ARLP035 Propagation de K7RA
ZCZC AP35
QST de W1AW
Propagation Forecast Bulletin 35 ARLP035
From Tad Cook, K7RA
Seattle, WA August 24, 2007
To all radio amateurs
SB PROP ARL ARLP035
ARLP035 Propagation de K7RA
Conditions were quiet this week, with no geomagnetic disturbances and most days had zero sunspots. For the past two days, August 22-23, the sunspot number was 11 and 12, indicative of a single sunspot group.
Slightly unsettled conditions are expected this weekend, with a planetary A index from August 24-30 expected at 8, 15, 15, 12, 8, 8 and 5. Sunspot activity is expected to remain low, as lone sunspot 969 moves across the sun.
Geophysical Institute Prague predicts quiet conditions for August 24, unsettled August 25, quiet to unsettled August 26, quiet August 27, unsettled August 28, and quiet again August 29-30.
Back in ARLP032 dated August 3, this bulletin said if the average sunspot number for August is above 20, then we will see another rise in our three-month moving average, which was also shown in that issue. Instead, for the three weeks and two days of this month we've had eight days of no sunspots, and the average sunspot number for the month thus far is 8.7. So perhaps early this spring was not the sunspot cycle minimum. Note the average sunspot numbers for March and April of this year were 9.8 and 6.9. Monthly averages seemed to be rising, until now.
Jerry Reimer, KK5CA wrote to us recently about NVIS propagation (Near Vertical Incidence Skywave, or high angle radiation for local or regional coverage). In his email, he wrote, ''NVIS experimenters and practitioners would do well to always consider the foF2 and fMUF values, available here:
http://www.sec.noaa.gov/ftpmenu/lists/iono_day.html . For most of the U.S., 40m is currently well above what is usable for NVIS propagation. Sometimes 60m is not usable, and this can sometimes also include 75/80m for some areas. Many people are confused when their low ''NVIS'' antenna (often a resonant horizontal wire dipole at 6-20 feet) is ineffective for high angle propagation above the fMUF, while it is effective in working stations over 200 miles away. Most of these antennas radiate signals at all angles, not just the highest angles, and the lower angle signals are refracted with more favorable S/N ratios than are the vertical signals, which pass through the F-layer. For reliable NVIS propagation, it is critical to select a frequency which is 50-80 percent below the fMUF''.
In that list that Jerry referenced, there are isosonde stations in North America, one of which may be local to you. Each page lists a latitude and longitude, but the format may be unfamiliar. They use an odd longitude reading that goes from zero degrees on the prime meridian east, covering the full 360 degrees. So if the number is E359, that would be one degree west of the meridian. For these stations in North America, just subtract the number shown from 360 to get the approximate location of the ionospheric sounding. For Dyess, it shows the location as N32E260. This would be 32 degrees north latitude, 100 degrees west longitude, because 360 minus 260 is
100.
Locations you might check, shown with the states they are in, are Millstone Hill (MA), Point Arguello (CA), Boulder (CO), Bear Lake (UT), Wallops (VA), Eglin (FL) and Dyess (TX).
The critical frequency you are looking for is in the foF2 column.
An interesting article about ionosondes is at
http://www.prc68.com/I/MWI.shtml .
Another list of stations is
http://www.ngdc.noaa.gov/stp/IONO/StationP12.html
, but I don't know where to get data from these.
(Source: Dave Raycroft/ODXA)
