In the wake of stratosphere/troposphere exchange events, the distribution of specific humidity in the mid-troposphere is an effective tracer for ozone of stratospheric origin. Both ozone and water vapor are important radiatively active gases in the troposphere and knowledge of their distribution on a global scale is relevant to both climate and photochemical modeling. Beginning with the analytic expression relating GOES-8/9 channel-3 water vapor radiance to upper tropospheric relative humidity, we have used model temperature grids to derive high horizontal resolution (8km) images of specific humidity. The accuracy of these images increases with dryness of the atmosphere; consequently, the images give new insight to the moisture content of events such as tropopause depressions in cutoff-lows, stratosphere/troposphere exchange behind fronts, and dry-air streamers. Depiction of water vapor as specific humidity rather than relative humidity allows it to be used as a conserved quantity. Observations based on this derived product, along with the dynamic tracer potential vorticity, show that we can explain both spatial and temporal variation in the vertical distribution of ozone. A summary of ozonesondes and NOAA P3 aircraft data from the North Atlantic Regional Experiment (NARE) September 1997 intensive will be presented that illustrates the impact of several dynamic events on the background level of free tropospheric ozone. The implications of this ability to interpret the mid-tropospheric circulation of water vapor on a global scale in terms of its relationship to the ozone budget of the troposphere will be discussed.
Symposium on Interdisciplinary Issues in Atmospheric Chemistry