Browsing by Author "Levin, I"

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    Assessment of regional atmospheric transport model performance using 222Radon observations
    (European Geosciences Union (EGU), 2020-05-04) Karstens, U; Levin, I; Ramonet, M; Gerbig, C; Arnold, S; Conil, S; Della Coletta, J; Frumau, A; Gheusi, F; Kazan V; Kubistin, D; Lindauer, M; Lopez, M; Maurer, L; Mihalopoulos, N; Pichon, JM; Spain, G
    The rather short life time of 222Radon of 5.5 days makes this radioactive noble gas an almost ideal tracer of atmospheric transport processes. 222Radon, the gaseous progeny of 226Radium, which is a trace constituent of all soils, can escape the soil grains and make its way from the unsaturated soil zone into the atmosphere. The exhalation rate of 222Radon from continental surfaces depends on soil type and permeability, but is orders of magnitude larger than that from ocean surfaces. Therefore, the atmospheric 222Radon activity concentration can be used as a measure of the residence time of air over continental surfaces or to distinguish continental from marine air masses. At continental sites, the short-term variability of 222Radon is mainly determined by diurnal or synoptic-scale boundary layer mixing processes. If its continental exhalation rate is known, 222Radon can even be applied as a quantitative tracer for evaluating regional scale transport model performance. In the present study we use 222Radon activity concentration measurements from the ICOS atmospheric station network and STILT transport model results to assess the ability of this routinely used model to correctly simulate the (diurnal) variation of boundary layer transport. This uncertainty assessment is an important step towards reliable estimates of the contribution of transport model error in GHGs inversion studies that aim at providing accurate fluxes from inversion of atmospheric GHGs observations in ICOS. © Author(s) 2020. This work is distributed under the Creative Commons Attribution 4.0 License.
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    Corrigendum to "Gas transport in firn: multiple-tracer characterisation and model intercomparison for NEEM, Northern Greenland'' published in Atmos. Chem. Phys., 12, 4259–-4277, 2012
    (Copernicus Publications, 2014-04-09) Buizert, C; Martinerie, P; Petrenko, VV; Severinghaus, JP; Trudinger, CM; Witrant, E; Rosen, JL; Orsi, AJ; Rubino, M; Etheridge, DM; Steele, LP; Hogan, C; Laube, JC; Sturges, WT; Levchenko, VA; Smith, AM; Levin, I; Conway, TJ; Dlugokencky, EJ; Lang, PM; Kawamura, K; Jenk, TM; White, JWC; Sowers, T; Schwander, J; Blunier, T
    It was kindly pointed out to us by M. Battle that Eq. (2) on p. 4263 contains a typo, and should instead be [X]corr(z) = [X]meas(z) ΔMδgrav(z)/1000 + 1 , (2) where [X]corr ([X]meas) is the gravity-corrected (measured) mixing ratio of gas species X, 1M = MX − Mair is the molar mass difference between gas X and air, and grav(z) is the gravitational fractionation per unit mass difference at depth z. All calculations in the study were done correctly, following Eq. (2) as given here. Furthermore, the present-day 1age value for NEEM is incorrect in the original manuscript, and underestimates Δage by 6 years. The correct value is 188+3 −9 yr. In our original, incorrect calculation we used the ice age in years before 2000 CE (b2k), while we should have used the ice age relative to the surface ice age. In the updated 1age calculation we use the ice age found by annual layer counting of the shallow NEEM 2011 S1 core (Sigl et al., 2013). The NEEM chronology published in Rasmussen et al. (2013) uses the correct, updated Δage estimate. Both errors addressed in this corrigendum affect neither the discussion nor the main conclusions of the original publication. © Author(s) 2014.
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    Evaluation of the boundary layer dynamics of the TM5 model over Europe
    (Copernicus Publications, 2016-09-14) Koffi, EN; Bergamaschi, P; Karstens, U; Krol, M; Segers, A; Schmidt, M; Levin, I; Vermeulen, AT; Fisher, RE; Kazan, V; Klein Baltink, H; Lowry, D; Manca, G; Meijer, HAJ; Moncrieff, J; Pal, S; Ramonet, M; Scheeren, HA; Williams, AG
    We evaluate the capability of the global atmospheric transport model TM5 to simulate the boundary layer dynamics and associated variability of trace gases close to the surface, using radon (222Rn). Focusing on the European scale, we compare the boundary layer height (BLH) in the TM5 model with observations from the National Oceanic and Atmospheric Admnistration (NOAA) Integrated Global Radiosonde Archive (IGRA) and also with ceilometer and lidar (light detection and ranging) BLH retrievals at two stations. Furthermore, we compare TM5 simulations of 222Rn activity concentrations, using a novel, process-based 222Rn flux map over Europe (Karstens et al., 2015), with harmonised 222Rn measurements at 10 stations. The TM5 model reproduces relatively well the daytime BLH (within 10–20 % for most of the stations), except for coastal sites, for which differences are usually larger due to model representation errors. During night, however, TM5 overestimates the shallow nocturnal BLHs, especially for the very low observed BLHs (< 100 m) during summer. The 222Rn activity concentration simulations based on the new 222Rn flux map show significant improvements especially regarding the average seasonal variability, compared to simulations using constant 222Rn fluxes. Nevertheless, the (relative) differences between simulated and observed daytime minimum 222Rn activity concentrations are larger for several stations (on the order of 50 %) than the (relative) differences between simulated and observed BLH at noon. Although the nocturnal BLH is often higher in the model than observed, simulated 222Rn nighttime maxima are actually larger at several continental stations. This counterintuitive behaviour points to potential deficiencies of TM5 to correctly simulate the vertical gradients within the nocturnal boundary layer, limitations of the 222Rn flux map, or issues related to the definition of the nocturnal BLH. At several stations the simulated decrease of 222Rn activity concentrations in the morning is faster than observed. In addition, simulated vertical 222Rn activity concentration gradients at Cabauw decrease faster than observations during the morning transition period, and are in general lower than observed gradients during daytime. Although these effects may be partially due to the slow response time of the radon detectors, they clearly point to too fast vertical mixing in the TM5 boundary layer during daytime. Furthermore, the capability of the TM5 model to simulate the diurnal BLH cycle is limited by the current coarse temporal resolution (3 h/6 h) of the TM5 input meteorology. © Author(s) 2016.
