bluuebunny/crossref_metadata_2025 huggingface dataset:
A numerical study of tropical cross-tropopause transport by convective overshoots during the TROCCINOX golden day
Authors: Chaboureau J.-P. , Cammas J.-P. , Duron J. , Mascart P. J. , Sitnikov N. M. , Voessing H.-J.
Published: April 2010

Abstract. Observations obtained during the Tropical Convection, Cirrus and Nitrogen Oxides (TROCCINOX) golden day have revealed the presence of ice particles up to 410 K (18.2 km) 2 km above the local tropopause. The case is investigated using a three-dimensional quadruply nested non-hydrostatic simulation and Meteosat Second Generation (MSG) observations. The simulation fairly well reproduces the measurements along the flight track. A reasonable agreement with MSG observations is also achieved: the 10.8-μm brightness temperature (BT) minimum of 187 K is reproduced (a value 6 K colder than the environmental cold-point temperature) as well as the positive BT difference between the 6.2- and 10.8-μm bands, an overshoot signature. The simulation produces several overshooting plumes up to 410 K yielding an upward transport of water vapour of a few tons per second across the tropical tropopause. The estimated mass flux agree with those derived from over tracer budgets indicating that convection transport mass across the tropopause.
Interference errors in infrared remote sounding of the atmosphere
Authors: Sussmann R. , Borsdorff T.
Published: April 2010

Abstract. More and more profiles of atmospheric state parameters are being retrieved from remote soundings in the infrared spectral domain. Classical error analysis, which was originally applied to microwave sounding systems, distinguishes between "smoothing errors," "forward model errors," "forward model parameter errors," and "retrieval noise errors". We show that for infrared soundings "interference errors", which have not been treated up to now, can be significant. Interference errors originate from "interfering species" that introduce signatures into the spectral measurement which overlap with the spectral features used for retrieval of the target species. This is a frequent situation in infrared atmospheric spectra where the vibration-rotation bands of different species often overlap; it is not the case in the microwave region. This paper presents a full theoretical formulation of interference errors. It requires a generalized state vector including profile entries for all interfering species. This leads to a generalized averaging kernel matrix made up of classical averaging kernels plus here defined "interference kernels". The latter are used together with climatological covariances for the profiles of the interfering species in order to quantify the interference errors. To illustrate the methods we apply them to a real sounding and show that interference errors have a significant impact on standard CO profile retrievals from ground-based mid-infrared solar absorption spectra. We also demonstrate how to minimize overall error, which is a trade-off between minimizing interference errors and the smoothing error. The approach used in this paper can be applied to soundings of all infrared-active atmospheric species, which includes more than two dozen different gases relevant to climate and ozone. And this holds for all kind of infrared remote sounding systems, i.e., retrievals from ground-based, balloon-borne, airborne, or satellite spectroradiometers.
Characterization of MIPAS elevation pointing
Authors: Kiefer M. , von Clarmann T. , Grabowski U. , De Laurentis M. , Mantovani R. , Milz M. , Ridolfi M.
Published: April 2010

Abstract. Sufficient knowledge of the pointing is essential for analyses of limb emission measurements. The scientific retrieval processor for MIPAS operated at IMK allows to retrieve pointing information in terms of tangent altitudes along with temperature. The retrieved tangent altitudes are independent of the engineering Line-Of-Sight (LOS) information delivered with the ESA Level 1b product. The difference of pointing retrieved from the reprocessed high resolution MIPAS spectra and the engineering pointing information was examined with respect to spatial/temporal behaviour. Among others the following characteristics of MIPAS pointing could be identified: Generally the engineering tangent altitudes are too high by 0–1.8 km with conspicuous variations in this range over time. Prior to December of 2003 there was a drift of about 50–100 m/h, which was due to a slow change in the satellite attitude. A correction of this attitude is done twice a day, which led to discontinuities in the order of up to 2 km in the tangent altitudes. There is a systematic difference in the mispointing between the poles which amounts to 1.5–2 km, i.e. there is a conspicuous orbit-periodic feature. The analysis of the correlation between the instrument's viewing angle azimuth and differential mispointing supports the hypotheses that a major part of this latter phenomenon can be attributed to an uncorrected roll angle of the satellite/instrument system of approximately 54 mdeg. Complementary to this, ESA operational LOS calibration results were used to characterize MIPAS pointing. For this purpose MIPAS is used as a radiometer while the passage of infrared bright stars through the instrument's field of view is recorded. Deviation from expected time of passage gives information about mispointing. A pronounced seasonal variation of the LOS is seen before a correction of on-board software took place in December of 2003. Further a pitch bias of 24 mdeg with respect to the platform attitude information is found.
Cloud condensation nucleus (CCN) behavior of organic aerosol particles generated by atomization of water and methanol solutions
Authors: Rissman T. A. , Varutbangkul V. , Surratt J. D. , Topping D. O. , McFiggans G. , Flagan R. C. , Seinfeld J. H.
Published: April 2010

