bluuebunny/crossref_metadata_2025 huggingface dataset:
High‐pressure flow study of the reactions OH + NOx→ HONOx: Errors in the falloff region
Authors: Donahue Neil M. , Dubey Manvendra K. , Mohrschladt Ralf , Demerjian Kenneth L. , Anderson James G.
Published: February 2004

We present data for the rate constant of the reaction NO2+ OH → HONO2in nitrogen from 2 to 600 torr at 300 K. This is the first application of our high‐pressure flow technique to a pressure‐dependent reaction. The pressure range in this experiment overlaps the ranges covered by traditional discharge flow studies and flash photolysis studies, allowing exploration of the transition between the low‐pressure and intermediate pressure regimes. The measured rate constants are in excellent agreement with previously published values; however, current recommendations systematically overestimate the room temperature rate constant by between 10 and 30% in the pressure range 20‐700 torr. A reanalysis of all available data yields a new recommendation in good agreement with most of the data over the entire observational pressure range. This analysis includes an explicit treatment of the collisional efficiencies of different bath gases and includes the extreme broadening of the pressure falloff curve caused by the very strong HO‐NO2bond. We also report room temperature results for the reaction NO + OH over a more limited pressure range (4 to 75 torr). Our data agree with the currently recommended rate constants over this range.
Vapor pressures in the ternary system water‐nitric acid‐sulfuric acid at low temperature: A reexamination
Authors: Taleb Djamel‐Eddine , Ponche Jean‐Luc , Mirabel Philippe
Published: February 2004

The equilibrium partial vapor pressures over the binary solutions H2O/HNO3, H2SO4/H2O, HNO3/H2SO4 and the ternary mixture H2SO4/HNO3/H2O have been re‐determined for temperatures below 25°C. The model presented here is valid over the entire range of concentrations, for temperatures in the range 190–298 K. The predictions of this model are compared with the existing measurements and other predictions, both at room temperature and at low temperatures down to about 190 K. The calculated partial pressures agree very well with the available experimental data
On the initiation of lightning discharge in a cloud: 2. The lightning initiation on precipitation particles
Authors: Nguyen Manh Duc , Michnowski Stanislaw
Published: February 2004

Assuming that transient values of an electric field and of a concentration of particles can be much higher in small local regions of a cloud than the maximum values measured within the thundercloud, the authors attempt to explain the lightning initiation mechanism. The discharges on neighbouring particles are considered in relation to the intensity of the ambient field and the distance between particles. It is shown that the electric field threshold for the appearance of breakdown discharge between close particles has lower values at certain distances between the particles than in the case of distant, well‐separated particles. The first breakdown discharge between two close, slightly conducting particles enhances the electric field in the nearest space outside the discharged particles along the direction of the ambient field, so the breakdown discharge to another nearest particle in this direction is privileged. The breakdown process in a densely populated area may proceed in chain with the increasing field at the tip of the progressing discharge. Such initiating mechanism might be expected in a limited volume with reduced electric field E/p=30 V cm−1 Tr−1 and with the concentration of about 15–500 l−1 of particles from about 0.1 to few millimeters in diameter. The suggested reasoning seems to be in a fairly good agreement with the recent observations of in‐cloud discharges, the structure of the cloud related to the initiation, and development of lightning flashes, and other features.
A global three‐dimensional time‐dependent lightning source of tropospheric NOx
Authors: Levy H. , Moxim W. J. , Kasibhatla P. S.
Published: February 2004

The spatial and temporal distribution for a global three‐dimensional, time‐dependent lightning source of NOxis constructed from a general circulation model's (GCM) deep moist convection statistics [Manabe et al., 1974;Manabe and Holloway, 1975], observations of cloud‐to‐cloud and intracloud lightning fractions and the vertical distribution of lightning discharge [Proctor, 1991], and empirical/theoretical estimates of relative lightning frequency resulting from deep moist convection over ocean and over land [Price and Rind, 1992]. We then bracket the annual global emission of NOxfrom lightning between 2 and 6 Tg N/yr, with a most probable range of 3 to 5 Tg N/yr, by comparing tropospheric NOxsimulations from the Geophysical Fluid Dynamics Laboratory Global Chemical Transport Model with measurements of NOxand/or NOyin the mid and upper troposphere where lightning is a major, if not the dominant, source. With this approach, the global magnitude of the lightning source is constrained by observed levels of NOx, while the temporal and spatial distributions of the source are under the control of the parent GCM. Although our lightning source is smaller than many previous estimates, it is still the major source of NOxand NOyin the mid and upper troposphere for a latitude belt running from 30°N to 30°S, an important contributor to summertime free tropospheric levels over the midlatitudes, and a major contributor, even in the lower troposphere, to the low NOxand NOylevels over the remote oceans.
An intercomparison of spectroscopic laser long‐path and ion‐assisted in situ measurements of hydroxyl concentrations during the Tropospheric OH Photochemistry Experiment, fall 1993
Authors: Mount George H. , Eisele Fred L. , Tanner David J. , Brault James W. , Johnston Paul V. , Harder Jerald W. , Williams Eric J. , Fried Alan , Shetter Richard
Published: February 2004

