bluuebunny/crossref_metadata_2025 huggingface dataset:
Statistical and spectral properties of some paleomagnetic/paleoclimatic time series
Authors: Viecelli J. A.
Published: February 2008

Power spectra were computed for the six paleomagnetic records in Wollin et al. (1977) and for composite time series formed by adding the six records sequentially. Use of the composite series reduces the noise associated with local magnetic and climatic variability. The statistical properties of the composite were found to be insensitive to the ordering of the individual records. Maximum likelihood estimates for the theoretical autocorrelation function of the composite data spaced at intervals of 10,000 years show that the data are described by a second order autoregressive process with first and second order coefficients 0.7 and −0.2. The theoretical power spectrum for these coefficients is monotonically increasing with period becoming nearly flat at periods longer than 100,000 years. Spectra with lag windows of 25 and 50 do not have peaks exceeding the 95% confidence limits. A 100 lag window spectrum has peaks exceeding the confidence limits at 105, 7.4×104 and 2.16×104 yr; however, since it is quite common for artificial paleomagnetic time series generated from the above second order autoregressive process to have significant peaks near one or more of the Earth's three orbital frequencies when using a 100 lag window, one must conclude that there is little if any reliable evidence for orbital forcing in the data studied.
SEASAT measurement system evaluation: Achievements and limitations
Authors: Lame D. B. , Born G. H.
Published: February 2008

The SEASAT project, which demonstrated the feasibility of microwave oceanographic remote sensing, was sponsored by the National Aeronautics and Space Administration and managed by the Jet Propulsion Laboratory. The evaluation of the measurement system (elements of the satellite, the sensors, the data handling, and data processing subsystems) was a key activity of the SEASAT project. This paper summarizes the primary achievements and highlights the generic limitations of the evaluation process. Other papers in this issue present details of the geophysical evaluation process carried out under the auspices of the SEASAT project.
An empirical determination of the effects of sea state bias on SEASAT altimetry
Authors: Born George H. , Richards Mark A. , Rosborough George W.
Published: February 2008

A simple linear empirical model has been developed to allow the user of SEASAT altimetry data to correct the altitude measurements for sea state bias effects. This bias is the result of two separate effects: one relating to instrumental effects and the other relating to a bias in the electromagnetic mean sea level relative to the geometric mean sea level. The electromagnetic bias is caused by the fact that the troughs of the ocean waves reflect the altimeter signal more strongly than the crests, thus causing the altimeter‐determined mean sea level to shift toward the wave troughs. An additional, but independent, instrument‐related bias is introduced because height corrections applied in the ground processor are not sufficient to compensate for simplifying assumptions made for the processor aboard SEASAT. This altitude bias also is predominately wave height dependent and directed toward the wave trough. The sum of these two effects is referred to as sea state bias. After applying appropriate corrections to the altimetry data, an empirical model for the sea state bias is obtained by differencing significant wave height and height measurements from coincident ground tracks. Ignoring small temporal variations in surface topography, the height differences on a given track should be zero; consequently, any residual height difference is attributed to sea state bias. The height differences are minimized by solving for the coefficient of a linear relationship between height differences and wave height differences that minimize the height differences. It is concluded that, for the altimeter data released by the Jet Propulsion Laboratory, 7% of the value of significant wave height should be subtracted from the SEASAT height measurements to correct for sea state bias. This correction reduced biases in the SEASAT data by more than 50% in the 36 cases examined here.
On the relationship between bedload and suspended sand transport on the inner shelf, Long Island, New York
Authors: Vincent Christopher E. , Young Robert A. , Swift Donald J. P.
Published: February 2008

Data obtained by a near‐bottom Profiling Concentration and Velocity system (PCV), deployed in 10 m water depth at a site 1 km from the Long Island coastline, are used to examine links between bedload and suspended sand concentrations. Calculations of bedload areal concentrationC*are based on the empirical results of Vincent et al. (1981) and use the theoretical formulations of Grant and Madsen (1978, 1979) to describe the interaction between wave and current boundary layers. Suspended sand concentrations were obtained directly from an Acoustic Concentration Meter (ACM). Average suspended sand profilesCzwere found to fit closely to a log‐linear profileCz=C1(1 ‐Alogez/Z1), whereC1is the sand concentration at a heightz1= 1 cm from the bed andAis empirically determined as 0.22±0.005. A linear correlation is observed between the areal bedload concentrationC*(the volume of bedload per unit area of the bed) and the suspended sand concentration 1 cm above the bedC1, with a correlation coefficient of 0.82 (significant at the 1% level), and supports the hypothesis of Einstein (1950) that bedload and suspended load are related through bedload concentration. It is also shown that the sedment threshold criterion of Komar and Miller (1973), when expressed as a ratio (here called the Komar ratio), can be used as a useful predictor forC1under conditions where the wave orbital currents are much greater than the mean flow. These relationships offer the opportunity for the calculation of both bedload and suspended sand transport rates from measurements of the steady current velocity and wave parameters, combined with information defining the surficial sediments and local bottom topography.
A detailed study of snow accumulation and stable isotope content in Dome C (Antarctica)
Authors: Petit J. R. , Jouzel J. , Pourchet M. , Merlivat L.
Published: February 2008

