:Product: Weekly Highlights and Forecasts
:Issued: 2011 Apr 19 1900 UTC
# Prepared by the US Dept. of Commerce, NOAA, Space Weather Prediction Center
# Product description and SWPC contact on the Web
# http://www.swpc.noaa.gov/weekly.html
#
# Weekly Highlights and Forecasts
#
Highlights of Solar and Geomagnetic Activity
11 - 17 April 2011

Solar activity was at low to moderate levels. Low activity occurred
during 11 - 14 April with C-class flares from Regions 1185 (N18,
L=025, class/area Cso/100 on 05 April), 1190 (N13, L=338, class/area
Eki/440 on 16 April), and 1193 (N17, L=266, class/area Eai/430 on 17
April). Activity increased to moderate levels on 15 April due to an
M1/1f flare at 15/1712 UTC from Region 1190 associated with minor
discrete radio emission. Region 1190 showed gradual spot growth
during 12 - 15 April and displayed a beta-gamma magnetic
configuration, then began to gradually decay on 16 April. Region
1193, which also contained a beta-gamma magnetic configuration,
showed gradual spot growth during 13 - 17 April. An Earth-directed
coronal mass ejection was observed early on 15 April, associated
with a filament disappearance from the northeast quadrant late on 14
April. Estimated plane-of-sky velocity was for the CME was 390 km/s,
based on an analysis of SOHO/LASCO coronagraph images. Activity
decreased to low levels during 16 - 17 April with C-class flares
from Regions 1185, 1190, and 1193.

No proton events were observed at geosynchronous orbit.

The greater than 2 MeV electron flux at geosynchronous orbit was at
normal to moderate levels during 11 - 13 April. Fluxes increased to
moderate to high levels during 14 - 16 April, then decreased to
normal to moderate levels during 16 - 17 April.

Geomagnetic activity was at quiet to active levels on 11 April.
Activity increased to quiet to minor storm levels on 12 April with
major storm periods observed at high latitudes. Activity decreased
to quiet to active levels on 13 April with minor to major storm
periods observed at high latitudes. Activity decreased to quiet to
unsettled levels on 14 April. A further decrease to quiet levels at
all latitudes occurred during 15 - 17 April. ACE solar wind
observations indicated the activity during 11 - 13 April was
associated with a coronal hole high-speed stream (CH HSS). The HSS
source was an equatorward extension of the southern polar CH. The CH
HSS commenced on 11 April following a negative- to positive-polarity
solar sector boundary crossing. Velocities increased during 11 - 12
April, eventually reaching a peak of 674 km/s at 12/1940, then
gradually decreased during the rest of the period. Interplanetary
magnetic field (IMF) changes associated with the onset of the CH HSS
included increased Bt (peak 17 nT at 11/2001 UTC) as well as
increased Bz variability with intermittent periods of southward Bz
(maximum deflection -9 nT at 12/0525 UTC). The CH HSS began to
gradually subside on 13 April.

Forecast of Solar and Geomagnetic Activity
20 April - 16 May 2011

Solar activity is expected to be low with C-class flares likely
during the period. There will be a chance for moderate activity
(isolated M-class flares) during the second half of the period due
to the return of previously active regions.

No proton events are expected at geosynchronous orbit.

The greater than 2 MeV electron flux at geosynchronous orbit is
expected to be at normal to moderate levels during most of the
period. However, high flux levels are expected during 22 - 23 April,
30 April - 03 May, and 11 - 13 May.

Geomagnetic field activity is expected to be to be at quiet to
unsettled levels during 20 - 22 April due to weak coronal hole
effects on 20 - 21 April and weak coronal mass ejection effects on
22 April (associated with the Earth-directed CME observed on 15
April). Activity is expected to decrease to quiet levels during 23 -
27 April. Field activity is expected to increase to quiet to active
levels during 28 April - 01 May due to recurrent coronal hole
effects. Activity is expected to decrease to quiet levels during 02
- 07 May. Activity is expected to increase to quiet to active levels
during 08 - 11 May due to recurrent coronal hole effects. Quiet
conditions are expected during 12 - 16 May.