On the role of the stratiform cloud scheme in the inter‐model spread of cloud feedback

Geoffroy, Olivier; Sherwood, Steven C.; Fuchs, David

doi:10.1002/2016ms000846

Cited by 27 publications

(31 citation statements)

References 58 publications

(104 reference statements)

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“…Most GCMs do not account for vertically varying cloud sinks in their computation of cloud fraction; for example, the most common type of cloud-fraction parameterization used in the combined CMIP3/CMIP5 ensemble is based on a diagnostic function of relative humidity alone (Geoffroy et al, 2017;Tompkins, 2005). This highlights the importance of correctly parameterizing the sinks of cloud condensates in global climate models (GCMs).…”

Section: Discussionmentioning

confidence: 99%

“…This highlights the importance of correctly parameterizing the sinks of cloud condensates in global climate models (GCMs). Most GCMs do not account for vertically varying cloud sinks in their computation of cloud fraction; for example, the most common type of cloud-fraction parameterization used in the combined CMIP3/CMIP5 ensemble is based on a diagnostic function of relative humidity alone (Geoffroy et al, 2017;Tompkins, 2005). Recent work by Wall and Hartmann (2018) has shown that one such RH-based scheme does not reproduce the observed anvil peak in the deeply convecting tropics of CAM5 (Neale et al, 2012).…”

Section: Discussionmentioning

confidence: 99%

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Formation of Tropical Anvil Clouds by Slow Evaporation

Seeley

Jeevanjee

Langhans

et al. 2019

Geophysical Research Letters

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Tropical anvil clouds play a large role in the Earth's radiation balance, but their effect on global warming is uncertain. The conventional paradigm for these clouds attributes their existence to the rapidly declining convective mass flux below the tropopause, which implies a large source of detraining cloudy air there. Here we test this paradigm by manipulating the sources and sinks of cloudy air in cloud‐resolving simulations. We find that anvils form in our simulations because of the long lifetime of upper‐tropospheric cloud condensates, not because of an enhanced source of cloudy air below the tropopause. We further show that cloud lifetimes are long in the cold upper troposphere because the saturation specific humidity is much smaller there than the condensed water loading of cloudy updrafts, which causes evaporative cloud decay to act very slowly. Our results highlight the need for novel cloud‐fraction schemes that align with this decay‐centric framework for anvil clouds.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Formation of Tropical Anvil Clouds by Slow Evaporation

Seeley

Jeevanjee

Langhans

et al. 2019

Geophysical Research Letters

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“…In addition, the LWP is extremely high, which could conceivably mean that the clouds are already relatively saturated with respect to further changes in droplet numbers, in line with the findings of Painemal and Minnis (2012) mentioned above. Geoffroy et al (2017) investigated the role of different stratiform cloud schemes to the inter-model spread of cloud feedbacks, looking at 14 models -four of which were used in the present study. They found that NorESM1-M, which diagnoses stratiform clouds based on relative humidity and atmospheric stability, had an opposite cloud feedback from models (including HadGEM2-ES, CSIRO-Mk3L-1-2 and IPSL-CM5A-LR) that diagnoses such clouds based solely on relative humidity.…”

Section: Discussionmentioning

confidence: 99%

Response to marine cloud brightening in a multi-model ensemble

et al. 2018

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Abstract. Here we show results from Earth system model simulations from the marine cloud brightening experiment G4cdnc of the Geoengineering Model Intercomparison Project (GeoMIP). The nine contributing models prescribe a 50 % increase in the cloud droplet number concentration (CDNC) of low clouds over the global oceans in an experiment dubbed G4cdnc, with the purpose of counteracting the radiative forcing due to anthropogenic greenhouse gases under the RCP4.5 scenario. The model ensemble median effective radiative forcing (ERF) amounts to −1.9 W m −2 , with a substantial inter-model spread of −0.6 to −2.5 W m −2 . The large spread is partly related to the considerable differences in clouds and their representation between the models, with an underestimation of low clouds in several of the models. All models predict a statistically significant temperature decrease with a median of (for years 2020-2069) −0.96 [−0.17 to −1.21] K relative to the RCP4.5 scenario, with particularly strong cooling over low-latitude continents. Globally averaged there is a weak but significant precipitation decrease of −2.35 [−0.57 to −2.96] % due to a colder climate, but at low latitudes there is a 1.19 % increase over land. This increase is part of a circulation change where a strong negative top-of-atmosphere (TOA) shortwave forcing over subtropical oceans, caused by increased albedo associated with the increasing CDNC, is compensated for by rising motion and positive TOA longwave signals over adjacent land regions.

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“…However, they should give a fair representation of geographical distribution, and numbers are comparable between models. To estimate the effective radiative forcing of increasing CDNC by 50 % in the different models, we use the method of Gregory et al (2004), whereby the topof-atmosphere (TOA) radiative flux imbalance is regressed against the globally averaged surface air temperature change compared to the RCP4.5 simulations. To estimate the effective radiative forcing of increasing CDNC by 50 % in the different models, we use the method of Gregory et al (2004), whereby the global mean top of atmosphere radiative flux imbalance is regressed against the globally averaged sur-face air temperature change compared to the RCP4.5 simulations.…”

Section: Postprocessing and Analysesmentioning

confidence: 99%