bluuebunny/crossref_metadata_2025 huggingface dataset:
Observed estimates of convergence in the Savu Sea, Indonesia
Authors: Potemra James T. , Sprintall Janet , Hautala Susan L. , Pandoe Wahyu
Published: May 2003

The Indonesian seas are known to be a region where various Pacific and Indian Ocean water masses converge and are transformed into uniquely characterized Indonesian Sea Water (ISW). The volume of Pacific surface waters that are stored in the Indonesian seas and the timescales for this volume to change are important factors in the formulation of ISW that ultimately enters the Indian Ocean as the Indonesian throughflow (ITF). In this study, data from a recent deployment of pressure gauges surrounding the Savu Sea are used to estimate volume, heat, and freshwater convergence within approximately the upper 100 m. A pair of gauges on the northeastern side (North Ombai and South Ombai) is used to estimate inflow from the Banda Sea through the Ombai Strait, and two pairs (Sumbawa/North Sumba and South Sumba/Roti) are used to estimate outflow to the Indian Ocean via the Sumba and Savu/Dao Straits. The data are used in conjunction with numerical model results to show that at times, for example, November and December of 1996, there can be up to a 10 Sv imbalance between the inflow and the outflow transport. Most of the variability in estimated convergence occurs intraseasonally and seems to be controlled by the flow through the Sumba Strait on the eastern side of the sea. The annual cycle of convergence is smaller and ranges from 4 Sv in December through February to −2 Sv (divergence) in August through October. Lower‐frequency variations based on model results are consistent with satellite derived sea level and sea surface temperatures in the Savu Sea and show that during recent El Niño‐Southern Oscillation events there is anomalous heat divergence (convergence) in the Savu Sea during El Niños (La Niñas).
Seasonal, interannual, and mesoscale variability of the Black Sea upper layer circulation derived from altimeter data
Authors: Korotaev Gennady , Oguz T. , Nikiforov A. , Koblinsky C.
Published: May 2003

TOPEX/Poseidon and ERS altimeter data comprising the period from May 1992 to May 1999 are assimilated into a shallow water model for providing a dynamically consistent interpretation of the sea surface height variations and estimation of the temporal and spatial characteristics of the upper layer circulation in the Black Sea. These 7‐year‐long observations offer a new capability for interpretation of major transient and quasi‐permanent features of the upper layer circulation. The instantaneous flow fields involve a complex, eddy‐dominated system with different types of structural organizations in which the eddies and the gyres of the interior cyclonic cell interact continuously among themselves and with meanders, and filaments of the Rim Current. The circulation possesses a distinct seasonal cycle whose major characteristic features repeat every year with some year‐to‐year variability. An organized two‐gyre winter circulation system disintegrates gradually into a series of interconnecting eddies in the summer and autumn months, which are also characterized by more pronounced and complex mesoscale activity in the peripheral flow system. Our analyses suggest a revised schematic circulation picture of the major quasi‐permanent and recurrent elements of the Black Sea.
Seasonal‐to‐interannual water mass formation in the upper tropical Indian Ocean
Authors: Schiller A.
Published: May 2003

An ocean general circulation model coupled to an atmospheric boundary‐layer model is used to investigate the seasonal cycle and interannual anomalies of water mass transformation in the upper tropical Indian Ocean. Within the thermocline of the tropical Indian Ocean diapycnal mixing as well as surface buoyancy fluxes are prime contributors to water mass formation. The seasonal cycle of thermocline water mass transformation in the Indian Ocean is associated with surface density fluxes and interior mixing. It is balanced by advection (overturning) and volumetric density changes due to the unsteadiness of the circulation. North of 7°S and during the Northeast Monsoon (DJFM), thermocline water is lost at a rate of up to 17 Sv. During the Southwest Monsoon (MJJASO), thermocline water gains volume at a rate of up to 8 Sv. On annual mean the upper tropical Indian Ocean loses water mass to the deeper layers (−3.1 Sv). Owing to the deep‐reaching overturning cell in the Indian Ocean seasonal formation rates of thermocline water are closely linked to the seasonal cycle of heat transport across 7°S. Regional formation is strongest in the equatorial Indian Ocean with a strong semiannual signal. Interannual variability in the tropical Indian Ocean generates diabatic changes of water mass characteristics in the upper ocean with significant anomaly amplitudes in the formation of thermocline water for the 1982‐1998 period (+6 Sv to −4 Sv). Furthermore, interannual anomalies of regional water mass formation correlate at −0.7 (western equatorial Indian Ocean) and at +0.8 (eastern equatorial Indian Ocean) with equatorial zonal wind stress anomalies. The model results suggest that interannual variability in the upper tropical Indian Ocean does not only contain a strong (predominantly adiabatic) east‐west component but also involves significant diabatic changes.
An improved single‐column model representation of ocean mixing associated with summertime leads: Results from a SHEBA case study
Authors: Holland Marika M.
Published: May 2003

