bluuebunny/crossref_metadata_2025 huggingface dataset:
Aircraft measurements of the concentrations of CO2, CH4, N2O, and CO and the carbon and oxygen isotopic ratios of CO2 in the troposphere over Russia
Authors: Nakazawa Takakiyo , Sugawara Satoshi , Inoue Gen , Machida Toshinobu , Makshyutov Shamil , Mukai Hitoshi
Published: February 2004

About 370 air samples were collected using aircraft in the troposphere over Russia in the summers of 1992, 1993, and 1994. These were then analyzed for the CO2, CH4, N2O and CO concentrations, as well as for δ13C and δ18O of CO2. Measured vertical profiles of tropospheric CO2 showed that the concentration increased with height over all locations. In the lower troposphere over the wetland and taiga regions, extremely low CO2 concentrations of 335–345 parts per million by volume (ppmv) were often observed. Measured values of δ13C and the CO2 concentration were negatively correlated with each other, the rate of change in δ13C with respect to the CO2 concentration being about −0.05‰/ppmv. This implies that the variations in the CO2 concentration observed over Russia in the summer are primarily caused by terrestrial biospheric activities. In the middle and upper troposphere, the CO2 concentration and δ13C showed systematic differences between each other in 1992, 1993, and 1994, probably due to their secular changes. The δ18O and CO2 observed in the lowest part of the troposphere over east and west Siberia were also negatively correlated with each other, with the rate of change in δ18O with respect to CO2 estimated to be about −0.1 l‰/ppmv. This relation may be caused by isotopic equilibrium of oxygen in CO2 with soil water through respiration of living plants and decomposition of organic matter and with chloroplast water in leaves through photosynthesis of living plants. In contrast to CO2, the CH4 concentration decreased with height. Extremely high CH4 concentrations were observed over the west Siberian lowland, owing to a large amount of CH4 emitted from wetlands. The N2O concentrations were fairly constant through the troposphere over all locations covered by this study, with an average value of about 311 parts per billion by volume (ppbv). The CO concentrations also showed vertical profiles, with a small gradient over natural wetlands, taiga, and tundra. High values of the CH4, CO, and CO2 concentrations were observed over Moscow, owing to emissions of the respective gases by human activities in an urban area. It was also found that over natural wetlands and tundra the CO2 and CH4 concentrations were negatively correlated with each other, reflecting a strong biospheric CO2 uptake and CH4 emissions from wetlands. The relationship between the CH4 and CO concentrations was strongly positive over areas with their anthropogenic and natural sources; the relationship was only slightly positive over wetlands, possibly due to CO emissions from wetlands and/or photochemically produced CO.
Measurement of surface radiation fluxes and cloud optical properties during the 1994 Arctic Ocean Section
Authors: Lubin Dan , Simpson A. Sabrina
Published: February 2004

During a voyage to the north pole from Alaska by the icebreakers USCGC Polar Sea and Canadian CGC Louis S. St.‐Laurent (the 1994 Arctic Ocean Section, July 24 to September 3) an atmospheric radiation and remote sensing experiment measured downwelling shortwave and longwave radiation reaching the sea ice surface. The experiment included a Fourier transform infrared (FTIR) spectroradiometer which measured zenith radiance at 1 cm−1 resolution in the middle infrared wavelength range 5–20 μm, an Eppley pyranometer measuring most of the downwelling shortwave flux (0.28–2.80 μm), an Eppley pyranometer measuring the downwelling near‐infrared flux (0.78–2.80 μm), and an Eppley pyrgeometer measuring the downwelling longwave flux. In conjunction with a discrete‐ordinates radiative transfer model, the FTIR emission spectra are used to estimate 8–12 μm cloud emissivity and effective radius of the cloud droplet size distribution. The broadband shortwave flux measurements are used to estimate shortwave cloud scattering optical depth. Most of the FTIR emission spectra recorded under overcast skies are consistent with cloud effective radius in the range 10–12 μm, but 27% of the spectra are more consistent with the range 4–6 μm, suggesting an occasional continental aerosol influence to Arctic cloud microphysics. The average daily shortwave cloud‐scattering optical depth ranged from 2 to 46, which is similar to a range inferred from radiometer data recorded at Barrow, Alaska, during the same season. The downwelling shortwave flux measurements and estimates of net surface flux are generally consistent with a four‐decade Russian climatology but also suggest that the frequency of cloud cover sampled during the 1994 Arctic Ocean Section was somewhat larger than the climatological average. These radiation measurement data from the 1994 Arctic Ocean Section should be useful for examining the treatment of atmospheric radiation and surface energy input in Arctic climate model simulations.
Global atmospheric angular momentum and Earth‐atmosphere exchange of angular momentum simulated in a general circulation model
Authors: Lejenäs Harald , Madden Roland A. , Hack James J.
Published: February 2004

