bluuebunny/crossref_metadata_2025 huggingface dataset:
Alpine lee cyclogenesis influence on air‐sea heat exchanges and marine atmospheric boundary layer thermodynamics over the western Mediterranean during a Tramontane/Mistral event
Authors: Flamant Cyrille
Published: May 2003

Data from a recent field campaign are used to analyze the nonstationary aspects of air‐sea heat exchanges and marine atmospheric boundary layer (MABL) thermodynamics over the Gulf of Lion (GoL) in connection with synoptic forcing. The data set includes measurements made from a wide range of platforms (sea‐borne, airborne, and space‐borne) as well as three‐dimensional atmospheric modeling. The analysis focuses on the 24 March 1998 Tramontane/Mistral event. It is shown that the nonstationary nature of the wind regime over the GoL was controlled by the multistage evolution of an Alpine lee cyclone over the Tyrrhenian Sea (between Sardinia and continental Italy). In the early stage (low at 1014 hPa) the Tramontane flow prevailed over the GoL. As the low deepened (1010 hPa), the prevailing wind regime shifted to a well‐established Mistral that peaked around 1200 UTC. In the afternoon the Mistral was progressively disrupted by a strengthening outflow coming from the Ligurian Sea in response to the deepening low over the Tyrrhenian Sea (1008 hPa) and the channelling induced by the presence of the Apennine range (Italy) and the Alps. In the evening the Mistral was again well established over the GoL as the depression continued to deepen (1002 hPa) but moved to the southeast, reducing the influence of outflow from the Ligurian Sea on the flow over the GoL. The air‐sea heat exchanges and the structure of the MABL over the GoL were observed to differ significantly between the established Mistral period and the disrupted Mistral period. In the latter period, surface latent and sensible heat fluxes were reduced by a factor of 2, on average. During that latter period, air‐sea moisture exchanges were mainly driven by dynamics, whereas during the former period, both winds and vertical moisture gradients controlled moisture exchanges. The MABL was shallower during the latter period (0.7 km instead of 1.2 km) because of reduced surface turbulent heat fluxes and increased wind shear at the top of the MABL in connection with the outflow from the Ligurian Sea. In the period of established Mistral, gravity waves above the MABL were observed to have an influence on the MABL structure. In the perturbed Mistral case this influence was not observed. Over the GoL the ubiquitous presence of sheltered regions (i.e., regions of reduced wind speed in the MABL) in the lee of the three major mountain ranges surrounding the GoL (namely, the Pyrénées, the Massif Central, and the Alps) was shown to have an impact on surface turbulent heat fluxes. The position of these sheltered regions, which evolved with the synoptic conditions, was the key to a correct interpretation of multiplatform surface turbulent flux measurements made over the GoL on 24 March 1998.
A method for computing horizontal pressure‐gradient force in an oceanic model with a nonaligned vertical coordinate
Authors: Shchepetkin Alexander F. , McWilliams James C.
Published: May 2003

Discretization of the pressure‐gradient force is a long‐standing problem in terrain‐following (or σ) coordinate oceanic modeling. When the isosurfaces of the vertical coordinate are not aligned with either geopotential surfaces or isopycnals, the horizontal pressure gradient consists of two large terms that tend to cancel; the associated pressure‐gradient error stems from interference of the discretization errors of these terms. The situation is further complicated by the nonorthogonality of the coordinate system and by the common practice of using highly nonuniform stretching for the vertical grids, which, unless special precautions are taken, causes both a loss of discretization accuracy overall and an increase in interference of the component errors. In the present study, we design a pressure‐gradient algorithm that achieves more accurate hydrostatic balance between the two components and does not lose as much accuracy with nonuniform vertical grids at relatively coarse resolution. This algorithm is based on the reconstruction of the density field and the physical z coordinate as continuous functions of transformed coordinates with subsequent analytical integration to compute the pressure‐gradient force. This approach allows not only a formally higher order of accuracy, but it also retains and expands several important symmetries of the original second‐order scheme to high orders [Mellor et al., 1994; Song, 1998], which is used as a prototype. It also has built‐in monotonicity constraining algorithm that prevents appearance of spurious oscillations of polynomial interpolant and, consequently, insures numerical stability and robustness of the model under the conditions of nonsmooth density field and coarse grid resolution. We further incorporate an alternative method of dealing with compressibility of seawater, which escapes pressure‐gradient errors associated with interference of the nonlinear nature of equation of state and difficulties to achieve accurate polynomial fits of resultant in situ density profiles. In doing so, we generalized the monotonicity constraint to guarantee nonnegative physical stratification of the reconstructed density profile in the case of compressible equation of state. To verify the new method, we perform traditional idealized (Seamount) and realistic test problems.
Numerical simulation of the Gulf Stream System: The Loop Current and the deep circulation
Authors: Lee Hyun‐Chul , Mellor George L.
Published: May 2003

