Joint USAF/NOAA Report of Solar and Geophysical Activity 20 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 20 2200 UTC

Joint USAF/NOAA Report of Solar and Geophysical Activity
SDF Number 111 Issued at 2200Z on 20 Apr 2012

IA. Analysis of Solar Active Regions and Activity from 19/2100Z
to 20/2100Z: Solar activity was low. New Region 1465 (S17E39 –
Dao/beta) emerged early in the period and showed significant growth.
It produced occasional C-class flares including a C1/1f
parallel-ribbon flare at 20/1501Z. Regions 1459 (S16E01 – Dai/beta),
1460 (N15W15 – Dkc/beta), and 1462 (S25W46 – Dho/beta) also showed
significant growth during the period. Region 1462 produced an
isolated C-class flare as it grew. There were no Earth-directed CMEs
during the period.

IB. Solar Activity Forecast: Solar activity is expected to be low
through the period (21 – 23 April) with a chance for an isolated
M-class flare.

IIA. Geophysical Activity Summary 19/2100Z to 20/2100Z:
Geomagnetic activity was at quiet to unsettled levels with brief
active periods at high latitudes. ACE solar wind data indicated the
minor increase in activity was due to a solar sector boundary
crossing (SSBC) at approximately 20/0700Z. The SSBC was associated
with increased IMF Bt (maximum 8 nT at 20/1059Z) and a period of
sustained southward IMF Bz (maximum deflections to -7 nT around
20/0400Z).

IIB. Geophysical Activity Forecast: Geomagnetic field activity is
expected to be at quiet levels during the first half of day 1 (21
April). Activity is forecast to increase to unsettled levels with a
chance for active levels beginning around 21/1500Z and continuing
into day 3 (23 April) due to expected glancing blows from the
partial-halo CMEs observed on 18 and 19 April. There will also be a
slight chance for minor storm levels on day 1.

III. Event Probabilities 21 Apr-23 Apr
Class M 30/30/30
Class X 01/01/01
Proton 01/01/01
PCAF green

IV. Penticton 10.7 cm Flux
Observed 20 Apr 142
Predicted 21 Apr-23 Apr 150/150/150
90 Day Mean 20 Apr 112

V. Geomagnetic A Indices
Observed Afr/Ap 19 Apr 005/005
Estimated Afr/Ap 20 Apr 007/007
Predicted Afr/Ap 21 Apr-23 Apr 014/015-011/012-010/012

VI. Geomagnetic Activity Probabilities 21 Apr-23 Apr
A. Middle Latitudes
Active 25/20/20
Minor storm 10/05/05
Major-severe storm 01/01/01
B. High Latitudes
Active 30/25/25
Minor storm 15/10/10
Major-severe storm 05/01/01