Ice/ocean mixed layer model simulations are run for a SHEBA field project case study from 5 July–8 August 1998. Observations indicate that during this time, calm winds occurred and coincided with a rapid warming and freshening of the surface of a lead near the SHEBA camp. A subsequent storm mixed down this warm, fresh water. Single‐column model simulations of this event are performed to isolate properties of the ocean system which must be accounted for to improve the representation of mixing in summertime leads. A traditional method of simulating the ice/ocean system in which a single ocean mixed layer calculation is forced with fluxes aggregated over the ice and open water portions of the domain is compared with simulations in which separate mixed layer calculations are done for the lead and under‐ice ocean systems. It is found that not only are multiple ocean mixed layer calculations needed to improve the simulations but the surface of the lead must be realistically embedded within the ice cover. When stable conditions occur, the lead surface remains isolated from the under‐ice system. Using this method considerably improves simulated lead vertical temperature and salinity profiles, allowing the lead surface to freshen to 20 ppt and reach temperatures greater than 1.4°C above freezing. This modifies the ice mass budgets, increasing lateral melt rates, open water formation, and the amount of absorbed solar radiation. This has implications for the accurate simulation of climate change and variability due to its effects on the albedo feedback mechanism.
Seasonal mixed layer heat budget of the tropical Atlantic Ocean
Authors: Foltz Gregory R. , Grodsky Semyon A. , Carton James A. , McPhaden Michael J.
Published: May 2003

This paper addresses the atmospheric and oceanic causes of the seasonal cycle of sea surface temperature (SST) in the tropical Atlantic on the basis of direct observations. Data sets include up to 4 years (September 1997 to February 2002) of measurements from moored buoys of the Pilot Research Array in the Tropical Atlantic (PIRATA), near‐surface drifting buoys, and a blended satellite in situ SST product. We analyze the mixed layer heat balance at eight PIRATA mooring locations and find that the seasonal cycles of latent heat loss and absorbed shortwave radiation are responsible for seasonal SST variability in the northwest basin (8°N–15°N along 38°W). Along the equator (10°W–35°W), contributions from latent heat loss are diminished, while horizontal temperature advection and vertical entrainment contribute significantly. Zonal temperature advection is especially important during boreal summer near the western edge of the cold tongue, while horizontal eddy temperature advection, which most likely results from tropical instability waves, opposes temperature advection by the mean flow. The dominant balance in the southeast (6°S–10°S along 10°W) is similar to that in the northwest, with both latent heat loss and absorbed solar radiation playing important roles.
Lateral diffusivity and Lagrangian scales in the Pacific Ocean as derived from drifter data
Authors: Zhurbas Victor , Oh Im Sang
Published: May 2003

The Global Drifter Program/Surface Velocity Program data set is used to derive maps of the lateral diffusivity and Lagrangian scales of velocity, length and time across the whole Pacific. For the lateral diffusivity, the minor principal component of both the Davis' diffusivity tensor and the half growth rate of the single‐particle dispersion tensor were calculated in 5° × 5° bins from drifters for the period 1979–1999. Estimates of the lateral diffusivity, K, obtained by means of the minor principal component approach, are shown to correspond well with other authors' estimates for the Pacific. The highest values of K (2–3 104 m2/s) are found in the eastern equatorial Pacific, while the lowest ones (2–3 103 m2/s) are typical for forty‐odd degrees in latitude northward of the subpolar fronts in both hemispheres and for the subtropics in the eastern part of the South Pacific. High values of K (about 1 × 104 m2/s) are also observed in the Kusoshio/Kuroshio Extension area and in the equatorial Pacific along the whole length of the equator. There are two approximately symmetrical tongues of high K value in the western Pacific centered around 21°N and 24°S, respectively. In general, K has a tendency to increase westward (eastward) in the midlatitudes (equatorial region) and toward the equator in both hemispheres. In the midlatitudes, the Lagrangian length scale L is found to be approximately equal to the first‐mode baroclinic radius of deformation, Ri, while the Rossby number defined as Ro = Tearth/T sinφ, where T is the Lagrangian timescale, Tearth is the period of the Earth's rotation, and φ is the latitude, is less than unity, implying that the quasigeostrophic mesoscale eddies are the main mechanism for lateral mixing. The lateral diffusivity in the midlatitudes is suggested to be parameterized as K = V2Ri, where V2 is the Lagrangian velocity scale inherent to a mesoscale eddy field. In the low latitudes, L becomes less than Ri, and the condition Ro ≤ 1 is no longer valid, which implies the change of the eddy‐controlled mechanism of lateral mixing by another mechanism.
Tidal currents on the central Oregon shelf: Models, data, and assimilation
Authors: Erofeeva Svetlana Y. , Egbert Gary D. , Kosro P. M.
Published: May 2003

Measurements of tidal currents on the central Oregon shelf are available from several sources, including recent high frequency (HF) coastal radar and Acoustic Doppler Profiler (ADP) deployments, and historical current moorings. In this paper we use a generalized inverse (GI) approach to compare these data to, and then assimilate them into, numerical models for the barotropic tides. Harmonic analysis of the data in short time windows using a modified admittance approach reveals that tidal currents on the Oregon shelf are highly variable in time, and can contain significant baroclinic components. Data from the winter months, when waters on the shelf are only weakly stratified, are found to be most nearly barotropic and thus most reasonable for assimilation into the shallow water equations model. The various data sources are used in several different combinations for assimilation and validation. Forcing the prior forward model with normal flow open boundary conditions obtained from a regional barotropic inverse model results in semidiurnal barotropic currents that are consistent (within estimated error limits) with all available data. In contrast, diurnal currents on the shelf are very sensitive to details of the model configuration, and are significantly improved by data assimilation. Very similar solutions result from assimilation of either the HF radar or ADP data sets. The high sensitivity of the diurnal band currents can be understood dynamically in terms of trapped shelf waves. A short (∼85 km long) section of shelf off the central Oregon coast is wide enough to allow first‐mode barotropic shelf waves at the subinertial diurnal frequencies. This results in locally resonant large amplitude diurnal tidal currents that are very sensitive to details in the local forcing, and hence quite variable in time.
Indo‐Pacific Ocean response to atmospheric intraseasonal variability: 1. Austral summer and the Madden‐Julian Oscillation
Authors: Waliser Duane E. , Murtugudde Ragu , Lucas Lisanne E.
Published: May 2003

