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Previous studies suggested that sudden stratospheric warmings (SSW) change the global atmosphere from troposphere to thermosphere/ionosphere. We report the low‐latitude O+ and H+ composition at 840‐km altitude during the 2009 SSW, with the DMSP satellite morning measurements. Our results indicate that the stratospheric variation around 30‐km altitude modulates the ion exchange between the ionosphere and protonosphere via the vertical and field‐aligned plasma drifts due to the enhanced lunar semidiurnal tides. The upward disturbance drift uplifts the ionospheric O+ into the protonosphere, and most O+ is changed to H+ via chemical coupling, while the O+/H+ transition height does not change under combined effects of the southward and upward disturbance drifts on 24–29 January. The disturbance drift turns downward, lowers the O+/H+ transition height, depletes the O+ density in the protonosphere, and the H+ at higher altitudes moves downward to supply the H+ at 840 km from 30 January to 5 February. Plain Language Summary The stratosphere is a layer of the atmosphere from ∼10–50 km altitudes. Roughly every 2 years, the Northern Hemisphere winter polar stratosphere suddenly warms over a course of few days, and the winds decelerate dramatically, even reversal to easterly winds, which is known as sudden stratospheric warmings (SSW). SSW causes large changes in global atmosphere including the troposphere, mesosphere, and thermosphere via the dynamic coupling. Studies in the last decade revealed that SSW can also lead to the remarkable changes in the ionospheric electron density around the 300–400 km F2 region. A question is whether or not the SSW effects can reach higher altitude. The main ions are O+ around the F2 peak, while change to light ions as the altitude increases. We use the DMSP satellite observations in the morning to present the O+ and H+ distributions at 840 km altitude during the 2009 SSW. The ion composition distributions provide us a channel to study the coupling between the protonosphere and ionosphere. The results illustrate that the SSW occurred at ∼30 km altitude can impact the protonospheric plasma environment in low latitudes that has been not presented previously. Key Points The sudden stratospheric warmings modulates the ion exchange between the ionosphere and protonosphere The O+/H+ transition height does not change under the combined effects of the upward and southward disturbance plasma drifts The enhanced semidiurnal lunar tides may contribute to the ion exchange between two layers

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 Hunga Ha’apai volcano eruption (20.536°S, 175.382°W in Tonga) reached its maximum outbreak on 15 January 2022, at 04:15 UT, leading to huge oceanic fluctuations and atmospheric disturbances. This study focuses on the response of the ionosphere to the eruption of Tonga volcano, based on observations from a low-latitude station of the Meridian Project at Fuke, Hainan (19.310°N, 109.080°E). We identified the anomalies in the plasma drift caused by the volcanic eruption and discussed the possible mechanisms. The following results were obtained: (1) The anomalies of ionospheric plasma drift were observed at Fuke Station, during the main eruption; (2) A sudden increase and inversion of the plasma drift velocity occurred on January 15, and a large fluctuation of the drift velocity occurred afterwards; (3) By comparing the anomalous propagation velocity with the background drift, it was confirmed that the anomaly was the response of the low latitude ionosphere to the Tonga volcano eruption. Furthermore, we analyzed a possible mechanism for the effect of volcanic eruptions on ionospheric plasma drift. A large number of charged particles could be brought out by the explosion to generate an atmospheric electric field, which may cause the ionospheric plasma to change its original motion.

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 Abstract

This study examines the ionospheric response to the intense geomagnetic storm of 9–12 October 2024 over the European sector. Digisonde data from mid-latitude European stations and in situ electron density measurements from Swarm A and B satellites were used to analyze variations in key ionospheric characteristics, including the critical frequency (foF2), peak height (hmF2) and plasma drift velocities. Significant uplift of the F2 layer and a corresponding reduction in foF2 were observed across latitudes, primarily driven by prompt penetration electric fields (PPEFs) and storm-induced thermospheric winds. Horizontal and vertical ion drifts showed large asymmetries and reversals, with zonal drift velocities exceeding 1000 m/s at some stations. Swarm observations confirmed plasma density enhancements during the main phase and notable depletions during recovery, particularly after 1:00 UT on 11 October. The midlatitude ionospheric trough (MIT) intensified during the recovery phase, as can be seen from Swarm B. These variations were shaped by electrodynamic forcing, compositional changes and disturbance dynamo electric fields (DDEFs). The results emphasize the role of solar wind drivers, latitude-dependent electrodynamic coupling and thermospheric dynamics in mid-latitude ionospheric variability during geomagnetic storms.

