Is El Niño Changing?

Abstract

Recent advances in observational and theoretical studies of El Nino have shed light on controversies concerning the possible effect of global warming on this phenomenon over the past few decades and in the future. El Nino is now understood to be one phase of a natural mode of oscillation-La Nina is the complementary phase-that results from unstable interactions between the tropical Pacific Ocean and the atmosphere. Random disturbances maintain this neutrally stable mode, whose properties depend on the background (time-averaged) climate state. Apparent changes in the properties of El Nino could reflect the importance of random disturbances, but they could also be a consequence of decadal variations of the background state. The possibility that global warming is affecting those variations cannot be excluded.

Decadal variability of the Indian Ocean dipole

“…T. Tozuka et al (personal communication, 2004) have recently suggested that decadal asymmetric occurrence of positive and negative IOD events may lead us to a decadal I OD-like picture because of linear statistical analysis methods. Such simulated association between the asymmetric interannual fluctuations of SST over the western pole of the IOD and its decadal component is presented in Figure 4b as an examp le (methodology similar to Figure 1a of Federov and Philander [2000] except that apart from the remova l of seasonal cycle and high frequency components, multidecadal and centenni al signals also have been removed) . The prospective role of the occurrence of asymmetric interannual events in such '' deca dal regime shifts '' i s a topic that has to be explored further.…”

Development of a four‐dimensional variational coupled data assimilation system for enhanced analysis and prediction of seasonal to interannual climate variations

“…The reason for this is that previous studies [e.g., Fedorov and Philander, 2000] suggested that the basic state of a coupled ocean-atmosphere field might be regulated by subsurface temperature in the upper ocean, which plays an essential role in air-sea interactions that develop on timescales equal to or longer than intraseasonal changes. A similar approach has already been attempted by Lee et al [2000] who used the drag coefficient and a Newtonian damping coefficient as control variables using a 4D-VAR CDA scheme, though they employed an intermediate model.…”

Why the properties of El Niño changed during the late 1970s

“…The propagation of SST anomalies is primarily determined by competitive effects between the vertical temperature advection, which promotes eastward propagation and the zonal temperature advection, which induces westward propagation [Fedorov and Philander, 2000]. From the pre-to the post-shift periods, the vertical advection plays a more important role than the zonal advection, thus prevailing westward propagation was replaced by stationary or eastward propagation.…”

“…The decadal changes in the vertical advection can be attributed to the mean thermocline depth change or the mean upwelling change [An and Jin, 2000]. Fedorov and Philander [2000] stressed the effect of changing the mean thermocline, whereas here we emphasize the effect of changing the mean upwelling.…”