Global Ocean Surface Research Articles

Variability of the Tropical Ocean Surface Temperatures at Decadal–Multidecadal Timescales. Part I: The Atlantic Ocean

Abstract Gridded time series from the Global Ocean Surface Temperature Atlas were analyzed with a variety of techniques to identify spatial structures and oscillation periods of the tropical Atlantic sea surface temperature (SST) variations at decadal timescales, and to develop physical interpretations of statistical patterns of decadal SST variations. Each time series was 110 yr (1882–1991) long. The tropical Atlantic SST variations were compared with decadal variations in a 74-yr-long (1912–85) north Nordeste Brazil rainfall time series and a 106-yr-long (1886–1991) tropical Atlantic cyclone activity index time series. The tropical Atlantic SST variations were also compared with decadal variations in the extratropical Atlantic SST. Multiyear to multidecadal variations in the cross-equatorial dipole pattern identified as a dominant empirical pattern of the tropical Atlantic SST variations in earlier and present studies are shown to be variations in the approximately north–south gradient of SST anomalies....

Analyses of global sea surface temperature 1856–1991

Global analyses of monthly sea surface temperature (SST) anomalies from 1856 to 1991 are produced using three statistically based methods: optimal smoothing (OS), the Kaiman filter (KF) and optimal interpolation (OI). Each of these is accompanied by estimates of the error covariance of the analyzed fields. The spatial covariance function these methods require is estimated from the available data; the timemarching model is a first‐order autoregressive model again estimated from data. The data input for the analyses are monthly anomalies from the United Kingdom Meteorological Office historical sea surface temperature data set (MOHSST5) [Parker et al., 1994] of the Global Ocean Surface Temperature Atlas (GOSTA) [Bottomley et al., 1990].These analyses are compared with each other, with GOSTA, and with an analysis generated by projection (P) onto a set of empirical orthogonal functions (as in Smith et al. [1996]). In theory, the quality of the analyses should rank in the order OS, KF, OI, P, and GOSTA. It is found that the first four give comparable results in the data‐rich periods (1951–1991), but at times when data is sparse the first three differ significantly from P and GOSTA. At these times the latter two often have extreme and fluctuating values, prima facie evidence of error. The statistical schemes are also verified against data not used in any of the analyses (proxy records derived from corals and air temperature records from coastal and island stations). We also present evidence that the analysis error estimates are indeed indicative of the quality of the products. At most times the OS and KF products are close to the OI product, but at times of especially poor coverage their use of information from other times is advantageous.The methods appear to reconstruct the major features of the global SST field from very sparse data. Comparison with other indications of the El Niño‐Southern Oscillation cycle show that the analyses provide usable information on interannual variability as far back as the 1860s.

El Niño‐Southern Oscillation sea surface temperature and wind anomalies, 1946–1993

El Niño‐Southern Oscillation (ENSO) periods, which occur irregularly every few years, are a major perturbation of the Earth's climate system that involves large‐scale changes in winds, rainfall, sea surface temperature (SST), and surface pressure. In some areas of the world there are disastrous droughts, and in others there is serious flooding. North American weather patterns are also affected. It is important to develop skillful forecasts for ENSO periods. Our goal here is to provide an overview of the global ocean and atmosphere surface changes that typically occur during ENSO periods. Knowledge of these anomaly patterns is needed in order to improve our understanding and forecasts of ENSO. With a global surface data set we describe the statistically significant patterns of SST, surface wind, and surface pressure changes that on average are associated with the 10 post‐World War II ENSO periods. We present these average anomaly results as an “ENSO composite.” It is useful to identify phases of the typical ENSO and examine the statistically significant elements phase by phase. An ENSO by ENSO period search indicates that about two thirds of these elements occur in 90% or more of the ENSO periods: we define a “Robust ENSO Composite” from these frequently occurring elements and find it to be an Indo‐Pacific phenomenon. Limitations in the surface data set make it possible that this study has not identified all the important aspects of ENSO periods; data are very sparse in both space and time over much of the tropics and the southern hemisphere. However, we suggest that any theory or model of ENSO should at least exhibit the features of this robust composite, and is unlikely to able to represent adequately the large‐scale environmental impacts of ENSO unless it does so.

