bluuebunny/crossref_metadata_2025 huggingface dataset:
Global sensitivity experiments of the radiative forcing due to mineral aerosols
Authors: Myhre Gunnar , Stordal Frode
Published: February 2004

The radiative effects of mineral dust in the atmosphere are uncertain. Further, the human contribution to the mineral aerosol concentration is difficult to quantify. We have performed several global sensitivity experiments to investigate the radiative forcing due to mineral dust. Two global data sets of mineral aerosol distribution are used. Radiative transfer schemes for thermal infrared and solar radiation are used in the calculations. We have investigated the sensitivity of the global radiative forcing to the spatial distribution of the aerosols, including the altitude, the size distribution, and optical parameters. Our strongest emphasis has been on the size distribution of the mineral aerosol, for which we have found a strong sensitivity. A range of −0.7 Wm−2 to 0.5 Wm−2 is estimated for the human influence on the global radiative forcing due to mineral aerosols. We find it almost as probable with a positive radiative forcing as with a negative forcing. Even if the global mean radiative forcing is small, there are large contributions of different sign in certain regions.
Surface energy balance and turbulence characteristics observed at the SHEBA Ice Camp during FIRE III
Authors: Duynkerke Peter G. , de Roode Stephan R.
Published: February 2004

The Institute for Marine and Atmospheric Research Utrecht (IMAU) participated in the First International Satellite Cloud Climatology Project (ISCCP) Regional Experiment (FIRE III) in May 1998. In this paper we describe surface layer measurements performed on the sea ice at the Surface Heat and Energy Balance of the Arctic Ocean (SHEBA) camp and compare these with measurements collected above a grass‐covered surface in Cabauw, the Netherlands. The observations consist of both high‐frequency turbulence measurements and mean‐profile measurements of wind, temperature, and humidity. In addition, we measured the upward and downward components of both the longwave and the shortwave radiation, and the snow and ice temperatures in the upper 40 cm. The observations give a detailed picture of all components of the energy balance of the Arctic sea‐ice surface. The turbulence measurements are used to study the surface layer scaling of the turbulence variables in the stable boundary layer. More specifically, we showed that the integral length scale of the vertical velocity fluctuations serves as the relevant turbulence length scale. The monthly averaged energy balance of the Arctic sea‐ice was dominated by radiative fluxes, whereas the sensible and latent heat flux and the energy flux into the surface were rather small. A detailed inspection of the diurnal variations in the turbulent fluxes, however, indicates that although the monthly averaged values are small, the hourly averaged values for these fluxes are significant in the surface energy balance.
From molecular clusters to nanoparticles: Role of ambient ionization in tropospheric aerosol formation
Authors: Yu Fangqun , Turco Richard P.
Published: February 2004

We investigate the role of background ionization, associated mainly with galactic cosmic radiation, in the generation and evolution of ultrafine particles in the marine boundary layer. We follow the entire course of aerosol evolution, from the initial buildup of molecular clusters (charged and uncharged) through their growth into stable nanoparticles. The model used for this purpose is based on a unified collisional (kinetic) mechanism that treats the interactions between vapors, neutral and charged clusters, and particles at all sizes. We show that air ions are likely to play a central role in the formation of new ultrafine particles. The nucleation of aerosols under atmospheric conditions involves a series of competing processes, including molecular aggregation, evaporation, and scavenging by preexisting particles. In this highly sensitive nonlinear system, electrically charged embryos have a competitive advantage over similar neutral embryos. The charged clusters experience enhanced growth and stability as a consequence of electrostatic interactions. Simulations of a major nucleation event observed during the Pacific Exploratory Mission (PEM) Tropics‐A can explain most of the observed features in the ultrafine particle behavior. The key parameters controlling this behavior are the concentrations of precursor vapors and the surface area of preexisting particles, as well as the background ionization rate. We find that systematic variations in ionization levels due to the modulation of galactic cosmic radiation by the solar cycle are sufficient to cause a notable variation in aerosol production. This effect is greatest when the ambient nucleation rate is limited principally by the availability of ions. Hence we conclude that the greatest influence of such ionization is likely to occur in and above the marine boundary layer. While a systematic change in the ultrafine particle production rate is likely to affect the population of cloud condensation nuclei and hence cloud optical properties, the magnitude of the effect cannot be directly inferred from the present analysis, and requires additional analysis based on specific aerosol‐cloud interactions.
Distinct circulation states of the Arctic atmosphere induced by natural climate variability
Authors: Dorn Wolfgang , Dethloff Klaus , Rinke Annette , Botzet Michael
Published: February 2004

The high‐resolution regional climate model HIRHAM4 with a horizontal resolution of 0.5°×0.5° was used to determine the influence of natural climate variations in the Arctic. The large‐scale lateral forcing and the lower boundary forcing for the HIRHAM4 were delivered from a long‐term run of the coupled circulation model ECHO‐G at T30 resolution. This run was carried out with prescribed constant external forcing for present‐day climate conditions. 600 years of this ECHO‐G simulation were analyzed to find periods persisting over several years either with mainly warm or mainly cold conditions during the Arctic winter. Two warm and two cold periods, each of 6 years duration, were selected for the regionalization of the Arctic climate in January. The performed model simulations show that a warm or cold Arctic winter climate is connected with two distinct circulation states of the Arctic atmosphere. These states are characterized by a different location and extension of the tropospheric vortex with a vortex center over the western Arctic in warm Januaries or over the eastern Arctic in cold Januaries, respectively. Moreover, there are indications that these different locations of the vortex are linked to a different synoptic activity in Alaska and the eastern part of the Arctic which is, in turn, related to a different meridional transport of heat and moisture into these regions. The resultant climate conditions in these regions differ from each other with statistical significance and are, finally, decisive for the warm or cold Arctic climate state.
Heterogeneous reactions of NO2 and HNO3 on oxides and mineral dust: A combined laboratory and modeling study
Authors: Underwood G. M. , Song C. H. , Phadnis M. , Carmichael G. R. , Grassian V. H.
Published: February 2004

