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
JournalJournal of Geophysical Research - Atmospheres
Date Published08/2015
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#jgrd52436-note-0001
DOI10.1002/2015JD023603
Journal: Journal of Geophysical Research - Atmospheres
Year of Publication: 2015
Date Published: 08/2015

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:
2015.  "Mixed-Phase Cloud Physics and Southern Ocean Cloud Feedback in Climate Models."  Journal of Geophysical Research - Atmospheres.  https://doi.org/10.1002/2015JD023603.