Project Title: Medium-Scale Atmospheric Waves: Coupling of Convection, Clouds, and Larger-Scale Dynamics
PI: M. Joan Alexander
Global climate and forecasting models are now capable of resolving both planetary-scale and some mesoscale waves. However, model intercomparisons and comparisons to observations suggest the properties of the smaller-scale resolved waves in such models are inaccurate both in a statistical climatological sense and in an event forecasting sense. This project aims to quantify the forcing, properties, and effects of atmospheric medium-scale waves with special emphasis on tropical waves generated by convection. Latent heating in convection generates waves on all scales, and the waves in turn organize the convection and can initiate new remote convective events. Representation of these processes in global models can be affected by the numerical resolution, the numerical methods used in the computation of the dynamical fields, and also the convective cloud parameterization.
We are using new Aura satellite observations to characterize the properties of medium-scale waves in the atmosphere. We will compare the observational results to theoretical models of wave generation by convection in case studies to test our understanding of the wave generation and propagation properties. These case study analyses can be expanded to the global scale as global-scale latent heating products from TRMM and CloudSat become available. We seek collaborations through CMAI to acquire and adapt these latent heating fields for use in our model studies. We will next compare the observed waves to those in the GEOS-5 assimilation fields and investigate the differences. Our project aims to improve the representation of these processes in global models, and we plan to examine the performance of the high-resolution assimilation model from this perspective. We seek collaborations through CMAI in acquiring the high-resolution assimilation products and in possibly developing diagnostics for wave and momentum budget studies.
Temperature fluctuations associated with medium-scale waves also influence cirrus cloud formation. At the tropical tropopause, wave-induced temperature fluctuations influence the growth and precipitation of cirrus and affect the global stratospheric water vapor budget. At high latitudes, mountain wave-induced ice clouds play a role in stratospheric ozone chemistry. Our collaborators at NASA Ames plan to use our results on wave temperature fluctations observed via satellite to improve their global models of cirrus formation.