bluuebunny/crossref_metadata_2025 huggingface dataset:
Contemporary seismicity, active faulting and seismic hazards of the coast ranges between San Francisco Bay and Healdsburg, California
Authors: Wong Ivan G.
Published: February 2008

Contemporary seismicity in the northern California Coast Ranges from San Francisco Bay to the town of Healdsburg and east of the seismically quiescent North Coast segment of the San Andreas fault is generally confined to the intensely deformed Santa Rosa block relative to the adjacent Sebastopol block. Much of this activity is concentrated along the Rodgers Creek, Healdsburg, Bennett Valley, and Maacama faults. A prominent gap in microseismicity exists along much of the 43 + km‐long Rodgers Creek fault, although paleoseismological evidence suggests that the fault has generated at least three paleoearthquakes of moment magnitude (Mw) 7 or greater during the late Holocene (Budding et al., 1991). Earthquakes in the region are generally confined to upper crustal depths of less than 10–12 km. Right‐lateral strike‐slip faulting on both northwest and north striking faults is currently the primary mode of regional crustal deformation based on observed focal mechanisms, although both reverse faulting, especially in the vicinity of the major Quaternary faults, and normal faulting occur within the region. The tectonic stress field in the region is dominated by north‐northeast to northeast directed compressive stresses. Although the Rodgers Creek fault may pose the highest known level of seismic hazard in the region in the next few decades, abundant geological evidence and the contemporary seismicity suggest that faults such as the Healdsburg, Bennett Valley, and Maacama faults also pose significant hazards because of their potential to generate Mw 6–7 ± earthquakes.
Strain accumulation across the Wasatch Fault near Ogden, Utah
Authors: Savage J. C. , Lisowski M. , Prescott W. H.
Published: February 2008

Deformation of a 70 by 40‐km trilateration network spanning the north trending Wasatch fault near Ogden, Utah, has been monitored from 1972 through 1990. All but nine of the 200 measurements are consistent with deformation that is linear in time. We presume that those nine observations are contaminated by some blunder in making the measurements and that deformation is linear in time. The strain rate over the 1972–1990 interval across a 40‐km‐wide zone west of the Wasatch fault (hanging wall block) is adequately approximated by a 0.04 ± 0.01 μstrain/yr N85°E±5° uniaxial extension. Adequate coverage of the footwall block is available only over the 1981–1990 interval, and the strain rate across a 30‐km‐wide zone there is approximated by a 0.07 ± 0.03 μstrain/yr N20°E±12° uniaxial extension. The observed extension of the hanging wall block in the direction normal to fault strike suggests that the Wasatch fault may be listric; a planar fault would produce a zone of contraction normal to the fault at the surface of the hanging wall block. The component of extension parallel to fault strike observed on the footwall block is unexplained.
Interface inversion using broadside seismic refraction data and three‐dimensional travel time calculations
Authors: Hole J. A. , Clowes R. M. , Ellis R. M.
Published: February 2008

A procedure has been developed to interpret densely sampled broadside seismic refraction data recorded from a large air gun array. First arrival travel times are inverted to find the structure on an interface beneath the shot line. Travel times are calculated for three‐dimensional velocity models using a rapid finite difference algorithm, adapted to allow variable sampling of the model and the determination of rays. A simple inversion parameterization eliminates the need for matrix inversion. The complete inversion procedure is computationally rapid yet allows the determination of detailed three‐dimensional structure. Broadside refraction data recorded in the Queen Charlotte Basin, offshore western Canada, during a multichannel reflection experiment are used to demonstrate the procedure. The data are inverted for the basement interface beneath the shot line, defining a rapidly varying thickness of sedimentary basin fill. The results of the inversion stimulate a reinterpretation of the reflection data and identify a new major basement fault. Structure out of the plane of the reflection section is determined, including the strike of the fault and other nearby features.
Application of continuum models to deformation of the Aleutian Island Arc
Authors: Geist Eric L. , Scholl David W.
Published: February 2008

Continuum models were constructed to describe large‐scale deformation of the Aleutian Island Arc over the past 5 m.y. These models consider the island arc as a continuum in the horizontal plane with the velocity boundary condition at the Pacific edge stated as a fraction of Pacific plate convergence transferred to the arc. First, a simple model of uniformly distributed strain is formulated to illustrate the mechanics of continuous deformation. Lineaments along the arc massif rotated about a vertical axis are matched by small‐element rotation calculated from the model. However, this model does not predict across‐arc variations in deformation and produces an unrealistic amount of crustal thickening after 5 m.y. A physically more meaningful model of deformation is the thin viscous sheet model based on averages of stress and rheology throughout the lithosphere. The amount of motion transferred from the Pacific plate to the arc is constrained by the rotated lineaments, while the effective stress‐strain exponent (n) and the ability the lithosphere has to sustain crustal thickness contrasts (the Argand number) are independent variables. Primarily, bathymetry, earthquake focal mechanisms, and styles of faulting are used to evaluate the models. The preferred model is one where the amount of motion transferred from the Pacific plate is greater in an arc‐parallel direction than in an arc‐normal direction, producing stresses consistent with strike‐slip faulting at the far western end of the arc and tensional stresses consistent with transverse normal faulting elsewhere in the arc massif. This model agrees with observations of slip vectors by Ekström and Engdahl (1989), who conclude that a portion of the arc‐parallel component of relative plate motion is taken up in the overriding plate. This model implies that compressive stress transferred to the arc is small in comparison to along‐arc shear stress and that stresses conducive to strikeslip faulting are prevalent throughout the arc.
Earthquake prediction and its optimization
Authors: Molchan G. M. , Kagan Y. Y.
Published: February 2008

