bluuebunny/crossref_metadata_2025 huggingface dataset:
A mechanistic model of Eulerian, Langrangian mean, and Lagrangian ozone transport by steady planetary waves
Authors: Rood Richard B. , Schoeberl Mark R.
Published: February 2008

Ozone transport is calculated for steady, dissipative planetary waves using the Eulerian, Lagrangian mean, and residual circulation. A Langrangian model of parcel dynamics is used to interpret planetary wave‐photochemistry interaction. In chemically active regions the mean field ozone changes are found to be significant only where there are large gradients in chemical sources and sinks along parcel trajectories. The largest changes in the mean field are found in the lower stratosphere and are due to the Lagrangian mean advection. When the Lagrangian mean advection is approximated by the residual circulation, errors in the transport velocities as large as 30% may occur.
Latitudinal distribution of ten stratospheric species deduced from simultaneous spectroscopic measurements
Authors: Girard A. , Fergant G. , Gramont L. , Lado‐Bordowsky O. , Laurent J. , Le Boiteux S. , Lemaitre M. P. , Louisnard N.
Published: February 2008

Solar infrared absorption spectra have been recorded from an aircraft during nine flights, in April–May 1980, at various latitudes between 62° north and 60° south. Using a solar occultation technique, the instrument is a spectrometer associated with a heliostat and designed for scanning automatically, in a repetitive sequency of measurements, a set of selected narrow spectral intervals within the spectral range 1000 to 4000 cm−1. Simultaneous measurements are presented concerning NO2, COS, H2O, CH4, N2O, O3, CO, HNO3, HF, and HCl. The results deduced from observations are the vertical column density above the flight altitude, near 11.5 km, the local concentration at the flight altitude, and qualitative information about the stratospheric vertical profile. A similar variation is observed for HNO3, HCl, and HF: for these three species, the vertical column density increases from the equator to the polar region in both hemispheres. The CO vertical column density decreases by a factor of 4 from the equator to high latitude in both hemispheres, with values slightly larger in the northern equatorial region than in the southern hemisphere at the same latitude. The latitudinal variation of H2O vertical column density is discussed in relation to the tropopause height. Some similarities are observed for latitudinal and seasonal variations of nitrogen dioxide and ozone.
On the dynamics of the ice sheets 2
Authors: Halfar P.
Published: February 2008

The equation which describes the motion of an ice sheet under its own weight has a cylindrically symmetric similarity solution. The initial value problem of the equation of motion which has been linearized in the deviations from this similarity solution is solved by an expansion of the solution in terms of eigenfunctions of the linearized equation. The linearized equation determines, for all ice sheets of the same volume, an asymptotically stable motion. These results are compared with the corresponding results of the two‐dimensional case (Halfar, 1981).
A frequency domain analysis of trends in Dobson total ozone records
Authors: Bloomfield Peter , Oehlert Gary , Thompson Mary Lou , Zeger Scott
Published: February 2008

A frequency domain statistical model for the Dobson total column ozone data is introduced. This model extends variance‐components analysis to the time series case and incorporates both temporal and spatial association found in the ozone data. A key feature of this model is the inclusion of a common global term representing natural global variations in ozone. The model is used to estimate global trends in ozone possibly related to the release of man‐made chlorofluorocarbons and other factors. We assess the ability of models to detect trends, given the current ozone data base.
On determining the large‐scale ocean circulation from satellite altimetry
Authors: Tai Chang‐Kou
Published: February 2008

To determine the surface geostrophic currents (which are proportional to the slope of the dynamic topography) from satellite altimetry, one needs an accurate and independent estimate of the geoid. Currently, these estimates are given in terms of spherical harmonics. While the high‐degree terms (short wavelengths) are either uncertain or completely unknown, the low‐degree terms (long wavelengths) are reasonably accurate. Furthermore, in terms of spherical harmonics, most of the dynamic topography's power is contained in the low‐degree terms. If the dynamic topography is treated as the signal and the geoid uncertainty as the noise, the signal to noise ratio is the highest for these low‐degree terms. Therefore a spherical harmonic expansion of the difference between the altimeter‐derived mean sea surface and the geoid estimate should reveal the large‐scale circulation of the ocean surface layer when one examines the low‐degree terms. Methods based on this principle are proposed and partially demonstrated over the Pacific Ocean using the mean sea surface derived from the SEASAT altimeter and the Goddard Earth Model 9 earth gravity model. The preliminary results show a well‐defined clockwise gyre in the North Pacific and a much less well defined counterclockwise gyre in the South Pacific. When the dynamic topography so obtained is compared to Wyrtki's (1975) dynamic topography derived from hydrographic data, the agreement is within the limit of geoid uncertainties and satellite orbital errors. To fully determine the three‐dimensional ocean circulation, one still needs hydrography: the three‐dimensional density distribution of the ocean. A method is presented for the determination of the ocean circulation and the improvement of the geoid in the combined problem of geodesy, hydrography, and satellite altimetry.
Particle transport processes in a small marine bay
Authors: Baker Edward T. , Cannon Glenn A. , Curl Herbert C.
Published: February 2008

