This paper investigates the monthly and daily responses of the zonal-mean O3 mass-mixing ratio to polar-vortex disturbances during the boreal winter of 2023/2024, using MERRA-2 data for the period 1 October 2023-30 April 2024. In addition to the expected latitudinal coupling during SSW events, the monthly ozone field exhibited a pronounced zonally asymmetric distribution, referred to as the zonally asymmetric ozone oscillation (ZAOO), most evident in the lower stratosphere throughout the core winter months. The monthly behaviour of the ozone tendency during the extended winter season under highly disturbed conditions was also investigated. To provide a plausible explanation for the observed features, a combination of the QBO, dynamical transport, and photochemical processes was considered. For the first time, TEM diagnostics were applied to individual winter season and specific sudden stratospheric warming (SSW) events, enabling detailed examination of ozone-tendency variability across latitude and altitude. The results provide clear quantification of the dynamical and net chemical contributions to both the monthly (October-April) and daily specific SSW event ozone tendencies. These findings support systematic assessments of each intriguing winter and SSW event, offering new opportunities to identify links between SSW type and the dominant mechanisms shaping the ozone-tendency response.

This study considers the thermo-dynamical anomalies, which occurred during the boreal winter 2023-2024 based on the MERRA-2 data for the period of October 2023-April 2024. The basic object of Part 2 is to examine in detail the major sudden stratospheric warming (SSW) event occurring in March 2024 while its secondary one is to investigate the spatial and temporal distribution of the MERRA-2 ozone anomalies and their association with the SSW events; a special attention is paid to the major SSW. The major SSW consists of two very different stages. By applying the EP Flux diagnostics, it has been found that while the first stage, responsible for the SSW onset on 04 March, is forced primarily by planetary waves (PWs) with zonal wavenumber 1 and a quite small part of wavenumber 2, the second stage is driven mainly by PWs with zonal wavenumber 2. However, the difference between these two stages is clearly demonstrated by tracing the evolution of the polar vortex; while a pair cyclone-anticyclone arrangements characterized the first stage of the SSW event, its second stage revealed comparatively rare configuration of an anticyclone located over the pole observed about a week. The obtained positive relationship between the geopotential height, temperature and MERRA-2 total content of ozone polar maps during the second major SSW stage indicates that the observed anticyclone over the pole is most likely caused by the presence of the respective TCO and T maxima over the pole. Part 2 has also considered the impact of the traveling PWs on the mean flow. It is found that the 7-d W1 and W2 PWs have exerted eastward forcing on the westward wind anomaly associated with the major SSW event, leading to its weakening, while the 17-and 21-d W1 PWs produced large ozone anomalies. (c) 2025 COSPAR. Published by Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

This study considers the thermo-dynamical anomalies occurred during the boreal winter 2023-2024 based on the MERRA-2 data for the period of October 2023--April 2024. Part 1 examines in detail only the two strong minor sudden stratospheric warming (SSW) events occurring in January and February 2024 as well as a so called "unrealized case of minor SSW" observed during the first two weeks in December 2023. The EP Flux diagnostics is applied for investigating the minor SSW phenomena. It has been found that both minor SSW events are forced by the planetary wave packet with zonal wavenumber 1 (PWN1) composed of traveling eastward E1 and westward W1 PWs as well as the stationary SPW1. The EP Flux diagnostics indicated that the effect from the distribution of the convergent and divergent zones at a given day is better evident on the dynamical anomalies during the next day. The distribution of the EP fluxes revealed interesting features during the recovery phase particularly of the first SSW event which suggested the traveling PWs contribution. It has been detected especially during the period of both minor SSW events that the E1 PWs have larger amplitudes than the W1 PWs. By applying the EP Flux diagnostics separately to the SPW1 and the E1 PWs it was found that the SPW1-mean flow coupling generates the minor SSW warming event, i.e. reverses the mean flow from eastward to westward, while the coupling between the E1 PWs and the mean flow leads to the recovery of the normal eastward winter circulation. (c) 2025 COSPAR. Published by Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

