New normalized constant modulus algorithms with relaxation

Published versio

A new family of blind adaptive equalization algorithms

Published versio

Residual echo signal in critically sampled subband acoustic echo cancellers based on IIR and FIR filter banks

Published versio

On the use of radon for quantifying the effects of atmospheric stability on urban emissions

Radon is increasingly being used as a tool for quantifying stability influences on urban pollutant concentrations. Bulk radon gradients are ideal for this purpose, since the vertical differencing substantially removes contributions from processes on timescales greater than diurnal and (assuming a constant radon source) gradients are directly related to the intensity of nocturnal mixing. More commonly, however, radon measurements are available only at a single height. In this study we argue that single-height radon observations should not be used quantitatively as an indicator of atmospheric stability without prior conditioning of the time series to remove contributions from larger-scale "non-local" processes. We outline a simple technique to obtain an approximation of the diurnal radon gradient signal from a single-height measurement time series, and use it to derive a four category classification scheme for atmospheric stability on a "whole night" basis. A selection of climatological and pollution observations in the Sydney region are then subdivided according to the radon-based scheme on an annual and seasonal basis. We compare the radon-based scheme against a commonly used Pasquill–Gifford (P–G) type stability classification and reveal that the most stable category in the P–G scheme is less selective of the strongly stable nights than the radon-based scheme; this lead to significant underestimation of pollutant concentrations on the most stable nights by the P–G scheme. Lastly, we applied the radon-based classification scheme to mixing height estimates calculated from the diurnal radon accumulation time series, which provided insight to the range of nocturnal mixing depths expected at the site for each of the stability classes. © 2015, Author(s)

Improved mixing height monitoring through a combination of lidar and radon measurements

Surface-based radon (222Rn) measurements can be combined with lidar backscatter to obtain a higher quality time series of mixing height within the planetary boundary layer (PBL) than is possible from lidar alone, and a more quantitative measure of mixing height than is possible from only radon. The reason why lidar measurements are improved is that there are times when lidar signals are ambiguous, and reliably attributing the mixing height to the correct aerosol layer presents a challenge. By combining lidar with a mixing length scale derived from a time series of radon concentration, automated and robust attribution is possible during the morning transition. Radon measurements provide mixing information during the night, but concentrations also depend on the strength of surface emissions. After processing radon in combination with lidar, we obtain nightly measurements of radon emissions and are able to normalise the mixing length scale for changing emissions. After calibration with lidar, the radonderived equivalent mixing height agrees with other measures of mixing on daily and hourly timescales and is a potential method for studying intermittent mixing in nocturnal boundary layers.© 2013, Copernicus Publications

Radon-based assessment of stability effects on potential radiological releases

It is a requirement of nuclear energy and research facilities to conduct continuous and comprehensive atmospheric monitoring in order to better forecast public or environmental exposure to routine or accidental releases of radioactive substances to the atmosphere. A key aspect of such monitoring programs is the assessment of the atmospheric mixing state (or “stability”). Whether these facilities are in dense urban areas, or surrounded by heavily vegetated exclusion zones, local roughness heterogeneity can hamper attempts to accurately categorise stability by conventional meteorological techniques. Based on an analysis of 8 months of hourly climatology and atmospheric radon observations from a 60 m tower at the IFIN-HH nuclear research facility (Bucharest, Romania), we develop and apply a continuous (i.e. not categorical) radon-based scheme for the classification of the nocturnal atmospheric stability state. We demonstrate the superior performance of the radon-based technique to Pasquill-Gifford or bulk Richardson number stability typing at this site where heterogeneous roughness elements reach to 15 m a.g.l. Under stable nocturnal conditions the Pasquill-Gifford scheme overestimates the atmosphere’s capacity to dilute pollutants with near-surface sources by 20% compared to the radon-based scheme. Under these conditions, near-surface wind speeds drop well below 1 m s-1 and nocturnal mixing depths vary from ~25 m to less than 10 m a.g.l. Climatological parameters are characterised by season and 4 arbitrarily-defined nocturnal stability categories. Benchmarks (based on 10/50/90th percentile distributions) of 30-60 m wind and temperature gradients are devised for each stability category for evaluation of model performance. Lastly, nocturnal radon-derived effective mixing depth estimates constrained by tower observations are used to better-constrain the seasonal variability in the Bucharest regional radon flux: 13 mBq m-2 s-1 (winter), 18 mBq m-2 s-1 (summer)

Characterising terrestrial influences on Antarctic air masses using Radon-222 measurements at King George Island

We report on one year of high-precision direct hourly radon observations at King Sejong Station (King George Island) beginning in February 2013. Findings are compared with historic and ongoing radon measurements from other Antarctic sites. Monthly median concentrations reduced from 72 mBq m−3 in late-summer to 44 mBq m−3 in late winter and early spring. Monthly 10th percentiles, ranging from 29 to 49 mBq m−3, were typical of oceanic baseline values. Diurnal cycles were rarely evident and local influences were minor, consistent with regional radon flux estimates one tenth of the global average for ice-free land. The predominant fetch region for terrestrially influenced air masses was South America (47–53° S), with minor influences also attributed to aged Australian air masses and local sources. Plume dilution factors of 2.8–4.0 were estimated for the most terrestrially influenced (South American) air masses, and a seasonal cycle in terrestrial influence on tropospheric air descending at the pole was identified and characterised. © Author(s) 201

Influence of turbulent mixing and air circulation in the lower atmosphere on fetch areas of selected WMO Global Atmosphere Watch baseline air pollution stations.

The World Meteorological Organisation (WMO) established the Global Atmosphere Watch (GAW) Programme in 1989. The scientific goals of GAW relate to investigating the role of atmospheric chemistry in global climate change, and include: understanding the complex mechanisms with respect to natural and anthropogenic atmospheric change; and improving the understanding of interactions between the atmosphere, ocean, and biosphere.American Meteorological Society; Stockholm Universit

Using radon-222 to distinguish between vertical transport processes at Jungfraujoch

Trace gases measured at Jungfrajoch, a key baseline monitoring station in the Swiss Alps, are tranported from the surface to the alpine ridge by several different processes. On clear days with weak synoptic forcing, thermally-driven upslope mountain winds (anabatic winds) are prevalent. Using hourly radon–222 observations, which are often used to identify air of terrestrial origin, we used the shape of the diurnal cycle to sort days according to the strength of anabatic winds. Radon is ideal as an airmass tracer because it is emitted from soil at a relatively constant rate, it is chemically inert, and decays with a half-life of 3.8 days. Because of its short half-life, radon concentrations are much lower in the free troposphere than in boundary-layer air over land. For comparable radon concentrations, anabatic wind days at Jungfraujoch are different from non-anabatic days in terms of the average wind speed, humidity, air temperature anomalies, and trace species. As a consequence, future studies could be devised which focus on a subset of days, e.g. by excluding anabatic days, with the intention of choosing a set of days which can be more accurately simulated by a transport model. © Author(s) 2014