:Product: Weekly Highlights and Forecasts
:Issued: 2001 Apr 10 2112 UT
Highlights of Solar and Geomagnetic Activity
02 - 08 April 2001

Solar activity reached high levels for the third consecutive week!
Region 9393 (N17, L = 151, class/area Fkc/2440 on 29 March) produced
two X-class flares on 02 April while crossing the west limb. One of
these flares, an X20 at 02/2151 UTC (X-ray peak estimated due to
GOES SRS saturation), had the largest X-ray magnitude seen to date
in Cycle 23. The X20 was associated with a 10,000 SFU Tenflare, a
partial-halo CME, and a solar proton event (see the discussion
below). Region 9393 also holds the distinction of being the largest
sunspot group yet seen during Cycle 23. Region 9415 (S21, L - 001,
class/area Eko/880 on 07 April) rotated into view just as Region
9393 was departing the disk. Region 9415 was an able successor to
Region 9393: it produced three major flares during the period, the
largest of which was an X5/Sf  (optical flare designation uncertain)
at 1921 UTC on 06 April (see the Energetic Event Summary for flare
times). Halo CMEs were associated with each of these major flares.
Region 9415 was also responsible for an M5 X-ray flare on 01 April,
a day before it rotated into view. It is currently near center disk,
classified as a large, magnetically complex (beta-gamma-delta)
E-type spot group with a strong persistent delta magnetic
configuration in its leader spots. Note: Region 9415 produced
additional major flares during 09 - 10 April; details will provided
in next week's issue.

Data were available from the Advanced Composition Explorer (ACE)
spacecraft for most of the period. Three CME passages occurred
during the period associated with major flare activity in Regions
9393 and 9415. The first CME, likely associated with an X-class
flare from Region 9393 on 02 April, reached the ACE spacecraft at
04/1422 UTC and caused abrupt increases in velocity, density,
temperature, IMF field intensity, and IMF Bz variability. Solar wind
speeds were as high as 800 km/sec with this passage. The second CME,
likely associated with an M5 flare from Region 9415 on 05 April,
reached ACE at 07/1700 UTC and caused relatively modest changes in
velocity, density, temperature, and Bz. The third CME, associated
with an X5 flare from Region 9415 on 06 April, reached ACE at
08/1034 UTC causing sudden increases in velocity (peak around 670
km/sec), IMF field intensity, temperature, Bz variability, and
density.

Greater than 10 MeV and greater than 100 MeV proton events followed
the X20 flare of 02 April. The greater than 10 MeV event began at
02/2340 UTC, reached a peak of 1110 PFU at 03/0740 UTC, and ended at
06/1340 UTC. The greater than 10 MeV proton flux remained at
enhanced levels for the rest of the period. The greater than 100 MeV
proton event began at 03/0120 UTC, reached a peak of 5.4 PFU at
03/0740 UTC, and ended at 03/2025 UTC.

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

The geomagnetic field was intermittently disturbed during the period
due to the CME passages mentioned above. The 04 April passage caused
unsettled to minor storm conditions during 04 - 05 April. Active to
major storm conditions occurred during the CME passages on 07 - 08
April.

Forecast of Solar and Geomagnetic Activity
11 April - 07 May 2001

Solar activity is expected to range from moderate to high levels
during the period. Region 9415 is expected to produce more major
flares before it rotates to the far side of the Sun on 16 April.
Isolated major flares will be possible during the rest of the period
due to the expected return of active longitudes associated with old
Region 9393 and Region 9415.

A solar proton event at greater than 10 MeV was in progress as the
period ended and is expected to continue for the next two days.
Additional proton events at greater than 10 and greater than 100 MeV
will be possible 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 field activity is expected to be at active to major
geomagnetic storm levels during 11 - 12 April in response to recent
major flares and accompanying halo-CMEs from Region 9415. Quiet to
active conditions are expected during the rest of the period.

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