bluuebunny/crossref_metadata_2025 huggingface dataset:
Estimation of sampling errors and scale parameters using two‐ and three‐dimensional rainfall data analyses
Authors: Soman Vishwas V. , Valdés Juan B. , North Gerald R.
Published: February 2004

This paper presents the analysis of rainfall data based on radar echoes collected in the vicinity of Darwin, Australia, during special observation periods in 1988. The study was conducted to estimate the scale parameters (such as timescale and length scale) present in the rainfall data, which are important in parameterizing many stochastic rainfall models. Another equally important issue addressed here is that of sampling errors in the rainfall observations from space. To address these issues, precipitation analyses were conducted in two and three dimensions. To perform two‐dimensional analyses, precipitation fields were averaged along one dimension (i.e., x, y, or t) at a time. Three‐dimensional analyses were performed on the complete time series of temporal‐hourly averaged spatially distributed observations. Important results obtained from the two‐dimensional analyses include isotropy of precipitation fields in space, variations in the rainfall data primarily in time, and length scales of 50 km (for Darwin I) and 52 km (for Darwin II) in both (i.e., north‐south and west‐east) directions. Length scales were estimated using the results from two‐dimensional analyses of the data. Time‐domain correlograms obtained for the time series of area‐averaged precipitation were used to estimate the timescales (6 hours for Darwin I and 8 hours for Darwin II). These results could be used in simulation studies using various stochastic rainfall models. The estimates of space‐time spectra obtained in three‐dimensional analyses were used to evaluate the sampling errors. The sampling errors thus estimated using these data sets were quite significant (about 25% to 30% for a 12‐hour sampling interval). Sampling errors were as high as 65% for Darwin I and 45% for Darwin II for a 24‐hour sampling time interval, which is a possibility if the Defense Meteorology Satellite Program (DMSP) satellite is used. These results are useful in satellite mission planning activities.
Long‐term observation of nitrate radicals at the Tor Station, Kap Arkona (Rügen)
Authors: Heintz F. , Platt U. , Flentje H. , Dubois R.
Published: February 2004

Long‐term observation of the trace gases NO2, ozone, and nitrate radicals (NO3) at a rural site in the Baltic Sea (near Kap Arkona, island Rügen) using differential optical absorption spectroscopy (DOAS) are presented here. The time series of these species cover more than 14 months of data. Additionally, meteorological data were taken from the Deutscher Wetterdienst station at Kap Arkona. The average nighttime NO3 concentration was determined at 7.8 ppt. Maximum lifetimes of more than 5000 s were observed, but average NO3 lifetimes are close to 250 s. As nitrate radicals are expected to play an important role in the nonphotochemical conversion of NOx to HNO3, long‐term observations offer a key for investigation of possible sink mechanisms of NO3 molecules mediated by both homogeneous and heterogeneous reactions. Analysis of the data shows that the NO3 lifetime is inversely proportional to the NO2 concentration, thus suggesting that the removal of N2O5 is actually the dominating NO3 loss process. The mean N2O5 concentration from this long‐term measurement was calculated at 1 ppb with an N2O5 lifetime between 1000 s and 20000 s covering 90% of the data.
Charging in ice‐ice collisions as a function of the ambient temperature and the larger particle average temperature
Authors: Avila Eldo E. , Varela Guillermo G. Aguirre , Caranti Giorgio M.
Published: February 2004

Measurements of charge transfer between ice particles are reported. The ambient temperature and the average graupel temperature are presented as an alternative pair of variables describing the charge transferred between ice particles during a collision. These variables are alternative to the generally used air temperature and liquid water content. A new charging diagram is also presented here. The results suggest that other variables would be necessary to better describe the phenomena. Some of the current hypotheses on charge transfer are also discussed. The data gathered in the present experiment correspond to collisions made in a wind tunnel between a cylinder growing by riming and ice spheres of 100 μm in diameter; the velocity was between 5 and 6 m s−1. The ambient temperature was between −8° and −24°C. The target temperature was adjusted with a Peltier element keeping the target always equal or above than the ambient temperature. The implications of these results to the thunderstorm electrification are discussed.
Assessing dependence among weights in a multiplicative cascade model of temporal rainfall
Authors: Cârsteanu Alin , Foufoula‐Georgiou Efi
Published: February 2004

“Classical” multifractal analysis shows, with a good degree of confidence, that the fit of multiplicative cascades to rainfall time series is appropriate, at least from the point of view of preserving the f(α) spectrum of scaling exponents. However, basing the analysis only on the f(α) curve allows only limited discrimination between different types of cascade models; thus other descriptors with more discriminating power are needed. Also, the question of whether cascades with independent weights are appropriate for rainfall remains unanswered and needs to be addressed. In the present work we address this question and provide an assessment of the dependence structure among weights in a multiplicative cascade model of temporal rainfall. We introduce a quantity based on oscillation coefficients (describing how many of the total n‐tuples of the series are obeying a certain pattern up‐down‐up etc.), and find that this quantity is invariant under aggregation for a multiplicative cascade model and has the ability to depict the presence and type of correlation in the weights of the cascade generator. Application of this development to high‐resolution temporal rainfall series consistently suggests the need for negative correlation in weights of a binary multiplicative cascade in order to match the oscillation coefficient structure of rainfall. This is interpreted as an indication of dependence in the splitting mechanisms of intensities cascading over successive scales and might have important implications for rainfall modeling and process understanding.
Summer and spring ozone profiles over the North Atlantic from ozonesonde measurements
Authors: Oltmans S. J. , Levy H. , Harris J. M. , Merrill J. T. , Moody J. L. , Lathrop J. A. , Cuevas E. , Trainer M. , O′Neill M. S. , Prospero J. M. , Vömel H. , Johnson B. J.
Published: February 2004

