Abstract. In this work, we study ionospheric disturbances excited by the passage of the solar terminator (ST) during tropical cyclones, using total electron content (TEC) data. We have considered 16 intense tropical cyclones (typhoons) that acted in the northwest of the Pacific Ocean near the territory of Japan. We analyze two-dimensional distributions of the number of registered wave packets (WPs) depending on various parameters: local time, WP maximum amplitude, and distance to typhoon. It is shown that in most cases the maximum number of WPs is observed at a distance less than 500-1500 km from the typhoon center and near the time of evening solar terminator passage. For typhoons occurring during autumn periods, the maximum number of WPs is recorded at daytime, and, apparently, is not associated with ST. Distributions of the number of WPs depending on their amplitude have a similar form for all the cases considered, with a maximum of about 0.2 TECU. At the same time, for some typhoons there are a large number of WPs with amplitude up to 0.6-0.8 TECU, which is significantly higher than WP amplitudes under quiet conditions. We briefly discuss the mechanism of possible interaction between ionospheric disturbances caused by two different sources (tropical cyclones and ST passage).
We study the level of total electron content (TEC) disturbance in ionospheric mid-latitude and high-latitude regions, which occurred during 2013. TEC behavior is calculated using data from two GPS stations: MOND (Mondy) and NRIL (Norilsk). TEC variations are estimated from dual-frequency phase measurements for all radio signal paths. We analyze the TEC variations in two time ranges: 10 and 40 min. These ranges correspond to medium- and large-scale ionospheric disturbances respectively. The TEC disturbance level is characterized using a special index WTEC. It allows us to receive multi-day continuous series of average TEC variation intensity. We reveal that at high latitudes WTEC variations correlate well with AE ones. The correlation between WTEC and Dst variations is much lower. The minimum level of TEC disturbance is independent of the season in the Arctic region; diurnal WTEC variations are more pronounced for medium-scale ionospheric disturbances than for large-scale ones. At mid-latitudes, the WTEC variation concurs with Dst and Kp variations only during strong magnetic storms. The minimum level of TEC disturbance is higher in summer than in winter. At middle latitudes, the sunset terminator generates gravity waves. In the Arctic region, terminator-induced waves are not observed.
Аннотация. Проведено исследование уровня возмущенности полного электронного содержания (ПЭС) в среднеширотных и высокоширотных обла-стях ионосферы в течение 2013 г. Ряды вариаций ПЭС рассчитывались по двухчастотным фазовым измерениям на всех радиолучах для GPS-станций MOND (Монды), NRIL (Норильск). Рассматрива-лись колебания ПЭС в двух диапазонах периодов: 10 и 40 мин, которые соответствуют средне-и круп-номасштабным ионосферным возмущениям. Для характеристики общего уровня возмущенности ПЭС использовался специальный индекс W TEC , который позволяет получать многодневные непре-рывные ряды усредненной интенсивности вариа-ций ПЭС. Выявлено, что в высоких широтах пове-дение W TEC хорошо согласуется с вариациями AE и хуже -с поведением индекса D st ; минимальный уровень возмущенности ПЭС не зависит от сезона; суточные вариации W TEC более выражены для сред-немасштабных ионосферных возмущений, чем для крупномасштабных. В средних широтах поведение W TEC хорошо согласуется с вариациями D st и K p только во время сильных магнитных бурь; значе-ние минимального уровня возмущенности летом выше, чем зимой; суточные вариации W TEC в средних широтах ярко выражены в течение года. В средних широтах солнечный терминатор генерирует грави-тационные волны, в Арктическом регионе возму-щения, вызванные солнечным терминатором, не наблюдаются.Ключевые слова: GPS, ионосфера, полное элек-тронное содержание, Арктический регион, геомаг-нитные вариации. Аbstract.We study the level of total electron content (TEC) disturbance in ionospheric mid-latitude and high-latitude regions during 2013. TEC behavior is calculated using data from two GPS stations: MOND (Mondy) and NRIL (Norilsk). TEC variations are calculated from two-frequency phase measurements for all radio rays. We analyze the TEC variations in two time ranges: 10 and 40 min. These ranges correspond to middle-and large-scale ionospheric disturbances respectively. The TEC disturbance level is characterized using the special index W TEC . W TEC allows us to receive multi-day continuous series of average TEC variation intensity. We reveal that at high latitudes W TEC variations agree well with AE ones. The correlation between W TEC and D st variations is much less. The minimum level of TEC disturbance is independent of the season in the Arctic region; diurnal W TEC variations are more pronounced for medium-scale ionospheric disturbances than for largescale ones. At mid-latitudes, the W TEC behavior agrees well with the D st and K p variations only during strong magnetic storms. The minimum level of TEC disturbance is higher in summer than in winter. At midlatitudes, the sunset terminator generates gravitational waves. In the Arctic region, terminator-generated waves are not observed.
We obtained the first experimental evidence for the magnetohydrodynamic (MHD) nature of ionospheric medium-scale travelling wave packets (MSTWP). We used data on total electron content (TEC) measurements obtained at the dense Japanese network GPS/GEONET (1220 stations) in [2008][2009]. We found that the diurnal, seasonal and spectral MSTWP characteristics are specified by the solar terminator (ST) dynamics. MSTWPs are the chains of narrow-band TEC oscillations with single packet's duration of about 1-2 hours and oscillation periods of 10-20 minutes. Their total duration is about 4-6 hours. The MSTWP spatial structure is characterized by a high degree of anisotropy and coherence at the distance of more than 10 wavelengths. The MSTWP direction of travelling is characterized by a high directivity regardless of seasons. Occurrence rate of daytime MSTWPs is high in winter and during equinoxes. Most of daytime MSWPs propagate southeastward (155±28 • ) at the velocity of 130±52 m/s. Occurrence rate of nighttime MSTIDs has its peak in summer. They propagate southwestward (245±15 • ) at the velocity of 110±43 m/s. These features are consistent with previous MS travelling ionosphere disturbance (TID) statistics obtained from 630-nm airglow imaging observations in Japan. In winter, MSTWPs in the northern hemisphere are observed 3-4 hours after the morning ST passage. In summer, MSTWPs are detected 1.5-2 hours before the evening ST occurrence at the point of observations, at the moment of the evening ST passage in the magneto-conjugate point. Both the high Q-factor of oscillatory system and synchronization of MSTWP occurrence with the solar terminator passage at the point of observations and in the magneto-conjugate area testify the MHD nature of ST-excited MSTWP generation. The obtained results are the first experimental evidence for the hypothesis of the ST-generated ion sound waves.
According to the data obtained on the equipment of the IEC SB RAS complex monitoring base for hazardous geological processes "Buguldeika" (Shared Research Facilities "Geodynamics and Geochronology" of IEC SB RAS) and Shared Research Facilities "Angara" of ISTP SB RAS an analysis of the characteristics of the Kudarinsky earthquake (09.12.2020) and the behaviour of the ionosphere during this event was carried out. The source parameters of the earthquake were obtained – the seismic moment of the earthquake (M0=3.02·1017 N·m), the moment magnitude (Mw=5.6), the source radius (2.43 km), and the stress drop (1.26 MPa).The analysis of the ionosphere behaviour carried out using GPS/GLONASS receivers did not reveal disturbances caused by the Kudarinsky earthquake, which is most likely due to the relatively small magnitude of this earthquake. An analysis of the observation series related to the Kudarinsky earthquake showed the efficiency of using the Core Facilities Centre equipment and complex monitoring bases for studying seismicity, which is the most dangerous natural process for the Baikal region.
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