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In this study, we utilize ICON observations from 2019 to 2022 to analyze the variability of vertical plasma drift and its relationship with the neutral winds. The results reveal that there are 19% of downward plasma drifts at 13–17 LT, which changes with seasons and longitudes. The downward plasma drift occurs less frequently compared to the contemporaneous counter electrojet during solstices. We identify the relationship between vertical plasma drifts and north foot magnetic zonal and meridional wind profiles at 90–300 km altitudes. As the vertical plasma drifts become small or downward, the zonal winds display diverse variations at the altitudes; that is, the disturbances are eastward at 95–120 km altitudes, westward at 120–160 km altitudes, and eastward above 180 km altitudes, while the meridional winds present weak changes in all altitudes. Additionally, we discuss the possible roles of the E‐ and F‐region dynamos on the vertical plasma drifts. Plain Language Summary The neutral wind in the Earth's upper atmosphere drives the ionospheric ions to cross the geomagnetic field lines and produces the dynamo effects in the E‐ and F‐regions. The electric field is created due to the divergence free of the total electrical current. The zonal electric field drives the ionospheric plasma to drift upward and downward due to the horizontal field lines, and influences the structures of low latitude ionosphere. One open question is that the vertical plasma drift shows the significant day‐to‐day variability and sometimes remarkably deviates from the climatological pattern during the quiet times. The ICON satellite provides the simultaneous observations of the plasma drifts and neutral winds in low latitudes, which provides us a good chance to investigate the day‐to‐day variability of the vertical plasma drift and its relationship to the neutral wind, as we discuss in the manuscript. Key Points The equatorial vertical plasma drifts show large variability and 19% downward plasma drift at 13–17 LT The occurrence of the downward plasma drift presents a significant longitudinal and seasonal variations The E‐ and F‐region zonal winds play vital roles on the large variability and the occurrence of the downward plasma drift

The background ionospheric conditions shaped by sunset electrodynamic processes are responsible for the development of equatorial plasma bubble (EPB)/equatorial spread F (ESF) irregularities of the post-sunset ionosphere. Distinct conditions exist for the EPB/ESF development also at later hours of the night. The plasma instability growth leading to EPB generation is dependent on the basic precursor conditions defined by the well-known parameters: the evening prereversal enhancement in vertical plasma drift (PRE), wave structure in plasma density and polarization electric field required to initiate/seed the instability, and the F layer bottom side density gradient, as a significant factor in controlling the growth rate. Competing roles of the zonal versus meridional thermospheric winds additionally control their development. Statistical as well as case studies have addressed aspects of the EPB development and occurrence under different geophysical conditions, generally focusing attention on any one of the above specific parameters. Little is known regarding the relative importance of concurrent presence of the precursor parameters (mentioned above) in shaping a given event. A large degree of day-to-day variability in these parameters arise from different sources of forcing, such as upward propagating atmospheric waves, and magnetic disturbance time electric fields in the form of prompt penetration and disturbance dynamo electric fields that often contribute to the widely observed short-term variabilities in EPB development and dynamics. In this paper, we will present and discuss some important aspects of the EPB/ESF short-term variability, focusing attention on their enhanced development, or suppression and, wherever possible, highlighting also the relative roles of the precursor parameters in such variability.

The Ion Velocity Meter (IVM) on NASA’s Ionospheric Connection Explorer (ICON) reports the in-situ ion density, ion temperature and 3-component ion drift velocity, retrieved from measurements by a retarding potential analyzer and an ion drift meter. ICON was launched during a deep solar minimum in late 2019, followed by a solar quiet (F10.7 < 80) period until September 2020. In order to quantify the uncertainties in the IVM’s drift velocity in a low plasma density environment, we compared IVM’s vertical drift velocity with eastward electric field (EEF) obtained from Swarm’s equatorial electrojet current measurements, the vertical drift from ground-based incoherent scatter radar (ISR) at Jicamarca Radio Observatory (JRO) and from Jicamarca Unattended Long-term studies of Ionosphere and Atmosphere (JULIA) coherent mode. The main results of this study show that (1) the vertical drift derived from Swarm’s EEF and ISR are in good agreement with the zonal electric field derived from JULIA’s vertical drift regardless of the F10.7 value. (2) The zonal electric field derived from IVM’s meridional drift is in good agreement with Swarm’s EEF in 2021, whereas the distribution is highly scattered in the deepest solar minimum in 2020. (3) An ad hoc IVM correction based on the 24-hour running mean of meridional drift can bring the IVM data into better agreement with Swarm and JULIA. An additional quality control based on O + fractional composition may be needed for some studies using IVM’s vertical drift. By using the same methodology presented in this work, future missions could calibrate their drift measurements to facilitate meaningful integration with ICON/IVM observations through the comparision with ground-based measurements.

