Language：English   Publishing type：Research paper (scientific journal)  

Abstract

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.

DOI： 10.1175/jcli-d-23-0627.1

Language：English   Publishing type：Research paper (scientific journal)  

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.

DOI： 10.1175/JCLI-D-23-0627.1

Repository Public URL： https://hdl.handle.net/2324/7179494

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.2151/sola.2021-016

Repository Public URL： https://hdl.handle.net/2324/7232580

Language：English   Publishing type：Research paper (scientific journal)  

<jats:title>Abstract</jats:title><jats:p>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.</jats:p>

DOI： 10.1175/jcli-d-20-0246.1

Language：English   Publishing type：Research paper (scientific journal)  

<p> 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.</p>

DOI： 10.2151/sola.2020-003

Event date： 2023.4

Language：English  

Country：Other  

Event date： 2022.5

Language：English  

Country：Other  

Event date： 2021.5 - 2021.6

Language：English  

Country：Other  

Event date： 2020.2

Language：English  

Country：Other  

Event date： 2023.12

Language：Japanese  

Country：Other  

Language：Japanese  

Language：Japanese  

It is well-known that El Niño typically brings warm winter in the Far East and that Western Pacific (WP) and Pacific/North American (PNA) often appear. However, significant events have opposite tendencies. To understand the cause of the difference, composite analysis has been conducted using long-term reanalysis datasets. Our analysis shows that about 63&#37; of El Niño events occurred from1948 are classified as the warm and about 37&#37; as the cold events. Furthermore, the WP and PNA seem to be mutually exclusive and are dominant during warm and cold winters, respectively. The SST anomaly in the Philippine Sea is negative more than that during cold winter. The SST anomaly distribution is corresponding to the Walker circulation anomaly. These differences are appeared from the fall and developed to the winter. Therefore, it is suggested that the disparate mid-latitude responses are associated with SST and the Walker circulation variations in the western Pacific Ocean.

Language：Japanese  

Language：Japanese  

In the Far East, El Niño (La Niña) typically brings warm (cold) winter via the teleconnections excited by the anomalous sea surface temperature (SST) in the tropics. Some ENSO events, however, have the opposite tendencies. To understand the mechanisms of the disparate mid-latitude responses during ENSO, composite analysis has been conducted using long-term reanalysis dataset. Our analysis shows that about 63&#37; (67&#37;) of all El Niño (La Niña) events are classified as typical warm (cold) winter around Japan and about 37&#37; (33&#37;) as atypical events. A Western Pacific (WP)-like pattern appears in typical events. Surprisingly, the Pacific/North American (PNA) pattern, which is a well-known feature during ENSO, is obscure during typical events. In fact, the PNA pattern dominates during atypical events with large amplitudes. In addition, SST distributions differ not only in the eastern Pacific Ocean but also in the western Pacific Ocean. These SST anomalies seem to cause differences divergence wind anomalies to cause different atmospheric responses in the mid-latitudes during ENSO.

Language：Japanese