bluuebunny/crossref_metadata_2025 huggingface dataset:
Differences in radar return from ice‐covered North Slope Lakes
Authors: Weeks W. F. , Fountain A. G. , Bryan M. L. , Elachi C.
Published: February 2008

Comparisons are made between L and X band synthetic aperture radar images of frozen lakes on the North Slope of Alaska and ground truth observations of the nature of their ice covers. It is shown that the differences in radar backscatter observed on different areas of a lake can be correlated with whether or not the lake is frozen completely to the bottom at the site in question. This explanation is reasonable inasmuch as the reflection coefficient associated with the high‐dielectric contrast ice/water interface is significantly higher than that associated with a low‐contrast ice/soil interface. However, the presence of the ice/water interface cannot be the only condition required for the higher backscatter because the ice/water interface per se would be specular at X and L band frequencies, causing the energy returned from the interface to be reflected away from the radar receiver. The other principal factor contributing to the return of energy from the ice/water interface to the receiver is believed to be the presence in the ice of numerous vertically elongated air bubbles which would act as scatters.
Use of the Butterworth low‐pass filter for oceanographic data
Authors: Roberts Jo , Roberts Thomas D.
Published: February 2008

The characteristics of the Butterworth low‐pass filter are well known in electrical engineering. Here we discuss its use for oceanographic records and compare its characteristics with other low‐pass filters now in use: the cosine‐Lanczos filter, the Gaussian filter, and the ideal filter. The Butterworth filter is recursive, i.e., past values of the output are used as input, so a phase shift is introduced unless the data are filtered forward and backward through the same filter. When this is done, the filtered signal differs only slightly from that of other low‐pass filters. Because the Butterworth filter uses fewer multiplicative constants for the same effect, there is a reduction in computer time over other low‐pass filters; the difference becomes more pronounced as more data points are used.
Molecular hydrogen in the near‐surface atmosphere and dissolved in waters of the tropical North Atlantic
Authors: Herr F. L. , Barger W. R.
Published: February 2008

The concentration of H2 has been measured in near‐surface air and at fifteen hydrographic stations across the tropical North Atlantic. For both air and seawater samples H2 was analyzed in the gas phase by the HgO technique. Air samples taken 10 m above the ocean surface gave a mean value of 0.65 ± 0.02 ppmv at mid‐ocean and showed higher values near Africa. A composite of all seawater analyses showed dissolved H2 varying in the upper 50 m from 4 to 73 nl H2/l H2O and averaging 18.5 nl/l. Below the mixed layer, H2 dropped quickly to near the equilibrium value (9.8 nl/l), but subsurface structure allowed occasional supersaturation to 20 nl/l. In the deepest water, below 1500 m, H2 was found to be undersaturated with respect to the present atmosphere. The northern hemispheric oceanic source strength has been calculated to be 0.33 × 1012 g H2/yr, which is only one quarter the previous estimate. Subsurface maxima within the pycnocline, reminiscent of methane maxima, were twice observed. The data indicate H2 dissolved in the open ocean may be much less variable than previously suspected from existing measurements.
On the distribution of the heights of sea waves: Some effects of nonlinearity and finite band width
Authors: Longuet‐Higgins Michael S.
Published: February 2008

It is shown that some recent data on the crest‐to‐trough heights of sea waves are fitted just as well as by the one‐parameter Rayleigh distribution as by the two‐parameter Weibull distribution, provided that the rms amplitude ā is taken as 0.925(2m0)1/2, where m0 is the lowest moment of the frequency spectrum. Reasons why the ratio ā/(2m0)1/2 should differ from unity are discussed. It is shown that the effect of finite wave steepness would be to increase the ratio by a factor [1 +
(ak)2] approximately, contrary to observation. The effect of finite band width is estimated from a model assuming low background noise superposed linearly on a delta function spectrum. For narrow band widths one obtains the formula ā2/2m0 = 1 − 0.734ν2, where ν is the rms spread of the noise about the mean frequency. Values of ν2 corresponding to Pierson‐Moskowicz spectra give results in close agreement with observation.
Mixing and circulation in the northwestern Gulf of St. Lawrence: A study of a buoyancy‐driven current system
Authors: Tang C. L.
Published: February 2008

Mixing and circulation near the entrance to the St. Lawrence estuary are studied by using the hydrographic and current meter data obtained in the summer of 1978. It is found that the currents in the upper 40 m are mainly buoyancy driven. As the low‐salinity water from the estuary flows eastward and encounters the more saline Gulf of St. Lawrence water, a wedge‐shaped layer of low‐salinity water and a density front are formed. Intense vertical mixing takes place along the boundary of the layer. The geostrophic current associated with the front flows southward and, upon reaching the shore, turns east. From there on it flows parallel to the coast and is reinforced by a basin‐wide cyclonic gyre forming a strong coastal jet, the Gaspe current. The salinity front divides the deep water into the two flow regimes. Eastward (westward) of the front the currents in the 40‐ to 100‐m depth are cyclonic (anticyclonic). The variability of the temperature and salinity fields is examined. The effect of the variability on the interpretation of the data is discussed.
The evolution of atmospheric ozone
Authors: Kasting J. F. , Donahue T. M.
Published: February 2008

