Signatures of moderate (M-class) and low (C and B class) intensity solar flares on the equatorial electrojet current: Case studies

NASA Astrophysics Data System (ADS)

Chakrabarty, D.; Bagiya, Mala S.; Thampi, Smitha V.; Pathan, B. M.; Sekar, R.

2013-12-01

The present investigation brings out, in contrast to the earlier works, the changes in the equatorial electrojet (EEJ) current in response to a few moderate (M-class) and low (C and B class) intensity solar flares during 2005-2010. Special care is taken to pick these flare events in the absence of prompt electric field perturbations associated with geomagnetic storms and substorms that also affect the electrojet current. Interestingly, only the normalized (with respect to the pre-flare level) deviations of daytime EEJ (and not the deviations alone) change linearly with the increases in the EUV and X-ray fluxes. These linear relationships break down during local morning hours when the E-region electric field approaches zero before reversal of polarity. This elicits that the response of EEJ strength corresponding to less-intense flares can be appropriately gauged only when the local time variation of the quiet time E-region zonal electric field is taken into account. The flare events enhanced the EEJ strength irrespective of normal or counter electrojet (CEJ) conditions that shows that solar flares change the E-region ionization density and not the electric field. In addition, the enhancements in the X-ray and EUV fluxes, for these flares occurring during this solar minimum period, are found to be significantly correlated as opposed to the solar maximum period, indicating the differences in the solar processes in different solar epochs.

Longitudinal variability of complexities associated with equatorial electrojet

NASA Astrophysics Data System (ADS)

Rabiu, A. B.; Ogunjo, S. T.; Fuwape, I. A.

2017-12-01

Equatorial electrojet indices obtained from ground based magnetometers at 6 representative stations across the magnetic equatorial belt for the year 2009 (mean annual sunspot number Rz = 3.1) were treated to nonlinear time series analysis technique to ascertain the longitudinal dependence of the chaos/complexities associated with the phenomena. The selected stations were along the magnetic equator in the South American (Huancayo, dip latitude -1.80°), African (Ilorin, dip latitude -1.82°; Addis Ababa, dip latitude - 0.18°), and Philippine (Langkawi, dip latitude -2.32°; Davao, dip latitude -1.02°; Yap, dip latitude -1.49°) sectors. The non-linear quantifiers engaged in this work include: Recurrence rate, determinism, diagonal line length, entropy, laminarity, Tsallis entropy, Lyapunov exponent and correlation dimension. Ordinarily the EEJ was found to undergo variability from one longitudinal representative station to another, with the strongest EEJ of about 192.5 nT at the South American axis at Huancayo. The degree of complexity in the EEJ was found to vary qualitatively from one sector to another. Probable physical mechanisms responsible for longitudinal variability of EEJ strength and its complexities were highlighted.

Spectral characteristics of geomagnetic field variations at low and equatorial latitudes

USGS Publications Warehouse

Campbell, W.H.

1977-01-01

Geomagnetic field spectra from eight standard observations at geomagnetic latitudes below 30?? were studied to determine the field characteristics unique to the equatorial region. Emphasis was placed upon those variations having periods between 5 min and 4 hr for a selection of magnetically quiet, average, and active days in 1965. The power spectral density at the equator was about ten times that the near 30?? latitude. The initial manifestation of the equatorial electrojet as evidenced by the east-west alignment of the horizontal field or the change in vertical amplitudes occurred below about 20?? latitude. Induced current effects upon the vertical component from which the Earth conductivity might be inferred could best be obtained at times and latitudes unaffected by the electrojet current. Values of about 1.6 ?? 103 mhos/m for an effective skin depth of 500-600 km were determined. The spectral amplitudes increased linearly with geomagnetic activity index, Ap. The spectral slope had a similar behavior at all latitudes. The slope changed systematically with Ap-index and showed a diurnal variation, centered on local noon, that changed form with geomagnetic activity.

Comparison of dayside current layers in Venus' ionosphere and earth's equatorial electrojet

NASA Technical Reports Server (NTRS)

Cole, Keith D.

1993-01-01

The major physical aspects of the equatorial electrojet of Earth and the dayside ionospheric current layers of Venus are compared, viz., the electric current intensity and total current, roles of electric field, pressure and gravity, diffusion time scales, and the Bernouille effect. The largest potential differences, of the order of 10 volts, horizontally across the dayside ionosphere of Venus, have important implications for possible dynamo action in the Venus ionosphere and the application of an electric field from the lower atmosphere or from the solar wind. An upper limit to the horizontal scale of vertical magnetic fields in the Venus ionosphere is estimated thereby for the first time. New upper limits on the velocity in, and thickness of, a possible S layer at Venus are presented. If an S layer exists, it is only for extreme conditions of the solar wind. A mechanism for formation of magnetic ropes in the Venus ionosphere is also proposed.

On the Occurrence of Afternoon Counter Electrojet Over Indian Longitudes During June Solstice in Solar Minimum

NASA Astrophysics Data System (ADS)

Pandey, Kuldeep; Sekar, R.; Anandarao, B. G.; Gupta, S. P.; Chakrabarty, D.

2018-03-01

Studies made earlier using ground-based observations of geomagnetic field over the Indian longitudes revealed that the occurrence of equatorial counter electrojet (CEJ) events in afternoon hours is more frequent during June solstice (May-June-July-August) in solar minimum than in other periods. In general, the June solstice solar minimum CEJ events occur between 1500 local time (LT) and 1800 LT with peak strength of about -10 nT at around 1600 LT. In order to understand the frequent occurrence of these CEJ events, an investigation is carried out using an equatorial electrojet model (Anandarao, 1976, https://doi.org/10.1029/GL003i009p00545) and the empirical vertical drift model by Fejer et al. (2008, https://doi.org/10.1029/2007JA012801). The strength, duration, peak value, and the occurrence time of CEJ obtained using electrojet model match remarkably well with the corresponding observation of average geomagnetic field variations. The occurrence of CEJ is found to be due to solar quiet (Sq) electric field in the westward direction which is manifested as downward drift in Fejer et al. (2008, https://doi.org/10.1029/2007JA012801) model output during 1500-1800 LT. Further, the occurrence of afternoon reversal of Sq electric field in this season is shown to be consistent with earlier studies from Indian sector. Therefore, this investigation provides explicit evidence for the role of westward Sq electric field on the generation of afternoon CEJ during June solstice in solar minimum periods over the Indian sector indicating the global nature of these CEJ events.

Equatorial Dynamics Observed by Rocket, Radar, and Satellite During the CADRE/MALTED Campaign. 1; Programmatics and small-scale fluctuations

NASA Technical Reports Server (NTRS)

Goldberg, Richard A.; Lehmacher, Gerald A.; Schmidlin, Frank J.; Fritts, David C.; Mitchell, J. D.; Croskey, C. L.; Friedrich, M.; Swartz, W. E.

1997-01-01

In August 1994, the Mesospheric and Lower Thermospheric Equatorial Dynamics (MALTED) Program was conducted from the Alcantara rocket site in northeastern Brazil as part of the International Guard Rocket Campaign to study equatorial dynamics, irregularities, and instabilities in the ionosphere. This site was selected because of its proximity to the geographic (2.3 deg S) and magnetic (approx. 0.5 deg S) equators. MALTED was concerned with planetary wave modulation of the diurnal tidal amplitude, which exhibits considerable amplitude variability at equatorial and subtropical latitudes. Our goals were to study this global modulation of the tidal motions where tidal influences on the thermal structure are maximum, to study the interaction of these tidal structures with gravity waves and turbulence at mesopause altitudes, and to gain a better understanding of dynamic influences and variability on the equatorial middle atmosphere. Four (two daytime and two nighttime) identical Nike-Orion payloads designed to investigate small-scale turbulence and irregularities were coordinated with 20 meteorological falling-sphere rockets designed to measure temperature and wind fields during a 10-day period. These in situ measurements were coordinated with observations of global-scale mesospheric motions that were provided by various ground based radars and the Upper Atmosphere Research Satellite (UARS) through the Coupling and Dynamics of Regions Equatorial (CADRE) campaign. The ground-based observatories included the Jicamarca radar observatory near Lima, Peru, and medium frequency (MF) radars in Hawaii, Christmas Island, and Adelaide. Since all four Nike-Orion flights penetrated and overflew the electrojet with apogees near 125 km, these flights provided additional information about the electrodynamics and irregularities in the equatorial ionospheric E region and may provide information on wave coupling between the mesosphere and the electrojet. Simultaneous with these flights, the CUPRI 50-MHz radar (Cornell University) provided local sounding of the electrojet region. A description of the campaign logistics and the measurements performed with the Nike-Orion instrumentation and their implications for turbulence due to gravity waves and tidal instability in the mesosphere and lower thermosphere (MLT) are presented here. From a study of electron density fluctuations measured by rocket probes, we have found evidence for equatorial mesospheric neutral-atmospheric turbulence between 85 and 90 km. Furthermore, falling-sphere data imply that gravity wave breaking was a source for this turbulence. Mean motions and the various planetary, tidal, and gravity wave structures and their coherence and variability are the subjects of a companion paper.

Equatorial dynamics observed by rocket, radar, and satellite during the CADRE/MALTED campaign 1. Programmatics and small-scale fluctuations

NASA Astrophysics Data System (ADS)

Goldberg, Richard A.; Lehmacher, Gerald A.; Schmidlin, Frank J.; Fritts, David C.; Mitchell, J. D.; Croskey, C. L.; Friedrich, M.; Swartz, W. E.

1997-11-01

In August 1994, the Mesospheric and Lower Thermospheric Equatorial Dynamics (MALTED) Program was conducted from the Alca‸ntara rocket site in northeastern Brazil as part of the International Guará Rocket Campaign to study equatorial dynamics, irregularities, and instabilities in the ionosphere. This site was selected because of its proximity to the geographic (2.3°S) and magnetic (~0.5°S) equators. MALTED was concerned with planetary wave modulation of the diurnal tidal amplitude, which exhibits considerable amplitude variability at equatorial and subtropical latitudes. Our goals were to study this global modulation of the tidal motions where tidal influences on the thermal structure are maximum, to study the interaction of these tidal structures with gravity waves and turbulence at mesopause altitudes, and to gain a better understanding of dynamic influences and variability on the equatorial middle atmosphere. Four (two daytime and two nighttime) identical Nike-Orion payloads designed to investigate small-scale turbulence and irregularities were coordinated with 20 meteorological falling-sphere rockets designed to measure temperature and wind fields during a 10-day period. These in situ measurements were coordinated with observations of global-scale mesospheric motions that were provided by various ground based radars and the Upper Atmosphere Research Satellite (UARS) through the Coupling and Dynamics of Regions Equatorial (CADRE) campaign. The ground-based observatories included the Jicamarca radar observatory near Lima, Peru, and medium frequency (MF) radars in Hawaii, Christmas Island, and Adelaide. Since all four Nike-Orion flights penetrated and overflew the electrojet with apogees near 125 km, these flights provided additional information about the electrodynamics and irregularities in the equatorial ionospheric E region and may provide information on wave coupling between the mesosphere and the electrojet. Simultaneous with these flights, the CUPRI 50-MHz radar (Cornell University) provided local sounding of the electrojet region. A description of the campaign logistics and the measurements performed with the Nike-Orion instrumentation and their implications for turbulence due to gravity waves and tidal instability in the mesosphere and lower thermosphere (MLT) are presented here. From a study of electron density fluctuations measured by rocket probes, we have found evidence for equatorial mesospheric neutral-atmospheric turbulence between 85 and 90 km. Furthermore, falling-sphere data imply that gravity wave breaking was a source for this turbulence. Mean motions and the various planetary, tidal, and gravity wave structures and their coherence and variability are the subjects of a companion paper.

ELF/VLF Wave Generation via HF Modulation of the Equatorial Electrojet at Arecibo Observatory

NASA Astrophysics Data System (ADS)

Flint, Q. A.; Moore, R. C.; Burch, H.; Erdman, A.; Wilkes, R.

2017-12-01

In this work we generate ELF/VLF waves by modulating the conductivity of the lower ionosphere using the HF heater at Arecibo. For many years, researchers have generated ELF/VLF waves using the powerful HF transmitters at HAARP, but few have attempted to do the same in the mid- to low- latitude region. While HAARP users have benefitted from the auroral electrojet, we attempt to exploit the equatorial electrojet to generate radio waves. On 31 July 2017, we transmitted at an HF frequency of 5.1 MHz (X-Mode) applying sinusoidal amplitude modulation in a step-like fashion from 0-5 kHz in 200 Hz steps over 10 seconds at 100% peak power to approximate a linear frequency ramp. We also transmitted 10-second-long fixed frequency tones spaced from 1 to 5 kHz. The frequency sweep is a helpful visual tool to identify generated waves, but is also used to determine optimal modulation frequencies for future campaigns. The tones allow us to perform higher SNR analysis. Ground-based B-field VLF receivers recorded the amplitude and phase of the generated radio waves. We employ time-of-arrival techniques to determine the altitude of the ELF/VLF signal source. In this paper, we present the initial analysis of these experimental results.

F2 layer characteristics and electrojet strength over an equatorial station

NASA Astrophysics Data System (ADS)

Adebesin, B. O.; Adeniyi, J. O.; Adimula, I. A.; Reinisch, B. W.; Yumoto, K.

2013-09-01

The data presented in this work describes the diurnal and seasonal variation in hmF2, NmF2, and the electrojet current strength over an African equatorial station during a period of low solar activity. The F2 region horizontal magnetic element H revealed that the Solar quiet Sq(H) daily variation rises from early morning period to maximum around local noon and falls to lower values towards evening. The F2 ionospheric current responsible for the magnetic field variations is inferred to build up at the early morning hours, attaining maximum strength around 1200 LT. The Sq variation across the entire months was higher during the daytime than nighttime. This is ascribed to the variability of the ionospheric parameters like conductivity and winds structure in this region. Seasonal daytime electrojet (EEJ) current strength for June solstice, March and September equinoxes, respectively had peak values ranging within 27-35 nT (at 1400 LT) , 30-40 nT (at 1200 LT) and 35-45 nT (at 1500 LT). The different peak periods of the EEJ strength were attributed to the combined effects of the peak electron density and electric field. Lastly, the EEJ strength was observed to be higher during the equinoxes than the solstice period.

The near-Earth magnetic field at 1980 determined from MAGSAT data

NASA Technical Reports Server (NTRS)

Langel, R. A.; Estes, R. H.

1984-01-01

Data from the MAGSAT spacecraft for November 1979 through April 1980 and from 91 magnetic observatories for 1978 through 1982 are used to derive a spherical harmonic model of the Earth's main magnetic field and its secular variation. Constant coefficients are determined through degree and order 13 and secular variation coefficients through degree and order 10. The first degree external terms and corresponding induced internal terms are given as a function of Dst. Preliminary modeling using separate data sets at dawn and dusk local time showed that the dusk data contains a substantial field contribution from the equatorial electrojet current. The final data set is selected first from dawn data and then augmented by dusk data to achieve a good geographic data distribution for each of three time periods: (1) November/December, 1979; (2) January/February; 1980; (3) March/April, 1980. A correction for the effects of the equatorial electrojet is applied to the dusk data utilized. The solution included calculation of fixed biases, or anomalies, for the observation data.

The near-earth magnetic field at 1980 determined from Magsat data

NASA Technical Reports Server (NTRS)

Langel, R. A.; Estes, R. H.

1985-01-01

Data from the Magsat spacecraft for November 1979 through April 1980 and from 91 magnetic observatories for 1978 through 1982 are used to derive a spherical harmonic model of the earth's main magnetic field and its secular variation. Constant coefficients are determined through degree and order 13 and secular variation coefficients through degree and order 10. The first degree external terms and corresponding induced internal terms are given as a function of Dst. Preliminary modeling using separate data sets at dawn and dusk local time showed that the dusk data contains a substantial field contribution from the equatorial electrojet current. The final data set is selected first from dawn data and then augmented by dusk data to achieve a good geographic data distribution for each of three time periods: (1) November/December, 1979; (2) January/February, 1980; (3) March/April, 1980. A correction for the effects of the equatorial electrojet is applied to the dusk data utilized. The solution included calculation of fixed biases, or anomalies, for the observation data.

Response of the Equatorial Ionosphere to the Geomagnetic DP 2 Current System

NASA Technical Reports Server (NTRS)

Yizengaw, E.; Moldwin, M. B.; Zesta, E.; Magoun, M.; Pradipta, R.; Biouele, C. M.; Rabiu, A. B.; Obrou, O. K.; Bamba, Z.; Paula, E. R. De

2016-01-01

The response of equatorial ionosphere to the magnetospheric origin DP 2 current system fluctuations is examined using ground-based multiinstrument observations. The interaction between the solar wind and fluctuations of the interplanetary magnetic field (IMF) Bz, penetrates nearly instantaneously to the dayside equatorial region at all longitudes and modulates the electrodynamics that governs the equatorial density distributions. In this paper, using magnetometers at high and equatorial latitudes, we demonstrate that the quasiperiodic DP 2 current system penetrates to the equator and causes the dayside equatorial electrojet (EEJ) and the independently measured ionospheric drift velocity to fluctuate coherently with the high-latitude DP 2 current as well as with the IMF Bz component. At the same time, radar observations show that the ionospheric density layers move up and down, causing the density to fluctuate up and down coherently with the EEJ and IMF Bz.

Latitude-dependent delay in the responses of the equatorial electrojet and Sq currents to X-class solar flares

NASA Astrophysics Data System (ADS)

Nogueira, Paulo A. B.; Abdu, Mangalathayil A.; Souza, Jonas R.; Denardini, Clezio M.; Barbosa Neto, Paulo F.; Serra de Souza da Costa, João P.; Silva, Ana P. M.

2018-01-01

We have analyzed low-latitude ionospheric current responses to two intense (X-class) solar flares that occurred on 13 May 2013 and 11 March 2015. Sudden intensifications, in response to solar flare radiation impulses, in the Sq and equatorial electrojet (EEJ) currents, as detected by magnetometers over equatorial and low-latitude sites in South America, are studied. In particular we show for the first time that a 5 to 8 min time delay is present in the peak effect in the EEJ, with respect that of Sq current outside the magnetic equator, in response to the flare radiation enhancement. The Sq current intensification peaks close to the flare X-ray peak, while the EEJ peak occurs 5 to 8 min later. We have used the Sheffield University Plasmasphere-Ionosphere Model at National Institute for Space Research (SUPIM-INPE) to simulate the E-region conductivity enhancement as caused by the flare enhanced solar extreme ultraviolet (EUV) and soft X-rays flux. We propose that the flare-induced enhancement in neutral wind occurring with a time delay (with respect to the flare radiation) could be responsible for a delayed zonal electric field disturbance driving the EEJ, in which the Cowling conductivity offers enhanced sensitivity to the driving zonal electric field.

Quiet Time Depression of the Equatorial Electrojet and Dynamics of the F-layer Ionosphere

NASA Astrophysics Data System (ADS)

Khadka, S.; Valladares, C. E.; Doherty, P.

2017-12-01

The depression of the equatorial electrojet (EEJ) is marked by a westward current due to streaming movement of laterally limited (±3°) charged particles in the ionospheric E region during the day along the magnetic equator. It is a complex low-latitude phenomenon and driven by various sources of electric fields associated with global neutral wind, solar tidal force, Interplanetary magnetic Field (IMF), etc. This unique physical property of the equatorial ionosphere holds a great promise for sorting out the governing mechanism of the dayside ionospheric electrodynamics and the onset of the enigmatic plasma structures in the ionospheric layers. Present study provides an overview of the special sequence of the longitudinal, seasonal, and occurrence rate variability of the depression of the EEJ, including its temporal variation, using data from an excellent chain of magnetic and ionospheric observatories along the low-latitude regions. A case and statistical study of the geomagnetically quiet time depression of EEJ strengths is presented using a pair of magnetometers, one located at the dip equator and another off the dip equator (±6° to ±9° away) in the American low-latitude regions. The significance of the variability of the depression of the EEJ current observed in the scenario of vertical drifts, sporadic E-layer, the equatorial F region plasma fountain, and height of the peak ionization in the F-layer, as well as GPS-TEC distributions, will be investigated.

(abstract) Dynamics of Meteor Trails Deposited in the Equatorial Electrojet

NASA Technical Reports Server (NTRS)

Chapin, Elaine; Kudeki, Erhan

1996-01-01

Previously we reported that the meteor echoes detected at the Jicamarca Radio Observatory exhibit some unusual properties. In summary, the echo durations are very long ..., radio wave scattering is non-specular ..., and the doppler spectra of the scattered signals contain components that are red-shifted ... immediately after the onset of the echoes.

Dependence of Lunar Tide of the Equatorial Electrojet on the Wintertime Polar Vortex, Solar Flux, and QBO

NASA Astrophysics Data System (ADS)

Siddiqui, T. A.; Yamazaki, Y.; Stolle, C.; Lühr, H.; Matzka, J.; Maute, A.; Pedatella, N.

2018-05-01

The lower atmospheric forcing effects on the ionosphere are particularly evident during extreme meteorological events known as sudden stratospheric warmings (SSWs). During SSWs, the polar stratosphere and ionosphere, two distant atmospheric regions, are coupled through the SSW-induced modulation of atmospheric migrating and nonmigrating tides. The changes in the migrating semidiurnal solar and lunar tides are the major source of ionospheric variabilities during SSWs. In this study, we use 55 years of ground-magnetometer observations to investigate the composite characteristics of the lunar tide of the equatorial electrojet (EEJ) during SSWs. These long-term observations allow us to capture the EEJ lunar tidal response to the SSWs in a statistical sense. Further, we examine the influence of solar flux conditions and the phases of quasi-biennial oscillation (QBO) on the lunar tide and find that the QBO phases and solar flux conditions modulate the EEJ lunar tidal response during SSWs in a similar way as they modulate the wintertime Arctic polar vortex. This work provides first evidence of modulation of the EEJ lunar tide due to QBO.

