Vertical Drift Research Articles

A Multivariable Study of a Traveling Ionosphere Disturbance Using the Arecibo Incoherent Scatter Radar

We present the first simultaneous observations of a traveling ionosphere wave (TID) event, measuring electron concentration (Ne), vertical plasma drift (Vz), and ion and electron temperatures (Ti, Te) using the Arecibo incoherent scatter radar. A TID with a period of 135 min was evident in all four state variables in the thermosphere. The amplitudes of Vz and relative Ti fluctuations show only small height variations from 200 to 500 km and their vertical wavelengths increase with altitude. The Te fluctuation shows different characteristics from EISCAT in both phase and amplitude. When the geomagnetic dip angle is 45°, half of the driving gravity wave’s (GW’s) equatorward velocity is mapped to Vz. This meridional-to-vertical velocity coupling amplifies GW’s effect in Ne through vertical transport. The amplifying and anisotropic effects of the geomagnetic field explain the ubiquitous presence of TIDs and their preferred equatorward propagation direction in the geomagnetic mid-latitudes, as well as the midnight collapse phenomenon observed at Arecibo.

Ionospheric Disturbances Observed Over the Peruvian Sector During the Mother's Day Storm (G5‐Level) on 10–12 May 2024

AbstractThis article presents the recent extreme and rare G5‐level geomagnetic storm (Mother's Day Storm) effects on the equatorial and low‐latitude ionosphere observed at the Peruvian sector by the Jicamarca (11.9°S, 76.8°W, magnetic dip 1°N) incoherent scatter radar and associated instruments. This storm was produced by multiple Earth‐directed coronal mass ejections, which generated significant modifications in the Earth's magnetic field, leading to the Sym‐H of ∼−518 nT. On the dayside, due to the strong eastward penetration electric field, vertical plasma drift and equatorial electrojet (EEJ) enhanced for 2–3 hr and remained consistent at values of ∼95 m/s and 260 nT between 1700 and 1900 UT (1200 and 1400 LT). At the same time, vertical E B plasma drift uplifted the equatorial ionosphere, producing the dusk‐side super plasma fountain and transferring electron density to higher latitudes. A huge increase (∼1,325%) in electron density (from 11 to 142 TECu) is observed at low and mid‐latitudes from ∼20°S to 50°S between 2000 and 0400 UT (1500–2300 LT). The strong westward penetration electric field suppressed pre‐reversal enhancement, leading to downward plasma drift (∼−96 m/s) at around 2400 UT (1900 LT). Overnight, vertical plasma drift fluctuated between ±90 m/s, and the combined effect of penetration and disturbance dynamo electric fields caused a significant increase (∼530 km) in ionospheric virtual height. In the main and early recovery phase, consistent short‐ and long‐duration electric field disturbances persisted for approximately 30 hr, with periods of ∼48 and 90 min.

Surface wave damping by a Robin boundary condition at a permeable seabed

We investigate the damping of inviscid surface gravity waves when they propagate over a permeable seabed. Traditionally, this problem is solved by considering the wave motion in the upper water layer interacting with the Darcy flow in the porous bottom layer through matching of the solutions at the permeable interface. The novel approach in this study is that we describe the interaction between the upper fluid layer and the permeable bottom layer by the application of a Robin boundary condition. By varying the magnitude of the Robin parameter R, we can model the bottom structure of the fluid layer from rigid to completely permeable. In the case when the bottom is a porous medium where Darcy’s law applies, or composed by densely packed vertical Hele-Shaw cells, R is small, and can by determined by comparison with analytical results for a two-layer structure. In this case the wave damping is small. For larger values of R, the damping increases, and for very large R, the wave is almost critically damped. For the nonlinear transport in spatially damped shallow-water waves, increasing bottom permeability (larger R), reduces the magnitude of the horizontal Stokes drift velocity, while the drift profile tends to become parabolic with height. The vertical Stokes drift in the limit of large permeability is linear with height, with a magnitude that is larger than the horizontal drift. It is suggested that the implementation of a permeable bottom bed in some cases could prevent shorelines from damaging erosion by incoming surface waves.

