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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. TEC Response to X-ray Solar Emissions Observed in the Equatorial and Low-latitude Brazilian Region

    NASA Astrophysics Data System (ADS)

    Becker-Guedes, F.; Nicoli Candido, C. M.; de Siqueira, P. M.; Paula, E. R.; Takahashi, H.; De Nardin, C. M.; Costa, J. E. R.

    2014-12-01

    Some spurious effects affecting radio communications happen when the X-ray solar flux in the interplanetary medium reaches values above a certain threshold. The magnitudes of these effects depend on the X-ray peak brightness and the duration, which drive the intensity of the ionosphere response when the associated electromagnetic wave hit the sunlit side of the Earth atmosphere. An important aspect defining the severity of damages to HF radio communications and LF navigation signals in a certain area is the local time when each event takes place. In order to improve the understanding of radio signal loss or degradation in the Brazilian sector due to solar X-ray emissions, we analyze total electron content (TEC) maps and curves at selected sites obtained by a GPS network formed by tents of dual-frequency receivers spread all over Brazilian territory. We observe ionospheric local changes during several X-ray events in the 0.1-0.8 nm range identified by GOES satellite. Considering the duration, peak brightness, and local time of the events, our goal is to understand the degree of changes suffered by the ionosphere after these solar X-ray emissions using GPS receivers, namely in the equatorial region and around the southern crest of the equatorial ionospheric anomaly.

  3. 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.

  4. 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.

  5. Impacts of CME on the TEC at middle and low latitudes during maximum of the 24th solar cycle

    NASA Astrophysics Data System (ADS)

    Migoya Orue, Yenca Olivia; Amory-Mazaudier, Christine; Radicella, Sandro; Nava, Bruno; Kashcheyev, Anton

    2015-04-01

    In this study we analyzed the impacts on the GNSS-derived Total Electron Content (TEC) of four selected CME hitting the Earth during the year 2013 at different stations of middle and low latitudes (Ebre, Rabat, Alexandria, San Fernando, M'barara, Matera and Dakar). In order to analyzed the seasonal behavior of TEC under these disturbed conditions in the mentioned stations we have selected four CME events occurred during the different seasons (January 19, March 17, July 9 and October 2) of year 2013, at a maximum of the sunspot cycle 24. At the beginning of each event there is an increase of TEC followed by a decrease. The first increase of TEC is a consequence of the Prompt Penetration of the Electric Field (PPEF). The depletion of the TEC is associated to the Disturbance Dynamo Electric Field (DDEF). In order to interpret the observations we analyzed the convection patterns at high latitudes given by the radar SUPERDARN. At low latitudes, we derived the ionospheric electric current disturbance Diono from ground magnetic variations. Diono is the sum of the DP2 (PPEF) and Ddyn (DDEF) electric current systems. Finally we found that the strength of the impact at middle and low latitudes depends on the time of the impact of the CME and the season.

  6. Performance evaluation of GNSS-TEC estimation techniques at the grid point in middle and low latitudes during different geomagnetic conditions

    NASA Astrophysics Data System (ADS)

    Abe, O. E.; Otero Villamide, X.; Paparini, C.; Radicella, S. M.; Nava, B.; Rodríguez-Bouza, M.

    2016-11-01

    Global Navigation Satellite Systems (GNSS) have become a powerful tool use in surveying and mapping, air and maritime navigation, ionospheric/space weather research and other applications. However, in some cases, its maximum efficiency could not be attained due to some uncorrelated errors associated with the system measurements, which is caused mainly by the dispersive nature of the ionosphere. Ionosphere has been represented using the total number of electrons along the signal path at a particular height known as Total Electron Content (TEC). However, there are many methods to estimate TEC but the outputs are not uniform, which could be due to the peculiarity in characterizing the biases inside the observables (measurements), and sometimes could be associated to the influence of mapping function. The errors in TEC estimation could lead to wrong conclusion and this could be more critical in case of safety-of-life application. This work investigated the performance of Ciraolo's and Gopi's GNSS-TEC calibration techniques, during 5 geomagnetic quiet and disturbed conditions in the month of October 2013, at the grid points located in low and middle latitudes. The data used are obtained from the GNSS ground-based receivers located at Borriana in Spain (40° N, 0° E; mid latitude) and Accra in Ghana (5.50° N, -0.20° E; low latitude). The results of the calibrated TEC are compared with the TEC obtained from European Geostationary Navigation Overlay System Processing Set (EGNOS PS) TEC algorithm, which is considered as a reference data. The TEC derived from Global Ionospheric Maps (GIM) through International GNSS service (IGS) was also examined at the same grid points. The results obtained in this work showed that Ciraolo's calibration technique (a calibration technique based on carrier-phase measurements only) estimates TEC better at middle latitude in comparison to Gopi's technique (a calibration technique based on code and carrier-phase measurements). At the same

  7. Performance evaluation of GNSS-TEC estimation techniques at the grid point in middle and low latitudes during different geomagnetic conditions

    NASA Astrophysics Data System (ADS)

    Abe, O. E.; Otero Villamide, X.; Paparini, C.; Radicella, S. M.; Nava, B.; Rodríguez-Bouza, M.

    2017-04-01

    Global Navigation Satellite Systems (GNSS) have become a powerful tool use in surveying and mapping, air and maritime navigation, ionospheric/space weather research and other applications. However, in some cases, its maximum efficiency could not be attained due to some uncorrelated errors associated with the system measurements, which is caused mainly by the dispersive nature of the ionosphere. Ionosphere has been represented using the total number of electrons along the signal path at a particular height known as Total Electron Content (TEC). However, there are many methods to estimate TEC but the outputs are not uniform, which could be due to the peculiarity in characterizing the biases inside the observables (measurements), and sometimes could be associated to the influence of mapping function. The errors in TEC estimation could lead to wrong conclusion and this could be more critical in case of safety-of-life application. This work investigated the performance of Ciraolo's and Gopi's GNSS-TEC calibration techniques, during 5 geomagnetic quiet and disturbed conditions in the month of October 2013, at the grid points located in low and middle latitudes. The data used are obtained from the GNSS ground-based receivers located at Borriana in Spain (40°N, 0°E; mid latitude) and Accra in Ghana (5.50°N, 0.20°E; low latitude). The results of the calibrated TEC are compared with the TEC obtained from European Geostationary Navigation Overlay System Processing Set (EGNOS PS) TEC algorithm, which is considered as a reference data. The TEC derived from Global Ionospheric Maps (GIM) through International GNSS service (IGS) was also examined at the same grid points. The results obtained in this work showed that Ciraolo's calibration technique (a calibration technique based on carrier-phase measurements only) estimates TEC better at middle latitude in comparison to Gopi's technique (a calibration technique based on code and carrier-phase measurements). At the same time

  8. Analysis of Ionospheric Scintillation spectral and TEC in the Chinese low latitude region

    NASA Astrophysics Data System (ADS)

    Li, Guozhu; Ning, Baiqi; Yuan, Hong

    GPS L-band scintillations and total electron content TEC were recorded at Sanya 18 33° N 109 52° E for the period July 2004 - July 2005 Automatic recorded raw digital scintillation data are analyzed to obtain the spectral characteristics of irregularities producing ionospheric scintillations and to estimate the correlation between amplitude scintillation and power spectral density Concurrent measurements of TEC were used to analyze ROTI defined as the standard deviation of the rate of change of TEC Results show that spectral slope and auto correlation interval correspond quite well with amplitude scintillation index S4 during the generation evolution and decay phase of scintillation activity which indicates the formation evolution and erosion of small-scale irregularities The statistical results of S4 indices and spectral slopes indicate that the spectral slopes increase with S4 indices for weak scintillation S4 0 3 but for moderate and strong scintillation spectral slopes tend to be in saturation It is also find that the large and small scale irregularities coexist when scintillation occurs In the analyzed dataset the ratio of ROTI S4 is found to vary between 0 3 and 8

  9. Analysis of ionospheric scintillation spectra and TEC in the Chinese low latitude region

    NASA Astrophysics Data System (ADS)

    Li, G.; Ning, B.; Yuan, H.

    2007-04-01

    GPS L-band scintillations and total electron content (TEC) were recorded at Sanya (18.33°N, 109.52°E) during the period July 2004-July 2005. Automatic recorded raw digital scintillation data are analyzed to obtain the spectral characteristics of irregularities producing ionospheric scintillations and to estimate the correlation between amplitude scintillation and power spectral density. Concurrent measurements of TEC are used to analyze ROTI, defined as the standard deviation of the rate of change of TECνll. The statistical results of S4 indices and power spectral indices indicate that the power spectral indices increase with S4 indices for weak scintillation (0.1 ≤ S4 < 0.3), but for moderate and strong scintillation, spectral indices tend to be saturated. In the analyzed data set, the ratio of ROTI/S4 is found to vary between 0.3 and 6, and the variation in estimated zonal drift velocities during geomagnetic quiet days (Kp < 3) shows that the motion of the irregularities is highly variable in the initial phase of irregularity development. After about 22:00 LT, the estimated drift velocities tend to follow the same pattern.

  10. Comparison of IRI model predictions with low latitude ionospheric observations

    NASA Astrophysics Data System (ADS)

    Bittencourt, J. A.; Chryssafidis, M.

    During a period of high solar activity (1979/1980), IRI-predicted electron density profiles were compared with measurements made at Fortaleza (Brazil), 2 degrees off the dip equator. A few discrepancies were found. They are attributed mainly to dynamical effects associated with low latitude E x B electromagnetic plasma drifts and thermospheric neutral winds that are not correctly reproduced in the CCIR numerical maps and in the IRI profile shapes as well. In particular, the dependence on the magnetic declination angle, which strongly affects the electrodynamical plasma motions at low latitudes, is not satisfactorily considered in the models.

  11. 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

  12. 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

  13. Mesopheric Temparature Inversions Observed in Long-Term Lidar Measurements at Mid- and Low-Latitudes

    NASA Technical Reports Server (NTRS)

    Leblanc, T.; McDermid, I. S.; Keckhut, P.; Hauchecorne, A.

    1998-01-01

    Results of an investigation of mesospheric temperature inversion layers using long-term lidar measurements at mid- and low-latitudes are reported. In this paper, new results from different lidar observations of the invasion layers will be presented.

  14. An additional layer in the low-latitude ionosphere in Indian longitudes: Total electron content observations and modeling

    NASA Astrophysics Data System (ADS)

    Thampi, Smitha V.; Balan, N.; Ravindran, Sudha; Pant, Tarun Kumar; Devasia, C. V.; Sreelatha, P.; Sridharan, R.; Bailey, G. J.

    2007-06-01

    The paper presents the observations and modeling of an additional layer in the low-latitude ionosphere in Indian longitudes. The signatures of the additional layer are observed as ledges or humps between the equatorial ionization anomaly trough and crest (EIA) in the latitudinal profiles of total electron content (TEC), measured using a single ground-based beacon receiver located at Trivandrum (8.5°N, 77°E, dip 0.5°N) in India. The ground-based ionograms also show the presence of the so-called F3 layer for a short duration corresponding to these signatures, and the layer is found to drift upward to the topside ionosphere. The study provides first observational evidence that the so-called "humps" in the latitudinal variation of TEC are nothing but the upward propagating F3 layer. This conclusion is supported by theoretical modeling using the Sheffield University Plasmasphere Ionosphere Model. It is shown that upward ExB drift and strong equatorward neutral wind (perturbed by atmospheric waves) can produce the humps in the latitudinal variation of TEC through the reduction in the downward diffusion of ionization along geomagnetic field lines. The model results also show that the F3 layer drifts to the topside and forms topside ledges.

  15. Ionosonde observations of daytime spread F at low latitudes

    NASA Astrophysics Data System (ADS)

    Jiang, Chunhua; Yang, Guobin; Liu, Jing; Yokoyama, Tatsuhiro; Komolmis, Tharadol; Song, Huan; Lan, Ting; Zhou, Chen; Zhang, Yuannong; Zhao, Zhengyu

    2016-12-01

    Spread F on ionograms has been considered to be a phenomenon mainly occurred at nighttime. This study presented a case study of daytime spread F observed by the ionosonde installed at Puer (PUR; 22.7°N, 101.05°E; dip latitude 12.9°N), where daytime spread F that lasted for more than 2 h (about 08:30 LT 10:45 LT) was observed on 14 November 2015. To investigate the possible mechanism, ionograms recorded at PUR and Chiang Mai (18.76°N, 98.93°E; dip latitude 9.04°N) were used in this study. We found that traveling ionospheric disturbances were observed before the occurrence of daytime spread F. Meanwhile, the movement of the peak height of the ionosphere was downward. We suggested that downward vertical neutral winds excited by traveling atmospheric disturbances/atmospheric gravity waves might play a significant role in forming daytime spread F over PUR during geomagnetic storms.

  16. 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

    2016-12-01

    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.

  17. Direct observational evidence for disturbance dynamo on the daytime low-latitude ionosphere: A case study based on the 28 June 2013 space weather event

    NASA Astrophysics Data System (ADS)

    Thampi, Smitha V.; Shreedevi, P. R.; Choudhary, R. K.; Pant, Tarun Kumar; Chakrabarty, D.; Sunda, S.; Mukherjee, S.; Bhardwaj, Anil

    2016-10-01

    A case of the westward disturbance dynamo (DD) electric field, influencing the daytime equatorial and low-latitude ionosphere, during a geomagnetic storm that occurred on 28-29 June 2013 is presented. The GPS total electron content (TEC) observations from a network of stations in the Indian equatorial, low and middle latitude regions along with the radio beacon TEC, ionosonde, and magnetic field observations are used to study the storm time behavior of the ionosphere. Negative ionospheric storm effects were seen over the low and middle latitudes during the storm time due to the presence of a westward DD electric field. Observations show that the suppression of the equatorial ionization anomaly (EIA) from the morning hours itself on 29 June 2013 took place due to the prevailing westward DD electric field, providing evidence for the model calculations by Balan et al. (2013). Simulations using the GITM model also agree well with our results. The present study gains importance as the direct observational evidences for disturbance dynamo effects on the daytime low-latitude ionosphere and the EIA are sparse, as it has been difficult to delineate it from the compositional disturbances.

  18. 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.

  19. Observation of energy spectrum of electron albedo in low latitude region at Hyderabad, India

    NASA Technical Reports Server (NTRS)

    Verma, S. D.; Bhatnagar, S. P.

    1985-01-01

    The preliminary results are presented of the measurement of the energy spectrum of low energy (5-24 MeV) albedo electrons, moving upward as well as downwards, at about 37 km (-4 mb) altitude, over Hyderabad, India, in low latitude region. The flux and energy spectrum was observed by a bi-directional, multidetector charged particle telescope which was flown in a high altitude balloon on 8th December 1984. Results based on a quick look data acquisition and analysis system are presented here.

  20. Simultaneous observation of whistlers and emissions during a geomagnetically quiet period at low latitude

    NASA Astrophysics Data System (ADS)

    Singh, Ashutosh K.; Singh, K. K.; Singh, A. K.; Lalmani

    2011-02-01

    A unique night-time natural electromagnetic disturbances in the VLF/ELF range received during a magnetically quite period at a low latitude Indian ground station, Jammu (geomag. lat. 19°26' N, L=1.17) has been reported. During the routine observation of VLF waves at Jammu, whistlers and different types of VLF/ELF emissions such as whistlers of varying dispersion confined to a small band limited frequency range, hisslers, pulsing hiss, discrete chorus emissions of rising and falling tones with multiple bands, oscillating tone discrete emission, whistler-triggered hook and discrete chorus risers emissions, etc. have been observed simultaneously during the quiet period on a single night. Such type of unique simultaneous observations has never been reported from any of the low latitude ground stations and this is the first observation of its kind. The results are discussed in the light of recorded features of whistlers and emissions. Generation and propagation mechanism are discussed briefly. Plasma parameters are further derived from the dispersion analysis of nighttime whistlers and emissions recorded simultaneously during magnetically quiet periods.

  1. Low-latitude total electron content enhancement at low geomagnetic activity observed over Japan

    NASA Astrophysics Data System (ADS)

    Kutiev, Ivan; Otsuka, Yuichi; Saito, Akinori; Tsugawa, Takuya

    2007-07-01

    Numerous total electron content (TEC) values derived from GPS signals are averaged within 1.5° × 1.5° cells in a 1-hour time frame, and the relative deviations of these average values from corresponding monthly medians are used to produce latitude-time plots over Japan. The paper analyzes the appearance and development of enhancements of TEC of equatorial origin (ETEs), occurring outside initial and main phases of geomagnetic storms. ETE structures appear mainly as single-crest structures in the evening hours local time, with TEC peak around 1900 LT. TEC usually decreases with latitude, and the structures disappear below 40°N. In some cases the TEC peak is found above the plot boundary of 24°N, as depletions toward the equator are also observed. The observed enhanced structures are linked to the well-known evening prereversal enhancement of ion drift in the equatorial F region. Double-crest ETEs are also observed, with the second peak occurring in early morning hours. Most of the ETE events appear in periods of low geomagnetic activity, 1-3 days after the main phase of the storms. In some cases the time of rising of ETE structures coincides with the increase of interplanetary electric field (IEF), a fact showing the importance of directly penetrating electric field in formation of ETEs. Often, ETEs appear repeatedly in 2 or 3 consecutive days. It is supposed that planetary atmospheric waves are responsible for this phenomenon. Most of the observed features of ETEs can be explained by the published results of simulations of the coupled thermosphere-ionosphere-plasmasphere (CTIP) model and the thermosphere/ionosphere/electrodynamic general circulation model (TIEGCM). It is suggested that ETE structures are produced mainly by a disturbance winds dynamo electric field, built up after the main phase of the storms. Some ETE events, appearing at the end of a prolonged period of low geomagnetic activity, can be linked to directly penetrating IEF in equatorial

  2. Chandra X-ray Observations of Jovian Low-latitude Emissions: Morphological, Temporal, and Spectral Characteristics

    NASA Technical Reports Server (NTRS)

    Bhardwaj, Anil; Elsner, Ronald F.; Gladstone, G. Randall; Cravens, Thomas E.; Waiate J. Hunter, Jr.; Branduardi-Raymont, Graziella; Ford, Peter

    2004-01-01

    Chandra observed X-rays from Jupiter during 24-26 February 2003 for about 40 hours with the ACIS-S and HRC-I instruments. The analysis of Jovian low-latitude "disk" Xray emissions are presented and compared with the high-latitude "auroral" emissions. We report the first Chandra ACIS-S measured X-ray spectrum (0.3-2 keV) of Jupiter's low-latitude disk The disk X-ray emission is harder and extends to higher energies than the auroral spectrum. The temporal variation in the Jovian disk X-rays is on an average consistent with those in the solar X-rays observed by GOES, and TIMED/SSE. Contrary to the auroral X-rays, the disk emissions are uniformly distributed over Jupiter; no indication of longitudinal dependence or correlation with surface magneh field strength is visible. Also, unlike the approx. 40 +/- 20 min periodic oscillations seen in the auroral X-ray emissions, the disk emissions do not show any periodic oscillations. The disk spectrum seems to be consistent with resonant and fluorescent scattering of solar X-rays by the Jovian upper atmosphere. Jupiter's disk is found to be about 50% dimmer in soft X-rays in February 2003 compared that in December 2000, which is consistent with the decrease in solar activity. No evidence of lightning-induced X-rays is seen in the Chandra X-ray data. The Jovian disk spectra observed with Chandra-ACIS is stronger than that observed with XMM-Newton two months later during April 28-29, 2003. The XMM-Newton Xray image of Jupiter shows evidence of limb darkening on the anti-sunward side as seen from Earth, as well as an asymmetry with respect to the subsolar point: suggesting a solar driven process.

  3. Ionospheric TEC observations from TOPEX satellite

    SciTech Connect

    Vladimer, J.A.; Ewell, V.R.; Lee, M.C.; Doherty, P.H.; Decker, D.T.; Anderson, D.N.; Klobuchar, J.A.

    1996-12-31

    Variability of Total Electron Content (TEC) in the equatorial anomaly region of the ionosphere can be studied extensively using the results of measurements taken by the NASA/CNES satellite, TOPEX/Poseidon. The NASA radar altimeter (NRA) is the first space-borne dual-frequency altimeter capable of accurately measuring vertical ionospheric TEC below 1,340 km. TOPEX TEC observations have already been used to support results from an ionospheric measurement campaign that was conducted in equatorial anomaly regions of South America by Phillips Laboratory in Spring, 1994. The best agreement in TEC values is seen during intervals of longitudinal proximity of the satellites` paths. The TOPEX over-ocean data can be used as a supplement to land based measurements in applications to ionospheric research at low and middle latitudes. This study focuses on comparisons between TOPEX vertical TEC data and GPS equivalent vertical TEC measurements taken near the East and West coastal regions of South America. Also the Phillips Laboratory Global Parameterized Ionospheric Model (PIM) is utilized in an effort to estimate slant to vertical conversion errors.

  4. 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.

  5. 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.

  6. Variability of Schumann resonance parameters observed at low latitude stations in China

    NASA Astrophysics Data System (ADS)

    Ouyang, X.-Y.; Xiao, Z.; Hao, Y.-Q.; Zhang, D.-H.

    2015-10-01

    This paper presents a comprehensive analysis of the Schumann resonance (SR) parameters observed at low latitude stations in China for the first time. Variations of SR peak frequency and intensity on different timescales (from minutes to years) are analyzed in detail. Diurnal and seasonal variations are shown and the source-observer distance is calculated to confirm the contributions of lightning activity. Differences in the profiles of SR intensity between the NS and EW components are due to the effects of the source-observer distance and the relative position of the observer to the sources. Diurnal frequency variations are more complicated and cannot be directly linked with the three thunderstorm centers. Seasonal variations are clear for intensity but not for frequency. The differences in the diurnal and seasonal variations between the SR intensity and frequency show that the greatest contributor to SR intensity is global lightning activity, while the SR frequency is not affected solely by lightning, as certain other factors involving ionosphere properties may play non-negligible roles. We also emphasize that our observations do not show a distinct day-night change in the SR parameters, and that the SR intensity does not show abrupt changes across terminators. This observation is consistent with previous simulations. Finally, the response of the SR to a solar flare is discussed. The flare leads to a sudden increase of about 0.2 Hz relative to the 2σ level of the SR frequencies in the first three modes, which is in agreement with other works in the literature. This frequency enhancement is explained using theoretical calculations.

  7. Observations of polarization electric fields and plasma drifts associated with low-latitude TIDs

    NASA Astrophysics Data System (ADS)

    Huang, C.

    2015-12-01

    Ionospheric plasma structures and TIDs are often observed in the conjugate hemispheres. It is widely believed that the polarization electric field is responsible for the conjugacy. However, observed conjugate disturbances so far are mostly in plasma density and TEC, and there is almost no report of observations of polarization electric fields associated with TIDs. We present the C/NOFS measurements of TID-like disturbances in the plasma density and drift velocity. The plasma drift perpendicular to the geomagnetic field is manifestation of the polarization electric field. Plasma flow parallel to the geomagnetic field is highly correlated with the polarization electric field and is consistent with the prediction of TID theories, confirming that the polarization electric field is caused by TIDs. Surprisingly, the polarization electric field is observed not only at night but also during daytime, implying that the polarization electric field is not shorted out by the dayside E layers. The satellite data are compared with the Jicamarca radar data when C/NOFS is 20 degrees away from the radar but nearly at the same magnetic latitude (along the same field lines). This may be the first observation of polarization electric field associated with TIDs and verifies that the polarization electric field can be indeed transmitted thousands of kilometers along the geomagnetic field lines. The observations provide direct evidence for justifying the mechanism for the generation of similar ionospheric disturbances in the conjugate hemispheres.

  8. 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.

  9. Electron density in the intermediate heights for low latitude stations: observations and models

    NASA Astrophysics Data System (ADS)

    Mosert, M.; Radicella, S. M.; Adeniyi, J. O.; Ezquer, R. G.; Jadur, C.

    The electron density (NF1) and height (hF1) of the F1 inflection point measured at three low latitude ionosonde stations were compared with the parameters of the N170 point (electron density at 170 km) and with those predicted by the IRI model. The validity of the empirical equation proposed by Radicella and Mosert to predict the height hF1 was checked. Daytime electron density profiles from Ibadan, Ouagadougou and Tucumán covering different seasonal and solar activity conditions were used in the study. The results indicate that the two points are close together most of the time and that the Radicella-Mosert formula descrbies the data better than the current IRI model.

  10. Ionospheric studies using a low-latitude ionospheric model (LION-model) and ground-based ionosonde observations.

    NASA Astrophysics Data System (ADS)

    Pillat, V. G.; Bittencourt, J. A.; Fagundes, P. R.

    Ionospheric observations made with ionosondes of the type CADI at S a o Jos e dos Campos 23 2 o S 45 9 o W dip latitude 17 6 o S and at Palmas 10 2 S 48 2 W dip latitude 5 7 S Brazil under conditions of high and low solar activity are presented and compared with ionospheric results obtained from a realistic fully time-dependent Low-Latitude Ionosphere Model denominated LION model which simulates the dynamic behavior of the low-latitude ionosphere In the LION model the time evolution and spatial distribution of the ionospheric particle densities and velocities are computed by numerically solving the time-dependent coupled nonlinear system of continuity and momentum equations for the ions O O 2 NO N 2 and N taking into account photoionization of the atmospheric species by the solar extreme ultraviolet radiation chemical and ionic production and loss reactions and plasma transport processes including the ionospheric effects of thermospheric neutral winds plasma diffusion and electromagnetic E x B plasma drift The Earth s magnetic field is represented by a tilted centered magnetic dipole This set of coupled nonlinear equations is solved along a given magnetic field line in a frame of reference moving vertically in the magnetic meridian plane with the electromagnetic plasma drift velocity The model results reproduce adequately the main characteristics and dynamic behavior of the low-latitude ionosphere under quiet

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. Ionospheric response to the 2006 sudden stratospheric warming event over the equatorial and low latitudes in the Brazilian sector using GPS observations

    NASA Astrophysics Data System (ADS)

    de Jesus, R.; Batista, I. S.; Fagundes, P. R.; Venkatesh, K.; de Abreu, A. J.

    2017-02-01

    The main purpose of this paper is to study the response of the ionospheric F-region using GPS-TEC measurements at equatorial and low latitude regions over the Brazilian sector during an sudden stratospheric warming (SSW) event in the year 2006. In this work, we present vertical total electron content (VTEC) and phase fluctuations derived from GPS network in Brazil. The continuous wavelet transform (CWT) was employed to check the periodicities of the ∆VTEC during the SSW event. The results show a strong decrease in VTEC and ∆VTEC values in the afternoon over low latitudes from DOY 05-39 (during the SSW event) mainly after the second SSW temperature peak. The ionospheric ∆VTEC pattern over Brazilian sector shows diurnal and semidiurnal oscillations during the 2006 SSW event. In addition, for the first time, variations in ∆VTEC (low latitude stations) with periods of about 02-08 day have been reported during an SSW event. Using GPS stations located in the Brazilian sector, it is reported for the first time that equatorial ionospheric irregularities were not suppressed by the SSW event.

  17. 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.

  18. 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.

  19. Studies of ionospheric variations during geomagnetic activities at the low-latitude station, Ile-Ife, Nigeria

    NASA Astrophysics Data System (ADS)

    Emmanuel, Ariyibi

    The dual frequency SCINDA NovAtel GSV 4004B GPS receiver installed at the Ile-Ife (low-latitude station) has been in operation since December 2009. Data records for the year 2010 were processed to obtain Total Electron Content (TEC) and S 4 index. These were interpreted to analyze the ionospheric condition during low geomagnetic activity period (when Dst is from -40 to 0 nT) and during geomagnetic storm events (with Dst about -100 nT). Seasonal variations of the TEC and S 4 index were also investigated. The occurrence of scintillations is closely linked to the peak value of TEC during the daytime; this is very evident during the equinox months when TEC ≥ 30 TECu. When the maximum TEC value is below 30 TECu, as shown by most of the days in the summer months, the scintillation phenomenon does not occur. During geomagnetic storms, the daytime segment of the TEC plot experiences fluctuations (even bifurcations) in values with the peak TEC value of about 40 TECu. From the interpreted data, the occurrence of geomagnetic storm does not necessarily suggest an increase in the level of scintillations at a low-latitude region. Also, there is a remarkable difference between the IRI 2007 model and the observed TEC values, as the daytime TEC peak differs in magnitude and time of occurrence from the observed TEC.

  20. Studies of ionospheric variations during geomagnetic activities at the low-latitude station, Ile-Ife, Nigeria

    NASA Astrophysics Data System (ADS)

    Ariyibi, Emmanuel; Joshua, Emanuel; Rabiu, Babatunde

    2013-02-01

    The dual frequency SCINDA NovAtel GSV 4004B GPS receiver installed at the Ile-Ife (low-latitude station) has been in operation since December 2009. Data records for the year 2010 were processed to obtain Total Electron Content (TEC) and S 4 index. These were interpreted to analyze the ionospheric condition during low geomagnetic activity period (when Dst is from -40 to 0 nT) and during geomagnetic storm events (with Dst about -100 nT). Seasonal variations of the TEC and S 4 index were also investigated. The occurrence of scintillations is closely linked to the peak value of TEC during the daytime; this is very evident during the equinox months when TEC ≥ 30 TECu. When the maximum TEC value is below 30 TECu, as shown by most of the days in the summer months, the scintillation phenomenon does not occur. During geomagnetic storms, the daytime segment of the TEC plot experiences fluctuations (even bifurcations) in values with the peak TEC value of about 40 TECu. From the interpreted data, the occurrence of geomagnetic storm does not necessarily suggest an increase in the level of scintillations at a low-latitude region. Also, there is a remarkable difference between the IRI 2007 model and the observed TEC values, as the daytime TEC peak differs in magnitude and time of occurrence from the observed TEC.

  1. Observations at Low Latitudes of Magnetic Merging Signatures Within a Flux Transfer Event During a Northward IMF

    NASA Technical Reports Server (NTRS)

    Chandler, M. O.; Avanov, L. A.

    2003-01-01

    Flux transfer events (FTE) have been postulated to result from transient magnetic merging. If so, the ion distributions within an event should exhibit features known to result from merging. Observations of a FTE by instruments on the Polar spacecraft revealed classical merging signatures that included: 1) D-shaped, accelerated, magnetosheath ion distributions, 2) a well defined de Hoffman-Teller frame, 3) local stress balance, and 4) a P-N magnetic field signature. This FTE was observed near the magnetic equator at approx. 13 MLT under conditions of a moderately northward interplanetary magnetic field (IMF) (clock angle of less than 10 deg). The nature of the ion distributions and the consistency of the measured cutoff speed with that calculated from the measured local magnetic field and the derived de Hoffman-Teller speed show the ion injection to be local. Coupled with the northward IMF these results lead to the conclusion that component merging in the low latitude region was responsible for the FTE.

  2. 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.

  3. 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.

  4. 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.

  5. Statistical description of low-latitude plasma blobs as observed by DMSP F15 and KOMPSAT-1

    NASA Astrophysics Data System (ADS)

    Park, J.; Min, K. W.; Kim, V. P.; Kil, H.; Kim, H. J.; Lee, J. J.; Lee, E.; Kim, S. J.; Lee, D. Y.; Hairston, M.

    The global distribution of low-latitude plasma blobs was investigated by in-situ plasma density measurements from the Korea Multi-Purpose Satellite-1 (KOMPSAT-1) and Defense Meteorological Satellite Program (DMSP) F15. In the observations, blobs occurred in the longitude sector where the activity of the equatorial plasma bubble (EPB) was appreciable, and additional blobs were found at the lower (KOMPSAT-1) altitude as in the EPBs. However, several notable differences exist between the distributions of EPBs and blobs. First, KOMPSAT-1 found few blobs around 0°E in March and June, as did DMSP F15 from 30°W to 120°E for every season. Second, the overall occurrences in December and March at the DMSP F15 (840 km) altitude were somewhat lower than expected from those of the EBPs. Third, at the DMSP F15 altitude, the occurrence probability of plasma blobs was less controlled by yearly variations in the solar activity. These results imply that topside ionospheric conditions as well as the existence of EPBs control further development of blobs. Additionally, it was found that the blob latitudes became higher as the yearly solar activity increased. Moreover, most of the blobs were encountered in the winter hemisphere, possibly due to the low ambient density.

  6. Ground and satellite observations of the low-latitude onsets of auroral substorm during a major magnetic storm

    NASA Astrophysics Data System (ADS)

    Ievenko, Igor; Parnikov, Stanislav; Alexeyev, Valeriy

    It is known that the first onset of auroral substorm expansion is connected with the brightness increase and breakup of the most equatorial arc. The subsequent substorm activizations can be observed in the intensification of auroral arcs at higher latitudes. As a result a formation of auroral bulge and poleward shift of a westward electrojet maximum takes place. The development of auroral bulge maps the precipitation dynamics of energetic particles during magnetospheric substorms. In this work the research results of auroral substorm during the major magnetic storm on March 20, 2001 (Dst =-150 nT) are submitted. The aurorae were registered at the Yakutsk meridian (130ºE; 200ºE, geom.) by the meridian-scanning and zenith photometers in the 630, 557.7 [OI], 427.8 (N2+) and 486.1 nm (H beta) emissions. Before the substorm onset the equatorial arc is observed at low geomagnetic latitudes of 55-57ºN (the dipole L=3.0-3.3). The zenith photometer registers an intense H beta emission in the arc (~400 R). The fast increase of the 427.8, 557.7 nm emission intensity during two equatorial arc breakups is accompanied by the decrease of H beta intensity by a factor of ~5. The aurora dynamics is compared with the measurements of precipitating flux of electrons and protons aboard DMSP F15 satellite, substorm injections at a geosynchronous orbit, variations in the solar wind and IMF and also images of the auroral oval from the IMAGE satellite. The ground and satellite observations are considered from a position of change of the magnetic field configuration during the low-latitude substorm. We assume that the sharp drop of H beta emission intensity (precipitating protons flux) during the breakups of equatorial arc may testify to a connection of its location with a proton isotropic boundary in the inner magnetosphere.

  7. Study of solar flare induced D-region ionosphere changes using VLF amplitude observations at a low latitude site

    NASA Astrophysics Data System (ADS)

    Tan, L. M.; Thu, N. N.; Ha, T. Q.; Marbouti, M.

    2014-06-01

    About 26 solar flare events from C2.56 to X3.2 classes were obtained and analyzed at Tay Nguyen University, Vietnam (12.56°N, 108.02°E) during May - December 2013 using very low frequency remote sensing to understand the responses of low latitude D-region ionosphere during solar flares. The observed VLF amplitude perturbations are used as the input parameters for the simulated Long Wavelength Propagation Capability (LWPC) program, using Wait's model of lower ionosphere, to calculate two Wait's parameters, viz. the reflection height (H') and the sharpness factor (?). The results reveal that when X-ray irradiance is increased, ? increased from 0.3 to 0.506 km-1, while H' decreased from 74 to 60 km. The electron density increased at the height of 74 km with 1-3 orders of magnitude during solar flares. These phenomena can be explained as: the ionization due to X-ray irradiance becomes greater than that due to cosmic rays and Lyman-α radiation, which increases the electron density profile. The present results are in agreement with the earlier results. The 3D representation of the electron density changes with altitude and time supports to fully understand the shape of the electron density changes due to X-ray flares. The shape variation of electron density is roughly followed to the variation of the amplitude perturbation and keeps this rule for different altitudes. It is also found that the electron density versus the height in lower latitude D-region ionosphere increases more rapidly during solar flares.

  8. Regional Arctic observations of TEC gradients and scintillations

    NASA Astrophysics Data System (ADS)

    Durgonics, Tibor; Høeg, Per; Benzon, Hans-Henrik

    2015-04-01

    In recent years, there has been growing scientific interest in Arctic ionospheric properties and variations. However our understanding of the fundamental ionospheric processes present in this area is still incomplete. GNSS networks present in Greenland today make it possible to acquire near-real time observations of the state and variations of the high-latitude ionosphere. This data can be employed to obtain relevant geophysical variables and statistics. In our study GPS-derived total electron content (TEC) measurements have been complemented with amplitude scintillation indices (S4), and phase scintillation indices (σφ). The investigation of the relationship between these geophysical variables will likely lead to new ways to study the underlying physical processes and to build tools for monitoring and predicting large-scale patterns in Arctic TEC and scintillations. A number of specific ionosphere events will be presented and the underlying geophysical process will be identified and described. In particular, results will be presented where large-scale gradients in the regional TEC are compared with the growth of scintillations. The statistics of the scintillations will be investigated, with emphasis on how well the scintillations follow the Nakagami-m distribution. The spectra of both the intensities and phase will be calculated, and the corner frequency of these spectra will also be determined. These corner frequencies will be used to compute a number of important geophysical and ionospheric parameters. Furthermore, we will discuss how the spectral characteristics of the scintillations during large TEC gradients vary, and how values of the power spectra slopes change during increasing scintillations. These values will be validated against values found in prior studies. TEC and scintillation time-series and maps will also be presented over the Greenlandic region. We will show how the expansion of the auroral oval during geomagnetic storms can be detected from

  9. 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.

  10. Electrodynamics of ionospheric weather over low latitudes

    NASA Astrophysics Data System (ADS)

    Abdu, Mangalathayil Ali

    2016-12-01

    The dynamic state of the ionosphere at low latitudes is largely controlled by electric fields originating from dynamo actions by atmospheric waves propagating from below and the solar wind-magnetosphere interaction from above. These electric fields cause structuring of the ionosphere in wide ranging spatial and temporal scales that impact on space-based communication and navigation systems constituting an important segment of our technology-based day-to-day lives. The largest of the ionosphere structures, the equatorial ionization anomaly, with global maximum of plasma densities can cause propagation delays on the GNSS signals. The sunset electrodynamics is responsible for the generation of plasma bubble wide spectrum irregularities that can cause scintillation or even disruptions of satellite communication/navigation signals. Driven basically by upward propagating tides, these electric fields can suffer significant modulations from perturbation winds due to gravity waves, planetary/Kelvin waves, and non-migrating tides, as recent observational and modeling results have demonstrated. The changing state of the plasma distribution arising from these highly variable electric fields constitutes an important component of the ionospheric weather disturbances. Another, often dominating, component arises from solar disturbances when coronal mass ejection (CME) interaction with the earth's magnetosphere results in energy transport to low latitudes in the form of storm time prompt penetration electric fields and thermospheric disturbance winds. As a result, drastic modifications can occur in the form of layer restructuring (Es-, F3 layers etc.), large total electron content (TEC) enhancements, equatorial ionization anomaly (EIA) latitudinal expansion/contraction, anomalous polarization electric fields/vertical drifts, enhanced growth/suppression of plasma structuring, etc. A brief review of our current understanding of the ionospheric weather variations and the

  11. 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).

  12. Statistical description of low-latitude plasma blobs as observed by DMSP F15 and KOMPSAT-1

    NASA Astrophysics Data System (ADS)

    Park, J.; Min, K. W.; Kim, V. P.; Kil, H.; Kim, H. J.; Lee, J. J.; Lee, E.; Kim, S. J.; Lee, D. Y.; Hairston, M.

    We investigated the global distribution of low-latitude plasma blobs using in-situ plasma density measurements from Korea Multi-Purpose Satellite-1 KOMPSAT-1 and Defense Meteorological Satellite Program DMSP F15 The seasonal-longitudinal S L distribution of blobs is generally consistent with that of equatorial plasma bubbles EPBs but between them exist two notable differences First during equinoxes the blob activity is inhibited around the Atlantic region Second during the June solstice the African peak is rather suppressed in the distribution KOMPSAT-1 at the lower altitude encountered blobs more frequently than DMSP F15 The occurrence probability of plasma blobs is less subjected to the yearly variation of solar activity And the latitudinal distribution of the blobs shows strong asymmetry during solstices Most of them are concentrated on the winter hemisphere where the background density is low and the inter-hemispheric plasma transport is poleward along the geomagnetic field line And the asymmetry becomes weak as the solar activity decreases suggesting that the blob generation bears connection with the fountain effect inside EPBs and the poleward plasma transport

  13. 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.

  14. 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

  15. Plasma drifts and polarization electric fields associated with TID-like disturbances in the low-latitude ionosphere: C/NOFS observations

    NASA Astrophysics Data System (ADS)

    Huang, Chao-Song

    2016-02-01

    Medium-scale traveling ionospheric disturbances are often observed at the magnetically conjugate points in the nighttime midlatitude ionosphere. It has been suggested that gravity waves disturb the ionosphere and induce electric fields in one hemisphere and that the electric fields are amplified by the Perkins instability and transmitted along the geomagnetic field lines to the conjugate ionosphere, creating similar disturbances there. However, direct observations of electric fields associated with traveling ionospheric disturbances (TIDs) are very few. In this study, we present low-latitude TID-like disturbances observed by the Communication/Navigation Outage Forecasting System (C/NOFS) satellite. It is found that ion velocity perturbations are generated in the directions parallel and perpendicular to the geomagnetic field within TIDs. Both the parallel and perpendicular ion velocity perturbations show an in-phase correlation with the ion density perturbations. For nighttime TIDs, the amplitude of both the parallel and meridional ion velocity perturbations increases almost linearly with the amplitude of the ion density perturbations, and the meridional ion drift is proportional to the parallel ion velocity. For daytime TIDs, the parallel ion velocity perturbation increases with the ion density perturbation, but the meridional ion velocity perturbation does not change much. The observations provide evidence that polarization electric field is generated within TIDs at low latitudes and maps along the geomagnetic field lines over a large distance.

  16. 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.

