Joint USAF/NOAA Report of Solar and Geophysical Activity 25 August 2011

:Product: Report of Solar-Geophysical Activity
:Issued: 2011 Aug 25 2200 UTC
# Prepared jointly by the U.S. Dept. of Commerce, NOAA,
# Space Weather Prediction Center and the U.S. Air Force.
#
Joint USAF/NOAA Report of Solar and Geophysical Activity
SDF Number 237 Issued at 2200Z on 25 Aug 2011
IA. Analysis of Solar Active Regions and Activity from 24/2100Z
to 25/2100Z: Solar activity was at very low levels. Region 1271
(N17W56) decayed in area and spot count, but developed a Delta
magnetic configuration in the large leader spot. The region produced
numerous low-level B-class events. Three new regions were numbered
during the period. In the western hemisphere, new Region 1278
(N16W40) emerged as a simple 4-spot bi-polar group. On the eastern
limb, new Region 1277 (N17E62) and new Region 1279 (N14E75) both
rotated onto the disk as large, uni-polar H-type groups. Region 1277
produced a B9 x-ray event at 25/0702Z while Region 1279 produced
another B9 x-ray event at 25/1652Z. The SOHO LASCO satellite
observed a slow-moving CME off the east limb, first observed in C2
imagery at 25/0856Z with an estimated plane-of-sky speed of 420
km/s. This CME does not appear to have an Earthward directed
component.
IB. Solar Activity Forecast: Solar activity is expected to be low
with a slight chance for an M-class event all three days (26 – 28
August).
IIA. Geophysical Activity Summary 24/2100Z to 25/2100Z:
The geomagnetic field was at quiet levels. Observations from the ACE
spacecraft indicated a steady decline in solar wind velocity during
the period from about 500 km/s to near 400 km/s. The Bz component
of the interplanetary magnetic field did not vary much beyond +/- 4
nT while the phi angle remained negative (toward) throughout the
period.
IIB. Geophysical Activity Forecast: The geomagnetic field is
expected to remain at quiet levels for days one and two (26 – 27
August). By day three (28 August), activity levels are expected to
increase to quiet to unsettled, with isolated active periods, due to
a geoeffective, recurrent coronal hole high speed stream.
III. Event Probabilities 26 Aug-28 Aug
Class M 10/10/10
Class X 01/01/01
Proton 01/01/01
PCAF Green
IV. Penticton 10.7 cm Flux
Observed 25 Aug 104
Predicted 26 Aug-28 Aug 110/115/115
90 Day Mean 25 Aug 097
V. Geomagnetic A Indices
Observed Afr/Ap 24 Aug 005/006
Estimated Afr/Ap 25 Aug 005/005
Predicted Afr/Ap 26 Aug-28 Aug 005/005-005/005-007/010
VI. Geomagnetic Activity Probabilities 26 Aug-28 Aug
A. Middle Latitudes
Active 15/15/20
Minor storm 01/01/05
Major-severe storm 01/01/01
B. High Latitudes
Active 15/15/30
Minor storm 01/01/15
Major-severe storm 01/01/01