ARRL

ARRL Propagation Bulletin ARLP015 (2001)

SB PROP @ ARL $ARLP015
ARLP015 Propagation de K7VVV

ZCZC AP15
QST de W1AW  
Propagation Forecast Bulletin 15  ARLP015
From Tad Cook, K7VVV
Seattle, WA  April 6, 2001
To all radio amateurs 

SB PROP ARL ARLP015
ARLP015 Propagation de K7VVV

This has been another week of remarkable solar activity, with
Sunspot 9393 producing more excitement. Sunspot numbers peaked on
March 28 and 30 at 352 and 349, and solar flux on March 27 and 28 at
273.4 and 273.5. Total visible sunspot area peaked on March 29 at
3940 millionths of the solar hemisphere. This week solar flares
tossed out enough energy to overwhelm the equipment that measures
10.7 cm solar flux.

At 2300z on April 2 the flux reading was 563.1, and on April 5 the
readings were 582.5 and 398.7 at 1700 and 2000z. These
flare-enhanced readings would certainly be a new record far beyond
any daily values reported for this solar cycle, but they are
discarded because they don't reflect actual 10.7 cm energy. So for
April 5, instead of a daily reading of 398.7, NOAA reported 210,
probably a guess based upon declining daily readings and a more
accurate 2300z reading of 207.5.

Following the new high in sunspot numbers, we have seen a number of
large solar flares and resulting aurora. On April 2 the most
powerful flare in at least 25 years erupted. Fortunately most of it
was aimed away from earth. A few days earlier on March 31 the
planetary A index soared to 155 and the planetary K index went as
high as 9 during a severe geomagnetic storm. There were incredible
auroral displays, seen as far south as Mexico. See an amazing
gallery of aurora images, many from southern regions that very
rarely see aurora, at
http://spaceweather.com/aurora/gallery_31mar01.html .

Since March and the first quarter of the year are both over, it is
time to report some numbers for those periods. Average solar flux
for March was 177.7. This is an increase, as the average daily solar
flux for December through February was 173.6, 166.6 and 147.2.
Average daily sunspot numbers for March were 166.7, and for December
through February were 146, 143 and 131. Quarterly average solar flux
for last year was 180.5, 182.9, 188.3 and 173.3.

For the first quarter of this year the average solar flux was 164.4.
The average daily sunspot number for the quarter just ended was
147.3, and the quarterly sunspot averages for last year were 168.9,
190.8, 193.1 and 145. Although this quarter really ended with quite
a bang, the quarterly averages for both solar flux and sunspots were
lower than the same period a year earlier.

Although the really active regions have now rotated off of the
visible solar disk, there are more rotating into view. Predicted
solar flux for the next few days, Friday through Monday, is 210,
210, 205 and 205. The predicted planetary A index for those days is
15, 8, 8 and 10.

Someone passed along some interesting comments that Paul Harden,
NA5N posted on Thursday to a discussion group for low power amateur
radio. He noted that there seemed to be an HF blackout below 20 MHz
caused by ionizing radiation reaching the D layer. E and F layer
enhancement of the ionosphere is good for HF propagation, but D
layer enhancement tends to absorb radio waves. He recommends the
NOAA Space Weather Now site at http://www.sec.noaa.gov/SWN/ , then
clicking on D-region absorption to go to
http://www.sec.noaa.gov/rt_plots/dregion.html.

For some time now W6EL's MiniProp program for propagation prediction
has been unavailable. This is the program used to generate the
occasional path predictions shown in this bulletin. I am extremely
happy to report that W6EL has just released a new free version of
his software, this time for Windows, and you can get it at
http://www.qsl.net/w6elprop/. It works with all recent versions of
Windows, including 95, 98, ME, NT and 2000. Be sure to give this a
try, and send W6EL a note of thanks. It is a great piece of software
for looking at seasonal, time of day, frequency and solar activity
variables and their effects on HF communications.

In closing, there was just too much to report this week, but thanks
to everyone who wrote. I should also note that DL9KAC mentioned in
last week's Propagation Forecast Bulletin ARLP014 is actually
DL6KAC.

Sunspot numbers for March 29 through April 4 were 315, 349, 326,
320, 223, 228 and 217 with a mean of 282.6. 10.7 cm flux was 261.7,
256.8, 245.6, 257.5, 228, 223.1 and 204.8, with a mean of 239.6, and
estimated planetary A indices were 22, 10, 155, 30, 20, 5 and 15
with a mean of 36.7.
NNNN
/EX