Validation of a derived product image for upper-tropospheric extratropical specific humidity

A method for quantifying specific humidity in the mid-to-upper troposphere has been developed, drawing from a parametric relationship between the logarithm of a weighted average of specific humidity and brightness temperature from the 6.7 um water vapor channel of the GOES-E/W imager, adjusted for variations in atmospheric temperature and satellite zenith angle. This derived product image (DPI) shares the horizontal resolution of the GOES water vapor image, and when atmospheric temperature information from model forecast fields is used, the DPI can be produced within one minute of the GOES image. Alternatively, model forecast fields can be used to forecast the water vapor channel at lower resolution. Results from a radiative transfer model characterize the robustness of this product in atmospheric cases of particular interest, including tropopause folds and depressions. Additionally, a number of case studies will be used to evaluate the quantitative and qualitative value of the DPI and its relationship to dynamic tracers such as potential vorticity. Two cases taken from the time periods of the Atmosphere-Ocean Chemistry Experiment (AEROCE 96) and North Atlantic Regional Experiment (NARE 97) atmospheric chemistry campaigns illustrate tropopause folds behind strong cold fronts, tapping into dry, ozone-rich stratospheric air whose advection and evolution can be followed in high spatial resolution with the DPI.