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The Role of Convective Moisture Sensitivity in Improving Major Systematic Biases in the Community Climate System Model (CCSM)

The Role of Convective Moisture Sensitivity in Improving Major Systematic Biases in the Community Climate System Model (CCSM)

Richard Neale - Rm 304 - rneale@ucar.edu
http://www.cgd.ucar.edu/cms/rneale
Climate Modelling Section, CGD, NCAR
P.O. Box 3000, Boulder, CO 80307-3000
Tel (303) 497-1380 Fax (303) 497-1324

The NCAR Community Climate System Model (CCSM3) exhibits persistent systematic errors in three important atmospheric phenomena: an excessive diurnal cycle amplitude over land, weak MJO-type variability at the wrong frequency and a strong ENSO with a fast 2-year period. All these phenomenon involve an intimate coupling relationship with convection and, therefore, the presence or absence of free tropospheric humidity.

Changing the existing undilute convective plume calculation to a dilute calculation to determine the height and strength of convection increases the sensitivity to tropospheric humidity and reduces the sensitivity to the surface. The change has a significant impact in dramatically improving these systematic errors. This talk will investigate how these key phenomena operate differently with the enhanced sensitivity to moisture provided by the scheme changes. We will also show that an association between improvements in MJO activity and the frequency of ENSO may involve significant scale interaction.