bluuebunny/crossref_metadata_2025 huggingface dataset:
Displacement and flexural stresses of a loaded elastic plate on a viscous liquid
Authors: Rehbinder G. , Yakubenko P. A.
Published: September 2002

The nonstationary deformation of an infinite thin elastic plate that is symmetrically loaded and floats on a highly viscous liquid is characterized by two similarity parameters and the shape of the load. The first similarity parameter is proportional to the rigidity of the plate and inversely proportional to the fourth power of the radial extent of the load. The second is proportional to the radial extent of the load raised to three halves and inversely proportional to the viscosity of the liquid. The equations describing the deformation of the plate and the motion of the liquid are solved analytically and applied to the rebound of Fennoscandia since the Weichselian glaciation. The corresponding interpretation of uplift data of the lithosphere in Scandinavia implies that the ice cap did not cover the southern part of Scandinavia. Moreover, the calculated flexural stresses of the lithosphere in Sweden are small in those regions where no weak earthquakes occur.
Modeling weather fronts to improve GPS heights: A new tool for GPS meteorology?
Authors: Gregorius Thierry L. H. , Blewitt Geoffrey
Published: September 2002

The precision of vertical position and atmospheric water vapor content determined by the Global Positioning System (GPS) is limited by errors due to tropospheric delay. One factor is the spatial and temporal variability in tropospheric refractivity caused by passing weather fronts. We can explain some of the temporal characteristics of estimated tropospheric delay in terms of a simple path delay model as a function of frontal parameters. These results suggest that GPS could be used to estimate the geometry and passage time of a frontal zone. We have developed indices which detect tropospheric variability from GPS data alone; the detection rate of fronts with this approach is up to 70%. Once detected, we eliminated days affected by fronts or other tropospheric variability from the time series of station height estimates, resulting in improved long‐term repeatability. The additional variance attributable to fronts is estimated to be up to 10 mm2at Herstmonceux, England, where fronts occur every 2–3 days. The effect of fronts on the horizontal station component is up to 80% smaller than for the vertical. Studies in the field of GPS meteorology may be improved by estimating frontal parameters.
A fluid inclusion and stable isotope study of hydrothermal circulation in a transform zone: Western Blanco Depression, northeast Pacific
Authors: Manac'h G. , Lécuyer C. , Juteau T.
Published: September 2002

The Blanco Trough (Juan de Fuca Ridge) exposes a continuous section of upper oceanic crust (basalts and diabases) that has been hydrothermally altered in a transform fault environment. Microthermometric measurements on fluid inclusions and stable oxygen isotope compositions of whole rocks and secondary minerals from pillow lava and diabase units were performed to determine the evolution of hydrothermal fluids. A few low δ18O values (down to +4.8‰) for diabase, and temperatures from 280 to 350°C obtained from fluid inclusions in quartz, attest to an early high temperature stage of hydrothermal circulation close to the ridge axis. A dense fracture network has maintained moderate temperature hydrothermal circulation (about 200°C) rooted down to the top of the diabase unit. Oxygen isotope profiles in two reference sections reveal that the upper part of the oceanic crust exposed in the Blanco Trough is significantly 18O‐enriched (+6.6‰) relative to its mantle source (5.7 ± 0.2‰). We propose that extensive off‐axis tectonic activity linked to the transform zone favored fluid circulation in crust at maximum temperatures of about 200°C. The low‐temperature water‐rock interactions (T < 200°C) were more pervasive in the Blanco crust, despite being 6 times younger than the crust at Hole 504B, which evolved far from any influence of transform fault activity. Transform faults, which are common in slow‐spreading ridge environments, may therefore significantly affect the hydrothermal activity, which contributes to the regulation of the chemical and isotope composition of seawater.
Regional atmospheric angular momentum contributions to polar motion excitation
Authors: Nastula Jolanta , Salstein David
Published: September 2002

We focus on a regional analysis of equatorial components of the effective atmospheric angular momentum (EAAM) functions that measure the excitation of polar motion. These functions are computed from National Centers for Environmental Prediction and National Center for Atmospheric Research (NCEP/NCAR) reanalysis data both globally and in 108 geographic sectors for the period 1968–1997. We investigate the relationship between the regional sector EAAM and the global functions responsible for polar motion excitation. We examine two excitation terms in parallel, with and without the inverted barometer (IB) approximation, which adjusts the atmosphere to account for an isostatic equilibrium response of the ocean to overlying pressure. In the case of pressure terms without IB the largest contributions to the equatorial components of polar motion excitation functions originate in the South Pacific, North Atlantic, and North Pacific regions. Applying the IB correction results in the dominance of Eurasia and North America instead, with nearly all Southern Hemisphere contributions disappearing. When comparing the regional functions to their global sum, such fluctuations are mainly coherent with variations over northern midlatitude land areas. In some sectors, oscillations in these functions tend to occur broadly across two frequency bands: 25–75 and 75–125 days in both prograde and retrograde directions, corresponding to counterclockwise and clockwise polar motion, respectively. Other sectors contain more continuous spectral bands, which are centered at ∼70 days. Coherence and cross‐spectral analyses lead us to identify a region over Eurasia that contributes importantly to exciting polar motion; we also note an eastwardly propagating signal toward this region in these excitation terms.
Estimation of nutation using the Global Positioning System
Authors: Rothacher M. , Beutler G. , Herring Thomas A. , Weber R.
Published: September 2002