Ozone profiles obtained by near‐daily ozonesonde observations during campaigns at several sites in the North Atlantic are used to construct time‐height cross sections of ozone concentration through the troposphere. Strong day‐to‐day ozone variability on the scale of synoptic meteorological disturbances is found both in the spring and in the summer throughout much of the troposphere. Layers of high ozone concentration (∼100 ppb) are frequently seen in the middle and upper troposphere and are invariably associated with transport characteristics that strongly support a stratospheric source for these layers. Regions of low ozone (<40 ppb) are seen in the middle and upper troposphere associated with higher relative humidity. The connection of these events with low surface mixing ratios suggests that convective processes mix air low in ozone up through the troposphere. Vertical layering of ozone mixing ratio, which is seen at all of the observing locations, is a result of differing sources of air in the different layers.
Comparison of tunable diode laser and long‐path ultraviolet/visible spectroscopic measurements of ambient formaldehyde concentrations during the 1993 OH Photochemistry Experiment
Authors: Harder J. W. , Fried Alan , Sewell Scott , Henry Bruce
Published: February 2004

Two different spectroscopic techniques for measuring atmospheric concentrations of formaldehyde were compared during a 6‐week field study in the mountains 17 km west of Boulder, Colorado, in August and September 1993. A long‐path ultraviolet/visible (UV/Vis) absorption spectrometer and an IR tunable diode laser absorption spectrometer (TDLAS) were the two instruments employed. The former measured ambient formaldehyde levels over a 10.3 km open path (20.6 km total path) extending between Fritz Peak Observatory and Idaho Hill, while the latter measured in situ levels at the Idaho Hill site. In addition to utilizing different spectral regions, both instruments employed different sampling and calibration approaches. Because of the closer proximity to anthropogenic sources the long‐path UV/Vis instrument generally detected higher formaldehyde concentrations than the TDLAS system at all times during the day. Averaged over the entire study for all wind regimes, the former resulted in formaldehyde concentrations 15% higher than the latter. The mean and median formaldehyde concentration measured by both instruments was around 1.5 ppbv and individual 5‐min averages varied from a maximum of about 5 ppbv down to levels 0.6 ppbv. However, during periods of strong westerly flow where anthropogenic and meteorological influences are minimized, both techniques were in agreement to within 5%. This regime, which constitutes 19% of the total mutual data set, resulted in a continental background formaldehyde concentration of 0.92±0.16 ppbv. The present instrument comparison thus bridges the gap in formaldehyde instrument comparison studies between those in the background free troposphere and those in polluted urban regimes. In addition to providing further confidence in both measurement techniques, the present comparison study also provided a valuable data set necessary for advancing our understanding of tropospheric oxidation mechanisms. A set of guidelines for future comparisons of long‐path and in situ measurements of formaldehyde at this site are also discussed.
A compilation of data on lead 210 concentration in surface air and fluxes at the air‐surface and water‐sediment interfaces
Authors: Preiss Nicolas , Mélières Marie‐Antoinette , Pourchet Michel
Published: February 2004

A 210Pb database has recently been constructed and is now available. This base includes approximately 800 210Pb measurements of concentration in air at the Earth's surface, together with deposition flux both at the atmosphere‐Earth and water‐sediment interfaces. Here the data are analyzed and summarized. The atmospheric data (concentration and deposition flux) are presented for the different geographical areas when sufficient measurements are available. The trends are discussed in terms of mechanisms (sources, atmospheric circulation, and climate]. Water‐sediment data are classified into four types of water reservoirs which differ in their sedimentation mechanisms or in their in situ 210Pb production. The corresponding histograms are compared with the air‐surface flux histogram. This database points out the complete lack of information in some large areas of the planet.
Role of coherent structures in the stochastic‐dynamic variability of precipitation
Authors: Kumar Praveen
Published: February 2004

Using time‐frequency‐scale elements obtained from wavelet packets as a basis, we describe a broad framework of analysis which can be used to reveal the essential dynamics, identified as coherent structures, of precipitation. We show that the matching pursuits algorithm with nearly symmetric orthogonal wavelets provides an optimal representation of the inner structure of rainfall time series and can describe features that range from scales of isolated singularity to synoptically forced large‐scale features. We describe the analysis of time series of several storms and show that there exist distinct scales of variation identifiable with rain cell and synoptic‐scale activity, which is in contradistinction to the scale invariance hypothesis.
Sprite observations above the U.S. High Plains in relation to their parent thunderstorm systems
Authors: Lyons Walter A.
Published: February 2004

