Browsing by Author "Fejer, B. G."
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Item Restricted Altitudinal dependence of evening equatorial F region vertical plasma drifts(American Geophysical Union, 2014-06-06) Fejer, B. G.; Hui, D.; Chau Chong Shing, Jorge Luis; Kudeki, E.We use Jicamarca incoherent scatter radar measurements to study for the first time the altitudinal variations of late afternoon and early night equatorial F region vertical plasma drifts. We also present the initial vertical drift measurements over the altitudinal range from about 200 to 2000 km. These data show that the afternoon drifts decrease weakly with altitude. Near their evening prereversal enhancements, the vertical drifts generally increase with altitude below about the F layer peak, decrease with height near the F layer peak and above, and are nearly height independent in the (solar flux dependent) topside ionosphere. The transition altitudes from height‐decreasing to height‐independent evening upward drifts decrease with altitude from solar maximum to solar minimum. After their reversal to downward, the vertical drifts do not change much with height. The altitudinal dependence of the evening vertical drifts has large day‐to‐day variability and is closely related to the time dependence of the zonal drifts, as expected from the curl‐free electric field condition.Item Restricted Assimilative modeling of the equatorial ionosphere for scintillation forecasting: modeling with vertical drifts(American Geophysical Union, 2005-11-19) Retterer, John M.; Decker, D. T.; Borer, W. S.; Daniell Jr., R. E.; Fejer, B. G.Knowledge of the vertical plasma drift velocity observed by the Jicamarca incoherent radar in seven events is assimilated into a theoretical model for the ambient F region plasma density. Comparisons of the calculated plasma density model and the observed plasma density show that, apart from the signature effects of equatorial plasma bubbles, the ambient model captures much of the detail of the plasma density profiles. Rayleigh‐Taylor growth rates calculated with the ambient model show a good correlation with the occurrence of spread F.Item Restricted Average vertical and zonal F region plasma drifts over Jicamarca(American Geophysical Union, 1991-08) Fejer, B. G.; De Paula, E. R; González, S. A; Woodman Pollitt, Ronald FranciscoThe seasonal averages of the equatorial F region vertical and zonal plasma drifts are determined using extensive incoherent scatter radar observations from Jicamarca during 1968–1988. The late afternoon and nighttime vertical and zonal drifts are strongly dependent on the 10.7-cm solar flux. We show that the evening prereversal enhancement of vertical drifts increases linearly with solar flux during equinox but tends to saturate for large fluxes during southern hemisphere winter. We examine in detail, for the first time, the seasonal variation of the zonal plasma drifts and their dependence on solar flux and magnetic activity. The seasonal effects on the zonal drifts are most pronounced in the midnight-morning sector. The nighttime eastward drifts increase with solar flux for all seasons but decrease slightly with magnetic activity. The daytime westward drifts are essentially independent of season, solar cycle, and magnetic activity.""The second-generation sounding system (SOUSY) 53.5-MHz mesosphere-stratosphere-troposphere (MST) radar at 78N, 16E on Svalbard has recently completed its inaugural summer, 2008, of polar mesospheric summer echoes (PMSE) observations. Here PMSE observations have been assembled in order to identify dates of the earliest and latest occurrences and how the frequency of PMSE occurrence correlates with dynamics and temperature, which are available from the collocated Nippon/Norway Svalbard Meteor 31-MHz Radar (NSMR). We find strong correlations between preferred PMSE altitude and low temperature, and between equatorward flow and occurrence rate. Temperature drops cause increases in PMSE occurrence: for the height interval 82–92 km, a drop of around 7 K increases the occurrence, typically by 1–2% d−1 and similarly for a 1 m s−1 increase in equatorward wind. A temperature drop of 5 K at 90 km altitude results in a lowering of the underlying preferred PMSE altitude by 1 km. This study therefore qualifies, at least for 78N, 16E and 2008, the dependence of PMSE occurrence rates and preferred heights on 90 km temperature and dynamics.Item Open Access Coherent and incoherent scatter radar study of the climatology and day-to-day variability of mean F-region vertical drifts and equatorial spread F(American Geophysical Union, 