Figure 1 presents a schematic of the components given in the vertically integrated energy budget of the atmosphere, along with simplified equations. Figures 2 and 3 present summary results of the total divergent energy transport and its divergence for two different Januaries, those of January 1989 (Fig. 2) and January 1998 (Fig. 3) based on the NCEP/NCAR reanalyses. The bottom panel shows the actual vectors of the vertically integrated transport and its potential function, while the top panel shows the divergence in W m-2. Because the changes in the top of the atmosphere fluxes are of the order of 10 W m-2, most of this field relates to the net fluxes at the surface out of the ocean. Similar results are obtained for the ECMWF reanalyses.
These two months are chosen because they occur at times of the peak in the most recent El Niño event (Fig. 3) and the last major La Niño in 1988-89 (Fig. 2). Therefore, comparing the tropical Pacific, we find that in 1989, when there was a strong cold dry tongue in the tropical eastern Pacific, the net flux is over 150 W m-2 into the ocean as the clear skies allow solar radiation to heat the ocean. In contrast, in 1998, under mature El Niño conditions the flux is mostly out of the ocean into the atmosphere, and this is no doubt a reason for the cooling of the ocean observed throughout this period and the record warmth seen in the global surface temperatures. The Pacific-North American (PNA) teleconnection pattern in the northern extratropics also reversed between these months. A strong negative PNA in January 1989 led to sea level pressure anomalies exceeding +18 mb at 45N in the Pacific in contrast to a deep Aleutian low with a sea level pressure anomaly of -10 mb in January 1998. The huge differences in the surface fluxes (Figs. 2 and 3) over the Kuroshio extension region are a direct consequence of this.
Also of note in these two figures is the contrast in the Labrador Sea, where a strong positive North Atlantic Oscillation (NAO) in January 1989 led to cold outbreaks over the northeast of Canada and Greenland, and over 250 W m-2 fluxes out of the ocean compared with a flux into the ocean in the same region in January 1998, when the NAO was weak.
Overall, the patterns seen here are reasonable: this is the northern winter when heat preferably goes into the southern oceans and out of the northern oceans, following the sun, and the main atmospheric transports are into the northern hemisphere. There is a strong land-sea contrast, as expected. Just a few weird features how up, such as positive values over parts of the southern oceans or Antarctica that are not reproducible and clearly relate to quality of the analyses. Results for other months will be presented.
This approach provides promise of better defining the atmosphere and ocean heat transports and the surface fluxes in a physically consistent framework. Prospects for determining the net diabatic heating associated with El Niño events are likely to lead to a paradigm change in how El Niño works and in defining its role in the global climate system.