:Product: Weekly Highlights and Forecasts
:Issued: 2001 Apr 03 2112 UT
Highlights of Solar and Geomagnetic Activity
26 March - 01 April 2001

Solar activity was at moderate to high levels. Activity was moderate
during 26 - 27 March due to isolated low-level M-class flares from
Regions 9393 (N17, L = 151, class/area Fkc/2440 on 29 March) and
9401 (N21, L = 134, class/area Eki/230 on 30 March). Region 9393
exhibited rapid growth through 29 March and became the largest spot
group observed during Cycle 23. The region began to gradual decay on
30 March, but remained extremely large and structurally complex
through the end of the period. Solar activity rose to high levels on
29 March as Region 9393 produced an X1/1n at 29/1015 UTC associated
with a 4700 sfu Tenflare, a solar proton event (see the description
below), and a full-halo CME. Region 9393 also produced numerous
low-level M-class flares during the period including an M4/Sf at
28/1240 UTC associated with a full-halo CME (please refer to the
Energetic Events listing for flare times). Activity decreased to
moderate levels during 30 - 31 March with isolated M-class flares
from Region 9393. Activity returned to high levels on 01 April due
to an M5 X-ray flare at 01/1217 UTC from a source just beyond the
southeast limb. Bright post-flare loops were seen at SE25 following
this flare as well as a spectacular non-Earth-directed CME. Note:
prior to publication of this report, Region 9393 produced the
largest X-ray event seen so far this cycle, with an estimated
magnitude of X20 at 02/2150 UTC; details will be provided in next
week's issue.

Data were available from the Advanced Composition Explorer (ACE)
spacecraft for most of the period. Multiple CME passages occurred
during the period. There were two passages on 27 March with CME
shock fronts observed at 27/0108 UTC and 27/1745 UTC.  A third CME
shock front was observed at 31/0023 UTC. This, by far, was the most
geoeffective of the three CMEs, with the following changes noted in
the solar wind flow: increased velocities with "gusts" to 830
km/sec, a strong jump in IMF total field intensity (to 73 nT),
increased densities, and prolonged periods of southward IMF Bz with
deflections as high as minus 46 nT (GSM).

A greater than 10 MeV proton event followed the X1/1n flare on 29
March. The event began at 29/1635 UTC, reached a peak of 35 PFU at
30/0610 UTC, and ended at 01/0600 UTC. Estimated maximum polar-cap
absorption associated with this event was 1.8 dB.

The greater than 2 MeV electron flux at geosynchronous orbit was at
normal to moderate levels.

The geomagnetic field was disturbed during most of the period due to
a number of CME passages. Field activity increased during 27 - 29
March with unsettled to minor storm periods at all latitudes and
major storm periods at high latitudes. Activity decreased to mostly
quiet to unsettled levels on 30 March. A severe geomagnetic storm
occurred during 31 March beginning with a sudden storm commencement
at 31/0051 UTC (114 nT, as measured by the Boulder USGS
magnetometer). Major to severe storm levels occurred at all
latitudes during this storm. Several magnetopause crossings were
detected by the GOES magnetometer as well. The final planetary
A-index for 31 March was 192. The storm began to subside on 01 April
with minor to major storm periods detected until 01/0900 UTC
followed by quiet to active conditions.

Forecast of Solar and Geomagnetic Activity
04 - 30 April 2001

Activity is expected to range from moderate to high levels during the
period. Region 9393 is expected to produce more major flares before
it crosses the west limb around 05 April. New Region 9415 (S22, L =
359, class/area Dko/470 on 03 April), which was the apparent source
for the M5 X-ray flare on 01 April, may also produce major flares
during the period.

Solar proton events at greater than 10 MeV and greater than 100 MeV
were in progress at issue time following the X20 flare of 02 April.
The proton event at greater than 100 MeV is expected to end late on
03 April while the greater than 10 MeV event is expected to continue
for the next couple days. Region 9393 may produce another proton
event before crossing the west limb. Region 9415 could also produce
a proton event during the period.

The greater than 2 MeV electron flux at geosynchronous orbit is
expected to be at normal to moderate levels during most of the
period.

Geomagnetic storm conditions are expected during 04 - 06 April in
response to recent major flares and accompanying halo-CMEs.
Unsettled conditions are expected during the rest of the period,
barring additional Earth-directed CME occurrences.


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