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Please use this identifier to cite or link to this item: http://apo.ansto.gov.au/dspace/handle/10238/4200

Title: Separating remote fetch and local mixing influences on vertical radon measurements in the lower atmosphere
Authors: Chambers, S
Williams, AG
Zahorowski, W
Griffiths, A
Crawford, J
Keywords: RADON
ATMOSPHERES
Radon 220
DAUGHTER PRODUCTS
DIFFUSION
RADON 222
Issue Date: 1-Nov-2011
Publisher: Wiley-Blackwell
Citation: Chambers, S., Williams, A. G., Zahorowski, W., Griffiths, A., Crawford, J. (2011). Separating remote fetch and local mixing influences on vertical radon measurements in the lower atmosphere. TELLUS SERIES B-CHEMICAL AND PHYSICAL METEOROLOGY, 63(5), 843-859.
Abstract: Two-point radon gradients provide a direct, unambiguous measure of near-surface atmospheric mixing. A 31-month data set of hourly radon measurements at 2 and 50 m is used to characterize the seasonality and diurnal variability of radon concentrations and gradients at a site near Sydney. Vertical differencing allows separation of remote (fetch-related) effects on measured radon concentrations from those due to diurnal variations in the strength and extent of vertical mixing. Diurnal composites, grouped according to the maximum nocturnal radon gradient (Delta C(max)), reveal strong connections between radon, wind, temperature and mixing depth on subdiurnal timescales. Comparison of the bulk Richardson Number (Ri(B)) and the turbulence kinetic energy (TKE) with the radon-derived bulk diffusivity (K(B)) helps to elucidate the relationship between thermal stability, turbulence intensity and the resultant mixing. On nights with large Delta C(max), K(B) and TKE levels are low and Ri(B) is well above the 'critical' value. Conversely, when Delta C(max) is small, K(B) and TKE levels are high and Ri(B) is near zero. For intermediate Delta C(max), however, Ri(B) remains small whereas TKE and K(B) both indicate significantly reduced mixing. The relationship between stability and turbulence is therefore non-linear, with even mildly stable conditions being sufficient to suppress mixing. © 2011, Wiley-Blackwell. The definitive version is available at www3.interscience.wiley.com
URI: http://dx.doi.org/10.1111/j.1600-0889.2011.00565.x
http://apo.ansto.gov.au/dspace/handle/10238/4200
ISSN: 0280-6509
Appears in Collections:Journal Articles

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