Observation of sporadic [formula omitted] layer altitude partially modulated by the Traveling Ionospheric Disturbances at high latitudes over Zhongshan station

At Zhongshan (69° S, 76° E) Antarctica we investigate the sporadic E (Es)-layer virtual height modulation, observed by an ionosonde, during the passage of the Medium-Scale Traveling Ionospheric Disturbances (MSTIDs), observed by a SuperDARN radar. Two events were identified, on 04 October 2011 at 07:00 - 12:00 UT and 29 February 2012 at 00:00 - 04:00 UT with periods of ∼15.0 and ∼12.0 min, respectively. The magnitude of average height modulation of the Es-layer was ∼3.7 to ∼17.1 and ∼0.5 to ∼7.3 km, respectively, with the same periods as the MSTIDs. Ray tracing during the events shows that the likely MSTID propagation was up to ∼300 km in the ionospheric F-region. The computed ion vertical drift velocity using SuperDARN radar and magnetometer data, and Es-layer altitude modulation observed by the ionosonde have moderate to strong positive correlation of 0.71 ± 0.22 and 0.51 ± 0.16, respectively. We show that the MSTIDs polarization electric field, which is mapped down from the F-region along the near-vertical magnetic field, moderately contributes to the modulation of the Es layer altitude via the E×B drift mechanism.

Investigation of characteristics of ionospheric vertical plasma drift during sunset over the mid-latitude station Nicosia, Cyprus

Investigation of characteristics of ionospheric vertical plasma drift during sunset over the mid-latitude station Nicosia, Cyprus

Data Assimilation of Ion Drift Measurements for Estimation of Ionospheric Plasma Drivers

AbstractDuring geomagnetic storms, the capabilities of current climate models in predicting ionospheric behavior are notably limited. A data assimilation tool, Estimating Model Parameters Reverse Engineering (EMPIRE), implements a Kalman filter to ingest electric density rate correcting the background electric potential and neutral wind. For the baseline setup, or case (1), EMPIRE ingests electron density global map output from the Ionospheric Data Assimilation 4‐Dimensional (IDA4D) algorithm. In this work, a new augmentation method is evaluated in which ion drift measurements are also assimilated into EMPIRE. The ion drift measurements used in the new augmentation method are obtained from Super Dual Auroral Radar Network (SuperDARN) sites in the mid‐to‐high latitude region of the northern hemisphere. Cases (2) and (3) are set up for evaluating the impacts from ingesting different types of observations: SuperDARN fit and grid data, respectively. Six independent data sources are used as validation data sets to compare outcomes with or without ingesting ion drifts. One is the vector ion velocities derived from the Millstone Hill Incoherent Scatter Radar (MHISR) and a second is the vertical drift from Arecibo site. The other four are SuperDARN ion velocity grid data from Saskatoon, Kapuskasing, Christmas Valley West, and Hokkaido East. Results show improvements in performance at mid‐latitudes by augmenting electron density rates with 3D spatially distributed line‐of‐sight ion drift measurements, with negligible improvements to low and high latitude estimations. The lack of improvement at high‐latitudes is attributed to the increase in EMPIRE ion drift error poleward of 60° magnetic.

On the Role of Physical Processes in Controlling Equatorial Plasma Bubble Morphology

AbstractIn this study, we present the results of an analysis of the morphological features of Equatorial Plasma Bubbles (EPBs) over South America. In this context, we analyzed data from the Disturbance Ionosphere indeX (DIX) maps calculated using around 450 Global Navigation Satellite System (GNSS) stations. To mitigate the influence of magnetic disturbances on bubble development, only data from geomagnetically quiet days were utilized. This study covered the period from the post‐peak of solar cycle 24 (2015) to the pre‐peak of solar cycle 25 (2023), totaling 1321 nights with EPB occurrences, representing the largest data set of EPBs ever compiled for South America. Our analysis unveiled several key findings regarding EPBs and their behavior over the South American region. First, we observed that the amplitude of plasma depletions, as reflected in the DIX values, and the EPB latitudinal development follow an approximately 11‐year cycle driven by solar radiation levels. Furthermore, our analysis highlights the significant influence of factors such as the angle between the solar terminator and the magnetic meridian (T‐M angle), which varies inversely with the vertical plasma drift velocity during the pre‐reversal enhancement (PRE). Additionally, we discuss the longitudinal variations associated with magnetic declination, as well as the saturation behavior of EPB development with extreme solar flux.

