The 2015 Summer Solstice Storm: One of the Major Geomagnetic Storms of Solar Cycle 24 Observed at Ground Level

Abstract

We report on the 22-23 June 2015 geomagnetic storm which occurred during the summer solstice time. There has been a shortage of intense geomagnetic storms during the current solar cycle 24 in relation to the previous cycle. This situation changed after mid-June 2015 when one of the biggest solar active regions (AR 2371) of current solar cycle 24, close to the central meridian produced several coronal mass ejections (CMEs) associated with M-class flares. The CMEs impact on the Earth's magnetosphere resulted in a moderately-severe G4-class geomagnetic storm on 22-23 June 2015 and a G2 (moderate) geomagnetic storms on 24 June. The G4 solstice storm was the second biggest (so far) geomagnetic storms of cycle 24. We highlight the ground level observations made by New-Tupi, Muonca and the CARPET El Leoncito cosmic ray detectors that are located within the South Atlantic Anomaly (SAA) region. These observations are studied in correlation with data obtained by space-borne detectors (ACE, GOES, SDO, and SOHO) and other ground-based experiments. The CME designations are from the Computer Aided CME Tracking (CACTus) automated catalog. As expected, Forbush Decreases (FD) associated with the passing CMEs were recorded by these detectors. We noticed a peculiar feature linked to a severe geomagnetic storm event. The 21 June 2015 CME 0091 was likely associated with the 22 June summer solstice FD event. The angular width of CME 0091 was very narrow and measured ∼ 56 • degrees seen from Earth. In most cases, only CME halos and partial halos, lead to severe geomagnetic storms. We performed a cross-check analysis of the FD events detected during the rise phase of the current solar cycle 24, the geomagnetic parameters, and the CACTus CME catalog. Our study suggests that narrow angular-width CMEs that erupt in the western region of the ecliptic plane can lead to moderate and severe geomagnetic storms. We also report on the strong solar proton radiation storm with onset on 21 June. We did not find a signal from this SEP at ground level. The details of these observations are presented.

Multi‐Instrumental Observation of Storm‐Induced Ionospheric Plasma Bubbles at Equatorial and Middle Latitudes

“…On 21–22 June 2015, two moderate and one giant coronal mass ejections (CMEs) reached the Earth magnetosphere and led to an occurrence of a severe geomagnetic storm (e.g., Augusto et al, ; NOAA Space Weather Highlights, ; Reiff et al, ). Figure illustrates the space weather conditions for 21–23 June 2015.…”

Relativistic Proton Levels from Region AR 12673 (GLE #72) and the Heliospheric Current Sheet as a Sun–Earth Magnetic Connection

“…Values of the pa close to 90 and 270°represent zero latitudes. The pa=90 0 and pa=270 0 coincides with the eastern side and with the western side of the ecliptic plane, respectively (Augusto et al 2018). In addition, from Figure 4 we can see that the shock wave velocities in the CME #0037 ranging from 104 to 2013 km h −1 , with a median velocity of 948 km h −1 and they have an almost uniform distribution, across the pa region (this happens only for a full-halo CME).…”

An Efficient, Time‐Dependent High Speed Stream Model and Application to Solar Wind Forecasts

“…These are the 17 March 2015 storm, strongest of the cycle with the Dst index reaching −234 nT (e.g., Kataoka et al., 2015), and the 26 August 2018 storm, third‐strongest of the cycle with the Dst index reaching −175 nT (e.g., Palmerio et al., 2022). The second‐strongest storm, on 23 June 2015 and with the Dst index reaching −198 nT, on the other hand, was driven by successive, interacting CMEs (e.g., Augusto et al., 2018). In the CME‐followed‐by‐HSS scenario, the fast solar wind that trails a CME compresses the material ahead of it, thus inhibiting (or at least lessening) expansion—this means that a CME is more likely to maintain high speeds, enhanced densities, and strong out‐of‐ecliptic fields.…”