Enhancement and suppression of urban heat plumes over Johannesburg

Goldreich, Yair; Tyson, Peter; Gogh, R. G. Von; Venter, Gyuri

doi:10.1007/bf00119372

Cited by 14 publications

(2 citation statements)

References 17 publications

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“…The difficulties of adjusting for the lapse rate effects on the temperature measurements at the elevated sites causes problems with their use in determining the urban-rural temperature difference. This is because previously published research by DeMarrais (1961), Goldreich et al (1981), Godowitch et al (1985) and Uno et al (1988) indicates that urban and open country vertical temperature profiles are not only considerably different to each other, but that it was difficult to generalize about average lapse rates over both areas between day and night, and over seasonal time periods. The lapse rate at one location could also be significantly different to another, even within the Melbourne region, as the lapse rate depends on other atmospheric conditions, such as pressure, temperature and humidity, which can be influenced by localized surface conditions.…”

Section: Methods Data and Site Descriptionmentioning

confidence: 97%

Associations between varying magnitudes of the urban heat island and the synoptic climatology in Melbourne, Australia

2000

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This paper examines the characteristics of the urban heat island (UHI) in a large Australian city (Melbourne) using local area weather data and the US National Centers for Environmental Prediction (NCEP) reanalyses data of mean sea level pressure (MSLP). Conventional methods to determine the UHI from climatological data often involve comparing minimum temperature data between urban and rural environments. The findings presented in this paper show that comparing simultaneous measurements of temperature at one urban and three nearby airport sites at 0600 (Australian eastern standard time (EST)) provided a better estimate of the UHI magnitude. Analyses of these data between 1973–1991 were grouped according to the daily UHI magnitude. For each UHI group of the daily data, mean anomalous synoptic conditions from the 19‐year mean monthly MSLP were examined for the influence of the different MSLP conditions on varying UHI magnitudes. These synoptic conditions included the entire range of weather conditions over the study period. Over the 19‐year period, daily analyses of the regional climatological 0600 EST temperature data revealed a UHI between −3.16° and 6.0°C. The reanalyses of the NCEP MSLP data, in association with the local area climatological data, suggest that statistically significant anomalous anticyclonic conditions were associated with the warmest 17% and coolest 1% of UHI events. The position of the centre of the anticyclone was critical to UHI genesis and development. Statistically significant mean low pressure anomalies were associated with UHI values between 0° and 1°C. These occurred on 40% of the days between 1973–1991. Melbourne's urban area, independent of the topography, was found to inhibit early morning advection events of warm continent air and result in an urban cool island (UCI). Copyright © 2000 Royal Meteorological Society

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Section: Methods Data and Site Descriptionmentioning

confidence: 97%

Associations between varying magnitudes of the urban heat island and the synoptic climatology in Melbourne, Australia

2000

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“…The relative position of a location within the urban heat island and the properties of the land use in the immediate area strongly influence the vertical thermal structure at night. However, many urban areas are located in regions where terrain (Goldreich et al, 1981) or water bodies can complicate or mask the urban effects on the thermal field.…”

Section: Spatial Variation Of the Nocturnal Urban Boundary Layermentioning

confidence: 99%

Spatial variation of the evolution and structure of the urban boundary layer

Godowitch

Ching

Clarke

1987

Boundary-Layer Meteorol

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The spatial variation of the nocturnal urban boundary-layer structure is described and the time variation of the mixing height, and the nocturnal inversion top and strength after sunrise is presented for urban sites located upwind, downwind, and near the center of the heat island, and at an upwind rural site. Observations were derived from high resolution temperature profiles obtained by a helicopter during 35 intensive morning experiments in St. Louis, Missouri.The nocturnal urban boundary layer increased in depth from the upwind edge of the urban area. Far downwind, in suburban and rural areas, a remnant of the urban boundary layer existed between a stable surface-based layer and an upper inversion that resembled the upwind rural inversion.The mixing height (base of the inversion) evolved in a parabolic manner after sunrise at the urban locations. A rise in the inversion top after sunrise at the urban locations is believed to be due to low-level convergence which caused the entire inversion layer to be lifted. Due to large horizontal temperature gradients associated with the urban heat island, cold air advection tended to counteract the urban-induced lifting effect by inhibiting mixing-height growth at urban locations upwind of the heat-island center. Advection also caused the maximum height and fastest growth rate of the urban mixed layer to be shifted downwind of the urban area with time. However, mean mixing-height growth rates at various urban locations did not differ significantly. The rural mixing-height growth rate was about twice as large as urban values for up to 3 hr after sunrise. Spatial differences in the mixing height became small near the time of inversion dissipation, which appeared to occur at about the same time at all locations.

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A case study of low level country breeze and inversion heights in the Johannesburg area

Goldreich¹,

Surridge²

1988

J. Climatol.

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Previous studies within a shallow valley east of the city centre of Johannesburg (South Africa) revealed the presence of some anomalies in the mesoscale, winter, nocturnal climate regime. Among them: the valley was relatively warmer during inversion nights; more than one thermal belt was discerned and valley winds dominated the early hours of the mornings. A tethered balloon and a mobile acoustic sounder were used to monitor temperature, wind and humidity profiles in the valley and vicinity, whilst ground mobile units measured temperature. Observations revealed a three layer wind system in which an elcvated country breeze is sandwiched between the katabatic flow near the ground and the gradient wind aloft. The double thermal belts observed on the valley's slopes are probably due to the oscillation of the country breere (the lower) and the meso-scale valley inversion top (the upper one). The inversion top over the ridge lines is probably caused by the regional nocturnal inversion or an elevated inversion erodcd by the urban heat island plume. KEY WORDS Mesoscale wind climatology Urban topo-climate interaction Country breeze Mountain and valley circulationWind and temperature profiles Winter climate of Southern Africa Plateau

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Enhancement and suppression of urban heat plumes over Johannesburg

Cited by 14 publications

References 17 publications

Associations between varying magnitudes of the urban heat island and the synoptic climatology in Melbourne, Australia

Associations between varying magnitudes of the urban heat island and the synoptic climatology in Melbourne, Australia

Spatial variation of the evolution and structure of the urban boundary layer

A case study of low level country breeze and inversion heights in the Johannesburg area

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