NOAA SEC Report of Solar-Geophysical Activity 28 Apr 2001
:Product: Report of Solar-Geophysical Activity
:Issued: 2001 Apr 28 2200 UT
# Prepared jointly by the U.S. Dept. of Commerce, NOAA,
#Space Environment Center and the U.S. Air Force.
Joint USAF/NOAA Report of Solar and Geophysical Activity
SDF Number 118 Issued at 2200Z on 28 Apr 2001
IA. Analysis of Solar Active Regions and Activity from 27/2100Z
to 28/2100Z: Solar activity dropped to low levels. Region 9433
(N17W50) produced isolated C-class flares, the largest of which was
a C7/1f at 28/0934 UTC. Gradual decay continued in the leading and
intermediate portions of this region. However, no decay was evident
within its trailing spots, where a strong magnetic delta
configuration remained. Region 9441 (N07E23) continued a gradual
growth phase that began on 27 April, but the region remained a
moderate-sized, simply-structured bipole. New Regions 9444 (S11E67)
and 9445 (N23E76) were assigned.
IB. Solar Activity Forecast: Solar activity is expected to be at
moderate to high levels. Region 9433 is expected to produce isolated
M-class flares. This region could also produce an isolated major
flare during the period.
IIA. Geophysical Activity Summary 27/2100Z to 28/2100Z:
Geomagnetic field activity ranged from quiet to minor storm levels.
An interplanetary shock at the leading edge of a CME passed the ACE
spacecraft at 28/0432 UTC, followed by a sudden impulse (SI) at
28/0520 UTC (76 nT, as measured by the Boulder USGS magnetometer).
The source for the CME was an M7/2b flare on 26 April. Field
activity increased to unsettled to minor storm levels following the
SI. The greater than 10 MeV proton flux at geosynchronous orbit
briefly crossed event threshold in response to the shock passage.
The greater than 10 MeV event began at 28/0430 UTC, reached a
maximum of 57 PFU at 28/0500 UTC, then ended at 28/0520 UTC. Proton
fluxes had decreased to near background levels by the close of the
IIB. Geophysical Activity Forecast: Geomagnetic field activity is
expected to be at unsettled to active levels through midday, 29
April as the disturbance gradually subsides. Quiet to unsettled
levels are expected for the remainder of the period. Region 9433
could produce another proton flare before it crosses the west limb
on 02 May. The greater than 2 MeV electron flux at geosynchronous
orbit may reach high levels during the first half of the period.
III. Event Probabilities 29 Apr-01 May
Class M 75/75/75
Class X 20/20/20
IV. Penticton 10.7 cm Flux
Observed 28 Apr 188
Predicted 29 Apr-01 May 185/180/175
90 Day Mean 28 Apr 167
V. Geomagnetic A Indices
Observed Afr/Ap 27 Apr 003/006
Estimated Afr/Ap 28 Apr 026/028
Predicted Afr/Ap 29 Apr-01 May 015/015-012/010-010/010
VI. Geomagnetic Activity Probabilities 29 Apr-01 May
A. Middle Latitudes
Minor storm 15/10/10
Major-severe storm 10/05/01
B. High Latitudes
Minor storm 20/15/10
Major-severe storm 15/10/05