Particle transport in Elliott Bay, a 20 km2 embayment in Puget Sound, Washington, was studied in an integrated program employing shipboard CTD/transmissometer observations, moored sediment traps, and moored transmissometer/current meter observations. Surface and bottom high/turbidity layers are present throughout the bay during both summer and winter seasons. Particles added to the surface layer by river input and phytoplankton production are rapidly advected out of the bay and provide only a minor contribution to the local sedimentation rate. The benthic nepheloid layer is maintained not by local resuspension but by particles advected into Elliott Bay with turbid deep water from the adjoining Main Basin of Puget Sound. A severalfold drop in mean current speed as Main Basin water enters Elliott Bay results in increased particle fallout within the benthic nepheloid layer, a high sedimentation rate, and the embayment functioning as a sink for particles from throughout Puget Sound.
L band SAR ocean wave observations during Marsen
Authors: Jain A. , Shemdin O. H.
Published: February 2008

The L Band Synthetic Aperture Radar (SAR) operated by the Jet Propulsion Laboratory (JPL) was flown over the Nordsee tower during the Marine Remote Sensing Experiment (MARSEN). The five‐sided flight pattern allowed viewing of the same ocean surface patch from five different directions. The results form a unique and useful base which is needed for evaluating existing wave imaging theories and developing more realistic models. The results derived from analysis of radar and in situ measurements suggest that (1) the focus dependence for optimum imaging is that for a surface moving with a speed that is approximately equal to the wave phase velocity, (2) azimuthally traveling waves can be as visible as range traveling waves when the necessary focus adjustments are made in the SAR processor, (3) visibility of azimuthally traveling waves does not improve with decreasing integration time, (4) spectra and images of azimuthally traveling waves do not show observable distortions compared to those for range traveling waves, and (5) comparisons of SAR image spectra for September 28, 1979, with in situ wave height spectra suggest that for a multi‐peaked wave system the SAR image spectrum and surface wave height spectrum are not connected by a simple relationship.
Measurements of wind velocity and pressure with a wave follower during Marsen
Authors: Hsiao S. V. , Shemdim O. H.
Published: February 2008

Near sea‐surface air pressure and wind velocities at several levels above the instantaneous water surface were measured using a wave follower during the Marine Remote Sensing (MARSEN) Experiment. The rate of momentum transfer from wind to waves is determined from the air pressure data. From the wind velocity measurements, the wave‐induced airflow and its coherence with waves are obtained for various wind velocities and phase speeds of the ocean waves. The pressure results indicate that momentum transfer to waves can be specified by the equation γi = 0.12 (μ − 1)2 in the ranges μ = 1 to 7.4, where γi is related to the imaginary part of the wave‐induced pressure, as defined by equation (2), μ = (8/3π)(U/c), U is wind speed at 10 m above the mean water level, and c is wave phase speed. The wind velocity results indicate that the wave‐induced airflow is much smaller than the mean wind speed. An empirical equation is proposed for the modulation of atmospheric transfer to short waves induced by the orbital velocity of long waves. Such modulation explains adequately the excess modulation of short waves by long waves as suggested by Wright et al. [1980] when the short waves are 13 cm long but not when they are 2.3 cm long. The agreement for the 13 cm waves supports their suggestion that the excess modulation is due to a modulation in atmospheric transfer. For the shorter 2.3 cm waves the less adequate agreement and the scatter in the results of Wright et al. suggest that other mechanisms such as short wave blocking by long wave orbital velocity, short wave breaking, and other strong nonlinear transfer among the short wave spectral components also may be contributing to the excess modulation of short waves by long waves.
Formaldehyde (HCHO) measurements in the nonurban atmosphere
Authors: Lowe David C. , Schmidt Ulrich
Published: February 2008

The mixing ratio of formaldehyde (HCHO) has been determined for air samples collected at a moderately polluted continental site (Jülich, Federal Republic of Germany) and for samples collected at coastal sites in Ireland and New Zealand. In addition the HCHO mixing ratio has been determined for air samples collected in the North and South Atlantic during a cruise of the F/S Meteor from Hamburg at 55°N to Montevideo at 35°S in October and November 1980. The HCHO mixing ratio in clean tropical marine air is of the order of 0.2 parts per billion by volume, about 50% lower than predicted by current photochemical models that include CH4 oxidation as the only source for HCHO. In the mid‐Atlantic, diurnal variations of the HCHO mixing ratio showing weak maxima during the early afternoon were occasionally observed. These variations may be attributed to the diurnal behavior of the photochemical and physical processes which determine the mixing ratio of HCHO during stable weather conditions. The results are discussed with regard to the currently accepted theory of the photochemistry of HCHO in the clean troposphere. It appears that the yield of HCHO formation through hydrocarbon photooxidation in the background marine troposphere is less than assumed from model considerations, most probably because of the lack of sufficiently high NO concentrations.
The composition of western Atlantic precipitation using shipboard collectors
Authors: Galloway James N. , Knap Anthony H. , Church Thomas M.
Published: February 2008

