bluuebunny/crossref_metadata_2025 huggingface dataset:
Observations and simulations of diurnal cycles of near‐surface wind speeds over land and sea
Authors: Barthelmie R. J. , Grisogono B. , Pryor S. C.
Published: February 2004

The role of stability and roughness changes in producing diurnal cycles of wind speed offshore is examined using experimental data and numerical simulations. Overnight, the transition from stable conditions over land to less stable conditions over sea combined with the lower roughness of the sea surface produces a marked increase in wind speeds offshore. However, during the day the transition from unstable conditions over land to stable conditions offshore means that the surface layer becomes decoupled from higher wind speeds aloft and the wind speed increase in the surface layer is smaller. Thus, in some cases the diurnal cycle of wind speeds offshore is inverted with respect to that at a typical land site; that is, highest wind speeds occur at night.
Consequence of forest‐to‐pasture conversion on CH4 fluxes in the Brazilian Amazon Basin
Authors: Steudler Paul A. , Melillo Jerry M. , Feigl Brigitte J. , Neill Christopher , Piccolo Marisa C. , Cerri Carlos C.
Published: February 2004

Methane (CH4) fluxes between soils and the atmosphere were measured in two tropical forest‐to‐pasture chronosequences in the state of Rondônia, Brazil. Forest soils always consumed atmospheric CH4 with maximum uptake rates in the dry season. Pasture soils consumed atmospheric CH4 during the dry season, but at lower rates than those in the forests. When soil moisture increased in the pasture soils, they became a source of CH4 to the atmosphere. Integrated over the year, forest soils were a net sink of approximately 470 mg CH4‐C/m2, while pastures were a net source of about 270 mg CH4‐C/m2. Thus forest‐to‐pasture conversion resulted in a net source of CH4 from the soil of about 1 g CH4/m2/yr. The total pasture‐related CH4 release for the entire Brazilian Amazon increased from 0.8 Tg CH4 in 1970 to about 2.5 Tg CH4 in 1990, with a maximum of 3.1 Tg CH4/yr in 1988. Soils accounted for a small part (about 5%) of the total CH4 release from the basin, while biomass burning and cattle emissions accounted for 95%. The average rate of increase in CH4 emission from pastures was about 0.2 Tg CH4/yr between 1975 and 1988. This represents between 12% and 14% of the global average rate of change in tropospheric CH4 content for this time period.
Gauge‐based monthly analysis of global land precipitation from 1971 to 1994
Authors: Xie Pingping , Rudolf Bruno , Schneider Udo , Arkin Phillip A.
Published: February 2004

Monthly gridded fields of global land precipitation have been constructed on 2.5° latitude/longitude grids for a 24‐year period from 1971 to 1994 by interpolating gauge observations at over 6000 stations contained in the Global Historical Climatology Network of the Carbon Dioxide Information Center of U.S. Department of Energy and the Climate Anomaly Monitoring System of the Climate Prediction Center of National Oceanic and Atmospheric Administration. Sensitivity tests indicated that this gauge‐based analysis has relatively high quality in general and that its quantitative accuracy increases with the gauge network density. Significant value‐dependent bias and random error, however, exist in the analysis over grid areas with few gauges. The mean distribution and annual cycle of the 24‐year gauge‐based analysis showed close agreement with those of several published long‐term means, and the inter‐annual variations in precipitation associated with the El Niño‐Southern Oscillation phenomenon were evident. Despite the ability of this gauge‐based analysis to describe large‐scale precipitation over global land areas, further efforts are needed to improve the interpolation algorithm, to increase gauge network density, and to combine the gauge analysis with other information sources based on satellite observations, especially over grid areas with poor gauge coverage.
Sulfur speciation in individual aerosol particles
Authors: Neubauer Kenneth R. , Sum Stephen T. , Johnston Murray V. , Wexler Anthony S.
Published: February 2004

Sulfur aerosols play an important role in acid deposition and the Earth's energy balance. Important species in these aerosols include methanesulfonates, hydroxymethanesulfonates, sulfates, and sulfites. Because the relative amounts of these species indicate different sources and atmospheric processes, it is important to distinguish them in single‐aerosol particles. To accomplish this task, we use rapid single‐particle mass spectrometry (RSMS), a technique that permits individual particles to be analyzed in an online mode. Each sulfur species produces a characteristic set of ions in the mass spectra. In simulated marine and urban aerosols the relative amounts of methanesulfonic acid (MSA) and sodium hydroxymethanesulfonate (NaHMSA) in a single particle can be determined from peak area ratios in the mass spectra. Improved quantitation is possible by application of the classification and regression tree (CART) algorithm to distinguish the mass spectra of particles having different compositions. Factors that influence speciation include particle size, morphology, and laser fluence.
Short‐term rainfall prediction method using a volume scanning radar and grid point value data from numerical weather prediction
Authors: Nakakita Eiichi , Ikebuchi Shuichi , Nakamura Tetsuya , Kanmuri Masayuki , Okuda Masahiro , Yamaji Akihiko , Takasao Takuma
Published: February 2004

