Sun in deep slumber: 10.7 solar flux hits record low value

NRC Canada’s FTP site which logs the daily 10.7 centimeter (2800 megahertz) radio flux from the sun just reported what appears to be a new record low in the observed data.

64.2 at 1700 UTC

Source data is here

The Solar Radio Monitoring Program is operated jointly by the National Research Council and the Canadian Space Agency, the web page for their monitoring program is here.

The 10.7cm solar radio flux is an indicator of the sun’s activity. Here is a brief description of it from the National Geophysical Data Center:

The sun emits radio energy with a slowly varying intensity. This radio flux, which originates from atmospheric layers high in the sun’s chromosphere and low in its corona, changes gradually from day-to-day, in response to the number of spot groups on the disk. Radio intensity levels consist of emission from three sources: from the undisturbed solar surface, from developing active regions, and from short-lived enhancements above the daily level. Solar flux density at 2800 megaHertz has been recorded routinely by radio telescopes near Ottawa (February 14, 1947-May 31, 1991) and Penticton, British Columbia, since the first of June, 1991. Each day, levels are determined at local noon (1700 GMT at Ottawa and 2000 GMT at Penticton) and then corrected to within a few percent for factors such as antenna gain, atmospheric absorption, bursts in progress, and background sky temperature.

Part of this has to due with the earth’s orbit and position relative to the sun in July, this from Australia’s IPS Radio and Space Services:

On July 18 1996, the observed value of the 10 cm solar flux dropped to a low of 64.9. In many books it is stated that the 10 cm solar flux can not go below a value of 67. For example, the formulae given in the June 1996 edition of the IPS Solar Geophysical Summary show 67.0 as the minimum value. So how can we get a value of 64.9?

The answer is quite interesting – it depends on the orbit of the earth! The earth’s orbit is not perfectly circular but is slightly elliptical. In July of each year we are a little further than average from the sun and so solar radiation, including the 10 cm flux, is very slightly weaker than average.

So the 10cm flux will tend to be lower in July than, for example, December when the earth is closer to the sun than its average value. The combination of the extra distance to the sun and the solar minimum conditions have acted to produce this very low flux value.

It is easy to correct for the earth-sun distance and, when this is done, a value of 67.0 is obtained. This is the text book value!

Values of the 10 cm flux are often given in two forms – first as directly observed values and secondly as values corrected for the earth-sun distance variation.

The last time that the observed 10cm flux was at a lower value was on July 26, 1964 when it stood at 64.8. The lowest value ever recored was on July 02, 1954 with a value of 64.4.

As we’ve seen from visiual cues and lack of sunpots recently, it is obvious that the sun is in a deep minimum. Expert forecasts that have called for the sun to be regularly active by now have been falsified by nature, and the question of the day is: how long before the sun becomes active again?

(h/t Basil)