bluuebunny/crossref_metadata_2025 huggingface dataset:
A three‐dimensional chemical transport model of the stratosphere: Midlatitude results
Authors: Kamiński Jacek W. , McConnell John C. , Boville Byron A.
Published: February 2004

A prototype robust three‐dimensional global chemical transport model (CTM) has been developed in order to facilitate a realistic simulation of stratospheric chemistry and dynamics. The current application is for a 100‐day run from August 10 to November 17 using the average (ensemble) of 10 dynamical runs (realizations) of the CCMl. The CTM results are compared with observations and two‐dimensional model results. A comparison of the midlatitude model results with satellite observations, stratospheric and mesospheric sounder (SAMS) and Halogen Occultation Experiment (HALOE), showed that the model can simulate relatively well, at least on the timescale of the simulation, the distribution and formation of long‐lived species (N2O, CH4, and H20). The distribution of short‐lived species was compared with some satellite measurements, limb infrared monitor of the stratosphere (LIMS) and Stratospheric Aerosol and Gas Experiment (SAGE II), and two‐dimensional model results, and was found to be consistent.
Atmospheric sulfur over the east Mediterranean region
Authors: Luria Menachem , Peleg Mordechai , Sharf Geula , Tov‐Alper Dafna Siman , Spitz Nadine , Ben Ami Yossef , Gawii Zohir , Lifschitz Batia , Yitzchaki Amir , Seter Ilan
Published: February 2004

Particulate sulfate has been measured intermittently at various ground sites in Israel and from an instrumented aircraft for a 10‐year period between 1984 and 1993. The measurements were accompanied by concurrent monitoring of primary and secondary air pollutants and meteorological parameters. In three studies, Etzion 1984–1986, Jerusalem 1987–1988, and Jerusalem 1990–1991, measurements were taken for at least a year. The other studies were performed during summer months when higher levels of secondary pollutants, including particulate sulfate, were observed. In most of the studies samples were taken for four sequential 6‐hour time segments. In one study, at Caesarea 1993, sulfate samples were taken only when wind flows were perpendicular to the coastline. The airborne measurements were performed along three north‐south paths inside the planetary boundary layer, over the Mediterranean coast, over the Judea‐Samaria mountains and over the Jordan Valley. Each flight path consisted of 30 to 45 minutes of continuous sampling of SO2 and one integrated sample of particulate sulfate. In all of our studies the concentration of particulate sulfate observed was relatively high compared with other world locations. The highest values, occasionally exceeding 500 nmole m−3, were found during the summer. Wintertime levels were in the range of 50–100 nmole m−3. The annual average, calculated for the three long studies, is 100 ± 15 nmole m−3, which is twice as high as predicted for the region by a global model and as high as reported for some of the more polluted regions in the US. Several indicators suggested that the origin of the sulfate in the region is not from local sources but the result of long range transport. The indicators include the lack of correlation between particulate sulfate and primary pollutants, the high sulfate to total sulfur values, the origin of the airmass back trajectories and the fact that similar levels were observed during concurrent periods at different sites. Throughout the study, higher concentration of particulate sulfate was found during the afternoon hours, especially during the summer and at the inland locations. The contribution to the afternoon elevated values could not be associated with long range transport and results probably from major sulfur emission sources located along the Israeli Mediterranean coast.
Microphysical and electrical evolution of a Florida thunderstorm: 1. Observations
Authors: French Jeffrey R. , Helsdon John H. , Detwiler Andrew G. , Smith Paul L.
Published: February 2004

This study deals with the microphysical and electrical evolution of a thunderstorm that occurred on August 9, 1991, during the Convection and Precipitation/Electrification (CaPE) Experiment in eastern Florida. During its approximately 1‐hour lifetime, the storm was penetrated several times by the Institute of Atmospheric Sciences' T‐28 aircraft at midlevels. It was also penetrated at low and middle‐levels by a National Oceanographic and Atmospheric Administration (NOAA) P‐3 and scanned by three radars, one of which had multiparameter capabilities, operated by the National Center for Atmospheric Research. Two stages of the storm's evolution are analyzed herein during which the storm grew to produce precipitation and lightning. The first stage, sampled during the first T‐28 penetration at 5.25 km (−3°C) and the P‐3 at 6.4 km (−10°C), was characterized by a 2‐ to 3‐km wide updraft (maximum 14 m s−1) with cloud liquid water contents up to 4 g m−3, low concentrations of graupel at −10°C, and small to medium raindrops in concentrations of less than 200 m−3 at −3°C. A downdraft region also existed that was devoid of cloud liquid water, but contained graupel up to 2 mm. Radar data (ZDR) are consistent with a coalescence‐dominated precipitation generation mechanism followed by transport of drops in the updraft to heights with temperatures colder than −7°C, where freezing formed graupel that continued to grow by riming. Electrification during this stage remained weak. The second stage, sampled during the second and third T‐28 penetrations and the second P‐3 penetration, was characterized at midlevels by a narrower updraft and a more diffuse, broad downdraft separated by a 1‐ to 2‐km wide transition zone. The updraft continued to show significant cloud liquid water (∼2 g m−3) with few precipitation particles, while the downdraft had very little cloud liquid with graupel in concentrations >1 𝓁−1. The transition zone shared both updraft and downdraft characteristics. The increase in ice concentration was accompanied by a rapid increase in the electrification of the cloud with peak electric fields reaching −20 kV m−1 at T‐28 altitude and the detection of lightning by ground‐based sensors and pilot report. As time progressed, precipitation particle concentrations reached several per liter at midlevels in both updrafts and downdrafts. The observations are consistent with electrification through a precipitation‐based mechanism involving the development of the ice phase.
Nonlinearity and self‐similarity of rainfall in time and a stochastic model
Authors: Veneziano Daniele , Bras Rafael L. , Niemann Jeffrey D.
Published: February 2004

