The Role of Gravity Waves in the Formation and Organization of Clouds During TWP-ICE

Michael Reeder Monash University
Todd Lane University of Melbourne
Christian Jakob Monash University
Andrew Heymsfield NCAR

Category: Modeling

Working Group: Cloud Life Cycle

All convective clouds emit gravity waves. While it is certain that convectively generated waves play important parts in determining the climate, their precise roles remain uncertain, and their effects are not generally represented in climate models. There are at least three ways in which convectively generated gravity waves affect climate. First, gravity waves have the potential to lift moist layers in the upper troposphere to produce extensive layers of cirrus. The vertical velocity and temperature perturbations associated with such waves may lead to supersaturation near the tropopause, which in turn leads to cirrus nucleation. This process has the potential to very significantly control the transport of water in to the lower stratosphere, since the cirrus crystals will grow, fall, and dehydrate the upper atmosphere. Conversely, the formation of cirrus layers may increase the temperature at upper levels by a degree or two, which in turn would increase the saturation mixing ratio with respect to ice, promoting greater transport of water into the lower stratosphere. Either way, the effect of thin cirrus clouds on the distribution of water in the upper troposphere and lower stratosphere, and hence the radiative budget, is almost certainly large. Second, it is known that the gravity waves emitted by deep convective clouds may themselves trigger and organize further convection, although the frequency with which this occurs and its significance remain uncertain. Third, gravity waves transport momentum and energy very large distances from the site of their generation, exerting a stress on the atmosphere wherever they dissipate. In this way, convectively generated gravity waves play a very influential role in determining the climate, and in particular the large-scale circulation, as they couple the troposphere to the upper atmosphere through the redistribution momentum and energy. This research project has only just begun, and the poster will describe the research plan and some preliminary results. The project will investigate the part played by convectively generated gravity waves in the formation of cirrus, in the initiation and organization of further convection, and in the subgrid-scale momentum transport and associated large-scale stresses imposed on the troposphere and stratosphere. This will be achieved through a combination of detailed numerical simulation and analysis of the observations taken during TWP-ICE.

This poster will be displayed at ASR Science Team Meeting.

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