This study combines laboratory measurements and modeling analysis to quantify the role of heterogeneous reactions of gaseous nitrogen dioxide and nitric acid on mineral oxide and mineral dust particles in tropospheric ozone formation. At least two types of heterogeneous reactions occur on the surface of these particles. Upon initial exposure of the oxide to NO2 there is a loss of NO2 from the gas phase by adsorption on the particle surface, i.e., NO2(g) → NO2(a). As the reaction proceeds, a reduction of gaseous NO2 to NO, NO2 (g) → NO (g) is found to occur. Initial uptake coefficients γ0 for NO2 on the surface of these particles have been measured at 298 K using a Knudsen cell reactor coupled to a mass spectrometer. For the oxides studied, α,γ‐Al2O3, α,γ‐Fe2O3, TiO2, SiO2, CaO, and MgO, γ0 ranges from <4×10−10 for SiO2 to 2×10−5 for CaO with most values in the 10−6 range. For authentic samples of China loess and Saharan sand, similar reactivity to the oxides is observed with γ0 values of 2×10−6 and 1×10−6, respectively. For HNO3 the reactivity is 1–2 orders of magnitude higher. Using these laboratory measurements, the impact of heterogeneous reactions of NO2 and HNO3 on mineral dust in tropospheric ozone formation and on O3‐precursor relationships is assessed using a time‐dependent, multiphase chemistry box model. Simulations with and without heterogeneous reactions were conducted to evaluate the possible influence of these heterogeneous reactions on ambient levels. Results show that values of the initial uptake for NO2 and HNO3, adjusted for roughness effects, must be greater than 10−4 to have an appreciable impact on NOx, HNO3, and O3 concentrations for the conditions modeled here. Thus the measured uptake coefficients for NO2 on dry surfaces are just below the lower limit to have an impact on the photochemical oxidant cycle, while the heterogeneous reactivity of HNO3 is sufficiently large to have an effect. Under conditions of high mineral dust mass loadings and/or smaller size distributions the importance of these reactions (both NO2 and HNO3) is expected to increase.
Physical and chemical characteristics of aerosols over the Negev Desert (Israel) during summer 1996
Authors: Formenti P. , Andreae M. O. , Andreae T. W. , Ichoku C. , Schebeske G. , Kettle J. , Maenhaut W. , Cafmeyer J. , Ptasinsky J. , Karnieli A. , Lelieveld J.
Published: February 2004

Sde Boker, in the Negev Desert of Israel (30°51′N, 34°47′E; 470 m above sea level (asl), is a long‐term station to investigate anthropogenic and natural aerosols in the eastern Mediterranean in the framework of the Aerosol, Radiation and Chemistry Experiment (ARACHNE). Ground‐level measurements of physical and chemical properties of aerosols and supporting trace gases were performed during an intensive campaign in summer 1996 (ARACHNE‐96). Fine non sea salt (nss)‐SO42− averaged 8±3 μg m−3 and fine black carbon averaged 1.4±0.5 μg m−3, comparable to values observed off the east coast of the United States. Optical parameters relevant for radiative forcing calculations were determined. The backscatter ratio for ARACHNE‐96 was β = 0.13±0.01. The mass absorption efficiency for fine black carbon (αa,BCEf) was estimated as 8.9±1.3 m2 g−1 at 550 nm, while the mass scattering efficiency for fine nss‐SO42− (αs,nss‐SO42−f) was 7.4±2.0 m2 g−1. The average dry single‐scattering albedo, ω0 characterizing polluted conditions was 0.89, whereas during “clean” periods ω0 was 0.94. The direct radiative effect of the pollution aerosols is estimated to be cooling. At low altitudes (below 800 hPa), the area was generally impacted by polluted air masses traveling over the Balkan region, Greece, and Turkey. Additional pollution was often added to these air masses along the Israeli Mediterranean coast, where population and industrial centers are concentrated. At higher altitudes (700 and 500 hPa), air masses came either from eastern Europe or from North Africa (Algerian or Egyptian deserts). The combination of measurements of SO2, CO, CN (condensation nuclei), and accumulation mode particles allowed to characterize the air masses impacting the site in terms of a mixture of local and long‐range transported pollution. In particular, the lack of correlation between SO2 and nss‐SO42− indicates that the conversion of regional SO2 into the particulate phase is not an efficient process in summer and that aged pollution dominates the accumulation mode particle concentrations.
GATOR‐GCMM: 2. A study of daytime and nighttime ozone layers aloft, ozone in national parks, and weather during the SARMAP field campaign
Authors: Jacobson Mark Z.
Published: February 2004

