Vertical incidence absorption calculated using electron density profiles from rocket experiments and comparison with observations during the winter anomaly

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In the first part of this paper ground-based measurements of vertical incidence absorption are compared with values calculated from electron density profiles from simultaneous rocket experiments. These data were obtained at Wallops Island during an investigation of the winter anomaly in radiowave absorption. The measurements were made at 3.03 MHz during five of the rocket flights and at 1.8 MHz on four others. Satisfactory agreement between observed and calculated values of absorption is obtained for an electron collision frequency model v m = 6.3 × 10 5 p where p is the pressure (in N m −2) from CIRA 1972. In the second part of the paper this electron collision frequency model is used in the calculation of vertical incidence absorption as a function of frequency between 1.7 and 3.0 MHz. The nine electron density profiles from the winter season are used together with five additional profiles from rocket flights in other seasons, all profiles being for a solar zenith angle of about 60°. Examination of the calculated values shows that the absorption is more sensitive to frequency changes than expected particularly for winter days, even at frequencies much less than ƒoE. The occurrence and number of multiple echoes in the ionograms is consistent with the calculated absorption values.