Hydroxyl plays a central role in the chemistry of the troposphere. Since the importance of OH was first recognized in the early 1970s, many experiments have attempted to measure OH, but very few have been successful, and much controversy has surrounded the measurements made [Crosley, this issue]. Thus, intercomparison of OH measurements is a requirement for community acceptance of derived OH concentrations, and accurate measurements of OH are essential to provide robust modeling of tropospheric chemistry since models typically allow OH concentrations to be determined within the model for lack of measurements. The Tropospheric OH Photochemistry Experiment held in the Colorado Rocky Mountains in fall 1993 brought together four instruments that to measure OH. In order to make a proper comparison, a number of other trace species and relevant jvalues were measured simultaneously with hydroxyl to provide a photochemical understanding of the measurements and an understanding of the airflow in the mountainous region in which this work was conducted. This region provided opportunities to measure both clean and polluted air over a wide dynamic range of species that affect the OH concentration. The measurements extended over a long enough period of time that a large quantity of data were collected under a variety of atmospheric conditions, thus allowing for a meaningful comparison of techniques. The long‐path spectroscopic laser system and the in situ selected ion chemical ionization mass spectrometry system determined OH concentrations for 4 weeks simultaneously. Generally, the derived concentrations from the two instruments agreed within the 2σ error bars over half the observation time. One quarter of the time, OH differences could be explained by different air masses between the long path and in situ site which contained different concentrations of trace species that affect OH abundance. Approximately one quarter of the data disagreed outside the observational errors with no obvious explanation. The long‐path experiment typically gave concentrations about 20% higher than the ion‐assisted experiment. This could be caused by inaccuracies in the absolute calibrations of the two instruments, or by trace species variations along the long path that differed from those at the in situ site. Generally, agreement between ion‐assisted and long‐path OH measurements was good, showing that measurements of hydroxyl in the troposphere can be performed with good accuracy on a routine basis.
Air‐water gas exchange of hexachlorocyclohexanes (HCHs) and the enantiomers of α‐HCH in Arctic regions
Authors: Jantunen Liisa M. , Bidleman Terry
Published: February 2004

In the summers of 1993 and 1994, air and water samples were taken in the Bering and Chukchi Seas and on a transect across the polar cap to the Greenland Sea to measure the air‐sea gas exchange of hexachlorocyclohexanes (HCHs) and the enantiomers of α‐HCH. Atmospheric concentrations of α‐ and γ‐HCH have decreased threefold or more since the mid‐1980s, whereas concentrations in surface water have shown little change. The saturation state of surface water (water/air fugacity ratio) was determined from the air and water concentrations of HCHs and their Henry's law constants as a function of temperature. Fugacity ratios >1.0 indicated net volatilization of α‐HCH in all regions except the Greenland Sea, where concentrations in air and water were close to equilibrium. Net deposition of γ‐HCH in the Chukchi Sea was indicated by fugacity ratios <1.0. In other regions, γ‐HCH was volatilizing or near air‐water equilibrium. Enantioselective degradation of (−)α‐HCH was found in surface water of the Bering and Chukchi Seas. The ER was reversed in the Canada Basin and Greenland Sea, where (+)α‐HCH was preferentially lost. The same order of enantioselective degradation was seen in air within the marine boundary layer of these regions, which provides direct evidence for sea‐to‐air transfer of α‐HCH.
Second European Stratospheric Arctic and Midlatitude Experiment campaign: Correlative measurements of aerosol in the northern polar atmosphere
Authors: Brogniez C. , Lenoble J. , Ramananahérisoa R. , Fricke K. H. , Shettle E. P. , Hoppel K. W. , Bevilacqua R. M. , Hornstein J. S. , Lumpe J. , Fromm M. D. , Krigman S. S.
Published: February 2004

The stratospheric aerosol layer in the Arctic winter was studied by three independent, height‐resolving, optical techniques close in space and time on February 2, 1994, above northern Scandinavia. The balloon‐borne Radiométre Ballon (RADIBAL) experiment measured altitude profiles of the radiance and polarization of scattered sunlight at two wavelengths: a ground‐based lidar measured vertical backscatter ratio profiles at one wavelength and the satellite‐borne Polar Ozone and Aerosol Measurement (POAM) Il solar occultation instrument measured atmospheric extinction at nine wavelengths. From the RADIBAL data the mode radius and variance of the aerosol size distribution are derived as well as the particle refractive index. This size distribution is used to convert the lidar backscatter ratio to an extinction coefficient. The POAM II aerosol extinction coefficients are derived under the assumption that the spectral dependence of the aerosol optical depth follows a quadratic law at all altitudes. This quadratic dependence is used to deduce the mode radius and variance of the aerosol size distribution and to interpolate the POAM data to the wavelengths of the other two instruments. In the common altitude range of measurements, from 15 to 23 km, the derived aerosol extinction profiles agree within the instrument measurement errors and the temporal and spatial variability of the aerosol layer. The geographic area of measurements was outside the polar vortex on that day. The effective aerosol particle radius decreases slightly with increasing altitude from 0.40 μm at 16 km to 0.25 μm at 22 km and the effective variance ranges from 0.15 to 0.25. The mean refractive index is 1.44 at 850 nm, which is compatible with a 75%‐sulfuric acid‐water aerosol. The aerosol number densities decrease from 5 to 1 cm−3 over the 16‐ to 22‐km altitude range and the surface area density decreases from 5 to less than 1 μm2 cm−3 over the same altitude range.
Annual variation of total ozone at Syowa Station, Antarctica
Authors: Chubachi Shigeru
Published: February 2004

