bluuebunny/crossref_metadata_2025 huggingface dataset:
Sea‐air flux of CO2 in the North Pacific using shipboard and satellite data
Authors: Stephens Mark P. , Samuels Geoffrey , Olson Donald B. , Fine Rana A. , Takahashi Taro
Published: February 2004

A method has been developed to produce high‐resolution maps of pCO2 in surface water for the North Pacific using satellite sea surface temperature (SST) data and statistical relationships between measured pCO2 and temperature. In the subtropical North Pacific the pCO2 in seawater is controlled primarily by temperature. Accordingly, pCO2 values that are calculated from the satellite SST data have good agreement with the measured values (rms deviation of ±17 μatm). In the northwestern subpolar region the pCO2 is controlled not only by temperature, but also by significant seasonal changes in the total CO2 concentration, which are caused by seasonal changes in primary production, mixing with subsurface waters, and sea‐air exchange. Consequently, the parameterization of oceanic pCO2 based on SST data alone is not totally successful in the northwestern region (rms deviation of ±40 μatm). The use of additional satellite products, such as wind and ocean color data, as planned for a future study, is considered necessary to account for the pCO2 variability caused by seasonal changes in the total CO2 concentration. The net CO2 flux for the area of the North Pacific included in this study (north of 10°N) has been calculated using the monthly pCO2 distributions computed, and monthly wind speeds from the European Centre for Medium‐Range Weather Forecasts. The region is found to be a net source to the atmosphere of 1.9×1012 to 5.8×1012 moles of CO2 per year (or 0.02–0.07 Gt C/yr), most of the outflux occurring in the sub tropics.
Rings of the North Brazil Current: Their structure and behavior inferred from observations and a numerical simulation
Authors: Fratantoni David M. , Johns William E. , Townsend Tamara L.
Published: February 2004

Large anticyclonic rings are shed from the retroflecting North Brazil Current (NBC) near 8°N in the tropical western Atlantic. New subsurface velocity and temperature measurements within three such rings are presented here and are found to be consistent with previous in situ and remotely sensed NBC ring measurements. A high‐resolution numerical model of the Atlantic Ocean forced by monthly wind stress and an imposed meridional overturning cell is found to shed NBC rings that approximate those observed. The model rings are more surface‐intensified than those observed and somewhat smaller in diameter. Both observed and modeled NBC rings move northwestward along the coast of South America with a speed of 8–16 cm/s, considerably slower than predicted by analytical theories describing westward ring propagation. At least 2–3 rings per year separate from the NBC retroflection. Annually, 1–3 rings translate intact from their formation region near 50°W to the islands of the southeastern Caribbean, where they disintegrate after a lifetime of about 100 days. The volume of fluid trapped within the core of an NBC ring and isolated from external mixing is estimated using potential vorticity as a tracer. The horizontal limits of the trapped core volume closely coincide with the radius of maximum swirl velocity, while the vertical limit of the core is typically less than the subsurface extent of significant swirl velocity. The core volume of a typical observed ring is 3.2±1.0×1013 m3. This corresponds to an annualized per‐ring mass transport near 1 Sv (106 m3/s), similar to previous estimates. This study is the first to make use of subsurface temperature and velocity data to compute the volume of the anomalous ring core. NBC rings may be responsible for 3–4 Sv of direct mass transport across the equatorial‐tropical gyre boundary or 20–25% of the total upper ocean cross‐gyre transport required by the Atlantic meridional overturning cell. Translating NBC rings may contribute 20% of the total meridional heat transport by the ocean at this latitude.
Polarimetric signatures of sea ice: 1. Theoretical model
Authors: Nghiem S. V. , Kwok R. , Yueh S. H. , Drinkwater M. R.
Published: February 2004

Physical, structural, and electromagnetic properties and interrelating processes in sea ice are used to develop a composite model for polarimetric backscattering signatures of sea ice. Physical properties of sea ice constituents such as ice, brine, air, and salt are presented in terms of their effects on electromagnetic wave interactions. Sea ice structure and geometry of scatterers are related to wave propagation, attenuation, and scattering. Temperature and salinity, which are determining factors for the thermodynamic phase distribution in sea ice, are consistently used to derive both effective permittivities and polarimetric scattering coefficients. Polarimetric signatures of sea ice depend on crystal sizes and brine volumes, which are affected by ice growth rates. Desalination by brine expulsion, drainage, or other mechanisms modifies wave penetration and scattering. Sea ice signatures are further complicated by surface conditions such as rough interfaces, hummocks, snow cover, brine skim, or slush layer. Based on the same set of geophysical parameters characterizing sea ice, a composite model is developed to calculate effective permittivities and backscattering covariance matrices at microwave frequencies for interpretation of sea ice polarimetric signatures.
Carbonate chemistry of the Sea of Japan
Authors: Chen Chen‐Tung Arthur , Wang Shu‐Lun , Bychkov Alexander S.
Published: February 2004

