Numerical Algorithm for Detecting Ion Diffusion Regions in the Geomagnetic Tail With Applications to MMS Tail Season 1 May to 30 September 2017


We present a numerical algorithm to identify ion diffusion regions (IDRs) in the geomagnetic tail and test its applicability. We use five criteria applied in three stages. (i) correlated reversals (within 90 s) of Vx and Bz (at least 2 nT about 0; geocentric solar magnetospheric coordinates); (ii) detection of Hall electric and magnetic field signatures; and (iii) strong (≥10 mV/m) electric fields. While no criterion alone is necessary and sufficient, the approach does provide a robust, if conservative, list of IDRs. We use data from the Magnetospheric Multiscale (MMS) mission spacecraft during a 5-month period (1 May to 30 September 2017) of near-tail orbits. We find 148 events satisfying Step 1, 37 satisfying Steps 1 and 2, and 17 satisfying all 3, of which 12 are confirmed as IDRs. All IDRs were within the X-range [−24, −15] RE and the majority occurred during traversals of a tailward moving X-line. Eleven of 12 IDRs were on the duskside despite approximately equal residence time in the plasma sheet (56.5% dusk vs. 43.5% dawn). MMS could identify signatures of four quadrants of the Hall B-structure in three events and three quadrants in seven events. The events we report commonly display Vx reversals greater than 400 km/s in magnitude, normal magnetic field reversals often >10 nT in magnitude, maximum DC | urn:x-wiley:jgra:media:jgra55058:jgra55058-math-0001|, which are often well in excess of the threshold for Stage 3. Our results are then compared with the set of IDRs identified by visual examination from Cluster in the years 2000–2005.

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JGR: Space Physics



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