Different atmospheric moisture divergence responses to extreme and moderate El Niños

Xu, Guangzhi, Osborn, Timothy J., Matthews, Adrian J. and Joshi, Manoj M. (2016) Different atmospheric moisture divergence responses to extreme and moderate El Niños. Climate Dynamics, 47 (1). pp. 393-410. ISSN 0930-7575

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      Abstract

      On seasonal and inter-annual time scales, vertically integrated moisture divergence provides a useful measure of the tropical atmospheric hydrological cycle. It reflects the combined dynamical and thermodynamical effects, and is not subject to the limitations that afflict observations of evaporation minus precipitation. An empirical orthogonal function (EOF) analysis of the tropical Pacific moisture divergence fields calculated from the ERA-Interim reanalysis reveals the dominant effects of the El Niño-Southern Oscillation (ENSO) on inter-annual time scales. Two EOFs are necessary to capture the ENSO signature, and regression relationships between their Principal Components and indices of equatorial Pacific sea surface temperature (SST) demonstrate that the transition from strong La Niña through to extreme El Niño events is not a linear one. The largest deviation from linearity is for the strongest El Niños, and we interpret that this arises at least partly because the EOF analysis cannot easily separate different patterns of responses that are not orthogonal to each other. To overcome the orthogonality constraints, a self-organizing map (SOM) analysis of the same moisture divergence fields was performed. The SOM analysis captures the range of responses to ENSO, including the distinction between the moderate and strong El Niños identified by the EOF analysis. The work demonstrates the potential for the application of SOM to large scale climatic analysis, by virtue of its easier interpretation, relaxation of orthogonality constraints and its versatility for serving as an alternative classification method. Both the EOF and SOM analyses suggest a classification of “moderate” and “extreme” El Niños by their differences in the magnitudes of the hydrological cycle responses, spatial patterns and evolutionary paths. Classification from the moisture divergence point of view shows consistency with results based on other physical variables such as SST.

      Item Type: Article
      Additional Information: © The Author(s) 2015. Open Access: This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
      Uncontrolled Keywords: el niño southern oscillation,self-organizing map ,hydrological cycle
      Faculty \ School: Faculty of Science > School of Environmental Sciences
      Depositing User: Pure Connector
      Date Deposited: 30 Oct 2015 10:00
      Last Modified: 11 Apr 2019 14:52
      URI: https://ueaeprints.uea.ac.uk/id/eprint/54958
      DOI: 10.1007/s00382-015-2844-2

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