The alkalinity and total CO2 data were collected during the Kuroshio Edge Exchange Processes‐Marginal Sea Studies expedition (July 28 to August 5, 1992) in the Sea of Japan. The concentrations of normalized alkalinity (NTA = TA × 35/S) (S represents salinity) and normalized total CO2 (NTCO2 = TCO2 × 35/S) in the deep water are fairly low relative to that of the northwest Pacific Ocean, indicating relatively little CaCO3 dissolution and organic carbon decomposition in the subsurface waters of the Sea of Japan. A benthic front between the deep water and the bottom water can be characterized by discontinuities of dissolved oxygen and NTCO2 at about 2000 m. The bottom water is quite homogeneous with θ = 0.1 ± 0.05°C, S = 34.07 ± 0.005, dissolved oxygen = 215 ± 5 μmol/kg, NTA = 2373 ± 5 μmol/kg, and NTCO2 = 2297 ± 5 μmol/kg. The inorganic carbon/organic carbon ratio shows that about a 15% increase in NTCO2 of the deep water is contributed by the inorganic CaCO3 dissolution. This is rather low compared to the open Pacific Ocean values of 30–40%. The degrees of saturation with respect to calcite and aragonite show that the deep water is undersaturated with respect to calcite below 1300 m. The water below 300 m is undersaturated with respect to aragonite. Excess CO2 is present from surface to bottom, confirming rapid turnover of the Sea of Japan deep water (100 years turnover time) reported previously based on tritium, fréons 11, 12, and 226Ra data. Previous age estimation of 300 years for deep waters based on 14C data was inconsistent with the above results. Recalculation based on proper prebomb Δ14C value gives an age of about 120 years for deep Sea of Japan water. Overall, the Sea of Japan contains 3.1±0.5×1014 g excess carbon.
Comparison of shear measurements and mixing predictions with a direct observation of diapycnal mixing in the Atlantic thermocline
Authors: Duda Timothy F. , Jacobs David C.
Published: February 2004

Four sets of velocity and density profiles have been measured with an autonomous profiler during an upper ocean intentional‐tracer (SF6) diapycnal diffusivity measurement, the North Atlantic Tracer Release Experiment (NATRE). The tracer was injected near 310 m depth in the Canary Basin. Two profile sets were collected 6 months after tracer release, and two were collected 1 year after release, all within the horizontal boundaries of the SF6 patch. Shear and strain can be combined with turbulent kinetic energy dissipation and diffusivity measurements (published elsewhere) to test existing expressions for dissipation and diffusivity due to shear‐induced turbulence. These expressions arise from internal‐wave decay modeling. One expression of dissipation parameterized in terms of shear, based on stochastic nonlinear internal‐wave interaction, has fared well empirically; its extension to estimate diffusivity is evaluated. Shear variance of the first two data sets was about 1.6 times GM76, and 2.5 to 3.0 times GM76 in the later sets. The average parameterized mixing estimate computed using all of the temporally limited shear measurements overestimates annual mean NATRE diffusivity, 1.5×10−5 m2 s−1, by a factor of 1.2. A modified parameterization gives an underestimate. To first order, this supports the present understanding of open‐ocean diffusivity in terms of fine‐scale shear and internal‐wave decay, that is, the slow diapycnal mixing was not a consequence of unusually low shear. Adjustment of the shear‐induced mixing models to better fit the data is not warranted because of the lack of direct comparability between the various measurements, the expected natural variability of the shear, and sampling errors.
Variability in the central equatorial Pacific, 1985–1989
Authors: Chiswell S. M. , Donohue K. A. , Wimbush M.
Published: February 2004

We describe variability in the equatorial Pacific Ocean near 160°W during the 5‐year period 1985–1989, encompassing “normal”, El Niño, and La Niña conditions. This description is based on conductivity‐temperature‐depth and acoustic Doppler current profiler data acquired during five cruises between 21°N and 4°S and on dynamic‐height time series from an array based mainly on the Line Islands. At Jarvis Island, near the equator, the time series of dynamic height and near‐surface temperature go back to 1981 and show the 1986–1987 El Niño anomalies starting later in the year and having longer duration than those of the 1982–1983 El Niño. Dynamic‐height anomaly was less strong for the 1986–1987 event, but the near‐surface temperature anomaly was of similar magnitude for the two El Niños. The Jarvis near‐surface temperature drop from 1986–1987 El Niño maximum to 1988–1989 La Niña minimum was 8°C. Empirical orthogonal function analysis of the time series shows that interannual and interseasonal variability in dynamic height was dominated by a mode with meridional form similar to a first‐vertical‐mode Kelvin wave, while intraseasonal variability had a primary mode with a single peak at 6°N and a secondary mode with peak at 6°N and trough at 2°N. While the equatorial thermocline deepened to the east and shoaled to the west during the 1986–1987 El Niño, at 160°W it did not change depth during either this El Niño or the subsequent La Niña. Nevertheless, just before El Niño and just after La Niña, the thermocline was observed to be about 50 m deeper than at other times. The South Equatorial Current and North Equatorial Countercurrent had markedly reduced (increased) transports during this El Niño (La Niña). However, the Northern Tsuchiya Jet strengthened during El Niño and weakened during La Niña.
Seabed drag coefficient under tidal currents in the eastern Irish Sea
Authors: Green Malcolm O. , McCave I. N.
Published: February 2004

