bluuebunny/crossref_metadata_2025 huggingface dataset:
Role of OH variability in the stalling of the global atmospheric CH4 growth rate from 1999 to 2006
Authors: McNorton J. , Chipperfield M. P. , Gloor M. , Wilson C. , Feng W. , Hayman G. D. , Rigby M. , Krummel P. B. , O'Doherty S. , Prinn R. G. , Weiss R. F. , Young D. , Dlugokencky E. , Montzka S. A.
Published: January 2016

Abstract. The growth in atmospheric methane (CH4) concentrations over the past two decades has shown large variability on a timescale of many years. Prior to 1999 the globally averaged CH4 concentration was increasing at a rate of 6.0 ppb/yr, but during a stagnation period from 1999 to 2006 this growth rate slowed to 0.6 ppb/yr. Since 2007 the growth rate has again increased to 4.9 ppb/yr. These changes in growth rate are usually ascribed to variations in CH4 emissions. We have used a 3-D global chemical transport model, driven by meteorological reanalyses and variations in global mean hydroxyl (OH) concentrations derived from CH3CCl3 observations from two independent networks, to investigate these CH4 growth variations. The model shows that between 1999 and 2006, changes in the CH4 atmospheric loss contributed significantly to the suppression in global CH4 concentrations relative to the pre-1999 trend. The largest factor in this is relatively small variations in global mean OH on a timescale of a few years, with minor contributions of atmospheric transport of CH4 to its sink region and atmospheric temperature. Although changes in emissions may be important during the stagnation period, these results imply a smaller variation is required to explain the observed CH4 trends. The contribution of OH variations to the renewed CH4 growth after 2007 cannot be determined with data currently available.
Growth of atmospheric clusters involving cluster-cluster collisions: comparison of different growth rate methods
Authors: Kontkanen J. , Olenius T. , Lehtipalo K. , Vehkamäki H. , Kulmala M. , Lehtinen K. E. J.
Published: January 2016

Abstract. We simulated the time evolution of atmospheric cluster concentrations in a one-component system where clusters grow not only by condensation of monomers, but where also cluster-cluster collisions significantly contribute to the growth of the clusters. Our aims were to investigate the consistency of the growth rates of sub-3 nm clusters determined with different methods, and the validity of the common approach to use them to estimate particle formation rates. We compared the growth rate corresponding to particle fluxes (FGR), the growth rate derived from the appearance times of clusters (AGR) and the growth rate calculated based on irreversible vapor condensation (CGR). We found that the relation between the different growth rates depends strongly on the external conditions and the properties of the model substance. The difference between the different growth rates was typically highest at the smallest, sub-2nm sizes. FGR was generally lower than AGR and CGR; at the smallest sizes the difference was often very large, while at sizes larger than 2 nm, the growth rates were closer to each other. AGR and CGR were in most cases close to each other at all sizes. The difference between the growth rates was generally lower in conditions where cluster concentrations were high, and evaporation and other losses thus less significant. Furthermore, our results show that the conventional method used to determine particle formation rates from growth rates may give estimates far from the true values. Thus, care must be taken not only in how the growth rate is determined, but also in how it is applied.
Validation of ash optical depth and layer height retrieved from passive satellite sensors using EARLINET and airborne lidar data: The case of the Eyjafjallajökull eruption
Authors: Balis D. , Koukouli M. E. , Siomos N. , Dimopoulos S. , Mona L. , Pappalardo G. , Marenco F. , Clarisse L. , Ventress L. J. , Carboni E. , Grainger R. G. , Wang P. , Theys N. , Zehner C.
Published: January 2016

Abstract. The vulnerability of the European airspace to volcanic eruptions was brought to the attention of the public and the scientific community by the 2010 eruptions of the Icelandic volcano Eyjafjallajökull. As a consequence of this event ash concentration thresholds replaced the ‘zero-tolerance to ash’ rule, drastically changing the requirements on satellite ash retrievals. In response to that, ESA funded several projects aiming at creating an optimal End-to-End System for Volcanic Ash Plume Monitoring and Prediction. Two of them, namely the SACS-2 and SMASH projects, developed and improved dedicated satellite-derived ash plume and sulphur dioxide level assessments. These estimates were extensively validated using ground-based and aircraft lidar measurements. The validation of volcanic ash levels and height extracted from the GOME-2 and IASI instruments on board the MetOp-A satellite is presented in this work. EARLINET lidar measurements are compared to different satellite retrievals for two eruptive episodes in April and May 2010. Comparisons were made between satellite retrievals and aircraft lidar data obtained with UK's BAe-146-301 Atmospheric Research Aircraft (managed by the Facility for Airborne Atmospheric Measurements, FAAM) over the United Kingdom and the surrounding regions. The validation results are promising for most satellite products and are within the estimated uncertainties of each of the comparative datasets, but more collocation scenes are needed to perform a comprehensive statistical analysis. The satellite estimates and the validation data sets are better correlated for high ash optical depth values, with correlation coefficients greater than 0.8. The IASI data show a better consistency concerning the ash optical depth and ash layer height when compared with the lidar data.
Scalar turbulent behavior in the roughness sublayer of an Amazonian forest
Authors: Zahn Einara , Dias Nelson L. , Araújo Alessandro , Sá Leonardo , Söergel Matthias , Trebs Ivonne , Wolff Stefan , Manzi Antônio
Published: January 2016