The large‐scale response of the Indo‐Pacific Ocean to atmospheric forcing associated with the Madden‐Julian Oscillation (MJO) is examined using an ocean general circulation model forced by canonical MJO conditions constructed from observations. The results show that for a number of equatorial areas, ocean advection processes can play an important role in determining the ocean response. In addition, mixed layer depth (MLD) variations are considerable and contribute to the sea surface temperature (SST) variability. SST variability also develops in the eastern equatorial Pacific via the propagation of ocean Kelvin waves. With regards to this variability the results suggest that advective processes, namely, meridional advection, play the most significant role. Sea level variability in the equatorial regions and eastern sides of the Indian and Pacific basins associated with the MJO is considerable. In conjunction with these sea level variations are also large variations in the Indonesian Throughflow. The results also show that the MJO forcing produces a low‐frequency rectified signal consisting of a weak cooling in the equatorial western Pacific and Indian Ocean regions, a relatively larger warming around the maritime continent, a fair amount of MLD shallowing in most of the above regions, and a westward equatorial Pacific Ocean current anomaly. In addition, the heat flux variations associated with the MJO produce systematic variations in the east‐west zonal gradient of Indian Ocean SST, which could influence the evolution of the Indian Ocean Zonal Mode. The implications and caveats associated with these results, the caveats associated with the model and forcing framework, and areas necessitating further study are discussed.
Constraining the inertial dissipation method using the vertical velocity variance
Authors: Dardier G. , Weill A. , Dupuis H. , Guerin C. , Drennan W. M. , Brachet S. , Lohou F. , Pedreros R.
Published: May 2003

The inertial dissipation method (IDM) is commonly used to measure turbulent fluxes over the ocean. It has the advantage over more direct methods in that it depends on the turbulent fluctuations only in the high frequencies of the so‐called inertial subrange. These frequencies are above those of typical ship motions and are considered to be relatively unaffected by flow distortion. However, a drawback in applying the method is that the problem is underdetermined: estimation of the fluxes requires knowledge of the Obukhov length L, which is itself a function of the fluxes. The problem is typically solved by iteration, using an initial L estimated from bulk formulae. This introduces a possible dependency on the initial bulk estimate along with problems of convergence. Recently, several authors have proposed improvements to the basic algorithm. For instance, Dupuis et al. [1997] proposed a parameterization of the “imbalance term” in the budget of turbulent kinetic energy (TKE). We explore an alternative approach to the problem. In order to constrain the equations resulting from the IDM we use the vertical velocity variance, σw, measured from the research vessel L'Atalante and an ASIS buoy, both deployed during the 1998 FETCH experiment. These data are compared to several parameterizations of σw on stability derived in experiments. For unstable cases, the data are found to be well described by the Panofsky and Dutton [1984] parameterization, although the scatter of the data is higher for swell conditions than for pure wind sea, indicating a likely sea state effect. Using measured values of σw along with this parameterization, the inertial dissipation problem is fully specified. The convergence of the method is satisfactory, and it offers u* estimates independent of bulk formulae.
Constraints on deep‐water formation from the oceanic distributions of 10Be
Authors: Luo Shangde , Ku Teh‐Lung
Published: May 2003

An analysis of the oceanic distribution of cosmogenic 10Be shows that deep waters are formed by descending of cold, dense surface waters at a rate of ∼18 Sv (106 m3 s−1) in the northern North Atlantic and ∼21 Sv (of which ∼17 Sv enters the Pacific) in the Antarctic over the last mixing cycle of ∼800 years, lending support to the estimates based on radiocarbon and nutrient distributions. It also indicates that deep‐water production in the northern North Atlantic is ∼50% higher averaging over the recent <100 years than over the last mixing cycle, suggesting a possible increase in the thermohaline ventilation of the North Atlantic during the past century.
Concentrations, isotopic compositions, and sources of size‐resolved, particulate organic carbon and oxalate in near‐surface marine air at Bermuda during spring
Authors: Turekian Vaughan C. , Macko Stephen A. , Keene William C.
Published: May 2003

