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Bela G Fejer - One of the best experts on this subject based on the ideXlab platform.
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multi instrumented observations of the equatorial f region during june Solstice large scale wave structures and spread f
Progress in Earth and Planetary Science, 2018Co-Authors: F S Rodrigues, Bela G Fejer, Dustin A Hickey, Weijia Zhan, C R Martinis, M A Milla, Juan F ArratiaAbstract:Typical equatorial spread-F events are often said to occur during post-sunset, equinox conditions in most longitude sectors. Recent studies, however, have found an unexpected high occurrence of ionospheric F-region irregularities during June Solstice, when conditions are believed to be unfavorable for the development of plasma instabilities responsible for equatorial spread-F (ESF). This study reports new results of a multi-instrumented investigation with the objective to better specify the occurrence of these atypical June Solstice ESF in the American sector and better understand the conditions prior to their development. We present the first observations of June Solstice ESF events over the Jicamarca Radio Observatory (11.95° S, 76.87° W, ∼ 1° dip latitude) made by a 14-panel version of the Advanced Modular Incoherent Scatter Radar system (AMISR-14). The observations were made between July 11 and August 4, 2016, under low solar flux conditions and in conjunction with dual-frequency GPS, airglow, and digisonde measurements. We found echoes occurring in the pre-, post-, and both pre- and post-midnight sectors. While at least some of these June Solstice ESF events could have been attributed to disturbed electric fields, a few events also occurred during geomagnetically quiet conditions. The late appearance (22:00 LT or later) of three of the observed events, during clear-sky nights, provided a unique opportunity to investigate the equatorial bottomside F-region conditions, prior to ESF, using nighttime airglow measurements. We found that the airglow measurements (630 nm) made by a collocated all-sky camera show the occurrence of ionospheric bottomside F-region perturbations prior to the detection of ESF echoes in all three nights. The airglow fluctuations appear as early as 1 hour prior to radar echoes, grow in amplitude, and then coincide with ESF structures observed by AMISR-14 and GPS TEC measurements. They also show some of the features of the so-called large-scale wave structures (LSWS) that have been detected, previously, using other types of observations and have been suggested to be precursors of ESF. The bottomside fluctuations have zonal spacings between 300 and 500 km, are aligned with the magnetic meridian, and extend at least a few degrees in magnetic latitude.
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direct comparison of nonmigrating tidal signatures in the electrojet vertical plasma drift and equatorial ionization anomaly
Journal of Atmospheric and Solar-Terrestrial Physics, 2012Co-Authors: H Luhr, Martin Rother, K Hausler, Bela G Fejer, P AlkenAbstract:Abstract This paper presents for the first time a full decomposition of tidal signatures in three important ionospheric quantities, the equatorial electrojet (EEJ), vertical plasma drift and the crest-to-trough ratio (CTR) of the equatorial ionization anomaly. Data sources are the EEJM-2 model, ROCSAT-1 data and CHAMP electron density measurements. The analysis is based on data sampled around the solar maximum 23 (2000–2004). Full spectra of the predominant nonmigrating tides were determined. The tidal component DE3 is dominating the spectrum during the months around August in all three quantities. Conversely, DE3 disappears around December Solstice everywhere. The August enhancement in EEJ strength is almost 3 times larger than that in plasma drift and CTR. The DE2 tide is strong during Solstice months and shows minima around equinoxes. The relative amplitudes of the annual variations are much the same for the three investigated quantities. The EEJ and the zonal wind around 100 km altitude exhibit almost identical DE2 and DE3 annual variations. Similarly, the vertical plasma drift and the zonal wind around 400 km altitude show much the same DE2 and DE3 annual variations. But their phase values are quite different, making a direct interaction less probable. Clear DE2 and DE3 tidal signature are only found in ionospheric quantities during daylight hours. There is a suite of other nonmigrating tides, which can be explained by the interaction of migrating diurnal and semi-diurnal solar tides with stationary longitudinal structures. These tides are prominent during Solstices and generally weak during equinoxes.
