bluuebunny/crossref_metadata_2025 huggingface dataset:
Variation of the mean sea level from TOPEX/POSEIDON data
Authors: Minster Jean‐François , Brossier Claude , Rogel Philippe
Published: February 2004

Variations of the 10‐day‐averaged sea level extracted from TOPEX/POSEIDON (T/P) altimeter data are examined from October 1992 to February 1995. Data are corrected from instrumental drifts, and recent precise orbit and ocean tide corrections are used. When data from the less accurate first eight cycles are excluded and atmospheric pressure effects are not corrected, the 10‐day mean sea level varies by 5.0 mm rms. Its variations can be described by a 4.1±1 mm/yr drift, a small annual signal of 2.7 mm amplitude and a residual signal of 3.5 mm rms amplitude, and Gaussian statistics close to formal error estimates. The mean sea level rise is difficult to explain by drifts of geophysical corrections, though the case for the wet tropospheric correction and that for the orbit are uncertain. Pressure effects should be corrected relative to the global pressure averaged over the ocean. The latter shows a seasonal signal of 1 cm amplitude and apparent fluctuations of 30‐ to 70‐day periods. These fluctuations could result from errors in the atmospheric pressure fields, but they seem to be mostly related to large regional pressure evolutions. Evidence is also found for a sampling effect by the T/P orbit of pressure signals at shorter than 10‐day periods. Pressure effects on sea level are then assumed to be an inverse barometer relative to 10‐day global atmospheric pressure over the ocean, which allows analysis of the geographical repartition of the mean sea level evolution due to other effects. The mean sea level rise is comparable in the northern (4.2±2.5 mm/yr) and southern (3.7±1.9 mm/yr) hemispheres. It seems mostly related to interannual variations of the tropical ocean (41% of the global signal) and of the northern hemisphere subtropical gyres (30% of the global signal); residual noise on these regional values seems inversely proportional to the square root of the number of data points in each area. The hemispheric seasonal pressure variation relative to the globally averaged pressure over the ocean is less than 3 mm amplitude; in our calculation it is implicitely assumed that it induces a small interhemispheric water mass exchange. The amplitudes of the seasonal hemispheric sea level variations are 27 and 18 mm in the northern and southern hemispheres, respectively. These amplitudes are very close to being inversely proportional to the ocean surface in each hemisphere. The maxima of sea level in these hemispheres are reached in the last weeks of September and March, respectively. At subpolar latitudes, semiannual components are observed in each hemisphere, which are consistent with those of sea surface temperature.
A theoretical investigation of boundary layer flow and bottom shear stress for smooth, transitional, and rough flow under waves
Authors: Wiberg Patricia L.
Published: February 2004

Velocity and shear stress distributions and the relationship between maximum near‐bottom orbital velocity uom and maximum shear velocity u*m in an oscillatory boundary layer are computed for hydraulically smooth, transitional, and rough turbulent flow using unsteady boundary layer theory and a single, continuous expression for eddy viscosity K. Velocity profiles over a half wave cycle calculated using a time‐independent form of K compare favorably with available measured profiles in smooth, transitional, and rough turbulent flows; computed shear stress profiles agree reasonably well with measured stress profiles. Use of a time‐dependent eddy viscosity generally improves the agreement between measured and computed velocity and shear stress near the bed but not in the outer boundary layer. Maximum computed bottom shear stress, however, does not differ significantly from values calculated with a time‐independent K owing to the choice of u*m as the turbulent velocity scale in K. The ratio of maximum orbital velocity to maximum shear velocity is computed as a function of two nondimensional parameters, a Reynolds number Re*=u*mδw/ν and an inverse Rossby number ξ0=ωz0/u*m; δW is wave boundary layer thickness, ω is wave frequency, ν is kinematic viscosity, and z0 is the bottom roughness parameter. These independent variables of the nondimensional unsteady boundary layer equation can be related to the more commonly used wave boundary layer parameters which are expressed in terms of orbital velocity instead of shear velocity. At the fully rough and fully smooth turbulent flow limits, u*m/uom is given by a single curve as a function of ξ0 or Re*, respectively. These curves compare favorably with available measurements and expressions for wave friction factor. The nondimensional equations also yield the dependence of u*m/uom on ξ0 and Re* for transitionally rough turbulent flow.
Simulations of three‐dimensional Langmuir circulation in water of constant density
Authors: Tandon Amit , Leibovich Sidney
Published: February 2004

Simulations of Langmuir circulation with constant eddy viscosity that reveal considerable levels of spatial and temporal complexity are reported. In field observations, the simulations could be interpreted as evidence of vacillation in space and time of measured features in the circulation system, and of the presence of defect structures in the windrow patterns in which the local spacing changes by a factor of 2 in a distance short compared to the windrow spacing. The results also suggest that the ratio of downwind jet speed to downwelling speeds (pitch) can be highly variable and is not a robust feature of Langmuir circulations.
Sensitivity of numerical prognoses to Antarctic sea ice distribution
Authors: Watkins Andrew B. , Simmonds Ian
Published: February 2004

