ARRL

ARRL Propagation Bulletin ARLP014 (2001)

SB PROP @ ARL $ARLP014
ARLP014 Propagation de K7VVV

ZCZC AP14
QST de W1AW  
Propagation Forecast Bulletin 14  ARLP014
From Tad Cook, K7VVV
Seattle, WA  March 30, 2001
To all radio amateurs 

SB PROP ARL ARLP014
ARLP014 Propagation de K7VVV

This has been an amazing week of high solar activity. For some time
now the assumption has been that activity was declining from last
year's peak, but now it seems that cycle 23 did not peak and then
begin declining in 2000 after all. This week's activity was so
remarkable that we put out mid-week bulletin ARLP013 a few days ago
to report it.

The peak solar flux values in 2000 were 262 on May 17 and 261.9 on
July 18. Then on Monday of this week a growing region 9393 produced
a new high for cycle 23 of 263.7. The next two days produced even
higher solar flux numbers of 273.4 and 273.5, breaking the cycle 23
record two more times. The highest recorded solar flux for the week
was actually at 2300z on Wednesday, at 293.8, but this one does not
count because the official daily number is always taken at 2000z in
Penticton, B.C.

It is interesting to look at the progression of all the recent solar
flux numbers, including the morning and afternoon readings.
Beginning at 1700z on March 18, and running through 2300z Thursday,
March 29, they were 135.3, 139.8, 143.1, 145.4, 147.0, 147.9, 157.2,
153.3, 158.1, 154.2, 159.4, 160.3, 180.4, 183.0, 184.0, 178.9,
180.0, 179.8, 201.1, 218.7, 216.6, 248.9, 216.8, 229.5, 247.6,
263.7, 261.1, 271.6, 273.4, 276.3, 272.4, 273.5, 293.8, 261.0,
261.7, and 276.1. We have not seen a value as high as 293.8 since
the period of January 30 through February 2, 1992 when they were
280, 303, 284 and 288.

Sunspot numbers also went very high this week, peaking at 352 on
Wednesday. This is not a record for cycle 23, which had a higher
sunspot number of 401 on July 20, 2000.

The cause of all this excitement is an explosion in the number and
size of sunspots recently, the largest being region 9393, which is
the largest sunspot to appear in the last 10 years. Astronomers rate
the size of sunspots in terms of millionths of the sun's earth-
facing hemisphere. A big sunspot measures 300 to 500 millionths, and
9393 registered about 2400 millionths on March 29. The biggest spot
of the current cycle, until now, was 9169 which measured 2140
millionths on September 20, 2000. There is also a statistic for the
total area of all the visible spots, and that has been growing
steadily and is still growing. The numbers for March 23 through 29
were 1210, 1760, 1870, 2290, 2830, 3830 and 3940.

Unfortunately, while earlier in the week we were blessed with low
geomagnetic indices (indicating good HF radio conditions and low
absorption), a frequent byproduct of high solar activity is solar
flares, and a bombardment of protons. The high A indices of last
week are back again, and there is more activity predicted for the
next few days due to a coronal mass ejection from sunspot 9393 on
Wednesday. The probable planetary A index for Friday and Saturday is
50, dropping to 30 on Sunday and 15 on Monday. Predicted solar flux
for the next few days (Friday through Monday) is 260, 255, 250 and
245. These numbers are difficult to predict though, because there is
so much new activity.

Quite a bit of email was received this week (via k7vvv@arrl.net)
concerning propagation reports. Most reported bands open louder and
longer. Of course, it helps that this activity follows the spring
equinox, when the northern and southern hemispheres are each
receiving a lot of solar radiation.

NG3Q reported working Cocos Keeling (a 10,400 mile path from
Cleveland) on Sunday with loud signals. W3FF heard and was called by
AP2JBZ in Pakistan on 12 meters, but W3FF was too weak for the AP2
to work him. Nothing remarkable about this, except that W3FF was
walking in Northern California and using a handheld antenna and
radio. NX9B in Southern Indiana noted that 15 meters was open later
than usual when he worked Pakistan at 0340z, and China at 0003z on
10 meters with a dipole. DL9KAC near Bonn on Tuesday said
propagation was very good to the Pacific and Asia on 10 and 15
meters. KF4ZAB in N.E. North Carolina had great luck with 35 watts
and a ground-mounted vertical working Europe on 10 and 17 meters.
3B8GO in Mauritius noticed a big peak in conditions around the 27th.
Unfortunately, the reports from 6 meters were unremarkable.

Once geomagnetic conditions quiet down, expect great conditions
again, with 20 meters open all night to the west and 15 meters open
into the evening. Monitor WWV at 18 minutes after the hour (or call
303-497-3235) and when K indices are 3 or less, good conditions may
return.

By the averages below, we can see that the average sunspot number
for this week was more than double last week's, rising from 101.7 to
248. Average solar flux rose nearly 86 points to 229.9. Average
figures one year ago were comparable to this week, although somewhat
lower, with sunspot numbers at 237.3 and solar flux at 210.6.

Sunspot numbers for March 22 through 28 were 129, 145, 204, 276,
339, 291 and 352 with a mean of 248. 10.7 cm flux was 183, 180,
218.7, 216.8, 263.7, 273.4 and 273.5, with a mean of 229.9, and
estimated planetary A indices were 10, 21, 13, 8, 6, 18 and 31 with
a mean of 15.3.
NNNN
/EX