Results from Cryo-PoF: Power over fiber for fundamental and applied physics at cryogenic temperature

The Power over Fiber (PoF) technology delivers electrical power by sending laser light through an optical fiber to a photovoltaic power converter, in order to power sensors or electrical devices. This solution offers several advantages: removal of noise induced by power lines, robustness in a hostile environment, spark free operation when electric fields are present and no interference with electromagnetic fields.This technology is at the basis of the Cryo-PoF project: an R&D funded by the Italian Institute for Nuclear Research (INFN) in Milano-Bicocca (Italy). This project is inspired by the needs of the DUNE Vertical Drift detector, where the VUV light of liquid argon must be collected at the cathode, i.e. on a surface whose voltage exceeds 300 kV. We developed a cryogenic system, which is solely based on optoelectronic devices and a single laser input line, to power both the Photon Detection devices and its electronic amplifier. The Milano-Bicocca setup employ a commercial GaAs laser source with 2 W maximum power and a photovoltaic power converter with efficiency of ∼ 30% at liquid nitrogen temperature. The results obtained in Milano Bicocca will be presented with emphasis on performance and potential application in the field of applied physics.

New Expression of the Field‐Line Integrated Rayleigh‐Taylor Instability Growth Rate

AbstractAn expression of Rayleigh‐Taylor (R‐T) instability growth rate based on the field‐line integrated theory is newly established. This expression can be directly utilized in ionosphere models with magnetic flux tube structure based on Modified Apex Coordinates. The R‐T instability growth rates are calculated using the thermospheric and ionospheric conditions based on the coupled Whole Atmosphere Model and Ionosphere Plasmasphere Electrodynamic model (WAM‐IPE). The parameters used in this calculation include the field‐line integrated conductivities and currents, which consider the Quasi‐Dipole Coordinates and the modifications to the equations of electrodynamics. Detailed description of the new formulas and comprehensive analyses of diurnal, longitudinal, and seasonal variations of the R‐T instability growth rate are carried out. The dependencies of growth rates on pre‐reversal enhancement (PRE) vertical drifts and solar activity are also examined. The results show that pronounced R‐T growth rates are captured between 18 and 22 local time (LT) when strong PRE occurs in the equatorial ionosphere. The simulated R‐T growth rate increases with increasing solar activity levels and demonstrates strong correlations with the angle between the sunset terminator and the geomagnetic field line. These results are consistent with plasma irregularity occurrence rates shown in various satellite observations, suggesting that the newly developed R‐T growth rate calculation can effectively capture the probability of irregularities by considering the changes along magnetic flux‐tubes in the ionosphere. Since the WAM‐IPE is running in operation at National Oceanic and Atmospheric Administration Space Weather Prediction Center, the new calculations can be potentially implemented in the near future to provide forecasted information of the R‐T growth rate.

The DUNE Far Detector Vertical Drift Technology. Technical Design Report

DUNE is an international experiment dedicated to addressing some of the questions at the forefront of particle physics and astrophysics, including themystifying preponderance of matter over antimatter in the early universe. The dual-site experiment will employ an intense neutrino beam focused on a near and a far detector as it aims to determine the neutrino mass hierarchy and to make high-precision measurements of the PMNS matrix parameters, including the CP-violating phase. It will also stand ready to observe supernova neutrino bursts, and seeks to observe nucleon decay as a signature of a grand unified theory underlying the standard model.The DUNE far detector implements liquid argon time-projection chamber (LArTPC) technology, and combines the many tens-of-kiloton fiducial mass necessary for rare event searches with the sub-centimeter spatial resolutionrequired to image those events with high precision. The addition of a photon detection system enhances physics capabilities for all DUNE physics drivers and opens prospects for further physics explorations. Given its size, the far detector will be implemented as a set of modules, with LArTPC designs that differ from one another as newer technologies arise.In the vertical drift LArTPC design, a horizontal cathode bisects the detector, creating two stacked drift volumes in which ionization charges drift towards anodes at either the top or bottom. The anodes are composed of perforated PCB layers with conductive strips, enabling reconstruction in 3D.Light-trap-style photon detection modules are placed both on the cryostat's side walls and on the central cathode where they are optically powered.This Technical Design Report describes in detail the technical implementations of each subsystem of this LArTPC that, together with the other far detector modules and the near detector, will enable DUNE to achieve its physics goals.

