Tab. 1

Classification of rainstorm grades"

Fig. 1

The distribution of rainstorm center of 20 selected precipitation cases and the diurnal variation of mean precipitation"

Tab. 2

Classification of precipitation processes"

Fig. 2

“In front of upper trough” category rainstorm’s mean wind field (barb, unit: m·s-1) and geopotential height field (isoline, unit: dagpm) at 500 hPa (a: before precipitation, b: after precipitation) and 200 hPa (c: before precipitation, d: after precipitation)"

Fig. 3

“In front of upper trough” category rainstorm’s mean moisture flux (vector, unit: kg·s-1·m-1) and divergence of moisture flux (shading, unit: 10-6 kg·s-1·m-2) at 850 hPa (a: before precipitation; b: after precipitation)"

Fig. 4

“Northwest side of the subtropical high” category rainstorm’s mean wind field (barb，unit: m·s-1) and geopotential height field (isoline, unit: dagpm) at 500 hPa (c: before precipitation, d: after precipitation) and 200 hPa (c: before precipitation, d: after precipitation)"

Fig. 5

“Northwest side of the subtropical high” category rainstorm’s mean moisture flux (vector, unit: 10-6 kg·s-1·m-1) and divergence of moisture flux (shading, unit: 10-6 kg·s-1·m-2) at 850 hPa (a: before precipitation; b: after precipitation)"

Fig. 6

Schematic diagram of 500 hPa trough ridge distribution and the corresponding rainstorm center (small figure on the lower right) in the precipitation process of the northwest class of subtropical high (solid line and red dot) and the upper trough front class (solid line and blue dot)"

Tab. 3

Characteristics of LLJ for 20 rainstorm events in the eastern region of Helan Mountain"

Fig. 7

Statistical characteristics of the relationship between the maximum rainfall intensity and the central velocity of LLJ (a), the central wind speed of LLJ (b) and relationship between the maximum process rainfall and central wind speed of LLJ (c)"

Fig. 8

Composite mean precipitation (a) of two categories precipitation (I：“Northwest side of the subtropical high” category rainstorm; II:“In front of upper trough” category rainstorm), schematic diagram of the center position (b) The larger the dot area, the higher the wind speed at the center of the jet stream) and evolution route (c) of LLJ during precipitation"

Fig. 9

Characteristics of LLJ for two categories precipitation processes"

Fig. 10

Wind direction frequency statistics of LLJ center"

Fig. 11

LLJ evolution route and 700 hPa flow field at the strongest moment of the jet and line chart of hourly precipitation at the center of rain intensity (unit:mm) in the typical case of two categories precipitation"