A one‐dimensional coupled chemistry and flow model of the earth's atmosphere is used to study the relationship between ozone content and oxygen level. The effects of the biogenic trace gases methane and nitrous oxide are considered, as well as the production of odd nitrogen in lightning discharges. The ozone column depth is found to increase monotonically with increasing oxygen content, in contrast with previous predictions that the column depth should peak at ∼10−1 PAL (present atmospheric level) of O2. The critical O2 level at which an effective ultraviolet shield is produced is in the neighborhood of 10−1 PAL. Implications of this result for the emergence of terrestrial land life are considered.
The statistical prediction of beach changes in southern California
Authors: Aubrey David G. , Inman Douglas L. , Winant Clinton D.
Published: February 2008

Changes in natural sand beaches induced by variations in incident waves were predicted by techniques of linear statistical estimation and empirical eigenfunction analysis. A 5‐year set of measured beach profiles and wave statistics from southern California constituted the data base for this two‐faceted statistical study. First, daily beach profile changes were predicted using four different spectral representations of the wave field. These profile changes were predictable using spectral representations of wave energy, radiation stress, energy flux, and wave steepness. Because of constraints on statistical reliability, a longer data set is required to select one of these as an optimal wave parameterization. Second, weekly beach profile changes were predicted using weekly averaged wave characteristics. Weekly beach changes were predictable using weekly mean and maximum values of wave energy and wave height. The best predictor of those tested was the weekly mean wave energy. When combined with a longshore transport model, this onshore/offshore transport estimator should be applicable to other coastal regions with different beach and wave characteristics.
Phase speeds of upwind and downwind traveling short gravity waves
Authors: Plant W. J. , Wright J. W.
Published: February 2008

Phase speeds of both upwind and downwind traveling, wind‐generated waves 4.1, 9.8, 16.5, and 36 cm in wavelength were measured by using microwave Doppler spectrometry. Advective effects of the wind drift could be separated from inertial pressure effects by taking sums and difference of the phase speeds of upwind and downwind directed waves. Boundary layer parameters inferred by fitting measured phase speeds to those predicted by first‐order perturbation of the interfacial flow are in general agreement with parameters derived from other measurements. Attempts to refine the interpretation by using available theories of phase speeds of finite amplitude, irrotational waves degraded the agreement; in fact, the measured fetch dependence of phase speeds was opposite that predicted by these theories.
Sources of the strongest RF radiation from lightning
Authors: Le Vine David M.
Published: February 2008

Experiments were performed at the Kennedy Space Center, Florida, during Trip 78 and later repeated at Wallops Island, Virginia, to identify sources of the strongest radio frequency radiation from lightning. This was done by monitoring the fast electric field changes associated with strong radiation in the HF to VHF range, using a field change system triggered on the output of an RF detector. The electric field changes associated with the strongest RF radiation were short duration (10–20 μs) bipolar pulses having an initial negative half cycle followed by a positive overshoot. The shape of these pulses was independent of the frequency of the RF radiation used to trigger the field change system. These fast pulses consistently were associated with more RF radiation than were return strokes and would appear to be a cloud discharge with characteristics suggestive of a very fast K change.
On the angular variation of solar reflectance of snow
Authors: Choudhury B. J. , Chang A. T. C.
Published: February 2008

Spectral and integrated solar reflectance of nonhomogeneous snowpacks are derived assuming surface reflection of direct radiation and subsurface multiple scattering. For surface reflection, a bidirectional reflectance distribution function derived for an isotropic Gaussian faceted surface is considered, and for subsurface multiple scattering an approximate solution of the radiative transfer equation is studied. Solar radiation incident on the snowpack is decomposed into direct and atmospherically scattered radiation. Spectral attenuation coefficients of ozone, carbon dioxide, water vapor, aerosol, and molecular scattering are included in the calculation of incident solar radiation. Illustrative numerical results are given for a case of North American winter atmospheric condition. The calculated dependence of spectrally integrated directional reflectance (or albedo) on solar elevation is in qualitative agreement with available observations.
Satellite and hydrographic observations of low‐frequency wave motions associated with a cold core Gulf Stream ring
Authors: Spence Thomas W. , Legeckis Richard
Published: February 2008

Thermal infrared data from the NOAA polar orbiting satellite and hydrographic observations from surface ships are used to estimate the eccentricity and the rotation rate of wavelike perturbations around the circumference of a Gulf Stream cyclonic eddy in April 1977. From the satellite data, the rotation rate is estimated at ω = (4.4 ± 0.1) × 10−6 s−1 for the period April 8–16. Estimates of ω are obtained from the trajectory of satellite‐tracked drifters and from changes in the sea surface temperature fields determined from expendable bathythermograph trace (XBT) surveys. A simple Eady model suggests the perturbations are stable modes of azimuthal wave number 2.
Thermally driven wind variability in the planetary boundary layer above Lima, Peru
Authors: Enfield D. B.
Published: February 2008

