:Product: Weekly Highlights and Forecasts
:Issued: 2000 Sep 20 2112 UT
HIGHLIGHTS OF SOLAR AND GEOMAGNETIC ACTIVITY
11 - 17 SEPTEMBER 2000

SOLAR ACTIVITY VARIED FROM LOW TO HIGH LEVELS. ACTIVITY WAS LOW ON
THE FIRST DAY OF THE PERIOD WITH ISOLATED C-CLASS SUBFLARES.
ACTIVITY INCREASED TO MODERATE LEVELS ON 12 SEPTEMBER DUE TO A
LONG-DURATION M1/2N HYDER FLARE AT 12/1213 UTC. THE TWO-RIBBON HYDER
FLARE WAS ASSOCIATED WITH A 23-DEGREE FILAMENT ERUPTION FROM THE
SOUTH-CENTRAL PORTION OF THE DISK. SOHO/LASCO IMAGES SHOWED A HALO
CME FOLLOWING THE ERUPTION. ACTIVITY DECREASED TO LOW LEVELS ON 13
SEPTEMBER WITH ISOLATED, OPTICALLY UNCORRELATED C-CLASS X-RAY
FLARES. ACTIVITY RETURNED TO MODERATE LEVELS ON 14 SEPTEMBER DUE TO
AN M1 X-RAY FLARE FROM REGION 9166 (S14, L = 124, CLASS/AREA EAI/340
ON 17 SEPTEMBER) AS IT ROTATED INTO VIEW. REGION 9165 (N13, L = 186,
CLASS/AREA DKC/400 ON 15 SEPTEMBER) PRODUCED TWO M-CLASS FLARES ON
15 SEPTEMBER - AN M2/SF AT 15/0532 UTC AND AN M2/1N FLARE AT 15/1437
UTC ASSOCIATED WITH A 190 SFU TENFLARE. THESE FLARES OCCURRED AS
REGION 9165 WAS IN A PERIOD OF RAPID DEVELOPMENT. ACTIVITY BECAME
HIGH ON 16 SEPTEMBER WITH AN M5/2B FLARE AT 16/0426 UTC FROM REGION
9165, WHICH HAD BEGUN TO DECAY AND SIMPLIFY. THIS FLARE WAS
ASSOCIATED WITH A 1100 SFU TENFLARE, TYPE II AND IV RADIO SWEEPS,
AND A HALO CME. REGION 9165 ALSO PRODUCED AN M3/2N AT 16/1428 UTC IN
ADDITION TO NUMEROUS C-CLASS FLARES DURING THE COURSE OF THE DAY.
ACTIVITY DECREASED TO LOW LEVELS ON THE FINAL DAY OF THE PERIOD DUE
TO C-CLASS SUBFLARES, THE LARGEST OF WHICH WAS A C5/1F AT 17/0643
UTC FROM REGION 9167 (N12, L = 092, CLASS/AREA DSO/170 ON 17
SEPTEMBER), WHICH HAD ROTATED INTO VIEW AS A DEVELOPING D-TYPE SPOT
GROUP.

DATA WERE AVAILABLE FROM THE ADVANCED COMPOSITION EXPLORER (ACE)
SPACECRAFT FOR MOST OF THE PERIOD. THERE WERE FOUR DISTURBANCES
NOTED IN THE SOLAR WIND FLOW. THE FIRST WAS A SHORT-LIVED HIGH SPEED
STREAM OBSERVED DURING 12 - 13 SEPTEMBER WITH PEAK VELOCITIES NEAR
460 KM/SEC AND A SHIFT TO A TOWARD (NEGATIVE POLARITY) SOLAR SECTOR.
THE SECOND WAS A CME PASSAGE AT ACE AT AROUND 15/0300 UTC ASSOCIATED
WITH A MINOR VELOCITY INCREASE, AN INITIAL NORTHWARD TURNING OF THE
BZ COMPONENT OF THE IMF FOLLOWED BY A PERIOD OF MOSTLY SOUTHWARD BZ,
AND INCREASED DENSITIES. THE THIRD DISTURBANCE OCCURRED WITH THE
ONSET OF ANOTHER HIGH SPEED STREAM, WHICH BEGAN DURING THE LATTER
HALF OF 16 SEPTEMBER, ASSOCIATED WITH A VELOCITY INCREASE FROM 350
TO 580 KM/SEC, DECREASED DENSITIES, AND VARIABLE BZ IN THE PLUS TO
MINUS 9 NT (GSM) RANGE. THE FOURTH DISTURBANCE WAS DUE TO ANOTHER
CME PASSAGE AT ACE AT AROUND 17/1400 UTC. THIS PASSAGE WAS
ACCOMPANIED BY AN INITIAL NORTHWARD TURNING OF BZ FOLLOWED BY A
STRONG SOUTHWARD TURN AT AROUND 17/2000 UTC WITH MAXIMUM DEFLECTIONS
TO MINUS 34 NT, INCREASED DENSITIES, AND VELOCITIES BRIEFLY REACHING
AS HIGH AS 860 KM/SEC. VELOCITIES REMAINED ELEVATED AT THE CLOSE OF
THE PERIOD AS THE HIGH SPEED STREAM CONTINUED.

