Defense Meteorological Satellite Program F13 Research Articles

Abnormal Sub‐Auroral Ion Drifts (ASAID) Developed in the Postmidnight (1–4) Magnetic Local Time Sector in 2013

AbstractWe investigate the Abnormal Sub‐Auroral Ion Drifts (ASAID) developed in the postmidnight (1–4) magnetic local time sector in 2013. Shown by the Defense Meteorological Satellite Program F15 horizontal ion velocity measurements, we specified 21 antisunward (eastward) ASAID flow channels (FCs) based on their respective underlying polar convections. Overall, the polar convection formed a two‐cell pattern with its convection axis tilted in the morning‐evening direction because of the underlying BY < 0 conditions. Its dawn cell intruded into the duskside from the dawnside where the eastward ASAID flows were streaming antisunward, opposite to the dawn cell sunward convection flows. Mostly, the ASAID FC appeared in the coinciding ring‐current–related ionospheric trough and flow‐stagnation–related main ionospheric trough in the South American sector because of the favorable conditions created by the South Atlantic Magnetic Anomaly promoting also the development of Stable Auroral Red (SAR) arc. Rarely observed, the ASAID FC was associated with the SAR arc detected over Rothera. Detected in the Mid Pacific longitude sector, a pair of northern‐southern ASAID FCs demonstrated northern‐southern conjugacy. With correlated observations, demonstrating magnetosphere‐ionosphere conjugacy, the inward (earthward) ASAID electric (E) field could also be investigated. These reveal the ASAID E field's fast‐time development by short‐circuiting when the hot‐ring‐current—cold‐plasmasphere interface developed and became impacted by finite Larmor radius effects because of the earthward intrusion of hot ring current protons. The ASAID E field's inner‐magnetosphere environment was characterized by the hot zone where heating was generated by low‐frequency waves and auroral kilometric radiations.

Antisunward Streaming Westward Sub‐Auroral Ion Drifts (SAID) Developed in the Postmidnight (1–4) Magnetic Local Time Sector During 2013

AbstractIn this study, we have surveyed the Defense Meteorological Satellite Program F15 plots of horizontal ion velocity measurements for the calendar year of 2013 and specified 15 antisunward (westward) sub‐auroral ion drifts (SAID) detections taken in the 1–4 magnetic local time (MLT) sector based on their respective underlying polar convections. We find that during these 15 SAID events, the strong duskside westward polar plasma convection extended across the midnight meridian into the postmidnight 1–4 MLT sector making there the westward SAID flows streaming antisunward. These antisunward (westward) SAID flows were observed only once as a northern‐southern conjugate pair over the Mid Pacific and repeatedly in the South American longitude sector's wider region. We could correlate six antisunward (westward) SAID flows with their respective nearby outward SAID E fields observed by one of the Van Allen Probe (VAP) satellites in the inner magnetosphere. These provided two strong correlations depicting inner‐magnetosphere—topside‐ionosphere conjugate observations and four weak correlations. The VAP observations illustrate (a) the newly‐formed outward SAID E field and (b) its plasma environment still showing (c) the signatures of short‐circuiting across (d) the newly‐formed plasmapause appearing with (e) the hot zone on the earthward/tailward side and sometimes with (f) a localized heat source. Implying different underlying heating mechanisms, the hot zone and the heat source were associated with energetic plasma particles accelerated by plasma turbulence, low‐frequency waves including electromagnetic ion cyclotron waves, and/or auroral kilometric radiation bursts.

DMSP Poynting Flux: Data Processing and Inter-Spacecraft Comparisons.

Poynting flux (PF) calculated from low Earth orbit spacecraft in situ ion drift and magnetic field measurements is an important measure of energy exchange between the magnetosphere and ionosphere. Defense Meteorological Satellite Program (DMSP) spacecraft provide an extensive back‐catalog of ion drift and magnetic perturbation measurements, from which quasi‐steady PF could be calculated. However, since DMSP are operations‐focused spacecraft, data must be carefully preprocessed for research use. We describe an automated approach for calculating earthward PF focusing on pre‐processing and quality control. We produce a PF data set using nine satellite‐years of DMSP F15, F16, and F18 observations. To validate our process we inter‐compare PF from different spacecraft using more than 2,000 magnetic conjunction events. We find no serious systematic differences. We further describe and apply an equal‐area binning technique to obtain average spatial patterns of PF, magnetic perturbation, electric field and ion drift velocity. We perform our analysis using all components of electric and magnetic field and comment on the adverse consequences of the typical single‐electric‐field‐component DMSP PF approximation on inter‐spacecraft agreement. Including full‐field components significantly increases the relative strength of near‐cusp PF and increases the integrated high‐latitude PF by ∼25%.