In the past the estimation of corrections to nutation models was uniquely reserved to very long baseline interferometry (VLBI) and lunar laser ranging (LLR) data processing. Although satellite space‐geodetic measurements have been used to determine UT1‐UTC rates (or length of day) for many years now, the estimation of nutation rates was not performed. There is no fundamental difference, however, between the estimation of rates in UT1‐UTC and nutation rates in obliquity and longitude from satellite data. A simple variance‐covariance analysis shows that significant contributions to nutation by the Global Positioning System (GPS) are possible for periods below about 16 days. Since March 1994, daily nutation rates have been computed at the Center for Orbit Determination Europe using the data collected by the global GPS network. The series of nutation rates now covers 3.5 years. It is used to compute corrections for a set of 34 nutation periods between 4 and 16 days. The formal uncertainties of the estimated nutation coefficients in obliquity Δε and longitude Δψ sin ε0grow linearly with period from several microarcseconds (μas) at periods of a few days to about 30 μas at periods of 16 days. The comparison of the GPS‐derived coefficients with the International Earth Rotation Service 1996 nutation model shows an overall agreement of 10 μas (median). The GPS results are also in very good agreement with the most recent model by Souchay and Kinoshita (1997.2), better than most of the VLBI and LLR results reported in the literature. GPS thus allows, although limited to high frequencies because of the satellite orbits involved, an independent check of the validity of theoretical nutation models and of results obtained from VLBI and LLR.
Fracture channel waves
Authors: Nihei Kurt T. , Yi Weidong , Myer Larry R. , Cook Neville G. W. , Schoenberg Michael
Published: September 2002

The properties of guided waves which propagate between two parallel fractures are examined. Plane wave analysis is used to obtain a dispersion equation for the velocities of fracture channel waves. Analysis of this equation demonstrates that parallel fractures form an elastic waveguide that supports two symmetric and two antisymmetric dispersive Rayleigh channel waves, each with particle motions and velocities that are sensitive to the normal and tangential stiffnesses of the fractures. These fracture channel waves degenerate to shear waves when the fracture stiffnesses are large, to Rayleigh waves and Rayleigh‐Lamb plate waves when the fracture stiffnesses are low, and to fracture interface waves when the fractures are either very closely spaced or widely separated. For intermediate fracture stiffnesses typical of fractured rock masses, fracture channel waves are dispersive and exhibit moderate to strong localization of guided wave energy between the fractures. The existence of these waves is examined using laboratory acoustic measurements on a fractured marble plate. This experiment confirms the distinct particle motion of the fundamental antisymmetric fracture channel wave (A0 mode) and demonstrates the ease with which a fracture channel wave can be generated and detected.
Thermochemical dynamics of magma chambers: A simple model
Authors: Mourtada‐Bonnefoi Catherine C. , Provost Ariel , Albarède Francis
Published: September 2002

A magma chamber may be considered as an open, non adiabatic chemical reactor that continuously receives new liquid, crystallizes, and erupts lava. Heat is transferred to the walls, and crystals settle on the chamber floor. Considering, for simplicity, the chamber magma as a thermally and chemically homogeneous two‐component liquid in which the solidification rate is a bell‐shaped function of temperature and composition, the system is governed by two coupled differential equations for the evolution of temperature and composition with time. For constant external factors, such as fresh‐magma input flow or heat loss flux, the magma chamber tends to a steady state. For a certain domain of external factor values, there are two stable steady state solutions instead of one. When the external factors vary slowly, the magma chamber state also drifts continuously, except when the external factors leave the bistability domain. Then all characteristics of the volcanic system undergo a sudden jump, for example, from basic to felsic composition and from high to low lava output flow when the fresh‐magma input flow of a waning volcano declines. The jump takes place over a time of the order of the magma residence time and is thus short compared to the lifetime of the chamber. Such a magmatic catastrophe, which may occur for a small and continuous evolution of the external conditions, results in a radical change in eruption style and volcanic products and may trigger an exceptionally large or violent eruption. This kind of event may explain the widespread observation of compositional gaps in lava series (e.g., the Daly gap), a number of radical changes in eruptive style, and certain eruptions which appear unique in the lifetime of some composite volcanoes.
Modeling particles and pelagic organisms in Chesapeake Bay: Convergent features control plankton distributions
Authors: Hood Raleigh R. , Wang Harry V. , Purcell Jennifer E. , Houde Edward D. , Harding Lawrence W.
Published: September 2002