We use physical arguments and statistical analysis to formulate stochastic models of rainfall intensity in time during intense convective storms. Special attention is given to the issue of multiplicative versus additive model structure and to the type of self‐similarity that can be displayed by rainfall under the constraints of stationarity and nonnegativity. We show that some multiscaling models proposed in the past do not satisfy these constraints. Using a set of six high‐resolution records, we find that the best fitting models are multiplicative, with a log (rain rate) spectrum of the segmented power type, i.e., of the form |ω|−β, with β that varies in different frequency ranges. Four spectral regimes are identified between scales from a few seconds to several hours. Nowhere do we find a log (rain rate) spectrum of the |ω|−1 type or scaling of the moments, which would be consistent with a conserved multifractal model. Other moment and spectral analyses as well as theoretical arguments lead us to reject also nonconserved multiscaling representations. The stochastic model we finally propose is lognormal with a segmented log spectrum and is not scaling. Two versions of the model are considered, one stationary for the central portion of the storm and the other nonstationary to include the buildup and decay phases. Compared to existing alternatives, the model is very easy to fit to data and to simulate.
Spatial resolution of a transport inversion technique
Authors: Vasconcelos Luis A. de P. , Kahl Jonathan D. W. , Liu Desong , Macias Edward S. , White Warren H.
Published: February 2004

A spatial calibration for conditional frequency analysis, the inversion technique applied to routine back trajectories to study the association between geographical regions and conditions at a receptor, is discussed for trajectories arriving at Hopi Point, Arizona. Several 0.5° × 0.5° cells were selected at three different distances from Hopi Point. These cells were used to mimic sources, with air residing over them considered contaminated by imaginary emissions. The distribution of back trajectory segment endpoints over a latitude‐longitude grid was then examined as a function of the trajectories sojourn over each imaginary source cell on their way to the receptor. The areal extent of significant associations, evaluated for different seasons and the various ideal source positions, suggests that this inversion technique can resolve the direction of potential sources but has limited resolution for their radial distance from the receptor.
An idealized ray model of gravity wave‐tidal interactions
Authors: Eckermann Stephen D. , Marks Crispin J.
Published: February 2004

The interaction of a gravity wave with a solar tide is analyzed using ray theory in order to assess whether the temporal oscillation of the tide has any significant effects on the interaction. We consider two types of solution: a “full ray solution,” in which tidal accelerations are included in the gravity wave ray‐tracing equations, and a second “Lindzen solution,” in which they are neglected; the latter is so named because it yields similar results to the parameterization of Lindzen [1981]. Initially, we consider an idealized tide of constant velocity amplitude in a steady isothermal atmosphere, as this allows analytical solutions to be derived. A numerical ray‐tracing code is employed to determine ray solutions within more complex tidal backgrounds. Full ray solutions often differ markedly in amplitude, wavenumber, and trajectory from Lindzen solutions for the same wave, highlighting the importance of tidal accelerations. Tidal accelerations have a stabilizing influence on gravity wave amplitudes by refracting waves to larger intrinsic phase speeds, thus reducing both the occurrence and intensity of tidally modulated gravity wave breaking. Even in the absence of dissipation, time‐varying refraction gives rise to time‐oscillating gravity wave action densities, ∂A/∂t, which in turn lead to wave momentum‐flux densities which are anticorrelated with tidal winds in agreement with mesospheric observations. Although ∂A/∂t averages to zero over one cycle of a constant‐amplitude tide, its phase locking to the tide implies transient flow accelerations which temporarily amplify tidal wind oscillations and might permanently change tidal amplitudes in a nonlinear interactive model. Numerical simulations through more complex tidal backgrounds show instances where permanent ∂A/∂t values are induced in a gravity wave through its interaction with the tide. Our results point to weaknesses in a Lindzen parameterization of gravity wave‐tidal interactions. A simple extension of the parameterization is suggested which incorporates some of these time‐varying influences.
Biogenic soil emissions of nitric oxide (NO) and nitrous oxide (N2O) from savannas in South Africa: The impact of wetting and burning
Authors: Levine Joel S. , Winstead Edward L. , Parsons Dirk A. B. , Scholes Mary C. , Scholes Robert J. , Cofer Wesley R. , Cahoon Donald R. , Sebacher Daniel I.
Published: February 2004