This paper continues the work by Molchan (1990, 1991b), who has considered earthquake prediction as a problem of the optimization of a certain loss function γ. Function γ is defined by specific social, economic, and geophysical goals. This problem can be fully solved for the loss function γ dependent on only two parameters: fraction of alarm time, τ, and fraction of failures to predict, ν. For such a loss function the tasks of geophysicists and decision makers are clearly denned and can be separated; the requirements of the prediction algorithm can be completely formulated in terms of hazard function. We also consider a more complex model of the loss function, introducing a finite number of various alarms. For each of these alarms, γ depends on three parameters; in addition to τ and ν, we take into account the total number of alarms, λ. For this model we find strategies which optimize the losses for each time unit (locally optimal). Contrary to the simple case of γ(τ, ν), such strategies may not be optimal globally (for the entire time interval). We determine the conditions under which the locally optimal strategy becomes globally optimal. We illustrate our results using the model of a short‐term earthquake prediction for central California. We emphasize that for this complex case, the tasks of geophysicists and decision makers in prediction are intertwined. Prediction and mitigation of many other natural disasters may benefit from the alert strategies discussed here.
The Aegir Ridge: Structure of an extinct spreading axis
Authors: Uenzelmann‐Neben Gabriele , Jokat Wilfried , Miller Heinz , Steinmetz Stefan
Published: February 2008

In 1988 a reflection seismic survey was carried out by the Alfred‐Wegener‐Institute for Polar and Marine Research to study structure and development of the Aegir Ridge, an extinct spreading axis in the Norway Basin. A number of volcanolike structures were detected in the central ridge. The emerging lava flows dip away from their source in ridge strike. Perpendicular to ridge strike, we observed lava flows dipping towards the ridge center. This pattern might represent a more general flow pattern at mid‐ocean ridges. After spreading ceased, sedimentation resulted in the deposition of 800 ms two‐way time (TWT) to 1300 ms TWT (about 900–1400 m) sediments in the central ridge. Distribution of the sediments indicate subsidence of the central ridge probably due to cooling after termination of spreading. This subsidence started no later than late Oligocene or early Miocene. We detected an area where migration of a fluid phase led to obstruction of the sedimentary layering and the formation of mounds and faults at the ocean bottom. Several sources for the fluid phase are discussed.
Hypocenter determination in strongly heterogeneous Earth models using the shortest path method
Authors: Moser T. J. , van Eck T. , Nolet G.
Published: February 2008

The shortest path method [Moser, 1991] for the calculation of seismic ray paths and travel times along them can be applied directly in the hypocenter location method proposed by Tarantola and Valette [1982]. It uses the analogy between seismic rays in the Earth and shortest paths in networks to construct first arrival times from one point to all other points of a three‐dimensional grid simultaneously in a fast, robust way, in Earth models of arbitrary complexity. Doing this for all stations of a seismic array, one can find the hypocenter location by minimizing the difference between the observed and the calculated travel times at the stations over the three‐dimensional grid. The concept of probability density functions allows then for a fully nonlinear examination of the uncertainties in the hypocenter location, due to uncertainties in the travel time data, numerical errors in the calculated travel times and, to a limited extent, incomplete knowledge about the Earth model. The result is a three‐dimensional contour map of regions of equal confidence for the earthquake location. The method becomes especially attractive when more than one event recorded by the same array is studied, because the calculation of the travel times, which is relatively the most time consuming operation, has to be done only once. The method is applied on the location of an event that occurred on January 18, 1989, in Israel.
Descriptive oceanography during the Frontal Air‐Sea Interaction Experiment: Medium‐ to large‐scale variability
Authors: Halliwell George R. , Cornillon Peter , Brink Kenneth H. , Pollard Raymond T. , Evans David L. , Regier Lloyd A. , Toole John M. , Schmitt Raymond W.
Published: February 2008

