Indications of topographically-induced eddies in stratified flow during a severe air pollution event

Abstract

During the last week of June 1978, Melbourne experienced a prolonged period of stagnation over the city, resulting in high levels of air pollutants. Internal Froude numbers through the period ranged from approxjmately 0.1 to 0.3, indicating that flow in the area should be strongly stratified. Wind patterns determined using data from thirteen anemographs within and immediately adjacent to the city revealed a pattern of eddies across the city each afternoon in a 'cavity' in the lee of upstream topography. That pattern evolved with time, and changed between days as the controlling meteorological conditions altered. The available mean sea level pressure data from the region for the same times indicated perturbations in that field which were consistent with the observed wind patterns.The eddy patterns were replaced at the surface overnight by katabatic winds as cooling took place and a ground-based inversion became reestablished. However, mean sea level pressure data and the anemograph records suggest that the eddy pattern may have continued overnight, aloft.Considerable recycling of air occurred, both within individual circulations and by wind reversal between daytime and nocturnal regimes. This aided the persistence of high pollutant concentrations.

Quantification of secondary organic aerosol in an Australian urban location

“…Autumn-early winter in Melbourne is marked by low wind speeds and cool temperatures, thus allowing pollutants to stagnate. [22] Levoglucosan measurements made on PM 10 filters collected at BAQS during 2007-09 confirm the presence of smoke in PM 10 aerosol during autumn-early winter. Environment Protection Authority Victoria (EPAV) air monitoring reports for 2005 and 2006 ascribe one exceedance of the Air NEPM for PM 10 during autumn of both 2005 and 2006 to prescribed burning.…”

Quantitative Analysis of Meteorological Conditions for a Comparative Risk Estimation of Nuclear Power Plants in Korea

“…In this method, the representative integral quantities for stagnation and recirculation are calculated on the basis of the measured wind speed and direction. The measured horizontal wind vectors are divided into 'east-west', i u and 'north-south', i v , components, respectively, as follows: (2) where i U is the wind speed and i is the wind direction from which the wind blows, clockwise from the north.…”

“…Lyons and Steedman reported the observations of marked decoupling of the surface layer and sudden nocturnal air temperature variations observed at a desert location in western Australia 1) . Tapp examined some of the meteorological features associated with an extended period of stagnation of the near-surface air mass in Melbourne, during which a severe and prolonged buildup of air pollutants occurred 2) . Katsoulis examined the meteorology of high concentration episodes and an air stagnation index for Athens 3) .…”

Atmospheric dispersion in mountain valleys and basins

“…,, Tapp (1985) Western Oregon has one of the highest meteorological potentials for air pollution in the United States (Holzworth, 1971). Stagnation periods occur in the basins (restricted valleys) along the Columbia and Willamette rivers during the northward movement of the Pacific anticyclone in summer and early fall, and with advection of warm air aloft from the souttl during late fall and winter (Olsson et al, 1974).…”