Techniques have been developed for the collection of rain on board ships. Chemical and meteorological analysis of rain events shows that rain can be collected for major ions on board ships in a contamination‐free manner by using collectors on the windward side of the ship. The results also support the conclusion of Jickells et al. (1982) that rain associated with North American air masses has elevated levels of SO4 = *, NO3−, and H+, while rain associated with eastern Atlantic air masses has background values.
Kinetic studies of raindrop chemistry: 1. Inorganic and organic processes
Authors: Graedel T. E. , Goldberg K. I.
Published: February 2008

The chemistry of raindrops, thought not long ago to be adequately represented by a few simple ions and their equilibrium constants, is now recognized to include the complex reactions of ions, radicals, and molecules of both acidic and basic moieties. To describe this system, we have formulated a model which includes both inorganic and organic processes (but not metal catalysis) totaling 94 reactions in 53 species. Three sets of computations were performed for raindrops of different diameters. In the first two, the initial chemistry of the raindrops was set by the cloud chemistry measurements of APEX (Atmospheric Precipitation Experiment) in the northeastern United States. In the simulations the drops were released into tropospheric air characteristic of either the suburban or urban northeast. In the third set of computations, designed to simulate urban centers on the U.S. west coast, raindrops with composition typical of those over the oceans were dropped in urban tropospheric air. Among the results are the following: (1) Photochemical processes, including the photolysis of H2O2 to produce OH˙ and the photolysis of NO3− to produce ozone, are significant in raindrops chemistry. (2) Organic chemical reactions of interest and importance occur in raindrops, particularly those of small size (and thus long lifetime), with the oxidation of aldehydes to organic acids being perhaps the most important. (3) Significant differences in some species concentrations occur at different altitudes during the raindrop's fall and for drops of different diameters. These differences are related to the scavenging efficiencies and lifetimes of the drops. (4) Given constant initial concentrations of trace species in raindrops, the calculations show that ion concentrations in rainwater increase as the rain rate decreases and that in a steady rainfall the concentrations of scavenged ions decrease as the concentrations of the gaseous precursors decrease. Neither effect is large, however. (5) The model results are consistent with experimental data, suggesting that below‐cloud processes do not significantly affect the concentration of strong inorganic acids in rain at ground level unless acid concentrations are low in droplets at cloud base.
The role of the ocean in the global atmospheric sulfur cycle
Authors: Nguyen B. C. , Bonsang B. , Gaudry A.
Published: February 2008

The background atmospheric SO2 concentration above the sea surface has been established at 0.1 × 10−6g/m3 (35 pptv). Several hypotheses to explain the origin of SO2 above the ocean, far from continental sources, have been discussed. We have shown that one of the mechanisms of SO2 formation is the biogenic production of reduced organic sulfur compounds in the ocean. Dimethyl sulfide (DMS) has been observed in oceanic areas, with concentrations ranging from 11 to 1150 × 10−9g l−1 in surface waters and from 0.2 to 400 × 10−9g m−3 (0.07 to 144 pptv) in marine atmosphere. This compound is emitted into the atmosphere and oxidized there by photochemically induced processes. That leads partly to SO2 formation, and subsequently, to sulfate. This hypothesis is corroborated by a correlation between atmospheric SO2 concentrations and the relation between atmospheric SO2 concentrations and biological activity. The flux of sulfur by this process (biological activity → organic sulfides → SO2 → SO2=) is estimated to range between 27 and 72×106 tons of sulfur per year. This biogenic production is comparable to atmospheric sulfur production by sea spray, which is about 44×106 T S/yr. Therefore, the oceanic production by these two processes could be estimated as being from 71 to 116×106 T S/yr.
The seasonal component of atmospheric CO2: Information from new approaches to the decomposition of seasonal time series
Authors: Cleveland William S. , Freeny Anne E. , Graedel T. E.
Published: February 2008

CO2 concentration data in the atmosphere are widely known to possess a seasonal cycle, largely due to plant photosynthesis and respiration, superimposed upon an upward trend that is largely due to increasing fossil fuel use. In this paper we assess the information contained in the seasonal component of atmospheric CO2 data by applying modern techniques of time series decomposition to monthly average CO2 observations at three locations. At Mauna Loa and South Pole, which have the longest time series, the amplitudes of the seasonal components are found to be increasing with time, from ∼5.6 ppm in 1958 to ∼6.2 ppm in 1978 at Mauna Loa and from ∼1.0 ppm in 1965 to ∼1.3 ppm in 1978 at the South Pole. We consider four possible causes of the CO2 seasonal behavior—changes in the seasonal pattern of fossil fuel use, increasing vegetation, increasing global photosynthetic activity, and changes in ocean temperature—and conclude that it is most likely that the CO2 seasonal behavior reflects an increase in global photosynthetic activity.
Modeling the diurnal dependence of the optical refractive index structure parameter
Authors: Kunkel K. E. , Walters D. L.
Published: February 2008

