The lower thermosphere coupling study of the cedar and wits programs

Abstract

The Lower Thermosphere Coupling Study (LTCS) is a coordinated investigation of the lower thermosphere (80 – 150 km) combining observational (optical and radar) and numerical modelling efforts with the ultimate goal of better understanding the dynamic and electrodynamic processes coupling the mesosphere, lower thermosphere, and upper thermosphere regions. The study, which is being conducted under the auspices of the CEDAR (Coupling, Energetics, and Dynamics of Atmospheric Regions) and WITS (World Ionosphere and Thermosphere Study) Programs, is intended to address such questions as: What is the relative importance of upward propagating tides, planetary waves, and gravity waves, related accelerations of the mean flow, and heating and momentum sources of magnetospheric origin, in determining neutral dynamical fields and ionospheric structures as a function of height between 90 and 150 km? What are the seasonal-latitudinal and diurnal variations in turbulent diffusivities due to gravity wave saturation, and related implications on the vertical transport of O and NO? What are the relative roles of magnetospheric currents, the E-region wind dynamo, and nighttime conductivities in determining ionospheric electric fields? Emphasis of the study will be placed on neutral winds, temperatures, electric fields, and currents during a series of coordinated measurements campaigns each consisting of a 30-day ‘background’ period and a 4–6 day ‘core period’. The first campaign was conducted during 15 September 1987 – 15 October 1987 with a core period during 21 – 25 September 1987. The scientific basis for the LTCS, its organization, and preliminary results from the 1987 campaign are reviewed in this paper.