bluuebunny/crossref_metadata_2025 huggingface dataset:
Geostrophic adjustment over submarine canyons
Authors: Klinck John M.
Published: February 2008

The geostrophic adjustment of a stratified coastal current in the presence of a submarine canyon is considered with a mathematical model in which the vertical structure of the fluid is handled with a “level” technique that represents vertical gradients by finite differences. Two situations are investigated in detail: a two‐level system where one level represents the shelf and one the canyon, and a three‐level system with two levels over the shelf and one in the canyon. There are four important length scales in the adjustment process: the initial width of the coastal current, the width of the canyon, and the internal and external radii of deformation. For each vertical mode, the shorter of the radius of deformation for that mode and the width of the coastal current determines the distance over which the perturbing influence of the canyon decays. For typical shelf situations, the external mode decays with the width of the coastal current, while the internal modes decay with the internal radius of deformation. The width of the canyon determines the strength of the cross‐canyon flow and thus, the strength of the canyon's effect on the overlying coastal current, with the interaction becoming smaller as the canyon width becomes smaller than the current width or the radius of deformation. As the cross‐canyon flow becomes small, the importance of the geostrophic balance decreases and the internal density gradients become more important in balancing pressure gradients. Therefore even in the case of flow over a narrow canyon, the isopycnals at the top of the canyon are distorted and there will be some residual circulation on the shelf that is forced by the presence of the canyon.
The damping of ocean waves by surface films: A new look at an old problem
Authors: Alpers Werner , Hühnerfuss Heinrich
Published: February 2008

A new theory is presented explaining why not only short surface ripples, but also longer ocean surface waves are damped by oil films floating on the sea surface. The wave attenuation by viscoelastic surface films is attributed to the Marangoni effect, which causes a strong resonance‐type wave damping in the short‐gravity‐wave region, and to nonlinear wave‐wave interaction, by means of which wave energy is transferred from the longer waves to the energy sink in the Marangoni resonance region. A viscoelastic surface film changes the free surface boundary condition in the tangential direction and thus strongly modifies the flow pattern in the boundary layer. As a consequence, wave energy is dissipated by enhanced viscous damping in the short‐gravity‐wave region due to large velocity gradients induced in the viscous boundary layer. Estimates of the influence of surface films on nonlinear transfer rates are given. Data on wave damping obtained in laboratory and field experiments by previous investigators are discussed in the light of the proposed theory. It is found that this theory is capable of explaining the observed strong wave damping by viscoelastic surface films. The theory predicts that in the equilibrium range of the spectrum, but outside the Marangoni resonance region, wave damping increases with wave number k as k3/2 and increases quadratically with wind speed (up to the limit where the film is “washed down”). The higher the elasticity of the surface film, the stronger is the wave damping.
Extracting the internal tide from data: Methods and observations from the Mixed Layer Dynamics Experiment
Authors: Levine Murray D. , Richman James G.
Published: February 2008

Several methods are developed for analyzing data containing a highly variable internal tide. In particular, the methods are aimed at the analysis of moored observations with relatively few measurements in the vertical. The analysis depends upon an “elliptical decomposition” that is a generalization of the familiar “rotary decomposition.” The technique is applied to velocity and temperature observations in the upper ocean made during the Mixed Layer Dynamics Experiment (MILDEX) in the northeast Pacific Ocean, about 700 km west of Santa Barbara, California, during October‐November 1983. The observed propagation direction and amplitude of the internal tide was highly variable in time. It was anticipated that the wave could be propagating from the continental shelf where it is presumed to be generated. However, most of the time the internal tide appears to be propagating parallel to the coast. This result suggests the importance of density and velocity structure at mesoscale and frontal scale in affecting the propagation of the internal tide.
A simple analytical formula to compute clear sky total and photosynthetically available solar irradiance at the ocean surface
Authors: Frouin Robert , Lingner David W. , Gautier Catherine , Baker Karen S. , Smith Ray C.
Published: February 2008

A simple yet accurate analytical formula is proposed to compute total and photosynthetically available solar irradiance at the ocean surface under clear skies. The formula takes into account the most important processes occurring within the atmosphere, namely, scattering by molecules and aerosols and absorption by water vapor, ozone, and aerosols. These processes are parameterized as a function of solar zenith angle, aerosol type, atmospheric visibility, and vertically integrated water vapor and ozone amounts. When compared with the radiative transfer model of Tanré et al. (1979), the formula shows excellent agreement (to within 1%) under most atmospheric conditions and solar zenith angles. There is also good agreement with formulas developed by other investigators to estimate total solar irradiance. Comparisons of calculated and measured total and photosynthetically available solar irradiances for several experiments in both tropical and mid‐latitude oceanic regions show 39 and 14 Wm−2 rms errors (6.5 and 4.7% of the average measured values) on an hourly time scale, respectively. The proposed formula is unique in its ability to predict surface solar irradiance in the photosynthetically active spectral interval. Furthermore, it may also be used for converting total irradiance measurements into photosynthetically available irradiance estimates. Combining the clear sky irradiance formula with satellite techniques to retrieve cloud effect on solar irradiance, pigment concentration, and sea surface temperature would provide useful primary productivity estimates over large oceanic areas and eventually the global oceans.
Probabilities and statistics for backscatter estimates obtained by a scatterometer
Authors: Pierson Willard J.
Published: February 2008

