As the atmosphere warms under climate change, it will hold more moisture. Latent heat released as water vapour condenses provides an important contribution to the atmospheric heat budget, affecting stability and providing complex feedbacks. Consequently, theories for the general circulation of the atmosphere proposed based on dry dynamics may not apply in moist simulations. In order to understand the possible changes to the Earth's atmospheric circulation as the climate warms, a deeper understanding of these feedbacks is required.
Changes to the atmospheric thermal structure and circulation as humidity is increased have been explored in an intermediate complexity general circulation model. To provide a reference climate more comparable with that of previous studies, and of the real world, a simple parameterisation of shortwave and longwave radiative transfer has been developed, which compares favourably with existing simple radiation schemes. Experiments have then been performed with fixed optical depths in which the moisture content of the model is varied.
In the zonal mean, increasing moisture content results in an increase in static stability throughout the atmosphere. Consequent changes to the Hadley cell, zonal jets, and storm track have been analysed using simple theories, and by comparison with an experiment in which the sea surface temperature in the tropics is increased. This reveals that the majority of the effects of increased moisture content on the circulation are generated by low latitude warming.
The simulations further reveal stronger midlatitude poleward transport of moist static energy as saturation vapour pressure is increased, and an unexpected increase in sensible heat transport in the cold sector of storms. A mechanism for the latter is proposed related to the environmental static stability against which the system develops. The experiments also suggest changes to the rate of conversion of available potential energy to eddy kinetic energy as moisture content increases.Open Acces
