Case Study of Hail Cloud Internal Structure Based on Rocket Sounding Data

Using rocket sounding data, a new generation of weather radar data and meteorological data is utilized to comprehensively analyze the hail cloud in Baota District, Yan'an County, on July 17, 2015. The results show the following aspects. (1) At 0800 BT (Beijing time), low vortex in the Hetao region split eastward, with a strong cold advection; the fast movement and a rising of surface temperature at 1400 BT caused this hail. (2) The hailstorm conditions inside the backward position, such as temperature and humidity, convection index (Tg), whole layer special humidity integral index (IQ), and total totals index (TT), are lower than those in the external natural atmosphere. The stratification stability index (K), lifted index (LI), and Showalter index (SI) show that hail clouds inside are smaller than those outside. The storm severity index (SSI) of the hail cloud, a thermal parameter, is lower than that in the natural atmosphere. The internal energy parameter, i.e., convective available potential energy (CAPE) is considerably lower than those in the natural atmosphere. The height of the 0°C layer inside the hail cloud is lower than the natural atmosphere outside the hail cloud. (3) Location of the rocket detection is opposite to the back of the hail cloud. The wind direction changes counterclockwise from downward to upward in the hail cloud.At the −20°C high-temperature layer, air flow is higher and stronger, and the whole layer has partial sinking airflow. (4) The temperature range that is near the 0°C layer in hail cloud is −1.8°C–5.0°C. The maximum humidity area is within the depth of 1.0 km, where humidity is over 80% and the maximum humidity is 87.1%. These provide water vapor conditions for hail formation. (5) There is a maximum horizontal wind speed of 19 m s⁻¹ rapid flow and a thickness of 0.022 km close to the lower layer of 0°C. The layer also maintains a horizontal wind speed of 13 m s⁻¹ or above in the temperature range of −4.8°C–5.0°C and a thickness within 1.6 km. These provide a dynamic field condition for hail formation. (6) There is a weak wind zone of ≤ 2 m s⁻¹ in areas where the temperature range is −8.7°C–9.2°C and the thickness is within 0.2 km. Below the weak wind zone, where the temperature range is −4.6°C–8.8°C and the thickness is within 0.889 km, it is the updraft. Here, the average rising speed is 1.79 m s^-1, and the maximum rising speed is 4 m s⁻¹. This configuration provides an environmental field for the growth of hail.