bluuebunny/crossref_metadata_2025 huggingface dataset:
Decade time scale variability of ventilation in the North Atlantic: High‐precision measurements of bomb radiocarbon in banded corals
Authors: Druffel Ellen R. M.
Published: February 2008

The first high‐precision radiocarbon measurements for the upper ocean are presented for banded corals from two sites in the North Atlantic Ocean. The striking dissimilarities between the post‐1950 records at Bermuda in the Sargasso Sea and the Florida Straits in the Gulf Stream illustrate the different mixing processes in the upper ocean at each site. Convective overturn associated with 18° degree water formation during late winter in the northern Sargasso Sea facilitates storage of considerable quantities of bomb radiocarbon at depth, which accounts for the damping of the Δ14C signal at Bermuda during the 1960s. A multibox isopycnal mixing model is used to estimate the ventilation rate of the upper 700 m of the water column in the Sargasso Sea from 1950 to 1983. An inverse model is used; that is, the water mass renewal rate was calculated for the post‐bomb period in order to satisfy the bomb radiocarbon time history in the corals. Sea water radiocarbon measurements made during the GEOSECS (1972–1973) and Transient Tracers in the Ocean (1980–1981) surveys are used to constrain the subsurface radiocarbon values calculated by the model. Results show that the rate of water mass renewal in the Sargasso Sea was high during 1963–1964, decreased during the late 1960s, and remained low during most of the 1970s. The 14C‐derived record of water mass renewal precedes by about 4 years that derived from isopycnal salinity in the Sargasso Sea [Jenkins, 1982], illustrating that the coral 14C record is controlled to a large extent by changes in ocean circulation rather than by atmospheric exchange of CO2.
A model of an Atlantic and Pacific hydrothermal plume
Authors: Speer Kevin G. , Rona Peter A.
Published: February 2008

A turbulent entrainment model of a hydrothermal plume was modified to include the effects of vertical structure in the background temperature and salinity fields. Owing to the stably stratified salinity field in the Pacific, relatively warm, salty water spreads at an equilibrium level, where the plume density equals the ambient density. In contrast, the unstable salinity profile in the Atlantic gives the plume added buoyancy, and it continues to rise to an equilibrium level where it is relatively cool and fresh. These attributes result from the mixing between the plume and the surrounding seawater at each level below the spreading layer. The equilibrium temperature anomaly is not directly proportional to the source strength but depends on the mixing and background salinity gradient. The net entrainment of surrounding seawater is greater in the Atlantic plume model than in the Pacific plume model for the same buoyancy flux. Recent data from the TAG hydrothermal field at 26°N on the Mid‐Atlantic Ridge and data from a vent field on the Endeavor segment of the Juan de Fuca Ridge are compared to model results. The model predicts the penetration height and θ‐S characteristics of the Atlantic plume, and it explains some of the differences between the observed Atlantic and Pacific hydrothermal plumes.
Trace petroliferous organic matter associated with hydrothermal minerals from the Mid‐Atlantic Ridge at the trans‐Atlantic geotraverse 26°N site
Authors: Brault M. , Simoneit B. R. T.
Published: February 2008

Hydrocarbons isolated from hydrothermal anhydrite, chalcopyrite, and sphalerite‐enriched samples from the mid‐Atlantic Ridge exhibit a high degree of thermal maturation, compared to a Fe‐oxide‐enriched sample, as evidenced by the high abundance of low molecular weight n‐alkanes ranging from C14 to C25 with a broad distribution of naphthenes. These trace hydrothermally‐derived petroleums contain some polycyclic aromatic hydrocarbons (PAH) and very low amounts of typical biomarkers (e.g., steroid hydrocarbons, triterpanes). The low levels of biomarkers may be due to removal by hydrothermal conversion to other products (e.g., aromatics) or have not yet formed. The Fe‐oxide‐enriched sample has a lower content of PAH than the other mineral samples; however, benzopyrenes and coronene are present at a significant level, and a series of mature triterpanes is also detectable. The loss of the lower molecular weight PAH in the Fe‐oxide‐enriched sample could be due to dissolution/oxidation processes. The presence of trace levels of petroleum strongly suggests its generation from contemporary organic detritus by hydrothermal activity and subsequent association with the minerals.
Statistics of bicoherence and biphase
Authors: Elgar Steve , Sebert Gloria
Published: February 2008

Statistics of estimates of bicoherence and biphase were obtained from numerical simulations of nonlinear random (harmonic) processes with known true bicoherence and biphase. Expressions for the bias, variance, and probability distributions of estimates of bicoherence and biphase as functions of the true bicoherence and number of degrees of freedom (dof) used in the estimates are presented. The probability distributions are consistent with theoretical distributions derived for the limit of infinite dof and are used to construct confidence limits on estimates of bicoherence and biphase. Maximum likelihood estimates of true values of bicoherence and biphase given observed values are also presented.
Research on erosive properties of cohesive sediments
Authors: Kuijper Cees , Cornelisse John M. , Winterwerp Johan C.
Published: February 2008

