Physics of auroral phenomena : proceedings of the 33rd Annual seminar, Apatity, 02 - 05 March, 2010 / [ed.: A.G. Yahnin, A. A. Mochalov]. - Апатиты : Издательство Кольского научного центра РАН, 2011. - 206 с. : ил.

“P hysics o f Auroral Phenom ena", Proc. XXXIII A n nua l Sem inar, Apatity, pp. 129 - 132, 2011 © Kola Science Centre, Russian Academy of Science, 2011 Polar Geophysical Institute THE ROLE OF ION D IFFU S ION IN FORMAT ION OF 3 -D SPAT IAL STRUCTURE OF THE PLASMASPHERE 0 .V . Martynenko, M .G. Botova (Murmansk State Technical University, Murmansk, Russia) A b stra c t. The influence of various factors on formation of 3D spatial structure of the Earth’s ionosphere and plasmasphere has been studying. In this work the role of ambipolar field-aligned diffusion in the process has been examined. 1. Introduction The ionosphere and plasmasphere refilling was studied in many of theoretical and experimental works (e. g.[ 1,2,3]). But we don't know researches which examined this process in 3D statement and reviewed details of spatial structure of resulting plasmasphere. Our work is intended to fill this gap. Our study was conducted by a computer simulation method using the global numerical model of the Earth's upper atmosphere UAM [4,5]. In order to select exclusively the role of the diffusion all other factors were eliminated in this calculation. Convection drift and neutral wind were set completely absent. In addition, the geographic and magnetic axes were superposed; the Sun was located exactly above the equator. The neutral temperature and composition distributions were stated as stationary in Solar-magnetic frame and ionospheric and plasmaspheric plasma rotated with the Earth, passing from day to night and back. In the initial state the ionosphere and plasmasphere were uniformly filled with plasma of very low density. Then the ionization started and the plasma began field-aligned motion into upper parts of the field tubes. In order to smooth the sharp changes the calculation started in pre-midnight hours for each longitude (night-time ionization by scattered radiation), and to the sunrise time the ion distribution became more natural. 2. Model result The overall picture after 5 days of simulation time is fairly realistic: the repetitive diurnal variation in the ionosphere and the plasmasphere which is virtually uniform in the longitudinal direction (Fig.l, 2). Thus, we can assume that the model with all above listed simplifications is still physically appropriate, and smaller structural features of the ionosphere-plasmasphere system can also be considered as physically meaningful. At the ionosphere level these structural details of plasma density and ion composition are most evident in the night sector. There are 3 latitudinal areas (symmetrical in both hemispheres) with increased plasma density (Fig.3, 4): sub-auroral (latitudes 60-65°), near-equatorial (near 10°) and mid-latitudinal (30-40°). Physical mechanisms of their formation will be discussed below. К *0____________ i *0____________ 8 20 9 .SO 10 to 6 to _____________* 90 В 20 9 SO 10 80 Figure 1. The horizontal cut o f the ion density at the base of plasmasphere after 1 and 5 days of modeling time 129