On the structure and evolution of ENSO‐related climate variability in the tropical Pacific: Lessons from TOGA

Abstract

Improved observations in the tropical Pacific during the Tropical Ocean‐Global Atmosphere (TOGA) program have served to corroborate preexisting notions concerning the seasonally dependent relationships between sea surface temperature, sea level pressure, wind stress, rainfall, upper tropospheric circulation, and ocean thermal structure anomalies in the El Niño‐Southern Oscillation (ENSO) phenomenon. However, the paradigm of a quasiperiodic “ENSO cycle,” phase locked with the annual march, does not capture the complexity of the evolution of the anomalies. The inadequacy of this model was particularly apparent during the second half of TOGA when the variability was highly aperiodic. Also, a single modal structure or empirical orthogonal function does not appear to be capable of representing the range of spatial patterns of ocean‐atmosphere interaction in the tropical Pacific. These results suggest the need for a more inclusive phenomenological description of ENSO. Data collected during TOGA serve to confirm the influence of tropical Atlantic sea surface temperature anomalies upon rainfall in northeast Brazil.

Multidecadal and interannual changes of stationary Rossby waves

“…Further, during the 1960s and 1970s, positive SST anomalies expanded westward, from the South American coast into the central equatorial Pacific. After 1980, positive SST anomalies propagated eastward across the basin, from the central Pacific, or developed concurrently in the central and eastern Pacific (Wallace et al, 1998). These changes in El Niño-Southern Oscillation (ENSO) properties are nearly synchronized with the decadal climate shift in the extratropical Pacific Ocean; specifically, an abrupt change in SST and large-scale winter circulation over the North Pacific, observed in the mid 1970s (Wang and An, 2001).…”

Intercomparison of global cloud cover fields over oceans from the VOS observations and NCEP/NCAR reanalysis

“…Larger SST anomalies during the positive ENSO phase in the eastern tropical Pacific reduce the zonal SST gradient and thus may weaken the Walker circulation, which in turn reduces the convectively driven cloudiness above the Pacific warm pool. Detailed analysis of the mechanisms of global and regional associations between ENSO and cloudiness is provided by Park and Leovy (2004) and Wallace et al (1998). In order to assess how the ENSO mode is represented in the total cloud cover anomalies in different data sets, we computed the EOFs of the boreal winter (JFM) cloud cover in the tropical Pacific (20°S-20°N) from the three products in the same manner as it was done for the North Atlantic.…”

The very strong coastal El Niño in 1925 in the far-eastern Pacific

“…Although the 1925-26 EN was relatively well documented at the time, some of the ideas that appeared well justified at the time, particularly the role of northerly winds (Schott 1931), have been discarded in the subsequent years with the establishment of the ENSO paradigm in the 1970s and 1980s (Wyrtki 1975;Wallace et al 1998;Neelin et al 1998), but without taking a close look at the 1925 EN. Thus, it is timely to revisit the 1925-26 EN in an integrated way, under the light of modern theory and expanded datasets, to recover potentially valuable information and insights on the nature of EN and its diversity.…”