The GATORG‐GCMM global‐ through urban‐scale nested air pollution/weather forecast model was applied to study ozone layers aloft, ozone in national parks, and weather during the August 3–6, 1990, SARMAP field campaign in northern and central California. Predictions of meteorological variables and mixing ratios of 20 gases were compared with observations. With nesting, the normalized gross error in predicted near‐surface Kelvin temperatures was 1.02% and that in near‐surface ozone above 50 ppbv was 22.5%. Statistics from outer nested domains indicated that the coarser the grid spacing, the greater the underprediction of ozone. In the absence of nesting, statistics deteriorated but not a lot. The model‐simulated observed nighttime ozone layers aloft and daytime ozone mixed layers in the San Joaquin Valley and San Francisco Bay Area. It also simulated observed daytime and nighttime ozone layers aloft over the San Francisco Bay near Hayward. The formation mechanism of these layers is discussed. The model was used to estimate that about 47–57% of peak daytime ozone in Sequoia and Yosemite National Parks during SARMAP was produced by anthropogenic gases, 13–3% was produced by biogenic hydrocarbons, and the rest (about 40%) was background.
On aggregation errors in atmospheric transport inversions
Authors: Kaminski Thomas , Rayner Peter J. , Heimann Martin , Enting Ian G.
Published: February 2004

This paper explores the consequences of resolution of surface fluxes on synthesis inversions of carbon dioxide. Synthesis inversion divides the Earth's surface into a set of regions and solves for the magnitudes of fluxes from these regions. The regions are generally quite large. By considering an inversion performed at the resolution of the underlying transport model we show that the aggregation to large regions can cause significant differences in the final results, with errors of the same order of magnitude as the fluxes themselves. Using a simple model, we derive an algorithm to reduce this error. This algorithm accounts for the extra data uncertainty that is caused by uncertainty in the small‐scale flux components. In the spatial synthesis inversion this extra data uncertainty reaches a maximum value of 3.5 ppmv. Accounting for it can halve the aggregation error. We provide suggestions for dealing with this problem when high‐resolution inversions are not feasible.
Enhancement of dust source area during past glacial periods due to changes of the Hadley circulation
Authors: Chylek Petr , Lesins Glen , Lohmann Ulrike
Published: February 2004

Tropical deserts (e.g., Sahara, Arabian desert, Australian desert) are located within the Hadley circulation. Most of the dust uplifted from these deserts is carried by trade winds and deposited in tropical oceans with very little, if any, transported to polar regions. During glacial periods the dust concentrations in polar ice cores were a factor of 10 to 100 higher than during interglacial periods, including the current Holocene. The early general circulation model simulations of the past glacial climate were not able to reproduce these high mineral dust concentrations; the most recent attempts achieve an increased dust transport to polar regions by extending dust source areas to higher latitudes. We present a hypothesis that during glacial periods the Hadley cell is confined closer to the equator. This contraction of the Hadley circulation leads to the geographical change of the boundary between the tropical and the midlatitude circulation regimes. During the glacial periods a considerable fraction of the current tropical deserts was located outside the region of the Hadley circulation. This allowed the dust to be uplifted and transported by midlatitude storm systems to the polar regions. We present a model for the contraction of the Hadley circulation during the past glacial periods based on the Schneider‐Lindzen and Held‐Hou model of symmetric tropical circulation and on the assumption that the tropical sea surface temperatures were lower during glacial periods than they are today.
Fluxes of oxygenated volatile organic compounds from a ponderosa pine plantation
Authors: Schade Gunnar W. , Goldstein Allen H.
Published: February 2004

We present the first canopy‐scale, continuous, long‐term flux measurements of a suite of oxygenated volatile organic compounds (OVOCs). Fluxes were measured above a ponderosa pine plantation, adjacent to the Blodgett Forest Research Station (38°53′42.9″N, 120°37′57.9″W, 1315 m elevation), with a fully automated relaxed eddy accumulation (REA) system coupled to a dual GC‐FID system. Quantified OVOCs included 2‐methyl‐3‐buten‐2‐ol (MBO), methanol, ethanol, acetaldehyde, and acetone. These compounds were the most abundant nonmethane VOCs at this site and were highly correlated with each other, especially during daytime. Fluxes were dominated by MBO and methanol with daytime average emissions of ∼1.3 mg C m−2 h−1. Ethanol, acetaldehyde, and acetone fluxes were approximately a factor of 5 lower. All fluxes showed diurnal cycles with maxima around noon and minima at night. Temperature and light were the main drivers for MBO emission, and the canopy level flux responses were virtually identical with previously measured leaf level fluxes from ponderosa pine trees at the same site. Ambient temperature appeared to be the most important driver of the other OVOC fluxes, but moisture also played a role, particularly for ethanol and acetone emissions, shown for the first time under field conditions. Soil and litter emissions, measured using a Pyrex glass chamber, contributed significantly to the canopy level fluxes of methanol, acetaldehyde, and acetone, and had a much smaller contribution to the canopy fluxes of ethanol. If the magnitude of these OVOC fluxes is similar in other ecosystems, they will have to be considered a major volatile organic compound emission to the atmosphere and a potentially significant carbon loss from the biosphere.
Compatibility evaluation of national precipitation gage measurements
Authors: Yang Daqing , Goodison Barry , Metcalfe John , Louie Paul , Elomaa Esko , Hanson Clayton , Golubev Valentin , Gunther Thilo , Milkovic Janja , Lapin Milan
Published: February 2004

