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Sample records for low-latitude tec observations

  1. SWARM Observations of the Motion of Low-latitude Plasma Depletions Coordinated with Ground-based TEC Measurements

    NASA Astrophysics Data System (ADS)

    Valladares, C. E.; Pradipta, R.; Sheehan, R. E.; Coisson, P.; Knudsen, D. J.

    2015-12-01

    During the early phase of the SWARM mission, the distance between the trajectories of all three satellites of the constellation was tens of km and the temporal separation was of order one minute. This unique geometry allows us to conduct multiple and almost simultaneous in-situ measurements through the same low-latitude plasma depletion to investigate their spatial coherence and the motion of structures embedded within the equatorial plasma bubbles. We have used the number density measured with the Electric Field Instrument (EFI) on-board the three satellites of the SWARM constellation during December 2013 and January 2014 and concurrent TEC values obtained by ground-based GPS receivers to fully diagnose the bubble characteristics at multiple scale sizes. We have applied correlation and cross-spectra analysis to the density values measured by the EFI probes to derive the longitudinal variability of plasma density structures and their velocity. Our results indicate a very strong variability of the plasma bubbles in longitude. More specifically, it shows that structures with scale sizes corresponding to 100 and 10 seconds are not in phase. TEC values measures on the ground indicated that TEC plasma depletions moved with a velocity of order 100 m/s and have a westward tilt of order 10°. This presentation will show results for several specific days of SWARM observations during passes in the American sector.

  2. Characterization of ionospheric variability in TEC using EOF and wavelets over low-latitude GNSS stations

    NASA Astrophysics Data System (ADS)

    Dabbakuti, J. R. K. Kumar; Venkata Ratnam, D.

    2016-06-01

    Investigation of ionospheric variability is essential for improving the daily ionospheric modeling and forecasting services of Global Navigation Satellite System (GNSS) applications. As India is a low-latitude region, more care has to be taken here to characterize the ionosphere due to irregularities and Equatorial Ionization Anomaly (EIA) conditions. Therefore, an appropriate method is required to diagnose the ionospheric variations during geomagnetic, solar and other disturbances. In this paper, the temporal ionospheric time delay variations were studied based on the Empirical Orthogonal Function (EOF) analysis and wavelet transforms (WT).These analyses were carried out with Total Electron Content (TEC) datasets obtained from three GNSS stations located in low-latitude regions. EOF analysis was performed on the TEC datasets, which were decomposed into a time series of orthogonal eigen values (or base functions) and associated coefficients. EOF base functions and their associated coefficients signify the hourly time variations and the day of the year variations. The results reveal that the first few EOFs represented the majority of TEC variability pertaining to the physical processes of the ionosphere. The accuracy of the EOF model was validated by the evaluation of observational TEC data with International Reference Ionosphere (IRI) 2012 models. The EOF model coefficients for each GNSS station showed a strong correlation with the IRI models and also described the correlation between the impacts of the level of geomagnetic activity on the ionosphere. The correlation coefficients for the first three EOFs were more than 0.95. The phase relationship of ionospheric TEC anomalies, with respect to the geomagnetic indices (Dst), were analyzed by wavelet transforms.

  3. Receiver DCB estimation and GPS vTEC study at a low latitude station in the South Pacific

    NASA Astrophysics Data System (ADS)

    Prasad, Ramendra; Kumar, Sushil; Jayachandran, P. T.

    2016-11-01

    The statistical estimation of receiver differential code bias (DCB) of the GSV4004B receiver at a low latitude station, Suva (lat. 18.15°S, long. 178.45°E, Geomag. Lat. 21.07°S), Fiji, and the subsequent behaviour of vTEC, are presented. By means of least squares linear regression fitting technique, the receiver DCB was determined using the GPS vTEC data recorded during the year 2010, CODE TEC and IRI-2012 model for 2010. To substantiate the results, minimization of the standard deviation (SD) method was also used for GPS vTEC data. The overall monthly DCB was estimated to be in the range of 62.6 TECU. The vTEC after removing the resultant monthly DCB was consistent with other low latitude observations. The GPS vTEC 2010 data after eliminating the resultant DCB were lower in comparison to Faraday rotation vTEC measurements at Suva during 1984 primarily due to higher solar activity during 1984 as compared to 2010. Seasonally, vTEC was maximum during summer and minimum during winter. The winter showed least vTEC variability whereas equinox showed the largest daytime variability. The geomagnetic disturbances effect showed that both vTEC and its variability were higher on magnetically disturbed days as compared to quiet days with maximum variability in the daytime. Two geomagnetic storms of moderate strengths with main phases in the local daytime showed long duration (∼52 h) increase in vTEC by 33-67% which can be accounted by changes in E×B drifts due to prompt penetration of storm-time auroral electric field in the daytime and disturbance dynamo electric field in the nighttime to low latitudes.

  4. Diagnostics of equatorial and low latitude ionosphere by TEC mapping over Brazil

    NASA Astrophysics Data System (ADS)

    Takahashi, H.; Costa, S.; Otsuka, Y.; Shiokawa, K.; Monico, J. F. G.; Paula, E.; Nogueira, P.; Denardini, C. M.; Becker-Guedes, F.; Wrasse, C. M.; Ivo, A. S.; Gomes, V. C. F.; Gargarela, W.; Sant'Anna, N.; Gatto, R.

    2014-08-01

    The total electron content (TEC) in the equatorial and low-latitude ionosphere over Brazil was monitored in two dimensions by using 2011 data from the ground-based global navigation satellite system (GNSS) receiver network operated by the Brazilian Institute for Geography and Statistics. It was possible to monitor the spatial and temporal variations in TEC over Brazil continuously during both day and night with a temporal interval of 10 min and a spatial resolution of about 400 km. The daytime equatorial ionization anomaly (EIA) and post-sunset plasma enhancement (PS-EIA) were monitored over an area corresponding to a longitudinal extension of 4000 km in South America. Considerable day-to-day variation was observed in EIA and PS-EIA. A large latitudinal and longitudinal gradient of TEC indicated a significant ionospheric range error in application of the GNSS positioning system. Large-scale plasma bubbles after sunset were also mapped over a wide range. Depletions with longitudinally separated by more than 800 km were observed. They were extended by more than 2000 km along the magnetic field lines and drifted eastward. It is expected that 2-dimensional TEC mapping can serve as a useful tool for diagnosing ionospheric weather, such as temporal and spatial variation in the equatorial plasma trough and crest, and particularly for monitoring the dynamics of plasma bubbles.

  5. Statistical analysis of TEC perturbations over a low latitude region during 2009-2013 ascending solar activity phase

    NASA Astrophysics Data System (ADS)

    Andima, Geoffrey; Jurua, Edward; Amabayo, Emirant Bertillas; Habarulema, John Bosco

    2015-12-01

    Total Electron Content (TEC) perturbations are manifestations of ionospheric irregularities which induce fluctuations in the amplitude and phase of trans-ionospheric radio signals. TEC data derived from Global Positioning System (GPS) receivers at Mbarara (Geogra. -0.60°N, 30.74°E and Geomag. -10.22°N, 102.36°E) and Entebbe (Geogra. 0.04°N, 32.44°E and Geomag. -9.53°N, 104.10°E) from 2009 to 2013 were used to study TEC perturbations over the low latitude region of Uganda. The results show that the frequency of occurrence of TEC perturbations of >4 TECU increased steadily from 2009 to 2013. TEC perturbations with amplitude <4 TECU occurred at all times. The likelihood of TEC perturbations exceeding 6 TECU was higher during the equinoxes than during the solstices in most of the years. Comparison of TEC perturbations with 10.7 cm solar radio flux (F10.7) data showed a weak positive correlation with this solar proxy. Wavelet analysis performed on the TEC perturbations revealed wave-like oscillations with periods typical of Traveling Ionospheric Disturbances (TID). These wave-like structures (WLS) dominated from 13:00 to 19:00 LT for most of the years analyzed. Though the WLS were observed to increase with solar activity, no seasonal pattern was recorded in their occurrence.

  6. TIDI observations relating to low latitude aeronomy

    NASA Astrophysics Data System (ADS)

    Niciejewski, R.; Killeen, T.; Kafkalidis, J.; Wu, Q.; Skinner, W.; Solomon, S.; Ortland, D.; Gell, D.; Gablehouse, D.; Johnson, R.

    2003-04-01

    The TIDI instrument aboard the TIMED satellite has been observing the neutral winds in the upper atmosphere on a routine basis since early January 2002. The instrument simultaneously samples the thin limb of the Earth with four separate telescopes providing two forward views and two rearward views, one of each on either side of the orbital path. At equator crossings, these two side views are separated by about 30 degrees of longitude at the tangent point altitude, or 2 hours of local time. Thus, on any orbit TIDI obtains two horizontal vector winds at the dayside equator crossing and two on the nightside equator crossing as well as for all low latitudes. This is significantly greater than the data output of either the HRDI or the DE-2 satellite observations. This paper will describe the climatology that has been obtained by the TIDI instrument since early 2002 for low latitudes. The precession rate of TIMED supports two month averaging of data sets in order to sample all local solar time. Tidal structure is evident in the resulting zonal and meridional winds for mesosphere and lower thermosphere altitudes.

  7. On the variabilities and uncertainties in the measurement of absolute (true) TEC over Indian equatorial and low latitude sectors

    NASA Astrophysics Data System (ADS)

    Rao Pvs, Rama; Kavutarapu, Venkatesh; Prasad, Dsvvd; Kandula, Niranjan

    The Indian sector encompasses the equatorial and low latitude regions where the ionosphere is highly dynamic and is characterized by the Equatorial Ionization Anomaly (EIA) resulting in large latitudinal electron density gradients causing ambiguities in the estimation of range delays in satellite based augmentation and navigation systems. The diurnal and latitudinal variations in the day-to-day variability of the Total Electron Content (TEC) in the Indian sector during the low sunspot period 2004-2005 are studied and presented. The diurnal and seasonal variations of standard deviations in the TEC measured at ten different Indian stations located from equator to the anomaly crest region and beyond are presented. The day-to-day variability in TEC is found to be lowest at the equatorial station, Trivandrum and increases with latitude up to the crest region of EIA and decreases beyond. Further, the measurements of TEC using grid based studies are also carried out with a view to ascertain the uncertainties in the measurement of the absolute value of TEC. The TEC derived from different satellite ray paths visible in the 50 x 50 grid over any particular location at any particular given point of time have shown significant differences in the TEC derived from one ray path to the other leading to the possibility of introducing errors in the interpolation technique. Also, the TEC values derived simultaneously along two different satellite ray paths simultaneously passing through the same sub-ionospheric point at the same point of time are found to be quite different from each other. These uncertainties are found to be more pronounced at and around the EIA anomaly crest region with larger variations particularly around noon-time hours.

  8. On the uncertainties in the measurement of absolute (true) TEC over Indian equatorial and low latitude sectors

    NASA Astrophysics Data System (ADS)

    Rama Rao, P. V. S.; Venkatesh, K.; Prasad, D. S. V. V. D.; Niranjan, K.

    2013-04-01

    The Indian sector encompasses the equatorial and low latitude regions where the ionosphere is highly dynamic and is characterized by the equatorial ionization anomaly (EIA) resulting in large latitudinal electron density gradients causing errors and uncertainties in the estimation of range delays in satellite based navigation systems. The diurnal and seasonal variations of standard deviations in the TEC data measured during the low sunspot period 2004-2005 at 10 different Indian stations located from equator to the anomaly crest region and beyond are examined and presented. The day-to-day variability in TEC is found to be lowest at the equatorial station and increases with latitude up to the crest region of EIA and decreases beyond.Further, the measured values of TEC using grid based system are also examined with a view to ascertain the uncertainties in the measurement of the absolute value of TEC. The VTEC values derived from different satellite ray paths visible in the 5° × 5° grid over any particular location at any given point of time have shown significant differences in the TEC derived from one ray path to the other ranging from a minimum of 10% to a maximum of about 50% leading to the possibility of introducing errors in the interpolation technique. Also, the TEC values derived simultaneously along two different satellite ray paths simultaneously passing through the same sub-ionospheric point at the same point of time are found to be significantly different from each other although they are expected to be same. These uncertainties are found to be more pronounced at and around the EIA anomaly crest region with larger variations particularly around noon-time hours.

  9. Study of the low latitude ionospheric turbulence observed by DEMETER

    NASA Astrophysics Data System (ADS)

    Li, F.; Lefeuvre, F.; Parrot, M.

    Following previous works from Molchanov et al 2002a 2002b 2004a 2004b and Hobara et al 2005 data bases dedicated to the systematic analysis of the power and spectral indices of the electric field have been elaborated Two data bases are considered one for the survey mode and the other for the burst mode For the survey mode estimations of the turbulence parameters are performed from the 8 first Fourier components of the averaged power spectra 0-150 Hz frequency band A single slope power law model f - alpha is assumed A quality factor allows to test that hypothesis For the burst mode the power spectra are derived from the waveforms One and two slope models are systematically tested Results are presented and the possibility to use these data bases for correlation with seismic activity is discussed Y Hobara F Lefeuvre M Parrot and O A Molchanov Low-latitude ionospheric turbulence observed by Aureol-3 satellite Annales Geophysicae 23 1259--1270 2005 Molchanov O A Hayakawa M Afonin V V Akentieva O A and Mareev E A Possible influence of seismicity by gravity waves on ionospheric equatorial anomaly from data of IK-24 satellite 1 Search for idea of seismo-ionosphere coupling Seismo Electromagnetics Lithosphere-Atmosphere-Ionosphere Coupling edited by Hayakawa M and Molchanov O A TERRAPUB Tokyo 275--285 2002a Molchanov O A Hayakawa M Afonin V V Akentieva O A Mareev E A and Trakhtengerts V Yu Possible influence of seismicity by gravity waves on ionospheric

  10. Characterisation of GPS-TEC in the African equatorial and low latitude region and the regional evaluation of the IRI model

    NASA Astrophysics Data System (ADS)

    Adebiyi, S. J.; Adimula, I. A.; Oladipo, O. A.

    2016-06-01

    With the increasing application of Global Navigation Satellite System (GNSS) products and services, knowledge of the Total Electron Content (TEC) variation is vital, particularly in historically under-sampled regions. The ionospheric induced-error, which is the largest and most variable error source of GNSS applications, is proportional to TEC along the satellite-receiver path. Simultaneous Global Positioning System (GPS) measurements from six African equatorial and low latitude stations in the southern hemisphere are used to investigate the latitudinal variation of TEC over the region during the year 2013, a year of moderate solar activity. The analysis reveals some detailed features of seasonal, month-to-month and solar activity dependence of TEC. The seasonal variation of TEC revealed that the daytime and the pre-midnight values of TEC for stations located close to the geographic equator is considerably higher in equinoxes and June solstice compared to stations farther from the equator, however, the difference is insignificant during the December solstice. The month-to-month variation of TEC shows semi-annual symmetry/asymmetry in TEC values for stations closer/farther from the equator. TEC sensitivity to solar activity shows significant seasonal and latitudinal characteristics. Generally, a relatively good correlation exists between TEC and F10.7 for stations around the Equatorial Ionization Anomaly (EIA) region compared to those found at stations close to the equator. Beyond the EIA region, the correlation coefficients drop in all seasons. TEC predicted by the three topside options of the International Reference Ionosphere (IRI) 2012 model [i.e. the NeQuick (NeQ), IRI-2001 Corrected (IRI-01 Corr) and the IRI-2001 (IRI-01) options] exhibits latitudinal and seasonal characteristics. The NeQ option performed better than the other two options at stations located within the equatorial region in most of the months and seasons. Outside the EIA region, the IRI-01 Corr

  11. East Asian observations of low-latitude aurora during the Carrington magnetic storm

    NASA Astrophysics Data System (ADS)

    Hayakawa, Hisashi; Iwahashi, Kiyomi; Tamazawa, Harufumi; Isobe, Hiroaki; Kataoka, Ryuho; Ebihara, Yusuke; Miyahara, Hiroko; Kawamura, Akito Davis; Shibata, Kazunari

    2016-10-01

    A magnetic storm around 1859 September 2, caused by a so-called Carrington flare, was the most intense in the history of modern scientific observations, and hence is considered to be a benchmark event concerning space weather. The magnetic storm caused worldwide observations of auroras, even at very low latitudes, such as Hawaii, Panama, or Santiago. Available magnetic-field measurements at Bombay, India, showed two peaks: the main was the Carrington event, which occurred in day time in East Asia; a second storm after the Carrington event occurred at night in East Asia. In this paper, we present results from surveys of aurora records in East Asia, which provide new information concerning the aurora activity of this important event. We found some new East Asian records of low-latitude aurora observations caused by a storm which occurred after the Carrington event. The size of the aurora belt of the second peak of the Carrington magnetic storm was even wider than that of usual low-latitude aurora events.

  12. Ionospheric irregularities in the low-latitude valley region observed with the Equatorial Atmosphere Radar

    NASA Astrophysics Data System (ADS)

    Yokoyama, T.; Patra, A. K.; Fukao, S.; Yamamoto, M.

    2005-10-01

    The geomagnetically low-latitude valley region between the upper E region and the lower F1 region is studied with the Equatorial Atmosphere Radar (EAR) in Indonesia. Three-meter-scale field-aligned irregularity echoes have been frequently observed in the valley region in association with the equatorial spread F (ESF) in the period from sunset to midnight. The valley region echoes usually appear at above 150 km and propagate downward with time. Rapid beam scanning of the EAR revealed that spatial structure, temporal variation, and drift velocity of the valley region echoes resemble those of ESF, which indicates that the dynamoelectric field in the equatorial F region controls the low-latitude valley region irregularities. Perturbed electric fields associated with ESF map down to the low-latitude valley region and can produce the perturbed plasma density structures as "images" of ESF structures. Image structure is effectively formed at altitudes below 200 km and is a source of the valley region irregularities observed with the EAR. It is suggested that intermediate layers should supply a plasma density gradient for excitation of 3-m-scale irregularities in the valley region through gradient drift instability.

  13. A multi-technique study of the 29-31 October 2003 geomagnetic storm effect on low latitude ionosphere over Indian region with magnetometer, ionosonde, and GPS observations

    NASA Astrophysics Data System (ADS)

    Panda, Sampad Kumar; Gedam, Shirish S.; Rajaram, Girija; Sripathi, S.; Pant, Tarun Kumar; Das, Rupesh M.

    2014-12-01

    The present study demonstrates the ionospheric response to the extreme geomagnetic storms during 29-31 Oct 2003 (the Halloween storm), in the low latitude anomaly Indian region, based on multi-instrument measurements namely magnetometer, ionosonde, and GPS observations. Unlike earlier reports, we have suitably chosen the best quiet days (CQ-Days) amongst 10 international quiet days (Q-Days), on the basis of equatorial electrojet strength and pattern, that drives the distribution of plasma over the low latitude. We stress that arbitrarily selecting the Control/Q-Days may lead to erroneous interpretations and will not yield a clearer understanding of the equatorial electrodynamics. Our analysis confirms the anomalous increase in TEC at all stations on 29 Oct 2003 and suppressed TEC across anomaly crest latitudes during 30-31 Oct 2003. The sharp transition in h'F is noticed during the progressive period of the storm, though it was relatively lower at the equator. The respective foF2 remained subordinate at Trivandrum. However, we did not notice such foF2 changes at Delhi. Observations at various latitudes confirm the maximum positive deviation of TEC at mid-latitude POL2 (140 %), followed by the low latitude Jodhpur (108 %), and the rest of the stations showing relatively lower enhancements with deviations ranging between 60-90 %. However, at Ahmedabad, the lowest divergence from the mean CQ-Days, attribute the typical quiet day formation of crest at this latitude. Although the results are well agreeing with earlier reports, miniature differences is noticeable due to our way of choosing the best reference days in the analysis.

  14. On the NH3 absorption depression observable at Northern low latitudes of Jupiter

    NASA Astrophysics Data System (ADS)

    Tejfel, Victor G.; Vdovichenko, Vladimir D.; Lysenko, Peter G.; Karimov, Alibek M.; Kirienko, Galina A.; Bondarenko, Natalya N.; Kharitonova, Galina

    2016-10-01

    From February to April of 2016, we carried out a special series of spectrophotometric observations of Jupiter to study the current behavior of the ammonia absorption at the low latitudes of the Northern hemisphere, where in 2004 we have found a well-defined depression of the 787 nm NH3 absorption band intensity (V.Tejfel et al., Bull.AAS, 2005, Vol. 37, p.682). In subsequent years, an existence of this depression was annually confirmed by spectral observations, although we were noticing its variable character. During observations of 2016 we obtained more than 2,500 CCD-spectrograms, including the spectra of the central meridian, the GRS, and 12 scans of Jovian disk on different dates (70 zonal spectra in each scan). The 787 nm NH3 absorption band was extracted with using of ratios of the Jovian spectra to the Saturn's disk spectrum that was taken as a reference. The depression of absorption in this band begins almost from the equator, and its maximum occurs at the planetographic latitude of 100N then the absorption increases again approaching to the latitude of 200N. The equivalent bandwidths corresponding to these latitudes are equal to 18.7 ± 1.4 A, 14.4 ± 1.0 A and 17.8 ± 0.8A. The 645 nm NH3 absorption band also shows depletion at the low latitudes of the Northern hemisphere, but it is less pronounced. At the temperate latitudes of the Northern hemisphere this band's absorption is systematically lower than the Southern Hemisphere's ones. We will continue research in this direction, especially because recently a significant depletion of gaseous NH3 has also been found with using of the VLA with high resolution (I. de Pater et al., Science, 2016, Vol. 352, Issue 6290, p.1290-1294) at the low latitudes of the Northern hemisphere in the region of the NEB.

  15. Subionospheric VLF perturbations observed at a low latitude station Varanasi (L = 1.07)

    NASA Astrophysics Data System (ADS)

    Singh, Ashutosh K.; Singh, A. K.; Singh, R.; Singh, R. P.; Adams, K.; Dowden, R. L.

    2015-01-01

    Initial results of subionospheric very low frequency (VLF) perturbations observed on NWC (19.8 kHz) and NPM (21.4 kHz) transmitter signals at low latitude ground station Varanasi, India, during the period January-June 2010, are presented. Characteristics and occurrence rates of these events mainly observed during nighttime are studied. Most of the early VLF events had slow recovery with amplitude perturbations of 0.5-4.5 dB and phase changes of 3-12°. Temporal variation of the events is studied. World Wide Lightning Location Network data along with the broadband VLF data are analyzed to find the location of causative lightning discharge and/or the sferics associated with these early VLF events. Lightning induced changes in D-region ionospheric conductivity are attributed to the perturbations in the VLF signals.

  16. On the observations of unique low latitude whistler-triggered VLF/ELF emissions

    NASA Astrophysics Data System (ADS)

    Altaf, M.; Singh, K. K.; Singh, A. K.; Lalmani

    A detailed analysis of the VLF/ELF wave data obtained during a whistler campaign under All India Coordinated Program of Ionosphere Thermosphere Studies (AICPITS) at our low latitude Indian ground station Jammu (geomag. lat. = 22° 26‧ N, L = 1.17) has yielded two types of unusual and unique whistler-triggered VLF/ELF emissions. These include (1) whistler-triggered hook emissions and (2) whistler-triggered long enduring discrete chorus riser emissions in VLF/ELF frequency range during night time. Such types of whistler-triggered emissions have not been reported earlier from any of the ground observations at low latitudes. In the present study, the observed characteristics of these emissions are described and interpreted. Dispersion analysis of these emissions show that the whistlers as well as emissions have propagated along a higher geomagnetic field line path with L-values lying ∼L = 4, suggesting that these triggered emissions are to be regarded as mid-latitude emissions. These waves could have propagated along the geomagnetic field lines either in a ducted mode or in a pro-longitudinal (PL) mode. The measured intensity of the triggered emissions is almost equal to that of the source waves and does not vary throughout the period of observation on that day. It is speculated that these emissions may have been generated through a process of resonant interaction of the whistler waves with energetic electrons. Parameters related to this interaction are computed for different values of L and wave amplitude. The proposed mechanism explains some aspects of the dynamic spectra.

  17. Patterns of GPS-TEC variation over low-latitude regions (African sector) during the deep solar minimum (2008 to 2009) and solar maximum (2012 to 2013) phases

    NASA Astrophysics Data System (ADS)

    Tariku, Yekoye Asmare

    2015-03-01

    Due to the unique geometry of the geomagnetic fields near the magnetic equator and low-latitude regions, the satellite communication system in the African sector is strongly influenced by the effects resulting from the accumulation of electrons in their ionosphere. Hence, this paper investigates the patterns of the vertical total electron content (VTEC) variation detected by the Global Positioning System (GPS) over low-latitude regions during a very low (2008 to 2009) and a high solar activity (2012 to 2013) phases. The study has been carried out by considering eight ground-based dual-frequency GPS receivers installed recently at different regions in Ethiopia. In this work, the diurnal, monthly, and seasonal variations in the GPS-VTEC have been analyzed. It has been found that the diurnal variability of VTEC has shown minimum values at around 0300 UT (0600 local time (LT)) and maximum values nearly between 1000 and 1300 UT (1300 and 1600 LT) during both the low and the high activity phases. Moreover, the maximum and minimum of monthly mean hourly VTEC values are observed in October and July, respectively, during both the low (2009) and the high solar activity (2012) phases. It has also been depicted that seasonal mean hourly VTEC values have shown maxima and minima in the March equinox and the June solstice, respectively, during both the low and the high solar activity phases.

  18. Observations of Low-Latitude Plasma Density Enhancements and their Associated Plasma Drifts

    NASA Technical Reports Server (NTRS)

    Klenzing, J. H.; Rowland, D. E.; Pfaff, R. F.; Le, G.; Freudenreich, H.; Haaser, R. A.; Burrell, A. G.; Stoneback, R. A.; Coley, W. R.; Heelis, R. A.

    2011-01-01

    Plasma density structures are frequently encountered in the nighttime low-latitude ionosphere by probes on the Communication/Navigation Outage Forecasting System (C/NOFS) satellite. Of particular interest to us here are plasma density enhancements, which are typically observed +/- 15 deg away from the magnetic equator. The low inclination of the C/NOFS satellite offers an unprecedented opportunity to examine these structures and their associated electric fields and plasma velocities, including their field-aligned components, along an east-west trajectory. Among other observations, the data reveal a clear asymmetry in the velocity structure within and around these density enhancements. Previous observations have shown that the peak change in drift velocity associated with a density enhancement occurs simultaneously both perpendicular and parallel to the magnetic field, while the 1results in this paper show that the peak change in parallel fl ow typically occurs 25-100 km to the east of the peak perpendicular ow. We discuss this and other aspects of the observations in relation to the characteristics of the plasma depletions formed near the magnetic equator detected by the same probes on the C/NOFS satellite and to previous observations and theories.

  19. Recent Plasma Observations Related to Dayside Magnetic Merging and the Low-latitude Boundary Layer

    NASA Technical Reports Server (NTRS)

    Chandler, Michael O.; Avanov, Levon A.; Craven, Paul D.; Mozer, Forrest S.; Moore, Thomas E.

    2007-01-01

    We have begun an investigation of the nature of the low-latitude boundary layer in the mid-altitude cusp region using data from the Polar spacecraft. This region has been routinely sampled for about three months each year for the periods 1999-2001 and 2004-2006. The low-to-mid-energy ion instruments frequently observed dense, magnetosheath-like plasma deep (in terms of distance from the magnetopause and in invariant latitude) in the magnetosphere. One such case, taken during a period of northward interplanetary magnetic field (IMF), shows magnetosheath ions within the magnetosphere with velocity distributions resulting from two separate merging sites along the same field lines. Cold ionospheric ions were also observed counterstreaming along the field lines, evidence that these field lines were closed. These results are consistent with the hypothesis that double merging can produce closed field lines populated by solar wind plasma. Through the use of individual cases such as this and statistical studies of a broader database we seek to understand the morphology of the LLBL as it projects from the sub-solar region into the cusp. We will present preliminary results of our ongoing study.

  20. Spectral features of lightning-induced ion cyclotron waves at low latitudes: DEMETER observations and simulation

    NASA Astrophysics Data System (ADS)

    Shklyar, D. R.; Storey, L. R. O.; Chum, J.; JiříčEk, F.; NěMec, F.; Parrot, M.; Santolik, O.; Titova, E. E.

    2012-12-01

    We use a comprehensive analysis of 6-component ELF wave data from the DEMETER satellite to study proton whistlers, placing emphasis on low-latitude events originating from lightning strokes in the hemisphere opposite to the hemisphere of observation. In this case, the formation of proton whistlers does not involve mode conversion caused by a strong mode coupling at a crossover frequency, although a polarization reversal remains an important element in formation of the phenomenon. DEMETER measurements of the six electromagnetic field components in the frequency band below 1000 Hz make it possible to determine not only the dynamic spectrum, but also the wave polarization, the wave normal angle, and the normalized parallel component of the Poynting vector. This permits us to address fine features of proton whistlers, in particular, we show that the deviation of the upper cutoff frequency from the equatorial cyclotron frequency is related to the Doppler shift. Experimental study of proton whistlers is supplemented by an investigation of ion cyclotron wave propagation in a multicomponent magnetoplasma and by numerical modeling of spectrograms, both in the frame of geometrical optics.

  1. MESSENGER observations of the dayside low-latitude boundary layer in Mercury's magnetosphere

    NASA Astrophysics Data System (ADS)

    Liljeblad, Elisabet; Karlsson, Tomas; Raines, Jim M.; Slavin, James A.; Kullen, Anita; Sundberg, T.; Zurbuchen, Thomas H.

    2015-10-01

    Observations from MErcury Surface Space ENvironment GEochemistry, and Ranging (MESSENGER)'s Magnetometer and Fast Imaging Plasma Spectrometer instruments during the first orbital year have resulted in the identification of 25 magnetopause crossings in Mercury's magnetosphere with significant low-latitude boundary layers (LLBLs). Of these crossings 72% are observed dawnside and 65% for northward interplanetary magnetic field. The estimated LLBL thickness is 450 ± 56 km and increases with distance to noon. The Na+ group ion is sporadically present in 14 of the boundary layers, with an observed average number density of 22 ± 11% of the proton density. Furthermore, the average Na+ group gyroradii in the layers is 220 ± 34 km, the same order of magnitude as the LLBL thickness. Magnetic shear, plasma β and reconnection rates have been estimated for the LLBL crossings and compared to those of a control group (non-LLBL) of 61 distinct magnetopause crossings which show signs of nearly no plasma inside the magnetopause. The results indicate that reconnection is significantly slower, or even suppressed, for the LLBL crossings compared to the non-LLBL cases. Possible processes that form or impact the LLBL are discussed. Protons injected through the cusp or flank may be important for the formation of the LLBL. Furthermore, the opposite asymmetry in the Kelvin-Helmholtz instability (KHI) as compared to the LLBL rules out the KHI as a dominant formation mechanism. However, the KHI and LLBL could be related to each other, either by the impact of sodium ions gyrating across the magnetopause or by the LLBL preventing the growth of KH waves on the dawnside.

  2. MESSENGER Observations of the Dayside Low-Latitude Boundary Layer in Mercury's Magnetosphere

    NASA Astrophysics Data System (ADS)

    Liljeblad, E. I.; Karlsson, T.; Raines, J. M.; Slavin, J. A.; Kullen, A.; Sundberg, T.; Zurbuchen, T.

    2015-12-01

    Observations from MESSENGER's MAG and FIPS instruments during the first orbital year have resulted in the identification of 25 magnetopause crossings in Mercury's magnetosphere with significant low-latitude boundary layers (LLBLs). The large majority of these crossings are observed on the dawnside and for northward interplanetary magnetic field. The estimated LLBL thickness is 450±56 km, and increases with distance to noon. The Na+-group ion is sporadically present in 14 of the boundary layers, with an observed average number density of 22±11 % of the proton density. Furthermore, the average Na+-group gyroradii in the layers is 220±34 km, the same order of magnitude as the LLBL thickness. Magnetic shear, plasma β and reconnection rates have been estimated for the LLBL crossings, and compared to those of a control group (non-LLBL) of 61 distinct magnetopause crossings which show signs of nearly no plasma inside the magnetopause. The results indicate that reconnection is significantly slower, or even suppressed, for the LLBL crossings compared to the non-LLBL cases. Possible processes that form or impact the LLBL are discussed. Protons injected through the cusp or flank may be important for the formation of the LLBL. Furthermore, the opposite asymmetry in the Kelvin-Helmholtz instability (KHI) as compared to the LLBL, rules out the KHI as a dominant formation mechanism. However, the KHI and LLBL could be related to each other, either by the impact of sodium ions gyrating across the magnetopause, or by the LLBL preventing the growth of KH waves on the dawnside.

  3. Observations of the intraseasonal oscillations over two Brazilian low latitude stations: A comparative study

    NASA Astrophysics Data System (ADS)

    Guharay, A.; Batista, P. P.; Clemesha, B. R.; Buriti, R. A.

    2014-12-01

    A comparative study of intraseasonal oscillations (ISO) in the period range 20-110 days is carried out in the mesosphere and lower thermosphere (MLT) zonal wind at two low latitude stations, Cariri (7.4°S, 36.5°W) and Cachoeira Paulista (22.7°S, 45°W) located far from the convective anomaly region. Considerable seasonal and interannual variability is observed. The ISO in the MLT and lower atmosphere are found to be well correlated during winter and spring indicating a coupling of the atmospheric regions through the ISO. On the other hand, relatively less correlation during summer and fall may suggest a dominance of the in situ excitation of the ISO in the MLT relative to the lower atmospheric contribution. The correlation between the MLT and lower atmosphere is found to be a little higher at Cachoeira Paulista than Cariri. The ISO in the MLT shows good correlation between the two stations, but correlation is insignificant in the case of lower atmosphere. The ISO is most prominent in the upper troposphere, upper stratosphere and MLT. The waves responsible for communicating the ISO signature from the troposphere to the middle atmosphere in the tropics are believed to refract through mid-latitudes in course of their propagation. An evident height variation of the high amplitude ISO in the upper troposphere is observed with a clear annual oscillation at Cariri. The observed behaviors of the ISO at the present sites are discussed in the light of plausible physical mechanisms.

  4. Magnetically Conjugate Observations of the Low Latitude Ionosphere in Western South America

    NASA Astrophysics Data System (ADS)

    Hickey, D. A.; Martinis, C. R.; Baumgardner, J. L.; Milla, M. A.; Mendillo, M.; Meriwether, J. W.

    2015-12-01

    An all-sky imager (ASI) installed at Villa de Leyva, Colombia (5.6° N, 73.5° W, 16.3° mag lat) in October 2014 is used in conjunction with another ASI near the magnetically conjugate point at El Leoncito in Argentina (31.8° S, 69.3° W, -19.6° mag lat) to study irregularities and perturbations in the ionosphere. A third ASI in Jicamarca, Peru (11.95° S, 76.87° W, 0.1° mag lat) provides context for the structures generated near the magnetic equator on the west coast of South America. The region sampled by these instruments covers from ~40° S to ~15° N and from ~ 80° W to ~65° W . The Jicamarca Radio Observatory has radar systems and other instruments that measure the upper atmosphere which, combined with the ASIs, allow us to uniquely study equatorial and low latitude processes. The ASIs are able to detect airglow depletions at 630 nm associated with equatorial spread F (ESF) that can also observed with coherent radar scatter measurements at Jicamarca. Simultaneous conjugate observations of ESF are compared to see how the large-scale structures behave at these locations. The ASIs are also used to look for a signature of the midnight temperature maximum (MTM) that is seen as an increase in brightness propagating poleward. Radar and Fabry-Perot interferometer data is used to measure this increase in temperature and combining them with the ASI data we will be able to probe the extent of MTM effects and investigate how they vary with latitude in both hemispheres.

  5. Observations of a Unique Type of ULF Waves by Low-Latitude Space Technology 5 Mission

    NASA Technical Reports Server (NTRS)

    Le, Guan; Chi, P.; Strangeway, R. J.; Slavin, J. A.

    2011-01-01

    We report a unique type of ULF waves observed by low-altitude Space Technology 5 (ST-5) constellation mission. ST-5 is a three micro-satellite constellation deployed into a 300 x 4500 km, dawn-dusk, and sun synchronous polar orbit with 105.6 inclination angle. Due to the Earth's rotation and the dipole tilt effect, the spacecraft's dawn-dusk orbit track can reach as low as sub auroral latitudes during the course of a day. Whenever the spacecraft traverse across the dayside closed field line region at sub auroral latitudes, they frequently observe strong transverse oscillations at 30-200 mHz, or in the Pc 2-3 frequency range. These Pc 2-3 waves appear as wave packets with durations in the order of 5-10 minutes. As the maximum separations of the ST-5 spacecraft are in the order of 10 minutes, the three ST -5 satellites often observe very similar wave packets, implying these wave oscillations occur in a localized region. The coordinated ground-based magnetic observations at the spacecraft footprints, however, do not see waves in the Pc 2-3 band; instead, the waves appear to be the common Pc 4-5 waves associated with field line resonances. We suggest that these unique Pc 2-3 waves seen by ST-5 are in fact the Doppler-shifted Pc 4-5 waves as a result of rapid traverse of the spacecraft across the resonant field lines azimuthally at low altitudes. The observations with the unique spacecraft dawn-disk orbits at proper altitudes and magnetic latitudes reveal the azimuthal characteristics of field-aligned resonances.

  6. Observations of a Unique Type of ULF Waves by Low-Latitude Space Technology 5 Mission

    NASA Technical Reports Server (NTRS)

    Le, G.; Chi, P.; Strangeway, R. J.; Slavin, J. A.

    2010-01-01

    We report a unique type of ULF waves observed by low-altitude Space Technology 5 (ST-5) constellation mission. ST-5 is a three micro-satellite constellation deployed into a 300 x 4500 km, dawn-dusk, and sun synchronous polar orbit with 105.6 degree inclination angle. Due to the Earth's rotation and the dipole tilt effect, the spacecraft's dawn-dusk orbit track can reach as low as subauroral latitudes during the course of a day. Whenever the spacecraft traverse across the dayside closed field line region at sub auroral latitudes, they frequently observe strong transverse oscillations at 30-200 mHz, or in the Pc 2-3 frequency range. These Pc 2-3 waves appear as wave packets with durations in the order of 5-10 minutes. As the maximum separations of the ST-5 spacecraft are in the order of 10 minutes, the three ST-5 satellites often observe very similar wave packets, implying these wave oscillations occur in a localized region. The coordinated ground-based magnetic observations at the spacecraft footprints, however, do not see waves in the Pc 2-3 band; instead, the waves appear to be the common Pc 4-5 waves associated with field line resonances. We suggest that these unique Pc 2-3 waves seen by ST-5 are in fact the Doppler-shifted Pc 4-5 waves as a result of rapid traverse of the spacecraft across the resonant field lines azimuthally at low altitudes. The observations with the unique spacecraft dawn-disk orbits at proper altitudes and magnetic latitudes reveal the azimuthal characteristics of field-aligned resonances.

  7. Observations of a Unique Type of ULF Waves by Low-Latitude Space Technology 5 Satellites

    NASA Technical Reports Server (NTRS)

    Le, G.; Chi, P. J.; Strangeway, R. J.; Slavin, J. A.

    2011-01-01

    We report a unique type of ULF waves observed by low-altitude Space Technology 5 (ST-5) constellation mission. ST-5 is a three micro-satellite constellation deployed into a 300 x 4500 km, dawn-dusk, and sun synchronous polar orbit with 105.6deg inclination angle. Due to the Earth s rotation and the dipole tilt effect, the spacecraft s dawn-dusk orbit track can reach as low as subauroral latitudes during the course of a day. Whenever the spacecraft traverse across the dayside closed field line region at subauroral latitudes, they frequently observe strong transverse oscillations at 30-200 mHz, or in the Pc 2-3 frequency range. These Pc 2-3 waves appear as wave packets with durations in the order of 5-10 minutes. As the maximum separations of the ST-5 spacecraft are in the order of 10 minutes, the three ST-5 satellites often observe very similar wave packets, implying these wave oscillations occur in a localized region. The coordinated ground-based magnetic observations at the spacecraft footprints, however, do not see waves in the Pc 2-3 band; instead, the waves appear to be the common Pc 4-5 waves associated with field line resonances. We suggest that this unique Pc 2-3 waves seen by ST-5 are in fact the Doppler-shifted Pc 4-5 waves as a result of rapid traverse of the spacecraft across the resonant field lines azimuthally at low altitudes. The observations with the unique spacecraft dawn-disk orbits at proper altitudes and magnetic latitudes reveal the azimuthal characteristics of field-aligned resonances.

  8. Observations of a Unique Type of ULF Waves by Low-Latitude Space Technology Five Mission

    NASA Technical Reports Server (NTRS)

    Le, G.; Chi, P.; Strangeway, R. J.; Slavin, J. A.

    2011-01-01

    We report a unique type of ULF waves observed by low-altitude Space Technology 5 (ST-5) constellation mission. ST-5 is a three micro-satellite constellation deployed into a 300 x 4500 km, dawn-dusk, and sun synchronous polar orbit with 105.6deg inclination angle. Due to the Earth s rotation and the dipole tilt effect, the spacecraft s dawn-dusk orbit track can reach as low as subauroral latitudes during the course of a day. Whenever the spacecraft traverse across the dayside closed field line region at subauroral latitudes, they frequently observe strong transverse oscillations at 30-200 mHz, or in the Pc 2-3 frequency range. These Pc 2-3 waves appear as wave packets with durations in the order of 5-10 minutes. As the maximum separations of the ST-5 spacecraft are in the order of 10 minutes, the three ST-5 satellites often observe very similar wave packets, implying these wave oscillations occur in a localized region. The coordinated ground-based magnetic observations at the spacecraft footprints, however, do not see waves in the Pc 2-3 band; instead, the waves appear to be the common Pc 4-5 waves associated with field line resonances. We suggest that these unique Pc 2-3 waves seen by ST-5 are in fact the Doppler-shifted Pc 4-5 waves as a result of rapid traverse of the spacecraft across the resonant field lines azimuthally at low altitudes. The observations with the unique spacecraft dawn-disk orbits at proper altitudes and magnetic latitudes reveal the azimuthal characteristics of field-aligned resonances.

  9. Response of equatorial and low latitude ionosphere to 2015 St. Patrick's Day super geomagnetic storm: Results from a chain of ground based observations over Indian region

    NASA Astrophysics Data System (ADS)

    Samireddipalle, Sripathi; Singh, Ram; Sreekumar, Sreeba; Suneel Kumar, Buduru

    2016-07-01

    In this paper, we present unique results of equatorial and low latitude ionosphere response to one of the major geomagnetic storms of the current solar cycle that occurred during 17-18 March 2015 where Dst reached its minimum of -228 nT. Here we utilized data from magnetometers, chain of ionosondes located at Tirunelveli (8.73°N, 77.70°E; geom: 0.320N), Hyderabad (17.360N, 78.470E; geom: 8.760N) and Allahabad (25.45°N, 81.85°E; geom: 16.50N) along with multi station GPS receivers over Indian sector. The observations showed a remarkable increase of h'F to as high as ~560 km over Tirunelveli (magnetic equator) with vertical drift of ~70 m/s at 13:30 UT due to direct penetration of storm time eastward electric fields which exactly coincided with the local time of Pre-Reversal Enhancement (PRE) and caused intense ESF irregularities in ionosondes and scintillations in GPS receivers at wide latitudes. Plasma irregularities are so intense that their signatures are seen in Allahabad/Lucknow. Stormtime thermospheric meridional winds as estimated using two ionosondes suggest the equatorward surge of gravity waves with period of ~2 hrs. Suppression of anomaly crest on the subsequent day of the storm suggests the complex role of disturbance dynamo electric fields and disturbance wind effects. Our results also show an interesting feature of Traveling Ionospheric Disturbances (TIDs) possibly associated with disturbance meridional wind surge during recovery phase. In addition, noteworthy observations are nighttime westward zonal drifts and PRE related TEC enhancements at anomaly crests during main phase and CEJ signatures during recovery phase.

  10. Equinoctial asymmetry in low latitude ionosphere as observed by SROSS-C2 satellite

    NASA Astrophysics Data System (ADS)

    Bardhan, Ananna; Aggarwal, Malini; Sharma, D. K.; Rai, J.

    2014-09-01

    The ionospheric plasma parameters (electron, ion temperatures and ion composition-Te, Ti, O+ and H+) measured by SROSS-C2 satellite at an average altitude of ~500 km has been investigated to study the behaviour of the ionosphere in equinoxes during half a solar cycle (year 1995-2000, F10.7 ~70-195). The region under study spans over 5-35°N geog. latitude and 65-95°E geog. longitude in the Indian sector. We found an equinoctial asymmetry in the diurnal behaviour of Te, Ti, O+ and H+ varying with increase in solar activity. The strength of equinoctial asymmetry in Te and Ti is strong during early morning and daytime and strength decreases with increase in solar activity whereas during night time no asymmetry/weaker is observed in low/high solar activity respectively. During the day time, a very strong equinoctial asymmetry in O+ is observed during solar minimum which diminishes with increase in solar activity. The similar diurnal behaviour of H+ as that of O+ is observed during low solar activity but no clear equinoctial asymmetry is observed during solar maximum, as H+ being highly dynamic. The transition height (O+/H+) is the lowest in early morning during solar minimum, which increases during local day-time. The rate of increase in transition height is different in both the equinoxes (higher in vernal than autumn) with respect to dependence on the solar activity, during daytime. Hence equinoctial asymmetry is stronger during solar minimum period than maximum, with higher/lower transition height in vernal during daytime/nighttime respectively.

  11. High Altitude Double Sodium Layer Observed at Low Latitude and Possible Formation: A Case Study

    NASA Astrophysics Data System (ADS)

    Xue, X.

    2012-12-01

    We report the lidar observations of a double sodium layer (DSL) at Lijiang, China, in March 2012, in which, a high-altitude secondary sodium layer (SeSL) and a sporadic sodium layer (SSL) are co-existed. The SeSL has a maximum density 120 cm-3, 6.7% of that of main layer, and starts at 122 km with full width at half maximum (FWHM) ~ 4-8 km. It does not merge into the main layer for whole observational period. The SSL with a peak density 5500 cm-3, 3 times larger than that of the main layer, appears at 105 km and accompanies with SeSL all the time. Further observations illustrate that multi-layer sporadic E (Es) layers are related to the formation of SeSL and SSL through meridional and zonal diurnal tidal (DT) wind shear mechanisms, respectively, whose efficiency differ at a given altitude according to the ratio of ion-neutral collision frequency to ion gyrofrequency.

  12. Low-latitude midnight brightness in 630.0 nm limb observations by FORMOSAT-2/ISUAL

    NASA Astrophysics Data System (ADS)

    Rajesh, P. K.; Chen, C. H.; Lin, C. H.; Liu, J. Y.; Huba, J. D.; Chen, A. B.; Hsu, R. R.; Chen, Y. T.

    2014-06-01

    This paper investigates the intense airglow brightness often observed in the 630.0 nm limb images taken using Imager of Sprites and Upper Atmospheric Lightnings (ISUAL), onboard FORMOSAT-2 satellite, where the tangent plane of the measurement falls in the local midnight sector. Most of the images show only single brightness, but in some cases there could be multiple peaks, which sometimes appears to be centered on geographic equator and in some cases falls on either sides of the magnetic equator. In order to understand such intense emission in the near-midnight hours, the observations are simulated using SAMI2 (SAMI2 is Another Model of the Ionosphere) model parameters based on the ISUAL viewing geometry. The simulations reproduced the measured airglow intensity pattern quite remarkably and suggested that the meridional neutral wind and the resulting plasma distribution are closely related with the observed brightness. The intensity and locations of the airglow brightness peaks could potentially be utilized to infer the strength of meridional neutral wind.

  13. An atlas of low latitude 6300A (01) night airglow from OGO-4 observations

    NASA Technical Reports Server (NTRS)

    Reed, E. I.; Fowler, W. B.; Blamont, J. E.

    1972-01-01

    The atomic oxygen emission line at 6300 A, measured in the nadir direction by a photometer on the polar orbiting satellite OGO-4, was plotted between 40 deg N and 40 deg S latitude on a series of maps for the moon-free periods between 30 August 1967 and 10 January 1968 The longitudinal and local time variations which occur during the northern fall-winter season are indicated. The northern tropical arc is more widespread while the southern arc is not present at all longitudes. The conditions under which the observations were made are described, and four airglow maps were selected to show the local time variations.

  14. Ground-satellite conjugate observations of low-latitude travelling ionospheric disturbances

    NASA Astrophysics Data System (ADS)

    Ceren Moral, Aysegul; Shiokawa, Kazuo; Otsuka, Yuichi; Suzuki, Shin; Liu, Huixin; Yatini, Clara

    2016-07-01

    Equatorial travelling ionospheric disturbances (TIDs) are studied by using three CHAMP satellite overpasses on ground-based 630-nm airglow images. The airglow images are obtained from Kototabang (KTB), Indonesia (geographic coordinates: 0.2S, 100.3E, geomagnetic latitude: 10.6S). From 7-year data from October 2002 to October 2009, April 30, 2006 (event 1), September 28, 2006 (event 2) and April 12, 2004 (event 3) are the only TID events found in both ground and satellite measurements. They show southward-moving structures in 630-nm airglow images. The events 1 and 2 are single pulse with horizontal scales of ~500-1000 km and event 3 show three wave fronts with horizontal scale sizes of 500-700 km. For events 1 and 3, the neutral density in CHAMP shows out-of-phase variations with the airglow intensity, while event 2 is in-phase. For event 1, the relation between electron density and airglow intensity is out of phase, while relationships of event 2 and 3 are unclear. These unclear relationships suggest that ionospheric plasma variation is not the cause of the TIDs. In the case if gravity waves in the thermosphere is the source of the observed TIDs, in-phase and out-of-phase relationships of neutral density and airglow intensity can be explained by different vertical wavelengths of the gravity wave. We estimate possible vertical wavelengths for those events using observed wave parameters and modeled neutral winds.

  15. Lightning-associated VLF perturbations observed at low latitude: Occurrence and scattering characteristics

    NASA Astrophysics Data System (ADS)

    Kumar, Sushil; Kumar, Abhikesh

    2013-01-01

    The occurrence of short-timescale (˜1-100 s) perturbations (early VLF events) on four Very Low Frequency (VLF) transmitter signals (call signs: NWC, NPM, VTX, NLK), recorded at Suva (18.1°S, 178.5°E, L = 1.16), shows the most frequent occurrence on the NWC signal and least on the VTX. Daytime early/fast events on the NWC transmission are (0.2-0.5 dB) with only negative amplitude perturbations with comparatively lower recovery times (10-30 s) as compared with most nighttime events with amplitude perturbations of 0.2-1.5 dB and recovery times of 20-80 s. The World-Wide Lightning Location Network detected causative lightnings for 74 of 453 early VLF events out of which 54 (73%) were produced due to narrow-angle scattering, and by 20 (27%) due to wide-angle scattering. The recovery (decay) of the scattered amplitude of early/fast events on the NWC signal shows both exponential and logarithmic forms, but the linear correlation coefficient is better with a logarithm fit. The first observations of early/slow events in daylight propagation are presented. Initial results on early/fast events with unusually long recoveries (≥5 min) and strong perturbations (≥1 dB) indicate that they are mainly observed on the transmissions from NPM and NLK in the nighttime only, with rare occurrence on other transmissions. Such unusually long recovery of early/fast events may be associated with large ionic conductivity perturbations associated with gigantic jets.

  16. Long Term Observations of the low Latitude (1,1) Diurnal Migrating Tide From WINDII, HRDI and TIDI

    NASA Astrophysics Data System (ADS)

    Niciejewski, R.; Skinner, W.; Gell, D.; Cooper, M.; Marshall, A.; Killeen, T.; Solomon, S.; Wu, Q.; Ortland, D.; Drob, D.; Emmert, J.; Shepherd, G.; Zhang, S.; Solheim, B.

    2006-05-01

    The dominant feature in the global scale wind field in the low latitude mesosphere and lower thermosphere (MLT) region is the solar diurnal migrating tide, classically represented by the (1,1) Hough function. The meridional component of the horizontal neutral wind vector is relatively stable in this region making it possible to estimate the daily (1,1) amplitude and phase*. Observations of the MLT winds have been performed from satellite platforms by HRDI and WINDII (UARS) and by TIDI (TIMED) since September 1991 providing a unique and continuous global perspective of the classical (1,1) tide for nearly 15 years. This paper will describe new results from HRDI, WINDII, and TIDI of the daily and annual variation of the (1,1) tide. A long-term interannual variability is clear in the data sets with the amplitude of the (1,1) tide peaking near 100 m/s within a week of the March equinox in 1993, 1995, 1999, 2002, and 2004. Lesser peaks occur during intervening years as well as about two weeks following the September equinox. A secondary result that will be discussed is the correspondence between coincident (1,1) tide observations by different pairs of experiments (HRDI/WINDII) and (HRDI/TIDI). *Burrage, M. D., M. E. Hagan, W. R. Skinner, D. L. Wu, and P. B. Hays, Long-term variability in the solar diurnal tide observed by HRDI and simulated by the GSWM, Geophys. Res. Lett., 22, 2641, 1995.

  17. Short- and Long-Timescale Thermospheric Variability as Observed from OI 630.0 nm Dayglow Emissions from Low Latitudes

    NASA Technical Reports Server (NTRS)

    Pallamraju, Duggirala; Das, Uma; Chakrabarti, Supriya

    2011-01-01

    We carried out high-cadence (5 min) and high-spatial resolution (2deg magnetic latitude) observations of daytime OI 630.0 nm airglow emission brightness from a low-latitude station to understand the behavior of neutral dynamics in the daytime. The results indicate that the wave periodicities of 12.20 min, and 2 h exist over a wide spatial range of around 8deg-12deg magnetic latitudes. The 20.80 min periodicities in the dayglow seem to appear more often in the measurements closer to the magnetic equator and not at latitudes farther away. Further, periodicities in that range are found to be frequent in the variations of the equatorial electrojet (EEJ) strength as well. We show that wave periodicities due to the neutral dynamics, at least until around 8deg magnetic latitude, are influenced by those that affect the EEJ strength variation as well. Furthermore, the average daily OI 630.0 nm emission brightness over 3 months varied in consonance with that of the sunspot numbers indicating a strong solar influence on the magnitudes of dayglow emissions.

  18. Short- and Long-Timescale Thermospheric Variability as Observed from OI 630.0 nm Dayglow Emissions from Low Latitudes

    NASA Technical Reports Server (NTRS)

    Pallamraju, Duggirala; Das, Uma; Chakrabarti, Supriya

    2010-01-01

    We carried out high-cadence (5 min) and high-spatial resolution (2deg magnetic latitude) observations of daytime OI 630.0 nm airglow emission brightness from a low-latitude station to understand the behavior of neutral dynamics in the daytime. The results indicate that the wave periodicities of 12.20 min, and 2 h exist over a wide spatial range of around 8deg-12deg magnetic latitudes. The 20.80 min periodicities in the dayglow seem to appear more often in the measurements closer to the magnetic equator and not at latitudes farther away. Further, periodicities in that range are found to be frequent in the variations of the equatorial electrojet (EEJ) strength as well. We show that wave periodicities due to the neutral dynamics, at least until around 8deg magnetic latitude, are influenced by those that affect the EEJ strength variation as well. Furthermore, the average daily OI 630.0 nm emission brightness over 3 months varied in consonance with that of the sunspot numbers indicating a strong solar influence on the magnitudes of dayglow emissions.

  19. Field-aligned current associated with low-latitude plasma blobs as observed by the CHAMP satellite

    NASA Astrophysics Data System (ADS)

    Park, J.; Lühr, H.; Stolle, C.; Rother, M.; Min, K. W.; Michaelis, I.

    2010-03-01

    Here we give two examples of low-latitude plasma blobs accompanied by linearly polarized perpendicular magnetic deflections which imply that associated field-aligned currents (FACs) have a 2-D sheet structure located at the blob walls. The estimated FAC density is of the order of 0.1 μA/m2. The direction of magnetic deflections points westward of the magnetic meridian and there is a linear correlation between perpendicular and parallel variations. All these properties are similar to those of equatorial plasma bubbles (EPBs). According to CHAMP observations from August 2000 to July 2004, blobs show except for these two good examples no clear signatures of 2-D FAC sheets at the walls. Generally, perpendicular magnetic deflections inside blobs are weaker than inside EPBs on average. Our results are consistent with existing theories: if a blob exists, (1) a significant part of EPB FAC will be closed through it, exhibiting similar perpendicular magnetic deflection inside EPBs and blobs, (2) the FAC closure through blobs leads to smaller perpendicular magnetic deflection at its poleward/downward side, and (3) superposition of different FAC elements might result in a complex magnetic signature around blobs.

  20. Observations of the coupling efficiency of VLF lightning-generated whistlers into the low-latitude plasmasphere

    NASA Astrophysics Data System (ADS)

    Jacobson, A. R.; Holzworth, R. H., II; Pfaff, R. F., Jr.; Heelis, R. A.

    2014-12-01

    The C/NOFS satellite [de La Beaujardiere, 2004] has provided a vast archive of multi-sensor data on the low-latitude ionosphere/plasmasphere since 2008. As part of the project, the VEFI payload [Pfaff et al., 2010] has recorded the 3-D electric field from DC through 16 kHz with high fidelity. The relative calibrations track between the three E-field antennas with sufficient accuracy and stability to allow retrieval of the wave polarization for a wide range of lightning-generated whistler waves [Jacobson et al., 2014]. The wave polarization in turn allows retrieval of the wavevector (within a sign ambiguity), which in turn allows an inverse-raytrace of the whistler raypath from the satellite to the ionospheric entry point. We will compare the raytrace predictions with ground-truth from the WWLLN global lightning-monitoring system [Lay et al., 2004; Rodger et al., 2005; Rodger et al., 2004]. In addition to providing location and time of lightning strokes, WWLLN provides an estimate of the radiated radio energy in the whistler passband [Hutchins et al., 2012]. Finally, the CINDI payload [Heelis et al., 2009] on C/NOFS provides ion composition at the satellite, permitting the index of refraction to be inferred. We will compare these estimates to the Poynting fluence density observed by VEFI, thereby providing a direct test of the coupling of lightning radio energy into plasmaspheric whistlers.

  1. A widespread low-latitude diurnal CO2 frost cycle on Mars revealed by Mars Climate Sounder observations

    NASA Astrophysics Data System (ADS)

    Piqueux, S.; Kleinboehl, A.; Hayne, P. O.; Kass, D. M.; McCleese, D. J.; Shirley, J. H.; Schofield, J. T.; Heavens, N. G.

    2015-12-01

    Surface observations by the Mars Climate Sounder (MCS) onboard the Mars Reconnaissance Orbiter document the widespread occurrence of atmospherically-corrected ground temperatures consistent with the presence of extensive CO2 frost deposits at low latitudes at 3AM. While the detection of CO2 ice has previously been reported outside the polar regions, in discrete locations associated with very high elevation terrains (i.e. associated with Elysium, Olympus Mons and the Tharsis Montes), our observations provide the first observational evidence of a global-scale diurnal CO2 cycle involving the atmosphere and the surface. MCS surface temperatures consistent with the presence of ephemeral diurnal CO2 frost deposits are strongly correlated with geologic terrains characterized by high emissivity, high albedo, and low thermal inertia. All of these properties are conducive to low nighttime temperatures. Thermal modeling of these low inertia terrains (i.e. < 75 J m-2K-1s-1/2), which cover a large fraction of the Martian surface, confirms that the regolith frequently reaches CO2 frost point temperatures at all latitudes near 3AM, with seasonal variations noticed. In addition, models used in conjunction with MCS temperature retrievals also predict that right before sunrise, nearly all of the Martian dusty low thermal inertia units are frosted at some point during the Mars Year. Energy/mass balance modeling suggests deposits with depths of up to several hundreds of microns of CO2 (<<0.1% of the Martian atmosphere). This is not sufficient to generate a measurable diurnal pressure cycle. The discovery of this diurnal CO2 cycle may nonetheless represent an important step forward in our understanding of the way the Mars atmosphere interacts with the surface.

  2. Semi-empirical low-latitude ionospheric model

    SciTech Connect

    Anderson, D.N.; Mendillo, M.; Herniter, B.

    1987-04-01

    Since current empirical models specifying low-latitude electron-density profiles severely underestimate the daytime plasma scale height and total electron content (TEC) values, a semiempirical low-latitude ionospheric model (SLIM) was developed that is not only computationally fast, but also more realistic. Electron-density profiles (180-1800 km) are theoretically calculated as a function of latitude (every 2 deg between 24 N and 24 S dip latitude) and local time (every half hour, over 24 hours LT) by solving the time-dependent plasma-continuity equation. Using simple exponential functions, sets of coefficients themselves are easily stored. quickly retrieved and form the basis for a fast, portable, semi-empirical computer code. This paper describes briefly the input parameters used to theoretically calculate the profiles and the procedures used to generate the coefficients. The SLIM profiles are compared with the Chiu and Bent empirical models for equinox, solar maximum conditions, while calculated at 6300 A airglow intensities and TEC values are compared with available observations. The SLIM profiles, their coefficients, TEC and 6300 A airglow intensities are available in tabular and computer formats.

  3. Observational evidence for plasma diffusion driven by Kelvin-Helmholtz vortices at the duskside of the low latitude boundary layer

    NASA Astrophysics Data System (ADS)

    Yan, G.; Mozer, F.; Shen, C.; Phan, T.; Parks, G. K.; McFadden, J. P.; Rème, H.; Chen, T.

    2015-12-01

    By revisiting two Kelvin-Helmholtz (K-H) vortex events under northward (Hasegawa et al, 2004) and southward (Yan et al, 2014) interplanetary magnetic field (IMF) observed by Cluster and THEMIS respectively, we investigated the ion density gradient at the dusk flank magnetopause with K-H vortices, by using the technique developed by Shen et al (2012) which can calculate the spatial gradient of a physical quantity even when only three-point simultaneous measurements are available or the tetrahedron is highly distorted. With three-point simultaneous observations, two components of the ion density gradient can be calculated in the vortex plane. In the results, we find that: (1) under either northward or southward IMF, cold dense plasma was found in the Kelvin-Helmholtz (K-H) vortices even when the IMF was southward; (2) in both events, there existed an ion density gradient as large as 0.5 cm-3/Mm for southward IMF and 2.0 cm-3/Mm for southward IMF alongside with K-H vortices in the low latitude boundary layer (LLBL); (3) the dominant direction of the ion density gradient in the vortex plane pointed outward to the magnetopause when the gradient is defined as the increasing direction; (4) in both events, the ion density gradient has positive correlation with the vorticity calculated by the same technique. The ion density gradient driven by K-H vortices indicates that plasma diffusion plays an important role as the micro-physical process of plasma transport into the magnetosphere directly through the LLBL with K-H vortices.

  4. Characterization of Vertical and Horizontal Wave Features in Dayglow Emissions as Observed from a Low-latitude Station, Hyderabad, INDIA.

    NASA Astrophysics Data System (ADS)

    Islam Laskar, Fazlul; Pallamraju, Duggirala; Chakrabarti, Supriya; Raghavarao, Ravipati; Vijaya Lakshmi, Thatiparthi; Anji Reddy, M.

    2012-07-01

    Due to the unique geomagnetic field configuration, equatorial upper atmosphere of the earth is affected by various electro-dynamical processes, such as, equatorial electrojet (EEJ), equatorial ionization anomaly (EIA), equatorial spread-F (ESF), equatorial temperature and wind anomaly (ETWA). Each of these processes leave their imprint on both the neutral and ionised components of the upper atmosphere. The plasma dynamics can be investigated by radio probing methods. Investigations on the neutral dynamics, however, are possible mainly through the optical measurements. As these phenomena spread over a large spatial extent, it is extremely important to measure their variability over a large field-of-view. Here, we present the results of the wave characteristics observed over a low latitude location, Hyderabad (Geographic: 17.5° N, 78.5° E; Geomagnetic: 8.6° N, 151.8° E), which were obtained using a high spectral-resolution multi-wavelength echelle-grating spectrograph. This instrument obtains oxygen dayglow emissions at 557.7 nm, 630.0 nm, and 777.4 nm wavelengths over a large field-of-view ( of about 140 degrees) that originate from peak altitudes of around 130 km, 230 km, and 300 km, respectively. Initial results from a total of 52 days of data reveal that the dominant wave periodicities in the intensities of these emissions are different for different emission heights. Significant latitudinal dependency is seen in case of 557.7 nm and 630.0 nm. The latitudinal behavior of the emissions show the influence of both the neutral dynamics and electrodynamics of the equatorial origin. The emission variabilities are compared with the empirical and physics based models to discern the dynamical component in them in order to understand the nature of the vertical coupling of atmospheric regions. These results will be presented in light of the electrodynamic effects on them.

  5. Towards Observing Tsunamis in the Ionosphere Using GPS TEC Measurements

    NASA Astrophysics Data System (ADS)

    Galvan, D. A.; Komjathy, A.; Mannucci, A.; Hickey, M. P.; Schubert, G.; Walterscheid, R. L.; Occhipinti, G.

    2009-12-01

    Recent modeling results and observations have demonstrated that the ionospheric signature of an ocean tsunami can potentially be detected as a traveling ionospheric disturbance (TID) produced by internal gravity waves propagating upward in the atmosphere [e.g., Hickey et al., (2009), Occhipinti et al., (2006)]. These tsunamigenic TID’s have been demonstrated to be present in total electron content (TEC) measurements using ground-based GPS radio signals [e.g., Artru et al., (2005)] and satellite-based altimeter radar [Occhipinti et al., (2006)]. There are many remaining unanswered questions regarding the reliability of detecting tsunamigenic TIDs, including how to distinguish them from TIDs of non-tsunamigenic origin, as well as factors affecting the propagation of internal gravity waves in the ionosphere. We present ongoing research analyzing ground-based GPS TEC observations during multiple known tsunami events. Specifically, fluctuations in TEC are obtained by comparing observed TEC with modeled TEC estimates using JPL’s Global Ionospheric Mapping (GIM) system. These small fluctuations are then band-passed filtered and Fourier analyzed, across multiple GPS satellites and ground stations, to search for wave patterns similar to the coincident ocean tsunami in the same geographic region. Results are discussed in terms of the degree to which a tsunamigenic TID is observed in each case, and the possible causes for failing to observe them. Comparisons between observations and results from theoretical models of tsunamigenic ionospheric wave propagation are also discussed for specific cases.

  6. Comparison of IRI-2012 with JASON-1 TEC and incoherent scatter radar observations during the 2008-2009 solar minimum period

    NASA Astrophysics Data System (ADS)

    Ji, Eun-Young; Jee, Geonhwa; Lee, Changsup

    2016-08-01

    The 2008-2009 solar minimum period was unprecedentedly deep and extended. We compare the IRI-2012 with global TEC data from JASON-1 satellite and with electron density profiles observed from incoherent scatter radars (ISRs) at middle and high latitudes for this solar minimum period. Global daily mean TECs are calculated from JASON-1 TECs to compare with the corresponding IRI TECs during the 2008-2009 period. It is found that IRI underestimates the global daily mean TEC by about 20-50%. The comparison of global TEC maps further reveals that IRI overall underestimates TEC for the whole globe except for the low-latitude region around the equatorial anomaly, regardless of season. The underestimation is particularly strong in the nighttime winter hemisphere where the ionosphere seems to almost disappear in IRI. In the daytime equatorial region, however, the overestimation of IRI is mainly due to the misrepresentation of the equatorial anomaly in IRI. Further comparison with ISR electron density profiles confirms the significant underestimation of IRI at night in the winter hemisphere.

  7. Study of total electron content variations over equatorial and low latitude ionosphere during extreme solar minimum

    NASA Astrophysics Data System (ADS)

    Sharma, Kavita; Dabas, R. S.; Ravindran, Sudha

    2012-10-01

    In recent years with the advancement in satellite based navigational applications, study of Total Electron Content (TEC) has gained significant importance. It is well known that due to dynamical behaviour of equatorial and low latitude ionosphere, the levels of ionization is relatively high herein. The sustained decrease in solar extreme ultraviolet radiations during the current minimum is greater than any in recent history. This gives us the opportunity to study the observations of global positioning system total electron content (GPS-TEC) dual frequency signals from the GPS satellites continuously recorded at Trivandrum (an equatorial station) and Delhi (a low latitude station) during the extremely low solar activity period from January 2007 to June 2009. This study illustrates the diurnal, seasonal and annual variations of TEC during the extended solar minimum period. This study also investigates the behaviour of daytime ionosphere around spring and autumn equinoxes at low solar activity period. The results clearly reveal the presence of equinoctial asymmetry which is more pronounced at equatorial station Trivandrum. The diurnal variation of TEC shows a short-lived day minimum which occurs between 0500 to 0600 LT at both the stations. Delhi TEC values show its steep increase and reach at its peak value between 1200 and 1400 LT, while at the equator the peak is broad and occurs around 1600 LT. Further, the daily maximum TEC ranges from about 5 to 40 TEC units at Trivandrum and about 10 to 40 TEC units at Delhi, which correspond to range delay variations of about 1 to 8 m at the GPS L1 frequency of 1.575 GHz. The Maximum values of TEC were observed during spring equinox rather than autumn equinox, showing presence of semi annual variation at both the locations. The minimum values of TEC were observed during the summer solstice at Trivandrum indicating the presence of winter anomaly at equatorial region while Delhi TEC values were minimum during winter solstice

  8. Low Latitude Aurora: Index of Solar Activity

    NASA Astrophysics Data System (ADS)

    Bekli, M. R.; Aissani, D.; Chadou, I.

    2010-10-01

    Observations of aurora borealis at low latitudes are rare, and are clearly associated with high solar activity. In this paper, we analyze some details of the solar activity during the years 1769-1792. Moreover, we describe in detail three low latitude auroras. The first event was reported by ash-Shalati and observed in North Africa (1770 AD). The second and third events were reported by l'Abbé Mann and observed in Europe (1770 and 1777 AD).

  9. Low-latitude ionospheric effects on SBAS

    NASA Astrophysics Data System (ADS)

    Arenas, J.; Sardón, E.; Sainz, A.; Ochoa, B.; Magdaleno, S.

    2016-06-01

    Satellite-based augmentation systems (SBAS) provide augmentation to Global Navigation Satellite Systems (GNSS) users in three areas: (1) broadcasting accurate corrections to GNSS satellite ephemeris, (2) providing a real-time empirical ionospheric model in the service area, and (3) providing integrity information in the form of estimates of the confidence of the ephemeris corrections and ionospheric delays. Ionospheric effects on SBAS are twofold: (a) the input data used by the SBAS will be affected by ionospheric effects, and (b) the more perturbed the ionosphere is, the more difficult it will be to provide accurate and reliable ionospheric information to the users. The ionosphere at low latitudes presents larger variability and more intense phenomena than at midlatitudes. Therefore, SBAS providing service to low-latitude regions will be more affected than those at other latitudes. From the different low-latitude ionospheric effects, this paper will focus on those having the largest impact on SBAS, which are total electron content temporal and spatial gradients, ionospheric scintillations, and depletions. This paper will present the impact of these effects on EGNOS (European Global Navigation Overlay System), the European SBAS. Although EGNOS can be considered as a midlatitude SBAS, it has to provide coverage down to rather low latitudes, so sometimes low-latitude ionospheric effects are observed in the EGNOS data. It will be shown how EGNOS performs under nominal conditions and how its performance is degraded when low-latitude ionospheric phenomena occur. Real EGNOS data affected by low-latitude ionospheric phenomena will be used.

  10. Persistent Longitudinal Variations of Plasma Density and DC Electric Fields in the Low Latitude Ionosphere Observed with Probes on the C/NOFS Satellite

    NASA Technical Reports Server (NTRS)

    Pfaff, R.; Freudenreich, H.; Klenzing, J.; Rowland, D.; Liebrecht, C.; Bromund, K.; Roddy, P.

    2010-01-01

    Continuous measurements using in situ probes on consecutive orbits of the C/N0FS satellite reveal that the plasma density is persistently organized by longitude, in both day and night conditions and at all locations within the satellite orbit, defined by its perigee and apogee of 401 km and 867 km, respectively, and its inclination of 13 degrees. Typical variations are a factor of 2 or 3 compared to mean values. Furthermore, simultaneous observations of DC electric fields and their associated E x B drifts in the low latitude ionosphere also reveal that their amplitudes are also strongly organized by longitude in a similar fashion. The drift variations with longitude are particularly pronounced in the meridional component perpendicular to the magnetic field although they are also present in the zonal component as well. The longitudes of the peak meridional drift and density values are significantly out of phase with respect to each other. Time constants for the plasma accumulation at higher altitudes with respect to the vertical drift velocity must be taken into account in order to properly interpret the detailed comparisons of the phase relationship of the plasma density and plasma velocity variations. Although for a given period corresponding to that of several days, typically one longitude region dominates the structuring of the plasma density and plasma drift data, there is also evidence for variations organized about multiple longitudes at the same time. Statistical averages will be shown that suggest a tidal "wave 4" structuring is present in both the plasma drift and plasma density data. We interpret the apparent association of the modulation of the E x B drifts with longitude as well as that of the ambient plasma density as a manifestation of tidal forces at work in the low latitude upper atmosphere. The observations demonstrate how the high duty cycle of the C/NOFS observations and its unique orbit expose fundamental processes at work in the low latitude

  11. Evidence of low-latitude daytime large-scale traveling ionospheric disturbances observed by high-frequency multistatic backscatter sounding system during a geomagnetically quiet period

    NASA Astrophysics Data System (ADS)

    Zhou, Chen; Zhao, Zhengyu; Yang, Guobin; Chen, Gang; Hu, Yaogai; Zhang, Yuannong

    2012-06-01

    Observations from the high-frequency multistatic backscatter sounding radars on a geomagnetically quiet day (minimum Dst = -14 nT) captured the anti-equatorward propagation of daytime large-scale traveling ionospheric disturbance (LSTID) at the low-latitude regions. The observed LSTID was characterized approximately by a meridional propagation speed of 347 ± 78 m/s and azimuthal angle of -4.7 ± 27.6° (counterclockwise from north), with a period of 76 min and a wavelength of 1583 ± 354 km by means of maximum entropy cross-spectral analysis. Vertical phase velocity was also evaluated to be <˜42 m/s through the Doppler measurements. These results provide evidence that the low-latitude ionosphere can undergo large-scale perturbations even under geomagnetically quiet conditions. We suggest that this observed LSTID could be due to the secondary gravity waves from thermospheric body forces created from the dissipation of primary gravity waves from deep tropospheric convection.

  12. Identifying Kinetic Plasma Wave Modes Observed in the Acceleration Regions in the Low-Latitude Boundary Layer.

    NASA Astrophysics Data System (ADS)

    Moore, T.; Nykyri, K.; Dimmock, A. P.

    2015-12-01

    Understanding plasma heating and transport across fluid, ion and electron scales is currently not well understood in astrophysical plasmas. We have recently identified (by determining the observational dispersion relation using multi-point spacecraft measurements) an ion-scale, large amplitude fast mode wave observed inside a fluid-scale Kelvin-Helmholtz vortex. The Poyinting flux of the fast mode wave packet was sufficient to produce the observed ~5 keV energy increase of ions of magnetosheath origin. In this followup work, we analyze in detail the other intervals with similar characteristics, where the cold magnetosheath population becomes significantly energized. We identify the plasma wave modes present and discuss whether their energy budget is sufficient for the observed level of energization.

  13. Analysis of local ionospheric variability based on SVD and MDS at low-latitude GNSS stations

    NASA Astrophysics Data System (ADS)

    Dabbakuti, J. R. K. Kumar; Devanaboyina, Venkata Ratnam; Kanchumarthi, S. Ramesh

    2016-06-01

    Investigation of ionospheric anomalies during equatorial and low latitude is of major concern for modeling and global navigation satellite system (GNSS) applications. Total electron content (TEC) varies with the ionospheric conditions, which will lead to the errors in the global positioning system (GPS) measurements. It is therefore a method that is necessary to characterize the ionospheric anomalies for satellite-based navigation systems. In this study, characterization of ionospheric variations based on the singular value decomposition (SVD) and classical multidimensional scaling (MDS) methods was studied. The yearly and daily variations are decomposed from the GPS-TEC, international reference ionosphere (IRI) 2007 and IRI 2012 models TEC over the three low-latitude GNSS stations located at Koneru Lakshmaiah University (KLU-Guntur), Hyderabad and Bangalore, respectively. From the results, it is found that there is a strong correlation between GPS-TEC and IRI models. The correlation coefficient for the first three singular values is more than 0.86. From this, it is possible to reconstruct more than 85 % of the variability contained in global GPS-derived VTEC data (for year 2013) by using only the first three modes. The semiannual variation has maximum value during March-April and September-October and has minimum value during June-July. It is observed that the annual variations have maximum value in summer and minimum value in winter, and the amplitudes decrease with increasing latitude. Further, opposite latitudinal asymmetry among annual and semiannual variations for three GNSS stations is noticed. SVD and MDS methods clearly show time-varying characteristics and the absence of the winter anomaly at low-latitude GNSS stations.

  14. DMSP F8 observations of the mid-latitude and low-latitude topside ionosphere near solar minimum

    SciTech Connect

    Greenspan, M.E.; Hughes, W.J. |; Burke, W.J.; Rich, F.J.; Heelis, R.A.

    1994-03-01

    The retarding potential analyzer on the DMSP F8 satellite measured ion density, composition, temperature, and ram flow velocity at 840-km altitude near the dawn and dusk meridians close to solar minimum. Nine days of data were selected for study to represent the summer and winter solstices and the autumnal equinox under quiet, moderately active, and disturbed geomagnetic conditions. The observations revealed extensive regions of light-ion dominance along both the dawn and dusk legs of the DMSP F8 orbit. These regions showed seasonal, longitudinal, and geomagnetic control, with light ions commonly predominating in places where the subsatellite ionosphere was relatively cold. Field-aligned plasma flows also were detected. In the morning, ions flowed toward the equator from both sides. In the evening, DMSP F8 detected flows that either diverged away from the equator or were directed toward the northern hemisphere. The effects of diurnal variations in plasma pressure gradients in the ionosphere and plasmasphere, momentum coupling between neutral winds and ions at the feet of field lines, and E {times} B drifts qualitatively explain most features of these composition and velocity measurements. 23 refs., 5 figs., 2 tabs.

  15. Ionosonde observations of F region parameters over Indian low latitude during different solar activity conditions and comparison with IRI model

    NASA Astrophysics Data System (ADS)

    Peddapati, PavanChaitanya; Patra, Amit

    2016-07-01

    In the equatorial region, the daytime F region exhibits three layers, namely F1, F2 and F3 layers. The detail characteristics of the F2 and F3 layers and their variabilities at different equatorial latitudes, however, have not been well defined. Given the fact that equatorial ionosphere is governed profoundly by dynamical and electro-dynamical forcing, electron density varies remarkably with latitude and altitude. A detailed characterization and study of the equatorial F region, thus, is necessary for improving ionospheric model, such as International Reference Ionosphere (IRI), applicable to the equatorial region. For this purpose, we have analyzed ionosonde observations from the dip equator and low magnetic latitude in the Indian sector to characterize the F2 and F3 layers in different seasons and solar activity conditions. In this paper, we present a detailed comparative analysis on the variabilities of the F2 and F3 layers as a function of local time, season and solar activity conditions. Finally, these results are compared with the IRI model parameters in an effort to evaluate the suitability of the IRI model representing the equatorial ionosphere in the Indian sector.

  16. Investigation of Ionospheric response to Geomagnetic Storms over a Low Latitude Station, Ile-Ife, Nigeria

    NASA Astrophysics Data System (ADS)

    Jimoh, Oluwaseyi E.; Yesufu, Thomas K.; Ariyibi, Emmanuel A.

    2016-05-01

    Due to several complexities associated with the equatorial ionosphere, and the significant role which the total electron content (TEC) variability plays in GPS signal transmission, there is the need to monitor irregularities in TEC during storm events. The GPS SCINDA receiver data at Ile-Ife, Nigeria, was analysed with a view to characterizing the ionospheric response to geomagnetic storms on 9 March and 1 October 2012. Presently, positive storm effects, peaks in TEC which were associated with prompt penetration of electric fields and changes in neutral gas composition were observed for the storms. The maximum percentage deviation in TEC of about 120 and 45% were observed for 9 March and 1 October 2012, respectively. An obvious negative percentage TEC deviation subsequent to sudden storm commencement (SSC) was observed and besides a geomagnetic storm does not necessarily suggest a high scintillation intensity (S4) index. The present results show that magnetic storm events at low latitude regions may have an adverse effect on navigation and communication systems.