Transient luminous events (sprites, blue jets, elves) above large mesoscale convective systems (MCSs) over the U.S. High Plains have been routinely monitored from the Yucca Ridge Field Station near Fort Collins, Colorado using ground‐based low‐light video systems. We analyzed 36 sprites above the Nebraska MCS of August 6, 1994. The results lend further support to the hypothesis that sprites are almost uniquely associated with positive cloud‐to‐ground (+CG) lightning flashes. Sprite‐associated +CGs also averaged substantially larger peak currents than the remaining +CG population (81 kA versus 30 kA in this storm system). There is some evidence that sprite‐associated +CGs also have higher stroke multiplicity. This study yields no evidence of sprites associated with negative CG events. In the central United States an additional requirement appears to be that the parent MCS has a contiguous radar reflectivity area exceeding 20–25,000 km2. The majority of the sprites occur above the large stratiform precipitation region and not the high‐reflectivity convective core of the MCS. Triangulation of a limited number of paired images (from September 7, 1994) suggests that the sprite is generally centered within 50 km of the parent +CG. Assuming the +CG provides the range, single‐image photogrammetric analyses provide estimates of the maximum vertical extent of the sprites. For this storm the sprite tops averaged 77 km with a maximum of 88 km. The bases averaged 50 km but with a few sprite tendrils extending as low as 31 km.
AVHRR remote sensing of aerosol optical properties in the Persian Gulf region, summer 1991
Authors: Nakajima Teruyuki , Higurashi Akiko
Published: February 2004

Satellite remote sensing is studied in this paper for retrieving aerosol parameters, i.e., aerosol optical thickness at 0.5 μm τ0.5, size exponent p, and absorption index κ, from channel 1 and 2 radiances of the NOAA 11 advanced very high resolution radiometer (AVHRR) in the Persian Gulf region in the summer of 1991. Results of the remote sensing are compared with ground‐based values obtained from solar radiation measurements with a sunphotometer and a pyranometer in Bushehr, Iran. It is found that tuning the calibration coefficients of AVHRR and introduction of a suitable aerosol absorption are needed for a good agreement between satellite‐derived and ground‐based values of τ0.5. The aerosol absorption index is also retrieved with two methods, i.e., simultaneous analyses with ground‐based τ0.5 and p, and the Fraser‐Kaufman method. Retrieved values of the aerosol single‐scattering albedo are ω≈0.75 and 0.70 from the two methods, respectively, for the Kuwait oil‐fire smoke layer. The single scattering albedo of another case, which is regarded as a sand‐dust layer, is estimated to be ω≈0.76 with the Fraser‐Kaufman method.
Sensitivity of paleoclimate simulation results to season definitions
Authors: Joussaume Sylvie , Braconnot Pascale
Published: February 2004

According to the Milankovitch theory, slow variations of the Earth's orbital parameters change the amplitude of the seasonal cycle of insolation and are considered to be the main forcing mechanism of glacial‐interglacial cycles. Because of the precession and changes in eccentricity the length of seasons also varies. No absolute phasing is then possible between the insolation curves of two different periods. Various solutions to compare different periods have been given either for astronomical computations [e.g., Berger and Loutre, 1991; Laskar et al., 1993] or for model simulations [e.g., Kutzbach and Otto‐Bliesner, 1982; Mitchell et al., 1988], but the sensitivity of model results to the different possible solutions has never been quantified. Our results, based on simulations of the last interglacial climate, 126 kyr B.P., where changes in the length of the seasons are large, clearly show that phase leads or lags between the various solutions used introduce biases in the analysis of insolation and climate change of the same order of magnitude as the Milankovitch forcing. Our main conclusions are that (1) when comparing various model simulations, the date of the vernal equinox (i.e., the phasing of the seasonal cycle of insolation) as well as the definition of seasons must be the same for all models in order to avoid artificial differences; (2) seasons based on astronomical positions are preferred to seasons defined with the same lengths as today, since they better account for the phasing of insolation curves. However, insolation is not the only forcing in most atmospheric general circulation model simulations. We also discuss the impact of the calendar hidden behind the definition of the seasonal cycle of the other boundary conditions, such as sea ice or sea surface temperatures.
Evolution of the infrared properties of the Mount Pinatubo aerosol cloud over Laramie, Wyoming
Authors: Massie Steven T. , Deshler Terry , Thomas Gary E. , Mergenthaler John L. , Russell James M.
Published: February 2004

Particle size distributions measured from May 1991 to April 1994 over Laramie, Wyoming, are used in Mie calculations to model the wavelength dependence and the time evolution of the extinction, single‐scattering albedo, and asymmetry parameters of stratospheric sulfate particles. The calculations cover the time period from 45 days before to 1080 days after the eruption of Mt. Pinatubo. The time evolution of the particle size distribution parameters and the evolution of the infrared extinction are examined concurrently and interrelated in terms of the variables present in the Mie equation for the extinction coefficient. The calculations are validated by comparing the theoretical model values to extinction measurements obtained by the Cryogenic Limb Array Etalon Spectrometer (CLAES), Improved Stratospheric and Mesospheric Sounder (ISAMS), Halogen Occultation Experiment (HALOE), and Stratospheric Aerosol and Gas Experiment (SAGE II) experiments. The Wyoming size distributions are also used to derive simple mathematical expressions from which area and volume densities can be estimated using CLAES extinction measurements.
UV‐visible absorption cross sections of gaseous Br2O and HOBr
Authors: Rattigan O. V. , Lary D. J. , Jones R. L. , Cox R. A.
Published: February 2004