Abstract. An important current problem in micrometeorology is the characterization of turbulence in the roughness sublayer (RSL), where most of the measurements above tall forests are made. There, scalar turbulent fluctuations display significant departures from the predictions of Monin–Obukhov similarity theory (MOST). In this work, we analyze turbulence data of virtual temperature, carbon dioxide and water vapor in the RSL above an Amazonian Forest (with a canopy height of 40 m), measured at 39.4 and 81.6 m above the ground under unstable conditions. We found that dimensionless statistics related to the rate of dissipation of turbulence kinetic energy (TKE) and the scalar variance display significant departures of MOST as expected, whereas the vertical velocity variance follows MOST much more closely. Much better agreement between the dimensionless statistics with the Obukhov similarity variable, however, was found for the subset of measurements made at low zenith angle Z, in the range 0 < |Z| < 20. We conjecture that this improvement is due to the relationship between sunlight incidence and “activation/deactivation” of scalar sinks and fonts verticaly distributed in the forest. Finally, we evaluated the relaxation coeficient of Relaxed Eddy Accumulation: it is also affected by zenith angle, with considerable improvement in the range 0 < |Z| < 20, and its values fall within the range reported in the literature for the unstable Surface Layer. In general, our results indicate the possibility of better stability-derived flux estimates for low zenith angle ranges.
Investigation of aerosol indirect effects on monsoon clouds using ground-based measurements over a high-altitude site in Western Ghats
Authors: Anil Kumar V. , Pandithurai G. , Leena P. P. , Dani K. K. , Murugavel P. , Sonbawne S. M. , Patil R. D. , Maheskumar R. S.
Published: January 2016

Abstract. The effect of aerosols on cloud droplet number concentration and droplet effective radius are investigated from ground-based measurements over a high-altitude site where in clouds pass over the surface. First aerosol indirect effect AIE estimates were made using i) relative changes in cloud droplet number concentration (AIEn) and ii) relative changes in droplet effective radius (AIEs) with relative changes in aerosol for different LWC values. AIE estimates from two different methods reveal that there is systematic overestimation in AIEn as compared to that of AIEs. Aerosol indirect effects (AIEn and AIEs) and Dispersion effect (DE) at different liquid water content (LWC) regimes ranging from 0.05 to 0.50 gm-3 were estimated. The analysis demonstrates that there is overestimation of AIEn as compared to AIEs which is mainly due to DE. Aerosol effects on spectral dispersion in droplet size distribution plays an important role in altering Twomey’s cooling effect and thereby changes in climate. This study shows that the higher DE in the medium LWC regime which offsets the AIE by 30%.
Global Observations and Modeling of Atmosphere-Surface Exchange of Elemental Mercury – A Critical Review
Authors: Zhu W. , Lin C.-J. , Wang X. , Sommar J. , Fu X. W. , Feng X.
Published: January 2016

Abstract. Reliable quantification of air-surfaces flux of elemental Hg vapor (Hg0) is crucial for understanding mercury (Hg) global biogeochemical cycles. There have been extensive measurements and modeling efforts devoting to estimating the exchange fluxes between the atmosphere and various surfaces (e.g., soil, canopies, water, snow, etc.) in past three decades. However, large uncertainty remains due to the complexity of Hg0 bi-directional exchange, limitations of flux quantification techniques and challenges in model parameterization. In this study, we provide a comprehensive review on the state of science in the atmosphere-surface exchange of Hg0. Specifically, the advancement of flux quantification techniques, mechanisms in driving the air-surfaces Hg exchange, and modeling efforts are presented. Due to the semi-volatile nature of Hg0 and redox transformation of Hg in environmental media, Hg deposition and evasion are influenced by multiple environmental variables including seasonality, vegetative coverage and its life cycle, temperature, light, moisture, atmospheric turbulence, presence of reactants (e.g., O3, radicals, etc.) that drives the physicochemical process of Hg in the media where Hg0 exchange occurs. However, effects of these processes on flux have not been fundamentally and quantitatively determined, which limits the accuracy of flux modeling. In this study, we compile an up-to-date global observational flux database and discuss the implication of flux data on global Hg budget. Mean Hg0 flux obtained by micrometeorological measurement did not appear to be significantly greater than the flux measured by dynamic flux chamber methods over unpolluted surfaces (p=0.16, one-tailed, Mann-Whitney U test). The spatio-temporal coverage of existing Hg0 flux measurements is highly heterogeneous with large data gaps existing in multiple continents (Africa, South Asia, Middle East, South America and Australia). The magnitude of evasion flux is strongly enhanced by human activities, particularly at contaminated sites. Hg0 flux observations in East Asia are comparatively larger in magnitude than the rest of the world, suggesting substantial reemission of previously deposited mercury from anthropogenic sources. Hg0 exchange over pristine surfaces (e.g., background soil and water) and vegetation need better constrains for global analysis of atmospheric Hg budget. The existing knowledge gap and the associated research needs for future measurements and modeling efforts for the air-surface exchange of Hg0 are discussed.
Why did the storm ex-Gaston (2010) fail to redevelop during the PREDICT experiment?
Authors: Freismuth T. M. , Rutherford B. , Boothe M. A. , Montgomery M. T.
Published: January 2016

