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Soil moisture in complex terrain: quantifying effects on atmospheric boundary layer flow and providing improved surface boundary conditions for mesoscale models


Soil moisture affects flow in the atmospheric boundary layer (ABL) through relative partitioning of surface energy fluxes. Surface conditions significantly affect flow in the ABL under quiescent synoptic conditions (weak forcing) over flat terrain, but strong wind forcing often dominates land surface effects. Over complex terrain, it is unclear what role soil moisture plays. Due to a lack of data at the appropriate resolution, surface conditions are often interpolated from coarse grids as part of a standard intialization procedure for mesoscale atmospheric models. In this work, simulations of the ABL are performed using the Advanced Regional Prediction System (ARPS) in a horizontally nested grid configuration for the complex terrain of Owens Valley, California, site of the Terrain-Induced Rotor Experiment (T-REX) in March and April, 2006. Effects of surface

conditions on simulations of ABL flow in complex terrain under both weak and strong synoptic

forcing are investigated through a sensitivity study and through comparisons to observations. Coupled hydrologic modeling using PF.CLM, a coupled groundwater-land-surface model, is presented as a physically-based alternative to standard initialization procedures. Soil moisture measurements were carried out during T-REX and are used to validate results of the coupled hydrologic modeling. Results of the sensitivity study indicate that simulations of the ABL are sensitive to surface soil moisture initialization under both weak and strong synoptic forcing. Comparisons of simulation results to observations show significant improvements in most simulations with more accurate soil moisture. Coupled hydrologic modeling is a promising alternative to standard initialization procedures; even simple two-dimensional simulations successfully capture soil moisture trends across Owens Valley. Simple adjustments to standard initial soil moisture based on field observations yield significant improvements in comparisons to observations as well.

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