Methods for the recovery of winds near the surface of the ocean from measurements of the normalized radar backscattering cross section must recognize and make use of the statistics (i.e., the sampling variability) of the backscatter measurements. Radar backscatter values from a scatterometer are random variables with expected values given by a model. A model relates backscatter to properties of the waves on the ocean, which are in turn generated by the winds in the atmospheric marine boundary layer. The effective wind speed and direction at a known height for a neutrally stratified atmosphere are the values to be recovered from the model. The probability density function for the backscatter values is a normal probability distribution with the notable feature that the variance is a known function of the expected value. The sources of signal variability, the effects of this variability on the wind speed estimation, and criteria for the acceptance or rejection of models are discussed. A modified maximum likelihood method for estimating wind vectors is described. Ways to make corrections for the kinds of errors found for the Seasat SASS model function are described, and applications to a new scatterometer are given.
Data interpretation and numerical modeling of the Mud and Suspended Sediment Experiment 1985
Authors: Lang G. , Schubert R. , Markofsky M. , Fanger H.‐U. , Grabemann I. , Krasemann H. L. , Neumann L. J. R. , Riethmüller R.
Published: February 2008

In 1985 a field survey was performed in the Weser estuary (northern Germany) covering a 30‐km‐long section to study the turbidity maximum in its complete extension. Moored instruments as well as shipborne vertical profilers were used in the survey. The measured data were employed in close connection with numerical simulations using a three‐dimensional finite‐difference model. The common aim of the investigations was to arrive at a better understanding of the hydrodynamics and the transient and spatial dynamics of the turbidity maximum in the Weser estuary. The overall behavior of the turbidity maximum resembles a cyclic process, wherein deposition, resuspension, and advection of resuspended sediments are the dominant processes. The conceptual model, derived from the measurements, was confirmed by the numerical simulations. This is demonstrated by the calculated distribution of suspended sediment along the estuary as well as by the calculated deposition and resuspension rates at the estuarine bed for a tidal cycle. Detailed analyses of measured data (moorings) demonstrate a close relationship between the local near‐bottom velocity gradient, stratification, and turbulence on the one hand and the suspended sediment concentration on the other. A comparison between numerical results and measured data leads to an improved parametrization of the bottom shear stress, wherein the bottom shear stress is calculated from the near‐bottom Reynolds stress, with consideration of the stratification. With this parametrization, it is shown that the model is able to reproduce some of the essential features reflected in the measured suspended sediment concentration.
Arctic sea ice 1973–1987: Seasonal, regional, and interannual variability
Authors: Parkinson Claire L. , Cavalieri Donald J.
Published: February 2008

Satellite passive‐microwave data, available for most of the period since 1972, have enabled a global description of the sea ice cover impossible prior to the 1970s. In this paper we analyze sea ice extents in the northern hemisphere over the period 1973–1987, using data derived from the Nimbus 5 electrically scanning microwave radiometer (ESMR) and the Nimbus 7 scanning multichannel microwave radiometer (SMMR). The record shows an average seasonal cycle ranging from a summer minimum of 8.5×106 km2 in September to a winter maximum of 15×106 km2 in March, with considerable interannual variability found both regionally and hemispherically. When yearly averaged sea ice extents are examined for trends, some regions (for example, Baffin Bay/Davis Strait) exhibit upward trends, while other regions (for example, the Kara and Barents seas) exhibit downward trends. The northern hemisphere overall shows no significant trend over the 1973–1987 period, although over the ESMR years (1973–1976) there was an upward trend and over the 8 full SMMR years (1979–1986) there was a lesser downward trend. The record as a whole gives no definitive indication from the varying sea ice extents of any consistent warming or cooling of the north polar region.
Autoregressive modeling for the spectral analysis of oceanographic data
Authors: Gangopadhyay Avijit , Cornillon Peter , Jackson Leland B.
Published: February 2008

