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ARRL Propagation Bulletin ARLP032 (2010)

ARLP032 Propagation de NW7US

QST de W1AW  
Propagation Forecast Bulletin 32  ARLP032
From Tomas Hood, NW7US
Stevensville, MT  August 13, 2010
To all radio amateurs 

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

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  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 and is available in high

While you are viewing movies, be sure to check out the movie located
at which shows a simulation of
Earth's magnetosphere on August 3.  About two-thirds into the movie,
you can see the arrival and then the passing of the coronal mass
ejection from the multiple-eruption event of August 1, 2010.  Browse
also to and watch the massive
filament eruption associated with the C-class flare of August 1,

The late Robert Brown, PhD, NM7M, proposed that the hard X-ray
energy present in the wavelengths from 1 to 8 Angstroms provide the
most effective ionizing energy throughout all of the ionospheric
layers in our atmosphere.  The GEOS satellites measure these
wavelengths and the resulting measurements are reported as the
background X-ray level throughout the day.  A daily average is
reported, as well.

Dr. Brown recorded the daily background X-ray levels for several
sunspot cycles, and discovered that during solar cycle minimum
periods, the background X-ray levels remained at the A class level.
During the rise and fall of a solar cycle, the background X-ray
energy levels remained mostly in the B range.  During peak solar
cycle periods, the background energy reached the C and sometimes
even M levels.

Armed with this information, can we discover any clues as to the
current status of Sunspot Cycle 24?  The Space Weather and Radio
Propagation page maintained by NW7US at
includes a graph showing the daily and monthly averaged hard X-ray
flux since the end of Sunspot Cycle 22.  The plot reveals a
noticeable rise in Cycle 24 activity.  We're seeing the energy rise
to the B level more often as 2010 progresses, supporting the view
that Cycle 24 is alive and moving along toward an eventual sunspot
cycle peak in several years.

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While solar activity was higher this week, geomagnetic activity has
been quiet, with daily planetary A indices ranging from 4 to 10, and
the daily mid-latitude A indices ranging from 2 to 9.  The predicted
planetary A index for August 13-14 is 5, then 8 on August 15, 12 on
August 16, then 5 on August 17-21.

NOAA/USAF expects geomagnetic activity to be mostly quiet for the
next week.  A very small coronal hole is rotating across the solar
disc, but will have little if any influence on the geomagnetic
activity this coming week.

If you would like to make a comment or have a tip for our readers,
email the author at,

For more information concerning radio propagation, see the ARRL
Technical Information Service at  For an explanation of
the numbers used in this bulletin, see  
An archive of past propagation bulletins
is at  Find more
good information and tutorials on propagation at  Monthly propagation
charts between four USA regions and twelve overseas locations are at  Instructions for starting or ending
email distribution of ARRL bulletins are at

Sunspot numbers for August 5 through August 11 were 54, 49, 47, 46,
53, 56, and 66 with a mean of 53. 10.7 cm flux was 82.7, 82.0, 90.5,
82.6, 84.1, 83.5, and 85.8 with a mean of 84.5.  Estimated planetary
A indices were 10, 8, 5, 4, 10, 8, and 10 with a mean of 7.9.
Estimated mid-latitude A indices were 7, 6, 4, 2, 7, 7, and 9 with a
mean of 6.


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