:Product: Weekly Highlights and Forecasts
:Issued: 2001 Apr 17 2112 UT
HIGHLIGHTS OF SOLAR AND GEOMAGNETIC ACTIVITY
09 - 15 APRIL 2001

SOLAR ACTIVITY REACHED HIGH LEVELS FOR THE FOURTH CONSECUTIVE WEEK.
REGION 9415 (S22, L = 001, CLASS/AREA EKO/880 ON 07 APRIL) PRODUCED
MAJOR FLARES ON APRIL 9, 10, 12, AND 15 (PLEASE REFER TO THE
ENERGETIC EVENT SUMMARY FOR FLARE SPECIFICS).  REGION 9415 WAS LARGE
AND MAGNETICALLY COMPLEX, BY VIRTUE OF A STRONG MAGNETIC DELTA
CONFIGURATION WITHIN THE LEADER PORTION OF THE REGION. REGION 9415
BEGAN TO GRADUALLY DECAY ON 09 APRIL, BUT THE STRONG DELTA PERSISTED
THROUGH 13 APRIL. THE DELTA APPEARED TO DISSIPATE ON 14 APRIL AS THE
REGION 9415, THEN CLASSED (MAGNETICALLY) AS A BETA-GAMMA, CONTINUED
TO SLOWLY DECAY. AS ITS DECAY PHASE CONTINUED, REGION 9415 PRODUCED
THE LARGEST FLARE OF THE PERIOD; AN X14/2B WHICH PEAKED AT 15/1350
UTC, MAKING IT THE SECOND LARGEST FLARE OBSERVED DURING CYCLE 23.
THIS FLARE WAS ASSOCIATED WITH A 48000 SFU TENFLARE, TYPE II AND IV
RADIO SWEEPS, SOLAR PROTON EVENTS AT GREATER THAN 100 MEV AND 10
MEV, AND A GROUND LEVEL EVENT (GLE). REGION WAS CROSSING THE WEST
LIMB AS THE PERIOD ENDED.

DATA WERE AVAILABLE FROM THE ADVANCED COMPOSITION EXPLORER (ACE)
SPACECRAFT FOR MOST OF THE PERIOD. HOWEVER, SWEPAM DATA WERE
UNRELIABLE DURING 15/1436  - 16/0300 UTC, DUE TO EFFECTS FROM THE
X14 FLARE. CORONAL MASS EJECTION (CME) PASSAGES OCCURRED ON 11 AND
13 APRIL. TWO CME SHOCK FRONTS REACHED ACE ON 11 APRIL. THE FIRST
SHOCK REACHED ACE AT ABOUT 11/1310 UTC, FOLLOWED BY A SECOND
STRONGER SHOCK AT 11/1520 UTC. SOLAR WIND VELOCITIES INCREASED TO
ABOUT 780 KM/SEC FOLLOWING THE SHOCKS, THEN GRADUALLY DECLINED. IMF
BZ SHOWED STRONG NORTH/SOUTH VARIATIONS FOLLOWING THE SECOND SHOCK
WITH A RANGE OF PLUS 29 TO MINUS 27 NT (GSM) BEFORE TURNING
NORTHWARD AT APPROXIMATELY 11/2300 UTC. THE 13 APRIL PASSAGE BEGAN
AS A SHOCK REACHED ACE AT 13/0707 UTC ACCOMPANIED BY INCREASED
VELOCITIES (PEAK AROUND 850 KM/SEC DURING 13/0900 - 1100 UTC), MINOR
INCREASES IN DENSITY AND TOTAL IMF FIELD INTENSITY; ALONG WITH
VARIABLE, BUT GENERALLY NORTHWARD, IMF BZ.

