Vertical Drift Research Articles

Ionospheric and magnetic signatures of extreme space weather events of 17 March and 23 June 2015 over the African sector

We have investigated responses of the African sector of the ionosphere to 17 March and 23 June 2015 severe geomagnetic storms. The vertical total electron content (TEC) measurements from Global Navigation Satellite System (GNSS) stations, which are located across the African continent, have been used to estimate the deviation of TEC (ΔTEC). The observed ionospheric response to these events was different at different locations. In the main phase of the 17 march 2015 storm, a significant positive ionospheric storm (ΔTEC maximum) occurred at Meli (245.8% enhancement) and Adis (105% enhancement) stations in the post-sunset period. On the other hand, during midnight negative ionospheric storms (ΔTEC minimum: ∼ 46%–68% depletion ) were observed at Dakr, Nklg, Wind, and Haro stations. The effects of 23 June 2015 storm are more pronounced during the initial phase. In the recovery phase of 23 June storm, negative storm effects observed at the eastern dip latitude and western equatorial stations. In contrast, at the northern and southern mid-latitude stations, we observed positive storm effect during the night periods. Night time TEC enhancement at mid-latitude stations probably caused by the vertical drift of the ionospheric plasma. We have also studied the magnetic signatures of the severe storms of 17 March and 23 June 2015 by analyzing their impacts on the horizontal (H-component) of the Earth’s magnetic field. By using a moving average filter, we have separated the effect of the magnetic disturbance (DP2) and the disturbance dynamo (Ddyn). The H-component analysis shows that there was maximum oscillation of DP2 and Ddyn currents occurrence when the IMF-Bz directed southward. In the main and recovery phases of the storm, this strong current oscillation is the driver for the development of positive ionospheric effect.

Relationships between ionospheric parameters derived from ionosonde observations and characteristics of post-sunset GHz scintillation during high solar activities (2012−2013) at Sanya (18.3°N, 109.6°E), China

In this study, we presented the characteristics of post-sunset GHz scintillation occurrence and ionospheric parameters derived from ionosonde observations, including the critical frequency of F2-layer (foF2), peak height of F2-layer (hmF2), minimum virtual height of F-layer (h’F), scale height around the F2-layer peak (Hm), virtual height (h’F5) and true height (hF5) measured at 5 MHz, in high solar activity years (2012-2013) of solar cycle 24 at Sanya (18.3°N, 109.6°E; dip lat.: 12.8°N), China. Furthermore, we investigated the relationships between the equinoctial asymmetry of scintillation and these ionospheric parameters. In addition, the growth rates of Rayleigh-Taylor instability were calculated on the basis of the ionosonde measurements and models, respectively. The results showed that the equinoctial asymmetry of scintillation onset time would be associated with the scale length of vertical electron density gradient (L), which affects the growth of Rayleigh-Taylor instability at the bottom of F-layer. The seasonal variations of foF2, Hm and scale length of vertical electron density gradient would be the reason to cause the seasonal variations of scintillation occurrence, and the equinoctial asymmetry of scintillation occurrence rate over low latitude can be related to the background electron density and the vertical drifts around sunset in F-layer. The correlations between the scintillation strength represented by the daily maximum S4 and the daily maximum values of foF2, hmF2, h’F, Hm, and also the drifts over low latitudes were weak, which need to be further studied.

Characterization of local time dependence of equatorial spread F responses to substorms in the American sector

