摘要
大多数深厚的局地对流是在条件不稳定的层结中发生的,这就有必要考虑较厚气层对由底部上升气块所可能产生的总影响。从能量角度讨论了条件不稳定问题中的不稳定能量和对流有效位能,并利用观测资料、结合实例分析了单站地面湿静力能与条件不稳定中不稳定能量的关系。主要结论如下:(1)从能量观点,对对流有效位能的两种定义进行了讨论,认为对流有效位能定义为正、负不稳定能量之差时,其与动能相联系的表达式中包含了低层抬升速度,可以更全面地用于强对流天气预报,尤其是中国南方暖季的强对流预报。(2)气块从底层上升时,无论经历的是干绝热还是湿绝热过程,湿静力能守恒,所以总能量的变化就是动能的变化,等于外界合力对气块做功的大小,不存在湿静力能向动能的转换。(3)从本质上来说,单站低层湿静力能的时序变化用于对流预报的意义在于预示着正、负不稳定能量的改变,从而影响不稳定能量的值。这可以弥补由于高空探测时间分辨率较粗,不能计算逐时正、负不稳定能量的不足。
Most of local deep convections are initiated in a conditionally unstable environment. Thereby it is necessary to con- sider the influence of a deep air layer to the air parcel that rises from the base level. Some questions related to conditional insta- bility, such as the unstable energy and Convective Available Potential Energy （CAPE）, are discussed from the perspective of energy. In addition, the relationship between the moist static energy of a single surface station and the unstable energy in a con- ditionally unstable environment is analyzed based on a case study using observational data. The main results are as follows. （1） From the perspective of energy, the original definition of CAPE should be followed. That means CAPE is equal to the differ- ence between positive and negative unstable energy. The lifting velocity in the lower level associated with the kinetic energy is implicitly included in the formulation of original CAPE, which is helpful for forecasting severe convective weather, especially in South China in the warm season. （2） The moist static energy remains constant when the air parcel is lifted from low to high levels during both the dry adiabatic and moist adiabatic processes, which indicates that the variation of total energy is only relat- ed to the variation of kinetic energy caused by external forcing. There exists no transformation from moist static energy to ki- netic energy. （3） Temporal variation of the moist static energy at a single surface station indicates the variation of positive and negative unstable energy, which is closely related to the calculation of unstable energy. Such temporal variations at various sta- tions can make up for the weaknesses caused by coarse resolution of soundings and the deficiency of hourly data of positive and negative unstable energy.
出处
《气象学报》
CAS
CSCD
北大核心
2017年第3期517-526,共10页
Acta Meteorologica Sinica
基金
国家自然科学基金项目(41475042)
我国华南春季对流性大风监测预报关键技术研究(GYHY201406002)
国家科技支撑计划项目(2015BAC03B06)