The atmospheric angular momentum budget as described by the National Center for Atmospheric Research community climate model has been studied. Model data from a 20‐year climate simulation have been used to study time variations of atmospheric angular momentum and Earth‐atmosphere exchange of angular momentum. Computed values of frictional torques, mountain torques, and atmospheric angular momentum as determined by the model were compared with observed values already published in the literature, as well as with values based on data obtained from the National Center for Environmental Prediction. Computed values of gravity wave drag torques are also presented. These values cannot be directly compared with observational data, but they give some idea of the possible role of wave drag on the angular momentum budget. A detailed comparison shows that the general circulation model simulates the seasonal variation of the angular momentum and frictional and mountain torques reasonably well. We also found that the model simulates the seasonal global atmospheric pressure variations owing to global redistributions of mass in a realistic way.
Seasonal variation of energy and water vapor exchange rates above and below a boreal jack pine forest canopy
Authors: Baldocchi Dennis D. , Vogel Christoph A. , Hall Brad
Published: February 2004

Fluxes of energy and water vapor over boreal forest stands are expected to vary during the growing season due to temporal variations in solar energy, soil and air temperature, soil moisture, photosynthetic capacity, and leaf area. To investigate this hypothesis, we measured fluxes of energy balance components (solar, latent and sensible heat, and soil and canopy heat storage) over and under a boreal jack pine forest in central Canada during the 1994 growing season. Temporal trends of daily‐integrated energy fluxes were significant during a 117 day period between spring and autumn. Mean fluxes of net radiation and latent heat peaked near the summer solstice. By the autumnal equinox their magnitudes were half of their peak values. On a day‐to‐day basis the presence or absence of clouds modulated solar energy fluxes, while evaporation rates were dependent on whether the canopy was dry or wet. When the canopy was dry, daily evaporation was generally less than 2.5 mm d−1. This amount was less than one‐half the rate of equilibrium evaporation and was low compared to evaporation from vegetation in temperate zones. When the canopy was wet, daily evaporation approached 3 mm d−1 and exceeded predicted rates of equilibrium evaporation. Evaporation from the dry forest was weakly coupled to available energy and was restricted by the canopy AEs low‐surface conductance. Biotic factors limiting the forest AEs surface conductance include the forest AEs low‐leaf area index and partial stomatal closure. Abiotic and physiological factors restricting stomatal opening included a scarce supply of soil moisture, limiting vapor pressure deficits and the low photosynthetic capacity of the needles. The fluxes of solar energy and latent and sensible heat at the floor of the forest were a significant portion of energy exchange between the forest and the atmosphere. Typically, 20 to 40% of the total energy exchange by the jack pine stand originated at the understory. Since a substantial amount of energy occurs under the forest, two‐layer, not a big‐leaf AE, evaporation models are recommended as a tool for estimating water vapor fluxes from this open forest stand.
Synoptic and mesoscale atmospheric features over the ice‐covered portion of the Fram Strait in spring
Authors: Rasmussen E. A. , Guest P. S. , Davidson K. L.
Published: February 2004

Data obtained during the Coordinated Eastern Arctic Experiment (CEAREX) from March 31 to April 20, 1989, from two ice camps in the pack ice region in the Fram Strait have been analyzed. The data show that the total period can be divided into two periods or regimes divided by a transition period. The first period was a radiative type, characterized by very low surface temperatures and low wind speeds. Fairly regular oscillations between southerly and northerly winds were caused by small‐scale disturbances in the surface pressure field, associated with upper level waves of large amplitude. During a transition period toward an “advective weather type” on April 11 a sharp frontal zone passed both ice camps. The front was associated with a small‐scale low which had formed over the ice on the shallow but intense baroclinic zone along the northeastern Greenland coast. Mesoscale vortices of this type may, if numerous enough, affect the horizontal transfer of heat from lower latitudes toward Arctic regions as well as the ice drift through the Fram Strait.
Convective electrification of clouds: A numerical study
Authors: Masuelli Sergio , Scavuzzo Carlos M. , Caranti Giorgio M.
Published: February 2004

Although the convective process of cloud electrification has been proposed long ago, there is a lack of numerical simulations in the literature that would put this mechanism to the test. A numerical model developed with the purpose of evaluating the electrification caused by the convective mechanism alone is presented. More precisely, in the model only the interaction between free ions and cloud and precipitation particles separates charge. The ability of this mechanism to reproduce the most important features of cloud electrification is discussed. The study is carried out on a slab symmetric domain of 16 km per side. The microphysics is represented by a bulk parameterization including four categories: cloud ice, cloud water, hail and rain. The model also includes aerosols and small ions, and it takes into account the difference in mobilities between positive and negative small ions. The influence of variables such as the number of particles, number of aerosols and ion pair formation rate is tested. A dipolar structure bounded by the cloud is obtained. The magnitude of electric field is too modest to produce any lightning after 10 min of simulation.
Distribution of methyl iodide, ethyl iodide, bromoform, and dibromomethane over the ocean (east and southeast Asian seas and the western Pacific)
Authors: Yokouchi Y. , Mukai H. , Yamamoto H. , Otsuki A. , Saitoh C. , Nojiri Y.
Published: February 2004

