Interplanetary Magnetic Field Control of PolarIonospheric Equivalent Current System Modes

TL;DR

This study investigates how different ionospheric current modes respond to variations in the interplanetary magnetic field, revealing multiple timescales of response linked to magnetospheric processes and confirming their physical basis.

Contribution

It identifies and quantifies the linear responses of specific ionospheric current modes to IMF components, elucidating their reconfiguration timescales and physical origins.

Findings

Modes are correlated with IMF components at specific time lags.

Responses include magnetopause merging and magnetotail reconnection timescales.

Longer lags show increased IMF influence, indicating conductivity feedbacks.

Abstract

We analyze the response of different ionospheric equivalent current modes to variations in the interplanetary magnetic field (IMF) components By and Bz. Each mode comprises a fixed spatial pattern whose amplitude varies in time, identified by a month-by-month empirical orthogonal function separation of surface measured magnetic field variance. Here we focus on four sets of modes that have been previously identified as DPY, DP2, NBZ, and DP1. We derive the cross-correlation function of each mode set with either IMF (B$_{y}$) or (B$_{z}$) for lags ranging from -10 to +600 mins with respect to the IMF state at the bow shock nose. For all four sets of modes, the average correlation can be reproduced by a sum of up to three linear responses to the IMF component, each centered on a different lag. These are interpreted as the statistical ionospheric responses to magnetopause merging (15- to 20-min lag) and magnetotail reconnection (60-min lag) and to IMF persistence. Of the mode sets, NBZ and DPY are the most predictable from a given IMF component, with DP1 (the substorm component) the least predictable. The proportion of mode variability explained by the IMF increases for the longer lags, thought to indicate conductivity feedbacks from substorms. In summary, we confirm the postulated physical basis of these modes and quantify their multiple reconfiguration timescales.