Snow samples have been taken in the Dome C area in order to study the variations of the accumulation rate and of the stable isotope content over the last century. Stake observations indicate a large spatial variability of the accumulation rate at a 1‐year scale (σs = 2.6 g cm−2 yr−1 for a mean value ā = 3.6 g cm−2 yr−1). The depth of the 1965 and 1955 layers determined from beta radioactivity measurements in 19 sites lets us deduce that the spatial variability becomes small at a 10‐year scale (σs = 0.3 g cm−2 yr−1), showing that the snow collected at one point is well representative of the fallen precipitation over this period. The rate of snow accumulation since 1965 is about 30% higher than during the 1955–1965 period. This conclusion is supported by measurements over a large geographical sector of East Antarctica. Shorter‐term changes of the snow accumulation have been studied by various means and in particular from detailed deuterium content profiles; by comparing with the beta and tritium radioactivity determinations it is shown that the deuterium variations do not allow us to obtain a seasonal record. In such a low‐accumulation area, different mechanisms (such as smoothing of the isotopic signal, roughness of the surface, irregularity of the accumulation) which may disturb the short‐term record are discussed. The interpretation of stratigraphie observations is not straightforward. However, it was possible to obtain a calibration down to the 1955 layer, which allows us to offer a dating of the snow layers over the last century. The mean accumulation so obtained (3.7 g cm−2 yr−1) is in good agreement with the value (3.6±0.5) deduced from lead 210 measurements. Geographical changes of the mean deuterium content are relatively small, showing that at a 10‐year scale the isotopic signal is well representative of the mean deuterium content of the precipitation. This ensures that the smoothed (10‐year running mean values) deuterium profile obtained over the last 160 years provides a good indication of the temperature secular trend in the Dome C area.
Direct measurements of ozone and nitrogen dioxide photolysis rates in the troposphere
Authors: Dickerson Russell R. , Stedman Donald H. , Delany Anthony C.
Published: February 2008

Direct measurements of the rate of O3 photolysis to O2(1Δg) and O(1D) and of NO2 photolysis to NO and O(3P) are reported as photolysis frequencies j(O3) and j(NO2). The effects of solar zenith angle, total ozone column, cloud cover, aerosol loading, temperature, pressure, and altitude are examined. For a clear sky, zero albedo, and zenith angle between 0° and 65°, the expression j (NO2) = 1.67 × 10−2 exp (−0.575 sec θ) (s−1) gives NO2 photolysis frequencies (photolysis rates per unit reactant) to within about 10% of the measured values, where θ is the solar zenith angle. Pressure has no measurable effect on j(NO2) between 0.15 and 1.2 bars. Temperature has only a small effect between 230 and 400 K, which can be described in terms of an effective activation energy of 0.48±0.05 kJ mol−1. Frequencies of ozone photolysis to O(1D) depend strongly on overhead ozone column and temperature as well as zenith angle; for 300 K, a clear sky, zero albedo, 45° zenith angle, 0.345‐cm ozone column, and altitude between 1.6 and 6 km, j(O3) = 1.6(±0.25) × 10−5 s−1. From 300 to 273 K, j(O3) drops by 40±3% for a 65° zenith angle and a 0.306‐cm ozone column; this value is not valid for different effective ozone columns. Measured photolysis frequencies show only weak dependence on altitude and aerosol loading. These frequencies were measured with instruments sensitive to radiation from the upward 2π sr only. Clouds dramatically reduce both photolysis frequencies, but they reduce the total radiation by a significantly larger factor. Airborne UV radiometers, calibrated against direct measurements of j(NO2), were used to measure albedos of many surfaces. While natural surfaces such as vegetation and oceans have albedos near zero, dense clouds and snow have an albedo near unity. With increasing altitude, molecular and particulate scattering often increase the effective albedo with respect to photolysis frequencies.
Methods for box models and ocean circulation tracers: Mathematical programing and nonlinear inverse theory
Authors: Wunsch Carl , Minster Jean‐François
Published: February 2008

Given the existing and forseeable oceanic data base, it is argued that practical determination of the general circulation of the oceans is probably impossible. Instead, by using a simple box model as an example, it is shown that mathematical models exist to determine both the range of possible solutions and the extreme values of important properties of all solutions. The specific techniques applied are linear and quadratic programing which are special cases of the more general techniques of optimization theory or mathematical programing. In addition, we provide an example of the use of a general nonlinear inversion technique for solving the problem. The methods should be adaptable to box models in much wider context and to much more elaborate diagnostic models.
On exchange of water between the Gulf of Alaska and the Bering Sea through Unimak Pass
Authors: Schumacher J. D. , Pearson C. A. , Overland J. E.
Published: February 2008

