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Nocturnal Temperatures in Edmonton, Alberta

K. D. HageDivision of Meteorology, University of Alberta, Edmonton, Alberta

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Abstract

A network of seven thermographs has been operated continuously within the city of Edmonton, Alberta, since February 1968 by Geoscience Research Associates, Ltd., under contract to the Department of Health of the Government of Alberta. Data from these stations, together with hourly observations from two rural airports and one urban airport in the Edmonton area, are inadequate for mapping the temperature field, but provide an unusual opportunity for the study of some climatological characteristics of urban temperatures over relatively flat terrain undisturbed by lake or sea influences. Annual variations in maximum heat island intensity based on monthly mean data are ill-defined because of large variations in month-to-month frequencies of favorable nights. Stratified monthly samples consisting only of nights with intense heat islands show weak annual maxima in January and June. A well-defined diurnal cycle in heat island intensity is found with a maximum 3–4 hr after sunset in all seasons. The time of maximum heat island intensity precedes the time of maximum vertical temperature gradient over the city in an seasons. In the presence of strong vertical wind shear, inversion breakdowns occur and these are found to be patchy and of small horizontal extent.

Abstract

A network of seven thermographs has been operated continuously within the city of Edmonton, Alberta, since February 1968 by Geoscience Research Associates, Ltd., under contract to the Department of Health of the Government of Alberta. Data from these stations, together with hourly observations from two rural airports and one urban airport in the Edmonton area, are inadequate for mapping the temperature field, but provide an unusual opportunity for the study of some climatological characteristics of urban temperatures over relatively flat terrain undisturbed by lake or sea influences. Annual variations in maximum heat island intensity based on monthly mean data are ill-defined because of large variations in month-to-month frequencies of favorable nights. Stratified monthly samples consisting only of nights with intense heat islands show weak annual maxima in January and June. A well-defined diurnal cycle in heat island intensity is found with a maximum 3–4 hr after sunset in all seasons. The time of maximum heat island intensity precedes the time of maximum vertical temperature gradient over the city in an seasons. In the presence of strong vertical wind shear, inversion breakdowns occur and these are found to be patchy and of small horizontal extent.

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