A GREATER THAN 10 MEV EVENT BEGAN ON 10 APRIL FOLLOWING A X2/3B FLARE
AT 10/0526 UTC. THE EVENT BEGAN AT 10/0850 UTC, REACHED A MAXIMUM OF
355 PFU AT 11/2055 UTC, AND ENDED AT 13/1055 UTC. A POLAR CAP
ABSORPTION EVENT WAS ASSOCIATED WITH THIS PROTON EVENT. A >100 MEV
PROTON EVENT BEGAN AT 12/1305 UTC FOLLOWING A X2 FLARE AT 12/1028
UTC. THIS EVENT REACHED A MAXIMUM OF 1.4 PFU AT 12/1725 UTC, THEN
ENDED AT 12/1950 UTC. PROTON EVENTS AT GREATER THAN 100 MEV AND
GREATER THAN 10 MEV, AND A GROUND LEVEL EVENT FOLLOWED THE X14 FLARE
ON 15 APRIL (THIS GLE WAS ONLY THE THIRD SEEN DURING CYCLE 23). THE
GREATER THAN 100 MEV EVENT BEGAN AT 15/1405 UTC, REACHED A MAXIMUM
OF 146 PFU AT 15/1525 UTC, AND WAS IN PROGRESS AS THE PERIOD ENDED.
THE >10 MEV EVENT BEGAN AT 15/1410 UTC, REACHED A MAXIMUM OF 951 PFU
AT 15/1920 UTC, AND WAS IN PROGRESS AS THE PERIOD ENDED. A POLAR CAP
ABSORPTION EVENT WAS ASSOCIATED WITH THIS PROTON EVENT.

THE GREATER THAN 2 MEV ELECTRON FLUX AT GEOSYNCHRONOUS ORBIT REACHED
HIGH LEVELS DURING 14 - 15 APRIL.

THE GEOMAGNETIC FIELD WAS INTERMITTENTLY DISTURBED DURING THE PERIOD
DUE TO THE CME PASSAGES MENTIONED ABOVE. A MAJOR GEOMAGNETIC STORM
BEGAN ON 11 APRIL WITH A SUDDEN STORM COMMENCEMENT (SSC) AT 11/1343
UTC (07 NT, BOULDER USGS MAGNETOMETER). THE SSC WAS FOLLOWED BY
MINOR TO SEVERE STORM LEVELS AT ALL LATITUDES. THE STORM SUBSIDED ON
12 APRIL. ANOTHER DISTURBANCE BEGAN ON 13 APRIL WITH A SUDDEN
IMPULSE (SI) AT 13/0735 UTC (19 NT, BOULDER USGS MAGNETOMETER). THE
SI WAS FOLLOWED BY ACTIVE TO MAJOR STORM LEVELS AT ALL LATITUDES
WITH SEVERE STORM LEVELS DETECTED AT HIGH LATITUDES. THIS
DISTURBANCE SUBSIDED ON 14 APRIL.

FORECAST OF SOLAR AND GEOMAGNETIC ACTIVITY
18 APRIL - 14 MAY 2001

SOLAR ACTIVITY IS EXPECTED TO RANGE FROM MODERATE TO HIGH LEVELS
DURING THE PERIOD. ISOLATED MAJOR FLARES WILL BE POSSIBLE DURING THE
PERIOD DUE TO THE EXPECTED RETURN ON 18 APRIL OF ACTIVE LONGITUDES
ASSOCIATED WITH OLD REGION 9393 (N16, L = 151, CLASS/AREA FKC/2440
ON 29 MARCH). (OLD) REGION 9415 IS EXPECTED TO RETURN TO THE VISIBLE
DISK ON 29 APRIL.

THE SOLAR PROTON EVENT AT GREATER THAN 100 MEV AND GREATER THAN 10
MEV THAT BEGAN ON 15 APRIL WERE IN PROGRESS AS THE PERIOD ENDED.
THESE EVENTS ARE EXPECTED TO END BY 18 APRIL. PROTON EVENTS WILL BE
POSSIBLE DURING THE PERIOD WITH EXPECTED RETURN OF OLD REGIONS 9393
AND 9415.

THE GREATER THAN 2 MEV ELECTRON FLUX AT GEOSYNCHRONOUS ORBIT IS
EXPECTED TO BE AT NORMAL TO MODERATE LEVELS DURING MOST OF THE
PERIOD.

GEOMAGNETIC FIELD ACTIVITY IS EXPECTED TO BE AT UNSETTLED TO MINOR
GEOMAGNETIC STORM LEVELS DURING 18 - 19 APRIL. MOSTLY UNSETTLED
LEVELS ARE EXPECTED DURING THE REST OF THE PERIOD, BARRING
EARTH-DIRECTED CME OCCURRENCES.


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