Multi‐instrumental Observations of the Quasi‐16‐Day Variations From the Lower Thermosphere to the Topside Ionosphere in the Low‐Latitude Eastern Asian Sector During the 2017 Sudden Stratospheric Warming Event

AbstractVariations of the low‐latitude ionosphere in the eastern Asian sector during the 2017 sudden stratospheric warming (SSW) were studied with multi‐instrumental observations that correspond to different altitudes. Specifically, the variations of the topside ionosphere as high as over 830 km were investigated with data from the Swarm B satellite (~500 km), the Defense Meteorological Satellite Program F15 satellite (~830 km), and the Meteorological Operational satellite‐A (~830 km). The main results are as follows. (1) Simultaneous variations were detected in the ionospheric parameters from the E region to the topside ionosphere around the first peak warming of the 2017 SSW. (2) These variations exhibited similar quasi‐16‐day (Q16D; ~14.5‐day) periods, and these periods were most significant just before the first peak warming. (3) These simultaneous Q16D variations were not due to the solar extreme ultraviolet irradiance or geomagnetic activities but were probably driven from below, by planetary waves or semidiurnal lunar tides that enhanced during the SSW. (4) The Q16D variation of the topside ionospheric electron density at ~830 km was probably driven not only by the upward mapping electric field modulated in the E region dynamo but also by the electric field modulated in the F region dynamo.

Abnormal Subauroral Ion Drifts (ASAID) and Pi2s During Cross‐Tail Current Disruptions Observed by Polar on the Magnetically Quiet Days of October 2003

AbstractIn this study we further investigate the development of abnormal subauroral ion drifts/polarization streams (ASAID/ASAPS) during the magnetically quiet days of 9–10 October 2003. Our main aim is to provide direct observational evidence verifying that the Defense Meteorological Satellite Program F15 detected quiet‐time ASAID/ASAPS features developed due to the formation of a magnetospheric cold plasma ripple‐hot ring current interface. By utilizing multisatellite and multi‐instrument Cluster_C2, Polar, and Defense Meteorological Satellite Program observations, we investigate plasma rippling and Pi2 pulsation events. In good agreement with the associated empirical scenario of plasma sheet rippling, we demonstrate with various C2 and Polar events the following observational results. (1) The rippling of the plasma sheet's inner edge was related to the process of cross‐tail current disruption and its earthward propagation. (2) The Pi2 pulsation of the cross‐tail EY field reversed the local convection flow when EY was dawnward directed and thus caused plasma ripples while (3) energy was provided by the earthward flows' braking/deceleration. (4) The ASAID/ASAPS feature's underlying EY is antisunward (or dawnward) and EZ is inward (or earthward). By tracking the cross‐tail current disruptions' tailward (by Cluster_C2) and earthward (by Polar) propagations, almost simultaneously, our results demonstrate also that the convection flows' local reversal by the dawnward EY is a common feature of both the tailward and the earthward flows. This study demonstrates also, with multiple plasmapause and EY detections made by Polar, the multiple and mixed occurrences of ASAID and SAID in the plasmasphere's rippled outer edge.

Poynting Flux in the Dayside Polar Cap Boundary Regions From DMSP F15 Satellite Measurements