A two‐dimensional Lagrangian particle trajectory model is described and used to study how surface currents transport particles and, by analogy, plankton in Chesapeake Bay, United States. It is shown that persistent patches of high particle concentration develop in well‐defined regions along the eastern shore and in the lower reaches of some western shore tributaries due to a combination of passive accumulation of particles in areas where the flushing rate is low and convergence. In the model the highest particle concentrations in the Chesapeake consistently develop in the lower bay (latitude 37.1°–37.7° N) in two specific regions near the shore of Cape Charles where convergence and downwelling occur. It is shown that one of these is associated with a strong and persistent, residual cyclonic eddy located over an abrupt change in bottom topography. Recent bay wide field surveys reveal that various planktonic groups, including phytoplankton, zooplankton, and bay anchovy eggs and larvae, have maximum abundances in the vicinity of this eddy. It is argued that these convergent areas are important features that have a strong influence on plankton distributions and that they provide consistently high food concentrations for higher trophic levels.
Location and dynamics of the Antarctic Polar Front from satellite sea surface temperature data
Authors: Moore J. Keith , Abbott Mark R. , Richman James G.
Published: September 2002

The location of the Antarctic Polar Front (PF) was mapped over a 7‐year period (1987–1993) within images of satellite‐derived sea surface temperature. The mean path of the PF is strongly steered by the topographic features of the Southern Ocean. The topography places vorticity constraints on the dynamics of the PF that strongly affect spatial and temporal variability. Over the deep ocean basins the surface expression of the PF is weakened, and the PF meanders over a wide latitudinal range. Near large topographic features, width and temperature change across the front increase, and large‐scale meandering is inhibited. Elevated mesoscale variability is seen within and downstream of these areas and may be the result of baroclinic instabilities initiated where the PF encounters large topographic features. The strong correlations between topography and PF dynamics can be understood in the context of the planetary potential vorticity (PPV or f/H) field. Mean PPV at the PF varies by more than a factor of 2 along its circumpolar path. However, at the mesoscale the PF remains within a relatively narrow range of PPV values around the local mean. Away from large topographic features, the PF returns to a preferred PPV value of ∼25 × 10−9 m−1 s−1 despite large latitudinal shifts. The mean paths of the surface and subsurface expressions of the PF are closely coupled over much of the Southern Ocean.
Comparison of airborne synthetic aperture radar imagery with in situ surface‐slope measurements across Gulf Stream slicks and a convergent front
Authors: Marmorino G. O. , Lyzenga D. R. , Kaiser J. A. C.
Published: September 2002

Synthetic aperture radar (SAR) imagery showing two types of features near the inshore edge of the Gulf Stream are compared with nearly simultaneous estimates of the sea surface slope field derived from optical shipboard measurements. One class of feature consists of a set of narrow, dark lines having radar signal modulations of about −10 dB at L band. These modulations are comparable to those observed in the in situ wave‐slope data over wavenumbers corresponding to the radar‐resonant Bragg waves. These modulations are also predicted by a simplified equilibrium wave spectrum model using a surface elasticity of about 25 mN/m (as determined from in situ measurements of surface tension) and a wind friction velocity of about 10 cm/s (from buoy and shipboard measurements). These results support Lyzenga and Marmorino's [1998] inference that the Gulf Stream dark lines represent relatively passive, biogenically derived surfactant slicks that are advected and strained by the large‐scale surface flow field. The second class of feature consists of a pair of bright‐dark signatures over the shallow continental shelf region near Cape Hatteras, North Carolina. These features are characterized by signal modulations of about +4 and −4 dB in both the L band SAR and in situ data. These modulations appear to be due to the interaction of surface waves with the current convergence and divergence regions associated with a rotary circulation in a shallow convergent front. Model calculations of this interaction by Lyzenga [1998] indicate that the positive perturbations associated with current convergence should be relatively independent of the wavenumber, which is in approximate agreement with the in situ measurements of the present paper. The model also indicates that the negative perturbations associated with the region of current divergence should decrease for wavenumbers higher than L band. That trend is observed in the SAR data but not in the in situ data, which show significant perturbations at higher wavenumbers. It is conjectured that this is due to the effects of surfactants and either along‐front or time variability in the frontal dynamics, which are not included in the model. Additional comparisons of this kind should be useful to further test and improve physical models of near‐surface phenomena.
Stocks and fluxes of biogenic silica in the western oligotrophic equatorial Pacific
Authors: Blain Stéphane , Tréguer Paul , Rodier Martine
Published: September 2002

During a cruise along the 165°E meridian (6°N–15°S), distributions of biogenic silica (BSi) and of chlorophyll a were studied. BSi ranged between 10 and 60 nmol L−1 in the nitrate‐depleted surface layer. A deep BSi maximum (DBSiM) layer was located at the base of the photic layer. The high mesoscale variability in BSi distribution is explained as resulting from a combination of physical and chemical forcings. For studying the response of the tropical/equatorial ecosystem to physical forcing, BSi is a more sensitive tracer than chlorophyll a. Daily variations of stocks and fluxes of biogenic silica in the 0–340 m layer were measured at a drifting station during a 5 day experiment at 0°S, 167°E. Displacement of the pycnocline occurred at the drifting station, allowing injection of new nutrients in the photic layer to which the ecosystem reacted by an increase of BSi in the DBSiM layer. We hypothesize that this BSi increase is explained by increased diatom growth (at a rate of 0.6 doublings d−1). At this drifting station, sediment traps were deployed below the photic layer (at 125, 175, 240, and 340 m depths) to estimate export fluxes of BSi. They ranged between 60 μmol m−2 d−1 at 125 m and 180 μmol m−2 d−1 at 340 m. Compared to a BSi production of 960 μmol m−2 d−1 measured 1 week later during the same cruise in similar oligotrophic equatorial waters, such low export fluxes suggest that dissolution of BSi might be high in the warm equatorial Pacific waters.
Sea‐ice impact on long‐term particle flux in the Greenland Sea's Is Odden‐Nordbukta region, 1985–1996
Authors: Ramseier René O. , Garrity Caren , Bauerfeind E. , Peinert R.
Published: September 2002

