bluuebunny/crossref_metadata_2025 huggingface dataset:
Dissipation methods, Taylor's hypothesis, and stability correction functions in the atmospheric surface layer
Authors: Hsieh Cheng‐I , Katul Gabriel G.
Published: February 2004

The traditional dissipation method and the new approaches suggested by Albertson et al. [1996] and Hsieh et al. [1996] to estimate momentum and heat fluxes were compared using velocity and temperature measurements in the atmospheric surface layer. These measurements were carried out above two different sites (grass and bare soil) over a wide range of atmospheric stability and turbulent intensity conditions. Taylor's hypothesis, flux divergence terms, and stability correction functions which play important roles in the dissipation methods were also evaluated. In highly turbulent intensity flows, deviations from Taylor's hypothesis may cause some errors in estimating dissipation rates and subsequent fluxes. Wyngaard and Clifford [1977] proposed a model to interpret the influence of departures from Taylor's hypothesis. In this study we evaluate this influence in the inertial subrange and discuss the usefulness of Wyngaard and Clifford's model in practice. We also found the flux divergence term in the temperature variance budget equation to be significant, relative to the production term in unstable conditions. Our measurements showed that discarding the flux divergence term resulted in systematic underpredictions of the sensible heat flux by the dissipation methods. The proposed dissipation method by Hsieh et al. [1996] for estimating sensible heat flux was extended to momentum flux, and its implications for stability correction functions were discussed. Good agreement between eddy correlation measured and predicted sensible heat fluxes by the methods of Albertson et al. [1997] and Hsieh et al. [1996] was noted.
Variations in tropospheric ozone related to transport at American Samoa
Authors: Harris Joyce M. , Oltmans Samuel J.
Published: February 2004

Ten years of isentropic trajectories were summarized using cluster analysis to describe flow patterns for American Samoa. The trajectories were then paired with surface ozone data to determine the dependence of surface ozone on transport. The two main transport regimes affecting surface ozone are trade wind transport, where trajectories show flow bringing ozone from the east in the tropical marine boundary layer, and midlatitude transport, where trajectories show strong westerly flow at higher elevations of southern midlatitudes, followed by descent with anticyclonic curvature. These two transport regimes yield ozone from distinctly different origins, having different mixing ratios. The seasonally changing frequency of transport type is shown to be partly responsible for the seasonal cycle and changes in variability of Samoa surface ozone. On average, 45% of winter ozone variation can be explained by differences in transport type. This strong relationship was absent, however, during 1991, probably because of UV blocking by aerosols from the eruption of Mount Pinatubo. Reduced total column ozone during winter 1992 may have contributed to this season having the lowest surface ozone levels of the study period.
Atmospheric aerosol and water vapor characteristics over north central Canada during BOREAS
Authors: Markham B. L. , Schafer J. S. , Holben B. N. , Halthore R. N.
Published: February 2004

A network of five automated and two handheld solar radiometers was operated during the 1994–1996 Boreal Ecosystem‐Atmosphere Study (BOREAS) in northern Saskatchewan and Manitoba, Canada, in order to characterize the atmospheric aerosol properties. Direct solar measurements were used to measure atmospheric transmission and infer aerosol optical thickness and water vapor column abundance. Near‐Sun sky radiance measurements (solar aureole) were used to estimate the aerosol size distribution. Aerosol conditions were heavily influenced by the presence or absence of forest fires. In 1996, when few fires occurred, conditions were uniform across the region with median aerosol optical thickness (AOT) at 500 nm of 0.12 and 90th percentile values of 0.27 for the May‐October period. During the 1994 and 1995 seasons, numerous fires occurred in the vicinity of the sites. The median AOT values were comparable with the 1996 values, though the 90th percentile values were larger, in general measuring 0.85 (southern 1994 season was 0.43). Median column water vapor measurements for the same 7 month period were in the range from 1.32 to 1.58 cm at both sites, with 1995 being the driest year of observation. Winter median values of AOT and water vapor were typically 0.09 and 0.34 cm, respectively. Size distributions derived from solar almucantar measurements show the predominance of small particles during smoke episodes when compared to that for background conditions. Spectral dependence of the AOT as characterized by the wavelength exponent, α, asymptotes at 1.8 for high optical depths for a 7 month season of cloud‐screened data at the northern young jack pine site. This observed wavelength exponent for boreal biomass burning conditions is within the range of values found during the burning season in a study in Brazil.
Regional‐scale surface flux observations across the boreal forest during BOREAS
Authors: Oncley Steven P. , Lenschow Donald H. , Campos Teresa L. , Davis Kenneth J. , Mann Jakob
Published: February 2004