AbstractPoynting flux, which describes electromagnetic energy flux, is an important energy source for the high‐latitude upper atmosphere. After the launch of Defense Meteorological Satellite Program (DMSP) F15 spacecraft with a boom‐mounted magnetometer on board, there was a new opportunity to calculate Earth‐directed Poynting flux at satellite altitudes (~850 km) in the upper atmosphere. A persistent enhancement of thermospheric density in the dayside polar cap boundary regions has been reported in the CHAMP satellite observations. To understand the significance of different physical mechanisms including Poynting flux and particle precipitation, and the correlation between them, a statistical study of Poytning flux and particle energy flux in the dayside cusp and low‐latitude boundary layer (LLBL) regions has been conducted based on DMSP F15 measurements. DMSP satellite observations showed a dominate downward Poynting flux for most cases in the cusp region. Our analysis of DMSP F15 data for five years (2000–2004) reveals that approximately 53% of 660 cusp crossings at 800–850 km showed strong downward Poynting flux (S > 10 mW/m2), 32% of the crossings had noticeable downward Poynting flux (S > 3 mW/m2), and 7% of the crossings did not show clear Poynting flux (S < 1 mW/m2). Only 13 out of 660 cusp crossings (~2%) showed noticeable upward Poynting flux. In the LLBL region, 35% of 11,641 LLBL crossings showed significant downward Poynting flux, 34% of the crossings had noticeable downward Poynting flux, and only 13% of the crossings did not show clear Poynting flux. On average, Poynting flux in LLBL is smaller than that in the cusp. The results show a slightly negative correlation between Poynting flux and particle precipitation energy flux in the dayside polar cap boundary regions. Statistically, Poynting flux in the cusp is enhanced during interplanetary magnetic field By positive conditions.

Motions of the Convection Reversal Boundary and Local Plasma in the High‐Latitude Ionosphere

AbstractWe present results from a systematic study of multisatellite samplings from the Defense Meteorological Satellite Program F13, F15, F16, F17, and F18 satellites over the period from 2007 to 2015 that describe the motion of the convection reversal boundary (CRB) and the local plasma flow across it. Focusing on the cases with continuous poleward and equatorward CRB motion sampled by three consecutive satellites within 50 min, 45% of the time the CRB motion may deviate from the local plasma motion near dawn and dusk where the reconnection process is unlikely to be present. Differences in the inferred CRB motion and the local plasma motion may arise from apparent motion induced by the local time displacement of consecutive samples across the CRB that is tilted with respect to a line of constant latitude. The presence of a viscous‐like interaction across the CRB can also contribute to the difference in the CRB and plasma motion. Accounting for these processes, the CRB motion and the motion of the plasma at the CRB are consistent only if a back and forth motion over a timescale of a few minutes is superimposed on a monotonic migration of the CRB over longer time periods.

Subauroral polarization stream on the outer boundary of the ring current during an energetic ion injection event

AbstractSubauroral polarization stream (SAPS) electric field can play an important role in the coupling between the inner magnetosphere and ionosphere; however, the production mechanism of SAPS has not been yet solved. During an energetic ion injection event on 26 March 2004, at latitudes lower than the equatorward boundaries of precipitating plasma sheet electrons and ions, the Defense Meteorological Satellite Program (DMSP) F13 satellite simultaneously observed a strong SAPS with the peak velocity of 1294 m/s and downward flowing field‐aligned currents (FACs). Conjugate observations of DMSP F13 and NOAA 15 satellites have shown that FACs flowing into the ionosphere just lie in the outer boundary of the ring current (RC). The downward flowing FACs were observed in a region of positive latitudinal gradients of the ion energy density, implying that the downward flowing FACs are more likely linked to the azimuthal gradient than the radial gradient of the RC ion pressure. Our result demonstrates that RC ion pressure gradients on the outer boundary of the RC in the evening sector during energetic ion injection events can lead to downward flowing FACs so as to cause strong SAPS in condition of low ionospheric conductivities.

Daytime ion and electron temperatures in the topside ionosphere at middle latitudes

AbstractIn the topside ionosphere during the daytime, the thermal electrons are directly heated by photoelectron fluxes from the local and conjugate hemispheres. The heat is lost primarily through conduction to the regions below where collisions with the ions provide the cooling. Ions are heated by collisions with both the electrons and ions and are cooled primarily by conduction to lower altitudes where the heat is lost to collisions with the neutral gas. Here we examine the effects of ion composition on the ion and electron temperatures in the midlatitude topside ionosphere during daytime using data from the Defense Meteorological Satellite Program F15 satellite in 2004–2006. The variations of electron and ion temperature with plasma density and composition indicate how the heat is exchanged between the different constituent ions and the role played by the solar zenith angle and the solar ionizing flux (F10.7). The observations show that the daytime temperature difference between the O+ and electron is smallest when the fractional contribution of H+ is the highest. In such an environment the electrons transfer heat to the H+ then to the O+ through ion‐ion collisions.

