Channel spread parameters for the high-latitude, near-vertical-incidence-skywave HF channel: Correlation with geomagnetic activity

Results of measurements on a high latitude, near vertical incidence, HF skywave channel are presented. The measurements are for a time period (May 1988), roughly two years after the peak of solar cycle #22, when the mean sunspot number was 85. The measurement periods include day, afternoon, night, and early morning times and cover a wide range of geomagnetic disturbance conditions. Signal amplitude, delay spread and Doppler spread are the channel characteristics of primary interest. The correlation of these channel characteristics with geomagnetic activity and with the position of the propagation path relative to selected regions of the auroral zone are examined. Ionogram characteristics for all measurements are briefly reviewed in light of geomagnetic and geographic factors. Four selected cases, representative of magnetically quiet daytime conditions, magnetically active daytime conditions, magnetically quiet night-time conditions, and magnetically active nighttime conditions are examined in detail. The measurement results indicate that, depending on geomagnetic and geographic factors, the received signals may be the result of simple reflection from a smoothly varying ionosphere, multipath reflection from an irregular ionosphere, or scattering (or a combination of multipath reflection and scattering) from an irregular ionosphere. Signals for the four groups are shown to be readily distinguishable on the basis of their characteristics and provide an estimate of the range of values of Doppler spread and spread factor that may be expected on the channel.