The absorption cross‐section of gaseous HOBr was determined over the wavelength range 235 to 430 nm with a spectral resolution of 0.6 nm full width at half maximum (FWHM) using a diode array spectrometer. The spectrum of HOBr shows two main absorption bands with maxima near 282 nm (σ = (3.1 ± 0.4) × 10−19 cm2 molecule−1 and 350 nm (σ = 12.5 ± 1.6) × 10−20 cm2 molecule−1) extending out to 430 nm. The absorption cross‐sections in the first absorption band are in good agreement with a recent determination; the cross‐sections in the second band however, are approximately a factor of 2.5 larger than previously determined. In addition we provide evidence in support of a weak band in HOBr around 440 nm (σ ≈ 7.5 × 10−21 cm2 molecule−1) as observed by Barnes et al. [1996]. The absorption cross‐section of Br2O, which was used to prepare HOBr, was determined over the wavelength range 230 to 750 nm. The spectrum shows four absorption bands with maxima at 314 nm (σ = (2.1 ± 0.3) × 10−18 cm2 molecule−1), 350 nm (σ = (1.9 ± 0.2) × 10−18 cm2 molecule−1), 520 nm (σ = (4.4 ± 0.5) × 10−20 cm2 molecule−1), and 665 nm (σ = (6.2 ± 0.9) × 10−20 cm2 molecule−1). The visible bands at 520 nm and 660 nm have not been observed previously. The equilibrium constant, for the reaction Br2O + H2O ⇔ 2HOBr was determined to be 0.037 ± 0.004 at 298 K. Measurement of the equilibrium constant as a function of temperature enabled values for ΔH298 K = (13.0 ± 0.5) kJ mol−1 and ΔS298 K = (16 ± 2) J mol−1 K−1 to be determined. The absorption cross‐section data for HOBr have been used in a photochemical box model to investigate the significance of these results in the lower stratosphere. The model results are compared with observations during a recent Stratospheric Photochemistry, Aerosols and Dynamics Expedition (SPADE) and show that the revised HOBr cross‐section, coupled to the rapid heterogeneous conversion of BrONO2 to HOBr, can account quantitatively for the abrupt morning rise in HOx.
Multi‐instrument zenith observations of noctilucent clouds over Greenland on July 30/31, 1995
Authors: Hecht James H. , Thayer Jeffrey P. , Gutierrez David J. , McKenzie David L.
Published: February 2004

Results are presented for zenith observations of a noctilucent cloud (NLC) display over the Sondrestrom atmospheric research facility near Kangerlussuaq, Greenland, on July 30/31, 1995. The observations were made with a Rayleigh lidar, which measured the NLC particle volume backscatter coefficient, and with a UV spectrograph, which measured the intensity and degree of linear polarization of solar light scattered from the NLC. The intensity and polarization measurements were made at solar depression angles of −1.8° to −4.6°. These data allowed the first simultaneous observation from the ground of the altitude and thickness of the NLC and of the radius of the NLC particles. The NLC was found to be between 86 and 84 km in altitude with a thickness of 1 to 2 km and the NLC particles had a radius at or below 0.07 μm. We also report the first observation of an NLC sublimating due to the passage of an AGW through the 85‐km altitude region. These observations are generally in agreement with models of noctilucent clouds.
A space‐time theory of mesoscale rainfall using random cascades
Authors: Over Thomas M. , Gupta Vijay K.
Published: February 2004

Following a brief review of relevant theoretical and empirical spatial results, a theory of space‐time rainfall, applicable to fields advecting without deformation of the coordinates, is presented and tested. In this theory, spatial rainfall fields are constructed from discrete multiplicative cascades of independent and identically distributed (iid) random variables called generators. An extension to space‐time assumes that these generators are iid stochastic processes indexed by time. This construction preserves the spatial structure of the cascades, while enabling it to evolve in response to a nonstationary large‐scale forcing, which is specified externally. The construction causes the time and space dimensions to have fundamentally different stochastic structures. The time dimension of the process has an evolutionary behavior that distinguishes between past and future, while the spatial dimensions have an isotropic stochastic structure. This anisotropy between time and space leads to the prediction of the breakdown of G. I. Taylor's hypothesis of fluid turbulence after a short time, as is observed empirically. General, nonparametric, predictions of the theory regarding the spatial scaling properties of two‐point temporal cross moments are developed and applied to a tracked rainfall field in a case study. These include the prediction of the empirically observed increase of correlation times as resolution decreases and the scaling of temporal cross moments, a new finding suggested by this theory.
Long‐lived tracer transport in the Antarctic stratosphere
Authors: Strahan S. E. , Nielsen J. E. , Cerniglia M. C.
Published: February 2004

