ARRL

ARRL Propagation Bulletin ARLP025 (2003)

SB PROP @ ARL $ARLP025
ARLP025 Propagation de K7RA

ZCZC AP25
QST de W1AW  
Propagation Forecast Bulletin 25  ARLP025
From Tad Cook, K7RA
Seattle, WA  June 20, 2003
To all radio amateurs 

SB PROP ARL ARLP025
ARLP025 Propagation de K7RA

Low sunspot numbers and geomagnetic disturbances in the
over-the-hill portion of the solar cycle continue. There are enough
sunspots for some good HF propagation, but we are about three years
past the cycle peak and about three and a half years ahead of the
next sunspot minimum. Complicating the situation is continued high
solar wind and flares, causing constant disturbance to geomagnetic
conditions. HF operators generally want stable geomagnetic indices,
such as a K index at 3 or below and a daily A index of 10 or less.

A chart in the recent NOAA Preliminary Report and Forecast of Solar
Geophysical Data at http://www.sec.noaa.gov/weekly/pdf/prf1450.pdf
shows the enhanced geomagnetic activity following the peak of a
solar cycle. Go to the last page of the report, and look at the bar
graphs for severe storm conditions, expressed as a planetary A index
over 100.

Note that for a few years after high solar activity the geomagnetic
indices are higher. Another report from last week at
http://www.sec.noaa.gov/weekly/pdf/prf1449.pdf projects our position
in the current cycle. Look at the last page, and see a rising
historical planetary A index. Look at the previous few pages, and
see the smoothed sunspot and solar flux projections.

The next minimum appears sometime around the end of 2006. By the
way, this publication is full of interesting information and appears
weekly at http://www.sec.noaa.gov/weekly/index.html.

William Hartman, N6FB forwarded a question from the eHam.net forum
about the relation between A and K indices, as well as a few other
questions. The K index is a measure of geomagnetic stability at
various magnetometers around the globe. During periods of activity,
the higher latitudes tend to have higher K indices. For mid-latitude
K values, an index of 3 is normal. Below 3 is nice and quiet, and
above is disturbed. Each point in the K index, which is published
every three hours, represents a big change. It is a non-linear
system.

The A index is published daily, and is made up of the eight K
indices over 24 hours. It is a linear scale, so a one point change
doesn't represent a big jump in activity. For instance, if you had a
constant K index of 2 for 24 hours this would produce an A index of
7. A constant K index of 3 is equal to an A of 15, and K of 4 equals
27. The K usually changes every three hours, so the A is somewhere
in between the values shown here. A web page that shows the
relationship is at http://www.ngdc.noaa.gov/stp/GEOMAG/kp_ap.html.

You can see recent mid-latitude, high and planetary A and K indices
at http://www.sec.noaa.gov/ftpdir/indices/DGD.txt. Note that on June
17 and 18, 2003 we had a planetary A index of 50 and 54, which is
very high.

June 17 and 18 activity was significant, and Al Olcott, K7ICW sent
an email commenting that the recent sporadic E skip on 144 and 222
MHz was of historic importance. He is in Las Vegas, and on June 17th
on 222 MHz, he worked K7MAC in Idaho. K7MAC was S7, and on 144 MHz
he was S9 into Nevada, a 544-mile path.

The June 17 and 18 numbers were the result of yet another robust
interplanetary shock wave, which swept over the earth around 0500z
on June 18. It was probably from a coronal mass ejection hurled from
sunspot 365 on June 15, the day that this sunspot reappeared.  In
May that same spot released two X-class solar flares, big ones.

Mark Williams, KF6YU wrote about an unusual experience on June 14
around 0000z. He was vacationing in Payson, Arizona and an AM
broadcast station he was listening to in his truck abruptly
disappeared. He switched to FM to listen to a Phoenix station, and
instead heard one in Sioux City, Iowa on that frequency. When he got
back to his cabin, he listened to dead air on HF, and the whole
phenomenon was over in about 30 minutes.

Someone had a question about what Carl Luetzelschwab, K9LA meant
when he referred to IMF in an email quoted in last week's bulletin.
IMF in this context doesn't refer to global banking or third-world
debt, but the Interplanetary Magnetic Field. When a strong solar
wind or interplanetary shock wave from the sun blasts earth, the IMF
tends to point south. This has been covered several times in this
bulletin over the past year, but now may be a good time to review
the IMF and its significance at
http://spaceweather.com/glossary/imf.html.

In addition, in last week's bulletin we hoped to come up with some
images showing the effects on the spectrograph at Project JOVE
during an x-ray event on June 9. Jim Sky, KH6SKY sent the link,
http://radiosky.com/wccro_spec_030609.html.  The strip charts were
produced with Radio-Skypipe software. Check
http://radiosky.com/skypipeishere.html for information.

Back to recent indices as well as a projection for the next few
days, we had average sunspot numbers drop nearly 37 points from last
week to 112.7 this week. Solar flux was also down. Not surprisingly
given the conditions and all the reports, the average planetary A
index increased from 21 to 30. Space weather was remarkably mild on
Thursday, June 19 with mid latitude and planetary K indices down to
2 or 3. However, the forecast shows more of the same enhanced
activity over the next few days, with a planetary A index of 25, 25,
20 and 20 for June 20-23. Solar flux should remain around 125 on
those days. On June 20 we should enter a solar wind stream flowing
from a coronal hole, which should cause those high A indices.

Sunspot numbers for June 12 through 18 were 168, 149, 91, 111, 91,
80, and 99, with a mean of 112.7. 10.7 cm flux was 163.5, 151,
133.5, 128.7, 122.6, 121.9, and 120.4, with a mean of 134.5.
Estimated planetary A indices were 11, 11, 32, 20, 32, 50, and 54,
with a mean of 30.
NNNN
/EX