Mechanisms of Convection-Wave Interactions

University Of Colorado At Boulder, Boulder CO

Investigators

Abstract

This project seeks to improve understanding of convection-wave interactions in the Tropics, with an emphasis on zonally-propagating, inertia-gravity wave disturbances with periods less than 2.5 days. Such disturbances are of interest owing to their strong ties to the diurnal cycle and potential role in the genesis of severe tropical storms, such as Hurricane Andrew 1992. Furthermore, space-time spectra of high-resolution satellite data show a dramatic westward bias in the propagation direction of these high-frequency wave modes, begging explanation and perhaps holding critical clues about wave-convection modulation mechanisms. A suite of carefully designed nested cloud-resolving model experiments on a uniform equatorial beta-plane will be performed using the Weather-Research Forecast (WRF) model system, to test hypotheses about what causes this asymmetry. Further insights will be gleaned from detailed diagnostic analyses, using techniques developed in previous work. These analyses will be applied to data from the idealized WRF model runs, as well as from other, much larger, realistic-boundary-condition model runs; and from observations. To assess the realism of the simulated wave structures, detailed comparisons will be made against composite radiosonde observations of temperature, moisture, and winds. Such observational composites already exist for low-frequency waves, but will be extended to diurnal and higher frequencies. The previously identified self-similarity of tropical convective wave life cycles across scales is expected to extend to these relatively short/fast waves, but with systematic differences across frequencies suggesting clues about the relative roles of temperature and moisture in wave dynamics. An important novelty of the observational component will be to bring in vertically-resolved cloud structure observations from CloudSat, which was launched in 2006. Scientific results of this work are expected to have broad impact in the atmospheric sciences by usefully informing efforts at improving convective parameterizations used in general-purpose regional and global models. Some of the modeling and diagnostic techniques will be packaged and offered as enhancements to the WRF model's "out-of-the-box" capabilities, as a service to the broader regional modeling community. This project will also contribute to the training and mentorship of a graduate student.