Gravity waves in the mesosphere generated by tropospheric convention

The observed cold temperatures in the summer mesosphere are dynamically maintained primarily through upwelling induced in response to the action of a zonal drag force caused by the breaking of upward propagating gravity waves. Tropospheric convective storms are believed to be important sources of gravity waves in the summer mesosphere, but little is known about the characteristics of mesospheric gravity waves generated by convection. As a first attempt to model such waves a nonhydrostatic cloud-resolving numerical model is used to simulate a 2-dimensional squall line in a domain of width 2048 km and depth 90 km. The simulation produces a broad spectrum of convectively generated gravity waves. These propagate into the middle atmosphere, forming a fan-like pattern of waves with amplitudes increasing with height, and eventually reach breaking amplitudes in the mesosphere. The resultant mesospheric wave-breaking produces strong zonal forcing, which is eastward to the east of the storm center and westward to the west of the storm center. Breaking of upward propagating waves also generates high frequency downward propagating secondary waves of short horizontal wavelength, and long vertical wavelength. The secondary waves have only a small influence on the net vertical transfer of momentum, but produce a strong signature in perturbation vertical velocity, featuring alternating positive and negative interference with the primary upward propagating modes.