To examine the effect of Antarctic sea ice concentration upon the atmosphere on synoptic timescales, a general circulation model was used in conjunction with the Australian Bureau of Meteorology's Global Assimilation and Prediction system analyses and the Defense Meteorological Satellite Program's Special Sensor Microwave/Imager sea ice data to perform a suite of 5‐day forecasts. As well as using a generic July sea ice concentration, further experiments were conducted with 0, 10, 25, 50, 80, and 100% sea ice concentrations. The 100% forecast was used as the control. Results show that the central pressure, structure and tracks of individual cyclones are sensitive to the “switch on” of different sea ice conditions. Composites of all forecasts made with each concentration showed considerable and statistically significant anomalies in the surface temperatures and turbulent heat fluxes over the sea ice. The magnitudes of these changes varied monotonically with the area of open water. The largest changes were simulated closest to the coast for all concentrations, except for the generic July sea ice run, which displayed maxima over the outer pack. Significant westerly anomalies were also induced over the ice in all cases. Mean sea level pressure (MSLP) anomalies occurred in all forecasts. Again, the generic July sea ice run displayed a distribution of the MSLP anomaly different from all other runs, with maxima occurring in the central to outer pack. All other forecasts displayed maxima at the coast. These results suggest that sea ice concentration induces anomalies in the atmospheric parameters in timescales of less than 5 days. Further, use of a realistic distribution of sea ice concentration produces results distinct from the constant concentration forecasts. Hence it is suggested that real‐time Antarctic sea ice data may be of considerable benefit to numerical weather prediction and analysis.
The Bernoulli function and flux of energy in the ocean
Authors: Saunders Peter M.
Published: February 2004

This short note explains how the Bernoulli function, the total energy of a fluid, can be calculated from recent work on the thermodynamics of seawater. The Bernoulli function for an incompressible fluid has been used in the past to infer the absolute circulation of the ocean from hydrographic data alone. This is now both undesirable and unnecessary. Constructing the Bernoulli function for a hydrographic section also provides a rigorous procedure for calculating the total energy flux across the section, a quantity dominated by the “heat flux”.
Effect of organic matter on bubble surface tension
Authors: Slauenwhite David E. , Johnson Bruce D.
Published: February 2004

Bubble surface tension (BST) is measured by spinning single bubbles in a rotating cell and relating the resulting bubble deformation to the Centrifugal number Ce. Using this method, bubbles in “clean” fresh water (distilled, deionized, passed through activated charcoal and filtered at 0.2 μm) are found to have a BST similar to that reported for the “clean” air‐water interface (72.4 mN/m), whereas adsorption of organic films are observed to decrease the BST, with the effect increasing as the bubbles are aged. In natural coastal sea water (North West Arm, Halifax Harbour (10 m)) the BST decreases to 70.5 mN/m, and in phytoplankton culture (Nitzschia pungens) decreases to 67 mN/m. Saturated stearic acid solution shows a BST of 57 mN/m. Coalescence of two bubbles with equilibrium surface film is accompanied by a rapid decrease in the surface tension, a decrease that we attribute to compression of the merging surface films at the newly created smaller interface. The decrease is most pronounced in water rich in organic surfactants.
Gulf Stream flow field and events near 68°W
Authors: Shay Thomas J. , Bane John M. , Watts D. Randolph , Tracey Karen L.
Published: February 2004

The SYNoptic Ocean Prediction (SYNOP) experiment was designed to provide an accurate understanding of the energetic mesoscale processes in the Gulf Stream. The Central Array measured velocity and temperature throughout the water column, with horizontal extent large enough nearly to span the meander envelope and Eulerian mean structure of the jet at 68°W. The 55‐ to 70‐km mooring spacing resolved mesoscale eddy interactions with the Gulf Stream, and the 26‐month duration allowed stable estimation of long‐term mean fields. Six steep meander troughs propagated into or developed within the array, each lasting around 30–60 days, thus impressing a small mean trough near 68°W in the predominantly eastward currents at jet level (1000 m and above). At the deep level (3500 m) the mean flow was southwest at the shoreward sites shallower than 4300 m, but it flowed cyclonically around a mean low‐pressure anomaly affecting all the deeper offshore sites. The eddy kinetic energy per unit mass (EK) decreased by a factor of about 2.5 with each depth increment from 400 to 700 to 1000 m but was only a factor of 2 smaller at 3500 m than at 1000 m. Values of EK in the upper central jet (400 m) were 100 to 230 mJ kg−1 and were 4–13 mJ kg−1 at 3500 m. Overall, EK in the upper 1000 m at 68°W was higher than previously published values at 55°W. Two extended case studies of meander propagation through the array demonstrate the development and intensification of deep cyclonic and anticyclonic flows beneath the Gulf Stream. The cyclonic flow at 3500 m, associated with amplifying meander troughs, often exceeded 0.35 m s−1, which was much larger than the typical 0.05 m s−1 deep mean velocities.
Are undiscovered hydrothermal vents in the southern Red Sea the main source of silica and helium 3 for the Red Sea Deep Water?
Authors: Cember Richard P.
Published: February 2004