Compatibility of precipitation measurements of various national gages commonly used in the Northern Hemisphere countries has been evaluated, based on the gage intercomparison data collected at 10 stations during the World Meteorological Organization (WMO) Solid Precipitation Measurement Intercomparison Project. Little difference (less than 5%) is found between national rainfall data, but a significant discrepancy (up to 110%) exists between national snowfall records. This difference is not constant and it varies with wind speed and temperature. It is certain that use of different precipitation gages in neighboring countries has introduced a significant discontinuity into precipitation records, particularly in cold and windy regions. Strong linear relations among daily national gage measurements have been defined for several national gages commonly used in the Northern Hemisphere. These linear relations provide a useful technique to adjust gage records when wind speed and temperature data are not available. The linear relations have been tested at selected WMO intercomparison stations, and good agreements of the adjusted amounts to other gage measurements are obtained at most of the test sites, indicating that the linear relations perform reasonably well at the selected WMO sites. Use of the proposed adjustment procedure will reduce inconsistency between precipitation measurements of national gages.
Sensitivity of cirrus bidirectional reflectance to vertical inhomogeneity of ice crystal habits and size distributions for two Moderate‐Resolution Imaging Spectroradiometer (MODIS) bands
Authors: Yang Ping , Gao Bo‐Cai , Baum Bryan A. , Wiscombe Warren J. , Hu Yong X. , Nasiri Shaima L. , Soulen Peter F. , Heymsfield Andrew J. , McFarquhar Greg M. , Miloshevich Larry M.
Published: February 2004

A common assumption in satellite imager‐based cirrus retrieval algorithms is that the radiative properties of a cirrus cloud may be represented by those associated with a specific ice crystal shape (or habit) and a single particle size distribution. However, observations of cirrus clouds have shown that the shapes and sizes of ice crystals may vary substantially with height within the clouds. In this study we investigate the sensitivity of the top‐of‐atmosphere bidirectional reflectances for two Moderate‐Resolution Imaging Spectroradiometer (MODIS) bands centered at 0.65 μm and 2.11 μm to cirrus models composed of either a single homogeneous layer or three distinct, but contiguous, layers. First, we define the single‐ and three‐layer cirrus cloud models with respect to ice crystal habit and size distributions on the basis of in situ replicator data acquired during the First International Satellite Cloud Climatology Project (ISCCP) Regional Experiment (FIRE‐II), held in Kansas during the fall of 1991. Subsequently, fundamental light‐scattering and radiative transfer theory is employed to determine the single‐scattering and the bulk radiative properties of the cirrus cloud. For radiative transfer computations we present a discrete form of the adding/doubling principle that is computationally straightforward and efficient. For the 0.65 μm band, at which absorption by ice is negligible, there is little difference between the bidirectional reflectances calculated for the one‐ and three‐layer cirrus models. This result suggests that the vertical inhomogeneity effect is relatively unimportant at 0.65 μm. At 2.11 μm the bidirectional reflectances computed for both optically thin (τ = 1) and thick (τ = 10) cirrus clouds show significant differences between the results for the one‐ and three‐layer models. The reflectances computed for the three‐layer cirrus model are substantially larger than those computed for the single‐layer cirrus. Furthermore, our analysis shows that the cirrus reflectances at both the 0.65 and 2.11 μm bands are very sensitive to the optical properties of the small crystals that predominate in the top layer of the three‐layer cirrus model. It is critical to define the most realistic geometric shape for the small “quasi‐spherical” ice crystals in the top layer for obtaining reliable single‐scattering parameters and bulk radiative properties of cirrus.
Latitudinal and longitudinal behavior of the mesospheric OH nightglow layer as observed by the Improved Stratospheric and Mesospheric Sounder on UARS
Authors: Zaragoza G. , Taylor F. W. , López‐Puertas M.
Published: February 2004

The mesospheric nightglow from the hydroxyl (OH) radical has been characterized using measurements taken by the Improved Stratospheric and Mesospheric Sounder (ISAMS) instrument on the UARS satellite. In this paper, the variations with latitude of the emission integrated vertically over the OH layer, for both solstice and equinox conditions, are analyzed and compared to other measurements and with model predictions. A semiannual variation with a minimum at solstice is found at low latitudes. An annual variation is found at high latitudes with a springtime minimum, which appears earlier than predicted by the models. Zonal maps of the OH emission show longitudinal structures with a timescale of days that suggest the effect of planetary waves on the emission process.
Voltages inside and just above thunderstorms
Authors: Marshall Thomas C. , Stolzenburg Maribeth
Published: February 2004

We estimate the voltage relative to the Earth inside thunderstorms and at cloud top from balloon soundings of electric field through convective regions and stratiform clouds. These are the first estimates we know of that give the voltage through the entire depth of storm clouds. Cloud top voltages were available for 13 soundings and ranged between −23 and +79 MV, with an average of +25 MV. The average cloud top voltage among the nine cases with positive values was +41 MV. These values support the Wilson [1920] hypothesis that thunderstorms drive the global electric circuit. The average cloud top voltage above electrified stratiform clouds was +32 MV, so these clouds may also make a substantial contribution to the global electric circuit. Within clouds the voltage values ranged between −102 and +94 MV in the 15 soundings. The voltage difference associated with intracloud and cloud‐to‐ground lightning flashes estimated from our soundings is in the range of about 20 to 130 MV. From the voltage differences inside storms we estimate the energy available for weak and strong lightning flashes as approximately 107 and 1010 J, respectively.
Observations of high‐frequency temporal gravity wave spectra in the middle upper stratosphere
Authors: Russell A. T. , Sica R. J.
Published: February 2004