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quiet time equatorial f region vertical plasma drift model derived from rocsat 1 observations
Journal of Geophysical Research, 2008Co-Authors: Bela G Fejer, John W Jensen, S Y SuAbstract:[1] We have used five years of measurements on board the ROCSAT-1 satellite to develop a detailed quiet time global empirical model for equatorial F region vertical plasma drifts. This model describes the local time, seasonal and longitudinal dependence of the vertical drifts for an altitude of 600 km under moderate and high solar flux conditions. The model results are in excellent agreement with measurements from the Jicamarca radar and also from other ground-based and in situ probes. We show that the longitudinal dependence of the daytime and nighttime vertical drifts is much stronger than reported earlier, especially during December and June Solstice. The late night downward drift velocities are larger in the eastern than in the western hemisphere at all seasons, the morning and afternoon December Solstice drifts have significantly different longitudinal dependence, and the daytime upward drifts have strong wave number-four signatures during equinox and June Solstice. The largest evening upward drifts occur during equinox and December Solstice near the American sector. The longitudinal variations of the evening prereversal velocity peaks during December and June Solstice are anti-correlated, which further indicates the importance of conductivity effects on the electrodynamics of the equatorial ionosphere.
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radar and satellite global equatorial f region vertical drift model
Journal of Geophysical Research, 1999Co-Authors: L Scherliess, Bela G FejerAbstract:We present the first global empirical model for the quiet time F region equatorial vertical drifts based on combined incoherent scatter radar observations at Jicamarca and Ion Drift Meter observations on board the Atmospheric Explorer E satellite. This analytical model, based on products of cubic-B splines and with nearly conservative electric fields, describes the diurnal and seasonal variations of the equatorial vertical drifts for a continuous range of all longitudes and solar flux values. Our results indicate that during solar minimum, the evening prereversal velocity enhancement exhibits only small longitudinal variations during equinox with amplitudes of about 15–20 m/s, is observed only in the American sector during December Solstice with amplitudes of about 5–10 m/s, and is absent at all longitudes during June Solstice. The solar minimum evening reversal times are fairly independent of longitude except during December Solstice. During solar maximum, the evening upward vertical drifts and reversal times exhibit large longitudinal variations, particularly during the Solstices. In this case, for a solar flux index of 180, the June Solstice evening peak drifts maximize in the Pacific region with drift amplitudes of up to 35 m/s, whereas the December Solstice velocities maximize in the American sector with comparable magnitudes. The equinoctial peak velocities vary between about 35 and 45 m/s. The morning reversal times and the daytime drifts exhibit only small variations with the phase of the solar cycle. The daytime drifts have largest amplitudes between about 0900 and 1100 LT with typical values of 25–30 m/s. We also show that our model results are in good agreement with other equatorial ground-based observations over India, Brazil, and Kwajalein.
Wenbin Wang - One of the best experts on this subject based on the ideXlab platform.
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seasonal and hemispheric variations of the total auroral precipitation energy flux from timed guvi
Journal of Geophysical Research, 2010Co-Authors: Xiaoli Luan, Wenbin Wang, A G Burns, Stanley C. Solomon, Y Zhang, L J PaxtonAbstract:[1] The auroral hemispheric power (HP) has been calculated from the averaged energy flux derived from Far-ultraviolet emission observations made by the global ultraviolet imager (GUVI) instrument on board the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite during 2002–2007. This HP was used to study how variations in seasonal and hemispheric asymmetries changed with changing geomagnetic activity. Our results showed that there were persistent seasonal and hemispheric differences in quiet conditions. There were HP differences of about 1–3 GW between the summer and winter seasons in each hemisphere and also between the two hemispheres during each Solstice period for low geomagnetic activity (Kp ≤ 3). The summer-winter asymmetry was 4%–35% when HP was low. These summer-winter differences became negligible when geomagnetic activity was moderate to active. Similarly, there were also HP differences of about 2 GW between local summers of the two hemispheres during geomagnetically quiet conditions (Kp < 3) but not during higher Kp conditions. The hemispheric asymmetries between the two summer Solstices were about 10%–20% during quiet conditions, whereas there was no apparent hemispheric asymmetry between the two winter Solstices under all Kp 1–5 conditions. Solar illumination effects were probably the primary cause of the seasonal and hemispheric variations of the auroral hemispheric power for these geomagnetically quiet conditions. During moderate and active conditions the conductivities were driven more by the production of ionization due to precipitation, so the precipitation was more symmetric.
