Injection of water vapor into the stratosphere in a convective system above Europe – a measurement perspective

Convective processes play a critical role in the atmosphere’s energy balance. In high updraft regimes, turbulent and diabatic processes redistribute moisture, heat, and aerosols, which lead to cloud formation affecting the radiation budget of the atmosphere. During the HALO airborne CIRRUS-HL mission in summer 2021, the outflow of a convective system over Northern Italy was probed at different altitudes. The system had an overshooting top accompanied by lightning and icing conditions. A suit of in-situ (aerosol, cloud probes, trace gases) and remote sensing (Lidar) instruments deployed on the research aircraft HALO combined with satellite observations  provided the opportunity to investigate the system from different perspectives. The in-situ H2O -O3 correlation revealed unexpected insights in the extra-tropical tropopause transition layer (exTL), characterized by enhanced water vapor  and ice crystal number in the exTL. The convective system penetrated into the exTL with O3 up to 450ppb. In contrast, the CO -O3 correlation shows minor influence, indicating that this convection event was little impacted by large scale mixing processes. The potential temperature around the upper cloud edge ranged from 330K to 350K. At higher potential temperatures (377-392K) no H2O enhancements were observed. Nevertheless, the irreversible injection of water vapor could lead to transport of moisture into the lower stratosphere in the following hours and days downwind of the system. Within the upper cloud part and in the vicinity of the cloud, water vapor and ice crystals are enhanced in comparison to the undisturbed surrounding, as visible in the Lidar curtain. Both, water vapor and ice crystals influence the hydration and dehydration of the exTL. While larger ice crystals sediment, smaller ice crystals may sublimate and contributing to a locally enhanced water vapor budget. Our measurements show, that strong convective systems can act as a potential moisture source of the lowermost stratosphere.