1,721,050 research outputs found
The probability of rapid climate change
Full text linkIf you look at a map of the air temperature of the surface of the Earth, you will see that North West Europe, including the UK, is warmer than Alaska, which is at the same latitude but on the Pacific rather than Atlantic Ocean. At school you were probably told that this was because of the Gulf Stream. However, there is a very similar current in the Pacific—the Kuroshio—which takes warm water north past Japan and then out into the Atlantic. Peter Challenor asks: What is the unique feature of the Atlantic that keeps us warm and could it change in the next few years?<br/
The probability of rapid climate change: II
No full textIn Significance December 2004, Peter Challenor described the statistical problem associated with the possible collapse in the thermohaline circulation in the North Atlantic—"the shutting down of the Gulf Stream". Here he brings us up to date with the latest results.<br/
Experimental design for the validation of kriging metamodels in computer experiments
No full textMetamodels (or emulators) are statistical tools for the analysis of large complex simulation models. They consist of a Gaussian (or second order) process (kriging) fitted to a designed set of simulator runs. Once an emulator has been built, it is important that it is validated against some independent runs of the simulator. This paper considers the design of experiments for the validation of the fitted metamodel. All the proposed designs are based on maximin Latin hypercubes and add an extra criterion to be optimised based on the distances between the points in the validation and original designs. Simulation experiments are carried out to determine how well each design performs against the alternative criteria
Relationship between remotely-sensed signatures of the ocean and subsurface structure
No full textThis is the first progress report under a Joint Research Council/Ministry of Defence research project on the relationship between remotely-sensed ocean signatures and subsurface structure and dynamics. It comprises an inventory of datasets and progress reports on sub-projects utilising in situ, altimetric and infrared data
Split-domain calibration of an ecosystem model using satellite ocean colour data
Full text linkThe application of satellite ocean colour data to the calibration of plankton
ecosystem models for large geographic domains, over which their ideal parameters cannot be assumed to be invariant, is investigated. A method is presented for seeking the number and geographic scope of parameter sets which allows the best fit to validation data to be achieved. These are independent data not used in the parameter estimation process. The goodness-of-fit of the optimally calibrated model to the validation data is an objective measure of merit for the model, together with its external forcing data. Importantly, this is a statistic which can be used for comparative evaluation of different models. The method makes use of observations from multiple locations, referred to as stations, distributed across the geographic domain. It relies on a technique for finding groups of stations which can be aggregated for parameter estimation purposes with minimal increase in the resulting misfit between model and observations.The results of testing this split-domain calibration method for a simple zero dimensional model, using observations from 30 stations in the North Atlantic, are presented. The stations are divided into separate calibration and validation sets.
One year of ocean colour data from each station were used in conjunction with a
climatological estimate of the station’s annual nitrate maximum. The results
demonstrate the practical utility of the method and imply that an optimal fit of the model to the validation data would be given by two parameter sets. The corresponding division of the North Atlantic domain into two provinces allows a misfit-based cost to be achieved which is 25% lower than that for the single parameter set obtained using all of the calibration stations. In general, parameters are poorly constrained, contributing to a high degree of uncertainty in model output for unobserved variables. This suggests that limited progress towards a definitive model calibration can be made without including other types of observations
A global analysis of the diurnal sea surface temperature cycle (abstract of paper to be presented at: AGU Ocean Sciences Meeting, 26-30 January 2004, Portland, Oregon)
No full textSatellite observations of the Pacific tropical instability wave characteristics and their interannual variability
No full textDescriptions of tropical instability wave (TIW) characteristics in the tropical Pacific Ocean as a function of the large-scale climate conditions and interannual variability, such as the El Nino southern oscillation, are made based on satellite data. As others have found, the TIW ocean–atmosphere coupling is caused by atmospheric boundary layer instability and mixing. Our observational investigation extends some of these previous findings and suggests that this mechanism of coupled variability of the wind and sea surface temperature may occur not only during La Nina years, when TIWs are more active, but whenever the TIWs are active. The sea surface temperature and height anomaly covariability phase shift might occur also independent of the TIW season activity. There is evidence that TIW activity increases when under strengthened wind stress conditions either in La Nina years or, by analogy, when oceanic numerical simulations are carried out with stronger wind stress. Observational results show larger TIW wavelengths and shorter periods when the ocean is under the action of strengthened wind stress. On this observational study this occurs when La Ninna conditions prevail on the equatorial Pacific
Cross calibration of Envisat, ERS-2, JASON, TOPEX-POSEIDON, and Geosat follow-on wind and wave data, based on comparisons with in-situ data and wave model analysis fields
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