2016-02) Smith, J. M.; Rodrigues, F. S.; Fejer, B. G.; Milla, MarcoWe conducted a comprehensive analysis of the vertical drifts and equatorial spread F (ESF) measurements made by the Jicamarca incoherent scatter radar (ISR) between 1994 and 2013. The ISR measurements allowed us to construct not only updated climatological curves of quiet-time vertical plasma drifts but also time-versus-height maps of ESF occurrence over the past two solar cycles. These curves and maps allowed us to better relate the observed ESF occurrence patterns to features in the vertical drift curves than previously possible. We identified an excessively high occurrence of post-midnight F region irregularities during December solstice and low solar flux conditions. More importantly, we also found a high occurrence of ESF events during sudden stratospheric warming (SSW) events. We also proposed and evaluated metrics of evening enhancement of the vertical drifts and ESF occurrence, which allowed us to quantify the relationship between evening drifts and ESF development. Based on a day-to-day analysis of these metrics, we offer estimates of the minimum pre-reversal enhancement (PRE) peak (and mean PRE) values observed prior to ESF development for different solar flux and seasonal conditions. We also found that ESF irregularities can reach the altitudes at least as high as 800 km at the magnetic equator even during low solar flux conditions.Item Restricted Dependence of equatorial F region vertical drifts on season and solar cycle(American Geophysical Union, 1979-10-01) Fejer, B. G.; Farley, D. T.; Woodman Pollitt, Ronald Francisco; Calderón, C.Vertical drift measurements have been made at Jicamarca for more than half a solar cycle. The data from periods of high and low activity are appreciably different. Daytime drift velocities during sunspot minimum are usually larger than during the maximum, while the opposite is true for nighttime periods. The evening reversal occurs earlier during sunspot minimum than during the maximum, but the morning reversal is not altered. The period of eastward electric field (upward drift) is thus shortest during sunspot minimum and local winter. By integrating the drift velocity data with respect to time, one can obtain a measure of the total potential drop between reversal points (near the terminators). This drop is largest at solar maximum. There is also a pronounced seasonal variation, with a minimum in mid-December during both solar minimum and maximum. The general features of the data cannot be explained solely on the basis of tidal winds driving an E region dynamo; polarization fields related to the F region dynamo are of major importance, particularly in helping to explain the enhancement of the daytime upward drift which often occurs shortly before the drift reverses to downward in the evening. In order to account quantitatively for the observed variations, however, numerical models considerably more sophisticated than those presently available are needed.Item Open Access Effects of the vertical plasma drift velocity on the generation and evolution of equatorial spread F(American Geophysical Union, 1999-09-01) Fejer, B. G.; Scherliess, L.; De Paula, E. R.We use radar observations from the Jicamarca Observatory from 1968 to 1992 to study the effects of the F region vertical plasma drift velocity on the generation and evolution of equatorial spread F. The dependence of these irregularities on season, solar cycle, and magnetic activity can be explained as resulting from the corresponding effects on the evening and nighttime vertical drifts. In the early night sector, the bottomside of the F layer is almost always unstable. The evolution of the unstable layer is controlled by the history of the vertical drift velocity. When the drift velocities are large enough, the necessary seeding mechanisms for the generation of strong spread F always appear to be present. The threshold drift velocity for the generation of strong early night irregularities increases linearly with solar flux. The geomagnetic control on the generation of spread F is season, solar cycle, and longitude dependent. These effects can be explained by the response of the equatorial vertical drift velocities to magnetospheric and ionospheric disturbance dynamo electric fields. The occurrence of early night spread F decreases significantly during equinox solar maximum magnetically disturbed conditions due to disturbance dynamo electric fields which decrease the upward drift velocities near sunset. The generation of late night spread F requires the reversal of the vertical velocity from downward to upward for periods longer