Could the next solar minimum arrive sooner than previously predicted?
American solar physicist David Hathaway thinks so. An article on the
'Science at NASA' website
http://science.nasa.gov/headlines/y2...larminimum.htm predicts
that the next solar minimum could occur in late 2006, about a year earlier
than previously thought. Hathaway bases his prediction on data from the last
eight solar cycles, which show that solar minimum follows the first
sunspot-free day on the sun by 34 months. In this solar cycle, the first
spotless day was on 28 January this year and more recently, on 11 and 12
October, there were two more spotless days. David Hathaway goes on to say
that the next solar maximum might also come early. "Solar activity
intensifies rapidly after solar minimum. In recent cycles, Solar Max has
followed Solar Min by just four years." If that is the case, the next solar
maximum should be in 2010.
(RSGB)

The Sun goes through a periodic rise and fall in activity which affects HF
communications; solar cycles vary in length from 9 to 14 years. At solar
minimum, only the lower frequencies of the HF band will be supported by the
ionosphere, while at solar maximum the higher frequencies will successfully
propagate, figure 1.4. This is because there is more radiation being emitted
from the Sun at solar maximum, producing more electrons in the ionosphere
which allows the use of higher frequencies.
(http://www.qsl.net/g3yrc/hf%20propag...ropagation.htm)