535. WE-Heraeus-Seminar: Water Vapor and Ice in the Atmosphere

Motivation

Despite recent major progress, significant gaps remain in the scientific understanding of atmospheric humidity in the upper troposphere/lower stratosphere region, ice nucleation, the life cycle of cirrus clouds and their impact on climate. Recently, a large effort was spent in instrument development and data retrievals, which helped to considerably improve the accuracy of observational data on water vapor distributions and cloud properties. Still it remains ambiguous, whether this progress suffices to adequately constrain theoretical studies on the dynamical forcing of ice nucleation at different scales, the humidity distribution at the onset of ice nucleation, the ice nucleation ability of atmospheric aerosols, ice crystal growths and sublimation, and the effects of ice crystal shape on the atmospheric radiation budget.
Objectives

Hence, it is the objective of the workshop to identify gaps in the scientific understanding of atmospheric ice nucleation processes, cloud feed-backs on the water vapor budget, the climate impact of ice clouds and UT/LS cirrus and humidity trends. In sight of upcoming aircraft missions, we will discuss instrument developments, results of observations from aircraft and satellite, laboratory experiments, theoretical studies and global modeling with the aim to reduce major uncertainties. Contrail studies may additionally serve as an atmospheric laboratory under defined conditions to answer selected questions. Summarized, the seminar will focus on measures and strategies to reduce uncertainties, close scientific gaps in water vapor and ice research and investigate future challenges. Plenty of time is reserved for the discussion of the "way forward".