QST de W1AW
Propagation Forecast Bulletin 21 ARLP021
From Tad Cook, K7RA
Seattle, WA May 23, 2003
To all radio amateurs
SB PROP ARL ARLP021
ARLP021 Propagation de K7RA
Carl Luetzelschwab, K9LA, is filling in for Tad Cook, K7RA, this week.
During the reporting period--Friday, May 16, through Thursday, May 22--solar activity was low. Geomagnetic field activity was generally quiet to unsettled during the first half of the period, then increased to active to minor storm at the end of the period due to increased solar wind from coronal hole activity that reached Earth on May 21.
Solar activity is forecast to be low for the next three days. Geomagnetic field activity for the next three days is forecast to have roughly a 40-percent probability of being active, with slightly quieter conditions as we move into the weekend.
Last week's bulletin included the comment, "Disturbed conditions occur more often when the solar cycle has passed the peak and is headed down." Historical data indeed show that geomagnetic storms (the "G" in the WWV report) occur more frequently during the decline of a solar cycle, whereas big solar flares that can cause polar cap absorption events (the "S" in the WWV report) and radio blackouts (the "R" in the WWV report) occur more frequently at the peak of a solar cycle. So the good news is that big solar flares probably won't be causing too many problems in the foreseeable future.
That leaves the bad news. The accompanying plot (covering the peak of Cycle 21 to the present) shows the smoothed sunspot number versus the number of days in the month when the planetary A index (Ap) was less than or equal to 7 (signifying quiet conditions). The thin green line following the spiky Ap data is a trend line to more clearly indicate what's happening.
The plot confirms that the declining phase of a solar cycle is the period with the most geomagnetic field activity (where the trend line is lowest). So for the next year or two we'll have to put up with a much higher probability of disturbed conditions. At least there's some seasonal relief to this, with the summer and winter months quieter than the months around the equinoxes.
The plot also shows that the quietest period--when the trend line is highest--is a year or two after solar minimum. Your author looks back fondly on the consistently excellent 160-meter propagation conditions during the winters of 1996 and 1997, when much DX was worked with his modest station. Those conditions will be back!
For contest enthusiasts, this weekend is CQ WPX CW. For a general picture of propagation for the contest, let's look at SSNe (the effective sunspot number--the sunspot number that forces the model of the F region to a best fit to real-time worldwide F region ionosonde data). Eyeballing the SSNe plot shows SSNe to be in the neighborhood of 60 and heading down (as of the evening of May 22). Plugging this value into your favorite propagation prediction software will show that 20 and 40 meters--and, to an extent, 75 meters--will be the workhorse bands for the contest. Fifteen meters will be right on the borderline between good and not good, and which way it goes will depend on the day-to-day variation of the ionosphere and the geomagnetic field activity.
Ten meters is going to be tough going for the contest, with a low probability of any consistent F region openings to the major overseas ham population areas (Europe and Japan). This is not surprising, as Cycle 23 is definitely in its decline. A good piece of advice for 10, 15 and 20 meters is to monitor the NCDXF beacons. If this isn't feasible, keep an eye on the trend of SSNe during the contest (it is updated hourly). Since it's tied to real-time F region ionosonde data, it will reflect to a certain degree the impact of geomagnetic field activity on the F region (for example, note the nice short duration increase in SSNe early on May 22 due to the effect of the solar wind speed increase the day before). If SSNe gets up to 80 or so, that may mean 15 meters will be productive, and it may even signal the possibility of a 10-meter opening.
And don't give up completely on 10, as we still could have domestic openings via sporadic E (CQ WPX format is everybody works everybody) and even transequatorial propagation into South America.
Regardless of the propagation conditions for WPX CW, jump in and have some fun. Contests are an excellent way to pick up new states, countries, and zones for your WAS, DXCC, and WAZ awards.
Sunspot numbers for May 15 through 21 were 97, 97, 81, 79, 75, 77 and 79, with a mean of 83.6. The 10.7-cm flux was 99.2, 102.6, 102.4, 109, 114.7, 117.1 and 119.3, with a mean of 109.2. Estimated planetary A indices were 23, 9, 9, 10, 12, 12 and 20, with a mean of 13.6.