Influence of the mean circulation on gravity wave generation

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Gravity waves (GW) represent a major coupling mechanism between the troposphere and the upper atmosphere by transporting the momentum, energy, and heat upward. Understanding and modeling the dynamical feedback of the mesosphere and lower thermosphere (MLT) to variations of the circulation in the lower atmosphere require a quantification of GW sources in the lower atmosphere. The main objective of the proposed study is to investigate GW excitation by the flow in the troposphere and the interactive response of MLT to variations of this forcing associated with different circulation regimes. A novel parameterization of GW sources will be coupled to a mainstream GW scheme and implemented in general circulation models (GCM). This will be a first parameterization that explicitly links GW generation to meteorological fields, and, thus, able to capture dynamical feedbacks between varying circulation patterns in the troposphere and MLT. We shall explore changes in GW forcing associated the different phases of the North Atlantic Oscillation and Arctic Oscillation. The major question will be how much MLT is controlled by the natural variability of the tropospheric circulation via the GW coupling mechanism.