高温和台风影响下的苏州城市粗糙子层湍流通量特征

利用苏州地区2011年12月20日—2012年8月13日的湍流观测资料对不同季节、高温、台风强天气过程下的湍流特征进行分析。结果表明:城市地区不同季节动量通量、感热通量、潜热通量日变化明显,各通量的夏季平均值、最大值均高于冬春季,夏季感热通量日最大值为160.2 W·m^-2,感热在城市地表能量平衡中的作用大于潜热,各季节潜热通量平均值仅为感热通量的40%~45%。降水量和植被覆盖度影响地表能量平衡,尤其影响地表热量在感热和潜热之间的分配。在高温天气过程中,感热通量增加明显,其峰值约是夏季平均的1.93倍。由于水汽较少,潜热通量明显减少,约为夏季日平均值的60%。速度三分量谱中u谱与w谱在低频区存在两个峰值,说明在城市复杂下垫面里,湍流激发机制中存在低频过程的影响。在台风天气过程中,动量通量大且变化快,感热输送弱,潜热输送波动大。速度谱w基本不符合"-5/3"次律,惯性子区最小且向高频移动,这和台风内部的复杂上升下沉气流有关。

Turbulence characteristics in roughness sublayer of Suzhou under the influence of high temperature and typhoon

The observation data of Suzhou from December 12, 2011 to August 13, 2012 was used to discuss the turbulence characteristics of different seasons and typical weather processes. Results show that: the diurnal variations of momentum fluxes, sensible heat fluxes and latent heat fluxes are obvious in different season in urban area. The average and maximum values of each flux in summer are higher than those in winter and spring,and the maximum sensible heat fluxes in summer is 160.2 W·m^-2. The latent heat flux accounts for about 40%-45% of the sensible heat flux, which proved that sensible heat plays a greater role in urban surface energy balance than latent heat. Precipitation and vegetation coverage affect surface energy balance, especially affecting the distribution of surface heat between sensible heat and latent heat. During the process of high-temperature weather, the sensible heat flux increases significantly, and its peak value is about 1.93 times the summer average. Although the heat is sufficient, the latent heat flux is significantly reduced due to less water vapor. It is about 60% of the summer average. There are two peaks of u spectrum and w spectrum in the low frequency region, which shows low-frequency processes contribute to the turbulence development of complex underlying surface. During the process of typhoon, the momentum flux is large and the change is fast, the sensible heat transport is weak, the latent heat transport is fluctuating and the strong upwards and downwards exchanges exist. The w spectrum in inertial subzone basically does not meet the "-5/3" law, it moves to the high frequency area. This may be related to the complex ascending or sinking airflow inside the typhoon.