ARRL

ARRL Propagation Bulletin ARLP030 (2010)

SB PROP @ ARL $ARLP030
ARLP030 Propagation de K7RA

ZCZC AP30
QST de W1AW  
Propagation Forecast Bulletin 30  ARLP030
From Tad Cook, K7RA
Seattle, WA  July 30, 2010
To all radio amateurs 

SB PROP ARL ARLP030
ARLP030 Propagation de K7RA

Sunspot activity increased again this week, but on Tuesday and
Wednesday (July 27-28), a stiff solar wind increased Earth's
geomagnetic activity, which is a negative for HF propagation.

Sunspot group 1089 grew, shrunk, and is growing again, visible a
total of 12 days as of early Friday.  Three more sunspot groups
appeared this week, with the latest, 1092 rapidly emerging on
Wednesday with a relative size of 180 millionths of a solar
hemisphere, growing to 210 on Thursday.  The relative size of group
1089 for July 19-29 was 130, 150, 310, 240, 200, 160, 140, 100, 70,
90 and 140.  Unfortunately, 1089 will shortly be out of view,
rotating across our Sun's western horizon.

Last week's bulletin ARLP029 mentioned rising weekly solar flux
averages (our reporting week for data at the bottom of each bulletin
runs from Thursday through Wednesday) and for the last four weeks it
was 72.8, 79.2, 80.6 and 85.3.  Average daily sunspot numbers over
the same weeks were 16, 18.9, 21.7 and 35.6.

Although the average for this week was greater than last, a glance
at a table of sunspot numbers at
http://www.swpc.noaa.gov/ftpdir/indices/DSD.txt shows that the
highest sunspot numbers for July were really centered around the
seven days from July 20-26.

Predicted solar flux (as of Thursday) is 87 for Friday and Saturday
(July 30-31), 85 on August 1-3, and 87 on August 4-6.  Predicted
planetary A index for those days is 8 on July 30-31 and 5 on August
1-9.  This is from the USAF and NOAA forecast at
http://www.swpc.noaa.gov/ftpmenu/forecasts/45DF.html, released daily
around 2100z.

Geophysical Institute Prague seems to agree with NOAA/USAF,
predicting quiet to unsettled conditions for July 30-31, and quiet
conditions August 1-5.

Steve Daniel, NN4T of Murfreesboro, Tennessee posed an interesting
question in an email this week.  "As the 6 meter sporadic E season
winds down (at least it seems to be winding down here in Tennessee)
I find myself thinking back to the 2000/2001 time frame when I was
first on 6.  That was at or near the peak of the last cycle and F2
propagation on 6 seemed quite common.  How high does solar activity
have to be for F2 propagation on 6 meters to occur?"

I posed that question to Carl Luetzelschwab, K9LA, and to several
others, including Jon Jones, N0JK and Vince Varnas, W7FA.

Vince commented, "The key to 6 meter F2 is solar flares. These
briefly enhance the F layer, raising the MUF to and above 50 MHz.
In cycle 19 it seemed to some as if there were daily openings to
Europe, South America, Africa and/or Japan. Such was not the case.
Even then, F2 was not a daily occurrence for most of us living in
the U.S. It is unlikely that we will ever have solar flux/sunspot
levels high enough to produce the same daily consistency and
dependability of F layer openings as is seen on 20 meters. The
bottom line is the higher the SSN/solar flux, the more likely to see
solar flares producing temporarily high enough MUF levels to cause F
layer propagation on 6 meters".

Jon noted that assuming lower activity during the current solar
cycle 24, there will be far less F2 propagation on 6 meters than in
cycle 23.

"From North America the 6 meter F2 propagation with low sunspot
numbers will be to South America and possibly Hawaii. Unlikely for
openings to Europe, Asia, Africa, etc. Big CMEs (Coronal Mass
Ejections) can occur at any time, even weak solar cycles. Recall the
Carrington solar flare of 1859 (the largest on record) occurred
during a weak solar cycle. However we may have to wait a while until
the next 'Carrington Flare' as ice cores show these major solar
events happen only once per 500 years."

Jon continued, "The primary terrestrial long haul 6 meter DX mode
for a weak cycle 24 will be E-layer for mid-latitude stations. TEP
(Trans-Equatorial Propagation) occurs even with low solar fluxes for
stations located at appropriate distances from the geomagnetic
equator. Occasional Es linking to TEP will take place. JT-65a EME
will play an increasing role for 6 Meter DXers".

Jon provided an excellent review of 6 meter F2 propagation by Jim
Kennedy K6MIO/KH6, at
http://www.uksmg.org/content/f2propagationmech.htm.

Carl referred us to his excellent article "Predicting 6 Meter F2
Propagation", which you can read on his web site.

On the K9LA web site at http://mysite.ncnetwork.net/k9la/, select
VHF, then the seventh article linked at the bottom of the list.

In response to the question from W3HKK in last week's bulletin
ARLP029, Lloyd Korb, K8DIO of Twinsburg, Ohio asked us to check "The
World Above 50 MHz" column in the current (August) issue of QST.
"There are two pages of great info on meteor scatter communications.
Maybe other VHF enthusiasts will recognize MS the next time they
hear a 'Ping'!!  I have been using MS for over 30 years on 50 MHz
and 2 meters.  Neat stuff!!"

Vince Varnas, W7FA commented, "What W3HKK was hearing on 6 meters
was: (1) meteor bursts, and (2) tropospheric fading. I often heard
this on 6 meters when I lived in Dayton, Ohio (K8REG)".

If you would like to make a comment or have a tip for our readers,
email the author at, k7ra@arrl.net.

For more information concerning radio propagation, see the ARRL
Technical Information Service at
http://arrl.org/propagation-of-rf-signals. For an explanation of the
numbers used in this bulletin, see
http://arrl.org/the-sun-the-earth-the-ionosphere. An archive of past
propagation bulletins is at
http://arrl.org/w1aw-bulletins-archive-propagation.  Find more good
information and tutorials on propagation at
http://mysite.ncnetwork.net/k9la/index.html.

Monthly propagation charts between four USA regions and twelve
overseas locations are at http://arrl.org/propagation.

Instructions for starting or ending email distribution of ARRL
bulletins are at http://arrl.org/bulletins.

Sunspot numbers for July 22 through 28 were 39, 45, 41, 39, 39, 15,
and 31 with a mean of 35.6.  10.7 cm flux was 87.7, 86.4, 85.2,
85.2, 84.4, 82.6 and 85.3 with a mean of 85.3. Estimated planetary A
indices were 5, 8, 5, 6, 6, 19 and 14 with a mean of 9. Estimated
mid-latitude A indices were 4, 6, 4, 5, 5, 11 and 10 with a mean of
6.4.
NNNN
/EX