Analysis of total ozone data from Syowa (69°S, 40°E) for the years 1982 to 1994 reveals several new features in the behavior of ozone depletion. There is no significant year‐to‐year trend or seasonal variation of total ozone during the polar night (June and July), and the mean value for these months provides a baseline for determining the springtime ozone decrease. Also, the constancy of the polar night data shows that the ozone depletion in spring does not affect the following wintertime total ozone. September mean total ozone relative to the mean total ozone during June and July varies linearly with that for August showing that the ozone destruction process is active in August and September; this relationship does not appear to continue through October when corruption or displacement of the polar vortex occurs. The magnitude of springtime ozone depletion has increased from the 1980s to the 1990s. Moreover, analysis of temperature at the 100‐hPa level shows that final warming at Syowa has been delayed 1.2 days per year. This suggests that the polar vortex is stabilized by the development of the Antarctic ozone hole.
Sensitivity of a linear detection procedure to the accuracy of empirical orthogonal functions
Authors: Kim Kwang‐Y.
Published: February 2004

Empirical orthogonal functions (EOFs) and the corresponding eigenvalues are an important ingredient in formulating the linear detection algorithm developed by North et al. [1995]. Naturally, reliability of this detection method is an important issue when only inaccurate EOFs and eigenvalues are available for constructing a detection filter. To address this issue, this study examines how sensitive the signal‐to‐noise ratio (SNR) is, which is an important property of a detection filter, to the accuracy of EOFs and eigenvalues. A relationship is derived between an error bound of the signal‐to‐noise ratio squared (SNR2) and EOF and eigenvalue errors [Kim, this issue]. The derived error bound estimate for SNR2 rather accurately delineates the actual SNR2 error due to an inaccurate filter providing that the EOFs and eigenvalues constructing a detection filter are “reasonably” accurate. Whether or not a set of EOFs and eigenvalues is reasonably accurate depends upon the magnitude of sampling error and is addressed in terms of the sampling insufficiency in space and time, and the cutoff eigenvalue which is the minimum eigenvalue retained for formulating a detection filter. If the cutoff eigenvalue is very low, an error bound tends to seriously underestimate an actual SNR2 error. The utility of the derived error bound is demonstrated by examining the relative uncertainty in the SNR of a hypothetical greenhouse warming signal when using two different sets of EOFs and eigenvalues.
Determination of aerosol optical depth and land surface directional reflectances using multiangle imagery
Authors: Martonchik John V.
Published: February 2004

Spectral aerosol optical depths, surface hemispherical‐directional reflectance factors, and bihemispherical reflectances (albedos) are retrieved for an area of Glacier National Park using spectral, multiangle imagery obtained with the airborne advanced solid state array spectroradiometer (ASAS). The retrieval algorithms are described and are identical in principle to those being devised for use by the multiangle imaging spectroradiometer (MISR) which will fly on the EOS‐AM1 spacecraft in 1998. As part of its science mission, MISR will produce global coverage of both aerosol amounts and land surface reflection properties. The results in this paper represent the initial effort in applying the MISR algorithms to real data. These algorithms will undergo additional testing and validation as more multiangle data become available.
Intercomparison of heating rates generated by global climate model longwave radiation codes
Authors: Baer F. , Arsky N. , Charney J. J. , Ellingson R. G.
Published: February 2004

Longwave radiative heating, which has a pronounced impact on climate prediction, is represented in Global Climate Models (GCMs) by an algorithm which converts model input parameters to heating rates. Since each GCM has a unique longwave radiative heating parameterization, an intercomparison of seven frequently used algorithms designed to assess their variability to input data was performed. The algorithms' heating rate calculation, which is perhaps the most important aspect of the parameterization in that it is a principal part which the GCM actually incorporates into its climate prediction, was evaluated by subjecting each to identical input parameters and comparing the resulting output. It should be noted that the overall shape of a given heating rate profile depends strongly on the depth of the model layers over which the average conditions were determined. But since GCMs ultimately see the heating rates only at model levels, this aspect of heating rate calculations is transparent to the models themselves. For clear sky conditions, the algorithms were tested with a diverse range of input data taken from different geographic locations and seasons and with various distributions of vertical levels. Analysis of the results from these clear sky experiments indicated that heating rate profiles generated by the algorithms were similar, with maximum variations of the order of 0.5°K/d. The differences in algorithm output became substantially more pronounced when clouds at one or more levels with varying thickness were introduced into the input conditions, particularly if the clouds were thicker than one model level. Indeed, for some cloud configurations the resulting profiles of heating rates appear to have no correspondence whatsoever to one another. How important these differences are to ultimate GCM climate predictions is currently under study.
Estimates of momentum flux associated with equatorial Kelvin and gravity waves
Authors: Sato Kaoru , Dunkerton Timothy J.
Published: February 2004