A major role of the National Center for Atmospheric Research (NCAR) Electra aircraft during the Boreal Ecosystem‐Atmosphere Study (BOREAS) was to measure fluxes of momentum, sensible and latent heat, carbon dioxide, and ozone on a transect that crossed the entire boreal forest biome. The observations spanned the growing season (late May to mid‐September 1994) and extended the fluxes obtained in two intensive study areas to larger spatial scales to help provide a data set that is useful for comparison with and validation of large‐scale models and satellite retrievals. We found the deciduous forests to be more photosynthetically active than nearby coniferous forests. Coniferous forest fluxes across the transect from the BOREAS southern to northern study areas show no apparent spatial trend, though smaller‐scale variability is large. The fluxes make a smooth transition from the BOREAS northern study area to the subarctic tundra. Typical midsummer, midday, large‐scale net ecosystem exchanges of carbon dioxide were about −10 μmol m−2 s−1 for primarily deciduous forests, about −6 μmol m−2 s−1 for the primarily coniferous regions between and including the two BOREAS study areas, and about −2 μmol m−2 s−1 for the subarctic tundra. The first two values are similar to those observed by flux towers in the region. Throughout the boreal forest the fluxes are influenced by the presence of lakes. Lake fraction is found to be a dominant source of variability in the fluxes observed along the transect. Lakes are also found to be large sinks of available radiant energy. Regional ground storage of heat is estimated to be about 30% of the net radiation over the forest, and 40% over the subarctic tundra, largely due to the presence of lakes.
Estimation of the cyclostationary dependence in geophysical data fields
Authors: OrtizBeviá M. J.
Published: February 2004

Geophysical multivariate data fields are frequently analyzed using linear inverse modelling. A cyclostationary dependence, whether annual, semiannual or diurnal, is usually present in these data. The dependence can be introduced in the inverse linear model in two different ways, known as the “fixed phase” and the “phase smoothed” approaches. When either of them is set to the analysis of real data, the interpretation of some of the diagnostics parameters is not straightforward. From statistical considerations, both methods are expected to perform rather loosely at some points. It is then hard to decide if those values of the parameters correspond to characteristics present in the observed field or to failures of the method. To settle this matter, we proceed in this work to analyze the same synthetic geophysical fields with both methods. The fields consist basically of geophysical waves of known frequency, upon which a cyclostationary dependence is imposed, that are embedded in noise. Different fields were generated by changing the phase of the cyclostationary dependence and the characteristics of the noise, and analyzed using both methods. Through this systematic procedure we assess the real meaning of the diagnostic parameters. Because the true signals and phase of the cyclostationary dependence are known, the performances of both approaches can be compared.
An operational atmospheric correction algorithm for Landsat Thematic Mapper imagery over the land
Authors: Liang Shunlin , Fallah‐Adl Hassan , Kalluri Satya , JáJá Joseph , Kaufman Yoram J. , Townshend John R. G.
Published: February 2004

An operational atmospheric correction algorithm for Thematic Mapper (TM) imagery has been developed for both sequential and parallel computer environments considering both aerosol and molecular scattering and absorption. The aerosol optical depth is estimated from the image itself using the dark object approach on a moving‐window basis, and the surface reflectance is then retrieved by searching lookup tables that are created using a numerical radiative transfer code. The dark object pixels are identified and their surface reflectance estimated using TM channel 7 (2.1 μm). A variety of techniques are employed to improve computational efficiency. This method is validated by measured aerosol optical depth and extensive visual evaluations accompanied by statistical analysis. Results indicate that the approach is highly stable and useful for both qualitative imagery interpretation (haze removal) and quantitative analysis. Future research activities are also highlighted. The computer codes are available to the general scientific community.
On the damping of temperature fluctuations in a circular tube relevant to the eddy covariance measurement technique
Authors: Rannik Üllar , Vesala Timo , Keskinen Raimo
Published: February 2004

A semiempirical model for the heat exchanger design to find out a minimum length to dampen temperature fluctuations is presented. Stationary heat transport processes through the tube wall are analyzed by means of Nusselt numbers. The conservative treatment of the problem reveals that the tube length should be of the order of 1000 times the inner diameter of the tube to neglect the corrections due to sensible heat flux in eddy covariance measurements of trace gases. The model is analytical and easy to use regarding the choice of tube and flow characteristics. Teflon tube is found to be practically as good a heat conductor as metals. The minimum length required for the damping is not affected by the possible heating of the tube outer surface.
Balloon‐borne measurements of the aerosol extinction‐to‐backscatter ratio
Authors: Rosen James M. , Kjome Norman T.
Published: February 2004

Aerosol extinction‐to‐backscatter ratio profiles from surface level to 25 km at 690 nm wavelength are derived from simultaneous nephelometersonde and backscattersonde measurements. The stratospheric values are altitude dependent and range from about 35 to 70 sr. These values are in satisfactory agreement with previously reported estimates employing other techniques and are consistent with optical calculations utilizing aerosol size distributions characteristic of the volcanically disturbed period during which the measurements were made (summer and fall 1992).
Simultaneous observations of nitrate and peroxy radicals in the marine boundary layer
Authors: Carslaw N. , Carpenter L. J. , Plane J. M. C. , Allan B. J. , Burgess R. A. , Clemitshaw K. C. , Coe H. , Penkett S. A.
Published: February 2004

