Field Strength Measurements Over a 2000 km Subauroral Path (Sodankylä-Lindau) Compared With the Absorption Observed at the Terminals

Field strength measurements have been carried out over the 2000 km subauroral Sodankylä-Lindau path and, at the same time, along two other lines: Norddeich-Lindau (D = 300 km) and Kemi-Sodankylä (D = 200 km). With the aid of oblique ionograms obtained from the Sodankylä-Lindau line and the vertical ionograms of Sodankylä, Uppsala and Lindau the field strength recordings of undisturbed winter days have been interpreted in terms of ionospheric D-region absorption. From the results of the analysis it is evident that anomalous winter absorption appears all over the three lines. The relative intensity of the effect seems to increase with increasing latitude.