Browsing by Author "Fejer, Bela G."
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Item Open Access Climatology of postsunset equatorial spread F over Jicamarca(American Geophysical Union, 2009-07) Chapagain, Narayan P.; Fejer, Bela G.; Chau Chong Shing, Jorge LuisWe use radar observations from 1996 to 2006 to study the climatology of postsunset equatorial 3-m spread F irregularities over Jicamarca during all seasons. We show that the spread F onset times do not change with solar flux and that their onset heights, which occur near the altitude of the evening F region velocity vortex, increase linearly from about 260 to 400 km from solar minimum to solar maximum. Higher onset heights generally lead to stronger radar echoes. During the equinox, spread F onset occurs near vertical drift evening reversal times, while during the December solstice, they occur near the drift reversal times close to solar minimum and near the time of the prereversal velocity peak for high solar flux conditions. On average, radar plume onset occurs earlier with increasing solar flux in all seasons. Plume onset and peak altitudes increase with solar activity, and the peak heights are generally highest during the equinox. The F region upward drift velocities that precede spread F onset increase from solar minimum to solar maximum and are approximately proportional to the maximum prereversal drift peak velocities.Item Restricted Daytime plasma drifts in the equatorial lower ionosphere(American Geophysical Union, 2015-10-19) Hui, Debrup; Fejer, Bela G.We have used extensive radar measurements from the Jicamarca Observatory during low solar flux periods to study the quiet time variability and altitudinal dependence of equatorial daytime vertical and zonal plasma drifts. The daytime vertical drifts are upward and have largest values during September–October. The day‐to‐day variability of these drifts does not change with height between 150 and 600 km, but the bimonthly variability is much larger in the F region than below about 200 km. These drifts vary linearly with height generally increasing in the morning and decreasing in the afternoon. The zonal drifts are westward during the day and have largest values during July–October. The 150 km region zonal drifts have much larger day‐to‐day, but much smaller bimonthly variability than the F region drifts. The daytime zonal drifts strongly increase with height up to about 300 km from March through October, and more weakly at higher altitudes. The December solstice zonal drifts have generally weaker altitudinal dependence, except perhaps below 200 km. Current theoretical and general circulation models do not reproduce the observed altitudinal variation of the daytime equatorial zonal drifts.Item Restricted Equatorial and low latitude ionospheric effects during sudden stratospheric warming events(Instituto Geofísico del Perú, 2011-08-13) Chau Chong Shing, Jorge Luis; Goncharenko, Larisa P.; Fejer, Bela G.; Liu, Han L.The sources of ionospheric forcing are from above (solar and magnetospheric forces), internal (chemistry, local neutral dynamics), and from below (lower atmosphere). In this work we review the observed ion-neutral coupling effects at equatorial and low latitudes during large meteorological events called sudden stratospheric warming (SSW). Research in this direction has been accelerated in recent years mainly due to: (1) extensive observing campaigns, and (2) solar minimum conditions. The former has been instrumental to catch the events before, during, and after the peak SSW temperatures. The latter has permitted a reduced forcing contribution from above and internal. The main ionospheric effects are clearly observed in the zonal electric fields (or vertical E×B drifts), total electron content, and peak electron densities. We include results from different ground- and satellite-based observations, covering different longitudes and years. We also present and discuss the modeling efforts that support most of the observations. Given that SSW can be forecast with a few days in advanced, there is potential for using the connection with the ionosphere for forecasting the occurrence and evolution of electrodynamic perturbations at low latitudes, and sometimes mid latitudes, during arctic winter warmings.Item Restricted Equatorial and low latitude ionospheric effects during sudden stratospheric warming events: Ionospheric effects during SSW events(Springer, 2012) Chau Chong Shing, Jorge Luis; Goncharenko, Larisa P.; Fejer, Bela G.; Liu, Han LiThere are several external sources of ionospheric