This paper describes the most extensive set of simultaneous measurements of the concentrations of nitrate (NO3) and peroxy (sum of HO2+RO2, R=alkyl and acyl) radicals to date. The measurements were made in the coastal marine boundary layer over the North Sea, at the Weybourne Atmospheric Observatory on the North Norfolk coast during the spring and autumn of 1994. In spring the average nighttime concentration of NO3 measured by differential optical absorption spectroscopy, was about 10 parts per trillion (ppt) (maximum 25 ppt). The corresponding peroxy radical concentration, measured by the chemical amplifier technique, averaged about 2 ppt (maximum 6 ppt), although this is likely to be an underestimate of the total radical concentration. There is a significant positive correlation between the two sets of radicals, which has not been reported previously. A box model of the marine boundary layer is used to show that this correlation arises from the processing of reactive organic species by NO3. During spring the relatively long lifetime of NO3 (up to 18 min) at night is controlled by reaction with dimethyl sulflde (DMS), and the model predicts significant production of HNO3, methyl tiomethylen (CH3SCH2O2) and other peroxy radicals, HCHO, and eventually sulfate. A nighttime production rate for the hydroxyl (OH) of about 2×104 molecules cm−3 s−1 is estimated. During one night in autumn the NO3 lifetime of about 3 min is too short to be explained by reaction with unsaturated hydrocarbons, but is satisfactorily accounted for by the heterogeneous loss of N2O5 on deliquesced aerosols in relatively polluted conditions.
A study of composite cirrus morphology using data from a 94‐GHz radar and correlations with temperature and large‐scale vertical motion
Authors: Mace Gerald G. , Ackerman Thomas P. , Clothiaux Eugene E. , Albrecht Bruce A.
Published: February 2004

In order to improve the representation of clouds in climate models, we require a better understanding of the relationship among cloud properties and the synoptic‐scale state of the atmosphere. In order to investigate this issue as it pertains to a specific class of cirrus clouds, we have combined a 2 month data set of radar reflectivities observed at State College, Pennsylvania, using a W‐band radar with output from a mesoscale model that uses 3‐hourly data assimilation. Products of the analysis include statistical distributions of fundamental cirrus cloud properties, such as frequency of occurrence, base, top and midcloud height, and layer thickness. We also consider the relationships between cirrus reflectivity and the large‐scale meteorological state defined by area‐averaged temperature and vertical velocity. Overall, cirrus clouds are observed 32% of the time, and 51% of those events occur in conjunction with lower‐level clouds. Most of the cirrus occur in thin layers (<1.5 km thickness). Cirrus occurrence appears to be related to largescale meteorological factors but the relationships are complex. The majority of the cirrus we observed occurred at temperatures lower than −35°C and there is little correlation between radar reflectivity and temperature. We also used this data set to examine the usefulness of a satellite‐borne W‐band radar.
Influence of line mixing on absorption by CO2 Q branches in atmospheric balloon‐borne spectra near 13 μm
Authors: Kochel Jeanne‐Marie , Hartmann Jean‐Michel , Camy‐Peyret Claude , Rodrigues Rodolphe , Payan Sébastien
Published: February 2004

Line mixing in CO2 Q branches is studied in the 13.2 μm region from balloon‐borne atmospheric transmission measurements. Eighty‐five spectra were recorded (at 67°N, 22°E) in the 660–960 cm−1 region using a Fourier transform spectrometer with an unapodized resolution (full width at half maximum) of 0.013 cm−1. They involve balloon altitudes and tangent heights from 13 to 30 km and a large range of optical thicknesses. The results of computations assuming Voigt line shapes as well as accounting for line mixing are compared with measured transmissions in three CO2 Q branches of different intensities and symmetries. They confirm the significant effect of line mixing and validate recent line coupling models. As a consequence of the accuracy of the forward approach the Q branches can be used for remote sensing; this should lead to improved precision of pressure/temperature retrievals since absorption in the Q branch wing region is particularly pressure sensitive.
A globally balanced two‐dimensional middle atmosphere model: Dynamical studies of mesopause meridional circulation and stratosphere‐mesosphere exchange
Authors: Zhu Xun , Swaminathan P. K. , Yee J. H. , Strobel D. F. , Anderson D.
Published: February 2004