A new indirect method is proposed to estimate momentum flux based on the theory of slowly varying gravity waves and equatorial waves in vertical shear by Dunkerton [this issue] which explains the discovery by Sato et al. [1994] that the cospectra of temperature and zonal wind fluctuations at Singapore (1.4°N, 104.0°E) are synchronized with the quasi‐biennial oscillation (QBO) of mean zonal wind in the stratosphere. The indirect estimates obtained from cospectra correspond to the summation of absolute values of momentum flux associated with each wave, whereas direct estimates from quadrature spectra give the summation of momentum flux. An analysis was made for twice daily rawinsonde data at Singapore. The direct estimate for Kelvin waves (5–20 day components) is 2–9×10−3 m s−2 and accords with the indirect estimate to within the estimation error. This result supports the validity of the indirect method. Although the indirect estimate depends on an assumed wave structure, large values of momentum flux are obtained for all possible equatorial modes having short periods (1–3 days). The indirect estimate for westerly shear is 20–60×10−3 m2 s−2 based on the theory of two‐dimensional gravity waves, while the direct estimate is only 0–4×10−3 m2 s−2. The reduction of indirect estimate under the assumption of equatorial waves is about 30–70%. The discrepancy between direct and indirect estimates indicates a large cancelation of positive and negative momentum fluxes. This is the case also for easterly shear. The indirect estimate for westerly shear is almost twice as large as that for easterly shear. The characteristics of waves near the source in the troposphere are thought to be independent of the QBO in the stratosphere, so that the difference in wave activity should be attributed to the differing characteristics of wave propagation under the strong QBO shear. Several possible explanations are discussed. Parameters such as phase velocity and zonal wavelength are estimated from the ratio of potential to kinetic energies assuming that the 1–3 day components are due to equatorial waves. The estimates in this paper were made assuming that the observed frequencies are actual ground‐based wave frequencies. If there is aliasing from higher frequencies than 1 day, the actual momentum fluxes can be significantly larger than the estimated values.
Impact of the atmosphere on surface radiative fluxes and snowmelt in the Arctic and Subarctic
Authors: Zhang T. , Bowling S. A. , Stamnes K.
Published: February 2004

A comprehensive atmospheric radiative transfer model combined with a surface energy balance equation was applied to investigate the impact of variations of the meteorological characteristics of the atmosphere on surface radiative fluxes and snowmelt in the Arctic and Subarctic. The discrete ordinate method was used to calculate the atmospheric radiative fluxes. Variations in the incoming longwave radiation could account for the inter‐annual variability of snowmelt in the Arctic and Subarctic. Under clear sky conditions, change in the atmospheric water vapor content is the most important single factor determining variations in incoming longwave radiation. The overall magnitude of the temperature inversion is another important factor. Radiative fluxes are very sensitive to the temperature of the inversion but insensitive to the depth of the inversion layer. For an atmosphere with no inversion, about 87% of the incoming longwave radiation comes from the lowest 500 m of the atmosphere, about 65% from the lowest 100 m, more than 20% from the lowest 10 m, and about 10% from the lowest 2 m. The coupling between the warmer, wetter atmosphere and snowmelt would enhance the warming in the Arctic and Subarctic predicted by global climate models in response to emissions of greenhouse gases.
Role of aerosol variations in anthropogenic ozone depletion in the polar regions
Authors: Portmann R. W. , Solomon S. , Garcia R. R. , Thomason L. W. , Poole L. R. , McCormick M. P.
Published: February 2004

A climatology of aerosol surface area inferred from satellite measurements is used as input in a two‐dimensional model to study the long‐term evolution of polar ozone depletion, especially the Antarctic ozone hole. It is found that volcanic aerosol inputs very likely modulate the severity of the ozone hole. In particular, the rapid deepening of the ozone hole in the early 1980s, as seen, for example, in the Halley Bay total ozone measurements, was probably caused by accelerated heterogeneous chemistry associated with an increase in aerosol surface area due to volcanic injection combined with the anthropogenic perturbation of stratospheric chlorine. This is further substantiated by the large Antarctic ozone decline observed and modeled after the eruption of Mount Pinatubo. A number of factors that influence the ozone hole are also investigated, including the effect of liquid versus frozen aerosol, the effects of denitrification and dehydration, the role of HOx in HCl and ClONO2 recovery, and the effect of chlorine partitioning at the start of winter. Denitrification tends to slightly increase modeled ozone loss, primarily between about 17 and 25 km late in the season, while dehydration tends to decrease the amount of ozone depletion. However, temperature and aerosol amount have the strongest control on the model ozone loss for a given chlorine loading. These findings suggest that future Arctic ozone depletion could be severe in unusually cold winters or years with large volcanic aerosol surface area.
The relative merits of surface layer and bulk similarity formulations for surface shear stress
Authors: Brutsaert Wilfried , Parlange Marc B.
Published: February 2004

Application of the bulk similarity formulation to the atmospheric boundary layer (ABL) requires the adoption of an external wind velocity and temperature scale. Recent versions of this approach have made use of the average wind speed and average temperature over the outer region or mixed layer of the ABL. The method is applied herein with wind profile data measured over the Landes forest in southwestern France to estimate the regional surface shear stress under unstable conditions. It is found that these estimates can be as reliable as those obtainable with Monin‐Obukhov similarity of the atmospheric surface layer.
Visibility‐reducing organic aerosols in the vicinity of Grand Canyon National Park: Properties observed by high resolution gas chromatography
Authors: Mazurek Monica , Masonjones Michael C. , Masonjones Heather D. , Salmon Lynn G. , Cass Glen R. , Hallock Kristen A. , Leach Martin
Published: February 2004

