The University of Tokyo · Environmental Science
Professor Tomoki Iwakiri's research lab specializes in climate dynamics, with a primary focus on the mechanisms and predictability of interannual climate variability, particularly the El Niño–Southern Oscillation (ENSO) and its multi-year variants. The lab investigates the physical processes underlying persistent La Niña events, the role of atmospheric and oceanic feedbacks, and the impacts of external forcings such as insolation changes on climate systems. Using a combination of observational data, reanalysis, and advanced climate model simulations—including large ensemble forecasts and CMIP6 models—the lab aims to improve understanding of ENSO dynamics and teleconnections, especially over regions like Japan and the Indian Ocean. Their work also extends to paleoclimate modeling, exploring how past climate states, such as the mid-Holocene, influenced ENSO and the Indian Ocean Dipole.
Figures are computed from collected data and may differ slightly.
El Niño-Southern Oscillation (ENSO), characterized by anomalous sea surface temperature in the central-eastern equatorial Pacific, is a dominant interannual variability, impacting worldwide weather and socioeconomics. The ENSO cycle contains irregularity, in which La Niña often persists for more than two years, called "multi-year La Niña". Observational records show that multi-year La Niña tends to accompany strong El Niño in the preceding year, but their physical linkage remains unclear. Here w
Abstract La Niña persisted from 2020 to 2023, but its mechanisms are still unclear. In this study, atmosphere and ocean reanalysis and 100‐member initialized forecasts using a state‐of‐the‐art climate model were analyzed to identify factors contributing to the persistence of the first‐ to second‐year La Niña during 2020–2022. We found that North Pacific high pressure anomalies in the winter of 2020/2021 forced a negative phase of the Pacific meridional mode through the following spring, forming
La Niña is the negative phase of the El Niño-Southern Oscillation (ENSO) cycle. It occurs in the equatorial Pacific, and events known as multiyear La Niña often persists for more than two years. During a conventional La Niña event, the seasonal cycle of surface temperature over Japan is amplified (i.e., hotter summer and colder winter than normal years), but the influence of multiyear events on temperatures over Japan is unclear. In this study, we evaluate the teleconnection associated with mult
Abstract El Niño–Southern Oscillation (ENSO) events occasionally recur one after the other in the same polarity, called multiyear ENSO. However, the dynamical processes are not well understood. This study aims to elucidate the unified mechanisms of multiyear ENSO using observations, phase 6 of the Coupled Model Intercomparison Project (CMIP6) models, and the theoretical linear recharge oscillator (RO) model. We found that multiyear El Niño and La Niña events are roughly symmetric except for case
Abstract This study presents modeling evidence that the Indian Ocean Dipole (IOD) is enhanced in its frequency and amplitude under mid‐Holocene (8‐ka) conditions. This enhancement is identified in a global climate model simulation driven by the 8‐ka insolation, in which negative sea surface temperature anomalies grow more than the present‐day simulation in the eastern Indian Ocean. The mechanism of IOD amplification is explained in terms of a positive feedback among sea surface temperature, prec
Abstract Off‐equatorial wind stress curl anomalies that mainly drive geostrophic transport are essential for the phase transition of the El Niño‐Southern Oscillation (ENSO) induced by a recharge‐discharge process. The ENSO‐induced zonal wind stress anomaly also drives surface Ekman currents, which may counteract the geostrophic transport, but its effect on ENSO periodicity remains unclear in the recharge oscillator theory. Here, we extended an ENSO diagnostic framework, called the Bjerknes‐Wyrtk
Abstract Paleo proxy records have suggested that El Niño–Southern Oscillation (ENSO) variability during the mid-Holocene [8200 to 4200 years ago (8.2–4.2 ka)] was weaker than during the instrumental periods, but the mechanisms remain unclear. We examined processes of ENSO suppression using a coupled general circulation model (CGCM) that simulates ENSO amplitude and skewness under the present climate reasonably well. Two long simulations were performed: one using the preindustrial condition (CTRL
Removing CO<sub>2</sub> from the atmosphere is emerging as a viable strategy to mitigate global warming, yet the responses of the climate system to CO<sub>2</sub> reduction remain uncertain. One of the most uncertain aspects of El Niño behavior is the change in periodicity in response to CO<sub>2</sub> forcing [O. Alizadeh, <i>Earth-Sci. Rev.</i> <b>235</b>, 104246 (2022)]. In this study, we show that climate models consistently project an abrupt shortening of El Niño periodicity once CO<sub>2</
El Ni&#241;o&#8211;Southern Oscillation (ENSO) events occasionally recur one after the other in the same polarity, called multiyear ENSO. However, the dynamical processes are not well understood. This study aims to elucidate the unified mechanisms of multiyear ENSO using observations, CMIP6 models, and the theoretical linear recharge oscillator (RO) model. We found that multiyear El Ni&#241;o and La Ni&#241;a events are roughly symmetric except in some cases. The composite multiy
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