The Loop Current and the deep circulation in the Gulf of Mexico are numerically investigated by a primitive equation, sigma coordinate ocean model with realistic surface fluxes obtained from an atmospheric forecast model. A deep cyclonic circulation, bounded by the deep basin in the eastern Gulf of Mexico, is spun up by the Loop Current; the deep cyclonic circulation is coincident with a southward current of the Loop Current eastern limb and weakens after Loop Current ring separation and cessation of the southward current. The anticyclonic, semienclosed Loop Current also induces anticyclonic lower layer columnar eddies in the eastern gulf. These lower layer eddies decouple from the upper layer Loop Current. The westward translation speed of a Loop Current ring is about 2.16–5.18 km d−1; the lower layer eddies have a higher speed and lead the rings into the central gulf. The time‐averaged surface circulation of the Gulf of Mexico basin is anticyclonic, mainly because of the transport of anticyclonic vorticity by Loop Current rings in the surface layer an average lower layer cyclonic circulation occurs along the continental slope of the basin.
Electromagnetic bias estimation using in situ and satellite data: 1. RMS wave slope
Authors: Millet Floyd W. , Arnold David V. , Warnick Karl F. , Smith Justin
Published: May 2003

The electromagnetic (EM) bias is the largest source of error in TOPEX/Poseidon and Jason‐1 satellite altimeter sea surface height (SSH) estimates. Current operational EM bias models are based on empirical relationships between the bias, wind speed, and significant wave height. These models are limited in their accuracy because wind speed and wave height do not capture enough information about the sea state to uniquely specify the bias. In order to improve EM bias estimation, we have studied the correlation between the EM bias and RMS long wave slope using data from tower‐based experiments in the Gulf of Mexico and Bass Straight, Australia. Models based on significant wave height and RMS slope are more accurate than models based on wave height and wind speed by at least 50% in RMS error between predicted and ground truth bias values. Furthermore, models which incorporate wave slope exhibit reduced regional variation between the two widely separated experiment locations.
Observation of hydrodynamic modulation of gravity‐capillary waves by dominant gravity waves
Authors: Hara Tetsu , Hanson Kurt A. , Bock Erik J. , Uz B. Mete
Published: May 2003

Accurate evaluation of the hydrodynamic modulation of short wind waves by dominant gravity waves is needed for various applications of microwave radar remote sensing of the ocean surface. Such knowledge is also essential for the studies of wind wave coupling and air–sea momentum/energy transfer. Here, we present direct field observations of the hydrodynamic modulation transfer function (MTF) during two field programs (High‐Resolution Remote Sensing Experiment (High‐Res) off Cape Hatteras, June 1993, and Coastal Ocean Processes (CoOP) experiment off the California coast, April and May 1995). Gravity‐capillary wave spectra were obtained using a scanning laser slope gauge (SLSG) for wave numbers between 25 and 800 rad m−1. An array of capacitive wave wires and a motion detection package were used for the measurement of surface gravity waves. These instruments were mounted on a research catamaran, which was towed to the side of a research vessel. The observations were mostly made under low wind conditions. The observed coherence is mostly below 0.1, suggesting that the modulation of short wind waves is not strongly correlated with dominant gravity waves. The coherence is slightly higher for wave numbers 50–100 rad m−1 than for wave numbers above 200 rad m−1. When wind and dominant waves are aligned and the water surface is clean, the magnitude of the hydrodynamic MTF is around 2–4 and its phase is close to 0. When surfactants are present and short wind wave spectra are reduced, the MTF magnitudes become significantly larger for wave numbers above 200 rad m−1. When wind and dominant waves are not aligned, the coherence becomes lower as expected. The results from the two field experiments are roughly consistent with each other. The existing relaxation model may predict the hydrodynamic MTF values that are roughly consistent with the observations if the effect of modulated wind stress over gravity waves is included.
Modeling wind‐driven circulation during the March 1998 sediment resuspension event in Lake Michigan
Authors: Beletsky Dmitry , Schwab David J. , Roebber Paul J. , McCormick Michael J. , Miller Gerald S. , Saylor James H.
Published: May 2003

A three‐dimensional primitive equation numerical ocean model was applied to Lake Michigan to simulate hydrodynamic conditions during the March 1998 sediment resuspension event in southern Lake Michigan caused by a storm with winds up to 20 m/s. The hydrodynamic model is driven with surface winds derived from observed meteorological conditions at 18 land stations and a meteorological buoy and also with surface winds calculated using a mesoscale meteorological model. Current observations from 11 subsurface moorings showed that the model driven with observed winds was able to qualitatively simulate wind‐driven currents but underestimated current speeds during the most significant wind event. In addition, a pronounced offshore flow in the area of observations was also underestimated. Hydrodynamic model results using the meteorological model winds as the forcing function showed significant improvement over model results which were based on observed winds proving the importance of mesoscale winds for current modeling in large lakes.
Nonlinear internal waves in the South China Sea: Observation of the conversion of depression internal waves to elevation internal waves
Authors: Orr Marshall H. , Mignerey Peter C.
Published: May 2003

The conversion of depression nonlinear internal solitons to elevation internal waves has been observed twice at the South China Sea continental shelf break. Shipboard X‐band radar, tow‐yo CTD, ADCP and high frequency acoustic flow visualization of the process are presented. The data focuses on up slope propagation of depression internal solitons from a water depth of ∼264 m to a water depth of ∼110 m. Dissipation by large amplitude shear instabilities was observed. The kinetic energy density was found to be a decreasing monotonic function of range with an energy dissipation rate coefficient of 0.063 km−1. The rate of energy dissipation over the ∼16.5 km soliton propagation path was 0.17 W/m/m. Simple numerical models of the waveform evolution are qualitatively compared to the observations. The observations, extracted scale parameters and dissipation rates should be useful for testing a variety of evolution equation representations of internal soliton propagation.
Directional wave measurements from three wave sensors during the FETCH experiment
Authors: Pettersson Heidi , Graber Hans C. , Hauser Danièle , Quentin Céline , Kahma Kimmo K. , Drennan William M. , Donelan Mark A.
Published: May 2003

