Wednesday, 17 January 2007: 4:15 PM
Quantifying the strength of soil moisture-precipitation coupling and its sensitivity to changes in surface water budget
213A (Henry B. Gonzalez Convention Center)
This paper presents a new index to quantify the strength of soil moisture-precipitation coupling in AGCMs based on intra-ensemble relative variance, and explores how the soil moisture-precipitation coupling in the CAM3-CLM3 model responds to a modification in the vegetation canopy interception parameterization that leads to significant surface water budget changes. Specifically, this study examines how these surface water budget changes influence (a) the strength of soil moisture-precipitation coupling as measured by the proposed new index, (b) the strength of soil moisture-precipitation coupling as measured by the index currently used in the Global Land-Atmosphere Coupling Experiment (GLACE), and (c) the memory of the coupled land-atmosphere system as measured by the correlation between soil moisture and subsequent precipitation and evapotranspiration. Two main differences are found between the newly proposed index and the index currently used in GLACE. First, the newly proposed index identifies Europe as a major region of modest-to-strong coupling in addition to what the GLACE index suggests. Secondly, as a result of the canopy interception parameterization changes that presumably favor a stronger soil moisture-precipitation coupling, the newly proposed index increases significantly but the GLACE index decreases in some major regions of strong coupling. Changes in the land-atmosphere system memory suggest an increase of coupling strength, consistent with results based on the proposed index. An excessive dependence of the GLACE index on the relative importance of atmospheric internal variability is identified as an important cause for the differences between the new index and the GLACE index in the regions of strong coupling they identify and in their response to model parameterization changes.