A physically based short‐term rainfall prediction method, which uses a volume scanning radar, is extended so that it utilizes grid point values from a numerical weather prediction model as supplementary information. The original short‐term prediction method mainly consists of a conceptual rainfall model that can predict rainfall distribution, particularly over mountainous regions, in a qualitative sense. On the other hand, the grid point values from the numerical weather prediction model, the Japan Spectral Model developed by the Japan Meteorological Agency, are operationally distributed as the grid point value (GPV) data. In the original short‐term prediction method the three‐dimensional wind field as well as initial distributions of the air temperature and water vapor were identified using topography and upper air observations. In the extended method, however, in identifying those initial values, the information from the GPV data is used instead of the upper air observations in order to accommodate large differences in temporal and spatial resolution between radar information and upper air observations. It is noted that this extended method does not use predicted GPV rainfall data. The conceptual rainfall model plays the role of bridging the gap between radar information and numerical weather prediction scales. This extended method is applied to a rainfall event which occurred in the bai‐u season (one of the rainy seasons of Japan) in July 1994. Results show that for the extended lead time of three and four hours, prediction of the expanding rainfall area was improved.
Multifractal characterization of rain fields with a strong orographic influence
Authors: Harris Daniel , Menabde Merab , Seed Alan , Austin Geoff
Published: February 2004

Data from networks of high time resolution (15 second) rain gauges forming a transect from the base to the divide of a mountain range are used to study the multifractal characteristics of precipitation at different locations along the transect. In particular, scaling power spectra, multiscaling moments and power law exceedence probability tails are analyzed from rain gauge time series of ∼35–70 hours in length. The parameters discussed are specifically the spectral scaling exponent, β, the intermittency parameter, C1 (a fundamental parameter of the moment scaling function, K(q)) and qcr, the power law probability tail exponent. Results show a systematic trend in the exponents, indicating a decrease in intermittency, the frequency of extreme values and smoothness of the time series with increasing altitude along the transect. K(q) and qcr are briefly discussed and derived as natural properties of multifractal cascades. It is concluded that the parameters of multifractal cascade models of rainfall are related to the physical processes which are qualitatively discussed in the context of the observed changes in the statistics.
Isotopic enrichment of heavy ozone in the stratosphere
Authors: Houston P. L. , Suits A. G. , Toumi R.
Published: February 2004

A mass‐independent, 3% enrichment of heavy ozone isotopes in the stratosphere can be assigned to a mechanism in which (1) short‐wavelength photodissociation of ozone produces O2(ν ≥ 26) + O, (2) the O2(ν ≥ 26) reacts with ground state O2 to produce O3 + O, and (3) each O atom recombines with O2 to form O3. The overall reaction scheme, O3 + hv + 3O2 → 3O3, produces more ozone than it consumes. The dissociation channel which begins this scheme is more probable for heavy ozone than for 48O3, and one of the oxygen atoms in the original O3 is incorporated into a new O3. Thus this new ozone source tends to “distill” heavy oxygen atoms into the O3 pool while depleting them from the O2 pool. The amount of enrichment produced by this mechanism, while significant, is still too small to account for the large observed stratospheric enrichment of heavy ozone.
A 5‐year simulation of supersonic aircraft emission transport using a three‐dimensional model
Authors: Weaver Clark J. , Douglass Anne R. , Considine David B.
Published: February 2004

A 5‐year simulation of supersonic aircraft exhaust using a three‐dimensional transport model has been completed using winds from the NASA/Goddard data assimilation system. A tracer based on emission rates of reactive nitrogen species (NOy) for all forecasted flight routes is continuously injected into the model. A parameterized upper stratospheric loss mechanism and a tropospheric sink due to rainout approximately balance the nitrogen emissions after several years of integration. Maximum values for exhaust NOy occur during the northern hemisphere (NH) summer months, and minimum values occur during winter. The pollutant is most zonally asymmetric during the NH summer. The peak values are never more than twice the zonal mean. This supports the use of zonally averaged two‐dimensional models to evaluate the impact of the exhaust on the lower stratospheric composition. Budget calculations from the transport model show that most exhaust released in the NH is transported downward into the troposphere, where it is destroyed. In the model, about 15–20% of exhaust released poleward of 30°N is transported into the tropics, where it is lofted. The stratospheric residence time for the exhaust is estimated to be 13 months.
Correlated millimeter wave measurements of ClO, N2O, and HNO3from McMurdo, Antarctica, during polar spring 1994
Authors: Klein Ulf , Crewell Susanne , De Zafra Robert L.
Published: February 2004