Medium‐ and large‐scale oceanographic variability in the Sargasso Sea is examined during the Frontal Air‐Sea Interaction Experiment (FASINEX), focusing primarily on processes that influence the formation of subtropical fronts. From Fall to Spring the mean meridional gradient of meridional Ekman transport in the Subtropical Convergence Zone (STCZ) enhances the meridional sea surface temperature (Ts) gradients between 26° and 32°N. In the presence of this enhanced mean gradient, baroclinic eddies with zonal wavelengths of ≈800 km and periods of ≈200 days exert the dominant influence on the formation of subtropical fronts at medium and large scales. These eddies generate westward propagating Ts anomaly features with the same dominant wavelengths and periods. They are confined between 26° and 32°N and have amplitudes that occasionally exceed ±1°C. Ts fronts tend to be found within bands ≈200 km wide that roughly follow the periphery of these anomaly features. Deformation in the horizontal eddy current field is primarily responsible for the existence of these frontal bands. The migration of the strong front originally bracketed by the FASINEX moored array was related to the westward propagation of the larger‐scale eddy/anomaly/frontal‐band pattern. The moored array was located within a warm‐anomaly feature during most of the experiment, which produced exceptionally warm conditions in the upper ocean. These anomalies are confined between 26° and 32°N, not only because the relatively large seasonal mean Tsy there allows horizontal eddy currents to force strong anomalies, but also because the baroclinic eddies with wavelengths of ≈800 km and periods of ≈200 days are confined to the STCZ. Large meridional variability exists in many properties of the eddy field, much of which can be traced to the influence of the Sargasso Sea mean current field on eddy variability.
Solitonlike solutions from the potential vorticity equation over topography
Authors: Nakamoto Shoichiro , Liu Juping , Kirwan A. D.
Published: February 2008

Using a general barotropic potential vorticity model that includes the time rate of change of the topographic vorticity, solitonlike solutions over variable bottom topography are obtained. To lowest order, the solution is the classic topographic wave. The solvability condition for the next order yields solitonlike solutions. The scaling regime for these solutions applies to topography steeper than that used in quasi‐geostrophic potential vorticity models of solitons.
Azimuth smearing in synthetic aperture radar ocean image spectra from the Norwegian Continental Shelf Experiment of 1988
Authors: Johnsen H. , Høgda K. A. , Guneriussen T. , Pedersen J. P.
Published: February 2008

Along‐track resolution loss in synthetic aperture radar ocean images is investigated using airborne C band data collected at different altitudes. A method is developed for qualifying and quantifying the amount of smearing. The smearing can be described as a low‐pass‐filtering process acting on the image spectra even in a nonlinear region of imaging. The dependency on the ratio of range to platform velocity and the radar incidence angle is presented. An intrinsic value for the subresolution velocity spread (i.e., the rms facet velocity) is estimated to be in the region σu = 0.59–0.73 m/s for the measurements available on March 11, 1988, with significant wave height ≈ 4 m and wind speed ≈ 8 m/s. These values for σu allow a conversion of the smearing to ERS 1 geometry giving a spatial smearing σx in the range 68–84 m which corresponds to a resolution varying between 300 and 370 m in the along‐track direction.
Zooplankton community pattern associated with a California Current cold filament
Authors: Mackas David L. , Washburn Libe , Smith Sharon L.
Published: February 2008

In July 1988 we sampled upper layer zooplankton distributions in and around a major cold filament located off Point Arena, California. Average zooplankton biomass levels declined inshore to offshore, but relatively high levels extended seaward along the cool side of the filament jet. A series of transverse station lines shows strong shifts in community composition across the axis of the filament. The cross‐filament compositional sequence was recognizably similar along each line, giving an impression (supported by cluster analysis and along‐flow versus cross‐flow spatial autocorrelation) of banding parallel to the filament axis. The “standard” sequence was characterized by local maxima of Dolioletta gegenbauri in nonfilament waters to the south and east, Euphausia pacifica along the southeast margin of the filament, Eucalanus californicus and euphausiid larvae within the cool core of the filament and extending partway across the strong seaward jet on the north and west margin of the filament, and heteropod larvae, chaetognaths, Dolioletta, and a mixture of small copepods (including several with southern and offshore faunal affinities) along the warm side of the jet and extending into nonfilament waters to the north and west. A “core” group of samples characterized by high abundance of Eucalanus matched the trajectories of drifters released at the upstream end of the filament. Both crossed geopotential anomaly contours (to larger Ф) as they moved out the filament, suggesting a cross‐jet component of motion.
Statistical properties of near‐surface flow in the California Coastal Transition Zone
Authors: Brink K. H. , Beardsley R. C. , Niiler P. P. , Abbott M. , Huyer A. , Ramp S. , Stanton T. , Stuart D.
Published: February 2008

During the summers of 1987 and 1988, 77 near‐surface satellite‐tracked drifters were deployed in or near cold filaments near Point Arena, California (39°N), and tracked for up to 6 months as part of the Coastal Transition Zone (CTZ) program. The drifters had large drogues centered at 15 m, and the resulting drifter trajectory data set has been analyzed in terms of its Eulerian and Lagrangian statistics. The CTZ drifter results show that the California Current can be characterized in summer and fall as a meandering coherent jet which on average flows southward to at least 30°N, the southern end of the study domain. From 39°N south to about 33°N, the typical core velocities are of O(50 cm s−1) and the current meanders have alongshore wavelengths of O (300 km) and onshore‐offshore amplitude of O(100–200 km). The lateral movement of this jet leads to large eddy kinetic energies and large eddy diffusivities, especially north of 36°N. The initial onshore‐offshore component of diffusivity is always greater than the alongshore component in the study domain, but at the southern end, the eddy diffusivity is more isotropic, with scalar single particle diffusivity (Kxx + Kyy) of O(8 × 107 cm2 s−1). The eddy diffusivity increases with increasing eddy energy. Finally, a simple volume budget for the 1988 filament observed near 37°N off Point Arena suggests that subduction can occur in a filament at an average rate of O (10 m d−1) some 200 km offshore, thus allowing the cold water initially in the filament core to sink below the warmer ambient water by the time the surface velocity core has turned back onshore. This process explains why satellite temperature and color imagery tend to “see” only flow proceeding offshore.
A comparison of observed and modeled sea surface topographic time series near the New England seamounts
Authors: Hallock Zachariah R. , Teague William J. , Thompson J. Dana
Published: February 2008

