Convective transport of water vapor into the lower stratosphere observed during double-tropopause events

Abstract

We present in situ observations of convectively injected water vapor in the lower stratosphere from instruments aboard two aircraft operated during the Deep Convective Clouds and Chemistry experiment. Water vapor mixing ratios in the injected air are observed to be 60–225 ppmv at altitudes 1–2 km above the tropopause (350–370 K potential temperature), well above observed background mixing ratios of 5–10 ppmv in the lower stratosphere. Radar observations of the responsible convective systems show deep overshooting at altitudes up to 4 km above the lapse rate tropopause and above the flight ceilings of the aircraft. Backward trajectories from the in situ observations show that convectively injected water vapor is observed from three distinct types of systems: isolated convection, a convective line, and a leading line-trailing stratiform mesoscale convective system. Significant transport of additional tropospheric or boundary layer trace gases is observed only for the leading line-trailing stratiform case. In addition, all observations of convective injection are found to occur within large-scale double-tropopause events from poleward Rossby wave breaking. Based on this relationship, we present a hypothesis on the role of the large-scale lower stratosphere during convective overshooting. In particular, the reduced lower stratosphere stability associated with double-tropopause environments may facilitate deeper levels of overshooting and convective injection.