Fine particle and total airborne particle samples were collected during August 1989 within the Grand Canyon (Indian Gardens (IG)) and on its south rim (Hopi Point (HP)) to define summertime organic aerosol concentration and composition as a function of elevation at Grand Canyon National Park. Inorganic chemical constituents were analyzed also to help place the relative importance of organics in perspective. Fine particle organic aerosols were approximately equal in concentration to sulfate aerosols at both sites. Monthly average mass concentrations for fine aerosol organics ranged from 1.1 μg m−3 (IG) to 1.3 μg m−3 (HP), while the organic aerosol concentration within total suspended particulate matter samples ranged from 1.9 μg m−3 (IG) to 2.1 μg m−3 (HP). Aerosol organics that could be evaluated by gas chromatography with flame ionization detection (GC‐FID) (elutable organics) constituted 27% to 53% of the total organics mass collected as fine or total aerosol. At each site, roughly half of the elutable organics fine aerosol fraction was composed of highly polar organic compounds. Distributions of the elutable organics were compared to Los Angeles fine aerosol samples and to distributions of authentic sources of aerosol organics. It was found that the Grand Canyon organic aerosol during August 1989 did not resemble diluted aged Los Angeles organic aerosol, indicating that most of the organic particulate matter at the Grand Canyon at the time studied originated from other sources.
Could high‐speed civil transport aircraft impact stratospheric and tropospheric temperatures measured by microwave sounding unit?
Authors: Shah Kathryn Pierce , Rind David , Lonergan Patrick
Published: February 2004

A radiative transfer postprocessor calculates microwave brightness temperatures Tb from climate experiments investigating supersonic aircraft exhaust impacts with the Global Climate/Middle Atmosphere Model (GCMAM) at the NASA Goddard Institute for Space Studies. Microwave signals from the exhaust‐perturbed GCMAM atmospheres are contrasted with observed interannual variability (natural “noise”) for 1982–1991 as measured by microwave sounding unit (MSU) channels across the lower troposphere, midtroposphere, and lower stratosphere. Exaggerated ozone and water vapor perturbations at supersonic cruise altitudes produce microwave signals easily detected against natural noise. Removal of ozone greenhouse action between 200 and 50 hPa cools all MSU channels with greatest Δ Tb of −8.3 K and signal‐to‐observed‐noise (S/N) ratios above 20 in the lower stratospheric channel. Doubling middle‐atmospheric water vapor above 100 hPa cools lower stratospheric Tb values by 1.5 K while warming tropospheric channels, particularly the tropopause channel. Detectable S/N ratios of 2–4 occur over the tropics and subtropics in the lower‐to‐middle troposphere and lower stratosphere. Realistic ozone and water vapor perturbations are based on the High‐Speed Research Program/Atmospheric Effects of Stratospheric Aircraft reports. These realistic stratospheric ozone and water vapor changes produce Δ Tb signals under 0.6 K and negligible S/N ratios. The slight climatic forcings are overwhelmed by natural feedbacks of high and low cloud formation, sea ice formation, and snow coverage. Thus the modeled realistic ozone and water vapor perturbations produce small and conflicting microwave signals, undetectable against natural variability and other sources of anthropogenic climatic forcing.
Subharmonics, cascades of period doubling, and chaotic behavior of photochemistry of the mesopause region
Authors: Sonnemann G. , Fichtelmann B.
Published: February 2004

Choosing a simple oxygen‐hydrogen model of the upper mesosphere, we study conditions necessary to create nonlinear effects such as cascades of period doubling and chaos. The model takes into account diurnal periodical excitation by solar radiation. The principal reaction of the model to water vapor changes and variations of the ratio of daytime hours to nighttime hours are studied in some detail. Although the model is rather simple as far as the considered photochemical processes are concerned, it is quite complex regarding the deterministic chaos because the phase space spans over five dimensions. Results of the calculations are discussed, including possible relations to measurements in the mesopause.
Aircraft observations of the effects of internal gravity waves on ozone over the western North Atlantic
Authors: Bian Xindi , Berkowitz Carl M. , Zhong Shiyuan
Published: February 2004

A series of wave‐like patterns in ozone mixing ratio, potential temperature, and dew point were observed during aircraft horizontal sampling at a constant elevation of approximately 1700 m over the Gulf of Maine and the western North Atlantic. Several hypotheses about the cause for such phenomena are examined. Both the observational evidence and a simple theoretical analysis suggest that the most likely explanation is the atmospheric perturbation associated with internal gravity waves trapped in a stable boundary layer.
Emission of NO from several higher plant species
Authors: Wildt J. , Kley D. , Rockel A. , Rockel P. , Segschneider H. J.
Published: February 2004

