KSGC: Development of a Multi-Planet Boundary Layer Model

The planetary boundary layer (PBL) is the region of the atmospherethat is the most familiar to most of us-the bottom few kilometers of the atmosphere in which fluid-surface interaction plays an important and direct role in atmospheric dynamics. The planetary boundary layer is a critical region for defining atmospheric behavior for any terrestrial planet. On Earth, the understanding and proper modeling of such phenomena as air-ocean carbon cycle interaction, diurnal cycle events, and pollution dispersal depend strongly on the proper definition of the boundary layer. On Mars, the PBL governs the formation, growth, and decline of global sandstorms. In the extreme case of tenuous atmospheres such as those on Triton and 10, the atmosphere is largely a planetary boundary layer that may only partially cover the planet surface. Despite, or perhaps because of, our familiarity with the PBL, there are a plethora of numerical . models designedto capture the dynamicsof this region. These modelstend to be highly parameterized, relying on data measurements of Earth's atmosphere to define a series of functions needed to close the equations governing the boundary layer. However, since the qualities of the planetary boundary layer vary significantly with time and location, these parameterized models often only work well in specific conditions and must be constantly tweaked as the local conditions change. Worse, planetary boundary layers do not tend to travel well to other worlds, as the Earth-based parameterizations must be recalibrated for the new environment, one in which the atmospheric data is at best limited (Mars) or essentially non-existent (Titan). Finally, even on Earth where data is plentiful, the validation of model performance is difficult since complete detailed measurements are rare and suffer from experimental uncertainties. The long-term goal of this project is to move towards a PBL model that is more universal, with a minimum of dependence on local data and parameters. Our procedure is to draw on engineering turbulence research, in which turbulence techniques are more readily validated against experiments and in which there are have been significant new developments in the past decade. At the same time, our goal is to keep the model as simple as possible to minimize the need for complicated parameterizations and to focus on model performance related to global, not local, phenomena. This model will be incorporated in the general circulation model (GeM) EPIC, the first GCM specifically designed with the goal of simulating all of the planetary atmospheres within the solar system. EPIC has already successfully simulated the vortex and wave dynamics of Jupiter, Saturn, and Neptune. While some preliminary work has been done on Venus, to expand EPIC firmly into the terrestrial realm requires a PBL model that is both accurate and flexible, evidencing reasonable behavior across a series of planets. Such a model will greatly facilitate comparative planetology research, in which the other atmospheres in our solar system serve as laboratories for studies that increase our understanding of Earth's meteorology and oceanography.