The paper reports the results of comprehensive observations of space weather manifestations during geophysical events at the end of October – beginning of November 2021 at the Yakut meridional geophysical network of SHICRA SB RAS equipped with a complex of various scientific instruments installed at the stations Yakutsk, Maimaga, Zhigansk, and Tixie Bay (neutron monitors, an ionosonde, a riometer, receivers of VLF radio noise and signals from navigation radio stations, magnetometers), as well as a complex of optical instruments installed in Maimaga. We present the results of the analysis of phenomena occurring in near-Earth space, Earth’s ionosphere and atmosphere in the North-Eastern sector of Siberia. We examine the properties of the geophysical effects of space weather observed at this time: Forbush decreases of cosmic rays, geomagnetic storm and substorm, riometric absorption, the occurrence of electrojet, quasi-periodic broadband radio hisses, assess changes in the effective height of the Earth—ionosphere waveguide, F2-layer critical frequencies, absorption of short-wave radio waves, temperature of the neutral atmosphere, radiant auroral band in 557.7 and 630.0 nm emissions, as well as the region of intense auroras and auroral red arc (SAR arc).

The paper examines conditions of occurrence and typical time scales of a polarization jet by measuring ionospheric parameters from DMSP satellites (h~830 km) and using data from the ground-based ionospheric station Yakutsk (YA462) during strong and long-term geomagnetic storms. The polarization jet at the ionospheric station Yakutsk was recorded in the dusk sector at the background of substorm disturbances when the geomagnetic index SME reached values from 1000 to ~3000 nT, and, according to data from the magnetic observatory Yakutsk (YAK), there was a positive bay ~50–100 nT in the geomagnetic field H component and ~100–200 nT in its Z component. We show that the lifetime of the polarization jet or narrow troughs in ionospheric plasma in the subauroral ionosphere during strong and long-term magnetic storms can be as long as 12 hrs.

Исследованы вариации ионосферных и термосферных параметров в северном полушарии на основе анализа данных высоко- и среднеширотной цепей евразийских ионозондов и приемников GPS/ГЛОНАСС в период сильной магнитной бури в октябре 2016 г. На главной фазе магнитной бури над Евразией наблюдался переход от положительного к отрицательному эффекту ионосферной бури как в высоких, так и средних широтах. Эффект отрицательной ионосферной бури на восстановительной фазе был вызван образованием обширных областей атмосферного газа с пониженным отношением концентраций [O]/[N2] над регионом высоких и средних широт Евразии. The variations of ionospheric and thermospheric parameters in the northern hemisphere were investigated based on the analysis of data from high- and mid-latitude Eurasian ionosonde chains and GPS/GLONASS receivers during a strong geomagnetic storm in October 2016. In the main phase of the geomagnetic storm over Eurasia, a transition from a positive to a negative ionospheric storm effect was observed in both high and mid-latitudes. The negative ionospheric storm effect during the recovery phase was caused by the formation of extensive areas of atmospheric gas with reduced concentration ratio [O]/[N2] over high and mid-latitude regions of Eurasia.

During magnetospheric substorms in the F region of the ionosphere and up to altitudes of 1000 km, a polarization jet (PJ) is developed. Measurements of energetic ring current ions on the AMPTE/CCE satellite and driftmeter data on the DMSP satellites evidence that the formation of PJ is associated with the injection of energetic ions (10–100 keV) into the inner magnetosphere during substorms. In the region of PJ development, the characteristics of the ionospheric plasma change: the plasma density decreases, sometimes by an order of magnitude, and at the same time, the plasma temperature increases significantly. In addition, simultaneously with the westward plasma drift, upward plasma drift is usually observed. The upward ion flux from the region of PJ development of 109 cm–2 s–1 is an order of magnitude greater than the average daytime ion flux from the ionosphere to the plasmasphere. Measurements on the MAGION-5 satellite in the plasmasphere on the same L-shells, where the polarization jet is recorded in the ionosphere, show an increase in the cold ion density. The density “humps” observed near the plasmapause are apparently formed due to plasma flows from the ionosphere accompanying the formation of the polarization jet. Thus, the consequences of substorms are observed throughout almost the entire magnetosphere.