Over a 2‐month period the seabed drag coefficient C100 at a site in the eastern Irish Sea (26‐m water depth) had a mean value of 0.0025, which is the value typically assumed, but was highly variable. The objective of the analysis was to unravel the causes of the variability in C100. An error analysis revealed that a considerable part of the variability could be due simply to random errors in the estimates of friction velocity, from which C100 was deduced, but the error bounds did not enclose all of the data. Wave‐current interaction was ruled out as the principal cause of the variability because waves were small and there was no noticeable correlation between C100 and ratio of wave‐orbital speed to tidal‐current speed. Classifying the boundary‐layer flow into smooth‐turbulent, transitional, and rough‐turbulent regimes implied that flow‐regime transitions could explain much of the variability, however, inspection of the data revealed a contradiction that made that explanation unlikely: the classification implied that the boundary‐layer flow was rough turbulent during neap tides but was smooth turbulent under peak spring‐tide currents. The classification scheme was based on the assumption of neutral stability, which, according to the stability parameter z / L, was violated for a considerable portion of the time. Boundary‐layer stratification by suspended sediment was found to provide a coherent explanation for drag coefficient variability; when z / L < 0.03, C100 was relatively constant, which reflected a relatively constant underlying bed roughness, but when z / L > 0.03, the buoyancy flux due to the suspended sediment caused C100 to vary widely. The analysis of the stratified‐flow dynamics includes the development of an equation (correct to second order in z / L, where z / L is small) for estimating bed shear stress from the velocity spectrum, which extends the applicability of the well‐known “inertial‐dissipation” method into the region z / L > 0.03.
Global ocean tides from ERS 1 and TOPEX/POSEIDON altimetry
Authors: Andersen Ole Baltazar
Published: February 2004

Ocean tide models representing all major diurnal and semidiurnal tidal constituents with a spatial resolution of 0.75°×0.75° have been estimated using the first 1.5 years of ERS 1 and TOPEX/POSEIDON altimetry. The ocean tide model was derived from the combined use of ERS 1 and TOPEX/POSEIDON data by using a modified orthotide formulation that simultaneously solves for all diurnal and semidiurnal constituents as well as the annual signal. An additional adjustment of the solar semidiurnal harmonic of the gravitational potential was applied in order to account for radiational forcing, particularly in the S2 constituent. TOPEX/POSEIDON provides excellent ocean tide estimates in the open ocean. However, especially in coastal regions, the track spacing of TOPEX/POSEIDON (315 km at the equator) is too coarse to determine large parts of the ocean tide signal. For these regions the inclusion of data from the ERS 1 35‐day repeat mission provides a valuable supplement, as the ERS 1 satellite has a track spacing which is around 3.6 times better than that of the TOPEX/POSEIDON satellite. The combined ERS 1 and TOPEX/POSEIDON ocean tide solution exhibits distinct sectoral geographical pattern of highs and lows when compared with the Cartwright and Ray (1990, 1991) ocean tide model. This indicates the presence of small but fundamental orbit errors present in the Cartwright and Ray ocean tide solution. Compared with a new set of 104 tide gauge readings compiled by Le Provost, the RMS differences of the combined ERS 1 and TOPEX solution are 2.51, 1.67, 1.58, and 1.13 cm for the M2, S2, K1, and O1 constituents, respectively. The increased spatial resolution of the combined ERS 1 and TOPEX model as compared to a TOPEX‐alone model is seen to reduce RMS differences from 37 to 22 cm for the M2 constituent, when compared to a selection of 90 pelagic and coastal tide gauges in the northwest European shelf region.
On the relationship between long‐term salinity variations and river discharge in the middle reach of the Delaware estuary
Authors: Wong Kuo‐Chuin
Published: February 2004

Daily averaged salinity measurements made in the middle reach of the Delaware estuary over the past three decades indicate the presence of significant subtidal variability. The salinity signals are dominated by variabilities at seasonal to interannual timescales. For any given month of the year the interannual variability accounted for more than 80% of the total deviations from the climatological mean monthly distributions. Variability at timescales shorter than a month is relatively insignificant. The long‐term variations in salinity are closely correlated with the Delaware River discharge, with higher discharge corresponding to lower salinity and vice versa. Contrary to expectation, the long‐term variations in the axial salinity gradient appear to have a negative correlation with the river discharge, with an increase in discharge corresponding to a reduction in the axial salinity gradient and vice versa. A number of factors, including the downstream movement of the salt intrusion limit beyond the observational station, the variation in the vertical salinity structure, and the possible existence of significant lateral variability may contribute to the observed response of the axial salinity gradient to different river discharge conditions.
Heat balance estimates using atmospheric analysis data: A case study for the Black Sea
Authors: Staneva J. V. , Stanev E. V. , Rachev N. H.
Published: February 2004

The heat balance for the Black Sea is estimated, based on classical bulk formulas, using the U. S. National Meteorological Center atmospheric analysis data and different types of sea surface temperature data. The main focus in the study is on the sensitivity of the heat fluxes to the input data. The contribution of the short‐period variability to the heat flux components is evaluated. It is shown that the use of monthly averaged atmospheric data produces substantial inconsistencies in the heat flux estimates due to inaccurate calculation of the nonlinear terms in the bulk formulas. Inventory of the past estimates for the Black Sea heat flux components and intercomparison with the ones calculated in this paper are carried out. Error estimates for experiments using independent sea surface temperature data are analyzed.
Upper ocean variability on the equator in the Pacific at 170°W
Authors: Weisberg Robert H. , Hayes Stanley P.
Published: February 2004