Substorms have been found to play an important role in ionospheric electrodynamics at low and equatorial latitudes. In this study, we have investigated the possible influence of substorm on the generation of equatorial spread F (ESF). Coherent backscatter radar (JULIA) and incoherent scatter radar measurements between 2000 and 2017 at the Jicamarca Radio Observatory (11.95° S, 76.87° W, ~0° dip lat) are used. In statistical analysis, 12,525 h of ESF measurements are considered and have been divided into two groups based on their local time: post-sunset (18–24 LT) and post-midnight (00–06 LT). The superposed epoch analysis shows that the substorm-caused disturbance on vertical plasma drift can last longer than 12 h, which further affects the occurrence rate of ESF during a substorm. The increase/decrease of ESF at the post-sunset/post-midnight sector with about a 1 h lag to the substorm commencement is attributed to the prompt penetration electric field (PPEF), while the disturbance dynamo electric field needs approximately 3.5 h to suppress/promote the post-sunset/post-midnight ESF after substorm. In addition, the absolute value of correlation coefficients between the AE index and the occurrence rate of ESF is the largest when a 3–3.5 h lag is considered, which implies that the effect of disturbance dynamo electric fields could be more significant than prompt penetration electric field for the generation (suppression) of post-midnight (post-sunset) ESF during a substorm.

A 100‐V trench power MOSFET with taper‐shielded gate and non‐uniform drift region doping profile

AbstractA 100‐V Taper‐Shielded trench Gate (TSG) power metal‐oxide‐semiconductor field‐effect transistor (MOSFET) with superior figure‐of‐merit (FOM) is proposed and investigated in this paper. The gate of the proposed TSG‐MOSFET has a tapered shape to reduce the gate‐to‐drain overlap capacitance (CGD) and the gate charge (QG). The vertical drift region doping profile of the proposed TSG‐MOSFET is enhanced in two ways. First is to use a multi‐step epitaxial growth to produce a non‐uniform doping profile. Second is to place a lightly doped n‐region at the trench bottom. The bulk electric field in the blocking state can be more evenly distributed, allowing a shorter drift region and lower specific ON‐resistance (RON,sp). Both technology computer‐aided design (TCAD) simulations and experiments were performed to evaluate the proposed device. The proposed device exhibits an improved RON,sp of 27 mΩ·mm2 with a breakdown voltage (BV) of 105 V. The third quadrant performance and the reverse recovery characteristics are also greatly improved. During reverse conduction, the amount of the excessive carriers stored in the drift region is reduced due to the shortened drift region and optimized drift region doping profile. The reverse recovery charge (Qrr) is decreased from 70 to 49 nC. When compared to its state‐of‐the‐art counterparts, the measured [RON × QG] FOM and the Qrr showed a reduction of 23% and 28%, respectively.

Explaining Ionospheric Ion Upflow in the Subauroral Polarization Streams

Ionospheric ion upflow is an important process for magnetosphere-ionosphere coupling via O+ source for the magnetosphere. This process occurs frequently in the subauroral polarization stream (SAPS) region where the SAPS-enhanced ion-neutral frictional heating tends to push ions upward because of enhanced upward pressure gradient force. However, the SAPS-induced neutral wind transport by ion-neutral friction may also play an important role in triggering ion upflow, which has been rarely studied. In this work, the thermosphere-ionosphere-electrodynamics general circulation model (TIEGCM) with/without an empirical SAPS model has been employed to investigate the impacts of SAPS on ion upflow in the topside ionosphere. Our results separate different transport processes in the ion continuity equation, showing that SAPS can accelerate upward ambipolar diffusion along its channel because of ion-neutral frictional heating, but SAPS-induced horizontal neutral wind may have a comparable or even larger contribution to vertical ion drift when SAPS are fully developed. In addition, the neutral wind can induce both upward and downward ion drift in the SAPS region, depending on the direction of the neutral wind and the local geomagnetic declination and inclination.

