bluuebunny/crossref_metadata_2025 huggingface dataset:
El Niño Chaos: The role of noise and stochastic resonance on the ENSO cycle
Authors: Stone Lewi , Saparin Peter I. , Huppert Amit , Price Colin
Published: February 2004

An alternative approach for explaining aperiodicity and chaos in the El‐Niño‐Southern‐Oscillation (ENSO) is proposed, which considers the ocean's equatorial wave dynamics as part of a nonlinear dynamical system driven by random environmental fluctuations. Noise excitation causes the model to jump chaotically between different interacting oscillations generated by the system's implied “Pacific ocean‐atmosphere” cycle and the seasonal cycle. The injection of noise induces chaotic dynamics, triggering an El Niño whenever the model's thermocline depth exceeds a threshold level. A “stochastic resonance” arises‐should noise intensity deviate substantially from optimal, the regular development and coherence of the ENSO cycle is impeded. The model's noise induced chaos provides an attractive explanation for the sporadic yet deterministic character of El Niño events.
Global oceanic precipitation: A joint view by TOPEX and the TOPEX microwave radiometer
Authors: Chen Ge , Chapron Bertrand , Tournadre Jean , Katsaros Kristina , Vandemark Douglas
Published: February 2004

The TOPEX/POSEIDON mission offers the first opportunity to observe rain cells over the ocean by a dual‐frequency radar altimeter (TOPEX) and simultaneously observe their natural radiative properties by a three‐frequency radiometer (TOPEX microwave radiometer (TMR)). This work is a feasibility study aimed at understanding the capability and potential of the active/passive TOPEX/TMR system for oceanic rainfall detection. On the basis of past experiences in rain flagging, a joint TOPEX/TMR rain probability index is proposed. This index integrates several advantages of the two sensors and provides a more reliable rain estimate than the radiometer alone. One year's TOPEX/TMR data are used to test the performance of the index. The resulting rain frequency statistics show quantitative agreement with those obtained from the Comprehensive Ocean‐Atmosphere Data Set (COADS) in the Intertropical Convergence Zone (ITCZ), while qualitative agreement is found for other regions of the world ocean. A recent finding that the latitudinal frequency of precipitation over the Southern Ocean increases steadily toward the Antarctic continent is confirmed by our result. Annual and seasonal precipitation maps are derived from the index. Notable features revealed include an overall similarity in rainfall pattern from the Pacific, the Atlantic, and the Indian Oceans and a general phase reversal between the two hemispheres, as well as a number of regional anomalies in terms of rain intensity. Comparisons with simultaneous Global Precipitation Climatology Project (GPCP) multisatellite precipitation rate and COADS rain climatology suggest that systematic differences also exist. One example is that the maximum rainfall in the ITCZ of the Indian Ocean appears to be more intensive and concentrated in our result compared to that of the GPCP. Another example is that the annual precipitation produced by TOPEX/TMR is constantly higher than those from GPCP and COADS in the extratropical regions of the northern hemisphere, especially in the northwest Pacific Ocean. Analyses of the seasonal variations of prominent rainy and dry zones in the tropics and subtropics show various behaviors such as systematic migration, expansion and contraction, merging and breakup, and pure intensity variations. The seasonality of regional features is largely influenced by local atmospheric events such as monsoon, storm, or snow activities. The results of this study suggest that TOPEX and its follow‐on may serve as a complementary sensor to the special sensor microwave/imager in observing global oceanic precipitation.
Physical and structural properties of the Greenland Ice Sheet Project 2 ice core: A review
Authors: Gow A. J. , Meese D. A. , Alley R. B. , Fitzpatrick J. J. , Anandakrishnan S. , Woods G. A. , Elder B. C.
Published: February 2004

