Based on the observation data from May 2012 to September 2012, the micrometeorological characteristics in the surface layer during gust, gale wind and hail were analyzed at the Pingliang Land Surface and Severe Weather Research Station. The results showed that there was strongly updraft a few hours before the occurrence of thunderstorm. The 30 minutes' average vertical velocity of the updraft could reach 0.25 m·s-1 at 14 meters above the ground. When suffering server thunderstorms, the vertical velocity in this region is almost 1 to 2 orders of magnitude greater than normal. When the thunderstorm passed the station, the near surface pressure increased rapidly, the temperature fell sharply and the updraft quickly changed to downdraft. These are all because of the influences of the strong and cool downdraft divergence flow. Besides, the 30 minutes' average vertical velocity of the downdraft can reach-0.18 m·s-1 at 14 meters above the ground. At the same time, there were strong temperature shear and the horizontal wind shear between the thunderstorm and the surrounding environment. They can lead to the extremely increasing in turbulence and sharply increasing of friction velocity, especially when gale wind and hail passed the station with the friction velocity twice than the maximum of its noon friction velocity. The turbulence spectrum analyses showed that the spectral energy of vertical velocity at low frequency region increased under the condition of the severe thunderstorm which not only increased sensible heat flux but also dominated turbulent flux. This may make development of thunderstorms.
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