Timing and duration of the Last Interglacial: evidence for a restricted interval of widespread coral reef growth

We report new mass spectrometric U-series ages for eight Last Interglacial fossil reefs along the continental margin of Western Australia. Corals were selected in growth position from localities that are characterized by apparently low levels of diagenesis and relative tectonic stability so that the fossil reefs provide critical information on Last Interglacial sea-levels without requiring corrections for tectonic movements. In addition, we have improved the constraint on the timing of onset of reef growth by recovering drill core coral from the base of the reefs. Uranium and thorium isotopes were measured with high levels of precision, leading to improvements in age resolution and allowing samples which have undergone diagenetic exchange of uranium and thorium to be more easily identified and discarded. These data supplement our previous results for Rottnest Island and Leander Point, leading to more than seventy mass spectrometric U-series ages from which constraints can be placed on the timing, duration and character of the Last Interglacial sea-level highstand. Reliable ages show that reef growth started contemporaneously at 128 ± 1 ka along the entire Western Australian coastline, while relative sea-levels were at least 3 m above the present level. Because Western Australia is located far from the former Penultimate Glacial Maximum ice sheets and are not significantly effected by glacial unloading, these data constrain the timing of onset of the Last Interglacial period to 128 ± 1 ka, assuming reef growth started soon after sea-level approached interglacial levels. A unique regressive reef sequence at Mangrove Bay constrains the timing of termination of the Last Interglacial period to 116 ± 1 ka. The major episode of reef building, however, both globally and locally along the Western Australian coast, is restricted to a very narrow interval occurring from ∼128 ka and ∼121 ka, suggesting that global ocean surface temperatures were warm and/or sea-levels were stable enough to allow prolific reef growth only during the earlier part of the Last Interglacial.

The early results from OCTS onboard ADEOS

The mission objectives of Ocean Color and Temperature Scanner (OCTS) are to measure global ocean color and sea surface temperature (SST), simultaneously, to retrieve marine biological processes, océanographic and geophysical parameters relating to carbon cycle and energy cycle such as global ocean primary product, ocean current, global aerosol over the ocean, air‐sea interactions, land cover and so on. OCTS is a visible and near infrared multi spectral radiometer to measure global ocean color and sea surface temperature with high sensitivity to provide quantitatively accurate measurement, after 10 years blank of operational ocean color sensor following the stop of CZCS operation. This paper describes the early results from data obtained during the ADEOS operational period started on November 26,1996 until the stop of operation on June 30, 1997.

Monthly mean ocean surface winds observed by NASA Scatterometer (NSCAT)

Winds are the critical factor in determining regional weather patterns and global climate. NASA Scatterometer (NSCAT) aboard Japan's Advanced Earth Observing Satellite (ADEOS, Midori) continually observed the global ocean surface wind speed and direction from September 1996 to June 1997. In the present article, the monthly mean global ocean surface winds observed by NSCAT will be shown. This provides a better description of atmospheric circulation over the global oceans.

Uncertainties in Global Ocean Surface Heat Flux Climatologies Derived from Ship Observations

Abstract A methodology to define uncertainties associated with ocean surface heat flux calculations has been developed and applied to a global climatology that utilizes a summary of the Comprehensive Ocean–Atmosphere Data Set surface observations. Systematic and random uncertainties in the net oceanic heat flux and each of its four components at individual grid points and for zonal averages have been estimated for each calendar month and for the annual mean. The most important uncertainties of the 2° × 2° grid cell values of each of the heat fluxes are described. Annual mean net shortwave flux random uncertainties associated with errors in estimating cloud cover in the Tropics yield total uncertainties that are greater than 25 W m−2. In the northern latitudes, where the large number of observations substantially reduces the influence of these random errors, the systematic uncertainties in the utilized parameterization are largely responsible for total uncertainties in the shortwave fluxes, which usually r...