Land‐sea thermal forcing of the coastal wind near Lima, Peru, is examined as a mechanism to explain the observed wind variability there, in particular the similarity between monthly anomalies of sea surface temperature and wind speeds on the interannual time scales typical of El Niño occurrences. Aerological and surface meteorological observations from Peru coastal sites are analyzed for two time scales: over 15–20 year periods (1958–1977) for monthly averaged data and over a year (1976–1977) for daily data. Wind profile characteristics and annual cycles, and their relation to the cross‐coastal temperature gradient are qualitatively and quantitatively consistent with the thermally forced boundary‐layer model proposed by Lettau (1978) to explain the Peru coastal wind. The cross‐coastal air temperature difference between Lima and Callao explained 55% of the variance in the surface wind speeds at Lima during 1976–1977. The mean annual cycles of the surface wind at Lima and other Peru coastal locations are in phase with the annual solar heating cycle where the seasonality of low cloudiness is large but with the annual cycle of the southeast trade circulation where it is not. This suggests that insolation over the desert is the principal source of thermal forcing variability. During El Niño periods the alongshore wind and the crosscoastal circulation above Lima intensify, in conjunction with anomalously warm sea surface temperatures. The planetary boundary layer is destabilized, and the base of the winter inversion is eroded upward. The observations are consistent with a reduction of desert cloudiness during El Niño events owing to air‐sea exchange and a consequent increase in the thermal forcing of the wind.
On the amplitude of beach cusps
Authors: Guza R. T. , Bowen A. J.
Published: February 2008

There is increasing evidence from field observations that beach cusps are often formed by subharmonic edge waves, edge waves which are generated by an instability in the incoming wind waves. A theoretical analysis suggests that the changing beach topography as the cusps grow provides a negative feedback to the excitation of the subharmonic edge waves. As the cusps grow, the edge waves subside. A maximum cusp amplitude is calculated, based on the assumption that some edge wave activity must persist to maintain the cusps. The theoretical prediction that cusp amplitude will increase with increasing beach slope and increasing incident wave period is in agreement with the trends suggested by some of the more detailed field observations of beach cusps.
Tides of the Caribbean Sea
Authors: Kjerfve Björn
Published: February 2008

Analysis of tidal characteristics from 45 gauge locations indicates that the Caribbean Sea hs a microtidal range, for the most part between 10 and 20 cm. The tide is primarily either mixed semidiurnal or mixed diurnal but a substantial section from Puerto Rico to Venezuela experiences diurnal tides. Empirical charts of six component tides (M2, S2, N2, K1, O1, and P1) show local detail of phase and amplitude. Each of the semidiurnal compnent tides is characterized by anticlockwise rotating amphidromes centered in the eastern Caribbean. There is evidence of strong radiational forcing of the S2 tide in the southwestern Caribbean. The diurnal component tides are largely uniform in both phase and amplitude for most of the western and central Caribbean. However, the diurnal phases increase rapidly toward the northwest and the Yucatan Channel.
Remote sensing of soil moisture content, over bare field at 1.4 GHz frequency
Authors: Wang J. R. , Choudhury B. J.
Published: February 2008

An algorithm for estimating moisture content of a bare soil from the observed brightness temperature at 1.4 GHz is discussed and applied to a limited data base. The method is based on a radiative transfer model calculation, which has been successfully used in the past to account for many observational results, with some modifications to take into account the effect of surface roughness. Besides the measured brightness temperatures, the three additional inputs required by the method are the effective soil thermodynamic temperature, the precise relation between moisture content and the smooth field brightness temperatures and a pair of parameters related to surface roughness. The procedures of estimating surface roughness parameters and of obtaining moisture content from observed brightness temperature are discussed. The algorithm is applied to observations from truck mounted and airborne radiometers. The estimated moisture contents compare favorably with the observations in the top 2 cm layer.
Sources of atmospheric methane: Measurements in rice paddies and a discussion
Authors: Cicerone Ralph J. , Shetter James D.
Published: February 2008

We have made field measurements of methane fluxes from rice paddies, fresh water lakes, and saltwater marshes to infer estimates of the size of these sources of atmospheric methane. The rice‐paddy measurements, the first of their kind, show that the principal means of methane escape is through the plants themselves as opposed to transport across the water‐air interface via bubbles or molecular diffusion. Nitrogen‐fertilized plants release much more methane than unfertilized plants but even these measured rates are only one fourth as large as those inferred earlier by Koyama and on which all global extrapolations have been based to date. We also compare our measured methane fluxes from lakes and marshes to similar earlier data and find that extant data and flux‐measurement methods are insufficient for reliable global extrapolations.
Diurnal analysis of local variabilities in atmospheric NO3
Authors: Gelinas Robert J. , Vajk J. Peter
Published: February 2008

A diurnal analysis of local NO3 variabilities is presented for selected atmospheric volume elements along the lines of sight which were observed by Noxon et al. (1978). In view of recent debates (Herman, 1980; Noxon et al., 1980a) concerning alternative interpretations of these measurements, the present analysis indicates that current photochemical theory is consistent with the experimental observations of diurnal variations in total NO3. Furthermore, diurnal variations in trace species column densities are shown to be potentially very sensitive tests of photochemical mechanisms and of physical perturbations when requisite levels of spatial and temporal resolution are achieved in observations.
The form of the near‐bed velocity profile in a tidally accelerating flow
Authors: Soulsby R. L. , Dyer K. R.
Published: February 2008