First Observations of Equatorial Ionospheric Electric Fields Driven by Storm‐Time Rapidly Recurrent Magnetospheric Substorms

AbstractGeomagnetic storm ionospheric electrodynamics at the magnetic equator are examined in detail using upgraded, higher time resolution, Jicamarca incoherent scatter radar drift observations, SuperMAG geomagnetic field, and solar wind data to study equatorial ionospheric electric fields during the 8 September 2017 storm main and early recovery phases. We show that during a period of mostly large and southward Interplanetary Magnetic Field (IMF) Bz there were numerous daytime prompt penetration vertical and zonal plasma drifts. These prompt penetration events were closely associated with rapidly recurring (quasi‐periods ∼30 − 60 min) magnetospheric substorms with expansion phases corresponding to upward and westward drift (eastward and downward electric field) perturbations, and recovery phases to opposite polarity changes. The magnitudes of the zonal prompt penetration drifts were about twice larger than those of the vertical drifts. Our study suggests that magnetospheric substorms are the main drivers of prompt penetration electric fields during extended periods (over ∼2 hr) of nearly steady southward IMF Bz. We also find that in general substorms are major driving factors for disturbance electric fields during geomagnetic active times. Our data highlight the powerful capabilities of the Jicamarca incoherent scatter radar as a tool for detailed studies of short‐lived solar wind‐magnetosphere‐ionosphere coupling processes.

On the Onset Time and Background Ionospheric Conditions of Postsunset Equatorial Plasma Bubble

AbstractOnset time and conditions of the postsunset equatorial plasma bubble (EPB) observed by the Gadanki Ionospheric Radar Interferometer are presented and discussed in the light of collocated digisonde observations of background ionosphere. Observations show two important findings: (a) onset time of EPB is linked with the sunset terminator and it varies between the low latitude E region sunset and apex F region sunset with a tendency of EPB onset to be close to low latitude E region sunset, and (b) higher height of the bottomside F layer (by 50–60 km) and vertical plasma drift (by 10–30 m s−1) observed over Gadanki are found to be associated with the EPBs growing in a narrow longitude zone of ±1° centered on Gadanki than those outside this zone. The early onset of EPB coinciding with the low latitude E region sunset is attributed to the early predominance of the F region dynamo leading to prereversal enhancement (PRE) of zonal electric field, consistent with theoretical expectation. Delay in the onset of EPB is attributed to the effect of flux tube integrated Pedersen conductivity owing to low latitude sporadic E activity and the F region meridional neutral wind that could change the F region plasma density along the flux tube through field‐aligned movement of plasma. Observations also show that ionosonde observations from a single location cannot be used to predict the growth of EPB at other location, including those close to the station but away from the station by about 120 km.

Fast Ionogram Observations of Ascending Thin Layers Locally Transported from the E to F Region at Equatorial and Low Latitudes

By using fast ionogram observations, we report the first simultaneous observations of ascending ion layers at equatorial and low latitudes. The ionosonde measurements at Sanya (18.3°N, 109.6°E; dip lat. 12.2°N) and Chumphon (10.7°N, 99.4°E; dip lat. 3.8°N) show that a high Es layer, which might contain metallic ions, was directly lifted upward from the local E region to F region bottomside at morning hours, in a pattern similar to the vertical drift of the F region background ionosphere driven by the daytime eastward electric field. A statistical analysis with Sanya ionosonde measurements shows that the low latitude ascending ion layer is not a rare phenomenon, with a maximum occurrence of 22% during equinox. The results indicate that at the latitudes far away from the magnetic equator, the local E region metallic ions could be directly brought into the F region with the ascending layer. It can be expected that fast ionogram measurements, which can easily capture the rapid evolution of the background ionosphere, will play an important role in studying the formation of some unexpected high altitude metallic layers.

Postoperative drift and dose-response of strabismus surgery in thyroid eye disease: predicting desired outcomes with intraoperative adjustable sutures

