ARLP013 Propagation de K7RA:
March 26, 2004

Propagation Forecast Bulletin 13 ARLP013
From Tad Cook, K7RA
Seattle, WA March 26, 2004
To all radio amateurs

ARLP013 Propagation de K7RA

Solar flux and sunspot numbers rose this week, and geomagnetic K and A indices were down. This is a perfect combination for the first days of spring. HF operators always love to see the K index lower than 3 and the A index below 10. There is nothing magic about those numbers, but lower numbers are better, and those are below the values (about K=3 and A=15) that we think of for unsettled conditions.

For quiet conditions, it's hard to beat this last Wednesday, March 24, when the mid-latitude K index was 0 for most of the reporting periods. With sunspot numbers rising amid quiet geomagnetic conditions, the springtime propagation over the past week has been fantastic.

Average daily sunspot numbers rose nearly 27 points to 92.7 this week (compared to last). The average daily planetary A index dropped nearly 7 points to 8.7. Sunspot numbers and solar flux are rising, and the predicted solar flux for this weekend, March 26-28 is 130, 135 and 130. This may be due to a pair of large sunspots emerging over the sun's northeastern limb.

But early spring is also a time when auroras are more intense, which of course is an indicator of elevated geomagnetic activity. This weekend is the CQ World Wide WPX SSB Contest, and the outlook for the next few days is good, with some active conditions probably returning around March 29-30.

A bulletin received earlier today from the Australian Government IPS Radio and Space Services warns that there may be rising geomagnetic activity this Saturday, March 27 due to solar wind from a coronal hole. One good daily resource for updates on solar wind streams is

Mark Dullea of Peabody, Massachusetts asked for a good source of daily Ap readings (planetary A index). The place to go is the NOAA Space Environment Center at This is also a good resource for comparing the daily variations in mid-latitude, high-latitude and planetary geomagnetic indices mentioned in the first paragraph.

Tony Salvate, N1TKS of Greenwich, Connecticut wrote for any thoughts regarding a friend who is going fishing about 150 miles south of the Arctic Circle in Northwest Canada this summer. He will be packing HF gear along with a solar panel and batteries, and Tony wonders about propagation to the Northeast United States. I noted that being so far north, propagation will be strongly affected by geomagnetic conditions, so hope for a K index lower than 3.

I also suggested calculating some paths with W6ELprop, the free propagation prediction program from I ran some projections for the end of June from Rae Lakes, Northwest Territories (which is roughly the area Tony described) to Tony's location and found some good possibilities for 40, 30 and 20 meters.

Users of Scott Craig's Solar Data Plotting Utility may or may not have noticed a leap year error a few weeks ago. If you look at the data file, February 29 is not there. Open the graph.dat file with a text editor such as Windows Notepad, and insert 81 for sunspot number and 110.0 for solar flux for the 29th.

If you haven't used Scott's program, you can download it from the WA4TTK web site at This program automatically sucks up the data from the end of each of these bulletins and displays it in a nice graph running from January 1, 1989.

For more information concerning propagation and an explanation of the numbers used in this bulletin see the Propagation page on the ARRL Web site at

Sunspot numbers for March 18 through 24 were 107, 89, 82, 65, 87, 110 and 109 with a mean of 92.7. 10.7 cm flux was 115.4, 112.2, 113.6, 111.2, 116.4, 118.3 and 119.7, with a mean of 115.3. Estimated planetary A indices were 10, 6, 9, 13, 11, 8 and 4, with a mean of 8.7.