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midlatitude summer nighttime anomaly of the ionospheric electron density observed by formosat 3 cosmic
Journal of Geophysical Research, 2010Co-Authors: C H Lin, Chiahung Chen, Jannyenq Liu, C H Liu, A G Burns, Wenbin WangAbstract:[1] This paper presents monthly variations of the midlatitude summer nighttime anomaly (MSNA) of the ionosphere for the first time by global observations of the FORMOSAT-3/COSMIC (F3/C) mission. The anomaly is characterized by the greater nighttime (1800 LT ∼ 0200 LT) ionospheric electron density than during daytime (0800 ∼ 1800 LT) at middle latitudes during months around June and December Solstices. The anomaly shown during December Solstice was known as the Weddell Sea Anomaly (WSA) occurring around the Antarctica and nearby the Pacific Ocean. This paper demonstrates that the WSA-like feature also exists in the Northern Hemisphere and is most prominent near the Northeast Asia, Europe/Africa, and Central Pacific longitudes around June Solstice. In both hemispheres, the anomalies with similar electron density characteristics and variations caused by the similar mechanism prompts us to name this phenomenon the MSNA. The monthly F3/C observations indicate that the anomaly appears as the most prominent structure of the global ionosphere around midnight hours.
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seasonal and solar activity variations of the weddell sea anomaly observed in the topex total electron content measurements
Journal of Geophysical Research, 2009Co-Authors: Geonhwa Jee, A G Burns, Yong Ha Kim, Wenbin WangAbstract:[1] The Weddell Sea Anomaly (WSA) in the ionosphere is characterized by higher plasma densities at night than during the day in the region near the Weddell Sea. According to previous studies on the WSA, it is known to occur mostly in southern summer and has not been reported in other seasons. We have utilized more than 13 years of TOPEX total electron content (TEC) measurements in order to study how the WSA varies with seasons and how it changes with solar activity. The TOPEX TEC data have been extensively utilized for climatological studies of the ionosphere because of their excellent spatial and temporal coverage. We investigate the seasonal and solar activity variations of the WSA using four seasonal cases (March equinox, June Solstice, September equinox, and December Solstice) and two solar activity conditions (F10.7 120 for solar maximum conditions) for geomagnetically quiet periods. Our analysis shows that (1) the WSA occurs only in the southern summer hemisphere for low F10.7, as in previous studies, but (2) the WSA occurs in all seasons except for winter when F10.7 is high; it is most prominent during the December Solstice (southern summer) and still strong during both equinoxes. The TOPEX TEC maps in the midlatitude and high-latitude ionosphere display significant global longitudinal variations for a given local time in the Southern Hemisphere, which varies with season and solar activity. The observed WSA appears to be an extreme manifestation of the longitudinal variations.
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ionospheric annual asymmetry observed by the cosmic radio occultation measurements and simulated by the tiegcm
Journal of Geophysical Research, 2008Co-Authors: Wenbin Wang, A G Burns, Zhen Zeng, Jiuhou Lei, Stan Solomon, Stig Syndergaard, Liying Qian, Yinghwa KuoAbstract:[1] Average F2-layer electron densities at December Solstice are higher than those at June Solstice. This phenomenon, which is often called the F2-layer annual asymmetry, has been observed for several decades, but its causes are still not fully understood. This study investigates global variations of this annual asymmetry observed from one year of the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) ionospheric radio occultation (IRO) measurements. The IRO observations show that there is a strong NmF2 annual asymmetry that has significant longitudinal and local time variations. A strong peak of the asymmetry occurs at about noon and another one at midnight, both located at around 25° geomagnetic latitude. Numerical simulations using the Thermosphere-Ionosphere Electrodynamics Global Circulation Model (TIEGCM) are in very good agreement with these observations. The modeled NmF2 annual asymmetry has a similar magnitude, and similar semidiurnal and longitudinal variations as those in the observations. TIEGCM simulations show that changes in solar extreme ultraviolet (EUV) radiation between the December and June Solstices and the displacement of the geomagnetic axis from the geographic axis are the two primary processes that cause the annual asymmetry and its associated longitudinal and local time variations. The tides propagating from lower altitudes also contribute to this asymmetry, but to a smaller extent.