During spring 1998, concentrations and stable isotopic compositions of organic carbon and oxalate were measured in size‐segregated aerosols at Bermuda to characterize sources and chemical processing. Marine‐derived organic carbon in super‐μm‐radius aerosol was enriched by an average of 724 ± 91 times relative to surface seawater. Carbon isotopic compositions indicated that, on average, marine‐derived carbon accounted for approximately 38% of carbon in both the super‐ and sub‐μm size fractions. Oxalate was present and significantly correlated with marine derived carbon in all size fractions. Most oxalate in super‐μm radius aerosol (>1 μm) originated from in situ production involving marine‐derived organic precursors, whereas oxalate in smaller size fractions originated primarily from condensation of oxalic acid vapor produced from the oxidation of gaseous marine precursors. The average dry‐deposition fluxes of marine organic carbon, continental organic carbon, and oxalate was 3.6, 7.3, and 0.15 μmol C m−2 day−1, respectively. Super‐μm aerosol dominated the dry‐deposition fluxes of marine (93%) and continental (96%) particulate carbon and oxalate (93%).
Vertical distribution of ozone at four sites in the United States
Authors: Newchurch M. J. , Ayoub M. A. , Oltmans S. , Johnson B. , Schmidlin F. J.
Published: May 2003

We report ozonesonde observations from the following four locations across the United States: Trinidad Head, California; Boulder, Colorado; Huntsville, Alabama; and Wallops Island, Virginia. These ozone profiles clearly indicate evidence of stratosphere‐troposphere exchange, boundary layer pollution, and strong seasonal variations. Significant variation at the shortest interlaunch frequencies (typically weekly) appears in all seasons, at all stations throughout the troposphere. Activity near the tropopause dominates in the winter and spring, while boundary layer ozone maximizes in the summer. The vertical extent and maximum values of boundary layer ozone are larger at the eastern stations. Comparisons to the TOMS overpasses indicate agreement to within 2% for the total‐column ozone at all stations, with station‐to‐station mean biases less than 2%. The seasonal variation of the total ozone column is essentially identical at Trinidad Head and Wallops Island, while the summertime values at Boulder are significantly smaller by comparison, and the amplitude of the annual cycle at Huntsville is smaller than the amplitude of the other three stations. The longitudinal character of upper tropospheric ozone shows amounts generally increasing westward from Huntsville, and in the lower troposphere, ozone decreases westward from Huntsville in all seasons. Values to the east of Huntsville increase at all altitudes and seasons, with the possible exception of August when Huntsville's boundary layer and free‐tropospheric ozone dominate.
Sea‐salt aerosol distribution during the Last Glacial Maximum and its implications for mineral dust
Authors: Reader M. C. , McFarlane N.
Published: May 2003

Sea‐salt aerosols and mineral dust in ice cores are complementary in their use as indicators of past climate because of their differing dependence on the various factors affecting their deposition rates, such as winds, precipitation, and soil properties. Here sea‐salt aerosol distributions for the Last Glacial Maximum (LGM) and for the modern climate are simulated using an online passive aerosol model in the Canadian Centre for Climate Modelling and Analysis second‐generation general circulation model. Comparison of simulated deposition rates of sea salt from the open ocean with polar ice core concentrations indicates that a 75‐fold enhancement, beyond that indicated by the model, is necessary for consistency with the Greenland ice core observations and an approximate tenfold additional enhancement is necessary for Antarctica. However, considering sea ice as a possible sea‐salt aerosol source allows greater simulated LGM deposition in Greenland, though there is a great deal of uncertainty in the possible magnitude of this. Using very simple models for which 1–2% of the total modern sea‐salt aerosol comes from ice‐covered areas, the ice core data can be accommodated by a sevenfold to tenfold overall additional LGM source enhancement. The fact that these additional enhancement factors are similar to the enhancement factor previously determined for mineral dust using the same general circulation model suggests that some combination of increased LGM surface winds and transport or deposition to ice core locations is necessary for agreement with the ice core data.
Thermal and dynamical changes of the stratosphere since 1979 and their link to ozone and CO2 changes
Authors: Langematz Ulrike , Kunze Markus , Krüger Kirstin , Labitzke Karin , Roff Gregory L.
Published: May 2003

This study examines which part of the observed stratospheric thermal and dynamical changes since 1979 can be attributed to the observed stratospheric ozone (O3) losses and CO2 increases. Further, the processes are studied that lead to temperature and circulation changes when stratospheric O3 and CO2 are modified. We compared results from simulations of the Freie Universität Berlin Climate Middle Atmosphere Model (FUB CMAM) using observed O3 and CO2 changes with observed trends of stratospheric temperature and circulation for the period 1979–2000 from FUB data and National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalyses. The observed O3 decrease leads in the FUB CMAM to a global mean stratospheric cooling, which is enhanced in the upper stratosphere by the imposed CO2 increase. While the model is able to reproduce the observed stratospheric cooling in the upper stratosphere, it underestimates the observed trends in the lower stratosphere, particularly in middle latitudes and during Northern Hemisphere (NH) spring. The observed intensification and increased lifetimes of the polar vortices in spring are captured by the model but with smaller magnitude than observed. It is suggested that the observed upper stratospheric temperature trends during the past two decades in low to middle latitudes are caused by radiative effects due to the O3 and CO2 changes, while the cooling of the polar stratosphere in winter is enhanced by changes in dynamical heating. However, in northern midlatitudes and in Arctic spring, other effects than O3 and CO2 changes must be considered to fully explain the observed changes in the lower stratosphere.
The influence of the global photochemical composition of the troposphere on European summer smog, Part I: Application of a global to mesoscale model chain
Authors: Langmann Bärbel , Bauer Susanne E. , Bey Isabelle
Published: May 2003

Elevated mixing ratios of ozone in the lower troposphere are a major summer time air pollution issue in Europe. Photochemical in‐situ production is the most important source of ozone in the planetary boundary layer and has been studied extensively. However, the contributions of background ozone due to stratospheric intrusions, lightning nitrogen oxide followed by ozone production, convective mixing and intercontinental transport are still poorly quantified. We analyze in this paper the influence of the large‐scale ozone background on near‐surface ozone throughout a summer smog period in July 1994 over Europe. For this purpose a chain of global to mesoscale models is applied with a nesting procedure coupling the individual model simulations. It is found that background ozone as determined by the global model dominates the results of the higher resolution limited area models increasingly with height. But improvements of limited area model results are not only restricted to the free troposphere. Strong convective events like thunderstorms couple free tropospheric and planetary boundary layer air masses so that ozone from above is injected into the planetary boundary layer contributing an amount of 5–10 ppbv to near‐surface ozone in the afternoon hours. A decrease in the same range of 5–10 ppbv in maximum near‐surface ozone over Central Europe is found in a model simulation where European anthropogenic emissions are reduced by 25%, an amount equal to the reported emission trends in Germany from 1994 to 2000. We conclude that intercontinental transport of pollution can obscure the results of local efforts to reduce critical exposure levels of ozone.
The monsoon aerosol extinction properties at Goa during INDOEX as measured with lidar
Authors: Chazette Patrick
Published: May 2003

The aerosol extinction properties in the framework of the Indian Ocean Experiment (INDOEX) are documented over the Goa area (western coast of India, 15.45°N, 73.08°E) between 1 and 15 March 1999. The temporal evolution and the vertical distribution of the aerosol trapped inside the winter monsoon plume have been studied using a ground‐based lidar system (micropulse lidar (MPL) emitting at 523 nm). Both the vertical structure and the optical properties of the particles have been assessed from the inversion of the lidar signals. A statistical approach has been used to determine the backscatter‐to‐extinction ratio (Φp), a key parameter to invert the lidar signal. Sun photometer‐retrieved optical thickness at 523 nm is used to constrain the inversion in daytime and leads to a mean value of Φp close to 0.03 sr−1 with a standard deviation of ∼0.010 sr−1. Black carbon concentration (BC) is shown to be a representative tracer of the surface scattering coefficient of aerosols (αs), the relative humidity (RH) effect seeming to be of a second order. A statistical linear relationship between BC and αs has been found and then used to constrain the lidar inversion during nighttime. During nighttime, about the same mean Φp has been assessed. The lidar‐derived optical thickness is shown to be more important during nighttime over the entire measurement period (a mean value of 0.76 ± 0.15 for nighttime instead of 0.55 ± 0.09 for daytime). A significant contribution to the optical thickness is shown to be due to an aerosol layer within 0.7 km above sea level (ASL). A second aerosol layer is found between 0.7 and ≈3.5 km ASL with an important diurnal variability in both its altitude extension and its optical thickness. Such a variability seems to be due to the sea breeze cycle. In the upper aerosol layer, optical thickness is 0.49 ± 0.14 during nighttime whereas it is only about 0.25 ± 0.07 during daytime.
Spatial and temporal distributions of U.S. winds and wind power at 80 m derived from measurements
Authors: Archer Cristina L. , Jacobson Mark Z.
Published: May 2003

This is a study to quantify U.S. wind power at 80 m (the hub height of large wind turbines) and to investigate whether winds from a network of farms can provide a steady and reliable source of electric power. Data from 1327 surface stations and 87 soundings in the United States for the year 2000 were used. Several methods were tested to extrapolate 10‐m wind measurements to 80 m. The most accurate, a least squares fit based on twice‐a‐day wind profiles from the soundings, resulted in 80‐m wind speeds that are, on average, 1.3–1.7 m/s faster than those obtained from the most common methods previously used to obtain elevated data for U.S. wind power maps, a logarithmic law and a power law, both with constant coefficients. The results suggest that U.S. wind power at 80 m may be substantially greater than previously estimated. It was found that 24% of all stations (and 37% of all coastal/offshore stations) are characterized by mean annual speeds ≥6.9 m/s at 80 m, implying that the winds over possibly one quarter of the United States are strong enough to provide electric power at a direct cost equal to that of a new natural gas or coal power plant. The greatest previously uncharted reservoir of wind power in the continental United States is offshore and nearshore along the southeastern and southern coasts. When multiple wind sites are considered, the number of days with no wind power and the standard deviation of the wind speed, integrated across all sites, are substantially reduced in comparison with when one wind site is considered. Therefore a network of wind farms in locations with high annual mean wind speeds may provide a reliable and abundant source of electric power.
Model analysis of the temporal and geographical origin of the CO distribution during the TOPSE campaign
Authors: Lamarque J.‐F. , Hess P. G.
Published: May 2003

The origin of carbon monoxide within the region covered by the Tropospheric Ozone Production about the Spring Equinox (TOPSE) measurement campaign during the winter and spring of 2000 is examined using a chemical transport model. The origin relates to the location (United States of America, Europe, Southeast Asia, and rest of the world) and time (June 1999 to May 2000) at which the CO was emitted from the surface. The model tracks CO from each source and from hydrocarbon oxidation, where each tagged CO reacts with OH. The analysis focuses on the relative distribution of each tagged CO. Changes in the transport and the photochemistry during the transition from the winter to spring months are particularly emphasized. In the high latitude lower troposphere, CO is strongly influenced by fresh emissions from Europe during the winter months. Otherwise, the analysis indicates the importance of the buildup of aged emissions during the winter season. The contribution from hydrocarbon oxidation is a significant fraction of the total CO, although the bulk of this oxidation occurs well away from the region of interest. During the spring months the transport of episodic emissions from Europe decreases in the lower troposphere and the age of CO generally decreases elsewhere.
Composition of cloud condensation nuclei
Authors: Ishizaka Yutaka , Adhikari Mandira
Published: May 2003

The composition of cloud condensation nuclei (CCN) was determined by thermal analysis, whereby CCN and aerosol particles were heated to temperatures up to 500°C. The CCN were observed in the urban atmosphere of Nagoya and in the coastal atmosphere of Mikuni, Japan. Automobile exhaust particles were also analyzed to examine the contribution of anthropogenic organic materials to CCN. The thermal analytical behavior of CCN at Nagoya and Mikuni showed that more than 80% of the total number concentration of CCN evaporated at or below 300°C and the concentration of CCN remained almost constant between 300° and 500°C. Thermal curves for inorganic ions such as NH4+, NO3−, and SO42− were similar to those for CCN, whereas the thermal curve of sea salt particles and total carbon (organic plus soot) particles were different from CCN. The results suggested that inorganic materials such as ammonium sulfate and ammonium nitrate contributed greatly to the CCN in the urban atmosphere and ammonium sulfate contributed considerably to the CCN in the coastal atmospheres. Anthropogenic organic materials, which evaporated below 300°C, contributed considerably to the CCN, whereas soot particles contributed hardly to the CCN.
Wintertime high‐altitude surface energy balance of a Bolivian glacier, Illimani, 6340 m above sea level
Authors: Wagnon Patrick , Sicart Jean‐Emmanuel , Berthier Etienne , Chazarin Jean‐Philippe
Published: May 2003

The objective of this study is to evaluate the surface energy balance (SEB) of a cold, high‐altitude tropical glacier, Illimani (16°39′S; 67°47′W, 6340 m above sea level (asl)), where a 137 m ice core was drilled down to the bedrock in June 1999. During the dry austral winter, tropical glaciers are known to experience strong sublimation, which may be responsible for snow composition changes through postdepositional processes. In order to help toward the interpretation of this climatic archive, SEB experiments were carried out in 1999, 2001, and 2002, during the dry season (mostly clear and cold atmosphere, strong westerly winds). The daily net all‐wave radiation is usually negative during this austral dry winter because of the highly reflective snow surface and because of reduced incoming long‐wave radiation due to a low cloudiness compared to outgoing long‐wave radiation. The turbulent heat fluxes were evaluated using the bulk aerodynamic approach, including stability correction. The roughness parameters are deduced from direct sublimation measurements and serve as calibration parameters. The sensible heat flux strongly heats the surface at night but changes to negative values during daytime unstable conditions (between 1000 and 1600 LT). The latent heat flux is always negative, which means that the surface loses mass through sublimation, particularly in the daytime (sublimation rates are −1.2 mm w.e. d−1, −0.7 mm w.e. d−1, and −0.8 mm w.e. d−1 during the 2001, 2002, and 1999 measuring periods, respectively, where w.e. is water equivalent). The winter SEB of this high‐altitude cold tropical glacier is comparable to the summer SEB over snow surfaces of the intermediate slopes of Antarctica.
TEM study of aerosol particles from clean and polluted marine boundary layers over the North Atlantic
Authors: Li Jia , Anderson James R. , Buseck Peter R.
Published: May 2003

Aerosol samples were collected from Punta del Hidalgo in the Canary Islands and Sagres in Portugal during June–July 1997 as part of the Aerosol Characterization Experiment‐2 (ACE‐2) over the North Atlantic Ocean. We studied individual aerosol particles using transmission and scanning electron microscopy. The major aerosol types include fresh and partly or completely reacted sea salt that consist of NaCl, mixed‐cation (Na, Mg, K, and Ca) sulfate, Na2SO4, and NaNO3; particles of industrial origin that include (NH4)2SO4, soot, flyash, silica, Fe oxide, and CaSO4; and minor terrestrial mineral dust. Because of their different geographic locations, samples from these two sites showed different degrees of impact from anthropogenic emissions from Europe. At Sagres, depending on the samples, between 0 and 30% of sea salt particles remain unreacted, while 0 to 50% were partly reacted, and 20 to 100% were completely converted to sulfate and nitrate through reactions with pollutants from the European continent. In contrast, at Punta del Hidalgo, the sea salt particles were much less affected by industrial pollution. Even during polluted periods, only less than 5% were completely reacted. The dramatic difference between the sea salt particles from Punta del Hidalgo and Sagres indicates dilution of pollution, rapid reaction, and exhaustion of reactive pollutants as they were transported to the open ocean.
Comparing MM5 radiative fluxes with observations gathered during the 1995 and 1999 Nashville southern oxidants studies
Authors: Zamora R. J. , Solomon S. , Dutton E. G. , Bao J. W. , Trainer M. , Portmann R. W. , White A. B. , Nelson D. W. , McNider R. T.
Published: May 2003