Abstract. An analysis is presented of the failed re-development of ex-Gaston during the 2010 PREDICT field campaign based on the European Centre for Medium Range Weather Forecast (ECMWF) analyses. We analyze the dynamics and kinematics of ex-Gaston to investigate the role of dry, environmental air in the failed redevelopment. The flow topology defined by the calculation of particle trajectories shows that ex-Gaston’s pouch was vulnerable to dry, environmental air on all days of observations. As early as 12:00 UTC 2 September 2010, a dry layer at and above 600 hPa results in a decrease in the vertical mass flux and vertical, relative vorticity. These findings support the hypothesis that entrained, dry air near 600 hPa thwarted convective updraughts and vertical mass flux, which in turn led to a reduction in vorticity and a compromised pouch at these middle levels. A compromised pouch allows further intrusion of dry air and inhibits vorticity amplification. This study supports recent work investigating the role of dry air in moist convection during tropical cyclogenesis.
Presentation of the EURODELTA III inter-comparison exercise – Evaluation of the chemistry transport models performance on criteria pollutants and joint analysis with meteorology
Authors: Bessagnet B. , Pirovano G. , Mircea M. , Cuvelier C. , Aulinger A. , Calori G. , Ciarelli G. , Manders A. , Stern R. , Tsyro S. , García Vivanco M. , Thunis P. , Pay M.-T. , Colette A. , Couvidat F. , Meleux F. , Rouïl L. , Ung A. , Aksoyoglu S. , Baldasano J. M. , Bieser J. , Briganti G. , Cappelletti A. , D'Isodoro M. , Finardi S. , Kranenburg R. , Silibello C. , Carnevale C. , Aas W. , Dupont J.-C. , Fagerli H. , Gonzalez L. , Menut L. , Prévôt A. S. H. , Roberts P. , White L.
Published: January 2016

Abstract. The EURODELTA III exercise allows a very comprehensive inter-comparison and evaluation of chemistry transport models performance. Participating models were applied over four different one month period, within a rather limited number of years (from June 2006 to March 2009) thus allowing evaluating the influence of different meteorological conditions on model performance. The exercise was performed under strict requirements concerning the input data. As a consequence, there were very limited differences in the models set up, representing a sort of sensitivity analysis to several aspects of the modelling chains. The models were evaluated mainly on background stations. Even if the meteorology was prescribed, some variables like the planetary boundary layer (PBL) height, the vertical diffusion coefficient are diagnosed in the model pre-processors and explain the spread of models results. For ozone, this study shows the importance of boundary conditions on model calculations and then on the regime of the gas and particle chemistry. The worst performances are observed for sulphur dioxide concentrations that are poorly captured by the models. The performances of models are rather good very similar for the nitrogen dioxide. On average, the models provide a rather good picture of the particulate matter (PM) concentrations over Europe even if the highest concentrations are underestimated. For the PM, the mean diurnal cycles show a general tendency to overestimate the effect of the PBL height rise while the afternoon chemistry (formation of secondary species) is certainly underestimated, PM observations show very flat diurnal profiles whatever the season. In general the day time PBL height is underestimated by all models, the largest variability of predicted PBL is observed over the ocean and seas. More generally, in most cases model performances are more influenced by the model setup than the season. The temporal evolution of wind speed is most responsible of model skilfulness in reproducing the daily variability of pollutant concentrations (e.g. the development of peak episodes), while the reconstruction of the PBL diurnal cycle seems more influencing in driving the corresponding pollutant diurnal cycle and hence the presence of systematic positive and negative biases detectable on daily basis.
Downscaling surface wind predictions from numerical weather prediction models in complex terrain with WindNinja
Authors: Wagenbrenner N. S. , Forthofer J. M. , Lamb B. K. , Shannon K. S. , Butler B. W.
Published: January 2016

Abstract. Wind predictions in complex terrain are important for a number of applications. Dynamic downscaling of numerical weather prediction (NWP) model winds with a high resolution wind model is one way to obtain a wind forecast that accounts for local terrain effects, such as wind speed-up over ridges, flow channeling in valleys, flow separation around terrain obstacles, and flows induced by local surface heating and cooling. In this paper we investigate the ability of a mass-consistent wind model for downscaling near-surface wind predictions from four NWP models in complex terrain. Model predictions are compared with surface observations from a tall, isolated mountain. Downscaling improved near-surface wind forecasts under high-wind (near-neutral atmospheric stability) conditions. Results were mixed during upslope and downslope (non-neutral atmospheric stability) flow periods, although wind direction predictions generally improved with downscaling. This work constitutes evaluation of a diagnostic wind model at unprecedented high spatial resolution in terrain with topographical ruggedness approaching that of typical landscapes in the western US susceptible to wildland fire.
Aerosol optical depth trend over the Middle East
Authors: Klingmüller K. , Pozzer A. , Metzger S. , Stenchikov G. , Lelieveld J.
Published: January 2016

