The latitudinal variations in plasma density parameters (total ion density, i.e. electron density, ion composition, and TEC) during the super geomagnetic storms on 10–11 May and 10–11 October 2024 are investigated in this study. Multiple peaks in the plasma density located at the low- and mid-latitudes on both hemispheres were measured by Swarm and DMSP satellites during these storms. The low-latitude peaks were formed by the plasma fountain processes associated with the equatorial electrodynamics, whereas the mid-latitude density peaks were governed by the sub-auroral phenomena. At the local afternoon sectors, the mid-latitude density peaks were situated around 40°–50° quasi-dipole (QD) latitudes, showing an increase in density of 5–6 times compared to the previous day geomagnetic quiet time values. The total electron content (TEC) obtained from the world-wide Global Navigation Satellite System (GNSS) receivers was used to understand the temporal and longitudinal variations in the latitudinal distribution of storm-time ionospheric densities. The dynamics and strength of the mid-latitude density peaks showed dependence on local time and phases of the geomagnetic storms. These mid-latitude density peaks were present at geomagnetic conjugate locations. However, the interhemispheric asymmetry in the density was observed at the mid-latitude density peaks during both storms, which could be due to the presence of storm-time strong interhemispheric neutral winds and thereby, differences in O/N2 values. The southern hemisphere showed a more prominent increase and variations in the plasma density than the northern hemisphere. The mid-latitude density enhancements became localized around 40° QD latitudes at the local midnight sectors after the main phase of the storms. These localized mid-latitude density enhancements persisted for several hours in the recovery phase of the storm. They propagated westward and gradually decreased in intensity over time. The mid-latitude enhanced density had greater zonal extent during the May geomagnetic storm than in October. The variations in the interplanetary magnetic and electric fields could be the factor for such difference. Overall, the similarities and key differences found in the latitudinal distribution of the plasma density parameters across longitudes and time are discussed in the case of these two geomagnetic superstorms.

I use yearly average noontime foF2 from six ionospheric stations from four continents, Juliusruh, Pruhonice, Roma, Boulder, Kokubunji and Canberra over periods 1976-1995 and 1996-2014, and six solar activity indices F10.7, F30, Mg II, solar H Lyman-α flux, sunspot numbers and He II. The results reveal somewhat and sometimes even substantially different trends of foF2 when the effect of solar cycle is removed/reduced from foF2 data with different solar activity proxies. Only F30 provides for all stations and both periods the trends of the same sign (negative), other indices reveal both positive and negative trends for different stations and periods. Therefore together with results of other criteria F30 is considered to be the most reliable solar activity index for long-term studies of midlatitude foF2.

We present a response of the ionized as well as neutral components of Earth's upper atmosphere to the 14th January 2022 moderate geomagnetic storm using ICON satellite observations. Global-scale analysis of ion density and thermospheric wind speed as a function of latitude and longitude covering 160-600 km altitude range provides descriptive illustrations of storm-time responses of different layers of the ionosphere. The storm induced disturbances at almost all altitudes considered in the study and the Hunga eruption caused high wind variations at lower altitudes (160-200 km). We also considered the effects of a co-incident Hunga Tonga volcanic eruption, while our focus remains on the ionosphere-thermosphere responses to the storm. Our analyses depicted strong equatorial and low latitude ion density enhancement on 14-01-2022 (12:01-23:59 LT) across almost all longitudes, which corresponds to the times after the sudden storm commencement (SSC). Compared to 13-14 January 2022 (00:00-12:00 LT), a high ion density is observed on 15-01-2022 (00:00-12:00 LT), especially over 0 degrees-200 degrees E longitudes. This ion density enhancement persists on 16-01-2022 (at all times of the day) with a similar scenario seen on 15-01-2022. Storm-enhanced wind speed irregularity decreases relatively with an increase in altitude. Ion density is higher in 12:01-23:59 LT than in 00:00-12:00 LT during all days considered. On 15-01-2022 (12:01-23:59 LT), fluctuating structure of ion density is observed in 100 degrees-200 degrees E longitudes over the dip equator region which was found to be associated with the Hunga eruption. Generally, the moderate geomagnetic storm caused a positive ionospheric storm, which enhanced ion density and triggered turbulence in the wind dynamics. (c) 2025 COSPAR. Published by Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