In this paper we report on the first measurements of microbial soil emissions of nitric oxide (NO) and nitrous oxide (N2O) from the savannas in South Africa. In addition to natural, unperturbed emission measurements, we investigated the impact of natural rainfall, artificial irrigation, and fire on these emissions. Wetting and burning resulted in a significant enhancement in the emissions of NO. Mean background NO emissions from the dry sites ranged from 0.4 to 6.2 ng N m−2s−1and from the wetted sites ranged from 4.7 to 34.0 ng N m−2s−1. After burning, the mean NO emissions from the dry sites increased and ranged from 13.3 to 15.2 ng N m−2s−1and from the wetted sites increased, exceeding 60 ng N m−2s−1. Measurements of biogenic emissions of N2O were attempted, but emissions were not detected throughout the measurement period, indicating emissions below the minimum delectability of the instrumentation (2 ng N m−2s−1).
Improved analysis of atmospheric absorption spectra by including the temperature dependence of NO2
Authors: Sanders R. W.
Published: February 2004

Absorption spectra of NO2 measured at several temperatures between room temperature and 197 K are used to improve the analysis of zenith view, atmospheric absorption data in the 405–430 nm spectral range. The size of persistent features in the residual spectrum of the analysis is reduced by up to 50%, which in principle facilitates measurement of weakly absorbing species, such as OClO and IO. Details of the reduction algorithm are discussed.
Peroxy radicals from photostationary state deviations and steady state calculations during the Tropospheric OH Photochemistry Experiment at Idaho Hill, Colorado, 1993
Authors: Cantrell Christopher A. , Shetter Richard E. , Calvert Jack G. , Eisele Fred L. , Williams Eric , Baumann Karsten , Brune William H. , Stevens Phillip S. , Mather James H.
Published: February 2004

Concentrations of peroxy radicals and a number of other trace gases were measured during the Tropospheric OH Photochemistry Experiment in August and September, 1993. The trace gas concentrations were used to derive two estimates of peroxy radical levels: deviations from the photostationary state, and theoretical calculations with the assumption of steady state radical concentrations. As in many previous studies, the photostationary state method yielded midday peroxy radical levels about twice those measured. Calculations were performed to assess the expected uncertainty in the photostationary state derived peroxy radical concentrations from the uncertainty of the input parameters. The agreement between measurements and steady state determinations was better than the photostationary state estimates, with the measurements slightly higher on average. Radical formation and destruction rates for clear sky conditions with low and high NOx were derived from the steady state calculations and the results demonstrate the processes that control peroxy radical levels in clean and polluted continental atmospheres.
Kinetic data imprecisions in photochemical rate calculations: Means, medians, and temperature dependence
Authors: Stewart Richard W. , Thompson Anne M.
Published: February 2004

The uncertainty in computed species concentrations resulting from measurement imprecision in reaction rate components is investigated in two tropospheric photochemical models. In this study, which extends Thompson and Stewart [1991], we perform statistical analysis on reaction rate coefficients to focus on two aspects of model uncertainty: (1) the change in the magnitude of concentration uncertainty as temperature varies throughout a model grid and (2) the difference resulting from selection of mean, as opposed to median, rates for model calculations. Reaction rates are treated as realizations of random variables having statistical properties given by component terms and their imprecisions. These assumptions lead to expressions for probability distributions of bimolecular rates and for the high‐ and low‐pressure limits for termolecular and thermolytic processes. They also imply that bimolecular rates and high‐ and low‐pressure limits used in photochemical models correspond to median values taken from a lognormal distribution. We derive analytic expressions for mean values, which are always larger than the medians, an intrinsic property of lognormal variables. We suggest that comparison of species concentrations computed using median and mean rates can provide some measure of the effect of rate imprecision in multidimensional models. We also find that the temperature dependence derived for the imprecision in bimolecular rates differs from that given in standard references, with our expression giving a smaller increase in imprecision as temperatures deviate from 298 K. Results are illustrated using a box and a one‐dimensional (1‐D) model.
Hydrogen peroxide, organic hydroperoxide, and formaldehyde as primary pollutants from biomass burning
Authors: Lee Meehye , Heikes Brian G. , Jacob Daniel J. , Sachse Glen , Anderson Bruce
Published: February 2004