During the Flux, Etat de la mer et Télédéction en Condition de fetcH variable (FETCH) experiment, directional wave measurements were made by an airborne radar RESSAC and by two moored buoys, an Air–Sea Interaction Spar (ASIS) and a Directional Waverider. In order to define the performance and compatibility of these wave sensors with different measuring principles, a comparison of the directional measurements in a variety of meteorological conditions during the experiment is presented in this paper. It was found that within the limits of their operational ranges, the sensors agreed on the one‐dimensional spectrum and the basic parameters derived from it—significant wave height and peak frequency. The sensors reported the directional features of the wave field and the mean direction consistently, but in some cases the two buoys disagreed on the directional width of the spectrum. Most of these cases were associated with a single swell‐dominated event.
Feature‐based classification of optical water types in the Northwest Atlantic based on satellite ocean color data
Authors: Martin Traykovski Linda V. , Sosik Heidi M.
Published: May 2003

We have developed an optical water type classification approach based on remotely sensed water leaving radiance, for application to the study of spatial and temporal dynamics of ecologically and biogeochemically important properties of the upper ocean. For CZCS and SeaWiFS imagery of the Northwest Atlantic region, pixels from several different locations projected into distinct clusters in water‐leaving radiance feature space, suggesting that these waters can be distinguished using a few spectral bands of ocean color data. Based on these clusters, we constructed a Northwest Atlantic Training Set and developed two different classification techniques. The Euclidean Distance Classifier minimizes the raw distance between each pixel and the centroid of the class to which it is assigned, whereas the Eigenvector Classifier is based on scaling the raw distances by the variance of each class, thereby accounting for the shape of each class in feature space. We conducted an initial evaluation of these two classification techniques by constructing water type classes based on only half of the pixels of each water type (randomly selected) in the Northwest Atlantic Training Set; classification was then carried out on the remaining half of the training set data. Applying the Euclidean Distance Classifier resulted in an average of 97.4% correctly classified pixels over 20 trials; even higher success rates were achieved with the Eigenvector Classifier, which gave an average of 99.1% correctly classified pixels. The Euclidean Distance Classifier performed well with spherical classes, but with more ellipsoidal classes, classification success improved considerably using the Eigenvector Classifier. We then applied these classifiers to ocean color images of the Northwest Atlantic to elucidate the geographical location and extent of each water type. We interpreted classifier results based on our Classification Goodness of Fit measure, which indicates how closely a given pixel is associated with its assigned class. This revealed that sharp boundaries exist between water masses of different optical types, with pixels on either side of the boundaries being strongly associated with their water type class. We anticipate that our classification techniques will facilitate long‐term time series studies by tracking optical water types through seasonal and interannual changes.
Ecosystem response to upwelling off the Oregon coast: Behavior of three nitrogen‐based models
Authors: Spitz Y. H. , Newberger P. A. , Allen J. S.
Published: May 2003

The behavior of three ecosystem models is analyzed for upwelling off the Oregon coast as a function of the number of model components. The first ecosystem model includes dissolved inorganic nitrogen‐phytoplankton‐zooplankton (NPZ), the second (NPZD) adds detritus, and the third (NNPZD) splits the nutrients into nitrate and ammonium. The models are made as equivalent as possible by choosing the same parameterizations for the biological interactions and are coupled to a two‐dimensional physical circulation model. Simulations with wind forcing from summer 1973 lead to similar spatial and temporal patterns for the three models. The mean phytoplankton concentration is maximum onshore of the upwelling jet while the mean zooplankton concentration is maximum farther offshore. The main difference among the models is a larger maximum zooplankton concentration for the NPZ simulation. This difference is attributed to the sinking of phytoplankton rather than detritus. We repeat the NNPZD summer 1973 simulation with wind forcing from 1999 and with constant wind stress. We also use the 1973 wind forcing and vary model parameters. The zooplankton maximum grazing rate is increased, the detritus sinking rate is reduced, and the inhibition of nitrate uptake by ammonium is removed. In all cases, the maximum of the zooplankton concentration is found offshore of the phytoplankton maximum. The locations and magnitudes depend upon the nature of the time variability of the wind forcing and on the biological parameters. The wind variability and the parameter values have little effect on the mean primary productivity, but have a larger effect on the f‐ratio.
An Oceanic General Circulation Model (OGCM) investigation of the Red Sea circulation: 2. Three‐dimensional circulation in the Red Sea
Authors: Sofianos Sarantis S. , Johns William E.
Published: May 2003