Over the last decade there has been a dramatic increase in the number and volume of data sets useful for oceanographic studies. Many of these data sets consist of long temporal or spatial series derived from satellites and large‐scale oceanographic experiments. These data sets are, however, often “gappy” in space, irregular in time, and always of finite length. The conventional Fourier transform (FT) approach to the spectral analysis is thus often inapplicable, or where applicable, it provides questionable results. Here, through comparative analysis with the FT for different oceanographic data sets, we discuss the possibilities offered by autoregressive (AR) modeling to perform spectral analysis of gappy, finite‐length series. The applications demonstrate that as the length of the time series becomes shorter, the resolving power of the AR approach as compared with that of the FT improves. For the longest data sets examined here, 98 points, the AR method performed only slightly better than the FT, but for the very short ones, 17 points, the AR method showed a dramatic improvement over the FT. The application of the AR method to a gappy time series, although a secondary concern of this manuscript, further underlines the value of this approach.
Temporal variability of currents in the eastern Ligurian Sea
Authors: Astraldi M. , Gasparini G. P. , Manzella G. M. R. , Hopkins T. S.
Published: February 2008

Surface and intermediate waters enter the Ligurian Sea from the Tyrrhenian and Algero‐Provencal basins via northward flows along the east and west coasts of Corsica. The temporal variability of these flows is examined by means of a 1‐year time series of current data (October 1986 to September 1987) and hydrographic data from December, March, and May cruises. The flow through the Corsica Channel increases suddenly during December and then gradually decreases after March, reaching its lowest values in late summer. The seasonal variability in the channel seems associated mainly with the steric sea level differences between the Tyrrhenian Sea and Ligurian Sea. The West Corsican Current appears more stable throughout the one year of data. The two flows converge just north of Corsica into the Ligurian Current. Because of the water‐masses differences between the two currents, in the area of convergence considerable smaller‐scaled structure is observed. During winter, the less dense Tyrrhenian water provides available potential energy to the Ligurian shelf area and thereby helps sustain the large‐scale cyclonic circulation in the Ligurian basin. During the other seasons the spatial structures over the Ligurian shelf are less organized and the spatial scale of the flow is a few tens of kilometers.
Variations in the structure of the anticyclonic gyres found in the Alboran Sea
Authors: Heburn George W. , La Violette Paul E.
Published: February 2008

Historical satellite, aircraft, and in situ data have shown that two anticyclonic gyres (the western and eastern Alboran gyres) are major ocean features of the Alboran Sea. An examination of several years of satellite imagery indicates that large variations in the surface expression of these two gyres occur and that on occasion one or the other gyre disappears (the disappearance of both gyres at the same time was not seen). The initial disappearance of either gyre occurs on a time scale of a week to 2 weeks, whereas the return may take from 3 weeks to 2 months. Various forcing mechanisms, i.e., winds, mass flux inflow through the Straits of Gibraltar and Sicily, and/or density, have been used in numerical ocean circulation models to study the dynamics of the western Mediterranean Sea. Various model results show relationships similar to those shown by the satellite imagery. However, no single forcing mechanism has been positively identified as the source of the disappearances, and the events may be a result of a combination of forcing mechanisms.
Geosat altimeter data analysis for the oceans around South Africa
Authors: Wakker K. F. , Zandbergen R. C. A. , Naeije M. C. , Ambrosius B. A. C.
Published: February 2008

Geosat altimeter data taken during a 1‐year period over the oceans around South Africa have been processed. This area is well known for its many interesting current systems and bathymetrie features. The investigation has focused on the elimination of the radial orbit errors by means of the crossover minimization technique and on the computation of mean sea surfaces and the determination of mesoscale sea surface variability. For three tracks over this area the collinear tracks analysis technique has been applied to investigate in detail both the mesoscale ocean surface variability and the horizontal component of the gravity disturbance vector. Various interesting geophysical and oceanographie features are discussed. In addition, the recovered Geosat radial orbit error over this area is analyzed, and the global distribution of the radial orbit errors is estimated.
Determination of the ocean circulation using Geosat altimetry
Authors: Nerem R. S. , Tapley B. D. , Shum C. K.
Published: February 2008

A spherical harmonic model of the sea surface topography complete to degree and order 10 and a model of the Earth's geopptential field complete to degree and order 50 have been obtained in a simultaneous solution using Geosat altimeter data and tracking data from 14 different satellites. The sea surface topography model compares well with oceanographic models computed using hydrographic data and ship drift data. Currently, errors in the estimated gravity field model limit the determination of the spherical harmonic coefficients of the general ocean circulation to degrees 10 and lower, corresponding to a minimum wavelength of 4000 km. Error analysis indicates that the correlation between the geoid and the sea surface topography model is less than 0.2, indicating good separation of the geoid and the sea surface topography at wavelengths of 4000 km or longer. Estimates of the scale factor for the significant wave height (H1/3), which is used to compute the electromagnetic bias correction and the bias for the Geosat altimeter, are obtained. The estimate of the H1/3 correction is 3.6±1.5%, and the height bias estimate is zero.
Measurements of tidal flow around a headland with a shipboard acoustic Doppler current profiler
Authors: Geyer W. Rockwell , Signell Richard
Published: February 2008

