:Product: Weekly Highlights and Forecasts
:Issued: 1999 May 18 2112 UT
HIGHLIGHTS OF SOLAR AND GEOMAGNETIC ACTIVITY
10 - 16 MAY 1999

SOLAR ACTIVITY RANGED FROM VERY LOW TO MODERATE LEVELS. SMALL- TO
MEDIUM-SIZED SUNSPOT GROUPS POPULATED THE DISK DURING THE PERIOD,
ALL OF WHICH WERE UNREMARKABLE IN TERMS OF STRUCTURE OR DYNAMICS. B-
AND C-CLASS SUBFLARES OCCURRED DURING MOST DAYS. ISOLATED, LOW-LEVEL
M-CLASS FLARES OCCURRED ON THE FIRST AND LAST DAYS OF THE PERIOD.
ONE OF THESE, AN M2/2N FROM REGION 8539 (N13, L=227, CLASS/AREA
DSO/050 ON 08 MAY) AT 10/0531UT, WAS ASSOCIATED WITH A TYPE IV RADIO
SWEEP AND A FULL-HALO CME.

REAL-TIME SOLAR WIND DATA WERE AVAILABLE FROM THE ADVANCED
COMPOSITION EXPLORER (ACE) SPACECRAFT FOR MOST OF THE PERIOD. A
CORONAL MASS EJECTION PASSAGE OCCURRED DURING 12 - 13 MAY. THE
PASSAGE CAUSED A VELOCITY INCREASE FROM 310 - 540 KM/SEC, INCREASED
IMF BZ VARIABILITY WITH MAXIMUM SOUTHERLY EXCURSIONS TO MINUS 14 NT
(GSM), A SHIFT TO A PREDOMINANTLY TOWARD (NEGATIVE POLARITY) SOLAR
SECTOR, AND A DENSITY INCREASE TO 30 P/CC.

A GREATER THAN 10 MEV PROTON FLUX ENHANCEMENT AT GEO-SYNCHRONOUS
ORBIT WAS IN PROGRESS AT THE START OF THE PERIOD (THE SOURCE WAS AN
M7 FLARE ON 09 MAY). THE ENHANCEMENT DECLINED TO BACKGROUND LEVELS
BY 10 MAY, THEN REMAINED SO FOR THE REST OF THE PERIOD.

THE GREATER THAN 2 MEV ELECTRON FLUX AT GEO-SYNCHRONOUS ORBIT WAS AT
MODERATE TO HIGH LEVELS THROUGH 12 MAY, THEN DECREASED TO NORMAL
LEVELS FOR THE BALANCE OF THE PERIOD.

THE GEOMAGNETIC FIELD WAS DISTURBED ON 13 MAY, MOST LIKELY IN
RESPONSE TO THE HALO-CME MENTIONED ABOVE. ACTIVE TO MINOR STORM
STORM LEVELS OCCURRED AT ALL LATITUDES DURING THE DISTURBANCE WITH
BRIEF MAJOR STORM PERIODS DETECTED AT HIGH LATITUDES. QUIET TO
UNSETTLED CONDITIONS PREVAILED DURING THE REST OF THE PERIOD.

FORECAST OF SOLAR AND GEOMAGNETIC ACTIVITY
19 MAY - 14 JUNE 1999

SOLAR ACTIVITY IS EXPECTED TO RANGE FROM LOW TO MODERATE LEVELS.
THERE IS ALSO A FAIR CHANCE FOR AN ISOLATED MAJOR FLARE SOMETIME
DURING THE PERIOD.

THERE WILL BE A SLIGHT CHANCE FOR A SOLAR PROTON ENHANCEMENT OR EVENT
AT GEO-SYNCHRONOUS ORBIT SOMETIME DURING THE PERIOD.

THE GREATER THAN 2 MEV ELECTRON FLUX AT GEO-SYNCHRONOUS ORBIT MAY
REACH HIGH LEVELS DURING 27 - 31 MAY. OTHERWISE, NORMAL TO MODERATE
LEVELS ARE EXPECTED.

GEOMAGNETIC FIELD ACTIVITY IS EXPECTED TO BE AT UNSETTLED TO ACTIVE
LEVELS DURING 19 MAY AND AGAIN DURING 26 - 28 MAY DUE TO CORONAL
HOLE EFFECTS. QUIET TO UNSETTLED CONDITIONS ARE EXPECTED DURING THE
REST OF THE PERIOD, BARRING ANY EARTH-DIRECTED CORONAL MASS
EJECTIONS.


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