Abstract. Cloud condensation nucleus (CCN) experiments were carried out for malonic acid, succinic acid, oxalacetic acid, DL-malic acid, glutaric acid, DL-glutamic acid monohydrate, and adipic acid, using both water and methanol as atomization solvents, at three operating supersaturations (0.11% 0.21%, and 0.32%) in the Caltech three-column CCN instrument (CCNC3). Predictions of CCN behavior for five of these compounds were made using the Aerosol Diameter Dependent Equilibrium Model (ADDEM). The experiments presented here expose important considerations associated with the laboratory measurement of the CCN behavior of organic compounds. Choice of atomization solvent results in significant differences in CCN activation for some of the compounds studied, which could result from residual solvent, particle morphology differences, and chemical reactions between the particle and gas phases. Also, significant changes in aerosol size distribution occurred after classification in a differential mobility analyzer (DMA) for malonic acid and glutaric acid. Filter analysis of adipic acid atomized from methanol solution indicates that gas-particle phase reactions may have taken place after atomization and before the methanol was removed from the sample gas stream. Careful consideration of these experimental issues is necessary for successful design and interpretation of laboratory CCN measurements.
Discriminating raining from non-raining clouds at mid-latitudes using multispectral satellite data
Authors: Nauss T. , Kokhanovsky A. A.
Published: April 2010

Abstract. We propose a new method for the delineation of precipitation using cloud properties derived from optical satellite data. This approach is not only sufficient for the detection of mainly convective driven precipitation by means of the commonly used connection between infrared cloud-top temperature and rainfall probability but enables the detection of stratiform precipitation (e.g., in connection with mid-latitude frontal systems). The scheme presented is based on the concept model, that precipitating clouds must have both a large enough vertical extent and large enough droplets. Therefore, we have analyzed Terra-MODIS scenes during the severe European summer floods in 2002 and retrieved functions for the computation of an auto-adaptive threshold value of the effective cloud droplet radius with respect to the corresponding optical thickness which links these cloud properties with rainfall areas on a pixel basis.
Analysis of the frequency-dependent response to wave forcing in the extratropics
Authors: Haklander A. J. , Siegmund P. C. , Kelder H. M.
Published: April 2010

Abstract. A quasigeostrophic model for the frequency-dependent response of the zonal-mean flow to planetary-wave forcing at Northern Hemisphere (NH) midlatitudes is applied to 4-D-Var ECMWF analysis data for six extended winter seasons. The theoretical response is a non-linear function of the frequency of the forcing, the thermal damping time α−1, and a scaling parameter μ which includes the aspect ratio of the meridional to the vertical length scale of the response. Non-linear regression of the calculated response from the analyses onto the theoretical response yields height-dependent estimates for both α−1 and μ. The thermal damping time estimated from this dynamical model is about 2 days in the troposphere, 7–10 days in the stratosphere, and 2–4 days in the lower mesosphere. These estimates generally lie within the range of existing estimates, although the values we find for the troposphere are significantly smaller than those calculated in several radiative transfer modeling studies. At most levels, the estimates for μ are significantly lower than can be derived from scaling arguments that apply outside the forcing region. We illustrate with an example how the response of the meridional circulation inside the forcing area can have a higher aspect ratio than the effective response outside the forcing area.
Development of a cloud microphysical model and parameterizations to describe the effect of CCN on warm cloud
Authors: Kuba N. , Fujiyoshi Y.
Published: April 2010

Abstract. First, a hybrid cloud microphysical model was developed that incorporates both Lagrangian and Eulerian frameworks to study quantitatively the effect of cloud condensation nuclei (CCN) on the precipitation of warm clouds. A parcel model and a grid model comprise the cloud model. The condensation growth of CCN in each parcel is estimated in a Lagrangian framework. Changes in cloud droplet size distribution arising from condensation and coalescence are calculated on grid points using a two-moment bin method in a semi-Lagrangian framework. Sedimentation and advection are estimated in the Eulerian framework between grid points. Results from the cloud model show that an increase in the number of CCN affects both the amount and the location of precipitation. Additionally, results from the hybrid microphysical model and Kessler's parameterization were compared. Second, new parameterizations were developed that estimate the number and size distribution of cloud droplets given the updraft velocity and the number of CCN. The parameterizations were derived from the results of numerous numerical experiments that used the cloud microphysical parcel model. The input information of CCN for these parameterizations is only several values of CCN spectrum (they are given by CCN counter for example). It is more convenient than conventional parameterizations those need values concerned with CCN spectrum, C and k in the equation of N=CSk, or, breadth, total number and median radius, for example. The new parameterizations' predictions of initial cloud droplet size distribution for the bin method were verified by using the aforesaid hybrid microphysical model. The newly developed parameterizations will save computing time, and can effectively approximate components of cloud microphysics in a non-hydrostatic cloud model. The parameterizations are useful not only in the bin method in the regional cloud-resolving model but also both for a two-moment bulk microphysical model and for a global model. The effects of sea salt, sulfate, and organic carbon particles were also studied with these parameterizations and global model.
Characterization of iodine particles with Volatilization-Humidification Tandem Differential Mobility Analyser (VH-TDMA), Raman and SEM techniques
Authors: Ristovski Z. D. , Fletcher C. , D’Anna B. , Johnson G. R. , Bostrom J. T.
Published: April 2010

