Dst prediction for a period of high-density plasmas in magnetic clouds

We examine geomagnetic effects for high-density plasmas in magnetic clouds and their relationship to solar sources. It is well known that Bz component of interplanetary magnetic field plays an important role for estimation of Dst from solar wind parameters (Burton et al.1975). However, magnetic clouds frequently carry high-density plasmas, which are interpreted as the remnants of filament. In order to clarify their geomagnetic effects, we try to estimate Dst by adopting different methods introducing effects of solar wind parameters. In our estimation the most important point is laid on the sense of Dst variation rather than its magnitude. The most suitable estimation is obtained by setting up a threshold for plasma density, in which for a case of plasma density greater than 20 /cc the Fenrich and Luhmann (1998)'s formula should be used, while in the other cases the Burton's formula are adopted. In both estimations the O'Brien and McPherron (2000)'s ring current decay time is employed. Furthermore, we examine the solar origin corresponding to the magnetic clouds and then compared characteristic signatures of the magnetic cloud with those observed on the solar surface. As a result, we confirm that the magnetic structure of interplanetary flux rope is in good agreement with the structures of the magnetic neutral line near disappearing filaments and heliospheric current sheet (HCS). On the basis of these studies, we suggest that for the geomagnetic disturbance forecast, the effect of high-density plasmas carried with magnetic clouds should be taken into account of as well as that of interplanetary magnetic field.