A shipboard acoustic Doppler current profiler (ADCP) and moored current meters were used to obtain detailed measurements of the spatial structure of the tidal flow around a headland in Vineyard Sound, Massachusetts, where tidal currents typically range from 50 to 70 cm s−1. Eight shipboard surveys were conducted, each of which followed one of five trapezoidal tracks in the vicinity of the headland, completing 11–12 circuits in the course of the tidal cycle (12.4 hours). The measurements from the ADCP compare favorably with moored velocity measurements at two locations (rms deviations of ±3 cm s−1), but the comparison showed more scatter at two other sites (rms deviations of ±7 cm s−1). The ADCP measurements from separate cruises were merged to form a composite spatial representation of the tidal and residual currents, providing resolution of the spatial structure of the flow around the headland at scales from several hundred meters to 10 km. The semidiurnal tidal flow is relatively uniform in space, roughly following the bathymetry around the headland, while a residual current field consists of counterrotating eddies on either side of the headland, with spatial scales of 5–8 km and velocities as high as 25 cm s−1. The instantaneous current field indicates the formation of transient eddies on the downstream side of the headland during flood and ebb, with clear evidence of flow separation near the tip of the headland.
A wind‐driven isopycnic coordinate model of the north and equatorial Atlantic Ocean: 1. Model development and supporting experiments
Authors: Bleck Rainer , Smith Linda T.
Published: February 2008

Numerical approximations to the dynamic equations are given which allow basin‐size ocean circulation models formulated in isopycnic coordinates to accommodate variable bottom topography and irregular coastlines. Emphasis is placed on computational economy through the use of a split‐explicit time integration scheme, on the proper formulation of the advection and Coriolis terms in the momentum equation in case of strongly varying layer thickness, and on the correct estimation of the horizontal pressure gradient force in grid boxes truncated by steep bottom slopes. The algorithms are tested in a series of two‐ and three‐layer double‐gyre experiments. In cases of steady forcing leading to a steady circulation, we are able to reproduce the expected motionless final state in coordinate layers that are below the direct influence of the wind forcing. This includes layers intersecting topographic obstacles. A long‐term (25–30 year) vacillation tentatively associated with the outcropping of isopycnals along the edge of the cyclonic gyre in a steadily forced model is documented. The paper forms the basis for a subsequent study in which circulation features obtained in a realistic North Atlantic setting will be discussed.
Drag coefficient at a stationary salt wedge
Authors: Sorgard Eirik , Martinsen Thomas , Aas Eyvind
Published: February 2008

The drag coefficient for the tangential stress at the interface between freshwater outflow and a salt wedge is estimated by fitting the analytic profile of two‐layered salt wedge models to the observed pycnocline. Satisfactory agreement is obtained only if the upper boundary of the pycnocline is chosen to represent the interface. A best fit procedure gives values of the drag coefficient at this interface between 1.1×10−4 and 2.7×10−4. This coefficient is defined by the ratio between the stress and the squared mean velocity of the upper layer. Direct measurements of the Reynolds stress by an ultrasonic current meter give the drag coefficient at the interface as (4.2±1.4)×10−4. If the coefficient is defined from the mean velocity of the upper layer relative to the velocity of the sliding interface, it obtains values in the range of 2 ‐ 7×10−3.
Asymptotic forms and solutions of the model for silica‐opal diagenesis in bioturbated sediments
Authors: Boudreau Bernard P.
Published: February 2008

Early diagenesis of the coupled dissolved silica‐opal system in bioturbated sediments may be explained by one of three possible models of increasing mathematical complexity, i.e. the simple, but unused constant‐opal model (abbreviated C.O.), the Schink et al. (1975) model (abbreviated SG&F) for which Wong and Grosch (1978) have supplied an analytical solution (designated as W&G), and the improved but much more sophisticated model proposed by Schink and Guinasso (1980) that must be solved numerically (S&G). Scaling analysis and computational comparisons show that the C.O. model and the SG&F model, as calculated via the W&G solution, are asymptotically valid forms of more complete S&G model for the limits of “large” and “small” opal concentrations, respectively. Specifically, the C.O. model is found to provide an excellent approximation to the vastly more complicated S&G model if the amount of opal preserved at depth in the sediment, b(∞), satisfies the inequality, b(∞) ≥ {[0.1(1 ‐ φ)DB][φγDS(CS ‐ CW)]−1 + ρb−1}−1, where φ is the porosity, DB is the mixing coefficient, DS is the tortuosity‐corrected molecular diffusivity of silica, CS is the solubility of opal, CW is the silica concentration in the overlying waters, ρb is the intrinsic density of opal and γ is a unit conversion constant if b and C are in different units. Schink and Guinasso (1980) have criticized Wong and Grosch (1978) for utilizing their solution of the earlier SG&F model to describe opal accumulation, a situation for which they believed the SG&F model was invalid. This study has found, however, that for conditions characteristic of the deep sea, the SG&F model and so the W&G solution remain reasonably accurate even if small amounts of opal escape dissolution and collect, but that radical divergence from the S&G model can be expected if the flux of silica is sufficient to create a siliceous ooze. This reflects the minor role played by the divergence of the advective flux in the balance of terms in the diagenetic conservation equations when little opal is preserved. These findings should resolve any uncertainty and controversy over the use of the W&G solution. Opal diagenesis in bioturbated shelf‐like sediments appears to be adequately described by the C.O. model alone. The C.O. model, coupled where necessary to the W&G solution, constitutes an attractive alternative to the S&G model because relatively simple analytical methods of solution may be employed rather than advanced numerical techniques.
Recurrence in truncated Boussinesq models for nonlinear waves in shallow water
Authors: Elgar Steve , Freilich M. H. , Guza R. T.
Published: February 2008

