1.1 A Perspective on Radiative Transfer and Cloud Microphysics in Climate Models (Invited Presentation)

Monday, 8 January 2018: 8:45 AM
Room 4ABC (ACC) (Austin, Texas)
Kuo-Nan Liou, Univ. of California, Los Angeles, CA

Clouds cover more than 50% of the sky and their function of sunlight reflection,

referred to as the solar albedo effect (SAE), results in a cooling component of the

earth-atmosphere system. At the same time, clouds trap thermal radiation emitted

to space, referred to as the greenhouse effect (GE). The competition of SAE and GE

with respect to earth’s climate system is regulated by cloud cover, vertical position

of different cloud types, thermodynamic phases, liquid/ice water content, and particle

size distribution. Low, middle, and vertically convective clouds are primarily

controlled by SAE; however, the role of high and thin clouds is not well understood

due to observational limitations from the ground, the air, and space. Thus, I should

largely confine my talk to ice clouds and radiative interactions for applications to

climate models. Due to computational requirements, interactions of radiation and ice

cloud macro- and micro-physics must be parameterized. Exact solutions for both

radiative transfer and cloud physics based on first principle could be accomplished

offline to complement ice-cloud model development. I will provide a number of

examples within the context of parameterization. Notwithstanding to complicate the

presentation, I will also discuss additional examples to illustrate the importance of

aerosol-ice interactions with respect to the formation of high-level clouds in climate

models for radiative forcing and feedback studies. Subsequently, I will show recent

progress using existing A-train datasets for ice clouds and climate research. Despite

this progress, new satellite observations for the vertical profile of ice-crystal size

distribution and related precipitation appear necessary to make a quantum advance

in the climate model performance in terms of validation and calibration to resolve the

role of ice clouds and aerosols in radiation fields as well as to reduce uncertainties in

climate simulations.

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