:Product: Weekly Highlights and Forecasts :Issued: 1999 Dec 21 2112 UT HIGHLIGHTS OF SOLAR AND GEOMAGNETIC ACTIVITY 13 - 19 DECEMBER 1999 SOLAR ACTIVITY RANGED FROM LOW TO MODERATE LEVELS. ACTIVITY WAS LOW THROUGH 16 DECEMBER DUE TO ISOLATED C-CLASS SUBFLARES, MOST OF WHICH CAME FROM REGION 8798 (S13, L = 171, CLASS/AREA DKC/550 ON 17 DECEMBER). THIS REGION BEGAN A GRADUAL GROWTH PHASE ON 15 DECEMBER AND BY THE END OF THE PERIOD HAD BECOME LARGE AND MAGNETICALLY COMPLEX. AN OPTICALLY UNASSOCIATED TYPE II RADIO SWEEP AT 16/0744UT MAY HAVE BEEN ASSOCIATED WITH FLARE ACTIVITY IN REGION 8798. REGION 8806 (N19, L = 115, CLASS/AREA FKC/890 ON 19 DECEMBER) ROTATED INTO VIEW ON 17 DECEMBER AS A LARGE, MAGNETICALLY COMPLEX SUNSPOT GROUP. IT PRODUCED AN M1 X-RAY FLARE AT 17/2141UT WITH AN ASSOCIATED LOOP PROMINENCE SYSTEM AND AN M1/1N FLARE AT 18/1912UT. ACTIVITY DECREASED TO LOW LEVELS ON 19 DECEMBER DUE TO OCCASIONAL C-CLASS FLARES FROM REGION 8806. REAL-TIME SOLAR WIND DATA WERE AVAILABLE FROM THE ADVANCED COMPOSITION EXPLORER (ACE) SPACECRAFT FOR MOST OF THE PERIOD. SOLAR WIND CHARACTERISTICS COMMONLY ASSOCIATED WITH CME EFFECTS WERE OBSERVED ON 13 DECEMBER WITH VELOCITIES AS HIGH AS 600 KM/SEC AND SUSTAINED PERIODS OF SOUTHWARD IMF BZ WITH DEFLECTIONS TO MINUS 13 NT (GSM). SOLAR WIND FLOW RETURNED TO NOMINAL CONDITIONS BY 14 DECEMBER. NO SIGNIFICANT CHANGES WERE OBSERVED IN THE SOLAR WIND FLOW FOR THE REST OF THE PERIOD. NO PROTON EVENTS WERE DETECTED AT GEOSYNCHRONOUS ORBIT DURING THE PERIOD. THE GREATER THAN 2 MEV ELECTRON FLUX AT GEOSYNCHRONOUS ORBIT WAS AT HIGH LEVELS AS THE PERIOD BEGAN, BUT DROPPED TO NORMAL LEVELS BY MIDDAY ON 13 DECEMBER. FLUXES REMAINED NORMAL FOR THE REST OF THE PERIOD. THE GEOMAGNETIC FIELD WAS DISTURBED ON 13 DECEMBER DUE TO CME EFFECTS. ACTIVE TO MAJOR STORM LEVELS OCCURRED DURING THE DISTURBANCE. ACTIVITY DROPPED TO MOSTLY QUIET LEVELS LATE ON 13 DECEMBER, THEN REMAINED SO FOR THE BALANCE OF THE PERIOD. FORECAST OF SOLAR AND GEOMAGNETIC ACTIVITY 22 DECEMBER 1999 - 17 JANUARY 2000 SOLAR ACTIVITY IS EXPECTED TO RANGE FROM LOW TO MODERATE LEVELS. OCCASIONAL TO FREQUENT C-CLASS FLARES AND ISOLATED M-CLASS FLARES LIKELY THROUGHOUT THE PERIOD. REGIONS 8798 AND 8806 EACH PROVIDE A CHANCE FOR AN ISOLATED MAJOR FLARE SOMETIME DURING THE PERIOD. THERE IS AN INCREASING CHANCE FOR A PROTON EVENT AT GEOSYNCHRONOUS ORBIT FROM REGIONS 8798 AND 8806. THE GREATER THAN 2 MEV ELECTRON FLUX AT GEOSYNCHRONOUS ALTITUDE IS EXPECTED TO BE AT MODERATE TO HIGH LEVELS DURING 01 - 05 JANUARY. OTHERWISE, NORMAL TO MODERATE LEVELS ARE EXPECTED. THE GEOMAGNETIC FIELD IS EXPECTED TO BE AT UNSETTLED TO MINOR STORM LEVELS DURING 31 DECEMBER - 03 JANUARY DUE TO RECURRENT CORONAL HOLE EFFECTS. QUIET TO UNSETTLED LEVELS ARE EXPECTED FOR THE REST OF THE PERIOD, BARRING ANY EARTH-DIRECTED CMES. .