ISSN 0010-9525, Cosmic Research, 2013, Vol. 51, No. 1, pp. 46–53. © Pleiades Publishing, Ltd., 2013. Original Russian Text © R. Lukianova, A. Kozlovsky, 2013, published in Kosmicheskie Issledovaniya, 2013, Vol. 51, No. 1, pp. 53–61. 46 1. INTRODUCTION Electrodynamic interaction between the solar wind (SW) energy and the Earth’s magnetosphere takes place, in the main, in the boundary layers and the magnetosphere tail, which are conjugate in the geo- magnetic field lines with the high-latitude areas: the auroral oval, cusp, and the polar cap (PC). In the cir- cumterrestrial space, the polar cap boundary (PCB) can be considered as a boundary between geomagnetic field lines that are open to SW and closed onto the opposite hemisphere. Field lines going out of the polar cap are stretched into the magnetosphere tail and open for penetration of SW plasma and the interplanetary electric field. It is a clear manifestation of the effects of the SW interaction with the magnetosphere, and an analysis of the PCB dynamics enables one to trace the development of many magnetospheric processes. In the Dungey cycle [1], during which the energy is injected from the SW into the magnetosphere and ion- osphere, plasma convection is determined by recon- nection of magnetic field lines on the daytime magne- topause and in the magnetosphere tail. It has been shown that, when day (night) reconnection domi- nates, as open magnetic flux increases (decreases), the polar cap is expanded (contracted), and, accordingly, PCB is shifted to the equator (pole). The PC contrac- tion–expansion also occurs in the substorm cycle [2– 4]. The auroral oval and PCB are asymmetric about the pole both along the noon–midnight meridian, and along the dawn–dusk meridian. Midline of the auroral oval is approximately at 78° and 68° MLat, and the oval thickness is about 3° and 10° (at К р = 3) on the day and night sides, respectively [5]. This line, as well as PCB, is shifted to the equator with increasing geomag- netic activity [6]. The PCB shift along the dawn–dusk meridian is controlled by a sign of the IMF B y , so that in the northern hemisphere at B y > 0 (B y < 0), the polar cap as a whole is shifted to the dawn (dusk) side [7–9]. In the southern hemisphere, the shift direction is opposite [10]. The PCB dynamics is complicated during geomag- netic storms. The main phase of a storm is usually ini- tiated by southward IMF of sufficiently large ampli- tude. According to an increase of the open magnetic flux in the magnetosphere, the PCB is shifted to the equator. During the main phase a large amount of energy is accumulated in the magnetosphere tail, and the occurring dissipative processes are largely nonlin- ear [11]. Consequently, the PCB dynamics during the storm can significantly differ from non-storm periods. A large number of images of the auroral oval made by the IMAGE satellite and progress in the methods of their processing [12] allow one to perform in-depth analysis the PCB evolution. In this paper, on the basis of the IMAGE measurements, the statistical depen- dences of PCB positions on the IMF parameters are obtained, and the PCB dynamics in different sectors Dynamics of Polar Boundary of the Auroral Oval Derived from the IMAGE Satellite Data R. Lukianova 1, 2 and A. Kozlovsky 3 1 Arctic and Antarctic Research Institute, ul. Beringa 38, St. Petersburg, 199397 Russia 2 Space Research Institute, Russian Academy of Sciences, Profsoyuznaya ul. 84/32, Moscow, 117997 Russia 3 Sodankyla@ Geophysical Observatory, University of Oulu, Finland e-mail: renata@aari.nw.ru, alexander.kozlovsky@oulu.fi Received March 29, 2012 Abstract—Based on a new database on positions of the auroral oval boundaries including measurements made by the IMAGE satellite in 2000–2002 with correct determination of the glow boundaries, statistical esti- mations of the latitudinal position of the polar cap boundary (PCB) are obtained depending on the IMF B y and B z , and the PCB evolution during a magnetic storm is analyzed. At zero IMF in the noon (midnight) sec- tor, PCB is located approximately at 80° (76°) CGMLat. The PCB displacement along the noon–midnight meridian is controlled by the IMF B z , and in the noon (midnight) sector it is equal to 0.45° (0.15°) CGMLat when B z changes by 1 nT. The PCB displacement along the dawn–dusk meridian depends on the IMF B y , and it equals 0.1° CGMLat when B y changes by 1 nT. Accordingly, the north polar cap as a whole is shifted to the dawn (dusk) side at B y > 0 (B y <0). After northward turn of the IMF during the storm’s recovery phase, the PCB on the dayside is shifted to the north practically without time delay. The night boundary requires 25 h or more in order to be shifted to the pole to a latitude corresponding to B z > 0. DOI: 10.1134/S0010952513010061