Seasonal and Solar Activity Changes of F-region Electron Density, Electron Temperature and Protonospheric Heat Flux during the Declining Part of Sunspot Cycle 20

251-256The daytime measurements of electron temperature (Te) and concentration (Ne) from incoherent scatter radar at Millstone Hill are analysed for the period Jan. 1968-Dec. 1973. This is the first analysis of the data for this period, which cover the solar maximum and a major portion of declining part of the sunspot cycle 20. The purpose of the analysis was to look for the seasonal and solar activity changes of F-region Ne, Te and protonospheric heat flux() during the declining part of the sunspot cycle 20 and also to compare the present results with the earlier results during the rising part of this sunspot cycle. It is found that while there is no major difference in the seasonal behaviour of F-region Ne and Te between the rising and the, declining parts of the sunspot cycle 20, the variation of daytime c. shows significant asymmetry between the rising and the declining phases of this sunspot cycle