We have analyzed spatial and temporal variations in ionospheric parameters over high and middle latitudes of Eurasia, using data from chains of high- and mid-latitude ionosondes during a severe magnetic storm in March 2015. To analyze the ionospheric response to the severe geomagnetic disturbance of solar cycle 24, we have employed ionosonde data on hourly average values of the critical frequency foF2 of the ionospheric F2 layer, the critical frequency of the sporadic layer foEs, and the minimum reflection frequency fmin. There are strong latitudinal and longitudinal differences between the features of temporal variations in the analyzed ionospheric parameters both under quiet conditions before the magnetic storm onset and during the storm. We discuss possible causes of the observed spatial variations in ionospheric parameters. The source of spatio-temporal variations in ionospheric ionization parameters may be inhomogeneities generated in the high-latitude ionosphere under conditions of increased helio-geomagnetic activity. During the magnetic storm main and recovery phases, periods of blackouts of radio signals from ionosondes were observed at both high and middle latitudes. During these periods, there was a significant increase in the absorption of radio waves used in ionosonde sounding, as well as in the frequency of occurrence of screening sporadic Es layers. The long-term effect of the negative ionospheric storm over high and middle latitudes of Europe is explained by the movement of the vast region of the reduced density ratio [O]/[N2] at thermosphere heights from the Far East and Siberia westward to Europe during the late recovery phase of the magnetic storm. Increased ionization of the ionospheric F2 layer with foF2 exceeding the level for quiet days before the onset of the magnetic disturbance over the vast region of Eastern, Western Siberia and Eastern Europe after the end of the magnetic storm in March 2015 is a manifestation of the aftereffect of magnetic storms. The increase in ionization was especially pronounced, as measured by the chain of mid-latitude ionosondes.

. We have examined longitudinal-temporal variations in ionospheric parameters over Eurasia by analyzing data from a chain of high-latitude ionosondes along a latitude circle ~70° N (geomagnetic latitudes 58°

В работе анализируются результаты многолетних комплексных экспериментов, выполненных на сети станций Якутского геофизического полигона и с помощью ионосферных и высоко-апогейных спутников. Наземные оптические измерения выполнялись в обсерватории Маймага (L = 3.2). Ионосферные наблюдения проводились в Якутске (L = 3.0), Жиганске (L = 4.0), Тикси (L = 5.6), Подкаменной Тунгуске (L = 3.0) и Магадане (L = 2.9) методами вертикального и наклонного зондирования с помощью высокопотенциальных двойных горизонтальных ромбических антенн. Настоящая работа суммирует физические свойства поляризационного джета с целью проведения геофизической верификация возможных механизмов его формирования. По ионограммам ионосферных станций при сопоставлении их со спутниковыми измерениями быстрых струйных течений плазмы выявлена сигнатура поляризационного джета. Это позволило использовать 15-минутные ионозондовые измерения обширной сети станций для исследования локального и быстро протекающего процесса развития поляризационного джета. Это также дало возможность провести сопоставление с измерениями энергичных ионов на спутнике AMPTE/CCE и установить, что поляризационный джет развиваются на внутренней границе кольцевого тока. По многолетним измерениям ионозондов было установлено, что поляризационный джет возникает в около-полуночном секторе на взрывной фазе суббури в области разрыва Харанга.

The data of simultaneous measurements of the polarization jet from the Yakutsk ground-based vertical radio sounding station and satellite observations of narrow electron density dips or fast westward drifts of the ionospheric plasma from satellites of the Defense Meteorological Satellite Program (DMSP) series. The events are based on ground-based ionospheric measurements and cover the time interval from March 1989 to December 2015, i.e. about 26 years. The simultaneity of observations is ensured by a time period of approximately ±1.5 h from the time of registration of signs of a polarization jet according to the data of a ground-based ionospheric sounding station or by the an orbital period of DMSP satellites around the Earth. Based on data of long-term simultaneous satellite and ground-based measurements (126 events), it was shown and confirmed that the presence of characteristic additional traces of reflections on ionograms indicates the presence of narrow and fast drifts of ionospheric plasma or a polarization jet near the zenith of the observation station. It is also shown that the quasi-instantaneous longitude extent of a polarization jet at subauroral latitudes can in some cases reach 8 h or 120° by longitude.

