Solar Terrestrial Activity Report

Last update August 12, 1999 at 04:00 UTC.

Recent development

The geomagnetic field was quiet to unsettled on August 11. Solar wind speed
ranged between 328 to 431 km/sec.

Solar flare activity was low. Solar flux was 127.9, the planetary A index
was 8 (3-hour K indices: 3312 2232, Boulder K indices: 2212 1222). Region
8657 was quiet and stable. Region 8661 decayed into spotless plage. Region
8662 did not change significantly and was quiet. The region could produce a
minor M flare. New region 8665 rotated into view at the southeast limb.
(The NOAA/SEC sunspot number of 76 is the lowest since April 26, 1999.) An
active region just behind the northeast limb should rotate into view in
about 2 days' time.

Flares and CMEs

Only 1 C class event was observed on August 11. It was a long duration C1.5
event associated with a prominence eruption near the northeast limb. A
large CME was observed off the northwest limb in connection with another
long duration event behind the northwest limb very early on August 12.
Several filaments in the southeast quadrant erupted during the day. A
partial halo CME was observed over the east limb and the south pole
starting at 06:06 UTC. Another partial halo CME covering at least nearly
all of the southern hemisphere and a part of the northwest limb was
observed starting at 15:55 in LASCO C2 (by that time the leading edge of
the CME had already expanded well past the solar limbs). This CME was
likely associated with LASCO EIT observed eruptive activity in filament(s)
to the north and northeast of region 8662, near the central meridian. The
CME could impact the earth sometime from late on August 14 to late on
August 15.

The background x-ray flux is at the class B5 level.

Coronal holes

A fairly small coronal hole in the southern hemisphere will likely rotate
into a geoeffective position on August 16-17.

Forecast

The geomagnetic field is expected to be quiet to unsettled on August 12-13.
Low frequency (below 2 MHz) radio wave propagation along east-west paths
over high and upper middle latitudes is fair to poor.

 Coronal holes (1)       Coronal mass      M and X class flares (3)
                         ejections (2)


1) Effects from a coronal hole could reach earth within the next 5 days.
2) Material from a CME is likely to impact earth within 96 hours.
3) There is a possibility of either M or X class flares within the next 48
hours.

Green: 0-20% probability, Yellow: 20-60% probability, Red: 60-100%