A study of the storm event on October 21–22, 1999 by the MHD simulation

K S Park,T Ogino

doi:10.1186/bf03351961

Abstract

Abstract We carried out a high resolution three-dimensional magnetohydrodynamic (MHD) simulation of the interaction between the solar wind and the Earth’s magnetosphere during a strong magnetic storm on October 21–22, 1999. The input to the simulation was from WIND solar wind observations. As the IMF is strongly southward (−20 nT to −30 nT) for 6 hours, the geomagnetic field lines in the dayside magnetopause are eroded to the geosynchronous orbit (GEO) region by reconnection. The associated magnetic flux is transferred from the dayside magnetosphere to the tail. The reconnection region still appears near GEO region on the dayside magnetopause, even though the IMF B z component becomes small or northward, because of the influence of the strong IMF B y (30 nT). IMF lines can successively reconnect with the naked and large geomagnetic field line in the dayside flank regions. Thus, the cross polar cap potential is maintained to be large value and convection in the ionosphere is enhanced. The cross polar cap potential is governed by IMF B y as well as B z (ф ≈250 kV for B z ≈ −20 nT and ф ≈ 300 kV for B z ≈ − 30 nT), and it saturates during the strong southward IMF. A large energy flux enters the ionosphere at very low latitudes (50°) and the inner edge of the plasma sheet becomes very close to the Earth X = −3.2 R E for a strong magnetic storms. The open-closed boundary extends to 60° latitudes on the nightside, 72° on the dayside, 62° on dawn, and 66° on dusk. Enhanced energy flux appears at low latitudes (50°) on the nightside in simulation. Moreover, the energy flux in the dusk region (19 MLT) appears down to 55° latitude in simulation, which is consistent with the low latitude boundary of the 0.02-20 keV particles detected by TED of the NOAA-15. A convective electric field, which is penetrating to the Earth-side of the NENL, is almost comparable to that of the solar wind. The present MHD simulation study give reasonable results even for extreme conditions and thereby its usefulness is demonstrated as a physical model for space weather studies.

Highlights

Simulations of the interaction between the solar wind and the magnetosphere (Lyon et al, 1981; Brecht et al, 1981; Ogino et al, 1985; Walker et al, 1993) were applied to ideal cases in which the solar wind and the interplanetary magnetic field (IMF) were constant.In recent years, global MHD simulations have been used to model magnetospheric events by using actual solar wind observations as input
The cross polar cap potential is governed by IMF By as well as Bz (φ ∼ 250 kV for Bz ∼ −20 nT and φ ∼ 300 kV for Bz ∼ −30 nT), and it saturates during the strong southward IMF
We have used a three-dimensional global MHD model to simulate the interaction of the solar wind with the Earth’s magnetosphere to study a strong magnetic storm on October 21–22, 1999, when the IMF was strongly southward (Bz = −20 to −30 nT) for ∼6 hours

Summary

Introduction

Simulations of the interaction between the solar wind and the magnetosphere (Lyon et al, 1981; Brecht et al, 1981; Ogino et al, 1985; Walker et al, 1993) were applied to ideal cases in which the solar wind and the interplanetary magnetic field (IMF) were constant.In recent years, global MHD simulations have been used to model magnetospheric events by using actual solar wind observations as input. The solar wind velocity was high and almost constant with 660 km/s and IMF By and Bz were about −6 nT and −6 nT, respectively, in that event They showed that closed field lines in the northern dusk region extended to higher latitudes due to the negative IMF By. In order to develop a Global Geospace Circulation Model (GGCM), MHD simulations were run for two time intervals on January 27, 1992 (1325–1715 UT and 1730–1930 UT) and were compared with observations (Raeder et al, 1998; Lyons, 1998). The IMF was northward on average, with a large By component (By = −20 nT), and the dynamic pressure (Dp ∼ 4 nPa) was about 2 to 3 times larger than normal. They found a Copyright c The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences; TERRAPUB

Results

Discussion

Conclusion