Dynamic Relationships Between the Horizontal Helicity and the Sandstorm

Abstract

Using the recorded data of upper wind and surface wind at 08 h and 20 h everyday from 2002 to 2006, we calculated the horizontal helicity from surface to 500 hPa. The results show that the more negative the horizontal helicity is, the higher the wind velocities from the surface to 500 hPa are and the stronger the westerly wind is. Consequently, the shear strength of the vertical air flow increases and the convergent vertical air flow thus enhances, which resulting in the formation of extremely severe dust storms. The negative core (or center) of the aforementioned horizontal helicity often reaches the maximum near by the Hexi Corridor, leading to the frequent occurrence of sandstorms in its downstream areas towards the southeast. Our calculated results demonstrate a strong relationship between the negativity of the helicities and the intensity of the related sandstorms. For example, if the horizontal helicity in its core is ≤–200 m2/s2, sand‐dust will probably occur within 24 hours with a better (>500 m) visibility. When the horizontal helicity in its core is ≤–600 m2/s2, strong sandstorms are likely to occur within 6 hours with a visibility less than 500 m. When the horizontal helicity in its core (or center) is ≤–1000 m2/s2, extremely strong sandstorms are most likely to occur within 6 hours with a visibility less than 50 m.