bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of the exchange of salt between the Baltic and the Kattegat through the Öresund using a three‐layer model
Authors: Mattsson Johan
Published: February 2004

The shallowness of the Öresund prevents a continuous inflow of saline Kattegat water to the Baltic. Instead, the salt is exchanged largely by fluctuating barotropic transports. Buffer effects and temporal storage of low‐salinity Baltic surface water complicate the exchange. The analysis of salt exchange through the Öresund requires use of a model of the stratification and baroclinically modified exchange processes. In this paper a three‐layer model of the Öresund, forced by the exchange with the Kattegat and the Baltic, is formulated and calibrated. Frontal dynamics, necessary to explain the retreat of the uppermost layer, are included. The model is calibrated using genetic algorithms, which provide an efficient and robust optimization method for this kind of model. An analysis of the exchange in view of the model results is presented. The paper also gives estimates of typical mean quantities. For the analyzed period of 11 years (1977–1987) the mean salt outflow rate from the Baltic during outflows is 311,000 kg s−1, and the mean salt inflow rate to the Baltic during inflows is 500,000 kg s−1. The net salt outflow from the Baltic is estimated to 19,000 kg s−1. The mean frontal speed is estimated at 0.25 m s−1 and the typical required length of an inflow event for high‐salinity Kattegat water to reach the Baltic is estimated at 4 days. Further results are also given. In addition, the baroclinic dynamics of the Öresund are discussed.
The development of the Odden ice tongue in the Greenland Sea during winter 1993 from remote sensing and field observations
Authors: Wadhams P. , Comiso J. C. , Prussen E. , Wells S. , Brandon M. , Aldworth E. , Viehoff T. , Allegrino R. , Crane D. R.
Published: February 2004

The Odden ice tongue in the central Greenland Sea, believed to be associated with midgyre convection, developed prominently during the winter of 1993 (January–April). During this period it was studied by a succession of cruises which formed part of the European Subpolar Ocean Programme and which included direct sampling and measurement of the frazil and pancake ice which constituted the material of the ice tongue as well as studies of the ocean structure. Passive microwave imagery was used to determine the evolution of Odden through the winter and, when combined with ERS 1 synthetic aperture radar studies and the field data, yielded estimates of ice extent and thickness through the winter. From these studies it was possible to estimate the salt flux into the ocean originating from brine release from sea ice during the growth phases of Odden.
Eddies in the northeastern North Atlantic: Statistics from observations from a moving ship
Authors: Bowerman Sarah J. , Leach Harry
Published: February 2004

Statistics of currents and hydrographic data collected from a moving ship in the northeastern North Atlantic have been used to investigate the role of eddies in the circulation of the ocean. The mean currents show, besides a North Atlantic Current of about 12 cm s−1, a significant westward flow, perhaps 4 cm s−1 just north of the Azores. Eddy kinetic energies in the Western Basin reach about 1000 cm2 s−2, while there is indication of a weak secondary maximum of about 300 cm2 s−2 in the Eastern Basin. Both the eddy kinetic energy and the thermohaline variability show a strong asymmetry with greater variability on the south side of the main branch of the North Atlantic Current at about 51°N. The momentum budget of the North Atlantic current shows a dominant geostrophic balance with terms of order 10 cm s−1. The gradients of the Reynolds stresses contribute about 0.1 cm s−1 and the nonlinear terms less than 0.01 cm s−1. The residual meridional velocity implied by the meridional heat transport is of order 3 cm s−1. The eddy scale was estimated by means of the average zero‐crossing length scale of the transverse velocity correlation function to be 46 km. There is significant interannual variability of both mean conditions and mesoscale variability in the region of the North Atlantic Current. The northward eddy heat transport appears to be zero in the mixed layer but may be a significant proportion of the total oceanic heat transport at the intergyre boundary in the thermocline. Estimates of the magnitudes of eddy diffusivities for both momentum and heat give values of about 104 m2 s−1.
Biogeochemical cycling in the Ross Sea: An introduction
Authors: Marra John
Published: February 2004

Twenty or 30 years ago, interest in the Southern Ocean was largely driven by its exceptional characteristics. The Southern Ocean was such an anomaly, with extremes of productivity (thought to be high), nutrients (also high), temperatures (low), populations of krill and whales, and, of course, the presence of ice. There was also created, perhaps, an allure because of its distance and because it was so unusual, relative to the familiarity of the North Atlantic, for example.

It has turned out, not surprisingly, that these exceptional characteristics illustrate the exceptional importance of the Southern Ocean to global ocean phenomena. By virtue of creating water masses the Southern Ocean may play a significant role in the ocean's nutrient distributions. Low temperatures over large areas mean that, potentially, it is a significant sink for dissolved gases such as oxygen and carbon dioxide. It is generally believed that Antarctica (as well as the Arctic) may be more susceptible to climate change than either temperate or tropical ecosystems, because these ecosystems function within a few degrees of the freezing point of water. Altogether, the processes here will tell us much about how the ocean works today and in the distant past.
Detection and monitoring of stratigraphic markers and temperature trends at the Greenland Ice Sheet Project 2 using passive‐microwave remote‐sensing data
Authors: Shuman C. A. , Alley R. B. , Fahnestock M. A. , Fawcett P. J. , Bindschadler R. A. , White J. W. C. , Grootes P. M. , Anandakrishnan S. , Stearns C. R.
Published: February 2004

