Insights from a refined decomposition of cloud feedbacks

Zelinka, Mark D.; Zhou, Chen; Klein, Stephen A.

doi:10.1002/2016gl069917

Cited by 172 publications

(223 citation statements)

References 77 publications

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“…i) It provides a physical basis for interpreting the result that the positive feedbacks due to rising high clouds under climate change are not limited to the tropics, but also extend to extratropical latitudes (36,37). The potential for cloud feedbacks at extratropical latitudes due to the static stability/iris mechanism (6) could be explored in future research.…”

Section: Discussionmentioning

confidence: 99%

Thermodynamic constraint on the depth of the global tropospheric circulation

Thompson

Bony

2017

Proc. Natl. Acad. Sci. U.S.A.

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The troposphere is the region of the atmosphere characterized by low static stability, vigorous diabatic mixing, and widespread condensational heating in clouds. Previous research has argued that in the tropics, the upper bound on tropospheric mixing and clouds is constrained by the rapid decrease with height of the saturation water vapor pressure and hence radiative cooling by water vapor in clear-sky regions. Here the authors contend that the same basic physics play a key role in constraining the vertical structure of tropospheric mixing, tropopause temperature, and cloud-top temperature throughout the globe. It is argued that radiative cooling by water vapor plays an important role in governing the depth and amplitude of large-scale dynamics at extratropical latitudes.climate dynamics | climate change | cloud feedbacks | extratropical dynamics | general circulation T he defining difference between the troposphere (the turning sphere) and the stratosphere (the layered sphere) is the amplitude of mixing within each region. The troposphere is marked by vigorous diabatic motions (i.e., motions that flux heat across isentropic surfaces); the stratosphere is characterized by relatively weak diabatic mixing.The top of the troposphere coincides closely to the level above which clouds rarely penetrate. In the tropics, the upper bound on tropospheric clouds is believed to be strongly constrained by the unique vertical structure of radiative cooling by water vapor. Saturation vapor pressure decreases rapidly with temperature in the tropical upper troposphere in accordance with the ClausiusClapeyron relationship. As the saturation vapor pressure decreases, so do water vapor concentrations, and hence so does the amplitude of the clear-sky radiative cooling (1, 2) and its associated downward mass flux (3). From continuity, the thermodynamic limit on sinking motion in clear-sky regions extends to rising motion in regions of deep convection (3). Because the rising motion in regions of deep convection is limited by saturation vapor pressures (and thus temperatures) in clear-sky regions and the static stabilities in clear-sky and cloudy regions of the tropics are comparable, it follows that cloud-top temperatures in the tropics are strongly constrained by the basic thermodynamics that govern clear-sky water vapor concentrations (3, 4).The physical linkages between clear-sky radiative cooling, the depth of tropospheric mixing, and clouds have been applied specifically to the case of tropical anvil clouds. Here we contend that the same physical linkages play an even broader role in the global atmosphere circulation. It is argued that clear-sky cooling by water vapor constrains the depth of tropospheric mixing, cloud-top temperatures, and the amplitude of large-scale atmospheric dynamics throughout the global atmosphere.A Thermodynamic Constraint on the Depth of the Troposphere At steady state, the thermodynamic energy equation can be expressed in pressure coordinates asWhere V · ∇ h T is the horizontal advection of temperature, ...

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Section: Discussionmentioning

confidence: 99%

Thermodynamic constraint on the depth of the global tropospheric circulation

Thompson

Bony

2017

Proc. Natl. Acad. Sci. U.S.A.

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“…LCC feedback is a major component of the overall cloud feedback (Clement et al, 2009; Qu et al, 2014; Zelinka et al, 2016). Previous regression analyses have shown that SST exerts a prime control on local and regional mean LCC variations, with inversion strength, a proxy for lower troposphere stability, being the next most important factor (Brient & Schneider, 2016; Qu et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

Observations of Local Positive Low Cloud Feedback Patterns and Their Role in Internal Variability and Climate Sensitivity

