QST de W1AW
Propagation Forecast Bulletin 10 ARLP010
From Tad Cook, K7VVV
Seattle, WA March 8, 2002
To all radio amateurs
SB PROP ARL ARLP010
ARLP010 Propagation de K7VVV
Sunspot numbers are down, and the sun is relatively quiet, although there has been a solar wind stimulating some geomagnetic activity this week. Average sunspot numbers dropped nearly 16 points this week from last, and average solar flux was down more than 14 points. Geomagnetic planetary A indices moved out of the single digits this week and averaged about double last week's average. The most active day was February 28, with planetary K indices as high as five. Contesters were grateful that conditions quieted down for the ARRL International DX Contest SSB weekend. There was also some geomagnetic activity on March 5-6, when the K index over the course of several periods was four.
The sun should be quiet over the next week, with solar flux below 200.
The first day of spring is less than two weeks away. The equinox is a great time for HF propagation. Ten meters should be good over the next few weeks, and fifteen meters will improve as we move later into spring.
Carl, K9LA, writes to report that subtraction and multiplication were not his high point last week. Here's the corrected version of the data he reported. The monthly median critical frequency foF2 at Dyess AFB (Abilene, Texas) for December 2000 was 11.65 MHz. For December 2001, it was 13.2 MHz. That's a difference of 1.55 MHz and is representative of the increased worldwide ionization in December 2001.
With the F2 region MUF for a 3000-km path being about three times the critical frequency, that 1.55-MHz difference in critical frequencies translates to a MUF roughly 5 MHz higher in December 2001 than December 2000. This increase was due to the recent resurgence in Cycle 23 and goes a long way in explaining why December 2001 (and the months around it) were so good for 6 meters compared to a year ago.
Sunspot numbers for February 28 through March 6 were 188, 153, 153, 169, 197, 168 and 191, with a mean of 174.1. The 10.7-cm flux was 204.2, 187.7, 191, 182.7, 174.9, 172.2 and 177.8, with a mean of 184.4. Estimated planetary A indices were 17, 11, 5, 10, 9, 15 and 15 with a mean of 11.7.