:Product: 19990923RSGA.txt :Issued: 1999 Sep 23 2200 UTC # Prepared jointly by the U.S. Dept. of Commerce, NOAA, # Space Environment Center and the U.S. Air Force. # JOINT USAF/NOAA REPORT OF SOLAR AND GEOPHYSICAL ACTIVITY SDF NUMBER 266 ISSUED AT 2200Z ON 23 SEP 1999 IA. ANALYSIS OF SOLAR ACTIVE REGIONS AND ACTIVITY FROM 22/2100Z TO 23/2100Z: SOLAR ACTIVITY WAS LOW. THE LARGEST EVENT OF THE PERIOD WAS AN IMPULSIVE C1/SF FROM 8706 (N20E25). REGION 8700 (N12W61) WAS THE MOST ACTIVE REGION THIS PERIOD AND PRODUCED SEVERAL MINOR SUBFLARES. A SIXTEEN DEGREE FILAMENT ERUPTED FROM NEAR S14W47 AT 23/1529Z. REMAINING REGIONS WERE MOSTLY QUIET. IB. SOLAR ACTIVITY FORECAST: SOLAR ACTIVITY IS EXPECTED TO REMAIN AT LOW LEVELS. ONLY ISOLATED C-CLASS X-RAY EVENTS ARE EXPECTED. IIA. GEOPHYSICAL ACTIVITY SUMMARY FROM 22/2100Z TO 23/2100Z: THE GEOMAGNETIC FIELD WAS AT QUIET TO MAJOR STORM LEVELS. THE GEOMAGNETIC STORM THAT FOLLOWED YESTERDAY'S SUDDEN IMPULSE AT 22/1222Z, CONTINUED THROUGH EARLY THIS PERIOD. THE STORM SUBSIDED RATHER QUICKLY AFTER 23/0600Z AND THE FIELD HAS BEEN MOSTLY QUIET TO UNSETTLED SINCE. IIB. GEOPHYSICAL ACTIVITY FORECAST: THE GEOMAGNETIC FIELD IS EXPECTED TO BE AT QUIET TO ACTIVE LEVELS. SOLAR WIND SPEED REMAINS ELEVATED FOLLOWING YESTERDAY'S INTERPLANETARY SHOCK. OCCASIONAL ACTIVE PERIODS ARE LIKELY DURING LOCAL NIGHTTIME HOURS ESPECIALLY AT HIGHER LATITUDES. III. EVENT PROBABILITIES 24 SEP-26 SEP CLASS M 10/10/10 CLASS X 01/01/01 PROTON 01/01/01 PCAF GREEN IV. PENTICTON 10.7 CM FLUX OBSERVED 23 SEP 137 PREDICTED 24 SEP-26 SEP 135/135/130 90 DAY MEAN 23 SEP 163 V. GEOMAGNETIC A INDICES OBSERVED AFR/AP 22 SEP 029/037 ESTIMATED AFR/AP 23 SEP 022/025 PREDICTED AFR/AP 24 SEP-26 SEP 012/015-010/012-010/010 VI. GEOMAGNETIC ACTIVITY PROBABILITIES 24 SEP-26 SEP A. MIDDLE LATITUDES ACTIVE 30/20/20 MINOR STORM 10/05/05 MAJOR-SEVERE STORM 05/01/01 B. HIGH LATITUDES ACTIVE 40/30/30 MINOR STORM 10/10/05 MAJOR-SEVERE STORM 05/01/01