A GREATER THAN 10 MEV PROTON EVENT WAS DETECTED AT GEOSYNCHRONOUS
ORBIT FOLLOWING THE LONG-DURATION M1/2N HYDER FLARE OF 12 SEPTEMBER.
IT BEGAN AT 12/1555 UTC, REACHED A MAXIMUM OF 321 PFU AT 13/0340
UTC, AND ENDED AT 15/2140 UTC. A POLAR-CAP ABSORPTION EVENT FOLLOWED
THE PROTON EVENT. IT BEGAN AROUND 12/1830 UTC, REACHED A MAXIMUM OF
4.6 DB (AS MEASURED BY THE THULE RIOMETER) AT 13/0600 UTC, THEN
ENDED AT 14/1532 UTC. THE GREATER THAN 100 MEV PROTON ALSO BECAME
ENHANCED FOLLOWING THE HYDER FLARE, BUT NEVER REACHED EVENT LEVELS.

THE GREATER THAN 2 MEV ELECTRON FLUX AT GEOSYNCHRONOUS ORBIT WAS AT
NORMAL TO MODERATE LEVELS.

GEOMAGNETIC FIELD ACTIVITY WAS AT QUIET TO UNSETTLED LEVELS UNTIL
12/0900 UTC, THEN INCREASED TO ACTIVE TO MINOR STORM LEVELS DURING
12/0900 - 1500 UTC. ACTIVITY DECREASED TO QUIET TO ACTIVE LEVELS
AFTER 12/1500 UTC. MOSTLY QUIET TO UNSETTLED LEVELS PERSISTED
THROUGH EARLY 15 SEPTEMBER. A CME-RELATED SUDDEN IMPULSE OCCURRED AT
15/0510 UTC (36 NT, BOULDER USGS MAGNETOMETER) FOLLOWED BY UNSETTLED
TO ACTIVE LEVELS WITH MINOR STORM LEVELS AT HIGH LATITUDES, WHICH
CONTINUED THROUGH 16 SEPTEMBER. ANOTHER SUDDEN IMPULSE OCCURRED AT
17/0333 UTC (53 NT, BOULDER MAGNETOMETER) FOLLOWED BY ACTIVE TO
MINOR STORM LEVELS. ACTIVITY INCREASED TO MINOR TO SEVERE STORM
LEVELS AFTER 17/2100 UTC FOLLOWING A CME-RELATED SHOCK PASSAGE AT
ACE.

FORECAST OF SOLAR AND GEOMAGNETIC ACTIVITY
20 SEPTEMBER - 16 OCTOBER 2000

SOLAR ACTIVITY IS EXPECTED TO BE AT LOW TO MODERATE LEVELS. THERE
WILL ALSO BE A CHANCE EARLY IN THE PERIOD FOR ISOLATED MAJOR FLARE
ACTIVITY FROM REGION 9165.

A PROTON EVENT IS POSSIBLE AT GEOSYNCHRONOUS ORBIT DURING THE FIRST
HALF OF THE PERIOD.

THE GREATER THAN 2 MEV ELECTRON FLUX AT GEOSYNCHRONOUS ORBIT MAY
REACH MODERATE TO HIGH LEVELS DURING 21 - 23 SEPTEMBER. NORMAL TO
MODERATE LEVELS ARE EXPECTED FOR THE REST OF THE PERIOD.

GEOMAGNETIC FIELD ACTIVITY IS EXPECTED TO BE AT ACTIVE TO MINOR STORM
LEVELS DURING 20 - 21 SEPTEMBER. QUIET TO UNSETTLED LEVELS ARE
EXPECTED DURING THE REST OF THE PERIOD, BARRING AN EARTH-DIRECTED
CME.


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