85th AMS Annual Meeting

Monday, 10 January 2005: 1:30 PM
Are Simulated Microwave Sounding Unit temperatures sensitive to the method by which they are generated?
J. J. Hnilo, LLNL, Livermore, CA; and B. D. Santer
Are Simulated Microwave Sounding Unit temperatures sensitive to the method by which they are generated?

J. J. Hnilo and B. D. Santer

Considerable scientific attention has been devoted to comparisons of observed and simulated Microwave Sounding Unit (MSU) temperatures. When simulating synthetic MSU temperatures, most studies apply a single static weighting function to the profiles of temperature. A variant of this procedure relies on different weighting functions for land and ocean regions to account for differences in surface emissivity values. A small number of investigations have also used full radiative transfer codes to derive synthetic MSU temperatures from model and/or reanalysis data. To date, few studies have rigorously quantified the sensitivity of simulated MSU temperatures to the choice of simulation method.

Here, we apply both the static weighting function and full radiative transfer code approaches to atmospheric temperature data from multiple reanalyses. Our motivation is to document the sensitivity of estimated synthetic MSU temperatures to a variety of different processing options.

The static weighting function approach is applied directly to monthly-mean pressure level data. Surface pressure is used to mask values that reside below the material surface. In addition to pressure level temperatures, the view-angle resolving radiative transfer code also utilizes skin temperatures and profiles of specific humidity. Regions of high topography are masked with surface pressure data, and there is explicit treatment of surface temperature data when surface pressure exceeds the lowest standard pressure level output (e.g., 1000hPa). Additionally, a land/sea mask is used to specify differing surface emissivity values. Further processing choices relate to the vertical resolution of the input temperature data and the treatment of upper-level moisture.

Results shown will highlight observed and simulated temperatures from the NCEP/NCAR, NCEP/DOE and ERA40 reanalyses data for MSU 2, MSU2LT and MSU4.

This work is supported under the auspices of the Office of Science, U.S. Department of Energy at the University of California Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48

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