ARLP053 Propagation de K7RA:
December 23, 2004

Propagation Forecast Bulletin 53 ARLP053
From Tad Cook, K7RA
Seattle, WA December 23, 2004
To all radio amateurs

ARLP053 Propagation de K7RA

After passing the longest night of the year, the northern hemisphere will have gradually increasing sunlight over the next six months. These seasonal variations have a big effect impact on propagation. As an example, using a popular propagation program to calculate a path from Seattle to Cleveland on December 22 with a sunspot number of 35 (average value for December 20-22), I looked at a projection for the 30 meter band. 30 meters should open toward Ohio around 8:00 AM Seattle time, around Seattle's sunrise. Expected signals should be good until sunset, when signals jump higher by 10-20 db. Then the chance of an opening stays low most of the night. From sunrise to sunset is 8 hours and 20 minutes.

Running the same values two months later, there are nearly two more hours of sunlight at the Seattle end. 30 meters looks good to Cleveland most times of the day and night, except for a low probability of an opening from after midnight until sunrise at the Seattle end.

Los Angeles sits in much more sunlight than Seattle in the dead of winter, with almost 10 hours from sunrise to sunset on the solstice. On December 22 the 30 meter path to Cleveland is open most hours of the day and night. The possibility of an opening drops during the hours of 6-9 PM LA time, and again from 2-5 AM. On February 22, LA sees over 11 hours from sunrise to sunset, and 30 meters should be open to Cleveland with strong signals at any time, except for a brief period with lower chance of an opening just before LA sunrise.

Jack Bock, K7ZR (SK) used to write about the ''Sufferin' Sevens'' in the Totem Tabloid, the newsletter for the Western Washington DX Club. He was referring to hams in Washington state and probably KL7, not Arizona. Having more light really does help.

For the past week, sunspot numbers were up and the A index was lower when compared to the previous week. Average daily sunspot numbers and solar flux values rose over 5 points, and the mid-latitude A index was down over two points.

For the next week, daily sunspot numbers should be moderately higher and solar flux should stay above 100 until the last day of the year. At that time, we can look at the average sunspot numbers for 2004, and compare them with previous years. Right now it looks like the average daily sunspot number for 2004 will come in about 40 points lower than 2003 and over 100 points lower than 2002.

If you would like to comment or have a tip, email the author at

For more information concerning propagation and an explanation of the numbers used in this bulletin see the ARRL Technical Information Service propagation page at

Sunspot numbers for December 16 through 22 were 14, 40, 40, 29, 30, 25 and 47 with a mean of 32.1. 10.7 cm flux was 90, 89.9, 90.6, 94, 93.9, 101 and 98.8, with a mean of 94. Estimated planetary A indices were 10, 15, 12, 4, 4, 12 and 19 with a mean of 10.9. Estimated mid-latitude A indices were 8, 9, 8, 1, 2, 6 and 12, with a mean of 6.6.