The geomagnetic cutoff rigidities at high latitudes for different solar wind and geomagnetic conditions

W Chu,G Qin

doi:10.5194/angeo-34-45-2016

Abstract

Abstract. Studying the access of the cosmic rays (CRs) into the magnetosphere is important to understand the coupling between the magnetosphere and the solar wind. In this paper we numerically studied CRs' magnetospheric access with vertical geomagnetic cutoff rigidities using the method proposed by Smart and Shea (1999). By the study of CRs' vertical geomagnetic cutoff rigidities at high latitudes we obtain the CRs' window (CRW) whose boundary is determined when the vertical geomagnetic cutoff rigidities drop to a value lower than a threshold value. Furthermore, we studied the area of CRWs and found out they are sensitive to different parameters, such as the z component of interplanetary magnetic field (IMF), the solar wind dynamic pressure, AE index, and Dst index. It was found that both the AE index and Dst index have a strong correlation with the area of CRWs during strong geomagnetic storms. However, during the medium storms, only AE index has a strong correlation with the area of CRWs, while Dst index has a much weaker correlation with the area of CRWs. This result on the CRW can be used for forecasting the variation of the cosmic rays during the geomagnetic storms.

Highlights

The ionosphere and atmosphere of the Earth at high and middle latitudes can be affected by the energetic particles which enter the magnetosphere at low altitudes (Nesse Tyssøy et al, 2013; Galand, 2001)
It is well believed that solar activity can significantly influence the polar region of the magnetosphere, so the cosmic rays window (CRW) varies with the different parameters of the interplanetary conditions
We vary one or two parameters with the rest solar wind parameters kept as the ones of the quiet period, so we get varying CRW corresponding to the varying solar wind parameters

Summary

Introduction

The ionosphere and atmosphere of the Earth at high and middle latitudes can be affected by the energetic particles which enter the magnetosphere at low altitudes (Nesse Tyssøy et al, 2013; Galand, 2001). Smart and Shea did a series of studies (Smart, 1999; Smart et al, 2000; Shea and Smart, 2001; Smart and Shea, 2003a, 2005) to determine the geomagnetic cutoff rigidities from charged particles trajectories by numerically solving Newton’s equation of motion This method is very accurate for calculating cosmic ray cutoff rigidities as long as the magnetospheric field is accurate enough and large-scale computer power is available. Tyssøy and Stadsnes (2014) used the measurements from the Medium Energy Proton and Electron Detector on all available Polar Orbit Environment Satellites (POES) to study the variation of the cutoff latitudes and provided a simple applicable parameterization as a function of the Dst index which represents the disturbed magnetic field at the dipole equator on the Earth’s surface, Bz, and solar wind pressure Pdyn.

Models and methods

Results

Solar wind parameters study of CRW

CRW during geomagnetic storms

Conclusions and discussions