Substantial data sets have been collected on the relaxation characteristics, density, grain size, c axis fabrics, and ultrasonic velocities of the Greenland Ice Sheet Project 2 (GISP2) core to its contact with bedrock at 3053.4 m. Changes in all these properties paralleled closely those found in cores from Byrd Station, Antarctica, and Dye 3, Greenland. Density increased progressively with depth to a maximum of 0.921 Mg/m3 at about 1400 m, at which depth the ice became bubble free. Below about 2000 m, in situ densities began to decrease in response to increasing ice sheet temperatures. Since drilling, much of the ice core has undergone significant volume expansion (relaxation) due to microcracking and the exsolving of enclathratized gases, especially in the brittle ice zone between 650 and 1400 m. Grain size increased linearly to about 1000 m, thereafter remaining fairly constant until the Younger Dryas event at 1678 m where a twofold to threefold decrease in grain size occurred. These grain size changes were accompanied by a progressive clustering of crystal c axes toward the vertical, including a small increase in c axis concentration across the Younger Dryas/Holocene boundary. Increased dust levels in the Wisconsin ice have contributed to the maintenance of a fine‐grained texture which, with its strong vertical c axis fabric, persisted to nearly 3000 m. However, beginning at about 2800 m, layers of coarse‐grained ice intermixed with the much finer‐grained matrix ice are observed. Below 3000 m the ice became very coarse grained. This change, attributed to annealing recrystallization at elevated temperatures in the ice sheet, was accompanied by a dispersed or ring‐like redistribution of the c axes about the vertical. Ultrasonic measurements of vertical and horizontal P wave velocities made at 10‐m intervals along the entire length of the GISP2 core fully confirmed the results of the crystallo‐optical observations. A return to fine‐grained ice coincided with the first appearance of brown, silty ice 13 m above bedrock. Bedrock material consisted of 48 cm of till, including boulders and cobbles, overlying gray biotite granite comprising the true bedrock. There is evidence that disturbed structure in the GISP2 cores begins little more than 70% of the way through the ice sheet. This disturbance increases with depth until it becomes large enough to cast suspicion on features lasting centuries or more in the bottom 10% of the ice sheet.
An improved composite surface model for the radar backscattering cross section of the ocean surface: 1. Theory of the model and optimization/validation by scatterometer data
Authors: Romeiser Roland , Alpers Werner , Wismann Volkmar
Published: February 2004

An improved composite surface model for the calculation of the normalized radar backscattering cross section (NRCS) of the ocean surface at moderate incidence angles is presented. The model is based on Bragg scattering theory. A Taylor expansion of the NRCS in the two‐dimensional surface slope yields nonzero second‐order terms which represent a first approximation for the effect of the geometric and hydrodynamic modulation of the Bragg scattering facets by all waves that are long compared to these facets. The corresponding expectation value of the NRCS varies with the wave height spectral density of all these waves, and it depends in a well‐defined way on frequency, polarization, incidence angle, and azimuthal look direction of the radar. We show that measured NRCS values at frequencies ranging from 1 GHz (L band) through 34 GHz (Kaband) and wind speeds between 2 and 20 m/s can be well reproduced by the proposed model after some reasonable tuning of the input ocean wave spectrum. Also, polarization effects and upwind/downwind differences of the NRCS appear to be relatively well represented. The model can thus be considered as an advanced wind scatterometer model which is based on physical principles rather than on empirical relationships. The most promising field of application, however, will be the calculation of NRCS variations associated with local distortions of the wave spectrum by surface current gradients or wind effects.
An improved composite surface model for the radar backscattering cross section of the ocean surface: 2. Model response to surface roughness variations and the radar imaging of underwater bottom topography
Authors: Romeiser Roland , Alpers Werner
Published: February 2004

In the companion paper we have presented an improved composite surface model for the calculation of normalized radar backscattering cross sections (NRCS) of the ocean surface. The proposed model accounts for the impact of the full two‐dimensional ocean wave spectrum on the radar backscatter and was shown to reproduce measured absolute NRCS values for a variety of radar configurations and wind speeds satisfactorily after some reasonable tuning of the input ocean wave spectrum. This paper focuses on the modulation of the NRCS in the presence of spatially varying surface currents. First, the sensitivity of the NRCS to intensity variations of different ocean wave spectral components is investigated. Then the hydrodynamic modulation of the wave spectrum over underwater bottom topography in tidal waters is computed in different ways, and the resulting radar signatures are discussed. The composite surface model yields comparable radar signatures at high (10 GHz, X band) and low (1 GHz, L band) radar frequencies, which is in much better agreement with experimental results than the predictions of a first‐order Bragg scattering model. On the other hand, measured variations of the NRCS at high radar frequencies appear to be still underestimated in some cases, which may be due to shortcomings of our description of the wave‐current interaction by conventional weak hydrodynamic interaction theory. Possible improvements of the theory are discussed, and requirements for future experiments are formulated.
Development of a spring thermocline at temperatures below the temperature of maximum density with application to the Baltic Sea
Authors: Eilola Kari
Published: February 2004

Local buoyancy supply associated with the pulsed horizontal advection of water of lower salinity at the sea surface can initiate the development of a shallow thermocline in spring. This process has been studied with an analysis of historical hydrographic data from the central parts of the Baltic proper and numerical experiments with a seasonal pycnocline model. It is shown that this situation occurs in the Baltic Sea when the temperature of the surface water is below the temperature of maximum water density and the buoyancy flux due to heating at the sea surface is negative.
A parametric model for the Yellow Sea thermal variability
Authors: Chu Peter C. , Fralick Charles R. , Haeger Steven D. , Carron Michael J.
Published: February 2004