This study examines the global behavior of the ionospheric TEC anomalies, i.e. their structures and temporal variability, during the initial, main and recovery phase of the geomagnetic storm occurring on 23-24 March 2023. For this purpose the global vertical TEC maps, generated by the NASA JPL IGS Ionosphere center, have been used and the geomagnetically forced anomalies have been presented in 2D (longitude-modip latitude) and polar maps. The main peculiar features of the TEC response could be summarized as: (i) the TOI-like event observed at the SH midnight hours during the main storm phase, and (ii) a clear longitude asymmetry between the TEC response at low and middle latitudes of the western and eastern hemispheres was seen; while the long-lasting positive response was evident for a full day in the western hemisphere the negative response or almost the lack of response was a characteristic of the eastern part. The study presented possible explanations of the above mentioned basic type of TEC anomalies by using the GUVY [O/N2] ratio maps and geomagnetic data from eight magnetometric stations situated at low latitudes for the separation of the effect generated by the DDEF. An attempt was made the observed TEC response during different storm phases to be reproduced. The presented reconstructions described in almost perfect way the real TEC responses and the RMSE assessments provided clear evidence for this evaluation. (c) 2024 COSPAR. Published by Elsevier B.V. All rights reserved.

The main idea of the present study is to investigate in detail the time evolution of the spatial inhomogeneities connected with the ionospheric response to the geomagnetic storm registered in the period of 10–11 May 2024. The obtained ionospheric anomalies represented by the relative deviations of the global Total Electron Content (TEC) data have been utilized in the analysis. The used global TEC data have been converted to a coordinate system with a modip latitude and geographical longitude. In addition to the maps illustrating the global spatial distribution of the geomagnetically forced ionospheric anomalies, a presentation of the observed longitudinal structures by sinusoidal approximation has also been used. The resulting positive and negative responses have been studied depending on the magnetic latitude, local times and the behavior of the geomagnetic activity parameters during the considered event. The interpretation takes into account the known mechanisms for the effect of the geomagnetic storm on the electron density. A special attention is focused on the differences in the two hemispheres at high and mid latitudes, where a simultaneous direct impact of the particle precipitation and the change in the temperature regime of the neutral atmosphere has been assumed. The low-latitude response as a result of the Equatorial Ionization Anomaly (EIA) associated with Disturbed Dynamo Electric Fields (DDEFs) and its relationship with local time has also been considered.

This paper presents climatological features of the longitudinal structures WN4, WN3, and WN2 and their drivers observed in the lower thermospheric temperatures and in the ionospheric TEC. For this purpose, two long-term data sets are utilized: the satellite SABER/TIMED temperature measurements, and the global TEC maps generated with the NASA JPL for the interval of 2002–2022. As the main drivers of the longitudinal structures are mainly nonmigrating tides, this study first investigates the climatology of those nonmigrating tides, which are the main contributors of the considered longitudinal structures; these are nonmigrating diurnal DE3, DE2, and DW2, and semidiurnal SW4 and SE2 tides. The climatology of WN4, WN3, and WN2 structures in the lower thermosphere reveals that WN4 is the strongest one with a magnitude of ~20 K observed at 10° S in August, followed by WN2 with ~13.9 K at 10° S in February, and the weakest is WN3 with ~12.4 K observed over the equator in July. In the ionosphere, WN3 is the strongest structure with a magnitude of 5.9 TECU located at −30° modip latitude in October, followed by WN2 with 5.4 TECU at 30 modip in March, and the last is WN4 with 3.7 TECU at −30 modip in August. Both the climatology of the WSA and the features of its drivers are investigated as well.