We have studied variations in ionospheric and geomagnetic parameters in the Northern Hemisphere during a series of magnetic storms in March 2012 by analyzing data from the Eurasian mid-latitude ionosonde chain, mid- and high-latitude chains of magnetometers of the global network INTERMAGNET. We have confirmed manifestations of the longitude inhomogeneity of ionospheric effects, which is associated with the irregular structure of the longitudinal variability of geomagnetic field components. The complex physics of the long magnetically disturbed period in March 2012 with switching between positive and negative phases of the ionospheric storm in the same period of the magnetic storm for different spatial regions is emphasized. The change in the effects of the ionospheric storm during this period might have been associated with the superposition in the mid-latitude region of the competing processes affecting the ionospheric ionization whose sources were in the auroral and equatorial ionosphere. We have compared the scenarios for the development of ionospheric disturbances under equinox conditions during magnetic storms in March 2012, October 2016, and March 2015.

We consider Doppler measurements at the Yakutsk subauroral ionospheric station in the periods of the formation and development of a polarization jet above the observing station. It is shown that the times at which the vertical and horizontal velocities of the plasma drift reach their maximum values may not coincide. Comparison of ground-based measurements when observing a polarization jet and calculation of the model of a high-latitude ionosphere demonstrate that the presence of mismatched peaks of the vertical and horizontal components of the plasma drift velocity at the altitudes of the F 2 layer leads to different variations in the basic parameters of the layer. It was found that in some cases, before the formation of a polarization jet, an increase in the critical frequency of the F 2 layer is observed. A decrease in the ion recombination rate due to an increase in the height of the layer maximum and, consequently, accumulation of ions at these altitudes, is a possible explanation for this behavior. Such an increase in the critical frequency of the F 2 layer may be an additional signature of the development of a polarization jet above the observing station.

Выполнено мультиинструментальное исследование вариаций ионосферных и геомагнитных параметров в северном полушарии в период сильной магнитной бури в октябре 2016 г. на основе анализа данных евразийской среднеширотной цепи ионозондов, средне-и высокоширотных цепей приёмников GPS/ГЛОНАСС и магнитометров сети INTERMAGNET.Подтверждены проявления долготной неоднородности ионосферных эффектов, связанной с нерегулярной структурой долготной изменчивости компонент геомагнитного поля

We present a joint analysis of longitude-temporal variations of ionospheric and geomagnetic parameters at middle and high latitudes in the Northern Hemisphere during the two severe magnetic storms in March and June 2015 by using data from the chains of magnetometers, ionosondes and GPS/GLONASS receivers. We identify the fixed longitudinal zones where the variability of the magnetic field is consistently high or low under quiet and disturbed geomagnetic conditions. The revealed longitudinal structure of the geomagnetic field variability in quiet geomagnetic conditions is caused by the discrepancy of the geographic and magnetic poles and by the spatial anomalies of different scales in the main magnetic field of the Earth. Variations of ionospheric parameters are shown to exhibit a pronounced longitudinal inhomogeneity with changing geomagnetic conditions. This inhomogeneity is associated with the longitudinal features of background and disturbed structure of the geomagnetic field. During the recovery phase of a storm, important role in dynamics of the mid-latitude ionosphere may belong to wave-like thermospheric disturbances of molecular gas, propagating westward for several days. Therefore, it is necessary to extend the time interval for studying the ionospheric effects of strong magnetic storms by a few days after the end of the magnetospheric source influence, while the disturbed regions in the thermosphere continues moving westward and causes the electron density decrease along the trajectories of propagation. (C) 2020 COSPAR. Published by Elsevier Ltd. All rights reserved.

The calculation results and experimental data on the formation and development of a polarization jet in subauroral latitudes are compared. It is shown that the alternation of vertical and horizontal components of the ionospheric plasma–drift velocity leads to different variations in the main parameters of the F2 layer. An increase in the critical frequency of the F2 layer is revealed in certain cases before the formation of a polarization jet. This behavior of the F2 layer may be caused by a decrease in the rate of the recombination of charged particles due to an increase in the altitude of the layer maximum, which results in particle accumulation at these altitudes. An increase in the critical frequency of the F2 layer can be an additional indicator of the development of a polarization jet over an observation station.