A model which simulates the diurnal dependence of the optical refractive index structure parameter within the atmospheric boundary layer is constructed by solving an energy balance equation for the ground surface temperature. This solution yields surface fluxes of sensible and latent heat. Empirical relationships are then used to calculate Cn2. Model results compare favorably with data obtained at a desert location under clear skies. A sensitivity analysis indicates that Cn2 is particularly sensitive to time of year, wind speed, the product of soil heat capacity and soil density, and soil moisture content. This model is applicable over relatively flat surfaces with little or no vegetation.
A 40‐ to 60‐day oscillation in the source region of the Somali Current during 1976
Authors: Mysak Lawrence A. , Mertz Gordon J.
Published: February 2008

Evidence is presented for a 40‐ to 60‐day oscillation in the longshore current and temperature fluctuations that were measured during 1976 in the Somali Current regime off Kenya by Düing and Schott (1978). It is suggested that this equatorial oceanic oscillation is excited by long‐period local wind fluctuations which are associated with the global tropical 40‐ to 50‐day day oscillation first detected by Madden and Julian (1971, 1972).
Modeling supercooling and ice formation in a turbulent Ekman layer
Authors: Omstedt Anders , Svensson Urban
Published: February 2008

A theoretical framework for studying supercooling and ice formation in turbulent waters is developed. The basic idea is that the problem can be described by a boundary layer theory in which buoyancy effects become important because of suspended ice crystals. A mathematical model based upon transient Ekman dynamics is formulated and explored. The model is based on the conservation equations for mean momentum, heat energy, salinity, and suspended ice concentration in their one‐dimensional form. The turbulent exchange coefficients are calculated with a two‐equation model of turbulence. The ice nucleation is assumed to be secondary, which means that ice crystals are assumed to be always present in the water as a result of mass exchange with the atmosphere. In the model the mass exchange is treated as a surface boundary condition for the ice concentration equation. Calculated time histories of temperature and ice concentration for different meteorological conditions and different rise velocities are presented and discussed. The results are in good qualitative agreement with field and laboratory measurements. The importance of the strong interaction between the ice formation process and the hydrodynamics of the boundary layer is emphasized.
Radial spreading of buoyant, surface plumes in coastal waters
Authors: Garvine Richard W.
Published: February 2008

Shallow buoyant, surface plumes in coastal waters sometimes develop by nearly radial spreading from a continuous source, such as at a river mouth. Such plumes often display a ring structure where buoyant water is concentrated between fronts at both the leading and trailing edges of the expanding ring. These rings often occur in multiple, concentric forms. A model of the radial, time dependent spreading of a shallow buoyant layer over a motionless, deep ambient layer is developed. It includes fronts as discontinuities and treats the remainder of the plume flow as inviscid, gravitational spreading controlled by nonlinear, internal waves. Calculations by the method of characteristics are presented that show the evolution of a clear ring structure. The combination of rapid spreading in the radial geometry together with reflection of internal waves off the frontal boundary at the plume leading edge is shown to be necessary for ring formation. A mechanism is suggested for the formation of multiple rings through the shear flow instability inherent in radial spreading.
An operational coupled hybrid wave prediction model
Authors: Janssen Peter A. E. M. , Komen Gerbrand J. , De Voogt Willem J. P.
Published: February 2008

GONO is a numerical wave prediction model used for the preparation of forecasts as well as hind‐casts. It is a hybrid model: the wind sea is described in a parametric way, but swell is treated in a spectral manner. For the wind sea there are two prognostic parameters: the zero‐moment wave height and the mean direction. Pure wind‐sea spectra are assumed to have a quasi‐universal shape: above the spectral peak, ƒ−5behavior is assumed; below the peak, a linear frequency dependence is taken. The directional dependence is of the cos2θ type. Empirical relations are used to derive the full set of wind‐sea parameters from the prognostic variables and the wind vector. The equations for the prognostic variables are solved on a discrete grid with the help of a simple finite‐difference scheme. For the accurate propagation of swell, possibly over large distances, a ray technique is used. The full two‐dimensional spectrum is reconstructed for selected grid points for which the results of the ray technique and the wind‐sea calculations are combined. The model is a shallow water model because bottom dissipation effects are taken into account, but effects of refraction are disregarded. Depending on wind speed, these effects may be important in areas where the depth is less than about 100 m. The model has not been applied in regions with depths less than 15 m, therefore extreme shallow water effects are not considered. The behavior of the model was studied in quite some detail during the recent Sea Wave Modeling Project (SWAMP) in a few idealized situations. Knowledge of the model behavior in more realistic situations stems from its routine operational application. Runs are made four times a day on a grid covering the North Sea and the Norwegian Sea, and the results are monitored continuously. Presently, we have a data base containing about four years of observations and model predictions. From this data base we discuss a few interesting storms, and we present a statistical analysis of all of the available material. As part of this analysis we consider the effect of the quality of the input winds on the model performance.
Observations of the vertical structure of the eddy field in the Kuroshio Extension
Authors: Schmitz William J.
Published: February 2008

