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Propagation of medium-scale gravity waves (GWs) in the thermosphere/ionosphere is observed remotely, using multi-frequency and multi-point continuous Doppler sounding system located in the western part of Czechia. Reflection heights of the sounding radio waves are determined from a nearby ionosonde. Phase velocity vectors of GWs are calculated from time/phase delays between signals corresponding to different transmitter–receiver pairs that reflect in the ionosphere at different locations. As various frequencies reflect at different heights, reflection points of radio signals are separated both horizontally and vertically, and the investigation of GW propagation in the ionosphere is performed in three dimensions. Results obtained for two 1-year periods representing the solar maximum (July 2014–June 2015) and current solar minimum (September 2018–August 2019) are presented. It is shown that GWs in the ionosphere usually propagated with wave vectors directed obliquely downward. A statistical distribution of wave vector elevation angles is presented. A model of neutral winds is used to estimate the wave characteristics in the wind-rest frame. It is found that the distribution of elevation angles is narrower in the wind-rest frame than in the Earth frame. Seasonal and diurnal changes of propagation directions and attenuations of GWs are discussed. The wind-rest frame wavelengths of the analyzed GWs were usually from ~ 80 to 300 km, and the propagation velocities were mostly between ~ 100 and ~ 220 m/s.

The aim of this paper is to statistically examine whether there are different patterns in daily numbers of deaths during the quiet periods of solar activity, in contrast to the periods of the strong solar storms. We considered three periods of solar storms (storm of 14 July 2000 Bastille Day Event, storm of 28 October 2003 Halloween Solar Storms, and storm of 17 March 2015 St. Patrick’s Day event) and three periods of continuous very low solar activity (13 September–24 October 1996, 21 July–20 August 2008, and 31 July–31 August 2009) during the Solar Cycles No. 23 and No. 24. In particular, we focus on diseases of the nervous system (group VI from ICD-10) and diseases of the circulatory system (group IX from ICD-10) separately for both sexes and two age groups (under 39 and 40+). We demonstrate that in the resulting graphical models there was a connection between the daily number of deaths and all indices of solar and geomagnetic activity in periods of low solar activity in contrast to periods of strong solar storms in some monitored groups according to age, sex, and group of diagnosis.

A statistical analysis of the relation between exceptional solar events and daily numbers of deaths in the Czech Republic is presented. In particular, we concentrate on diseases of the nervous system (group VI from ICD-10—International Statistical Classification of Diseases and Related Health Problems 10th Revision) and diseases of the circulatory system (group IX from ICD-10). We demonstrate that the neurological diseases exhibit greater instability during the period of rising and falling solar activity. We study the daily numbers of deaths, separately for both sexes and two age groups (under 39 and 40+), during the Solar Cycles No. 23 and No. 24. We focus on exceptionally strong solar events in this period, such as the “Bastille Day event” on 14 July 2000, “Halloween solar storm” on 28 October 2003, and events on 7 January 1997, 2 April 2000, and on 7 September 2005. Special attention is paid to “St. Patrick’s Day storm” on 17 March 2015, the strongest geomagnetic storm of the Solar Cycle No. 24 that occurred following a coronal mass ejection (CME). We investigate the changes in the daily numbers of deaths during 1 month before and 1 month after these exceptional solar events. We take specific storm dynamics of their geophysical parameters into consideration. It has been verified that, for diseases of the nervous system, women are generally more sensitive than men. On the contrary, this differences between men and women have not been found for diseases of the circulatory system. Our findings suggest that the impact of the hazardous space weather conditions on human health depends on the specific dynamic and strength of the solar storm.

A severe meteorological storm system on the frontal border of cyclone Fabienne passing above central Europe was observed on 23–24 September 2018. Large meteorological systems are considered to be important sources of the wave-like variability visible/detectable through the atmosphere and even up to ionospheric heights. Significant departures from regular courses of atmospheric and ionospheric parameters were detected in all analyzed datasets through atmospheric heights. Above Europe, stratospheric temperature and wind significantly changed in coincidence with fast frontal transition (100–110 km h−1). Zonal wind at 1 and 0.1 hPa changes from the usual westward before the storm to eastward after the storm. With this change are connected changes in temperature where at 1 hPa the analyzed area is colder and at 0.1 hPa warmer. Within ionospheric parameters, we have detected significant wave-like activity occurring shortly after the cold front crossed the observational point. During the storm event, both by Digisonde DPS-4D and continuous Doppler sounding equipment, we have observed strong horizontal plasma flow shears and time-limited increase plasma flow in both the northern and western components of ionospheric drift. The vertical component of plasma flow during the storm event is smaller with respect to the corresponding values on preceding days. The analyzed event of an exceptionally fast cold front of cyclone Fabienne fell into the recovery phase of a minor–moderate geomagnetic storm observed as a negative ionospheric storm at European mid-latitudes. Hence, ionospheric observations consist both of disturbances induced by moderate geomagnetic storms and effects originating in convective activity in the troposphere. Nevertheless, taking into account a significant change in the global circulation pattern in the stratosphere, we conclude that most of the observed wave-like oscillations in the ionosphere during the night of 23–24 September can be directly attributed to the propagation of atmospheric waves launched on the frontal border (cold front) of cyclone Fabienne. The frontal system acted as an effective source of atmospheric waves propagating upward up to the ionosphere.