The monitoring of upper ocean velocity, temperature, and surface winds at 0°, 170°W was initiated in May 1988 as part of the Tropical Ocean‐Global Atmosphere program. Located between regions of warm (cold) sea surface temperature in the western (eastern) equatorial Pacific, this west central region exhibits large interannual variations in surface wind stress associated with the El Niño‐Southern Oscillation. Here we report on the first 3 years of data collected at 0°, 170°W, exclusive of an El Niño event. The west central Pacific is a region through which the Equatorial Undercurrent (EUC) accelerates downstream. The vertical position of the EUC core, the vertical penetration of the South Equatorial Current (SEC), and the vertically integrated zonal volume transport all show large annual cycles. Annual and higher‐frequency transport variations are due primarily to fluctuations occurring above the thermocline, as opposed to within the EUC itself. Unlike the EUC position, the EUC core speed remains relatively steady annually, except during boreal fall and winter, when short duration, zonal momentum pulses generated as Kelvin waves to the west reduce the EUC to minimal values. Interannually, the EUC core speed was highest in 1988, and it has decreased, on average, since then. Also during 1988, tropical instability waves, generally observed farther east, were well developed at 170°W, while not in subsequent years. This suggests the same role interannually as annually for these waves: to smooth out heat and momentum gradients that form in response to the wind stress. (The winds in 1988, following the 1986–1987 El Niño, were stronger than in subsequent years.) At higher frequencies, evidence exists for an inertial‐gravity wave mode previously identified in nearby Canton Island sea level records.
An examination of the North Pacific Ocean in the spectral domain using Geosat altimeter data and a numerical ocean model
Authors: Jacobs G. A. , Teague W. J. , Mitchell J. L. , Hurlburt H. E.
Published: February 2004

The sea surface height (SSH) variations of the North Pacific ocean and the Kuroshio Extension region, in particular, are examined by frequency and wavenumber decompositions of a 1/8°, six‐layer primitive equation Pacific Ocean model and of the Geosat Exact Repeat Mission (ERM) data. Both data sets exhibit peaks in variability at 1 and 2 cycles per year over much of the Kuroshio Extension region. This study is restricted to these two frequencies. Annual variations of equatorial currents in both data sets are similar in both space and time, with the variations in the South Equatorial Current appearing as annual westward propagations. Annual variations in the strength of the Kuroshio Extension are manifested mainly through changes in the strength of the recirculation gyres on the southern side of the current. Annual transport maxima for the Kuroshio Extension occur around late October for both the model and Geosat. Large‐scale variations (length scales greater than 1000 km) of the model and Geosat have comparable amplitudes. The main differences between the model SSH and the Geosat ERM data occur over regions where seasonal steric variations are significant (from 20°N to 30°N). Wavenumber spectra over the Kuroshio Extension region reveal similar dynamics in both data sets. Much of the energy in wavenumber spectra appears as westward propagating SSH anomalies near the theoretical Rossby wave dispersion relations. As the Rossby wave dispersion relation changes with latitude (shifting to shorter wavelengths with higher latitudes), the peaks in the wavenumber decompositions follow. Thus the dynamics are generally consistent with quasi‐geostrophic dynamics in both the model and altimeter data. Wavelengths of propagating SSH anomalies which have spectral peaks near the Rossby dispersion curve are longer in the Geosat and model than wavelengths indicated by theory. In the semiannual frequency below 35°N, westward propagation dominates over eastward propagation in both Geosat and the model. Most differences in the dynamics of the model and Geosat occur at shorter length and timescales, with Geosat showing higher amplitudes at the shorter scales than the model.
Effects of turbulence intermittency on growth inhibition of a red tide dinoflagellate, Gonyaulax polyedra Stein
Authors: Gibson Carl H. , Thomas William H.
Published: February 2004

Thomas and Gibson (1990a, b) quantified the rate of strain γ required to inhibit the growth of the red tide dinoflagellate Gonyaulax polyedra Stein in a Couette flow device that produces an effectively constant γ value to represent the small‐scale shear encountered by dinoflagellates in turbulent flow. A continuous γ value of about 8 rad s−1 was found to cause zero‐growth rates, >8 caused negative growth, and < 2 caused no effect. Measurements of the same organism in the same device with intermittent γ show that the daily average γ threshold for zero growth
does not require continuous shear but decreases to values smaller than 0.09 rad s−1 with increasing intermittency (decreasing fraction of the time of shear application) up to a limiting minimum time period of 5–15 min. When γ values of 9 rad s−1 were applied for periods of only 2.5,1, and 0.25 hours during a day, increasingly negative growth rates were observed (although 5 min had no effect). Thus
was reduced by 2 orders of magnitude by intermittency of the simulated turbulence. Because turbulence near the sea surface is intermittent, especially when waves are breaking, the effects on dinoflagellate growth inhibition will be larger and extend to much greater depths than might be expected from only the
profile. Comparison with the lagged correlations of wind wave spectral components versus oceanic phytoplankton growth (Tynan, 1993), showing larger negative correlations between dinoflagellate concentration and waves than with winds, suggests a similar response exists between dinoflagellate growth inhibition in natural populations and turbulence intermittency and strength. Diatoms exhibit the opposite response, with growth enhancement.
Orbit and tide error reduction for the first 2 years of TOPEX/POSEIDON data
Authors: Tai Chang‐Kou , Kuhn John
Published: February 2004

