Journal Article

PreJuSER-1795

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Cirrus clouds formation and ice supersaturated regions in a global climate model

Lohmann, U. ; Spichtinger, P. ; Jess, S. ; Peter, T. ; Smit, H. G. J.FZJ*

2008
IOP Publ. Bristol

This record in other databases:  

Please use a persistent id in citations: doi:10.1088/1748-9326/3/4/045022

Abstract: At temperatures below 238 K, cirrus clouds can form by homogeneous and heterogeneous ice nucleation mechanisms. ECHAM5 contains a two-moment cloud microphysics scheme and permits cirrus formation by homogeneous freezing of solution droplets and heterogeneous freezing on immersed dust nuclei. On changing the mass accommodation coefficient, alpha, of water vapor on ice crystals from 0.5 in the standard ECHAM5 simulation to 0.006 as suggested by previous laboratory experiments, the number of ice crystals increases by a factor of 14, as a result of the delayed relaxation of supersaturation. At the same time, the ice water path increases by only 29% in the global annual mean, indicating that the ice crystals are much smaller in the case of low alpha. As a consequence, the short wave and long wave cloud forcing at the top of the atmosphere increase by 15 and 18 W m(-2), respectively. Assuming heterogeneous freezing caused by immersed dust particles instead of homogeneous freezing, the effect is much weaker, decreasing the global annual mean short wave and long wave cloud forcing by 2.7 and 4.7 W m(-2). Overall, these results provide little support, if any, for kinetic growth limitation of ice particles (i.e. a very low alpha).

Keyword(s): J ; cirrus clouds (auto) ; ice supersaturated regions (auto) ; climate modeling (auto)

Note: We thank the two anonymous reviewers for their helpful comments and suggestions, Claudia Stubenrauch for providing the TOVS data, Sylvaine Ferrachat and Rebekka Posselt for technical help and the German (DKRZ) and Swiss Computing Centres (CSCS) for computing time. This study contributed towards the Swiss climate research program NCCR Climate. It was partly supported by the EC within the framework of the MC fellowship 'Impact of mesoscale dynamics and aerosols on the life cycle of cirrus clouds' and partly by the Integrated Project SCOUT- O3.

---

Research Program(s):

1. Atmosphäre und Klima (P22)

Appears in the scientific report 2008

---