The influence of extratropical cloud phase and amount feedbacks on climate sensitivity

Frey, William R.; Kay, J. E.

doi:10.1007/s00382-017-3796-5

Cited by 91 publications

(112 citation statements)

References 74 publications

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“…The need for improving cloud microphysical processes that influence thermodynamic phase is underscored by the impact of these processes on Arctic amplification. Given the tendency of most climate models to underestimate the proportion of supercooled liquid in mixed‐phase clouds, eliminating this low bias in climate models by correcting the cloud microphysical processes at the root of the issue should be a priority, as it would not only potentially increase climate sensitivity estimates (Frey & Kay, ; Tan et al, ) but also simultaneously impact Arctic amplification estimates. CALIOP‐SLF2 in particular demonstrates that attention to details in the cloud microphysical processes that influence SLF can be critical, especially in the Arctic, where mixed‐phase clouds are ubiquitous and unique thermodynamic conditions interact with the microphysical processes (Morrison et al, ).…”

Section: Discussionmentioning

confidence: 99%

“…Since liquid droplets tend to be both more abundant and smaller in size compared to their solid counterparts (Pruppacher & Klett, ), fewer ice‐to‐liquid transitions in clouds equate to smaller increases in cloud optical depth post‐CO 2 doubling which ultimately causes ECS to increase by reducing the shortwave radiation reflected back to space. When the same version of the model was instead coupled to a thermodynamic mixed‐layer ocean model, ECS was increased by a comparable amount of 1.5 °C, largely due to a weakened cloud phase feedback (Frey & Kay, ).…”

Section: Introductionmentioning

confidence: 99%

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Evidence of Strong Contributions From Mixed‐Phase Clouds to Arctic Climate Change

Tan

Storelvmo

2019

Geophysical Research Letters

114

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Underestimation of the proportion of supercooled liquid in mixed‐phase clouds in climate models has called into question its impact on Arctic climate change. We show that correcting for this bias in the CESM model can either enhance or reduce Arctic amplification depending on the microphysical characteristics of the clouds as a corollary to the cloud phase feedback. Replacement of ice with liquid in the cloud phase feedback results in more downward longwave radiation, which is effectively trapped as heat at the surface in the Arctic due to its unique stable stratification conditions, and this ultimately leads to a more positive lapse rate feedback. The larger the ice particles are to begin with, the stronger Arctic amplification becomes due to the lower precipitation efficiency of liquid droplets compared to ice crystals. Our results emphasize the importance of realistic representations of microphysical processes in mixed‐phase clouds, particularly in the Arctic.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Evidence of Strong Contributions From Mixed‐Phase Clouds to Arctic Climate Change

Tan

Storelvmo

2019

Geophysical Research Letters

114

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“…Do we see evidence for cloud thinning at warm temperatures from an increased drying efficiency from cloud top mixing? Cloud thinning with warming through this mechanism has been reported in large‐eddy simulations (Bretherton et al, ; Rieck et al, ) and climate models (Frey & Kay, ). However, the relevance of this process is dependent on the strength of the inversion staying constant with warming.…”

Section: Evidence For Mechanismsmentioning

confidence: 99%

Mechanisms Behind the Extratropical Stratiform Low‐Cloud Optical Depth Response to Temperature in ARM Site Observations

et al. 2019

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Ground‐based observations from three middle‐ and high‐latitude sites managed by the U.S. Department of Energy's Atmospheric Radiation Measurement (ARM) program are used to determine the sensitivity of the low‐cloud optical depth to temperature and to test whether observations support mechanisms previously proposed to affect the optical depth feedback. Analysis of cloud optical depth retrievals support previous satellite findings that the optical depth decreases or stays constant with increases in temperature when the cloud is warm but increases when the cloud is cold. The cloud liquid water path sensitivity to warming largely explains the optical depth sensitivity at all sites. Mechanisms examined in this study involve the temperature dependence of (a) the moist‐adiabatic lapse rate, (b) cloud phase partitioning, (c) drying efficiency of cloud top mixing, (d) cloud top inversion strength, and (e) boundary layer decoupling. Mechanism (a) is present across all clouds and explains 30% to 50% of the increase in liquid water path with warming at temperatures below 0 °C. However, the cloud's adiabaticity, the ratio between the liquid water path and its theoretical maximum, is at least as important and determines how the liquid water path sensitivity to temperature varies with temperature. At temperatures below 0 °C, the adiabaticity increases with warming, and the data support mechanism (b). At warmer temperatures, the adiabaticity decreases with warming, overwhelming mechanism (a) and resulting in the liquid water path decreasing with warming. This adiabaticity decrease arises primarily because of mechanism (d), and to a lesser degree because of mechanism (e). No evidence is found supporting mechanism (c).

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“…This mechanism is pertinent to mixed‐phase clouds, that is, clouds that are comprised of mixtures of supercooled liquid droplets and ice crystals. Thermodynamic phase shifts from ice to liquid hydrometeors in mixed‐phase clouds occur as the atmosphere warms in what is known as the “cloud phase feedback” (Mitchell et al, ; McCoy et al, ; Tsushima et al, ; Tan et al, ; Frey & Kay, ). Since liquid droplets are typically more abundant and smaller in size compared to their solid counterparts (Pruppacher & Klett, ), shifts from the ice to liquid phase within mixed‐phase clouds can increase τ due to the fact that extinction is inversely proportional to effective radius; therefore, for a fixed water content, τ increases (decreases) when ice (liquid) is replaced with liquid (ice).…”

Section: Introductionmentioning

confidence: 99%

The Role of Thermodynamic Phase Shifts in Cloud Optical Depth Variations With Temperature

Tan

Oreopoulos²,

Cho

2019

Geophysical Research Letters

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We present a novel method that identifies the contributions of thermodynamic phase shifts and processes governing supercooled liquid and ice clouds to cloud optical depth variations with temperature using Moderate Resolution Imaging Spectroradiometer observations. Our findings suggest that thermodynamic phase shifts outweigh the net influence of processes governing supercooled liquid and ice clouds in causing increases in midlatitudinal cold cloud optical depth with temperature. Cloud regime analysis suggests that dynamical conditions appear to have little influence on the contribution of thermodynamic phase shifts to cloud optical depth variations with temperature. Thermodynamic phase shifts also contribute more to increases in cloud optical depth during colder seasons due to the enhanced optical thickness contrast between liquid and ice clouds. The results of this study highlight the importance of thermodynamic phase shifts in explaining cold cloud optical depth increases with temperature in the current climate and may elucidate their role in the cloud optical depth feedback.

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The influence of extratropical cloud phase and amount feedbacks on climate sensitivity

Cited by 91 publications

References 74 publications

Evidence of Strong Contributions From Mixed‐Phase Clouds to Arctic Climate Change

Evidence of Strong Contributions From Mixed‐Phase Clouds to Arctic Climate Change

Mechanisms Behind the Extratropical Stratiform Low‐Cloud Optical Depth Response to Temperature in ARM Site Observations

The Role of Thermodynamic Phase Shifts in Cloud Optical Depth Variations With Temperature

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