  17. Intensity of low-latitude nighttime F-region ionospheric density irregularities observed by ROCSAT and ground-based GPS receivers in solar maximum

    NASA Astrophysics Data System (ADS)

    Sun, Yang-Yi; Liu, Jann-Yenq; Chao, Chi-Kuang; Chen, Chia-Hung

    2015-02-01

    This study examines the global correlation between the instantaneous total amplitude of ion density fluctuations observed by ROCSAT and the phase fluctuation of the total electron content (TEC) recorded by worldwide ground-based Global Positioning System (GPS) receivers during the high solar activity period of March 1999-December 2002 for Kp<3. The Hilbert-Huang transform (HHT) is applied to compute the instantaneous total amplitude of ROCSAT ion densities. The event-based and climatological comparisons of the total amplitude and occurrence probability of irregularities observed by ROCSAT show that the total amplitude can reveal both the occurrence probability of irregularities and the associated intensity. The noise level of the total amplitude is about 103.5 (near 3000) ions/cm3. The high correlation (correlation coefficient=0.81) between the GPS TEC phase fluctuation index FP and instantaneous total amplitude of ROCSAT electron densities suggests that the total amplitude can be used to globally monitor the intensity of irregularities at equatorial and within the latitude belt of ±15°. The relationship between the ionospheric background ionization and the irregularity intensity is further investigated.

  18. Low-latitude ionospheric effects of energetic electrons during a recurrent magnetic storm

    NASA Astrophysics Data System (ADS)

    Suvorova, A. V.; Huang, C.-M.; Matsumoto, H.; Dmitriev, A. V.; Kunitsyn, V. E.; Andreeva, E. S.; Nesterov, I. A.; Tsai, L.-C.

    2014-11-01

    We study a magnetosphere-ionosphere coupling at low latitudes during a moderate (corotating interaction regions/high-speed solar wind streams-driven) geomagnetic storm on 22 July 2009. Recently, it has been shown that during major (coronal mass ejection-driven) storms, quasi-trapped >30 keV electrons largely enhance below the radiation belt in the forbidden zone and produce an additional ionization in the topside ionosphere. In this work, we examine a case of the recurrent storm when the magnetosphere-ionosphere coupling through the quasi-trapped electrons also may take place. Data from NOAA/Polar-orbiting Operational Environmental Satellite and Japanese Greenhouse gases Observing Satellite were used to identify the forbidden electron enhancement (FEE). We find a positive vertical gradient of the electron fluxes that indicates to the radiation belt as a source of FEE. Using global ionospheric maps, radiotomography reconstructions from beacon data and COSMIC/FORMOSAT-3 radio occultation measurements, we have observed an unusually large area in the nighttime ionosphere with increased total electron content (TEC) and prominent elevation of the F layer at low latitudes that coincides with FEEs spatially and temporarily. Ionizing particles are considered as an addition source of ionization along with generally accepted mechanisms for storm time TEC increase (a positive ionospheric storm). We discuss relative contributions of the FEE and disturbance dynamo electric field in the TEC increases during the storm recovery phase.

  19. Recent Plasma Observations Related to Magnetic Merging and the Low-Latitude Boundary Layer. Case Study by Polar, March 18, 2006

    NASA Technical Reports Server (NTRS)

    Chandler, M.; Avanov, L.; Craven, P.; Mozer, F.; Moore, T. E.

    2007-01-01

    We have begun an investigation of the nature of the low-latitude boundary layer in the mid-altitude cusp region using data from the Polar spacecraft. Magnetosheath-like plasma is frequently observed deep (in terms of distance from the magnetopause and in invariant latitude) in the magnetosphere. One such case, taken during a long period of northward interplanetary magnetic field (IMP) on March 18, 2006, shows injected magnetosheath ions within the magnetosphere with velocity distributions resulting from two separate merging sites along the same field lines. Cold ionospheric ions were also observed counterstreaming along the field lines, evidence that these field lines were closed. Our results support the idea of double reconnection under northward IMP on the same group of field lines can provide a source for the LLBL. However, the flow direction of the accelerated magnetosheath ions antiparallel to the local magnetic field and given location of the spacecraft suggest that these two injection sites are located northward of the spacecraft position. Observed convection velocities of the magnetic field lines are inconsistent with those expected for double post-cusp reconnection in both hemispheres. These observations favor a scenario in which a group of newly closed field lines was created by a combination of high shear merging at high latitudes in the northern hemisphere and low shear merging at lower latitudes at the dayside magnetopause.

  20. Observing Traveling Ionospheric Disturbances Caused by Tsunamis Using GPS TEC Measurements

    NASA Technical Reports Server (NTRS)

    Galvan, David A.; Komjathy, Attila; Hickey, Michael; Foster, James; Mannucci, Anthony J.

    2010-01-01

    Ground-based Global Positioning System (GPS) measurements of ionospheric Total Electron Content (TEC) show variations consistent with atmospheric internal gravity waves caused by ocean tsunamis following two recent seismic events: the American Samoa earthquake of September 29, 2009, and the Chile earthquake of February 27, 2010. Fluctuations in TEC correlated in time, space, and wave properties with these tsunamis were observed in TEC estimates processed using JPL's Global Ionospheric Mapping Software. These TEC estimates were band-pass filtered to remove ionospheric TEC variations with wavelengths and periods outside the typical range of internal gravity waves caused by tsunamis. Observable variations in TEC appear correlated with the tsunamis in certain locations, but not in others. Where variations are observed, the typical amplitude tends to be on the order of 1% of the background TEC value. Variations with amplitudes 0.1 - 0.2 TECU are observable with periods and timing affiliated with the tsunami. These observations are compared to estimates of expected tsunami-driven TEC variations produced by Embry Riddle Aeronautical University's Spectral Full Wave Model, an atmosphere-ionosphere coupling model, and found to be in good agreement in some locations, though there are cases when the model predicts an observable tsunami-driven signature and none is observed. These TEC variations are not always seen when a tsunami is present, but in these two events the regions where a strong ocean tsunami was observed did coincide with clear TEC observations, while a lack of clear TEC observations coincided with smaller tsunami amplitudes. There exists the potential to apply these detection techniques to real-time GPS TEC data, providing estimates of tsunami speed and amplitude that may be useful for early warning systems.

  1. TEC variations over Europe during the solar eclipse of March 20, 2015 using GLONASS observations

    NASA Astrophysics Data System (ADS)

    Shagimuratov, Irk; Cherniak, Iurii; Krankowski, Andrzej; Zakharenkova, Irina; Yakimova, Galina; Tepenitzina, Nadezhda

    2016-07-01

    We report the features of the ionospheric TEC variations derived from the GLONASS measurements during the partial solar eclipse of March 20, 2015. Over Europe the maximal phase of the eclipse was observed around 10 UT. The eclipse took place during period when the ionosphere changed from night to day conditions. This eclipse occurred on the recovery phase of the strong geomagnetic storm of March 17, 2015. The effect of the eclipse was detected in diurnal variations of TEC over the individual GNSS stations as a trough-like variation with a gradual decrease and a succeeding increase of TEC at the time of the eclipse. The eclipse effect on the TEC distribution was observed more distinctly along individual satellite passes. Over the Kaliningrad GNSS station (54N, 20E) we registered the maximal TEC depression of about 4-6 TECU along several satellite passes. We should note that analysis of the ionospheric effects of the solar eclipse was complicated by the geomagnetic storm of March 17. The superposition of the storm and the eclipse make it difficult to separate the absolute TEC changes caused by the eclipse. At the same time the strong changes of the spatial structure of the TEC distribution were registered on the TEC maps. To analyze the spatial TEC distribution during the eclipse the TEC maps with high spatial-temporal resolution were produced. We used the GLONSS measurements derived from 150-180 stations of the dense European GNSS network. Dynamics of the ionospheric plasma density was analyzed using the mixture GLONASS-GPS TEC maps produced with 5 min sampling rate. The spatial structure of the ionosphere changed essentially during the eclipse comparing with the control days. The occurred TEC gradients were quite different comparing with previous and subsequent days. The complex pattern in the spatial-temporal TEC distribution highlights the important role of the dynamic processes in the ionosphere during the eclipse.

  2. Low-latitude ionosphere response to super geomagnetic storm of 17/18 March 2015: Results from a chain of ground-based observations over Indian sector

    NASA Astrophysics Data System (ADS)

    Ramsingh; Sripathi, S.; Sreekumar, Sreeba; Banola, S.; Emperumal, K.; Tiwari, P.; Kumar, Burudu Suneel

    2015-12-01

    In this paper, we present unique results of equatorial and low-latitude ionosphere response to one of the major geomagnetic storms of the current solar cycle that occurred during 17-18 March 2015, where Dst reached its minimum of -228 nT. Here we utilized data from magnetometers, chain of ionosondes located at Tirunelveli (8.73°N, 77.70°E; geometry: 0.32°N), Hyderabad (17.36°N, 78.47°E; geometry 8.76°N), and Allahabad (25.45°N, 81.85°E; geometry 16.5°N) along with multistation GPS receivers over Indian sector. The observations showed a remarkable increase of h'F to as high as ~560 km over Tirunelveli (magnetic equator) with vertical drift of ~70 m/s at 13:30 UT due to direct penetration of storm time eastward electric fields which exactly coincided with the local time of pre-reversal enhancement (PRE) and caused intense equatorial spread F irregularities in ionosondes and scintillations in GPS receivers at wide latitudes. Plasma irregularities are so intense that their signatures are seen in Allahabad/Lucknow. Storm time thermospheric meridional winds as estimated using two ionosondes suggest the equatorward surge of gravity waves with period of ~2 h. Suppression of anomaly crest on the subsequent day of the storm suggests the complex role of disturbance dynamo electric fields and disturbance wind effects. Our results also show an interesting feature of traveling ionospheric disturbances possibly associated with disturbance meridional wind surge during recovery phase. In addition, noteworthy observations are nighttime westward zonal drifts and PRE-related total electron content enhancements at anomaly crests during main phase and counter electrojet signatures during recovery phase.

  3. Middle- and low-latitude ionosphere response to 2015 St. Patrick's Day geomagnetic storm

    NASA Astrophysics Data System (ADS)

    Nava, B.; Rodríguez-Zuluaga, J.; Alazo-Cuartas, K.; Kashcheyev, A.; Migoya-Orué, Y.; Radicella, S. M.; Amory-Mazaudier, C.; Fleury, R.

    2016-04-01

    This paper presents a study of the St Patrick's Day storm of 2015, with its ionospheric response at middle and low latitudes. The effects of the storm in each longitudinal sector (Asian, African, American, and Pacific) are characterized using global and regional electron content. At the beginning of the storm, one or two ionospheric positive storm effects are observed depending on the longitudinal zones. After the main phase of the storm, a strong decrease in ionization is observed at all longitudes, lasting several days. The American region exhibits the most remarkable increase in vertical total electron content (vTEC), while in the Asian sector, the largest decrease in vTEC is observed. At low latitudes, using spectral analysis, we were able to separate the effects of the prompt penetration of the magnetospheric convection electric field (PPEF) and of the disturbance dynamo electric field (DDEF) on the basis of ground magnetic data. Concerning the PPEF, Earth's magnetic field oscillations occur simultaneously in the Asian, African, and American sectors, during southward magnetization of the Bz component of the interplanetary magnetic field. Concerning the DDEF, diurnal magnetic oscillations in the horizontal component H of the Earth's magnetic field exhibit a behavior that is opposed to the regular one. These diurnal oscillations are recognized to last several days in all longitudinal sectors. The observational data obtained by all sensors used in the present paper can be interpreted on the basis of existing theoretical models.

  4. Accounting for observational uncertainties in the evaluation of low latitude turbulent air-sea fluxes simulated in a suite of IPSL model versions

    NASA Astrophysics Data System (ADS)

    Servonnat, Jerome; Braconnot, Pascale; Gainusa-Bogdan, Alina

    2015-04-01

    Turbulent momentum and heat (sensible and latent) fluxes at the air-sea interface are key components of the whole energetic of the Earth's climate and their good representation in climate models is of prime importance. In this work, we use the methodology developed by Braconnot & Frankignoul (1993) to perform a Hotelling T2 test on spatio-temporal fields (annual cycles). This statistic provides a quantitative measure accounting for an estimate of the observational uncertainty for the evaluation of low-latitude turbulent air-sea fluxes in a suite of IPSL model versions. The spread within the observational ensemble of turbulent flux data products assembled by Gainusa-Bogdan et al (submitted) is used as an estimate of the observational uncertainty for the different turbulent fluxes. The methodology holds on a selection of a small number of dominating variability patterns (EOFs) that are common to both the model and the observations for the comparison. Consequently it focuses on the large-scale variability patterns and avoids the possibly noisy smaller scales. The results show that different versions of the IPSL couple model share common large scale model biases, but also that there the skill on sea surface temperature is not necessarily directly related to the skill in the representation of the different turbulent fluxes. Despite the large error bars on the observations the test clearly distinguish the different merits of the different model version. The analyses of the common EOF patterns and related time series provide guidance on the major differences with the observations. This work is a first attempt to use such statistic on the evaluation of the spatio-temporal variability of the turbulent fluxes, accounting for an observational uncertainty, and represents an efficient tool for systematic evaluation of simulated air-seafluxes, considering both the fluxes and the related atmospheric variables. References Braconnot, P., and C. Frankignoul (1993), Testing Model

  5. Low Latitude Gravity Wave Variances in the MLT Derived from Saber Temperature Observation and Compared with Model Simulations of Waves Generated By Deep Tropical Convection

    NASA Astrophysics Data System (ADS)

    Walterscheid, R. L.; Christensen, A. B.

    2014-12-01

    Equatorial regions are the scene of prolific generation of gravity waves by deep tropical convection. Waves generated by deep convection have appreciable energy at frequencies and spatial scales that are able to reach altitudes in the Middle Atmosphere and Lower Thermosphere (MLT) and above where they may attain significant amplitudes. A portion of these waves have scales and amplitudes large enough to be detected by space borne instruments. We have analyzed temperature data from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the Thermosphere Ionosphere Mesosphere Energetics Dynamics (TIMED) satellite for sub-tidal scale fluctuations. Filtering was applied both vertically and horizontally to extract wave variances. We have examined the variances at equatorial latitudes for the altitude region between 70 and 120 km and have have characterized them as a function of season, local time intervals, geographical location and altitude. We find large variances in locations of where convection is particularly prolific (e.g., western South Pacific) and at altitudes where wave trapping is known to be favored (e.g., the lower thermospheric duct). The locations of significant variances persist from year to year. Variances of on the order of a few tens of degrees are found. We have also performed simulations of the response to deep tropical convection with the The Aerospace Corporation Dynamical Model (ADM). This model is a time dependent, high-resolution fully compressible dynamical model that has been used to examine the MLT wave response to intense cellular convection in northern Australia. The background thermal structure for the present simulations was obtained from TIMED/SABER data averaged over low latitudes by season and local time. Our simulations give wave amplitudes that agree reasonably well with the observed amplitudes and show layering that is consistent with the observations. We will show the results of our analysis of

  6. Modulation of the ionosphere by Pc5 waves observed simultaneously by GPS/TEC and EISCAT

    NASA Astrophysics Data System (ADS)

    Belakhovsky, V.; Pilipenko, V.; Murr, D.; Fedorov, E.; Kozlovsky, A.

    2016-06-01

    Earlier studies demonstrated that the monitoring of the ionospheric total electron content (TEC) by global satellite navigation systems is a powerful method to study the propagation of transient disturbances in the ionosphere, induced by internal gravity waves. This technique has turned out to be sensitive enough to detect ionospheric signatures of magnetohydrodynamic waves as well. However, the effect of TEC modulation by ULF waves is not well examined as a responsible mechanism has not been firmly identified. During periods with intense Pc5 waves distinct pulsations with the same periodicity were found in the TEC data from high-latitude GPS receivers in Scandinavia. We analyze jointly responses in TEC variations and EISCAT ionospheric parameters to global Pc5 pulsations during the recovery phase of the strong magnetic storms on October 31, 2003. Comparison of periodic fluctuations of the electron density at different altitudes from EISCAT data shows that main contribution into TEC pulsations is provided by the lower ionosphere, up to ~150 km, that is the E-layer and lower F-layer. This observational fact favors the TEC modulation mechanism by field-aligned plasma transport induced by Alfven wave. Analytical estimates and numerical modeling support the effectiveness of this mechanism. Though the proposed hypothesis is basically consistent with the analyzed event, the correspondence between magnetic and ionospheric oscillations is not always perfect, so further studies need to be conducted to understand fully the TEC modulations associated with Pc5 pulsations.

  7. Performance evaluation of selected ionospheric delay models during geomagnetic storm conditions in low-latitude region

    NASA Astrophysics Data System (ADS)

    Venkata Ratnam, D.; Sarma, A. D.; Satya Srinivas, V.; Sreelatha, P.

    2011-06-01

    Investigation of space weather effects on GPS satellite navigation systems is very crucial in high-precision positional applications such as aircraft landings and missile guidance, etc. The geomagnetic storms can drastically affect the total electron content (TEC) of the ionosphere even in low latitudes, especially for Indian region as it comes under low-latitude region. Hence, the performance of three prominent ionospheric models is investigated for adverse ionospheric conditions using 17 GPS TEC stations data. The models characterized the ionospheric disturbances due to two magnetic storms well.

  8. Widespread Low-Latitude Diurnal CO2 Frost on Mars

    NASA Astrophysics Data System (ADS)

    Piqueux, S.; Kleinböhl, A.; Hayne, P. O.; Heavens, N. G.; Kass, D. M.; McCleese, D. J.; Schofield, J. T.; Shirley, J. H.

    2016-09-01

    We map and characterize MCS nighttime surface temperature observations consistent with the occurrence of CO2 frost on Mars. Low-latitude nighttime CO2 frost is widespread, with potential implications for the physical nature of the surface layer.

  9. Assessment of IRI and IRI-Plas models over the African equatorial and low-latitude region

    NASA Astrophysics Data System (ADS)

    Adebiyi, S. J.; Adimula, I. A.; Oladipo, O. A.; Joshua, B. W.

    2016-07-01

    A reliable ionospheric specification by empirical models is important to mitigate the effects of the ionosphere on the operations of satellite-based positioning and navigation systems. This study evaluates the capability of the International Reference Ionosphere (IRI) and IRI extended to the plasmasphere (IRI-Plas) models in predicting the total electron content (TEC) over stations located in the southern hemisphere of the African equatorial and low-latitude region. TEC derived from Global Positioning System (GPS) measurements were compared with TEC predicted by both the IRI-Plas 2015 model and the three topside options of the IRI 2012 model (i.e., NeQuick (NeQ), IRI 2001 corrected factor (IRI-01 Corr), and the IRI 2001(IRI-01)). Generally, the diurnal and the seasonal structures of modeled TEC follow quite well with the observed TEC in all the stations, although with some upward and downward offsets observed during the daytime and nighttime. The prediction errors of both models exhibit latitudinal variation and these showed seasonal trends. The values generally decrease with increase in latitude. The TEC data-model divergence of both models is most significant at stations in the equatorial region during the daytime and nighttime. Conversely, both models demonstrate most pronounced convergence during the nighttime at stations outside the equatorial region. The IRI-Plas model, in general, performed better in months and seasons when the three options of the IRI model underestimate TEC. Factors such as the height limitation of the IRI model, the inaccurate predictions of the bottomside and topside electron density profiles were used to explain the data-model discrepancies.

  10. Geomorphological impacts of high-latitude storm waves on low-latitude reef islands - Observations of the December 2008 event on Nukutoa, Takuu, Papua New Guinea

    NASA Astrophysics Data System (ADS)

    Smithers, S. G.; Hoeke, R. K.

    2014-10-01

    Low-latitude reefs and reef islands usually experience relatively benign climatic and hydrodynamic conditions due to their location near to the equator, outside of the major storm belts, and they typically exhibit geomorphological traits that reflect the prevailing low-energy conditions. For example, algal ridges are poorly developed, reef flat boulder zones are modest or lacking, rubble banks are rare, and reef islands tend to be low and dominated by sand. Nukutoa is a low-lying triangular-shaped reef island of ~ 6 ha located on the eastern rim of Takuu atoll (4°45‧S, 157°2‧E), Papua New Guinea, approximately 300 km northeast of Bougainville. The approximately 450 residents of Takuu all live on Nukutoa. In December 2008 Takuu was struck by several days of very high water levels and waves, which washed completely over approximately 50% of Nukutoa. GPS shoreline mapping and topographic surveys of the island were undertaken in the days immediately prior to the event, and were repeated immediately after. Homes and village infrastructure were damaged during this event, which eroded around 60% of the shoreline, and deposited a sand sheet averaging around 50 mm thick over approximately 13% of the island. This event was generated by two distant storms - one located > 6000 km away near 50°N, and affected a wide area of the Western Pacific. Oral histories record at least five similar events since the 1940s. In this paper we document the geomorphic impacts of the December 2008 event and discuss the possible significance of similar events in the past, and in the future.

  11. A detection algorithm for scale analysis of post-sunset low-latitude plasma depletions as observed by the Swarm constellation mission

    NASA Astrophysics Data System (ADS)

    Kervalishvili, Guram; Stolle, Claudia; Xiong, Chao

    2016-04-01

    ESA's constellation mission Swarm was successfully launched on 22 November 2013. The three satellites achieved their final constellation on 17 April 2014 and since then Swarm-A and Swarm-C orbiting the Earth at about 470 km (flying side-by-side) and Swarm-B at about 520 km altitude. The satellites carry instruments to monitor the F-region electron density with a sampling frequency of 2 Hz. This paper will present a detection algorithm for low-latitude post-sunset plasma bubbles (depletions), which uses local minima and maxima to detect depletions directly from electron density readings from Swarm. Our analyses were performed in the magnetic latitude (MLat) and local time (MLT) coordinate system. The detection procedure also captures the amplitude of depletion, which is called depth in the following. The width of a bubble corresponds to the length the satellite is located inside a depletion. We discuss the global distribution of depth and width of plasma bubbles and its seasonal and local time dependence for all three Swarm satellites from April 2015 through September 2015. As expected, on global average the bubble occurrence rate is highest for combined equinoxes (Mar, Apr, Sep, and Oct) and smallest for June solstice (May, Jun, Jul, and Aug). MLT distribution of the bubble occurrence number shows a sharp increase at about 19 MLT and decreases towards post-midnight hours. Interestingly, there is an inverse relation between depth and width of bubbles as function of MLT. This is true for all seasons and for all Swarm satellites. The bubble depth (width) is decreasing (increasing) from post-sunset to post-midnight for December solstice (Jan, Feb, Nov, and Dec) and combined equinoxes with about the same amplitude values for bubbles depth (width). Therefore we suggest that at post midnight when the depletions are less steep the structures of the depletions is broader than early after sunset. However for June solstice the depletions are less deep and the bubble depth and

  12. Comparison of GPS-TEC observations over Addis Ababa with IRI-2012 model predictions during 2010-2013

    NASA Astrophysics Data System (ADS)

    Akala, A. O.; Somoye, E. O.; Adewale, A. O.; Ojutalayo, E. W.; Karia, S. P.; Idolor, R. O.; Okoh, D.; Doherty, P. H.

    2015-10-01

    This study presents Global Positioning System-Total Electron Content (GPS-TEC) observations over Addis Ababa (Lat: 9.03°N Lon: 38.77°E Mag. lat: 0.18°N) and an evaluation of the accuracy of International Reference Ionosphere-2012 (IRI-2012) model predictions during 2010-2013. Generally, on a diurnal scale, TEC recorded minimum values at 0400-0600 LT and maximum at 1400-1600 LT. Seasonally, TEC recorded maximum values during December solstice and September equinox, and minimum during June solstice. On a year-by-year basis, 2013 recorded the highest values of TEC for both the observed and the model measurements, while 2010 recorded the lowest, implying the solar activity dependence of TEC. Furthermore, we observed discrepancies in the comparison of the GPS-TEC measurements with those derived from IRI-2012 model, after the exclusion of the contributions of plasmaspheric electron content (PEC) from the GPS-observed TEC. All the three options of IRI-2012 model overestimated TEC during early morning and post-sunset hours. Comparatively, of the three options of IRI-2012 model, NeQuick appears to be the most accurate for TEC estimation over Addis Ababa, although at a very close performance capability with the IRI01 CORR option, while IRI2001 is the least accurate.

  13. Latitudinal and Seasonal Investigations of Storm-Time TEC Variation

    NASA Astrophysics Data System (ADS)

    Adimula, I. A.; Oladipo, O. A.; Adebiyi, S. J.

    2016-07-01

    The ionosphere responds markedly and unpredictably to varying magnetospheric energy inputs caused by solar disturbances on the geospace. Knowledge of the impact of the space weather events on the ionosphere is important to assess the environmental effect on the operations of ground- and space-based technologies. Thus, global positioning system (GPS) measurements from the international GNSS service (IGS) database were used to investigate the ionospheric response to 56 geomagnetic storm events at six different latitudes comprising the northern and southern hemispheres in the Afro-European sector. Statistical distributions of total electron content (TEC) response show that during the main phase of the storms, enhancement of TEC is more pronounced in most of the seasons, regardless of the latitude and hemisphere. However, a strong seasonal dependence appears in the TEC response during the recovery phase. Depletion of TEC is majorly observed at the high latitude stations, and its appearance at lower latitudes is seasonally dependent. In summer hemisphere, the depletion of TEC is more pronounced in nearly all the latitudinal bands. In winter hemisphere, enhancement as well as depletion of TEC is observed over the high latitude, while enhancement is majorly observed over the mid and low latitudes. In equinoxes, the storm-time TEC distribution shows a fairly consistent characteristic with the summer distribution, particularly in the northern hemisphere.

  14. Very low latitude (L = 1.08) whistlers

    NASA Astrophysics Data System (ADS)

    Singh, Rajesh; Cohen, Morris B.; Maurya, Ajeet K.; Veenadhari, B.; Kumar, Sushil; Pant, P.; Said, Ryan K.; Inan, Umran S.

    2012-12-01

    For decades, whistlers observed on the ground at mid and high latitudes have been used for diagnostics of Earth's plasmasphere. Whistlers have also been observed at low latitudes however, the propagation characteristics of low latitude whistlers are poorly understood thus they have not been used effectively as a diagnostic for the low latitude ionosphere. One key limitation with past studies has been lack of knowledge of the whistler source lightning location. Here we present the first cases of low latitude ground whistlers most likely linked with their causative lightning discharges in the conjugate zone. The Global Lightning Dataset 360 (GLD360) detected lightning discharges were found to be located close to the conjugate location of the recording stations, providing direct evidence of inter-hemispheric propagation at the low latitudes. A total of 864 whistlers were observed at Allahabad, India (Geomag. lat. 16.05°N Geomag. long. 155.34°E L = 1.08) during the night of 26 January 2011. Using GLD360 network data, we show the occurrence of thunderstorm activity between 200 and 450 km from the conjugate point of Allahabad. We also report the distribution of peak currents of whistler-producing lightning, which demonstrate a cutoff at 30 kA.

  15. Highly Structured Plasma Density and Associated Electric and Magnetic Field Irregularities at Sub-Auroral, Middle, and Low Latitudes in the Topside Ionosphere Observed with the DEMETER and DMSP Satellites

    NASA Technical Reports Server (NTRS)

    Pfaff, Robert F.; Liebrecht, C; Berthelier, Jean-Jacques; Parrot, M.; Lebreton, Jean-Pierre

    2007-01-01

    Detailed observations of the plasma structure and irregularities that characterize the topside ionosphere at sub-auroral, middle, and low-latitudes are gathered with probes on the DEMETER and DMSP satellites. In particular, we present DEMETER observations near 700 km altitude that reveal: (1) the electric field irregularities and density depletions at mid-latitudes are remarkably similar to those associated with equatorial spread-F at low latitudes; (2) the mid-latitude density structures contain both depletions and enhancements with scale lengths along the spacecraft trajectory that typically vary from 10's to 100's of km; (3) in some cases, ELF magnetic field irregularities are observed in association with the electric field irregularities on the walls of the plasma density structures and appear to be related to finely-structured spatial currents and/or Alfven waves; (4) during severe geomagnetic storms, broad regions of nightside plasma density structures are typically present, in some instances extending from the equator to the subauroral regions; and (5) intense, broadband electric and magnetic field irregularities are observed at sub-auroral latitudes during geomagnetic storm periods that are typically associated with the trough region. Data from successive DEMETER orbits during storm periods in both the daytime and nighttime illustrate how enhancements of both the ambient plasma density, as well as sub-auroral and mid-latitude density structures, correlate and evolve with changes in the Dst. The DEMETER data are compared with near simultaneous observations gathered by the DMSP satellites near 840 km. The observations are related to theories of sub-auroral and mid-latitude plasma density structuring during geomagnetic storms and penetration electric fields and are highly germane to understanding space weather effects regarding disruption of communication and navigation signals in the near-space environment.

  16. Effects of geomagnetic storm on low latitude ionospheric total electron content: A case study from Indian sector

    NASA Astrophysics Data System (ADS)

    Chakraborty, Monti; Kumar, Sanjay; De, Barin Kumar; Guha, Anirban

    2015-07-01

    The effect of geomagnetic storms on low latitude ionosphere has been investigated with the help of Global Positioning System Total Electron Content (GPS-TEC) data. The investigation has been done with the aid of TEC data from the Indian equatorial region, Port Blair (PBR) and equatorial ionization anomaly region, Agartala (AGR). During the geomagnetic storms on 24th April and 15th July 2012, significant enhancement up to 150% and depression up to 72% in VTEC is observed in comparison to the normal day variation. The variations in VTEC observed from equatorial to EIA latitudes during the storm period have been explained with the help of electro-dynamic effects (prompt penetration electric field (PPEF) and disturbance dynamo electric field (DDEF)) as well as mechanical effects (storm-induced equatorward neutral wind effect and thermospheric composition changes). The current study points to the fact that the electro-dynamic effect of geomagnetic storms around EIA region is more effective than at the lower latitude region. Drastic difference has been observed over equatorial region (positive storm impact) and EIA region (negative storm impact) around same longitude sector, during storm period on 24th April. This drastic change as observed in GPS-TEC on 24th April has been further confirmed by using the O/N2 ratio data from GUVI (Global Ultraviolet Imager) as well as VTEC map constructed from IGS data. The results presented in the paper are important for the application of satellite-based communication and navigational system.

  17. Comparison of Ionospheric TEC Derived from GPS and IRI 2012 Model during Geomagnetic Storms at Indonesia

    NASA Astrophysics Data System (ADS)

    Marlia, Dessi; Wu, Falin

    2016-07-01

    This paper investigates the variations of vertical Total Electron Content (VTEC) at Manado, Indonesia (geographic coordinates : lat 1.34 ° S and long 124.82 ° E) for period 2013. The GPS measured TEC is compared with the TEC derived from the IRI (International Reference Ionosphere) 2012 model. Vertical TEC measurements obtained from dual frequency GPS receiver that is GISTM (GPS Ionospheric Scintillations and TEC monitor). Variation of TEC validate to IRI 2012 model at Manado station has been compared with the model for three different topside of electron density namely NeQuick, IRI-01-Corr and IRI2001.There is a need to investigation on diurnal, seasonal variations, solar activity dependence of TEC and including effects of space weather related events to TEC and modeling of TEC. In this paper, diurnal and seasonal variations of VTEC and the effect of VTEC due to space weather events like Geomagnetic storms are analyzed. The result show that the TEC prediction using IRI-2001 model overestimated the GPS TEC measurements, while IRI-NeQuick and IRI-01-corr show a tendency to underestimates the observed TEC during the day time particularly in low latitude region in the maximum solar activity period (2013). The variations of VTEC during 17th March, 2013, 29th June, 2013 storms are analyzed. During 17th March,2013 storm enhancement in VTEC with Kp value 6 and Disturbance storm index (DST) -132 nT. During 29th June, 2013 storm VTEC depletion with value 7 and DST -98 nT. Significant deviations in VTEC during the main phase of the storms are observed. It is found that the response of ionospheric TEC consist of effects of both enhancement and depletions in ionospheric structures (positive and negative storm). Keywords: TEC ionosphere, GPS, GISTM, IRI 2012 model, solar activity, geomagnetic storm

  18. DEMETER Observations of Highly Structured Plasma Density and Associated ELF Electric Field and Magnetic Field Irregularities at Middle and Low Latitudes

    NASA Technical Reports Server (NTRS)

    Pfaff, R.; Liebrecht, C.; Berthelier, J.-J.; Parrot, M.; Lebreton, J.-P.

    2008-01-01

    The DEMETER spacecraft frequently encounters structured plasma and electric field irregularities associated with equatorial spread-F. However, during severe geonagnetic storms, the spacecraft detects broader regions of density structures that extend to higher latitudes, in some instances to the sub-auroral regions. In addition to the electric field irregularities, ELF magnetic field irregularities are sometimes observed. for example, on the walls of the density structures, and appear related to finely-structured spatial currents and/or Alfven waves. The mid-latitude irregularities are compared with those of equatorial spread-F as well as wit11 intense irregularities associated with the trough region observed at sub-auroral latitudes.

  19. LISN: Measurement of TEC values, and TID characteristics over South and Central America (Invited)

    NASA Astrophysics Data System (ADS)

    Valladares, C. E.

    2013-12-01

    The Low-latitude Ionospheric Sensor Network (LISN) is a distributed observatory designed to provide the climatology and weather of the low latitude ionosphere over the South American continent. Presently, the LISN observatory consists of 47 GPS receivers able to transmit TEC and scintillation values to a central server in a real-time basis. Historical TEC values from these receivers and from about 300 other GPSs that operated in South and Central America between 2008 and 2012 were used to derive regional maps of TEC and TIDs. A prominent feature of the TEC maps is the intense day-to-day variability that is observed during all seasons and under quiet and active magnetic conditions. To assess the TEC dependencies a non-linear least-square fit was conducted to simultaneously extract the solar flux, magnetic and seasonal variability for each square cell of the TEC maps and for each 30-min local time sector. It was found that TEC values and the anomaly intensity increase as a function of the solar flux. The latitudinal separation increases with magnetic activity, and TEC values in Central America become the largest when Kp is equal to 5o or more. TIDs are seen quite frequently over the Caribbean region and in the northern part of South America. To calculate the TIDs travel velocities, their propagation direction, and the scale-size of the disturbances a multi-site multi-dimension cross-correlation method was applied to the TEC database. Phase velocities of order 150 m/s and scale sizes between 100 and 400 km were typically observed. This paper will present the morphology and statistics of TIDs as a function of latitude, longitude, local time and season. It is also introduced the results of an investigation to correlate the appearance, phase velocity and angle of propagation of TIDs and tropospheric phenomena observed with the TRMM satellite.

  20. Electric Field and Plasma Density Observations of Irregularities and Plasma Instabilities in the Low Latitude Ionosphere Gathered by the C/NOFS Satellite

    NASA Technical Reports Server (NTRS)

    Pfaff, Robert F.; Freudenreich, H.; Rowland, D.; Klenzing, J.; Liebrecht, C.

    2012-01-01

    The Vector Electric Field Investigation (VEFI) on the C/NOFS equatorial satellite provides a unique data set which includes detailed measurements of irregularities associated with the equatorial ionosphere and in particular with spread-F depletions. We present vector AC electric field observations gathered on C/NOFS that address a variety of key questions regarding how plasma irregularities, from meter to kilometer scales, are created and evolve. The talk focuses on occasions where the ionosphere F-peak has been elevated above the C/NOFS satellite perigee of 400 km as solar activity has increased. In particular, during the equinox periods of 2011, the satellite consistently journeyed below the F-peak whenever the orbit was in the region of the South Atlantic anomaly after sunset. During these passes, data from the electric field and plasma density probes on the satellite have revealed two types of instabilities which had not previously been observed in the C/NOFS data set: The first is evidence for 400-500km-scale bottomside "undulations" that appear in the density and electric field data. In one case, these large scale waves are associated with a strong shear in the zonal E x B flow, as evidenced by variations in the meridional (outward) electric fields observed above and below the F-peak. These undulations are devoid of smaller scale structures in the early evening, yet appear at later local times along the same orbit associated with fully-developed spread-F with smaller scale structures. This suggests that they may be precursor waves for spread-F, driven by a collisional shear instability, following ideas advanced previously by researchers using data from the Jicamarca radar. A second result is the appearance of km-scale irregularities that are a common feature in the electric field and plasma density data that also appear when the satellite is near or below the F-peak at night. The vector electric field instrument on C/NOFS clearly shows that the electric field

  1. AzTEC 1.1 mm OBSERVATIONS OF THE MBM12 MOLECULAR CLOUD

    SciTech Connect

    Kim, M. J.; Kim, S.; Youn, S.; Kang, Y.-W.; Yun, M. S.; Wilson, G. W.; Aretxaga, I.; Hughes, D. H.; Humphrey, A.; Williams, J. P.; Austermann, J. E.; Perera, T. A.; Mauskopf, P. D.; Magnani, L.

    2012-02-10

    We present 1.1 mm observations of the dust continuum emission from the MBM12 high-latitude molecular cloud observed with the Astronomical Thermal Emission Camera (AzTEC) mounted on the James Clerk Maxwell Telescope on Mauna Kea, Hawaii. We surveyed 6.34 deg{sup 2} centered on MBM12, making this the largest area that has ever been surveyed in this region with submillimeter and millimeter telescopes. Eight secure individual sources were detected with a signal-to-noise ratio of over 4.4. These eight AzTEC sources can be considered to be real astronomical objects compared to the other candidates based on calculations of the false detection rate. The distribution of the detected 1.1 mm sources or compact 1.1 mm peaks is spatially anti-correlated with that of the 100 {mu}m emission and the {sup 12}CO emission. We detected the 1.1 mm dust continuum emitting sources associated with two classical T Tauri stars, LkH{alpha}262 and LkH{alpha}264. Observations of spectral energy distributions (SEDs) indicate that LkH{alpha}262 is likely to be Class II (pre-main-sequence star), but there are also indications that it could be a late Class I (protostar). A flared disk and a bipolar cavity in the models of Class I sources lead to more complicated SEDs. From the present AzTEC observations of the MBM12 region, it appears that other sources detected with AzTEC are likely to be extragalactic and located behind MBM12. Some of these have radio counterparts and their star formation rates are derived from a fit of the SEDs to the photometric evolution of galaxies in which the effects of a dusty interstellar medium have been included.

  2. Atmosphere-Ionosphere coupling -manifestations in the low latitude ionosphere

    NASA Astrophysics Data System (ADS)

    Pant, Tarun; Sumod, S. G.; Vineeth, C.; Thampi, Smitha; Jose, Lijo; Kishore Kumar, K.; Sreeja, V.; Manju, G.; Ravindran, Sudha; Sridharan, R.; Niranjan, K.; Dabas, R. S.; Das, Rupesh; Alex, S.; Tiwari, Diwakar

    As is known, the extent of the impact of the geomagnetic storms on the vertical coupling of the MLTI regions, especially over low latitudes, is not very well understood. To investigate this aspect of the MLTI coupling, a multi-instrument campaign was conducted during March-April 2006, a period when a few moderate geomagnetic storms occurred, in India. During the campaign period, a Multiwavelength dayglow Photometer (MWDPM) was operated along with ionosonde, magnetometer and a meteor radar from Trivandrum (8.5oN, 76.5oE, 0.5oN diplat.), the dip equatorial station in India. The MWDPM provided the optically estimated daytime mesopause temperature while the meteor radar measured the wind and temperature in the lower thermosphere-upper mesosphere region. The MWDPM also provided the near simultaneous measurements on the thermospheric dayglow (O1D 630 nm). GPS satellite based measurements of total electron content (TEC) over a number of locations in India provided the latitudinal distribution of ionization. The new and important observations made during this campaign are the following: (a) The optically measured daytime mesopause temperature shows a prominent decrease in the afternoon hours during the initial and main phases of the geomagnetic storms. This observation, perhaps, is new and unique. (b) Quasi 2 and 5 day oscillations appear to be modulating the mesopause temperature indicating the presence of planetary waves therein. The wind and temperature variability in the lower thermosphere, obtained using the collocated radar further corroborate with these optical measurements and establish the origin of these waves to be in the lower atmosphere. (c) The Equatorial Electrojet (EEJ) induced magnetic field on the ground also exhibit similar variability indicating the presence of these planetary scale oscillations, also in the ionospheric dynamo region. (d) The simultaneously measured thermospheric dayglow (O1D 630 nm) also shows an intensification of a quasi 2-and 5-day

  3. Study of daytime vertical E × B drift velocities inferred from ground-based magnetometer observations of ΔH, at low latitudes under geomagnetically disturbed conditions

    NASA Astrophysics Data System (ADS)

    Subhadra Devi, P. K.; Unnikrishnan, K.

    2014-03-01

    In this study, 30 storm sudden commencement (SSC) events during the period 2001-2007 for which daytime vertical E × B drift velocities from JULIA radar, Jicamarca (geographic latitude 11.91°S, geographic longitude 283.11°E, 0.81°N dip latitude), Peru and ΔH component of geomagnetic field measured as the difference between the magnitudes of the horizontal (H) components between two magnetometers deployed at two different locations Jicamarca (geographic latitude 11.91°S, geographic longitude 283.11°E, 0.81°N dip latitude) and Piura (geographic latitude 5.21°S, geographic longitude 279.41°E, 6.81°N dip latitude), in Peru, were considered. It is observed that a positive correlation exists between peak value of daytime vertical E × B drift velocity and peak value of ΔH for the three consecutive days of SSC. A qualitative analysis made after selecting the peak values of daytime vertical E × B drift velocity and ΔH showed that 57% of the events have daytime vertical E × B drift velocity peak in the magnitude range 20-30 m/s and 63% of the events have ΔH peak in the range 80-100 nT. The maximum probable (45%) range of time of occurrence of peak value for both vertical E × B drift velocity and ΔH during the daytime hours were found to be the same, i.e., 10:00-12:00 LT. A strong positive correlation was also found to exist between the daytime vertical E × B drift velocity and ΔH for all the three consecutive days of SSC, for all the events considered. To establish a quantitative relationship between day time vertical E × B drift velocity and ΔH, linear and polynomial (order 2 and 3) regression analysis (Least Square Method (LSM)) were carried out, considering the fully disturbed day after the commencement of the storm as ‘disturbed period’ for the SSC events selected for analysis. The formulae indicating the relationship between daytime vertical E × B drift velocity and ΔH, for the ‘disturbed periods’, obtained through the regression analysis

  4. Low latitude middle atmosphere ionization studies

    NASA Technical Reports Server (NTRS)

    Bassi, J. P.

    1976-01-01

    Low latitude middle atmosphere ionization was studied with data obtained from three blunt conductivity probes and one Gerdien condenser. An investigation was conducted into the effects of various ionization sources in the 40 to 65 Km altitude range. An observed enhancement of positive ion conductivity taking place during the night can be explained by an atmsopheric effect, with cosmic rays being the only source of ionization only if the ion-ion recombination coefficient (alpha sub i) is small(10 to the -7 power cu cm/s) and varies greatly with altitude. More generally accepted values of alpha sub i ( approximately equal to 3x10 to the -7 power cu cm/s) require an additional source of ionization peaking at about 65 Km, and corresponding approximately to the integrated effect of an X-ray flux measured on a rocket flown in conjunction with the ionization measurements. The reasonable assumption of an alpha sub i which does not vary with altitude in the 50-70 Km range implies an even greater value alpha sub i and a more intense and harder X-ray spectrum.

  5. Atmospheric Mercury Speciation &Ozone Depletion Events Observed At Low Latitude On The Shore of The Hudson Bay In Northern Quebec (kuujjuarapik: 55n) Along To Bro (doas) Measurments

    NASA Astrophysics Data System (ADS)

    Poissant, L.; Hoenninger, G.; Pilote, M.; Leser, H.; Sebastian, O.; Platt, U.

    Atmospheric mercury and ozone depletion events have been recently observed in the high Arctic region (eg., Alert, Canada) during polar sunrise. Although the mechanisms are still enigmatic, bromine (Br) radicals have been pointed out in the literature as a potential oxidation species. Besides their significant contribution to the destruction of ozone in the polar stratosphere reactive bromine species play the key role in bound- ary layer ozone depletion and can be an effective oxidant for mercury. From April 15th to May 8th 2001, an international intensive field campaign has been achieved in the Hudson Bay area at Kuujjuarapik, Québec, Canada (Lat. 55 N) in regards to Mercury Depletion Events (MDE) in low Arctic regions. Mercury speciation concen- trations (Total Gaseous Mercury (TGM), Total Particulate Mercury (TPM) &Reactive Gaseous Mercury (RGM)) using new mercury speciation units namely Tekran 1130 &1135, were measured along with Ozone (Teco 49C), BrO mixing ratio (Differential Optical Absorption Spectroscopy, DOAS) and meteorological parameters (eg. temper- ature, wind, etc.). Results indicated during that period, median concentrations were as following : TGM (1.93 ng/m3); TPM (183 pg/m3); RGM (22 pg/m3); O3 (36.5 ppb) and BrO (0.35 ppt). Median ratio of TPM/RGM was 9.2. Furthermore, BrO mixing ra- tio was anti-correlated with TGM (TGM = -0.05 BrO + 1.99 : R2 = 0.35) and O3 (O3 = -1.0 BrO + 38.9 : R2 = 0.33) whereas it was correlated with RGM (RGM = 4.6 BrO + 21.3 : R2 = 0.54). Interestingly, larger BrO mixing ratio (>5 ppt) and RGM concen- trations (>60 pg/m3) appeared only at cold temperature (~< minus 8 C). Moreover, mercury and ozone depletions were recorded correlated to high amounts of BrO for air masses originating from the north, which were in contact with the Hudson Bay sea ice for several days. One of the most important effect of temperature seemed to ap- 1 pear on TPM concentrations. Indeed, TPM correlated significantly with temperature (TPM = 8.8 T

  6. Global features of ionospheric slab thickness derived from JPL TEC and COSMIC observations

    NASA Astrophysics Data System (ADS)

    Huang, He; Liu, Libo

    2016-04-01

    The ionospheric equivalent slab thickness (EST) is the ratio of total electron content (TEC) to F2-layer peak electron density (NmF2), describing the thickness of the ionospheric profile. In this study, we retrieve EST from Jet Propulsion Laboratory (JPL) TEC data and NmF2 retrieved from Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) ionospheric radio occultation data. The diurnal, seasonal and solar activity variations of global EST are analyzed as the excellent spatial coverage of JPL TEC and COSMIC data. During solstices, daytime EST in the summer hemisphere is larger than that in the winter hemisphere, except in some high-latitude regions; and the reverse is true for the nighttime EST. The peaks of EST often appear at 0400 local time. The pre-sunrise enhancement in EST appears in all seasons, while the post-sunset enhancement in EST is not readily observed in equinox. The dependence of EST on solar activity is very complicated. Furthermore, an interesting phenomenon is found that EST is enhanced from 0° to 120° E in longitude and 30° to 75° S in latitude during nighttime, just to the east of Weddell Sea Anomaly, during equinox and southern hemisphere summer.

  7. TEC variations along an East Euro-African chain during 5th April 2010 geomagnetic storm

    NASA Astrophysics Data System (ADS)

    Shimeis, A.; Borries, C.; Amory-Mazaudier, C.; Fleury, R.; Mahrous, A. M.; Hassan, A. F.; Nawar, S.

    2015-05-01

    In this paper, we analyzed the variations of TEC along a latitudinal East Euro-African chain, during the storm of April 5, 2010. We observed a large asymmetry between the two hemispheres. We detected the presence of a TID in the Northern hemisphere on April 5. The propagation time of the TID from high to low latitudes and the speed of the TID was determined. On April 5, 6 and 7, we observed a decrease of the TEC and changes of the NO+ in the Northern hemisphere. This depletion is caused by the large-scale thermospheric wind disturbances due to Joule heating dissipation in the auroral zone.

  8. Characteristics of GPS TEC variations in the polar cap ionosphere

    NASA Astrophysics Data System (ADS)

    Watson, Chris; Jayachandran, P. T.; MacDougall, John W.

    2016-05-01

    This paper presents statistical characteristics (occurrence rate, amplitude, and frequency) of low-frequency (<100 mHz) variations in total electron content (TEC) observed in the polar cap ionosphere. TEC variations were primarily associated with mesoscale (tens to hundreds of kilometers) ionization structures and were observed by five Global Positioning System (GPS) receivers over a 6 year period (2009-2014). The altitude of ionization structures was estimated by using colocated ionosonde radars. High data rate receivers combined with broad spatial coverage of multisatellite TEC measurements provided high-resolution magnetic local time/latitude maps of TEC variation characteristics, which were examined as a function of solar cycle and season. These high-resolution maps improve upon the current observational picture of mesoscale structuring in the polar cap and provide accurate links to particular magnetospheric source regions. Occurrence of TEC variations was consistently highest in dayside regions mapping to low latitude and plasma mantle boundary layers, while largest-amplitude TEC variations were observed in dayside regions close to the polar cusp, and lower latitudes around midnight. Occurrence and amplitude of TEC variations increased significantly during the ascending phase of the solar cycle, independent of solar wind conditions, while seasonal statistics showed highest dayside occurrence and amplitude in winter months, lowest in summer, and highest nightside occurrence and amplitude around equinox. A surprising result in the frequency distributions of TEC variations was discrete frequencies of about 2 and 4 mHz, which appeared to originate from regions corresponding to the plasma mantle, immediately poleward of the polar cusp.

  9. A comparative study of the ionospheric F-region observations in the Brazilian low latitude region and the TIMEGCM model results during the super geomagnetic storm of 20 November 2003

    NASA Astrophysics Data System (ADS)

    Becker-Guedes, F.; Sahai, Y.; Fagundes, P.; Crowley, G.; Lima, W.

    The TIMEGCM is a global 1st principles model of the ionosphere-thermosphere I-T system with fully coupled and interactive ionospheric and thermospheric components The model requires a specification of the high latitude electric potential distribution for each time step along with specification of the auroral particle precipitation Each of these parameters is obtained by use of the AMIE Assimilative Mapping of Ionospheric Electrodynamics technique which assimilates data from nearly 200 ground-based magnetometers several DMSP satellites and the SuperDARN radar network In this paper we compare ionospheric observations from two low-latitude ionospheric sounding stations with predictions from the TIMEGCM during the super geomagnetic storm of 20 November 2003 The super geomagnetic storm with SSC at 08 03 UT on 20 November attained vert Dst vert max 472 nT at 20 00 UT 20 11 The digital ionosondes using the Canadian Advanced Digital Ionosondes CADIs are located at Palmas PAL 10 2 r S 48 2 r W dip latitude 5 5 r S a near equatorial station and S a o Jos e dos Campos SJC 23 2 r S 45 9 r W dip latitude 17 6 r S station located under the crest of equatorial ionospheric anomaly Brazil Comparisons of model predictions with ionospheric observations during intense geomagnetic disturbances are important studies related to space weather forecasting Salient features from this comparative study are presented and discussed in this paper

  10. Peculiar features of the low-latitude and midlatitude ionospheric response to the St. Patrick's Day geomagnetic storm of 17 March 2015

    NASA Astrophysics Data System (ADS)

    Nayak, Chinmaya; Tsai, L.-C.; Su, S.-Y.; Galkin, I. A.; Tan, Adrian Teck Keng; Nofri, Ed; Jamjareegulgarn, Punyawi

    2016-08-01

    The current study aims at investigating and identifying the ionospheric effects of the geomagnetic storm that occurred during 17-19 March 2015. Incidentally, with SYM-H hitting a minimum of -232 nT, this was the strongest storm of the current solar cycle 24. The study investigates how the storm has affected the equatorial, low-latitude, and midlatitude ionosphere in the American and the European sectors using available ground-based ionosonde and GPS TEC (total electron content) data. The possible effects of prompt electric field penetration is observed in both sectors during the main phase of the storm. In the American sector, the coexistence of both positive and negative ionospheric storm phases are observed at low latitudes and midlatitudes to high latitudes, respectively. The positive storm phase is mainly due to the prompt penetration electric fields. The negative storm phase in the midlatitude region is a combined effect of disturbance dynamo electric fields, the equatorward shift of the midlatitude density trough, and the equatorward compression of the plasmapause in combination with chemical compositional changes. Strong negative ionospheric storm phase is observed in both ionosonde and TEC observations during the recovery phase which also shows a strong hemispherical asymmetry. Additionally, the variation of equatorial ionization anomaly as seen through the SWARM constellation plasma measurements across different longitudes has been discussed. We, also, take a look at the performance of the IRI Real-Time Assimilative Mapping during this storm as an ionospheric space weather tool.

  11. Comparison of Two IRI Plasmasphere Extensions with GPS-TEC Observations

    NASA Technical Reports Server (NTRS)

    Gulyacva, Tamara; Gallagher, Dennis

    2005-01-01

    Two plasmasphere extensions of the International Reference Ionosphere are made available for the users. It is aimed to estimate the effect of charged particles on technical devices in the Earth's environment and to define the ionosphere-plasmasphere operational conditions compatible with existing and future systems of radio communication, radio navigation and other relevant radio technologies in the ranges of medium and higher frequencies. The Global Core Plasma Model (GCPM-2000) of Gallagher et al. (2000) is an empirical description of thermal plasma densities in the plasmasphere, plasmapause, magnetospheric trough, and polar cap. GCPM-2000 uses the Kp index and is coupled to IRI in the transition region 500-600 km. The IZMIRAN plasmasphere model (Chasovitin et al., 1998; Gulyaeva et al., 2002) is an empirical model based on whistler and satellite observations. It presents global vertical analytical profiles of electron density smoothly fitted to IRI electron density profile at 1000 km altitude and extended towards the plasmapause (up to 36,000 km). For the smooth fitting of the two models, the shape of the IRI topside electron density profile is improved using ISIS 1, ISIS 2, and IK19 satellite inputs (Gulyaeva, 2003). The plasmasphere model depends on solar activity and magnetic activity (kp-index). The two IRI plasmasphere extensions are compared in the present study with the total electron content derived from records of Global Positioning Satellites (GPS-TEC) observations for different latitudinal, solar activity, magnetic activity, diurnal and seasonal conditions. The differences of model TEC with observed TEC in the topside ionosphere and plasmasphere are discussed.

  12. A global picture of ionospheric slab thickness derived from GIM TEC and COSMIC radio occultation observations

    NASA Astrophysics Data System (ADS)

    Huang, He; Liu, Libo; Chen, Yiding; Le, Huijun; Wan, Weixing

    2016-01-01

    The ionospheric equivalent slab thickness (EST), defined as the ratio of total electron content (TEC) to F2 layer peak electron density (NmF2), describes the thickness of the ionospheric profile. In this study, we retrieve EST from TEC data obtained from Global Ionospheric Map (GIM) and NmF2 retrieved from Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) ionospheric radio occultation data. The diurnal, seasonal, and solar activity variations of global EST are analyzed as the excellent spatial coverage of GIM and COSMIC data. During solstices, daytime EST in the summer hemisphere is larger than that in the winter hemisphere, except in some high-latitude regions, and the reverse is true for the nighttime EST. The peaks of EST often appear at 0400 local time. The presunrise enhancement in EST appears in all seasons, while the postsunset enhancement in EST is not readily observed in equinox. Both enhancements are attributed to the more remarkable electron density decay of NmF2 compared to that of TEC. The dependence of EST on solar activity is related to the inconsistent solar activity dependences of electron density at different altitudes. Furthermore, it is interesting that EST is enhanced from 0° to 120°E in longitude and 30° to 75°S in latitude during nighttime, just to the east of Weddell Sea Anomaly, during equinox and the Southern Hemisphere summer. This phenomenon is supposed to be related to the effects of geomagnetic declination-related plasma vertical drifts.

  13. Low latitude Ionospheric response to the recent super storm of 17 March 2015: Modeling perspectives and recent findings

    NASA Astrophysics Data System (ADS)

    Joshi, L. M.; Sripathi, S.; Singh, R.

    2015-12-01

    In this paper, simulation of low latitude ionospheric response to the recent super geomagnetic storm of 17 March 2015 at Indian longitude, utilizing SAMI2 codes by incorporating Doppler EXB drift, relevant to the storm period, is being presented. Intense enhancement in the EXB drift of 60 to 70 m/s over magnetic equator was observed in the evening hours of 17 March due to the prompt penetration of the high latitude electric field. This remarkable intensification of EXB drift transported the F layer to beyond 550 km altitude, quite unusual in the Indian sector. Model EXB drift in the day time during the recovery phase of the super storm was slightly westward, unlike the eastward EXB drift during the quiet day. This has been found to be linked with the disturbance dynamo during the recovery phase. SAMI2 model, utilizing the Doppler EXB drift during the evening hours and model EXB drift during the rest of the period, could simulate the intense F layer height rise and latitudinal expansion of EIA during storm main phase. Equator ward disturbance thermospheric winds during the recovery phase have also been incorporated in the simulation. Simulation results also indicated a complete suppression of the equatorial ionization anomaly (EIA) during the recovery phase, linked with the westward disturbance dynamo electric field. Model simulations indicate the role of the disturbance neutral winds during the recovery phase in enhancing the plasma density, however, the development of the EIA has been found to be controlled by the zonal electric field. The model results have been compared with the ground observations of the total electron content (TEC). TEC map over the Indian region shows a remarkable suppression of the EIA during the recovery phase of the geomagnetic storm. Peculiarities of this super storm will also be discussed in the light of the current understanding of the space weather impact on the low latitude ionosphere.

  14. Modelling of ionospheric irregularities during geomagnetic storms over African low latitude region

    NASA Astrophysics Data System (ADS)

    Mungufeni, Patrick

    2016-07-01

    In this study, empirical models of occurrence of ionospheric irregularities over low latitude African region during geomagnetic storms have been developed. The geomagnetic storms considered consisted of Dst ≤ -50 nT. GNSS-derived ionospheric Total Electron Content (TEC) data over Libreville, Gabon (NKLG) (0.35° N, 9.68° E, geographic, 8.05° S, magnetic) and Malindi, Kenya (MAL2) (2.99° S, 40.19° E, geographic, 12.42° S, magnetic) during 2000 - 2014 were used. Ionospheric irregularities at scale- lengths of a few kilometers and ˜400 m were represented with the rate of change of TEC index (ROTI). The inputs for the models are the local time, solar flux index, Auroral Electrojet index, day of the year, and the Dst index, while the output is the median ROTI during these given conditions. To develop the models, the ROTI index values were binned based on the input parameters and cubic B splines were then fitted to the binned data. Developed models using data over NKLG and MAL2 were validated with independent data over stations within 510 km and 680 km radius, respectively. The models captured the enhancements and inhibitions of the occurrence of the ionospheric irregularities during the storm period. The models even emulated these patterns in the various seasons, during medium and high solar activity conditions. The correlation coefficients for the validations were statistically significant and ranged from 0.58 - 0.73, while the percentage of the variance in the observed data explained by the modelled data ranged from 34 - 53.

  15. Space Weather Studies Using the Low-Latitude Ionospheric Sensor Network (LISN)

    NASA Astrophysics Data System (ADS)

    Valladares, C. E.; Pacheco, E.

    2014-12-01

    LISN is an array of small instruments that operates as a real-time distributed observatory to understand the complex day-to-day variability and the extreme state of disturbance that occurs in the South American low-latitude ionosphere nearly every day after sunset. The LISN observatory aims to forecast the initiation and transport of plasma bubbles across the South American continent. The occurrence of this type of plasma structures and their embedded irregularities poses a prominent natural hazard to communication, navigation and high precision pointing systems. As commercial and military aviation is increasingly reliant on Global Navigation Satellite Systems (GNSS) any interruption due to ionospheric irregularities or errors due to large density gradients constitutes a serious threat to passengers and crew. Therefore, it is important to understand the conditions and sources that contribute to the formation of these irregularities. To achieve high quality regional nowcasts and forecasts, the LISN system was designed to include a dense coverage of the South American landmass with 47 GPS receivers, 5 flux-gate magnetometers distributed on 2 base lines and 3 Vertical Incidence Pulsed Ionospheric Radar (VIPIR) ionosondes deployed along the same magnetic meridian that intersects the magnetic equator at 68° W. This presentation will provide a summary of recent instrument installations and new processing techniques that have been developed under the LISN project. We will also present the results of recent efforts to detect TIDs and TEC plasma depletions on a near real-time basis. We will describe a method to estimate the zonal velocity and tilt of the plasma bubbles/depletions by combining observations of TEC depletions acquired with adjacent receivers, making it possible to predict precisely their future locations.

  16. Assimilated Low Latitude Ionosphere Variability During the First CAWSES Space Wether Campaign

    NASA Astrophysics Data System (ADS)

    Sojka, J. J.; Schunk, R. W.; Scherliess, L.; Thompson, D. C.

    2004-12-01

    The Utah State University (SUS) Global Assimilation of Ionospheric Measurements (GAIM) has been used to study the first CAWSES Space Weather Campaign period (March 25 through April 5). This period is noteworthy in two distinct ways. First, there is an extended three-day very quiet geomagnetic period, which is followed almost immediately by a marked change in the ionosphere associated with severe geomagnetic activity. GAIM, for this study, assimilated over 500 groundbased GPS TEC and 18 digisonde measurements. The background ionosphere was driven by climatology models that responded to the geomagnetic Kp and solar F10.7 indices. The GAIM assimilation results show that the ionosphere at low latitudes is highly responsive to (a) quiet time variability from "drivers" that are relatively unknown, and (b) during the storm from drivers assumed to be associated with high latitude auroral inputs, but again relatively unspecific. However, the strength of the assimilation approach is that the observed electron density and total electron density, when assimilated, redistributes the background model ionosphere to reveal both the quiet-time and disturbed ionospheric variability. These GAIM results will be presented with comparison to the purely climatology background.

  17. On the mutual relationship of the equatorial electrojet, TEC and scintillation in the Peruvian sector

    NASA Astrophysics Data System (ADS)

    Khadka, Sovit M.; Valladares, Cesar; Pradipta, Rezy; Pacheco, Edgardo; Condor, Percy

    2016-06-01

    This paper presents the interrelationship between the equatorial electrojet (EEJ) strength, Global Positioning System (GPS)-derived total electron content (TEC), and postsunset scintillation from ground observations with the aim of finding reliable precursors of the occurrence of ionospheric irregularities. Mutual relationship studies provide a possible route to predict the occurrence of TEC fluctuation and scintillation in the ionosphere during the late afternoon and night respectively based on daytime measurement of the equatorial ionosphere. Data from ground based observations in the low latitudes of the west American longitude sector were examined during the 2008 solar minimum. We find a strong relationship exists between the noontime equatorial electrojet and GPS-derived TEC distributions during the afternoon mediated by vertical E × B drift via the fountain effect, but there is little or no relationship with postsunset ionospheric scintillation.

  18. Studies of Plasma Bubbles & Comparision of TEC Fluctuations and Scintillations at Varanasi Using GPS Data

    NASA Astrophysics Data System (ADS)

    Priyadarshi, Shishir; Kumar, Sanjay; Singh, Abhay Kumar

    Ionospheric total electron content (TEC) and scintillations have been recorded continuously since January 2009 using a dual frequency GPS receiver at Varanasi, India (geographic lat. 25.30 N, long. 82.990 E). The trajectory of a GPS satellite plays an important role in observing the bubble characteristics. The GPS data with a sampling interval of 60 s were analyzed to determine TEC, the rate of change of TEC (ROT) and as well as ROTI, defined as the standard deviation of ROT. In this work we compare the S4 index of GPS scintillations with the ROTI values and there by investigated the evolution of large and small scale irregularities at scale length of few kilometers and 400 m respectively observed at low latitude station Varanasi. The effects of geomagnetic activity and geomagnetic storm on the generation of bubbles are studied using Kp index and Dst index respectively. Kew words: GPS, Plasma bubble, ROT, ROTI

  19. The influence of ionospheric thin shell height on TEC retrieval from GPS observation

    NASA Astrophysics Data System (ADS)

    Wang, Xiao-Lan; Wan, Qing-Tao; Ma, Guan-Yi; Li, Jing-Hua; Fan, Jiang-Tao

    2016-07-01

    We investigate the influence of assumed height for the thin shell ionosphere model on the Total Electron Content (TEC) derived from a small scale Global Positioning System (GPS) network. TEC and instrumental bias are determined by applying a grid-based algorithm to the data on several geomagnetically quiet days covering a 10 month period in 2006. Comparisons of TEC and instrumental bias are made among assumed heights from 250 km to 700 km with an interval of 10 km. While the TEC variations with time follow the same trend, TEC tends to increase with the height of the thin shell. The difference in TEC between heights 250 km and 700 km can be as large as ∼ 8 TECU in both daytime and nighttime. The times at which the TEC reaches its peak or valley do not vary much with the assumed heights. The instrumental biases, especially bias from the satellite, can vary irregularly with assumed height. Several satellites show a large deviation of ∼ 3 ns for heights larger than 550 km. The goodness of fit for different assumed heights is also examined. The data can be generally well-fitted for heights from 350 km to 700 km. A large deviation happens at heights lower than 350 km. Using the grid-based algorithm, there is no consensus on assumed height as related to data fitting. A thin shell height in the range 350 – 500 km can be a reasonable compromise between data fitting and peak height of the ionosphere.

  20. The influence of ionospheric thin shell height on TEC retrieval from GPS observation

    NASA Astrophysics Data System (ADS)

    Wang, Xiao-Lan; Wan, Qing-Tao; Ma, Guan-Yi; Li, Jing-Hua; Fan, Jiang-Tao

    2016-07-01

    We investigate the influence of assumed height for the thin shell ionosphere model on the Total Electron Content (TEC) derived from a small scale Global Positioning System (GPS) network. TEC and instrumental bias are determined by applying a grid-based algorithm to the data on several geomagnetically quiet days covering a 10 month period in 2006. Comparisons of TEC and instrumental bias are made among assumed heights from 250 km to 700 km with an interval of 10 km. While the TEC variations with time follow the same trend, TEC tends to increase with the height of the thin shell. The difference in TEC between heights 250 km and 700 km can be as large as ˜ 8 TECU in both daytime and nighttime. The times at which the TEC reaches its peak or valley do not vary much with the assumed heights. The instrumental biases, especially bias from the satellite, can vary irregularly with assumed height. Several satellites show a large deviation of ˜ 3 ns for heights larger than 550 km. The goodness of fit for different assumed heights is also examined. The data can be generally well-fitted for heights from 350 km to 700 km. A large deviation happens at heights lower than 350 km. Using the grid-based algorithm, there is no consensus on assumed height as related to data fitting. A thin shell height in the range 350 - 500 km can be a reasonable compromise between data fitting and peak height of the ionosphere.

  1. The influence of ionospheric thin shell height on TEC retrieval from GPS observation

    NASA Astrophysics Data System (ADS)

    Wang, Xiao-Lan; Wan, Qing-Tao; Ma, Guan-Yi; Li, Jing-Hua; Fan, Jiang-Tao

    2016-07-01

    We investigate the influence of assumed height for the thin shell ionosphere model on the Total Electron Content (TEC) derived from a small scale Global Positioning System (GPS) network. TEC and instrumental bias are determined by applying a grid-based algorithm to the data on several geomagnetically quiet days covering a 10 month period in 2006. Comparisons of TEC and instrumental bias are made among assumed heights from 250 km to 700 km with an interval of 10 km. While the TEC variations with time follow the same trend, TEC tends to increase with the height of the thin shell. The difference in TEC between heights 250 km and 700 km can be as large as ˜ 8 TECU in both daytime and nighttime. The times at which the TEC reaches its peak or valley do not vary much with the assumed heights. The instrumental biases, especially bias from the satellite, can vary irregularly with assumed height. Several satellites show a large deviation of ˜ 3 ns for heights larger than 550 km. The goodness of fit for different assumed heights is also examined. The data can be generally well-fitted for heights from 350 km to 700 km. A large deviation happens at heights lower than 350 km. Using the grid-based algorithm, there is no consensus on assumed height as related to data fitting. A thin shell height in the range 350 – 500 km can be a reasonable compromise between data fitting and peak height of the ionosphere.

  2. Comparison of standard TEC models with a Neural Network based TEC model using multistation GPS TEC around the northern crest of Equatorial Ionization Anomaly in the Indian longitude sector during the low and moderate solar activity levels of the 24th solar cycle

    NASA Astrophysics Data System (ADS)

    Sur, D.; Paul, A.

    2013-09-01

    The highest Total Electron Content (TEC) values in the world normally occur at Equatorial Ionization Anomaly (EIA) region resulting in largest ionospheric range delay values observed for any potential Space Based Augmentation System (SBAS). Reliable forecasting of TEC is crucial for satellite based navigation systems. The day to day variability of the location of the anomaly peak and its intensity is very large. This imposes severe limitations on the applicability of commonly used ionospheric models to the low latitude regions. It is necessary to generate a mathematical ionospheric forecasting and mapping model for TEC based on physical ionospheric influencing parameters. A model, IRPE-TEC, has been developed based on real time low latitude total electron content data using GPS measurements from a number of stations situated around the northern crest of the EIA during 2007 through 2011 to predict the vertical TEC values during the low and moderate solar activity levels of the 24th solar cycle. This model is compared with standard ionospheric models like International Reference Ionosphere (IRI) and Parameterized Ionospheric Model (PIM) to establish its applicability in the equatorial region for accurate predictions.

  3. Comparative study on the ionospheric response to minor and major sudden stratospheric events in the Brazilian equatorial and low latitudes

    NASA Astrophysics Data System (ADS)

    Fagundes, Paulo Roberto; Kavutarapu, Venkatesh; Gil Pillat, Valdir; Vieira, Francisco

    2016-07-01

    The Total electron Content (TEC), derivate from GPS, becomes one of the most powerful techniques to study the space-time ionospheric (F-region) electrodynamics, during the quiet and disturbed periods. The number of GPS stations in Brazil increased significantly during the last few years; currently more than 100 GPS stations are in operation over the Brazilian region. The GPS-TEC values are derived using the differential delay technique from the dual frequency measurements at L1 and L2 frequencies over the considered locations at equatorial and low latitudes. The present study investigates the ionospheric total electron content (GPS-TEC) response in the Southern Hemisphere equatorial and low latitudes, due to major and minor sudden stratospheric warming (SSW) events, which took place during 2009 and 2012. During both the SSW events, the TEC values are depleted to the order of 20-30% all over the Brazil from equator to beyond Equatorial Ionization Anomaly (EIA) regions. In addition, the EIA were suppressed during the SSW events for several days. However, the TEC depletion and EIA suppression lasted for a longer period during SSW-2012 when compared with the SSW-2009; despite the SSW-2012 is considerd as a minor event.

  4. Mapping the East African Ionosphere Using Ground-based GPS TEC Measurements

    NASA Astrophysics Data System (ADS)

    Mengist, Chalachew Kindie; Kim, Yong Ha; Yeshita, Baylie Damtie; Workayehu, Abyiot Bires

    2016-03-01

    The East African ionosphere (3°S-18°N, 32°E-50°E) was mapped using Total Electron Content (TEC) measurements from ground-based GPS receivers situated at Asmara, Mekelle, Bahir Dar, Robe, Arbaminch, and Nairobi. Assuming a thin shell ionosphere at 350 km altitude, we project the Ionospheric Pierce Point (IPP) of a slant TEC measurement with an elevation angle of >10° to its corresponding location on the map. We then infer the estimated values at any point of interest from the vertical TEC values at the projected locations by means of interpolation. The total number of projected IPPs is in the range of 24-66 at any one time. Since the distribution of the projected IPPs is irregularly spaced, we have used an inverse distance weighted interpolation method to obtain a spatial grid resolution of 1°×1° latitude and longitude, respectively. The TEC maps were generated for the year 2008, with a 2 hr temporal resolution. We note that TEC varies diurnally, with a peak in the late afternoon (at 1700 LT), due to the equatorial ionospheric anomaly. We have observed higher TEC values at low latitudes in both hemispheres compared to the magnetic equatorial region, capturing the ionospheric distribution of the equatorial anomaly. We have also confirmed the equatorial seasonal variation in the ionosphere, characterized by minimum TEC values during the solstices and maximum values during the equinoxes. We evaluate the reliability of the map, demonstrating a mean error (difference between the measured and interpolated values) range of 0.04-0.2 TECU (Total Electron Content Unit). As more measured TEC values become available in this region, the TEC map will be more reliable, thereby allowing us to study in detail the equatorial ionosphere of the African sector, where ionospheric measurements are currently very few.

  5. Scintillations and TEC gradients from Europe to Africa: a picture by the MISW project

    NASA Astrophysics Data System (ADS)

    Alfonsi, Lucilla; Spogli, Luca; Cesaroni, Claudio; Vadakke Veettil, Sreeja; Aquino, Marcio; Zin, Alberto; Wilhelm, Nicolas; Serant, Damien; Forte, Biagio; Mitchell, Cathryn N.; Grzesiak, Marcin; Kos, Timoslav; von Benzon, Hans-Henrik; Zurn, Martin; Enell, Carl-Fredrik; Haggstrom, Ingemar

    2016-04-01

    MISW (Mitigation of space weather threats to GNSS services) is an EU/FP7 project with the purpose of tackling the research challenges associated with Space Weather effects on GNSS (Global Navigation Satellite System). In particular, the objective of MISW is to develop suitable algorithms capable of enabling Satellite Based Augmentation Systems (e.g. EGNOS) in the low-latitude African sector. For this purpose, MISW has created a detailed picture of extreme space weather events that occurred in the past and in the current solar cycle. Despite its weakness, the current solar cycle exhibited two superstorms that happened during the descending phase, in March and in June 2015. The latter has been studied in detail through a careful analysis of GNSS data acquired by TEC (Total Electron Content) and scintillation monitors and by IGS and regional geodetic networks located in Europe and in Africa. The investigation enabled creating the actual scenarios of TEC gradients and scintillation that occurred over a wide latitudinal extent between 21 and 30 June 2015. The investigation is based on calibrated TEC from different receivers, aiming at the estimation of east-west and north-south TEC gradients and on the integration of calibrated TEC and TEC gradients with the scintillation data. The impact of the storm on GNSS performance has also been investigated in terms of losses of lock. The results of this study highlight the importance of assessing the latitudinal and the longitudinal TEC gradients as crucial information to identify to what extent different ionospheric sectors are severely affected by scintillation. On the other hand, this study also shows evidences of how TEC gradients are not always responsible for the observed scintillation. Finally, the outcomes of the study demonstrate the complex relation between scintillation, TEC gradients and losses of GNSS satellites lock.

  6. A study on ionospheric TEC forecast using genetic algorithm and neural network

    NASA Astrophysics Data System (ADS)

    Huang, Zhi; Yuan, Hong

    Back propagation artificial neural network (ANN) augmented by genetic algorithm (GA) is introduced to forecast ionospheric TEC with the dual-frequency GPS measurements from the low and high solar activity years in this paper due to ionosphere space characterizing by the highly nonlinear and time-varying with random variations. First, with different number of neurons in the hidden layer, different transfer function and training function, the training performance of network model is analyzed and then optimized network structure is determined. The ionospheric TEC values one hour in advance are forecasted and further the prediction performance of the developed network model is evaluated at the given criterions. The results show that predicted TEC using BP neural network improved by genetic algorithm has good agreement with observed data. In addition, the prediction errors are smaller in middle and high latitudes than in low latitudes, smaller in low solar activity than in high solar activity. Compared with BP Network with three layers structure, Prediction precision of network model optimized by genetic algorithm is further improved. The resolution quality indicate that the proposed algorithm can offer a powerful and reliable alternative to the design of ionospheric TEC forecast technologies, and provide advice for the regional ionospheric TEC maps. Key words: Neural network, Genetic algorithm, Ionospheric TEC, Forecast,

  7. Performance of ionospheric maps in support of long baseline GNSS kinematic positioning at low latitudes

    NASA Astrophysics Data System (ADS)

    Park, J.; Sreeja, V.; Aquino, M.; Cesaroni, C.; Spogli, L.; Dodson, A.; De Franceschi, G.

    2016-05-01

    Ionospheric scintillation occurs mainly at high and low latitude regions of the Earth and may impose serious degradation on GNSS (Global Navigation Satellite System) functionality. The Brazilian territory sits on one of the most affected areas of the globe, where the ionosphere behaves very unpredictably, with strong scintillation frequently occurring in the local postsunset hours. The correlation between scintillation occurrence and sharp variations in the ionospheric total electron content (TEC) in Brazil is demonstrated in Spogli et al. (2013). The compounded effect of these associated ionospheric disturbances on long baseline GNSS kinematic positioning is studied in this paper, in particular when ionospheric maps are used to aid the positioning solution. The experiments have been conducted using data from GNSS reference stations in Brazil. The use of a regional TEC map generated under the CALIBRA (Countering GNSS high-Accuracy applications Limitations due to Ionospheric disturbances in BRAzil) project, referred to as CALIBRA TEC map (CTM), was compared to the use of the Global Ionosphere Map (GIM), provided by the International GNSS Service (IGS). Results show that the use of the CTM greatly improves the kinematic positioning solution as compared with that using the GIM, especially under disturbed ionospheric conditions. Additionally, different hypotheses were tested regarding the precision of the TEC values obtained from ionospheric maps, and its effect on the long baseline kinematic solution evaluated. Finally, this study compares two interpolation methods for ionospheric maps, namely, the Inverse Distance Weight and the Natural Neighbor.

  8. Semi-empirical low-latitude ionospheric model. Environmental research papers

    SciTech Connect

    Anderson, D.N.; Mendillo; Herniter

    1985-10-10

    Since current empirical models specifying low-latitude electron density profiles severely underestimate the daytime plasma density scale-height and total electron content (TEC), a Semi-empirical, Low-latitude, Ionospheric Model (SLIM) was developed that is not only more realistic but is also computationally fast. Electron-density profiles (180 to 1800 km) are theoretically calculated as a function of latitude (every 2/sup 0/ between 24 N and 24 S dip latitude) and local time (every half-hour over 24 hours LT) by solving the time-dependent plasma-continuity equation. Assuming a Chapman-like profile, sets coefficients are then generated that reproduce these individual profiles. The coefficients themselves are easily stored, quickly retrieved, and form the basis for a fast, portable, semi-empirical computer code. This report describes briefly the input parameters used to theoretically calculate profiles and the procedures used to generate the coefficients. The SLIM profiles are compared with the Chiu and Bent empirical models for Equinox, solar-maximum conditions. Finally, electron densities, the coefficients, TEC and 6300 A airglow intensities are listed in tabular form for three seasons (Equinox, June solstice, and December solstice) and two solar-cycle periods (solar maximum and solar minimum).

  9. The response of the ionosphere to intense geomagnetic storms in 2012 using GPS-TEC data from East Africa longitudinal sector

    NASA Astrophysics Data System (ADS)

    Tesema, F.; Damtie, B.; Nigussie, M.

    2015-12-01

    The response of the ionosphere to intense magnetic storms has been studied using total electron content (TEC). TEC data recorded by a series of GPS receivers at a longitude ∼ 35 ° E covering a wide range of latitudes (32 ° S to 68 ° N, geographic) is analyzed to study spatio-temporal modifications of the vertical TEC (vTEC) during storms on 07 and 09 March 2012 and on 14 July 2012. We have observed main phase positive response at equatorial ionization anomaly (EIA) crests and mid latitude regions in all the storms. These main phase positive responses are associated with vertical drift enhancement (intensified equatorial electrojet (EEJ)) and the mechanical effect of equatorward neutral wind after an auroral activity. A daytime substantial depletion of TEC at low latitude region was observed on 08 March 2012. This is due to the combined effects of oversheilding and disturbance dynamo electric field that drive large downward drifts during the day. The low latitude and equatorial ionospheric response in the recovery phase days of March storm is found to be largely associated with the disturbance dynamo field that suppressed the upward E × B drift from EEJ observations. The summer negative and winter positive response in July storm as well as mid latitude positive response in March storm was associated with the composition changes as depicted by the O to N2 ratio from GUVI measurements.

  10. Analysis of total electron content (TEC) variations in the low- and middle-latitude ionosphere

    NASA Astrophysics Data System (ADS)

    Shim, Ja Soon

    Detailed study of the spatial correlations of day-to-day ionospheric TEC variations on a global scale was performed for four 30-day-long periods in 2004 (January, March/April, June/July, September/October) using observations from more than 1000 ground-based GPS receivers. In order to obtain the spatial correlations, initially, the day-to-day variability was calculated by first mapping the observed slant TEC values for each 5-minute GPS ground receiver-satellite pair to the vertical and then differencing it with its corresponding value from the previous day. This resulted in more than 150 million values of day-to-day change in TEC (DeltaTEC). Next, statistics were performed on the DeltaTEC values. The study indicates strong correlations between geomagnetic conjugate points, and these correlations are larger at low latitudes than at middle latitudes. Typical correlation lengths, defined as the angular separation at which the correlation coefficient drops to 0.7, were found to be larger at middle latitudes than at low latitudes. The correlation lengths are larger during daytime than during nighttime. The results indicate that the spatial correlation is largely independent of season. These spatial correlations are important for understanding the physical mechanisms that cause ionospheric weather variability and are also relevant to data assimilation. In an effort to better understand the effects of neutral wind and electric field on the TEC variability, a physics-based numerical Ionosphere/Plasmasphere Model (IPM) was used. The model solves the transport equations for the six ions, O+,NO +, O+2,N+2, H+, and He+, on convecting flux tubes that realistically follow the geomagnetic field. Two of the inputs required by the IPM are the thermospheric neutral wind and the low-latitude electric field, which can be given by existing empirical model or externally specified by the user. To study the relative importance of the neutral wind and the electric field for the TEC

  11. Unusual nighttime impulsive foF2 enhancements at low latitudes: Phenomenology and possible explanations

    NASA Astrophysics Data System (ADS)

    Perna, L.; Pezzopane, M.; Zuccheretti, E.; Fagundes, P. R.; de Jesus, R.; Cabrera, M. A.; Ezquer, R. G.

