Response of MCS Low-Frequency Gravity Waves to Vertical Wind Shear and Nocturnal Thermodynamic Environments

Faith P. Groff aDepartment of Atmospheric Science, Colorado State University, Fort Collins, Colorado

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Rebecca D. Adams-Selin bAtmospheric and Environmental Research, Inc., Lexington, Massachusetts

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Russ S. Schumacher aDepartment of Atmospheric Science, Colorado State University, Fort Collins, Colorado

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Abstract

This study investigates the sensitivities of mesoscale convective system (MCS) low-frequency gravity waves to changes in the vertical wind and thermodynamic profile through idealized cloud model simulations, highlighting how internal MCS processes impact low-frequency gravity wave generation, propagation, and environmental influence. Spectral analysis is performed on the rates of latent heat release, updraft velocity, and deep-tropospheric descent ahead of the convection as a signal for vertical wavenumber n=1 wave passage. Results show that perturbations in midlevel descent up to 100 km ahead of the MCS occur at the same frequency as n=1 gravity wave generation prompted by fluctuations in latent heat release due to the cellular variations of the MCS updrafts. Within a nocturnal environment, the frequency of the cellularity of the updrafts increases, subsequently increasing the frequency of n=1 wave generation. In an environment with low-level unidirectional shear, results indicate that n=2 wave generation mechanisms and environmental influence are similar among the simulated daytime and nocturnal MCSs. When deep vertical wind shear is incorporated, many of the low-frequency waves are strong enough to support cloud development ahead of the MCS as well as sustain and support convection.

Groff’s current affiliation: CPP Wind Engineering and Air Quality Consultants, Windsor, Colorado.

© 2021 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Corresponding author: Faith P. Groff, Fgroff@cppwind.com

Abstract

This study investigates the sensitivities of mesoscale convective system (MCS) low-frequency gravity waves to changes in the vertical wind and thermodynamic profile through idealized cloud model simulations, highlighting how internal MCS processes impact low-frequency gravity wave generation, propagation, and environmental influence. Spectral analysis is performed on the rates of latent heat release, updraft velocity, and deep-tropospheric descent ahead of the convection as a signal for vertical wavenumber n=1 wave passage. Results show that perturbations in midlevel descent up to 100 km ahead of the MCS occur at the same frequency as n=1 gravity wave generation prompted by fluctuations in latent heat release due to the cellular variations of the MCS updrafts. Within a nocturnal environment, the frequency of the cellularity of the updrafts increases, subsequently increasing the frequency of n=1 wave generation. In an environment with low-level unidirectional shear, results indicate that n=2 wave generation mechanisms and environmental influence are similar among the simulated daytime and nocturnal MCSs. When deep vertical wind shear is incorporated, many of the low-frequency waves are strong enough to support cloud development ahead of the MCS as well as sustain and support convection.

Groff’s current affiliation: CPP Wind Engineering and Air Quality Consultants, Windsor, Colorado.

© 2021 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Corresponding author: Faith P. Groff, Fgroff@cppwind.com
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