Normalized kinetic energy frequency distributions at a site in the Kuroshio Extension along 152°E are independent of depth as a good first approximation. The lowest frequencies are strongly vertically coherent from 350 to 6000 m depths (nominal). None of the other vertical sets of time series previously examined possess these characteristics to such a degree, coherence being typically much lower between the thermocline and abyssal depths, with spectral shape changing significantly as well. The vertical distributions of eddy kinetic energy at this Kuroshio Extension site and for the Gulf Stream along 55°W are very similar, if a depth independent contribution of approximately 100 cm2 s−2 be added to the former. The latter observation suggests the existence of a more energetic weakly depth‐dependent component for the eddy field in the North Atlantic than for the North Pacific, at special locations in the vicinity of their mid‐latitude jets, possibly a signature of distinct instability mechanisms.
Remotely sensed sea surface temperature variability off California during a “Santa Ana” clearing
Authors: Lynn Ronald J. , Svejkovsky Jan
Published: February 2008

During a prolonged clearing with particularly dry atmospheric conditions over the Southern California Bight, four NOAA 6 satellite overpasses at 12‐hour intervals were recorded while a research vessel measured ocean temperatures within the field of view of the satellite. This data set is used to evaluate two versions of an equation for estimating sea surface temperature from satellite data and for examining short‐term changes in surface temperature caused by diurnal variation and surface layer movement. Surface temperatures calculated from data taken during a daytime overpass, using two slightly differing versions of a multiwindow atmospheric correction equation, match the ocean temperatures within the expected range of scatter: ±0.6°C. One version has a mean daytime bias of +0.5°C, the other has −0.4°C, and thus the two versions differ by 0.9°C. The satellite‐derived sea surface temperatures show a diurnal variation in the range of 0.25° to 1.0°C. Hence the bias of calculated satellite temperatures for the nighttime overpasses differ from those for the daytime; the bias in one version is +1.2°C and in the other is +0.4°C. It is suggested that these biases are caused by inherent problems in the selection and matching of satellite and ocean data sets used to determine the equation coefficients as well as poorly understood diurnal variation of the surface temperature as measured by satellite. Advection, evidenced by an image‐to‐image shift of thermal gradients over 12‐ and 24‐hour periods can produce local temperature changes that add to the problem. Noise in one of the satellite data channels, another part of the problem, is shown to be amenable to filtering techniques. Diurnal differences in satellite‐observed surface temperatures are found to vary regionally; larger variation is found in waters that are turbid and have a shallow thermocline. Near surface in situ temperature measurements suggest a diurnal layer variation of 0.2°C, much less than the variation observed by satellite. An estimation of diurnal sea surface temperature variation based on heat budget calculations supports the in situ observations.
Equatorial sea level response during the 1982–1983 El Niño
Authors: Lukas Roger , Hayes Stanley P. , Wyrtki Klaus
Published: February 2008

During the 1982–83 El Niño/Southern Oscillation event, sea level across the width of the equatorial Pacific adjusted to the reversal of the equatorial trade winds, and by the end of 1982 the normal sea level slope across the Pacific had been eliminated. The transfer of warm upper‐ocean water from the western Pacific to the eastern Pacific was accomplished by a combination of direct wind forcing as the wind anomaly crossed the basin and by mass flux induced by free equatorial waves. The importance of equatorially trapped Kelvin waves of first and second vertical mode during the onset of the 1982–83 El Niño is inferred from the cross‐correlation statistics between central and eastern Pacific sea level stations and between wind variations in the western Pacific and equatorial sea level stations to the east. The different propagation speeds of these two modes appears to be responsible for the observed change inshape of the major sea level signals during the 1982–83 event. Tentative evidence for first baroclinic mode, first meridional‐mode Rossby waves is also presented.
Effect of the Emperor Seamounts on the mesoscale thermohaline structure during the summer of 1982
Authors: Roden Gunnar I. , Taft Bruce A.
Published: February 2008

The influence of the Emperor Seamount Chain upon the mesoscale thermohaline structure and upon geopotential height are investigated on the basis of a field experiment in the summer of 1982. The seamounts have a twofold effect: they deflect the oncoming flow of the Kuroshio Extension, and they give rise to secondary perturbations of small horizontal extent but of large vertical amplitude. The Kuroshio Extension approached the seamounts on a southeastward course and was deflected by Kinmei Seamount in an anticyclonic loop. The deflection led to a weakening of this current over this seamount and to reintensification on the downstream side. Uplift of isopycnals near seamount peaks and vertical displacement along seamount flanks were generally observed, but the details varied considerably from one seamount to the next. Uplift occurred over some peaks; on others it was displaced 50–100 km from it. In some instances there was intense downward displacement on the west and upward displacement on the east side; in others this was not the case. A Taylor columnlike feature occurred over Suiko Seamount. A very large and asymmetric density dome was found 40 km west of Jingu Seamount, atop which a density front was located, which suggests flow intensification to the left of the seamount. In the main gap between the northern and southern seamounts, prominent wedgelike intrusions or subarctic and Kuroshio‐type waters were observed in the upper few hundred meters. The isopycnals in the main gap sloped sharply to the south, indicating a strong eastward baroclinic flow component. The geopotential heights over the Emperor Seamounts indicate strong local perturbations superimposed upon larger‐scale slopes. A geopotential low was observed west of the seamounts, and a high was found near the seamount top or to the east of it, indicating anticyclonic flow. In terms of geometric distance, perturbation dynamic heights reached 0.32 m, and maximum sea surface slopes were 5·10−6. The slopes produce baroclinic currents up to 0.5 m s−1 around the seamounts.
Atmospheric forcing of interannual variability in the northeast Pacific Ocean: Connections with El Niño
Authors: Emery William J. , Hamilton Kevin
Published: February 2008

