Climatological analysis of warm conveyor belt contributions to UTLS moisture content

The Upper Troposphere-Lower Stratosphere (UTLS) is a transition region for coupled dynamical, chemical and microphysical processes. These coupled processes play an essential role in climate change. Water vapor, ozone and aerosols in the UTLS region have important impacts on the Earth’s radiation budget. Systematic biases in UTLS moisture are known to exist in global climate models. Understanding the sources of UTLS moisture and quantifying the transport processes that control water vapor and clouds in the UTLS can provide important insights into the model uncertainties and improve model simulations. In the extratropics ascending airstreams in extratropical cyclones, particularly the warm conveyor belt (WCB), and deep convection are thought to be the most important sources of UTLS moisture. Here, we utilize ERA5 reanalysis data and IAGOS aircraft measurements to quantify the contribution of WCBs to UTLS moisture for the decade 2010 to 2019. WCB outflow regions are defined using Lagrangian trajectories. The moisture anomaly in the WCB outflow compared to average UTLS moisture content is quantified as well as its evolution over the 2 days after WCB ascent. ERA5 suggests significant positive moisture anomalies in the WCB outflow that persists over several days. Finally, ERA5 UTLS moisture content is compared to IAGOS humidity measurements with a particular focus on WCB outflow regions. In summary, we present a comprehensive climatological picture of the role of WCB moisture transport for the UTLS composition.