In an accelerating tidal flow the near‐bed velocity profile departs from the usual logarithmic form. The amount of the departure may not necessarily be large, but is nevertheless important when the profiles are used to calculate the bed roughness length and shear stress. A form for the accelerated profile is derived in terms of an ‘acceleration length’. Profiles measured off the SW coast of England are fitted to this expression, and give a value for a constant γ appearing in it. Published laboratory oscillatory flow profiles are also fitted; in this case the constant γ is larger due to the greater relative bed roughness. Von Karman's constant is obtained from the field data and found to be equal to 0.40, closer to laboratory values than to the now widely used atmospheric value of 0.35. Some evidence is found, however, to support a slow decrease in von Karman's constant with increasing boundary‐layer thickness to roughness length ratio.
Symposium on middle atmosphere dynamics and transport
Authors: Gille John C. , VanZandt Thomas E.
Published: February 2008

Several recent developments have led to a strong upsurge of interest in the dynamics of the middle atmosphere, which is that portion of the atmosphere between the tropopause (8‐16 km) and 100 km altitude. One is the development of new theoretical insights and capabilities, notably the renewed interest in traveling planetary waves, and in the Lagrangian approach to atmospheric dynamics, with the demonstration that it provides illuminating insights into the interactions between waves and the mean flow. The number and scope of computer models has also grown rapidly.
Turbulence and stress owing to gravity wave and tidal breakdown
Authors: Lindzen R. S.
Published: February 2008

It has been suggested (Lindzen, 1967, 1968a, b; Lindzen and Blake, 1971; Hodges, 1969) that turbulence in the upper mesosphere arises from the unstable breakdown of tides and gravity waves. Crudely speaking, it was expected that sufficient turbulence would be generated to prevent the growth of wave amplitude with height (roughly as (basic pressure)−1/2). This work has been extended to allow for the generation of turbulence by smaller amplitude waves, the effects of mean winds on the waves, and the effects of the waves on the mean momentum budget. The effects of mean winds, while of relatively small importance for tides, are crucial for internal gravity waves originating in the troposphere. Winds in the troposphere and stratosphere sharply limit the phase speeds of waves capable of reaching the upper mesosphere. In addition, the existence of critical levels in the mesosphere significantly limits the ability of gravity waves to generate turbulence, while the breakdown of gravity waves contributes to the development of critical levels. The results of the present study suggest that at middle latitudes in winter, eddy coefficients may peak at relatively low altitudes (50 km) and at higher altitudes in summer and during sudden warmings (70–80 km), and decrease with height rather sharply above these levels. Rocket observations are used to estimate momentum deposition by gravity waves. Accelerations of about 100 m/s/day are suggested. Such accelerations are entirely capable of producing the warm winter and cold summer mesopauses.
The instability of atmospheric gravity waves through wave‐wave interactions
Authors: Yeh K. C. , Liu C. H.
Published: February 2008

We investigate the possibility of a propagating primary wave decaying into secondary waves through three‐wave interactions. Such a possibility exists in an inviscid isothermal atmosphere when the vertical wavelength is small compared to the scale height. Initially, the amplitude of the secondary waves grows exponentially, and this growth time decreases exponentially with height. This means that as the primary wave propagates upward its energy is continuously transfered to the secondary waves. This transfer becomes increasingly rapid with increasing height. It is shown that this process can take place even when the local Richardson number is more than 100, indicating dynamic stability.
Earth radiation budgets
Authors: Stephens G. L. , Campbell G. G. , Haar T. H. Vonder
Published: February 2008

This paper presents the annual and seasonal averaged earth atmosphere radiation budgets derived from the most complete set of satellite observations available in late 1979. The budgets are derived from a composite of 48 monthly mean radiation budget maps. The annual, global average emitted infrared flux is 234 W m−2, planetary albedo is 0.30, and the net flux is zero within measurement uncertainty. The annual cycle of net flux is also studied in detail, and the observed globally averaged net flux displays an annual cycle that is of similar magnitude and phase to the annual cycle imposed by the influence of sun‐earth distance variations on solar radiation input into the atmosphere. A study of the geographical distribution of the annual variability of the net flux reveals that generally greater than 95% of this variability occurs as a result of the semi and annual cycles that may be forced by the regular variation of solar declination throughout the year. However, the amounts of energy contained in the variance from year to year is large. Thus, we direct radiation modeling studies to these regions and situations where the potential for climate impact due to radiation budget variability is the greatest. The individual components of emitted flux and planetary albedo display expectedly more high‐frequency variability particularly equatorward of 30° latitude governed by weather features and their attendant cloud distributions. Radiative transfer model simulations of the observed budget quantities at the ‘top‐of‐the‐atmosphere’ are good at least for the zonally averaged case. Significant differences exist between the present surface radiation budget calculations and those previously estimated. The differences, largely a result of the exclusion of enhanced absorption in the window region (8–14 μm) in earlier budget calculations, provide some 35 W m−2 more radiant energy into the oceans in the tropics than previously estimated. The validity of this result was verified by using GATE radiation budget measurements.
Wind wave prediction in shallow water: Theory and applications
Authors: Cavaleri Luigi , Rizzoli Paola Malanotte
Published: February 2008

