Joint USAF/NOAA Report of Solar and Geophysical Activity 17 September 2011

:Product: Report of Solar-Geophysical Activity
:Issued: 2011 Sep 17 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 260 Issued at 2200Z on 17 Sep 2011
IA. Analysis of Solar Active Regions and Activity from 16/2100Z
to 17/2100Z: Solar activity was low during the past 24 hours.
Regions 1289 (N22W67) and 1290 (S13W84) each produced C-class
events, the largest a long duration C2 event from Region 1289 at
16/2351Z. An associated CME first became visible on LASCO C2 imagery
at 16/2348Z and had an estimated plane-of-sky speed of 575 km/s.
Further analysis will be conducted to determine geoeffectiveness.
IB. Solar Activity Forecast: Solar activity is expected to be low
with a chance for isolated M-class flares for the next three days
(18-20 September).
IIA. Geophysical Activity Summary 16/2100Z to 17/2100Z:
The geomagnetic field was quiet until approximately 17/0400Z when
effects from the 14 September CME arrived at Earth. A shock was
observed at ACE at 17/0256Z which was followed by a sudden impulse
of 21 nT observed by the Boulder magnetometer. Solar wind speeds
increased from approximately 350 km/s to 450 km/s along with a
noticeable increase in temperature and density. The interplanetary
magnetic field Bt reached +14 nT and there were several extended
periods of southward Bz with a maximum deviation of -12 nT.
Conditions at Earth increased to active levels following shock
arrival with an isolated minor storm period at 17/1800Z. Solar wind
speeds peaked at 550 km/s around 17/1115Z but have since decreased
to approximately 450 km/s. The greater than 2 MeV electron flux at
geosynchronous orbit reached high levels during the period.
IIB. Geophysical Activity Forecast: The geomagnetic field is
expected to be quiet to unsettled with a slight chance for isolated
active periods on day one (18 September) as effects from the 14
September CME subside. Mostly quiet conditions are expected for days
two and three (19-20 September).
III. Event Probabilities 18 Sep-20 Sep
Class M 30/35/35
Class X 01/01/01
Proton 01/01/01
PCAF green
IV. Penticton 10.7 cm Flux
Observed 17 Sep 145
Predicted 18 Sep-20 Sep 145/145/145
90 Day Mean 17 Sep 102
V. Geomagnetic A Indices
Observed Afr/Ap 16 Sep 002/002
Estimated Afr/Ap 17 Sep 023/032
Predicted Afr/Ap 18 Sep-20 Sep 010/010-005/005-005/005
VI. Geomagnetic Activity Probabilities 18 Sep-20 Sep
A. Middle Latitudes
Active 20/10/05
Minor storm 10/01/01
Major-severe storm 01/01/01
B. High Latitudes
Active 25/15/05
Minor storm 15/05/01
Major-severe storm 01/01/01