scholarly journals Thermodynamic Control on the Poleward Shift of the Extratropical Jet in Climate Change Simulations: The Role of Rising High Clouds and Their Radiative Effects

2019 ◽  
Vol 32 (3) ◽  
pp. 917-934 ◽  
Author(s):  
Ying Li ◽  
David W. J. Thompson ◽  
Sandrine Bony ◽  
Timothy M. Merlis
Keyword(s):  
Climate Change ◽  
Radiative Effects ◽  
Considerable Uncertainty ◽  
Surface Warming ◽  
Thermodynamic Constraint ◽  
Poleward Shift ◽  
Cloud Radiative Effects ◽  
Underlying Mechanisms ◽  
High Clouds

Extratropical eddy-driven jets are predicted to shift poleward in a warmer climate. Recent studies have suggested that cloud radiative effects (CRE) may enhance the amplitude of such shifts. But there is still considerable uncertainty about the underlying mechanisms, whereby CRE govern the jet response to climate change. This study provides new insights into the role of CRE in the jet response to climate change by exploiting the output from six global warming simulations run with and without atmospheric CRE (ACRE). Consistent with previous studies, it is found that the magnitude of the jet shift under climate change is substantially increased in simulations run with ACRE. It is hypothesized that ACRE enhance the jet response to climate change by increasing the upper-tropospheric baroclinicity due to the radiative effects of rising high clouds. The lifting of the tropopause and high clouds in response to surface warming arises from the thermodynamic constraints placed on water vapor concentrations. Hence, the influence of ACRE on the jet shift in climate change simulations may be viewed as an additional “robust” thermodynamic constraint placed on climate change by the Clausius–Clapeyron relation. The hypothesis is tested in simulations run with an idealized dry GCM, in which the model is perturbed with a thermal forcing that resembles the ACRE response to surface warming. It is demonstrated that 1) the enhanced jet shifts found in climate change simulations run with ACRE are consistent with the atmospheric response to the radiative warming associated with rising high clouds, and 2) the amplitude of the jet shift scales linearly with the amplitude of the ACRE forcing.

scholarly journals Radiative Effects of Clouds and Water Vapor on an Axisymmetric Monsoon

2020 ◽  
Vol 33 (20) ◽  
pp. 8789-8811 ◽  
Author(s):  
Michael P. Byrne ◽  
Laure Zanna
Keyword(s):  
Climate Change ◽  
Water Vapor ◽  
Monsoon Circulation ◽  
Radiative Effects ◽  
Surface Cooling ◽  
Radiative Processes ◽  
Cloud Radiative Effects ◽  
Cloud Effect ◽  
New Perspective ◽  
The Tropics

AbstractMonsoons are summertime circulations shaping climates and societies across the tropics and subtropics. Here the radiative effects controlling an axisymmetric monsoon and its response to climate change are investigated using aquaplanet simulations. The influences of clouds, water vapor, and CO2 on the axisymmetric monsoon are decomposed using the radiation-locking technique. Seasonal variations in clouds and water vapor strongly modulate the axisymmetric monsoon, reducing net precipitation by approximately half. Warming and moistening of the axisymmetric monsoon by seasonal longwave cloud and water vapor effects are counteracted by a strong shortwave cloud effect. The shortwave cloud effect also expedites onset of the axisymmetric monsoon by approximately two weeks, whereas longwave cloud and water vapor effects delay onset. A conceptual model relates the timing of monsoon onset to the efficiency of surface cooling. In climate change simulations CO2 forcing and the water vapor feedback have similar influences on the axisymmetric monsoon, warming the surface and moistening the region. In contrast, clouds have a negligible effect on surface temperature yet dominate the monsoon circulation response. A new perspective for understanding how cloud radiative effects shape the monsoon circulation response to climate change is introduced. The radiation-locking simulations and analyses advance understanding of how radiative processes influence an axisymmetric monsoon, and establish a framework for interpreting monsoon–radiation coupling in observations, in state-of-the-art models, and in different climate states.

scholarly journals Aerosol–cloud interactions studied with the chemistry-climate model EMAC