than about half an hour. These irregularities occur most often at ∼0400 local time when the prompt penetration and disturbance dynamo vertical drifts have largest amplitudes. The occurrence of late night spread F is highest near solar minimum and decreases with increasing solar activity probably due to the large increase of the nighttime downward drifts with increasing solar flux.Item Restricted Enhanced lunar semidiurnal equatorial vertical plasma drifts during sudden stratospheric warmings(American Geophysical Union, 2011-11-15) Fejer, B. G.; Tracy, B. D.; Olson, M. E.; Chau Chong Shing, Jorge LuisLarge scale electrodynamic and plasma density variations in the low latitude ionosphere have recently been associated with sudden stratospheric warming (SSW) events. We present empirical models of largely enhanced lunar semidiurnal equatorial vertical plasma drift perturbations during arctic winter low and high solar flux SSW events. These perturbations play a dominant role in the electrodynamic response of the low latitude ionosphere to SSWs. Our models indicate that the amplitudes of the enhanced lunar semidiurnal drifts are strongly local time and solar flux dependent, with largest values during early morning low solar flux SSW periods. These results suggest that ionospheric conductance strongly modulate low latitude ionospheric changes during SSWs. They also indicate that lunar semidiurnal effects need to be taken into account by global ionospheric models for their improved forecasting of the low latitude ionospheric response to SSW events, especially for low solar flux conditions.Item Restricted Equatorial electric fields during magnetically disturbed conditions 1. The effect of the interplanetary magnetic field(American Geophysical Union, 1979-10-01) Woodman Pollitt, Ronald Francisco; Kelley, M. C.; Farley, D. T.; Fejer, B. G.; Gonzáles, S. A.Radar measurements of E and F region drift velocities have been used to look for correlations between changes in equatorial electric fields and the interplanetary magnetic field (IMF). The east-west component of the IMF appears to be unimportant, but the north-south component has some effect; rapid reversals from south to north are sometimes correlated with reversals of the equatorial east-west electric field during both daytime and nighttime. This is not always true, however, the IMF may reverse without any apparent effect at the equator. Furthermore, large equatorial field perturbations are sometimes observed when the IMF Bz is large and southward but not varying drastically. In this latter case the equatorial perturbations start nearly simultaneously with the onset of auroral substorms, while in the previous case they usually correlate with the onset of the substorm recovery phase. These observations indicate that the IMF does not affect the equatorial electric fields directly. Rather, it is changes in the magnetospheric electric fields and the auroral zone electric field and conductivity distribution (which may or may not be triggered by IMF changes) which alter the worldwide ionospheric current flow and electric field pattern, of which the equatorial observations are an indication.Item Restricted Equatorial electric fields during magnetically disturbed conditions 2. Implications of simultaneous auroral and equatorial measurements(American Geophysical Union, 1979-10-01) Gonzales, C.A.; Kelley, M. C.; Fejer, B. G.; Vickrey, J. F.; Woodman Pollitt, Ronald FranciscoSimultaneous auroral and equatorial electric field data are used along with magnetic field data to study anomalous electric field patterns during disturbed times. During some substorms, accompanied by ring current activity, the worldwide equatorial zonal electric field component reverses from the normal pattern. This is interpreted as a partial closure of high latitude field aligned currents in the dayside, low latitude ionosphere. These currents flow westward across the dayside. In several cases the zonal equatorial electric field component was nearly identical in form to the zonal auroral component, indicating the close electrical coupling between these regions. Less certain, but equally intriguing, is the evidence presented for a close relationship between the zonal equatorial electric field and the time derivative of the ring current induced magnetic field. Another class of events seems related to rapid changes of magnetospheric convection and a temporary imbalance between the field external to the plasmasphere and the shielding charges in the Alfven layer. Examples of both rapid increases and decreases are presented. The latter seems often to be related to a northward