Interannual variabilty of the earth’s radiation budget: some regional studies

A detailed study is presented of the interannual variability of the Earth's radiation budget (ERB) at the top of the atmosphere in three equatorial regions: the western Pacific over Indonesia, the eastern Pacific off the west coast of South America and the eastern Atlantic off the west coast of Africa. The objective is to try and understand the cloud, surface and ERB interactions that occur in these areas, each of which shows a large interannual signal in the net radiation balance. The period studied extends from March 1979 through to April 1985, for which coincident ERB and cloud data are available from the Nimbus-7 ERB and Cloud Climatology data sets. This period encompasses the exceptional 1982–1983 ENSO as well as the 1984 Atlantic warming event. Additionally, sea-surface temperature data from the Global Ocean Surface Temperature Atlas (GOSTA) data set are used in combination with the ERB data to partition the outgoing longwave radiation into surface emission and greenhouse-effect components. The methodology involves examination of the time series of anomalies in all of these quantities together with the formulation of statistical relationships amongst them. These methods firstly allow the shortwave (SW) and longwave (LW) components of the ERB anomalies to be identified. The SW and LW anomalies are themselves seen to be made up of different components and, much like the net balance, are often the residuals of two competing effects. This is exemplified in the eastern Pacific and Atlantic regions, which both experienced periods of anomalously high SSTs. In such areas the SW anomaly can arise due to an imbalance between the cooling effect of increased high cloudiness and warming due to reduction of low level cloud, whilst the LW anomaly is composed of warming due to the increase in high cloud amount and cooling due to increased surface emission. The result is that anomalies in the net balance term, which is ultimately the most important with regard to climate variability, are seen to arise as a result of complex interactions between the atmosphere, cloudiness and surface. © 1997 the Royal Meteorologcal Society.

Interannual variabilty of the earth's radiation budget: some regional studies

A detailed study is presented of the interannual variability of the Earth's radiation budget (ERB) at the top of the atmosphere in three equatorial regions: the western Pacific over Indonesia, the eastern Pacific off the west coast of South America and the eastern Atlantic off the west coast of Africa. The objective is to try and understand the cloud, surface and ERB interactions that occur in these areas, each of which shows a large interannual signal in the net radiation balance. The period studied extends from March 1979 through to April 1985, for which coincident ERB and cloud data are available from the Nimbus-7 ERB and Cloud Climatology data sets. This period encompasses the exceptional 1982–1983 ENSO as well as the 1984 Atlantic warming event. Additionally, sea-surface temperature data from the Global Ocean Surface Temperature Atlas (GOSTA) data set are used in combination with the ERB data to partition the outgoing longwave radiation into surface emission and greenhouse-effect components. The methodology involves examination of the time series of anomalies in all of these quantities together with the formulation of statistical relationships amongst them. These methods firstly allow the shortwave (SW) and longwave (LW) components of the ERB anomalies to be identified. The SW and LW anomalies are themselves seen to be made up of different components and, much like the net balance, are often the residuals of two competing effects. This is exemplified in the eastern Pacific and Atlantic regions, which both experienced periods of anomalously high SSTs. In such areas the SW anomaly can arise due to an imbalance between the cooling effect of increased high cloudiness and warming due to reduction of low level cloud, whilst the LW anomaly is composed of warming due to the increase in high cloud amount and cooling due to increased surface emission. The result is that anomalies in the net balance term, which is ultimately the most important with regard to climate variability, are seen to arise as a result of complex interactions between the atmosphere, cloudiness and surface. © 1997 the Royal Meteorologcal Society.

