:Product: Weekly Highlights and Forecasts
:Issued: 2013 May 20 0139 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
13 - 19 May 2013

Solar activity reached high levels during the week, in fact the
highest levels of activity since 2013 began. Between 13 and 14 May,
newly-numbered Region 1748 (N11, L=296, class/area=Eki/310) produced
an X2/1n flare at 13/1605Z and an X3/2b flare at 14/0111Z. Both
events produced several radio emissions. Three Tenflares were
observed at 14/0115Z (640 sfu), 14/0141Z (190 sfu), and 14/0203Z
(370 sfu). A Type-II radio sweep was observed at 14/0107Z with an
estimated velocity of 1514 km/s, in conjunction with a Type-IV radio
sweep at 14/0113Z. SDO/AIA 193A showed a flare on the East limb at
N12 from 14/0009-0154 and 14/0206-0224Z. A dimming and wave was
observed over the east hemisphere and North Pole. Two distinct halo
coronal mass ejections (CMEs) were subsequently observed on LASCO
imagery. The first appeard in C2 coronagraph imagery at 14/0125Z and
grew to a full HALO CME by 14/0224Z. The second event appeared at
14/0200Z with loop edge over the East and expanded to a partial HALO
280 degrees in width.

Solar activity remained at high levels on 15 May. Region 1748 grew
to a Dki/beta-gamma-delta and produced an X1/2n flare at 15/0148Z
associated with a Type II radio sweep (estimated shock speed 501
km/s), a Type IV radio sweep, a 440 sfu Tenflare; and a fast,
assymetric halo CME. The CME speed was observed in LASCO C2
coronagraph imagery at 15/0148Z and expanded to a full HALO CME by
15/0248Z. SDO/AIA 193/211/304 showed the flare at 15/0124-0212Z
which produced a faint dimming in the Northeast and North direction
and a wave over the East hemisphere. The CME had and earthward
component and its western flank reached Earth on 18 May at 0112Z.

Activity declined to moderate levels on 16 May with a single M1
flare from Region 1748 at 16/2153Z. Moderate levels continued
through 17 May when Region 1748 produced an M3/2b flare at 17/0857Z.
Type II (376 km/s) and Type IV radio bursts, as well as a 420 sfu
Tenflare, were observed with this event. At 17/0912Z, LASCO/C2
coronagraph imagery observed a CME erupting from the east limb. It
grew to a full halo CME by 17/0948Z and was estimated to be moving
at approximately 1498 km/s. The CME reached Earth on 19 May at
2221Z.

The remainder of the week was dominated by low levels of activity as
Region 1748 shrank to less than half its largest extent. The largest
flare of the latter part of the week was a C9 observed on the east
limb at 19/1750Z. The other regions on the visible disk throughout
the week were relatively inactive, producing only low-level C-class
activity.

A 10 MeV proton flux greater than 10 pfu at geosynchronous orbit
event began at 15/1325Z, reached a maximum flux of 41 pfu at
17/1720Z, and ended at 18/1445Z. The 10 MeV flux remains enhanced at
the time of this report. The event was attributed to the X1/2n flare
at 15/0148Z.

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

Geomagnetic field activity ranged from quiet to minor storm levels
with the arrival of two CMEs during the week. The first CME, which
was observed leaving the sun on 15 May, passed the ACE spacecraft at
18/0023Z and arrived at Earth at 18/0112Z with a 31nT sudden
impulse. Activity reached minor storm levels by 18/0300Z and
remained there through the end of the 0300-0600Z synoptic period.
Activity then dropped to active, unsettled, then quiet levels during
the subsequent periods. The following evening, active levels were
observed during the 0000-0300Z synoptic period.

The second CME, which left the sun on 17 May, passed the ACE
spacecraft at 19/2221Z and arrived at Earth at 19/2306Z with a 29nT
sudden impulse. Activity increased to active levels during the
2100-0000Z synoptic period.

Forecast of Solar and Geomagnetic Activity
20 May - 15 June 2013

Solar activity is expected to be low to moderate throughout the
forecast period. High levels of activity are possible through 25 May
and again after 7 June associated with Region 1748.

There is a chance for proton events at geosynchronous orbit,
particularly through 25 May and again after 7 June associated with
Region 1748.

The greater than 2 MeV electron flux at geosynchronous orbit is
expected to be at high levels from 24-31 May associated with a
recurrent coronal hole high speed stream.

Geomagnetic field activity is expected to reach minor to major storm
levels on 20 May in response to the 17 May coronal mass ejection. In
the absence of any Earth-directed coronal mass ejections, the
remainder of the forecast period is expected to be characterized by
quiet to unsettled levels of activity with the possible exception of
28 May, when another geoeffective coronal hole high speed stream
becomes geoeffective and brings active levels.