The vertical component of the plasma drift, especially the evening-time pre-reversal drift, constitutes an important aspect of the nighttime electrodynamics of the equatorial ionosphere. Over the years, several studies using measurements and models have been performed to understand the characteristics of this process and its implications for the development of the instabilities leading to the plasma bubble formation and ionospheric scintillation. However, the Brazilian region presents some unique features that bring some difficulties for the vertical drift prognosis, which is required for the scintillation forecasting. These features are mainly related to the geomagnetic field lines topology that presents strong differences when compared to those of other equatorial longitudes. In this work, some of the difficulties for the pre-reversal vertical drift modeling and estimation are discussed; also, a dataset containing long-term observation (2001–2009) is compared with a widely used empirical model. The results show an intrinsic trend of underestimation by the model, which seems to be independent of latitude and seasonality thus suggesting an additional contribution arising from sources other than solely the geomagnetic topology. Also, the results indicate that the deviation can vary in the range of 0–40 m/s and the percentage error enhances with increasing values of pre-reversal vertical drift peak and reduces with increasing F10.7 values, thereby, indicating a clear possibility of meridional winds contribution which is not included in the empirical model used and may account for these differences.

Different methods are used to research and monitor the ionospheric dynamics using ground measurements: Digisonde Drift Measurements (DDM) and Continuous Doppler Sounding (CDS). For the first time, we present comparison between both methods on specific examples. Both methods provide information about the vertical drift velocity component. The DDM provides more information about the drift velocity vector and detected reflection points. However, the method is limited by the relatively low time resolution. In contrast, the strength of CDS is its high time resolution. The discussed methods can be used for real-time monitoring of medium scale travelling ionospheric disturbances. We conclude that it is advantageous to use both methods simultaneously if possible. The CDS is then applied for the disturbance detection and analysis, and the DDM is applied for the reflection height control.

This study uses multiple ground and satellite‐based measurements to investigate the extreme ionospheric response to the Mother's Day storm on May 10–11, 2024. Prompt penetration electric field caused a significant enhancement in the ionospheric vertical drift (∼${\\sim} $95 m/s) and the equatorial electrojet strength (∼${\\sim} $  275 nT) over Jicamarca. These extreme eastward electric field perturbations, along with the large meridional wind, significantly altered the F‐region plasma fountain at different local times. The afternoon equatorial ionization anomaly (EIA) not only sustained for an exceptionally long duration (∼${\\sim} $12 hr) but also expanded spatially over time. The separation between the two peaks of EIA crests exceeded ∼48°${\\sim} 48{}^{\\circ}$and ∼70°${\\sim} 70{}^{\\circ}$in the morning and evening sectors, respectively. This study shows, for the first time, that unusually strong EIA can not only develop at different local times but can also sustain for long duration under favorable conditions, which has implications for space weather applications. Plain Language Summary The Earth's upper atmosphere is significantly influenced by space weather events, particularly geomagnetic storms. In this study, we investigate the impact of an intense geomagnetic storm that occurred on 10–11 May 2024 (popularly known as Mother's Day storm) on the equatorial and low‐latitude ionosphere. Using datasets from various ground and satellites‐based (SWARM, and GOLD satellites, Global GNSS receivers, Incoherent Scatter Radar (ISR), Fabry‐ Perot interferometers (FPI), and magnetometer) measurements, we show the impact of extreme prompt penetration of electric field on the development of plasma fountain during the storm. We observe a significant increase in electron density and TEC during the main phase of the storm. Our findings highlight the role of extreme space weather disturbances on the generation of EIA at different local times and the impact of the plasma distribution on the globe. We also observe different types of electric field perturbations on low latitude ionosphere during this severe geomagnetic storm. Key Points The plasma fountain during the Mother's Day storm was unusually strong across different local time sectors The combined effects of a strong penetration electric field and meridional wind sustained the plasma fountains for an extended period The EIA crest over the Jicamarca sector merged with the expanded auroral region