Optimal aperture synthesis radar imaging

NASA Astrophysics Data System (ADS)

Hysell, D. L.; Chau, J. L.

2006-03-01

Aperture synthesis radar imaging has been used to investigate coherent backscatter from ionospheric plasma irregularities at Jicamarca and elsewhere for several years. Phenomena of interest include equatorial spread F, 150-km echoes, the equatorial electrojet, range-spread meteor trails, and mesospheric echoes. The sought-after images are related to spaced-receiver data mathematically through an integral transform, but direct inversion is generally impractical or suboptimal. We instead turn to statistical inverse theory, endeavoring to utilize fully all available information in the data inversion. The imaging algorithm used at Jicamarca is based on an implementation of the MaxEnt method developed for radio astronomy. Its strategy is to limit the space of candidate images to those that are positive definite, consistent with data to the degree required by experimental confidence limits; smooth (in some sense); and most representative of the class of possible solutions. The algorithm was improved recently by (1) incorporating the antenna radiation pattern in the prior probability and (2) estimating and including the full error covariance matrix in the constraints. The revised algorithm is evaluated using new 28-baseline electrojet data from Jicamarca.

Equatorial electrojet responses to intense solar flares under geomagnetic disturbance time electric fields

NASA Astrophysics Data System (ADS)

Abdu, M. A.; Nogueira, P. A. B.; Souza, J. R.; Batista, I. S.; Dutra, S. L. G.; Sobral, J. H. A.

2017-03-01

Large enhancement in the equatorial electrojet (EEJ) current can occur due to sudden increase in the E layer density arising from solar flare associated ionizing radiations, as also from background electric fields modified by magnetospheric disturbances when present before or during a solar flare. We investigate the EEJ responses at widely separated longitudes during two X-class flares that occurred at different activity phases surrounding the magnetic super storm sequences of 28-29 October 2003. During the 28 October flare we observed intense reverse electrojet under strong westward electric field in the sunrise sector over Jicamarca. Sources of westward disturbance electric fields driving large EEJ current are identified for the first time. Model calculations on the E layer density, with and without flare, and comparison of the results between Jicamarca and Sao Luis suggested enhanced westward electric field due to the flare occurring close to sunrise (over Jicamarca). During the flare on 29 October, which occurred during a rapid AE recovery, a strong overshielding electric field of westward polarity over Jicamarca delayed an expected EEJ eastward growth due to flare-induced ionization enhancement in the afternoon. This EEJ response yielded a measure of the overshielding decay time determined by the storm time Region 2 field-aligned current. This paper will present a detailed analysis of the EEJ responses during the two flares, including a quantitative evaluation of the flare-induced electron density enhancements and identification of electric field sources that played dominant roles in the large westward EEJ at the sunrise sector over Jicamarca.

Statistical analysis of the correlation between the equatorial electrojet and the occurrence of the equatorial ionisation anomaly over the East African sector

NASA Astrophysics Data System (ADS)

Mungufeni, Patrick; Bosco Habarulema, John; Migoya-Orué, Yenca; Jurua, Edward

2018-06-01

This study presents statistical quantification of the correlation between the equatorial electrojet (EEJ) and the occurrence of the equatorial ionisation anomaly (EIA) over the East African sector. The data used were for quiet geomagnetic conditions (Kp ≤ 3) during the period 2011-2013. The horizontal components, H, of geomagnetic fields measured by magnetometers located at Addis Ababa, Ethiopia (dip lat. ˜ 1° N), and Adigrat, Ethiopia (dip lat. ˜ 6° N), were used to determine the EEJ using differential techniques. The total electron content (TEC) derived from Global Navigation Satellite System (GNSS) signals using 19 receivers located along the 30-40° longitude sector was used to determine the EIA strengths over the region. This was done by determining the ratio of TEC over the crest to that over the trough, denoted as the CT : TEC ratio. This technique necessitated characterisation of the morphology of the EIA over the region. We found that the trough lies slightly south of the magnetic equator (0-4° S). This slight southward shift of the EIA trough might be due to the fact that over the East African region, the general centre of the EEJ is also shifted slightly south of the magnetic equator. For the first time over the East African sector, we determined a threshold daytime EEJ strength of ˜ 40 nT that is mostly associated with prominent EIA occurrence during a high solar activity period. The study also revealed that there is a positive correlation between daytime EEJ and EIA strengths, with a strong positive correlation occurring during the period 13:00-15:00 LT.

ROCSAT and HF Doppler sounder observations of the DP2-type electric field during the global Pc5 magnetic pulsation event

NASA Astrophysics Data System (ADS)

Hashimoto, K. K.; Kikuchi, T.; Nagatsuma, T.; Tomizawa, I.

2016-12-01

During the stormtime Pc5 magnetic pulsations on 31 October 2003, we detected large amplitude oscillations in the ionospheric electric field with the HF Doppler sounders at midlatitude for 10 hours from 11 to 21 LT. Similar oscillations were recorded on the magnetometer data at high-to-equatorial latitudes with significant amplitude enhancement at the dayside equator. We deduced the equatorial electrojet (EEJ) by subtracting the low latitude Pc5 from the equatorial Pc5 and found that the midlatitude electric field (EF) is well correlated with the EEJ with correlation coefficients (0.80-0.95) and that the EEJ to EF ratio reached maximum at 11 LT and dramatically decreased until 18 LT in a function of cos0.6(solar zenith angle). With these observations, we suggest that the midlatitude electric field (EF) is associated with the DP2 type ionospheric currents transmitted from high latitude to the equator. It is to be noted that the EF is well correlated with the EEJ during the night after 18 LT, indicating that the Pc5 electric field is so strong as to drive equatorial electrojet in the nighttime ionosphere. Using the electric field measured by ROCSAT-1/IPEI, we confirmed that the Pc5 electric field in the mid- and low-latitude ionosphere is comparable to or even stronger than those observed by the HF Doppler sounders. High correlations between the ground- and satellite-based observations over 15 minutes indicate that the Pc5 electric field distribute uniform over 6500 km along the ROCSAT orbit which is consistent with the large-scale DP2 electric field.

The interplanetary and magnetospheric causes of extreme dB/dt at equatorial locations

NASA Astrophysics Data System (ADS)

Adebesin, Babatunde O.; Pulkkinen, Antti; Ngwira, Chigomezyo M.

2016-11-01

The 1 min resolution solar wind and geomagnetic data obtained from seven equatorial/low-latitude stations during four extreme geomagnetic activities are used to investigate the extreme dB/dt perturbations. Simulations of the magnetospheric-ionospheric environment were also performed for varying amplitudes of the solar proton density. Simulations were carried out using the Space Weather Modeling Framework/BATS-R-US + RCM model. Both the observations and simulations demonstrated that the appearance time of the extreme dB/dt perturbations at equatorial stations during disturbed conditions is instantaneous and equitable to those experienced at auroral regions yielding time lags of the order of a few seconds. We find that the rapid dB/dt enhancements are caused by the electric field of magnetospheric current origin, which is being enhanced by solar wind density and ram pressure variations and boosted by the equatorial electrojet. Our results indicate that the solar wind proton density variations could be used as a predictor of extreme dB/dt enhancement at equatorial latitudes.

Simulations of neutral wind shear effect on the equatorial ionosphere irregularities

NASA Astrophysics Data System (ADS)

Kim, J.; Chagelishvili, G.; Horton, W.

2005-12-01

We present numerical calculations of the large-scale electron density driven by the gradient drift instability in the daytime equatorial electrojet. Under two-fluid theory the linear analysis for kilometer scale waves lead to the result that all the perturbations are transformed to small scales through linear convection by shear and then damped by diffusion. The inclusion of the nonlinearity enables inverse energy cascade to provide energy to long scale. The feedback between velocity shear and nonlinearity keeps waves growing and leads to the turbulence. In strongly turbulent regime, the nonlinear states are saturated [1]. Since the convective nonlinearities are isotropic while the interactions of velocity shear with waves are anisotropic, the feedback do not necessarily enable waves to grow. The growth of waves are highly variable on k-space configuration [2]. Our simulations show that the directional relationship between vorticity of irregularities and shear are one of key factors. Thus during the transient period, the irregularities show the anisotropy of the vorticity power spectrum. We report the evolution of the power spectrum of the vorticity and density of irregularties and its anistropic nature as observed. The work was supported in part by the Department of NSF Grant ATM-0229863 and ISTC Grant G-553. C. Ronchi, R.N. Sudan, and D.T. Farley. Numerical simulations of large-scale plasma turbulece in teh day time equatorial electrojet. J. Geophys. Res., 96:21263--21279, 1991. G.D. Chagelishvili, R.G. Chanishvili, T.S. Hristov, and J.G. Lominadze. A turbulence model in unbounded smooth shear flows : The weak turbulence approach. JETP, 94(2):434--445, 2002.

Longitude-dependent lunar tidal modulation of the equatorial electrojet during stratospheric sudden warmings

NASA Astrophysics Data System (ADS)

Siddiqui, Tarique A.; Stolle, Claudia; Lühr, Hermann

2017-03-01

The effects of coupling between different layers of the atmosphere during Stratospheric Sudden Warming (SSW) events have been studied quite extensively in the past few years, and in this context large lunitidal enhancements in the equatorial ionosphere have also been widely discussed. In this study we report about the longitudinal variabilities in lunitidal enhancement in the equatorial electrojet (EEJ) during SSWs through ground and space observations in the Peruvian and Indian sectors. We observe that the amplification of lunitidal oscillations in EEJ is significantly larger over the Peruvian sector in comparison to the Indian sector. We further compare the lunitidal oscillations in both the sectors during the 2005-2006 and 2008-2009 major SSW events and during a non-SSW winter of 2006-2007. It is found that the lunitidal amplitude in EEJ over the Peruvian sector showed similar enhancements during both the major SSWs, but the enhancements were notably different in the Indian sector. Independent from SSW events, we have also performed a climatological analysis of the lunar modulation of the EEJ during December solstice over both the sectors by using 10 years of CHAMP magnetic measurements and found larger lunitidal amplitudes over the Peruvian sector confirming the results from ground magnetometer observations. We have also analyzed the semidiurnal lunar tidal amplitude in neutral temperature measurements from Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) at 110 km and found lesser longitudinal variability than the lunitidal amplitude in EEJ. Our results suggest that the longitudinal variabilities in lunitidal modulation of the EEJ during SSWs could be related to electrodynamics in the E region dynamo.

A Proxy Method for Estimation of EE-index using MAGDAS/CPMN Data

NASA Astrophysics Data System (ADS)

Ueno, T.; Yumoto, K.; Uozumi, T.; Numata, Y.; Group, M.

2008-12-01

EE-index (EDst, EU, and EL) is a new index proposed by Space Environment Research Center, Kyushu University (see Uozumi et al., 2008) to monitor temporal and long-term variations of the equatorial electrojet (EEJ). EU and EL mainly represent the range of EEJ and CEJ (equatorial counter electrojet) components, respectively. The baseline levels of EU and EL are obtained by averaging the H-component magnetic variations observed at the nightside (LT = 18-06) MAGDAS/CPMN stations along the magnetic equator. EDst, defined by Uozumi et al. (2008) fluctuates depending on the number of stations in the nightside sector (LT = 18-06). If the number is few, EDst may include some local fluctuations: the partial ring current component, substorm component and so on. Such local components cause some error in estimating the baseline level of EU or EL. Therefore, we need to use as many stations' data as possible in order to derive EU and EL properly. Pacific region is one of the most difficult areas to measure the magnetic field near the dip equator, because there are few islands. In the present paper, we developed a new method to use the data obtained from Ewa Beach (EWA; G. Lat. = 21.32N, G. Long. = 158.0W, Dip Lat. = 38.03), Hawaii, USA for estimation of EDst. EWA is not the equatorial station, but its nighttime H-component magnetic variations are found to be similar to those of Christmas Island (CXI; G. Lat. = 2.05N, G. Long. = 157.5W, Dip Lat. = 5.24), Kiribati. Data from EWA can be used as a proxy of that from CXI for monitoring temporal and long-term variations of the equatorial electrojet (EEJ) in real time. Acknowledgements: Authors appreciate Prof. Hisashi Utada of Earthquake Research Institute, University of Tokyo for supplying the magnetometer data from Christmas Island, Kiribati. Our deepest gratitude goes to all the members of the MAGDAS/CPMN project for their ceaseless support. Especially, we wish to thank the staffs of the observation stations: Dr. Baylie Damtie (Bahir Dar University, Ethiopia; AAB), Dr. Ronald Woodman Pollitt and Dr. Jose Ishitsuka (Instituto Geofisico del Peru; ANC), Fr. Daniel McNamara (Manila Observatory, Philippines; DAV), Ms. Lynn Kaisan (NOAA Pacific Tsunami Warning Center, HI, USA; EWA), Dr. Mazlan Othman and Dr. Mohd Fairos (National Space Agency, Ministry of Science, Technology and Innovation, Malaysia; LKW) and Prof. Archana Bhattacharya (Indian Institute of Geomagnetism, India; TIR) for their kind cooperation.

Equatorial ionospheric electrodynamics during solar flares

NASA Astrophysics Data System (ADS)

Zhang, Ruilong; Liu, Libo; Le, Huijun; Chen, Yiding

2017-05-01

Previous investigations on ionospheric responses to solar flares focused mainly on the photoionization caused by the increased X-rays and extreme ultraviolet irradiance. However, little attention was paid to the related electrodynamics. In this letter, we explored the equatorial electric field (EEF) and electrojet (EEJ) in the ionosphere at Jicamarca during flares from 1998 to 2008. It is verified that solar flares increase dayside eastward EEJ but decrease dayside eastward EEF, revealing a negative correlation between EEJ and EEF. The decreased EEF weakens the equatorial fountain effect and depresses the low-latitude electron density. During flares, the enhancement in the Cowling conductivity may modulate ionospheric dynamo and decrease the EEF. Besides, the decreased EEF is closely related to the enhanced ASY-H index that qualitatively reflects Region 2 field-aligned current (R2 FAC). We speculated that solar flares may also decrease EEF through enhancing R2 FAC that leads to an overshielding-like effect.

Investigating the effect of geomagnetic storm and equatorial electrojet on equatorial ionospheric irregularity over East African sector

NASA Astrophysics Data System (ADS)

Seba, Ephrem Beshir; Nigussie, Melessew

2016-11-01

The variability of the equatorial ionosphere is still a big challenge for ionospheric dependent radio wave technology users. To mitigate the effect of equatorial ionospheric irregularity on trans-ionospheric radio waves considerable efforts are being done to understand and model the equatorial electrodynamics and its connection to the creation of ionospheric irregularity. However, the effect of the East-African ionospheric electrodynamics on ionospheric irregularity is not yet well studied due to lack of multiple ground based instruments. But, as a result of International Heliophysical Year (IHY) initiative, which was launched in 2007, some facilities are being deployed in Africa since then. Therefore, recently deployed instruments, in the Ethiopian sector, such as SCINDA-GPS receiver (2.64°N dip angle) for TEC and amplitude scintillation index (S4) data and two magnetometers, which are deployed on and off the magnetic equator, data collected in the March equinoctial months of the years 2011, 2012, and 2015 have been used for this study in conjunction with geomagnetic storm data obtained from high resolution OMNI WEB data center. We have investigated the triggering and inhibition mechanisms for ionospheric irregularities using, scintillation index (S4), equatorial electrojet (EEJ), interplanetary electric field (IEFy), symH index, AE index and interplanetary magnetic field (IMF) Bz on five selected storm and two storm free days. We have found that when the eastward EEJ fluctuates in magnitude due to storm time induced electric fields at around noontime, the post-sunset scintillation is inhibited. All observed post-sunset scintillations in equinox season are resulted when the daytime EEJ is non fluctuating. The strength of noontime EEJ magnitude has shown direct relation with the strength of the post-sunset scintillations. This indicates that non-fluctuating EEJ stronger than 20 nT, can be precursor for the occurrence of the evening time ionospheric irregularities. It is also found that prolonged eastward undershielding electric field during the daytime intensified the daytime EEJ magnitude and resulted in strong post-sunset scintillations. We have also observed that the rate of change of BZ (i.e. electric field produced by Faraday's Induction law) and eastward IEFy around the PRE hour is nicely correlated with strong post-sunset scintillations. Moreover, discussions about the causes for the appearance and disappearance of ionospheric scintillation are presented in this paper.

Annual and semiannual variations of the geomagnetic field at equatorial locations

USGS Publications Warehouse

Campbell, W.H.

1981-01-01

For a year of quiet solar-activity level, geomagnetic records from American hemisphere observatories located between about 0?? and 30?? north geomagnetic latitude were used to compare the annual and semiannual variations of the geomagnetic field associated with three separate contributions: (a) the quiet-day midnight level, MDT; (b) the solar-quiet daily variation, Sq; (c) the quiet-time lunar semidiurnal tidal variation, L(12). Four Fourier spectral constituents (24, 12, 8, 6 h periods) of Sq were individually treated. All three orthogonal elements (H, D and Z) were included in the study. The MDT changes show a dominant semiannual variation having a range of about 7 gammas in H and a dominant annual variation in Z having a range of over 8 gammas. These changes seem to be a seasonal response to the nightside distortions by magnetospheric currents. There is a slow decrease in MDT amplitudes with increasing latitude. The Sq changes follow the patterns expected from an equatorial ionospheric dynamo electrojet current system. The dominant seasonal variations occur in H having a range of over 21 gammas for the 24 h period and over 12 gammas for the 12 h period spectral components. The higher-order components are relatively smaller in size. The Sq(H) amplitudes decrease rapidly with increasing latitude. Magnetospheric contributions to the equatorial Sq must be less than a few per cent of the observed magnitude. The L(12) variation shows the ionospheric electrojet features by the dominance of H and the rapid decrease in amplitude with latitude away from the equator. However, the seasonal variation range of over 7 gammas has a maximum in early February and minimum in late June that is not presently explainable by the known ionospheric conductivity and tidal behavior. ?? 1981.

Winds in the meteor zone over Trivandrum

NASA Astrophysics Data System (ADS)

Reddi, C. R.; Rajeev, K.; Ramakumar, Geetha

1991-04-01

The height profiles of the zonal and meridional wind obtained from the meteor wind radar data recorded at Trivandrum (8 deg 36 min N, 77 deg E) are presented. Large wind shears were found to exist in the meteor zone over Trivandrum. The profiles showed quasi-sinusoidal variations with altitude and vertical wavelength of the oscillation in the range 15-25 km. Further, there was a large day-to-day variability in the profiles obtained for the same local time on consecutive days. The results are discussed in the light of the winds due to tides and equatorial waves in the low latitudes. The implications of the large wind shears with reference to the local wind effects on the equatorial electrojet are outlined.

Achievements of ATS-6 beacon experiment over Indian sub-continent

NASA Technical Reports Server (NTRS)

Deshpande, M. R.; Rastogi, R. G.; Vats, H. O.; Sethia, G.; Chandra, H.; Davies, K.; Grubb, R. N.; Jones, J. E.

1978-01-01

The repositioning of the ATS-6 satellite at 34 deg E enabled the scientific community of India to use the satellite's radio beacon for ionospheric studies. Two scientific projects were undertaken. The objective of the first project was to map ionospheric electron content, range rate errors, traveling ionospheric phenomena, solar flare effect, and magnetic phenomena. The second project was aimed at studying geophysical phenomena associated with the equatorial electrojet. The principal results of these studies are described.

Impact of Stratospheric Sudden Warming on the Occurrence of the Equatorial Spread-F

NASA Astrophysics Data System (ADS)

Jose, Lijo; Vineeth, C.; Pant, T. K.

2017-12-01

This study presents the influence of stratospheric sudden warming (SSW) events in modulating the start time of the equatorial spread-F (ESF) through enhanced planetary wave (PW) activity during the winter months of the SSW years. The analysis based on the data from a digital ionosonde and proton precession magnetometer over Trivandrum (8.5°N, 77°E, 0.5°N dip lat.) revealed that the PWs of quasi-16 day periodicity influence the start time of the ESF to a significant extent during the SSW years. On the other hand, during a normal year such effect is not very evidently present. It has been observed that the quasi-16 day wave propagates to ionospheric dynamo region from the atmosphere below and modifies the electrodynamical processes like the equatorial electrojet and prereversal enhancement, which is more pronounced during both the SSW periods. Such a modification in the electrodynamics can modulate the equatorial plasma fountain and influence the F region neutral dynamics, which in turn can affect the occurrence of ESF by modifying the seeding conditions.

Equatorial ionospheric currents derived from MAGSAT data

NASA Technical Reports Server (NTRS)

Roy, M. (Principal Investigator)

1983-01-01

The MAGSAT data on the three component's of the geomagnetic field are subjected to ring current correction and crustal anomaly elimination near the dip equator. The evidence of a strong west east electrojet current below the satellite height (approximately 350 km) is confirmed. Strong evidence of east-west component of the field suggests the existence of a vertical current originating at the jet level and extending upwards. A model calculation shows that such a current system can explain the satellite data as well as the ground data.

GAIA modeling of electrodynamics in the lower ionosphere during a severe solar flare event

NASA Astrophysics Data System (ADS)

Matsumura, M.; Shiokawa, K.; Shinagawa, H.; Jin, H.; Fujiwara, H.; Miyoshi, Y.; Otsuka, Y.

2016-12-01

Recent studies indicated that the ionospheric F-region disturbances due to solar flare irradiance are controlled not only by photoionization but also by electrodynamical changes of the ionosphere [Liu et al., 2007; Qian et al., 2012]. The electric field changes during solar flare events occur mainly in the E-region due to the X-ray flux enhancement, and in the equatorial counter electrojet regions the eastward electric field turns into westward below 107-km altitude [Manju and Viswanathan, 2005]. The TIME-GCM model has been used to investigate the flare-related electrodynamics of the ionosphere [Qian et al., 2012]. However, the model did not consider the flare effects at altitudes below 97 km due to the ionospheric lower boundary of the model. On the other hand, the GAIA model [Jin et al., 2011] can simulate electron density variations and electrodynamics around and below 100 km because the model does not have the limitation of the lower boundary. We have improved the GAIA model to incorporate the Flare Irradiance Spectral Model (FISM) [Chamberlin et al., 2007; 2008] to understand the global response of the whole ionosphere including E and D regions to the solar flares. We have performed a simulation for the X17 flare event of October 28, 2003, and have showed that soft X-ray considerably enhances conductivity even at an altitude of 80 km. We will report its effect on the ionospheric electric field and the equatorial electrojet currents.

