Forecast of solar ejecta arrival at 1 AU from radial speed

Abstract

Solar ejecta produce changes in the interplanetary magnetic field of the terrestrial environment. When the magnetic polarity of the ejecta is suitable, it may trigger intense geomagnetic storms. Therefore, prediction of the arrival of solar ejecta in the geospace is of crucial importance for space weather applications. We implement a simple model, developed by Gopalswamy et al., (2000) to estimate the time of arrival for solar ejecta at 1AU. This model requires just one input parameter: the radial speed of the associated coronal mass ejection (CME) at the moment of its expulsion from the Sun. When the speed of the CME is measured from a location on the Sun-Earth line, only the plane of the sky speed can be obtained. Since the prediction model depends on the initial speed of the CMEs observed remotely, it is important to obtain this speed as accurately as possible. One of the major uncertainties in the measured initial speed is the extent of projection effects. We attempt to correct for projection effects using the solar surface location of the eruption and assuming a width to the CME. We found that the correction is in agreement with a model obtained from stereoscopic observations from the past.