Hydrogen peroxide, organic hydroperoxide species, and formaldehyde were found to be enhanced within biomass burning plumes during the Transport and Atmospheric Chemistry near the Equator ‐ Atlantic (TRACE A) experiment. This enhancement could have resulted from direct emission by the fires or by secondary photochemical production. In this study, direct production of hydroperoxide and formaldehyde from biomass burning is proposed and examined through comparisons of hydroperoxide and formaldehyde measurements, obtained from three fire flights in TRACE A, with model estimates, with other measurement data, and with results from fire experiments at the University of Rhode Island (URI). For highest concentrations of hydroperoxide and formaldehyde, model predictions fall short of those observed, and an additional source is required. H2O2and CH3OOH were noted to increase with CO and were significantly correlated with other measured species known to be produced from biomass burning. The enhancements of H2O2and CH3OOH relative to CO were different between flights in which the relative enhancements of CO to CO2were also different. The enhancement ratio of H2O2and CH3OOH relative to CO was 1–5×10−2and 2–4×10−3, respectively. CH2O was correlated with CO. The enhancement ratios of CH2O were determined in relation to both CO and CO2for three flights and were 7–19×10−3and 3–5×10−4, respectively. The correlations of CH2O with other measured combustion species were more significant than those of H2O2and CH3OOH. To determine whether hydroperoxide and formaldehyde can be directly produced from biomass burning, simple biomass fire experiments were performed at URI. These species were observed to be clearly elevated in test biomass fires. These experiments present unequivocal evidence for the direct production of hydrogen peroxide and formaldehyde from biomass burning. The results from both TRACE A and our fire experiments also fit possible mechanisms of direct formation of hydroperoxide and formaldehyde in combustion processes. The atmospheric implication of the direct production of these species from biomass burning is their contribution to odd‐hydrogen radical production, thereby affecting the oxidizing capacity of the atmosphere before O3would be photochemically developed. In TRACE A, odd‐hydrogen radical production from the direct source of these species is estimated to be near 30% of the total radical production.
Photosynthates as dominant source of CH4 and CO2 in soil water and CH4 emitted to the atmosphere from paddy fields
Authors: Minoda Tomomi , Kimura Mamoto , Wada Eitaro
Published: February 2004

Emission rates of CH4 from paddy soil with and without rice straw applications were measured with pot experiments to estimate the contribution of rice straw to the total CH4 emission during the growth period of rice plants. The CH4 derived from rice straw was calculated to be 44% of the total emission. 13CO2 uptake experiments were also carried out four times from June 30 to September 13, 1994, to estimate the contribution of photosynthesized carbon to CH4 emission. The contribution percentages of photosynthesized carbon to the total CH4 emitted to the atmosphere were 3.8% around June 30, 31% around July 25, 30% around August 19, and 14% around September 13 in the treatment with rice straw applications, and 52% around July 25, 28% around August 19, and 15% around September 13 in the treatment without rice straw applications. They were calculated to be 22% and 29% for the entire growth period in the treatments with and without rice straw applications, respectively. The contribution percentages of photosynthesized carbon to the total CH4 and inorganic carbon (Σ CO2) dissolved in soil water were 1.3%, 30%, 29%, and 34% for dissolved CH4 and 3.0%, 36%, 30% and 28% for dissolved inorganic carbon around June 30, July 25, August l9, and September 13, respectively, in the treatment with rice straw applications. They were 70%, 23%, and 32% for dissolved CH4 and 31%, 16%, and 19% for dissolved inorganic carbon around July 25, August 19, and September 13, respectively, in the treatment without rice straw applications.
Characteristics of atmospheric waves in the tidal period range derived from zenith observations of O2(0–1) Atmospheric and OH(6‐2) airglow at lower midlatitudes
Authors: Reisin Esteban R. , Scheer Jürgen
Published: February 2004

From about 100 nights of ground‐based measurements of fluctuations in airglow brightness and rotational temperature, taken from two sites at 32°S and 37°N, a considerable number of new determinations of complex values of Krassovsky's η are derived, and compared with observations by other investigators and model predictions. Our findings support the model of Hines, Tarasick, and Shepherd (HTS), which leads to practical consequences regarding the usefulness of airglow observations for deriving vertical propagation of atmospheric waves in the mesopause region. It is shown, at least in part, that the vertical wave propagation can be inferred from zenith observations of one airglow emission, alone, and that consistent information can be obtained simultaneously for the two airglow layers. The analysis presented comprises the range of observed periods between 3 and 24 hours. The salient feature is that η values are essentially limited to the fourth quadrant, for both the O2 and OH emissions, which means, according to the HTS model, that the majority of the waves observed propagate upward, with vertical wavelengths between 20 and 60 km, and only a few are possibly evanescent. This would not contradict the interpretation that most if not all of the wave signatures may be due to the semidiurnal tide, or tidal transients.
Glacial‐interglacial variability of atmospheric CO2 due to changing continental silicate rock weathering: A model study
Authors: Munhoven Guy , François Louis M.
Published: February 2004

