Abstract
Abstract. Cirrus clouds impose high uncertainties on climate prediction, as knowledge on important processes is still incomplete. For instance it remains unclear how cloud microphysical and radiative properties change as the cirrus evolves. Recent studies classify cirrus clouds into categories including in situ, orographic, convective and liquid origin clouds and investigate their specific impact. Following this line, we present a novel scheme for the classification of cirrus clouds that addresses the need to determine specific stages of cirrus evolution. Our classification scheme is based on airborne Differential Absorption and High Spectral Resolution Lidar measurements of atmospheric water vapor, aerosol depolarization, and backscatter, together with model temperature fields and simplified parameterizations of freezing onset conditions. It identifies regions of supersaturation with respect to ice (ice-supersaturated regions, ISSRs), heterogeneous and homogeneous nucleation, depositional growth, and ice sublimation and sedimentation with high spatial resolution. Thus, all relevant stages of cirrus evolution can be classified and characterized. In a case study of a gravity lee-wave-influenced cirrus cloud, encountered during the ML-CIRRUS flight campaign, the applicability of our classification is demonstrated. Revealing the structure of cirrus clouds, this valuable tool might help to examine the influence of evolution stages on the cloud's net radiative effect and to investigate the specific variability of optical and microphysical cloud properties in upcoming research.
Highlights
Cirrus play an important role for weather and climate: besides their influence on the water vapor budget in the upper troposphere through condensation and evaporation (Dinh et al, 2014) and dynamics due to latent heat (Spichtinger, 2014), they modify the radiation balance of the Earth and atmosphere
The classification scheme that we present is based on atmospheric lidar cross sections and facilitates the detailed investigation of evolution stages, their vertical and horizontal order, the impact of atmospheric dynamics, and their specific optical properties
WALES is capable of providing collocated measurements of humidity in the form of water vapor volume mixing ratio rw, backscatter ratio (BSR), and aerosol depolarization ratio (ADEP)
Summary
Cirrus play an important role for weather and climate: besides their influence on the water vapor budget in the upper troposphere through condensation and evaporation (Dinh et al, 2014) and dynamics due to latent heat (Spichtinger, 2014), they modify the radiation balance of the Earth and atmosphere. The classification scheme that we present is based on atmospheric lidar cross sections and facilitates the detailed investigation of evolution stages, their vertical and horizontal order, the impact of atmospheric dynamics, and their specific optical properties Such a classification needs information on RHi and temperature, as they are two governing variables in ice particle formation, growth, and disappearance (Pruppacher and Klett, 2010). The airborne Differential Absorption Lidar WALES (WAter vapour Lidar Experiment in Space), flown aboard the German research aircraft HALO (High Altitude and LOng range, model: Gulfstream G550), makes major parts of the needed data available It provides an unique data set of collocated, high spatial resolution measurements of atmospheric backscatter, depolarization, and water vapor, enabling us to distinguish incloud and cloud-free regions, to identify the relevant aerosol type in the vicinity of the cloud, and to calculate relative humidity. We end with a summary of the classification scheme and a brief outline of its potential in cirrus cloud research
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