There is a paucity of high‐frequency temporal gravity wave spectra in the middle upper stratosphere (30–40 km) as most instruments that are capable of accessing this region do not have the capability to make measurements for any extended period of time. The spectral analysis of density fluctuations obtained with the Purple Crow Rayleigh scatter lidar has shown that middle upper stratospheric temporal spectra follow the expected −1.5 to −2.0 power law relationship for frequencies less than 1×10−3 s−1. At frequencies greater than 1×10−3 s−1, the shape of the temporal spectrum is much more variable, with strong quasi‐monochromatic features appearing intermittently on certain nights. These higher‐frequency features have been attributed to nonlinear wave interactions and suggest that estimates of gravity wave activity in the middle upper stratosphere may be larger and much more variable than previously assumed. This variability also suggests that middle upper stratospheric energy dissipation and eddy diffusion values may be much larger and more variable than previously assumed. Current parameterizations of subgrid dynamical processes in general circulation models that resolve this region may need to be reexamined in this light.
Aircraft observations of thin cirrus clouds near the tropical tropopause
Authors: Pfister Leonhard , Selkirk Henry B. , Jensen Eric J. , Schoeberl Mark R. , Toon Owen B. , Browell Edward V. , Grant William B. , Gary Bruce , Mahoney Michael J. , Bui Thaopaul V. , Hintsa Eric
Published: February 2004

This work describes aircraft‐based lidar observations of thin cirrus clouds at the tropical tropopause in the central Pacific obtained during the Tropical Ozone Transport Experiment/Vortex Ozone Transport Experiment (TOTE/VOTE) in December 1995 and February 1996. Thin cirrus clouds were found at the tropopause on each of the four flights which penetrated within 15° of the equator at 200–210 east longitude. South of 15°N, thin cirrus were detected above the aircraft about 65% of the time that data were available. The altitudes of these clouds exceeded 18 km at times. The cirrus observations could be divided into two basic types: thin quasi‐laminar wisps and thicker, more textured structures. On the basis of trajectory analyses and temperature histories, these two types were usually formed respectively by (1) in situ cooling on both a synoptic scale and mesoscale and (2) recent (a few days) outflow from convection. There is evidence from one case that the thicker clouds can also be formed by in situ cooling. The actual presence or absence of thin cirrus clouds was also consistent with the temperature and convective histories derived from back trajectory calculations. Notably, at any given time, only a relatively small portion (at most 25%) of the west central tropical Pacific has been influenced by convection within the previous 10 days. The structures of some of the thin cirrus clouds formed in situ strongly resembled long‐wavelength (500–1000 km) gravity waves observed nearly simultaneously by the ER‐2 on one of the flights. Comparison with in situ water vapor profiles made by the NASA ER‐2 aircraft provide some observational support for the hypothesis that thin cirrus clouds play an important role in dehydrating tropospheric air as it enters the stratosphere.
Chemistry and oxidation capacity of the nitrate radical in the continental boundary layer near Berlin
Authors: Geyer Andreas , Alicke Björn , Konrad Stephan , Schmitz Thomas , Stutz Jochen , Platt Ulrich
Published: February 2004

The nitrate radical is in many situations the most important nighttime oxidizing species, removing, for example, hydrocarbons, which would otherwise be available to daytime ozone formation. In spite of its importance in the night and probably also under certain conditions during the day, our understanding of the NO3 chemistry and its impact on the oxidation capacity of the atmosphere is still incomplete. Here we present measurements of NO3 by differential optical absorption spectroscopy (DOAS) and a number of other atmospheric trace gases performed during the Berliner Ozonexperiment (BERLIOZ) campaign at Pabstthum near Berlin, Germany, to quantify the contribution of NO3 to the atmospheric oxidation rate of volatile organic compounds (VOCs) and NOx removal. The measurements show that only two NO3 sinks were of importance: (1) About 50–30% (depending on the distance (0.1–3 km) to a near forest) of the NO3 was lost due to reaction with biogenic hydrocarbons. (2) The major part of the remaining loss probably can be attributed to the indirect loss via the reaction of N2O5 on aerosol surfaces. Assuming that heterogeneous hydrolysis of N2O5 is occurring, the nonphotolytical conversion of NOx to HNO3 via N2O5 was found to be comparable with daytime conversion by the reaction of OH with NO2. In combination with measurements of the OH concentration, it was possible for the first time to derive a relative contribution of 28% (24‐hour average) for the NO3‐initiated oxidation to the total VOC degradation.
Ozone profile retrieval from backscattered ultraviolet radiances: The inverse problem solved by regularization
Authors: Hasekamp Otto P. , Landgraf Jochen
Published: February 2004