Geochemical Ocean Sections Study (GEOSECS) Indian Ocean Expedition data show that silica and 3He in the Red Sea Deep Water are linearly correlated, suggesting a common hydrothermal source. Silica sections for the Red Sea from the GEOSECS and Mer Rouge (MEROU) expeditions show a strong vertical silica maximum centered at 500 to 600 m depth. The MEROU sections, which have higher horizontal resolution than the GEOSECS sections, suggest that the primary silica source lies in the south at that depth. The interpretation is that the large‐scale silica and 3He distributions are due to the dispersal in the Red Sea Deep Water of warm or hot hydrothermal vent waters associated with the seafloor spreading center of the southern Red Sea. The helium‐ and silica‐rich hot brines of the central Red Sea probably cannot provide the large fluxes of silica or 3He required to maintain the inventory of either of these deep water properties in steady state. The hypothesis of a common hydrothermal source for silica and 3He can most readily be tested by measurements of the germanium‐silicon ratio in Red Sea Deep Water.
Simulation of the mixed‐layer circulation in the Arctic Ocean
Authors: Holland David M. , Mysak Lawrence A. , Oberhuber Josef M.
Published: February 2004

A numerical simulation of the mixed‐layer circulation of the Arctic Ocean is presented using Oberhuber's [1993a] coupled sea ice‐mixed layer‐isopycnal ocean general circulation model. The model domain includes the Arctic Ocean and the Greenland‐Iceland‐Norwegian (GIN) Sea. The horizontal resolution is 2°. The vertical is resolved using five isopycnal layers, of which the uppermost layer is a turbulent mixed layer. The sea ice is modeled using a thermodynamic‐dynamic model which includes a viscous‐plastic rheology. Monthly climatological atmospheric forcing is used to spin up the model into a cyclostationary equilibrium. Model results are presented and discussed with respect to observational and previous modeling studies. The mixed layer shows a circulation pattern similar to that inferred from indirect observations and other modeling studies. In an attempt to determine the main driving mechanism for the mixed‐layer circulation as produced by the Oberhuber model, a set of sensitivity experiments is carried out. In particular, the relative importance of (1) ice cover, (2) atmospheric winds, (3) surface freshwater fluxes, and (4) initialization with Levitus [1982] data is examined to determine the contribution each makes to the modeled circulation. The key conclusion is that buoyancy forcing is critical to maintaining the mixed‐layer circulation.
Coastal ocean fronts and eddies imaged with ERS 1 synthetic aperture radar
Authors: Johannessen J. A. , Shuchman R. A. , Digranes G. , Lyzenga D. R. , Wackerman C. , Johannessen O. M. , Vachon P. W.
Published: February 2004

ERS 1 C band synthetic aperture radar (SAR) data were collected during the Norwegian Continental Shelf Experiment (NORCSEX) both in November 1991 during the ERS 1 commissioning phase and at different seasons in 1992 and 1993. Characteristic SAR image expressions are observed in relation to perturbation of the surface current‐short wave interaction across the Norwegian Coastal Current front for winds less than 10–12 m s−1. In situ measurements document the existence of alternating zones of convergence and divergence coexisting with a strong near‐surface current shear of nearly 4f (where f is the Coriolis parameter) across a distance of a few kilometers. Under calm to moderate winds, i.e., 4–7 m s−1, characteristic expressions of upper ocean circulation features also include the manifestation of eddies through the presence of surface film, which damps the Bragg waves. Comparison of a near‐coincident National Oceanic and Atmospheric Administration advanced very high resolution radiometer image and an ERS 1 SAR image supports the interpretation that surface current fronts are imaged by SAR. In combination with a SAR image simulation model, the relative quantitative importance of shear, convergence, and divergence along the front is examined. Although the model formulation is simple and the absolute magnitude of the perturbations is uncertain, the study shows that the SAR images can sometimes be used to interpret frontal dynamics, including growth and decay of meanders.
Scattering of shelf waves by a spatially varying mean current
Authors: Yankovsky Alexander E. , Chapman David C.
Published: February 2004

A linearized shallow water model is used to investigate the scattering of barotropic shelf waves by spatial variations of a sheared mean current flowing in the same direction as free‐wave phase propagation. The mean current is specified to follow smooth changes in the bottom topography through a scattering region of finite length. The mean current scatters the shelf waves by changing the background potential vorticity, as well as reducing the number of propagating modes available to carry energy downstream of the scattering region. Scattering increases as the strength of the mean current increases, and large‐amplitude evanescent modes may be generated which decay slowly downstream of the scattering region. When combined with the mean current, the evanescent modes appear as compact, mesoscale flows between the mean current and the coast. In some cases, energy is extracted from the mean current and transferred to the shelf waves within the scattering region, such that the scattering process becomes a source of energy for the propagating shelf waves rather than a sink.
The fate of river discharge on the continental shelf: 1. Modeling the river plume and the inner shelf coastal current
Authors: Kourafalou Vassiliki H. , Oey Lie‐Yauw , Wang John D. , Lee Thomas N.
Published: February 2004