Predawn plasma bubble cluster observed in Southeast Asia

AbstractPredawn plasma bubble was detected as deep plasma depletion by GNU Radio Beacon Receiver (GRBR) network and in situ measurement onboard Defense Meteorological Satellite Program F15 (DMSPF15) satellite and was confirmed by sparse GPS network in Southeast Asia. In addition to the deep depletion, the GPS network revealed the coexisting submesoscale irregularities. A deep depletion is regarded as a primary bubble. Submesoscale irregularities are regarded as secondary bubbles. Primary bubble and secondary bubbles appeared together as a cluster with zonal wavelength of 50 km. An altitude of secondary bubbles happened to be lower than that of the primary bubble in the same cluster. The observed pattern of plasma bubble cluster is consistent with the simulation result of the recent high‐resolution bubble (HIRB) model. This event is only a single event out of 76 satellite passes at nighttime during 3–25 March 2012 that significantly shows plasma depletion at plasma bubble wall. The inside structure of the primary bubble was clearly revealed from the in situ density data of DMSPF15 satellite and the ground‐based GRBR total electron content.

Ionospheric observations during the geomagnetic storm events on 24–27 July 2004: Long‐duration positive storm effects

Ionospheric storms represent large global disturbances of the ionospheric F region electron density in response to geomagnetic storms. In this study, we use a combination of ionospheric total electron content (TEC) global maps and data from in‐situ satellite measurements, such as solar wind data from the Advanced Composition Explorer (ACE), the Defense Meteorological Satellite Program (DMSP), and TOPographic EXplorer (TOPEX) and JASON‐1 satellites, to investigate the ionospheric response during the geomagnetic storm event on 24–27 July 2004. A chain of ground‐based Global Positioning System (GPS) stations and ionosonde measurements across South Africa have been used to give a comprehensive coverage over this midlatitude location. The most pronounced ionospheric effects of the storm occurred at low‐ and midlatitudes in the Southern hemisphere, with the most significant enhancements, observed on 25 and 27 July, presented here. The DMSP F15 satellite observed a sharp density enhancement over the midlatitudes. Over South Africa, the enhancement on 25 July was about twice as large as that observed on 27 July. The positive storm enhancements on 25 and 27 July both lasted over 7 hours, and can be classified as long‐duration positive storm effects. Also, IMF Bz had southward orientation for an extended number of hours (exceeding 9 hours) and could have been the means by which energy was continuously fed into the magnetosphere and ionosphere. In addition, the F region critical frequency (foF2) values observed at two ionosonde stations showed marked positive responses that were associated with an increase in the ionospheric peak height (hmF2).

Response of the ionospheric F-region in the Brazilian sector during the super geomagnetic storm in April 2000 observed by GPS

The response of the ionospheric F-region in the equatorial and low latitude regions in the Brazilian sector during the super geomagnetic storm on 06–07 April 2000 has been studied in the present investigation. The geomagnetic storm reached a minimum D st of −288 nT at 0100 UT on 07 April. In this paper, we present vertical total electron content (VTEC) and phase fluctuations (in TECU/min) from GPS observations obtained at Imperatriz (5.5°S, 47.5°W; IMPZ), Brasília (15.9°S, 47.9°W; BRAZ), Presidente Prudente (22.12°S, 51.4°W; UEPP), and Porto Alegre (30.1°S, 51.1°W; POAL) during the period 05–08 April. Also, several GPS-based TEC maps are presented from the global GPS network, showing widespread and drastic TEC changes during the different phases of the geomagnetic storm. In addition, ion density measurements on-board the satellite Defense Meteorological Satellite Program (DMSP) F15 orbiting at an altitude of 840 km and the first Republic of China satellite (ROCSAT-1) orbiting at an altitude of 600 km are presented. The observations indicate that one of the orbits of the DMSP satellite is fairly close to the 4 GPS stations and both the DMSP F15 ion-density plots and the phase fluctuations from GPS observations show no ionospheric irregularities in the Brazilian sector before 2358 UT on the night of 06–07 April 2000. During the fast decrease of D st on 06 April, there is a prompt penetration of electric field of magnetospheric origin resulting in decrease of VTEC at IMPZ, an equatorial station and large increase in VTEC at POAL, a low latitude station. This resulted in strong phase fluctuations on the night of 06–07 April, up to POAL. During the daytime on 07 April during the recovery phase, the VTEC observations show positive ionospheric storm at all the GPS stations, from IMPZ to POAL, and the effect increasing from IMPZ to POAL. This is possibly linked to the equatorward directed meridional wind. During the daytime on 08 April (the recovery phase continues), the VTEC observations show very small negative ionospheric storm at IMPZ but the positive ionospheric storm effect is observed from BRAZ to POAL possibly linked to enhancement of the equatorial ionospheric anomaly.