turning of the interplanetary magnetic field.Item Open Access Equatorial ExB drifts during sudden stratospheric warming events(Instituto Geofísico del Perú, 2009) Chau Chong Shing, Jorge Luis; Galindo, F. R.; Fejer, B. G.; Goncharenko, L. P.Diapositivas presentadas en: CEDAR Workshop 2009 del 28 de junio al 2 de julio de 2009 en Santa Fe, Nuevo México, USA.Item Restricted Equatorial F region vertical plasma drifts during solar maxima(American Geophysical Union, 1989-09-01) Fejer, B. G.; De Paula, E. R.; Batista, I. S.; Bonelli, E.; Woodman Pollitt, Ronald FranciscoIncoherent scatter radar measurements at Jicamarca are used to study the effects of large solar fluxes and magnetic activity on the F region vertical plasma drifts. The average drifts from the two last solar maxima are almost identical except in the late afternoon-early evening sector where their variations with solar flux and magnetic activity are strongly season dependent. The average evening winter (May-August) drifts appear to remain almost constant after a certain solar flux level is reached but increase with magnetic activity. The equinoctial evening drifts increase systematically with solar-flux but decrease with magnetic activity. Very large prereversal enhancement velocities, up to about 80 m/s, were often observed during the 1978–1981 equinoctial periods when the solar flux was very high. Comparison of incoherent scatter radar drifts with vertical velocities inferred from ionosonde observations indicate that the latter technique substantially underestimates the plasma drifts during periods of large solar fluxes except during winter.Item Open Access Equatorial ionospheric electric fields during the November 2004 magnetic storm(American Geophysical Union, 2007-10) Fejer, B. G.; Jensen, J. W.; Kikuchi, T.; Abdu, M. A.; Chau Chong Shing, Jorge LuisWe use radar measurements from the Jicamarca Radio Observatory, magnetometer observations from the Pacific sector and ionosonde data from Brazil to study equatorial ionospheric electric fields during the November 2004 geomagnetic storm. Our data show very large eastward and westward daytime electrojet current perturbations with lifetimes of about an hour (indicative of undershielding and overshielding prompt penetration electric fields) in the Pacific equatorial region during the November 7 main phase of the storm, when the southward IMF, the solar wind and reconnection electric fields, and the polar cap potential drops had very large and nearly steady values. This result is inconsistent with the recent suggestion that solar wind electric fields penetrate without attenuation into the equatorial ionosphere for several hours during storm main phase. The largest daytime prompt penetration electric fields (about 3 mV/m) ever observed over Jicamarca occurred during the November 9 storm main phase, when large equatorial electrojet current and drift perturbations were also present in the Pacific and Brazilian equatorial regions. The rise and decay times of these equatorial electric fields were about 20 min longer than of the corresponding solar wind electric fields. The ratios of prompt penetration electric fields and corresponding solar wind electric field changes were highly variable even during the day, and had largest values near dawn. Also, the prompt penetration electric fields did not show polar cap potential drop saturation effects. Our results clearly highlight that the relationships of prompt penetration and solar wind electric fields, and polar cap potentials are far more complex than implied by simple proportionality factors.Item Open Access Equatorial ionospheric electrodynamic perturbations during Southern Hemisphere stratospheric warming events(American Geophysical Union, 2013-03) Olson, M. E.; Fejer, B. G.; Stolle, C.; Lühr, H.; Chau Chong Shing, Jorge LuisWe use ground-based and satellite measurements to examine, for the first time, the characteristics of equatorial electrodynamic perturbations measured during the 2002 major and 2010 minor Southern Hemisphere sudden stratospheric warming (SSW) events. Our data suggest the occurrence of enhanced quasi-two fluctuations during the 2002 early autumnal equinoctial warming. They also show a moderately large multi-day perturbation pattern, resembling those during arctic SSW events, during 2002 late equinox, as the major SSW was weakening. We also compare these data with extensive recent results that showed the fundamentally important role of lunar semidiurnal tidal effects on low latitude electrodynamic perturbations during of arctic SSW events.Item Open Access Equatorial zonal electric fields during the 