The impact of radiative transfer processes on MM5 air‐quality forecasts during the Nashville Southern Oxidants Experiments is addressed. We find that an incorrect specification of aerosol scattering, aerosol absorption, and ozone absorption in the model can lead to positive errors in the instantaneous total solar irradiance at the surface of 100 W m−2 using the Dudhia solar parameterization. This increased solar irradiance upsets the surface energy balance in the model causing errors in the surface heat fluxes and mixing depth estimation. We also show that a systematic 80 W m−2 increase in the forecast downwelling long‐wave radiation can inhibit the formation of ground‐based nocturnal inversions in the model when the Dudhia long‐wave radiation routine is used. Thus we find that accurate specification of radiative processes, including some driven by local pollution, can be important for mesoscale meteorological forecasting. A method for including ozone absorption in MM5 is introduced, and optimum choices for running the model in aerosol rich geographic regions are discussed.
A model to extend spectral and multiwavelength UV irradiances time series: Model development and validation
Authors: Díaz Susana , Nelson Don , Deferrari Guillermo , Camilión Carolina
Published: May 2003

Measurements of spectral and multichannel UV radiation became more common in the middle and late eighties after the discovery of the “ozone hole,” but time series for these measurements are still relatively short for the determination of trends to be applied in geophysical and biological studies. However, systematic measurements of total column ozone have been performed since the late 1950s at several stations, and global coverage has been available since the late 1970s. Also, long‐term time series of broadband instruments (Pyranometers, UV and erythemally weighted) are available from many sites around the world. In this paper a multiregressive model that enables the inference of spectral or narrow band UV irradiances from total ozone column and broadband irradiance, in places where relatively short time series of UV spectral irradiances are available, is proposed. To test the model, measurements of irradiances performed at three of the stations in the NSF UV Radiation Monitoring Network, under all weather, solar zenith angle and surface conditions, were used. The model generated very good results over a wide variety of situations. Pyranometer data from the NOAA/CMDL surface radiation budget database for South Pole and Barrow Stations were used to estimate daily integrated narrow band irradiances. A time series of monthly means for the narrowband (303.030–307.692 nm) were then computed, dating back to the late 1970s.
Sources and chemistry of nitrogen oxides over the tropical Pacific
Authors: Staudt A. C. , Jacob D. J. , Ravetta F. , Logan J. A. , Bachiochi D. , Krishnamurti T. N. , Sandholm S. , Ridley B. , Singh H. B. , Talbot B.
Published: May 2003

We examine the sources and chemistry affecting nitrogen oxides (NOx = NO + NO2) over the tropical Pacific (30°S–20°N) using observations from the Pacific Exploratory Mission to the Tropics B (PEM‐Tropics B) aircraft mission conducted in March–April 1999. A global model of tropospheric chemistry driven by assimilated meteorological data is used to interpret the observations. Median concentrations observed over the South Pacific during PEM‐Tropics B were 7 pptv NO, 16 pptv peroxyacetyl nitrate (PAN), and 34 pptv nitric acid (HNO3); the model generally reproduces these observations but overestimates those over the North Pacific. Lightning was the largest source of these species in the equatorial and South Pacific tropospheric column and in the tropical North Pacific upper troposphere. The oceanic source of acetone implied by high observations of acetone concentrations (mean 431 pptv) allows an improved simulation of PAN/NOx chemistry. However, the high acetaldehyde concentrations (mean 78 pptv) measured throughout the troposphere are inconsistent with our understanding of acetaldehyde and PAN chemistry. Simulated concentrations of HNO3 and HNO3/NOx are highly sensitive to the model representation of deep convection and associated HNO3 scavenging. Chemical losses of NOx during PEM‐Tropics B exceed chemical sources by a factor of 2 in the South Pacific upper troposphere. The chemical imbalance, also apparent in the low observed HNO3/NOx ratio, is explained by NOx injection from lightning and by frequent convective overturning which depletes HNO3. The observed imbalance was less during the PEM‐Tropics A campaign in September 1996, when aged biomass burning effluents over the South Pacific pushed the NOx budget toward chemical steady state.
Effects of humidity on aerosols in southern Africa during the biomass burning season
Authors: Magi Brian I. , Hobbs Peter V.
Published: May 2003

Measurements of the aerosol total light scattering coefficient, σsp, and the aerosol hemispheric backscatter ratio, β(1), as functions of relative humidity (RH in %) (so‐called humidographs) at three wavelengths (450, 550, and 700 nm) were obtained in the dry season in southern Africa (1) in ambient air in South Africa, Botswana, Mozambique and Zambia, (2) at various distances downwind in identifiable smoke plumes from biomass fires, and (3) along the southwest coast of Africa. The ratio of σsp at an RH of 80% to that at 30% provides a measure of the effects of RH on σsp, and similarly for β(1). For the three broad sampling categories given above, and at a wavelength of 550 nm, these ratios varied from 1.42 ± 0.05 to 2.07 ± 0.03 for σsp, and from 0.69 ± 0.05 to 0.99 ± 0.14 for β(1). In general, humidographs for the ambient air samples showed a greater dependence on RH than those for smoke from identifiable biomass fires. During a period when dense, aged smoke was transported to the region from the north, the humidographs for σsp for ambient air samples were similar to those for identifiable smoke plume samples just ∼10‐ to 50‐min old. This suggests that as far as the effects of RH on σsp are concerned the effects of aging of smoke and its mixing with ambient air are realized within less than about an hour.
A study of infrared diabatic forcing of ice clouds in the tropical atmosphere
Authors: Maestri Tiziano , Rizzi Rolando
Published: May 2003