We present the first long‐term current and bottom pressure observations from Unimak Pass, Alaska, and adjacent locations on the Gulf of Alaska and Bering Sea shelves. Vector mean current recorded between March and August 1980 was ∼12 cm/s toward 284°T or onto the Bering Sea shelf, however, magnitude decreased from ∼20 cm/s to ∼6 cm/s between the first and second halves of the record. At shorter periods (3–10 days), current fluctuations in the pass were strongly coherent (K2 ≧ 0.7) with the pressure difference measured along the axis of the pass, and this was coherent with geostrophic wind estimates. The results indicated that wind‐induced sea level perturbation was the dominant forcing mechanism for fluctuations. Relations among current, bottom pressure, pressure difference, and geostrophic wind time series also showed that dynamic variaton on the Gulf of Alaska shelf was primarily responsible for current fluctuations in the pass. Hydrographic data indicated that a baroclinic current existed along the Gulf of Alaska coast, and this flow became the long‐term mean flow through the pass. We suggest that this feature was the extension of the Kenai Current. The historic supposition that water is transported from the Gulf of Alaska into the Bering Sea was verified; however, the waters are of coastal origin rather than from the Alaskan Stream.
A simple formula for vertical eddy diffusion coefficients under conditions of nonneutral stability
Authors: Henderson‐Sellers B.
Published: February 2008

Vertical turbulent transport of heat and momentum in water bodies is often parameterized as the neutral value of the appropriate (vertical) eddy diffusion coefficient, multiplied by a function of the gradient Richardson number. An analysis of previously published formulae for these stability functions shows that they are not consistent with observed values for the ratio between nonneutral and neutral values of the vertical eddy diffusion coefficients [Ueda et al., 1981] nor with observed values of the turbulent Prandtl number or the flux Richardson number [Linden, 1979]. A new formulation for the stability function in the case of turbulent heat transfer is proposed which is of an inverse quadratic form. It is shown that this representation, together with an appropriate inverse linear form in the case of momentum transfer, is in excellent agreement with recent data.
Mars water vapor, near‐surface
Authors: Ryan J. A. , Sharman R. D. , Lucich R. D.
Published: February 2008

In a previous paper we concluded that the temperature sensors aboard the Viking landers (VL‐1 and VL‐2) were detecting the water vapor frost point. Analysis of one Mars year of data at both lander sites substantiates this conclusion. At VL‐1 it is found that the water vapor mixing ratio is constant with height through the bulk of the atmosphere, most of the time. Exceptions are during the onset phases of the two major dust storms when temporary enhancement of near‐surface vapor occurs (the same phenomenon is observed at VL‐2), and some depletion of near‐surface vapor during the decay phase of the first storm, possibly the second storm as well. The former suggests near‐surface, northward transport of water vapor with the storms. The latter suggests adsorption of vapor on dust particles followed by surface deposition. At VL‐2, severe near‐surface depletion of water vapor occurs during northern autumn and winter. The residual vapor is in equilibrium with the surface condensate observed at the site during this period, indicating that the source region for the condensate must be aloft with downward transport by dust fall‐out. Since the near‐surface water vapor mixing ratio and concentration at VL‐1 generally parallels the column abundance over VL‐1 obtained by the orbiters, this suggests that VL‐1 can be used to give a measure of column abundance for as long as the temperature sensors remain operational.
Estimation of nearshore tidal currents on nonsmooth continental shelves
Authors: Battisti David S. , Clarke Allan J.
Published: February 2008

The theory of Battisti and Clarke (1982) to calculate analytically barotropic tidal currents across ‘smooth’ continental margin topography is shown to be valid near shore on ‘nonsmooth’ continental shelves. The theory includes longshore gradients and friction and produces formulae easily evaluated with coastal sea level data. The tidal currents across three such shelves (West Florida, south of Long Island, and Vancouver Island) are calculated and compared with those observed.
Clouds and wet removal as causes of variability in the trace‐gas composition of the marine troposphere
Authors: Thompson Anne M. , Cicerone Ralph J.
Published: February 2008

We describe a modeling study of the effects of clouds and wet removal on the chemistry of the remote marine troposphere. Using a time‐dependent model with parameterized vertical transport to calculate trace‐gas concentrations, we find that large variations in key species (e.g., HNO3, H2CO, and H2O2) result from simulations of sporadic rainfall, changes in cloud cover, and external inputs such as surface NO sources. Depending on the frequency and intensity of an event, the effects of these perturbations may persist for several days, thereby invalidating assumptions of photochemical equilibrium in the interpretation of measurements. Long‐term integrations with fixed boundary conditions and regularly occurring cloud and rain episodes demonstrate a strong sensitivity of the mean concentration of longer‐lived soluble gases to precipitation frequency but also confirm the validity of using properly chosen parameterizations of wet removal in steady state calculations. The marine atmosphere is represented in our model by selecting boundary conditions such as oceanic albedo and lower background NOx and hydrocarbons than observed over continents. The numerical model includes fairly complete gas‐phase photochemistry, multiple scattering optics, and a simple parameterization of a marine boundary layer. Although a simple one‐dimensional vertical transport is assumed, we demonstrate clearly that rainfall and cloud‐cover changes contribute to species variability. Sensitivities to exchange rates of gases with the sea surface are also discussed.
The optical and radiation field signatures produced by lightning return strokes
Authors: Guo Changming , Krider E. Philip
Published: February 2008