ObjectifPrésenter les résultats de la correction chirurgicale du strabisme secondaire à l'ophtalmopathie thyroïdienne réalisée par l'insertion de sutures de type « nœud papillon » (bow-knot) ajustables en cours de chirurgie sous anesthésie locale et concevoir des modèles de prédiction de la correction chirurgicale et de la déviation postopératoire en fonction de la relation dose-effet de l'intervention. MéthodesNous avons procédé à une analyse rétrospective des dossiers de patients opérés entre 2016 et 2021. Le résultat était jugé satisfaisant si la diplopie avait disparu et s'accompagnait d'un alignement vertical (< 5 DP) et horizontal (< 10 DP) stable en position primaire du regard. La correction de la diplopie subjective au moyen de prismes permettant un alignement moteur était considérée comme un résultat passable. Dans les autres cas, le résultat était jugé médiocre. RésultatsAu total, 73 patients ont été admis à cette étude (60 femmes, soit 82 %). Les déviations horizontales et verticales moyennes en période préopératoire se chiffraient à 26,9 DP (é.-t. : 19,1) et à 11,8 DP (é.-t. : 7,6), respectivement. La déviation horizontale moyenne était de –3,2 DP (é.-t. : 5,2), tandis que la déviation verticale moyenne était de –3,4 DP (é.-t. : 3,3). Une analyse de régression linéaire a permis d’établir une relation dose-effet de 2,37 DP/mm pour la récession du droit médial (p < 0,0001; r2 = 0,777) et de 3,75 DP/mm pour la récession unilatérale du droit inférieur (p < 0,0001; r2 = 0,922). Les taux de réussite se déclinaient comme suit : satisfaisant chez 62 patients (85 %), passable chez 7 patients (10 %) et médiocre chez 4 patients (5 %). ConclusionsLa récession musculaire réalisée au moyen de sutures ajustables pendant l'intervention est une technique efficace pour corriger le strabisme secondaire à l'ophtalmopathie thyroïdienne. Il est possible d'obtenir une relation dose-effet prévisible avec une tendance vers une surcorrection. Une sous-correction proportionnelle à l'ampleur de la chirurgie prévue devrait être la cible de choix en période postopératoire immédiate. On n'a pas pu établir de corrélation entre d'autres variables, notamment la décompression orbitaire et la chirurgie à la fois verticale et horizontale, et la relation dose-effet ou la déviation postopératoire. Cela dit, d'autres études devront être réalisées afin de valider nos résultats.

The Temporal Evolution of F-Region Equatorial Ionization Anomaly Owing to the 2022 Tonga Volcanic Eruption

The dynamic evolutions of the noon ionospheric Equatorial Ionization Anomaly (EIA) owing to the 2022 Tonga volcanic eruption were investigated using the ionospheric plasma measurements from the Swarm satellite, the science experiment of the Constellation Observing Systems for Meteorology, Ionosphere, and Climate (COSMIC) mission, and the thermospheric wind observations from the Ionospheric Connection Explorer (ICON). At 14.1 universal time (UT), the noon EIA was enhanced for the upward plasma drifts, when the F2-layer was significantly uplifted from 360 km to 410 km. At 15.6 UT, because of the downward drifts, the intensity of the EIA reduced, and hmF2 decreased to 270 km. At 17–18 UT, the EIA recovered and reformed, and hmF2 increased to 350 km. A two-peak structure in the plasma was observed at Swarm altitudes. The temporal evolution might be related to the vertical plasma drifts (both downward and upward) from the E-region electric field.

Development of a Collisional Radiative Model for Hydrogen-Cesium Plasmas and Its Application to SPIDER

SPIDER is the full scale prototype for the ITER Heating Neutral Beam (HNB) source. The production of negative ions in the source mostly relies on the conversion of H/D atoms and positive ions on a 1.6 m <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times0.8$ </tex-math></inline-formula> m converter surface, which is covered with cesium in order to reduce its work function and maximize the conversion efficiency. In SPIDER, optical emission spectroscopy (OES) is used to study the light emitted by the plasma. In particular, the intensities of the cesium emission lines are tracked and used to reconstruct the distribution of its excited states. By coupling these measurements with a collisional radiative (CR) model, estimates of the cesium ground-state density and plasma parameters can be obtained in various parts of the source which are unreachable by other diagnostics. This work describes such a model and its use in conjunction with OES during the first operation with cesium in SPIDER. The electron density at the bottom of the source was found to be much larger than the rest, as a consequence of vertical drifts caused by the horizontal filter field, which would likely indicate a lower negative-ion availability for the beam. The effect of increasing the cesium evaporation rate on the negative-ion and electron densities was also investigated.