H Luhr - One of the best experts on this subject based on the ideXlab platform.
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nonmigrating tidal signatures in the magnitude and the inter hemispheric asymmetry of the equatorial ionization anomaly
Annales Geophysicae, 2013Co-Authors: Chao Xiong, H LuhrAbstract:Abstract. Based on nine years of observations from the satellites CHAMP and GRACE the tidal signatures in the magnitude and the inter-hemisphere asymmetry of the equatorial ionization anomaly (EIA) have been investigated in this study. The EIA magnitude parameters show longitudinal wavenumber 4 and 3 (WN4/WN3) patterns during the months around August and December, respectively, while for different EIA parameters the contributions of the various tidal parameters are different. For the crest-to-trough ratio (CTR) the dominating nonmigrating tidal component contributing to WN4 is DE3 during the months around August, while during the months around December Solstice the stationary planetary wave, SPW3, takes a comparable role to DE2 in contributing to WN3. For the apex height index (ApexHC) of the EIA fluxtube the stationary planetary waves, SPW4/SPW3, exceed the amplitudes of DE3/DE2 taking the leading role in causing the longitudinal WN4/WN3 patterns. During the months around December Solstice the SW3 tide is prominent in both CTR and ApexHC. SW3 shows a strong dependence on the solar flux level, while it is hardly dependent on magnetic activity. For the EIA inter-hemispheric asymmetry only WN1 and WN2 longitudinal patterns can be seen. During June Solstice months the pattern can be explained by stationary planetary waves SPW1 and SPW2. Conversely, around December Solstice months longitudinal features exhibit some local time evolution, in particular the diurnal nonmigrating tide D0 takes the leading role.
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direct comparison of nonmigrating tidal signatures in the electrojet vertical plasma drift and equatorial ionization anomaly
Journal of Atmospheric and Solar-Terrestrial Physics, 2012Co-Authors: H Luhr, Martin Rother, K Hausler, Bela G Fejer, P AlkenAbstract:Abstract This paper presents for the first time a full decomposition of tidal signatures in three important ionospheric quantities, the equatorial electrojet (EEJ), vertical plasma drift and the crest-to-trough ratio (CTR) of the equatorial ionization anomaly. Data sources are the EEJM-2 model, ROCSAT-1 data and CHAMP electron density measurements. The analysis is based on data sampled around the solar maximum 23 (2000–2004). Full spectra of the predominant nonmigrating tides were determined. The tidal component DE3 is dominating the spectrum during the months around August in all three quantities. Conversely, DE3 disappears around December Solstice everywhere. The August enhancement in EEJ strength is almost 3 times larger than that in plasma drift and CTR. The DE2 tide is strong during Solstice months and shows minima around equinoxes. The relative amplitudes of the annual variations are much the same for the three investigated quantities. The EEJ and the zonal wind around 100 km altitude exhibit almost identical DE2 and DE3 annual variations. Similarly, the vertical plasma drift and the zonal wind around 400 km altitude show much the same DE2 and DE3 annual variations. But their phase values are quite different, making a direct interaction less probable. Clear DE2 and DE3 tidal signature are only found in ionospheric quantities during daylight hours. There is a suite of other nonmigrating tides, which can be explained by the interaction of migrating diurnal and semi-diurnal solar tides with stationary longitudinal structures. These tides are prominent during Solstices and generally weak during equinoxes.
