Observing and Understanding the Variability of Water in Weather and Climate
17TH Conference on Hydrology


Lidar characterizations of water vapor measurements over the ARM SGP Site

Richard A. Ferrare, NASA/LRC, Hampton, VA; and E. V. Browell, S. Ismail, J. Barrick, G. Diskin, S. Kooi, L. H. Brasseur, V. G. Brackett, M. Clayton, B. Lesht, L. Miloshevich, J. Podolske, F. Schmidlin, D. D. Turner, and D. Whiteman

NASA's Lidar Atmospheric Sensing Experiment (LASE) system was operated during the ARM/FIRE Water Vapor Experiment (AFWEX) to characterize the upper tropospheric (UT) water vapor field over the ARM Center Facility (CF) as part of the third Water Vapor Intensive Observation Period (WVIOP3). LASE was operated from the NASA DC-8 aircraft in the nadir and zenith modes simultaneously. Seven DC-8 flights were made during November 27 to December 10, 2000 over the CF, and LASE collected approximately 30 hours of profile data over the SGP using a combination of water vapor absorption cross-sections. These LASE water vapor measurements have been used to evaluate UT water vapor measurements acquired by the ground-based CART and NASA GSFC Raman lidars; DC-8 in situ cryogenic hygrometer and diode laser hygrometer (DLH); and Vaisala RS80-H, Sippican, Inc. (formerly VIZ Manufacturing Company) carbon hygristor, and chilled mirror radiosondes.

Initial comparisons with LASE upper troposphere water vapor (UTWV) measurements acquired during AFWEX showed the CART Raman lidar (CARL) UTWV profiles were about 6% wetter than LASE in the upper troposphere, and the Vaisala RS80-H and chilled mirror sondes were about 8-10% drier than LASE. Scaling the Vaisala water vapor profiles to match the precipitable water vapor (PWV) measured by the SGP microwave radiometer (MWR) did not change these results significantly. However, the differences between the LASE, CARL, and Vaisala radiosonde profiles were reduced to about 5%, and within the 10% goal in mean differences in UTWV, by accounting for altitude and temperature dependencies of the CARL water vapor profiles, and by employing schemes to correct the Vaisala RS80-H calibration equation and the time lag of the Vaisala RS80H humidity sensor. The radiosonde chilled mirror UTWV measurements were generally drier than the LASE UTWV measurements, but were still within about 10% on average.

The LASE and DC-8 in situ DLH UTWV measurements generally agreed to within about 3%, although the DC-8 in situ cryogenic hygrometer measurements were generally 10-20% drier than the LASE measurements. This larger difference is most likely due to response characteristics dictated by physical properties (or constraints) of the chilled-mirror instrument and measurement technique. Precipitable water vapor (PWV) derived from the LASE profiles agrees within about 3% on average with PWV derived from the ARM SGP microwave radiometer. The agreement between the LASE and MWR PWV and the LASE and CARL UTWV measurements supports the hypotheses that MWR measurements of the 22 GHz water vapor line can accurately constrain the total water vapor amount and that the CART Raman lidar, when calibrated using the MWR PWV, can provide an accurate, stable reference for characterizing upper troposphere water vapor. We also shall discuss how these CART Raman lidar measurements have been used to examine the vertical and temporal variability of water vapor and aerosols over the ARM SGP site.

extended abstract  Extended Abstract (280K)

Joint Poster Session 2, Instrumentation and Remote Sensing (Joint with the Symposium on Observing and Understanding the Variability of Water in Weather and Climate and the 17th Conference on Hydrology)
Tuesday, 11 February 2003, 9:45 AM-9:45 AM

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