A thermal parametric model has been developed for analyzing observed regional sea temperature profiles based on a layered structure of temperature fields (mixed layer, thermocline, and deep layers). It contains three major components: (1) a first‐guess parametric model, (2) high‐resolution profiles interpolated from observed profiles, and (3) fitting of high‐resolution profiles to the parametric model. The output of this parametric model is a set of major characteristics of each profile: sea surface temperature, mixed‐layer depth, thermocline depth, thermocline temperature gradient, and deep layer stratification. Analyzing nearly 15,000 Yellow Sea historical (1950–1988) temperature profiles (conductivity‐temperature‐depth station, 4825; expendable bathythermograph, 3213; bathythermograph, 6965) from the Naval Oceanographic Office's Master Oceanographic Observation Data Set by this parametric model, the Yellow Sea thermal field reveals dual structure: one layer (vertically uniform) during winter and multilayer (mixed layer, thermocline, sublayer) during summer. Strong seasonal variations were also found in mixed‐layer depth, thermocline depth, and thermocline strength.
Sensitivity of a global sea ice model to the treatment of ice thermodynamics and dynamics
Authors: Fichefet T. , Maqueda M. A. Morales
Published: February 2004

The sensitivity of a global thermodynamic‐dynamic sea ice model coupled to a one‐dimensional upper ocean model to degradations of the model physics is investigated. The thermodynamic component of the sea ice model takes into consideration the presence of snow on top of sea ice, the storage of sensible and latent heat inside the snow‐ice system, the influence of the subgrid‐scale snow and ice thickness distributions on sea ice thermodynamics, the transformation of snow into snow ice when snow depth increases to the point where the snow‐ice interface sinks below the waterline, and the existence of leads and polynyas (areas of open water) within the ice cover. Ice dynamics is treated basically as by Hibler [1979]. Regarding the upper ocean model, it is made up of an integral mixed layer model and of a diffusive model of the pycnocline. Advection of heat and salt by oceanic currents is implicitly accounted for by restoring the temperatures and salinities of the water column to annual mean data. It is very important to note that a single set of parameter values is employed to simultaneously simulate the Arctic and Antarctic ice regimes. A control run carried out with the model demonstrates that it does reasonably well in simulating the seasonal waxing and waning of both ice packs. The sensitivity study focuses on physical processes pertaining to (1) the vertical growth and decay of sea ice (thermal inertia of snow and ice, heat conduction, and snow cover), (2) the lateral growth and decay of sea ice (leads and polynyas), and (3) the sea ice dynamics (ice motion and shear strength). A total of nine sensitivity experiments have been performed. Each experiment consisted of removing a particular parameterization from the control run computer code. It appears that the thermal inertia of the snow‐ice system is negligible in the Antarctic but not in the Arctic, where the total heat content of sea ice is chiefly dictated by internal storage of latent heat in brine pockets, sensible heat storage being of very minor consequence. It is also found that the inclusion of a prognostic snow layer and of a scheme of snow ice formation is important for sea ice modeling in the southern hemisphere. Furthermore, our results suggest that the thermodynamic effect of the subgrid‐scale snow and ice thickness distributions, the existence of open water areas within the ice cover, and the ice motion play a crucial role in determining the seasonal behavior of both ice packs. The ice shear strength seems to be of lesser importance, although it has a nonnegligible effect in both hemispheres. We can therefore conclude that all these processes should be represented in global climate models.
A comparison of the volcanic records over the past 4000 years from the Greenland Ice Core Project and Dye 3 Greenland ice cores
Authors: Clausen Henrik B. , Hammer Claus U. , Hvidberg Christine S. , Dahl‐Jensen Dorthe , Steffensen Jørgen P. , Kipfstuhl Josef , Legrand Michel
Published: February 2004

Since 1980 the electrical conductivity method (ECM) has been used to infer volcanic acid signals in Greenland ice cores. The method reveals the great majority of major volcanic eruptions, including several known from historic records. Subsequent ion chromatographic analyses of the acid volcanic layers show the chemical composition, i.e., the concentration of the volcanic acids H2SO4, HCI, and HF plus, e.g., the nonvolcanically derived HNO3. While ECM data are available from a large number of shallow depth Greenland ice cores, covering the past 500–1500 years, only the Greenland Ice Core Project (GRIP), Greenland Ice Sheet Project 2 (GISP2), and Dye 3 deep ice cores exist for a detailed comparative study of volcanic signals in Greenland ice cores representing several thousand years. Comparison of the volcanic signals registered in the GRIP and GISP2 cores will be presented elsewhere. The latter cores were augered 30 km apart and essentially represent the same atmospheric conditions such as temperature, snow accumulation, and chemical composition of the air. Here we present a comparison between the major volcanic signals over the past 4000 years in the GRIP core from central Greenland and the Dye 3 core from SE Greenland in order to investigate the depositional differences. Many of the major signals are detected in both cores, but some of the differences in the records can be used to infer the latitudinal band of some eruption sites. Furthermore, the influence of the amount of annual precipitation and glaciological postdepositional processes on the volcanic signals is discussed.
Long‐period changes in the bottom water flowing through Vema Channel
Authors: Hogg Nelson G. , Zenk Walter
Published: February 2004