Five sediment traps deployed in the Greenland Sea at a depth of 500 m between 72°N and 75°N by the Sonderforschungsbereich 313, Kiel, Germany, provide the necessary data to compare particle flux with ambient ice regimes. Sedimentation in this seasonally ice‐covered region is dependent upon the following three basic parameters: (1) ice concentration, (2) duration of ice cover, and (3) distance from the ice edge. These factors vary significantly with time and space. We develop algorithms that provide annual sedimentation amounts for the area contained by 71°N to 76°N, the Greenland coast, and 10°E. For a severe ice year the area of seasonal ice cover and an 80‐km‐wide band extending along the maximum extent of the ice edge, the Biological Marginal Ice Zone (BMIZ), combine to provide 92% of the total sedimentation. For particulate organic carbon and silica this zone accounts for 89% each of the total sedimentation. In a light ice year the respective percentages are 84% for dry weight, 87% for particulate organic carbon, and 81% for biogenic particulate silica. These figures are slightly less than sedimentation for a severe ice year. If the Is Odden‐Nordbukta region is replaced by open ocean for purposes of comparison, the BMIZ out produces the open ocean for POC by a factor of 3.2. Projecting the algorithms for the Is Odden‐Nordbukta region to the rest of the Greenland Sea, we conclude that the Is Odden‐Nordbukta region is a substantial producer of sedimentation.
Introduction to special section: Biogeochemical conditions in the equatorial Pacific in late 1994
Authors: Dandonneau Yves
Published: September 2002

The equatorial Pacific has been intensively studied since 1989 when Joint Global Ocean Flux Study (JGOFS) promoted an international study of this region [JGOFS, 1990]. Attention was focused on the equatorial Pacific for several reasons. Upwelling in this region brings nutrients into the euphotic zone over a wide area. It also brings up waters with high inorganic carbon content which cause CO2 outgasing to the atmosphere.
The velocity and vorticity structure of the Agulhas Current at 32°S
Authors: Beal Lisa M. , Bryden Harry L.
Published: September 2002

The full depth velocity field of the Agulhas Current, the Western Boundary Current of the southwest Indian Ocean, has been directly measured using a lowered acoustic Doppler current profiler (LADCP). Fifteen combined conductivity‐temperature‐depth (CTD) and LADCP stations were occupied across the current at 32°S off the east coast of South Africa in February‐March 1995, as part of the World Ocean Circulation Experiment Indian Ocean program. The deep velocity structure of the Agulhas Current was found to be very different than previously described using geostrophic estimates. In particular, LADCP results reveal a V‐shaped pattern for the level of no motion across the Agulhas Current and an Agulhas Undercurrent is observed flowing equatorward below 800 m depth, directly beneath the surface core of the poleward flowing Agulhas Current. Comparisons of direct and geostrophic velocities suggest that the velocity structure of the Agulhas Current is essentially geostrophic below about 200 m depth, where differences are generally less than estimated errors. Above these depths the LADCP‐measured shears and geostrophic shears exhibit differences and velocities can diverge. Shipboard ADCP data support LADCP results near the surface, indicating that both instruments are measuring real signals. The geostrophic and LADCP‐measured shears are well matched away from the surface, and a depth‐averaged fit (below 200 m) between them exhibits small standard deviations. The geostrophic volume transport of the Agulhas Current, as referenced to LADCP, is 73 Sv, and is just 3% different from the direct LADCP transport estimate. The most recent full depth estimate of Agulhas Current transport in the literature is given by Toole and Warren [1993], who estimate a geostrophic volume transport of 85 Sv. The baroclinic velocity structures from their section and from this work are similar, indicating that the difference in the transport estimates is due to the choice of geostrophic reference level and ultimately to the presence of the previously unobserved Agulhas Undercurrent. Combined CTD/LADCP data are very useful for potential vorticity analysis, since velocity and density measurements are simultaneous and coincident. The vorticity structure of the Agulhas Current suggests the presence of a “mixing boundary” at middepths, similar to features observed in the Gulf Stream. The feature appears to be associated with a sharp upturn in isopycnals, coincident with the foot of the continental slope. The boundary inhibits cross‐stream mixing of intermediate water masses and may help explain the appearance of a discrete filament of Red Sea Water inshore of Antarctic Intermediate Waters in the same density layer, despite intense cross‐stream shears.
Open‐ocean deep convection due to thermobaricity: 1. Scaling argument
Authors: Akitomo Kazunori
Published: September 2002