Yuan

Oreopoulos

Platnick

et al. 2018

Geophysical Research Letters

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Modeling studies have shown that cloud feedbacks are sensitive to the spatial pattern of sea surface temperature (SST) anomalies, while cloud feedbacks themselves strongly influence the magnitude of SST anomalies. Observational counterparts to such patterned interactions are still needed. Here we show that distinct large‐scale patterns of SST and low‐cloud cover (LCC) emerge naturally from objective analyses of observations and demonstrate their close coupling in a positive local SST‐LCC feedback loop that may be important for both internal variability and climate change. The two patterns that explain the maximum amount of covariance between SST and LCC correspond to the Interdecadal Pacific Oscillation and the Atlantic Multidecadal Oscillation, leading modes of multidecadal internal variability. Spatial patterns and time series of SST and LCC anomalies associated with both modes point to a strong positive local SST‐LCC feedback. In many current climate models, our analyses suggest that SST‐LCC feedback strength is too weak compared to observations. Modeled local SST‐LCC feedback strength affects simulated internal variability so that stronger feedback produces more intense and more realistic patterns of internal variability. To the extent that the physics of the local positive SST‐LCC feedback inferred from observed climate variability applies to future greenhouse warming, we anticipate significant amount of delayed warming because of SST‐LCC feedback when anthropogenic SST warming eventually overwhelm the effects of internal variability that may mute anthropogenic warming over parts of the ocean. We postulate that many climate models may be underestimating both future warming and the magnitude of modeled internal variability because of their weak SST‐LCC feedback.

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“…Focusing only on the cloud feedback mechanisms, Zelinka et al (2012a) and others used this approach to isolate the role of each of the fundamental cloud variables that contribute to the cloud radiative response: cloud cover, cloud optical depth or water phase (liquid or ice), and cloud altitude (or cloud temperature). The shortwave (SW) cloud feedback is primarily driven by changes in cloud cover and cloud optical depth, whereas the longwave (LW) cloud feedback is driven by changes in cloud cover, cloud optical depth, and cloud vertical distribution (e.g., Klein and Jakob, 1999;Zelinka et al, 2012bZelinka et al, , 2013Zelinka et al, , 2016.…”

Section: Introductionmentioning

confidence: 99%

The link between outgoing longwave radiation and the altitude at which a spaceborne lidar beam is fully attenuated

et al. 2017

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Abstract. According to climate model simulations, the changing altitude of middle and high clouds is the dominant contributor to the positive global mean longwave cloud feedback. Nevertheless, the mechanisms of this longwave cloud altitude feedback and its magnitude have not yet been verified by observations. Accurate, stable, and long-term observations of a metric-characterizing cloud vertical distribution that are related to the longwave cloud radiative effect are needed to achieve a better understanding of the mechanism of longwave cloud altitude feedback. This study shows that the direct measurement of the altitude of atmospheric lidar opacity is a good candidate for the necessary observational metric. The opacity altitude is the level at which a spaceborne lidar beam is fully attenuated when probing an opaque cloud. By combining this altitude with the direct lidar measurement of the cloud-top altitude, we derive the effective radiative temperature of opaque clouds which linearly drives (as we will show) the outgoing longwave radiation. We find that, for an opaque cloud, a cloud temperature change of 1 K modifies its cloud radiative effect by 2 W m −2 . Similarly, the longwave cloud radiative effect of optically thin clouds can be derived from their top and base altitudes and an estimate of their emissivity. We show with radiative transfer simulations that these relationships hold true at single atmospheric column scale, on the scale of the Clouds and the Earth's Radiant Energy System (CERES) instantaneous footprint, and at monthly mean 2 • × 2 • scale. Opaque clouds cover 35 % of the ice-free ocean and contribute to 73 % of the global mean cloud radiative effect. Thin-cloud coverage is 36 % and contributes 27 % of the global mean cloud radiative effect. The link between outgoing longwave radiation and the altitude at which a spaceborne lidar beam is fully attenuated provides a simple formulation of the cloud radiative effect in the longwave domain and so helps us to understand the longwave cloud altitude feedback mechanism.

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Insights from a refined decomposition of cloud feedbacks

Cited by 172 publications

References 77 publications

Thermodynamic constraint on the depth of the global tropospheric circulation

Thermodynamic constraint on the depth of the global tropospheric circulation

Observations of Local Positive Low Cloud Feedback Patterns and Their Role in Internal Variability and Climate Sensitivity

The link between outgoing longwave radiation and the altitude at which a spaceborne lidar beam is fully attenuated

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