Joint USAF/NOAA Report of Solar and Geophysical Activity 20 April 2011

:Product: Report of Solar-Geophysical Activity
:Issued: 2011 Apr 20 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 110 Issued at 2200Z on 20 Apr 2011
IA. Analysis of Solar Active Regions and Activity from 19/2100Z
to 20/2100Z: Solar activity has been at low levels for the past 24
hours. Regions 1195 (S17E55) and 1193 (N16W20) remain areas of
interest producing several B/C class events. The largest event was a
C4/Sf at 20/1939Z from Region 1195. Behind Region 1195, just
rotating onto the east limb, New Region 1196 (S27E69) is already
producing C-class events. Note: The Penticton 10.7 cm radio flux
appears to be flare enhanced.
IB. Solar Activity Forecast: Solar activity is expected to be at
low levels with a slight chance for M-class events for the next
three days (21-23 April).
IIA. Geophysical Activity Summary 19/2100Z to 20/2100Z:
The geomagnetic field has been unsettled to active with isolated
minor storm periods observed at high latitudes. The increase in
activity was due to the arrival of a coronal hole high-speed stream
(CH HSS). Observations at the ACE spacecraft, over the past 24
hours, have shown the solar wind speed increase from 350-550 km/s
and back down 500 km/s.
IIB. Geophysical Activity Forecast: The geomagnetic field is
expected to be at quiet to unsettled levels for the next 2 days
(21-22 April) as the effects of the CH HSS subside. Late on 21
April, a slow moving CME is expected to become geoeffective with
quiet to unsettled conditions lasting for 24 hours. On day three (23
April), quiet conditions are expected to prevail.
III. Event Probabilities 21 Apr-23 Apr
Class M 15/15/15
Class X 01/01/01
Proton 01/01/01
PCAF green
IV. Penticton 10.7 cm Flux
Observed 20 Apr 117
Predicted 21 Apr-23 Apr 115/115/115
90 Day Mean 20 Apr 104
V. Geomagnetic A Indices
Observed Afr/Ap 19 Apr 004/006
Estimated Afr/Ap 20 Apr 010/010
Predicted Afr/Ap 21 Apr-23 Apr 010/010-008/008-005/005
VI. Geomagnetic Activity Probabilities 21 Apr-23 Apr
A. Middle Latitudes
Active 25/20/10
Minor storm 05/05/01
Major-severe storm 01/01/01
B. High Latitudes
Active 30/20/10
Minor storm 10/10/01
Major-severe storm 01/01/01