A Madden‐Julian Oscillation event remotely accelerates ocean upwelling to abruptly terminate the 1997/1998 super El Niño

Abstract

The termination of the superintense 1997/1998 El Niño was extraordinarily abrupt. The May 1998 Madden‐Julian Oscillation (MJO), a massive complex of stormy tropical clouds, is among possible contributors to the abrupt termination. Despite having been sensationally proposed 18 years ago, the role of the MJO remained controversial and speculative because of the difficulty of sufficiently simulating the El Niño and MJO simultaneously. An ensemble simulation series using a newly developed, fully ocean‐coupled version of a global cloud system resolving numerical model replicated the specific atmosphere and ocean conditions of May 1998 in unprecedented detail, extending the prediction skill of the MJO to 46 days. Simulation ensemble members with stronger MJO activities over the Maritime Continent experienced quicker sea surface temperature drop in the eastern Pacific, confirming that the easterly winds associated with the remote MJO accelerated ocean upwelling to abruptly terminate the El Niño.

Global Cloud-Resolving Models

“…For instance, simulations with 3.5, 7, and 14 km mesh show similar multiscale structure of convective systems embedded in super-cloud clusters or MJOs [64,65,70]. Hence, this multiresolution approach is proving to be a popular way to accelerate GCRM studies and enabling the use of NICAM over multi-decadal timescales [71][72][73], for larger ensemble simulations [74,75], for collaborative studies with Earth observations [28,76,77], and to explore the impact of increased complexity of physics schemes and coupling to other ocean and land models [78].…”

“…In the case of NICAM, the coupled model NICOCO, albeit at coarser resolution, has been used to investigate an MJO effect on ENSO [78]. Next-generation models will fully resolve both the atmosphere and ocean mesoscale and improve the physical foundation for climate prediction.…”

NICAM Predictability of the Monsoon Gyre over the Western North Pacific during August 2016

“…Cumulus parameterization was switched off and cloud processes were explicitly calculated using the NICAM Single-moment Water 6 (NSW6) cloud microphysics method (Tomita 2008). Although the 14 km mesh size is relatively coarser than that of typical cloud-resolving models without a cumulus para meterization scheme, our model effectively captures large-scale convective organization in the tropics, including MJOs, as described by Miyakawa et al (2014Miyakawa et al ( , 2017, Miura et al (2007), Kodama et al (2015), and Satoh et al (2017). We used the mstrnX-AR5 radiation transfer scheme (Sekiguchi and Nakajima 2008).…”

Coupling library Jcup3: its philosophy and application

“…The tripolar grid has an irregular grid shape, such that the North pole is stretched to the North American and Eurasian continents. In fact, a study using the NICAM-COCO coupled model with Jcup has already been conducted by Miyakawa et al (2017). In this way, both NICAM and COCO are irregular gridsystem models covering a spherical surface, and a large number of calculations are required to determine the grid point correspondence and interpolation coefficients necessary for coupling.…”