The optical signals radiated by Florida lightning in the 0.4‐ to 1.1‐μm wavelength interval have been recorded in correlation with wide‐band electric field signatures. The initial light signal from a return stroke tends to be linear for about 15 μs and then rises more slowly to a peak that is delayed by about 60 μs from the electric field peak. The transition between the fast linear portion and the slower rise may be due to the return stroke entering the cloud base. A small percentage of the records indicate that two different branches of the same stepped leader can initiate separate return strokes. The light pulses from cloud discharges tend to be smaller and more slowly varying than those from return strokes. The total optical power radiated by first strokes in the 5‐ to 35‐km range has a mean and standard deviation of 2.3±1.8×109 W at peak. Normal subsequent strokes produce 4.8±3.6×108 W at peak, and subsequent strokes preceded by a dart‐stepped leader produce 5.4±2.2×108 W. The characteristic widths of 23 subsequent stroke signals range from 103 to 235 μs, with a mean and standard deviation of 158±33 μs. Analyses of the initial linear slopes of the light signals suggest that the space‐ and time‐averaged radiance of first strokes is about 1.0±0.9×106 W/m during the bright phase and that normal and dart‐stepped subsequent strokes produce about 2.5±1.8×105 W/m and 4.3±3.1×105 W/m, respectively. Further analyses suggest that the dependence of the average radiance on the peak electric field, and probably the peak current, is neither linear nor quadratic.
Vertical overturns: A comparison of Thorpe and Ozmidov length scales
Authors: Dillon T. M.
Published: February 2008

An objective measure of the length scale of turbulent overturning events, the Thorpe scale, LT, is compared to the Ozmidov scale L0 = (ε/N3)1/2, where N is the buoyancy frequency and ε is the kinetic energy dissipation rate. Far from the surface in wind‐forced mixing layers and in the seasonal thermocline, L0 and LT are of the same order, but near the surface of a mixing layer, L0 is significantly larger than LT. The change in the ratio L0/LT is attributed to a decrease in the gradient Richardson number in the highly energetic zone near the surface. Another length scale, LB = (DCx/N)1/2, where Cx is the Cox number and D is the molecular diffusivity of temperature, is the same order as LT near the surface of a mixing layer as well as in the layer interior and in the seasonal thermocline. It is shown, by using the turbulent kinetic energy budget, that LB/LT is only weakly dependent on the gradient Richardson number as long as the ratio of eddy viscosity to eddy diffusivity is constant. The temperature variance dissipation rate is compared to the product of the buoyancy frequency and the existing temperature variance. Temperature fluctuations are defined as the temperature difference between the observed temperature profile and the Thorpe profile (the temperature profile which would result if an overturning patch gravitationally collapsed without dissipation). It is shown that the major balance in the temperature variance equation is between the rate at which variance is produced and the rate at which it is dissipated and that the rate of change of temperature variance can be an important modification to this balance only if the variance decays in a time much smaller than a buoyancy period.
Ground‐based infrared spectroscopic measurements of atmospheric hydrogen cyanide
Authors: Rinsland C. P. , Smith M. A. H. , Rinsland P. L. , Goldman A. , Brault J. W. , Stokes G. M.
Published: February 2008

A number of lines of the ν3 band of hydrogen cyanide have been detected in solar absorption spectra recorded near sunrise and sunset at Kitt Peak National Observatory (elevation 2095 m) with a 0.01 cm−1 resolution Fourier transform spectrometer. Analysis of two of the strongest and best isolated lines has led to a value of 2.73×1015 molecules cm−2 for the vertical column abundance of HCN above Kitt Peak. The accuracy of this value is estimated as ±25%. This result, combined with the stratospheric concentration of HCN derived by Coffey, Mankin, and Cicerone (1981), yields 166 parts per trillion by volume for the average mixing ratio of HCN between 2 and 12 km. This is the first determination of the HCN concentration in the nonurban troposphere.
Changes in concentrations of cloud and precipitation particles in the highly electrified regions of thundercloud
Authors: Kamra A. K.
Published: February 2008

Velocities of charged cloud and precipitation particles in thunderclouds change because of the electrical forces acting on them. It is shown in this paper that this change in their velocities will cause a change in their concentrations in the regions of the cloud having intense electrification. These changes in the concentrations of cloud and precipitation particles have been calculated here in a simplified model. In accordance with the recent observations, small regions of the cloud having strong electric fields imbedded in large scale but comparatively weaker electric fields have been assumed to exist over short periods of time inside thunderclouds. No particular charge generating mechanism has been considered. However, cloud particles have been assumed to carry positive charge and the precipitation particles negative charge. A uniform and constant updraft has been assumed to exist for short periods of time in these small regions of the cloud. The results depict accumulation of the particles of certain sizes and charge densities in the regions of cloud having intense electrification. Dependence of this accumulation of particles on the electric field, charge and size of the particles, updraft velocity, and the size of the region of intense electrification has been studied. Variations of these accumulations with time have also been examined. Some possible consequences and implications of these calculations have been broadly discussed.
Distribution of and changes in industrial carbon dioxide production
Authors: Rotty Ralph M.
Published: February 2008

The burning of fossil fuels is believed to be the major source responsible for an observed increase in the concentration of carbon dioxide in the atmosphere now measured at many locations around the world. This paper revises earlier published data on the annual amounts of carbon released to the atmosphere during the period 1950–1978 and updates the record through 1980. A latitudinal distribution of the fossil fuel source is presented as an aid in explaining the differences in the observed CO2 concentrations at several stations.

