4.7
Improved retrievals of temperature and water vapor profiles with a twelve-channel microwave radiometer
James C. Liljegren, ANL, Argonne, IL
The Atmospheric Radiation Measurement (ARM) Program has operated a twelve-channel microwave radiometer profiler (MWRP) built by Radiometrics Corporation since February 2000. This instrument provides real-time vertical profiles of temperature, water vapor, and limited-resolution cloud liquid water from the surface to 10 km in nearly all weather conditions at approximately 10-minute intervals. Figure 1 shows a frontal passage (~1200 hr) captured by the MWRP. In contrast to radiosondes, the MWRP provides substantially improved temporal resolution but coarser vertical spatial resolution, which declines in proportion to the height above ground level. In this regard it more closely matches the temporal and vertical resolution of numerical weather forecast models.
Although the MWRP is currently deployed at the ARM Southern Great Plains (SGP) central facility near Lamont, OK, it has also been successfully operated at the ARM North Slope of Alaska (NSA) facility at Barrow, AK. Since its initial deployment at SGP significant biases between measured and modeled brightness temperatures in the five channels between 22-30 GHz have been observed. These brightness temperature biases resulted in significant biases in the retrieved profiles of water vapor and temperature and also adversely affected the vertical resolution. In this paper the brightness temperature biases are eliminated by substituting the air-broadened half width of the 22.235 GHz water vapor line from the HITRAN compilation (Rothman et al., 1992) for the Rosenkranz (1998) half width in the model calculations. An a priori statistical retrieval based on the revised model is shown to yield significant improvements in the accuracy and vertical resolution of the retrieved temperature and water vapor profiles. Additional improvements are then demonstrated by combining the MWRP retrievals with those from the GOES-8 sounder and Rapid Update Cycle (RUC) model.
This work was supported by the Environmental Sciences Division, U. S. Department of Energy, Office of Science, Office of Biological and Environmental Research, under contract W-31-109-Eng-38, as part of the Atmospheric Radiation Measurement Program. Argonne National Laboratory is operated by the University of Chicago for the U. S. Department of Energy.
Session 4, Atmospheric Observations: Part Two (Room 618)
Tuesday, 13 January 2004, 8:30 AM-2:45 PM, Room 618
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