Satellite passive‐microwave sensors provide a sensitive means of studying ice‐sheet surface processes that assists ice‐core interpretation and can extend local observations across regional scales. Analysis of special sensor microwave/imager (SSM/I) brightness temperature (TB) data supports ice‐core research in two specific ways. First, the summer hoar complex layers used to date the Holocene portion of the Greenland Ice Sheet Project 2 ice core can be defined temporally and spatially by SSM/I 37‐GHz vertically (V) and horizontally (H) polarized B ratio (V/H) trends. Second, comparison of automatic weather station temperatures to SSM/I 37‐GHz V TB data shows that they are an effective proxy temperature record in this region. Also, the TB data can be correlated with proxy temperature trends from stable‐isotope‐ratio (δ18O and δD) profiles from snow pits and this allows the assignment of dates to specific snow depths.
Observations and predictions of run‐up
Authors: Raubenheimer B. , Guza R. T.
Published: February 2004

For a significant range of offshore wave conditions and foreshore slopes, run‐up observations are compared to semiempirical formulations and predictions of an existing numerical model based on the depth‐averaged one‐dimensional nonlinear shallow water equations with bore‐like breaking wave dissipation and quadratic bottom friction. The numerical model is initialized with time series of sea surface elevation and cross‐shore velocity observed in 80 cm mean water depth (approximately 50 m offshore of the mean shoreline) on a gently sloping beach and in 175 cm water depth (100 m offshore of the shoreline) on a steep concave beach. Run‐up was measured with a stack of resistance wires at elevations 5, 10, 15, 20, and 25 cm above and parallel to the beach face. At sea swell frequencies (nominally 0.05 < f ≤ 0.18 Hz), run‐up energy is limited by surf zone dissipation of shoreward propagating waves so that increasing the offshore wave height above a threshold value does not substantially increase the predicted or observed sea swell run‐up excursions (e.g., run‐up is “saturated”). Existing semiempirical saturation formulations are most consistent with the observations and numerical model predictions of run‐up excursions nearest the bed. In contrast, at infragravity frequencies (0.004 < f ≤ 0.05 Hz) where surf zone dissipation is relatively weak and reflection from the beach face is strong (e.g., saturation formulas are not applicable), the run‐up excursions increase approximately linearly with increasing offshore wave height. The numerical model also accurately predicts that the tongue‐like shape of the run‐up results in sensitivity of run‐up measurements to wire elevation. For instance, run‐up excursions and mean vertical superelevation (above the offshore still water level) increase with decreasing wire elevation, and continuous thinning of the run‐up tongue during the wave uprush can result in large phase differences between run‐up excursions measured at different wire elevations. Numerical model simulations suggest that run‐up measured more than a few centimeters above the bed cannot be used to infer even the sign of the fluid velocities in the run‐up tongue.
Seasonal characteristics of the perennial ice cover of the Beaufort Sea
Authors: Kwok R. , Comiso J. C. , Cunningham G. F.
Published: February 2004

By definition, ice which survives the summer is classified as multiyear ice. Thus the area covered by multiyear ice during the winter should be nearly equivalent to the ice area during the previous summer's minima. This condition provides a reasonable criterion for the evaluation of ice concentration and ice type retrieval algorithms using remote‐sensing data sets. From special sensor microwave imager (SSM/I) data the NASA Team algorithm estimates the multiyear, first‐year, and total ice concentrations during the winter using combinations of the polarization and spectral gradient ratios. The Team algorithm provides only estimates of ice concentration in the summer. From ERS 1 synthetic aperture radar (SAR) data the remarkably stable contrast between multiyear ice and first‐year ice in winter provides consistent estimates of multiyear ice concentrations. In the summer, multiyear ice concentration cannot be estimated from SAR or SSM/I data because free water on the surface effectively masks the backscatter and emissivity signature of this ice type. From SAR data a technique which takes advantage of the high backscatter of wind‐roughened open water as a discrimination feature is used to estimate the total ice concentration in the summer. With a year‐long (January 1992 to January 1993) data set from the Beaufort Sea we found that the multiyear ice concentration estimates from the SAR data are stable and are nearly equivalent to the ice concentration estimated at the end of the previous summer. We contrast this with the variability of the multiyear ice concentration and ice fraction estimates obtained using SSM/I data. The Team algorithm produces ice concentration and multiyear ice estimates which are consistently lower than those from the SAR data. We discuss reasons for these discrepancies and the implications of the higher than previously noted multiyear ice concentrations.
Electrical measurements on the Greenland Ice Sheet Project 2 Core
Authors: Taylor Kendrick C. , Alley Richard B. , Lamorey Gregg W. , Mayewski Paul
Published: February 2004

The Greenland Ice Sheet Project 2 (GISP2) electrical conductivity measurement (ECM) record is an indication of the concentration of H + in the core. The ECM detected seasonal variations in the nitrate concentration of the core which were used to assist in dating the core by annual layer counting. Volcanic eruptions that produce acidic aerosols are recorded in the ECM record. Evidence of biomass burning is detected by the ECM because fire‐related ammonium emissions neutralize the acids in the core. Rapid climate transitions associated with the Younger Dryas and Dansgaard/Oeschger interstadial events alter the concentration of alkaline dust and are detected by the ECM. The ECM has been used to develop stratigraphic ties between the GISP2 and the Greenland Ice Core Project cores. Users of the data should be aware of some instrument‐related artifacts in the ECM record.
An evaluation of expendable bathythermograph and Tropical Atmosphere‐Ocean Array data for monitoring tropical ocean variability
Authors: Smith Neville R. , Meyers Gary
Published: February 2004

