Mixed-phase cloud physics and Southern Ocean cloud feedback in climate models

Increasing optical depth poleward of 45° is a robust response to warming in global climate models. Much of this cloud optical depth increase has been hypothesized to be due to transitions from ice‐dominated to liquid‐dominated mixed‐phase cloud. In this study, the importance of liquid‐ice partitioni...

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Bibliographic Details
Published in:Journal of Geophysical Research: Atmospheres
Main Authors: McCoy, DT, Hartmann, DL, Zelinka, MD, Ceppi, P, Grosvenor, DP
Format: Article in Journal/Newspaper
Language:English
Published: American Geophysical Union 2015
Subjects:
Science & Technology
Physical Sciences
Meteorology & Atmospheric Sciences
climate
Southern Ocean
feedbacks
mixed phase
clouds
STRATIFORM CLOUDS
LAYER CLOUD
WATER
STRATOCUMULUS
SIMULATIONS
MULTIMODEL
TRANSITION
SATELLITE
COVER
CMIP5
Online Access:http://hdl.handle.net/10044/1/76096
https://doi.org/10.1002/2015JD023603
Description
Summary:Increasing optical depth poleward of 45° is a robust response to warming in global climate models. Much of this cloud optical depth increase has been hypothesized to be due to transitions from ice‐dominated to liquid‐dominated mixed‐phase cloud. In this study, the importance of liquid‐ice partitioning for the optical depth feedback is quantified for 19 Coupled Model Intercomparison Project Phase 5 models. All models show a monotonic partitioning of ice and liquid as a function of temperature, but the temperature at which ice and liquid are equally mixed (the glaciation temperature) varies by as much as 40 K across models. Models that have a higher glaciation temperature are found to have a smaller climatological liquid water path (LWP) and condensed water path and experience a larger increase in LWP as the climate warms. The ice‐liquid partitioning curve of each model may be used to calculate the response of LWP to warming. It is found that the repartitioning between ice and liquid in a warming climate contributes at least 20% to 80% of the increase in LWP as the climate warms, depending on model. Intermodel differences in the climatological partitioning between ice and liquid are estimated to contribute at least 20% to the intermodel spread in the high‐latitude LWP response in the mixed‐phase region poleward of 45°S. It is hypothesized that a more thorough evaluation and constraint of global climate model mixed‐phase cloud parameterizations and validation of the total condensate and ice‐liquid apportionment against observations will yield a substantial reduction in model uncertainty in the high‐latitude cloud response to warming.

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