The nature and causes of the observed interannual variability of oceanic conditions in the Northeast Pacific were investigated using a variety of meteorological and oceanographic data sets. An examination of a long series of seasonal mean atmospheric sea level pressure (SLP) charts showed that when the winter average SLP pattern in the North Pacific varies significantly from climatology, it tends to do this in one of two characteristic ways. In particular, in some winters there is an anomalously strong circulation which differs from climatology mainly in having an intensified Aleutian low. In other winters there is an anomalously weak atmospheric circulation; this is almost invariably associated with the westward displacement of the Aleutian low and the production of a separate but much weaker low in the Gulf of Alaska. The North Pacific winter SLP appears to have some relation to the Southern Oscillation (SO) and oceanic temperatures in the tropics. In particular, El Niño/Southern Oscillation (ENSO) episodes are generally coincident with strong North Pacific SLP patterns and often follow winters with weak SLP patterns. However, this relationship is far from being perfectly regular and predictable. Interannual variations in the intensity of the North Pacific atmospheric surface circulation were found to be strongly correlated with the anomalies of both sea surface temperature (SST) and sea level height (SLH) at stations along the British Columbia coast. An intense Aleutian low is invariably associated with warm coastal waters and high coastal sea levels. By comparing a large number of Pacific SLP and SST maps, it was possible to verify that the relation between North Pacific SLP and oceanic surface temperature actually applies to the SST over much of the northeast Pacific (at least as far west as 150°W). The relationship of North Pacific SLP with the SO, together with the relationship between North Pacific SLP and oceanic conditions in the Northeast Pacific, can account for the observed general tendency for SST and SLH along the west coast of North America to be anomalously high during tropical ENSO episodes. On the other hand, the lack of a truly predictable relation between the Southern Oscillation and North Pacific SLP explains the fact that not all ENSO events are associated with wanning of the northeast Pacific.
An algorithm to measure sea ice concentration with microwave radiometers
Authors: Swift C. T. , Fedor L. S. , Ramseier R. O.
Published: February 2008

An algorithm is developed which uses two microwave radiometer channels to estimate quantitative fractions of first‐year and multiyear sea ice types. The algorithm is applied to data obtained from satellite sensors, and the data trends are used to refine values of the emissivities. The algorithm was tested, and results were in reasonable agreement with visual observations, where mixtures of first‐year sea ice and multiyear sea ice were known to coexist. However, on a synoptic basis the satellite estimates differ from visual and radar means of classifying ice that has survived at least one melt season (old ice). A possible explanation for the discrepancy is that the emissivity of sea ice changes over time periods longer than one melt season.
On the Bering Sea ice edge front
Authors: Muench Robin D. , Schumacher James D.
Published: February 2008

An oceanographic field program was carried out along the Bering Sea ice edge in winter 1982–83 to investigate the temperature/salinity front associated with and paralleling the winter ice edge. Currents were measured using taut‐wire moorings that were in place over winter, and an intensive CTD survey was carried out of the frontal structure in midwinter (February–March). The midwinter front separated cold (<−1.5°C), low salinity (<32‰), middle Bering shelf water from warmer (>0°C), more saline (>32.5‰) outer‐shelf water. The front had northwestward baroclinic currents paralleling the front/ice edge with near‐surface speeds of 5–6 cm/s and an associated transport of about 0.3×106 m3/s. These baroclinic currents were superimposed on a regional barotropic along‐isobath flow, resulting in north‐westward midwinter upper‐layer flows with monthly mean speeds exceeding 10 cm/s. An upper‐layer flow component was directed beneath the ice and provided heat adequate to melt the ice and limit advance of the edge. The resulting low‐salinity meltwater was mixed vertically, to maintain the front, by wind acting across a highly mobile, hydrodynamically rough ice cover. Subtidal fluctuations were not significantly affected by the front or the ice cover, and local winds accounted for less than one quarter of the observed current variability, the remainder being probably due to regional variations in the barotropic flow.
Drifter trajectories through a current meter array at Drake Passage
Authors: Peterson Ray G.
Published: February 2008