Abstract. Particles formed upon photo-oxidation of CH2I2 and particles of I2O5 and HIO3 have been studied using a Volatilisation and Humidification Tandem Differential Mobility Analyser (VH-TDMA) system. Volatilization and hygroscopic behaviour have been investigated as function of temperature (from 25 to 400°C), humidity (RH from 80 to 98%), initial aerosol sizes (from 27 to 100 nm mobility diameter) and in nitrogen or air as the sheath gasses. The volatility behaviour of particles formed upon photo-oxidation of CH2I2 is more similar to that of HIO3 particles in a filtered sheath air than in nitrogen, with the particle shrinkage occurring at 190°C and accompanied by hygroscopic growth. Despite its high solubility, HIO3 was found not to be hygroscopic at room temperature with no significant growth displayed until the thermodenuder temperature reached 200°C or above when the particles have transformed into I2O5. Diiodopentaoxide (I2O5) particles exhibit relatively low hygroscopic growth factors of 1.2–2 in the humidity range investigated. Scanning Electron Microscopy (SEM) of particles formed upon photo-oxidation of CH2I2 shows that their primary elemental components were iodine and oxygen in a stoichiometric ratio of approximately 1:2 with 10% error. Both Raman spectra and SEM show poor crystallinity for all the aerosols produced.
Model intercomparison of indirect aerosol effects
Authors: Penner J. E. , Quaas J. , Storelvmo T. , Takemura T. , Boucher O. , Guo H. , Kirkevåg A. , Kristjánsson J. E. , Seland Ø.
Published: April 2010

Abstract. Modeled differences in predicted effects are increasingly used to help quantify the uncertainty of these effects. Here, we examine modeled differences in the aerosol indirect effect in a series of experiments that help to quantify how and why model-predicted aerosol indirect forcing varies between models. The experiments start with an experiment in which aerosol concentrations, the parameterization of droplet concentrations and the autoconversion scheme are all specified and end with an experiment that examines the predicted aerosol indirect forcing when only aerosol sources are specified. Although there are large differences in the predicted liquid water path among the models, the predicted aerosol indirect effect for the first experiment is rather similar. Changes to the autoconversion scheme can lead to large changes in the liquid water path of the models and to the response of the liquid water path to changes in aerosols. Nevertheless, these changes do not necessarily lead to large changes in the radiative forcing. The parameterization of cloud fraction within models is not sensitive to the aerosol concentration, and, therefore, the response of the modeled cloud fraction within the present models appears to be smaller than that which would be associated with model ''noise''. The prediction of aerosol concentrations, given a fixed set of sources, leads to some of the largest differences in the predicted aerosol indirect radiative forcing among the models. Thus, this aspect of modeling requires significant improvement in order to improve the prediction of aerosol indirect effects.
The Heidelberg iterative cloud retrieval utilities (HICRU) and its application to GOME data
Authors: Grzegorski M. , Wenig M. , Platt U. , Stammes P. , Fournier N. , Wagner T.
Published: April 2010

Abstract. Information about clouds, in particular the accurate identification of cloud free pixels, is crucial for the retrieval of tropospheric vertical column densities from space. The Heidelberg Iterative Cloud Retrieval Utilities (HICRU) retrieve effective cloud fraction using spectra of two instruments designed for trace gas retrievals from space: The Global Ozone Monitoring Experiment (GOME) on the European Remote Sensing Satellite (ERS-2) and the SCanning Imaging Absorption SpectroMeter for Atmospheric CHartographY (SCIAMACHY) on ENVISAT. HICRU applies the widely used threshold method to the so-called Polarization Monitoring Devices (PMDs) with higher spatial resolution compared to the channels used for trace gas retrievals. Cloud retrieval and in particular the identification of cloud free pixels is improved by HICRU through a sophisticated, iterative retrieval of the thresholds which takes their dependency on different instrumental and geometrical parameters into account. The lower thresholds, which represent the surface albedo and strongly affect the results of the algorithm, are retrieved accurately through a four stage classification scheme using image sequence analysis. The design and the results of the algorithm applied to GOME data are described and compared to several other cloud algorithms for GOME. The differences to other cloud algorithms are discussed with respect to the particular characteristics of the algorithms.
The impact of cirrus clouds on tropical troposphere-to-stratosphere transport
Authors: Corti T. , Luo B. P. , Fu Q. , Vömel H. , Peter T.
Published: April 2010

Abstract. Although it is well known that air enters the stratosphere preferentially through upwelling in the tropics, the exact mechanisms of troposphere-to-stratosphere transport (TST) are still unknown. Previously proposed mechanisms have been found either to be too slow (e.g., clear sky upwelling) to provide agreement with in situ tracer measurements, or to be insufficient in mass flux to act as a major supply for the Brewer-Dobson circulation (e.g., convective overshooting). In this study we evaluate whether the lofting of air via cirrus cloud-radiation interaction might offer an alternative path for TST, which is responsible for a significant fraction of the observed air mass transport. We find that a combination of deep convection and subsequent upwelling associated with cirrus clouds and clear sky can explain the supply of air for the Brewer-Dobson circulation. Thus, upwelling associated with cirrus clouds offers a mechanism for the missing second stage, which links the first stage of TST, deep convection, to the third stage, the Brewer-Dobson circulation.
The semianalytical cloud retrieval algorithm for SCIAMACHY II. The application to MERIS and SCIAMACHY data
Authors: Kokhanovsky A. A. , von Hoyningen-Huene W. , Rozanov V. V. , Noël S. , Gerilowski K. , Bovensmann H. , Bramstedt K. , Buchwitz M. , Burrows J. P.
Published: April 2010