To describe the transport of cohesive sediments, it is necessary to specify the erosion flux at the bed. Experiments on the erosion of soft mud layers in a steady flow were performed in the Delft Tidal Flume and in an annular flume. The results were analyzed using the erosion rate function as derived by Parchure and Mehta. It is concluded that a reasonable description is possible. However, the floc erosion rate appeared to be a function of the bed shear stress. In one case the erosion rate function needed to be adjusted slightly in order to obtain agreement between measured and calculated suspension concentrations.
Calibration of a general optical equation for remote sensing of suspended sediments in a moderately turbid estuary
Authors: Stumpf Richard P. , Pennock Jonathan R.
Published: February 2008

A general algorithm for determining suspended sediment concentrations in the surface waters of estuaries has been developed for use with satellite data. The algorithm uses a three‐parameter general optical equation to relate suspended sediment concentrations to water reflectances that have been corrected for sun angle effects, atmospheric path radiance, and tidal excursion. Using data collected by the advanced very high resolution radiometer on five different dates, reflectances were determined using two different methods, one providing maximum correction for haze and the other providing minimum sensitivity to pigments. For both methods, in situ and remotely sensed samples from Delaware Bay acquired within 3.5 hours of each other agreed to within 60% at the 95% confidence level. Pixel and subpixel scale spatial variations and variability associated with in situ measurements produced about 50% of the differences. Chlorophyll concentrations of >50 μg/L produced a discrepancy in the reflectance method that provided the best haze correction. The parameter values may be adjusted to allow for variations in sediment size and pigment variations, allowing application of the calibration to estuaries having optically different suspended sediments.
Experimental study of the evolution of a solitary wave at an abrupt junction
Authors: Losada M. A. , Vidal C. , Medina R.
Published: February 2008

This paper describes physical and numerical experiments that were carried out to investigate the scattering of nonbreaking solitary waves of moderate amplitude on encountering an abrupt discontinuity in depth from h1 to h2. It is shown that in the neighborhood of the step from deeper to shallower depth the wave amplitude undergoes a rapid evolution which depends on the amount of reflection and energy losses and on dispersive and nonlinear wave effects. On the shallower shelf, the wave amplitude reaches a minimum value after the step. It is proposed that the wave characteristics (shape and volume) recorded at this point be used to predict the far field wave evolution on the shelf. From the experimental results an evolution modes diagram is drawn which distinguishes four types of wave evolution on the shelf: (1) fission, (2) fission and peaking of the first soliton, (3) transition, and (4) plunging. The diagram includes lines of constant breaking index ab/h2, where ab is the breaking wave amplitude and h2 is the shelf depth. Following Mei (1985), an energy loss coefficient fe is presented. For large values of a1/(h1–h2), the experimental data conform with the values given by the steady state formula of Daily and Harleman (1966).
A numerical model of mesoscale physical‐biological interactions in the Fram Strait marginal ice zone
Authors: Niebauer H. J. , Smith Walker O.
Published: February 2008

A numerical model of marginal ice zones is presented which includes ice‐atmosphere‐ocean interactions and couples biological processes to the physical dynamics of the ice edge. We have used initial conditions from the Fram Strait in spring when stratification is increasing, nutrient concentrations are high, and solar radiation is increasing, conditions which are found prior to an ice edge phytoplankton bloom. We present three sets of experiments: (1) a standard case (and variations resulting from different initial conditions) with oceanic and ice melt stratification, but no winds or eddies, (2) one with wind forcing and ice cover but no eddies, and (3) cases with cyclonic and anticyclonic eddies under ice cover. In general, stratification within the upper layers accelerates the growth and accumulation of phytoplankton. When the stratification is due to ice melt only, the bloom is horizontally constrained between the ice and the ice edge frontal structure. Maximum primary productivity occurs 7 to 10 days after the introduction of stratification, and chlorophyll reaches a maximum approximately 3 days later. The bloom's biomass is eventually limited by nutrients. Wind‐driven ice edge upwelling alone was ineffective in stimulating phytoplankton growth. However, any wind‐induced horizontal movement of ice either uncovers nutrient‐rich water or advects nutrients into open water, which stimulates phytoplankton growth. When a cyclonic eddy rotates under the ice, a surface divergence results, causing the ice to open in the center, while upwelling at the eddy core injects nutrients into the euphotic zone. Anticyclonic eddies induce downwelling at the eddy's core and upwelling and surface divergence at the outer edges. With the increased irradiance and high nutrient concentrations, phytoplankton biomass within the eddy increases rapidly.
Ice drift and momentum exchange in winter Antarctic pack ice
Authors: Martinson Douglas G. , Wamser Christian
Published: February 2008

