Comparison of magnetic perturbation data from LEO satellite constellations: Statistics of DMSP and AMPERE

Abstract

During the past decade engineering-grade magnetic field measurements from the low Earth orbiting (LEO) Iridium constellation of communication satellites have been available to the geospace science community as a tool to map field-aligned currents. The Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) applied to Iridium measurements markedly improved the temporal and spatial resolution of these data. We developed new methods to compare data from the latest improvement to AMPERE with those from a constellation of four LEO Defense Meteorological Satellite Program (DMSP) spacecraft that carry high-resolution magnetometers. To perform the comparisons, we transformed all data to a common coordinate frame and altitude (110 km) and developed a means of computing spacecraft magnetic conjunctions. These conjunctions yield discrepancies in the magnetic field perturbations measured at each proximate spacecraft. During the geomagnetic disturbance of 29-30 May 2010, the vector differences in the horizontal perturbations at closest approach (typically a few tens of kilometers) had mean, median, and standard deviation values of 132 nT, 112 nT, and 90 nT, respectively. The DMSP spacecraft tend to report larger perturbations in the northern polar cap and cusp regions, especially during active intervals. We attribute some of the differences to limitations of spacecraft-attitude knowledge that propagate into AMPERE data. Overall, for the magnetic storm, we provide clear evidence that AMPERE data can provide high-resolution auroral zone data in good agreement with DMSP data for use in data assimilation algorithms. Such dual-use commercial data can provide important global augmentation to the nation's space weather monitoring capabilities. Background and MotivationEarth's thermosphere, where most low Earth orbiting (LEO) satellites operate, is subject to a variety of space weather disturbances. As first discussed in Cummings and Dessler [1967], many of these disturbances are closely linked to variations in magnetic field-aligned currents (FAC), which are often referred to as Birkeland currents. Although hundreds of satellites have operated in LEO, until this millennium only about a dozen had been equipped with high-quality vector magnetometers needed for characterizing FAC behavior. From the 1970's to the turn of the century, direct knowledge of FAC structure and behavior was ascertained from individual or sequential passes of LEO (or LEO-approach) missions that included the following: Satellite 1963-38C [Zmuda et al

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

“…The cross‐validation analysis suggests that the procedure can yield the spatial prediction of DMSP perturbation magnetic fields from AMPERE data alone with a median discrepancy of 30–50 nT. The large discrepancy between the prediction and observation is generally consistent with the previously identified discrepancy between DMSP and AMPERE data sets reported in Knipp et al []. In other words, the current procedure's accuracy is validated up to the level of consistency between these two data sets.…”

“…For the purpose of cross validation, the magnetic perturbation fields at the reference altitude h r predicted by using only the AMPERE data are compared to the DMSP F‐15, F‐16, F‐17, and F‐18 observations mapped to h r . Figures a and b shows predicted and observed magnetic field , where k = 1,2, for 13:20–13:24 UT on 29 May 2010, which corresponds to an example shown in Figure 11 of Knipp et al []. The agreement is good except for the high‐latitude morning sector, where there are no AMPERE data in the area and the discrepancy is greater for (eastward).…”

“…Note that the AMPERE data, as referred to throughout the paper, should not be mistaken with the AMPERE data product resulting from the AMPERE inversion procedure and that the spliced data used in place of low‐quality data to stabilize regression analysis in the AMPERE inversion procedure are excluded from the current analysis. Knipp et al [] examined the correspondence between AMPERE and DMSP data through magnetic conjunction analysis and confirmed an overall consistency of these data sets. DMSP data are later used in this study for validation of the spatial prediction of magnetic perturbations obtained from AMPERE data, and, in combination with AMPERE data, for estimation of the toroidal magnetic potential and FAC analysis.…”

“…DMSP data are later used in this study for validation of the spatial prediction of magnetic perturbations obtained from AMPERE data, and, in combination with AMPERE data, for estimation of the toroidal magnetic potential and FAC analysis. In spite of the overall agreement, discrepancies of up to a few hundreds of nanoteslas are identified in some cases [ Knipp et al , ], so the observational error is set centered at 200 nT in the current analysis. In the method described in section 3.3 the observational errors for the individual data points are given by the data quality flag provided by AMPERE scaled to be centered around 200 nT, and the median value of the AMPERE quality flag is assigned to the DMSP data.…”

Magnetic Signatures of Ionospheric and Magnetospheric Current Systems During Geomagnetic Quiet Conditions—An Overview

“…The majority of magnetic satellites belong to the second category. Their data have been used very successfully for studying ionospheric and magnetospheric processes, especially during geomagnetic disturbed conditions when the signal of those sources is particularly strong (e.g., Knipp et al 2014, and references therein). However, many interesting external phenomena have amplitudes of only a few nanotesla; still they provide crucial information on ionospheric and magnetospheric processes.…”