Ambient concentrations of four marine‐derived halocarbons (methyl iodide, ethyl iodide, bromoform and dibromomethane) and two man‐made halocarbons (trichloroethylene and tetrachloroethylene) were measured during western Pacific cruises and east and southeast Asian cruises. Ethyl iodide was detected in the atmosphere for the first time and was identified as an atmospheric iodine source compound. Bromoform concentrations were positively correlated with those of dibromomethane, and methyl iodide showed variations similar to those of ethyl iodide. However, there was no correlation between the bromocarbons and the iodocarbons. The concentrations of methyl iodide and ethyl iodide changed more markedly, possibly owing to higher rates of photodecomposition of iodocarbons.
Temperature dependence of ternary solution particle volumes as observed by lidar in the Arctic stratosphere during winter 1992/1993
Authors: Beyerle Georg , Luo Beiping , Neuber Roland , Peter Thomas , McDermid I. Stuart
Published: February 2004

Multiwavelength lidar measurements of stratospheric aerosols performed at the Arctic Network for the Detection of Stratospheric Change station on Spitsbergen during winter 1992/1993 are analyzed. Altitude profiles of particle median radius and volume density are derived for measurements with aerosol depolarization smaller than 0.01. Below an altitude corresponding to 450 K potential temperature the Pinatubo aerosol layer dominated the stratospheric aerosol content with volume densities of more than 5 μm3 cm−3, whereas above 450 K, volume densities were close to background values of 0.1 μm3 cm−3. However, at all altitude levels between 350 and 550 K, volume densities consistently increased by a factor of 2–30 when temperatures approached the frost point. The observations are compared to results from thermodynamic model calculations at altitude levels of 400, 440, and 480 K. Good agreement between the observed and theoretically derived temperature dependencies of volume density suggests that nondepolarizing polar stratospheric cloud particles, as well as volcanic aerosols, at low temperatures are composed of a ternary liquid solution of sulfuric and nitric acid. At all altitude levels, model results indicated more than 90% HNO3 gas phase depletion as temperatures approached the frost point. A mean profile of total H2SO4 volume mixing ratio is derived, decreasing from about 4 parts per billion by volume (ppbv) at 350 K to about 0.5 ppbv above 450 K.
Refraction and atmospheric photochemistry
Authors: Balluch M. , Lary D. J.
Published: February 2004

A new model for calculating the effects of refraction is introduced. This model was invented independently of the one described by DeMajistre et al.[1995], but it is shown that the two models are analytically equivalent. However, the numerical implementation of the model introduced here is vastly more economical and efficient than that of the model by DeMajistre et al. This is because the two differential equations solved numerically by DeMajistre et al. have been solved analytically for the new model, prior to the numerical implementation, which reduced them to only one simple expression. The effects of refraction on stratospheric chemistry calculated with this new model are shown to be greatest in the polar lower stratosphere close to the onset and completion of polar night. The main effect is to change the shape of the seasonal cycle of reactive species produced by photolysis such as NO, NO2, OH, HO2, Cl, ClO, Br, and BrO during the onset and completion of polar night.
Millimeter wave spectroscopic measurements over the South Pole: 4. O3 and N2O during 1995 and their correlations for two quasi‐annual cycles
Authors: Cheng Dongjie , Crewell Susanne , Klein Ulf , de Zafra Robert L. , Chamberlin R. A.
Published: February 2004

In two separate papers we have previously reported observations of stratospheric O3 and N2O over the South Pole during the 1993 annual cycle. Here we present (1) new O3 and N2O observations at the South Pole in 1995 and (2) correlations between O3 and N2O for two 11‐month observations during February 1993 to January 1994 and January‐December 1995. Strong similarities exist between the two quasi‐annual cycles for both O3 and N2O. A double‐peaked profile again dominates O3 vertical distribution in 1995 as in 1993. Features such as a pronounced summer‐fall decline in mid‐stratospheric O3 followed by an early winter increase, a downward trend in the O3 contour pattern associated with vertical transport, a transient enhancement of middle to upper stratospheric O3 just before local sunrise, the timing of the ozone hole onset, and a dramatic increase of stratospheric O3 during and following vortex breakup all show good consistency between the two annual cycles. N2O observations show a good agreement between the two 11‐month cycles in atmospheric descent rate during fall and winter, and in the timing of N2O recovery from diminished values during spring. We use O3‐N2O correlations to further investigate the double‐peaked vertical distribution of O3. During springtime warmings the O3/N2O ratio shows a tight coupling between O3 and N2O around 20 km, as transport creates the lowaltitude O3 peak. A rapid and systematic decrease of the O3/N2O ratio during summer in the 25 to 30 km region (while N2O is essentially stable) supports the increasingly dominant role of photochemistry in producing the vertical profile for O3 above ∼25 km while leaving a transport‐produced layer with a relatively large mixing ratio below ∼25 km. The resulting double‐peaked O3 distribution, which persists for many months, can alter the normally negative correlations between O3 and N2O in the lower and middle stratosphere, although in measurements of the N2O/O3 ratios for polar air these perturbations have often been taken to be a hallmark of catalytic ozone depletion by chlorine. The present analysis should help to clarify the influence of the relatively unique O3 vertical distribution of polar ozone when interpreting O3‐N2O correlations.
Remote sensing of carbonaceous aerosol production by African savanna biomass burning
Authors: Liousse C. , Dulac F. , Cachier H. , Tanré D.
Published: February 2004