Climatology of TEC Longitudinal Difference in Middle Latitudes of East Asia

In this paper, a statistical analysis of the diurnal, seasonal and solar cycle variation in the TEC longitudinal difference in midlatitudes of East Asia is presented using CODE GIMs data in 2015–2019. Moreover, the empirical neutral wind model HWM-14 and geomagnetic field model IGRF-2020 were employed to analyze the influence of geomagnetic configuration-neutral wind mechanism on the TEC longitudinal difference, and the F2 layer peak electron density (NmF2) data from the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) were also used to study the role of local electron density in the TEC longitudinal difference. For the high solar activity year, the results show that east-west TEC longitudinal difference index Re/w is negative in the noon and positive at evening-night. Moreover, the longitudinal difference of daytime TEC is most evident in summer, less in autumn and least in spring and winter, while the nighttime difference is most obvious in equinox, followed by summer and winter during nighttime. The model simulation shows that the TEC longitude difference around noon is mainly caused by the zonal wind-declination mechanism, and a 4-h time delay seems to be an optimal result for the vertical drift velocity to cause the longitudinal TEC difference during pre-noon hours. At night, the uplifting electron flux, which is a product of local electron density and vertical drift velocity, shows a good correlation with Re/w, indicating that the local electron density is also an important factor affecting the TEC longitudinal difference during the nighttime. Moreover, there was about a 3-h time delay between the TEC longitudinal variations and the uplifting electron flux at night. For the low solar activity years, the western TEC is greater than eastern TEC during most of the year except in the summer nighttime. The TEC diurnal variation in the east and west suggested that the nighttime Re/w should be related to other physical process, such as the midlatitude summer nighttime anomaly (MSNA) in the east and the ionospheric nighttime enhancement (INE). The current study provides evidence for the longitudinal difference of NmF2 in East Asian midlatitudes and geomagnetic configuration-neutral wind mechanism proposed in previous studies and finds some new features which need further studying to improve our current understanding of ionospheric longitudinal difference in the low solar activity years. The results provide new insight into TEC longitudinal variations at midlatitudes, and they can contribute to understanding the ionosphere-thermosphere coupling system.

Geospace Concussion: Global Reversal of Ionospheric Vertical Plasma Drift in Response to a Sudden Commencement.

An interplanetary shock can abruptly compress the magnetosphere, excite magnetospheric waves and field-aligned currents, and cause a ground magnetic response known as a sudden commencement (SC). However, the transient (<∼1min) response of the ionosphere-thermosphere system during an SC has been little studied due to limited temporal resolution in previous investigations. Here, we report observations of a global reversal of ionospheric vertical plasma motion during an SC on 24 October 2011 using ∼6s resolution Super Dual Auroral Radar Network ground scatter data. The dayside ionosphere suddenly moved downward during the magnetospheric compression due to the SC, lasting for only ∼1min before moving upward. By contrast, the post-midnight ionosphere briefly moved upward then moved downward during the SC. Simulations with a coupled geospace model suggest that the reversed vertical drift is caused by a global reversal of ionospheric zonal electric field induced by magnetospheric compression during the SC.

Drift characteristics and the multi-field coupling stress mechanism of the pantograph-catenary arc under low air pressure

The fault caused by a pantograph-catenary arc is the main factor that threatens the stability of high-speed railway energy transmission. Pantograph-catenary arc vertical drift is more severe than the case under normal pressure, as it is easy to develop the rigid busbar, which may lead to the flashover occurring around the support insulators. We establish a pantograph-catenary arc experiment and diagnosis platform to simulate low pressure and strong airflow environment. Meanwhile, the variation law of arc drift height with time under different air pressures and airflow velocities is analyzed. Moreover, arc drift characteristics and influencing factors are explored. The physical process of the arc column drifting to the rigid busbar with the jumping mechanism of the arc root on the rigid busbar is summarized. In order to further explore the mechanism of the above physical process, a multi-field stress coupling model is built, as the multi-stress variation law of arc is quantitatively evaluated. The dynamic action mechanism of multi-field stress on arc drifting characteristics is explored, as the physical mechanism of arc drifting under low pressure is theoretically explained. The research results provide theoretical support for arc suppression in high-altitude areas.

