Dynamic processes in the magnetic field and in the ionosphere during the 30 August–2 September, 2019 geospace storm

Abstract. Back at the end of the last century, L. F. Chernogor validated the concept that geospace storms are comprised of synergistically coupled magnetic storms, ionospheric storms, atmospheric storms, and storms in the electric field originating in the magnetosphere, the ionosphere and the atmosphere (i.e., electric storms). Their joint studies require the employment of multiple-method approach to the Sun–interplanetary medium–magnetosphere–ionosphere–atmosphere – Earth system. This study provides general analysis of the 30 August–2 September, 2019 geospace storm, the analysis of disturbances in the geomagnetic field and in the ionosphere, as well as the influence of the ionospheric storm on the characteristics of HF radio waves over the People's Republic of China. A unique feature of the geospace storm under study is its duration, of up to four days. The main results of the study are as follows. The energy and power of the geospace storm have been estimated to be 1.5 PJ and 15 GW, and thus this storm is weak. The energy and power of the magnetic storm have been estimated to be 1.5 PJ and 9 GW, i.e., this storm is moderate, and a unique feature of this storm is the duration of the main phase, of up to two days. The recovery phase also was lengthy, no less than two days. On 31 August 2019 and on 1 September 2019, the variations in the H and D components attained 60–70 nT, while the Z-component variations did not exceed 20 nT. On 31 August 2019 and on 1 September 2019, the level of fluctuations in the geomagnetic field in the 100–1000 s period range increased from from 0.2–0.3 nT to 2–4 nT, while the energy of the oscillations showed a maximum in the 300–400 s to 700–900 s period range. The geospace storm was accompanied by a moderate to strong negative ionospheric storm. During 31 August 2019 and 1 September 2019, the electron density in the ionospheric F region reduced by a factor of 1.4 to 2.4 times as compared to the values on the reference day. The geospace storm gave rise to appreciable disturbances also in the ionospheric E region, as well as in the Es layer. In the course of the ionospheric storm, the altitude of reflection of radiowaves could sharply increase from about 150 km to approximately 300–310 km. The geospace storm was accompanied by the generation of atmospheric gravity waves modulating the ionospheric electron density. For the about 30 min period oscillation, the amplitude of the electron density disturbances could attain about 40 %, while it did not exceed 6 % for the about 15 min period. The results obtained have made a contribution to understanding of the geospace storm physics, to developing theoretical and empirical models of geospace storms, to the acquisition of detailed understanding of the adverse effects that geospace storms have on radiowave propagation and to applying that knowledge to effective forecasting these adverse influences.