We present an estimate of the yearly flux of total and black carbon aerosols emitted by savanna biomass burning in Africa from satellite data and ground‐based measurements. Smoke plumes are identified using visible, near‐infrared, and thermal infrared derived information. In the savanna region of our study, these structures could either decrease or increase the visible albedo of advanced very high resolution radiometer (AVHRR). It is hypothesized that variations of chemical composition and particulate size distribution may create such differences. The 5S model [Tanré et al., 1990] is used to simulate radiative transfer through smoke plumes and background atmosphere. The overall uncertainty of the derived aerosol optical depth (τa) is 75% and mainly due to the choice in particulate composition and size distribution aerosol. Impact of the aerosol mixture (internal versus external mixture) has been also tested. For smoke plumes a typical value of τa(at 0.55 μm) is 0.5, and 0.1 for the background atmosphere. Specific extinction cross sections are calculated using Mie theory applied to different representative aerosol models, allowing the retrieval of aerosol columnar concentrations from aerosol optical depth values and integrated aerosol mass loadings in fire plumes. The overall uncertainty on the determination of aerosol load is estimated to be lower than a factor of 5. The atmospheric carbonaceous aerosol flux from savanna burning in Africa was estimated to be 6.5 Tg C yr−1, which compares with that obtained from emission factor on‐site measurements (13±5 Tg C yr−1).
Effect of wind on surface hoar growth on snow
Authors: Hachikubo Akihiro , Akitaya Eizi
Published: February 2004

Field observations of surface hoar formation were carried out with the measurements of water vapor condensation rate, snow surface temperature, air temperature, humidity, wind speed, and net radiation. Large surface hoar crystals were observed to form under the breezy wind, 1 to 2 m s−1, at 0.1m high. The condensation rate increased linearly with the product of the vapor pressure gradient and the wind speed. The bulk transfer coefficient of water vapor Ce was roughly constant when the surface hoar crystals were small, whereas it showed some increase as the hoar crystals grew to several millimeters in height. A possible cause of this increase in Ce is that the developed surface hoar crystals modify the aerodynamic roughness and consequently increase the turbulent transfer of water vapor.
An integrated air pollution modeling system for urban and regional scales: 2. Simulations for SCAQS 1987
Authors: Lu Rong , Turco Richard P. , Jacobson Mark Z.
Published: February 2004

A new air quality modeling system, the surface meteorology and ozone generation (SMOG) model, is used to investigate the evolution and properties of air pollution in the Los Angeles basin during the southern California air quality study (SCAQS) intensive field program. The SMOG model includes four major components: a meteorological model, a tracer transport code, a chemistry and aerosol microphysics model, and a radiative transfer code. The fidelity of the coupled modeling system is evaluated by comparing model predictions against SCAQS data. Predictions of surface winds and temperatures are found to be in excellent agreement with measurements during daylight hours, when a strong sea breeze and mountain‐upslope flows are predominant but are less reliable at night when winds are typically lighter and more variable. Winds aloft, including shear and temporal variations, are also simulated quite well, although the forecasts (which are not constrained through continuous data assimilation) tend to drift from actual conditions as time progresses. Accordingly, the large‐scale flow is reinitialized each morning in the simulations. The dispersion patterns of two inert tracers released during the SCAQS period are accurately reproduced by the model. The two releases, one in the early morning hours and one around noon, led to quite different transport rates and distributions owing to the evolution of the sea breeze over die course of the day. Overall, the three‐dimensional development of thermally induced winds and their influences on tracer transport in the Los Angeles basin are accurately captured by the model. The predicted surface concentrations of ozone and other key pollutants have been spatially and temporally correlated with measured abundance, and the values agree to within 25–30% for ozone, with somewhat larger mean differences for several other species. In the case of the vertical distribution of ozone, the SMOG simulations generate dense oxidant (ozone) layers embedded in the temperature inversion, explaining for the first time similar features seen during SCAQS. Sources of error and uncertainty in the simulations are identified and discussed. The broad agreement between SMOG model predictions and SCAQS observations suggests that an integrated modeling approach is well suited for representing the coupled effects of mesoscale meteorology, tracer dispersion, and chemical transformations on urban and regional air quality.
Comparison between vertical ozone soundings and reconstructed potential vorticity maps by contour advection with surgery
Authors: Mariotti A. , Moustaoui M. , Legras B. , Teitelbaum H.
Published: February 2004

Sudden jumps and deep laminations, observed on vertical stratospheric ozone profiles during the European Arctic Stratospheric Ozone Experiment (EASOE) (winter 1991–1992) are explained as resulting from transport on isentropic layers. This is obtained by comparing the ozone profiles with high‐resolution reconstruction of the potential vorticity. Multilayer isentropic contour advection with surgery (CAS) is performed using European Center for Medium Range Weather Forecasts (ECMWF) analyzed winds. The results presented in this work are based on analyzing the location of the edge of the polar vortex, the horizontal and vertical extents of filamentary structures and intrusions within the polar vortex. The results are consistent with the assumption of high ozone content within the polar vortex which is valid during normal winter conditions of the northern hemisphere. The resolution required to carry out this study is much higher than that of current operational analysis by weather centers, while it is achievable by CAS reconstructions, which provide a dynamical understanding of the ozone variations.
Nitrogen oxides and ozone production in the North Atlantic marine boundary layer
Authors: Carsey Thomas P. , Churchill Dean D. , Farmer Michael L. , Fischer Charles J. , Pszenny Alexander A. , Ross Victor B. , Saltzman Eric S. , Springer‐Young M. , Bonsang Bernard
Published: February 2004