Climatologically, the wintertime-evolved stratospheric polar vortex comprises zonal wind, which is westerly. During extreme events like Sudden Stratospheric Warming (SSW), the polar vortex disrupts, showing easterly wind at stratospheric altitudes. Defining extreme events in the stratosphere, like SSW at a definite pressure scale, depends on the region explaining its effects. For instance, the standard definition of SSW is 10 hPa pressure suites primarily for the lower atmosphere. SSW's current definition is unsuitable for the upper atmosphere, especially the ionosphere. So, with this viewpoint, we study the fundamental behaviour of the zonal mean of temperature during the reversal of the zonal mean of zonal wind by using superposed epoch analysis. We use the MERRA2 dataset for this analysis. From MERRA-2, we analyse the zonal mean of temperature and zonal wind from 1980 – 2022 northern hemispheric winters. The analyses are done at 10 hPa, where the standard definition of SSW is defined, and at 1 hPa, 0.5 hPa and 0.1 hPa. Temperature behaviours at different reversal periods are studied at various latitudinal values, starting at 60oN and ending at 90oN. With this analysis, a more general picture of the temperature–wind relation can be understood, which will help to understand and define SSW in a much better way for upper atmospheric studies.

Polar stratospheric chemistry is highly sensitive even to minor disruptions in water vapor or temperature. Unusual behavior in temperature and water vapor has been identified in the southern polar winter stratosphere in 2023. The potential correlation between the post-Hunga-Tonga eruption elevation of water vapor (detected in the tropics), temperature changes, and ozone anomalies is under discussion, as these parameters play a crucial role in stratospheric chemistry and dynamics. In the winter of 2023 in the Southern Hemisphere, an unexpected decrease in ozone levels and the emergence of a substantial ozone hole were observed. This event marked one of the most significant ozone decreases in the past 15 years, with an unusually large ozone hole occurring during this period, and it appears to be at least partly associated with the Hunga Tonga eruption.

Abstract. The total electron content (TEC) is an important parameter for the ionospheric dynamics, GNSS/GPS signal propagation and related applications of GNSS/GPS signals. Despite this fact the long-term trends in TEC have been studied a little only. Here we analyze the homogeneous series JPL-35 of global TEC data for 1994–2014 for selection of the optimum solar activity proxy for TEC analyses, and the UPC TEC data over 2003–2023 for estimating long-term trends in TEC. TEC trends are very predominantly negative. TEC trends reveal a clear wavenumber 2 longitudinal structure in low/equatorial latitudes with strong negative trends in belts 0–60° E and 180–240° E and weak trends in 90–150° E and 270–330° E. For more detailed information on TEC trends a longer series of reliable TEC data is required.

Polar stratospheric chemistry is highly sensitive to changes in water vapor content and temperature. We identified an unusual behavior of water vapor and temperature in the southern polar winter stratosphere in 2023. The relationships between the Hunga-Tonga eruption injection of water vapor (detected in the tropics) and its transport to SH high latitudes, temperature changes and ozone anomalies at southern high latitudes are discussed, as well as the roles of zonal wind and the meridional flux of zonal mean zonal momentum. These parameters exhibit a consistent pattern in anomalous year 2023. In the winter of 2023 in the Southern Hemisphere, an unexpected decrease in ozone levels and the emergence of an excessive ozone hole were observed. This event marked one of the deepest Antarctic ozone holes with the largest area since 2011. This appears to be associated with the Hunga Tonga eruption anomalous water vapor injection. This study highlights importance of water vapor for evolution of the Antarctic stratosphere.

The increasing concentration of greenhouse gases, which heats the troposphere, cools the upper atmosphere (mesosphere, thermosphere, and ionosphere) via the infrared radiation. This has consequences for various upper atmosphere parameters, which are briefly described in this paper. We describe also the important role of the Institute of Atmospheric Physics both in investigations as well as coordination of the international collaboration.

