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Recent studies suggest that there are two types of El Nino events, which differ in terms of zonal distribution of sea-surface temperature (SST) anomalies. In this study, we investigate mechanisms in controlling simulation of two-types of El Nino using three different versions of the Seoul National University (SNU) air-sea coupled general circulation models. The occurrences of two types of El Nino are related to the simulated climatological SST over the eastern Pacific. It is found that a model with relatively less canonical (or frequent Warm Pool or Central Pacific) El Nino occurrence has colder cold tongue in the equatorial central Pacific. Due to the cold mean SST and associated dryness over the eastern Pacific, positive El Nino-related SST anomalies over the eastern Pacific cannot trigger local convection effectively. The eastern Pacific dryness leads to the confinement of anomalous convective activity in the western Pacific, which results in weak canonical El Nino and reduction in canonical El Nino occurrence. Instead, the confined convective activity in the western Pacific can lead to strong SST anomalies over western-central Pacific through local air-sea interaction, which can increase Warm Pool (WP) El Nino occurrence. In addition, we found that mean equatorial thermocline structure is also related to the occurrences of WP El Nino and canonical El Nino that is, a model with deep thermocline depth simulates less WP El Nino occurrence, consistent with Yeh et al. (2009) .

Previous analyses on the estimates of water vapor and cloud-related feedbacks in the tropics usually use observations over the Earth Radiation Budget Ex- periment (ERBE) period (1985-89). To examine the sam- ple dependence of previous estimates, the authors extend the analysis to two additional periods: 1990-94 and 1995-99. The results confirm our hypothesis, i.e., the values of the feedbacks depend on the period of data cov- erage. The differences in the feedbacks from cloud radia- tive forcings (CRFs) estimated from the three periods are particularly significant. Two possible causes for these differences are proposed. First, a regime behavior in the CRFs-Sea Surface Temperature Anomaly (SSTA) rela- tionship over the cold tongue region is revealed: when SSTA is below -0.5C, the CRF anomalies are insensitive to the SSTA; when the SSTA is between -0.5C and 2.0C, the CRF anomalies are positively correlated with the SSTA; however, when the SSTA exceeds 2.0C, the CRF anomalies decrease with the SSTA. This regime be- havior is due to the regime behavior of cirrostratus and deep convective clouds. Second, the CRFs-SSTA rela- tionship is regulated by remote forcings. Warming of the far eastern equatorial Pacific would reduce the water va- por convergence over the central Pacific by weakening the trade wind over the southeastern Pacific, thereby re- ducing the feeding of moisture to the convective flow. The results suggest that CRFs-SSTA relationships during ENSO events are nonlinear and strongly depend on the magnitude and the spatial distribution of the SSTA.

Recent reconstructions of Mg and Ca concentrations of seawater indicate that seawater Mg/Ca changed significantly over the last 5 million years (Ma). Tropical sea surface temperature (SST) records for the last 5 Ma based on foraminiferal Mg/Ca paleothermometry assume constant seawater Mg/Ca. These SST records suggest that average equatorial Pacific SSTs remained thermally stable from 5 to 2 Ma, after which significant cooling occurred only in the eastern equatorial Pacific. This study examines the implications of adjusting available equatorial Pacific SST records based on Mg/Ca paleothermometry to account for the inferred past variations of seawater Mg/Ca. The results suggest that both the cold and the warm regions of the equatorial Pacific were much warmer during the early Pliocene (30–31 °C), and that both regions experienced a marked cooling from ∼ 4 Ma to ∼ 1 Ma. This new interpretation of foraminiferal Mg/Ca creates a discrepancy with alkenone unsaturation-based SST records from the eastern equatorial Pacific, which might be due to either overestimation of changes in past seawater Mg/Ca or to factors affecting the interpretation of the U K' 37 index. The adjusted SST records are consistent with the hypothesis that higher levels of greenhouse gases maintained the warmth of the early Pliocene.

We use the hydrographic data obtained during the joint survey of the Yellow Sea by the First Institute of Oceanography, China and the Korea Ocean Research and Development Institute, Korea, to quantify the spatial structures and temporal evolution of the southern Yellow Sea Cold Water Mass (YSCWM). It is indicated that the southern YSCWM is a water mass that develops in summer and decays in fall. In winter, due to the intrusion of the Yellow Sea Warm Current (YSWC), the central area (approximately between 34 degrees N and 35 degrees N, 122 degrees E and 124 degrees E) of the Yellow Sea is mainly occupied by relatively high temperature water (T > 10 degrees C). By contrast, from early summer to fall, under the seasonal thermocline, the central area of Yellow Sea is occupied by cold water (T < 10 degrees C). In summer, the southern YSCWM has two cold cores. One is formed locally southeast of Shandong Peninsula, and the other one has a tongue-like feature occupying the area approximately between 34 degrees N and 37 degrees N, 123 degrees E and 126 degrees E. The bottom layer temperature anomalies from February to July in the cold tongue region, along with the trajectories of the bottom floaters, suggest that the cold water mass in the northeast region has a displacement from the north to the central area of the Yellow Sea during the summer. (c) 2007 Elsevier Ltd. All rights reserved.