Properties of open‐ocean deep convection due to thermobaricity at high latitudes have been investigated by the scaling argument. Two types of open‐ocean deep convection are found. The first type appears in a homogeneous ocean or in a deepening mixed layer. The increased apparent buoyancy flux due to thermobaricity makes scales of convective properties larger than those without thermobaricity. The ratio of thermobaric to nonthermobaric scales is determined only by l0/Hα, where l0 and Hα are the size of nonthermobaric convection and the characteristic depth for thermobaricity to be effective, respectively. In a nonrotating frame, then, thermobaricity becomes effective when the ocean depth H is comparable with Hα, as previous studies show. In a rotating frame, thermobaricity is most effective with slow rotation (the Coriolis parameter ƒ ≪ 10−4 s−1) and low temperatures (approximately the freezing point of seawater), since l0/Hα becomes largest. In the actual situation (ƒ ∼ 10−4 s−1), thus thermobaricity is not so effective because the Earth rotation confines l0 to a smaller level, i.e., l0/Hα < 1. The second type of deep convection is driven by pure thermobaric instability in a two‐layer ocean where a cold, fresh mixed layer overlies a warm, saline deep layer, as often observed in polar oceans. It causes an abrupt overturning of the water column. Scales of convective properties are dependent on the difference of water temperature between the two layers, the initial size of plume, and the Coriolis parameter (or time), but not on the surface cooling rate directly. With actual parameters, convective properties and the associated buoyancy flux are much larger than those of the first type. Observed vertical profiles of water temperature and salinity suggest that the first type of deep convection could occur in the Greenland Basin while the second type could occur in the Weddell Sea.
Local mixed layer response to wind and buoyancy forcing in the western equatorial Pacific
Authors: Zhang Kate Q. , Rothstein Lewis M.
Published: September 2002

The behavior of three types of widely used one‐dimensional mixed layer models (bulk, turbulence closure, and shear instability) is evaluated under idealized conditions representative of atmospheric forcing over the western equatorial Pacific Ocean. Results show that under heavy precipitation (frequently observed in this region), models with a shear instability mixing component capture the fundamental behavior of the mixed layer better than do those without. On the basis of this comparison, a version of the Price‐Weller‐Pinkel (PWP) [Price et al., 1986; Schudlich and Price, 1992] mixed layer model is selected for the purpose of simulating near‐surface temperature and salinity measurements in this region. Heat and salt budgets calculated from observations taken during the Tropical Ocean Global Atmosphere‐Coupled Ocean‐Atmosphere Response Experiment (TOGA‐COARE) pilot study suggest that above the top of the thermocline, local atmospheric forcing is indeed of first‐order importance in the evolution of the temperature field. Horizontal advection of salt, however, is observed to be as important as local forcing (evaporation minus precipitation) in the evolution of the salinity field. Driven by observed fluxes, numerical simulation using the PWP model confirm the primary importance of local forcing for the temperature field and the importance of salinity advection for the salinity field. During the TOGA‐COARE intensive observing period, simulated and observed temperatures agree well at 9 m depth under weak winds, but the model/data discrepancy gradually increases during periods of stronger westerly winds. The addition of a simplified meridional temperature advection term, based on the mean observed temperature gradient, reduces but does not eliminate the model data discrepancy. The magnitude of model/data salinity discrepancies is consistent with concurrent measurements of instantaneous horizontal salinity gradients and velocities, but not with their time‐mean values.
Patterns of distribution of sound‐scattering zooplankton in warm‐ and cold‐core eddies in the Gulf of Mexico, from a narrowband acoustic Doppler current profiler survey
Authors: Zimmerman Robert A. , Biggs Douglas C.
Published: September 2002

The acoustic backscatter intensity (ABI) reflected from epipelagic zooplankton communities in the central Gulf of Mexico was measured during June 1995 with a vessel‐mounted, narrowband‐153‐kHz acoustic Doppler current profiler (ADCP). Horizontal and vertical variations in ABI were documented in three kinds of mesoscale hydrographic features commonly found in the Gulf of Mexico: the warm‐core Loop Current (LC), a warm‐core Loop Current eddy (LCE), and a cold‐core region that separated the two warm‐core features. Since new nitrogen domes close to surface waters in cold‐core features whereas surface waters of warm‐core features are nutrient depleted, the cold‐core region was expected to have higher biological stocks as a result of locally higher primary production. Both ABI and net tow data confirmed that the cold‐core region was in fact a zone of local aggregation of zooplankton and micronekton. During both day and night, ABI when integrated for the upper 50 and 100 m in the cold‐core region was significantly greater than in the LC or in the LCE, and ABI was positively correlated with standing stock biomass taken by the net tows. Further investigations into the biological differences between Gulf of Mexico divergence and convergence regimes are warranted, and the ADCP will be a useful tool for examination of the distribution of sound scatterers in such features.
Analysis of underwater radiance observations: Apparent optical properties and analytic functions describing the angular radiance distribution
Authors: Aas Eyvind , Højerslev Niels K.
Published: September 2002

