Research Article

A regional space weather hazard variation index utilising Swarm FAST data

British Geological Survey, The Lyell Centre Research Park, Currie EH14 4AP, Edinburgh, UK

^* Corresponding author: lauren@bgs.ac.uk

Received: 17 June 2024
Accepted: 25 September 2024

Abstract

We develop a new method for the determination of a regional hazard indicator using Swarm satellite near-real-time Fast Track (‘FAST’) data based on pre-computed threshold exceedances. The European Space Agency (ESA) aim to deliver the FAST data promptly (currently twice daily) compared to the standard four-day lag with Swarm operational (‘OPER’) data. This provides an opportunity to map localized intense field variation during geomagnetic storms in areas without fixed ground-based magnetometers. To determine the location-dependent threshold above which we consider the magnetic field to be highly active, we compute the 20-s standard deviation of the magnetic field along the track and create baseline thresholds derived from 10 years of Swarm data. Using the standard 1 Hz Level1b LR MAG product, we first remove models of the core, crust and magnetosphere before analysing the ionospheric residuals to determine geomagnetically quiet and active thresholds. We bin the residuals into 20,840 quasi-uniform grid cells globally and compute the typical magnetic field variance expected in each cell. From the binned magnetic variances, we can determine thresholds for exceedance e.g. at the 99th percentile in each grid cell. If the value of the magnetic variation computed from Swarm FAST data, using the same method, exceeds the pre-determined thresholds within the bin, this indicates a highly variable magnetic field in the region, implying a localized increase in space weather hazard risk in regions without ground observatories. We present our Swarm-specific index which we can compare to other geomagnetic indices such as Kp. Our index compares well to Kp and the higher-cadence Hp60 and captures activity levels during both geomagnetic storms and quiet times. Using FAST data, we can quickly quantify the hazard on a per-orbit (or shorter) basis, thus providing as close to real-time geomagnetic activity monitoring as presently feasible. The methodology can also be used by other satellite missions surveying magnetic fields.