A wind wave forecasting model is described, based upon the ray technique, which is specifically designed for shallow water areas. The model explicitly includes wave generation, refraction, and shoaling, while nonlinear dissipative processes (breaking and bottom friction) are introduced through a suitable parametrization. The forecast is provided at a specified time and target position, in terms of a directional spectrum, from which the one‐dimensional spectrum and the significant wave height are derived. The model has been used to hindcast storms both in shallow water (Northern Adriatic Sea) and in deep water conditions (Tyrrhenian Sea). The results have been compared with local measurements, and the rms error for the significant wave height is between 10 and 20%. A major problem has been found in the correct evaluation of the wind field.
The temperature difference across the cool skin of the ocean
Authors: Paulson C. A. , Simpson J. J.
Published: February 2008

The temperature difference ΔT across the cool skin of the ocean was determined from radiometric measurements of surface brightness temperature and conventional measurements of temperature at a depth of 1 m. Eleven days of measurements were made from the R/P Flip in February 1974 about 800 miles north of Hawaii (35°N, 155°W). The surface brightness temperature was corrected for nonblackness of the surface to obtain an estimate of the true surface temperature. The constant λ in Saunders' (1967a) formula, ΔT = λvQ/kU* was found to be λ = 6.5±0.6, where v is kinematic viscosity, Q the upward heat flux just below, the interface, k the thermal conductivity, and U* the friction velocity. The constant is independent of wind speed for winds ranging from 3 to 11 m/s. The use of subsurface rather than surface temperature in the bulk aerodynamic formulas results in an increase in the sum of the sensible and latent heat fluxes equal to 4‐5% of Q. However, the percentage change in sensible and latent heat fluxes may be much greater. Spectra of surface and subsurface sea temperature exhibit a peak at low frequencies and fall off approximately proportional to ƒ−3/2; with increasing frequency ƒ. The variability of sea surface temperature was caused about equally by the variability of subsurface temperature and the variability of ΔT. Caution should therefore be exercised in the interpretation of radiometric surface temperature measurements as representative of subsurface temperature.
Evidence for 18.6 year MN signal in temperature and drought conditions in North America since AD 1800
Authors: Currie Robert G.
Published: February 2008

Evidence for the 18.6 year lunar nodal MN term in air temperature is found at 30 stations in eastern North America. Since AD 1800 the mean discrepancy in epoch between maxima in temperature and maxima in the Drought Area Index (DAI) for the western United States vis‐a‐vis, the maxima in the MN tide is 0.9 and 0.1 yr, respectively. Also, a cluster of 9 stations in western Canada yields the 18.6 yr term which is out of phase with stations in eastern North America and is indicative of a standing tidal wave in the atmosphere. This suggests that enhanced drought conditions in the western United States are neither ‘recurrent’ nor ‘rhythmic’ on a time scale of 20 yr, but rather periodic with a period of 18.6 yr. Finally, the Rocky Mountain system is seen as an influence for atmospheric tidal phenomena at epochs of maximum in the MN tide as well as for maxima in the temperature records and the DAI.
Measurements of C2–C5 hydrocarbons over the North Atlantic
Authors: Rudolph J. , Ehhalt D. H.
Published: February 2008

Latitudinal distributions of ethane, propane, propene, and acetylene in air over the Atlantic from 48°N to 4°S are reported. In addition, measurements of saturated and unsaturated hydrocarbons (C2–C5) at low latitudes and from 55°N to 80°N are presented. The mixing ratios of ethane, propane, and acetylene were found to vary systematically between a few tenths of a ppb and a few ppb. The alkene and higher alkane (C4 and C5) mixing ratios were found to be in the ppt range. The data are discussed with respect to the source distributions and atmospheric lifetimes of the different hydrocarbons.
On sulfate aerosol formation mechanism and its role in stratospheric pollution
Authors: Kabanov A. S. , Khmelevtsov S. S.
Published: February 2008

While describing the condensation growth of droplets in a homogeneous environment, the authors have come to the conclusion that the condensation process of vapors from small droplets onto large ones is continuously taking place, the concentration of droplets decreasing and the average radius increasing. This process determining the evolution of aerosol, the problem is reduced to finding an asymptotic solution of a set of equations. The solutions are obtained and analyzed. The comparison of the spectra received with the experimental one shows a good qualitative agreement of the theory and the experiment.
Influence of dissolved organic materials on turbid water optical properties and remote‐sensing reflectance
Authors: Witte W. G. , Whitlock C. H. , Harriss R. C. , Usry J. W. , Poole L. R. , Houghton W. M. , Morris W. D. , Gurganus E. A.
Published: February 2008