This paper presents a climatological global view on the spatial structure and interannual variability of the high-frequency migrating quarterdiurnal tide (QW4) built on a large statistics of the 21 years (2002-2022) SABER/ TIMED temperature measurements. The obtained consistent picture for the vertical structure and phase coher-ence provide strong support that the observed oscillation is a tide which is a permanent feature of middle at-mospheric dynamics while the repeating seasonal variability during all 21 years reaffirms the validity and effectiveness of the satellite data analysis method previously proposed by the same authors and used for analyzing the satellite data. The climatological tidal amplitudes rapidly growth with the height, as the 21-yearly mean amplitude changes from-1.6 K at 84 km to-7.9 K at 110 km; the latter is the largest climatologically mean tidal amplitude observed at latitude of 20 degrees S. The tide is stronger in the SH than that in the NH particularly in the lower thermosphere and it is stronger at low latitudes than that at middle latitudes at all considered heights in the & PLUSMN;50 degrees latitude range. The latitude tidal structure changes quite rapidly with height. While it is definitely asymmetric about the equator in the lower thermosphere with main enhancements at 110 km height situated around the equator, at-20 degrees S and around & PLUSMN;(40-50 degrees), the tidal structures at lower height levels become more symmetric as that at 84 km height with enhancements at the equator, & PLUSMN;35 degrees and around & PLUSMN;50 degrees. The seasonal variability based on the latitude and altitude climatological tidal structures indicated that at least four seasonal components have to be included in correctly describing the tidal seasonal behavior. The 21-year QW4 clima-tology reports for the first time the presence of the vertically upward propagating QW4 tide around the latitudes of -(0 degrees -20 degrees N) with a wavelength of-30 km, hence for correct description of the QW4 tide it is necessary besides the trapped and propagating Hough modes with very large wavelengths some propagating modes with shorter wavelengths to be included as well. This study also presents the QW4 responses to the 11-year solar cycle and the quasi-biennial oscillation at 30 hPa which define the tidal interannual variability.

The paper presents climatology of the poorly known, particularly at high latitudes, short-period (8- and 6-h) tides observed by meteor radars at high latitudinal stations Tromsø (70°N, 19°E) and Svalbard (78°N, 16°E) based on 16 years (2003–2018) and 18 years (2001–2018) of measurements, respectively. The main focus of this study is to clarify the seasonal variability and vertical structure of the two tides observed at both sites. It is found that at the two not very distant high-latitude stations Tromsø and Svalbard both tides have not only different seasonal variability but also some distinction in the altitude structure as well. In general the short-period tides at both sites are vertically upward propagating waves but with seasonally depending vertical wavelength. The two tides at Tromsø and the 8-h one at Svalbard reveal some inter-annual variability with a period of quasi-2 years. An assessment of the solar heating as the main mechanism for the generation of the 8- and 6-h tides simulated by the model WACCM6 is presented as well. The results could be used as benchmarks for model simulations and for understanding better the forcing mechanisms of these short-period tides at high latitudes.

The paper presents climatology of the mean winds and diurnal and semidiurnal tides observed by meteor radars at high latitudinal stations Svalbard (78 degrees N, 16 degrees E) and Tromso (70 degrees N, 19 degrees E) based on 18 years (2001-2018) and 16 years (2003-2018) of measurements, respectively. The main focus of the study is to clarify the features of the diurnal tide (DT) because it is poorly known particularly at high latitudes. The detailed analysis of both tidal amplitudes and phases indicated that the seasonal and altitude structure of the DT at these two not very distant stations are significantly different. Moreover, a very unusual vertical structure of the DT at Tromso has been found where above altitudes of similar to 88-90 km the zonal and meridional components have opposite directions of vertical propagation. This unusual vertical tidal feature has been supported by the climatology of the DT obtained by the MF radar situated at Tromso for the period of time 1997-2019. The paper presents also the comparison of the radar observations with two models: the assimilated CMAM-DAS and the specified dynamics (SD) WACCM-X. The WACCM-X simulated DT supports to large extent the climatology of the DT at Tromso while the assimilated CMAM-DAS reproduced the evanescent character of the tide in summer up to altitude of -88 km with almost the same amplitudes and phases as the observed ones. These results could be used as benchmarks for model simulations for understanding the forcing mechanisms of the DT at high latitudes of the considered region.