Effect of the seed perturbation amplitude on the equatorial spread F initiation during solar minimum

The contribution of gravity wave (GW) to the initiation/development of spread F during a solar minimum year was investigated through the comparison of the observed precursory parameters and characteristics of the corresponding equatorial spread F (ESF) events. The ionospheric parameters were recorded at the magnetic equatorial station Sao Luis (2.3°S, 44°W, dip latitude 2°S) during March and October 2010. These data were used to estimate the influence of the relative gravity wave amplitude and the ambient ionospheric condition on the diurnal variation of the spread F initiation. The vertical velocity drift indicated a clear control and defines the threshold for the seasonal variability of the ESF occurrence. However, it was insufficient to solely determine or predict the day to day variation of ESF occurrence. Thus, few days with contrasting ambient ionospheric condition and magnitude of GW amplitude were analysed in order to investigate the role of the different precursory factors in the observed diurnal variation of the plasma irregularity development. The density scale length and gravity wave amplitude were shown to immensely contribute to the linear instability growth rate, especially during the days with a low post-sunset rise. Thus, the experimental observations have demonstrated the strong inter-dependence between the precursory factors and they have also highlighted the probable control of the ESF morphology.

Temporal and altitudinal variability of the spread F observed by the VHF radar over Christmas Island

Abstract. The goal of this work is to study the time and altitude echo characteristics under different solar and seasonality conditions using the VHF radar range–time–intensity (RTI) images. The occurrence of equatorial spread F depends on the existence of conditions that can seed the Rayleigh–Taylor instability, and these conditions can change with solar flux, seasonality, longitude distributions, and day-to-day variability. So, the equatorial spread F is observed as its time and altitude occurrence. The VHF radar of Christmas Island (2.0∘ N, 157.4∘ W, 2.9∘ N dip latitude) has been operational in the equatorial region for some time, allowing long-term observations. The occurrence of echoes during solar minimum conditions is observed throughout the night since the post-reversal westward electric field is weaker than the solar maximum and the possibilities of the vertical plasma drift becoming positive are larger. On the other hand, echoes during solar maximum will be controlled by dynamics near the time of the pre-reversal peak (PRE). Our results indicate that the peak time occurrence of echoes along this period shows a well-defined pattern, with echoes distributed as closer to local sunset during solar maximum and around/closer to midnight during solar minimum conditions; meanwhile, the peak altitude occurrence of echoes shows a slightly regular pattern with higher-altitude occurrences during solar maxima and lower altitudes during solar minimum conditions.

Investigating the Role of Gravity Waves on Equatorial Ionospheric Irregularities Using TIMED/SABER and C/NOFS Satellite Observations

In this paper, for the first time, simultaneous atmospheric temperature perturbation profiles obtained from the TIMED/SABER satellite and equatorial ion density and vertical plasma drift velocity observations with and without ESF activity obtained from the C/NOFS satellite are used to investigate the effect of gravity waves (GW) on ESF. The horizontal and vertical wavelengths of ionospheric oscillations and GWs are estimated by applying wavelet analysis techniques. In addition, vertically propagating GWs that dissipate energy in the ionosphere-thermosphere system are investigated using the spectral analysis technique. We find that the vertical wavelength of GW, corresponding to dominant wavelet power, ranges from 12 to 31 km regardless of the conditions of the ionosphere; however, GWs with vertical wavelengths between about 1 to 13 km are found every day, saturated between 90 and 110 km at different longitudinal sectors. Filtering out vertical wavelengths above 13 km from temperature perturbations, ranges of zonal wavelengths of GW (i.e., from about 290 to 950 km) are found corresponding to irregular and non-irregular ionosphere. Similarly, corresponding to dominant oscillations, the zonal wavelength of ion density perturbations is found within 16 to 1520 km. Moreover, we find an excellent agreement among the median zonal wavelengths of GW for the cases of irregular and non-irregular ionosphere and ion density perturbations that are 518, 495, and 491 km, respectively. The results imply that seed perturbations due to GW with a vertical wavelength from about 1 to 13 km evolve to ion density irregularity and may be amplified due to post-sunset vertical upward drift velocity.