A new algorithm is presented for the retrieval of ozone profiles from backscattered ultraviolet radiation, as measured by the Global Ozone Monitoring Experiment (GOME). It is the first algorithm for ozone profile retrieval from this type of measurement that does not depend on climatological information about the ozone profile. For the inversion, Phillips‐Tikhonov regularization is used in combination with the L curve criterion for choosing the regularization parameter. This inversion technique allows one to retrieve a maximal possible information amount from the measurement, while at the same time the influence of the measurement noise on the retrieved profile is minimized. In this paper, we show the suitability of this method for ozone profile retrieval from GOME radiance measurements. The average vertical resolution of the retrieved profiles varies between 8 and 10 km. The GOME ozone profiles are validated with 163 ozonesonde profiles spread over seven stations. The root‐mean‐square differences between the sonde and GOME ozone profiles are generally 5–10% in the stratosphere. Differences in the mean profile are in the range 1–7% in the stratosphere.
Estimating relationships between air mass origin and chemical composition
Authors: Methven John , Evans Mathew , Simmonds Peter , Spain Gerard
Published: February 2004

Observations of a chemical at a point in the atmosphere typically show sudden transitions between episodes of high and low concentration. Often these are associated with a rapid change in the origin of air arriving at the site. Lagrangian chemical models riding along trajectories can reproduce such transitions, but small timing errors from trajectory phase errors dramatically reduce the correlation between modeled concentrations and observations. Here the origin averaging technique is introduced to obtain maps of average concentration as a function of air mass origin for the East Atlantic Summer Experiment 1996 (EASE96, a ground‐based chemistry campaign). These maps are used to construct origin averaged time series which enable comparison between a chemistry model and observations with phase errors factored out. The amount of the observed signal explained by trajectory changes can be quantified, as can the systematic model errors as a function of air mass origin. The Cambridge Tropospheric Trajectory model of Chemistry and Transport (CiTTyCAT) can account for over 70% of the observed ozone signal variance during EASE96 when phase errors are side‐stepped by origin averaging. The dramatic increase in correlation (from 23% without averaging) cannot be achieved by time averaging. The success of the model is attributed to the strong relationship between changes in ozone along trajectories and their origin and its ability to simulate those changes. The model performs less well for longer‐lived chemical constituents because the initial conditions 5 days before arrival are insufficiently well known.
Surface albedo measurements over snow and blue ice in thematic mapper bands 2 and 4 in Dronning Maud Land, Antarctica
Authors: Reijmer C. H. , Bintanja R. , Greuell W.
Published: February 2004

Ground‐based observations of broadband, narrowband (in Landsat thematic mapper bands 2, 0.52–0.60 μm, and 4, 0.76–0.90 μm), and bidirectional reflectance are used to study the albedo of blue ice and snow. The measured broadband albedos for blue ice and snow are 0.60 and 0.78, respectively. The narrowband albedos in bands 2 and 4 for snow are 0.97 and 0.86, respectively, and for blue ice are 0.87 and 0.51, respectively. The measurements are point values and used to verify existing weighting functions between the broadband and narrowband albedos. Blue ice data do not comply with the existing functions. Furthermore, a new function for blue ice is derived. A simple two‐stream model is used to illustrate the behavior of the snow and ice albedo as a function of reflection and absorption. The bidirectional reflectance measurements are used to derive bidirectional reflectance distribution functions (BRDFs) for snow and blue ice. The BRDF of blue ice exhibits a maximum brightening in the forward limb around a zenith angle close to the solar zenith angle, indicating specular reflectance of blue ice which is not visible for snow and glacier ice surfaces.
Summarizing multiple aspects of model performance in a single diagram
Authors: Taylor Karl E.
Published: February 2004

A diagram has been devised that can provide a concise statistical summary of how well patterns match each other in terms of their correlation, their root‐mean‐square difference, and the ratio of their variances. Although the form of this diagram is general, it is especially useful in evaluating complex models, such as those used to study geophysical phenomena. Examples are given showing that the diagram can be used to summarize the relative merits of a collection of different models or to track changes in performance of a model as it is modified. Methods are suggested for indicating on these diagrams the statistical significance of apparent differences and the degree to which observational uncertainty and unforced internal variability limit the expected agreement between model‐simulated and observed behaviors. The geometric relationship between the statistics plotted on the diagram also provides some guidance for devising skill scores that appropriately weight among the various measures of pattern correspondence.
Mechanisms for pollutant transport between the boundary layer and the free troposphere
Authors: Donnell Elisabeth A. , Fish Deb J. , Dicks Ed M. , Thorpe Alan J.
Published: February 2004

Pollutants are longer‐lived in the free troposphere than the boundary layer, hence the transport of pollutants from the boundary layer to the free troposphere has significant implications for long‐range transport and global warming. It is important to quantify the transport of air between the boundary layer and the free troposphere and to understand the role different meteorological mechanisms play. Idealised passive tracer experiments, with tracer initially only in the boundary layer, are performed in a numerical model for three case study days with different synoptic conditions. After 24 hours, more than 50% of the tracer resides in the free troposphere for the two frontal cases, and 40% resides there for the high‐pressure case. The tracer was transported to maximum heights of 8 km. To elucidate the role of different mechanisms for each case, the tracer amount transported by advection only, advection and turbulent mixing, and advection and convection was calculated. Advection is found to be the most important mechanism in transporting the tracer to the free troposphere; however, the addition of upright convection and turbulent mixing increases the amount by up to 24% with convection transporting the tracer to heights of 5 km. The inclusion of convection and turbulent mixing to the advection are not linearly additive processes. This study shows the possibility of a large proportion of the pollutant emitted in the boundary layer being transported to the free troposphere in a short time and the importance of representing all the meteorological processes.
April 1998 Asian dust event over the Columbia Plateau
Authors: Vaughan Joseph K. , Claiborn Candis , Finn Dennis
Published: February 2004

