Geomagnetic storm

Late on 15 June, another geomagnetic storm has been recorded for solar cycle 25 (SC25). The source was a high speed wind stream associated with an extension from the southern polar coronal hole. Solar wind speed reached values near 600km/s, while Bz briefly peaked near -10nT. The coronal hole can be seen in the SDO/AIA 193 image from 13 June underneath when it was passing the Sun's central meridian.

 

Over the last couple of months, we have had already several instances when geomagnetic storming conditions were reached. On 12 May, there was even a strong geomagnetic storm following the arrival of an interplanetary coronal mass ejection. So how does this geomagnetic activity relate to the previous solar cycles (SC)? In the graph underneath (data from WDC Kyoto), for each SC since 1976 (SC21 thru SC25), and for the period covering 18 months after the respective solar cycle minimum (see the dedicated SILSO solar cycle page), the number of geomagnetic storming days (vertical axis) are represented and binned per level of Kp from Kp=5 to Kp=9 (horizontal axis). Please check out the STCE SWx Classification page for more info on geomagnetic indices and levels of geomagnetic activity. Though the numbers for June 2021 are not complete yet, the overall tendency is clear. The graph shows that -so far- SC25 has been geomagnetically more active than the previous SC24, in particular concerning the number of days with minor storming. Nonetheless, both SC24 and SC25 numbers pale in comparison to SC23 and especially SC21 and 22. Note that no extremely severe storms have been observed yet, in none of the 5 SCs, which is fairly OK considering we are still at the start of the SC, but also because this kind of storms are isolated events and thus better evaluated over a much longer period, e.g. an entire solar cycle.

 

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