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The Influence of Forests on Atmospheric Heating during the Snowmelt Season

Takeshi YamazakiGeophysical Institute, Tohoku University, Sendai, Japan

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Abstract

Atmospheric heating during the snowmelt season has been studied by means of data analysis and numerical model experiments. As a result of the data analysis, it was shown that in some examples the daytime air temperature rose above 0°C, even if the ground surface was covered by snow. Moreover, it was found that the number of days when the daytime air temperature rose above 0°C was large when the duration of sunshine increased. However, the increase was not related to the wind speed. Therefore, the air temperature over snow cover increases during the daytime if the sunshine is strong even under calm conditions (weak advection). On the other hand, the following result was obtained with the use of a local circulation model combined with a canopy heat balance model. The atmosphere was heated over the plains if forested areas existed around the plains, even if the plains surfaces were covered by snow without forests. An upward sensible heat flux was supplied from the forest canopy, resulting in atmospheric heating. It was concluded that the existence of forests was one of the main causes of atmospheric heating during the snowmelt season.

Abstract

Atmospheric heating during the snowmelt season has been studied by means of data analysis and numerical model experiments. As a result of the data analysis, it was shown that in some examples the daytime air temperature rose above 0°C, even if the ground surface was covered by snow. Moreover, it was found that the number of days when the daytime air temperature rose above 0°C was large when the duration of sunshine increased. However, the increase was not related to the wind speed. Therefore, the air temperature over snow cover increases during the daytime if the sunshine is strong even under calm conditions (weak advection). On the other hand, the following result was obtained with the use of a local circulation model combined with a canopy heat balance model. The atmosphere was heated over the plains if forested areas existed around the plains, even if the plains surfaces were covered by snow without forests. An upward sensible heat flux was supplied from the forest canopy, resulting in atmospheric heating. It was concluded that the existence of forests was one of the main causes of atmospheric heating during the snowmelt season.

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