  17. A study on the low-latitude daytime E region plasma irregularities using coordinated VHF radar, rocket-borne, and ionosonde observations

    NASA Astrophysics Data System (ADS)

    Patra, A. K.; Venkateswara Rao, N.; Phanikumar, D. V.; Chandra, H.; Das, U.; Sinha, H. S. S.; Pant, T. K.; Sripathi, S.

    2009-11-01

    In this paper we study the off-electrojet low-latitude daytime E region plasma irregularities using first multi-instrument observations in India made during July 2004 by the MST radar from Gadanki (13.5°N, 79.2°E, magnetic latitude 6.4°N), Langmuir probe on board the RH-300 Mk II rocket, and ionosonde from Sriharikota (13.6°N, 80.2°E, magnetic latitude 6.4°N). Radar echoes were confined to altitudes below 105 km and were observed in the form of a descending echoing layer with the descent rate of 1 km/h. Virtual height of the E layer, as observed by ionosonde, shows identical descending behavior. A detailed analysis based on the radar and ionosonde observations shows that the radar echoes are related to the range spread in the ionogram. Rocket observations made on 23 July 2004 revealed weak plasma irregularities with scale sizes more than 100 m and no noticeable irregularity at shorter scales. The spectral slope of the irregularities observed by the rocket probe is found to be -4 for scales in between 1 km and 100 m. During the rocket launch, radar did not detect any echo conforming that the small-scale irregularities were not present. Examination of concurrent observations of neutral wind made by TIMED Doppler interferometry suggests that zonal wind plays a crucial role in forming electron density layers, which become unstable via the gradient drift instability with background electric field or/and zonal neutral wind generating low-latitude E region plasma irregularities.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

    2016-06-01

    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.

  2. 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.

  3. Seasonal variations of nighttime D-region ionosphere in 2013 solar maximum observed from a low-latitude station

    NASA Astrophysics Data System (ADS)

    Tan, Le Minh; Thu, Nguyen Ngoc; Ha, Tran Quoc; Nguyen-Luong, Quang

    2015-10-01

    We present the observation of tweek atmospherics with harmonics m = 1-8 during the solar maximum year, 2013, at Tay Nguyen University, Vietnam (Geog. 12.65° N, 108.02° E). The analysis of 33,690 tweeks on ten international quiet days during 2 months each season, summer (May, August), winter (February, November), and equinox (March, September), shows that tweeks occur about 51 % during summer, 22 % during winter, and 27 % during equinox. The D-region ionosphere is more sharply bounded for harmonics m = 5-6 around an altitude of 85.5 km. The environment of the D-region is more inhomogeneous during winter and equinox seasons. The mean electron density varies from 28.4-225 cm -3, which corresponds to the harmonics m = 1-8 at the mean reflection height of 81.5-87.7 km. The results reveal that the lower reference height in our work as compared to other works is due to the higher level of solar activity. The equivalent electron density profile of the nighttime D-region ionosphere using tweek method during summer, equinox, and winter seasons shows lower values of electron density by 12-58 %, 3-67 %, and 24-76 % than those obtained using the International Reference Ionosphere (IRI-2012) model.

  4. The relationship between high- and low-latitude Pi2 pulsations simultaneously observed by DE-1, AMPTE/CCE, and ground stations

    NASA Astrophysics Data System (ADS)

    Teramoto, M.; Nose, M.; Takahashi, K.; Sutcliffe, P. R.

    2007-12-01

    Pi2 pulsations (period from 40s to 150s) are observed at substorm onset. Cavity mode resonance is the possible scenario of low-latitude Pi2 pulsations. It is an open question whether the resonance boundary, plasmapause, is good reflector or not. We investigated Pi2 pulsations observed simultaneously by the polar orbiting DE-1 satellite (an apogee: about 3.6 Re altitude and a perigee: about 500km altitude), equatorial orbiting AMPTE/CCE satellite (an apogee: about 8.8 Re altitude and a perigee: about 1100km altitude), and ground stations at 1132-1136 UT on November 14, 1986. DE-1 was located at polar region (Geomagnetic latitude=-83.42 degrees). AMPTE/CCE was located at L=4.57 and 23.6 MLT. AMPTE/CCE might be located outside the plasmasphere. They are observed Pi2 pulsations in the compressional component. The AL index began to decrease at 1114 UT. It showed substorm onset. They had high coherence with that observed at Kakioka (KAK) in the H component, which was located at L=1.25 and 3.21 MLT. The phase difference between KAK and DE-1 and between KAK and AMPTE/CCE were 180 and 90 degrees at 14 mHz. These Pi2 pulsations had high coherence with that observed by Hermanus (HER), which was located at L=1.8 and 12.8 MLT. These observational results may support that the plasmapause is imperfect boundary. Pi2 pulsations at low latitude are excited by the plasmaspheric virtual resonance mode, in which the ambient magnetic fields outside plasmasphere oscillated with the cavity mode resonance. And Pi2 pulsations at the polar cap are also excited by PVR mode. In this presentation, we will show these Pi2 pulsations observed by DE-1, AMPTE/CCE, HER and KAK, in addition to other ground stations (Port Aux Francais, Furstenfeldbruck, and Wingst) and conduct statistical study of Pi2 pulsations, which were simultaneously observed by the DE-1 and AMPTE/CCE satellite.

  5. 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.

  6. In situ Electric Field Observations of Schumann Resonances in the Low Latitude Ionosphere and Their Implications for Tropospheric-Ionospheric Electromagnetic Coupling Mechanisms

    NASA Astrophysics Data System (ADS)

    Simoes, F.; Pfaff, R. F.; Freudenreich, H.; Bromund, K. R.; Martin, S. C.

    2010-12-01

    The Communications/Navigation Outage Forecasting System (C/NOFS) satellite investigates the electrodynamics of the low latitude ionosphere using a low inclination (13 degree) orbit with perigee and apogee of 401 and 867 km, respectively. The satellite is equipped with a three-axis double probe electric field detector, which provides continuous DC and AC electric field measurements. Among the most intriguing data acquired thus far, the electric field probe on C/NOFS unexpectedly detected Schumann resonances in the nightside ionosphere on a number of orbits within the satellite altitude sampling region. The Schumann resonance data are generally very low amplitude (~ 1 µV/m) signatures with a distinct spectral structure that corresponds precisely to the frequency modes predicted by the Schumman resonance waveguide cavity response; up to 10 ten peaks have been observed. These observations suggest major implications for Extremely Low Frequency (ELF) electromagnetic wave propagation in the earth’s ionosphere, namely the global electric circuit, lightning detection, and cavity leakage mechanisms. These findings provide a fresh approach to the study of tropospheric-space weather coupling mechanisms and transient luminous events, imply the need for a significant revision of the “standard” ELF wave propagation model, and offer a new, remote sensing technique for the investigation of planetary atmospheric electricity.

  7. Case study of simultaneous observations of sporadic sodium layer, E-region field-aligned irregularities and sporadic E layer at low latitude of China

    NASA Astrophysics Data System (ADS)

    Xie, H. Y.; Ning, B. Q.; Zhao, X. K.; Hu, L. H.

    2017-03-01

    Using the Na lidar at Haikou (20.0°N, 110.3°E), the VHF coherent radar and the digital ionosonde both at Sanya (18.4°N, 109.6°E), cases of simultaneous observations of sporadic sodium layer (SSL), E-region field-aligned irregularities (FAI) and sporadic E layer (Es) in the mesosphere and lower thermosphere (MLT) region at low latitude of China are studied. It is found that SSL occurs simultaneously or follows the enhancement of Es and FAI. The Es, FAI and SSL descend slowly with time which is mostly controlled by the diurnal tide (DT). Besides, the interaction of gravity wave (GW) with tides can cause oscillations in FAI and SSL. Our observations support the neutralization of ions for SSL formation: when the metallic ions layer descents to the altitudes where models predict, the sodium ions convert rapidly to atomic Na that may form an SSL event. Moreover, the SSL peak density will increase (decrease) in the convergence (divergence) vertical shear region of zonal wind.

  8. X-rays and solar proton event induced changes in the first mode Schumann resonance frequency observed at a low latitude station Agra, India

    NASA Astrophysics Data System (ADS)

    Singh, Birbal; Tyagi, Rajesh; Hobara, Yasuhide; Hayakawa, Masashi

    2014-06-01

    Effects of two events of X-ray bursts followed by solar proton events (SPEs) occurred on 22 September, 2011 and 06 July, 2012 on the variation of first mode Schumann resonance (SR) frequency monitored at a low latitude station, Agra (Geograph. lat. 27.2°N, long. 78°E) India are examined. The variation of average first mode SR frequency shows a sudden increase in coincidence with the X-ray bursts and a decrease associated with the peak flux of SPE. The increases in the frequency in the two cases are 8.4% and 10.9% and corresponding decreases are 4.3% and 3.3% respectively. The increases in the frequency are interpreted in terms of growth of ionization in the upper part of D-region ionosphere due to X-ray bursts and decreases during SPE are caused by the high ionization in the lower D-region (altitude about 50-60 km) in the polar region. The variation of SR frequency is observed to be consistent with other observatories at middle and high latitudes. The effects of X-ray flares on the D-region of the ionosphere at low and equatorial latitudes are also examined by analyzing the amplitude data of VLF transmitter signal (NWC, f=19.8 kHz) monitored at Agra. The flare effect observed prior to sun-set hours shows increase of electron density above 60 km in the ionosphere.

  9. Accounting for observation uncertainties in an evaluation metric of low latitude turbulent air-sea fluxes: application to the comparison of a suite of IPSL model versions

    NASA Astrophysics Data System (ADS)

    Servonnat, Jérôme; Găinuşă-Bogdan, Alina; Braconnot, Pascale

    2016-11-01

    Turbulent momentum and heat (sensible heat and latent heat) fluxes at the air-sea interface are key components of the whole energetic of the Earth's climate. The evaluation of these fluxes in the climate models is still difficult because of the large uncertainties associated with the reference products. In this paper we present an objective metric accounting for reference uncertainties to evaluate the annual cycle of the low latitude turbulent fluxes of a suite of IPSL climate models. This metric consists in a Hotelling T 2 test between the simulated and observed field in a reduce space characterized by the dominant modes of variability that are common to both the model and the reference, taking into account the observational uncertainty. The test is thus more severe when uncertainties are small as it is the case for sea surface temperature (SST). The results of the test show that for almost all variables and all model versions the model-reference differences are not zero. It is not possible to distinguish between model versions for sensible heat and meridional wind stress, certainly due to the large observational uncertainties. All model versions share similar biases for the different variables. There is no improvement between the reference versions of the IPSL model used for CMIP3 and CMIP5. The test also reveals that the higher horizontal resolution fails to improve the representation of the turbulent surface fluxes compared to the other versions. The representation of the fluxes is further degraded in a version with improved atmospheric physics with an amplification of some of the biases in the Indian Ocean and in the intertropical convergence zone. The ranking of the model versions for the turbulent fluxes is not correlated with the ranking found for SST. This highlights that despite the fact that SST gradients are important for the large-scale atmospheric circulation patterns, other factors such as wind speed, and air-sea temperature contrast play an

  10. 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.

  11. 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.

  12. Equatorial and low-latitude ionospheric response due to 2009 sudden stratospheric warming, South American sector.

    NASA Astrophysics Data System (ADS)

    Fagundes, Paulo Roberto; Gende, Mauricio; De Jesus, Rodolfo; Goncharenko, Larisa; Coster, Anthea; Kavutarapu, Venkatesh; De Abreu, Alessandro; Pillat, ValdirGil; Pezzopane, Michael

    The equatorial and low-latitude ionosphere/thermosphere system is permanently disturbed by waves (MSTIDs, tides, and planetary waves), which are generated in the lower atmosphere or in situ, as well as electric fields and TIDs produced by geomagnetic storm and UV, EUV, and X-ray solar radiation. Until recently it was thought, that during geomagnetic quiet conditions the equatorial and low-latitude F-layer was mainly perturbed by waves that were generated not far away from the observed location or electric fields generated by electroject. On the contrary during geomagnetic storms when the energy sources are in high latitudes the waves (TIDs) travel a very long distance from high latitude to equatorial region and electric fields can be mapped via magnetic field lines. However, recently an unexpected coupling between high latitude, -mid latitude, and -equatorial/low-latitude was discovered during sudden stratospheric warming (SSW). The exploration of all aspects involved in this process must be investigated in order to improve our knowledge about the Earth's atmosphere. This investigation, studies the consequences of the vertical coupling from lower to upper atmosphere during a major Northern Hemisphere sudden stratospheric warming, which took place in January 2009, on the equatorial and low-latitude ionosphere in the Southern Hemisphere. Using 16 ground-based GPS stations over the Brazilian sector, spanning from latitude 2.8N to 30.1S and longitude 62.0W to 37.7W, it was possible to notice that the ionosphere was disturbed by SSW from the Equator to low latitude. The TEC at all 16 stations was severely disturbed during several days after the SSW temperature peak.

  13. 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

  14. Statistical comparison of TEC derived from GPS and ISR observations at high latitudes

    NASA Astrophysics Data System (ADS)

    Makarevich, Roman A.; Nicolls, Michael J.

    2013-07-01

    A comprehensive data set collected with the Poker Flat Incoherent Scatter Radar (PFISR) and GPS receiver in Fairbanks, Alaska (magnetic latitude = 65.4°N) in 2007-2010 is employed to analyze and compare the total electron content (TEC) estimates derived from two radio techniques at high latitudes. The average TEC trends are shown to be largely similar and consistent with expectations based on solar conditions. The TEC residuals expressed as the difference and ratio between the PFISR- and GPS-derived TEC are evaluated to be below 2 total electron content units (TECU = 1016 electronsm-2) and 0.7-0.8, respectively, with some dependence on solar conditions. The agreement between TEC estimates is examined by limiting the difference between the GPS satellite and PFISR beam elevations to 2.5° and postintegrating GPS measurements over the period of each PFISR measurement. Factors controlling the agreement are investigated, including possible roles of GPS satellite bias, GPS elevation angle, and topside contribution to TEC. It is demonstrated that the best agreement, expressed as a linear correlation and a fraction of points consistent with the linear trend, is achieved with satellites at the largest elevation angles and smallest distances from PFISR, which are a possible effect of small spatial differences and unremoved differential biases. Estimates of the topside contribution to TEC range between 14% and 30% and are most consistent during daytime hours, while observations near the solar terminator and during the night suffer from large uncertainties.

  15. TEC, Trigger and Check, preparing LOFAR for Lunar observations

    NASA Astrophysics Data System (ADS)

    ter Veen, Sander; Mevius, Maaijke; Bonardi, Antonio; Buitink, Stijn; Corstanje, Arthur; Enriquez, J. Emilio; Falcke, Heino; Hörandel, Jörg R.; Mitra, Pragati; Mulrey, Katey; Nelles, Anna; Rachen, Jörg Paul; Rossetto, Laura; Schellart, Pim; Scholten, Olaf; Thoudam, Satyendra; Trinh, Gia; Winchen, Tobias

    2017-03-01

    One of the main ways to use radio to detect Ultra High Energy Neutrinos and Cosmic Rays is the Lunar Askaryan technique, that uses the Moon as a target and searches for nanosecond pulses with large radio telescopes. To use low frequency aperture arrays, such as LOFAR and the SKA, pose new challenges and possibilities in detection techniques of short radio pulses and to measure the Total Electron Content (TEC). As a prepatory work, we have used other measurements that use similar techniques, or that can answer a specific question, with the LOFAR radio telescope. This contribution reports on our work on triggering on short radio signals, post-event imaging of radio signals from buffered data and methods to determine the TEC-value.

  16. Statistical Characterization of Storm Enhanced Density based on GPS TEC Observations

    NASA Astrophysics Data System (ADS)

    Coster, A. J.; Colerico, M.; Rideout, W.; Taylor, B.; Foster, J.; Rich, F.

    2005-12-01

    Storm enhanced density (SED) involves the redistribution of plasmas in the ionosphere and magnetosphere driven by disturbance electric fields. Associated with SED events are large scale gradients in the total electron density (TEC) over relatively short distances. These TEC gradients can have direct impact on navigation and communication users. For example, marine users have horizontal positioning requirements of 2-5 meters at a 95 percent confidence level for safety of navigation in inland waterways. TEC gradients observed during 2003 SED events resulted in positioning errors larger than 20 meters on differential GPS baselines as short as 200 km. Large TEC gradients associated with SED events (greater than 100 TEC units per degree) have been observed near many large airports in the Northeast and Northwest continental US. Better SED characterization has been needed to improve current ionospheric models and to further our understanding of this phenomenon. The Madrigal database at MIT Haystack Observatory now contains TEC data with an unprecedented combination of global spatial coverage and high temporal resolution. Data from more than 2000 receivers are being incorporated into the daily 2005 TEC maps. This database has allowed for long term statistical studies of the presence of SED. In this paper, we present statistics of SED plumes observed during multiple storms during the 2000-2005 time period. The location, size of gradients, and time evolution of multiple SED events has been statistically characterized using an automated gradient analysis tool. Examples of magnetically conjugate SED plumes over northern Europe and the American longitude sectors will be discussed. Inter-hemispheric comparisons of the TEC magnitude of the observed SED events at the base, as well as within the plume, will be presented. The results also include observations of magnetically conjugate sub-auroral polarization streams (SAPS) which accompany the SED events using DMSP ion drift

  17. Equatorial and Low-Latitudes Ionospheric Reaction to Solar Flares

    NASA Astrophysics Data System (ADS)

    Nicoli Candido, C. M.; Becker-Guedes, F.; Paula, E. R.; Takahashi, H.

    2015-12-01

    Solar X-ray and extreme ultraviolet (EUV) photons are responsible for ionizing the terrestrial atmosphere and create the ionosphere. During solar flares, a fast increase in the electron density at different altitude regions takes place due to the abrupt enhance of the X-ray and EUV fluxes reaching Earth. With these changes in the ionosphere, radio communication and navigation can be drastically affected. The magnitudes of these Space Weather events can be related to the X-ray peak brightness and duration, which drive the intensity of the ionosphere response when the associated electromagnetic wave hit the sunlit side of the Earth's atmosphere. Other aspects defining these changes in a particular region are the local time, the solar zenith angle, and the position of the flare in the solar disc for each event. In order to improve the understand of radio signal degradation and loss in the Brazilian sector due to solar abrupt electromagnetic emissions, total electron content (TEC) data obtained by a GPS network formed by tents of dual-frequency receivers spread all over Brazilian territory were analyzed. It was observed different ionospheric local changes during several X-ray events identified by GOES satellite regarding the 0.1-0.8 nm range, and some case studies were ponder for a more detailed analysis of these effects. Considering the results, we have made an estimation of the ionospheric disturbances range for a particular event with great chance to affect space based communications in the equatorial and low-latitude regions.

  18. TEC Variations Over Korean Peninsula During Magnetic Storm

    NASA Astrophysics Data System (ADS)

    Ji, E.-Y.; Choi, B.-K.; Kim, K.-H.; Lee, D.-H.; Cho, J.-H.; Chung, J.-K.; Park, J.-U.

    2008-03-01

    By analyzing the observations from a number of ground- and space-based instruments, including ionosonde, magnetometers, and ACE interplanetary data, we examine the response of the ionospheric TEC over Korea during 2003 magnetic storms. We found that the variation of vertical TEC is correlated with the southward turning of the interplanetary magnetic field B_z. It is suggested that the electric fields produced by the dynamo process in the high-latitude region and the prompt penetration in the low-latitude region are responsible for TEC increases. During the June 16 event, dayside TEC values increase more than 15%. And the ionospheric F2-layer peak height (hmF2) was ˜300km higher and the vertical E×B drift (estimated from ground-based magnetometer equatorial electrojet delta H) showed downward drift, which may be due to the ionospheric disturbance dynamo electric field produced by the large amount of energy dissipation into high-latitude regions. In contr! ast, during November 20 event, the nightside TEC increases may be due to the prompt penetration westward electric field. The ionospheric F2-layer peak height was below 200km and the vertical E×B drift showed downward drift. Also, a strong correlation is observed between enhanced vertical TEC and enhanced interplanetary electric field. It is shown that, even though TEC increases are caused by the different processes, the electric field disturbances in the ionosphere play an important role in the variation of TEC over Korea.

  19. Signature of ionospheric irregularities under different geophysical conditions on SBAS performance in the western African low-latitude region

    NASA Astrophysics Data System (ADS)

    Abe, Oladipo Emmanuel; Villamide, Xurxo Otero; Paparini, Claudia; Ngaya, Rodrigue Herbert; Radicella, Sandro M.; Nava, Bruno

    2017-01-01

    Rate of change of TEC (ROT) and its index (ROTI) are considered a good proxy to characterize the occurrence of ionospheric plasma irregularities like those observed after sunset at low latitudes. SBASs (satellite-based augmentation systems) are civil aviation systems that provide wide-area or regional improvement to single-frequency satellite navigation using GNSS (Global Navigation Satellite System) constellations. Plasma irregularities in the path of the GNSS signal after sunset cause severe phase fluctuations and loss of locks of the signals in GNSS receiver at low-latitude regions. ROTI is used in this paper to characterize plasma density ionospheric irregularities in central-western Africa under nominal and disturbed conditions and identified some days of irregularity inhibition. A specific low-latitude algorithm is used to emulate potential possible SBAS message using real GNSS data in the western African low-latitude region. The performance of a possible SBAS operation in the region under different ionospheric conditions is analysed. These conditions include effects of geomagnetic disturbed periods when SBAS performance appears to be enhanced due to ionospheric irregularity inhibition. The results of this paper could contribute to a feasibility assessment of a European Geostationary Navigation Overlay System-based SBAS in the sub-Saharan African region.

  20. Equatorial and Low-Latitude Ionospheric Response to the Extreme Space Weather Event of March 2015, in the Brazilian Sector.

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    Fagundes PR, Cardoso FA and Venkatesh KPhysics and Astronomy Laboratory, Universidade do Vale do Paraiba (UNIVAP), Sao Jose dos Campos, Sao Paulo, Brazil In the present investigation we discuss the results on the response of the ionosphere (F-region) in the Brazilian sector, during extreme space weather event of March 2015. This geomagnetic storm has been considered as one of strongest storms in the solar cycle 24 where, the Dst index reached a minimum of -227 nT at 23:00 UT (17/03/2015) with KP reaching to 8-, and the monthly mean F10.7 solar flux was 125 sfu. This space weather event was studied using a large network of 110 GPS stations. It has been noticed that the Total Electron Content (TEC) was severely disturbed during the geomagnetic storm main and recovery phases. A wavelike oscillation with three peaks is observed from equator to low latitudes during the storm main phase on 17th and 18th March, 2015. Using a latitudinal chain of 8 GPS stations from equatorial region to low latitudes the storm time behavior of the Equatorial Ionization Anomaly (EIA) is investigated. It was noticed that the wavelike oscillation peak latitudinal extent decreases from the beginning of main phase to the recovery phase. The first maximum extends beyond from 2oS to 20oS, the second one from 8oS to 18oS and the third one from 13oS to 17oS. In addition, a strong negative phase in TEC variations is observed during the recovery phase on March 18, 2015. This negative phase is found to be stronger at low-latitude compared to the equatorial region. An anomalous behavior of EIA caused by the wavelike oscillations is observed during the main phase on March 17, 2015. Also, due to the strong negative phase in TEC resulted in strong EIA suppression on March 18, 2015.

  1. 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.

  2. GPS observation of continent-size traveling TEC pulsations at the start of geomagnetic storms

    NASA Astrophysics Data System (ADS)

    Pradipta, R.; Valladares, C. E.; Doherty, P. H.

    2014-08-01

    We report our experimental observation of continent-size traveling plasma disturbances using GPS measurements of total electron content (TEC) over the North American sector. These plasma disturbances occurred at the beginning of geomagnetic storms, immediately after the shock arrived, and prior to the appearance of large-scale traveling ionospheric disturbances (LSTIDs) from the auroral region. Specifically, these supersize TEC perturbations were observed when the interplanetary magnetic field Bz was oscillating between northward and southward directions. They were found to propagate zonally with a propagation speed of 2-3 km/s. We interpret these TEC pulsations as ion drift waves in the magnetosphere/plasmasphere that propagate azimuthally inside the GPS orbit.

  3. 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.

  4. Comparison of Two IRI plasmasphere Extensions with GPS-TEC Observations

    NASA Technical Reports Server (NTRS)

    Gulyaeva, T. L.; Gallagher, Dennis L.

    2006-01-01

    Comparisons of two model results with Global Positioning System GPS-TEC measurements have been carried out for different latitudinal, solar activity, magnetic activity, diurnal and seasonal conditions. The models evaluated are the Global Core Plasma Model (GCPM-2000) and the IRI extension with Russian plasmasphere model (IRI*).Data of 23 observatories providing GPS-TEC and ionosonde data have been used. It is shown that IRI* plasmasphere electron density is greater than GCPM results by an order of magnitude at 6370 km altitude (one Earth's radius) with this excess growing to 2-3 orders of magnitude towards the GPS satellite altitude of 20000 km. Another source of model and GPS-TEC differences is a way of selection of the F2 layer peak parameters driving the models either with ITU-R (former CCIR) maps or ionosonde observations. Plasmasphere amendment to IRI improves accuracy of TEC model predictions because the plasmasphere contribution to the total TEC varies from 10% by daytime under quiet magnetic conditions to more than 50% by night under stormy conditions.

  5. Seismo-Ionospheric Coupling as Intensified EIA Observed by Satellite Electron Density and GPS-TEC Data

    NASA Astrophysics Data System (ADS)

    Ryu, K.; Jangsoo, C.; Kim, S. G.; Jeong, K. S.; Parrot, M.; Pulinets, S. A.; Oyama, K. I.

    2014-12-01

    Examples of intensified EIA features temporally and spatially related to large earthquakes observed by satellites and GPS-TEC are introduced. The precursory, concurrent, and ex-post enhancements of EIA represented by the equatorial electron density, which are thought to be related to the M8.7 Northern Sumatra earthquake of March 2005, the M8.0 Pisco earthquake of August 2007, and the M7.9 Wenchuan Earthquake of 12 May 2008, are shown with space weather condition. Based on the case studies, statistical analysis on the ionospheric electron density data measured by the Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions satellite (DEMETER) over a period of 2005-2010 was executed in order to investigate the correlation between seismic activity and equatorial plasma density variations. To simplify the analysis, three equatorial regions with frequent earthquakes were selected and then one-dimensional time series analysis between the daily seismic activity indices and the EIA intensity indices were performed for each region with excluding the possible effects from the geomagnetic and solar activity. The statistically significant values of the lagged cross-correlation function, particularly in the region with minimal effects of longitudinal asymmetry, indicate that some of the very large earthquakes with M > 7.0 in the low latitude region can accompany observable seismo-ionospheric coupling phenomena in the form of EIA enhancements, even though the seismic activity is not the most significant driver of the equatorial ionospheric evolution. The physical mechanisms of the seismo-ionospheric coupling to explain the observation and the possibility of earthquake prediction using the EIA intensity variation are discussed.

  6. 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.

  7. Comparison of GPS TEC variations with IRI-2007 TEC prediction at equatorial latitudes during a low solar activity (2009-2011) phase over the Kenyan region

    NASA Astrophysics Data System (ADS)

    Olwendo, O. J.; Baki, P.; Cilliers, P. J.; Mito, C.; Doherty, P.

    2013-11-01

    This work presents an analysis of the Total Electron Content (TEC) derived from the International GNSS Service (IGS) receivers at Malindi (mal2: 2.9oS, 40.1oE, dip -26.813o), Kasarani (rcmn: 36.89oE, 1.2oS, dip -23.970o), Eldoret (moiu: 35.3oE, 0.3oN, dip -21.037o) and GPS-SCINDA (36.8oE, 1.3oS, dip -24.117o) receiver located in Nairobi for the period 2009-2011. The diurnal, monthly and seasonal variations of the GPS derived TEC (GPS-TEC) and effects of space weather on TEC are compared with TEC from the 2007 International Reference Ionosphere model (IRI-TEC) using the NeQuick option for the topside electron density. The diurnal peaks in GPS-TEC is maximum during equinoctial months (March, April, October) and in December and minimum in June solstice months (May, June, July). The variability in GPS-TEC is minimal in all seasons between 0:00 and 04:00 UT and maximum near noon between 10:00 and 14:00 UT. Significant variability in TEC at post sunset hours after 16:00 UT (19:00 LT) has been noted in all the seasons except in June solstice. The TEC variability of the post sunset hours is associated with the occurrence of the ionization anomaly crest which enhances nighttime TEC over this region. A comparison between the GPS-TEC and IRI-TEC indicates that both the model and observation depicts a similar trend in the monthly and seasonal variations. However seasonal averages show that IRI-TEC values are higher than the GPS-TEC. The IRI-TEC also depicts a double peak in diurnal values unlike the GPS-TEC. This overestimation which is primarily during daytime hours could be due to the model overestimation of the equatorial anomaly effect on levels of ionospheric ionization over the low latitude regions. The IRI-TEC also does not show any response to geomagnetic activity, despite the STORM option being selected in the model; the IRI model generally remains smooth and underestimates TEC during a storm. The GPS-TEC variability indicated by standard deviation seasonal averages

  8. Low-latitude daytime F region irregularities observed in two geomagnetically quiet days by the Hainan coherent scatter phased array radar (HCOPAR)

    NASA Astrophysics Data System (ADS)

    Chen, Gang; Jin, Han; Yan, Jingye; Zhang, Shaodong; Li, Guozhu; Yokoyama, Tatsuhiro; Yang, Guotao; Yan, Chunxiao; Wu, Chen; Wang, Jin; Zhong, Dingkun; Li, Yaxian; Wang, Zhihua

    2017-02-01

    Hainan coherent scatter phased array radar (HCOPAR) located at low latitude of China has recorded the extremely rare daytime F region irregularities at noon of 22 July 2013 and 23 May 2016. The two field-aligned irregularities (FAIs) appeared in the topside F2 layer and presented small Doppler velocities and narrow spectral widths. The fan sector maps show that the FAIs moved northward with almost no zonal speed. The irregularities emerged in the geomagnetically quiet condition and were irrelevant to the storm-induced eastward electric field as other daytime cases. More than 2 h after the emergency of the daytime irregularities over Hainan, the Shaoyang digisonde situated 870 km north to the HCOPAR recorded the spread-F in ionospheric F1 layer. According to the echo altitudes, the spread-F may connect the daytime bubbles via magnetic field line. The strong photoionization after sunrise made it difficult to generate the plasma bubbles in the sunlit ionosphere. Consequently, the two midday FAIs over Hainan may drift along the magnetic field lines from higher altitudes in the south and are most likely the remnant of previous night's bubbles.

  9. The Low-latitude Ionospheric Sensor Network: The Initial Campaigns

    NASA Astrophysics Data System (ADS)

    Doherty, P. H.; Valladares, C. E.; Carrano, C.

    2009-05-01

    The Low-latitude Ionospheric Sensor Network (LISN) is a distributed observatory designed to provide regional coverage in South America and high-temporal resolution measurements to diagnose the initiation and development of plasma structures and the state and dynamics of the low latitude ionosphere. It combines inexpensive GPS receivers and state-of-the-art radars such as the Vertical Incidence Pulsed Ionospheric Radar (VIPIR) ionosondes and magnetometers. This paper describes the characteristics of the LISN distributed observatory and discusses the results of the first two campaigns. LISN will be comprised of nearly 70 GPS receivers with the capability to measure Total Electron Content (TEC), amplitude and phase scintillation and Traveling Ionospheric Disturbances (TIDs). LISN will also include 5 ionosondes able to measure nighttime E-region densities and 5 collocated magnetometers that will be placed along the same magnetic meridian. The first campaign was dedicated to detect medium-scale (~100 km) TIDs and was conducted at Huancayo, Peru in July 2008 using 3 GPS receivers spaced by 4-5 km arranged in a triangular configuration. TEC data corresponding to 3 consecutive days indicate that the TIDs phase velocity was close to 120 m/s and directed northward during the early evening hours. The second campaign was conducted in February 2009 using 3 GPS receivers installed near Ancon and coordinated with the VIPIR ionosonde running in an interferometer mode. We will discuss the implications of these new results within the frame of the current theories of plasma bubble onset.

  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. Comparison of two IRI electron-density plasmasphere extensions with GPS-TEC observations

    NASA Astrophysics Data System (ADS)

    Gulyaeva, T. L.; Gallagher, D. L.

    Comparisons of two model results with Global Positioning System, GPS-TEC, measurements have been carried out for different latitudinal, solar activity, magnetic activity, diurnal, and seasonal conditions. The models evaluated are the Global Core Plasma Model (GCPM-2000) and the IRI extension (IRI ∗) with the Russian plasmasphere model. Data from 23 observatories providing GPS-TEC and ionosonde data have been used. It is shown that the IRI ∗ plasmasphere electron densities are greater than the GCPM results by an order of magnitude at 6370 km altitude (one Earth radius), becoming two to three orders of magnitude larger at the GPS satellite orbital altitude of 20,200 km. Another source of model and GPS-TEC differences is the selection of the ionospheric F2 layer peak parameters driving the models, either with ITU-R (former CCIR) maps or ionosonde observations. The plasmasphere model extension of IRI improves the accuracy of the TEC model predictions taking into account the plasmasphere contribution to the total electron content which could vary from 10% during daytime under quiet magnetic conditions to more than 50% during the night under storm-time conditions.

  12. Observed TEC Anomalies by GNSS Sites Preceding the Aegean Sea Earthquake of 2014

    NASA Astrophysics Data System (ADS)

    Ulukavak, Mustafa; Yal&ccedul; ınkaya, Mualla

    2016-11-01

    In recent years, Total Electron Content (TEC) data, obtained from Global Navigation Satellites Systems (GNSS) receivers, has been widely used to detect seismo-ionospheric anomalies. In this study, Global Positioning System - Total Electron Content (GPS-TEC) data were used to investigate ionospheric abnormal behaviors prior to the 2014 Aegean Sea earthquake (40.305°N 25.453°E, 24 May 2014, 09:25:03 UT, Mw:6.9). The data obtained from three Continuously Operating Reference Stations in Turkey (CORS-TR) and two International GNSS Service (IGS) sites near the epicenter of the earthquake is used to detect ionospheric anomalies before the earthquake. Solar activity index (F10.7) and geomagnetic activity index (Dst), which are both related to space weather conditions, were used to analyze these pre-earthquake ionospheric anomalies. An examination of these indices indicated high solar activity between May 8 and 15, 2014. The first significant increase (positive anomalies) in Vertical Total Electron Content (VTEC) was detected on May 14, 2014 or 10 days before the earthquake. This positive anomaly can be attributed to the high solar activity. The indices do not imply high solar or geomagnetic activity after May 15, 2014. Abnormal ionospheric TEC changes (negative anomaly) were observed at all stations one day before the earthquake. These changes were lower than the lower bound by approximately 10-20 TEC unit (TECU), and may be considered as the ionospheric precursor of the 2014 Aegean Sea earthquake

  13. 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

  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. 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.

  16. 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

  17. Observations of TEC fluctuations from an explosion on the Earth`s surface

    SciTech Connect

    Massey, R.S.; Carlos, R.C.; Jacobson, A.R.; Wu, G.

    1994-09-01

    The authors report observations of perturbations in the ionosphere total electron content (TEC) caused by acoustic waves propagating from a large chemical explosion in souther New Mexico at the earth`s surface. Fluctuations in TEC were measured by two arrays of receivers that monitor the phase of the 136 MHz beacons on two geostationary satellites. One array, located in northern New Mexico, observed fluctuations in the region where acoustic waves from the blast impinged directly on the ionosphere, while the second array, in Texas, was located to observe fluctuations caused by ducted acoustic waves. The TEC disturbance at the New Mexico array had an amplitude of about 2 {times} 10{sup 14} m{sup {minus}2} (more than 10 times the array noise level), while the amplitude at the Texas array, at a range of 900 km, was only a few times the instrumental noise level. Noise background analysis shows that the probability that a comparable or larger response at the New Mexico array might have been caused by a background noise event was less than 1%. The corresponding probability for the Texas array was 3%.

  18. 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.

  19. 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.

  20. Modeling of ionospheric irregularities during geomagnetically disturbed conditions over African low-latitude region

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

    In this study, station-specific models of ionospheric irregularities over low-latitude African region during geomagnetically disturbed days (Dst≤-50 nT) have been developed. Global Navigation Satellite Systems (GNSS)-derived ionospheric total electron content (TEC) data during 1998-2014 were used. Ionospheric irregularities were represented with the rate of change of TEC index (ROTI). The inputs for the models are the local time, solar flux index, day number of the year, auroral electrojet, and the disturbance storm time indices, while the output is the hourly 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 were validated with independent data over stations within 680 km radius. The models reproduced fairly well the inhibitions and the occurrences of ionospheric irregularities during geomagnetically disturbed days. The models even emulated these patterns in the various seasons, during medium and high solar activity conditions. During validations of the models, the percentages of the number of errors (difference between the observed and the modeled ROTI) <0.05 total electron content unit, 1TECU = 1016 el m-2 (TECU)/Min at all the stations were all >70% and the root-mean-square error were mostly < 0.1 TECU/Min. Furthermore, the correlation coefficients ranged from 0.47 to 0.76.

  1. First Observations of Equatorial TEC and Scintillation With Multiple Dual-Frequency Software-Defined GPS Receivers

    NASA Astrophysics Data System (ADS)

    O'Hanlon, B.; Kintner, P. M.; de Paula, E. R.

    2009-05-01

    A dual-frequency software-defined GPS receiver has been developed and used for monitoring total electron content (TEC) and observing equatorial ionospheric scintillation. The Cornell University GPS Receiver Implemented on a DSP (GRID) utilizes the GPS L1 C/A and L2 C signals to measure TEC and observe scintillation. The GRID receiver measured TEC and GPS signal amplitude and phase at 10 Hz. Also employed were two similar GPS digital storage receivers (non-real-time) that made the same measurements at 50 Hz. These receivers were arranged in a linear array and utilized in January, 2009 in Natal, Brazil (magnetic latitude 2.42°) to make these observations. Mild scintillation of the L1 C/A and L2 C signals was observed. TEC measurements agreed well with those taken by a collocated GPSV 4004B Scintillation/TEC Monitor. We demonstrate the use of multiple receivers to measure drifts and report on the first fast (10Hz-50Hz) multiple receiver TEC measurements in the equatorial ionosphere.

  2. 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.

  3. Hemispheric asymmetry in transition from equatorial plasma bubble to blob as deduced from 630.0 nm airglow observations at low latitudes

    NASA Astrophysics Data System (ADS)

    Park, Jaeheung; Martinis, Carlos R.; Lühr, Hermann; Pfaff, Robert F.; Kwak, Young-Sil

    2016-01-01

    Transitions from depletions to enhancements of 630.0 nm nighttime airglow have been observed at Arecibo. Numerical simulations by Krall et al. (2009) predicted that they should occur only in one hemisphere, which has not yet been confirmed observationally. In this study we investigate the hemispheric conjugacy of the depletion-to-enhancement transition using multiple instruments. We focus on one event observed in the American longitude sector on 22 December 2014: 630.0 nm airglow depletions evolved into enhancements in the Northern Hemisphere while the evolution did not occur in the conjugate location in the Southern Hemisphere. Concurrent plasma density measured by low Earth orbit (LEO) satellites and 777.4 nm airglow images support that the depletions and enhancements of 630.0 nm nighttime airglow reflect plasma density decreases and increases (blobs), respectively. Characteristics of the airglow depletions, in the context of the LEO satellite data, further suggest that the plasma density depletion deduced from the airglow data represents equatorial plasma bubbles (EPBs) rather than medium-scale traveling ionospheric disturbances from midlatitudes. Hence, the event in this study can be interpreted as EPB-to-blob transition.

  4. 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

  5. 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.

  6. Small spatial scale field aligned currents in middle and low latitudes as observed by the CHAMP satellite and verification of their current circuit model

    NASA Astrophysics Data System (ADS)

    Nakanishi, K.; Iyemori, T.; Luhr, H.

    2013-12-01

    The magnetic field observation by the CHAMP satellite shows the global and frequent appearance of small scale (1-5 nT) magnetic fluctuations with period around a few tens seconds along the satellites. They have the following characteristics. 1. The signal is perpendicular to the geomagnetic main field, and the amplitude of the zonal component is larger than that of the meridional component. 2. Around the dip equator, as the latitude becomes lower, the period and amplitudes of the two components perpendicular to the main field respectively tend to become longer and smaller (to nearly zero on the dip equator). 3. The amplitude of the magnetic fluctuations on the dayside is larger than that on the night side by around one order in magnitude, which highly correlates to the electric conductivity of the ionospheric dynamo layer. 4. The amplitude shows symmetry about the magnetic dip equator which indicates a magnetic conjugacy to a certain extent. 5. The amplitude shows almost no dependence on the solar wind parameters such as the IMF cone angle nor the solar wind speed, which strongly suggests no association with the Pc3 micro pulsation. 6. The amplitude also shows almost no dependence on the geomagnetic activity. 7. The amplitude has a clear seasonal dependence with topographical characteristics. They can be interpreted as the spatial structure of small scale field-aligned currents generated by the ionospheric dynamo driven by atmospheric gravity waves propagating from the lower atmosphere. The mechanism is the following; first, the gravity waves generated by the lower atmospheric disturbance propagate to the ionosphere; the neutral winds oscillate, cause ionospheric dynamo and Pedersen and Hall currents flow; because the dynamo region is finite, the currents cause polarized electric fields; and the polarized electric fields propagate along the geomagnetic filed as Alfven waves accompanied by field-aligned currents, at the same time, the ionospheric currents divert to

  7. Comment on 'Observations of Low-Latitude Electron Precipitation' by R. Lieu, J. Watermann, K. Wilhelm, J. J. Quenby, and W. I. Axford

    NASA Technical Reports Server (NTRS)

    Rassoul, H. K.; Hanson, W. B.

