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The K7RA Solar Update


Here we are at the summer solstice for the Northern Hemisphere, which was at 0504 UTC today, June 21. If you are west of the Central time zone, to you it was last evening. Today is the longest day of the year, but the length of your day varies considerably depending on your latitude.  In San Diego, the sunrise is at 5:48 AM, and it sets 14 hours later at 7:53 PM. In Seattle the sun rises today at 5:21 AM and sets at 9:01 PM, 15 hours and 40 minutes later. But in Fairbanks, Alaska, the sun rises today at 3:39 AM and doesn’t set until tomorrow at 12:06 AM, 20 hours and 27 minutes later!

Right now many of us are interested in what HF radio conditions should be for this weekend during ARRL Field Day. Until June 3, the prediction for June 21-23 was for quiet geomagnetic conditions, with a planetary A index of five for all three days.  Then on June 3 it changed, and the predicted planetary A index for those days was 25, 18 and 10, quite a difference. On June 15 the forecast changed to 10, 18 and 10, then on June 19 it became 18, 12 and 8, and finally yesterday it changed to 25, 15 and 10, closer to what it was on June 3.

Remember, we want those numbers to be low.

You can check for daily updates after 2100 UTC, and at it is updated every three hours with new K indices.

As of Thursday afternoon, predicted solar flux is 130 on June 21, 135 on June 22-24, 130 on June 25, 125 on June 26-27, 120 on June 28, 115 on June 29-30, hitting a minimum of 100 on July 5-7 and rising to a peak of 130 on July 19-21.

Predicted planetary A index is 25, 15 and 10 on June 21-23, 5 on June 24-27, then 30, 20, 10 and 8 on June 28 through July 1, then 5 on July 2-4, 10 on July 5-6, then 5 on July 7-13, and 8 on July 15-16.

Over the past week average daily sunspot numbers rose from 39.6 to 97, and average daily solar flux was up from 99.2 points to 115.3.

Petr Kolman, OK1MGW predicts quiet to active geomagnetic conditions June 21-23, quiet to unsettled June 24, quiet June 25-26, quiet to active June 27, active to disturbed June 28-29, quiet to unsettled June 30 through July 2, quiet to active July 3-4, and mostly quiet July 5-6.

Pavel Costa, CO7WT sent this observation: “In past winters I have noticed that when a cold front is passing over Cuba, the front of the wave some times acts as a very good reflector for VHF signals, precisely the 2 meter band that is commonly used here in Cuba for FM signals.”

“As Cuba is a kind of thin and long island, the propagation behaves differently depending on the angle of the incoming cold front. Sometimes when the front comes perpendicular to the island, the propagation is good for signals bouncing off the front of the wave. Other times when the wave comes parallel to the island the propagation is improved island wide.”

“This phenomenon is not always seen with all cold fronts, and its duration is from 1 to 4 hours for ranges about 100 to 500 Km, I have noticed.”

“Last winter I remember a cold front that made possible communications from hand held radios on 2 meter simplex with rubber duck antennas from two locations around 100 km apart with about 5 watts. That was around last December, maybe E skip helped that time, but I think the cold front was responsible for that.”

K1KT, Ken Tata of Warwick, Rhode Island noted on June 18 an intense 2 meter opening in Europe, and said a MUF map showed a spot over the Adriatic with MUF of 280 MHz.

Jeff Hartley, N8II of West Virginia mentioned on June 16, “The bands have sounded pretty good despite the low solar flux, except for 12 and 10 meters. 15 meters is often open in our evening into Europe. 17 meters is open most days to Europe and Western Asia around 0200-0300Z, and I worked about 10 European and Asian stations on 15 meters via Es into F2 (beacon from VE1 heard on 10M) on Friday at 0230-0315Z. 15 meters was fantastic over long stretches in the All Asia contest, JA's were loud Sunday for over 2 hours 1330-1530Z. This is a fairly rare opening for us.”

For more information concerning radio propagation, see the ARRL Technical Information Service at For an explanation of the numbers used in this bulletin, see An archive of past propagation bulletins is at More good information and tutorials on propagation are at

Monthly propagation charts between four USA regions and twelve overseas locations are at

Instructions for starting or ending email distribution of ARRL bulletins are at

Sunspot numbers for June 13 through 19 were 45, 73, 101, 104, 110, 120, and 126, with a mean of 97. 10.7 cm flux was 98.9, 109.1, 111, 115.9, 123.8, 125, and 123.4, with a mean of 115.3. Estimated planetary A indices were 4, 4, 5, 3, 4, 5, and 5, with a mean of 4.3. Estimated mid-latitude A indices were 6, 5, 4, 3, 5, 7, and 4, with a mean of 4.9.



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