An 11‐box model of the oceanic carbon cycle including sedimentary processes is used to explore the role chemical weathering of continental silicate rocks might play in driving atmospheric CO2 levels on glacial‐interglacial timescales. Histories for the consumption of CO2 by silicate rock weathering processes are derived from the marine Ge/Si record. Taking the major uncertainties in the knowledge of the Ge and Si cycles into account, several histories for the evolution of the riverine dissolved silica fluxes are calculated from this record. The investigation of the systematics between riverine dissolved silica and bicarbonate fluxes under different weathering regimes leads us to the tentative conclusion that although there is no correlation between dissolved silica and total bicarbonate concentrations in the major rivers, there may exist a negative correlation between weathering intensity and the ratio of dissolved silica to bicarbonate derived from silicate weathering alone. With this correlation as a working hypothesis, it is possible to interpret the dissolved silica fluxes in terms of equivalent CO2 consumption rates. The calculated histories indicate that glacial rates of CO2 consumption by chemical silicate rock weathering could have been twice, and possibly up to 3.5 times, as high as they are today. When used to force the carbon cycle model, they are responsible for glacial‐interglacial pCO2 variations in the atmosphere of typically 50–60 ppm and up to 95–110 ppm. These variations are superimposed to a basic oscillation of 60 ppm generated by the model, mainly in response to coral reef buildup and erosion processes. The total pCO2 signal has an amplitude of about 80–90 ppm and up to 125–135 ppm. Although these large amplitudes indicate that silicate weathering processes should be taken into account when studying glacial‐interglacial changes of CO2 in the atmosphere, it also raises new problems, such as too high CO2 levels during the period from 110–70 kyr B.P., requiring further study.
Nonmethane hydrocarbon measurements during the Tropospheric OH Photochemistry Experiment
Authors: Goldan Paul D. , Kuster William C. , Fehsenfeld Fred C.
Published: February 2004

In the rural troposphere, the nonmethane hydrocarbon compounds (NMHCs) play a significant role in establishing the absolute, as well as, the relative concentration of the odd‐hydrogen radicals. In order to provide data which could be used to estimate OH reactive loss rates with hydrocarbons directly, and to broaden our understanding of the production of biogenic NMHCs in and the transport of anthropogenic NMHCs into the Colorado mountains, in situ hydrocarbon measurements were made during the Tropospheric OH Photochemistry Experiment in the fall of 1993. NMHC measurements were made using an automated gas chromatographic system that was capable of quantifying alkanes C3 (propane) through C10 (decane), alkenes C4 (butene) through C10 (decene), light alcohols from C1 (methanol) through C5 (pentanol), light ketones from C3 (acetone) through C5 (pentanone), aromatics from C6 (benzene) through C9 (trimethylbenzenes), C10 monoterpenes, and acetaldehyde. During periods of influx of urban air masses, the NMHCs appeared to be the dominant sink for OH radicals.
Comparisons between instantaneous wind measurements made at Saskatoon (52N, 107W) using the colocated medium frequency radars and Fabry‐Perot interferometer instruments: Climatologies (1988–1992) and case studies
Authors: Manson Alan , Yi Fan , Hall Greg , Meek Chris
Published: February 2004

Winds and waves measured by the Medium Frequency Radars (MFR) at Saskatoon (52N, 107W), Robsart (49N, 109W), and Sylvan Lake (52N, 114W), and the Fabry‐Perot Interferometer (FPI) at Saskatoon are compared. Particular care has been taken to exclude FPI airglow (558 nm, green line) contamination by aurora or scatter from clouds; radar data were selected from high signal‐to‐noise conditions. Comparisons between the MFR/FPI in seasonal wind climatologies (at a radar height of 98 km) and wind speed ratios and direction‐difference histograms for the Saskatoon systems show excellent agreement. Zonal and meridional wind comparisons (scatter plots) also show no significant differences in mean winds between the FPI and MFR. Differences between instantaneous measurements, as seen on 91 individual days, are categorized into four types of events, depending upon FPI/MFR similarities and differences and the dominance of the solar tide. A gravity wave model is then used to demonstrate the effects of waves, with scales from hundreds to several thousand of kilometers, upon such optical and radar systems, each of which has a different inherent spatial averaging. The model is largely successful in explaining the differences between the instantaneous MFR and FPI measurements. The relevance of such comparisons to satellite/ground‐based collaborations is briefly discussed.
Relationship between rain composition in Spain and its sources
Authors: Hernández Emiliano , Gimeno Luis , Sánchez Modesto , Rua Antonio , Méndez Rafael
Published: February 2004

Factor analysis is used to evaluate relationships among inorganic ions to provide a qualitative determination of the kind of ion sources Spanish wet deposition. This procedure identifies four factors: sea, soil, aerosol, and industrial. The factor that reproduces a larger fraction of the variance is the soil or soil/aerosol and the factor reproducing a lower fraction of the variance is the industrial. The conditional probability function (CPF) [Ashbaugh et al., 1985] is used to identify possible sources for each ion, in geographical terms. The Mediterranean region is the most important source of inorganic ions and the British Isles the single source, although intermediate, of acid rain.
Nocturnal vertical distribution of stratospheric O3, NO2 and NO3 from balloon measurements
Authors: Renard Jean‐Baptiste , Pirre Michel , Robert Claude , Moreau Guy , Huguenin Daniel , Russell James M.
Published: February 2004

Simultaneous measurements of NO2, O3, NO3, and aerosol extinction coefficient vertical distribution have been made in the middle of the night by the AMON (Absorption par Minoritaires Ozone et Nox) instrument on October 16, 1993, from a balloon platform at float altitude, above Aire sur l'Adour in the south of France. Amon measures atmospheric transmission in the UV Visible range, using the star occultation method. Vertical distributions, obtained between 20 and 40 km, are calculated by a tangent ray inversion technique. Measurements of NO and NO2 by the HALOE (HALogen Occultation Experiment) instrument aboard UARS were also available on October 17, 1993, close to Aire sur l'Adour. Comparison with box model simulations, including heterogeneous reactions, shows that while an increase of NO3 concentration at 38 km could be explained by an occasionally steep vertical gradient of temperature concentrations, another increase of both NO2 and NO3 measured by AMON between 22 to 25 km, i.e. in the upper part of the aerosol layer, cannot be explained by the model. Such an increase is also present on one HALOE profile close to Aire sur l'Adour, for the same altitude range.
Water table control of CH4 emission enhancement by vascular plants in boreal peatlands
Authors: Waddington J. M. , Roulet N. T. , Swanson R. V.
Published: February 2004