Lateral 1200V SiC schottky barrier diode with single event burnout tolerance

For a power device to be used in space, it must be able to recover from a single event effect caused by heavy ion radiation. Conventional vertical silicon carbide (SiC) power devices such as automotive diodes and MOSFETs, can only meet this requirement if they are heavily derated, a 1200 V device typically unusable above 200 V. In this paper, a lateral RESURF Schottky diode has been designed in TCAD simulation using a radiation-hard (rad-hard) by design methodology. By preventing anode-to-cathode shorting that occurs in a vertical drift region, the lateral design is shown to recover after a heavy ion traverses the device with a linear energy transfer (LET) of 60 MeV·cm2/mg, while the device is blocking 1200 V. The design splits the drift region into a higher doping zone closer to the cathode (Zone 2) of 1.5×1017 cm−3 and a lower doping zone closer to the anode (Zone 1) of 1×1016 cm−3. The electric field spikes were reduced while the device was recovering. This design keeps the local temperature in the device to under 1000 K if the heavy ion penetrates the device in a direction perpendicular to the surface. Other entry positions and directions are also simulated and a maximum temperature of 1733 K occurs when the ion path is horizontal, entering at 1 μm below the surface. However, this temperature peak occurs at the cathode, which is not expected to lead to lasting leakage damage. A deep P+ pillar embedded into the anode acts as a collector for holes generated during the single event. Simulations show that a deeper P+ pillar, to a depth of up to 5 μm, reduces the hole density in the N-drift region and P-epi layer during recovery. This also allows the Zone 1 doping to be increased to as much as 5×1016 cm−3, thereby reducing on-state losses.

Ionospheric Virtual Height (h′F2) Response and its Vertical Ion Drifts Characteristics at an Equatorial Station

The Ionospheric virtual heights (h’F2) obtained from the DPS-4.2 Version of the GIRO’s site, as a computing parameter for vertical E × B ion drifts in this present study using the international quiet days (IQDs) is engaged. Vertical ion drifts () computed from virtual heights was studied over Ilorin (lat. 8.31°N, long. 4.34°E, dip lat. 2.95o) during a solar minimum (SM), a station situated at the equatorial dip. The hourly averages of vertical ion drifts, were computed from 10-international quiet days (IQDs) hourly h’F2 averages for the four seasonal months adopted. Seasonally, was having same behavourial patterns of pre-noon and post-noon peaks, but in h’F2, it had noontime, post-sunset and pre-sunrise peaks occurred in all seasons. The pre-noon peaks magnitudes are 6.8, 14.4 and 15.0 m/s in June Solsticial, Equinoctial and December Solsticial respectively; and its post-noon peaks magnitudes are 0.8, 7.4 and 7.9 m/s in December and June Solsticials, and Equinoctial seasons respectively. The h’F2 noontime peaks magnitudes are (321–410) km, post-sunset peaks magnitudes are (253–329) km and pre-sunrise peaks magnitudes are (228–318) km in all seasons. Also, depicted pre-reversal enhancement (PRE) night peaks in all seasons. The PRE peaks magnitudes are [(-4.0)–(-13.4)] m/s at 2000 LT, [(-4.9)–(-9.3)] m/s between 2200 LT and 2300 LT in all seasons. Similar phenomenal observations occurred in the h’F2 and annual patterns plots. In general, the h’F2 and magnitudes were greatest in Solsticial seasons and least in Equinoctial season. The h’F2 and stable and continual descent indicates generally that the electrons briskly drifting away from the equator triggered by solar ionization in the equatorial region. As well, seasonal peaks occurred in general are assumed to be controlled by the enhanced vertical E × B ion drifts upsurge, which adapts with former aftermaths at some stations in the West African sector during closely related solar activity

Low Latitude Estimated Virtual Vertical Plasma Drifts Variation During Solar Minimum