Six low‐profile undrogued buoys drifted through the Drake Passage during 1979 where an extensive array of current meters was moored. Geostrophic currents at the buoy positions are estimated by extrapolating the shallow 40‐hour low‐pass filtered current measurements to the surface by using vertical shear relationships derived from hydrographie stations taken over a 5‐year period within the passage. The buoy tracks are also filtered, followed by the removal of the extrapolated geostrophic currents. The residual drifts are then compared with the 10‐m winds, which are estimated twice daily by applying the similarity theory for a neutral barotropic boundary layer to sea level atmospheric pressure fields. The residual drifts are found to respond within a few hours to variations in the wind. Buoy motions against the interior flow, persisting for as long as 6 days, along with loops and reversals which are not observed in the subsurface currents are well accounted for by the wind. During times of nearly steady wind conditions the residual drift is found to average 3.4%±1.4% of the 10‐m wind speed at 25.0°±12.0° to the left of the wind.
Selection of a numerical filtering method: Convolution or transform windowing?
Authors: Evans J. C.
Published: February 2008

Filtering by transform windows and convolution are compared. Windows are procedurally easier to design and use, especially for more complicated applications such as band‐pass filtering. For comparable frequency response functions, the same amount of data will be lost at the ends of the time series regardless of which method is selected. In the case of windowing, the impulse response function must be calculated by inverting the frequency response function to determine the data loss. If large numbers of long time series are involved, computational efficiency of the filtering method becomes important. A simple index of relative efficiency is derived which shows that windowing is often but not always the more efficient technique. Even for eliminating deterministic signals such as tides, windows can sometimes improve computational efficiency when used in combination with least squares weights design.
Computation of errors in current meters attached to near‐surface moorings
Authors: Chhabra Narender K.
Published: February 2008

Current measurements from moored buoy systems are contaminated by mooring motion. A few examples of moored buoy systems are studied to illustrate the use of computer simulations for computing errors introduced by surface waves in the current meters attached to near‐surface moorings. Results presented show that for all cases studied the standard deviations of true flow components (relative to the current meters) are greater than the standard deviations of wave orbital velocities, except near the surface. Also, in one case which is closest to a surface‐following mooring, the standard deviations of true flow components (relative to the current meters) increase, rather than decrease, with depth over the upper 40–45 m depth. Effect of mooring line characteristics, environment and vertical cosine response on the simulated current meter error is shown. In all cases, for current meters located near the ocean surface, the error is comparable to the surface wave induced Stokes drift. Significant errors (>1 cm s−1) were computed at depths greater (up to 2 and 3 times) than the depth where Stokes drift becomes negligible. Simulations also show a great deal of variation (several centimeters per second, the order of Stokes drift) in the error due to variations in mooring line characteristics and environments.
The distribution of bomb radiocarbon in the ocean
Authors: Broecker Wallace S. , Peng Tsung‐Hung , Ostlund Gote , Stuiver Minze
Published: February 2008

Water column inventories are calculated for bomb radiocarbon at all the stations occupied during the GEOSECS and NORPAX expeditions and for the available TTO stations. The pattern of global inventories obtained in this way suggests that a sizable portion of the bomb radiocarbon that entered the Antarctic, the northern Pacific, and the tropical ocean has been transported to the adjacent temperate zones. A strategy for utilizing these inventory anomalies as constraints on global ocean circulation models is presented. Essential to this strategy are the improvement of our knowledge of the pattern of wind speed over the ocean, the establishment of the wind speed dependence of the rate of gas exchange between the atmosphere and sea, and the continued mapping of the distribution of bomb‐produced radiocarbon in the sea.
Gas exchange and CO2 flux in the tropical Atlantic Ocean determined from 222Rn and pCO2 measurements
Authors: Smethie William M. , Takahashi Taro , Chipman David W. , Ledwell James R.
Published: February 2008

Measurements of 222Rn vertical profiles and pCO2 in the surface water and the atmosphere were made simultaneously in the tropical Atlantic ocean as part of the TTO/TAS program. The gas exchange rate or piston velocity was determined from the 222Rn profiles, and the ΔpCO2 between the surface ocean and the atmosphere was determiend from the pCO2 measurements. The net flux of CO2 across the sea‐air interface was calculated from these two data sets. The piston velocity ranged from 1.4 to 6.9 m/d and was correlated with wind speed. The slope of piston velocity versus wind speed was estimated to be between 0.3 and 1.1 (m/d)/(m/s). The ΔpCO2 ranged from −35 μatm at 15°N, 55°W to +64 /zatm at 5°S, 28°W, with the zero ΔpCO2 isopleth located at about 10°N. The high ΔpCO2 values can be explained by lateral advection of surface water from the east with heating and biological consumption of CO2 and alkalinity during transit. The net flux of CO2 was into the ocean north of 10°N latitude with values reaching a maximum of 1.4 mol m−2 yr−1 at 15°N, 50°W. South of 10°N, the net flux was out of the ocean, reaching a maximum value of 2.7 mol m−2 yr−1 at 8°S, 28°W. The average net flux from 10°N to 10°S was 1.3 mol m−2 yr−1 out of the ocean, which is equivalent to 0.15 gigatons of carbon per year if the flux determined applied throughout the year.
A laboratory study of gyres and uplift near the Strait of Gibraltar
Authors: Whitehead J. A.
Published: February 2008

