Browsing by Author "Element, A"

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    Comparison of in-situ water vapour isotope analysers
    (American Geophysical Union, 2011-12-05) Element, A; Parkes, SD; Griffith, DWT; Wang, L; McCabe, MF
    Recently there have been a number of spectroscopic based in-situ water vapour isotope analysers developed. These analysers are capable of providing datasets that are useful for a range studies including interpreting rapid fluctuations associated with land atmosphere exchange processes, and validation of process based models that work on different spatial and temporal scales. Here we present a comparison of three spectroscopic analysers that provide in-situ analysis of water vapour isotopes. These include a Fourier Transform InfraRed (FTIR) spectroscopy based system (broad band technique), a system based on Off-Axis Integrated Cavity Output Spectroscopy (OA-ICOS), and a Wavelength-Scanned Cavity Ring-Down Spectroscopy (WS-CRDS) system. Using a continuous flow calibration system, liquid isotopic standards were vaporised and used to determine the response of the three analysers to changes isotopic composition and the water vapour mixing ratio. Based on these experiments it was shown that all three analysers required significant corrections to move the raw data onto the Standard Mean Ocean Water (SMOW) scale. We then deployed the three analysers at a coastal location near Sydney, Australia where diurnal temperature variations are relatively small and high mixing ratios are generally observed. The WS-CRDS and OA-ICOS were then deployed in central NSW, Australia where large diurnal temperature variations and relatively low mixing ratios were observed. The in-situ isotope data collected from the three analysers is then compared between these two locations.
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    Improved estimation of total boundary layer radon for budget studies and regional integrations.
    (European Geosciences Union, 2010-05-02) Williams, AG; Zahorowski, W; Chambers, SD; Element, A; Werczynski, S; Griffiths, AD
    Estimation of the total amount of the natural radioactive tracer radon-222 (radon) in a vertical column through the troposphere is a critical step in the process of calculating regionally integrated emissions of important greenhouse gases using radon-calibrated budget techniques. As continuous long-term radon time series used for such calculations are typically gathered at sites located at or near the surface, a rigorous column radon estimate would require knowledge of the vertical distribution of radon through the atmospheric boundary layer (ABL). The most frequent approach to addressing this issue is to assume a uniform radon profile within the ABL, and no radon in the free atmosphere above. This study aims at refining these traditional assumptions by presenting vertical integrations of high-resolution radon profiles, gathered using a motorised glider in and above daytime boundary layers over rural inland Australia under a range of stability and cloud conditions. On cloudless days, a large drop in radon concentrations across the inversion is evident from the vertical radon profiles. This is a result of radon depletion in the free atmosphere by radioactive decay (radon’s half-life is 3.8 days), and the “top-down” diffusion process associated with entrainment of this radon-depleted air into the ABL results in a range of radon gradients observed in the upper part of the mixed layer. When actively coupled boundary layer clouds are present, the profiles indicate strongly enhanced vertical mixing and venting of radon from the sub-cloud layer into the cloud layer. Under these conditions, the proportion of total-column radon remaining in the sub-cloud layer can sometimes be as low as 30%. Based on the enhanced understanding of vertical radon distributions in daytime terrestrial boundary layers gained from these airborne studies, refinements are suggested to the traditional estimation of total column radon from datasets where only surface-based radon measurements are available. These refinements are shown to result in improved estimates of total boundary layer radon in both clear and cloudy conditions. © Author(s) 2010
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    In-situ measurements of the stable isotopic composition of atmospheric water vapour using FTIR spectroscopy
    (Université Pierre et Marie Curie, 2010-04-27) Parkes, SD; Griffith, DWT; Williams, AG; Element, A; Chambers, SD; McCabe, MF
    The stable isotopic composition of atmospheric water vapour is related to the hydrological processes that occur along the back trajectory of an air mass, including evaporation at the moisture source, atmospheric mixing and precipitation. Thus, by collecting continuous measurements of the stable isotopes in water vapour a record of the hydrological history of air passing a site can be compiled. To collect such a record a FTIR instrument capable of making real‐time in‐situ measurements of the stable isotopes in water vapour has been developed. The instrument has been deployed at a site near Sydney, Australia for approximately 18 months. During this time we have shown that the FTIR instrument compares well with laser based analysers that are capable of making similar real‐time measurements. In addition to the comparison between the different analysers, we have been investigating some of the large signals that are observed in the time series of isotopic measurements. The analysis of the dataset indicates that the lowest isotope values are generally associated with cold fronts that pass over the South East of the Australian Continent and then over the Sydney region. When a cold front passes over or near the measurement site, the deuterium isotope value can be observed to change by up to 100 per mille within the space of a few hours. In addition, cold frontal passages with contrasting moisture source and precipitation histories exhibit systematic differences in water vapour stable isotope signals as they pass over Sydney. On the other hand, higher and more slowly changing isotope values are generally associated with anticyclonic conditions. The study shows that for our site the variations in the stable isotope values are strongly influenced by the hydrological history of air parcels at a synoptic scale.