Abstract. We use the combined Dark Target/Deep Blue aerosol optical depth (AOD) satellite product of the Moderate-resolution Imaging Spectroradiometer (MODIS) collection 6 to study trends over the Middle East between 2000 and 2015. Our analysis corroborates a previously identified positive AOD trend over large parts of the Middle East during the period 2001 to 2012. We relate the annual AOD to precipitation, soil moisture and surface winds to identify regions where these attributes are directly related to the AOD over Saudi Arabia, Iraq and Iran. Regarding precipitation and soil moisture, a relatively small area in and surrounding Iraq turns out to be of prime importance for the AOD over these countries. Regarding surface wind speed, the African Red Sea coastal area is relevant for the Saudi Arabian AOD. Using multiple linear regression we show that AOD trends and interannual variability can be attributed to soil moisture, precipitation and surface winds, being the main factors controlling the dust cycle. Our results confirm the dust driven AOD trends and variability, supported by a decreasing MODIS-derived Ångström exponent and a decreasing AERONET-derived fine mode fraction that accompany the AOD increase over Saudi Arabia. The positive AOD trend relates to a negative soil moisture trend. As a lower soil moisture translates into enhanced dust emissions, it is not needed to assume growing anthropogenic aerosol and aerosol precursor emissions to explain the observations. Instead, our results suggest that increasing temperature and decreasing relative humidity in the last decade have promoted soil drying, leading to increased dust emissions and AOD; consequently an AOD increase is expected due to climate change.
Detection of Saharan dust and biomass burning events using near real-time intensive aerosol optical properties in the northwestern Mediterranean
Authors: Ealo M. , Alastuey A. , Ripoll A. , Pérez N. , Minguillón M. C. , Querol X. , Pandolfi M.
Published: January 2016

Abstract. The study of Saharan dust events (SDE) and biomass burning (BB) emissions are both topic of great scientific interest since they are frequent and important polluting scenarios affecting air quality and climate. The main aim of this work is evaluating the feasibility of using near real-time in situ aerosol optical measurements for the detection of these atmospheric events in the Western Mediterranean Basin (WMB). With this aim, intensive aerosol optical properties (SAE: scattering Ångström exponent, AAE: absorption Ångström exponent, SSAAE: single scattering albedo Ångström exponent, and g: asymmetry parameter) were derived from multi-wavelength aerosol light scattering, hemispheric backscattering and absorption measurements performed at regional (Montseny; MSY, 720 m a.s.l.) and continental (Montsec; MSA, 1570 m a.s.l.) background sites in the WMB. A sensitivity study aiming at calibrating the measured intensive optical properties for SDE and BB detection is presented and discussed. The detection of Saharan dust events (SDE) by means of the SSAAE parameter and Ångström matrix depended on the altitude of the measurement station, and on SDE intensity. At MSA (mountain-top site) SSAAE detected around 85% of SDE compared with 50% at MSY station, where pollution episodes dominated by fine anthropogenic particles frequently masked the effect of mineral dust on optical properties during less intense SDE. Furthermore, an interesting feature of SSAAE was its capability to detect the presence of mineral dust after the end of SDE. Thus, resuspension processes driven by summer regional atmospheric circulations and dry conditions after SDE favored the accumulation of mineral dust at regional level having important consequences for air quality. On average, SAE, AAE and g ranged between -0.7 and 1, 1.3 and 2.5, and 0.5 and 0.75, respectively, during SDE. Based on the Aethalometer model, biomass burning (BB) contribution to equivalent black carbon (BC) accounted for 36% and 40% at MSY and MSA respectively. Linear relationships were found between AAE and %BCbb, with AAE values reaching around 1.5 when %BCbb was higher than 50%. BB contribution to organic matter (OM) at MSY was around 30%. Thus FF combustion sources showed important contributions to both BC and OM in the region under study. Results for OM source apportionment showed good agreement with simultaneous biomass burning organic aerosol (BBOA) and hydrocarbon-like organic aerosol (HOA) calculated from Positive Matrix Factorization (PMF) applied to simultaneous Aerosol Mass Spectrometer (ACSM) measurements. A wildfire episode was identified at MSY, showing AAE values up to 2 when daily BB contributions to BC and OM were 73% and 78% respectively.
Simulating secondary organic aerosol from missing diesel-related intermediate-volatility organic compound emissions during the Clean Air for London (ClearfLo) campaign
Authors: Ots R. , Young D. E. , Vieno M. , Xu L. , Dunmore R. E. , Allan J. D. , Coe H. , Williams L. R. , Herndon S. C. , Ng N. L. , Hamilton J. F. , Bergström R. , Di Marco C. , Nemitz E. , Mackenzie I. A. , Kuenen J. J. P. , Green D. C. , Reis S. , Heal M. R.
Published: January 2016

Abstract. We present high-resolution atmospheric chemistry transport model (ACTM) simulations of secondary organic aerosol (SOA) formation over the UK for 2012. Our simulations include additional diesel-related intermediate volatility organic compound (IVOC) emissions derived directly from comprehensive field measurements at an urban background site in London during the 2012 Clean Air for London (ClearfLo) campaign. Our IVOC emissions are added proportionally to VOC emissions, as opposed to proportionally to primary organic aerosol (POA) as has been done by previous ACTM studies seeking to simulate the effects of these missing emissions. Modelled concentrations are evaluated against hourly and daily measurements of organic aerosol (OA) components derived from aerosol mass spectrometer (AMS) measurements also made during the ClearfLo campaign at three sites in the London area. Good hourly performance in comparison to the measurements was shown, giving confidence in the SOA prediction skill of the ACTM system used. According to the model simulations, diesel-related IVOCs can explain on average ~30% of the annual SOA in and around London. Furthermore, the 90-th percentile of modelled daily SOA concentrations for the whole year is 3.8 μg m−3 (more than 40% of which is produced from the missing diesel precursors), constituting a notable addition to total particulate matter. More measurements of these precursors (currently not included in official emissions inventories) is recommended. During the period of concurrent measurements, SOA concentrations at the Detling rural background location east of London were greater than at the central London location. The model shows that this was caused by an intense pollution plume with a strong gradient of imported SOA passing over the rural location. This demonstrates the value of modelling for supporting the interpretation of measurements taken at different sites or for short durations.
Simulated 2050 aviation radiative forcing
Authors: Chen C.-C. , Gettelman A.
Published: January 2016