Emission of nitric oxide (NO) from a variety of plant species was observed in a continuously stirred tank reactor. During daytime and at NO concentrations below 1 ppb in the chamber air, NO emissions were observed for all studied nitrate‐nourished plant species. A relation was found between the NO emission rates during daytime and the uptake rates of CO2. The ratio of the NO emission rate to the CO2 uptake was similar for all plants. Changes of the net rate of photosynthesis induced by variations of light intensity or changes of CO2 concentrations changed the NO emission rates correspondingly. The link between NO emissions and CO2 uptake during daytime allowed estimation of the potential of the vegetation to evolve NO on a global scale as 0.23 Tg N yr−1. Strong NO emissions during nights were observed when the nitrate concentration in the nutrient solution was enhanced. Then NO emissions were observed with flux densities comparable to the highest emission rates found from soils.
Area‐average rainfall and lightning activity
Authors: Chèze Jean‐Luc , Sauvageot Henri
Published: February 2004

The aim of the paper is to discuss the statistical relations between the average rainfall parameters for an ensemble of convective cells and the mean lightning occurrence inside this area. The study is based on a data set gathered in France using C and S band radars and two different lightning detection networks. One of them is used to measure L, the cloud to ground flash number. The other one is used to measure Sa, the total cloud to ground and intracloud flash number. The rainfall parameters are 〈R〉 and F(τ), the mean areal rain rate and the fractional rainfall area above a threshold τ, respectively. The results demonstrate that for a single event (i.e., on the spatiotemporal scale of a rain system), significant correlations (1) between the average rainfall parameters, (2) between L and Sa, and (3) between the lightning and the average rainfall parameters are observed. As expected, the correlation between 〈R〉 and F(τ) (1) is very tight for the individual cases as well as for the cluster of the data. The correlations between L and Sa and between the lightning and the average rainfall parameters (i.e., 2 and 3) can be tight in convectively and electrically very active systems (the correlation coefficient between L and F(τ) reaches 0.96). Yet, the parameters of the relations change from one case to another. So, when considered on a climatological scale (i.e., all the data for a season processed together), the 2 and 3 types of correlation diminish or even vanish. However, it is suggested that for homogeneous climatological conditions associated with very active convective clouds, such as, for example, the conditions observed in some tropical areas, and for a homogeneous regime of convection, a tight relation with stable parameters could be expected.
Growth of freshly nucleated particles in the troposphere: Roles of NH3, H2SO4, HNO3, and HCl
Authors: Kerminen Veli‐Matti , Wexler Anthony S. , Potukuchi Sudhakar
Published: February 2004

Growth of airborn, nanometer‐size nuclei was examined in a H2SO4‐HNO3‐HCl‐NH3‐H2O system using a single‐particle condensation model. Under conditions typical of the lower troposphere, growth is driven initially by the flux of sulfuric acid, followed by thermodynamic equilibration by the more abundant water and ammonia vapors. Pure sulfuric acid‐water‐ammonia condensation was shown to be rather slow and unable to produce cloud condensation nuclei (CCN) in the atmosphere. Under favorable conditions and after reaching a certain size, nuclei may start to absorb large quantities of nitric or hydrochloric acid together with ammonia, which produces CCN‐size particles over a timescale of a few minutes. The resulting CCN are susceptible to evaporation as the ambient conditions change but may become stable via cloud processing. The fast, HNO3‐HCl‐NH3‐driven condensation was estimated to occur frequently in continental aerosol systems. Marine CCN production cannot be explained by this process; it requires either the participation of other condensable vapors, such as organics, or a different growth mechanism.
Ground‐based observation of ozone, carbon monoxide, and sulfur dioxide at Kenting, Taiwan, during the PEM‐West B campaign
Authors: Liu Chung‐Ming , Buhr Martin , Merrill John T.
Published: February 2004

Intensive measurements of chemical species were conducted during February–March, 1994 at Renting, which is at the southern tip of Taiwan, in accord with the Pacific Exploratory Measurements in the western Pacific ocean (PEM‐West B) experiment. In general, frequent outbreaks of cold polar air mass dominated the synoptic weather pattern, which was led by a fast moving cold front and followed by steady northeasterly winds over the Taiwan region. There was frontal passage only eight times, each taking about 48 hours to complete. Steady northeasterly winds prevailed during most of the study period and were associated with a negligible diurnal variation of the chemical species. The median level of ozone, CO, and SO2 in the northeasterly wind was 45.7, 198, and 0.08 ppbv, respectively. Dramatic changes in the levels of O3, CO, and SO2 occurred during each frontal passage, which was characterized by a drop in the surface pressure, a swift change in the wind direction, and a reduction in the wind speed. The ozone level dropped from 40–55 ppbv to about 6–15 ppbv at 12–18 hours after the time of the surface pressure minimum, and then it took about 6–18 hours to be restored to its original level. In the meantime, the levels of CO and SO2 also decreased in the beginning but increased dramatically up to 400–556 ppbv and 1–9.51 ppbv, respectively, right after the frontal passage. Later on, their concentration dropped back to the original steady level in a northeasterly wind.
Accuracy of the independent pixel approximation for satellite estimates of oceanic boundary layer cloud optical depth
Authors: Chambers L. H. , Wielicki B. A. , Evans K. F.
Published: February 2004

