| 1. |
Masahiro Shiozaki, Hiroki Tokinaga, Masato Mori, What Determines the East Asian Winter Temperature during El Niño? — Role of the Early-Onset El Niño and Tropical Indian Ocean Warming, Journal of Climate, 10.1175/JCLI-D-23-0627.1, 2024.04, Atmospheric teleconnections from the Pacific El Niño are key to determining the East Asian winter climate. Using the database for Policy Decision-making for Future climate change (d4PDF) large ensemble simulations, the present study investigates a mechanism for the warm and cold East Asian winters during El Niño with a focus on atmospheric teleconnections triggered by anomalous sea surface temperature (SST) patterns in the tropical Indo-Pacific. Our results show that the Western Pacific (WP) teleconnection pattern plays a primary role in the warm winters in East Asia. The WP pattern tends to appear in years when both an early El Niño and the positive phase of the Indian Ocean dipole mode (IOD) develop in boreal autumn. In those years, the tropical Indian Ocean (TIO) strongly warms in the following winter, forming a distinct zonal contrast in precipitation anomalies over the tropical Indo-Pacific through a reduced Walker circulation. The Rossby wave source anomalies indicate that the WP pattern is associated with the weakened Indo-Pacific Walker circulation. By contrast, the WP pattern does not dominate in the cold winters due to the absence of strong TIO warming. The present study proposes a mechanism that promotes excitation of the WP pattern through the upper-troposphere divergence in East Asia associated with the Walker circulation modulated by the tropical Indo-Pacific interbasin interaction.. |
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Masahiro Shiozaki, Takeshi Enomoto, Two Types of Mid-Latitudes Responses during La Niña, SOLA, 10.2151/sola.2021-016, 17, 0, 103-108, 2021.05. |
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Masahiro Shiozaki, Takeshi Enomoto, Koutarou Takaya, Disparate Midlatitude Responses to the Eastern Pacific El Niño, Journal of Climate, 10.1175/jcli-d-20-0246.1, 34, 2, 773-786, 2021.01, Abstract To investigate the disparate influences of the eastern Pacific (EP) El Niño on the winter climate in the Far East, we conducted composite analyses using long-term reanalysis datasets. Our analysis shows that the western Pacific (WP) pattern dominates in the warm winter (typical) composite and the Pacific–North American (PNA) pattern dominates in the non-warm winter (atypical) composite. In the warm winter case, the amplitudes of the negative sea surface temperature (SST) anomalies in the western Pacific Ocean are large whereas in the non-warm winter case, these amplitudes are small. In addition, the Indian Ocean basin warming occurs following the Indian Ocean dipole mode, as seen in the warm winter composite. We investigated the dynamical mechanisms responsible for the disparate midlatitude responses to the EP El Niño by focusing on Rossby wave sources and propagation. These SST anomalies modulate the Walker and Hadley circulations and the convective activity in the western Pacific Ocean. Upper-tropospheric divergences at the midlatitudes due to the anomalous Hadley circulation result in different teleconnection patterns. In the warm winter composite, the anticyclonic anomaly in the southern part of the WP pattern is created by the upstream negative Rossby wave source, while the other cyclonic anomaly is reinforced by the northward Rossby wave propagation. The cyclonic second and fourth centers of action of the PNA pattern are created by the positive Rossby wave sources. Furthermore, the equatorial SST gradient near the date line is found be a good precursor of the winter climate in the Far East. . |
| 4. |
Shiozaki Masahrio, Enomoto Takeshi, Comparison of the 2015/16 El Niño with the two previous strongest events, SOLA, 10.2151/sola.2020-003, 16, 12-16, 2020.01, The 2015/16 El Niño is compared with the two previous strongest events, the 1982/83 and 1997/98 El Niño. The 2015/16 winter features a basin warming in the Indian Ocean, a negative sea surface temperature (SST) anomaly shifted to the north in the western Pacific Ocean in addition to a positive SST anomaly shifted to the west in the eastern Pacific Ocean. These SST distributions lead to suppressed convection in the Maritime Continent, and to a weakened Hadley circulation in the western Pacific Ocean. The eastern Asian monsoon in the 2015/16 winter was also weakened due to the dominance of the western Pacific (WP) pattern. On the other hand, the third and fourth centers of action of Pacific/North American (PNA) pattern in the 2015/16 case are obscure. This may be due to weak divergence in the eastern Pacific Ocean. . |