This study has examined both: (i) the global structure and seasonal variability of the eastward- and westward-travelling quasi 6-day waves (Q6DWs) observed in the geopotential height (GPH) NOGAPS-ALPHA hourly forecast data during the time interval of 14 months (January 2009–February 2010), and (ii) the climatology and interannual variability of the Q6DWs observed in the satellite MLS/Aura GPH data for an extended period of 10 years (January 2005–December 2014). Both data sets are analyzed by using the same approach. The detailed analysis revealed that the westward-travelling Q6DWs have been identified mainly at mid-high latitudes with zonal wave numbers 1 and 2. Two different types of eastward-travelling waves have been found: (i) waves at middle and high latitudes with zonal wave numbers 1 and 2, which are observed in the local winters, and (ii) waves observed over the equator with zonal wave number 1, which maximize mainly between June and September with a secondary enhancement between January–March belonging to the fast Kelvin waves. Some signatures of the solar cycle and SSW impact on the interannual variability as well as ∼2–3-year variability have been distinguished in the different ∼6-day waves. This study draws attention to both the rarely studied winter-time eastward-travelling PWs and the impact of the SSW events, particularly the major ones, on the short- and long-term variability of the PW populations.

An empirical total electron content (TEC) model response to external forcing over Balkan Peninsula (35 degrees N-50 degrees N; 15 degrees E-30 degrees E) is built by using the Center for Orbit Determination of Europe (CODE) TEC data for full 17 years, January 1999 - December 2015. The external forcing includes geomagnetic activity described by the K-p-index and solar activity described by the solar radio flux F10.7. The model describes the most probable spatial distribution and temporal variability of the externally forced TEC anomalies assuming that they depend mainly on latitude, K-p- index, F10.7 and LT. The anomalies are expressed by the relative deviation of the TEC from its 15-day mean, rTEC, as the mean value is calculated from the 15 preceding days. The approach for building this regional model is similar to that of the global TEC model reported by Mukhtarov et al. (2013a) however it includes two important improvements related to short-term variability of the solar activity and amended geomagnetic forcing by using a "modified" Kp index. The quality assessment of the new constructing model procedure in terms of modeling error calculated for the period of 1999-2015 indicates significant improvement in accordance with the global TEC model (Mukhtarov et al., 2013a). The short-term prediction capabilities of the model based on the error calculations for 2016 are improved as well. in order to demonstrate how the model is able to reproduce the rTEC response to external forcing three geomagnetic storms, accompanied also with short-term solar activity variations, which occur at different seasons and solar activity conditions are presented.

A quasi 2-day wave (QTDW) during the austral summer period usually coincides with a sudden stratospheric warming (SSW) event in the winter hemisphere, while the SSW influences on QTDWs are not totally understood. In this work, the hourly Navy Operational Global Atmospheric Prediction System-Advanced Level Physics High Altitude reanalysis data sets during January/February 2006 are utilized to study the contribution of a major SSW on the anomalous QTDW activities during the same period. Our new findings are generalized as follows: (1) The summer easterly is enhanced during a SSW event due to the interhemispheric coupling, which is clearly indicated by the anomalous cross-equator circulation from the winter to summer mesosphere. (2) The enhanced summer easterly could sustain critical layers for QTDWs with larger phase speeds (e.g., smaller zonal wave number or shortwave period) and strengthen the summer easterly barotropic/baroclinic instabilities, which are essential for the QTDW amplification through wave-mean flow interactions. This is why a strong westward QTDW with zonal wave number 2 is identified besides the conventionally dominant wave mode of wave number 3, and their periods are only similar to 42-45 hr during January 2006. (3) The strong winter planetary waves during SSW periods facilitate the occurrence of the nonlinear interaction between QTDWs and stationary planetary waves, which is strongly suggested by the abnormal temporal variations of wave number 2 and wave number 3 QTDWs. We conclude that the anomalous QTDW behaviors in summer mesosphere during January 2006 are associated with the major SSW event in the winter stratosphere.