A globally balanced two‐dimensional middle atmosphere model has been developed. The dynamical fields are obtained by numerically solving two elliptic equations for the mass stream function of the residual circulation and the geopotential field. By comparison with exact solutions, it is demonstrated that this model is more accurate than two‐dimensional models in which the nonlinear advection equations are solved numerically. General features of the dynamical fields from the model and a focused study of meridional circulation in the mesopause region are presented. The simulated zonal mean temperature and zonal wind are consistent with the CIRA (1986) model atmosphere and the direct wind measurements from the high‐resolution Doppler imager (HRDI) and wind imaging interferometer (WINDII) instruments on board the Upper Atmosphere Research Satellite (UARS). The predicted meridional component of the residual circulation
around 92 km is approximately 25 m s−1 with maximum near the summer mesopause. In the mesopause region the salient features in the UARS data are peak zonal mean meridional velocities of 20–30 m s−1 and substantial latitudinal gradients from equator to midlatitude maxima. The consistency between the model and the direct measurements supports the hypothesis that the mesospheric circulation is forced by gravity wave induced drag. The model tracer fields indicate the existence of a mesospheric “depletion zone” and “tracer front” similar to the “surf zone” and “barrier” in the lower stratosphere. The depletion zone and tracer front are generated by divergent and convergent
fields analogous to tropospheric frontogenesis by a deformation field. In addition, the model shows that the most active region for the stratosphere‐mesosphere mass exchange is at the summer polar stratopause. The active exchange is driven by a strong summer mesospheric drag force through the “downward control” principle.
On tropospheric chemical oscillations
Authors: Hess Peter G. , Madronich Sasha
Published: February 2004

Tropospheric chemical mechanisms can generate oscillations in which the concentrations of all reactive chemical species oscillate on timescales ranging from days to years, depending on certain parameter ranges of specified sources for NOxand a reduced species (e.g., carbon monoxide, isoprene, or methane). A simple carbon monoxide oxidation mechanism is presented that exhibits oscillatory solutions qualitatively similar to those found in more complex mechanisms. This allows the derivation of a two‐variable oscillatory model for ozone and carbon monoxide. Using this model, an analytic estimation of the oscillation period is given, the chemical sources required for oscillatory solutions are evaluated, and the mechanism for the oscillation is elucidated. Some of these results can be extended to more complex oscillatory mechanisms.
On the response of a three‐dimensional general circulation model to imposed changes in the ozone distribution
Authors: Christiansen B. , Guldberg A. , Hansen A. W. , Riishøjgaard L. P.
Published: February 2004

A series of idealized ozone perturbations has been studied with the French community general circulation model Arpège. The perturbations are uniform 50% and 75% reductions and an ozone hole type reduction concentrated in the lower part of the stratosphere and the upper part of the troposphere. We compare the radiative drive, the temperature response under the fixed dynamical heating approximation, and the full dynamical response. In all experiments the main effect of the dynamics is a weakening of the diabatic meridional circulation and an associated latitudinal smoothing of the temperature response. The weakening of the diabatic meridional circulation is in agreement with a reduction of the wave forcing, associated with an extended tongue of low refractive index close to the tropopause. While the fixed dynamical heating approximation in general represents the pattern of the temperature response well, the strength of the response is altered when allowing dynamical effects. In the lower stratosphere this adjustment is 25%–50% of the fixed dynamical heating response. The mean zonal wind is very stable to uniform reductions, but the strength of the winter stratospheric jet increases drastically in the hole type experiment. The ozone perturbations decrease the variability in the winter hemisphere, which in the control experiment and the uniform reduction experiments is of oscillatory nature with a timescale of 50 to 100 days.
Quantification of lower stratospheric mixing processes using aircraft data
Authors: Balluch M. G. , Haynes P. H.
Published: February 2004

The reduction in scale of filamentary structures in stratospheric tracers due to stretching by the large‐scale flow must ultimately be halted by processes that lead to molecular mixing. A quantitative bound on the strength of such processes, represented by an effective diffusivity D, is here inferred from high‐resolution tracer data from recent airborne campaigns, using simple mathematical models representing the stretching and mixing processes. The mathematical models are based on the hypothesis that the filamentary structure observed along quasi‐horizontal aircraft flight tracks corresponds in reality to the intersection of the flight track with sloping sheets of tracer. The aircraft data are analyzed to identify tracer features that unambiguously correspond to filamentary structures on isentropic surfaces. Clearly identifiable filaments are seen down to scales of less than 100 km, with transitions in tracer values at the edge of such filaments over scales of less than 10 km. Backward trajectories starting in the neighborhood of such filaments show convincingly that the air inside and outside the filaments has different origin. Integration of an equation for tracer gradient along forward trajectories allows the scale and orientation of the sloping tracer sheets corresponding to the observed filamentary structure to be deduced. On the assumption that the scale of the tracer sheets is small compared to the scale of variation of the velocity field, a diffusion equation may be derived that governs the spatial structure of the sheets. The diffusion coefficient in this equation is the product of the actual diffusivity D and a time‐varying function that depends on the tracer gradient. The latter is determined by the forward integration along trajectories. The diffusion equation is integrated for different values of the diffusivity D. If the value of D is sufficiently large, the integration implies that the filament would diffuse away too rapidly to be consistent with the observations. Finding the maximum acceptable value of D gives an estimate of an upper bound on D for the real atmosphere. The results suggest that the value of D relevant to these filaments can be no more than 10−2 m2 s−1 and in some cases considerably less. Comparison is made with a recent analysis by Waugh et al., [1997], who considered observed filaments that could, on the basis of the relation between mixing ratios of different tracers, be deduced to be partially mixed. Applying our method of analysis to the same observations suggests that the diffusivity D is about 1.4×10−2 m2 s−1. This is consistent, if typical aspect ratios of horizontal to vertical scales are taken into account, with Waugh et al.'s estimate for an equivalent horizontal diffusivity.
Evolution of Mount Pinatubo's aerosol size distributions over the continental United States: Two wavelength lidar retrievals and in situ measurements
Authors: Post Madison J. , Grund Christian J. , Wang Dongliang , Deshler Terry
Published: February 2004