Two important sources of information for monitoring and predicting the El Niño‐Southern Oscillation are the Tropical Atmosphere Ocean (TAO) buoy array and the volunteer observing ship expendable bathythermograph (VOS XBT) network. The subsurface ocean temperature measurements of these two networks are evaluated in the context of analysis and monitoring of medium‐ to low‐frequency variability in the tropical Pacific Ocean. It is shown that both systems capture the principal features that characterize variability in the equatorial central and eastern Pacific Ocean but only TAO can capture the higher temporal fluctuations in detail. In the western Pacific, the VOS XBT network is able to capture the slowly moving, westward propagating Rossby waves and their reflection and interaction with the western boundary. TAO is limited in this respect because of its equatorial focus. The accuracy of temperature maps is estimated using the rms analysis error variance. The accuracy of the VOS XBT network fluctuates in space and time but is relatively steady averaged over the tropical region, while that of TAO has gradually improved as the basin wide array has been implemented. Case studies using VOS XBT data only, TAO data only, and the combined full data set indicate the networks are complementary and supportive, evaluated basin wide and over the tropical region. The high temporal resolution and regularity of the equatorially focused TAO network are complemented by the broad‐scale, irregular tropical VOS XBT sampling in the equatorial region and by VOS coverage outside the domain of TAO. A proxy for net information content is derived from the estimated rms error variance of the analysis. For the equatorial region, TAO now provides in excess of 70% of the information, its dominance beginning in 1992. For the tropical region (20°S–20°N) the net information content of the respective systems is of comparable magnitude, each equivalent to in excess of 100 independent samples per 10‐day period in 1994, reinforcing the notion that both systems are valuable sources of subsurface ocean information for monitoring medium‐ to low‐frequency tropical variability.
A dynamical model for wind‐driven ice motion: Application to ice drift on the Labrador Shelf
Authors: Tang C. L. , Gui Q.
Published: February 2004

A three‐dimensional coupled ice‐ocean model has been developed to study short‐term ice motion over the eastern Canadian continental shelf. The model consists of a Hibler ice model and a diagnostic ocean model. Ice is coupled to the ocean through a surface Ekman layer. The model is implemented for the Labrador Sea using 6‐hourly winds and atmospheric pressures as input forcings. The results show that the model is able to produce many desired features of ice motion and ocean currents including wind‐generated coastal currents, an ice velocity field reflecting the influence of permanent and transient currents, and an increased sea surface tilt and ice internal stress at the coast. The model is used to simulate ice drift trajectories from six ice beacons deployed over the Labrador and Newfoundland Shelves in 1992. In the subtidal frequency range the modeled and observed ice velocities are in excellent agreement. Model errors, measured by the rms separation between the modeled and observed positions, increase with time. The increase is 10 km d−1 in the first 2 days and slower after 2 days. The model results are compared with a model run without ice‐ocean coupling and a calculation using an empirical relationship and parameters (speed ratio and turning angle). The errors are 20% (no ice‐ocean coupling) and 70% (empirical relationship) larger than the errors in the coupled model in the first 2 days and much larger after several days.
Mapping submarine sand waves with multiband imaging radar: 1. Model development and sensitivity analysis
Authors: Vogelzang J.
Published: February 2004

In 1989 and 1991, unexpected modulations caused by submarine sand waves were observed with the airborne imaging radar (AIR), a P, L, and C band synthetic aperture radar. The measurements were performed in a sand wave area off the Dutch coast. The sand waves have an asymmetric, sawtooth‐shaped profile with the steep slope oriented toward the northeast. During the experiments, wind and current had opposite directions: the wind was directed toward the northeast and the current toward the southwest. Under these conditions, existing models for the imaging mechanism predict that the modulation depth decreases with increasing radar frequency and that the steep slopes show up as dark lines in radar images. The AIR images show a relation between modulation depth and radar frequency as predicted. However, only the P band image of 1989 shows the steep slopes of the sand waves as dark lines. The P band image of 1991 and the L band images of 1989 and 1991 show a sawtooth‐shaped modulation which cannot be explained by existing theory. A new model is developed that is one dimensional in position space and fully two dimensional in wavenumber space. The radar cross section is calculated using both first‐order Bragg and an integral equation scattering model in which the cross section originates from a spectral band rather than a single value. The new model contains two improvements over previous ones. First, wave blocking or, better, wave reflection is included, though in an approximate manner. It is shown to be of importance at P band only. Second, the contribution to the radar cross section from waves moving both to and from the radar is included, whereas some previous models consider only one of these contributions. This explains the observed modulations, at least qualitatively, under the assumptions that the angular distribution of short waves is almost constant and that waves moving against the wind have small relaxation rates.
Ocean gravity waves: A nonlinear analysis of observations
Authors: Frison Theodore W. , Abarbanel Henry D. I.
Published: February 2004