Abstract. The Semianalytical CloUd Retrieval Algorithm (SACURA) is applied to the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) data. In particular, for the first time we derive simultaneously cloud optical thickness (COT), liquid water path (LWP), cloud top height (CTH), and cloud droplet radius (CDR) using SCIAMACHY measurements in the visible (442 nm, COT), in the oxygen A-band (755–775 nm, CTH) and in the infrared (1550 nm, CDR). Some of the results obtained are compared with those derived from the Medium Resolution Imaging Spectrometer (MERIS), which has better spatial resolution and observe almost the same scene as SCIAMACHY.
A Lagrangian analysis of the impact of transport and transformation on the ozone stratification observed in the free troposphere during the ESCOMPTE campaign
Authors: Colette A. , Ancellet G. , Menut L. , Arnold S. R.
Published: April 2010

Abstract. The ozone variability observed by tropospheric ozone lidars during the ESCOMPTE campaign is analyzed by means of a hybrid-Lagrangian modeling study. Transport processes responsible for the formation of ozone-rich layers are identified using a semi-Lagrangian analysis of mesoscale simulations to identify the planetary boundary layer (PBL) footprint in the free troposphere. High ozone concentrations are related to polluted air masses exported from the Iberian PBL. The chemical composition of air masses coming from the PBL and transported in the free troposphere is evaluated using a Lagrangian chemistry model. The initial concentrations are provided by a model of chemistry and transport. Different scenarios are tested for the initial conditions and for the impact of mixing with background air in order to perform a quantitative comparison with the lidar observations. For this meteorological situation, the characteristic mixing time is of the order of 2 to 5 days depending on the initial conditions. Ozone is produced in the free troposphere within most air masses exported from the Iberian PBL at an average rate of 0.2 ppbv h-1, with a maximum ozone production of 0.4 ppbv h-1. Transport processes from the PBL are responsible for an increase of 13.3 ppbv of ozone concentrations in the free troposphere compared to background levels; about 45% of this increase is attributed to in situ production during the transport rather than direct export of ozone.
Technical note: Characterization of a static thermal-gradient CCN counter
Authors: Frank G. P. , Dusek U. , Andreae M. O.
Published: April 2010

Abstract. The static (parallel-plate thermal-gradient) diffusion chamber (SDC) was one of the first instruments designed to measure cloud condensation nuclei (CCN) concentrations as a function of supersaturation. It has probably also been the most widely used type of CCN counter. This paper describes the detailed experimental characterization of a SDC CCN counter, including calibration with respect to supersaturation and particle number concentration. In addition, we investigated the proposed effect of lowered supersaturation because of water vapor depletion with increasing particle concentration. The results obtained gives a larger understanding why and in which way it is necessary to calibrate the SDC CCN counter. The calibration method is described in detail as well. The method can, in parts, be used for calibrations also for other types of CCN counters. We conclude the following: 1) it is important to experimentally calibrate SDC CCN counters with respect to supersaturation, and not only base the supersaturation on the theoretical description of the instrument; 2) the number concentration calibration needs to be performed as a function of supersaturation, also for SDC CCN counter using the photographic technique; and 3) we observed no evidence that water vapor depletion lowered the supersaturation.
Comparison of GOME tropospheric NO2 columns with NO2 profiles deduced from ground-based in situ measurements
Authors: Schaub D. , Boersma K. F. , Kaiser J. W. , Weiss A. K. , Folini D. , Eskes H. J. , Buchmann B.
Published: April 2010

Abstract. Nitrogen dioxide (NO2) vertical tropospheric column densities (VTCs) retrieved from the Global Ozone Monitoring Experiment (GOME) are compared to coincident ground-based tropospheric NO2 columns. The ground-based columns are deduced from in situ measurements at different altitudes in the Alps for 1997 to June 2003, yielding a unique long-term comparison of GOME NO2 VTC data retrieved by KNMI/BIRA with independently derived tropospheric NO2 profiles. A first comparison relates the GOME columns to the ground-based NO2 profiles that are directly integrated to tropospheric columns. A second comparison includes averaging kernel (AK) information, which makes the comparison independent from the a priori NO2 profile used in the GOME retrieval. This allows splitting the total difference between the column data sets into two contributions: one that is due to differences between the a priori and the ground-based NO2 profile shapes, and another that can be attributed to uncertainties in both the remaining retrieval parameters and the ground-based in situ NO2 profiles. For anticyclonic clear sky conditions the comparison indicates a good agreement between the columns (n=157, R=0.70/0.74 without/with AK included). Both data sets show a similar seasonal behaviour with a distinct maximum of spring NO2 VTCs. The mean relative difference (with respect to the ground-based columns) is −7% with a standard deviation of 40% and GOME on average slightly underestimating the ground-based columns. Further analysis indicates small GOME columns being systematically smaller than the ground-based ones. The influence of different shapes in the a priori and the ground-based NO2 profile is analysed by considering AK information. It is moderate and indicates similar shapes of the profiles for clear sky conditions. Only for large GOME columns, differences between the profile shapes explain the larger part of the relative difference. In contrast, the other error sources give rise to the larger relative differences found towards smaller columns. Further, for the clear sky cases, errors from different sources are found to compensate each other partially. The comparison for cloudy cases indicates a poorer agreement between the columns (n=60, R=0.61). The mean relative difference between the columns is 60% with a standard deviation of 118% and GOME on average overestimating the ground-based columns. The clear improvement after inclusion of AK information (n=60, R=0.87) suggests larger errors in the a priori NO2 profiles under cloudy conditions and demonstrates the importance of using the kernel information for (partially) clouded scenes.
Evaluated kinetic and photochemical data for atmospheric chemistry: Volume III – reactions of inorganic halogens
Authors: Atkinson R. , Baulch D. L. , Cox R. A. , Crowley J. N. , Hampson R. F. , Hynes R. G. , Jenkin M. E. , Rossi M. J. , Troe J.
Published: April 2010

