| 1. |
Influence of El Nino on Winter Climate of Japan
Influence of the ENSO (El Niño/Southern Oscillation) on East Asian winter monsoon is examined. It is widely accepted that the El Niño tends to bring warm climate in December-January-February (DJF) winter season in Japan. However, our study reveal that in the DJF-averaged fields the ENSO has little impact on the near-surface temperature anomalies there. In particular, near-surface temperature anomaly fields in the late winter show neutral signals. Simultaneously, the Pacific-Northern American (PNA) pattern is dominant in the upper troposphere while no strong signals are found near Japan. In contrast, in the early winter, the WP pattern with positive phase are dominant so that winter tends to be warm in Western Japan. The opposite is true for La Niña. Dynamical mechanisms of such seasonal evolutions in the upper-level height field from early winter to late winter are not yet clarified yet and thus remain for future work.. |
| 2. |
Tropical Sea Surface Temperature Anomaly and the Winter Climate of Japan during ENSO
In the Far East, El Niño (La Niña) typically brings warm (cold) winter. However, significantENSO events have the opposite tendencies. To understand the cause of the disparate mid-latituderesponses, composite analysis has been conducted using long-term reanalysis dataset to find the seasurface temperature (SST) in the Pacific Ocean and the atmospheric responses corresponding to warm orcold winter in the Far East. Our analysis shows that about 70% of all ENSO are classified as the typicalwarm and about 30% as the atypical events. A Western Pacific (WP)-like meridional dipole patternappears in the typical events. Surprisingly, Pacific/North American (PNA) pattern, which is a remarkablefeature during ENSO, is obscure during the typical events. In fact, PNA pattern dominates during atypicalevents, with large amplitude. In addition, SST distributions differ in the west Pacific Ocean. During thetypical events, the amplitude of SST anomaly in the Philippine sea is large. In contrast to it, the anomalyis not clear in the atypical events. This SST anomaly in the west Pacific Ocean may cause atmosphericresponses in the mid-latitude consistent with the winter climate in the Far East during ENSO.. |
| 3. |
The Relationship between Upper-level Atmospheric Responses and Japanese Winter Climate during El Nino
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% (67%) of all El Niño (La Niña) events are classified as typical warm (cold) winter around Japan and about 37% (33%) 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.. |
| 4. |
The Mid-latitude Responses Categorized by the Winter Climate in the Far East during El Nino
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% of El Niño events occurred from1948 are classified as the warm and about 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.. |
| 5. |
WP/PNAインデックスと熱帯海面水温偏差との関係. |
| 6. |
極東域におけるEl Ninoの冬季気候への影響. |
| 7. |
Influence of El Nino on Winter Climate of Japan. |
| 8. |
Tropical Sea Surface Temperature Anomaly and the Winter Climate of Japan during ENSO. |
| 9. |
ENSOと極東域の寒暖との関係. |
| 10. |
The Relationship between Upper‐level Atmospheric Responses and Japanese Winter Climate during El Nino. |
| 11. |
NINO.3インデックスと日本付近における冬の寒暖との関係. |
| 12. |
El Nino時における冬季極東域への異なる影響に対応する熱帯太平洋・インド洋SST偏差パターン. |
| 13. |
The Mid‐latitude Responses Categorized by the Winter Climate in the Far East during El Nino. |