    1989-01-01

    Observations made by an electron spectrometer aboard Spacelab 1 and presented by Lieu et al. (1988) are examined critically. The precipitation of electrons in the energy range of 0.1-12.5 keV was measured on December 6 and 7, 1983. Data for 16 passes near 240 km altitude, between + and - 30 deg geographic latitude, outside the South Atlantic Anomaly were included. It is argued that there is no geophysical confirmation of the large electron fluxes reported by Lieu et al. In their response, Lieu et al. discuss the sampling bias in the Spacelab 1 data and the magnetic shielding deficiencies of the calibration facility below about 500 eV.

  8. Analysis of ionospheric TEC from GNSS observables over the Turkish region and predictability of IRI and SPIM models

    NASA Astrophysics Data System (ADS)

    Ansari, Kutubuddin; Corumluoglu, Ozsen; Panda, Sampad Kumar

    2017-04-01

    The present study investigates the ionospheric Total Electron Content (TEC) variations in the lower mid-latitude Turkish region from the Turkish Permanent GNSS Network (TPGN) and International GNSS Services (IGS) observations during the period from January 2015 to December 2015. The corresponding TEC predicted by the International Reference Ionosphere (IRI 2012) and Standard Plasmasphere-Ionosphere Model (SPIM), and interpolated from Global Ionosphere Maps (GIMs) are evaluated to realize their reliability over the region. We studied the diurnal and monthly behavior of TEC and the relative TEC deviations along with the upper and lower quartiles to represent its spatio-temporal variability. The diurnal variation of GNSS-derived TEC indicates its maximum peak value around 10.00 UT which decreases gradually to attain minimum value after midnight. The monthly maximum value of TEC is observed in March followed by May and August, and the lowest value is seen during September. Studies show that the monthly relative deviation of TEC variability lies in the range of -1 to 4 units for all stations with the maximum difference between positive and negative variability remaining around 5. The studies also cover seasonal variation, grand-mean of ionospheric TEC and TEC intensity from the TPGN. The seasonal ionospheric VTEC pattern over all stations depicts slight increment in VTEC distribution during March equinox compared to September equinox. The December solstice perceived relatively higher VTEC than June solstice. The overall of VTEC values enhanced at all stations towards end of the year 2015 compare to mid of year due the high solar activity. The maximum grand-mean of VTEC is registered in March equinox while the lowest value is seen in September irrespective of all stations. The measured grand-mean intensity variations of VTEC values are in ascending phase during March, May, August and November months, but in descending phase during February, April, June and September

  9. 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.

  10. Low latitude electrodynamic plasma drifts - A review

    NASA Technical Reports Server (NTRS)

    Fejer, B. G.

    1991-01-01

    The characteristics and driving mechanisms of low latitude ExB plasma drifts and electric fields particularly at F-region heights are reviewed. It is concluded that the general characteristics of the quiet-time plasma can be explained as resulting from E- and F-region dynamo and interhemispheric coupling processes. The disturbance dynamo effects are found to be responsible for the drift perturbations following the periods of enhanced magnetic activity. The prompt penetration of high-latitude electric fields to lower latitudes produces large perturbations on the upward/poleward drifts, but has no significant effect on the low-latitude and the equatorial zonal drifts. Detailed low-latitude and global numerical models for studying the characteristics of plasma drifts are capable of reproducing the latitudinal variation of the perturbation electric fields and their diurnal variations.

  11. Low latitude ionospheric scintillation and zonal irregularity drifts observed with GPS-SCINDA system and closely spaced VHF receivers in Kenya

    NASA Astrophysics Data System (ADS)

    Olwendo, O. J.; Baluku, T.; Baki, P.; Cilliers, P. J.; Mito, C.; Doherty, P.

    2013-05-01

    In this study we have used VHF and GPS-SCINDA receivers located at Nairobi (36.8°E, 1.3°S, dip -24.1°) in Kenya, to investigate the ionospheric scintillation and zonal drift irregularities of a few hundred meter-scale irregularities associated with equatorial plasma density bubbles for the period 2011. From simultaneous observations of amplitude scintillation at VHF and L-band frequencies, it is evident that the scintillation activity is higher during the post sunset hours of the equinoctial months than at the solstice. While it is noted that there is practically no signatures of the L-band scintillation in solstice months (June, July, December, January) and after midnight, VHF scintillation does occur in the solstice months and show post midnight activity through all the seasons. VHF scintillation is characterized by long duration of activity and slow fading that lasts till early morning hours (05:00 LT). Equinoctial asymmetry in scintillation occurs with higher occurrence in March-April than in September-October. The occurrence of post midnight VHF scintillation in this region is unusual and suggests some mechanisms for the formation of scintillation structure that might not be clearly understood. Zonal drift velocities of irregularities were measured using cross-correlation analysis with time series of the VHF scintillation structure from two closely spaced antennas. Statistical analyses of the distribution of zonal drift velocities after sunset hours indicate that the range of the velocities is 30-160 m/s. This is the first analysis of the zonal plasma drift velocity over this region. Based on these results we suggest that the east-west component of the plasma drift velocity may be related to the evolution of plasma bubble irregularities caused by the prereversal enhancement of the eastward electric fields. The equinoctial asymmetry of the drift velocities and scintillation could be attributed to the asymmetry of neutral winds in the thermosphere that drives

  12. Simulation of nose whistlers: An application to low latitude whistlers

    NASA Astrophysics Data System (ADS)

    Singh, Kalpana; Singh, R. P.; Kumar Singh, Abhay; Singh, R. N.

    2006-05-01

    Simulation technique for whistler mode signal propagating through inhomogeneous plasma using WKB approximation has been developed (Singh, K., Singh, R.P., Ferencz, O.E., 2004. Simulation of whistler mode propagation for low latitude stations. Earth Planet Space 56, 979-987). In the present paper, we have used it for the analysis of recorded signals at low latitudes and estimated the nose frequency, which is not observed on the dynamic spectra. At low latitudes nose frequency is ˜100 kHz or more and therefore it is absent in the dynamic spectra due to attenuation of the signal at higher frequencies. The importance of nose frequency is in determining the exact path of propagation, which is required in probing of ambient medium. It is shown that the method permits to study the nose frequency variation, it can be used to deduce physical parameters as the global electric field. A case study permits to get a reasonable value of the electric field, which up to now could not be done at very low latitude.

  13. Ionospheric TEC Weather Map Over South America

    NASA Astrophysics Data System (ADS)

    Takahashi, H.; Wrasse, C. M.; Denardini, C. M.; Pádua, M. B.; Paula, E. R.; Costa, S. M. A.; Otsuka, Y.; Shiokawa, K.; Monico, J. F. Galera; Ivo, A.; Sant'Anna, N.

    2016-11-01

    Ionospheric weather maps using the total electron content (TEC) monitored by ground-based Global Navigation Satellite Systems (GNSS) receivers over South American continent, TECMAP, have been operationally produced by Instituto Nacional de Pesquisas Espaciais's Space Weather Study and Monitoring Program (Estudo e Monitoramento Brasileiro de Clima Especial) since 2013. In order to cover the whole continent, four GNSS receiver networks, (Rede Brasileiro de Monitoramento Contínuo) RBMC/Brazilian Institute for Geography and Statistics, Low-latitude Ionospheric Sensor Network, International GNSS Service, and Red Argentina de Monitoreo Satelital Continuo, in total 140 sites, have been used. TECMAPs with a time resolution of 10 min are produced in 12 h time delay. Spatial resolution of the map is rather low, varying between 50 and 500 km depending on the density of the observation points. Large day-to-day variabilities of the equatorial ionization anomaly have been observed. Spatial gradient of TEC from the anomaly trough (total electron content unit, 1 TECU = 1016 el m-2 (TECU) <10) to the crest region (TECU > 80) causes a large ionospheric range delay in the GNSS positioning system. Ionospheric plasma bubbles, their seeding and development, could be monitored. This plasma density (spatial and temporal) variability causes not only the GNSS-based positioning error but also radio wave scintillations. Monitoring of these phenomena by TEC mapping becomes an important issue for space weather concern for high-technology positioning system and telecommunication.

  14. GPS Observation of Fast-moving Continent-size Traveling TEC Pulsations at the Start of Geomagnetic Storms

    NASA Astrophysics Data System (ADS)

    Pradipta, R.; Valladares, C. E.; Doherty, P. H.

    2014-12-01

    Using network of GPS receiver stations in North and South America, we have recently observed fast-moving continent-size traveling plasma disturbances in the mapped total electron content (TEC) data. These space plasma disturbances occurred at the beginning of geomagnetic storms, immediately after the storm's suddent commencement (SSC) and prior to the appearance of large-scale traveling ionospheric disturbances (LSTIDs) from the auroral regions. More specifically, these supersize TEC perturbations were observed when the IMF Bz was oscillating between northward and southward directions. They were found to propagate zonally westward with a propagation speed of 2-3 km/s, if projected onto an ionospheric-equivalent altitude of 350 km. Based on their general characteristics and comparison with ground-based ionosonde data, we interpret these TEC pulsations as ion drift waves in the magnetosphere/plasmasphere that propagate azimuthally inside the GPS orbit.

  15. Global response of the low-latitude to midlatitude ionosphere due to the Bastille Day flare

    NASA Astrophysics Data System (ADS)

    Huba, J. D.; Warren, H. P.; Joyce, G.; Pi, X.; Iijima, B.; Coker, C.

    2005-08-01

    The first global simulation study and comparison to data of the ionospheric effects associated with the enhanced EUV irradiance of the Bastille Day flare are presented. This is done by incorporating a time-dependent EUV spectrum, based on data and hydrodynamic modeling, into the NRL ionosphere model SAMI3. The simulation results indicate that the total electron content (TEC) increases to over 7 TEC units in the daytime, low-latitude ionosphere. In addition, it is predicted that the maximum density in the F-layer (NmF2) increases by $\\lesssim$20% and that the height of the maximum electron density (HmF2) decreases by $\\lesssim$20%. These results are explained by the increased ionization at altitudes <400 km which increases TEC and NmF2 while decreasing HmF2. The results are in reasonably good agreement with data obtained from GPS satellites and the TOPEX satellite.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. The Low-latitude Ionospheric Sensor Network (LISN): Initial Measurements

    NASA Astrophysics Data System (ADS)

    Valladares, C. E.

    2008-12-01

    This paper describes the characteristics and illustrates the early measurements of the first distributed observatory that is being installed in the South American region to study the low-latitude ionosphere and upper atmosphere. The LISN distributed observatory will be comprised of nearly 70 GPS receivers with the capability to measure Total Electron Content (TEC), amplitude and phase scintillation and Traveling Ionospheric Disturbances (TIDs). The network will include 5 ionosondes able to measure nighttime E-region densities and 5 collocated magnetometers that will be placed along the same magnetic meridian. This network of GPS receivers and ionospheric sensors span from north to south in the South American continent west of the 55o West meridian. In addition to introducing the present capabilities of the LISN network, this paper will present the results of the first LISN campaign dedicated to detect medium-scale (~100 km) TIDs that was conducted at Huancayo using 3 closely-spaced GPS receivers. This paper also presents initial calculations of the vertical drift velocity using 3 magnetometers, two of them placed off the equator in opposite hemispheres and a detailed description of the measurements of the first LISN ionosonde that is presently operating near the magnetic equator.

  1. 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.

  2. 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.

  3. 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.

    1977-01-01

    In situ measurements of variational electric fields at low latitudes, taken by OGO 6 satellite instruments, are analyzed. The observations are compared with other data on F region and spread-F structures. Conformity of the electric field fluctuations with the overall picture of low-latitude irregularities is examined empirically and theoretically, and candidate processes for generation of the observed irregularities are considered. Three distinct types of irregularities are delineated and compared.

  4. 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.

  5. Multifractal analysis of low-latitude geomagnetic fluctuations

    NASA Astrophysics Data System (ADS)

    Bolzan, M. J. A.; Rosa, R. R.; Sahai, Y.

    2009-02-01

    The technique of large deviation multifractal spectrum has shown that the high-latitude (77.5° N, 69.2° W) geomagnetic fluctuations can be described from direct dissipation process or loading-unloading regimes of the solar wind-magnetosphere coupling. In this paper, we analyze the H-component of low-latitude (22.4° S, 43.6° W) geomagnetic field variability observed during the month of July 2000 at the Geomagnetic Observatory, Vassouras, RJ, Brazil. The variability pattern during this period is a mixture of quiet and disturbed days including the Bastille Day intense geomagnetic storm on 15 July. Due to the complexity of this data, we pursue a detailed analysis of the geomagnetic fluctuations in different time scales including a multifractal approach using the singular power spectrum deviations obtained from the wavelet transform modulus maxima (WTMM). The results suggest, as observed from high-latitude data, the occurrence of low-latitude multifractal processes driving the intermittent coupling between the solar wind-magnetosphere and geomagnetic field variations. On finer scales possible physical mechanisms in the context of nonlinear magnetosphere response are discussed.

  6. Ionospheric disturbances detected by high-resolution GPS-TEC observations after an earthquake and a tornado

    NASA Astrophysics Data System (ADS)

    Tsugawa, Takuya; Otsuka, Yuichi; Saito, Akinori; Ishii, Mamoru; Nishioka, Michi

    Ionospheric disturbances following the 2011 Tohoku earthquake and the 2013 Moore tornado were observed by high-resolution GPS total electron content (TEC) observations using dense GPS receiver networks. After the 2011 Tohoku earthquake, concentric waves with short propagation distance propagated in the radial direction in the propagation velocity of 3,457, 783, 423 m/s for the first, second, third peak, respectively. Following these waves, concentric waves with long propagation distance appeared to propagate at the velocity of 138-288 m/s. In the vicinity of the epicenter, sudden TEC depletions and short-period oscillations with a period of approximately 4 minutes were also observed. The center of these ionospheric variations, termed the "ionospheric epicenter", corresponded to the tsunami source. Comparing to the results of a numerical simulation using non-hydrostatic compressible atmosphere-ionosphere model, the first peak of circular wave would be caused by the acoustic waves generated from the propagating Rayleigh wave. The second and third waves would be caused by atmospheric gravity waves excited in the lower ionosphere due to the acoustic wave propagations from the tsunami source. The fourth and following waves are considered to be caused by the atmospheric gravity waves induced by the wavefronts of traveling tsunami. After the EF5 tornado hit Moore, Oklahoma, USA, on 20 May 2013, clear concentric waves and short-period oscillations were observed. These concentric waves were non-dispersive waves with a horizontal wavelength of approximately 120 km and a period of approximately 13 minutes. They were observed for more than seven hours throughout North America. TEC oscillations with a period of approximately 4 minutes were also observed in the south of Moore for more than eight hours. Comparison between the GPS-TEC observations and the infrared cloud images from the GOES satellite indicates that the concentric waves and the short-period oscillations would be

  7. 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.

  8. Theory of the low-latitude boundary layer

    NASA Technical Reports Server (NTRS)

    Sonnerup, B. U. OE.

    1980-01-01

    A one-dimensional steady state fluid mechanical model is developed of the low-latitude plasma boundary layer inside the dawn and dusk magnetopause. Momentum transfer in the layer is produced by viscosity and/or mass diffusion. Coupling to the ionosphere is achieved via field-aligned currents, the magnitude of which is limited by parallel potential drops. These currents flow into and out of the ionosphere in the manner described by Iijima and Potemra. The higher-latitude (region 1) currents are associated with the boundary layer proper, while the lower-latitude (region 2) ones are associated with a region of sunward return flow adjacent to the boundary layer. The parallel potential drops have a magnitude of typically 2-3 kV and a north-south extent of 100-200 km. The calculated potential profile corresponds reasonably well to observed inverted V precipitation events.

  9. 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.

  10. 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).

  11. 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.

  12. 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)

  13. Real-time reconstruction of topside ionosphere scale height from coordinated GPS-TEC and ionosonde observations

    NASA Astrophysics Data System (ADS)

    Gulyaeva, Tamara; Poustovalova, Ljubov

    The International Reference Ionosphere model extended to the plasmasphere, IRI-Plas, has been recently updated for assimilation of total electron content, TEC, derived from observations with Global Navigation Satellite System, GNSS. The ionosonde products of the F2 layer peak density (NmF2) and height (hmF2) ensure true electron density maximum at the F2 peak. The daily solar and magnetic indices used by IRI-Plas code are compiled in data files including the 3-hour ap and kp magnetic index from 1958 onward, 12-monthly smoothed sunspot number R12 and Global Electron Content GEC12, daily solar radio flux F10.7 and daily sunspot number Ri. The 3-h ap-index is available in Real Time, RT, mode from GFZ, Potsdam, Germany, daily update of F10.7 is provided by Space Weather Canada service, and daily estimated international sunspot number Ri is provided by Solar Influences Data Analysis Center, SIDC, Belgium. For IRI-Plas-RT operation in regime of the daily update and prediction of the F2 layer peak parameters, the proxy kp and ap forecast for 3 to 24 hours ahead based on data for preceding 12 hours is applied online at http://www.izmiran.ru/services/iweather/. The topside electron density profile of IRI-Plas code is expressed with complementary half-peak density anchor height above hmF2 which corresponds to transition O+/H+ height. The present investigation is focused on reconstruction of topside ionosphere scale height using vertical total electron content (TEC) data derived from the Global Positioning System GPS observations and the ionosonde derived F2 layer peak parameters from 25 observatories ingested into IRI-Plas model. GPS-TEC and ionosonde measurements at solar maximum (September, 2002, and October, 2003) for quiet, positively disturbed, and negatively disturbed days of the month are used to obtain the topside scale height, Htop, representing the range of altitudes from hmF2 to the height where NmF2 decay by e times occurs. Mapping of the F2 layer peak parameters

  14. Longitudinal Variation in GPS -TEC and Topside Electron Density Associated with the Wave Number Four Structures over South American Sector

    NASA Astrophysics Data System (ADS)

    Nogueira, P. A.; Abdu, M. A.; Souza, J. R.; Bailey, G. J.; Shume, E. B.; Denardini, C. M.

    2012-12-01

    Recent observations of the low-latitude ionospheric electron density have revealed a longitudinal structure in the Equatorial Ionization Anomaly (EIA) intensity, which is characterized by a wave number-four pattern when plotted at a constant-local-time frame. It has been proposed that neutral wind driven dynamo electric fields from the E-region due to non migrating tidal modes are responsible for this pattern. In the present work we have used measurements from the Defense Meteorological Satellite Program (DMSP) to investigate the four peaks structure in the topside electron density of the low latitude ionosphere. We also compare the climatology of the Total Electron Content (TEC) as observed by GPS receivers in two equatorial stations over South America, São Luís (2.33 S, 315.8E, declination = -19 degree) in Brazil and Arequipa (16.5S, 288.5E, declination = 0.5 degree) in Peru. TEC variations for three solar activity levels (high, moderate and low) have been analyzed. TEC values over São Luís are found to be larger than that ones over Arequipa independent of the season, local time and solar cycle conditions. We estimated the vertical plasma drifts over these stations using magnetometer data during daytime and using ionosonde data for evening hours. We fed the Sheffield University Plasmasphere Ionosphere Model (SUPIM) with this drifts in an attempt to partially explain the differences in the TEC over these stations. The SUPIM was also used to evaluate the effect of thermospheric wind to cause the four peaks structure in the plasma density. Therefore, we analyze the equatorial ionospheric response to combined effects of thermospheric neutral winds and zonal electric field causing the longitudinal variation in TEC observed in the South American longitude sector.

  15. 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.

  16. Characteristics of the low latitude ionospheric storm in the East-Asian region

    NASA Astrophysics Data System (ADS)

    Zhao, B.; Wan, W.; Liu, L.

    2009-04-01

    First, an classification of ionospheric storm effects in the sub-equatorial ionization anomaly(SEIA) region at 120°E has been performed through the analysis of ionogram data at two ionosonde stations, Wuhan (114.4°, 30.5°) and Chung-Li (121.2°, 25°), and total electron content (TEC) derived from GPS network distributed around 120°E during the year 1999-2004. Three types of negative phase are identified. One is shown to be varied in phase of F-layer height variation and the other two out of phase. Two types of positive phase are also found. The mechanisms to cause these types of ionospheric effects has been considered to be related with storm meridional thermospheric wind including traveling atmosphere disturbance(TAD), electric fields and composition changes. Then based on the 50 years of ionosonde and 8 years of global ionospheric maps (GIMs) data, features of low latitude ionospheric storm were obtained. Results shows that positive phases during 18:00-2400 LT with its center near the 21:00 LT and 24:00-08:00 LT with its center near the sunrise time have predomination in controlling the storm behavior at low latitudes. It is shown that the distortion of EIA under the effects of the above factors have significant influence on the behavior of SEIA ionogram parameters.

  17. 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.

  18. An ensemble average method to estimate absolute TEC using radio beacon-based differential phase measurements: Applicability to regions of large latitudinal gradients in plasma density

    NASA Astrophysics Data System (ADS)

    Thampi, Smitha V.; Bagiya, Mala S.; Chakrabarty, D.; Acharya, Y. B.; Yamamoto, M.

    2014-12-01

    A GNU Radio Beacon Receiver (GRBR) system for total electron content (TEC) measurements using 150 and 400 MHz transmissions from Low-Earth Orbiting Satellites (LEOS) is fabricated in house and made operational at Ahmedabad (23.04°N, 72.54°E geographic, dip latitude 17°N) since May 2013. This system receives the 150 and 400 MHz transmissions from high-inclination LEOS. The first few days of observations are presented in this work to bring out the efficacy of an ensemble average method to convert the relative TECs to absolute TECs. This method is a modified version of the differential Doppler-based method proposed by de Mendonca (1962) and suitable even for ionospheric regions with large spatial gradients. Comparison of TECs derived from a collocated GPS receiver shows that the absolute TECs estimated by this method are reliable estimates over regions with large spatial gradient. This method is useful even when only one receiving station is available. The differences between these observations are discussed to bring out the importance of the spatial differences between the ionospheric pierce points of these satellites. A few examples of the latitudinal variation of TEC during different local times using GRBR measurements are also presented, which demonstrates the potential of radio beacon measurements in capturing the large-scale plasma transport processes in the low-latitude ionosphere.

  19. Low Latitude Aeronomy Study in Africa

    DTIC Science & Technology

    2016-02-09

    by improvising we were able to construct a small FPI and have it deployed in Abuja, Nigeria and obtained thermospheric winds in West...collaboration in the future. 15. SUBJECT TERMS Equatorial ionosphere, plasma bubble, thermospheric wind observations. 16. SECURITY CLASSIFICATION OF: 17...longitudinal variations of the plasma bubble and its association with the thermospheric wind . To achieve this goal, we proposed to deploy a Fabry-Perot

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. Counter-streaming magnetosheath ions in the dayside low latitude boundary layer

    NASA Technical Reports Server (NTRS)

    Fuselier, S. A.; Klumpar, D. M.; Shelley, E. G.

    1992-01-01

    Observations in the subsolar low-latitude boundary layer (LLBL) during reconnection show counterstreaming suprathermal ions on rare occasions. Composition measurements for one event presented here indicate that the ions are from the magnetosheath although no similar equal energy per charge suprathermal He(2+) and H(+) populations were observed there. Acceleration of magnetosheath ions either across the magnetopause or in the LLBL followed by magnetic mirroring of the initially parallel suprathermal ions best explains these observations.

  6. Turbulent oceanic western-boundary layers at low latitude

    NASA Astrophysics Data System (ADS)

    Quam Cyrille Akuetevi, Cataria; Wirth, Achim

    2013-04-01

    Low latitude oceanic western-boundary layers range within the most turbulent regions in the worlds ocean. The Somali current system with the Great Whirl and the Brazilian current system with its eddy shedding are the most prominent examples. Results from analytical calculations and integration of a one layer reduced-gravity fine resolution shallow water model is used to entangle this turbulent dynamics. Two types of wind-forcing are applied: a remote Trade wind forcing with maximum shear along the equator and a local Monsoon wind forcing with maximum shear in the vicinity of the boundary. For high values of the viscosity (> 1000m2s-1) the stationary solutions compare well to analytical predictions using Munk and inertial layer theory. When lowering the friction parameter time dependence results. The onset of instability is strongly influenced by inertial effects. The unstable boundary current proceeds as a succession of anti-cyclonic coherent eddies performing a chaotic dynamics in a turbulent flow. The dynamics is governed by the turbulent fluxes of mass and momentum. We determine these fluxes by analyzing the (potential) vorticity dynamics. We demonstrate that the boundary-layer can be separated in four sub-layers, which are (starting from the boundary): (1) the viscous sub-layer (2) the turbulent buffer-layer (3) the layer containing the coherent structures and (4) the extended boundary layer. The characteristics of each sub-layer and the corresponding turbulent fluxes are determined, as are the dependence on latitude and the type of forcing. A new pragmatic method of determining the eddy viscosity, based on Munk-layer theory, is proposed. Results are compared to observations and solutions of the multi-level primitive equation model (DRAKKAR).

  7. 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.

  8. Large enhancements in low latitude total electron content during 15 May 2005 geomagnetic storm in Indian zone

    NASA Astrophysics Data System (ADS)

    Dashora, N.; Sharma, S.; Dabas, R. S.; Alex, S.; Pandey, R.

    2009-05-01

    Results pertaining to the response of the equatorial and low latitude ionosphere to a major geomagnetic storm that occurred on 15 May 2005 are presented. These results are also the first from the Indian zone in terms of (i) GPS derived total electron content (TEC) variations following the storm (ii) Local low latitude electrodynamics response to penetration of high latitude convection electric field (iii) effect of storm induced traveling atmospheric disturbances (TAD's) on GPS-TEC in equatorial ionization anomaly (EIA) zone. Data set comprising of ionospheric TEC obtained from GPS measurements, ionograms from an EIA zone station, New Delhi (Geog. Lat. 28.42° N, Geog. Long. 77.21° E), ground based magnetometers in equatorial and low latitude stations and solar wind data obtained from Advanced Composition Explorer (ACE) has been used in the present study. GPS receivers located at Udaipur (Geog. Lat. 24.73° N, Geog. Long. 73.73° E) and Hyderabad (Geog. Lat. 17.33° N, Geog. Long. 78.47° E) have been used for wider spatial coverage in the Indian zone. Storm induced features in vertical TEC (VTEC) have been obtained comparing them with the mean VTEC of quiet days. Variations in solar wind parameters, as obtained from ACE and in the SYM-H index, indicate that the storm commenced on 15 May 2005 at 02:39 UT. The main phase of the storm commenced at 06:00 UT on 15 May with a sudden southward turning of the Z-component of interplanetary magnetic field (IMF-Bz) and subsequent decrease in SYM-H index. The dawn-to-dusk convection electric field of high latitude origin penetrated to low and equatorial latitudes simultaneously as corroborated by the magnetometer data from the Indian zone. Subsequent northward turning of the IMF-Bz, and the penetration of the dusk-to-dawn electric field over the dip equator is also discernible. Response of the low latitude ionosphere to this storm may be characterized in terms of (i) enhanced background level of VTEC as compared to the mean

  9. Low-latitude gravity wave variances in the mesosphere and lower thermosphere derived from SABER temperature observation and compared with model simulation of waves generated by deep tropical convection

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

    A portion of waves generated by deep convection have scales and amplitudes large enough to be detected by spaceborne 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 subtidal-scale fluctuations. Filtering was applied both vertically and horizontally to extract wave variances. We have analyzed the altitude region between 70 and 130 km and focus on the variances at equatorial latitudes for the altitude region between 70 and 120 km as a function of season, local time intervals, geographical location, and altitude. We find significant variances where convection is particularly prolific (Intertropical Convergence Zone) 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. Standard deviations of a few tens of kelvins are found. We have also performed simulations of the response to deep tropical convection with a time-dependent, high-resolution fully compressible dynamical model. Our simulations give wave amplitudes that agree reasonably well with the observed amplitudes and show layering that is consistent with the observations. Our main finding is that significant variations seen in TIMED/SABER temperature data have a convective wave source and are concentrated in layers where thermal ducts occur.

  10. E-region radar echoes from low-latitude field aligned irregularities due to gravity waves and tides: A case study using radar, lidar and radiosonde observations and simulations

    NASA Astrophysics Data System (ADS)

    Sundararajan, Sridharan; M, Sandhya

    On the night of 5 February 2011, the height-time plot of echo from E-region field aligned irregularities (FAI) received by the Indian MST radar at Gadanki (13.5(°) N, 79.2(°) E) shows a slow descending layered structures separated by nearly 8 km in the height region 80-100 km and vertically elongated structures with quasi-periodic (QP) variations at higher heights. The stratospheric thermal structure also shows similar slowly descending structures with nearly 8 km separation. Hodograph of 7-9 km band-pass filtered radiosonde zonal and meridional winds over Gadanki form clearly an ellipse and the dominant period obtained from the ratio of major to minor axes of the ellipse is nearly 24 h indicating the presence of a non-migrating diurnal tide with vertical wavelength 8 km. The two-dimensional spectrum of temperature perturbations, which are assumed to be due to gravity waves, shows dominant periods near 1 h and 1.5 h. The spectrum of FAI echo also shows similar dominant periods. Altitude-time cross section of vertical ion velocity is computed using winds comprising of observed gravity wave and tidal parameters. As the diurnal tide over Tirunelveli (8.7(°) N, 77.8(°) E) shows weaker amplitudes above 90 km, the removal of tidal contribution clearly reveals the observed FAI echo structure of vertically slanting plasma blob structures at higher heights and slowly descending continuous structures separated by 8 km at lower heights. The present study clearly demonstrates the role of tides and gravity waves in the formation of descending echo structures and quasi-periodic echoes respectively.

  11. E region radar echoes from low-latitude field-aligned irregularities due to gravity waves and tides: A case study using radar, lidar, and radiosonde observations and simulations

    NASA Astrophysics Data System (ADS)

    Sridharan, S.; Sandhya, M.

    2014-04-01

    On the night of 5 February 2011, the height-time plot of echo from E region field-aligned irregularities (FAI) received by the Indian mesosphere-stratosphere-troposphere radar at Gadanki (13.5°N, 79.2°E) shows a slow-descending layered structures separated by nearly 8 km in the height region 80-100 km and vertically elongated structures with quasiperiodic variations at higher heights. The stratospheric thermal structure also shows similar slowly descending structures with nearly 8 km separation. Hodograph of 7-9 km band-pass filtered radiosonde zonal and meridional winds over Gadanki form clearly an ellipse, and the dominant period obtained from the ratio of major to minor axes of the ellipse is nearly 24 h indicating the presence of a nonmigrating diurnal tide with vertical wavelength of 8 km. The two-dimensional spectrum of temperature perturbations, which are assumed to be due to gravity waves, shows dominant periods near 1 h and 1.5 h. The spectrum of FAI echo also shows similar dominant periods. Altitude-time cross section of vertical ion velocity is computed using winds composed of observed gravity wave and tidal parameters. As the diurnal tide over Tirunelveli (8.7°N, 77.8°E) shows weaker amplitudes above 90 km, the removal of tidal contribution clearly reveals the observed FAI echo structure of vertically slanting plasma blob structures at higher heights and slowly descending continuous structures separated by 8 km at lower heights. The present study clearly demonstrates the role of tides and gravity waves in the formation of descending echo structures and quasiperiodic echoes respectively.

  12. The Low-latitude Ionospheric Sensor Network (LISN)

    NASA Astrophysics Data System (ADS)

    Valladares, Cesar

    This paper describes the characteristics and illustrates the early measurements of the first distributed observatory that is being installed in the South American region to study the lowlatitude ionosphere and upper atmosphere. The LISN distributed observatory will be comprised of nearly 70 GPS receivers with the capability to measure Total Electron Content (TEC), amplitude and phase scintillation and Traveling Ionospheric Disturbances (TIDs). The network will include 5 ionosondes able to measure nighttime E-region densities and 5 collocated magnetometers that will be placed along the same magnetic meridian. This network of GPS receivers and ionospheric sensors span from north to south in the South American continent and west of the 55o West meridian. They will complement each other to provide new, time continuous and spatially extended observations of the background ionosphere, its motion and the embedded structures over this large dynamic region. The LISN network is being complemented with a physics-based data-inversion that incorporates a ionosphere model and a field-line-integrated electric field model to provide a consistent representation of the ionospheric electron density, conductivities, E×B plasma drifts, and neutral winds. This new distributed observatory will bring the opportunity to understand the day-to-day variability and the stability of the lowlatitude ionosphere and to make forecasts on a regional basis. This paper describes the instrumentation, presents the first measurements and discusses the scientific benefits of the LISN network.

  13. Magnetic field maxima in the low latitude boundary layer

    NASA Technical Reports Server (NTRS)

    Sonnerup, B.; Paschmann, G.; Phan, T.-D.; Luehr, H.

    1992-01-01

    The magnetic field often exhibits a maximum in the earth's low-latitude boundary layer. Examples of this behavior are shown using data from the AMPTE/IRM spacecraft, and it is argued that two fundamentally distinct causes exist for the excess field: (1) a depression, within the layer, of the population of medium-energy ions of magnetospheric origin and (2) field curvature effects associated with undulations of the magnetopause itself.

  14. 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.

  15. Spatial analyses on seismo-ionospheric precursors observed by GIM TEC and DEMETER during the 2008 M8.0 Wenchuan earthquake

    NASA Astrophysics Data System (ADS)

    Liu, Jann-Yenq; Chen, Yuh-Ing; Huang, Ching-Chi; Parrot, Michel; Pulinets, Sergey; Ouzounov, Dimitar

    2015-04-01

    This paper examines seismo-ionospheric precursors (SIPs) in the total electron content (TEC) of the global ionosphere map (GIM) and observations in the French satellite DEMETER (Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions) during the 12 May 2008 M8.0 Wenchuan earthquake. The temporal and spatial analyses on the GIM TEC are used to search SIPs of the Wenchuan earthquake. Meanwhile, both daytime and nighttime electron density (Ne), electron temperature (Te), ion density (Ni) and ion temperature (Ti) probed by DEMETER are investigated. A statistical analysis of the box-and-whisker method is utilized to see if the four DEMETER data sets 1-6 days before and after the earthquake are significantly different. The analysis is employed to investigate the epicenter and three reference areas along the same magnetic latitude discriminating the SIPs from global effects. Results show that the nighttime Ne and Ni (daytime Ti) over the epicenter significantly decrease (increase) 1-6 days before the earthquake. The intersections of the global distribution of the significant differences (or anomalous changes) in the nighttime Ne, the nighttime Ni, and the daytime Ti 1-6 days before and after the earthquake specifically appear over the epicenter. The spatial analyses confirm that SIPs of GIM TEC and DEMETER observations appearing 2-6 days before are related to the 2008 M8.0 Wenchuan earthquake.

  16. 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

  17. Using GPS-SCINDA observations to study the correlation between scintillation, total electron content enhancement and depletions over the Kenyan region

    NASA Astrophysics Data System (ADS)

    Olwendo, J. O.; Cilliers, P. J.; Baki, P.; Mito, C.

    2012-05-01

    This paper presents the first results of total electron content (TEC) depletions and enhancement associated with ionospheric irregularities in the low latitude region over Kenya. At the low latitude ionosphere the diurnal behavior of scintillation is driven by the formation of large scale equatorial depletions which are formed by post-sunset plasma instabilities via the Rayleigh-Taylor instability near the magnetic equator. Data from the GPS scintillation receiver (GPS-SCINDA) located at the University of Nairobi (36.8°E, 1.27°S) for March 2011 was used in this study. The TEC depletions have been detected from satellite passes along the line of sight of the signal and the detected depletions have good correspondence with the occurrence of scintillation patches. TEC enhancement has been observed and is not correlated with increases in S4 index and consecutive enhancements and depletions in TEC have also been observed which results into scintillation patches related to TEC depletions. The TEC depletions have been interpreted as plasma irregularities and inhomogeneities in the F region caused by plasma instabilities, while TEC enhancement have been interpreted as the manifestation of plasma density enhancements mainly associated with the equatorial ionization anomaly crest over this region. Occurrence of scintillation does happen at and around the ionization anomaly crest over Kenyan region. The presence of high ambient electron densities and large electron density gradients associated with small scale irregularities in the ionization anomaly regions have been linked to the occurrence of scintillation.

  18. Modelling of ionospheric Medium Scale Travelling Disturbances and a comparison with simultaneous ground-based TEC measurements and DEMETER plasma observations at 650 kilometres

    NASA Astrophysics Data System (ADS)

    Onishi, Tatsuo; Wang, Xiaoni; Berthelier, Jean-Jacques

    2010-05-01

    Medium-scale Travelling Ionospheric Disturbances (MSTIDs) are quasi periodic ionospheric disturbances with typical periods of 15 to 60 minutes and wavelengths of several hundreds of kilometers. They are triggered by Atmospheric Gravity Waves (AGWs) mostly generated at high latitudes. Simultaneous measurements of the Total Electron Content (TEC) by the US dense GPS receiver network and of the thermal ions by the CNES DEMETER micro-satellite at 650 km altitude have provided several examples of MSTID and shown typical variations of the ion density and velocity component parallel to the Earth's magnetic field during these events. A quantitative interpretation of such ionospheric disturbances has been undertaken by means of the SAMI2 ionospheric model. A representative pattern of an Atmospheric Gravity with a wave velocity toward the equator was developed to infer the variations of the neutral density and of the meridional component of the neutral velocity. These variations are introduced in the model and directly couples with the ionospheric plasma in the collisional region of the ionosphere. At higher altitudes, when the neutral atmosphere is too faint to have a direct effect on the ions, the resulting plasma disturbance propagates along the magnetic field lines. The computed variations of the plasma parameters along the orbit of DEMETER and of the TEC are analyzed for various parameters of the Atmospheric Gravity Wave. They are compared to the GPS-TEC and DEMETER observations in order to retrieve the AGW characteristics and study the propagation mechanism of the ionospheric plasma disturbance.

  19. 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.

  20. LION: A dynamic computer model for the low-latitude ionosphere

    NASA Astrophysics Data System (ADS)

    Bittencourt, J. A.; Pillat, V. G.; Fagundes, P. R.; Sahai, Y.; Pimenta, A. A.

    2007-11-01

    A realistic fully time-dependent computer model, denominated LION (Low-latitude Ionospheric) model, that simulates the dynamic behavior of the low-latitude ionosphere is presented. The time evolution and spatial distribution of the ionospheric particle densities and velocities are computed by numerically solving the time-dependent, coupled, nonlinear system of continuity and momentum equations for the ions O+, O2+, NO+, N2+ and N+, taking into account photoionization of the atmospheric species by the solar extreme ultraviolet radiation, chemical and ionic production and loss reactions, and plasma transport processes, including the ionospheric effects of thermospheric neutral winds, plasma diffusion and electromagnetic E×B plasma drifts. The Earth's magnetic field is represented by a tilted centered magnetic dipole. This set of coupled nonlinear equations is solved along a given magnetic field line in a Lagrangian frame of reference moving vertically, in the magnetic meridian plane, with the electromagnetic E×B plasma drift velocity. The spatial and time distribution of the thermospheric neutral wind velocities and the pattern of the electromagnetic drifts are taken as known quantities, given through specified analytical or empirical models. The model simulation results are presented in the form of computer-generated color maps and reproduce the typical ionization distribution and time evolution normally observed in the low-latitude ionosphere, including details of the equatorial Appleton anomaly dynamics. The specific effects on the ionosphere due to changes in the thermospheric neutral winds and the electromagnetic plasma drifts can be investigated using different wind and drift models, including the important longitudinal effects associated with magnetic declination dependence and latitudinal separation between geographic and geomagnetic equators. The model runs in a normal personal computer (PC) and generates color maps illustrating the typical behavior of the

  1. 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.

  2. 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

  3. 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.

  4. Large ionospheric TEC depletion induced by the 2016 North Korea rocket

    NASA Astrophysics Data System (ADS)

    Choi, Byung-Kyu; Kil, Hyosub

    2017-01-01

    A rocket called Kwangmyongsong-4 was launched from North Korea at 00:30 UT on February 7, 2016. We investigated ionospheric total electron content (TEC) depletions induced by the rocket using the Global Navigation Satellite System (GNSS) stations in South Korea. A sudden depletion in TEC variations appeared ∼6 min after the rocket launch. The drops in slant TEC exceeded 17 TEC unit (TECU) and those in vertical TEC were approximately 7 TECU. It is remarkable that the TEC drop by the 2016 Kwangmyongsong-4 rocket is larger (almost by three times) than that by the 2012 Unha-3 rocket. There are the differences of the background TEC values at the 2012 and the 2016 cases. These results suggest that the difference of the background electron density affects the magnitude of TEC depletion. The horizonal velocity of the rocket was 1.6 km/s, which was estimated from horizontal distances with an initial time of TEC disturbances. However, the 2012 Unha-3 rocket (∼2.5 km/s) moved faster horizontally than the 2016 Kwangmyongsong-4 rocket. Furthermore, when the rocket moved from high latitudes to low latitudes, TEC disturbances reduced gradually, and then, the depletion persisted for a longer time at the west side (the right side of southern direction).

  5. Velocity fields in a low-latitude coronal hole - Results from the Solar Maximum Mission

    NASA Technical Reports Server (NTRS)

    Mullan, D. J.; Waldron, W. L.

    1987-01-01

    The Solar Maximum Mission (SMM) satellite has been used to observe Doppler signatures in C IV in a low-latitude coronal hole as it crossed the central meridian (1985 February 2-8). Scatter plots of C IV emission intensity versus velocity do not show the pronounced positive correlation which has been reported in other regions on the sun. These data suggest that the coronal hole may control the gross velocity field in the solar atmosphere at the level where C IV is formed. Some localized regions of upflow coincide with EUV bright points in the coronal hole.

