Water vapor retrievals: new applications and implications for cal/val

Recent examination of observations of water vapor and halogen-containing chemical compounds in the lower stratosphere has suggested an interaction between continental convection during summer and ozone chemistry capable of substantial depletion of column ozone amounts. Understanding this interaction, its interannual variability, and possible trends in the coming decades requires robust climatologies of water vapor. The transient nature of stratospheric water vapor enhancements associated with convective events defines the spatial (both horizontal and vertical) and temporal sampling required to derive robust climatologies from different types of observing systems, including satellites. Moreover, climatological water vapor mixing ratios in the stratospheric regions of interest are very low, creating a demanding situation for validation of retrieval products. This paper will examine the relevant aspects of sampling issues and measurement uncertainty issues relevant to cal/val as defined by this new stratospheric science application.