Virtual vertical plasma drifts estimated from hourly virtual heights (h’F2) extracted from the digisonde found on GIRO’s website are used in this recent study by engaging the international quiet days (IQDs) conditions. Virtual vertical plasma drifts () estimated from low latitude F2-region virtual heights was examined over Ilorin (lat. 8.31°N, long. 4.34°E, dip lat. 2.95o) during solar minimum (SM), a station Located along the latitudinal hollow. The 10-international quiet days (IQDs) monthly averages across each hourly period of the day were used for the estimation. Two characteristics of highlighted are the pre-noon and the post-noon peaks of the diurnal patterns for each season. The pre-noon peaks magnitudes between 0800 LT and 0900 LT are 6.8, 14.4 and 15.0 m/s for June Solstice, Equinox and December Solstice respectively; and its post-noon peaks magnitudes around 1800 LT evening time are 0.8, 7.4 and 7.9 m/s foe December and June Solstices, and Equinox respectively. displayed an enhanced phenomenon of slight-transitory spikes having magnitudes of -0.3 m/s (December Solstice) and -0.8 m/s (Equinox), and 3.6 m/s (June Solstice) around 1200 LT noontime. Finally, depicted pre-reversal enhancement (PRE) night peaks for the entire season. The PRE peaks magnitudes are [(-4.0)–(-13.4)] m/s at 2000 LT, [(-4.9)–(-9.3)] m/s between 2200 LT and 2300 LT, [(-3.6)–(-6.6)] m/s between 0100 LT and 0200 LT and [(-3.0)–(-6.4)] m/s between 0300 LT and 0400 LT respectively for all seasons. Same phenomenon in the annual pattern as showcased in the diurnal patterns occurred. In general, magnitudes were highest in Solstices and lowest in Equinox during solar minimum. The gradually and continuous decay is ensued by the electrons hastily turnoff movement from the low latitude due to solar ionization for all seasons

Diffusive‐Convection Staircase Merger Events Mediated by Subsurface Eddies in the Canada Basin

AbstractDiffusive‐convection (DC) staircases, characterized by interleaving well‐mixed layers and high‐gradient interfaces of thermohaline properties, are commonly observed in the Canada Basin, Arctic. Previous studies suggested a quasi‐steady state of the thermohaline structures of these staircases. In this work, we employ mooring and Ice‐Tethered Profiler (ITP) data to show emergent merger events of staircases mediated by subsurface eddies with warm cores located at 300–500 m depths in 2005, 2007 and 2009. Two types of merger events, the B‐merger (resulting from strengthening of stronger interfaces at the expense of weaker ones) and the H‐merger (produced by vertical drift and collision of staircase interfaces), are documented during the passage of subsurface eddies. The merging staircases are located at 320–450 m depths, with layers of up to 70 m thick and high‐gradient interfaces thinner than 5 m. Mooring measurements reveal the emergence of staircase mergers associated with a background Richardson number dropping from a typical magnitude of – to , indicating the persistence of DC staircases in the presence of strong shears. In parallel, ITP data suggest the formation of B‐mergers (H‐mergers) to be favored within the eddy core (flank). The vertical heat fluxes associated with the B‐merger (H‐merger) staircases are estimated to be ∼3 W/m2 (∼1.5 W/m2), which substantially exceed the typical staircase‐driven heat fluxes of W/m2. These observations imply the significance of subsurface eddies in shaping the halocline structures and thus the vertical heat fluxes in the Arctic Ocean, particularly in a warming climate.

Tidal Control of Equatorial Vertical E × B Drift Under Solar Minimum Conditions

AbstractObservations show that equatorial ionospheric vertical drifts during solar minimum differ from the climatology between late afternoon and midnight. By analyzing WACCM‐X simulations, which reproduce this solar cycle dependence, we show that the interplay of the dominant migrating tides, their propagating and in situ forced components, and their solar cycle dependence impact the F‐region wind dynamo. In particular, the amplitude and phase of the propagating migrating semidiurnal tide (SW2) in the F‐region plays a key role. Under solar minimum conditions, the SW2 tide propagate to and beyond the F‐region in the winter hemisphere, and consequently its zonal wind amplitude in the F‐region is much stronger than that under solar maximum conditions. Furthermore, its phase shift leads to a strong eastward wind perturbation near local midnight. This in turn drives a F‐region dynamo with an equatorial upward drift between 18 and 1 hr local times.

