Joint USAF/NOAA Report of Solar and Geophysical Activity 18 April 2011

:Product: Report of Solar-Geophysical Activity
:Issued: 2011 Apr 18 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 108 Issued at 2200Z on 18 Apr 2011
IA. Analysis of Solar Active Regions and Activity from 17/2100Z
to 18/2100Z: Solar activity has been at low levels for the past 24
hours. Region 1193 (N17E05) has been the most active, producing two
low-level C-class events. Region 1193 has remained rather stable but
continues to grow in sunspot number and magnetic complexity. At
18/0348Z, a C1 flare was observed off the west limb. There was a
non-earth directed CME associated with this event visible in LASCO
C2 imagery at 18/0412Z.
IB. Solar Activity Forecast: Solar activity is expected to be at
low levels with a chance for M-class events for the next three days
(19-21 April). Region 1190 (N13W68) is expected to rotate off the
visible disk in the next two days, while a new flux Region, visible
in STEREO Behind EIT imagery, is forecast to rotate onto the
southeast limb early on 19 April.
IIA. Geophysical Activity Summary 17/2100Z to 18/2100Z:
The geomagnetic field has been at quiet to unsettled levels for the
past 24 hours. Quiet levels were observed till around 18/0634Z when
a 24 nT Sudden Impulse (SI) was observed by the Boulder
magnetometer. Following the arrival of this shock, mostly unsettled
levels were observed at mid latitudes with isolated active periods
at high latitudes. This increase in activity was due to the arrival
of a slow moving CME, observed lifting off the solar disk on 15
April.
IIB. Geophysical Activity Forecast: The geomagnetic field is
expected to be at quiet levels on day 1 (19 April). An increase to
unsettled geomagnetic levels with a chance for active periods is
expected on days 2 and 3 (20-21 April), due to the forecasted
arrival of a coronal hole high speed stream.
III. Event Probabilities 19 Apr-21 Apr
Class M 20/20/20
Class X 01/01/01
Proton 01/01/01
PCAF Green
IV. Penticton 10.7 cm Flux
Observed 18 Apr 111
Predicted 19 Apr-21 Apr 115/115/115
90 Day Mean 18 Apr 104
V. Geomagnetic A Indices
Observed Afr/Ap 17 Apr 002/005
Estimated Afr/Ap 18 Apr 007/008
Predicted Afr/Ap 19 Apr-21 Apr 005/005-010/010-010/010
VI. Geomagnetic Activity Probabilities 19 Apr-21 Apr
A. Middle Latitudes
Active 10/35/25
Minor storm 01/10/05
Major-severe storm 01/01/01
B. High Latitudes
Active 10/40/30
Minor storm 01/15/10
Major-severe storm 01/00/01