Microwave Emission Brightness Temperature Histograms (METH) Rain Rates for Climate Studies: Remote Sensing Systems SSM/I Version-6 Results

Abstract A satellite microwave emission brightness temperature histograms (METH) technique has been applied to Special Sensor Microwave Imager (SSM/I) data taken on board the Defense Meteorological Satellite Program (DMSP) satellites and preprocessed by Remote Sensing Systems (RSS) Co. to produce 21 yr (July 1987–present) of oceanic rainfall products. These rain products are used as input to the Global Precipitation Climatology Project (GPCP) rain maps. Analysis of the METH product using SSM/I version-4 (V4) data shows jumps in vertically polarized 19-GHz brightness temperatures that are attributed to changes in DMSP satellites. A version-6 (V6) SSM/I that corrects for intersatellite differences was released by RSS in 2006. The jumps in the time series are reduced, with most of the changes occurring in the early part of the DMSP F13 data. The bias between RSS V6 and V4 of brightness temperature at 19 and 22 GHz is less than 0.5 K. METH rain rates were reprocessed using V6 data and were analyzed. The 20-yr global mean difference between the METH V4 and V6 is less than 0.3%, with differences as large as 3% in individual years. Trend analyses show increases in the oceanic rain belts, such as the intertropical convergence zone and the South Pacific convergence zone, and in the Bay of Bengal. These rain-rate trends, from both linear trend analysis and empirical mode decomposition analysis, are comparable to the version-2 GPCP analyses but are smaller than those found in the unified microwave ocean retrieval algorithm.

A Comparison of Oceanic Precipitation Estimates in the Tropics and Subtropics

Abstract A number of Earth remote sensing satellites are currently carrying passive microwave radiometers. A variety of different retrieval algorithms are used to estimate surface rain rates over the ocean from the microwave radiances observed by the radiometers. This study compares several different satellite algorithms with each other and with independent data from rain gauges on ocean buoys. The rain gauge data are from buoys operated by the NOAA Pacific Marine Environmental Laboratory. Potential errors and biases in the gauge data are evaluated. Satellite data are from the Tropical Rainfall Measuring Mission Microwave Imager and from the Special Sensor Microwave Imager instruments on the operational Defense Meteorological Satellite Program F13, F14, and F15 satellites. These data have been processed into rain-rate estimates by the NASA Precipitation Measurement Mission and by Remote Sensing Systems, Inc. Biases between the different datasets are estimated by computing differences between long-term time averages. Most of the satellite datasets agree with each other, and with the gauge data, to within 10% or less. The biases tend to be proportional to the mean rain rate, but the geographical patterns of bias vary depending on the choice of data source and algorithm. Some datasets, however, show biases as large as about 25%, so care should be taken when using these data for climatological studies.

Influences of geomagnetic fields on longitudinal variations of vertical plasma drifts in the presunset equatorial topside ionosphere

On the basis of the measurements from the ion drift meter on the Defense Meteorological Satellite Program F13 Satellite from 2000 to 2002, the relative longitudinal variations of E × B vertical plasma drifts in the presunset equatorial topside ionosphere at 1745 LT are examined. Obvious influences of geomagnetic fields on longitudinal variations of E × B vertical plasma drifts, which also show a seasonal dependence, have been found. During the June solstice, the relative vertical plasma drifts is most significantly influenced by the geomagnetic field declination. However, the relative vertical plasma drifts during the December solstice more strongly correlates with the geomagnetic field strength. Although the relative vertical plasma drifts during equinox are also influenced by the geomagnetic field declination, an underlying dependence on magnetic field magnitude, as seen in December, is also present.