Yearlong data records from four arrays of inverted echo sounders (IES) equipped with pressure sensors from the northwest Atlantic and 2‐year records from a two‐layer, primitive‐equation numerical model of this region (including a prescribed deep western boundary current) are compared. Standard deviations of barotropic and total sea surface topographic variability and the correlations between them are examined as a function of horizontal position. Variances contained in three spectral bands (secular, longer than 150 days; mesoscale, 20–150 days; and high frequency 2–20 days) are also examined. The eastward penetration scale of modeled Gulf Stream variability shows a significant improvement over a previous comparison (Hallock et al., 1989). Standard deviations of observed sea surface height components compare favorably with those derived from model output, with maxima of about 30 cm (10 cm for the barotropic contribution). High correlations (0.6–0.8) between surface height and the barotropic component are found for both model and observations. Spectral shape is dominated by the temporal mesoscale east of the New England Seamounts for both observed and modeled variability. West of the seamounts, the secular (low frequency) band becomes more important, particularly for the surface height variability; this result is more pronounced for model output. Gulf Stream geostrophic current direction statistics from IES dynamic heights compare favorably with those derived from model dynamic heights upstream and downstream of the seamounts.
Carbon and oxygen isotope time series from an 18‐year Caribbean reef coral
Authors: Winter Amos , Goenaga Carlos , Maul George A.
Published: February 2008

Colonies of Montastrea annularis live near La Parguera, Puerto Rico, and may be 700 years old. Time series from 1964 to 1982 of δ13C and δ18O from a continuous core of these corals are compared to an adjacent environmental record. At the intraannual level, δ18O correlates well with water temperature. Changes in the amplitude of the δ18O signal between 1967 and 1976 are attributed to sampling frequency but may be also due to environmental changes such as salinity. Average annual δ18O, δ13C and sea surface temperature show similar trends for the period from 1964 to 1982 but especially from 1969 onwards. Changes in average annual values during this time interval are most likely due to water mass changes brought about by interannual variability of the North Atlantic circulation. Since water temperatures at La Parguera are representative of changes occurring in the wider Caribbean, the isotope record from La Parguera corals could be used as a proxy for large‐scale environmental changes beyond the historical record through the Little Ice Age.
Focusing of synthetic aperture radar ocean images with long integration times
Authors: Kasilingam Dayalan P. , Hayt David W. , Shemdin Omar H.
Published: February 2008

Synthetic aperture radar (SAR) images obtained in the SAR and X Band Ocean Nonlinearities: Chesapeake Light Tower (SAXON:CLT) experiment are processed with long integration times (6 s) and analyzed to study the effects of focusing. Two images with near‐azimuth‐traveling waves were chosen for the study. The first image consists of relatively short wavelength wind waves traveling in the same general direction as the aircraft. The second image consists of a long Atlantic swell traveling in the opposite direction to the aircraft. At these long integration times the image spectral intensities are found to be sensitive to the focus setting. The spectral intensity at the optimum focus is 400% of that at zero focus for the first image and 167% for the second image. The focusing curves for both images agree well with those predicted by a model developed by several groups and referred to here as the “consensus” model. This model predicts an optimum focus setting that is equal to one half of the effective phase speed of the dominant wave in the azimuth direction. The velocity bunching model underpredicts the optimum focus setting significantly. The study concludes that in long‐integration‐time SAR processing of surface waves, such as the spotlight mode, the image contrast is sensitively dependent on the focus setting and that the optimum focus setting is given by one half of the effective phase speed of the dominant surface wave.
Mesoscale flow and thermohaline structure around Fieberling seamount
Authors: Roden Gunnar I.
Published: February 2008

The circulation and thermohaline structure around Fieberling and the three neighboring seamounts to the ESE are examined on the basis of high‐resolution observations in August 1989. In the upper layers, the primary interaction is with well‐defined intrusions of water of subtropical and subarctic origin, linked to the outer boundary of a southward meandering California current. The effects of flow‐topography interaction are complex and vary with depth. At the level of Fieberling's top, about 450 m, the impinging subtropical flow is deflected anticyclonically, and several eddies are generated. Uplift of isopycnals suggestive of upwelling is observed above the tops of all four seamounts. The height of the upwelling cones varies between 120 and 240 m, depending upon background stratification, and their axes are sometimes tilted, apparently by shear of the large‐scale flow. Strong subsurface jets, 10–20 km wide and 500–1000 m thick, with speeds up to 30 cm/s, have been found in the vicinity of the seamounts. In the lower layers the primary interaction is with large‐scale flow from the southeast. The flow is deflected anticyclonically around the seamount group as a whole, with individual branches of this flow passing through the larger gaps between seamounts. The observations are compared with simple models of subinertial flow past individual and multiple seamounts. Though suggestive in predicting some of the observed features, the models need further development based on less restrictive assumptions on the impinging mean flow and the ambient density stratification.
A two‐dimensional model of boundary mixing
Authors: Salmon Haydee , Killworth Peter D. , Blundell Jeffrey R.
Published: February 2008

