Jeffrey M. Forbes

Department of Aerospace Engineering Sciences, University of Colorado, Boulder, CO

Abstract:

The mesosphere/lower thermosphere and ionosphere (MLTI) region (ca. 80-150 km) hosts a
complex interplay between dynamics, energetics, electrodynamics and chemistry over a range
of spatial and temporal scales. The MLTI includes the mesopause (ca. 85-95 km), the coldest
temperature minimum in the atmosphere. Phenomena typically associated with the region
include tides; gravity waves and planetary waves; wave dissipation; non-LTE CO2 cooling;
radiative cooling by NO; absorption of EUV solar radiation, joule heating; turbulent and
molecular diffusion of heat and momentum; transport of constituents; magnetic field influences
and ion-neutral collisions; plasma instabilities and irregularities. The dynamics of the MLTI is
dominated by meteorological influences in the lower part of the domain, transitioning to solar
and geomagnetic driving at higher altitudes; hence many of the above phenomena and processes
possess a characteristic transition height within the MLTI determined by competing time scales.
Optical emissions often represent the final manifestation of a chain of dynamical and chemical
processes, and therefore offer a valued means of assessing and validating models. The objective
of this talk is to provide a broad overview of the primary dynamical phenomena occurring in
the MLTI, and to identify the crucial issues for future study.