Abstract. The radiative forcing from aviation is investigated by using a comprehensive general circulation model in the present (2006) and the future (through 2050). Global flight distance is projected to increase by a factor of 4 between 2006 and 2050. However, simulated contrail cirrus radiative forcing in 2050 can reach 87 mW m−2, an increase by a factor of 7 from 2006, and thus does not scale linearly with fuel emission mass. This is due to non-uniform regional increase in air traffic and different sensitivities for contrail radiative forcing in different regions. Simulations indicate that negative radiative forcing induced by the indirect effect of aviation sulfate aerosols on liquid clouds in 2050 can be as large as −160 mW m−2, an increase by a factor of 4 from 2006. As a result, the net 2050 aviation radiative forcing has a cooling effect on the planet. Aviation sulfate aerosols emitted at cruise altitude can be transported down to the lower troposphere, increasing the aerosol concentration, thus increasing the cloud drop number concentration and persistence of low-level clouds. Aviation black carbon aerosols produce a negligible net forcing globally in 2006 and 2050.
A study of the influence of forest gaps on fire-atmosphere interactions
Authors: Kiefer Michael T. , Heilman Warren E. , Zhong Shiyuan , Charney Joseph J. , Bian Xindi
Published: January 2016

Abstract. Much uncertainty exists regarding the possible role that gaps in forest canopies play in modulating fire-atmosphere interactions in otherwise horizontally homogeneous forests. This study examines the impact of forest gaps on fire-atmosphere interactions using the ARPS-CANOPY model, a version of the Advanced Regional Prediction System (ARPS) model with a canopy parameterization. A series of numerical experiments are conducted with a stationary low-intensity fire, represented in the model as a line of enhanced surface sensible heat flux. Experiments are conducted with and without forest gaps, and with gaps in different positions relative to the fireline. For each of the four cases considered, an additional simulation is performed without the fire to facilitate comparison of the fire-perturbed atmosphere and the background state. Analyses of both mean and instantaneous wind velocity, turbulent kinetic energy, air temperature, and turbulent mixing of heat are presented in order to examine the fire-perturbed atmosphere on multiple time scales. Results of the analyses indicate that the impact of the fire on the atmosphere is greatest in the case with the gap centered on the fire, and weakest in the case with the gap upstream of the fire. It is shown that gaps in forest canopies have the potential to play a substantial role in the vertical as well as horizontal transport of heat away from the fire. Results also suggest that in order to understand how the fire will alter wind and turbulence in a heterogeneous forest, one needs to first understand how the forest heterogeneity itself influences the wind and turbulence fields without the fire.
Three Northern Regions Shelter Forest contributed to long-term increasing trend of biogenic isoprene emissions in Northern China
Authors: Zhang Xiaodong , Huang Tao , Zhang Leiming , Shen Yanjie , Zhao Yuan , Gao Hong , Mao Xiaoxuan , Jia Chenhui , Ma Jianmin
Published: January 2016

Abstract. To assess the long-term trends of isoprene emissions in Northern China and the impact of the Three Northern Regions Shelter Forest (TNRSF) on these trends, a database of historical biogenic isoprene emissions from 1982 to 2010 was developed for this region using a biogenic emission model for gases and aerosols. The total amount of the biogenic isoprene emissions during the three decades was 4.4 Tg in Northern China and 1.6 Tg in the TNRSF, with annual emissions ranged from 132,000 to 176,000 ton yr-1 and from 45,000 to 70,000 ton yr-1, respectively, in the two regions. Isoprene emission fluxes have increased substantially in many places of the TNRSF over the last three decades due to the growing trees and vegetation coverage, especially in the Central-North China region where the highest emission incline reached to 58 % from 1982 to 2010. Biogenic isoprene emissions produced from anthropogenic forests tended to surpass those produced from stead-state natural forests, such as boreal forests in Northeastern China. The estimated isoprene emissions suggest that the TNRSF has altered the long-term emission trend in North China from a decreasing trend during 1982 to 2010 (slope = −0.533, R2 = 0.05) to an increasing trend for the same period of time (slope = 0.347, R2 = 0014), providing strong evidence for the change in the emissions of biogenic volatile organic compounds (BVOCs) induced by the human activities on decadal or longer time scales.
Physics of Stratocumulus Top (POST): turbulence characteristics
Authors: Jen-La Plante I. , Ma Y-F. , Nurowska K. , Gerber H. , Khelif D. , Karpinska K. , Kopec M. K. , Kumala W. , Malinowski S. P.
Published: January 2016

