Прояви слабких варіацій космічної погоди в системі іоносфера-плазмосфера: результати спостережень та моделювання

Abstract

Thesis submitted for obtaining the Doctor of Philosophy degree in Natural Sciences, Speciality – 104 Physics and Astronomy. – National Technical University “Kharkiv Polytechnic Institute”, Ministry of Education and Science of Ukraine, Kharkiv, 2021. The object of the study is geospace plasma and processes in it in the range of altitudes of 200-7000 km. The subject of the study is variations in the ionosphere-plasmasphere system caused by the effect of weak space weather disturbances and the physical mechanisms responsible for these variations. The thesis is devoted to study the effect of weak space weather changes on the ionosphere-plasmasphere system using multi-instrumental research and modeling of physical processes. Research methods. Observations of the ionosphere during periods of weak space weather changes were carried out by remote radiophysical methods of incoherent scatter (IS) and vertical sounding of the ionosphere. Methods of mathematical statistics and statistical radiophysics were used to analyze the results of observations. Experimental data were processed using original software developed at the Institute of Ionosphere (upgraded UPRISE software package). Investigations of the physical mechanisms responsible for the observed changes in the ionosphere-plasmasphere system were performed using physical modeling. A feature of the modeling method is using of ionospheric observations as input parameters for the physical model Field Line Interhemispheric Plasma (FLIP). This research method is unique because it avoids the significant uncertainties in the input parameters of the physical that are common to most other theoretical studies due to the low accuracy of empirical models of the thermosphere and ionosphere commonly used as a source of input for physical modeling. Validation of the simulated variations of plasma environment parameters was carried out by comparing with the observational data of international ionospheric and plasmaspheric satellite missions. The scientific novelty of the dissertation is as follows: for the first time demonstrated that even weak variations of space weather lead to significant rearrangement interaction in the ionosphere-plasmasphere system, causing, in particular, strong modulation of ionospheric-plasmospheric fluxes of hydrogen ions (H+); the mechanisms responsible for changes in the interaction of the ionosphere and plasmasphere have been established using physical modeling. The main reasons of changes are vertical motion of the ionosphere or partial depletion of the plasmasphere; it is established that the most sensitive parameter of ionospheric plasma to weak space weather changes is the relative concentration of hydrogen ions H+. This finding allowed us to explain the long-standing problem of low predictive capabilities of the topside ion composition model of the international empirical standard International Reference Ionosphere. The practical significance of the results is as follows. New data and knowledge about the response of the ionosphere-plasmasphere system to weak space weather changes will contribute to deepening the understanding of the impact of the Sun on the near-Earth space and allow us to advance in solving actual problems of space weather forecasting and adjusting models of the near-Earth plasma environment to reliably predict the negative impact of the ionosphere and plasmasphere on the motion and operation of spacecraft, satellite communications, radar and global positioning. The introduction substantiates the relevance of the dissertation, formulates the purpose and objectives of the study, defines the object, subject and methods of research, shows the relationship of work with scientific topics, describes the scientific novelty and practical significance of the results, indicates the personal contribution of the author, provides information about approbation of work and publication of research results. The first chapter provides overview of modern ideas about solar-terrestrial relations and the main physical mechanisms that determine space weather, describes the process of geomagnetic field perturbation and classification of geomagnetic storms by geomagnetic indices, describes the general structure of the Earth’s ionosphere and plasmasphere and considers the main drivers of perturbations in the ionosphere and plasmasphere. The analysis of the current state of near-Earth space environment research, methods and techniques of its diagnostics (remote radiophysical and satellites) as well as current models of the ionosphere and plasmasphere are presented separately. The choice of research problems, necessity and relevance for solving the problems of dissertation are substantiated. The second chapter presents the results of analysis of temporal variations of the Earth's plasma environment parameters obtained by incoherent scatter radar of the Institute of Ionosphere before, during and after weak variations in space weather for different seasons at different phases of the solar cycle (23-rd and 24-th). Comparative analysis of the results of observations of the relative concentration of hydrogen ions with estimates of international ion composition model IRI-2016/TBT-2015 was carried out. The main results of second chapter are as follows. It was revealed that for most of the studied periods weak variations in space weather do not lead to significant changes in electron density variations both in the F2 layer peak region and topside ionosphere; the exception is December 2017 when the plasma density decreased by twice after weak geomagnetic disturbance during nighttime; it was found that during all the investigated periods accompanied by weak space weather changes there were not significant variations in the electron temperature; this indicates the absence of significant increase of the ring current, which could affect variations in the F2 layer peak electron density and the topside ionosphere; it was found that the relative concentration of hydrogen ions in the topside ionosphere changed significantly during weak space weather disturbances in contrast to other plasma parameters. The relative concentration of hydrogen ions can change up to 2-3 times even with a very weak increase in geomagnetic activity (Kp≤3). Moreover increase in geomagnetic activity leads to decrease in N(H+)/N while weakening to increase; it was revealed that the best agreement between the results of observations and model estimates of the relative concentration of H+ ions occurs with increase in geomagnetic activity; differences increase with decrease of magnetic activity. The third chapter is devoted to modeling of physical processes in the ionosphere-plasmasphere system using Kharkiv incoherent scatter radar data. The following results were obtained: it is demonstrated that even weak variations of space weather lead to significant reorganization of the interaction in the ionosphere - plasmasphere system. This rearrangement occurs due to strong modulation of ionospheric-plasmospheric fluxes of hydrogen ions; the key physical mechanisms responsible for changes in the interaction of the ionosphere and plasmasphere and connection of these mechanisms with weak variations of space weather are established. The main reasons of changes in the vertical motion of plasma, which causes modulation of hydrogen ion fluxes during space weather disturbances may be two factors: enhancement of horizontal thermospheric winds directed to the equator during nighttime (due to heating of auroral zones) and penetration of zonal magnetospheric electric fields to middle latitudes; validation of the simulated variations of plasma environment parameters was carried out by comparing with IS radar and international ionospheric and plasmaspheric satellite missions data; the main reasons of significant differences between observed variations of N(H+)/N and predictions of the ion composition model IRI-2016/TBT-2015 in quiet geomagnetic conditions are explained; multi-instrumental studies of ionospheric plasma variations in two distant regions of the Northern Hemisphere – European (Kharkiv, Ukraine) and Asian (Shigaraki, Japan) was carried out. It is established that different reaction of the ionosphere to weak space weather changes over the Central Europe and Asian region can be explained by the local time effect. The simulation results are consistent with data from ionospheric (Swarm) and plasmaspheric (DMSP) satellite missions.