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

Abstract

[1] 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 l h $ 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 l h $ 30-40 km and periods of t $ 20-30 min. The OH intensity perturbations are enhanced because the vertical wavelengths l z 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.

Compressible f‐plane solutions to body forces, heatings, and coolings, and application to the primary and secondary gravity waves generated by a deep convective plume

“…The best‐fit depth and duration have been found to be ∼10 km and χ ∼10 min, respectively. This duration is consistent with high‐time‐resolution NEXRAD data, which found that a new plume within a thunderstorm typically appears every 15–20 min [ Vadas and Yue , ]. Note that this 15–20 min time period includes the growth and collapse of the plume plus the time for the formation of a new plume.…”

“…We determine F 0 by calculating the body force solution numerically in time and linearly scaling by the maximum updraft velocity. The “best‐fit” plume duration and depth have been determined primarily via comparison of the model results with the amplitudes and parameters of concentric GWs from convective plumes as observed in the OH airglow near the mesopause [ Vadas et al ., , , ]. The best‐fit depth and duration have been found to be ∼10 km and χ ∼10 min, respectively.…”

“…This approximation is satisfied for vertical depths of . These solutions were used to calculate the primary GWs excited by deep convective plumes (modeled as vertical body forces), for example [ Vadas and Fritts , ; Vadas and Yue , ]. However, compressibility is expected to be important for GWs with excited by force/heat/coolings with .…”

Upper atmospheric gravity wave details revealed in nightglow satellite imagery

“…Typical wavelengths for such events fall in the range of ∼20-30 km. In the presence of wind shear, the rings are morphed into asymmetric, banded, or linearly oriented patterns (40). The DNB provides a more complete picture of these structures than surface-based systems, particularly for cloudy scenes or remote regions (e.g., Fig.…”

Combination of Lidar and Model Data for Studying Deep Gravity Wave Propagation

“…The most energetic part of the gravity wave spectrum is excited in the troposphere, with prominent source mechanisms being the flow over topography (e.g., Smith et al 2008), convection (e.g., Vadas et al 2012), flow deformation, and vertical shear at upper-level fronts (Plougonven and Zhang 2014). As internal gravity waves distribute energy and momentum in the atmosphere, they represent a prominent coupling mechanism between the troposphere and the middle atmosphere (e.g., Fritts and Alexander 2003).…”