Measurements of reactive nitrogen gases (NO, NO2, NOy), as well as related chemical (O3, CO, aerosol black carbon, radon, selected nonmethane hydrocarbons) and meteorological parameters were made on board the R/V Malcolm Baldridge prior to and subsequent to the 1992 ASTEX (Atlantic Stratocumulus Transition Experiment) in the North Atlantic Ocean during June and July 1992. Results showed indications of well‐defined plumes from North America and Europe from both chemistry and back trajectory data. Elevated ozone concentrations were also observed in airmasses from uninhabited continental regions. Chemical and meteorological data were incorporated into a simple photochemical model in which ozone destruction predominated over generation. The principal reaction leading to ozone destruction was O(1D) + H2O → 2OH.
A modeling and observational study of the detailed microphysical structure of tropical cirrus anvils
Authors: Chen Jen‐Ping , McFarquhar Greg M. , Heymsfield Andrew J. , Ramanathan V.
Published: February 2004

A detailed microphysical analysis of ice particles in a cirrus anvil is presented, using a combination of observational data and model simulations for missions flown during the Central Equatorial Pacific Experiment (CEPEX). The observational data are obtained mainly from the two‐dimensional cloud probe, measuring particles as small as 100 μm in diameter; the model simulations are done with a detailed microphysical model that categorizes cloud particles according to their size, shape, and solute content. Detailed analyses of the simulated particle size spectra are made for the size range of 1 μm to several millimeters, which are then compared with the observational results. The evolution of the cirrus anvil is divided into four stages: the deep convection, the precipitating anvil, the extended anvil and the detached anvil. Discussions on the properties of the simulated cloud systems are given in detail for each stage. Model results show that the number concentration of ice particles in the anvils can reach over 1000 per liter. Frozen cloud droplets and interstitial aerosol particles are the main sources of these ice particles. In the precipitating anvils, a trimodal size distribution is prevalent at the upper portion, whereas bimodal or unimodal distributions are more common at the lower levels. The size distributions in the extended anvils exhibit a bimodal shape at the upper levels and a unimodal shape at the lower levels. The properties of the extended anvil compare fairly well with the observational results for one case but not as well for the other two cases. Nevertheless, both the observations and simulations show that smaller particles (diameter < 100 μm) are fractionally more important to the total number concentration and ice water content at higher altitudes in the anvil, whereas larger particles (diameter >100 μm) are more abundant in the middle to lower sections. Sedimentation sorting plays a significant role in determining the structures and evolution of the cirrus anvils. A sensitivity test indicates that the amount of condensation nuclei in the convective inflow may have a strong influence on the number concentration of ice particles, as well as the structure and lifetime of tropical cirrus anvils.
Angular dependence of observed reflectances: A comparison with plane parallel theory
Authors: Loeb Norman G. , Davies Roger
Published: February 2004

In this study, a direct comparison between plane parallel model calculations and one year of Earth Radiation Budget Satellite (ERBS) shortwave scanner observations over ocean between 30°S and 30°N is performed. Considering only cloud‐contaminated pixels, plane parallel model calculations are first normalized to observations at nadir at high Sun elevations on a pixel‐by‐pixel basis by adjusting cloud fraction and cloud optical depth. These are then used to generate plane parallel model reflectances as a function of view, solar zenith, and relative azimuth angle, which are directly compared with the observations on a statistical basis. At moderate to high solar elevations (θo≲63°), the relative view angle dependence of plane parallel reflectances remains, on a statistical basis, within ≈10% (relative difference) of that of the observations. For larger solar zenith angles, however, observed and plane parallel reflectances show systematic differences at all view angles that increase with increasing solar zenith angle. Provided atmospheric effects above the cloud are accounted for in the calculations, observed reflectances exceed plane parallel values in the backscattering direction by roughly a constant amount at all view angles for θo≳63°. In the forward scattering direction, observed reflectances generally fall within the range of plane parallel model values (for a range of model assumptions) but show a very different view angle dependence; observed reflectances level off at view angles between 60° and 73°, whereas the calculations increase steadily. When stratified by pixel brightness, the plane parallel model generally provides a better approximation to the observed reflectance dependence on view angle for darker (i.e., optically thinner) pixels than for brighter (optically thicker) pixels. For the brightest pixels, reflectance differences are largest at nadir in the backscattering direction and at oblique view angles in the forward direction. Overall, the relative dependence on azimuthal angle is similar for the observations and plane parallel model, irrespective of cloud thickness. Neglecting pixel area expansion with view angle in the calculations is shown to have only a minor influence. Finally, the marked difference in the reflectance dependence on solar zenith angle between observations and calculations is suggested as the likely reason why the principle of directional reciprocity applied to satellite measurements breaks down at ERBS pixel scales.
Intercomparison of measurements of sulfur dioxide in ambient air by carbonate‐impregnated filters and Teco pulsed‐fluorescence analyzers
Authors: Ferek Ronald J. , Covert Paul A. , Luke Winston
Published: February 2004

