Land surface and orographic controls on precipitation patterns in the Sierra Madre Occidental and Western Ghats

land surface-atmosphere interaction;diurnal cycle;mesoscale meteorology

Flynn, Wendilyn

关键词: land surface-atmosphere interaction;    diurnal cycle;    mesoscale meteorology;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/42354/Wendilyn_Flynn.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

Several aspects of land surface-atmosphere interactions cannot be adequately captured by climate models, due in part to inadequacies in representing small scale processes in space and time, such as diurnal cycles, convection, and cloud microphysics. Individual and collaborative efforts using climate models and reanalyses have established various parameters that attempt to diagnose the magnitude of connections between land surface conditions and atmospheric responses, such as soil moisture and precipitation. As global precipitation patterns change, the regions that experience high degrees of coupling between the land surface and atmosphere are likely to be impacted most. Within this study, we focus on two regions where we suspect coupling between the land surface, topography, and the atmosphere is significant: the areas surrounding the Sierra Madre Occidental mountains of western Mexico, and the Western Ghats of India, and investigate the processes behind these connections in detail. While these regions possess their own unique meteorological challenges, including sparse observational networks of land surface and meteorological fields, the orography in each case acts as the primary regulator of heat and moisture in monsoonal flows. We use the recently developed Land Information System (LIS) to generate realistic land surface conditions to use in sensitivity tests with the Weather Research and Forecasting model (WRF) at high resolutions (5 km) over seasonal time scales to capture the intricacies of dynamical processes occurring between the land surface, terrain, and atmosphere. We find that fluxes of heat and moisture from the surface in these regions of complex terrain act as additional, but secondary, controls on orographic precipitation that modulate the flow of moisture onshore and upslope. Both regions exhibit strong diurnal cycles in meteorological fields, land surface parameters, and convective parameters which lead to diurnal cycles of precipitation. Impacts of contrasting initial soil conditions on precipitation intensity, timing,and accumulation immediate to the orography are largely negligible on seasonal timescales, but are robust for up to 30 days into the simulations. Areas further inland, in the lee of the mountains, exhibit much stronger land surface-atmosphere interactions on short-term and seasonal timescales.