Enhanced Stratospheric Water Vapor over the Summertime Continental United States and the Role of Overshooting Convection

Other literature type English OPEN
Herman, Robert L. ; Ray, Eric A. ; Rosenlof, Karen H. ; Bedka, Kristopher M. ; Schwartz, Michael J. ; Read, William G. ; Troy, Robert F. ; Chin, Keith ; Christensen, Lance E ; Fu, Dejian ; Stachnik, Robert A. ; Bui, T. Paul ; Dean-Day, Jonathan M. (2016)

The NASA ER-2 aircraft sampled the UTLS region over North America during the NASA Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC<sup>4</sup>RS) field mission. This study reports three case studies of convectively-influenced air parcels with enhanced water vapor in the overworld stratosphere over the summertime continental United States. Water vapor mixing ratios greater than 10&thinsp;ppmv, more than twice the stratospheric background levels, were measured by the JPL Laser Hygrometer (JLH Mark2) at pressure levels between 80 and 160&thinsp;hPa. Through satellite observations and analysis, we make the connection between these in situ water measurements and overshooting cloud tops. The overshooting tops (OT) are identified from a SEAC<sup>4</sup>RS OT detection product based on satellite infrared window channel brightness temperature gradients. Back trajectory analysis ties enhanced water to OT one to seven days prior to the intercept by the aircraft. The trajectory paths are dominated by the North American Monsoon (NAM) anticyclonic circulation. This connection suggests that ice is convectively transported to the overworld stratosphere in OT events and subsequently sublimated; such events may irreversibly enhance stratospheric water vapor in the summer over Mexico and the United States. Regional context is provided by water observations from the Aura Microwave Limb Sounder (MLS).
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