Spatial Variation in the Responses of the Surface External and Induced Magnetic Field to the Solar Wind

R M Shore,M P Freeman,J W Gjerloev,N Olsen,E G Thomas,J C Coxon

doi:10.1029/2019ja026543

Abstract

AbstractWe analyze the spatial variation in the response of the surface geomagnetic field (or the equivalent ionospheric current) to variations in the solar wind. Specifically, we regress a reanalysis of surface external and induced magnetic field (SEIMF) variations onto measurements of the solar wind. The regression is performed in monthly sets, independently for 559 regularly spaced locations covering the entire northern polar region above 50° magnetic latitude. At each location, we find the lag applied to the solar wind data that maximizes the correlation with the SEIMF. The resulting spatial maps of these independent lags and regression coefficients provide a model of the localized SEIMF response to variations in the solar wind, which we call “Spatial Information from Distributed Exogenous Regression.” We find that the lag and regression coefficients vary systematically with ionospheric region, season, and solar wind driver. In the polar cap region the SEIMF is best described by the By component of the interplanetary magnetic field (50–75% of total variance explained) at a lag ∼20–25 min. Conversely, in the auroral zone the SEIMF is best described by the solar wind ϵ function (60–80% of total variance explained), with a lag that varies with season and magnetic local time (MLT), from ∼15–20 min for dayside and afternoon MLT (except in Oct–Dec) to typically 30–40 min for nightside and morning MLT and even longer (60–65 min) around midnight MLT.

Highlights

Interaction between the solar wind and the Earth's magnetic field drives a system of electrical currents which couple the magnetosphere and ionosphere in near-Earth space, caused by disturbances occurring on the Sun (Milan et al, 2017)
We regress a reanalysis of surface external and induced magnetic field (SEIMF) variations onto measurements of the solar wind
In the auroral zone the SEIMF is best described by the solar wind ε function (60–80% of total variance explained), with a lag that varies with season and magnetic local time (MLT), from ∼15–20 min for dayside and afternoon MLT to typically 30–40 min for nightside and morning MLT and even longer (60–65 min) around midnight MLT

Summary

Introduction

Interaction between the solar wind and the Earth's magnetic field drives a system of electrical currents which couple the magnetosphere and ionosphere in near-Earth space, caused by disturbances occurring on the Sun (Milan et al, 2017). We demonstrate a technique of regressing equivalent current variations onto measurements of specific solar wind parameters, which is performed independently for each locality This allows us to explore the localization of two key controlling factors of the solar-terrestrial coupling, which have until now been investigated only in spatially and temporally smoothed terms. To minimize the (smoothing) assumptions, we make about the equivalent current behavior when describing its relationship to the solar wind; we base our investigation on the data set developed by Shore et al (2018) This is a reanalysis of the Earth's surface external and induced magnetic field (SEIMF) variations, made from the SuperMAG archive (Gjerloev, 2009, 2012).

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