A technique for estimating a plasma drift velocity distribution in the ionosphere is presented. This technique is based on a framework for representing a global vector field on a sphere by using a set of localized basis functions which is newly derived as a variant of the spherical elementary current system (SECS). A vector field on a sphere can be divided into its divergence-free (DF) component and curl-free (CF) component. The DF and CF components can then be represented by weighted sums of the DF and CF vector-valued basis functions, respectively. While the SECS basis functions have a singular point, the new basis functions do not diverge over a sphere. This property of the new basis function allows us to achieve robust prediction of the drift velocity at any point in the ionosphere. Assuming that the ionospheric plasma drift velocity has no divergence, its distribution can be represented by a weighted sum of the DF basis functions. The proposed technique estimates the ionospheric plasma drift velocity distribution from the SuperDARN data by using the DF basis functions. Since there are some wide gaps in the spatial coverage of the SuperDARN, an empirical convection model is combined with the framework based on the new basis functions. It is demonstrated that the proposed technique is useful for the estimation and modeling of the ionospheric plasma velocity distribution.

We introduce a new numerical model developed to assist with Data Interpretation and Numerical Analysis of ionospheric Missions and Observations (DINAMO). DINAMO derives the ionospheric electrostatic potential at low- and mid-latitudes from a two-dimensional dynamo equation and user-specified inputs for the state of the ionosphere and thermosphere (I–T) system. The potential is used to specify the electric fields and associated F-region E × B plasma drifts. Most of the model was written in Python to facilitate the setup of numerical experiments and to engage students in numerical modeling applied to space sciences. Here, we illustrate applications and results of DINAMO in two different analyses. First, DINAMO is used to assess the ability of widely used I–T climatological models (IRI-2016, NRLMSISE-00, and HWM14), when used as drivers, to produce a realistic representation of the low-latitude electrodynamics. In order to evaluate the results, model E × B drifts are compared with observed climatology of the drifts derived from long-term observations made by the Jicamarca incoherent scatter radar. We found that the climatological I–T models are able to drive many of the features of the plasma drifts including the diurnal, seasonal, altitudinal and solar cycle variability. We also identified discrepancies between modeled and observed drifts under certain conditions. This is, in particular, the case of vertical equatorial plasma drifts during low solar flux conditions, which were attributed to a poor specification of the E-region neutral wind dynamo. DINAMO is then used to quantify the impact of meridional currents on the morphology of F-region zonal plasma drifts. Analytic representations of the equatorial drifts are commonly used to interpret observations. These representations, however, commonly ignore contributions from meridional currents. Using DINAMO we show that that these currents can modify zonal plasma drifts by up to ~ 16 m/s in the bottom-side post-sunset F-region, and up to ~ 10 m/s between 0700 and 1000 LT for altitudes above 500 km. Finally, DINAMO results show the relationship between the pre-reversal enhancement (PRE) of the vertical drifts and the vertical shear in the zonal plasma drifts with implications for equatorial spread F.

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.

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.

The Ionospheric CONnections (ICON) mission has been continuously operating during the period from January 2020 to December 2021 providing simultaneous measurements of the thermal plasma properties near 600 km altitude and the neutral atmosphere and ionosphere in the altitude range 100 km to 500 km at low and middle latitudes. During this period of extremely low to moderately low solar activity, the evolving properties of the topside ionospheric density, composition, temperature and drift velocity at the satellite location are described using measurements from the Ion Velocity Meter (IVM). In the early months of 2020, the very low solar activity and relatively high abundance of H + in the total plasma density present a challenge to a robust description of the full local time distribution of the topside ion drifts. However, the quality of measurements of the ionospheric composition and temperature are not impacted by low solar activity conditions and changes in the O + and H + concentrations and their effects on the energy balance in the topside can be investigated as solar activity changes. As the relative abundance of O + increases, the susceptibility of the ion drift determination to the local plasma environment around the spacecraft is reduced and a more robust determination of the ion drift at all local times is possible. From October 2020 onward, the relationships between the topside ionospheric dynamics and the ionospheric density and temperature can be investigated and the relationships between the plasma drifts and the underlying neutral wind drivers can be established.