ZCZC AP45
QST de W1AW
Propagation Forecast Bulletin 45 ARLP045
From Tad Cook, K7VVV
Seattle, WA November 7, 1997
To all radio amateurs
SB PROP ARL ARLP045
ARLP045 Propagation de K7VVV
Solar Cycle 23 showed renewed activity this week, as solar flux values went well over 100. Average solar flux for the week was up about 19 points, and average daily sunspot numbers were up about 36 points. The average solar flux for the previous 90 days went up two points from 87 to 89 over the week, and daily values were above this average on every day, indicating a strong upward trend. Flux values are measured three times per day at an observatory in Penticton, British Columbia. The one reported here is the noon measurement at 2000 UTC, but the highest flux measured for the week was actually 120.6 at 2200 UTC on November 4.
As solar activity was rising, geomagnetic conditions were very quiet, especially on November 2 and 3, when K indices were at one or zero most of the time. This meant that absorption of radio waves in the upper latitudes and over polar paths was minimized, and conditions on higher HF bands improved. These conditions did not last, and as this bulletin is being written on Thursday evening, the K index is six, and a major geomagnetic storm is raging. This is from a major flare that burst from the solar surface at 0558 UTC on Tuesday. Protons from this flare are slow moving, so it takes a couple of days to affect the Earth. There was another major flare on Thursday morning at 1155 UTC, so poor conditions may continue, although at this point it is uncertain if the new flare will hit the Earth directly with protons or not.
In last week's bulletin ARLP044 it was mentioned that active geomagnetic conditions created havoc in the recent CQ Worldwide DX Contest. Actually that was mostly true from a west coast contester's perspective, since contest stations in that region use a polar path to reach Europe. The east coast was not affected nearly as much, since that path to Europe is further to the east. It is mainly high latitude paths which are bothered during periods of geomagnetic activity.
For the short term, expect poor conditions until effects from these solar flares pass. If we are not affected by the latter flare, conditions may be back to normal by the middle of next week. Solar flux is expected to drop below 100 by November 11, below 90 two days later, and to the mid-eighties after the middle of the month. It should rise above 90 again around November 23, and above right after Thanksgiving. Periods of unsettled to active geomagnetic conditions are forecast around November 20-23, a recurrence of the conditions during the recent DX contest.
For updates on the storm, check WWV at 18 minutes after the hour, or call 303-497-3235. Conditions should be back toward normal when the K index is three or less, although the ionosphere may take some time to recover. Some good sites on the web to check for alerts and information are Cary Oler's Solar Terrestrial Dispatch page at http://holly.cc.uleth.ca/solar/ or NOAA's Space Environment Center at http://solar.sec.noaa.gov.
Sunspot Numbers for October 30 through November 5 were 51, 55, 62, 74, 66, 68 and 51 with a mean of 61. 10.7 cm flux was 88.2, 90.5, 93, 97.8, 109.8, 117.9 and 113.8, with a mean of 101.6, and estimated planetary A indices were 10, 4, 8, 3, 3, 9, and 9, with a mean of 6.6.