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the influence of nonmigrating tides on the longitudinal variation of the equatorial electrojet
Journal of Geophysical Research, 2008Co-Authors: H Luhr, Martin Rother, K Hausler, P Alken, Stefan MausAbstract:[1] The climatological model of the equatorial electrojet, EEJM-1, derived from Orsted, CHAMP and SAC-C satellite measurements provides the opportunity to investigate the longitudinal variation of the current strength in detail. Special emphasis is put in this study on the effect of nonmigrating tides. We have found that the influence of the diurnal eastward-propagating mode with wavenumber-3, DE3, is particularly strong. In polar orbiting satellite observations the DE3 tidal signal appears as a four-peaked longitudinal structure. We have put special emphasis in our analysis to isolate the DE3 contribution from other sources contributing to the wavenumber-4 structure in satellite data. The amplitude of the DE3 signature in the EEJ not only peaks during equinox seasons, but is also strong around the June Solstice. When looking at the modulation of the EEJ intensity the DE3 accounts for about 25% during the months of April through September. It is thus the dominant cause for longitudinal variations. During December Solstice months the influence of DE3 is negligible. A secondary three-peaked longitudinal pattern emerges during Solstice seasons when the DE3 influence is removed. From the data available it is, however, not clear whether this pattern is related to any tidal drivers.
A G Burns - One of the best experts on this subject based on the ideXlab platform.
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seasonal and hemispheric variations of the total auroral precipitation energy flux from timed guvi
Journal of Geophysical Research, 2010Co-Authors: Xiaoli Luan, Wenbin Wang, A G Burns, Stanley C. Solomon, Y Zhang, L J PaxtonAbstract:[1] The auroral hemispheric power (HP) has been calculated from the averaged energy flux derived from Far-ultraviolet emission observations made by the global ultraviolet imager (GUVI) instrument on board the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite during 2002–2007. This HP was used to study how variations in seasonal and hemispheric asymmetries changed with changing geomagnetic activity. Our results showed that there were persistent seasonal and hemispheric differences in quiet conditions. There were HP differences of about 1–3 GW between the summer and winter seasons in each hemisphere and also between the two hemispheres during each Solstice period for low geomagnetic activity (Kp ≤ 3). The summer-winter asymmetry was 4%–35% when HP was low. These summer-winter differences became negligible when geomagnetic activity was moderate to active. Similarly, there were also HP differences of about 2 GW between local summers of the two hemispheres during geomagnetically quiet conditions (Kp < 3) but not during higher Kp conditions. The hemispheric asymmetries between the two summer Solstices were about 10%–20% during quiet conditions, whereas there was no apparent hemispheric asymmetry between the two winter Solstices under all Kp 1–5 conditions. Solar illumination effects were probably the primary cause of the seasonal and hemispheric variations of the auroral hemispheric power for these geomagnetically quiet conditions. During moderate and active conditions the conductivities were driven more by the production of ionization due to precipitation, so the precipitation was more symmetric.
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midlatitude summer nighttime anomaly of the ionospheric electron density observed by formosat 3 cosmic
Journal of Geophysical Research, 2010Co-Authors: C H Lin, Chiahung Chen, Jannyenq Liu, C H Liu, A G Burns, Wenbin WangAbstract:[1] This paper presents monthly variations of the midlatitude summer nighttime anomaly (MSNA) of the ionosphere for the first time by global observations of the FORMOSAT-3/COSMIC (F3/C) mission. The anomaly is characterized by the greater nighttime (1800 LT ∼ 0200 LT) ionospheric electron density than during daytime (0800 ∼ 1800 LT) at middle latitudes during months around June and December Solstices. The anomaly shown during December Solstice was known as the Weddell Sea Anomaly (WSA) occurring around the Antarctica and nearby the Pacific Ocean. This paper demonstrates that the WSA-like feature also exists in the Northern Hemisphere and is most prominent near the Northeast Asia, Europe/Africa, and Central Pacific longitudes around June Solstice. In both hemispheres, the anomalies with similar electron density characteristics and variations caused by the similar mechanism prompts us to name this phenomenon the MSNA. The monthly F3/C observations indicate that the anomaly appears as the most prominent structure of the global ionosphere around midnight hours.