During the peak days of the 2019 Leonids and Geminids (16–19 November and 10–16 December), two ionograms/minute and one Skymap/minute campaign measurements were carried out at the Sopron (47.63°N, 16.72°E) and Průhonice (50.00°N, 14.60°E) Digisonde stations. The stations used frequencies between 1 and 17 MHz for the ionograms, and the Skymaps were made at 2.5 MHz. A temporary optical camera was also installed at Sopron with a lower brightness limit of +1 visual magnitude. The manual scaling of ionograms for November and December 2019 to study the behavior of the regular sporadic E layer was also completed. Although the distributions of the stations were similar, there were interesting differences despite the relative proximity of the stations. The optical measurements detected 88 meteors. A total of 376 meteor-induced traces were found on the Digisonde ionograms at a most probable amplitude (MPA) threshold of 4 dB and of these, 40 cases could be linked to reflections on the Skymaps, too. Of the 88 optical detections, 31 could be identified on the ionograms. The success of detections depends on the sensitivity of the instruments and the noise-filtering. Geometrically, meteors above 80 km and with an altitude angle of 40° or higher can be detected using the Digisondes.

Mesoscale convective systems are effective sources of atmospheric disturbances that can reach ionospheric heights and significantly alter atmospheric and ionospheric conditions. Convective systems can affect the Earth’s atmosphere on a continental scale and up to F-layer heights. Extratropical cyclone “Zyprian” occurred at the beginning of July, 2021 and dominated weather over the whole of Europe. An extensive cold front associated with “Zyprian” moved from the western part to the eastern part of Europe, followed by ground-level convergence and the formation of organized convective thunderstorm systems. Torrential rains in the Czech Republic have caused a great deal of damage and casualties. Storm-related signatures were developed in ground microbarograph measurements of infrasound and gravity waves. Within the stratosphere, a shift of the polar jet stream and increase in specific humidity related to the storm system were observed. At the ionospheric heights, irregular stratification and radio wave reflection plane undulation were observed. An increase in wave-like activity was detected based on ionograms and narrowband very-low-frequency (VLF) data. On directograms and SKYmaps (both products of digisonde measurements), strong and rapid changes in the horizontal plasma motion were recorded. However, no prevailing plasma motion direction was identified within the F-layer. Increased variability within the ionosphere is attributed mainly to the “Zyprian” cyclone as it developed during low geomagnetic activity and stable solar forcing.

For a better understanding of atmospheric dynamics, it is very important to know the general conditions (dynamics and chemistry) of the atmosphere. Planetary waves (PWs) are global-scale waves, which are well-known as main drivers of the large-scale weather patterns in mid-latitudes on timescales from several days up to weeks in the troposphere. When PWs break, they often cut pressure cells off the jet stream. A specific example is so-called streamer events, which occur predominantly in the lower stratosphere at mid-latitudes and high latitudes. For streamer events, we check whether there are any changes in gravity wave (GW) or infrasound characteristics related to these events in ionospheric and surface measurements (continuous Doppler soundings, two arrays of microbarometers) in the Czech Republic.

For a better understanding of atmospheric dynamics, it is very important to know the general conditions (dynamics and chemistry) of the atmosphere. Planetary waves (PWs) are global-scale waves, which are well-known as main drivers of the large-scale weather patterns in mid-latitudes on timescales from several days up to weeks in the troposphere. When PWs break, they often cut pressure cells off the jet stream. A specific example is so-called streamer events, which occur predominantly in the lower stratosphere at mid-latitudes and high latitudes. For streamer events, we check whether there are any changes in gravity wave (GW) or infrasound characteristics related to these events in ionospheric and surface measurements (continuous Doppler soundings, two arrays of microbarometers) in the Czech Republic. Phenomena in infrasound arrival parameters undoubtedly related to streamer events were not identified in observations of two stations located in Central Europe. Simulations of infrasound propagation show influences of the streamer events on the waveguide formed near the tropopause. Microbarom propagation is influenced by the tropopause waveguide in a limited azimuth sector and at limited distances. Due to the typical occurrence of the streamer events over the North Atlantic, infrasound stations in western Europe can be of particular interest for future studies of streamer event signatures in infrasound arrivals. Arrivals to Central Europe are through the waveguide formed between the ground and the upper stratosphere. The upper-stratosphere waveguide is not influenced by the streamer events. Supplementary ground-based measurements of GW using the WBCI array in the troposphere showed that GW propagation azimuths were more random during streamer and streamer-like events compared to those observed during calm conditions. GW propagation characteristics observed in the ionosphere by continuous Doppler soundings during streamer events did not differ from those expected for the given time period.