Indian Ocean impact on ENSO evolution 2014-2016 in a set of seasonal forecasting experiments

Autor(en)

Michael Mayer, Magdalena Alonso-Balmaseda

Abstrakt

This study investigates the influence of the anomalously warm Indian Ocean state on the unprecedentedly weak Indonesian Throughflow (ITF) and the unexpected evolution of El Niño-Southern Oscillation (ENSO) during 2014–2016. It uses 25-month-long coupled twin forecast experiments with modified Indian Ocean initial conditions sampling observed decadal variations. An unperturbed experiment initialized in Feb 2014 forecasts moderately warm ENSO conditions in year 1 and year 2 and an anomalously weak ITF throughout, which acts to keep tropical Pacific ocean heat content (OHC) anomalously high. Changing only the Indian Ocean to cooler 1997 conditions substantially alters the 2-year forecast of Tropical Pacific conditions. Differences include (i) increased probability of strong El Niño in 2014 and La Niña in 2015, (ii) significantly increased ITF transports and (iii), as a consequence, stronger Pacific ocean heat divergence and thus a reduction of Pacific OHC over the two years. The Indian Ocean’s impact in year 1 is via the atmospheric bridge arising from altered Indian Ocean Dipole conditions. Effects of altered ITF and associated ocean heat divergence (oceanic tunnel) become apparent by year 2, including modified ENSO probabilities and Tropical Pacific OHC. A mirrored twin experiment starting from unperturbed 1997 conditions and several sensitivity experiments corroborate these findings. This work demonstrates the importance of the Indian Ocean’s decadal variations on ENSO and highlights the previously underappreciated role of the oceanic tunnel. Results also indicate that, given the physical links between year-to-year ENSO variations, 2-year-long forecasts can provide additional guidance for interpretation of forecasted year-1 ENSO probabilities.

Organisation(en)

Institut für Meteorologie und Geophysik

Externe Organisation(en)

European Centre for Medium-Range Weather Forecasts (ECMWF)

Journal

Climate Dynamics

Band

56

Seiten

2631–2649

Anzahl der Seiten

19

ISSN

0930-7575

DOI

https://doi.org/10.1007/s00382-020-05607-6

Publikationsdatum

2020

Peer-reviewed

Ja

ÖFOS 2012

105206 Meteorologie

ASJC Scopus Sachgebiete

Atmospheric Science

Link zum Portal

https://ucrisportal.univie.ac.at/de/publications/indian-ocean-impact-on-enso-evolution-20142016-in-a-set-of-seasonal-forecasting-experiments(ba6b7ee0-c30c-44cb-8044-6c9bc9363d21).html