:Product: Weekly Highlights and Forecasts
:Issued: 2001 May 02 2112 UT
Highlights of Solar and Geomagnetic Activity
23 - 29 April 2001

Solar activity ranged from low to high levels. Region 9433 (N17, L =
153, class/area Fki/1070 on 25 April) produced low-level M-class
flares through 25 April as it showed gradual spot growth within its
interior and trailing portions (a magnetic delta configuration
persisted in the trailer portion through the period). Activity
reached high levels on 25 April by virtue of five low-level M-class
flares from Region 9433, all of which were impulsive. Activity
increased to high levels again on 26 April as Region 9433 produced
the sole major flare of the period: an M7/2b at 26/1312 UTC with an
associated 360 SFU Tenflare, and Type II and IV radio sweeps.
SOHO/LASCO images also showed a full-halo coronal mass ejection
(CME) associated with this flare. Region 9433 entered a gradual
decay phase following the major flare, exhibiting gradual loss of
spots in the leading and intermediate portions of the group.
However, the trailer portion of the region remained complex as the
delta persisted through the remainder of the period. Activity
declined to moderate levels on 27 April with isolated low-level
M-class flares from Region 9433. Activity dropped to low levels on
28 April and remained so for the balance of the period with isolated
C-class subflares, mostly from Regions 9433 and 9441 (N08, L = 078,
class/area Dai/190 on 29 April). Region 9441 produced isolated
C-class subflares during a minor growth phase that occurred during
27 - 29 April, followed by gradual decay during the rest of the
period. Region 9433 began to cross the west limb at the close of the
period.

Data were available from the Advanced Composition Explorer (ACE)
spacecraft for most of the period. A CME passage occurred during 28
- 29 April. The CME shock front reached the ACE spacecraft at
28/0342 UTC. The frontal passage was followed by abrupt increases in
velocity (peak to 810 km/sec shortly following the passage) and
total IMF intensity, along with a modest increase in densities. IMF
Bz was initially variable following the shock passage, then turned
mostly southward during 28/0900 - 1500 UTC with maximum southerly
deflections to minus 18 nT (GSM). CME effects gradually subsided
during 29 April.

A proton enhancement at greater than 10 MeV occurred during 26 - 27
April in the wake of the M7/2b flare of 26 April. A brief greater
than 10 MeV proton event occurred on 28 April associated with the
shock passage mentioned above. The event began at 28/0430 UTC,
reached a maximum of 57 PFU at 28/0500 UTC, and ended at 28/0520
UTC. Proton fluxes returned to background levels on 29 April.

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

The geomagnetic field was disturbed on 28 - 29 April due to the CME
passage described above. The disturbance began with a sudden impulse
at 28/0503 UTC (76 nT, as measured by the Boulder USGS magnetometer)
followed by unsettled to major storm levels. The disturbance ended
around midday on 29 April. Quiet to unsettled conditions occurred
during the remainder of the period.

Forecast of Solar and Geomagnetic Activity
02 - 28 May 2001

Solar activity is expected to range from low to moderate levels
during the period. Isolated M-class flares will be possible during
the period.

No proton events are expected 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.

The geomagnetic field is expected to be disturbed around 4 May due
to coronal hole effects. Unsettled to active conditions will be
possible during this disturbance. Quiet to unsettled levels are
expected during the remainder of the period, barring an
Earth-directed CME.


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