Variability of transionospheric signal time delay at subauroral latitudes

Abstract

Faraday observations were conducted at Anchorage, AK ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">61.04\deg</tex> N, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">149.75\deg</tex> W), utilizing beacon transmissions from a geostationary satellite during the period just following the minimum phase of solar cycle 21, and, for comparison purpose, during a short period following the maximum phase of that same cycle. Near the minimum phase average maximum monthly values of total electron content (TEC), which is proportional to transionospheric signal time delay, were below <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15 \times 10^{16}</tex> el m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> , while individual daily maximum values never exceeded <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20 \times 10^{16}</tex> el m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> . Near the maximum phase TEC average monthly values were larger by a factor of two. Seasonal and day-to-day variabilities were observed. Unique representation of the data has permitted the study of day-to-day variability of TEC. For example, near minimum phase during all seasons the TEC structure appears uniform from day to day during the buildup and decay phases of the local ionosphere. During the maximum and minimum of the diurnal phase, the TEC structure variability is seasonally dependent. During periods of magnetic sudden commencements, which rarely occurred in the observation periods, significant positive phase responses of TEC did not materialize near solar minimum, but were correlated near solar maximum.