bluuebunny/crossref_metadata_2025 huggingface dataset:
Observations of meridional scale frequency dependence in the coupled tropical ocean‐atmosphere system
Authors: Wang Chunzai , Weisberg Robert H.
Published: February 2004

It is generally observed in models of the coupled tropical ocean‐atmosphere system that the meridional scales for oscillations at interannual periods are larger than an oceanic equatorial Rossby radius of deformation. Using 9 years of the high‐resolution optimum interpolation sea surface temperature (SST) product of the National Oceanic and Atmospheric Administration (NOAA)/National Centers for Environmental Prediction (NCEP), analyses are made on the frequency dependence of the observed meridional scales, with emphasis on the latitudinal structures in the central Pacific at 140°W. On the relatively short intraseasonal and seasonal timescales the SST variations are found to occur over a meridional scale of the oceanic equatorial Rossby radius of deformation suggested by conventional equatorially trapped wave theory. In contrast to this, on the longer annual and interannual timescales the meridional scales are found to increase beyond the oceanic equatorial Rossby radius of deformation. A physical explanation for this meridional scale increase with decreasing frequency in the coupled tropical ocean‐atmosphere system is discussed.
Effective environmental half‐lives of 90Sr and 137Cs in the coastal seawater of Japan
Authors: Kasamatsu Fujio , Inatomi Naohiko
Published: February 2004

The effective environmental half‐lives of 137Cs and 90Sr together with their variations in concentrations in the coastal seawater of Japan were examined based on results of long‐term and systematic measurements during 1984–1994. Concentrations of these radionuclides in surface water from 12 areas in the region of the Kuroshio and the Tsushima Currents along Japan were similar and higher than in surface waters of the cold current of Oyashio. Relatively constant concentrations were observed in seawater above 200 m depth that appears to be well mixed, as generally assumed, with sharp gradient below 200 m depth. The observed mean concentrations of 137Cs in coastal waters of Japan decreased from 3.1 ± 0.2 mBq/L in the surface mixed layer (0–200 m depth) to 1.8 ± 0.2 mBq/L at 500 m depth (a decrease of 58%). The observed mean concentration of 90Sr in coastal waters of Japan decreased from 2.2 ± 0.2 mBq/L at the surface mixed layer to 1.4 ± 0.2 mBq/L at 500 m depth (a decrease of 64%). The vertical distribution of 137Cs/90Sr activity ratio ranged from 1.45 at surface to 1.31 at a depth of 450–500 m, suggesting a possible difference in the behavior between 90Sr and 137Cs in coastal seawater. Concentrations of 90Sr and 137Cs in the surface mixed layer were 3.3 ± 0.4 mBq/L (n=40) and 4.3 ± 0.5 mBq/L (n=40), respectively, in 1984. The concentrations dropped fairly steadily from 1984 to 1994, except for a clear increase of 137Cs in the spring of 1986 (5.0 ± 1.1 mBq/L, n=34) due to Chernobyl deposit. The concentrations of 90Sr and 137Cs in 1994 were 2.2 ± 0.2 mBq/L (n=51) and 3.1 ± 0.2 mBq/L (n=51), respectively. Effective environmental half‐lives of 90Sr and 137Cs of the surface mixed layer in the Tsushima Current system are calculated to be 17.3 years (95% confidence interval 16.1–18.7 years) during 1984–1994 and 18.7 years (13.4–31.2 years) during 1987–1994, respectively.
Photochemical production of carbon disulphide in seawater
Authors: Xie Huixiang , Moore Robert M. , Miller William L.
Published: February 2004

It is generally accepted that the ocean is an important source for atmospheric CS2, which makes a major contribution to the formation of COS in the atmosphere. The processes producing CS2 in seawater, however, are essentially unknown. We report for the first time to our knowledge that marine photochemical reactions are identified as a significant source for oceanic CS2. Apparent quantum yield spectra of CS2 production were obtained using water samples collected in the northeast Atlantic. Results indicate that it is mainly UV solar radiation (290–340 nm) which is responsible for CS2 photoproduction. The photoproduction rate of CS2 is positively correlated with absorbance at 350 nm, suggesting that the reactions are mediated by chromophoric dissolved organic matter (CDOM). Laboratory irradiations have confirmed that cysteine and cystine are efficient precursors of CS2 and that OH radicals are likely to be important intermediates. Both the field survey and laboratory work point to similar mechanisms for photochemical production of CS2 and COS in marine waters. A CS2 production rate of 0.49 Tg yr−1 for the world oceans has been estimated using the quantum yield spectra from this work and the sea surface light field provided by Leifer [1988]. This estimate is of the same order of magnitude as the present estimate of the CS2 flux from the ocean to the atmosphere based on surface saturation and wind speed.
The Tropical Ocean‐Global Atmosphere observing system: A decade of progress
Authors: McPhaden Michael J. , Busalacchi Antonio J. , Cheney Robert , Donguy Jean‐René , Gage Kenneth S. , Halpern David , Ji Ming , Julian Paul , Meyers Gary , Mitchum Gary T. , Niiler Pearn P. , Picaut Joel , Reynolds Richard W. , Smith Neville , Takeuchi Kensuke
Published: February 2004