Reliable estimation of vertical plasma drift in the ionosphere is crucial for interpreting ionospheric dynamics and enhancing the accuracy of space weather models. This study provides a comparative assessment of direct Digisonde Drift Measurements (DDM) and indirect ionogram-based methods using parameters such as hmF2, h′F2, h′(3.5 MHz), and h′(0.8foF2). Two high cadence measurement campaigns were conducted at the mid-latitude observatory in Pruhonice, Czech Republic, during different phases of the solar cycle. The analysis focuses on evaluating measurement consistency, temporal coherence, and the influence of sampling step and averaging strategy on drift estimation. While DDM yields stable and robust results even at 1 min resolution, ionogram-derived methods are strongly affected by measurement uncertainty and ambiguity in virtual height interpretation – particularly at short time scales. However, at night, all methods converge when a 15 min time interval is consistently applied both as the computation step and for subsequent smoothing. Under these conditions, coherent wave-like features in the vertical drift are reliably captured. The study outlines the strengths and limitations of each technique and provides recommendations for optimizing temporal resolution in ionospheric drift measurements, supporting improved methodology for future observational campaigns and model validation.

In this work, we report the simultaneous emergence of the X‐pattern of equatorial ionization anomaly (EIA) in the American and Asian sectors during a geomagnetically quiet day for the first time through the Global‐scale Observations of the Limb and Disk and Global Ionosphere Specification data assimilation products. The Ionospheric Connection Explorer (ICON) flying over the X‐pattern shows that vertical ion drift is downward around the cross and upward on both sides, along with the simultaneously observed neutral winds. The morphology of the EIA‐X is successfully reproduced by the Whole Atmosphere Community Climate Model‐Xtended with the constraint lower atmosphere (SD‐WACCMX). The mechanism behind the simultaneous EIA‐X is further clarified. We find that the EIA‐X cross coincides with the amplitude peaks of zonal neutral winds associated with the diurnal tide, and is primarily driven by downward ion drift resulting from the E‐region dynamo modulated by these zonal winds.

This study investigates the non‐solar trends and variability in Jupiter's sub‐auroral ionosphere from Pioneer, Voyager, Galileo, and Juno radio occultation electron density profiles. We show that these data are correlated with magnetic field geometry via primarily westward and equatorward thermospheric neutral winds driving field‐aligned plasma transport. This process separates Jupiter's ionosphere into variable vertical plasma drift regions, which organize most of the observed spatial and local time variability in electron density data. However, the ionospheric structure appears to be more variable when wind‐driven transport is weak, shaped by additional drivers that need further investigation. Nonetheless, Jupiter's sub‐auroral ionosphere appears to primarily be a closed system with remarkably stable vertical structure over ∼ ${\\sim} $6 decades.

Drifting fish eggs are a type of fish egg with a slightly higher density than water, requiring floating for successful hatching. While it is acknowledged that interaction with the riverbed surface can cause mortality of the eggs, the impact of this process on their downstream transport remains unclear. In this paper, we theoretically explore the transport of drifting fish eggs in turbulent open channel flows, taking into account both gravitational settling and riverbed mortality effects. This is done by incorporating a vertical drift term in the governing advection‐diffusion equation and an absorbing boundary condition for the riverbed surface, respectively. For the first time, we derive an analytical solution by the method of separation of variables for the vertical distribution of eggs during transport. Our analysis shows that in principle, settling can lead to egg accumulation near the riverbed, reducing the population's mean velocity, while conversely, riverbed mortality can decrease near‐bed accumulation and accelerate drifting to some extent. However, by estimating values of the mortality rate parameter in the real rivers, we conclude that while it can significantly affect the population size, it has a negligible effect on the vertical concentration distribution in practice, allowing for a considerable simplification of the analytical solution. Furthermore, we deduce an analytical solution for the mean velocity of the egg population, indicating variations of the deceleration rate compared to mean flow velocity, which is capable of assisting in the identification of spawning grounds. The obtained analytical solutions are validated by various numerical and experimental results.