Results from both field measurements and laboratory simulations are used to assess the effects of dissolved organic materials on turbid‐water optical properties. Upwelled reflectance, attenuation, absorption, and backscatter spectral properties at wavelengths from 450 to 800 nm are examined in relation to water chemistry. From these data it is clear that dissolved organic materials decrease upwelled reflectance from turbid waters. Depending on wavelength, the decrease in reflectance is a nonlinear function of concentration with largest gradients at low carbon concentrations. Large increases in absorption coefficient (particularly at blue wavelengths) are observed with increases in dissolved organic material. Changes in backscatter coefficient are moderate, indicating minimal changes in particle scattering. Upwelled reflectance is highly correlated with two backscatter‐absorption parameters used in certain optical models. Both backscatter‐absorption parameters prove to be nonlinear with dissolved organic material concentration change.
Water drag coefficient of first‐year sea ice
Authors: Langleben M. P.
Published: February 2008

In May 1977, eddy flux measurements of momentum were made with a three‐component ultrasonic current meter in the oceanic boundary layer under a first‐year floe of fast sea ice in Barrow Strait, N.W.T. By using eddy correlation methods, values of horizontal Reynolds' stress were computed from each of 20 data runs of about 1‐hour duration during which the mean current was reasonably steady. A least squares analysis in which water stress was assumed proportional to the square of the mean current yielded a value for the 1‐m water drag coefficient of 1.32×10−3 with a standard deviation of 0.06×10−3. The diameter of the floe was greater than 1 km and its mean thickness was 128 cm, with a standard deviation of 4 cm and a maximum deviation of 7 cm.
Statistical analysis of the tsunamis of the Italian Coasts
Authors: Caputo Michele , Faita G. F.
Published: February 2008

A study of a catalog of 138 tsunamis of the Italian coasts has been made. Intensities of 106 tsunamis has been assigned and cataloged. The statistical analysis of this data fits a density distribution of the form log n = 3.00 ‐ 0.425 I, where n is the number of tsunamis of intensity I per thousand years.
Determination of surface albedos and aerosol extinction characteristics from satellite imagery
Authors: Kaufman Yoram J. , Joseph Joachim H.
Published: February 2008

A procedure is developed for calculation of atmospheric extinction characteristics (optical thickness, scattering height, and single scattering albedo) and surface albedo from radiometric images made at satellite altitudes. The procedure is a fast, computerized method, suitable for high volume processing of satellite imagery data, and thus can be used to map temporal and spatial distribution of aerosol parameters. Based on an analytical approximate solution of the equation of radiative transfer in a plane parallel atmosphere, the procedure is primarily applicable in the 0.4 μm to 0.8 μm wavelength range for solar zenith angles from 10° to 60°, surface albedos between 0.03 to about 0.5, and atmospheric optical thicknesses from 0.2 to 2. If there exists a step‐like change in the surface albedo (e.g., a seashore or river bank or other similar change of terrain), both surface reflectivity and atmospheric optical thickness can be derived from radiance measurements. In this case, the resultant optical thickness is not based on a known surface reflectivity and is essentially independent of the radiometer calibration. A sensitivity study (in Appendix 1) shows that the procedure is highly sensitive to single scattering albedo and optical thickness. This high sensitivity enables one to obtain good results for the single scattering albedo and optical thickness, even with errors in the measured radiances as high as 20%. The resultant optical thickness and single scattering albedo, calculated at a specific wavelength, are not sensitive to aerosol size distribution. Methods for reducing the errors—due to variations in surface albedo, nonuniformity of the aerosol layer (over small distances), and statistical errors of the digital data—are discussed. The procedure is applied to a Landsat image of the African coast where supporting surface measurements are available. Comparison of the resulting atmospherical optical thickness, sea albedo, and land albedo to ground measurements shows that the optical thickness can be retrieved with an error of 0.05. The sea albedo was retrieved within 0.01. The dependence of the procedure on ω0 is investigated.
A relationship between wind stress and wave slope
Authors: Plant William J.
Published: February 2008

Recently published data taken in wind‐wave tanks and on the ocean are shown to yield a growth rate, β, describing the transfer of energy and momentum directly from wind to surface waves, that is well described by the relation β = [(0.04±0.02)u*2ω cos θ]/c2 over a wide range of frequencies. Here u* is air friction velocity, ω is radian wave frequency, c is phase speed, and θ is the angle between wind and waves. Using this form and the requirement that the momentum flux from wind to waves not exceed the wind stress, we show that the total mean‐square, upwind/downwind wave slope between the frequencies g/2πU10 and 20 Hz must be less than ρa/[ρω(0.04±0.02)], where ρa and ρω are air and water densities, g is gravitational acceleration, and U10 is wind speed at 10 m. Measurements of mean square slope both in wavetanks and on the ocean seem to show agreement with this limitation as long as the air‐water interface is well defined. One implication of such a slope limitation is that mean slope spectral densities are limited to values which decrease as the peak frequency of a wind wave spectrum decreases. This may provide an explanation for the observation that mean‐square, dominant wave slopes are typically smaller on the ocean than in wavetanks.
Using sea ice to measure vertical heat flux in the ocean
Authors: McPhee Miles G. , Untersteiner Norbert
Published: February 2008