forcing, including these are solar wind-magnetospheric processes and lower atmospheric winds and waves. In this work we review the observed ion-neutral coupling effects at equatorial and low latitudes during large meteorological events called sudden stratospheric warming (SSW). Research in this direction has been accelerated in recent years mainly due to: (1) extensive observing campaigns, and (2) solar minimum conditions. The former has been instrumental to capture the events before, during, and after the peak SSW temperatures and wind perturbations. The latter has permitted a reduced forcing contribution from solar wind-magnetospheric processes. The main ionospheric effects are clearly observed in the zonal electric fields (or vertical E×B drifts), total electron content, and electron and neutral densities. We include results from different ground- and satellite-based observations, covering different longitudes and years. We also present and discuss the modeling efforts that support most of the observations. Given that SSW can be forecasted with a few days in advance, there is potential for using the connection with the ionosphere for forecasting the occurrence and evolution of electrodynamic perturbations at low latitudes, and sometimes also mid latitudes, during arctic winter warmings.Item Restricted Equatorial zonal plasma drifts measured by the C/NOFS satellite during the 2008–2011 solar minimum(American Geophysical Union, 2013-06-26) Fejer, Bela G.; Tracy, Brian D.; Pfaff, Robert F.We use the measurements by the Vector Electric Field Investigation (VEFI) on board the Communication/Navigation Outage Forecasting System (C/NOFS) satellite to study the local time and seasonal‐ and longitudinal‐dependent climatology of equatorial F region zonal plasma drifts during 2008–2011. These drifts are essentially westward during the day and eastward at night. Over Jicamarca Radio Observatory, the satellite measurements are in good agreement with incoherent scatter radar drifts. Our data show strong longitudinal variations, particularly in the South American sector during the solstices. The equinoctial data exhibit short‐lived and largely enhanced westward drifts near sunrise and wave‐4 structures from the early afternoon to late night equinoctial periods. The nighttime eastward drifts are largest near the western American sector at all seasons. The June solstice postmidnight eastward drifts decrease sharply at longitudes of about 310° and have much smaller values in the entire Eastern Hemisphere. We also briefly discuss the relationship between the longitude‐dependent vertical and zonal plasma drifts.Item Restricted Lunar tidal effects in the electrodynamics of the low latitude ionosphere(Elsevier, 2013-02-04) Fejer, Bela G.; Tracy, Brian D.The low latitude ionosphere is highly variable over a large range of temporal and spatial scales even during geomagnetically quiet periods, largely as a result of electrodynamic plasma drift effects. Several recent experimental and modeling studies have investigated the electrodynamic response of the low latitude ionosphere to high latitude and lower atmospheric wave activity, particularly during sudden stratospheric warmings. In this work, we review some recent results on the short-term variability of equatorial vertical plasma drifts measured mostly at the Jicamarca Radio Observatory and their effects on equatorial short-scale spread F irregularities. We show that lunar tidal semidiurnal and diurnal effects, which have been largely ignored in most studies, can play significant roles in low latitude ionospheric variability.Item Restricted Lunar tide in the equatorial F region vertical ion drift velocity(American Geophysical Union, 2001-01-01) Stening, Robert J.; Fejer, Bela G.Vertical ion drift velocity data from Jicamarca have been analyzed for a lunar semidiurnal tide using a least squares fitting method. Amplitudes of up to 6 m s−1 are obtained with phases in agreement with lunar tidal determinations of other associated physical parameters. Variations between season, solar activity, and day to night are also examined. Generally, amplitudes are larger in the southern summer. Much of the phase variation with season is very similar for solar maximum and minimum years. There is a summer to winter phase change that is most distinct at solar maximum nighttime. A day‐to‐night phase reversal can also been seen in some seasons. Hints of this are also found in the lunar tide in the F region height and in the magnetic variations at Huancayo.Item Restricted MELISSA: system description and