East-west Sea Surface Temperature Research Articles

1997/98エル・ニーニョに関係したインド洋上の東西非対称偏差の誘発過程

Anomalous east-west asymmetric anomalies were seen in sea surface temperature (SST), and convective activity over the equatorial Indian Ocean during October-December 1997. Using NCEP/NCAR reanalysis and sea surface height data obtained from TOPEX/POSEIDON satellite altimeter, its triggering process and strengthening mechanism are identified. The climatological wind over the equatorial Indian Ocean exhibits different seasonal cycle between its western and eastern region. During the summer monsoon season, westerly wind prevails over the western Indian Ocean, on the other hand, easterly wind is dominant over the eastern Indian Ocean at almost the same time. During the 1997 summer, divergent easterly wind anomalies were obvious over the equatorial Indian Ocean due to a warm episode of the El Nino, which weakened (accelerated) the climatological westerly (easterly) wind over the western (eastern) Indian Ocean. As a result, the east-west SST contrast was produced in the succeeding autumn through changing evaporative cooling and upwelling. Corresponding to these SST changes, the convective activities were enhanced (suppressed) over the western (eastern) Indian Ocean and actual wind became easterly in place of climatological westerly wind during October-December 1997. The above easterly anomalies induced westward-moving downwelling Rossby waves, and led to the maximum SST in January 1998 in the western Indian Ocean. On the other hand, eastward-moving downwelling Kelvin waves were generated after the termination of easterly wind anomalies, which were consistent with the SST warming in the eastern Indian Ocean for the period February-June 1998. In this manner, a coupling process between the modulated Walker Circulation associated with the El Nino event and the monsoon circulation from summer to autumn is a crucial factor for inducing the above asymmetric anomalies. Moreover, the oceanic waves are found to be closely related with enhancement of these asymmetric structures.

Rapid changes in ocean circulation and heat flux in the Nordic seas during the last interglacial period

THE apparent similarity of climate variability in the North Atlantic region in the last interglacial period1–5 and the present interglacial (Holocene) has recently been challenged by the rapid oscillations in climate conditions indicated by some marine6,7 and terrestrial climate records8–10 for the last interglacial. Ocean circulation in the northern North Atlantic seems to be intimately coupled to the processes of climate change on various time-scales11,12, so that climate variability—and the associated mechanisms of change—should be well recorded by sediments from these high latitudes. Previous studies in this region5,13 have indeed indicated an apparently less stable last-interglacial climate than at middle latitudes of the North Atlantic Ocean4. Here we present detailed records from marine sediments in the Nordic seas of oceanographic conditions during the last interglacial. The records show three large sea surface temperature fluctuations, a weakening of the east–west sea surface temperature gradient with time, and changes in deep-water properties. In contrast, similar analyses of a core from the same region indicate that sea surface temperature during the Holocene has been relatively stable. Our data—along with those from the Labrador Sea7—indicate rapid changes in ocean circulation and oceanic heat fluxes at high northern latitudes during the last interglacial, which may have been associated with marked temperature changes on adjacent continents.

Implications for the creation of warm saline deep water: Late Paleocene reconstructions and global climate model simulations

A global warming trend began during the late Paleocene that culminated in the early Eocene with the highest global temperatures of the Cenozoic. We have reconstructed late Paleocene surficial boundary conditions and modeled atmospheric conditions using the Goddard Institute for Space Studies general circulation model version II (GISS GCM II). These experiments were conducted to test the hypothesis that warm saline deep water formed during the late Paleocene and to understand atmospheric circulation near the beginning of a period of global warming. The warming is attributed primarily to increased sea surface temperatures at high latitudes. The sensitivity of the climate to ocean temperature was tested using two sea surface temperature distributions, each delimited latitudinally by oxygen isotope values, but with different east-west gradients. The simulations discussed here contain several features unique among warm climate experiments. The first experiment (P-1) used latitudinally constant (zonal) sea surface temperatures. The zonally distributed sea surface temperatures strengthen the general circulation of the atmosphere. In particular, Hadley Cell circulation is intensified, leading to extremes of precipitation in the equatorial region and extreme evaporation across subtropical oceans. The unusual results prompted a second experiment with modern east-west sea surface temperature gradients superimposed and referred to as P-Gradient (P-Grad). The east-west gradients in the sea surface temperature field exert a strong influence on the general atmospheric circulation, but the extreme zonality prevails. Under extreme zonal conditions it is possible to create a model where evaporation is in excess of precipitation by as much as 3 mm/day. If this occurred in restricted areas in a generally warmer ocean, such as the late Paleocene eastern Tethys Ocean and parts of the South Atlantic Ocean, it should be possible to create very saline water, which could become a component in warm saline deep water formation.

Seasonality in the Associations between Surface Temperatures over the United States and the North Pacific Ocean

Abstract Thirty-one years of monthly data are used to evaluate the seasonal dependence of the associations between large-scale temperature anomalies over the United States and the North Pacific Ocean. Both station (grid-point) values and empirical orthogonal functions of temperature are used in the correlative analysis. The North Pacific sea surface temperature (SST) anomalies correlate most highly with temperature fluctuations over the southeastern and the far western states. Correlations with the SST anomalies have opposite signs in the two portions of the United States. The associations with the SST anomalies are independent of season only in the western states. The association involving the southeastern states is strongest during the winter and insignificant during the summer. The pattern of North Pacific SST that correlates most highly with the United States temperature is an east-west SST gradient between the West Coast and 35°N, 160°W. Statistically significant fractions of temperature variance ove...

Associations between Sea Surface Temperature Gradient and Overlying Mid-Tropospheric Circulation in the North Pacific Region

Abstract An attempt was made to verify and further investigate a proposed relationship between the location of the maximum east-west sea surface temperature anomaly gradient (ΔSSTA) and the location of the maximum meridional component of the anomalous 700 mb geostrophic wind (VgA) in the North Pacific on a monthly and seasonal time scale. Previous empirical studies, mostly of a case study type, had suggested collocation of maximum values of these variables in the same time period, particularly during the cold seasons. Using 31 years of monthly sea surface temperature and 700 mb height data for the North Pacific, the two variables wore computed for each month and 3-month periods for each 10° longitude sector from 125°W to 155°E, and for each of three latitude bands (55–40°N, 40–25°N, 55–25°N). From these calculations, the spatial relationships of the two variables wore determined by counting frequencies of the collocation of maximum VgA and ΔSSTA for each month or season and latitude band, and by computing...