We study the development and evolution of buoyant river plumes on the continental shelf. Our calculations are based on three‐dimensional numerical simulations, where the river runoff is introduced as a volume of zero salinity water in the continuity equation and mixing is provided by the model's turbulence closure scheme and wind forcing. In the absence of wind forcing, the modeled river plumes typically consist of an offshore bulge and a coastal current in the direction of Kelvin wave propagation. We propose a plume classification scheme based on a bulk Richardson number, which expresses the relative magnitude of the buoyancy‐induced stratification versus the available mixing. When the ratio of the discharge and shear velocities is greater (less) than 1, the plume is categorized as supercritical (subcritical); that is, the width of the bulge is greater (less) than the width of the coastal current. Supercritical plumes are often characterized by a meandering pattern along the coastal current, caused by a baroclinic instability process. For a given discharge, subcritical plumes are produced by large mixing and/or shallow water depths. In the presence of wind forcing, the favorable conditions for offshore removal of coastal low‐salinity waters include high river runoff and strong upwelling‐favorable wind stress. When the rivers are treated as individual sources of freshwater (“point source” behavior), the wind‐driven flow may exhibit substantial spatial variability. Under the above removal conditions, strong offshore transport takes place in “jetlike” flow regions within the river plume, in contrast to the downwind acceleration of adjacent waters. When the rivers are treated as a long “line source” of freshwater, the plume region resembles a coastal low‐salinity band, and the above removal conditions trigger offshore transport that is most pronounced at the “head” of the source.
Evaluation of TOPEX and basin‐wide Tropical Ocean and Global Atmosphere‐Tropical Atmosphere Ocean sea surface topographies and derived geostrophic currents
Authors: Menkes Christophe , Boulanger Jean‐Philippe , Busalacchi Antonio J.
Published: February 2004

Fields of TOPEX‐derived sea level anomalies are validated against and compared with fields of Tropical Ocean and Global Atmosphere‐Tropical Atmosphere Ocean (TOGA‐TAO) dynamic height anomalies for the first 470 days of the TOPEX/POSEIDON mission. At periods longer than 35 days, TOPEX sea level anomalies compare extremely well with TOGA‐TAO dynamic height anomalies throughout the whole basin, with a mean correlation of 0.79 and mean rms differences of 2.6 cm. Zonal geostrophic current anomalies are then derived from both data sets and validated against in situ current meter measurements at the equator. TOPEX‐derived geostrophic current anomalies at the equator are in good agreement with in situ currents at 0°–165°E, 0°–170°W, 0°–140°W, and 0°–110°W. TOGA‐TAO‐derived current anomalies compare well with in situ currents at 0°–110°W, 0°–140°W, and 0°–170°W, but poor comparisons at 0°–165°E are thought to be linked to the absence of instantaneous salinity measurements in the dynamic height calculation. Despite localized discrepancies, basin‐wide TOGA‐TAO geostrophic currents compare reasonably well with TOPEX‐derived geostrophic currents. The discrepancies in the comparison between TOPEX and TAO are shown to be mostly associated with gaps in TOGA‐TAO space‐time sampling and subsequent gridding procedures.
Low‐frequency variability in the region of the Agulhas Retroflection
Authors: Wang Liping , Koblinsky Chester J.
Published: February 2004

Using sea level data collected by TOPEX/POSEIDON altimeter, we studied the low‐frequency variability in the region of the Agulhas Retroflection and Return Current. We found that characteristics of the low‐frequency variability are fundamentally different from those associated with the high‐frequency mesoscale variability. As in the Kuroshio Extension region, strong low‐frequency variability is found to cluster around strong current. Although bottom topography is found to have strong influence on the low‐frequency variability, correspondence between the spatial structure of low‐frequency variability and major bottom topographic features is significantly different from that in the Kuroshio Extension region.
Comparison of actual and simulated synthetic aperture radar image spectra of ocean waves
Authors: Zurk L. M. , Plant William J.
Published: February 2004

We have simulated synthetic aperture radar (SAR) image spectra of ocean waves, which were focused for stationary scenes using three popular formulations of SAR ocean imaging theory: the time‐dependent, velocity‐bunching, and quasi‐linear models. All three models require functional forms for surface wave spectra, modulation transfer functions, and correlation times; these were obtained from data taken during the SAR and X Band Ocean Nonlinearities (SAXON)‐Forschungsplatform Nordsee (FPN) experiment of November 1990. These measurements were made on and near the German research platform Nordsee during the same period of time that SAR images of ocean waves at X, C, and L bands were obtained by aircraft near the tower. We compare the results of our simulations to the actual SAR spectra for a variety of integration times, range‐to‐velocity ratios (R/V), and azimuth angles. We find that all three models reproduce the observed image spectra well when integration times are small and R/V ratios are low to moderate. Some adjustments of the parameters measured on the tower are occasionally necessary in order to produce this agreement, but in most cases these adjustments are small and within measurement errors; in all cases the same parameters suffice for all models. However, we reproduce a result previously obtained by Brüning et al. [1994] that measured modulated transfer functions do not properly account for imagery of range‐traveling waves propagating downwind. We also find that our calculated velocity spreads seem to be too large to reproduce the observations when the significant wave height is above about 1.5 m and R/V is appreciable. For long integration times and high R/V ratios, the velocity‐bunching model smears the spectrum more than the time‐dependent model and more than the observations. We find that the velocity‐bunching formulation is viable up to an integration time that is a function of R/V; for lower ratios, velocity bunching is viable up to longer integration times, and we offer an explanation of why this is so. Finally, we find that for large R/V ratios the quasi‐linear model fails to produce the low‐frequency components observed in actual image spectra and produced by velocity‐bunching and time‐dependent models.
Observations of the deepwater flow into the Baltic Sea
Authors: Liljebladh Bengt , Stigebrandt Anders
Published: February 2004