The three‐dimensional circulation of the Red Sea is studied using a set of Miami Isopycnic Coordinate Ocean Model (MICOM) simulations. The model performance is tested against the few available observations in the basin and shows generally good agreement with the main observed features of the circulation. The main findings of this analysis include an intensification of the along‐axis flow toward the coasts, with a transition from western intensified boundary flow in the south to eastern intensified flow in the north, and a series of strong seasonal or permanent eddy‐like features. Model experiments conducted with different forcing fields (wind‐stress forcing only, surface buoyancy forcing only, or both forcings combined) showed that the circulation produced by the buoyancy forcing is stronger overall and dominates the wind‐driven part of the circulation. The main circulation pattern is related to the seasonal buoyancy flux (mostly due to the evaporation), which causes the density to increase northward in the basin and produces a northward surface pressure gradient associated with the downward sloping of the sea surface. The response of the eastern boundary to the associated mean cross‐basin geostrophic current depends on the stratification and β‐effect. In the northern part of the basin this results in an eastward intensification of the northward surface flow associated with the presence of Kelvin waves while in the south the traditional westward intensification due to Rossby waves takes place. The most prominent gyre circulation pattern occurs in the north where a permanent cyclonic gyre is present that is involved in the formation of Red Sea Outflow Water (RSOW). Beneath the surface boundary currents are similarly intensified southward undercurrents that carry the RSOW to the sill to flow out of the basin into the Indian Ocean.
Structure and eastward extension of the Changjiang River plume in the East China Sea
Authors: Lie Heung‐Jae , Cho Cheol‐Ho , Lee Jae‐Hak , Lee Seok
Published: May 2003

The hydrographic structure and offshore extension of freshwater plume discharged from the Changjiang (also known as the Yangtze) River in the northern East China Sea were investigated by analyzing conductivity‐temperature‐depth (CTD) data and drifter trajectories collected during the summers of 1997 and 1998. From June to early September, when southerly winds prevail, the plume tends to move northeast in the Chinese coastal area and then separates from the coastal zone to travel eastward over 400 km offshore across the western shelf of the northern East China Sea. During other seasons, when northerly winds prevail, the plume is confined to the Chinese coast. In the summer the plume in the midshelf, confined to a thin surface layer 10 to 15 m thick, extends eastward in the form of patches of low‐salinity water rather than spreading as a tongue‐shaped pattern from the Changjiang mouth. The eastward movement of patches in the western shelf is primarily due to upwelling favorable southerly winds. Upon reaching the vicinity of Cheju‐do, an island in the middle of northern East China Sea, the patches are advected to the Korea/Tsushima Strait by either the Cheju Warm Current or a northward‐flowing mean current of the Kuroshio Branch Current and then finally flow into the East/Japan Sea.
Bio‐optical relationships and ocean color algorithms for the north polar region of the Atlantic
Authors: Stramska Malgorzata , Stramski Dariusz , Hapter Ryszard , Kaczmarek Slawomir , Stoń Joanna
Published: May 2003

Up to now, relatively few bio‐optical measurements have been made in the high northern latitude waters, which allow sound relationships for ocean color remote sensing to be determined. We collected optical and chlorophyll a concentration, Chl, data in the north polar region of the Atlantic in summer season. The investigated region includes subarctic and arctic waters between 70°N and 80°N within the meridional zone between 1°E and 20°E. Our measurements show that the current NASA global algorithms, OC2, OC4, and chlor‐MODIS, generally overpredict Chl in the investigated waters by a factor of about 2 at low pigment concentrations (<0.2 mg m−3) and underpredict Chl at higher concentrations (20–50% at 2–3 mg m−3). For our data set, the best two‐band algorithm for Chl involves the ratio of remote‐sensing reflectance, Rrs(442)/Rrs(555), at 442‐nm and 555‐nm light wavebands. We found that the general trend of variation in the blue‐to‐green reflectance ratio, Rrs(442)/Rrs(555) or Rrs(490)/Rrs(555), with Chl was driven primarily by Chl‐dependent change in the green‐to‐blue ratio of absorption by pure seawater and particles. The effect of the blue‐to‐green backscattering ratio was of secondary importance. We observed a characteristic optical differentiation of waters within the investigated region. The majority of waters, which are here hypothesized to be dominated by diatoms, exhibited a relatively high blue‐to‐green reflectance ratio. The waters at several other stations, presumably dominated by dinoflagellates and/or prymnesiophytes, showed much lower reflectance ratio. Our data also show that the seemingly random variations in particulate absorption and backscattering coefficients at any given Chl are significant (more than a factor of 2) in the investigated waters.
The arctic ice thickness anomaly of the 1990s: A consistent view from observations and models
Authors: Rothrock D. A. , Zhang J. , Yu Y.
Published: May 2003

Observations of sea‐ice draft from submarine cruises in much of the Arctic Ocean show that the ice cover was unusually thin in the mid‐1990s. Here we limit our examination to digitally recorded draft data from eight cruises spanning the years 1987 to 1997 and find a decrease of about 1 m over the 11‐year span. Comparisons of our modeled draft with observed draft show good agreement in the temporal change. Comparing average draft over entire cruises, the RMS discrepancy between modeled and observed draft is 0.3 m and the correlation is 0.98. Agreement in the spatial patterns of draft is somewhat lower; the RMS discrepancy of 50‐km averages of draft is 0.7 m and the correlation is 0.73. We review reports of interannual variations of ice thickness or volume from other model studies. All models agree that thickness decreased by between 0.6 and 0.9 m from 1987 to 1996. Our model shows a modest recovery in thickness from 1996 to 1999. For the 1950s, 1960s, and 1970s, models tend to disagree on the size and to a lesser extent the timing or phase of interannual variations.
Assimilation of drifter observations for the reconstruction of the Eulerian circulation field
Authors: Molcard Anne , Piterbarg Leonid I. , Griffa Annalisa , Özgökmen Tamay M. , Mariano Arthur J.
Published: May 2003

