Weekly Highlights of Solar and Geomagnetic Activity, 15 - 21 April 2013

[SWPC.We...@noaa.gov]

:Product: Weekly Highlights and Forecasts
:Issued: 2013 Apr 22 0431 UTC
# Prepared by the US Dept. of Commerce, NOAA, Space Weather Prediction Center
# Product description and SWPC contact on the Web
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# Weekly Highlights and Forecasts
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Highlights of Solar and Geomagnetic Activity
15 - 21 April 2013

Solar activity was at low levels during the period. The first half
of the period (15 - 18 April) was dominated with mostly low-level
C-class activity from Regions 1719 (N11, L=077, class/area Eki/290
on 12 April) and 1723 (S18, L=001, class/area Dai/200 on 17 April).
The largest event during this time frame was a long duration C6 at
18/1823 UTC from Region 1719. Associated with the event was a Type
II signature with an estimated plane-of-sky speed of 1273 km/s and a
coronal mass ejection (CME) observed off the west limb. The
remainder of the period (19 - 21 April) witnessed the rapid
emergence on the disk of Region 1726 (N12, L=326, class/area Ekc/260
on 21 April). During this time frame, Region 1726 produced a total
of 20 C-class flares. The largest flare was a C4/Sf at 21/1838 UTC.
At the time of this report, Region 1726 was continuing its growth
phase and maintaining its complex beta-gamma-delta magnetic
configuration.

No proton events were observed at geosynchronous orbit. However, the
greater than 10 MeV proton flux increased slightly above background
levels beginning at about 21/1005 UTC and peaked at about 3 pfu at
21/1640 UTC. The enhancement was likely triggered by activity beyond
the west limb from old Region 1719 (N11, L=077).

The greater than 2 MeV electron flux at geosynchronous orbit was at
normal to moderate levels.

Geomagnetic field activity was at predominately quiet levels with an
isolated unsettled reading observed during the period 15/1800 - 2100
UTC. The period began under the waning influence of a weak CME.
Solar wind speeds were at mostly nominal levels, beginning the
period near 450 km/s and exhibited a steady decline to end the
period at about 285 km/s. Total interplanetary magnetic field (IMF)
readings ranged from a high of 12 nT early on 15 April, declined to
4 nT by early on 16 April and varied between 4 - 6 nT for the
remainder of the period. The Bz component of the IMF ranged from +11
nT early on 15 April and declined to about +5 nT by midday on 15
April. Through the remainder of the period, Bz did not vary much
beyond +/-4 nT. The Phi angle was in a negative (toward) orientation
through early on 16 April and switched to a predominately positive
(away) orientation through about 20/1900 UTC when it became variable
through the remainder of the period.

Forecast of Solar and Geomagnetic Activity
22 April - 18 May 2013

Solar activity is expected to be at predominately low levels through
the outlook period. A chance for M-class activity and a slight
chance for x-class activity exists due to active regions that
currently populate the visible disk and active regions due to rotate
onto the disk throughout the outlook period.

A slight chance for a 10 MeV proton event at geosynchronous orbit is
possible due to active regions that currently populate the visible
disk and active regions due to rotate onto the disk throughout the
outlook period..

The greater than 2 MeV electron flux at geosynchronous orbit is
expected to be at moderate to high levels from 24 April - 02 May in
the wake of a coronal hole high speed stream (CH HSS). Normal to
moderate levels will predominate from 03 - 18 May.

Geomagnetic field activity is expected to be at quiet to unsettled
levels on 22 April in response to a possible glancing blow from the
18 April CME. Mostly unsettled to active levels with isolated minor
storm periods are possible from 23 - 26 April due to recurrent (CH
HSS) effects. Predominately quiet levels are expected from 27 April
- 18 May.