This article reviews main progress in investigations of long-term trends in the mesosphere, thermosphere, and ionosphere over the period 2018-2022. Overall this progress may be considered significant. The research was most active in the area of trends in the mesosphere and lower thermosphere (MLT). Contradictions on CO2 concentration trends in the MLT region have been solved; in the mesosphere trends do not differ statistically from trends near the surface. The results of temperature trends in the MLT region are generally consistent with older results but are developed and detailed further. Trends in temperatures might significantly vary with local time and height in the whole height range of 30-110 km. Observational data indicate different wind trends in the MLT region up to the sign of the trend in different geographic regions, which is supported by model simulations. Changes in semidiurnal tide were found to differ according to altitude and latitude. Water vapor concentration was found to be the main driver of positive trends in brightness and occurrence frequency of noctilucent clouds (NLCs), whereas cooling through mesospheric shrinking is responsible for a slight decrease in NLC heights. The research activity in the thermosphere was substantially lower. The negative trend of thermospheric density continues without any evidence of a clear dependence on solar activity, which results in an increasing concentration of dangerous space debris. Significant progress was reached in long-term trends in the E-region ionosphere, namely in foE (critical frequency of E region, corresponding to its maximum electron density). These trends were found to depend principally on local time up to their sign; this dependence is strong at European high midlatitudes but much less pronounced at European low midlatitudes. In the ionospheric F2 region very long data series (starting at 1947) of foF2 (critical frequency of F2 region, corresponding to the maximum electron density in the ionosphere) revealed very weak but statistically significant negative trends. First results of long-term trends were reported for the topside ionosphere electron densities (near 840 km), the equatorial plasma bubbles, and the polar mesospheric summer echoes. The most important driver of trends in the upper atmosphere is the increasing concentration of CO2, but other drivers also play a role. The most studied one was the effect of the secular change in the Earth's magnetic field. The results of extensive modeling reveal the dominance of secular magnetic change in trends in foF2 and its height (hmF2), total electron content, and electron temperature in the sector of about 50 degrees S-20 degrees N, 60 degrees W-20 degrees E. However, its effect is locally both positive and negative, so in the global average this effect is negligible. The first global simulation with WACCM-X (Whole Atmosphere Community Climate Model eXtended) for changes in temperature excited by anthropogenic trace gases simultaneously from the surface to the base of the exosphere provides results generally consistent with observational patterns of trends. Simulation of ionospheric trends over the whole Holocene (9455 BCE-2015) was reported for the first time. Various problems of long-term-trend calculations are also discussed. There are still various challenges in the further development of our understanding of long-term trends in the upper atmosphere. The key problem is the long-term trends in dynamics, particularly in activity of atmospheric waves, which affect all layers of the upper atmosphere. At present we only know that these trends might be regionally different, even opposite.

The most studied ionospheric parameter for long-term trends is foF2. The dominant factor of foF2 variability is the solar cycle, which is much stronger than the long-term trends. Therefore its effect in data must be removed. However, several decade long homogeneous measurements of the solar EUV fluxes are not available, so various solar activity proxies (solar activity indices) must be used. The aim of this paper is to study the impact of selection of different solar activity proxies on foF2 long-term trends and to find the best solar activity proxy for foF2 trends at middle latitudes. The results based on yearly average data of six midlatitude stations from four continents (1976-2014) and of six solar activity proxies show that the long-term trends in foF2 depend substantially on the solar activity proxy used, and the only solar proxy, which provides trends of the same sign for all stations and both sub-periods, is F30. Based on results of this paper and that of Lastovi & ccaron;ka and Buresova(2023), I can recommend F30 as the best solar proxy for studying long-term trends of foF2 at middle latitudes (at least for yearly average values).(c) 2023 COSPAR. Published by Elsevier B.V. All rights reserved.

