A General Circulation Model Study of January Climate Anomaly Patterns Associated with Interannual Variation of Equatorial Pacific Sea Surface Temperatures

The relationships of sea surface temperature (SST) anomalies with atmospheric general circulation and with momentum and heat fluxes are investigated in order to show the dominant structures in the North Pacific in the ENSO cycle (ES: 2-5 years) and decadal (DC: longer than 5 years) time scales, using newly computed monthly 5ox5o (longitude x latitude) gridded datasets for SST, wind stress, and net surface heating fields and National Meteorological Center (NMC) geopotential height data for the 40-year period of The Pacific/North American (PNA) like pattern that has three centers in the 150oW-170oW longitudinal band in the wintertime 500hPa height field is prominent in the decadal changes of wintertime SST anomalies. Stronger (weaker) westerlies are located south (north) of the normal jet stream position during periods of below-normal (above-normal) SST anomalies in most of the entire extratropical North Pacific. Those SST anomalies are caused by the enhanced (suppressed) heat release along the Kuroshio and its extension, and by stronger (weaker) southward Ekman transport. However the dominant pattern of the wind field on the ES time scale is quite different from that on the DC time scale. The westerly jet in the central North Pacific is stronger than normal, but shifts northward of its mean position in years of ENSO warm episodes. On the other hand, the northwesterly wind is weaker, hence heat release is suppressed in the western North Pacific. A Western Pacific (WP) like pattern then appears in the atmospheric geopotential height field over the ocean with a below-normal center in the Bering Sea and an above-normal center south of Japan. The situation is reversed in the years of ENSO cold episodes.The differences in the spatial patterns of SST anomalies on the DC and ES time scales are associated with differences in the atmospheric circulation, such as the predominance of PNA-like versus WP-like patterns. The corresponding change in the wind system then brings about a change of heat release and Ekman transport that form the SST anomalies. It appears that the distinctions between these two atmospheric patterns are responsible for the differences in the spatial structure of tropical SST anomalies on the DC and ES time scales.

Section: Analysis Toolsmentioning

confidence: 99%

Relationships between Sea Surface Temperature, the Atmospheric Circulation and Air-sea Fluxes on Multiple Time Scales

Tanimoto

Iwasaka²,

Hanawa

1997

“…It is generally accepted that the lower latitude sea surface temperature (SST) anomaly has a large influence on mid-latitude tropospheric circulations (e. g. Blackmon et al, 1983). Fig.…”

Section: Sst Anomalymentioning

confidence: 99%

A Possible Influence of Sea Surface Temperature Variation on the Recent Development of Ozone Hole

Kodera¹,

Yamazaki²

1989

A possible cause of the recent decrease of planetary wave activity and Antarctic ozone depletion in spring is proposed. The tropospheric stationary wave structure in the southern hemisphere shows substantial variation during 1979 to 1988. Before the 1980's, especially in 1979, a well-developed tropospheric ridge was situated in the South Pacific and the stationary wave propagated into the stratosphere, while after 1985 the tropospheric ridge became weaker and split into two ridges, and no vertical propagation was clearly seen. In 1988, however, the vertically propagating wave number 1 structure was recovered. This change of planetary wave structure in the South Pacific seems to be related to the sea surface temperature anomaly in the low latitude South Pacific. A possible role of the sea surface temperature variation in the recent development of the ozone hole is also discussed.

“…is considered to be a major forcing from the ocean to the atmosphere on seasonal time scales. A number of GCM studies have been made regarding the influence of El Nino on the global atmospheric circulation, first, using the composite El Nino SST anomaly by Rasmusson and Carpenter (1982) (Shukia and Wallace, 1983;Blackmon et al 1983;Tokioka et al 1986;Palmer and Mansfield, 1986a), and later, using real SST anomalies for particular El Nino Events (e.g. Palmer and Mansfield, 1986b, Owen and Palmer, 1987, Fennessy and Shukla, 1991.…”

Section: Introductionmentioning

confidence: 99%

A Study of SST-forced Variability and Potential Predictability of Seasonal Mean Fields using the JMA Global Model

Sugi

Kawamura

Sato

1997

An ensemble climate simulation experiment has been conducted using the Japan Meteorological Agency (JMA) global model to study the SST-forced atmospheric variability and potential predictability of seasonal mean fields. The ensemble consists of three model integrations each for the same 34-year period. The three integrations use the same observed SST for the period 1955-1988 but start from different atmospheric initial states.The variance ratios of the SST-forced variability to the total variability of the seasonal mean fields are computed. The ratios are considered to represent "potential predictability" (possible maximum predictability when SST is perfectly predicted). The variance ratios of pressure fields are generally high (50-90%) in the tropics but low (less than 30%) in the extratropics, suggesting that the potential predictability of the seasonal mean fields is high in the tropics but low in the extratropics. The variance ratios of precipitation take a wide range of values within the tropics from 74% for N.E. Brazil rainfall to 31% for Indian summer monsoon rainfall, indicating large regional differences in the potential predictability of seasonal mean rainfall within the tropics. The variance ratio of globally-averaged global mean land surface air temperature is high (66%) but the ratio is low (less than 30%) for the seasonal mean local surface air temperature over most land area. This suggests that the potential predictability of local land surface air temperature is low.