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Nighttime Surface-Layer Temperature Tendencies with and without Chinooks

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  • 1 Department of Geography, The University of Calgary, Calgary, Canada
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Abstract

Investigation into the nature and size of the divergence of net radiation at night in Canada's chinook belt showed that the mean rate of radiative cooling exceeded the measured cooling rate by a statistically significant 2.26 in the layer z1–10 mm in chinook-free weather. Nocturnal changes in both rates were generally in phase. Downward flux of sensible heat from the air column towards the ground accounted for the difference between the two rates. With a chinook at the ground, the mean radiative cooling rate remained virtually unchanged from its chinookless values but the measured rate of cooling was significantly lower. In prechinooks, the surface layer was radiatively warmed but the warming was overcompensated for by the horizontal advection of cold air.

Abstract

Investigation into the nature and size of the divergence of net radiation at night in Canada's chinook belt showed that the mean rate of radiative cooling exceeded the measured cooling rate by a statistically significant 2.26 in the layer z1–10 mm in chinook-free weather. Nocturnal changes in both rates were generally in phase. Downward flux of sensible heat from the air column towards the ground accounted for the difference between the two rates. With a chinook at the ground, the mean radiative cooling rate remained virtually unchanged from its chinookless values but the measured rate of cooling was significantly lower. In prechinooks, the surface layer was radiatively warmed but the warming was overcompensated for by the horizontal advection of cold air.

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