A primary data set consisting of 70 series of angular radiance distributions observed in clear blue western Mediterranean water and a secondary set of 12 series from the more green and turbid Lake Pend Oreille, Idaho, have been analyzed. The results demonstrate that the main variation of the shape of the downward radiance distribution occurs within the Snell cone. Outside the cone the variation of the shape decreases with increasing zenith angle. The most important shape changes of the upward radiance appear within the zenith angle range 90°–130°. The variation in shape reaches its minimum around nadir, where an almost constant upward radiance distribution implies that a flat sea surface acts like a Lambert emitter within ±8% in the zenith angle interval 140°–180° in air. The ratio Q of upward irradiance and nadir radiance, as well as the average cosines μd and μu for downward and upward radiance, respectively, have rather small standard deviations, ≤10%, within the local water type. In contrast, the irradiance reflectance R has been observed to change up to 400% with depth in the western Mediterranean, while the maximum observed change of Q with depth is only 40%. The dependence of Q on the solar elevation for blue light at 5 m depth in the Mediterranean coincides with observations from the central Atlantic as well as with model computations. The corresponding dependence of μd shows that diffuse light may have a significant influence on its value. Two simple functions describing the observed angular radiance distributions are proposed, and both functions can be determined by two field observations as input parameters. The ε function approximates the azimuthal means of downward radiance with an average error ≤7% and of upward radiance with an error of ∼1%. The α function describes the zenith angle dependence of the azimuthal means of upward radiance with an average error ≤7% in clear ocean water, increasing to ≤20% in turbid lake water. The a function suggests that the range of variation for μu falls between 0 and 1/2, and for Q it is between π and 2π. The limits of both ranges are confirmed by observations. By combining the ε and α functions, a complete angular description of the upward radiance field is achieved.
Diurnal tides over Kashevarov Bank, Okhotsk Sea
Authors: Kowalik Zygmunt , Polyakov Igor
Published: September 2002

Diurnal tidal waves K1 and O1 were studied using a primitive equation ocean circulation model with fine vertical resolution. The study focused on Kashevarov Bank, a shallow submarine bank at the northern continental slope of the Sea of Okhotsk. Owing to resonance, the currents over the bank are 20–30 times stronger than the off‐bank currents. The large current amplitudes of the basic tidal waves K1 and O1, through nonlinear interactions, generate residual currents and new oscillations in the semidiurnal, fortnightly and other bands. The model predicts a strong clockwise residual circulation, with barotropic and baroclinic components. The latter is about 50% of the total residual flow over the bank top. To elucidate the role of various terms in maintenance of the residual motion, the time‐averaged momentum and heat balance equations were analyzed. The time‐averaged flow over the bank top is ageostrophic, and the horizontal advection is dominant in the tidal rectification. To demonstrate the influence of the tides on the thermohaline structure over Kashevarov Bank, horizontally uniform and vertically stratified initial temperature and salinity distributions were considered. Strong tidal mixing results in an almost homogeneous thermohaline structure and well‐developed internal tides over the bank summit. This fact demonstrates the role of tides in establishing the observed homogeneous stratification over Kashevarov Bank.
The application of radiotracers to a study of Black Sea circulation: Validation of numerical simulations against observed weapons testing and Chernobyl 137Cs data
Authors: Staneva Joanna V. , Buesseler Ken O. , Stanev Emil V. , Livingston Hugh D.
Published: September 2002

In this paper, we use the distribution of the artificial radionuclide, 137Cs, to investigate mixing and ventilation in the Black Sea. Timeseries data of vertical radionuclide distributions are combined with model simulations in order to follow the magnitude and depth of penetration of surface oxic water into intermediate depths, below the oxic/anoxic interface. Simulated data are produced by a three‐dimensional circulation model that includes a new parameterization of the Bosphorus inflow/plume to simulate the effects of Mediterranean water on internal mixing. A radioactive tracer model for pre‐Chernobyl 137Cs (weapons testing 137Cs) and Chernobyl 137Cs is coupled to the circulation model. The model results are compared to field data collected between 1986 and 1992. The main output from the simulations is the identification of the contribution of entrainment in the mixing of surface waters into subsurface layers. The trend of tracer penetration into the deeper layers following isopycnal surfaces is well demonstrated in the model and is consistent with the known circulation and physics of the Black Sea. The correlation between the activities of radionuclides and salinity, found in the field data, is supported by the simulations. These model results illustrate that the time‐space abundance of the existing field data is sufficient for reconstructing the distribution of tracers in space and time, provided reliable estimates of Black Sea circulation exist.
Weakly nonlinear theory and sea state bias estimations
Authors: Elfouhaily Tanos , Thompson Donald , Vandemark Douglas , Chapron Bertrand
Published: September 2002