A major accomplishment of the recently completed Tropical Ocean‐Global Atmosphere (TOGA) Program was the development of an ocean observing system to support seasonal‐to‐interannual climate studies. This paper reviews the scientific motivations for the development of that observing system, the technological advances that made it possible, and the scientific advances that resulted from the availability of a significantly expanded observational database. A primary phenomenological focus of TOGA was interannual variability of the coupled ocean‐atmosphere system associated with El Niño and the Southern Oscillation (ENSO).Prior to the start of TOGA, our understanding of the physical processes responsible for the ENSO cycle was limited, our ability to monitor variability in the tropical oceans was primitive, and the capability to predict ENSO was nonexistent. TOGA therefore initiated and/or supported efforts to provide real‐time measurements of the following key oceanographic variables: surface winds, sea surface temperature, subsurface temperature, sea level and ocean velocity. Specific in situ observational programs developed to provide these data sets included the Tropical Atmosphere‐Ocean (TAO) array of moored buoys in the Pacific, a surface drifting buoy program, an island and coastal tide gauge network, and a volunteer observing ship network of expendable bathythermograph measurements. Complementing these in situ efforts were satellite missions which provided near‐global coverage of surface winds, sea surface temperature, and sea level. These new TOGA data sets led to fundamental progress in our understanding of the physical processes responsible for ENSO and to the development of coupled ocean‐atmosphere models for ENSO prediction.
Formation of 26.8–26.9 σθ water in the Kuril Basin of the Sea of Okhotsk as a possible origin of North Pacific Intermediate Water
Authors: Watanabe Tatsuro , Wakatsuchi Masaaki
Published: February 2004

By using all Japanese hydrographic data obtained south of 55°N in latitude in the Sea of Okhotsk, we compile a data set for this study. Our investigations with these data show that a large quantity of relatively cold, fresh, oxygen‐rich homogeneous intermediate water with a density range of 26.8 to 26.9 σθ exists in the Kuril Basin; we name this intermediate water the Kuril Basin Intermediate Water (KBIW). Results of isosteric analyses show that a possible origin of KBIW is located in a region off the Hokkaido coast in the southwestern Sea of Okhotsk. We suggest that KBIW is produced by the isopycnal mixing of relatively dense Soya Warm Water, which appears only in early spring, with the colder, fresher water which originates from the northwestern Okhotsk. Finally, we demonstrate that KBIW may be a source water of the North Pacific Intermediate Water (NPIW) because it has the same density range and water properties.
Hyperpycnal and buoyant plumes from a sediment‐laden river
Authors: Chao Shenn‐yu
Published: February 2004

The interaction of river plumes and sediment transport is examined using a three‐dimensional numerical model which couples the hydrodynamics and sediment transport. Only large rivers in midlatitudes are considered so that the effect of Coriolis deflection becomes important. Winds and tides are excluded. In an initially quiescent coastal sea, sediment‐freshwater mixture is released from the inner reaches of a river. A high ratio of sediment to buoyancy input is chosen so that the initial sediment‐freshwater mixture is denser than the receiving seawater. As the dense underflow enters the adjacent sea, release of sediment to the sea floor changes the plume from hyperpycnal to buoyant. The forced convection of freshwater from depths triggers an expansive buoyant plume expanding in the direction of Kelvin wave propagation. The resulting buoyant plume is far more expansive than a typical buoyant plume in clear seawater produced by a comparable buoyancy input. Circulation associated with the plume is anticyclonic throughout the water column, lacking a cyclonic gyre underneath the anticyclone as one would expect from a typical buoyant plume in clear seawater. A heuristic argument follows to explain the lack of baroclinic flow structure in plumes forced by the sediment‐freshwater mixture.
Toward the true near‐surface wind speed: Error modeling and calibration using triple collocation
Authors: Stoffelen Ad
Published: February 2004

Wind is a very important geophysical variable to accurately measure. However, a statistical phenomenon important for the validation or calibration of winds is the small dynamic range relative to the typical measurement uncertainty, i.e., the generally small signal‐to‐noise ratio. In such cases, pseudobiases may occur when standard validation or calibration methods are applied, such as regression or bin‐average analyses. Moreover, nonlinear transformation of random error, for instance, between wind components and speed and direction, may give rise to substantial pseudobiases. In fact, validation or calibration can only be done properly when the full error characteristics of the data are known. In practice, the problem is that prior knowledge on the error characteristics is seldom available. In this paper we show that simultaneous error modeling and calibration can be achieved by using triple collocations. This is a fundamental finding that is generally relevant to all geophysical validation. To illustrate the statistical analysis using triple collocations, in situ, ERS scatterometer, and forecast model winds are used. Wind component error analysis is shown to be more convenient than wind speed and direction error analysis. The anemometer winds from the National Oceanic and Atmospheric Administration (NOAA) buoys are shown to have the largest error variance, followed by the scatterometer and the National Centers for Environmental Prediction (NCEP) forecast model winds proved the most accurate. When using the in situ winds as a reference, the scatterometer wind components are biased low by −4%. The NCEP forecast model winds are found to be biased high by −6%, After applying a higher‐order calibration procedure an improved ERS scatterometer wind retrieval is proposed. The systematic and random error analysis is relevant for the use of nearsurface winds to compute fluxes of momentum, humidity, or heat or to drive ocean wave or circulation models.
Insignificant evaporation from escaping sea spray droplets
Authors: Wu Jin
Published: February 2004

Production spectra of sea spray droplets obtained by Smith et al. [1993] at various wind velocities are used in conjunction with a sharp dropoff on the large‐radius side proposed by Wu [1990, 1993]. Most spray droplets described by these composite spectra are shown to be suspended. The maximum possible flux of water from these droplets which escape the sea is shown to be insignificant.
Seasonal and interannual variability of surface photosynthetically available radiation in the Arabian Sea
Authors: Arnone Robert A. , Ladner Sherwin , La Violette Paul E. , Brock John C. , Rochford Peter A.
Published: February 2004

The regional and monthly intensity of photosynthetically available radiation (PAR) (350–700 nm) just below the sea surface (EdPAR−) for the Arabian Sea is determined from solar irradiance models and 7 years of satellite data (1979–1985). Model results of high spatial resolution (18 km) PAR distribution computed from actual monthly measurements (aerosols, cloud cover, and ozone) displayed small‐scale patchiness that is not observed in PAR climatology models. Two elevated PAR periods are observed each year, as opposed to a single elevated period per year observed in the North Atlantic during the summer. When the biannual cycle for each of the 7 years is compared with the 7‐year average, interannual changes in intensity and time are observed. Additionally, the PAR cycle is found to vary regionally within the Arabian Sea. The bimodal PAR distribution shows elevated peaks in May and October and minima in December (corresponding to the winter equinox) and July. The second minima occurs at the onset of the southwest monsoon, apparently in response to increased cloud cover and aerosols associated with the monsoon. This summer minima varied latitudinally. It originates in the southern regions (0°–10° latitude) in April and migrates north as the influence of the southwest monsoon moves northward, reaching the northern Oman coast (20° latitude) in August. Additionally, the summer minima is less pronounced as the southwest monsoon moves northward. Maximum PAR intensity is observed in early spring (preceding the minima), originating in the southern Arabian Sea and extending northward into the central Arabian Sea. The timing of the northward movement of this spring maximum is slightly different each year. The net yearly PAR intensity for each of the 7 years appears to remain approximately the same, despite the interannual variability in the cycle and regional variability. The timing and location of PAR cycles are important since they must be coupled with nutrient availability to understand biological cycles. We determined that for the Arabian Sea, PAR cycles determined by climatology may be inadequate to define the submarine light field and that high‐resolution PAR cycles are needed to resolve realistic bio‐optical and nutrient cycles.
Internal wave reflection and mixing at Fieberling Guyot
Authors: Eriksen Charles C.
Published: February 2004

The structure of internal wave reflection off a sloping bottom on the steep flank of a tall North Pacific Ocean seamount is observed in year‐long moored array records to differ substantially from the form predicted by linear theory, although linear theory accounts for several qualitative features of the process. This study documents new features of wave reflection as described below. Wave reflection is detectable as far as 750 m above the bottom. Motions are dominated by a single empirical mode whose phase structure obeys linear internal wave dispersion but whose amplitude decays with a scale comparable to the wavenumber. While the dominant mode has scales appropriate to the reflection of a first baroclinic mode wave incident from the open ocean, its decay from the bottom is such that current vectors in the vertical plane rotate clockwise in time when viewed with shallow water to the right. This flow resembles the lower half of the deepest cell pattern predicted by linear reflection from a uniform slope. At the local internal wave critical frequency, the dominant mode has nearly a vanishing wavenumber rather than the infinite wavenumber predicted by linear reflection. Reflected waves are aligned parallel to the bottom slope measured on wave spatial scales, rather than shorter ones. Wave reflection causes large, frequent density overturns, implying mixing. The rate and strength of these overturns imply a local vertical eddy viscosity of 2–6 × 10−4 m2/s over the bottom few hundred meters. The contribution of bottom‐intensified mixing to the open deep ocean is roughly equivalent to that found in situ, although reflection from gentler slopes or at lower latitude may produce greater contribution from internal wave‐reflection‐induced mixing.
Upper ocean heat and salt balances in response to a westerly wind burst in the western equatorial Pacific during TOGA COARE
Authors: Feng Ming , Hacker Peter , Lukas Roger
Published: February 2004

Two volume control methods are used to analyze the upper ocean heat and salt balances in response to a westerly wind burst event in the western equatorial Pacific during the Tropical Ocean Global Atmosphere Coupled Ocean‐Atmosphere Response Experiment. One method uses a fixed‐thickness surface layer, and the other uses an isopycnal depth as the lower boundary. Horizontal advection terms in the budget calculations are estimated using the R/V Wecoma repeat hydrographic survey data within a 133 km × 133 km region. In both methods, the upper ocean heat budget is balanced within 10 W m−2 of the surface air‐sea flux observations during a 19‐day time period, which covers the December 1992 westerly wind burst and a low‐wind recovery period in early January 1993. The standard error in the estimation of heat advection is 11 W m−2. The salt budget yields a rain rate estimate of 15.4 mmd−1 with an error bar of 4 mmd−1. This estimate is within 20% of the optical rain gauge measurements. The advection terms are important in both the heat and salt balances. Meridional advection dominates over zonal and vertical advection, acting to decrease temperature and increase salinity in the surface layer. From the isopycnal boundary method, the diapycnal turbulent flux transports a mean heat flux of 17 W m−2 into the thermocline. Diapycnal advection is almost equally important, so that the total heat flux into the thermocline is estimated to be more than 30 W m−2 during the study time period. Both terms are also important in the salt budget.
Impacts of precipitation in the upper ocean in the western Pacific warm pool during TOGA‐COARE
Authors: Li Xiaofan , Sui C.‐H. , Adamec D. , Lau K.‐M.
Published: February 2004

An ocean mixed‐layer model with a modified Kraus‐Turner parameterization scheme is used to investigate the impacts of precipitation in the upper ocean in the western Pacific warm pool during Tropical Ocean Global Atmosphere‐Coupled Ocean Atmosphere Response Experiment (TOGA‐COARE). Heat and salt budgets calculated in the upper ocean indicate local balance between surface forcing and the ocean response. Thus the mixed‐layer model captures the dominant processes governing heat and salt variability. The model responses are analyzed and compared with the observed upper ocean in three distinctive layers determined by Monin‐Obukhov length scales. In the top layer (the top 5 m), about 90% of the surface buoyancy flux is absorbed, and strong diurnal and intraseasonal variations are excited. The second layer, 5–20 m, contains intraseasonal variability that is characterized by nearly neutral stratification during strong westerly wind events, strong thermal stratification during clear‐sky days, and strong saline stratification during heavy precipitation. The dominant effect of precipitation is to generate a stable stratification and to form a barrier layer. The third layer, 20–50 m, has intraseasonal variations due to mixing during westerly wind events. Heavy precipitation amplifies mixed‐layer temperature fluctuations by a cycle of strong surface cooling and entrainment warming through the following processes. Heavy precipitation causes a shallower mixed layer and a larger cooling rate. Surface temperature drops rapidly, and the upper ocean becomes thermally unstable. The salinity maintains a weak density stability, which causes strong entrainment warming. Surface freshwater flux is the key factor controlling saline structure when advection is excluded. However, experiments without the entrainment process show a significant bias toward a lower salinity, indicating that the entrainment process must be properly treated in the model to prevent a biased trend.
Modeling nitrate fluxes in an open coastal environment (Gulf of Lions): Transport versus biogeochemical processes
Authors: Tusseau‐Vuillemin Marie‐Hélène , Mortier Laurent , Herbaut Christophe
Published: February 2004

A 13‐compartment model of primary production and degradation of dissolved organic matter has been coupled with a general circulation model in an open coastal environment (Gulf of Lions, Mediterranean) so as to quantify exchanges with the open sea. The biogeochemical model had been previously calibrated with a one‐dimensional vertical version on a 1‐year data set, and this simulation provides boundary conditions for the three‐dimensional model. After a 1‐year spin‐up simulation, quasi‐equilibrium is obtained for all the compartments, and the results of an additional annual simulation are compared with coastal zone color scanner images and other data collected in the area: the simulation of chlorophyll a, nutrient concentrations, and primary production is quite satisfactory, although the spring bloom starts slightly earlier than usual. Total gross community production is estimated at 76 g C m−2 y−1, and New Gross Community Production at 45 g Carbon m−2 y−1 (f = 0.37). The model was used to understand the nitrate annual cycle in the coastal zone of the Gulf of Lions. Nitrate input from the Rhône river, from the sediment, and from marine advection are compared in terms of potential fertilization. Model results indicate that, regarding the open sea, the margin acts most of the time as a sink for nitrate. However, during winter, when phytoplankton growth is reduced and cascading of dense waters is active along the shelf, the margin is shown to export nitrate toward the open sea. These results may qualitatively apply to other open Mediterranean margins, although the intensity of the fluxes would be modulated by local features.
Variability of the near‐surface eddy kinetic energy in the California Current based on altimetric, drifter, and moored current data
Authors: Kelly Kathryn A. , Beardsley Robert C. , Limeburner Richard , Brink Kenneth H. , Paduan Jeffrey D. , Chereskin Teresa K.
Published: February 2004

Low‐pass‐filtered velocities obtained from World Ocean Circulation Experiment (WOCE) surface drifters deployed in the California Current off northern California during 1993–1995 have been compared with surface geostrophic velocity estimates made along subtracks of the TOPEX/POSEIDON altimeter and with moored acoustic Doppler current profiler (ADCP) data. To obtain absolute geostrophic velocities, a mean sea surface height (SSH) field was estimated using the mean drifter velocities and historical hydrographic data and was added to the altimetric SSH anomalies. The correlation between collocated drifter and altimetric velocities is 0.73, significant at the 95% level. The component of the drifter velocity which was uncorrelated with the altimetric velocity was correlated with the wind in the Ekman transport sense. Monthly averages of eddy kinetic energy (EKE), estimated using all drifter and altimeter data within the domain (124°–132°W, 33°–40.5°N), show energy levels for the drifters that are about 13% greater than those for the altimeter. Drifter, altimeter, and ADCP measurements all exhibit similar seasonal cycles in EKE, with the altimeter data reaching maximum values of about 0.03 m2 s−2 in late summer/fall. Wavenumber spectra of the altimeter velocity indicate that the velocity fluctuations were dominated by features with wavelengths of 240–370 km, while the ADCP data suggest that the temporal scales of these fluctuations are at least several months. Between 36° and 40.5°N, the region of monthly maximum EKE migrates westward to about 128°W on a seasonal timescale. This region of maximum EKE coincides with the maximum zonal SSH gradient, with increased EKE associated with increased southward flow. A simple model shows that much of the seasonal cycle of the SSH anomalies can be produced by linear processes forced by the curl of the wind stress, although the model cannot explain the offshore movement of the front.
Observation of atmospheric and climate dynamics from a high resolution ice core record of a passive tracer over the last glaciation
Authors: Marsh Nigel D. , Ditlevsen Peter D.
Published: February 2004

Here we present a temporal analysis of diluted calcium from the Greenland Ice Core Project Summit ice core over a length corresponding to the duration of the last glacial period (92–8 ka). Our analysis suggests that this signal can be split into two distinct temporal components whose dynamics are characterized by respective timescale regimes. Timescales longer than approximately 200 years show a strong negative correlation with the temperature proxy δ18O signal. This we interpret as a result of the temperature dependence of processes governing source area efficiency. At faster timescales, ≤200 years, correlation with the temperature proxy is significantly weakened, while its variability or mean absolute deviation is negatively correlated with the δ18O; this we believe is a sign of the turbulent nature or “storminess” of the atmosphere during the glacial climate. Furthermore, this component of the signal displays intermittency and multifractality supporting our interpretation of an observation of atmospheric dynamics. This then provides a signal of atmospheric and climate dynamics back to 92 ka.
An uncertainty budget for ground‐based Fourier transform infrared column measurements of HCl, HF, N2O, and HNO3 deduced from results of side‐by‐side instrument intercomparisons
Authors: Walsh C. Paton , Bell W. , Gardiner T. , Swann N. , Woods P. , Notholt J. , Schütt H. , Galle B. , Arlander W. , Mellqvist J.
Published: February 2004

The results of side‐by‐side instrument intercomparisons of Fourier transform infrared (FTIR) spectrometers at Ny‐Ålesund, Spitzbergen (79°N, 12°E), during May/June 1995 and at Harestua, Norway (60°N, 10°E), during September/October 1994 are reported. The spectrometers were operated simultaneously recording atmospheric spectra in the midinfrared using the Sun as a source. The differences in vertical columns of HCl, HF, N2O, and HNO3 measured simultaneously by different instruments were as large as 5.8, 7.7, 2.8, and 4.3%, respectively, having mean absolute values 0.5, 1.6, 1.0, and 1.6%, respectively. These results were used to derive 1σ overall uncertainties of 9.7% for HCl, 7.7% for HF, 6.4% for N2O, and 14.3% for HNO3. Separate uncertainties are quoted for the precision of daily column measurements which exclude the contribution due to uncertainty in the line parameters. These are 7.7% for HCl, 5.7% for HF, 4.9% for N2O, and 6.8% for HNO3. These numbers are estimated for the local conditions at the intercomparison sites but will differ from site to site depending on the knowledge of local atmospheric conditions at the time of measurement.
Initial comparison of lightning mapping with operational time‐of‐arrival and interferometric systems
Authors: Mazur Vladislav , Williams Earle , Boldi Robert , Maier Launa , Proctor David E.
Published: February 2004

The mapping of lightning radiation sources produced by the operational Time‐of‐Arrival National Aeronautics and Space Administration/Lightning Detection and Ranging (NASA/LDAR) system is compared with that of the Interferometric French Office National D'Etudes et de Recherches Aerospatiales (ONERA‐3D) system. The comparison comprises lightning activity in three Florida storms and also individual flashes in one of these storms. Although limited in scope, the comparison and analysis show a significant difference in the representation of lightning radiation by each mapping system. During the duration of a flash, the LDAR data show a continuity in time and a three‐dimensional structure of radiation sources. The ONERA‐3D radiation source data are more intermittent in time and have a more two‐dimensional structure. The distinction between the radiation sources mapped by the two systems is also reflected in the difference between their propagation speeds, 104–105 m s−l, estimated by the LDAR system, and 107–108 m s−1, estimated by the ONERA‐3D system. We infer that this difference occurs because most of the radiation sources mapped with LDAR are associated with virgin breakdown processes typical of slowly propagating negative leaders. On the other hand, most of the radiation sources mapped with ONERA‐3D are produced by fast intermittent negative breakdown processes typical of dart leaders and K changes as they traverse the previously ionized channels. Thus each operational system may emphasize different stages of the lightning flash, but neither appears to map the entire flash.
Aerosols and climate: Anthropogenic emissions and trends for 50 years
Authors: Wolf Martinus E. , Hidy G. M.
Published: February 2004

A global inventory has been prepared for anthropogenic particulate emissions into the troposphere that covers the period 1990–2040. The inventory provides estimates for both primary particulate emissions and secondary contributions from atmospheric chemical reactions, particularly of SO2. Using a conventional method, total worldwide anthropogenic emissions of particles <10 μm diameter are estimated at 345 Tg/yr, excluding secondary NO3−and organics. Approximately 35% of the particles entering the troposphere is airborne sulfate from oxidation of SO2emissions. Emissions worldwide are dominated by fossil fuel combustion, particularly coal, and biomass burning. These emissions are projected to grow by 1.5 2.1 times in 2040, largely from fossil fuel combustion. Growth is expected to be greatest in the developing countries, especially India and China. Present anthropogenic emissions appear to be a small fraction of emissions from natural sources. However, the man‐derived component could become comparable to natural emissions by 2040. Increased haziness may enhance negative climate forcing both directly by increased radiative scattering and indirectly by modifying cloud albedo and cover. The forcing will be spatially non‐uniform, superimposed on the forcing derived from greenhouse gases.
A study of general circulation model climate feedbacks determined from perturbed sea surface temperature experiments
Authors: Colman R. A. , McAvaney B. J.
Published: February 2004

The response of a general circulation model (GCM) to global perturbations in sea surface temperatures (SSTs) is examined. The feedback strengths in the model are diagnosed by the response of top of atmosphere (TOA) radiative fluxes determined after substitution of fields from the “perturbed” climate into the “control.” Total feedback is divided into terms due to water vapour, lapse rate, surface temperature, and clouds (in turn analysed in terms of cloud amount, height and types). The “standard experiment” prescribes a globally uniform SST perturbation with fixed soil moisture. Four additional experiments vary the number of model vertical levels, the pattern of SST changes, the convection scheme, and the soil moisture. The SST pattern change chosen follows that of an equilibrium 2×CO2 experiment, which shows polar amplification of the surface warming. Variations in the clear sky sensitivity of the model are shown to depend primarily on changes in the long wave response due to competing (positive) water vapor and (generally negative) lapse rate feedbacks. Results here indicate that these feedbacks may be very different for differing experimental boundary conditions. The long wave feedback due to cloud amount changes is negative in all experiments, due to a very consistent decrease in high and middle cloud fractions. Conversely, cloud height feedback is positive due to a general increase in the altitude of (particularly high) cloud. Cloud height feedback is very sensitive to the choice of the convection scheme and to the change in vertical resolution. Greatest changes in the strength of the short wave cloud feedback results from modifications to the soil moisture specification and the convection scheme. The results here indicate that large differences in cloud feedback may be diagnosed from a single model, even without changes being made to the cloud parametrization. The value of the sensitivity can thus be expected to be a function not only of the physical parametrizations chosen for the model (e.g. the penetrative convection scheme), but also of the details of the manner in which the experiment was performed (e.g. SST and soil moisture specifications). The TOA radiation perturbation analysis method proves to be a powerful technique for diagnosing and understanding the physical processes responsible for the range in climate sensitivity found between the experiments.
Satellite‐derived atmospheric characteristics of spiral and comma‐shaped southern hemisphere mesocyclones
Authors: McMurdie Lynn A. , Claud Chantal , Atakturk Serhad
Published: February 2004

Mesoscale cyclones in cold airstreams poleward of major frontal zones are generated frequently over the Southern Ocean. Quantitative information regarding the atmospheric water and wind fields of these systems can be retrieved from satellite‐borne microwave instruments. These instruments include the Special Sensor Microwave Imager (SSM/I), the first European Remote Sensing satellite (ERS‐1) scatterometer and the TIROS‐N operational vertical sounder (TOVS). In this study, we summarize the structures found in the SSM/I‐derived integrated water vapor (IWV), cloud liquid water, wind speed, and liquid and solid precipitation fields for 33 Southern Ocean mesolows. We present the ERS‐1 scatterometer surface wind vector fields for nine of these mesolows, and we analyze the TOVS‐derived geopotential thickness fields for one case. This study confirms earlier results and also examines several features not previously investigated in Southern Ocean mesolows. We find that (1) solid precipitation is more prevalent than liquid precipitation in most mesocyclones; (2) the higher‐latitude, smaller‐scale mesolows with spiral‐shaped cloud systems have lower IWV content than comma‐shaped mesolows; and (3) the surface cyclonic circulation of the mesolows is confirmed by the ERS‐1 winds. Surface fluxes of heat and moisture were estimated from European Centre for Medium‐Range Weather Forecasting (ECMWF) gridded fields for two highlighted cases and found to be moderate during the formation of the mesolow that occurred near the Antarctic ice edge and low for a comma cloud case. In addition, TOVS‐derived thickness patterns show that the Antarctic case lacked strong baroclinic structure, whereas comma cloud cases tend to develop in baroclinic environments.
Feedbacks between climate and surface water in northern Africa during the middle Holocene
Authors: Coe Michael T. , Bonan Gordon B.
Published: February 2004

