Preprints
https://doi.org/10.5194/wcd-2020-22
https://doi.org/10.5194/wcd-2020-22

  13 May 2020

13 May 2020

Review status: a revised version of this preprint is currently under review for the journal WCD.

Influence of ENSO on North American subseasonal surface air temperature variability

Patrick Martineau1, Hisashi Nakamura1,2, and Yu Kosaka1 Patrick Martineau et al.
  • 1Research Center for Advanced Science and Technology, The University of Tokyo, Tokyo, Japan
  • 2Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan

Abstract. The wintertime influence of El Niño-Southern Oscillation (ENSO) on subseasonal variability is revisited by identifying the dominant mode of covariability between 10–60 day band-pass-filtered surface air temperature (SAT) variability over the North American continent and winter-mean sea surface temperature (SST) over the North Pacific sector. We find, in agreement with previous studies, that La Niña conditions tend to enhance the subseasonal SAT variability over western North America. This modulation of subseasonal variability is achieved through interactions between subseasonal eddies and La Niña-related changes in the winter-mean circulation. Specifically, eastward-propagating quasi-stationary eddies over the North Pacific are more efficient in extracting energy from the mean flow through the baroclinic conversion of energy over the North Pacific sector during La Niña. Changes in the vertical structure of these wave anomalies are crucial to enhance the efficiency of energy conversion via amplified downgradient heat fluxes that energize subseasonal eddy thermal anomalies. The combination of increased subseasonal SAT variability and the cold winter-mean response to La Niña both contribute to enhancing the likelihood of cold extremes over western North America.

Patrick Martineau et al.

 
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Status: final response (author comments only)
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Patrick Martineau et al.

Patrick Martineau et al.

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Short summary
To understand better the factors that impact the weather in North America, this study explores the influence of El Niño-Southern Oscillation on wintertime surface air temperature variability using reanalysis data. Results show that La Niña enhances subseasonal variability over western North America by amplifying the baroclinic conversion of energy from the winter-mean circulation to subseasonal eddies. Changes in the vertical structure of these eddies are crucial for this amplification.