    2014-08-01

    This paper is focused on unusual nighttime impulsive electron density enhancements that are rarely observed at low latitudes on a wide region of South America, under quiet and medium/high geomagnetic conditions. The phenomenon under investigation is very peculiar because besides being of brief duration, it is characterized by a pronounced compression of the ionosphere. The phenomenon was studied and analyzed using both the F2 layer critical frequency (foF2) and the virtual height of the base of the F region (h‧F) values recorded at five ionospheric stations widely distributed in space, namely: Jicamarca (-12.0°, -76.8°, magnetic latitude -2.0°), Peru; Sao Luis (-2.6°, -44.2°, magnetic latitude +6.2°), Cachoeira Paulista (-22.4°, -44.6°, magnetic latitude -13.4°), and São José dos Campos (-23.2°, -45.9°, magnetic latitude -14.1°), Brazil; Tucumán (-26.9°, -65.4°, magnetic latitude -16.8°), Argentina. In a more restricted region over Tucumán, the phenomenon was also investigated by the total electron content (TEC) maps computed by using measurements from 12 GPS receivers. A detailed analysis of isoheight ionosonde plots suggests that traveling ionospheric disturbances (TIDs) caused by gravity wave (GW) propagation could play a significant role in causing the phenomenon both for quiet and for medium/high geomagnetic activity; in the latter case however a recharging of the fountain effect, due to electric fields penetrating from the magnetosphere, joins the TID propagation and plays an as much significant role in causing impulsive electron density enhancements.

  12. Positive and negative GPS-TEC ionospheric storm effects during the extreme space weather event of March 2015 over the Brazilian Sector

    NASA Astrophysics Data System (ADS)

    Fagundes, Paulo Roberto; Fejer, B. G.; Kavutarapu, Venkatesh; Gil Pillat, Valdir; Cardoso, Felipe Antonio; Ribeiro, Brunno Augusto

    2016-07-01

    We studied the response of the ionosphere (F-region) in the Brazilian sector during extreme space weather event of 17 March 2015 using a large network of 102 GPS-TEC stations. It is observed that the Vertical Total Electron Content (VTEC) was severely disturbed during the storm main and recovery phases. A wavelike oscillation with three peaks was observed in the TEC diurnal variation from equator to low latitudes during the storm main phase on 17th and 18th March, 2015. The latitudinal extent of the wavelike oscillation peaks decreased from the beginning of main phase towards the recovery phase. The first peak extended from beyond 0S to 30S, the second occurred from 6S to 25S, whereas the third diurnal peaks was confined from 13S to 25S. In addition, a strong negative phase in VTEC variations was observed during the recovery phase on March 18-19, 2015. This ionospheric negative phase was stronger at low-latitudes than in the equatorial region. Also, two latitudinal chains of GPS-TEC stations from equatorial region to low latitudes in the East and West Brazilian sectors are used to investigate the storm time behavior of the Equatorial Ionization Anomaly (EIA) in the East and West Brazilian sectors. We observed an anomalous behavior in EIA caused by the wavelike oscillations during the storm main phase on 17 March, and suppression of the EIA, resulting from the negative phase in VTEC, in the storm recovery phase.

  13. Low-latitude particle precipitation and associated local magnetic disturbances

    SciTech Connect

    Rassoul, H.K. ); Rohrbaugh, R.P.; Tinsley, B.A. )

    1992-04-01

    The time variations of optical emissions during low-latitude auroral events have been shown to correlate well with those of magnetograms in the region where the aurorae are observed. Two events not previously reported are analyzed and are shown to confirm the nature of the correlations found for two earlier events. The maximum optical emissions at mid-latitudes occur in concert with the maximum positive (northward) excursions in the H trace and with rapid fluctuations in the D trace of nearby magnetograms. The fluctuation in {Delta}D is usually from the east (positive) to the west (negative) in the vicinity of the {Delta}H perturbation. The positive excursions in H at low-latitude observatories at the time of the maximum optical emissions are associated with negative H excursions at high latitude observatories in the same longitude sector. The source of the particles has been inferred to be the ring current, with precipitation occurring when the {vert bar}Dst{vert bar} index is large at the time of the large short term excursions in the local magnetic field. This result is consistent with the funding of Voss and Smith (1979), derived from a series of rocket measurements of precipitating heavy particles, that the flux correlates better with the product of {vert bar}Dst{vert bar} and the exponential of K{sub p} than with either alone. In the present case it is shown that the product of {vert bar}Dst{vert bar} and the amplitude of the short term excursions in the horizontal component in local magnetograms has better time resolution and better correlation with the observed emission rates than the index using K{sub p}.

  14. Low-latitude mountain glacier evidence for abrupt climate changes

    NASA Astrophysics Data System (ADS)

    Thompson, L. G.; Mosley-Thompson, E. S.; Lin, P.; Davis, M. E.; Mashiotta, T. A.; Brecher, H. H.

    2004-12-01

    Clear evidence that a widespread warming of Earth's climate system is now underway comes from low latitude mountain glaciers. Proxy temperature histories reconstructed from ice cores, and the rapidly accelerating loss of both the total ice area and ice volume on a near global scale suggest that these glaciers responding to increasing rates of melting. In situ observations reveal the startling rates at which many tropical glaciers are disappearing. For example, the retreat of the terminus of the Qori Kalis Glacier in Peru is roughly 200 meters per year, 40 times faster than its retreat rate in 1978. Similarly, in 1912 the ice on Mount Kilimanjaro covered 12.1 km2, but today it covers only 2.6 km2. If the current rate of retreat continues, the perennial ice fields may disappear within the next few decades, making this the first time in the past 11,700 years that Kilimanjaro will be devoid of the ice that shrouds its summit. Tropical glaciers may be considered ``the canaries in the coal mine'' for the global climate system as they integrate and respond to key climatological variables, such as temperature, precipitation, cloudiness, humidity, and incident solar radiation. A composite of the decadally-averaged oxygen isotopic records from three Andean and three Tibetan ice cores extending back over the last two millennia shows an isotopic enrichment in the 20th century that suggests a large-scale warming is underway at lower latitudes. Multiple lines of evidence from Africa, the Middle East, Europe and South America indicate an abrupt mid-Holocene climate event in the low latitudes. If such an event were to occur now with a global human population of 6.3 billion people, the consequences could be severe. Clearly, we need to understand the nature and cause of abrupt climate events.

  15. The solar eclipse and its associated ionospheric TEC variations over Indian stations on January 15, 2010

    NASA Astrophysics Data System (ADS)

    Vyas, B. M.; Sunda, Surendra

    2012-02-01

    An annular solar eclipse occurred over the Indian subcontinent during the afternoon hours of January 15, 2010. This event was unique in the sense that solar activity was minimum and the eclipse period coincides with the peak ionization time at the Indian equatorial and low latitudes. The number of GPS receivers situated along the path of solar eclipse were used to investigate the response of total electron content (TEC) under the influence of this solar eclipse. These GPS receivers are part of the Indian Satellite Based Augmentation System (SBAS) named as 'GAGAN' (GPS Aided Geo Augmented Navigation) program. The eight GPS stations located over the wide range of longitudes allows us to differentiate between the various factors induced due to solar eclipse over the equatorial and low latitude ionosphere. The effect of the eclipse was detected in diurnal variations of TEC at all the stations along the eclipse path. The solar eclipse has altered the ionospheric behavior along its path by inducing atmospheric gravity waves, localized counter-electrojet and attenuation of solar radiation intensity. These three factors primarily control the production, loss and transport of plasma over the equatorial and low latitudes. The localized counter-electrojet had inhibited the equatorial ionization anomaly (EIA) in the longitude belt of 72°E-85°E. Thus, there was a negative deviation of the order of 20-40% at the equatorial anomaly stations lying in this 'inhibited EIA region'. The negative deviation of only 10-20% is observed for the stations lying outside the 'inhibited EIA region'. The pre-eclipse effect in the form of early morning enhancement of TEC associated with atmospheric gravity waves was also observed during this solar eclipse. More clear and distinctive spatial and temporal variations of TEC were detected along the individual satellite passes. It is also observed that TEC starts responding to the eclipse after 30 min from start of eclipse and the delay of the

  16. Thermal imbalance and shock wave effects on low latitude ionosphere : asymmetric case of a total solar eclipse

    NASA Astrophysics Data System (ADS)

    Vila, P. M.; Fleury, R.; Le Roux, Y.; Kone, E.

    2003-04-01

    frequency, as well as on GPS TEC values. Analogic analysis of these modes show that local atmospheric shock waves were generated by the rapid eclipse totality cooling from sources at troposphere, mesosphere and lower thermosphere levels. For the general case of low latitudes Africa, we infer that similar oscillations from atmospheric storms can disturb the equatorial ionosphere during daytime (e.g. electrojet shears, layer strata) and nighttime (the irregular ESF seed component).

  17. Penetrating of high-latitude-electric-field effects to low latitudes during SUNDIAL 1984

    NASA Astrophysics Data System (ADS)

    Spiro, R. W.; Wolf, R. A.; Fejer, B. G.

    1988-02-01

    Electric-field-penetration events have been identified using F-region vertical-drift measurements obtained in the October 6-13, 1984 period by the Jicamarcan incoherent-backscatter radar and corresponding h-prime F measurements from ionosondes at Fortaleza, Cachoeira Paulista, and Dakar. Predictions made using the Rice Convection Model for the pattern, strength, and duration of the low-latitude electric field occurring in response to an increasing high-latitude convection agree with observations. The observed 1-2 h duration of the low-latitude response to decreased convection can be explained by the fossil-wind theory of Richmond (1983).

  18. Penetrating of high-latitude-electric-field effects to low latitudes during SUNDIAL 1984

    NASA Technical Reports Server (NTRS)

    Spiro, R. W.; Wolf, R. A.; Fejer, B. G.

    1988-01-01

    Electric-field-penetration events have been identified using F-region vertical-drift measurements obtained in the October 6-13, 1984 period by the Jicamarcan incoherent-backscatter radar and corresponding h-prime F measurements from ionosondes at Fortaleza, Cachoeira Paulista, and Dakar. Predictions made using the Rice Convection Model for the pattern, strength, and duration of the low-latitude electric field occurring in response to an increasing high-latitude convection agree with observations. The observed 1-2 h duration of the low-latitude response to decreased convection can be explained by the fossil-wind theory of Richmond (1983).

  19. Studies of Total Electron Content variations at low-latitude stations within the Equatorial Ionization Anomaly zone

    NASA Astrophysics Data System (ADS)

    Lilian, Olatunbosun

    2016-07-01

    The total electron content (TEC) is an important parameter to monitor for possible space weather impacts. The radio waves that pass through the earth's ionosphere travel more slowly than their free space velocity due to group path delay of the ionosphere. This group path delay is directly proportional to the TEC of the ionosphere. Using dual frequency GPS receiver at low latitude stations of Ile-Ife (7.52oN, 4.28oE), Addis Ababa (9.04oN, 38.77oE) and Bangalore (13.03oE, 77.57oE), all located within 0 - 15oN of the equatorial anomaly region, the measurement of ionospheric TEC for 2012 has been carried out. The data from the three stations were used to study the diurnal, monthly and seasonal variations of TEC. The diurnal variations maximize between 10:00 - 16:00UT, 08:00 - 14:00UT and 06:00 - 12:00UT for Ile-Ife, Addis Ababa and Bangalore stations respectively. The diurnal variations showed wave-like pertubation during disturbed and quiet periods at Bangalore and Addis Ababa stations. The monthly average TEC variations showed that the month of March recorded the highest TEC value of ~59TECu at about 16:00UT in Ile-Ife station, while TEC at Addis Ababa and Bangalore maximize in October with ~72TECu and 65TECu at about 11:00UT and 09:00UT respectively. Seasonal variations showed that TEC maximizes during the equinoctial months and least in summer, over the three stations. Keywords: Total Electron Content, Equatorial Ionization Anomaly, Global Positioning System co-author:E.A. Ariyibi(Department of Physics and Engineering Physics, Obafemi Awolowo University, Ile-Ife, Nigeria)

  20. Comparison with IRI-PLUS and IRI-2012-TEC values of GPS-TEC values

    NASA Astrophysics Data System (ADS)

    Atıcı, Ramazan; Saǧır, Selçuk

    2016-07-01

    This study presents a comparison with IRI-PLUS and IRI-2012 Total Electron Content (TEC) values of Total Electron Content (TEC) values obtained from Ankara station (39,7 N; 32,76 E) of Global Position System (GPS) of Turkey on equinox and solstice days of 2009 year. For all days, it is observed that GPS-TEC values are greater than IRI-2012-TEC values, while IRI-PLUS-TEC values are very close to GPS-TEC values. When GPS-TEC values for both equinoxes are compared, it is seen that TEC values on September equinox are greater than one on March equinox. However, it is observed that GPS-TEC values on June solstice are greater than one on December solstice. Also, the relationship between GPS-TEC values and geomagnetic indexes is investigated.

  1. Influence of planetary scale waves on the upper atmospheric optical dayglow emissions over equatorial-low-latitude

    NASA Astrophysics Data System (ADS)

    Laskar, F. I.; Duggirala, P. R.; Thatiparthi, V. L.; Chakrabarti, S.; Reddy, M.; Raghavarao, R.; Pathan, B. M.; Khekale, P. V.

    2012-12-01

    Systematic measurement of optical dayglow emissions at multiple wavelengths, namely, 557.7nm , 630.0nm, and 777.4nm have been carried out over a large field-of-view using a newly built Multiwavelength Imaging Spectograph using Echelle-grating (MISE) during January-February 2011 from a low latitude station, Hyderabad (Geographic: 17.5 deg. N, 78.5 deg. E; Mag.: 8.6 deg. N, 151.8 deg. E), India. Several large and small scale features are seen in all the wavelengths. In contrast to the earlier measurement of OI-630.0nm red-line emission during the high solar activity period (2001), current optical dayglow measurements during relatively low solar epoch (2011) show no similarity with that of the solar flux. However, it is noted that the variation in strength of the equatorial electrojet (EEJ) seems to be similar to that of optical measurements in 2011. This is also in contrast with the measurements in 2001, where no similarity was seen between EEJ and OI-630.0nm dayglow intensity. Periodogram analysis of these two data sets (optical and EEJ) show a marked difference in the occurrence of the quasi-16-day planetary wave periods before noon and in the afternoon hours. In order to investigate the coupling of atmospheric regions, periodogram analysis of total electron content (TEC) and SABER measured mesosphere and lower thermosphere (MLT) temperature data were carried out. Interestingly, the TEC data from Bangalore (Mag. Lat 4 deg. N) shows contrasting behaviour in terms of periodicities before noon and afternoon similar to those in optical dayglow intensities, SABER temperatures, and the strength of the EEJ while the TEC periodicities of another further away station (Ahmedabad, Mag. Lat 15 deg. N) does not show any such behaviour. It is suggested that planetary wave of periods of quasi-9-day and quasi-16-day, which are observed in MLT have their influence on the behaviour of the upper atmosphere as seen in optical, radio and magnetic measurements. These results point to

  2. Structure of the low latitude boundary layer

    NASA Technical Reports Server (NTRS)

    Sckopke, N.; Paschmann, G.; Haerendel, G.; Sonnerup, B. U. O.; Bame, S. J.; Forbes, T. G.; Hones, E. W., Jr.; Russell, C. T.

    1980-01-01

    Observations at high temporal resolution of the frontside magnetopause and plasma boundary layer, made with the LASL/MPE fast plasma analyzer onboard the ISEE 1 and 2 spacecraft, revealed a complex quasiperiodic structure of some of the observed boundary layers. A cool tailward streaming boundary layer plasma was seen intermittently, with intervening periods of hot tenuous plasma which has properties similar to the magnetospheric population. While individual encounters with the boundary layer plasma last only a few minutes, the total observation time may extend over one hour or more.

  3. Low-latitude Es capable of controlling the onset of equatorial spread F

    NASA Astrophysics Data System (ADS)

    Joshi, L. M.; Patra, A. K.; Rao, S. V. B.

    2013-03-01

    investigate their role on the occurrence of equatorial spread F (ESF), the low-latitude E region in the evening hours has been characterized in terms of sporadic E (Es) activity based on ionosonde observations from Sriharikota, a low-latitude station in India. While prior to the sunset, either Chapman type E layer, or Es, or a combination of the two was observed, after sunset, when observed, the E layer was exclusively Es. Es, however, could be either blanketing or nonblanketing type. Observations revealed that while the occurrence of ESF had a broad relationship with the type of Es, a detailed investigation suggested that (1) ESF occurred (did not occur) irrespective of Es type if the virtual height of the F layer base (h'F) was greater than ~360 km (less than ~290 km), and (2) ESF occurrence depended strongly on the type of Es if 290 km < h'F < 360 km. Model computation shows that low-latitude Es can significantly influence the growth of the Rayleigh-Taylor instability for the cases corresponding to category 2 by increasing the total field-line integrated Pedersen conductivity, consistent with the observations. The results presented in this paper highlight under what circumstances the low-latitude Es would play a critical role in the occurrence of ESF, which can be used to understand the day-to-day variability of ESF.

  4. Analytical study of nighttime scintillations using GPS at low latitude station Bhopal

    SciTech Connect

    Maski, Kalpana; Vijay, S. K.

    2015-07-31

    Sporadically structured ionosphere (i.e. in-homogeneities in refractive index) can cause fluctuations (due to refraction effects) on the radio signal that is passing through it. These fluctuations are called ionospheric scintillations. Low latitude region is suitable for studying these scintillations. The influence of the ionosphere on the propagation of the radio wave becomes very marked with reference to communication or navigational radio system at very low frequency (VLF) to a high frequency (HF), which operate over the distances of 1000 km or more. Radio wave communication at different frequencies depends on structure of the ionosphere. With the advent of the artificial satellites, they are used as a prime mode of radio wave communication. Some natural perturbation termed as irregularities, are present in the form of electron density of the ionosphere that cause disruption in the radio and satellite communications. Therefore the study of the ionospheric irregularities is of practical importance, if one wishes to understand the upper atmosphere completely. In order to make these communications uninterrupted the knowledge of irregularities, which are present in the ionosphere are very important. These irregularities can be located and estimated with the help of Ionospheric TEC and Scintillation. Scintillation is generally confined to nighttime hours, particularly around equatorial and low latitudes.

  5. Equatorial ionization anomaly development as studied by GPS TEC and foF2 over Brazil: A comparison of observations with model results from SUPIM and IRI-2012

    NASA Astrophysics Data System (ADS)

    Nogueira, P. A. B.; Abdu, M. A.; Souza, J. R.; Batista, I. S.; Bailey, G. J.; Santos, A. M.; Takahashi, H.

    2013-11-01

    The equatorial ionization anomaly (EIA) development is studied using the total electron content (TEC) observed by the Global Positioning System (GPS) satellites, the F2-layer critical frequency (foF2) as measured by digisondes operated in the Brazilian sector, and by model simulation using the SUPIM (Sheffield University Plasmasphere Ionosphere Model). We have used two indices based on foF2 and TEC to represent the strength of the EIA Southern Anomaly Crest (SAC), which are denoted, respectively, by SAC(foF2) and SAC(TEC). Significant differences in the local time variations of the EIA intensity, as represented by these two indices, are investigated. The observed SAC indices are compared with their values modeled by the SUPIM and also by the International Reference Ionosphere (IRI)-2012. The SUPIM simulations that use the standard E×B plasma drift and neutral air wind models are found to provide acceptable representations of the observed foF2 and TEC, and hence the indices SAC(foF2) and SAC(TEC) during daytime, whereas the IRI-2012 model is not, except during the post-midnight/sunrise hours. It is found that the differences in the local time variations between the SAC(foF2) and SAC(TEC) can be reduced by limiting the TEC integrations in height up to an altitude of 630 km in the SUPIM calculations. It is also found that when the EIA intensity is calculated for an intermediate dip latitude (12°S) the difference between the local time variation patterns of the two corresponding indices in the experimental data and in the SUPIM results is reduced. For the IRI-2012 values, the subequatorial station modification does not appear to have any effect.

  6. Low-Latitude Ethane Rain on Titan

    NASA Technical Reports Server (NTRS)

    Dalba, Paul A.; Buratti, Bonnie J.; Brown, R. H.; Barnes, J. W.; Baines, K. H.; Sotin, C.; Clark, R. N.; Lawrence, K. J.; Nicholson, P. D.

    2012-01-01

    Cassini ISS observed multiple widespread changes in surface brightness in Titan's equatorial regions over the past three years. These brightness variations are attributed to rainfall from cloud systems that appear to form seasonally. Determining the composition of this rainfall is an important step in understanding the "methanological" cycle on Titan. I use data from Cassini VIMS to complete a spectroscopic investigation of multiple rain-wetted areas. I compute "before-and-after" spectral ratios of any areas that show either deposition or evaporation of rain. By comparing these spectral ratios to a model of liquid ethane, I find that the rain is most likely composed of liquid ethane. The spectrum of liquid ethane contains multiple absorption features that fall within the 2-micron and 5-micron spectral windows in Titan's atmosphere. I show that these features are visible in the spectra taken of Titan's surface and that they are characteristically different than those in the spectrum of liquid methane. Furthermore, just as ISS saw the surface brightness reverting to its original state after a period of time, I show that VIMS observations of later flybys show the surface composition in different stages of returning to its initial form.

  7. Disturbed time observations of the temporal dependence and dynamics of TEC, scintillation, and ionospheric irregularity zonal drifts

    NASA Astrophysics Data System (ADS)

    Muella, Marcio; de Paula, Eurico; Kintner, Paul; Kantor, Ivan; Cerruti, Alessandro; Mitchell, Cathryn; Crowley, Geoff; Smorigo, Paulo; Batista, Inez

    GPS amplitude scintillations at the L1 frequency (1.575 GHz) and integral data of total electron content (TEC) obtained from measurements of the Brazilian ground-based GPS network are used to study specific relationships between TEC, scintillations and ionospheric electron density imaged at near the southern crest of the Equatorial Ionization Anomaly (EIA). Using a time-dependent tomographic model, 3-dimensional images are created to couple the geophysical quantities measured by the GPS receivers during the storm time period of November 18-23. It allows studying large variations in the temporal and spatial evolution of the electron density affecting the behavior and dynamics of the scintillations. Estimations of the ionospheric irregularity zonal drift velocities at 350 km obtained from two-spaced GPS receivers observations, and the coupling of the neutral atmosphere and the ionosphere obtained from the ASPEN- TIMEGCM model results are also used in the investigation. The model is used to analyze the north-south symmetry/asymmetry conditions in the ionization distribution of the equatorial anomaly produced by a meridional/transequatorial wind, and its effect to the development and evolution of the scintillations associated to the ionospheric irregularities. In this work we present some relevant aspects of the ionospheric dynamics and the thermosphere-ionosphere coupling system, which are some of the most important topics of study during the occurrence of geomagnetic storms.

  8. Low-Latitude Ethane Rain on Titan

    NASA Astrophysics Data System (ADS)

    Dalba, Paul; Buratti, B. J.; Brown, R. H.; Barnes, J. W.; Baines, K. H.; Sotin, C.; Clark, R. N.; Lawrence, K. J.; Nicholson, P. D.

    2012-10-01

    Cassini ISS observed multiple widespread changes in surface brightness in Titan's equatorial regions over the past three years (Barnes, J. W. et al. 2012, Icarus, submitted). These brightness variations are attributed to rainfall from cloud systems that appear to form seasonally (Turtle, E. P. et al. 2011, Science, 331, 1414-1417). Determining the composition of this rainfall is an important step in understanding the “methanological” cycle that dominates Titan's surface and atmosphere. In this study, we use data from Cassini VIMS to complete a thorough spectroscopic investigation of rain-wetted areas near Yalaing Terra, Hetpet Regio and central Adiri on Titan. We compute “before-and-after” spectral ratios of any areas that show either deposition or evaporation of rain at any point in the time span of August 2009 to January 2012. By comparing these spectral ratios to a model of liquid ethane that was calculated to match the resolution and sampling interval of VIMS (Brown, R. H. et al. 2008, Nature, 454, 607-610), we find that the rain is most likely composed of liquid ethane. The spectrum of liquid ethane contains multiple absorption features that fortunately fall within the 2-micron and 5-micron spectral windows in Titan's atmosphere. We show that these features are visible in the spectra taken of Titan's surface and that they are characteristically different than those in the spectrum of liquid methane. Furthermore, just as ISS saw the surface brightness reverting to its original state after a period of time, we show that VIMS observations of later flybys show the surface composition in different stages of returning to its initial form as well. This research was carried out at the Jet Propulsion Laboratory, California Institute of Technology under contract to the National Aeronautics and Space Administration. Copyright 2012. All rights reserved.

  9. Low-latitude ethane rain on Titan

    NASA Astrophysics Data System (ADS)

    Dalba, P. A.; Buratti, B. J.; Brown, R. H.; Barnes, J. W.; Baines, K. H.; Sotin, C.; Clark, R. N.; Lawrence, K. J.; Nicholson, P. D.

    2012-12-01

    Cassini ISS observed multiple widespread changes in surface brightness in Titan's equatorial regions over the past three years (Barnes, J. W. et al. 2012, Icarus, submitted). These brightness variations are attributed to rainfall from cloud systems that appear to form seasonally (Turtle, E. P. et al. 2011, Science, 331, 1414-1417). Determining the composition of this rainfall is an important step in understanding the "methanological" cycle that dominates Titan's surface and atmosphere. In this study, we use data from Cassini VIMS to complete a thorough spectroscopic investigation of rain-wetted areas near Yalaing Terra, Hetpet Regio and central Adiri on Titan. We compute "before-and-after" spectral ratios of any areas that show either deposition or evaporation of rain at any point in the time span of August 2009 to January 2012. By comparing these spectral ratios to a model of liquid ethane that was calculated to match the resolution and sampling interval of VIMS (Brown, R. H. et al. 2008, Nature, 454, 607-610), we find that the rain is most likely composed of liquid ethane. The spectrum of liquid ethane contains multiple absorption features that fortunately fall within the 2-micron and 5-micron spectral windows in Titan's atmosphere. We show that these features are visible in the spectra taken of Titan's surface and that they are characteristically different than those in the spectrum of liquid methane. Furthermore, just as ISS saw the surface brightness reverting to its original state after a period of time, we show that VIMS observations of later flybys show the surface composition in different stages of returning to its initial form as well. Funded by NASA.

  10. Statistical characteristics of low-latitude ionospheric scintillation over China

    NASA Astrophysics Data System (ADS)

    Liu, Kangkang; Li, Guozhu; Ning, Baiqi; Hu, Lianhuan; Li, Hongke

    2015-03-01

    The Global Positioning System (GPS) L-band ionospheric scintillation produced by electron density irregularities in the ionospheric E- and F-regions, is mainly a low- and high-latitude phenomenon. In this study, the statistical behavior of GPS ionospheric scintillation over a Chinese low-latitude station Sanya (18.3°N, 109.6°E; dip lat: 12.8°N) has been investigated. A detailed study on the seasonal and solar activity dependence of scintillation occurrence during July 2004-December 2012 show that the amplitude scintillation pattern, with a maximum occurrence during equinox of solar maximum, agrees with plasma bubble observations by in situ satellites in this longitude. A few daytime periodic scintillation events are found during June solstice months of solar minimum. Interestingly, a significant equinoctial asymmetry of scintillation onset time is found in 2011-2012. The initiation of scintillation during September-October is on average earlier than that of March-April about 25 min. Meanwhile, the zonal drifts of irregularities estimated using two spatially separated GPS receivers over Sanya show a similar behavior during the two equinoxes, slowly decreasing from 150 m/s at post-sunset to 50 m/s near midnight. The possible mechanisms responsible for the occurrence characteristics of GPS scintillation over Sanya, and relevant aspects of the zonal drifts of the irregularities are discussed.

  11. Inner Plasma Structure of the Low-Latitude Reconnection Layer

    NASA Technical Reports Server (NTRS)

    Zhang, Q.-H.; Dunlop, M. W.; Lockwood, M.; Lavraud, B.; Bogdanova, Y. V.; Hasegawa, H.; Yang, H. -G.; Liu, R. -Y.; Hu, H. -Q.; Zhang, B. -C.; Pu, Z. -Y.; Yang, Z. -W.; Wang, J.; Taylor, M. G. G. T.; Berchem, J.; Constantinescu, D.; Volwerk, M.; Frey, H.; Fazakerley, A. N.; Shen, C.; Shi, J. -K.; Sibeck, D.; Escoubet, P.; Wild, J. A.

    2012-01-01

    We report a clear transition through a reconnection layer at the low-latitude magnetopause which shows a complete traversal across all reconnected field lines during northwestward interplanetary magnetic field (IMF) conditions. The associated plasma populations confirm details of the electron and ion mixing and the time history and acceleration through the current layer. This case has low magnetic shear with a strong guide field and the reconnection layer contains a single density depletion layer on the magnetosheath side which we suggest results from nearly field-aligned magnetosheath flows. Within the reconnection boundary layer, there are two plasma boundaries, close to the inferred separatrices on the magnetosphere and magnetosheath sides (Ssp and Ssh) and two boundaries associated with the Alfvén waves (or Rotational Discontinuities, RDsp and RDsh). The data are consistent with these being launched from the reconnection site and the plasma distributions are well ordered and suggestive of the time elapsed since reconnection of the field lines observed. In each sub-layer between the boundaries the plasma distribution is different and is centered around the current sheet, responsible for magnetosheath acceleration. We show evidence for a velocity dispersion effect in the electron anisotropy that is consistent with the time elapsed since reconnection. In addition, new evidence is presented for the occurrence of partial reflection of magnetosheath electrons at the magnetopause current layer.

  12. Low-latitude Ionospheric Heating during Solar Flares

    NASA Astrophysics Data System (ADS)

    Klenzing, J.; Chamberlin, P. C.; Qian, L.; Haaser, R. A.; Burrell, A. G.; Earle, G. D.; Heelis, R. A.; Simoes, F. A.

    2013-12-01

    The advent of the Solar Dynamics Observatory (SDO) represents a leap forward in our capability to measure rapidly changing transient events on the sun. SDO measurements are paired with the comprehensive low latitude measurements of the ionosphere and thermosphere provided by the Communication/Navigation Outage Forecast System (C/NOFS) satellite and state-of-the-art general circulation models to discuss the coupling between the terrestrial upper atmosphere and solar radiation. Here we discuss ionospheric heating as detected by the Coupled Ion-Neutral Dynamics Investigation (CINDI) instrument suite on the C/NOFS satellite during solar flares. Also discusses is the necessity of decoupling the heating due to increased EUV irradiance and that due to geomagnetic storms, which sometimes occur with flares. Increases in both the ion temperature and ion density in the subsolar topside ionosphere are detected within 77 minutes of the 23 Jan 2012 M-class flare, and the observed results are compared with the Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model (TIME-GCM) using the Flare Irradiance Spectral Model (FISM) as an input.

  13. Singular Plasma Disturbance in the Low-Latitude F Region

    NASA Technical Reports Server (NTRS)

    Singh, Sardul; Johnson, F. S.; Heelis, R. A.

    1999-01-01

    We describe here a new phenomenon characterized by unusual patterns of ion drifts inside ion density depletion regions observed by the AE-E satellite in the low-latitude F region. In about 30 depletions, vertical ion drift relative to the background was upward on the western sides, downward on the eastern sides, and zero near the middle where the density depletion was greatest. These drift characteristics are distinct from those observed in plasma bubble depletions. The structures reported here were observed on circular orbits below 300 km altitude and had density depletions of up to 2 orders of magnitude or more below the ambient ion density. The upward and downward drift excursions were up to 200 m/s relative to the background. Almost all these structures were observed over oceans or near coasts and largely between +/- 10 deg and +/- 30 deg clip latitude. The structures were observed mostly as isolated, single depletion regions with the majority of them about 250 km wide in the east-west direction. They occurred during quiet magnetic conditions with near-equal occurrence frequencies in the premidnight and postmidnight periods. The characteristic density and drift signatures indicate westward propagating disturbances in which the bottomside F layer is first lifted and then returned back to its original position, leaving the ionosphere undisturbed after the disturbance passes by. The estimated speed of these disturbances is of the order of 200 m/s. These unique solitary plasma disturbances, which we designate as singular plasma disturbances, are associated with a propagating source of E x B drift, not driven by neutral perturbations at the altitude of observation.

  14. Model for the low-latitude ionosphere with coefficients for different seasonal and solar cycle conditions. Final report, 1 October 1981-30 June 1986

    SciTech Connect

    Mendillo, M.; Herniter, B.

    1986-11-01

    A new ionospheric model for the low-latitude ionosphere was constructed to provide easy access to electron density profiles (Ne(h)), total electron content (TEC) and 6300A airglow under a variety of conditions. Results from the rigorous theoretical calculations for ionospheric structure at a given time and a site were parameterized to a set of six coefficients that reproduce the individual Ne(h) profiles using a simple algebraic formula. This report summarizes the rationale for such a model, describes the input parameters and methods used to generate the coefficients, and provides a comprehensive set of coefficients. The model covers the low-latitude ionosphere (24 N to 24 S every 4 deg of dip latitude), over the altitude range 180 to 1000km, for every hour of local time. The tabulated coefficients, TEC and 6300 airglow are presented for three seasons (Equinox, June solstice, and December solstice) and two solar cycles (solar maximum and solar minimum).

  15. Small, highly reflective ice crystals in low-latitude cirrus

    NASA Astrophysics Data System (ADS)

    Garrett, T. J.; Gerber, H.; Baumgardner, D. G.; Twohy, C. H.; Weinstock, E. M.

    2003-11-01

    At low latitudes, cirrus are ubiquitous and can be in excess of 100°C colder than the surface, limiting the amount of sunlight absorbed by the earth's atmosphere and surface, and reducing its loss of heat. Here we present aircraft measurements within cirrus over southern Florida indicating that ice crystals have smaller sizes and are more reflective than is assumed in most current climate models. If the measurements are generally representative of low-latitude cirrus, they point to a first-order correction to representations of how these clouds affect the earth's climate.

  16. Ionosphere-Thermosphere Coupling in Jupiter's Low Latitudes

    NASA Astrophysics Data System (ADS)

    Stallard, T.; Melin, H.; Johnson, R.; O'Donoghue, J.; Moore, L.; Miller, S.; Tao, C.; Achilleos, N. A.; Smith, C.; Ray, L. C.; Yates, J. N.

    2015-12-01

    One of the leading problems in our understanding of Jupiter's atmosphere, known colloquially as the 'energy crisis', is that the upper atmosphere has global temperatures far in excess of that predicted by solar heating. Unlike the Earth, solar heating has only a small effect on the thermosphere, varying little in temperature with local time, and with equatorial neutrals co-rotating with the planet due to meridional advection. Within the auroral region, ionosphere-thermosphere coupling produces strong flows and results in huge Joule Heating from auroral currents. In this region, the temperature excess can be explained, but Jupiter's fast rotation means that Coriolis forces prevent energy in the poles from transferring equatorward, so there remains no explanation of why low latitudes are overheated by a factor of 3-5 over that predicted by solar heating alone.Despite this anomaly, although the past twenty years has seen a wealth of new data and results in Jupiter's auroral region, studies of the equatorial region have been somewhat limited. This lack of investigation comes partly from the apparent uniform nature of the equatorial region, and partly from the difficulty in observing this region. It is only in the past three years that observers begun to re-examine this region, revealing evidence of complex interactions between the thermosphere and ionosphere, including what appears to be thermospheric weather patterns at a fixed planetary longitudes, stable over two decades; perhaps caused by continuous flows from the auroral region. Here, we introduce our recent research, in order to compare and contrast what has been observed at Jupiter with the more well understood interactions between Earth's ionosphere and thermosphere. We hope that this will open a discussion between the communities that will improve our understanding of the underlying physical processes, as they occur at both planets.

  17. Response of the equatorial and low-latitude ionosphere in the Indian sector to the geomagnetic storms of January 2005

    NASA Astrophysics Data System (ADS)

    Sreeja, V.; Devasia, C. V.; Ravindran, Sudha; Pant, Tarun Kumar; Sridharan, R.

    2009-06-01

    The equatorial and low-latitude ionospheric response to three moderate geomagnetic storms (17, 18, and 22 January) during the period from 16 to 23 January 2005 is investigated in the context of development/inhibition of the Equatorial Ionization Anomaly (EIA) and the subsequent occurrence/nonoccurrence of Equatorial Spread F (ESF) irregularities on these days. The study is carried out using the Total Electron Content (TEC) measured with the GPS receivers along the ˜80°E longitude sector and the F-layer bottom height obtained from the Ionosonde located over the dip equatorial location of Trivandrum (8.5°N, 77°E, dip latitude ˜0.5°N) in India. It is observed that, for the storms on days 17 and 22, the development of the anomaly was inhibited, probably due to the westward disturbance dynamo electric fields. Subsequently, the post sunset enhancement in the vertical drift of the equatorial F region was also inhibited significantly compared to the quiet day pattern and, as anticipated, no ESF was observed on these days. A large vertical drift of the equatorial F region followed by nearly simultaneous onset of weak ESF was observed on day 18. The late development of the EIA on this day could be due to the eastward prompt penetration electric field associated with the southward turning of the interplanetary magnetic field. Also, strong and distinct F3 layer appeared for a short time in the morning, reappeared later in the noon time, and then quickly ascended to the topside ionosphere during the main phase of the storm on day 18.

  18. A comparative analysis of the model calculated and GPS-observed TEC variations before the Haiti, 2010 and Japan, 2011 earthquakes

    NASA Astrophysics Data System (ADS)

    Namgaladze, Alexander; Karpov, Mikhail; Zolotov, Oleg

    2013-04-01

    Model simulations of the ionosphere Total Electron Content (TEC) variations have been performed for the Haiti January 12, 2010 and Japan March 11, 2011 earthquakes. Calculations have been carried out using the global numerical Upper Atmosphere Model (UAM). The seismogenic impacts in the model have been set as lower boundary conditions for the electric potential equation. Namely, the vertical electric currents of ~ 20 nA/m2 flowing from the ionosphere to the Earth have been set at the near-epicenter area of ~ 250 by 2000 km. The simulated relative (%) TEC disturbances for both events have been compared to each other and to the corresponding GPS-observed data. The common features persisting at both observed and modeled TEC variations are: (1) the appearance of positive disturbances 20 - 40% by magnitude at night hours for 2 - 4 days before the earthquake, (2) the geomagnetic conjugation of the effects and (3) the lack of migration (movements) of the TEC deviations during their lifetime (of ~ 8 hours). Main differences between the considered events (Haiti and Japan), both modeled and observed, are most evidently pronounced in the TEC disturbances' maximum location relative to the geomagnetic equator. In case of the Haiti earthquake the strongest by magnitude TEC disturbances are located near the magnetically conjugated to the earthquake's epicenter region at the Southern hemisphere, while in case of the Japan earthquake - near the epicenter at the Northern hemisphere. We have attributed this difference to the different seasons the events have taken place in. The asymmetry of the Haiti model TEC disturbances relative to the magnetic meridian of the earthquake's epicenter is in agreement with the GPS-observed one. In case of the Japan earthquake the asymmetry of the TEC deviations relative to the magnetic meridian of the earthquake's epicenter is negligible in the observations, while in the model results it is similar to the Haiti case. In order to remove this asymmetry

  19. Origin of high-frequency TEC disturbances observed by GPS over the European mid-latitude region

    NASA Astrophysics Data System (ADS)

    Wautelet, Gilles; Warnant, Rene

    2015-10-01

    High-frequency variability of the ionospheric Total Electron Content (TEC) can strongly affect precise positioning with GNSS. The occurrence rate as well as the amplitude of such disturbances has been extensively studied over the last decade. Mainly, one can distinguish disturbances due to space-weather events and the others, qualified as "quiet-time" as they are observed during quiet geomagnetic conditions. The latter, which represent more than 75% of the total number of disturbances over mid-latitudes, are then divided into two categories: the Winter Daytime (WD) and the Summer Nighttime (SN). The first category, representing the bulk of quiet-time disturbances, corresponds to classical Medium-Scale Traveling Ionospheric Disturbances (MSTIDs), that are the result of the interaction of gravity waves and the ionospheric plasma. On the other hand, SN disturbances are generally understood as non-classical MSTIDs of electrical origin. The paper investigates the origin of these two types of disturbance based on GPS measurements, ionospheric soundings and wind speed data at a tropospheric level. If one cannot exclude the solar terminator as a potential source of gravity waves responsible for WD events, it is thought that the major contribution comes from the lower atmosphere. More precisely, tropospheric jetstream is considered as the favorite candidate for daytime MSTIDs. Turning to SN disturbances, our analysis reveals that they are related to spread-F phenomenon, linked to the appearance of sporadic E-layers. The related instabilities are responsible for field-aligned irregularities in the F-region, which are thought to be responsible for noise-like fluctuations of the GPS TEC observed during SN events.

  20. Comparison of equatorial GPS-TEC observations over an African station and an American station during the minimum and ascending phases of solar cycle 24

    NASA Astrophysics Data System (ADS)

    Akala, A. O.; Seemala, G. K.; Doherty, P. H.; Valladares, C. E.; Carrano, C. S.; Espinoza, J.; Oluyo, S.

    2013-11-01

    GPS-TEC data were observed at the same local time at two equatorial stations on both longitudes: Lagos (6.52° N, 3.4° E, 3.04° S magnetic latitude), Nigeria; and Pucallpa (8.38° S, 74.57° W, 4.25° N magnetic latitude), Peru during the minimum (2009, 2010) and ascending (2011) phases of solar cycle 24. These data were grouped into daily, seasonal and solar activity sets. The day-to-day variations in vertical TEC (VTEC) recorded the maximum during 14:00-16:00 LT and minimum during 04:00-06:00 LT at both longitudes. Seasonally, during solar minimum, maximum VTEC values were observed during March equinox and minimum during solstices. However, during the ascending phase of the solar activity, the maximum values were recorded during the December solstice and minimum during the June solstice. VTEC also increased with solar activity at both longitudes. On longitude by longitude comparison, the African GPS station generally recorded higher VTEC values than the American GPS station. Furthermore, harmonic analysis technique was used to extract the annual and semi-annual components of the amplitudes of the TEC series at both stations. The semi-annual variations dominated the TEC series over the African equatorial station, while the annual variations dominated those over the American equatorial station. The GPS-TEC-derived averages for non-storm days were compared with the corresponding values derived by the IRI-2007 with the NeQuick topside option. The NeQuick option of IRI-2007 showed better performance at the American sector than the African sector, but generally underestimating TEC during the early morning hours at both longitudes.

  1. On the Connection Between Solar Activity and Low-Latitude Aurorae in the Period 1715 - 1860

    NASA Astrophysics Data System (ADS)

    Vázquez, M.; Vaquero, J. M.; Curto, J. J.

    2006-11-01

    Observations of aurorae borealis at low latitudes are very rare and are clearly associated with strong geomagnetic storms. Morphologically, they are characterized by a diffuse red colour with no rapid motions. The main aim of this paper is to analyse two hitherto ignored aurorae that were observed at two low-latitude sites, Tenerife (28°N 18°W) and Mexico City (19°N 99°W), in 1770 and 1789, respectively. These observations can give supplementary information about the level of solar activity at those times where direct solar observations were rather scarce. Studying also the behaviour of the heliosphere during this period using different proxies, we find that the open magnetic field better describes auroral occurrences. The variation over time in geomagnetic latitude at the two sites is also calculated.

  2. Ulysses sees differences in solar wind at high, low latitudes

    NASA Astrophysics Data System (ADS)

    1995-06-01

    Scientists presenting results today of their data at the spring meeting of the American Geophysical Union in Baltimore, Md., said the speed of the solar wind over the southern pole is high, compared to its low velocity near the Sun's equator. The solar wind is the hot ionized gas that escapes from the solar corona and expands into interplanetary space. At the present minimum of the solar activity cycle, the angle between the Sun's rotational and magnetic equators has decreased -- in these conditions Ulysses found that the region of low-speed solar winds were confined more closely to the rotational equator than in earlier portions of the solar cycle. Now on its way to the northern solar pole, Ulysses is nearly 62 degrees north of the Sun's equator today. The second phase of the primary mission -- to explore the northern pole of the Sun -- will begin on June 19, when the spacecraft reaches 70 degrees north latitude, The spacecraft will reach a maximum northern latitude of 80,2 degrees on 31 July 1995. Ulysses' trajectory from 80 degrees south of the equator in September 1994, back down to the Sun's equator in March 1995, also brought the spacecraft within 1.3 astronomical units (121 million miles, 194 million km) of the Sun, the closest Ulysses would ever travel to the Sun since it was launched on October 6, 1990. The spacecraft picked up speed during this phase allowing the entire region to be scanned in just six months time. Scientists refer to this phase of the mapping as the "fast latitude scan", Ulysses had left the equatorial plane in early 1992 after a gravitational swingby of Jupiter, and had gradually climbed in latitude until reaching 80 degrees south in September 1994. Ulysses' observations during the fast latitude scan have shown that the solar wind being continuously emitted by the Sun is distinctly different at high and low latitudes, said Dr. Edward J. Smith, Ulysses project scientist at NASA's Jet Propulsion Laboratory, for the joint NASA

  3. Ionospheric control of polarization of low-latitude geomagnetic micropulsations at sunrise

    NASA Astrophysics Data System (ADS)

    Saka, O.; Itonaga, M.; Kitamura, T.

    1982-08-01

    The ionospheric control of low latitude pulsation polarization characteristics suggested by Saka et al. (1980) has been confirmed through continuous low latitude Pc3 and Pc4 geomagnetic micropulsation observations. The D-component amplitude increases as much as that of the H-component after sunrise, effecting the tilting of the major polarization ellipse axis from north to northwest. This coincides with the appearance of the E-layer in the ionosphere within an hour, and the time of the coincidence shifts from season to season in parallel with changes of sunrise. The ellipticity of the horizontal plane polarization is not appreciably affected by sunrise. It is suggested that the Hall conductivity increment associated with the E-layer sunrise enhancement affects the characteristics of the D-component on the ground.

  4. Low latitude aurorae as a diagnostic for energetic particle injections and their environment

    NASA Astrophysics Data System (ADS)

    Thaller, S. A.; Wygant, J. R.; Dai, L.; Dombeck, J. P.; Cattell, C. A.; Mozer, F.; Russell, C. T.; Fennell, J. F.; Claudepierre, S. G.; Mende, S. B.; Frey, H. U.

    2012-12-01

    The region between the inner magnetosphere and the geomagnetic tail/plasma sheet is highly dynamic during geomagnetic storms and hosts many important magnetospheric phenomenon and structures, including particle injections and the outer radiation belt. The energy transport mechanisms in this region during major storms are not yet fully understood, however there is increasing evidence that in the range of invariant latitudes (ILAT) mapping to this dipole-tail boundary region, Alfven waves are an important energy source for the aurora. This range of latitudes, which is roughly 50 to 68 degrees ILAT varying somewhat on the level of magnetospheric disturbance, is low latitude for the aurora. We present a study of intense earthward Alfvenic Poynting flux at the location of, and concomitant with, energetic electron injections during dipolarizations, on field lines mapping to low latitude aurorae. The Poynting flux, when mapped to an ionospheric altitude of 100km, is of sufficient intensity to power the magnetically conjugate auroral luminosities. The preliminary results suggest that wave Poynting flux is an important link between injection events and low latitude aurorae. Thus the observation of the intensification and dynamic behavior of low latitude auroral arcs, i.e. those on field lines that during storms map to the near- tail boundary where particle injections are observed, are an important diagnostic for the occurrence, location, and plasma dynamics associated with energetic particle injections. This has important implications for the Radiation Belt Storm Probes (RBSP) mission. The data gathered by RBSP can be used in conjunction with auroral data from the THEMIS all-sky imaging array in Canada, providing a richer context for the study of radiation belt physics.

  5. Recent low-latitude freeze thaw on Mars

    NASA Astrophysics Data System (ADS)

    Page, David P.

    2007-07-01

    Outside polar latitudes, features corresponding to surface thaw have yet to be identified on Mars. The youthful gully landforms observed at mid-high latitude [Malin, M., Edgett, K., 2000. Science 288, 2330-2335] are the nearest candidate, but the source (and nature) of the gully carving agent remains controversial [e.g., Musselwhite, D.S., Swindle, T.D., Lunine, J.I., 2001. Geophys. Res. Lett. 28, 1283-1285; Mellon, M.T., Phillips, R.J., 2001. J. Geophys. Res. 106, 1-15; Knauth, L.P., Burt, D.M., 2002. Icarus 158, 267-271; Costard, F., Forget, F., Mangold, N., Peulvast, J.P., 2002. Science 295, 110-113; Christensen, P.R., 2003. Nature 422, 45-48; Treiman, A.H., 2003. J. Geophys. Res. 108]. At higher obliquity than the present epoch, near-surface ground ice should be present globally [Mellon, M.T., Jakosky, B.M., 1995. J. Geophys. Res. 100 (E6), 11781-11799], populated by condensation of atmospheric water vapour in the top few metres of the regolith, or emplaced as dusty ice sheets reaching down towards the equator. The latitudinal restriction of these gullies to regions poleward of ±30° appears to argue against a thaw component to their formation—since ground ice is present and stable at all latitudes at high obliquity, the current (low) obliquity regime should result in ground ice thaw at low latitudes, where insolation and daytime temperatures are currently greatest, and this is not observed. A previously undescribed meltwater sequence in the Cerberus plains, at 20° N/187° E, shows that comparable, but much more continuous, and mappable melting and surface runoff have occurred in the geologically recent past at near-equatorial latitudes on Mars. Polygonal ground in the Cerberus plains is seen by the Mars Global Surveyor Mars Orbiter Camera (MOC) to suffer sequential, regional-scale volatile-loss consistent with thaw of near-surface ground ice under periglacial conditions. This degradation is continuously sampled by a single MOC strip, showing an icy

  6. Gravity wave activity observed in the mesosphere and ionosphere on September 16th 2015 by an all-sky imager and dTEC maps over Brazil

    NASA Astrophysics Data System (ADS)

    Wrasse, Cristiano M.; Gobbi, Delano; Buriti, Ricardo; Bageston, José Valentin; Medeiros, Amauri; Paulino, Igo; Cosme Alexandre Figueiredo, M.; Takahashi, Hisao; Azambuja, Rodrigo

    2016-07-01

    All-sky imager was used to observe the wave activity in the mesosphere and a ground network of GPS receivers were used to make detrended Total Electron Content (dTEC) maps to monitor the ionosphere. The wave activity was observed on September 16th 2015 over the southeast region in Brazil. The gravity wave characteristics and the atmospheric conditions for wave propagation will be presented and discussed. The gravity wave source was associated with strong tropospheric convection.

  7. Positive and negative GPS-TEC ionospheric storm effects during the extreme space weather event of March 2015 over the Brazilian sector

    NASA Astrophysics Data System (ADS)

    Fagundes, P. R.; Cardoso, F. A.; Fejer, B. G.; Venkatesh, K.; Ribeiro, B. A. G.; Pillat, V. G.

    2016-06-01

    We studied the response of the ionosphere (F region) in the Brazilian sector during extreme space weather event of 17 March 2015 using a large network of 102 GPS- total electron content (TEC) stations. It is observed that the vertical total electron content (VTEC) was severely disturbed during the storm main and recovery phases. A wavelike oscillation with three peaks was observed in the TEC diurnal variation from equator to low latitudes during the storm main phase on 17-18 March 2015. The latitudinal extent of the wavelike oscillation peaks decreased from the beginning of the main phase toward the recovery phase. The first peak extended from beyond 0°S to 30°S, the second occurred from 6°S to 25°S, whereas the third diurnal peaks was confined from 13°S to 25°S. In addition, a strong negative phase in VTEC variations was observed during the recovery phase on 18-19 March 2015. This ionospheric negative phase was stronger at low latitudes than in the equatorial region. Also, two latitudinal chains of GPS-TEC stations from equatorial region to low latitudes in the east and west Brazilian sectors are used to investigate the storm time behavior of the equatorial ionization anomaly (EIA) in the east and west Brazilian sectors. We observed an anomalous behavior in EIA caused by the wavelike oscillations during the storm main phase on 17 March, and suppression of the EIA, resulting from the negative phase in VTEC, in the storm recovery phase.

  8. Tomographic imaging of the equatorial and low-latitude ionosphere over central-eastern Brazil

    NASA Astrophysics Data System (ADS)

    Muella, Marcio T. A. H.; de Paula, Eurico R.; Mitchell, Cathryn N.; Kintner, Paul M.; Paes, Ricardo R.; Batista, Inez S.

    2011-02-01

    A four-dimensional time-dependent tomographic algorithm, named Multi Instrument Data Analysis System (MIDAS), is used to image the equatorial and low-latitude ionosphere over the central-eastern sides of the Brazilian territory. From differential phase data obtained by a chain of ground-based GPS receiver the total electron content (TEC) is estimated and then, together with a modeled ionosphere from International Reference Ionosphere (IRI) model, the electron density distribution is reconstructed and the parameters of the F 2-peak layer are accessed from the images. This paper presents the first study of ionospheric tomography using real dual-frequency data from the Brazilian Network for Continuous GPS Monitoring (RBMC). Ionospheric F 2-peak electron density ( N m F 2) accessed from the images are compared to concurrent measurements from three ionosondes installed across Brazil. One year of data during the solar maximum period from March/2001 to February/2002 is used to analyze the seasonal and hourly variation of the F 2-layer peak density. The accuracy with which MIDAS images the electron density during geomagnetic quiet periods is investigated through its correlation and deviation with the ionosonde and IRI model data, respectively. The main aspects of the reconstruction results at the equatorial ionization anomaly (EIA) region over Brazil are highlighted and discussed.

  9. Multifractal behaviour of the ionospheric scintillation index time series over an Indian low latitude station Surat

    NASA Astrophysics Data System (ADS)

    Tanna, H. J.; Pathak, K. N.

    2014-03-01

    The amplitude scintillation information recorded by the GSV4004B GISTM (Global Ionospheric Scintillation TEC Monitor) GPS receiver at an Indian low latitude station Surat (21.16°N, 72.78°E) for 48 months during the years 2009, 2010, 2011 and 2012 are utilized in the present work. Multifractal detrended fluctuation analysis (MF-DFA) have been carried out along with computation of q-order fluctuation function, q-order Hurst exponent, q-order mass exponent and multifractal spectrums for each monthly post-sunset S4 index time series. The non-linear dependence of mass exponent and dependence of q-order Hurst exponent on q-values reflect the existence of nonlinear interaction between different scales and multifractal structure in the system, respectively. The comparison of broadness and shape of spectra with the occurrence of scintillation activities registered in the same period reveal the existence of multifractality/complexity in the turbulent ionosphere, which is influenced by the small-scale intermittency and solar flux indices. The truncation of the spectrum is the evidence of manifestation of small-scale intermittency of the turbulent ionosphere. The higher values of the Hölder exponent α0, calculated from the spectrum, imply the irregular nature of the underlying process. The present study suggests that, MF-DFA may act as an important non-linear technique for identifying the effect of large and small-scale fluctuations in complex and turbulent ionosphere.

  10. Biomarkers of a Low-Latitude Neoproterozoic Glaciation

    NASA Astrophysics Data System (ADS)

    Olcott, A. N.; Sessions, A. L.; Corsetti, F. A.; Kaufman, A. J.

    2005-12-01

    Neoproterozoic low-latitude glaciations are often considered times of great biologic limitation because of the hypothesized presence of thick, global sea ice. Alternatively, climate models have suggested that tropical oceans could have remained ice-free, or covered by only thin sea ice, allowing life to continue unimpeded throughout the glaciations. The analysis of organic remains from synglacial sediments provides an approach to address the debate. Here we describe molecular, isotopic, and petrographic analyses of organic rich strata (up to 3.0 percent TOC) deposited in southeastern Brazil during Neoproterozoic low-latitude glaciation ca. 700 Ma. These strata contain extractable biomarkers, including 2-α-methyl hopanes, 2,3,6-trimethylarylisoprenoids, C29-C31 hopanes, and C27-C29 steranes. The preserved biomarkers reflect the presence of a complex and productive ecosystem comprised of both aerobic and anaerobic phototrophs, heterotrophs, and eukaryotes. The biomarker data indicate euxinia extending into the photic zone, providing evidence that the oceans were strongly stratified. Significantly, the occurrence of photosynthetic cyanobacteria and green sulfur bacteria at this time indicates that sea-ice cover at this location was thin to nonexistent, and is incompatible with models for snowball Earth that envision kilometers of ice thickness.

  11. Continuum observations of M 51 and M 83 at 1.1 mm with AzTEC

    NASA Astrophysics Data System (ADS)

    Wall, W. F.; Puerari, I.; Tilanus, R.; Israel, F. P.; Austermann, J. E.; Aretxaga, I.; Wilson, G.; Yun, M.; Scott, K. S.; Perera, T. A.; Roberts, C. M.; Hughes, D. H.

    2016-06-01

    We observed the spiral galaxies M 51 and M 83 at 20 arscec spatial resolution with the bolometer array Aztronomical Thermal Emission Camera (AzTEC) on the JCMT in the 1.1 mm continuum, recovering the extended emission out to galactocentric radii of more than 12 kpc in both galaxies. The 1.1 mm-continuum fluxes are 5.6 ± 0.7 and 9.9 ± 1.4 Jy, with associated gas masses estimated at 9.4 × 109 M⊙ and 7.2 × 109 M⊙ for M 51 and M 83, respectively. In the interarm regions of both galaxies, the N(H2)/I(CO) (or X-factor) ratios exceed those in the arms by factors of ˜1.5-2. In the inner discs of both galaxies, the X-factor is about 1 × 1020 cm- 2 (K km s- 1)- 1. In the outer parts, the CO-dark molecular gas becomes more important. While the spiral density wave in M 51 appears to influence the interstellar medium and stars in a similar way, the bar potential in M 83 influences the interstellar medium and the stars differently. We confirm the result of Foyle et al. that the arms merely heighten the star formation rate (SFR) and the gas surface density in the same proportion. Our maps reveal a threshold gas surface density for an SFR increase by two or more orders of magnitude. In both galaxy centres, the molecular gas depletion time is about 1 Gyr climbing to 10-20 Gyr at radii of 6-8 kpc. This is consistent with an inside-out depletion of the molecular gas in the discs of spiral galaxies.

  12. Winter-time dependence of the global TEC on the stratospheric temperature and solar radiation

    NASA Astrophysics Data System (ADS)

    Mukhtarov, Plamen; Pancheva, Dora

    2015-12-01

    This paper presents a simple linear regression model that enables to quantify the contribution of high-latitude stratospheric temperature and solar radiation (describes by its proxy F10.7) to the variability of the low-latitude TEC during winter. The model is based on cross-correlation analysis performed on the Aura MLS temperature measurements and the global CODE TEC data for the period of time 2005-2010, i.e. at low to moderate solar activity (F10.7 changes between ~65 and ~140 solar flux units). It revealed that the temperature at altitude of ~40 km and latitude of ~60°N describes the most typical winter conditions and shows the largest negative correlation with the low-latitude TEC. This temperature namely is included in the regression model. The model results have been compared with the TEC data by calculating the standard deviation (STD). The comparison indicated that the regression model describes almost half of the real variability of the global TEC and that the contribution of the temperature (that is only a part of forcing from below) is almost half of the solar variability (i.e. external forcing related to the photo-ionization). A possible mechanism for explaining the relationship between the high-latitude stratospheric increase of the temperature and low-latitude decrease of the TEC is suggested.

  13. Simulation of low latitude ionospheric response to 2015 St. Patrick's Day super geomagnetic storm over Indian longitude sector

    NASA Astrophysics Data System (ADS)

    Mohan Joshi, Lalit; Sripathi, Samireddipelle; Singh, Ram

    2016-07-01

    We present low latitude ionospheric response over Indian longitude to the recent super geomagnetic storm of 17 March 2015, using the SAMI2 model which incorporates ionosonde derived vertical drift impacted by prompt penetration eastward electric field occurring during the evening Prereversal Enhancement (PRE) in the vertical drift. The importance of this storm is that (a) Dst reaches as low as -228 nT and (b) prompt penetration of eastward electric field coincided with evening hours PRE. The daytime vertical EXB drifts in the SAMI2 model are, however, considered based on Scherliess-Fejer model. The simulations indicate a significant enhancement in F layer height and equatorial ionization anomaly (EIA) in the post sunset hours on 17 March 2015 vis-a-vis quiet day. The model simulations during recovery phase, considering disturbance dynamo vertical EXB drift along with equatorward disturbance wind, indicates suppression of the daytime EIA. SAMI2 simulations considering the disturbance wind during the recovery phase suggests that equatorward wind enhances the ionospheric density in the low latitude, however, its role in the formation of the EIA depends on the polarity of the zonal electric field. Comparison of model derived total electron content (TEC) with the TEC from ground GPS receivers indicate that model does reproduce enhancement of the EIA during the main phase and suppression of the EIA during the recovery phase of the super storm. However, peculiarities pertaining to the ionospheric response to prompt penetration electric field in the Indian sector vis-a-vis earlier reports from American sector will be discussed.

  14. Impact of the 15 January 2010 annular solar eclipse on the equatorial and low latitude ionosphere over the Indian region

    NASA Astrophysics Data System (ADS)

    Panda, S. K.; Gedam, S. S.; Rajaram, G.; Sripathi, S.; Bhaskar, A.

    2015-12-01

    The annular solar eclipse of 15 January 2010 over southern India was studied with a multi-instrument network consisting of magnetometer, ionosonde and GPS receivers. The presence of a counter electrojet (weakened or westward zonal electric field) during the eclipse and adjacent days suggests the strong gravitational tidal effect associated with the exceptional Sun-Moon-Earth alignment around the eclipse day. With a strong backup of magnetometer recordings on the day of eclipse, its adjacent days and the normal electrojet day, it is argued that the regular eastward electric field for the whole day at the equator was not just weakened, but actually was flipped for several hours by the influence of enhanced lunar tides. The effect of flipping the electric field was clearly seen in the equatorial ionosonde data and through the large array of GPS receivers that produced the total electron content (TEC) data. The main impact of flipping the electric field was poor feeding of equatorial ionization anomaly (EIA) due to the severely weakened fountain effect on the eclipse day, with the regular anomaly crest shifting towards the equator. The equatorial ionosonde profile was also showing an enhanced F2 region peak in spite of a reduced vertical TEC. While the plasma density depletion at the lower F region altitude over the equator was due to the temporary lack of photo-ionization, the reductions in high altitude plasma density beyond the equator were caused by the electrodynamics taking place around the eclipse. The important finding of this analysis is that the electrodynamical consequences on the low latitude ionosphere were mainly due to the combination of eclipse and lunar tides which were far more significant and influenced the EIA density rather than eclipse alone. Based on these findings, it is argued that the prevailing lunar tidal impact also needs to be taken into account while seeking to understand the electrodynamical impact of the solar eclipse on the low

  15. Observation of TEC perturbation associated with medium-scale traveling ionospheric disturbance and possible seeding mechanism of atmospheric gravity wave at a Brazilian sector

    NASA Astrophysics Data System (ADS)

    Jonah, O. F.; Kherani, E. A.; De Paula, E. R.

    2016-03-01

    In the present study, we document daytime total electron content (TEC) disturbances associated with medium-scale traveling ionospheric disturbances (MSTIDs), on few chosen geomagnetically quiet days over Southern Hemisphere of Brazilian longitude sector. These disturbances are derived from TEC data obtained using Global Navigation Satellite System (GNSS) receiver networks. From the keograms and cross-correlation maps, the TEC disturbances are identified as the MSTIDs that are propagating equatorward-eastward, having most of their average wavelengths longer in latitude than in longitude direction. These are the important outcomes of the present study which suggest that the daytime MSTIDs over Southern Hemisphere are similar to their counterparts in the Northern Hemisphere. Another important outcome is that the occurrence characteristics of these MSTIDs and that of atmospheric gravity wave (AGW) activities in the thermosphere are found to be similar on day-to-day basis. This suggests a possible connection between them, confirming the widely accepted AGW forcing mechanism for the generation of these daytime MSTIDs. The source of this AGW is investigated using the Geostationary Operational Environmental Satellite system (GOES) and Constellation Observing System for Meteorology, Ionosphere, and Climate satellite data. Finally, we provided evidences that AGWs are generated by convection activities from the tropospheric region.

  16. Orbital control of low-latitude seasonality during the Eemian

    USGS Publications Warehouse

    Winter, A.; Paul, A.; Nyberg, J.; Oba, T.; Lundberg, J.; Schrag, D.; Taggart, B.

    2003-01-01

    We used Sr/Ca and stable isotope data from well dated and preserved corals from the northeastern Caribbean to determine the seasonal environmental conditions for four continuous years during the Eemian, the last time the Earth was in a prolonged warm phase. We determined that the seasonal range in SST during the Eemian was 25??-30?? C. This is ???1-2?? larger than at present and caused primarily by winter cooling and, only to a small degree, by summer warming. As climate modeling studies indicate, the bias towards colder winters can be explained by changes in low latitude insolation induced by altered orbital parameters, modulated by atmospheric CO2 levels that were lower than today. Milankovitch forcing at higher latitudes was probably less important.

  17. Low latitude auroras prior to 1200 C.E. and Ezekiel’s vision

    NASA Astrophysics Data System (ADS)

    Silverman, S. M.

    2006-01-01

    In another paper in this volume the auroral events of August 28 and September 2, 1859 have been discussed in the context of other events from that time to the present. Elsewhere, Siscoe, Silverman and Siebert have presented persuasive arguments for the proposition that the first chapter of the Biblical book of Ezekiel was a description of an aurora. The present paper discusses a number of low latitude auroras beginning with an unusually active period around 1100 C.E., proceeding through the period of the beginning of the Common Era, to the time of Ezekiel and Assyrian and Babylonian observations.

  18. Low-Latitude Auroras: The Magnetic Storm of 14-15 May 1921

    NASA Technical Reports Server (NTRS)

    Silverman, S. M.; Cliver, E. W.

    2001-01-01

    We review solar geophysical data relating to the great magnetic storm of 14-15 May 1921, with emphasis on observations of the low-latitude visual aurora. From the reports we have gathered for this event the lowest geomagnetic latitude of definite overhead aurora (coronal form) was 40 deg and the lowest geomagnetic latitude from which auroras were observed on the poleward horizon in the northern hemisphere was 30 deg. For comparison, corresponding overhead/low-latitude values of 48 deg/32 deg and 41 deg/20 deg were reported for the great auroras on 28-29 August and 1-2 September 1859, respectively. However for the 1921 event, there is a report of aurora from Apia, Samoa, in the southern hemisphere, within 13 deg of the geomagnetic equator. This report by professional observers appears to be credible, based on the aurora description and timing, but is puzzling because of the discrepancy with the lowest latitude of observation in the northern hemisphere and the great implied aurora height (approximately 2000 km, assuming overhead aurora at Auckland, New Zealand). We discuss various possibilities that might account for this observation.

  19. A high-latitude, low-latitude boundary layer model of the convection current system

    SciTech Connect

    Siscoe, G.L. ); Lotko, W.; Sonnerup, B.U.O. )

    1991-03-01

    Observations suggest that both the high- and low-latitude boundary layers contribute to magnetospheric convection, and that their contributions are linked. In the interpretation pursued here, the high-latitude boundary layer (HBL) generates the voltage while the low-latitude boundary layer (LBL) generates the current for the part of the convection electric circuit that closes through the ionosphere. This paper gives a model that joins the high- and low-latitude boundary layers consistently with the ionospheric Ohm's law. It describes an electric circuit linking both boundary layers, the region 1 Birkeland currents, and the ionospheric Pedersen closure currents. The model works by using the convection electric field that the ionosphere receives from the HBL to determine two boundary conditions to the equations that govern viscous LBL-ionosphere coupling. The result provides the needed self-consistent coupling between the two boundary layers and fully specifies the solution for the viscous LBL-ionosphere coupling equations. The solution shows that in providing the current required by the ionospheric Ohm's law, the LBL needs only a tenth of the voltage that spans the HBL. The solution also gives the latitude profiles of the ionospheric electric field, parallel currents, and parallel potential. It predicts that the plasma in the inner part of the LBL moves sunward instead of antisunward and that, as the transpolar potential decreases below about 40 kV, reverse polarity (region 0) currents appear at the poleward border of the region 1 currents. A possible problem with the model is its prediction of a thin boundary layer ({approximately}1000 km), whereas thicknesses inferred from satellite data tend to be greater.

  20. Investigation of low-latitude E and valley region irregularities: Their relationship to equatorial plasma bubble bifurcation

    NASA Astrophysics Data System (ADS)

    Li, Guozhu; Ning, Baiqi; Patra, A. K.; Wan, Weixing; Hu, Lianhuan

    2011-11-01

    The low-latitude E, valley and F region 3 m scale irregularities are studied with the Sanya (18.4°N, 109.6°E, dip latitude 12.8°N) VHF coherent scatter radar. The observations show that the E region irregularities (ERIs) often weaken or disappear during the development of postsunset equatorial plasma bubbles (EPBs) in equinoctial months. However, the valley region irregularities (VRIs) are found to occur during the EPB development and show structures with close relation to those of EPBs. The interesting aspect is that the ERI disruption and VRI generation are simultaneously detected. In terms of the electric field coupling from the equatorial F region down to low-latitude E and valley regions, the polarization electric fields (PEFs) associated with the EPB bifurcation are suggested to play key roles in the evolution of ERIs and VRIs. It is shown that the mapping of upward and eastward PEFs generated within the equatorial west tilted bubble would inhibit the occurrence of low-latitude ERIs. However, for the east tilted bubble structure, the associated downward PEFs might map to the low-latitude valley region and play an active role for the development of 3 m scale irregularities through gradient drift instability.

  1. Climatology of low latitude ionosphere under effect of varying solar flux during solar cycle 23 and 24

    NASA Astrophysics Data System (ADS)

    Dashora, Nirvikar; Suresh, Sunanda

    2016-07-01

    The characteristics of quiet time equatorial and low latitude total electron content (TEC) over the Indian sector using GIM data (1998-2014) is obtained. For the first time the analysis is carried filtering out the solar flare and storm effects and time series of quiet time VTEC data from three locations namely dip equator and two low latitude conjugate locations in Indian sector are obtained. It is well known that a complex interplay among drivers of equatorial electrodynamics like Solar flux, dynamo electric field and meridional winds determine the daytime ionization and distribution in equatorial ionization anomaly zone. In this study, we have critically examined the role of varying solar flux and response of low latitude ionosphere with new and standardized definitions. The results are examined and interpreted in the context of large number of previous studies. The newly found features from this study are as follows. Marked difference in nature of equinoctial asymmetry is noted between solar cycle 23 and 24. Long absence of winter anomaly both during low and high solar activity (HSA) in LL (low latitude) regions is found. Climatology of the diurnal cycle is provided in four categories using new criteria for demarcation of solar activity levels. Highest correlation (~77%) between GIM ionospheric electron content (IEC) and PI (solar EUV proxy index) is noted over equator in contrast to previous studies. The minimum positive contribution of PI in variation of IEC requires minimum of 2 years of data and if more than 7-8 years of data is used, it saturates. RMS (root mean square) width of PI can be used to define the HSA. Strong QBO (quasi biennial oscillations) in IEC is noted in tune with the one in PI over both the LL location but QBO remains surprisingly subdued over equator. The semi-annual oscillations in GIM-IEC are found to be stronger at all locations during high solar activity and weaker between 2005 and 2011, whereas, the annual oscillations are found to

  2. Simulation of the low latitude ionosphere response to disturbed winds and electric fields: Brazilian region

    NASA Astrophysics Data System (ADS)

    Batista, Inez S.; Souza, Jonas; Bailey, Graham; Bravo, Manuel

    2016-07-01

    Modeling the ionosphere during disturbed periods is one of the most challenging tasks due to the complexity of the phenomena that affect the electric fields and the thermosphere environment as whole. It is well known that depending on the direction of the interplanetary magnetic field disturbance electric fields (undershielding or overshielding) can penetrate from high to low latitudes causing significant disturbances in the electron density distribution and in the equatorial ionization anomaly (EIA) development. Besides that, the large amount of energy deposited in the polar region during disturbed periods will be responsible for the generation of disturbed winds that will flow towards the equator where they produce a disturbance dynamo which also affects the EIA density distribution. The TIDs and TADs are also sources of disturbances that propagate at high velocity reaching the equator 2-3 hours after the beginning of the magnetic storm. In this work we use the Sheffield University Plasmasphere-Ionosphere Model at INPE (SUPIM-INPE), to simulate the drastic effects that were observed at the low latitude ionosphere in the Brazilian region during a very intense magnetic storm event. A few models are tested for the disturbed electric field and wind. The simulation results showed that the observations are better explained when considering a traveling waveform disturbance propagating from north to south at a velocity equal to 200 m/s.

  3. Low-latitude plasma drifts from a simulation of the global atmospheric dynamo

    SciTech Connect

    Crain, D.J. ); Heelis, R.A. ); Bailey, G.J. ); Richmond, A.D. )

    1993-04-01

    The authors work with a dynamo model to address questions about plasma drifts in the E region, primarily at low latitudes. Tidal winds have been known to have a big influence on electric fields in the E region, and magnetic fields and ion drifts in the equatorial F region. Recent work has centered on self consistency in simulations, using realistic wind distributions, 3-D current distributions, and more accurate measures of the currents and conductivities. The wind dynamo in the ionosphere is well accepted as the main source of electric fields in the low and mid latitudes. The authors present a self consistent model of the plasma distribution and the dynamo driven electric potential distribution. Their results are compared with other simulations. A major concern in their model was reproducing ion drift observations in the equatorial region. Their conclusion is that the F region plays a significant role in the low latitude dyanamo effects, much larger than was previously assumed. When they build into their model realistic ionospheric conditions, allow for appropriate wind distributions, and allow a self consistent redistribution of plasma in the night, they find the model simulates measured ion drifts more closely. Their model is normalized against observations at Jicamarca. By allowing E [times] B drifts in the ionosphere, and F region zonal winds they can reproduce many of the night changes in the ion drifts at Jicamarca.

  4. Ionospheric slab thickness in middle and low latitudes

    SciTech Connect

    Davies, K.; Liu, X.M. )

    1991-08-01

    The equivalent slab thickness of the ionosphere at 15 stations in middle and low latitudes was studied to determine its dependence on solar cycle and location. The data were grouped by season. The following are the major conclusions. There appears to be little or no geographical, or geomagnetic, dependence. The slab thickness varies approximately linearly with the 12-month smoothed values of the 10.7-cm solar radio flux. In middle latitudes the winter midnight thickness is essentially independent of the flux, whereas in summer and equinox the midnight thickness increases with increase of solar flux. The noon thickness increases with increase of solar flux in all seasons. The zero-order Fourier coeffficients for the diurnal curves at all 15 stations were expressed as linear functions of the 10.7-cm flux. The higher harmonic coefficients showed no appreciable dependence on solar flux. The pronounced predawn increase in slab thickness is caused by low values of the maximum electron density, not by increase of total electron content. 10 refs.

  5. GNSS-TEC observations of the atmospheric resonance excited by the 2015 April Plinian eruptions of the Calbuco volcano, Chile: Comparison with the 2014 Kelud eruption

    NASA Astrophysics Data System (ADS)

    Nakashima, Y.; Heki, K.

    2015-12-01

    GNSS-Total Electron Content (TEC) method is a useful tool to observe the ionosphere. We observed ionospheric disturbances caused by the lower atmospheric resonance excited by two recent Plinian volcanic eruptions. In the case of the 2014 eruption of the Kelud volcano, Indonesia (Nakashima et al., submitted), the lower atmospheric resonance excited by the continuing eruption caused long-lasting harmonic oscillations not only in the ionosphere but also in the solid earth. This year, we add the new case of the 2015 eruption of the Calbuco volcano, Chile. Two large eruptions occurred at the Calbuco volcano over the days 22- 23 April 2015. The first sub-Plinian eruption started at ~16:04 UT, Apr. 22, and continued for about 1.5 hours. The second one started at ~4:00 UT, Apr. 23, and lasted for 6 hours. We detected continuous oscillations of ionospheric TEC corresponding to the two eruptions using GPS and GLONASS data from stations of the Argentine GNSS Array: RAMSAC. The waves propagated with a speed of ~1.0 km/s from the volcano. The frequency spectra of the TEC variation in the first eruption on Apr. 22 showed clear peaks at 3.7 and 4.4 mHz, the lower atmospheric resonance frequencies. The perturbation also showed overtone peaks and a 10 mHz pulse-like signal at the onset of the continuous oscillation. The results suggest that a Vulcanian explosion occurred prior to the Plinian eruption. On the other hand, the second eruption on Apr. 23 showed only a weaker peak at 4.4 mHz without overtones, suggesting that the second eruption was weaker but lasted longer than the first one. We are going to present detailed records of the 2015 Calbuco case, and compare it with past cases of ionospheric disturbances by volcanic eruptions, e.g. the 2014 Kelud volcano eruption.

  6. The domination of Saturn's low-latitude ionosphere by ring 'rain'.

    PubMed

    O'Donoghue, J; Stallard, T S; Melin, H; Jones, G H; Cowley, S W H; Miller, S; Baines, K H; Blake, J S D

    2013-04-11

    Saturn's ionosphere is produced when the otherwise neutral atmosphere is exposed to a flow of energetic charged particles or solar radiation. At low latitudes the solar radiation should result in a weak planet-wide glow in the infrared, corresponding to the planet's uniform illumination by the Sun. The observed electron density of the low-latitude ionosphere, however, is lower and its temperature higher than predicted by models. A planet-to-ring magnetic connection has been previously suggested, in which an influx of water from the rings could explain the lower-than-expected electron densities in Saturn's atmosphere. Here we report the detection of a pattern of features, extending across a broad latitude band from 25 to 60 degrees, that is superposed on the lower-latitude background glow, with peaks in emission that map along the planet's magnetic field lines to gaps in Saturn's rings. This pattern implies the transfer of charged species derived from water from the ring-plane to the ionosphere, an influx on a global scale, flooding between 30 to 43 per cent of the surface of Saturn's upper atmosphere. This ring 'rain' is important in modulating ionospheric emissions and suppressing electron densities. PMID:23579676

  7. The domination of Saturn's low-latitude ionosphere by ring `rain'

    NASA Astrophysics Data System (ADS)

    O'Donoghue, J.; Stallard, T. S.; Melin, H.; Jones, G. H.; Cowley, S. W. H.; Miller, S.; Baines, K. H.; Blake, J. S. D.

    2013-04-01

    Saturn's ionosphere is produced when the otherwise neutral atmosphere is exposed to a flow of energetic charged particles or solar radiation. At low latitudes the solar radiation should result in a weak planet-wide glow in the infrared, corresponding to the planet's uniform illumination by the Sun. The observed electron density of the low-latitude ionosphere, however, is lower and its temperature higher than predicted by models. A planet-to-ring magnetic connection has been previously suggested, in which an influx of water from the rings could explain the lower-than-expected electron densities in Saturn's atmosphere. Here we report the detection of a pattern of features, extending across a broad latitude band from 25 to 60 degrees, that is superposed on the lower-latitude background glow, with peaks in emission that map along the planet's magnetic field lines to gaps in Saturn's rings. This pattern implies the transfer of charged species derived from water from the ring-plane to the ionosphere, an influx on a global scale, flooding between 30 to 43 per cent of the surface of Saturn's upper atmosphere. This ring `rain' is important in modulating ionospheric emissions and suppressing electron densities.

  8. Possible precipitation of ice at low latitudes of Mars during periods of high obliquity

    USGS Publications Warehouse

    Jakosky, B.M.; Carr, M.H.

    1985-01-01

    Most of the old cratered highlands of Mars are dissected by branching river valleys that appear to have been cut by running water1,2 yet liquid water is unstable everywhere on the martian surface. In the equatorial region, where most of the valleys are observed, even ice is unstable3,4. It has been suggested, therefore, that Mars had an early denser atmosphere with sufficient greenhouse warming to allow the existence of liquid water 5. Here, we suggest instead that during periods of very high obliquities, ice could accumulate at low latitudes as a result of sustained sublimation of ice from the poles and transport of the water vapour equatorwards. At low latitudes, the water vapour would saturate the atmosphere and condense onto the surface where it would accumulate until lower obliquities prevailed. The mechanism is efficient only at the very high obliquities that occurred before formation of Tharsis very early in the planet's history, but limited equatorial ice accumulation could also have occurred at the highest obliquities during the rest of the planet's history. Partial melting of the ice could have provided runoff to form the channels or replenish the groundwater system. ?? 1985 Nature Publishing Group.

  9. Possible precipitation of ice at low latitudes of Mars during periods of high obliquity

    NASA Technical Reports Server (NTRS)

    Jakosky, B. M.; Carr, M. H.