Data from Mauna Loa Observatory, the South Pole, and elsewhere around the world [Keeling et al., 1978a, b; Bolin and Bischof, 1970; Herbert, 1980] show an increase in the concentration of carbon dioxide in the atmosphere. Attempts to deduce from these records information about the global carbon cycle depend upon data pertaining to the sources of CO2 introduced by man‐burning of fossil fuels and conversion of the world's forests. The latitudinal distribution of the fossil fuel production of CO2 should be an important aid in carbon‐cycle analysis.

Observations in the atmosphere show that the Northern Hemisphere CO2 concentration is increasing more rapidly than the Southern Hemisphere concentration and that the most rapid increase is at 50°–60°N latitude. The greatest seasonal variation also occurs in this latitude band. This paper updates and documents the fossil fuel sources of CO2. It revises global CO2 emission values for 1950–1978 published earlier; it demonstrates that a change in the rate of increase of annual CO2 emissions occurred in 1973; and it attempts to delineate the regional distribution of this source of CO2.
Semiautomatic nondispersive infrared analyzer apparatus for CO2 air sample analyses
Authors: Komhyr W. D. , Waterman L. S. , Taylor W. R.
Published: February 2008

A semiautomatic nondispersive infrared analyzer apparatus has been developed for analysis of up to 50 CO2 air samples per day. The samples are collected in 500‐ml glass flasks and are transferred to the analyzer with a novel, free‐floating piston pump. Sample and calibration gas transfer operations are controlled by a microprocessor, and data are recorded, analyzed, and output by a Hewlett‐Packard 9845A/S desktop computer. The apparatus is described, including operating and test modes, and performance characteristics determined from 2 years of operation are given.
Chlorocarbon emission scenarios: Potential impact on stratospheric ozone
Authors: Wuebbles Donald J.
Published: February 2008

Prior analyses of chlorocarbons and their effects on stratospheric ozone have primarily concentrated on examining potential perturbations from two chlorofluorocarbons, CFCℓ3 (CFC‐11) and CF2Cℓ2 (CFC‐12). The purpose of this study is to provide an updated theoretical analysis of the potential effect on ozone due to past and future chlorocarbon emissions. To assess the overall impact from chlorinated emissions on the ozone layer, all chlorocarbons presently thought to be of likely concern are examined. A broad spectrum of scenarios is evaluated in order to provide an envelope including conceivable changes in future chlorocarbon emissions. Results indicate that CFCℓ2CF2Cℓ (CFC‐113), CH3CCℓ3, and CCℓ4 could contribute significantly to predicted changes in total ozone based on their current emission rates.
Registration of thunderstorm centers by automatic atmospherics stations
Authors: Volland H. , Schäfer J. , Ingmann P. , Harth W. , Heydt G. , Eriksson A. J. , Manes A.
Published: February 2008

A new generation of VLF‐atmospherics receivers and analyzers is presented that operates completely automatically and allows the realtime identification of thunderstorm activity centers. The mean azimuth and angular spread of each thunderstorm center within the detection range as well as the mean statistical properties of three measured spectral parameters of the atmospherics originating at that center are determined within each measuring period (20 min) by a desktop computer. Using a suitable statistical procedure for determining the mean angular and spectral parameters and applying a new extended model for VLF‐propagation as function of the solar zenith angle and of the magnetic field component along the propagation path, the operation program determines in real time the distances and strengths (atmospherics/min) of the activity centers so that all data can be immediately printed out and stored on the internal magnetic tape cartridge. Additionally, an external plotter is used for marking the thunderstorm centers on a map. No maintenance is required apart from changing the data tape cartridge once every month. At present, two systems of this new kind are installed at Pretoria (South Africa), Tel Aviv (Israel), and a somewhat older one at Berlin. Three more stations are to be established toward the end of this year. First results show the characteristics of the method, the short‐ and long‐range capability and resolution, and the reliability of the thunderstorm localizations.
Surface elevation contours of greenland and Antarctic Ice Sheets
Authors: Zwally H. Jay , Bindschadler R. A. , Brenner A. C. , Martin T. V. , Thomas R. H.
Published: February 2008

Surface elevations of the ice sheets are contoured at 50‐m intervals for the region of Greenland covered by SEASAT radar altimetry south of 72°N and at 100‐m intervals for a region of East Antarctica north of 72°S. The surface elevations were obtained from computer retracking of the radar altimeter waveforms, which were recorded at 0.1‐s intervals corresponding to 662‐m spacings on the surface. The precision of the elevation measurements before adjustment for radial orbit errors is 1.9 m as shown by analysis of elevation differences at orbital crossover points. This precision is partly determined by radial errors of approximately 1.0 m in orbit determination and partly by noise due to ice surface irregularities. Adjustment of the radial components of the orbits to minimize the differences in elevations at crossovers over a small, relatively flat region reduces the rms difference to 0.25 m, which is indicative of the optimum precision obtainable over the ice sheets. However, the precision degrades as the slope of the surface or amplitude of the undulations increases, yielding an overall precision of ±1.6 m. The preliminary contour maps are not corrected for slope‐induced displacements. A 2‐m contour map in a region of highest data density illustrates the three‐dimensional characteristics of some surface undulations.
On a satellite scatterometer as an anemometer
Authors: Brown R. A.
Published: February 2008

