| 1. |
- Blanco, Joaquin, 1985-, et al.
(author)
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A Cloud-Controlling Factor Perspective on the Hemispheric Asymmetry of Extratropical Cloud Albedo
- 2023
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In: Journal of Climate. - 0894-8755 .- 1520-0442. ; 36:6, s. 1793-1804
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Journal article (peer-reviewed)abstract
- The Northern and Southern Hemispheres reflect on average almost equal amounts of sunlight due to compensating hemispheric asymmetries in clear-sky and cloud albedo. Recent work indicates that the cloud albedo asymmetry is largely due to clouds in extratropical oceanic regions. Here, we investigate the proximate causes of this extratropical cloud albedo asymmetry using a cloud-controlling factor (CCF) approach. We develop a simple index that measures the skill of CCFs, either individually or in combination, in predicting the asymmetry. The index captures the contribution to the asymmetry due to interhemispheric differences in the probability distribution function of daily CCF values. Cloud albedo is quantified using daily MODIS satellite retrievals, and is related to range of CCFs derived from the ERA5 product. We find that sea surface temperature is the CCF that individually explains the largest fraction of the asymmetry, followed by surface wind. The asymmetry is predominantly due to low clouds, and our results are consistent with prior local-scale modeling work showing that marine boundary layer clouds become thicker and more extensive as surface wind increases and surface temperature cools. The asymmetry is consistent with large-scale control of storm-track intensity and surface winds by meridional temperature gradients: persistently cold and windy conditions in the Southern Hemisphere keep cloud albedo high year-round. Our results have important implications for global-scale cloud feedbacks and contribute to efforts to develop a theory for planetary albedo and its symmetry.
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| 2. |
- Datseris, George, et al.
(author)
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Agents.jl : a performant and feature-full agent-based modeling software of minimal code complexity
- 2022
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In: Simulation (San Diego, Calif.). - : SAGE Publications. - 0037-5497 .- 1741-3133.
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Journal article (peer-reviewed)abstract
- Agent-based modeling is a simulation method in which autonomous agents interact with their environment and one another, given a predefined set of rules. It is an integral method for modeling and simulating complex systems, such as socio-economic problems. Since agent-based models are not described by simple and concise mathematical equations, the code that generates them is typically complicated, large, and slow. Here we present Agents.jl, a Julia-based software that provides an ABM analysis platform with minimal code complexity. We compare our software with some of the most popular ABM software in other programming languages. We find that Agents.jl is not only the most performant but also the least complicated software, providing the same (and sometimes more) features as the competitors with less input required from the user. Agents.jl also integrates excellently with the entire Julia ecosystem, including interactive applications, differential equations, parameter optimization, and so on. This removes any extensions library requirement from Agents.jl, which is paramount in many other tools.
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| 3. |
- Datseris, George, et al.
(author)
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Minimal Recipes for Global Cloudiness
- 2022
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In: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 49:20
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Journal article (peer-reviewed)abstract
- Clouds are primary modulators of Earth's energy balance. It is thus important to understand the links connecting variabilities in cloudiness to variabilities in other state variables of the climate system, and also describe how these links would change in a changing climate. A conceptual model of global cloudiness can help elucidate these points. In this work we derive simple representations of cloudiness, that can be useful in creating a theory of global cloudiness. These representations illustrate how both spatial and temporal variability of cloudiness can be expressed in terms of basic state variables. Specifically, cloud albedo is captured by a nonlinear combination of pressure velocity and a measure of the low-level stability, and cloud longwave effect is captured by surface temperature, pressure velocity, and standard deviation of pressure velocity. We conclude with a short discussion on the usefulness of this work in the context of global warming response studies.
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| 4. |
- Hadas, Or, et al.
(author)
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The role of baroclinic activity in controlling Earth's albedo in the present and future climates
- 2023
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In: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 120:5
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Journal article (peer-reviewed)abstract
- Clouds are one of the most influential components of Earth's climate system. Specifically, the midlatitude clouds play a vital role in shaping Earth's albedo. This study investigates the connection between baroclinic activity, which dominates the midlatitude climate, and cloud-albedo and how it relates to Earth's existing hemispheric albedo symmetry. We show that baroclinic activity and cloud-albedo are highly correlated. By using Lagrangian tracking of cyclones and anticyclones and analyzing their individual cloud properties at different vertical levels, we explain why their cloud-albedo increases monotonically with intensity. We find that while for anticyclones, the relation between strength and cloudiness is mostly linear, for cyclones, in which clouds are more prevalent, the relation saturates with strength. Using the cloud-albedo strength relationships and the climatology of baroclinic activity, we demonstrate that the observed hemispheric difference in cloud-albedo is well explained by the difference in the population of cyclones and anticyclones, which counter-balances the difference in clear-sky albedo. Finally, we discuss the robustness of the hemispheric albedo symmetry in the future climate. Seemingly, the symmetry should break, as the northern hemisphere's storm track response differs from that of the southern hemisphere due to Arctic amplification. However, we show that the saturation of the cloud response to storm intensity implies that the increase in the skewness of the southern hemisphere storm distribution toward strong storms will decrease future cloud-albedo in the southern hemisphere. This complex response explains how albedo symmetry might persist even with the predicted asymmetric hemispheric change in baroclinicity under climate change.
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