Steric Sea Level in the Los Alamos POP Code—Non-Boussinesq Effects

ABSTRACT The recent availability of accurate global ocean surface elevation data from satellites permits intercomparison with model results, and therefore raises the question of the accuracy of the computed sea level in ocean models. Most models, even those that incorporate a free surface, make use of the Boussinesq approximation—that is, they assume an incompressible fluid and conserve volume rather than mass. This results in an error in predicting steric sea level changes. The Los Alamos POP model, a free-surface Bryan-Cox type of ocean model developed for parallel computers, is in this category. We generalize the POP (Parallel Ocean Program) model to account for non-zero dilatation (non-zero velocity divergence—the primary non-Boussinesq effect) due to a variety of causes, such as expansion due to thermal and salinity mixing, as well as compressibility. We then compute both local and global changes of the sea level due to these effects and conclude that overall global dynamic effects are entirely negligible. There are some small local effects such as a very small increase in the Antarctic Circumpolar Current transport, for example. We also observe a global mean sea level decrease at a rate on the order of a half-metre per Century. While in this case this is most likely due to the ocean relaxing toward equilibrium (the computation is not initiated from a state of equilibrium), this does indicate that mean ocean expansion/contraction may be Significant from the point of view of climate and ought to be included in models.

Decadal Variability of the Tropical Atlantic Ocean Surface Temperature in Shipboard Measurements and in a Global Ocean-Atmosphere Model

Sea surface temperature (SST) variability was investigated in a 200-yr integration of a global model of the coupled oceanic and atmospheric general circulations developed at the Geophysical Fluid Dynamics Laboratory (GFDL). The second 100 yr of SST in the coupled model's tropical Atlantic region were analyzed with a variety of techniques. Analyses of SST time series, averaged over approximately the same subregions as the Global Ocean Surface Temperature Atlas (GOSTA) time series, showed that the GFDL SST anomalies also undergo pronounced quasi-oscillatory decadal and multidecadal variability but at somewhat shorter timescales than the GOSTA SST anomalies. Further analyses of the horizontal structures of the decadal timescale variability in the GFDL coupled model showed the existence of two types of variability in general agreement with results of the GOSTA SST time series analyses. One type, characterized by timescales between 8 and 11 yr, has high spatial coherence within each hemisphere but not between the two hemispheres of the tropical Atlantic. A second type, characterized by timescales between 12 and 20 yr, has high spatial coherence between the two hemispheres. The second type of variability is considerably weaker than the first. As in the GOSTA time series, the multidecadal variability in the GFDL SST time series has approximately opposite phases between the tropical North and South Atlantic Oceans. Empirical orthogonal function analyses of the tropical Atlantic SST anomalies revealed a north-south bipolar pattern as the dominant pattern of decadal variability. It is suggested that the bipolar pattern can be interpreted as decadal variability of the interhemispheric gradient of SST anomalies. The decadal and multidecadal timescale variability of the tropical Atlantic SST, both in the actual and in the GFDL model, stands out significantly above the background 'red noise' and is coherent within each of the time series, suggesting that specific sets of processes may be responsible for the choice of the decadal and multidecadal timescales. Finally, it must be emphasized that the GFDL coupled ocean-atmosphere model generates the decadal and multidecadal timescale variability without any externally applied force, solar or lunar, at those timescales.

The interrelationship between temperature changes in the free atmosphere and sea surface temperature changes

Fields of sea surface temperature anomalies from the Global Ocean Surface Temperature Atlas (GOSTA) and microwave sounding measurements (MSU) of temperature in the troposphere are examined separately and together for the 1979–1988 period. Global correlation patterns of both sets of fields are investigated at a range of leads and lags up to 6 months and exhibit a wide range of correlation structure. There are regions, such as the tropical eastern Pacific, where sea surface temperature anomalies persist for several months and are associated with local air temperature anomalies; in this particular example, about 0.7°C air temperature change is associated with a 1.0°C sea temperature change. By contrast, some ocean regions and many atmospheric regions, mostly in middle and high latitude, show only local spatial correlations that disappear completely in a month or two. The most persistent and extensive spatial correlation patterns are quite different for the sea and the air. In the sea the “butterfly” pattern of the Pacific is the most important and reverses sign between the eastern equatorial Pacific and the western Pacific and subtropics. In the warm phase the temperature anomalies associated with this pattern are similar to the correlation pattern. For the atmosphere the main correlation pattern is an equatorial belt with no sign changes in the tropics; this pattern is linked to the oceanic El Niño mode. In the warm phase the temperature anomalies show peak values on both sides of the equator in the eastern and central Pacific. Based mainly on the results from the spatial patterns, certain regions are selected for intercomparison of time series. In the tropical eastern Pacific the sea leads the air by about a month while in the Gulf Stream and Kuroshio regions the sequence is reversed.

