Friday, September 21, 2012

AR 1574's C1 Flare on Sept 20th

The above image was taken September 20th at 11:39:00 UTC by the Atmospheric Imaging Assembly (AIA), at 304 Angstroms, aboard the Solar Dynamics Observatory (SDO). This was during the time of a C1 solar flare, produced by Active Region 1574 (AR 1574) on the southwestern (lower right) limb. Image Credit: SDO/AIA

For the end of September 19th and most of the 20th, the solar activity was low. Active Region 1574 (AR 1574) produced a C1 solar flare on the 20th at 11:39 UTC. And AR 1574 has grown over the period, from a simple unipolar spot to a 4-spot bipolar group. All of the other spotted ARs had little change. No Earth-directed coronal mass ejections (CMEs) were observed. The forecast through September 23rd: The solar activity is expected to be at low levels with a slight chance for M-class activity.

Above Earth, the geomagnetic field was at predominately quiet to unsettled levels with a period of active conditions on the 19th between 21:00 UTC and 24:00 UTC. The period began with wind speeds, as measured at the Advanced Composition Explorer (ACE) spacecraft, steady at 400 km/s while the Bz component of the interplanetary magnetic field (IMF) was mostly south at about -10 nT. At about 23:00 UTC, wind speed and temperature indicated slight increases while IMF Bz began fluctuating between +8 to -6 nT. By the 20th at about 01:00 UTC, the phi angle changed from a positive (away) to a negative (toward) orientation. These changes were all indicative of a co-rotating interaction region in advance of a coronal hole high-speed stream. By the end of the period, wind velocities were steady at about 575 km/s while IMF Bz did not vary much beyond +/- 2 nT. The forecast through September 23rd: The geomagnetic field is expected to be at quiet to unsettled levels with isolated active intervals for the 21st and 22nd as a coronal hole high-speed stream (CH HSS) remains geoeffective. By the 23rd, mostly quiet to unsettled levels are expected as CH HSS effects wane. Stay tuned...

To monitor solar flare activity minute by minute, visit the "Today's Space Weather" page of NOAA's Space Weather Prediction Center (

To learn more about the sun and to stay current on solar activity, visit the mission home pages of the Solar Dynamics Observatory (SDO) (, the Solar and Heliospheric Observatory (SOHO) (, the Advanced Composition Explorer (ACE) (, and the Solar Terrestrial Relations Observatory (STEREO) (


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