In light of the increasing number of drifting buoys in the ocean and recent advances in the realism of ocean general circulation models toward oceanic forecasting, the problem of assimilation of Lagrangian observations data in Eulerian models is investigated. A new and general rigorous approach is developed based on optimal interpolation (OI) methods, which takes into account directly the Lagrangian nature of the observations. An idealized version of this general formulation is tested in the framework of identical twin experiments using a reduced gravity, quasi‐geostrophic model. An extensive study is conducted to quantify the effectiveness of Lagrangian data assimilation as a function of the number of drifters, the frequency of assimilation, and the uncertainties associated with the forcing functions driving the ocean model. The performance of the Lagrangian assimilation technique is also compared to that of conventional methods of assimilating drifters as moving current meters, and assimilation of Eulerian data, such as fixed‐point velocities. Overall, the results are very favorable for the assimilation of Lagrangian observations to improve the Eulerian velocity field in ocean models. The results of our assimilation twin experiments imply an optimal sampling frequency for oceanic Lagrangian instruments in the range of 20–50% of the Lagrangian integral timescale of the flow field.
Flow induced by upwelling winds in an equatorward facing bay: Gulf of Arauco, Chile
Authors: Valle‐Levinson Arnoldo , Atkinson Larry P. , Figueroa Dante , Castro Leonardo
Published: May 2003

Shipborne observations of hydrographic and flow velocity profiles were combined with wind velocity measurements to describe the characteristics of the wind‐induced flow in an equatorward facing bay of central Chile in South America. The measurements, which were taken from two transects and one anchor station, were made during late austral spring, between 4 and 10 December 2000. Most observations concentrated on Boca Grande, a transect that crossed the deep, northern (equatorward) entrance to the bay. The other transect crossed the smaller and shallower, westward entrance to the bay, Boca Chica. The anchor station was located inside the bay, close to Boca Chica. The period of observations was characterized by persistent upwelling winds of up to 17 m/s. The direction of the wind showed very little variability, but its magnitude exhibited well‐defined diurnal fluctuations. Wind speeds peaked at around sunset (2100 local time), which coincided with the deepest pycnocline location. The shallowest pycnocline depth appeared a couple of hours after sunrise. These pycnocline oscillations had amplitudes of ∼5 m and were believed to propagate poleward along the coast and dissipate at the shallow entrance in Boca Chica. This mechanism could have mixed low‐oxygen, nutrient‐rich waters into the photic zone and enhanced the primary productivity. Observed flows at the Boca Grande transect consisted of downwind flow over the shallow ends and upwind flow in the deepest part. This wind‐induced pattern is believed to cause a pair of counterrotating gyres that allow near‐surface divergence and ventilation of upwelled subsurface waters at the southern end of the bay. This is the region where the highest concentrations of chlorophyll are identified in color imagery.
Short‐range forecast experiments of the Kuroshio path variabilities south of Japan using TOPEX/Poseidon altimetric data
Authors: Komori Nobumasa , Awaji Toshiyuki , Ishikawa Yoichi , Kuragano Tsurane
Published: May 2003

Capability for short‐range forecasting of the Kuroshio path variabilities south of Japan is studied by assimilating the absolute sea surface dynamic height data, which are derived from in situ hydrography and TOPEX/Poseidon (T/P) altimetry, into a high‐resolution 1‐1/2 layer primitive equation model every 15 days for 5 years from 1993 to 1997. The initialization scheme used is the variational method, which contains the nonlinear dynamics of the model as a weak constraint and is suitable for initialization in the western boundary current regions where initialization by simple optimal interpolation is inappropriate. The time series of the analysis field well represents the Kuroshio path variations during the study period. For example, the root‐mean‐square (RMS) differences from the observations falls within 0.3° for the location in latitude of the current axis off Enshu‐nada and 11.4 cm for the sea level at Hachijo‐jima Island while their observed RMS variabilities are 0.5° and 30.7 cm, respectively. By using the resulting fields as the initial conditions, 116 cases of 90‐day forecast experiments for the Kuroshio path variations are then performed to assess the statistical properties of our assimilation system. Though significant bias is found in the forecast field southeast of Kyushu, the accuracy of our forecasted field south of Japan is much higher than that of persistence experiments, and the typical evolution of the Kuroshio into a large‐amplitude path off Enshu‐nada is successfully reproduced after the initialization. In particular, the eastward progression speed and the horizontal scale of the meander are quite similar to those observed. These results and the comparison with the RMS variability of the analysis field enable us to infer that roughly 60‐day forecasts of the Kuroshio path variabilities south of Japan are possible. This indicates that our assimilation system is suitable for the operational short‐range forecasting of the upper Kuroshio.
Hydraulic estimates of Denmark Strait overflow
Authors: Nikolopoulos Anna , Borenäs Karin , Hietala Riikka , Lundberg Peter
Published: May 2003

