Presentation on theme: "Upper Tropospheric Humidity: A Comparison of Satellite, Radiosonde, Lidar and Aircraft Measurements Satellite Lidar Aircraft Radiosonde."— Presentation transcript:
Upper Tropospheric Humidity: A Comparison of Satellite, Radiosonde, Lidar and Aircraft Measurements Satellite Lidar Aircraft Radiosonde
Collaborators Rich Ferrare et al., NASA/LaRC John Goldsmith, DOE/LANL Barry Lesht, DOE/ANL Larry Milosevich, NCAR Frank Schmidlin, NASA/GSFC Bill Smith et al., NASA/LaRC Dave Tobin et al., Univ. of Wisconsin Dave Turner, DOE/PNNL David Whiteman et al., NASA/GSFC
Objective To assess of the accuracy of current measurements of upper tropospheric water vapor. Assuming: a) There is no perfect observation of upper tropospheric water vapor. b) We should assess the consistency of different measurements, rather than attempting to validate against a specific benchmark. c) Satellites can provide a common reference for comparing disparate measurements to assess their relative consistency.
Why Monitor Upper Tropospheric Water Vapor?
Change in Water Vapor at 2xCO 2 : GFDL GCM Increase in tropopause RH amplifies wv feedback by ~10% Most change attributable to increase in saturation vapor pressure
Satellite Measurement of Upper Tropospheric Humidity
What do IR “water vapor” radiances measure? The 6.7 m radiances are sensitive to relative humidity averaged over a deep layer of the upper troposphere (~ hPa). * Use satellite 6.7 m T b to provide a common, stable benchmark for intercomparing other measurements.
Step 1: Insert lidar/sonde moisture profile (and coincident sonde temperature profile) into radiative transfer model. * Compare observed and forward-simulated T b. How do you compare satellite measurements with a water vapor profile? Step 2: Transform both observed and simulated T b into Upper Tropospheric relative Humidity ( UTH ) ln (UTH p 0 / cos ) = a + b T 6.7 (1) * Use UTH translation to interpret T b comparison. 1 K error in T b equals ~10% relative error in UTH. "Profile-to-Radiance" Comparison Procedure
Temporal Comparisons of Upper Tropospheric Water Vapor Radiosonde – Satellite: Upper Tropospheric Humidity
Satellites provide a common reference for intercomparing different UTWV measurements and assessing their relative consistency
ARM Water Vapor Intensive Observation Periods Lidar Humidity Profiles: ARM /CART Raman Lidar (CARL) GSFC Scanning Raman Lidar (SRL) NASA/LaRC DIAL Lidar (LASE) Radiosonde Humidity Profiles Vaisala RS80 VIZ Carbon Hygristor Frostpoint Chilled Mirror Radiances NASA/LaRC Airborne Interferometer (NAST-I) GOES 6.7 m Imager The Atmospheric Radiation Measurement (ARM) Program has conducted a series of Water Vapor IOPs over their Central U.S. field site: 1996 WV IOP, 1997 WV IOP, 1999 Lidar IOP, 2000 WV IOP, 2000 AFWEX
ARM Measurement Intercomparison
Impact of Radiosonde Corrections
Measurement Intercomparison: Radiosonde Radiosondes are drier by ~20-30% relative to satellite. cloud
Measurement Intercomparison: Lidars Raman (CARL, SRL) and DIAL (LASE) lidar agree to within ~10%. cloud
Measurement Intercomparison: NAST-I NAST-I intereferometer and GOES-8 radiances agree to within ~1 K.
Bias Summary Uncorrected sondes are ~30% drier than GOES in the upper trop (~20% drier than lidar). Temp-lag corrections can reduce this bias to ~10% wrt lidar. Lidars, aircraft intereferometer, and satellite agree to ~10%. RadiosondesLidars & NAST
Vertical Structure of Biases Direct assimilation of satellite radiances offers potential to greatly improve the radiosonde humidity profiles in the upper troposphere.
Summary Satellite IR measurements can provide an effective tool for intercomparing upper tropospheric humidity from different instruments. Vaisala RS80 radiosondes exhibit a systematic dry bias relative to both satellite and lidar measurements. Existing ARM radiosonde corrections were ineffective in the upper troposphere, however some new corrections show promise (i.e., Miloshevich). Direct assimilation of satellite radiances offers potential to improve the radiosonde humidity profiles in the upper troposphere when other corrections are not available (e.g., for historical records).
Vertical Structure of Biases Existing ARM correction methods improve total column water vapor, but have little impact on the upper troposphere.