[Propagation+Space Weather] Today's Space Weather Forecast Discussion on 2015 May 16 1230 UTC

[nw7us@sunspotwatch.com]

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Here is the current forecast discussion on space weather and geophysical activity, issued 2015 May 16 1230 UTC.

Solar Activity

24 hr Summary: Solar activity remained at low levels with weak C-class activity observed from Region 2342 (N18W26, Cao/beta). The largest events of the period were two C2 flares. The first was a C2/Sf observed from region 2342 at 15/2230 UTC and the second was a C2 flare at 15/2329 UTC from Region 2339 (N12W65, Fac/beta-gamma).

Region 2339 remained the largest and most complex spot group on the disk. Consolidation and growth within the regions trailer spots occurred early in the period, but showed some signs of decay later in the period; while the regions leader spots decayed gradually throughout the period. Region 2339 continued to show a beta-gamma magnetic complexity, however some weakening in the structure occurred. Region 2346 (S08E07, Cro/beta) was in decay as the leader spots lost penumbral area and spot count decreased. The remaining regions were quiet and stable.

Several eruptive filament structures occurred during the period as observed in SDO/AIA and GONG/H-alpha imagery. The most impressive was an eruptive prominence (EPL) from the NE limb and a connected highly active and partially eruptive filament from the NE quadrant. The EPL (N42E90) erupted at approximately 15/2322 UTC. Initial analysis suggests most material erupted north and eastward and would likely be off the Sun-Earth line, however we are awaiting updated SOHO/LASCO coronagraph imagery for further analysis. An approximately 13 degree long filament centered near N23E55 became highly active and partially eruptive beginning about the same time as the EPL. Initial analysis of available imagery suggests most material lost from the filament was likely reabsorbed.

Another filament, approximately 7 degrees long and centered near N10W29, became highly active and slowly disappeared between approximately 15/2252-16/0051 UTC. Initial analysis of all available imagery suggests it was likely reabsorbed.

Two CMEs occurred from near the south polar crown but were not geoeffective. A third CME, likely resultant from the EPL event was noted on SOHO/LASCO C2 coronagraph imagery, but not enough imagery was available yet for model input to determine geoeffectiveness.

Forecast: Solar activity is expected to be low with a slight chance for M-class (R1-R2/Minor-Moderate) flare activity over the next three days (16-18 May) with Region 2339 remaining the likely source.

Energetic Particle

24 hr Summary: The greater than 2 MeV electron flux reached high levels with a peak flux of 8787 pfu at 15/1455 UTC. The greater than 10 MeV proton flux remained at background levels.

Forecast: The greater than 2 MeV electron flux is expected to persist at moderate to high levels in response to coronal hole high speed stream (CH HSS) effects. The greater than 10 MeV proton flux is expected to remain below S1 (Minor) thresholds for the forecast period (16-18 May).

Solar Wind

24 hr Summary: Solar wind parameters at the ACE satellite gradually decreased, despite a slight uptick between 16/0000-0100 UTC from about 475 km/s to near 520 km/s. Overall, the solar wind speed lowered from about 540 km/s to near 430 km/s by periods end. Total magnetic field (Bt) strength remained fairly steady between 2-3 nT, except for a slight strengthening to about 4 nT from 16/0000-0200 UTC. The Bz component was variable but predominantly southward during the period with maximum negative deviation reaching near -4 nT. The phi angle remained in a predominantly negative (towards) orientation.

Forecast: The solar wind speed is expected to slowly decrease through day one (16 May) as the high speed stream effects diminish. On day two (17 May), a glancing blow from the 13 May CME is expected to impact the ACE satellite with an increase in density and a slight increase in wind speeds. A positive polarity, equatorial CH HSS is expected to keep wind speeds enhanced through day three (18 May).

Geospace

24 hr Summary: The geomagnetic field was at quiet levels due to waning CH HSS effects.

Forecast: The geomagnetic field is expected to be at mostly quiet levels for the rest of the UTC day on day one (16 May) as effects from the negative polarity CH HSS continue to wane. By late on day one to early on day two (16-17 May) conditions are expected to reach active to minor storm levels (G1-Minor) due to glancing blow effects from the 13 May CME. By day three (18 May), field conditions are expected to be at quiet to active levels under CME influences coupled with the expected arrival of a positive polarity, equatorial CH HSS.

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