    1985-01-01

    Most of the old cratered highlands of Mars are dissected by branching river valleys that appear to have been cut by running water, yet liquid water is unstable everywhere on the Martian surface. In the equatorial region, where most of the valleys are observed, even ice is unstable. It has been suggested, therefore, that Mars had an early denser atmosphere with sufficient greenhouse warming to allow the existence of liquid water. Here, it is suggested instead that during periods of very high obliquities, ice could accumulate at low latitudes as a result of sustained sublimation of ice from the poles and transport of the water vapor equatorwards. At low latitudes, the water vapor would saturate the atmosphere and condense onto the surface, where it would accumulate until lower obliquities prevailed. The mechanism is efficient only at the very high obliquities that occurred before formation of Tharsis very early in the planet's history, but limited equatorial ice accumulation could also have occurred at the highest obliquities during the rest of the planet's history. Partial melting of the ice could have provided runoff to form the channels or replenish the groundwater system.

  10. Discovery of a widespread low-latitude diurnal CO2 frost cycle on Mars

    NASA Astrophysics Data System (ADS)

    Piqueux, Sylvain; Kleinböhl, Armin; Hayne, Paul O.; Heavens, Nicholas G.; Kass, David M.; McCleese, Daniel J.; Schofield, John T.; Shirley, James H.

    2016-07-01

    While the detection of CO2 ice has only been reported outside the Martian polar regions at very high elevation (i.e., Elysium, Olympus Mons, and the Tharsis Montes), nighttime surface observations by the Mars Climate Sounder on board the Mars Reconnaissance Orbiter document the widespread occurrence of atmospherically corrected ground temperatures consistent with the presence of extensive carbon dioxide frost deposits in the dusty low thermal inertia units at middle/low latitudes. Thermal infrared emissivities, interpreted in conjunction with mass balance modeling, suggest micrometer size CO2 ice crystals forming optically thin layers never exceeding a few hundreds of microns in thickness (i.e., 10-2 kg m-2) locally, which is insufficient to generate a measurable diurnal pressure cycle (<<0.1% of the Martian atmosphere). Atmospheric temperatures at middle/low latitudes are not consistent with precipitation of CO2 ice, suggesting that condensation occurs on the surface. The recurring growth and sublimation of CO2 ice on Martian dusty terrains may be an important process preventing soil induration and promoting dynamic phenomena (soil avalanching and fluidization and regolith gardening), maintaining a reservoir of micrometer size dust particles that are mobile and available for lifting. The discovery of this diurnal CO2 cycle represents an important step forward in our understanding of the way the Martian atmosphere interacts with the surface.

  11. Ionospheric variability over Indian low latitude linked with the 2009 sudden stratospheric warming

    NASA Astrophysics Data System (ADS)

    Patra, Amit; Alex, Sobhana; Samireddipalle, Sripathi; Peddapati, PavanChaitanya

    In this paper, we analyze radar observations of ExB drift and plasma irregularities, ionosonde observations of E- and F-layer parameters including spread F, and magnetic field observations made from Indian low latitudes linked with the 2009 sudden stratospheric warming (SSW) event. ExB drift variations presented here are the first of their kind from the Indian sector as far as the effect of SSW is concerned. Difference of magnetic fields observed from the equator and low latitude (∆H) and ExB drift show linear relation and both show remarkably large positive values in the morning and negative values in the afternoon exhibiting semidiurnal behavior. Remarkable changing patterns in the critical frequency of F2 layer (foF2) and F3 layer (foF3) were observed after the occurrence of SSW. Large variations with quasi-16-day periodicity were observed in ∆H, foF2 and foF3. Both semidiurnal and quasi-16-day wave modulation observed after the 2009 SSW event are consistent with those reported earlier. We also noted quasi-6 day variations in ∆H and foF2 soon after the SSW commencement, not much reported before. During the counter-electrojet events linked with the SSW event, while equatorial Es (Esq) disappeared as expected, there were no blanketing Es (Esb), a finding not reported and discussed earlier. Esb was also not formed at the off-equatorial location, indicating the absence of required vertical wind shear, but E region plasma irregularities were observed by the ionosonde and radar with a close relationship between the two. Weak F region irregularities were observed in the post-midnight hours and case studies suggest the possible role of SSW related background electric field in the manifestation of post-midnight F region irregularities.

  12. Ionospheric variability over Indian low latitude linked with the 2009 sudden stratospheric warming

    NASA Astrophysics Data System (ADS)

    Patra, A. K.; Pavan Chaitanya, P.; Sripathi, S.; Alex, S.

    2014-05-01

    In this paper, we analyze radar observations of E × B drift and plasma irregularities, ionosonde observations of E and F layer parameters including spread F, and magnetic field observations made from Indian low latitudes linked with the 2009 sudden stratospheric warming (SSW) event. E × B drift variations presented here are the first of their kind from the Indian sector as far as the effect of SSW is concerned. Difference of magnetic fields observed from the equator and low-latitude (∆H) and E × B drift show linear relation, and both show remarkably large positive values in the morning and negative values in the afternoon exhibiting semidiurnal behavior. Remarkable changing patterns in the critical frequency of F2 layer (foF2) and F3 layer (foF3) were observed after the occurrence of SSW. Large variations with quasi 16 day periodicity were observed in ∆H, foF2, and foF3. Both semidiurnal and quasi 16 day wave modulation observed after the 2009 SSW event are consistent with those reported earlier. We also noted quasi 6 day variations in ∆H and foF2 soon after the SSW commencement, not much reported before. During the counterelectrojet events linked with the SSW event, while equatorial Es (Esq) disappeared as expected, there were no blanketing Es (Esb), a finding not reported and discussed earlier. Esb was also not formed at the off-equatorial location, indicating the absence of required vertical wind shear, but E region plasma irregularities were observed by the ionosonde and radar with a close relationship between the two. Weak F region irregularities were observed in the postmidnight hours, and case studies suggest the possible role of SSW-related background electric field in the manifestation of postmidnight F region irregularities.

  13. AzTEC/ASTE Millimeter-wave Monitoring and Target-of-opportunity Observations of Selected Radio-bright Fermi-detected Gamma-ray Blazars and GRBs

    NASA Astrophysics Data System (ADS)

    Stacy, J. Gregory; Wilson, G.; AzTEC/ASTE Collaboration

    2010-11-01

    We report on correlative millimeter-wave radio observations at 1.1 mm of high-priority Fermi-detected gamma-ray blazars using the AzTEC bolometer-array camera mounted on the 10-m ASTE radio telescope in northern Chile. These observations were carried out during the latter part of the 2008 observing season, overlapping with the first months of operation of the Fermi Observatory. High-priority blazars were monitored and we responded as well to Fermi alerts of elevated gamma-ray emission or flaring activity. We also report on the upper limits obtained to millimeter-wave emission in the early afterglow from GRB 081121. These correlative measurements constituted a pilot observing program that will be extended and expanded to include numerous additional gamma-ray targets for the Large Millimeter Telescope as part of its commissioning operations over the coming year. This work is supported in part by the National Science Foundation.

  14. Variabilities of low latitude mesospheric and E region echoes: linked to common sources?

    NASA Astrophysics Data System (ADS)

    Dharmalingam, Selvaraj; Patra, Amit; Sathishkumar, Sundararaman; Narayana Rao, D.

    2016-07-01

    Variability in dynamics of the mesospheric and E region echoes have been studied in isolation. Both echoing phenomena are directly or indirectly coupled with each other through neutral dynamics. This is especially so for the low-latitudes outside the equatorial electrojet belt, where E region plasma irregularities causing radar echoes are governed by neutral dynamics, such as tides and gravity waves. Although these regions are close to each other, no effort has been made yet to understand the dynamical coupling processes manifesting the observed variabilities in the two echoing phenomena. To investigate linkage between the two phenomena, if any, we conducted systematic observations of low latitude mesospheric and E region echoes during 2011-2012 using the Gadanki MST radar and used these in conjunction with SABER temperature, MF radar wind, and sporadic E observations. Both echoes are found to occur in the height regions where temperature observations show negative gradients. Mesospheric echoes are collocated with temperature gradient associated with mesospheric temperature inversion while the E region echoes are collocated with negative temperature gradient close to the mesopause. Observations have revealed a common signature of semi-annual variations in the occurrence of both mesospheric and ionospheric E-region - occurrences peak in the equinoxes. The E region echoes have an additional peak occurring in the summer and this occurrence is well correlated with the enhancement in the diurnal tidal amplitude. We surmise that the enhancement in the diurnal tidal amplitude is linked with non-migrating tide of tropospheric weather phenomena in summer. Intriguingly, mesospheric echoing layers display descending pattern quite similar to the E region echoes and sporadic E layer, which have been used to invoke tidal dynamics in manifesting similar morphology in both mesospheric and E region echoes. These results will be presented and the role of tidal dynamics on the

  15. Relation Between Low Latitude Pc3 Magnetic Micropulsations and Solar Wind (P6)

    NASA Astrophysics Data System (ADS)

    Ansari, I. A.

    2006-11-01

    iaaamphysics@yahoo.co.in iaaphysicsamu@yahoo.com.au Geomagnetic pulsations recorded on the ground are the signatures of the integrated signals from the magnetosphere. Pc3 Geomagnetic pulsations are quasi-sinusoidal variations in the Earth’s Magnetic field in the period range 10-45 seconds. The magnitude of these pulsations ranges from fraction of a nT (nano Tesla) to several nT. These pulsations can be observed in a number of ways. However the application of ground based magnetometer arrays has proven to be one of the most successful methods of studying the spatial structure of hydromagnetic waves in the Earth’s Magnetosphere. The solar wind provides the energy for the Earth’s magnetospheric processes. Pc3-5 geomagnetic pulsations can be generated either externally or internally with respect to the magnetosphere. The Pc3 studies undertaken in the past have been confined to middle and high latitudes. The spatial and temporal variations observed in Pc3 occurrence are of vital importance because they provide evidence which can be directly related to wave generation mechanisms both inside and external to the magnetosphere. At low latitudes (L < 3) wave energy predominates in the Pc3 band and the spatial characteristics of these pulsations have received little attention in the past. An array of four low latitude induction coil magnetometers was established in south-east Australia over a longitudinal range of 17 degrees at L=1.8 to 2.7 for carrying out the study of the effect of the solar wind velocity on these pulsations. Digital dynamic spectra showing Pc3 pulsation activity over a period of about six months have been used to evaluate Pc3 pulsation occurrence. Pc3 occurrence probability at low latitudes has been found to be dominant for the solar wind velocity in the range 400-700 Km/sec. The results suggest that solar wind controls Pc3 occurrence through a mechanism in which Pc3 wave energy is convected through the magnetosheath and coupled to the standing

  16. LSWS linked with the low-latitude Es and its implications for the growth of the R-T instability

    NASA Astrophysics Data System (ADS)

    Joshi, L. M.

    2016-07-01

    A comprehensive investigation of spread F irregularities over the Indian sector has been carried out using VHF radar and ionosonde observations. Two different categories of spread F observations, one where the onset of the range spread F (RSF) was concurrent with the peak h'F (category 1) and another where the RSF onset happened ~90 min after the peak h'F time (category 2), are presented. RSF in category 2 was preceded by the presence of oblique echoes in ionograms, indicating the irregularity genesis westward of Sriharikota. The average peak h'F in category 1 was ~30 km higher than that in category 2 indicating the presence of standing large-scale wave structure (LSWS). Occurrence of the blanketing Es during 19:30 to 20:30 Indian Standard Time in category 1 (category 2) was 0% (>50%). Model computation is also carried out to further substantiate the observational results. Model computation indicates that zonal variation of low-latitude Es can generate zonal modulation in the F layer height rise. It is found that the modulation of the F layer height, linked with the low-latitude Es, assists the equatorial spread F onset by modifying both the growth rate of the collisional Rayleigh-Taylor (R-T) instability and also its efficiency. A predominant presence of low-latitude Es has been observed, but the increase in the F layer height and the R-T instability growth in the evening hours will maximize with complete absence of low-latitude Es. A new mechanism for the generation of LSWS and its implications on R-T instability is discussed.

  17. Investigation of low-latitude ionospheric irregularities and their relationship to equatorial plasma bubbles using Sanya VHF radar

    NASA Astrophysics Data System (ADS)

    Ning, B.; Li, G.; Hu, L.

    2011-12-01

    A VHF radar has been set up at Sanya (18.34° N, 109.62° E, geomagnetic latitude 7.04°N), China in 2009. On the basis of the E, valley and F region irregularity observations detected by the Sanya VHF radar during equinoctial months, we focus on the simultaneous observations of E region irregularities disruption and valley region irregularities generation during the presence of post-sunset F region bubble structures. We stress that both the low latitude the E region irregularities (ERI) disruption and valley region irregularities (VRI) generation are associated with the development of post-sunset equatorial plasma bubble (EPB) structures. It is suggested that the electric field coupling from the unstable equatorial F region to low-latitude E and valley region could trigger and inhibit the occurrence of irregularities, depending on the polarity of the polarization electric field associated with the bifurcation of equatorial plasma bubbles. The mapping of upward/eastward and downward/eastward electric field associated with the west-tilted and east-tilted bubble structures, may be responsible for the disruption of E region irregularities, and the generation of valley region irregularities, respectively. However, more observations from multi instruments will be required to confirm such a scenario that the multi bifurcated EPBs play crucial roles for the simultaneous occurrence of low latitude ERI disruption and VRI generation.

  18. Mid- and low-latitude prompt-penetration ionospheric zonal plasma drifts

    NASA Astrophysics Data System (ADS)

    Fejer, Bela G.; Scherliess, Ludger

    We have used ion drift observations from the DE-2 satellite to determine the latitudinal variation and the temporal evolution of mid- and low-latitude prompt penetration zonal plasma drifts driven by magnetospheric electric fields. Our results indicate that sudden increases in convection lead to predominantly westward perturbation drifts which decrease equartorwards and have largest amplitudes in the dusk-midnight sector. The diurnal perturbation drift patterns shift to later local times with increasing storm time and decay to new quasi-equilibrium values in about 2 hours, as the ring current readjusts to the new polar cap potential. The daily and latitudinal variations and temporal evolution of the DE-2 prompt penetration drifts are generally in good agreement with predictions from the Rice Convection Model, although the experimental results show larger amplitudes and longer shielding time constants.

  19. An Investigation of the Low-Latitude Boundary Layer at Mid-Altitudes in the Cusp

    NASA Technical Reports Server (NTRS)

    Chandler, Michael O.; Avanov, Levon A.

    2006-01-01

    We have begun an investigation of the nature of the low-latitude boundary layer in the mid-altitude cusp region using data from the Polar spacecraft. This region has been routinely sampled for about three months each year for the periods 1999-2001 and 2004-2006. The low-to-mid-energy ion instruments frequently observed dense, magnetosheath-like plasma deep (in terms of distance from the magnetopause and in invariant latitude) in the magnetosphere. We seek to understand the morphology of the LLBL as it projects from the sub-solar region into the cusp and determine the influences on this morphology. An initial survey of the data is ongoing and we present here an overview of our intended study and some preliminary results.

  20. Trends of ionospheric irregularities over African low latitude region during quiet geomagnetic conditions

    NASA Astrophysics Data System (ADS)

    Mungufeni, Patrick; Habarulema, John Bosco; Jurua, Edward

    2016-02-01

    The occurrence patterns of ionospheric irregularities during quiet geomagnetic conditions over the African low latitude region were analysed. GNSS-derived Total Electron Content of the ionosphere data during the period 2001-2012 were used. The data were obtained from Libreville, Gabon (0.35°N, 9.68°E, geographic, 8.05°S, magnetic), Mbarara, Uganda (0.60°S, 30.74°E, geographic, 10.22°S, magnetic), and Malindi, Kenya (2.99°S, 40.19°E, geographic, 12.42°S, magnetic). The rate of change of total electron content index greater than 0.5 TECU/Min were considered as severe ionospheric irregularities. For most of the time, the strength of ionospheric irregularities in March equinox were greater than those during September equinox over East Africa and an opposite observation was made over West Africa. These asymmetries might be due to the direction of the meridional winds during equinoxes over the different stations. Severity of ionospheric irregularity reduced from west towards the east. This might have been related to the decreasing geomagnetic field strength from east towards the west. This is the first study that reveals the equinoctial asymmetry is different in the West and East African sectors. Moreover, the importance of this study lies in the fact that it has used extensive data to examine the isolated and un-explained earlier observations of equinoctial asymmetry and longitudinal variation of ionospheric irregularities over the African low latitude region.

  1. Recent results on daytime upper atmospheric wave dynamics at low latitudes and their dependence on equatorial electrodynamics

    NASA Astrophysics Data System (ADS)

    Pallamraju, Duggirala; Vijaya Lakshmi, Thatiparthi; Anji Reddy, M.; Karan, Deepak; Phadke, Kedar

    2016-07-01

    Investigations using optical emissions originating over large spatial extents (latitudes/longitudes) and multiple wavelengths revealed several interesting aspects of vertical and horizontal coupling in the low-latitude thermosphere during daytime. The daytime measurements were enabled by multi-wavelength high spectral resolution echelle grating spectrograph (MISE) that is operating from a low-latitude observational site, Hyderabad (Geographic: 17.5 ^{o} N, 78.5 ^{o} E; Geomagnetic: 8.6 ^{o} N, 151.8 ^{o} E), in India. MISE is capable of obtaining daytime optical emissions over a large field-of-view (140 ^{o}) at high-data cadence (around 5 min.) at oxygen emission wavelengths at 557.7 nm, 630.0 nm, and 777.4 nm that originate at 130 km, 230 km, and peak height of the F-region, respectively. Wave dynamics prevalent in multiple altitudes have been obtained during different background conditions. Based on this information various aspects of vertical coupling are investigated. It is seen that there is a preferred phase of solar activity when vertical coupling is enabled more readily. Further, the solar flux seems to affect the wave dynamics differently at different altitudes. The low-latitude electrodynamics also plays an important role in governing the neutral dynamical behaviour which is reflected in the neutral dayglow emissions at multiple wavelengths. These new results reveal greater insights into the fundamental nature of coupling between the thermospheric regions in the daytime. Some of the salient features of these results will be presented.

  2. Relations Between Traveling Convection Vortex (TCV) Signatures in Near-Cusp Ground Data, at Geosynchronous Orbit, and in Low Latitude Ground Data

    NASA Astrophysics Data System (ADS)

    Camarena, H.; Engebretson, M. J.; Posch, J. L.; Murr, D.; Singer, H. J.; Sibeck, D. G.

    2015-12-01

    Traveling Convection Vortices (TCVs) occur as solitary localized ~2- 5 mHz transients near the ionospheric footpoint of the dayside magnetopause. Ion foreshock instabilities are now understood to drive all or nearly all TCVs; they generate localized changes in dynamic pressure at the dayside magnetospheric boundary, resulting in transient magnetic field variations that generate field-aligned currents that propagate to the high latitude ionosphere and also compressional waves that produce signatures at geosynchronous orbit and lower latitudes on the ground. In this work we extend earlier multistation event studies by means of a statistical study comparing isolated TCV events observed between 2010 and 2014 by the MACCS array (Magnetometer Array for Cusp and Cleft Studies) in Arctic Canada, GOES-13, and several low-latitude INTERMAGNET magnetic observatories, all in the same longitude sector. We found essentially no correlation between the amplitude of TCV events and the amplitude of magnetic field compressions (ΔB) at GOES-13 and low-latitude ground stations. Comparing TCV amplitudes to time derivatives (dB/dt) at geosynchronous orbit and low latitudes, as suggested by published approximate theoretical analyses, resulted in modest correlations. Consistent with earlier studies, the low latitude response was strongest at stations under or very near the equatorial electrojet. We also analyzed a set of sudden impulse (SI) events with bipolar high-latitude signatures; the geostationary and low latitude compressions associated with them were relatively higher than those for TCVs.

  3. Ionospheric variations over Indian low latitudes close to the equator and comparison with IRI-2012

    NASA Astrophysics Data System (ADS)

    Pavan Chaitanya, P.; Patra, A. K.; Balan, N.; Rao, S. V. B.

    2015-08-01

    In this paper, we analyze daytime observations of the critical frequencies of the F2 (foF2) and F3 (foF3) layers based on ionosonde observations made from Indian low latitudes close to the magnetic equator and study their local time, seasonal, planetary-scale variations (including the solar rotation effect), and solar activity dependence. Given the occurrence of the F3 layer, which has remarkable local time, seasonal and solar activity dependences, variations in foF2 have been evaluated. Local time variations in foF2 and foF3 show noon "bite-out" in all seasons and in all solar activity conditions, which are attributed to vertically upward plasma transport by the zonal electric field and meridional neutral wind. Comparison of observed foF2 with those of the IRI-2012 model clearly shows that the model values are always higher than observed values and the largest difference is observed during noontime owing to the noon bite-out phenomenon. Peak frequency of the F layer (foF2 / foF3), however, is found to have better agreement with IRI-2012 model. Seasonal variations of foF2 and foF3 show stronger asymmetry at the solstices than at the equinoxes. The strong asymmetry at the solstice is attributed to the asymmetry in the meridional neutral wind with a secondary contribution from E × B drifts, and the relatively weak asymmetry observed at the equinox is attributed to the asymmetry in E × B drifts. Variations in foF2 and foF3 with solar flux clearly show the saturation effect when F10.7 exceeds ~ 120 sfu, which is different from that of the mid-latitudes. Irrespective of solar flux, both foF2 and foF3 in summer, however, are found to be remarkably lower than those observed in other seasons. Variations in foF2 show dominant periods of ~ 27, ~ 16 and ~ 6 days. Intriguingly, amplitudes of ~ 27-day variations in foF2 are found to be maximum in low solar activity (LSA), moderate in medium solar activity (MSA) and minimum in high solar activity (HSA), while the amplitudes of

  4. Electrical coupling between the E and F regions and its effect on low-latitude electrodynamic drifts produced by the atmospheric dynamo

    SciTech Connect

    Crain, D.J.

    1991-01-01

    The global ionospheric electrostatic potential distribution is determined using a realistic first-principle ionosphere model and simple wind distributions. The low-latitude ion drifts are calculated for various wind distributions and for self-consistent plasma and potential distributions. These drifts are compared with the plasma drifts observed at Jicamarca, and show considerable improvement over previous dynamo models. The role of the F-region dynamo is determined to be significantly greater than previously assumed. The zonal neutral wind in the F region is shown to be the major source of low-latitude electric fields and the reversal of this wind is linked to the formation of enhanced electric fields in the post-sunset period. The reversal of this wind and the large size of the conductivity ratio are the principal factors that determine the behavior of the post-sunset enhancement of vertical ion drift at low latitudes.

  5. On the Release of Energetic Electrons from the Jovian Magnetosphere: Evidence for a Low Latitude Cusp

    NASA Astrophysics Data System (ADS)

    Jones, D. E.; Murphy, N.

    2001-12-01

    Magnetic field data from Pioneers 10 and 11 have been used to develop a model magnetosphere for Jupiter consisting of an offset, tilted planetary dipole, a bent and twisted current disc represented by an array of concentric current rings, a dayside tail-like dusk-dawn current sheet, and an image dipole (Jones et al, 1980; Jones et al., 1981, Thomas and Jones, 1984). Such a model also fits the Ulysses magnetic field data as well (Jones et al., 1993). In all cases, the magnetosphere has a low latitude cusp. In this paper we compare the model magnetosphere shape and cusp location with the location of periodic energetic particle bursts observed by outbound Pioneer 11 (Fillius, 1976). It is found that the observed peaks occur very near the model cusp field lines, suggesting that this is where energetic particles leave the magnetosphere to propagate on interplanetary magnetic field lines connecting Jupiter with the sun (Conlon et al., 1974). Moiroka and Tsuchiya (1996) have found that the release of energetic electrons is controlled by the solar wind at Jupiter, as expected if they are released at the cusps. D.L. Chenette, T. F. Conlon, and J. A. Simpson, Bursts of relativistic electrons from Jupiter observed in interplanetary space with the time variations of the planetary rotation period, J. Geophys. Res., 79, 3551-3558, 1974 D. E. Jones, J. G. Melville II, and M. L. Blake, Modeling Jupiter's current disc: Pioneer 10 outbound, J. Geophys. Res., 85, 3329, 1980. D. E. Jones, B. T. Thomas, Equatorial disk and dawn-dusk currents in the frontside magnetosphere of Jupiter: Pioneers 10 and 11, J. Geophys. Res., 86, 1738, 1981. B. T. Thomas and D. E. Jones, Modeling Jupiter's magnetospheric currents using Pioneer data: Evidence for a low-latitude cusp, J. Geophys. Res., 89, 6663, 1984. D. E. Jones, E. J. Smith, N. Murphy, D. Winterhalter, A. Balogh, and D. J. Southwood, A model Jovian magnetospheric current system based upon magnetic field data obtained by the Ulysses helium

  6. Characteristics of Total Electron Content (TEC) observed from a chain of stations near the northern crest of the Equatorial Ionization Anomaly (EIA) along 88.5°E meridian in India

    NASA Astrophysics Data System (ADS)

    Paul, K. S.; Das, A.; Ray, S.; Paul, A.

    2016-01-01

    The equatorial ionosphere presents some of the highest TEC values in the world coupled with observations of periodic structures. Total Electron Content (TEC) and scintillation data were analyzed from a chain of stations Calcutta (22.58°N, 88.38°E geographic; 32°N magnetic dip), Baharampore (24.09°N, 88.25°E geographic; 35°N magnetic dip) and Farakka (24.79°N, 87.89°E geographic; 36.04°N magnetic dip) situated almost same meridian (88.5°E) during September 2011 and March-April 2012 for elevation greater than 20° so that the ionosphere can be tracked from the 15.50°N south of Calcutta to 31.80°N north of Farakka. Periodic variation of TEC was noticed before TEC bite out, predominantly within a particular latitudinal swath (19°N ‒26°N) along 88.5°E meridian. No periodic structures were observed over the magnetic equator during the observation period on ionosonde records from the magnetic equator station Trivandrum and COSMIC, GRACE and C/NOFS electron density measurements. The present paper reports, perhaps for the first time from the Indian longitude sector, confinement of such periodic structures in TEC primarily within a latitude swath of 19.00-26.00 °N almost along the same longitude of 88.5 °E.

  7. Pulsating nighttime magnetic background noise in the upper ULF band at low latitudes

    NASA Astrophysics Data System (ADS)

    Bösinger, T.; Demekhov, A. G.; Ermakova, E. N.; Haldoupis, C.; Zhou, Q.

    2014-05-01

    We model long-period (~2 h) irregular pulsations in the ellipticity of magnetic background noise (MBN) in the upper ULF band which were frequently observed during nighttime at a low-latitude site on the Island of Crete. It is shown that such pulsations cannot be reproduced in the calculations when using the ionosphere parameters from the statistical IRI (International Reference Ionosphere) model, while regular diurnal signatures of the ellipticity spectrum at sunset and sunrise are successfully reproduced. We apply the same approach to the location of the Arecibo incoherent scatter radar and show that using actually measured ionosphere profiles (up to a height of 400 km) instead of IRI profiles produces the ellipticity pulsations very similar to those observed at Crete. Comparison of model results with the calculated behavior of Alfvén mode refractive index allows us to conclude that the observed nighttime long-period irregular pulsations in the MBN ellipticity are caused by dynamic processes at the upper boundary of the ionospheric E-F valley which serves as a subionospheric Alfvén resonator. Irregular widening, shrinking, and/or deepening of the valley with time scales of 1 to 4 h affect the electrodynamical properties of this resonator and manifest themselves in the magnetic background noise properties.

  8. Low-Latitude Solar Wind During the Fall 1998 SOHO-Ulysses Quadrature

    NASA Technical Reports Server (NTRS)

    Poletto, G.; Suess, Steven T.; Biesecker, D.; Esser, R.; Gloeckler, G.; Zurbuchen, T.; Whitaker, Ann F. (Technical Monitor)

    2001-01-01

    The Fall 1998 SOlar-Heliospheric Observatory (SOHO) - Ulysses quadrature occurred when Ulysses was at 5.2 AU, 17.4 deg South of the equator, and off the West line of the Sun. SOHO coronal observations, at heliocentric distances of a few solar radii, showed that the line through the solar center and Ulysses crossed, over the first days of observations, a dark, weakly emitting area and through the northern edge of a streamer complex during the second half of the quadrature campaign. Ulysses in situ observations showed this transition to correspond to a decrease from higher speed wind typical of coronal hole flow to low speed wind. Physical parameters (density, temperature, flow speed) of the low latitude coronal plasma sampled over the campaign are determined using constraints from what is the same plasma measured later in situ and simulating the intensities of the Hydrogen Lyman-alpha and OVI 1032 and 1037 Angstrom lines, measured by the Ultra Violet Coronagraph Spectrometer (UVCS) on SOHO. The densities, temperatures and outflow speed are compared with the same characteristic flow parameters for high-latitude fast wind streams and typical slow solar wind.

  9. Anomalous ionospheric variations prior to major earthquakes during 2015 affecting Indian low latitude station Delhi

    NASA Astrophysics Data System (ADS)

    Gupta, Sumedha; Upadhayaya, Arun Kumar

    2016-07-01

    We have analyzed five major earthquakes (M>6) that occurred during the year 2015, affecting Indian ionosphere, using F2 layer critical frequency (foF2) data obtained using Digisonde from a low latitude station, Delhi (28.6°N, 77.2°E, 42.4°N dip). Normal day-to-day variability occurring in ionosphere is segregated by calculating F2 layer critical frequency variations (ΔfoF2) from the normal quiet time behavior apart from calculating interquartile range. We find that ionospheric F2 region across Delhi by and large shows some significant perturbations 3-4 days prior to these earthquake events. These observed perturbations indicate towards seismo-ionospheric coupling as solar and geomagnetic indices were normally quiet and stable during the period of these events. Further, it was also observed that the effect of earthquake was prominently observed even outside the earthquake preparation zone, calculated using Dobrovolsky et al. [1979].

  10. Simulation of low-latitude ionospheric response to 2015 St. Patrick's Day super geomagnetic storm using ionosonde-derived PRE vertical drifts over Indian region

    NASA Astrophysics Data System (ADS)

    Joshi, L. M.; Sripathi, S.; Singh, Ram

    2016-03-01

    In this paper, we present low-latitude ionospheric response over Indian longitude to the recent super geomagnetic storm of 17 March 2015, using the Sami2 is Another Model of the Ionosphere (SAMI2) model which incorporates ionosonde-derived vertical drift impacted by prompt penetration eastward electric field occurring during the evening prereversal enhancement (PRE) in the vertical drift. The importance of this storm is that (1) Dst reaches as low as -228 nT and (2) prompt penetration of eastward electric field coincided with evening hours PRE. The daytime vertical E × B drifts in the SAMI2 model are, however, considered based on Scherliess-Fejer model. The simulations indicate a significant enhancement in F layer height and equatorial ionization anomaly (EIA) in the post sunset hours on 17 March 2015 vis-a-vis quiet day. The model simulations during recovery phase, considering disturbance dynamo vertical E × B drift along with equatorward disturbance wind, indicate suppression of the daytime EIA. SAMI2 simulations considering the disturbance wind during the recovery phase suggest that equatorward wind enhances the ionospheric density in the low latitude; however, its role in the formation of the EIA depends on the polarity of the zonal electric field. Comparison of model derived total electron content (TEC) with the TEC from ground GPS receivers indicates that model does reproduce enhancement of the EIA during the main phase and suppression of the EIA during the recovery phase of the superstorm. However, peculiarities pertaining to the ionospheric response to prompt penetration electric field in the Indian sector vis-a-vis earlier reports from American sector have been discussed.

  11. Isotopic composition of low-latitude paleoprecipitation during the Early Cretaceous

    USGS Publications Warehouse

    Suarez, M.B.; Gonzalez, Luis A.; Ludvigson, Greg A.; Vega, F.J.; Alvarado-Ortega, J.

    2009-01-01

    likely underestimated tropical to subtropical precipitation and evaporation fluxes. The limited latitudinal constraints for earlier isotope mass balance modeling of the Albian hydrologic cycle of the Northern Hemisphere Americas resulted in extrapolated low-latitude precipitation ??18O values that were much heavier (up to 3???) than the values observed in this study. The lighter values identified in this study indicate a more pronounced rainout effect for tropical regions and quite possibly a more vigorous evaporation effect. These and additional low-latitude data are required to better constrain changes in the hydrologic cycle during the Cretaceous greenhouse period, and to reduce the uncertainties resulting from limited geographic coverage of proxy data. ?? 2009 Geological Society of America.

  12. Determining the Current and Future Health of Low-Latitude Andean Glaciers Using an Equilibrium Line Altitude Model and Hypsometric Data from the Randolph Glacier Inventory

    NASA Astrophysics Data System (ADS)

    Malone, A.; MacAyeal, D. R.

    2015-12-01

    Mountain glaciers have been described as the water towers of world, and for many populations in the low-latitude South American Andes, glacial runoff is vital for agricultural, industrial, and basic water needs. Previous studies of low-latitude Andean glaciers suggest a precarious future due to contemporary warming. These studies have looked at trends in freezing level heights or observations of contemporary retreat. However, regional-scale understanding of low-latitude glacial responses to present and future climate change is limited, in part due to incomplete information about the extent and elevation distribution of low-latitude glaciers. The recently published Randolph Glacier Inventory (RGI) (5.0) provides the necessary information about the size and elevation distribution of low-latitude glaciers to begin such studies. We determine the contemporary equilibrium line altitudes (ELAs) for low-latitude Andean glaciers in the RGI, using a numerical energy balance ablation model driven with reanalysis and gridded data products. Contemporary ELAs tend to fall around the peak of the elevation histogram, with an exception being the southern-most outer tropical glaciers whose modeled ELAs tend to be higher than the elevation histogram for that region (see below figure). Also, we use the linear tends in temperature and precipitation from the contemporary climatology to extrapolate 21stcentury climate forcings. Modeled ELAs by the middle on the century are universally predicted to rise, with outer tropical ELAs rising more than the inner tropical glaciers. These trends continue through the end of the century. Finally, we explore how climate variables and parameters in our numerical model may vary for different warming scenarios from United Nation's IPCC AR5 report. We quantify the impacts of these changes on ELAs for various climate change trajectories. These results support previous work on the precarious future of low latitude Andean glaciers, while providing a richer

  13. Low-latitude Pi2 pulsations during intervals of quiet geomagnetic conditions (Kp≤1)

    NASA Astrophysics Data System (ADS)

    Kwon, H.-J.; Kim, K.-H.; Jun, C.-W.; Takahashi, K.; Lee, D.-H.; Lee, E.; Jin, H.; Seon, J.; Park, Y.-D.; Hwang, J.

    2013-10-01

    It has been reported that Pi2 pulsations can be excited under extremely quiet geomagnetic conditions (Kp=0). However, there have been few comprehensive reports of Pi2 pulsations in such a near ground state magnetosphere. To understand the characteristics of quiet-time Pi2 pulsations, we statistically examined Pi2 events observed on the nightside between 1800 and 0600 local time at the low-latitude Bohyun (BOH, L = 1.35) station in South Korea. We chose year 2008 for analysis because geomagnetic activity was unusually low in that year. A total of 982 Pi2 events were identified when Kp≤1. About 80% of the Pi2 pulsations had a period between 110 and 300 s, which significantly differs from the conventional Pi2 period from 40 to 150 s. Comparing Pi2 periods and solar wind conditions, we found that Pi2 periods decrease with increasing solar wind speed, consistent with the result of Troitskaya (1967). The observed wave properties are discussed in terms of plasmaspheric resonance, which has been proposed for Pi2 pulsations in the inner magnetosphere. We also found that Pi2 pulsations occur quasi-periodically with a repetition period of ˜23-38 min. We will discuss what determines such a recurrence time of Pi2 pulsations under quiet geomagnetic conditions.

  14. Calculated distributions of hydrogen and helium ions in the low-latitude ionosphere.

    NASA Technical Reports Server (NTRS)

    Moffett, R. J.; Hanson, W. B.

    1973-01-01

    The simultaneous time-dependent continuity equations for O(+), H(+) and He(+) in the low latitude F-region are solved. Account is taken of E x B drift, a meridional neutral wind, and ion-ion and ion-neutral drag. The calculated profiles of O(+) and H(+) concentrations at 1630 LT are in fair agreement with the observations of Hanson et al. The He(+) field-aligned velocity is almost matched to the O(+) field-aligned velocity and, above the chemical equilibrium region and around the He(+) peak, the He(+) concentration is determined largely by production and transport. There is disagreement between the theoretical vertical He(+) profile and the profile observed by Hanson et al. Satisfactory agreement is obtained with Taylor's satellite results at fixed height for O(+) and H(+). It is found that the He(+) concentration is greater in the winter hemisphere than in the summer hemisphere, even if the neutral helium distribution is symmetrical about the Equator. The He(+) results are consistent with Taylor's results.

  15. Jellyfish Patch Detecting Using Low Latitude Remote Sensing System

    NASA Astrophysics Data System (ADS)

    Lee, J. S.; Jo, Y. H.

    2015-12-01

    Jellyfish can be asexual and sexual reproduction depending on the environment, and it has excellent environmental adaptability and reproduction than other sea creatures. If the marine environment become worse, jellyfish can take advantage in the competition for survival. Marine environmental changes caused by rapid climate change, dyke construction and land reclamation will increase the amount of jellyfish and as a result can lead to a various social and economic problems. In this study, jellyfish were observed in coastal area using a low-altitude Helikite remote sensing system for the first time. Helikite is a type of helium balloon plus a kite that can get the data with optical sensors for the desired spatial resolutions by adjusting the altitudes. In addition, it has an advantage that can monitor any objects for a long time at one place as long as the electric power and helium last. In this study, we observed the jellyfish patches using a digital camera in the Chesapeake Bay and estimate populations and size of jellyfish patches through image processing. Research results suggests that we can have long-term real-time observations for not only jellyfish, but also other harmful marine creatures.

  16. Modeling the 6,300- angstrom low-latitude nightglow

    SciTech Connect

    Fesen, C.G. ); Abreu, V.J. )

    1987-02-01

    Observations of the 6,300-{angstrom} nightglow form the Visible Airglow Experiment (VAE) instrument on AE-E are presented for spring equinox, solar cycle maximum conditions. The data comprise altitude profiles and integrated column brightness maps from {approximately}1,800 to 0400 LT and within {plus minus}30{degrees} of the dip equator. The data clearly show near-midnight enhancements of the 6,300-{angstrom} emission. Attempts to model the column brightness maps indicated that these enhancements are due to tidal effects: the enhancements were only reproduced in the theoretical calculations which included upward propagating tidal components in the neutral winds. Further, low equatorial intensities were observed by the VCAE which could only be simulated by assuming that the phase of the E {times} B drift by shifted 1 hour LT; i.e., upward drift persists until 2,000 LT instead of 1,900 LT. The VAE observations could be reasonably simulated with the phase shift in the E {times} B drift and with the dip and geographic equators offset. The major discrepancy is in the magnitude of the nightglow maxima: the calculated intensities are a maximum of 2 times too large. Possible sources are uncertainties in the neutral densities, chemistry, and rate coefficients and in the neutral winds.

  17. Dynamics of the low latitude thermosphere and ionosphere

    SciTech Connect

    Burnside, R.G.

    1984-01-01

    Nighttime thermospheric neutral wind velocities were determined at Arecibo, Puerto Rico, by using a Fabry-Perot interferometer, which measures the Doppler shift of the O(/sup 1/D) airglow emission. In summer, the winds are observed to flow toward the southeast between sunset and midnight. After midnight in summer, the meridional component of the wind usually slackens, while the zonal component may reverse. By contrast, in winter, the meridional wind is often small, and the predominant flow is eastward throughout the night. Vertical winds are inferred from the divergence of the horizontal flow. A maximum downward flow of about 5 m s..pi../sup 1/ is observed near midnight in summer. Incoherent scatter radar measurements were used to calculate the O/sup +/ diffusion velocity and infer the vertical profile of the meridional wind. Horizontal temperature gradients and ion-drag forces were evaluated from radar measurements. It is concluded that it may sometimes be necesary to include viscous forces to balance the meridional equation of motion for the neutral gas. Electrical conductivities of the E and F layers of the nighttime ionosphere were determined. The F layer Pedersen conductivity at the magnetically conjugate point was evaluated using ionosonde data. The F layer dynamo mechanism was found to be the source of most of the nighttime electric fields observed at Arecibo.

  18. Insights into low-latitude cloud feedbacks from high-resolution models.

    PubMed

    Bretherton, Christopher S

    2015-11-13

    Cloud feedbacks are a leading source of uncertainty in the climate sensitivity simulated by global climate models (GCMs). Low-latitude boundary-layer and cumulus cloud regimes are particularly problematic, because they are sustained by tight interactions between clouds and unresolved turbulent circulations. Turbulence-resolving models better simulate such cloud regimes and support the GCM consensus that they contribute to positive global cloud feedbacks. Large-eddy simulations using sub-100 m grid spacings over small computational domains elucidate marine boundary-layer cloud response to greenhouse warming. Four observationally supported mechanisms contribute: 'thermodynamic' cloudiness reduction from warming of the atmosphere-ocean column, 'radiative' cloudiness reduction from CO2- and H2O-induced increase in atmospheric emissivity aloft, 'stability-induced' cloud increase from increased lower tropospheric stratification, and 'dynamical' cloudiness increase from reduced subsidence. The cloudiness reduction mechanisms typically dominate, giving positive shortwave cloud feedback. Cloud-resolving models with horizontal grid spacings of a few kilometres illuminate how cumulonimbus cloud systems affect climate feedbacks. Limited-area simulations and superparameterized GCMs show upward shift and slight reduction of cloud cover in a warmer climate, implying positive cloud feedbacks. A global cloud-resolving model suggests tropical cirrus increases in a warmer climate, producing positive longwave cloud feedback, but results are sensitive to subgrid turbulence and ice microphysics schemes.

  19. Variational electric fields at low latitudes and their relation to spread F and plasma irregularities

    NASA Technical Reports Server (NTRS)

    Holtet, J. A.; Maynard, N. C.; Heppner, J. P.

    1976-01-01

    Recordings from OGO 6 show that electric field irregularities are frequently present between + or - 35 deg geomagnetic latitude in the 2000 - 0600 local time sector. The signatures are very clear, and are easily distinguished from the normal AC background noise, and whistler and emission activity. The spectral appearance of the fields makes it meaningful to distinguish between 3 different types of irregularities: strong irregularities, weak irregularities, and weak irregularities with a rising spectrum. Strong irregularities seem most likely to occur in regions where gradients in ionization are present. Changes in plasma composition, resulting in an increase in the mean ion mass, are also often observed in the irregularity regions. Comparison with ground based ionosondes indicates a connection between strong irregularities and low latitude spread F. A good correlation is also present between strong fields and small scale fluctuations in ionization, delta N/N 1 percent. From the data it appears as if a gradient driven instability is the most likely source of the strong irregularities.

  20. Solar Cycle Effects on Equatorial Electrojet Strength and Low Latitude Ionospheric Variability (P10)

    NASA Astrophysics Data System (ADS)

    Veenadhari, B.; Alex, S.

    2006-11-01

    veena_iig@yahoo.co.in The most obvious indicators of the activity of a solar cycle are sunspots, flares, plages, and soon. These are intimately linked to the solar magnetic fields, heliospheric processes which exhibit complex but systematic variations. The changes in geomagnetic activity, as observed in the ground magnetic records follow systematic correspondence with the solar activity conditions. Thus the transient variations in the magnetic field get modified by differing solar conditions. Also the solar cycle influences the Earth causing changes in geomagnetic activity, the magnetosphere and the ionosphere. Daily variations in the ground magnetic field are produced by different current systems in the earth’s space environment flowing in the ionosphere and magnetosphere which has a strong dependence on latitude and longitude of the location. The north-south (Horizontal) configuration of the earth’s magnetic field over the equator is responsible for the narrow band of current system over the equatorial latitudes and is called the Equatorial electrojet (EEJ) and is a primary driver for Equatorial Ionization anomaly (EIA). Equatorial electric fields and plasma drifts play the fundamental roles on the morphology of the low latitude ionosphere and strongly vary during geomagnetically quiet and disturbed periods. Quantitative study is done to illustrate the development process of EEJ and its influence on ionospheric parameters. An attempt is also made to examine and discuss the response of the equatorial electrojet parameters to the fast varying conditions of solar wind and interplanetary parameters.

  1. Electrostatic waves due to field-aligned electron beams in the low-latitude boundary layer

    NASA Technical Reports Server (NTRS)

    Peroomian, V.; Ashour-Abdalla, M.; Fuselier, S. A.; Schriver, D.; Peterson, W. K.; Strangeway, R. J.

    1992-01-01

    Mass-resolved ion, electron, and plasma wave data obtained from several low-latitude boundary layer (LLBL) crossings by the AMPTE CCE satellite are analyzed. The data clearly separate the LLBL from the adjacent magnetosheath and magnetosphere. Attention was focused on wave-particle interactions involving electrons. Electron beams were found to be present in the LLBL during the southward interplanetary magnetic field, along with a simultaneous enhancement of electrostatic waves with parallel polarization. Linear theory analysis shows that for plasma conditions in the LLBL, electron beams are unstable to electrostatic waves that propagate parallel to the local magnetic field, in agreement with observations. A numerical simulation study of the beam-plasma interaction in the LLBL shows that the instability saturates by thermalization of the beam but that a beamlike structure can still remain in the electron distribution for certain initial parameters. It is suggested that peaks in the electron velocity distribution function may be found in the LLBL away from the beam source region.

  2. Insights into low-latitude cloud feedbacks from high-resolution models.

    PubMed

    Bretherton, Christopher S

    2015-11-13

    Cloud feedbacks are a leading source of uncertainty in the climate sensitivity simulated by global climate models (GCMs). Low-latitude boundary-layer and cumulus cloud regimes are particularly problematic, because they are sustained by tight interactions between clouds and unresolved turbulent circulations. Turbulence-resolving models better simulate such cloud regimes and support the GCM consensus that they contribute to positive global cloud feedbacks. Large-eddy simulations using sub-100 m grid spacings over small computational domains elucidate marine boundary-layer cloud response to greenhouse warming. Four observationally supported mechanisms contribute: 'thermodynamic' cloudiness reduction from warming of the atmosphere-ocean column, 'radiative' cloudiness reduction from CO2- and H2O-induced increase in atmospheric emissivity aloft, 'stability-induced' cloud increase from increased lower tropospheric stratification, and 'dynamical' cloudiness increase from reduced subsidence. The cloudiness reduction mechanisms typically dominate, giving positive shortwave cloud feedback. Cloud-resolving models with horizontal grid spacings of a few kilometres illuminate how cumulonimbus cloud systems affect climate feedbacks. Limited-area simulations and superparameterized GCMs show upward shift and slight reduction of cloud cover in a warmer climate, implying positive cloud feedbacks. A global cloud-resolving model suggests tropical cirrus increases in a warmer climate, producing positive longwave cloud feedback, but results are sensitive to subgrid turbulence and ice microphysics schemes. PMID:26438280

  3. Hydromagnetic waves at low latitudes - A symposium review from the fifth IAGA assembly

    NASA Technical Reports Server (NTRS)

    Fraser, B. J.

    1986-01-01

    The aim of the symposium was to bring together investigators with interests in low latitude hydromagnetic waves in order to review the present state of knowledge in this area of magnetospheric physics. Of particular importance is the means by which wave energy is transferred to low latitudes to produce geomagnetic pulsations on the ground. The group of contributed papers reviewed shows that definitive experiments are underway and new theories capable of providing resonant wave energy at low latitudes are being developed. Particular topics covered by the review include solar wind control, wave spectra, array studies of wave parameters, storm time waves, and global wave resonance theory involving the coupling of compressional and transverse waves in the magnetosphere.

  4. High latitude regulation of low latitude thermocline ventilation and planktic foraminifer populations across glacial-interglacial cycles

    NASA Astrophysics Data System (ADS)

    Sexton, Philip F.; Norris, Richard D.

    2011-11-01

    One of the earliest discoveries in palaeoceanography was the observation in 1935 that the (sub)tropical planktic foraminifer Globorotalia menardii became absent or extremely rare in the Atlantic Ocean during glacials of the late Pleistocene. Yet a mechanistic explanation for G. menardii's extraordinary biogeographic behaviour has eluded palaeoceanographers for 75 years. Here we show that modern G. menardii, along with two other species that also suffer Atlantic population collapses during glacials, track poorly ventilated waters globally in their thermocline habitats. The ventilation states of low latitude thermoclines are 'set', to a first order, by intermediate water masses originating at high latitudes. In the modern Atlantic this control on low latitude thermocline ventilation is exerted by relatively poorly ventilated, southern-sourced Antarctic Intermediate Water (AAIW) and sub-Antarctic Mode Water (SAMW). We suggest that the glacial Atlantic foraminifer population collapses were a consequence of a low latitude thermocline that was better ventilated during glacials than it is today, in line with geochemical evidence, and driven primarily by a well-ventilated, northern-sourced intermediate water mass. A ventilation mechanism driving the glacial population collapses is further supported by our new constraints on the precise timing of these species' Atlantic proliferation during the last deglaciation — occurring in parallel with a wholesale, bipolar reorganisation of the Atlantic's thermocline-to-abyssal overturning circulation. Our findings demonstrate that a bipolar seesaw in the formation of high latitude intermediate waters has played an important role in regulating the population dynamics of thermocline-dwelling plankton at lower latitudes.

  5. Multispecies spawning sites for fishes on a low-latitude coral reef: spatial and temporal patterns.

    PubMed

    Claydon, J A B; McCormick, M I; Jones, G P

    2014-04-01

    Spawning sites used by one or more species were located by intensively searching nearshore coral reefs of Kimbe Bay (New Britain, Papua New Guinea). Once identified, the spawning sites were surveyed repeatedly within fixed 5 m radius circular areas, for  > 2000 h of observations ranging from before dawn to after dusk spanning 190 days between July 2001 and May 2004. A total of 38 spawning sites were identified on the seven study reefs distributed at an average of one site every 60 m of reef edge. Pelagic spawning was observed in 41 fish species from six families. On three intensively studied reefs, all 17 spawning sites identified were used by at least three species, with a maximum of 30 different species observed spawning at a single site. Spawning was observed during every month of the study, on all days of the lunar month, at all states of the tide and at most hours of the day studied. Nevertheless, the majority of species were observed spawning on proportionately more days from December to April, on more days around the new moon and in association with higher tides. The strongest temporal association, however, was with species-specific diel spawning times spanning < 3 h for most species. While dawn spawning, afternoon spawning and dusk spawning species were differentiated, the time of spawning for the striated surgeonfish Ctenochaetus striatus also differed significantly among sites. The large number of species spawning at the same restricted locations during predictable times suggests that these sites are extremely important on this low-latitude coral reef.

  6. Anomalous variations of ionosphere associated with the strong earthquake at Pakistan-Iran border at a low latitude station Agra, India

    NASA Astrophysics Data System (ADS)

    Pundhir, Devbrat; Singh, Birbal; Singh, O. P.; Gupta, Saral K.

    2016-05-01

    In this paper, we analyze the TEC data for April 2013 observed at Agra station, India (geogr. lat. 27.2° N, long. 78° E) to examine the effect of earthquake of magnitude M = 7.8 which occurred on 16 April 2013 at Pakistan-Iran border region. We process the TEC data using the σ statistical criterion to find out anomalous variation in TEC data. We also study the VLF propagation signal from NPM, Hawaii (21.42° N, 158° W), which is monitored at the same station (Agra station) in the light of this earthquake as well as solar flares. The nighttime fluctuation method is used to analyze the VLF data for the period of ±5 days from the day of earthquake (11-21 April 2013). The anomalous enhancements and depletions are found in TEC data on 1-9 days before the occurrence of event.

  7. Modeling Longitude Dependence of Stormtime Low-Latitude Prompt-Penetration Electric Fields

    NASA Astrophysics Data System (ADS)

    Spiro, R. W.; Sazykin, S.; Wolf, R. A.; Toffoletto, F.

    2011-12-01

    Transient large-scale electric fields of magnetospheric origin, known as prompt penetration electric fields, can strongly affect low-latitude ionospheric dynamics during geomagnetically active periods. We present results from a study of computed prompt penetration electric fields associated with rising solar cycle storms using a reformulated version of the Rice Convection Model (RCM), generalized to include arbitrary internal geomagnetic field. In this study we assume an IGRF internal magnetic field and an event-driven storm-time Tsyganenko external field to investigate longitude and By effects on the resulting pattern of low-latitude electric field penetration during periods of modest magnetic storms.

  8. HF radar signatures of the cusp and low-latitude boundary layer

    NASA Technical Reports Server (NTRS)

    Baker, K. B.; Dudeney, J. R.; Greenwald, R. A.; Pinnock, M.; Newell, P. T.; Rodger, A. S.; Mattin, N.; Meng, C.-I.

    1995-01-01

    Continuous ground-based observations of ionospheric and magnetospheric regions are critical to the Geospace Environmental Modeling (GEM) program. It is therefore important to establish clear intercalibrations between different ground-based instruments and satellites in order to clearly place the ground-based observations in context with the corresponding in situ satellite measurements. HF-radars operating at high latitudes are capable of observing very large spatial regions of the ionosphere on a nearly continuous basis. In this paper we report on an intercalibration study made using the Polar Anglo-American Conjugate Radar Experiment radars located at Goose Bay, Labrador, and Halley Station, Antarctica, and the Defense Meteorological Satellite Program (DMSP) satellites. The DMSP satellite data are used to provide clear identifications of the ionospheric cusp and the low-latitude boundary layer (LLBL). The radar data for eight cusp events and eight LLBL events have been examined in order to determine a radar signature of these ionospheric regions. This intercalibraion indicates that the cusp is always characterized by wide, complex Doppler power spectra, whereas the LLBL is usually found to have spectra dominated by a single component. The distribution of spectral widths in the cusp is of a generally Gaussian form with a peak at about 220 m/s. The distribution of spectral widths in the LLBL is more like an exponential distribution, with the peak of the distribution occurring at about 50 m/s. There are a few cases in the LLBL where the Doppler power spectra are strikingly similar to those observed in the cusp.

  9. The Kinetic Scale Structure of the Low Latitude Boundary Layer: Initial MMS Results

    NASA Astrophysics Data System (ADS)

    Dorelli, John; Gershman, Dan; Avanov, Levon; Pollock, Craig; Giles, Barbara; Gliese, Ulrik; Barrie, Alexander; Holland, Matthew; Salo, Chad; Dickson, Charles; Coffey, Victoria; Chandler, Michael; Sato, Yoshifumi; Strangeway, Robert; Russell, Christopher; Baumjohann, Wolfgang; Khotyainstev, Yuri; Torbert, Roy; Burch, James

    2016-04-01

    Since its launch in March of 2015, NASA's Magnetospheric Multiscale (MMS) mission has captured thousands of high resolution magnetopause crossings, routinely resolving the sub-Larmor radius structure of the magnetopause boundary layer for the first time. The primary goal of MMS is to understand the microphysics of magnetic reconnection, and it is well on its way to achieving this objective. However, MMS is also making routine measurements of the electron and ion gyroviscous and heat flux tensors with unprecedented resolution and accuracy. This opens up the possibility of directly observing the physical processes that facilitate momentum and energy transport across the magnetopause boundary layer under arbitrary conditions (e.g., magnetic field geometry and flow shear) far from the reconnection X line. Currently, our global magnetosphere fluid models (e.g., resistive or Hall MHD) do not include accurate descriptions of viscosity and heat flow, both of which are known to be critical players at the magnetopause (not just at the reconnection sites), and several groups are attempting to make progress on this difficult fluid closure problem. In this talk, we will address the fluid closure problem in the context of MMS observations of the Low Latitude Boundary Layer (LLBL), focusing on high resolution particle observations by the Fast Plasma Investigation (FPI). FPI electron bulk velocities are accurate enough to compute current density in both the high density magnetosheath and low density magnetosphere and have already revealed that the LLBL has a complex parallel current structure on the proton Larmor radius scale. We discuss the relationship between these parallel currents and the Hall electric field structures predicted by kinetic models. We also present first observations of the ion and electron gyroviscous and heat flux tensors in the LLBL and discuss implications for the fluid closure problem at Earth's magnetopause.

  10. Comparison study on ionospheric spread-F between high and low latitude regions during the storm time

    NASA Astrophysics Data System (ADS)

    Shi, Jiankui; Tao, Wei; Wang, Guojun; Wang, Xiao; Zherebtsov, Gelii; Pirog, Olga; Romanova, Elena

    We use DPS-4 digisonde measurement data from ionospheric station Hainan (19.4N, 109.0E), China, and Yakutsk (62N, 129E) and Zhigansk (66N, 123E), Russia to study ionospheric Spread-F (SF) properties during the magnetic storm time. The results show that: (1) The SF can take place in any phase (suddenly commencement, main phase and recovery phase). (2) The SF always take place from about 2000LT to around midnight, and the more the latitude is, the earlier the SF takes place. (3) Yakutsk station has a higher occurrence of SF than that both in the higher latitude station (Zhigansk) and lower latitude station (Hainan). (4) The frequency SF, range SF and mixed SF can be observed at any latitude station. The strong range SF can only be observed at Hainan station (low latitude station) and it confirms that the strong range SF concerns the equatorial plasma bubble. Our results indicate that ionospheric disturbance which causes the SF, during the storm time, is original from the higher latitude region and propagate to the lower region. Sometimes it could excite out SF at low latitude region and sometimes it could not.

  11. On the seasonal variations of reflectivity and turbulence characteristics of low-latitude mesospheric echoes over Gadanki

    NASA Astrophysics Data System (ADS)

    Selvaraj, D.; Patra, A. K.; Narayana Rao, D.

    2016-06-01

    Gadanki radar observations of the low-latitude mesospheric echoes studied earlier have shown that while both occurrence rate and signal-to-noise ratio of the mesospheric echoes peak in the equinoxes turbulent kinetic energy (TKE) dissipation rate and eddy diffusivity, estimated using spectral width of these echoes, peak in the summer. This seasonal difference is apparently inconsistent with the understanding that the mesospheric echoes are generated by turbulence. In this paper, we analyze Gadanki radar observations of mesospheric echoes made during 2011 and 2012 and study seasonal variations in reflectivity and TKE dissipation rate in an attempt to address the aforementioned puzzle. We show that both reflectivity and TKE dissipation rate in the mesosphere show semiannual variations peaking in the equinoxes, which are vastly different from those reported earlier. We also show that seasonal variations in reflectivity and TKE dissipation rate have a close correspondence with gravity wave activity. These results are found to be consistent with the gravity wave breaking hypothesis generating turbulence and radar echoes in the low-latitude mesosphere.

  12. Equatorial and low-latitude ionosphere-thermosphere system response to the space weather event of August 2005

    NASA Astrophysics Data System (ADS)

    Sreeja, V.; Ravindran, Sudha; Pant, Tarun Kumar; Devasia, C. V.; Paxton, L. J.

    2009-12-01

    The response of the equatorial and low-latitude ionosphere-thermosphere system to the geomagnetic storm during 23-26 August 2005 is investigated. The study is carried out using the vertical total electron content (VTEC) measured by GPS receivers along the 77-78°E longitude and the O/N2 ratio obtained from the Global Ultraviolet Imager instrument on board the TIMED satellite. The equatorial ionization anomaly (EIA) shows a poleward latitudinal expansion on 24 August, probably associated with an eastward prompt-penetration electric field. The equatorial and low latitudes show an increase in VTEC during the main phase of the storm on 24 August. The prompt-penetration eastward electric field, along with an increase in the O/N2 ratio, could be responsible for this observed positive phase. The VTEC variations on 24 August also reveal the signature of a large-scale acoustic gravity wave/traveling atmospheric disturbance propagating with a horizontal velocity of ˜750 m/s. Suppression of the EIA is observed during the storm recovery phase on 25 August, which probably is associated with the westward disturbance dynamo electric field and the equatorward expansion of the neutral composition changes (O/N2 depletion).

  13. Study of propagation characteristics of very low latitude whistlers by means of three-dimensional ray-tracing computations

    NASA Astrophysics Data System (ADS)

    Ohta, Kenji; Nishimura, Yasuhiro; Kitagawa, Tomomi; Hayakawa, Masashi

    1997-04-01

    The propagation mechanism of very low latitude (geomagnetic latitudes of less than 10-15°) whistlers is poorly understood. There is a controversy on their propagation; some workers using the observational facts have suggested field-aligned propagation, but some theoretical (ray tracing) works have all indicated nonducted propagation. This paper reexamines the propagation characteristics of nonducted propagation, but we use three-dimensional ray tracing (different from previous works) for realistic ionosphere/magnetosphere models (the electron density profile with latitudinal and longitudinal gradients and the International Geomagnetic Reference Field (IGRF) magnetic field model instead of the conventional dipole model). By assuming small possible tilts (in the latitudinal and longitudinal direction) of the initial wave normal angle in the input southern hemisphere, we have found that it is possible for us to detect simultaneously, at a very low latitude position in the northern ionosphere, one-hop whistler rays started from slightly spaced locations in the south with different initial wave normal angles and that some of them can penetrate through the ionosphere, but some others cannot. On the basis of systematic analysis of important parameters, we come to the general conclusion that it is possible for us to find a closely spaced set of paths to reproduce the one-hop and three-hop whistlers in the north and to have the dispersion ratio of 1:3. The echo train whistlers, as were often observed by Hayakawa et al. [1990], are realized also by this nonducted propagation without any serious requirements.

  14. Early science with the Large Millimetre Telescope: Deep LMT/AzTEC millimetre observations of ɛ Eridani and its surroundings

    NASA Astrophysics Data System (ADS)

    Chavez-Dagostino, M.; Bertone, E.; Cruz-Saenz de Miera, F.; Marshall, J. P.; Wilson, G. W.; Sánchez-Argüelles, D.; Hughes, D. H.; Kennedy, G.; Vega, O.; De la Luz, V.; Dent, W. R. F.; Eiroa, C.; Gómez-Ruiz, A. I.; Greaves, J. S.; Lizano, S.; López-Valdivia, R.; Mamajek, E.; Montaña, A.; Olmedo, M.; Rodríguez-Montoya, I.; Schloerb, F. P.; Yun, Min S.; Zavala, J. A.; Zeballos, M.

    2016-11-01

    ɛ Eridani is a nearby, young Sun-like star that hosts a ring of cool debris analogous to the Solar system's Edgeworth-Kuiper belt. Early observations at (sub-)mm wavelengths gave tentative evidence of the presence of inhomogeneities in the ring, which have been ascribed to the effect of a putative low eccentricity planet, orbiting close to the ring. The existence of these structures has been recently challenged by high-resolution interferometric millimetre observations. Here, we present the deepest single-dish image of ɛ Eridani at millimetre wavelengths, obtained with the Large Millimetre Telescope Alfonso Serrano (LMT). The main goal of these LMT observations is to confirm (or refute) the presence of non-axisymmetric structure in the disc. The dusty ring is detected for the first time along its full projected elliptical shape. The radial extent of the ring is not spatially resolved and shows no evidence, to within the uncertainties, of dust density enhancements. Additional features of the 1.1 mm map are: (i) the presence of significant flux in the gap between the ring and the star, probably providing the first exo-solar evidence of Poynting-Robertson drag, (ii) an unambiguous detection of emission at the stellar position with a flux significantly above that expected from ɛ Eridani's photosphere, and (iii) the identification of numerous unresolved sources which could correspond to background dusty star-forming galaxies.

  15. Ionospheric response to the 17-18 March 2015 geomagnetic storm as seen from multiple TEC and NmF2 measurements along 100°E

    NASA Astrophysics Data System (ADS)

    Bhuyan, Pradip; Yokoyama, Tatsuhiro; Kalita, Bitap Raj; Seemala, G. K.; Hazarika, Rumajyoti; Komolmis, Tharadol; Yatini, Clara; Chakrabarty, Dibyendu; Supnithi, Pornchai

    2016-07-01

    The response of the ionosphere along 100°E to the strong geomagnetic storm of 17-18 March 2015 has been investigated combining TEC and NmF2 data from multiple stations spanning low latitudes in the northern and southern hemispheres to the equator. The GPS TEC data measured over Dibrugarh (27.4°N, 95°E), Kohima (25.6°N, 94.1°E) and Ahmedabad (23.0°N, 72.5°E) and NmF2 measured along a chain of ionosonde stations Dibrugarh (27.5°N, 95°E), Chiang Mai (18.76ºN, 98.93ºE), Chumphon (10.72ºN,99.37ºE), Kototabang (0.2ºS,100.32ºE) and Cocos Island (12.2ºS,96.8ºE ) were used to examine the signature of the storm around the low-mid latitude ionosphere in this sector. Nearly similar TEC variation has been observed over Dibrugarh and Kohima located at the northern edge of the EIA. The maximum TEC on 18 March over Dibrugarh and Kohima was reduced by more than ~80 TECU compared to that on the geomagnetically quiet day of 16 March 2015. In contrast to the substantial reduction in TEC over ~100°E TEC from the ~75°E longitude station Ahmedabad showed insignificant variations on the same day. Strong reduction in NmF2 at the crest of the anomaly in both northern and southern hemisphere (Dibrugarh, Ching Mai and Cocos Island) and enhancement near the equator (Cumphon and Kototbang) has been observed. The O/N2 ratio as obtained from the TIMED/GUVI reduced substantially along 100°E on 18 March compared to other longitude sectors. Equatorward meridional winds depleted the ionization at the crest region and enhanced the same near the equator. No L band scintillation was observed in the evening of 17 March at Dibrugarh and Kohima indicating absence of F region irregularity along this longitude while strong scintillations were observed at 75°E. The reversal of the IMF Bz from southward to northward direction in the dusk to evening sector inhibited the growth of the irregularity due to reversal of the PPEF at 100°E while the PPEF favoured generation and growth of Spread F

  16. Influence of hydrologic attributes on brown trout recruitment in low-latitude range margins.

    PubMed

    Nicola, Graciela G; Almodóvar, Ana; Elvira, Benigno

    2009-06-01

    Factors controlling brown trout Salmo trutta recruitment in Mediterranean areas are largely unknown, despite the relevance this may have for fisheries management. The effect of hydrological variability on survival of young brown trout was studied during seven consecutive years in five resident populations from the southern range of the species distribution. Recruit density at the end of summer varied markedly among year-classes and rivers during the study period. Previous work showed that egg density the previous fall did not account for more than 50% of the observed variation in recruitment density. Thus, we expected that climatic patterns, as determinants of discharge and water temperature, would play a role in the control of young trout abundance. We tested this by analyzing the effects of flow variation and predictability on young trout survival during the spawning to emergence and the summer drought periods. Both hatching and emergence times and length of hatching and emergence periods were similar between years within each river but varied considerably among populations, due to differences in water temperature. Interannual variation in flow attributes during spawning to emergence and summer drought affected juvenile survival in all populations, once the effect of endogenous factors was removed. Survival rate was significantly related to the timing, magnitude and duration of extreme water conditions, and to the rate of change in discharge during hatching and emergence times in most rivers. The magnitude and duration of low flows during summer drought appeared to be a critical factor for survival of young trout. Our findings suggest that density-independent factors, i.e., hydrological variability, play a central role in the population dynamics of brown trout in populations from low-latitude range margins. Reported effects of hydrologic attributes on trout survival are likely to be increasingly important if, as predicted, climate change leads to greater extremes

  17. Variability of Total Electron Content at Low Latitude Region During Solar Minimum 2008: Impact of High Speed Streams, HSSs

    NASA Astrophysics Data System (ADS)

    Nicoli Candido, C. M.; Batista, I. S.; Becker-Guedes, F.; Klausner, V.

    2015-12-01

    The solar minimum period of solar cycle 23 was unusually long and quiet in comparison to other solar minima in last century. Several reports have analyzed its features and its impact under diverse points-of-view. In this work, we analyze the low latitude ionosphere behavior in Brazil and its response during this peculiar period. The ionospheric variation is analyzed through typical parameters such as vertical total electron content (VTEC), the peak height of F2 layer and its critical frequency, hmF2 and foF2, in 2008, around the southern crest of the Equatorial Ionization Anomaly (EIA), in Cachoeira Paulista (22.5o S, 45.0 o W, mag. lat: 16 o S, dip angle: -32.3o) and at an equatorial station, São Luís (2.33o S, 44.2o W, dip angle: -6.7o). VTEC values present a semiannual variation pattern and two well-defined peaks in March and October. Daily maximum values are observed around 15:00 LT. It was observed periodicities observed of 9, 13.5 and 27 days in VTEC and hmF2, mainly at the first and the second half of 2008. These periods match with the observed periods in solar and geomagnetic indexes such as Vsw, Kp and AE and are associated with occurrence of high speed streams (HSS) coming from solar coronal holes. A complex response of the low latitude ionosphere is observed, with prominent increases and decreases of VTEC at daytime during the interval of occurrence of HSSs. It is suggested that a combination of several factors such as prompt penetration of electric field, disturbed dynamo electric field, meridional winds, thermal expansion of thermosphere and composition changes of neutral atmosphere are responsible for the high day-to-day variability of the ionosphere

  18. Longitudinal Variations of Low-Latitude Gravity Waves and Their Impacts on the Ionosphere

    NASA Astrophysics Data System (ADS)

    Cullens, C. Y.; England, S.; Immel, T. J.

    2014-12-01

    The lower atmospheric forcing has important roles in the ionospheric variability. However, influences of lower atmospheric gravity waves on the ionospheric variability are still not clear due to the simplified gravity wave parameterizations and the limited knowledge of gravity wave distributions. In this study, we aim to study the longitudinal variations of gravity waves and their impacts of longitudinal variations of low-latitude gravity waves on the ionospheric variability. Our SABER results show that longitudinal variations of gravity waves at the lower boundary of TIME-GCM are the largest in June-August and January-February. We have implemented these low-latitude gravity wave variations from SABER instrument into TIME-GCM model. TIME-GCM simulation results of ionospheric responses to longitudinal variations of gravity waves and physical mechanisms will be discussed.

  19. a Study of Ionospheric Low Latitude Velocity and Density Irregularity Correlations during Solar Minimum

    NASA Astrophysics Data System (ADS)

    Haaser, R. A.; Earle, G. D.; Heelis, R. A.; Klenzing, J. H.; Coley, W. R.; Stoneback, R. A.; Burrell, A. B.

    2010-12-01

    The C/NOFS satellite has measured ionospheric plasma density irregularities at low latitudes on scales larger than 10 km over a full set of seasons. The focus of this study is on data from the Ion Velocity Meter (IVM) from Jan-Dec 2009 for pre-midnight and post-midnight times when the data are most reliable. Correlations between the normalized changes in density and velocity (dni/n and dv-horz,vert) during spread-F events (plasma bubbles through the f-peak) and localized plasma enhancements associated with those events are analyzed and compared to investigate seasonal, spatial, and temporal properties during the 2009 solar minimum conditions. The correlations presented and their relationship to the unusually quiescent background conditions in this epoch challenge our understanding and add significantly to our knowledge of ionospheric irregularity events and distribution statistics at low latitudes during solar minimum.

  20. Signatures of solar event at middle and low latitudes in the Europe-African sector, during geomagnetic storms, October 2013

    NASA Astrophysics Data System (ADS)

    Azzouzi, I.; Migoya-Orué, Y.; Amory Mazaudier, C.; Fleury, R.; Radicella, S. M.; Touzani, A.

    2015-11-01

    This paper presents the variability of the total electron content, VTEC, the ROTI index (proxy of the scintillation index) and the transient variations of the Earth's magnetic field associated to the impacts of solar events during October 2013. The observations are from middle and low latitudes in European African longitude sector. During October 2013, there are four solar events reaching the Earth. The two first events, on October 2 and October 8 are CME, the third event on October 14, is a jet of fast solar wind flowing from a solar coronal hole, and the last event on October 30 is a slow solar wind with southward excursions of the Bz component of the interplanetary magnetic field, associated to CME passing near the Earth. For the four events, the variation of VTEC at middle latitudes is the same and presents an increase of VTEC at the time of the impact followed by a decrease of VTEC, lasting one or several days. At low latitudes, no clear common pattern for all the events appears. For the four events the variation of the ROTI index over Africa is different showing the asymmetry between West and East Africa. For the first event, on October 2, the scintillations are not inhibited, for the second and the fourth events on October 8 and 30, the scintillations are inhibited on East Africa and for the third event (high speed solar wind stream), on October 14, the scintillations are inhibited over the whole Africa. The available data allow the full explanation of the observations of October 14, indeed, on this day, there is no post sunset increase of the virtual height h‧F2 at Ascension Island. There is no Pre Reversal Enhancement (PRE) of the eastward electric field; it is this electric field which moves up the F layer, the necessary condition for the existence of scintillation. The analysis of the variations of the Earth's magnetic field at low latitudes highlights the presence of the ionospheric disturbance dynamo on October 14, which produces a decrease of the

  1. Investigation of ionospheric TEC over China based on GNSS data

    NASA Astrophysics Data System (ADS)

    Xiong, Bo; Wan, Weixing; Yu, You; Hu, Lianhuan

    2016-09-01

    In this paper, the ionospheric total electron content (TEC) is derived from 250 Global Navigation Satellite Systems (GNSS) receivers over China. The GNSS TEC data are utilized to study the diurnal and day-to-day variability of ionosphere, ionospheric east-west differences and to construct regional ionospheric map. The GNSS-TEC curves clearly show sunrise and sunset enhancements in the diurnal variation. The peak value of TEC is lower in January 2015 than in May 2014. There is 2 h difference in the occurrence time of TEC maximum/minimum between May and January. Compared with the observations of Global Positioning System (GPS) and Global Navigation Satellite System (GLONASS), the measurements from the Geostationary Earth Orbit (GEO) satellites of BeiDou Navigation Satellite System (BDS) clearly present the ionospheric day-to-day variability and east-west differences in a region with small longitude differences (3.52-11.31°). The east-west differences in TEC are more obvious in larger longitude differences at 11:30 local time on 23 January 2015. The maximum east-west difference in TEC is about 7 total electron content unit (TECU, 1 TECU = 1016 el m-2) in longitude difference of 11.31°. Our analysis shows that the TEC for east-west small longitude differences may be associated with the east-west gradient of geomagnetic declination. Based on 250 GNSS stations, a regional TEC map constructed by Kriging method can well capture the main spatial structure of ionosphere in China. A comparison between TEC maps obtained by Kriging method and provided by Jet Propulsion Laboratory displays that there are large deviations in the North of China, which is mainly caused by the difference in the number of used GNSS stations. In addition, comprehensive investigation presents that GNSS has more advantages over GPS and GLONASS in the ionosphere research over China.

  2. Biotic turnover driven by eutrophication before the Sturtian low-latitude glaciation

    NASA Astrophysics Data System (ADS)

    Nagy, Robin M.; Porter, Susannah M.; Dehler, Carol M.; Shen, Yanan

    2009-06-01

    Reconstructions of the diversity of Precambrian microorganisms suggest a pronounced biotic turnover coinciding with the onset of Neoproterozoic low-latitude glaciation, in which diverse assemblages of organic-walled microfossils known as acritarchs were replaced by assemblages of simple, smooth-walled forms called leiosphaerids, and the remnants of bacterial blooms. This turnover has been interpreted as the mass extinction of eukaryotic phytoplankton and the subsequent proliferation of bacteria. However, the causes of this mass extinction and its exact temporal relationship to the glaciations remain unclear. Here we present palaeontological data from the >742+/-6-Myr-old Chuar Group from Arizona, which indicate that the biotic turnover occurred before the first low-latitude (Sturtian) glaciation, constrained to be between 726 and 660Myr in age. In our record, the turnover is associated with the appearance of abundant and diverse protozoan fossils and a shift to rising total organic carbon, suggestive of increased primary productivity spurred by the influx of nutrients. This is followed by an increase in the ratio of highly reactive iron to total iron, which we interpret as persistent water column anoxia. We therefore conclude that the biotic turnover recorded in the Chuar Group was driven by widespread eutrophication of surface waters, rather than low-latitude glaciation.

  3. Weather disturbances in the ionosphere-thermosphere system at middle and low latitudes

    NASA Astrophysics Data System (ADS)

    Schunk, Robert

    It has been clearly established that the ionosphere-thermosphere system exhibits both a back-ground state (climatology) and a disturbed state (weather). At mid-latitudes, the background ionospheric state is characterized by an electron density distribution that tends to be uniform, with a gradual transition from high electron densities on the dayside to low electron densities on the nightside. At low latitudes, the main characteristic feature is the Equatorial Ionization Anomaly (EIA), which corresponds to ionization peaks that are located on both sides of the magnetic equator. The background thermospheric state at mid-and low-latitudes tends to be uniform, with gentle winds blowing around the globe from the sub-solar point. However, su-perimposed on these background states are storm-time disturbances, mesoscale (100-1000 km) structures, and plasma irregularities. For the ionosphere, these include traveling ionospheric disturbances (TIDs), sporadic E layers, He+ layers in the topside ionosphere, descending inter-mediate layers, ridges of enhanced ionization (Storm Enhanced Densities), a 4-wave signature, spread-F, and equatorial plasma bubbles. For the thermosphere, the weather disturbances include upward propagating waves from the lower atmosphere (planetary, tidal and gravity waves), Traveling Atmospheric Disturbances (TADs) generated at high latitudes, storm-time O/N2 depletions, and neutral gas perturbations at the terminator and in the regions contain-ing equatorial plasma bubbles. These and other weather disturbances in the middle and low latitude ionosphere-thermosphere system will be discussed.

  4. Effects of the magnetic storm in April 2000 in the low latitude ionosphere near longitude 120E

    NASA Astrophysics Data System (ADS)

    Liu, L.; Wan, W.; Lee, C.

    A halo-CME induced interplanetary shock wave that passed the Earth around 1648 UT on April 6, 2000 triggered a geomagnetic storm with a minimum value of about -300 nT in Dst index. In this paper, digisonde data from ionospheric stations at Chungli, Wuhan, and Kokubunji are included to investigate the ionospheric responses of low latitudes near longitude 120 E to this storm. At three low latitudes near longitude 120 E during this storm, the significant ionospheric responses was an anomalous rapid and large increase in the ionospheric heights occurred around the beginning of the main phase, and the lifts in h'F and hmF2 lasted for about 2 hours. The nearsimultaneous ionosphere increase was also observed at Chungli, Taiwan. And a wave like disturbance appeared on daytime of the second day. The near simultaneity of the ionospheric lifts at these stations in the nighttime ionospheric heights after the SSC suggested that an ExB plasma drift due to the storm related perturbed east-west electric fields. The empirical models of storm time equatorial zonal electric fields (Fejer and Scherliess, 1997) attributed those rapid and large lifts to the effect of solar wind-magnetosphere dynamo origin, which penetrate to low latitudes and equatorial regions. The following wave like disturbance was suggested to be caused by storm induced Travelling atmospheric disturbances (TADs). A method developed by Liu et al. (2002) and Luan et al. (2002) was used to derive the vertical effective winds from ionospheric measurements. It also shows that there was a significantly downward and upward vertical drift during the storm, which verifies the existence of the storm related perturbed east-west electric fields. Finally, the ionospheric storm time derivation from its monthly median level at these stations was also used to validate the predication ability of STORM, a storm empirical model of Araujo-Pradere et al. (2001), which is now included in the international reference ionosphere model IRI

  5. The observation and simulation of ionospheric response to CIR/high-speed streams-induced geomagnetic activity on 4 April 2005

    NASA Astrophysics Data System (ADS)

    Chen, Yanhong; Wang, Wenbin; Qiu, Na; Liu, Siqing; Gong, Jiancun; Huang, Wengeng

    2016-08-01

    The ionospheric response to corotating interaction region (CIR)-induced geomagnetic activity on 4 April 2005 has been studied using in situ electron density measurements, ground GPS-total electron content (TEC) observations, and numerical simulations of the National Center for Atmospheric Research Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIE-GCM). The case study resulted that the ionospheric positive response occurred from high to low latitudes. The positive effect at low latitudes could continue for 4 days, whereas at middle to high latitudes the disturbance mainly lasted only for 1 day. The modeled Ne and TEC from TIE-GCM had a good agreement with those from observations. The simulation results showed that penetration electric fields were responsible for the daytime positive response during the initial and main phases of the geomagnetic storm, while neutral winds were responsible for the presunset positive effects. The long-lasting positive storm effect during the storm recovery time at low latitudes was related to the thermospheric composition (O/N2) changes during the storm event.

  6. Modelling the probability of ionospheric irregularity occurrence over African low latitude region

    NASA Astrophysics Data System (ADS)

    Mungufeni, Patrick; Jurua, Edward; Bosco Habarulema, John; Anguma Katrini, Simon

    2015-06-01

    This study presents models of geomagnetically quiet time probability of occurrence of ionospheric irregularities over the African low latitude region. GNSS-derived ionospheric total electron content data from Mbarara, Uganda (0.60°S, 30.74°E, geographic, 10.22°S, magnetic) and Libreville, Gabon (0.35°N, 9.68°E, geographic, 8.05°S, magnetic) during the period 2001-2012 were used. First, we established the rate of change of total electron content index (ROTI) value associated with background ionospheric irregularity over the region. This was done by analysing GNSS carrier-phases at L-band frequencies L1 and L2 with the aim of identifying cycle slip events associated with ionospheric irregularities. We identified at both stations a total of 699 events of cycle slips. The corresponding median ROTI value at the epochs of the cycle slip events was 0.54 TECU/min. The probability of occurrence of ionospheric irregularities associated with ROTI ≥ 0.5 TECU / min was then modelled by fitting cubic B-splines to the data. The aspects the model captured included diurnal, seasonal, and solar flux dependence patterns of the probability of occurrence of ionospheric irregularities. The model developed over Mbarara was validated with data over Mt. Baker, Uganda (0.35°N, 29.90°E, geographic, 9.25°S, magnetic), Kigali, Rwanda (1.94°S, 30.09°E, geographic, 11.62°S, magnetic), and Kampala, Uganda (0.34°N, 32.60°E, geographic, 9.29°S, magnetic). For the period validated at Mt. Baker (approximately, 137.64 km, north west), Kigali (approximately, 162.42 km, south west), and Kampala (approximately, 237.61 km, north east) the percentages of the number of errors (difference between the observed and the modelled probability of occurrence of ionospheric irregularity) less than 0.05 are 97.3, 89.4, and 81.3, respectively.

