An examination of elevated frequency propagation over a transpolar path



[1] A Chirpsounder® system has been installed to evaluate the communication path between Svalbard (Spitsbergen) and Barrow, Alaska. This system of measurements is used to update operational ionospheric propagation models we use to nowcast the effectiveness of high-frequency (HF) communications over polar paths. Operations have been virtually continuous since December 2000, during which time Radio Propagation Services Inc. has made measurements of the propagation effects that have been encountered. Oblique sounder patterns have been diverse, ranging from standard (i.e., classical) ionograms with a sharp “nose” near the anticipated maximum useable frequency to rather diffuse patterns. However, the most interesting patterns consist of nonclimatological patterns of signals associated with EMOFs. These were first observed to occur during the winter, but they are in evidence throughout the year. The strong signal strengths associated with these EMOF patterns are transient and consistent with independent ionospheric layers or modulations of existing layers. The EMOF signals have been analyzed statistically, and the paper will describe the diurnal and seasonal behaviors. We will also investigate the association of these observations with polar patches and blobs, which have been observed to convect across the polar cap, especially in the winter. These observations are not simply scientific curiosities. The character and persistence of these signals have a significant impact on communication effectiveness for over-the-pole air transport operations. Issues of radio spectrum, service provider location, and dynamic frequency management are directly related to the phenomena observed.