| Land Breeze and Thermals： A Scale Threshold to Distinguish Their Effects |
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| 作者姓名： | Yongqiang LIU |
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| 作者单位： | Forestry Sciences Laboratory, USDA Forest Service, 320 Green Street, Athens, GA 30602, USA |
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| 摘 要： | Land breeze is a type of mesoscale circulation developed due to thermal forcing over a heterogeneous landscape. It can contribute to atmospheric dynamic and hydrologic processes through affecting heat and water fluxes on the land-atmosphere interface and generating shallow convective precipitation. If the scale of the landscape heterogeneity is smaller than a certain size, however, the resulting land breeze becomes weak and becomes mixed up with other thermal convections like thermals. This study seeks to identify a scale threshold to distinguish the effects between land breeze and thermals. Two-dimensional simulations were performed with the Regional Atmospheric Modeling System （RAMS） to simulate thermals and land breeze. Their horizontal scale features were analyzed using the wavelet transform. The thermals developed over a homogeneous landscape under dry or wet conditions have an initial scale of 2-5 km during their early stage of development. The scale jumps to 10-15 km when condensation occurs. The solution of an analytical model indicates that the reduced degree of atmospheric instability due to the release of condensation potential heat could be one of the contributing factors for the increase in scale. The land breeze, on the other hand, has a major scale identical to the size of the landscape heterogeneity throughout various stages of development. The results suggest that the effects of land breeze can be clearly distinguished from those of thermals only if the size of the landscape heterogeneity is larger than the scale threshold of about 5 km for dry atmospheric processes or about 15 km for moist ones.
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| 关 键 词： | 陆地 热量 表面平衡 天气预报 表面温度 |
| 收稿时间： | 2004-12-16 |
| 修稿时间： | 2005-07-25 |
Land breeze and thermals: A scale threshold to distinguish their effects |
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| Yongqiang LIU.Land breeze and thermals: A scale threshold to distinguish their effects[J].Advances in Atmospheric Sciences,2005,22(6):889-902. |
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| Authors: | Yongqiang Liu |
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| Institution: | Forestry Sciences Laboratory, USDA Forest Service, 320 Green Street, Athens, GA 30602, USA |
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| Abstract: | Land breeze is a type of mesoscale circulation developed due to thermal forcing over a heterogeneous landscape. It can contribute to atmospheric dynamic and hydrologic processes through affecting heat and water fluxes on the land-atmosphere interface and generating shallow convective precipitation. If the scale of the landscape heterogeneity is smaller than a certain size, however, the resulting land breeze becomes weak and becomes mixed up with other thermal convections like thermals. This study seeks to identify a scale threshold to distinguish the effects between land breeze and thermals. Two-dimensional simulations were performed with the Regional Atmospheric Modeling System (RAMS) to simulate thermals and land breeze. Their horizontal scale features were analyzed using the wavelet transform. The thermals developed over a homogeneous landscape under dry or wet conditions have an initial scale of 2-5 km during their early stage of development. The scale jumps to 10-15 km when condensation occurs. The solution of an analytical model indicates that the reduced degree of atmospheric instability due to the release of condensation potential heat could be one of the contributing factors for the increase in scale.The land breeze, on the other hand, has a major scale identical to the size of the landscape heterogeneity throughout various stages of development. The results suggest that the effects of land breeze can be clearly distinguished from those of thermals only if the size of the landscape heterogeneity is larger than the scale threshold of about 5 km for dry atmospheric processes or about 15 km for moist ones. |
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| Keywords: | land breeze thermals horizontal scale large-eddy simulation wavelet transform |
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