The rapid spatial recurrence of weakly nonlinear, weakly dispersive, progressive shallow‐water waves is examined with numerical simulations using a discretized and truncated (i.e., finite number of allowed frequency modes) form of the Boussinesq equations. Laboratory observations of sandbar formation under recurring, mechanically generated monochromatic waves with small Ursell number have motivated others to suggest that recurrence in naturally occurring random waves contributes to the establishment of periodic longshore sandbars on beaches. The present study primarily examines recurrence in wave fields with Ursell numberO(1) and characterizes the sensitivity of recurrence to initial spectral shape and number of allowed frequency modes. It is shown that rapid spatial recurrence is not an inherent property of discretized and truncated Boussinesq systems for evolution distances of 10–50 wavelengths. When a small number of Fourier modes are used to represent an initially monochromatic wave field with significant nonlinearity (the Ursell number isO(1)), there is a trend toward recurrence of initial modal amplitudes, consistent with the known periodic solutions for a primary wave and its harmonic. However, for 32 modes or more, numerical simulations indicate only a few cycles of a damped recurrence, followed by disordered evolution of the Fourier amplitudes. For initial conditions similar to ocean field measurements of frequency‐sorted swell with Ursell numberO(1) and many (>300) modes in the numerical model, the Fourier coefficients of the wave field do not recur rapidly. Thus in these cases the predictions of many rapid recurrence cycles by few‐mode models is an artifact of severe truncation. On the other hand, even with many allowed modes, pronounced recurrence is predicted when the Ursell number is small and the initial wave field is monochromatic. In this case, few‐ and many‐mode solutions are similar.
Evolution of the southern ocean winter mixed layer and sea ice: Open ocean deepwater formation and ventilation
Authors: Martinson Douglas G.
Published: February 2008

An analytical model has been developed to describe the nature of the winter ocean/sea ice interaction in the southern ocean, to determine the principal processes responsible for maintaining stability in this marginally stable region, and to predict the response to changes in the external forcing and initial conditions. The model accurately describes the sparse winter observations and the general temporal evolution of the ice, mixed layer depth, and salinity for the period following the elimination of the seasonal pycnocline by rapid fall ice growth. A scale analysis and sensitivity study reveal the system parameter dependence. This indicates that the magnitude of entrainment is proportional to Fst/(h0∇S), where Fs is the external salt flux; h0, the depth of the winter mixed layer; and ∇S, the salinity gradient through the pycnocline. Thermodynamic ice growth reflects predominantly the competition between the oceanic diffusive heat gain across the base of the mixed layer and the loss to the atmosphere through the ice and leads. A strong thermal gradient across the pycnocline leads to a significant diffusive flux which balances most of the heat lost to the atmosphere. This limits the amount of ice growth possible and plays the principal role in maintaining the system stability, since the ice growth is required for destabilization through haline rejection during the growth process. The system is also sensitive to the large ratio of heat to salt in the pycnocline. This introduces a negative feedback where increasing ice growth induces entrainment by the associated salt flux, which in turn drives an entrainment heat flux which compensates for heat lost to the atmosphere. This moderates the ability to grow ice and drive further entrainment. The absolute strength of the salinity gradient, on the other hand, dictates the effectiveness which a same magnitude external salt flux will have in driving entrainment. The effectiveness with which changes in these parameters (as well as several other external parameters) can influence the southern ocean stability is explicitly evaluated through the sensitivity study and analysis.
Geodetic and oceanographic results from the analysis of 1 year of Geosat data
Authors: Denker Heiner , Rapp Richard H.
Published: February 2008

