:Product: Weekly Highlights and Forecasts
:Issued: 2015 Dec 21 0423 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
14 - 20 December 2015

Solar activity was at low levels. The period was dominated by low to
mid-level C-class flare activity from a number of active regions,
the largest of which was a C6/1f flare at 16/0903 UTC from Region
2468 (S15, L=128, class/area=Dao/120 on 10 Dec). Region 2468 was the
most productive region on the visible disk throughout the summary
period, however, an unnumbered region behind the northeast limb
produced multiple mid-level C-class flares within quick succession
and caused a slow increase in the background GOES-15 x-ray flux late
in the period.

Two asymmetrical full-halo coronal mass ejections (CMEs) were
observed in SOHO/LASCO C2 coronagraph imagery on 16 Dec. The first
CME was observed in C2 imagery beginning at 16/0924 UTC and was
associated with the C6/1F flare mentioned above. The second CME,
associated with a filament eruption, was first observed in
coronagraph imagery at 16/1436 UTC. Both CMEs were determined to be
Earth-directed and arrived at Earth late on 19 Dec. See the
geomagnetic summary below for further information on this event.

No proton events were observed at geosynchronous orbit.

The greater than 2 MeV electron flux at geosynchronous orbit reached
high levels on 14 Dec and 19 Dec with moderate levels observed
throughout the remainder of the period.

Geomagnetic field activity reached active to G1 (Minor) geomagnetic
storm levels late on 14 Dec and early on 15 Dec due to the influence
of a corotating interaction region followed by the onset of a
negative polarity coronal hole high speed stream (CH HSS). Isolated
active field conditions were observed early on 16 Dec and again late
on 17 Dec due to weak substorming. The CMEs from 16 Dec presumably
merged in the interplanetary medium and impacted the Earth at
19/1528 UTC. During the passage of the interplanetary shock, solar
wind parameters aboard the ACE spacecraft became suddenly enhanced.
Total field strength values initially increased from 5 nT to 17 nT
and the Bz component went strongly southward shortly after the
initial shock passage. The prolonged period of southward magnetic
field (-Bz) associated with the passage of the 16 Dec CMEs caused
periods of active conditions late on 19 Dec and active to G2
(Moderate) geomagnetic storm levels on 20 Dec. G2 storm conditions
were observed between 20/0300-0600 UTC and 20/1500-2359 UTC.

Forecast of Solar and Geomagnetic Activity
21 December - 16 January 2016

Solar activity is expected to be low throughout the period with a
chance for M-class flares (R1-R2 (Minor-Moderate) Radio Blackouts)
on 21 Dec through 03 Jan to the increased flare activity from an
unnumbered region behind the east limb.

No proton events are expected at geosynchronous orbit.

The greater than 2 MeV electron flux at geosynchronous orbit is
expected to be at normal levels on 21-27 Dec, moderate levels on 31
Dec-02 Jan, and 14-16 Jan. High flux levels are expected on 28-30
Dec and 03-13 Jan.

Geomagnetic field activity is expected to be at active to G2
(Moderate) geomagnetic storm levels early on 21 Dec due to the
waning effects of the 16 Dec coronal mass ejections. G1 (Minor)
geomagnetic storms are likely on 02, 06, and 10 Jan due to the
influence of recurrent coronal hole high speed streams.