Surface‐based radiometers can be used to assess the atmospheric aerosol burden. During 1998, two multifilter rotating shadow‐band radiometers (MFRSRs), operated by Washington State University (WSU) and by the USDA UV‐B program, were used to collect data on the Columbia Plateau atmosphere. Analysis of these data by an automated Langley algorithm provided retrievals for total optical thickness, allowing for calculation of aerosol optical thickness (AOT) and the top‐of‐atmosphere (TOA) instrument signal. Statistical evaluation of the TOA signal permitted recalculation of optical thickness using the Bouguer‐Lambert‐Beer law and resulted in improved estimates of aerosol optical thickness (AOT). Results for AOT and the associated Ångström parameters are presented here for an April 1998 dust event for two colocated Columbia Plateau sites. AOT at 500 nm went from background levels (seasonally dominated by regional windblown dust) of ∼0.2 to more than 0.4 during the event maximum on April 27, not returning to normal levels until April 30. Comparison of 500‐nm AOT between the two MFRSR showed a root‐mean‐square (RMS) difference of 0.016. The Ångström exponent α reached a minimum of ∼0.2, and the β coefficient reached a maximum of ∼0.35, both on April 27, coincident with the AOT maximum. Contemporaneous aerosol sampling in Spokane, Washington, provided (1) elemental data that strongly support our interpretation of this event as an influx of Asian dust without significant sulfur enrichment and (2) event maximum PM10measurements ∼80 μg/m3consistent with Pullman event maximum AOT results, assuming a 3–4 km thick dust layer.
Isotopic composition of stratospheric water vapor: Implications for transport
Authors: Johnson David G. , Jucks Kenneth W. , Traub Wesley A. , Chance Kelly V.
Published: February 2004

We develop a series of models of transport in the upper tropical troposphere in order to explain the observed abundance and isotopic composition of stratospheric water vapor. We start with the Rayleigh fractionation process and add the effects of mixing and recirculation of stratospheric air through the upper troposphere. We compare our measurements with model calculations for a range of input parameters and find that the observations are best explained by a model that mixes vapor from roughly 11 km (carried aloft either as condensate or through radiative heating and uplift) with air that has been dehydrated (in a large convective system) to a mixing ratio substantially below the saturation mixing ratio of the mean tropical tropopause. The result is that while most of the moisture comes from convective outflow near 11 km, most of the air in the upper troposphere consists of dehydrated air from convective systems with cloud top temperatures below that of the mean tropical tropopause. We also find that the water vapor mixing ratio in the stratosphere is determined not only by the temperature of the tropical tropopause but also by the relative importance of radiative heating, recirculation of stratospheric air, and deep convection in supplying air to the upper troposphere. Our results show that water vapor isotope ratios are a powerful diagnostic tool for testing the results of general circulation models.
Aerosol optical depth measurements during the Aerosols99 experiment
Authors: Voss Kenneth J. , Welton Ellsworth J. , Quinn Patricia K. , Frouin Robert , Miller Mark , Reynolds R. Michael
Published: February 2004

The Aerosols99 cruise took place during the period from January 14 to February 8, 1999, on the R/V Ronald Brown. The cruise track was almost a straight line in the southeast direction from Norfolk, Virginia, to Cape Town, South Africa, and afforded the opportunity to sample several different aerosol regimes over the North and South Atlantic. Handheld sunphotometers, a shadowband radiometer (FRSR), and a LIDAR were used to measure the aerosol optical depth (AOD) during the cruise. The AOD and angstrom exponent α (spectral dependence of the AOD) varied strongly between regimes. Maritime regions typically had AOD (500 nm) of approximately 0.10±0.03, with α around 0.3±0.3. An African dust event was encountered in which the AOD (500 nm) averaged 0.29±0.05 with an α of 0.36±0.13. At the Intertropical Convergence Zone (ITCZ), no measurements were obtained because of cloudiness; however, after the ITCZ we encountered a biomass burning aerosol with high average AOD (500 nm) of 0.36±0.13, and a high α (0.88±0.30). Farther south the aerosol went back to the low levels of a typical marine aerosol.
Vertical profiling of optical and physical particle properties over the tropical Indian Ocean with six‐wavelength lidar: 1. Seasonal cycle
Authors: Müller Detlef , Franke Kathleen , Wagner Frank , Althausen Dietrich , Ansmann Albert , Heintzenberg Jost
Published: February 2004

