At 10:45 PM 11/29/06, cesco12342000 wrote: > > Near the equator, > > there is little frequency spread (< 4 Hz), but it is larger > > in near-polar paths and can be very large (up to 40 Hz) > > under disturbed conditions. > >A question: where does the frequency spread come from ? >Is this a doppler effect of a moving ionosphere, or are >there other causes ?
Yes. It's Doppler spreading because of turbulent motions within the ionosphere. >why is the effect bigger in polar regions ? Because the most turbulent regions of the ionosphere are the Auroral zones that are located near the poles. The Auroral zones are regions in which a lot of energy gets dissipated in a relatively small volume. That leads to the same kind of instability and turbulence that one sees in a pot of boiling water. The regions closest to the poles, the polar caps, are significantly less turbulent than the Auroral zones which bound the caps on the equatorward side. The other place that significant Doppler spreading is observed to occur is in the equatorial ionosphere during so-called "spread-F" conditions. 73, Mike K1MK Michael Keane K1MK [EMAIL PROTECTED]
