The measurement of diurnal variations of electron concentration in the 60-100 km ionosphere at Arecibo

The Arecibo 430 MHz incoherent scatter radar was used to observe the diurnal variation of electron concentration in the 6-100 km altitude region on 14 August 1977. This report is an evaluation of the technique and includes a fairly complete discussion of errors involved. Although interference remains a serious problem, the results are useful down to about 60 km altitude and a minimum density of about 50 electrons cm^-3. Characteristic statistical plus systematic errors indicate that an observed 100 electrons cm^-3 value actually lies between 50 and 180 electrons cm^-3 assuming no interference. Observed variations of electron concentration include not only those due to basic solar control but also at least one wavelike feature characterized by phase shift with altitude. These results should prove particularly useful as constraints to time dependent models of the D-region chemistry.