Browsing by Author "Meijer, HAJ"

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    Atmospheric transport and chemistry of trace gases in LMDz5B: evaluation and implications for inverse modelling
    (Copernicus Publications, 2015-02-03) Locatelli, R; Bousquet, P; Hourdin, F; Saunois, M; Cozic, A; Couvreux, F; Grandpeix, JY; Lefebvre, MP; Rio, C; Bergamaschi, P; Chambers, SD; Karstens, U; Kazan, V; van der Laan, S; Meijer, HAJ; Moncrieff, J; Ramonet, M; Scheeren, HA; Schlosser, C; Schmidt, M; Vermeulen, AT; Williams, AG
    Representation of atmospheric transport is a major source of error in the estimation of greenhouse gas sources and sinks by inverse modelling. Here we assess the impact on trace gas mole fractions of the new physical parameterizations recently implemented in the atmospheric global climate model LMDz to improve vertical diffusion, mesoscale mixing by thermal plumes in the planetary boundary layer (PBL), and deep convection in the troposphere. At the same time, the horizontal and vertical resolution of the model used in the inverse system has been increased. The aim of this paper is to evaluate the impact of these developments on the representation of trace gas transport and chemistry, and to anticipate the implications for inversions of greenhouse gas emissions using such an updated model. © Author(s, 2015.
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    Compatibility of atmospheric 14CO2 measurements: comparing the heidelberg low-level counting facility to international accelerator mass spectrometry (AMS) laboratories
    (Cambridge University Press, 2016-09-19) Hammer, S; Friedrich, R; Kromer, B; Cherkinsky, A; Lehman, SJ; Meijer, HAJ; Nakamura, T; Palonen, V; Reimer, RW; Smith, AM; Southen, JR; Szidat, S; Turnbull, J; Uchida, M
    Combining atmospheric Δ14CO2 data sets from different networks or laboratories requires secure knowledge on their compatibility. In the present study, we compare Δ14CO2 results from the Heidelberg low-level counting (LLC) laboratory to 12 international accelerator mass spectrometry (AMS) laboratories using distributed aliquots of five pure CO2 samples. The averaged result of the LLC laboratory has a measurement bias of –0.3±0.5‰ with respect to the consensus value of the AMS laboratories for the investigated atmospheric Δ14C range of 9.6 to 40.4‰. Thus, the LLC measurements on average are not significantly different from the AMS laboratories, and the most likely measurement bias is smaller than the World Meteorological Organization (WMO) interlaboratory compatibility goal for Δ14CO2 of 0.5‰. The number of intercomparison samples was, however, too small to determine whether the measurement biases of the individual AMS laboratories fulfilled the WMO goal. © 2016 by the Arizona Board of Regents on behalf of the University of Arizona
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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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    Initial results of an intercomparison of AMS-based atmospheric 14CO2 measurements
    (Cambridge University Press, 2016-02-16) Miller, J; Lehman, SJ; Wolak, C; Turnbull, J; Dunn, G; Graven, H; Keeling, RF; Meijer, HAJ; Aerts-Bijma, AT; Palstra, SWL; Smith, AM; Allison, CE; Southon, J; Xu, XM; Nakazawa, T; Aoki, S; Nakamura, T; Guilderson, TP; LaFranchi, B; Mukai, M; Terao, Y; Uchida, M; Kondo, M
    This article presents results from the first 3 rounds of an international intercomparison of measurements of Δ14CO2 in liter-scale samples of whole air by groups using accelerator mass spectrometry (AMS). The ultimate goal of the intercomparison is to allow the merging of Δ14CO2 data from different groups, with the confidence that differences in the data are geophysical gradients and not artifacts of calibration. Eight groups have participated in at least 1 round of the intercomparison, which has so far included 3 rounds of air distribution between 2007 and 2010. The comparison is intended to be ongoing, so that: a) the community obtains a regular assessment of differences between laboratories; and b) individual laboratories can begin to assess the long-term repeatability of their measurements of the same source air. Air used in the intercomparison was compressed into 2 high-pressure cylinders in 2005 and 2006 at Niwot Ridge, Colorado (USA), with one of the tanks "spiked" with fossil CO2, so that the 2 tanks span the range of Δ14CO2 typically encountered when measuring air from both remote background locations and polluted urban ones. Three groups show interlaboratory comparability within 1‰ for ambient level Δ14CO2. For high CO2/low Δ14CO2 air, 4 laboratories showed comparability within 2‰. This approaches the goals set out by the World Meteorological Organization (WMO) CO2 Measurements Experts Group in 2005. One important observation is that single-sample precisions typically reported by the AMS community cannot always explain the observed differences within and between laboratories. This emphasizes the need to use long-term repeatability as a metric for measurement precision, especially in the context of long-term atmospheric monitoring. © 2013 by the Arizona Board of Regents on behalf of the University of Arizona.