The first year of the Geosat Exact Repeat Mission has been analyzed to obtain improved orbits, gravity model, and representation of sea surface topography. The starting point for this study were the original geophysical data records merged with orbits by Haines et. al. (1990) computed with the GEM‐T1 gravity model. A radial orbit error model following the development of Engelis (1987a) was modified to account for resonant effects above degree 36. Twenty‐four 17‐day arcs were analyzed. Separate 17‐day and a single 1‐year solution for a gravity model and a spherical harmonic representation of the sea surface topography to degree 10 were found. The root‐mean‐square crossover discrepancy with the a priori (i.e., GEM‐T1) model was ±1.1 m, which was reduced to ±0.22 m with the 1‐year solution. Comparison of overlaps in the arcs showed discrepancies of ±1.3 m with the a priori field which were reduced to ±0.07 m with the 1‐year solution. The determination of the degree (1, 0) term in the sea surface topography was not possible in this analysis because of the high correlation of this term with an orbit error term. In addition, the (1, 1) terms showed serious incompatibility with that implied by historical oceanographic information. The final solution used here incorporated the degree 1 coefficients from oceanographic data. The problem with the (1, 1) coefficients may imply a small center of mass offset in the tracking station positions used in the orbit calculations or may result from the poor distribution of the available tracking stations. Error analysis indicated a ±10 cm sea surface topography commission error to degree 10. The geoid commission error to degree 36 was ±9 cm in the ocean areas. The new potential coefficient model was compared with terrestrial data, in a manner to that done by Engelis and Knudsen (1989) to show the improvement of the new model.
One hundred years of Arctic ice cover variations as simulated by a one‐dimensional, ice‐ocean model
Authors: Häkkinen S. , Mellor G. L.
Published: February 2008

A one‐dimensional ice‐ocean model consisting of a second moment, turbulent closure, mixed layer model and a three‐layer snow‐ice model has been applied to the simulation of Arctic ice mass and mixed layer properties. The results for the climatological seasonal cycle are discussed first and include the salt and heat balance in the upper ocean. The coupled model is then applied to the period 1880–1985, using the surface air temperature fluctuations from Hansen et al. (1983) and from Wigley et al. (1981). The analysis of the simulated large variations of the Arctic ice mass during this period (with similar changes in the mixed layer salinity) shows that the variability in the summer melt determines to a high degree the variability in the average ice thickness. The annual oceanic heat flux from the deep ocean and the maximum freezing rate and associated nearly constant minimum surface salinity flux did not vary significantly interannually. This also implies that the oceanic influence on the Arctic ice mass is minimal for the range of atmospheric variability tested.
Sea surface heights in the Mediterranean Sea from Geosat altimeter data
Authors: Arabelos D. , Tziavos I. N.
Published: February 2008

The preprocessing and the crossover adjustment of Geosat altimeter data are carried out in order to obtain a precise approximation of the sea surface heights in the Mediterranean Sea. Altimeter data from the U.S. National Oceanographic Data Center (NODC) have been used covering a time period of about 1 year. With the rejection of outliers and subsatellite points whose root‐mean‐square (rms) error exceeds 0.09 m, the rms crossover discrepancy was 3.5 m. When a crossover adjustment was performed, the RMS crossover discrepancy decreased to 0.14 m. After the fit and crossover adjustment model were applied, about the same rms crossover discrepancy was found (0.16 m). The latter solution was applied successfully in the test area as indicated by the results obtained from the comparisons of Geosat sea surface heights with OSU81 geoidal heights as well as with locally computed gravimetric geoidal heights by the fast Fourier transform (FFT) method. These comparisons showed a very good agreement at the level of 0.70 m.
Influence of wet tropospheric correction on mesoscale dynamic topography as derived from satellite altimetry
Authors: Jourdan D. , Boissier C. , Braun A. , Minster J. F.
Published: February 2008

We study the influence of the wet tropospheric correction on mesoscale dynamic topography as derived from satellite altimetry. For this purpose, we use Geosat altimeter data in the northeast Atlantic, and we process separately the tropospheric correction derived from the PERIDOT model following the technique for analysing altimeter height profiles. We show that the humidity spatial scales are larger than those of the dynamic topography. Consequently, the wet tropospheric effect is considerably reduced when orbit error corrections are applied; after long‐wavelength filtering, the along‐track rms of the correction is 13% of that of the oceanic signal. In addition, contrary to the dynamic topographic signal, the tropospheric signal is temporally decorrelated between two successive adjacent tracks so that the wet tropospheric contribution to the objectively analysed synoptic maps is only 10% of the signal of mesoscale variability.
A note on the attenuation of surface gravity waves by rainfall
Authors: Nystuen Jeffrey A.
Published: February 2008

Rainfall has long been associated with damping of short surface gravity waves. A theory is presented which uses a thin rain‐induced turbulent surface layer to explain the enhanced attenuation. In the presence of a thin turbulent surface layer, the e‐folding attenuation time for the 30‐cm wavelength surface gravity waves needed for remote sensing of the ocean surface using synthetic aperture radar (SAR) is reduced from several minutes to several seconds. This explains the observation of low SAR radar return from regions of high rainfall. Longer wavelengths are also affected depending on the strength of the mixing and the thickness of the turbulent layer.
Seasat scatterometer versus scanning multichannel microwave radiometer wind speeds: A comparison on a global scale
Authors: Boutin J. , Etcheto J.
Published: February 2008