Results of an experiment performed at drifting ice station FRAM I in the Arctic Ocean northwest of Spitzbergen during March–May 1979 indicate that sensible heat flux from the ocean to the ice cover was less than 2 W m−2. The estimate is based on measurements of temperature gradient, growth rate, and salinity of young sea ice. Uncertainty in the magnitude of the heat flux results more from evidence of horizontal inhomogeneity in the growing ice sheet than from measurement errors.
Sea‐state‐related altitude errors in the SEASAT radar altimeter
Authors: Hayne G. S. , Hanock D. W.
Published: February 2008

For the work reported here, a six‐parameter model waveform is least squares fitted to 10‐s averages of the data from the 63 waveform sampling gates in the SEASAT radar altimeter. One of the fitted parameters is a time‐origin parameter that provides a measure of the position of the actual mean radar waveform relative to the sampling gate set and thus provides a correction to the instrument's altitude measurement. For the data set analyzed this correction appears to vary quadratically as a function of the significant waveheight (SWH). The result to date is that the correction ΔG, in centimeters, which should be added to the surface elevation measurements on the SEASAT geophysical data record (GDR), is given by ΔG = 0.593 SG + 0.476 SG2 where SG is the GDR value for SWH, in meters. The discussion in this paper reviews waveform assumptions built into the SEASAT onboard altitude tracker and subsequent altitude data processing and lists several additional important effects that were not included in that processing but which are incorporated into the SEASAT waveform analysis reported here.
Large‐scale heat exchange and ice production in the central Arctic
Authors: Maykut Gary A.
Published: February 2008

The arctic ice pack is a mixture of ice of many different thicknesses. Ice growth and heat exchange are strongly influenced by thickness, particularly when the ice is thin. For this reason measurements at a particular location do not necessarily represent conditions elsewhere within the region. Large‐scale heat exchange estimates must take into account contributions made by different thicknesses of ice. This requires information on the relative area covered by ice of any given thickness and on how each flux varies with thickness. Strain histories derived from the motions of several buoy and drifting station arrays were combined with climatological data on air temperatures and incoming radiation to estimate time dependent changes in the distribution of ice thickness in the Central Arctic. Thermodynamic ice models were used to determine the dependence of heat exchange and ice production on ice thickness. Large‐scale fluxes were then obtained by summing the area weighted contributions made by each ice thickness category. Differences between the large‐scale fluxes and those based on local measurements over perennial ice were due almost entirely to the effects of young ice less than a meter in thickness. Net annual ice production in areas of thin ice totaled about 1 m when averaged over the entire area of the strain array. In contrast to the very small annual values measured over multiyear ice, large‐scale turbulent heat losses were close to 200 MJ m−2 year−1, similar in magnitude to the net radiation. Absorption of shortwave radiation by summer leads resulted in annual net radiation totals for the region which were more than double those over the ice. Solar energy absorbed in the water played a major role in the mass balance of the ice cover. Intermediate thicknesses (0.2–0.8 m) of young ice, rather than open leads, exerted the greatest influence on ice production, heat input to the atmosphere, and salt input to the ocean. Monthly and annual heat flux totals obtained with different strain histories showed little correlation with the average divergence, suggesting that the variability of the strain field may be more important than the long‐term average of the strain components.
Threshold friction velocities and rupture moduli for crusted desert soils for the input of soil particles into the air
Authors: Gillette Dale A. , Adams John , Muhs Daniel , Kihl Rolf
Published: February 2008

Desert soils having clay crusts, mostly from the Mojave Desert, were tested for threshold friction velocity (the friction velocity at which soil erosion begins) with an open‐bottomed wind tunnel. The soils were also tested for content of clay, water‐soluble material, calcium carbonate, organic material, mineralogy of clay and of salts, soil moisture, modulus of rupture, and crust thickness. If no loose material existed on the soil surface, crusts having modulus of rupture greater than 0.7 bar and crust thickness of 0.7 cm to 0.3 cm were effective in protecting against wind erosion. Disturbed clay crusts having modulus of rupture before disturbance greater than 2 bar with thickness less than 1.9 cm did not experience significant wind erosion. Modulus of rupture was related to composition of soil but was shown to depend mostly on clay content. Soil composition is related to modulus of rupture in an empirical equation.
Winds between San Diego and San Clemente Island
Authors: Dorman Clive E.
Published: February 2008