Ground‐based observations of stratospheric ClO, N2O, and HNO3were made almost continuously at McMurdo Station, Antarctica (77.9°S, 166.6°E), during the austral spring of 1994, using two separate microwave receivers. Vertical profiles of these trace gases have been retrieved from the pressure broadened emission spectra between September 4 and October 8, 1994. In early September, McMurdo was located well inside the polar vortex, and high mixing ratios of chlorine monoxide (up to 1.8 ppbv) were measured in the lower stratosphere. Because of vortex movement, later measurements were taken in edge regions, where ClO was found to be quite variable. This vortex movement also provided an opportunity to study relative changes between all three species. Almost no HNO3was seen below 20 km during the measurement period, indicating that stratospheric air had been efficiently denitrified by polar stratospheric cloud formation. A significant increase of the nitric acid column was observed only around September 20, when McMurdo was closer to the outer edge of the vortex. At the beginning of the measurements, the vertical profiles of the inert tracer N2O had already descended so far that very little N2O was present above 20 km. During the observation period, the N2O distribution did not show strong changes except for a slight downward trend which increased with altitude. This indicates, as noted in previous years, that subsidence continued in the stratosphere over McMurdo Station until at least early October, when measurements were stopped. The temporal correlations between the behavior of ClO, N2O, HNO3, altitude, and temperature at the 50‐hPa level, and of ozone measured by local ozonesondes show that changes in the atmospheric composition were partly due to dynamic effects. A backward trajectory analysis was performed to interpret the ClO data in an attempt to clarify some irregularities.
Open‐path Fourier transform infrared studies of large‐scale laboratory biomass fires
Authors: Yokelson Robert J. , Griffith David W. T. , Ward Darold E.
Published: February 2004

A series of nine large‐scale, open fires was conducted in the Intermountain Fire Sciences Laboratory (IFSL) controlled‐environment combustion facility. The fuels were pure pine needles or sagebrush or mixed fuels simulating forest‐floor, ground fires; crown fires; broadcast burns; and slash pile burns. Mid‐infrared spectra of the smoke were recorded throughout each fire by open path Fourier transform infrared (FTIR) spectroscopy at 0.12 cm−1resolution over a 3 m cross‐stack pathlength and analyzed to provide pseudocontinuous, simultaneous concentrations of up to 16 compounds. Simultaneous measurements were made of fuel mass loss, stack gas temperature, and total mass flow up the stack. The products detected are classified by the type of process that dominates in producing them. Carbon dioxide is the dominant emission of (and primarily produced by) flaming combustion, from which we also measure nitric oxide, nitrogen dioxide, sulfur dioxide, and most of the water vapor from combustion and fuel moisture. Carbon monoxide is the dominant emission formed primarily by smoldering combustion from which we also measure carbon dioxide, methane, ammonia, and ethane. A significant fraction of the total emissions is unoxidized pyrolysis products; examples are methanol, formaldehyde, acetic and formic acid, ethene (ethylene), ethyne (acetylene), and hydrogen cyanide. Relatively few previous data exist for many of these compounds and they are likely to have an important but as yet poorly understood role in plume chemistry. Large differences in emissions occur from different fire and fuel types, and the observed temporal behavior of the emissions is found to depend strongly on the fuel bed and product type.
Role of mineral aerosol as a reactive surface in the global troposphere
Authors: Dentener Frank J. , Carmichael Gregory R. , Zhang Yang , Lelieveld Jos , Crutzen Paul J.
Published: February 2004

A global three‐dimensional model of the troposphere is used to simulate the sources, abundances, and sinks of mineral aerosol and the species involved in the photochemical oxidant, nitrogen, and sulfur cycles. Although the calculated heterogeneous removal rates on mineral aerosol are highly uncertain, mainly due to poorly known heterogeneous reaction rates, the reaction of SO2 on calcium‐rich mineral aerosol is likely to play an important role downwind of arid source regions. This is especially important for regions in Asia, which are important and increasing emitters of sulfur compounds. Our results indicate that the assumption that sulfate aerosol follows an accumulation mode size distribution, is particularly in Asia likely to overestimate the sulfate aerosol climate‐cooling effect. An even larger fraction of gas phase nitric acid may be associated with and neutralized by mineral aerosol. Interactions of N2O5, O3, and HO2‐radicals with dust are calculated to affect the photochemical oxidant cycle, causing ozone decreases up to 10% in and nearby the dust source areas. Comparison of these results with limited available measurements indicates that the proposed reactions can indeed take place, although due to a lack of measurements a rigorous evaluation is not possible at this time.
Model for multiscale disaggregation of spatial rainfall based on coupling meteorological and scaling descriptions
Authors: Perica S. , Foufoula‐Georgiou E.
Published: February 2004

The precipitation output of a mesoscale atmospheric numerical model is usually interpreted as the average rainfall intensity over the grid cell of the model (typically 30 × 30 km to 60×60 km). However, rainfall exhibits considerable heterogeneity over subgrid scales (i.e., scales smaller than the grid cell), so it is necessary for hydrologic applications to recreate or simulate the small‐scale rainfall variability given its large‐scale average. Rainfall disaggregation is usually done statistically. In this paper, a new subgrid scale rainfall disaggregation model is developed. It has the ability to statistically reproduce the rainfall variability at scales unresolved by mesoscale models while being conditioned on large‐scale rainfall averages and physical properties of the prestorm environment. The model is based on two extensively tested hypotheses for midlatitude mesoscale convective systems [Perica and Foufoula‐Georgiou, 1996]: (1) standardized rainfall fluctuations (defined via a wavelet transform) exhibit simple scaling over the mesoscale, and (2) statistical scaling parameters of rainfall fluctuations relate to the convective available potential energy (CAPE), a measure of the convective instability of the prestorm environment. Preliminary evaluation of the model showed that the model is capable of reconstructing the small‐scale statistical variability of rainfall as well as the fraction of area covered with rain at all analyzed subgrid scales. The performance evaluation was based on comparison of summary statistics and spatial pattern measures of simulated fields with those of known fields observed during the Oklahoma‐Kansas Preliminary Regional Experiment for Storm‐Central (PRE‐STORM).
A general model of how fire emissions and chemistry produce African/oceanic plumes (O3, CO, PAN, smoke) in TRACE A
Authors: Chatfield Robert B. , Vastano John A. , Singh H. B. , Sachse G.
Published: February 2004

