Inverse procedure for high‐latitude ionospheric electrodynamics: Analysis of satellite‐borne magnetometer data

Abstract

This paper presents an analysis of data from the magnetometers on board the Defense Meteorological Satellite Program (DMSP) F-15, F-16, F-17, and F-18 satellites and the Iridium satellite constellation, using an inverse procedure for high-latitude ionospheric electrodynamics, during the period of 29-30 May 2010. The Iridium magnetometer data are made available through the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) program. The method presented here is built upon the assimilative mapping of ionospheric electrodynamics procedure but with a more complete treatment of the prior model uncertainty to facilitate an optimal inference of complete polar maps of electrodynamic variables from irregularly distributed observational data. The procedure can provide an objective measure of uncertainty associated with the analysis. The cross-validation analysis, in which the DMSP data are used as independent validation data sets, suggests that the procedure yields the spatial prediction of DMSP perturbation magnetic fields from AMPERE data alone with a median discrepancy of 30-50 nT. Discrepancies larger than 100 nT are seen in about 20% of total samples, whose location and magnitude are generally consistent with the previously identified discrepancy between DMSP and AMPERE data sets. Resulting field-aligned current (FAC) patterns exhibit more distinct spatial patterns without spurious high-frequency oscillatory features in comparison to the FAC products provided by AMPERE. Maps of the toroidal magnetic potential and FAC estimated from both AMPERE and DMSP data under four distinctive interplanetary magnetic field (IMF) conditions during a magnetic cloud event demonstrate the IMF control of high-latitude electrodynamics and the opportunity for future scientific investigation.

Modes of (FACs) Variability and Their Hemispheric Asymmetry Revealed by Inverse and Assimilative Analysis of Iridium Magnetometer Data

“…In the high‐latitude region, we assume FACs are in the radial direction and produce mostly toroidal magnetic perturbation at the altitude of Iridium satellites. The toroidal and poloidal decomposition of the magnetic field can be simplified under this assumption following Matsuo et al () to where is the magnetic field vector, Ψ is the toroidal magnetic potential, and is a unit vector pointing upward. FAC J can then be calculated from magnetic field vectors following Ampere's law assuming an electrostatic condition as …”

“…The magnetic perturbation data y can be related to the coefficient vector x as where y is a column vector containing all at location i and time j ; H is a matrix containing 244 basis functions evaluated at the observation locations, and ϵ accounts for observational and truncation errors (Matsuo et al, ). H represents a linear relationship between x and y in this case and can be computed following Richmond et al (1995) as where λ m and ϕ m are latitude and longitude; and …”

“…In the high-latitude region, we assume FACs are in the radial direction and produce mostly toroidal magnetic perturbation at the altitude of Iridium satellites. The toroidal and poloidal decomposition of the magnetic field can be simplified under this assumption following Matsuo et al (2015) to…”

Comparison of predictive estimates of high‐latitude electrodynamics with observations of global‐scale Birkeland currents

“…Using AMPERE data, the Assimilative Mapping of Ionospheric Electrodynamics has been applied to a number of geomagnetic storms [cf. Matsuo et al, 2015]. Wilder et al [2012] obtained dramatic differences in ionospheric Joule heating rates and distributions relative to assimilations using only ground magnetometer, radar, and operational low Earth orbit satellite observations.…”

“…Using AMPERE data, the Assimilative Mapping of Ionospheric Electrodynamics has been applied to a number of geomagnetic storms [cf. Matsuo et al ., ]. Wilder et al .…”