Recent observations made by the Cryogenic Limb Array Etalon Spectrometer (CLAES) on the Upper Atmosphere Research Satellite (UARS) indicate that during the austral fall, CH4 zonal mean isopleths in the Antarctic vortex appear to descend more rapidly than those of N2O. How is this possible in an isolated region such as the vortex when photochemical sinks are insignificant? To understand these observations, we have run a simulation of the 1992 austral fall using the Goddard Global Spectral Mechanistic Model (GSMM) and the three‐dimensional Chemistry and Transport Model (CTM). Model tracer fields show good agreement with the observations over a 4‐month period beginning in mid‐February. Both the observations and the simulation show that the apparent differential descent occurs during periods of wave activity, while during quiet vortex periods N2O and CH4 descend at approximately the same rate. To understand how wave activity may drive the observed differences between N2O and CH4 behavior, we calculate the terms of the zonal mean tracer tendency equation in the transformed Eulerian Mean (TEM) formulation of Andrews et al. [1987]. Analysis of the terms of the tracer tendency equation shows that each tracer's response to eddy forcing is the source of the apparent differential descent. While descent is the dominant motion inside the vortex, horizontal mixing becomes significant during periods of wave activity and differences in the tracers' meridional gradients affect the relative amounts of each tracer transported into the vortex. This analysis demonstrates the relationship between wave activity, eddy transport, and tracer mixing ratios inside the vortex throughout the fall. In addition, CLAES observations deep in the vortex (70°–80°S) show gradually increasing CH4 mixing ratios from March to September, implying the importance of eddy‐driven mixing within the vortex in winter.
Spectrometric inflight measurement of aircraft exhaust emissions: First results of the June 1995 campaign
Authors: Haschberger P. , Lindermeir E.
Published: February 2004

A customized Fourier transform infrared spectrometer onboard an aircraft performs in‐flight measurements of the jet engine's exhaust emissions. For this purpose the instrument is mounted in the aircraft's cabin receiving infrared radiation emitted by the hot jet about 1 m downstream from the nozzle exit. From the measured infrared spectra the concentrations and emission indices of the gas species NO, CO, H2O, and CO2 and the gas temperature are calculated. The estimated accuracy of the measurements is in the range of 5 to 20%. The results reveal the high precision of the acquired data which are compared to model calculations.
Dispersion of aircraft exhausts in the free atmosphere
Authors: Dürbeck Tilman , Gerz Thomas
Published: February 2004

The effective diffusion of aircraft emissions and the growth of plume cross‐sections at cruising altitudes of commercial airliners are examined by means of large‐eddy simulation in a domain of size 4.3 × 1.1 × 1.1 km3. It is assumed that aircraft‐induced turbulence has ceased and that the exhaust plumes can be represented by line sources with Gaussian cross‐sections. On the basis of a previous study where the effective diffusion in a stratified atmosphere with negligible wind shear was investigated [Dürbeck and Gerz, 1995], the work is extended here to situations with shear rates typical for the free atmosphere ranging between 0.001 s−1 and 0.007 s−1, covering bulk Richardson numbers Ri between 0.13 and 360. Along a flight track the atmosphere is usually only weakly turbulent (Ri > 1); an aircraft encounters strong but highly intermittent turbulence (Ri < 0.25) only occasionally. Both situations are examined here. It is found that when Ri > 1, shear has no significant influence on horizontal or vertical effective diffusivities which lay, for a stratification of 0.019 s−1, in the range of 15 m2s−1 ≤ Dh ≤ 23 m2s−1 and 0.15 m2s−1 ≤ Dv ≤ 0.18 m2s−1, respectively. But shear in combination with diffusion enlarges the cross‐section of an exhaust plume and increases the entrainment rate. When Ri ≈ 0.1, the diffusivity Dh grows by a factor of about 3 and Dv by a factor of about 20 compared to shearfree situations. With increasing shear and time, only Dv and shear control plume sizes and entrainment rates, whereas Dh has a diminishing influence. The results agree very well with data from recent in situ flight measurements in the North Atlantic flight corridor in the tropopause region.
On the initiation of lightning discharge in a cloud: 1. The high field regions in a thundercloud
Authors: Nguyen Manh Duc , Michnowski Stanislaw
Published: February 2004

A question of the existence of high electric field regions in thunderclouds and possible local enhancements of this field is discussed. The effects of precipitation particle motions on the local electric field distribution are estimated. It is shown that the high field regions, of the order of 300–400 kV m−1 or more, can appear within a cloud on the boundary of large charge centers. The higher transient field needed for lightning initiation can appear in small regions between the charge centers, especially when an advancing draft or precipitation is coming. The very high field regions have not been detected because of their small space‐time scale.
Cross‐tropopause mixing of ozone through gravity wave breaking: Observation and modeling
Authors: Lamarque J.‐F. , Langford A. O. , Proffitt M. H.
Published: February 2004

In the companion paper [Langford et al., this issue] clear signatures of ozone modulation by gravity waves in the lower and middle troposphere have been described from lidar observations over Fritz Peak Observatory (39.9°N, 105.3°W) during September 3–4, 1993, and analyzed using a linear model. It is emphasized in that paper that the linear analysis breaks down at the tropopause level. The purpose of this paper is to interpret the ozone observation in the upper troposphere using a high‐resolution mesoscale model and analyze the physical processes responsible for the structures in the upper troposphere and lower stratosphere. In particular, it is shown that topographically excited gravity waves that break at the tropopause level are responsible for an irreversible exchange of ozone from the stratosphere to the troposphere.
Some long‐run properties of rainfall records in Italy
Authors: Montanari Alberto , Rosso Renzo , Taqqu Murad S.
Published: February 2004