Ocean gravity waves measured at the Harvest Platform off the coast of California were analyzed using tools derived from methods of nonlinear dynamics. We compare these with laboratory data of random surface wave fields. The Harvest data show clear signs of low‐dimensional dynamics in action and have an embedding dimension of six or seven. The largest Lyapunov exponent, a measure of future uncertainty, shows that the data are from a chaotic system and that predictions are limited to a horizon of about two major periods of the predominate wavelength. These results underscore the utility of nonlinear time domain methods for signal analysis and for extracting dynamical information not visible with linear methods.
Observations and modeling of the 1991–1992 El Niño signal off central California
Authors: Ramp Steven R. , McClean Julie L. , Collins Curtis A. , Semtner Albert J. , Hays Kevin A. S.
Published: February 2004

Five research cruises were conducted over the continental shelf and slope near the Farallon Islands, California, in February, May, August, and October/November 1991 and February 1992. The observations consisted of shipboard hydrographic and acoustic Doppler current profiler data and moored current meter measurements. Water mass anomalies were calculated for each cruise by subtracting seasonal means based on historical data. In general, the maximum anomalies were observed subsurface in the 100‐to 150‐m range. In May 1991, equatorward, upwelling favorable winds elevated the thermocline resulting in cold, salty anomalies nearshore, with cold, fresh anomalies offshore associated with the advection of Pacific Subarctic Water into the region from the north. Warm, fresh anomalies and a strongly depressed thermocline were observed during the February 1992 cruise. A combination of coastal sea level and wind stress data and output from the Los Alamos National Laboratory parallel ocean program model was used to explain the cause of these anomalies. The February 1992 anomalies were shown to be due to both the deepening of the Aleutian low in the North Pacific associated with the 1991–1993 El Nino/Southern Oscillation event in the equatorial Pacific and poleward propagating intraseasonal coastal trapped Kelvin waves also arising from this event. The anomalous poleward wind forcing produced onshore flow, deepening of the thermocline, and downwelling at progressively southward locations. The “downwelling” Kelvin waves propagated northward with the two signals meeting somewhere near the cruise region. Both the model and the coastal sea level data showed the phase speed of the waves to slow by about 50% after passing the Gulf of California. This may be due to the scattering of energy from the fastest baroclinic mode into a slower mode. The strongest wave signal in the equatorial Pacific did not necessarily produce the strongest anomalies off central California.
Measurements of upper ocean surface current shear with high‐frequency radar
Authors: Fernandez Daniel M. , Vesecky John F. , Teague Calvin C.
Published: February 2004

Estimates of the variation with depth of both the speed and direction of near‐surface ocean currents within the top meter have been made using time series data collected from a dual‐frequency, high‐frequency radar located on the California coast, south of Monterey. Long‐term averages derived from this data set over 3 different years consistently revealed an expected reduction in the speed of the near‐surface current as a function of depth, consistent with a logarithmic vertical current profile. An unexpected and previously unmeasured clockwise rotation with increasing depth of the near‐surface current was also observed. Hypotheses are suggested for the apparent rotation.
Sea level anomalies in the tropical Atlantic from Geosat data assimilated in a linear model, 1986–1988
Authors: Gourdeau L. , Minster J. F. , Gennero M. C.
Published: February 2004

Along‐track sea level anomalies derived from Geosat altimeter data from November 1986 to November 1988 are assimilated by Kalman filtering into a wind‐forced second‐baroclinic vertical mode linear model of the tropical Atlantic Ocean. To save computer time, the filter is degraded, mostly by fixing the error covariance matrix of the estimate once the filter has reached its asymptotic behavior. Geosat altimeter data have been processed using improved corrections. The sea surface height variability signal is extracted using the classical along‐track technique, relative to a complete reference cycle, and using only tracks longer than 2200 km. This processing has preserved oceanic signals both on large scales (above 1000 km) and on the mesoscale (around 200 km). Sea level anomalies predicted at Principe Island are close to in situ tide gage data, though some differences can be partly related to tidal or orbit error corrections. Oceanographic signals are analyzed from two different sets of fields: one issued from anisotropic space‐time objective analysis of Geosat data and the other from the model assimilation. The latter appears as an interesting method to extract low‐frequency and propagating signals. Along the equator, eastward propagating features are consistent with Kelvin waves correlated with zonal wind stress anomalies. Upwelling in the Gulf of Guinea is 1 month earlier in 1987 than in 1988. After elimination of the annual and semiannual signals by harmonic analysis, the residual signal over the whole tropical basin, decomposed into complex empirical orthogonal functions, is found dominated by variations between the 2 years, equatorial and tropical signals being anticorrelated.
Seasonal variability of sea surface Δ14C in the equatorial Pacific in an ocean circulation model
Authors: Rodgers Keith B. , Cane Mark A. , Schrag Daniel P.
Published: February 2004