The theory of “weakly” nonlinear (WNL) waves is commonly used in generating higher statistical moments of a random surface wave field. These moments can be used, for example, to estimate the sea state bias (SSB) in radar altimetry under a geometric optical assumption. The present investigation suggests that several previous SSB studies appear to have misapplied this WNL theory by violating its condition of validity. As a result, a pronounced inconsistency appears even for lower‐order moments. This inconsistency appears as a difference between the statistical moments of the nonlinear surface generated by the application of the WNL theory and those of the linear input (or bare) spectrum. If measured spectra, which yield measured moments (such as rms elevation and slope), are chosen as an input to WNL theory, then the corresponding moments of resulting output spectra may be severely overestimated. To strictly avoid the inconsistency, WNL theory must only be applied to long gravity waves where the wave‐wave interactions are weak, hence the WNL epithet. To further illustrate this problem, we present an inversion scheme that determines the proper input spectrum by forcing the low‐order moments of the output spectrum to equal the measured moments. Analytical solutions are given for this inversion based on an explicit formulation of the low‐order nonlinear moments and a simplified one‐dimensional power law spectrum. The solutions show that the high‐frequency portion (wave components shorter than about 10 m) of the input (or bare) spectrum must be significantly less energetic than that of the output spectrum. Our results emphasize the importance of the shorter‐scale waves in the SSB mechanism.
Spatially growing Rossby lee waves: Implications for a coupled ocean‐atmosphere global circulation model
Authors: Hughes Roger L. , O'Farrell Siobhan P.
Published: September 2002

Large‐amplitude Rossby lee waves are observed in the Southern Ocean of an ocean general circulation model. These waves result in a reduced ability of an associated coupled ocean‐atmosphere general circulation model to model the observed sea ice distribution around Antarctica. To understand this behavior, Rossby lee waves within a meridionally sheared eastward directed ocean current are investigated theoretically. It is found that shearing the current results in a significant asymmetry in the lee wave field, the amplitude of which increases linearly downstream. In the regions where the meridional gradient of the shear exceeds β but is of opposite sign, there are no Rossby lee waves. Waves are trapped to the region where β dominates. Investigation of the ocean general circulation model shows that the meridional shear does not exceed β. However, the meridional gradient of Ertel's potential vorticity, a more appropriate quantity in a continuously stratified ocean general circulation model, is negative as required.
Aerosol chemical composition and distribution during the Pacific Exploratory Mission (PEM) Tropics
Authors: Dibb J. E. , Talbot R. W. , Scheuer E. M. , Blake D. R. , Blake N. J. , Gregory G. L. , Sachse G. W. , Thornton D. C.
Published: September 2002

Distributions of aerosol‐associated soluble ions over much of the South Pacific were determined by sampling from the NASA DC‐8 as part of the Pacific Exploratory Mission (PEM) Tropics campaign. The mixing ratios of all ionic species were surprisingly low throughout the free troposphere (2–12 km), despite the pervasive influence from biomass burning plumes advecting over the South Pacific from the west during PEM‐Tropics. At the same time, the specific activity of 7Be frequently exceeded 1000 fCi m−3 through much of the depth of the troposphere. These distributions indicate that the plumes must have been efficiently scavenged by precipitation (removing the soluble ions), but that the scavenging must have occurred far upwind of the DC‐8 sampling regions (otherwise 7Be activities would also have been low). This inference is supported by large enhancements of HNO3 and carboxylic acids in many of the plumes, as these soluble acidic gases would also be readily scavenged in any precipitation events. Decreasing mixing ratios of NH4+ with altitude in all South Pacific regions sampled provide support for recent suggestions that oceanic emissions of NH3 constitute a significant source far from continents. Our sampling below 2 km reaffirms the latitudinal pattern in the methylsulfonate/non‐sea‐salt sulfate (MSA/nss SO4=) molar ratio established through surface‐based and shipboard sampling, with values increasing from <0.05 in the tropics to nearly 0.6 at 70°S. However, we also found very high values of this ratio (0.2–0.5) at 10 km altitude above the intertropical convergence zone near 10°N. It appears that wet convective pumping of dimethylsulfide from the tropical marine boundary layer is responsible for the high values of the MSA/nss SO4= ratio in the tropical upper troposphere. This finding complicates use of this ratio to infer the zonal origin of biogenic S transported long distances.
Hygroscopic properties of aerosol formed by oxidation of limonene, α‐pinene, and β‐pinene
Authors: Virkkula Aki , Van Dingenen Rita , Raes Frank , Hjorth Jens
Published: September 2002

The hygroscopic properties of aerosol formed by oxidation of three monoterpenes, limonene, α‐pinene, and β‐pinene, were measured using a tandem differential mobility analyzer (TDMA). The experiments were performed in the European Photoreactor (EUPHORE) in Valencia, Spain. The experiments included ozonolysis and photooxidation with and without ammonium sulfate seed aerosol. Pure organic particles, formed by oxidation of the terpenes in the absence of the seed aerosol, proved to be slightly hygroscopic. The hygroscopic growth factor (G) was close to 1.10 at relative humidity 84% ± 1%, which is often observed as the G of the less hygroscopic mode of atmospheric aerosol in field measurements. In the experiments with ammonium sulfate seed aerosol G decreased from approximately 1.5 before the start of terpene oxidation to approximately 1.1 as the oxidation products condensed on the particles. G was not proportional to the organic layer thickness but decreased with increasing organic volume fraction. Our analysis shows that in the internally mixed particles, ammonium sulfate and the organic products take up water independently of one another.
Factors influencing changes in rainwater composition from urban versus remote regions of the Yellow Sea
Authors: Zhang J. , Chen S. Z. , Yu Z. G. , Wang C. S. , Wu Q. M.
Published: September 2002

