Prelude to El Niño early in summer 2009

Lively Data, July 17, 2009

Maps of merged SLA (in cm) in the equatorial Pacific Ocean, on June 15, 2009.
Zonal component of geostrophic current, called U (in cm/s) in the equatorial Pacific Ocean, on June 15, 2009. To create this map with the LAS, choose NRT, Global, (Maps of) Geostrophic Velocity Anomalies, and the variable U (Zonal Velocity (cm/s)). Select the geographic area Equatorial Pacific. To overlay colors and lines, select Color filled and lines in the Options Contour style. The colors are defined in Color filled levels (-70,70,10)(85) and lines in Contour levels : 10C.

While current observations indicate El Niño conditions are increasing across the equatorial Pacific Ocean, a quick look with the LAS on recent Sea Level Anomalies evolutions confirms that El Niño conditions are present.

The latest map of NRT Sea Level shows positive anomalies in the western Pacific Ocean and in the Niño 3.4 region (170°W-120°W, 5°S-5°N).

A previous Lively Data (La Niña, westerly current, Jan. 22, 2008) showed that the zonal component of geostrophic current (U) is marked by positive values during El Niño episode, describing easterly current. It's currently also the case, even early in the evolution of an ENSO event.

Merged sea level anomalies Hovmoller diagram over the equatorial Pacific, from June 2008 to June 15, 2009, at 4.9°N. To plot such diagram, choose your variable NRT Global - (Maps of) Sea Level Anomalies Merged, select Longitude-time Hofmoeller (xt) in Select view, choose a latitude and interesting longitudes. Then, you can choose a period.

A previous Lively Data (Rossby waves in ENSO events, May 15, 2008) described the importance of equatorial Rossby waves in the mechanisms of the ENSO phenomenon, having a key role in recharge of the equatorial band in warm water before an ENSO event.

Further information: