Boundary-layer observations in the Pilbara coastal region

Abstract

Rapid industrialisation is taking place in a number of coastal areas of Western Australia's Pilbara region, as a result of the processing and export of offshore natural gas and mineral resources from inland. Air quality models are being applied to further our knowledge of the dispersion and resulting ground-level concentrations of various industrial pollutants. However, meteorological data for the region are sparse, and there is a need to understand low-level stability profiles under different synoptic weather regimes in order to reduce uncertainty in the results from these models. To this end, boundary-layer wind, temperature and humidity data were gathered from radiosonde flights throughout the day at coastal and inland (7 km) locations at Port Hedland over two observing periods, each six days in duration, and designed to include the dominant synoptic wind patterns. Under offshore synoptic winds (typically April through August), the stability profile in sea breeze onshore flow was found to be dependent on whether the temperature of the early morning offshore flow was greater or less than the sea surface temperature. Mixed-layer heights throughout the day were restricted to less than 250 m at the coastal site and 500 m at the inland site. On days of synoptic onshore wind patterns (typically September through March), winds were onshore throughout the day and most of the night, with an unstable temperature profile extending to a height of a few hundred metres, capped by a stable layer to typically 1000 m. A deeper, less-stable layer above extended to 2000 m. The data are used to develop generic models of stability profiles as a function of synoptic wind regime, primarily for use in DISPMOD, a Gaussian-plume based air quality dispersion model.