Abstract. This article, the third in the series, presents kinetic and photochemical data evaluated by the IUPAC Subcommittee on Gas Kinetic Data Evaluation for Atmospheric Chemistry. It covers the gas phase and photochemical reactions of inorganic halogen species, which were last published in J. Phys. Chem. Ref. Data in 2000 (Atkinson et al., 2000), and were updated on the IUPAC website in 2003. The article consists of a summary sheet, containing the recommended kinetic parameters for the evaluated reactions, and five appendices containing the data sheets, which provide information upon which the recommendations are made.
Mesoscale circulations over complex terrain in the Valencia coastal region, Spain, Part 1: simulation of diurnal circulation regimes
Authors: Pérez-Landa G. , Ciais P. , Sanz M. J. , Gioli B. , Miglietta F. , Palau J. L. , Gangoiti G. , Millán M. M.
Published: April 2010

Abstract. We collected ground-based and aircraft data on meteorological parameters and CO2 fluxes and concentrations during a 2-week intensive campaign over the Valencia basin, as part of a process study to understand how mesoscale circulations over complex terrain develop and affect the atmospheric transport acting on surface CO2 fluxes. In this paper, we interpret the meteorological data during a selected case, with the help of a very high resolution mesoscale model to understand the diurnal cycle of mesoscale flow regimes, characterized by night-time katabatic drainage, morning sea-breeze development and subsequent coupling with mountain up-slopes, and evening flow-veering under larger-scale influences. At each step, a careful statistical analysis of the model performances is carried out. Despite the inherent complexity of the processes interacting with each other, and large model uncertainties for soil moisture boundary conditions and turbulence parameterizations, we show that it is possible to simulate faithfully the flow regimes, especially the inland progression and organization of the sea breeze. This provides confidence with respect to the future applicability of mesoscale models to establish a missing link between surface sources of CO2 and atmospheric concentration signals over complex terrain.
Mesoscale circulations over complex terrain in the Valencia coastal region, Spain, Part 2: linking CO2 surface fluxes with observed concentrations
Authors: Pérez-Landa G. , Ciais P. , Gangoiti G. , Palau J. L. , Carrara A. , Gioli B. , Miglietta F. , Schumacher M. , Millán M. M. , Sanz M. J.
Published: April 2010

Abstract. Several consecutive vertical profiles of CO2 concentration and meteorological parameters were collected during an intensive summer campaign in a coastal complex terrain region within the frame of the European Project RECAB (Regional Assessment and Modelling of the Carbon Balance in Europe). The region presents a marked diurnal cycle in the wind flow (analyzed in detail in a companion paper) as a consequence of the development of mesoscale circulations. In terms of the different stages of the diurnal cycle in the meteorology, these circulations result in an important coupling between atmospheric transport and surface CO2 fluxes. To understand the effects of this interaction on the spatial variability of the observed CO2 concentrations, we conduct a high-resolution simulation with a coupled biosphere-atmosphere model in the area of interest during a representative case study. Our model approach consists of estimating the regional NEE distribution by using a set of eddy-covariance measurements that are transported by a mesoscale model coupled to a Lagrangian particle dispersion model. Our simulations were able to successfully reproduce crucial processes controlling the mesoscale transport of CO2. Availability of both simulations and observations for our analysis allowed us to characterize the influence of the coupling between mesoscale circulations and biological processes in the spatial gradients of the CO2 concentrations. Temporal averages in the simulated CO2 distribution show a 3-D rectification effect consisting of: 1) horizontally, a CO2 deficit over land, mirrored by a CO2 excess over the sea and 2) vertically, the prevalence of mean CO2 depletion between 500 and 2000 m, and the permanent build-up of CO2 in the lower levels.
From molecular clusters to nanoparticles: second-generation ion-mediated nucleation model
Authors: Yu F.
Published: April 2010

Abstract. Ions, which are generated in the atmosphere by galactic cosmic rays and other ionization sources, may play an important role in the formation of atmospheric aerosols. In the paper, a new second-generation ion-mediated nucleation (IMN) model is presented. The new model explicitly treats the evaporation of neutral and charged clusters and it describes the evolution of the size spectra and composition of both charged and neutral clusters/particles ranging from small clusters of few molecules to large particles of several micrometers in diameter. Schemes used to calculate the evaporation coefficients for small neutral and charged clusters are consistent with the experimental data within the uncertainty range. The present IMN model, which is size-, composition-, and type-resolved, is a powerful tool for investigating the dominant mechanisms and key parameters controlling the formation and subsequent growth of nanoparticles in the atmosphere. This model can be used to analyze simultaneous measurements of the ion-mobility spectra and particle size distributions, which became available only recently. General features of the spectra for ions smaller than the critical size, size-dependent fractions of charged nanoparticles, and asymmetrical charging of freshly nucleated particles predicted by the new IMN model are consistent with recent measurements. Results obtained using the second generation IMN model, in which the most recent thermodynamic data for neutral and charged H2SO4-H2O clusters were used, suggest that ion-mediated nucleation of H2SO4-H2O can lead to a significant production of new particles in the lower atmosphere (including the boundary layer) under favorable conditions. It has been shown that freshly nucleated particles of few nanometers in size can grow by the condensation of low volatile organic compounds to the size of cloud condensation nuclei. In such cases, the chemical composition of nucleated particles larger than ~10 nm is dominated by organics.
A modified band approach for the accurate calculation of on-line photolysis rates in stratospheric-tropospheric Chemical Transport Models
Authors: Williams J. E. , Landgraf J. , Bregman A. , Walter H.
Published: April 2010

Abstract. Here we present an efficient and accurate method for the online calculation of photolysis rates relevant to both the stratosphere and troposphere for use in global Chemistry Transport Models. The method is a modified version of the band model introduced by Landgraf and Crutzen (1998) which has been updated to improve the performance of the approach for solar zenith angles >75° without the use of any implicit parameterisations. For this purpose, additional sets of band parameters have been defined for instances where the incident angle of the light beam is between 75–93°, in conjunction with a scaling component for the far UV region of the spectrum (λ=176.6–202.0 nm). For incident angles between 85–93° we introduce a modification for pseudo-sphericity that improves the accuracy of the 2-stream approximation. We show that this modified version of PIFM is accurate for angles <93° by comparing the resulting height resolved actinic fluxes with a recently developed full spherical reference model. We also show that the modified band method is more accurate than the original, with errors generally being ±10% throughout the atmospheric column for a diverse range of chemical species. Moreover, we perform certain sensitivity studies that indicate it is robust and performs well over a wide range of conditions relevant to the atmosphere.
Effects of methane outgassing on the Black Sea atmosphere
Authors: Kourtidis K. , Kioutsioukis I. , Rapsomanikis S.
Published: April 2010

Abstract. Methane in air and seawater was measured in the Eastern Black Sea during the 10–18 December 1999 BIGBLACK project cruise. The measurements allowed for the calculation of supersaturation ratios and methane fluxes across the air-sea interface. CH4 mixing ratios in air were generally in the 1.8–2.0 ppmv range, while surface (4 m depth) seawater concentrations varied from 5 to 100 ppmv. Above active seep areas, the water was supersaturated at around 500% with respect to the overlying atmosphere. Accordingly, flux densities varied greatly and were up to 4000 umol m-2 day-1. In the Sevastopol harbour, supersaturations up to around 3000%, similar to those at the Danube Delta, were observed, while in the Istanbul harbour supersaturations could not be determined because the very high values of water concentrations have led to detector saturation. Simple modelling shows that the observed fluxes do not have any substantial impact in the methane content of the Black Sea atmosphere, as they could only raise its concentrations by less than 1 ppb. On the other hand, calculations performed as part of the CRIMEA project, show that mud volcano eruptions could episodically raise the methane concentrations well above their regional background for several tens of kilometres downwind.
Polar tropospheric ozone depletion events observed in IGY
Authors: Roscoe H. K. , Roscoe J.
Published: April 2010

Abstract. The Royal Society expedition to Antarctica established a base at Halley Bay, in support of the International Geophysical Year of 1957–1958. Surface ozone was measured during 1958 only, using a prototype Brewer-Mast sonde. The envelope of maximum ozone was an annual cycle from 10 ppbv in January to 22 ppbv in August. These values are 35% less at the start of the year and 15% less at the end than modern values from Neumayer, also a coastal site. This may reflect a general increase in surface ozone since 1958 and differences in summer at the less windy site of Halley, or it may reflect ozone loss on the inlet together with long-term conditioning. There were short periods in September when ozone values decreased rapidly to near-zero, and some in August when ozone values were rapidly halved. Such ozone-loss episodes, catalysed by bromine compounds, became well-known in the Artic in the 1980s, and were observed more recently in the Antarctic. In 1958, very small ozone values were recorded for a week in midwinter during clear weather with light winds. The absence of similar midwinter reductions at Neumayer, or at Halley in the few measurements during 1987, means we must remain suspicious of these small values, but we can find no obvious reason to discount them. The dark reaction of ozone and seawater ice observed in the laboratory may be fast enough to explain them if the salinity and surface area of the ice is sufficiently amplified by frost flowers.
Atmospheric carbon gases retrieved from SCIAMACHY by WFM-DOAS: improved global CO and CH4 and initial verification of CO2 over Park Falls (46° N, 90° W)
Authors: de Beek R. , Buchwitz M. , Noël S. , Burrows J. P. , Bovensmann H. , Bruns M. , Bremer H. , Bergamaschi P. , Körner S. , Heimann M.
Published: April 2010