Further details of the “warming” of bottom water flowing through the Vema Channel, first reported by Zenk and Hogg [1996], are given. Because cross‐channel gradients of temperature are large and the channel is narrow, careful analysis is required to determine whether or not the bottom water temperature minimum was adequately sampled by a particular station or cruise. During a period from 1972 to 1996, at least 14 visits with quality hydrographic measurements have been made to the region. Of these, 11 were judged successful, and their data indicate an abrupt rise in potential temperature by 0.03°C from −0.18°C to −0.15°C in the early 1990s that has remained until the latest observation in the spring of 1996. Although this observation is consistent with the report of warming of Antarctic Bottom Water in the Argentine Basin by Coles et al [1996], their associated conclusion that this water mass has also freshened by 0.008 psu (on potential density surfaces) is in contradiction with our finding of no measurable change.
Effects of small‐scale wind on coastal upwelling with application to Point Conception
Authors: Wang Dong‐Ping
Published: February 2004

A three‐dimensional, limited‐area, ocean general circulation model is used to study the response of the coastal ocean to small‐scale wind forcing. The model considers an idealized forcing of a semi‐infinite, upwelling‐favorable wind with a large positive wind curl at one end. Such a wind pattern is commonly found in the vicinity of capes and points where the synoptic‐scale wind is disturbed by coastal mountain ranges. The model study includes both process and hindcast studies. The process study considers the upwelling spinup and relaxation, driven by a positive wind curl. It also examines the model sensitivity to wind patterns and an external pressure force. The model results show that a strong poleward alongshore pressure gradient is set up by a positive wind curl. This pressure force drives an inshore poleward current into the upwelling region during active wind forcing, and it causes a surge of warm water into the upwelling zone during wind relaxation. The hindcast study is applied to the 1983 Organization of Persistent Upwelling Structures (OPUS) observations near Point Conception off central California. The simulation uses an idealized geometry but with observed winds. During OPUS, a sudden reversal of the surface equatorward currents occurred in the midst of a steady upwelling‐favorable wind. This unexpected coastal flow feature was faithfully reproduced in the model simulation.
A convection‐diffusion model for suspended sediment in the surf zone
Authors: Duy Nguyen The , Shibayama Tomoya
Published: February 2004

A model is developed to simulate the temporal and spatial distributions of suspended sediment in the surf zone. The model is solved numerically in a time domain and in a two‐dimensional vertical plane. At each time step of computation, the upper moving boundary (water surface) and the velocity field are determined through the solution of a hydrodynamic model which is based on the Reynolds equations of motion. The sediment concentration field is then determined by solving the convection‐diffusion equation of the sediment mass. The comparisons with laboratory data of various experimental conditions show reasonable agreements for the simulated wave field and the concentration field in the surf zone.
Thermohaline circulation and interaction between ice shelf cavities and the adjacent open ocean
Authors: Grosfeld K. , Gerdes R. , Determann J.
Published: February 2004

The circulation system in an ice shelf cavity is driven by buoyancy fluxes due to melting and freezing of ice and horizontal pressure gradients at the interface between the cavity and the open ocean. Hence the inflow and outflow pattern and the hydrography in the open ocean influence the general hydrographic condition in the cavity, which at least provides the potential for melting and freezing processes. Applying a three‐dimensional ocean general circulation model to an idealized ice shelf cavity geometry coupled with an open ocean at a topographic ice shelf barrier, we found an important parameter controlling the interaction between these two systems. Idealized studies for different ice shelf and sea bottom topographies and forcing mechanisms for the open ocean show that the ice shelf edge represents a natural barrier for barotropic interaction, because of the sudden decrease in water column thickness. Since the water column thickness and the Coriolis force determine the characteristics for geostrophic flow, separated circulation systems arise for the open ocean and the ice shelf cavity. Only in areas where constant water column thickness and, from the oceanographic point of view, constant ƒ/H contours can be observed across the barrier, an increased barotropic current can surmount the ice edge and ventilate the water mass beneath the ice shelf. This is only the case at lateral sloping sidewalls or at deep depressions, which can be found, for example, in the southern Weddell Sea. In all other cases the circulation in the ice shelf cavity is closed and almost unaffected by the hydrography outside the barrier.
Flow and recirculation of Antarctic Intermediate Water across the Rio Grande Rise
Authors: Boebel Olaf , Schmid Claudia , Zenk Walter
Published: February 2004