Upper bounds of the Denmark Strait deep‐water overflow from the Nordic seas into the North Atlantic are estimated using rotating hydraulic theory. The calculations are made for the real bottom topography of the strait and are based on hydrographic sections surveyed during a dedicated field experiment in the area. Results are presented for zero as well as finite (but constant) potential vorticity, and it is shown that the differences in outcome between these two approaches are only minor. The calculated interface configurations are found to be in good agreement with those observed, and the theoretically obtained transports conform with earlier estimates.
Shoaling transformation of wave frequency‐directional spectra
Authors: Herbers T. H. C. , Orzech Mark , Elgar Steve , Guza R. T.
Published: May 2003

A Boussinesq model for the nonlinear transformation of the frequency‐directional spectrum and bispectrum of surface gravity waves propagating over a gently sloping, alongshore uniform beach is compared with field and laboratory observations. Outside the surf zone the model predicts the observed spectral evolution, including energy transfers to harmonic components traveling in the direction of the dominant waves, and the cross‐interactions of waves traveling in different directions that transfer energy to components with the vector sum wavenumber. The sea surface elevation skewness and asymmetry, third‐order moments believed to be important for sediment transport, also are predicted well. Effects of surf zone wave breaking are incorporated with a heuristic frequency‐dependent dissipation term in the spectral energy balance equation and an empirical relaxation of the bispectrum to Gaussian statistics. The associated coefficients are calibrated with observations that span a wide range of surf zone conditions. With calibrated coefficients, the model predicts observed surf zone frequency spectra well and surf zone skewness and asymmetry fairly well. The observed directional spectra inside the surf zone are broader than the predicted spectra, suggesting that neglected scattering effects associated with the random onset of wave breaking or with higher‐order nonlinearity may be important.
FROSTFIRE: An experimental approach to predicting the climate feedbacks from the changing boreal fire regime
Authors: Hinzman Larry D. , Fukuda Masami , Sandberg David V. , Chapin F. Stuart , Dash David
Published: May 2003

The FROSTFIRE research project conducted a prescribed burn of a 970 ha watershed in interior Alaska. To the best of our knowledge, this is the first experimental burn of a watershed and the most thoroughly documented prescribed fire in history. Although extensive fire research has been conducted in more temperate regions, relatively little had been done in the boreal forest and almost none in areas of discontinuous permafrost. The goal of this project was to examine the impacts of weather and vegetation on fire behavior and the resulting effects of fire on feedbacks to climate. The research was conducted in the Caribou‐Poker Creeks Research Watersheds near Fairbanks, Alaska. Intensive preburn surveys quantified the preburn environment, ecology, hydrology, and fuel status of the experimental watershed. This information was compared with measurements taken during and after the fire. Although the fire was artificially ignited, the fire behavior and fire effects were similar to those of naturally occurring fires. Close collaboration among agencies and among scientists of several countries was critical to the success of the project.
A comparison of particle mass spectrometers during the 1999 Atlanta Supersite Project
Authors: Middlebrook Ann M. , Murphy Daniel M. , Lee Shan‐Hu , Thomson David S. , Prather Kimberly A. , Wenzel Ryan J. , Liu Don‐Yuan , Phares Denis J. , Rhoads Kevin P. , Wexler Anthony S. , Johnston Murray V. , Jimenez José L. , Jayne John T. , Worsnop Douglas R. , Yourshaw Ivan , Seinfeld John H. , Flagan Richard C.
Published: May 2003

During the Atlanta Supersite Project, four particle mass spectrometers were operated together for the first time: NOAA's Particle Analysis by Laser Mass Spectrometer (PALMS), University of California at Riverside's Aerosol Time‐of‐Flight Mass Spectrometer (ATOFMS), University of Delaware's Rapid Single‐Particle Mass Spectrometer II (RSMS‐II), and Aerodyne's Aerosol Mass Spectrometer (AMS). Although these mass spectrometers are generally classified as similar instruments, they clearly have different characteristics due to their unique designs. One primary difference is related to the volatilization/ionization method: PALMS, ATOFMS, and RSMS‐II utilize laser desorption/ionization, whereas particles in the AMS instrument are volatilized by impaction onto a heated surface with the resulting components ionized by electron impact. Thus mass spectral data from the AMS are representative of the ensemble of particles sampled, and those from the laser‐based instruments are representative of individual particles. In addition, the AMS instrument cannot analyze refractory material such as soot, sodium chloride, and crustal elements, and some sulfate or water‐rich particles may not always be analyzed with every laser‐based instrument. A main difference among the laser‐based mass spectrometers is that the RSMS‐II instrument can obtain size‐resolved single particle composition information for particles with aerodynamic diameters as small as 15 nm. The minimum sizes analyzed by ATOFMS and PALMS are 0.2 and about 0.35 μm, respectively, in aerodynamic diameter. Furthermore, PALMS, ATOFMS, and RSMS‐II use different laser ionization conditions. Despite these differences the laser‐based instruments found similar individual particle classifications, and their relative fractions among comparable sized particles from Atlanta were broadly consistent. Finally, the AMS measurements of the nitrate/sulfate mole ratio were highly correlated with composite measurements (r2 = 0.93). In contrast, the PALMS nitrate/sulfate ion ratios were only moderately correlated (r2 ∼ 0.7).
BIBLE A whole‐air sampling as a window on Asian biogeochemistry
Authors: Elliott Scott , Blake Donald R. , Blake Nicola J. , Dubey Manvendra K. , Rowland F. Sherwood , Sive Barkley C. , Smith Felisa A.
Published: May 2003

