Measurements of neutral N2 density from mass spectrometers on five satellites (AE‐B, Ogo 6, San Marco 3, Aeros A, and AE‐C) and neutral temperatures inferred from incoherent scatter measurements at four ground stations (Arecibo, Jicamarca, Millstone Hill, and St. Santin) have been combined to produce a model of thermospheric neutral temperatures and N2 densities similar to the Ogo 6 empirical model. The satellite‐ and ground‐based measurements provide unique and complementary information on the structure of the thermosphere. Incoherent scatter data have good local time coverage at the station locations and provide data for studies of long‐term trends. Measurements from satellites provide information at different altitudes, latitudes, longitudes, solar activities, and seasons. The overall data set covers the time period from the end of 1965 to mid‐1975. The global average temperature from the new model for an F10.7 of 150 is 1041°K or 56°K lower than that from the Ogo 6 model. The annual temperature variation is about two‐thirds that of the Ogo 6 model, but variations in lower bound density (inferred from low‐altitude AE‐C data) and lower bound temperature (from incoherent scatter data) result in annual density variations at high altitude very similar to those in the Ogo 6 model. Diurnal and semidiurnal variations in lower bound density and temperature gradient parameters are also introduced. Model diurnal exospheric temperature variations reflect the observed changes with season seen in incoherent scatter measurements. Data used in the model cover a wide range of solar activities (mean F10.7 of 75–180), and the annual and diurnal temperature amplitudes are found to increase with solar activity at twice the rate of the mean temperature. The model fits moderate magnetic activity better than the Ogo 6 model but does not include observed longitude variations. The overall good agreement of the individual data sets with the model confirms the basic consistency of the various measurements taken in different time periods.

Recent studies have shown that exospheric temperatures can be obtained from incoherent scatter experiments. A method proposed by Carru et al. (1967) is extended to yield the atomic oxygen density and a temperature shape parameter. The method involves the determination, by means of a nonlinear regression analysis, of the values of neutral temperature and oxygen density that best reproduce the measured ion temperature profile, given measured profiles of electron density and electron temperature. By this method, it is possible to obtain a continuous daytime variation of the neutral parameters with a relative accuracy of 15-20%. The first results exhibit a definite day-to-night variation of the atomic oxygen density, which is compared to the variation given by the Jacchia and Cira models. Measurements of the parameters of the neu-tral atmosphere originate mainly from satellite or rocket experiments or from satellite drag studies. These types of observation provide either good altitude resolution or wide geographic coverage; however, satellite experiments have poor time resolution in a given place, and rocket experiments offer only instantaneous measurements, most often thinly scattered in space and time. Carru et al. [1967a] have shown that the incoherent scatter system of St. Santin-Nan•ay [Du Castel et al., 1966] can be used to determine the exospheric temperature T• of the neutral atmosphere, provided that a shape is assumed for the temperature profile and that. a value is assumed for the neutral atomic oxygen density at some altitude.This method has been extended so as to yield, through use of a nonlinear regression technique, a simultaneous determination of the following three parameters: T•, the exospheric tempera-X Now at Arecibo Ionospheric Observatory, Arecibo, Puerto Rico. ture; (O), the neutral atomic oxygen density; and s, the shape parameter of an exponential neutral temperature profile.We first discuss the principles upon which the method is based, then consider the validity and the limitations of the method; finally, preliminary results are given and are compared with several empirical models of the atmosphere.

The Atmosphere Explorer-C satellite (AE-C) is uniquely suited for correlative studies with groundbased stations because its on-board propulsion system enables a desired ground station overflight condition to be maintained for a period of several weeks. It also provides the first low-altitude (below 260 km) comparison of satellite and incoherent scatter electron and ion temperatures. More than 40 comparisons of remote and in situ measurements were made by using data from AE-C and four incoherent scatter stations (Arecibo, Chatanika, Millstone Hill, and St. Santin). The results indicate very good agreement between satellite and ground measurements of the ion temperature, the average satellite retarding potential analyzer temperatures differing from the average incoherent scatter temperatures by -2% at St. Santin, +3% at Millstone Hill, and +2% at Arecibo. The electron temperatures also agree well, the average satellite temperatures exceeding the average incoherent scatter temperatures by 3% at St. Santin, 2% at Arecibo, and 11% at Millstone Hill. Several temperature comparisons were made between AE-C and Chatanika. In spite of the highly variable ionosphere often encountered at this high-latitude location, good agreement was obtained between the in situ and remote measurements of electron and ion temperatures. Longitudinal variations are found to be very important in the comparisons of electron temperature in some locations. The agreement between the electron temperatures is considerably better than that found in some earlier comparisons involving satellites at higher altitudes.In some of these instances the ratio of probe temperature (Te)•, to incoherent scatter temperature (Te)s was as high as 1.7-1.9 [Hanson et al., 1969; Carlson and Sayers, 1970]. Others have found smaller discrepancies ((Te)•,/(Te)s -1.15) [McClure et al., 1973] or no significant discrepancy [Evans, 1965; Taylor and Wrenn, 1970; Wrenn et al., 1973]. The diversity of these findings may have been due to the lack of simultaneity of the observations and/or to the spatial separation of the ionospheric samples being examined in the different experiments. Comparisons involving rocket-borne electrostatic probes flown in the vicinity of an incoherent scatter station have not indicated a large discrepancy; i.e., (Te)p/(Te)s was generally less than 1.2 [Brace et al., 1969; Sagalyn and Wand, 1971], but these comparisons were limited to altitudes below 300 km. An indication of an altitude dependence was obtained in a rocket probe-incoherent scatter comparison that extended to 700 km [Brace and McClure, 1971 ]. Below 350 km, (Te)p/(Te)s -• 1.0, whereas at 700 km the ratio had attained a value of 1.8. The results of this experiment, however, may have been influenced by the large separation (nearly 5000 km) in longRude between the rocket trajectory and the incoherent scatter beam. An altitude dependence was also suggested by a related temperature comparison in which simultaneous in situ measurements were made from the same vehicle [Benson, 1973]. In this case...

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