Six rainfall data time series, collected in various sites in Italy, are analyzed in order to determine whether a linear trend or long memory is present. Various techniques for estimating the intensity of long memory are applied, including the rescaled range statistic, the aggregated variance method, the periodogram method and maximum likelihood. A modified variance‐type estimator is used in order to detect long memory even when some types of nonstationarity are potentially present. The results indicate that a decreasing trend, though not statistically significant, is present in every record, and that long memory is significant in only two series.
Laboratory measurements of mineral dust scattering phase function and linear polarization
Authors: West Robert A. , Doose Lyn R. , Eibl Andrew M. , Tomasko Martin G. , Mishchenko Michael I.
Published: February 2004

With the goal of improving our understanding of how small mineral dust particles scatter light at visible and near‐infrared wavelengths, we measured the scattering phase function and linear polarization of small mineral dust particles over the scattering angle range 15°–170° at three wavelengths (0.47, 0.652, and 0.937 μm). Particle samples were obtained from Duke Scientific Corp., and include aluminum oxide, silicon carbide, aluminum silicate, antimony oxide, calcium carbonate, and cerium oxide. Particle equivalent‐sphere radii range from a few tenths of a micron to about 10 μm. The particles were injected into a laboratory chamber, where they scattered light as they fell through the air. They were collected on a scanning electron micrograph (SEM) substrate. Particle shapes and sizes were then measured from the SEM images. We compare measured phase functions with those calculated for spheroids with a distribution of axial ratios and sizes, random orientation, and refractive index 1.53+0.008i [Mishchenko et al., this issue]. Two of the samples (one of which has a refractive index close to that used in theoretical computations) produced scattering phase functions that were quite similar to those for spheroids. Two samples produced phase functions whose variation between 15° and 170° was much less than that for the spheroids or for the other samples. We suspect this difference may be due to the very high refractive index of those particles, although differences in particle microstructure may also be important. Two samples produced positive linear polarization which had a single broad maximum near 100° scattering angle, and a magnitude greater than 40% at some wavelengths. Two samples had generally positive linear polarization but a more complicated structure, and two samples produced mostly negative polarization whose amplitude was small. We do not have numerical results for the appropriate refractive index and size parameter with which to compare the polarization measurements. We hope the questions raised by this work will stimulate additional effort to develop and test numerical codes for scattering by nonspherical particles.
Application of infrared interferometer spectrometer clear sky spectral radiance to investigations of climate variability
Authors: Iacono Michael J. , Clough Shepard A.
Published: February 2004

An investigation of clear sky spectral radiances and their applicability as a diagnostic for climate variability is described. Global observations of outgoing longwave radiation during 1970 from the infrared interferometer spectrometer (IRIS) aboard Nimbus 4 cover nearly a full annual cycle, and the spectral content of the data provides unique information for examining regional and seasonal variations of spectral radiance. The IRIS radiances have been validated against a line‐by‐line radiative transfer model and are found to compare favorably with calculated radiances. A brightness temperature threshold technique is used to separate clear and cloudy spectra, and seasonal means of clear sky spectra are analyzed for tropical and northern midlatitude ocean areas. Brightness temperature standard deviations are also examined spectrally. Values of 1–2 K in the tropics and 2–3 K at midlatitudes in the 800–1200 cm−1 window region are consistent with observed ocean temperature variability. Spectral features in the standard deviations reflect the variation of surface temperature, tropospheric temperature, and water vapor in the tropics and the increased variability of ozone during winter in the northern hemisphere. Spectral differences between seasonal and annual mean outgoing radiance are associated with variations in atmospheric parameters, and a linear retrieval algorithm is used to quantify these changes in the tropics. Retrieved seasonal sea surface temperature (SST) differences are typically within 0.7 K of the observed SST differences. Interseasonal water column variations during this annual cycle are 5–10% over the tropical Pacific and Atlantic and 10–20% over the equatorial Indian Ocean. In general, the retrieved seasonal changes in temperature and water vapor parameters are consistent with the known conditions of the 1970 tropical ocean and atmosphere. These variations are detectable as signatures in outgoing spectral radiances and provide significant information relevant to climate change.
Long‐term daily monitoring of Saharan dust load over ocean using Meteosat ISCCP‐B2 data: 2. Accuracy of the method and validation using Sun photometer measurements
Authors: Moulin C. , Dulac F. , Lambert C. E. , Chazette P. , Jankowiak I. , Chatenet B. , Lavenu F.
Published: February 2004

