Absorption in the D and E regions and its time variation

Abstract

It is important to separate the D and E layer contributions, respectively, when interpreting results obtained by the usual determination of the apparent reflection coefficient. One criterion which can be used is the different frequency variation of both non-deviative and deviative absorption. Hitherto, for deviative absorption, a one parametric formula depending upon the E layer critical frequency has been used. This procedure failed when blanketing Es was present; for a fixed frequency, a higher reflection coefficient was obtained than for even the thick, normal E layer. With a thin layer model for sporadic E, a new formula has been obtained which depends upon two parameters, f o E and the cusp frequency, f r . One and a half years' data for noon were reduced on this basis. Results may be described in terms of a parameter B (characterizing the non-deviative absorption) and a parameter C (essentially proportional to the product of collision frequency and half thickness of the E layer). A greater seasonal variation was found for C than for B. The summer maximum of absorption was found to arise from deviative absorption. During summer the E layer occurs at lower altitudes; i.e. in a region of higher collissional frequency. The value of B is nearly constant from February through August and appears to have its minimum in November. The well known winter anomaly is an effect of non-deviative absorption and has its maximum during January. The daily variation has been checked using three days of observation each month. For the parameter C, the daily variation was small, so that the maximum of absorption near noon is essentially an effect of non-deviative absorption. Another interesting result was noted during SID periods: the value B became very large whereas C remained unchanged. The day to day dispersion of absorption is not greater than that of other ionospheric characteristics. The quartile dispersion is ±10 per cent for B and ± 14 per cent for C. Again, the variability of conditions in the E region is rather large in comparison to those of the D region.