This paper uses the Winter Weddell Sea Project 1986, winter Antarctic data set to (1) describe the nature of observed sea ice drift and momentum exchange and (2) determine relevant drag coefficients (linear and quadratic) and parameter values for three formulations of the momentum balance. The large‐scale mean divergence of the ice justifies, with some penalty, use of the steady free drift equation in which the air‐ice stress is balanced by ice‐ocean drag and the Coriolis force. Three forms of the free drift equation are considered: (1) stresses are parameterized with a quadratic drag law, (2) stresses are parameterized with a linear drag law (useful because of its analytically manageable form), and (3) the Coriolis force is ignored (owing to the thin, 0.6‐m ice), so ice speed is proportional to wind speed at a specified angle. All three formulations simulate the observed ice drift with the same degree of accuracy. The linear drag law is an excellent approximation to the quadratic law over a broad range of forcing only when the air‐ice and ice‐water stresses are both parameterized using the linear law (otherwise the ice‐water drag coefficient is a nonconstant function of wind speed). The linear drag coefficient and constant of proportionality relating ice speed to wind speed can both be computed directly from knowledge of the quadratic values. These calculations result in estimates within ≤2% of the optimum fitted values. Because of the ∼95% ice coverage, ice interaction is frequently significant. During such periods, the ice‐water drag coefficient represents an “effective” drag, artificially inflated to include the forces arising from this interaction. We break the ice drift data into 6‐hour nonoverlapping windows to allow isolation of periods of true free drift. Both true drag coefficient values and effective values are then estimated. The effective values show a strong correlation to the 4‐day average large‐scale ice divergence. They also show that the ice‐water stress is typically ∼1/3 the air‐ice stress, indicating a significant role of ice interaction (free drift still provides an excellent parameterization of ice drift but at the expense of neglecting the details of these physics). The optimum quadratic drag coefficient is 1.62×10−3 with turning angle 15.2°; the effective value is 3.22×10−3 with turning angle 18.1°; the linear drag coefficient is 0.80×10−3 with turning angle 18.1°; the effective value is 1.48×10−3 with turning angle 19.6°, and in general, the ice drifts at ∼3% of the wind speed, ∼23° to its left.
Interannual differences of Geosat altimeter heights and sea level: The importance of a datum
Authors: Wyrtki Klaus , Mitchum Gary
Published: February 2008

Sea surface height data from the Geosat altimeter are compared with island sea level data from 18 gauges in the western and central tropical Pacific during December 1986 to November 1987. Care was taken to ensure that the two data sets are referenced to the same mean surface. This was done by requiring that both data sets have a zero mean sea level over the period April 1985 to April 1986. When the annual means are computed at each station in the later time period, we find that the annual mean sea surface height values have drifted away from the corresponding sea level values by as much as 16 cm. Further, the pattern of differences that develop between the two data sets is not random but is spatially coherent with a strong east‐west gradient. These observations illustrate the necessity for sea surface height data to be referred to a well‐defined zero point, a datum, in order to reliably monitor interannual changes in the sea surface topography. Until these differences can be eliminated, it will be necessary to use tide gauge data as benchmarks for the altimeter sea surface height data.
Fluxes through diffusive staircases: A new formulation
Authors: Kelley Dan E.
Published: February 2008

This paper deals with two aspects of the flux law for diffusive convection: (1) the dependence on density ratio, and (2) the dependence on ΔT. Empirical formulations of the dependence of temperature and salinity fluxes on density ratio are developed using published measurements. At high density ratios (Rρ > 4) our temperature fluxes agree with those given by Marmorino and Caldwell's (1976) formulation, but at low density ratios (Rρ < 2.5) our temperature fluxes are smaller by half. However, it is suggested that any formulation of the 4/3 flux law should be used with caution. A simple convection theory implies that fluxes are not proportional to ΔT4/3, as the 4/3 law states, but rather are proportional to ΔT raised to an power closer to 5/4. The theory accurately matches measurements of velocity and heat flux in thermal convection. There are insufficient data to test (or even fully formulate) the theory for diffusive convection, but if the thermal convection results carry over to the diffusive case, then the 4/3 flux law overestimates oceanic fluxes by up to about 30%.
A study of differences between environmental reports by ships in the voluntary observing program and measurements from NOAA buoys
Authors: Wilkerson John C. , Earle Marshall D.
Published: February 2008

Four years of weather observations from ships in the World Meteorological Organization Voluntary Observing Program were compared with common parameters measured simultaneously by NOAA moored buoys when ships were within 100 km of buoy stations. Common parameters were wind speed, wind direction, atmospheric pressure, surface air and sea temperatures, wave height, and wave period. From a data base containing as many as 63,354 pairs of ship‐buoy reports (in the case of wind speed), the analysis provided an overall set of difference statistics as well as separate sets of difference statistics for each of the following data categories to reveal possible correlations: year, season, geographical region, buoy location, and separation between ship and buoy to a distance of 100 km. The results showed little correlation with any of these subcategories. Ship‐reported wind speeds were on average 2–4 kn higher than buoy‐reported winds, with standard deviations of 7–8 kn (1 kn = 0.51 m/s). Mean differences in wind direction of about 7° and standard deviations of direction differences of 45° were typical. Mean differences and standard deviations of differences for the remaining parameters were atmospheric pressure (−0.5 mbar, 4.2 mbar), air temperature (1.1°C, 4.3°C), sea temperature (0.1°C, 3.5°C), wave height (0.1 m, 2.2 m), and wave period (−0.2 s, 2.4 s). Factors responsible for these differences are noted, particularly for surface winds. This analysis represents the first known quantitative comparison of simultaneous observations made by ships and buoys for such a large data base.
Suggestions for the measurement and derivation of fluxes and flux divergences from a satellite
Authors: Wu Man‐Li C.
Published: February 2008