  7. Wp index: A new substorm index derived from high-resolution geomagnetic field data at low latitude

    NASA Astrophysics Data System (ADS)

    Nosé, M.; Iyemori, T.; Wang, L.; Hitchman, A.; Matzka, J.; Feller, M.; Egdorf, S.; Gilder, S.; Kumasaka, N.; Koga, K.; Matsumoto, H.; Koshiishi, H.; Cifuentes-Nava, G.; Curto, J. J.; Segarra, A.; ćElik, C.

    2012-08-01

    Geomagnetic field data with high time resolution (typically 1 s) have recently become more commonly acquired by ground stations. Such high time resolution data enable identifying Pi2 pulsations which have periods of 40-150 s and irregular (damped) waveforms. It is well-known that pulsations of this type are clearly observed at mid- and low-latitude ground stations on the nightside at substorm onset. Therefore, with 1-s data from multiple stations distributed in longitude around the Earth's circumference, substorm onset can be regularly monitored. In the present study we propose a new substorm index, the Wp index (Wave and planetary), which reflects Pi2 wave power at low-latitude, using geomagnetic field data from 11 ground stations. We compare the Wp index with the AE and ASY indices as well as the electron flux and magnetic field data at geosynchronous altitudes for 11 March 2010. We find that significant enhancements of the Wp index mostly coincide with those of the other data. Thus the Wp index can be considered a good indicator of substorm onset. The Wp index, other geomagnetic indices, and geosynchronous satellite data are plotted in a stack for quick and easy search of substorm onset. The stack plots and digital data of the Wp index are available at the Web site (http://s-cubed.info) for public use. These products would be useful to investigate and understand space weather events, because substorms cause injection of intense fluxes of energetic electrons into the inner magnetosphere and potentially have deleterious impacts on satellites by inducing surface charging.

  8. Magnetic Field Measurement on the C/NOFS Satellite: Geomagnetic Storm Effects in the Low Latitude Ionosphere

    NASA Technical Reports Server (NTRS)

    Le, Guan; Pfaff, Rob; Kepko, Larry; Rowland, Doug; Bromund, Ken; Freudenreich, Henry; Martin, Steve; Liebrecht, C.; Maus, S.

    2010-01-01

    The Vector Electric Field Investigation (VEFI) suite onboard the Communications/Navigation Outage Forecasting System (C/NOFS) spacecraft includes a sensitive fluxgate magnetometer to measure DC and ULF magnetic fields in the low latitude ionosphere. The instrument includes a DC vector measurement at 1 sample/sec with a range of +/- 45,000 nT whose primary objective is to provide direct measurements of both V x B and E x B that are more accurate than those obtained using a simple magnetic field model. These data can also be used for scientific research to provide information of large-scale ionospheric and magnetospheric current systems, which, when analyzed in conjunction with the C/NOFS DC electric field measurements, promise to advance our understanding of the electrodynamics of the low latitude ionosphere. In this study, we use the magnetic field data to study the temporal and local time variations of the ring currents during geomagnetic storms. We first compare the in situ measurements with the POMME (the POtsdam Magnetic Model of the Earth) model in order to provide an in-flight "calibration" of the data as well as compute magnetic field residuals essential for revealing large scale external current systems. We then compare the magnetic field residuals observed both during quiet times and during geomagnetic storms at the same geographic locations to deduce the magnetic field signatures of the ring current. As will be shown, the low inclination of the C/NOFS satellite provides a unique opportunity to study the evolution of the ring current as a function of local time, which is particularly insightful during periods of magnetic storms. This paper will present the initial results of this study.

  9. The new PhysTEC program at Boston University

    NASA Astrophysics Data System (ADS)

    Jenkins, Juliet; Duffy, Andrew

    2011-11-01

    The Boston University Physics Department was recently awarded a three-year grant from the Physics Teacher Education Coalition (PhysTEC). PhysTEC's main aims are to improve the education of future physics teachers, and to increase the number of qualified physics teachers in the school system. Although there have been over 20 PhysTEC-funded sites across the country, BU is the first PhysTEC site in New England. Our goals with this poster are to raise awareness about PhysTEC, and to talk about what we are doing and what we plan to do at BU with our PhysTEC funding. A key part of the PhysTEC program is the teacher-in-residence (TIR), an experienced physics teacher who comes to campus for a year to promote physics teaching as a profession and to lend their experience to education-related efforts. Our first TIR is Juliet Jenkins. The poster will discuss Ms. Jenkins' role in the Department of Physics and in the School of Education as we move forward with new efforts to promote teaching, including a Learning Assistant program, a pilot studio section of one of our introductory physics courses, and a new education course that allows undergraduate students to observe teachers in the classroom.

  10. Analysis of propagation delays of compressional Pi 2 waves between geosynchronous altitude and low latitudes

    NASA Astrophysics Data System (ADS)

    Imajo, Shun; Yumoto, Kiyohumi; Uozumi, Teiji; Kawano, Hideaki; Abe, Shuji; Ikeda, Akihiro; Koga, Kiyokazu; Matsumoto, Haruhisa; Obara, Takahiro; Marshall, Richard; Akulichev, Victor A.; Mahrous, Ayman; Liedloff, Adam; Yoshikawa, Akimasa

    2014-12-01

    The propagation of compressional Pi 2 waves in the inner magnetosphere is investigated by analyzing the onset delay times between the ground and the geosynchronous altitude. We use the compressional component (northward) of magnetic data from low-latitude stations and the geosynchronous satellite ETS-VIII (GMLat. = -10.8°, GMLon. = 217.5°). The onset delays are determined by a cross-correlation analysis, and we analyzed the events with high waveform correlations (correlation coefficient greater than 0.75). Some of these high-correlation events have the properties of propagating waves; Pi 2 waveforms at the ground stations and the satellite were synchronized with each other when the data were shifted by onset delays. The results of the statistical analysis show that 87% of the Pi 2 onsets at a ground station (Kuju, GMLat. = 26.13°, GMLon. = 202.96°) were delayed from the Pi 2 onsets at ETS-VIII, and the average of the delay times was 29 sec. This clearly shows Pi 2 onsets (initial perturbations of Pi 2) propagated from the geosynchronous altitude to the low-latitude ground. The delay times tended to be larger around the midnight sector than around the dawn and dusk sectors. These results are consistent with two-dimensional propagation of fast waves estimated by the model of Uozumi et al. (J Geophys Res 114:A11207, 2009). The delay times are nearly identical to the travel time of fast waves from geosynchronous altitude to the low-latitude ground, and the local time variation of the delay shows the azimuthal propagation along the geosynchronous orbit. We conclude that the initial compressional perturbations of Pi 2 waves propagate radially and longitudinally as a fast wave in the inner magnetosphere.

  11. High-time resolution of the low-latitude asymmetric disturbance in the geomagnetic field.

    NASA Technical Reports Server (NTRS)

    Crooker, N. U.

    1972-01-01

    The low-latitude asymmetric disturbance field is investigated by means of a Fourier harmonic analysis performed on 2.5-min interspaced values of magnetic records from eight stations, in lieu of the hourly values used in Crooker and Siscoe's (1971) study. The major advantage of the higher time resolution is that substorm activity, which has a time scale of 1-2 hr, can be studied in detail. Data covering four active periods in 1965 and five active periods in 1967 are used.

  12. Importance of electric field measurement over low latitudes at stratospheric heights by balloons

    NASA Astrophysics Data System (ADS)

    Gupta, S. P.

    The vertical field in the stratosphere around 35 km is predominantly of atmospheric origin whereas the horizontal electric field at these altitude is mainly of ionospheric origin. The electrical coupling between ionosphere and atmosphere is not known for low latitudes. Balloon borne electric field measurements are planned from Hyderabad, India (geographic latitude 17.5 deg N) to understand this coupling. Measurement of stratospheric electric fields are also important from the point of view of the sun-weather relationship. It is suggested that the balloon borne electric field measurements are important to understand the electrodynamics of the middle atmosphere.

  13. Diurnal and seasonal effects in E region low-latitude nitric oxide

    NASA Technical Reports Server (NTRS)

    Stewart, A. I.; Cravens, T. E.

    1978-01-01

    Measurements of nitric oxide in the lower E region made by the ultraviolet nitric oxide experiment on Atmosphere Explorer C during 1974 are used to demonstrate diurnal and seasonal effects at low latitudes. At the equator, NO increases by about a factor of 2 between sunrise and the early afternoon: this is followed by a small decline toward sunset. Seasonally, NO shows an asymmetry about the equator with more NO on the summer side than on the winter side; at equinox the asymmetry vanishes. These effects are in qualitative accord with the current theoretical understanding of thermospheric nitric oxide.

  14. Low-latitude arc-continent collision as a driver for global cooling.

    PubMed

    Jagoutz, Oliver; Macdonald, Francis A; Royden, Leigh

    2016-05-01

    New constraints on the tectonic evolution of the Neo-Tethys Ocean indicate that at ∼90-70 Ma and at ∼50-40 Ma, vast quantities of mafic and ultramafic rocks were emplaced at low latitude onto continental crust within the tropical humid belt. These emplacement events correspond temporally with, and are potential agents for, the global climatic cooling events that terminated the Cretaceous Thermal Maximum and the Early Eocene Climatic Optimum. We model the temporal effects of CO2 drawdown from the atmosphere due to chemical weathering of these obducted ophiolites, and of CO2 addition to the atmosphere from arc volcanism in the Neo-Tethys, between 100 and 40 Ma. Modeled variations in net CO2-drawdown rates are in excellent agreement with contemporaneous variation of ocean bottom water temperatures over this time interval, indicating that ophiolite emplacement may have played a major role in changing global climate. We demonstrate that both the lithology of the obducted rocks (mafic/ultramafic) and a tropical humid climate with high precipitation rate are needed to produce significant consumption of CO2 Based on these results, we suggest that the low-latitude closure of ocean basins along east-west trending plate boundaries may also have initiated other long-term global cooling events, such as Middle to Late Ordovician cooling and glaciation associated with the closure of the Iapetus Ocean. PMID:27091966

  15. Climatological response of Indian low-latitude ionosphere to geomagnetic storms

    NASA Astrophysics Data System (ADS)

    Suresh, Sunanda; Dashora, N.

    2016-05-01

    A climatological response of low-latitude ionosphere to geomagnetic storms is presented using long-term global ionospheric maps data from June 1998 to June 2015 covering two solar cycles 23 and 24. The results are presented for daytime forenoon and afternoon sectors under minor, moderate, and major ionospheric storm categories based on minimum Dst index criterion. For the first time the effectiveness of storms is identified using monthly standard deviation as an indicator of the day to day variability in equatorial and low-latitude ionosphere. Thus, results on climatology are definitive and form a database that would be comparable to statistical results from any other longitude and time. Seasonal statistics for total storms, effective positive and negative storms, and amplitude of mean seasonal perturbation in total electron content are obtained. Total and effective storms are found to be higher in solar cycle 23 than in 24 and only a couple of effective storms occurred during low solar activity 2007-2009 that too in minor category. Afternoon sector is found to be favorable for occurrence of maximum number of effective positive storms. A latitudinal preference is found for a given storm to be effective in either time sectors. Equinoctial asymmetry in ionospheric response both in terms of occurrence and perturbation amplitude is found. September equinoxes are found to bear maximum total, effective positive and negative storms. Winters are found more prone to negative storms, whereas summers have recorded minimum number of either of storms and minimum perturbation amplitudes.

  16. Low-latitude arc-continent collision as a driver for global cooling

    NASA Astrophysics Data System (ADS)

    Jagoutz, Oliver; Macdonald, Francis A.

    2016-05-01

    New constraints on the tectonic evolution of the Neo-Tethys Ocean indicate that at ˜90-70 Ma and at ˜50-40 Ma, vast quantities of mafic and ultramafic rocks were emplaced at low latitude onto continental crust within the tropical humid belt. These emplacement events correspond temporally with, and are potential agents for, the global climatic cooling events that terminated the Cretaceous Thermal Maximum and the Early Eocene Climatic Optimum. We model the temporal effects of CO2 drawdown from the atmosphere due to chemical weathering of these obducted ophiolites, and of CO2 addition to the atmosphere from arc volcanism in the Neo-Tethys, between 100 and 40 Ma. Modeled variations in net CO2-drawdown rates are in excellent agreement with contemporaneous variation of ocean bottom water temperatures over this time interval, indicating that ophiolite emplacement may have played a major role in changing global climate. We demonstrate that both the lithology of the obducted rocks (mafic/ultramafic) and a tropical humid climate with high precipitation rate are needed to produce significant consumption of CO2. Based on these results, we suggest that the low-latitude closure of ocean basins along east-west trending plate boundaries may also have initiated other long-term global cooling events, such as Middle to Late Ordovician cooling and glaciation associated with the closure of the Iapetus Ocean.

  17. Reevaluation of conflicting Eocene tropical temperature estimates: Molluskan oxygen isotope evidence for warm low latitudes

    NASA Astrophysics Data System (ADS)

    Kobashi, Takuro; Grossman, Ethan L.; Yancey, Thomas E.; Dockery, David T., III

    2001-11-01

    Oxygen isotope data from planktonic foraminifera for the warm Eocene epoch suggest that tropical sea-surface temperatures (SSTs) may have been cooler than at present. Such data have stimulated various explanations involving, e.g., major changes in ocean heat transport. However, the planktonic data disagree with terrestrial climate proxies, which suggest significantly warmer low-latitude temperatures. We examined this discrepancy by analyzing seasonal oxygen isotope variations in shallow-marine mollusks from the Mississippi Embayment. Results indicate that mean annual SSTs decreased from 26 27 °C in the early Eocene to 22 23 °C in the Oligocene, agreeing well with temperatures inferred from terrestrial climate proxies. These cooling trends, with more significant winter cooling (5 °C) than summer cooling (3 °C), are consistent with the predicted consequences of decreasing atmospheric CO2 concentration through the Paleogene, suggesting that atmospheric CO2 change was a major controlling factor for Paleogene climate change. That winter SST estimates from the mollusks agree well with the foraminiferal SST estimates suggests that planktonic foraminiferal growth in low latitudes occurred mainly during the cooler winter months throughout the Eocene. We hypothesize that the unusual hydrography of Eocene oceans shifted foraminiferal productivity primarily to winter, biasing foraminiferal SST estimates of mean annual SSTs.

  18. Investigating planetary wave and seasonal variability in mesospheric temperature at mid- and low-latitudes

    NASA Astrophysics Data System (ADS)

    Zhao, Y.; Taylor, M.; Gardner, C.; Liu, A.

    The Utah State University Mesospheric Temperature Mapper MTM is a high performance CCD imaging system developed as part of the US CEDAR program This imager sequentially measures the nocturnal OH 6 2 band intensity and rotational temperature peak altitude sim 87km and the O 2 0 1 Atmospheric band intensity and temperature peak altitude sim 94km with a precision of 1-2 K in 3 minutes The MTM is capable of autonomous operation and since 1998 long-term seasonal measurements were obtained from the mid-latitude Starfire Optical Range SOR facility 35 r N NM duration 14 months Subsequently the imager was relocated to the low-latitude 21 r N at USAF AEOS facility at Maui Hawaii and long-term measurements were obtained as part of the Maui-MALT program 2001-2005 Over 500 nights of quality data have been obtained to date These measurements are constitute an important dataset for seasonal studies and were obtained in coordination with the University of Illinois Na wind temperature lidar which operated on a campaign basis from both of these facilities Together these two datasets have been used to investigate the occurrence and signatures of planetary waves and to compare seasonal variability in mesospheric temperature at mid- and low-latitudes

  19. C/NOFS Measurements of Magnetic Perturbations in the Low-Latitude Ionosphere During Magnetic Storms

    NASA Technical Reports Server (NTRS)

    Le, Guan; Burke, William J.; Pfaff, Robert F.; Freudenreich, Henry; Maus, Stefan; Luhr, Hermann

    2011-01-01

    The Vector Electric Field Investigation suite on the C/NOFS satellite includes a fluxgate magnetometer to monitor the Earth s magnetic fields in the low-latitude ionosphere. Measurements yield full magnetic vectors every second over the range of +/-45,000 nT with a one-bit resolution of 1.37 nT (16 bit A/D) in each component. The sensor s primary responsibility is to support calculations of both V x B and E x B with greater accuracy than can be obtained using standard magnetic field models. The data also contain information about large-scale current systems that, when analyzed in conjunction with electric field measurements, promise to significantly expand understanding of equatorial electrodynamics. We first compare in situ measurements with the POMME (Potsdam Magnetic Model of the Earth) model to establish in-flight sensor "calibrations" and to compute magnetic residuals. At low latitudes the residuals are predominately products of the storm time ring current. Since C/NOFS provides a complete coverage of all local times every 97 min, magnetic field data allow studies of the temporal evolution and local time variations of storm time ring current. The analysis demonstrates the feasibility of using instrumented spacecraft in low-inclination orbits to extract a timely proxy for the provisional Dst index and to specify the ring current s evolution.

  20. Low-latitude arc-continent collision as a driver for global cooling.

    PubMed

    Jagoutz, Oliver; Macdonald, Francis A; Royden, Leigh

    2016-05-01

    New constraints on the tectonic evolution of the Neo-Tethys Ocean indicate that at ∼90-70 Ma and at ∼50-40 Ma, vast quantities of mafic and ultramafic rocks were emplaced at low latitude onto continental crust within the tropical humid belt. These emplacement events correspond temporally with, and are potential agents for, the global climatic cooling events that terminated the Cretaceous Thermal Maximum and the Early Eocene Climatic Optimum. We model the temporal effects of CO2 drawdown from the atmosphere due to chemical weathering of these obducted ophiolites, and of CO2 addition to the atmosphere from arc volcanism in the Neo-Tethys, between 100 and 40 Ma. Modeled variations in net CO2-drawdown rates are in excellent agreement with contemporaneous variation of ocean bottom water temperatures over this time interval, indicating that ophiolite emplacement may have played a major role in changing global climate. We demonstrate that both the lithology of the obducted rocks (mafic/ultramafic) and a tropical humid climate with high precipitation rate are needed to produce significant consumption of CO2 Based on these results, we suggest that the low-latitude closure of ocean basins along east-west trending plate boundaries may also have initiated other long-term global cooling events, such as Middle to Late Ordovician cooling and glaciation associated with the closure of the Iapetus Ocean.

  1. Low-latitude arc–continent collision as a driver for global cooling

    PubMed Central

    Jagoutz, Oliver; Macdonald, Francis A.; Royden, Leigh

    2016-01-01

    New constraints on the tectonic evolution of the Neo-Tethys Ocean indicate that at ∼90–70 Ma and at ∼50–40 Ma, vast quantities of mafic and ultramafic rocks were emplaced at low latitude onto continental crust within the tropical humid belt. These emplacement events correspond temporally with, and are potential agents for, the global climatic cooling events that terminated the Cretaceous Thermal Maximum and the Early Eocene Climatic Optimum. We model the temporal effects of CO2 drawdown from the atmosphere due to chemical weathering of these obducted ophiolites, and of CO2 addition to the atmosphere from arc volcanism in the Neo-Tethys, between 100 and 40 Ma. Modeled variations in net CO2-drawdown rates are in excellent agreement with contemporaneous variation of ocean bottom water temperatures over this time interval, indicating that ophiolite emplacement may have played a major role in changing global climate. We demonstrate that both the lithology of the obducted rocks (mafic/ultramafic) and a tropical humid climate with high precipitation rate are needed to produce significant consumption of CO2. Based on these results, we suggest that the low-latitude closure of ocean basins along east–west trending plate boundaries may also have initiated other long-term global cooling events, such as Middle to Late Ordovician cooling and glaciation associated with the closure of the Iapetus Ocean. PMID:27091966

  2. C/NOFS Measurements of Stormtime Magnetic Perturbations in the Low-latitude Ionosphere

    NASA Technical Reports Server (NTRS)

    Le, Guan; Burke, William J.; Pfaff, Robert F.; Freudenreich, Henry; Maus, Stefan; Luehr, Hermann

    2012-01-01

    The Vector Electric Field Investigation suite on the C/NOFS satellite includes a fluxgate magnetometer to monitor the Earth's magnetic fields in the low-latitude ionosphere. Measurements yield full magnetic vectors every second over the range of +/- 45,000 nT with a one-bit resolution of 1.37 nT (16 bit AID) in each component. The sensor's primary responsibility is to support calculations of both VxB and ExB with greater accuracy than can be obtained using standard magnetic field models. The data also contain information about large-scale current systems, that, when analyzed in conjunction with electric field measurements, promise to significantly expand understanding of equatorial electrodynamics. We first compare in situ measurements with the POMME (POtsdam Magnetic Model of the Earth) model to establish in-flight sensor "calibrations" and to compute magnetic residuals. At low latitudes the residuals are predominately products of the stormtime ring current. Since C/NOFS provides a complete coverage of all local times every 97 minutes, magnetic field data allow studies of the temporal evolution and local-time variations of stormtime ring current. The analysis demonstrates the feasibility of using instrumented spacecraft in low-inclination orbits to extract a timely proxy for the provisional Dst index and to specify the ring current's evolution.

  3. Combustion heated cold sealed TEC

    SciTech Connect

    Yarygin, V.I.; Klepikov, V.V.; Meleta, Y.A.; Mikheyev, A.S.; Yarygin, D.V.; Wolff, L.R.

    1997-12-31

    The development of a thermionic domestic boiler system using natural gas, which as performed under an ECS-project in 1992 to 1994 by a Russian-Dutch team of researchers, will be continued again. Thanks to financial support on the part of the Netherlands Organization for Scientific Research (NWO), the major effort in 1997 to 1999 will be focused on the development, manufacture and testing of an improved, easier to fabricate, more repairable and less expensive combustion heated TEC with a longer life-time. The achievement of the aim of this project will make it possible to expand the field of the terrestrial thermionics application and to embark on the commercialization stage. This report discusses the concept of the combustion heated Cold Seal TEC. A Cold Seal TEC will be developed and tested, in which the rubber O-ring seal will electrically insulate the hot shell from the collector heat pipe. The Cold Seal TEC will use a noble gas + cesium as the working medium (the idea of such a TEC was first proposed in 1973 by Professor Musa from Romania). In its cold state, the cesium will short circuit the emitter and the collector. During operation, the interelectrode space will be filled with cesium vapor. The upper part of a Cold Seal TEC will be filled with a noble gas. This noble gas will prevent the O-ring seal from being attacked by the cesium. The TEC output characteristics will be considerably improved by using electrode materials that were developed earlier in the course of an ECS-project for the development of low temperature TEC electrodes.

  4. Quantitative Evaluation of Ionosphere Models for Reproducing Regional TEC During Geomagnetic Storms

    NASA Astrophysics Data System (ADS)

    Shim, J. S.; Kuznetsova, M.; Rastaetter, L.; Bilitza, D.; Codrescu, M.; Coster, A. J.; Emery, B.; Foster, B.; Fuller-Rowell, T. J.; Goncharenko, L. P.; Huba, J.; Mitchell, C. N.; Ridley, A. J.; Fedrizzi, M.; Scherliess, L.; Schunk, R. W.; Sojka, J. J.; Zhu, L.

    2015-12-01

    TEC (Total Electron Content) is one of the key parameters in description of the ionospheric variability that has influence on the accuracy of navigation and communication systems. To assess current TEC modeling capability of ionospheric models during geomagnetic storms and to establish a baseline against which future improvement can be compared, we quantified the ionospheric models' performance by comparing modeled vertical TEC values with ground-based GPS TEC measurements and Multi-Instrument Data Analysis System (MIDAS) TEC. The comparison focused on North America and Europe sectors during selected two storm events: 2006 AGU storm (14-15 Dec. 2006) and 2013 March storm (17-19 Mar. 2013). The ionospheric models used for this study range from empirical to physics-based, and physics-based data assimilation models. We investigated spatial and temporal variations of TEC during the storms. In addition, we considered several parameters to quantify storm impacts on TEC: TEC changes compared to quiet time, rate of TEC change, and maximum increase/decrease during the storms. In this presentation, we focus on preliminary results of the comparison of the models performance in reproducing the storm-time TEC variations using the parameters and skill scores. This study has been supported by the Community Coordinated Modeling Center (CCMC) at the Goddard Space Flight Center. Model outputs and observational data used for the study will be permanently posted at the CCMC website (http://ccmc.gsfc.nasa.gov) for the space science communities to use.

  5. Longitude and IMF By Effects on Stormtime Low-Latitude Prompt-Penetration Electric Fields

    NASA Astrophysics Data System (ADS)

    Spiro, R. W.; Sazykin, S.; Song, Y.; Toffoletto, F.; Wolf, R. A.

    2010-12-01

    During geomagnetically disturbed periods, transient large-scale electric fields of magnetospheric origin, known as prompt penetration electric fields, are known to strongly affect ionospheric dynamics. We examine storm-associated prompt-penetration electric fields in the low-latitude ionosphere using a recently reformulated version of the Rice Convection Model (RCM), a numerical model of the inner magnetosphere and its coupling to the ionosphere. This reformulated version of the RCM was designed to accept an arbitrary intrinsic geomagnetic field and to represent the lack of symmetry in the magnetospheric magnetic field due to the partial penetration of IMF By. In this study we assume an IGRF internal magnetic field together with an event-driven storm-time Tsyganenko external field to investigate the longitudinal dependence of the prompt penetration electric field pattern and the effects of IMF By penetration.

  6. A Unified Fluid Model for Low-latitude Ionosphere Turbulence Causes Radiowave Scintillations

    NASA Astrophysics Data System (ADS)

    Hassan, E.; Horton, W.

    2012-12-01

    Nonlinear dynamics of the low latitudes E-layer simulated with a systems of differential equations describing the neutral wind driven Farley-Buneman instability and the density-gradient-drift instability as rising bubbles and falling higher electron density spikes. The simulations extent earlier nonlinear studies by using empirical models for the atmosphere and ionosphere backgrounds to give realistic local time-altitude parameters within a Python wrapped F90 simulations. New equations that keep both the compressional and rotational ion flows that apply in the lower F layer are analyzed to describe plumes extending to the peak of the F layer. A ray-tracing technique is used to describe the small angle scattering at high frequency [Gigahertz] GNSS signals treated as rays in the turbulent ionospheric plasma.

  7. Space weather disturbances in the ionosphere-thermosphere-electrodynamics system at middle and low latitudes

    NASA Astrophysics Data System (ADS)

    Schunk, Robert

    2012-07-01

    It has been clearly established that the ionosphere-thermosphere-electrodynamics system can vary significantly from hour to hour and from day to day. The hour-to-hour variations are associated with weather disturbances, which can produce mesoscale (100-1000 km) structures and plasma irregularities. For the ionosphere, these weather disturbances include Traveling Ionospheric Disturbances (TIDs), sporadic E layers, He ^{+} layers in the topside ionosphere, descending intermediate layers, ridges of enhanced ionization (Storm Enhanced Densities), a 4-wave signature, spread-F, and equatorial plasma bubbles. For the thermosphere, the weather disturbances include upward propagating waves from the lower atmosphere (planetary, tidal and gravity waves), Traveling Atmospheric Disturbances (TADs) generated at high latitudes, storm-time O/N _{2} depletions, and neutral gas perturbations both at the terminator and in the regions containing equatorial plasma bubbles. The current state of our knowledge of weather disturbances in the middle and low latitude ionosphere-thermosphere-electrodynamics system will be reviewed.

  8. Preliminary analyses of solar flare effects on geomagnetic H component at equatorial and low latitudes

    NASA Astrophysics Data System (ADS)

    Ugonabo, Obiageli Josephine; Ugwu, Ernest Benjamin Ikechukwu; Nneka Okeke, Francisca

    The study of solar flare effect (SFE) on geomagnetic H component at mid latitudes was carried out using data from INTERMAGNET website. M and X solar flare effects on three stations, Addis Ababa (AAE), Bangui (BNG), and Tamanrasset (TAM) were investigated. It was found that the ratio is greater than zero for all the three stations used, hence SFE enhances geomagnetic field in the equatorial and low latitudes. It was equally noted that the SFE on geomagnetic field is not just a simple augmentation at the pre-flare ionospheric currents over these stations. It is concluded that both pre-flare and solar flare amplitude variations of H are high in low and equatorial stations. Keywords: Solar flare, geomagnetic component, latitudes.

  9. Color-magnitude diagrams for six metal-rich, low-latitude globular clusters

    NASA Technical Reports Server (NTRS)

    Armandroff, Taft E.

    1988-01-01

    Colors and magnitudes for stars on CCD frames for six metal-rich, low-latitude, previously unstudied globular clusters and one well-studied, metal-rich cluster (47 Tuc) have been derived and color-magnitude diagrams have been constructed. The photometry for stars in 47 Tuc are in good agreement with previous studies, while the V magnitudes of the horizontal-branch stars in the six program clusters do not agree with estimates based on secondary methods. The distances to these clusters are different from prior estimates. Redding values are derived for each program cluster. The horizontal branches of the program clusters all appear to lie entirely redwards of the red edge of the instability strip, as is normal for their metallicities.

  10. Ion-neutral coupling effects on low-latitude thermospheric evening winds

    NASA Astrophysics Data System (ADS)

    Evonosky, W.; Richmond, A. D.; Fang, T.-W.; Maute, A.

    2016-05-01

    We examine the forces that determine zonal wind structure in the low-latitude evening thermosphere and its relation with ion-neutral coupling. These winds drive the evening F region dynamo that affects the equatorial ionization anomaly (EIA) and the generation of plasma irregularities. Forces are calculated using the Thermosphere-Ionosphere-Electrodynamics General Circulation Model coupled with the Global Ionosphere-Plasmasphere model. At 19 LT, the horizontal pressure gradient dominates the net acceleration of neutral winds below ˜220 km, while it tends to be offset by ion drag and viscosity higher up. The eastward pressure-gradient acceleration above 200 km increases approximately linearly with height and tends to be similar for different latitudes and different levels of solar activity. The pressure-gradient and ion-drag forces in the central F region approximately balance for field lines that pass through the EIA. Viscosity is an important additional force at non-EIA latitudes and in the bottomside and topside EIA ionosphere. An increase in E region drag on plasma convection due to increased nighttime ionization causes both the ion and neutral velocities in the F region to decrease, while the velocity difference tends to be maintained. The presence of a low-latitude evening time vertical shear in the zonal wind is associated primarily with a strong eastward pressure-gradient acceleration at high altitude that reverses the daytime westward wind and a weak low-altitude pressure-gradient acceleration of either eastward or westward direction that fails to reverse the low-altitude westward wind present in the afternoon.

  11. A Statistical Study of TEC Variations during the Passage of TCV Events

    NASA Astrophysics Data System (ADS)

    Murr, D.; Beyene, F.

    2015-12-01

    The field-aligned current system associated with traveling convection vortices (TCVs) is rather difficult to characterize due to its transient nature and occurrence at high latitudes on the dayside. Previous studies have demonstrated that for sufficiently large events, TEC variations can be observed during the passage of TCVs. We present the results of a statistical study using high latitude ground magnetometers and TEC receivers to investigate TEC variations during TCV events.

  12. Risk assessment of the extreme interplanetary shock of 23 July 2012 on low-latitude power networks

    NASA Astrophysics Data System (ADS)

    Zhang, J. J.; Wang, C.; Sun, T. R.; Liu, Y. D.

    2016-03-01

    Geomagnetic sudden commencements (SCs), characterized by a rapid enhancement in the rate of change of the geomagnetic field perturbation (dB/dt), are considered to be an important source of large geomagnetically induced currents (GICs) in middle- and low-latitude power grids. In this study, the extreme interplanetary shock of 23 July 2012 is simulated under the assumption that it had hit the Earth with the result indicating the shock-caused SC would be 123 nT. Based on statistics, the occurrence frequency of SCs with amplitudes larger than the simulated one is estimated to be approximately 0.2% during the past 147 years on the Earth. During this extreme event, the simulation indicates that dB/dt, which is usually used as a proxy for GICs, at a dayside low-latitude substation would exceed 100 nT/min; this is very large for low-latitude regions. We then assess the GIC threat level based on the simulated geomagnetic perturbations by using the method proposed by Marshall et al. (2011). The results indicate that the risk remains at "low" level for the low-latitude power network on a global perspective. However, the GIC risk may reach "moderate" or even "high" levels for some equatorial power networks due to the influence of the equatorial electrojet. Results of this study feature substantial implications for risk management, planning, and design of low-latitude electric power networks.

  13. Revisiting the question: Does high-latitude solar activity lead low-latitude solar activity in time phase?

    SciTech Connect

    Kong, D. F.; Qu, Z. N.; Guo, Q. L.

    2014-05-01

    Cross-correlation analysis and wavelet transform methods are used to investigate whether high-latitude solar activity leads low-latitude solar activity in time phase or not, using the data of the Carte Synoptique solar filaments archive from 1919 March to 1989 December. From the cross-correlation analysis, high-latitude solar filaments have a time lead of 12 Carrington solar rotations with respect to low-latitude ones. Both the cross-wavelet transform and wavelet coherence indicate that high-latitude solar filaments lead low-latitude ones in time phase. Furthermore, low-latitude solar activity is better correlated with high-latitude solar activity of the previous cycle than with that of the following cycle, which is statistically significant. Thus, the present study confirms that high-latitude solar activity in the polar regions is indeed better correlated with the low-latitude solar activity of the following cycle than with that of the previous cycle, namely, leading in time phase.

  14. Dynamics of American Sector Mid and Low Latitude Ionospheric and Thermospheric Response During the November 2004 Superstorm

    NASA Astrophysics Data System (ADS)

    Erickson, P. J.; Goncharenko, L. P.; Nicolls, M. J.; Crowley, G.; Kelley, M. C.

    2007-12-01

    Interplanetary electric field (IEF) penetration into the inner magnetosphere and plasmasphere can occur during intense geomagnetic storms, enhancing eastward electric fields over the sunlit ionosphere. Such events can serve as triggers for complex ionosphere-magnetosphere feedback mechanisms which increase ionospheric convection and neutral winds both locally and globally. We present a study of ionospheric dynamics and physical drivers during several events contained within the November 9 - 11, 2004 superstorm. This event was marked by excellent coverage from the full American sector incoherent scatter radar chain at Jicamarca, Arecibo, Millstone Hill, and Sondrestrom, which allows wide latitude diagnostics of E and F region electric fields, plasma densities and temperatures, and neutral wind vectors. We also employ CARISMA magnetometer chain observations, DMSP SSIES topside ion drifts, and GPS derived total electron content (TEC) maps to place the radar data in context. Penetrating eastward electric fields were seen from Millstone Hill equatorwards to Jicamarca for over 15 hours on November 9 and 10, accompanied by very low TEC values and a plasmasphere boundary layer midway between Millstone Hill and Arecibo. Equatorward neutral wind surges of ~ 300 m/s were driven locally by substorms at Millstone Hill and Arecibo, with associated dynamo effects creating prompt electric fields and large F layer downdrafts. Substorm timing during three separate events as identified from CARISMA magnetometers is consistent with Millstone Hill observed neutral wind surges. We also present results from TIMEGCM model runs and compare predictions of ionospheric conditions along the radar chain to gain insight into the complex physical drivers during this superstorm event.

  15. Space Weather Activities of IONOLAB Group: TEC Mapping

    NASA Astrophysics Data System (ADS)

    Arikan, F.; Yilmaz, A.; Arikan, O.; Sayin, I.; Gurun, M.; Akdogan, K. E.; Yildirim, S. A.

    2009-04-01

    Being a key player in Space Weather, ionospheric variability affects the performance of both communication and navigation systems. To improve the performance of these systems, ionosphere has to be monitored. Total Electron Content (TEC), line integral of the electron density along a ray path, is an important parameter to investigate the ionospheric variability. A cost-effective way of obtaining TEC is by using dual-frequency GPS receivers. Since these measurements are sparse in space, accurate and robust interpolation techniques are needed to interpolate (or map) the TEC distribution for a given region in space. However, the TEC data derived from GPS measurements contain measurement noise, model and computational errors. Thus, it is necessary to analyze the interpolation performance of the techniques on synthetic data sets that can represent various ionospheric states. By this way, interpolation performance of the techniques can be compared over many parameters that can be controlled to represent the desired ionospheric states. In this study, Multiquadrics, Inverse Distance Weighting (IDW), Cubic Splines, Ordinary and Universal Kriging, Random Field Priors (RFP), Multi-Layer Perceptron Neural Network (MLP-NN), and Radial Basis Function Neural Network (RBF-NN) are employed as the spatial interpolation algorithms. These mapping techniques are initially tried on synthetic TEC surfaces for parameter and coefficient optimization and determination of error bounds. Interpolation performance of these methods are compared on synthetic TEC surfaces over the parameters of sampling pattern, number of samples, the variability of the surface and the trend type in the TEC surfaces. By examining the performance of the interpolation methods, it is observed that both Kriging, RFP and NN have important advantages and possible disadvantages depending on the given constraints. It is also observed that the determining parameter in the error performance is the trend in the Ionosphere

  16. A general comment on low latitude problems in the IRI (and a specific one to the following paper)

    NASA Astrophysics Data System (ADS)

    Piggott, W. R.

    1995-02-01

    It appears to me that much of the important work done in the 1960 to 1970 period has been forgotten to the great loss of understanding what is happening. It is essential to consider the effect of the geometry of the Earth's magnetic field near the magnetic equator. Thus apparent upword movements of hmF2 are physically horizontal movements away from the magnetic equator and vice versa. In addition the Consultative Committee on International Radiopropagation (CCIR) maps show an additional peak of ionization which moves down in latitude until it joins the main low latitude structure. Its changes with season are also shown on the CCIR maps. The theoretical papers of King and Kohl (1968) are particularly important, together with the simplifying work of Rishbeth (1972) who showed that the observed data could be represented adequately by using modified values for the main parameters used by King and Kohl. A few typical examples can be found in the ITU Telecommunication Journal published in Geneva and in more detail in an Advisory Group Aeronautical Research Development (AGARD) publication (1970). Note also the work of Vila (1971) who, flying an ionosonde in an aircraft across the magnetic equator in the Nigerian sector, showed that the actual peaks of ionization are very narrow in latitude. Unfortunately, these peaks move in latitude day to day. Therefore, is the upper quartile of NmF2 or foF2 a better guide to a realistic forecast than the median?

  17. Latitudinal TEC gradients over polar ionosphere using high latitude GPS measurements

    NASA Astrophysics Data System (ADS)

    Shagimuratov, Irk; Cherniak, Iurii; Zakharenkova, Irina; Tepenitsyna, Nadezhda; Yakimova, Galina; Ephishov, I. I.

    The GPS observations of Greenland network were used to analyze the latitudinal variations of TEC at the high-latitudes ionosphere. This network provides unique opportunity to monitor TEC variability in polar ionosphere on a regular base. GPS stations are arranged along the latitude over the range 60-83°N (65°-87° Corrected Geomagnetic Latitude) near of 30°-40° longitudes. More than 20 GPS stations are located closely with one another along latitude. The distance between stations is about 1°-2°.Such spatial resolution provides the possibility to analyze the detailed structure of latitudinal TEC profiles. The standard procedure of processing GPS observations was used for TEC estimation. On this base it was obtained the diurnal TEC variations over all Greenland stations. The TEC data is used to form latitudinal profiles (TEC section) covered subauroral, auroral and polar ionosphere. In the report the observations of TEC for quiet and disturbed ionosphere during several geomagnetic storms occurred in September 2011 are presented. During quiet conditions in the night-time TEC profiles demonstrated invariable values about of 4-6 TECU in latitudinal region of 60°-75°N; then it presented THE increase towards the higher latitude and reached the value of 10 TECU near 80°N. The daytime profiles revealed TEC decrease toward high latitude in keeping with 0.8 TECU/degree. During storm the structure of latitudinal TEC profiles was essentially changed with agreement to the development of geomagnetic storm. The positive effect was observed at subauroral and auroral latitudes, negative effect was prevailed at the polar region. During the night time the ionospheric trough can be observed. In the report features of the behavior of latitudinal profiles at high-latitude ionosphere for September 2011 events were discussed.

  18. The trophic structure and predation impact of a low latitude midwater fish assemblage

    NASA Astrophysics Data System (ADS)

    Hopkins, Thomas L.; Sutton, Tracey T.; Lancraft, Thomas M.

    The trophic ecology of a midwater fish assemblage was investigated in the eastern Gulf of Mexico, a regime exhibiting the principal physical-biological characteristics of oligotrophic low latitude ecosystems. In all, the diets of 164 species of midwater fishes were examined, with data for 121 being sufficient for analytical comparisons. Cluster analysis grouped the assemblage into 15 feeding guilds, with these falling into two major groups, those including zooplanktivores with largely crustacean diets, and those including predators on large prey, most of which were piscivores. Among the zooplanktivores, the principal predators were the Myctophidae, Sternoptychidae and Gonostomatidae which, respectively, consumed 31%, 27% and 14% of the food biomass eaten daily by the midwater fish assemblage. The myctophids alone accounted for 53% of the copepod and 40% of the euphausiid biomass ingested. The copepod genus Pleuromamma was especially important forage, constituting 40% of the copepod biomass consumed by the midwater fish assemblage. The Stomiidae were the dominant piscivores and accounted for 20% of the total food ingested daily and 61% of the fish eaten, with the majority of their prey being myctophids. Literature comparisons reveal that diet patterns for the eastern Gulf midwater assemblage closely resemble those for mid- to- low latitude oligotrophic regimes in general. Daily consumption of the entire assemblage is estimated at 2.5-4.3 kg C km -2 in the upper 1000 m. Four fifths of this is zooplankton while the balance is large prey, mostly fishes. The ingestion rate accounts for only 5-10% of the daily production of zooplankton, but 95% of fish daily production. While the latter is obviously an overestimate it does suggest a tighter nutritional coupling of the midwater fish assemblage with the upper trophic levels of the ecosystem than with zooplankton. Midwater fishes and shrimps, the two dominant groups of micronekton, together account for only 25% of

  19. How Strong is the Case for Proterozoic Low-Latitude Glaciation?

    NASA Astrophysics Data System (ADS)

    Evans, D. A.

    2004-05-01

    The most recent global compilations of paleomagnetic depositional latitudes for Proterozoic glaciogenic formations indicate a dominant mode near the paleo-equator (Evans 2000 AJS; Evans 2003 Tectonophysics). This result would therefore support either the snowball Earth or the large-obliquity hypotheses for Precambrian ice ages, but would reject the uniformitarian comparison to polar-temperate-restricted Phanerozoic glaciogenic deposits. The most reliable low-latitude results come from the Australian Marinoan succession, but a recent summary of these units has suggested that a glaciogenic origin is not yet demonstrated (Eyles and Januszczak 2004 Earth-Sci Reviews). It becomes useful, then, to review the global evidence for Proterozoic low-latitude glaciation. Eyles and Januszczak (ibid.) identified 13 Neoproterozoic deposits with "demonstrated" glacial influence. Among these, poor age constraints and lack of paleomagnetic data prohibit estimation of depositional paleolatitudes for the Fiq, Sturtian, Vreeland, Taoudeni, East Greenland, Port Askaig, and Zhengmuguan units. Moderate paleolatitudes are reasonably well supported for the South China, Gaskiers, Smalfjord, and Moelv units. Among the three remaining units, the Rapitan Group can be assigned a near-equatorial paleolatitude indirectly through use of the Galeros and Franklin-Natkusiak paleomagnetic results, as long as the Rapitan age lies within 750-720 Ma as generally expected. The Moonlight Valley Formation in northern Australia may be assigned a tropical paleolatitude according to high-quality paleomagnetic results from compellingly correlated Marinoan strata in southern Australia. Those strata, including the famous Elatina Formation, have yielded a robust paleomagnetic signature that is commonly interpreted to imply frigid climate (manifest in part by frost-wedge polygons) at near-equatorial latitudes. Concerns that the Neoproterozoic geomagnetic field was either nonaxial or nondipolar are valid in principle

  20. Trends, spectral characteristics, and rainfall relationships of low-latitude sea surface temperatures at different longitudes

    NASA Astrophysics Data System (ADS)

    Kane, R. P.

    2000-01-01

    The sea surface temperature (SST) data for low latitudes in the Pacific, Atlantic, and Indian Oceans for 1950-1996 (47 years) showed different seasonal variation patterns at different longitudes. When the seasonal patterns were subtracted from the monthly values, the deseasoned residuals showed considerable anomalies (interannual variability). In the Pacific the main features were the El Niño events. In the Atlantic, North and South Atlantic SST showed dissimilar anomalies, and these did not have any fixed lag or lead relationships with the Pacific events. The same was true for the low-latitude Indian Ocean SST. The correlation of Pacific SST with Atlantic or Indian Oceans' SST was less than ˜0.65, yielding a common variance (square of the correlation) of less than ˜40%. Thus, whereas SST anomalies might have some common origin, the manifestation of SST anomalies at different longitudes was erratic, with no preference for any longitude to start with, nor any definite sequence of occurrence in the Pacific relative to the Atlantic or Indian Oceans. A spectral analysis showed that all regions had quasi-biennial, quasi-triennial, and higher periodicities, but the exact values of these periodicities differed significantly at different longitudes. All parameters had long-term trends. These were mostly nonuniform, almost negligible in the first half (1950-1973) and mostly upward in the second half (1973-1996), indicating warming in recent decades, which is also reflected in decreases in snow cover area in the Northern Hemisphere. Rainfalls in various regions are considerably influenced by local SST regimes. For northeast Brazil, Atlantic SST influence is overpowering and often operates independently of the Pacific SST (El Niños). Hence the emphasis given in mass media (press, radio, and television) to the role of El Niño events only in influencing the rainfalls may turn out to be misleading, as seems to have happened for the 1997 El Niño. This El Niño started in

  1. A GIS-based assessment of the suitability of SCIAMACHY satellite sensor measurements for estimating reliable CO concentrations in a low-latitude climate.

    PubMed

    Fagbeja, Mofoluso A; Hill, Jennifer L; Chatterton, Tim J; Longhurst, James W S

    2015-02-01

    An assessment of the reliability of the Scanning Imaging Absorption Spectrometer for Atmospheric Cartography (SCIAMACHY) satellite sensor measurements to interpolate tropospheric concentrations of carbon monoxide considering the low-latitude climate of the Niger Delta region in Nigeria was conducted. Monthly SCIAMACHY carbon monoxide (CO) column measurements from January 2,003 to December 2005 were interpolated using ordinary kriging technique. The spatio-temporal variations observed in the reliability were based on proximity to the Atlantic Ocean, seasonal variations in the intensities of rainfall and relative humidity, the presence of dust particles from the Sahara desert, industrialization in Southwest Nigeria and biomass burning during the dry season in Northern Nigeria. Spatial reliabilities of 74 and 42 % are observed for the inland and coastal areas, respectively. Temporally, average reliability of 61 and 55 % occur during the dry and wet seasons, respectively. Reliability in the inland and coastal areas was 72 and 38 % during the wet season, and 75 and 46 % during the dry season, respectively. Based on the results, the WFM-DOAS SCIAMACHY CO data product used for this study is therefore relevant in the assessment of CO concentrations in developing countries within the low latitudes that could not afford monitoring infrastructure due to the required high costs. Although the SCIAMACHY sensor is no longer available, it provided cost-effective, reliable and accessible data that could support air quality assessment in developing countries. PMID:25626562

  2. High-latitude controls of thermocline nutrients and low latitude biological productivity.

    PubMed

    Sarmiento, J L; Gruber, N; Brzezinski, M A; Dunne, J P

    2004-01-01

    The ocean's biological pump strips nutrients out of the surface waters and exports them into the thermocline and deep waters. If there were no return path of nutrients from deep waters, the biological pump would eventually deplete the surface waters and thermocline of nutrients; surface biological productivity would plummet. Here we make use of the combined distributions of silicic acid and nitrate to trace the main nutrient return path from deep waters by upwelling in the Southern Ocean and subsequent entrainment into subantarctic mode water. We show that the subantarctic mode water, which spreads throughout the entire Southern Hemisphere and North Atlantic Ocean, is the main source of nutrients for the thermocline. We also find that an additional return path exists in the northwest corner of the Pacific Ocean, where enhanced vertical mixing, perhaps driven by tides, brings abyssal nutrients to the surface and supplies them to the thermocline of the North Pacific. Our analysis has important implications for our understanding of large-scale controls on the nature and magnitude of low-latitude biological productivity and its sensitivity to climate change.

  3. Low energy, low latitude wave-dominated shallow marine depositional systems: examples from northern Borneo

    NASA Astrophysics Data System (ADS)

    Lambiase, Joseph J.; Suraya Tulot

    2013-12-01

    The depositional environments of the wave-dominant successions in the middle to late Miocene Belait and Sandakan Formations in northwestern and northern Borneo, respectively, were determined based on grain size distributions, sedimentary structures and facies successions, as well as trace and microfossil assemblages. Generally, progradational shoreface successions in the Belait Formation were deposited in very low wave energy environments where longshore currents were too weak to generate trough cross-bedding. Shoreface sands are laterally continuous for several km and follow the basin contours, suggesting attached beaches similar to the modern Brunei coastline. In contrast, trough cross-bedding is common in the coarser Sandakan Formation and back-barrier mangrove swamp deposits cap the progradational succession as on the modern northern Dent Peninsula coastline, indicating barrier development and higher wave energy conditions than in the Belait Formation. The Borneo examples indicate that barrier systems that include significant tidal facies form under higher wave energy conditions than attached beaches with virtually no tidal facies. Also, Borneo's low latitude climate promotes back-barrier mangrove which reduces tidal exchange and reduces tidal influence relative to comparable temperate climate systems. The results of the study indicate that depositional systems on low energy, wave-dominated coasts are highly variable, as are the sand bodies and facies associations they generate.

  4. Interactive Ion-Neutral Dynamics in the Low Latitude Evening Ionosphere

    NASA Astrophysics Data System (ADS)

    Evonosky, W. R.; Richmond, A. D.; Fang, T. W.; Maute, A. I.

    2015-12-01

    Neutral winds in the ionosphere drive global electrodynamic phenomena which alter theupper-atmosphere so significantly that they can affect the orbit of satellites andground-to-spacecraft communications. Understanding these winds and what drives them is centralto prediction and risk management associated with such a dynamic upper atmosphere. This studyexamined the relationship between accelerations acting on neutral winds in the ionosphere and theformation of a vertical shear of those winds in low latitudes (between ±30 magnetic) and earlyevening local times (16-22 LT). Accelerations were calculated using variables output by thethermosphere ionosphere electrodynamics general circulation model (TIEGCM) under differentsolar activity and night-time ionization conditions and visualized both spatially and temporally. Ingeneral, with acceleration values averaged along magnetic latitudes between ±30 degrees(inclusive) and only considering medium solar activity conditions, we found that the ionosphereexhibits distinct layering defined by the dominant accelerations in each layer. We also found hintsthat during different night-time ionization levels, ion drag acceleration tends to remain constantwhile ion and neutral velocities change to conserve the difference between them. When consideringspecific latitudes and solar conditions, previously unreported structures appear which involveinteractions between the ion drag and viscous forces.

  5. Dynamics of turbulent western-boundary currents at low latitude in a shallow-water model

    NASA Astrophysics Data System (ADS)

    Akuetevi, C. Q. C.; Wirth, A.

    2015-06-01

    The dynamics of low latitude turbulent western-boundary currents (WBCs) crossing the Equator are considered using numerical results from integrations of a reduced-gravity shallow-water model. For viscosity values of 1000 m2 s-1 and greater, the boundary layer dynamics compares well to the analytical Munk-layer solution. When the viscosity is reduced, the boundary layer becomes turbulent and coherent structures in the form of anticyclonic eddies, bursts (violent detachments of the viscous sub-layer, VSL) and dipoles appear. Three distinct boundary layers emerge, the VSL, the advective boundary layer and the extended boundary layer. The first is characterized by a dominant vorticity balance between the viscous transport and the advective transport of vorticity; the second by a balance between the advection of planetary vorticity and the advective transport of relative vorticity. The extended boundary layer is the area to which turbulent motion from the boundary extends. The scaling of the three boundary layer thicknesses with viscosity is evaluated. Characteristic scales of the dynamics and dissipation are determined. A pragmatic approach to determine the eddy viscosity diagnostically for coarse-resolution numerical models is proposed.

  6. Dynamics of turbulent western boundary currents at low latitude in a shallow water model

    NASA Astrophysics Data System (ADS)

    Akuetevi, C. Q. C.; Wirth, A.

    2014-11-01

    The dynamics of low latitude turbulent western boundary currents crossing the equator is considered using numerical results from integrations of a reduced gravity shallow-water model. For viscosity values of 1000 m2 s-1 and more, the boundary layer dynamics compares well to the analytical Munk-layer solution. When the viscosity is reduced, the boundary layer becomes turbulent and coherent structures in form of anticyclonic eddies, bursts (violent detachments of the viscous sub-layer) and dipoles appear. Three distinct boundary layers emerge, the viscous sub-layer, the advective boundary layer and the extended boundary layer. The first is characterized by a dominant vorticity balance between the viscous transport and the advective transport of vorticity. The second by a balance between the advection of planetary vorticity and the advective transport of relative vorticity. The extended boundary layer is the area to which turbulent motion from the boundary extends. The scaling of the three boundary layer thicknesses with viscosity is evaluated. Characteristic scales of the dynamics and dissipation are determined. A pragmatic approach to determine the eddy viscosity diagnostically for coarse resolution numerical models is proposed.

  7. Dynamics of turbulent western boundary currents at low latitude in a shallow water model

    NASA Astrophysics Data System (ADS)

    Akuetevi, C. Q. C.; Wirth, A.

    2014-03-01

    The dynamics of low latitude turbulent western boundary currents, subject to two different types of idealized wind forcing, Monsoon Wind and Trade Wind, is considered using numerical results from integrations of a reduced gravity shallow-water model. For viscosity values of 1000 m2 s-1 and above, the boundary layer dynamics compares well to the analytical solutions of the Munk-layer and the inertial-layer, derived from quasigeostrophic theory. Modifications due to variations in the layer thickness (vortex stretching) are only important close to the boundary. When the viscosity is reduced the boundary layer becomes turbulent and coherent structures in form of anticyclonic eddies, bursts (violent detachments of the viscous sub-layer) and dipoles appear. Three distinct boundary layers emerge, the viscous sub-layer, the advective boundary layer and the extended boundary layer. The first is characterized by a dominant vorticity balance between the viscous transport and the advective transport of vorticity. The second by a balance between the advection of planetary vorticity and the advective transport of relative vorticity. The extended boundary layer is the area to which turbulent motion from the boundary extends. The scaling of the three boundary layer thicknesses with viscosity is evaluated. A pragmatic approach to determine the eddy viscosity diagnostically for coarse resolution numerical models is proposed.

  8. Combined Impedance Probe and Langmuir Probe Studies of the Low-Latitude E Region

    NASA Technical Reports Server (NTRS)

    Rowland, D. E.; Pfaff, R. F.; Steigies, C. T.

    2008-01-01

    The EQUIS-2 sounding rocket and radar campaign, launched from Kwajalein Atoll in 2004, included a mission to study low-latitude irregularities and electrodynamics, led by NASA GSFC. This mission included two instrumented rockets launched into the nighttime E region (apogee near 120 km), which included comprehensive electrodynamics and neutral density instrumentation. These rockets carried the first of a new generation of impedance probes, that utilize a wide-band drive signal to simultaneously measure the impedance of an antenna in a plasma as a function of frequency from 7 kEIz to 4 MHz. at a rapid cadence. This technique promises to permit true plasma spectroscopy, and resulted in the identification of multiple plasma resonances and accurate measurements of the plasma density, even in the low density nighttime E region. We present analyses of the technique and resulting spectra, and show how these data may be combined with fixed-bias Langmuir Probe data to infer the temperature structure of the E region as well as providing accurate absolute calibrations for the very high time resolution fixed-bias probe data. The data is shown to agree well with data from ionosonde, the ALTAIR radar, and the Peruvian beacon experiment.

  9. High-latitude controls of thermocline nutrients and low latitude biological productivity.

    PubMed

    Sarmiento, J L; Gruber, N; Brzezinski, M A; Dunne, J P

    2004-01-01

    The ocean's biological pump strips nutrients out of the surface waters and exports them into the thermocline and deep waters. If there were no return path of nutrients from deep waters, the biological pump would eventually deplete the surface waters and thermocline of nutrients; surface biological productivity would plummet. Here we make use of the combined distributions of silicic acid and nitrate to trace the main nutrient return path from deep waters by upwelling in the Southern Ocean and subsequent entrainment into subantarctic mode water. We show that the subantarctic mode water, which spreads throughout the entire Southern Hemisphere and North Atlantic Ocean, is the main source of nutrients for the thermocline. We also find that an additional return path exists in the northwest corner of the Pacific Ocean, where enhanced vertical mixing, perhaps driven by tides, brings abyssal nutrients to the surface and supplies them to the thermocline of the North Pacific. Our analysis has important implications for our understanding of large-scale controls on the nature and magnitude of low-latitude biological productivity and its sensitivity to climate change. PMID:14702082

  10. A Statistical Study of the Sudden Impulses of Geomagnetic Field at Mid and Low Latitudes

    NASA Astrophysics Data System (ADS)

    Shi, C.

    2015-12-01

    Sudden impulses (SI) of geomagnetic field are associated with the sudden increases of the solar wind dynamic pressure, which is typically caused by the interplanetary shocks. In the mid and low latitudes at the ground, the SIs are the sudden increases of the northward magnetic field. Using a set of 447 SI cases and the SMR index (local Dst index provided by SuperMAG), we find that the responses of the geomagnetic field to the jump of the square root of solar wind dynamic pressure show a strong local time dependence with the strongest responses located in the midnight and the weakest responses located in the dawn side. We also find that geomagnetic responses, especially the noon and midnight responses, have quite different amplitudes under north and south interplanetary magnetic field. By calculating the normalized sudden impulses, we find that there is a seasonal variation with the peak around summer and the valley around winter. We also find that the shock normal orientation affects the amplitude of the sudden impulses: the more parallel the shock normal orientation is to the sun-earth line, the stronger the sudden impulses will be.

  11. South Carolina TEC Student Code.

    ERIC Educational Resources Information Center

    Edwards, C. A., Ed.; Kiser, J. A., Ed.

    This student code has statewide application to South Carolina Technical Colleges and Technical Education Centers (TEC). Provisions are divided into eight articles: (1) General Provisions, including the purpose of a student code, the precept of internal solution of problems, and definitions; (2) Student Rights, including Bill of Rights protections;…

  12. Tropical Atlantic climate response to low-latitude and extratropical sea-surface temperature: A Little Ice Age perspective

    NASA Astrophysics Data System (ADS)

    Saenger, Casey; Chang, Ping; Ji, Link; Oppo, Delia W.; Cohen, Anne L.

    2009-06-01

    Proxy reconstructions and model simulations suggest that steeper interhemispheric sea surface temperature (SST) gradients lead to southerly Intertropical Convergence Zone (ITCZ) migrations during periods of North Atlantic cooling, the most recent of which was the Little Ice Age (LIA; ˜100-450 yBP). Evidence suggesting low-latitude Atlantic cooling during the LIA was relatively small (<1°C) raises the possibility that the ITCZ may have responded to a hemispheric SST gradient originating in the extratropics. We use an atmospheric general circulation model (AGCM) to investigate the relative influence of low-latitude and extratropical SSTs on the meridional position of the ITCZ. Our results suggest that the ITCZ responds primarily to local, low-latitude SST anomalies and that small cool anomalies (<0.5°C) can reproduce the LIA precipitation pattern suggested by paleoclimate proxies. Conversely, even large extratropical cooling does not significantly impact low-latitude hydrology in the absence of ocean-atmosphere interaction.

  13. Ionospheric and magnetic signatures of a high speed solar wind in low latitudes on 13 October 2012

    NASA Astrophysics Data System (ADS)

    Migoya-Orue, Y. O.; Azzouzi, I.; Coisson, P.; Amory Mazaudier, C.; Fleury, R.; Radicella, S. M.

    2016-03-01

    This paper presents the impact of a fast solar wind on the ionosphere, in low latitudes, on 13 October 2012. On that day, the high speed solar wind reached the Earth around 16:00UT, during the recovery phase of a geomagnetic storm which started around 00:00UT. The solar wind speed was determined to be 580km/s, on the same day, around 17:00UT. Its impact was observed in low and equatorial latitudes, in Africa and in Eastern South America, on the F layer and on the geomagnetic field variations. Through the analysis of magnetic indices, ionosonde characteristics and the horizontal component of the geomagnetic field, we found that the 13 October 2012 event exhibited a local impact, affecting the observatories situated in a longitude sector between 315°E and 45°E. Particularly, the F layer in Africa (observed by the ionosonde at Ascension Island) did not present any lift, and there was a delay for approximately two hours of the ascent of the F layer in America (the ionosonde at Fortaleza). In this case, there was an evident inhibition on the development of spread F at the time of the Pre Reversal Enhancement (PRE) in Africa and Eastern America, while the ionograms of the days before and after presented clear spread F traces. The disturbances of the ionospheric equivalent electric current (Diono) deduced from the variations of the geomagnetic field at M'Bour near Dakar (Africa) and at Kourou (Eastern America) exhibited on the dayside, an anti Sq current which is signature of the influence of the Disturbance Dynamo Electric Field (DDEF).

  14. Seasonal Variability in OH Mesospheric Temperatures at Low-Latitudes and Comparison with Timed-Saber Temperatures

    NASA Astrophysics Data System (ADS)

    Taylor, Michael J.; Zhao, Yucheng; Russell, J. M., III

    The Utah State University Mesospheric Temperature Mapper (MTM) is a high performance, solid state imaging system capable of determining variations in the rotational temperatures of two upper mesospheric near infrared nightglow emissions: the OH (6,2) Meinel band (peak altitude 87 km) and the O2(0,1) Atmospheric band emission (peak altitude 94 km), with a precision of typically 1-2K in 3 min. For the past 5 years (November 201-December 2006), the MTM was operated near-continuously from the Air Force AMOS Facility, near the summit of Haleakala Crater, Maui, HI (24.8 N, 204 E), 2970 m). Autonomous observations were made as part of the Maui-MALT program which is a joint initiative between the National Science Foundation (NSF) and the US Air Force Office of Scientific research (AFOSR) to investigate the dynamics of the upper atmosphere in unprecedented detail. Over 1000 nights of high-quality data have been obtained, providing novel information on the nocturnal behavior of mesospheric temperature and its variability enabling a detailed comparative study with TIMED-SABER temperature measurements at low-latitudes. Here we focus on a seasonal comparison with MTM OH temperatures. The variability of the MTM and SABER temperatures track well on day-to-day and seasonal time scales giving high confidence in the compatibility of the two data sets. However, there appears to be a 5 K systematic offset between these data with the MTM temperatures warmer. A similar offset has been observed at mid-latitudes and this new study extends this comparison to lower latitudes where non-LTE effects are not significant. The origin and variability in this offset will be investigated as a function of season.

  15. Investigating short-period mesospheric gravity wave propagation and momentum flux at low-latitudes using simultaneous Na lidar and temperature mapper measurements

    NASA Astrophysics Data System (ADS)

    Ejiri, M. K.; Taylor, M. J.; Pautet, P. D.; Zhao, Y.; Liu, A. Z.

    The US Maui-MALT program is designed to investigate the properties and dynamics of the low-latitude mesosphere and lower thermosphere region MLT in exceptional detail A key component of this study is the investigation of short-period gravity waves and their propagation and dissipation characteristics at MLT height High-resolution measurements of the background wind temperature field using the University of Illinois Na wind temperature lidar have been combined with simultaneous image measurements of the NIR OH and O 2 airglow intensity and rotational temperature obtained by the Utah State University Mesospheric Temperature Mapper MTM to perform an in-depth investigation of five selected short-period less than 20 min gravity wave events In each case the waves were observed under differing background conditions and we have determined their intrinsic properties and nature of propagation i e freely propagating or ducted This has allowed us to quantify their associated horizontal momentum fluxes at two different altitudes 87 and 94 km within MLT and hence investigate their impact on this region at low-latitudes

  16. Investigation of the morphology and Wait's parameter variations of the low-latitude D region ionosphere using the multiple harmonics of tweeks

    NASA Astrophysics Data System (ADS)

    Tan, Le Minh

    2016-06-01

    Recording the tweeks with a maximum up to eight harmonics using the receiver installed at Tay Nguyen University (12.65° N, 108.02° E) during 2013-2014, we investigated the morphology of the nighttime D-region ionosphere. Tweeks were recorded on 5 quiet nights per month. The results show that the mean reflection height in 2014 (Rz = 79.3) is lower by 3.3 km than that in 2013 (Rz = 64.9). The reflection height at low latitudes is higher than that at high latitudes. The mean reference height h‧ in 2013 is higher about 0.9 km than that in 2014 and the mean sharpness factor β in 2013 is higher by 0.07 km-1 than that in 2014. The short-term variation of reflection heights for tweeks with harmonics m = 1-3 and sunspot number have the negative correlation coefficients. However, the correlations between them are not clear. On some nights, from 19:00-21:00 LT, the reflection height temporal variability shows a moderate to strong negative correlation with the tweek occurrence. This suggests that the reflection height variation may be caused by QE fields generated by lightning discharges. The variations of tweek reflection heights observed during 2013-2014, at low latitudes could be significantly caused by the ionization effect by Lyman- α and Lyman- β coming from geocorona, variation of neutral density, particle precipitations, and by direct energy coupling between lightning and lower ionosphere.

  17. Monthly mean foF2 model for an African low-latitude station and comparison with IRI

    NASA Astrophysics Data System (ADS)

    Ikubanni, S. O.; Adeniyi, J. O.; Obrou, O. K.

    2014-02-01

    We have employed the hourly values of the ionospheric F-region critical frequency (foF2) obtained from Ouagadougou ionosonde, Burkina Faso (geographic coordinates 12° N, 1.8° W) during the interval of 1985-1995 (solar cycle 22) and solar radio flux of 10 cm wavelength (F10.7) to develop a local model (LM) for the African low-latitude station. The model was developed from regression analysis method, using the two-segmented regression analysis. We validated LM with foF2 data from Korhogo observatory, Cote d'Ivorie (geographical coordinates 9.3° N, 5.4° W). LM as well as the International Reference Ionosphere (IRI) agrees well with observations. LM gave some improvement on the IRI-predicted foF2 values at the sunrise (06 LT) at all solar flux levels and in all seasons except June solstice. The performance of the models at the representing the salient features of the equatorial foF2 was presented. Considering daytime and nighttime performances, LM and IRI are comparable in low solar activity (LSA), LM performed better than IRI in moderate solar activity (MSA), while IRI performed better than LM in high solar activity (HSA). CCIR has a root mean square error (r.m.s.e), which is only 0.10 MHz lower than that of LM while LM has r.m.s.e, which is about 0.05 MHz lower than that of URSI. In general, our result shows that performance of IRI, especially the CCIR option of the IRI, is quite comparable with the LM. The improved performance of IRI is a reflection of the numerous contributions of ionospheric physicists in the African region, larger volume of data for the IRI and the diversity of data sources, as well as the successes of the IRI task force activities.

  18. Occurrence and characteristics of nighttime ULF waves at low latitude: The results of a comprehensive analysis

    NASA Astrophysics Data System (ADS)

    Villante, Umberto; Tiberi, Pietro

    2016-05-01

    The occurrence and characteristics of ULF events (f ≈ 10-100 mHz) detected during the night at low latitude (L'Aquila, Italy, λ ≈ 36.3°), during quiet and moderately perturbed magnetospheric conditions, have been examined by means of a long-term analysis between 1996 and 2012. Clearly defined events (≈8000 on each component) are typically more energetic in H than in D and basically consist of penetrating upstream waves, resonances of local field lines, and Pi2 waves. The global event occurrence shows a strong asymmetry about midnight, with a much higher wave activity before dawn than after dusk: it mostly comes from the intense penetration of upstream waves through the dawn flank of the magnetopause. D events are more frequent in summer and H events more frequent in winter, suggesting a different influence of the ionospheric modification of the downgoing signals. Between f ≈ 30 and 45 mHz, the reversal of the dominant polarization across midnight reveals tailward propagation of penetrating waves. Below f ≈ 25 mHz, intermingled with continuous Pc3 and Pc4 waves, a large fraction of events exhibit Pi2 characteristics: the dominant left-handed polarization and the switch of the tilt angle of the major axis of the polarization ellipses are consistent with the pattern expected for waves related to the substorm current wedge. A relevant percentage of the power spectra shows a second enhancement above f ≈ 55 mHz, revealing resonance of local field lines also during the night.

  19. Holocene biomass burning recorded in polar and low-latitude ice cores

    NASA Astrophysics Data System (ADS)

    Kehrwald, N. M.; Zennaro, P.; Zangrando, R.; Gabrielli, P.; Thompson, L. G.; Gambaro, A.; Barbante, C.

    2011-12-01

    Ice cores contain specific molecular markers including levoglucosan (1,6-anhydro-β-D-glucopyranose) and other pyrochemical evidence that provides much-needed information on the role of fire in regions with no existing data of past fire activity. Levoglucosan is a cellulose combustion product produced at burning temperatures of 300°C or greater. We first trace fire emissions from a boreal forest source in the Canadian Shield through transport and deposition at Summit, Greenland. Atmospheric and surface samples suggest that levoglucosan in snow can record biomass burning events up to 1000s of kilometers away. Levoglucosan does degrade by interacting with hydroxyl radicals in the atmosphere, but it is emitted in large quantities, allowing the use as a biomass burning tracer. These quantified atmospheric biomass burning emissions and associated parallel oxalate and levoglucosan peaks in snow pit samples validates levoglucosan as a proxy for past biomass burning in snow records and by extension in ice cores. The temporal and spatial resolution of chemical markers in ice cores matches the core in which they are measured. The longest temporal resolution extends back approximately eight glacial cycles in the EPICA Dome C ice core, but many ice cores provide high-resolution Holocene records. The spatial resolution of chemical markers in ice cores depends on the core location where low-latitude ice cores primarily reflect regional climate parameters, and polar ice cores integrate hemispheric signals. Here, we compare levoglucosan flux measured during the late Holocene in the Kilimanjaro (3°04.6'S; 37°21.2'E, 5893 masl) and NEEM, Greenland (77°27' N; 51°3'W, 2454 masl) ice cores. We contrast the Holocene results with levoglucosan flux across the past 600,000 years in the EPICA Dome C (75°06'S, 123°21'E, 3233 masl) ice core.

  20. Isotopic evolution of saline lakes in the low-latitude and polar regions

    SciTech Connect

    Horita, Juske

    2009-01-01

    Isotopic fractionations associated with two primary processes (evaporation and freezing of water) are discussed, which are responsible for the formation and evolution of saline lakes in deserts from both low-latitude and the Polar regions. In an evaporative system, atmospheric parameters (humidity and isotopic composition of water vapor) have strong influence on the isotopic behavior of saline lakes, and in a freezing system, salinity build-up largely controls the extent of freezing and associated isotope fractionation. In both systems, salinity has a direct impact on the isotopic evolution of saline lakes. It is proposed that a steady-state terminal lake model with short-term hydrologic and environmental perturbations can serve as a useful framework for investigating both evaporative and freezing processes of perennial saline lakes. Through re-assessment of own work and literature data for saline lakes, it was demonstrated that effective uses of the isotope activity compositions of brines and salinity-chemistry data could reveal dynamic changes and evolution in the isotopic compositions of saline lakes in response to hydrologic and environmental changes. The residence time of isotopic water molecules in lakes determines the nature of responses in the isotopic compositions following perturbations in the water and isotope balances (e.g., dilution by inflow, water deficit by increased evaporation, and/ or reduction in inflow). The isotopic profiles of some saline lakes from the Polar regions show that they switched the two contrasting modes of operation between evaporative and freezing systems, in response to climate and hydrological changes in the past.

  1. Isotopic Evolution of Saline Lakes in the Low-Latitude and Polar Regions

    SciTech Connect

    Horita, Juske

    2009-01-01

    Isotopic fractionations associated with two primary processes (evaporation and freezing of water) are discussed, which are responsible for the formation and evolution of saline lakes in deserts from both low-latitude and the Polar regions. In an evaporative system, atmospheric parameters (humidity and isotopic composition of water vapor) have strong influence on the isotopic behavior of saline lakes, and in a freezing system, salinity build-up largely controls the extent of freezing and associated isotope fractionation. In both systems, salinity has a direct impact on the isotopic evolution of saline lakes. It is proposed that a steady-state 'terminal lake' model with short-term hydrologic and environmental perturbations can serve as a useful framework for investigating both evaporative and freezing processes of perennial saline lakes. Through re-assessment of own work and literature data for saline lakes, it was demonstrated that effective uses of the isotope activity compositions of brines and salinity-chemistry data could reveal dynamic changes and evolution in the isotopic compositions of saline lakes in response to hydrologic and environmental changes. The residence time of isotopic water molecules in lakes determines the nature of responses in the isotopic compositions following perturbations in the water and isotope balances (e.g., dilution by inflow, water deficit by increased evaporation, and/or reduction in inflow). The isotopic profiles of some saline lakes from the Polar regions show that they switched the two contrasting modes of operation between evaporative and freezing systems, in response to climate and hydrological changes in the past.

  2. Ionospheric TEC variations at mid-latitudes obsereved using SBAS L1/L5 signals.

    NASA Astrophysics Data System (ADS)

    Padokhin, A. M.; Kunitsyn, V.; Kurbatov, G.; Yasyukevich, Y.

    2014-12-01

    With the development of Satellite based augmentation systems (SBAS) the dual frequency L1/L5 observations from a number of geostationary satellites are now available. It provides the possibility to retrieve ionospheric total electron content (TEC) from these observations using the same approach as for dual frequency GPS/GLONASS observations. In this work we study L1/L5 signals of Indian GAGAN geostationary satellites observed with geodetic GNSS receivers at several stations at mid-latitudes and estimate corresponding geostationary TEC and errors of such estimations. TEC RMS was found to reach up to 1.5 TECU with typical values of 0.25-0.5 TECU which is several times greater than for common GPS/GLONASS observations. TEC RMS also manifests UT-dynamics which is specific for the chosen geostationary satellite and not relevant to the receiver site and signal paths. SBAS TEC was found to be in good agreement with the data of nearest ionosondes taking into account low elevation angles of SBAS satellites already at mid-latitudes and spatial gradients of electron density along the ray paths. We also present the wavelet analysis of geostationary TEC, providing typical periods of observed variations at different time scales (from tens of minutes to tens of days) and discuss the capabilities of SBAS TEC observations in connection with ionospheric effects of solar flares.

  3. Connection between high-latitude arcs and the low-latitude boundary layer during periods of northward IMF

    NASA Astrophysics Data System (ADS)

    Maggiolo, R.; Fontaine, D.; Hosokawa, K.; Maes, L.; Zhang, Y.; Fear, R. C.; Cumnock, J. A.; Kozlovsky, A.; Kullen, A.; Milan, S. E.; Shiokawa, K.; Echim, M.

    2014-12-01

    High-latitude auroral arcs are a typical feature of periods of northward IMF. They consist in thin and elongated optical emission similar to discrete auroral arcs but located in the polar ionosphere. Their formation mechanism and the magnetospheric regions to which they are connected are still not well understood. On November 10, 2005, high-latitude arcs were detected by an all-sky camera at Resolute Bay in Canada and by the TIMED/GUVI and DMSP/SUSIE space-based imagers. These observations indicate that they were detaching from the duskside auroral oval and then drifting poleward while pointing in the cusp direction. The same day, the Cluster spacecraft were flying in the dawn-dusk direction from the lobe region at altitudes ~5 RE to the magnetospheric equatorial plane at geocentric distances ~19 RE. Cluster observations reveal the presence of field-aligned acceleration regions above the polar ionosphere associated with the high-latitude arcs detected by the imagers. We analyze Cluster particle observations from the lobe region to the duskside magnetopause. In the high-latitude arcs region, Cluster detects upgoing ions and precipitating electrons accelerated by a quasi-static electric field. These accelerated particles coexist with plasmasheet-like plasma embedded in the lobe region. A comparison between the 4 Cluster spacecraft electron measurements for the most poleward arc reveals that the plasmasheet-like electron population is vanishing on a time scale of a few minutes while the plasmasheet-like ion population doesn't display any temporal evolution. The most equatorward arc is separated from the auroral oval by a "transition" region where weak fluxes of ions with plasmasheet like temperatures are detected. Then the Cluster spacecraft cross the plasmasheet until they reach the low-latitude boundary layer (LLBL) characterized by a mixture of plasmasheet and magnetosheath plasma. The "transition" region and the LLBL are magnetically connected. Using Cluster

  4. Temporal and spatial distributions of TEC depletions with scintillations and ROTI over south China

    NASA Astrophysics Data System (ADS)

    Deng, Baichang; Huang, Jiang; Kong, Debao; Xu, Jie; Wan, Dehuan; Lin, Guoguo

    2015-01-01

    This study investigated the temporal and spatial distributions of TEC depletions with scintillations and ROTI over south China. Data were collected from two GPS receiver stations in south China from 2011 to 2012. Our results revealed that maxima of distribution of TEC depletions were observed in vernal and autumnal equinox months. During pre-midnight hours and in the region of northern crest of equatorial anomaly, deep TEC depletions (approximately 20 TECU) well coincided with the occurrences of intense scintillations (S4 > 0.5) and large ROTI (approximately 2). But around midnight hours or at the outer edge of northern anomaly crest, only shallow TEC depletions (<10 TECU) were recorded with small ROTI (<1) and no scintillation. Our results suggest that the temporal and spatial variability of TEC depletions during equinox months over south China could be considered as a representative of the evolution phase of the plasma bubbles during post-sunset hours.

  5. Energetic and magnetosheath energy particle signatures of the low-latitude boundary layer at low altitudes near noon

    NASA Technical Reports Server (NTRS)

    Roeder, J. L.; Lyons, L. R.

    1992-01-01

    The low-latitude boundary layer (LBL) and its separation from the cusp have previously been identified using observations of particle precipitation at magnetosheath energies. Using S3-3 satellite observations, we have determined that these identifications can also be made from energetic particle observations on polar-orbiting satellites. It is found that the equatorward boundary of the LBL is identifiable as an approximately discontinuous decrease in 33-keV electron fluxes from low to high latitudes. Both the energetic ion and electron fluxes decrease discontinuously at the boundary between the LBL and the cusp or polar cap. A distinct LBL is nearly always identifiable in energetic particle measurements in the 10-14 MLT region when counting rates are statistically significant. The identifications obtained using the energetic particle measurements have been compared to those obtained using criteria developed by Newell and Meng (1988, 1989) for magnetosheath energy particle precipitation. In this way, we have evaluated the accuracy of both techniques and used the energetic particle measurements to supplement the identifications obtained using the Newell and Meng criteria. We propose that the Newell and Meng threshold on ion energy flux can be reduced by a factor of 6. This modification provides identification of the LBL for lower ion intensity levels than has previously been thought possible. Source, acceleration, and scattering processes have also been studied within and in the vicinity of the LBL. Observed trapped pitch angle distributions of energetic electrons imply that the LBL is at least partially on closed field lines. Strong scattering of energetic protons is found within and equatorward of the LBL and thus must occur at least partially along closed field lines. Field-aligned electron acceleration by parallel electric fields can be discerned within and poleward of the LBL, but a more detailed analysis is necessary for a statistical study. Conical ion

  6. Solar terminator effects on middle- to low-latitude Pi2 pulsations

    NASA Astrophysics Data System (ADS)

    Imajo, Shun; Yoshikawa, Akimasa; Uozumi, Teiji; Ohtani, Shinichi; Nakamizo, Aoi; Demberel, Sodnomsambuu; Shevtsov, Boris Mikhailovich

    2016-08-01

    To clarify the effect of the dawn and dusk terminators on Pi2 pulsations, we statistically analyzed the longitudinal phase and amplitude structures of Pi2 pulsations at middle- to low-latitude stations (GMLat = 5.30°-46.18°) around both the dawn and dusk terminators. Although the H (north-south) component Pi2s were affected by neither the local time (LT) nor the terminator location (at 100 km altitude in the highly conducting E region), some features of the D (east-west) component Pi2s depended on the location of the terminator rather than the LT. The phase reversal of the D component occurred 0.5-1 h after sunrise and 1-2 h before sunset. These phase reversals can be attributed to a change in the contributing currents from field-aligned currents (FACs) on the nightside to the meridional ionospheric currents on the sunlit side of the terminator, and vice versa. The phase reversal of the dawn terminator was more frequent than that of the dusk terminator. The D-to- H amplitude ratio on the dawn side began to increase at sunrise, reaching a peak approximately 2 h after sunrise (the sunward side of the phase reversal region), whereas the ratio on the dusk side reached a peak at sunset (the antisunward side). The dawn-dusk asymmetric features suggest that the magnetic contribution of the nightside FAC relative to the meridional ionospheric current on the dusk side is stronger than that on the dawn side, indicating that the center of Pi2-associated FACs, which probably corresponds to the Pi2 energy source, tends to be shifted duskward on average. Different features and weak sunrise/sunset dependences at the middle-latitude station (Paratunka, GMLat = 46.18°) can be attributed to the larger annual variation in the sunrise/sunset time and a stronger magnetic effect because of closeness from FACs. The D-to- H amplitude ratio decreased with decreasing latitude, suggesting that the azimuthal magnetic field produced by the FACs in darkness and the meridional ionospheric

  7. Low-latitude equinoctial spread-F occurrence at different longitude sectors under low solar activity

    NASA Astrophysics Data System (ADS)

    Pezzopane, M.; Zuccheretti, E.; Abadi, P.; de Abreu, A. J.; de Jesus, R.; Fagundes, P. R.; Supnithi, P.; Rungraengwajiake, S.; Nagatsuma, T.; Tsugawa, T.; Cabrera, M. A.; Ezquer, R. G.