Asian trace gas and aerosol emissions into carbon, nitrogen, and other elemental cycles will figure prominently in near term Earth system evolution. Atmospheric hydrocarbon measurements resolve numerous chemical species and can be used to investigate sourcing for key geocarriers. A recent aircraft study of biomass burning and lightning (BIBLE A) explored the East Asian atmosphere and was unique in centering on the Indonesian archipelago. Samples of volatile organics taken over/between the islands of Japan, Saipan, Java, and Borneo are here examined as a guide to whole‐air‐based studies of future Asian biogeochemistry. The midlatitude onshore/offshore pulse and tropical convection strongly influence concentration distributions. As species of increasing molecular weight are considered, rural, combustion, and industrial source regimes emerge. Methane‐rich inputs such as waste treatment and rice cultivation are evidenced in the geostrophic outflow. The Indonesian atmosphere is rich in biomass burning markers and also those of vehicular activity. Complexity of air chemistry in the archipelago is a direct reflection of diverse topography, land use, and local economies in a rapidly developing nation. Conspicuous in its absence is the fingerprint for liquefied petroleum gas leakage, but it can be expected to appear as demand for clean fossil fuels rises along with per capita incomes. Combustion tracers indicate high nitrogen mobilization rates, linking regional terrestrial geocycles with open marine ecosystems. Sea to air fluxes are superimposed on continental and marine backgrounds for the methyl halides. However, ocean hot spots are not coordinated and suggest an intricate subsurface kinetics. Levels of long‐lived anthropogenic halocarbons attest to the success of international environmental treaties while reactive chlorine containing species track industrial air masses. The dozens of hydrocarbons resolvable by gas chromatographic methods will enable monitoring of upcoming Asian modernization. Crucial uncertainties are underscored. Signatures for Asian combustion processes and megacities have been obtained only indirectly or at a distance. Detailed fingerprinting must be combined with regular aircraft and ground station measurements to maximize utility of the database.
Hydrocarbon measurements at Pabstthum during the BERLIOZ campaign and modeling of free radicals
Authors: Konrad S. , Schmitz Th. , Buers H.‐J. , Houben N. , Mannschreck K. , Mihelcic D. , Müsgen P. , Pätz H.‐W. , Holland F. , Hofzumahaus A. , Schäfer H.‐J. , Schröder S. , Volz‐Thomas A. , Bächmann K. , Schlomski S. , Moortgat G. , Großmann D.
Published: May 2003

The Photochemistry Experiment in BERLIOZ (PHOEBE) was conducted in July/August 1998 at a rural site located near the small village Pabstthum, about 50 km NW of downtown Berlin. More than 60 nonmethane hydrocarbons (NMHC) in the range of C2–C10 were measured using two in situ gas chromatography (GC) systems. The first (GC1) was capable of measuring C2–C10 hydrocarbons with a relatively high separation efficiency but low time resolution (80–90 min), while GC2 provided quasi‐continuous measurements of C5–C10 hydrocarbons with a time resolution of 20 min but with a poorer separation efficiency than GC1. The advantages of both systems were joined by interpolation between two data points of GC1 with the pattern given by GC2. For compounds that could not be reliably measured with GC2, patterns of compounds with similar reactivity were used. Air masses with the lowest photochemical age as estimated from the toluene/benzene ratio and the highest hydrocarbon mixing ratios were observed on 20 and 21 July when air was advected from the direction of Berlin. Alkanes were the most abundant hydrocarbons (∼60%) on a molecular basis, followed by alkenes and aromatics. The reactivity of the hydrocarbons toward OH was dominated by the alkenes (>60%), with isoprene and α‐pinene constituting the major part. The hydrocarbon data were used together with the other trace gases measured at Pabstthum to simulate OH, HO2, and RO2 concentrations with the condensed chemical box model RACM. Relatively good agreement of the simulated radical concentrations with the spectroscopic measurements made at Pabstthum is observed for NOx mixing ratios >5 ppb, whereas the model overestimates OH and HO2 by 100% and 40%, respectively, at low NOx. The discrepancy between measured and modeled OH does not correlate with the concentration of particles. The RO2 concentrations are in good agreement with the measurements over the entire range of NOx. Sensitivity studies show that peroxyacetyl nitrate (PAN) is an important radical source and that missing volatile organic compound (VOC) reactivity is an unlikely explanation for the overestimation of HOx: By doubling of the VOC reactivity, OH and HO2 can be brought into agreement. However, the model then overestimates the organic RO2 concentrations by almost a factor of 2. Another important finding is that RACM overestimates the measured NO/NO2 ratio by 25%. This and the overestimation of HO2 lead to an overprediction of the local ozone formation rate by about 40% at low NOx mixing ratios.
Weak impact of mixing on chlorine deactivation during SOLVE/THESEO 2000: Lagrangian modeling (CLaMS) versus ER‐2 in situ observations
Authors: Konopka Paul , Grooß Jens‐Uwe , Günther Gebhard , McKenna Daniel S. , Müller Rolf , Elkins James W. , Fahey David , Popp Peter
Published: May 2003

