Relationships Between Tropical Ascent and High Cloud Fraction Changes With Warming Revealed by Perturbation Physics Experiments in CAM5

Schiro, Kathleen A.; Su, Hui; Wang, Yuan; Langenbrunner, Baird; Jiang, Jonathan H.; Neelin, J. David

doi:10.1029/2019gl083026

Cited by 13 publications

(17 citation statements)

References 53 publications

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“…But what we actually see is a decrease in up , because the mean heating rate in the ascending region is also intensifying, and at a faster rate than the cooling over the descending region (i.e., −Q up ∕Q dn increases). This provides support for the suggestion of Schiro et al (2019) that changes to convection in the ascending region are closely linked to changes in ascent area with warming.…”

Section: Mean Circulationsupporting

confidence: 81%

“…Simulations of the future climate are sensitive to convective parameterizations (e.g., Maher et al, 2018). Models participating in the Coupled Model Intercomparison Project Phase 5 vary widely in their projections of the strength of the mean tropical circulation (Byrne et al, 2018), mostly due to differences in convective parameterizations between the models (Schiro et al, 2019). The resulting uncertainties can be avoided by using global convection-resolving models (CRMs; e.g., Stevens et al, 2019), but for now the high computational cost of such models limits their use in global climate change simulations.…”

Section: Modelmentioning

confidence: 99%

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Understanding the Response of Tropical Ascent to Warming Using an Energy Balance Framework

Jenney

Randall

Branson

2020

J Adv Model Earth Syst

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Previous work has established that warming is associated with an increase in dry static stability, a weakening of the tropical circulation, and a decrease in the convective mass flux. Using a set of idealized simulations with specified surface warming and superparameterized convection, we find support for these previous conclusions. We use an energy and mass balance framework to develop a simple diagnostic that links the fractional area covered by the region of upward motion to the strength of the mean circulation. We demonstrate that the diagnostic works well for our idealized simulations and use it to understand how changes in tropical ascent area and the strength of the mean circulation relate to changes in heating in the ascending and descending regions. We show that the decrease in the strength of the mean circulation can be explained by the relatively slow rate at which atmospheric radiative cooling intensifies with warming. In our simulations, decreases in tropical ascent area are balanced by increases in nonradiative heating in convective regions. Consistent with previous work, we find a warming-induced decrease in the mean convective mass flux. However, when we condition by the sign of the mean vertical motion, the warming-induced changes in the convective mass flux are nonmonotonic and opposite between the ascending and descending regions. Plain Language SummaryThe circulation of the atmosphere is expected to weaken in a future warmer climate. Despite an expected increase in precipitation, studies show that the average strength of stormy updrafts (as measured by the average speed of the updrafts multiplied by their area) will also decrease. We use simulations with realistic representations of storms to test these ideas and derive an equation that may help us better understand how the strength of the circulation is linked to changes in its energy balance.

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Section: Mean Circulationsupporting

confidence: 81%

Section: Modelmentioning

confidence: 99%

Understanding the Response of Tropical Ascent to Warming Using an Energy Balance Framework

Jenney

Randall

Branson

2020

J Adv Model Earth Syst

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“…Even with the same SST patterns in all the AMIP runs, the differences in the model physics, especially the moist convective schemes (Schiro et al, ), can still create large intermodel spread in the tightening trend, as shown in Figure and Table S2. Su et al () found that model differences in the cloud radiative effects at the top of atmosphere over deep convective regions are highly correlated with the diverse responses in the ascent intensity and area changes, indicating a strong coupling between circulation and clouds.…”

Section: Resultsmentioning

confidence: 99%

Observed Tightening of Tropical Ascent in Recent Decades and Linkage to Regional Precipitation Changes

Zhai

et al. 2020

Geophysical Research Letters

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Climate models predict that the tropical ascending region should tighten under global warming, but observational quantification of the tightening rate is limited. Here we show that the observed spatial extent of the relatively moist, rainy and cloudy regions in the tropics associated with large‐scale ascent has been decreasing at a rate of −1%/decade (−5%/K) from 1979 to 2016, resulting from combined effects of interdecadal variability and anthropogenic forcings, with the former contributing more than the latter. The tightening of tropical ascent is associated with an increase in the occurrence frequency of extremely strong ascent, leading to an increase in the average precipitation rate in the top 1% of monthly rainfall in the tropics. At the margins of the convective zones such as the Southeast Amazonia region, the contraction of large‐scale ascent is related to a long‐term drying trend about −3.2%/decade in the past 38 years.