In two previous University of Washington field programs, airborne measurements of SO2 using carbonate‐impregnated filters and a Teco pulsed‐fluorescence analyzer showed excellent agreement over a range of ambient concentrations from 2 to 127 ppbv. As part of the Gas‐Phase Sulfur Intercomparison Experiment (GASIE), ambient air, diluted fivefold to tenfold with zero air, was sampled in the concentration range of 0.02 to 4 ppbv. With the bulk of the measurements in the range of 40 to 230 parts per trillion by volume (pptv), agreement between the two techniques was again very good (regression equation: Teco =1.07(filter)+4.5 pptv, r=0.93). Using careful precleaning, impregnation, storage, and handling techniques for the filter substrates, at sub‐100 pptv concentrations, the filter method is capable of an accuracy of better than ±10% with a ±7 pptv uncertainty (due to blank variability) for 6 m3 samples. In addition, the Teco model 43S is capable of rather precise measurements of sub‐100 pptv concentrations (approximately ±16 pptv) provided a suitable averaging time is employed (at least 10 min).
Effect of composition variations in cloud droplet populations on aqueous‐phase chemistry
Authors: Gurciullo Christopher S. , Pandis Spyros N.
Published: February 2004

We prove that the use of a cloud or fog droplet population's volume weighted average pH results in the underestimation of the actual rate of sulfate production for most atmospheric conditions. To quantify the magnitude of this error, we have developed two aqueous‐phase chemistry models: a droplet size‐resolved model and a bulk chemistry model. The discrepancy between the results of these two models indicates the magnitude of the error introduced by using bulk aqueous‐phase properties. This error depends mainly on the availability of gas‐phase species (SO2, O3, H2O2, and NH3), the aerosol size/composition distribution, and the residence time of the air parcel in cloud containing air. The ratio of predicted sulfate production between the two models for the cases studied here varies from as low as unity to as high as 30. The largest ratios occur during the first few minutes of cloud formation. After this peak the difference in sulfate production rates between the two models decreases rapidly. For the scenarios simulated, the largest error introduced by the bulk modeling approach at the end of a cloud event was underprediction of the sulfate production by a factor of 2. The magnitude of the sulfate underprediction by the bulk model decreases with increasing initial levels of gas‐phase NH3 and H2O2 and is rather insensitive to the gas‐phase O3 and SO2 concentrations.
Measurements of new particle formation and ultrafine particle growth rates at a clean continental site
Authors: Weber R. J. , Marti J. J. , McMurry P. H. , Eisele F. L. , Tanner D. J. , Jefferson A.
Published: February 2004

Simultaneous measurements of aerosol particles and their expected gas phase precursors were made at Idaho Hill, Colorado, a remote continental site. This study used apparatus and techniques similar to those employed in an earlier study at the Mauna Loa Observatory, Hawaii [Weber et al., 1995]. New particle formation, identified by the presence of ultrafine particles (nominally 3 to 4 nm diameter), was commonly observed in downslope (westerly) air and was correlated with high sulfuric acid (H2SO4) concentrations, low relative humidity and low particle surface area concentrations. The data point to H2SO4 as a principle nucleation precursor species with typical daytime concentrations between 106 and 107 molecules cm−3. Particle production was observed at H2SO4 concentrations that are well below predicted values for binary nucleation of H2O and H2SO4, suggesting that another species participated. Particle growth rates were estimated from the data with two independent approaches and in both cases were ∼5 to 10 times higher than can be explained by condensation of H2SO4 and its associated water. This suggests that species in addition to H2S04 were also making large contributions to ultrafine particle growth. Finally, calculated steady‐state H2SO4 concentrations were found to be in good agreement with measured values if the mass accommodation coefficient for H2SO4 on aerosol surfaces was assumed equal to ∼1.
Timescales for the stratospheric circulation derived from tracers
Authors: Hall Timothy M. , Waugh Darryn W.
Published: February 2004

A class of atmospheric constituents used as tracers of stratospheric flow are chemically long‐lived in comparison with timescales of interest and exhibit gradients due primarily to time‐dependent mixing ratios at the tropopause. In general, the stratospheric transport properties derived from such tracers depend on the nature of their time variation. To explore the relationship between timescales associated with the propagation of tracer mixing ratio signals and bulk transport properties, we have used two three‐dimensional chemical transport models to simulate the age spectrum (the distribution of transit times of mass present in air parcels) of the stratosphere. From the age spectrum the stratospheric response to any time‐varying tropospheric forcing may be deduced. The modeled age spectra are broad, indicating a range of transit times present in air parcels, and asymmetric, so that the mean transit time, called the mean age, is much larger than the modal transit time. Furthermore, the phase lag time of an oscillating signal (e.g., the annual CO2 cycle and lower stratospheric H2O) and the mean age are not timescales characterizing the same transport property. Periodic signal phase lags do not represent “mean transit times” and, in general, cannot be readily related to bulk transport properties. However, if the age spectrum is peaked enough, as it appears to be in the lower tropical stratosphere, periodic signal phase lags approximate the modal time.
Effect of cloud inhomogeneities on the solar zenith angle dependence of nadir reflectance
Authors: Loeb Norman G. , Várnai Tamás , Davies Roger
Published: February 2004