The steady flow in and near a turbulent boundary layer on a sloping boundary is considered, for a nonrotating stratified fluid. It is shown that the effect of nonuniform stratification in the interior (i.e., away from the turbulent layer) is to induce a convergent‐divergent flow in the boundary layer which results in an inflow or outflow to the interior. This inflow‐outflow acts in a divergent‐convergent manner on the interior isopycnals. Use of a filling‐box argument for the slow time variation of the interior then produces an approximate expression for an effective interior vertical diffusivity. The parameter dependence of this diffusivity is very strong; however, with realistic geophysical values (subject to the omission of rotation), e.g., a mixed layer depth of 50 m, Munk's canonical value of 10−4 m2 s−1 can easily be achieved. This work thus supports the view that boundary mixing is likely to be an important process in setting the vertical density profile in the ocean.
Airborne observations of thermal mesoscale circulations in the coastal marine boundary layer
Authors: Tjernström Michael
Published: February 2008

Detailed observations obtained from airborne meteorological measurements in an area along the Baltic coast in the southeast of Sweden are presented. The measurements were taken during late spring/early summer when the water in the Baltic is generally cool compared to typical daytime land surface temperatures which generated significant surface temperature contrasts between land and water. The measurements show the coastal marine boundary layer to be very far from the homogeneity often assumed in numerical models. The cases presented focus mainly on mesoscale circulations driven or modified by this temperature contrast and related turbulence structure such as thermal jets and sea breeze circulations and show a high degree of temporal as well as small‐scale spatial variability. Even though the synoptic scale wind direction in this area is highly variable, due to traveling mid‐latitude cyclones, the surface temperature patterns show great consistency from day to day, with the coldest water always being along the coast with a pronounced minimum localized at the southeastern part of the coastline. It is not clear to what extent the sea surface temperature inhomogeneities are responsible for some of the observed small‐scale variability, nor is it clear if they are results of ocean processes alone or are interacting in any significant way with the marine boundary layer close to the coast.
A comparison of sea ice parameters computed from advanced very high resolution radiometer and Landsat satellite imagery and from airborne passive microwave radiometry
Authors: Emery W. J. , Radebaugh M. , Fowler C. W. , Cavalieri D. , Steffen K.
Published: February 2008

The advanced very high resolution radiometer (AVHRR), flying on the NOAA polar‐orbiting weather satellites, can be used to map both sea ice concentration and ice edge, under cloud‐free conditions. In order to evaluate the accuracy and reliability of these AVHRR ice parameters, we have compared AVHRR‐derived sea ice parameters from the Bering Sea with those computed from nearly coincident (within 6 hours) Landsat multispectral scanner (MSS) imagery and from the aircraft multichannel microwave radiometer (AMMR) flown on the NASA DC‐8. The higher spatial and spectral resolutions of the Landsat data make them appropriate to use as a reference for the AVHRR inferred sea ice parameters while the lower‐altitude aircraft microwave sensor also provides a good source of comparison data. Both the AVHRR near‐infrared (channel 2) and thermal infrared (channel 4) images were used to compute ice concentration. Mean ice concentration differences between the channel 2 AVHRR and Landsat MSS data (Landsat‐AVHRR) ranged from −0.8 to 1.8% with a mean value of 0.5%. Root‐mean‐square (rms) differences ranged from 6.8 to 17.7%. Mean differences were larger for the channel 4 AVHRR ice concentrations ranging from −2.2 to 8.4% with rms differences from 8.6 to 26.8%. Mean differences between AVHRR channel 2 concentrations and the AMMR data (AMMR‐AVHRR) ranged from −19.7 to 18.9% while rms values went from 17.0 to 44.8%. Mean ice edge differences between the Landsat and AVHRR images were 1.8 km for channel 2 and 2.9 km for channel 4 with rms differences of 3.2 km and 4.4 km, respectively. The AVHRR ice edge was south and west of the Landsat edge.
Microbial populations in surface films: Amino acid dynamics in nearshore and offshore waters off southern California
Authors: Carlucci A. F. , Wolgast D. M. , Craven D. B.
Published: February 2008