A theoretical study has been conducted on the effects of cloud horizontal inhomogeneity on the retrieval of optical depth by remote sensing of visible reflectance. Forty‐five Landsat scenes of oceanic boundary layer clouds provide a sampling of real cloud fields, including trade cumulus, open and closed cell broken stratocumulus, and solid stratocumulus. The spherical harmonic discrete ordinate method (SHDOM) radiative transfer model is used to calculate two‐dimensional reflectances from subsampled cloud strips representing the Landsat scenes. The independent pixel approximation (IPA) is used to retrieve optical depth for comparison to the original input. Results for τIPA versus τref are presented on scales from the Landsat pixel scale (28.5 m) to an imager pixel scale (6 km) to near mesoscale (60 km). The random error decreases as the averaging scale increases, but error due to inhomogeneity remains. At the 60 km scale the average error is about 6% for high Sun, 2% for low Sun. Individual scenes, however, have retrieved optical depth errors as high as 45% due to horizontal radiative transport. The ability to retrieve higher statistical moments of the frequency distribution of optical depth is also assessed. Sigma, (σ), the standard deviation of τ, is retrieved quite well up to a point, then is underestimated due to the smoothing effect of horizontal radiative transport. The gamma function parameter ν, another measure of the width of the τ frequency distribution, is retrieved quite well over a wide range but with a systematic bias which varies with solar zenith angle, again due to horizontal radiative transport. A method is sought to reduce the optical depth retrieval error using a simple correction based on remotely sensed cloud properties. Of those considered, cloud physical aspect ratio (computed here from one possible relation which depends on properties obtainable from remote sensing) is found to be the most effective correction parameter. The aspect ratio correction reduces the retrieved optical depth bias error by 50 to 100% and the RMS error by 20 to 50%. Correction coefficients are presented at three solar zenith angles. This work is limited by its consideration of only single‐level marine boundary layer clouds, assumptions of conservative scattering, constant cloud droplet size, no gas absorption or surface reflectance, and restriction to two‐dimensional radiative transport. Future work will attempt to remove some of these limitations. The Landsat data used are also limited due to radiative smoothing.
An intercomparison of oceanic precipitation frequencies from 10 special sensor microwave/imager rain rate algorithms and shipboard present weather reports
Authors: Petty Grant W.
Published: February 2004

Oceanic precipitation frequencies produced by 10 satellite microwave algorithms submitted to the first Precipitation Intercomparison Project are compared with frequencies derived from ship reports. It is found that most algorithms yield distributions in reasonable agreement with the ship‐derived climatology at low latitudes, but the majority fail to register more than very infrequent (∼1%) precipitation at latitudes poleward of about 45°, in contrast to the much larger (∼10%) frequencies indicated by surface reports. Only two algorithms, both of which were based on the brightness temperature transformations of Petty [1994a, b], appear to approximately reproduce ship‐observed precipitation frequency patterns at both tropical and high latitudes. All 10 algorithms, however, appear to have difficulty producing realistic precipitation frequencies in the “dry” subtropical trade belts. This problem is tentatively attributed to the unique physical characteristics of precipitation in those regions.
UARS first global N2O5 data sets: Application to a stratospheric warming event in January 1992
Authors: Kumer J. B. , Kawa S. R. , Roche A. E. , Mergenthaler J. L. , Smith S. E. , Taylor F. W. , Connell P. S. , Douglass A. R.
Published: February 2004

For the first time, global measurements of N2O5 are available for study. N2O5 has long been a missing link in large‐scale observations of stratospheric nitrogen species, the chemical family that comprises the major global loss cycle for ozone above about 25 km [McElroy et al., 1992]. N2O5 is also an important intermediate in conversion of NOx to HNO3, thus limiting the effect of nitrogen‐catalyzed ozone destruction below about 25 km [Fahey et al., 1993]. The new N2O5 observations come from both the Cryogenic Limb Array Etalon Spectrometer (CLAES) and Improved Stratospheric and Mesospheric Sounder (ISAMS) instruments on the Upper Atmosphere Research Satellite (UARS), providing near‐global coverage at high spatial and temporal resolution for almost 20 months. Here we focus on data obtained near 40 km during a stratospheric warming in January 1992. The N2O5 fields show globally coherent structures with large variation in response to global transport coupled with highly temperature dependent chemistry. Comparison of the data with chemistry and transport models indicates that our understanding of processes controlling N2O5 amounts and the interaction with other reactive nitrogen species is largely accurate under most conditions; however, an exceptional disagreement is found in the prolonged polar dark. This example demonstrates the utility of global data to understand the combined effects of chemistry and transport on N2O5 under a wide range of conditions.
Measurement of geopotential heights by GPS radio occultation
Authors: Leroy Stephen S.
Published: February 2004