Using long-term data from Yakut meridional chain of Yakutsk — Zhigansk — Batagay — Tixie ionospheric stations, we study ionospheric signatures of fast subauroral ion drift. Sharp drops or “falls” of critical frequencies (FCF) of the ionospheric F layer are shown to be one of the main signatures of the development of fast subauroral ion drifts near or at the zenith of the observation station. Comparison between long-term ground-based and satellite measurements indicates that there is good agreement between seasonal variation in the probability of occurrence of FCF derived from ground-based data and subauroral ion drifts derived from DMSP satellite data. Such a coincidence implies that both satellite and ground-based measurement methods register the same phenomenon in the boundary layers of the plasmasphere, namely, the appearance and development of electric fields of magnetospheric origin. The local time for recording of falls of the critical frequency derived from the ground-based data is shown to closely coincide with the appearance time of subauroral polarization streams of plasma according to satellite data. We can therefore conclude that most of the observed FCFs derived from ground-based data refer to intense storms.

The paper was carried out as a part of the project devoted to a comprehensive study of the longitudinal variations of the Earth's magnetic field in middle and high latitudes of the Northern hemisphere and related variations in the midlatitude ionosphere in disturbed and quiet geomagnetic conditions in 2011-2017. The analyzed period covers the years of growth, maximum and decline of the 24th cycle of solar activity. To study the geomagnetic field variations, data from the INTERMAGNET global network of magnetometers in the Northern hemisphere were used. In the analyzed time period 122 events of magnetic storms were identified: 102 moderate , 18 strong and 2 severe . A statistical analysis of the distribution of magnetic storms by years and seasons was performed. New interesting results are obtained on the irregular structure of the longitudinal variability of the geomagnetic field components in quiet conditions due to the discrepancy between the Northern geographical and geomagnetic poles, as well as the presence of anomalies of different spatial scales in the background magnetic field of the Earth. The longitudinal-temporal variations of the geomagnetic field components under disturbed conditions also show a strong dependence on the individual features of the magnetic storms. On the case study of the development of two severe magnetic storms in 2015, the longitudinal-temporal variations of the parameters of the midlatitude ionosphere over the Eurasian continent were analyzed based on the analysis of the ionosonde chain data. The presence of longitudinal features of the background structure and variations of the geomagnetic field leads to the fact that the registered ionospheric effects also exhibit a significant longitudinal inhomogeneity. We assume that the storm-associated ionosphere dynamics is determined by the lower thermosphere disturbances due to the auroral electrojet amplifications producing the enhanced neutral wind and turbulences; these, in turn, uplift the molecular gas to the ionospheric heights. This process decreases the [O]/[N 2 ] ratio and, consequently, the electron density.

Doppler measurement data from the Yakutsk subauroral ionospheric station have been used to reveal for the first time new and previously unknown dynamic phenomena during the development of the polarization jet. This study of horizontal and vertical velocities of ionospheric drifts reveals that the peaks of vertical and horizontal velocity components do not always coincide during the observation of a polarization jet. The horizontal plasma drift velocities are ~300–600 m/s on average (there are events with velocities of 900–1000 m/s). The vertical drift velocities are 30–50 m/s on average (there are events with velocities of 100–150 m/s). Analysis of ground-based ionospheric data has revealed that all events with the development of the polarization jet over Yakutsk were uniformly divided into four cases. In the first case, the vertical velocities in the polarization jet band reached a maximum simultaneously with horizontal velocities. In the other two cases, the times of the vertical velocity peaks are shifted to both sides of the reference time by ±1 h. In the latter case, the vertical velocities have similar peaks on both sides of horizontal velocity peaks.

Complex optical and ionospheric measurements in the region of the formation of red arcs accompanying the polarization jet development are analyzed. Optical measurements were done at subauroral station Maimaga, and ionospheric measurements were fulfilled at subauroral stations Yakutsk and Zhigansk. Spatial location and intensity of red-arcs were detected by the meridional scanning photometer. The temperature of the neutral atmosphere was recorded by Fabry-Perot interferometer. It is shown that the temperature of the neutral atmosphere increases in the red arc region and changes in accordance with variations in the emission. On 02 December 1989 the neutral temperature increased by 500 K in the red arc relative to the undisturbed level determined for quiet days during the month. This evidences on the strong heating process in the red arc region. According to ionospheric and satellite data on 18 February 1999 the red arc was observed simultaneously with polarization jet development - fast westward plasma drift in the poleward electric field. The magnitude of this electric field was 50-80 mV/m. Due to frictional interaction of ions and neutrals, ions were heated up to 5000-6000 K and neutrals gain energy of some hundreds degrees.