We use lidar measurements at wavelengths of 10.59 and 0.694 μm, together with contemporaneous in situ measurements of aerosol size distribution width, to retrieve the time‐height evolution of lognormal median radius and number density for stratospheric aerosols over the central United States during the first two years after the eruption of Mount Pinatubo. Comparisons with the in situ measurements of median radius and number density are favorable only if the 10.59‐μm backscatter is doubled, indicating a calibration bias in NOAA's climatological data set. The time histories of lidar‐retrieved parameters at lower altitudes indicate that material from a new source appeared in the stratospheric aerosol cloud in the fall of 1992, about 500 days after the eruption of Mount Pinatubo.
Exploring the effects of forcing quasi‐biennial oscillations in a two‐dimensional model
Authors: Politowicz Philip A. , Hitchman Matthew H.
Published: February 2004

Analytic forcing of the stratospheric quasi‐biennial oscillation (QBO) is introduced into a two‐dimensional middle atmosphere model containing interactive radiation, dynamics, photochemistry and climatological aerosols. The “WISCAR” model integrates the temperature equation in time, but diagnoses the meridional stream function and zonal wind. An analytic forcing function for the QBO is derived from zonal wind observations and employed in three different ways: (1) as a “thermal nudge” in the temperature equation, or in the diagnostic meridional stream function equation as (2) additional heating or (3) equivalent wave driving. A different amplification factor for each method is required to achieve good agreement with the observed QBO in column ozone. This lends insight into the relationship among thermal perturbations, heating, and vertical motion. The vertical variation of QBO amplitude leads to a vertical dependence of the phase relationship among vertical motion, temperature, and zonal wind. Equatorial upward motions range from nearly zero to twice the time mean. Feedbacks in the model result in different extratropical responses for the two hemispheres and modulation of the equatorial semiannual oscillation. Chemical feedbacks and phase relationships are explored for the two ozone regimes: photochemical control above 30 km and advective control beneath. Confirming other studies, QBO vertical motions alter the distribution of odd nitrogen species above 30 km, which, together with the temperature dependence of reaction rates, combine to exert a strong control on ozone perturbations.
Chemical reaction rate sensitivity and uncertainty in a two‐dimensional middle atmospheric ozone model
Authors: Chen Li , Rabitz Herschel , Considine David B. , Jackman Charles H. , Shorter Jeffrey A.
Published: February 2004

The NASA Goddard Space Flight Center two‐dimensional (2‐D) model has been used to study the sensitivity of model ozone concentrations to input chemical reaction rates, and the uncertainty of the model‐calculated concentrations. Ozone sensitivity coefficients to changes in chemical reaction rates are defined as logarithmic partial derivatives of the ozone concentration with respect to the chemical reaction rates. These logarithmic derivatives are estimated using a finite difference technique. The ozone sensitivity coefficients to 96 gas phase chemical reactions in the 2‐D model show that the ozone concentration is sensitive to the rates of about 25 reactions. The magnitude of the ozone sensitivity coefficients varies from 0.05 to 0.9. The latitude‐altitude distributions of the ozone sensitivity coefficients to several reactions are presented. The uncertainty of the model‐calculated ozone concentration is evaluated using a guided Monte Carlo (GMC) method from a probability distribution function. The GMC method judiciously combines uncertainty estimates derived from the sensitivity information with Monte Carlo runs of the model. The uncertainty of the model ozone concentration due to uncertainties in gas phase reaction rates is calculated from published chemical rate uncertainties and varies from 10–20% in the lower stratosphere to 30–40% in the mesosphere. Details concerning the GMC method are discussed, and the latitude‐altitude distribution of the uncertainty of the model‐calculated ozone is presented.
Surface measurements of formaldehyde and formic and acetic acids at a subtropical semiarid site in India
Authors: Khare Puja , Satsangi G. S. , Kumar N. , Kumari K. M. , Srivastava S. S.
Published: February 2004

