Deciphering characteristics of Central and Eastern Pacific ENSOs from the amplitude-modulated seasonal cycles.
Abstract
The qualitative and quantitative definitions of ENSO continued to challenge climate scientists, particularly so in the warming world. The signals of ENSO extracted in the previous studies, with a few exceptions, are based on the anomalies with respect to a long-term mean annual cycle: an approach that has been ignoring the need to account for the year-to-year changes in amplitudes of leading seasonal modes. Therefore, it is hard to assess the roles of individual modes modulations from the traditional anomalies. A few leading seasonal modes of climate variables are extracted via a diagnostic strategy that allows dynamically consistent interannual amplitude-modulations among five key variables. We show that all warm/cold event-types in the Pacific are the abnormal modulations of two seasonal modes of SST, having their significant variances in the Eastern and Central Pacific (EP and CP), respectively. When the positive amplitude-modulations are large enough to merge two consecutive positive phases of the EP-Mode of SST, a strong or an extreme El Nino occurs. The absence of such mergers during the negative amplitude-modulations contributes significantly to the positive skewness of EP SST anomalies. We also show that the CP-ENSO and Pacific Meridional Mode are manifestations of the CP-modes' interannual amplitude changes. Thus, this disentanglement of low-frequency variability of different dynamical origins has brought more clarity in the warm/cold event's identifications and their co-varying spatio-temporal characteristics. The lack of secular trends in both CP and EP SST-modes and the absence of any systematic decadal changes in their zonal propagation characteristics challenge the notion of changing ENSO in a warming world- an ongoing scientific concern. An overriding insight culled from these analyses is that the same sets of physical and dynamical processes drive the seasonal cycles and ENSO.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFM.A23E..02K