:Product: Weekly Highlights and Forecasts
:Issued: 2001 Oct 02 2112 UT
Highlights of Solar and Geomagnetic Activity
24 - 30 September 2001

Solar activity reached high levels for the fourth consecutive week.
The period began with activity at high levels due to an X2/2b flare
at 24/1038 UTC from Region 9632 (S18, L = 272, class/area Dki/790 on
24 September) associated with a 7500 SFU Tenflare, a Type IV radio
sweep, a fast full-halo CME, and a solar proton event (see the
description below).  This region was large and magnetically complex
through the period. It began to gradually decay on 29 September and
was approaching the west limb as the period ended. Activity remained
high on 25 September due to an M7/1n flare at 25/1027 UTC from
Region 9628 (S18, L = 292, class/area Fkc/880 on 25 September)
associated with a Type II radio sweep. This region also produced
isolated, low-level M-class flares during the period (for flare
specifics, please refer to the Energetic Events and Optical Flare
lists). Region 9628 began to gradually decay on 29 September, though
it remained large and magnetically complex as it began crossing the
west limb at the close of the period. Region 9636 (N14, L = 227,
class/area Eai/400 on 26 September), a moderately complex,
reversed-polarity sunspot group; produced isolated M-class flares
during the period including a long-duration M3/2n flare at 28/0830
UTC associated with Type II and IV radio sweeps and a partial-halo
CME. The daily (Penticton) 10.7 cm solar radio flux readings of 279
sfu on 24 September and 283 sfu on 26 September were the highest
observed since the start of Cycle 23.

Solar Wind data were available from the NASA Advanced Composition
Explorer (ACE) spacecraft for most of the period. SWEPAM data
(speed, density, and temperature) were unreliable during 26/1600 -
27/1000 UTC due to proton contamination. A few CME passages and a
possible high-speed stream occurred during the period. A CME front
passed the ACE spacecraft beginning at about 25/2000 UTC. IMF Bz
varied rapidly following the passage with a range of plus 20 to
minus 17 nT (GSM) before turning north at around 26/0900 UTC.
Velocities were elevated and densities were low during 27 - 29
September, possibly due to a positive-polarity coronal hole. Another
CME passage began around 29/0830 UTC accompanied by increased
velocities (peak to 750 km/sec) and increased IMF Bz variability
(plus 13 to minus 12 nT). Another CME passed the spacecraft
beginning around 30/1848 UTC associated with increased velocity
(brief peak to 570 km/sec), total IMF field intensity, density, and
temperature. IMF Bz was variable in the plus to minus 15 nT range
following this passage.

Proton events at greater than 100 MeV and greater than 10 MeV
followed the X2 flare on 24 September. The greater than 100 MeV
event began at 24/1440 UTC, reached a maximum of 31.2 PFU at 25/0755
UTC, and ended at 26/1940 UTC. The greater than 10 MeV event began
at 24/1215 UTC, reached a maximum of 12,900 PFU at 25/2235 UTC, then
ended at 30/1710 UTC.

The greater than 2 MeV electron flux at geosynchronous orbit ranged
from normal to moderate levels during most of the period. However,
there were brief periods of high fluxes observed on 28 September.

The geomagnetic field was quiet until late on 25 September. A
CME-induced sudden impulse occurred at 25/2025 UTC (25 nT, as
measured by the Boulder USGS magnetometer) followed by active to
(brief) major storm levels. Activity declined to quiet to unsettled
levels during the latter half of 26 September. Quiet to unsettled
levels prevailed until early 29 September. Another CME-induced
disturbance began on 29 September with a sudden impulse at 29/0940
UTC (17 nT, as measured by the Boulder USGS magnetometer) followed
by active to major storm levels. Active conditions also occurred
late on 30 September, following another CME passage at Earth.

Forecast of Solar and Geomagnetic Activity
03 - 29 October 2001

Solar activity is expected to range from low to high levels. Isolated
M-class flares are expected. There will be a fair chance for
isolated major flare activity during the period.

A greater than 10 MeV proton event began on 01 October and was in
progress as the period began (details will be provided in next
week's issue). It is expected to end on 03 October. There will be a
slight chance for another 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. However, high flux levels will be possible around 28
October.

Active periods will be possible during 12 and 25 - 26 October due to
recurrent coronal hole effects. Quiet to unsettled conditions are
expected during the remainder of the period.


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