The SEASAT‐A satellite scatterometer (SASS) wind‐algorithm was tested against surface wind fields. Three classes of surface wind fields were used; point measurements, an isotach field over an intensively measured triangle with 200 km sides, and synoptic scale winds determined from pressure and temperature fields and a planetary boundary layer model. These comparisons can verify optimal capabilities of SASS at accuracies of ±2 m s−1 and ±20°. SASS ability to locate fronts accurately is also established. Complications in nonsteady, highly variable fields indicate problems exist in unqualified application of the SASS algorithm to all conditions.
Scylla and Charybdis observed from space
Authors: Alpers Werner , Salusti Ettore
Published: February 2008

Scylla and Charybdis are, in Greek mythology, two immortal and irresistible monsters who beset the narrow waters separating the Italian peninsula from Sicily. They give poetic expressions to exceptional oceanographic features encountered in the Strait of Messina. Recently, the SEASAT satellite has added new information on the oceanography of this strait. For the first time, experimental evidence is presented that internal waves are generated in the Strait of Messina. The generation mechanism is linked to tidal currents washing over the shallow sill within the strait. The experimental data originate from a synthetic aperture radar (SAR) image obtained from the SEASAT satellite on Sept, 15, 1978, and from subsequent in situ measurements carried out from the Italian research vessel Bannock in Nov. 1980. The circular wave pattern visible on the SEASAT SAR image is interpreted in terms of internal solitons. Furthermore, the SEASAT SAR image also reveals ‘tagli,’ special types of tidal bores, encountered in the Strait of Messina.
The effect of oceanic whitecaps and foams on pulse‐limited radar altimeters
Authors: Zheng Q. A. , Klemas V. , Hayne G. S. , Huang N. E.
Published: February 2008

Based on electromagnetic field theory of stratified media, the microwave reflectivity of a sea surface covered by whitecaps and foams at 13.9 GHz was computed. The computed results show that the reflectivity declines with increasing thickness of foams. The reflectivity of the sea surface without any whitecaps or foams is 0.6066 (20°C, S∶35‰), but it will be less than 0.15 when the thickness of foam cover is more than 0.3 cm. While gathering the data of whitecap and foam coverage in situ and reviewing whitecapping models, it can be shown that the effect of oceanic whitecaps and foams on the measured results of a pulse‐limited radar altimeter working at high frequencies will not be negligible in high sea state conditions.
Effects of a shelf polynya on flow and water properties in the northern Bering Sea
Authors: Schumacher J. D. , Aagaard K. , Pease C. H. , Tripp R. B.
Published: February 2008

We present long‐term (∼230‐day) measurements from three moorings in the vicinity of Saint Lawrence Island on the northern Bering Sea shelf. One mooring was deployed near the polynya which often exists south of the island. These data confirm the existence of strong (∼0.15 m s−1) flow toward Bering Strait northwest of the island (in Anadyr Strait) and suggest that regional circulation results in a moderate (∼ 0.03 5 m s−1) mean flow eastward along the southern coast of Saint Lawrence Island. Coherent variations in the regional circulation and variations in the geostrophic wind account for much of the low‐frequency current fluctuation south of Saint Lawrence Island. However, there were 11 events when offshore (northerly) winds coincided with the temperature following the freezing point, increasing salinity, and reversal of the current. This suggests that ice formation and the ensuing brine rejection affect flow in the vicinity of the polynya. Scaling of a simplified momentum equation indicates that the cross‐shelf density gradient was a possible mechanism for some of the reversals. Salinity data show a seasonal cycle as well as individual events of brine rejection. During an average event time of 65 hours, the salinity increased by 8×10−3 g kg−1 h−1; the heat flux can be estimated as 535 Wm−2. These fluxes correspond to an ice production of ∼5 m during winter 1981. Extrapolation of our results and comparison with the freshwater cycle suggest that brine rejection is an important component of the regional salt budget.
On the seasonal sea ice cover of the Sea of Okhotsk
Authors: Parkinson Claire L. , Gratz Andrew J.
Published: February 2008

Free of ice 4 months of the year, the Sea of Okhotsk begins to freeze over in a few coastal locations in November, attains its maximum ice coverage usually in mid March, and by June retains ice in only a few coastal regions. This sequence is well recorded by satellite imagery from the Electrically Scanning Microwave Radiometer (ESMR) on board Nimbus 5. Four years of ESMR data reveal significant interannual variations in the maximum ice cover and in the smoothness of the growth and retreat periods. Of the years 1973–1976, the heaviest ice cover occurred in 1973, and the growth period most interrupted by temporary ice edge retreats was in 1974. Comparison of the general features of the cycle of sea ice distribution with basic oceanographic factors shows that ice forms first in cold, shallow, low‐salinity waters and then seems to drift in a direction approximating the Okhotsk‐Kuril current system. Two basic patterns of ice edge positioning which occur frequently in the ESMR data are identified as a rectangular structure and a wedge structure. Each of these is strongly correlated with the bathymetry of the region and with the known current system, suggesting that convective depth and ocean currents play an important role in determining ice patterns. Certain major interannual variations in the ice extents are accounted for by interannual contrasts in the atmospheric pressure fields.
On some possible interactions between internal waves and sea ice in the marginal ice zone
Authors: Muench Robin D. , LeBlond Paul H. , Hachmeister Lon E.
Published: February 2008

