城乡过渡地带低空温度平流和边界层特征的观测分析

Observational Study on Character of Boundary Layer andLow-Level Tempearture Advection over TransitionZone between Urban and Rural

利用兰州河谷盆地城乡过渡区边界层观测资料,分析了该地区的温度平流和边界层特征。分析表明:(1)夜间热岛环流明显,白天则较弱;(2)夜间200m高度以下有较强的冷平流,在250～400m高度有较弱的暖平流,冷暖温度平流对测点上空边界层温度和层结变化有显著影响;(3)由声雷达确定的夜间边界层高度对应于Ri<1.0的高度,在这一高度范围内存在逆位温和强的风切变。本地区下垫面和复杂的地形导致夜间边界层高度随时间周期性地升高和降低,变化周期约3h。

Using the observational data over transition zone between urban and rural areas in the basin of the Yellow River(Lanzhou) valley, the characteristics of boundary layer and the heat advection were analyzed. The analysis shows: (1) nocturnal heat island circle is distinct, while it is obscure in daytime; (2) there is strong cool advection below highs of 200 m, while the weak warm advection between the heights of 250 m and 400 m. The heat advection have significantly influence on the temperature and stratification of boundary layer; (3) the height of nocturnal boundary layer retrieved from sodar facsimile is corresponding to the height of %R-i<1.0%, there are inversion and strong wind shear in this layer. The complex underlying surface and terrain result in increasing and decreasing of the nocturnal boundary layer periodically, and the period is about three hours.