Skorokhod T. Internal gravity waves in the thermosphere according to direct satellite measurements

The purpose of the dissertation research is to study the thermospheric wave field by the analyzing the measurements of thermospheric parameters on board of LEO satellites. The work consists of four main sections. In section 1 (Internal gravity waves in the Earth upper atmosphere, review of the literature), the development of scientific ideas about the atmospheric gravity waves (GW) is described. In section 2 (Selection of wave disturbances in satellite measurement data) and in section 3 (Analysis of wave disturbances spectra on the basis of GW theory), an integral method for satellite measurements data processing has been developed. The method is realized in set of algorithms and mathematical software. Two key stages are united in this method. At the beginning the selection of GW wave form distribution along the satellite orbit is carried out and the corresponding wave number spectrum is calculated. At the second stage the "unobserved" spectral parameters (frequency , wave numbers ) are theoretically estimated. In the dissertation the task of GW measurement errors estimation was formulated and solved for the first time. For this purpose the error analysis was allocated from the spatial-temporal to the spectral domain. It was demonstrated that registration of spectrum can be done with a high precision. The estimation of is approximate; it is done with an error of a half of the wave spectrum width. Thus, the researcher is able to obtain a fairly accurate information on the intensity distribution of the wave field along the satellite orbit, and only approximate information on the wave frequency, wavelength, propagation direction, and phase and group velocity. These restrictions are caused by initial physical principles and can not be eliminated by "more thorough" data processing. The corner stone of the dissertation research is the step-by-step control of the changes that processing contributes into the data frequency domain. Due to this it was possible to find out the nature of the complexity of wave disturbance separation from the trend component. The problem is not the presence of the trend by itself, but it is in the trend spectrum spreading - the artefact of digital signal processing, which leads to the overlapping of trend and GW spectra. Correspondingly, the technique of wave disturbances selection needs the double data filtering. At the first step a rough trend deletion is carried out in order to reduce the spreading component, and then GW band-pass filtering has to be done. The data processing algorithm is implemented in the form of software package, using which the analysis of several months of measurements on the satellite DE 2 was carried out. Obtained results are recorded in the GW catalogue, which actually is a statistical basis for the GW further study. In section 4 (Characteristics of GW field in upper thermosphere), a representative data sample that describes a thermosphere wave activity at 250-500 km altitudes is suggested. Basing on this, the thermospheric disturbances spectral compositions are investigated. In particular, it was established that the structural element of the thermospheric wave field is the wave packages localized both in spatial-temporal and in spectral domains. The observed composition of wave disturbances is following: the main component is GW, the second one by the intensity and registration frequency - is the thermospheric ducted modes, and the third one - is the acoustic mode. (Planetary waves were not investigated in this work). The geographic distribution of thermospheric waves demonstrates the presence of the strongly perturbed high-latitude regions and the quiet low-latitude area. Both polar caps are completely filled with GW of auroral origin with amplitudes (according to the relative density perturbation of the neutral atmosphere). In these regions GW acts as an important factor in the formation of thermospheric energy balance (after the direct heating by EUV solar radiation and at the same level as thermal conductivity caused). In the quiet zone only some GW bursts are recorded with the amplitudes . In the largest part of the quiet zone the intensity of the waves falls below the level of their detection. The relations of the thermospheric perturbations and the earthquakes were established. The areas in which the generation of GW as earthquake precursors happens were defined in space (distance is about 2000 km) and in time (about -6 h).