The wind speeds obtained from the Seasat A scatterometer system (SASS) and scanning multichannel microwave radiometer (SMMR) using two different algorithms were compared on a global scale. The temperature dependence of the sea surface emissivity was shown to be incorrectly modelled. After correcting this effect, regional differences up to ± 3 m s−1 are still observed between both instruments, even though they balance in global averaging, resulting in no bias between the global data sets. Validation experiments of satellite wind speeds should take into account this possibility of regional biases and insure the validity of the measurements everywhere in the global ocean.
Triggered lightning in New Mexico
Authors: Hubert P. , Laroche P. , Eybert‐Berard A. , Barret L.
Published: February 2008

Triggered lightning experiments with rockets pulling a grounded wire were performed at Langmuir Laboratory in 1981. Out of 56 firings, 35 events were triggered among which 29 had a peak current intensity above 2 kA and 27 were hybrid flashes. The highest current peak is 40 kA±10%. The median value of the transported charge is 35 C, including a contribution of 28 C from the continuous component. The largest charge is in a flash carrying a mixture of +235 and −240 C±10%. The median number of pulses is 15 above 2 kA, 10 above 3 kA, and 2 above 10 kA. Comparison with natural lightning reveals a large excess of small current pulses in the triggered case, but there is a great similarity in shape, size, and number between the subsequent strokes of natural flashes and the largest among the pulses in the triggered events.
Correcting satellite Doppler data for tropospheric effects
Authors: Black H. D. , Eisner A.
Published: February 2008

Using a simple geometrical model, and one fitted parameter, tropospheric effects can be effectively removed from satellite Doppler data at microwave frequencies. Both the wet and the dry parts of the tropospheric refraction effect are removed. The technique works best for low (say, 1200 km or less) altitude satellites. For these satellites, the pass (transit) duration limits the required atmospheric correlation time to about 20 min. The effective thickness of the neutral atmosphere (10 km for the wet and 45 km for the dry) limits the required correlation distance to a few degrees in latitude and longitude. These conditions are satisfied often enough to make the fitting technique highly useful. The fitted parameter together with minimal dependence on model structure appears to skirt a difficult problem, modeling the water vapor distribution in a poorly mixed atmosphere. Experimental results (for a limited time period) confirm that the approach is valid on a global basis. In another context, this technique can be used to intensively sample the precipitable water vapor in the atmosphere without using balloons.
Seasonal, latitudinal, and secular variations in the abundance and isotopic ratios of atmospheric CO2: 2. Results from oceanographic cruises in the tropical Pacific Ocean
Authors: Keeling Charles D. , Carter Alane F. , Mook Willem G.
Published: February 2008

Between March 1979 and June 1980, air was collected on the Hawaii‐Tahiti shuttle expedition of the Global Atmospheric Research Program. A north‐south track was repeatedly sampled and the air analyzed to provide eight sets of data on the concentration, 13C/12C, and 18O/16O ratios of atmospheric carbon dioxide between 20°N and 17°S latitude near 155°W. In the northern hemisphere the 13C/12C ratio of the CO2 seasonally added to and withdrawn from the atmosphere was found to be nearly constant at circa 30‰ less than standard PDB. This ratio is consistent with photosynthesis and respiration of terrestrial vegetation as the cause of the seasonal cycle. The ratio was progressively less negative southward, reaching about −13‰ at 17°S. This shift in ratio suggests that air‐sea exchange is important in producing the seasonal variation in the southern hemisphere, since this exchange probably occurs with little kinetic isotopic fractionation. The seasonally adjusted 13C/12C ratio of atmospheric CO2 increased steadily southward from −7.55‰ near 16°N to −7.47‰ near 17°S, as expected from a predominantly northern hemisphere source of a CO2 from fossil fuel combustion and a barrier to atmospheric mixing in the tropics. A peak in CO2 concentration near the equator was not found in the north‐south trend in 13C/12C ratio. This lack of an isotopic peak suggests that the high concentrations of CO2 near the equator is produced by the release of CO2 from sea water and is not related to biological activity of land vegetation.
Sinks of the anthropogenically enhanced carbon cycle in surface fresh waters
Authors: Kempe Stephan
Published: February 2008

The carbon chemistry of rivers and lakes has been severely affected by man's activities. This is evident from the data base of the SCOPE/UNEP project, Carbon Transport in Major World Rivers. Increase of erosion following deforestation and agriculture removes carbon from the biosphere into inland deposition centers, lakes, and reservoirs and causes the organic carbon load of rivers to increase. Organic sewage and eroded soil carbon fuel respiration in rivers thus increases the CO2 pressure and diminishes the O2 and NO3 loads in relation to the total organic content. Nutrient release causes eutrophication of lakes and coastal seas, resulting in enhanced primary productivity and CO2 sequestering. Loss of CaCO3 in upstream lakes and boosting PCO2 cause increasing undersaturation of streams with respect to carbonate minerals. In estuaries this undersaturation leads to the corrosion of marine carbonate, as is experimentally shown for the River Elbe, fixing riverine free CO2 as bicarbonate permanently. All sinks combined, up to 1015 g C per year can additionally be sequestered from the anthropogenically enhanced carbon cycle.
On the determinants of the near surface temperature regime on the South Polar Plateau
Authors: Carroll John J.
Published: February 2008