Abstract. Turbulence observed during the Physics of Stratocumulus Top (POST) research campaign is analyzed. Using in-flight measurements of dynamic and thermodynamic variables at the interface between the stratocumulus cloud top and free troposphere, the cloud top region is classified into sublayers, and the thicknesses of these sublayers are estimated. The data are used to calculate turbulence characteristics, including the bulk Richardson number, meansquare velocity fluctuations, turbulent kinetic energy (TKE), and estimates of the TKE dissipation rate. A comparison of these properties among different sublayers indicates that the entrainment interfacial layer consists of two significantly different sublayers: the turbulent inversion sublayer (TISL) and the moist, yet statically stable, cloud top mixing sublayer (CTMSL). Both sublayers are marginally turbulent; turbulence is produced by shear and damped by buoyancy such that the sublayer thicknesses adapt to temperature and wind variations across them. Turbulence in both sublayers is highly anisotropic, with Corrsin and Ozmidov scales as small as ~ 30cm and ~ 3m in the TISL and CTMSL, respectively.
Using airborne HIAPER Pole-to-Pole Observations (HIPPO) to evaluate model and remote sensing estimates of atmospheric carbon dioxide
Authors: Frankenberg C. , Kulawik S. S. , Wofsy S. , Chevallier F. , Daube B. , Kort E. A. , O'Dell C. , Olsen E. T. , Osterman G.
Published: January 2016

Abstract. In recent years, space-borne observations of atmospheric carbon-dioxide (CO2) have become increasingly used in global carbon-cycle studies. In order to obtain added value from space-borne measurements, they have to suffice stringent accuracy and precision requirements, with the latter being less crucial as it can be reduced by just enhanced sample size. Validation of CO2 column averaged dry air mole fractions (XCO2) heavily relies on measurements of the Total Carbon Column Observing Network TCCON. Owing to the sparseness of the network and the requirements imposed on space-based measurements, independent additional validation is highly valuable. Here, we use observations from the HIAPER Pole-to-Pole Observations (HIPPO) flights from January 2009 through September 2011 to validate CO2 measurements from satellites (GOSAT, TES, AIRS) and atmospheric inversion models (CarbonTracker CT2013B, MACC v13r1). We find that the atmospheric models capture the XCO2 variability observed in HIPPO flights very well, with correlation coefficients (r2) of 0.93 and 0.95 for CT2013B and MACC, respectively. Some larger discrepancies can be observed in profile comparisons at higher latitudes, esp. at 300 hPa during the peaks of either carbon uptake or release. These deviations can be up to 4 ppm and hint at misrepresentation of vertical transport. Comparisons with the GOSAT satellite are of comparable quality, with an r2 of 0.85, a mean bias μ of −0.06 ppm and a standard deviation σ of 0.45 ppm. TES exhibits an r2 of 0.75, μ of 0.34 ppm and σ of 1.13 ppm. For AIRS, we find an r2 of 0.37, μ of 1.11 ppm and σ of 1.46 ppm, with latitude-dependent biases. For these comparisons at least 6, 20 and 50 atmospheric soundings have been averaged for GOSAT, TES and AIRS, respectively. Overall, we find that GOSAT soundings over the remote pacific ocean mostly meet the stringent accuracy requirements of about 0.5 ppm for space-based CO2 observations.
What effect does VOC sampling time have on derived OH reactivity?
Authors: Sonderfeld H. , White I. R. , Goodall I. C. A. , Hopkins J. R. , Lewis A. C. , Koppmann R. , Monks P. S.
Published: January 2016

Abstract. State of the art techniques allow for rapid measurements of total OH reactivity. Unknown sinks of OH and oxidation processes in the atmosphere have been attributed to what has been termed "missing" OH reactivity. Often overlooked are the differences in timescales over which the diverse measurement techniques operate. Volatile organic compounds (VOC) acting as sinks of OH are often measured by gas chromatography (GC) methods which provide low frequency measurements on a timescale of hours, while sampling times are generally only a few minutes. Here, the effect of the sampling time and thus the contribution of unmeasured VOC variability on OH reactivity is investigated. Measurements of VOC mixing ratios by proton transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS) conducted during two field campaigns (ClearfLo and PARADE) in an urban and a semi-rural environment were used to calculate OH reactivity. VOC were selected to represent variability for different compound classes. Data were averaged over different time intervals to simulate lower time resolutions and were then compared to the mean hourly OH reactivity. The results show deviations in the range of 1 to 25%. The observed impact of VOC variability is found to be greater for the semi-rural site. The selected compounds were scaled by the contribution of their compound class to the total OH reactivity from VOC based on concurrent gas chromatography measurements conducted during the ClearfLo campaign. Prior to being scaled, the variable signal of aromatic compounds results in larger deviations in OH reactivity for short sampling intervals compared to oxygenated VOC (OVOC). However, once scaled with their lower share during the ClearfLo campaign this effect was reduced. No seasonal effect on the OH reactivity distribution across different VOC was observed at the urban site.
Size resolved morphological properties of the high Arctic summer aerosol during ASCOS-2008
Authors: Hamacher-Barth E. , Leck C. , Jansson K.
Published: January 2016