Observations indicate that the area of lakes and wetlands in northern Africa was considerably greater during the middle Holocene than at present. Simulations are designed to examine whether expanded surface waters may have had a significant impact on the strength of the summer monsoon of northern Africa. Three experiments with the National Center for Atmospheric Research community climate model (NCAR CCM3) are analyzed, a modern and two middle Holocene (6000 years before present) simulations, one with and one without prescribed expanded surface water. There is a significant increase in the strength of the summer monsoon in the middle Holocene simulation due to the enhanced seasonal insolation cycle. The addition of surface waters result in a June, July, and August mean increase in the net surface radiation (5%), an increase in the latent heat flux (30%), a decrease in the sensible heat flux (10%), and an increase in the near‐surface specific humidity (>5%) compared to the middle Holocene simulation without surface water changes. The changes in these simulated climate variables are comparable in scale to changes due to orbital forcing alone. The expanded surface waters result in a cooling of the atmosphere and anticyclonic flow over the large water bodies in summer relative to the simulation without surface water changes. The combination of increased atmospheric moisture and altered circulation results in significant changes to the precipitation distribution in northern Africa including a small increase in the zonal mean July precipitation to the north of the lakes and a decrease to the south. The geographic distribution of the precipitation with surface water changes is qualitatively in better agreement with observations than the distribution with orbital forcing alone but still does not fully match the expansion implied by observations nor the expansion required to produce the simulated middle Holocene surface waters used in this study. The results of this study suggest that surface waters were an important factor in the climate of northern Africa during the middle and early Holocene and that they must be included for accurate simulation of this climate.
Comparison of Arctic and Antarctic trace gas column abundances from ground‐based Fourier transform infrared spectrometry
Authors: Notholt J. , Toon G. C. , Lehmann R. , Sen B. , Blavier J.‐F.
Published: February 2004

Column abundances of several atmospheric trace gases have been derived from solar absorption spectra measured from McMurdo, Antarctica (77.9°S, 166.7°E), in September and October 1986 and from solar and lunar absorption spectra recorded in Ny Ålesund, Spitsbergen (78.9°N, 11.9°E), during winter and spring 1992–1995. The same analysis software, including the molecular spectroscopic parameters and initial volume mixing ratio profile shapes, was employed for both data sets to minimize the possibility of introducing systematic biases. The results clearly show that denitrification in the Antarctic lower stratosphere results in much smaller column abundances of HNO3 than in the Arctic. The springtime recovery of HCl in the Antarctic showed a stronger increase than in the Arctic. The ClONO2 peak occurred about 1 month later in the Antarctic and was found to be less pronounced than in the Arctic. After accounting for the 30% increase in total chlorine between 1986 and 1993, the minimum values for HCl + ClONO2 are similar in the Arctic and the Antarctic, indicating that both polar regions show nearly the same activation of chlorine during the polar night. However, in the Arctic the low values of HCl + ClONO2 start to recover in February, whereas in the Antarctic the lack of NO2, caused by the denitrification, delays the increase of HCl + ClONO2 by about 1 month. A simple one‐dimensional model was able to reproduce the behavior of HCl and ClONO2, simply by assuming a one month later date for the last Antarctic polar stratospheric clouds together with greater latitude excursions of the Arctic air parcel trajectories. The model runs imply that in the Antarctic the reconversion of ClONO2 to HCl occurs about 1 month later than in the Arctic. Furthermore, the results imply that any differences in the O3 depletion are caused mainly by differences in the stratospheric temperatures and dynamics and only to a small extent by the increased chlorine loading. The total column abundances of the short‐lived tropospheric trace gases C2H6, C2H2, CO, and CH2O are found to be up to 10 times higher in the Arctic compared with the Antarctic, reflecting the hemispheric imbalance in production.
Modeling the size distribution of a soil aerosol produced by sandblasting
Authors: Alfaro Stéphane C. , Gaudichet Annie , Gomes Laurent , Maillé Michel
Published: February 2004

In order to develop a model providing the mass size distribution of the dust raised from the ground by the sandblasting process, mechanical characteristics of 240 μm saltating sand grains meant to be used as projectiles in wind tunnel sandblasting experiments were carefully determined. It was found that for values of the measured friction velocity less than about 55 cm/s, the constraint of the relatively small dimensions of the wind tunnel test section did not prevent saltation from developing freely. The kinetic energy of the sand grains was also determined. Aerosols were then produced in the wind tunnel by bombarding a clay target with the saltating 240 μm quartz grains. The size distributions of these aerosols were measured for three wind speeds with an optical particle analyzer. For the lowest wind speed the size distribution of the aerosol was similar to that of the 8.6 μm aggregates originally constituting the agglomerates of clay, but disaggregation into smaller particles became more important when wind speed increased. A theory of sandblasting was then developed that gave theoretical results agreeing with the experimental ones. A consequence of this theory was that submicron particles could be released from aggregates for high wind speeds. Experiments meant to check this implication were carried out and confirmed it. Cohesion energies of kaolin particles of three different sizes, 8.6, 2.8, and approximately 0.5 μm, were calculated and found to be a decreasing exponential function of the particle size. This explains (1) why the soil‐derived aerosol size distributions present a common mode in the 1–10 μm size range, these particles being readily released even in not particularly energetic conditions, and (2) why observation of a submicron mode in natural aerosols requires a higher friction velocity than for the common 1–10 μm mode.
Carbon dioxide in the atmosphere: Isotopic exchange with ozone and its use as a tracer in the middle atmosphere
Authors: Yung Yuk L. , Lee Anthony Y. T. , Irion Frederick W. , DeMore William B. , Wen Jason
Published: February 2004

