What is it about?
Sea surface temperatures (SST) in the North Atlantic Ocean exhibit multidecadal fluctuations and known to influence Asian climate. We explored the relation between summer climate over South and East Asia and its dependence on the SST patterns associated with positive and negative phases of Atlantic multidecadal oscillation using sets of idealized model experiments.
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Why is it important?
Our findings shows that the Atlantic multidecadal oscillation (AMO) influences the summer climate of East Asia through an extratropical atmospheric circulation pathway (i.e. Rossby wave train), whereas South Asian summer monsoon precipitation is linked to the AMO partly via a tropical pathway (i.e. Intertropical Convergence Zone). These tropical and extratropical pathways that cause a response of the South and East Asia summer climate to the AMO are sensitive to the pattern of AMO SST anomalies, and to whether they are confined to the North Atlantic/Arctic or outside the North Atlantic that are still associated with the AMO. The results obtained in this study help in understanding further the potential for the AMO to generate multidecadal variability in South and East Asian climate.
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This page is a summary of: The Influence of Atlantic Variability on Asian Summer Climate Is Sensitive to the Pattern of the Sea Surface Temperature Anomaly, Journal of Climate, July 2020, American Meteorological Society, DOI: 10.1175/jcli-d-20-0039.1.
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Identifying teleconnections and multidecadal variability of East Asian surface temperature during the last millennium in CMIP5 simulations
We examine the relationships in models and reconstructions between the multidecadal variability of surface temperature in East Asia and two extratropical modes of variability: the Atlantic Multidecadal Oscillation (AMO) and the Pacific Decadal Oscillation (PDO). We analyse the spatial, temporal and spectral characteristics of the climate modes in the last millennium, historical and pre-industrial control simulations of seven Coupled Model Intercomparison Project phase 5 (CMIP5)/Paleoclimate Model Intercomparison Project phase 3 (PMIP3) global climate models (GCMs) to assess the relative influences of external forcing and unforced variability. These models produce PDO and AMO variability with realistic spatial patterns but widely varying spectral characteristics. AMO internal variability significantly influences East Asian temperature in five models (MPI, HadCM3, MRI, IPSL and CSIRO) but has a weak influence in the other two (BCC and CCSM4). In most models, external forcing greatly strengthens these statistical associations and hence the apparent teleconnection with the AMO. PDO internal variability strongly influences East Asian temperature in two out of seven models, but external forcing makes this apparent teleconnection much weaker. This indicates that the AMO–East Asian temperature relationship is partly driven by external forcing, whereas the PDO–temperature relationship is largely from internal variability within the climate system. Our findings suggest that external forcing confounds attempts to diagnose the teleconnections of internal multidecadal variability. Using AMO and PDO indices that represent internal variability more closely and minimising the influence of external forcing on East Asian temperature can partly ameliorate this confounding effect. Nevertheless, these approaches still yield differences between the forced and control simulations and they cannot always be applied to paleoclimate reconstructions. Thus, we recommend caution when interpreting teleconnections diagnosed from reconstructions that contain both forced and internal variations.
INTEGRATE: climate model simulations data to study the Asian climate response to Atlantic Multidecadal Oscillation (AMO) using the Intermediate General Circulation Model version 4 (IGCM4)
This dataset contains model simulated data to study the response of Asian summer climate to AMO-like (Atlantic Multidecadal Oscillation) sea surface temperature (SST) anomalies using the Intermediate General Circulation Model version 4 (IGCM4; Joshi et al., 2015). This dataset also contains the AMO SST patterns from seven Coupled Model Intercomparison Project (CMIP5)/Paleoclimate Modelling Intercomparison Project Phase (PMIP3) global climate models (Ratna et al., 2019), which are used to explore the sensitivity of the atmospheric response to the SST pattern. These data were collected as part of the Natural Environment Research Council (NERC) funded 'An integrated data-model study of interactions between tropical monsoons and extra-tropical climate variability and extremes (INTEGRATE)' project (2016-2020) at the Climatic Research Unit, University of East Anglia. The project studied the interactions between tropics and extratropical climate variability.
An integrated data-model study of interactions between tropical monsoons and extra-tropical climate variability and extremes
In order to predict the evolution of inter-regional linkages this century, it is crucial to understand how they have evolved in the past. This is particularly important because extremes such as drought are modulated by decadal variability. Our study is motivated by recent identification of multidecadal links between 2000-year reconstructions of Tibetan Plateau precipitation and Northern Hemisphere temperature. We will go far beyond this initial finding by combining insights gained from coupled climate models and observations (instrumental, tree-ring and documentary records) to identify large-scale modes that link the variability of tropical monsoons and northern extratropical climates on multiple timescales. We will (i) better understand the teleconnections between monsoon and extratropical regions (with particular emphasis on the Arctic), (ii) evaluate the ability of climate models to reproduce observed behaviour including regional extremes, (iii) explore mechanisms that drive the observed behaviour and understand how the linkages may evolve under future climate change using simulations with a hierarchy of models. Paleoclimate records, including temperature- sensitive tree-ring records from the Eurasian Arctic and precipitation-sensitive series from the Asian monsoon regions provide a unique opportunity to identify associations on annual to multidecadal timescales. CMIP5 and CMIP6 "control" and "last millennium" runs will be used to assess simulated unforced variability and response to forcings such as volcanoes and to consider SST and atmospheric circulation patterns associated with periods of extremes in the monsoon, extratropical and Arctic regions. New simulations with imposed anomalies (e.g. sea or land surface temperatures in particular regions) in conjunction with external forcing will be designed to explore the roles of basin-wide changes or land-surface interactions in generating and synchronising decadal variability. Implications for future climate change will be considered using model simulations and our improved understanding of mechanisms.
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