Vapor phase formaldehyde, formic acid, and acetic acid (HCHO, HCOOH, and CH3COOH) were measured at Dayalbagh, a suburban site in Agra. The average mixing ratios of formaldehyde, formic acid and acetic acid for the entire data set (N=60) were 0.8±0.5 parts per billion by volume (ppbv), 1.4±0.8 ppbv, and 0.9±0.3 ppbv, respectively. Maximum levels of HCHO were observed between 1500 and 1900 hours (LT) possibly because of an increase in in situ formation up to 1600 hours. The extension of maximum concentration up to 1900 hours was probably due to low rates of HCHO removal as a result of diminished insolation and a decrease in OH concentration. Formic and acetic acids showed elevated levels between 1000 and 1600 hours, probably due to active photochemistry and direct emissions. HCOOH and CH3COOH correlated significantly with each other but not with HCHO. This finding suggested the origin of both the acids from the same sources, while HCHO had different pathways. Rates of direct emission, in situ formation, and removal by dry deposition were estimated for both acids. In situ reaction produced more formic acid than acetic acid. Production of acetic acid was seen to be dominated by direct emissions. The production estimates exceed removal by a factor of ≈2.5; these fall within the uncertainty limits.
POAM II retrieval algorithm and error analysis
Authors: Lumpe J. D. , Bevilacqua R. M. , Hoppel K. W. , Krigman S. S. , Kriebel D. L. , Debrestian D. J. , Randall C. E. , Rusch D. W. , Brogniez C. , Ramananahérisoa R. , Shettle E. P. , Olivero J. J. , Lenoble J. , Pruvost P.
Published: February 2004

We present a detailed discussion of the version 5 algorithms used to analyze the Polar Ozone and Aerosol Measurement II (POAM II) solar occultation data. As this version is primarily an ozone and aerosol retrieval, the scope of the paper is limited to these constituents. Forward model algorithms for calculating atmospheric transmittance in the nine POAM II spectral channels are presented, as well as detailed instrument simulation models used to generate synthetic data. Inversion of POAM II data is accomplished in two sequential steps, using the method of optimal estimation. A nonlinear spectral inversion is performed first, which simultaneously inverts the measured slant optical depth profiles in all channels to obtain the separate gas and aerosol optical depth components. Inversion of the slant path line of sight integral then yields altitude profiles of constituent density and aerosol extinction. Examples of both real and simulated retrievals are presented, and comparisons are made between retrievals obtained with the version 5 operational algorithm and an independent algorithm developed at the Laboratoire d'Optique Atmosphérique, University of Lille, Lille, France. A detailed error analysis is also presented, providing estimates of the total random and systematic error budget for the ozone and aerosol retrievals. The results of this analysis indicate random errors of 5% or less in the ozone retrievals in the 10‐ to 50‐km range. Random errors in the retrieved aerosol extinction are estimated to be 10 to 20% in the primary 1060‐nm channel, increasing to 20 to 30% at 352 nm. Total systematic errors are estimated to be less than 5% for ozone and as much as 10 to 15% in the 1060‐nm aerosol extinction and are primarily caused by systematic biases in the National Center for Environmental Prediction (NCEP) temperatures used in the analysis. Analysis of the retrieval averaging kernels shows that under present aerosol loading conditions, aerosol feedback into the ozone retrievals introduces biases of less than 2% at all altitudes.
Heterogeneous chemistry in aircraft wakes: Constraints for uptake coefficients
Authors: Kärcher B.
Published: February 2004

Recent in situ measurements in subsonic and supersonic aircraft plumes show the presence of high aerosol abundances. Given the large initial surface areas of the exhaust particles (volatile aerosols, soot, and ice) of 103–105 μm2 cm−3 or more, heterogeneous processing can potentially become important. Based on an analytical model to predict the temporal evolution of the surface areas, the potential for heterogeneous chemistry during the lifetime of single aircraft wakes is investigated. The model surface areas are constrained by plume observations and compared to numerical simulations of aerosol formation and growth. Efficient heterogeneous processing on volatile aerosols and soot on timescales below 1 day generally requires uptake coefficients ≳0.003–0.007, depending on the specific surface area of soot. For low available surface areas and slow reactions, the lifetime of emitted exhaust species sensitively depends on the wake mixing properties. Shutting off uptake by volatile particles inhibits heterogeneous processing unless high soot surface areas and reaction probabilities are prescribed. Depending on the lifetime of ice contrails, uptake coefficients ≳0.1 are required for rapid uptake of exhaust species on the ice particles. This lower limit becomes relaxed if contrails are long‐lived or develop into persistent cirrus or polar stratospheric clouds, rendering activation of chlorine potentially important. The model is applied to investigate the uptake of gaseous HNO2 and SO2 by the observed particles in the plume of the Concorde in the lower stratosphere.
Self‐similar random fields and rainfall simulation
Authors: Menabde Merab , Seed Alan , Harris Daniel , Austin Geoff
Published: February 2004

The theory of self‐similar random fields is applied to the statistical description and simulation of rainfall. Fluctuations in rainfields measured by a high resolution weather radar covering a 15 km square are shown to satisfy the condition of self‐similarity. The probability density function of the logarithm of the breakdown coefficients (defined as the ratio of two field means, each computed at different resolutions) of the rainfall fluctuation field generally belongs to the class of infinitely divisible distributions. The theoretical framework for scaling self‐similar fields is presented and related to results from alternate frameworks, presented in the literature. A simple procedure for the parameterization and modeling of the experimentally measured probability density function is presented. The obtained generator is then used for rainfall simulation by multiplicative cascades. Simulated results exhibit a good statistical and visual agreement with the measured data.
Detection of tropospheric OH radicals by long‐path differential‐optical‐absorption spectroscopy: Experimental setup, accuracy, and precision
Authors: Hausmann Martin , Brandenburger Uwe , Brauers Theo , Dorn Hans‐Peter
Published: February 2004

