A Cluster Analysis Approach to comparing Atmospheric Radiation Measurement (ARM) Data with Global Climate Model (GCM) Results

A cluster analysis approach is employed to compare Atmospheric Radiation Measurement (ARM) program observational data at the Southern Great Plains (SGP) site with the corresponding output from an integration of the Community Climate System Model (CCSM3) run under the IPCC SRES A2 business as usual scenario for the current decade. A parallel clustering algorithm developed at Oak Ridge National Laboratory (ORNL) designed for analyzing very large datasets was applied to obtain various atmospheric column regimes/states at the SGP site from the observations and, separately, from the CCSM3 model results based on vertical temperature, humidity and wind speed tropospheric profiles and surface pressure. A three way process was implemented to compare ARM data with GCM output, where CCSM3 output is projected on to ARM data derived regimes as a first approach, ARM data is projected onto CCSM3 output derived regimes as a second approach, and finally regimes derived from a merged data pool of ARM data and CCSM3 output are analyzed. The analysis reveals distinct singular regimes that exist in ARM observations and CCSM3 output, which are not replicated in the other. These distinct regimes in CCSM3 output and ARM observations suggest misrepresentation of atmospheric states in CCSM3 over the SGP site. The comparisons also indicate that the inter-annual variability of CCSM3 is comparatively lesser than that of ARM observations on the multi-variate basis with a strong seasonal locking of regimes in CCSM3 not observed in ARM data. This study introduces cluster analysis as a superior technique, to compare observations and GCM on a multi-variate basis proD R A F T March 14, 2012, 4:02pm D R A F T MAHAJAN ET AL.: CLUSTER ANALYSIS OF ARM DATA AND GCM RESULTS X 3 viding the capability to compare comprehensive all-inclusive atmospheric states, over traditional univariate comparisons. D R A F T March 14, 2012, 4:02pm D R A F T X 4 MAHAJAN ET AL.: CLUSTER ANALYSIS OF ARM DATA AND GCM RESULTS