More than 2 years of TOPEX/POSEIDON data (repeat cycles 1–81) are processed with orbit and tide error reduction schemes that preserve the oceanic signal. The rms crossover difference (XD) between heights belonging to the same cycle is a good measure of the errors because the real oceanic variability manifests little of itself in times less than 10 days. This rms XD is reduced from 10.8 to 8.1 cm after the tide error correction and to 6.0 cm after the orbit error reduction and editing, a more than threefold reduction in power, even for the remarkably error‐free TOPEX/POSEIDON data. If the mesoscale variability that manages to reveal itself in less than 10 days (e.g., in the western boundary currents) and residual coastal tide errors are screened out, the global area‐weighted residual XD is only 4.3 cm, implying that for variability studies the residual error is only 3.0 cm for instantaneous point measurements of altimetric sea level away from coastal regions, far exceeding the prelaunch mission requirement. The important issue of signal preservation (which has been shown analytically elsewhere) is addressed here directly using data treated with orbit reduction as well as untreated data. It is shown that the time‐compartmentalized orbit error reduction leaves the annual heating and cooling cycle intact as anticipated by the analytical proof, whereas conventional orbit error removal procedures would wreak havoc. The error of the Cartwright and Ray (1991) tide model is estimated to be in excess of 5 cm (global area‐weighted rms including shallow seas). The crossover‐difference‐inducing part of the orbit correction (which includes any short‐term, large‐scale, along‐track variations) is estimated to be 3.3 cm (along‐track rms) for the Joint Gravity Model 2 orbit. The total orbit error is estimated to be 3.5 cm, an independent confirmation of estimates based on satellite tracking and other means.
Seasonal simulation of the Southern Ocean coupled ice‐ocean system
Authors: Häkkinen Sirpa
Published: February 2004

The Southern Ocean ice‐ocean system is investigated using a coupled model developed at Princeton University. The ocean model uses the primitive equations and solves the second‐moment closure for turbulent mixing; the snow‐ice model uses a three‐level thermodynamic scheme resembling Semtner's (1976) model. The focus here is to study the seasonal variability of the ice covered areas and water mass formation. The model simulates reasonably well the seasonal cycle of the ice cover in the Southern Ocean. The annual rapid advance of the ice extent is tied to the ice advection away from the coast toward the Antarctic Circumpolar Current (ACC), where it melts rapidly with the increase of radiative fluxes in the austral spring. The European Center for Medium‐Range Weather Forecasts climatology tends to produce too little ice in the Pacific sector, for which the primary cause is a weak meridional wind stress. The oceanic heat fluxes are up to 100 W m−2 in open water areas and along the coastal areas except in the Weddell and Ross Seas, which are occupied by a year‐round sea ice cover and have average heat flux of 20 W m−2 or less. However, there is a small region in the Ross Sea with high heat loss suggesting deep convection. The meridional and zonal heat fluxes are in reasonable agreement with observational estimates. The Atlantic meridional heat flux is zero at 34°S (northern boundary of the model), which is an inadequacy in the model. In the Indian Ocean sector the flux is southward, while in the Pacific sector it is weak and equatorward. From the water mass balance we can deduce that the Antarctic Bottom Water (AABW) (σt > 27.85) annual production is 12 Sv in the Atlantic sector and 5 Sv in the Ross Sea. The total production of 17 Sv is in excellent agreement with the observational estimates of 10–20 Sv. Intermediate water types are produced in the Indian Ocean sector, where some of the AABW is lost during that conversion. In the Atlantic sector, 6 Sv of the annually formed AABW is advected north across the ACC. In the Pacific sector the northward AABW flow is 7.5 Sv, which is in excess of the Ross Sea production, suggesting that a considerable portion of the AABW formed in the Weddell Sea is contributing to that flux.
Subgrid parameterization of surface heat and momentum fluxes over polar oceans
Authors: Vihma Timo
Published: February 2004

The parameterization of heat and momentum fluxes over a heterogeneous surface consisting of sea ice and large areas of open ocean (polynyas) has been studied. Various theories required to calculate grid‐averaged fluxes are discussed, and a two‐dimensional mesoscale boundary layer model has been applied to simulate the flow and heat exchange processes inside a single grid element of a hypothetical atmospheric general circulation model. The theories are compared with model results. Considering the surface fluxes of sensible and latent heat, a mosaic method, based on the use of estimates for local surface temperature, air temperature, specific humidity, and wind speed over the ice‐covered and ice‐free parts of the grid square, performed well in the comparison. Parameterizing the net longwave radiation, an estimate for the subgrid distribution of cloudiness was useful. Parameterization of surface momentum flux seemed to be most reasonable on the basis of the surface pressure field and a geostrophic drag coefficient depending on the air‐surface temperature difference.
Solar heating of the Arctic mixed layer
Authors: Maykut G. A. , McPhee Miles G.
Published: February 2004