Dense ship observations off San Diego were used to capture the diurnal and seasonal wind trends. The land breeze regime extends to 40 km off San Diego in the winter, but goes to less than 10 km when averaged for the winter. Significant diurnal variations in wind speed occur in all seasons from the coast to beyond 140 km. Ship observations were averaged over 0.2° of latitude and longitude. These have significant structure that is obscured in other studies based upon 1° averages. Wind speeds decrease by a factor of 2 or more from 140 km offshore to the coast in both the northerly and westerly component. The mean flow has a weak summer southerly component. This is in opposition to earlier studies which indicated northerly mean monthly flow all year. Ship observations were compared to San Diego Airport and San Clemente Island measurements in order to check the accuracy of allowing land measurements to substitute for over water measurements. San Diego winds were found to be very representative of the nearest 10 km of ocean in wind speed and direction on the diurnal and seasonal scales. San Diego would be a good proxy station from which to infer the long‐term near shore meteorlogical conditions. San Clemente Island wind speeds are systematically less than the ship observed wind speeds in the easterly component. But the correspondence between the northerly component at San Clemente and ships is irregular in the diurnal and monthly means. This station could not be used to infer the northerly component without an uncertain and elaborate correction.
Ambient airborne solids concentrations including volcanic ash at Hanford, Washington sampling sites subsequent to the Mount St. Helens eruption
Authors: Sehmel George A.
Published: February 2008

A major eruption of Mount St. Helens occurred on May 18, 1980. Subsequently, airborne solid concentrations were measured as a function of time at two sites within the southern edge of the fallout plume about 211 km east of Mount St. Helens. This ash was a source for investigating area‐wide resuspension. Rain had a variable effect on decreasing airborne concentrations from resuspension. From 0.5 to 1.5 cm of rain were required to significantly reduce airborne solid concentrations through July. For a more aged resuspension source in September, a rain of 2.0 cm had a negligible effect. A monthly average threshold‐wind speed for resuspension was defined as 3.6 m/s. For monthly‐average wind speeds less than the threshold wind speed, monthly‐average airborne concentrations tended to decrease with time. A decrease was recorded between September and October. For this 4‐month time period, the half‐life was on the order of 50 days, corresponding to a weathering rate of 5.1 year−1.
Cross‐equatorial tracer transport in the upper waters of the Pacific Ocean
Authors: Fine Rana A. , Peterson William H. , Rooth Claës G. H. , Östlund H. Göte
Published: February 2008

Tritium samples have been analyzed from several cross‐equatorial transects in the Pacific under the NORPAX and EPOCS programs. Together with earlier sections from the GEOSECS program, they allow description of the equatorial Pacific tritium transient over a period extending between approximately the tenth and the fifteenth year after the major nuclear tests. South of the equator within the upper water layers at temperatures above 16°, an increase of 25–60% in the decay‐corrected tritium concentration is found. A northern hemisphere source for the tritium increase is unequivocally indicated, but the details of the exchange are as yet uncertain. The tritium transient evolution is consistent with recent suggestions that the net cross‐equatorial oceanic heat transport in the Pacific is small on the scale of the global atmospheric heat transport processes. An additional result relevant to the equatorial heat budget is that the tritium data put a lower bound of 16° on the temperature of the water up welling at the equator.
Effect of coupled anthropogenic perturbations on stratospheric ozone
Authors: Wuebbles D. J. , Luther F. M. , Penner J. E.
Published: February 2008

Since 1976 the greatest concern about potential perturbations to stratospheric ozone has been in regard to the atmospheric release of chlorofluorocarbons. Consequently, atmospheric measurements of ozone have usually been compared with model calculations in which only chlorocarbon perturbations are considered. However, in order to compare theoretical calculations with recent measurements of ozone and to project expected changes to atmospheric ozone levels over the next few decades, one must consider the effect from other perturbations as well. In this paper, we consider the coupling between several possible anthropogenic atmospheric perturbations. Namely, we examine the effects of past and possible future increases of chlorocarbons, CO2, N2O, and NOx. The focus of these calculations is on the potential changes in ozone due to chlorocarbon emissions, how other anthropogenic perturbations may have influenced the actual change in ozone over the last decade, and how these perturbations may influence future changes in ozone. Although calculations including future chlorocarbon emissions alone result in significant reductions in ozone, there is very little change in total ozone over the coming decades when other anthropogenic sources are included. Increasing CO2concentrations have the largest offsetting effect on the change in total ozone due to chlorocarbons. Owing to the necessity of considering emissions from a number of trace gases simultaneously, determining expected global‐scale chemical and climatic effects is more complex than was previously recognized.
Island shadows in wave directional spectra
Authors: Pawka S. S.
Published: February 2008

Shadows of individual islands are observed in directional spectra sampled with a high resolution linear array at Torrey Pines Beach, California. A detailed investigation of the spectra indicates that the Channel Islands restrict the wave energy density to certain narrow directional sectors. A deep spectral trough, associated with San Clemente Island, is a predominant feature in the well resolved spectra (wave frequencies ∼0.06–0.15 Hz). Negligible values of energy density in the center of this directional ‘gap’ were consistently observed in the range 0.082–0.114 Hz. Measurable but low gap energy density values are seen in the high and low frequency regimes. Generation of high frequency waves (f≥0.13 Hz) by local winds generally smears the island windowing effects and even creates a spectral peak in a directional sector which is blocked from deep ocean exposure. Several estimation techniques are used in the directional spectrum analysis. These include the Maximum Likelihood Method (MLM) and two methods developed in this work. The two new techniques show significant improvement over the MLM in the definition of gaps in the spectrum. Although none of these methods is considered an ‘Optimal’ estimator for general use, each displays some superior merit in particular directional spectrum estimation problems.