The object of this modeling study is to identify the physical mechanisms responsible for seasonal variability in sea surface Δ14C for the equatorial Pacific Ocean. Analyses of Δ14C in corals from Guam, Galapagos, Fanning, and Canton reveal seasonal variability between 30 and 50 per mil during the 1970s and early 1980s. Given that this variability occurs on seasonal timescales, whereas air‐sea isotopic equilibration occurs on a timescale of 5 to 10 years, the variability must be due to seasonal variability in the physical circulation of the ocean. We use the primitive equation ocean circulation model of Gent and Cane [1989], along with the hybrid mixed layer model of Chen et al. [1994a], to study the dynamical mechanisms responsible. Upwelling in the eastern equatorial Pacific brings up Δ14C‐depleted waters, and air‐sea exchange creates high Δ14C in the western equatorial Pacific, establishing horizontal gradients in sea surface Δ14C. Seasonally varying lateral advection, acting on these gradients, is the dominant mechanism for Δ14C variability in the equatorial Pacific. In addition to the runs which were forced with seasonally varying winds, a run which used interannual winds between 1971 and 1985 was performed. The substantial interannual Δ14C variability present in this run is associated with advective anomalies in the equatorial waveguide.
Shannon entropy as an indicator of age for turbulent overturns in the oceanic thermocline
Authors: Wijesekera Hemantha W. , Dillon Thomas M.
Published: February 2004

The Shannon entropy is a measure of the degree of intricacy contained in any graphable n‐dimensional realization of an observable quantity. We use the Shannon entropy to measure the intricacy of density overturns in the oceanic thermocline and find that the Shannon entropy is related to the Thorpe scale LT [Thorpe, 1977] and the Ozmidov scale LO [Ozmidov, 1965]. We find that (1) small Shannon entropy corresponds to small values of ROT (≡LO/LT), while large Shannon entropy is associated with large values of ROT; (2) density spectra are typically more steep than inertial subrange spectra when both Shannon entropy and ROT are small, whereas the spectral slope tends to be flatter than inertial subrange spectra when both Shannon entropy and ROT are large; (3) the Grashof number is very large (O(1010)) when Shannon entropy is small, indicating that these patches are extremely density unstable; (4) spectral bandwidth is much larger for patches with small Shannon entropy than for those with large entropy, indicating that large‐scale, or “bulk” Reynolds number is large when entropy is small. We discuss the hypothesis that the degree of intricacy, and hence the Shannon entropy, increases with increasing time in a turbulent overturn and is observed to decrease only when the resolution limits of the measuring system are exceeded. On the basis of these arguments we suggest that some classes of overturns are created with Thorpe scale larger than the Ozmidov scale. In these overturns the kinetic energy dissipation rate (ε) is small during the initial growth of the overturn. Later, a small‐scale structure develops, and a more complex, higher‐order flow evolves. This behavior is discussed and compared with gridgenerated laboratory turbulence, in which initially small, energetic, rapidly growing boundary layers detached from the grid and advect downstream, forcing ROT to be largest adjacent to the grid and thereafter decrease as a result of entrainment.
Synoptic settings of westerly wind bursts
Authors: Hartten Leslie M.
Published: February 2004

The morphology of westerly wind bursts (WWBs) during the 1980s is investigated using 1000‐mbar winds analyzed by the European Center for Medium‐Range Weather Forecasts (ECMWF). The variety of synoptic situations in which WWBs occur are explored so that the dynamics of WWB generation and maintenance can be studied and so that those interested in short‐ and long‐term forecasts of conditions over the equatorial Pacific will have an increased knowledge of those elements associated with WWBs. WWBs are identified by searching for episodes in which the zonal wind was at least 5 m s−1 over at least 10° longitude for two or more days. This definition, based on surface winds rather than elevated winds or wind anomalies, reflects the impact WWBs have on air/sea interaction processes. The spatial and temporal criteria provide a synoptic‐scale envelope for such interactions and mitigate against erroneous analyses. According to these criteria, 131 distinct WWBs occurred during the 1980s. A new two‐dimensional classification scheme has been developed; the nine patterns in it describe the near‐surface flow during 90% of these WWBs. A single cyclone or a series of cyclones in one or both hemispheres and several different types of cross‐equatorial flow are the major components of the patterns. Only 8% of the bursts were associated with concurrent cyclones in both the northern and southern hemispheres. Four bursts involving cross‐equatorial flow are subjected to further study. The flow is decomposed into barotropic and baroclinic parts and into rotational and divergent baroclinic components. One of the bursts was predominantly barotropic and another predominantly baroclinic; the cross‐equatorial flow in all four cases was predominantly divergent in nature. The information from these cases, coupled with the typical vertical structures and small meridional length scales associated with the various synoptic patterns, suggests that simple baroclinic models of circulations driven by near‐equatorial heating are not adequate to describe the dynamics during WWBs.
Accuracy and precision of cryogenic limb array etalon spectrometer (CLAES) temperature retrievals
Authors: Gille John C. , Bailey Paul L. , Massie Steven T. , Lyjak Lawrence V. , Edwards David P. , Roche Aidan E. , Kumer John B. , Mergenthaler John L. , Gross Michael R. , Hauchecorne Alain , Keckhut Phillip , McGee Thomas J. , McDermid Ian S. , Miller Alvin J. , Singh Upendra
Published: February 2004