It has earlier been hypothesized that the deep water flowing into the Baltic Sea forms a bottom pool in the Arkona Sea, just inside the entrance sills. The flow from the pool farther into the Baltic Sea was assumed to be baroclinic geostrophic and controlled by the pool stratification. This was supported by a realistic statistical description of the deepwater flow into the Baltic Sea, computed using historical vertical density profiles from a hydrographical station in the Arkona Sea. However, basin‐wide synoptic measurements of density and currents were not available for a direct verification of the pool model. A hydrographic survey was undertaken in the Arkona Sea shortly after a major inflow event in the beginning of 1993. The conductivity‐temperature‐depth sections reveal a thick bottom pool of deep water separated by a halocline from the surface water of Baltic origin. Approaching the northern coastal boundary from the central parts of the pool, the halocline sank by about 20 m before hitting the bottom. The ship‐mounted acoustic Doppler current profiler recorded a complicated current field. However, subtraction of the assumed barotropic part gives a current field quite similar to the baroclinic geostrophic current field computed from the density distribution. Thus, a dense bottom pool, including a baroclinic geostrophic boundary current along the northern flank of the pool, is quite evident from our measurements.
The Indo‐Pacific throughflow in the Timor Passage
Authors: Molcard R. , Fieux M. , Ilahude A. G.
Published: February 2004

Two current meter moorings were deployed from the R/V Marion Dufresne in March 1992 between Roti Island and the Ashmore Reef and were recovered in April 1993 onboard the R/V Baruna Jaya 1. The mean transport was estimated between 3.4 and 5.3 Sv (1 Sv = 106 m3/s) for the Pacific water flowing toward the Indian Ocean through the Timor Passage. The upper part of the transport, from the surface to 500 m, shows a weak maximum during the southwest monsoon. An unexpected deep flow toward the Indian Ocean between 500 and 1550 m brings an important contribution to the total transport, which is minimum during August–September. As already noted in previous experiments, there is significant variability in the form of a succession of events within the 20‐ to 60‐day range.
Impact of dimethylsulfide photochemistry on methyl sulfur cycling in the equatorial Pacific Ocean
Authors: Kieber David J. , Jiao Jianfu , Kiene Ronald P. , Bates Timothy S.
Published: February 2004

Shipboard experiments were conducted in the equatorial Pacific Ocean to ascertain the relative importance of atmospheric ventilation, biological consumption, and photolysis in the removal of dimethylsulfide (DMS) from seawater. Comparisons were made at a series of sampling locations in a transect from 12°N 140°W to 12°S 135°W, as part of the International Global Atmospheric Chemistry project's Marine Aerosol and Gas Exchange cruise in February–March 1992. Turnover rate constants for DMS were used to compare the different removal pathways over three depth intervals (0–1 m, 0–20 m, and 0–60 m). In the surface mixed layer (0–60 m), the DMS turnover rate constants ranged from 0.02 to 0.19 day−1 for atmospheric ventilation, 0.04 to 0.66 day−1 for biological consumption, and 0.05 to 0.15 day−1 for photolysis. When all three processes are considered, the corresponding turnover time for DMS ranges from 1 to 4 days, with photolysis accounting for 7%–40% of the total turnover of DMS. Laboratory irradiations were conducted with stored seawater samples to study the kinetics and wavelength dependence of DMS photolysis. Salient results were (1) the photolysis of DMS followed pseudo first‐order kinetics, (2) dimethylsulfoxide was a minor (14%) product of DMS photolysis, and (3) the photolysis of DMS in seawater under natural light conditions occurred primarily at wavelengths between 380 and 460 nm. On the basis of these results, we predict that the photolysis of DMS will occur at appreciable depths in the photic zone in oligotrophic marine environments (∼60 m). An important finding of this study is that atmospheric loss, biological consumption, and photolysis are all important removal pathways for DMS in the photic zone of the equatorial Pacific Ocean. The relative importance of each pathway is a function of the depth interval considered, sampling location, and meteorological conditions.
Tritium distributions in an isopycnic model of the North Atlantic
Authors: Jia Yanli , Richards Kelvin J.
Published: February 2004

An ocean general circulation model with an isopycnic coordinate in the vertical is used to simulate the North Atlantic circulation. Tritium and helium are injected into the model after an initial spin‐up phase to assist our understanding of the model response and to validate the model itself by comparing the model data with available tracer observations. In this paper, the distribution of tritium is presented and compared with observations in 1972 (Geochemical Ocean Sections Study) and 1981 (Transient Tracers in the Ocean (TTO)). The vertical penetration of tritium in the model compares well with observations, reflecting the ventilation patterns in the subtropical and subpolar gyres and the deep overflows from the Greenland and Norwegian basin through the Denmark Strait and across the Iceland‐Faeroes rise. However, the distributions of tritium on various isopycnic layers do show discrepancies with observations, and the magnitude of tritium concentration is too high in the model. It is found that the model produces a pronounced maximum tritium concentration in the interior of the North Atlantic subtropical gyre in 1972, which is not observed. The presence of this maximum suggests that the ratio of diffusion to advection timescales (the Péclet number) is too high in the model. A simple two‐dimensional advection‐diffusion model is used to explore the relationships between the distributions of tritium and the timescales of advection and diffusion processes. These experiments suggest an upper bound on the Péclet number. A further experiment using the Atlantic isopycnic model with a decreased Péclet number shows some improvement to the distribution of tritium on the isopycnic layers. Comparisons of tritium‐helium age in 1981 between the model results and TTO data show that the model has a too rapid circulation. The lack of mixing by eddies in the model is also believed to be partially responsible for the discrepancies between the modeled tritium distributions and the observations. The good correspondence between our tritium simulation with the Atlantic isopycnic model and observations leads us to believe that the model captures the major pathways of deep ocean circulation in the North Atlantic. The model should be useful for other tracer sequestration studies. Combining models of varying complexity has proved useful in identifying and (partially) correcting deficiencies in the model and will be used in future tracer studies.
Open‐ocean boundary conditions from interior data: Local and remote forcing of Massachusetts Bay
Authors: Bogden Philip S. , Malanotte‐Rizzoli Paola , Signell Rich
Published: February 2004