A full‐chemistry simulation of the Great African Plume gives one example of a broad conceptual model of the intercontinental pollution of the tropical middle troposphere by lofted biomass burning plumes. This two‐dimensional idealization “calibrated” by carbon monoxide distributions links conventional estimates of burning emissions to oceanic concentrations of pollutants. This paper makes use of GRACES, a modular photochemical simulation system, in two forms. The results of the chemically intensive two‐dimensional form, using idealized winds, mixing, deposition, and rainout, match the general concentration patterns of a three‐dimensional GRACES model study of CO during the TRACE A/SAFARI period of October 1992 (reported separately). The study highlights the importance of simulating the vertical and diurnal variation of the planetary boundary layer and cloud activity. These correlate temporally with the intensity of tropical agricultural burning. We emphasize one situation, the drift northward and eastward of pollution into the interocean convergence region, where it rises by small‐scale motions and rides out westward in the lower midtroposphere (<5 km). These effects help set in place large strata of enhanced CO, ozone, and other pollution over the equatorial Atlantic Ocean. Overall, our comparisons of simulations with the TRACE A data on the cycling of CO, NOx, and O3in the tropical atmosphere suggest substantial agreement of current emission estimates and atmospheric concentrations. In certain regions, ozone is simulated slightly below observed levels. The striking major disagreements are in NOy, (total reactive nitrogen) and HNO3, which are intimately related to CO and O3; this suggests that current theory omits at least one fundamental process.
Wave breaking signatures in sodium densities and OH nightglow: 2. Simulation of wave and instability structures
Authors: Fritts David C. , Isler Joseph R. , Hecht James H. , Walterscheid Richard L. , Andreassen Øyvind
Published: February 2004

Measurements of atmospheric structure and dynamics near the mesopause were performed using a sodium lidar, an MF radar, and a night‐glow CCD camera during the CORN campaign performed in central Illinois during September 1992. The major features of the observed structure on September 27/28 include a low‐frequency, large‐scale wave accounting for persistent overturning of the temperature and sodium density fields, superposed higher‐frequency motions, small‐scale transient ripples in the nightglow images suggestive of instability structures, and large‐scale wind shear near the height of apparent instability. We describe four simulations of wave breaking with a three‐dimensional model designed to assist in the interpretation of these observations. Two simulations address the instability of a low‐frequency wave in a background shear flow with and without higher‐frequency modulation. These show higher‐frequency motions to be important in assigning the spatial and temporal scales of instability structures. Two other simulations examine the instabilities accompanying a convectively unstable inertia‐gravity wave with and without higher‐frequency modulation without mean shear. These show the instability structure to remain aligned in the direction of wave propagation, with only weak influences by the high‐frequency motion. Our results suggest that instability due to a superposition of waves accounts best for the nightglow features observed during the CORN campaign and that streamwise convective instabilities observed due to wave breaking at higher intrinsic frequencies continue to dominate instability structure for internal waves for which inertial effects are important.
Sensitivity of multiangle remote sensing observations to aerosol sphericity
Authors: Kahn Ralph , West Robert , McDonald Duncan , Rheingans Brian , Mishchenko Michael I.
Published: February 2004

Multiangle, multispectral remote sensing observations, such as those anticipated from the Earth Observing System (EOS) multiangle imaging spectroradiometer (MISR), can distinguish spherical from nonspherical particles over calm ocean for mineral‐dust‐like particles with the range of sizes and column amounts expected under natural conditions. The ability to make such distinctions is critical if remote sensing of atmospheric aerosol properties is to provide significant new contributions to our understanding of the global‐scale, clear‐sky solar radiation balance. According to theoretical simulations the measurements can retrieve column optical depth for nonspherical particles to an accuracy of at least 0.05 or 10%, whichever is larger. In addition, three to four distinct size groups between 0.1 and 2.0 microns effective radius can be identified at most latitudes.
Annual variation of rainfall over Brazil and water vapor characteristics over South America
Authors: Rao Vadlamudi Brahmananda , Cavalcanti Iracema F. A. , Hada Kioshi
Published: February 2004