Possible factors controlling global marine temperature variations over the past century

Data from the Global Ocean Surface Temperature Atlas (GOSTA), which includes 60 million ship reports for the 1856–1988 period, have been used to study global night marine air temperature (MAT) and sea surface temperature (SST) interannual variations. Linear regression has been used to establish trends over two periods: 1888–1988, a period often used for land station analyses, and 1856–1988. For global MAT the trends for the century beginning in 1888 computed for these periods are 0.49°C and 0.29°C, respectively. Stepwise linear regression is used to relate the marine time series to three physical variables thought to influence surface temperatures, namely, changes in solar radiation output, changes in atmospheric transmission for solar radiation, and changes in the global surface pressure field. Indices of these variables used are new computations of solar irradiance, atmospheric turbidity at Sonnblick, Austria, supported by sunshine records from Japan, and the Southern Oscillation Index (SOI). When MAT and SST series are examined for the globe, northern and southern hemisphere separately, the largest fraction of the variance (45% for the global MAT, 35% for global SST) is accounted for by turbidity changes, while the tropical east Pacific shows the largest fraction (45% for MAT, 49% for SST) associated with SOI changes. Modeled solar irradiance variations contribute the second most important factor in controlling marine temperature fluctuations in the southern hemisphere. The tropical west Pacific SST is relatively insensitive to the three parameters, in accordance with previous suggestions that the temperature there is limited by evaporation. When the residuals are examined after account is taken of these factors, the global MAT trend for 1888–1988 is reduced to 0.24°C. With the present approach the apparent twentieth century temperature increases can be viewed as partly due to a recovery from cooling at the turn of the century, probably associated with volcanic activity.

On Climatological Monthly Mean Wind Stress and Wind Stress Curl Fields over the World Ocean

Abstract Using a version of the global surface marine observation historical data set, a new 1° spatial resolution global ocean surface wind stress climatology has been evaluated using the Large and Pond surface drag coefficient formulation. These new results are compared, after spatial smoothing, with those of Hellerman and Rosenstein, who used a different drag coefficient form. It is found that the new stresses are almost everywhere smaller than those of Hellerman and Rosenstein, often by 20%–30%, which is greater than the formal error estimates from their calculations. The stress differences show large-scale spatial structure, as would he expected given the spatial variation of the surface stability parameter and the known different wind variability regions. Basin zonally averaged Ekman transports are computed to provide perspective on the significance of the stress differences; annual mean differences can exceed 10 Sv (Sv = 106 m3 s−1) equatorward of 20° lat, but are smaller poleward. Wind stress curl...

Mean surface energy fluxes over the global ocean

A newly available consolidated data set from the U.S. Navy's Fleet Numerical Weather Central in Monterey, California, is utilized to investigate global energy fluxes at the sea‐air interface. Sea surface temperature data from January 1949 to December 1979 were extracted from the data set along with air temperature, sea level pressure, dew point temperature, wind speed, wind direction, and cloud cover. Five degree latitude by five degree longitude spatial averaging and monthly temporal averaging were applied to the parameters in the data set for the purpose of studying long‐term large‐scale fluctuations. The heat balance of the global ocean surface layer is calculated using bulk flux formulations. Maps of the long‐term monthly and annual means of the net surface energy flux together with the four components of the total flux (latent heat flux, sensible heat flux, incoming radiation, and outgoing radiation) for the global oceans are presented. Incoming solar radiation and latent heat flux are the two dominant components that control net surface energy fluxes. Wind speed, cloud cover, and the gradient of specific humidity are the three most important meteorological parameters in determining surface flux. Errors associated with the bulk formula calculations and the significant features of the energy balance at the ocean surface are discussed.