  6. 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.

  7. 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.

  8. 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

  9. 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.

  10. Analysis of the atmospheric upward radiation in low latitude area

    NASA Astrophysics Data System (ADS)

    Li, Haiying; Wu, Zhensen; Lin, Leke; Lu, Changsheng

    2016-10-01

    Remote sensing using THz wave has irreplaceable advantage comparing to the microwave and the infrared waves, and study on the THz remote sensing become more and more popular in recent years. The major applications of the remote sensing in THz wavelengths are the retrieval of the atmospheric parameters and the microphysical information of the ice cloud. The remote sensing of the atmosphere is based on the radiation of THz wave along the earth-space path of which the most significant part is the upward radiation of the atmosphere. The upward radiation of the atmosphere in sunny day in the low latitude area is computed and analyzed in this paper. The absorption of THz wave by the atmosphere is calculated using the formulations illustrated in the Recommendation ITU-R P.676 to save machine hour, the frequency range is then restricted below 1THz. The frequencies used for the retrieval of atmospheric parameters such as temperature and water content are usually a few hundred GHz, at the lower end of THz wavelengths, so this frequency range is sufficient. The radiation contribution of every atmospheric layer for typical frequencies such as absorption window frequencies and peak frequencies are analyzed. Results show that at frequencies which absorption is severe, information about lower atmosphere cannot reach the receiver onboard a satellite or other high platforms due to the strong absorption along the path.

  11. Mathematical modeling of plasma drifts over equatorial low latitude regions

    NASA Astrophysics Data System (ADS)

    Sundaresan, S.; Nageswara Rao, B.

    2010-09-01

    This paper presents a mathematical model to simulate ionospheric plasma drifts at equatorial low latitude regions by coupling of E- and F-regions. The governing non-linear differential equations (of elliptic and parabolic nature) are solved numerically through finite-difference schemes and obtained neutral winds and electric fields. The temperature and electron density profiles are generated utilizing MSIS-86 atmospheric model. The continuity equation is employed to obtain night-time E-region density profile using measured ionograms at Trivandrum (India). The computed vertical and zonal plasma drifts are comparable with measured Jacamarca plasma drifts with little variations during noon and evening times. The plasma drifts at Trivandrum (8.5° N, 76.5° E, dip 0.5° N) are compared with those of Jicamarca (12° S, 76.9° W, dip 2° N). Neutral wind simulations of present model agree well with those of horizontal wind model (HWM-93). The post-sunset enhancement and its reversal are also discussed.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. Signatures of Self-Organized Criticality in Low-Latitude Magnetosphere

    NASA Astrophysics Data System (ADS)

    Wanliss, J.; Uritsky, V.

    2007-05-01

    In a series of previous publications (see e.g. Consolini, 1997; Uritsky and Pudovkin, 1998; Uritsky et al., 2002, 2006; Lui et al., 2000; Chapman and Watkins, 2001) it has been shown that spatiotemporal activity in high-latitude magnetosphere exhibits signatures of self-organized criticality (SOC) - a robust multiscale stochastic regime observed in driven nonlinear systems with many couple degrees of freedom. This regime has been identified by a set of mutually consistent scaling laws describing dynamical and statistical properties of magnetospheric substorms. Here, we report the existence of SOC in the dynamics of SYM-H index, whish is a marker of space storms and other types of low-latitude geomagnetic disturbances. The ensemble average dynamics of activity bursts in the SYM-H index are scale-free and are characterized by spreading critical scaling exponents whose values are consistent with the shape of the scaling of burst sizes versus bust lifetimes. The probability distributions for the lifetime and the size of the SYM-H bursts show robust power laws which are essentially independent of the lower activity threshold used to detect the bursts, and they extend over many orders of magnitude. The avalanche distribution exponents are also in agreement with theoretical predictions for SOC systems. All of these results, together with previous studies (Wanliss and Weygand, [2007]), begin to paint a coherent picture of critical state in the inner magnetosphere possibly associated with SOC dynamics of the ring current and other constituents of low-latitude activity.

  17. 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

  18. 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

  19. 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.

  20. Role of Geomagnetic Disturbances on VLF Whistler Wave Activity at Low Latitudes (P32)

    NASA Astrophysics Data System (ADS)

    Patel, R. P.; Singh, S.; Singh, A. K.; Singh, R. P.

    2006-11-01

    rppatel123@rediffmail.com The disturbances on solar surfaces lead to the enhanced injection of energetic charged particles in to the inner magnetosphere, which modifies the electrodynamic features of ionosphere and magnetosphere. The electrodynamic properties control the generation and propagation characteristics of VLF waves. At Varanasi station, which is one of the low latitude stations in India, we have recorded VLF waves from 1992 onwards. The source of VLF wave is natural lightning discharges. Whistler activity varies with latitude having maximum around 500 geomagnetic latitude. The occurrence rate is low at low latitudes and also depends on the solar and geomagnetic conditions. In this paper, we report the results derived from the statistical analysis of whistler waves recorded at Varanasi during the period January 1990 December 1999. The monthly occurrence rate is obtained which shows maximum during January to March. Seasonal variation of the occurrence rate is also studied. In order to study the role of geomagnetic disturbances on the occurrence rate, we have used Kp index and its variation. It is observed that the occurrence probability monotonically increases with ∑Kp values. It is observed that when ∑Kp > 10, the occurrence rate is greater than the average value. This tendency is found to be in good agreement with those reported by other workers. In addition, we also present the probability of observation of whistler waves during the weak/intense geomagnetic storm. Detailed result of occurrence of whistler waves during the main phase and recovery phase of geomagnetic storms will also be presented. An attempt will be made to present explanation of these statistical results.

  1. Linear theory of the Kelvin-Helmholtz instability in the low-latitude boundary layer

    NASA Technical Reports Server (NTRS)

    Rajaram, R.; Sibeck, D. G.; Mcentire, R. W.

    1991-01-01

    The feasibility is examined of establishing characteristic profiles across the magnetospheric low-latitude boundary layer for the Kelvin-Helmholtz mode so that these profiles can be compared with satellite observations or a latitudinal chain of ground stations. An anisotropic collisionless fluid model is used instead of conventional MHD, and the finite thickness of the boundary layer and the thickness and position of the current layer are taken into account. The instability is found to be enhanced by a decrease in the thickness of the shear layer and of the current layer and by the proximity of the 'current layer' to the outer edge of the shear layer. The velocity threshold for the onset of instability is insensitive to the thickness. Characteristic profiles of the variation of plasma and field parameters across the boundary are obtained, and the importance of parameters specifying the current layer position and thickness is demonstrated.

  2. Simulation of PPEF effects in dayside low-latitude ionosphere for the October 30, 2003, Superstorm

    NASA Astrophysics Data System (ADS)

    Verkhoglyadova, Olga P.; Tsurutani, Bruce T.; Mannucci, Anthony J.; Saito, Akinori; Araki, Tohru; Anderson, David; Abdu, M.; Sobral, J. H. A.

    One of the important signatures during strong magnetic storms is prompt penetrating electric fields (PPEFs) into the ionosphere, which causes the dayside ionospheric superfountain (DIS). Interplanetary-ionosphere coupling for the October 30, 2003, superstorm is analyzed by using ACE and ground-based measurements. The relationships between the interplanetary magnetic field Bz component, ionospheric vertical velocities above Jicamarca, and horizontal magnetic field components measured at Huancayo are presented. DIS is associated with uplift, displacement, and enhancement of the equatorial ionospheric anomalies. We apply an extended SAMI-2 ionospheric model to simulate DIS effects above Jicamarca for this superstorm. An agreement between our results and observed ƒ0F2 during the main phase of the storm is reported. It is shown that the PPEF approach and corresponding modeling results capture the main physics of the dayside low-latitude ionospheric response during the first couple hours of the magnetic superstorm.

  3. 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.

  4. Ionosphere/thermosphere dynamics as deduced from meridional ionosonde chain at low latitudes

    NASA Astrophysics Data System (ADS)

    Maruyama, Takashi; Uemoto, Junpei; Tsugawa, Takuya; Hidekatsu, Jin; Kubota, Minoru; Saito, Susumu

    Multipoint ionosonde observation was conducted to study ionosphere/thermosphere dynamics in Southeast Asia. For this study, data from three ionosonde stations aligned at 100° E were analyzed. Two of them are near the magnetic conjugate points in Northern Thailand and West Sumatra, Indonesia, and the other is near the magnetic equator in the Malay Peninsula; these are three of five SEALION (Southeast Asia low latitude ionospheric network) ionosonde stations. The F-layer critical frequency (foF2), the propagation factor (M3000F2), and the F-layer virtual height (h'F) were scaled from quarter hourly ionograms at the three stations. The ionospheric height is closely related to the thermospheric dynamics (neutral drags) as well as electromagnetic forces (EXB drifts) and chemical processes (productions and losses). Because h'F strongly depends on the chemical process during daytime, it is better to examine the peak height (hmF2) for the discussion of dynamics. hmF2 was determined from M3000F2 using the modified Shimazaki's formula. The peak height obtained by this method is less accurate near the magnetic equator because the electron density vertical profile around the peak is greatly distorted from the parabolic distribution and the formation of an additional layer (sometimes called the F3 layer). The peak heights at the low-latitude conjugate points were compared for the whole day. The height difference between the two stations is a good indicator of the transequatorial neutral wind as the equatorward wind lifts the ionosphere up, while the poleward wind lowers it. The diurnal variation of the transequatorial wind inferred from the height differences is examined for various seasons. We found that there exists a strong terdiurnal component, which was most significant around the March equinox. Also the results were compared with the HWM model wind. The terdiurnal amplitude inferred in this study was larger than the model wind and the phases of the diurnal variation

  5. Regional GPS TEC modeling; Attempted spatial and temporal extrapolation of TEC using neural networks

    NASA Astrophysics Data System (ADS)

    Habarulema, John Bosco; McKinnell, Lee-Anne; Opperman, Ben D. L.

    2011-04-01

    In this paper, the potential extrapolation capabilities and limitations of artificial neural networks (ANNs) are investigated. This is primarily done by generating total electron content (TEC) predictions using the regional southern Africa total electron content prediction (SATECP) model based on the Global Positioning System (GPS) data and ANNs with the aid of multiple inputs intended to enable the software to learn and correlate the relationship between their variations and the target parameter, TEC. TEC values are predicted over regions that were not covered in the model's development, although it is difficult to validate their accuracy in some cases. The SATECP model is also used to forecast hourly TEC variability 1 year ahead in order to assess the forecasting capability of ANNs in generalizing TEC patterns. The developed SATECP model has also been independently validated by ionosonde data and TEC values derived from the adapted University of New Brunswick Ionospheric Mapping Technique (UNB-IMT) over southern Africa. From the comparison of prediction results with actual GPS data, it is observed that ANNs extrapolate relatively well during quiet periods while the accuracy is low during geomagnetically disturbed conditions. However, ANNs correctly identify both positive and negative storm effects observed in GPS TEC data analyzed within the input space.

  6. Analysis of low latitude Noctilucent Cloud occurrences using satellite data and modeling

    NASA Astrophysics Data System (ADS)

    Russell, J. M.; Rong, P.; Hervig, M. E.; Bailey, S. M.; Gumbel, J.; Lambert, A.

    2012-12-01

    Numerous NLC sightings have occurred in recent years at latitudes as low as ~ 40N in the skies over Chicago, Illinois, Boulder, Colorado, Omaha, Nebraska, Logan, Utah, Seattle, Washington, Calar Alto, Spain and Paris, France. While no confirming evidence has come forth thus far, such sightings raise the natural question about whether there are systematic NLC increases occurring at these low latitudes. This question is investigated using observations of temperature made by the SABER instrument on the TIMED satellite over the 2002 to 2011 time period, a 7-year water vapor climatology developed from data collected by the MLS instrument on the Aura satellite for 2005 to 2011, and Polar Mesospheric Cloud (PMC) measurements made by the OSIRIS instrument on the Odin satellite for the 2002 to 2011 period. These data are used in conjunction with a 0-D thermodynamic equilibrium model [Hervig et al., 2009] that assumes mesospheric ice is in equilibrium with available water vapor. The 0-D model has proven to be effective in reproducing variations of the observed ice mass density, ice layer centroid height [Russell et al., 2010], and daily PMC occurrence frequency on intra-seasonal scales. Inter-annual and decadal scale variations in the northern PMC season are examined in this paper. All analyses were performed on the 0.00464 hPa surface or ~ 84 km, which is the northern hemisphere mean cloud height. Both MLS 0-D and OSIRIS measured PMCs agree well with the SABER 0-D results for 2005 to 2011. Results show a statistically significant upward trend in the number of 0-D derived PMCs per season in the latitude range 40-55N for 2002 - 201l. The long-term increases in cloud number are accompanied by temperature decreases over the same time period. Analysis of temperature and cloud number anomaly data indicates that the low latitude cloud number changes are driven by temperature. Solar cycle effects have not yet been considered in this analysis.

  7. A high-altitude balloon experiment to probe stratospheric electric fields from low latitudes

    NASA Astrophysics Data System (ADS)

    Gurubaran, Subramanian; Shanmugam, Manu; Jawahar, Kaliappan; Emperumal, Kaliappan; Mahavarkar, Prasanna; Buduru, Suneel Kumar

    2017-02-01

    The Earth's electrical environment hosts a giant electrical circuit, often referred to as the global electric circuit (GEC), linking the various sources of electrical generators located in the lower atmosphere, the ionosphere and the magnetosphere. The middle atmosphere (stratosphere and mesosphere) has been traditionally believed to be passively transmitting electric fields generated elsewhere. Some observations have reported anomalously large electric fields at these altitudes, and the scientific community has had to revisit the earlier hypothesis time and again. At stratospheric altitudes and especially at low latitudes, horizontal electric fields are believed to be of ionospheric origin. Though measurements of these fields from a balloon platform are challenging because of their small magnitudes (around a few mV m-1), a suitably designed long-duration balloon experiment capable of detecting such small fields can provide useful information on the time evolution of ionospheric electric fields, which is otherwise possible only using radar or satellite in situ measurements. We present herein details of one such experiment, BEENS (Balloon Experiment on the Electrodynamics of Near Space), carried out from a low-latitude site in India. The instrument package for this experiment is comprised of four deployable booms for measurements of horizontal electric fields and one inclined boom for vertical electric field measurements, all equipped with conducting spheres at the tip. The experiment was conducted from Hyderabad (17.5° N, 78.6° E) during the post-midnight hours on 14 December 2013. In spite of a few shortcomings we report herein, a noticeable feature of the observations has been the detection of horizontal electric fields of ˜ 5 mV m-1 at the stratospheric altitudes of ˜ 35 km.

  8. Latitudinal GRBR-TEC estimation in Southeast Asia region based on the two-station method

    NASA Astrophysics Data System (ADS)

    Watthanasangmechai, Kornyanat; Yamamoto, Mamoru; Saito, Akinori; Tsugawa, Takuya; Yokoyama, Tatsuhiro; Supnithi, Pornchai; Yatini, Clara Yono

    2014-10-01

    Total electron content (TEC) is an important parameter for revealing latitudinal ionospheric structures, such as the equatorial ionization anomaly (EIA) in Southeast Asia. Understanding the EIA is beneficial for studying equatorial spread F. To reveal the structures, the absolute TEC as a function of latitude must be accurately determined. In early 2012, we expanded a GNU Radio Beacon Receiver (GRBR) network to provide latitudinal coverage in the Thailand-Indonesia sector. We employed the GRBR network to receive VHF and UHF signals from polar low-Earth-orbit satellites. The TEC offset is an unknown parameter in the absolute TEC estimation process. We propose a new technique based on the two-station method to estimate the offset for the latitudinal TEC estimation, and it works better than the original method for a sparse network. The TEC estimation system requires two iterations to minimize the root-mean-square error (RMSE). Once the RMSE reaches the global minimum, the absolute TECs are estimated simultaneously over five GRBR stations. GPS-TECs from local stations are used as the initial guess of the offset estimation. The height of the ionospheric pierce point is determined from the ionosonde hmF2. As a result, the latitudinal GRBR-TEC was successfully estimated from the polar orbit satellites. The two EIA humps were clearly captured by the GRBR-TEC. The result was well verified with the TEC reconstructed from the C/NOFS density data and the ionosonde bottomside data. This is a significant step showing that the GRBR is a useful tool for the study of low-latitude ionospheric features.

  9. Is high obliquity a still plausible explanation for Neoproterozoic low-latitude glaciations ?

    NASA Astrophysics Data System (ADS)

    Levrard, B.; Laskar, J.

    2003-04-01

    The observations of enigmatic low-latitude glaciogenic sequences during the Sturtian (˜ 750-700 Ma) and the Varanger (˜ 620-570 Ma) glacial intervals of the Neopropterozo& uml;i c era remain the subject of controversial debates concerning possible scenarii. Of the many models that have been proposed to account for theses paradoxical features, the high-obliquity scenario invoked by G.E. Williams (1975) appears to be still largely considered. However, a such scenario requires a dissipative mechanism to bring back the Earth's obliquity from a value higher than 55o to the present value (˜ 23.5o) in less than 200 Ma. Williams (1993) suggested that core-mantle friction could have explained this substantial decrease. However, it was demonstrated by Néron de Surgy and Laskar (1997) and confirmed by Pais et al. (1999) that, not only it requires abnormal values of effective viscosity, but due to the conservation of the angular momentum, it is also largely conflicting with the paleorotation data. D.M Williams et al. (Nature, 1998) recently proposed that ``climate friction" could have produced this decrease in less than 100 Ma between ˜ 600 Ma and 500 Ma. We have revisited in details this mecanism (Levrard and Laskar, submitted to Geo. J. Int., 2002) for the Neoproterozoic glaciations. In response to periodic variations in the obliquity, the redistribution of ice/water mass and the isostatic adjusment to the surface loading affect the dynamical ellipticity of the Earth. Delayed responses in the mass redistribution may introduce a secular term in the obliquity evolution (Bills, 1994; Rubincam, 1995; Ito et al, 1995). We analyze the obliquity-oblateness feedback using non-linear response of ice sheets (Imbrie and Imbrie, 1980) to insolation forcing and layered models with Maxwell visco-elastic rheology. Possible increase in the non-linear response of ice sheets to insolation forcing and latitudinal changes in this forcing strongly limit the contribution of the obliquity

  10. 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.

  11. 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

  12. A simplified indexing of F-region geophysical noise at low latitudes

    NASA Technical Reports Server (NTRS)

    Aggarwal, S.; Lakshmi, D. R.; Reddy, B. M.

    1979-01-01

    A simple method of deriving an F-region index that can warn the prediction users at low latitudes as to the specific months when they have to be more careful in using the long term predictions is described.

  13. 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.

  14. 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.

  15. 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.

  16. A Semi-Empirical Low-Latitude Ionospheric Model

    DTIC Science & Technology

    1988-10-06

    the atmosphere, P., a value of marca incoherent scatter radar observations reported 5.5 x 10- s ’ represents solar cycle maximum con- by Fejer et al...bottomside components of the overall profiles with N(h) = N ex [c -:. - e)] good results. It was decided, therefore, to define a (h- h...) "generalized" or

  17. Statistical Evaluation of Forecasts Over the Low-Latitudes.

    DTIC Science & Technology

    1985-08-01

    o o .x 1. Introduction .. . ........ .. .- 2. The Models . . . . . . . . . . . ... ... 4 2.1 Filtered barotropic modelo . ....... ... 4 2.1.1...and Dynamic Meteorology. John Wiley and Sons, Inc., 477 pp . Hebert, P.J., 1980: Atlantic hurricane season of 1979. Mon. Wea. Rev., 108, 973-990. Julian...for the special observing periods. NOAA Data Report ERL GFDL-6, 237 pp . Mathur, M.B., 1970: A note on an improved quasi-Lagrangian advective scheme

  18. 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.

  19. 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

  20. Statistical Study of Low Latitude Pc3 Geomagnetic Pulsations: Diurnal and Seasonal Characteristics

    NASA Astrophysics Data System (ADS)

    Ansari, I. A.

    2006-05-01

    Using an array of four low latitude induction coil magnetometers, geomagnetic pulsations in the Pc3 period range were recorded simultaneously in southeast Australia. The data recording stations were situated at Woomera, Broken Hill, Newcastle and Launceston over a latitudinal range of 100 and a longitudinal range of 170 at L=1.8 to 2.7. Geomagnetic data for a period of about six months were digitized and analysis was carried out employing digital sonagram technique. The Pc3 occurrence was found to be evenly distributed with magnetic activity over the Kp = 2 - 5 range. Launceston, however, showed lower occurrences at low Kp values (Kp <2+) than the other three stations. The Pc3 occurrence probability normalized with respect to Kp occurrence was maximum for Kp = 4+ at all the four stations. It is also worth noting that Pc3 in winter was observed during intense magnetic activity when 5 < Kp <9. Finally, a gradual increase in the Pc3 average, lower and upper frequencies limit with Kp was observed during the local winter months for Kp <5. Key words - Pc3 geomagnetic pulsations, digital sonagram, diurnal variation of Pc3 occurrence, seasonal variation of Pc3 occurrence, Kp dependence.

  1. 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.

  2. Day-to-day changes in ionospheric electron content at low latitudes

    NASA Astrophysics Data System (ADS)

    Dabas, R. S.; Bhuyan, P. K.; Tyagi, T. R.; Bhardwaj, R. K.; Lal, J. B.

    1984-06-01

    For a number of years, the ionospheric electron content (IEC) over the Indian subcontinent has been determined on the basis of the Faraday rotation of satellite radio beacon transmissions. In these determinations, use was made of the orbiting satellites BE-B and BE-C, and, for a limited period, of the geostationary satellite ATS 6. A large variability in day-to-day values of IEC was reported, and it was tried to correlate this phenomenon with magnetic activity, solar flux, or the effect of neutral winds. Tyagi (1978) observed that the day-to-day changes in IEC occur in the form of single day abnormality, and alternate day abnormality. Long-term fluctuations were found with a periodicity of about 45 days. The present investigation is concerned with a more detailed study of the observed variations. An analysis is conducted of IEC data recorded during the low phase of the solar cycle, taking into account data from six low-latitude stations covering a latitude range from approximately 15.0 deg N to 30.0 deg N.

  3. Assessment of Modeling Capability for Reproducing Storm Impacts on TEC

    NASA Astrophysics Data System (ADS)

    Shim, J. S.; Kuznetsova, M. M.; Rastaetter, L.; Bilitza, D.; Codrescu, M.; Coster, A. J.; Emery, B. A.; Foerster, M.; Foster, B.; Fuller-Rowell, T. J.; Huba, J. D.; Goncharenko, L. P.; Mannucci, A. J.; Namgaladze, A. A.; Pi, X.; Prokhorov, B. E.; Ridley, A. J.; Scherliess, L.; Schunk, R. W.; Sojka, J. J.; Zhu, L.

    2014-12-01

    During geomagnetic storm, the energy transfer from solar wind to magnetosphere-ionosphere system adversely affects the communication and navigation systems. Quantifying storm impacts on TEC (Total Electron Content) and assessment of modeling capability of reproducing storm impacts on TEC are of importance to specifying and forecasting space weather. In order to quantify storm impacts on TEC, we considered several parameters: TEC changes compared to quiet time (the day before storm), TEC difference between 24-hour intervals, and maximum increase/decrease during the storm. We investigated the spatial and temporal variations of the parameters during the 2006 AGU storm event (14-15 Dec. 2006) using ground-based GPS TEC measurements in the selected 5 degree eight longitude sectors. The latitudinal variations were also studied in two longitude sectors among the eight sectors where data coverage is relatively better. We obtained modeled TEC from various ionosphere/thermosphere (IT) models. The parameters from the models were compared with each other and with the observed values. We quantified performance of the models in reproducing the TEC variations during the storm using 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.

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

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

    The paper investigates the O(+) ion and NO(+) ion temperature and temperature anisotropy for a spatially homogeneous auroral F region in the presence of large electric fields perpendicular to the geomagnetic field. The maximum optical emissions at midlatitudes 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 source of the particles is inferred to be the ring current, with precipitation occurring when the Dst index is large at the time of the large short-term excursions in the local magnetic field. This result is consistent with the finding 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 Dst and the exponential of Kp than with either alone. It is shown that the product of Dst 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 Kp.

  5. TEC variation during high and low solar activities over South American sector

    NASA Astrophysics Data System (ADS)

    Jonah, O. F.; de Paula, E. R.; Muella, M. T. A. H.; Dutra, S. L. G.; Kherani, E. A.; Negreti, P. M. S.; Otsuka, Y.

    2015-12-01

    Using dual frequency GPS receivers in the South American sector, the measurement of absolute ionospheric Total Electron Content (TEC) has been estimated applying the Nagoya ionospheric model for both the years of 2009 and 2001, which represent low and high solar activities, respectively. The diurnal, day-to-day, monthly, seasonal, latitudinal and longitudinal variations of TEC were studied for equatorial and low latitude regions of South America. The strength and characteristics of the Equatorial Ionization Anomaly (EIA) were equally analyzed. The analyses reveal the diurnal, seasonal and semidiurnal TEC variation, as well as the nighttime variability during the low and high solar activities. Wavelet power spectra analysis was employed to check the periodicities of the TEC data, F10.7 and zonal and meridional wind velocities measured by Meteor radar at ∼100 km altitude. Periods such as 27, 16, 8-10, 1-5 days were found to be dominant in the zonal and meridional wind velocity corresponding with those of TEC periodicities. Hence, besides the solar radiation, we suggest that there are contributions of tides and planetary waves in spatial and temporal TEC enhancement and variations during the geomagnetic quiet periods of both solar activities.

  6. 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.

  7. 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.

    2016-06-01

    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 s 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.

  8. Modeling storm-time electrodynamics of the low-latitude ionosphere thermosphere system: Can long lasting disturbance electric fields be accounted for?

    NASA Astrophysics Data System (ADS)

    Maruyama, Naomi; Sazykin, Stanislav; Spiro, Robert W.; Anderson, David; Anghel, Adela; Wolf, Richard A.; Toffoletto, Frank R.; Fuller-Rowell, Timothy J.; Codrescu, Mihail V.; Richmond, Arthur D.; Millward, George H.

    2007-07-01

    Storm-time ionospheric disturbance electric fields are studied for two large geomagnetic storms, March 31, 2001 and April 17 18, 2002, by comparing low-latitude observations of ionospheric plasma drifts with results from numerical simulations based on a combination of first-principles models. The simulation machinery combines the Rice convection model (RCM), used to calculate inner magnetospheric electric fields, and the coupled thermosphere ionosphere plasmasphere electrodynamics (CTIPe) model, driven, in part, by RCM-computed electric fields. Comparison of model results with measured or estimated low-latitude vertical drift velocities (zonal electric fields) shows that the coupled model is capable of reproducing measurements under a variety of conditions. In particular, our model results suggest, from theoretical grounds, a possibility of long-lasting penetration of magnetospheric electric fields to low latitudes during prolonged periods of enhanced convection associated with southward-directed interplanetary magnetic field, although the model probably overestimates the magnitude and duration of such penetration during extremely disturbed conditions. During periods of moderate disturbance, we found surprisingly good overall agreement between model predictions and data, with penetration electric fields accounting for early main phase changes and oscillations in low-latitude vertical drift, while the disturbance dynamo mechanism becomes increasingly important later in the modeled events. Discrepancies between the model results and the observations indicate some of the difficulties in validating these combined numerical models, and the limitations of the available experimental data.

  9. Attenuation of lightning-produced sferics in the Earth-ionosphere waveguide and low-latitude ionosphere

    NASA Astrophysics Data System (ADS)

    Burkholder, Brian S.; Hutchins, Michael L.; McCarthy, Michael P.; Pfaff, Robert F.; Holzworth, Robert H.

    2013-06-01

    We compare radio atmospherics (sferics) detected by the World Wide Lightning Location Network (WWLLN) to very low frequency (VLF) whistler waves observed in the low-latitude ionosphere by the Vector Electric Field Instrument of the Communications/Navigation Outage Forecasting System (C/NOFS) satellite. We also model the propagation of these sferics through the Earth-ionosphere waveguide to the subsatellite point using the Long-Wavelength Propagation Capability software and compare this result to the same C/NOFS data set. This unprecedentedly expansive data set allows comparison to theory and prior observation of VLF radio wave propagation in the Earth-ionosphere waveguide and low-latitude ionosphere. We show that WWLLN and C/NOFS observe the well-known effect of variable attenuation with direction within the Earth-ionosphere waveguide. Propagation within the ionosphere is also examined, and a lack of attenuation above 400 km is observed. Finally, in comparison to recent works using Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions (DEMETER) data by Fiser et al. and Chum et al., we find that C/NOFS successfully detects whistlers with comparable amplitudes at much greater distances, compared to those reported for DEMETER.

  10. 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.

  11. 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.

  12. 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.

  13. Some evidence of ground power enhancements at frequencies of global magnetospheric modes at low latitude

    NASA Astrophysics Data System (ADS)

    Francia, P.; Villante, U.

    1997-01-01

    A statistical analysis of the power spectra of the geomagnetic field components H and D for periods ranging between 3 min and 1 h was conducted at a low-latitude observatory (LÁquila, L=1.6) at the minimum and maximum of the solar cycle. For both components, during daytime intervals, we found evidence of power enhancements at frequencies predicted for global modes of the Earthś magnetosphere and occasionally observed at auroral latitudes in the F-region drift velocities (approximately at 1.3, 1.9, 2.6, and 3.4 mHz). Nighttime observations reveal a relative low frequency H enhancement associated with the bay occurrence together with a peak in the H/D power ratio which sharply emerges at 1.2 mHz in the premidnight sector. The strong similarity between solar minimum and maximum suggests that these modes can be considered permanent magnetospheric features. A separate analysis on a two-month interval shows that the observed spectral characteristics are amplified by conditions of high-velocity solar wind. Acknowledgements. The authors are grateful to Prof. D. J. Southwood (Imperial College, London), J. C. Samson (University of Alberta, Edmonton), L. J. Lanzerotti (AT&T Bell Laboratories), A. Wolfe (New York City Technical College) and to Dr. M. Vellante (University of LÁquila) for helpful discussions. They also thank Dr. A. Meloni (Istituto Nazionale di Geofisica, Roma) who made available geomagnetic field observations from LÁquila Geomagnetic Observatory. This research activity at LÁquila is supported by MURST (40% and 60% contracts) and by GIFCO/CNR. Topical Editor K.-H. Glaßmeier thanks C. Waters and S. Fujita for their help in evaluating this paper.->

  14. Responses of the low-latitude ionosphere to very intense geomagnetic storms

    NASA Astrophysics Data System (ADS)

    Sobral, J. H. A.; Abdu, M. A.; Yamashita, C. S.; Gonzalez, W. D.; de Gonzalez, A. C.; Batista, I. S.; Zamlutti, C. J.; Tsurutani, B. T.

    2001-01-01

    In this work, we investigate the ionospheric responses to exceptionally high-intensity and long-duration magnetic storms over Brazil. Disturbed ionospheric F-region vertical drifts and peak electron density changes observed at the equatorial station Fortaleza - Fz (/3°55'S /38°25'W /dip-3.5°) and the low-latitude station Cachoeira Paulista - CP /(22°41'S /45°00'W dip24°S), for three magnetospheric storm events that occurred in December 1980, April 1981 and September 1982, are analyzed. These storms had minimum Dst indexes /-240,-311 and /-289nT, respectively. The interplanetary magnetic field (Bz) data from the ISEE-3 satellite, the auroral activity index AE, and the ring current index Dst are used as indicators of the magnetospheric conditions. The ionospheric response features are analyzed using the F-layer critical parameters h'F, hpF2 and foF2, from ionograms obtained at Fz and CP. The Bz and the AE index variations were much higher than those in many previous studies. Therefore, many of the observations reported here either have not been observed or are not readily explained by current models for predicting the penetration//dynamo disturbance electric fields. The altitude of the nocturnal ionospheric F-layer at low latitudes may undergo significant variations during storm-time, caused by magnitude variations on the local zonal component of the F-region electric field intensity. During the period studied here, clear association of the F-layer rise (vertical velocity and altitude) and spread-F occurrence is observed. It is shown that the storm-time layer rise has a dominant role on the equatorial spread-F. An attempt is made to identify the origin of electric fields responsible for the disturbed F-layer alterations. The main conclusions of this study are that (a) some effects on the F-layer height and peak electron concentrations are consistent with model predictions. Some others are in discrepancy or have not been either predicted by model studies or

  15. 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.

  16. 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.

  17. Characteristics of low-latitude whistlers and their relation with f0F2 and magnetic activity

    SciTech Connect

    Bao, Z.; Wang, T.; Xu, J.; Chen, S.; Liang, B.

    1982-01-01

    Characteristics of low-latitude whistlers observed with instrumentation at three locations in China over a three-year period are discussed. The whistler maxima were always detected after midnight, local time, and none occurred during the daytime or evening. The rate of occurrence at the three sites was less than 1/min. A similarity was found between the diurnal variation of the median value of the critical frequency of the F2 region and that of the whistler dispersion. A set of algebraic equations was employed to calculate the electron concentration in the equatorial plane at the top of the propagation path (Neq) and the tube content (NT). The whistler dispersion and f0F2 (the critical frequency) were then converted into Neq and NT, resulting in calculated median values which agreed with satellite observations. Finally, a positive correlation was obtained between the daily variation of Kp and whistler dispersion, supporting the hypothesis that the whistler occurrence rate at low latitudes peaks one or two days after a geomagnetic storm day.

  18. Source Region Identification for Low Latitude Whistlers (L=1.08)

    NASA Astrophysics Data System (ADS)

    Gokani, S. A.; Singh, R.; Maurya, A. K.; Bhaskara, V.; Cohen, M.; Kumar, S.; Lichtenberger, J.

    2014-12-01

    Though whistlers are known and studied from past one century, the scientific community still strives to understand the generation and propagation mechanism of whistlers in very low latitude region. One of the solutions comes from locating the causative lightning discharges and source region of low latitude whistlers. In the present study, ~ 2000 whistlers recorded during period of one year (Dec, 2010 to Jan, 2011) at Allahabad (Geomag. lat. 16.79o N; L=1.08), India are correlated with lightning activity detected by World Wide Lightning Location Network (WWLLN) at and around conjugate region. About 63% of whistlers are correlated with the lightning strikes around conjugate region. Further to confirm this correlation, arrival azimuths of causative sferics are determined and the obtained azimuths points towards conjugate region of Allahabad. The characteristics of thunder cloud generating these whistlers are examined and found that the clouds with South-East alignment are more prone to trigger whistler waves. The seasonal and diurnal variation of whistler parameters such as occurrence rate, power spectral density and dispersion are also studied and explained on the basis of ionospheric conditions in low latitudes. The results obtained open a new window to look for the propagation mechanism of low latitude whistlers.

  19. Distinct responses of the low-latitude ionosphere to CME and HSSWS: The role of the IMF Bz oscillation frequency

    NASA Astrophysics Data System (ADS)

    Rodríguez-Zuluaga, J.; Radicella, S. M.; Nava, B.; Amory-Mazaudier, C.; Mora-Páez, H.; Alazo-Cuartas, K.

    2016-11-01

    In this work an attempt to identify the role of the interplanetary magnetic field (IMF) in the response of the ionosphere to different solar phenomena is presented. For this purpose, the day-to-day variability of the equatorial ionospheric anomaly (EIA) and the main ionospheric disturbances are analyzed during one coronal mass ejection (CME) and two high-speed solar wind streams (HSSWSs). The EIA parameters considered are the zonal electric field and both the strength and position of its northern crest. The disturbances being the prompt penetration of magnetospheric electric field (PPMEF) and disturbance dynamo electric field (DDEF) are studied using the magnetic response of their equivalent current systems. In accordance, ground-based Global Navigation Satellite Systems receivers and magnetometers at geomagnetic low latitudes in the American sector are used. During both phenomena, patterns of PPMEF related to fluctuations of the IMF are observed. Diurnal and semidiurnal magnetic oscillations are found to be likely related to DDEF. Comparisons among the EIA parameters and the DDEF magnetic response exhibit poor relation during the CME in contrast to good relation during the HSSWSs. It is concluded that the response of the low-latitude ionosphere to solar phenomena is largely determined through the oscillation frequency of the IMF Bz by affecting the generation of the PPMEF and DDEF differently. This is seen as an effect of how the energy from the solar wind is transferred into the magnetosphere-ionosphere system.

  20. IRI-vTEC versus GPS-vTEC for Nigerian SCINDA GPS stations

    NASA Astrophysics Data System (ADS)

    Okoh, Daniel; McKinnell, Lee-Anne; Cilliers, Pierre; Okere, Bonaventure; Okonkwo, Chinelo; Rabiu, Babatunde

    2015-04-01

    Following the recent proliferation of dual-frequency GPS (Global Positioning System) receiver systems across the African continent, there is a growing number of papers that compare vertical Total Electron Content (vTEC) values derived from the International Reference Ionosphere (IRI) model with those obtained from the GPS receiver measurements. In this work we report an investigation of IRI-vTEC versus GPS-vTEC comparisons for three Nigerian SCINDAGPS stations (Nsukka, Ilorin, and Lagos) for which data are available in the year 2012, and present a further review of the differences/similarities observed between them. Since a major interest in this work is to use the GPS measurements to improve the predictions of the IRI model for the region, we present a detailed regression analysis of differences between the two sources in a manner that will benefit this application.

  1. Causative mechanisms for the occurrence of a triple layered mesospheric inversion event over low latitudes

    NASA Astrophysics Data System (ADS)

    Ramesh, K.; Sridharan, S.; Vijaya Bhaskara Rao, S.

    2014-05-01

    The temperature profile obtained from the space borne instrument "Sounding of Atmosphere by Broadband Emission Radiometry" instrument onboard "Thermosphere Ionosphere Mesosphere Energetics and Dynamics" shows a triple layered mesospheric inversion event on the night of 23 September 2011, when there is an overpass near the low-latitude sites Gadanki (13.5°N, 79.2°E) and Tirunelveli (8.7°N, 77.8°E). The three mesospheric inversion layers (MILs) are formed in the height region around ~70 (lower), ~80 (middle), and ~90 km (upper) with amplitudes ~11, ~44, and ~109 K and thickness of 3.4, 4.9, and 6.6 km, respectively. The formation of the lower and middle MILs can only be observed in the Rayleigh lidar temperature profiles over Gadanki due to upper height limitation of the system. Nearly all the dominant causative mechanisms are examined for the occurrence of the MIL event. The lower MIL at ~70 km is inferred to be due to planetary wave dissipation, as there is a sudden decrease of planetary wave activity above 70 km. Further, it is demonstrated that the middle MIL at ~80 km is due to the turbulence generated by gravity wave breaking which is in turn due to gravity wave-semi-diurnal tidal interaction, though the height of the middle MIL descends at the rate of ~1 km/h, which is nearly the vertical phase speed of diurnal tide, whereas the upper MIL at above 90 km is due to the large chemical heating rate (~45 K/day) generated by the dominant exothermic reaction O + O + M → O2 + M.

  2. Post-Storm Middle and Low-Latitude Ionospheric Electric Fields Effects

    NASA Astrophysics Data System (ADS)

    Fejer, B. G.; Blanc, M.; Richmond, A. D.

    2017-03-01

    The Earth's upper atmosphere and ionosphere undergoes large and complex perturbations during and after geomagnetic storms. Thermospheric winds driven by enhanced energy and momentum due to geomagnetic activity generate large disturbance electric fields, plasma drifts and currents with a broad range of temporal and spatial scales from high to equatorial latitudes. This disturbance dynamo mechanism plays a fundamental role on the response of the middle and low-latitude ionosphere to geomagnetic activity. In this review, we initially describe the early evidence for the importance of this process and the first simulation study which already was able to explain its main effects on the electrodynamics of the middle and low-latitude ionosphere. We then describe the results of more recent simulations and the extensive experimental work that highlights the importance of this mechanism for ionospheric space weather studies extending to post-storms periods, and present some suggestions for future studies.

  3. Post-Storm Middle and Low-Latitude Ionospheric Electric Fields Effects

    NASA Astrophysics Data System (ADS)

    Fejer, B. G.; Blanc, M.; Richmond, A. D.

    2016-12-01

    The Earth's upper atmosphere and ionosphere undergoes large and complex perturbations during and after geomagnetic storms. Thermospheric winds driven by enhanced energy and momentum due to geomagnetic activity generate large disturbance electric fields, plasma drifts and currents with a broad range of temporal and spatial scales from high to equatorial latitudes. This disturbance dynamo mechanism plays a fundamental role on the response of the middle and low-latitude ionosphere to geomagnetic activity. In this review, we initially describe the early evidence for the importance of this process and the first simulation study which already was able to explain its main effects on the electrodynamics of the middle and low-latitude ionosphere. We then describe the results of more recent simulations and the extensive experimental work that highlights the importance of this mechanism for ionospheric space weather studies extending to post-storms periods, and present some suggestions for future studies.

  4. 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

  5. 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.