Geopotential heights of constant pressure surfaces are retrieved from global positioning system (GPS) radio occultation data. In order to assess accuracy a subset of data obtained by GPS/MET during spring 1995 and summer 1995 are compared to the output of the European Centre for Medium‐Range Weather Forecasts (ECMWF) global model. The root‐mean‐square measurement error is 20 m throughout the upper troposphere and lower stratosphere. Furthermore, the ECMWF global model contains enhanced errors in the southeast Pacific. In probing the data for potential utility in climate studies, a Bayesian interpolation technique is used to map the geopotential height fields in the upper troposphere during the summer. Despite limitations of the GPS/MET data set the global average 300‐mbar geopotential height over a 2‐week period in summer 1995 is determined with an accuracy of 7 m. By obtaining greater coverage and partially resolving synoptic variability, a future constellation of 16 orbiting receivers could obtain global average geopotential height estimates in the upper troposphere with an accuracy of l m each day. Accuracy would be somewhat worse for regional studies, except in the tropics where synoptic variability is depressed.
Role of radiative transfer in the modeled mesoscale development of summertime arctic stratus
Authors: Pinto James O. , Curry Judith A.
Published: February 2004

Improvements have been made in the treatment of radiation in Version 5 of the Pennsylvania State University‐National Center for Atmospheric Research (NCAR) Mesoscale Model (MM5) to simulate boundary layer stratus observed during the summertime Arctic Stratus Experiment of 1980. Shortwave radiation is treated using a two‐stream, delta‐Eddington approximation developed for Version 2 of the NCAR Community Climate Model. This code offers many improvements over the original radiative transfer code developed by Dudhia [1989], including a more detailed treatment of surface albedo, solar absorption by ozone, and improved treatment of liquid, ice, and mixed‐phase clouds. Longwave radiative calculations are performed with the broadband radiative transfer code currently employed in Version 3 of the European Centre for Medium‐Range Weather Forecasts (EC3) model. Improvements offered by EC3 include longwave radiative absorption by ozone and trace gases and the explicit radiative treatment of mixed‐phase clouds. The importance of radiation in the formation of low‐level Arctic stratus and the evolution of an anticyclone is illustrated with three simulations: (1) baseline simulation using the Dudhia [1989] radiative transfer, (2) improved radiative transfer (i.e., CCM2 shortwave and EC3 longwave), and (3) radiative transfer neglected. The area extent of low clouds is reduced toward observed values when improved radiative transfer is implemented. The temperature, moisture, and cloud water profiles show significant sensitivity to the treatment of radiative transfer as well. Comparisons between observations and model results show that the new radiation package improves the area extent of cloud cover and the quality of the simulated surface radiative fluxes. The importance of radiative cooling in the evolution of a Beaufort Sea anticyclone is demonstrated.
Aircraft‐borne detection of stratospheric column amounts of O3, NO2, OClO, ClNO3, HNO3, and aerosols around the arctic vortex (79°N to 39°N) during spring 1993: 1. Observational data
Authors: Pfeilsticker K. , Blom O. E. , Brandtjen R. , Fischer H. , Glatthor N. , Grendel A. , Gulde T. , Höpfner M. , Perner D. , Piesch C. , Platt U. , Renger W. , Sessler J. , Wirth M.
Published: February 2004

Using several remote sensing techniques on board a research aircraft (Transall C‐160), we measured the stratospheric column amounts of O3, NO2, OClO, ClNO3, and HNO3, and the height‐resolved aerosol backscattering ratios during March 7–10, 1993. During this period the polar vortex extended from the Arctic well into the Mediterranean (35°N). Several underflights of the vortex and its edge region were conducted, covering Arctic (79°N) to Mediterranean latitudes (39°N). During all the flights, moderate amounts of NO2 (0.7–2·1015/cm2), elevated amounts of HNO3 (1.75–2.35·1016/cm2), ClNO3 (2.4–5.4·1015/cm2), and OClO (6–13·1012/cm2) were found inside the vortex, indicating that the air masses of the vortex were still chemically disturbed. The observation is interpreted as the polar vortex going from the stage of its wintertime denoxification (conversion of NOx into NOy;) and chlorine activation (conversion of HCl and ClNO3 into chlorine oxides) to the springtime reverse processes via the formation of enhanced amounts of ClNO3. In addition, first measurements of OClO (6–1012/cm2 at solar zenith angle 90°) and high amounts of ClNO3 (4–1015/cm2) around 40°N are reported.
Coupled aerosol‐chemical modeling of UARS HNO3 and N2O5 measurements in the Arctic upper stratosphere
Authors: Bekki S. , Chipperfield M. P. , Pyle J. A. , Remedios J. J. , Smith S. E. , Grainger R. G. , Lambert A. , Kumer J. B. , Mergenthaler J. L.
Published: February 2004

Gas‐phase photochemical models do not account for the formation of a secondary altitude HNO3 maximum in the upper stratosphere at high latitudes during winter, suggesting that some processes are missing in the currently accepted chemistry of reactive nitrogen species [Kawa et al, 1995]. Heterogeneous chemistry on aerosol particles had been discounted as the cause because the aerosol surface area is expected to be very low at these altitudes. We have coupled a sulphate aerosol microphysical model to a chemical transport model to investigate this model deficiency in the Arctic during January 1992. The aerosol model predicts the formation of small sulphate particles at 1100 K. Comparisons with cryogenic limb array etalon spectrometer (CLAES) HNO3 and improved stratospheric and mesospheric sounder (ISAMS) N2O5 observations show that the heterogeneous conversion of N2O5 to HNO3 on the modeled small sulphate particles can account for some of the unexpected features seen in Upper Atmosphere Research Satellite (UARS) observations.