[K6BW] Solar Info from K6TR - a very useful overview stolen fromsolarcycle24.com

[Lars Williamson]

Thanks Bill, for sharing the petty pilferage.
Great review - concise, inclusive, and helpful.
Lars W6RMY/NNN0HJH-inactive

  ----- Original Message ----- 
  From: Bill Smith<mailto:hbco2 at sbcglobal.net> 
  To: HWA<mailto:k6bw at mailman.qth.net> 
  Sent: Wednesday, September 23, 2009 8:00 PM
  Subject: [K6BW] Solar Info from K6TR - a very useful overview stolen fromsolarcycle24.com


  Hams in North America have HF allocations on 1.8, 3.5, 7.0, 10.0, 14.0, 18, 21, 24 and 28 MHz. We have VHF Allocations on 50 and 144 MHz. Some countries in Europe also allocate 70 MHz to hams but we don't have that here. Propagation works differently between HF and VHF. HF Communications is capable of achieving worldwide distances when reflecting off the F Layer of the Ionosphere. The Maximum Usable Frequency is determined by a number of factors but the key is Ionization from the UV Radiation generated by Sunspots. Other factors which determine the MUF are the season and the time of day. The MUF peaks in early afternoon. During solar Minimum the MUF rarely rises above 14 MHz and at night drops to 7 to 10 MHz. Because this Solar Minimum is so low it is currently dropping to 6 MHz. At the peak of the Solar Cycle the MUF can reach into the VHF Spectrum but that rarely lasts more than a year. The Cycle 21 and 22 Peaks brought exceptional conditions to 50 MHz. Cycle 23 was lower a
   nd we had marginal conditions on 50 MHz. We did have very good conditions on the higher HF bands 21, 24, and 28 MHz. On the low bands 1.8, 3.5 and 7 it is possible to work around the world but it takes Big Antennas and lots of power to overcome the Ionospheric D-Layer Absorption. The higher bands don't have that problem. So at the peak of the Solar Cycle one can throw a wire out the window and work the world with 100 watts when the band is open.

  Now to VHF. There the dominant modes are Sporadic E, Ground Wave, and Auroral E. If you have the money you can also run moonbounce but that is trending toward UHF. Anyway E Layer communications runs about 500 to 1000 miles if you use Aurora. Aurora happens when the E-Layer is ionized in the Polar region of the globe by a geomagnetic storm. This storms can generated by a Solar Wind from a Coronal Hole or from a burst from a Sunspot CME. Either can happen at anytime. But the source of the disturbance has to strike the earth in order for it to create a Geomagnetic Storm. They are more frequent as the Cycle becomes more active.

  Regarding the flares we had today they came from Region 1026 which was not in a Geoeffective Position at the time of the flare so it is unlikely they will generate a storm. In terms of CMEs we get our first hint as to whether they will hit earth 4 minutes after the event. While good for VHF Propagation CMEs and Coronal Holes are bad for HF Propagation.

  The key to HF Propagation as I stated earlier is UV Radiation. And we need a steady flow of it. We will not see much in the way of improved HF Prop until the Solar Flux rises above 90 and stays there for a while. If it briefly pops above 90 and then recedes like it did in March 2008 that will do nothing for us. The Ionosphere really needs to be cooked ! For 28 MHz to come alive the SF has to remain above 125. The 50 MHz band needs a minimum sustained SF of 175 and 200 is more realistic. With the weak cycle that is being predicted we will be lucky to have more than a year of good conditions on 28 MHz. 50 MHz F Layer looks to be out of the question this go round. But right now even a minor open on 21 MHz would be a pleasant surprise after the minimum we've been through.
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