The ice edges of the world ocean are generally the site, at times when winds are blowing off the ice, of regularly spaced surface bands of ice floes. These bands have size scales of the order of 1–10 km, and their long axes are oriented approximately normal to the wind direction. Available oceanic temperature and salinity data from the Bering and Greenland Sea ice edge regions suggest that these ice bands are commonly underlain by a two‐layered density structure which is maintained by net melting along the ice edges. Linear internal wave theory is applied to these data to compute first‐mode interfacial wave phase speeds. A simple analytical model is developed that demonstrates the feasibility of generation of such interfacial internal waves by the stress discontinuity due to off‐ice winds blowing over either a stationary or a moving ice edge. It is qualitatively shown that the computed internal wave phase speeds and wavelengths are, under many conditions, compatible with the speeds and spacings of the surface ice bands. This compatibility suggests, in turn, that coupling between internal waves and ice bands may commonly occur. Some possible implications of the generation and presence of these internal waves upon other ice edge processes, such as air‐sea heat and momentum transfer, are qualitatively discussed.
Turbulent heat and momentum transfer in the oceanic boundary layer under melting pack ice
Authors: McPhee Miles G.
Published: February 2008

A theory for momentum flux in the planetary boundary layer (PBL) stabilized by continuous surface buoyancy is extended to include turbulent flux of an arbitrary scalar contaminant and then used to estimate how wind‐driven sea ice melts as it encounters temperatures in the oceanic boundary layer that are above the melting point. Given wind stress and temperature difference Δθ across the oceanic PBL, the theory predicts melt rate and ice drift velocity. Results indicate that the effect of buoyancy on PBL turbulence is significant even with small values of Δθ(<0.5 K). Curves of melt rate and ice speed as functions of u*, the interfacial friction velocity, show that melting is strongly dependent on stress at the interface and that the effective drag on the ice undersurface is significantly reduced at oceanic temperatures commonly observed in the marginal ice zone. The latter suggests that divergence will occur at the ice margin when off‐ice winds advect the pack over water above the melting temperature. The structure of mean currents beneath the ice is also investigated; results indicate that advection will play an important, if not dominant, role in determining water column properties near an ice edge front.
A model of grease ice growth in small leads
Authors: Bauer Jane , Martin Seelye
Published: February 2008

When a strong, cold wind blows over open polar leads, ice grows in the form of small crystals which are herded downwind by both wind waves and a wind‐driven surface current to pile up at the downwind edge of the lead. As this process continues, the piled‐up ice, called ‘grease ice,’ advances upwind until the entire lead is ice covered. In a numerical model of ice growth in a horizontally one‐dimensional lead with a wind blowing along its length we use the heat flux taken from existing formulations to determine the ice production rate. Similarly, we use the wave field and surface current, which are functions of wind speed and fetch, to calculate the ice pileup depth and the ice cover advance rate. Because this ice growth mechanism allows water at its freezing point to remain in contact with the cold air, high heat and salt fluxes are maintained. The ice growth predicted from this model is an order of magnitude greater than one‐dimensional vertical growth.
New measurements of sulfate and chlorinity in natural sea ice
Authors: Reeburgh W. S. , Springer‐Young M.
Published: February 2008

Precise determinations of sulfate and chlorinity were made on SIPRE core samples of natural sea ice. One ice was a multiyear ice that had remained attached to T‐3 (Fletcher's Ice Island) for over 20 years and the other was a shore‐fast annual ice collected near Barrow, Alaska. Our results show sulfate: chlorinity ratios different from the seawater ratio. A mixing model shows that on warming and aging, sulfate and chlorinity are lost in a constant ratio, indicating conservative behavior. Fractionation in sea ice appears to be determined in the freezing process and further enrichment does not take place with aging. The effects of sulfate fractionation in sea ice are too small and the residence times of both sea ice and Arctic Ocean surface water are too short to permit detectable modification of seawater composition by freezing.
Some comments on the exchange of CO2 across the air‐sea interface
Authors: Lal D. , Suess H. E.
Published: February 2008

Boundary values are estimated for the long‐term rate of exchange of carbon dioxide between the atmosphere and the ocean, based on the analyses of the experimentally determined shapes of ‘wiggles’ in the atmospheric 14C/12C ratios, for which accurate tree ring data are available for the past 8 millenia. It is shown that the high frequency wiggles (characteristic period of about 200 years) can be explained as entirely due to temporal variations in the global production rate of 14C (estimated maximum range: ±25%) arising from solar modulation of galactic cosmic ray flux provided the mean residence time of carbon dioxide in the atmosphere lies in the range (3–25) years. These calculations are based on a four‐box model for the carbon cycle, with a wide range of parameters for the mixed layer of the ocean to simulate the carbon dioxide exchange.
Global mesoscale variability from collinear tracks of SEASAT altimeter data
Authors: Cheney Robert E. , Marsh James G. , Beckley Brian D.
Published: February 2008