Rainwater samples were collected from three stations at the Yellow Sea in 1992–1993 and analyzed for some major species (Ca2+, K+, Na+, Mg2+, NO3−, NH4+, pH, PO43−, and SO42−). Absolute concentrations and element‐to‐sodium ratios show clear seasonal variations with higher levels in winter and lower levels in summer for most of the species. Levels of major species from urban areas can be twice as high as those of remote regions, in terms of both absolute concentration and element‐to‐sodium ratio. The contrasts between urban and remote and between low and high elevations can be explained by proximity to the ocean, local pollution sources, and scavenging processes. Comparison with other world areas shows rather high levels of chemical species in rainwater from the Yellow Sea relative to remote world oceans or even some other coastal urban areas. Using sodium as a sea‐salt tracer, it was estimated that more than 50% of major species in rainwater could come from non‐marine contributions, and for some species like NH4+, NO3−, and SO42−, anthropogenic emissions are definitely the major source. The high concentration of nitrogen species and elevated N/P ratio of rainwater, as compared to riverine input, suggest the significance of atmospheric wet deposition to the marine production and biogeochemical circulation of nutrients in this region.
Middle Atmosphere High Resolution Spectrograph Investigation
Authors: Conway Robert R. , Stevens Michael H. , Brown Charles M. , Cardon Joel G. , Zasadil Scott E. , Mount George H.
Published: September 2002

The Middle Atmosphere High Resolution Spectrograph Investigation (MAHRSI) was developed specifically to measure the vertical density profiles of hydroxyl (OH) and nitric oxide (NO) in the middle atmosphere from space. MAHRSI was launched on its first flight in November 1994 on the CRISTA‐SPAS satellite that was deployed and retrieved by the space shuttle. The instrument measured the radiance profiles of ultraviolet solar resonance fluorescence on the Earth's limb with a spectral resolving power of 15,600 at a wavelength of 308 nm and 7200 at 215 nm. The instantaneous height of the field of view projected to the tangent point was about 300 m. OH limb radiance measurements were made between altitudes of 90 and 30 km, and each limb scan extended over a horizontal distance of 1200 km. For NO a limb scan extended between altitudes of 140 and 76 km and over a horizontal distance 700 km. Observations were made from 52°S latitude to 62°N latitude. The OH measurements have been inverted to provide the first global maps of the vertical distribution of OH between 90 and 50 km. The data show a detailed history of the morning formation of a strongly peaked layer of OH at an altitude of 68 km. This layer was produced by solar photodissociation of a thin layer of water vapor peaked at 65 km extending between 30°S and 35°N observed contemporaneously by the Halogen Occultation Experiment (HALOE) on the Upper Atmosphere Research Satellite. MAHRSI was successfully flown for a second time in August 1997 under conditions that extended the geographical coverage to 72°N latitude and local solar time coverage through the afternoon hours. This paper provides a detailed description of the experiment and instrumentation, of the algorithms used to reduce the spectral data and perform the inversions, and presents examples of key results from the 1994 flight.
Sensitivity analysis: Could better methods be used?
Authors: Saltelli Andrea
Published: September 2002

Some recent articles are reviewed where sensitivity analysis (SA) is implemented via either an elementary “one factor at a time” (OAT) approach or via a derivative‐based method. In these works, as customary, SA is used for mechanism identification and/or model selection. OAT and derivative based methods have important limitations: (1) Only a reduced portion of the space of the input factors is explored, (2) the possibility that factors might interact is discounted, (3) the methods do not allow self‐verification. Given that all models involved are highly nonlinear and potentially nonadditive, the adopted methods might fail to provide the full effect of any given factor on the output. This could deceive the analyst, unless the analysis were really meant to focus on a narrow range around the nominal value, where linearity may be assumed. Different methods are suggested, such as a rationalized OAT screening test, a regression‐based method, and two implementations of global quantitative sensitivity analysis measures. Computational cost, efficiency, and limitations of the proposed strategies are discussed, and an example is offered.
A reconstructed view of polar stratospheric chemistry
Authors: Coffey M. T. , Mankin William G. , Hannigan J. W.
Published: September 2002

We describe a technique that uses relatively sparse observations from aircraft of vertical column amounts together with a quasi‐conserved parameter, potential vorticity (PV), to reconstruct column abundances on a near‐global scale. Stratospheric column amounts for a number of gases (including HF, NO, NO2, HNO3, ClONO2, O3, and HCl) were measured during airborne field deployments to both polar regions in four separate years. Functions are determined that relate vertical column amounts to the isentropic potential vorticity at two potential temperature levels (440 K and 520 K) at the observation points. Gridded PV values, derived from National Center for Environmental Prediction temperature and heights, are used to reconstruct column distributions for an entire polar region. Reconstructed fields are used to explore the usefulness of column observations to describe vertically averaged properties of the polar vortex and to compare one year and hemisphere with another.