spectral features of pre‐ and post‐midnight F‐region echoes(American Geophysical Union, 2019-12) Rodrigues, Fabiano S.; Zhan, Weijia; Milla, Marco; Fejer, Bela G.; De Paula, Eurico R.; Neto, Acacio C.; Santos, Angela M.; Batista, Inez S.Most of the low‐latitude ionospheric radar observations in South America come from the Jicamarca Radio Observatory, located in the western longitude sector (∼75°W). The deployment of the 30 MHz FAPESP Clemson‐INPE (FCI) coherent backscatter radar in the magnetic equatorial site of São Luis, Brazil, in 2001 allowed observations to be made in the eastern sector (∼45°W). However, despite being operational for several years (2001–2012), FCI only made observations during daytime and pre midnight hours, with a few exceptions. Here, we describe an upgraded system that replaced the FCI radar and present results of full‐night F‐region observations. This radar is referred to as Measurements of Equatorial and Low‐latitude Ionospheric irregularities over São Luís, South America (MELISSA), and made observations between March 2014 and December 2018. We present results of our analyses of pre‐ and post‐midnight F region echoes with focus on the spectral features of post‐midnight echoes and how they compare to spectra of echoes observed in the post‐sunset sector. The radar observations indicate that post‐midnight F‐region irregularities were generated locally and were not a result of “fossil” structures generated much earlier in time (in other longitude sectors) and that drifted into the radar field‐of‐view. This also includes cases where the echoes are weak and that would be associated with decaying equatorial spread F (ESF) structures. Collocated digisonde observations show modest but noticeable F‐region apparent uplifts prior to post‐midnight ESF events. We associate the equatorial uplifts with disturbed dynamo effects and with destabilizing F‐region conditions leading to ESF development.Item Open Access Multi-instrumented observations of the equatorial F-region during June solstice: large-scale wave structures and spread-F(SpringerOpen, 2018-03) Rodrigues, Fabiano S.; Hickey, Dustin A.; Zhan, Weijia; Martinis, Carlos R.; Fejer, Bela G.; Milla, Marco; Arratia, Juan F.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.Item Open Access Multi-process driven unusually large equatorial perturbation electric fields during the April 2023 geomagnetic storm(Frontiers Media, 2024-02-05) Fejer, Bela G.; Laranja, Sophia R.; Condor Patilongo, PercyThe low latitude ionosphere and thermosphere are strongly disturbed during and shortly after geomagnetic storms. We use novel Jicamarca radar measurements, ACE satellite solar wind, and SuperMAG geomagnetic field observations to study the electrodynamic response of the equatorial ionosphere to the 23, 24 April 2023 geomagnetic storm. We also compare our data with results from previous experimental and modeling studies of equatorial storm-time electrodynamics. We show, for the first time, unusually large equatorial vertical and zonal plasma drift (zonal and meridional electric field) perturbations driven simultaneously by multi storm-time electric field mechanisms during both the storm main and recovery phases. These include daytime undershielding and overshielding prompt penetration electric fields driven by solar wind electric fields and dynamic pressure changes, substorms, as well as disturbance dynamo electric fields, which are not well reproduced by current empirical models. Our nighttime measurements, over an extended period of large and slowly decreasing southward IMF Bz, show very large, substorm-driven, vertical and zonal drift fluctuations superposed on large undershield driven upward and westward drifts up to about 01 LT, and the occurrence of equatorial spread F irregularities with very strong spatial and temporal structuring. These nighttime observations cannot be explained by present models of equatorial storm-time electrodynamics.Item Open Access Storm-time equatorial thermospheric dynamics and electrodynamics(Utah State University, 2020) Navarro Dominguez, Luis A.; Fejer, Bela G.It presents the first comprehensive study of the equatorial thermospheric dynamics and ionospheric electrodynamics over Peru following enhanced energy depositions into the high-latitude ionosphere during geomagnetic storms. We used extensive observations of ionospheric plasma drifts and of night-time thermospheric neutral winds from the Jicamarca Incoherent Scatter Radar and from the network of Fabry-Perot Interferometers deployed in the central region of Peru respectively.