A large region in central Brazil is characterized by summer rainfall and winter dry conditions. During the 6‐month period of September, October, November, December, January, and February (SONDJF) this region receives 70% or more of its annual rainfall. Calculations of vertically integrated water vapor flux and its divergence are made for South America. The results suggest that the Amazon basin is the principal source of moisture for central Brazil during the period SONDJF. Water vapor flux from the equatorial Atlantic associated with trade winds is the main moisture source for the Amazon basin.
Comparison of 6.7‐μm radiances computed from aircraft soundings and observed from GOES
Authors: Salathé Eric P. , Smith Ronald B.
Published: February 2004

Radiances observed by the GOES 6.7‐μm channel are compared to computations from simultaneous aircraft soundings of the temperature and moisture profiles. The soundings were measured using high precision instruments aboard the National Center for Atmospheric Research Sabreliner. An advanced line‐by‐line radiative transfer model is used to simulate the satellite observations. This comparison shows that the computed brightness temperatures overestimate the observed brightness temperatures but reproduce the full range in observed brightness temperatures. The computed brightness temperatures are, on average, 2.6 K higher than observed. Possible sources for this bias are investigated, such as transmission through a cloudy lower boundary, scattering by thin high‐level cirrus, and water vapor continuum absorption. It is likely that a combination of uncertainties in the radiative properties of water and unaccountable ice or aerosol absorption contributes to the disparity.
Evidence for nonlinear coupling of planetary waves and tides in the Antarctic mesopause
Authors: Kamalabadi F. , Forbes J. M. , Makarov N. M. , Portnyagin Yu. I.
Published: February 2004

Analyses of hourly‐mean meridional and zonal winds near 95 km, observed with the meteor radar system at Molodezhnaya station (68°S, 45°E) during 1990, reveal the presence of long‐period (2–18 day) waves with dominant periods corresponding to those of Rossby normal modes modified by mean zonal winds. Time–varying analyses indicate that although significant contributions at planetary wave periods persist with nearly constant periods for intervals of days to weeks, temporal variability of these periods is observed over longer intervals. Tidal motions, which mainly consist of the semidiurnal and the diurnal periods, demonstrate considerable modulation of their amplitudes that vary with time. The observed tidal amplitude modulations are investigated through bispectral analyses. The results of these analyses suggest nonlinear interactions of quadratic form between oscillations with periods in the range of 2 to 19 days and the diurnal and semidiurnal tides at various intervals during 1990.
Remote sensing of aerosols over land surfaces including polarization measurements and application to POLDER measurements
Authors: Herman M. , Deuzé J. L. , Devaux C. , Goloub P. , Bréon F. M. , Tanré D.
Published: February 2004

Ground‐based measurements of the diffuse skylight and airborne measurements of the light reflected by land surfaces are examined, especially with regard to their polarization properties. The reported land surface reflections correspond to multidirectional polarized measurements performed by the Polarization and Directionality of Earth Reflectances (POLDER) airborne version on very clear days. These observations are analyzed for retrieving the polarization properties of scattering by terrestrial aerosols and reflection by ground targets, respectively. The results suggest that the polarized light is much more sensitive to atmospheric scattering than to reflection by natural surfaces, especially by vegetative cover. Theoretical modeling supports this hypothesis. Finally, application of these results to aerosol remote sensing over land surfaces from POLDER measurements is discussed.
Modeling phase functions for dustlike tropospheric aerosols using a shape mixture of randomly oriented polydisperse spheroids
Authors: Mishchenko Michael I. , Travis Larry D. , Kahn Ralph A. , West Robert A.
Published: February 2004

Laboratory and in situ measurements show that scattering properties of natural nonspherical particles can be significantly different from those of volume‐or surface‐equivalent spheres, thus suggesting that Mie theory may not be suitable for interpreting satellite reflectance measurements for dustlike tropospheric aerosols. In this paper we use the rigorous T‐matrix method to extensively compute light scattering by shape distributions of polydisperse, randomly oriented spheroids with refractive indices and size distributions representative of naturally occurring dust aerosols. Our calculations show that even after size and orientation averaging, a single spheroidal shape always produces a unique, shape‐specific phase function distinctly different from those produced by other spheroidal shapes. However, phase functions averaged over a wide aspect‐ratio distribution of prolate and oblate spheroids are smooth, featureless, and nearly flat at side‐scattering angles and closely resemble those measured for natural soil and dust particles. Thus, although natural dust particles are, of course, not perfect spheroids, they are always mixtures of highly variable shapes, and their phase function can be adequately modeled using a wide aspect‐ratio distribution of prolate and oblate spheroidal grains. Our comparisons of nonspherical versus projected‐area‐equivalent spherical particles show that spherical‐nonspherical differences in the scattering phase function can be large and therefore can cause significant errors in the retrieved aerosol optical thickness if Mie theory is used to analyze reflectance measurements of nonspherical aerosols. On the other hand, the differences in the total optical cross sections, single‐scattering albedo, asymmetry parameter of the phase function, and backscattered fraction are much smaller and in most cases do not exceed 10%. This may suggest that for a given aerosol optical thickness the influence of particle shape on the aerosol radiative forcing is negligibly small. Spherical‐nonspherical differences in the extinction‐to‐backscatter ratio are very large and should be explicitly taken into account in inverting lidar measurements of dustlike aerosols.
Comment on “A spectroscopic tour through the liquid aerosol interface: Implications for atmospheric chemistry” by J.‐X. Zhang, D. P. Aiello, and P. M. Aker
Authors: Campillo A. J. , Eversole J. D. , Lin H.‐B.
Published: February 2004

