A dynamical interpretation of the global response to equatorial Pacific SST anomalies
- European Centre for Medium-Range Weather Forecast, Reading (United Kingdom)
The Northern Hemisphere winter 1988/89 was characterized by large persistent anomalies in both the tropics and the extratropics. A strong cold anomaly in the sea surface temperature (SST) was present in the eastern equatorial Pacific and the Walker circulation was very intense over the Pacific. In the northern extratropics, positive geopotential anomalies over western Europe and the eastern Pacific Ocean persisted through January and February; a major amplification of the Pacific ridge occurred at the beginning of February, with the onset of a Pacific block that caused a severe cold spell over the western coast of North America. The role of the SST anomaly in the maintenance of the seasonal anomaly over the northern extratropics has been investigated at ECMWF by comparing results of 90-day integrations with observed and with climatological SST. The extratropical response to the [open quotes]La Nina[close quotes] SST pattern accounts for a large proportion of the January-February anomaly. A 90-day experiment showed that the changes in the tropical circulation induced by the extratropical relaxation are clearly positively correlated with those induced by the SST anomaly. A second [open quotes]relaxation[close quotes] experiment shows that these changes are indeed able to reinforce the extratropical response, suggesting the existence of a positive feedback, the manifestation of global-scale regimes that exist independently of SST anomalies, but whose occurrence and stability properties can be significantly altered by a strong, persistent boundary forcing. This model can explain a number of qualitative aspects of tropical-midlatitude interactions simulated by the GCM integrations herein. 28 refs., 16 figs., 2 tabs.
- OSTI ID:
- 6317625
- Journal Information:
- Journal of Climate; (United States), Vol. 6:5; ISSN 0894-8755
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ATMOSPHERIC CIRCULATION
GLOBAL ASPECTS
TEMPERATURE DEPENDENCE
OCEANIC CIRCULATION
SURFACE WATERS
TEMPERATURE MONITORING
AMPLIFICATION
EUROPE
FEEDBACK
GENERAL CIRCULATION MODELS
NORTH AMERICA
NORTHERN HEMISPHERE
PACIFIC OCEAN
SEAS
SOUTHERN OSCILLATION
WIND
EARTH PLANET
MATHEMATICAL MODELS
MONITORING
PLANETS
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