SB PROP @ ARL $ARLP011   
   ARLP011 Propagation de K7RA   
      
   ZCZC AP11   
   QST de W1AW     
   Propagation Forecast Bulletin 11  ARLP011   
   From Tad Cook, K7RA   
   Seattle, WA  March 18, 2011   
   To all radio amateurs    
      
   SB PROP ARL ARLP011   
   ARLP011 Propagation de K7RA   
      
   Average daily sunspot numbers this week plummeted 45 points to 69,   
   and average daily solar flux was off over 26 points to 113.1.  In a   
   brief report for the ARRL Letter we said that average flux was off   
   nearly 25 points to 114.5.  The average changed because the   
   observatory in Penticton reported the solar flux for Wednesday,   
   March 16 as 104.9, but later it was adjusted down to 95 by NOAA's   
   Space Weather Prediction Center.   
      
   This happens sometimes when energy from a Coronal Mass Ejection   
   overwhelms the 2.8 GHz (10.7 cm wavelength) receiver at the Dominion   
   Radio Astrophysical Observatory in Penticton, British Columbia.  A   
   good example was on March 7, 2011 when the noon solar flux reading   
   was 938.6.  This was an obvious outlier, caused by a solar flare out   
   of sunspot group 1166 that was positioned near optimal   
   geoeffectiveness. As a result, the official number was adjusted down   
   to 122.  But Wednesday's number didn't seem so obviously out of   
   line, and the timing didn't seem to line up with the only event I   
   knew of, an eruption from sunspot group 1169, which was nearly over   
   the solar horizon.   
      
   When I saw an image at http://www.spaceweather.com showing the CME   
   on the western limb with a time stamp of 2048z, I assumed this meant   
   the event occurred 48 minutes after the 2000z flux reading.  But it   
   turned out to be a long duration event.   
      
   Rob Steenburgh, KA8JBY works at the Space Weather Prediction Center   
   in Boulder, and looked into this for us.  He checked with the   
   forecasters, who wrote:   
      
   "The Penticton noon flux did come at 105 but was flare enhanced. We   
   estimated a value of 95 based on the morning flux.   
      
   "The long duration event (LDE) began at 16/1752Z, max at 16/2034Z   
   and end at 16/2324Z. It peaked at C3.7 from Region 1169 (N18W75).   
   The Penticton noon reading is taken between the hours of 1900 -   
   2000Z, so right in the middle of the LDE.  It was an extremely   
   impressive looking event on GOES-15 SXI."   
      
   So I didn't realize that the noon reading was actually taken over   
   the course of the hour before noon, not just a snapshot right at   
   local noon (2000z).  Rob clarified this, and said there are four   
   readings taken over the hour.  One is ignored (the outlier, or the   
   one most different from the other three) and the rest are averaged   
   to produce the noon solar flux.  So that estimate for Wednesday was   
   95, and the measured value for Thursday was 90.1, which seems   
   consistent with the declining sunspot numbers for Wednesday and   
   Thursday, 50 and 45, and the shrinkage of total sunspot area, 300   
   and 170 millionths of a solar hemisphere.   
      
   Last Friday, March 11 the planetary A index reached 40 due to a   
   powerful X1.5 class solar flare at 2323z on March 9.  This is   
   another definite indication that solar Cycle 24 is ramping up.   
   After four years of no X class flares, there have been two in the   
   last month.   
      
   The past few days have seen very quiet geomagnetic conditions, with   
   the K index in most locations at 0.   
      
   The latest forecast shows quiet conditions with planetary A index   
   around 5 until March 27-30, when predicted planetary A index is   
   expected to rise to 7, 7, 19 and 7.   
      
   Geophysical Institute Prague predicts quiet conditions March 18-19,   
   unsettled March 20, quiet to unsettled March 21, unsettled March 22,   
   quiet to unsettled March 23, and quiet on March 24.   
      
   Predicted solar flux for March 18-25 is 85, 80, 85, 90, 95, 100,   
   105, 110, and 85 on March 26-29.   
      
   This Sunday is the Spring Equinox in the Northern Hemisphere, a   
   welcome sign for DXers everywhere, when both the northern and   
   southern hemispheres are bathed in an equal amount of solar   
   radiation.   
      
   In the bulletin preview yesterday, we promised to explain how the   
   geomagnetic A index for the day is calculated using the eight K   
   index values throughout the day.  Here is how it works.   
      
   The K index value is not linear, and is based on magnetic   
   measurements in units called nano-Teslas.  K index of 0 corresponds   
   to a three-hour measurement of 0-5 nT, 1 is 5 >nT, K of 2 is >10, 3   
   is >20, 4 is >40, 5 is >70, 6 is >120, 7 is >200, 8 is >339, and 9   
   is >500 nT.  The idea of the A index is to take an average of the K   
   index to express a value for the whole day, but because the K index   
   is not a linear scale, it is not realistic to just average the eight   
   K index measurements.  Instead, we convert each K index into a   
   linear scale called the A index, then average those, and that yields   
   the A index value for the day, which is always expressed in whole   
   numbers.   
      