  6. Induction effects of geomagnetic disturbances in the geo-electric field variations at low latitudes

    NASA Astrophysics Data System (ADS)

    Doumbia, Vafi; Boka, Kouadio; Kouassi, Nguessan; Didier Franck Grodji, Oswald; Amory-Mazaudier, Christine; Menvielle, Michel

    2017-01-01

    In this study we examined the influences of geomagnetic activity on the Earth surface electric field variations at low latitudes. During the International Equatorial Electrojet Year (IEEY) various experiments were performed along 5° W in West Africa from 1992 to 1995. Among other instruments, 10 stations equipped with magnetometers and telluric electric field lines operated along a meridian chain across the geomagnetic dip equator from November 1992 to December 1994. In the present work, the induced effects of space-weather-related geomagnetic disturbances in the equatorial electrojet (EEJ) influence area in West Africa were examined. For that purpose, variations in the north-south (Ex) and east-west (Ey) components of telluric electric field were analyzed, along with that of the three components (H, D and Z) of the geomagnetic field during the geomagnetic storm of 17 February 1993 and the solar flare observed on 4 April 1993. The most important induction effects during these events are associated with brisk impulses like storm sudden commencement (ssc) and solar flare effect (sfe) in the geomagnetic field variations. For the moderate geomagnetic storm that occurred on 17 February 1993, with a minimum Dst index of -110 nT, the geo-electric field responses to the impulse around 11:00 LT at LAM are Ex = 520 mV km-1 and Ey = 400 mV km-1. The geo-electric field responses to the sfe that occurred around 14:30 LT on 4 April 1993 are clearly observed at different stations as well. At LAM the crest-to-crest amplitude of the geo-electric field components associated with the sfe are Ex = 550 mV km-1 and Ey = 340 mV km-1. Note that the sfe impact on the geo-electric field variations decreases with the increasing distance of the stations from the subsolar point, which is located at about 5.13° N on 4 April. This trend does not reflect the sfe increasing amplitude near the dip equator due the high Cowling conductivity in the EEJ belt.

  7. New historical records and relationships among 14C production rates, abundance and color of low latitude auroras and sunspot abundance

    NASA Astrophysics Data System (ADS)

    Abbott, Dallas; Juhl, Robert

    2016-12-01

    Incursions of high-energy particles from space, specifically solar energetic particles and galactic cosmic rays, have significant effects on the Earth, including disruption of the Earth's magnetic field, generation of electric fields strong enough to damage electronic devices as well as the production of auroras at low-latitudes, within 45° of the magnetic equator. We examine the relationships among 14C production, auroral abundance, auroral color and sunspot abundance using existing data supplemented by a new dataset. The new dataset, based on Chinese and Korean records from A.D. 1100-1700, includes 46 new or revised records of sunspots and 279 records of low-latitude auroras. Low-latitude auroras are predominantly red (66%, 835 events) with lesser proportions of white (20%, 253 events) and black auroras (6%, 67 events). All other auroral colors (green, yellow, multicolored, blue and purple) aggregate to a total of 100 events (8%). Overall, white auroras are more frequent during times of higher 14C production. We use two empirical methods of evaluating the flux of high-energy particles: modeled peaks and lows in 14C production and peaks and lows in the 14C calibration curve. We find that comparison to modeled 14C production gives significant results. White auroras are significantly more abundant (98% probability) at times of high production of 14C. Red auroras are somewhat more abundant (88% probability) at times of low production of 14C. The abundances of black, multicolored, green, yellow, and blue auroras between times of low and high 14C production are not significantly different. Violet/purple auroras are significantly more abundant (98% probability) at times of low 14C production. The positive correlation of violet/purple auroras with times of low14C production rate and the lack of correlation of blue auroras with times of high14C production is surprising, for this portion of the visible spectrum contains strong emission lines and some lines with high

  8. 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.

  9. Contributions of the low-latitude boundary layer to the finite width magnetotail convection model

    NASA Technical Reports Server (NTRS)

    Spence, H. E.; Kivelson, M. G.

    1993-01-01

    Convection of plasma within the terrestrial nightside plasma sheet contributes to the structure and, possibly, the dynamical evolution of the magnetotail. In order to characterize the steady state convection process, we have extended the finite tail width model of magnetotail plasma sheet convection. The model assumes uniform plasma sources and accounts for both the duskward gradient/curvature drift and the earthward E x B drift of ions in a two-dimensional magnetic geometry. During periods of slow convection (i.e., when the cross-tail electric potential energy is small relative to the source plasma's thermal energy), there is a significant net duskward displacement of the pressure-bearing ions. The electrons are assumed to be cold, and we argue that this assumption is appropriate for plasma sheet parameters. We generalize solutions previously obtained along the midnight meridian to describe the variation of the plasma pressure and number density across the width of the tail. For a uniform deep-tail source of particles, the plasma pressure and number density are unrealistically low along the near-tail dawn flank. We therefore add a secondary source of plasma originating from the dawnside low-latitude boundary layer (LLBL). The dual plasma sources contribute to the plasma pressure and number density throughout the magnetic equatorial plane. Model results indicate that the LLBL may be a significant source of near-tail central plasma sheet plasma during periods of weak convection. The model predicts a cross-tail pressure gradient from dawn to dusk in the near magnetotail. We suggest that the plasma pressure gradient is balanced in part by an oppositely directed magnetic pressure gradient for which there is observational evidence. Finally, the pressure to number density ratio is used to define the plasma 'temperature.' We stress that such quantities as temperature and polytropic index must be interpreted with care as they lose their nominal physical significance in

  10. Variability of Ionospheric TEC and the Performance of the IRI-2012 Model at the BJFS Station, China

    NASA Astrophysics Data System (ADS)

    Li, Shuhui; Li, Lihua; Peng, Junhuan

    2016-10-01

    We studied variation characteristics of ionospheric total electron contents (TEC) and performance of the International Reference Ionosphere (IRI)-2012 model in predicting TEC at the BJFS (Beijing Fangshan station), China. Diurnal and seasonal variations were analyzed with TEC data derived from dual-frequency global positioning system (GPS) observations along with the solar activity dependence of TEC at the BJFS station. Data interpolated with information from IGS Global Ionosphere Maps (GIMs) were also used in the analysis. Results showed that the IRI-2012 model can reflect the climatic characteristics and solar activity dependence of ionospheric TEC. By using time series decomposition method, ionospheric daily averaged TEC values were divided into the periodic components, geomagnetic activity component, solar activity component and secular trend. Solar activity component and periodic components are supposed to be the main reasons which account for the difference between the GIMs TEC and the TEC from the IRI-2012 model.

  11. 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.

  12. TEC enhancement immediately before M9 mega-thrust earthquakes

    NASA Astrophysics Data System (ADS)

    Heki, Kosuke

    2012-07-01

    Earthquakes are often preceded by electromagnetic precursors, e.g. electric currents in the ground and propagation anomalies of radio waves. By monitoring the differences of the L1 and L2 carrier phases from GPS satellites, we can infer ionospheric Total Electron Content (TEC). Here I report that positive anomalies of ionospheric TEC appeared immediately before the 2011 Tohoku-Oki (Mw9.0), 2010 Chile (Maule) (Mw8.8), 2007 Bengkulu (Mw8.6), and 2004 Sumatra-Andaman (Mw9.2) earthquakes. Coseismic vertical movements of the surface excite acoustic and internal gravity waves, causing coseismic ionospheric disturbances (CID), and GPS-TEC data showed that they occurred about ten minutes after these earthquakes. In addition to them, positive TEC anomalies were found to start 60-40 minutes before these earthquakes above the focal regions, and to last until the onsets of CID. In the Tohoku-Oki case, the anomaly was reached about one tenth of the background TEC immediately before the earthquake. TEC enhancements often occur irrespective of earthquakes, for example, sudden increase of TEC due to solar flares and large-scale traveling ionospheric disturbances (LSTID) propagating from the auroral oval to mid-latitude regions. These disturbances can be distinguished by carefully observing their spatial extents and movements. Geomagnetic activities were relatively high in the 2004 Sumatra-Andaman and 2011 Tohoku-Oki events, but were low in the 2007 Bengkulu and 2010 Chile events. For the Tohoku-Oki and the Bengkulu earthquakes, we analyzed the TEC time series of the same satellite and receiver pair over 120 days before and after the earthquakes, and confirmed that the precursory anomalies of the earthquakes were the largest in these periods. We also investigated three M8 class earthquakes, the 1994 Hokkaido-Toho-Oki (Mw8.3), 2006 Kuril (Mw8.2), and the 2003 Tokachi-Oki (Mw8.0) earthquakes. However, only weak precursory TEC anomalies were seen in the 1994 event, and not in the 2003

  13. 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.

  14. A robust TEC depletion detector algorithm for satellite based navigation in Indian zone and depletion analysis for GAGAN

    NASA Astrophysics Data System (ADS)

    Dashora, Nirvikar

    2012-07-01

    Equatorial plasma bubble (EPB) and associated plasma irregularities are known to cause severe scintillation for the satellite signals and produce range errors, which eventually result either in loss of lock of the signal or in random fluctuation in TEC, respectively, affecting precise positioning and navigation solutions. The EPBs manifest as sudden reduction in line of sight TEC, which are more often called TEC depletions, and are spread over thousands of km in meridional direction and a few hundred km in zonal direction. They change shape and size while drifting from one longitude to another in nighttime ionosphere. For a satellite based navigation system, like GAGAN in India that depends upon (i) multiple satellites (i.e. GPS) (ii) multiple ground reference stations and (iii) a near real time data processing, such EPBs are of grave concern. A TEC model generally provides a near real-time grid based ionospheric vertical errors (GIVEs) over hypothetically spread 5x5 degree latitude-longitude grid points. But, on night when a TEC depletion occurs in a given longitude sector, it is almost impossible for any system to give a forecast of GIVEs. If loss-of-lock events occur due to scintillation, there is no way to improve the situation. But, when large and random depletions in TEC occur with scintillations and without loss-of-lock, it affects low latitude TEC in two ways. (a) Multiple satellites show depleted TEC which may be very different from model-TEC values and hence the GIVE would be incorrect over various grid points (ii) the user may be affected by depletions which are not sampled by reference stations and hence interpolated GIVE within one square would be grossly erroneous. The most general solution (and the far most difficult as well) is having advance knowledge of spatio-temporal occurrence and precise magnitude of such depletions. While forecasting TEC depletions in spatio-temporal domain are a scientific challenge (as we show below), operational systems

  15. 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.

  16. High and Low Latitude types of the Downstream Influences of the North Atlantic Oscillation

    NASA Astrophysics Data System (ADS)

    Song, J.

    2013-12-01

    Using reanalysis data, we find that the downstream-propagating quasi-stationary Rossby wave train associated with the North Atlantic Oscillation (NAO) generally propagates along a high (low)-latitude pathway during warm (cold) El Niño-Southern Oscillation (ENSO) boreal winters. Consistent with the different propagation directions of the NAO-related downstream wave train, during the warm (cold) ENSO winters, the NAO is associated with significant 300 hPa geopotential height anomalies over eastern Siberia (the Arabian Sea, the east coast of Asia at around 40N, and the North Pacific), and the near-surface air temperature (SAT) perturbations associated with the NAO over the high latitudes of Asia are relatively strong (weak). Based on these differences, we argue that the NAO has two distinct types of downstream influence: a high-latitude type and a low-latitude type. Furthermore, we argue that the two types of NAO's downstream influence are modulated by the intensity of the subtropical potential vorticity (PV) meridional gradient over Africa. When this gradient is weak (strong), as in the warm (cold) ENSO winters, the NAO's downstream influence tends to be of the high (low)-latitude type. These results are further supported by analysis of intraseasonal NAO events. We separate NAO events into two categories in terms of the intensity of the subtropical PV gradient over Africa. Composites of the NAO events accompanied by a weak (strong) subtropical PV gradient show that the NAO-related downstream wave train tends to propagate along a high (low)-latitude pathway. Fig. 1 Regressed monthly anomalous meridional wind at 300 hPa (V 300hPa, thin contours, interval is 1 m/s) onto the monthly NAO index and the corresponding stationary wave activity fluxes (vectors, unit is m2s-2) during a) the warm ENSO winters and b) cold ENSO winters. Solid (dashed) contours represent positive (negative) values and the zero contours are omitted. The regressed results at the 95% confidence level

  17. Some studies of zonal and meridional wind characteristics at low latitude Indian stations

    NASA Technical Reports Server (NTRS)

    Nagpal, O. P.; Kumar, S.

    1985-01-01

    At the beginning of the Indian Middle Atmosphere Programme (IMAP), it was decided that the preparation of consolidation reports of already available parameters for the middle atmosphere would be useful. Atmospheric wind data obtained by rockets and balloons constituted one such parameter which had to be consolidated. The present paper summaries the results of this consolidation study. Both zonal and meridional components of winds at four low latitude Indian stations namely Thumba, Shar, Hyderabad, and Balasore, have been analyzed to yield reference wind profiles for each month. The montly mean values have been used to bring out the amplitudes and phases of the annual, semiannual and quasi-biennial oscillations.

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

    PubMed

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

    2016-05-03

    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.

  19. 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.

  20. 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.

  1. 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.

  2. Detailed study of Pi2 damped oscillations from low latitude magnetic observatory

    NASA Astrophysics Data System (ADS)

    Bulusu, Jayashree; Arora, Kusumita; Nagarajan, Nandini

    2017-03-01

    The study of low latitude damped Pi2 oscillations (40-150 s) are investigated using archived data from Choutuppal (CPL), geomagnetic observatory, operated by CSIR-NGRI, Hyderabad, India. The period of investigation is during solar cycle 21 (1975-1983). All the Pi2 events identified during this period are subjected to detailed analysis for their association with substorm and non-substorm events. It is interesting to note that there is equal probability of occurrence of Pi2s with or without a substorm. The Pi2 frequencies associated with substorms showed an increased value in the post-midnight sector than compared to the Pre-midnight sectors. The non-substorm Pi2s are seen to be associated with lower levels of geomagnetic activity. The corresponding period of Pi2s decreases with increasing level of activity. While the generation of Pi2s are generally attributed to substorm onset, it is seen that the quiet time non-substorm events are related to plasmaspheric cavity mode resonances at low latitudes.

  3. 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

  4. Airborne pseudolite aiding BeiDou system to improve positioning precision in low latitude areas

    NASA Astrophysics Data System (ADS)

    Ma, Weihua; Yuan, Jianping; Luo, Jianjun

    2005-11-01

    The BeiDou System (BDS), which has three satellites in Geostationary Earth Orbit (GEO), is a regional satellite navigation system of China and its positioning performance is notorious in low latitude areas. The two mending plans using Airborne Pseudolite (APL) aiding BDS to improve navigation precision in such areas are put forward. Plan I uses three BDS satellites and one APS to supply navigation data and Plan II employs two BDS satellites, one APS and altimeter to work. Both of the plans adopt point positioning with code pseudo-range algorithm. Geometric Dilution of Precision (GDOP), which is calculated by Positioning Error Transfer Coefficient Matrix (PETCM), is used to evaluate the positioning performance of new plans. PETCM is predigested when user is in low latitude areas. The key elements of predigested PETCM that effect the Geometric Dilution of Precision (GDOP) are analyzed. The character of GDOP is forecasted easily with the predigested PETCM. The simulations show that the precision of plans are expected to be hundreds of meters except some region where the latitudes of user and APL are close to each other and Plan II is better than plan I. The phenomenal consists with the theoretical analysis.

  5. Where does the plasmasphere begin? Revisit to topside ionospheric profiles in comparison with plasmaspheric TEC from Jason-1

    NASA Astrophysics Data System (ADS)

    Lee, Han-Byul; Kim, Yong Ha; Kim, Eunsol; Hong, Junseok; Kwak, Young-Sil

    2016-10-01

    Topside ionospheric profiles have been measured by Alouette 1 and ISIS 1/2 in the periods of 1962-1972 and 1972-1979, respectively. The profiles cover from the orbital altitude of 1000 km to the F2 peak and show large variations over local time, latitude, and seasons. We here analyze these variations in comparison with plasmaspheric total electron contents (pTECs) that were measured by Jason-1 satellite from the altitude of 1336 km to 20,200 km (GPS orbit). The scale heights of the profiles are generally smaller in the daytime than nighttime but show large day-to-day variations, implying that the ionospheric profiles at 1000 km are changing dynamically, rather than being in diffusive equilibrium. We also derived transition heights between O+ and H+, which show a clear minimum at dawn for low-latitude profiles due to decreasing O+ density at night. To compare with pTEC, we compute topside ionospheric total electron content (tiTEC) by integrating over 800-1336 km using the slope of the profiles. The tiTEC varies in a clear diurnal pattern from 0.3 to 1 and 3 total electron content unit (TECU, 1 TECU = 1016 el m-2) for low and high solar activity, respectively, whereas Jason-1 pTEC values are distributed over 2-6 TECU and 4-8 TECU for low and high solar activity, respectively, with no apparent diurnal modulation. Latitudinal variations of tiTEC show distinctive hemispheric asymmetry while that of Jason-1 pTEC is closely symmetric about the magnetic equator. The local time and latitudinal variations of tiTEC basically resemble those of the ionosphere but are characteristically different from those of Jason-1 pTEC. Based on the difference between tiTEC and pTEC variations, we propose that the region above 1300 km should be considered as the plasmasphere. Lower altitudes for the base of "plasmaspheric TEC," as used in some studies, would cause contamination of ionospheric influence.

  6. 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.

  7. 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.

  8. E- and F- region incoherent scatter radar spectral measurements at mid and low-latitudes

    NASA Astrophysics Data System (ADS)

    Kudeki, Erhan; Milla, Marco

    2016-07-01

    In this talk we will contrast and compare incoherent scatter radar spectral measurements conducted using the Arecibo, ALTAIR, and Jicamarca incoherent scatter radars at ionospheric heights ranging from E-region into the topside F-region. Arecibo measurements from mid-latitudes exemplify high SNR ISR techniques utilized with large magnetic aspect angles. Low-latitude measurements at ALTAIR and Jicamarca make use of and combine large and small magnetic aspect angle techniques. Examples presented will include both natural and naturally enhanced electron and ion lines detected in the lower F region near the geomagnetic equator as well as the results of search for proton gyro-resonance peaks in the Jicamarca topside spectra.

  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. Thermospheric meridional wind at low latitude from measurements of F layer peak height

    NASA Astrophysics Data System (ADS)

    de Medeiros, R. T.; Abdu, M. A.; Batista, I. S.

    1997-07-01

    Thermospheric meridional winds are calculated in this paper for the low-latitude station, Cachoeira Paulista, in Brazil using ionospheric F layer peak height hmax as the primary database for different seasons and solar activity conditions. A servo model is used that expresses the ionospheric F layer peak height displacements as a function of chemical loss, diffusion, thermospheric meridional wind and vertical plasma drift. The method used is similar to, and an extension of, the one used in recent years for midlatitudes, where the effect of vertical plasma drift is considered negligible. We have included in our analysis the effect of vertical plasma drift on hmax over Cachoeira Paulista by using a vertical drift model which is a field line extension of an equatorial electric field model developed for our longitude, for which the radar data from Jicamarca, Peru, are complemented, in the sunset sector, by vertical drift from ionosonde data over Fortaleza. A numerical model on the electrodynamic coupling of the E and F regions is used to obtain the equatorial height dependence of the vertical drift needed for its field line mapping to low latitude. Meridional winds were calculated using the servo equations in which the vertical plasma drifts, and hmax values deduced from Cachoeira Paulista ionograms, were the main inputs. The magnetic meridional winds calculated for the summer equinoctial and winter months of high and low solar activity epochs are compared with the HWM-90 and with the measurements by Fabri-Perot technique available for Cachoeira Paulista. The results show varying agreements. The paper presents details of the method of analysis and the comparison of the results.

  11. A new method for estimation of TEC from GNSS receivers during multiple cycle slips and data loss due to ionospheric irregularities

    NASA Astrophysics Data System (ADS)

    Dashora, Nirvikar

    2012-07-01

    Estimation of total electron content (TEC) is a must to utilize the GNSS signal for ionospheric research. The estimation of absolute ionospheric TEC from raw GNSS data itself is a lengthy and complex task and requires knowledge of sophisticated computer programming skills, satellite orbital geometry and many other aspects like GNSS signal structure, satellite and receiver specific information etc. Not many software are available that automatize the complex task of cycle slip detection and correction. The estimation of satellite and receiver biases is one more step left before getting true TEC. In equatorial and low latitudes, where the nighttime ionospheric irregularities are oft-occurring phenomena, estimation of TEC becomes a challenge. This is because, during TEC depletions and scintillations, the loss of lock in the receiver results either in data loss or sharp gradients in the recorded delays; more often for phase than code. Raw data in form of accumulated phase in radians and total code-range in meters show random occurrences of multiple cycle slips and data loss of several minutes in the data file. Thus, such phase and code data has to be corrected first before processing it to obtain TEC. Almost all available software/algorithms suggest flagging such data for no further use. Hence, TEC cannot be estimated during multiple cycle slip events within few minutes from raw GPS data. But, for ionospheric research the time of occurrence, evolution and drift of depletions are very useful. This paper details a complete new software for pre-processing the raw RINEX (receiver independent exchange format) data and retrieval of TEC using code and carrier-phase measurements from an stand alone dual frequency GPS receiver. We use modified and new sets of algorithms a GNSS receiver. It is significant to note that we are able to retrieves almost all the the corrupted TEC data points due to random multiple cycle slip events which are oft-occurring phenomena during ESF in

  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. Study of TEC fluctuation via stochastic models and Bayesian inversion

    NASA Astrophysics Data System (ADS)

    Bires, A.; Roininen, L.; Damtie, B.; Nigussie, M.; Vanhamäki, H.

    2016-11-01

    We propose stochastic processes to be used to model the total electron content (TEC) observation. Based on this, we model the rate of change of TEC (ROT) variation during ionospheric quiet conditions with stationary processes. During ionospheric disturbed conditions, for example, when irregularity in ionospheric electron density distribution occurs, stationarity assumption over long time periods is no longer valid. In these cases, we make the parameter estimation for short time scales, during which we can assume stationarity. We show the relationship between the new method and commonly used TEC characterization parameters ROT and the ROT Index (ROTI). We construct our parametric model within the framework of Bayesian statistical inverse problems and hence give the solution as an a posteriori probability distribution. Bayesian framework allows us to model measurement errors systematically. Similarly, we mitigate variation of TEC due to factors which are not of ionospheric origin, like due to the motion of satellites relative to the receiver, by incorporating a priori knowledge in the Bayesian model. In practical computations, we draw the so-called maximum a posteriori estimates, which are our ROT and ROTI estimates, from the posterior distribution. Because the algorithm allows to estimate ROTI at each observation time, the estimator does not depend on the period of time for ROTI computation. We verify the method by analyzing TEC data recorded by GPS receiver located in Ethiopia (11.6°N, 37.4°E). The results indicate that the TEC fluctuations caused by the ionospheric irregularity can be effectively detected and quantified from the estimated ROT and ROTI values.

  15. Theoretical scaling laws for the spectrum of density irregularities in the high- and low-latitude ionosphere

    SciTech Connect

    Keskinen, M.J.

    1990-05-03

    Constraints on and scaling laws associated with the spectrum of density irregularities in the high and low latitude ionosphere are derived using conservation laws implied by the fundamental nonlinear plasma fluid equations describing low frequency, long wavelength ionospheric plasma dynamics and structure. For the high latitude case we discuss the spectrum implied by interchange-like plasma instabilities and apply our results to convecting ionospheric plasma enhancements, blobs, patches, and polar cap arcs. For the low latitude ionosphere, we derive scaling laws for the density spectrum associated with the Rayleigh-Taylor instability and make applications to equatorial spread-F. For both the high and low latitude cases, we distinguish the spectral behavior to be expected in both the lower and upper ionosphere.

  16. 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

  17. Middle- and low-latitude emissions from energetic neutral atom precipitation seen from ATLAS 1 under quiet magnetic conditions

    NASA Technical Reports Server (NTRS)

    Tinsley, B. A.; Rohrbaugh, R. P.; Ishimoto, M.; Torr, M. R.; Torr, D. G.

    1994-01-01

    During the ATLAS 1 mission spectral observations were made at middle and low latitudes of features expected from the precipitation of energetic neutral atoms. The Imaging Spectrometric Observatory was used at night in the UV and visible with maximum gain. The tangent ray heights of the look directions ranged from near 100 km to near 200 km, and the geomagnetic conditions were quiet during the observations, which were made March 28 to April 3, 1992. The N2(+) 1N 391.4-nm and O I 130.4 and 135.6-nm emissions were observed at all latitudes, with lower emission rates at lower magnetic dip latitudes, except that enhancements in the O I lines were seen within 30 deg of the dip equator to radiative recombination of ionospheric plasma. The latitude profile observed for the N2(+) 1N emission did not show an equatorial or midlatitude peak. This implies that the source of energetic neutrals is more consistent with prompt charge exchange loss of freshly injected trapped ions with relatively low mirror heights (i.e., ions on higher L shells with equatorial pitch angle distributions nearly isotropic to the loss cone) than loss of highly eroded populations of particles with high mirror heights (i.e., ions on lower L shells with pancake equatorial pitch angle distributions). The N2(+) 1N emission rates have been compared with models of atmospheric emission due to fluxes of O/O(+) and H/H(+) in the thermosphere, as produced by energetic neutral oxygen or hydrogen atom precipitation. Energy deposition rates are inferred.

  18. Difficulties in the study of cosmic radio noise absorption at 30 MHz using riometer at low latitude station, Kolhapur (Lat-16.8°N, Long-74.25°E)

    NASA Astrophysics Data System (ADS)

    Nikte, S. S.; Sharma, A. K.; Nade, D. P.; Rokade, M. V.; Ghodpage, R. N.; Patil, P. T.; Bhonsle, R. V.

    2014-01-01

    A dual dipole antenna has been installed at low latitude station Kolhapur (Geographic 16.8°N, 74.25°E), Maharashtra, India for the study of cosmic radio noise absorption using Solid State Riometer (which operates at 30 MHz) during pre phase of 24th solar maxima. The aim for this type of study over Kolhapur was to know the response of lower (D region) ionosphere over low latitude by cosmic radio noise absorption using riometer technique during quite period as well as sudden ionospheric disturbances (SID). The observations are being taken for 3 years. Two different sites (˜40 km away from each other) were used for the installation of riometer equipment assuming minimum local noise. It is found that solar noise to cosmic radio noise hence resulting in signal saturation. The night time signal is relatively free of interference but sometimes local noise is responsible for spike-like signatures. Hence it is concluded that Kolhapur (a low latitude station) is not suitable for the study of cosmic radio noise absorption on 30 MHz with riometer and dual dipole antenna. Proper choice for operating frequency of riometer and antenna gain is suggested for low latitude use of this technique for ionospheric deviative and nondeviative absorption studies.

  19. Long-term prediction of the Arctic ionospheric TEC based on time-varying periodograms.

    PubMed

    Liu, Jingbin; Chen, Ruizhi; Wang, Zemin; An, Jiachun; Hyyppä, Juha

    2014-01-01

    Knowledge of the polar ionospheric total electron content (TEC) and its future variations is of scientific and engineering relevance. In this study, a new method is developed to predict Arctic mean TEC on the scale of a solar cycle using previous data covering 14 years. The Arctic TEC is derived from global positioning system measurements using the spherical cap harmonic analysis mapping method. The study indicates that the variability of the Arctic TEC results in highly time-varying periodograms, which are utilized for prediction in the proposed method. The TEC time series is divided into two components of periodic oscillations and the average TEC. The newly developed method of TEC prediction is based on an extrapolation method that requires no input of physical observations of the time interval of prediction, and it is performed in both temporally backward and forward directions by summing the extrapolation of the two components. The backward prediction indicates that the Arctic TEC variability includes a 9 years period for the study duration, in addition to the well-established periods. The long-term prediction has an uncertainty of 4.8-5.6 TECU for different period sets.

  20. Characterizing quasi-periodic disturbances in GPS TEC data and their drivers

    NASA Astrophysics Data System (ADS)

    Wurtz, J.; Coster, A. J.; Goncharenko, L.; Zhang, S.

    2012-12-01

    We examine a large data set (2003-2009) of total electron content (TEC) values derived from a global network of differential GPS receivers that was downloaded from the Madrigal database. We report on TEC oscillations at multiple periods ranging from 5 to ~30 days. A significant portion of oscillations with 9-day and 13.5-day periods is driven by the recurrent geomagnetic activity, as evident from the analysis of geomagnetic indices. The TEC disturbances in response to the recurrent geomagnetic activity are stronger at middle and high latitudes, and are less pronounced at lower latitudes (< 30 degrees). We also observe a correlation between TEC and the 28-day lunar cycle that is more evident at lower (equatorial) latitudes in both northern and southern hemispheres. The TEC disturbances associated with the lunar cycle are well pronounced during the northern hemisphere winter and equinox seasons.

  1. The 630 nm MIG and the vertical neutral wind in the low latitude nighttime thermosphere

    NASA Technical Reports Server (NTRS)

    Herrero, F. A.; Meriwether, J. W., Jr.

    1994-01-01

    It is shown that large negative divergences (gradients) in the horizontal neutral wind in the equatorial thermosphere can support downward neutral winds in excess of 20 m/s. With attention to the meridional and vertical winds only, the pressure tendency equation is used to derive the expression U(sub z0) approximately equals (Partial derivative U(sub y)/Partial derivative y)H for the vertical wind U(sub z0) at the reference altitude for the pressure tendency equation; H is the atmospheric density scale height, and (Partial derivative U(sub y)/Partial derivative y) is the meridional wind gradient. The velocity gradient associated with the Meridional Intensity Gradient (MIG) of the O((sup 1)D) emission (630 nm) at low latitudes is used to estimate the vertical neutral wind in the MIG region. Velocity gradients derived from MIG data are about 0.5 (m/s)/km) or more, indicating that the MIG region may contain downward neutral winds in excess of 20 m/s. Though direct measurements of the vertical wind are scarce, Fabry-Perot interferometer data of the equatorial F-region above Natal, Brazil, showed downward winds of 30 m/s occurring during a strong meridional wind convergence in 1982. In-situ measurements with the WATS instrument on the DE-2 satellite also show large vertical neutral winds in the equatorial region.

  2. 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.

  3. Reassessment of the thermospheric response to geomagnetic activity at low latitudes

    NASA Astrophysics Data System (ADS)

    Berger, C.; Barlier, F.; Ill, M.

    1988-10-01

    The present study takes advantage of measurements made at low latitudes by the Cactus accelerometer. From such measurements, the response of several thermospheric parameters to geomagnetic activity can be simultaneously and reliably retrieved: total density, density scale height, vertical density scale height gradient, temperature, O/N2 ratio and mean molecular mass. Their behavior exhibits a diurnal variation, some features of which have not been described, especially in the case of strong geomagnetic storms; the night scale height response appears to be stronger than the day one, while its vertical gradients increase by day and slightly decrease at night. The temperature increase is higher by day while the O/N2 ratio decreases by day, and increases at night at constant pressure level as well as at fixed height. By day, significant vertical temperature gradients are also found. These results as well as others are analyzed in the light of existing theories and compared to the predictions of existing thermospheric models. Strong meridional winds at night, heat transport through thermal conductivity, as well as wave dissipation during the day, might be factors helping to account for such behavior.

  4. 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.

  5. Origin and magnitude of low latitude terrestrial precipitation and temperature anomalies during Heinrich events and deglaciation

    NASA Astrophysics Data System (ADS)

    Donders, T. H.; de Boer, H. J.; Finsinger, W.; Grimm, E. C.; Dekker, S. C.; Reichart, G. J.; Wagner-Cremer, F.

    2009-04-01

    Repetitive phases of increased pine at Lake Tulane, Florida have previously been related to strong stadials terminated by so-called Heinrich events. The climatic significance of these pine phases has been interpreted in different ways. Using a pollen-climate inference model, we quantified the climate changes and consistently found mean summer precipitation (PJJA) increases (0.5-0.9 mm/day) and mean November temperature increases (2.0-3.0∘C) that are coeval with Heinrich events and the Younger Dryas. Comparison with marine sea surface temperature records point to a potential source for these heat and moisture anomalies in the Gulf of Mexico or the western tropical Atlantic. A climate model sensitivity analysis indicates that a positive heat anomaly in the Gulf of Mexico and equatorial Atlantic best approximates the pollen-inferred climate reconstructions from Lake Tulane during the Heinrich events and Younger Dryas. We explain the low latitude warming by an increased Loop Current facilitated by the persistence of the Atlantic Warm Pool during summer.

  6. Characteristics of Low-latitude Coronal Holes near the Maximum of Solar Cycle 24

    NASA Astrophysics Data System (ADS)

    Hofmeister, Stefan J.; Veronig, Astrid; Reiss, Martin A.; Temmer, Manuela; Vennerstrom, Susanne; Vršnak, Bojan; Heber, Bernd

    2017-02-01

    We investigate the statistics of 288 low-latitude coronal holes extracted from SDO/AIA-193 filtergrams over the time range of 2011 January 01–2013 December 31. We analyze the distribution of characteristic coronal hole properties, such as the areas, mean AIA-193 intensities, and mean magnetic field densities, the local distribution of the SDO/AIA-193 intensity and the magnetic field within the coronal holes, and the distribution of magnetic flux tubes in coronal holes. We find that the mean magnetic field density of all coronal holes under study is 3.0 ± 1.6 G, and the percentaged unbalanced magnetic flux is 49 ± 16%. The mean magnetic field density, the mean unsigned magnetic field density, and the percentaged unbalanced magnetic flux of coronal holes depend strongly pairwise on each other, with correlation coefficients cc > 0.92. Furthermore, we find that the unbalanced magnetic flux of the coronal holes is predominantly concentrated in magnetic flux tubes: 38% (81%) of the unbalanced magnetic flux of coronal holes arises from only 1% (10%) of the coronal hole area, clustered in magnetic flux tubes with field strengths >50 G (10 G). The average magnetic field density and the unbalanced magnetic flux derived from the magnetic flux tubes correlate with the mean magnetic field density and the unbalanced magnetic flux of the overall coronal hole (cc > 0.93). These findings give evidence that the overall magnetic characteristics of coronal holes are governed by the characteristics of the magnetic flux tubes.

  7. Storm-time ionization enhancements at the topside low-latitude ionosphere

    NASA Astrophysics Data System (ADS)

    Dmitriev, A.; Yeh, H.-C.

    2008-05-01

    Ion density enhancements at the topside low-latitude ionosphere during a Bastille storm on 15-16 July 2000 and Halloween storms on 29-31 October 2003 were studied using data from ROCSAT-1/IPEI experiment. Prominent ion density enhancements demonstrate similar temporal dynamics both in the sunlit and in the nightside hemispheres. The ion density increases dramatically (up to two orders of magnitude) during the main phase of the geomagnetic storms and reaches peak values at the storm maximum. The density enhancements are mostly localized in the region of a South Atlantic Anomaly (SAA), which is characterized by very intense fluxes of energetic particles. The dynamics of near-Earth radiation was studied using SAMPEX/LEICA data on >0.6 MeV electrons and >0.8 MeV protons at around 600 km altitude. During the magnetic storms the energetic particle fluxes in the SAA region and in its vicinity increase more than three orders of magnitude. The location of increased fluxes overlaps well with the regions of ion density enhancements. Two mechanisms were considered to be responsible for the generation of storm-time ion density enhancements: prompt penetration of the interplanetary electric field and abundant ionization of the ionosphere by enhanced precipitation of energetic particles from the radiation belt.

  8. Performance of Emcore Third Generation CPV Modules in the Low Latitude Marine Environment of Hawaii

    NASA Astrophysics Data System (ADS)

    Hoffman, Richard; Buie, Damien; King, David; Glesne, Thomas

    2011-12-01

    Emcore third generation concentrating photovoltaic (CPV) modules were evaluated in the low latitude location of Kihei, Hawaii. For comparison, the best available monocrystalline silicon flat panel modules were included in both dual-axis tracked and fixed mount configurations. The daily DC uncorrected efficiency value for the CPV modules averaged over the six-month performance period was 25.9% compared to 16% to 17% for the flat panels. Higher daily energy was obtained from CPV modules than tracked flat panels when daily direct solar insolation was greater than 5 kWh/m2 and more than fixed mount flat panel when direct insolation was greater than 3 kWh/m2. The module energy conversion performance was demonstrated to be predictable using a parametric model developed by Sandia National Laboratory. Soiling accumulation on module entrance surface was surprisingly rapid in the local environment. Measured energy loss rate due to soiling were two to six times larger for CPV compared to flat panel losses.

  9. 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.

  10. 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.

  11. TEC variations and IRI-2012 performance at equatorial latitudes over Africa during low solar activity

    NASA Astrophysics Data System (ADS)

    Olawepo, A. O.; Adeniyi, J. O.; Oluwadare, E. J.

    2017-04-01

    GPS-TEC data obtained from Asmara (Geomag. Lat 11.42N, Long. 113.31E), Bahir Dar (Geomag. Lat. 8.04N, Long. 111.19E), and Eldoret (Geomag. Lat. 2.71S, Long. 107.30E), three stations in the equatorial region of the African sector, have been used to study the variations in the vertical total electron content (vTEC) and to investigate the performance of the three topside options in the IRI-2012 during the year 2010, a year of low solar activity (Rz = 16). The results revealed that TEC exhibits diurnal, seasonal and latitudinal characteristics. TEC values over the three stations are minimum during the sunrise hour of 0600LT and maximum around 1200LT-1500LT irrespective of the season. Daytime peak is followed by a steady decay in TEC which continues into the mid-night. TEC values during the equinoxes are observed to be greater than those of the solstices. TEC values during March equinox are higher than those of September equinox for the stations in the northern hemisphere. June solstices exhibit the lowest values for all the stations. For the station in the southern hemisphere, TEC values during December solstice values are slightly higher than those of September equinox. The three topside options in IRI-2012 reproduce the morphology of TEC at the three stations with correlation coefficient ranging between 0.97 and 0.99. The performance of NeQuick option at predicting TEC at these stations is observed to be the best compared to the other two options irrespective of the season.

  12. 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.

  13. Nighttime D-region electron density measurements from ELF-VLF tweek radio atmospherics recorded at low latitudes

    NASA Astrophysics Data System (ADS)

    Maurya, A. K.; Veenadhari, B.; Singh, R.; Kumar, S.; Cohen, M.

    2012-12-01

    Dispersive atmospherics (tweeks) observed during 2010 simultaneously at two low latitude stations, Allahabad (geomagnetic lat., 16.79° N) and Nainital (geomagnetic lat. 20.48° N), have been utilized to estimate the nighttime D-region electron density at the ionospheric reflection height under the local nighttime propagation (21:00 - 02:00 LT or 15:30 - 20:30 UT). The analysis of simultaneously recorded tweeks at both the stations on five international quiet days during one month each from summer (June), winter (January) and equinox (March) seasons shows that the D-region electron density varies 21.5-24.5 cm-3 over the ionospheric reflection height of 85-95 km. The average values of Wait lower ionospheric parameters: ionospheric reference height h‧ and sharpness factor β are almost same during winter (86.1-85.9 km, 0.51-0.52 km-1) and equinox (85.6-85.7 km, 0.54 km-1) seasons. The values of h‧ and β during summer season are about 83.5 km and 0.60 km-1 at both stations. Overall, equivalent electron density profile obtained using tweek method shows lower values of electron density by about 5-60% than those obtained using IRI-2007 model and lower/higher by 2-68% than those obtained using rocket technique. The electron density estimated using all three techniques (tweek, IRI 2007, Rocket) is consistent in the altitude range of 82-98 km. The estimated geographic locations of causative lightnings of tweeks were matched with the locations and times of lightnings detected by the World-Wide Lightning Location Network (WWLLN). The WWLLN detected about 27.5% of causative lightnings of tweeks simultaneously observed at both the stations.

  14. Auroral activity associated with Kelvin-Helmholtz instability at the inner edge of the low-latitude boundary layer

    NASA Technical Reports Server (NTRS)

    Farrugia, C. J.; Sandholt, P. E.; Burlaga, L. F.

    1994-01-01

    Auroral activity occurred in the late afternoon sector (approx. 16 MLT) in the northern hemisphere during the passage at Earth of an interplanetary magnetic cloud on January 14, 1988. The auroral activity consisted of a very dynamic display which was preceded and followed by quiet auroral displays. During the quiet displays, discrete rayed arcs aligned along the geomagnetic L shells were observed. In the active stage, rapidly evolving spiral forms centered on magnetic zenith were evident. The activity persisted for many minutes and was characterized by the absence of directed motion. They were strongly suggestive of intense filaments of upward field-aligned currents embedded in the large-scale region 1 current system. Distortions of the flux ropes as they connect from the equatorial magnetosphere to the ionosphere were witnessed. We assess as possible generating mechanisms three nonlocal sources known to be associated with field-aligned currents. Of these, partial compressions of the magnetosphere due to variations of solar wind dynamic pressure seem an unlikely source. The possibility that the auroral forms are due to reconnection is investigated but is excluded because the active aurora were observed on the closed field line region just equatorward of the convection reversal boundary. To support this conclusion further, we apply recent results on the mapping of ionospheric regions to the equatorial plane based on the Tsyganenko 1989 model (Kaufmann et al., 1993). We find that for comparable magnetic activity the aurora map to the equatorial plane at X(sub GSM) = approx. 3 R(sub E) and approx. 2 R(sub E) inward of the magnetopause, that is, the inner edge of the boundary layer close to dusk. Since the auroral forms are manifestly associated with magnetic field shear, a vortical motion at the equatorial end of the flux rope is indicated, making the Kelvin-Helmholtz instability acting at the inner edge of the low-latitude boundary layer the most probable generating

  15. 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).

