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Abstract
The use of the eddy correlation technique is demonstrated for the measurement of sensible heat transfer in an urban area. The problems of time and space sampling (in the horizontal and vertical) are investigated. Based on 27 summer days of observations from a roof-top site in the central built-up part of Vancouver, the diurnal variation of sensible heat transfer above an urban area is described. The flux of heat at 1.2, 4 and 20 m above roof level largely reflected time and magnitude changes in the net radiation field. While being in phase with net radiation, the sensible heat flow commonly exhibited unusually high values in the late afternoon. Nocturnal urban sensible heat flow was quite unlike the normal rural pattern, often being directed into the atmosphere. Also at night the existence of flux divergence is suggested.
Abstract
The use of the eddy correlation technique is demonstrated for the measurement of sensible heat transfer in an urban area. The problems of time and space sampling (in the horizontal and vertical) are investigated. Based on 27 summer days of observations from a roof-top site in the central built-up part of Vancouver, the diurnal variation of sensible heat transfer above an urban area is described. The flux of heat at 1.2, 4 and 20 m above roof level largely reflected time and magnitude changes in the net radiation field. While being in phase with net radiation, the sensible heat flow commonly exhibited unusually high values in the late afternoon. Nocturnal urban sensible heat flow was quite unlike the normal rural pattern, often being directed into the atmosphere. Also at night the existence of flux divergence is suggested.
Abstract
This paper examines the medium-range forecast of a typhoon using a global model. The focus of this study is on a comparison of two longwave radiative transfer calculations, one is based on an emissivity formulation while the other utilizes a band model. A more realistic prediction of low clouds in the storm environment by the band model leads to stronger cooling rates and the resulting destabilization contributes to the maintenance of conditional instability. The inflowing air supplies this instability for the maintenance of a longer-lasting storm. The emissivity model fails to predict a sufficient abundance of low clouds resulting in weaker cooling rates hence the resulting destabilization is weak and leads to decay of the storm. The important role of radiatively active shallow clouds in maintaining the conditional instability of the storm environment is illustrated for a long-range integration. An analysis of these aspects of storm environment destabilization is presented in this paper.
Abstract
This paper examines the medium-range forecast of a typhoon using a global model. The focus of this study is on a comparison of two longwave radiative transfer calculations, one is based on an emissivity formulation while the other utilizes a band model. A more realistic prediction of low clouds in the storm environment by the band model leads to stronger cooling rates and the resulting destabilization contributes to the maintenance of conditional instability. The inflowing air supplies this instability for the maintenance of a longer-lasting storm. The emissivity model fails to predict a sufficient abundance of low clouds resulting in weaker cooling rates hence the resulting destabilization is weak and leads to decay of the storm. The important role of radiatively active shallow clouds in maintaining the conditional instability of the storm environment is illustrated for a long-range integration. An analysis of these aspects of storm environment destabilization is presented in this paper.
Abstract
A yaw sphere-thermometer assembly, to measure sensible heat flux density by the eddy correlation method, was built following the design of Tanner and Thurtell. Wind tunnel experiments indicate that the sphere constant should be 1.57, which is significantly less than the theoretical value of 2.25. The effects of tilt indicate that heat fluxes may be in error by 5% per degree of tilt In unstable conditions and up to 11% per degree in stable conditions. Field comparisons of the heat fluxes measured by the yaw sphere-thermometer system and a Bowen ratio apparatus produced satisfactory agreement.
Abstract
A yaw sphere-thermometer assembly, to measure sensible heat flux density by the eddy correlation method, was built following the design of Tanner and Thurtell. Wind tunnel experiments indicate that the sphere constant should be 1.57, which is significantly less than the theoretical value of 2.25. The effects of tilt indicate that heat fluxes may be in error by 5% per degree of tilt In unstable conditions and up to 11% per degree in stable conditions. Field comparisons of the heat fluxes measured by the yaw sphere-thermometer system and a Bowen ratio apparatus produced satisfactory agreement.
