Browsing by Author "Vermeulen, AT"
Now showing 1 - 6 of 6
Results Per Page
Sort Options
- Item222Rn vertical gradient measurements and its use for transport model calibration.(Energy Research Centre for the Netherlands, 2008-06) Vermeulen, AT; Verheggen, B; Zahorowski, W
- ItemAtmospheric transport and chemistry of trace gases in LMDz5B(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, AGRepresentation 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.
- ItemContinuous hourly radon gradient observations at Cabauw, the Netherlands - a review of main features of the 2007-2009 dataset(Copernicus Publications, 2010-05-02) Zahorowski, W; Vermeulen, AT; Williams, AG; Chambers, SD; Verheggen, BWe report on results of the first three years of radon time series and radon gradient observations at the Cabauw site in the Netherlands (51.971°N, 4.927°E). Two 1500 L dual flow loop, two filter radon detectors with a sensitivity better than 40 mBq m-3 are installed at the site, ensuring that gradients can be defined to the required precision every hour. The inlets are mounted on the main meteorological tower at 20 m and 200 m above ground level. The Cabauw site, located 50 km inland on a polder in an agricultural region, has a simple orography with surface elevations changing by a few metres at most within a 20 km radius. The radon gradient observations are part of our larger program to characterise turbulent mixing processes throughout the lower atmosphere. The two other related measurement projects are the continuous hourly measurements of radon gradients in the surface layer on a 50 m tower at Lucas Heights, Australia (34.053ºS, 150.981ºE; see Chambers et al, this conference), and campaign-style measurements of radon profiles up to altitudes of 4000 m above ground level using light aircraft (see Williams et al., this conference). We observe well pronounced absolute radon and radon gradient signals at Cabauw, influenced by atmospheric processes occurring on seasonal, synoptic, and diurnal time scales. Seasonal variability - the lowest radon concentrations were observed in winter and summer, when the dominant air mass fetch was the Atlantic Ocean. In spring and autumn, concentrations were generally high, as the air mass fetch was primarily over western and/or central Europe. Even when the fetch was oceanic during the latter seasons, it was often over the North Sea where radon concentrations are perturbed by land emissions. In autumn, radon concentrations from the mainland European fetch were more than three times larger than the corresponding concentration from the Atlantic/North Sea regions. Synoptic variability - the radon signal is typically a combination of local and remote influences. Synoptic and diurnal components can be separated by comparing the radon signal at 20 m and 200 m, and by using wind speed as a selecting condition. For most of the data, the diurnal signal is strongly pronounced in the 20 m data, especially when wind speeds are lower than 3 ms-1. In low wind conditions, local influences dominate and the radon signal is predominantly a combination of local source variations and diurnal changes in the local mixing depth. On the other hand, under high wind conditions (> 7 ms-1) the remote signal dominates at both levels, reflecting variations in the radon source function over a wider fetch area, the geographic extent of which is defined by the radon half-life and prevailing wind conditions. The separation of these two signals provides an opportunity to compare subsets of radon time series and gradient observations with a column or regional model and thus evaluate mixing and transport schemes characteristic for the site and the region. Diurnal variability - diurnal composite plots show that the 20 m signal is characterized by an early morning maximum and early afternoon minimum, predominantly reflecting changes in the boundary layer mixing depth on this time scale. The amplitude of this cycle ranged from 450 mBq m-3 in winter to 1460 mBq m-3 in spring. The 200 m Cabauw data exhibited a modest mid-morning maximum, consistent with upward mixing of radon from the surface as the nocturnal inversion breaks down.
- ItemEvaluation 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, AGWe 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.
- ItemH(2) Vertical profiles in the continental boundary layer: measurements at the Cabauw tall tower in the Netherlands(Copernicus Gesellschaft MBH, 2011-07-01) Popa, ME; Vermeulen, AT; van den Bulk, WCM; Jongejan, PAC; Batenburg, AM; Zahorowski, W; Röckmann, TIn-situ, quasi-continuous measurements of atmospheric hydrogen (H(2)) have been performed since October 2007 at the Cabauw tall tower station in the Netherlands. Mole fractions of H(2), CO and several greenhouse gases are determined simultaneously in air sampled successively at four heights, between 20 and 200 m above ground level. (222)Rn measurements are performed in air sampled at 20 and 200 m. This H(2) dataset represents the first in-situ, quasi-continuous long-term measurement series of vertical profiles of H(2) in the lower continental boundary layer. Seasonal cycles are present at all heights in both H(2) and CO, and their amplitude varies with the sampling height. The seasonality is evident in both the "baseline" values and in the short term (diurnal to synoptic time scales) variability, the latter being significantly larger during winter. The observed H(2) short term signals and vertical gradients are in many cases well correlated to other species, especially to CO. On the other hand, H(2) has at times a unique behaviour, due to its particular distribution of sources and sinks. Our estimation for the regional H(2) soil uptake flux, using the radon tracer method, is (-1.89 +/- 0.26) x10(-5) g/(m(2) h), significantly smaller than other recent results from Europe. H(2)/CO ratios of the traffic emissions computed from our data, with an average of 0.54 +/- 0.07 mol: mol, are larger and more variable than estimated in some of the previous studies in Europe. This difference can be explained by a different driving regime, due to the frequent traffic jams in the influence area of Cabauw. The H(2)/CO ratios of the large scale pollution events have an average of 0.36 +/- 0.05 mol:mol; these ratios were observed to slightly increase with sampling height, possibly due to a stronger influence of soil uptake at the lower sampling heights. © Author(s) 2011.
- ItemRadon-222 observations for atmospheric transport, mixing and pollution studies: a review(South Pacific Radioactivity Association, 2010-08-31) Chambers, SD; Zahorowski, W; Williams, AG; Crawford, J; Cohen, DD; Vermeulen, AT; Verheggen, BOver the past century the simple source/sink mechanisms of Radon-222 (radon), and its 3.8-day half E life, have led to its extensive use as a passive atmospheric tracer. This presentation will outline the main contemporary applications of radon in atmospheric research. Two of these applications — air mass transport, and vertical mixing in the lower atmosphere — will then be illustrated by four separate case studies: (1) Using radon to identify the geographical extent, strength and seasonal variability of land and oceanic emissions; (2) Using radon in pollution studies to improve the performance of clustering algorithms used for defining source regions; (3) Using hourly tower-based T, radon gradient observations to investigate mixing processes in the lower boundary layer and stable nocturnal boundary layer with changing atmospheric stability; and (4) Using vertical radon profile "snapshots" measured from light aircraft up to 4 km above ground level to contrast boundary layer entrainment rates between clear-sky, convective and stratiform cloud cases.