  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. 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

  18. A comprehensive analysis of the occurrence and characteristics of midperiod ULF waves at low latitude

    NASA Astrophysics Data System (ADS)

    Villante, Umberto; Tiberi, Pietro

    2015-03-01

    A long-term analysis (1985-2012) allowed to investigate the occurrence and characteristics of clearly defined ULF events (f ≈ 10-100 mHz) detected during daytime at low-latitude (L'Aquila, Italy; L ≈ 1.6) during quiet and moderately perturbed magnetospheric conditions. Selected events (≈30,000 on each component) typically have much greater amplitude on the H component with respect to D. They often reveal two prominent spectral peaks, one in band A (f < ≈ 45 mHz), mostly related to the transmission of upstream waves, and the other one in band B (f > ≈ 55 mHz), including resonances of local field lines and higher-frequency upstream waves. The occurrence of resonant phenomena on the D component is also clearly evidenced. The solar wind speed is confirmed as the key element for the manifestation of events; by contrast, their appearance is inhibited during extremely low solar wind densities. The events mostly manifest between dawn and early afternoon, with highest occurrence at ≈08:00-10:00 LT, as might be expected for the usual distribution of the interplanetary magnetic field orientation determining more or less favorable conditions for a foreshock region on the morning flank of the bow shock. No evidence is found for a favorite occurrence for low cone angles (θXB < ≈ 10°) rather, they preferentially manifest for θXB ≈ 25°-40°. The polarization pattern, much more definite in the afternoon, is consistent with the expected antisunward propagation; in the morning sector, it also suggests the possible occurrence of sunward propagating modes, mostly at f < ≈ 22 mHz. The tilt angle of the major axis of the polarization ellipses during daytime hours is oriented in the NW/SE quadrant and experiences remarkable changes at sunrise and sunset; it also shows a seasonal modulation with larger angles in the winter.

  19. 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.

  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. Ionospheric effects at low latitudes during the March 22, 1979, geomagnetic storm

    SciTech Connect

    Fesen, C.G. ); Crowley, G.; Roble, R.G. )

    1989-05-01

    This paper investigates the response of the equatorial ionosphere to the neutral atmosphere perturbations produced by the magnetic storm of March 22, 1979. A numerical model of the equatorial ionosphere is used to calculate the maximum electron densities and F layer heights associated with a storm-perturbed neutral atmosphere and circulation model. Possible electric field perturbations due to the storm are ignored. The neutral atmosphere and dynamics are simulated by the National Center for Atmospheric Research thermospheric general circulation model (TGCM) for the storm day of March 22, 1979, and the preceding quiet day. The most striking feature of the TGCM storm day simulations is the presence of waves in the neutral composition, wind, and temperature fields which propagate from high latitudes to the equator. The TGCM-calculated fields for the two days are input into a low-latitude ionosphere model which calculates n{sub max} and h{sub max} between {plus minus}20{degree}dip latitude. The calculated nighttime 6300-{angstrom} airglow emission and the altitude profiles of electron concentration are also highly perturbed by the storm. Examination of ionosonde data for March 22, 1979, shows remarkable agreement between the measured and predicted changes in f{sub 0}F{sub 2} and h{sub max} near 140{degree}W. Poorer agreement near 70{degree}W may be due to the neglect of electric field perturbations and the approximations inherent in the modeling. The results of these simulations indicate that the major factor influencing the storm time ionospheric behavior in this case is the neutral wind.

  2. Day-to-day variability of geomagnetic hourly amplitudes at low latitudes

    NASA Astrophysics Data System (ADS)

    Okeke, F. N.; Agodi Onwumechili, C.; Rabiu, Babatunde A.

    1998-08-01

    A study of the variability of the amplitude of Sq at a fixed hour from one day to the next at nine stations from the dip equator to about 22° north of it has produced interesting results. The amplitude and sign of the variability change virtually randomly, making the mean practically zero. The variability occurs at all hours of the day. Its magnitudes in the components D, H and Z have the same diurnal variation, which peaks in the noon period like Sq(H) in low latitudes, and a weak seasonal variation that peaks at the June solstice (local summer). It is demonstrated that changes in the current intensities of the equatorial electrojet (EEJ) and the worldwide part of the Sq (WSq) current layers have contrasting phases and can sometimes be in antiphase. Indeed, the changes are mostly independent. Inclusion of the magnetic element D revealed that the EEJ current system has not only an east-west but also a north-south component. The study shows that the meridional component of the EEJ current intensity evidenced at the Kodaikanal and Annamalainagar stations is an integral part of the zonal component at Trivandrum. This confirms the results of Rastogi (1996) and validates those of Onwumechili (1997). The results suggest that ionospheric conductivity mainly controls the magnitude, while the electric field and ultimately winds mainly control the phase and randomness of the day-to-day variability of the hourly amplitudes of Sq. The random component is attributed to local and/or regional atmospheric winds, probably of gravity wave origin.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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

  8. 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.

  9. The morningside low-latitude boundary layer as determined from electric and magnetic field measurements on Geotail

    NASA Technical Reports Server (NTRS)

    Mozer, F. S.; Hayakawa, H.; Kokubun, S.; Nakamura, M.; Okada, T.; Yamamoto, T.; Tsuruda, K.

    1994-01-01

    On October 17, 1992, the Geotail satellite crossed the dawnside magnetopause approximately 41 times. At the majority of these crossings, the magnetic field and the normal component of the electric field were larger and the plasma density was smaller in a low-latitude boundary layer than they were in either the nearby magnetosheath or in the magnetosphere. These results are intepreted in terms of the Kelvin-Helmholtz instability associated with velocity shear at the magnetopause. Consistent with this interpretation, it is shown that the low-latitude boundary layer was the region where the flow decreased from its magnetosheath to magnetospheric value. Evidence is presented that the magnetopause was locally oriented within less than 20 deg of its nominal geometry on these crossings and that it moved with an amplitude of 1500-6000 kilometers. The thickness of the low-latitude boundary layer averaged 800 kilometers and the electric potential across it averaged 4 kilovolts with a spread of a factor of 2. Thus, the viscous interaction and similar processes are not significant contributors to magnetospheric convection.

  10. Effects of disturbed electric fields in the low-latitude and equatorial ionosphere during the 2015 St. Patrick's Day storm

    NASA Astrophysics Data System (ADS)

    Kuai, Jiawei; Liu, Libo; Liu, Jing; Sripathi, S.; Zhao, Biqiang; Chen, Yiding; Le, Huijun; Hu, Lianhuan

    2016-09-01

    The 2015 St. Patrick's Day geomagnetic storm with SYM-H value of -233 nT is an extreme space weather event in the current 24th solar cycle. In this work, we investigated the main mechanisms of the profound ionospheric disturbances over equatorial and low latitudes in the Asian-Australian sector and the American sector during this super storm event. The results reveal that the disturbed electric fields, which comprise penetration electric fields (PEFs) and disturbance dynamo electric fields (DDEFs), play a decisive role in the ionospheric storm effects in low latitude and equatorial regions. PEFs occur on 17 March in both the American sector and the Asian-Australian sector. The effects of DDEFs are also remarkable in the two longitudinal sectors. Both the DDEFs and PEFs show the notable local time dependence, which causes the sector differences in the characteristics of the disturbed electric fields. This differences would further lead to the sector differences in the low-latitude ionospheric response during this storm. The negative storm effects caused by the long-duration DDEFs are intense over the Asian-Australian sector, while the repeated elevations of hmF2 and the equatorial ionization anomaly intensifications caused by the multiple strong PEFs are more distinctive over the American sector. Especially, the storm time F3 layer features are caught on 17 March in the American equatorial region, proving the effects of the multiple strong eastward PEFs.

  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. Latitudinal variation of the specific local time of postmidnight enhancement peaks in F layer electron density at low latitudes: A case study

    NASA Astrophysics Data System (ADS)

    Jiang, Chunhua; Deng, Chi; Yang, Guobin; Liu, Jing; Zhu, Peng; Yokoyama, Tatsuhiro; Song, Huan; Lan, Ting; Zhou, Chen; Wu, Xiongbin; Zhang, Yuannong; Zhao, Zhengyu; Komolmis, Tharadol; Supnithi, Pornchai; Yatini, Clara Y.

    2016-04-01

    Ionospheric nighttime enhancements are manifested in an increase of the electron density at nighttime. This paper studies the latitudinal variation of the specific local time of postmidnight enhancement peaks using ionosondes distributed at low latitudes. To obtain the parameters of the ionosphere, we manually extracted ionograms recorded by ionosondes. Cases show that there are significant latitudinal variations in the observed local time of the postmidnight enhancement peaks. Results show that the lower the geomagnetic latitude, the earlier the enhancement peak occurred in the geomagnetic northern hemisphere. Additionally, the enhancement peaks occurred earlier in the geomagnetic southern hemisphere than that in the geomagnetic northern hemisphere for these present cases. We suggest that the combined effect of the geomagnetic inclination and transequatorial meridional wind might be the main driving force for latitudinal variation of the local time of the occurrence.

  13. Study of zonal large scale wave structure (LSWS) and equatorial scintillation with low-latitude GRBR network over Southeast Asia and African sectors

    NASA Astrophysics Data System (ADS)

    Ram Sudarsanam, Tulasi; Yamamoto, Mamoru; Gurubaran, Subramanian; Tsunoda, Roland

    2012-07-01

    The day-to-day variability of Equatorial Spread-F, when and where the equatorial plasma bubbles (EPBs) may initiate, were the challenging problems that puzzling the space weather researchers for several decades. The zonal large scale wave structure (LSWS) at the base of F-layer is the earliest manifestation of seed perturbation for the evolution of EPBs by R-T instability processes, hence, found to play deterministic role on the development of ESF. Yet, only a little is known about LSWS with lack of sufficient observations, primarily because of inability to detect the LSWS with the currently existing instruments except with steerable incoherent scatter radar such as ALTAIR radar. This situation, however, was recently changed with launch of C/NOFS in a unique low-inclination (13 ^{o}) orbit. With the availability of CERTO beacon transmissions from C/NOFS in a near equatorial orbit, it is now possible to detect and resolve the roles by LSWS on a regular basis. A ground based low-latitude GNU Radio Beacon Receiver (GRBR) Network has been recently established that provide coverage of Southeast Asia, Pacific and African low-latitude regions. Recent observations suggest that these wave structures with zonal wave lengths varying between 200 and 800 km can be earliest detected even before E-region sunset and found to grow significantly after sunset, probably, aided by the polarization electric fields. Further, these zonal structures consistently found to be aligned with field lines for several hundreds of kilometers and EPBs were found to grow from the westward walls of upwellings. The characteristic differences on the strength of LSWS between the Asian and African longitudes were identified during the recent increasing solar activity and discussed in this paper.

  14. Photochemical and microbial transformation of terrestrial dissolved organic matter - Lena River vs. rivers in mid and low latitudes

    NASA Astrophysics Data System (ADS)

    Vähätalo, A. V.; Aarnos, H.; Paolucci, E. M.; Musibono, D. E.; Khan, S. R.; Gelinas, Y.; Shantz, A.; Huang, Q.; Schneider, W.; Rezende, C. E.; Petrescu, E.; Reader, H. E.

    2012-04-01

    biodegradability model based on a reactivity continuum to the observed biodegradation of DOC. In the dark control samples, the biodegradation of DOC was moderate, but the irradiation speeded up the decomposition of DOC a lot. The potential photodecomposition of DOM can be realized with a few hundred kilometers from the mouth of those rivers discharging to the mid- or low-latitude ocean. For the DOM of Lena River, the potential photodegradation is realized only partially in the receiving Laptev Sea having seasons with no or little solar radiation and additionally covered by sea ice over most of year.

  15. Variation of TEC and related parameters over the Indian EIA region from ground and space based GPS observations during the low solar activity period of May 2007-April 2008

    NASA Astrophysics Data System (ADS)

    Chakravarty, S. C.; Nagaraja, Kamsali; Jakowski, N.

    2017-03-01

    The annual variations of ionospheric Total Electron Content (TEC), F-region peak ionisation (NmF2) and the ionospheric slab thickness (τ) over the Indian region during the low solar activity period of May 2007-April 2008 have been studied. For this purpose the ground based TEC data obtained from GAGAN measurements and the space based data from GPS radio occultation technique using CHAMP have been utilised. The results of these independent measurements are combined to derive additional parameters such as the equivalent slab thickness of the total and the bottom-side ionospheric regions (τT and τB). The one year hourly average values of all these parameters over the ionospheric anomaly latitude region (10-26°N) are presented here along with the statistical error estimates. It is expected that these results are potentially suited to be used as base level values during geomagnetically quiet and undisturbed solar conditions.

  16. L-Band TEC Measurements and Lower Frequency Scintillation

    NASA Astrophysics Data System (ADS)

    Pedersen, T. R.; Beach, T. L.

    2003-12-01

    Signal amplitude measurements from the GPS satellites are currently limited to L-band frequencies above 1 GHz, which often remain unaffected by conditions causing even severe scintillation at more sensitive lower frequencies. Use of differential carrier phase data from dual frequency receivers to drive phase screen models and estimate scintillation at other frequencies is one potential means of monitoring scintillation over a wider range of frequencies. However, this process is complicated by the presence of a diffractive component in the L-band signal phase which can obscure the true structure in total electron content (TEC) needed as input to phase screen models. Signal amplitudes and phases at L1 and L2 frequencies (1.57 and 1.23 GHz, respectively) are calculated after propagation through one-dimensional power-law phase screens and then the resulting differential carrier phase compared with the initial phase values in the screen. Scintillation at a variety of frequencies is then computed from both the original screen and the simulated differential carrier phase, and the two results compared to examine the effects of the unobservable diffractive phase component contained in observational TEC data. Initial results show an increase of ~10% in S4 index computed at 250 MHz from simulated differential carrier phase compared to the direct phase screen computation. These results suggest that under many conditions L-band TEC observations can be used effectively to estimate VHF and UHF scintillation over a wide range of scintillation levels, and that the differences resulting from use of observed TEC instead of true ionospheric phase can be accounted for by a relatively simple correction factor.

  17. Humpback whale “super-groups” – A novel low-latitude feeding behaviour of Southern Hemisphere humpback whales (Megaptera novaeangliae) in the Benguela Upwelling System

    PubMed Central

    Seakamela, S. Mduduzi; Meÿer, Michael A.; Kirkman, Stephen P.; Barendse, Jaco; Cade, David E.; Hurwitz, David; Kennedy, Amy S.; Kotze, Pieter G. H.; McCue, Steven A.; Thornton, Meredith; Vargas-Fonseca, O. Alejandra; Wilke, Christopher G.

    2017-01-01

    Southern Hemisphere humpback whales (Megaptera novaeangliae) generally undertake annual migrations from polar summer feeding grounds to winter calving and nursery grounds in subtropical and tropical coastal waters. Evidence for such migrations arises from seasonality of historic whaling catches by latitude, Discovery and natural mark returns, and results of satellite tagging studies. Feeding is generally believed to be limited to the southern polar region, where Antarctic krill (Euphausia superba) has been identified as the primary prey item. Non-migrations and / or suspended migrations to the polar feeding grounds have previously been reported from a summer presence of whales in the Benguela System, where feeding on euphausiids (E. lucens), hyperiid amphipods (Themisto gaudichaudii), mantis shrimp (Pterygosquilla armata capensis) and clupeid fish has been described. Three recent research cruises (in October/November 2011, October/November 2014 and October/November 2015) identified large tightly-spaced groups (20 to 200 individuals) of feeding humpback whales aggregated over at least a one-month period across a 220 nautical mile region of the southern Benguela System. Feeding behaviour was identified by lunges, strong milling and repetitive and consecutive diving behaviours, associated bird and seal feeding, defecations and the pungent “fishy” smell of whale blows. Although no dedicated prey sampling could be carried out within the tightly spaced feeding aggregations, observations of E. lucens in the region of groups and the full stomach contents of mantis shrimp from both a co-occurring predatory fish species (Thyrsites atun) and one entangled humpback whale mortality suggest these may be the primary prey items of at least some of the feeding aggregations. Reasons for this recent novel behaviour pattern remain speculative, but may relate to increasing summer humpback whale abundance in the region. These novel, predictable, inter-annual, low latitude feeding

  18. Humpback whale "super-groups" - A novel low-latitude feeding behaviour of Southern Hemisphere humpback whales (Megaptera novaeangliae) in the Benguela Upwelling System.

    PubMed

    Findlay, Ken P; Seakamela, S Mduduzi; Meÿer, Michael A; Kirkman, Stephen P; Barendse, Jaco; Cade, David E; Hurwitz, David; Kennedy, Amy S; Kotze, Pieter G H; McCue, Steven A; Thornton, Meredith; Vargas-Fonseca, O Alejandra; Wilke, Christopher G

    2017-01-01

    Southern Hemisphere humpback whales (Megaptera novaeangliae) generally undertake annual migrations from polar summer feeding grounds to winter calving and nursery grounds in subtropical and tropical coastal waters. Evidence for such migrations arises from seasonality of historic whaling catches by latitude, Discovery and natural mark returns, and results of satellite tagging studies. Feeding is generally believed to be limited to the southern polar region, where Antarctic krill (Euphausia superba) has been identified as the primary prey item. Non-migrations and / or suspended migrations to the polar feeding grounds have previously been reported from a summer presence of whales in the Benguela System, where feeding on euphausiids (E. lucens), hyperiid amphipods (Themisto gaudichaudii), mantis shrimp (Pterygosquilla armata capensis) and clupeid fish has been described. Three recent research cruises (in October/November 2011, October/November 2014 and October/November 2015) identified large tightly-spaced groups (20 to 200 individuals) of feeding humpback whales aggregated over at least a one-month period across a 220 nautical mile region of the southern Benguela System. Feeding behaviour was identified by lunges, strong milling and repetitive and consecutive diving behaviours, associated bird and seal feeding, defecations and the pungent "fishy" smell of whale blows. Although no dedicated prey sampling could be carried out within the tightly spaced feeding aggregations, observations of E. lucens in the region of groups and the full stomach contents of mantis shrimp from both a co-occurring predatory fish species (Thyrsites atun) and one entangled humpback whale mortality suggest these may be the primary prey items of at least some of the feeding aggregations. Reasons for this recent novel behaviour pattern remain speculative, but may relate to increasing summer humpback whale abundance in the region. These novel, predictable, inter-annual, low latitude feeding events

  19. 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.

  20. On the dynamics of low latitude, wide and shallow coastal system: numerical simulations of the Upper Gulf of Thailand

    NASA Astrophysics Data System (ADS)

    Saramul, Suriyan; Ezer, Tal

    2014-04-01

    A high-resolution (˜1 km horizontal grid and 21 vertical layers) numerical model based on the Princeton Ocean Model (POM) has been used to study the 3D dynamics of the Upper Gulf of Thailand (UGOT). While influenced by tides and rivers like other estuarine systems, the UGOT is unique because it is wide (˜100 km × 100 km), it is shallow (average depth of only ˜15 m), it is located in low latitudes (˜12.5°N-13.5°N), and it is influenced by the seasonal monsoon. Sensitivity studies were thus conducted to evaluate the impact that surface heat fluxes, monsoonal winds, river runoffs, and the low latitude may have on the dynamics; the latter has been evaluated by modifying the Coriolis parameter and comparing simulations representing low and mid latitudes. The circulation in the UGOT changes seasonally from counter-clockwise during the northeast monsoon (dry season) to clockwise during the southwest monsoon (wet season). River discharges generate coastal jets, whereas river plumes tend to be more symmetric near the river mouth and remain closer to the coast in low latitudes, compared with mid-latitude simulations. River plumes are also dispersed along the coast in different directions during different stages of the monsoonal winds. The model results are compared favorably with a simple wind-driven analytical estuarine model. Comparisons between an El Niño year (1998) and a La Niña year (2000) suggest that water temperatures, warmer by as much as 2 °C in 1998 relative to 2000, are largely driven by decrease cloudiness during the El Niño year. The developed model of the UGOT could be used in the future to address various environmental problems affecting the region.

  1. Review of variations in Mw < 7 earthquake motions on position and TEC (Mw = 6.5 Aegean Sea earthquake sample)

    NASA Astrophysics Data System (ADS)

    Yildirim, Omer; Inyurt, Samed; Mekik, Cetin

    2016-02-01

    Turkey is a country located in the middle latitude zone, where tectonic activity is intensive. Recently, an earthquake of magnitude 6.5 Mw occurred offshore in the Aegean Sea on 24 May 2014 at 09:25 UTC, which lasted about 40 s. The earthquake was also felt in Greece, Romania, and Bulgaria in addition to Turkey. In recent years, ionospheric anomaly detection studies have been carried out because of seismicity with total electron content (TEC) computed from the global navigation satellite system's (GNSS) signal delays and several interesting findings have been published. In this study, both TEC and positional variations have been examined separately following a moderate size earthquake in the Aegean Sea. The correlation of the aforementioned ionospheric variation with the positional variation has also been investigated. For this purpose, a total of 15 stations was used, including four continuously operating reference stations in Turkey (CORS-TR) and stations in the seismic zone (AYVL, CANA, IPSA, and YENC), as well as international GNSS service (IGS) and European reference frame permanent network (EPN) stations. The ionospheric and positional variations of the AYVL, CANA, IPSA, and YENC stations were examined using Bernese v5.0 software. When the precise point positioning TEC (PPP-TEC) values were examined, it was observed that the TEC values were approximately 4 TECU (total electron content unit) above the upper-limit TEC value at four stations located in Turkey, 3 days before the earthquake at 08:00 and 10:00 UTC. At the same stations, on the day before the earthquake at 06:00, 08:00, and 10:00 UTC, the TEC values were approximately 5 TECU below the lower-limit TEC value. The global ionosphere model TEC (GIM-TEC) values published by the Centre for Orbit Determination in Europe (CODE) were also examined. Three days before the earthquake, at all stations, it was observed that the TEC values in the time period between 08:00 and 10:00 UTC were approximately 2 TECU

  2. Spatial Structure and Dynamics of Intermediate -scale Irregularities in the Post-sunset Low-latitude Ionosphere (Invited)

    NASA Astrophysics Data System (ADS)

    Bhattacharyya, A.

    2013-12-01

    Efforts to forecast the strength and latitudinal extent of scintillations on VHF and higher frequency trans-ionospheric radio signals recorded in low-latitude regions require a knowledge of the evolution of the spectrum of ionospheric irregularities in the intermediate scale range (~ 100m - few km), and dynamics of the irregularities. At present, the 3-D models that have been developed to simulate the evolution of equatorial plasma bubbles (EPBs), capture the dynamics of EPBs but do not have adequate spatial resolution to yield the intermediate scale irregularity spectrum. Power spectra of weak scintillations recorded on a VHF, UHF, or L-band signal provide direct information about the intermediate scale irregularity spectrum. However, for strong scintillations, it is not possible to derive the irregularity spectral slopes from scintillation spectra, and information about the irregularity spectrum is deduced from other characteristics, such as the coherence scale of the ground scintillation pattern of intensity, which depends on the irregularity spectrum as seen from model calculation results presented here. Information about the spatio-temporal evolution of intermediate scale irregularities is derived from scintillation data on the basis of these theoretical results. For this study, spaced receiver measurements of intensity scintillations on a VHF signal transmitted from a geo-stationary satellite and recorded at an equatorial station are used. Generally, in the initial phase of EPB development after sunset, there is a large de-correlation between the spaced receiver signals, that may be attributed to fluctuations in the velocity of the irregularities due to the perturbation electric fields associated with the interchange instability, which gives rise to the irregularities. The 'random velocity' parameter, computed from spaced receiver intensity scintillation measurements, is a measure of the de-correlation. The coherence scale and the random velocity, together

  3. Oxygen and carbon stable isotopes of modern land snail shells as environmental indicators from a low-latitude oceanic island

    NASA Astrophysics Data System (ADS)

    Yanes, Yurena; Romanek, Christopher S.; Delgado, Antonio; Brant, Heather A.; Noakes, John E.; Alonso, María R.; Ibáñez, Miguel

    2009-07-01

    Land snails provide a unique opportunity to study terrestrial paleoenvironments because their shells, which are generally highly abundant and well-preserved in the fossil record, contain a temporal record of environmental change in the form of isotope codes. To evaluate the utility of this approach for a low-latitude oceanic setting, 207 modern shells of 18 species of land snail were analyzed for their oxygen and carbon isotope composition along a north and south facing altitudinal gradient (10-2160 m a.s.l.) in Tenerife Island (˜28°N) of the Canary Archipelago. Shells collected at each locality showed a relatively large range in isotope composition which was greater along the south facing transect (drier and hotter), suggesting that the variance in shell isotope values may be related to water-stress. Although pooled isotope values did not generally show strong relationships with environmental variables (i.e., altitude, temperature and precipitation), mean isotope values were strongly associated with some climatic factors when grouped by site. The mean δ 18O value of the shell (δ 18O shell) by site displayed a negative correlation with elevation, which is consistent with the positive relationship observed between temperature and the δ 18O value of rain (δ 18O rain). Calculated δ 18O values of the snail body water (δ 18O body) derived from observed temperatures and δ 18O shell values (using the equation of Grossman and Ku [Grossman E. L. and Ku T. L. (1986) Oxygen and carbon isotope fractionation in biogenic aragonite. Chem. Geol. (Isotope Geosci. Sec.)59, 59-74]) displayed a trend with respect to altitude that was similar to measured and hypothetical δ 18O values for local rain water. The calculated δ 18O body values from the shell declined 0.17‰ (VSMOW) per 100 m, which is consistent with the "altitude effect" observed for tropical rains in Western Africa, and it correlated negatively with rainfall amount. Accordingly, lower δ 18O shell values

  4. GPS TEC variations in the polar cap ionosphere: Solar wind and IMF dependence

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

    This statistical study examines the solar wind dependence of total electron content (TEC) variations arising from mesoscale (tens to hundreds of kilometers) structuring of the polar cap ionosphere. Six years of TEC measurements were collected from five high-data rate Global Positioning System (GPS) receivers of the Canadian High Arctic Ionospheric Network (CHAIN), from which high-resolution magnetic local time-latitude maps of TEC variation occurrence rate and amplitude were created. Ionosonde radars were used to identify TEC variations arising from ionization of the E and F region ionospheres. Statistical TEC maps were examined as a function of solar wind and interplanetary magnetic field (IMF) measurements. Statistical results showed that occurrence rate of TEC variations was highest in localized dayside regions, with exact local time and latitude of peak occurrence depending primarily on the dayside coupling rate of the solar wind and magnetosphere, as well as IMF orientation and magnitude in the Y-Z plane. Occurrence of TEC variations throughout the polar cap increased with solar wind-magnetosphere coupling rate and IMF magnitude. The solar wind dependence of occurrence rate largely reflected the location and rate of dayside magnetic reconnection and subsequent particle precipitation and polar cap convection. Amplitudes of TEC variations were largest around noon and increased throughout the polar cap with increased solar wind-magnetosphere coupling rate. These statistical results improve upon the existing observational picture of the polar ionosphere and will potentially facilitate development of models and techniques for mitigating impacts of the polar ionosphere on navigation signals and communication links.

  5. 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).

  6. 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.

  7. 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.

  8. 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

  9. Observations of equatorial ionization anomaly over Africa and Middle East during a year of deep minimum

    NASA Astrophysics Data System (ADS)

    Bolaji, Olawale; Owolabi, Oluwafisayo; Falayi, Elijah; Jimoh, Emmanuel; Kotoye, Afolabi; Odeyemi, Olumide; Rabiu, Babatunde; Doherty, Patricia; Yizengaw, Endawoke; Yamazaki, Yosuke; Adeniyi, Jacob; Kaka, Rafiat; Onanuga, Kehinde

    2017-01-01

    In this work, we investigated the veracity of an ion continuity equation in controlling equatorial ionization anomaly (EIA) morphology using total electron content (TEC) of 22 GPS receivers and three ground-based magnetometers (Magnetic Data Acquisition System, MAGDAS) over Africa and the Middle East (Africa-Middle East) during the quietest periods. Apart from further confirmation of the roles of equatorial electrojet (EEJ) and integrated equatorial electrojet (IEEJ) in determining hemispheric extent of EIA crest over higher latitudes, we found some additional roles played by thermospheric meridional neutral wind. Interestingly, the simultaneous observations of EIA crests in both hemispheres of Africa-Middle East showed different morphology compared to that reported over Asia. We also observed interesting latitudinal twin EIA crests domiciled at the low latitudes of the Northern Hemisphere. Our results further showed that weak EEJ strength associated with counter electrojet (CEJ) during sunrise hours could also trigger twin EIA crests over higher latitudes.

  10. Transmission of the electric fields to the low latitude ionosphere in the magnetosphere-ionosphere current circuit

    NASA Astrophysics Data System (ADS)

    Kikuchi, Takashi; Hashimoto, Kumiko K.

    2016-12-01

    The solar wind energy is transmitted to low latitude ionosphere in a current circuit from a dynamo in the magnetosphere to the equatorial ionosphere via the polar ionosphere. During the substorm growth phase and storm main phase, the dawn-to-dusk convection electric field is intensified by the southward interplanetary magnetic field (IMF), driving the ionospheric DP2 currents composed of two-cell Hall current vortices in high latitudes and Pedersen currents amplified at the dayside equator (EEJ). The EEJ-Region-1 field-aligned current (R1 FAC) circuit is completed via the Pedersen currents in midlatitude. On the other hand, the shielding electric field and the Region-2 FACs develop in the inner magnetosphere, tending to cancel the convection electric field at the mid-equatorial latitudes. The shielding often causes overshielding when the convection electric field reduces substantially and the EEJ is overcome by the counter electrojet (CEJ), leading to that even the quasi-periodic DP2 fluctuations are contributed by the overshielding as being composed of the EEJ and CEJ. The overshielding develop significantly during substorms and storms, leading to that the mid and low latitude ionosphere is under strong influence of the overshielding as well as the convection electric fields. The electric fields on the day- and night sides are in opposite direction to each other, but the electric fields in the evening are anomalously enhanced in the same direction as in the day. The evening anomaly is a unique feature of the electric potential distribution in the global ionosphere. DP2-type electric field and currents develop during the transient/short-term geomagnetic disturbances like the geomagnetic sudden commencements (SC), which appear simultaneously at high latitude and equator within the temporal resolution of 10 s. Using the SC, we can confirm that the electric potential and currents are transmitted near-instantaneously to low latitude ionosphere on both day- and night

  11. Solar Flux Effect on the Reproducibility of Global/Local-Time Variations of Ion Density Structure at Low-Latitude Ionosphere

    NASA Astrophysics Data System (ADS)

    Su, Shin-Yi

    Longitudinal/seasonal (l/s) variations of ion density structures at the 600-km low-latitude ionosphere observed by ROCSAT-1 between two similar solar activity years of 2000 and 2002 are examined at four different local-time (LT) regions. The gross feature of l/s density structure is almost identical to each other at the four LT regions examined. A complete reproducibility of density structure can be assumed, including the shape of equatorial ionization anomaly (EIA), for identical solar flux input that also implicitly affect other atmospheric components such as the neutral O/N2 ratio and neutral wind variation. The fact that the solar variability effect is thought as the ultimate driver to shape the global ionospheric structure can be confirmed with the reproduction of ROCSAT observations with the simulation results of the TIEGCM model runs using the observed solar flux inputs for various seasons. However, the EIA crestto-valley ratio or no-valley signature in this background density structure can not be used to infer the post-sunset irregularity occurrence rates because the l/s variation of the magnetic declination effect that determines the post-sunset ionospheric conductivity for the ionospheric electrodynamics can not be readily obtained from this ionospheric background structure.

  12. Statistical analysis of ionospheric TEC anomalies before global M w ≥ 7.0 earthquakes using data of CODE GIM

    NASA Astrophysics Data System (ADS)

    Liu, Wenjing; Xu, Liang

    2016-12-01

    Based on Center of Orbit Determination in Europe (CODE) global ionospheric map (GIM) data, a statistical analysis of local total electron content (TEC) anomalies before 121 low-depth (D ≤ 100 km) strong (M w ≥ 7.0) earthquakes has been made using the sliding median differential calculation method combining with a new approach of image processing technique. The results show that significant local TEC anomalies could be observed 0-6 days before 80 earthquakes, about 66.1% out of the total. The positive anomalies occur more often than negative ones. For 26 cases, both positive and negative anomalies are observed before the shock. The pre-earthquake TEC anomalies show local time recurrence for 38 earthquakes, which occur around the same local time on different days. The local time distribution of the pre-earthquake TEC anomalies mainly concentrates between 19 and 06 LT, roughly from the sunset to sunrise. Most of the pre-earthquake TEC anomalies do not locate above the epicenter but shift to the south. The pre-earthquake TEC anomalies could be extracted near the magnetic conjugate point of the epicenter for 40 events, which is 50% out of the total 80 cases with significant local TEC anomalies. In general, the signs of the anomalies around epicenter and its conjugate point are the same, but the abnormal magnitude and lasting time are not.

  13. 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.

  14. Expanding the PhysTEC Coalition

    NASA Astrophysics Data System (ADS)

    Stein, Fredrick

    2003-04-01

    The Physics Teacher Education Coalition (PhysTEC) is a community of physics departments representing scientists and educators at institutions dedicated to improving the science preparation of future K-12 teachers. Now in its second year, PhysTEC requires physics and education faculty to work together to provide an education for future teachers that emphasizes interactive engagement and a student-centered approach to learning science. The first six Coalition members are the physics departments at Ball State University, Oregon State University, University of Arizona, University of Arkansas, Western Michigan University, and Xavier University of Louisiana. PhysTEC is creating a broad, active Coalition of physics departments that have implemented or are interested in implementing one or more of the PhysTEC Program Components. · A long-term, active collaboration among the physics department, the department of education, and the local schools. · A Teacher-in-Residence (TIR) program that provides for a full-time participant in assisting faculty in course revisions. · The redesign of physics courses based on results from physics education research. · The redesign of elementary and secondary science methods courses with an emphasis on inquiry-based teaching and learning. · The establishment of a mentoring program to provide a valuable induction experience for novice science teachers. · The participation of physics faculty in the improvement and expansion of school experiences. www.phystec.org

  15. B/TEC Opens Doors for You.

    ERIC Educational Resources Information Center

    Business and Technician Education Council, London (England).

    This package contains a paper summarizing the aims and services provided by the Business and Technician Education Council (B/TEC). Established to advance the quality and availability of a wide range of employment-related education to persons in the United Kingdom who are studying at or beyond the equivalent of the American associate-degree level,…

  16. 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…

  17. 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…

  18. Precursory TEC enhancement immediately before the 2011 Tohoku-Oki earthquake

    NASA Astrophysics Data System (ADS)

    Heki, K.

    2011-12-01

    Earthquakes are often preceded by electromagnetic precursors, and we have been searching for them in, e.g. electric currents in the ground and propagation anomalies of radio waves. Here I report that a positive anomaly of ionospheric Total Electron Content (TEC) appeared immediately before the 2011 Tohoku-Oki earthquake (Mw9.0). Microwave signals from GPS satellites experience delays inversely proportional to the square of the frequency as they propagate through the ionosphere. By monitoring the differences of the L1 and L2 carrier phases with the dense GPS array, we can infer 2-D distribution of TEC above Japan. Coseismic vertical crustal movements excite acoustic waves, and they arrive at the ionosphere in ~10 minutes and cause coseismic ionospheric disturbances (CID). Raw TEC time series on March 11 show such CID in addition to slow background variations due to the changes in elevation and diurnal variation of vertical TEC (VTEC). We modeled the VTEC over the studied time window of ~5 hours with a cubic polynomial of time, and defined the departure from the model as TEC anomalies. Positive anomaly was found to start ~40 minutes before the earthquake in data of four GPS satellites 9, 15, 26, 27. The anomaly was larger at points closer to the epicenter, and reached ~1/10 of the background TEC immediately before the earthquake. The anomaly disappeared after the passage of CID. TEC increases often occur irrespective of earthquakes. For example, enhanced UV flux due to solar flares causes sudden increase of TEC. This, however, occurs on the whole sun-lit hemisphere, and never localizes above the focal region. Large-scale traveling ionospheric disturbances (LSTID) excited in the auroral oval often propagate southward and reach Japan. This can be distinguished by carefully observing their movements. I analyzed the TEC time series of satellite 15 observed at 93009 over 120 days from January to April, 2011. The precursory anomaly on March 11 showed the largest departure

  19. 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.

  20. Disturbances of the Low Latitude Ionosphere During Extremes of Geomagnetic Activity

    DTIC Science & Technology

    2003-09-30

    Boston University, we have made a coordinated series of observations at Arequipa (Peru) near the magnetic equator and at Tucuman (Argentina) at 14o...conditions were found to be more rapid at the anomaly site (Argentina) than at the site on the magnetic equator (Peru). These results from Arequipa and...view of the three southern hemisphere imaging systems shown in Figure 1 (a), Arequipa , Tucuman and El Leoncito, in order to extend the latitudinal

  1. 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.

  2. Dropwindsonde observations of the mean boundary layer structure in the low-latitude Pacific during SOP-1

    NASA Technical Reports Server (NTRS)

    Firestone, James K.

    1986-01-01

    The low-level mean thermodynamic and wind profiles in the transition between the trade winds and the ICZ are described using the FGGE level II-b dropwindsonde data set collected during the period of SOP-1 (January 15-February 20, 1979). The results illustrate the influence of decaying midlatitude frontal systems in the northwesternmost region, the general tradelike nature of the eastern regions, and the highly convective nature of a region near the equator. Contrary to the results obtained with the traditional approach to the tropical boundary layer, the FGGE data indicate a trade inversion that remains quasi-horizontal in the north-south direction despite an equatorward decrease in its frequency of occurrence, indicating that subsidence may be more important in equatorial regions than was previously thought.

  3. 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.

  4. Analysis of NeQuick topside TEC over the Antarctic Region

    NASA Astrophysics Data System (ADS)

    Nava, Bruno; Alazo-Cuartas, Katy; Pietrella, Marco; Migoya-Orue, Yenca; Scotto, Carlo; Pezzopane, Michael

    2016-04-01

    In the present work the NeQuick 2 capabilities to estimate the ionospheric topside Total Electron Content (TEC) in the Antarctic Region have been investigated. The topside TEC at a given location has been determined as the difference between a GNSS-derived vertical TEC and the corresponding integrated bottomside electron density profile, as obtained by a co-located ionosonde. In particular, the relevant electron density profiles have been provided in the framework of the AUSPICIO (AUtomatic Scaling of Polar Ionograms and Cooperative Ionospheric Observations) project by the Adaptive Ionospheric Profiler (AIP) applied to ionograms recorded at selected high-latitude and polar ionosondes. The GNSS-derived vertical TEC have been obtained from single receivers belonging to the IGS Network. To allow a direct comparison between the NeQuick and the GNSS-derived topside TEC, a matching for the peak density and height is needed. Therefore a data ingestion technique has been implemented in order to adapt the NeQuick model to the measured foF2 and hmF2 values. The performance of the NeQuick 2 in reconstructing the electron density above the F2 layer peak height has been evaluated in terms of statistical comparisons between experimental and model-retrieved ionospheric topside TEC. The analysis results indicate that the model tends to slightly underestimate the topside TEC, especially during periods of high solar activity. Indeed, considering the inhomogeneity of the data sets, it is not possible to infer a general trend of the NeQuick performance as a function of latitude. Thus the statistics related to individual stations will be presented.

  5. Semi-annual oscillations in Saturn's low-latitude stratospheric temperatures.

    PubMed

    Orton, Glenn S; Yanamandra-Fisher, Padma A; Fisher, Brendan M; Friedson, A James; Parrish, Paul D; Nelson, Jesse F; Bauermeister, Amber Swenson; Fletcher, Leigh; Gezari, Daniel Y; Varosi, Frank; Tokunaga, Alan T; Caldwell, John; Baines, Kevin H; Hora, Joseph L; Ressler, Michael E; Fujiyoshi, Takuya; Fuse, Tetsuharu; Hagopian, Hagop; Martin, Terry Z; Bergstralh, Jay T; Howett, Carly; Hoffmann, William F; Deutsch, Lynne K; Van Cleve, Jeffrey E; Noe, Eldar; Adams, Joseph D; Kassis, Marc; Tollestrup, Eric

    2008-05-08

    Observations of oscillations of temperature and wind in planetary atmospheres provide a means of generalizing models for atmospheric dynamics in a diverse set of planets in the Solar System and elsewhere. An equatorial oscillation similar to one in the Earth's atmosphere has been discovered in Jupiter. Here we report the existence of similar oscillations in Saturn's atmosphere, from an analysis of over two decades of spatially resolved observations of its 7.8-microm methane and 12.2-microm ethane stratospheric emissions, where we compare zonal-mean stratospheric brightness temperatures at planetographic latitudes of 3.6 degrees and 15.5 degrees in both the northern and the southern hemispheres. These results support the interpretation of vertical and meridional variability of temperatures in Saturn's stratosphere as a manifestation of a wave phenomenon similar to that on the Earth and in Jupiter. The period of this oscillation is 14.8 +/- 1.2 terrestrial years, roughly half of Saturn's year, suggesting the influence of seasonal forcing, as is the case with the Earth's semi-annual oscillation.

  6. 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.

  7. Role of geomagnetic disturbance on whistler occurrence at a low latitude station

    NASA Astrophysics Data System (ADS)

    Singh, Shubha; Patel, R. P.; Singh, Krishna K.; Singh, A. K.; Singh, R. P.

    2007-07-01

    In this paper, we report the results derived from a statistical analysis of whistlers recorded at Varanasi during the period January 1990-December 1999. The monthly occurrence rate shows a maximum during January to March. In order to study the role of geomagnetic disturbance on the whistler occurrence rate, we have used the KP index and its variation. It is found that the occurrence probability monotonically increases with ∑ KP (daily sum) values. It is found that, when ∑ KP>20, the occurrence rate is greater than the average value, in good agreement with results reported by other workers. In addition, we also present the probability of the observation of whistlers during weak/intense geomagnetic storms and also during the main phase and recovery phase of geomagnetic storms.