The Sidebands of the Equatorial Electrojet: General Characteristic of the Westward Currents, as Deduced From CHAMP

NASA Astrophysics Data System (ADS)

Zhou, Yun-Liang; Lühr, Hermann; Alken, Patrick

2018-02-01

Based on 5 years (2001-2005) of magnetic field measurements made by the CHAMP satellite, latitudinal profiles of the equatorial electrojet (EEJ) have been derived. This study provides a comprehensive characterization of the reverse current EEJ sidebands. These westward currents peak at ±5° quasi-dipole latitude with typical amplitudes of 35% of the main EEJ. The diurnal amplitude variation is quite comparable with that of the EEJ. Similarly to the EEJ, the intensity is increasing with solar EUV flux, but with a steeper slope, indicating that not only the conductivity plays a role. For the longitude distribution we find, in general, larger amplitudes in the Western than in the Eastern Hemisphere. It is presently a common understanding that the reverse current EEJ sidebands are generated by eastward zonal winds at altitudes above about 120 km. In particular, a positive vertical gradient of wind speed generates westward currents at magnetic latitudes outside of 2° dip latitude. Interesting information about these features can be deduced from the sidebands' tidal characteristics. The longitudinal variation of the amplitude is dominated by a wave-1 pattern, which can primarily be attributed to the tidal components SPW1 and SW3. In case of the hemispheric amplitude differences these same two wave-1 components dominate. The ratio between sideband amplitude and main EEJ is largely controlled by the tidal features of the EEJ. The longitudinal patterns of the latitude, where the sidebands peak, resemble to some extent those of the amplitude. Current densities become larger when the peaks move closer to the magnetic equator.

An evidence for prompt electric field disturbance driven by changes in the solar wind density under northward IMF Bz condition

DOE PAGES

Rout, Diptiranjan; Chakrabarty, D.; Sekar, R.; ...

2016-05-26

Before the onset of a geomagnetic storm on 22 January 2012 (Ap = 24), an enhancement in solar wind number density from 10/cm 3 to 22/cm 3 during 0440–0510 UT under northward interplanetary magnetic field (IMF Bz) condition is shown to have enhanced the high-latitude ionospheric convection and also caused variations in the geomagnetic field globally. Some conspicuous changes in ΔX are observed not only at longitudinally separated low-latitude stations over Indian (prenoon), South American (midnight), Japanese (afternoon), Pacific (afternoon) and African (morning) sectors but also at latitudinally separated stations located over high and middle latitudes. The latitudinal variation ofmore » the amplitude of the ΔX during 0440–0510 UT is shown to be consistent with the characteristics of prompt penetration electric field disturbances. Most importantly, the density pulse event caused enhancements in the equatorial electrojet strength and the peak height of the F layer (h mF 2) over the Indian dip equatorial sector. Furthermore, the concomitant enhancements in electrojet current and F layer movement over the dip equator observed during this space weather event suggest a common driver of prompt electric field disturbance at this time. Such simultaneous variations are found to be absent during magnetically quiet days. In the absence of significant change in solar wind velocity and magnetospheric substorm activity, these observations point toward perceptible prompt electric field disturbance over the dip equator driven by the overcompression of the magnetosphere by solar wind density enhancement.« less

Global scale equatorial ionization anomaly (EIA) response to magnetospheric disturbances based on the May-June 1987 SUNDIAL-coordinated observations

NASA Astrophysics Data System (ADS)

Abdu, M. A.; Walker, G. O.; Reddy, B. M.; de Paula, E. R.; Sobral, J. H. A.; Fejer, B. G.

1993-07-01

Equatorial ionization anomaly (EIA) responses to magnetospheric disturbances have been investigated using ionosonde and geomagnetic data sets obtained for different longitude sectors during the 9-day (28 May-7 June) globally-coordinated SUNDIAL 87 campaign. Attention is focused on the EIA response features of the two magnetically most-disturbed days of the campaign window, 29 May and 6 June. Anomalous EIA inhibition and development were simultaneously observed at widely separated (American and Asian) longitude sectors, accompanied respectively by events of morning electrojet reversal and evening partial ring current development. A numerical model of the low-latitude ionosphere has been used to quantify the role that a disturbance electric field could play in the observed EIA response features. The implications of the results on the global low-latitude disturbance electric field pattern is discussed.

Source and identification of heavy ions in the equatorial F layer.

NASA Technical Reports Server (NTRS)

Hanson, W. B.; Sterling, D. L.; Woodman, R. F.

1972-01-01

Further evidence is presented to show that the interpretation of some Ogo 6 retarding potential analyzer (RPA) results in terms of ambient Fe+ ions is correct. The Fe+ ions are observed only within dip latitudes of plus or minus 30 deg, and the reason for this latitudinal specificity is discussed in terms of a low-altitude source region and F region diffusion and electrodynamic drift. It is shown that the polarization field associated with the equatorial electrojet will raise ions to 160 km out of a chemical source region below 100 km but it will do so only in a narrow region centered on the dip equator. Subsequent vertical ExB drift, coupled with motions along the magnetic fields, can move the ions to greater heights and greater latitudes. There should be a resultant fountain of metallic ions rising near the equator that subsequently descends back to the E and D layers at tropical latitudes.

Solar quiet day ionospheric source current in the West African region.

PubMed

Obiekezie, Theresa N; Okeke, Francisca N

2013-05-01

The Solar Quiet (Sq) day source current were calculated using the magnetic data obtained from a chain of 10 magnetotelluric stations installed in the African sector during the French participation in the International Equatorial Electrojet Year (IEEY) experiment in Africa. The components of geomagnetic field recorded at the stations from January-December in 1993 during the experiment were separated into the source and (induced) components of Sq using Spherical Harmonics Analysis (SHA) method. The range of the source current was calculated and this enabled the viewing of a full year's change in the source current system of Sq.

Corrigendum to "Characteristics of equatorial electrojet derived from Swarm satellites" [Adv. Space Res. 59 (2017) 1526-1538

NASA Astrophysics Data System (ADS)

Thomas, Neethal; Vichare, Geeta; Sinha, A. K.

2018-02-01

The authors regret that a typographical error in Abstract and Section 5 should be corrected. Figure 7b of Thomas et al. [2017] presents the variation of total westward return current (y-axis) with total eastward forward current (x-axis). The slopes vary between 1 and 0.1. This indicates that ratio of total westward return currents to total eastward forward current vary between 0.1 to 1. However in Abstract and Section 5, the authors have erroneously written the ratio as between "total eastward forward current to total westward return current".

Sq field characteristics at Phu Thuy, Vietnam, during solar cycle 23: comparisons with Sq field in other longitude sectors

NASA Astrophysics Data System (ADS)

Pham Thi Thu, H.; Amory-Mazaudier, C.; Le Huy, M.

2011-01-01

Quiet days variations in the Earth's magnetic field (the Sq current system) are compared and contrasted for the Asian, African and American sectors using a new dataset from Vietnam. This is the first presentation of the variation of the Earth's magnetic field (Sq), during the solar cycle 23, at Phu Thuy, Vietnam (geographic latitudes 21.03° N and longitude: 105.95° E). Phu Thuy observatory is located below the crest of the equatorial fountain in the Asian longitude sector of the Northern Hemisphere. The morphology of the Sq daily variation is presented as a function of solar cycle and seasons. The diurnal variation of Phu Thuy is compared to those obtained in different magnetic observatories over the world to highlight the characteristics of the Phu Thuy observations. In other longitude sectors we find different patterns. At Phu Thuy the solar cycle variation of the amplitude of the daily variation of the X component is correlated to the F.10.7 cm solar radiation (~0.74). This correlation factor is greater than the correlation factor obtained in two observatories located at the same magnetic latitudes in other longitude sectors: at Tamanrasset in the African sector (~0.42, geographic latitude ~22.79) and San Juan in the American sector (~0.03, geographic latitude ~18.38). At Phu Thuy, the Sq field exhibits an equinoctial and a diurnal asymmetry: - The seasonal variation of the monthly mean of X component exhibits the well known semiannual pattern with 2 equinox maxima, but the X component is larger in spring than in autumn. Depending of the phase of the sunspot cycle, the maximum amplitude of the X component varies in spring from 30 nT to 75 nT and in autumn from 20 nT to 60 nT. The maximum amplitude of the X component exhibits roughly the same variation in both solstices, varying from about ~20 nT to 50 nT, depending on the position into the solar cycle. - In all seasons, the mean equinoctial diurnal Y component has a morning maximum Larger than the afternoon minimum i.e. the equivalent current flow over a day is more southward than northward. During winter, the asymmetry is maximum, it erases the afternoon minimum. At the Gnangara observatory, in Asian Southern Hemisphere, the diurnal Y pattern is opposite and the current flow is more northward. It seems that in the Asian sector, the northern and southern Sq current cells both contribute strongly to the equatorial electrojet. The pattern is different in the African and American sectors where the northern Sq current cell contribution to the equatorial electrojet is smaller than the southern one. These observations can explain the unexpected maximum of amplitude of the equatorial electrojet observed in the Asian sector where the internal field is very large. During winter the Y component flow presents an anomaly, it is always southward during the whole day and there is no afternoon northward circulation.

The climatology of low latitude ionospheric currents derived from CHAMP observations

NASA Astrophysics Data System (ADS)

Stolle, Claudia; Alken, Patrik

2010-05-01

The multi-year data base of magnetic field and ionospheric measurements from the CHAMP satellite contain enormous potential to investigate the behaviour and the origin of currents in the E and F region ionosphere. Special advantage is drawn from the satellite's near polar orbit and the full data coverage over all longitudes and local times. This paper will present findings about two prominent features of the low latitude ionosphere: equatorial plasma irregularities and the equatorial electrojet (EEJ). Equatorial plasma irregularities (commonly known as "bubbles") severely disturb the post sunset F region ionosphere and cause the strongest radio wave scintillations globally during solar maximum years. Using CHAMP vector magnetic field data, it was possible for the first time to show on a long term basis that equatorial plasma irregularities have signatures in all components of the magnetic field. The first ever global climatology of the occurrence rate of these magnetic signatures has been compiled. Such a data base of disturbed orbits is especially useful for core and crustal magnetic field modellers. The magnetic field observations of CHAMP, Ørsted, and SAC-C were employed to develop a climatological model of the EEJ. Measurements of the EEJ and empirical values from electron density and thermospheric density and winds have in addition enabled the development of a climatological model of the equatorial electric field. These results provide excellent opportunity to investigate the seasonal/longitudinal characteristics of the EEJ and the influence of atmospheric waves on E region dynamics.

Geomagnetically Induced Currents Around the World During the 17 March 2015 Storm

NASA Technical Reports Server (NTRS)

Carter, B. A.; Yizengaw, E.; Pradipta, R.; Weygand, J. M.; Piersanti, M.; Pulkkinen, Antti Aleksi; Moldwin, M. B.; Norman, R.; Zhang, K.

2016-01-01

Geomagnetically induced currents (GICs) represent a significant space weather issue for power grid and pipeline infrastructure, particularly during severe geomagnetic storms. In this study, magnetometer data collected from around the world are analyzed to investigate the GICs caused by the 2015 St. Patricks Day storm. While significant GIC activity in the high-latitude regions due to storm time substorm activity is shown for this event, enhanced GIC activity was also measured at two equatorial stations in the American and Southeast Asian sectors. This equatorial GIC activity is closely examined, and it is shown that it is present both during the arrival of the interplanetary shock at the storm sudden commencement (SSC) in Southeast Asia and during the main phase of the storm approximately 10 h later in South America. The SSC caused magnetic field variations at the equator in Southeast Asia that were twice the magnitude of those observed only a few degrees to the north, strongly indicating that the equatorial electrojet (EEJ) played a significant role. The large equatorial magnetic field variations measured in South America are also examined, and the coincident solar wind data are used to investigate the causes of the sudden changes in the EEJ approximately 10 h into the storm. From this analysis it is concluded that sudden magnetopause current increases due to increases in the solarwind dynamic pressure, and the sudden changes in the resultant magnetospheric and ionospheric current systems, are the primary drivers of equatorial GICs.

Pulsed Artificial Electrojet Generation

NASA Astrophysics Data System (ADS)

Papadopoulos, K.

2008-12-01

Traditional techniques for generating low frequency signals in the ULF/ELF range (.1-100 Hz) and rely on ground based Horizontal Electric Dipole (HED) antennas. It is, furthermore, well known that a Vertical Electric Dipole (VED) is by more than 50 dB more efficient than a HED with the same dipole current moment. However, the prohibitively long length of VED antennas in the ELF/ULF range coupled with voltage limitations due to corona discharge in the atmosphere make them totally impracticable. In this paper we discuss a novel concept, inspired by the physics of the equatorial electrojet, that allows for the conversion of a ground based HED to a VED in the E-region of the equatorial ionosphere with current moment comparable to the driving HED. The paper focuses in locations near the dip-equator, where the earth's magnetic is in predominantly in the horizontal direction. The horizontal electric field associated with a pulsed HED drives a large Hall current in the ionospheric E-region, resulting in a vertical current. It is shown that the pulsed vertical current in the altitude range 80-130 km, driven by a horizontal electric field of, approximately, .1 mV/m at 100 km altitude, is of the order of kA. This results in a pulsed VED larger than 106 A-m. Such a pulsed VED will drive ELF/ULF pulses with amplitude in excess of .1 nT at a lateral range larger than few hundred kilometers. This is by three orders of magnitude larger than the one expected by a HED with comparable current moment. The paper will conclude with the description of a sneak-through technique that allows for creating pulsed electric fields in the ionosphere much larger than expected from steady state oscillatory HED antennas.

Understanding the Longitudinal Variability of Equatorial Electrodynamics using integrated Ground- and Space-based Observations

NASA Astrophysics Data System (ADS)

Yizengaw, E.; Moldwin, M.; Zesta, E.

2015-12-01

The currently funded African Meridian B-Field Education and Research (AMBER) magnetometer array comprises more than thirteen magnetometers stationed globally in the vicinity of geomagnetic equator. One of the main objectives of AMBER network is to understand the longitudinal variability of equatorial electrodynamics as function of local time, magnetic activity, and season. While providing complete meridian observation in the region and filling the largest land-based gap in global magnetometer coverage, the AMBER array addresses two fundamental areas of space physics: first, the processes governing electrodynamics of the equatorial ionosphere as a function of latitude (or L-shell), local time, longitude, magnetic activity, and season, and second, ULF pulsation strength at low/mid-latitude regions and its connection with equatorial electrojet and density fluctuation. The global AMBER network can also be used to augment observations from space-based instruments, such us the triplet SWARM mission and the upcoming ICON missions. Thus, in coordination with space-based and other ground-based observations, the AMBER magnetometer network provides a great opportunity to understand the electrodynamics that governs equatorial ionosphere motions. In this paper we present the longitudinal variability of the equatorial electrodynamics using the combination of instruments onboard SWARM and C/NOFS satellites and ground-based AMBER network. Both ground- and pace-based observations show stronger dayside and evening sector equatorial electrodynamics in the American and Asian sectors compared to the African sector. On the other hand, the African sector is home to stronger and year-round ionospheric bubbles/irregularities compared to the American and Asian sectors. This raises the question if the evening sector equatorial electrodynamics (vertical drift), which is believed to be the main cause for the enhancement of Rayleigh-Taylor (RT) instability growth rate, is stronger in the American sector and weaker in the African sector - why are the occurrence and amplitude of equatorial irregularities stronger in the African sector?

Formation and Identification of Counter Electrojet (CEJ) 1. Department of Physics and Astronomy, University of Nigeria, Nsukka, Nigeria. 2. Centre for Basic Space Science, University of Nigeria, Nsukka, Nigeria. 3. Department of Physics, University of Agriculture, Makurdi, Nigeria 1.Corresponding Author: franciscaokeke@yahoo.com OR francisca.okeke@unn.edu.ng

NASA Astrophysics Data System (ADS)

Okeke, F. N.; Okoro, E. C.; Isikwue, B. C.; Hanson, E.

2012-12-01

This study investigates the possible occurrence of counter equatorial electrojet (CEJ) and a quicker method for identification of CEJ. Data from a chain of magnetic observatories of World Data Center for Geomagnetism in Tokyo, Japan, was employed. It is strikingly interesting to observe that most CEJ occurred from morning through nighttime, with almost the same pattern of dHin depression. In Ascension Island [ASC], Huancayo [HUA] and Pondicherry [PND], most changes in horizontal component were found to be less than zero, which reveals an indication of full CEJ. Partial CEJ occurrences were observed during some hours at these stations where changes in horizontal component were found to be greater than zero. It is suggested that IMF turning north indicates CEJ, hence storm effects could also be attributed to CEJ existence. Some of our new findings are at variance with results of some previous workers; hence further work is suggested for further clarification. A quick method of easy identification of CEJ is suggested.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Roussel-Dupre, R.; Fitzgerald, T.J.; Symbalisty, E.

In this paper the authors report on recent radar measurements taken during the month of October 1994 with the LDG HF radar in the Ivory Coast, Africa as part of the International Equatorial Electrojet Year. The purpose of this experimental effort in part was to study the effects of thunderstorms on the ionosphere. At the same time, the authors decided to carry out a set of experiments of an exploratory nature to look for echoes that could potentially arise from ionization produced in the mesosphere. The two leading candidates for producing transient ionization in the mesosphere are meteors and high-altitudemore » discharges. Each is discussed in the context of these measurements.« less

Solar quiet day ionospheric source current in the West African region

PubMed Central

Obiekezie, Theresa N.; Okeke, Francisca N.

2012-01-01

The Solar Quiet (Sq) day source current were calculated using the magnetic data obtained from a chain of 10 magnetotelluric stations installed in the African sector during the French participation in the International Equatorial Electrojet Year (IEEY) experiment in Africa. The components of geomagnetic field recorded at the stations from January–December in 1993 during the experiment were separated into the source and (induced) components of Sq using Spherical Harmonics Analysis (SHA) method. The range of the source current was calculated and this enabled the viewing of a full year’s change in the source current system of Sq. PMID:25685434

Continuous day-time time series of E-region equatorial electric fields derived from ground magnetic observatory data

NASA Astrophysics Data System (ADS)

Alken, P.; Chulliat, A.; Maus, S.

2012-12-01

The day-time eastward equatorial electric field (EEF) in the ionospheric E-region plays an important role in equatorial ionospheric dynamics. It is responsible for driving the equatorial electrojet (EEJ) current system, equatorial vertical ion drifts, and the equatorial ionization anomaly (EIA). Due to its importance, there is much interest in accurately measuring and modeling the EEF. However, there are limited sources of direct EEF measurements with full temporal and spatial coverage of the equatorial ionosphere. In this work, we propose a method of estimating a continuous day-time time series of the EEF at any longitude, provided there is a pair of ground magnetic observatories in the region which can accurately track changes in the strength of the EEJ. First, we derive a climatological unit latitudinal current profile from direct overflights of the CHAMP satellite and use delta H measurements from the ground observatory pair to determine the magnitude of the current. The time series of current profiles is then inverted for the EEF by solving the governing electrodynamic equations. While this method has previously been applied and validated in the Peruvian sector, in this work we demonstrate the method using a pair of magnetometers in Africa (Samogossoni, SAM, 0.18 degrees magnetic latitude and Tamanrasset, TAM, 11.5 degrees magnetic latitude) and validate the resulting EEF values against the CINDI ion velocity meter (IVM) instrument on the C/NOFS satellite. We find a very good 80% correlation with C/NOFS IVM measurements and a root-mean-square difference of 9 m/s in vertical drift velocity. This technique can be extended to any pair of ground observatories which can capture the day-time strength of the EEJ. We plan to apply this work to more observatory pairs around the globe and distribute real-time equatorial electric field values to the community.

Characteristics of Equatorial and Low-Latitude Plasma Irregularities as Investigated Using a Meridional Chain of Radio Experiments Over India

NASA Astrophysics Data System (ADS)

Sripathi, S.; Sreekumar, Sreeba; Banola, S.

2018-05-01

The characteristics of equatorial and low-latitude plasma irregularities are studied using a meridional chain of ionosondes located at Tirunelveli, Hyderabad, and Allahabad and Global Positioning System (GPS) receivers located at Tirunelveli, Mumbai, and Nagpur during the year 2015. The observations suggest that while stronger and longer duration of equatorial spread F irregularities occur in the postsunset sector during equinoxes and winter, they occur mostly in the postmidnight sector during summer, while being weaker in strength and shorter in duration. Further, the postsunset spread F occurs first at the equator followed by their occurrence at low latitudes during equinoxes and winter, while the postmidnight spread F during summer are found to be stronger and earlier at low latitudes followed by their occurrence at the equator. While plasma irregularities are observed by both the ionosondes and GPS receivers during both equinoxes and winter, it is observed mostly by the ionosondes during summer. The results further strengthen the view that while postsunset spread F in equinoxes and winter are generated by the equatorial processes, postmidnight spread F in the summer may be linked to the nonequatorial processes. The results also reemphasize the asymmetric distribution of plasma irregularities or scintillations during equinoxes wherein vernal (autumn) equinox shows more intense plasma irregularities than autumn (vernal) equinox during certain years. Also, using a larger data set of simultaneous GPS and ionosonde observations, the relationship of prereversal enhancement and strength of L-band scintillations with solar flux, Kp index, and equatorial electrojet strength are examined.

Equatorial E Region Electric Fields and Sporadic E Layer Responses to the Recovery Phase of the November 2004 Geomagnetic Storm

NASA Astrophysics Data System (ADS)

Moro, J.; Resende, L. C. A.; Denardini, C. M.; Xu, J.; Batista, I. S.; Andrioli, V. F.; Carrasco, A. J.; Batista, P. P.; Schuch, N. J.