The flow of the low‐salinity Antarctic Intermediate Water (AAIW) at 700–1150 m depth across the Rio Grande Rise and the lower Santos Plateau is studied under the auspices of the World Ocean Circulation Experiment (WOCE) in the context of the Deep Basin Experiment. Our data set consists of several hydrographic sections, a collection of 15 RAFOS float trajectories, and records from 14 moored current meters. The data were gathered during different intervals between 1990 and 1994. The inferred flow field strongly supports a basinwide anticyclonic recirculation cell in the subtropical South Atlantic underneath the wind‐driven gyre. Its center, which appears to be southeast of the Rio Grande Rise, separates the eastward advection of AAIW below the South Atlantic Current from the westward flowing, recirculating AAIW. The two near‐shelf limbs closing the circumference of AAIW flow are formed in the east by the deep Benguela Current, potentially modulated by salty inflow of Indian Ocean Intermediate Water, and in the west by the Brazil Current system. Further important circulation elements are the Brazil‐Falkland (Malvinas) Confluence Zone at 40°S and an unnamed divergence at 28°S close to the 1000 m isobath. The resulting broad southward flow of AAIW augments the share of modified, i.e., saltier, intermediate water in the source region of the South Atlantic Current, while the smaller northward flow marks the source of a narrow equatorward Western Intermediate Boundary Current, ultimately leaving the South Atlantic. This shelf‐trapped jet is clearly documented in hydrographic data from 19°S and in nearby current meter records. The jet contrasts a sluggish flow across this latitude east of 35°W. A continuous flow of AAIW from its subpolar region in the southwestern Argentine Basin all along the western slope toward the equator appears unlikely between 35°S and 25°S.
Validity of the temperature reconstruction from water isotopes in ice cores
Authors: Jouzel J. , Alley R. B. , Cuffey K. M. , Dansgaard W. , Grootes P. , Hoffmann G. , Johnsen S. J. , Koster R. D. , Peel D. , Shuman C. A. , Stievenard M. , Stuiver M. , White J.
Published: February 2004

Well‐documented present‐day distributions of stable water isotopes (HDO and H218O) show the existence, in middle and high latitudes, of a linear relationship between the mean annual isotope content of precipitation (δD and δ18O) and the mean annual temperature at the precipitation site. Paleoclimatologists have used this relationship, which is particularly well obeyed over Greenland and Antarctica, to infer paleotemperatures from ice core data. There is, however, growing evidence that spatial and temporal isotope/surface temperature slopes differ, thus complicating the use of stable water isotopes as paleothermometers. In this paper we review empirical estimates of temporal slopes in polar regions and relevant information that can be inferred from isotope models: simple, Rayleigh‐type distillation models and (particularly over Greenland) general circulation models (GCMs) fitted with isotope tracer diagnostics. Empirical estimates of temporal slopes appear consistently lower than present‐day spatial slopes and are dependent on the timescale considered. This difference is most probably due to changes in the evaporative origins of moisture, changes in the seasonality of the precipitation, changes in the strength of the inversion layer, or some combination of these changes. Isotope models have not yet been used to evaluate the relative influences of these different factors. The apparent disagreement in the temporal and spatial slopes clearly makes calibrating the isotope paleothermometer difficult. Nevertheless, the use of a (calibrated) isotope paleothermometer appears justified; empirical estimates and most (though not all) GCM results support the practice of interpreting ice core isotope records in terms of local temperature changes.
Modeling spectra of breaking surface waves in shallow water
Authors: Chen Yongze , Guza R. T. , Elgar Steve
Published: February 2004

Predictions from Boussinesq‐equation‐based models for the evolution of breaking surface gravity waves in shallow water are compared with field and laboratory observations. In the majority of the 10 cases investigated, the observed spectral evolution across the surf zone is modeled more accurately by a dissipation that increases at high frequency than by a frequency‐independent dissipation. However, in each case the predicted spectra are qualitatively accurate for a wide range of frequency‐dependent dissipations, apparently because preferential reduction of high‐frequency energy (by dissipation that increases with increasing frequency) is largely compensated by increased nonlinear energy transfers to high frequencies. In contrast to the insensitivity of predicted spectral levels, model predictions of skewness and asymmetry (statistical measures of the wave shapes) are sensitive to the frequency dependence of the dissipation. The observed spatial evolution of skewness and asymmetry is predicted qualitatively well by the model with frequency‐dependent dissipation, but is predicted poorly with frequency‐independent dissipation. Although the extension of the Boussinesq equations to breaking waves is ad hoc, a dissipation depending on the frequency squared (as previously suggested) reproduces well the observed evolution of wave frequency spectra, skewness, and asymmetry.
Evaluation and diagnosis of surface currents in the National Centers for Environmental Prediction's ocean analyses
Authors: Acero‐Schertzer Carmen E. , Hansen Donald V. , Swenson Mark S.
Published: February 2004