Removal of the vascular vegetation (Eriophorum vaginatum) at two sites in a Swedish boreal peatland decreased the seasonal CH4 flux by 55 to 85%, while the daily CH4 flux at a Canadian boreal peatland with Carex rostrata removed decreased by over 30%. Dissolved CH4 pore water concentrations in the rooting zone were 1.2 to 2.5 times greater than the storage at similar sites where vegetation was removed by clipping, suggesting that the removal of vascular vegetation decreased CH4 production. Moreover, nighttime CH4 flux enhancement was coincident with the diurnal peak in dissolved CH4 pore water concentration. A positive correlation between mean daily net ecosystem production and mean daily CH4 flux (r2 = 0.655, n = 8) at lawn sites with sedge vegetation suggests that sites with greater CO2 fixation had a higher CH4 flux, likely through enhanced methanogenesis and transport. The degree of vascular vegetation CH4 flux enhancement, however, changed throughout the growing season and was correlated to the position of the water table. Under low water table conditions the presence of vascular plant cover has a lesser effect in enhancing CH4 emissions, indicating that CH4 and net ecosystem exchange coupling is limited to vascular plants and only to sites that remain wet with the water table near the surface.
Regional climate model of the Arctic atmosphere
Authors: Dethloff Klaus , Rinke Annette , Lehmann Ralph , Christensen Jens H. , Botzet Michael , Machenhauer Bennert
Published: February 2004

A regional climate model of the whole Arctic using the dynamical package of the High‐Resolution Limited Area Model (HIRLAM) and the physical parameterizations of the Hamburg General Circulation Model (ECHAM3) has been applied to simulate the climate of the Arctic north of 65°N at a 50‐km horizontal resolution. The model has been forced by the European Centre for Medium‐Range Weather Forecasts (ECMWF) analyses at the lateral boundaries and with climatological or actual observed sea surface temperatures and sea ice cover at the lower boundary. The results of simulating the Arctic climate of the troposphere and lower stratosphere for January 1991 and July 1990 have been described. In both months the model rather closely reproduces the observed monthly mean circulation. While the general spatial patterns of surface air temperature, mean sea level pressure, and geopotential are consistent with the ECMWF analyses, the model shows biases when the results are examined in detail. The largest biases appear during winter in the planetary boundary layer and at the surface. The underestimated vertical heat and humidity transport in the model indicates the necessity of improvements in the parameterizations of vertical transfer due to boundary layer processes. The tropospheric differences between model simulations and analyses decrease with increasing height. The temperature bias in the planetary boundary layer can be reduced by increasing the model sea ice thickness. The use of actual observed sea surface temperatures and sea ice cover leads only to small improvements of the model bias in comparison with climatological sea surface temperatures and sea ice cover. The validation of model computed geopotential, radiative fluxes, surface sensible and latent heat fluxes and clouds against selected station data shows deviations between model simulations and observations due to shortcomings of the model. This first validation indicates that improvements in the physical parameterization packages of radiation and in the description of sea ice thickness and sea ice fraction are necessary to reduce the model bias.
Effective area of a horizontal long‐wire antenna collecting the atmospheric electric vertical current
Authors: Tammet H. , Israelsson S. , Knudsen E. , Tuomi T. J.
Published: February 2004

The effective area of an antenna collecting the vertical air‐Earth current is a coefficient of proportionality between the collected current and the air‐Earth current density. The effective area can be correctly defined only if the model behind the proportionality relation is adequate. The current collected by a horizontal long‐wire antenna is not exactly proportional to the vertical air‐Earth Maxwell current density because of the different behavior of the displacement and conduction components of the current. Thus, two different effective areas are separately defined for the displacement and nondisplacement components. First, the dynamic effective area characterizes rapid variations of the displacement current. It is calculated assuming that the air does not contain any space charges and that the electric current flow lines match the electric field lines. Second, the static effective area characterizes the nondisplacement current, and it is calculated by taking into account the facts that the conductivity close to the wire surface is unipolar, that the wind‐determined horizontal ion trajectories do not match the electric field lines, and that there are space charges due to the electrode effect of the wire and of the ground. Traditionally, the atmospheric electric vertical current density measurements have been interpreted by using the dynamic effective area as a calibration coefficient. This turns out to be a satisfactory approximation in the case of strong turbulence when the near‐ground space charge layer is high and the static effective area approaches the dynamic effective area. In the limit of low turbulence the traditional interpretation results in errors of several tens percent. A reduced height of the antenna helps to keep the static effective area close to the dynamic effective area and to suppress the errors.
Three‐dimensional study of the relative contributions of the different nitrogen sources in the troposphere
Authors: Lamarque J.‐F. , Brasseur G. P. , Hess P. G. , Müller J.‐F.
Published: February 2004