2017-12-01

Equatorial E region electric fields (EEFs) inferred from coherent radar data, sporadic-E (Es) layers observed from a digital ionosonde data, and modeling results are used to study the responses of the equatorial E region over São Luís (SLZ, 2.3°S, 44.2°W, -7° dip angle), Brazil, during the super storm of November 2004. The EEF is presented in terms of the zonal (Ey) and vertical (Ez) components in order to analyze the corresponding characteristics of different types of Es seen in ionograms and simulated with the E region ionospheric model. We bring out the variabilities of Ey and Ez components with storm time changes in the equatorial E region. In addition, some aspects of the electric fields and Es behavior in three cases of weak, very weak, and strong Type II occurrences during the recovery phase of the geomagnetic storm are discussed. The connection between the enhanced occurrence and suppressions of the Type II irregularities and the q-type Es (Esq) controlled by electric fields, with the development or disruption of the blanketing sporadic E (Esb) layers produced by wind shear mechanism, is also presented. The mutual presence of Esq along with the Esb occurrences is a clear indicator of the secular drift of the magnetic equator and hence that of the equatorial electrojet (EEJ) over SLZ. The results show evidence about the EEJ and Es layer electrodynamics and coupling during geomagnetic disturbance time electric fields.

Electric currents in E-like planetary ionospheres

NASA Technical Reports Server (NTRS)

Cole, K. D.

1990-01-01

In this paper an MHD approach is used to consider the conduction of electric current in a lightly ionized gas, taking into account the gradients of pressure in the ion and electron gases, in addition to the electric field. The coefficients of electrical conductivity are found for each driver of current. New expressions for the components of heat dissipation associated with each driver of current are developed, which are fully consistent with kinetic theory. The relationship of the results to those obtained by kinetic theory is discussed. New components of currents associated with planetary equatorial electrojets are found. A new diffusion equation for magnetic induction is found, applicable in E-like regions of planetary ionospheres, and stellar photospheres.

Study of the Equatorial and Low-Latitude Electrodynamic and Ionospheric Disturbances During the 22-23 June 2015 Geomagnetic Storm Using Ground-Based and Spaceborne Techniques

NASA Astrophysics Data System (ADS)

Astafyeva, E.; Zakharenkova, I.; Hozumi, K.; Alken, P.; Coïsson, P.; Hairston, M. R.; Coley, W. R.

2018-03-01

We use a set of ground-based instruments (Global Positioning System receivers, ionosondes, magnetometers) along with data of multiple satellite missions (Swarm, C/NOFS, DMSP, GUVI) to analyze the equatorial and low-latitude electrodynamic and ionospheric disturbances caused by the geomagnetic storm of 22-23 June 2015, which is the second largest storm in the current solar cycle. Our results show that at the beginning of the storm, the equatorial electrojet (EEJ) and the equatorial zonal electric fields were largely impacted by the prompt penetration electric fields (PPEF). The PPEF were first directed eastward and caused significant ionospheric uplift and positive ionospheric storm on the dayside, and downward drift on the nightside. Furthermore, about 45 min after the storm commencement, the interplanetary magnetic field (IMF) Bz component turned northward, leading to the EEJ changing sign to westward, and to overall decrease of the vertical total electron content (VTEC) and electron density on the dayside. At the end of the main phase of the storm, and with the second long-term IMF Bz southward turn, we observed several oscillations of the EEJ, which led us to conclude that at this stage of the storm, the disturbance dynamo effect was already in effect, competing with the PPEF and reducing it. Our analysis showed no significant upward or downward plasma motion during this period of time; however, the electron density and the VTEC drastically increased on the dayside (over the Asian region). We show that this second positive storm was largely influenced by the disturbed thermospheric conditions.

Equatorial E region electric fields at the dip equator: 2. Seasonal variabilities and effects over Brazil due to the secular variation of the magnetic equator

NASA Astrophysics Data System (ADS)

Moro, J.; Denardini, C. M.; Resende, L. C. A.; Chen, S. S.; Schuch, N. J.

2016-10-01

In this work, the seasonal dependency of the E region electric field (EEF) at the dip equator is examined. The eastward zonal (Ey) and the daytime vertical (Ez) electric fields are responsible for the overall phenomenology of the equatorial and low-latitude ionosphere, including the equatorial electrojet (EEJ) and its plasma instability. The electric field components are studied based on long-term backscatter radars soundings (348 days for both systems) collected during geomagnetic quiet days (Kp ≤ 3+), from 2001 to 2010, at the São Luís Space Observatory (SLZ), Brazil (2.33°S, 44.20°W), and at the Jicamarca Radio Observatory (JRO), Peru (11.95°S, 76.87°W). Among the results, we observe, for the first time, a seasonal difference between the EEF in these two sectors in South America based on coherent radar measurements. The EEF is more intense in summer at SLZ, in equinox at JRO, and has been highly variable with season in the Brazilian sector compared to the Peruvian sector. In addition, the secular variation on the geomagnetic field and its effect on the EEJ over Brazil resulted that as much farther away is the magnetic equator from SLZ, later more the EEJ is observed (10 h LT) and sooner it ends (16 h LT). Moreover, the time interval of type II occurrence decreased significantly after the year 2004, which is a clear indication that SLZ is no longer an equatorial station due to the secular variation of the geomagnetic field.

Auroral electrojets and evening sector electron dropouts at synchronous orbit

NASA Technical Reports Server (NTRS)

Erickson, K. N.; Winckler, J. R.

1973-01-01

Evidence is presented in support of the concept that, during magnetospheric substorms, ionospheric auroral electrojet currents are directly coupled to the proton partial ring current in the outer magnetosphere. It has been found that for sufficiently isolated substorms the timing of the start of the electron dropout and of its maximum depression is in good agreement with the start and maximum of electrojet activity as indicated by the auroral electrojet index. This correlation suggests a direct coupling between the electrojet currents and the proton partial ring current.

Theoretical Studies of Low Frequency Instabilities in the Ionosphere. Final Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dimant, Y. S.

2003-08-20

The objective of the current project is to provide a theoretical basis for better understanding of numerous radar and rocket observations of density irregularities and related effects in the lower equatorial and high-latitude ionospheres. The research focused on: (1) continuing efforts to develop a theory of nonlinear saturation of the Farley-Buneman instability; (2) revision of the kinetic theory of electron-thermal instability at low altitudes; (3) studying the effects of strong anomalous electron heating in the high-latitude electrojet; (4) analytical and numerical studies of the combined Farley-Bunemadion-thermal instabilities in the E-region ionosphere; (5) studying the effect of dust charging in Polarmore » Mesospheric Clouds. Revision of the kinetic theory of electron thermal instability at low altitudes.« less

Ionospheric very low frequency transmitter

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kuo, Spencer P.

2015-02-15

The theme of this paper is to establish a reliable ionospheric very low frequency (VLF) transmitter, which is also broad band. Two approaches are studied that generate VLF waves in the ionosphere. The first, classic approach employs a ground-based HF heater to directly modulate the high latitude ionospheric, or auroral electrojet. In the classic approach, the intensity-modulated HF heater induces an alternating current in the electrojet, which serves as a virtual antenna to transmit VLF waves. The spatial and temporal variations of the electrojet impact the reliability of the classic approach. The second, beat-wave approach also employs a ground-based HFmore » heater; however, in this approach, the heater operates in a continuous wave mode at two HF frequencies separated by the desired VLF frequency. Theories for both approaches are formulated, calculations performed with numerical model simulations, and the calculations are compared to experimental results. Theory for the classic approach shows that an HF heater wave, intensity-modulated at VLF, modulates the electron temperature dependent electrical conductivity of the ionospheric electrojet, which, in turn, induces an ac electrojet current. Thus, the electrojet becomes a virtual VLF antenna. The numerical results show that the radiation intensity of the modulated electrojet decreases with an increase in VLF radiation frequency. Theory for the beat wave approach shows that the VLF radiation intensity depends upon the HF heater intensity rather than the electrojet strength, and yet this approach can also modulate the electrojet when present. HF heater experiments were conducted for both the intensity modulated and beat wave approaches. VLF radiations were generated and the experimental results confirm the numerical simulations. Theory and experimental results both show that in the absence of the electrojet, VLF radiation from the F-region is generated via the beat wave approach. Additionally, the beat wave approach generates VLF radiations over a larger frequency band than by the modulated electrojet.« less

Vernal Point and Plate Tectonics: Indo-Australian

NASA Astrophysics Data System (ADS)

Chavez C, Teodosio; Chavez-Sumarriva, Israel; Chavez S, Nadia

2013-04-01

A precession coordinate system (eccentricity -100Ka, obliquity -40Ka and precession -25Ka) developed by Milankovicht was the precession of the equinoxes, where the vernal point retrograde 1° every 72 years approximately and enter (0°) into the Aquarius constellation on March 20, 1940. On earth this entry was verify through: a) stability of the magnetic equator in the south central zone of Peru and in the north zone of Bolivia, b) the greater intensity of equatorial electrojet (EEJ) in Peru and Bolivia since 1940. The vernal point is a maximum conductivity sensitive axis in the EEJ given at the equinoxes. There was a relationship between the equatorial electrojet - magnetic equator - crust, and besides there was a long history of studies of coupling between earthquake-ionosphere that can be founded in the following revisions: Liperovsky et al. (1990); Gaivoronskaya (1991); Liperovsky et al. (1992); Parrot et al. (1993); Pulinets et al. (1994) and Gokhberg et al. (1995). In IUGG (2007), Cusco was propose as a prime meridian (72° W == 0°) that was parallel to the Andes; the objective was to synchronize the earth sciences phenomena (e.g. geology, geophysics, etc.). The coordinate system had the vernal point from meridian (72° W == 0°) and March 20, 1940. The retrograde movement of the vernal point was the first precessional degree (2012 = 1940 + 72); from the new prime meridian (72° W == 0°) it has obtained the opposite meridian (72° E == 180°). The first precessional degree (2012) near the meridian (72 ° E) was related to the date of April 11, 2012 where a massive earthquake of 8.6 on the Richter scale, followed by several aftershocks, one of 8.2 degrees struck Indonesia with epicenter near Banda Aceh. Five months after that date, Matthias Delescluse et.al (2012), Han Yue et.al (2012), and Fred F. Pollitz et.al, (2012), explained that the two violent earthquakes would be evidence of a break in the Indo-Australian Plate Tectonics caused earthquakes around the world. It is noted that in one of the opposite meridian there was a correlation between the vernal point and the indo-australian plate.

Relationship between lunar tidal enhancements in the equatorial electrojet and tropospheric eddy heat flux during stratospheric sudden warmings

NASA Astrophysics Data System (ADS)

Siddiqui, T. A.; Yamazaki, Y.; Stolle, C.; Lühr, H.; Matzka, J.

2017-12-01

A number of studies in recent years have reported about the lunar tidal enhancements in the equatorial electrojet (EEJ) from ground- and space-based magnetometer measurements during stratospheric sudden warming (SSW) events. In this study, we make use of the ground magnetometer recordings at Huancayo observatory in Peru for the years 1978 - 2013 to derive a relationship between the lunar tidal enhancements in the EEJ and tropospheric eddy heat fluxes at 100 hPa during the SSW events. Tropospheric eddy heat fluxes are used to quantify the amount of wave activity entering the stratosphere. Anomalously large upward wave activity is known to precede the polar vortex breakdown during SSWs. We make use of the superposed epoch analysis method to determine the temporal relations between lunar tidal enhancements and eddy heat flux anomalies during SSWs, in order to demonstrate the causal relationship between these two phenomena. We also compare the lunar tidal enhancements and eddy heat flux anomalies for vortex split and for vortex displaced SSWs. It is found that larger lunar tidal enhancements are recorded for vortex split events, as compared to vortex displaced events. This confirms earlier observation; larger heat flux anomalies are recorded during vortex split SSW events than the heat flux anomalies during vortex displaced SSW events. Further, the temporal relations of lunar tidal enhancements in the EEJ have been compared separately for both the QBO phases and with the phases of the moon with respect to the central epoch of SSWs by means of the superposed epoch analysis approach. The EEJ lunar tidal enhancements in the east phase of QBO are found to be larger than the lunar tidal enhancements in the west phase of QBO. The phase of moon relative to the central SSW epoch also affects the lunar tidal enhancement in the EEJ. It is found that the lunar tidal enhancements are significantly larger when the day of new or full moon lies near the central SSW epoch, as compared to cases when new or full moon occur further away from the central SSW epoch.

Geophysics Integrated Studies in the Sun Earth System: A Cooperative Project of Vietnam, Europe, and Africa

NASA Astrophysics Data System (ADS)

Amory-Mazaudier, C.; et al.

2006-11-01

lhminh@igp.ncst.ac.vn The Hanoi Institute of Geophysics (Vietnam) will participate to international Heliophysical Year. This paper presents Vietnam‘s participation into this International cooperative project : the Vietnamese network of magnetometers, meteorological stations, ionosondes and GPS receivers involved in campaigns of measurements, the research field selected for the training of young Vietnamese scientists, and the Institutes involve in this training. This paper also presents some particularities of geophysical parameters in Vietnam : the strong amplitude of the equatorial electrojet observed by satellite data and confirmed by magnetic observations at the ground level presented for the first time to the international community, the monsoon signature etc. Finally the differences between the Asian sector and the African sector lead to the development of comparative studies between Asia and Africa.

The convection electrojet and the substorm electrojet

NASA Astrophysics Data System (ADS)

Kamide, Y.; Nakamura, R.

1996-06-01

Enhancements in the auroral electrojets associated with magnetospheric substorms result from those in either the electric field or the ionospheric conductivities, or both. Their relative importance varies significantly, even during a single substorm, depending on the location as well as on the substorm phases. It is predicted that different parts of the electrojets tend to respond in different ways to substorm activity. The unprecedented, unique opportunity for CLUSTER spacecraft observations of electric/magnetic fields and precipitating particles, combined with radar measurements of ionospheric quantities and with ground magnetometers, will provide us with crucial information regarding the physical nature of the separation between the electric field-dominant'' and conductivity-dominant'' auroral electrojets. This study also discusses the implications of these two auroral-electrojet components in terms of solar wind-magnetosphere-ionosphere interactions. Acknowledgements. This study is supported in part by the Ministry of Education, Science, Sports, and Culture in Japan, under a Grant-in-Aid for Scientific Research (Category B). Topical Editor D. Alcaydé thanks M. Lockwood and N. J. Fox for their help in evaluating this paper.--> Correspondence to: Y. Kamide-->

First Application of the Zeeman Technique to Remotely Measure Auroral Electrojet Intensity From Space

NASA Technical Reports Server (NTRS)

Yee, J. H.; Gjerloev, J.; Wu, D.; Schwartz, M. J.

2017-01-01

Using the O2 118 GHz spectral radiance measurements obtained by the Microwave Limb Sounder instrument on board the Aura spacecraft, we demonstrate that the Zeeman effect can be used to remotely measure the magnetic field perturbations produced by the auroral electrojet near the Hall current closure altitudes. Our derived current-induced magnetic field perturbations are found to be highly correlated with those coincidently obtained by ground magnetometers. These perturbations are also found to be linearly correlated with auroral electrojet strength. The statistically derived polar maps of our measured magnetic field perturbation reveal a spatial-temporal morphology consistent with that produced by the Hall current during substorms and storms. With today's technology, a constellation of compact, low-power, high spectral-resolution cubesats would have the capability to provide high precision and spatiotemporal magnetic field samplings needed for auroral electrojet measurements to gain insights into the spatiotemporal behavior of the auroral electrojet system.

Towards developing an analytical procedure of defining the equatorial electrojet for correcting satellite magnetic anomaly data

NASA Technical Reports Server (NTRS)

Ravat, Dhananjay; Hinze, William J.

1991-01-01

Analysis of the total magnetic intensity MAGSAT data has identified and characterized the variability of ionospheric current effects as reflected in the geomagnetic field as a function of longitude, elevation, and time (daily as well as monthly variations). This analysis verifies previous observations in POGO data and provides important boundary conditions for theoretical studies of ionospheric currents. Furthermore, the observations have led to a procedure to remove these temporal perturbations from lithospheric MAGSAT magnetic anomaly data based on 'along-the-dip-latitude' averages from dawn and dusk data sets grouped according to longitudes, time (months), and elevation. Using this method, high-resolution lithospheric magnetic anomaly maps have been prepared of the earth over a plus or minus 50 deg latitude band. These maps have proven useful in the study of the structures, nature, and processes of the lithosphere.

The impacts of the St. Patrick's Day superstorm on selected technologies

NASA Astrophysics Data System (ADS)

Carter, B. A.; Yizengaw, E.; Lin, C. S.; Pradipta, R.; Norman, R.; Tseng, T.; Bennett, J.; Bishop, R. L.; Weygand, J. M.; Francis, M.; Terkildsen, M. B.; Groves, K. M.; Caton, R. G.; Tripathi, N.; Zhang, K.

2015-12-01

In the past, significant research efforts have been directed towards understanding how severe geomagnetic storms affect the near-Earth space environment. From this research, we have learned that many technologies are affected by these severe space weather events. The 2015 St. Patrick's Day geomagnetic storm has provided a great opportunity to analyze three selected space weather phenomena that adversely impact modern technologies; (1) Geomagnetically Induced Currents (GICs), (2) increased thermospheric mass density, and (3) the occurrence of Equatorial Plasma Bubbles (EPBs). The serious effects of GICs on power grids in the high-latitude regions is well known. Recent research has indicated that the equatorial region is also susceptible to increased GIC activity due to the equatorial electrojet. Thus, an examination of the equatorial magnetometer data during the St. Patrick's Day storm will be presented. It is also well understood that during geomagnetic storms, the thermospheric mass density at a given altitude increases due to the increase in Joule heating in the high-latitude regions. As a consequence of this, low-Earth orbiting satellites and space debris experience increased atmospheric drag. Changes in atmospheric drag causes orbits to be perturbed, resulting in less accurate orbit predictions. An investigation of the orbits of several low-Earth orbiting satellites will be presented and discussed in the context of collision avoidance, as part of the ongoing space debris problem. Finally, Equatorial Plasma Bubbles (EPBs) are a common phenomenon in the nighttime low-latitude ionosphere. EPBs are known to cause random fluctuations (i.e., scintillations) in the amplitude and phase of trans-ionospheric radio signals. While EPBs have been reported during both geomagnetically quiet and disturbed periods, research clearly indicates that the occurrence of EPBs is dependent on the geomagnetic activity level. The occurrence of EPBs around the world will be presented using data from both ground- and space-based EPB detection platforms. The results will be interpreted in the context of the disturbed ionosphere-thermosphere state and the subsequent impacts on the Generalized Rayleigh-Taylor plasma instability during the St. Patrick's Day storm.

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.

The complete spectrum of the equatorial electrojet related to solar tides: CHAMP observations

NASA Astrophysics Data System (ADS)

Lühr, H.; Manoj, C.

2013-08-01

Based on 10 yr of magnetic field measurements by the CHAMP satellite we draw a detailed picture of the equatorial electrojet (EEJ) tidal variations. For the first time the complete EEJ spectrum related to average solar tides has been compiled. A large fraction of the resulting spectrum is related to the switch on/off of the EEJ between day and night. This effect has carefully been considered when interpreting the results. As expected, largest amplitudes are caused by the migrating tides representing the mean diurnal variation. Higher harmonics of the daily variations show a 1/f fall-off in amplitude. Such a spectrum is required to represent the vanishing of the EEJ current at night. The migrating tidal signal exhibits a distinct annual variation with large amplitudes during December solstice and equinox seasons but a depression by a factor of 1.7 around June-July. A rich spectrum of non-migrating tidal effects is deduced. Most prominent is the four-peaked longitudinal pattern around August. Almost 90% of the structure can be attributed to the diurnal eastward-propagating tide DE3. In addition the westward-propagating DW5 is contributing to wave-4. The second-largest non-migrating tide is the semi-diurnal SW4 around December solstice. It causes a wave-2 feature in satellite observations. The three-peaked longitudinal pattern, often quoted as typical for the December season, is significantly weaker. During the months around May-June a prominent wave-1 feature appears. To first order it represents a stationary planetary wave SPW1 which causes an intensification of the EEJ at western longitudes beyond 60° W and a weakening over Africa/India. In addition, a prominent ter-diurnal non-migrating tide TW4 causes the EEJ to peak later, at hours past 14:00 local time in the western sector. A particularly interesting non-migrating tide is the semi-diurnal SW3. It causes largest EEJ amplitudes from October through December. This tidal component shows a strong dependence on solar flux level with increasing amplitudes towards solar maximum. We are not aware of any previous studies mentioning this behaviour of SW3. The main focus of this study is to present the observed EEJ spectrum and its relation to tidal driving. For several of the identified spectral components we cannot offer convincing explanations for the generation mechanisms.

Three-dimensional Electromagnetic Modeling of the Hawaiian Swell

NASA Astrophysics Data System (ADS)

Avdeev, D.; Utada, H.; Kuvshinov, A.; Koyama, T.