The impact of the Hunga Tonga–Hunga Ha’apai volcanic eruption on the Peruvian atmosphere: from the sea surface to the ionosphere

The eruption of the Hunga Tonga Hunga Ha’apai volcano on 15 January 2022 significantly impacted the lower and upper atmosphere globally. Using multi-instrument observations, we described disturbances from the sea surface to the ionosphere associated with atmospheric waves generated by the volcanic eruption. Perturbations were detected in atmospheric pressure, horizontal magnetic field, equatorial electrojet (EEJ), ionospheric plasma drifts, total electron content (TEC), mesospheric and lower thermospheric (MLT) neutral winds, and ionospheric virtual height measured at low magnetic latitudes in the western South American sector (mainly in Peru). The eastward Lamb wave propagation was observed at the Jicamarca Radio Observatory on the day of the eruption at 13:50 UT and on its way back from the antipodal point (westward) on the next day at 07:05 UT. Perturbations in the horizontal component of the magnetic field (indicative of EEJ variations) were detected between 12:00 and 22:00 UT. During the same period, GNSS-TEC measurements of traveling ionospheric disturbances (TIDs) coincided approximately with the arrival time of Lamb and tsunami waves. On the other hand, a large westward variation of MLT winds occurred near 18:00 UT over Peru. However, MLT perturbations due to possible westward waves from the antipode have not been identified. In addition, daytime vertical plasma drifts showed an unusual downward behavior between 12:00 and 16:00 UT, followed by an upward enhancement between 16:00 and 19:00 UT. Untypical daytime eastward zonal plasma drifts were observed when westward drifts were expected. Variations in the EEJ are highly correlated with perturbations in the vertical plasma drift exhibiting a counter-equatorial electrojet (CEEJ) between 12:00 and 16:00 UT. These observations of plasma drifts and EEJ are, so far, the only ground-based radar measurements of these parameters in the western South American region after the eruption. We attributed the ion drift and EEJ perturbations to large-scale thermospheric wind variations produced by the eruption, which altered the dynamo electric field in the Hall and Pedersen regions. These types of multiple and simultaneous observations can contribute to advancing our understanding of the ionospheric processes associated with natural hazard events and the interaction with lower atmospheric layers.Graphical

Response of total electron content to the October 25, 2022 partial solar eclipse from high to low latitudes in the Euro-Asian region

Solar eclipses (SEs) pertain to high-energy sources. They are capable of causing significant disturbances in all geoshells and geophysical fields. Despite the almost century-long history of studying the influence of eclipses on geoshells, the task of observing and analyzing disturbances in them remains relevant. This is explained by the fact that the response of the media significantly depends on the state of atmospheric and space weather, the location and time of observation, the SE magnitude, etc. The aim of this paper is to present the results of a statistical analysis of the features of the total electron content (TEC) variations during the October 25, 2022 SE from high to low latitudes in the Euro-Asian region. Data from Global Navigation Satellite System were used for the analysis. The error in estimating TEC in the vertical column did not exceed 0.1 TECU. For the first time, the response of the ionosphere to an SE has been studied on a global scale (from the Reykjavik station to the Novosibirsk station) using methods of statistical analysis, including the time moments after sunset. The decrease in TEC reached 1.0–19.0 TECU, and the relative decrease was approximately –0.32. Changes in all TEC disturbance parameters depended in a complex manner on the relative obscuration area of the solar disk. This can be explained by non-monotonic changes in electron density during the daytime, by the intensification of the ionosphere–plasmasphere coupling, the disturbance of the ionospheric current system, vertical plasma drift in crossed electric and magnetic fields, as well as the generation of wave disturbances during the SE period. The delay time of the maximum ionospheric response (maximum |δV| value) with respect to the maximum magnitude of the eclipse was 15–25 min. The duration of the ionospheric response to the SE slightly exceeded the duration of the perturbing source influence.