2014 ◽  
Vol 14 (15) ◽  
pp. 21975-22043 ◽  
Author(s):  
D. Y. Chang ◽  
H. Tost ◽  
B. Steil ◽  
J. Lelieveld
Keyword(s):  
Cloud Cover ◽  
Climate Model ◽  
Osmotic Coefficient ◽  
Cloud Droplet ◽  
Radiative Effects ◽  
Aerosol Cloud ◽  
Cloud Radiative Effect ◽  
Albedo Effect ◽  
Cloud Radiative Effects ◽  
High Clouds

Abstract. This study uses the EMAC atmospheric chemistry-climate model to simulate cloud properties and estimate cloud radiative effects induced by aerosols. We have tested two prognostic cloud droplet nucleation parameterizations, i.e., the standard STN (osmotic coefficient model) and hybrid (HYB, replacing the osmotic coefficient by the κ hygroscopicity parameter) schemes to calculate aerosol hygroscopicity and critical supersaturation, and consider aerosol–cloud feedbacks with a focus on warm clouds. Both prognostic schemes (STN and HYB) account for aerosol number, size and composition effects on droplet nucleation, and are tested in combination with two different cloud cover parameterizations, i.e., a relative humidity threshold and a statistical cloud cover scheme (RH-CLC and ST-CLC). The use of either STN and HYB leads to very different cloud radiative effects, particularly over the continents. The STN scheme predicts highly effective CCN activation in warm clouds and hazes/fogs near the surface. The enhanced CCN activity increases the cloud albedo effect of aerosols and cools the Earth's surface. The cooler surface enhances the hydrostatic stability of the lower continental troposphere and thereby reduces convection and convective precipitation. In contrast, the HYB simulations calculate lower, more realistic CCN activation and consequent cloud albedo effect, leading to relatively stronger convection and high cloud formation. The enhanced high clouds increase greenhouse warming and moderate the cooling effect of the low clouds. With respect to the cloud radiative effects, the statistical ST-CLC scheme shows much higher sensitivity to aerosol–cloud coupling for all continental regions than the RH-CLC threshold scheme, most pronounced for low clouds but also for high clouds. Simulations of the short wave cloud radiative effect at the top of the atmosphere in ST-CLC are a factor of 2–8 more sensitive to aerosol coupling than the RH-CLC configurations. The long wave cloud radiative effect responds about a factor of 2 more sensitively. Our results show that the coupling with the HYB scheme (κ approach) outperforms the coupling with STN (osmotic coefficient), and also provides a more straightforward approach to account for physicochemical effects on aerosol activation into cloud droplets. Accordingly, the sensitivity of CCN activation to chemical composition is highest in HYB. Overall, the prognostic schemes of cloud cover and cloud droplet formation help improve the agreement between model results and observations, and for the ST-CLC scheme it seems to be a necessity.

Response Interference as a Mechanism Underlying Implicit Measures

2008 ◽  
Vol 24 (4) ◽  
pp. 218-225 ◽  
Author(s):  
Bertram Gawronski ◽  
Roland Deutsch ◽  
Etienne P. LeBel ◽  
Kurt R. Peters
Keyword(s):  
Task Performance ◽  
Psychological Research ◽  
Implicit Measures ◽  
Mediation Model ◽  
Response Interference ◽  
Relevant Evidence ◽  
Moderated Mediation Model ◽  
Stimulus Features ◽  
Underlying Mechanisms

Over the last decade, implicit measures of mental associations (e.g., Implicit Association Test, sequential priming) have become increasingly popular in many areas of psychological research. Even though successful applications provide preliminary support for the validity of these measures, their underlying mechanisms are still controversial. The present article addresses the role of a particular mechanism that is hypothesized to mediate the influence of activated associations on task performance in many implicit measures: response interference (RI). Based on a review of relevant evidence, we argue that RI effects in implicit measures depend on participants’ attention to association-relevant stimulus features, which in turn can influence the reliability and the construct validity of these measures. Drawing on a moderated-mediation model (MMM) of task performance in RI paradigms, we provide several suggestions on how to address these problems in research using implicit measures.

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