Search Results

You are looking at 1 - 10 of 12 items for

  • Author or Editor: Sydney Levitus x
  • Refine by Access: All Content x
Clear All Modify Search
Sydney Levitus

Abstract

Results or a Fourier analysis of climatological fields of the monthly rate of change of heat storage for the world ocean are presented. The amplitude and Phase of the first harmonic are shown, as well as the percent variance of the annual cycle accounted for by this harmonic. These distributions are presented to describe the global geographical characteristics of the annual cycle of the rate of change of heat storage of the world ocean integrated through a depth of 275 m. We have used the results of our Fourier analysis at each gridpoint to synthesize monthly mean estimates of the rate of change of heat storage based on the annual mean and first two harmonies of the annual cycle. We have zonally averaged these time-smoothed monthly estimates over the world ocean and individual ocean basins and present time-latitude plots of these zonal averages.

The climatological monthly temperature fields used to estimate heat storage are one-degree objectively analyzed fields which are based on the approximately 1.5 million temperature soundings on file at the National Ocean-ographic Data Center, Washington, DC, as of 1978.

The amplitude of the first harmonic shows maxima exceeding 300 W m−2 along 40°N in the Pacific and Atlantic Oceans and in midlatitudes of the Southern Hemisphere. Values exceeding 200 W m−2 are found in the tropics. The results show large propagation of phase in the tropical Pacific and Atlantic.

Full access
Sydney Levitus

Abstract

Monthly climatological estimates of wind stress have been used to compute Ekman volume fluxes in the world ocean. Specifically, meridional and zonal Ekman volume fluxes have been computed and from the divergence of these horizontal components, the vertical Ekman volume flux at the base of the Ekman layer has been computed. We have zonally integrated the meridional and vertical components across the world ocean and individual ocean basins, and present maps of the time-latitude variation of these transports. The contribution of the Pacific Ocean dominates the global zonal integrals in the extratropics. lle Indian Ocean exhibits a large annual cycle in meridional Ekman volume flux. Ekman upwelling in the tropics of the Atlantic and Pacific occurs from June through November. The maximum upward vertical Ekman volume flux slightly exceeds 2.5 sverdrup in the Pacific and 1.0 sverdrup in the Atlantic and occurs centered around 10°N in each ocean.

Full access
Sydney Levitus

Abstract

The annual cycle of temperature and heat storage for the world ocean and individual ocean basins is described based on climatological monthly-mean temperature fields. One well-known feature observed in the fields of temperature and heat storage is the large annual cycle at midlatitudes of both hemispheres that lags the maximum of incoming solar radiation by about three months. Another major feature observed in the heat storage of the Northern Hemisphere is a large annual cycle located at about 12°N. The heat storage in this region is approximately three to four months out of phase with the annual cycle at midlatitudes of the Northern Hemisphere with the maximum at 12°N occurring around May. The annual range of heat storage at 12°N is as large as the annual range at midlatitudes of the Northern Hemisphere. In tropical oceans the 1argest variability in temperature occurs at subsurface levels and appears to be associated with large-scale redistribution of heat and displacements of the thermocline.

Full access
Sydney Levitus

Abstract

The annual cycle of salinity in the upper 500 m of the world ocean is described, based on climatological seasonal salinity analyses presented in a previous study. The annual cycle is examined using zonally integrated seasonal sections for the various oceans, seasonal fields for the sea surface, and maps of the zonally integrated annual range. Major features include relatively large annual cycles in the tropical Pacific (8°N) and off the coast of Labrador. For the North Atlantic, good agreement exists with the work of Smed for the sea surface.

Full access
Sydney Levitus

Abstract

A comparison of the annual cycle of two monthly sea surface temperature climatologies for the world ocean is presented. One set of the climatological fields used consist of one-degree objectively analyzed monthly means, based on approximately 1.5 million temperature soundings held by the National Oceanographic Data Center, Washington, DC. The second climatology used is based on monthly objective analyses of a subset of the 70 million historical merchant ship reports from the Cooperative Ocean–Atmosphere Data Set. The comparison is performed by examining the amplitude and phase of the first two harmonics of each climatology, as well as the percent variance contributed by each harmonic to the annual cycle. There is excellent agreement between the two sea surface temperature climatologies in the first two harmonics. In the Northern Hemisphere, maxima in the amplitude of the first harmonic are found off Japan (approximately 7.5°C–8.0°C) and off the east coast of the United States (8.0°C–9.0°C off Cape Hatteras) and Canada (8.0°C in the Gulf of St. Lawrence). In the Southern Hemisphere, open ocean maxima of 3.0°C–4.0°C are found at latitudes 28° to 32°S in the Pacific, Atlantic and Indian Oceans. In the tropics of the eastern Atlantic and eastern Pacific, maxima appear as tongues extending from the continents to the northwest. Another maximum is observed along the east coast of South America centered at 35°S, 58°W with a value of about 5.5°C. The results show large propagation of phase in the tropical Pacific and Atlantic. The results presented are the fist global estimates of these quantities and are in agreement with previous results published in the literature for limited ocean domains.