The Cryogenic Limb Array Etalon Spectrometer (CLAES) measured emission from the 792 cm−1 Q branch of CO2, from which temperature distributions in the stratosphere and low mesosphere were derived. Here we briefly review the measurement technique, concentrating on aspects that affect the temperature determination. Comparison of many pairs of retrievals at the same location (near 32°N or 32°S) measured on sequential orbits (time separation of 96 min) shows a precision ranging from approximately 0.8 K at 68 mbar to about 3.5 K at 0.2 mbar, which agrees with simulations incorporating random noise and short‐period spacecraft motions. Comparisons of globally analyzed CLAES data with National Meteorological Center (NMC) and U.K. Meteorological Office (UKMO) analyses show general agreement, with CLAES tending to be cooler by about 2 K, except in the tropics and high‐latitude winter conditions. This is supported by comparisons with individual radiosondes and several lidars that indicate that the agreement is within 2 K throughout the profile (except for a narrow layer around 3 mbar). An error analysis also indicates that systematic errors should be roughly 2 K, independent of altitude. The systematic differences at low latitudes appear to be due to tropical waves, which have vertical wavelengths too short to be seen by the TIROS Operational Vertical Sounder (TOVS) instruments. There are no correlative rocketsondes or lidars to help resolve the reasons for the high‐latitude differences. Comparisons with other Upper Atmosphere Research Satellite (UARS) data should shed additional light on this question.
Atmospheric fate and greenhouse warming potentials of HFC 236fa and HFC 236ea
Authors: Gierczak Tomasz , Talukdar Ranajit K. , Burkholder James B. , Portmann R. W. , Daniel J. S. , Solomon S. , Ravishankara A. R.
Published: February 2004

The rate coefficient for the reaction OH + CF3CH2CF3 (1,1,1,3,3,3‐hexafluoropropane, HFC236fa) was measured between 269 and 413 K using the pulsed photolysis‐laser induced fluorescence technique to be k1 = (1.60 ± 0.40) × 10−12 exp (−(2450 ± 150)/T) cm3 molecule−1 s−1. The rate coefficient, k2b, for the destruction of CF3CH2CF3 via reaction with O(1D) was measured to be (4.5 ± 1.9) × 10−12 cm3 molecule−1 s−1 using the laser photolysis‐resonance fluorescence technique. From these data, along with previously published rate coefficients for OH reaction with HFC236ea, the atmospheric lifetimes of HFC236fa and HFC236ea were calculated to be 210 and 8.1 years, respectively. The room temperature infrared absorption cross sections for these two compounds were measured over the range 650 to 1350 cm−1. The global warming potentials (GWPs) of HFC236fa and HFC236ea, respectively, were calculated to be 5610 and 2200 for a 20‐year horizon and 5160 and 220 for a 500‐year horizon.
Global uncertainty analysis of a regional‐scale gas‐phase chemical mechanism
Authors: Gao Dongfen , Stockwell William R. , Milford Jana B.
Published: February 2004

A global uncertainty analysis of the Regional Acid Deposition Model version 2 chemical mechanism was conducted to estimate the effect of uncertainties in rate parameters and product yields on predicted concentrations of ozone and other secondary pollutants. Uncertainties were also estimated for changes in ozone due to 25% reductions in reactive organic gases (ROG), nitrogen oxides (NOx) or both. The analyses were performed for single‐day box model simulations of summertime smog episodes, with uncertainties propagated using a Latin hypercube sampling scheme. The resulting uncertainties in peak ozone concentrations range from about 20 to 50% (±1σ relative to the mean). Uncertainties in predicted concentrations range from 15 to 30% for HNO3, 20 to 30% for HCHO, and 40 to 70% for peroxyacetyl nitrate (PAN). Except with very low concentrations, uncertainties in H2O2 range from 30 to 45%. For the cases studied the choice between ROG or NOx reductions as most effective for lowering ozone concentrations is insensitive to uncertainties in chemical parameters. Product concentrations are most strongly affected by uncertainties in rate parameters for PAN chemistry, HNO3 formation, aromatics oxidation, the reaction of HO2 + NO, and photolysis of HCHO, NO2, and O3, and uncertainties in peroxy radical yields from aromatics and olefins oxidation.
Analysis of small‐scale patterns of atmospheric motion in a sheared, convective boundary layer
Authors: Ludwig F. L. , Street R. L. , Schneider J. M. , Costigan K. R.
Published: February 2004

Multiresolution feature analysis has been applied to data from NOAA's Phoenix II dual Doppler radar observations of a convective boundary layer near Boulder, Colorado, during June 1984 and to large eddy simulation (LES) results (using the regional atmospheric modeling system (RAMS) developed at Colorado State University) corresponding to a subset of that data. The data and LES results provide winds on a three‐dimensional grid with spacing of ∼200 m to a depth of about 2 km over a 9 × 9 km square for the observations. LES results were for an elongated (in the east‐west direction) volume. The prevailing circulation maintained a strong shear (synoptic westerlies aloft above upslope easterlies at the surface) despite strong afternoon heating. The analysis defined preferred motion patterns (for both the observed and the simulated data) over 3 × 3 × 3 grid points using empirical orthogonal functions. In the case of the observations the patterns strengthened or weakened the shear locally for the most stable cases, but other patterns became relatively more important with increasing convection. Among these were a vortical pattern tilted in the shear direction. Differences in the peak intensity statistics for two different smoothings were used to estimate their support dimension from the observed data during moderately unstable conditions; most fell between 2.2 and 2.6. When the LES results corresponding to a moderately unstable observed atmosphere were analyzed, they showed that the preferred motion patterns were more like the observed stable case than the unstable cases, and the support dimension estimates were all greater than 2.6, indicating less intermittency than was observed.
Gas chromatography mass spectrometry analysis of volatile organic trace gases at Mauna Loa Observatory, Hawaii
Authors: Helmig Detlev , Pollock Walter , Greenberg Jim , Zimmerman Pat
Published: February 2004