The theoretical studies shown here indicate that the best bands to measure and derive the total outgoing longwave radiation (OLR), surface downward flux (SDF), and cooling rates (CRs) using linear regression are (1) the band between 800 and 1200 cm−1 for OLR, (2) the band between 500 and 660 cm−1 or 660 and 800 cm−1 for SDF, and (3) the band between 660 and 800 cm−1 for CRs. These results are obtained from scatter plots of total fluxes and cooling rates associated with the various bands. The advanced very high resolution radiometer OLR is damped compared with the Nimbus 7 Earth radiation budget (ERB) OLR, which is derived from the broadband, narrow field of view ERB instrument, owing to its use of only one narrow band (centered around the 11‐μm window region) measurement.
Temperature dependence of the charge and aerosol production associated with a breaking wave in a whitecap simulation tank
Authors: Bowyer P. A. , Woolf D. K. , Monahan E. C.
Published: February 2008

The size spectrum of the particles produced by the bursting of bubbles in a laboratory‐produced seawater whitecap, and the total charge carried by these particles, was investigated. The charge was found to increase strongly with water temperature. Production of aerosols of diameter greater than 3 micrometers was found to increase, though less strongly, while the production of smaller aerosols, if anything, decreased with water temperature. These results are consistent with the hypothesis that the charge is carried by a fraction of the larger particles.
Low‐frequency shelf/slope responses induced by localized offshore forcings
Authors: Qiu Bo
Published: February 2008

Using a two‐layer β plane model with bottom friction, we investigated the shelf/slope responses induced by localized offshore forcing sources which (1) propagate in the along‐slope direction and (2) have oscillating amplitudes. The two cases represent typical forcing patterns of cutoff eddy propagations and unstable meanders in western boundary currents. When the localized forcing source propagates in the along‐slope direction, it tends to induce components of bottom‐trapped topographic Rossby waves (TRWs) with a similar cross‐slope structure, and the shelf/slope response depends strongly upon the magnitude of the propagating speed c. In the in viscid limit, maximum response occurs when c is such that the induced bottom‐trapped TRW components may freely cross the slope region. When bottom friction is considered, however, the shelf/slope response due to the bottom‐trapped TRWs is important only in large c value cases. In small c value cases, we found the shelf/slope response is determined by surface‐intensified wave components, whose existence is due to the planetary β effect. For observed warm eddies with c = 3 ∼ 5 cm s−1, the result of the present study suggests that both bottom‐trapped TRWs and surface‐intensified baroclinic waves are significant in determining the shelf/slope response. In cases when the localized forcing source oscillates in amplitude, we found that a localized response peak exists in the shelf/slope region. Along a fixed cross‐slope section this response peak in the frictional case tends to shift offshore as the oscillating period of the forcing source increases. This result is opposed to the inviscid result, which shows that the response peak is independent of the forcing's oscillating period. The result for the frictional case is qualitatively consistent with that observed across the continental rise south of Cape Cod, thus suggesting the importance of bottom friction in determining the shelf/slope response.
Evidence for the influence of wave‐current interaction in a tidal boundary layer
Authors: Green Malcolm O. , Rees Jon M. , Pearson Nick D.
Published: February 2008

Near‐bed velocity profiles were measured in 24‐m water depth off the northeast coast of England. Measurements were made over two complete tidal cycles which spanned the waning stage of a storm. Superimposed on the tidal mean flow were progressively decaying wave‐orbital motions: the data thus span a wide range of relative wave and current energies and so offer an ideal opportunity to test wave‐current boundary layer theory. The magnitude of the tide‐modulated friction velocity, inferred from measured velocity profiles, appeared to decrease concurrently with the near‐bed wave energy, which is consistent with wave‐current theory. Also, the discrepancy between roughness inferred from the measured velocity profiles above the wave boundary layer and the “expected” roughness was greatest when the waves were most energetic. This, too, is consistent with wave‐current theory. The best evidence for a dynamic effect of the waves on the mean flow above the wave boundary layer was the correlation of the roughness discrepancy with the regular tidal variation in the strength of the wave‐orbital velocity relative to the mean flow. A model of the wave‐current boundary layer was used to predict the time‐averaged friction velocity, and the model predictions compared well with the observations with exceptions that, formed two groups. The first group, in which the model predictions were underestimates of the observations, comprised observations from the time of peak observed bed shear stress. A plausible explanation for the discrepancy is that an evolving ripple field and/or near‐bed saltating layer contributed an extra component of roughness that was unaccounted for in the predictions. The second group, in which the model predictions were overestimates of the observations, comprised observations from the times of minimum observed bed shear stress. These bursts also had the lowest observed roughness Reynolds numbers, all of which fell below the critical value for transition to fully rough turbulent flow. Since laboratory measurements imply wave‐current interaction does not occur in the smooth‐turbulent combined flow boundary layer, the predictions of time‐averaged friction velocity were repeated using a smooth‐turbulent pure‐current model. The predictions were significantly improved, thus supporting that contention.
The regional optimization of infrared measurements of sea surface temperature from space
Authors: Minnett P. J.
Published: February 2008