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    Gas transport in firn: multiple-tracer characterisation and model intercomparison for NEEM, Northern Greenland
    (Copernicus Publications, 2012-05-14) Buizert, C; Martinerie, P; Petrenko, VV; Severinghaus, JP; Trudinger, CM; Witrant, E; Rosen, JL; Orsi, AJ; Rubino, M; Etheridge, DM; Steele, LP; Hogan, C; Laube, JC; Sturges, WT; Levchenko, VA; Smith, AM; Levin, I; Conway, TJ; Dlugokencky, EJ; Lang, PM; Kawamura, K; Jenk, TM; White, JWC; Sowers, T; Schwander, J; Blunier, T
    Air was sampled from the porous firn layer at the NEEM site in Northern Greenland. We use an ensemble of ten reference tracers of known atmospheric history to characterise the transport properties of the site. By analysing uncertainties in both data and the reference gas atmospheric histories, we can objectively assign weights to each of the gases used for the depth-diffusivity reconstruction. We define an objective root mean square criterion that is minimised in the model tuning procedure. Each tracer constrains the firn profile differently through its unique atmospheric history and free air diffusivity, making our multiple-tracer characterisation method a clear improvement over the commonly used single-tracer tuning. Six firn air transport models are tuned to the NEEM site; all models successfully reproduce the data within a 1σ Gaussian distribution. A comparison between two replicate boreholes drilled 64 m apart shows differences in measured mixing ratio profiles that exceed the experimental error. We find evidence that diffusivity does not vanish completely in the lock-in zone, as is commonly assumed. The ice age- gas age difference (Δage) at the firn-ice transition is calculated to be 182+3−9 yr. We further present the first intercomparison study of firn air models, where we introduce diagnostic scenarios designed to probe specific aspects of the model physics. Our results show that there are major differences in the way the models handle advective transport. Furthermore, diffusive fractionation of isotopes in the firn is poorly constrained by the models, which has consequences for attempts to reconstruct the isotopic composition of trace gases back in time using firn air and ice core records. © Author(s) 2012.
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    TransCom continuous experiment: comparison of 222Rn transport at hourly time scales at three stations in Germany
    (Copernicus, 2011) Taguchi, S; Law, RM; Rödenbeck, C; Patra, PK; Maksyutov, S; Zahorowski, W; Sartorious, H; Levin, I
    Fourteen global atmospheric transport models were evaluated by comparing the simulation of 222Rn against measurements at three continental stations in Germany: Heidelberg, Freiburg and Schauinsland. Hourly concentrations simulated by the models using a common 222Rn-flux without temporal variations were investigated for 2002 and 2003. We found that the mean simulated concentrations in Heidelberg are related to the diurnal amplitude of boundary layer height in each model. Summer mean concentrations simulated by individual models were negatively correlated with the seasonal mean of diurnal amplitude of boundary layer height, while in winter the correlation was positive. We also found that the correlations between simulated and measured concentrations at Schauinsland were higher when the simulated concentrations were interpolated to the station altitude in most models. Temporal variations of the mismatch between simulated and measured concentrations suggest that there are significant interannual variations in the 222Rn exhalation rate in this region. We found that the local inversion layer during daytime in summer in Freiburg has a significant effect on 222Rn concentrations. We recommend Freiburg concentrations for validation of models that resolve local stable layers and those at Heidelberg for models without this capability. © 2011, © Author(s) 2011.
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    TransCom continuous experiments: comparison of radon concentrations at inland stations
    (Global Carbon Project, 2008-06) Taguchi, S; Law, RM; Peters, W; Rodenbeck, C; Patra, PK; Maksyutov, S; Zahorowski, W; Sartorius, H; Levin, I