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<h1>Report 52:&nbsp; Sampling Strategies for the

Comparison of Climate Model Calculated and Satellite Observed Brightness

Temperatures</font>

<ul><b>&nbsp;Engelen,</b> Richard J., Laura D. Fowler, Peter J. Gleckler

and Michael F. Wehner

<p>June 1999, 38 pp.&nbsp;

<p>Brightness temperatures derived from polar orbiting satellites are valuable

for the evaluation of global climate models. However, the effect of orbital

constraints must be accounted to ensure valid comparisons. As part of the

AMIP II climate model comparisons, this study seeks to evaluate the bias

of possible model output sampling strategies, and whether they can be practically

implemented to provide meaningful comparisons with these satellite observations.

We compare various sampling strategies with a proxy satellite data set

constructed from model output and actual TOVS orbital trajectories, rather

than with the observations themselves. To a large extent, this enables

isolation of the sampling error from biases caused by deficiencies in the

modeled climate processes. Our results suggest that the traditional method

of calculating brightness temperatures from monthly mean temperature and

moisture profiles yields biases from both nonlinear effects and the removal

of the diurnal cycle, that may be unacceptable in many applications. However,

our results also suggest that a brightness temperature calculation every

six hours of the simulation provides substantially lower sampling biases

provided that there are two or more properly aligned satellites. This is

encouraging because it means for many applications modelers need not accurately

mimic actual satellite trajectories in the sampling of their simulations.

However, if only one satellite is available for comparison with simulations,

more sophisticated sampling seems necessary. For such circumstances, we

introduce a simple procedure that serves as a useful approximation to the

rather complex procedure required to sample a model exactly as a polar

orbiting satellite does the Earth.<i><a href="pdf/52.pdf">(pdf file)</a></i>

<font size=-1><a href="report.html">Return to PCMDI Report Series</a></font>

<p><font size=-1>UCRL-MI-123395</font></ul>