Weekly Space Weather Highlights

Highlights of Solar and Geomagnetic Activity
14 - 20 August 2017

Solar activity ranged from very low levels to moderate levels over
the period. Very low levels were observed on 16-17 Aug, low levels
were observed on 14-15 Aug and again from 18-19 Aug, while moderate
levels were observed on 20 Aug. 

The period began with Region 2671 (N11, L=305, class/area Fkc/410 on
18 Aug) rotating around the east limb. The region was in a growth
phase through 18 Aug and rapidly developed from a simple Hax/alpha
spot group to an Fkc/beta-gamma group by 17 Aug with an extent
reaching 20 heliographic degrees by 20 Aug. Although a magnetically
complex spot group, it only managed 11 C-class flares. The largest
was a C7/Sf, with an associated Type II (928 km/s) radio sweep, at
19/2155 UTC. Although coronal dimming was observed in SDO/AIA 193
imagery beginning at 19/2143 UTC, there was no observable
indications of an associated coronal mass ejection (CME) in
coronagraph imagery. Another region began producing C-class activity
on the east limb beginning on 18 Aug. By 20 Aug, the region rotated
into view and was numbered 2672 (N05, L=225, class/area Dao/beta on
20 Aug). This region produced an M1 flare (R1-Minor) at 20/0152 UTC.
No Earth-directed CMEs were observed during the period. 

No proton events were observed at geosynchronous orbit.

The greater than 2 MeV electron flux at geosynchronous orbit reached
high levels from 14-16 Aug and again from 18-20 Aug. A decrease to
moderate levels was observed on 17 Aug coinciding with the arrival
of a positive polarity coronal hole high speed stream (CH HSS). The
largest flux value of the period was 23,392 pfu observed at 20/1540

Geomagnetic field activity ranged from quiet to G1 (Minor)
geomagnetic storm levels. The period began under the waning
influence of a negative polarity CH HSS. Solar wind speed decreased
from near 600 km/s to around 360 km/s by 16 Aug while total field
was between 3-5 nT. Early on 16 Aug, total field began to increase
to a maximum of 13 nT at 17/0740 UTC while the solar wind speed
slowly increased to around 780 km/s by late on 19 Aug as a polar
connected, positive polarity CH HSS became geoeffective. By the end
of the period, solar wind speeds decreased to near 650 km/s while
total field values had decreased to 3 nT. The geomagnetic field
responded with quiet levels from 14-16 Aug, followed by quiet to G1
(Minor) storm levels from 17-20 Aug. 

Forecast of Solar and Geomagnetic Activity
21 August - 16 September 2017

Solar activity is expected to be at low levels with a chance for
M-class (R1-R2, Minor-Moderate) activity from Regions 2671 and 2672
from 21 Aug-02 Sep and again from 08-16 Sep when both regions return
to the visible disk. Very low levels are expected from 03-07 Sep. 

No proton events are expected at geosynchronous orbit.

The greater than 2 MeV electron flux at geosynchronous orbit is
expected to reach high levels from 21-30 Aug, 01-07 Sep, 11-13 Sep,
and again from 15-16 Sep due to recurrent CH HSS influence. 

Geomagnetic field activity is expected to be at unsettled to active
levels from 21-22 Aug, 30 Aug-02 Sep, 08-09 Sep, and from 13-16 Sep
with G1 (Minor) storm levels likely on 31 Aug, and 13-16 Sep due to
recurrent CH HSS activity.