Massachusetts and Cape Cod Bays form a semienclosed coastal basin that opens onto the much larger Gulf of Maine. Subtidal circulation in the bay is driven by local winds and remotely driven flows from the gulf. The local‐wind forced flow is estimated with a regional shallow water model driven by wind measurements. The model uses a gravity wave radiation condition along the open‐ocean boundary. Results compare reasonably well with observed currents near the coast. In some offshore regions, however, modeled flows are an order of magnitude less energetic than the data. Strong flows are observed even during periods of weak local wind forcing. Poor model‐data comparisons are attributable, at least in part, to open‐ocean boundary conditions that neglect the effects of remote forcing. Velocity measurements from within Massachusetts Bay are used to estimate the remotely forced component of the flow. The data are combined with shallow water dynamics in an inverse‐model formulation that follows the theory of Bennett and McIntosh [1982], who considered tides. We extend their analysis to consider the subtidal response to transient forcing. The inverse model adjusts the a priori open‐ocean boundary condition, thereby minimizing a combined measure of model‐data misfit and boundary condition adjustment. A “consistency criterion” determines the optimal trade‐off between the two. The criterion is based on a measure of plausibility for the inverse solution. The “consistent” inverse solution reproduces 56% of the average squared variation in the data. The local‐wind‐driven flow alone accounts for half of the model skill. The other half is attributable to remotely forced flows from the Gulf of Maine. The unexplained 44% comes from measurement errors and model errors that are not accounted for in the analysis.
Impact of aerosols and clouds on the troposphere and stratosphere radiation field with application to twilight photochemistry at 20 km
Authors: Anderson Donald E. , DeMajistre Robert , Lloyd Steven A. , Swaminathan P. K.
Published: February 2004

A series of coordinated investigations of polar stratospheric chemistry, radiation, and dynamics has resolved and generated many questions regarding ozone depletion in the Earth's atmosphere. Photodissociation plays a key role, and the radiation field models utilized have often been singled out as possible sources of uncertainty. Mean intensities (source functions) are compared for three independent models: discrete‐ordinate, integral equation, and Monte Carlo simulation. It was found that the results differ by <10% for clear, cloudy, and aerosol conditions over an altitude range of 0–50 km, wavelength interval of 175–800 nm and a wide range of solar zenith angles. It is shown that in the presence of Pinatubolike aerosol concentrations, twilight photodissociation rates within an aerosol layer centered at 20 km can be reduced by more than an order of magnitude, whereas for solar zenith angles <60°, photodissociation rate changes are a few percent or less. Assessment of the effects of the aerosols on twilight stratospheric chemistry within the aerosol layer shows that radiation field perturbations on the homogeneous photochemistry are small and that heterogeneous processes are the major source of the altered photochemistry.
Gravity waves and turbulence associated with cumulus convection observed with the UHF/VHF clear‐air Doppler radars
Authors: Sato Kaoru , Hashiguchi Hiroyuki , Fukao Shoichiro
Published: February 2004

Vertical wind disturbances are frequently observed during midsummer afternoons in association with cumulus convection. To examine the relation of these wind disturbances to atmospheric stability and turbulence intensity, we carried out intensive observations of wind, temperature and humidity over a large vertical region extending from the boundary layer to the lower stratosphere using UHF/VHF radars and radiosondes at Shiga, Japan (35°N, 136°E). The wind disturbances propagate quickly into the upper troposphere just after 1500 local standard time (LST) when the level of free convection (LFC) descends below the top of the mixed layer, while before that, the disturbances are confined in the mixed layer. However, strong turbulence is largely confined to the region below 3 km even after 1500 LST, suggesting that the height of 3 km corresponds to the top of cumuli, while the wind disturbances above are due to gravity waves generated in association with cumulus convection. In addition, stratospheric disturbances were examined for 12 cases of midsummer disturbances using routine observational data taken with a VHF radar in a height region of 5–24 km. Wind disturbances are observed in the lower stratosphere when turbulence as well as wind disturbances are strong in the whole troposphere. The stratospheric disturbances are dominant in two regions below and above a height of 18 km where the background horizontal wind is weak. Long‐period disturbances are observed only in the lower region. This fact suggests that the height of 18 km is a critical level for the long‐period gravity waves. The existence of a strong turbulent layer around 18 km is consistent with this inference.
Retrieval error comparison for several inversion techniques used in limb‐scanning millimeter‐wave spectroscopy
Authors: Puliafito E. , Bevilacqua R. , Olivero J. , Degenhardt W.
Published: February 2004