2004-12-01

An anomalous behavior of the geomagnetic deep sounding (GDS) responses at the Honolulu geomagnetic observatory has been reported by many researchers. Kuvshinov et al (2004) found that the predicted GDS Dst C-response does not match the experimental data -- 10-20% disagreement occurs for all periods of 2 to 30 days, qualitatively implying a more resistive, rather than conductive, structure beneath the Hawaiian Islands. Simpson et al. (2000) found that the GDS Sq C-response at the Honolulu observatory is about 4 times larger than that at a Hawaii island site, again suggesting a more resistive (than elsewhere around) structure beneath the observatory. Constable and Heinson (2004, http://mahi.ucsd.edu/Steve/swell.pdf), presenting a 2-D interpretation of the magnetotelluric (MT) and GDS responses recently obtained at 7 seafloor sites to the south of the Hawaii Islands, concluded that the dataset require the presence of a narrow conducting plume just beneath the islands. The main motivation of our work is to reveal the reason of the anomalous behavior of the Honolulu response. Obviously, the cause may be due to heterogeneity of either the conductivity or the source field. We examine this problem in some detail with reference to the Constable and Heinson's seafloor dataset, as well as the available dataset from the Honolulu observatory. To address the problem we apply numerical modeling using the three-dimensional (3-D) forward modeling code of Avdeev et al. (1997, 2002). With this code we simulate various regional 3-D conductivity models that may produce EM responses that better fit the experimental datasets, at least qualitatively. Also, to explain some features of the experimental long-period GDS responses we numerically studied a possible effect in the responses caused by the equatorial electrojet. Our 3-D modeling results show that, in particular: (1) The GDS responses are better explained by models with a resistive lithosphere whereas the MT data are better fit by models without one; (2) A conductive plume under the Hawaiian Islands may not be required by the MT and GDS datasets considered; (3) An equatorial electrojet might affect the imaginary part of the GDS responses at periods of 2 h and more; (4) The anomalous large value of 0.4 observed in the real part of the seafloor GDS responses still cannot be explained by the 3-D models considered. It seems to require more complicated models.

Characteristics of the equatorial plasma drifts as obtained by using Canadian Doppler ionosonde over southern tip of India

NASA Astrophysics Data System (ADS)

Sripathi, S.; Singh, Ram; Banola, S.; Sreekumar, Sreeba; Emperumal, K.; Selvaraj, C.

2016-08-01

We present here characteristics of the Doppler drift measurements over Tirunelveli (8.73°N, 77.70°E; dip 0.5°N), an equatorial site over Southern India using Doppler interferometry technique of Canadian ionosonde. Three-dimensional bulk motions of the scatterers as reflected from the ionosphere are derived by using Doppler interferometry technique at selected frequencies using spaced receivers arranged in magnetic E-W and N-S directions. After having compared with Lowell's digisonde drifts at Trivandrum, we studied the temporal and seasonal variabilities of quiet time drifts for the year 2012. The observations showed higher vertical drifts during post sunset in the equinox followed by winter and summer seasons. The comparison of Doppler vertical drifts with the drifts obtained from (a) virtual height and (b) Fejer drift model suggests that Doppler vertical drifts are relatively higher as compared to the drifts obtained from model and virtual height methods. Further, it is seen that vertical drifts exhibited equinoctial asymmetry in prereversal enhancement quite similar to such asymmetry observed in the spread F in the ionograms and GPS L band scintillations. The zonal drifts, on the other hand, showed westward during daytime with mean drifts of ~150-200 m/s and correlated well with equatorial electrojet strength indicating the role of E region dynamo during daytime, while they are eastward during nighttime with mean drifts of ~100 m/s resembling F region dynamo process. Also, zonal drifts showed large westward prior to the spread F onset during autumn equinox than vernal equinox, suggesting strong zonal shears which might cause equinoctial asymmetry in spread F.

A case study of Ionospheric storm effects during long-lasting southward IMF Bz driven geomagnetic storm

NASA Astrophysics Data System (ADS)

Liu, J., Sr.

2014-12-01

Multiple instrumental observations including GPS TEC, foF2 and hmF2 from ionosondes, vertical ion drift measurements from C/NOFS, magnetometer data and far-ultraviolet airglow measured by TIMED/GUVI are used to investigate the profound ionospheric disturbances at mid- and low-latitudes during the 14-17 July 2012 geomagnetic storm event, which was featured by prolonged southward interplanetary geomagnetic field component for about 30 hours below -10 nT. In the East Asian/Australian sector, latitudinal profile of TEC variations in the main phase were characterized by three bands of increments and separated by weak depressions in the Equatorial Ionospheric Anomaly (EIA) crest regions, which were caused by the combined effects of disturbance dynamo electric fields (DDEF) and equatorward neutral winds. In the recovery phase, strong inhibition of EIA occurred and the summer crest of EIA disappeared on 16 July due to the combined effects of intrusion of neutral composition disturbance zone as shown by the TIME/GUVI O/N2 measurements and long-lasting daytime westward DDEF inferred from the equatorial electric electrojet (EEJ) observations. The transit time of DDEF over the dip equator from westward to eastward is around 2200 LT. In the American longitude, the salient ionospheric disturbances in the summer hemisphere were characterized by daytime periodical intrusion of negative phase for three consecutive days in the recovery phase, preceded by storm enhanced density (SED) plume in the initial phase. In addition, multiple short-lived prompt penetration electric fields (PPEF) appeared during stable southward IMF Bz in the recovery phase and were responsible for enhanced the EIA and equatorial ionospheric uplift around sunset.

A case study of ionospheric storm effects during long-lasting southward IMF Bz-driven geomagnetic storm

NASA Astrophysics Data System (ADS)

Liu, Jing; Liu, Libo; Nakamura, Takuji; Zhao, Biqiang; Ning, Baiqi; Yoshikawa, A.

2014-09-01

Multiple instrumental observations including GPS total electron content (TEC), foF2 and hmF2 from ionosondes, vertical ion drift measurements from Communication/Navigation Outage Forecasting System, magnetometer data, and far ultraviolet airglow measured by Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics/Global Ultraviolet Imager (TIMED/GUVI) are used to investigate the profound ionospheric disturbances at midlatitude and low latitude during the 14-17 July 2012 geomagnetic storm event, which was featured by prolonged southward interplanetary geomagnetic field component for about 30 h below -10 nT. In the East Asian/Australian sector, latitudinal profile of TEC variations in the main phase were characterized by three bands of increments and separated by weak depressions in the equatorial ionospheric anomaly (EIA) crest regions, which were caused by the combined effects of disturbance dynamo electric fields (DDEF) and equatorward neutral winds. In the recovery phase, strong inhibition of EIA occurred and the summer crest of EIA disappeared on 16 July due to the combined effects of intrusion of neutral composition disturbance zone as shown by the TIMED/GUVI O/N2 measurements and long-lasting daytime westward DDEF inferred from the equatorial electrojet observations. The transit time of DDEF over the dip equator from westward to eastward is around 2200 LT. In the American longitude, the salient ionospheric disturbances in the summer hemisphere were characterized by daytime periodical intrusion of negative phase for three consecutive days in the recovery phase, preceded by storm-enhanced density plume in the initial phase. In addition, multiple short-lived prompt penetration electric fields appeared during stable southward interplanetary magnetic field (IMF) Bz in the recovery phase and were responsible for enhanced the EIA and equatorial ionospheric uplift around sunset.

Characterization of the Auroral Electrojet and the Ambient and Modified D Region for HAARP Using Long-Path VLF Diagnostics

DTIC Science & Technology

2001-03-15

order to characterize the auroral electrojet and the ambient and modified D-region directly above and near the HAARP (High Frequency Active Auroral...near the HAARP facility and along the west coast of Alaska. In addition in order to characterize the auroral electrojet on a continental scale and to...United States and Canada. Data from the complete array of D-region diagnostic systems was acquired during a number of Fall and Spring HAARP campaigns

Effect of the solar wind and interplanetary magnetic field parameter variations to the enhancement and dynamics of auroral electrojet during superstrong magnetic storms

NASA Astrophysics Data System (ADS)

Solovyev, Stepan; Boroev, Roman; Moiseyev, Alexey; Du, Aimin; Yumoto, Kiyohumi

According to the global ground geomagnetic observations in the six meridian chains and analysis of satellite measurements the auroral elektrojet features at various conditions in the solar wind (SW) and the IMF: during a sharp rise of dynamic pressure up to 15-60 nPa and variations in the intensity and sign of the IMF Bz-component to -40 --50 nT. The data obtained during super strong magnetic storms of October 29-30, 2003, November 20-21, 2003, November 07-08, 2004 and November 09-10, 2004 (Dst = -300 --400 nT) are analysed. The following scientific results are obtained: • It is shown that a sharp increase of the SW dynamic pressure (Pd) and the excitation of a sudden impulse (SC) during IMF Bz negative (Bz<0) leads to a simultaneous (with accuracy 1-3 min) increase of DP2 current system and the intensity of the western elec-trojet (Jw) in a broad sector of longitudes and expansion of Jw to the pole up to the polar cap latitudes with the velocity of VN = 1-3 km/s. • It is found that during the sharp rise of Pd up to 60 nPa for IMF Bz positive (Bz>0) 35 nT is the amplification of eastward magnetopause currents and DP2 current system are observed. Strengthening and dynamics of the westward electrojet is not observed. • We find that during periods of intensity growth of negative values of IMF Bz to -50 nT within a few hours there is a shift of the centers of auroral electrojet to the equator up to latitudes about 10-20 degrees along the meridian with a speed of 1-4 km/s with a simultaneous amplifications of Jw repeated in 1-2 hours with a duration of 1-2 hours at latitudes from low to auroral latitudes and with a possible extension to electrojets up to the polar cap latitudes and the abrupt extension of the subsequent Jw electrojets localization region by azimuth. • It is shown that after the electrojet displacement to the equator during southward direc-tion of IMF Bz and enhancement of the SW electric field the IMF Bz turning to the north accompanied by the poleward expansion of Jw electrojet at a speed of 1 km/s in a wide range of longitudes is observed. • It is found that the electrojet expansion to the pole during superstorms often occurs up to the polar cap latitudes due to the extension of the precipitating particles and increased ionospheric conductivity region from the low and auroral latitudes, but not due to the movement of localized westward electrojet along the meridian, as is the case in the substorm. The report discusses the possible causes of the dynamics of auroral electrojets under different geophysical conditions. This work was supported by the Presidium of the Russian Academy of Sciences (program 16, part 3), by the RFBR grant No.09-05-98546 and also supported by the SB RAS project No.69.

Electric field formation in three different plasmas: A fusion reactor, arc discharge, and the ionosphere

NASA Astrophysics Data System (ADS)

Lee, Kwan Chul

2017-11-01

Three examples of electric field formation in the plasma are analyzed based on a new mechanism driven by ion-neutral collisions. The Gyro-Center Shift analysis uses the iteration of three equations including perpendicular current induced by the momentum exchange between ions and neutrals when there is asymmetry over the gyro-motion. This method includes non-zero divergence of current that leads the solution of time dependent state. The first example is radial electric field formation at the boundary of the nuclear fusion device, which is a key factor in the high-confinement mode operation of future fusion reactors. The second example is the reversed rotation of the arc discharge cathode spot, which has been a mysterious subject for more than one hundred years. The third example is electric field formations in the earth's ionosphere, which are important components of the equatorial electrojet and black aurora. The use of one method that explains various examples from different plasmas is reported, along with a discussion of the applications.

Investigating the auroral electrojets using Swarm

NASA Astrophysics Data System (ADS)

Smith, Ashley; Macmillan, Susan; Beggan, Ciaran; Whaler, Kathy

2016-04-01

The auroral electrojets are large horizontal currents that flow within the ionosphere in ovals around the polar regions. They are an important aspect of space weather and their position and intensity vary with solar wind conditions and geomagnetic activity. The electrojet positions are also governed by the Earth's main magnetic field. During more active periods, the auroral electrojets typically move equatorward and become more intense. This causes a range of effects on Earth and in space, including geomagnetically induced currents in power transmission networks, disturbance to radio communications and increased drag on satellites due to expansion of the atmosphere. They are also indicative of where the aurora are visible. Monitoring of the auroral electrojets in the pre-satellite era was limited to the network of ground-based magnetic observatories, from which the traditional AE activity indices are produced. These suffer in particular from the stations' poor distribution in position and so this motivates the use of satellite-based measurements. With polar low-Earth orbit satellites carrying magnetometers, all latitudes can be sampled with excellent resolution. This poster presents an investigation using Swarm's magnetometer data to detect the electrojets as the spacecraft move above them. We compare and contrast two approaches, one which uses vector data and the other which uses scalar data (Hamilton and Macmillan 2013, Vennerstrom and Moretto, 2013). Using ideas from both approaches we determine the oval positions and intensities from Swarm and earlier satellites. The variation in latitude and intensity with solar wind conditions, geomagnetic activity and secular variation of the main field is investigated. We aim to elucidate the relative importance of these factors. Hamilton, B. and Macmillan, S., 2013. Investigation of decadal scale changes in the auroral oval positions using Magsat and CHAMP data. Poster at IAGA 12th Scientific Assembly, 2013. http://nora.nerc.ac.uk/503037/ Vennerstrom, S. and Moretto, T., 2013. Monitoring auroral electrojets with satellite data. Space Weather, VOL. 11, 509-519, doi:10.1002/swe.20090

A case-study of the evolution of polar-cap currents and auroral electrojets during polar geomagnetic disturbances with IMS magnetometer data

NASA Technical Reports Server (NTRS)

Iijima, T.; Kim, J. S.; Sugiura, M.

1984-01-01

The development of the polar cap current and the relationship of that development to the evolution of auroral electrojets during individual polar geomagnetic disturbances is studied using 1 min average data from US-Canada IMS network stations and standard magnetograms from sites on the polar cap and in the auroral zone. It is found that even when the auroral electrojet activity is weak, polar cap currents producing fields of magnitude approximately 100-200 nT almost always exist. A normal convection current system exists quasi-persistently in the polar cap during extended quiet or weakly disturbed periods of auroral electrojet activity. After one such period, some drastic changes occur in the polar cap currents, which are followed by phases of growth, expansion, and recovery. Polar cap currents cannot all be completely ascribed to a single source mechanism.

RAL Low-cost Ionosonde System

NASA Astrophysics Data System (ADS)

Stamper, R.; Davis, C. J.; Bradford, W. J.; Hapgood, M. A.; McCrea, I. W.

2009-04-01

Ionosondes continue to be important for the study of the ionosphere; they are relatively cheap and simple to install and operate, so can be distributed widely across the globe; they can give information on plasma density, structure and motion; their direct measurements of electron densities are also important for calibrating other more complicated observation methods such as incoherent scatter radar, satellite beacon tomography and radio occultation. The low cost of sounders, however, is relative to facilities such as space-based instrumentation and incoherent scatter radars; one type of ionosonde widely used for monitoring costs in excess of €150,000, representing a significant investment for many organisations. A new instrument design is under development at RAL for a low-power sounder using pulse-coding techniques to get good signal-to-noise. The design uses COTS components wherever possible, and has a projected cost in the region of €6,000 for the simplest version, making such a system accessible to all. The design is tiered so that the simplest version would give information about layer heights and electron densities, but adding multiple receivers would enable plasma velocities and echo direction to be determined, increasing the science output. The intention is that sounders of this new design be installed widely, in particular in developing nations. This would be especially beneficial for study of the equatorial and low-latitude ionosphere, which is relatively poorly understood because of a relative lack of instrumentation in this region. A wide range of studies would be enabled or enhanced by a much denser network of ionosondes across Africa, South America and Asia including: study of planetary-scale oscillations and gravity waves in the ionosphere; investigation of longitudinal variation in the equatorial electrojet and equatorial anomaly; examination of mechanisms for vertical coupling in the atmosphere with, for example, global thunderstorm activity being concentrated in Africa and South America; the study of ionospheric scintillation mechanisms and occurrence in the equatorial region; thorough characterisation of ionospheric variability on a wide range of spatial and temporal scales across a wide range of longitudes.

RAL Low-Cost Ionosonde System

NASA Astrophysics Data System (ADS)

Stamper, R.; Davis, C.; Bradford, J.

2005-12-01

Ionosondes continue to be important for the study of the ionosphere; they are relatively cheap and simple to install and operate, so can be distributed widely across the globe; they can give information on plasma density, structure and motion; their direct measurements of electron densities are also important for calibrating other more complicated observation methods such as incoherent scatter radar, satellite beacon tomography and radio occultation. The low cost of sounders, however, is relative to facilities such as space-based instrumentation and incoherent scatter radars; one type of ionosonde widely used for monitoring costs in excess of 200,000, representing a significant investment for many organisations. A new instrument design is under development at RAL for a low-power sounder using pulse-coding techniques to get good signal-to-noise. The design uses COTS components wherever possible, and has a projected cost in the region of 7,500 for the simplest version, making such a system accessible to all. The design is tiered so that the simplest version would give information about layer heights and electron densities, but adding multiple receivers would enable plasma velocities and echo direction to be determined, increasing the science output. The intention is that sounders of this new design be installed widely, in particular in developing nations. This would be especially beneficial for study of the equatorial and low-latitude ionosphere, which is relatively poorly understood because of a relative lack of instrumentation in this region. A wide range of studies would be enabled or enhanced by a much denser network of ionosondes across Africa, South America and Asia including: study of planetary-scale oscillations and gravity waves in the ionosphere; investigation of longitudinal variation in the equatorial electrojet and equatorial anomaly; examination of mechanisms for vertical coupling in the atmosphere with, for example, global thunderstorm activity being concentrated in Africa and South America; the study of ionospheric scintillation mechanisms and occurrence in the equatorial region; thorough characterisation of ionospheric variability on a wide range of spatial and temporal scales across a wide range of longitudes.

Observations of Pc5 micropulsation-related electric field oscillations in equatorial ionosphere

NASA Technical Reports Server (NTRS)

Reddy, C. A.; Ravindran, Sudha; Viswanathan, K. S.; Murthy, B. V. Krishna; Rao, D. R. K.; Araki, T.

1994-01-01

A 54.95-MHz coherent backscatter radar, an ionosonde and the magnetometer located at Trivandrum in India (8.5 deg N, 77 deg E, 0.5 deg N dip angle) recorded large-amplitude ionospheric fluctuations and magnetic field fluctuations associated with a Pc5 micropulsation event, which occurred during an intense magnetic storm on 24 March 1991 (A(sub p) = 161). Simultaneous 100-n T-level fluctuations are also observed in the H-component at Brorfelde, Denmark (55.6 deg N gm) and at Narsarsuaq, Greenland (70.6 deg N gm). Our study of the above observations shows that the E-W electric field fluctuations in the E- and F-regions and the magnetic field fluctuations at Thumba are dominated by a near-sinusoidal oscillation of 10 min during 1730-1900 IST (1200-1330 UT), the amplitude of the electric field oscillation in the equatorial electrojet (EEJ) is 0.1-0.25 mV/m and it increases with height, while it is about 1.0 mV/m in the F-region, the ground-level H-component oscillation can be accounted for by the ionospheric current oscillation generated by the observed electric field oscillation in the EEJ and the H-component oscillations at Trivandrum and Brofelde are in phase with each other. The observations are interpreted in terms of a compressional cavity mode resonance in the inner magnetosphere and the assoicated ionospheric electric field penetrating from high latitudes to the magnetic equator.

Evidence of prompt penetration electric fields during HILDCAA events

NASA Astrophysics Data System (ADS)

Pereira Silva, Regia; Sobral, Jose Humberto Andrade; Koga, Daiki; Rodrigues Souza, Jonas

2017-10-01

High-intensity, long-duration continuous auroral electrojet (AE) activity (HILDCAA) events may occur during a long-lasting recovery phase of a geomagnetic storm. They are a special kind of geomagnetic activity, different from magnetic storms or substorms. Ionized particles are pumped into the auroral region by the action of Alfvén waves, increasing the auroral current system. The Dst index, however, does not present a significant downward swing as it occurs during geomagnetic storms. During the HILDCAA occurrence, the AE index presents an intense and continuous activity. In this paper, the response of Brazilian equatorial ionosphere is studied during three HILDCAA events that occurred in the year of 2006 (the descending phase of solar cycle 23) using the digisonde data located at São Luís, Brazil (2.33° S, 44.2° W; dip latitude 1.75° S). Geomagnetic indices and interplanetary parameters were used to calculate a cross-correlation coefficient between the Ey component of the interplanetary electric field and the F2 electron density peak height variations during two situations: the first of them for two sets daytime and nighttime ranges, and the second one for the time around the pre-reversal enhancement (PRE) peak. The results showed that the pumping action of particle precipitation into the auroral zone has moderately modified the equatorial F2 peak height. However, F2 peak height seems to be more sensitive to HILDCAA effects during PRE time, showing the highest variations and sinusoidal oscillations in the cross-correlation indices.

Long-term EEJ variations by using the improved EE-index

NASA Astrophysics Data System (ADS)

Fujimoto, A.; Uozumi, T.; Abe, Sh.; Matsushita, H.; Imajo, Sh.; Ishitsuka, J. K.; Yoshikawa, A.

2016-03-01

In 2008, International Center for Space Weather Science and Education, Kyushu University (ICSWSE) proposed the EE-index, which is an index to monitor the equatorial geomagnetic phenomena. EE-index has been improved with the development of the MAGnetic Data Acquisition System and the Circum-pan Pacific Magnetometer Network (MAGDAS/CPMN) and the enormous archive of MAGDAS/CPMN data over 10 years since the initial article. Using the improved EE-index, we examined the solar cycle variation of equatorial electrojet (EEJ) by the time series analysis for EUEL (one part of EE-index) at Ancon in Peru and the solar activity from September 18, 1998 to March 31, 2015. We found that the long-term variation of daily EEJ peak intensity has a trend similar to that of F10.7 (the solar activity). The power spectrum of the daily EEJ peak has clearly two dominant peaks throughout the analysis interval: 14.5 days and 180 days (semi-annual). The solar cycle variation of daily EEJ peak correlates well with that of F10.7 (the correlation coefficient 0.99). We conclude that the daily EEJ peak intensity is roughly determined as the summation of the long-period trend of the solar activity resulting from the solar cycle and day-to-day variations caused by various sources such as lunar tides, geometric effects, magnetospheric phenomena and atmospheric phenomena. This work presents the primary evidence for solar cycle variations of EEJ on the long-term study of the EE-index

Relation between precipitation of energetic electrons, field-aligned currents, and the westward electrojet

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dronov, A.V.; Tsirs, V.E.