Abstract. The three carbon gases carbon monoxide (CO), carbon dioxide (CO2), and methane (CH4) are important atmospheric constituents affecting air quality and climate. The nadir spectra of reflected and scattered solar radiation in the near-infrared region, as observed by SCIAMACHY/ENVISAT, contain information on the vertical columns of these gases. A modified DOAS algorithm (WFM-DOAS) has been developed to retrieve this information. The main SCIAMACHY/WFM-DOAS data products are CO vertical columns and dry-air column averaged mixing ratios of methane and CO2, denoted XCH4 and XCO2, respectively. For CO and methane we present new results obtained with an improved version of WFM-DOAS (v0.5). The SCIAMACHY data products have been compared with global reference data (MOPITT for CO, TM5 model simulations for XCH4). The comparisons indicate that major problems of the previous version of WFM-DOAS (v0.4x) related to the varying ice-layer on the SCIAMACHY channel 8 detector have been solved. On average, the SCIAMACHY CO agrees within 10% (standard deviation 30%) with MOPITT but regionally, especially over northern South America, large differences have been found (up to about 80%). For methane we present global and regional maps which are compared to TM5 model simulations performed using standard emission inventories. Overall, there is good agreement but regionally there are substantial differences, e.g., due to limitations of current methane emission inventories. It still needs to be assessed by how much emission inventories can be improved by using the SCIAMACHY data. Concerning CO2 we present a comparison of SCIAMACHY XCO2 (WFM-DOAS v0.4) with TM3 model simulations over Park Falls, Wisconsin, USA. The peak-to-peak XCO2 variability as measured by SCIAMACHY (seasonal cycle of year 2003–2005 data) is ~13 ppmv, in good agreement with preliminary analysis of ground-based Fourier Transform Spectrometer (FTS) measurements, which is a factor of 2.3 larger than the XCO2 variability of TM3 model simulation for 2003. Park Falls is one of the few FTS ground stations which measure column averaged CO2 and detailed comparison with these measurements (after data release) will help identifying the reason for the observed differences between SCIAMACHY and global (atmospheric) carbon models such as TM3 as reported here and in previous studies. For all three carbon gases we present regional results including seasonal variation focusing on China.
Combined observational and modeling based study of the aerosol indirect effect
Authors: Storelvmo T. , Kristjansson J. E. , Myhre G. , Johnsrud M. , Stordal F.
Published: April 2010

Abstract. The indirect effect of aerosols via liquid clouds is investigated by comparing aerosol and cloud characteristics from the Global Climate Model CAM-Oslo to those observed by the MODIS instrument onboard the TERRA and AQUA satellites (http://modis.gsfc.nasa.gov). The comparison is carried out for 15 selected regions ranging from remote and clean to densely populated and polluted. For each region, the regression coefficient and correlation coefficient for the following parameters are calculated: Aerosol Optical Depth vs. Liquid Cloud Optical Thickness, Aerosol Optical Depth vs. Liquid Cloud Droplet Effective Radius and Aerosol Optical Depth vs. Cloud Liquid Water Path. Modeled and observed correlation coefficients and regression coefficients are then compared for a 3-year period starting in January 2001. Additionally, global maps for a number of aerosol and cloud parameters crucial for the understanding of the aerosol indirect effect are compared for the same period of time. Significant differences are found between MODIS and CAM-Oslo both in the regional and global comparison. However, both the model and the observations show a positive correlation between Aerosol Optical Depth and Cloud Optical Depth in practically all regions and for all seasons, in agreement with the current understanding of aerosol-cloud interactions. The correlation between Aerosol Optical Depth and Liquid Cloud Droplet Effective Radius is variable both in the model and the observations. However, the model reports the expected negative correlation more often than the MODIS data. Aerosol Optical Depth is overall positively correlated to Cloud Liquid Water Path both in the model and the observations, with a few regional exceptions.
Scavenging of ultrafine particles by rainfall at a boreal site: observations and model estimations
Authors: Andronache C. , Grönholm T. , Laakso L. , Phillips V. , Venäläinen A.
Published: April 2010

Abstract. Values of the scavenging coefficient were determined from observations of ultrafine particles (with diameters in the range 10–510 nm) during rain events at a boreal forest site in Southern Finland between 1996 and 2001. The estimated range of values of the scavenging coefficient was [7×10−6–4×10−5] s−1, which is generally higher than model calculations based only on below-cloud processes (Brownian diffusion, interception, and typical charge effects). A new model that includes below-cloud scavenging processes, mixing of ultrafine particles from the boundary layer (BL) into cloud, followed by cloud condensation nuclei activation and in-cloud removal by rainfall, is presented. The effective scavenging coefficients estimated from this new model have values comparable with those obtained from observations. Results show that ultrafine particle removal by rain depends on aerosol size, rainfall intensity, mixing processes between BL and cloud elements, in-cloud scavenged fraction, in-cloud collection efficiency, and in-cloud coagulation with cloud droplets. Implications for the treatment of scavenging of BL ultrafine particles in numerical models are discussed.
Atmospheric sulphuric acid and aerosol formation: implications from atmospheric measurements for nucleation and early growth mechanisms
Authors: Sihto S.-L. , Kulmala M. , Kerminen V.-M. , Dal Maso M. , Petäjä T. , Riipinen I. , Korhonen H. , Arnold F. , Janson R. , Boy M. , Laaksonen A. , Lehtinen K. E. J.
Published: April 2010