Microbial biomass and utilization (incorporation plus respiration) of dissolved free amino acids (DFAA) were studied in sea surface films or microlayers in nearshore and offshore waters off the coast of southern California during 1988 (September) and 1989 (October). Microbial biomass (bacterial numbers via cell counts and total microbial biomass via adenosine triphosphate concentrations), DFAA, and dissolved combined amino acids (DCAA) were always enriched in films compared with subsurface waters, with enrichment factors (ratio of microlayer value compared to 10‐cm control value) often exceeding those measured previously in microlayers from diverse Atlantic and Pacific coastal and island environments. Higher enrichment factors were generally obtained for offshore stations than for nearshore sites. Glutamic acid utilization was greater in microlayers than in control waters at 9 of 13 stations. At those sites where higher utilization occurred in the 10‐cm waters, the microbial populations were highly active and had been subjected to substantial wind mixing prior to sampling. Glutamic acid concentrations were increased in subsurface waters at these sites relative to other stations, apparently by the input of dissolved film constituents. Calculated turnover times were longer for films than for 10‐cm waters, in large pan because of the substantially larger glutamic acid pools in the films. Individual amino acids were not enriched in films compared with 10‐cm waters to the same degree in both the DFAA and DCAA. The relative levels of the individual amino acids in the free and combined pools may have been influenced by their differential production or preferential utilization.
A wave tank study of the dependence of X band cross sections on wind speed and water temperature
Authors: Keller Mary Ruth , Keller William C. , Plant William J.
Published: February 2008

Measurements of normalized radar cross sections of wind‐generated waves were made at X band for both vertical and horizontal polarization for incidence angles of 10°, 28°, 48°, and 68°. The study, conducted in the Naval Research Laboratory wind‐wave facility, sought to measure effects on the backscatter of varying water temperature, wind speed, and wind stress. The cross‐section measurements were averaged for 2.13 min simultaneously with wind speed and wind stress. Air and water temperature were measured periodically with mercury thermometers. The results were compared with the empirical model functions developed for the Seasat‐A satellite scatterometer, SASS I and SASS II, and with the physically based models of Burden and Vesecky, Plant, and Donelan and Pierson. In order to use the SASS I and SASS II models for these comparisons, differences between Ku and X bands were assumed to be small; where possible, the other models were evaluated at X band. It was found that none of the models was consistently accurate at all wind speeds, incidence angles, and polarizations. Part of the inconsistency can be assigned to the fact that the models were developed for open ocean conditions with much higher sea states. However, Plant's model can easily be adjusted to account for this effect by using a relationship between mean squared slope and wind stress appropriate for tank conditions. When this was done, the model did fit the data better but the improvement was not dramatic. This indicates that inaccuracies in the models are probably due to other factors as well. When plotted versus 19.5‐m winds on a log‐log scale, the measured cross sections do not fall on straight lines. Thus a power law dependence of cross section on wind speed is not a good representation of that relationship over our whole wind speed range. The data exhibit large variations at low wind speeds, however, which are not related to system noise. This may indicate that the statistics of backscatter depend markedly on wind speed. When these low wind speed data were omitted, a power law was found to fit the remaining data rather well. Although the water temperature was varied from 9°C to 36°C when the measurements were made at a 48° incidence angle, no temperature dependence was detectable above the low‐wind‐speed variability. The wave tank data compare well enough with 10 GHz, 3.0 cm (X band) aircraft measurements, and with the 14.6 GHz, 2.1 cm (Ku band) satellite data used in the SASS II model to cast doubt on the hypothesis that cross section depends on antenna altitude.
Simulation of the 1979 spring bloom in the Mid‐Atlantic Bight: A coupled physical/biological/optical model
Authors: Gregg Watson W. , Walsh John J.
Published: February 2008

A coupled physical/biological/optical model was developed to investigate the causes of phytoplankton variability in the spring 1979 Mid‐Atlantic Bight (MAB) as observed in Coastal Zone Color Scanner (CZCS) imagery, and to estimate the magnitude and variability of primary production. The model incorporated advection, mixing, sinking, growth as a function of light, temperature, and nutrient availability, and death as a function of ingestion. These variables were assumed to determine the large‐scale, low‐frequency variability of phytoplankton distributions. The model also contained two phytoplankton groups, netplankton and nanoplankton, which differed in maximum growth rate, sinking rate, and specific light absorption. The model produced chlorophyll concentrations within the first attenuation depth within 1 standard deviation of CZCS imagery on large scale (i.e., over regions about 50 km in width). This suggested the model represented the physical/biological coupling often observed in imagery. The two phytoplankton groups used in the model were initialized to equal distributions throughout the model domain and organized in the course of the model run into distributions corresponding to long‐term observations in the MAB; netplankton dominated the coast and nanoplankton dominated the slope. This suggested that the model incorporated the mechanisms causing these distributions in the real ocean, namely, the interaction between mixing, differential growth rates, and differential sinking rates. Finally, primary production estimates were within reasonable agreement with those measured in situ, suggesting the applicability of the model in estimating regional‐scale primary production.
Differences in global data sets of atmospheric and surface parameters and their impact on outgoing longwave radiation and surface downward flux calculations
Authors: Wu Man Li C. , Chang Lihsiung Aron
Published: February 2008