The Rodgers formal retrieval error analysis allows the quantitative determination of such important retrieval properties as the total retrieval error, the contributions from the relevant error sources, the vertical resolution, and the inversion bias. Therefore it is a powerful tool for the objective evaluation and comparison of retrieval techniques. We have applied this error analysis to five numerical inversion techniques (the direct inversion, the linear constrained inversion, the optimal estimation inversion, the general relaxation inversion, and the Twomey‐modified Chahine relaxation inversion) used for the retrieval of middle atmospheric constituent concentrations from limb‐scanning millimeter‐wave spectroscopic measurements. As an example of such measurements, we use the geometry and instrument characteristic of the millimeter‐wave atmospheric sounder (MAS) experiment, which has flown on the first three ATLAS series of spacelab shuttle missions (March 1992, April 1993, and November 1994). We find that the relaxation methods have somewhat better vertical resolution but are slightly more sensitive to measurement errors than the constrained matrix methods. However, for the assumed MAS instrument characteristics, the total retrieval error is similar for all of the inversion schemes. We also tested the error predicted by the theoretical analysis against numerical simulations and find good agreement. Trade‐offs of these retrieval characteristics for several cases of measurement error and a priori profile uncertainty are presented.
Two‐dimensional and three‐dimensional model simulations, measurements, and interpretation of the influence of the October 1989 solar proton events on the middle atmosphere
Authors: Jackman Charles H. , Cerniglia Mark C. , Nielsen J. Eric , Allen Dale J. , Zawodny Joseph M. , McPeters Richard D. , Douglass Anne R. , Rosenfield Joan E. , Rood Richard B.
Published: February 2004

The very large solar proton events (SPEs) which occurred from October 19 to 27, 1989, earned substantial middle‐atmospheric HOx and NOx constituent increases. Although no measurements of HOx increases were made during these SPEs, increases in NO were observed by rocket instruments which are in good agreement with calculated NO increases from our proton energy degradation code. Both the HOx and the NOx increases can cause ozone decreases; however, the HOx‐induced ozone changes are relatively short‐lived because HOx species have lifetimes of only hours in the middle atmosphere. Our two‐dimensional model, when used to simulate effects of the longer‐lived NOx, predicted lower‐stratospheric polar ozone decreases of greater than 2% persisting for one and a half years past these SPEs. Previous three‐dimensional model simulations of these SPEs (Jackman et al., 1993) indicated the importance of properly representing the polar vortices and warming events when accounting for the ozone decreases observed by the solar backscattered ultraviolet 2 instrument two months past these atmospheric perturbations. In an expansion of that study, we found that it was necessary to simulate the November 1, 1989, to April 2, 1990, time period and the November 1, 1986, to April 2, 1987, time period with our three‐dimensional model in order to more directly compare to the stratospheric aerosol and gas experiment (SAGE) II observations of lower stratospheric NO2 and ozone changes between the end of March 1987 and 1990 at 70°N. Both the NOx increases from the October 1989 SPEs and the larger downward transport in the 1989–1990 northern winter compared to the 1986–1987 northern winter contributed to the large enhancements in NO2 in the lower stratosphere observed in the SAGE II measurements at the end of March 1990. Our three‐dimensional model simulations predict smaller ozone decreases than those observed by SAGE II in the lower stratosphere near the end of March 1990, indicating that other factors, such as heterogeneous chemistry, might also be influencing the constituents of this region.
Formation of low‐ozone pockets in the middle stratospheric anticyclone during winter
Authors: Manney G. L. , Froidevaux L. , Waters J. W. , Zurek R. W. , Gille J. C. , Kumer J. B. , Mergenthaler J. L. , Roche A. E. , O'Neill A. , Swinbank R.
Published: February 2004

Microwave limb sounder observations of midstratospheric ozone during stratospheric warmings show tongues of high ozone drawn up from low latitudes into the developing anticyclone. Several days later, an isolated pocket of low ozone mixing ratios appears, centered in the anticyclone, and extending in the vertical from ≈15 to 5 hPa, with higher mixing ratios both above and below. These low ozone mixing ratios during northern hemisphere warmings are comparable to values well inside the vortex and are ≈3 parts per million by volume lower than typical midlatitude extra‐vortex mixing ratios. This type of feature is seen whenever the anticyclone is strong and persistent, including during relatively strong minor warmings in the southern hemisphere. Three‐dimensional back trajectory calculations indicate that the air in the region of the low‐ozone pockets originates at higher altitudes and low latitudes, where ozone mixing ratios are much higher. The air parcels studied here are typically confined together for 1 to 3 weeks before the lowest ozone mixing ratios are observed. The trajectory calculations and comparisons with passive tracer data confirm that the observed low‐ozone regions in the midstratosphere could not result solely from transport processes.
Stratospheric Ozone Intercomparison Campaign (STOIC) 1989: Overview
Authors: Margitan J. J. , Barnes R. A. , Brothers G. B. , Butler J. , Burris J. , Connor B. J. , Ferrare R. A. , Kerr J. B. , Komhyr W. D. , McCormick M. P. , McDermid I. S. , McElroy C. T. , McGee T. J. , Miller A. J. , Owens M. , Parrish A. D. , Parsons C. L. , Torres A. L. , Tsou J. J. , Walsh T. D. , Whiteman D.
Published: February 2004

