:Product: Weekly Highlights and Forecasts
:Issued: 1999 Sep 28 2112 UT
HIGHLIGHTS OF SOLAR AND GEOMAGNETIC ACTIVITY
20 - 26 SEPTEMBER 1999

SOLAR ACTIVITY RANGED FROM VERY LOW TO LOW LEVELS. THE VISIBLE DISK
WAS POPULATED BY A NUMBER OF SMALL, SIMPLY-STRUCTURED SUNSPOT GROUPS
WHICH PRODUCED B- AND C-CLASS SUBFLARES. THE LARGEST FLARE OF THE
WEEK WAS A C9/SF AT 21/0352UT ASSOCIATED WITH A WEAK TYPE II RADIO
SWEEP FROM REGION 8706 (N20, L=207, CLASS/AREA CSO/120 ON 20
SEPTEMBER).

REAL-TIME SOLAR WIND DATA WERE AVAILABLE FROM THE ADVANCED
COMPOSITION EXPLORER (ACE) SPACECRAFT FOR MOST OF THE PERIOD. THERE
WERE TWO DISTURBANCES DETECTED IN THE SOLAR WIND FLOW. THE FIRST
DISTURBANCE OCCURRED DURING 22 - 23 SEPTEMBER AND WAS ASSOCIATED
WITH A VELOCITY INCREASE (360 TO 630 KM/SEC), SOUTHWARD IMF BZ
DEFLECTIONS TO MINUS 20 NT (GSM), AND BRIEF INCREASES IN DENSITY AND
ION TEMPERATURE. THE SECOND DISTURBANCE WAS DETECTED ON 26 SEPTEMBER
AS A HIGH-SPEED CORONAL HOLE WIND STREAM PASSED THE SPACECRAFT. THE
DISTURBANCE WAS ACCOMPANIED BY A VELOCITY INCREASE FROM 390 TO 570
KM/SEC, A DROP IN PARTICLE DENSITIES, INTERVALS OF SOUTHWARD IMF BZ
WITH MAXIMUM DEFLECTIONS TO MINUS 12 NT (GSM), AND A SUSTAINED
PERIOD OF ELEVATED ION TEMPERATURES.

NO PROTON EVENTS WERE DETECTED AT GEO-SYNCHRONOUS ORBIT DURING THE
PERIOD.

THE GREATER THAN 2 MEV ELECTRON FLUX WAS AT MODERATE TO HIGH LEVELS
DURING 20 - 21 SEPTEMBER, THEN DECREASED TO NORMAL TO MODERATE
LEVELS FOR THE BALANCE OF THE PERIOD.

TWO GEOMAGNETIC FIELD DISTURBANCES WERE DETECTED DURING THE WEEK. THE
FIRST OCCURRED DURING 22 - 23 SEPTEMBER AND BEGAN WITH AN 08 NT
SUDDEN IMPULSE AT 22/1222UT FOLLOWED BY ACTIVE TO MAJOR STORM
PERIODS AT ALL LATITUDES AND BRIEF SEVERE STORM PERIODS AT HIGH
LATITUDES. THE SOLAR ORIGIN OF THIS DISTURBANCE WAS NOT READILY
DISCERNIBLE. THE SECOND DISTURBANCE BEGAN ON 26 SEPTEMBER AND WAS IN
PROGRESS AS THE PERIOD ENDED. ACTIVE TO MAJOR STORM LEVELS WERE
DETECTED DURING THIS DISTURBANCE WITH THE MAJOR STORM LEVELS LIMITED
TO HIGH LATITUDES. AN ISOLATED, TRANSEQUATORIAL CORONAL HOLE
(POSITIVE POLARITY) WAS THE SOURCE FOR THIS DISTURBANCE.

FORECAST OF SOLAR AND GEOMAGNETIC ACTIVITY
29 SEPTEMBER - 25 OCTOBER 1999

SOLAR ACTIVITY IS EXPECTED TO BE AT LOW TO MODERATE LEVELS. ISOLATED
M-CLASS FLARE ACTIVITY  MAY OCCUR AROUND 08 - 20 OCTOBER.

NO SIGNIFICANT PROTON EVENTS ARE EXPECTED AT GEO-SYNCHRONOUS ORBIT.

THE GREATER THAN 2 MEV ELECTRON FLUX AT GEO-SYNCHRONOUS ALTITUDE IS
EXPECTED TO BE AT MODERATE TO HIGH LEVELS DURING 29 SEPTEMBER - 01
OCTOBER, 10 - 18 OCTOBER, AND 24 - 25 OCTOBER. OTHERWISE, FLUXES ARE
EXPECTED TO BE IN THE NORMAL TO MODERATE RANGE.

GEOMAGNETIC FIELD ACTIVITY IS EXPECTED VARY FROM QUIET TO UNSETTLED
LEVELS DURING MOST OF THE PERIOD. HOWEVER, ACTIVE LEVELS ARE
POSSIBLE DURING 09 - 15 AND 23 - 24 OCTOBER DUE TO RECURRENT CORONAL
HOLE EFFECTS.


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