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The La Niña OLR Index

The La Niña outgoing longwave radiation (OLR) index tabulates synoptic-scale breaks in deep-atmospheric convection activity over the western tropical Pacific. Over the time for which satellite-based OLR information has been available, the La Niña events distinguished by their OLR behavior (the index's large peaks in the Annual Integral figure) have predominantly accounted for the familiar La Niña weather associations over North America (Chiodi and Harrison 2015a). The convection breaks tabulated by the index are associated with near-surface easterly wind surges that drive La Niña type sea surface temperature anomaly patterns when they occur in sufficient numbers over the tropical Pacific (Chiodi and Harrison 2015b). NOAA/PMEL hosts an El Niño theme page with further information on the tropical Pacific.

The Annual Integrals figure shows the number of convection-break days observed each year, starting from Northen Hemisphere spring. This year, the total has been updated through . The To date Integrals figure shows the number of convection break days observed up to this date each year. The Recent Activity figure plots the running-sum of convection break days since spring of .


Data source

The index is calculated using NOAA's OLR-Daily CDR , made available through the University of Maryland OLR CDR Portal, and is updated daily, subject to data availability (last update ).   get series (netcdf 352kB) » 

Calculation

The index tabulates the occurence of daily-averaged absolute OLR values greater than 267.5 W/m^2, averaged over the region 150°E - 180°, 5°S - 5°N, starting from April 1st of each year.

References

Chiodi, A. M. and D. E. Harrison, 2015: Global Seasonal Precipitation Anomalies Robustly Associated with El Niño and La Niña Events - An OLR perspective. J. Climate, 28, 6133-6159. doi:10.1175/JCLI-D-14-00387.1

Chiodi, A.M., and D.E. Harrison 2015: Equatorial Pacific easterly wind surges and the onset of La Niña events. J. Climate, 28(2), 776.792, doi: 10.1175/JCLI-D-14-00227.1

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