   The equivalent A values for each K value are, K of 1 is 3, 2 is 7, 3   
   is 15, 4 is 27, 5 is 48, 6 is 80, 7 is 140, 8 is 240 and 9 is 400.   
      
   So looking at http://www.swpc.noaa.gov/ftpdir/indices/DGD.txt, note   
   the high-latitude A index (measured at the University of Alaska at   
   Fairbanks) on March 11, 2011 is 56, a high value.  The eight K index   
   values are 4, 4, 5, 5, 5, 7, 6 and 4.  Those convert to A values of   
   27, 27, 48, 48, 48, 140, 80 and 27.  The sum of those is 445.   
   Divide by eight, and the average is 55.625, which rounds out to 56,   
   the A index for the day.   
      
   Bert Ingalls, KH6HI, operates a 6-meter beacon in Hawaii on the   
   island of Oahu.  The KH6HI/B beacon is on 50.0645 MHz and runs 20   
   watts into a pair of horizontally polarized loop antennas stacked   
   vertically at about 2/3 wavelength, or 12 feet apart.  It is at a   
   commercial broadcast site in the Waianae mountain range (see   
   http://www.6meterbeaconproject.org/kh6hi.html) at 2,500 feet with an   
   unobstructed shot to the horizon in all directions.   
      
   On Saturday, March 12, LW3EX in Buenos Aires reported hearing the   
   beacon at 2349z with an RST of 539.  Between grid squares BL01 and   
   GF05 is a distance of about 7,600 miles.  Bert wrote, "I believe the   
   following report is the first TE/F2 to South America from Hawaii for   
   Cycle 24.  It occurred at 1:49 PM local time which is typical for   
   TE/F2 in that direction during previous solar cycles.  I would   
   expect that propagation to ZL/VK and other South Pacific islands   
   will begin to occur as well providing the solar flux continues to   
   remain at current or higher levels."   
      
   Bob Forsman, WK5X of Stuarts Draft, Virginia wrote about the recent   
   report of possibly very long distance Argentina to North Carolina 2   
   meter propagation, and notes that this type of report isn't   
   unprecedented.  He found a couple of reports from 1979 and 1981 in   
   the March 2010 "World Above 50 MHz" column in QST, and included   
   these with some of his own comments.   
      
   "1) The December 1981 "The World Above....." column details a   
   September 23, 1981 (evening) occurrence of 2-Meter propagation   
   between CP5CL (Cochabamba, Bolivia) and the WB5QFM 2-Meter repeater   
   near Arcadia, Louisiana. It is interesting that this path, along   
   with last week's path, both occurred during an equinoctial (but   
   opposite) period. The South American station was full quieting into   
   the Louisiana repeater for 30 minutes, and then dropped to about 3 X   
   5 for a couple of hours.   
      
   "2) LU1DMA reports a QSO on 2-Meter SSB with Steve, WB9YWN (now   
   AF9X) on March 1, 1979 (last week's report was from March 2). After   
   tracking down AF9X, it was determined that Steve was likely   
   operating either maritime mobile from the vicinity of Bermuda, or   
   fixed from Charleston, South Carolina. These paths are not   
   dissimilar to the path reported last week."   
      
   If you would like to make a comment or have a tip for our readers,   
   email the author at, k7ra@arrl.net.   
      
   For more information concerning radio propagation, see the ARRL   
   Technical Information Service web page at   
   http://arrl.org/propagation-of-rf-signals. For an explanation of the   
   numbers used in this bulletin, see   
   http://arrl.org/the-sun-the-earth-the-ionosphere. An archive of past   
   propagation bulletins is at   
   http://arrl.org/w1aw-bulletins-archive-propagation. Find more good   
   information and tutorials on propagation at   
   http://mysite.ncnetwork.net/k9la/index.html.   
      
   Monthly propagation charts between four USA regions and twelve   
   overseas locations are at http://arrl.org/propagation.   
      
   Instructions for starting or ending email distribution of ARRL   
   bulletins are at http://arrl.org/bulletins.   
      
   Sunspot numbers for March 10 through 16 were 88, 105, 78, 64, 51,   
   47, and 50, with a mean of 69. 10.7 cm flux was 131.3, 123.1, 120.7,   
   112.9, 107.4, 101.5, and 95, with a mean of 113.1. Estimated   
   planetary A indices were 20, 40, 13, 6, 6, 0, and 0, with a mean of   
   12.1. Estimated mid-latitude A indices were 14, 18, 10, 5, 2, 0, and   
   1, with a mean of 7.1.   
   NNNN   
   /EX   
      
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   neighbors and community isn't just a good thing to do,  it's   
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