:Product: Weekly Highlights and Forecasts
:Issued: 1999 Sep 21 2112 UT
HIGHLIGHTS OF SOLAR AND GEOMAGNETIC ACTIVITY
13 - 19 SEPTEMBER 1999

SOLAR ACTIVITY WAS PREDOMINATELY LOW WITH A SINGLE MODERATE EVENT
OCCURRING DURING THE PERIOD. REGION 8690 (N16, L=025, CLASS/AREA
EAO/310 ON 17 SEPTEMBER) PRODUCED AN M1/SF FLARE AT 17/0120UT. A
PARTIAL-HALO CORONAL MASS EJECTION (CME) WAS OBSERVED BY THE
LASCO/SOHO SPACECRAFT FOLLOWING A 50-DEGREE DISAPPEARING SOLAR
FILAMENT (DSF) THAT OCCURRED 16/1508-1615UT. REGION 8699 (N23,
L=003, CLASS/AREA ESO/170 ON 19 SEPTEMBER) SHOWED RAPID GROWTH AT
THE BEGINNING OF THE PERIOD, AND THEN STABILIZED FOR THE REMAINDER,
PRODUCING MINOR C-CLASS SUBFLARES. THE OTHER REGION OF NOTE WAS
REGION 8700 (N12, L=290, CLASS/AREA DRI/070 ON 19 SEPTEMBER) WHICH
DEVELOPED A MIXED POLARITY SUNSPOT GROUP AND PRODUCED NUMEROUS
C-CLASS FLARES.

REAL-TIME SOLAR WIND DATA WERE AVAILABLE FROM THE ADVANCED
COMPOSITION EXPLORER (ACE) SPACECRAFT FOR MOST OF THE PERIOD. THE
MAJORITY OF THE PERIOD WAS DOMINATED BY HIGH SPEED CORONAL HOLE
CONDITIONS. WIND SPEEDS WERE HIGH, RANGING FROM 550 TO 650 KM/SEC
UNTIL SEPTEMBER 19TH WHEN THE WIND SPEED DROPPED TO 410 KM/SEC. IMF
BZ FLUCTUATED BETWEEN NORTHWARD AND SOUTHWARD FOR MOST OF THE WEEK
WITH PROLONGED PERIODS OF PREDOMINATELY SOUTHWARD CONDITIONS. ACE
REAL-TIME SOLAR WIND MEASUREMENTS INDICATED THE ARRIVAL OF A HIGH
SPEED SHOCK AT 15/0700UT. AT THAT TIME THE WIND SPEED INCREASED TO
700 KM/SEC WITH A SHORT PERIOD OF SUSTAINED SOUTHWARD BZ THAT
REACHED A MAXIMUM OF MINUS 15 NT. THIS EVENT WAS FOLLOWED BY A
SUDDEN IMPULSE AT EARTH AT 15/2019UT (8 NT, AS MEASURED BY THE
BOULDER USGS MAGNETOMETER).

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

THE GREATER THAN 2 MEV ELECTRON FLUX ROSE TO HIGH LEVELS FROM
SEPTEMBER 17-19.

THE GEOMAGNETIC FIELD WAS AT QUIET TO MINOR STORM CONDITIONS, WITH
MINOR TO MAJOR CONDITIONS OCCURRING AT HIGH LATITUDES. THESE
CONDITIONS WERE ASSOCIATED WITH A HIGH-SPEED CORONAL HOLE STREAM.
CONDITIONS ON SEPTEMBER 15 INCREASED TO MINOR STORM LEVELS AT MID
LATITUDES AND SEVERE STORMING AT HIGH LATITUDES IN CONJUNCTION WITH
THE HIGH SPEED SHOCK DISCUSSED ABOVE. THE EFFECTS OF THE HIGH SPEED
STREAM BEGAN TO DIMINISH ON SEPTEMBER 19TH WITH QUIET TO UNSETTLED
CONDITIONS.

FORECAST OF SOLAR AND GEOMAGNETIC ACTIVITY
22 SEPTEMBER - 18 OCTOBER 1999

SOLAR ACTIVITY IS EXPECTED TO RANGE FROM LOW TO MODERATE LEVELS WITH
A SLIGHT CHANCE FOR MAJOR FLARES.

THERE WILL BE A SLIGHT FOR A PROTON EVENT AT GEO-SYNCHRONOUS ORBIT.

THE GREATER THAN 2 MEV ELECTRON FLUX AT GEO-SYNCHRONOUS ALTITUDE IS
EXPECTED TO BE AT MODERATE TO HIGH LEVELS.

GEOMAGNETIC FIELD ACTIVITY IS EXPECTED VARY FROM QUIET TO UNSETTLED
LEVELS DURING MOST OF THE PERIOD.

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