scholarly journals Attributing Historical and Future Evolution of Radiative Feedbacks to Regional Warming Patterns using a Green’s Function Approach: The Preeminence of the Western Pacific

2018 ◽  
Author(s):  
Yue Dong ◽  
Cristian Proistosescu ◽  
Kyle Armour ◽  
David Battisti
Keyword(s):  
Green’S Function ◽  
Green's Function ◽  
Western Pacific ◽  
Function Approach ◽  
Regional Warming ◽  
Future Evolution ◽  
Radiative Feedbacks ◽  
The Western Pacific

scholarly journals Attributing Historical and Future Evolution of Radiative Feedbacks to Regional Warming Patterns using a Green’s Function Approach: The Preeminence of the Western Pacific

2019 ◽  
Vol 32 (17) ◽  
pp. 5471-5491 ◽  
Author(s):  
Yue Dong ◽  
Cristian Proistosescu ◽  
Kyle C. Armour ◽  
David S. Battisti
Keyword(s):  
Green’S Function ◽  
Green's Function ◽  
Climate Sensitivity ◽  
Climate Model ◽  
Global Climate Model ◽  
Western Pacific ◽  
Surface Warming ◽  
The Future ◽  
Radiative Feedbacks ◽  
The Western Pacific

Abstract Global radiative feedbacks have been found to vary in global climate model (GCM) simulations. Atmospheric GCMs (AGCMs) driven with historical patterns of sea surface temperatures (SSTs) and sea ice concentrations produce radiative feedbacks that trend toward more negative values, implying low climate sensitivity, over recent decades. Freely evolving coupled GCMs driven by increasing CO2 produce radiative feedbacks that trend toward more positive values, implying increasing climate sensitivity, in the future. While this time variation in feedbacks has been linked to evolving SST patterns, the role of particular regions has not been quantified. Here, a Green’s function is derived from a suite of simulations within an AGCM (NCAR’s CAM4), allowing an attribution of global feedback changes to surface warming in each region. The results highlight the radiative response to surface warming in ascent regions of the western tropical Pacific as the dominant control on global radiative feedback changes. Historical warming from the 1950s to 2000s preferentially occurred in the western Pacific, yielding a strong global outgoing radiative response at the top of the atmosphere (TOA) and thus a strongly negative global feedback. Long-term warming in coupled GCMs occurs preferentially in tropical descent regions and in high latitudes, where surface warming yields small global TOA radiation change but large global surface air temperature change, and thus a less-negative global feedback. These results illuminate the importance of determining mechanisms of warm pool warming for understanding how feedbacks have varied historically and will evolve in the future.

scholarly journals Analysis of the interaction of thermoacoustic modes with a Green’s function approach

2018 ◽  
Vol 10 (4) ◽  
pp. 326-336 ◽  
Author(s):  
Alessandra Bigongiari ◽  
Maria Heckl
Keyword(s):  
Green’S Function ◽  
Green's Function ◽  
Initial Perturbation ◽  
Time History ◽  
Function Approach ◽  
Stability Maps ◽  
Flame Describing Function ◽  
The Stability ◽  
Dynamics Simulations ◽  
Fast Prediction

In this paper, we will present a fast prediction tool based on a one-dimensional Green's function approach that can be used to bypass numerically expensive computational fluid dynamics simulations. The Green’s function approach has the advantage of providing a clear picture of the physics behind the generation and evolution of combustion instabilities. In addition, the method allows us to perform a modal analysis; single acoustic modes can be treated in isolation or in combination with other modes. In this article, we will investigate the role of higher-order modes in determining the stability of the system. We will initially produce the stability maps for the first and second mode separately. Then the time history of the perturbation will be computed, where both the modes are present. The flame will be modelled by a generic Flame Describing Function, i.e. by an amplitude-dependent Flame Transfer Function. The time-history calculations show the evolution of the two modes resulting from an initial perturbation; both transient and limit-cycle oscillations are revealed. Our study represents a first step towards the modelling of nonlinearity and non-normality in combustion processes.

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