  8. Deglacial origin of barrier reefs along low-latitude mixed siliciclastic and carbonate continental shelf edges.

    PubMed

    Droxler, André W; Jorry, Stéphan J

    2013-01-01

    Because the initial phase of barrier reef evolution is often buried under more recent phases of coralgal growth, the origins of modern barrier reefs have remained elusive. Direct observations on the nature of the substrate on top of which barrier reefs have developed are lacking, and simple questions about whether the substrate contributes to their overall linear morphology have remained unanswered. We present here a review dedicated to late-Quaternary shelf-edge deposition in tropical mixed siliciclastic-carbonate systems. These modern analogs are used to develop a quantitative understanding of shelf-edge barrier reef formation during different segments of relatively well-established sea-level cycles. The onset of rapid sea-level rise during early deglaciations, when siliciclastics were deposited along newly formed coasts at up-dip positions, provided opportune time windows for coralgal communities to establish themselves on top of maximum lowstand siliciclastic coastal deposits, such as beach ridges and lowstand shelf-edge deltas.

  9. Equatorial ionization anomaly in the low-latitude topside ionosphere: Local time evolution and longitudinal difference

    NASA Astrophysics Data System (ADS)

    Chen, Yiding; Liu, Libo; Le, Huijun; Wan, Weixing; Zhang, Hui

    2016-07-01

    Although the equatorial ionization anomaly (EIA) has been widely studied, it was seldom investigated from observations for the topside ionosphere. In this paper, the climatology characteristics of the latitudinal structure of topside ion density (Ni) were investigated in detail using ROCSAT-1 and DMSP Ni observations. EIA double-peak structure may exist at 600 km, depending on longitude, local time, season, and solar activity, while it is not a prevalent characteristic at 840 km even at solar maximum sunset. Local time evolution of the EIA at 600 km was presented. The double-peak structure begins to appear at noontime, being later than the appearance of the EIA in F2 peak region. The pronounced EIA induced by the strong prereversal enhancement at solar maximum begins to appear at 19:00 LT and can last to premidnight; EIA crest-to-trough ratio is largest (lowest) at March equinox (June solstice) and reaches a maximum at 20:00 LT in all seasons. EIA structure shows evident longitudinal difference. Pronounced EIA exists around about 100°E at 13:00 LT at the two equinoxes and June solstice, while it exists at more extensive longitudes (about 90°E to 240°E) at December solstice. The trans-equator plasma transport induced by neutral winds can weaken the double-peak structure in the topside ionosphere. The longitudinal difference in the EIA structure at 600 km is related to the longitudinal variations of equatorial upward plasma drift and geomagnetic declination.

  10. Positive and negative ionospheric responses to the March 2015 geomagnetic storm from BDS observations

    NASA Astrophysics Data System (ADS)

    Jin, Shuanggen; Jin, Rui; Kutoglu, H.

    2017-01-01

    The most intense geomagnetic storm in solar cycle 24 occurred on March 17, 2015, and the detailed ionospheric storm morphologies are difficultly obtained from traditional observations. In this paper, the Geostationary Earth Orbit (GEO) observations of BeiDou Navigation Satellite System (BDS) are for the first time used to investigate the ionospheric responses to the geomagnetic storm. Using BDS GEO and GIMs TEC series, negative and positive responses to the March 2015 storm are found at local and global scales. During the main phase, positive ionospheric storm is the main response to the geomagnetic storm, while in the recovery phase, negative phases are pronounced at all latitudes. Maximum amplitudes of negative and positive phases appear in the afternoon and post-dusk sectors during both main and recovery phases. Furthermore, dual-peak positive phases in main phase and repeated negative phase during the recovery are found from BDS GEO observations. The geomagnetic latitudes corresponding to the maximum disturbances during the main and recovery phases show large differences, but they are quasi-symmetrical between southern and northern hemispheres. No clear zonal propagation of traveling ionospheric disturbances is detected in the GNSS TEC disturbances at high and low latitudes. The thermospheric composition variations could be the dominant source of the observed ionospheric storm effect from GUVI [O]/[N2] ratio data as well as storm-time electric fields. Our study demonstrates that the BDS (especially the GEO) observations are an important data source to observe ionospheric responses to the geomagnetic storm.

  11. 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.

  12. Mesospheric turbulence studies using over low latitude: campaign of July, 2004

    NASA Astrophysics Data System (ADS)

    Chandra, H.; Sinha, H. S.; Misra, R. N.; Das, S. R.; Kota, Uma; Datta, J.; Chakravarty, S. C.; Patra, A. K.; Rao, D. N.

    Details of the coordinated rocket and MST radar campaign for mesospheric turbulence studies carried out during July 19-27 2004 are presented One RH-300 MK II rocket instrumented with a Langmuir probe and spherical probe was launched from SHAR 13 7 N 80 2 E at 1142 h IST on July 23 2004 when strong mesospheric echoes were observed by the MST radar at Gadandki 13 5 N 79 2 E Also as a part of the campaign one RH-200 rocket was launched from SHAR within an hour of the RH-300 rocket flight for measurements of winds by radar tracking of metallic chaff The Langmuir probe detected electron density irregularities with scale sizes in the range of 1m to a few km in the altitude ranges of 67 5-71 km 74 9-78 km and 84-89 km during the rocket ascent MST radar detected strong echoes in the height region of 73-77 km and relatively weak ones around 68 km Winds obtained by chaff release experiment indicates strong shear in the zonal flow around 75 km The turbulence parameters obtained from rocket borne Langmuir probe and MST radar data are compared

  13. 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.

  14. 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.

  15. Dawn-dusk asymmetries in the low-latitude boundary layer arising from the Kelvin-Helmholtz instability: A particle simulation

    NASA Technical Reports Server (NTRS)

    Wilber, M.; Winglee, R. M.

    1995-01-01

    Along the low-latitude boundary layer (LLBL), the Kelvin-Helmholtz (K-H) instability can provide a means for injection of solar wind plasma across closed field lines of the magnetosphere. A fully electromagnetic, two-dimensional (three-velocity) particle code is used to investigate dawn-dusk asymmetries that can arise from velocity differences due to gradient drifts and electric field gradients, and ion acceleration across the narrow field transition layers in the dawn and dusk flanks. The model includes the dawn and dusk sides of the LLBL simultaneously in a slab geometry, incorporating seperate populations of ions and electrons for the magnetosphere and the magnetosheath plasmas. We report several effects: (1) asymmetries in the observed morphology of the turbulent structures, with familiar fluidlike vortex formation on the duskside, but tongues of magnetosheath plasma penetrating into the magnetosphere on the dawnside; (2) the formation of discrete current layers, characterized by strong currents and sharp gradients in the magnetic field, and discrete charge layers, having net charges and constant, weaker currents; (3) increasing asymmetry in dawn/dusk behavior with a decrease of initial currents; (3) increasing asymmetry in dawn/dusk behavior with a decrease of initial boundary layer width; and (4) enhancement of the dawn-to-dusk electric field as magnetosheath particles and momenta are transported across the magnetopause.

  16. 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.

  17. Physical mechanisms of low-latitude cloud feedback on climate change (Invited)

    NASA Astrophysics Data System (ADS)

    Bretherton, C. S.

    2009-12-01

    feedbacks are not represented well in most GCMs, and are even difficult to sort out in LES models. Lastly, we will critically discuss recent observational studies claiming relevance to cloud feedbacks on climate change and suggest some possible methodological improvements.

  18. New method in computer simulations of electron and ion densities and temperatures in the plasmasphere and low-latitude ionosphere

    NASA Astrophysics Data System (ADS)

    Pavlov, A. V.

    2003-07-01

    are electron-ion Coulomb collisions, vibrational excitation of N2 and O2, and rotational excitation of N2. It is shown that the increase in the loss rate of O+(4S) ions due to the vibrational excited N2 and O2 leads to the decrease in the calculated NmF2 by a factor of 1.06 1.44 and to the increase in the calculated hmF2, up to the maximum value of 32 km in the low-latitude ionosphere between 30 and +30° of the geomagnetic latitude. Inclusion of vibrationally excited N2 and O2 brings the model and data into better agreement.

  19. 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.

  20. 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

    1998-12-03

    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.

  1. 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.

  2. 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.

  3. 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.

  4. Reconstruction of east-west deep water exchange in the low latitude Atlantic Ocean over the past 25,000 years

    NASA Astrophysics Data System (ADS)

    Howe, Jacob N. W.; Piotrowski, Alexander M.; Hu, Rong; Bory, Aloys

    2017-01-01

    Radiogenic neodymium isotopes have been used as a water mass mixing proxy to investigate past changes in ocean circulation. Here we present a new depth transect of deglacial neodymium isotope records measured on uncleaned planktic foraminifera from five cores spanning from 3300 to 4900 m on the Mauritanian margin, in the tropical eastern Atlantic as well as an additional record from 4000 m on the Ceara Rise in the equatorial western Atlantic. Despite being located under the Saharan dust plume, the eastern Atlantic records differ from the composition of detrital inputs through time and exhibit similar values to the western Atlantic foraminiferal Nd across the deglaciation. Therefore we interpret the foraminiferal values as recording deep water Nd isotope changes. All six cores shift to less radiogenic values across the deglaciation, indicating that they were bathed by a lower proportion of North Atlantic Deep Water during the Last Glacial Maximum (LGM) relative to the Holocene. The eastern Atlantic records also show that a neodymium isotope gradient was present during the LGM and during the deglaciation, with more radiogenic values observed at the deepest sites. A homogeneous water mass observed below 3750 m in the deepest eastern Atlantic during the LGM is attributed to the mixing of deep water by rough topography as it passes from the western Atlantic through the fracture zones in the Mid-Atlantic Ridge. This implies that during the LGM the low latitude deep eastern Atlantic was ventilated from the western Atlantic via advection through fracture zones in the same manner as occurs in the modern ocean. Comparison with carbon isotopes indicates there was more respired carbon in the deep eastern than deep western Atlantic during the LGM, as is also seen in the modern Atlantic Ocean.

  5. 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.

  6. 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.

  7. The NASA thermionic-conversion (TEC-ART) program

    NASA Technical Reports Server (NTRS)

    Morris, J. F.

    1977-01-01

    The current emphasis is on out-of-core thermionic conversion (TEC). The additional degrees of freedom offer new potentialities, but high-temperature material effects determine the level and lifetime of TEC performance: New electrodes not only raise power outputs but also maintain them regardless of emitter-vapor deposition on collectors. In addition, effective electrodes serve compatibly with hot-shell alloys. Space TEC withstands external and internal high-temperature vaporization problems, and terrestrial TEC tolerates hot corrosive atmospheres outside and near-vacuum inside. Finally, reduction of losses between converter electrodes is essential even though rather demanding geometries appear to be required for some modes of enhanced operation.

  8. Review of variations in Mw < 7 earthquake motions on position and tec (Mw = 6.5 aegean sea earthquake sample)

    NASA Astrophysics Data System (ADS)

    Yildirim, O.; Inyurt, S.; Mekik, C.

    2015-10-01

    Turkey is a country located in Middle Latitude zone and in which tectonic activity is intensive. Lastly, an earthquake of magnitude 6.5Mw occurred at Aegean Sea offshore on date 24 May 2014 at 12:25 UTC and it lasted approximately 40 s. The said earthquake was felt also in Greece, Romania and Bulgaria in addition to Turkey. In recent years seismic origin ionospheric anomaly detection studies have been done with TEC (Total Electron Contents) generated from GNSS (Global Navigation Satellite System) signals and the findings obtained have been revealed. In this study, TEC and positional variations have been examined seperately regarding the earthquake which occurred in the Aegean Sea. Then The correlation of the said ionospheric variation with the positional variation has been investigated. For this purpose, total fifteen stations have been used among which the data of four numbers of CORS-TR stations in the seismic zone (AYVL, CANA, IPSA, YENC) and IGS and EUREF stations are used. The ionospheric and positional variations of AYVL, CANA, IPSA and YENC stations have been examined by Bernese 5.0v software. When the (PPP-TEC) values produced as result of the analysis are examined, it has been understood that in the four stations located in Turkey, three days before the earthquake at 08:00 and 10:00 UTC, the TEC values were approximately 4 TECU above the upper limit TEC value. Still in the same stations, one day before the earthquake at 06:00, 08:00 and 10:00 UTC, it is being shown that the TEC values were approximately 5 TECU below the lower limit TEC value. On the other hand, the GIM-TEC values published by the CODE center have been examined. Still in all stations, it has been observed that three days before the earthquake the TEC values in the time portions of 08:00 and 10:00 UTC were approximately 2 TECU above, one day before the earthquake at 06:00, 08:00 and 10:00 UTC, the TEC values were approximately 4 TECU below the lower limit TEC value. Again, by using the same

  9. 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

  10. Temperature climatology of the middle atmosphere from long-term lidar measurements at mid- and low-latitudes

    NASA Technical Reports Server (NTRS)

    McDermid, I. Stuart; Leblanc, Thierry; Keckhut, Philippe; Hauchecorne, Alain; She, C. Y.; Krueger, David A.

    1998-01-01

    The temperature structure of the middle atmosphere has been studied for several decades using a variety of techniques. However, temperature profiles derived from lidar measurements can provide improved vertical resolution and accuracy. Lidars can also provide long-term data series relatively absent of instrumental drift, and integration of the measurements over several hours removes most of the gravity wave-like short-scale disturbances. This paper describes a seasonal climatology of the middle atmosphere temperature derived from lidar measurements obtained at several mid- and low-latitude locations. Results from the following lidars, which have all obtained a long-term measurement record, were used in this study: the two Rayleigh lidars of the Service d'Aeronomie du CNRS, France, located at the Observatoire de Haute Provence (OHP, 44.0 deg N) and at the Centre d'Essais des Landes (CEL, 44.0 deg N), the two Rayleigh/Raman lidars of the Jet Propulsion Laboratory, USA, located at Table Mountain, California (TMF, 34.4 deg N) and at Mauna Loa, Hawaii (MLO, 19.5 deg N), and the Colorado State University, USA, sodium lidar located at Fort Collins, Colorado (CSU, 40.6 deg N). The overall data set extends from 1978 to 1997 with different periods of measurements depending on the instrument. Three of the instruments are located at primary or complementary stations (OHP, TMF, MLO) within the Network for Detection of Stratospheric Change (NDSC). Several aspects of the temperature climatology obtained by lidar in the middle atmosphere are presented, including the climatological temperature average through the year; the annual and semi-annual components, and the differences compared to the CIRA-86 climatological model.

  11. Masking of interannual climate proxy signals by residual tropical cyclone rainwater: Evidence and challenges for low-latitude speleothem paleoclimatology

    NASA Astrophysics Data System (ADS)

    Frappier, Amy Benoit

    2013-09-01

    The anomalously low oxygen isotope ratio (δ18O values) of tropical cyclone rainfall can transfer proxy information about past tropical cyclone activity to stalagmite oxygen isotope records. Isotopically distinct stormwater reaches the growing crystal surface as a coherent slug, or after attenuation by mixing with isotopically normal vadose groundwaters. A high-resolution micromilled stalagmite stable isotope record from Belize shows that residual tropical cyclone water from Hurricane Mitch masked the oxygen isotope record of a major El Niño event. On decadal time scales, measured δ18O values are affected by changes in local tropical cyclone frequency. Despite the tropical cyclone masking effect, the structure of the "missing" El Niño event is preserved in the ATM-7 carbon isotope ratios (δ13C values). In tropical cyclone-prone regions, the fidelity of stalagmite oxygen isotope proxy data to recording background climate signals is modulated by temporal variations in local tropical cyclone rainfall, and the sensitivity of individual stalagmites to tropical cyclone masking varies with hydrology. Speleothem δ13C values, unaffected by tropical cyclones, can preserve the underlying structure of climatic variability. For low-latitude speleothems with C-O isotope covariance, intervals in which the δ18O values are significantly lower than δ13C values predict may indicate periods when local tropical cyclone masking of isotope-derived precipitation records is enhanced by greater infiltration of tropical cyclone rain. The temporal structure in stalagmite C-O isotope covariance has paleoenvironmental meaning that may be revealed by exploring factors associated with independent behavior in each isotope ratio, respectively. Tropical cyclone masking presents new challenges to paleoclimatology and a source of hypotheses for paleotempestology.

  12. A new TEC interpolation method based on the least squares collocation for high accuracy regional ionospheric maps

    NASA Astrophysics Data System (ADS)

    Krypiak-Gregorczyk, Anna; Wielgosz, Paweł; Jarmołowski, Wojciech

    2017-04-01

    The ionosphere plays a crucial role in space weather that affects satellite navigation as the ionospheric delay is one of the major errors in GNSS. On the other hand, GNSS observations are widely used to determine the amount of ionospheric total electron content (TEC). An important aspect in the electron content estimation at regional and global scale is adopting the appropriate interpolation strategy. In this paper we propose and validate a new method for regional TEC modeling based on least squares collocation (LSC) with noise variance estimation. This method allows for providing accurate TEC maps with high spatial and temporal resolution. Such maps may be used to support precise GNSS positioning and navigation, e.g. in RTK mode and also in the ionosphere studies. To test applicability of new TEC maps to positioning, double-difference ionospheric corrections were derived from the maps and their accuracy was analyzed. In addition, the corrections were applied to GNSS positioning and validated in ambiguity resolution domain. The tests were carried out during a strong ionospheric storm when the ionosphere is particularly difficult to model. The performance of the new approach was compared to IGS and UPC global, and CODE regional TEC maps. The results showed an advantage of our solution with resulting accuracy of the relative ionospheric corrections usually better than 10 cm, even during the ionospheric disturbances. This proves suitability of our regional TEC maps for, e.g. supporting fast ambiguity resolution in kinematic GNSS positioning.

  13. Differential validation of the US-TEC model

    NASA Astrophysics Data System (ADS)

    Araujo-Pradere, E. A.; Fuller-Rowell, T. J.; Spencer, P. S. J.; Minter, C. F.

    2007-06-01

    This paper presents a validation and accuracy assessment of the total electron content (TEC) from US-TEC, a new product presented by the Space Environment Center over the contiguous United States (CONUS). US-TEC is a real-time operational implementation of the MAGIC code and provides TEC maps every 15 min and the line-of-sight electron content between any point within the CONUS and all GPS satellites in view. Validation of TEC is difficult since there are no absolute or true values of TEC. All methods of obtaining TEC, for instance, from GPS, ocean surface monitors (TOPEX), and lightning detectors (FORTE), have challenges that limit their accuracy. GPS data have interfrequency biases; TOPEX also has biases, and data are collected only over the oceans; and FORTE can eliminate biases, but because of the lower operating frequency, the signals suffer greater bending on the rays. Because of the difficulty in obtaining an absolute unbiased TEC measurement, a "differential" accuracy estimate has been performed. The method relies on the fact that uninterrupted GPS data along a particular receiver-satellite link with no cycle slips are very precise. The phase difference (scaled to TEC units) from one epoch to the next can be determined with an accuracy of less than 0.01 TEC units. This fact can be utilized to estimate the uncertainty in the US-TEC vertical and slant path maps. By integrating through US-TEC inversion maps at two different times, the difference in the slant TEC can be compared with the direct phase difference in the original RINEX data file for nine receivers not used in the US-TEC calculations. The results of this study, for the period of April-September 2004, showed an average root mean square error of 2.4 TEC units, which is equivalent to less than 40 cm of signal delay at the GPS L1 frequency. The accuracy estimates from this "differential" method are similar to the results from a companion paper utilizing an "absolute" validation method by comparing with

  14. Ionospheric Indices Based on GPS TEC

    NASA Astrophysics Data System (ADS)

    Noguera, C.; Sojka, J. J.; Thompson, D. C.; Schunk, R. W.

    2005-12-01

    The solar terrestrial environment is presently characterized by a suite of indices that represent the system's dynamics and indicate the degree of space weather effects. These indices an have extended heritage based on measurements that are well calibrated and readily available. Examples of these are the solar radio flux at 10.7 cm (F10.7), magnetospheric currents inferred from ground-based magnetographs (Dst), and auroral electrojet also based on ground-based magnetograms (AE family of indices). At the present time, the ionosphere's dynamics and response to space weather are not characterized by a "true" ionosphere index. However, since ionospheric plasma variability has a major adverse effect on human space technologies, the creation of such an index may be appropriate. The major adverse effects are associated with radio wave propagation through the ionosphere either communications or navigation. Over the past decade thousands of ground-based dual frequency GPS receivers have been deployed. Each of these measures ionospheric total electron content (TEC) continuously in multiple directions. Hence, with the standardized formatting of these measurements and their near real-time nature, a unique ionospheric data stream exists from which indices can, in principle, be developed. This study is an initial exploration of how a purely ionospheric index could be derived from these GPS TEC data. Regional versus global issues are addressed, as well as diurnal issues.

  15. Test and Evaluation of Training Extension Course (TEC).

    ERIC Educational Resources Information Center

    Jacobs, T. O.; Hardy, Richard A., Jr.

    The effectiveness of a Training Extension Course (TEC) as a means of increasing the Military Occupational Specialty (MOS) proficiency of Army personnel was evaluated. TEC was implemented by the Combat Arms Training Board using sound/slide as the basic media for 56 lessons. Training material relevant to MOS 11B40, Light Weapons Infantryman, was…

  16. 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

  17. 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

  18. 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.

  19. Total electron content (TEC) variability at Los Alamos, New Mexico: A comparative study: 2. Comparisons with other TEC sources

    NASA Astrophysics Data System (ADS)

    Huang, Zhen; Roussel-Dupré, Robert

    2006-12-01

    In this study, the Fast On-Orbit Recording of Transient Events (FORTE) derived TEC variabilities on a diurnal cycle, seasonal cycle, 11-year solar cycle, and 27-day solar cycle are compared with the TEC estimates from the Los Alamos ionospheric transfer function implemented with the International Reference Ionosphere model, the GPS-derived TEC maps from NOAA, the GPS measurements made at Los Alamos, and the ionosonde critical frequency data at the closest station, Boulder, Colorado. The results show good agreement on average (monthly, annual, or multiyear means) in TEC variability at Los Alamos between the various data sources with relative RMS errors of about 5-10%. The results also show RMS errors larger than 30% for point-to-point comparisons, with the most significant errors found during high solar activity years, during summer seasons, and during strong geomagnetic storm conditions. This comparative study suggests that the FORTE-derived TECs combined with other TEC sources can help to better understand the TEC variability at Los Alamos in providing more accurate time-dependent site TECs than those derived from a single source or extrapolated from global model predictions.

  20. 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

  1. Impact of multi-scale oscillations at high and low latitudes on two persistent heavy rainfall events in the middle and lower reaches of the Yangtze River

    NASA Astrophysics Data System (ADS)

    Hui, Pinhong; Fang, Juan

    2016-08-01

    To investigate the multi-scale features in two persistent heavy rainfall (PHR) events in the middle and lower reaches of the Yangtze River (MLRYR) in June of 1982 and 1998, this study examines the impact of multi-scale oscillations in the north and south of 30°N on the PHR events by performing sensitivity experiments with the Weather Research and Forecast (WRF) model. It is found that the 60-day lowpass perturbation made a trivial contribution to the MLRYR precipitation during the PHR event in 1982. This PHR event resulted mainly from the combined effects of 30-60-day oscillation at low latitudes and 10-30-day oscillation at both high and low latitudes. The southwesterly anomalies associated with the 30-60-day anticyclonic anomaly over the northwestern Pacific facilitated moisture transport from the ocean to the MLRYR and enhanced the low-level convergence and ascending motion in the MLRYR. This similarly occurred in the 10-30-day oscillation as well. Moreover, the 10-30-day anomalies at high latitudes played a role in strengthening the large-scale low-level convergence over the MLRYR. The PHR event in 1998 was mainly related to the 60-day oscillation at both high and low latitudes and 30-60-day oscillation at low latitudes. The 60-day low-pass filtered anomalous cyclone at high latitudes in the north of 30°N contributed to the development of low-level convergence and ascending motion in northern MLRYR while the anomalous anticyclone at low latitudes in the south of 30°N not only increased the moisture in the MLRYR but also preconditioned the dynamical factors favorable for PHR over the whole area. The 30-60-day perturbations located north and south of 30°N worked together producing positive moisture anomaly in the MLRYR. In addition, the anomalous circulation in the south of 30°N tended to favor the development of ascending motion and low-level convergence in the MLRYR.

  2. 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.

  3. Comparison of GPS based TEC measurements with the IRI-2012 model for the period of low to moderate solar activity (2009-2012) at the crest of equatorial anomaly in Indian region

    NASA Astrophysics Data System (ADS)

    Karia, S. P.; Patel, N. C.; Pathak, K. N.

    2015-04-01

    The measurements of total electron content (TEC) are conducted at Surat (21° 9‧ N, 72° 47‧ E) in India, which lies under the northern crest of the equatorial anomaly region, for a period of four years from low to moderate solar activity (2009-2012) using a Global Positioning System (GPS) receiver. These results are compared with the TEC derived from IRI-2012 using three different options of topside electron density: NeQuick, IRI01-corr and IRI-2001. As there is difference between the upper limit of integration in the GPS TEC (20,200 km) and the IRI model (2000 km), to have a fair comparison of measured TEC with that of modeled TEC, the plasmaspheric contribution to the GPS TEC is removed. The measured TEC are compared with the model derived TEC for different times of the day for all months of four years (2009-2012). The IRI-2012 estimates the TEC well for the dusk hours 1800LT and noon hour 1200LT from 2010 to 2012. However, the estimation shows discrepancies with the observed TEC in the year 2009. For 0600LT it is observed that, from 2009 to 2011 the predictions made by IRI-2012 (options NeQuick and IRI01-corr) shifts from over estimation (0-50%) to under estimation (50-75%) and estimate the TEC well in the year 2012. In general, from 2009 to 2012, it is observed that with ascending phase of solar cycle the discrepancies in IRI prediction decreases for 0600LT, 1200LT and 1800LT hours of the day. Further, the comparison is also done for TEC at peak hour 1430LT for four months i.e. April, June, October and December (representing four seasons). It is observed that the peak hour TEC obtained by model overestimates the TEC for a low solar activity year 2009 but estimates well in 2010 and 2012 (except June). Further, model underestimates the peak hour TEC for moderate solar activity year 2011.

  4. Adjustments of the TaD electron density reconstruction model with GNSS-TEC parameters for operational application purposes

    NASA Astrophysics Data System (ADS)

    Kutiev, Ivan; Marinov, Pencho; Fidanova, Stefka; Belehaki, Anna; Tsagouri, Ioanna

    2012-12-01

    Validation results on the latest version of TaD model (TaDv2) show realistic reconstruction of the electron density profiles (EDPs) with an average error of 3 TECU, similar to the error obtained from GNSS-TEC calculated paremeters. The work presented here has the aim to further improve the accuracy of the TaD topside reconstruction, adjusting the TEC parameter calculated from TaD model with the TEC parameter calculated by GNSS transmitting RINEX files provided by receivers co-located with the Digisondes. The performance of the new version is tested during a storm period demonstrating further improvements in respect to the previous version. Statistical comparison of modeled and observed TEC confirms the validity of the proposed adjustment. A significant benefit of the proposed upgrade is that it facilitates the real-time implementation of TaD. The model needs a reliable measure of the scale height at the peak height, which is supposed to be provided by Digisondes. Oftenly, the automatic scaling software fails to correctly calculate the scale height at the peak, Hm, due to interferences in the receiving signal. Consequently the model estimated topside scale height is wrongly calculated leading to unrealistic results for the modeled EDP. The proposed TEC adjustment forces the model to correctly reproduce the topside scale height, despite the inaccurate values of Hm. This adjustment is very important for the application of TaD in an operational environment.

  5. 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

  6. 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.

  7. The auroral ionosphere TEC response to an interplanetary shock

    NASA Astrophysics Data System (ADS)

    Jin, Yaqi; Zhou, Xiaoyan; Moen, Jøran I.; Hairston, Marc

    2016-03-01

    This letter investigates the global total electron content (TEC) response in the auroral ionosphere to an interplanetary shock on 8 March 2012, using GPS TEC data from three pierce point chains. One is a longitudinal chain along ~65° magnetic latitude (MLAT) from ~19 magnetic local time (MLT) through dayside to 03 MLT clockwise; one meridional chain is around 14 MLT from 88° to 59° MLAT; and the third one is a chain along ~75° MLAT from ~14 to 00 MLT clockwise. The first chain clearly presents a TEC signal propagation away from ~14 MLT, indicating the shock impact location. Such a propagation is well consistent with the diffuse shock aurora propagation, and the impact location is well predicted by the shock normal direction calculated using the Geotail solar wind and interplanetary magnetic field data. The meridional chain reveals a very fast TEC signal equatorward expansion at ~45 km/s, which is the manifestation of the shock impact and further compression near the subsolar magnetopause. While TEC along the high-latitude chain varies randomly, lacking any pattern, it is consistent with the discrete aurora dynamics along the poleward boundary of the auroral oval. These findings strongly support the shock aurora mechanisms of adiabatic compression and field-aligned current establishment or enhancement, suggest that due to the same mechanisms a shock-generated TEC variation is a "duplication" of the shock aurora from the global picture to the auroral forms and their dynamics, and open the door for the TEC to be an important tool to understand the solar wind and geospace coupling. These results, for the first time, reveal the prompt, intense, and global ionospheric TEC response to the interplanetary fast-forward shock.

  8. 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.

  9. 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.

  10. 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.

  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. Daylight photodynamic therapy - Experience and safety in treatment of actinic keratoses of the face and scalp in low latitude and high brightness region*

    PubMed Central

    Galvão, Luiz Eduardo Garcia; Gonçalves, Heitor de Sá; Botelho, Karine Paschoal; Caldas, Juliana Chagas

    2017-01-01

    Daylight photodynamic therapy has been used in countries with high latitudes during the summer for actinic keratoses treatment with reports of similar efficacy to conventional photodynamic therapy. We evaluate its safety in 20 patients in the city of Fortaleza, a local with low latitude and high brightness. Sixteen patients did not report any discomfort due to the procedure. Daylight photodynamic therapy is an easy application method with great tolerability by the patient and has the possibility of being performed throughout the year in these regions. It can mean a promising tool in the control of skin cancer. PMID:28225978

  13. 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.

  14. Low solar activity variability and IRI 2007 predictability of equatorial Africa GPS TEC

    NASA Astrophysics Data System (ADS)

    Adewale, A. O.; Oyeyemi, E. O.; Cilliers, P. J.; McKinnell, L. A.; Adeloye, A. B.

    2012-01-01

    Diurnal, seasonal and latitudinal variations of Vertical Total Electron Content (VTEC) over the equatorial region of the African continent and a comparison with IRI-2007 derived TEC (IRI-TEC), using all three options (namely; NeQuick, IRI01-corr and IRI-2001), are presented in this paper. The variability and comparison are presented for 2009, a year of low solar activity, using data from thirteen Global Positioning System (GPS) receivers. VTEC values were grouped into four seasons namely March Equinox (February, March, April), June Solstice (May, June, July), September Equinox (August, September, October), and December Solstice (November, December, January). VTEC generally increases from 06h00 LT and reaches its maximum value at approximately 15h00-17h00 LT during all seasons and at all locations. The NeQuick and IRI01-corr options of the IRI model predict reasonably well the observed diurnal and seasonal variation patterns of VTEC values. However, the IRI-2001 option gave a relatively poor prediction when compared with the other options. The post-midnight and post-sunset deviations between modeled and observed VTEC could arise because NmF2 or the shape of the electron density profile, or both, are not well predicted by the model; hence some improvements are still required in order to obtain improved predictions of TEC over the equatorial region of the Africa sector.

  15. Statistics of ionospheric disturbances over the Antarctic Peninsula as derived from TEC measurements

    NASA Astrophysics Data System (ADS)

    Galushko, V. G.; Paznukhov, V. V.; Sopin, A. A.; Yampolski, Y. M.

    2016-04-01

    Results of ionospheric disturbances observations using multisite total electron content (TEC) measurements over the Antarctic Peninsula for the period from 2009 to 2012 are presented. Diurnal dependencies of the disturbance occurrence frequency, velocity, and direction of motion are established. Parameters of the disturbances are calculated using dynamic approach to the problem of ionospheric disturbances diagnostics which has been extended to allow for an arbitrary waveform of TEC perturbations. Specific data quality constraints are introduced to determine the presence of wavelike disturbances in the TEC records and to satisfy the required accuracy of parameter reconstruction. Statistical treatment of the results shows that during the daytime disturbances propagate predominantly in the northern and northeastern directions. In the evening and nocturnal hours the northwestern direction is prevailing, with the characteristic disturbance velocities ranging from 10 to 250 m/s. The most probable velocities are tens of meters per second, while the mean values are equal to about 100-130 m/s. In the daytime the velocities of the ionospheric disturbances are even higher. During the Antarctic winter time disturbances are usually observed at local noon time, in sharp contrast with the summer time, when they are present during the nights and mornings.

  16. TIME3D-IGGCAS: A new three-dimension mid- and low-latitude theoretical ionospheric model in realistic geomagnetic fields

    NASA Astrophysics Data System (ADS)

    Ren, Zhipeng; Wan, Weixing; Liu, Libo; Le, Huijun

    2012-05-01

    Based on the previous work, a new three-dimension mid- and low-latitude theoretical ionospheric model in realistic geomagnetic fields is developed, named Three-Dimension Theoretical Ionospheric Model of the Earth in the Institute of Geology and Geophysics, Chinese Academy of Sciences (TIME3D-IGGCAS). This new model covers the mid- and low-latitude ionosphere and whole plasmasphere. It self-consistently solves the equations of mass continuity, motion and energy of electron and ions to give out the time-dependent three-dimensional structures of the main ionospheric and plasmaspheric parameters in realistic geomagnetic fields, including ion number densities of O+, H+, He+, NO+, O2+, N2+ and electron; electron and ion temperature; and ion velocity vectors. We carry out simulations in March Equinox and in June Solstice, and compare the simulated results with that from IRI empirical model. TIME3D-IGGCAS can well reproduce the main ionospheric features in all simulations. We also simulate the ionospheric differences between different kinds of geomagnetic fields. The results suggest that the geomagnetic field configuration obviously affect the ionospheric plasma density, and the differences between NmF2 in realistic geomagnetic fields and that in tilted dipole fields can be larger than 40%.

  17. A recurrent neural network approach to quantitatively studying solar wind effects on TEC derived from GPS; preliminary results

    NASA Astrophysics Data System (ADS)

    Habarulema, J. B.; McKinnell, L.-A.; Opperman, B. D. L.

    2009-05-01

    This paper attempts to describe the search for the parameter(s) to represent solar wind effects in Global Positioning System total electron content (GPS TEC) modelling using the technique of neural networks (NNs). A study is carried out by including solar wind velocity (Vsw), proton number density (Np) and the Bz component of the interplanetary magnetic field (IMF Bz) obtained from the Advanced Composition Explorer (ACE) satellite as separate inputs to the NN each along with day number of the year (DN), hour (HR), a 4-month running mean of the daily sunspot number (R4) and the running mean of the previous eight 3-hourly magnetic A index values (A8). Hourly GPS TEC values derived from a dual frequency receiver located at Sutherland (32.38° S, 20.81° E), South Africa for 8 years (2000-2007) have been used to train the Elman neural network (ENN) and the result has been used to predict TEC variations for a GPS station located at Cape Town (33.95° S, 18.47° E). Quantitative results indicate that each of the parameters considered may have some degree of influence on GPS TEC at certain periods although a decrease in prediction accuracy is also observed for some parameters for different days and seasons. It is also evident that there is still a difficulty in predicting TEC values during disturbed conditions. The improvements and degradation in prediction accuracies are both close to the benchmark values which lends weight to the belief that diurnal, seasonal, solar and magnetic variabilities may be the major determinants of TEC variability.

  18. Non-parametric Data Analysis of Low-latitude Auroras and Naked-eye Sunspots in the Medieval Epoch

    NASA Astrophysics Data System (ADS)

    Bekli, Mohamed Reda; Zougab, Nabil; Belabbas, Abdelmoumene; Chadou, Ilhem

    2017-04-01

    We have studied solar activity by analyzing naked-eye sunspot observations and aurorae borealis observed at latitudes below 45°. We focused on the medieval epoch by considering the non-telescopic observations of sunspots from AD 974 to 1278 and aurorae borealis from AD 965 to 1273 that are reported in several Far East historical sources, primarily in China and Korea. After setting selection rules, we analyzed the distribution of these individual events following the months of the Gregorian calendar. In December, an unusual peak is observed with data recorded in both China and Japan, but not within Korean data.

  19. 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.

  20. GIM-TEC adaptive ionospheric weather assessment and forecast system

    NASA Astrophysics Data System (ADS)

    Gulyaeva, T. L.; Arikan, F.; Hernandez-Pajares, M.; Stanislawska, I.

    2013-09-01

    The Ionospheric Weather Assessment and Forecast (IWAF) system is a computer software package designed to assess and predict the world-wide representation of 3-D electron density profiles from the Global Ionospheric Maps of Total Electron Content (GIM-TEC). The unique system products include daily-hourly numerical global maps of the F2 layer critical frequency (foF2) and the peak height (hmF2) generated with the International Reference Ionosphere extended to the plasmasphere, IRI-Plas, upgraded by importing the daily-hourly GIM-TEC as a new model driving parameter. Since GIM-TEC maps are provided with 1- or 2-days latency, the global maps forecast for 1 day and 2 days ahead are derived using an harmonic analysis applied to the temporal changes of TEC, foF2 and hmF2 at 5112 grid points of a map encapsulated in IONEX format (-87.5°:2.5°:87.5°N in latitude, -180°:5°:180°E in longitude). The system provides online the ionospheric disturbance warnings in the global W-index map establishing categories of the ionospheric weather from the quiet state (W=±1) to intense storm (W=±4) according to the thresholds set for instant TEC perturbations regarding quiet reference median for the preceding 7 days. The accuracy of IWAF system predictions of TEC, foF2 and hmF2 maps is superior to the standard persistence model with prediction equal to the most recent ‘true’ map. The paper presents outcomes of the new service expressed by the global ionospheric foF2, hmF2 and W-index maps demonstrating the process of origin and propagation of positive and negative ionosphere disturbances in space and time and their forecast under different scenarios.

  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. Flight testing TECS - The Total Energy Control System

    NASA Technical Reports Server (NTRS)

    Kelly, James R.; Person, Lee H., Jr.; Bruce, Kevin R.

    1986-01-01

    This paper describes some of the unique features of an integrated throttle-elevator control law known as the Total Energy Control System (TECS) which has been flight tested on NASA Langley's Transport Systems Research Vehicle. The TECS concept is designed around total energy principles. It utilizes a full-time autothrottle to control the total energy of the aircraft and the elevator to distribute the energy between speed and flight path objectives. Time histories of selected parameters generated from flight data are used to illustrate the pilot-like control strategy of the system and the priority logic employed when throttle limiting is encountered.

  3. 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

  4. 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.

  5. Unusual Calcium Carbonate, Glass-Like Shards, and Low Latitude Diatoms in the GISP2 Ice Core --What Are They Telling Us?

    NASA Astrophysics Data System (ADS)

    Abbott, D. H.; Breger, D.; Burckle, L. H.; Biscaye, P.; Cole-Dai, J.

    2010-12-01

    We have studied samples extracted from the GISP2 (Greenland) ice core using Scanning-Electron Microscopy and Energy-Dispersive X-Ray Fluorescence Analysis. The seven samples studied span the time from 534.9 to 539 A.D. (361.72 m to 361.04 m depth). Through this interval, melted-ice ion data show peaks in dissolved sulfate of 91.0 ug/l centered at 536.8 A.D. and 92.9 ug/l centered at 538.1 A.D. Other sulfate values from the lowermost sample and from within this interval are 46.5 ug/l or lower. The particles extracted from the ice in this interval include Ni-Fe oxide, glass-like shards, zircons, Fe-O spherules, K bearing silicate spherules, calcium carbonate crystals (some with interpenetrating microtwins), feldspar, barite, magnetite and a low-latitude assemblage of marine diatoms. These data can be interpreted as the effects of a bolide impact during the mid-Sixth Century A.D. into an oceanic continental shelf at low latitudes. Larger grained, glassy material probably initially impacted the Greenland ice cap on ballistic trajectories. Later, finer grained particles (minerals, microspherules, and marine microfossils), elevated by the impact, were carried to Greenland by atmospheric winds. The rainout of debris lasted from 536 to 539 A.D. This proposed oceanic impact covers the same time period as that of a severe global climate downturn recorded by tree rings and in historical records.

  6. A mitochondrial phylogeny and biogeographical scenario for Asiatic water shrews of the genus Chimarrogale: implications for taxonomy and low-latitude migration routes.

    PubMed

    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

  7. Integrating both interaction pathways between warming and pesticide exposure on upper thermal tolerance in high- and low-latitude populations of an aquatic insect.