A three‐dimensional study of the relative importance of the different odd nitrogen sources in the troposphere is discussed. In order to consistently simulate the chemistry, all the sources are considered simultaneously but each nitrogen emitted is characterized by a given flavor. This allows us to follow the evolution of nitrogen from each source without affecting the overall chemical system of the atmosphere. The model results suggest that the NOx concentration in the southern hemisphere is mostly dominated by the lightning source, while the northern hemisphere odd nitrogen burden results mainly from the influence of fossil fuel combustion, aircraft, and lightning emissions. In particular, in the upper tropospheric northern hemisphere midlatitudes, approximately 25–30% of the NOx is due to aircraft, 15–20% to fossil fuel combustion sources at the surface, and 15–20% to lightning, assuming that the global fleet of aircraft releases 0.44 TgN/yr and that lightning produces 5 TgN/yr. The sensitivity of these figures to several parameters (aircraft and soil source strengths, as well as the lightning source strength and its vertical distribution) is also studied.
First estimates of the radiative forcing of aerosols generated from biomass burning using satellite data
Authors: Christopher Sundar A. , Kliche Donna V. , Chou Joyce , Welch Ronald M.
Published: February 2004

Collocated measurements from the Advanced Very High Resolution Radiometer (AVHRR) and the Earth Radiation Budget Experiment (ERBE) scanner are used to examine the radiative forcing of atmospheric aerosols generated from biomass burning for 13 images in South America. Using the AVHRR, Local Area Coverage (LAC) data, a new technique based on a combination of spectral and textural measures is developed for detecting these aerosols. Then, the instantaneous shortwave, longwave, and net radiative forcing values are computed from the ERBE instantaneous scanner data. Results for the selected samples from 13 images show that the mean instantaneous net radiative forcing for areas with heavy aerosol loading is about −36 W/m2 and that for the optically thin aerosols are about −16 W/m2. These results, although preliminary, provide the first estimates of radiative forcing of atmospheric aerosols from biomass burning using satellite data.
Comparisons of humidity observations and Eta model analyses and forecasts for water balance studies
Authors: Yarosh E. S. , Ropelewski C. F. , Mitchell K. E.
Published: February 2004

Direct comparison was performed between observed radiosonde humidity and vapor transport profiles and the National Centers for Environmental Prediction (NCEP) (formerly the National Meteorological Center) mesoscale Eta model analyses and forecasts. The data for this comparison were gathered during the Global Energy and Water Cycle Experiment's Continental‐Scale International Project Integrated Systems Test (GIST) for the period July 15 to August 31, 1994, which fell within the preoperational evaluation phase of the new NCEP mesoscale Eta model and associated data assimilation system. These intercomparisons show good agreement between Eta model analyses and observations in humidity and the zonal and meridional components of the humidity transport. Typical root‐mean‐square (RMS) errors relative to observed standard deviations were of the order of 0.4–0.5 at all levels between the surface and 300 hPa. The relative RMS humidity errors associated with the forecasts ranged between 0.9 and 1.4 in the lowest 300 hPa for all forecast times examined (3 to 36 hours). The RMS humidity transport errors for the forecasts tend to be somewhat less. During the GIST period, this study found the Eta model performance for water balance studies to be somewhat degraded over mountainous terrain. On the basis of this GIST finding and other corroborating evidence, NCEP corrected an error in the Eta model data assimilation system. The Eta‐model‐derived, vertically integrated moisture flux divergence compares favorably with similar estimates based on radiosonde observations alone. In these comparisons, the Eta model estimates of evaporation minus precipitation agree with the radiosonde estimates within 10% of the mean precipitation over the Mississippi River Basin. The agreement is less (around 50% of the mean precipitation) for a smaller basin. The analysis suggests that the Eta model forecasts may be useful over larger basins for various water budget study issues, such as diurnal variability and impacts of observation sampling density.
Nonstationary gravity wave forcing of the stratospheric zonal mean wind
Authors: Alexander M. J. , Rosenlof K. H.
Published: February 2004

The role of gravity wave forcing in the zonal mean circulation of the stratosphere is discussed. Starting from some very simple assumptions about the momentum flux spectrum of nonstationary (non‐zero phase speed) waves at forcing levels in the troposphere, a linear model is used to calculate wave propagation through climatological zonal mean winds at solstice seasons. As the wave amplitudes exceed their stable limits, a saturation criterion is imposed to account for nonlinear wave breakdown effects, and the resulting vertical gradient in the wave momentum flux is then used to estimate the mean flow forcing per unit mass. Evidence from global, assimilated data sets are used to constrain these forcing estimates. The results suggest the gravity‐wave‐driven force is accelerative (has the same sign as the mean wind) throughout most of the stratosphere above 20 km. The sense of the gravity wave forcing in the stratosphere is thus opposite to that in the mesosphere, where gravity wave drag is widely believed to play a principal role in decelerating the mesospheric jets. The forcing estimates are further compared to existing gravity wave parameterizations for the same climatological zonal mean conditions. Substantial disagreement is evident in the stratosphere, and we discuss the reasons for the disagreement. The results suggest limits on typical gravity wave amplitudes near source levels in the troposphere at solstice seasons. The gravity wave forcing in the stratosphere appears to have a substantial effect on lower stratospheric temperatures during southern hemisphere summer and thus may be relevant to climate.
Photodissociation parameterization for stratospheric photochemical modeling
Authors: Zhao Xuepeng , Turco Richard P.
Published: February 2004

