Showing papers on "World Ocean Atlas published in 2005"

Seasonal global mean sea level change from satellite altimeter, GRACE, and geophysical models

Abstract: We estimate seasonal global mean sea level changes using different data resources, including sea level anomalies from satellite radar altimetry, ocean temperature and salinity from the World Ocean Atlas 2001, time-variable gravity observations from the Gravity Recovery and Climate Experiment (GRACE) mission, and terrestrial water storage and atmospheric water vapor changes from the NASA global land data assimilation system and National Centers for Environmental Prediction reanalysis atmospheric model. The results from all estimates are consistent in amplitude and phase at the annual period, in some cases with remarkably good agreement. The results provide a good measure of average annual variation of water stored within atmospheric, land, and ocean reservoirs. We examine how varied treatments of degree-2 and degree-1 spherical harmonics from GRACE, laser ranging, and Earth rotation variations affect GRACE mean sea level change estimates. We also show that correcting the standard equilibrium ocean pole tide correction for mass conservation is needed when using satellite altimeter data in global mean sea level studies. These encouraging results indicate that is reasonable to consider estimating longer-term time series of water storage in these reservoirs, as a way of tracking climate change.

Seasonal heat budget of the Mediterranean Sea

Abstract: [1] We calculate the monthly components of the Mediterranean Sea heat budget, namely the net shortwave, net longwave, latent, sensible heat fluxes, and heat storage change, for years 1984–2000. The radiative components of the seasonal heat budget are derived by a radiation transfer model, while in most other studies bulk formulae are used. A variety of data are required to run the model, among which are cloud data from International Satellite Cloud Climatology Project (ISCCP) D2 data set, aerosol data from Global Aerosol Data Set (GADS), temperature and humidity from National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) and European Centre for Medium-range Weather Forecasts (ECMWF) Re-Analysis (ERA-40), and oceanographical data from Mediterranean Data Archaeology and Rescue (MEDAR) MEDATLAS database and the World Ocean Atlas 2001. We compare two methods for the estimation of the monthly latent heat flux and evaporation: the bulk aerodynamic and the heat balance. The average annual evaporation rate for the Mediterranean Sea, based on the heat balance method, is estimated at 1500 ± 190 mm yr−1. The bulk aerodynamic method produces estimates of the annual evaporation rate in the range 1060–1280 mm yr−1, depending on the source of the input data. The analysis of the heat content shows that the solar heat absorbed by the sea during summer is redistributed to winter evaporation via heat storage by the sea. Thus the peak evaporation occurs in winter and is mainly driven by energy released (100–150 Wm−2) from sea heat storage.

Timeseries of Polar Water properties in Fram Strait

Abstract: [1] Timeseries of temperature and salinity of Polar Water in the East Greenland Current (EGC) and on the East Greenland shelf at 79°N are presented. The observations in the EGC are made in the 45–74 dbar layer carrying liquid freshwater from the Arctic Ocean to subarctic seas. The properties on the outer fringe of the EGC are dominated by shifts of the position of the East Greenland Front (EGF). In the inner part of the EGC and on the shelf the seasonal cycle of the properties are dominated by the annual cycle of sea ice freezing and melting. Comparing the observations with the World Ocean Atlas (WOA) and other climatologies demonstrates that the climatologies in the EGC and on the shelf at 79°N are poor due to poor data coverage.

Interannual to decadal sea level change in south-western Europe from satellite altimetry and in-situ measurements

Abstract: Interannual to decadal sea level changes are investigated in the Iberian Peninsula in the interval 1993–2001 using satellite altimetry and tide gauge measurements Eleven locations, six in the Mediterranean Sea and five in the Atlantic Ocean, are selected Monthly de-seasoned sea level values are low-pass filtered to focus on signals with periods longer than one year The correlation of altimetry and tide gauge monthly values is higher than 07 and significant at the 95% level at many of the locations, is regionally dependent and increases when using low-pass filtered data The long-term components of the sea level height differences are mostly smaller than +/- 3 mm/yr The sea level is inversely correlated to the North Atlantic Oscillation climatic index and the correlation increases at interannual time scales A relative maximum in sea level in the years 1996–1997 coincides with a relative minimum of the North Atlantic Oscillation index A maximum in the same time interval is observed in steric heights computed from hydrographic databases, that correspond to the change in sea level due to volume change The correlation between steric heights and tide gauge yearly values in 1993–1998 is regionally dependent and significant at the 90% level at a few locations in the Mediterranean Sea Highest values are reached with steric and thermo-steric heights of Medar/Medatlas in Malaga (07) and with thermo-steric heights of World Ocean Atlas 1998 in Ceuta and Algeciras (08)

Errors in Estimated Temporal Tracer Trends Due to Changes in the Historical Observation Network: A Case Study of Oxygen Trends in the Southern Ocean

Abstract: Several models predict large and potentially abrupt ocean circulation changes due to anthropogenic greenhouse-gas emissions. These circulation changes drive-in the models-considerable oceanic oxygen trend. A sound estimate of the observed oxygen trends can hence be a powerful tool to constrain predictions of future changes in oceanic deepwater formation, heat and carbon dioxide uptake. Estimating decadal scale oxygen trends is, however, a nontrivial task and previous studies have come to contradicting conclusions. One key potential problem is that changes in the historical observation network might introduce considerable errors. Here we estimate the likely magnitude of these errors for a subset of the available observations in the Southern Ocean. We test three common data analysis methods south of Australia and focus on the decadal-scale trends between the 1970's and the 1990's. Specifically, we estimate errors due to sparsely sampled observations using a known signal (the time invariant, temporally averaged, World Ocean Atlas 2001) as a negative control. The crossover analysis and the objective analysis methods are for less prone to spatial sampling location biases than the area averaging method. Subject to numerous caveats, we find that errors due to sparse sampling for the area averaging method are on the order of several micro-moles . for the crossover and the objective analysis method, these errors are much smaller. For the analyzed example, the biases due to changes in the spatial design of the historical observation network are relatively small compared to the tends predicted by many model simulations. This raises the possibility to use historic oxygen trends to constrain model simulations, even in sparsely sampled ocean basins.

A potential use of satellite derived upper ocean heat content for studying climate variability: an example for the South Atlantic

Abstract: The lack of continuous long-term hydrographic observations, especially in the South Atlantic Ocean, makes satellite-derived data an extremely useful tool to investigate time and spatial variability on a basin scale. Altimeter data, which is not affected by cloud coverage as infrared-derived data, provides extremely useful information on the vertical thermal and dynamical structure of the upper ocean when combined with climatological hydrographic through a diagnostic model. We present a semi-dynamic model that combines sea surface height anomalies from TOPEX/POSEIDON, infrared satellite-derived sea surface temperature, and World Ocean Atlas 2001 hydrographic data to generate maps of the Upper Ocean Heat Content Anomaly which is suitable for climate variability studies.