Global Data Assimilation Experiments with Scatterometer Winds from SEASAT-A

Abstract Two days of global scatterometer-derived oceanic surface winds during the period of 0000 GMT 16 July-0000 GMT 18 July 1978 from the SEASAT-A satellite are used in the NMC's global data assimilation and forecast experiments to gain a preliminary appreciation of the impact of this dataset. The NMC's global data assimilation system used in this study is described. The nature of the scatterometer winds and their error characteristics are discussed. Two parallel 48-hour data assimilation experiments are conducted: one including scatterometer wind data (SASS), the other without (NCSASS). After 48 hours of assimilation, large differences have evolved between SASS and NOSASS analyses due to the scatterometer winds. Comparison of the analyses with the operational analysis generated by the Australian Bureau of Meteorology suggests that the influence of scatterometer winds was beneficial in the Southern Hemisphere.

Central swath mapping by a future satellite-borne fan-beam microwave scatterometer for inferring global ocean wind fields

The SeaSat-A satellite scatterometer is a microwave sensor designed to provide a capability for mapping the global ocean surface wind speed and direction. Four fan beams whose major axes are oriented at \pm45 and \pm135\deg to the flight vector cover a swath width of 1900 km, but a central region remains that is inadequately mapped. In this paper, two additional fan beams are suggested for a future scatterometer that provide a more complete coverage of the central region.

Sur la biogenèse de la pyrimidine de la thiamine

Climatological mean monthly distributions of pH in the total H+ scale, total CO2 concentration (TCO2), and the degree of CaCO3 saturation for the global surface ocean waters (excluding coastal areas) are calculated using a data set for pCO2, alkalinity and nutrient concentrations in surface waters (depths < 50 m), which is built upon the GLODAP, CARINA and LDEO databases. The mutual consistency among these measured parameters is demonstrated using the inorganic carbon chemistry model with the dissociation constants for carbonic acid by Lueker et al. (2000) and for boric acid by Dickson (1990). Linear potential alkalinity-salinity relationships are established for 24 regions of the global ocean. The mean monthly distributions of pH and carbon chemistry parameters for the reference year 2005 are computed using the climatological mean monthly pCO2 data adjusted to a reference year 2005 and the alkalinity estimated from the potential alkalinity-salinity relationships. The equatorial zone (4°N-4°S) of the Pacific is excluded from the analysis because of the large interannual changes associated with ENSO events. The pH thus calculated ranges from 7.9 to 8.2. Lower values are located in the upwelling regions in the tropical Pacific and in the Arabian and Bering Seas; higher values are found in the subpolar and polar waters during the spring-summer months of intense photosynthetic production. The vast areas of subtropical oceans have seasonally varying pH values ranging from 8.05 during warmer months to 8.15 during colder months. The warm tropical and subtropical waters are supersaturated by a factor of as much as 4.2 with respect to aragonite and 6.3 for calcite, whereas the cold subpolar and polar waters are supersaturated by 1.2 for aragonite and 2.0 for calcite because of the lower pH values resulting from greater TCO2 concentrations. In the western Arctic Ocean, aragonite undersaturation is observed. The time-series data from the Bermuda (BATS), Hawaii (HOT), Canary (ESTOC) and the Drake Passage show that pH has been declining at a mean rate of about -0.02 pH per decade, and that pCO2 has been increasing at about 19 μatm per decade tracking the atmospheric pCO2 increase rate. This suggests that the ocean acidification is caused primarily by the uptake of atmospheric CO2. The relative importance of the four environmental drivers (temperature, salinity, alkalinity and total CO2 concentration) controlling the seasonal variability of carbonate chemistry at these sites is quantitatively assessed. The ocean carbon chemistry is governed sensitively by the TA/TCO2 ratio, and the rate of change in TA is equally important for the future ocean environment as is the TCO2 in ocean waters increases in the future.