Data from the 1975 Arctic Ice Dynamics Joint Experiment (AIDJEX) are used to examine energy exchange between the Arctic mixed layer and the ice pack. Conductivity‐temperature‐depth profiles from four drifting stations reveal significant heat storage in the upper 50 m of the water column during summer, with mixed layer temperature elevation above freezing δT reaching as high as 0.4°C. Combining δT with turbulent friction velocity obtained from local ice motion provides an estimate of heat flux from the ocean to the ice Fw which was found to be strongly seasonal, with maximum values reaching 40–60 W m−2 in August. The annual average value of Fw was 5.1 W m−2, about half again as large as oceanic heat flux inferred from bottom ablation measurements in undeformed ice at the central station. Solar heat input to the upper ocean through open leads and thin ice, estimated using an ice thickness distribution model, totaled about 150 MJ m−2, in general agreement with integrated values of Fw. Results indicate that oceanic heat flux to the ice in the central Arctic is derived mainly from shortwave radiation entering the ocean through the ice pack, rather than from diffusion of warm water from below. Indeed, during the AIDJEX project the mixed layer appears to have contributed 15–20 MJ m−2 of heat to the upper pycnocline. During the summer, Fw was found to vary by as much as 10–30 W m−2 over separations of 100 to 200 km and thus represents an important term in the surface heat budget not controlled by purely local deformation and thermodynamics.
Barotropic tides in the global oceans from a nonlinear tidal model assimilating altimetric tides: 1. Model description and results
Authors: Kantha Lakshmi H.
Published: February 2004

In this first part of a two‐part paper we present results from a high‐resolution, data‐assimilative, fully nonlinear barotropic tidal model of the global oceans that excludes the Arctic. The model assimilates, in waters deeper than 1000 m, altimetric tides derived from the analysis of 2 years of TOPEX altimetric data. It also assimilates tide gage data from coastal tide gages. The model domain includes that covered by the altimeter and extends to the Antarctic. In the first part we present tidal results for the primary semidiurnal (M2, S2, N2, and K2) and diurnal (K1, O1, P1, and Q1) constituents. The second part deals with applications (Kantha, et al., this issue). The model results are compared with observational data from pelagic gages. These comparisons show that overall in the open ocean, in deep waters away from the margins of the primary basins, the model performance is comparable to other tidal models derived using TOPEX data, except for M2 and S2. However, one advantage of this model compared with those based solely on the analysis of altimetric data is that the altimetry‐derived tides are subjected to dynamical constraints by the model. This results in reduction of subtidal variability often folded into tidal signals by TOPEX data analysis. It is also shown that in shallow waters along the margins, especially in east Asian marginal seas, the model differs substantially from these other models. In addition to sea surface heights, we also present dynamically consistent barotropic currents in the form of tidal ellipses for M2 and K1 constituents. Since the goal of this research is a global tidal model uniformly valid in both deep and shallow waters, we finally present tidal elevations and currents on two well‐known shallow water areas, the northwest European shelf and the northeast American shelf, and a semienclosed western Pacific marginal sea, the Bering Sea. The model results are compared with independent observations and, where possible, with results from other numerical models. The results highlight the importance of bottom topography; on the northwest European shelf, where accurate bottom topography was included in the model, the results are much better than on the northeast American shelf, where the Digital Bathymetric Data Base 5 (DBDB5) topographic database has significant errors. Results from the Bering Sea, where the topography is more accurate than the DBDB5, compare well with known tides in the region.
Intercomparison of recent ocean tide models
Authors: Andersen O. B. , Woodworth P. L. , Flather R. A.
Published: February 2004

One of the tremendous achievements of the TOPEX/POSEIDON (T/P) satellite mission is the release of 12 new global ocean tide models during 1994. Virtually all of these models are based on the high‐precision altimetry obtainable from the T/P satellite, and all of the models are superior to both the Cartwright and Ray (1990, 1991) model as well as to the Schwiderski (1980a, b) model when compared to tide gauges. In the present intercomparison, only global ocean tide models released during 1994 have been tested. As T/P continues to operate, new ocean tide models will continue to be released and existing ocean models will be updated. Hence this intercomparison can only present a snapshot of the “state of the art” within ocean tide modeling. However, the intercomparison demonstrates the high accuracy and consistency of all these recent ocean tide models. From a comparison with a common 104 tide gauge data set compiled by Le Provost and others (unpublished data), the general result is that, six of the new ocean tide models have RMS agreement better than 3 cm. The obtainable accuracy with different tide gauge types raises the question about the accuracy of “ground truth.” As ocean tide models become increasingly more accurate, the accuracy of the harmonic constants derived from the tide gauge recordings becomes significant. Generally, the RMS agreement between models based on 2 years of T/P altimetry is significantly better than the agreement between models based on 1 year of T/P altimetry. For models based on two years of T/P altimetry the RMS agreement has values around 2.0, 1.4, 1.0, and 0.7 cm for the M2, S2, K1and O1constituents, respectively. As a preliminary evaluation, these values might be taken as a measure of the consistency of ocean tides estimated from the first part of the T/P mission, which is extremely promising for future ocean tide models derived from T/P altimetry using 3 or more years of data. This also suggests that further improvement using 3 or more years of data will only be marginal. The differences arise when studying the ocean tides on continental shelves surrounding the ocean. Major differences are seen, especially on the Patagonian shelf. As the continental shelves are critical for tidal dissipation, it will be very important to improve tide models on the shelves in future global ocean tide models.
Generation and propagation of infragravity waves
Authors: Herbers T. H. C. , Elgar Steve , Guza R. T.
Published: February 2004

