Mid-Latitude and Arctic Cirrus Clouds: Analyzing Their Origins and Freezing Mechanisms By Means of the Large Scale Lagrangian Model CLaMS-Ice

CLaMS-Ice is a newly developed large-scale Lagrangian cirrus forecast and analysis tool. The CLaMS-Ice model consists of a detailed microphysical cirrus cloud box model (Spichtinger and Gierens, 2009) which can be operated along atmospheric trajectories of the global Lagrangian model CLaMS (Chemical LAgrangian Model of the Stratosphere, see McKenna et al., 2002). The two-moment bulk microphysics scheme includes the main mechanisms of cirrus forming directly from the gas phase (in-situ origin cirrus, Krämer et al., 2016): heterogeneous ice nucleation on ice nucleating particles (INP), and homogeneous nucleation of liquid solution particles of sulphuric acid. Further, depositional growth and sublimation as well as sedimentation of ice crystals are treated in the model. In addition to in-situ origin cirrus clouds that form directly from the gas phase, CLaMS-Ice also represents cirrus originating from uplifted frozen liquid drops (liquid origin cirrus, Luebke et al, 2016; Krämer et al., 2016) by transferring liquid and ice water content from ECMWF meteorological fields into the cirrus temperature regime (< 238 K) under the assumption that all liquid water freezes as soon as a trajectory crosses the temperature threshold of 238 K.

Based on ClaMS-Ice simulations, it is possible to track the origin of cirrus clouds, their formation mechanisms together with the frequency of occurrence of the respective cloud types. Thus, from CLaMS- Ice simulations, new insights on cirrus clouds microphysical and thus radiative properties are expected. As a first, important step, CLaMS-Ice is evaluated based on in-situ observations from the HALO campaign ML-CIRRUS 2014 in mid-latitude spring (Rolf et al., 2016).

Here, we apply ClaMS-Ice to mid-latitude in comparison to Arctic regions. We analyze in-situ and liquid origin cirrus: overall, in-situ cirrus are more frequent than liquid origin cirrus. However, liquid origin cirrus occur more often at mid-latitudes than in the Arctic, which we attribute to the generally slower updraft velocities in this region. In line with this, in the Arctic thin cirrus are more common.

Analysis of the freezing mechanisms of in-situ and liquid origin cirrus yields that for in-situ cirrus over the complete temperature range, homogeneous freezing occurs most frequently in thick cirrus formed in higher updrafts, while heterogeneous freezing prevails in thin cirrus formed in lower updrafts. For thick as well as thin liquid origin cirrus hetereogeneous freezing is dominating at the higher cirrus temperature range, but at colder temperatures additional homogeneous freezing occurs more often, especially in the Arctic.

References

Krämer et al. (2016): A microphysics guide to cirrus clouds – Part 1: Cirrus types, Atmos. Chem. Phys., 16, 3463-3483, doi:10.5194/acp-16-3463-2016.

McKenna et al. (2001): A new Chemical Lagrangian Model of the Stratosphere (CLaMS) - 1. Formulation of advection and mixing, Journal of Geophysical Research-atmospheres, 107, 4309, doi:10.1029/2000JD000114.

Rolf et al. (2016): Reconciliation of in-situ observations and large-scale simulations of mid-latitude cirrus clouds, 17th ICCP Conference, Manchester, July 25-29.

Spichtinger and Gierens (2009): Modelling of cirrus clouds - Part 1a: Model description and validation, Atmospheric Chemistry and Physics, 9, 685–706, 2009.