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seasonal and solar activity variations of the weddell sea anomaly observed in the topex total electron content measurements
Journal of Geophysical Research, 2009Co-Authors: Geonhwa Jee, A G Burns, Yong Ha Kim, Wenbin WangAbstract:[1] The Weddell Sea Anomaly (WSA) in the ionosphere is characterized by higher plasma densities at night than during the day in the region near the Weddell Sea. According to previous studies on the WSA, it is known to occur mostly in southern summer and has not been reported in other seasons. We have utilized more than 13 years of TOPEX total electron content (TEC) measurements in order to study how the WSA varies with seasons and how it changes with solar activity. The TOPEX TEC data have been extensively utilized for climatological studies of the ionosphere because of their excellent spatial and temporal coverage. We investigate the seasonal and solar activity variations of the WSA using four seasonal cases (March equinox, June Solstice, September equinox, and December Solstice) and two solar activity conditions (F10.7 120 for solar maximum conditions) for geomagnetically quiet periods. Our analysis shows that (1) the WSA occurs only in the southern summer hemisphere for low F10.7, as in previous studies, but (2) the WSA occurs in all seasons except for winter when F10.7 is high; it is most prominent during the December Solstice (southern summer) and still strong during both equinoxes. The TOPEX TEC maps in the midlatitude and high-latitude ionosphere display significant global longitudinal variations for a given local time in the Southern Hemisphere, which varies with season and solar activity. The observed WSA appears to be an extreme manifestation of the longitudinal variations.
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ionospheric annual asymmetry observed by the cosmic radio occultation measurements and simulated by the tiegcm
Journal of Geophysical Research, 2008Co-Authors: Wenbin Wang, A G Burns, Zhen Zeng, Jiuhou Lei, Stan Solomon, Stig Syndergaard, Liying Qian, Yinghwa KuoAbstract:[1] Average F2-layer electron densities at December Solstice are higher than those at June Solstice. This phenomenon, which is often called the F2-layer annual asymmetry, has been observed for several decades, but its causes are still not fully understood. This study investigates global variations of this annual asymmetry observed from one year of the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) ionospheric radio occultation (IRO) measurements. The IRO observations show that there is a strong NmF2 annual asymmetry that has significant longitudinal and local time variations. A strong peak of the asymmetry occurs at about noon and another one at midnight, both located at around 25° geomagnetic latitude. Numerical simulations using the Thermosphere-Ionosphere Electrodynamics Global Circulation Model (TIEGCM) are in very good agreement with these observations. The modeled NmF2 annual asymmetry has a similar magnitude, and similar semidiurnal and longitudinal variations as those in the observations. TIEGCM simulations show that changes in solar extreme ultraviolet (EUV) radiation between the December and June Solstices and the displacement of the geomagnetic axis from the geographic axis are the two primary processes that cause the annual asymmetry and its associated longitudinal and local time variations. The tides propagating from lower altitudes also contribute to this asymmetry, but to a smaller extent.
S Y Su - One of the best experts on this subject based on the ideXlab platform.
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quiet time equatorial f region vertical plasma drift model derived from rocsat 1 observations
Journal of Geophysical Research, 2008Co-Authors: Bela G Fejer, John W Jensen, S Y SuAbstract:[1] We have used five years of measurements on board the ROCSAT-1 satellite to develop a detailed quiet time global empirical model for equatorial F region vertical plasma drifts. This model describes the local time, seasonal and longitudinal dependence of the vertical drifts for an altitude of 600 km under moderate and high solar flux conditions. The model results are in excellent agreement with measurements from the Jicamarca radar and also from other ground-based and in situ probes. We show that the longitudinal dependence of the daytime and nighttime vertical drifts is much stronger than reported earlier, especially during December and June Solstice. The late night downward drift velocities are larger in the eastern than in the western hemisphere at all seasons, the morning and afternoon December Solstice drifts have significantly different longitudinal dependence, and the daytime upward drifts have strong wave number-four signatures during equinox and June Solstice. The largest evening upward drifts occur during equinox and December Solstice near the American sector. The longitudinal variations of the evening prereversal velocity peaks during December and June Solstice are anti-correlated, which further indicates the importance of conductivity effects on the electrodynamics of the equatorial ionosphere.