Using an atmosphere-ionosphere coupled model, the excitation source and temporal (seasonal and interannual) variations in non-migrating tides are investigated in this study. We first focus our attention on temporal variations in eastward moving diurnal tide with zonal wavenumber 3 (DE3), which is the largest of all the non migrating tides in the mesosphere and lower thermosphere (MLT). Our simulation results indicate that upward propagation of the DE3 excited in the troposphere is sensitive to the zonal mean zonal wind in the stratosphere and mesosphere. The DE3 amplitude is enhanced in the region where the vertical shear of the zonal mean zonal wind is positive (westerly shear). Quasi-2-year variation in the DE3 amplitude in the MLT region is generated by quasi-2-year variation in the zonal mean zonal wind between 40 and 70 km, which is modulated by the stratospheric QBO. The excitation mechanisms of SW3 (westward moving semidiurnal tide with zonal wavenumber 3) and SW1 (westward moving semidiurnal tide with zonal wavenumber 1) are also investigated. During equinoxes, the SW3 and SW1 are excited by tropospheric heating (latent heat release and solar radiative heating) associated with cumulus convection in the tropics, and propagate upward into the MLT region. On the other hand, during solstices, SW3 and SW1 are generated in the winter stratosphere and mesosphere through the nonlinear interaction between the stationary planetary wave and migrating semidiurnal tide, and propagate upward to the lower thermosphere. The excitation sources of other non-migrating tides are also discussed.

The paper presents the climatology and interannual variability of both eastward- and westward-propagating ∼2-day waves (QTDW) observed in the MLS/Aura geopotential height data for a period of 10 full years (2005–2014). The climatology of the QTDWs has been studied in two steps: (i) by using average 2D-wavelet spectra both the dominant modes of variability and how these modes vary in time and space have been determined, and (ii) by applying a 2D decomposition procedure, where all planetary waves are simultaneously extracted from the data, the average global spatio-temporal distributions of all defined by the 2D-wavelet analysis modes have been obtained. It is found that the westward-propagating waves at mid-high latitudes have zonal wave numbers 2, 3 and 4 and are observed mainly in summer hemisphere. Two different types of eastward-propagating waves have been identified: (i) waves at mid-high latitudes with zonal wave numbers 2 and 3 observed in the winter hemisphere, and (ii) waves observed predominantly over the equator with zonal wave number 2, which do not have a well-defined seasonal variability but show some enhancement in both solstices. While the climatological features of the MLS/Aura QTDWs for the considered period are robust the interannual variations have to be adopted cautiously. The primary reason is that the length of the considered period of 10 years is not enough for finding clear variability pattern. The only long-term variability which appears to have some robustness is that of the W3 wave in the Southern Hemisphere where the influence of the solar cycle has been distinguished.

impact of the SSW on QTDW at other hemisphere. The authors have carried out a number of analyses using satellite observations and reanalysis data to establish their conclusions. However, the findings do not illustrate any novelty in their characteristics. In this context it should be pointed out that earlier study by Gu et al. (2016c) already investigated on the SSW and QTDW (W2, W3) relationship using greater number of warming events including the present warming episode of 2006. Noting the listed issues the paper requires substantial revision before it could be considered for publication.

This study examines the structure and variability of the ionospheric TEC anomalies driven by geomagnetic storms. For this purpose the CODE global ionospheric TEC data from four geomagnetically disturbed periods (29 October–1 November 2003, 7–10 November 2004, 14–15 December 2006, and 5–6 August 2011) have been considered. By applying the tidal analysis to the geomagnetically forced TEC anomalies we made an attempt to identify the tidal or stationary planetary wave (SPW) signatures that may contribute to the generation of these anomalies. It has been found that three types of positive anomalies with different origin and different latitudinal appearance are observed. These are: (i) anomalies located near latitudes of ±40° and related to the enhancement and poleward moving of the equatorial ionization anomaly (EIA) crests; (ii) anomalies located near latitudes of ±60° and seen predominantly in the night-side ionosphere, and (iii) very high latitude anomalies having mainly zonally symmetric structure and related to the auroral heating and thermospheric expansion. The decomposition analysis revealed that these anomalies can be reconstructed as a result of superposition of the following components: zonal mean (ZM), diurnal migrating (DW1), zonally symmetric diurnal (D0), and stationary planetary wave 1 (SPW1).