1988-11-01

We have investigated the relation between the precipitation of energetic electrons and protons (>30 keV), field aligned currents, and the position of the westward electrojet during the active phase of substorms. Our work is based on measurements by Kosmos-426 in November 11-12 and 22-25, 1971, and by Kosmos-900 and Interkosmos-17 in December 1-2, 1977. Maximum fluxes of precipitating energetic electrons arrive in the region of outflowing current. Maximum fluxes of protons are precipitated preferentially in regions of inflowing current. During the active phase of substorms, the maximum fluxes of energetic electrons are recorded at the leading edge of the westwardmore » electrojet.« less

Coordinated satellite and incoherent scatter observations. [of the ionosphere

NASA Technical Reports Server (NTRS)

Calderon, C. H. J.

1975-01-01

Measurements taken at the Jicamarca Radar Observatory at Lima, Peru during the Cooperative Sounding Rocket Program are reported. The following types of data were acquired: (1) electron density and temperature, (2) vertical plasma drift, (3) electrojet relative echo power density, (4) electrojet Doppler shift and condition, and (5) 150 km echoing region.

Ionosphere VHF scintillations over Vaddeswaram (Geographic Latitude 16.31°N, Geographic Longitude 80.30°E, Dip 18°N), a latitude Indian station - A case study

NASA Astrophysics Data System (ADS)

Brahmanandam, P. S.; Uma, G.; Pant, T. K.

2017-10-01

This research reports the 250 MHz amplitude ionosphere scintillations recorded at Vaddeswaram (Geographic Latitude 16.31°N, Geographic Longitude 80.30°E, Dip 18°N), a low-latitude station in India. Though amplitude scintillations were recorded for four continuous days (05-08 November 2011), the presence of intense and long-duration scintillations on 06 November 2011 instigated us to verify the ionosphere background conditions. This research, therefore, is also used important databases including, diurnal variations of h‧F (virtual height of the F-layer) and the vertical drifts as measured by an advanced digital ionosonde radar located at an Indian equatorial station i.e. Trivandrum (Geographic Latitude 8.5°N, Geographic Longitude 77°E, Dip 0.5°N), equatorial Electrojet (EEJ) ground strength measured using magnetometers and the total electron content (TEC) maps provided by the International GPS Service (IGS) to study the background ionosphere conditions. The interesting observations are higher E × B drifts, the occurrence of long-duration range-type spread F signatures at Trivandrum and, thereafter, intense scintillations over Vaddeswaram. It was found a secondary peak at around 1600 LT in EEJ strength followed by a higher upward drift velocity (more than 60 m/s) with a significant raise of the F region up to 470 km over the magnetic equator on 06 November 2011. The possible physical mechanisms of these important observational results are discussed in the light of available literature.

Study of Sun-Earth interactions using equatorial VHF scintillation in the Indian region

NASA Astrophysics Data System (ADS)

Banola, Sridhar

Plasma density irregularities in the ionosphere (associated with ESF, plasma bubbles and Spo-radic E layers) cause scintillations in various frequency ranges. VHF radio wave scintillation technique is extensively used to study plasma density irregularities of sub-kilometre size . Ef-fects of magnetic and solar activity on ionospheric irregularities are studied so as to ascertain their role in the space weather of the near earth environment in space. Indian Institute of Ge-omagnetism operated a ground network of 13 stations monitoring amplitude scintillations on 244/251 MHz (FLEETSAT 73° E) signals in placecountry-regionIndia for more than a decade under AICPITS. At present VHF scintillation is being recorded at Mumbai by monitoring 251 MHz signal transmitted by geostationary satellite UFO2(71.2 E). sampling at 20 Hz. During CAWSES campaign (March-April 2006, low sunspot period) occurrence of daytime scintilla-tions was observed higher than the nighttime scintillations. This could be due to the fact that during low sunspot years occurrence of spread-F is limited to a narrow latitude region near the dip equator. To study solar cycle association of scintillations, long series of simultaneous amplitude scintillation data for period Jan 1989 to Dec 2000 at Indian low-latitude stations Tirunelveli/Trivandrum, close to dip equator, Pondicherry/Karur, located at the fringe of elec-trojet, Mumbai (dip lat. 13.5o N), a temperate station and Ujjain (dip lat. 18.6o N), close to anomaly crest region are utilized. Nighttime scintillation occurrence is solar activity dependent. Equatorial scintillations are inhibited with increase in geomagnetic activity.

Recent Advances in Atmospheric, Solar-Terrestrial Physics and Space Weather From a North-South network of scientists [2006-2016] PART B : Results and Capacity Building

NASA Astrophysics Data System (ADS)

Amory-Mazaudier, C.; Fleury, R.; Petitdidier, M.; Soula, S.; Masson, F.; Davila, J.; Doherty, P.; Elias, A.; Gadimova, S.; Makela, J.; Nava, B.; Radicella, S.; Richardson, J.; Touzani, A.; Girgea Team

2017-12-01

This paper reviews scientific advances achieved by a North-South network between 2006 and 2016. These scientific advances concern solar terrestrial physics, atmospheric physics and space weather. This part B is devoted to the results and capacity building. Our network began in 1991, in solar terrestrial physics, by our participation in the two projects: International Equatorial Electrojet Year IEEY [1992-1993] and International Heliophysical Year IHY [2007-2009]. These two projects were mainly focused on the equatorial ionosphere in Africa. In Atmospheric physics our research focused on gravity waves in the framework of the African Multidisciplinary Monsoon Analysis project n°1 [2005-2009 ], on hydrology in the Congo river basin and on lightning in Central Africa, the most lightning part of the world. In Vietnam the study of a broad climate data base highlighted global warming. In space weather, our results essentially concern the impact of solar events on global navigation satellite system GNSS and on the effects of solar events on the circulation of electric currents in the earth (GIC). This research began in the framework of the international space weather initiative project ISWI [2010-2012]. Finally, all these scientific projects have enabled young scientists from the South to publish original results and to obtain positions in their countries. These projects have also crossed disciplinary boundaries and defined a more diversified education which led to the training of specialists in a specific field with knowledge of related scientific fields.

Improved spatial and temporal characteristics of ionospheric irregularities and polar mesospheric summer echoes using coherent MIMO and aperture synthesis radar imaging

NASA Astrophysics Data System (ADS)

Chau, J. L.; Urco, J. M.; Milla, M. A.; Vierinen, J.

2017-12-01

We have recently implemented Multiple-input multiple-output (MIMO) radar techniques to resolve temporal and spatial ambiguities of ionospheric and atmospheric irregularities, with improve capabilities than previously experiments using single-input multi-output (SIMO) techniques. SIMO techniques in the atmospheric and ionospheric coherent scatter radar field are usually called aperture synthesis radar imaging. Our implementations have done at the Jicamarca Radio Observatory (JRO) in Lima, Peru, and at the Middle Atmosphere Alomar Radar System (MAARSY) in Andenes, Norway, to study equatorial electrojet (EEJ) field-aligned irregularities and polar mesospheric summer echoes (PMSE), respectively. Figure 1 shows an example of a configuration used at MAARSY and the comparison between the SIMO and MIMO resulting antenna point spread functions, respectively. Although in this work we present the details of the implementations at each facility, we will focus on the observed peculiarities of each phenomenon, making emphasis in the underlying physical mechanisms that govern their existence and their spatial and temporal modulation. For example, what are the typical horizontal scales of PMSE variability in both intensity and wind field?

Field-aligned currents and the auroral electrojet

NASA Technical Reports Server (NTRS)

Cahill, L. J.; Potter, W. E.; Kintner, P. M.; Arnoldy, R. L.; Choy, L. W.

1974-01-01

A Nike Tomahawk with fields and particles payload was launched on Nov. 18, 1970, over a strong westward electrojet current and auroral forms moving rapidly to the east. Electron fluxes moving up and down the magnetic field lines were measured. Upward-moving electrons below 1-keV energy were dominant and were equivalent to a net downward electric current that fluctuated between .2 and .6 microamp/sq m during the flight above 130 km. As the rocket traversed this broad region of downward electric current over and to the north of the auroral forms, the horizontal electric field slowly rotated from east to west. The magnetic measurements indicate that the westward electrojet was a horizontal sheet of current several hundred kilometers in north-south extent.

Rocket investigations of the auroral electrojet

NASA Technical Reports Server (NTRS)

Davis, T. N.

1973-01-01

Five Nike-Tomahawk rockets were flown to measure perturbations in the magnitude of the geomagnetic field due to auroral electrojets. The dates and locations of the rocket launches are given along with a brief explanation of payloads and instrumentation. Papers published as a result of the project are listed. An abstract is included which outlines the scientific results from one of the flights.

Global characteristics of auroral Hall currents derived from the Swarm constellation: dependences on season and IMF orientation

NASA Astrophysics Data System (ADS)

Huang, Tao; Lühr, Hermann; Wang, Hui

2017-11-01

On the basis of field-aligned currents (FACs) and Hall currents derived from high-resolution magnetic field data of the Swarm constellation, the average characteristics of these two current systems in the auroral regions are comprehensively investigated by statistical methods. This is the first study considering both current types determined simultaneously by the same spacecraft in both hemispheres. The FAC distribution, derived from the novel Swarm dual-spacecraft approach, reveals the well-known features of Region 1 (R1) and Region 2 (R2) FACs. At high latitudes, Region 0 (R0) FACs appear on the dayside. Their flow direction, up or down, depends on the orientation of the interplanetary magnetic field (IMF) By component. Of particular interest is the distribution of auroral Hall currents. The prominent auroral electrojets are found to be closely controlled by the solar wind input, but we find no dependence of their intensity on the IMF By orientation. The eastward electrojet is about 1.5 times stronger in local summer than in winter. Conversely, the westward electrojet shows less dependence on season. As to higher latitudes, part of the electrojet current is closed over the polar cap. Here the seasonal variation of conductivity mainly controls the current density. During local summer of the Northern Hemisphere, there is a clear channeling of return currents over the polar cap. For positive (negative) IMF By a dominant eastward (westward) Hall current circuit is formed from the afternoon (morning) electrojet towards the dawn side (dusk side) polar cap return current. The direction of polar cap Hall currents in the noon sector depends directly on the orientation of the IMF By. This is true for both signs of the IMF Bz component. Comparable Hall current distributions can be observed in the Southern Hemisphere but for opposite IMF By signs. Around the midnight sector the westward substorm electrojet is dominating. As expected, it is highly dependent on magnetic activity, but it shows only little response to season and IMF By polarity. An important finding is that all the IMF By dependences of FACs and Hall currents practically disappear in the dark winter hemisphere.

Field-aligned current and auroral Hall current characteristics derived from the Swarm constellation

NASA Astrophysics Data System (ADS)

Huang, Tao; Wang, Hui; Hermann, Luehr

2017-04-01

On the basis of field-aligned currents (FACs) and Hall currents derived from high-resolution magnetic field data of the Swarm constellation the average characteristics of these two current systems in the auroral regions are comprehensively investigated by statistical methods. This is the first study considering both current types simultaneously and for both hemispheres. The FAC distribution, derived from the Swarm dual-spacecraft approach, reveals the well-known features of Region 1 (R1) and Region 2 (R2) FACs. At high latitudes, Region 0 (R0) FACs appear on the dayside. Their direction depends on the orientation of the interplanetary magnetic field (IMF) By component. Of particular interest is the distribution of auroral Hall currents. The most prominent auroral electrojets are found to be closely controlled by the solar wind input. But there is no dependence on the IMF By orientation. The eastward electrojet is about twice as strong in summer as in winter. Conversely, the westward electrojet shows less dependence on season. Part of the electrojet current is closed over the polar cap. Here the seasonal variation of conductivity mainly controls the current density. There is a clear channeling of return currents over the polar cap. Depending on IMF By orientation most of the current is flowing either on the dawn or dusk side. The direction of Hall currents in the noon sector depends directly on the orientation of the IMF By. This is true for both signs of the IMF Bz component. But largest differences between summer and winter seasons are found for northward IMF Bz. Around the midnight sector the westward substorm electrojet is dominating. As expected, it is highly dependent on magnetic activity, but shows only little response to the IMF By polarity.

Custom auroral electrojet indices calculated by using MANGO value-added services

NASA Astrophysics Data System (ADS)

Bargatze, L. F.; Moore, W. B.; King, T. A.

2009-12-01

A set of computational routines called MANGO, Magnetogram Analysis for the Network of Geophysical Observatories, is utilized to calculate customized versions of the auroral electrojet indices, AE, AL, and AU. MANGO is part of an effort to enhance data services available to users of the Heliophysics VxOs, specifically for the Virtual Magnetospheric Observatory (VMO). The MANGO value-added service package is composed of a set of IDL routines that decompose ground magnetic field observations to isolate secular, diurnal, and disturbance variations of magnetic field disturbance, station-by-station. Each MANGO subroutine has been written in modular fashion to allow "plug and play"-style flexibility and each has been designed to account for failure modes and noisy data so that the programs will run to completion producing as much derived data as possible. The capabilities of the MANGO service package will be demonstrated through their application to the study of auroral electrojet current flow during magnetic substorms. Traditionally, the AE indices are calculated by using data from about twelve ground stations located at northern auroral zone latitudes spread longitudinally around the world. Magnetogram data are corrected for secular variation prior to calculating the standard version of the indices but the data are not corrected for diurnal variations. A custom version of the AE indices will be created by using the MANGO routines including a step to subtract diurnal curves from the magnetic field data at each station. The custom AE indices provide more accurate measures of auroral electrojet activity due to isolation of the sunstorm electrojet magnetic field signiture. The improvements in the accuracy of the custom AE indices over the tradition indices are largest during the northern hemisphere summer when the range of diurnal variation reaches its maximum.

Investigation of the magnetospheric convection influence on equatorial electrojet and electric field at the geomagnetic equator in quiet conditions on the basis of the GSM TIP

NASA Astrophysics Data System (ADS)

Klimenko, M. V.; Klimenko, V. V.; Bryukhanov, V. V.

Inclusion in the Global Self-consistent Model of the Thermosphere Ionosphere and Protonosphere GSM TIP developed in WD IZMIRAN of the new block of the electric field calculation allows to carry out the investigation of the equatorial ionosphere In this block the decision of the three-dimensional equation of the full current density conservation in the ionosphere of the Earth is realized by adduction it to the two-dimensional by integration on thickness of the current conductive layer along geomagnetic field lines which are expected equipotential In the given work are presented the calculation results on the basis of the model GSM TIP in which the composition and the temperature of neutral atmosphere computed on the basis of model MSIS The calculations were carried out for the quiet equinox conditions in the minimum of the solar activity The magnetosphere convection field calculated in the model by two ways paid in models - by setting of the field aligned currents of the first zone or potential difference across the polar caps Herewith in the first variant of calculations the currents of the first zone were selected so as got the potential difference through the polar caps was approximately such as assigned in the second variant There are considered two events - an absence of the screening by Alfven layer electric field that is to say the absence of the field aligned currents of the second zone and presence of such screening under given field aligned currents of the second zone All calculations were carried out with taking into account of

Salient features of the dayside low latitude ionospheric response to the main phase step-I of the 17 March 2015 geomagnetic storm

NASA Astrophysics Data System (ADS)

Bagiya, Mala S.; Sunil, A. S.; Chakrabarty, D.; Sunda, Surendra

2017-10-01

Based on TEC observations by India's GPS Aided GEO Augmented Navigation (GAGAN) GPS network, we report the dayside low latitude ionospheric variations over the Indian region during the moderate main phase step-I of the 17 March 2015 geomagnetic storm. In addition, we assess the efficacy of GPS inferred TEC maps by International GNSS service (IGS) in capturing large scale diurnal features of equatorial ionization anomaly (EIA) over the Indian region during this period. Following the prompt penetration electric field (PPE) at ∼0605 UT, equatorial electrojet (EEJ) enhances by ∼55 nT over 75 ± 3oE longitudes where main phase step-I is coincided with local noon. Initial moderate EIA gradually strengthens with the storm commencement. Although GAGAN TEC exhibits more intense EIA evolution compare to IGS TEC maps, latitudinal extent of EIA are comparable in both. The enhanced EEJ reverses by ∼0918 UT under the effect of overshielding electric field, the later is accompanied by northward turning of interplanetary magnetic field (IMF) Bz. The weakening of well evolved EIA reflects in IGS TEC maps after ∼45 min of the overshielding occurrence. In contrary, GAGAN TEC shows the corresponding feature after ∼0115 h. Resurgence of EIA, following the PPE ∼1115 UT, shows up in GAGAN TEC but IGS TEC maps fails in capturing this feature. The observed low latitude TEC variations and EIA modulations are explained in terms of the varying storm time disturbance electric fields. The anomalies between the GAGAN TEC and IGS TEC maps are discussed in terms of the possible limitations of the IGS TEC maps in capturing storm time EIA variability over the Indian region.

Diurnal, monthly and seasonal variation of mean winds in the MLT region observed over Kolhapur using MF radar

NASA Astrophysics Data System (ADS)

Sharma, A. K.; Gaikwad, H. P.; Ratnam, M. Venkat; Gurav, O. B.; Ramanjaneyulu, L.; Chavan, G. A.; Sathishkumar, S.

2018-04-01

Medium Frequency (MF) radar located at Kolhapur (16.8°N, 74.2°E) has been upgraded in August 2013. Since then continuous measurements of zonal and meridional winds are obtained covering larger altitudes from the Mesosphere and Lower Thermosphere (MLT) region. Diurnal, monthly and seasonal variation of these mean winds is presented in this study using four years (2013-2017) of observations. The percentage occurrence of radar echoes show maximum between 80 and 105 km. The mean meridional wind shows Annual Oscillation (AO) between 80 and 90 km altitudes with pole-ward motion during December solstice and equatorial motion during June solstice. Quasi-biennial oscillation (QBO) with weaker amplitudes are also observed between 90 and 104 km. Zonal winds show semi-annual oscillation (SAO) with westward winds during equinoxes and eastward winds during solstices between 80 and 90 km. AO with eastward winds during December solstice and westward wind in the June solstice is also observed in the mean zonal wind between 100 and 110 km. These results match well with that reported from other latitudes within Indian region between 80 and 90 km. However, above 90 km the results presented here provide true mean background winds for the first time over Indian low latitude region as the present station is away from equatorial electro-jet and are not contaminated by ionospheric processes. Further, the results presented earlier with an old version of this radar are found contaminated due to unknown reasons and are corrected in the present work. This upgraded MF radar together with other MLT radars in the Indian region forms unique network to investigate the vertical and lateral coupling.

Detection of the 'continuous' H3(+) electrojet in the Jovian Aurora

NASA Astrophysics Data System (ADS)

Stallard, T. S.; Miller, S.; Achilleos, N.; Rego, D.; Prange, R.; Dougherty, M.; Joseph, R. D.

1999-09-01

Recently we have published the first detection of an auroral electrojet - a fast ion wind circulating around the auroral oval - on Jupiter (Rego et al., Nature, 399, 121-123). The detection was made during an unusual "auroral event", but raised the possibility that such electrojets might be detectable under "normal" auroral conditions. This work, currently in progress, is directed towards that aim. To accomplish this, high resolution infrared spectra and images of the Jovian aurora were taken on the nights of September 7-11(th) 1998, observing the nu_ {2} Q(1,0(-) ) line of H(+}_{3) at 3.953 mu m. The slit was aligned across the planet, perpendicular to the rotational axis, and the spectra were taken at 1 arcsec steps across the planet through the region of aurora. Each spectrum has been fitted row by row with a gaussian using height, width, background and central position as free parameters. This results in a measurement of how the relative central position varies across each spectra. Having processed the data, removing any systematic array effects, rotation, and instrumentally based spatial effects, we intend to show a measurable electrojet from the dopler shift it causes. This will be in the form of LOS maps of the auroral region at different CML taken over the 5 night observation period.

Global ionospheric dynamics and electrodynamics during geomagnetic storms (Invited)

NASA Astrophysics Data System (ADS)

Mannucci, A. J.; Tsurutani, B.; Verkhoglyadova, O. P.; Komjathy, A.; Butala, M. D.

2013-12-01

Globally distributed total electron content (TEC) data has become an important tool for exploring the consequences of storm-time electrodynamics. Magnetosphere-ionosphere coupling during the main phase is responsible for the largest ionospheric effects observed during geomagnetic storms, mediated by global scale electrodynamics. Recent research using case studies reveals a complex picture of M-I coupling and its relationship to interplanetary drivers such as the solar wind electric field. Periods of direct coupling exist where the solar wind electric field is strongly correlated with prompt penetration electric fields, observed as enhanced vertical plasma drifts or an enhanced electrojet in the daytime equatorial ionosphere. Periods of decoupling between low latitude electric fields and the solar wind electric field are also observed, but the factors distinguishing these two types of response have not been clearly identified. Recent studies during superstorms suggest a role for the transverse (y-component) of the interplanetary magnetic field, which affects magnetospheric current systems and therefore may affect M-I coupling, with significant ionospheric consequences. Observations of the global ionospheric response to a range of geomagnetic storm intensities are presented. Scientific understanding of the different factors that affect electrodynamic aspects of M-I coupling are discussed.

Generation of Currents in Weakly Ionized Plasmas through a Collisional Dynamo

NASA Astrophysics Data System (ADS)

Dimant, Yakov; Oppenheim, Meers; Fletcher, Alex

2016-10-01

Intense electric currents called electrojets occur in weakly ionized magnetized plasmas. An example occurs in the Earth's ionosphere near the magnetic equator where neutral winds drive the plasma across the geomagnetic field. Similar processes take place in the Solar chromosphere and MHD generators. We argue that not all convective neutral flows generate electrojets and it introduces the corresponding universal criterion for the current formation, ∇ × (U-> × B->) ≠ ∂ B-> / ∂ t , where U-> is the neutral flow velocity, B-> is the magnetic field, and t is time. This criterion does not depend on the conductivity tensor, σ̂ . For many systems, the displacement current, ∂ B-> / ∂ t , is negligible, making the criterion even simpler. This theory also shows that the neutral-dynamo driver that generates electrojets plays the same role as the DC electric current plays for the generation of the magnetic field in the Biot-Savart law. Work supported by NSF/DOE Grant PHY-1500439.