Laboratory experiments were conducted in which a rotating basin of stratified salty water in a field of gravity with a free surface was connected to a basin of fresh water by a narrow, shallow channel. The resulting density‐driven flow in the channel consisted of two currents: a freshwater flow at the top from the fresh basin to the salty basin and a saltwater flow at the bottom in the opposite direction. It models the flow in the Strait of Gibraltar, which connects the Atlantic Ocean to the saltier Mediterranean Sea. Selective withdrawal of deep water up to and over the sill depth is observed in the stratified salty (Mediterranean) basin. The governing dimensionless numbers are the ratio of the Rossby radius of deformation within the strait to the width of the strait and the ratio of Rossby radius in the stratified (Med.) water to Rossby radius of deformation within the strait. The experiments were deliberately scaled to correspond to the parameters of the real Mediterranean/Gibraltar region or not as we wished. With the most correct parameters the water at a depth corresponding to 700 m in the Mediterranean was selectively withdrawn up to sill depth and out of the salty basin, the water at a depth corresponding to 900 m was not. With double the correctly scaled stratification the water at a depth corresponding to 500 m was drawn out, and the water at a depth corresponding to 700 m was not. With no stratification, water of a depth corresponding to 1200 m was drawn out. The results are qualitatively consistent with the ideas of Stommel et al. (1973) that water at great depth in the Mediterranean is drawn up and out at the Strait of Gibraltar, although quantitatively the scaled experimental depths of withdrawal are not as great. There are some indications that the gyre of Atlantic water corresponding to the Alboran Sea gyre may enhance the selective withdrawal process, but the mechanism is unclear.
The exchange of water in fjords: The efflux/reflux theory of advective reaches separated by mixing zones
Authors: Cokelet E. D. , Stewart R. J.
Published: February 2008

Many fjords consist of deep, stratified reaches separated by shallower sills above which most of the mixing between water masses occurs. On a long time scale, each reach can be modeled as a steady, two‐layer advective flow. These flows intermingle in turbulent mixing zones, where the flow from any incoming layer can be split into two parts: an efflux fraction, which continues on into the next reach, and a reflux fraction, which mixes vertically and recirculates into its original reach. Using conservation of mass, we define these fractions and express them in terms of the salinities observed in the reaches. The processes of the complex mixing zones need not be considered in detail. These ideas are applicable to complicated branched fjords and linked sequences of reaches. Where more than two reaches meet at a multiple junction the conservation of two tracers (usually fresh water and salt) is insufficient to determine completely the efflux/reflux fractions. We propose an entropy maximization technique to resolve the uncertainty. Long‐term pollutant concentrations relate directly to the circulation via the new efflux/reflux formulation. The method demonstrates that refluxing leads to conservative pollutants being broadcast throughout the fjord system with magnified concentrations. A new quantity, the mean tracer age, provides a relevant time scale that includes the effects of recirculation and to which the rates of non‐conservative processes should be compared. Conservative pollutants may be retained for a surprisingly long time in a refluxing system.
Chronology of warm‐core ring 82B
Authors: Evans Robert H. , Baker Karen S. , Brown Otis B. , Smith Raymond C.
Published: February 2008

A chronology constructed from satellite‐derived thermal imagery is presented to describe the formation and life history of warm‐core ring 82B. This overview provides insight into a classification of features and discrete events associated with Gulf Stream warm‐core rings and allows these events, as well as our limited shipboard observations, to be placed in a broader spatial and temporal context than would otherwise be possible without the satellite data. Events influencing the evolution of 82B include environmental factors, such as meteorological influences and Gulf Stream interactions, as well as those stimulated by encounters with changes in bottom topography. The interactions of the ring with surrounding waters are especially noteworthy, and the existence of vortex‐vortex interactions is shown to be a significant cause of local water advection through streamer activity. Ring events are documented by following changes in ring size, shape, translation, and surface thermal structure. Our satellite observations are supported by extensive contemporaneous shipboard observations, including XBT, CTD, BOPS (biooptical profiling system) temperature profiles, and along‐track sea surface temperature measurements. In addition, acoustic velocity profiling and drifter trajectories have been used to corroborate hydrographic features of the ring and environs. These ship and satellite data form a coherent space/time overview of the ring and its environment and show them to be closely related and continually interacting.
222Rn surpluses in warm‐core rings
Authors: Orr James C. , Guinasso Norman L. , Schink David R.
Published: February 2008

Measurements of 222Rn and 226Ra were made in the western Atlantic Ocean as part of the Warm Core Rings Program. A significant number of measurements on waters taken from the surface and deeper waters showed 222Rn concentrations in excess of those supported by the parent 226Ra. Since the source of these 222Rn surpluses is near‐bottom shelf or slope water, and since the half‐life of 222Rn is only 3.8 days, such 222Rn surpluses are indicative of rapid offshore advective and or mixing processes. Concentrations of 226Ra exhibit a small but measurable increase when moving from the Sargasso Sea, through the slope water, and up onto the shelf.