A global thermospheric model based on mass spectrometer and incoherent scatter data MSIS, 1. N₂density and temperature

Abstract

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.

NRLMSISE‐00 empirical model of the atmosphere: Statistical comparisons and scientific issues

“…Hedin et al [1977] described the selection process, which was designed to ensure the widest coverage of the hyperspace of subroutine arguments (e.g., day of year, latitude, longitude) while satisfying constraints imposed by computing and storage limitations. The data selection method of Hedin et al avoids dominance of the model coefficients by only a few large data sets, although this can also be accomplished by proper weighting of data-model residuals in computing c 2 .…”

“…Even though only a subset of the MSIS database is used to evaluate the model coefficients [Hedin et al, 1977], the number of data points is still quite sizable ($3 Â 10 5 ), rendering an all inclusive Levenberg-Marquardt calculation [Press et al, 1992] compute-intensive and cumbersome. Because the NRLMSIS thermospheric data are separable by mass number (species, temperature, total mass density), one can partition the process into a series of separate Levenberg-Marquardt (LM) c 2 minimization calculations for coefficient and data subsets covering different altitude regions, species, magnetic activity levels, and scales and types of variability.…”

The 30 cm radio flux as a solar proxy for thermosphere density modelling

“…To account for this effect, it is customary for models to use two solar inputs (Hedin et al 1977): slow variations are represented by a trend, defined as the running mean of the flux over the last 81 days, while fast variations are described by the detrended flux, i.e. the difference between daily values and trend.…”

Variations of the nighttime thermospheric mass density at low and middle latitudes

“…For instance, the Jacchia thermospheric models are developed using thermospheric mass densities retrieved from satellite orbit decays [Jacchia and Slowey, 1968;Jacchia, 1977;Bilitza, 1992]. The Mass Spectrometer and Incoherent Scatter Radar (MSIS) model is constructed from satellite-born mass spectrometer data [Hedin et al, 1974[Hedin et al, , 1977Hedin, 1983Hedin, , 1987. Thermospheric mass density can also be obtained from satellite-born accelerometer measurements [Boudon et al, 1979;Falin et al, 1981;Reigber et al, 2002].…”