:Product: Weekly Highlights and Forecasts
:Issued: 2021 May 24 0337 UTC
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# Weekly Highlights and Forecasts
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Highlights of Solar and Geomagnetic Activity
17 - 23 May 2021

Solar activity ranged from very low to moderate levels with the
majority of the flare activity caused by Region 2824 (N21, L=195,
class/area Csi/190 on 22 May). Very low levels were observed on 17
and 19-20 May with Low levels occurring on 18 and 21 May. Activity
increased to moderate levels on 22-23 May due to a series of M1
flares from Region 2824 at 22/1711, 22/2136, and 23/1108 UTC. In
addition to the M-class flares were several noteworthy C-class
flares, including an impulsive C6/1n at 22/0256 UTC with an
associated Type II (1530 km/s) Radio sweep, an impulsive C6/1n with
an associated Type II (653 km/s), and a long duration C1 at 22/0844
UTC. Multiple CME signatures were observed from the region
associated with these flares (and others). Each were modelled and
put into a consolidated WSA-ENLIL run showing arrival times
beginning late on 25 May.

No proton events were observed at geosynchronous orbit.

The greater than 2 MeV electron flux at geosynchronous orbit was at
normal to moderate levels with a peak flux of 1,040 pfu which was
briefly reached at 22/1635 UTC.

Geomagnetic field activity ranged from quiet to G1 (Minor)
geomagnetic storm levels. The period began with nominal solar wind
values in the 325-420 km/s range through early on 20 May. An
isolated active period was observed early on 18 May due to possible
weak CME influence from 13 May. The geomagnetic field was quiet on
17 May, quiet to active on 18 May, and quiet to unsettled on 19 May.
Beginning at 20/1845 UTC, total field increased to 19 nT while solar
wind speed subsequently increased to near 575 km/s due to the onset
of a negative polarity coronal hole high speed stream (CH HSS).
Solar wind speed slowly decreased back to nominal levels by the end
of the period. The geomagnetic field responded with quiet to G1
(Minor) storm levels on 20 May, quiet to unsettled on 21 May, and
quiet levels thereafter.

Forecast of Solar and Geomagnetic Activity
24 May - 19 June 2021

Solar activity is expected to be low with a chance for further
M-class flares on 24-30 May as Region 2824 rotates across the
visible disk. Very low levels are expected on 31 May - 11 Jun. Low
levels are expected to return on 12-19 Jun as Region 2824 rotates
back onto the visible disk.

No proton events are expected at geosynchronous orbit.

The greater than 2 MeV electron flux at geosynchronous orbit is
expected to reach high levels on 26-29 May due to CME enhancements.

Geomagnetic field activity is expected to reach G1 (Minor) storm
levels on 25-27 May with G2 (Moderate) storming on 26 May due to the
arrival of multiple CMEs from 22-23 May. G1 (Minor) storming is also
likely on 16 Jun as a recurrent, negative polarity CH HSS is
expected to become geoeffective.