The accuracy with which well‐calibrated satellite infrared radiometers can measure sea surface temperature is limited by the validity of the correction applied for the modification of the electromagnetic radiation before it reaches the radiometer. An accurate numerical line‐by‐line model of the radiative transfer through the atmosphere is used to simulate measurements of the advanced very high resolution radiometer (AVHRR/2) on the NOAA series of near‐polar‐orbiting satellites for conditions of the region of the Greenland, Iceland, and Norwegian Sea. A set of regionally optimized zenith‐angle dependent coefficients for the “split‐window” algorithm is derived and its error characteristics are discussed. While the benefit of using such coefficients is demonstrated, the errors resulting from failing to account properly for seasonal changes in this particular region are shown to be relatively small.
Physical processes affecting the objective determination of near‐surface velocity from satellite data
Authors: Wahl Darrin D. , Simpson James J.
Published: February 2008

A flexible implementation of an objective method for estimating sea surface velocities from remotely sensed sea surface temperature (SST) patterns is given. The method assumes, like previous methods, that the motion of thermal features results from advection. Other near‐surface processes (i.e., diffusion and air‐sea heat exchange), however, can also affect the near‐surface thermal structure. It therefore becomes necessary to determine how these physical processes affect the perceived velocity determined from thermal gradient structure. Models were developed to quantitatively analyze the method's relative sensitivity to the degradation of thermal features due to near‐surface physical processes. The results are used to quantify the attainable accuracy of the method for estimating near‐surface velocity from satellite data.
Observations of shear and vertical stability from a neutrally buoyant float
Authors: Kunze Eric , Williams A. J. , Briscoe Melbourne G.
Published: February 2008

Measurements of 1‐ to 5‐m shear and strain from a neutrally buoyant float are used to examine the statistics and causes of shear instability in a 9‐day record. “Unstable” conditions (defined as VZ/N > 2 where Vz = |Vz|) are due to higher‐than‐average shear rather than lower‐than‐average buoyancy frequency and there are no instances of unstable buoyancy frequency, or overturns, on the ≥0.5‐m spacing of the thermistors. Shear is dominated by upward propagating near‐inertial motions. Unstable events were more frequent when a near‐inertial wave packet occupied the water parcel tracked by the float. Groups of unstable events occur roughly every 5–7 hours at scales <2.5 m and much less often at larger scales. Events typically last 10 min (one buoyancy period) or longer. These time scales appear to be controlled by vertical advection of ∼1‐m fine structure past the float sensors so do not represent the intrinsic time scales of instability. Turbulent and mixing quantities are estimated from these fine‐scale measurements, giving a dissipation rate of ε ∼ (2.3–16) × 10−10 W/kg and an eddy diffusivity of Kρ ∼ 3 × 10−6 m2/s, in agreement with direct microstructure estimates. Therefore the float adequately resolves those quantities needed to estimate turbulent dissipation and could be used to monitor turbulent mixing in the ocean.
On Kuroshio front fluctuations in the East China Sea using satellite and in situ observational data
Authors: Qiu Bo , Toda Takashi , Imasato Norihisa
Published: February 2008

Fluctuations of the Kuroshio front in the East China Sea and their relation to variations of the Kuroshio stream around the Tokara Strait are investigated using consecutive satellite images, sea level data, as well as water temperature records from a Japan Meteorological Agency buoy station and a ferryboat which crosses the Tokara Strait. Meanders of the Kuroshio front with typical horizontal scales of 100 to 150 km and wave periods of 14 to 20 days are found to appear ubiquitously in the East China Sea. The front meanders originate upstream over the continental slope and evolve rapidly, while propagating downstream at speeds of 20 to 26 cm s−1. Downstream southwest of Kyushu, the fully developed meanders sometimes take the form of warm filaments, and when the volume transport of the Kuroshio is large, they may develop into shed‐off warm eddies. Previous observations based on ferryboat temperature records have revealed the repeated northward migration of a clear sea surface temperature (SST) front across the Tokara Strait. It is shown that this northward migration of the SST front corresponds to the passage of the Kuroshio front meanders across the Tokara Strait, and that the unclear southward migration of the SST front is due to the presence of mixed water behind each meander. The Kuroshio front meanders in the East China Sea are further found to be closely related to the north‐southward movement of the entire Kuroshio stream in the Tokara Strait. A lag of about 10 days exists between the time the front meanders reach the Tokara Strait and the Kuroshio stream there shifts to its northernmost position.
Meridional and seasonal variations in the satellite‐sensed fraction of euphotic zone chlorophyll
Authors: Strass Volker H.
Published: February 2008