Full access
Sydney Levitus

Abstract

Monthly climatological estimates of wind stress and sea surface temperature are used to compute meridional Ekman heat fluxes in the world ocean. Qualitatively the annual cycles of the Atlantic and Pacific oceans are quite similar, but quantitatively, the Pacific estimates are up to several times larger than the Atlantic estimates. The Indian Ocean exhibits an annual mean southward flux over nearly all of the 24.5°N–31.5°S latitude belt, which qualitatively supports an annual mean net southward heat flux for this region as determined by surface heat balance requirements. A large southward heat flux in the Indian Ocean centered at about 7.5°N during Northern Hemisphere summer is responsible for a global Ekman heat flux distribution, with an annual cycle in the tropics that qualitatively resembles the results of Oort and Vonder Haar.

Full access
Sydney Levitus and Grigory Isayev

Abstract

No abstract available

Full access
Rong-Hua Zhang and Sydney Levitus

Abstract

Upper-ocean temperature and surface marine meteorological observations are used to examine interannual variability of the coupled tropical Pacific climate system. The basinwide structure and evolution of meteorological and oceanographic fields associated with ENSO events are described using composites, empirical orthogonal functions, and a lagged correlation analysis.

The analyses reveal well-defined spatial structures and coherent phase relations among various anomaly fields. There are prominent seesaw patterns and orderly movement of subsurface ocean thermal anomalies. During an El Niño year, positive temperature anomalies occur in the eastern and central tropical Pacific upper ocean. Westerly wind anomalies, displaced well to the west of SST anomalies, occur over the western and central equatorial region. These patterns are accompanied by subsurface negative temperature anomalies in the west, with maxima located at thermocline depths off the equator. A reverse pattern is observed during La Niña.

The ENSO evolution is characterized by a very slow propagation of subsurface thermal anomalies around the tropical Pacific basin, showing consistent and coherent oceanic variations in the west and in the east, at subsurface depths and at the sea surface, and on the equator and off the equator of the tropical North Pacific. A common feature associated with the onset of El Niño is an appearance of subsurface thermal anomalies in the western Pacific Ocean, which propagate systematically eastward along the equator. Their arrival to the east results in a reversal of SST anomaly polarity, which then correspondingly produces surface wind anomalies in the west, which in turn produce and intensify the subsurface anomalies off the equator, thus terminating one phase of the Southern Oscillation. At the same time, the continual anomaly movement at depth from east to west off the equator provides a phase transition mechanism back to the west. In due course, opposite anomalies are located in the subsurface equatorial western Pacific, introducing an opposite SO phase and beginning a new cycle. Therefore, the phase transitions at the sea surface in the east and at depth in the west are both caused by these preferential, slowly propagating subsurface temperature anomalies, which are essential to the ENSO evolution. Their cycling time around the tropical Pacific basin may determine the period of the El Niño occurrence.

The authors’ data analyses show an important role of the thermocline displacement in producing and phasing SST anomalies in the eastern and central equatorial Pacific. The coherent subsurface anomaly movement and its phase relation with SST and surface winds determine the nature of interannual variability and provide an oscillation mechanism for the tropical Pacific climate system. It appears that interannual variability represents a slowly evolving air–sea coupled mode, rather than individual free oceanic Rossby and Kelvin wave modes. These results provide an observational basis for verifying theoretical studies and model simulations.

Full access
Rong-Hua Zhang and Sydney Levitus

Abstract

Yearly upper-ocean in situ temperature anomaly data for the period 1961–90 are analyzed to reveal spatial structure and evolution of decadal variability in the North Pacific Ocean. An EOF analysis has been performed on individual temperature anomaly fields at upper-ocean standard levels, as well as simultaneously on the entire upper-ocean data to depict the combined three-dimensional structure in a coherent manner. Time evolution of anomaly fields is depicted by using a regression analysis.

The analyses detect the principal basin-scale structure of decadal warm period (DWP) and decadal cold period (DCP). There is a well-defined subsurface thermal anomaly pattern, characterized by a prominent seesaw structure with opposite anomaly polarity between the midlatitude North Pacific and the subtropical regions. During a DWP, a positive temperature anomaly is found in the central midlatitude upper ocean, with the maximum at about 100-m depth. This is accompanied by a corresponding negative anomaly in the American coastal region and in the subtropics. A reverse pattern of these anomalies is observed during the DCP. Evolution between the DWP and the DCP involves significant zonal and meridional propagation of anomaly phase around the North Pacific, showing consistent and coherent variations from subsurface to sea surface, from central midlatitudes to the American coastal regions, and to the subtropical Pacific Ocean. This phase propagation is much more well-organized at subsurface depths than that at the sea surface, suggesting an anomaly decadal-scale cycle circulating clockwise around the subtropical gyre, which supports earlier findings by . There is a systematic and coherent westward transpacific phase propagation in the subtropical region.

These analyses present evidence of the manner in which upper-ocean temperature anomalies evolved in the North Pacific, thus providing an observational basis for evaluating theoretical studies and model simulations. The dynamical implication for physical understanding and prediction of decadal climate variability are discussed.

Full access
Sydney Levitus and Abraham H. Oort

A project to objectively analyze a large quantity of oceanographic data for the world ocean is described. Preliminary results are encouraging within the limits of data available. Results are being used in a variety of ways but at present primarily for studies of the ocean's role in the global heat balance. A brief discussion of the data used, the method of analysis, and some preliminary results is presented.

Full access