    2013-02-01

    We present the results of a comparative study of spread-F signatures over five low-latitude sites: Chiangmai (CGM; 18.8° N, 98.9° E, mag. Lat. 8.8° N), Thailand; Tanjungsari (TNJ; 6.9° S, 107.6° E, mag. Lat. 16.9° S), Indonesia; Palmas (PAL; 10.2° S, 311.8° E, mag. Lat. 0.9° S) and São José Dos Campos (SJC; 23.2° S, 314.1° E, mag. Lat. 14.0° S), Brazil; and Tucumán (TUC; 26.9° S, 294.6° E, mag. Lat. 16.8° S), Argentina. The investigation was based on simultaneous ionograms recorded by an FMCW (frequency-modulated continuous-wave) at CGM, an IPS-71 (digital ionosonde from KEL aerospace) at TNJ, a CADI (Canadian Advanced Digital Ionosonde) at PAL and SJC, and an AIS-INGV (Advanced Ionospheric Sounder - Istituto Nazionale di Geofisica e Vulcanologia) at TUC, during the equinoctial periods March-April (R12 = 2.0 and R12 = 2.2) and September-October (R12 = 6.1 and R12 = 7.0) 2009, for very low solar activity. Spread-F signatures were categorized into two types: the range spread-F (RSF) and the frequency spread-F (FSF). The study confirms that the dynamics and the physical processes responsible for these phenomena are actually complicated. In fact, the features that arise from the investigation are different, depending on both the longitude sector and on the hemisphere. For instance, TUC, under the southern crest of the ionospheric equatorial ionization anomaly (EIA), shows a predominance of RSF signatures, while both SJC, under the southern crest of EIA but in a different longitude sector, and CGM, under the northern crest of EIA, show a predominance of FSF signatures. Moreover, the spread-F occurrence over the longitude sector that includes CGM and TNJ is significantly lower than the spread-F occurrence over the longitude sector of PAL, SJC, and TUC.

  8. A simple expression for sound attenuation due to surface duct energy leakage in low-latitude oceans.

    PubMed

    Duan, Rui; Yang, Kunde; Ma, Yuanliang; Chapman, N Ross

    2016-05-01

    This paper presents an expression for the attenuation of sound energy in an ocean surface duct due to energy leakage outside the duct. Dominant parameters determining the attenuation are the sound frequency and the surface duct thickness. The attenuation is found to be exponentially dependent on a scaled frequency that combines the two parameters. Data from experiments in low-latitude oceans with three different surface duct thicknesses are used to verify the exponential expression derived for the attenuation.

  9. Investigation of Sbas L1/L5 Signals and Their Application to the Ionospheric TEC Studies

    NASA Astrophysics Data System (ADS)

    Padokhin, A. M.; Kunitsyn, V.; Andreeva, E. S.; Nesterov, I. A.; Kurbatov, G. A.

    2013-12-01

    With the development of SBAS systems the dual frequency L1/L5 observations from a number of geostationary satellites are now available. It provides the possibility to retrieve ionospheric TEC from these observations using the same approach as for dual frequency GPS/GLONASS observations. In this work we study the properties of L1/L5 signals of American WAAS and Indian GAGAN geostationary satellites observed with geodetic GNSS receivers located at equatorial and mid-latitudes and estimate corresponding TEC and errors of such estimations. Along with the advantages of geostationary TEC observations, such as almost motionless underionospheric point, there are points that should be taken into account when analyzing geostationary TEC data, including larger amount of plasmaspheric electron content in geostationary TEC compared to GNSS observations, and very low elevation angles of geostationary satellites already at midlatitudes, so the spatial gradients of electron density should be considered. We present long term datasets of geostationary TEC variations during current Solar cycle in various heliogeophysical conditions at equatorial and midlatitude stations and their comparison with the data of nearest ionosondes and high-orbital radiotomography, as well as spectral and wavelet analysis of geostationary TEC variations data, providing typical periods of observed TEC variations at different time scales (e.g. diurnal variations, disturbances associated with sunset and sunrise terminator etc.). We also study the possibility to include the geostationary TEC data to the ionospheric tomography procedures. The authors acknowledge the support of the Russian Foundation for Basic Research (12-05-33065, 12-05-31231, 13-05-01122, 13-05-10080, 14-05-31445), grant of the President of Russian Federation MK-2544.2012.5 and Lomonosov Moscow State University Program of Development.

  10. Potential impacts of wintertime soil moisture anomalies from agricultural irrigation at low latitudes on regional and global climates

    NASA Astrophysics Data System (ADS)

    Wey, Hao-Wei; Lo, Min-Hui; Lee, Shih-Yu; Yu, Jin-Yi; Hsu, Huang-Hsiung

    2015-10-01

    Anthropogenic water management can change surface energy budgets and the water cycle. In this study, we focused on impacts of Asian low-latitude irrigation on regional and global climates during boreal wintertime. A state-of-the-art Earth system model is used to simulate the land-air interaction processes affected by irrigation and the consequent responses in atmospheric circulation. Perturbed experiments show that wet soil moisture anomalies at low latitudes can reduce the surface temperature on a continental scale through atmospheric feedback. The intensity of prevailing monsoon circulation becomes stronger because of larger land-sea thermal contrast. Furthermore, anomalous upper level convergence over South Asia and midlatitude climatic changes indicate tropical-extratropical teleconnections. The wintertime Aleutian low is deepened and an anomalous warm surface temperature is found in North America. Previous studies have noted this warming but left it unexplained, and we provide plausible mechanisms for these remote impacts coming from the irrigation over Asian low-latitude regions.

  11. On the Origin of the Crestone Crater: Low-Latitude Periglacial Features in San Luis Valley, Colorado

    NASA Astrophysics Data System (ADS)

    Schwans, E.; Meng, T. M.; Prudhomme, K.; Morgan, M. L.

    2015-12-01

    this claim. Results indicate that the Crestone Crater and nearby similar structures are relic collapsed hydraulic pingos, formed during Pleistocene periglacial activity. This conclusion provides further insight into periglacial landforms at low latitudes while demonstrating the value of LiDAR analysis of small geologic features on a regional scale.

  12. Ionospheric TEC Estimations with the Signals of Various Geostationary Navigational Satellites

    NASA Astrophysics Data System (ADS)

    Kurbatov, G. A.; Padokhin, A. M.; Kunitsyn, V.; Yasyukevich, Y.

    2015-12-01

    The development of GNSS and SBAS systems provides the possibility to retrieve ionospheric TEC from the dual frequency observations from a number of geostationary satellites using the same approach as for dual frequency GPS/GLONASS observations. In this connection, the quality of geostationary data, first of all the level of noise in TEC estimations is of great interest and importance. In this work we present the results of the comparison of the noise patterns in TEC estimations using signals of geostationary satellites of augumentation systems - indian GAGAN, european EGNOS and american WAAS, as well as the signals of chinees COMPASS/Beidou navigational system. We show that among above mentioned systems geostationary COMPASS/Beidou satellites provide best noise level in TEC estimations (RMS~0.1TECU), which corresponds to those of GPS/GLONASS, while GAGAN and WAAS TEC RMS could reach up to 1.5 TECU with typical values of 0.25-0.5 TECU which is up to one order greater than for common GPS/GLONASS observations. EGNOS TEC estimations being even more noisy (TEC RMS up to 10TECU) than WAAS and GAGAN ones at present time are not suitable for ionospheric studies. We also present geostationary TEC response to increasing solar X-Ray and EUV ionizing radiation during several recent X-class flares. Good correlation was found between TEC and EUV flux for the stations at the sunlit hemisphere. We also present geostationary TEC response to geomagnetic field variations during strong and moderate geomagnetic storms (including G4 St. Patricks Day Storm of 2015) showing examples of both positive and negative TEC anomalies of order of tens of TECU during main storm phase. Our results show the capability of geostationary GNSS and SBAS observations for continuous monitoring of ionospheric TEC. Intensively growing networks of dedicated receivers (for example MGEX network) and increasing number of dual-frequency geostationary satellites in SBAS and GNSS constellations potentially make it a

  13. Obliquity signals at low latitudes: a result of the cross-equatorial tropical insolation gradient?

    NASA Astrophysics Data System (ADS)

    Bosmans, Joyce; Hilgen, Frederik; Lourens, Lucas

    2013-04-01

    Despite the near-zero obliquity-induced insolation changes at the tropics, an obliquity signal is present in various sediment records at low latitudes. A number of hypotheses have been brought forward to explain the presence of obliquity at the tropics, especially in North-African records of monsoon strength. Firstly, the latitude of the tropics changes from 22° to 24.5°, shifting the area under the influence of the monsoon by ~300 km, which could influence its poleward penetration. A second hypothesis involves the strengthening of the austral winter insolation gradient at times of high obliquity, forcing stronger trade winds which become part of the North-African monsoonal south-westerlies, intensifying the North-African summer monsoon. Thirdly, influences of higher latitudes, where obliquity-induced changes in insolation are larger, could strengthen the North-African monsoon through increased northerly moisture transport into the monsoon region and a strengthened Asian low pressure system. The fourth hypothesis is based on the insolation gradient, specifically the cross-equatorial insolation gradient between the Tropics of Cancer and Capricorn. This insolation gradient drives the differential sensible heating between the two limbs of the winter hemisphere Hadley Cell and therefore the strength of the monsoon. This hypothesis suggests that the obliquity signal in the tropics arises without influence from higher latitudes. Using a high-resolution coupled climate model, EC-Earth, we can oppose the first three hypotheses. Comparing two experiments of low and high obliquity we find a more northward North-African monsoon during high obliquity, as suggested by the first hypothesis. However, we find that precession has a much larger effect on the northward extend of the North-African monsoon. Also, we find a very small increase in trade wind strength over the South-Atlantic for obliquity. Furthermore, spectral analysis shows that the winter hemispheric insolation

  14. Threshold magnitude for Ionospheric TEC response to earthquakes

    NASA Astrophysics Data System (ADS)

    Perevalova, N. P.; Sankov, V. A.; Astafyeva, E. I.; Zhupityaeva, A. S.

    2014-02-01

    We have analyzed ionospheric response to earthquakes with magnitudes of 4.1-8.8 which occurred under quiet geomagnetic conditions in different regions of the world (the Baikal region, Kuril Islands, Japan, Greece, Indonesia, China, New Zealand, Salvador, and Chile). This investigation relied on measurements of total electron content (TEC) variations made by ground-based dual-frequency GPS receivers. To perform the analysis, we selected earthquakes with permanent GPS stations installed close by. Data processing has revealed that after 4.1-6.3-magnitude earthquakes wave disturbances in TEC variations are undetectable. We have thoroughly analyzed publications over the period of 1965-2013 which reported on registration of wave TIDs after earthquakes. This analysis demonstrated that the magnitude of the earthquakes having a wave response in the ionosphere was no less than 6.5. Based on our results and on the data from other researchers, we can conclude that there is a threshold magnitude (near 6.5) below which there are no pronounced earthquake-induced wave TEC disturbances. The probability of detection of post-earthquake TIDs with a magnitude close to the threshold depends strongly on geophysical conditions. In addition, reliable identification of the source of such TIDs generally requires many GPS stations in an earthquake zone. At low magnitudes, seismic energy is likely to be insufficient to generate waves in the neutral atmosphere which are able to induce TEC disturbances observable at the level of background fluctuations.

  15. Comparison of the dynamical response of low latitude middle atmosphere to the major stratospheric warming events in the Northern and Southern Hemispheres

    NASA Astrophysics Data System (ADS)

    Bhagavathiammal, G. J.; Sathishkumar, S.; Sridharan, S.; Gurubaran, S.

    2016-08-01

    This study presents comparison of low-latitude dynamical responses to boreal 2008/09 and austral 2002 winter Major Stratospheric Warming (MSW) events, as both events are of vortex split type. During these winters, planetary wave (PW) variability and changes in low-latitude circulation are examined using European Center for Medium Range Weather Forecasting (ECMWF) reanalysis (ERA)-interim data sets and mesospheric wind data acquired by the MF radars at Tirunelveli (8.7°N) and Rarotonga (22°S). Eliassen-Palm diagnostic is used to provide an evidence for the lateral PW energy propagation from high to low-latitudes during both the MSW events. The PW flux reaches much lower latitudes during the boreal event than during the austral event. The low-latitude westward winds at stratospheric heights are stronger (weaker) during the boreal (austral) MSW. Weak (strong) PW wave activity at low latitude mesospheric heights during boreal (austral) MSW indicates the influence of low-latitude stratospheric westward winds on the vertical propagation of PW to low-latitude mesosphere.

  16. TEC disturbances during major Sudden Stratospheric Warmings in the mid-latitude ionosphere.

    NASA Astrophysics Data System (ADS)

    Polyakova, Anna; Voeykov, Sergey; Chernigovskaya, Marina; Perevalova, Natalia

    Using total electron content (TEC) global ionospheric maps, dual-frequency GPS receivers TEC data and MLS (Microwave Limb Sounder, EOS Aura) atmospheric temperature data the ionospheric disturbances during the strong sudden stratospheric warmings (SSWs) of 2008/2009 and 2012/2013 winters are investigated in Russia's Asia region. It is established that during the SSW maximum the midday TEC decrease and the night/morning TEC increase compared to quiet days are observed in the mid-latitude ionosphere. As a result it caused the decrease of the diurnal TEC variations amplitude of about two times in comparison with the undisturbed level. The analysis of TEC deviations from the background level during the SSWs has shown that deviations dynamics vary depending on the observation point position. Negative deviations of TEC are registered in the ionosphere above the region of maximum stratosphere heating (the region of the stratospheric circulation change) as well as above the anticyclone. On the contrary, TEC values increase compared to the quiet day's values above the stratosphere cyclone. It is shown that during maximum phase of a warming, and within several days after it the amplification of wave TEC variations intensity with periods of up to 60 min is registered in ionosphere. The indicated effects may be attributed to the vertical transfer of molecular gas from a stratospheric heating region to the thermosphere as well as to the increase in activity of planetary and gravity waves which is usually observed during strong SSWs. The study is supported by the RF President Grant of Public Support for RF Leading Scientific Schools (NSh-2942.2014.5), the RF President Grant No. MK-3771.2012.5 and RFBR Grant No. 12-05-00865_а.

  17. V-TECS Guide for Computer Operator.

    ERIC Educational Resources Information Center

    South Carolina State Dept. of Education, Columbia. Office of Vocational Education.

    This V-TECS (Vocational-Technical Consortium of States) Guide is an extension or continuation of the V-TECS catalog for the occupation of computer operator. The guide is designed to help South Carolina teachers to promote the art of learning while teaching subject matter. The guide addresses the three domains of learning: psychomotor, cognitive,…

  18. The AzTEC Mathematics Project (AMP).

    ERIC Educational Resources Information Center

    Johnson, Gae R.

    The AzTEC Mathematics Project (AMP) is a statewide partnership among Arizona's Regents universities and state community colleges, partner school districts, and economic communities. AzTec is committed to preparing highly qualified K-12 mathematics and science teachers. AMP targeted Native American teachers and teachers of Native American students…

  19. Analysis of observations backing up the existence of VLF and ionospheric TEC anomalies before the Mw6.1 earthquake in Greece, January 26, 2014

    NASA Astrophysics Data System (ADS)

    Sanchez-Dulcet, F.; Rodríguez-Bouza, M.; Silva, H. G.; Herraiz, M.; Bezzeghoud, M.; Biagi, P. F.

    The present work integrates ground-based ionosphere measurements using very-low-frequency radio transmissions with satellite measurements of the total electron content to draw common conclusions about the possible impact that the Mw6.1 earthquake that took place in Greece on January 26, 2014, had on the ionosphere. Very-low-frequency radio signals reveal the existence of an ∼4-day anomaly in the wavelet spectra of the signals received inside the earthquake preparation zone and a significant increase in the normalized variance of the signals prior to the earthquake (approximately 1 day before). Through total electron content analysis, it was possible to identify a clear anomaly from 15:00 until 20:00 UT on the day before the earthquake that appears again on the day of the earthquake between 07:00 UT and 08:00 UT. The anomalous values reach TEC∗Sigma ∼4.36 and 3.11, respectively. Their spatial and temporal distributions give grounds to assume a possible link with the earthquake preparation. The geomagnetic, solar and weather conditions during the considered period are presented and taken into account. This work is an initial and original step towards a multi-parameter approach to the problem of the possible earthquake-related effects on the ionosphere joining observations made from both ground stations and satellites. A well-founded knowledge of these phenomena is clearly necessary before dealing with their application to earthquake prediction purposes.

  20. On the climate response of the low-latitude Pacific Ocean to changes in the global freshwater cycle

    NASA Astrophysics Data System (ADS)

    Williams, P. D.; Guilyardi, E.; Sutton, R. T.; Gregory, J. M.; Madec, G.

    2006-11-01

    Under global warming, the predicted intensification of the global freshwater cycle will modify the net freshwater flux at the ocean surface. Since the freshwater flux maintains ocean salinity structures, changes to the density-driven ocean circulation are likely. A modified ocean circulation could further alter the climate, potentially allowing rapid changes, as seen in the past. The relevant feedback mechanisms and timescales are poorly understood in detail, however, especially at low latitudes where the effects of salinity are relatively subtle. In an attempt to resolve some of these outstanding issues, we present an investigation of the climate response of the low-latitude Pacific region to changes in freshwater forcing. Initiated from the present-day thermohaline structure, a control run of a coupled ocean atmosphere general circulation model is compared with a perturbation run in which the net freshwater flux is prescribed to be zero over the ocean. Such an extreme experiment helps to elucidate the general adjustment mechanisms and their timescales. The atmospheric greenhouse gas concentrations are held constant, and we restrict our attention to the adjustment of the upper 1,000 m of the Pacific Ocean between 40°N and 40°S, over 100 years. In the perturbation run, changes to the surface buoyancy, near-surface vertical mixing and mixed-layer depth are established within 1 year. Subsequently, relative to the control run, the surface of the low-latitude Pacific Ocean in the perturbation run warms by an average of 0.6°C, and the interior cools by up to 1.1°C, after a few decades. This vertical re-arrangement of the ocean heat content is shown to be achieved by a gradual shutdown of the heat flux due to isopycnal (i.e. along surfaces of constant density) mixing, the vertical component of which is downwards at low latitudes. This heat transfer depends crucially upon the existence of density-compensating temperature and salinity gradients on isopycnal surfaces

  1. Solar Wind Activity Dependence of the Occurrence of Field-Line Resonance at low Latitudes (L~1.3)

    NASA Astrophysics Data System (ADS)

    Takasaki, S.; Kawano, H.; Tanaka, Y.; Yoshikawa, A.; Seto, M.; Iijima, M.; Yumoto, K.

    2002-12-01

    It is known that the field line resonance (FLR below) is caused by hydromagnetic waves in the magnetosphere. The fundamental field line eigenfrequency can be expressed by the magnetic field line length, the magnetic field intensity, and the plasma density at the magnetic field line. We can measure the fundamental field line eigenfrequency by ground-based observation. The field line length and the magnetic field intensity can be calculated from some magnetic field model (such as the IGRF model) of the magnetosphere. Then, it is possible that the plasma density at the magnetic field line is determined by these factors. The final aim of this study is to monitor and study time-dependent changes in the plasmaspheric plasma distributions by using ground magnetic field observations. For this purpose, we are working in the following three research phases. The first phase is to confirm the possibility of identifying FLR at low-latitudes (L~1.3). The second phase is to examine the correlation between FLR and solar wind parameters. The third phase is to estimate the plasma density from the FLR data, and monitor the density in a continuous manner. We are now in the third phase, and we report here the results of the first two phase. In the first phase, in order to investigate features of FLR close to the Earth, we installed three magnetometers in Japan at L~1.3 (at Kawatabi, Zaou, and Iitate), and started observing ULF geomagnetic pulsations. Each adjacent stations are separated in latitude by 50 to 100 km. The magnetic field data from these stations and Kakioka geomagnetic observatory, Japan, were analyzed by using the amplitude-ratio method and the cross-phase method. As a result, we identified FLR events whose frequency decreased with decreasing geomagnetic latitude; we infer that this feature was caused by heavy ion mass loading to low-L field lines. In the second phase, we studied the dependence of the occurrence probability of the above-identified FLR events on solar wind

  2. The response of local power grid at low-latitude to geomagnetic storm: An application of the Hilbert Huang transform

    NASA Astrophysics Data System (ADS)

    Liu, Jin; Wang, Chuan-Bing; Liu, Lu; Sun, Wei-Huai

    2016-04-01

    The Hilbert-Huang transform (HHT) is an adaptive data analysis method that can accommodate the variety of data generated by nonlinear and nonstationary processes in nature. In this paper, we focus on the small geomagnetically induced current (GIC) at the local substations in low-latitude power grid of China, responding to a moderate storm on 14-18 July 2012. The HHT is applied to analyze the neutral point currents (NPCs) of transformers measured at different substations, and the GIC indices converted from local geomagnetic field measurements. The original data are decomposed into intrinsic mode functions (IMFs) using the ensemble empirical mode decomposition. After removal of the quasi-diurnal components related with the solar quiet variation, the IMFs representing storm disturbances are transformed into Hilbert energy spectra. The results show that some transformers have more or less responses to the moderate storm in the form of Hilbert energy spectra with the frequency around 2-3 mHz. A comparison on the amplitude changes of the spectra total energy of NPCs' perturbation during storm time intervals at different sites suggests that a shell type of three-phase single transformer group seems to be more vulnerable in the storm. Although the low-latitude power grids usually show very small GIC, these can be used to investigate the potential risk of space weather to the system.

  3. Thermionic Energy Conversion (TEC) topping thermoelectrics

    NASA Technical Reports Server (NTRS)

    Morris, J. F.

    1981-01-01

    Performance expectations for thermionic and thermoelectric energy conversion systems are reviewed. It is noted that internal radiation effects diminish thermoelectric figures of merit significantly at 1000 K and substantially at 2000 K; the effective thermal conductivity contribution of intrathermoelectric radiative dissipation increases with the third power of temperature. It is argued that a consideration of thermoelectric power generation with high temperature heat sources should include utilization of thermionic energy conversion (TEC) topping thermoelectrics. However TEC alone or TEC topping more efficient conversion systems like steam or gas turbines, combined cycles, or Stirling engines would be more desirable generally.

  4. An empirical model of ionospheric total electron content (TEC) near the crest of the equatorial ionization anomaly (EIA)

    NASA Astrophysics Data System (ADS)

    Hajra, Rajkumar; Chakraborty, Shyamal Kumar; Tsurutani, Bruce T.; DasGupta, Ashish; Echer, Ezequiel; Brum, Christiano G. M.; Gonzalez, Walter D.; Sobral, José Humberto Andrade

    2016-07-01

    We present a geomagnetic quiet time (Dst > -50 nT) empirical model of ionospheric total electron content (TEC) for the northern equatorial ionization anomaly (EIA) crest over Calcutta, India. The model is based on the 1980-1990 TEC measurements from the geostationary Engineering Test Satellite-2 (ETS-2) at the Haringhata (University of Calcutta, India: 22.58° N, 88.38° E geographic; 12.09° N, 160.46° E geomagnetic) ionospheric field station using the technique of Faraday rotation of plane polarized VHF (136.11 MHz) signals. The ground station is situated virtually underneath the northern EIA crest. The monthly mean TEC increases linearly with F10.7 solar ionizing flux, with a significantly high correlation coefficient (r = 0.89-0.99) between the two. For the same solar flux level, the TEC values are found to be significantly different between the descending and ascending phases of the solar cycle. This ionospheric hysteresis effect depends on the local time as well as on the solar flux level. On an annual scale, TEC exhibits semiannual variations with maximum TEC values occurring during the two equinoxes and minimum at summer solstice. The semiannual variation is strongest during local noon with a summer-to-equinox variability of ~50-100 TEC units. The diurnal pattern of TEC is characterized by a pre-sunrise (0400-0500 LT) minimum and near-noon (1300-1400 LT) maximum. Equatorial electrodynamics is dominated by the equatorial electrojet which in turn controls the daytime TEC variation and its maximum. We combine these long-term analyses to develop an empirical model of monthly mean TEC. The model is validated using both ETS-2 measurements and recent GNSS measurements. It is found that the present model efficiently estimates the TEC values within a 1-σ range from the observed mean values.

  5. Diurnal and seasonal variation of the nighttime OH (8-3) emission at low latitudes

    SciTech Connect

    Abreu, V.J.; Yee, J.H. )

    1989-09-01

    Nighttime morphological maps of the hydroxyl emission (8-3 band) measured by the Visible Airglow Experiment on board the Atmosphere Explorer E satellite are presented for solstice and equinox conditions. The volume emission rate profile of the emission was determined by inverting satellite perigee observations. This profile was later used to convert limb measurements into zenith intensities of the emission. A theoretical model has been used to correct twilight observations for the presence of the thermospheric O{sup +}({sup 2}P) emission at 7,320-7,330 {angstrom}. The derived morphology agrees well with ground based measurements and theoretical simulations.

  6. Variations in ion composition at middle and low latitudes from Isis 2 satellite

    NASA Technical Reports Server (NTRS)

    Breig, E. L.; Hoffman, J. H.

    1975-01-01

    The paper describes absolute ion concentration measurements with an ion mass spectrometer on the Isis 2 satellite and discusses features of the ion composition near a fixed altitude of 1400 km as they relate to longitudinal and latitudinal variations at low and middle latitudes. Two distinct classes of daytime ionospheric behavior are observed. The data obtained confirm the strong solar-geomagnetic seasonal control over the topside ion distribution. The new phenomena associated with the observed longitudinal dependence of the ion composition at 1400 km demonstrate the existence of complex physical processes which take place in this region of the ionosphere.

  7. Response of the low-latitude D region ionosphere to extreme space weather event of 14-16 December 2006

    NASA Astrophysics Data System (ADS)

    Kumar, Sushil; Kumar, Abhikesh; Menk, Frederick; Maurya, Ajeet K.; Singh, Rajesh; Veenadhari, B.

    2015-01-01

    response of the D region low-latitude ionosphere has been examined for extreme space weather event of 14-16 December 2006 associated with a X1.5 solar flare and an intense geomagnetic storm (Dst = -146 nT) using VLF signals from Northwest Cape, Australia (NWC) (19.8 kHz) and Lualualei, Hawaii (callsign NPM) (21.4 kHz) transmitters monitored at Suva (Geographic Coordinates, 18.10°S, 178.40°E), Fiji. Modeling of flare associated amplitude and phase enhancements of NWC (3.6 dB, 223°) and NPM (5 dB, 153°) using Long-Wave Propagation Capability code shows reduction in the D region reflection height (H') by 11.1 km and 9.4 km, and enhancement in ionization gradients described by increases in the exponential sharpness factor (β) by 0.122 and 0.126 km-1, for the NWC and NPM paths, respectively. During the storm the daytime signal strengths of the NWC and NPM signals were reduced by 3.2 dB on 15 and 16 December (for about 46 h) and recovered by 17 December. Modeling for the NWC path shows that storm time values of H' and β were reduced by 1.2 km and 0.06 km-1, respectively. Morlet wavelet analysis of signal amplitudes shows no clearly strong signatures of gravity wave propagation to low latitudes during the main and recovery phases. The reduction in VLF signal strength is due to increased signal attenuation and absorption by the Earth-ionosphere waveguide due to storm-induced D region ionization changes and hence changes in D region parameters. The long duration of the storm effect results from the slow diffusion of changed composition/ionization at D region altitudes compared with higher altitudes in the ionosphere.

  8. First results on climatological response of Indian low latitude ionosphere to geomagnetic storms during solar cycle 23 and 24

    NASA Astrophysics Data System (ADS)

    Suresh, Sunanda; Dashora, Nirvikar

    2016-07-01

    For the first time, a climatological response of low latitude ionosphere to geomagnetic storms is presented using long term global ionospheric maps (GIM) data from June 1998 to June 2015 covering two solar cycles 23 and 24. The results are not only the first from Indian region but also the first around the globe to bring latitudinal character of daytime ionospheric storms with use of newly defined criteria. The results are presented for daytime forenoon and afternoon sectors under minor, moderate and major ionospheric storm categories based on minimum Dst index criterion. For the first time the effectiveness of storms is identified using monthly standard deviation as an indicator of the day-to-day variability in equatorial and low latitude ionosphere. Thus results on climatology are definitive and form a data base that would be comparable to statistical results from any other longitude and time. Seasonal statistics for total storms, effective positive and negative storms, and amplitude of mean seasonal perturbation in total electron content are obtained. Total and effective storms are found to be higher in solar cycle 23 than in 24 and only couple of effective storms occurred during low solar activity 2007-2009 that also in minor category. Afternoon sector is found to be favourable for occurrence of maximum number of effective positive storms. A latitudinal preference is found for a given storm to be effective in either time sectors. Equinoctial asymmetry in ionospheric response both in terms of occurrence and perturbation amplitude is found. September equinoxes are found to bear maximum total, effective positive and negative storms. Winters are found more prone to negative storms whereas summers have recorded minimum number of either of storms and minimum perturbation amplitudes.

  9. Lightning-Generated Whistler Waves Observed by Probes On The Communication/Navigation Outage Forecast System Satellite at Low Latitudes

    NASA Technical Reports Server (NTRS)

    Holzworth, R. H.; McCarthy, M. P.; Pfaff, R. F.; Jacobson, A. R.; Willcockson, W. L.; Rowland, D. E.

    2011-01-01

    Direct evidence is presented for a causal relationship between lightning and strong electric field transients inside equatorial ionospheric density depletions. In fact, these whistler mode plasma waves may be the dominant electric field signal within such depletions. Optical lightning data from the Communication/Navigation Outage Forecast System (C/NOFS) satellite and global lightning location information from the World Wide Lightning Location Network are presented as independent verification that these electric field transients are caused by lightning. The electric field instrument on C/NOFS routinely measures lightning ]related electric field wave packets or sferics, associated with simultaneous measurements of optical flashes at all altitudes encountered by the satellite (401.867 km). Lightning ]generated whistler waves have abundant access to the topside ionosphere, even close to the magnetic equator.

  10. The role of the zonal ExB plasma drift in the low latitude ionosphere at solar minimum and maximum near equinox

    NASA Astrophysics Data System (ADS)

    Pavlov, Anatoli

    The F2-layer peak density, NmF2, and peak altitude, hmF2, which were observed by 12 ionospheric sounders during the geomagnetically quiet time periods at solar minimum (20 September 1964) and maximum (12-13 April 1958) are compared with those calculated by the threedimensional time-dependent theoretical model of the Earth's low and middle latitude ionosphere and plasmasphere. Major features of the data are reproduced by the model. The changes in NmF2 due to the zonal E ×B plasma drift are found to be inessential by day. It is shown that the model, which does not take into account the zonal E ×B plasma drift, underestimates night-time NmF2 up to the maximum factors of 2 (solar minimum) and 2.3 (solar maximum) at low geomagnetic latitudes. The night-time increase of NmF2 caused by the zonal E ×B plasma drift is less pronounced at -20° and 20° geomagnetic latitudes in comparison with that between -10° and 10° geomagnetic latitude. The longitude dependence of the calculated nighttime low latitude influence of the zonal E ×B plasma drift on NmF2 is explained in terms of the longitudinal asymmetry in B (the eccentric magnetic dipole is displaced from the Earth's center and the Earth's eccentric tilted magnetic dipole moment is inclined with respect to the Earth's rotational axis), and the variations of the wind induced plasma drift and the meridional E ×B plasma drift in geomagnetic longitude. The difference between the calculated value of hmF2 and that obtained when the zonal E ×B drift is omitted is essential by night and is not exceeding 17 km in the low latitude ionosphere. The model calculations show that over the geomagnetic equator the zonal E ×B plasma drift produces the increase in the electron density up to the maximum factors of 1.5 and 1.3 (solar minimum) and 2 and 1.6 (solar maximum) at 700 km and 1000 km altitude, respectively, and this increase is not significant above about 1500 km. The maximum effects of the zonal E ×B plasma drift on the

  11. Radar, satellite, and modelling studies of the low-latitude protonosphere. Ph.D. Thesis

    SciTech Connect

    Gonzalez, S.A.

    1994-01-01

    A study of the variations in the composition of the topside ionosphere at low and equatorial latitudes is presented. Observations of (H+)/n(sub e) are used to study the behavior of the transition altitude over Arecibo during summer solstice for both solar minimum and solar maximum conditions. The solar maximum observations are complemented with DE-2 RPA data from passes over Arecibo to estimate the concentration of helium ions in the topside at that location. The transition altitude over Arecibo is found to be very dependent on solar activity level. For summer solar maximum conditions, the transition altitude varies anywhere from 2000 to 2500 km in altitude during the day (depending on solar flux) down to 1000 km at night. The DE-2 composition data show that during solar maximum conditions, helium ions are an important fraction of the total ionospheric plasma near 900 km over Arecibo with typical concentrations od 1-3 x 10(exp 4) ions cm(sup {minus}3). Observations from the BIMS and RPA instruments aboard the AEE spacecraft are used to study O+, H+, and He+ concentrations in the equatorial topside ionosphere during solar minimum conditions. For these conditions He+ is found to be a minor species and essentially negligible at all times. The transition altitude is found to be near 800 km during the day and below 600 km during the night for all seasons. Finally, the authors present simulations using the University of Sheffield coupled ionosphere thermosphere theoretical model. The results of these simulations are used to try to reproduce their observations and also to study the effect of equatorial E x B drifts on the transition altitude. The model reproduces the major diurnal features in qualitative agreement with the Arecibo solar maximum conditions, the simulations predict peak helium ion concentrations in the topside over Arecibo for equinox with the lowest concentrations occurring during summer solstice.

  12. A low latitude Auroras catalogue from 1766 to 1797 (Padua, Italy)

    NASA Astrophysics Data System (ADS)

    De La Guía, M. C.; Dominguez-Castro, F.; Vaquero, J. M.; Bertolin, C.; Gallego, M. C.; Camuffo, D.

    2015-12-01

    It is presented a long term catalogue of aurorae from the observations done by Joseph Toaldo between 1766-1797 at La Specola (the Observatory) in Padua (Italy, 45º24'07.5''N, 11º52'06.8''E). Toaldo was interested in astrometeorology and was the prime mover and the first director of the Astronomic Observatory where he carried out valuable daily observations on both fields. He also taught astronomy and meteorology at the University of Padua. The data was collected from different historical document sources including the original manuscripts made by Toaldo which also contain meteorological readings. A total of 148 aurorae events were recovered from Toaldo's manuscripts. The data reliability was validated using time and season, percentage of the moon illuminated and aurorae directionality. The data shows a secular maximum of the auroral activity around 1780 that occurred at planetary scale. From 1789 onwards there is a sharp decrease of this activity marking the onset of the Dalton Minimum although the solar activity decreases less rapidly. It has also been collected geomagnetic declination measurements taken in Padua between 1725-1799. These geomagnetic observations are consistent with the geomagnetic model gufm1.

  13. Investigation of TEC Variations over Mid-Latitude during Quit and Disturbed Days of March 2015

    NASA Astrophysics Data System (ADS)

    Atıcı, Ramazan; Saǧır, Selçuk; Güzel, Esat

    2016-07-01

    The variations during 09-14-March-2015 quit days and 15-20 March 2015 disturbed days of Total Electron Content (TEC) values (provided by IONOLAB group) obtained by analysis the data from Ankara Global Position System (GPS) station of Turkey located at mid-latitude, IRI -2012 model the and IRI-PLUS model are investigated. Also, the variations of the geomagnetic, interplanetary and solar wind parameters are examined. As a result of investigations, TEC values from all three models are not change too much at quit days. Unlike, at the disturbed days, although IRI-2012 and IRI-PLUS TEC values are not change too much, a noticeable change in GPS-TEC values is occurred. GPS-TEC values are rapidly increased on 17-March 2015 to be severe magnetic storm (Dst = -124 nT). Then, on following days it was observed to significantly decrease. Thus, it is said that GPS-TEC values are more sensitive than IRI-2012 and IRI-PLUS models to variations occurred on disturbed days.

  14. Average low-latitude meridional electric fields from DE 2 during solar maximum

    SciTech Connect

    Maynard, N.; Aggson, T.; Herrero, F.; Liebrecht, M.

    1988-05-01

    Electric-field data from the double-probe vector electric-field instrument (VEFI) on the DE 2 spacecraft were analyzed to determine the average meridional electric-field (zonal ion flow) patterns in the region between + or - 30 deg magnetic latitude during solar maximum conditions. Over 300 passes were used to compile the data set. Data were projected to a constant 300-km altitude and to the equatorial plane assuming that the electric field along the magnetic field was zero. The average data set displayed a rapid increase of the downward meridional electric field with local time near 1800 MLT with the higher latitudes seeing the change first. A secondary nighttime maximum of this electric-field component was observed past midnight with the crossover to upward electric fields (westward ion flow) occurring between 0400 and 0500 MLT. A sharp return to near zero was observed between 1200 and 1300. Typical average amplitudes range between 3 and 6 mV/m. No consistent variations with magnetic activity were observed. Although the daily variation in the zonal ion flow is dominated by the diurnal term, a net superrotation is evident in the harmonic analysis. The superrotation is strongest near the equator and decreases with latitude, because of the disturbance dynamo. The higher order harmonics up through the quatrediurnal term are also of significant magnitude in the analysis of the shape of the daily variation. Close similarity is seen to the zonal neutral winds indicating that they form the principal driving force. The magnitudes of the electric field derived ion drift are somewhat higher than the average F-region neutral-wind values.

  15. Average low-latitude meridional electric fields from DE 2 during solar maximum

    SciTech Connect

    Maynard, N.C. ); Aggson, T.L.; Herrero, F.A. ); Liebrecht, M.C. )

    1988-05-01

    Electric field data from the double probe vector electric field instrument (VEFI) on the DE 2 spacecraft have been analyzed to determine the average meridional electric field (zonal ion flow) patterns in the region between {plus minus} 30{degree} magnetic latitude during solar maximum conditions. The average data set displayed a rapid increase of the downward meridional electric field with local time near 1,800 MLT with the higher latitudes seeing the change first. A secondary nighttime maximum of this electric field component was observed post midnight with the crossover to upward electric fields (westward ion flow) occurring between 0400 and 0500 MLT. A sharp return to near zero was observed between 1,200 and 1,300. Typical average amplitudes range between 3 and 6 mV/m. No consistent variations with magnetic activity were observed. Although the daily variation in the zonal ion flow is dominated by the diurnal term, a net superrotation is evident in the harmonic analysis. The superrotation is strongest near the equator and decreases with latitude, because of the disturbance dynamo. The higher order harmonics up through the quatrediurnal term are also of significant magnitude in the analysis of the shape of the daily variation. Cose similarity is seen to the zonal neutral winds indicating that they form the principal driving force. The magnitudes of the electric field derived ion drift are somewhat higher than the average F region neutral wind values. This along with the higher order harmonic content argues for the need to develop fully coupled E and F region model depicting the ionosphere and thermosphere interactions in a self-consistent fashion.

  16. Scintillation-producing Fresnel-scale irregularities associated with the regions of steepest TEC gradients adjacent to the equatorial ionization anomaly

    NASA Astrophysics Data System (ADS)

    Muella, M. T. A. H.; Kherani, E. A.; de Paula, E. R.; Cerruti, A. P.; Kintner, P. M.; Kantor, I. J.; Mitchell, C. N.; Batista, I. S.; Abdu, M. A.

    2010-03-01

    Using ground-based GPS and digital ionosonde instruments, we have built up at latitudes of the equatorial ionization anomaly (EIA), in the Brazilian sector, a time-evolving picture of total electron content (TEC), L-band amplitude scintillations, and F region heights, and we have investigated likely reasons for the occurrence or suppression of equatorial scintillations during the disturbed period of 18-23 November 2003. During the prestorm quiet nights, scintillations are occurring postsunset, as expected; however, during the storm time period, their spatial-temporal characteristics and intensity modify significantly owing to the dramatic changes in the ionospheric plasma density distribution and in the temporal evolution of TEC. The two-dimensional maps showing both TEC and amplitude scintillations revealed strong evidence of turbulences at the Fresnel length (causing scintillations) concurrent with those regions of steepest TEC gradients adjacent to the crests of the EIA. The largest density gradients have been found to occur in an environment of increased background electron density, and their spatial distribution and location during the disturbed period may differ significantly from the magnetic quiet night pattern. However, in terms of magnitude the gradients at equatorial and low latitudes appear to not change during both magnetic quiet and disturbed conditions. The scenarios for the formation or suppression of scintillation-producing Fresnel-scale irregularities during the prestorm quiet nights and disturbed nights are discussed in view of different competing effects computed from numerical simulation techniques.

  17. Mapping of water frost and ice at low latitudes on Mars

    NASA Astrophysics Data System (ADS)

    Carrozzo, F. G.; Bellucci, G.; Altieri, F.; D'Aversa, E.; Bibring, J.-P.

    2009-10-01

    This paper reports on mapping of water frost and ice on Mars, in the range of latitudes between 30°S and 30°N. The study has been carried out by analysing 2485 orbits acquired during almost one martian year by the Mars Express/OMEGA imaging spectrometer. Water frost/ice is identified by the presence of ˜1.5 μm, ˜2 μm and ˜3.0 μm absorptions. Although the orbits analysed in this study cover all seasons, water frost/ice is observed only near the aphelion seasons, at Ls = 19° and at Ls = 98-150°. Water frost/ice is detected mainly on the southern hemisphere between 15°S and 30°S latitude while it has not been identified within 15°S-15°N. In the northern hemisphere, the water frost/ice detection is complicated by the presence of clouds. Usually, water frost/ice is found in shadowed areas, while in few cases it is exposed to the sunlight. This indicates a clear relationship with the local illumination conditions on the slopes which favour the water frost/ice deposition on the surface when the temperatures are very low. OMEGA observations span from 10 to 17 LT and the frost/ice is detected mainly between 15 and 16 LT, with practically no detection before 13 LT. We think this is due to the fact that the 10-12 LT observations occur at large distances and it is not a local time effect. A thermal model is used to determine the deposition conditions on the sloped surfaces where water frost/ice has been found. There, daily atmospheric saturation does not occur on pole facing 10-25° slopes with current water vapour abundances but only by assuming values greater than 40 pr μm. Moreover, the water frost/ice is not detected during the northern winter, even if the thermal model foresees daily saturation on 25° slopes.

  18. TEC Longitude Difference Using GIMS and the IRI Model

    NASA Astrophysics Data System (ADS)

    Natali, Maria Paula; Meza, Amalia Margarita; Mendoza, Gastón

    2016-07-01

    The main geomagnetic field declination has a global distribution with positive and negative values showing maximum east-west differences over North America and Oceania and minimum differences over America and Asia. Several authors study one or more of these regions using TEC data derived from GNSS observations to describe variations in TEC. They reported a pronounced longitudinal variation respect to zero magnetic declination. One of the important factors that cause the longitude difference at mid-latitude is a combined effect of the longitude variations of magnetic declination and the variations of the zonal thermospheric winds with local time. We propose to study this effect using Global Ionospheric Maps (GIMs) and the respective TEC values generated from the International Reference Ionospheric (IRI) model, during a solar cycle, applying Principal Component Analysis (PCA). Our works is focused over different local times and regions at mid-latitude. PCA involves a mathematical procedure that transforms a number of correlated variables into a number of uncorrelated variables using the data itself. The spatial structure of the ionosphere variability and its temporal evolution, together are called modes, and there are ordered according to their percentage of the variability of data from highest to lowest. In this analysis the first mode has more than the 90 % of the variability, representing the nominal behavior of the ionosphere, and the second and third modes are the more important for our analysis, because they show the strong longitudinal variation in the different regions using either GIMs or the IRI model.

  19. Global structure of ionospheric TEC anomalies driven by geomagnetic storms

    NASA Astrophysics Data System (ADS)

    Pancheva, D.; Mukhtarov, P.; Andonov, B.

    2016-07-01

    This study examines the structure and variability of the ionospheric TEC anomalies driven by geomagnetic storms. For this purpose the CODE global ionospheric TEC data from four geomagnetically disturbed periods (29 October-1 November 2003, 7-10 November 2004, 14-15 December 2006, and 5-6 August 2011) have been considered. By applying the tidal analysis to the geomagnetically forced TEC anomalies we made an attempt to identify the tidal or stationary planetary wave (SPW) signatures that may contribute to the generation of these anomalies. It has been found that three types of positive anomalies with different origin and different latitudinal appearance are observed. These are: (i) anomalies located near latitudes of ±40° and related to the enhancement and poleward moving of the equatorial ionization anomaly (EIA) crests; (ii) anomalies located near latitudes of ±60° and seen predominantly in the night-side ionosphere, and (iii) very high latitude anomalies having mainly zonally symmetric structure and related to the auroral heating and thermospheric expansion. The decomposition analysis revealed that these anomalies can be reconstructed as a result of superposition of the following components: zonal mean (ZM), diurnal migrating (DW1), zonally symmetric diurnal (D0), and stationary planetary wave 1 (SPW1).

  20. Low-Latitude Solar Wind During the Fall 1998 SOHO-Ulysses Quadrature

    NASA Technical Reports Server (NTRS)

    Poletto, G.; Suess, S. T.; Biesecker, D. A.; Esser, R.; Gloeckler, G.; Ko, Y.-K.; Zurbuchen, T. H.

    2002-01-01

    Solar and Heliospheric Observatory (SOH0)-Ulysses quadratures occur when the SOHO-Sun-Ulysses-included angle is 90 deg. These offer the opportunity to directly compare properties of plasma parcels, observed by SOHO [Dorningo et al.] in the low corona, with properties of the same parcels measured, in due time, in situ, by Ulysses [ Wenzel et al]. We refer the reader to Suess et al. for an extended discussion of SOHO-Ulysses quadrature geometry. Here it suffices to recall that there are two quadratures per year, as SOHO makes its one-year revolution around the Sun. This, because SOHO is at the L1 Lagrangian point, in essentially the same place as the Earth, while Ulysses is in a near-polar -5-year solar orbit with a perihelion of 1.34 AU and aphelion of 5.4 AU.

  1. Dual-propagation-path entry of lightning-generated whistlers into the low-latitude magnetosphere

    NASA Astrophysics Data System (ADS)

    Jacobson, A. R.; Holzworth, R.; Pfaff, R. F., Jr.; Heelis, R. A.

    2015-12-01

    Using burst-mode VLF recordings from the VEFI payload on the C/NOFS satellite, we have studied dual-propagation-path penetration of lightning-generated whistlers into the magnetosphere. We use a unique automated retrieval of the wave dispersion(s) of whistler-like features in the recordings, not constrained by assuming single dispersion. We use the measured polarization of the wave, plus ion composition from the CINDI payload, to infer initial wavevector for launching a reverse raytrace to infer the transionospheric path from the Earth's atmosphere to the satellite. We use the WWLLN lightning-location system to ground-truth the origin of many of the whistlers observed at C/NOFS. We combine these elements to elucidate the presence of more than one propagation path for the outbound whistlers.

  2. On the ionospheric impact of recent storm events on satellite-based augmentation systems in middle and low-latitude sectors

    NASA Technical Reports Server (NTRS)

    Komjathy, Attila; Sparks, Lawrence; Mannucci, Anthony J.; Pi, Xiaoqing

    2003-01-01

    The Ionospheric correction algorithms have been characterized extensively for the mid-latitude region of the ionosphere where benign conditions usually exist. The United States Federal Aviation Administration's (FAA) Wide Area Augmentation System (WAAS) for civil aircraft navigation is focused primarily on the Conterminous United States (CONUS). Other Satellite-based Augmentation Systems (SBAS) include the European Geostationary Navigation Overlay Service (EGNOS) and the Japanese Global Navigation Satellite System (MSAS). Researchers are facing a more serious challenge in addressing the ionospheric impact on navigation using SBAS in other parts of the world such as the South American region on India. At equatorial latitudes, geophysical conditions lead to the so-called Appleton-Hartree (equatorial) anomaly phenomenon, which results in significantly larger ionospheric range delays and range delay spatial gradients than is observed in the CONUS or European sectors. In this paper, we use GPS measurements of geomagnetic storm days to perform a quantitative assessment of WAAS-type ionospheric correction algorithms in other parts of the world such as the low-latitude Brazil and mid-latitude Europe. For the study, we access a world-wide network of 400+ dual frequency GPS receivers.

  3. Long-term Trends in Mesospheric Temperatures at high and low latitudes derived from OH airglow spectra of Kiruna FTS and Sloan Digital Sky Survey

    NASA Astrophysics Data System (ADS)

    Kim, Yongha; Kim, Jeong-Han; Kim, Gawon; Lee, Youngsun

    2016-07-01

    We have analyzed mesospheric temperatures from OH airglow measurements with Fourier Transform Spectrometer (FTS) in the period of 2003 - 2012 at Kiruna (67.9°N, 21.1°E). We also derived mesospheric temperatures from rotational emission lines of the OH airglow (8-3) band in the sky spectra of Sloan Digital Sky Survey (SDSS) in the period of 2000 - 2014. The main objective of SDSS is to make a detailed 3-dimensional map of the universe by observing images and spectra of various celestial objects at Apache Point Observatory (APO, 32°N 105°W). From both temperature sets we first estimated the solar responses of mesospheric temperatures to F10.7 variation and the seasonal variation of mesospheric temperatures. After removing the solar response, we found the long-term mesospheric temperature trends of -4 ˜-6.6 K/decade at Kiruna and -0.02 ± 0.7 K/decade at Apache Point. Our results indicate significant cooling trend at the high latitude but very little or no cooling at the low latitude. Although both trends are comparable and consistent with other studies, the temperature trend from SDSS spectra should be regarded as unique contribution to global monitoring of climate change because the SDSS project is completely independent of climate studies.

  4. Two encounters with the flank low-latitude boundary layer - Further evidence for closed field topology and investigation of the internal structure

    NASA Technical Reports Server (NTRS)

    Traver, D. P.; Mitchell, D. G.; Williams, D. J.; Frank, L. A.; Huang, C. Y.

    1991-01-01

    The structure of the flank low-latitude boundary layer (LLBL) is examined through differential energy spectra and particle angular anisotropies for traversals of the dawn flank (December 19, 1977) and dusk flank (July 7, 1978) during periods of predominantly northward magnetosheath field orientation. Spectra are presented that were obtained from combined ISEE 1 low-energy-proton and electron-differential-energy-analyzer and medium-energy-particle-instrument data extending over the 200-eV/q to 2-MeV energy range for the plasma sheet, stagnation region, outer LLBL, and magnetosheath regions. The stagnation region and the outer LLBL are each a mixture of plasma-sheet and magnetosheath populations, but the stagnation region contains a relatively higher fraction of plasma sheet particles, consistent with its placement earthward of the outer LLBL. Evidence for energization of thermal electrons appears during the dusk flank crossing. Bidirectional field-aligned ion distributions are observed with typically 5-to-1 enhancement of the flux along the magnetic field during certain portions of the dusk flank crossing.

  5. Inevitability of low-latitude melting on Mars: implications for the sedimentary record

    NASA Astrophysics Data System (ADS)

    Kite, E. S.; Manga, M.; Halevy, I.

    2010-12-01

    The recently published MOC-NA database of sedimentary rock locations shows an extraordinary concentration of sedimentary rocks near the equator - 64% at <10° latitude (59% when Valles Marineris is excluded). These rocks overwhelmingly date from the late Noachian to the middle Hesperian, when many sulfate-bearing deposits formed. With the reasonable assumption that liquid water is required for lithification, we hypothesize that liquid water only occurred near the equator during this era. As an initial test of this hypothesis, we model melting on Early Mars assuming a weak greenhouse effect similar to today. Combining the Laskar group's chaotic diffusion parameterization of orbital evolution with simple assumptions about ice stability, we show that melting under a weak greenhouse is most likely when (1) obliquity is high, (2) eccentricity is moderately high, (3) at equinox, (4) when the longitude of perihelion corresponds to equinox, and (5) at the equator. We compare discharge results from a snowpack Energy Balance Model to published discharge constraints at three Early Mars locations - SW Melas, Gale-Aeolis-Zephyria, and Meridiani. If these discharges cannot be reproduced under a weak greenhouse similar to today, then a stronger Early Mars greenhouse effect is required to explain these observations. We show how the fraction of a precession cycle during which melting occurs - the 'stratigraphic wet fraction' - can be used to set a lower bound on the strength of the Early Mars greenhouse effect. The stratigraphic wet fraction can be measured by MSL at Gale.

  6. Energetic particles and ionization in the nighttime middle and low latitude ionosphere

    NASA Technical Reports Server (NTRS)

    Voss, H. D.; Smith, L. G.

    1977-01-01

    Seven Nike Apache rockets, each equipped with an energetic particle spectrometer (12 E 80 keV) and electron-density experiments, were launched from Wallops Island, Virginia and Chilca, Peru, under varying geomagnetic conditions near midnight. At Wallops Island the energetic particle flux (E 40 keV) is found to be strongly dependent on Kp. The pitch-angle distribution is asymmetrical about a peak at 90 D signifying a predominately quasi-trapped flux and explaining the linear increase of count rate with altitute in the altitude region 120 to 200 km. The height-averaged ionization rates derived from the electron-density profiles are consistent with the rates calculated from the observed total particle flux for magnetic index Kp 3. In the region 90 to 110 km it is found that the nighttime ionization is primarily a result of Ly-beta radiation from the geocorona and interplanetary hydrogen for even very disturbed conditions. Below 90 km during rather disturbed conditions energetic electrons can be a significant ionization source. Two energetic particle precipitation zones have been identified at midlatitudes.

  7. Holocene geomagnetic field variations from low latitude site: contribution from the Canary Islands

    NASA Astrophysics Data System (ADS)

    Kissel, Catherine; Laj, Carlo; Rodriguez-Gonzalez, Alejandro; Perez-Torrado, Francisco; Carrracedo, Juan-Carlos; Wandres, Camille

    2016-04-01

    Islands, our data allow to construct a curve illustrating the Earth magnetic field intensity fluctuations for Southwestern Europe/Western Africa. This curve shows three maximum broad intensity features which are also observed in the Middle East and in Central Asia indicating that they have a very large geographical extent. These maxima do not all appear clearly in the models of variations of the dipolar field intensity which have an insufficient resolution. Within the broad maxima characterizing the first millenium BC, regional variability is observed in particular with high PI around 1000 BC in the middle East and around 600 BC in southwestern Europe. This corresponds to a westward drift rate of 0.1° longitude/yr, consistent with the values generally accepted for the westward drift of the non-dipole field.

  8. Low-latitude ionospheric D region dependence on solar zenith angle

    NASA Astrophysics Data System (ADS)

    Thomson, Neil R.; Clilverd, Mark A.; Rodger, Craig J.

    2014-08-01

    Phase and amplitude measurements of VLF radio signals on a short, nearly all-sea path between two Hawaiian Islands are used to find the height and sharpness of the lower edge of the daytime tropical D region as a function of solar zenith angle (SZA). The path used was from U.S. Navy transmitter NPM (21.4 kHz) on Oahu to Keauhou, 306 km away, on the west coast of the Big Island of Hawaii, where ionospheric sensitivity was high due to the destructive interference between the ionospherically reflected wave and the ground wave, particularly around the middle of the day. The height and sharpness are thus found to vary from H' = 69.3 ± 0.3 km and β = 0.49 ± 0.02 km-1 for SZA ~10°, at midday, to H' > 80 km and β ~ 0.30 km-1 as the SZA approached ~70°-90°, near dawn and dusk for this tropical path. Additional values for the variations of H' and β with solar zenith angle are also found from VLF phase and amplitude observations on other similar paths: the short path, NWC to Karratha (in NW Australia), and the long paths, NWC to Kyoto in Japan and NAU, Puerto Rico, to St. John's Canada. Significant differences in the SZA variations of H' and β were found between low and middle latitudes resulting from the latitudinally varying interplay between Lyman α and galactic cosmic rays in forming the lower D region. Both latitude ranges showed β < 0.30 km-1 during sunrise/sunset conditions.

  9. Evaluation of NeQuick 2 derived vertical TEC at three northern mid-latitude locations

    NASA Astrophysics Data System (ADS)

    Alazo Cuartas, Katy; Radicella, Sandro M.; Nava, Bruno; Lazo Olazabal, Bienvenido; Migoya Orue, Yenca O.

    2013-04-01

    NeQuick 2 is the latest version of the three-dimensional and time dependent ionospheric electron density model developed at the T/ICT4D (former ARPL) of the Abdus Salam International Centre for Theoretical Physics (ICTP) - Trieste, Italy and at the Institute for Geophysics, Astrophysics and Meteorology of the University of Graz, Austria. The purpose of this work is to identify possible limitations of the model. Therefore, the ability of NeQuick 2 in reproducing the vertical Total Electron Content (vTEC) derived from GPS observations using different input sources has been evaluated. The daily solar flux in 10.7 cm, the monthly smoothed solar flux and the hourly daily ionosonde derived F2 peak parameters, foF2 and hmF2, have been therefore used as model drivers to compute the vTEC at the relevant locations. Peak parameter values from three ionosonde stations (Ebre, El Arenosillo and Ramey) and GPS-derived vTEC data obtained from the corresponding co-located receivers (ebre, sfer, pur3) have been processed for the present work. The available data for the years 2000 and 2004, corresponding to high and moderate solar activity periods, have been considered to be able to estimate the model performance in a wide range of geophysical conditions. For each location, the data analysis has been based on statistical comparisons between experimental and retrieved vTEC. The results indicate that the differences between NeQuick 2-computed and GPS-derived vTEC exhibit well defined diurnal and seasonal patterns that depend on the location and period considered. On average, NeQuick 2 underestimates the vTEC during nighttime, mainly in the winter months and slightly during the summer months. In the daytime hours on the European locations, the model generally overestimates the vTEC in winter months, having an opposite behavior in the summer months. At PRJ18/pur3 location the NeQuick 2 response is more complex. During high solar activity, the daily difference between modeled and GPS

  10. Validation of IRI-2012 TEC model over Ethiopia during solar minimum (2009) and solar maximum (2013) phases

    NASA Astrophysics Data System (ADS)

    Asmare, Yekoye; Kassa, Tsegaye; Nigussie, Melessew

    2014-06-01

    This paper investigates the capacity of the latest version of the International Reference Ionosphere (IRI-2012) model in predicting the vertical Total Electron Content (vTEC) over Ethiopian regions during solar minimum (2009) and solar maximum (2013) phases. This has been carried out by comparing the IRI-2012 modeled and experimental vTEC inferred from eight ground based dual frequency GPS (Global Positioning System) receivers installed recently at different regions of the country. In this work, the diurnal, monthly and seasonal variation in the measured vTEC have been analyzed and compared with the IRI-2012 modeled vTEC. During the solar minimum phase, the lowest and highest diurnal peak of the experimental vTEC are observed in July and October, respectively. In general, the diurnal variability of vTEC has shown minimum values around 0300 UT (0600 LT) and maximum values between around 1000 and 1300 UT (1300 and 1600 LT) during both solar activity phases. Moreover, the maximum and minimum monthly and seasonal mean hourly vTEC values are observed in October and July and in the March equinox and June solstice, respectively. It is also shown that the IRI-2012-model better predicts the diurnal vTEC in the time interval of about 0000-0300 UT (0300-0600 LT) during the solar minimum phase. However, the model generally overestimates the diurnal vTEC except in the time interval of about 0900-1500 UT (1200-1800 LT) during the solar maximum phase. The overall result of this work shows that the diurnal vTEC prediction performance of the model is generally better during the solar minimum phase than during solar maximum phase. Regarding the monthly and seasonal prediction capacity of the model, there is a good agreement between the modeled and measured monthly and seasonal mean hourly vTEC values in January and December solstice, respectively. Another result of the work depicts that unlike the GPS-TEC the IRI-2012 TEC does not respond to the effect resulted from geomagnetic

  11. SEVAN particle-detector network located at Middle-Low latitudes for Solar Physics and Space Weather research

    NASA Astrophysics Data System (ADS)

    Chilingarian, Ashot

    A network of middle to low latitude particle detectors called SEVAN (Space Environmental Viewing and Analysis Network) is planned in the framework of the International Heliophysical Year (IHY), to improve fundamental research of the Solar accelerators and Space Weather conditions. The network will detect changing fluxes of secondary cosmic rays at different altitudes, latitudes and altitudes those constituting powerful integrated device in exploration of solar modulation effects. Surface particle detectors measure time series of secondary particles born in cascades originated in the atmosphere by nuclear interactions of the "primary" protons and nuclei accelerated in galaxy. During violent solar explosions additional particles, accelerated at sun's environments, can add to this "background" flux. If solar particles are energetic enough they also will generate secondary particles reaching earth surface. Therefore, registration of changing time series of secondary particles shed light on the high-energy particle acceleration mechanisms by solar flares and Coronal Mass Ejection driven shocks. Network of particle detectors located at middle-to-low latitudes is sensitive to the highest energy solar particles. The enigma of particle acceleration in supernovae remnants, super-massive black holes, clusters of galaxies can be researched using particle beams accelerated by sun and detected at earth. The shock acceleration is a universal process responsible for the same physical process (particle acceleration) on the different scales. Time series of intensities of high energy particles can also provide highly cost-effective information on the key characteristics of the disturbances of interplanetary magnetic field. Recent results on of the detection of the extreme solar events (2003, 2005) by the monitors of the Aragats Space-Environmental Center (ASEC) illustrate wide possibilities opening with introduction of new particle detectors measuring neutron, electron and muon

  12. Response of low latitude D-region ionosphere to the Total Solar Eclipse of 22 July 2009, deduced from ELF/VLF analysis

    NASA Astrophysics Data System (ADS)

    Singh, A. K.; Singh, R.; Singh, A. K.

    2011-12-01

    Response of the D-region of the ionosphere to the total solar eclipse of 22 July 2009 at low latitude, Varanasi (geomagnetic lat = 140 55'N, longitude = 1540 E, dip. angle = 37.30) was investigated using ELF/VLF radio signal. The solar eclipse started at 05:30:04.4 hrs IST and lasted up to 07:27 hrs IST with totally from 6.25 IST to 6.27 IST.The changes in D-region ionospheric VLF reflection heights and electron density during eclipse have been estimated from tweek analysis. The reflection height increased from ~90 km from the first occurrence of tweek to about 93-94 km at the totality and then decreased to ~89 km at the end of the eclipse. The reflection heights are lower by 2-3 km as compared to the usual nighttime tweek reflection heights. The electron density is found to vary between 25-27 cm-3 at the reflection heights. The significant increase in tweek reflection height of about 15 km during the eclipse as compared to the daytime (morning) reflection heights of ~ 78 km is observed. Observations suggest that about 30-40% obscuration of solar disc can lead to the tweeks occurrence which otherwise occur only in the nighttime. A significant increase of 3dB in the strength of the amplitude of VLF signal is observed around the time of TSE as compared to a control day. These low latitude ionospheric perturbations on the eclipse day are discussed and compared with other normal days. During a solar eclipse, the decrease in solar flux due to moon's shadow causes sudden change in the D-region physical and chemical processes. During the totality due to blocking of Lyman-α 1215Å (major D-region ionizing radiation) by moon's umbral shadow, the electron density decreases drastically towards the nighttime values [Smith, 1972]. During the TSE, there was no production of ionization in the ionosphere and the ions and electrons in the lowest part of it recombined at a rapid rate resulting a depletion in the electron density in the 'D' region of the Ionosphere and hence an

  13. Low latitude palaeoclimate dynamics

    NASA Astrophysics Data System (ADS)

    Kawahata, H.; Maeda, L.

    2003-04-01

    Large heat storage capacity in the western equatorial Pacific (WEP) has played an important role in modulating global climate. The drying up of the huge continental platform around Indonesian Maritime continent during low sea level increased the supply rate of lithogenic matter to the ocean. Positive correlation between lithogenic content and the relative abundance of fern spores suggests that lithogenics in C4402 (3N, 135E, 4402 m water depth) could be derived from coastal lowland of New Guinea. Less rainfall during glacial times (OIS 2, 3, 4 and 4/5 boundary) generally enhanced transport of pollen by wind to Site C4402. Comparison of MAR of organic carbon (MARoc), reflecting primary production, showed big contrast between Pacific and Indian sides. Core C4402 showed high MARoc in OIS 2, 3, late 6, 6/7 boundary and 8. The record in core C2188 (4N, 141E, 2188 m water depth)located in less productive area of the WEP exhibited less fluctuation with higher values during glacial times; OIS 2, 3, 4 and late 8 except for the middle 5. The MARoc data in core O3187 (1N, 160E, 3187 m water depth) from the oligotrophic WEP displayed low values with little fluctuation. In association with the shallow thermocline, biological productivity was controlled by wind-induced surface water mixing or terrestrial inputs around Site C4402 while more intense upwelling driven by stronger winds might have made little difference to the low to medium productivity because the deeper thermocline prevented nutrient-bearing water from upwelling even during the glacial times. In contrast, MARoc in core GC5 (14S, 121E, 2472m water depth)increased gradually from OIS 6 to 3, peaked in OIS 1/2 boundary and rapidly decreased to Holocene. This profile is quite different from those obtained from the WEP. Although both sites are under influence of Asian monsoon, Site GC5 (Indian side) might have experienced continental environmental environmental change more while Site C4402 (Pacific side) remained under oceanic condition because of hundreds km from New Guinea.

  14. The transient variation in the complexes of the low-latitude ionosphere within the equatorial ionization anomaly region of Nigeria

    NASA Astrophysics Data System (ADS)

    Rabiu, A. B.; Ogunsua, B. O.; Fuwape, I. A.; Laoye, J. A.

    2015-09-01

    The quest to find an index for proper characterization and description of the dynamical response of the ionosphere to external influences and its various internal irregularities has led to the study of the day-to-day variations of the chaoticity and dynamical complexity of the ionosphere. This study was conducted using Global Positioning System (GPS) total electron content (TEC) time series, measured in the year 2011, from five GPS receiver stations in Nigeria, which lies within the equatorial ionization anomaly region. The non-linear aspects of the TEC time series were obtained by detrending the data. The detrended TEC time series were subjected to various analyses to obtain the phase space reconstruction and to compute the chaotic quantifiers, which are Lyapunov exponents LE, correlation dimension, and Tsallis entropy, for the study of dynamical complexity. Considering all the days of the year, the daily/transient variations show no definite pattern for each month, but day-to-day values of Lyapunov exponents for the entire year show a wavelike semiannual variation pattern with lower values around March, April, September and October. This can be seen from the correlation dimension with values between 2.7 and 3.2, with lower values occurring mostly during storm periods, demonstrating a phase transition from higher dimension during the quiet periods to lower dimension during storms for most of the stations. The values of Tsallis entropy show a similar variation pattern to that of the Lyapunov exponent, with both quantifiers correlating within the range of 0.79 to 0.82. These results show that both quantifiers can be further used together as indices in the study of the variations of the dynamical complexity of the ionosphere. The presence of chaos and high variations in the dynamical complexity, even in quiet periods in the ionosphere, may be due to the internal dynamics and inherent irregularities of the ionosphere which exhibit non-linear properties. However, this

  15. Tec family kinases in inflammation and disease.

    PubMed

    Horwood, Nicole J; Urbaniak, Ania M; Danks, Lynett

    2012-04-01

    Over the last decade, the Tec family of nonreceptor tyrosine kinases (Btk, Tec, Bmx, Itk, and Rlk) have been shown to play a key role in inflammation and bone destruction. Bruton's tyrosine kinase (Btk) has been the most widely studied due to the critical role of this kinase in B-cell development and recent evidence showing that blocking Btk signaling is effective in ameliorating lymphoma progression and experimental arthritis. This review will examine the role of TFK in myeloid cell function and the potential of targeting these kinases as a therapeutic intervention in autoimmune disorders such as rheumatoid arthritis. PMID:22449071

  16. Antarctic-type blue whale calls recorded at low latitudes in the Indian and eastern Pacific Oceans

    NASA Astrophysics Data System (ADS)

    Stafford, Kathleen M.; Bohnenstiehl, DelWayne R.; Tolstoy, Maya; Chapp, Emily; Mellinger, David K.; Moore, Sue E.

    2004-10-01

    Blue whales, Balaenoptera musculus, were once abundant around the Antarctic during the austral summer, but intensive whaling during the first half of the 20th century reduced their numbers by over 99%. Although interannual variability of blue whale occurrence on the Antarctic feeding grounds was documented by whalers, little was known about where the whales spent the winter months. Antarctic blue whales produce calls that are distinct from those produced by blue whales elsewhere in the world. To investigate potential winter migratory destinations of Antarctic blue whales, we examined acoustic data for these signals from two low-latitude locales: the eastern tropical Pacific Ocean and the Indian Ocean. Antarctic-type blue whale calls were detected on hydrophones in both regions during the austral autumn and winter (May-September), with peak detections in July. Calls occurred over relatively brief periods in both oceans, suggesting that there may be only a few animals migrating so far north and/or producing calls. Antarctic blue whales appear to use both the Indian and eastern Pacific Oceans concurrently, indicating that there is not a single migratory destination. Acoustic data from the South Atlantic and from mid-latitudes in the Indian or Pacific Oceans are needed for a more global understanding of migratory patterns and destinations of Antarctic blue whales.

  17. Low-latitude glaciation and rapid changes in the Earth's obliquity explained by obliquity-oblateness feedback.

    PubMed

    Williams, D M; Kasting, J F; Frakes, L A

    1998-12-01

    Palaeomagnetic data suggest that the Earth was glaciated at low latitudes during the Palaeoproterozoic (about 2.4-2.2 Gyr ago) and Neoproterozoic (about 820-550 Myr ago) eras, although some of the Neoproterozoic data are disputed. If the Earth's magnetic field was aligned more or less with its spin axis, as it is today, then either the polar ice caps must have extended well down into the tropics-the 'snowball Earth' hypothesis-or the present zonation of climate with respect to latitude must have been reversed. Williams has suggested that the Earth's obliquity may have been greater than 54 degrees during most of its history, which would have made the Equator the coldest part of the planet. But this would require a mechanism to bring the obliquity down to its present value of 23.5 degrees. Here we propose that obliquity-oblateness feedback could have reduced the Earth's obliquity by tens of degrees in less than 100 Myr if the continents were situated so as to promote the formation of large polar ice sheets. A high obliquity for the early Earth may also provide a natural explanation for the present inclination of the lunar orbit with respect to the ecliptic (5 degrees), which is otherwise difficult to explain.

  18. Analysis of the disturbed electric field effects in the sporadic E-layers at equatorial and low latitude regions

    NASA Astrophysics Data System (ADS)

    Araujo Resende, Laysa Cristina; Moro, Juliano; Denardini, Clezio Marcos; Carrasco, Alexander J.; Batista, Paulo; Chen, Sony Su; Batista, Inez S.; Andrioli, Vania Fatima

    2016-07-01

    In the present work we analyze the disturbed electric field effects in the sporadic E-layers at equatorial regions, Jicamarca (11.57°S, 76.52°O, I: -2°) and São Luís (2°S, 44° O, I: -2.3°), and at low latitude regions, Fortaleza (3.9°S, 38.45°O, I: -9°) and Cachoeira Paulista (22.42°S, 45°O, I: -15°). We have conducted a deep analysis to investigate these effects using a theoretical model for the ionospheric E region, called MIRE. This model is able to simulate the Es layers taking into account the E region winds and electric fields. It calculates the densities for the main molecular (NO^{+}, O_{2}^{+}, N_{2}^{+}) and metallic ions (Fe^{+}, Mg^{+}) by solving the continuity and momentum equations for each species. The main purpose of this analysis is to verify the disturbed electric fields role in the occurrence or disruption of Es layers through simulations. The analysis show that the Es layer formation and dynamics can be influenced by the prompt penetration electric fields that occur during magnetic disturbances. Therefore, the simulations present interesting results that helps to improve the understanding of Es layer behavior during the disturbed periods.

  19. V-TECS Fifth Annual Report, July 1978.

    ERIC Educational Resources Information Center

    Southern Association of Colleges and Schools, Atlanta, GA. Commission on Occupational Education Institutions.

    This annual report of the V-TECS (Vocational-Technical Education Consortium of States) includes a progress report and an explanation of V-TECS itself. (V-TECS is a consortium whose principal objective is to produce catalogs of performance objectives, and performance guides for use in vocational-technical curriculum development.) First, the…

  20. Detecting ionospheric TEC perturbations caused by natural hazards using a global network of GPS receivers: The Tohoku case study

    NASA Astrophysics Data System (ADS)

    Komjathy, A.; Galvan, D. A.; Stephens, P.; Butala, M. D.; Akopian, V.; Wilson, B.; Verkhoglyadova, O.; Mannucci, A. J.; Hickey, M.

    2012-12-01

    Recent advances in GPS data processing have demonstrated that ground-based GPS receivers are capable of detecting ionospheric TEC perturbations caused by surface-generated Rayleigh, acoustic and gravity waves. There have been a number of publications discussing TEC perturbations immediately following the M 9.0 Tohoku earthquake in Japan on March 11, 2011. Most investigators have focused on the ionospheric responses up to a few hours following the earthquake and tsunami. In our research, in addition to March 11, 2011 we investigate global ionospheric TEC perturbations a day before and after the event. We also compare indices of geomagnetic activity on all three days with perturbations in TEC, revealing strong geomagnetic storm conditions that are also apparent in processed GEONET TEC observations. In addition to the traveling ionospheric disturbances (TIDs) produced by the earthquake and tsunami, we also detect "regular" TIDs across Japan about 5 hours following the Tohoku event, concluding these are likely due to geomagnetic activity. The variety of observed TEC perturbations are consistent with tsunami-generated gravity waves, auroral activity, regular TIDs and equatorial fluctuations induced by increased geomagnetic activity. We demonstrate our capabilities to monitor TEC fluctuations using JPL's real-time Global Assimilative Ionospheric Model (GAIM) system. We show that a real-time global TEC monitoring network is able to detect the acoustic and gravity waves generated by the earthquake and tsunami. With additional real-time stations deployed, this new capability has the potential to provide real-time monitoring of TEC perturbations that could potentially serve as a plug-in to enhance existing early warning systems.

  1. A spatial analysis of the ionospheric TEC anomalies prior to M7.0+ earthquakes during 2003-2014

    NASA Astrophysics Data System (ADS)

    Zhu, Fuying; Lin, Jian; Su, Fanfan; Zhou, Yiyan

    2016-11-01

    In the present paper, by using the global navigation satellite system total electron content (GNSS TEC), we conducted a statistical study on the spatial distribution of the seismo-ionospheric precursors (SIPs) before the occurrence of 133 shallow earthquakes of magnitude M ⩾ 7.0 in the global area during 2003-2014. To exclude the effect of space weather and geomagnetic disturbance, we considered the variations in the geomagnetic Dst indices, Kp indices, and the F10.7 indices; the GNSS TEC over the regions of ±10° near the epicenters is then investigated, and the spatial distribution of ionospheric TEC anomalies 0-15 days before the earthquakes is reported for the first time. We also statistically analyzed and compared the counts of the TEC anomalies over the epicenters in the eastern, southern, western, and northern directions 0-15 days prior to the earthquakes. Results show that the maximum occurrence number of ionospheric TEC negative anomalies specially appears over the epicenters and the anomalous behaviors of the ionospheric TEC attenuate slightly with the distance to the epicenters. However, the ionospheric TEC positive anomalies in the western direction have the biggest chance of occurring. Finally, the spatial distribution characteristics of the observed SIPs are explained by the electric-field-coupling model.

  2. Substitution of Ionosonde Data for GPS TEC Data in GAIM-GM: A Regional Study

    NASA Astrophysics Data System (ADS)

    Sojka, J. J.; Schunk, R. W.; Gardner, L. C.; Scherliess, L.; Rice, D.; Tobiska, W.; Heaton, L. E.; Fulgham, J. A.

    2011-12-01

    The Utah State University (USU) Global Assimilation of Ionospheric Measurement - Gauss Markov (GAIM-GM) model is run in real-time by the US Air Force Weather Agency (AFWA) to provide both specification and forecast of the ionosphere. At USU for development, validation, and testing versions of GAIM-GM are run in the Space Weather Center (SWC). This study describes the results of one such set of test runs and their validation. The standard GAIM-GM operates on as little as ground-based GPS total electron content (TEC) input. Other data sets are used as they become available in real-time, e.g., ionosonde electron density profiles (EDP), COSMIC satellite TEC, in-situ DMSP plasma measurements, etc. In this study the basic GAIM-GM is ran with only GPS TEC ground-based observations and then a second version is run with only ionosonde data. The two tests are conducted over the same period using real-time available observations. Note the current USU-SWC GAIM operations uses a 3 hour latency period hence "real-time" observations include all observations available to USU-SWC within the past three hours. Fundamentally, the two types of observations, TEC and ionosonde EDP are very different. The former is the integral over an ionospheric path that is roughly represented by the latter, the EDP. An ionosonde, ground-based, can only observe up to the F-layer peak, hence less than 50% of the TEC path. This study is regional and covers a region where the number of ionosondes and GPS receivers are similar. Hence, comparing the two GAIM-GM simulations will provide an insight into how the assimilation technique differentiates between the two different data types. This information will then provide better appreciation of how GAIM-GM operates when both data types are combined. The combined TEC plus EDP forms a third GAIM-GM simulation which will also be presented.

  3. The 1980 V-TECS Marketing Study.

    ERIC Educational Resources Information Center

    Hattwick, Richard E.; And Others

    The Vocational-Technical Education Consortium of States (V-TECS) conducted a marketing study that considered the implications of six options for the organization's future. The first option is continuation of the status quo, which is dangerous because existing members may leave the consortium. The second option is the status quo combined with an…

  4. V-TECS Career Cluster Frameworks.

    ERIC Educational Resources Information Center

    Vocational Technical Education Consortium of States, Decatur, GA.

    This document includes 16 vocational-technical crosswalk wheels relating the 14 Vocational Technical Education Consortium of States (V-TECS) Career Families to the 16 Career Clusters developed by the U.S. Department of Education. The career clusters are based on the common academic, workplace, and technical knowledge and skills that cut across all…

  5. Altitudinal variation of midlatitude localized TEC enhancement from ground- and space-based measurements

    NASA Astrophysics Data System (ADS)

    Datta-Barua, S.; Mannucci, A. J.; Walter, T.; Enge, P.

    2008-10-01

    We present terrestrial and space-based dual-frequency observations of a region of enhanced total electron content (TEC) over the southeastern United States at local nighttime during the geomagnetic storm of 29-31 October 2003. The apparently localized, large-amplitude, and nearly Earth-fixed midlatitude ionosphere disturbance contained about 10 m higher delay at Global Positioning System (GPS) L1 frequency than the nighttime background ionosphere TEC. Using the dual-frequency altimeter on board the Jason satellite, we show evidence that nearly all of the electron content was below its orbital altitude of 1300 km at 0000 local time on 31 October 2003. Dual frequency GPS measurements from the receiver on board the SAC-C satellite indicate that some portion of the electron content existed above the 700 km orbit altitude of SAC-C. We develop a horizontally piecewise constant regional model of the enhancement. We compare the model prediction of TEC with the SAC-C satellite GPS data to constrain the altitude of this enhanced TEC region. Our model indicates that the peak density of the anomalous region is at slightly higher altitude and greater in amplitude than that of the background. The TEC enhancement provides a concrete case study of an extreme scenario that both space-based and ground-based GPS augmentation systems must take into account in order to offer high-accuracy, high-integrity corrections to GPS for safety-of-life applications.

  6. Ionospheric response of equatorial and low latitude F-region during the intense geomagnetic storm on 24-25 August 2005

    NASA Astrophysics Data System (ADS)

    de Jesus, R.; Sahai, Y.; Guarnieri, F. L.; Fagundes, P. R.; de Abreu, A. J.; Bittencourt, J. A.; Nagatsuma, T.; Huang, C.-S.; Lan, H. T.; Pillat, V. G.