The accuracy of a method for long‐term monitoring of the desert aerosol optical thickness over the oceans using Meteosat low‐resolution images, presented in a companion paper, is assessed. We present Sun photometer measurements of aerosol optical thickness and Angström wavelength exponent obtained in 1986–1994 at different sites and seasons in the tropical Atlantic and northwestern Mediterranean. Results suggest that in the absence of dust outbreak the optical effects of the marine aerosol are dominated by continental anthropogenic sulphates in the Mediterranean Sea and by continental desert dust in the tropical Atlantic. We rely on this data set to constrain the desert aerosol model used in the Meteosat data inversion. We obtain the best agreement between Meteosat‐ and Sun‐photometer‐derived aerosol optical thickness with a size distribution typical of background desert aerosol and a refractive index of 1.50 ‐ i 0.010. The main theoretical uncertainties on the desert aerosol optical thickness estimated from Meteosat are due to the sensor calibration and to the radiometric sensitivity. Comparison of Meteosat‐derived estimates of the desert aerosol optical thickness with independent Sun photometer measurements exhibits a maximum dispersion of 25%.
Interannual variations of the quasi‐16‐day oscillation in the polar summer mesospheric temperature
Authors: Espy P. J. , Stegman J. , Witt G.
Published: February 2004

Nighttime measurements of the hydroxyl Meinel (4,2) rotational band have been used to infer the mesospheric temperature over Scandinavia from June to August during the years 1992–1995. While the nightly averaged temperatures show a statistically significant, quasi‐16‐day oscillation in the 1992 and 1994 summer data, none is observed during 1993 and 1995. When present, the period, amplitude, and temporal behavior of this oscillation agree with both model predictions and previous wind measurements of the (1,3) Rossby normal mode in the summer mesosphere. Thus this temperature oscillation appears to correspond to the thermal signature of the 16‐day Rossby mode. Its appearance in the summer mesosphere is shown to occur when the oscillating zonal flows in the upper stratosphere near the equator are in an eastward phase, while it appears to be blocked during the westward phases. This correspondence of the 16‐day wave in the summer mesosphere with the eastward equatorial wind would favor the explanation that it is generated in the winter hemisphere and propagates vertically and toward the summer pole following the westerly mean winds.
OH radical formation yields from the gas‐phase reactions of O3 with alkenes and monoterpenes
Authors: Chew Andrew A. , Atkinson Roger
Published: February 2004

The compound 2‐butanol has been used to scavenge ≥95% of the OH radicals formed in the reactions of O3 with the alkenes 2,3‐dimethyl‐2‐butene and 2‐methyl‐2‐butene and with the monoterpenes α‐pinene and sabinene at 296±2 K and atmospheric pressure of air, with the OH radical formation yields from these O3 reactions being obtained from the amounts of 2‐butanone formed. The rate constant for the reaction of the OH radical with 2‐butanol was measured using a relative rate method; the rate constant was determined to be (9.2±2.4) × 10−12 cm3 molecule−1 s−1 at 296±2 K, where the indicated error includes the estimated overall uncertainties in the rate constant for the reference organic (cyclohexane). The formation yield of 2‐butanone from the reaction of the OH radical with 2‐butanol was determined to be 0.695±0.073. Using this 2‐butanone formation yield from the OH radical reaction with 2‐butanol, the OH radical formation yields from the reactions of O3 with 2,3‐dimethyl‐2‐butene, 2‐methyl‐2‐butene, α‐pinene, and sabinene were determined to be 0.80±0.12, 0.93±0.14, 0.76±0.11, and 0.33±0.06, respectively. These OH radical formation yields agree to within ±25% with the yields previously derived using cyclohexane to scavenge OH radicals and measuring the amounts of cyclohexanone plus cyclohexanol formed. Our present OH radical formation yield for 2,3‐dimethyl‐2‐butene is also in good agreement with the value of 0.7 previously reported from a comprehensive product study.
On the magnitude of transport out of the Antarctic polar vortex
Authors: Wauben Wiel M. F. , Bintanja Richard , van Velthoven Peter F. J. , Kelder Hennie
Published: February 2004

The degree of isolation of the Antarctic stratospheric vortex in late winter and spring is investigated quantitatively by using a three‐dimensional global tracer transport model, in which the transport is computed from European Centre for Medium‐Range Weather Forecasts analyzed data. The evolution of the spatial distribution of passive tracers provides information about variations in the vortex structure, as well as about the magnitude of the transport out of the Antarctic vortex. The vortex structure revealed by tracers released inside the vortex at 72.5 hPa corresponds well with the satellite‐derived distribution of total ozone. The model computations indicate that in late winter and spring of the years 1990–1993, there is a quasi‐horizontal cross‐vortex transport of about 0.24% per day of the total tracer amount, while per day, 0.83% of the vortex mass descends into the troposphere. This indicates that roughly 65% of the vortex air is flushed out during August‐September‐October, the approximate lifetime of the Antarctic vortex. This number is insensitive to changes in model resolution, although the quasi‐horizontal outflow into the midlatitude stratosphere increases at the expense of the downward outflow if a coarser resolution is used. It is concluded that during late winter and early spring (i.e., the period of major ozone depletion), the vortex is a fairly well isolated air mass.
Effect of temperature and air movement on the flux of elemental mercury from substrate to the atmosphere
Authors: Gustin Mae Sexauer , Taylor George E. , Maxey Rachel A.
Published: February 2004

