Evolution of Convectively Injected Water Vapor in the Lower Stratosphere During the SEAC4RS Campaign

Elevated stratospheric water vapor was observed over the continental United States during the NASA Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC⁴RS) mission in summer 2013. Water vapor mixing ratios greater than 10 ppmv, much higher than background 4 to 6 ppmv of the overworld stratosphere, were measured by the JPL Laser Hygrometer (JLH Mark2) at altitudes between 16.0 and 17.5 km (potential temperatures of approximately 380 K to 410 K) on 8 August 2013. Earlier studies based on back-trajectory analysis hypothesized that the source of this excess water was convective storm systems that occurred four days earlier and hundreds of miles away by overshooting the tropopause and irreversibly depositing ice in the stratosphere. Weather and Research Forecast (WRF) model simulations of the atmosphere have been carried out for this case study. We find that the WRF simulations of upper tropospheric and lower stratospheric water vapor are sensitive to the initial and boundary conditions from reanalysis. Replacing initial and boundary conditions with vertically-interpolated Aura MLS temperature and water vapor improves the simulations of moisture anomalies. The WRF model disperses the convectively injected excess water so quickly that spikes of elevated water vapor in the 8 August 2013 aircraft in situ data are more likely from local storms than from the transport of high water vapor perturbations caused by distant storms four days earlier. Additional observations are provided by the Aura Microwave Limb Sounder (MLS). We use these observations to estimate the impact of deep convection on regional water vapor distributions.