Publication Date:
2020-11-30
Description:
Past studies have suggested that regional trends in anthropogenic aerosols can influence the Pacific Decadal Oscillation (PDO) through modulation of the Aleutian Low. However, the robustness of this connection is debated. This study analyses changes to the Aleutian Low in an ensemble of climate models forced with large, idealised global and regional black carbon (BC) and sulphate aerosol perturbations. To isolate the role of ocean feedbacks, the experiments are performed with an interactive ocean and with prescribed sea surface temperatures. The results show a robust weakening of the Aleutian Low forced by a global 10-fold increase in BC in both experiment configurations. A linearised steady-state primitive equation model is forced with diabatic heating anomalies to investigate the mechanisms through which heating from BC emissions influences the Aleutian Low. The heating from BC absorption over India and east Asia generates Rossby wave trains that propagate into the North Pacific sector, forming an upper tropospheric ridge. Sources of BC outside of east Asia enhance the weakening of the Aleutian Low. The responses to a global 5-fold and regional 10-fold increase in sulphate aerosols over Asia show poor consistency across climate models, with a multi-model mean response that does not project strongly onto the Aleutian Low. These findings for a large, idealised step increase in regional sulphate aerosol differ from previous studies that suggest the transient increase in sulphate aerosols over Asia during the early 21st century weakened the Aleutian Low and induced a transition to a negative PDO phase.
Print ISSN:
0894-8755
Electronic ISSN:
1520-0442
Topics:
Geography
,
Geosciences
,
Physics
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