Using 63 and 56 yr of continuous observations, we investigate the long‐term oscillations and residual linear trends, respectively, in the E‐ and F‐region ionosonde measured parameters of frequencies and height over Juliusruh, Europe. Using the Lomb‐Scargle periodogram (LSP) long‐term variations are estimated before the trend calculation. We found that the amplitude of the annual oscillation is higher than the 11‐yr solar cycle variation in the critical frequencies of the daytime E (foE) and Es (foEs) layers. In the F‐region, except for daytime hmF2, and nighttime foF2, the amplitude of the 11‐yr solar cycle variation is higher than the annual oscillation. The combination of the LSP estimated periods and their corresponding amplitudes and traditional regression analysis are used to construct a model for E‐ and F‐region ionospheric parameters. The modeled estimates are in good agreement with the observations. The trend calculation is derived by applying a least‐squares fit analysis to the residuals, subtracting the model from the observation. In the F‐region, both day (nighttime) foF2 and hmF2 show negative trends of −4.44 ± 1.78 (−4.30 ± 1.63) kHz/yr and −413 ± 47 (−574 ± 75) m/yr, respectively. The Piecewise linear trend of foF2 provides negative and positive trends in 1964–1996 and 1997–2019, respectively. In the E‐region, foEs show a negative trend of −2.00 ± 0.61 kHz/yr. The present investigation suggests that the greenhouse cooling effect and negative trend in the atomic oxygen (O) as well as wind shear variability could be the main drivers for the observed negative trends in the hmF2, foF2, and foEs, respectively.

The massive explosive eruption of the Hunga volcano on 15 January 2022 generated atmospheric waves that were recorded around the globe and affected the ionosphere. The paper focuses on observations of atmospheric waves in the troposphere and ionosphere in Europe, however, a comparison with observations in East Asia, South Africa and South America is also provided. Unlike most recent studies of waves in the ionosphere based on the detection of changes in the total electron content, this study builds on detection of ionospheric motions at specific altitudes using continuous Doppler sounding. In addition, much attention is paid to long-period infrasound (periods longer than similar to 50 s), which in Europe is observed simultaneously in the troposphere and ionosphere about an hour after the arrival of the first horizontally propagating pressure pulse (Lamb wave). It is shown that the long-period infrasound propagated approximately along the shorter great circle path, similar to the previously detected pressure pulse in the troposphere. It is suggested that the infrasound propagated in the ionosphere probably due to imperfect refraction in the lower thermosphere. The observation of infrasound in the ionosphere at such large distances from the source (over 16 000 km) is rare and differs from ionospheric infrasound detected at large distances from the epicenters of strong earthquakes, because in the latter case the infrasound is generated locally by seismic waves. An unusually large traveling ionospheric disturbance (TID) observed in Europe and associated with the pressure pulse from the Hunga eruption is also discussed. Doppler sounders in East Asia, South Africa and South America did not record such a significant TID. However, TIDs were observed in East Asia around times when Lamb waves passed the magnetically conjugate points. A probable observation of wave in the mesopause region in Europe approximately 25 min after the arrival of pressure pulse in the troposphere using a 23.4 kHz signal from a transmitter 557 km away and a coincident pulse in electric field data are also discussed.

Background: Specific antibodies are important for post-vaccination and post-infection immune responses against severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). The role of antibodies in preventing and treating Coronavirus disease 2019 (COVID-19) in high-risk populations has been highlighted through the use of virusspecific monoclonal antibodies, which has raised the question of immunoglobulin replacement therapy (IRT) used in immunocompromised patients. Methods: Virus-specific anti-receptor-binding domain (RBD) and anti-nucleocapsid protein (NCAP) antibodies (assessed using a chemiluminescence assay and virus-neutralizing antibodies (virus neutralization test against Delta and Omicron variants)) were analyzed in 20 batches of 10 % (100 mg/mL) immunoglobulin solutions for intravenous IRT from two commercially available producers between January 2022 and March 2023 for clinical use. Results: Anti-RBD and anti-NCAP antibodies were detected in all 20 batches of assessed IRT solutions (mean concentrations of 2817 IU/mL and 2380 IU/mL, respectively). Notably, the concentration of the virus-specific antibodies increased continuously during the follow-up period (from 822.5 IU/mL to 4066.4 IU/mL and 102 IU/mL to 3455.9 IU/mL). These antibodies demonstrated high virus-neutralizing activity against the Delta variant (mean titers of 436 and 325) but were limited to the Omicron variant (mean titers 78 and 70). The differences observed between the two brands were not statistically significant. Conclusion: IRT solutions contain high concentrations of anti-SARS-CoV-2 specific antibodies, which may prevent COVID-19; however, the efficacy can be influenced by variable virus-neutralizing activities against different viral strains. Therefore, appropriate IRT should be combined with other approaches, such as vaccination or pre- and post-exposure prophylaxis. Passively transmitted specific antibodies may also lead to false-positive serological test results.

