2001 Fiscal Year Final Research Report Summary
A STUDY OFTHE INTERACTION BETWEEN THEASIAN SUMMER MONSOONAND EL NINO-SOUTHERN OSCILLATION
| Project/Area Number |
11640430
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Meteorology/Physical oceanography/Hydrology
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| Research Institution | TOYAMA UNIVERSITY |
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Principal Investigator |
KAWAMURA Ryuichi TOYAMA UNIVERSITY, FACULTY OF SCIENCE, ASSOCIATE PROFESSOR, 理学部, 助教授 (30303209)
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| Project Period (FY) |
1999 – 2001
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| Keywords | MONSOON / ENSO / EL NINO |
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| Research Abstract |
Using an ocean general circulation model (OGCM) and NCEP/NCAR reanalysis, we obtained two major impacts (i.e., ES and EA impacts) of El Nino-Southern Oscillation (ENSO) on the South Asian summer monsoon interannual variability. The ES impact, which is dominated by TBO-like ENSO in the Indian Ocean and the Pacific Ocean, tends to prevail during the period from the 1960s to mid-1970s. Eastward migration of anomalous Walker circulation relevant to the growth of ENSO can be seen over the tropical Indian Ocean. Associated with this is the prominence of zonally asymmetric SST anomalies between the western and eastern parts of the Indian Ocean in late summer. Low-level twins anomalous circulation across the equator is induced over the Indian Ocean from summer to fall and its northern counterpart is dynamically linked with anomalous monsoon rainfall over India especially in late summer. If the TBO-like ENSO regime has a precise biennial periodicity, the summer monsoon season always corresponds
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to the growth phase of ENSO, which means that the monsoon is always affected by the ES impact.
By contrast, the EA impact requires the prolonged ENSO that does not terminate in boreal spring because persistent anomalous convective heating in the vicinity of the Philippines from the preceding winter to late spring triggers a WES feedback regime in the Indian Ocean. Due to the frequent occurrence of the prolonged warm and cold events, the EA impact at the decay phase of ENSO becomes significant after the late 1970s. The ES impact at the growth phase of TBO-like ENSO brings about the strong ENSO-monsoon coupling prior to the late 1970s, while the occurrence of the prolonged ENSO after the late 1970s induces the EA impact on the monsoon at the decay phase of ENSO that is significant at the early stage of the monsoon season. Compared to the ES impact, the EA impact is indirect and not persistent until late summer. Furthermore, the monsoon after the late 1970s tends to experience both the ES and EA impacts of ENSO although the ES impact becomes less clear. We conclude that these features lead to the decline of the ENSO-monsoon relationship after the late 1970s. Less
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Research Products
(14 results)
