ISSN 00167932, Geomagnetism and Aeronomy, 2014, Vol. 54, No. 4, pp. 445–448. © Pleiades Publishing, Ltd., 2014. Original Russian Text © E.S. Belenkaya, D.A. Parunakian, I.I. Alekseev, V.V. Kalegaev, M.S. Blokhina, M.S. Grigoryan, 2014, published in Geomagnetizm i Aeronomiya, 2014, Vol. 54, No. 4, pp. 485–488. 445 1. INTRODUCTION Events connected with sharp variations in the solarwind pressure have been actively studied in past years (typical variations in the solarwind parameters are reviewed, e.g., in (Zastenker, 2007)). Sharp (<10 min) and strong (>20%) variations in solarwind ion fluxes in 1996–1999, unrelated to shock waves, were studied in (Riazantseva et al., 2005). The condi tion for keeping the pressure balance (thermal and magnetic) at sharp boundaries was fulfilled only in 55% of the cases. These cases could represent tangen tial discontinuities (or similar structures). Events are known from literature where a solarwind dynamic pressure jump was caused only by a density jump, with other parameters being invariable. Most cases of small and middlescale structures with sharp bound aries considered in (Riazantseva et al., 2005) relates to such events. The solarwind pulse length attains sev eral hours, and the front length reaches tens of min utes. It has been noted in (Dalin et al., 2002) that most cases of a very sharp increase in the solarwind pres sure (from seconds to minutes) are connected with an increase in the density, while the pressure balance is violated most often. Thus, unsteady structures develop in solar wind during propagation toward the Earth, which cause strong disturbances in the magnetosphere (magnetopause motion and variations in the magnetic field). The authors have emphasized that <10% of the cases of a sharp increase in the pressure is connected with shock waves. Events during which only the veloc ity varies and other parameters remain invariable are rare. They do not relate to CIRs or CMEs. The struc ture of interplanetary coronal mass ejections was stud ied, e.g., in the work (Sharma and Srivastava, 2012). It has been noted (Pukkinen et al., 2008) that a high solarwind velocity results in high ionospheric activity, and the velocity value is more significant than the azimuthal component of the electric field. Accord ing to observations, the propagation velocity of the disturbance front in the magnetosphere is higher under sharp variations in pressure than in the solar wind (this reflects the wave character of the process in the magnetosphere). Solarwind discontinuities are connected with variations in the pressure. The total pressure p sw con sists of three components: the dynamic pressure n sw m sw , the thermal pressure n sw kT sw , and the mag netic pressure /2μ 0 , where n sw is the density of charged particles, mainly protons (alpha particles, the density of which is about 1/25 of the proton density, are not considered), m sw is the mass of charged parti cles (the proton mass m sw = 1.67 × 10 –27 kg), V sw is the solarwind flux velocity, k = 1.38 × 10 –23 J K –1 is the Boltzmann constant, T sw is the temperature of charged particles of solar wind, μ 0 = 4π × 10 –7 H m –1 is the vac uum permeability, and B sw is the value of the solar wind magnetic field (IMF). The first component pre vails in the solar wind. In this work, we consider how a jump of each solarwind parameter, entering into the dynamic pressure, affects the lowlatitude geomag netic field disturbance in the magnetosphere. 2 sw V 2 sw B LowLatitude Variations in the Geomagnetic Field Caused by Solar Wind Disturbances E. S. Belenkaya, D. A. Parunakian, I. I. Alekseev, V. V. Kalegaev, M. S. Blokhina, and M. S. Grigoryan Skobeltsyn Institute of Nuclear Physics, Moscow State University, Moscow, 119991 Russia email: elena@decl.sinp.msu.ru Received July 5, 2013; in final form, December 16, 2013 Abstract—In view of the actual question regarding the effect of a solarwind pressure jump on disturbances in the Earth’s magnetosphere, events with high velocity and density gradients are of special interest. In this work, we consider the response of the current at the dayside magnetopause to these events and the corre sponding strengthening of the geomagnetic field in the lowlatitude magnetosphere. A transient process is studied that accompanies reconfiguration of the magnetosphere under the effect of disturbances of solar wind parameters. An analytical equation is received for estimation of an increase in the northern component of lowlatitude magnetic field of the magnetosphere in a transient current system (transient ring current) versus initial values of the solarwind velocity and density and their disturbances. DOI: 10.1134/S0016793214040070