Our data contradicts the claim of Zhang et al. [1994] that water droplets from a vibrating orifice aerosol generator are chemically modified.
Understanding the production and interconversion of the hydroxyl radical during the Tropospheric OH Photochemistry Experiment
Authors: Eisele Fred L. , Mount George H. , Tanner David , Jefferson Anne , Shetter Richard , Harder Jerald W. , Williams Eric J.
Published: February 2004

The hydroxyl radical plays a critical role in the chemistry of the lower atmosphere. Understanding its production, interconversion, and sinks is central to modeling and predicting the chemistry of the troposphere. The OH measurements made during the 1993 Tropospheric OH Photochemistry Experiment provide a detailed look at these mechanisms since NOx, j(O3), RO2, HO2, nonmethane hydrocarbons (NMHC), and many other relevant species were measured simultaneously. The relationship of OH to NOx and to primary production is extensively examined. Close agreement with theory is shown in the NOx/OH relation with OH concentrations increasing with increasing NO to a maximum at 1–2 ppbv due to conversion of HO2 to OH, and then OH decreasing with further increasing NOx due to conversion of NO2 to HNO3. Close correlations of OH concentrations with primary production (water, ozone,j(O3)) are also shown both on average and on rapid timescales.
A three‐dimensional global episodic tracer transport model: 1. Evaluation of its transport processes by radon 222 simulations
Authors: Li Yonghong , Chang Julius S.
Published: February 2004

A three‐dimensional, Eulerian, global episodic tracer transport model is developed in this study. This model is designed to represent those episodic processes that are important for the transport and removal of short‐lived tropospheric constituents better than most other global tracer models. It is also designed to be consistent with a regional model so that a nested modeling system in future studies can provide the much‐needed finer resolutions over industrial regions with concentrated anthropogenic emissions. This model subdivides the atmosphere into 18 levels and 128 by 64 horizontal grids and calculates tracer concentrations by numerically solving the mass conservation equation on the basis of high temporal resolution, local meteorological conditions in an event‐based manner. It represents the first attempt to utilize a mesoscale‐type description of cloud effects on tropospheric chemical species for individual clouds in a globe‐scale tracer transport model. The vertical transport by clouds is represented by a one‐dimensional mixing model with subgrid‐scale mass adjustment and entrainment effects. A modified Bott's [1989a, b] scheme for spherical geometry is used for the advection calculations, which are mass conservative, positive definite, efficient, and accurate. Three parameterization schemes are provided for the description of mixing process in the planetary boundary layer (PBL), one of which has a nonlocal submodule for the convective PBL. An evaluation of the model transport processes is conducted by simulating radon 222 using 2 months of the National Center for Atmospheric Research Community Climate Model version 2 meteorology. Model‐simulated surface concentrations fall within the observed ranges over both continents and oceans. The model average vertical profile over midlatitude northern hemisphere and the percentages of radon mass above 2 and 5.5 km are in reasonable agreement with available observations. Much better agreement with observations is achieved when direct, subgrid‐scale cloud transport is included than when it is not. Model results suggest that cloud vertical transport contributes substantially to the radon in the middle and upper troposphere at northern midlatitudes and in the upper troposphere at low latitudes. One implication of these results is that subgrid cloud convection may play a dominant role in bringing surface emissions of reactive chemical compounds into the upper troposphere.
Model‐estimated microwave emissions from rain systems for remote sensing applications
Authors: Smirnov Mikhail T. , Meischner Peter F.
Published: February 2004

A simple model for estimating the upward and downward microwave emission from rain layer types above ground is presented. The emission properties of the rain layers are estimated from physical quantities such as the optical depth, the single‐scattering albedo, the physical temperature, and a given drop size distribution for Mie scattering calculations. The underlying surface is characterized by the emissivity and the physical temperature. The transparency coefficientqand the reflection coefficientrof the rain layer are expressed by these physical quantities. The brightness temperature then is given by the physical temperatureT,q, andr. The radiation transfer is estimated by the method of layer addition, described bySobolev[1956], which avoids the necessity of solving the equation of radiation transfer. The accuracy of this simple model was estimated by comparisons with three‐dimensional Monte Carlo calculations. The error is estimated to be less than 3 K for common situations and less than 8 K for unrealistic high optical depths. It is shown that any one of the quantities rain rate, rain layer depth, and physical temperature can be estimated with sufficient accuracy if the others are known. The basic model has been extended for application to inhomogeneous cloud layers and to include differences in brightness temperatures for horizontal and vertical polarizations for oblate raindrops. The main intended application of this model is rain rate estimation from space with low data processing efforts, especially for the Priroda mission. The model was tested for the downwelling emission during the field experiment CLEOPATRA by measurements with a polarimetric weather radar and rain gauges. The results verify the principles, and promising agreement was found at least for stratiform rain. The polarimetric extension of the model too showed promising results under quite different measurement conditions in Russia and southern Germany.
Atmospheric correction of ocean color imagery in the Earth Observing System era
Authors: Gordon Howard R.
Published: February 2004

