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NASA NTRS1995

Vertical structure of the midlatitude temperature from stratosphere to mesopause (30 - 105 km)

Data sets from Rayleigh lidar (1979-93) at the Observatory of Haute-Provence (44 deg N, 6 deg E) and at Biscarrosse (44 deg N, 1 deg W) of southern France, and from narrowband Na lidar (1991-4) at Fort Collins, Colorado (41 deg N, 105 deg W) are used to deduce the vertical temperature structure of the midlatitude middle atmosphere from 30 - 105 km. Nightly averaged temperatures measured across the Atlantic at comparable latitudes between 81 and 90 km showed seasonal variations tracking one another. Harmonic analyses of the measured profiles at these sites have been compared to the reference atmosphere, CIRA 1986. Considerable differences are noted in the annual mean temperautres in the mesopause region. Two temperature minima at 86 and 99 m are observed, suggesting heating and cooling mechnanisms not previously incorporated into the reference atmosphere. Using the new 3D TIME-General Circulation Model (GCM) of Roble and Ridley which includes both dynamical and chemical processes, we account for this anomalous behavior by model simulation for the first time. Except the existence of strong semi-annual oscillations, the observed annual and semi-annual temperature variations are compatible with CIRA 1986. Observed annual temperature and solar flux forcing are out-of-phase between 65 and 99 km, reflecting dynamics dominated atmosphere at these altitudes.

She, C. Y.↗

NASA NTRS1987

Orbital atmospheric physics and dynamics

There are two ways of modeling the upper atmosphere. One is the empirical model that makes use of experimental data on means and excursions from the mean and fits the data in a self-consistent manner. The other approach is to deal directly with the physical processes. This is difficult since what is happening is extremely complex. Data measured using an interferometer to give Doppler shifts of airglow lines showed 300 to 800 m/sec winds with a complex structure in the upper region of the thermosphere at high latitudes. Ionospheric electric fields, strongly influenced by interaction with the solar wind, drive the ionized component and large neutral winds result due to momentum transfer between the charged particles and the neutrals. Frictional heating results from movement of ions through the neutrals, which also influences the compositional structure. These are examples of the complex interactions involved. The NCAR General Circulation Model (tropospheric) was adapted for use at thermospheric altitudes: the Thermospheric General Circulation Model (TGCM). The model makes use partly of primitive equations and partly of empirical data for some quantities such as electron density, magnetic field, and ion drift.

Roble, Raymond↗