In 1978, during the last 25 days of the SEASAT mission, the satellite ground tracks repeated within 2.5 km every 3 days. This yielded eight to nine sets of global collinear altimeter data with a cross‐track grid spacing of approximately 900 km at the equator and 600 km at mid‐latitude. Because the geoid is time‐invariant, such observations can reveal sea surface height variability due to dynamic ocean phenomena. We have solved for variations due to deep‐ocean mesoscale features by eliminating the longer wavelength deviations. Modeled tidal heights were first subtracted from the altimeter data, and linear trends were then removed from collinear segments approximately 2000 km in length. This second step eliminates relative orbit error together with any residual tide model errors. The resulting sea height profiles have a precision of a few centimeters, and the global variability map constructed from these data reveals a strikingly realistic view of mesoscale energetics. Maximum values of 20–40 cm rms variability are generated by meanders and eddies of five major current systems: Gulf Stream, Kuroshio, Agulhas, Antarctic Circumpolar, and Falkland/Brazil confluence. Perhaps a more significant discovery was the dominance of exceedingly small variability over vast regions of the oceans; approximately 70% of all global values were less than 5 cm. This category included the eastern North Pacific, eastern South Pacific, and almost the entire South Atlantic where values as small as 1–2 cm were common. With such a low level of background noise, even some currents with relatively small sea height signatures could be detected. In both the Atlantic and the Pacific, for example, the North Equatorial Current systems were clearly expressed as zonal bands of higher variability.
Temporal variations of beam attenuation coefficient on the continental rise off Nova Scotia
Authors: Pak Hasong , Zaneveld J. Ronald V.
Published: February 2008

Two separate time series observations of light transmission in the bottom water on the Continental Rise off Nova Scotia show fluctuations of light transmission in a wide range, 0–50% transmission at λ = 660 nm. The range corresponds approximately to SPM concentrations of 12 mg/l to 150 μg/l. The former is the maximum value determined by filtration (Biscaye, 1980), and the latter is determined by an empirical relation between beam attenuation coefficient and particle volume determined by a particle counter. Nepheloid layers of significant turbidity, called benthic storms, were observed in 30 and 10% of the time, respectively, for the two observations, and each storm lasted 2–5 days. High frequency fluctuations represented by pulse lengths less than 10 min were observed superimposed on the low frequency fluctuations during 16 and 4% of the time. Both the major storms and the high frequency pulses are interpreted to be a result of resuspension of bottom sediments at varying distances from the instrument; the high frequency pulses are thought to be a result of erosion at a relatively short distance, while the low frequency fluctuations result from erosion at greater distance.
Nonlinear features of internal waves off Baja California as observed from the SEASAT imaging radar
Authors: Apel John R. , Gonzalez Frank I.
Published: February 2008

The synthetic aperture radar (SAR) on SEASAT has yielded well‐defined images of quasi‐periodic internal waves in the waters on the west side of Baja California. These waves occur in groupings separated by 15–23 km, each group having 2–20 striations with wavelengths of the order of 300 m or longer. They appear in water approximately 200 m deep, shoreward of several banks at the continental shelf edge whose depths are as shallow as 15 m. The wave surface signatures exhibit clear nonlinear features: higher‐than‐linear group velocities, and decreases in wavelength, crest length, and amplitude toward the rear of the packet. Environmental data for the area have been examined, and these show a well‐developed mixed layer, low winds, and vigorous tidal action. Thus, stratification, wind speed, tidal current, and bottom topography apparently combine to establish proper conditions for tidal generation of internal waves. The images have been analyzed from the standpoint of nonlinear wave theory, and it is shown that the vertical displacement of an isopycnal surface can be estimated from a combination of SAR imagery, vertical density profiles, and simple theoretical expressions. Numerical examples are given.
Nearshore coastal currents on the South Carolina continental shelf
Authors: Schwing Franklin B. , Kjerfve Björn , Sneed James E.
Published: February 2008

Simultaneous current, sea level, wind, and atmospheric pressure data from the South Carolina nearshore shelf during the summer are analyzed and compared. The current record was taken in the nearshore region at 10m depth, an area where the current regime has not been well studied. Most of the variance in the series is concentrated in two frequency bands; (1) 2–12 days (meteorological) and (2) 12–25 hours (tidal and daily). The variance of the two bands is approximately equal in both the alongshore and the cross‐shore current components, but net flow is primarily due to low frequency events. The nearshore current flows predominantly to the northeast, possibly an Ekman response to the northerly blowing wind regime. Current reversals occur in response to frontal passages approximately every 6 days. Low frequency alongshore currents and winds are highly coherent at 2–12 days, with the currents having a phase lag of about 3 hours. Cross‐shore currents are not coherent with cross‐shore winds, but have a statistically significant 7 hour lag to alongshore currents. Coastal sea level is also coherent with alongshore currents, lagging by 15 hours at 4.4 days, indicating that the nearshore current may drive sea level changes. The reason for the significant lag in sea level is not clearly understood.