Most studies of the physical climatology of the Antarctic interior focus on the local surface energy budget. The results of these studies are reviewed leading to the often cited conclusion that atmospheric heat transport is required from lower latitudes to maintain the temperature against the large radiative losses by the snow‐atmosphere system of the interior plateau. Micrometeorological data taken over a 3 year period at the south pole are presented, illustrating the annual cycle of the surface energy budget. In addition, these data, coupled with local 500 mbar data, are used to examine the role of vertical and horizontal transport mechanisms in determining the near‐surface temperature variations. The major conclusions are as follows. The interannual variability in the radiation budget components is very small. Day to day variations in the longwave and sensible heat flux are high and related to variability in the synoptic conditions such as cloudiness, wind flow at the surface, and wind and temperature variations at 500 mbar. Except during the summer season, the variability in surface temperature is highly correlated with wind speed, which in turn is strongly correlated with wind direction. Down slope flows are generally low speed and associated with cooling. Cross slope and up slope flows are generally stronger and associated with warming. In summer, there is no correlaton between local temperature and surface wind speed, but down slope flows are generally associated with local cooling. Horizontal thermal advection in the lower troposphere has a very pronounced effect on the surface temperature in summer but only a moderate to weak effect in the other seasons. Except in summer, strong winds (i.e., cross and up slope winds) are associated with weakened thermal stratification; weak winds (down slope) are associated with increased thermal stratification. In addition to the radiation budget, downward mixing through the boundary layer and transient horizontal advection appear far more important than local divergence or convergence effects in determining the local temperature.
Traveling atmospheric pressure waves measured during a solar eclipse
Authors: McIntosh B. A. , ReVelle D. O.
Published: February 2008

An array of microbarographs near Saskatoon, Saskatchewan, detected traveling pressure waves at a time and with a direction of motion that indicates an association with the solar eclipse of February 26, 1979. The velocity was 10 m/s moving toward azimuth 65°; the wave period and amplitude were approximately 120 s and 12.0 Pa, respectively; the duration of the wave train was approximately 3 hours. The probability that it was a free gravity wave is examined and rejected. A plausible source mechanism similar to the low level nocturnal jet is suggested.
Average ozone profiles for 1979 from the NIMBUS 7 SBUV instrument
Authors: McPeters R. D. , Heath D. F. , Bhartia P. K.
Published: February 2008

Monthly average ozone profiles from the first year of operation of the solar backscattered ultraviolet (SBUV) instrument on the NIMBUS 7 satellite (November 1978 through October 1979) are tabulated for 10° latitude bands from 80°S to 80°N. For each month and latitude zone we list layer ozone amounts and standard deviations for 12 Umkehr layers (approximately 0–60 km) and the average total ozone for each zone. The ozone mixing ratio and number density at the center of each layer are also given. We find that the average SBUV profiles agree with average Umkehr profiles measured at Boulder to within 10% over most of the range. The Krueger‐Minizner model is found to be a good representative ozone model for 45°N, agreeing with an annual average of our measured profiles to better than 10% between 20 and 60 km.
A summary of results from the first NIMBUS 7 SMMR observations
Authors: Gloersen P. , Cavalieri D. J. , Chang A. T. C. , Wilheit T. T. , Campbell W. J. , Johannessen O. M. , Katsaros K. B. , Kunzi K. F. , Ross D. B. , Staelin D. , Windsor E. P. L. , Barath F. T. , Gudmandsen P. , Langham E. , Ramseier R. O.
Published: February 2008

Selected data obtained during the first year of operation of the scanning multichannel microwave radiometer (SMMR) on board the NIMBUS 7 satellite (launched in late October 1978) have been used to calculate, on a global basis, various geophysical parameters over open oceans, polar regions, and terrain. Over open oceans these calculations have provided values for sea surface temperatures, near‐surface winds, atmospheric water vapor in a column, and rainfall rates. In polar regions, sea ice concentration, multiyear ice fraction, and radiating temperatures have been obtained. Finally, the extent and water equivalence of snow cover over terrain have been calculated. These parameters have been compared with in situ measurements of the same geophysical parameters, where available, and the results of these comparisons are described. The self‐consistency of the global displays of all the parameters is discussed along with the plans for archiving them for subsequent research purposes. A description of the SMMR calibration and data processing scheme is also given.