Ensemble average currents from the 15 m depth level of the National Centers for Environmental Prediction's (NCEP) analyses of the tropical Pacific Ocean are evaluated against surface mixed layer current observations obtained from an extensive set of satellite‐tracked drifting buoys. These averages display many climatological characteristics of the region but are not intended to serve as a climatology because the data from the analyses are trimmed to match the time‐space distribution of the observations. Substantial discrepancies between the analyses and the observations are revealed. First, the near‐equatorial meridional currents and divergence have approximately twice the magnitude in the analyses as in the observations. This discrepancy is largely independent of whether temperature profile data are assimilated or not and is attributed to the parameterization of vertical viscosity. Second, the zonal flow in both the North Equatorial Countercurrent (NECC) and the South Equatorial Current (SEC) is much stronger in the analyses than in the observations, especially in the western Pacific. This discrepancy is associated with assimilation of temperature profile data. It arises because salinity is an active variable in the underlying analysis model but is not controlled by boundary fluxes or other observations. Under the uncontrolled influence of advection and strong horizontal diffusion the salinity distribution becomes nearly homogeneous. Consequently, the analyses do not account for observed temperature‐salinity correlations when density is computed following assimilation of temperature profile data. This leads to erroneous pressure gradients that drive excessively strong geostrophic currents and force large accelerations near the western boundary. Our results indicate that it is important to consider the consequences on the density structure of neglecting salinity during the assimilation of temperature data. We recommend that surface salinity observations from drifting buoys and volunteer observing ships be initiated to improve the ocean analyses.
Analyses of global sea surface temperature 1856–1991
Authors: Kaplan Alexey , Cane Mark A. , Kushnir Yochanan , Clement Amy C. , Blumenthal M. Benno , Rajagopalan Balaji
Published: February 2004

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.
Air content along the Greenland Ice Core Project core: A record of surface climatic parameters and elevation in central Greenland
Authors: Raynaud Dominique , Chappellaz Jerôme , Ritz Catherine , Martinerie Patricia
Published: February 2004

We present here measurements of the air content of the ice, V, performed along the Greenland Ice Core Project (GRIP) ice core. The main features of the long‐term trends are (1) a decrease of 13% between the last glacial maximum (LGM) and the earliest part of the Holocene, and (2) an increase of 8% during the Holocene. The resultsare discussed in terms of changes in atmospheric pressure, surface elevation and porosityat close‐off. The V record contains a significant signal of past changes of surface elevation in qualitative agreement with ice sheet modeling simulations. It suggests a thickening of central Greenland during the transition from the LGM to the early Holocene, and a significant thinning through the Holocene period. It also stresses the large influence on past V variations of changes in ice porosity, which are not explained by the present‐day spatial relationship with temperature and may reflect changes in other surface climatic parameters (like precipitation seasonality or wind stress). The potential role of temporalvariations of atmospheric pressure patterns is also evaluated. Air content results in the GRIP ice older than 110 ka indicate values approximately in the same range as those observed during the last 40,000 years, with generally higher air content corresponding to isotopically warmer ice.
Error analysis of empirical ocean tide models estimated from TOPEX/POSEIDON altimetry
Authors: Desai Shailen D. , Wahr John M. , Chao Yi
Published: February 2004

An error budget is proposed for the TOPEX/POSEIDON (T/P) empirical ocean tide models estimated during the primary mission. The error budget evaluates the individual contribution of errors in each of the altimetric range corrections, orbit errors caused by errors in the background ocean tide potential, and errors caused by the general circulation of the oceans, to errors in the ocean tide models of the eight principal diurnal and semidiurnal tidal components, and the two principal long‐period tidal components. The effect of continually updating the T/P empirical ocean tide models during the primary T/P mission is illustrated through tide gauge comparisons and then used to predict the impact of further updates during the extended mission. Both the tide gauge comparisons and the error analysis predict errors in the tide models for the eight principal diurnal and semidiurnal constituents to be of the order of 2–3 cm root‐sum‐square. The dominant source of errors in the T/P ocean tide models appears to be caused by the general circulation of the oceans observed by the T/P altimeter. Further updates of the T/P empirical ocean tide models during the extended mission should not provide significant improvements in the diurnal and semidiurnal ocean tide models but should provide significant improvements in the long‐period ocean tide models, particularly in the monthly (Mm) tidal component.
Effects of a sewage plume on the biology, optical characteristics, and particle size distributions of coastal waters
Authors: Petrenko A. A. , Jones B. H. , Dickey T. D. , LeHaitre M. , Moore C.
Published: February 2004

The effect of a sewage plume on the biology, optical characteristics, and particle size distributions of coastal waters was evaluated around the Sand Island, Hawaii, outfall diffuser. In situ physical and biooptical data and Niskin bottle samples were collected during a 1‐week cruise from September 25 to October 1, 1994. One or two layers affected by sewage could be distinguished in the water column: recently discharged (“new”) sewage plume waters and “old” plume waters. In conditions characterized by high Froude number the distribution of chlorophyll fluorescence in new plume waters was the same as for ambient waters, while for low Froude number, chlorophyll fluorescence increased within the plume, demonstrating the importance of physical forcing on effluent and phytoplankton interactions. New plume waters were associated with at least 2.7‐fold increases in particle load, high concentrations of particles larger than 70 μm, increases in ammonium, phosphate, and silicate, and high levels of heterotrophic bacteria and Prochlorococcus compared to surrounding waters. Both new and old plume layers, but not phytoplankton layers, showed distinct increases in fluorescence for the excitation/emission (Ex/Em) wavelength pair Ex/Em=228/340 in nm, interpreted as particulate tryptophan‐like fluorescence. Such fluorescence may be useful as a new in situ real‐time indicator of waters affected by effluent discharges.
Correlations between altimetric sea surface height and radiometric sea surface temperature in the South Atlantic
Authors: Jones Matthew S. , Allen Myles , Guymer Trevor , Saunders Mark
Published: February 2004

