ARLP031 Propagation de K7RA:
August 1, 2003

Propagation Forecast Bulletin 31 ARLP031
From Tad Cook, K7RA
Seattle, WA August 1, 2003
To all radio amateurs

ARLP031 Propagation de K7RA

Strong geomagnetic activity continues. The estimated Planetary A Index is a number derived from observations at geomagnetic observatories around the world. The higher the A index, the higher the geomagnetic activity, and generally this is worse for HF propagation.

We like to see low geomagnetic activity with lots of sunspots for great HF propagation. Unfortunately, after the peak of a solar cycle we can experience long periods of active geomagnetic conditions. This week the average daily planetary A index jumped to 21.9 from 16.1 the previous week.

Sunspots and solar flux were down quite a bit from the previous week. Average daily sunspot numbers dropped from 195.3 to 74.6, and average daily solar flux went from 147.7 to 106.2.

Daily solar flux values are expected to stay around 105-115 from August 1-8, and then rise to around 140 from August 12-18. The planetary A index for Friday through Monday, August 1-4 is expected to be 25, 20, 15 and 10. August 4-6 is expected to be a quiet geomagnetic period, worth a try for reasonable HF propagation.

Now that July has passed, we can look at some monthly averages for solar flux and sunspot numbers.

Due to some high values around the middle of the month, July actually had higher average daily sunspot numbers than any month since January. The monthly average sunspot numbers, January through July, were 150, 87.9, 119.7, 114.3, 89.6, 118.4 and 132.8.

July's average daily solar flux was just a little lower than the June values. Average daily solar flux values for January through July were 144, 124.5, 133.5, 126.8, 116.6, 129.4 and 127.7.

The fall equinox is a little over seven weeks away. HF conditions should improve as the days grow shorter and we move from summer to fall propagation.

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

Sunspot numbers for July 24 through 30 were 134, 94, 52, 60, 56, 63, and 63, with a mean of 74.6. 10.7 cm flux was 125.2, 111.6, 102.6, 101.7, 103.4, 99.9, and 98.7, with a mean of 106.2. Estimated planetary A indices were 10, 11, 26, 24, 17, 36, and 29, with a mean of 21.9.