Mesospheric concentric gravity waves generated by multiple convective storms over the North American Great Plain

We report on six continuous hours of OH airglow imager observations (at z ∼ 87 km) of convectively generated gravity waves (GWs) near Fort Collins, Colorado, on the evening of 08 September 2005. These GWs appeared as nearly concentric rings, and had epicenters near the locations of deep convection in three thunderstorms in Colorado, Nebraska and South Dakota. Using GOES satellite and weather radar observations, we show that the GWs closely follow the thunderstorms. Using the background wind from a nearby radar, the intrinsic wave parameters and vertical wavelengths are calculated. The temperature perturbations are estimated to be T '/ T ¯ ∼ 1-3% for GWs with horizontal wavelengths λh ∼ 20-40 km and horizontal phase speeds ∼40-60 m/s. The horizontal wavelengths of GWs from a convective cluster decreased in time from 30 to 15 km. We employ convective plume and ray-trace models to simulate the GW-induced OH intensity perturbations from convective plumes, clusters and complexes. We find that the results using the background model wind (radiosonde/TIME-GCM) agree well with the late-time observations, when the images are dominated by southwestward, short-wavelength, high-frequency GWs. These late-time GWs propagate against the background wind, and have λh ∼ 30--40 km and periods of τ ∼ 20-30 min. The OH intensity perturbations are enhanced because the vertical wavelengths λz increased, T '/ T ¯ increased, and the vertical velocity perturbations w' decreased (because the GWs were near their reflection levels). We also find that these short-wavelength GWs were created ∼5 h earlier by an extremely energetic, deep convective plume in South Dakota, thereby showing that small-scale, convective GWs directly link the troposphere and mesopause region.