Volatile organic trace gases in the remote troposphere at the Mauna Loa Observatory were identified in July and August 1992 during the Mauna Loa Observatory Photochemical Experiment (MLOPEX 2) using an in situ fully automated gas chromatography mass spectrometry (GCMS) instrument. Identification was obtained for 65 organic compounds, 7 additional compounds were identified tentatively. Four target parts per trillion (ppt)‐level species were detected in the selected ion monitoring mode (SIM). The experimental data show typical background air characteristics; for example, abundance of long‐lived compounds such as halogenated hydrocarbons during all measurement periods. Volatile organic compounds (VOCs) from local sources from the island were also seen during daytime upslope flow conditions. These included short‐lived biogenic hydrocarbons such as isoprene and monoterpenes and typical emissions from combustion processes such as alkylated aromatics.
Theoretical, actinometric, and radiometric determinations of the photolysis rate coefficient of NO2 during the Mauna Loa Observatory Photochemistry Experiment 2
Authors: Lantz K. O. , Shetter R. E. , Cantrell C. A. , Flocke S. J. , Calvert J. G. , Madronich S.
Published: February 2004

Measurements of the photolysis rate coefficient of NO2 (jNO2) were made using a chemical actinometer during the fall (September 15 to October 23, 1991), winter (January 15 to February 15, 1992), spring (April 15 to May 15, 1992), and summer (July 15 to August 15, 1992) intensives during the second Mauna Loa Observatory Photochemistry Experiment (MLOPEX 2), Hawaii. The measured clear sky jNO2 values of MLOPEX 2 for all four intensives have substantially increased over the measured jNO2 values of MLOPEX 1 (May, 1988); a 37% increase occurs in midday clear sky jNO2 from the spring intensive of MLOPEX 1 to the spring intensive of MLOPEX 2. The ratio of actinometer measurements to theoretical calculations of jNO2 are 1.44 ± 0.03, 1.45 ± 0.02, 1.43 ± 0.03, and 1.34 ± 0.02 for the fall, winter, spring, and summer intensives, respectively. Inclusion of stratospheric aerosols or aerosols of any reasonable optical parameters in a detailed discrete ordinate model cannot account for the discrepancy between measurements and model. The photolysis rate coefficient of NO2 is also derived from simultaneous measurements of the ultraviolet irradiance measured with an Eppley radiometer using a semiempirical relationship for each of the four intensives. A simplified cloud model is proposed to explain jNO2 values that exceed clear sky values during days that have partial cloud coverage.
A numerical model for the simulation of stable isotope profiles in drying soils
Authors: Mathieu Renaud , Bariac Thierry
Published: February 2004

A numerical model was developed for the simulation of vertical profiles of water content and stable isotope concentration in a drying soil. It allows the calculation of stationary isotopic profiles occurring in steady state conditions as well as the evolution of the profiles at the first and second drying stages in transient conditions for any initial profile, atmospheric conditions, and temperature distribution. A parameterization of the kinetic fractionation in relation to surface water content is proposed to allow the simulation of its evolution during the development of a dry superficial layer in nonsteady conditions. After a qualitative study of the isotopic enrichment the model creates, it is validated by comparison with existing analytical solutions which are limited to the stationary state. A numerical application in nonsteady conditions allowed us to simulate the evolution of the isotopic profile for a drying soil and to compare it with the stationary profile. The discussion emphasizes the lack of experimental examination of the liquid‐vapor isotopic equilibrium and the liquid phase isotopic homogeneity in porous media, both major assumptions in the theory of water and stable isotope transfers in soils.
A real‐time monitoring system for airborne particle shape and size analysis
Authors: Kaye P. H. , Alexander‐Buckley K. , Hirst E. , Saunders S. , Clark J. M.
Published: February 2004

This paper describes a new instrument for the study of airborne particles. The instrument performs a rapid analysis of the transient spatial intensity distribution of laser‐light scattered by individual aerosol particles drawn from an ambient environment and uses this to characterize the particles in terms of both size and shape parameters. Analyses are carried out at peak particle throughput rates of up to 10,000 particles per second, and semiquantitative data relating to the size and shape (or more correctly asymmetry) spectra of the sampled particles are provided to the user via a graphical display which is refreshed or updated at 5‐s intervals. In addition to the real‐time display of data, continuous data recording allows subsequent replay of measurements at either normal or high speed. Preliminary experimental results are given for aerosols of both spherical and nonspherical particle types, and these suggest the instrument may find use in environmental monitoring of aerosols or clouds where some real‐time semiquantitative assessment of particulate size and shape spectra may be desirable as an aid to characterizing the aerosol and its constituent particulate species.
Atmospheric deposition of reactive nitrogen oxides and ozone in a temperate deciduous forest and a subarctic woodland: 1. Measurements and mechanisms
Authors: Munger J. William , Wofsy Steven C. , Bakwin Peter S. , Fan Song‐Miao , Goulden Michael L. , Daube Bruce C. , Goldstein Allen H. , Moore Kathleen E. , Fitzjarrald David R.
Published: February 2004

