Interdecadal changes in El Nino onset in the last four decades

Journal Article · Wed Feb 01 04:00:00 EST 1995 · Journal of Climate

DOI:https://doi.org/10.1175/1520-0442(1995)008<0267:ICIENO>2.0.CO;2· OSTI ID:79393

Wang, B ^[1]

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1. Univ. of Hawaii, Honolulu, HI (United States)

The characteristics of the onset of the Pacific basin-wide warming have experienced notable changes since the late 1970s. The changes are caused by a concurrent change in the background state on which El Nino evolves. For the most significant warm episodes before the late 1970s (1957, 1965, and 1972), the atmospheric anomalies in the onset phase (November to December of the year preceding the El Nino) were characterized by a giant anomalous cyclone over east Australia whose eastward movement brought anomalous westerlies into the western equatorial Pacific, causing development of the basin-wide warming. Meanwhile, the trades in the southeastern Pacific relaxed back to their weakest stage, resulting in a South American coastal warming, which led the central Pacific warming about three seasons. Conversely, in the warm episodes after the late 1970s (1982, 1986-87, and 1991), the onset phase was characterized by an anomalous cyclone over the Philippine Sea whose intensification established anomalous westerlies in the western equatorial Pacific. Concurrently, the trades were enhanced in the southeastern Pacific, so that the coastal warming off Ecuado occurred after the central Pacific warming. It is found that the atmospheric anomalies occurring in the onset phase are controlled by background SSTs that exhibit a significant secular variation. In the late 1970s, the tropical Pacific between 20{degrees}S and 20{degrees}N experienced an abrupt interdecadal warming, concurrent with a cooling in the extratropical North Pacific and South Pacific and a deepening of the Aleutian Low. The interdecadal change of the background state affected El Nino onset by altering the formation of the onset cyclone and equatorial westerly anomalies and through changing the trades in the southeast Pacific, which determine whether a South American coastal warming leads or follows the warming at the central equatorial Pacific. 49 refs., 13 figs.

• OSTI ID: 79393
• Journal Information: Journal of Climate, Journal Name: Journal of Climate Journal Issue: 2 Vol. 8; ISSN JLCLEL; ISSN 0894-8755
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
AIR-WATER INTERACTIONS
CLIMATIC CHANGE
CORRELATIONS
PACIFIC OCEAN
SOUTHERN OSCILLATION
TEMPERATURE DISTRIBUTION
VARIATIONS