This paper demonstrates the pitfalls in applying 2D spectral and decomposition methods for studying planetary waves (PWs) during winter. A new approach for examining the travelling PWs provides the opportunity for them to be investigated by considering the amplitude and phase variability of the stationary planetary waves. The presented two simulations of a purely modulated stationary planetary wave with zonal wave number one, SPW1, with different periods of amplitude and phase modulations indicated that the 2D spectral and decomposition results show artificial zonally travelling waves with periods of modulations. When the period of the phase modulation is shorter (longer) than that of the amplitude modulation then eastward (westward) propagating waves are stronger than the westward (eastward) ones.

This study presents the analysis of 14 months (January 2009 to February 2010) of continuous hourly Navy Operational Global Atmospheric Prediction System-Advanced Level Physics High Altitude reanalysis data used for examining the quasi 2 day wave (QTDW). The global structure and seasonal variability of the eastward and westward traveling QTDWs in all meteorological fields (geopotential height, zonal and meridional wind, and temperature) have been studied. The use of hourly reanalysis data allows a comprehensive understanding of the global spatial-temporal QTDW distribution by simultaneous separations of all tides and planetary waves. The wave characteristics (amplitudes and phases) are presented in latitude range +/-80 degrees and altitudes from 15 to 95 km. Two different types of eastward traveling waves are identified: (i) waves at middle and high latitudes with zonal wave numbers 2 and 3, which are observed in the local winters, and (ii) waves observed predominantly over the equator with zonal wave number 2, which do not have a well-defined seasonal variability but show some enhancement between June and August. While the first type waves are seen in all meteorological fields, the second ones are not seen in the meridional wind and belong to the ultrafast Kelvin waves. Two different types of westward traveling waves have been identified as well: (i) waves at middle and high latitudes with zonal wave numbers 2, 3, and 4, which are observed mainly in summer hemisphere, and (ii) waves observed predominantly over the equator with zonal wave numbers 1, 2, and 3, enhanced predominantly at both solstices but are seen in other seasons as well. While the first type waves are seen in all meteorological fields, the second ones are observed in the meridional wind and are Rossby-gravity normal modes.

This study investigates the impact of dynamical processes in the neutral atmosphere on the high-midlatitude ionosphere during two sudden stratospheric warming (SSW) events. For this purpose, the reanalysis meteorological data of the National Centers for Environmental Prediction / National Center for Atmospheric Research (NCEP/NCAR) and UK Met Office (UKMO) were used in addition to that from the high-midlatitude chain of Russian ionosonde stations. The results show that the ionospheric response to the SSW events at high-midlatitudes depends on the position of the ionosonde stations relative to the stratospheric circulation pattern. Two well-pronounced effects were detected in this study. The first effect, observed in January 2009, was a negative effect in critical frequency (f o F2) and a positive effect in F2 layer maximum (h m F2) above the border of a stratospheric cyclone and an anticyclone with northward flow direction. During a 6-day period, the ionosphere exhibited a sharply inhomogeneous longitudinal structure when ionosondes, displaced at a longitude of approximately 20°, showed differences of approximately 1 MHz in f o F2 and more than 50 km in h m F2. The second feature, which was clearly observed in January 2013, implied a positive effect in f o F2 up to approximately 2.5 MHz and a negative effect in h m F2 at approximately 10 km above the center of the stratospheric cyclone. We conclude that these effects were caused by upward transport of molecular gas to the lower thermosphere for the first case and a pulldown forcing of molecular species above the low-pressure zone inside the cyclone for the second case. Changes in the O + /N 2 ratio in the lower thermosphere altered the O + recombination rate and the corresponding variations of ionosphere parameters.

The paper presents for the first time the global ionospheric response to the major SSW in January 2009 seen in the critical f(o)F2 frequency measured by ground-based ionosonde stations. Particular attention is paid on the latitudinal features of the f(o)F2 response. The ionospheric response is studied by considering the variability of the main Fourier components (24-, 12- and 8-h) of the critical frequency f(o)F2 around the central day of the SSW, i.e. around 23 January. The obtained ionosonde f(o)F2 results have been compared with the analogous f(o)F2 ones but obtained from the satellite system FORMOSAT-3/COSMIC.