Response of the auroral electrojet indices to abrupt southward IMF turnings

NASA Astrophysics Data System (ADS)

Gjerloev, J. W.; Hoffman, R. A.; Ohtani, S.; Weygand, J.; Barnes, R.

2010-05-01

We present results from a study of the behavior of the auroral electrojet indices following abrupt southward turnings of the IMF Bz. The auroral electrojet indices are calculated from observations made by more than 100 ground based stations provided by the SuperMAG collaborators. Based on three simple criteria we selected 73 events. In each event the interval of analysis started at the time of the IMF Bz southward turning and ended 45 minutes later or at the onset of any abrupt energy unloading event in the magnetosphere, regardless of size. We refer to this period as the "pre-unloading phase". To isolate the dependence of the auroral electrojets on the solar induced ionospheric conductivity during this phase we separated the standard AU/AL indices into two new sets of indices defined by the upper and lower envelope of the north-south component for all sunlit stations (AUs/ALs) and for all stations in darkness (AUd/ALd). Based on events and statistical analyses we can conclude that following a southward turning of the IMF Bz the AUd/ALd indices show no measurable response while the AUs/ALs indices clearly intensify. The intensifications of AUs/ALs are dependent on the intensity of the solar wind driver (as measured by IMF Bz or the Akasofu ɛ parameter). The lack of AUd/ALd response does not depend on the intensity of any subsequent substorm. We find that during these isolated events the ionospheric current system is primarily confined to the sunlit ionosphere. This truncated version of the classical global DP-2 current system suggests that auroral electrojet continuity is not maintained across the terminator. Because of its conductivity dependence on the solar zenith angle, this truncated global current pattern is expected to be highly dependent on UT and season and thus can be asymmetric between hemispheres. Thus we argue that the global two-cell DP-2 current system is not a consequence only of a southward turning of the IMF but requires also the reduction of the conductivity gradient at the terminator.

Geomagnetic Field Distortion by a Solar Stream as a Mechanism for the Production of Polar Aurora and Electrojets

NASA Technical Reports Server (NTRS)

Kern, J. W.

1961-01-01

This paper describes a mechanism for charge separation in the geomagnetically trapped radiation which may account for some observed phenomena associated with the polar aurora and the electrojet current systems. The following development is proposed: given that there exist eastward or westward longitudinal gradients in the geomagnetic field resulting from distortion of the geomagnetic field by solar streams, if the trapped radiation is adiabatic in character, radial drift separation of positive and negative charged particles must occur. It follows that, for bounded or irregular distributions of plasma number density in such an adiabatic - drift region, electric fields will arise. The origin of such electric fields will not arrest the drift separation of the charged particles, but will contribute to exponential growth of irregularities in the trapped plasma density. An adiabatic acceleration mechanism is described, which is based on incorporating the electrostatic energy of the particle in the energy function for the particle. Direct consequences of polarization of the geomagnetically trapped radiation will be the polar electrojet current systems and the polar aurora.

Energy density of ionospheric and solar wind origin ions in the near-Earth magnetotail during substorms

NASA Technical Reports Server (NTRS)

Daglis, Loannis A.; Livi, Stefano; Sarris, Emmanuel T.; Wilken, Berend

1994-01-01

Comprehensive energy density studies provide an important measure of the participation of various sources in energization processes and have been relatively rare in the literature. We present a statistical study of the energy density of the near-Earth magnetotail major ions (H(+), O(+), He(++), He(+)) during substorm expansion phase and discuss its implications for the solar wind/magnetosphere/ionosphere coupling. Our aim is to examine the relation between auroral activity and the particle energization during substorms through the correlation between the AE indices and the energy density of the major magnetospheric ions. The data we used here were collected by the charge-energy-mass (CHEM) spectrometer on board the Active Magnetospheric Particle Trace Explorer (AMPTE)/Charge Composition Explorer (CCE) satellite in the near-equatorial nightside magnetosphere, at geocentric distances approximately 7 to 9 R(sub E). CHEM provided the opportunity to conduct the first statistical study of energy density in the near-Earth magnetotail with multispecies particle data extending into the higher energy range (greater than or equal to 20 keV/E). the use of 1-min AE indices in this study should be emphasized, as the use (in previous statistical studies) of the (3-hour) Kp index or of long-time averages of AE indices essentially smoothed out all the information on substorms. Most distinct feature of our study is the excellent correlation of O(+) energy density with the AE index, in contrast with the remarkably poor He(++) energy density - AE index correlation. Furthermore, we examined the relation of the ion energy density to the electrojet activity during substorm growth phase. The O(+) energy density is strongly correlated with the pre-onset AU index, that is the eastward electrojet intensity, which represents the growth phase current system. Our investigation shows that the near-Earth magnetotail is increasingly fed with energetic ionospheric ions during periods of enhanced dissipation of auroral currents. The participation of the ionosphere in the substorm energization processes seems to be closely, although not solely, associated with the solar wind/magnetosphere coupling. That is, the ionosphere influences actively the substorm energization processes by responding to the increased solar wind/magnetosphere coupling as well as to the unloading dissipation of stored energy, with the increased feeding of new material into the magnetosphere.

Improving geomagnetic observatory data in the South Atlantic Anomaly

NASA Astrophysics Data System (ADS)

Matzka, Jürgen; Morschhauser, Achim; Brando Soares, Gabriel; Pinheiro, Katia

2016-04-01

The Swarm mission clearly proofs the benefit of coordinated geomagnetic measurements from a well-tailored constellation in order to recover as good as possible the contributions of the various geomagnetic field sources. A similar truth applies to geomagnetic observatories. Their scientific value can be maximised by properly arranging the position of individual observatories with respect to the geometry of the external current systems in the ionosphere and magnetosphere, with respect to regions of particular interest for secular variation, and with respect to regions of anomalous electric conductivity in the ground. Here, we report on our plans and recent efforts to upgrade geomagnetic observatories and to recover unpublished data from geomagnetic observatories at low latitudes in the South Atlantic Anomaly. In particular, we target the magnetic equator with the equatorial electrojet and low latitudes to characterise the Sq- and ring current. The observatory network that we present allows also to study the longitudinal structure of these external current systems. The South Atlantic Anomaly region is very interesting due to its secular variation. We will show newly recovered data and comparisons with existing data sets. On the technical side, we introduce low-power data loggers. In addition, we use mobile phone data transfer, which is rapidly evolving in the region and allows timely data access and quality control at remote sites that previously were not connected to the internet.

Monitoring of Space and Earth electromagnetic environment by MAGDAS project: Collaboration with IKIR - Introduction to ICSWSE/MAGDAS project

NASA Astrophysics Data System (ADS)

Yoshikawa, Akimasa; Fujimoto, Akiko; Ikeda, Akihiro; Uozumi, Teiji; Abe, Shuji

2017-10-01

For study of coupling processes in the Solar-Terrestrial System, International Center for Space Weather Science and Education (ICSWSE), Kyushu University has developed a real time magnetic data acquisition system (the MAGDAS project) around the world. The number of observational sites is increasing every year with the collaboration of host countries. Now at this time, the MAGDAS Project has installed 78 real time magnetometers - so it is the largest magnetometer array in the world. The history of global observation at Kyushu University is over 30 years and number of developed observational sites is over 140. Especially, Collaboration between IKIR is extended back to 1990's. Now a time, we are operating Flux-gate magnetometer and FM-CW Radar. It is one of most important collaboration for space weather monitoring. By using MAGDAS data, ICSWSE produces many types of space weather index, such as EE-index (for monitoring long tern and shot term variation of equatorial electrojet), Pc5 index (for monitoring solar-wind velocity and high energy electron flux), Sq-index (for monitoring global change of ionospheric low and middle latitudinal current system), and Pc3 index (for monitoring of plasma density variation at low latitudes). In this report, we will introduce recent development of MAGDAS/ICSWSE Indexes project and topics for new open policy for MAGDAS data will be also discussed.

Observations of the Earth's magnetic field from the Space Station: Measurement at high and extremely low altitude using Space Station-controlled free-flyers

NASA Technical Reports Server (NTRS)

Webster, W., Jr.; Frawley, J. J.; Stefanik, M.

1984-01-01

Simulation studies established that the main (core), crustal and electrojet components of the Earth's magnetic field can be observed with greater resolution or over a longer time-base than is presently possible by using the capabilities provided by the space station. Two systems are studied. The first, a large lifetime, magnetic monitor would observe the main field and its time variation. The second, a remotely-piloted, magnetic probe would observe the crustal field at low altitude and the electrojet field in situ. The system design and the scientific performance of these systems is assessed. The advantages of the space station are reviewed.

Monitoring Auroral Electrojet from Polar Cap Stations

NASA Astrophysics Data System (ADS)

Tan, A.; Lyatsky, W.; Lyatskaya, S.

2004-12-01

The auroral electrojet AL and AE geomagnetic activity indices are important for monitoring geomagnetic substorms. In the northern hemisphere these indices are derived from measurements at a set of geomagnetic observatories located in the auroral zone. In the southern hemisphere the major portion of the auroral zone is located on the ocean; this does not allow us to derive the auroral electrojet indices in the same way. We showed that monitoring the auroral electrojet is possible from magnetic field measurements at polar cap stations. For this purpose we used hourly values of geomagnetic field variations at four polar cap stations, distributed along polar cap boundary and occupying a longitudinal sector of about 14 hours, and calculated mean values of the total magnetic field disturbance T = (X2 + Y2 + Z2)1/2 where X, Y, and Z are geomagnetic field components measured at these polar cap stations. The set of the obtained values were called the T index. This index has a clear physical mining: it is the summary of geomagnetic disturbance in all three components averaged over the polar cap boundary. We found that correlation coefficients for the dependence of the T index on both AL and AE indices are as high as ~0.9 and higher. The high correlation of the T index with the AL and AE indices takes place for any UT hour when the stations were located at the night side. The T index further shows good correlation with solar wind parameters: the correlation coefficient for the dependence of the T index on the solar wind-geomagnetic activity coupling function is ~0.8 and higher, which is close to the correlation coefficient for AL index. The T index may be especially important in the cases when ground-based measurements in the auroral zone are impossible as in the southern hemisphere.

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 sides, which is explained by means of the light speed propagation of the TM0 mode waves in the Earth-ionosphere waveguide.

Transmission of the Magnetospheric Electric Fields to the Low Latitude Ionosphere during Storm and Substorms

NASA Astrophysics Data System (ADS)

Kikuchi, T.; Hashimoto, K. K.; Ebihara, Y.; Tanaka, T.; Tomizawa, I.; Nagatsuma, T.

2016-12-01

The solar wind energy is transmitted to the 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. 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 also develop during the transient/short-term geomagnetic disturbances like the geomagnetic sudden commencements (SC) and ULF pulsations, which appear simultaneously at high latitude and equator within the temporal resolution of 10 sec. Using the SC, we can confirm that the electric potential and currents are transmitted near-instantaneously to low latitude ionosphere on both the day- and night-sides, which is explained by means of the light speed propagation of the TM0 mode waves in the Earth-ionosphere waveguide.

Ionospheric and Birkeland current distributions inferred from the MAGSAT magnetometer data

NASA Technical Reports Server (NTRS)

Zanetti, L. J.; Potemra, T. A.; Baumjohann, W.

1983-01-01

Ionospheric and field-aligned sheet current density distributions are presently inferred by means of MAGSAT vector magnetometer data, together with an accurate magnetic field model. By comparing Hall current densities inferred from the MAGSAT data and those inferred from simultaneously recorded ground based data acquired by the Scandinavian magnetometer array, it is determined that the former have previously been underestimated due to high damping of magnetic variations with high spatial wave numbers between the ionosphere and the MAGSAT orbit. Among important results of this study is noted the fact that the Birkeland and electrojet current systems are colocated. The analyses have shown a tendency for triangular rather than constant electrojet current distributions as a function of latitude, consistent with the statistical, uniform regions 1 and 2 Birkeland current patterns.

Toward a global multi-scale heliophysics observatory

NASA Astrophysics Data System (ADS)

Semeter, J. L.

2017-12-01

We live within the only known stellar-planetary system that supports life. What we learn about this system is not only relevant to human society and its expanding reach beyond Earth's surface, but also to our understanding of the origins and evolution of life in the universe. Heliophysics is focused on solar-terrestrial interactions mediated by the magnetic and plasma environment surrounding the planet. A defining feature of energy flow through this environment is interaction across physical scales. A solar disturbance aimed at Earth can excite geospace variability on scales ranging from thousands of kilometers (e.g., global convection, region 1 and 2 currents, electrojet intensifications) to 10's of meters (e.g., equatorial spread-F, dispersive Alfven waves, plasma instabilities). Most "geospace observatory" concepts are focused on a single modality (e.g., HF/UHF radar, magnetometer, optical) providing a limited parameter set over a particular spatiotemporal resolution. Data assimilation methods have been developed to couple heterogeneous and distributed observations, but resolution has typically been prescribed a-priori and according to physical assumptions. This paper develops a conceptual framework for the next generation multi-scale heliophysics observatory, capable of revealing and quantifying the complete spectrum of cross-scale interactions occurring globally within the geospace system. The envisioned concept leverages existing assets, enlists citizen scientists, and exploits low-cost access to the geospace environment. Examples are presented where distributed multi-scale observations have resulted in substantial new insight into the inner workings of our stellar-planetary system.

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.

Studies of Westward Electrojets and Field-Aligned Currents in the Magnetotail During Substorms: Implications for Magnetic Field Models

NASA Technical Reports Server (NTRS)

Spence, Harlan E.

1996-01-01

This section outlines those tasks undertaken in the final year that contribute integrally to the overarching project goals. Fast, during the final year, it is important to note that the project benefited greatly with the addition of a Boston University graduate student, Ms. Karen Hirsch. Jointly, we made substantial progress on the development of and improvements to magnetotail magnetic field and plasma models. The ultimate aim of this specific task was to assess critically the utility of such models for mapping low-altitude phenomena into the magnetotail (and vice-versa). The bulk of this effort centered around the finite-width- magnetotail convection model developed by and described by Spence and Kivelson (J. Geophys. Res., 98, 15,487, 1993). This analytic, theoretical model specifies the bulk plasma characteristics of the magnetotail plasma sheet (number density, temperature, pressure) across the full width of the tail from the inner edge of the plasma sheet to lunar distances. Model outputs are specified by boundary conditions of the source particle populations as well as the magnetic and electric field configuration. During the reporting period, we modified this code such that it can be interfaced with the auroral particle precipitation model developed by Dr. Terry Onsager. Together, our models provide a simple analytic specification of the equatorial distribution of fields and plasma along with their low-altitude consequences. Specifically, we have built a simple, yet powerful tool which allows us to indirectly 'map' auroral precipitation signatures (VDIS, inverted-V's, etc.) measured by polar orbiting spacecraft in the ionosphere, to the magnetospheric equatorial plane. The combined models allow us to associate latitudinal gradients measured in the ion energy fluxes at low-altitudes with the large-scale pressure gradients in the equatorial plane. Given this global, quasi-static association, we can then make fairly strong statements regarding the location of discrete features in the context of the global picture. We reported on our initial study at national and international meetings and published the results of our predictions of the low-altitude signatures of the plasma sheet. In addition, the PI was invited to contribute a publication to the so-called 'Great Debate in Space Physics' series that is a feature of EOS. The topic was on the nature of magnetospheric substorms. Specific questions of the when and where a substorm occurs and the connection between the auroral and magnetospheric components were discussed in that paper. This paper therefore was derived exclusively from the research supported by this grant. Attachment: Empirical modeling of the quite time nightside magnetosphere.' 'CRRES observations of particle flux dropout event.' The what, where, when, and why of magnetospheric substorm triggers'. and 'Low altitude signature of the plasma sheet: model prediction of local time dependence'.

Infrasonic waves generated by supersonic auroral arcs

NASA Astrophysics Data System (ADS)

Pasko, Victor P.

2012-10-01

A finite-difference time-domain (FDTD) model of infrasound propagation in a realistic atmosphere is used to provide quantitative interpretation of infrasonic waves produced by auroral arcs moving with supersonic speed. The Lorentz force and Joule heating are discussed in the existing literature as primary sources producing infrasound waves in the frequency range 0.1-0.01 Hz associated with the auroral electrojet. The results are consistent with original ideas of Swift (1973) and demonstrate that the synchronization of the speed of auroral arc and phase speed of the acoustic wave in the electrojet volume is an important condition for generation of magnitudes and frequency contents of infrasonic waves observable on the ground. The reported modeling also allows accurate quantitative reproduction of previously observed complex infrasonic waveforms including direct shock and reflected shockwaves, which are refracted back to the earth by the thermosphere.

Ultra-low-frequency wave power in the magnetotail lobes. I - Relation to substorm onsets and the auroral electrojet index

NASA Technical Reports Server (NTRS)

Smith, R. A.; Goertz, C. K.; Harrold, B. G.; Goldstein, M. L.; Lepping, R. P.; Fitch, C. A.; Sands, M. R.

1990-01-01

Time-series observations of the magnetotail-lobe magnetic field have been Fourier analyzed to compute the frequency-weighted energy density Pfz in the range 1-30 mHz. Pfz is generally observed in the range 0.0001-0.01 gamma-squared Hz with a mean value of 0.0012 during substorm growth phases and 0.001 in the comparison intervals. No strong correlation of Pfz is found with the auroral electrojet index in either set of intervals, but during substorm growth phases Pfz may vary by an order of magnitude over time scales of 30 min, with a tendency for higher power levels to occur later in the growth phase. Increases in Pfz precede by about 10 min localized expansive phase activity observed in individual magnetograms.

First demonstration of HF-driven ionospheric currents

NASA Astrophysics Data System (ADS)

Papadopoulos, K.; Chang, C.-L.; Labenski, J.; Wallace, T.

2011-10-01

The first experimental demonstration of HF driven currents in the ionosphere at low ELF/ULF frequencies without relying in the presence of electrojets is presented. The effect was predicted by theoretical/computational means in a recent letter and given the name Ionospheric Current Drive (ICD). The effect relies on modulated F-region HF heating to generate Magneto-Sonic (MS) waves that drive Hall currents when they reach the E-region. The Hall currents inject ELF waves into the Earth-Ionosphere waveguide and helicon and Shear Alfven (SA) waves in the magnetosphere. The proof-of-concept experiments were conducted using the HAARP heater in Alaska under the BRIOCHE program. Waves between 0.1-70 Hz were measured at both near and far sites. The letter discusses the differences between ICD generated waves and those relying on modulation of electrojets.

Radiation shielding estimates for manned Mars space flight.

PubMed

Dudkin, V E; Kovalev, E E; Kolomensky, A V; Sakovich, V A; Semenov, V F; Demin, V P; Benton, E V

1992-01-01

In the analysis of the required radiation shielding protection of spacecraft during a Mars flight, specific effects of solar activity (SA) on the intensity of galactic and solar cosmic rays were taken into consideration. Three spaceflight periods were considered: (1) maximum SA; (2) minimum SA; and (3) intermediate SA, when intensities of both galactic and solar cosmic rays are moderately high. Scenarios of spaceflights utilizing liquid-propellant rocket engines, low- and intermediate-thrust nuclear electrojet engines, and nuclear rocket engines, all of which have been designed in the Soviet Union, are reviewed. Calculations were performed on the basis of a set of standards for radiation protection approved by the U.S.S.R. State Committee for Standards. It was found that the lowest estimated mass of a Mars spacecraft, including the radiation shielding mass, obtained using a combination of a liquid propellant engine with low and intermediate thrust nuclear electrojet engines, would be 500-550 metric tons.

Simultaneous observation of the poleward expansion of substorm electrojet activity and the tailward expansion of current sheet disruption in the near-earth magnetotail

NASA Technical Reports Server (NTRS)

Lopez, R. E.; Koskinen, H. E. J.; Pulkkinen, T. I.; Bosinger, T.; Mcentire, R. W.; Potemra, T. A.

1993-01-01

A substorm that occurred on 7 June 1985 at 2209 UT for which simultaneous measurements from ground stations and CCE are available is considered. The event occurred during a close conjunction between CCE, the EISCAT magnetometer cross, and the STARE radar, allowing a detailed comparison of satellite and ground-based data. Two discrete activations took place during the first few minutes of this substorm: the expansion phase onset at 2209 UT and an intensification at 2212 UT, corresponding to a poleward expansion of activity. The energetic particle data indicate that the active region of the magnetotail during the 2212 UT intensification was located tailward of the active region at 2209 UT. This is direct evidence for a correspondence between tailward expansion of localized activity in the near-earth magnetotail (current disruption and particle energization) and poleward expansion of activity (electrojet formation) in the ionosphere.

Electrical changes of the polar ionosphere during magnetospheric substorms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ahn, B.H.; Kamide, Y.; Akasofu, S.H.