Penetrating Electric Field Simulated by the MAGE and Comparison With ICON Observation

AbstractUsing the newly developed, Multiscale Atmosphere‐Geospace Environment (MAGE) model, we simulated the penetrating electric field in the equatorial region under different interplanetary magnetic field (IMF) BZ conditions during September 2020. Two intervals were selected for detailed analysis and the latter one was compared with the vertical ion drift data from the NASA Ionospheric Connection Explorer (ICON) satellite. The MAGE simulations show that in southward IMF (S‐IMF) cases, the dawn‐dusk electric potential drop at the equator is about 12% of the cross polar cap potential difference. Based on the MAGE simulation, the dawn‐dusk potential drop at the equator varies nearly instantaneously on the order of a few minutes with the changes in the IMF BZ or interplanetary electric field, which in turn alters the vertical ion drift. The daytime changes of the equatorial vertical ion drift in response to the penetrating electric field related to the IMF BZ are only half of that during the nighttime. ICON data, though not inconsistent with the simulation, were not able to verify the occurrence of penetrating electric field because of its unfavorable location at the time. The MAGE simulation shows a pre‐reversal enhancement (PRE) during southward IMF cases, but the PRE was absent in the ICON IVM observations. Further observations and modeling are needed to resolve this discrepancy.

Modeling Equatorial F‐Region Ionospheric Instability Using a Regional Ionospheric Irregularity Model and WAM‐IPE

AbstractThis paper uses a regional simulation of plasma convective instability in the postsunset equatorial ionosphere together with a global atmosphere/ionosphere/plasmasphere GCM (WAM‐IPE) to forecast irregularities associated with equatorial spread F (ESF) for 1–2 hr after sunset. First, the regional simulation is initialized and forced using ionosphere state parameters derived from campaign data from the Jicamarca Radio Observatory and from empirical models. The irregularities produced by these simulations are found to be quantitatively similar to those observed. Next, the aforementioned state parameters are replaced with parameters from WAM‐IPE, and the resulting departures between the simulated and observed irregularities are noted. In one of five cases, the forecast failed to accurately predict ESF irregularities due to the late reversal of the zonal thermospheric winds. In four of five cases, significant differences between the observed and predicted prereversal enhancement (PRE) of the background vertical drifts resulted in degraded forecast accuracy. This highlights the need for improved PRE forecasting in the global‐scale model.

ICON Observations of Equatorial Ionospheric Vertical ExB and Field‐Aligned Plasma Drifts During the 2020–2021 SSW

AbstractPrevious studies have revealed large anomalies in vertical ExB drift during the sudden stratospheric warming (SSW), and little attention focused on the behaviors of field‐aligned plasma drift. We report the first simultaneous observations of the equatorial ionospheric vertical ExB and field‐aligned plasma drifts and neutral winds during the 2020–2021 SSW, using the Ionospheric Connections Explorer (ICON) satellite measurements. The downward ExB drift is observed in the afternoon equatorial topside ionosphere in longitudes of ∼180°–270°E, in good agreement with the Jicamarca incoherent scatter radar measurements. What is more, the ICON records the afternoon northward disturbance in field‐aligned plasma drift, which is mainly due to the disturbance meridional wind. The enhanced semidiurnal tides maybe contribute to the disturbances in equatorial topside plasma drifts and neutral winds. This study indicates that the field‐aligned motion is an important factor in the ionosphere‐thermosphere responses to SSW.