SB PROP @ ARL $ARLP030<br />ARLP030 Propagation de K7VVV<br /><br />ZCZC AP30<br />QST de W1AW <br />Propagation Forecast Bulletin 30 ARLP030<br />>From Tad Cook, K7VVV<br />Seattle, WA July 19, 2002<br />To all radio amateurs <br /><br />SB PROP ARL ARLP030<br />ARLP030 Propagation de K7VVV<br /><br />A big, big sunspot had crossed the earth-facing side of the sun this<br />week. Sunspot 30 brought a nice short-term rise in the sunspot count<br />and solar flux, but also caused geomagnetic instability, with more<br />to come.<br /><br />Sunspot 30 first peeked around the eastern limb of the visible solar<br />disk about 10 days ago, and was directly facing earth around July<br />16. The sunspot number peaked at 209 on July 15, and on the same day<br />the Penticton observatory read a solar flux value of 323.6, clearly<br />off the scale anomaly. NOAA produced an adjusted value of 160 for<br />the day, which is the official solar flux number. A dramatic photo<br />of the sunspot group is currently displayed at<br />http://spaceweather.com/swpod/18jul02/peoples1.jpg . An amateur<br />captured this photo with a digital camera and a telescope with a<br />solar filter.<br /><br />A full-halo coronal mass ejection blasted away from the sun on<br />Tuesday, which caused unsettled to active conditions on Wednesday.<br />On Thursday there was a solar flare at 0745z.<br /><br />The average daily sunspot count for the week was up over sixteen<br />points when contrasted with the previous week, and average solar<br />flux rose by nearly sixteen points. Without the downward adjustment<br />of the flux value on July 15, the average for the week would have<br />risen by nearly forty points.<br /><br />If you go to gopher://sec.noaa.gov/00/indices/DSD you can see the<br />daily solar flux, sunspot number and sunspot area, along with some<br />other indices. It is interesting how the sunspot area kept<br />increasing between July 12 and 17, but the sunspot number peaked on<br />July 15. The daily sunspot number is calculated by taking the number<br />of groups of sunspots and multiplying by 10, then adding the product<br />of this calculation to the number of individual sunspots. So for<br />example, if 12 groups of sunspots were observed, but there were 43<br />individual spots, the sunspot number would be 163. The actual daily<br />number is calculated by taking observations from a number of places<br />around the globe. This is how it is possible for the total area<br />covered by sunspots to keep rising after the daily sunspot number<br />has declined, because while sunspots may be darkening a larger area,<br />this can happen when the number of spots and groups of spots is<br />lessening.<br /><br />You can grab some files of yearly sunspot data going way back to<br />1818 at ftp://ftp.ngdc.noaa.gov/STP/SOLARDATA/SUNSPOTNUMBERS/ .<br /><br />For the next few days the estimated planetary A index is expected to<br />rise to 20 on Friday, then 15 on Saturday and back to around 20 on<br />Sunday. Solar flux is expected to rise from 185 on Friday and<br />Saturday to 190 on Sunday, then 195 on Monday and Tuesday.<br /><br />We are in a summertime propagation mode, which is generally not as<br />good for HF communications as spring or fall. High noise levels and<br />shorter periods of darkness in the northern hemisphere make<br />propagation on 160 and 80 meters difficult.<br /><br />10 meters is not nearly as good as in the spring or fall, although<br />there is some sporadic E layer skip. 20 and 15 meters are probably<br />the best bet for long distance propagation, with 20 meters being<br />great to the Far East and the Pacific late at night. South America<br />is an easy shot from North America, with 80 and 40 meters good after<br />dark, and 30 meters opening earlier in the evening. 20 meters is<br />also good at night in this direction, but opening earlier than the<br />path to the Pacific. 15 meters is great over this trans-equatorial<br />path from the middle of the day to the early morning hours, closing<br />before sunset. Toward Europe, 20 meters is the best bet, but during<br />the evening hours, not during the day as it was in the spring.<br /><br />After last week's mention of the variation in the observed solar<br />flux tracking with the slight change in distance from the sun, W7YED<br />asked if this caused higher solar flux numbers in the winter than in<br />summer. Actually the variation in observed flux values caused by the<br />change in distance is slight, only a few points. This is not enough<br />to really affect HF propagation as much as week to week changes in<br />solar activity, particularly in the years around the peak of the<br />solar cycle.<br /><br />Sunspot numbers for July 11 through 17 were 99, 93, 141, 152, 209,<br />182 and 179, with a mean of 150.7. 10.7 cm flux was 136.4, 133.2,<br />134.9, 143.8, 160, 171.5, and 180, with a mean of 151.4. Estimated<br />planetary A indices were 9, 20, 8, 6, 8, 11, and 18, with a mean of<br />11.4.<br />NNNN<br />/EX