The effect of clouds on the computation of longwave radiation budget parameters is studied using two sets of cloud fields that are obtained from two different satellite systems using two different retrieval schemes: the High Resolution Infrared Sounder 2 (HIRS2)/Microwave Sounding Unit (MSU) retrievals at Goddard Laboratory for Atmospheres (GLA) and the International Satellite Cloud Climatology Project (ISCCP) products at Goddard Institute for Space Studies. The 60% global mean coverage from the ISCCP‐produced cloud amount is much larger than the 43% global mean coverage from the HIRS2‐retrieved cloud amount. Despite this fact, the ISCCP‐derived outgoing longwave radiation (OLR) is very close to the HIRS2‐derived OLR; the global mean OLR difference between the two data sources is −2.6 W m−2, with a standard deviation of 7 W m−2. The small difference is due to the higher cloud‐top pressure obtained in the ISCCP data, which tends to counterbalance the differences in coverage between the ISCCP and HIRS2 data sets. However, the produced surface downward flux using the ISCCP‐derived cloud fields is much larger than that produced from HIRS2 (the global mean difference is around 11.7 W m−2, with a standard deviation of 13 W m−2), reflecting the differences in cloud coverage of the two data sets. The effect of temperature‐humidity fields on the computation of longwave radiation budget parameters is studied using five sets of temperature‐humidity fields produced at different agencies which use different retrieval systems/assimilation systems (HIRS2 retrievals at GLA, TIROS Operational Vertical Sounder retrievals at the National Environmental Satellite Data Information Service, European Centre for Medium‐range Weather Forecasts assimilation, National Meteorological Center assimilation, and GLA assimilation). Despite all differences found in the geophysical parameters, the derived OLR fields are close to each other. The global mean differences among these five OLRs vary from 0.28 to 4.4 W m−2 with a standard deviation ranging from 4.2 to 7 W m −2. However, large differences are found in the computation of surface downward flux. The global mean differences vary from 3.5 to 19.4 W m−2, with standard deviations ranging from 12.3 to 20.6 W m−2. Most discrepancies in the OLR fields using different cloud fields and geophysical parameters are less than 10 W m−2, which is within the accuracy of current satellite techniques. The discrepancies in the surface downward flux are much larger than 10 W m−2.
Conductivity and electric field variations with altitude in the stratosphere
Authors: Holzworth Robert H.
Published: February 2008

Electric field and conductivity measurements were made in the altitude range from 10 to 27 km during the Electrodynamics of the Middle Atmosphere superpressure balloon experiment in 1983 and 1984. These balloons primarily floated at a constant altitude of 26 km, but due to the eventual loss of superpressure near the end of each flight, daily altutide variations at sunset and sunrise occurred. This paper presents electric field, conductivity and derived current density data from the two EMA flights which underwent the longest periods of this daily altitude variation. This includes data from 18 days in late 1983 and early 1984 when the balloons were between longitudes of 50° and 100°E and between magnetic L values of 4.3 and 9.5 in the southern hemisphere. The average conductivity for all the data is well represented by the fit to the EMA6 flight where <σ(Z)> = (1.8±0.2)×10−13 exp(z/7.5) S/m and Z is the altitude in kilometers. The vertical electric field is also shown to be well fit in this altitude range by a similar single term exponential with a scale height of the opposite sign but similar magnitude. No convincing evidence for variation of the current density with altitude was found. While the average scale height was about 7.5 km, it is also shown that data from individual days are also well fit by an exponential, but with values which can be significantly different (up to +8.9 km in one case). The paper also presents evidence for a small (25% maximum) perturbation in the conductivity caused by the balloon wake. The paper concludes with a comparison of these data to other measurements and to various models of the stratospheric conductivity. It is found that the EMA conductivity measurements are quite similar to other previous measurements, yet significantly different from some model predictions.
Use of satellite data to constrain the model‐calculated atmospheric lifetime for N2O: Implications for other trace gases
Authors: Ko Malcolm K. W. , Sze Nien Dak , Weisenstein Debra K.
Published: February 2008

The source gases, such as nitrous oxide (N2O) and chlorofluorocarbons (CFCs), are released into the atmosphere at the Earth's surface and are removed mainly by photolysis in the stratosphere. The atmospheric abundance of a source gas is proportional to its emission rate and atmospheric lifetime. The lifetime is, in turn, determined by the local photochemical removal rate of the gas and the efficiency of transport that carries the gas from where it is emitted to the dominant photochemical removal region. The latter is particularly important for source gases for which the removal is restricted to the tropical stratosphere, a region where both the photolysis rates and concentrations are highest. We calculate that approximately 80% Of N2O is removed in the stratosphere between 30°N and 30°S. Using the data for N2O obtained from the stratospheric and mesospheric sounder (SAMS) instrument on the Nimbus 7 satellite to constrain the model‐calculated distributions, we concluded that previous models may have underestimated the magnitude of vertical transport over the tropics and that the calculated lifetimes for N2O and CFC source gases could be 30% shorter than previously reported values. The calculated lifetime for N2O of 110 years would imply a source strength of 13×106 tons (N) yr−1, compared to a source strength of 9.2×106 tons (N) per year for a lifetime of 160 years. A shorter lifetime for the CFCs (47 years for CFC‐11 and 95 years for CFC‐12) would imply a more rapid decrease in the atmospheric chlorine content once the CFC emissions are stopped, making it possible to reach the pre‐ozone hole value of 2 ppbv as early as 2045. Accurate determination of the lifetime of CFC‐11 is particularly important, since the lifetime is used in the definitions of the ozone depletion potentials (ODP), chlorine loading potentials (CLP), and greenhouse warming potentials (GWP) of the replacement chemicals for the CFCs. A shorter lifetime for CFC‐11 would elevate the magnitudes of ODP, CLP, and GWP for these chemicals.
Calculation of longwave radiation fluxes in atmospheres
Authors: Feigelson E. M. , Fomin B. A. , Gorchakova I. A. , Rozanov E. V. , Timofeyev Yu. M. , Trotsenko A. N. , Schwarzkopf M. Daniel
Published: February 2008