    2012-02-01

    In this investigation, we present and discuss the response of the ionospheric F-region in the South American and East Asian sectors during an intense geomagnetic storm in August 2005. The geomagnetic storm studied reached a minimum Dst of -216 nT at 12:00 UT on 24 August. In this work ionospheric sounding data obtained of 24, 25, and 26 August 2005 at Palmas (PAL; 10.2° S, 48.2° W; dip latitude 6.6° S), São José dos Campos (SJC, 23.2° S, 45.9° W; dip latitude 17.6° S), Brazil, Ho Chi Minh City, (HCM; 10.5° N, 106.3° E; dip latitude 2.9° N), Vietnam, Okinawa (OKI; 26.3° N, 127.8° E; dip latitude 21.2° N), Japan, are presented. Also, the GPS observations obtained at different stations in the equatorial and low-latitude regions in the Brazilian sector are presented. On the night of 24-25 August 2005, the h‧F variations show traveling ionospheric disturbances associated with Joule heating in the auroral zone from SJC to PAL. The foF2 variations show a positive storm phase on the night of 24-25 August at PAL and SJC during the recovery phase. Also, the GPS-VTEC observations at several stations in the Brazilian sector show a fairly similar positive storm phase on 24 August. During the fast decrease of Dst (between 10:00 and 11:00 UT) on 24 August, there is a prompt penetration of electric field of magnetospheric origin that result in abrupt increase (˜12:00 UT) in foF2 at PAL, SJC (Brazil) and OKI (Japan) and in VTEC at IMPZ, BOMJ, PARA and SMAR (Brazil). OKI showed strong oscillations of the F-region on the night 24 August resulted to the propagation of traveling atmospheric disturbances (TADs) by Joule heating in the auroral region. These effects result a strong positive observed at OKI station. During the daytime on 25 August, in the recovery phase, the foF2 observations showed positive ionospheric storm at HCM station. Some differences in the latitudinal response of the F-region is also observed in the South American and East Asian sectors.

  7. Imaging the topside ionosphere and plasmasphere with ionospheric tomography using COSMIC GPS TEC

    NASA Astrophysics Data System (ADS)

    Pinto Jayawardena, Talini S.; Chartier, Alex T.; Spencer, Paul; Mitchell, Cathryn N.

    2016-01-01

    GPS-based ionospheric tomography is a well-known technique for imaging the total electron content (TEC) between GPS satellites and receivers. However, as an integral measurement of electron concentration, TEC typically encompasses both the ionosphere and plasmasphere, masking signatures from the topside ionosphere-plasmasphere due to the dominant ionosphere. Imaging these regions requires a technique that isolates TEC in the topside ionosphere-plasmasphere. Multi-Instrument Data Analysis System (MIDAS) employs tomography to image the electron distribution in the ionosphere. Its implementation for regions beyond is yet to be seen due to the different dynamics present above the ionosphere. This paper discusses the extension of MIDAS to image these altitudes using GPS phase-based TEC measurements and follows the work by Spencer and Mitchell (2011). Plasma is constrained to dipole field lines described by Euler potentials, resulting in a distribution symmetrical about the geomagnetic equator. A simulation of an empirical plasmaspheric model by Gallagher et al. (1988) is used to verify the technique by comparing reconstructions of the simulation with the empirical model. The Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) is used as GPS receiver locations. The verification is followed by a validation of the modified MIDAS algorithm, where the regions' TEC is reconstructed from COSMIC GPS phase measurements and qualitatively compared with previous studies using Jason-1 and COSMIC data. Results show that MIDAS can successfully image features/trends of the topside ionosphere-plasmasphere observed in other studies, with deviations in absolute TEC attributed to differences in data set properties and the resolution of the images.

  8. Investigating the performance of neural network backpropagation algorithms for TEC estimations using South African GPS data

    NASA Astrophysics Data System (ADS)

    Habarulema, J. B.; McKinnell, L.-A.

    2012-05-01

    In this work, results obtained by investigating the application of different neural network backpropagation training algorithms are presented. This was done to assess the performance accuracy of each training algorithm in total electron content (TEC) estimations using identical datasets in models development and verification processes. Investigated training algorithms are standard backpropagation (SBP), backpropagation with weight delay (BPWD), backpropagation with momentum (BPM) term, backpropagation with chunkwise weight update (BPC) and backpropagation for batch (BPB) training. These five algorithms are inbuilt functions within the Stuttgart Neural Network Simulator (SNNS) and the main objective was to find out the training algorithm that generates the minimum error between the TEC derived from Global Positioning System (GPS) observations and the modelled TEC data. Another investigated algorithm is the MatLab based Levenberg-Marquardt backpropagation (L-MBP), which achieves convergence after the least number of iterations during training. In this paper, neural network (NN) models were developed using hourly TEC data (for 8 years: 2000-2007) derived from GPS observations over a receiver station located at Sutherland (SUTH) (32.38° S, 20.81° E), South Africa. Verification of the NN models for all algorithms considered was performed on both "seen" and "unseen" data. Hourly TEC values over SUTH for 2003 formed the "seen" dataset. The "unseen" dataset consisted of hourly TEC data for 2002 and 2008 over Cape Town (CPTN) (33.95° S, 18.47° E) and SUTH, respectively. The models' verification showed that all algorithms investigated provide comparable results statistically, but differ significantly in terms of time required to achieve convergence during input-output data training/learning. This paper therefore provides a guide to neural network users for choosing appropriate algorithms based on the availability of computation capabilities used for research.

  9. Compound Specific δD Values Across a Tropical Precipitation Gradient: Implications for Low-latitude Paleoclimate Reconstructions

    NASA Astrophysics Data System (ADS)

    Douglas, P. M.; Pagani, M.; Brenner, M.; Curtis, J. H.; Hodell, D. A.

    2009-12-01

    Hydrogen isotopes (δD) of terrestrial and aquatic plant lipids have been used to reconstruct past continental hydrological change in low-latitude settings. Generally, lipid δD values correlate strongly with the isotopic composition of precipitation, although evapotranspiration and biosynthetic fractionation are important influences on the δD of leaf waxes. Few studies have focused on constraining the controls on δD values of lipids in the tropics, where high evaporation rates impact both leaf and lake water isotopic composition. We measured δD values in surface waters and lipids extracted from leaves, lake sediments and soils along a latitudinal transect across Mexico, Guatemala and Honduras, a region with distinct dry and wet seasons. The δD values of leaf waxes extracted from lake sediments are positively correlated with surface water δD values (r = 0.73). The apparent fractionation between stream waters (inferred to represent plant source water) and leaf waxes (ɛlw) is negatively correlated with mean annual precipitation (r = -0.89), likely due to greater evapotranspiration and D-enriched leaf water in drier climates. δD values of leaf waxes extracted directly from leaves collected during the rainy season (August 2008) are similarly correlated with surface water δD values (r = 0.85). Leaf ɛlw values, however, are not significantly correlated with mean annual precipitation. It is possible that the correlation between ɛlw and mean annual precipitation in lake sediment leaf waxes is related to seasonal variability in evapotranspiration. Specifically, lake sediment leaf waxes could predominantly represent production during the dry season when evapotranspiration effects are strongest and when many tropical tree species shed their leaves. Possible seasonal variability in fractionation between source water and leaf wax lipids should be taken into account when interpreting leaf wax δD records from tropical locations, both in terms of controlling for long

  10. Using a three dimensional Ionospheric Data Assimilation and Analysis System (IDAAS) to study the slant-to-vertical deviation in two dimensional TEC mapping over ionosphere equatorial anomaly

    NASA Astrophysics Data System (ADS)

    Yu, T.

    2013-12-01

    By using International Reference Ionosphere (IRI) model as a background ionosphere and applying the Kalman filter to update the state with observations, we develop an Ionosphere Data Assimilation Analysis System (IDAAS) to reconstruct a 3-dimensional ionosphere with the GPS slant TEC and ionosonde data in China. The preliminary results with GPS data collected over east-south Asia on June 30 2005 show that inversed slant TEC has very good correlation with the observations both for the GPS sites being and not being involved in reconstruction. The inversed NmF2 and vertical TEC both demonstrate great improvement of agreement with those observed from ionosondes and TOPEX satellite independently. Based on IDAAS, simulations are carried out to investigate the deviation relative to slant-to-vertical conversion (STV) TEC by using the slant TEC derived from Nequick model as a replacement of measurement data. It is shown that the relative deviation induced by slant-to-vertical conversion may be significant in some cases, and it varies from 0% to 40% when elevation decreasing from 90° to 15°, while relative deviation of IDAAS is much smaller and varies from -5% to 15% without elevation dependence. Comparing with the ';true TEC' map derived from the empirical model, there are big differences in STV TEC map, but no obvious discrepancy in IDAAS map. Generally, IDAAS TEC map is much closer to the 'true TEC' map than the 2-D TEC map does. It is suggested that 3-dimensional inversion techniques are necessary when using GPS observation with low elevation rays at equatorial anomaly region, where the high horizontal gradient of electron density could lead to a significant slant-to-vertical deviation by 2-dimensional inversion method.

  11. Towards Better Understanding of GPS-based Ionospheric TEC Perturbations Caused by Natural Hazards

    NASA Astrophysics Data System (ADS)

    Komjathy, A.; Galvan, D. A.; Butala, M. D.; Stephens, P.; Mannucci, A. J.; Hickey, M. P.

    2011-12-01

    Natural hazards including earthquakes, volcanic eruptions, and tsunamis, have been significant threats to humans throughout recorded history. The Global Positioning System satellites have become primary sensors to measure signatures associated with such natural hazards. These signatures typically include GPS-derived seismic deformation measurements, co-seismic vertical displacements, and real-time GPS-derived ocean buoy positioning estimates. Another way to use GPS observables is to compute the ionospheric total electron content (TEC) to measure and monitor post-seismic ionospheric disturbances caused by earthquakes, volcano eruptions, and tsunamis. Recent advances in GPS data processing have demonstrated that ground-based GPS receivers are capable of detecting ionospheric TEC perturbations generated by surface Rayleigh, acoustic and gravity waves. There have been a number of papers published discussing TEC perturbations immediately following the Tohoku earthquake in Japan on March 11, 2011. Due to the dense GPS network in Japan (GEONET) and high earthquake magnitude, these reports are the clearest observations to date of the effect of a major earthquake and tsunami on the ionosphere near the epicenter. Most investigators have focused on the ionospheric response up to a few hours following the earthquake and tsunami. In our research we investigate the ionospheric TEC perturbations up to a few days before and after the event. We also address the impact of geomagnetic activity during March 11. We compare TEC perturbations on that day with other days showing similar geomagnetic activities. Initial results have revealed that the earthquake and tsunami generated TEC perturbations that were observable and detectable in the GEONET data for up to 24 hours following the Tohoku event. We will investigate optimized GPS processing techniques to derive high-precision TEC perturbations. The primary application involving the ionosphere will be the real-time monitoring of the

  12. TEC anomalies before the Haiti Jan. 12, 2010 and China May 12, 2008 earthquakes

    NASA Astrophysics Data System (ADS)

    Zolotov, Oleg; Prokhorov, Boris; Namgaladze, Alexander; Martynenko, Oleg

    The anomalous TEC (total electron content) variations as seismo-ionospheric earthquake signa-tures have been investigated for the cases of a) China (Eastern Sichuan) earthquake of May 12, 2008, M 7.9 (31.0° N; 103.4° E) and b) Haiti seismic event of Jan. 12, 2010, M 7.0 (18.46° N; 72.5° W). The anomalies look like strong local long-living TEC enhancements relative to the non-disturbed level linked to the near-epicenter area. They are followed by similar effects at the magnetically conjugated regions. The geomagnetic conditions are quiet for the considered periods, i.e. those anomalies are not caused by the solar or geomagnetic activity. To analyze those disturbances we have calculated differential TEC maps for a few days before the earthquakes using Ionospheric TEC Maps provided by the NASA in IONEX file format. The background TEC levels are calculated as a) running median for 3 days before and 7 days after the current calculation moment and as b) running median for 7-days before the calculation moment. Both seismic events show the very similar to each other pre-earthquake TEC anomalies mani-festations independently on the background level calculations: a) the enhancement area is of ˜10° in latitude, ˜40° in longitude for the Chinese earthquake and ˜15° in latitude and ˜25° in longitude for the Haiti earthquake; b) TEC deviation maximum reaches more than 60% in magnitude for the Chinese earthquake and than 40% for the Haiti case; c) the enhancements area existed from 06UT till 12UT May 9, 2008 for the Chinese earthquake and from Jan. 10, 22UT till Jan. 12, 08UT, 2010 for the Haiti one; d) the TEC enhancements were observed at the magnetically conjugated areas in both cases. Magnetic conjugation of the observed anomalies strongly evidences in favour of the hypothesis of the F2-region ionospheric plasma vertical drift under influence of the zonal electric field of seismic origin as the principle reason of the observed phenomena. The work was partially

  13. Investigation of the TEC Changes in the vicinity of the Earthquake Preparation Zone

    NASA Astrophysics Data System (ADS)

    Ulukavak, Mustafa; Yalcinkaya, Mualla

    2016-04-01

    Recently, investigation of the anomalies in the ionosphere before the earthquake has taken too much attention. The Total Electron Content (TEC) data has been used to monitor the changes in the ionosphere. Hence, researchers use the TEC changes before the strong earthquakes to monitor the anomalies in the ionosphere. In this study, the GPS-TEC variations, obtained from the GNSS stations in the vicinity of the earthquake preparation zone, was investigated. Nidra earthquake (M6.5), which was occurred on the north-west of Greece on November 17th, 2015 (38.755°N, 20.552°E), was selected for this study. First, the equation proposed by Dobrovolsky et al. (1979) was used to calculate the radius of the earthquake preparation zone. International GNSS Service (IGS) stations in the region were classified with respect to the radius of the earthquake preparation zone. The observation data of each station was obtained from the Crustal Dynamics Data and Information System (CDDIS) archive to estimate GPS-TEC variations between 16 October 2015 and 16 December 2015. Global Ionosphere Maps (GIM) products, obtained from the IGS, was used to check the robustness of the GPS-TEC variations. Possible anomalies were analyzed for each GNSS station by using the 15-day moving median method. In order to analyze these pre-earthquake ionospheric anomalies, we investigated three indices (Kp, F10.7 and Dst) related to the space weather conditions between 16 October 2015 and 16 December 2015. Solar and geomagnetic indices were obtained from The Oceanic and Atmospheric Administration (NOAA), The Canadian Space Weather Forecast Centre (CSWFC), and the Data Analysis Center for Geomagnetism and Space Magnetism Graduate School of Science, Kyoto University (WDC). This study aims at investigating the possible effects of the earthquake on the TEC variations.

  14. Detection of Geomagnetic Pulsations of the Earth Using GPS-TEC Data

    NASA Astrophysics Data System (ADS)

    Koroglu, Ozan; Arikan, Feza; Köroǧlu, Meltem; Sabri Ozkazanc, Yakup

    2016-07-01

    The magnetosphere of the Earth is made up of both magnetic fields and plasma. In this layer, plasma waves propagate as Ultra Low Frequency (ULF) waves having mHz scale frequencies. ULF waves are produced due to complicated solar-geomagnetic interactions. In the literature, these ULF waves are defined as pulsations. The geomagnetic pulsations are classified into main two groups as continuous pulsations (Pc) and irregular pulsations (Pi). These pulsations can be determined by ionospheric parameters due to the complex lithosphere-ionosphere-magnetosphere coupling processes. Total Electron Content (TEC) is one of the most important parameters for investigating the variability of ionosphere. Global Positioning System (GPS) provides a cost-effective means for estimating TEC from GPS satellite orbital height of 20,000 km to the ground based receivers. Therefore, the time series of GPS-TEC inherently contains the above mentioned ULF waves. In this study, time series analysis of GPS-TEC is carried out by applying periodogram method to the mid-latitude annual TEC data. After the analysis of GPS-TEC data obtained for GPS stations located in Central Europe and Turkey for 2011, it is observed that some of the fundamental frequencies that are indicators of Pc waves, diurnal and semi-diurnal periodicity and earth-free oscillations can be identified. These results will be used in determination of low frequency trend structure of magnetosphere and ionosphere. Further investigation of remaining relatively low magnitude frequencies, all Pi and Pc can be identified by using time and frequency domain techniques such as wavelet analysis. This study is supported by the joint TUBITAK 115E915 and joint TUBITAK114E092 and AS CR 14/001 projects.

  15. Bottom-side profile parameters (B0, B1) characteristics over the Brazilian equatorial and low latitudes and their comparison with different options in the IRI-2012 model during the 24th solar minimum (2010-2011)

    NASA Astrophysics Data System (ADS)

    Venkatesh, K.; Fagundes, P. R.

    2016-08-01

    The present study reports the characteristics of the bottom-side profile thickness (B0) and shape (B1) parameters from ionosonde and IRI-2012 model over the Brazilian sector. The ionosonde data from an equatorial station Fortaleza and a low latitude station Cachoera Paulista during a two year period from 2010 to 2011 are considered in this study. Simultaneous comparison is made on the performance of three different options 'Gul-1987', 'Bil-2000' and the 'ABT-2009' for bottom-side profile estimation in the latest available IRI-2012. The diurnal and seasonal characteristics of the B0 and B1 from ionosonde measurements are studied and compared with those from the IRI-2012 model using the three different options. It is seen that the Gul-1987 method shows better predictions of the observed B0 at the equatorial and low latitudes values when compared with the other options. The latest option 'ABT-2009' has shown improved predictions in the estimation of B1 compared with those from the other methods particularly during the night-time hours. A comparison on the seasonal characteristics of the day maximum values of B0 between observations and the three different options in IRI-2012 reveals that the Gul-1987 method shows better predictions of the seasonal variations in B0 while ABT-2009 method shows better predictions of seasonal variations in B1. Further, an insight into the percentage of deviations in the estimation of B0 and B1 reveals that the models overestimate the B0 during night-time and underestimate the B0 (at equator) during day-time while they underestimate the B1 during night-time hours at both locations. Also, the variations in the bottom-side total electron content are studied using the three different methods in the IRI-2012 model and compared with those derived from the ionosonde observations.

  16. Changes in opal fluxes along the northwest African margin during the last glacial period; linking high and low latitude patterns of productivity

    NASA Astrophysics Data System (ADS)

    Bradtmiller, L. I.; Galgay, M.; McGee, D.; Kinsley, C. W.; Anderson, R. F.

    2014-12-01

    Recent studies have proposed competing hypotheses to explain increased opal fluxes in high and low latitudes during the most recent deglaciation. Anderson et al. (2009) rely on increased wind-driven upwelling in the Southern Ocean to explain the increased availability of Si in both the Southern Ocean and tropical thermoclines, leading to increased opal fluxes in both regions coincident with the deglacial rise in CO2. Meckler et al. (2013) suggest that a decrease in the presence of North Atlantic intermediate water (GNAIW) during the deglaciation allowed Si-rich southern-sourced waters to fill the tropical Atlantic leading to increased opal burial. We attempt to distinguish between these two mechanisms by reconstructing opal fluxes and fluxes of windblown dust over the past ~65ka at four sites along the northwest African margin. The records include the deglaciation, including Heinrich Event 1 (H1) and the Younger Dryas (YD), as well as several earlier Heinrich events. We find that opal and dust fluxes increase simultaneously during the deglaciation, and more highly resolved cores record H1 and the YD as distinct peaks within the deglaciation. Furthermore, opal and dust fluxes scale approximately linearly with one another during these events. We observe opal peaks associated with most Heinrich Events through H6. Finally, we observe a strong similarity between patterns of opal flux in the Southern Ocean and along the African Margin. This suggests that the pattern of diatom productivity and opal flux along the African Margin reflects a combination of changes in wind strength due to shifting temperature gradients, and changes in the export of silica-rich water from the Southern Ocean, both as a result of the global scale climate changes associated with Heinrich Events. Anderson, R. F., S. Ali, L. I. Bradtmiller, S. H. H. Nielsen, M. Q. Fleisher, B. E. Anderson and L. H. Burckle. Wind-Driven Upwelling in the Southern Ocean and the Deglacial Rise in Atmospheric CO2

  17. The mapping of ionospheric TEC for central Russian and European regions on the base of GPS and GLONASS measurements

    NASA Astrophysics Data System (ADS)

    Shagimuratov, Irk; Cherniak, Iurii; Zakharenkova, Irina; Ephishov, Ivan; Krankowski, Andrzej; Radievsky, Alexander

    2014-05-01

    The total electron content (TEC) is a key parameter not only for space radio communication but also for addressing the fundamental problems of the ionosphere physics and near Earth space. Currently, the main sources of information on the TEC in the global scale are GNSS signals measurements. The spatial-temporal behavior of the ionosphere can be most effectively analyzed using TEC maps. To date, global IGS global ionospheric maps with a resolution of 2.5 degree in latitude and 5 in longitude and a time resolution of 2 h are most widely used. To study the detailed structure of the ionospheric gradients and rapid process as well as for precise positioning task it is necessary to use more precise regional TEC maps. The Regional TEC maps are currently constructed by different research groups for different regions: USA, Europe, Japan etc. The West Department of IZMIRAN research group is a one in Russia who works on the task of regional ionosphere mapping since 2000. It was developed the methodology for obtaining information on the spatial TEC distribution, TEC maps of the ionosphere on the basis of the algorithm for multi-station processing of GNSS observations. Using a set of algorithms and programs, regional TEC maps with a spatial resolution of 1° and a time resolution up to 15 min can be produced. Here is developed the approach to establish the regular online internet service for regional ionosphere mapping of the Western Russia and Eastern Europe. Nowadays the development of GLONASS navigation system is completely finished and it consists of a constellation of more than 24 satellites. It is good perspective for investigations of the ionosphere structure and dynamics on the base of the simultaneous observations of GPS and GLONASS systems. The GLONASS satellites have the inclination about 64 degrees as against GPS satellites with 56. So the GLONASS provides opportunity to study the high latitude ionosphere. The different scale electron density irregularities

  18. On the latitudinal changes in ionospheric electrodynamics and composition based on observations over the 76-77°E meridian from both hemispheres during a geomagnetic storm

    NASA Astrophysics Data System (ADS)

    Shreedevi, P. R.; Thampi, Smitha V.; Chakrabarty, D.; Choudhary, R. K.; Pant, Tarun Kumar; Bhardwaj, Anil; Mukherjee, S.

    2016-02-01

    The relative contributions of the composition disturbances and the disturbance electric fields in the redistribution of ionospheric plasma is investigated in detail by taking the case of a long-duration positive ionospheric storm that occurred during 18-21 February 2014. GPS total electron content (TEC) data from the Indian Antarctic station, Bharti (69.4°S, 76.2°E geographic), the northern midlatitude station Hanle (32.8°N, 78.9°E geographic), northern low-latitude station lying in the vicinity of the anomaly crest, Ahmedabad (23.04°N, 72.54°E geographic, dip latitude 17°N), and the geomagnetic equatorial station, Trivandrum (8.5°N, 77°E geographic, dip latitude 0.01°S) are used in the study. These are the first simultaneous observations of TEC from Bharti and Hanle during a geomagnetic storm. The impact of the intense geomagnetic storm (Dst˜-130 nT) on the southern hemisphere high-latitude station was a drastic reduction in the TEC (negative ionospheric storm) starting from around 0330 Indian standard time (IST) on 19 February which continued till 21 February, the maximum reduction in TEC at Bharti being ˜35 TEC units on 19 February. In the northern hemisphere midlatitude and equatorial stations, a positive ionospheric storm started on 19 February at around 0900 IST and lasted for 3 days. The maximum enhancement in TEC at Hanle was about ˜25 TECU on 19 February while over Trivandrum it was ˜10 TECU. This long-duration positive ionospheric storm provided an opportunity to assess the relative contributions of disturbance electric fields and composition changes latitudinally. The results indicate that the negative ionospheric storm over Bharti and the positive ionospheric storm over Hanle are the effect of the changes in the global wind system and the storm-induced composition changes. At the equatorial latitudes, the positive ionospheric storm was due to the interplay of prompt penetration electric field and disturbance dynamo electric field.

  19. Investigation of the Ionospheric Fluctuations Caused by Space Weather Effects Using GNSS TEC Measurements

    NASA Astrophysics Data System (ADS)

    Shagimuratov, Irk; Krankowski, Andrzej; Cherniak, Iurii; Ephishov, Ivan; Zakharenkova, Irina; Yakimova, Galina

    2013-04-01

    It is known that GPS radio signals passing through the ionosphere suffer varying degrees of rapid variations of their amplitude and phase - signal scintillations. The scintillations are caused by the presence of wide range of scale size irregularities in the ionosphere. It is very important to estimate scintillation and phase fluctuation effects on GNSS navigation system (GPS/GLONASS) performance and consequently on the precession of the obtained position. Effects of the ionospheric irregularities on the GPS signals can be evaluated by measurements of the differential phase time rate of dual frequency GPS signals. GPS observations carried out at the Arctic IGS (International GNSS Service) stations were used to study the development of TEC fluctuations in the high latitude ionosphere. Standard GPS measurements with 30s sampling rate allow the detection of middle- and large-scale ionospheric irregularities. For detection of ionospheric fluctuations the rate of TEC (ROT, in the unit of TECU/min) at 1 min interval was used. The temporal occurrence of TEC fluctuations is clearly observed in time variations in the dual frequency carrier phase along satellite passes. As a measure of the fluctuation activity level the Rate of TEC Index (ROTI) based on standard deviation of ROT was also used. ROTI was estimated in 10-minute interval. These techniques and IGS data were used to study the occurrence of TEC fluctuations at the northern latitude ionosphere for selected geomagnetic storms occurred at the end of 23rd and beginning of new 24th solar cycles. Results demonstrate that fluctuation activity of GPS signals in the high latitude ionosphere is depended on geomagnetic conditions. Intensity of fluctuations essentially increases during geomagnetic storms. The strongest TEC fluctuations occurred as short time rate of TEC enhancements of a factor of 2-5 relative to the quiet time. During geomagnetic disturbed conditions strong phase fluctuations can register at latitudes low

  20. Assessment of precursor signature of TEC anomalies over Japan area

    NASA Astrophysics Data System (ADS)

    Hattori, K.; Han, P.

    2015-12-01

    To reduce the effect of strong geomagnetic activities, the TEC data of 2 days after Dst index exceed -60 nT were excluded in previous statistical studies of earthquake related TEC anomalies. Actually, the influences of a magnetic storm on TEC variations depend on the intensity and onset time of the storm. In this study, to clarify such dependences, we applied classification analysis to the storm data (Dst) and discussed the response of TEC variation to each type of storm. We picked out all the 294 geomagnetic storms during 1998-2013, and classified them into 3 types in magnitude and 4 types in onset time (local time). We checked the TEC data from 2 days before till 5 days after the onset of each geomagnetic storm. A bootstrap method is used to calculate the average variation of the TEC for each type of storm. The average variation can be regarded as an average response of TEC to the related type of storm. If the average value of TEC exceeds the mean±2σ threshold, we consider it being affected by the storm. By this mean, we could find the accurate period affected by each type of storm. We employed the results obtained above to remove the TEC data associated with geomagnetic storms. Next we performed statistical analysis of the TEC anomalies possibly associated with large earthquakes in Japan area during 1998/05-2013/12. There are statistical significance of TEC anomalies 1-5 days before and 16-20 days after M>=6.0 earthquakes. The significance of pre-earthquake anomalies is consistent with the results reported by Kon et al., 2011. The significance of 16-20 days after earthquakes may be due to aftershock effects of the Tohoku earthquake. To remove the influences of any per- and after- shock effects, we proposed a new method which considers 'isolate EQs' only. 'Isolate EQs' are earthquakes which is unique in a 61 days window centered by the day of the EQ. The result shows there are clear high possibilities of TEC anomalies 1-5 days prior to M>=6 earthquakes. Finally

  1. Long time series analysis of ionospheric TEC disturbance over seismically region in southwest China during low solar activity

    NASA Astrophysics Data System (ADS)

    Yan, Xiangxiang; Yu, Tao; Shan, Xinjian; Liu, Zhan; Wang, Zhenjie

    2016-04-01

    Recently, there are growing interests in studying the seismo-ionospheric disturbance prior to earthquakes, mainly including the anomalies in the electric field, magnetic field and plasma parameters. However, there are still some controversies over this topic, mainly because of strong day-to-day variability of the ionosphere itself. It is hard to determine whether the different forms of ionospheric disturbances are associated with earthquakes or not. Using data of Crustal Movement Observation Network of China (CMONC) and IGS (International GNSS Service), we attempt to give a statistical investigation about the total electron content (TEC) perturbation before 30 Mw6.0+ earthquakes during January 2000 to December 2010 in China. To determine the abnormal TEC signals, a quartile-based process is performed. At each time point we calculated the median M using the TEC values at the same local time for the preceding 15 days. In addition, we calculated the maps of differential TEC from global ionosphere maps (GIM) in the above period. It is shown that TEC anomalies were detected before 20 earthquakes, nearly 67%. The anomalies represent positive before most events and occurred mostly within 2-6 days before the shocks, significantly during the afternoon period, 1200-2000LT. Part of perturbations appeared more than one time. Moreover, the affected area of TEC is not coincide with the vertical projection of the epicenter but shifts equatorward and is controlled by equatorial ionization anomaly (EIA) crest. On the other hand, we analyzed variations of TEC over southwest China during a period of low solar and geomagnetic activity in April-October 2008, based on the data of CMONC. During that time, six large earthquakes with magnitude M≧6.0 occurred around the southwest region of China. The method to detect abnormal TEC signals is same with above statistical study. Known that the decisive role in the ionosphere state is performed by space weather effects, we compared the TEC

  2. Validation of the inferred ionospheric currents during a Sudden Impulse with GNSS TEC data over Italy.

    NASA Astrophysics Data System (ADS)

    Piersanti, Mirko; Cesaroni, Claudio; Spogli, Luca; Villante, Umberto; De Franceschi, Giorgiana; Musicò, Elvirà; Avallone, Antonio

    2016-04-01

    The definite identification of the characteristics of the geomagnetic response to Solar Wind (SW) pressure changes represents an interesting element of the magnetospheric dynamics that is also important in the Space Weather context. In the present analysis, we discriminate between magnetospheric (DL) and ionospheric (DP) contributions in the ground response comparing SEGMA array (South European Geomagnetic Array) and geostationary observations with the predictions of the Tsyganenko model for the different magnetospheric current systems (from the magnetopause, ring current, tail current, etc.) for different case events. To obtain the Ionospheric contribution we subtracted the field aligned currents (FAC) MFACE model (Model of FACs through Empirical Orthogonal Function analysis, He et al., [2012]) from the residual DP field at each ground station. Meaningful changes in the ionospheric currents reflect into meaningful variation of the total electron content in the ionosphere. Thus, to validate our approach in determining the ionospheric currents, we analyse calibrated TEC and TEC spatial gradients data over the Italian sites of the SEGMA array derived with a network of GNSS receivers, termed RING (Rete Integrata Nazionale GPS). RING is a dense network of about 180 stations covering the Italian territory, by means of which it is possible to obtain maps of TEC derived products with very fine spatial resolution (0.1° x0.1° , lat x long). The aim of this validation is to catch the correspondences between ionospheric current variations and the morphology and dynamics of the TEC in the mid latitude ionosphere on selected case events.

  3. Data assimilation of plasmasphere and upper ionosphere using COSMIC/GPS slant TEC measurements

    NASA Astrophysics Data System (ADS)

    Wu, M. J.; Guo, P.; Xu, T. L.; Fu, N. F.; Xu, X. S.; Jin, H. L.; Hu, X. G.

    2015-11-01

    Increasing total electron content (TEC) measurements from the low Earth orbiting satellites to Global Positioning System satellites flourish the exploration of the ionosphere and plasmasphere for decades. This paper indicates a method that 3-D Var is applied to assimilate precise orbit determination antenna TEC measurements of Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) satellites into the background global core plasma model (GCPM). The slant TEC data archived in the COSMIC Data Analysis and Archive Center from 500 km to 20,200 km are used to reconstruct a new electron density model. This model has a temporal resolution of 2 h and spatial resolutions of 2.5° in geomagnetic latitude, 5° in longitude, 50 km in the upper ionosphere, and several hundred kilometers in the plasmasphere. Preliminary results show that the data assimilation modifies the initial GCPM forecast to be better coincident with actual COSMIC measurements in internal quality check. Furthermore, independent validation with upper ionosphere-retrieved electron density and TEC of global ionosphere maps implies a reasonable improvement in the estimation of plasmaspheric electron density after the assimilation.

  4. Probability Distribution Extraction from TEC Estimates based on Kernel Density Estimation

    NASA Astrophysics Data System (ADS)

    Demir, Uygar; Toker, Cenk; Çenet, Duygu

    2016-07-01

    Statistical analysis of the ionosphere, specifically the Total Electron Content (TEC), may reveal important information about its temporal and spatial characteristics. One of the core metrics that express the statistical properties of a stochastic process is its Probability Density Function (pdf). Furthermore, statistical parameters such as mean, variance and kurtosis, which can be derived from the pdf, may provide information about the spatial uniformity or clustering of the electron content. For example, the variance differentiates between a quiet ionosphere and a disturbed one, whereas kurtosis differentiates between a geomagnetic storm and an earthquake. Therefore, valuable information about the state of the ionosphere (and the natural phenomena that cause the disturbance) can be obtained by looking at the statistical parameters. In the literature, there are publications which try to fit the histogram of TEC estimates to some well-known pdf.s such as Gaussian, Exponential, etc. However, constraining a histogram to fit to a function with a fixed shape will increase estimation error, and all the information extracted from such pdf will continue to contain this error. In such techniques, it is highly likely to observe some artificial characteristics in the estimated pdf which is not present in the original data. In the present study, we use the Kernel Density Estimation (KDE) technique to estimate the pdf of the TEC. KDE is a non-parametric approach which does not impose a specific form on the TEC. As a result, better pdf estimates that almost perfectly fit to the observed TEC values can be obtained as compared to the techniques mentioned above. KDE is particularly good at representing the tail probabilities, and outliers. We also calculate the mean, variance and kurtosis of the measured TEC values. The technique is applied to the ionosphere over Turkey where the TEC values are estimated from the GNSS measurement from the TNPGN-Active (Turkish National Permanent

  5. StarTEC: A Technology Project in Education Reform.

    ERIC Educational Resources Information Center

    Hawley, Helen; Benavides, Otto; Duffy, Sharon; Georgi, David; Guay, Diane; Redmond, Pamela; Richmond, James

    StarTEC (Staff, Teacher, and Restructured Technology Education Consortium) was a 3-year technology catalyst program funded by the U.S. Department of Education, and continued for a third year to complete its activities. The goal of StarTEC was to ensure that all teachers prepared by partners in the Consortium would meet the new California standard…

  6. Web services interface for Space Weather: NeQuick 2 web and experimental TEC Calibration

    NASA Astrophysics Data System (ADS)

    Migoya Orue, Yenca O.; Nava, Bruno; Radicella, Sandro M.; Alazo Cuartas, Katy; Luigi, Ciraolo

    2013-04-01

    A web front-end has been recently developed and released to allow retrieving and plotting ionospheric parameters computed by the latest version of the model, NeQuick 2. NeQuick is a quick-run ionospheric electron density model particularly designed for trans-ionospheric propagation applications. It has been developed at the Aeronomy and Radiopropagation Laboratory (now T/ICT4D Laboratory) of the Abdus Salam International Centre for Theoretical Physics (ICTP) - Trieste, Italy with the collaboration of the Institute for Geophysics, Astrophysics and Meteorology (IGAM) of the University of Graz, Austria. To describe the electron density of the ionosphere up to the peak of the F2 layer, NeQuick uses a profile formulation which includes five semi-Epstein layers with modelled thickness parameters. Through a simple web interface users can exploit all the model features including the possibility of computing the electron density and visualizing the corresponding Total Electron Content (TEC) along any ground-to-satellite straight line ray-path. Indeed, the TEC is the ionospheric parameter retrieved from the GPS measurements. It complements the experimental data obtained with diverse kinds of sensors and can be considered a major source of ionospheric information. Since the TEC is not a direct measurement, a "de-biasing" procedure or calibration has to be applied to obtain the relevant values from the raw GPS observables. Using the observation and navigation RINEX files corresponding to a single receiver as input data, the web application allows the user to compute the slant and/or vertical TEC following the concept of the "arc-by-arc" offsets estimation. The combined use of both tools, freely available from the T/ICT4D Web site, will allow the comparison of experimentally derived slant and vertical TEC with modelled values. An online demonstration of the capabilities of the mentioned web services will be illustrated.

  7. Concentration and 14C Content of Total Organic Carbon and Black Carbon in Small (<100 ug C) Samples from Low-Latitude Alpine Ice Cores

    NASA Astrophysics Data System (ADS)

    Kehrwald, N. M.; Czimczik, C. I.; Santos, G. M.; Thompson, L. G.; Ziolkowski, L.

    2008-12-01

    Many low latitude glaciers are receding with consequences for the regional energy budget and hydrology. Ice loss has been linked to climate change and the deposition of organic aerosols such as black carbon (BC) which is formed during incomplete combustion. Little is known about how the contents of BC and total organic carbon (TOC) in aerosols change over time and how anthropogenic activities (e.g. land-use change) impact this variability. Low-latitude ice cores are located closer to population centers than polar ice caps and can provide a regional synthesis of TOC and BC variability. Radiocarbon (14C) may be used to partition BC aerosols into fossil (>50 kyrs) and modern sources (e.g. fossil-fuels vs. wildfires). We quantified TOC, BC, and their 14C content in three low-latitude ice cores: Naimona'nyi (30°27'N, 81°91'E) and Dasuopu (28°23'N, 85°43'E), Tibet, and Quelccaya (13°56'S; 70°50'W), Peru. Aerosols (52-256 g ice on filters) were separated into TOC and BC using thermal oxidation (CTO- 375). 14C was measured by AMS. TOC contents were 0.11-0.87, 0.05-0.43, and 0.06-0.19 μg C (g ice) -1 for Naimona'nyi, Dasuopu, and Quelccaya, respectively. BC contents were 18±8, 27±4, and 29±12 %TOC. Procedural blanks were 0.8 ± 0.4 μg C (TOC) and 1.2 ± 0.6 μg C (BC). In ice cores well dated through annual layer counting and/or independent ages (e.g. volcanic horizons) such as Quelccaya, the ability to separate BC from TOC, as well as partition BC into fossil and modern contributions has potential for reconstructing pre- and post-industrial changes in aerosol composition and their impact on the energy budget.

  8. Firefly Algorithm in detection of TEC seismo-ionospheric anomalies

    NASA Astrophysics Data System (ADS)

    Akhoondzadeh, Mehdi

    2015-07-01

    Anomaly detection in time series of different earthquake precursors is an essential introduction to create an early warning system with an allowable uncertainty. Since these time series are more often non linear, complex and massive, therefore the applied predictor method should be able to detect the discord patterns from a large data in a short time. This study acknowledges Firefly Algorithm (FA) as a simple and robust predictor to detect the TEC (Total Electron Content) seismo-ionospheric anomalies around the time of the some powerful earthquakes including Chile (27 February 2010), Varzeghan (11 August 2012) and Saravan (16 April 2013). Outstanding anomalies were observed 7 and 5 days before the Chile and Varzeghan earthquakes, respectively and also 3 and 8 days prior to the Saravan earthquake.

  9. A regional ionospheric TEC mapping technique over China and adjacent areas on the basis of data assimilation

    NASA Astrophysics Data System (ADS)

    Aa, Ercha; Huang, Wengeng; Yu, Shimei; Liu, Siqing; Shi, Liqin; Gong, Jiancun; Chen, Yanhong; Shen, Hua

    2015-06-01

    In this paper, a regional total electron content (TEC) mapping technique over China and adjacent areas (70°E-140°E and 15°N-55°N) is developed on the basis of a Kalman filter data assimilation scheme driven by Global Navigation Satellite Systems (GNSS) data from the Crustal Movement Observation Network of China and International GNSS Service. The regional TEC maps can be generated accordingly with the spatial and temporal resolution being 1°×1° and 5 min, respectively. The accuracy and quality of the TEC mapping technique have been validated through the comparison with GNSS observations, the International Reference Ionosphere model values, the global ionosphere maps from Center for Orbit Determination of Europe, and the Massachusetts Institute of Technology Automated Processing of GPS TEC data from Madrigal database. The verification results indicate that great systematic improvements can be obtained when data are assimilated into the background model, which demonstrates the effectiveness of this technique in providing accurate regional specification of the ionospheric TEC over China and adjacent areas.

  10. Analysis of geomagnetically induced currents at a low-latitude region over the solar cycles 23 and 24: comparison between measurements and calculations

    NASA Astrophysics Data System (ADS)

    Barbosa, Cleiton; Alves, Livia; Caraballo, Ramon; Hartmann, Gelvam A.; Papa, Andres R. R.; Pirjola, Risto J.

    2015-11-01

    Geomagnetically Induced Currents (GIC) are a space weather effect, which affects ground-based technological structures at all latitudes on the Earth's surface. GIC occurrence and amplitudes have been monitored in power grids located at high and middle latitudes since 1970s and 1980s, respectively. This monitoring provides information about the GIC intensity and the frequency of occurrence during geomagnetic storms. In this paper, we investigate GIC occurrence in a power network at low latitudes (in the central Brazilian region) during the solar cycles 23 and 24. Calculated and measured GIC data are compared for the most intense geomagnetic storms (i.e. -50 < Dst < -50 nT) of the solar cycle 24. The results obtained from this comparison show a good agreement. The success of the model employed for the calculation of GIC leads to the possibility of determining GIC for events during the solar cycle 23 as well. Calculated GIC in one transformer reached ca. 30 A during the "Halloween storm" in 2003 whilst most frequent intensities lie below 10 A. The normalized inverse cumulative frequency for GIC data was calculated for the solar cycle 23 in order to perform a statistical analysis. It was found that a q-exponential Tsallis distribution fits the calculated GIC frequency distribution for more than 99% of the data. This analysis provides an overview of the long-term GIC monitoring at low latitudes and suggests new insight into critical phenomena involved in the GIC generation.

  11. Major shifts in calcareous phytoplankton assemblages through the Eocene-Oligocene transition of Tanzania and their implications for low-latitude primary production

    NASA Astrophysics Data System (ADS)

    Dunkley Jones, Tom; Bown, Paul R.; Pearson, Paul N.; Wade, Bridget S.; Coxall, Helen K.; Lear, Caroline H.

    2008-12-01

    A high-resolution record of exceptionally well preserved calcareous nannofossil assemblages from Tanzania is marked by two key transitions closely related to the climatic events of the Eocene-Oligocene transition (EOT). The first transition, at ˜34.0 Ma, precedes the first positive shift in δ18O and coincides with a distinct interval of very low nannofossil abundance and a cooling in sea surface temperatures (SST). The second, at ˜33.63 Ma, is immediately above the Eocene-Oligocene boundary (EOB) and is associated with a significant drop in nannofossil diversity. Both transitions involve significant reductions in the abundance of holococcoliths and other oligotrophic taxa. These changes in calcareous phytoplankton assemblages indicate (1) a widespread and significant perturbation to the low-latitude surface ocean closely tied to the EOB, (2) a potential role for reduced carbonate primary production at the onset of global cooling, and (3) a significant increase in nutrient availability in the low-latitude surface ocean through the EOT.

  12. Potentialities of TEC topping: A simplified view of parametric effects

    NASA Technical Reports Server (NTRS)

    Morris, J. F.

    1980-01-01

    An examination of the benefits of thermionic-energy-conversion (TEC)-topped power plants and methods of increasing conversion efficiency are discussed. Reductions in the cost of TEC modules yield direct decreases in the cost of electricity (COE) from TEC-topped central station power plants. Simplified COE, overall-efficiency charts presented illustrate this trend. Additional capital-cost diminution results from designing more compact furnaces with considerably increased heat transfer rates allowable and desirable for high temperature TEC and heat pipes. Such improvements can evolve of the protection from hot corrosion and slag as well as the thermal expansion compatibilities offered by silicon-carbide clads on TEC-heating surfaces. Greater efficiencies and far fewer modules are possible with high-temperature, high-power-density TEC: This decreases capital and fuel costs much more and substantially increases electric power outputs for fixed fuel inputs. In addition to more electricity, less pollution, and lower costs, TEC topping used directly in coal-combustion products contributes balance-of-payment gains.

  13. Evaluation of six ionospheric models as predictors of TEC

    SciTech Connect

    Brown, L.D.; Daniell, R.E.; Fox, M.W.; Klobuchar, J.A.; Doherty, P.H.

    1990-05-03

    The authors have gathered TEC data from a wide range of latitudes and longitudes for a complete range of solar activity. This data was used to evaluate the performance of six ionospheric models as predictors of Total Electron Content (TFC). The TEC parameter is important in correcting modern DOD space systems, which propagate radio signals from the earth to satellites, for the time delay effects of the ionosphere. The TEC data were obtained from polarimeter receivers located in North America, the Pacific, and the East Coast of Asia. The ionospheric models evaluated are: (1) the International Reference Ionosphere (IRI); (2) the Bent model; (3) the Ionospheric Conductivity and Electron Density (ICED) model; (4) the Penn State model; (5) the Fully Analytic Ionospheric Model (FAIM, a modification of the Chiu model); and (6) the Damen-Hartranft model. They will present extensive comparisons between monthly mean TEC at all local times and model TEC obtained by integrating electron density profiles produced by the six models. These comparisons demonstrate that even thought most of the models do very well at representing f0F2, none of them do very well with TEC, probably because of inaccurate representation of the topside scale height. They suggest that one approach to obtaining better representations of TEC is the use of f0E2 from coefficients coupled with a new slab thickness developed at Boston University.

  14. Towards Robust Estimation and Correction of Ionospheric TEC Signatures in Low Frequency Spaceborne SAR data

    NASA Astrophysics Data System (ADS)

    Liao, H.; Meyer, F. J.

    2013-12-01

    In the last decade, abundant research has proven the existence of ionospheric distortions in data acquired by spaceborne low-frequency Synthetic Aperture Radar (SAR) systems. The most prominent of these distortions are resolution degradation, distortions of the image geometry, biased phase information, and Faraday rotation, a rotation of the signal's polarization vector. For a given system, all these distortions are characterized by the ionospheric Total Electron Content (TEC). Hence, global correction of SAR would require accurate knowledge of TEC. While a variety of techniques for TEC estimation are available, the performance of these algorithms is limited as they do not exploit the entirety of ionosphere induced signatures available in a SAR data set. Instead, only a subset of information is selected by identifying the parameter of highest sensitivity for correcting a specific SAR observable. Therefore, more research is needed to improve the robustness and accuracy of ionospheric correction methods. The goal of our research is to improve ionospheric estimation performance through combining existing ionospheric correction methods with complementary strengths. Firstly, the implementational details of three ionospheric estimation methods will be presented. These include: (1) A Faraday rotation (FR)-based method where FR is first estimated from quad-polarized SAR data using the classical Bickel and Bates estimator. Ionospheric TEC is then derived from the FR measurements based on satellite observation geometry and a three-dimensional geomagnetic field model; (2) a second method exploits the fact that ionospheric group delay is dependent on the signal frequency. A lower and a higher-frequency sub-look image are firstly extracted from a wide-band SAR acquisition and ionosphere-induced range shifts between these sub-looks are then calculated using image cross-correlation methods. The advantage of this method is that it only requires a one-band image to determine

  15. The role of Tec family kinases in the regulation of T-helper-cell differentiation.

    PubMed

    Boucheron, Nicole; Ellmeier, Wilfried

    2012-04-01

    ABSTRACT Members of the Tec kinase family (Tec, Btk, Itk, Rlk, and Bmx) play an important role during innate and adaptive immune responses, and mutations in Tec family kinases are linked with immunodeficiencies in humans and mice. Three members of the Tec kinase family are expressed in T cells (Tec, Itk, and Rlk), and biochemical and genetic studies have revealed important roles for Tec family kinases during T-cell development and in the control of T-cell function. Here the authors review the role of Tec family kinases in the regulation of T-helper-cell differentiation. PMID:22449074

  16. TEC protein tyrosine kinase is involved in the Erk signaling pathway induced by HGF

    SciTech Connect

    Li, Feifei; Jiang, Yinan; Zheng, Qiping; Yang, Xiaoming; Wang, Siying

    2011-01-07

    Research highlights: {yields} TEC is rapidly tyrosine-phosphorylated and activated by HGF-stimulation in vivo or after partial hepatectomy in mice. {yields} TEC enhances the activity of Elk and serum response element (SRE) in HGF signaling pathway in hepatocyte. {yields} TEC promotes hepatocyte proliferation through the Erk-MAPK pathway. -- Abstract: Background/aims: TEC, a member of the TEC family of non-receptor type protein tyrosine kinases, has recently been suggested to play a role in hepatocyte proliferation and liver regeneration. This study aims to investigate the putative mechanisms of TEC kinase regulation of hepatocyte differentiation, i.e. to explore which signaling pathway TEC is involved in, and how TEC is activated in hepatocyte after hepatectomy and hepatocyte growth factor (HGF) stimulation. Methods: We performed immunoprecipitation (IP) and immunoblotting (IB) to examine TEC tyrosine phosphorylation after partial hepatectomy in mice and HGF stimulation in WB F-344 hepatic cells. The TEC kinase activity was determined by in vitro kinase assay. Reporter gene assay, antisense oligonucleotide and TEC dominant negative mutant (TEC{sup KM}) were used to examine the possible signaling pathways in which TEC is involved. The cell proliferation rate was evaluated by {sup 3}H-TdR incorporation. Results: TEC phosphorylation and kinase activity were increased in 1 h after hepatectomy or HGF treatment. TEC enhanced the activity of Elk and serum response element (SRE). Inhibition of MEK1 suppressed TEC phosphorylation. Blocking TEC activity dramatically decreased the activation of Erk. Reduced TEC kinase activity also suppressed the proliferation of WB F-344 cells. These results suggest TEC is involved in the Ras-MAPK pathway and acts between MEK1 and Erk. Conclusions: TEC promotes hepatocyte proliferation and regeneration and is involved in HGF-induced Erk signaling pathway.

  17. Real-time GPS Ionospheric TEC Estimation over South Korea

    NASA Astrophysics Data System (ADS)

    Choi, Byung-Kyu; Yoo, Sung-Moon; Roh, Kyoung-Min; Lee, Sang-Jeong

    2013-09-01

    Ionosphere is one of the largest error sources when the navigational signals produced by Global Positioning System (GPS) satellites are transmitted. Therefore it is very important to estimate total electron contents (TEC) in ionosphere precisely for navigation, precise positioning and some other applications. When we provide ionospheric TEC values in real-time, its application can be expanded to other areas. In this study we have used data obtained from nine Global Navigation Satellite System (GNSS) reference stations which have been operated by Korea Astronomy and Space Science Institute (KASI) to detect ionospheric TEC over South Korea in real-time. We performed data processing that covers converting 1Hz raw data delivered from GNSS reference stations to Receiver INdependent Exchange (RINEX) format files at intervals of 5 minutes. We also analyzed the elevation angles of GPS satellites, vertical TEC (VTEC) values and their changes.

  18. Space Weather Activities of IONOLAB Group: IONOLAB-TEC

    NASA Astrophysics Data System (ADS)

    Arikan, F.; Sezen, U.; Arikan, O.; Ugurlu, O.; Nayir, H.

    2009-04-01

    Space Weather (SW) is the concept of changing environmental conditions in outer space and affect Earth and its technological systems. SW is a consequence of the solar activities and the coupling of solar energy on Earth's atmosphere due to the Earth's magnetic field. The monitoring and prediction of SW has utmost importance for HF communication, Satellite communication, navigation and guidance systems, Low Earth Orbit (LEO) satellite systems, Space Craft exit and entry into the atmosphere. Ionosphere is the plasma layer of the atmosphere that is ionized by solar radiation and it is a key player of SW. Ionosphere is a temporally and spatially varying, dispersive, anisotropic and inhomogeneous medium that is characterized primarily by its electron density distribution. IONOLAB is a group of researchers of various disciplines, getting together to handle challenges of the Earth's ionosphere. The team has researchers from Hacettepe University and Bilkent University, Department of Electrical and Electronics Engineering and General Command of Mapping of Turkish Army. One of the most important contributions of IONOLAB group is the automated web-based computation service for Total Electron Content (TEC). TEC corresponds to the line integral of electron density distribution on a given path. TEC can also be expressed as the amount of free electrons within 1 m2 cross-sectional area of the cylinder on the ray path. Global Position System (GPS) provides a cost-effective medium for monitoring of ionosphere using the signals recorded by stationary GPS receivers in estimating TEC. IONOLAB group has developed IONOLAB-TEC for reliable and robust estimates for all latitudes and both calm and disturbed days by using RINEX, IONEX and satellite ephemeris data provided from the IGS centers. IONOLAB-TEC consists of a regularized signal estimation algorithm which combines signals from all GPS satellites for a given instant and a given receiver, for a desired time period or for 24 hours

  19. TEC Programmes Evaluated: Student Progress and Employer Perceptions.

    ERIC Educational Resources Information Center

    Moor, Christine

    1984-01-01

    An evaluation of Technician Education Council (TEC) programs sought to determine the extent to which this British job training project meets the needs of students and employers as well as the changing requirements of industry. (SK)

  20. Space-time ARIMA modelling of global TEC maps

    NASA Astrophysics Data System (ADS)

    Choliy, V.

    2009-04-01

    Autoregressive integrated moving average modelling technique is used to global TEC maps from Ionex for the purpose of forecasting. When used on parallel or CUDA-based computers this methodology produces very quick forecasts without loose of details.

  1. Dependences of statistical characteristics of NmE on the month of the year at middle and low latitudes under daytime geomagnetically quiet conditions at low solar activity

    NASA Astrophysics Data System (ADS)

    Pavlov, A. V.; Pavlova, N. M.

    2016-07-01

    Month-to-month changes in the statistical characteristics of the ionospheric E layer peak electron density NmE at medium and low geomagnetic latitudes under daytime geomagnetically quiet conditions are investigated. Critical frequencies of the ionospheric E layer measured by the middle latitude ionosonde Boulder and low latitude ionosondes Huancayo and Jicamarca at low solar activity from 1957 to 2015 have been used in the conducted statistical analysis. The mathematical expectation of NmE, standard deviation of NmE from the expectation of NmE, and NmE variation coefficient have been calculated for each month of the year. The months of the formation of extrema of these statistical parameters of NmE were found.

  2. Statistical study of the ULF Pc4-Pc5 range fluctuations in the vicinity of Earth's magnetopause and correlation with the Low Latitude Boundary Layer thickness

    NASA Astrophysics Data System (ADS)

    Nykyri, K.; Dimmock, A. P.

    2016-07-01

    The main generation mechanisms for the Earth's Low Latitude Boundary Layer (LLBL) are considered to be magnetic reconnection, viscous interactions such as Kelvin-Helmholtz instability and associated plasma mixing and diffusion. We have performed a statistical study of the Ultra Low Frequency (ULF) fluctuation power at the Pc4-Pc5 range using ≈6 years of THEMIS measurements of the plasma velocity and magnetic field. The results reveal a clear dawn-dusk asymmetry showing that the fluctuation power is typically more enhanced in the vicinity of the magnetopause downstream of the quasi-parallel shock. The statistical study of the Vx-component of the plasma velocity indicates that the LLBL is also thicker on the dawn-sector. These results may suggest that the physical mechanisms that provide power in the Pc4-Pc5 range are more effective on the dawn-sector and provide a means for a more effective LLBL generation.

  3. Investigation of low-latitude hydrogen emission in terms of a two-component interstellar gas model

    NASA Technical Reports Server (NTRS)

    Baker, P. L.; Burton, W. B.

    1975-01-01

    High-resolution 21-cm hydrogen line observations at low galactic latitude are analyzed to determine the large-scale distribution of galactic hydrogen. Distribution parameters are found by model fitting, optical depth effects are computed using a two-component gas model suggested by the observations, and calculations are made for a one-component uniform spin-temperature gas model to show the systematic departures between this model and data obtained by incorrect treatment of the optical depth effects. Synthetic 21-cm line profiles are computed from the two-component model, and the large-scale trends of the observed emission profiles are reproduced together with the magnitude of the small-scale emission irregularities. Values are determined for the thickness of the galactic hydrogen disk between half density points, the total observed neutral hydrogen mass of the galaxy, and the central number density of the intercloud hydrogen atoms. It is shown that typical hydrogen clouds must be between 1 and 13 pc in diameter and that optical thinness exists on large-scale despite the presence of optically thin gas.

  4. The 4D-TECS integration for NASA TSRV airplane

    NASA Technical Reports Server (NTRS)

    Kaminer, I.; Oshaughnessy, P. R.

    1989-01-01

    The integration of the Total Energy Control System (TECS) concept with 4D navigation is described. This integration was made to increase the operational capacity of modern aircraft and encourage incorporation of this increased capability with the evolving National Airspace System (NAS). Described herein is: 4D smoothing, the basic concepts of TECS, the spoiler integration concept, an algorithm for nulling out time error, speed and altitude profile modes, manual spoiler implementation, 4D logic, and the results of linear and nonlinear analysis.

  5. A Mitochondrial Phylogeny and Biogeographical Scenario for Asiatic Water Shrews of the Genus Chimarrogale: Implications for Taxonomy and Low-Latitude Migration Routes

    PubMed Central

    Yuan, Shou-Li; Jiang, Xue-Long; Li, Zhen-Ji; He, Kai; Harada, Masashi; Oshida, Tatsuo; Lin, Liang-Kong

    2013-01-01

    The six species and three subspecies in the genus Chimarrogale (Soricomorpha: Soricidae) are commonly referred to as Asiatic water shrews. The Chimarrogale are the most widely distributed group of Nectogaline shrews, extending throughout the Oriental region and Japan. Because of the limited numbers of specimens available for study, the phylogenetic relationships and biogeographical history of this genus have not been comprehensively discussed. We used mitochondrial cytochrome b gene sequences to estimate phylogenetic relationships and divergence times among four Chimarrogale species, including all three subspecies of Chimarrogale himalayica. We also conducted a species delimitation analysis and tested two alternative migration scenarios in Asia through species distribution modeling and a reconstruction of the ancestral distribution. Here, we present the first proposed hypothesis regarding the Asiatic water shrew phylogeny and reveal ten putative species within the four recognized species. Distinct phylogenetic statuses of Chimarrogale phaeura, Chimarrogale platycephala, and Chimarrogale styani were confirmed. Chimarrogale himalayica was strongly supported as paraphyletic. We suggest that three subspecies of Chimarrogale himalayica should be reconsidered as distinct species. However, these suggestions must be considered with caution because only a single locus of a mtDNA gene was used. Four additional putative species, possibly distributed in central southwestern China and Taiwan, are currently undescribed; therefore, comprehensive morphological analyses are warranted to test their taxonomic statuses. The estimated molecular divergence times indicated that rapid speciation occurred during the early Pliocene, and current distribution patterns may have been affected by global cooling during the Pliocene/Pleistocene boundary. Reconstruction of the ancestral distribution and species distribution modeling for Asiatic water shrews revealed a low-latitude migration route

  6. First Evaluation of the Climatological Calibration Algorithm in the Real-time TMPA Precipitation Estimates over Two Basins at High and Low Latitudes

    NASA Technical Reports Server (NTRS)

    Yong, Bin; Ren, Liliang; Hong, Yang; Gourley, Jonathan; Tian, Yudong; Huffman, George J.; Chen, Xi; Wang, Weiguang; Wen, Yixin

    2013-01-01

    The TRMM Multi-satellite Precipitation Analysis (TMPA) system underwent a crucial upgrade in early 2009 to include a climatological calibration algorithm (CCA) to its realtime product 3B42RT, and this algorithm will continue to be applied in the future Global Precipitation Measurement era constellation precipitation products. In this study, efforts are focused on the comparison and validation of the Version 6 3B42RT estimates before and after the climatological calibration is applied. The evaluation is accomplished using independent rain gauge networks located within the high-latitude Laohahe basin and the low-latitude Mishui basin, both in China. The analyses indicate the CCA can effectively reduce the systematic errors over the low-latitude Mishui basin but misrepresent the intensity distribution pattern of medium-high rain rates. This behavior could adversely affect TMPA's hydrological applications, especially for extreme events (e.g., floods and landslides). Results also show that the CCA tends to perform slightly worse, in particular, during summer and winter, over the high-latitude Laohahe basin. This is possibly due to the simplified calibration-processing scheme in the CCA that directly applies the climatological calibrators developed within 40 degrees latitude to the latitude belts of 40 degrees N-50 degrees N. Caution should therefore be exercised when using the calibrated 3B42RT for heavy rainfall-related flood forecasting (or landslide warning) over high-latitude regions, as the employment of the smooth-fill scheme in the CCA bias correction could homogenize the varying rainstorm characteristics. Finally, this study highlights that accurate detection and estimation of snow at high latitudes is still a challenging task for the future development of satellite precipitation retrievals.

  7. First evaluation of the climatological calibration algorithm in the real-time TMPA precipitation estimates over two basins at high and low latitudes

    NASA Astrophysics Data System (ADS)

    Yong, Bin; Ren, Liliang; Hong, Yang; Gourley, Jonathan J.; Tian, Yudong; Huffman, George J.; Chen, Xi; Wang, Weiguang; Wen, Yixin

    2013-05-01

    The TRMM Multi-satellite Precipitation Analysis (TMPA) system underwent a crucial upgrade in early 2009 to include a climatological calibration algorithm (CCA) to its real-time product 3B42RT, and this algorithm will continue to be applied in the future Global Precipitation Measurement era constellation precipitation products. In this study, efforts are focused on the comparison and validation of the Version 6 3B42RT estimates before and after the climatological calibration is applied. The evaluation is accomplished using independent rain gauge networks located within the high-latitude Laohahe basin and the low-latitude Mishui basin, both in China. The analyses indicate the CCA can effectively reduce the systematic errors over the low-latitude Mishui basin but misrepresent the intensity distribution pattern of medium-high rain rates. This behavior could adversely affect TMPA's hydrological applications, especially for extreme events (e.g., floods and landslides). Results also show that the CCA tends to perform slightly worse, in particular, during summer and winter, over the high-latitude Laohahe basin. This is possibly due to the simplified calibration-processing scheme in the CCA that directly applies the climatological calibrators developed within 40° latitude to the latitude belts of 40°N-50°N. Caution should therefore be exercised when using the calibrated 3B42RT for heavy rainfall-related flood forecasting (or landslide warning) over high-latitude regions, as the employment of the smooth-fill scheme in the CCA bias correction could homogenize the varying rainstorm characteristics. Finally, this study highlights that accurate detection and estimation of snow at high latitudes is still a challenging task for the future development of satellite precipitation retrievals.

  8. Spatio-temporal variability of ionospheric Total Electron Content (TEC) over the Indian subcontinent derived from geodetic GPS network

    NASA Astrophysics Data System (ADS)

    Vijayan, M.; Kannoth, S.; Varghese, G.; Earnest, A.; Jade, S.; Bhatt, B. C.; Gupta, S. S.

    2013-12-01

    We present, for the first time, Ionospheric Total Electron Content (TEC) computed from dual frequency GPS data observed by Indian geodetic GPS network and neighboring IGS stations for more than a decade (2001-2012) (figure 1). Indian geodetic GPS network has more than 30 stations well spread across the Indian subcontinent, primarily, to study the tectonics of the Indian plate. Each station has geodetic grade dual frequency GPS receiver which are operated in continuous mode by making observations at every 30s since 2001. The ionospheric TEC presented here is computed from the code and phase GPS measurements using the software IONODETECT developed at CSIR 4PI. This decadal scale ionospheric data set covers from maxima of 23rd to maxima of 24th solar cycle with a broad spatial coverage from 35S to 56N and 38E to 134E (figure1). The GPS TEC computed at every 30 seconds over each sub-ionospheric point correlates well with International Reference Ionosphere(IRI) 2012 model in longer time scale, however, a strong spatio-temporal dependence in correlation is clearly observed. In addition a site specific, nearly systematic night time bias between GPS TEC and IRI-12 is noted. The advantage of using the systematic bias for correcting Differential Code Bias (DCB) in computing GPS TEC is discussed. We also discuss in detail the equatorial ionospheric processes and regional characteristics of Equatorial Ionization Anomaly (EIA) through latitudinal, diurnal, seasonal, and inter-annual variability of decadal scale GPS TEC computed over Indian subcontinent. EIA anomaly crust maxima during local noon on 30th November 2004 is clearly visible in the figure 1. The TEC variations associated with solar flares and solar maxima and minima during the solar cycles are also discussed to understand the impact of space weather on equatorial and mid latitude ionosphere as well as on navigation. Vertical TEC (VTEC) at each sub ionospheric pierce points (SIP) on 30th November 2004 from 0UTC to

  9. Geomorphic evidence for former lobate debris aprons at low latitudes on Mars: Indicators of the Martian paleoclimate

    USGS Publications Warehouse

    Hauber, E.; Van Gasselt, S.; Chapman, M.G.; Neukum, G.

    2008-01-01

    Circumferential depressions enclosing mesas and plateaus in the northern Kasei Valles and in the Tartarus Colles regions of Mars are interpreted as indicators of the former extent of lobate debris aprons, thought to be mixtures of ice and elastic particles. These former lobate debris aprons existed about 1 Ga ago and were embayed by lavas or other flow deposits. After the lobate debris aprons had been removed by sublimation and deflation, topographic depressions with a depth of 50 m and a width of several kilometers were left behind between the mesa or plateau scarp and the solidified flow materials. These depressions or moats are located equatorward of ??30?? at significantly lower latitudes than generally observed for occurrences of modem, intact lobate debris aprons. This observation provides evidence that the paleoclimate at that time was different than today, probably due to a higher averaged obliquity of the planet's rotational axis. Copyright 2008 by the American Geophysical Union.

  10. Modeling of Heat and Mass Transfer in a TEC-Driven Lyophilizer

    NASA Technical Reports Server (NTRS)

    Yuan, Zeng-Guang; Hegde, Uday; Litwiller, Eric; Flynn, Michael; Fisher, John

    2006-01-01

    Dewatering of wet waste during space exploration missions is important for crew safety as it stabilizes the waste. It may also be used to recover water and serve as a preconditioning step for waste compaction. A thermoelectric cooler (TEC)-driven lyophilizer is under development at NASA Ames Research Center for this purpose. It has three major components: (i) an evaporator section where water vapor sublimes from the frozen waste, (ii) a condenser section where this water vapor deposits as ice, and (iii) a TEC section which serves as a heat pump to transfer heat from the condenser to the evaporator. This paper analyses the heat and mass transfer processes in the lyophilizer in an effort to understand the ice formation behavior in the condenser. The analysis is supported by experimental observations of ice formation patterns in two different condenser units.

  11. Application of neural networks to South African GPS TEC modelling

    NASA Astrophysics Data System (ADS)

    Habarulema, John Bosco; McKinnell, Lee-Anne; Cilliers, Pierre J.; Opperman, Ben D. L.

    2009-06-01

    The propagation of radio signals in the Earth's atmosphere is dominantly affected by the ionosphere due to its dispersive nature. Global Positioning System (GPS) data provides relevant information that leads to the derivation of total electron content (TEC) which can be considered as the ionosphere's measure of ionisation. This paper presents part of a feasibility study for the development of a Neural Network (NN) based model for the prediction of South African GPS derived TEC. The South African GPS receiver network is operated and maintained by the Chief Directorate Surveys and Mapping (CDSM) in Cape Town, South Africa. Vertical total electron content (VTEC) was calculated for four GPS receiver stations using the Adjusted Spherical Harmonic (ASHA) model. Factors that influence TEC were then identified and used to derive input parameters for the NN. The well established factors used are seasonal variation, diurnal variation, solar activity and magnetic activity. Comparison of diurnal predicted TEC values from both the NN model and the International Reference Ionosphere (IRI-2001) with GPS TEC revealed that the IRI provides more accurate predictions than the NN model during the spring equinoxes. However, on average the NN model predicts GPS TEC more accurately than the IRI model over the GPS locations considered within South Africa.

  12. Potentialities of TEC topping: a simplified view of parametric effects

    SciTech Connect

    Morris, J.F.

    1980-01-01

    Reductions in the cost of thermionic-energy-conversion (TEC) modules yield direct decreases in cost of electricity (COE) from TEC-topped central-station power plants. Simplified COE, overall-efficiency charts presented illustrate this trend. Additional capital-cost diminution will result from designing more compact furnaces with considerably increased heat-transfer rates allowable and desirable for high-temperature TEC and heat pipes. Such improvements can evolve because of the protection from hot corrosion and slag as well as the thermal-expansion compatibilities offered by silicon-carbide clads on TEC-heating surfaces. Greater efficiencies and far fewer modules are possible with high-temperature, high-power-density TEC: This will decrease capital and fuel costs much more - and substantially increase electric-power outputs for fixed fuel inputs. In addition to more electricity, less pollution, and lower costs, TEC topping used directly in coal-combustion products will contribute to balance-of-payment gains and national energy independence.

  13. CFD Extraction Tool for TecPlot From DPLR Solutions

    NASA Technical Reports Server (NTRS)

    Norman, David

    2013-01-01

    This invention is a TecPlot macro of a computer program in the TecPlot programming language that processes data from DPLR solutions in TecPlot format. DPLR (Data-Parallel Line Relaxation) is a NASA computational fluid dynamics (CFD) code, and TecPlot is a commercial CFD post-processing tool. The Tec- Plot data is in SI units (same as DPLR output). The invention converts the SI units into British units. The macro modifies the TecPlot data with unit conversions, and adds some extra calculations. After unit conversions, the macro cuts a slice, and adds vectors on the current plot for output format. The macro can also process surface solutions. Existing solutions use manual conversion and superposition. The conversion is complicated because it must be applied to a range of inter-related scalars and vectors to describe a 2D or 3D flow field. It processes the CFD solution to create superposition/comparison of scalars and vectors. The existing manual solution is cumbersome, open to errors, slow, and cannot be inserted into an automated process. This invention is quick and easy to use, and can be inserted into an automated data-processing algorithm.

  14. Structure of small-scale field-aligned currents at middle and low latitudes having lower atmospheric origin

    NASA Astrophysics Data System (ADS)

    Nakanishi, K.; Iyemori, T.; Luhr, H.; Aoyama, T.

    2014-12-01

    The CHAMP magnetic data indicate that small amplitude (1-5 nT) magnetic fluctuations with period around a few tens of seconds along the orbit exist globally and almost all the time. Characteristics of the magnetic fluctuations including seasonal dependence having geographical characteristics strongly suggest that they are the small-scale spatial structure of field-aligned currents with lower atmospheric origin (Nakanishi et al., 2014). We suppose that gravity waves generated by lower atmospheric disturbances propagate to the ionosphere and drive the E-layer dynamo. The currents in the ionosphere divert along the magnetic field into the other hemisphere and make a closed circuit. To confirm the above scenario and to find the scale of the current circuit in longitudinal direction, we use the magnetic data observed by the SWARM satellites. By analysis of the magnetic data observed by the SWARM satellites, the magnetic fluctuations as recorded earlier by CHAMP are confirmed to have the same characteristics i.e., the magnetic fluctuation is perpendicular to the geomagnetic field; the amplitude on the dayside is much larger than that on the nightside; towards the dip equator the period tends to get longer. Because the three Swarm satellites have various spatial relations in 3-D space between their orbits, we could easily confirm that the objective magnetic fluctuations are not temporal but spatial structures. The longitudinal scale seems to be of the order of 100 km. We shall show the above results and some other characteristics of the current circuit and discuss whether or not our suggested model fits the observed characteristics.

  15. GPS scintillation and TEC depletion near the northern crest of equatorial anomaly over South China

    NASA Astrophysics Data System (ADS)

    Deng, Baichang; Huang, Jiang; Liu, Weifeng; Xu, Jie; Huang, Lingfeng

    2013-02-01

    This study presents a statistical analysis of GPS L-band scintillation with data observed from July 2008 to March 2012 at the northern crest of equatorial anomaly stations in Guangzhou and Shenzhen of South China. The variations of the scintillation with local time, season, solar activity and duration of scintillation patches were investigated. The relationship between the scintillation and TEC depletion was also reported. Our results revealed that GPS scintillation occurred from 19:30 LT (pre-midnight) to 03:00 LT (post-midnight). During quiet solar activity years, the scintillation was only observed in pre-midnight hours of equinox months and patches durations were mostly less than 60 min. During high solar activity years, more scintillation occurred in the pre-midnight hours of equinox and winter months; and GPS scintillation started to occur in the post-midnight hours of summer and winter. The duration of scintillation patches extended to 180 min in high solar activity years. Solar activity had a larger effect to strong scintillations (S4 > 0.6) than to weak scintillations (0.6 ⩾ S4 > 0.2). Strong scintillations were accompanied by TEC depletion especially in equinox months. We also discussed the relationship between TEC depletion and plasma bubble.

  16. Statistical Analysis of Ionospheric Storms on GPS TEC measurements between 2000 and 2014 in mid-latitude

    NASA Astrophysics Data System (ADS)

    Chung, J. K.

    2015-12-01

    The ionospheric storms that may generate the spatial/temporal gradient or irregularities of electron densities are very interest phenomena for two reasons. First, they occur by the increasing solar EUV/X-ray fluxes as well as by the equatorward or poleward plasma transportations by the global changes of the neutral winds and electric fields responded to geomagnetic storms. Second, they have been the practical interests in the satellite navigations and radio communications, especially in the mid-latitudes of the dense population regions in these days though ionosphere in mid-latitudes is quiet compared with high and low latitudes. In this presentation, the statistical analysis of the occurrences of the ionospheric storms in Korea are presented. They are examined from Korea GPS TEC dataset between 2000 and 2014 over the full-solar cycle coverage. We examine the two super geomagnetic storms cases of 29-31 October 2003 and 8-10 November 2004 to discuss the possible physical mechanisms for ionospheric storm of positive and negative phases and their affection on GPS positioning. The parameters to define the ionospheric storms are suggested to increase our understanding of their physical characteristic and then to apply the practical cases.

  17. A comparison of H-alpha intensity and radio wave scattering on eight low-latitude lines of sight

    NASA Technical Reports Server (NTRS)

    Spangler, Steven R.; Reynolds, Ronald J.

    1990-01-01

    Radio scattering and H-alpha measurements for eight sources in Cygnus are compared. The diameter of the radio scattering disk at 1 GHz is found to be correlated with emission measure as determined from the H-alpha measurements, and that strong radio scattering characterized by a diameter of about 30 milliarcsec is produced in regions with emission measures of about 100/cm exp 6 pc or less. The slope of diameter-emission measure correlation is steeper than would be the case if all lines of sight were characterized by the same turbulent outer scale and modulation index. It is suggested that the lines of sight to unscattered or lightly scattered sources traverse only a diffuse medium which is revealed by H-alpha observations at high latitudes. Heavily scattered sources are viewed through an additional component of interstellar H II which has turbulence with different properties.

  18. GPS meteorology in a low-latitude region: Remote sensing of atmospheric water vapor over the Malaysian Peninsula

    NASA Astrophysics Data System (ADS)

    Musa, T. A.; Amir, S.; Othman, R.; Ses, S.; Omar, K.; Abdullah, K.; Lim, S.; Rizos, C.

    2011-10-01

    This paper presents an accuracy assessment of IWV data obtained from one year of GPS measurements in Peninsular Malaysia and the correlation between this GPS-derived IWV and radiosonde-derived IWV. Four GPS stations in close proximity to existing radiosonde stations are assessed; the root mean square errors of the GPS-derived IWVs are 3.447 kg/m2, 3.786 kg/m2, 4.122 kg/m2 and 4.253 kg/m2 and their linear correlation coefficients are 0.877, 0.797, 0.851 and 0.849, respectively. Such strong correlations indicate that GPS data has the potential to be used for water vapor observation in Peninsular Malaysia for locations with few weather stations.

  19. Low latitude ionospheric scintillation and zonal plasma irregularity drifts climatology around the equatorial anomaly crest over Kenya

    NASA Astrophysics Data System (ADS)

    Olwendo, O. J.; Baki, P.; Cilliers, P. J.; Doherty, P.; Radicella, S.

    2016-02-01

    In this study we have used a VHF and GPS-SCINDA receiver located at Nairobi (36.8°E, 1.3°S, dip -24.1°) in Kenya to investigate the climatology of ionospheric L-band scintillation occurrences for the period 2009 to 2012; and seasonal variation of the zonal plasma drift irregularities derived from a VHF receiver for the period 2011. The annual and diurnal variations of L-band scintillation indicate occurrence at post sunset hours and peaks in the equinoctial months. However VHF scintillation occurs at all seasons around the year and is characterized by longer duration of activity and a slow fading that continues till early morning hours unlike in the L-band where they cease after midnight hours. A directional analysis has shown that the spatial distribution of scintillation events is mainly on the Southern and Western part of the sky over Nairobi station closer to the edges of the crest of the Equatorial Ionization Anomaly. The distribution of zonal drift velocities of the VHF related scintillation structures indicates that they move at velocities in the range of 20-160 m/s and their dimension in the East-West direction is in the range of 100-00 km. The December solstice is associated with the largest plasma bubbles in the range of 600-900 km. The most significant observation from this study is the occurrence of post-midnight scintillation without pre-midnight scintillations during magnetically quiet periods. The mechanism leading to the formation of the plasma density irregularity causing scintillation is believed to be via the Rayleigh Tailor Instability; it is however not clear whether we can also attribute the post-midnight plasma bubbles during magnetic quiet times to the same mechanism. From our observations in this study, we suggest that a more likely cause of the east ward zonal electric fields at post-midnight hours is the coupling of the ionosphere with the lower atmosphere during nighttime. This however needs a further investigation based on relevant

  20. Dipole tilt angle effects on the latitude of the cusp and cleft/low-latitude boundary layer

    SciTech Connect

    Newell, P.T.; Meng, C.I. )

    1989-06-01

    A large data set of approximately 12,000 Defense Meteorological Satellite Program satellite F7 crossings of the cusp or the cleft (i.e., the dayside magnetospheric boundary layer) over a 3-year period is studied for seasonal dependence in latitudinal position. A carefully tested algorithm is used to distinguish the various dayside particle precipitation regions and boundaries. It is found that in the 1,100-1,300 MLT sector, the cusp proper exhibits about {minus}0.06{degree} magnetic latitude (MLAT) shift for each degree increase in dipole tilt angle. Thus the difference between the average summer and winter cusp positions is close to 4{degree} MLAT, approximately symmetric about equinox. For the cleft (magnetospheric boundary layer) the variation is smaller. For example, in the 0700-0900 MLT sector the cleft equatorward boundary shift is {minus} 0.027{degree} MLAT/1{degree} dipole tilt. These results are in general agreement with the predictions of empirical magnetospheric magnetic field models. Various ground-based and low-altitude observations can be systematically affected by the seasonal latitudinal shift herein documented.

  1. Equatorial ionospheric irregularities using GPS TEC derived index

    NASA Astrophysics Data System (ADS)

    Oladipo, O. A.; Schüler, Torben

    2013-01-01

    We have used the rate of change of TEC (ROT) derived fluctuation index to study irregularities in the ionosphere at Franceville in Gabon (Lat.= -1.63°, Long.=13.55°, Geomag. Lat.= -0.71°), an equatorial station in the African sector. Based on a preliminary study at two equatorial stations at different longitude an average ROTI index which gives the fluctuation level over half an hour at a particular station was put forward. This index eliminates the noise spikes or extreme value usually present in ROTI index estimate. The new index ROTI was used to study ionospheric irregularity occurrence at Franceville. As far as we know, this is the first time irregularity occurrence study is being done at this station using GNSS data. The results obtained showed that ionospheric irregularity season at Franceville is from March to November and that there is a kind of minimum around June. Very low irregularities activity is also observed around January. Pre-midnight fluctuation is observed to be more pronounced at Franceville during the period studied.

  2. Aurorae Observed at the Canary Islands

    NASA Astrophysics Data System (ADS)

    Vázquez, M.; Vaquero, J. M.

    2010-12-01

    Descriptions of eleven aurorae observed in the Canary Islands during the period 1770 - 2010 have been found in different documents. Most of them are coincident with periods of strong solar activity, with the geomagnetic latitude playing a minor role. Coronal mass ejections are the most probable solar source of these low-latitude events. The absence of low-latitude aurorae is verified in our sample during the Dalton Minimum and the first half of the twentieth century.

  3. Formation of monitoring and evening electron temperature peaks in the low latitude F region during 19-21 March 1988

    NASA Astrophysics Data System (ADS)

    Pavlov, A. V.; Fukao, S.; Kawamura, S.