A significant discrepancy has been noted between satellite measurements of shortwave reflectance at nadir and the results of plane‐parallel model calculations: For moderate to large solar zenith angles, observed nadir reflectances increase with solar zenith angle, whereas plane‐parallel values decrease. Consequently, cloud optical depths retrieved using one‐dimensional (1‐D) theory have a bias which increases systematically with solar zenith angle. Using Monte Carlo model simulations of photon transport through stochastic, isotropic, scale‐invariant cloud fields with variable cloud top heights and volume extinction coefficients, we show that nadir reflectances from three‐dimensional cloud fields increase with solar zenith angle, consistent with the observations. The difference from the 1‐D case is shown to be explainable by cloudside illumination as well as by the presence of structured (i.e., non‐flat) cloud tops. Cloud sides enhance the amount of incident solar radiation intercepted by cloud, allowing more radiation to be scattered upward in the nadir direction. Structured cloud tops change the slope of illuminated cloud top surfaces, such that nadir reflectance at low solar elevations increases with the slope of the illuminated surface. For simple cloud geometries the two effects make equivalent contributions to the increase in nadir reflectance with solar zenith angle. While this increase is most pronounced for vertically extensive broken cloud fields, it also affects reflectances from overcast cloud fields with inhomogeneous (bumpy) cloud tops. Thus the observed solar zenith angle bias in cloud optical depth for the general cloud scene likely also occurs for extensive overcast cloud fields. Internal inhomogeneities due to small‐scale liquid water content variations within clouds are shown to cause no changes at low Sun and only slight decreases in nadir reflectance for high solar elevations.
A Lagrangian dispersion model for predicting CO2sources, sinks, and fluxes in a uniform loblolly pine (Pinus taeda L.) stand
Authors: Katul Gabriel , Oren Ram , Ellsworth David , Hsieh Cheng‐I , Phillips Nathan , Lewin Keith
Published: February 2004

A canopy Lagrangian turbulent scalar transport model for predicting scalar fluxes, sources, and sinks within a forested canopy was tested using CO2concentration and flux measurements. The model formulation is based on the localized near‐field theory (LNF) proposed byRaupach[1989a, b]. Using the measured mean CO2concentration profile, the vertical velocity variance profile, and the Lagrangian integral timescale profile within and above a forested canopy, the proposed model predicted the CO2flux and source (or sink) profiles. The model testing was carried out using eddy correlation measurements at 9 m in a uniform 13 m tallPinus taeda L.(loblolly pine) stand at the Blackwood division of the Duke Forest near Durham, North Carolina. The tree height and spacing are relatively uniform throughout. The measured vertical profile leaf area index (LAI) was characterized by three peaks, with a maximum LAI occurring at 6.5 m, in qualitative agreement with the LNF source‐sink predicted profile. The LNF CO2flux predictions were in better agreement with eddy correlation measurements (coefficient of determinationr2= 0.58; and standard error of estimate equal to 0.16 mg kg−1m s−1) thanKtheory. The model reproduced the mean diurnal CO2flux, suggesting better performance over longer averaging time periods. Two key simplifications to the LNF formulation were considered, namely, the near‐Gaussian approximation to the vertical velocity and the absence of longitudinal advection. It was found that both of these assumptions were violated throughout the day, but the resulting CO2flux error at 9 m was not strongly related to these approximations. In contrast to the forward LNF approach utilized by other studies, this investigation demonstrated that the inverse LNF approach is sensitive to near‐field corrections.
Profiles and partitioning of reactive nitrogen over the Pacific Ocean in winter and early spring
Authors: Kondo Y. , Koike M. , Kawakami S. , Singh H. B. , Nakajima H. , Gregory G. L. , Blake D. R. , Sachse G. W. , Merrill J. T. , Newell R. E.
Published: February 2004

Measurements of NO, NOy, PAN, HNO3, O3, CO, CH4, nonmethane hydrocarbons (NMHCs), and H2O were made over the Pacific Ocean in February and March during the Pacific Exploratory Mission West B (PEM‐West B). NOx, was calculated from NO using a photochemical model. These data were classified according to six air mass categories: western Pacific maritime, tropical, tropical convective, western Pacific continental, high latitude, and stratospheric. It has been found that the mixing ratios of many of the observed species and partitioning of NOy varied significantly depending on altitude, air mass, and season. These variations have been interpreted in terms of chemical and transport processes. In the maritime air below 7 km, the mixing ratios of calculated NOx ((NOx)mc), PAN, and NOy were lower than those in the continental air masses. The lowest values of PAN, HNO3, NOy, and O3 were observed in the tropical region below 5 km. In the continental air, NOy, PAN, CO, and NMHC levels below 4 km were much higher than those obtained in September and October during PEM‐West A, due to rapid transport of these species from anthropogenic sources on the continent to the Pacific Ocean by the westerly winds which dominated in early winter and spring. Reduced photochemistry during winter also contributed to the higher values of CO and NMHCs. Above 7 km the values of these species were lower during PEM‐West B, possibly due to much weaker convective activity in early spring. In spite of the weaker vertical transport, the median values of (NOx)mc and the (NOx)mc/C3H8 ratio at 10 km were 110–140 parts per trillion by volume (pptv) and 2.9–3.4 pptv/pptv, respectively, in the continental and maritime air masses, indicating the importance of in situ NOx production in the upper troposphere. In the continental air the PAN/NOy and HNO3/NOy ratios ranged between 0.2 and 0.5, showing clear anticorrelation. The PAN/NOy ratio was also anticorrelated with the temperature. In the high‐latitude air between 1 and 7 km the PAN/NO3, ratio was 0.5–0.8, and the (NOx)mc/NOy ratio was less than 0.05. Temperature and the concentrations of OH and NMHCs are considered to have strongly influenced the partitioning of NOy at middle and high latitudes. Generally, the sum of (NOx)mc, PAN, and HNO3 constituted 90±10% of the observed NOy from the boundary layer up to 7 km in all types of air masses. This finding improves our basic understanding on the chemistry and budget of the reactive nitrogen.
Surface mesonet for BOREAS
Authors: Shewchuk Stanley R.
Published: February 2004