A Numerical Study on the Impact of E × B Drift on the Vertical Distribution of the Plasma Density Over the Geomagnetic Equatorial Ionospheric Region

AbstractUsing an in–house developed Quasi Two–Dimensional (QTD) physics–based ionospheric model, the impact of E × B drift velocity on the vertical distribution of the electron density over the equatorial latitude has been investigated. The vertical drift measurements from (a) drift analysis software of Digisonde (b) derived from Digisonde ionograms (c) calculated from the Scherliess–Fejer (SF) model, and (d) obtained from the magnetometer ΔH measurements have been used in this study. Four quiet days in a low solar activity year, representing four seasons of the year 2010, have been chosen for the study. The model–derived electron density profiles using the vertical drifts from all four methods matched well with the Digisonde observation below ∼150 km at all the Local Times (LTs) for all 4 days. However, since the Digisonde–derived drifts were very low, centered mostly around zero, it led to the overestimation/underestimation of the F–region peak plasma density (nmF2)/height (hmF2). The model simulated electron density profiles using the SF model, and ΔH derived vertical drifts showed good agreement with the observation up to an altitude of ∼350 km. The study showed that vertical drift is a factor that controls the nmF2 trough around noon over the equatorial latitude. It is seen that plasma diffusion occurs only beyond an altitude of 350 km, while the range of altitudes between 320 and 350 km acts as the “diffusion threshold height.” This finding has significant implications for understanding plasma dynamics in the equatorial ionosphere.

The Impact of Vertical Plasma Motion on the Evolution of Predawn Equatorial Plasma Bubbles on the Dayside

AbstractThis study investigates the impact of vertical ionospheric drift during daytime on the evolution of predawn equatorial plasma bubbles by conducting model simulations using “Sami3 is Another Model of the Ionosphere.” The upward drift of the ionosphere transports bubbles to higher altitudes, where their lifetime is set by the atomic oxygen photoionization rate. While the bubbles generated at predawn persist into dayside, the bubbles generated shortly after sunset diminish before sunrise. Therefore, post‐sunset bubbles do not contribute to daytime electron density irregularities. Bubbles maintain their field‐aligned characteristics throughout the daytime regardless of the vertical ionospheric drift. This property allows bubbles to exist near the magnetic equator despite poleward plasma transport by the fountain process. The shift of irregularity concentration to higher latitudes over time in satellite observations is explained by the combined effect of transport of bubbles to higher altitudes and rapid refilling of depletions near the magnetic equator.

Variability of the equatorial ionization anomaly over the South American sector: Effects of electric field and effective meridional wind

Vertical Total Electron Content (VTEC) Maps over the South American Continent were utilized to investigate the temporal and longitudinal climatology of Equatorial Ionization Anomaly (EIA) using more than 350 Global Navigation Satellite Systems (GNSS) receivers. At a temporal resolution of 10 min, the EIA motions, morphologies, and evolutions were mapped using VTEC keogram along magnetic meridians lines. Between 2014 and 2019, characteristics of the EIA were studied at two different South American magnetic meridians (i.e., 3.36° E and 7.58° E) separated by ∼555 km at an altitude of 300 km. The aim of this study is to examine the EIA’s variability, monthly variations and occurrences at evenly spaced longitudinal sectors. The effects of effective meridional winds component and E × B drift velocity on the daytime asymmetry of EIA anomalies were studied using a physics-based numerical model, Sheffield University Plasmasphere-Ionosphere model at Instituto Nacional de Pesquisas Espaciais (SUPIM-INPE). We found that the EIA parameters such as strength, shape, intensity, and latitudinal positions are affected by the eastward electric field and effective meridional wind. The monthly variations in the EIA over two magnetic meridian sectors demonstrate a semiannual variation. The EIA crests were more symmetric in equinox than in solstice seasons. The asymmetries of the EIA observed during the December solstice are more intense than during the June solstice, whereas September equinox is less symmetric than March equinox seasons. Moreover, this study indicates that the vertical drift and the meridional neutral wind plays a very significant role in the development of the EIA asymmetry by transporting the plasma up the field lines. There was a notable contraction of the EIA southern hemispheric (SH) crests from the December solstice to the June solstice. Meanwhile, the EIA crest positions in the northern hemisphere (NH) expand from the December solstice to the June solstice. According to our observations, the March equinox season had the most EIA occurrences, which were then followed by the September equinox, the December and June solstices. The intensities of the EIA crests also considerably decreased with solar descending phases. Through modeling, this work provides the scientific community with new insights into the evolution/development of EIA and their latitudinal asymmetry, as well as the role of E × B drift and thermospheric neutral wind in assessing the statistical analysis of EIA variability using the largest VTEC database over the South American sector.