A global thermospheric model based on mass spectrometer and incoherent scatter data MSIS, 1. N2 density and temperature


  • A. E. Hedin,

  • J. E. Salah,

  • J. V. Evans,

  • C. A. Reber,

  • G. P. Newton,

  • N. W. Spencer,

  • D. C. Kayser,

  • D. Alcaydé,

  • P. Bauer,

  • L. Cogger,

  • J. P. McClure


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.