The generation and propagation of infragravity waves (frequencies nominally 0.004–0.04 Hz) are investigated with data from a 24‐element, coherent array of pressure sensors deployed for 9 months in 13‐m depth, 2 km from shore. The high correlation between observed ratios of upcoast to downcoast energy fluxes in the infragravity (FupIG/FdownIG) and swell (Fupswell/Fdownswell) frequency bands indicates that the directional properties of infragravity waves are strongly dependent on incident swell propagation directions. However, FupIG/FdownIG is usually much closer to 1 (i.e., comparable upcoast and downcoast fluxes) than is Fupswell/Fdownswell, suggesting that upcoast propagating swell drives both upcoast and downcoast propagating infragravity waves. These observations agree well with predictions of a spectral WKB model based on the long‐standing hypothesis that infragravity waves, forced by nonlinear interactions of nonbreaking, shoreward propagating swell, are released as free waves in the surf zone and subsequently reflect from the beach. The radiated free infragravity waves are predicted to be directionally broad and predominantly refractively trapped on a gently sloping shelf. The observed ratios FseaIG/FshoreIG of the seaward and shoreward infragravity energy fluxes are indeed scattered about the theoretical value 1 for trapped waves when the swell energy is moderate, but the ratios deviate significantly from 1 with both low‐ and high‐energy swell. Directionally narrow, shoreward propagating infragravity waves, observed with low‐energy swell, likely have a remote (possibly trans‐oceanic) energy source. High values (up to 5) of FseaIG/FshoreIG, observed with high‐energy swell, suggest that high‐mode edge waves generated near the shore can be suppressed by nonlinear dissipation processes (e.g., bottom friction) on the shelf.
Modeling the heating and melting of sea ice through light absorption by microalgae
Authors: Zeebe Richard E. , Eicken Hajo , Robinson Dale H. , Wolf‐Gladrow Dieter , Dieckmann Gerhard S.
Published: February 2004

In sea ice of polar regions, high concentrations of microalgae are observed during the spring. Algal standing stocks may attain peak values of over 300 mg chl a m−2 in the congelation ice habitat. As of yet, the effect of additional heating of sea ice through conversion of solar radiation into heat by algae has not been investigated in detail. Local effects, such as a decrease in albedo, increasing melt rates, and a decrease of the physical strength of ice sheets may occur. To investigate the effects of microalgae on the thermal regime of sea ice, a time‐dependent, one‐dimensional thermodynamic model of sea ice was coupled to a bio‐optical model. A spectral one‐stream model was employed to determine spectral attenuation by snow, sea ice, and microalgae. Beer's law was assumed to hold for every wavelength. Energy absorption was obtained by calculating the divergence of irradiance in every layer of the model (Δz = 1 cm). Changes in sea ice temperature profiles were calculated by solving the heat conduction equation with a finite difference scheme. Model results indicate that when algal biomass is concentrated at the bottom of congelation ice, melting of ice resulting from the additional conversion of solar radiation into heat may effectively destroy the algal habitat, thereby releasing algal biomass into the water column. An algal layer located in the top of the ice sheet induced a significant increase in sea ice temperature (ΔT > 0.3 K) for snow depths less than 5 cm and algal standing stocks higher than 150 mg chl a m−2. Furthermore, under these conditions, brine volume increased by 21% from 181 to 219 parts per thousand, which decreased the physical strength of the ice.
Observations of atmosphere‐ocean coupling in midlatitude western boundary currents
Authors: Kelly Kathryn A. , Caruso Michael J. , Singh Sandipa , Qiu Bo
Published: February 2004

Oceanographic fields derived from the Geosat altimeter and atmospheric fields from the European Centre for Medium‐Range Weather Forecasts (ECMWF) were examined for both the western North Pacific Ocean and the western North Atlantic Ocean to determine the nature of the coupling. Despite the short data records, approximately 2.5 years, correlation analyses of nonseasonal fluctuations showed similar relationships for both oceans. Correlations between the height difference across the jets (surface transport) and the path of the western boundary currents suggested that there is a structural change of the recirculation gyres, associated with a path change, with timescales of 5–9 months. Both wind stress and wind stress curl were clearly correlated with the surface transport and path in each ocean. Although net surface heat flux and wind stress were correlated, there was no clear correlation between net surface heat flux from ECMWF and surface transport over the entire study region. Additional regional analyses of the North Atlantic showed a consistent relationship between cooling, sea surface temperature (SST), and surface transport west of 62°W; anomalous cooling (accompanied by cyclonic wind anomalies) corresponds to a weaker SST gradient across the Gulf Stream and decreasing surface transport. Because the surface transport fluctuations to the west and east of 62°W in the western North Atlantic are not correlated, structural changes in the recirculation gyres, which have their maximum variations east of 62°W, may not be related to surface heat flux variations.
An ocean large‐eddy simulation model with application to deep convection in the Greenland Sea
Authors: Denbo Donald W. , Skyllingstad Eric D.
Published: February 2004