The NASA Upper Atmosphere Research Program organized a Stratospheric Ozone Intercomparison Campaign (STOIC) held in July–August 1989 at the Table Mountain Facility (TMF) of the Jet Propulsion Laboratory (JPL). The primary instruments participating in this campaign were several that had been developed by NASA for the Network for the Detection of Stratospheric Change: the JPL ozone lidar at TMF, the Goddard Space Flight Center trailer‐mounted ozone lidar which was moved to TMF for this comparison, and the Millitech/LaRC microwave radiometer. To assess the performance of these new instruments, a validation/intercomparison campaign was undertaken using established techniques: balloon ozonesondes launched by personnel from the Wallops Flight Facility and from NOAA Geophysical Monitoring for Climate Change (GMCC) (now Climate Monitoring and Diagnostics Laboratory), a NOAA GMCC Dobson spectrophotometer, and a Brewer spectrometer from the Atmospheric Environment Service of Canada, both being used for column as well as Umkehr profile retrievals. All of these instruments were located at TMF and measurements were made as close together in time as possible to minimize atmospheric variability as a factor in the comparisons. Daytime rocket measurements of ozone were made by Wallops Flight Facility personnel using ROCOZ‐A instruments launched from San Nicholas Island. The entire campaign was conducted as a blind intercomparison, with the investigators not seeing each others data until all data had been submitted to a referee and archived at the end of the 2‐week period (July 20 to August 2, 1989). Satellite data were also obtained from the Stratospheric Aerosol and Gas Experiment (SAGE II) aboard the Earth Radiation Budget Satellite and the total ozone mapping spectrometer (TOMS) aboard Nimbus 7. An examination of the data has found excellent agreement among the techniques, especially in the 20‐ to 40‐km range. As expected, there was little atmospheric variability during the intercomparison, allowing for detailed statistical comparisons at a high level of precision. This overview paper will summarize the campaign and provide a “road map” to subsequent papers in this issue by the individual instrument teams which will present more detailed analysis of the data and conclusions.
On the lack of southern hemisphere polar mesosphere summer echoes
Authors: Balsley B. B. , Woodman R. F. , Sarango M. , Rodríguez R. , Urbina J. , Ragaini E. , Carey J. , Huaman M. , Giraldez A.
Published: February 2004

We report VHF radar observations of the southern high‐latitude mesopause region using wind profilers that were installed recently on King George Island, Antarctica, and Ushuaia, Argentina. Briefly, our observations, which were made during January and February 1993, show almost no evidence of so‐called polar mesosphere summer echoes, or PMSE. Since these echoes are a predominant feature of the northern high‐latitude mesosphere in summer, their absence in the southern hemisphere is both surprising and intriguing. In this paper we present evidence demonstrating the virtual absence of the echoes and demonstrate that our systems were capable of detecting them had they been present. We also outline some of the consequences of this intriguing result, which are supported by observed hemispheric differences in polar mesospheric clouds, mesospheric temperatures, upper atmospheric gravity wave activity, and mean circulation patterns.
Factors influencing the concentration of gas phase hydrogen peroxide during the summer at Niwot Ridge, Colorado
Authors: Watkins B. A. , Parrish D. D. , Trainer M. , Norton R. B. , Yee J. E. , Fehsenfeld F. C. , Heikes B. G.
Published: February 2004

Measurements of H2O2 and several chemical and meteorological parameters were made during two summer studies at Niwot Ridge, Colorado, a rural site with low humidity, low SO2 concentrations, and low but varying levels of NOX. During two meteorological conditions, a strong nocturnal inversion and precipitation occurence, depositional processes play a major role in controlling the variability of H2O2. Selection of data from sunny, dry, and midday periods reduce these major effects and allow the influences of photochemistry to be discerned. Even during these selected periods, removal processes must be very rapid to balance the high production rates implied by measured and modeled levels of peroxy radicals. The relationships of the resulting near steady state concentrations of H2O2 with other parameters indicate that H2O2 is highest in air masses with low levels of NOX, highly aged NOY (as indicated by low NOX to NOY ratios), and high levels of O3. These relationships also provide indirect evidence that isoprene is a significant precursor of H2O2. A significant negative correlation with relative humidity is found, which may reflect the dependence of the removal processes upon this parameter. The observed ratios of H2O2 to HNO3 indicate that the photochemical oxidant formation is NOX limited.
Scattered ultraviolet radiation in the upper stratosphere 2: Models and measurements
Authors: Minschwaner K. , Anderson G. P. , Hall L. A. , Chetwynd J. H. , Thomas R. J. , Rusch D. W. , Berk A. , Conant J. A.
Published: February 2004

Scattered ultraviolet radiation in the 40 to 46 km altitude range is evaluated using an analytic, single‐scattering description and results from the atmospheric ultraviolet radiance integrated code (AURIC). The calculations are compared with measurements obtained from a balloon‐borne spectrometer at 1.5‐nm resolution. The analytic approach is useful for approximating the angular and spectral dependence of scattered UV radiation; however, use of a single scale height to describe the vertical distribution of absorbers and scatterers leads to errors of 50% or greater at intermediate ozone opacities. Results from AURIC generally are compatible with the observations, particularly below 210 nm where large discrepancies have been noted in prior model/measurement comparisons.