Biological and Environmental Research - Earth and Environmental System Sciences
Earth and Environmental System Modeling

Mixed-Phase Cloud Physics and Southern Ocean Cloud Feedback in Climate Models

TitleMixed-Phase Cloud Physics and Southern Ocean Cloud Feedback in Climate Models
Publication TypeJournal Article
Year of Publication2015
AuthorsMcCoy, Daniel T., Hartmann Dennis L., Zelinka Mark D., Ceppi Paulo, and Grosvenor Daniel P.
JournalJournal of Geophysical Research - Atmospheres
Volume120
Number18
Pages9539-9554
Abstract / 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 CMIP5 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 40K 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 re-partitioning 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. Inter-model differences in the climatological partitioning between ice and liquid are estimated to contribute at least 20% to the inter-model 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 GCM 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.

URLhttp://onlinelibrary.wiley.com/doi/10.1002/2015JD023603/full
DOI10.1002/2015JD023603
Journal: Journal of Geophysical Research - Atmospheres
Year of Publication: 2015
Volume: 120
Number: 18
Pages: 9539-9554
Publication Date: 09/2015

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 CMIP5 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 40K 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 re-partitioning 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. Inter-model differences in the climatological partitioning between ice and liquid are estimated to contribute at least 20% to the inter-model 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 GCM 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.

DOI: 10.1002/2015JD023603
Citation:
McCoy, DT, DL Hartmann, MD Zelinka, P Ceppi, and DP Grosvenor.  2015.  "Mixed-Phase Cloud Physics and Southern Ocean Cloud Feedback in Climate Models."  Journal of Geophysical Research - Atmospheres 120(18): 9539-9554.  https://doi.org/10.1002/2015JD023603.