Abstract. The representation of aerosol properties and processes in climate models is fraught with large uncertainties. Especially at high northern latitudes a strong under-prediction of aerosol concentrations and nucleation events is observed and can only be constrained by in situ observations based on the analysis of individual aerosol particles. To further reduce the uncertainties surrounding aerosol properties and their potential role as cloud condensation nuclei this study provides observational data resolved over size on morphological and chemical properties of aerosol particles collected in the summer high Arctic, north of 80° N. Aerosol particles were imaged with scanning and transmission electron microscopy and further evaluated with digital image analysis. In total 3903 particles were imaged and categorized according to morphological similarities into three gross morphological groups, single particles, gel particles and halo particles. Single particles were observed between 15 nm and 800 nm in diameter and represent the dominating type of particles (82%). The majority of particles appeared to be marine gels with a broad Aitken mode peaking at 70 nm accompanied by a minor fraction of ammonium (bi)sulfate with a maximum in number concentration at 170 nm. Gel particles (11% of all particles) were observed between 45 nm and 800 nm with a maximum in number concentration at 154 nm. Imaging with transmission electron microscopy allowed further morphological discrimination of gel particles in “aggregate” particles, “aggregate with film” particles and “mucus-like” particles.
Controls on phase composition and ice water content in a convection permitting model simulation of a tropical mesoscale convective system
Authors: Franklin C. N. , Protat A. , Leroy D. , Fontaine E.
Published: January 2016

Abstract. Simulations of tropical convection from an operational numerical weather prediction model are evaluated with the focus on the model's ability to simulate the observed high ice water contents associated with the outflow of deep convection and to investigate the modelled processes that control the phase composition of tropical convective clouds. The intensification and decay of convective strength across the mesoscale convective system lifecycle is simulated well, however, the areas with reflectivities > 30 dBZ are overestimated due to too much rain above the freezing level, stronger updrafts and larger particle sizes in the model. The inclusion of a heterogeneous rain freezing parameterisation and the use of different ice size distributions show better agreement with the observed reflectivity distributions, however, this simulation still produces a broader profile with many high reflectivity outliers demonstrating the greater occurrence of convective cells in the simulations. It is shown that the growth of ice is less dependent on vertical velocity than is liquid water, with the control on liquid water content being the updraft strength due to stronger updrafts having minimal entrainment and higher supersaturations. Larger liquid water contents are produced when cloud droplet number concentrations are increased or when a parameterisation of heterogeneous freezing of rain is included. These changes reduce the efficiency of the warm rain processes in the model generating greater supercooled liquid water contents. The control on ice water content in the model is the ice sizes and available liquid water, with the larger ice particles growing more efficiently via accretion and riming. Limiting or excluding graupel produces larger ice water contents for warmer temperatures due to the greater ice mass contained in slow falling snow particles. This results in longer in-cloud residence times and more efficient removal of liquid water. It is demon strated that entrainment in the mixed-phase regions of convective updrafts is most sensitive to the turbulence formulation in the model. Greater mixing of environmental air into cloudy updrafts in the region of -30 to 0 degrees Celsius produces more detrainment at these temperatures and the generation of a larger stratiform area. Above these levels in the purely ice region of the updrafts, the entrainment and buoyancy of air parcels is controlled by the ice particle sizes, demonstrating the importance of the microphysical processes on the convective dynamics.
Will a perfect model agree with perfect observations? The impact of spatial sampling
Authors: Schutgens N. A. J. , Gryspeerdt E. , Weigum N. , Tsyro S. , Goto D. , Schulz M. , Stier P.
Published: January 2016

Abstract. The spatial resolution of global climate models with interactive aerosol and the observations used to evaluate them is very different. Current models use grid-spacings of ∼ 200 km, while satellite observations of aerosol use so-called pixels of ∼ 10 km. Ground site or air-borne observations concern even smaller spatial scales. We study the errors incurred due to different resolutions by aggregating high-resolution simulations (10 km grid-spacing) over either the large areas of global model grid-boxes ("perfect" model data) or small areas corresponding to the pixels of satellite measurements or the field-of-view of ground-sites ("perfect" observations). Our analysis suggests that instantaneous RMS differences between these perfect observations and perfect global models can easily amount to 30–160%, for a range of observables like AOT (Aerosol Optical Thickness), extinction, black carbon mass concentrations, PM2.5, number densities and CCN (Cloud Condensation Nuclei). These differences, due entirely to different spatial sampling of models and observations, are often larger than measurement errors in real observations. Temporal averaging over a month of data reduces these differences more strongly for some observables (e.g. a three-fold reduction i.c. AOT), than for others (e.g. a two-fold reduction for surface black carbon concentrations), but significant RMS differences remain (10-75%). Note that this study ignores the issue of temporal sampling of real observations, which is likely to affect our present monthly error estimates. We examine several other strategies (e.g. spatial aggregation of observations, interpolation of model data) for reducing these differences and show their effectiveness. Finally, we examine consequences for the use of flight campaign data in global model evaluation and show that significant biases may be introduced depending on the flight strategy used.
Monthly and Spatially Resolved Black Carbon Emission Inventory of India: Uncertainty Analyses
Authors: Paliwal U. , Sharma M. , Burkhart J. F.
Published: January 2016