    A comparison between the election, T_e, and ion, T_i, temperatures measured by the middle and upper atmosphere (MU) radar Shigaraki (34.85° N, 136.10° E, Japan) and those produced by the model of the ionosphere and plasmasphere is presented for 19-21 March 1988. We compare the modeled NmF2 and hmF2 with those observed bz the Akita, Kokubunji, Yamagawa,Okinawa, Chung-Li, Manila, Vanimo, and Darwin sounders and by the MU radar during the the 19-21 March 1988 geomagnetically quiet time period near 201° geomagnetic longitude. The variations of T_e are characterized by morning and evening peaks over the Darwin Yamagawa, Kokubunji and Akita ionosonde stations and over the MU radar while the model produces morning and daytime peaks in T_e above the Vanimo, Manila, Chung-Li, and Okinawa, ionosonde stations. There is a rapid heating of daytime electrons by photoelectrons, and the difference between T_e and T_i is increased after sunrise because the night-time electron density, N_e, is less than that by day, and the resulting electron cooling is less than that by day. After the abrupt morning increase, T_e decreases due to the electron cooling increase caused by the increase in N_e. We found that the night-time downward ExB drift causes the decrease in NmF2 before sunrise and the resulting increase in the magnitude, of the T_e morning peak. This plasma drift becomes more effective in lowering N_e with lowering the geomagnetic latitude, ϕ, i. e. the decrease in |ϕ| leads to the decrease in the night-time N_e before sunrise and the resulting increase in the magnitude of the morning T_e peak. The effect of the plasma drift, W, due to the neutral wind on the formation of the morning T_e peak is decreased with lowering ϕ. The increase in |ϕ| leads to the increase of the effect to the night-time W on N_e, the increase in the night-time N_e before sunrise, and the resulting decrease in the morning T_e peak, created by an evening N_e decrease, becomes strong. The decrease in

  4. Erratum: ``A Low-Latitude Halo Stream around the Milky Way'' (ApJ, 588, 824 [2003])

    NASA Astrophysics Data System (ADS)

    Yanny, Brian; Newberg, Heidi Jo; Grebel, Eva K.; Kent, Steve; Odenkirchen, Michael; Rockosi, Connie M.; Schlegel, David; Subbarao, Mark; Brinkmann, Jon; Fukugita, Masataka; Ivezic, Željko; Lamb, Don Q.; Schneider, Donald P.; York, Donald G.

    2004-04-01

    The zero points of the stellar templates used to measure radial velocity in the main body of this paper have been found to be systematically in error. Correction of the radial velocities significantly increases the derived circular velocity of the stars in the planar stream, to 215+/-25 km s-1. The velocity dispersion of the stream is somewhat lower than earlier results with the modified analysis. Two types of stars were studied in this paper. The original template for stars of type F, used to study the ``Monoceros arc'' Galactic structure, was incorrectly zero-pointed by 20 km s-1. The original template for stars of type A, used to measure the Sagittarius dwarf tidal stream, produced radial velocities systematically shifted by 49 km s-1. In both cases, the sign of the error is such that for nearly all stars, the correct values of the heliocentric radial velocities are lower than those originally quoted. A cross-correlation of Sloan Digital Sky Survey (SDSS) spectra with templates from the ELODIE survey (C. Soubiran, D. Katz, & R. Cayrel, ApJ, 588, 824 [2003]) was performed to find new radial velocities for each star (D. Schlegel 2003, private communication). This showed that our radial velocities were systematically shifted by an amount that depends on the type of the star observed and the original template against which it was cross-correlated. To determine the measurement error with the new templates, we identified 445 F-type stars and 1109 A-type stars that had been observed twice by the SDSS. These stars were chosen with the color and magnitude criteria used to select stars in Figures 6 and 9. The errors in the F stars were a good match to a Gaussian with a σ of 28 km s-1. The errors in the A star comparison were significantly non-Gaussian, with large tails. A χ2 fit to a Gaussian (similar to the technique we use in this paper to measure the width of the streams) yielded a σ of 35 km s-1. Dividing by sqrt(2) to reflect two independent measurements, we

  5. Principal component analysis for the research of TEC variations' dynamic in the Ionosphere

    NASA Astrophysics Data System (ADS)

    Maslennikova, Yulia; Bochkarev, Vladimir

    Principal Component Analysis (it is also known as Proper Orthogonal Decomposition (POD)) is one of the basic ways to research of spatial structure of various geophysical parameters. POD involves a mathematical procedure that transforms a number of possibly correlated variables into a smaller number of uncorrelated variables called principal components. However it is requires considering the features both physical processes in investigated system and form of representation of experimental data for this method to be used. Problems that appear through using POD and some possible ways of solution of those problems (through example of variations of the Total Electronic Content (TEC) of ionosphere) are represented in that report. The maps of TEC are given by the Jet Propulsion Laboratory (JPL) during the 1998-2009 years. When PCA is used it is necessary to consider the dominating periodicity in observable date (first of all daily and seasonal). The proposed solution of that problem is using of co-moving frame of reference in which the "subsolar" point remains motionless. That trick allows a better way to investigate the spatial structure of the first components than using a geographical coordinate system. It appears that a type of scalar product of a data vectors has an influence on the decomposition components' orthogonality definition. One of the main goals of this research is to investigate the influence of scalar multiplication's type on adequacy of decomposition in consideration of a relative position of graticule points and of a TEC data' preprocessing method. The TEC decomposition's reproducibility checking is made by using a statistical modeling. Another goal of this research is to investigate the influence of the distribution type of geophysical parameters' fluctuation on quality of a mode separation. Decomposition is performed using nonparametric estimation of degree of correlation. It is shown that the proposed method makes it possible to improve a mode

  6. Temporal and spatial distribution of GPS-TEC anomalies prior to the strong earthquakes

    NASA Astrophysics Data System (ADS)

    Zhu, Fuying; Wu, Yun; Zhou, Yiyan; Gao, Yang

    2013-06-01

    Earthquakes are one of the most destructive and harmful natural disasters, especially in recent years, the 2008/5/12 Wenchuan M7.9 earthquake, the 2011/3/11 Tohoku M9.0 earthquake and the 2012/4/11 Sumatra M8.6 earthquake have caused a significant impact to the human life. In this paper, we make a study of the temporal and spatial distribution of the Global Positioning System Total Electron Content (GPS TEC) anomalies prior to the three strong earthquakes by the method of statistical analysis. Our results show that the pre-earthquake ionospheric anomalies are mainly positive anomalies and take the shape of a double-crest structure with a trough near the epicenter. The ionospheric anomalies do not coincide with the vertical projection of the epicenter of the subsequent earthquake, but mainly localize in the near-epicenter region and corresponding ionospheric anomalies are also simultaneously observed in the magnetic conjugate region prior to the three earthquakes. In addition, the amplitude and scale-size of the ionospheric ΔTEC are different with the magnitude of the earthquake, and the horizontal scale-size of the greatest anomalies before the Tohoku M9.0 earthquake is ˜30∘ in longitude and ˜10∘ in latitude, with the maximum amplitude of TEC disturbances reaching ˜20 TECu relative to the background. The peak of anomaly enhancement usually occurs in the afternoon to sunset (i.e. between 14:00 and 18:00 local time) which lasts for approximate 2 hours. Possible causes of these anomalies are discussed, and after eliminating the effect of solar activities and magnetic storms it can be concluded that the detected obvious and regular anomalous behavior in TEC within just a few days before the earthquakes is related with the forthcoming earthquakes with high probability.

  7. Impacts of December 2006 Solar Radio Bursts on the African Equatorial GPS-TEC

    NASA Astrophysics Data System (ADS)

    Akala, A. O.; Somoye, E.; Akiode, A.

    2013-12-01

    Abstract Strong solar activities were observed on the 6 and 13th December, 2006; a minimum phase of solar cycle 23. These flares, in the magnitude of X6.5 and X3.4 on December 6 and 13, 2006 respectively, were absolutely unexpected, with attendant eruptions of solar energetic particles (SEPs) into the earth's ionosphere. This study presents the impacts of the solar flares on African equatorial TEC measurements. TEC data from three African equatorial GPS stations, namely; Libreville (0.36°N, 9.67°E, 8.04oS mag. lat), Gabon; Mbarara (0.60°S, 30.74°E, 9.00oS mag. lat), Uganda; and Malindi (3.00oS, 40.20oE, 10.98oS mag. lat), Kenya were used for the study. Both flares caused noticeable enhancements in TEC measurements at the three stations. These results further revealed the need for the space science community to also pay attention to the impacts of space weather on space and ground based systems during the minimum phases of solar cycles.

  8. First tomographic observations of the Midlatitude Summer Nighttime Anomaly over Japan

    NASA Astrophysics Data System (ADS)

    Thampi, Smitha V.; Lin, Charles; Liu, Huixin; Yamamoto, Mamoru

    2009-10-01

    Recently, a chain of digital beacon receivers has been established over Japan, mainly for the tomographic imaging of the ionosphere. These receivers are installed at Shionomisaki (33.45°N, 135.8°E), Shigaraki (34.85°N, 136.1°E), and Fukui (36.06°N,136°E), which continuously track the Low Earth Orbiting Satellites (LEOS), and the simultaneous line-of-sight Total Electron Content (TEC) data are used for tomographic reconstruction. In the images obtained during July 2008, it is seen that the nighttime electron densities exceed the daytime values on almost all days over latitudes >33-34°N. On several days, these northern latitudes show enhanced electron densities compared to the low-latitude region during nighttime. These are the prominent features of the “Midlatitude Summer Nighttime Anomaly (MSNA)” that is recently observed in the northern hemisphere and is considered similar to the nighttime Weddell Sea Anomaly (WSA). This is the first study of the MSNA using tomographic technique and found its significant day-to-day variability. The ionosonde data from Wakkanai (45.4°N, 141.7° E), ground-based GPS TEC observations using the GEONET, CHAMP in situ electron density measurements, and Formosat3/COSMIC (F3/C) occultation measurements are also used to confirm the presence of MSNA over this region and to examine its variability. It is seen that, in general, during the local summer period, electron density over the northern latitudes is highest at ˜2000-2100 LT and the latitudinal enhancement in electron density also begins to appear around the same time, which continues to exist even at later hours.

  9. First Tomographic Observations of the Mid-latitude Summer Nighttime Anomaly (MSNA) over Japan

    NASA Astrophysics Data System (ADS)

    Yamamoto, M.; Thampi, S.; Lin, C.; Liu, H.

    2009-12-01

    Recently, a chain of digital beacon receivers has been established over Japan, mainly for the tomographic imaging of the ionosphere. These receivers are installed at Shionomisaki (33.45°N, 135.8°E), Shigaraki (34.85°N, 136.1°E) and Fukui (36.06°N,136°E), which continuously track the Low Earth Orbiting Satellites (LEOS), and the simultaneous line-of-sight relative Total Electron Content (TEC) data are used for tomographic reconstruction. In the images obtained during July 2008, it is seen that the nighttime electron densities exceed the daytime values on almost all days over latitudes >33-34°N. On several days, these northern latitudes show enhanced electron densities compared to the low-latitude region during nighttime. These are the prominent features of the ‘Mid-latitude Summer Nighttime Anomaly (MSNA)’ that is recently observed in the northern hemisphere and is considered similar to the nighttime Weddell Sea Anomaly (WSA). This is the first study of the MSNA using tomographic technique, and found its significant day-to-day variability. The Formosat3/COSMIC occultation measurements, ionosonde data from Wakkanai (45.4°N, 141.7° E), ground-based GPS TEC observations using the GEONET, and CHAMP in situ electron density measurements are also used to confirm the presence of MSNA over this region and to examine its variability. It is seen that in general, during the local summer period, electron density over the northern latitudes is highest at ~2000-2100 LT and the latitudinal enhancement in electron density also begins to appear around the same time, which continues to exist even at later hours. This feature is explained by considering the neutral wind effect in the geomagnetic frame.

  10. Analysis of traveling ionospheric disturbances (TIDs) in GPS TEC launched by the 2011 Tohoku earthquake

    NASA Astrophysics Data System (ADS)

    Crowley, Geoff; Azeem, Irfan; Reynolds, Adam; Duly, Timothy M.; McBride, Patrick; Winkler, Clive; Hunton, Don

    2016-05-01

    Traveling ionospheric disturbances (TIDs) have been detected using various measurement techniques, including HF sounders, incoherent scatter radars, in situ measurements, and optical techniques. However, observations of TIDs have tended to be sparse and there is a need for additional observations to provide new scientific insight into the geophysical source phenomenology and wave propagation physics. The dense network of GPS receivers around the globe offers a relatively new data source to observe and monitor TIDs. In this paper, we use total electron content (TEC) measurements from ~4000 GPS receivers throughout the continental United States to observe TIDs associated with the 11 March 2011 Tohoku tsunami. The tsunami propagated across the Pacific to the U.S. west coast over several hours, and we show that corresponding TIDs were observed in the US. Using this network of GPS receivers we present a 2D imaging of TEC perturbations and calculate various TID parameters, including horizontal wavelength, speed, and period. Well-formed, planar TIDs were detected over the west coast of the U.S. ~10 h after the earthquake. Fast Fourier transform analysis of the observed waveforms revealed that the period of the wave was 15.1 min with a horizontal wavelength of 194.8 km, phase velocity of 233.0 m/s, and an azimuth of 105.2° (propagating nearly due east in the direction of the tsunami wave). These results are consistent with the TID observations in airglow measurements from Hawaii earlier in the day and with other GPS TEC observations.

  11. Modulation of low-latitude west wind on abnormal track and intensity of tropical cyclone Nargis (2008) in the Bay of Bengal

    NASA Astrophysics Data System (ADS)

    Li, Wei-Wei; Wang, Chunzai; Wang, Dongxiao; Yang, Lei; Deng, Yi

    2012-03-01

    Tropical cyclone (TC) Nargis (2008) made landfall in Myanmar on 02 May 2008, bringing a storm surge, major flooding, and resulting in a significant death toll. TC Nargis (2008) displayed abnormal features, including rare eastward motion in its late stage, rapid intensification before landing. Using reanalysis data and a numerical model, we investigated how a low-latitude westerly wind modulated TC Nargis' (2008) track and provided favorable atmospheric conditions for its rapid intensification. More importantly, we found a possible counterbalance effect of flows from the two hemispheres on the TC track in the Bay of Bengal. Our analysis indicates that a strong westerly wind burst across the Bay of Bengal, resulting in TC Nargis' (2008) eastward movement after its recurvature. This sudden enhancement of westerly wind was mainly due to the rapidly intensified mid-level cross-equatorial flow. Our results show that a high-pressure system in the Southern Hemisphere induced this strong, mid-level, cross-equatorial flow. During the rapid intensification period of TC Nargis (2008), this strong and broad westerly wind also transported a large amount of water vapor to TC Nargis (2008). Sufficient water vapor gave rise to continuously high and increased mid-level relative humidity, which was favorable to TC Nargis' (2008) intensification. Condensation of water vapor increased the energy supply, which eventuated the intensification of TC Nargis (2008) to a category 4 on the Saffir-Simpson scale.

  12. Spread-F during the magnetic storm of 22 January 2004 at low latitudes: Effect of IMF-Bz in relation to local sunset time

    NASA Astrophysics Data System (ADS)

    Rastogi, R. G.; Chandra, H.; Janardhan, P.; Hoang, Thai Lan; Condori, Louis; Pant, T. K.; Prasad, D. S. V. V. D.; Reinisch, B.

    2014-08-01

    The paper describes the results of spread-F at low latitude stations around the world during the magnetic storm starting at 0130 UT on 22 January 2004. The storm can be divided into two phases, first phase up to 1000 UT when interplanetary magnetic field IMF-Bz was highly fluctuating around a small positive value and the second phase after a sudden large southward turning of IMF-Bz at 1030 UT. The first phase produced strong spread-F at Jicamarca, Sao Luis, and Ascension Island and caused complete inhibition of spread-F at Thumba and Waltair in India. It generated weak spread-F at Ho Chi Minh City in Vietnam and strong spread-F at Hainan and Chung Li. The strong spread-F at Hainan and Chung Li were caused by the positive IMF-Bz during the first phase of the storm and not by the negative pulse of IMF-Bz at 1000 UT.

  13. Comparative sequence stratigraphy of low-latitude versus high-latitude lacustrine rift basins: Seismic data examples from the East African and Baikal rifts

    USGS Publications Warehouse

    Scholz, C.A.; Moore, T.C.; Hutchinson, D.R.; Golmshtok, A. Ja; Klitgord, Kim D.; Kurotchkin, A.G.

    1998-01-01

    Lakes Baikal, Malawi and Tanganyika are the world's three largest rift valley lakes and are the classic modem examples of lacustrine rift basins. All the rift lakes are segmented into half-graben basins, and seismic reflection datasets reveal how this segmentation controls the filling of the rift basins through time. In the early stages of rifting, basins are fed primarily by flexural margin and axial margin drainage systems. At the climax of syn-rift sedimentation, however, when the basins are deeply subsided, almost all the margins are walled off by rift shoulder uplifts, and sediment flux into the basins is concentrated at accommodation zone and axial margin river deltas. Flexural margin unconformities are commonplace in the tropical lakes but less so in high-latitude Lake Baikal. Lake levels are extremely dynamic in the tropical lakes and in low-latitude systems in general because of the predominance of evaporation in the hydrologic cycle in those systems. Evaporation is minimized in relation to inflow in the high-latitude Lake Baikal and in most high-latitude systems, and consequently, major sequence boundaries tend to be tectonically controlled in that type of system. The acoustic stratigraphies of the tropical lakes are dominated by high-frequency and high-amplitude lake level shifts, whereas in high-latitude Lake Baikal, stratigraphic cycles are dominated by tectonism and sediment-supply variations.

  14. Research of the effects of TEC on UFPA noise performance

    NASA Astrophysics Data System (ADS)

    Jiang, Qiao; Xie, Guangzhong; Xiong, Lixia; Liao, Baobin; Que, Longcheng; Zhou, Yun; Lv, Jian

    2012-10-01

    Infrared detection technology plays a more and more important role in military and business. Uncooled infrared focal plane array (UFPA) is a kind of thermal detector, which detects the infrared radiation of target through the microbolometer's photoelectric conversion. Based on the thermal model of UFPA, stable and accordant substrate temperature of microbolometer array is extreme important to improve the UFPA's noise performance. After researching the effects of substrate temperature act on UFPA's noise performance and responsivity, a low noise data capture system with TEC controller for UFPA is designed. And a 320x240 microbolometer array's noise is tested with this system. With the TEC controller, the substrate temperature fluctuates at a margin of only 0.006 ºC. The test result shows that a 12.1% decrease in RMS noise, a 14.5% decrease in FPN noise and improvement of responsivity non-uniformity over time have been obtained after using TEC controller in UFPA.

  15. Ionospheric Disturbances Observed during Earthquakes and Solar Eclipses at Tashkent and Kitab GPS Stations

    NASA Astrophysics Data System (ADS)

    Ahmedov, Bobomurat

    2016-07-01

    Since the Global Positioning System (GPS) data can be used to measure the ionospheric TEC, the technique has received our attention as a potential tool to detect ionospheric perturbations related to the earthquakes and we mainly analysed GPS derived TEC disturbances from two GPS stations located in Tashkent and Kitab, for possible earthquake ionospheric precursors. This talk reports the ionospheric anomalies observed during strong local earthquakes (M greater than 5.0) which occurred mostly in and around Uzbekistan in seismically active zones, during years 2010 to 2015 within 1000 km from the observing GPS stations located in Tashkent and Kitab. The solar and geomagnetic conditions were quiet during occurrence of the selected more than 30 earthquakes. We produced TEC time series over both sites and apply them to detect anomalous TEC signals preceding or accompanying the earthquakes. The results show anomalous enhancements which are examined in the earthquakes. In general the anomalies occurred 1-6 days before the earthquakes as ionospheric electromagnetic precursors. To identify the anomalous values of TEC we calculated differential TEC (dTEC). dTEC is obtained by subtracting 15 days backward running mean of vTEC from the values of observed vTEC at each epoch. This procedure removes normal variations in TEC. For a detail study of the data, we have calculated dTEC values for all the months and examined the anomalous TEC variations before the earthquakes. A thorough analysis of the data shows abnormal variations in TEC and ionospheric anomalies, such as variations in the electron density few days before the earthquakes, may play a role of one of the electromagnetic precursory signals of earthquakes. TEC decrease during the solar eclipses is also obtained from data at GPS station in Tashkent and Kitab. During the solar flares occurrence the amplitude of TEC is amplified with compare to the nondisturbed initial monthly mean background value after the flare.

  16. A MLP neural network as an investigator of TEC time series to detect seismo-ionospheric anomalies

    NASA Astrophysics Data System (ADS)

    Akhoondzadeh, M.

    2013-06-01

    Anomaly detection is extremely important for earthquake parameters estimation. In this paper, an application of Artificial Neural Networks (ANNs) in the earthquake precursor's domain has been developed. This study is concerned with investigating the Total Electron Content (TEC) time series by using a Multi-Layer Perceptron (MLP) neural network to detect seismo-ionospheric anomalous variations induced by the powerful Tohoku earthquake of March 11, 2011.The duration of TEC time series dataset is 120 days at time resolution of 2 h. The results show that the MLP presents anomalies better than referenced and conventional methods such as Auto-Regressive Integrated Moving Average (ARIMA) technique. In this study, also the detected TEC anomalies using the proposed method, are compared to the previous results (Akhoondzadeh, 2012) dealing with the observed TEC anomalies by applying the mean, median, wavelet and Kalman filter methods. The MLP detected anomalies are similar to those detected using the previous methods applied on the same case study. The results indicate that a MLP feed-forward neural network can be a suitable non-parametric method to detect changes of a non linear time series such as variations of earthquake precursors.

  17. X-Ray Crystal Structure of Bone Marrow Kinase in the X Chromosome: A Tec Family Kinase

    SciTech Connect

    Muckelbauer, Jodi; Sack, John S.; Ahmed, Nazia; Burke, James; Chang, ChiehYing Y.; Gao, Mian; Tino, Joseph; Xie, Dianlin; Tebben, Andrew J.

    2012-06-27

    Bone marrow kinase in the X chromosome, a member of the Tec family of tyrosine kinases, plays a role in both monocyte/macrophage trafficking as well as cytokine secretion. Although the structures of Tec family kinases Bruton's tyrosine kinase and IL-2-inducible T-cell kinase are known, the crystal structures of other Tec family kinases have remained elusive. We report the X-ray crystal structures of bone marrow kinase in the X chromosome in complex with dasatinib at 2.4 {angstrom} resolution and PP2 at 1.9 {angstrom} resolution. The bone marrow kinase in the X chromosome structures reveal a typical kinase protein fold; with well-ordered protein conformation that includes an open/extended activation loop and a stabilized DFG-motif rendering the kinase in an inactive conformation. Dasatinib and PP2 bind to bone marrow kinase in the X chromosome in the ATP binding pocket and display similar binding modes to that observed in other Tec and Src protein kinases. The bone marrow kinase in the X chromosome structures identify conformational elements of the DFG-motif that could potentially be utilized to design potent and/or selective bone marrow kinase in the X chromosome inhibitors.

  18. The estimation of the ionosphere state over Mexico region based on TEC data

    NASA Astrophysics Data System (ADS)

    Sergeeva, Maria; Maltseva, Olga; Mejia-Ambriz, Julio-Cesar; Gonzalez-Esparza, Americo; De La Luz-Rodriguez, Victor Hugo; Romero-Hernández, Esmeralda

    2016-07-01

    In recent years, increasing interest toward Space Weather (SW) issues comes not only from researches but the general public as well because SW events can influence unfavorably all aspects of human life and technology. To prevent negative impacts the constant monitoring of the near-Earth space is required based on radio methods and with the help of satellites, magnetometers, all-sky imagers, other ground-based instruments, including Total Electron Content (TEC) studies and modeling. In October of 2014 the Mexican Space Weather Service (SCiESMEX) was established. The objectives of this new service include the study, analysis and forecast of changes in the ionosphere over the Mexican region (geographic latitudes 14º - 32º N, geomagnetic latitudes 23º - 38º N). From the beginning of September 2015 the continuous monitoring of TEC variations over Mexico is performed to monitor the Space Weather conditions. The traditional parameters describing these conditions in the ionosphere are the critical frequency of the F2-layer foF2 and its maximum height hmF2 measured by ground ionosondes. Since Mexico at the moment has no ionosonde in operation but has a rather dense network of GPS receivers the present paper discusses the possibility of evaluating the ionosphere state with use of the vertical total electron content (vTEC) reconstructed using the data of GPS receivers. To verify such prospect the comparison was made between the results for Mexico and for the adjacent regions having ionosondes. Three problems are being solved: (1) comparison of two options to obtain TEC values (global ionospheric maps and values from local receivers calculated on the base of software complex provided by Institute of Solar-Terrestrial Physics, Siberian Branch, Russian Academy of Sciences) based on daily and seasonal variations of monthly medians, (2) comparison of instantaneous values during disturbances, (3) determination of foF2 from observational values of TEC using the medians of the

  19. Ionospheric Signatures of Tohoku-Oki Tsunami in GPS TEC: Comparisons with Models Near the Epicenter and Far Afield

    NASA Astrophysics Data System (ADS)

    Galvan, D. A.; Komjathy, A.; Hickey, M. P.; Foster, J. H.; Song, Y.

    2011-12-01

    Ocean tsunamis can produce atmospheric internal gravity waves that propagate to the ionosphere, creating disturbances in ionospheric electron density that travel with the ocean waves below. These traveling ionospheric disturbances (TIDs) can be observed using measurements of total electron content (TEC) between Global Positioning System (GPS) satellites and receivers on the ground. We present observations of ionospheric perturbations caused by multiple tsunami events, including the Tohoku tsunami of March 11, 2011 in regions both near the epicenter and far afield throughout the Pacific Ocean. We have investigated measurements of ionospheric TEC from 1198 GPS receivers in the Japanese GEONET network, dozens of receivers on the Hawaiian Islands, and hundreds more receivers on the west coasts of North and South America. We compare the observed TEC perturbation magnitudes to those produced by the atmosphere-ionosphere coupling model of Hickey et al, 2009. We also compare the position and velocity of the ionospheric gravity wave front with that of the ocean tsunami as estimated by the tsunami sea-surface model of Song, 2007, the Method Of Splitting Tsunami (MOST) model of NOAA, and various observations by Deep-ocean Assessment and Reporting of Tsunamis (DART) buoys. GPS TEC measurements show a TID magnitude in agreement with the atmosphere-ionosphere coupling model, and often aligned with the position of the modeled ocean tsunami wavefront. TIDs from the Tohoku earthquake and tsunami were observed moving away from the epicenter at approximate speeds of 3400 m/s, 1000 m/s and 200-300 m/s, consistent with Rayleigh waves, acoustic waves, and gravity waves, respectively. The gravity wave perturbations, seen as soon as 30 minutes after the earthquake, are mostly between 0.5 to 1.5 TECU, but in some regions were as high as 3 TECU (1 TECU = 10^16 el/m2), representing ~10% of the background TEC. Due to the dense GPS network and high earthquake magnitude, these are the clearest

  20. Plasmasphere pulsations observed simultaneously by midlatitude SuperDARN radars, ground magnetometers and THEMIS spacecraft during an auroral substorm

    NASA Astrophysics Data System (ADS)

    Ruohoniemi, J. M.; Shi, X.; Baker, J. B. H.; Frissell, N. A.; Hartinger, M.; Liu, J.

    2015-12-01

    We present simultaneous ground and space-based observations of ultra-low frequency (ULF) pulsations which occurred during an auroral substorm on September 25th, 2014. Expansion phase onset began at 06:04 UT at which time three midlatitude SuperDARN radars observed strong pulsations in the Pi2 frequency range with peak to peak amplitude reaching as high as 1km/s. Similar pulsations occurred during a later auroral intensification which started at 06:20 UT. Both sets of pulsations were detected in a region of radar backscatter located inside the subauroral polarization stream (SAPS) equatorward of the auroral oval specified by THEMIS all sky imagers and inside the midlatitude density trough as mapped by GPS/TEC measurements. The amplitude of the pulsations was large enough to reverse the direction of the SAPS flow from westward to eastward. Similar pulsations were detected by electric field instrument aboard the THEMIS probe D located inside the plasmasphere. Simultaneous observations from several low-latitude ground magnetometers (some located on the dayside) further illustrate the global nature of the pulsations and suggest they may have been associated with a plasmaspheric cavity resonance (PCR). Pulsed tailward plasma flow observed by THEMIS probe E at the geosynchronous orbit suggests that the compressional energy to generate the PCR was from the Bursty Bulk Flows (BBFs) braking against the magnetospheric dipolar region.

  1. Tidal variability during stratospheric sudden warming in 2009: Comparison between GAIA model and COSMIC and TIMED/SABER observations

    NASA Astrophysics Data System (ADS)

    Jin, Hidekatsu; Miyoshi, Yasunobu; Fujiwara, Hitoshi; Shinagawa, Hiroyuki; Pancheva, Dora; Mukhtarov, Plamen

    2012-07-01

    We compare results from a whole atmosphere-ionosphere coupled model, GAIA, and from the COSMIC and TIMED/SABER observations during 2008/2009 northern winter season. The GAIA model has assimilated meteorological reanalysis data by a nudging method. The comparison shows excellent agreements in the major features from the stratosphere to the ionosphere including the growth and decay of the major stratospheric sudden warming (SSW) event in 2009. During the major SSW period, a pronounced semidiurnal variation in the F-region electron density and its local-time phase shift similar to the previous observations are reproduced by the model and COSMIC observation. The model suggests that the TEC variation is caused by an enhanced semidiurnal variation in the EXB drift, which is probably related to an amplified semidiurnal migrating tide (SW2) in the lower thermosphere. The model and TIMED/SABER observation show that the SW2 tide amplifies at low latitudes from the stratosphere to the thermosphere as well as the phase variation. Possible mechanisms will be discussed in the presentation.

  2. Remote Sensing of Low and Mid-Latitude Ionospheric Disturbances During Solar Minimum Using CITRIS and CERTO Measurements of TEC and Radio Scintillation

    NASA Astrophysics Data System (ADS)

    Siefring, C. L.; Bernhardt, P. A.

    2010-12-01

    Unique data on ionospheric plasma disturbances from the Naval Research Laboratory CITRIS (Scintillation and TEC Receiver in Space) instrument will be presented. CITRIS is a multi-band receiver that recorded TEC (Total Electron Content) and radio scintillations from Low-Earth Orbit (LEO) on STPSat1. The 555+/5 km altitude 35° inclination orbit covers low and mid-latitudes. The measurements require propagation from a transmitter to a receiver through the F-region plasma. CITRIS used both 1) satellite beacons in LEO, such as the NRL CERTO (Coherent Electromagnetic Radio TOmography) three-frequency beacons transmitting at 150/400/1067 MHz and 2) the French global network of ground-based DORIS (Doppler Orbitography and Radiopositioning Integrated by Satellite) beacons transmitting at 401.25 and 2036.25 MHz. CITRIS was operated in a complementary fashion with the C/NOFS satellite during most of its first year of operations; C/NOFS carries CERTO beacon along with in-situ diagnostics. CITRIS and ground receivers can simultaneously measure TEC and scintillations on different paths using CERTO on C/NOFS. When C/NOFS is not in view, CITRIS makes measurements from DORIS beacons and other LEO satellites. Because of the orbits CITRIS will always make measurements at the same longitude within 48 min of C/NOFS. The ability to look at multiple paths is unique and useful for studying the spatial extent and time duration of disturbances. The combination of TEC and scintillation measurements provides information on a range of scale-sizes from >1 km to about 100 m. The joint data set on plasma structures at low-latitudes is a focus of our presentation, with the addition of comparisons to CITRIS data taken at mid-latitude. Several types of irregularities have been studied including Spread-F and the newly discovered dawn-side depletions. The data covers large portions of the Earth (including the Pacific, African and South American sectors) during an unusually quite portion of the most

  3. Analysis of the fluctuations of the total electron content (TEC) measured at Goose Bay using tools of nonlinear methods

    NASA Astrophysics Data System (ADS)

    Kumar, K. Satheesh; Kumar, C. V. A.; George, Benny; Renuka, G.; Venugopal, C.

    2004-02-01

    In this paper we report the evidence of a low-dimensional chaos in a set of data observed outside laboratories. The dynamic behavior of the time series of the fluctuations of the total electron content (TEC) measured at Goose Bay, which is a high-latitude station, is analyzed in detail using the tools of nonlinear dynamics. The low-dimensional character of the dynamics is evident from the estimated value of the fraction of false neighbors for various dimensions and the correlation dimension. The deterministic nature of the dynamics is investigated using recurrence plots and spatiotemporal entropy. The chaotic nature of the underlying dynamics of the fluctuations of TEC is shown by the power spectrum indicating exponential decay and the calculated positive value of Lyapunov exponent. This is also supported by the results of the comparison of the chaotic characteristics of the time series of variations of TEC with the pseudochaotic characteristic of the colored noise time series. The results of the tests based on the prediction error and the time reversal asymmetry statistic reject the hypothesis that TEC belongs to the family of linear stochastic signals. The nonlinear non-Gaussian nature of the oscillations of variations of TEC is further investigated by the surrogate data test based on several geometrical and dynamical characteristics of the variations of TEC such as mutual information, the fraction of the false nearest neighbours, the local slopes of the correlation sums, the curves giving Lyapunov exponents, and finally, the value of Lyapunov exponents. The results of this analysis show that low-dimensional chaotic dynamics could be a possible and fruitful concept which can be utilized to study the disturbance in the ionosphere as in the case of magnetospheric dynamics. We feel that the dynamical invariants like Lyapunov exponents and correlation dimension can describe the disturbance in the variations of TEC and thus the disturbance in the ionosphere. Hence the

  4. Te/C nanocomposites for Li-Te Secondary Batteries

    PubMed Central

    Seo, Jeong-Uk; Seong, Gun-Kyu; Park, Cheol-Min

    2015-01-01

    New battery systems having high energy density are actively being researched in order to satisfy the rapidly developing market for longer-lasting mobile electronics and hybrid electric vehicles. Here, we report a new Li-Te secondary battery system with a redox potential of ~1.7 V (vs. Li+/Li) adapted on a Li metal anode and an advanced Te/C nanocomposite cathode. Using a simple concept of transforming TeO2 into nanocrystalline Te by mechanical reduction, we designed an advanced, mechanically reduced Te/C nanocomposite electrode material with high energy density (initial discharge/charge: 1088/740 mA h cm−3), excellent cyclability (ca. 705 mA h cm−3 over 100 cycles), and fast rate capability (ca. 550 mA h cm−3 at 5C rate). The mechanically reduced Te/C nanocomposite electrodes were found to be suitable for use as either the cathode in Li-Te secondary batteries or a high-potential anode in rechargeable Li-ion batteries. We firmly believe that the mechanically reduced Te/C nanocomposite constitutes a breakthrough for the realization and mass production of excellent energy storage systems. PMID:25609035

  5. C-TEC: Ohio's First All-Green School

    ERIC Educational Resources Information Center

    Krall, Angie

    2009-01-01

    In Ohio's Licking County, the Career and Technology Education Centers (C-TEC) is a leader in the green movement. This eco-friendly school incorporates environmental sustainability in all aspects of its programming and is the first Leadership in Energy and Environmental Design (LEED)-certified public building in the state. While eco-friendly…

  6. Te/C nanocomposites for Li-Te Secondary Batteries.

    PubMed

    Seo, Jeong-Uk; Seong, Gun-Kyu; Park, Cheol-Min

    2015-01-01

    New battery systems having high energy density are actively being researched in order to satisfy the rapidly developing market for longer-lasting mobile electronics and hybrid electric vehicles. Here, we report a new Li-Te secondary battery system with a redox potential of ~1.7 V (vs. Li(+)/Li) adapted on a Li metal anode and an advanced Te/C nanocomposite cathode. Using a simple concept of transforming TeO2 into nanocrystalline Te by mechanical reduction, we designed an advanced, mechanically reduced Te/C nanocomposite electrode material with high energy density (initial discharge/charge: 1088/740 mA h cm(-3)), excellent cyclability (ca. 705 mA h cm(-3) over 100 cycles), and fast rate capability (ca. 550 mA h cm(-3) at 5C rate). The mechanically reduced Te/C nanocomposite electrodes were found to be suitable for use as either the cathode in Li-Te secondary batteries or a high-potential anode in rechargeable Li-ion batteries. We firmly believe that the mechanically reduced Te/C nanocomposite constitutes a breakthrough for the realization and mass production of excellent energy storage systems.

  7. Te/C nanocomposites for Li-Te Secondary Batteries

    NASA Astrophysics Data System (ADS)

    Seo, Jeong-Uk; Seong, Gun-Kyu; Park, Cheol-Min

    2015-01-01

    New battery systems having high energy density are actively being researched in order to satisfy the rapidly developing market for longer-lasting mobile electronics and hybrid electric vehicles. Here, we report a new Li-Te secondary battery system with a redox potential of ~1.7 V (vs. Li+/Li) adapted on a Li metal anode and an advanced Te/C nanocomposite cathode. Using a simple concept of transforming TeO2 into nanocrystalline Te by mechanical reduction, we designed an advanced, mechanically reduced Te/C nanocomposite electrode material with high energy density (initial discharge/charge: 1088/740 mA h cm-3), excellent cyclability (ca. 705 mA h cm-3 over 100 cycles), and fast rate capability (ca. 550 mA h cm-3 at 5C rate). The mechanically reduced Te/C nanocomposite electrodes were found to be suitable for use as either the cathode in Li-Te secondary batteries or a high-potential anode in rechargeable Li-ion batteries. We firmly believe that the mechanically reduced Te/C nanocomposite constitutes a breakthrough for the realization and mass production of excellent energy storage systems.

  8. Industrial Maintenance Technology (IM-TEC). Student Manual.

    ERIC Educational Resources Information Center

    Fusch, Gene E.

    This student manual explains an innovative strategy through which Bellingham Technical College's (Washington) evening Industrial Electrician and Millwright Apprenticeships were aggregated with workforce upgrade course offerings to form the college's first evening degree program in Industrial Maintenance Technology (IM-TEC). Section 1 contains a…

  9. A novel protein tyrosine kinase Tec identified in lamprey, Lampetra japonica.

    PubMed

    Li, Ranran; Su, Peng; Liu, Chang; Zhang, Qiong; Zhu, Ting; Pang, Yue; Liu, Xin; Li, Qingwei

    2015-08-01

    Protein tyrosine kinase Tec, a kind of non-receptor tyrosine kinase, is primarily found to be expressed in T cells, B cells, hematopoietic cells, and liver cells as a cytoplasmic protein. Tec has been proved to be a critical modulator of T cell receptor signaling pathway. In the present study, a homolog of Tec was identified in the lamprey, Lampetra japonica. The full-length Tec cDNA of L. japonica (Lja-Tec) contains a 1923 bp open reading frame that encodes a 641-amino acid protein. The multi-alignment of the deduced amino acid sequence of Lja-Tec with typical vertebrate Tecs showed that it possesses all conserved domains of the Tec family proteins, indicating that an ortholog of Tec exists in the extant jawless vertebrate. In the phylogenetic tree that was reconstructed with 24 homologs of jawless and jawed vertebrates, the Tecs from lampreys and hagfish were clustered as a single clade. The genetic distance between the outgroup and agnathan Tecs' group is closer than that between outgroup and gnathostome Tecs' group, indicating that its origin was far earlier than any of the jawed vertebrates. The mRNA levels of Lja-Tec in lymphocyte-like cells and gills were detected by real-time quantitative polymerase chain reaction. Results showed that it was significantly upregulated under stimulation with mixed pathogens. This result was further confirmed by western blot analysis. All these results indicated that Lja-Tec plays an important role in immune response. Our data will provide a reference for the further study of lamprey Tec and its immunological function in jawless vertebrates. PMID:26079172

  10. A novel protein tyrosine kinase Tec identified in lamprey, Lampetra japonica.

    PubMed

    Li, Ranran; Su, Peng; Liu, Chang; Zhang, Qiong; Zhu, Ting; Pang, Yue; Liu, Xin; Li, Qingwei

    2015-08-01

    Protein tyrosine kinase Tec, a kind of non-receptor tyrosine kinase, is primarily found to be expressed in T cells, B cells, hematopoietic cells, and liver cells as a cytoplasmic protein. Tec has been proved to be a critical modulator of T cell receptor signaling pathway. In the present study, a homolog of Tec was identified in the lamprey, Lampetra japonica. The full-length Tec cDNA of L. japonica (Lja-Tec) contains a 1923 bp open reading frame that encodes a 641-amino acid protein. The multi-alignment of the deduced amino acid sequence of Lja-Tec with typical vertebrate Tecs showed that it possesses all conserved domains of the Tec family proteins, indicating that an ortholog of Tec exists in the extant jawless vertebrate. In the phylogenetic tree that was reconstructed with 24 homologs of jawless and jawed vertebrates, the Tecs from lampreys and hagfish were clustered as a single clade. The genetic distance between the outgroup and agnathan Tecs' group is closer than that between outgroup and gnathostome Tecs' group, indicating that its origin was far earlier than any of the jawed vertebrates. The mRNA levels of Lja-Tec in lymphocyte-like cells and gills were detected by real-time quantitative polymerase chain reaction. Results showed that it was significantly upregulated under stimulation with mixed pathogens. This result was further confirmed by western blot analysis. All these results indicated that Lja-Tec plays an important role in immune response. Our data will provide a reference for the further study of lamprey Tec and its immunological function in jawless vertebrates.

  11. The role of the zonal E×B plasma drift in the low-latitude ionosphere at high solar activity near equinox from a new three-dimensional theoretical model

    NASA Astrophysics Data System (ADS)

    Pavlov, A. V.

    2006-10-01

    A new three-dimensional, time-dependent theoretical model of the Earth's low and middle latitude ionosphere and plasmasphere has been developed, to take into account the effects of the zonal E×B plasma drift on the electron and ion number densities and temperatures, where E and B are the electric and geomagnetic fields, respectively. The model calculates the number densities of O+(4S), H+, NO+, O2+, N2+, O+(2D), O+(2P), O+(4P), and O+(2P*) ions, the electron density, the electron and ion temperatures using a combination of the Eulerian and Lagrangian approaches and an eccentric tilted dipole approximation for the geomagnetic field. The F2-layer peak density, NmF2, and peak altitude, hmF2, which were observed by 16 ionospheric sounders during the 12-13 April 1958 geomagnetically quiet time high solar activity period are compared with those from the model simulation. The reasonable agreement between the measured and modeled NmF2 and hmF2 requires the modified equatorial meridional E×B plasma drift given by the Scherliess and Fejer (1999) model and the modified NRLMSISE-00 atomic oxygen density. In agreement with the generally accepted assumption, the changes in NmF2 due to the zonal E×B plasma drift are found to be inessential by day, and the influence of the zonal E×B plasma drift on NmF2 and hmF2 is found to be negligible above about 25° and below about -26° geomagnetic latitude, by day and by night. Contrary to common belief, it is shown, for the first time, that the model, which does not take into account the zonal E×B plasma drift, underestimates night-time NmF2 up to the maximum factor of 2.3 at low geomagnetic latitudes, and this plasma transport in geomagnetic longitude is found to be important in the calculations of NmF2 and hmF2 by night from about -20° to about 20° geomagnetic latitude. The longitude dependence of the night-time low-latitude influence of the zonal E×B plasma drift on NmF2, which is found for the first time, is explained in terms

  12. A comparative study of TEC response for the African equatorial and mid-latitudes during storm conditions

    NASA Astrophysics Data System (ADS)

    Habarulema, John Bosco; McKinnell, Lee-Anne; Burešová, Dalia; Zhang, Yongliang; Seemala, Gopi; Ngwira, Chigomezyo; Chum, Jaroslav; Opperman, Ben

    2013-09-01

    The solar wind effects on the Earth's environment are studied for their basic scientific values and crucial practical impacts on technological systems. This paper reports results of Total Electron Content (TEC) changes during two successive ionospheric storms of 7-12 November 2004 using GPS data derived from dual frequency receivers located at African equatorial and midlatitudes. In the geographic coordinate system, equatorial TEC variability is considered over Libreville (0.36°N, 9.67°E), Gabon and Mbarara (0.60°S, 30.74°E), Uganda. TEC over midlatitude stations Sutherland (32.38°S, 20.81°E) and Springbok (29.67°S, 17.88°E), South Africa are analysed. The analysis of the storm time ionospheric variability over South Africa was undertaken by comparing the critical frequency of the F2 layer (foF2) and the peak height of the F2 layer (hmF2) values obtained from Grahamstown (33.30°S, 26.53°E) and Madimbo (22.4°S, 30.9°E) ionosonde measurements. During the analysed storm period it is observed that GPS TEC for midlatitudes was depleted significantly with a corresponding depletion in foF2, due to the reduction in GUVI O/N2 ratio as observed from its global maps. Over the equatorial latitudes, positive storm effects are more dominant especially during the storm main phase. Negative storm effects are observed over both mid and equatorial latitudes during the recovery phase. A shift in equatorial TEC enhancement (from one GPS station to another) is observed during magnetic storms and has been partially attributed to passage of Travelling Ionospheric Disturbances (TIDs). Magnetometer data over the International Real-time Magnetic Observatory Network (intermagnet) station, Addis Ababa, AAE (9.03°N, 38.77°E) has been used to help with the explanation of possible causes of equatorial ionospheric TEC dynamics during the analysed magnetic storm period.

  13. Evaluation of Hi-Tec Implant Restoration in Mandibular First Molar Region- A Prospective Clinical Study

    PubMed Central

    Sreeram, Roopa Rani. S.; Prasad, L Krishna; Chakravarthi, P Srinivas; Devi, Naga Neelima; Sreeram, Sanjay Krishna

    2015-01-01

    Background and Aims Missing teeth lead to loss of structural balance, inefficient function, poor aesthetics and psychological effects on human beings, which needs restoration for normal contour, function and aesthetics. Several natural or synthetic substitutes are being used for replacement of missing tooth since centuries. Implants are the latest modality of replacement. So, the study was aimed to assess clinical success rate of Hi-Tec implant; which is economical and new in market. Results of the study will help clinician for appropriate implant selection. Materials and Methods The study included 10 patients from 19 to 31 years and needed restoration of missing mandibular first molar. Restoration had done using Hi Tec Single-tooth implants with metal-ceramic single crown prosthesis after three months of osseointegration. The implants were evaluated clinically (bleeding on probing, probing depth, implant mobility- periotest) and radiographically (marginal bone loss and peri-implant radiolucency) for six years. The observers were blinded for the duration of the study to prevent bias. Results All the patients had uneventful post-surgical healing. No bleeding on probing, Implant mobility, peri-implant radiolucency with minimal marginal bone loss and constant probing depths were observed well within the normal range during follow-up periods. Conclusion Two stage single-tooth Hi Tec implant restoration can be used as a successful treatment modality for replacing mandibular first molar in an economic way. However, these results were obtained after 6 years of follow up with a smaller sample size, so long term multi center studies with a larger sample size is recommended for the predictability of success rate conclusively. PMID:26436053

  14. GPS-TEC of the Ionospheric Disturbances as a Tool for Early Tsunami Warning

    NASA Astrophysics Data System (ADS)

    Kunitsyn, Viacheslav E.; Nesterov, Ivan A.; Shalimov, Sergey L.; Krysanov, Boris Yu.; Padokhin, Artem M.; Rekenthaler, Douglas

    2013-04-01

    Recently, the GPS measurements were used for retrieving the information on the various types of ionospheric responses to seismic events (earthquakes, seismic Rayleigh waves, and tsunami) which generate atmospheric waves propagating up to the ionospheric altitudes where the collisions between the neutrals and charge particles give rise to the motion of the ionospheric plasma. These experimental results can well be used in architecture of the future tsunami warning system. The point is an earlier (in comparison with seismological methods) detection of the ionospheric signal that can indicate the moment of tsunami generation. As an example we consider the two-dimensional distributions of the vertical total electron content (TEC) variations in the ionosphere both close to and far from the epicenter of the Japan undersea earthquake of March 11, 2011 using radio tomographic (RT) reconstruction of high-temporal-resolution (2-minute) data from the Japan and the US GPS networks. Near-zone TEC variations shows a diverging ionospheric perturbation with multi-component spectral composition emerging after the main shock. The initial phase of the disturbance can be used as an indicator of the tsunami generation and subsequently for the tsunami early warning. Far-zone TEC variations reveals distinct wave train associated with gravity waves generated by tsunami. According to observations tsunami arrives at Hawaii and further at the coast of Southern California with delay relative to the gravity waves. Therefore the gravity wave pattern can be used in the early tsunami warning. We support this scenario by the results of modeling with the parameters of the ocean surface perturbation corresponding to the considered earthquake. In addition it was observed in the modeling that at long distance from the source the gravity wave can pass ahead of the tsunami. The work was supported by the Russian Foundation for Basic Research (grants 11-05-01157 and 12-05-33065).

  15. Regional optimization of the IRI-2012 output (TEC, foF2) by using derived GPS-TEC

    NASA Astrophysics Data System (ADS)

    Ssessanga, Nicholas

    2016-07-01

    Accurate measurement and determination of the state of the ionosphere has become a key point as ground-based communication systems become more space dependent. However, due to limited infrastructure, a number of global models have been developed with extensive interpolation techniques to comprehensively describe ionospheric dynamics. As a result, most global models do not perform adequately in regions with a paucity of ionospheric measurements. In this paper, the most recent International Reference Ionosphere (IRI-2012) model output, Total Electron Content (TEC) and F2 layer critical frequency (foF2), are optimized (over a range of 120 ° E-150 ° E and 20 ° N-50 ° N in longitude and latitude, respectively). To obtain the optimal solution, we adjust two input parameters, the 12-month running mean sun spot number (R12) and the ionospheric index (IG12), in relation to the derived Global Positioning System (GPS) vertical TEC (VTEC). The results are compared to the measured TEC and foF2 from GPS receivers and ionosondes, respectively. The analysis shows that the modified IRI-2012 model is more accurate at estimating both the TEC and the foF2 values than the original model during days of geomagnetic quiet and disturbance.

  16. First observations of poleward large-scale traveling ionospheric disturbances over the African sector during geomagnetic storm conditions

    NASA Astrophysics Data System (ADS)

    Habarulema, John Bosco; Katamzi, Zama Thobeka; Yizengaw, Endawoke

    2015-08-01

    This paper presents first observations of poleward traveling ionospheric disturbances (TIDs) during strong geomagnetic conditions over the African sector. By analyzing different data sets we have observed both positive and negative ionospheric responses during the storm period of 08-10 March 2012. Considering the African region as a whole, three longitudinal sectors were strategically selected to establish the entire regional response. On both sides of the geomagnetic equator, results show poleward shift in peak total electron content (TEC) enhancements/depletions at different times which are associated to large-scale TIDs. The observed phenomena are linked to the global ionospheric response and electrodynamics. The understanding has been established using data from International GNSS Service receiver network, radio occultation electron density profiles, derived E×B drift measurements from magnetometer observations and regional ground-based and satellite data. Contrary to other related studies, generated regional TEC perturbation maps were not enough to show obvious directions of the large-scale TIDs due to insufficient data over the northern hemispheric part of the African sector. There appears to be a switch between positive and negative storm phases during the same storm period especially in the Southern Hemisphere part of the African region where "enough" data were available. However, a detailed analysis revealed that the positive storm phase corresponded to the expansion of the equatorial ionization anomaly (EIA) toward some parts of midlatitude regions (and possibly with the contribution from low-latitude electrodynamics associated to equatorial electrojet), while the other part recorded a negative storm phase due to storm-induced changes from the auroral origin. We have observed a simultaneous occurrence of both poleward and equatorward propagating TIDs over the African sector during the same geomagnetic storm period. Our results show that short-lived large

  17. Wave Propagation in the Ionosphere Associated With Earthquakes Revealed by GPS- TEC 4D Tomography

    NASA Astrophysics Data System (ADS)

    Watada, S.; Obayashi, M.; Ozawa, S.

    2008-12-01

    Hi-density high-rate sampling GPS network data is ideal for imaging quickly changing 3D structures in the ionosphere. GPS-TEC observation by GEONET in Japan during the 2003 Tokachi-Oki earthquake shows a clear propagating ionospheric disturbance. Heki and Ping (2005) interpreted the phenomena as a propagating sound wave in the thermosphere which was originally radiated into the atmosphere from the earthquake source region. To understand the ionosphere disturbance directly, we developed 4D ionosphere tomography method as an extension of a mantle tomography method to retrieve 3D seismic velocity structure of the mantle from traveltimes of seismic body waves from earthquakes to the seismic stations. We applied this tomography method to 1 Hz GPS-TEC data from GEONET which provides a dense line of sight coverage of space and time above and around the Japanese islands during and the after the earthquake. The image results show dispersive propagating waves, i.e., the phase speed of the waves is different from the wave energy propagation speed. The first phase, which appears first 100 km above the epicenter area, propagates horizontally with a phase speed about 1km/s and the secondary phase propagates slower. A close examination of the propagation of the first phase shows dispersion of the phase. The positive peak of the first phase travels 10% faster than the negative peak so that the peak shape broadens as it proceeds. The amplitude of the positive peak diminishes as it propagates over 1400 km distance from the source region. In contrast to the positive peak, the negative peak first appears as small amplitude and grows after traveling over 1000 km from the source region. Study of the evolution of the 4D GPS-TEC disturbance will provide rich information about the mechanisms of generation and propagation of ionospheric disturbance through the solid-earth-atmosphere-ionosphere coupling. Ionospheric disturbance can be generated from land surface deformation and the ocean

  18. Millennial-Scale Abrupt Changes in Strength of the Monsoons During the Last Glacial: Event Sequence During Low Latitude Stadial/Interstadial Transitions

    NASA Astrophysics Data System (ADS)

    Higginson, M. J.; Altabet, M. A.; Wincze, L.; Herbert, T. D.; Murray, D. W.; Murray, R. W.

    2003-12-01

    We exploit the unprecedented ability to synchronize two high-resolution sedimentary records from the Oman and Pakistan margins of the Arabian Sea to derive sea surface temperature (SST) gradient estimates over the last 65 Kyr. Millennial-scale cycles in monsoon dominance parallel Dansgaard-Oeschger events recorded in Greenland. Switches occurred during the last glacial period between a strong summer monsoon climate mode (inter-stadials) and an intensified winter monsoon (during stadials). The amplitude of individual monsoon events and Greenland temperature extremes appears broadly comparable, suggesting that the response to, and likely forcing for, such events was quasi-global in nature. The fidelity of the sedimentary nitrogen isotope record has allowed us to identify a 20cm interval at ODP Site 723 on the Oman margin containing a stadial/inter-stadial between 43-42 Kyr BP. We employ sedimentary δ 15N, chlorin pigment and alkenone abundances, major and minor element analyses of 2mm samples across this interval to generate a comprehensive, multi-proxy data set to understand the sequence of climatic events, especially the relative intensity of summer and winter monsoons, during these times. A lack of evidence for bioturbation in excess of our sampling resolution facilitates decadal-scale climatic reconstructions. Using a four-component flux-dilution model, we show that the deposition of carbonate decreased in parallel with an increase in TOM flux from stadial to inter-stadial time. This interval is also marked by a significant drop in lithogenic flux, analogous to a similar decrease noted during deglaciation in the western Arabian Sea. Combined with alkenone UK'37-derived estimates for SST, we conclude that the climatological shift from stadial to inter-stadial conditions at low latitudes was characterized by several switches in mean monsoon state. The winter monsoon was the dominant mode during maximum stadial conditions, and conversely that the summer monsoon was

  19. GPS scintillation and TEC gradients at equatorial latitudes in April 2006

    NASA Astrophysics Data System (ADS)

    Alfonsi, L.; Spogli, L.; Tong, J. R.; de Franceschi, G.; Romano, V.; Bourdillon, A.; Le Huy, M.; Mitchell, C. N.

    2011-05-01

    We use observations of ionospheric scintillation at equatorial latitudes from two GPS receivers specially modified for recording, at a sampling rate of 50 Hz, the phase and the amplitude of the L1 signal and the Total Electron Content (TEC) from L1 and L2. The receivers, called GISTM (GPS Ionospheric Scintillation and TEC Monitor), are located in Vietnam (Hue, 16.4°N, 107.6°E; Hoc Mon, 10.9°N, 106.6°E). These experimental observations are analysed together with the tomographic reconstruction of the ionosphere produced by the Multi-Instrument Data Analysis System (MIDAS) for investigating the moderate geomagnetic storm which occurred on early April 2006, under low solar activity. The synergic adoption of the ionospheric imaging and of the GISTM measurements supports the identification of the scale-sizes of the ionospheric irregularities causing scintillations and helps the interpretation of the physical mechanisms generating or inhibiting the appearance of the equatorial F layer irregularities. In particular, our study attributes to the turning of the IMF (Interplanetary Magnetic Field) between northward and southward direction an important role in the inhibition of the generation of spread F irregularities resulting in a lack of scintillation enhancement in the post-sunset hours.

  20. Nature of the 1100 Micron AzTEC-COSMOS Sources

    NASA Astrophysics Data System (ADS)

    Yun, Min Su; Aguirre, J.; Aretxaga, I.; Austermann, J.; Bock, J.; Fazio, G.; Huang, J.; Hughes, D.; Kang, Y.; Kim, S.; Lowenthal, J.; Ma, C.; Mauskopf, P.; Perera, T.; Sanders, D.; Scott, K.; Scoville, N.; Wilson, G.; Yoon, I.

    2006-12-01

    The Cosmic Evolution Survey (COSMOS) is a 2 square degree HST/ACS survey specifically designed to probe galaxy evolution as a function of time and environment (PI: N. Scoville). To take advantage of the extensive complementary databases already available through the COSMOS collaboration, we have undertaken a 1100 micron imaging survey of a 30' x 30' field centered just north of the earlier mm/submm surveys by the Bolocam on CSO and MAMBO on the IRAM 30-m telescope. In this poster paper, we will compare the results of the AzTEC and Bolocam surveys and discuss the nature of the AzTEC sources based on the existing multi-wavelength data in hand.

  1. The TEA transcription factor Tec1 links TOR and MAPK pathways to coordinate yeast development.

    PubMed

    Brückner, Stefan; Kern, Sandra; Birke, Raphael; Saugar, Irene; Ulrich, Helle D; Mösch, Hans-Ulrich

    2011-10-01

    In Saccharomyces cerevisiae, the TEA transcription factor Tec1 controls several developmental programs in response to nutrients and pheromones. Tec1 is targeted by the pheromone-responsive Fus3/Kss1 mitogen-activated protein kinase (MAPK) cascade, which destabilizes the transcription factor to ensure efficient mating of sexual partner cells. The regulation of Tec1 by signaling pathways that control cell division and development in response to nutrients, however, is not known. Here, we show that Tec1 protein stability is under control of the nutrient-sensitive target of rapamycin complex 1 (TORC1) signaling pathway via the Tip41-Tap42-Sit4 branch. We further show that degradation of Tec1 upon inhibition of TORC1 by rapamycin does not involve polyubiquitylation and appears to be proteasome independent. However, rapamycin-induced Tec1 degradation depends on the HECT ubiquitin ligase Rsp5, which physically interacts with Tec1 via conserved PxY motives. We further demonstrate that rapamycin and mating pheromone control Tec1 protein stability through distinct mechanisms by targeting different domains of the transcription factor. Finally, we show that Tec1 is a positive regulator of yeast chronological lifespan (CLS), a known TORC1-regulated process. Our findings indicate that in yeast, Tec1 links TORC1 and MAPK signaling pathways to coordinate control of cellular development in response to different stimuli. PMID:21840851

  2. Informal report on measurements of slant TEC by FORTE

    SciTech Connect

    Massey, R.S.

    1997-11-21

    Los Alamos National Laboratory`s Space and Atmospheric Sciences group is now operating the FORTE satellite, which has two sets of instruments: optical detectors and radio detectors. In this report the author describes work with one set of radio detectors that allow measurements of the total electron content (TEC) traversed by VHF radiation originating at an electromagnetic pulse (EMP) generator located at Los Alamos.

  3. THE REDSHIFT AND NATURE OF AzTEC/COSMOS 1: A STARBURST GALAXY AT z = 4.6

    SciTech Connect

    Smolcic, V.; Capak, P.; Blain, A. W.; Salvato, M.; Masters, D.; Moric, I.; Riechers, D. A.; Ilbert, O.; Aretxaga, I.; Hughes, D.; Schinnerer, E.; Sheth, K.; Aravena, M.; Aussel, H.; Aguirre, J.; Berta, S.; Carilli, C. L.; Civano, F.; Fazio, G.; Huang, J.

    2011-04-20

    Based on broadband/narrowband photometry and Keck DEIMOS spectroscopy, we report a redshift of z = 4.64{sup +0.06}{sub -0.08} for AzTEC/COSMOS 1, the brightest submillimeter galaxy (SMG) in the AzTEC/COSMOS field. In addition to the COSMOS-survey X-ray to radio data, we report observations of the source with Herschel/PACS (100, 160 {mu}m), CSO/SHARC II (350 {mu}m), and CARMA and PdBI (3 mm). We do not detect CO(5 {yields} 4) line emission in the covered redshift ranges, 4.56-4.76 (PdBI/CARMA) and 4.94-5.02 (CARMA). If the line is within this bandwidth, this sets 3{sigma} upper limits on the gas mass to {approx}<8 x 10{sup 9} M{sub sun} and {approx}<5 x 10{sup 10} M{sub sun}, respectively (assuming similar conditions as observed in z {approx} 2 SMGs). This could be explained by a low CO-excitation in the source. Our analysis of the UV-IR spectral energy distribution of AzTEC 1 shows that it is an extremely young ({approx}<50 Myr), massive (M{sub *} {approx} 10{sup 11} M{sub sun}), but compact ({approx}<2 kpc) galaxy, forming stars at a rate of {approx}1300 M{sub sun} yr{sup -1}. Our results imply that AzTEC 1 is forming stars in a 'gravitationally bound' regime in which gravity prohibits the formation of a superwind, leading to matter accumulation within the galaxy and further generations of star formation.

  4. Large Scale Ionospheric Response During March 17, 2013 Geomagnetic Storm: Reanalysis Based on Multiple Satellites Observations and TIEGCM Simulations

    NASA Astrophysics Data System (ADS)

    Yue, X.; Wang, W.; Schreiner, W. S.; Kuo, Y. H.; Lei, J.; Liu, J.; Burns, A. G.; Zhang, Y.; Zhang, S.

    2015-12-01

    Based on slant total electron content (TEC) observations made by ~10 satellites and ~450 ground IGS GNSS stations, we constructed a 4-D ionospheric electron density reanalysis during the March 17, 2013 geomagnetic storm. Four main large-scale ionospheric disturbances are identified from reanalysis: (1) The positive storm during the initial phase; (2) The SED (storm enhanced density) structure in both northern and southern hemisphere; (3) The large positive storm in main phase; (4) The significant negative storm in middle and low latitude during recovery phase. We then run the NCAR-TIEGCM model with Heelis electric potential empirical model as polar input. The TIEGCM can reproduce 3 of 4 large-scale structures (except SED) very well. We then further analyzed the altitudinal variations of these large-scale disturbances and found several interesting things, such as the altitude variation of SED, the rotation of positive/negative storm phase with local time. Those structures could not be identified clearly by traditional used data sources, which either has no gloval coverage or no vertical resolution. The drivers such as neutral wind/density and electric field from TIEGCM simulations are also analyzed to self-consistantly explain the identified disturbance features.

  5. Wide-field Imaging Survey of Dust Continuum Emissions at lambda = 1.1 mm toward the Chamaeleon and Lupus Regions with AzTEC on ASTE

    SciTech Connect

    Momose, Munetake; Hiramatsu, Masaaki; Tsukagoshi, Takashi; Shimajiri, Yoshito; Ezawa, Hajime; Kawabe, Ryohei; Ikeda, Norio; Kitamura, Yoshimi; Kamegai, Kazuhisa; Saito, Masao

    2009-08-05

    We carried out an imaging survey of dust continuum emissions toward the Chamaeleon and Lupus regions. Observations were made with the 144-element bolometer array camera AzTEC mounted on the 10-meter sub-millimeter telescope ASTE during 2007-2008. The preliminary results of disk search and the cloud structure of Lupus III are presented.

  6. Vegetation and climate change inferred from two marine pollen records in the low latitude west Pacific during the Marine Isotope Stage (MIS) 3

    NASA Astrophysics Data System (ADS)

    Bian, Y.; Li, J.; Jian, Z.; Chu, F.; Kuhnt, W.; Chu, Z.

    2013-12-01

    The climate change in the low latitude area since the last glacial is one of the most hotspot for Quaternary climate research, and the West Pacific Warm Pool (WPWP) is thought to play a key role in the propagation and amplification of climate changes through its influence on the global distribution of heat and water vapour. Meanwhile tropical vegetation is the most outstanding and obvious feature of South-East Asian landscapes, is expected to provide valuable information for the palaeoclmatic conditions. Pollen records from the tropical West Pacific indicate that the tropical vegetation is much sensitive to the environment and climate change, and their good correspondence with palaeocliamte change in glacial/interglacial timescales. Due to the low resolution of sediment cores, few of previous vegetation studies concerned on rapid climate change. In this study, pollen analysis from the sediment cores MD06-3075 retrieved from the Davao Gulf off Southern Philippine and MD98-2178 from western Sulawesi sea are used to reconstruct the vegetation and climate history of the tropical West Pacific and short timescale variation during the MIS 3. Based on AMS14C dating and plankton foraminifera oxygen isotope, the sedimentary records of the last 50,000 years at station MD06-3075 was obtained with a sample resolution of 400 years; records of almost the last 90,000 was included in sediments at station MD98-2178, where pollen analysis includes records of the last 77,000 years with a temporal resolution of 400-800 years. Pollen records from these two marine core show significant periodinal changes during MIS 3. The mangrove pollen content increase at 43-39 ka B.P. and 31-29 ka B.P., while the tropical mid-upper montane rainforest pollen decrease at that two periods from MD06-3075. The MD98-2178 record present that those two groups fluctuate during the 57-51 ka B.P., 48-44 ka B.P. and 38-28 ka B.P. Considering the oxygen isotope value and the SSTMg/Ca record , the temperature

  7. Application of IRI-Plas in Ionospheric Tomography and HF Communication Studies with Assimilation of GPS-TEC

    NASA Astrophysics Data System (ADS)

    Arikan, Feza; Gulyaeva, Tamara; Sezen, Umut; Arikan, Orhan; Toker, Cenk; Hakan Tuna, MR.; Erdem, Esra

    2016-07-01

    International Reference Ionosphere is the most acknowledged climatic model of ionosphere that provides electron density profile and hourly, monthly median values of critical layer parameters of the ionosphere for a desired location, date and time between 60 to 2,000 km altitude. IRI is also accepted as the International Standard Ionosphere model. Recently, the IRI model is extended to the Global Positioning System (GPS) satellite orbital range of 20,000 km. The new version is called IRI-Plas and it can be obtained from http://ftp.izmiran.ru/pub/izmiran /SPIM/. A user-friendly online version is also provided at www.ionolab.org as a space weather service. Total Electron Content (TEC), which is defined as the line integral of electron density on a given ray path, is an observable parameter that can be estimated from earth based GPS receivers in a cost-effective manner as GPS-TEC. One of the most important advantages of IRI-Plas is the possible input of GPS-TEC to update the background deterministic ionospheric model to the current ionospheric state. This option is highly useful in regional and global tomography studies and HF link assessments. IONOLAB group currently implements IRI-Plas as a background model and updates the ionospheric state using GPS-TEC in IONOLAB-CIT and IONOLAB-RAY algorithms. The improved state of ionosphere allows the most reliable 4-D imaging of electron density profiles and HF and satellite communication link simulations.This study is supported by TUBITAK 115E915 and joint TUBITAK 114E092 and AS CR 14/001.

  8. Using TEC and radio scintillation data from the CITRIS radio beacon receiver to study low and midlatitude ionospheric irregularities

    NASA Astrophysics Data System (ADS)

    Siefring, Carl L.; Bernhardt, Paul A.; Koch, Douglas E.; Galysh, Ivan J.

    2011-12-01

    Unique data on ionospheric plasma irregularities from the Naval Research Laboratory Scintillation and TEC Receiver in Space (CITRIS) instrument is presented. CITRIS is a multiband receiver that recorded Total Electron Content (TEC) and radio scintillations from Low-Earth Orbit (LEO) on STPSat1. The 555 ± 5 km altitude 35° inclination orbit covers low and midlatitudes. The measurements require propagation from a transmitter to a receiver through the F region plasma. CITRIS used both 1) satellite beacons in LEO and 2) the French sponsored global network of ground-based Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) beacons. This paper is both a brief review of the CITRIS experiment and the first combined TEC and scintillation study of ionospheric irregularities using a satellite-borne beacon receiver. It primarily focuses on CITRIS/DORIS observations and is a case study of the ionospheric irregularities and associated scintillation characteristics at 401.25 MHz during the 2008 equinox solar minimum. In addition, CITRIS was operated in a complementary fashion with the Communication/Navigations Outages Forecasting System (C/NOFS) satellite during C/NOFS' first year of operations and comparison with measured C/NOFS irregularity characteristics are made. Several types of irregularities have been studied including Spread-F and the newly discovered dawn-side depletions.

  9. Total Electron Content (TEC) disturbances over Brazilian region during the minor sudden stratospheric warming (SSW 2012) event of January 2012

    NASA Astrophysics Data System (ADS)

    Vieira, Francisco; Fagundes, Paulo Roberto; Kavutarapu, Venkatesh; Gil Pillat, Valdir

    2016-07-01

    The effects of Sudden Stratospheric Warming on ionosphere have been investigated by several scientists, using different observational techniques and model simulations. However, the 2011-2012 minor event is one of those that are less studied. Since, the zonal westward wind is slowed without reversing to eastward, this SSW was consider as a minor event. The stratospheric temperature started increasing on December 26, 2011, reached its peak on January 18, 2012, and afterwards started decreasing slowly. In addition, there was moderate geomagnetic storm on January 22-25, 2012, after the SSW temperature peak. In the present study, the GPS-TEC measurements from a network of 72 receivers over the Brazilian region are considered. This network of 72 GPS-TEC locations lies between 5 N and 30 S (35 degrees) latitudes and 35 W and 65 W (30 degrees) longitudes. Further, two chains of GPS receivers are used to study the response of Equatorial Ionization Anomaly (EIA) changes in the Brazilian East and West sectors, as well as its day-to-day variability before and during the SSW2012. It was noted that the TEC is depleted to the order of 30% all over the Brazilian region, from equator to beyond the EIA regions and from East to West sectors. It is also noticed that the EIA strengths at East and West sectors were suppressed after the stratospheric temperature peak. However, the Brazilian West sector was found to be more disturbed compared to the East sector during this SSW event.

  10. Geomagnetic storm effect on the occurrence of ionospheric irregularities over African equatorial sector using GPS-TEC

    NASA Astrophysics Data System (ADS)

    Amaechi, Paul; Oyeyemi, Elijah; Akala, Andrew

    2016-07-01

    Total electron content (TEC) derived from Global Navigation Satellite Systems (GNSS) measurements provided by the International GNSS Service (IGS) network have been used to study the occurrence of large scale ionospheric irregularities over the African equatorial sector. The rate of change of TEC (ROT) as well as its standard deviation over five minutes (ROTI) were used to monitor the level of irregularities over 3 stations distributed across the three longitudinal sectors of Africa (eastern, central and western longitudinal sectors). The storm effect on irregularities occurrence has been studied in conjunction with the disturbance storm time (Dst) and the z component of the Interplanetary magnetic field (IMFBz) indices during four intense storms which were classified according to their season of occurrence during the year 2015. Irregularities were associated with GPS-TEC fluctuations as seen in the increased ROT and ROTI values especially in the post sunset period. Irregularities were inhibited over all the stations during the storm of March plausibly as a result of electric field conditioned by the southward turning of IMFBz during the pre and post midnight periods. The triggering of irregularities over the western and central stations and their inhibition over the eastern station during the storm of June was controlled by the ring current. The storm effect on irregularities was not evident over the western and central stations but inhibition of irregularities was observed over the eastern station during the storm of September.

  11. Propagating planetary wave coupling in SABER MLT temperatures and GPS TEC during the 2005/2006 austral summer

    NASA Astrophysics Data System (ADS)

    Chang, Loren C.; Liu, Jann-Yenq; Palo, Scott E.

    2011-10-01

    It has long been suggested that the existence of ionospheric oscillations at multiday periodicities can be explained in part, by the penetration of propagating planetary waves into the E region ionospheric dynamo. In this study, global-scale observations of mesosphere and lower thermosphere (MLT) temperatures from TIMED/SABER and total electron content (TEC) results from GPS derived global ionosphere maps are examined for signs of potential upward planetary wave coupling, around the time of an intense quasi 2 day wave (QTDW) event in the MLT region during 1 December 2005 to 28 February 2006. The periodicity and zonal wave number of westward 3 (W3) and westward 2 (W2) QTDWs are resolved continuously in equatorial ionization anomaly (EIA) latitude TEC values at the same times as corresponding QTDW events in SABER temperatures. Additionally, signatures of an E1 ultrafast Kelvin (UFK) or inertia-gravity wave with period around 60 h (2.5 d) are also resolved. While the TECs also show signs of geomagnetic activity, the coherence and consistency of the aforementioned disturbances between the MLT and the ionosphere suggest that they cannot be attributed to geomagnetic forcing. We find that such propagating planetary waves can produce transient variability of the EIAs, though the effectiveness and hemispheric symmetry of such coupling also depends on factors other than the maximum planetary wave amplitude in the MLT.

  12. Bimodal solar system based on a ultra-high-temperature TEC

    NASA Astrophysics Data System (ADS)

    Ogloblin, B. G.; Kirillov, E. Ya.; Klimov, A. V.; Shalaev, A. I.; Shumov, D. P.; Ender, A. Ya.; Kuznetsov, V. I.; Sitnov, V. I.

    1996-03-01

    The paper considers an ecological, solar, bimodal system with ultra-high temperature thermionic energy converter (TEC). The solar bimodal Space Electric Propulsion System (SEPS) characteristics are presented.

  13. The dynamics and spectral characteristics of the GPS TEC wave packets excited by the solar terminator

    NASA Astrophysics Data System (ADS)

    Afraimovich, E. L.; Edemsky, I. K.; Voeykov, S. V.; Yasukevich, Y. V.; Zhivetiev, I. V.

    2009-04-01

    The great variety of solar terminator (ST) -linked phenomena in the atmosphere gave rise to a num¬ber of studies on the analysis of ionosphere parameter variations obtained by different ionosphere sounding methods. Main part of experimental data was obtained using methods for analyzing the spectrum of ionosphere parameter variations in separate local points. To identify ST-generated wave disturbances it is necessary to measure the dynamic and spectral characteristics of the wave disturbances and to compare it with spatial-temporal characteristics of ST. Using TEC measurements from the dense network of GPS sites GEONET (Japan), we have obtained the first GPS-TEC image of the space structure of medium-scale traveling wave packets (MS TWP) excited by the solar terminator. We use two known forms of the 2D GPS-TEC image for our presentation of the space structure of ST-generated MS TWP: 1) - the diagram "distance-time"; 2) - the 2D-space distribution of the values of filtered TEC series dI (λ, φ, t) on the latitude φ and longitude λ for each 30-sec TEC counts. We found that the time period and wave-length of ST-generated wave packets are about 10-20 min and 200-300 km, respectively. Dynamic images analysis of dI (λ, φ, t) gives precise estimation of velocity and azimuth of TWP wave front propagation. We use the method of determining velocity of traveling ionosphere disturbances (SADM-GPS), which take into account the relative moving of subionosphere points. We found that the velocity of the TWP phase front, traveling along GEONET sites, varies in accordance with the velocity of the ST line displacement. The space image of MS TWP manifests itself in pronounced anisotropy and high coherence over a long distance of about 2000 km. The TWP wave front extends along the ST line with the angular shift of about 20°. The hypothesis on the connection between the TWP generation and the solar terminator can be tested in the terminator local time (TLT) system: d

  14. Cassini ISS observations of Titan's surface and changes in its south-polar lakes

    NASA Astrophysics Data System (ADS)

    Turtle, Elizabeth; Perry, Jason; McEwen, Alfred; Hayes, Alexander; West, Robert

    Cassini's Imaging Science Subsystem (ISS) has been returning images of Titan since early 2004, continuing through the 65 close Titan encounters that have been performed to date. These ob-servations have been combined to produce a 938-nm albedo map of the surface with resolutions ranging from several kilometers to several hundred meters. The morphologies observed on Titan's surface reflect a wide variety of geological features [1]: roughly east-west streamlined shapes, suggestive of aeolian processes, consistent with Cassini RADAR observations of dunes at low latitudes [2]; narrow, curvilinear channels; dark lakes and seas at high latitudes [e.g., 3]; rare impact structures, further evidence for a geologically young surface; and possible tec-tonic and cryovolcanic structures. Changes have also been observed: a new large dark area appeared between July 2004 and June 2005 [3] and may have subsequently faded. Recent ISS observations of Ontario Lacus suggest that its shoreline may have receded as well [cf. 4]. Such changes are interpreted to be the result of precipitation and ponding of liquid methane and the subsequent infiltration into the subsurface or evaporation thereof [3]. No changes have been observed to date in the lakes and seas at high northern latitudes. We will present ISS' most recent map of Titan's surface, documenting changes that may have resulted from weather and seasonal changes and their implications for Titan's active methane cycle. References: [1] Porco et al. (2005) Nature 434, 159-168. [2] Lorenz et al. (2006) Science 312, 724-727. [3] Turtle et al. (2009) GRL 36, DOI 0.1029/2008GL036186. [4] Hayes et al. (2009) Eos Trans. AGU, 90, Abstract P54C-02.

  15. Ionospheric disturbances by volcanic eruptions by GNSS-TEC: Comparison between Vulcanian and Plinian eruptions

    NASA Astrophysics Data System (ADS)

    Nakashima, Y.; Heki, K.; Takeo, A.; Cahyadi, M. N.; Aditiya, A.

    2014-12-01

    Acoustic waves from volcanic eruptions are often observed as infrasound in near fields. Part of them propagate upward and disturb the ionosphere, and can be observed in Total Electron Content (TEC) data derived by Global Navigation Satellite System (GNSS) receivers. In the past, Heki (2006 GRL) detected ionospheric disturbances by the 2004 explosion of the Asama Volcano, central Japan, and Dautermann et al. (2009 JGR) studied the 2003 eruption of the Soufriere Hills volcano in Montserrat, West Indies. Here we present new examples, and try to characterize such disturbances. We first show TEC disturbances by the 2014 February Plinian eruption (VEI 4) of the Kelud volcano, East Java, Indonesia (Figure), observed with a regional GNSS network.The 2014 Kelud eruption broke a lava dome made by 2007 eruption and created a new creator. Significant disturbances were detected with four GPS and two GLONASS satellites, and the wavelet analyses showed that harmonic oscillations started at ~16:25 UT and continued nearly one hour. The frequency of the oscillation was ~3.8 mHz, which coincides with the atmospheric fundamental mode. We also confirmed concentric wavefronts, moving outward by ~0.8m/sec (stronger signals on the northern side). These features are similar to the 2003 Soufriere Hills case, although the signals in the present Kelud case is much clearer. Next, we compare them with ionospheric disturbances by Vulcanian explosions that occurred recently in Japan, i.e. the 2004 Asama case and the 2009 Sakurajima, and the 2011 Shin-moedake eruptions. They are characterized with one-time N-shaped disturbances possibly excited by the compression of the air above the vents. On the other hand, data from nearby seismometers suggested that atmospheric oscillations of various frequencies were excited by this continuous Plinian eruption. Part of such oscillations would have grown large due to atmospheric resonance.

  16. NMobTec-EnvEdu: M-Learning System for Environmental Education

    ERIC Educational Resources Information Center

    Cavus, Nadire

    2008-01-01

    This paper introduced the implementation of a New Mobile Technologies and Environmental Education System (NMobTec-EnvEdu) designed for m-learning environments. The NMobTec-EnvEdu system has been developed to provide environmental education in a collaborative framework to undergraduate students through the Internet using mobile phones. The study…

  17. Use of GPS TEC Maps for Calibrating Single Band VLBI Sessions

    NASA Technical Reports Server (NTRS)

    Gordon, David

    2010-01-01

    GPS TEC ionosphere maps were first applied to a series of K and Q band VLBA astrometry sessions to try to eliminate a declination bias in estimated source positions. Their usage has been expanded to calibrate X-band only VLBI observations as well. At K-band, approx.60% of the declination bias appears to be removed with the application of GPS ionosphere calibrations. At X-band however, it appears that up to 90% or more of the declination bias is removed, with a corresponding increase in RA and declination uncertainties of approx.0.5 mas. GPS ionosphere calibrations may be very useful for improving the estimated positions of the X-only and S-only sources in the VCS and RDV sessions.

  18. Comparison of COSMIC RO Data with European Digisondes and GPS TEC measurements

    NASA Astrophysics Data System (ADS)

    Zakharenkova, Irina; Krypiak-Gregorczyk, Anna; Shagimuratov, Irk; Krankowski, Andrzej; Lagovsky, Anatoly

    variation of NmF2 for the considered seasons depending on day-time and night-time conditions. Also it was analyzed the total elec-tron content values calculated for the nearest ground-based GPS stations located in European region. To compare GPS TEC with RO and ionosondes' data these profiles were integrated. In general bottom parts of CO