Joint USAF/NOAA Report of Solar and Geophysical Activity 21 April 2012

Prepared jointly by the U.S. Dept. of Commerce, NOAA,
Space Weather Prediction Center and the U.S. Air Force.
Updated 2012 Apr 21 2200 UTC

Joint USAF/NOAA Report of Solar and Geophysical Activity
SDF Number 112 Issued at 2200Z on 21 Apr 2012

IA. Analysis of Solar Active Regions and Activity from 20/2100Z
to 21/2100Z: Solar activity was low. Regions 1460 (N16W27 –
Dkc/beta) and 1465 (S17E27 – Dso/beta) each produced a low-level
C-class flare. Region 1460 showed minor interior spot growth and
some mixed polarities in its trailer portion. Minor interior spot
growth also occurred in Region 1465 as well as penumbral growth in
its trailer. Region 1459 (S14W13 – Eac/beta) showed penumbral growth
in its interior portion and maintained a simple beta magnetic
configuration. No Earth-directed CMEs were observed during the
period. No new regions were numbered.

IB. Solar Activity Forecast: Solar activity is expected to be low
during the period (22 – 24 April) with a chance for an isolated
M-class flare.

IIA. Geophysical Activity Summary 20/2100Z to 21/2100Z:
Geomagnetic field activity was at quiet levels until around 21/1900Z,
then increased to quiet to unsettled levels. The increase was
associated with a weak interplanetary shock (IPS) passage, detected
at ACE at around 21/1611Z, and followed by a weak geomagnetic field
response at around 21/1712Z (no Sudden Geomagnetic Impulse
observed). ACE solar wind data showed a change to mostly southward
IMF Bz following the IPS passage (maximum deflections to -8 nT) as
well as a gradual increase in IMF Bt (peaks to 9 nT). A minor
increase in wind speeds also followed the IPS passage. It is likely
the CME passage was associated with the partial-halo CME observed on
18 April.

IIB. Geophysical Activity Forecast: Geomagnetic field activity is
expected to be at quiet to unsettled levels during the period (22 –
24 April) with a chance for active levels. Weak CME-passage effects
are expected during 22 – 23 April (another CME is expected to arrive
late on 22 April). A recurrent coronal hole high-speed stream is
expected to become geoeffective on 24 April.

III. Event Probabilities 22 Apr-24 Apr
Class M 30/30/30
Class X 01/01/01
Proton 01/01/01
PCAF green

IV. Penticton 10.7 cm Flux
Observed 21 Apr 149
Predicted 22 Apr-24 Apr 150/150/145
90 Day Mean 21 Apr 112

V. Geomagnetic A Indices
Observed Afr/Ap 20 Apr 007/008
Estimated Afr/Ap 21 Apr 006/007
Predicted Afr/Ap 22 Apr-24 Apr 011/012-010/010-010/010

VI. Geomagnetic Activity Probabilities 22 Apr-24 Apr
A. Middle Latitudes
Active 20/20/25
Minor storm 10/10/15
Major-severe storm 01/01/01
B. High Latitudes
Active 25/25/35
Minor storm 15/15/25
Major-severe storm 05/05/10