A nonhydrostatic, Boussinesq, three‐dimensional model, the ocean large‐eddy simulation model (OLEM), has been developed to study deep oceanic convection. The model uses a subgrid‐scale parameterization of turbulence developed for large‐eddy simulation models, and the advection of scalars is accomplished using a monotonic scheme. A set of experiments was performed using OLEM to provide a direct comparison with laboratory results and aircraft measurements of the atmospheric convective boundary layer. The results from these experiments are in excellent agreement with laboratory and atmospheric convective boundary layer measurements of the mean profiles of zonal and vertical velocity variance, potential temperature variance, and heat flux. The horizontal wavenumber spectra of zonal and vertical velocity are also in good agreement with laboratory measurements and Kolmogorov's theoretical inertial subrange spectrum. A set of experiments using a potential temperature‐salinity profile from the central Greenland Sea for model initialization was conducted to study the effect of the thermobaric instability and rotation on the structure and evolution of deep oceanic convection. The artificial removal of the thermobaric instability suppresses penetrative convection, which is responsible for rapid changes in water properties at depths much greater than occurs for convective, mixed‐layer deepening. The vertical velocity and diameter, −0.08 m s−1 and 300 m, respectively, of the penetrative plumes are in good agreement with observations from the Greenland Sea. A period of strong penetrative convection is followed by a gradual transition to convective, mixed‐layer deepening. During penetrative convection, the values of heat flux are about 2 times greater than convective, mixed‐layer deepening. In the absence of rotation, the evolution of penetrative convection occurs more rapidly, and vertical motions are more vigorous. The presence of the horizontal component of rotation forces asymmetries in the circulation around a penetrative plume. These experiments clearly demonstrate the importance of thermobaric instability and rotation on deep convection. To properly model large‐scale flows in regions of penetrative convection, it is necessary to include these effects in the vertical mixing parameterization.
Propagation and reflection of long equatorial waves in the Pacific Ocean during the 1992–1993 El Niño
Authors: Boulanger Jean‐Philippe , Menkes Christophe
Published: February 2004

The TOPEX/POSEIDON satellite, together with the Tropical Ocean and Global Atmosphere‐Tropical Atmosphere Ocean (TOGA‐TAO) array, provides oceanographic and atmospheric observations which allow a detailed study of the equatorial Pacific variability. During the November 1992 to December 1993 El Niño period, sea level, dynamic height, wind stress, sea surface temperature, and surface zonal current data derived from TOPEX/POSEIDON and TOGA‐TAO measurements were used to describe the Pacific ocean‐atmosphere system and to understand the role played by long equatorial waves. A potentially important mechanism of the El Niño‐Southern Oscillation (ENSO), commonly referred to as the delayed action oscillator, involves Kelvin and long Rossby waves and their reflections at the Pacific western boundary. In order to investigate if this process was at work during the period under study, a method for projecting TOPEX sea level, TOGA‐TAO dynamic height, and zonal wind stress onto meridional wave structures was designed both in unbounded and bounded regions. The Kelvin and first three Rossby waves of the first baroclinic mode are propagating at theoretical wave speeds in all data sets. Zonal wind stress projections show that oceanic propagating wave features are strongly linked to wind variability. Reflections are then examined at both boundaries. At the eastern boundary most of the signal reflected from incoming Kelvin waves is either counteracted by unfavorable wind forcing or strongly reinforced and therefore does not seem to play a significant role for generating the major Rossby wave signals during the period under study. In the western Pacific, wind forcing, rather than western boundary reflections, appears to be the main trigger for returning Kelvin waves from the western Pacific to the eastern Pacific. Simultaneously with the weakening of the extended 1991–1993 ENSO event, an upwelling Kelvin wave is observed propagating from the western Pacific in September 1993 to the eastern Pacific in November 1993. This scenario is consistent with some features of the delayed action oscillator mechanism, where an upwelling Kelvin wave is systematically seen returning from the western boundary to the east at the end of warm events. However, here, contrary to the delayed action oscillator, most of this returning Kelvin wave seems to be forced by a strong easterly anomaly located in the western Pacific, rather than by reflection of an upwelling first Rossby wave at the western boundary.
Barents Sea tidal and inertial motions from Argos ice buoys during the Coordinated Eastern Arctic Experiment
Authors: Pease C. H. , Turet P. , Pritchard R. S.
Published: February 2004

A harmonic analysis, constrained to estimate separately ice motions forced by tides and inertial oscillations, was applied to observed positions of Argos buoys deployed on drifting multiyear sea ice in the eastern Arctic Ocean and Barents Sea during the Coordinated Eastern Arctic Experiment (1988–1989). Individual tidal components were estimated at 15‐day intervals, and inertial oscillations were estimated at 3‐day intervals. The S2 tidal component was distinguishable from inertial motions south of 79°N, and the M2 tidal component was distinguishable from the inertial motion north of 77.5°N. Computed ice velocities of up to 70 cm s−1 for M2 tidal motion over Spitsbergen Bank southeast of Svalbard agreed reasonably well with the regional tidal models (no ice cover) of Gjevik and of Kowalik. Regional differences in the energy distribution in the Arctic Basin (low), Barents shelf (high), and Spitsbergen Bank (extreme) were emphasized by this technique. The M4 tidal component in the ice motion was typically as large over the Barents shelf as the inertial oscillation.