Comparison of incoherent scatter observations of electron density, and electron and ion temperature at Millstone Hill with the International Reference Ionosphere

Abstract

Millstone Hill incoherent scatter (IS) observations of electron density ( N e , electron temperature ( T e ) and ion temperature ( T i ) are compared with the International Reference Ionosphere (IRI-86) for both noon and midnight, for summer, equinox and winter, at both solar maximum (1979–1980) and solar minimum (1985–1986). The largest difference in N e is found in the topside, where values of N e given by IRI-86 are generally larger than those obtained from IS measurements, by a factor which increases with increasing height, and which has a mean value near two at 600 km. Apart from the bottom of the profile, which is tied to the CIRA neutral temperature, the IRI-86 T e model has no solar cycle variation. However, the IS measurements during the summer reveal larger T e at solar maximum than at solar minimum. At other seasons higher T e at solar maximum occurs only during the daytime at the greater heights. Nighttime T e is shown by the IS radar to be generally larger in winter than in summer, an effect not included in the IRI. This is apparently due to photoelectron heating during winter from the sunlit ionosphere conjugate to Millstone Hill. The day-night difference in T i given by IRI-86 above 600km is not as large in the IS measurements.