In the last decade, satellite altimetric measurements of sea surface height (SSH) and infrared radiometric measurements of sea surface temperature (SST) have provided a wealth of information about ocean circulation and atmosphere‐ocean interactions. SSH is a depth‐integrated quantity dependent upon the temperature and salinity structure of the water column and on the depth independent barotropic contribution. SST from infrared radiometers is a surface parameter representing the temperature of the top few microns of the ocean surface. Hence any relationship between SST and SSH provides dynamical information about the coupling between the ocean surface and subsurface. It also offers a promise of new techniques such as interpolating SSH data using SST and of improved calculations of eddy kinetic energy. We use SST data from the along‐track scanning radiometer on ERS‐I and SSH data from the TOPEX/POSEIDON instrument to examine the relationship between SST and SSH anomalies within the South Atlantic region for 1993 and 1994. We find that positive (≈0.2–0.6) spatial cross correlations between SST and SSH anomalies at zero lag are present throughout the region at large scales (wavelengths >1000 km). Small‐scale correlations, however, are high (≈0.7) only in areas associated with fronts and mesoscale variability. These small‐scale correlations are seasonal, being strongest in winter and weakest in summer. We discuss the application of these correlations to various techniques requiring the synergistic use of SSH and SST data.
Actual and potential information in dual‐view radiometric observations of sea surface temperature from ATSR
Authors: Murray M. J. , Allen M. R. , Mutlow C. T. , Závody A. M. , Jones M. S. , Forrester T. N.
Published: February 2004

The along‐track scanning radiometer (ATSR) on ERS‐1 has delivered a continuous global record of radiometric (skin) sea surface temperature (SST) since August 1991. We present a comprehensive analysis of the large‐scale and low‐frequency characteristics of the data set using direct comparison with other global SST analyses to develop a quantitative understanding of the various factors contributing to the accuracy of and sources of bias in the first 4 years of the ATSR SST record. Such a global analysis is a necessary complement to direct validation against in situ observations, since large‐scale sources of bias may be indistinguishable from instrument noise or sampling uncertainty in individual validation campaigns. No large‐scale features attributable to atmospheric contamination through aerosols or water vapor are discernible in the difference between the three‐channel, dual‐view ATSR SSTs and the National Oceanic and Atmospheric Administration (NOAA) blended analysis of advanced very high resolution radiometer (AVHRR) and in situ SST observations. Features in the difference field can be traced to known deficiencies in the data used in the NOAA operational analysis or tentatively related to skin‐bulk temperature differences in certain regions. Atmospheric contamination is, however, evident in the ATSR two‐channel SST retrieval (used in daytime and after the failure of the 3.7 μm channel) compared to the NOAA operational analysis. The Pinatubo aerosol plume is the dominant feature of the difference field in the first year of ATSR operation. In all cases, however, the amplitude of the atmospheric signature is significantly lower in dual‐view than in corresponding single‐view ATSR SSTs, indicating that the potential remains for unbiased two‐channel SST retrieval even in the presence of aerosol.
Physical forcing of phytoplankton dynamics in the southwestern Ross Sea
Authors: Arrigo Kevin R. , Weiss Andrea M. , Smith Walker O.
Published: February 2004

Coastal zone color scanner (CZCS) imagery of phytoplankton pigments and passive microwave imagery of sea ice distributions in the southwestern Ross Sea are presented for three different seasons (1978–1989, 1979–1980, and 1981–1982) and were analyzed in conjunction with meteorological data obtained from a series of automatic weather stations (AWS). Dynamics of the phytoplankton bloom in Terra Nova Bay differed from those in the Ross Sea owing to spatial differences in katabatic wind fields which determine when the surface waters stratify. Interannual variation in the timing of formation of the Ross Sea polynya appears to be controlled by winter temperatures, which determine sea ice thickness and integrity, rather than variability or intensity in wind stress. Together, CZCS, AWS, and passive microwave data suggest that when the Ross Sea polynya forms early, stronger and more frequent katabatic winds result in increased advective losses of phytoplankton in surface waters and a delay in the phytoplankton bloom. If polynya formation is delayed until after the winds diminish in frequency, the phytoplankton bloom will develop earlier. The observation that diatoms dominate both the marginal ice zone and Terra Nova Bay, which are hydrographically similar, while Phaeocystis antarctica is found in unstable waters north of the Ross Ice Shelf, suggests that stratification plays an important role in determining species composition in the Ross Sea.
Salinity effects in a tropical ocean model
Authors: Murtugudde Ragu , Busalacchi Antonio J.
Published: February 2004

