Sunday, May 28, 2017

Observed El Niño SSTA development and the effects of easterly and westerly wind events in 2014/15

Wintertime La Niña pattern. (Credit: NOAA Climate.gov)In a paper published on the Journal of Climate, Chiodi (University of Washington) and Harrison (PMEL) show that wind stress information from easterly and westerly events in 2014  can accurately simulate the development of sea surface temperatures in 2014 and 2015, when wind data from the TAO/TRITON array was unusually sparse. 

The authors state that in order to forecast equatorial Pacific sea surface temperature developments in years such as 2014 and 2015, it may be necessary to learn to predict easterly and westerly wind characteristics. 

This study was supported by the CPO Ocean Observation and Monitoring Division.

Read the paper:  Chiodi, A.M. and D.E. Harrison (2017). Observed El Niño SSTA Development and the Effects of Easterly and Westerly Wind Events in 2014/15. Journal of Climate, 30, 1505–1519. doi: 10.1175/JCLI-D-16-0385.1

Abstract:

The unexpected halt of warm sea surface temperature anomaly (SSTA) growth in 2014 and development of a major El Niño in 2015 has drawn attention to our ability to understand and predict El Niño development. Wind stress–forced ocean model studies have satisfactorily reproduced observed equatorial Pacific SSTAs during periods when data return from the TAO/TRITON buoy network was high. Unfortunately, TAO/TRITON data return in 2014 was poor. To study 2014 SSTA development, the observed wind gaps must be filled. The hypothesis that subseasonal wind events provided the dominant driver of observed waveguide SSTA development in 2014 and 2015 is used along with the available buoy winds to construct an oceanic waveguide-wide surface stress field of westerly wind events (WWEs) and easterly wind surges (EWSs). It is found that the observed Niño-3.4 SSTA development in 2014 and 2015 can thereby be reproduced satisfactorily. Previous 2014 studies used other wind fields and reached differing conclusions about the importance of WWEs and EWSs. Experiment results herein help explain these inconsistencies, and clarify the relative importance of WWEs and EWSs. It is found that the springtime surplus of WWEs and summertime balance between WWEs and EWSs (yielding small net wind stress anomaly) accounts for the early development and midyear reversal of El Niño–like SSTA development in 2014. A strong abundance of WWEs in 2015 accounts for the rapid SSTA warming observed then. Accurately forecasting equatorial Pacific SSTA in years like 2014 and 2015 may require learning to predict WWE and EWS occurrence characteristics.

Thursday, April 13, 2017/Categories: Climate Observation Division, General News

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