Convectively Transported Water Vapor Plumes in the Midlatitude Lower Stratosphere

Abstract

Deep convective overshooting has been shown to transport water vapor into the midlatitude lower stratosphere. However, it has not been demonstrated how the convective water vapor plumes evolve after the overshoots collapse. Furthermore, there is a lack of characterization of the convective water vapor plumes, nor is it clear whether satellite instruments can observe the characteristics. We use a high-resolution numerical weather prediction model to study a convective system over North America. Multiple overshoots transport water vapor in the overworld stratosphere, forming a moist layer between 16.2 and 16.8 km (389.8–399.7 K), with horizontal diameters of about 300–400 km, and a maximum water vapor mixing ratio of 10.0 ppmv (4.3 ppmv anomaly). Lagrangian trajectories and mass integrations show the overworld water vapor plumes are maintained after the convective system weakens. In the lowermost stratosphere (LMS), water vapor plumes are less stable and ice is present, because there is perturbation by ongoing convection. Lagrangian trajectories and mass integrations show the LMS parcels partly return to the troposphere, and that the LMS water vapor mass is reduced by half after the convection weakens. On average, the LMS moistening is between 15.0 and 15.8 km (362.6–382.0 K), with horizontal diameters of about 150 km, and a maximum water vapor mixing ratio of 31.1 ppmv (18.4 ppmv anomaly). Although current satellites have difficulty observing the fine structure of the convective water vapor plumes, a new satellite instrument under development (SHOW) with 1-km vertical and 100-km horizontal resolution will be able to verify the plume characteristics.