A reduced gravity, primitive equation, ocean general circulation model (GCM) with a variable depth mixed layer and a natural boundary condition for freshwater fluxes is employed to investigate the role of salinity in tropical ocean dynamics and thermodynamics. Surface heat fluxes are computed without any feedback to observations by an advective atmospheric mixed layer (AML) model which is coupled to the ocean GCM. We analyze the differences in the tropical Atlantic, Pacific, and the Indo‐Pacific basins between control runs (simulations with complete hydrology) and simulations where (1) precipitation (P) is neglected, (2) salinity effects are neglected, or (3) salinity is held constant in each layer. Salinity contributes to pressure gradient forces, mixed layer processes, and vertical stability/mixing. Setting P = 0 in the tropical Atlantic produces larger sea surface temperature (SST) changes than previously estimated due to the realistic oceanic mixed layer model and surface flux formulation. Neglecting salinity effects leads to a different choice of mixing parameters, which feeds back into model dynamics and thermodynamics. Salinity anomalies produce an asymmetric response across the equator in the Atlantic due to differences in the air‐sea interactions. Including salinity effects in the tropical Pacific leads to an improved cold tongue simulation. The result is a reduced SST gradient at the equator which will have significant feedback in a coupled system. The same experiment with a restoring surface heat flux leads to an increased SST gradient, indicating that the surface flux parameterization is crucial for interpreting the role of salinity. The Indonesian throughflow (ITF) is reduced when salinity is neglected or held constant. The NINO3 and NINO4 SST indices are almost identical for the control run and the simulations when climatological P is used. However, associated subsurface temperature differences are larger, and they may play a role on decadal timescales. It is thus shown with a comprehensive set of experiments that even in the tropics, salinity plays an important role in the model dynamics and thermodynamics.
Statistical properties of global significant wave heights and their use for validation
Authors: Bauer Eva , Staabs Christoph
Published: February 2004

Global data sets of significant wave height (Hs) from altimeter measurements and from the wave model WAM are analyzed statistically to assess the quality of the data.Hsderived from the altimeters aboard Seasat (1978), Geosat (1988), ERS‐1 (1993, 1994), and TOPEX (1993, 1994) and from WAM (1988, 1993) and, in addition, from in situ data of Ocean Weather Station M in the North Atlantic are used. First, collocated data sets are compared through linear regression and principal component analysis. From this, a good agreement betweenHsof the ERS‐1 altimeter (1993) and the WAM model is inferred. Second, theHsfrequency distributions are described by the first four moments. Using the first four moments of linear order statistics, the lognormal and the general extreme value distribution function are found to approximate distributions ofHsbest.Hsfrom Seasat and ERS‐1 (1993) deviate from these empirical distribution functions, manifesting weaknesses in the data. AlthoughHsfrom ERS‐1 have weaknesses, their assimilation into WAM has a positive impact. The assessment of the quality of this existingHsdata provides a prerequisite for the coming assimilation schemes using wave data from synthetic aperture radars and also for climate research studies.
On the implementation of passive open boundary conditions for a general circulation model: The barotropic mode
Authors: Palma Elbio D. , Matano Ricardo P.
Published: February 2004

The objective of this study is to evaluate the performance of several open boundary conditions applied to the Princeton ocean model. The focus is on passive open boundary conditions applied to the external mode, i.e., conditions that are applied when the mean flow at the open boundary is unknown and the values of the variables must be assumed or extrapolated from the interior solution. Three types of open boundary conditions (OBCs) are tested: (1) radiation conditions, (2) characteristic methods, (3) relaxation schemes. Numerical experiments are conducted in a zonal channel that include different forms of bottom topography. The experiments are designed to emphasize flow conditions dominated by direct wind forcing or wave radiation. Three sets of experiments are discussed: (1) forcing by a uniform, alongshelf wind stress; (2) the barotropic adjustment of an initial perturbation in the sea surface elevation; and (3) forcing by a traveling storm. The results of these experiments are compared with analytical solutions and the results of experiments using cyclic boundary conditions, or expanded domains. According to our results all radiation schemes of Orlanski/s type perform poorly in either flows with strong nonlinear components or when the model response is dominated by the propagation of dispersive wave packets. The characteristic method recommended by Roed and Cooper [1987] provided reasonable responses in most cases, but we found problems in handling dispersive waves or variable wind forcing at the open boundaries. Although there were limitations in all the OBCs that we tested the best overall performances were for the conditions proposed by Flather [1976], combined with a local solution approach proposed by Roed and Smesdtad [1984], and the flow relaxation scheme developed by Martinsen and Engedahl [1987].