    PubMed

    Op de Beeck, Lin; Verheyen, Julie; Stoks, Robby

    2017-05-01

    Global warming and chemical pollution are key anthropogenic stressors with the potential to interact. While warming can change the impact of pollutants and pollutants can change the sensitivity to warming, both interaction pathways have never been integrated in a single experiment. Therefore, we tested the effects of warming and multiple pesticide pulses (allowing accumulation) of chlorpyrifos on upper thermal tolerance (CTmax) and associated physiological traits related to aerobic/anaerobic energy production in the damselfly Ischnura elegans. To also assess the role of latitude-specific thermal adaptation in shaping the impact of warming and pesticide exposure on thermal tolerance, we exposed larvae from replicated high- and low-latitude populations to the pesticide in a common garden rearing experiment at 20 and 24 °C, the mean summer water temperatures at high and low latitudes. As expected, exposure to chlorpyrifos resulted in a lower CTmax. Yet, this pesticide effect on CTmax was lower at 24 °C compared to 20 °C because of a lower accumulation of chlorpyrifos in the medium at 24 °C. The effects on CTmax could partly be explained by reduction of the aerobic scope. Given that these effects did not differ between latitudes, gradual thermal evolution is not expected to counteract the negative effect of the pesticide on thermal tolerance. By for the first time integrating both interaction pathways we were not only able to provide support for both of them, but more importantly demonstrate that they can directly affect each other. Indeed, the warming-induced reduction in pesticide impact generated a lower pesticide-induced climate change sensitivity (in terms of decreased upper thermal tolerance). Our results indicate that, assuming no increase in pesticide input, global warming might reduce the negative effect of multiple pulse exposures to pesticides on sensitivity to elevated temperatures.

  8. The role of thermocline water temperature in tropical climate change: a Holocene proxy-record from the low-latitude western Pacific

    NASA Astrophysics Data System (ADS)

    Dang, H.; Jian, Z.; Bassinot, F.; Qiao, P.; Cheng, X.

    2011-12-01

    To better understand the tropical climatic feedback and amplification mechanism, it is essential to learn, not only the sea surface temperature, but more importantly the variability in the tropical thermocline. By analyzing planktonic foraminiferal Mg/Ca from a sediment core recovered in the western tropical Philippine Sea, we have reconstructed the variability in both sea surface and thermocline water temperatures (SST and TWT, respectively) over the last 13 kyr. The results show: (1) during the late deglaciation, the SST gradually warmed and reached the Holocene mean level until 9.6 ka, while the TWT rose more rapidly to a distinct peak around 11.8-9.6 ka; (2) through the Holocene, the SST maintained roughly stable (or, decreased by ~0.5°C as suggested by some previous reconstructions from the Indo-Pacific Warm Pool, IPWP), but the TWT declined by 2°C, accordingly resulting in an increased ΔTG-P (the difference between SST and TWT) of ~1.5-2°C. The decreasing TWT over the Holocene tightly followed the decreasing trend in boreal summer insolation, and exhibited similar pattern as some tropical climate records as well as the extra-tropical Pacific SST and Antarctic air temperature records. Therefore, it implied that, over the Holocene the upper ocean heat storage and its thermal gradient (which could be represented by the TWT and ΔTG-P, respectively) could be involved into some feedbacks closely related to the boreal summer insolation, and probably act as potential high-low latitude climatic linkages to connect the dynamic IPWP and the extra-tropical regions through the movement of Inter-Tropical Convergence Zone (ITCZ) and the ventilation of mid-low latitude thermocline.

  9. Pathogenic fungi and parasitoids of aphids present in air captures of migratory alates in the low-latitude plateau of Yunnan, China.

    PubMed

    Huang, Zhi-Hong; Feng, Ming-Guang; Chen, Xue-Xin; Liu, Shu-Sheng

    2008-10-01

    To survey fungal pathogens and parasitoids of aphids in the low-latitude plateau of Yunnan, southwest China, 3,553 migratory alates of Brevicoryne brassicae, Lipaphis erysimi, and Myzus persicae were attracted to a yellow-plus-plant trap from air during a full-year period and individually reared on cabbage leaves for 7-14 d at 18-22 degrees C and L:D 12:12. Among the trapped alates, 19.2% were killed by 10 species of aphid-pathogenic fungi after survival of 2.3 d (range, 1-7 d). Another 2.8% were mummified by the wasps Aphidius gifuensis, Diaeretella rapae, Ephedrus plagiator, and Aphelinus mali after survival of 4.9 d (range, 1-11 d). Most of the mycosed alates (77.8%) died from Entomophthorales predominated by Pandora neoaphidis (42.7%) and Zoophthora radicans (14.5%), followed by P. nouryi, Neozygites fresenii, Conidiobiolus spp., Entomophthora planchoniana, and Z. aphidis in decreasing frequencies. A mitosporic fungus, Lecanicillium lecanii, was found frequently in L. erysimi alates trapped in rainy season. However, B. brassicae alates captured in dry season were infected or parasitized very occasionally. The predeath fecundity of the infected or parasitized alates warranted successful colonization on plants, although greatly reduced, and was well shown by the fitted probability for a given fecundity per capita and the increasing mean size of their progeny colonies. Contagious transmission of the alate-borne mycosis in most of the colonies caused high progeny mortalities within 14 d. The results highlight for the first time the diversity of aphid pathogens and the spread of both pathogens and parasitoids with host dispersal flight in the low-latitude plateau.

  10. Geomorphic evidence for former lobate debris aprons at low latitudes on Mars: Indicators of the Martian paleoclimate

    NASA Astrophysics Data System (ADS)

    Hauber, E.; van Gasselt, S.; Chapman, M. G.; Neukum, G.

    2008-02-01

    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 clastic 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 modern, 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.

  11. 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.

  12. The Polar Cap Tongue of Ionization: A survey of GPS TEC mappings from 2000 to 2014

    NASA Astrophysics Data System (ADS)

    David, M.; Sojka, J. J.; Schunk, R. W.; Coster, A. J.

    2015-12-01

    The tongue of ionization (TOI) is a sporadic large-scale feature of the F-region polar ionosphere; a volume of high density plasma transported anti-sunward across the polar cap by the magnetospheric convection electric field. Sometimes the TOI may exist in the form of polar cap patches, owing to the solar wind and M-I coupling causing variations in convection, breaking up the TOI into discrete patchy structures. Figure 1 shows an example of a TOI under quiet geomagnetic conditions, from the GPS TEC map for 1637 UT on 05 Nov 2012, a day on which the Kp index was never higher than 1.7. The data is taken from Millstone Hill's on-line Madrigal data base. The TOI is often thought of as a storm-time phenomenon; this work challenges that assumption by examining observations from all levels of geomagnetic activity throughout the period of availability of the GPS TEC maps (2000-2014).Sojka et al [1994] carried out a modeling study to determine the seasonal and universal time dependence of the tongue of ionization (and polar cap patches); Figure 2 is reproduced from that paper. In essence, this figure is intended to indicate the times when a TOI may and may not exist. A notable feature is the "hole" that is seen during winter days between 0600 and 1200 UT. At the time of that publication it was not possible to test the prediction, but there now exists a wealth of data in the form of maps of total electron content (TEC), available from the on-line Madrigal data base. These TEC maps, especially in the northern hemisphere, cover the mid-latitude and polar cap regions with sufficient resolution to determine whether or not a TOI exists, for nearly every day from the year 2000 to the present time, at 5 minute intervals. In this study we make a comprehensive survey of this immense data base and outline the conditions under which TOIs have been seen in the northern hemisphere, based on seasonal and UT dependencies, as well as levels of geomagnetic disturbance. The winter "hole" in

  13. 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

  14. 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.

  15. Invesion of tsunami height using GPS TEC data. The case of the 2012 Haida Gwaii tsunami and Earthquake.

    NASA Astrophysics Data System (ADS)

    Rakoto, V.; Lognonne, P. H.; Rolland, L. M.

    2015-12-01

    Large earthquakes (i.eM>6) and tsunamis associated are responsible for ionospheric perturbations. These perturbations can be observed in the total electron content (TEC) measured from multi- frequency Global Navigation Satellite systems (GNSS) data (e.g GPS). We will focus on the studies of the Haïda Gwaii earthquake and tsunami case. It happened the 28 october 2012 along the Queen Charlotte fault of the Canada Western Coast. First, we compare GPS data of perturbation TEC to our model. We model the TEC perturbation in several steps. (1) First, we compute tsunami normal modes modes in atmosphere in using PREM model with 4.7km of oceanic layer. (2) We sum all the tsunami modes to obtain the neutral displacement. (3) We couple the ionosphere with the neutral atmosphere. (4) We integrate the perturbed electron density along each satellite station line of sight. At last, we present first results of TEC inversion in order to retrieve the waveform of the tsunami. This inversion has been done on synthetics data assuming Queen Charlotte Earthquake and Tsunami can be considered as a point source in far field.

  16. 77 FR 19719 - Whirlpool Corporation Including On-Site Leased Workers From Career Solutions TEC Staffing, IBM...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-04-02

    ... Solutions TEC Staffing, IBM Corporation, TEK Systems Penske Logistics, Eurest, Canteen, Kelly Services, Inc...-site leased workers from Career Solutions TEC Staffing, IBM Corporation, TEK Systems, Penske...

  17. Comparing the H-alpha Intensity and Radio Wave Scattering on Eight Low-Latitude Lines of Sight

    NASA Astrophysics Data System (ADS)

    Simonetti, J. H.; Dennison, B.; Topasna, G. A.

    1995-12-01

    Spangler and Reynolds compared H-alpha intensities, measured using the Wisconsin Fabry-Perot interferometer, with radio-wave scattering sizes of eight extragalactic sources along low-latitiude lines of sight. They find that some correlation exists between scattering and H-alpha intensity, as one might expect. However, the H-alpha observations were made with a 50(') beam size; higher resolution observations might provide a more accurate measure of the intensity along the scattering line of sight. We made sensitive, arcminute resolution H-alpha images of the same fields to upgrade the accuracy of their results. We find that many of their measured H-alpha intensities are accurate, but some of the higher intensities are biased upward by the presence of clumped emission. Appropriate reduction of these large intensities increases the degree of correlation between scattering and H-alpha intensity, thus strengthening their original conclusions. This work is a first step towards using our spectral-line imaging system for a more extensive study of the relationship between the warm ionized medium and scattering of radio waves. This research was supported by NSF grant AST-9319670 and a grant from the Horton Foundation to Virginia Tech.

  18. 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

  19. Isoform-dependent interaction of BRDG1 with Tec kinase.

    PubMed

    Yokohari, K; Yamashita, Y; Okada, S; Ohya, K; Oda, S; Hatano, M; Mano, H; Hirasawa, H; Tokuhisa, T

    2001-11-30

    Tec is the prototype of an emerging family of protein-tyrosine kinases. Tec and Btk, another member of this family, together participate in the development of B-cell immune system. We previously identified one of the downstream messengers for human Tec kinase, BRDG1. BRDG1 is associated with Tec and becomes tyrosine-phosphorylated in B-cells by the engagement of B-cell antigen receptor (BCR). Here we show that overexpression of BRDG1 strongly augments BCR-mediated activation of cAMP-response element binding protein (CREB) but not that of c-Jun and the promoters of c-MYC and BCL-xL genes. Furthermore, we isolated the murine orthologue of BRDG1. Three isoforms of BRDG1 are generated by alternative splicing of the message. Two of them have a deletion of 33 amino acids in a Pleckstrin homology (PH) domain of BRDG1. Both the tyrosine-phosphorylation and CREB-activating ability of BRDG1 were isoform-dependent, suggesting a role of the PH domain of BRDG1. These data have identified a novel regulatory mechanism of CREB family of transcriptional factors.

  20. V-TECS Guide for Bookkeeping/Accounting/Payroll Clerk.

    ERIC Educational Resources Information Center

    Gregory, Margaret R.; Benson, Robert T.

    This guide, an extension of the Vocational-Technical Education Consortium of States (V-TECS) catalog, includes such considerations as background information, decision-making skills, attitudes, and learning methods surrounding the occupations of bookkeeper/accountant/payroll clerk. The guide provides job-relevant task, performance objectives,…

  1. 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…

  2. 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.

  3. Te/C nanocomposites for Li-Te Secondary Batteries.

    PubMed

    Seo, Jeong-Uk; Seong, Gun-Kyu; Park, Cheol-Min

    2015-01-22

    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.

  4. Epizootic rabbit enteropathy inoculum (TEC4): antibiograms and antibiotic fractionation.

    PubMed

    Huybens, Nathalie; Houeix, Julien; Licois, Dominique; Mainil, Jacques; Marlier, Didier

    2011-01-01

    Epizootic rabbit enteropathy (ERE) emerged and spread in Europe within the last 13 years causing major economical loss. The aims of the study was to evaluate antibiograms of TEC4, an inoculum composed of an extract of intestinal content of affected rabbits, and to test the potential of different antibiotic-based TEC4 fractions to reproduce the disease. Twenty nine different antibiotic discs were incubated for determining bacteria resistance. In a complementary study, nine tubes of liquid medium were inoculated with TEC4, incubated and added individually with amoxicillin/clavulanic acid, bacitracin, ceftiofur, doxycycline, novobiocin, streptomycyin, tylosin, vancomycin and 0.9% saline solution as control. The content of each tube was washed by centrifugation and suspended in saline. The three most effective antibiotics are florfenicol, amoxycillin/clavulanic acid and tylosin. A high concentration of Clostridium sordelli and Bacillus firmus were isolated in all fractions. Species never cultured from TEC4 were identified as Fusobacterium necrogenes (in vancomycin fraction), Cellulomonas sp (in novobiocin fraction) and Bacteroides distasonis (in doxycycline fraction). The ERE was reproduced when bacitracin, doxycycline and 0.9% fractions were inoculated. Rabbits showed ERE clinical signs with the specific drop in daily weight gain.

  5. An Evaluation of Lockheed Technology Emphasis Camp (TEC) Summer 1984.

    ERIC Educational Resources Information Center

    Jonas, Edward D., Jr.; And Others

    This report presents an evaluation of Lockheed TEC, a pilot program established by the Lockheed Georgia Company as a joint summer employment venture with other Georgia institutions. The goal of this program for economically qualified high school juniors and seniors was to expose them to aerospace technology through four program objectives. These…

  6. Multifractal analysis of vertical total electron content (VTEC) at equatorial region and low latitude, during low solar activity

    NASA Astrophysics Data System (ADS)

    Bolzan, M. J. A.; Tardelli, A.; Pillat, V. G.; Fagundes, P. R.; Rosa, R. R.

    2013-01-01

    This paper analyses the multifractal aspects of the GPS data (measured during a period of low solar activity) obtained from two Brazilian stations: Belém (01.3° S, 48.3° W) and São José dos Campos (SJC) (23.2° S, 45.9° W). The results show that the respective geographic sites show important scaling differences as well as similarities when their multifractal signatures for vertical total electron content (VTEC) are compared. The f(α) spectra have a narrow shape for great scales, which indicates the predominance of deterministic phenomena, such as solar rotation (27 days) over intermittent phenomena. Furthermore, the f(α) spectra for both sites have a strong multifractality degree at small scales. This strong multifractality degree observed at small scales (1 to 12 h) at both sites is because the ionosphere over Brazil is a non-equilibrium system. The differences found were that Belém presented a stronger multifractality at small scales (1 h to 12 h) compared with SJC, particularly in 2006. The reason for this behaviour may be associated with the location of Belém, near the geomagnetic equator, where at this location the actions of X-rays, ultraviolet, and another wavelength from the Sun are more direct, strong, and constant throughout the whole year. Although the SJC site is near ionospheric equatorial anomaly (IEA) peaks, this interpretation could explain the higher values found for the intermittent parameter μ for Belém compared with SJC. Belém also showed the presence of one or two flattening regions for f(α) spectra at the same scales mentioned before. These differences and similarities also were interpreted in terms of the IEA content, where this phenomenon is an important source of intermittence due the presence of the VTEC peaks at ±20° geomagnetic latitudes.

  7. Statistical characteristics of ionogram spread-F and satellite traces over a Chinese low-latitude station Sanya

    NASA Astrophysics Data System (ADS)

    Zhu, Zhengping; Lan, Jiaping; Luo, Weihua; Sun, Fenglou; Chen, Kun; Chang, Shanshan

    2015-11-01

    Ionosonde ionogram measurements over Sanya (18°N, 109°E; 13°N dip latitude), China during 2012-2013 are used to investigate the occurrence characteristics of spread-F (SF) and satellite traces (STs), and the possible correlation between them under the weak solar maximum of solar cycle 24. The SF and STs were manually identified from ionograms. The results show that the diurnal pattern of SF peaks at post-sunset during equinox, and at post-midnight during summer months, respectively. By classifying the SF into range spread-F (RSF) and frequency spread-F (FSF), it is found that the SF during equinox are mostly RSF associated with the equatorial F-region irregularities and can be explained by the generalized Rayleigh-Taylor instability. A statistics on the RSF and STs shows that not all RSF events were preceded by STs, and not all STs led to RSF development. The monthly mean value of the sunset ionospheric F2 layer peak height (hmF2) on RSF days is apparently higher than that on non RSF days. This result provides statistically consistent evidence that both the sunset rapid rising of the F-layer and the presence of F-region bottomside density perturbations (as indicated by STs) are important factors for the equinoctial RSF onset and development. However in summer months, the occurrences of RSF and FSF are comparable. Most FSF initiated at midnight. And there was no close relationship between the summer time FSF, F-layer height increase and STs. We suggest that the midnight FSF during summer months observed over Sanya might not be resulting from the decaying of post-sunset RSF initiated at equatorial latitude, but due to the quite localized generation of F-region irregularities.

  8. Multiple causes of sexual segregation in European red deer: enlightenments from varying breeding phenology at high and low latitude.

    PubMed Central

    Bonenfant, Christophe; Loe, Leif E.; Mysterud, Atle; Langvatn, Rolf; Stenseth, Nils Chr; Gaillard, Jean-Michel; Klein, François

    2004-01-01

    Sexual segregation outside the mating season occurs in most species of sexually dimorphic ungulates and has been extensively described in the literature, but the mechanisms causing segregation are still debated. The detailed pattern of sexual segregation throughout the year has rarely been presented for mammals, and no study, to our knowledge, has used latitudinal-related variation in breeding phenology to shed light on the underlying mechanisms. Recent methodological developments have made it possible to quantify separate components of segregation (social, habitat) and activity synchrony in animal groups, but these major improvements have so far been little used. We observed European red deer year round at two widely different latitudes (France and Norway) and tested three different mechanistic hypotheses of segregation related to: (i) predation risk; (ii) body-size-related forage selection; and (iii) activity budget. Habitat segregation peaked during calving in both populations and dropped rapidly after calving. Females with calves were more segregated from males than were females without calves, pointing to a key role of antipredator behaviour even though large predators are absent in France and extremely rare in Norway. However, at both sites individuals also grouped with their own sex within habitat types (i.e. social segregation), and individuals in mixed-sex groups were less synchronized in activity type than individuals in either unisex male or unisex female groups, suggesting that differences in activity budgets are involved. Social segregation peaked during calving and was lowest during the rut (indicating aggregation) in both populations; these activities occurred one month later in the Northern populations, corresponding well with known differences in breeding phenology. We conclude that latitude-dependent breeding phenology shapes the seasonal pattern of sexual segregation and that sexual segregation in ungulates has multiple causes. PMID:15255042

  9. 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

  10. 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

  11. Validation of NeQuick TEC data ingestion technique against C/NOFS and EISCAT electron density measurements

    NASA Astrophysics Data System (ADS)

    Nigussie, M.; Radicella, S. M.; Damtie, B.; Yizengaw, E.; Nava, B.; Roininen, L.

    2016-07-01

    This paper investigates a technique to estimate near-real-time electron density structure of the ionosphere. Ground-based GPS receiver total electron content (TEC) at low and high latitudes has been used to assist the NeQuick 2 model. First, we compute model input (effective ionization level) when the modeled slant TEC (sTEC) best fits the measured sTEC by single GPS receiver (reference station). Then we run the model at different locations nearby the reference station and produce the spatial distribution of the density profiles of the ionosphere in the East African region. We investigate the performance of the model, before and after data ingestion in estimating the topside ionosphere density profiles. This is carried out by extracting in situ density from the model at the corresponding location of C/NOFS (Communication/Navigation Outage Forecast System) satellite orbit and comparing the modeled ion density with the in situ ion density observed by Planar Langmuir Probe onboard C/NOFS. It is shown that the performance of the model after data ingestion reproduces the topside ionosphere better up to about 824 km away from the reference station than that before adaptation. Similarly, for high-latitude region, NeQuick 2 adapted to sTEC obtained from high-latitude (Tromsø in Norway) GPS receiver and the model used to reproduce parameters measured by European Incoherent Scatter Scientific Association (EISCAT) VHF radar. It is shown that the model after adaptation shows considerable improvement in estimating EISCAT measurements of electron density profile, F2 peak density, and height.

  12. 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.

  13. 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.

  14. 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.

  15. 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

  16. 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.

  17. 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.

  18. 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.

  19. Study of GPS-TEC related to Wenchuan earthquake (M=7.9) of 12 May 2008 and their fractal analysis

    NASA Astrophysics Data System (ADS)

    Singh, O. P.; Chauhan, Vishal; Singh, Birbal

    2010-05-01

    Daily variation of vertical TEC data recorded at Bichpuri Agra station (Geographic Lat. 27.20N, Geographic Long. 780E, Geomagnetic Lat. 17.100N) employing a GPS receiver has been studied for a period of three months from 1 April to 30 June 2008 in relation to Wenchuan earthquake (M=7.9) of 12 May 2008. A significant enhancement has been observed in TEC 22 days before this earthquake. This result is interpreted in terms of E×B drift mechanism, where E is electric field of seismic origin. Further, fractal analysis of TEC data has also been carried out using Burlaga- Klein method and it is found that fractal dimension gradually increases long before the occurrence of this earthquake. These results are not influenced by magnetic storms and are attributed strongly to earthquake.

  20. Ionospheric Data Assimilation with GPS data: Slant versus Vertical TEC

    NASA Astrophysics Data System (ADS)

    Feldt, J. A.; Moldwin, M.; Mannucci, A. J.; Ridley, A. J.; Komjathy, A.; Wilson, B. D.; Stephens, P.; Butala, M. D.

    2011-12-01

    There are a number of Global Positioning System (GPS) total electron content (TEC) data sets widely used in the ionospheric community including the MIT Madrigal and the NASA Jet Propulsion Laboratory (JPL) database. Understanding the differences of the datasets are important for empirical and physics-based modeling efforts especially those involving ionospheric data assimilation. For this study, we are comparing the Madrigal database's World Wide GPS receiver network with JPL processed GPS data from nearly 200 stations. We will investigate two data assimilation models using these data: University of Michigan's Global Ionosphere Thermosphere Model (GITM) and the JPL Global Assimilative Ionospheric Model (GAIM). The Madrigal data product provides gridded vertical total electron content (VTEC) based on data from a worldwide network of GPS receivers, in an easily accessible format without the need to process individual line of sight measurements. JPL uses raw data (RINEX files) from each GPS receiver to produce slant TEC (STEC) output between each receiver and satellite line of sight. Interfrequency biases at JPL are estimated using a model-assisted global mapping approach. We compare the Madrigal and JPL TEC data products to analyze differences in their ionospheric and bias estimation algorithms. This study will also compare data assimilation results using with VTEC and STEC.

  1. Dynamics of the Tec-family tyrosine kinase SH3 domains.

    PubMed

    Roberts, Justin M; Tarafdar, Sreya; Joseph, Raji E; Andreotti, Amy H; Smithgall, Thomas E; Engen, John R; Wales, Thomas E

    2016-04-01

    The Src Homology 3 (SH3) domain is an important regulatory domain found in many signaling proteins. X-ray crystallography and NMR structures of SH3 domains are generally conserved but other studies indicate that protein flexibility and dynamics are not. We previously reported that based on hydrogen exchange mass spectrometry (HX MS) studies, there is variable flexibility and dynamics among the SH3 domains of the Src-family tyrosine kinases and related proteins. Here we have extended our studies to the SH3 domains of the Tec family tyrosine kinases (Itk, Btk, Tec, Txk, Bmx). The SH3 domains of members of this family augment the variety in dynamics observed in previous SH3 domains. Txk and Bmx SH3 were found to be highly dynamic in solution by HX MS and Bmx was unstructured by NMR. Itk and Btk SH3 underwent a clear EX1 cooperative unfolding event, which was localized using pepsin digestion and mass spectrometry after hydrogen exchange labeling. The unfolding was localized to peptide regions that had been previously identified in the Src-family and related protein SH3 domains, yet the kinetics of unfolding were not. Sequence alignment does not provide an easy explanation for the observed dynamics behavior, yet the similarity of location of EX1 unfolding suggests that higher-order structural properties may play a role. While the exact reason for such dynamics is not clear, such motions can be exploited in intra- and intermolecular binding assays of proteins containing the domains.

  2. 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.

  3. Ionospheric disturbances triggered by the 25 April, 2015 M7.8 Gorkha earthquake, Nepal: Constraints from GPS TEC measurements

    NASA Astrophysics Data System (ADS)

    Catherine, J. K.; Uma Maheshwari, D.; Gahalaut, V. K.; Roy, P. N. S.; Khan, P. K.; Puviarasan, N.

    2017-01-01

    The ionosphere response to the April 11, 2015 (Mw 7.8) Gorkha earthquake, occurring in the Himalayan arc, is analysed using GPS Total Electron Content (TEC) measurements, from GPS sites in Nepal and India, situated both close to and far from the epicentre. In the near field, the Coseismic Ionospheric disturbance (CID) following the earthquake rupture propagation arrive east of the epicentre, within 5-7 min with a propagation velocity of 980 m/s, equal to the speed of the shock acoustic waves at the ionospheric heights, and on to the west with a reduced speed of 650 m/s, within 8-11 min, after the earthquake occurrence. The phenomenon of CID splitting into two modes, east and west of the epicentre is observed. In the far-field region, up to epicentral distances of 2200 km, Rayleigh wave induced ionospheric disturbance are recorded with a propagation speed of 2.6 km/s. Higher TEC amplitude of 0.2-1.5 TECU is observed east of the epicentre compared to the west with 0.1-0.3 TECU. The characteristics of this dip-slip earthquake are well projected in the TEC waveforms. The ambient magnetic field in the mid-latitudes prohibited the propagation of ionospheric disturbance in the northward direction. In the present study the observed primary CID is essentially in congruence with the rupture propagation of the earthquake in E-SE direction.

  4. 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.

  5. A comparison of benthic foraminiferal Mn / Ca and sedimentary Mn / Al as proxies of relative bottom-water oxygenation in the low-latitude NE Atlantic upwelling system

    NASA Astrophysics Data System (ADS)

    McKay, C. L.; Groeneveld, J.; Filipsson, H. L.; Gallego-Torres, D.; Whitehouse, M. J.; Toyofuku, T.; Romero, O. E.

    2015-09-01

    Trace element incorporation into foraminiferal shells (tests) is governed by physical and chemical conditions of the surrounding marine environment, and therefore foraminiferal geochemistry provides a means of palaeo-oceanographic reconstructions. With the availability of high-spatial-resolution instrumentation with high precision, foraminiferal geochemistry has become a major research topic over recent years. However, reconstructions of past bottom-water oxygenation using foraminiferal tests remain in their infancy. In this study we explore the potential of using Mn / Ca determined by secondary ion mass spectrometry (SIMS) as well as by flow-through inductively coupled plasma optical emission spectroscopy (FT-ICP-OES) in the benthic foraminiferal species Eubuliminella exilis as a proxy for recording changes in bottom-water oxygen conditions in the low-latitude NE Atlantic upwelling system. Furthermore, we compare the SIMS and FT-ICP-OES results with published Mn sediment bulk measurements from the same sediment core. This is the first time that benthic foraminiferal Mn / Ca is directly compared with Mn bulk measurements, which largely agree on the former oxygen conditions. Samples were selected to include different productivity regimes related to Marine Isotope Stage 3 (35-28 ka), the Last Glacial Maximum (28-19 ka), Heinrich Event 1 (18-15.5 ka), Bølling Allerød (15.5-13.5 ka) and the Younger Dryas (13.5-11.5 ka). Foraminiferal Mn / Ca determined by SIMS and FT-ICP-OES is comparable. Mn / Ca was higher during periods with high primary productivity, such as during the Younger Dryas, which indicates low-oxygen conditions. This is further supported by the benthic foraminiferal faunal composition. Our results highlight the proxy potential of Mn / Ca in benthic foraminifera from upwelling systems for reconstructing past variations in oxygen conditions of the sea floor environment as well as the need to use it in combination with other proxy records such as faunal

  6. 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.

  7. Wide-field Imaging Survey of Dust Continuum Emissions at λ = 1.1 mm toward the Chamaeleon and Lupus Regions with AzTEC on ASTE

    NASA Astrophysics Data System (ADS)

    Momose, Munetake; Hiramatsu, Masaaki; Tsukagoshi, Takashi; Shimajiri, Yoshito; Ikeda, Norio; Kitamura, Yoshimi; Kamegai, Kazuhisa; Ezawa, Hajime; Kawabe, Ryohei; Saito, Masao

    2009-08-01

    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.

  8. 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.

  9. Distinct and Overlapping Functions of TEC Kinase and BTK in B Cell Receptor Signaling.

    PubMed

    de Bruijn, Marjolein J W; Rip, Jasper; van der Ploeg, Esmee K; van Greuningen, Lars W; Ta, Van T B; Kil, Laurens P; Langerak, Anton W; Rimmelzwaan, Guus F; Ellmeier, Wilfried; Hendriks, Rudi W; Corneth, Odilia B J

    2017-04-15

    The Tec tyrosine kinase is expressed in many cell types, including hematopoietic cells, and is a member of the Tec kinase family that also includes Btk. Although the role of Btk in B cells has been extensively studied, the role of Tec kinase in B cells remains largely unclear. It was previously shown that Tec kinase has the ability to partly compensate for loss of Btk activity in B cell differentiation, although the underlying mechanism is unknown. In this study, we confirm that Tec kinase is not essential for normal B cell development when Btk is present, but we also found that Tec-deficient mature B cells showed increased activation, proliferation, and survival upon BCR stimulation, even in the presence of Btk. Whereas Tec deficiency did not affect phosphorylation of phospholipase Cγ or Ca(2+) influx, it was associated with significantly increased activation of the intracellular Akt/S6 kinase signaling pathway upon BCR and CD40 stimulation. The increased S6 kinase phosphorylation in Tec-deficient B cells was dependent on Btk kinase activity, as ibrutinib treatment restored pS6 to wild-type levels, although Btk protein and phosphorylation levels were comparable to controls. In Tec-deficient mice in vivo, B cell responses to model Ags and humoral immunity upon influenza infection were enhanced. Moreover, aged mice lacking Tec kinase developed a mild autoimmune phenotype. Taken together, these data indicate that in mature B cells, Tec and Btk may compete for activation of the Akt signaling pathway, whereby the activating capacity of Btk is limited by the presence of Tec kinase.

  10. 76 FR 73683 - Whirlpool Corporation, Including On-Site Leased Workers From Career Solutions TEC Staffing...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-11-29

    ... Solutions TEC Staffing, Andrews International, IBM Corporation, TEK Systems Penske Logistics, Eurest... Systems, Penske Logistics, Eurest, Canteen, Kelly Services, Inc., Prodriver, and Arkansas Warehouse,...

  11. 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.

  12. Modeling of Equatorial Anomaly Development and Collapse at Dusk Observed by TIMED/GUVI Over Indian Longitudes

    NASA Astrophysics Data System (ADS)

    Basu, S.; Huba, J.; Makela, J.; Ray, S.; Groves, K.

    2007-05-01

    The GUVI instrument on NASA's TIMED satellite acquires images of 135.6-nm emission in the Earth's ionosphere/thermosphere system. The brightness of the GUVI images is approximately proportional to the square of the electron density and, as such, the images can be used to monitor the equatorial F region ionization anomaly. The intensity and separation of these bands are controlled by the equatorial E-B drift and the meridional neutral wind. Further, the collapse of the anomaly has been linked to the suppression of irregularities causing scintillations. The SAMI3, another model of the ionosphere, has been utilized to model the evening collapse of the anomaly in the Indian longitude sector where measurements of TEC, scintillations and estimates of the daytime vertical drifts are available. Preliminary results from SAMI3 show that the collapse of the anomaly at dusk can be simulated by a reduction of the vertical drift, and its reversal in mid-afternoon in agreement with the drift estimates from magnetometer observations. Introduction of neutral winds into SAMI3 reproduces the dusk behavior of TEC at low latitude stations in India. While preliminary results from SAMI3 provide some insights into the day-to-day variation of scintillations, much further work is necessary, particularly on the relative effects of the pre-reversal enhancement of the vertical drifts, time of reversal, neutral winds and the conductivity in the E-region on the generation and suppression of instabilities. We hope these modeling efforts will eventually lead to the isolation of a unique set of drivers that control large and small scale plasma structuring.

  13. 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.

  14. 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.

  15. Debris-covered piedmont glaciers along the northwest flank of the Olympus Mons scarp: Evidence for low-latitude ice accumulation during the Late Amazonian of Mars

    NASA Astrophysics Data System (ADS)

    Milkovich, Sarah M.; Head, James W.; Marchant, David R.

    2006-04-01

    association with these lobate features that might suggest: (1) near-surface groundwater as a source for ice in the alcoves in the lobe source region at the base of the scarp, or (2) basal melting and drainage emanating from the lobes that might indicate wet-based glacial conditions. Instead, the array of features is consistent with cold-based glacial processes. The glacial interpretations outlined here are consistent with recent geological evidence for low-latitude ice-rich features at similar positions on the Tharsis Montes as well as with orbital dynamic and climate models indicating extensive snow and ice accumulation associated with episodes of increased obliquity during the Late Amazonian period of the history of Mars.

  16. GS-TEC: the Gaia spectrophotometry transient events classifier

    NASA Astrophysics Data System (ADS)

    Blagorodnova, Nadejda; Koposov, Sergey E.; Wyrzykowski, Łukasz; Irwin, Mike; Walton, Nicholas A.

    2014-07-01

    We present an algorithm for classifying the nearby transient objects detected by the Gaia satellite. The algorithm will use the low-resolution spectra from the blue and red spectrophotometers on board the satellite. Taking a Bayesian approach, we model the spectra using the newly constructed reference spectral library and literature-driven priors. We find that for magnitudes brighter than 19 in Gaia G magnitude, around 75 per cent of the transients will be robustly classified. The efficiency of the algorithm for Type Ia supernovae (SNe I) is higher than 80 per cent for magnitudes G ≤ 18, dropping to approximately 60 per cent at magnitude G = 19. For SNe II, the efficiency varies from 75 to 60 per cent for G ≤ 18, falling to 50 per cent at G = 19. The purity of our classifier is around 95 per cent for SNe I for all magnitudes. For SNe II, it is over 90 per cent for objects with G ≤ 19. GS-TEC also estimates the redshifts with errors of σz ≤ 0.01 and epochs with uncertainties σt ≃ 13 and 32 d for SNe I and SNe II, respectively. GS-TEC has been designed to be used on partially calibrated Gaia data. However, the concept could be extended to other kinds of low-resolution spectra classification for ongoing surveys.

  17. The PhysTEC Teacher Education Program at FIU

    NASA Astrophysics Data System (ADS)

    Kramer, Laird

    2010-10-01

    The FIU PhysTEC Project is an integral component of the Physics Department's educational transformation that has led to more than a ten-fold increase in majors. The transformation seeks to increase the quality and quantity of physics majors and future physics teachers, including those from historically underrepresented groups. Elements of the efforts include transformed introductory physics courses, establishment of a physics research and learning community, engagement of stakeholders spanning high school through the university administration, and advocacy by a physics education research group. The PhysTEC Project supports future physics teachers through a Learning Assistant program coupled to newly revised secondary education programs. The Learning Assistant program is an experiential program that recruits new students into teaching careers while providing a mechanism for transforming courses - undergraduates experience the rewards and intellectual challenges of teaching through providing interactive engagement learning experiences for their peers in introductory physics courses. Students that continue in the program enroll in a multidisciplinary teacher preparation program and may receive significant financial support. FIU is a minority-serving urban public research institution in Miami, Florida serving over 39,000 students, of which 64% are Hispanic, 13% are Black, and 56% are women. Programmatic strategies and impacts of the program will be provided.

  18. 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.

  19. 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…

  20. 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.

  1. 75 FR 44051 - Resolicitation of Applications for the Railroad Safety Technology Program Grant Program (RS-TEC...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-07-27

    ... Grant Program (RS-TEC-10-001) AGENCY: Federal Railroad Administration (FRA), Department of Transportation (DOT). ACTION: Notice of Funds Availability, Resolicitation of Applications (RS-TEC-10-001... Railroad Safety Technology Grant Program ] (Funding Opportunity RS-TEC-10-001), the Federal...

  2. The PhysTec Project of APS, AIP, and AAPT

    NASA Astrophysics Data System (ADS)

    Jansen, Henri

    2002-04-01

    We will describe the development of the PhysTEC program at Oregon State University. The goal of this program is to enhance the number of secondary physics teachers and to improve the physics training of primary teachers and secondary teachers in related fields. Key elements of the plan include: (1) a seamless five-year program leading to a M.S. in science education and a B.S. in physics with a specialty in physics education, which takes advantage of our unique undergraduate physics curriculum (the Paradigms project); (2) a teacher-in-residence with joint duties in the Department of Physics and the Department of Science and Math Education; (3) inquiry-based and pedagogically-oriented lab and recitation sections in calculus-based introductory physics; (4) an inquiry-based physical science course for preservice elementary teachers; (5) outreach projects that enhance the preservice experience and support the methods and pedagogy training offered elsewhere in the curriculum.

  3. Impact of Uncertainty in Solar Forcing on TEC

    NASA Astrophysics Data System (ADS)

    Shim, Ja Soon; Fuller-Rowell, Tim; Codrescu, Mihail; Fedrizzi, Mariangel; Mays, M. Leila; Taktakishvilli, Aleksandre; Kuznetsova, Maria; Rastätter, Lutz

    2016-07-01

    The Community Coordinated Modeling Center (CCMC), which is an interagency partnership to enable, support and perform the research and development for next-generation space science and space weather models, has been leading community-wide model validation efforts for Ionosphere/Thermosphere (IT) models along with other models that cover different domains of the Sun-Earth system such as heliosphere and magnetosphere. Uncertainty quantification plays a critical role in model validation. As a preliminary study on uncertainty analysis, we investigate how uncertainty in external forcing such as the solar radio flux at 10.7 cm (F10.7 index) and the interplanetary magnetic field (IMF) impacts on the IT model results during geomagnetic storm times (e.g., 2013 Mar. event). For this study, CTIPe (Coupled Thermosphere Ionosphere Plasmasphere Electrodynamics) model is used. In this paper, we focus on the impact of the uncertainty of the parameters (F10.7 and IMF) on regional TEC (North American sector).

  4. Recent Progress in Understanding Natural-Hazards-Generated TEC Perturbations: Measurements and Modeling Results

    NASA Astrophysics Data System (ADS)

    Komjathy, A.; Yang, Y. M.; Meng, X.; Verkhoglyadova, O. P.; Mannucci, A. J.; Langley, R. B.

    2015-12-01

    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, volcanic eruptions, and tsunamis. Research at the University of New Brunswick (UNB) laid the foundations to model the three-dimensional ionosphere at NASA's Jet Propulsion Laboratory by ingesting ground- and space-based GPS measurements into the state-of-the-art Global Assimilative Ionosphere Modeling (GAIM) software. As an outcome of the UNB and NASA research, new and innovative GPS applications have been invented including the use of ionospheric measurements to detect tiny fluctuations in the GPS signals between the spacecraft and GPS receivers caused by natural hazards occurring on or near the Earth's surface.We will show examples for early detection of natural hazards generated ionospheric signatures using ground-based and space-borne GPS receivers. We will also discuss recent results from the U.S. Real-time Earthquake Analysis for Disaster Mitigation Network (READI) exercises utilizing our algorithms. By studying the propagation properties of ionospheric perturbations generated by natural hazards along with applying sophisticated first-principles physics-based modeling, we are on track to develop new technologies that can potentially save human lives and minimize property damage. It is also expected that ionospheric monitoring of TEC perturbations might become an integral part of existing natural hazards warning systems.

  5. GNSS ionospheric scintillation and TEC at high latitudes: INGV monitoring and studies

    NASA Astrophysics Data System (ADS)

    Alfonsi, L.; de Franceschi, G.; Spogli, L.; Romano, V.

    2009-12-01

    The Istituto Nazionale di Geofisica e Vulcanologia (INGV) is monitoring the high latitude ionospheric irregularities causing GNSS signals corruption since 2003 when a GISTM receiver (GPS Ionospheric Scintillation and TEC Monitor) was deployed in Ny Alesund (Svalbard). Currently, INGV manages three GISTMs at Svalbard (two in Ny Alesund, another one in Longyearbyen) and two receivers in Antarctica at Concordia and Mario Zucchelli Stations. The GISTM receivers consist of NovAtel OEM4 dual-frequency receivers with special firmware specifically able to compute in near real time the amplitude and the phase scintillation from the GPS L1 frequency signals, and the ionospheric TEC (Total Electron Content) from the GPS L1 and L2 carrier phase signals. From this ground-based network, we are able to capture the dynamics of ionospheric plasma in a wide latitudinal range, from auroral to cusp/cap regions, considering the contribution of both hemispheres, in a bi-polar framework. The data collected are structured and archived in a dedicated database: www.eswua.ingv.it. The INGV activities in the field of the observation and the investigation of the ionospheric irregularities are included in several international collaborations addressing scientific issues as well as technological applications. This paper would like to give an overview of our recent activities about polar ionospheric imaging, scintillation climatology and scintillation mitigation matured also under the umbrella of the SCAR ICESTAR community and, currently, part of the initiatives of the SCAR Action Group “GPS Weather and Space Weather Forecast”chaired by INGV.

  6. TEC data ingestion into IRI and NeQuick over the antarctic region

    NASA Astrophysics Data System (ADS)

    Nava, Bruno; Pezzopane, Michael; Radicella, Sandro M.; Scotto, Carlo; Pietrella, Marco; Migoya Orue, Yenca; Alazo Cuartas, Katy; Kashcheyev, Anton