This paper describes a newly developed long‐path differential‐optical‐absorption‐spectroscopy instrument used for the measurement of tropospheric OH radicals. The instrument consists of a high resolution echelle spectrometer in conjunction with a multiple‐reflection cell of 38.5 m base length and a UV laser light source that provides a spectral line width of 0.41 nm. Local in situ absorption measurements at total path lengths of either 1.85 or 3.1 km can be performed. The simultaneous observation of six atmospheric OH rotational absorption lines (Q1(2), Q21(2), R2(2), Q1(3), Q21(3), and P1(1)) around 308 nm allows OH measurements with high specificity. A new method to accurately determine the precision and the detection limit of each individual OH measurement data point is presented. Presently, a 2σ‐detection limit of 1.5×106 OH cm−3 is achieved (based on 1.85 km absorption path length and about 6 min integration time), which corresponds to a minimum detectable optical density of 2.5×10−5. The absolute instrumental accuracy was calculated to be better than 6.5%, which emphasizes the qualification of the longpath absorption technique as an absolute method. Examples of field experiments are reported to illustrate the present performance.
Photochemical oxidant formation over southern Switzerland: 1. Results from summer 1994
Authors: Staffelbach T. , Neftel A. , Blatter A. , Gut A. , Fahrni M. , Stähelin J. , Prévôt A. , Hering A. , Lehning M. , Neininger B. , Bäumle M. , Kok G. L. , Dommen J. , Hutterli M. , Anklin M.
Published: February 2004

We present ground‐based and aircraft measurements of photochemically relevant trace gases from the southern part of Switzerland from summer 1994. The region is adjacent to the Po Valley and exhibits the highest ozone concentrations within Switzerland. O3 concentrations of up to 166 parts per billion by volume (ppbv) were measured. Isoprene was 3 ppbv on the ground and 0.3 ppbv at 1000 m altitude on average in the afternoon and dominates the volatile organic compound (VOC) reactivity toward OH at the ground. Measured HONO concentrations of 0.2 ppbv in the afternoon are much higher, as can be explained from gas phase reactions alone. Radical concentrations are derived from steady state calculations using ground‐based measurements in the afternoon. The resulting concentrations for OH, HO2, and RO2 are 3.1×106, 1.1×109, and 1.3×109 molecules cm−3, respectively. Isoprene and NO have the largest influence on the estimated OH concentration, followed by O3, photolysis frequency of O3, and HONO. HO2 and RO2 concentrations are most sensitive to changes in HONO, O3, and photolysis frequency of O3. The estimated radical production is larger than the NOx emissions, suggesting low‐NOx chemistry. We calculated indicators for NOx or VOC sensitivity and show that reduction of NOx emissions would be more efficient in reducing O3 than VOC reduction upwind of the measurement site.
Large‐scale variability of wind erosion mass flux rates at Owens Lake: 1. Vertical profiles of horizontal mass fluxes of wind‐eroded particles with diameter greater than 50 μm
Authors: Gillette Dale A. , Fryrear D. W. , Xiao Jing Bing , Stockton Paul , Ono Duane , Helm Paula J. , Gill Thomas E. , Ley Trevor
Published: February 2004

A field experiment at Owens (dry) Lake, California, tested whether and how the relative profiles of airborne horizontal mass fluxes for >50‐μm wind‐eroded particles changed with friction velocity. The horizontal mass flux at almost all measured heights increased proportionally to the cube of friction velocity above an apparent threshold friction velocity for all sediment tested and increased with height except at one coarse‐sand site where the relative horizontal mass flux profile did not change with friction velocity. Size distributions for long‐time‐averaged horizontal mass flux samples showed a saltation layer from the surface to a height between 30 and 50 cm, above which suspended particles dominate. Measurements from a large dust source area on a line parallel to the wind showed that even though the saltation flux reached equilibrium ∼650 m downwind of the starting point of erosion, weakly suspended particles were still input into the atmosphere 1567 m downwind of the starting point; thus the saltating fraction of the total mass flux decreased after 650 m. The scale length difference and ratio of 70/30 suspended mass flux to saltation mass flux at the farthest down wind sampling site confirm that suspended particles are very important for mass budgets in large source areas and that saltation mass flux can be a variable fraction of total horizontal mass flux for soils with a substantial fraction of <100‐μm particles.
A scalar three‐dimensional spectral model with variable anisotropy
Authors: Dalaudier Francis , Gurvich Alexandre S.
Published: February 2004

