Internal energy balance and energy transfer in the lower thermosphere

The earth's upper atmosphere is drastically out of local thermodynamic equilibrium as a result of solar irradiation and the consequent photochemistry and as a result of the transport of energy by both radiative and fluid mechanical mechanisms, so that the lower thermosphere provides an excellent potential laboratory for the observation of nonequilibrium processes. The atmospheric energy partition in different degrees of freedom (translational, rotational, vibrational, electronic, chemical, and ionization) is presented over the altitude range 0-300 km in terms of effective population temperatures for these different forms of energy. The vibration of molecular oxygen and nitrogen is excited mainly by chemical and energy transfer mechanisms and de-excited by vibration-vibration and vibration-translation energy transfer processes. The vibrational population temperature for various molecules may be either lower or higher than the kinetic temperature, and a number of models for the vibrational population of various atmospheric molecules are outlined here.