Joining moored-buoy and satellite winds to better understand and forecast El Nino and La Nina events

What is it about?

Near surface wind variability over the tropical Pacific is a dominant driver of the sea surface temperature anomaly (SSTA) changes associated with El Nino and La Nina events. Reliably monitoring and understanding event development requires being able to accurately estimate wind stress across the full basin. Various types of wind data are available to researchers, but they are not equally useful for this purpose. This study evaluates several approaches and finds that joining the winds from tropical Pacific moored-buoy array with the right kind of satellite winds provides a remarkably accurate basis for simulating El Nino and La Nina-associated SSTA development with an ocean model. The utility of the wind stress fields produced by the joint buoy-satellite approach is further examined by using them to study the reasons for the unexpected development of a La Nina in 2017 and attempting to predict the state of the commonly referred-to Nino 3.4 index during the northern hemisphere's winter season (when El Nino and La Nina impacts on seasonal weather conditions are strongest). Results show that a series of easterly wind surges in the latter half of 2017 drove the central Pacific SSTA cooling associated with the 2017 La Nina. They also show that the forecast skill of the wind stress integral approach to predicting Nino 3.4 over the period for which both the required satellite and buoy winds have been available is as good as our best performing coupled-model forecast systems.

Featured Image

Why is it important?

The western Pacific is a locus of weather-scale westerly wind events that play an important role in the development of El Nino events. At present, nearly all of the moored-buoys that formerly comprised the western Pacific (a.k.a "TRITON") part of the tropical Pacific mooring-array have been removed. This work identifies a useful band-aid for the missing buoy winds, thereby enabling our ability to monitor and study the development of El Nino events. An open-access copy of the paper is available from the Journal of Climate's web site.

Perspectives