Effects of Convectively Generated Gravity Waves and Rotation on the Organization of Convection

Changhai Liu National Center for Atmospheric Research,* Boulder, Colorado

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Mitchell W. Moncrieff National Center for Atmospheric Research,* Boulder, Colorado

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Abstract

The effects of latent heating, gravity waves, and planetary rotation on numerically simulated convective cloud systems are investigated. First, the nonlinear response of an initially motionless, uniformly stratified, dry atmosphere to steady heating that interacts with the environment through inertial–gravity waves is examined. Planetary rotation confines the subsidence-induced adiabatic warming to the neighborhood of the heated region on a time scale comparable to the lifetime of mesoscale convective systems. In a moist atmosphere, rotation-induced localized descent stabilizes and dries the near environment and decreases the convective available potential energy. The Tropics is therefore a preferred region for convective clustering.

This hypothesis is tested in two sets of multiday convection-resolving simulations on f planes representative of the Tropics, subtropics, and midlatitudes. Convection is maintained by radiative cooling and surface fluxes of heat and moisture. In a motionless mean state, convective clustering is most prominent in the Tropics. In constant easterly flow, tropical convection organizes on three scales. Eastward-propagating convectively coupled gravity waves generate large-scale envelopes of cloudiness. Embedded within these envelopes are westward-traveling mesoscale convective systems that, in turn, contain westward-traveling deep convective cores.

Corresponding author address: Dr. Changhai Liu, National Center for Atmospheric Research, P. O. Box 3000, Boulder, CO 80307-3000. Email: chliu@ucar.edu

Abstract

The effects of latent heating, gravity waves, and planetary rotation on numerically simulated convective cloud systems are investigated. First, the nonlinear response of an initially motionless, uniformly stratified, dry atmosphere to steady heating that interacts with the environment through inertial–gravity waves is examined. Planetary rotation confines the subsidence-induced adiabatic warming to the neighborhood of the heated region on a time scale comparable to the lifetime of mesoscale convective systems. In a moist atmosphere, rotation-induced localized descent stabilizes and dries the near environment and decreases the convective available potential energy. The Tropics is therefore a preferred region for convective clustering.

This hypothesis is tested in two sets of multiday convection-resolving simulations on f planes representative of the Tropics, subtropics, and midlatitudes. Convection is maintained by radiative cooling and surface fluxes of heat and moisture. In a motionless mean state, convective clustering is most prominent in the Tropics. In constant easterly flow, tropical convection organizes on three scales. Eastward-propagating convectively coupled gravity waves generate large-scale envelopes of cloudiness. Embedded within these envelopes are westward-traveling mesoscale convective systems that, in turn, contain westward-traveling deep convective cores.

Corresponding author address: Dr. Changhai Liu, National Center for Atmospheric Research, P. O. Box 3000, Boulder, CO 80307-3000. Email: chliu@ucar.edu

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