1986-05-01

Changes of the distribution of the potential, electric fields, ionospheric currents, field-aligned currents, the Joule heat production rate, the particle energy injection rate and the total energy dissipation rate are examined in detail by comparing them at a presubstorm epoch and the maximum epoch for several substorms on March 17, 18, and 19, 1978. The data sets are obtained on the basis of the magnetic records from the six International Magnetospheric Study meridian chains of observatories by using the computer code developed by Kamide e-italict-italic a-italicl-italic. (1981) and the conductivity model developed by Ahn et al. (1983b). A number ofmore » global features that are found to be common to most of the substorms examined in this study include the following: (1) The positive potential cell in the morning sector extends into the evening sector during substorms. (2) When it is intensified, the westward electrojet on the nightside tends to flow equatorward of the positive potential ridge. (3) The so-called ''Harang discontinuity'' may be identified as the ridge of the negative potential cell. (4) The distribution of field- aligned currents determined by our method is more complicated than the statistical pattern obtained by polar orbiting satellites. (5) The basic ionospheric current pattern is fundamentally the same during a fairly quiet period, a slightly disturbed period and a substorm period. (6) The highest Joule heat production occurs along the westward extension of the westward electrojet, while the particle energy injection rate is high along the westward electrojet in the morning sector.« less

The Ionospheric Impact of an ICME-Driven Sheath Region Over Indian and American Sectors in the Absence of a Typical Geomagnetic Storm

NASA Astrophysics Data System (ADS)

Rout, Diptiranjan; Chakrabarty, D.; Sarkhel, S.; Sekar, R.; Fejer, B. G.; Reeves, G. D.; Kulkarni, Atul S.; Aponte, Nestor; Sulzer, Mike; Mathews, John D.; Kerr, Robert B.; Noto, John

2018-05-01

On 13 April 2013, the ACE spacecraft detected arrival of an interplanetary shock at 2250 UT, which is followed by the passage of the sheath region of an interplanetary coronal mass ejection (ICME) for a prolonged (18-hr) period. The polarity of interplanetary magnetic field Bz was northward inside the magnetic cloud region of the ICME. The ring current (SYM-H) index did not go below -7 nT during this event suggesting the absence of a typical geomagnetic storm. The responses of the global ionospheric electric field associated with the passage of the ICME sheath region have been investigated using incoherent scatter radar measurements of Jicamarca and Arecibo (postmidnight sector) along with the variations of equatorial electrojet strength over India (day sector). It is found that westward and eastward prompt penetration (PP) electric fields affected ionosphere over Jicamarca/Arecibo and Indian sectors, respectively, during 0545-0800 UT. The polarities of the PP electric field perturbations over the day/night sectors are consistent with model predictions. In fact, DP2-type electric field perturbations with ˜40-min periodicity are found to affect the ionosphere over both the sectors for about 2.25 hr during the passage of the ICME sheath region. This result shows that SYM-H index may not capture the full geoeffectivenss of the ICME sheath-driven storms and suggests that the PP electric field perturbations should be evaluated for geoeffectiveness of ICME when the polarity of interplanetary magnetic field Bz is northward inside the magnetic cloud region of the ICME.

Extreme EEJ and Topside Ionospheric Response to the 22-23 June 2015 Geomagnetic Storm

NASA Astrophysics Data System (ADS)

Astafyeva, E.; Zakharenkova, I.; Alken, P.; Coisson, P.

2016-12-01

In this work, we study the ionospheric and thermospheric response to the intense geomagnetic storm of 22-23 June 2015. With the minimum SYM-H excursion of -207 nT, this storm is so far the 2nd strongest geomagnetic storm in the current 24th solar cycle. The storm started with the arrival of a coronal mass ejection at 18:37UT on 22 June 2015. The interplanetary magnetic field (IMF) Bz component changed polarity several times during this storm. Consequently, the interplanetary electric field Ey component repeated this oscillatory behavior, and varied from -15 to +20 mV/m, which is comparable with storm-time levels. Data from multiple ground-based and space-borne instruments showed that both positive and negative ionospheric storms occurred during this storm at middle and low latitudes on both day and night sides. To study the drivers of the observed ionospheric effects, we further analyze variations of thermospheric parameters (neutral mass density and thermospheric O/N2 ratio), as well as the equatorial electrojet (EEJ) data as retrieved from magnetic measurements onboard Swarm satellites. One of the most interesting features of the June 2015 storm is observation of extremely high EEJ values (both eastward and westward), that correlate with variations of the IEF Ey. We find that the storm-time penetration electric fields were, most likely, the main driver of the observed ionospheric effects at the initial phase of the storm, and at the beginning of the main phase. At the end of the main phase, the thermospheric composition changes seemed to contribute as well.

The Role of the Auroral Processes in the Formation of the Outer Electron Radiation Belt

NASA Astrophysics Data System (ADS)

Stepanova, M. V.; Antonova, E. E.; Pinto, V. A.; Moya, P. S.; Riazantseva, M.; Ovchinnikov, I.

2016-12-01

The role of the auroral processes in the formation of the outer electron radiation belt during storms is analyzed using the data of RBSP mission, low orbiting satellites and ground based observations. We analyze fluxes of the low energy precipitating ions using data of the Defense Meteorological Satellite Program (DMSP). The location of the auroral electrojet is obtained from the IMAGE magnetometer network, and of the electron distribution in the outer radiation belt from the RBSP mission. We take into account the latest results on the auroral oval mapping in accordance with which the most part of the auroral oval maps not to the plasma sheet. It maps into the surrounding the Earth plasma ring in which transverse currents are closed inside the magnetosphere. Such currents constitute the high latitude continuation of the ordinary ring current. The development of the ring current and its high latitude continuation generates strong distortion of the Earth's magnetic field and corresponding adiabatic variation of the relativistic electron fluxes. This adiabatic variation should be considered for the analysis of the processes of the acceleration of relativistic electrons and formation of the outer radiation belt. We also analyze the plasma pressure profiles during storms and demonstrate the formation of sharp plasma pressure peak at the equatorial boundary of the auroral oval. It is shown that the observed this peak is directly connected to the creation of the seed population of relativistic electrons. We discuss the possibility to predict the position of new radiation belt during recovery phase of the magnetic storm using data of low orbiting and ground based observations.

NmF2 and hmF2 measurements at 95° E and 127° E around the EIA northern crest during 2010-2014

NASA Astrophysics Data System (ADS)

Kalita, Bitap Raj; Bhuyan, Pradip Kumar; Yoshikawa, Akimasa

2015-11-01

The characteristics of the F2 layer parameters NmF2 and hmF2 over Dibrugarh (27.5° N, 95° E, 17° N geomagnetic, 43° dip) measured by a Canadian Advanced Digital Ionosonde (CADI) for the period of August 2010 to July 2014 are reported for the first time from this low mid-latitude station lying within the daytime peak of the longitudinal wave number 4 structure of equatorial anomaly (EIA) around the northern edge of anomaly crest. Equinoctial asymmetry is clearly observed at all solar activity levels whereas the midday winter anomaly is observed only during high solar activity years and disappears during the temporary dip in solar activity in 2013 but forenoon winter anomaly can be observed even at moderate solar activity. The NmF2/hmF2 variations over Dibrugarh are compared with that of Okinawa (26.5° N, 127° E, 17° N geomagnetic), and the eastward propagation speed of the wave number 4 longitudinal structure from 95° E to 127° E is estimated. The speed is found to be close to the theoretical speed of the wave number 4 (WN4) structure. The correlation of daily NmF2 over Dibrugarh and Okinawa with solar activity exhibits diurnal and seasonal variations. The highest correlation in daytime is observed during the forenoon hours in equinox. The correlation of daily NmF2 (linear or non-linear) with solar activity exhibits diurnal variation. A tendency for amplification with solar activity is observed in the forenoon and late evening period of March equinox and the postsunset period of December solstice. NmF2 saturation effect is observed only in the midday period of equinox. Non-linear variation of neutral composition at higher altitudes and variation of recombination rates with solar activity via temperature dependence may be related to the non-linear trend. The noon time maximum NmF2 over Dibrugarh exhibits better correlation with equatorial electrojet (EEJ) than with solar activity and, therefore, new low-latitude NmF2 index is proposed taking both solar activity and EEJ strength into account.

An empirical probability density distribution of planetary ionosphere storms with geomagnetic precursors

NASA Astrophysics Data System (ADS)

Gulyaeva, Tamara; Stanislawska, Iwona; Arikan, Feza; Arikan, Orhan

The probability of occurrence of the positive and negative planetary ionosphere storms is evaluated using the W index maps produced from Global Ionospheric Maps of Total Electron Content, GIM-TEC, provided by Jet Propulsion Laboratory, and transformed from geographic coordinates to magnetic coordinates frame. The auroral electrojet AE index and the equatorial disturbance storm time Dst index are investigated as precursors of the global ionosphere storm. The superposed epoch analysis is performed for 77 intense storms (Dst≤-100 nT) and 227 moderate storms (-100

Global ionospheric current distributions during substorms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ahn, B.; Kamide, Y.; Akasofu, S.

1984-03-01

The growth and decay of global ionospheric currents during magnetospheric substorms on March 17, 18, and 19, 1978 are examined on the basis of magnetic records from the six IMS meridian chains of observatories and others (the total number being 71). The computer code developed by Kamide et al. (1981) and the conductivity model developed by Ahn et al. (1983) are used. Several substorms centered around 1000-1200 UT are chosen in this presentation, since the simultaneous all-sky and riometer records are essential in timing the substorm epochs. Several global feautes that are common to most substorms during the three-day intervalmore » include the following: (1) During a quiet period, currents are often present in the cusp and/or polar cap regions. The cusp current consists of a pair of east-west currents and the polar cap current consists of several vortices. (2) When the interplanetary magnetic field (IMF) B/sub z/ component is positive, but decreases in magnitude, a well-defined westward electrojet develops in the midnight sector. However, this development is not evident in the AE index. (3) A gradual, but distinct growth (often followed by a rapid and large increase) in the AE index is indentified as the intensification of a weaksubstorm current system, which was mentioned in (2), accompanied by typical auroral substorm features, including riometer absorption. (4) The subsequent sharp increase of the AE index arises primarily from a deep intrusion of the westward electrojet into the pre-midnight sector and its equatorward shift. (5) The overall increase of the global current can be significantly differnt fromm what a sharp increase of the AE index indicates. (6) During the recovery phase, the intruded westward electrojet recedes towards the dawn sector.« less

The relationship between VHF radar auroral backscatter amplitude and Doppler velocity: a statistical study

NASA Astrophysics Data System (ADS)

Shand, B. A.; Lester, M.; Yeoman, T. K.

1996-08-01

A statistical investigation of the relationship between VHF radar auroral backscatter intensity and Doppler velocity has been undertaken with data collected from 8 years operation of the Wick site of the Sweden And Britain Radar-auroral Experiment (SABRE). The results indicate three different regimes within the statistical data set; firstly, for Doppler velocities <200 m s-1, the backscatter intensity (measured in decibels) remains relatively constant. Secondly, a linear relationship is observed between the backscatter intensity (in decibels) and Doppler velocity for velocities between 200 m s-1 and 700 m s-1. At velocities greater than 700 m s-1 the backscatter intensity saturates at a maximum value as the Doppler velocity increases. There are three possible geophysical mechanisms for the saturation in the backscatter intensity at high phase speeds: a saturation in the irregularity turbulence level, a maximisation of the scattering volume, and a modification of the local ambient electron density. There is also a difference in the dependence of the backscatter intensity on Doppler velocity for the flow towards and away from the radar. The results for flow towards the radar exhibit a consistent relationship between backscatter intensity and measured velocities throughout the solar cycle. For flow away from the radar, however, the relationship between backscatter intensity and Doppler velocity varies during the solar cycle. The geometry of the SABRE system ensures that flow towards the radar is predominantly associated with the eastward electrojet, and flow away is associated with the westward electrojet. The difference in the backscatter intensity variation as a function of Doppler velocity is attributed to asymmetries between the eastward and westward electrojets and the geophysical parameters controlling the backscatter amplitude.

Ground and Satellite Observations of ULF Waves Artificially Produced by HAARP

NASA Astrophysics Data System (ADS)

Chang, C.; Labenski, J.; Shroff, H.; Doxas, I.; Papadopoulos, D.; Milikh, G.; Parrot, M.

2008-12-01

Modulated ionospheric heating at ULF frequencies using the HAARP heater was performed from April 28 to May 3, 2008 (http://www.haarp.alaska.edu). Simultaneous ground-based ULF measurements were made locally at Gakona, AK and at Lake Ozette, WA that is 2000 km away. The ground-based results showed that ULF amplitudes measured at Gakona are mostly proportional to the electrojet strength above HAARP, indicating electrojet modulation to be the source of the local ULF waves. However, the timing of ULF events recorded at Lake Ozette did not correlated with the electrojet strength at Gakona, indicating that modulation of F region pressure is the more likely source for distant ULF waves. These observations are consistent with the theoretical understanding that ULF waves generated by current modulation are shear Alfven waves propagating along the magnetic field line, thus at high latitude their observations are limited to the vicinity of the heated spot. On the other hand, propagation of ULF waves at significant lateral distances requires generation of magnetosonic waves since they are the only mode that propagates isotropically and can thus couple efficiently in the Alfvenic duct. In addition to ground-based observations, the DEMETER satellite also provided space measurements of the heating effects during its passes over HAARP. The DEMETER results showed direct detection of HAARP ULF waves at 0.1 Hz. Moreover, density dips were observed every time HAARP was operated at CW mode, which provides clear evidence of duct formation by direct HF heating at F peak. Details of these results will be presented at the meeting. We would like to acknowledge the support provided by the HAARP facility during our ULF experiments.

Analysis of data from the Lockheed Experiment on ATS-5. [magnetic storms and auroras in the ionosphere

NASA Technical Reports Server (NTRS)

Sharp, R. D.

1975-01-01

Satellite observations of auroral electrojets, electron fluxes, and magnetic storm activity are presented and discussed. Plasma-particle interactions are examined for the earth's magnetosphere, and data (i.e., magnetograms) of the satellite observations are analyzed.

Investigation of ELF/VLF waves created by a "beat-wave" HF ionospheric heating at high latitudes

NASA Astrophysics Data System (ADS)

Shumilov, Oleg; Tereshchenko, Evgeniy; Kasatkina, Elena; Gomonov, Alexandr

2015-04-01

The generation of extremely low frequency (ELF, 3-3000 Hz) and very low frequency (VLF, 3-30 kHz) electromagnetic waves by modulated ionospheric high frequency (HF, 2-30 MHz) heating is one of the main directions of ionospheric modification experiments. In this work, we present observations of ELF waves generated during a "beat-wave" heating experiments at the EISCAT heating facility. ELF waves were registered with the ELF receiver located at Lovozero (68 N, 35 E), 660 km east from the EISCAT Tromso heating facility (69.6 N, 19.2 E). Frequency shifts between the generated beat-wave and received ELF waves were detected in all sessions. It is shown that the amplitudes of ELF waves depend on the auroral electrojet current strength. Our results showing a strong dependence of ELF signal intensities on the substorm development seem to support the conclusion that electrojet currents may affect the BW generation of ELF/VLF waves.

Simulation of the westward traveling surge and Pi 2 pulsations during substorms

NASA Technical Reports Server (NTRS)

Kan, J. R.; Sun, W.

1985-01-01

The westward traveling surge and the Pi2 pulsations are simulated as a consequence of an enhanced magnetospheric convection in a model of magnetosphere coupling. The coupling is characterized by the bouncing of Alfven waves launched by the enhanced convection. The reflection of Alfven waves from the ionosphere is treated in which the height-integrated conductivity is allowed to be highly nonuniform and fully anisotropic. The reflection of Alfven waves from the magnetosphere is characterized by the coefficient Rm, depending on whether the field lines are open or closed. The conductivity in the model is self-consistently enhanced with increasing upward field-aligned current density. The results of the simulation, including the convection pattern, the electrojets, the field-aligned current, the conductivity enhancement, the oscillation of the westward electrojet, and the average speed of the westward surge are in reasonable agreement with the features of the westward traveling surge and the Pi 2 pulsations observed during substorms.

Near-earth magnetic disturbance in total field at high latitudes. I - Summary of data from Ogo 2, 4, and 6. II - Interpretation of data from Ogo 2, 4, and 6

NASA Technical Reports Server (NTRS)

Langel, R. A.

1974-01-01

A complete survey of the near-earth magnetic field magnitude was carried out by the Polar Orbiting Geophysical Observatories (Ogo 2, 4, and 6). The average properties of variations in total magnetic field strength at invariant latitudes greater than 55 deg are given. Data from all degrees of magnetic disturbance are included, the emphasis being on periods when Kp = 2- to 3+. Although individual satellite passes at low altitudes confirm the existence of electrojet currents, neither individual satellite passes nor contours of average delta B are consistent with latitudinally narrow electrojet currents as the principal source of delta B at the satellite. The total field variations at the satellite form a region of positive delta B between about 2200 and 1000 MLT and a region of negative delta B between about 1000 and 2200 MLT. The ratio of delta B magnitudes in these positive and negative regions is variable.

Rocket observations at the northern edge of the eastward electrojet

NASA Technical Reports Server (NTRS)

Cahill, L. J., Jr.; Arnoldy, R. L.; Taylor, W. W. L.

1980-01-01

The paper discusses a Nike-Tomahawk rocket launched north over quiet, late evening auroral arcs in March 1975. A northward magnetic disturbance was observed on the ground under the rocket trajectory; south of the arcs the northward electric field was 60 mV/m, indicating strong westward plasma flow. An eastward electrojet current layer was penetrated in the upward flight, and precipitating electrons were observed over each arc. Using the observed electron flux and a model of the ionosphere, the Hall and Pedersen conductivities were calculated which were used to compute the eastward and northward components of the horizontal ionospheric currents. The joule power decreased abruptly in the auroral arcs, as the precipitating electron power increased; the total dissipated power was the same inside the arcs, between them and southward. North of the aurora the electric field and dissipated power remained low; field-aligned currents carried by the observed electrons were about a factor of 3 lower than those inferred from the magnetic field measurements.

Atmospheric Pressure and Velocity Fluctuations Near the Auroral Electrojet.

DTIC Science & Technology

1982-01-15

various aspects of the atmosphere’s dynamical response to auroral activity have been carried out by Blumen and Hendl (1969), Testud (1970), Francis...Geophys. Res. 80, 2839, 1975. Testud , 3., Gravity waves generated during magnetic substorms, 3. Atmos. Terr. Phys. 32, 1793, 1970. Waco, D. E., A

Evidence for OI 630.0 nm dayglow variations over low latitudes during onset of a substorm

NASA Astrophysics Data System (ADS)

Chakrabarty, D.; Sekar, R.; Sastri, J. H.; Pathan, B. M.; Reeves, G. D.; Yumoto, K.; Kikuchi, T.

2010-10-01

Observations of OI 630.0 nm dayglow intensity from Mt. Abu (magnetic latitude (MLAT): 16.2°N magnetic longitude (MLONG): 148°E) at two different directions corresponding to two different magnetic latitudes (MLATZenith: 16.2°N and MLAT20°Elevation: 22.2°N) revealed nearly simultaneous intensity enhancements on 2 February 2002 (Ap = 19) during 0554-0635 universal time (UT) (1124-1205 Indian Standard Time (IST); IST = UT + 5.5 h). This feature is found to be absent on a typical control day (3 February 2002; Ap = 4). The dayglow enhancements were concomitant with enhancements in the E-region zonal electric field inferred from deviations of the northward component of magnetic field (ΔH) obtained from a meridional chain of magnetometers encompassing the dip equatorial and low-latitude regions. Simultaneous positive bay signatures in ΔH were also recorded at all stations along the 210° magnetic meridian (MM) in the afternoon sector (˜1454-1535 magnetic local time). The changes in the solar wind parameters including the dawn-to-dusk component of IEF and ram pressure are found negligible during 0554-0635 UT. However, the variations in the auroral electrojet and ring current indices indicate the presence of a substorm during 0554-0635 UT. Sudden enhancements in the energetic particle fluxes measured by the Los Alamos National Laboratory (LANL) 1991-080 satellite at geosynchronous altitude provide evidence for the onset of the expansion phase of a magnetospheric substorm. Therefore, the present investigation adduces the response of 630.0 nm dayglow intensities over low latitudes corresponding to the onset of the expansion phase of an auroral/magnetospheric substorm.

Active experiments in the ionosphere and variations of geophysical and meteorological parameters

NASA Astrophysics Data System (ADS)

Sivokon, Vladimir; Cherneva, Nina; Shevtsov, Boris

Energy distribution in ionospheric-magnetospheric relations, as one of the possible external climatological factors, may be traced on the basis of the analysis of natural geophysical phenomena such as ionosphere artificial radio radiation and magnetic storms. Development of magnetic disturbances is, to some extent, associated with current variations in electrojet. In its turn, some technologies are known which may affect electrojet and its characteristics. The method, developed by the authors, is based on a complex comparison of different geophysical fields and allows us to determine the degree of active experiment effect on energy change in ionospheric-magnetospheric relations and to evaluate on this basis the degree of active experiment effect on climate in the ionosphere. Within the framework of RAS Presidium Program Project “Determination of climate-forming characteristic changes on the basis of monitoring of geophysical field variations”, investigations have been carried out, which showed the possibility of ionosphere modification effect on the energy of magnetospheric-ionospheric relations. Evaluation of possible climate changes considering ionospheric-magnetospheric relations has not been previously discussed.

Solar and lunar tidal variabilities in GPS-TEC and geomagnetic field variations: Seasonal as well as during the sudden stratospheric warming of 2010

NASA Astrophysics Data System (ADS)

Sridharan, S.

2017-04-01

The Global Positioning System (GPS) deduced total electron content (TEC) data at 15°N (geomagnetic), which is the northern crest region of equatorial ionization anomaly, are used to study solar and lunar tidal variabilities during the years 2008 and 2009 and also during the 2009-2010 winter, when a major sudden stratospheric warming (SSW) event has occurred. The diurnal and semidiurnal tidal amplitudes show semiannual variation with maximum amplitudes during February-March and September-November, whereas terdiurnal tide is larger during April-September. They show significant longitudinal variability with larger (smaller) amplitudes over 250°E-150°E (200°E-250°E). Lunar semidiurnal tidal amplitudes show sporadic enhancements during northern winter months and negligible amplitudes during northern summer months. They also show notable longitudinal variabilities. The solar migrating tides DW1 and SW2 show semiannual variation with larger amplitudes during spring equinox months, whereas TW3 maximizes during northern summer. DW2 shows larger amplitudes during summer months. During the SSW, except TW3, the migrating tides DW1 and SW2 show considerable enhancements. Among solar nonmigrating tides, SW1, TW2, and DS0 show larger enhancements. Solar tides in TEC and equatorial electrojet strength over Tirunelveli vary with the time scale of 60 days during October 2009-March 2010 similar to ozone mass mixing ratio at 10 hPa, and this confirms the vital role of ozone in tidal variabilities in ionospheric parameters. Lunar tidal amplitudes in changes in horizontal component of geomagnetic field (ΔH) are larger over Tirunelveli, a station near dip equator. Solar semidiurnal tides in ΔH have larger amplitudes than lunar tides over polar stations, Mawson and Godhavn.