A new technique is described for calculating molecular photodissociation rates using a novel empirical formulation. This technique is shown to be applicable for stratospheric photochemical modeling and atmospheric photochemical systems in general. The two basic independent variables that control photodissociation rates in the atmosphere are the column abundances of ozone and molecular oxygen; these are the main absorbers that control solar ultraviolet radiation in the atmosphere. Hence they are the key variables used to parameterize photodissociation processes. In this approach, the spectral integrals normally associated with photodissociation rate calculations are eliminated by substituting for the integrals empirical functions that depend only on the column abundances of O2 and O3. The particular empirical functions adopted here related to the curve of growth for the transmission of radiation through absorbing media, particularly through spectrally highly structured absorbers. The simple expressions that we derived can be applied to calculate photodissociation rates at most solar zenith angles for a wide variety of molecular species, including O2, O3, NO2, HO2, H2O, H2O2, N2O5, HNO3, N2O, HNO2, CO2, CH2O, SO2, OCS, HCl, CF2Cl2, CFCl3, CCl4, CH3Cl, ClO, ClO2, OClO, ClONO2, HOCl, CH3Br, BrNO3, and CH4O2. The accuracy and applicability of the empirical formulas, corrections for radiation scattering effects, variations in the solar ultraviolet spectrum, and temperature variations, are discussed.
The water‐soluble fraction of atmospheric aerosol particles and its influence on cloud microphysics
Authors: Eichel Cornelia , Krämer Martina , Schütz Lothar , Wurzler Sabine
Published: February 2004

The water‐soluble fraction of atmospheric aerosol particles is a major property dividing the particle population into cloud condensation nuclei and interstitial particles during cloud formation. Likewise, this property influences cloud microphysics and chemistry as well as direct and indirect aerosol forcing of climate. Up to now this important parameter has been only poorly determined experimentally. Here, we present SoFA, a new method to determine the water‐Soluble Fraction of large and giant Aerosol particles in five narrow size bands with geometrical radii of 0.4, 0.6, 0.9, 1.3, 1.8 μm and one band for particles with radius larger than 2.3 μm. First results show three different types of aerosol particles (AP I, II, III). AP I were characterized by 9% water‐soluble material, and AP II by 50% and correspond to those found in earlier studies for small particles. The new AP III consists of 88% water‐soluble material. In those size bands, where all three particle types could be detected (0.9, 1.3, and 1.8 μm because of detection limits of SoFA, only two types of particles could be detected in the remaining size bands), about 50% of the total number of analyzed particles belong to AP III, whereas about 25% belong to both APII and I. These numbers lead to 59% water‐soluble material on average. Particles of AP III are assumed to be cloud‐processed particles, those of AP I might be of biological origin. The impact of the water‐soluble fraction of particles on cloud microphysics is investigated by comparing two cloud situations using an entraining air parcel model with detailed microphysics. The model simulations show an influence on nucleation scavenging, cloud interstitial aerosol, and in particular, drop size population. Most notable is that the same aerosol particle number distribution causes either a precipitating or a non precipitating cloud, depending only upon different water‐soluble fractions of the particles.
First International Satellite Land Surface Climatology Field Experiment 1987 sonde budget revisited
Authors: Betts Alan K. , Barr Alan G.
Published: February 2004

We recompute estimates of boundary layer top entrainment from the 1987 FIFE sonde data, using a better averaging method, and get a mean value for the entrainment parameter AR of 0.39 ± 0.19, about 10% smaller than before. We also show the dependence of AR on wind speed and time of day. The increase in entrainment with wind speed is quite marked. Our mean asymptotic value of AR, representative of free convection at low wind speeds, is now only 0.31.
Spatiotemporal predictions of polar mesospheric summer echoes
Authors: Hall C. M.
Published: February 2004

Radar operating in the VHF band, at least, are capable of detecting unusually strong echoes from the mesopause region during summer. These polar mesospheric summer echoes (PMSE) have been reported mostly from radar situated in arctic regions, but midlatitude observations are not uncommon. First, the origins of PMSE are reviewed to give a background for what follows. The widely held assumption is that the presence of such echoes is related to the low temperatures found only at and around the summer mesopause, and given this assumption, we identify the times, from scales of 1 year to 1 hour, and geographic locations at which PMSE are expected to be observable. Other timescales, climatic to turbulent, are discussed qualitatively, and the whole study is presented as a planning tool for observations of the mesosphere which might have to take PMSE into account.