Dynamics of the Magnetospheric Magnetic Field during Strong Magnetic Storms in 2015 According to Measurements on Board Van Allen Probes and Modeling Results

The results of studies of proton flux dynamics of the ring current and magnetic field in the middle of radiation belts during two strong magnetic storms in 2015 (March 17-18, 2015 and June 22-23, 2015) with a close amplitude of Dst-variations (|Dst(max)| 200 nT) are presented. An analysis of the experimental data obtained on board two space vehicles named Van Allen Probes (earlier: Radiation Belt Storm Probes, RBSP), located at an orbit close to equatorial is performed. Modeling of the ring current and magnetic field in the frames of the paraboloid model of Earth's magnetosphere ?2000 is conducted. Confirmation of the existence of a mechanism for ring current development and, respectively, geomagnetic storm under the action of a strong pulse of solar-wind pressure is obtained as a result of comparative analysis of ring current dynamics and the magnetic field in the middle of radiation belts during the main phases of two storms in 2015. It is found that during the magnetic storm of June 22-23, 2015, the development of the ring current during the main phase continued despite the northward turn of the interplanetary magnetic field (IMF) and the following period with positive B-z in the solar wind. The effect observed during June 22-23, 2015 is explained by the intensification of storm ring current due to a long and powerful pulse of the solar wind pressure that led to a nonadiabatic transport of the ring current particles to lower L shells.