Interaction of chemical heating and the diurnal tide in the mesosphere

Much of the solar energy deposited into the upper part of the middle atmosphere is realized as heat as a consequence of exothermic chemical reactions. The heating varies with time primarily in response to variations in composition due to photochemistry and to vertical advection by tides and other processes. Diurnal variations in the heating can, in turn, cause modifications in the tidal amplitude and structure. Using a three-dimensional chemical-dynamical model, we show that the advection of atomic oxygen by tidal winds has a significant impact on the location, timing, and magnitude of the heating but that the feedback of this on the tidal amplitude is weak (less than 10%). The day/night cycle in chemical heating associated with photochemistry also contributes to the local amplification or damping of the tide. Tidal transport affects the overall composition and therefore also the total heating by solar energy. When tides are removed, the total global mean amount of solar heating (chemical heating plus direct solar heating) decreases by as much as 40% in the mesosphere.