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    Map of radon flux at the Australian land surface.
    (European Geosciences Union, 2010-06-09) Griffiths, AD; Zahorowski, W; Element, A; Werczynski, S
    A time-dependent map of radon-222 flux density at the Australian land surface has been constructed with a spatial resolution of 0.05° and temporal resolution of one month. Radon flux density was calculated from a simple model utilising data from national gamma-ray aerial surveys, modelled soil moisture, and maps of soil properties. The model was calibrated against a large data set of accumulation-chamber measurements, thereby constraining it with experimental data. A notable application of the map is in atmospheric mixing and transport studies which use radon as a tracer, where it is a clear improvement on the common assumption of uniform radon flux density. © Author(s) 2010
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    The vertical distribution of radon in clear and cloudy daytime terrestrial boundary layers
    (American Meteorological Society, 2011-01-01) Williams, AG; Zahorowski, W; Chambers, SD; Griffiths, AD; Hacker, JM; Element, A; Wercanski, S
    Radon ((222)Rn) is a powerful natural tracer of mixing and exchange processes in the atmospheric boundary layer. The authors present and discuss the main features of a unique dataset of 50 high-resolution vertical radon profiles up to 3500 m above ground level, obtained in clear and cloudy daytime terrestrial boundary layers over an inland rural site in Australia using an instrumented motorized research glider. It is demonstrated that boundary layer radon profiles frequently exhibit a complex layered structure as a result of mixing and exchange processes of varying strengths and extents working in clear and cloudy conditions within the context of the diurnal cycle and the synoptic meteorology. Normalized aircraft radon measurements are presented, revealing the characteristic structure and variability of three major classes of daytime boundary layer: 1) dry convective boundary layers, 2) mixed layers topped with residual layers, and 3) convective boundary layers topped with coupled nonprecipitating clouds. Robust and unambiguous signatures of important atmospheric processes in the boundary layer are identifiable in the radon profiles, including "top-down" mixing associated with entrainment in clear-sky cases and strongly enhanced venting and subcloud-layer mixing when substantial active cumulus are present. In poorly mixed conditions, radon gradients in the daytime atmospheric surface layer significantly exceed those predicted by Monin-Obukhov similarity theory. In two case studies, it is demonstrated for the first time that a sequence of vertical radon profiles measured over the course of a single day can consistently reproduce major structural features of the evolving boundary layer.© 2011, American Meteorological Society.
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    Vertical radon-222 profiles in the atmospheric boundary layer
    (CSIRO and the Bureau of Meteorology, 2011-11-15) Zahorowski, W; Williams, AG; Chambers, SD; Griffiths, AD; Crawford, J; Werczynski, S; Element, A
    Radon-222 (radon) is a naturally occurring radioactive tracer of air mass transport on different time and space scales. In particular, the vertical distribution of radon has been demonstrated to be useful for characterisation of exchange and mixing processes within the atmospheric boundary layer. In 2006 we started a program of research, using radon-222 to advance our understanding of these processes as part of a broader goal to improve parameterisation schemes for vertical mixing in the lower atmosphere. Two types of experiments have been conducted. The first is based on continuous hourly estimates of radon-222 concentration gradients at two meteorological towers, one focussing on near-surface gradients (2-50m) recorded on a 50m tower at Lucas Heights in New South Wales (34.05ºS, 150.98ºE), and the other on boundary layer gradients (20-200 m) measured on a 213m tower at the Cabauw Experimental Site for Atmospheric Research in the Netherlands (51.971ºN, 4.927ºE). The second experiment type relies on the collection of high resolution radon-222 vertical profiles up to 4,000 m above ground level using radon samplers mounted on an instrumented motorised research glider. In this presentation, we discuss selected results from a unique set of high resolution vertical radon profiles measured in 2007-2010 in clear and cloudy daytime terrestrial boundary layers over rural New South Wales. The profile examples reveal the characteristic structure and variability of three major types of daytime boundary layer: 1) dry convective boundary layers, 2) mixed layers topped with residual layers, and 3) convective boundary layers topped with coupled non-precipitating clouds. We demonstrate that important boundary layer processes are identifiable in the observed radon profiles, including ‘‘top down’’ mixing associated with entrainment in clear-sky cases and strongly enhanced venting and sub-cloud layer mixing when substantial active cumulus are present. A related presentation (Chambers et al. 2011) outlines some recent results based on our radon gradient measurements at the Lucas Heights tower. © 2011 CSIRO and the Bureau of Meteorology.