A new objective technique for assessing global climate teleconnections

Abstract

Teleconnections are one of the main sources of intra-annual to inter-decadal variation in weather and climate and are one way that changes at the largest scales can be cascaded to adjustments at the smaller scales. This thesis aims to identify how atmospheric teleconnections might change with a warmer climate. A new method based on point correlation maps and self-organising maps (SOMs) is presented. Proof of concept is demonstrated using 60 years of National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) sea level pressure (SLP) re-analysis data and the medium complexity climate model FORTE (Fast Ocean Rapid Troposphere Experiment). It is shown that the method can identify known teleconnections from historical data and be used to assess how realistically teleconnections are reproduced in a climate model. The method is then applied to an assessment of the capability of three CMIP5 (Climate Model Intercomparison Project 5) models to simulate realistic teleconnections, as a precursor to understanding how teleconnections change with different climate forcings. The three models used are CM5B-LR, GFDL-ESM2G and HadGEM-ES. The performance is variable by region, with each model having different strengths and weaknesses. There are areas where all models perform relatively well, such as the North Atlantic Oscillation, and others where all three models perform badly, such as the Indian monsoon. The teleconnections modelled using historical conditions and under two Representative Concentration Pathways (RCP4.5 and RCP8.5) are compared. There is a lack of agreement between the models as to the changes expected, with few changes being statistically significant. There is no large-scale rearrangement of teleconnections or any new forms of teleconnections in any of the models. Suggested improvements to the method and ideas for further investigation are presented.

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ORCID for Freja Hunt: orcid.org/0000-0003-4045-2856

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