2002-2003 sudden stratospheric warming event(Instituto Geofísico del Perú, 2009) Olson, Michael E.; Fejer, B. G.; Stolle, C.; Chau Chong Shing, Jorge Luis; Goncharenko, L. P.For nearly fifty years, the Jicamarca Radio Observatory (11.95°S, 76.87°W, 2°N dip latitude) near Lima, Peru, has measured ionospheric plasma drifts. Over the last ten years, measurements of plasma drift velocities have also been measured using radar observations of the equatorial 150 km altitude región (Kudeki and Fawcett, 1993; Chau and Woodman, 2004).Item Restricted Evolution of equatorial ionospheric bubbles during a large auroral electrojet index increase in the recovery phase of a magnetic storm(American Geophysical Union, 2006-02-10) Keskinen, M. J.; Ossakow, S. L.; Fejer, B. G.; Emmert, JohnWe present a model and observations of the evolution of equatorial ionospheric bubbles during a large auroral electrojet (AE) index increase in the recovery phase of a geomagnetic storm. Using a three‐dimensional time‐dependent numerical simulation model, we find, for the 19–21 October 1998 storm, that the equatorial bubble evolution is different during storm time as compared to quiet time conditions. We have found that the storm time vertical drift in conjunction with reduced off‐equatorial E region shorting is the primary mechanism that distinguishes the large AE increase recovery phase storm time evolution from the quiet time case. Comparison of the simulation model with ground‐based storm time radar observations is made.Item Restricted F region east-west drifts at Jicamarca(American Geophysical Union, 1981-01-01) Fejer, B. G.; Farley, D. T.; Gonzales, C. A.; Woodman Pollitt, Ronald Francisco; Calderon, C.F region east-west drifts have been measured at Jicamarca for almost 10 years, using incoherent scatter. The drifts are westward during the day and eastward at night. The daytime drift velocities are about 50 m/s and change very little with season or solar cycle. The evening reversal occurs at about 1600 local time throughout the solar cycle. The maximum nighttime eastward drifts are about 105 and 130 m/s during solar minimum and maximum, respectively. The daytime and nighttime drifts show very litle variation with magnetic activity. These Jicamarca incoherent scatter results (especially the reversal times) differ appreciably from results obtained using other techniques, but there appear to be fairly simple explanations for the apparent disagreements.Item Restricted F3 layer during penetration electric field(American Geophysical Union, 2008-09-04) Balan, N.; Thampi, S. V.; Lynn, K.; Otsuka, Y.; Alleyne, H.; Watanabe, S.; Abdu, M. A.; Fejer, B. G.The occurrence of an additional layer, called F3 layer, in the equatorial ionosphere at American, Indian, and Australian longitudes during the super double geomagnetic storm of 7–11 November 2004 is presented using observations and modeling. The observations show the occurrence, reoccurrence, and quick ascent to the topside ionosphere of unusually strong F3 layer in Australian longitude during the first super storm (8 November) and in Indian longitude during the second super storm (10 November), all with large reductions in peak electron density (Nmax) and total electron content (GPS‐TEC). The unusual F3 layers can arise mainly from unusually strong fluctuations in the daytime vertical E × B drift as indicated by the observations and modeling in American longitude. The strongest upward E × B drift (or eastward prompt penetration electric field, PPEF) ever recorded (at Jicamarca) produces unusually strong F3 layer in the afternoon hours (≈1400–1600 LT) of PPEF, with large reductions in Nmax and TEC; the layer also reappears in the following evening (≈1700–1800 LT) owing to an unusually large downward drift. At night, when the drift is unusually upward and strong, the F region splits into two layers.Item Restricted Longitudinal ionospheric effects in the South Atlantic evening sector during solar maximum(American Geophysical Union, 2002-07-10) De Paula, E. R.; Souza, J. R.; Fejer, B. G.; Bailey, G. J.; Heelis, R. A.Large-scale horizontal gradients in ion density and vertical drift observed by the Atmospheric Explorer E satellite in the South Atlantic region (latitudes 10S–20S, longitudes 50W–10E) during the June solstice at solar maximum are presented and analyzed. These features occur during the nighttime period. The observations near 450-km altitude show vertically downward ion drift velocities exceeding 120 m s−1 and depleted regions where the ion density is around 2 × 104 cm−3. It is shown, using values modeled by the Sheffield University Plasmasphere Ionosphere