The key to estimating ocean primary production from satellite color images is to project accurately the total euphotic zone chlorophyll content from the remotely sensed signal, emitted from merely the near‐surface reaches. In situ profiles of chlorophyll fluorescence and solar irradiance (and temperature), collected at different times of the phytoplankton growth season with a towed undulator along a section running from the Azores toward Greenland, are used for simulating satellite measurements. Given by the simulations, the satellite‐sensed fraction of the euphotic zone chlorophyll content accounts for only 7.5% on average, and it varies meridionally and seasonally by several times of its mean value. The major variations are attributed to changes in the chlorophyll vertical distribution, which are related to the succession of growth phases during the phytoplankton seasonal cycle: the onset of the spring bloom, the development of the bloom to full spate, and the transition to oligotrophy. To improve satellite‐based estimates of integral euphotic zone chlorophyll quantities, it is suggested that use be made of the sea surface temperature field as a predictor of the time‐dependent meridional transitions between the different growth phases.
Preliminary investigations on the influence of rain on the production, concentration, and vertical distribution of sea salt aerosol
Authors: Marks Roman
Published: February 2008

During the Humidity Exchange Over the Sea Main Experiment (HEXMAX) in October–November 1986, the vertical profile of a sea salt aerosol measured at 4.5 m, 12 m, and 18.3 m elevations, and its size distribution at 12 m elevation were investigated. Several data sets were collected under conditions of rainfall into the sea. These data indicate that the mass of marine aerosol is dramatically enhanced when the wind speed exceeds about 10 m s−1. The vertical distribution of sea salt aerosol measured under such conditions showed a substantial mass accumulation within a few meters over the sea. With increasing wind speed, a marked shift in the size distribution of sea salt aerosol mass toward smaller particles, as well as a gradual shift toward larger sizes of particles, was observed. This indicates that under rainy and windy weather conditions, the direct splashing of raindrops and the bursting of bubbles produced as a result of drop impact may greatly enhance exchange processes between the air and the sea.
The annual cycle of the eddy momentum flux due to the planetary‐scale Northern Hemisphere 500‐mbar seasonally forced waves
Authors: Lejenäs Harald
Published: February 2008

Thirty years of daily data have been used to estimate the annual cycle of the large‐scale 500‐mbar geopotential height fields. The resulting Fourier coefficients, describing the smooth annual cycle, have been used to study the annual cycle of the planetary‐scale northern hemisphere seasonally forced waves. Monthly mean maps of the first three waves are presented, as well as the annual cycle of the eddy momentum flux caused by these waves. It is shown that, during the winter circulation regime, zonal wave number 2 transports momentum toward the south, while wave numbers 1 and 3 transport momentum toward the north. During the summer circulation regime, the fluxes are weak. It is found that there is a connection between a suddenly increased equatorward momentum flux for zonal wave number 2 in late November and the onset of the winter circulation regime.
The measurement of extractable particulate organic matter at a nonurban area in the northeastern United States
Authors: Lioy Paul J. , Kneip Theodore J. , Daisey Joan M.
Published: February 2008

The concentrations of atmospheric extractable particulate organic matter (EOM) were measured at Sterling Forest, New York and Ringwood, New Jersey during the period 1977 through 1979. The samples were taken on a monthly basis for Sterling Forest and were measured as 3‐day composites at Ringwood. The study indicated there was significant variability in the concentrations measured at these rural sites when compared to New York City, which is located 50 miles (80 km) to the southeast. The highest concentrations measured at the rural sites were for the polar fraction (as identified by acetone extractable organic mass). The wintertime levels of EOM were very low when compared to New York City, indicating the lack of many local sources for space heating. The summertime EOM levels, at the rural sites, however, did show episodic excursions, which appeared to be associated with periods influenced by regional photochemical smog. When compared to data taken at remote locations of the world, the average EOM levels observed in this study were higher. This would be expected because the sites are periodically downwind of major industrial and urban centers.
Comment on “Hy‐wire measurements of atmospheric potential” by R. H. Holzworth
Authors: Markson Ralph
Published: February 2008

Measurement of the temporal variation of the global electrical circuit is becoming of increasing interest to the scientific community. Holzworth (1983) suggests that a tethered balloon at about 500 m over Wallops Island may have recorded variations of the global electrical circuit. This note discussed the general problem of how meteorological processes in the lower atmosphere control the variation of atmospheric potential and thus mask the global signal. It is shown that the reported tethered balloon potential measurements occurred (1) when changes in aerosol number density spectrum would have been expected and (2) when changes in convection may have occurred. These meteorological processes modulate the atmospheric electric field intensity locally. There is no correlation when the curve determined by the UT hourly average of the tethered balloon potentials is correlated with the hourly UT variation of the global circuit as represented by the Carnegie curve. For the abrupt drops in potential that occurred coincident with the breakup of fog or discontinuation of the morning rise in temperature to be due to changes in the global circuit would require more than 50% of the several thousand global thunderstorms to stop abruptly; this is unlikely. Because of the occurrence of fog and convection of hazy air rich in space charge, a coastal region is particularly inappropriate for attempts to measure the global circuit variation. Aside from problems related to location, the excessive voltages reported in the tethered balloon data suggest some problem with the measuring technique itself. These data give potentials at 530 m which are 48% higher than comparable aircraft measurements. Extrapolated to the ionosphere, the tethered balloon potential profiles would generally give ionospheric potentials on the order of 500 kV, which is well beyond the values measured in any other program.
On the chemistry of stratospheric SO2 from volcanic eruptions
Authors: McKeen S. A. , Liu S. C. , Kiang C. S.
Published: February 2008

