Sang‐Wook Yeh

Abstract El Niño and Southern Oscillation (ENSO) is the most prominent year‐to‐year climate fluctuation on Earth, alternating between anomalously warm (El Niño) and cold (La Niña) sea surface temperature (SST) conditions in the tropical Pacific. ENSO exerts its impacts on remote regions of the globe through atmospheric teleconnections, affecting extreme weather events worldwide. However, these teleconnections are inherently nonlinear and sensitive to ENSO SST anomaly patterns and amplitudes. In

[1] There is an evidence of the increasing intensity as well as occurrence frequency of the so-called central Pacific (CP) El Niño events since the 1990s. We examine whether such an increase in the frequency of CP El Niño may be a manifestation of natural climate variability. A control simulation of the Kiel Climate Model, run for 4200 years with the present values of greenhouse gases, exhibit large variations of the occurrence frequency of the CP El Niño versus the eastern Pacific (EP) El Niño.

Abstract This study examined connections between the North Pacific climate variability and occurrence of the central Pacific (CP) El Niño for the period from 1950 to 2012. A composite analysis indicated that the relationship between the North Pacific sea surface temperature (SST), along with its overlying atmospheric circulation, and the CP El Niño during the developing and mature phases was changed when the occurrence frequency of the CP El Niño significantly increased after 1990. Empirical ort

Abstract This paper examines characteristic changes in North Pacific sea surface temperature (SST) variability during the boreal winter (December–February) for two subperiods (1956–88 and 1977–2009) during which the 1976/77 and the 1988/89 climate transitions occurred. It is found that the Pacific decadal oscillation (PDO)-like SST variability plays a dominant role in the 1976/77 climate transition, while both the North Pacific Gyre Oscillation (NPGO)-like and PDO-like SST variability contribute

This study assesses the changes in the tropical Pacific Ocean sea surface temperature (SST) trend and ENSO amplitude by comparing a historical run of the World Climate Research Programme Coupled Model Intercomparison Project (CMIP) phase-5 multimodel ensemble dataset (CMIP5) and the CMIP phase-3 dataset (CMIP3). The results indicate that the magnitude of the SST trend in the tropical Pacific basin has been significantly reduced from CMIP3 to CMIP5, which may be associated with the overestimation

Connections between decadal changes in the tropical Pacific mean state and El Niño–Southern Oscillation (ENSO) decadal modulation are examined using three runs of a coupled general circulation model (CGCM). The differences between the three simulations, i.e., a standard coupled model (one AGCM is coupled to a single OGCM) and two interactive ensemble models (six or twelve AGCMs are coupled to a single OGCM), are confined to the amplitude of internal atmospheric variability. All three simulations

Abstract It is important to understand the dynamical processes that cause heat waves at regional scales. This study examined the physical mechanism that was responsible for a heat wave in South Korea in August 2016. Unlike previous August heat waves over the Korean Peninsula, the intensity of the geopotential height over the Kamchatka Peninsula in August 2016 was the strongest since 1979, which acted as an atmospheric blocking in the downstream region of the Korean Peninsula. Therefore, the anom

Connections between Pacific decadal variability (PDV) and low‐frequency modulation of El Niño and Southern Oscillation (ENSO) amplitude are analyzed using observed sea surface temperature (SST) during 1900–2001. The variability of the first two Empirical Orthogonal Functions (EOFs) of PDV, i.e., the PDV1 and PDV2, are compared to decadal variations of ENSO amplitude. The PDV1, which is called the Pacific decadal oscillation or decadal ENSO‐like variability, is not related to the modulation of EN

Abstract Four climate system models are chosen here for an analysis of ENSO amplitude changes in 4 × CO2 climate change projections. Despite the large changes in the tropical Pacific mean state, the changes in ENSO amplitude are highly model dependant. To investigate why similar mean state changes lead to very different ENSO amplitude changes, the characteristics of sea surface temperature anomaly (SSTA) variability simulated in two coupled general circulation models (CGCMs) are analyzed: the Me

Abstract The North Pacific Oscillation (NPO), which is characterized by a north‐south dipole‐like pattern of sea level pressure (SLP) in the North Pacific, is an atmospheric circulation that is a key to understanding tropical‐extratropical interactions in the Pacific. We show that the center of the southern lobe SLP in the NPO during boreal winter (December‐January‐February) is shifted to the east after the mid‐1990s compared to before the mid‐1990s. This leads to the change in the relationship

Abstract This study analyzes differences in the mechanisms leading to anomalously high‐temperature weather events, such as heat waves and tropical nights, in Korea. We identify pure heat wave and pure tropical night events during the period from 1979 to 2016. Based on composite analyses for each case, we identify different mechanisms leading to pure heat waves and pure tropical nights. The structures including low‐level atmospheric circulations, specific humidity, wind, and the atmospheric stabi