Weekly Highlights of Solar and Geomagnetic Activity, 08 - 14 April 2013

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

:Product: Weekly Highlights and Forecasts
:Issued: 2013 Apr 15 0630 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
08 - 14 April 2013

Solar activity was at very low to high levels during the period. The
period began at low levels that persisted until early on 11 April.
At 11/0716 UTC, solar activity reached high levels as Region 1719
(N11, L=077, class/area Eki/290 on 12 April) produced an M6/3b flare
with Type II (estimated speed 1370 km/s) and Type IV radio sweeps, a
Tenflare (470 sfu), and an associated asymmetric full halo coronal
mass ejection (CME) with an estimated plane-of-sky speed of 1142
km/s. On 12 April, solar activity reached moderate levels as Region
1718 (N21, L=109, class/area Dkc/510) produced an M3 flare at
12/2038 UTC. Solar activity decreased to low levels on 13 April with
a further decrease to very low levels on 14 April as the majority of
the regions on the visible disk decreased in either area or
complexity.

Greater than 10 MeV and greater than 100 MeV proton events were
observed during the period associated with the 11 April M6/3b flare.
The greater than 10 MeV proton event began at 11/1055 UTC, reached a
peak flux of 114 pfu at 11/1645 UTC, and ended at 12/2210 UTC. The
greater than 100 MeV proton event began at 11/0940 UTC, reached a
peak flux of 2 pfu at 11/1400 UTC, and ended at 11/1955 UTC.

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

Geomagnetic field activity was at quiet levels until late on 13
April when a geomagnetic shock was observed in ACE/SWEPAM data
associated with the 11 April CME. At 13/2215 UTC, the total field
(Bt) increased from 4 nT to 10 - 13 nT, while the solar wind speed
increased from approximately 365 km/s to 480 km/s. An associated
geomagnetic sudden impulse was observed in the Boulder magnetometer
(29 nT) at 13/2255 UTC. This produced an unsettled period to end the
UTC day on 13 April. By 14 April, the geomagnetic field continued to
be under the influence of the 11 April CME. Total field was variable
between 4 and 14 nT while the Bz component of the interplanetary
magnetic field was mostly positive between 1 - 12 nT with brief
southward deflections to a maximum of -7 nT. Solar wind speed
reached a maximum of 558 km/s at 14/0443 UTC before slowly
decreasing to end the period near 460 km/s. The geomagnetic field
responded with quiet to unsettled conditions on 14 April with a
brief period of active to minor storm conditions mid-day at high
latitudes.

Forecast of Solar and Geomagnetic Activity
15 April - 11 May 2013

Solar activity is expected to be at very low to low levels with a
chance for an M-class flare from 15 April to 18 April when Regions
1718 and 1719 depart the visible disk. Very low to low levels are
expected from 19 April to 28 April. From 29 April to 11 May, solar
activity is expected to be at very low to low levels with a chance
for M-class flaring as Regions 1718 and 1719 return to the visible
disk.

No proton events are expected at geosynchronous orbit.

The greater than 2 MeV electron flux at geosynchronous orbit is
expected to be at moderate to high levels on 16 - 18 April due to
CME effects. Moderate to high levels are expected again on 25 April
- 02 May due to coronal hole high speed stream (CH HSS) effects.
Normal to moderate levels are expected for the rest of the period.

Geomagnetic field activity is expected to be quiet to unsettled on
15 April due to residual effects from the 11 April CME. Mostly quiet
conditions are expected from 16 - 22 April. On 23 April, a recurrent
CH HSS is expected to move into geoeffective position causing
unsettled to active conditions with continuing quiet to unsettled
conditions on 24 April. From 25 - 26 April, another recurrent CH HSS
is expected to become geoeffective causing unsettled to active
conditions. From 27 April until the end of the forecast period,
mostly quiet conditions are expected to prevail.