Influence of solar flare's location and heliospheric current sheet on the associated shock's arrival at Earth

摘要

We study the source locations of 130 solar flare-type II radio burst events with the associated interplanetary shocks observed by L1 spacecraft (type A events) and 217 flare-type II events without such shocks observed at L1 (type B events) during February 1997–August 2002. In particular, we investigate the relative positions between the flare sources, the heliospheric current sheet (HCS), and the Earth. We found the following results: (1) Solar flares are usually distributed within [S30°, N30°] in heliographic latitude and [S30°, N30°] × [E10°, W30°] is the predominant source region on the solar disk that includes the majority of geoeffective solar flares. (2) The shocks with the associated flares located near the HCS would have a lower probably of reaching the Earth. For the Earth-encountered shocks, their initial speeds are distinctly higher when their associated flares are located near the HCS. (3) The angular distance from the flare source to the Earth (defined as Ψ below) also contributes to the probability of the associated shock being observed at the Earth. The shock arrival probability decreases with the increment of Ψ and the mean initial shock speed increases with Ψ for those Earth-encountered shocks. (4) The so-called “same-opposite side effect” of the HCS is confirmed to exist. That is, the shocks whose associated flares are located on the same side of the HCS as the Earth (called as “same side events”) have a greater chance of reaching the Earth than those shocks with their associated flares on the opposite side (“opposite side events”). Here for the first time, a comprehensive sample of solar transient events of both arriving and nonarriving ones (at Earth) is used to testify to the same-opposite side effect. These results would be valuable in understanding the solar-terrestrial relations, and helpful for space weather prediction.