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“…All the simulations are found to reach an equilibrium state within 30 years (the top-of-atmosphere [TOA] net radiation flux close to 0 and surface temperature stabilized), and our analyses are based on the averages of the last 10 years. Note that for those parameter-perturbed experiments, the new equilibrium states are slightly different with the present-day climate in terms of the TOA atmospheric radiative fluxes and/or global mean surface temperature, but the responses in the atmospheric states are still valuable to reflect the importance of certain model parameters, as done in many previous modeling works (Qian et al, 2015;Schiro et al, 2019;Tan et al, 2016). We choose not to tune the TOA radiative fluxes back to the observational values, because such a tuning can exert marked influence on the model's climate sensitivity and overshadow the effects of parameter perturbation in this study.…”

Section: Model Descriptionmentioning

confidence: 99%

“…Over the tropics, radiative warming arising from high-altitude ice cloud can be as large as +80 W m −2 at the top of atmosphere (Stephens et al, 2002). Hence, radiative properties of ice clouds are crucial in regulating the Earth's radiation and energy balance and altering the climate feedbacks and climate sensitivity (e.g., Sanderson et al, 2007;Schiro et al, 2019;Su et al, 2017). Ice particle size is a critical physical property which is closely related with the cross section for longwave absorption and efficiency of shortwave scattering (Fu & Liou, 1993;Liu et al, 2014).…”

Section: Motivation and Backgroundmentioning

confidence: 99%

Impact of Cloud Ice Particle Size Uncertainty in a Climate Model and Implications for Future Satellite Missions

Wang

Jiang

et al. 2020

JGR Atmospheres

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Ice particle size is pivotal to determining ice cloud radiative effect and precipitating rate. However, there is a lack of accurate ice particle effective radius (Rei) observation on the global scale to constrain its representation in climate models. In support of future mission design, here we present a modeling assessment of the sensitivity of climate simulations to Rei and quantify the impact of the proposed mission concept on reducing the uncertainty in climate sensitivity. We perturb the parameters pertaining to ice fall speed parameter and Rei in radiation scheme, respectively, in National Center for Atmospheric Research CESM1 model with a slab ocean configuration. The model sensitivity experiments show that a settling velocity increase due to a larger Rei results in a longwave cooling dominating over a shortwave warming, a global mean surface temperature decrease, and precipitation suppression. A similar competition between longwave and shortwave cloud forcing changes also exists when perturbing Rei in the radiation scheme. Linearity generally holds for the climate response for Rei related parameters. When perturbing falling snow particle size (Res) in a similar way, we find much less sensitivity of climate responses. Our quadrupling CO2 experiments with different parameter settings reveal that Rei and Res can account for changes in climate sensitivity significantly from +12.3% to −6.2%. By reducing the uncertainty ranges of Rei and Res from a factor of 2 to ±25%, a future satellite mission under design is expected to improve the climate state simulations and reduce the climate sensitivity uncertainty pertaining to ice particle size by approximately 60%. Our results highlight the importance of better observational constraints on Rei by satellite missions.

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Relationships Between Tropical Ascent and High Cloud Fraction Changes With Warming Revealed by Perturbation Physics Experiments in CAM5

Cited by 13 publications

References 53 publications

Understanding the Response of Tropical Ascent to Warming Using an Energy Balance Framework

Understanding the Response of Tropical Ascent to Warming Using an Energy Balance Framework

Observed Tightening of Tropical Ascent in Recent Decades and Linkage to Regional Precipitation Changes

Impact of Cloud Ice Particle Size Uncertainty in a Climate Model and Implications for Future Satellite Missions

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