In this case we are looking at temperature anomalies. T-bar is the mean temperature, T' is the temperature anomaly and when added together, one gets T which is the observed temperature.
Some Lecture Links:
Hi, Mappers. . . The attached PDF illustrates the growing impacts of the oceanic Kelvin wave. Each slide is a daily realization of 5-day mean subsurface ocean temperature (top) and ocean temperature anomalies (bottom). Paging through the slides from the start demonstrates pronounced eastward propagation. The wave had its earliest origins in an MJO-related westerly wind burst more than a month ago over the West Pacific, but has been forced since by repeated westerly wind burst activity that has migrated eastward with the wave.
Note the upward sloping region of concentrated isotherms in the East Pacific, and some near vertical isotherms. This region of concentrated isotherms constitutes an upward sloping thermocline. The Kelvin wave is predominantly a disturbance of that thermocline. Since the thermocline slopes upward, the wave will be forced to shoal, or propagate upward, much like a gravity wave propagating upward toward a shoreline. Similar to that wave on the shore, this wave is likely to break as it shoals. Instead of breaking above the ocean surface as a coastal wave, however, it would break by pushing the east Pacific thermocline downward and by pulling a few of the nearly vertical isotherms eastward. It might even pull the 25-26 degree isotherms to the Galopagos.
Recently in Roundy and Kravitz (2009, J. Climate), we showed that Kelvin waves that are associated with westerly local wind anomalies over the eastern equatorial Pacific are associated with adjustment toward El Nino, whereas Kelvin waves that approach the East Pacific when the local intraseasonal wind anomalies are easterly attenuate and are not associated with surface warming. I mention this association because several wave modes of the tropical atmosphere appear to be coming together over the next couple of weeks to enhance westerly anomalies over the right region to support El Nino growth. The GFS agrees with this scenario (although it frequently handles modes of large scale organized tropical convection poorly).
Should these near-equatorial westerly anomalies develop as suggested along the trajectory of the Kelvin wave, subsurface ocean temperature anomalies are likely to reach 5-7C over the next 3 weeks. Surface tempature anomalies will likely temporarily reach +2C, before declining somewhat to between 1.25 and 2C across the equatorial E. Pacific west of the Gallopagos.
In any case, this makes for the prospect of an interesting winter!
Paul Roundy
