Propagation News

ARLP032 Propagation de NW7US



This week's bulletin was written by Tomas Hood, NW7US.  Tomas is filling in for your regular reporter Tad Cook, K7RA.

Sunspot numbers and solar flux increased this week, with average daily sunspot numbers up over 32 points to 53, and the average daily
10.7-cm solar flux up over 3 points to 84.5.  These are the numbers from last Thursday through this Wednesday, August 5 through August
11.

The sunspot count on August 11 was 66, consisting of four active sunspot regions, NOAA Active Regions 1093, 1095, 1096, and 1097.
The largest of these was 1093 with a relative size of 130 millionths of a solar hemisphere.  The sunspot count of 66 is the highest yet
recorded in Sunspot Cycle 24.  Another note-worthy development this week is that five active sunspot regions were reported on August 12.
However, most of the spots were small, resulting in a daily sunspot count of 50.

Another news-worthy event was the M-class X-ray flare that erupted from active sunspot region 1093 on August 7.  This flare was 10
times more powerful than the C-class flare on August 1 that caused so much News Media attention on August 3 through August 5.  This
M1.0 magnitude solar flare peaked at 1824 UTC on August 7 and ejected a huge mass of coronal plasma.  Many hoped that the coronal
mass ejection, or CME, originating from the sunspot region 1093 would trigger auroral displays around the world just like those that
occurred last week.  However, because this CME was not fully Earth-directed, most of the CME missed the magnetosphere, resulting
in only the slightest increase in geomagnetic activity between August 10 and 11.

This flare, one of the biggest since the start of Cycle 24, also triggered a metric type II radio burst.  This kind of radio burst
can be heard from a radio receiver tuned to, say, a six-meter frequency as the burst occurs.  The burst sounds like rushing wind.
You can hear a recording of a type II radio burst as recorded on 50 MHz by Thomas Ashcraft on April 2, 2001 at 2151 UTC that occurred
during the X22.0-magnitude X-ray flare, by browsing to http://tinyurl.com/50MT2RB.  Incidentally, the April 2, 2001 flare
is the second largest event on record after the X28.0-magnitude mega-flare that occurred on November 4, 2003.

A movie of the August 7 M-class flare showing a series of filtered views of the event as seen by the Solar Dynamics Observatory's
Atmospheric Imaging Assembly can be viewed at http://tinyurl.com/20100807mflare and is available in high
definition.