The diabatic exchange occurring in the atmosphere and within ice cloud layers in tropical standard conditions is investigated. The crossover from the spectral region in which the cloud's layer experiences a net emission (roughly the far infrared) to the region in which it experiences net absorption (window) does not significantly depend on the ice amount, but appears strictly connected with cloud's height and atmospheric temperature structure. For a fixed atmosphere, the cloud's internal structure of radiative heating and cooling is highly dependent on cloud trasmissivity. The energy absorbed by ice crystals at the base of a cirrus is different from that absorbed by the air molecules occupying the same layer and the effects of scattering are quantified and compared to particle's emission. Simulations have been done in case of spherical and hexagonal column‐shaped ice particles. Small differences are obtained in the integrated quantities due to compensating effects which appear fairly unimportant when compared to uncertainties caused by our inadequate knowledge of some of the main properties of ice clouds, such as ice amount and effective radius. Of larger magnitude are variations in layer's absorbed flux due to changes in the water vapor concentration.
Investigation of the effect of water complexes in the determination of peroxy radical ambient concentrations: Implications for the atmosphere
Authors: Reichert L. , Andrés Hernández M. D. , Stöbener D. , Burkert J. , Burrows J. P.
Published: May 2003

The objective of this study has been to investigate the origin of the water vapor effect on the chain length (CL) of peroxy radical chemical amplifiers (PERCA). Results of the investigation of the water interference in the determination of peroxy radicals by using the PERCA technique are presented. The experimental conditions have been analyzed and modeled. A nonlinear dependence of the CL on the relative humidity (RH) has been accurately determined. The combined analysis of experimental and simulated results rules out wall loses as a single explanation of the CL variation observed and indicates three reactions, which possibly account for this water effect: (1) nonradical products, (2) , and (3) nonradical products (e.g., HNO3). Assuming a mechanism involving the formation of a HO2–nH2O complex, the corresponding rate coefficients and their water dependence have been estimated. The quadratic dependence of these rate coefficients upon the RH implies the participation of two H2O molecules in the proposed reactions. The study has shown that at a RH of 80% an effective second‐order rate coefficient of 10−15 cm3 molecule−1 s−1 for the reaction of CO with HO2, or 10−13 cm3 molecule−1 s−1 for the reaction of HO2 with NO, explains the observed behavior. Both these complex reactions have potential significance for the chemistry of the marine boundary layer (MBL) and their atmospheric implications are discussed.
Mapping isoprene emissions over North America using formaldehyde column observations from space
Authors: Palmer Paul I. , Jacob Daniel J. , Fiore Arlene M. , Martin Randall V. , Chance Kelly , Kurosu Thomas P.
Published: May 2003

We present a methodology for deriving emissions of volatile organic compounds (VOC) using space‐based column observations of formaldehyde (HCHO) and apply it to data from the Global Ozone Monitoring Experiment (GOME) satellite instrument over North America during July 1996. The HCHO column is related to local VOC emissions, with a spatial smearing that increases with the VOC lifetime. Isoprene is the dominant HCHO precursor over North America in summer, and its lifetime (≃1 hour) is sufficiently short that the smearing can be neglected. We use the Goddard Earth Observing System global 3‐D model of tropospheric chemistry (GEOS‐CHEM) to derive the relationship between isoprene emissions and HCHO columns over North America and use these relationships to convert the GOME HCHO columns to isoprene emissions. We also use the GEOS‐CHEM model as an intermediary to validate the GOME HCHO column measurements by comparison with in situ observations. The GEOS‐CHEM model including the Global Emissions Inventory Activity (GEIA) isoprene emission inventory provides a good simulation of both the GOME data (r2 = 0.69, n = 756, bias = +11%) and the in situ summertime HCHO measurements over North America (r2 = 0.47, n = 10, bias = −3%). The GOME observations show high values over regions of known high isoprene emissions and a day‐to‐day variability that is consistent with the temperature dependence of isoprene emission. Isoprene emissions inferred from the GOME data are 20% less than GEIA on average over North America and twice those from the U.S. EPA Biogenic Emissions Inventory System (BEIS2) inventory. The GOME isoprene inventory when implemented in the GEOS‐CHEM model provides a better simulation of the HCHO in situ measurements than either GEIA or BEIS2 (r2 = 0.71, n = 10, bias = −10%).
Clean air slots amid dense atmospheric pollution in southern Africa
Authors: Hobbs Peter V.
Published: May 2003

During the flights of the University of Washington's Convair‐580 in the Southern African Regional Science Initiative (SAFARI 2000) in southern Africa, a phenomenon was observed that has not been reported previously. This was the occurrence of thin layers of remarkably clean air, sandwiched between heavily polluted air, which persisted for many hours during the day. Photographs are shown of these clean air slots (CAS), and particle concentrations and light scattering coefficients in and around such slot are presented. An explanation is proposed for the propensity of CAS to form in southern Africa during the dry season.