This paper introduces a simple three‐dimensional (3‐D) spectral model for scalar fluctuations with variable anisotropy. This heuristic model is useful in the study of statistical properties of stably stratified flows. It goes a step further than existing analogues by explicitly taking into account variation of anisotropy with the size of the fluctuations. The spectral model is specified by its isovalue surfaces and by its generalized energy spectrum. These surfaces are ellipsoids, (variably) elongated in the vertical direction. The model depends on two arbitrary functions of the spectral parameter. The possibilities of such variable anisotropy models are demonstrated by choosing specific functions. The choice was guided by maximal simplicity requirement and by the “tradition” of turbulent studies which heavily uses “power law” functions. These examples show how quantitative predictions are obtained using such 3‐D spectral models. They were selected in order to display characteristics that depend explicitly on the variable anisotropy and that could not have been obtained with previous models. The first example is the calculation of the one‐dimensional spectrum of temperature for arbitrary direction of measurement and the natural prediction of a change in slope for quasi‐horizontal spectra, while the oblique and vertical spectra retain the same slope. The second example is to account for radar echo aspect sensitivity, with angular contrast depending on the radar wavelength. The main advantages of the present model are its great flexibility provided by the use of two arbitrary functions and also the (relative) simplicity of its mathematical formulation.
On using inverse methods for resolving emissions with large spatial inhomogeneities
Authors: Chang Michael E. , Hartley Dana E. , Cardelino Carlos , Haas‐Laursen Danielle , Chang Wen‐Ling
Published: February 2004

We apply an inverse method to estimate the carbon monoxide emissions in Atlanta, Georgia. The resultant carbon monoxide inventory is unrealistically characterized by temporal oscillations on the frequency of 1 hour. We suspect that the difficulty in deducing the emissions is due to inhomogeneities in the spatial distribution of the emissions. In several controlled experiments we reproduce the oscillations by introducing relatively small errors into the spatial distribution of the emission inventory. In similar experiments with isoprene in which the emissions are more homogeneous, we do not find this problem. These results are discussed in the context of previous inverse studies of carbon monoxide and isoprene.
Biogenic isoprene emission: Model evaluation in a southeastern United States bottomland deciduous forest
Authors: Geron Christopher D. , Nie Dalin , Arnts Robert R. , Sharkey Thomas D. , Singsaas Eric L. , Vanderveer Peter J. , Guenther Alex , Sickles Joe E. , Kleindienst Tad E.
Published: February 2004

Isoprene is usually the dominant natural volatile organic compound emission from forest ecosystems, especially those with a major broadleaf deciduous component. Here we report isoprene emission model performance versus leaf and canopy level isoprene emission measurements made at the Duke University Research Forest near Chapel Hill, North Carolina. Emission factors, light and temperature response, canopy environment models, foliar mass, leaf area, and canopy level isoprene emission were evaluated in the field and compared with model estimates. Model components performed reasonably well and generally yielded estimates within 20% of values measured at the site. However, measured emission factors were much higher in early summer following an unusually dry spring. These decreased later in the summer but remained higher than values currently used in emission models. There was also a pronounced decline in basal emission rates in lower portions of the canopy which could not be entirely explained by decreasing specific leaf weight. Foliar biomass estimates by genera using basal area ratios adjusted for crown form were in excellent agreement with values measured by litterfall. Overall, the stand level isoprene emissions determined by relaxed eddy accumulation techniques agreed reasonably well with those predicted by the model, although there is some evidence for underprediction at ambient temperatures approaching 30°C, and overprediction during October as the canopy foliage senesced. A “Big Leaf” model considers the canopy as a single multispecies layer and expresses isoprene emission as a function of leaf area rather than mass. This simple model performs nearly as well as the other biomass‐based models. We speculate that seasonal water balance may impact isoprene emission. Possible improvements to the canopy environment model and other components are discussed.
The role of convective processes over the Zaire‐Congo Basin to the southern hemispheric ozone maximum
Authors: Jenkins Gregory S. , Mohr Karen , Morris Vernon R. , Arino Olivier
Published: February 2004

During October, satellite measurements show that there is a region of elevated tropospheric ozone over the tropical southern Atlantic Ocean. The cause of the high ozone concentrations has been related to biomass burning in South America and Africa. In this paper, we present evidence from satellite sources, European Center for Medium‐Range Weather Forecast analyses, and a mesoscale simulation during October, suggesting that afternoon and evening deep convection in central Africa is responsible for some of the abnormally high concentrations of ozone in the Tropical South Atlantic which extend southeast over southern Africa into the Indian Ocean. The mechanisms for enhancing tropospheric O3 includes (1) the removal of ozone, NOx, and hydrocarbon rich air from fires in eastern Africa within the planetary boundary layer to the middle and upper troposphere by deep convection; (2) the production Of NOx from lightning associated with mesoscale convective systems and the subsequent photochemical production of O3, and (3) the entrainment of O3 rich air from the lower stratosphere into the upper troposphere by deep convection. During the next few years an international field campaign in central Africa (the experiment for regional sources and sinks of oxidants‐EXPRESSO), global lightning data, and the launch of the Tropical Rainfall Measuring Mission (TRMM) will help to identify the relative importance of each of the processes over central Africa that could be responsible for high O3 concentrations over the tropical south Atlantic.