During the second and third segment of the SOLVE campaign in February and March 2000, the Arctic polar vortex began to be disturbed by planetary waves and upper stratospheric warming events. The perturbations of the vortex were associated with transport of air from low and middle latitudes into the polar region. Filaments with a lifetime exceeding two weeks were generated in regions of strong baroclinicity and peeled off the vortex edge.The Chemical Lagrangian Model of the Stratosphere (CLaMS) is used for the interpretation of filamentary structures in chemical tracer fields measured on board the ER‐2 during the March flights across the edge of the polar vortex. Both the mixing and the impact of mixing on the chemistry are considered. The isentropic version of CLaMS is initialized on 10 February at four isentropic levels: θ = 400, 425, 450, and 475 K. A comparison of the measured CH4/Halon‐1211 correlation curves and time series with corresponding CLaMS results obtained for spatial resolution of about 45 km indicates weak mixing between vortex and midlatitude air without pronounced anomalous mixing events. Thus the Arctic vortex in the altitude range 400–475 K was well isolated during the considered period without significant mass exchange across the vortex edge. The mixing intensity in CLaMS is controlled by the finite time Lyapunov exponent λ measuring the deformation rate of the horizontal wind and switching on mixing in the flow regions where λ exceeds a critical value λc. The CLaMS simulations suggest a temporally and spatially inhomogeneous mixing in the lower stratosphere with a lateral (across the wind) effective diffusion coefficient of the order 103 m2 s−1. The amount of ClONO2 formed due to chemistry induced by mixing of the activated vortex air with NOx‐rich midlatitude air does not exceed 3%. The impact of mixing on the accumulated ozone loss is less than 1%. The ClONO2 collar observed during the flight on 11 March can be understood as a result of deactivation of ClOx through the NOx produced owing to the chemical decomposition of HNO3 without a significant contribution of mixing with NOx‐rich midlatitude air.
Balloonborne in situ gas chromatograph for measurements in the troposphere and stratosphere
Authors: Moore F. L. , Elkins J. W. , Ray E. A. , Dutton G. S. , Dunn R. E. , Fahey D. W. , McLaughlin R. J. , Thompson T. L. , Romashkin P. A. , Hurst D. F. , Wamsley P. R.
Published: May 2003

An in situ gas chromatograph (GC) instrument on a balloonborne package is described in detail and data from seven science deployments are presented. This instrument, the Lightweight Airborne Chromatograph Experiment (LACE), operates on the Observations of the Middle Stratosphere (OMS) in situ gondola and has taken data from the upper troposphere to near 32 km with a vertical resolution of better than 300 m. LACE chromatography has been developed to measure halon‐1211, the chlorofluorocarbons (CFC‐11, CFC‐113, CFC‐12), nitrous oxide (N2O), and sulfur hexafluoride (SF6) every 70 s and methyl chloroform (CH3CCl3), carbon tetrachloride (CCl4), hydrogen (H2), methane (CH4), and carbon monoxide (CO) every 140 s. In the introduction we present scientific motivation for choosing this suite of molecules and for the use of faster sample rates resulting in unprecedented vertical resolution from an in situ GC. Results from an intercomparison with the Airborne Chromatograph for Atmospheric Trace Species (ACATS‐IV) instrument are shown to quantitatively connect this LACE data set to the complementary data set generated on board the NASA ER‐2 aircraft.
Spatial and temporal patterns of active layer thickness at Circumpolar Active Layer Monitoring (CALM) sites in northern Alaska, 1995–2000
Authors: Hinkel K. M. , Nelson F. E.
Published: May 2003

Maximum annual development of the active layer above permafrost has been monitored at seven 1‐km2 Circumpolar Active Layer Monitoring (CALM) sites in northern Alaska since 1995. Grid nodes are spaced at 100‐m intervals, yielding a regular array of 121 (11 × 11) data collection points. Three sites are located in the Arctic Foothills physiographic province, and four are on the Arctic Coastal Plain. Air and soil temperature measurements are made at each site, and soil moisture is monitored at most. Six years of record permit several general conclusions: (1) At the landscape scale, end‐of‐season thaw depth is strongly correlated with local air temperature on an interannual basis. All sites experienced maximum average thaw depth in 1998 and a minimum in 2000, consistent with the warmest and coolest summers during the period of record. The active layer, however, may exhibit Markovian behavior over multidecadal periods. (2) There is significant intrasite variation in thaw depth and near‐surface soil moisture content within each 1‐km2 grid, reflecting the local influence of vegetation, substrate properties, snow cover dynamics, and terrain. (3) On the Coastal Plain, thaw depth is significantly greater in drained thaw‐lake basins, resulting in a bimodal distribution of thaw depth related to primary landscape elements. (4) Foothills sites demonstrate large spatial and interannual variability resulting from microtopography and temporal variations of soil moisture content, making predictive mapping of thaw depth problematic at the scale and resolution of the grids. The spatial pattern of thaw depth across sites on the Coastal Plain is relatively consistent, although lake margins exhibit more complex patterns attributable to fluctuating water levels.