Impact of the solar wind dynamic pressure on the Region 2 field‐aligned currents

The relationship between the Region 2 field‐aligned currents and the solar wind dynamic pressure is investigated using magnetic field data from Defense Meteorological Satellite Program‐F13 (DMSP‐F13). The generation of the Region 2 currents is associated with the direction of the magnetic pressure gradient in the magnetosphere, in relation to that of the thermal pressure gradient. Past spacecraft observations have suggested that the spatial distribution of the magnetic pressure in the magnetosphere varies with the solar wind dynamic pressure. Therefore, we can expect that the Region 2 currents would depend on the solar wind dynamic pressure. We compared the Region 2 field‐aligned current intensity at the altitude of the ionosphere, as derived using magnetic field data from DMSP‐F13, with the solar wind dynamic pressure derived from OMNI2 hourly data. It was confirmed that the Region 2 current intensity depends on the solar wind dynamic pressure during magnetic storms. During nonstorm times, however, the correlation between the Region 2 currents and the solar wind dynamic pressure is weak. The weak correlation during nonstorm times suggests that the plasma pressure in the ring current region is also essential for the effect of the solar wind dynamic pressure on the Region 2 currents.

Variational Assimilation of Global Microwave Rainfall Retrievals: Physical and Dynamical Impact on GEOS Analyses

Abstract Global microwave rainfall retrievals from a five-satellite constellation, including the Tropical Rainfall Measuring Mission Microwave Imager, Special Sensor Microwave Imager from the Defense Meteorological Satellite Program F13, F14, and F15, and the Advanced Microwave Scanning Radiometer from the Earth Observing System Aqua, are assimilated into the NASA Goddard Earth Observing System (GEOS) Data Assimilation System using a 1D variational continuous assimilation (VCA) algorithm. The physical and dynamical impact of rainfall assimilation on GEOS analyses is examined at various temporal and spatial scales. This study demonstrates that the 1D VCA algorithm, which was originally developed and evaluated for rainfall assimilations over tropical oceans, can effectively assimilate satellite microwave rainfall retrievals and improve GEOS analyses over both the Tropics and the extratropics where the atmospheric processes are dominated by different large-scale dynamics and moist physics, and also over land, where rainfall estimates from passive microwave radiometers are believed to be less accurate. Results show that rainfall assimilation renders the GEOS analysis physically and dynamically more consistent with the observed precipitation at the monthly mean and 6-h time scales. Over regions where the model precipitation tends to misbehave in distinctly different rainy regimes, the 1D VCA algorithm, by compensating for errors in the model’s moist time tendency in a 6-h analysis window, is able to bring the rainfall analysis closer to the observed. The radiation and cloud fields also tend to be in better agreement with independent satellite observations in the rainfall–assimilation run especially over regions where rainfall analyses indicate large improvements. Assimilation experiments with and without rainfall data for a midlatitude frontal system clearly indicate that the GEOS analysis is improved through changes in the thermodynamic and dynamic fields that respond to the rainfall assimilation. The synoptic structures of temperature, moisture, winds, divergence, and vertical motion, as well as vorticity, are more realistically captured across the front.

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

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

Spike‐like change of the vertical E × B drift in the equatorial region during very large geomagnetic storms

We investigate the characteristics of the storm‐time disturbance electric fields in the equatorial region using the measurements of the vertical ion velocity from the Defense Meteorological Satellite Program F13 and the first Republic of China Satellite during the selected 43 geomagnetic storms of Dst <−100 nT in 2000–2004. The distinguishing feature in both observations is the occurrence of the spike‐like vertical E × B drift during the main phase of very large storms (Dst <−150 nT). The spikes occur simultaneously at different local times but the direction of the spikes shows a dependence on the local time. The spikes are upward on the dayside and downward on the nightside. The observed characteristics of the spikes can be explained by the penetration of the dawn‐to‐dusk polar cap electric field to low latitude.

Ionospheric disturbances during the magnetic storm of 15 July 2000: Role of the fountain effect and plasma bubbles for the formation of large equatorial plasma density depletions

[1] We investigate the role of the fountain effect and plasma bubbles for the formation of the large equatorial plasma depletions during the geomagnetic storm of 15 July 2000. The large equatorial plasma depletions are detected in the Atlantic sector on the night of the 15th by the Defense Meteorological Satellite Program (DMSP) F15 and the first Republic of China Satellite (ROCSAT-1). The observations show discontinuous drop of the plasma density at the walls of the depletions, flat plasma density inside the depletions, and persistence or growth of the depletions over night. These properties are not consistent with the trough morphology induced by the fountain effect. The coincident ionospheric observations of DMSP F15 and ROCSAT-1 demonstrate that the large depletions are created in the longitude regions where plasma bubbles are present. The occurrence of the large depletions after sunset, elongation in the north-south direction, formation of steep walls, and colocation with plasma bubbles at lower altitudes or earlier times suggest that the large depletions are closely associated with plasma bubbles.