Abstract. We have investigated the formation and early growth of atmospheric secondary aerosol particles building on atmospheric measurements. The measurements were part of the QUEST 2 campaign which took place in spring 2003 in Hyytiälä (Finland). During the campaign numerous new aerosol particle formation events occurred of which 15 were accompanied by gaseous sulphuric acid measurements. Our detailed analysis of these 15 events is focussed on nucleation and early growth (to a diameter of 3 nm) of fresh particles. It revealed that new particle formation seems to be a function of the gaseous sulphuric acid concentration to the power from one to two. The former would be consistent with the recently developed activation theory while the latter would be consistent with the kinetic nucleation theory. We find that some events are dominated by the activation mechanism and some are dominated by the kinetic mechanism. Inferred coefficients for the two nucleation mechanisms are correlated with the product of gaseous sulphuric acid and ammonia concentrations. This indicates that besides gaseous sulphuric acid also ammonia has a role in nucleation. Early growth of fresh particles to a diameter of 3 nm has a mean rate of 1.2 nm/h and is clearly correlated with the gaseous sulphuric acid concentration.
Re-evaluation of the 1950–1962 total ozone record from Longyearbyen, Svalbard
Authors: Vogler C. , Brönnimann S. , Hansen G.
Published: April 2010

Abstract. The historical total ozone measurements taken with Dobson Spectrophotometer #8 at Longyearbyen, Svalbard, Norway, in the period 1950–1962 have been re-analyzed and homogenized based on the original measurement logs, using updated relevant parameters. In lack of sufficient calibration information, an empirical quality assessment was performed, based on a climatological comparison with ozone measurements in Tromsø, using TOMS data at both sites in the period 1979–2001, and Dobson data in the period 1950–1962. The assessment revealed that, as in the case of the Tromsø measurements, the C wavelength pair direct-sun measurements are most trustworthy (and most frequent), while the WMO standard reference mode AD direct-sun has a systematic bias relative to this data set. Zenith-blue (ZB) measurements at solar zenith angles (SZA) <80° were homogenized using two different polynomials before and from 1957; also ZB measurements at larger SZAs were homogenized by means of a normalization function derived from days with measurements over a wide range of SZAs. CC' zenith-cloudy measurements, which are particularly frequent during the summer months, were homogenized by applying correction factors for only two different cloud types: high thin clouds and medium/low/thick clouds; a further diversification of corrections reflecting cloud conditions did not prove significant. The combination of all measurements yields a total of 4837 single values, covering 1676 days from September 1950 to September 1962; moon measurements during the polar night add another 137 daily means. The re-evaluated data show a convincing agreement with measurements since 1979 (TOMS, SAOZ, Dobson) as well as with the 1957–1962 data stored at the World Ozone and UV Data Centre (WOUDC).
The 1986–1989 ENSO cycle in a chemical climate model
Authors: Brönnimann S. , Schraner M. , Müller B. , Fischer A. , Brunner D. , Rozanov E. , Egorova T.
Published: April 2010

Abstract. A pronounced ENSO cycle occurred from 1986 to 1989, accompanied by distinct dynamical and chemical anomalies in the global troposphere and stratosphere. Reproducing these effects with current climate models not only provides a model test but also contributes to our still limited understanding of ENSO's effect on stratosphere-troposphere coupling. We performed several sets of ensemble simulations with a chemical climate model (SOCOL) forced with global sea surface temperatures. Results were compared with observations and with large-ensemble simulations performed with an atmospheric general circulation model (MRF9). We focus our analysis on the extratropical stratosphere and its coupling with the troposphere. In this context, the circulation over the North Atlantic sector is particularly important. Observed differences between the El Niño winter 1987 and the La Niña winter 1989 include a negative North Atlantic Oscillation index with corresponding changes in temperature and precipitation patterns, a weak polar vortex, a warm Arctic middle stratosphere, negative and positive total ozone anomalies in the tropics and at middle to high latitudes, respectively, as well as anomalous upward and poleward Eliassen-Palm (EP) flux in the midlatitude lower stratosphere. Most of the tropospheric features are well reproduced in the ensemble means in both models, though the amplitudes are underestimated. In the stratosphere, the SOCOL simulations compare well with observations with respect to zonal wind, temperature, EP flux, and ozone, but magnitudes are underestimated in the middle stratosphere. The polar vortex strength is well reproduced, but within-ensemble variability is too large for obtaining a significant signal in Arctic temperature and ozone. With respect to the mechanisms relating ENSO to stratospheric circulation, the results suggest that both, upward and poleward components of anomalous EP flux are important for obtaining the stratospheric signal and that an increase in strength of the Brewer-Dobson circulation is part of that signal.