Sudden Stratospheric Warming (SSW) is an extreme dynamical event observed in the middle atmosphere. During this event, there will be changes in circulation behaviour in the middle atmosphere followed by a sudden warming in the polar stratosphere. The warming scenario is preceded by the polar vortex disruption due to the non-linear interaction of extra-tropical planetary waves from the troposphere with the mean flow. SSW affects both the upper and lower atmosphere, irrespective of latitude. It is known that warming events are more frequent in the northern hemisphere than in the southern hemisphere. The study investigates the evolution of warming events in both the northern and southern hemispheres. We use the reanalysis data to compare the 2013 - 2014 northern hemisphere and 2002 southern hemisphere SSW. To understand the forcing and responses in both hemispheres, we conducted meteorological and statistical analyses of SSW using temperature, zonal wind, meridional wind, and geopotential height. The factors that modulate the intensity of warming events in both hemispheres have been discussed in detail.

Background : Common variable immunodeficiency (CVID) is characterized by an impaired post-vaccination response, high susceptibility to respiratory tract infections, and a broad spectrum of non-infectious complications. Thus, patients with CVID are at high risk of coronavirus disease 2019 (COVID-19), and vaccination’s role in prevention is questionable. The main aim of this study was to evaluate the clinical outcomes, safety, and dynamics of humoral and T-cell immune responses induced by the mRNA vaccine BNT162b2 in CVID. Methods : This prospective observational cohort study focused on the clinical outcomes (proportion of infected patients, disease severity), safety (adverse-event incidence, laboratory-parameter changes), and dynamics of humoral (specific post-vaccination and virus-neutralizing-antibody assessment) and T-cell immune responses (anti-SARS-CoV-2 specific T-cell detection) in 21 patients with CVID after a two-dose administration of BNT162b2. The patients were followed for 6 months. Results : Humoral response was observed in 52% (11/21) of patients at month 1 post-vaccination but continuously decreased to 33.3% (5/15) at month 6. Nevertheless, they had a remarkably lower anti-SARS-CoV-2 neutralizing antibody titer than healthy controls. The T-cell response was measurable in 33% (6/17) of patients with CVID at month 1, and it persisted for the study period. Mild infection occurred in three patients (14.3%) within the follow-up period. The vaccine also exhibited a favorable safety profile. Conclusions : The BNT162b2 vaccine elicited a measurable antibody response in a high proportion of patients, but it was limited by low titer of the virus-neutralizing antibodies and rapid waning of anti-RBD SARS-CoV-2 specific antibodies. T-cell response was detected in one-third of the patients and remained stable within the follow-up period. Vaccination has favorable safety and clinical-related outcomes in preventing severe COVID-19.

