QST de W1AW
Propagation Forecast Bulletin 47 ARLP047
From Tad Cook, K7RA
Seattle, WA November 21, 2003
To all radio amateurs
SB PROP ARL ARLP047
ARLP047 Propagation de K7RA
The three sunspots that raised so much havoc at the end of October are back after journeying across the sun's far side. The planetary A index of 117 on Thursday, November 20 indicates a very strong geomagnetic storm. The mid-latitude A index was 67, and Alaska's College A index was 161. Average daily sunspot numbers for the week rose to 63 from 32.6 last week. Average daily solar flux rose from 94.8 to 117.7, and average daily planetary A index went from 23.4 to 31.7.
Over last weekend, a solar wind disturbed Earth's magnetic field. Conditions were disturbed until November 19, when the planetary and mid-latitude A indices were in a normal range. The day before, Tuesday, November 18, sunspot 486 pushed a coronal mass toward Earth. This was the event that caused all the upset two days later on November 20.
Ken Brown, N4SO, on the USNS Bowditch, a surveying ship in the Military Sealift Command reports from somewhere around the South China Sea that he copied the W1AW AMTOR FEC signal on 14.095 MHz at 2315 UTC on November 18. His equipment consisted of a Global Marine Distress and Safety System (GMDSS) receiver and a whip antenna. The path is more than 8000 miles. A projection with the W6ELprop software for that day shows 2300-0000 UTC may have been the end of a short opening that probably began around 2130 UTC.
Rough conditions should subside over the weekend. Current projection shows the planetary A index from Friday to Monday, November 21-24, at 45, 35, 20 and 20. Predicted solar flux values over the same period are 180, 190, 200 and 210. High sunspot and solar flux levels are expected to remain through Thanksgiving, November 27.
Diane Leveque, NH6HE, suggested the Lockheed Martin Solar and Astrophysics Laboratory Web site. It shows dramatic photos and measurements of solar events.
John Huffman, NA8M, asks: "Conditions here in the northern latitudes of Michigan are much different than for those folks in Florida and Texas. Which propagation indicators should I look for to see if the north, in particular, is going to have lousy conditions?"
John should check the mid-latitude K index transmitted by WWV at 18 minutes after each hour. It is updated every three hours. When this value rises above 3, conditions will get rough, and the higher latitudes will feel it more than the lower latitudes. Every K index point represents a significant change, and at the end of the day, the K indices are used to calculate the A index for that date. A full day of K indices at 3 would yield an A index at 15. A full day of K equal to 4 would be A equal to 27, and with K equal to 5 the A would be 48.
On Thursday, November 20, the mid-latitude A index was 67. Starting early in the UTC day (Wednesday evening in North America) the K index was only 1, then it rose to 3, 5, 6, 5, 7, 7 and then 6.
Likewise, when the K index goes lower, the geomagnetic field is more stable and HF paths should become more reliable. It can go all the way down to zero.
In addition to getting the K index from WWV, you can check the WWV message on line. You can also check recent A and K indices for mid-latitude, planetary and high latitude values. Yet another option is to call 303-497-3235, which provides a recording of the latest WWV message. Live WWV audio is available by telephone too, at 303-499-7111.
Because of the Thanksgiving holiday, next week's Solar Update will be issued Wednesday, November 26.
For more information about propagation and an explanation of the numbers used in this bulletin see the Propagation page on the ARRL Web site.
Sunspot numbers for November 13 through 19 were 25, 34, 52, 54, 72, 90 and 114, with a mean of 63. The 10.7 cm flux was 102.1, 98.9, 97.8, 104.4, 121, 144.3 and 155.1, with a mean of 117.7. Estimated planetary A indices were 42, 37, 40, 35, 34, 20 and 14, with a mean of 31.7.