Model (SUPIM) along the satellite trajectory, that the large ion density depletions appear as a result of large downward ion drifts driven by large southward winds along the magnetic meridian and by diffusion. During others seasons such behavior is not observed by the AE-E satellite, neither by SUPIM results. The roles played by the different physical processes responsible for the large downward drift velocities are investigated. The model results highlight the relationship between longitudinal variation of the ion densities and the location of the equatorial anomaly crest in the South Atlantic region.Item Restricted Low latitude storm time ionospheric electrodynamics(Elsevier, 2002-04-30) Fejer, B. G.The response of the low latitude ionosphere to high latitude convection has long been the subject of considerable interest. Radar, ionosonde, magnetometer, and satellite measurements have been extensively used for studying the time-dependent characteristics of low-latitude disturbance electric fields and currents, and their coupling to the high latitude convection. Several global convection models have been used to explore the relationship between inner magnetospheric processes, and mid- and low-latitude ionospheric electrodynamic effects during geomagnetically active times. Recently, significant progress has been made in quantifying the average storm time-dependent responses of low latitude electrodynamic plasma drifts and currents to changes in the high latitude convection, and in the validation of global convection and ionospheric disturbance models. However, there are several fundamental questions dealing mostly with the large variability of the disturbance electric fields. In this review, we examine the latest progress in these studies and discuss a number of outstanding problems.Item Restricted Low-latitude ionospheric disturbance electric field effects during the recovery phase of the 19-21 October 1998 magnetic storm(American Geophysical Union, 2003-12-23) Fejer, B. G.; Emmert, J. T.Low‐latitude ionospheric electric fields and currents are often strongly disturbed during periods of enhanced geomagnetic activity. These perturbations can last for several hours after geomagnetic quieting. We use incoherent scatter radar measurements from Jicamarca and Arecibo during 19–21 October 1998 to study, for the first time, the low‐latitude disturbance electric fields during the recovery phase of a large magnetic storm. On 19 October the Jicamarca data showed initially large and short‐lived (time scale of about 10–20 min) upward and westward drift perturbations in the early afternoon sector, due to the penetration of strong magnetospheric electric fields probably driven by an increase in the solar wind dynamic pressure. Following the decrease of auroral activity, very strong afternoon and nighttime zonal and vertical disturbance dynamo drifts were observed over Jicamarca but, surprisingly, only small and sporadic perturbation drifts were present over Arecibo. The latitudinal variation of the daytime zonal disturbance dynamo drifts during this day is in good agreement with that previously observed for thermospheric disturbance winds. The disturbance dynamo drifts also indicate significantly different local, storm time, and possibly latitudinal dependences for their vertical/perpendicular and zonal drift components, suggesting large variations in both the amplitude and direction of the disturbance dynamo electric field vector. In the next day, during moderately disturbed conditions, the daytime perturbation drifts were small, but following transient increases in geomagnetic activity, large upward/perpendicular drifts were observed near dusk over Jicamarca and Arecibo, where simultaneous westward perturbation drifts were also seen. These perturbations are consistent with the occurrence of strong prompt penetration electric fields reaching the magnetic equator. The measured prompt penetration drift patterns are generally in good agreement with predictions from global convection models. Later at night, under moderately disturbed conditions, relatively large zonal and meridional disturbance dynamo electric fields were observed by the two radars. Our results illustrate the large variability of the low‐latitude perturbation electric fields relative to their climatological values after large storms, probably due to the importance of additional disturbance processes. They also indicate that a much deeper understanding of solar‐wind/magnetospheric/ionospheric processes is required for accurate predictions of these electric fields.
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