August '09

Solar Conditions

The mostly calm propagation conditions will continue and the only minor variations will be August 6-10 when the Boulder 'A' index will peak at 8. Things will then settle down to the recent 'norm' of A=5 and K=2. The Solar Flux should also remain between 68 and 70 during this period.

We saw a run of eight days with a large sunspot during July, but none have emerged since. Unlike other recent spots, this one did not appear just for one or two days and then vanish. Sunspot numbers for July 9-15 were 15, 13, 0, 0, 0, 0 and 0 with a mean of 4. The Solar flux was 69.1, 67.8, 68.2, 68, 67.2, 66.6 and 66.5 with a mean of 67.6. The estimated planetary A indices were 6, 7, 4, 5, 10, 8 and 5 with a mean of 6.4. The estimated mid-latitude A indices were 6, 7, 2, 4, 5, 6 and 3 with a mean of 4.7.

Previous Solar Cycles

Solar Cycle 23 began in October 1996, so Solar Cycle 24 should have had an impact on Solar conditions by now, as Solar cycles typically last 11 years, but the ‘false alarms’ continue as we see the occasional burst of Solar activity followed by yet another period of ‘Quiet to Unsettled’. In October 1991, Solar Cycle 22 reached its peak in a short period, but Solar Cycles 17, 20 and 23 were very similar to each other. Here is another website which has both text and graphical charts which show this quite clearly: http://www.solen.info/solar/

The WM7d forecast is easy to understand as it gets to the point without going through too much detailed data: http://www.wm7d.net/hamradio/solar/27d_forecast.shtml

A 45 day text based forecast can be found at: http://www.swpc.noaa.gov/ftpmenu/forecasts/45DF.html

Here is yet another site dedicated to HF propagation conditions: http://dx.qsl.net/propagation/

Sunspot Numbers:
Observers around the world compute daily sunspot numbers by multiplying the number of observed sunspot groups by ten and then adding this product to his total count of individual spots. Results vary greatly, since the measurement strongly depends on observer interpretation and experience and on the stability of the Earth's atmosphere above the observing site.
Moreover, the use of Earth as a platform from which to record these numbers contributes to their variability, too, because the sun rotates and the evolving spot groups are distributed unevenly across solar longitudes.
To compensate for these limitations, each daily international number is computed as a weighted average of measurements made from a network of cooperating observatories. Sunspot counts rise and fall approximately every 11.1 years. The cycle, though, is not symmetrical, for the spot count takes on the average about 4.8 years to rise from a minimum to a maximum and another 6.2 years to fall to a minimum once again. The largest annual mean number (190.2) occurred in 1957.
There is a comprehensive FAQ’s page about Sunspot numbers and Space Weather in general at: http://www.space.com/spacewatch/solar_faq.html#g1

ASAP Software
Bradford University have a software download called ASAP (Automated Solar Activity Prediction) which shows real time Solar data on your PC, although I haven’t tried it yet. Details at: http://spaceweather.inf.brad.ac.uk/asap.html

Thanks to Mike Terry and Ken Fletcher for regular updates.