Ionospheric propagation correlation statistics for service planning

The present paper extends the spatial correlation results in Gibson et al. (1993) to a longer period of data and other receiver separations. New analyses are presented of correlations of signals at separated frequencies and with geomagnetic activity. Data were collected at frequencies from 7.9 to 19.1 MHz on a 2600 km path from Cricklade in England to the Kandilli Observatory near Istanbul during the period from April 1992 to February 1993, with a different second receiving site during each of the first three months. Small (quiet-time) variations of signal strength from day to day may involve fluctuations in f0F2, hmF2, and f0Es, whose causes cannot usually be identified and hence are called ´geophysical noise´. Larger variations, as reviewed for example by Davies (1990) and references therein, tend to be associated with events on the sun, including sudden ionospheric disturbances, ionospheric storms, polar cap absorption events, large scale travelling ionospheric disturbances, and associated disturbances in the geomagnetic field