NOAA SEC Report of Solar-Geophysical Activity 10 Apr 2001

:Product: Report of Solar-Geophysical Activity
:Issued: 2001 Apr 10 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 100 Issued at 2200Z on 10 Apr 2001
IA.  Analysis of Solar Active Regions and Activity from  09/2100Z
to 10/2100Z:  Solar activity remained at high levels. Region 9415
(S23W19) produced a long-duration X2/3b parallel-ribbon flare at
10/0526 UTC. This flare was associated with a 4000 SFU Tenflare,
Type II and IV radio sweeps, a 14-degree filament disappearance, and
a fast full-halo CME. Region 9415 showed decay in its trailer spots,
but maintained a strong magnetic delta configuration in its leader
portion, where a minor increase in spots was noted. Minor growth
occurred in Region 9417 (S08W39). It produced a C6/Sf at 10/1451
UTC. Minor growth was also observed in Region 9425 (S25W49). The
remaining regions were simply-structured and stable. No new regions
were assigned.
IB.  Solar Activity Forecast:  Solar activity is expected to be at
moderate to high levels. Region 9415 is expected to produce another
major flare during the period.
IIA.  Geophysical Activity Summary 09/2100Z to 10/2100Z:
Geomagnetic field activity ranged from quiet to active levels. A
greater than 10 MeV proton event followed today's X2/3b flare. It
began at 10/0850 UTC and was in progress as the period ended. The
greater than 10 MeV proton flux was near 100 PFU at the close of the
period and gradually increasing. A greater than 100 MeV proton flux
enhancement was also associated with the X2/3b flare. A polar cap
absorption (PCA) event began around 10/1200 UTC and continued as the
period ended. Thus far, maximum absorption associated with the PCA
event has been estimated at 8.5 dB. The greater than 2 MeV electron
flux reached high levels during the period.
IIB.  Geophysical Activity Forecast:  A major geomagnetic storm is
expected during 11 - 12 April in response to halo-CMEs observed on
09 - 10 April. Active to major storm levels are expected during this
disturbance with brief severe storm levels possible at high
latitudes. Unsettled to minor storm levels are expected on 13 April
as the storm subsides. The greater than 10 MeV proton event is
expected to continue through most of the period. The PCA event is
expected to end during the latter half of the period. The greater
than 2 MeV electron flux is expected to be at moderate to high
levels during the period.
III.  Event Probabilities 11 Apr-13 Apr
Class M    80/80/80
Class X    25/25/25
Proton     90/80/25
PCAF       In Progress
IV.  Penticton 10.7 cm Flux
Observed           10 Apr 170
Predicted   11 Apr-13 Apr  165/165/160
90 Day Mean        10 Apr 167
V.  Geomagnetic A Indices
Observed Afr/Ap 09 Apr  017/019
Estimated Afr/Ap 10 Apr  013/009
Predicted Afr/Ap 11 Apr-13 Apr  050/040-050/090-020/030
VI.  Geomagnetic Activity Probabilities 11 Apr-13 Apr
A.  Middle Latitudes
Active                15/15/35
Minor storm           25/25/15
Major-severe storm    45/45/10
B.  High Latitudes
Active                15/25/35
Minor storm           30/30/20
Major-severe storm    50/35/15