A technique for the computation of longwave radiative quantities using the line‐by‐line approach has been developed in the Soviet Union. The method has been applied to obtain fluxes and cooling rates for standard atmospheric profiles used in the Intercomparison of Radiation Codes Used in Climate Models (ICRCCM) sponsored by the World Meteorological Organization. The sensitivity of the result to changes in the vertical quadrature scheme, the angular integration, and the spectral line shape is evaluated. Fluxes and cooling rates in the troposphere are in general agreement with those obtained with different line‐by‐line models. Results from parameterized models, including a wideband statistical model and one employing the integral transmission function, have been compared to the line‐by‐line results. Flux errors in the simplified schemes are of the order of 10 W/m2. The sensitivity of these models to changes in atmospheric profiles, or to an increase in CO2 amount, is similar to that of the line‐by‐line calculations.
Total ozone from the TIROS operational vertical sounder during the formation of the 1987 “ozone hole”
Authors: Lefèvre F. , Cariolle D. , Muller S. , Karcher F.
Published: February 2008

Total ozone maps obtained from the infrared radiances measured by the TOVS/HIRS2 instrument on board the NOAA 10 satellite are used to study the formation of the 1987 Antarctic “ozone hole.”We use in this study an improved version of the retrieval algorithm described by Muller and Cayla (1983), now calibrated for middle and high latitudes and taking into account the unusually depleted ozone profiles of the Antarctic spring. Error analysis indicates that our method has an accuracy of the order of 5–7% in clear sky conditions. Values determined from the TIROS operational vertical sounder (TOVS) are in good agreement with Dobson measurements in the mid‐latitudes and with the ozonesondes launched from the Antarctic stations during the Airborne Antarctic Ozone Experiment (AAOE). The agreement with the total ozone mapping spectrometer (TOMS) data at mid‐latitudes is also good, but significant differences are found in early September in the high latitudes. In particular, the large‐scale zonally symmetric minimum representative of the ozone hole appears later in the TOVS maps than in the TOMS data. The ozone hole was already apparent in the TOMS map on the first days of September, while TOVS detected only localized ozone deep minima associated with optically thick polar stratospheric clouds (PSCs) and did not observe any circular depletion structure until September 17. This discrepancy seems to be the consequence of high solar zenith angles and climatological errors in the TOMS algorithm, which tends to underestimate the ozone content in late winter. It is only in mid‐September that TOVS data show a rapid ozone decrease affecting the whole vortex. The low ozone amounts are first recorded in the vicinity of the PSCs detected in the ozone field and then spread into the vortex. TOVS observations suggest that a rapid ozone decrease might take place during or just after the formation of major water ice PSCs. Since the vortex is exposed to UV sunlight in mid‐September, this could be the direct consequence of both a sudden increase of free chlorine and an efficient denitrification occurring during type 2 PSC events. It is concluded that since the algorithm presented in this paper allows reliable ozone determinations in middle and high latitudes and accurate type 2 PSC detection, measurements from TOVS could play an important role in the ozone layer monitoring, especially in the wintertime polar regions where UV techniques are ineffective or affected by the lack of intense sunlight.
Acoustic signature of thunder from seismic records
Authors: Kappus Mary E. , Vernon Frank L.
Published: February 2008

Thunder, the sound wave through the air associated with lightning, transfers sufficient energy to the ground to trigger seismometers set to record regional earthquakes. The acoustic signature recorded on seismometers, in the form of ground velocity as a function of time, contains the same type features as pressure variations recorded with microphones in air. At a seismic station in Kislovodsk, USSR, a nearly direct lightning strike caused electronic failure of borehole instruments while leaving a brief impulsive acoustic signature on the surface instruments. The peak frequency of 25–55 Hz is consistent with previously published values for cloud‐to‐ground lightning strikes, but spectra from this station are contaminated by very strong wind noise in this band. A thunderstorm near a similar station in Karasu triggered more than a dozen records of individual lightning strikes during a 2‐hour period. The spectra for these events are fairly broadband, with peaks at low frequencies, varying from 6 to 13 Hz. The spectra were all computed by multitaper analysis, which deals appropriately with the nonstationary thunder signal. These independent measurements of low‐frequency peaks corroborate the occasional occurrences in traditional microphone records, but a theory concerning the physical mechanism to account for them is still in question. Examined separately, the individual claps in each record have similar frequency distributions, discounting a need for multiple mechanisms to explain different phases of the thunder sequence. Particle motion, determined from polarization analysis of the three‐component records, is predominantly vertical downward, with smaller horizontal components indicative of the direction to the lightning bolt. In three of the records the azimuth to the lightning bolt changes with time, confirming a significant horizontal component to the lightning channel itself.