Processes controlling Southern Ocean shortwave climate feedbacks in CESM

Kay, J. E.; Medeiros, Brian; Hwang, Yean Ren; Gettelman, Andrew; Perket, J.; Flanner, M.

doi:10.1002/2013gl058315

Cited by 64 publications

(77 citation statements)

References 52 publications

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“…We will now discuss how model mixed‐phase behavior appears to influence the cloud feedback. The GCM‐predicted LWP increase with warming that drives the robust negative optical depth cloud feedback at high latitudes (Figure a) [ Gordon and Klein , ; Kay et al ., ; Zelinka et al ., ] has been shown to exhibit a strong dependence on model T5050 [ McCoy et al ., ]. Based on this mechanism we evaluate the dependence of SW cloud feedback on T5050.…”

Section: Resultsmentioning

confidence: 99%

On the relationships among cloud cover, mixed‐phase partitioning, and planetary albedo in GCMs

McCoy

Tan

Hartmann

et al. 2016

J Adv Model Earth Syst

146

137

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In this study, it is shown that CMIP5 global climate models (GCMs) that convert supercooled water to ice at relatively warm temperatures tend to have a greater mean-state cloud fraction and more negative cloud feedback in the middle and high latitude Southern Hemisphere. We investigate possible reasons for these relationships by analyzing the mixed-phase parameterizations in 26 GCMs. The atmospheric temperature where ice and liquid are equally prevalent (T5050) is used to characterize the mixed-phase parameterization in each GCM. Liquid clouds have a higher albedo than ice clouds, so, all else being equal, models with more supercooled liquid water would also have a higher planetary albedo. The lower cloud fraction in these models compensates the higher cloud reflectivity and results in clouds that reflect shortwave radiation (SW) in reasonable agreement with observations, but gives clouds that are too bright and too few. The temperature at which supercooled liquid can remain unfrozen is strongly anti-correlated with cloud fraction in the climate mean state across the model ensemble, but we know of no robust physical mechanism to explain this behavior, especially because this anti-correlation extends through the subtropics. A set of perturbed physics simulations with the Community Atmospheric Model Version 4 (CAM4) shows that, if its temperature-dependent phase partitioning is varied and the critical relative humidity for cloud formation in each model run is also tuned to bring reflected SW into agreement with observations, then cloud fraction increases and liquid water path (LWP) decreases with T5050, as in the CMIP5 ensemble.

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Section: Resultsmentioning

confidence: 99%

On the relationships among cloud cover, mixed‐phase partitioning, and planetary albedo in GCMs

McCoy

Tan

Hartmann

et al. 2016

J Adv Model Earth Syst

146

137

View full text Add to dashboard Cite

show abstract

“…The L-only fingerprint F(L) is increasingly apparent in both observational datasets and is incompatible with internal variability. We note, however, that several authors have suggested that cloud shifts may not be trivially related to changes in the jet (Grise and Polvani 2014;Ceppi et al 2014;Kay et al 2014), and further study of the interaction between clouds and the circulation is necessary to understand this response. This is in agreement with previous studies that suggest models fail to capture the observed poleward expansion (Johanson and Fu 2009;Seidel et al 2008).…”

Section: A Observed Poleward Migration Incompatible With Forced Modelsmentioning

confidence: 87%

External Influences on Modeled and Observed Cloud Trends

et al. 2015

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Understanding the cloud response to external forcing is a major challenge for climate science. This crucial goal is complicated by intermodel differences in simulating present and future cloud cover and by observational uncertainty. This is the first formal detection and attribution study of cloud changes over the satellite era.Presented herein are CMIP5 model-derived fingerprints of externally forced changes to three cloud properties: the latitudes at which the zonally averaged total cloud fraction (CLT) is maximized or minimized, the zonal average CLT at these latitudes, and the height of high clouds at these latitudes. By considering simultaneous changes in all three properties, the authors define a coherent multivariate fingerprint of cloud response to external forcing and use models from phase 5 of CMIP (CMIP5) to calculate the average time to detect these changes. It is found that given perfect satellite cloud observations beginning in 1983, the models indicate that a detectable multivariate signal should have already emerged. A search is then made for signals of external forcing in two observational datasets: ISCCP and PATMOS-x. The datasets are both found to show a poleward migration of the zonal CLT pattern that is incompatible with forced CMIP5 models. Nevertheless, a detectable multivariate signal is predicted by models over the PATMOS-x time period and is indeed present in the dataset. Despite persistent observational uncertainties, these results present a strong case for continued efforts to improve these existing satellite observations, in addition to planning for new missions.

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“…Long-term output of CGCM simulations involving a dynamical sea-ice model may be helpful to further explore the observed relationships with atmospheric variability (Kay et al 2014), because the observational data record of the Antarctic SIC is relatively short and insufficient to conclusively establish a statistical link between sea ice and atmospheric variability. The 150 yr output from the control run (CTR) experiment with the SINTEX-F2 model (Fig.…”

Section: Simulated Sea-ice Variability and Its Impact On Atmospheric mentioning

confidence: 99%

Role of Weddell Sea ice in South Atlantic atmospheric variability

Morioka¹,

Engelbrecht²,

Behera³

2017

Clim. Res.

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We investigated the role of Weddell Sea ice in atmospheric variability over the South Atlantic by conducting observational data analysis and coupled general circulation model (CGCM) experiments. Weddell Sea ice exhibits a pronounced interannual variability in early austral summer (November−January). Low sea-ice concentration (SIC) anomalies in the Weddell Sea are strongly associated with anticyclonic atmospheric circulation anomalies in the South Atlantic. Composite analysis reveals that the low SIC anomalies in the Weddell Sea may be attributed to increased solar radiation and northwesterly wind anomalies. The low SIC anomalies, in turn, contribute to warmer skin temperature in the band of 60−70°S and enhance the near-surface atmospheric stability north of this band, implying favorable conditions for sustaining the anticyclonic circulation anomalies in the South Atlantic. This intriguing association between the SIC and atmospheric circulation anomalies is also simulated in CGCM experiments, e.g. when the interannual sea surface temperature variability in the tropics and mid-latitudes is suppressed. These results suggest that Weddell Sea ice, which may undergo interannual variation via air−sea−ice interactions in the high latitudes, influences atmospheric variability over the South Atlantic.

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Processes controlling Southern Ocean shortwave climate feedbacks in CESM

Cited by 64 publications

References 52 publications

On the relationships among cloud cover, mixed‐phase partitioning, and planetary albedo in GCMs

On the relationships among cloud cover, mixed‐phase partitioning, and planetary albedo in GCMs

External Influences on Modeled and Observed Cloud Trends

Role of Weddell Sea ice in South Atlantic atmospheric variability

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