This paper describes the mesonet sensor equipment installed by the Saskatchewan Research Council (SRC) for the Boreal Ecosystem‐Atmosphere Study (BOREAS) project as well as the data collection methods and modifications made to overcome environment‐related problems. The surface mesoscale atmospheric sciences mesonet for BOREAS is made up of 10 meteorological monitoring sites in western Canada designed to complement the two intensive sites for the BOREAS project. All stations monitored the atmosphere continuously from the start of the project in early 1994 to the end of the project in 1996. One site within the mesonet, the Saskatchewan Research Council's Climatological Reference Station, had over three decades of records. The BOREAS years of 1994 and 1995 had warmer air temperatures than normal; the year 1994 was 0.7°C above the long‐term annual average.
Winter and spring thaw as observed with imaging radar at BOREAS
Authors: Way JoBea , Zimmermann Reiner , Rignot Eric , McDonald Kyle , Oren Ram
Published: February 2004

Measurements of the length of the growing season in the boreal regions, during which significant carbon exchange due to metabolic activity occurs, may improve current estimates of annual CO2 fluxes at high northern latitudes. For coniferous, evergreen forest species, the summer frost free period bounds the growing season length and period of net carbon uptake. Spring soil thaw bounds the period of soil respiration and decomposition and thus carbon release. The balance of these two exchanges determines whether the boreal region is a net carbon source or sink. Imaging radar data can potentially be used to monitor these periods of soil and canopy thaw due to the sensitivity of radar to surface freeze/thaw state. In considering the use of imaging radar, two issues must be addressed. First, the temporal relationship between the time of freezing and thawing of the forest canopy and soil and the periods of photosynthetic and respiration activity must be ascertained. Second, the sensitivity of imaging radar to freeze/thaw processes in each of the forest components must be assessed. Of particular interest is the extent to which radar is selectively sensitive to tree and soil thawing. In 1994, in situ soil, stem and root temperatures, and stem xylem flux were measured over a complete annual cycle at the Boreal Ecosystem‐Atmosphere Study (BOREAS) test sites in Canada. Imaging radar data from the European Space Agency Remote Sensing (ERS‐1) satellite were also acquired throughout 1994. The in situ temperature data show clear transitions in soil and stem thawing related to the start of soil respiration and canopy photosynthesis, respectively. The imaging radar data show clear shifts in backscatter related directly to soil thaw, and possibly to canopy thaw, as two independent transitions. These results are compared to seasonal ecosystem model results for carbon exchange.
Equatorial dynamics observed by rocket, radar, and satellite during the CADRE/MALTED campaign: 2. Mean and wave structures, coherence, and variability
Authors: Fritts David C. , Garten James F. , Riggin Dennis M. , Goldberg Richard A. , Lehmacher Gerald A. , Schmidlin Frank J. , McCarthy Sean , Kudeki Erhan , Fawcett Clinton D. , Hitchman Mathew H. , Lieberman Ruth S. , Reid Iain M. , Vincent Robert A.
Published: February 2004

We present an analysis of the wind and temperature measurements made by rocket, radar, and satellite instrumentation in the equatorial and subtropical middle atmosphere accompanying the MALTED/CADRE campaign conducted at Alcantara, Brazil during August 1994. Measured mean winds and temperatures extended from ∼10 to 110 km, exhibited general consistency between instruments, and revealed an oscillatory nature of the mean zonal wind with altitude at equatorial latitudes. MF radar measurements of tidal structures showed these to exhibit variability on ∼8‐ and 16‐day periods, but to be largely uncorrelated in time. Two‐day wave structures displayed the same periodicities, but were well correlated among sites at northern and equatorial latitudes. Rocket and radar measurements at smaller scales of motion revealed inertia‐gravity waves having significant temporal coherence, quadrature correlations between components indicating clear directions of propagation, and momentum flux and mean wind correlations indicative of gravity wave filtering processes. Rocket estimates of diurnal tidal amplitudes suggest that the diurnal tide achieves convectively unstable amplitudes in the upper equatorial mesosphere.