The April 4, 1982, eruption of El Chichón in southern Mexico introduced several megatons of gaseous sulfur into the stratosphere, mostly as SO2 or H2S. Available kinetic information indicates that H2S is converted to SO2 much faster than SO2 is oxidized to sulfate by homogeneous gas phase reactions. The process by which SO2 is chemically converted to sulfate is not precisely known, and various reaction mechanisms have been proposed. The rate‐limiting step of SO2 oxidation is believed to be reaction with the OH radical to form the HOSO2 radical. Depending on the fate of HOSO2, odd hydrogen may or may not be regenerated in the overall oxidation sequence. A decrease in OH due to volcanic SO2 should be observable through the gaseous species that depend on OH, and in particular SO2 itself. One‐ and two‐dimensional model results are presented that estimate the photochemical effects of the SO2 from the El Chichón volcano under various assumptions of HOSO2 to sulfate conversion. It is found that the chemical lifetime for the volcanic SO2 would be greater than 100 days for a large portion of the cloud if HOSO2 does not regenerate odd hydrogen during conversion to sulfate and if heterogeneous losses of SO2 are not competitive. However, observations of sulfate particle formation and SO2 imply a chemical lifetime of 30–40 days, which is consistent with HOSO2 conversion regenerating odd hydrogen. The implications of this finding for the problem of sulfate formation in the polluted troposphere is briefly reviewed.
The Limb Infrared Monitor of the Stratosphere: Experiment Description, Performance, and Results
Authors: Gille John C. , Russell James M.
Published: February 2008

The Limb Infrared Monitor of the Stratosphere experiment was launched on the NIMBUS 7 spacecraft to test the capabilities of infrared limb scanning radiometry to sound the composition and structure of the middle atmosphere. The instrument, a six channel radiometer, operated from October 25, 1978, to May 28, 1979, returning each day more than 7000 profiles of radiance as a function of vertical position across the limb. These radiances were subsequently inverted to determine temperature, ozone, water vapor, nitric acid, and nitrogen dioxide distributions in the stratosphere and mesosphere. This paper describes the experiment and its results. The measurement requirements are discussed, and critical instrument parameters are identified. Next, the instrument and its laboratory calibration are described. In orbit, its operation was stable and nearly flawless. The operational data reduction involved calibrating the radiances, performing a nonlinear inversion based on the emissivity growth approximation, and mapping the data. The methods of validating the data through simulation, internal checks, and intercomparisons are summarized, and conservative estimates for accuracy and precision are obtained. Temperature accuracy and precision are estimated to be 2 K and ∼0.4 K, respectively. Accuracy of the trace gases is ∼25%, comparable to the estimated accuracy of the in situ comparison data; their precision is ∼0.25 ppmv (O3 and H2O) and 0.2 ppbv (HNO3 and NO2). Examples of the vertical profiles, maps, and cross sections of the data show previously unobserved variations with latitude, altitude, and time. The results demonstrate that infrared limb scanning is an extremely powerful method for sounding the middle atmosphere.
Sulfur dioxide in remote oceanic air: Cloud transport of reactive precursors
Authors: Chatfield Robert B. , Crutzen Paul J.
Published: February 2008

Reactive surface emissions of reduced sulfur gases can produce SO2 in the middle and upper troposphere at the levels of 80±30 pptv measured high over the remote oceans. We present simulations with a two‐dimensional “Staubsauger” or “vacuum cleaner” model that combines a photochemical model with a description of vertical transport of trace species by convective clouds within larger synoptic circulations. Emissions of 20–60 Tg (S)/yr of (CH3)2S, H2S, or CS2, may produce the observed SO2. Roughly equal production rates of SO2 and methane sulfonic acid may be expected. The amount and exact vertical distribution of the SO2 produced remain uncertain: the greatest chemical uncertainties are the reaction yield of SO2 expectable under clean tropospheric conditions and also the liquid‐phase removal of SO2, and the oxidation rate. The amount of upper tropospheric SO2 produced depends substantially on the proximity of strong reduced S sources to regions of active convection. However, the character of the solutions we present is invariably distinctly different from those obtained with one‐ or two‐dimensional models employing the eddy‐diffusion hypothesis. The results of the model point beyond its original conception, and stress the likely importance of the rainy tropical jungles and mid‐latitude industrial regions, since both regions have large sulfur emissions arid frequently active cumulonimbus convection. This process, however, should contribute mainly to upper‐tropospheric SO2. Other chemical implications are that tropospheric OH may depend critically on HOOH levels as well as the hydrocarbon and nitrogen oxide cycles. Cloud transport may play an important role in these cycles. The hydroxyl radical concentration depends as much on assumptions regarding HOOH reaction and transport as it does on NO levels.
High‐resolution frequency analysis of geological time series
Authors: Siddiqui M. M. , Wang Chien‐Chun
Published: February 2008

