The Solar Numbers
Understanding the daily solar data used for H.F. propagation forecasting
BY ARNIE CORO
Host of "Dxers Unlimited"
SEND YOUR COMMENTS, QUESTIONS AND IDEAS DIRECTLY TO ME AT: arnie@radiohc.org
It all started in the late nineteen-forties... a Canadian scientist, Prof. Dr. Arthur Covington, developed a technnique to measure solar activity OBJECTIVELY.
Covington's findings were inmediately accepted by the scientific community, and from 1947-48 on, the 2750 mHz solar noise measurements became a standard "yardstick" for solar activity.
Today, almost 50 years after the pioneering research work, the daily 10.7 cM wavelength solar noise measurements provide the information we all need to follow the Sun's daily changes with higher precision than ever before.
No, don't worry, I won't go into astrophysics, or the sophisticated area of Solar-Terrestrial relationships....
What I want Dxers Unlimited's listeners to learn is more about those daily "solar numbers" -- what they really mean and, above all, how you can put them to work to improve your chances of picking up Dx stations, listening to the best possible shortwave broadcast band, or sometimes, maybe when to do some nice reading or antenna maintenance work ... if the "numbers" tell you that propagation is going to be very poor.
Covington's research at a Canadian observatory involved the use of two basic instruments... a Solar Radiotelescope, and a Dicke type Radiometer. By coupling the solar radiotelescope to the radiometer, he was able to measure the NOISE generated by the Sun's activity at different frequencies.
Among this distinguished Canadian scientist's contributions to solar astrophysical research was his finding that at a frequency very near 2800 mHz -- actually he did his experimental work at 2750 mHz -- the SOLAR FLUX measured CORRELATED very nicely with the up-till-then accepted standard for measuring solar activity -- the so-called WOLF number, or SUNSPOT COUNT.
In another article soon to be appearing here, you will learn more about the WOLF number, but now I must explain very briefly that WOLF number data is NOT OBJECTIVE to the same extent that Covington's 10.7 cM SOLAR FLUX measurements are. The reason for this is the fact that the WOLF number is derived from VISUAL OBSERVATIONS done by HUMANS, not by actual SCIENTIFIC INSTRUMENTS.
So, the WOLF number has to take into account the kind of telescope used, the location of the observatory and provide a "weighting factor" for the actual observer -- that's the scientist doing the daily observations by watching the sun via her or his telescope -- in order to come out with some sort of averaging for observations taking place at many different observatories worldwide.
The merit of Covington's 10.7 cM Solar Flux Measurements are now evident: a scientific instrument that can be calibrated very easily will provide OBJECTIVE data, regardless of who is operating it, or its actual location.
I hope that the above explanation makes things more clear about why 10.7 Solar Flux is now favored by scientist as the "yardstick" for measuring solar activity.
HOW THE TWO CORRELATE?
Yes, both Wolf numbers and 10.7 Solar Flux Measurements correlate. I won't go into the sophisticated math concepts involved; instead I will offer you a very simple and easy-to-use table that relates "APPROXIMATELY" 10.7 cm Flux and Wolf numbers:
There is a formula that correlates both measurements, the objective 10.7 cm solar flux and the weighted or subjective WOLF number. The formula may prove a little difficult to handle to those not familiar with mathematics, so I just left it out.
The lowest-ever recorded Solar Flux in almost 50 years was 65.8 units, while the maximum went all the way up to 458 units. For all practical purposes, the range of 66 to 180 solar flux units is what we are going to see during the next 18 months or so. After mid 1999, or perhaps a little earlier, we may see daily solar flux figures going above 180!!!
In another feature article here at Dxers Unlimited's webpage, I'll explain how solar activity is described, from VERY LOW to VERY HIGH and what this means.
Now, when you pick up the SOLAR FLUX numbers via the INTERNET or listening to the radio, you can very easily tell with a reasonable approximation the EQUIVALENT NUMBER OF SUNSPOTS. But beware ... the EFFECTIVE SUNSPOT NUMBER is yet another different concept, of which I'll tell you in yet another article.
73 and enjoy the hobby!!!
Havana, Cuba
30 December, 1997