Spatial and temporal analysis of the seasonal and interannual variability in the tropical Pacific simulated with a coupled GCM

J. F. Álvarez García, W. D. Cabos Narváez, M. J. O. Beviá

Abstract


In the first part of this work, the dominant time scales that explain the tropical variability of the first SINTEX
simulation (ECHAM4(T30)-ORCA) are identified through a spectral analysis. Higher order spectral analysis is
used to examine the interactions among these time scales. The time series analyzed are an average of sea surface
temperature over the Niño3 region. The time scales obtained are compared with those identified in another coupled
GCM simulation (ECHAM4(T42)-OPYC3). The higher importance of the biannual time scale in this last is explained partly by the strength of the coupling between the annual and the biannual time scales. There is no such strong coupling in the SINTEX simulation. Important differences among the generation of the simulated warm (or cold) event suggest the need of a systematic classification to isolate their relevant features. Therefore in the second part of this work, we address this problem. A space-time cluster analysis is performed on a data set built by collecting the values of the heat content anomalies in the tropical Pacific region, in the fifteen months previous to a peak in the Niño3 Index that has been identified as a ?warm? (or ?cold?) event. In the case of the warm events,
three types of generation schemes are found. In two of them, there are anomalies of heat content in the west, north
and south of the equator, more than nine months before the events start. In the third case, the anomalies appear and
grow in the central equatorial Pacific. Only two types are needed to classify the generation of cold events. Negative
sea level height anomalies appear six months before the Niño3 Index reaches the (local) minimum. They are located north of the equator in one of the groups, and south of it in the other. Some of these characteristic traits also appear in observations of warm and cold events.

Keywords


coupled model;El Niño-Southern Oscillation;seasonal;interannual;heat content;clusters

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References


DOI: https://doi.org/10.4401/ag-3384
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Published by INGV, Istituto Nazionale di Geofisica e Vulcanologia - ISSN: 2037-416X