Atmospheric heavy ozone is enriched in the isotopes 18O and 17O. The magnitude of this enhancement, of the order of 100‰, is very large compared with that commonly known in atmospheric chemistry and geochemistry. The heavy oxygen atom in heavy ozone is therefore useful as a tracer of chemical species and pathways that involve ozone or its derived products. As a test of the isotopic exchange reactions, we successfully carry out a series of numerical experiments to simulate the results of the laboratory experiments performed by Wen and Thiemens [1993] on ozone and CO2. A small discrepancy between the experimental and the model values for 17O exchange is also revealed. The results are used to compute the magnitude of isotopic exchange between ozone and carbon dioxide via the excited atom O(1D) in the middle atmosphere. The model for 18O is in good agreement with the observed values.
Measurements of dimethyl sulfide, dimethyl sulfoxide, dimethyl sulfone, and aerosol ions at Palmer Station, Antarctica
Authors: Berresheim H. , Huey J. W. , Thorn R. P. , Eisele F. L. , Tanner D. J. , Jefferson A.
Published: February 2004

In January and February 1994, measurements of dimethylsulfide (DMS) in air and seawater were conducted at Palmer Station, Antarctica, during project SCATE (Sulfur Chemistry in the Antarctic Troposphere Experiment). Corresponding values ranged between 6 and 595 pptv (median: 94 pptv) and 0.7 and 3.7 nM (median: 2 nM), respectively. Atmospheric DMS levels were significantly enhanced during a storm episode in connection with large‐scale low‐pressure systems passing through the study area. DMS sea‐to‐air fluxes ranged between 0.03 and 19 (median: 1.1) μmol m−2 d−1 based on seawater DMS and wind speed measurements. The atmospheric DMS lifetime is estimated to be 9 days based on a 24‐hour averaged OH concentration of 1.1 × 105 cm−3. Atmospheric dimethylsulfoxide (DMSO) and dimethylsulfone (DMSO2) mixing ratios varied mostly between <0.2 and 15 pptv. These variations consisted of many short‐term spikes which may be explained by downward mixing of these compounds from the free troposphere [Davis et al., this issue]. The DMSO photochemical lifetime with respect to the 24‐hour average OH concentration is approximately 25 hours in the coastal Antarctic troposphere in summer. However, present calculations show that the dominant sink of both DMSO and DMSO2 could be surface loss, yielding atmospheric lifetimes of a few hours for both compounds [see also Davis et al., this issue]. A good correlation was found between DMSO and DMSO2. Aerosol MSA and excess sulfate concentrations also showed a good correlation, with a slope of 0.73. However, DMS was not correlated with any of its measured oxidation products, probably because of its long atmospheric residence time over Antarctica.
Nitrogen oxide emissions from a banana plantation in the humid tropics
Authors: Veldkamp Edzo , Keller Michael
Published: February 2004

Use of nitrogen fertilizer is thought to contribute significantly to the increase of atmospheric nitrous oxide (N2O) and nitric oxide (NO). While the current increase of fertilizer use is concentrated in tropical areas, nearly all studies of nitrogen oxide emissions have been conducted in agricultural systems in temperate areas. We measured N2O and NO fluxes from a fertilized banana plantation in the humid tropics of Costa Rica, where 360 kg N ha−1yr−1is applied. Using chamber techniques, we sampled an Andisol and an Inceptisol on a monthly basis. Twice on each soil type, we sampled intensively in time following fertilizer applications. There is a strong spatial and temporal dependence of nitrogen oxide emissions on place and time of fertilizer application. We find greater mean N2O and NO emissions from the Andisol (31.4 ng N2O‐N cm−2h−1and 55.6 ng NO‐N cm−2h−1) than from the Inceptisol (9.3 ng N2O‐N cm−2h−1and 41.1 ng NO‐N cm−2h−1) under the plants where fertilizer is typically applied. The percentages of applied fertilizer‐N that are converted into nitrogen oxide (“yield”) are between 1.26 and 2.91% for N2O and between 5.09 and 5.66% for NO depending on soil type. We consistently calculate higher nitrogen oxide yields based on intensive sampling versus monthly sampling. Temporal variation in nitrogen oxide emissions probably causes monthly sampling to underestimate mean annual fluxes. Our results suggest that in some tropical systems a higher percentage of applied nitrogen may be lost in gaseous form than in temperate agriculture. Current global estimates of N2O and NO sources from tropical agriculture are based on information from temperate areas and may cause an underestimate of the contribution of tropical agriculture to the budgets of these trace gases.