For the first time the seasonal cycle of optical and physical particle properties over the Indian Ocean was observed with a six‐wavelength aerosol lidar. The measurements were performed in the framework of the Indian Ocean Experiment at the Maldives International Airport in Hulule island (4.1° N, 73.3° E) from February 1999 until March 2000. The advection of air masses from India and Southeast Asia during the northeast monsoon season showed multiple particle layers with strong backscatter and extinction coefficients to heights of 4 km. Approximately 30–45% of the monthly‐mean optical depth was contributed by elevated particle layers above 1000 m height. Mean optical depths of ∼0.32 at 530 nm and mean extinction‐to‐backscatter (lidar) ratios from 45 to 75 sr at 532 nm indicated heavily polluted aerosols. Observations during March 2000 showed that 56% of the mean optical depth of 0.29 was contributed by elevated particle layers. Lidar ratios between 45 and 60 sr were in the same range as in the previous year. The southwest monsoon season was characterized by the advection of particles in maximum heights of 5000 m from Africa and Arabia. Backscatter coefficients were considerably less compared to the findings during the winter monsoon. Low mean optical depths of 0.15, with a contribution of 48% from layers above 1000 m, and lidar ratios from 35–55 sr indicated a mixture of clean‐marine and clean‐continental aerosol conditions. During the intermonsoon season, clean‐marine conditions prevailed with particles to maximum heights of 2.5 km, mean optical depths of 0.13, and lidar ratios from 20 to 30 sr.
A model for prediction of desert dust cycle in the atmosphere
Authors: Nickovic Slobodan , Kallos George , Papadopoulos Anastasios , Kakaliagou Olga
Published: February 2004

An integrated modeling system has been developed to accurately describe the dust cycle in the atmosphere. It is based on the SKIRON/Eta modeling system and the Eta/NCEP regional atmospheric model. The dust modules of the entire system incorporate the state of the art parameterizations of all the major phases of the atmospheric dust life such as production, diffusion, advection, and removal. These modules also include effects of the particle size distribution on aerosol dispersion. The dust production mechanism is based on the viscous/turbulent mixing, shear‐free convection diffusion, and soil moisture. In addition to these sophisticated mechanisms, very high resolution databases, including elevation, soil properties, and vegetation cover are utilized. The entire system is easily configurable and transferable to any place on the Earth, it can cover domains on almost any size, and its horizontal resolution can vary from about 100 km up to approximately 4 km. It can run on one‐way‐nested form if necessary. The performance of the system has been tested for various dust storm episodes, in various places and resolution using gridded analysis or forecasting fields from various sources (ECMWF and NCEP) for initial and boundary conditions. The system is in operational use during the last two years, providing 72 hour forecasts for the Mediterranean region. The results are available on the internet (http://www.icod.org.mt and http://forecast.uoa.gr).
Quasi‐biennial oscillation in vertical velocity inferred from trace gas data in the equatorial lower stratosphere
Authors: Niwano Masanori , Shiotani Masato
Published: February 2004

Vertical velocity variations associated with the quasi‐biennial oscillation (QBO) in the equatorial lower stratosphere are investigated with the Halogen Occultation Experiment (HALOE) data from 1993 to 1998. The vertical velocity is inferred from ascent rates of an annual cycle in total water ([H2O] + 2[CH4]) profiles around the 20–60 hPa layer over the equator. The zonally averaged ascent rates of total water anomalies exhibit QBO‐related variations with anomalies of 0.10–0.15 mm s−1 between 20 and 40 hPa at the equator, whereas there scarcely exists an annual cycle in the ascent rates. The QBO variation of the ascent rates shows that its positive anomalies precede negative anomalies of temperature and ozone variations by about 2–3 months at the equator and 30–60 hPa. This phase relationship is in conflict with former results from several two‐dimensional model studies, which have reported that vertical velocity variations are almost out of phase with temperature anomalies preceding ozone anomalies by a few months. It is supposed that these differences could be caused by the observed large tendency of temperature anomalies, which is related to the observed rapid acceleration of the QBO westerly. An estimate of vertical advection of zonal momentum expected from the ascent rates suggests that the asymmetric acceleration of the zonal wind QBO can be explained by the QBO‐induced vertical velocity being asymmetric between the easterly and the westerly shear zones.
Vertical profiles of cloud condensation nuclei above Wyoming
Authors: Delene David J. , Deshler Terry
Published: February 2004

High‐resolution (125 m) profiles of cloud condensation nucleus (CCN) number concentration at 1.0% supersaturation were measured 12 times at Laramie, Wyoming (41°N), and twice at Lauder, New Zealand (45°S), extending from the surface to 200 mbar. The balloon‐borne instruments included a condensation nucleus (CN) counter to measure particles with diameter greater than ∼10 nm and an optical particle counter to measure particles with diameter >0.3 μm (D0.3). Within vertical profiles, variations in CCN concentration were typically positively correlated with changes in CN and D0.3 concentrations and often corresponded with changes in relative humidity, typically positively, but occasionally negatively correlated. The aerosol profiles generally show several distinct layers that can be defined by equivalent potential temperature and relative humidity. These layers are used to summarize the 14 vertical profiles by classifying aerosol measurements into five distinct atmospheric layers: surface, lower tropospheric, upper tropospheric, stratospheric and regions of high humidity. Laramie summer and winter profiles show that the mean CCN concentration decreases between the lower and upper tropospheric layers (450 to 130 cm−3 in summer, 150 to 65 cm−3 in winter). The average summer CCN/CN ratio in Wyoming shows an increase from 0.09 in the lower troposphere to 0.17 in the upper troposphere. The summer CCN concentrations at Lauder, New Zealand, were about twice the summer CCN concentrations measured at Laramie, Wyoming, while the CN and D0.3 concentrations were approximately the same.