Sensors that can be used for the observation of ocean color in NASA's Earth Observing System era (SeaWiFS, MODIS, and MISR) have been designed with 2–4 times the radiometric sensitivity of the proof‐of‐concept ocean color instrument CZCS (coastal zone color scanner). To realize an improvement in the retrieval of biologically important ocean parameters, e.g., the concentration of the photosynthetic pigment chlorophyll a, from this increased sensitivity, significantly better atmospheric correction than was applied to CZCS is required. Atmospheric correction improvement necessitates the inclusion of the effects of multiple scattering, which are strongly dependent on the aerosol size distribution, concentration, and absorption properties. We review the basic concepts of atmospheric correction over the oceans and provide the details of the algorithms currently being developed for SeaWiFS, MODIS, and MISR. An alternate correction algorithm that could be of significant value in the coastal zone is described for MISR. Related issues such as the influence of aerosol vertical structure in the troposphere, polarization of the light field, sea surface roughness, and oceanic whitecaps on the sea surface are evaluated and plans for their inclusion in the algorithm are described. Unresolved issues, such as the presence of stratospheric aerosol, the appropriateness of the aerosol models used in the assessment of multiple scattering, and the identification of, and difficulties associated with the correction for, the presence of absorbing aerosols, e.g., urban pollution or mineral dust, are identified, and suggestions are provided for their resolution.
Aerosol characteristics at Idaho Hill during the OH Photochemistry Experiment
Authors: Murphy D. M. , Thomson D. S. , Kaluzhny M. , Marti J. J. , Weber R. J.
Published: February 2004

This paper supports other measurements at Idaho Hill by describing measurements of the aerosol surface area, volume, and size distribution. The aerosol size distributions at the Idaho Hill site showed nuclei and accumulation modes similar to other clean continental sites. However, there were fewer large aerosols. Principal components analysis verifies that the modes present in the size distribution also had distinct time behavior. The coarse aerosol mode had two components with distinctly different time behavior: aerosols larger than 2 μm displayed a great deal of short‐term variability not present in smaller aerosols. Accumulation mode aerosols had separate correlations with fresh and aged pollution, whereas smaller aerosols were correlated only with fresh pollution. Aerosols larger than 15 nm showed no diurnal variation in downslope conditions and an afternoon maximum in upslope conditions. Aerosol surface areas were too small to directly affect OH chemistry even if OH or HO2 had fast surface losses. Aerosol volumes indicate that aerosol nitrate is not a likely candidate to balance the NOy shortfall.
Retrieval of atmospheric properties and surface bidirectional reflectances over land from POLDER/ADEOS
Authors: Leroy M. , Deuzé J. L. , Bréon F. M. , Hautecoeur O. , Herman M. , Buriez J. C. , Tanré D. , Bouffiès S. , Chazette P. , Roujean J. L.
Published: February 2004

Polarization and Directionality of the Earth's Reflectances (POLDER) is a new instrument devoted to the global observation of the polarization and directionality of solar radiation reflected by the Earth‐atmosphere system. It will fly onboard the ADEOS platform in 1996. This paper outlines the improvements expected from POLDER in the description of atmospheric aerosols and water vapor over land, and of surface bidirectional reflectances. It then gives a detailed description of the operational algorithms which are implemented in the “land surface and atmosphere over land” processing line. This line is part of an effort initiated by Centre National d'Etudes Spatiales (the French Space Agency) to develop lines of products in order to facilitate the exploration of POLDER's new capabilities by the international science community. Emphasis is given in this paper to the presentation of the principles, physical rationale, and elements of validation of the algorithms of this processing line. The main products are (1) for each orbit segment, the amount and type of aerosols, the water vapor content, and bidirectional reflectances corrected for atmospheric effects, and (2) every 10 days, global maps of surface directional signatures, of hemispherical surface reflectances, and of parameters describing the statistical distribution of aerosol and water vapor content. These products will be made available to all interested investigators. The most innovative algorithms of the processing line are (1) cloud detection, based on a series of tests involving reflectance thresholds, oxygen pressure estimates, and analysis of polarized radiance in the rainbow direction, (2) retrieval of aerosol optical thickness and type from directional polarized radiance measurements, and (3) retrieval of surface directional signature through an adjustment of a time series of directional reflectance measurements with a semiempirical bidirectional reflectance model.
Temporal and spatial variations of the carbon isotopic ratio of atmospheric carbon dioxide in the western Pacific region
Authors: Nakazawa Takakiyo , Morimoto Shinji , Aoki Shuhji , Tanaka Masayuki
Published: February 2004

