The first super geomagnetic storm of solar cycle 24: “The St. Patrick’s day event (17 March 2015)”

Abstract

The first super geomagnetic storm (Dst < −200 nT) of solar cycle 24 occurred on "St. Patrick's day" (17 March 2015). Notably, it was a two-step storm. The source of the storm can be traced back to the solar event on 15 March 2015. At ~2:10 UT on that day, SOHO/LASCO C3 recorded a partial halo coronal mass ejection (CME), which was associated with a C9.1/1F flare (S22W25) and a series of type II/IV radio bursts. The initial propagation speed of this CME is estimated to be ~668 km/s. An interplanetary (IP) shock, likely driven by a magnetic cloud (MC), arrived at the Wind spacecraft at 03:59 UT on 17 March and caused a sudden storm commencement. The storm intensified during the Earth's crossing of the ICME/shock sheath and then recovered slightly after the interplanetary magnetic field (IMF) turned northward. The IMF started turning southward again due to a large MC field itself, which caused the second storm intensification, reaching a minimum value (Dst = −223 nT). It is found that the first step is caused by a southward IMF component in the sheath (between the upstream shock and the front of the MC), whereas the second step is associated with the passage of the MC. The CME that erupted on 15 March is the sole solar source of the MC. We also discuss the CME/ storm event with detailed data from observations (Wind and SOHO) and our algorithm for predicting the intensity of a geomagnetic storm (Dst min ) from known IP parameter values. We found that choosing the correct Dst min estimating formula for predicting the intensity of MC-associated geomagnetic storms is crucial for space weather predictions.

MAVEN observations of the solar cycle 24 space weather conditions at Mars

“…This active region rotated over the east solar limb as viewed at Earth and produced an M8.9 class flare that was observed by MAVEN EUVM and GOES on 7 March 2015. As this active region rotated toward the direction of Earth on the solar disk, it produced a number of 10.1002/2016JA023495 flares and CMEs, including the activity that triggered first super geomagnetic storm of solar cycle 24 at Earth ("St. Patrick's Day Storm" [Wu et al, 2016]). …”

Use of spherical elementary currents to map the polar current systems associated with the geomagnetic sudden commencements on 2013 and 2015 St. Patrick's Day storms

“…According to this method, the wavefront associated with the 2013 event has incidence angles of 21° within the equatorial plane ( x‐y plane in GSM coordinates) and 6° in the meridional ( x‐z ) plane, whereas the corresponding 2015 angles are 5° ( x‐y ) and 16° ( x‐z ), meaning that the wave comes from the northern hemisphere afternoon sector in both cases. Using these wavefront orientations, along with the spacecraft positions and their onset times (not shown here), the speed of the wavefront is found to be about 640 km/s for the 2013 event and 580 km/s for the 2015 event [see Wu et al ., ]. It should be noted, however, that the above quantities have a considerable uncertainty due to gaps in the satellite data, especially around the onset of the 2013 event.…”

Ionospheric Response to the St. Patrick's Day Space Weather Events in March 2012, 2013, and 2015 at Southern Low and Middle Latitudes

“…This storm of 17–18 March 2015 with a minimum Dst index of −222 nT developed through a two‐step development in the ring current as shown in Figure a. The first step was caused by a southward IMF B Z in the sheath region and the second step by the passage of a MC (Wu et al, ), thus showing sheath‐sheath‐ejecta scenario for the multistep development of this superstorm. The second step of the storm development was of longer duration that was consistent with an intense (−10 to −20 nT) and long duration of southward IMF B Z in the MC that intensified the storm.…”

“…The interplanetary parameters and solar wind conditions associated with the 17–18 March 2015 storm have been presented by several researchers (e.g., Alberti et al, ; Guerrero et al, ; Marubashi et al, ; Verkhoglyadova et al, ; Wu et al, ). The IMF B Z variation during 16–19 March 2015 (Figure c) shows two southward turnings of IMF B Z with the second one strong (< −15 nT) and of longer duration (>10 hr).…”