3.3 Linkage of STEVE with substorm activity
We analyzed the GOES spacecraft magnetic field and particle flux data to identify the substorm associated injection at the geostationary orbit for STEVE events. Interestingly, we found that most of the STEVE events (20 events) were accompanied by the substorm associated injection at the geostationary orbit approximately 30 mins prior to the detachment of STEVE. Although we have used different GOES spacecrafts to identify the feature of diapolarization and substorm associated injection for all 26 STEVE events spanning from 2006 to 2019, here we have shown only three examples using GOES-15 particle flux (both electron and proton) data. Figure 11 shows three examples of energetic electron and proton fluxes from GOES-15 spacecraft as a function of L-value, MLT, and UT for STEVE events of (A) 18 August 2018, (B) 02 March 2019, and (C) 02 May 2019. GOES‐15 was in the premidnight sector at ∼2000 MLT for these three events. The longitudinal difference of GOES-15 and Athabasca ASI is ~63 degree. The detachment time of STEVE arc is highlighted by purple dashed line, as observed in the red-line ASI images at Athabasca. The black dotted lines indicate the start of dispersionless enhancement for both electron and proton fluxes. The dispersionless enhancement with a simultaneous increase of the electron (by a factor of ~1.5-3.0) and ion fluxes (by a factor of ~2 to an order of magnitude) at ~0527-0552 UT was observed on 18 August 2018 (A) and STEVE started at 0600 UT. Similarly, at 0525-0532 UT, dispersionless enhancement by a factor of ~4 was observed for 02 March 2019 (B) and STEVE observed at 0600 UT. For the event of 02 May 2019, STEVE began at 0450 UT and the dispersionless enhancement by a factor of ~2-4 was observed at ~0415-0435 UT. The enhancement of proton flux was found to be around one order of magnitude higher for lower energies (95 and 140 keV) for 02 May 2019 (C). Since GOES-15 observes near simultaneous dispersionless injections for both protons and electrons, the location of the injections must be close to the location of GOES-15 at ∼2000 MLT. GOES particle flux data confirm substorm onset before the STEVE events. Although not shown here, the events of diapolarization and substorm associated injection were also observed for red and red+green arcs.