CO2 samples were collected on board container ships between Japan and Australia and between Japan and the United States from April 1984 to December 1991. They were then analyzed for their δ13C values with a precision of 0.02‰. The seasonal cycle of δ13C was clearly observable at latitudes from 55°N to the equator. Peak‐to‐peak amplitude of the average seasonal cycle of δ13C was about 0.8‰ at latitudes north of 40°N and decreased going southward to 0.2‰ at the equator. The comparison of the observed seasonal cycles of δ13C with those of the CO2 concentration suggests that the seasonal CO2 cycles observed at latitudes north of the equator are due to the seasonal change in terrestrial biospheric activities. However, air transport from the southern hemisphere is also thought to be partly responsible for the seasonal CO2 cycles at northern low latitudes. Values of δ13C decreased secularly at a rate of about −0.03‰/year, owing mainly to increased amounts of isotopically light CO2 produced in fossil fuel combustion and deforestation. Interannual variations of the long‐term trend of δ13C in association with the El Niño–Southern Oscillation (ENSO) event and other factors were clearly observed, which were almost opposite in phase with those of the CO2 concentration. From the comparison of the observed long‐term trend of δ13C with those calculated using a box diffusion model, it is suggested that an imbalance of the CO2 exchange between the atmosphere and the terrestrial biosphere could be responsible for such interannual variations.
High resolution Doppler imager observations of Kelvin waves in the equatorial mesosphere and lower thermosphere
Authors: Lieberman Ruth S. , Riggin Dennis
Published: February 2004

The behavior of Kelvin waves in the mesosphere and lower thermosphere is examined in three 10‐day sequences of high resolution Doppler imager mesospheric and lower thermospheric zonal winds at solstice. Eastward propagating signatures are observed in wavenumbers 1, 2, and 3 of the zonal wind field with periods near 3 and 5 days. These structures are coherent in latitude and altitude, and maximize near or on the equator. In the mesosphere, lines of constant phase move downward in time, implying that these waves are forced from below. Above 90 km the phase lines of Kelvin zonal wavenumbers 2 and 3 traverse upward in time, suggesting in situ or higherlevel sources. Estimates of the Eliassen‐Palm fluxes indicate that wavenumber 1 may significantly contribute to the eastward momentum budget of the equatorial lower thermosphere.
Evaluation and intercomparison of global atmospheric transport models using222Rn and other short‐lived tracers
Authors: Jacob Daniel J. , Prather Michael J. , Rasch Philip J. , Shia Run‐Lie , Balkanski Yves J. , Beagley Stephen R. , Bergmann Daniel J. , Blackshear W. T. , Brown Margaret , Chiba Masaru , Chipperfield Martyn P. , de Grandpré J. , Dignon Jane E. , Feichter Johann , Genthon Christophe , Grose W. L. , Kasibhatla Prasad S. , Köhler Ines , Kritz Mark A. , Law Kathy , Penner Joyce E. , Ramonet Michel , Reeves Claire E. , Rotman Douglas A. , Stockwell Deianeira Z. , Van Velthoven Peter F. J. , Verver Gé , Wild Oliver , Yang Hu , Zimmermann Peter
Published: February 2004

Simulations of222Rn and other short‐lived tracers are used to evaluate and intercompare the representations of convective and synoptic processes in 20 global atmospheric transport models. Results show that most established three‐dimensional models simulate vertical mixing in the troposphere to within the constraints offered by the observed mean222Rn concentrations and that subgrid parameterization of convection is essential for this purpose. However, none of the models captures the observed variability of222Rn concentrations in the upper troposphere, and none reproduces the high222Rn concentrations measured at 200 hPa over Hawaii. The established three‐dimensional models reproduce the frequency and magnitude of high‐222Rn episodes observed at Crozet Island in the Indian Ocean, demonstrating that they can resolve the synoptic‐scale transport of continental plumes with no significant numerical diffusion. Large differences between models are found in the rates of meridional transport in the upper troposphere (interhemispheric exchange, exchange between tropics and high latitudes). The four two‐dimensional models which participated in the intercomparison tend to underestimate the rate of vertical transport from the lower to the upper troposphere but show concentrations of222Rn in the lower troposphere that are comparable to the zonal mean values in the three‐dimensional models.
A comparison of the stratospheric aerosol background periods of 1979 and 1989–1991
Authors: Thomason L. W. , Kent G. S. , Trepte C. R. , Poole L. R.
Published: February 2004

A comparison of global stratospheric aerosol levels measured in 1979 by the Stratospheric Aerosol and Gas Experiment (SAGE) and in 1989–1991 by SAGE II is presented. These periods exhibit the lowest stratospheric aerosol levels in the era of modern measurements and are often referred to as background periods. We find that, depending on latitude, the 1‐μm aerosol optical depth in 1989–1991 was 10 to 30% higher than that observed in 1979. We demonstrate that the latter period (prior to the June 1991 eruption of Mount Pinatubo) was characterized by an ongoing global recovery from the eruptions of El Chichón in 1982 and Nevado del Ruiz in 1985, with a further complication introduced by the February 1990 Kelut eruption. Therefore the differences between 1979 and 1989–1991 cannot be completely attributed to nonvolcanic sources.