We present 5 years of NOy and O3 eddy flux and concentration measurements and NOx concentration measurements at Harvard Forest (1990–1994), a mixed deciduous forest in central Massachusetts, and 2 months of data for a spruce woodland near Schefferville, Quebec, during the NASA ABLE3B/Northern Wetlands Study (1990). Mean midday values of net dry NOy flux from atmosphere to canopy were 3.4 and 3.2 μmole m−2 hr−1 at Harvard Forest in summer and winter, respectively, and 0.5 μmole m−2hr−1 at Schefferville during summer. Nighttime values were 1.3, 2.0, and 0.15 μmole m−2 hr−1, respectively. For 1990–1994, the net annual dry deposition of nitrogen oxides was 17.9 mmole m−2 yr−1 (2.49 kgN ha−1 y−1). Oxidized species such as HNO3 dominated N deposition, with minor contributions from direct deposition of NO2. Emissions of NO from the forest soil were negligible compared to deposition. Comparison of NOy deposition at Harvard Forest and Schefferville and analysis of the dependence on meteorological parameters show that anthropogenic sources dominate the nitrogen oxide inputs over much of North America. Heterogeneous reactions account for >90% of the conversion of NO2 to HNO3 in winter, leading to rates for dry deposition of NOy similar to fluxes in summer despite 10‐fold decrease in OH concentrations. In summer, formation of HNO3 by heterogeneous reactions (mainly at night) could provide 25–45% of the NO2 oxidation.
Semidiurnal and diurnal temperature tides (30–55 km): Climatology and effect on UARS‐LIDAR data comparisons
Authors: Keckhut Philippe , Gelman M. E. , Wild J. D. , Tissot F. , Miller A. J. , Hauchecorne A. , Chanin M.‐L. , Fishbein E. F. , Gille J. , Russell J. M. , Taylor F. W.
Published: February 2004

Very good agreement is shown for diurnal and semidiurnal temperature variations calculated from lidar measurements in southern France and from data of the microwave limb sounder of the Upper Atmosphere Research Satellite (UARS). Tides induce temperature deviations observed in southern France to be as large as ±3 K, with a maximum at the stratopause. The amplitudes and phases of the semidiurnal variation change significantly with season and location. Seasonal changes up to 2 K have been clearly identified for the diurnal component. An analytic model of the diurnal component, based on sinusoidal functions, fits the data well, but is less successful for the semidiurnal component. Substantial agreement is also reported for the diurnal component between the results of our analytical model and the published results of a two‐dimensional global‐scale wave model. In contrast, the semidiurnal component is in total disagreement with numerical simulations that report very small amplitudes, as compared with the observations reported here. The confidence in detecting bias in data comparisons is improved if data used are limited to periods from April to September and if time‐of‐day adjustments are applied. Comparison between lidar and nearly coincident UARS temperature measurements have revealed, systematically, for the 4 experiments aboard UARS, a significant residual mean difference of up to 3 K around 35–43 km. A comparison using simultaneous measurements suggests that the bias is associated with the variability of migrating tides and/or the presence of nonmigrating tides rather than instrumental characteristics.
Kinetic studies of the reactions of BrO and IO radicals
Authors: Laszlo Barna , Huie Robert E. , Kurylo Michael J. , Miziolek Andrzej W.
Published: February 2004

The 193‐nm laser photolysis Of Br2/N2O mixtures in N2 buffer has been utilized to determine the absorption cross section of BrO and to study the reactions of O(3P) with Br2, O(3P) with BrO, and the self reaction of BrO at room temperature. The measured kinetic data are in good agreement with the literature values. Molecular bromine formation in the self‐reaction of BrO can be described by the concerted steps of Br+BrO→BrOBr and Br+BrOBr→Br2+BrO. From a curve fitting of the simultaneously monitored BrO and IO decays in the Br2/I2/N2O system, room temperature rate constants for the BrO+IO→Products and I+BrO→IO+Br reactions of (6.9±2.7)×10−11 cm3/molecule/s and (1.2±0.6)×10−11 cm3molecule/s, respectively, were derived. Similar experiments using IBr, instead of Br2/I2, revealed a marked sensitivity of the rate constant analysis to the accessible ratio of radical concentrations. Kinetic analysis of this complex reaction system is presented.
High‐latitude climate change in a global coupled ocean‐atmosphere‐sea ice model with increased atmospheric CO2
Authors: Washington Warren M. , Meehl Gerald A.
Published: February 2004

A global atmospheric general circulation model (GCM) coupled to a global 1‐degree, 20‐level ocean GCM with dynamic and thermodynamic sea ice is integrated with CO2 increasing at 1% per year compounded for 75 years (CO2 doubles at about year 70). Flux correction is not used in the experiment. The increase of globally averaged surface air temperature at the time of CO2 doubling is 3.8°C. The warm subsurface Atlantic layer at intermediate depths in the Arctic is maintained mainly by the sinking and intrusion of water from the West Spitsbergen Current in the model and the observations. With increased CO2 in the model, the warmer surface waters are intruded into the upper portion of the Atlantic layer producing an anomalous warming in the model at depths between 200 and 400 m. This resembles an anomalous warm layer near those depths recently observed in the Arctic. As the climate warms and sea ice retreats, low clouds increase over the newly exposed water. Yet the consequent increase of cloud albedo over these regions is more than compensated for by the decrease of surface albedo due to the melting of sea ice. This produces a net decrease of planetary albedo in the Arctic that contributes to a strong ice‐albedo feedback and the comparatively high sensitivity of the model.