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B8 - Role of uncertainty in ice microphysical processes in warm conveyor belts

Project leaders: Prof. Dr. Corinna Hoose, Dr. Christian Grams, Dr. Annette Miltenberger


Latent heat release due to condensation in the warm sector of an extratropical cyclone is embedded into a rapidly ascending air stream – the warm conveyor belt (WCB). WCBs transport air cross-isentropically from low levels to the tropopause over a horizontal distance of O(1000 km) within about 2 days. This injection of air into the upper troposphere has a significant impact on the large scale and affects the life cycle of blocking anticyclones. However, there is significant uncertainty about the role of microphysical processes in WCBs and how they affect the intensity of WCB outflow. In particular, the representation of ice formation processes is uncertain, so that the phase partitioning is often poorly represented in numerical weather prediction (NWP) models.

This project addresses the impact of cloud microphysical processes in the extratropics across multiple scales ranging from cloud particles to the large-scale circulation. Therefore, we will develop an innovative diagnostic framework to quantify the relative contributions of microphysical processes on latent heating in WCBs and their effects on WCB evolution and intensity. A large ensemble will be used to scan the phase space of environmental conditions, e.g. temperature and humidity (profiles), availability and properties of aerosol, and cloud microphysical parameters, e.g. efficiency of secondary ice formation and diameter-fallspeed relations. Statistical emulation will allow us to quantify the relative sensitivity of the WCB ascent and outflow to the the input variables and processes. Furthermore, the microphysical latent heating contributions will be analyzed from a Lagrangian perspective with recently developed online trajectories. Finally, the feedback on the large-scale circulation will be targeted with sensitivity experiments and the analysis of variables describing the upper tropospheric flow.