<p>To study ionospheric climate and to study its long-term changes and trends we need solar activity proxies, because long and homogeneous data series of solar ionizing flux are not available. Also models like IRI are based on solar proxies. To select the optimum solar activity proxies, we use yearly average foF2 data of six ionospheric stations from middle latitudes of four continents over 1976-2014 and six solar activity proxies, F10.7, sunspot numbers, F30, Mg II, He II and solar Lyman-α flux. The highest percentage of total variance of yearly foF2 is described equally by F30 and Mg II. However, when we divide period 1976-2014 into two parts, 1976-1995 and 1996-2014, F30 is the only proxy which reveals the same dependence of foF2 on solar proxy. Moreover, F30 is available since March 1957 whereas Mg II only since November 1978. Thus for long-term studies of yearly foF2 at middle latitudes F30 is the most suitable solar activity proxy.</p> <p>Change of the dependence of foF2 on solar activity proxies from 1976-1995 to 1996-2014 appears to be of solar origin; it is related to changes of interdependences among solar proxies between the first and second periods.</p>

Abstract To study ionospheric climate, to model the ionosphere (e.g., the International Reference Ionosphere—IRI) and to investigate its long‐term changes and trends, solar activity proxies/indices have been used, because long and homogeneous data series of solar ionizing flux are not available. To identify the optimum solar activity proxies, we use yearly average foF2 data of 11 ionospheric stations from middle and low/equatorial latitudes of four continents over 1976–2014 and six solar activity proxies, F10.7, sunspot numbers, F30, Mg II, He II, and solar H Lyman‐α flux. Mg II and F30 are found to be the best solar proxies for variability of foF2 at middle latitudes, not the usually used F10.7 or sunspot numbers. At equatorial latitudes the situation seems to be different with likely He II as the optimum solar proxy but all low/equatorial results are very preliminary. Solar activity describes 99% of the total variance of yearly foF2 and the foF2 dependence on solar proxies is highly linear at middle latitudes. The dependence of foF2 on F10.7 and sunspot numbers is significantly steeper in 1996–2014 than in 1976–1995, whereas for F30 both intervals provide the same dependence. We recommend for investigating the midlatitude yearly values of foF2 the solar proxy F30 followed by Mg II as the second one, not traditional F10.7 or sunspot numbers.

Climate change is characterized by global surface warming associated with the increase of greenhouse gas population since the start of the industrial era. Growing evidence shows that the upper atmosphere is experiencing appreciable cooling over the last several decades. The seminal modeling study by Roble and Dickinson (1989) suggested potential effects of increased greenhouse gases on the ionosphere and thermosphere cooling which appear consistent with some observations. However, several outstanding issues remain regarding the role of CO2, other important contributors, and impacts of the cooling trend in the ionosphere and thermosphere: for example, (1) what is the regional variability of the trends? (2) the very strong ionospheric cooling observed by multiple incoherent scatter radars that does not fit with the prevailing theory based on the argument of anthropogenic greenhouse gas increases, why? (3) what is the effect of secular changes in Earth’s main magnetic field? Is it visible now in the ionospheric data and can it explain some of the regional variability in the observed ionospheric trends? (4) what is the impact of long-term cooling in the thermosphere on operational systems? (5) what are the appropriate strategic plans to ensure the long-term monitoring of the critical space climate?

In the present study, using sixty-three and fifty-six years of continuous observations, we investigate the long-term oscillations and residual trends, respectively, in the E-and F-region ionosonde measured parameters over Juliusruh, Europe.Using the Lomb-Scargle periodogram (LSP) long-term variations are estimated before the trend estimation.We found that the amplitude of the annual oscillation is higher than the 11-year solar cycle variation in the critical frequencies of the daytime E (foE) and Es (foEs) layers.A weak semi-annual oscillation is also identified in the foE.In the F-region, except for daytime hmF2, and nighttime foF2, the amplitude of the 11-year solar cycle variation is higher than the annual oscillation.The LSP estimated periods and their corresponding amplitudes are used to construct a model E-and F-region ionospheric parameters that are in good agreement with the observation.The linear trend estimation is derived by applying a least-squares fit analysis to the residuals, subtracting the model from the observation.Except for the daytime foF2, all the other parameters like nighttime foF2, day and nighttime h'F, and hmF2 show a negative trend.Present results suggest that the greenhouse effect is a prime driver for the observed long-term trend in the F-region.Interestingly, weak negative trends in the foE and foEs are found which contradicts an earlier investigation.The present study suggests that the changes in the upper stratospheric ozone and mesosphere wind shear variability could be the main driver for the observed weak negative trends in the foE, and foEs, respectively.