螺旋度在对流天气预报中的应用研究进展

螺旋度表征流体旋转与沿旋转方向运动的强度，在等熵流体中具有守恒性。螺旋性是维持大气运动的基本物理图案：边界层流体、湍流、强风暴、热带气旋等都有较强的螺旋结构；对流风暴常发生在螺旋度值大的地方，流体稳定性与螺旋度密切相关，高螺旋度阻碍了扰动能量串级，对超级单体风暴的维持有重要作用；z螺旋度对大范围暴雨有较好的指示意义。风暴相对螺旋度对决定对流风暴类型有重要作用，其大小决定超级单体是否能形成中气旋，同时，其对冰雹预报有一定的指示意义；风暴相对螺旋度用于预报时计算的难点在于确定预报风暴移动速度。热力场与螺旋度有内在联系，地面相对螺旋度可视为地转风或实际风引起温度平流的一个量度。

Progress in Researches on Application of Helicity to Convective Weather Prediction

Helicity denotes the conjunct intensity of rotation and the movement along the rotation, and it is conservative in isentropic fluid. Helicity is the basic physical pattern for the maintenance of atmospheric activities. Boundary layer fluids, turbulences, severe storms and tropical cyclones are highly helical in their structures. Severe storms often occur in highly helical environments. The stability of fluid is closely associated with helicity. High helicity prevents transient energy from leaping to other energy classes, thus has great importance for the maintenance of supercell. Z-helicity is a good indicator of heavy rainfall. The relative helicity of a storm has great importance in the evolution of the storm. The occurrence of a meso-cyclone is highly depended on the value of helicity. The relative helicity of a storm is also a good indicator of hail occurrence. It is difficult for the application of relative storm helicity in predicting storms for the uncertainty of storm velocity. There exists inherent relationship between atmospheric temperature and helicity, and the surface relative helicity can be used to measure the temperature advection caused by geostrophic flow.