Abstract. Black Carbon (BC) emissions from India for the year 2011 is estimated to be 892.12 ± 151.53 Gg/yr based on a new ground-up, GIS-based inventory. The grid-based, spatially resolved emission inventory includes, in addition to conventional sources, emissions from kerosene lamps, forest fires, diesel-powered irrigation pumps and electricity generators at mobile towers. The emissions have been estimated at district level and were spatially distributed into grids at a resolution of 40 × 40 km2. The uncertainty in emissions has been estimated using Monte Carlo simulation by considering the variability in activity data and emission factors. Monthly variation of BC emissions has also been estimated to account for the seasonal variability. To the total BC emissions, Domestic Fuels contributed most significantly (48 %), followed by Industry (22 %), Transport (17 %), Open Burning (12 %) and Others (1 %). The spatial and seasonal resolution of the inventory will be useful for modeling BC transport in the atmosphere for air quality, global warming, and other process-level studies that require greater temporal resolution than traditional inventories.
A biogenic CO2 flux adjustment scheme for the mitigation of large-scale biases in global atmospheric CO2 analyses and forecasts
Authors: Agustí-Panareda A. , Massart S. , Chevallier F. , Balsamo G. , Boussetta S. , Dutra E. , Beljaars A.
Published: January 2016

Abstract. Forecasting atmospheric CO2 daily at the global scale with a good accuracy like it is done for the weather is a challenging task. However, it is also one of the key areas of development to bridge the gaps between weather, air quality and climate models. The challenge stems from the fact that atmospheric CO2 is largely controlled by the CO2 fluxes at the surface, which are difficult to constrain with observations. In particular, the biogenic fluxes simulated by land surface models show skill in detecting synoptic and regional-scale disturbances up to sub-seasonal time-scales, but they are subject to large seasonal and annual budget errors at global scale, usually requiring a posteriori calibration. This paper presents a scheme to diagnose and mitigate model errors associated with biogenic fluxes within an atmospheric CO2 forecasting system. The scheme is an adaptive calibration referred to as Biogenic Flux Adjustment Scheme (BFAS) and it can be applied automatically in real time throughout the forecast. The BFAS method improves the continental budget of CO2 fluxes in the model by combining information from three sources: (1) retrospective fluxes estimated by a global flux inversion system, (2) land-use information, (3) simulated fluxes from the model. The method is shown to produce enhanced skill in the daily CO2 10-day forecasts without requiring continuous manual intervention. Therefore, it is particularly suitable for near-real-time CO2 analysis and forecasting systems.
Interannual variability of the boreal summer tropical UTLS in observations and CCMVal-2 simulations
Authors: Kunze Markus , Braesicke Peter , Langematz Ulrike , Stiller Gabriele
Published: January 2016

Abstract. During boreal summer the upper troposphere/lower stratosphere (UTLS) in the northern hemisphere shows a distinct maximum in water vapour (H2O) mixing ratios and a coincident minimum in ozone (O3) mixing ratios, both confined within the Asian monsoon anticyclone (AMA). This well known feature has been related to transport processes emerging above the convective systems during the Asian summer monsoon (ASM), further modified by the dynamics of the AMA. We assess the ability of chemistry climate models (CCMs) to reproduce the climatological characteristics and variability of H2O, O3 and temperature in the UTLS during the boreal summer in comparison to MIPAS satellite observations and ERA-Interim reanalyses. By using a multiple linear regression model the main driving factors, the strength of the ASM, the quasi-biennial oscillation (QBO), and the El Niño-Southern Oscillation (ENSO), are separated. The results of the regression analysis show for ERA-Interim and the CCMs enhanced H2O and reduced O3 mixing ratios within the AMA for stronger ASM seasons. The CCM results can further confirm earlier studies which emphasize the importance of the Tibetan Plateau/southern slope of the Himalayas as the main source region for H2O in the AMA. The results suggest that H2O is transported towards higher latitudes at the north–eastern edge of the AMA, rather than transported towards low equatorial latitudes to be fed into the tropical pipe. The regression patterns related to ENSO show a coherent signal for temperatures and H2O mixing ratios for ERA-Interim and the CCMs, and suggest a weakening of the ASM during ENSO warm events. The QBO modulation of the lower stratospheric temperature near the Equator is well represented in the CCMs. Its influence on H2O and O3 mixing ratios is consistent but weaker.
The impact of the diurnal cycle of the atmospheric boundary layer on physical variables relevant for wind energy applications
Authors: Englberger Antonia , Dörnbrack Andreas
Published: January 2016

Abstract. This paper provides a quantification of the temporal evolution of physical variables in the atmospheric boundary layer (ABL) relevant for wind energy applications. For this purpose, we use the unique dataset gathered during the BLLAST (Boundary Layer Late Afternoon and Sunset Turbulence) field experiment to validate a large-eddy simulation (LES) model by simulating the complete diurnal cycle of the ABL. In this way, this contribution to the special issue of ACP "The Boundary-Layer Late Afternoon and Sunset Turbulence project" satisfies the purpose of the BLLAST experiment: to provide a dataset for the validation of numerical simulations aiming to study transient BL processes. For wind energy applications, we are investigating the behaviour of different physical parameters which are relevant in the height region where a wind turbine operates. This results in a quantification of the diurnal cycle influence on the vertical wind shear, the stratification and the turbulence intensity in the atmosphere. Further, the impact of different heterogeneous surface conditions on shear near the surface layer of the ABL is investigated.