A method of high‐resolution frequency analysis is applied to three geological time series. It is shown that the characteristic frequencies in these series are almost identical with some of the major characteristic frequencies of the earth's orbital elements and their linear combinations. The analysis supports the Milankovitch orbital theory of long‐term climatic changes.
Synoptic sea ice‐atmosphere interactions in the Chukchi and Beaufort Seas from NIMBUS 5 ESMR data
Authors: Carleton Andrew M.
Published: February 2008

Three case studies are used to evaluate the interactions between individual synoptic events and the sea ice cover of parts of the western Arctic in October 1976. Changes in both ice extent and concentration are assessed quantitatively by using 2‐day averaged passive microwave data from the NIMBUS 5 ESMR (electrically scanning microwave radiometer). These are related to daily 850‐mbar resultant wind patterns for the periods considered. Strong anticyclonic conditions are associated with relatively static surface brightness temperatures (TB) and hence with generally stable ice conditions. Conversely, a quasi‐stationary cyclonic system produces marked TB variations involving rapid changes in ice edge position and ice concentrations. Transient atmospheric (temperature, moisture) fluctuations, associated with the passage of synoptic systems, are found not to be negligible in the interpretation of microwave sea ice TB signatures on short time scales.
Cloud optical thickness feedbacks in the CO2 climate problem
Authors: Somerville Richard C. J. , Remer Lorraine A.
Published: February 2008

A radiative‐convective equilibrium model is developed and applied to study cloud optical thickness feedbacks in the CO2 climate problem. The basic hypothesis is that in the warmer and moister CO2‐rich atmosphere, cloud liquid water content will generally be larger too. For clouds other than thin cirrus the result is to increase the albedo more than to increase the greenhouse effect. Thus the sign of the feedback is negative: cloud optical properties act as a thermostat and alter in such a way as to reduce the surface and tropospheric warming caused by the addition of CO2. This negative feedback can be substantial. When observational estimates of the temperature dependence of cloud liquid water content are employed in the model, the surface temperature change caused by doubling CO2 is reduced by about one half. This result is obtained for global and annual average conditions, no change in cloud amount or altitude, and constant relative humidity. These idealizations, together with other simplifications typical of one‐dimensional radiative‐convective climate models, render the result tentative. Further study of cloud optical property feedbacks is warranted, however, because the climate is apparently so sensitive to them.
Atmospheric methane in the recent and ancient atmospheres: Concentrations, trends, and interhemispheric gradient
Authors: Rasmussen R. A. , Khalil M. A. K.
Published: February 2008

The concentrations of methane in the old and ancient atmospheres of the earth can be deduced by analyzing the air in bubbles embedded in polar ice cores. Upon analyzing some 80 ice core samples from the polar regions we found that the concentration of methane 250 years ago and earlier was only 700 (±30) ppbv, or about 45% of present levels. A rapid and significant increase of atmospheric methane started about 150 years ago. The rate of increase has escalated since then and is about 1.3%/yr at present. We also found that the concentration of methane in the atmosphere 250 years ago and earlier, when methane was not increasing, was 10% (±4%) higher in the Arctic as compared to the Antarctic. This finding is consistent with the expected ratio of about 1.07–1.11 obtained from a global mass balance model and the primarily land‐based natural sources of methane, estimated to be about 280 Tg/yr, which may have been the only sources several hundred years ago, when human activities did not contribute significantly to the global methane cycle.
Determination of cloud parameters from infrared sounder data
Authors: Yeh Hwa‐Young M.
Published: February 2008

A method for remote sensing of cloud parameters by using infrared sounder data has been developed on the basis of the parameterized infrared transfer equation applicable to cloudy atmospheres. The method is utilized for the retrieval of cloud height, amount, and emissivity in the 11‐μm region. Numerical analyses and retrieval experiments have been carried out by using synthetic sounder data for the theoretical study. The sensitivity of the numerical procedures to the measurement errors are also examined. The retrieved results are physically discussed and numerically compared with the model atmospheres. Comparisons reveal that the recovered cloud parameters agree reasonably well with the pre‐assumed values. However, for cases when relatively thin clouds and/or small cloud fractional cover within a field of view are present, the recovered cloud parameters show considerable fluctuations. Experiments on the proposed algorithm are carried out by utilizing High Resolution Infrared Sounder (HIRS/2) data of NOAA 6 and TIROS‐N. Results of experiments are difficult to verify quantitatively, but the retrieved cloud amounts show reasonably good comparisons with the surface reports and GOES satellite images.