NOAA SEC Report of Solar-Geophysical Activity 18 Apr 2002

:Product: Report of Solar-Geophysical Activity

:Issued: 2002 Apr 18 2210 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 108 Issued at 2200Z on 18 Apr 2002

IA.  Analysis of Solar Active Regions and Activity from  17/2100Z

to 18/2100Z:  Solar activity was low. Only C-class flares occurred

over the past 24 hours. Some of these flares did not have an obvious

source on the visible disk and may have originated from beyond the

limb. Region 9906 (S14W55) remains large and complex but has shown

some sunspot decay and magnetic simplification. New Regions 9911

(S13E23) and 9912 (N11E28) were numbered.

IB.  Solar Activity Forecast:  Solar activity is expected to be

moderate. M-class activity is expected in Region 9906. A major flare

in this region remains a possibility.

IIA.  Geophysical Activity Summary 17/2100Z to 18/2100Z:

The geomagnetic field ranged from quiet to severe storm levels in

response to the CME that impacted the Earth early yesterday. ACE

solar wind information suggests that this CME has passed. The

geomagnetic field is currently at active levels. Yesterday’s greater

than 10 MeV proton event has ended: start 17/1530 UTC, maximum flux

(24 pfu) 17/1540 UTC, and end 18/0035 UTC.

IIB.  Geophysical Activity Forecast:  The geomagnetic field is

expected to be at unsettled to active levels through the end of 18

April UTC. Another CME is expected to impact the Earth early on 19

April UTC froptin LDE/CME that occurred on 17 April. Minor to major

storm conditions are possible for the 24-48 hours following this

CME’s arrival. Geomagnetic activity is expected to decline to

unsettled to active levels by the end of the 3-day forecast period.

Another greater than 10 MeV proton event is possible if Region 9906

generates a major flare.

III.  Event Probabilities 19 Apr-21 Apr

Class M    75/50/40

Class X    10/05/01

Proton     10/05/01

PCAF       yellow

IV.  Penticton 10.7 cm Flux

Observed           18 Apr 188

Predicted   19 Apr-21 Apr  180/175/170

90 Day Mean        18 Apr 201

V.  Geomagnetic A Indices

Observed Afr/Ap 17 Apr  027/041

Estimated Afr/Ap 18 Apr  045/050

Predicted Afr/Ap 19 Apr-21 Apr  040/040-030/050-012/020

VI.  Geomagnetic Activity Probabilities 19 Apr-21 Apr

A.  Middle Latitudes

Active                50/50/30

Minor storm           30/20/10

Major-severe storm    20/10/05

B.  High Latitudes

Active                35/50/30

Minor storm           40/30/20

Major-severe storm    25/15/05