The flux of elemental mercury vapor from intact mill tailings (36 to 1270 μg Hg/g), soil (7 μg Hg/g), and cinnabar ore (934 μg Hg/g) was measured as a function of temperature (20°–60°C) and wind velocity (0.2–0.8 m/s) using a controlled environment, open gas‐exchange system. Continuous air movement over core surfaces in the gas‐exchange chamber resulted in a logarithmic decline in mercury flux with time. Measurement of the effect of environmental parameters on mercury flux was done after attainment of a quasi steady state of flux. Prior to attainment of this state the activation energy for mercury flux was less than the molar heat of vaporization of element mercury (14 kcal/mol). At steady state the substrate‐to‐air flux of mercury vapor increased logarithmically with temperature, mimicking the element's vapor pressure curve; and activation energies (16.4 to 25.7 kcal/mol) for mercury flux were higher than the molar heat of vaporization of elemental mercury due to physicochemical properties of the soil (e.g., porosity, organic matter, clay content) that affect gas‐phase mercury transport and fate. A change in wind velocity from 0.2 to 0.8 m/s resulted in an increase in mercury flux by a factor of 2 for a core with >150 μg Hg/g and no significant response from two cores with <150 μg Hg/g. Using data from gas‐exchange experiments, equations were derived for predicting the response of mercury flux to a range of temperatures and wind velocities for a variety of substrate mercury concentrations. The equations and the results of this study are used to predict the flux of mercury to the atmosphere from substrate enriched in mercury.
Atmospheric carbon monoxide budget of the southern hemisphere: Implications of 13C/12C measurements
Authors: Manning M. R. , Brenninkmeijer C. A. M. , Allan W.
Published: February 2004

A large seasonal cycle has been observed in the 13C/12C isotopic ratio of CO in clean air in the extratropical southern hemisphere. This ratio is determined by the mixture of CO from isotopically distinct sources and is strongly influenced by the relative contributions of surface sources and the oxidation of CH4. We use a zonally averaged atmospheric model to relate atmospheric CO mixing ratios and 13C/12C isotopic ratios to the magnitude and distribution of CO sources and to explain the average seasonal cycles observed. The average 13C/12C ratio of CO emitted by surface sources in the southern hemisphere is larger than in the northern hemisphere and the southward flux of CO into the extratropical southern hemisphere is additionally enriched in 13C as a result of oxidation during transport. These effects partially offset the effect of highly depleted 13C/12C ratios in CO produced by CH4 oxidation. In the extratropical southern hemisphere, seasonal variation in the fraction of atmospheric CO derived from CH4 oxidation produces large changes in 13C/12 C which are partially offset by seasonal variations of surface sources. A good fit to observed average cycles can be obtained using surface source strengths consistent with previous estimates. However, the southern hemisphere data place strong constraints on the CH4 oxidation source and imply that either the CO yield per molecule of CH4 is about 0.7, compared with previous estimates of around 0.8, or that unidentified processes associated with CH4 oxidation cause 13C enrichment of about 4‰ in the CO produced.
Biogenic sulphur emissions and inferred non‐sea‐salt‐sulphate cloud condensation nuclei in and around Antarctica
Authors: O'Dowd Colin D. , Lowe Jason A. , Smith Michael H. , Davison Brian , Hewitt C. Nicholas , Harrison Roy M.
Published: February 2004

Accumulation mode aerosol properties and biogenic sulphur emissions over the South Atlantic and Antarctic Oceans are examined. Two contrasting air masses, polar and maritime, each possessing distinct aerosol properties, were encountered during the summer months. By examining aerosol volatile properties, polar air masses arriving from the Antarctic continent were shown to consist primarily Of H2SO4 in the accumulation mode size range, with inferred NH+4 to SO=4 molar ratios close to zero. By comparison, air masses of temperate maritime origin were significantly neutralized with molar ratios of ≈1. These results suggest a deficit of ammonia in polar air masses compared with that in maritime air masses. Dimethyl sulphide (DMS) exhibited no correlation with its putative aerosol oxidation products, although spatial coherence in atmospheric concentrations of DMS, methane sulphonic acid (MSA), and non‐sea‐salt (nss)‐sulphate mass was observed. Volatility analysis, used to infer nss‐sulphate cloud condensation nuclei (nss‐sCCN) active at a supersaturation of ≈0.2%, indicates that nss‐sCCN mass and number concentration were best correlated with MSA mass (r≈0.63). Aerosol volatility identified the presence of MSA in submicron non‐sea‐salt aerosol; however, its contribution to the aerosol mass was small relative to the contribution of sulphuric acid and ammonium bisulphate/sulphate aerosol. The marine sulphur cycle appears strongly coupled to the sea‐salt cycle with, typically, 80–90% of nss‐sulphate thought to be internally mixed with sea‐salt aerosol. During the austral Summer of 1992/1993, a period of strong biological productivity in the Weddell Sea and sub‐Antarctic Ocean, particularly during ice‐melt, the cruise‐average DMS flux of 61 μg m−2 d−1 corresponded to a very modest average nss‐sCCN concentration of 21 cm−3. Observed peak values of DMS flux and inferred nss‐CCN concentrations during the cruise were 477 μg m−2 d−1 and 64 cm−3, respectively. Events of new particle formation were identified in the Weddell Sea and occurred under conditions of high DMS flux and low aerosol surface area.