Lagrangian analysis of ice supersaturated air masses in connection with low level fronts of extratropical cyclones

Abstract

Ice supersaturation is often found in the upper troposphere. The so-called ice supersaturated regions (ISSRs), i.e. air masses in the status of supersaturation with respect to ice, are formation regions of in-situ cirrus clouds. While an ISSR alone has a rather small effect on the radiation budget, this changes significantly when cirrus clouds develop within the ISSR. Hence, the transition from an ISSR to a cirrus cloud has important implications. In order to understand how ISSR and the embedded in-situ cirrus clouds form and develop, the transport pathways of water vapour have to be understood. Therefore, to better understand the life cycle of extratropical ice-supersaturated regions (ISSRs), we utilize backward and forward trajectories initiated within ISSRs and analyze them. Furthermore, we connect these trajectories with information about the location of low-level frontal systems to investigate connections between ISSRs and extratropical cyclones. Particularly interesting is the relative position to the so-called warm conveyor belt (WCB) trajectories.