climate feedbacks; climate change; climate modeling; cloud physics
Dietlicher Remo, Neubauer David, Lohmann Ulrike (2019), Elucidating ice formation pathways in the aerosol-climate model ECHAM6-HAM2, in Atmospheric Chemistry and Physics Discussions
Järvinen Emma, Jourdan Olivier, Neubauer David, Yao Bin, Liu Chao, Andreae Meinrat O., Lohmann Ulrike, Wendisch Manfred, McFarquhar Greg M., Leisner Thomas, Schnaiter Martin (2018), Additional Global Climate Cooling by Clouds due to Ice Crystal Complexity, in Atmospheric Chemistry and Physics Discussions
Lohmann Ulrike, Neubauer David (2018), The importance of mixed-phase and ice clouds for climate sensitivity in the global aerosol–climate model ECHAM6-HAM2, in Atmospheric Chemistry and Physics
, 18(12), 8807-8828.
Dietlicher Remo, Neubauer David, Lohmann Ulrike (2018), Prognostic parameterization of cloud ice with a single category in the aerosol-climate model ECHAM(v6.3.0)-HAM(v2.3), in Geoscientific Model Development
, 11(4), 1557-1576.
Gasparini B., Meyer A., Neubauer D., Münch S., Lohmann U. (2018), Cirrus Cloud Properties as Seen by the CALIPSO Satellite and ECHAM-HAM Global Climate Model, in Journal of Climate
, 31(5), 1983-2003.
Clouds are important in the climate system because of their large influence on the radiation budget. They scatter solar radiation and with that cool the climate (albedo effect of clouds). On the other hand, they absorb and re-emit terrestrial radiation, which causes a warming (greenhouse effect of clouds). Clouds are also an integral part in the hydrological cycle. In mid-latitudes most of the precipitation originates via the ice phase and melts on the way to the surface. However, the ice phase in clouds is much less understood than the warm phase. General circulation models (GCMs) need to parameterize precipitation formation, because it occurs on subgrid scales. Following on Kessler's (1969) concept, a distinction is made between cloud droplets, which have a negligible fall velocity and thus float within the cloud, and larger raindrops, which fall out of the cloud. It is less clear how to treat the ice phase, because even pristine ice crystals not necessarily remain in the cloud, but may grow to sizes large enough to have a noticeable fall velocity and leave the cloud. Nevertheless, most GCMs including ECHAM6-HAM treat the ice phase analogously to the liquid phase and separate smaller ice crystals from larger snow flakes. In November 2012, a workshop on the parameterization of clouds in numerical models held at the European Centre for Medium-Range Weather Forecasts (ECMWF) recommended with highest priority that ice and snow species should be combined into one species. This recommendation arises because the separation into ice crystals and snow flakes is an artificial distinction of unnecessary complexity and possibly a source of model biases in terms of precipitation intensity and distribution. Therefore I am proposing to simplify the parameterization of ice microphysics in the ECHAM6-HAM GCM by combining ice and snow into a single ice phase category for both stratiform and convective clouds. The improved ECHAM6-HAM GCM will be coupled to Max Planck Institute Ocean and sea-ice Model (MPIOM) to conduct simulations of the future climate. We will investigate the cloud response to global warming and possible feedbacks involving Arctic clouds and sea ice.