Weekly Highlights of Solar and Geomagnetic Activity, 22 - 28 April 2013

[SWPC.We...@noaa.gov]

:Product: Weekly Highlights and Forecasts
:Issued: 2013 Apr 29 0434 UTC
# Prepared by the US Dept. of Commerce, NOAA, Space Weather Prediction Center
# Product description and SWPC contact on the Web
# http://www.swpc.noaa.gov/weekly.html
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# Weekly Highlights and Forecasts
#
Highlights of Solar and Geomagnetic Activity
22 - 28 April 2013

Solar activity was at low to moderate levels during the period. The
period began at very low levels, but quickly rose to moderate levels
as an impulsive M1 flare and associated Type IV radio sweep occurred
at 22/1029 UTC from Region 1726 (N13, L=331, class/area Fkc/1000 on
25 Apr). An associated coronal mass ejection (CME) was observed in
LASCO C2 imagery off the west limb at 21/1036 UTC, but was only
partially Earth-directed and did not result in noticeable impacts.
Activity returned to low levels following the M1 flare, but remained
fairly active throughout the period, producing over 60 C-class
flares. The most active region was Region 1726, which produced over
33 C-class flares on its own. As soon as Region 1726 rotated off the
visible disk on 25 Apr, Region 1731 (N09, L=187, class/area Dkc/420
on 28 Apr) emerged and quickly became the area of interest,
producing a total of 12 C-class flares. Region 1733 (S17, L=254,
class/area Cso/30 on 28 Apr) produced a C4/1n flare associated with
Type II (576 km/s) and Type IV radio emissions at the end of the
forecast period, and had an associated potentially Earth-directed
CME. Further analysis is pending.

No proton events were observed at geosynchronous orbit.

The greater than 2 MeV electron flux at geosynchronous orbit was
normal to moderate levels from 22 Apr to 26 Apr. Flux values
increased to high levels on 27 Apr, reaching a max of 2920 pfu at
27/1625 UTC, and remained at moderate to high levels until late on
28 Apr as a result of effects from coronal hole high speed stream
(CH HSS) activity.

Geomagnetic field activity was at quiet to unsettled levels on 22-23
Apr. Activity increased to unsettled to active levels on 24 Apr due
to effects from a favorably positioned CH HSS. Solar wind speeds
increased to near 430 km/s, the total interplanetary magnetic field
(IMF) reached a maximum 23.4 nT, and the Bz component dropped to
-18.9 nT. Solar wind speed continued to increase on 25 Apr to the
500 km/s range, total fields decreased to approximately 5 nT, and
the Bz component of the IMF was variable between +/- 3 nT. The
ionosphere responded with a short-lived G1 (Minor) geomagnetic storm
early on 26 Apr, but conditions quickly returned to unsettled levels
for the remainder of the day. Quiet levels returned by 27 Apr and
remained there through the end of the period as CH HSS effects
diminished.

Forecast of Solar and Geomagnetic Activity
29 April - 25 May 2013

Solar activity is expected to be low with a chance for M-class
flares through 07 May as Region 1731 remains on the visible disk.
Activity is expected to decrease to very low to low levels through
08 May. Activity will likely increase to low with M-class flares
likely when we see Region 1726 return on 09 May. Region 1731 returns
on 20 May, keeping levels low with M-class flares likely through the
end of the forecast period.

No proton events are expected at geosynchronous orbit.

The greater than 2 MeV electron flux at geosynchronous orbit is
expected to be at moderate to high levels through 02 May due to CH
HSS effects. Values should decrease to normal to moderate levels
from 03 May through 21 May. Another increase to moderate to high
levels in response to recurrent CH HSS effects is expected from
22-25 May.

Geomagnetic field activity is expected to be mostly quiet through 20
May. Conditions should increase to unsettled to active with isolated
periods of minor storming possible from 21-23 in response to
recurrent CH HSS effects. Mostly quiet levels should return on 24
and 25 May.