| In this paper, wind profile radar data at Dali station, GPS/MET moisture observations and NCEP/NCAR reanalysis data are used to study the heavy rainfall events. The results show that:The value of signal-to noise increases, vertical velocity decreases quickly and the number of level of the signal-to-noise and vertical velocity possessing same values adds with the approach of rainfall. For the most of rainfall events, the rainfall reaches the maximum as the signal-to-noise increases, and the rainfall reaches the minimum as the vertical velocity decreases. The number of the events with wind speed more than 12m/s increases and the number with wind speed less than 8m/s decreases with the approach of rainfall. The more the wind intensity is, the more the ratio of the wind maximum emerged above 5000m becomes obvious. In ether case, the wind maximum seldom emerges less than 1000m. Short-time strong rainfall can be produced even no low-level jet; the low-level-jet is sufficient condition to produce strong rainfall, not necessary condition. The relation between maximal observational height and rainfall intensity is not obvious, the rainfall may be related to different weather systems, and the maximal observational heights of stratiform clouds are lower than those of convective clouds. Anyway, whether it is signal-to-noise or vertical velocity, the characteristics of addition (or reduction) are very obvious one hour before rainfall. The vertical shear of horizontal wind always exits one to three hours before rainfall, but it decreases quickly as the rainfall emerges and produces difficulty to forecast.The abundant moisture and appropriate triggered conditions are often favorable to produce short-time rainfall. The quick addition of moisture and more than 2mm/h is the sign of short-time strong rainfall. Without abundant moisture, the short-time strong rainfall seldom emerges even if the triggered condition is appropriate.The moisture always reach its maximum on mid-level, the values on low-level and high-level are less than that of mid-level when the short-time strong rainfall emerges. The moisture increases with the height under 500-700hPa, the relative moisture is about 80-95% on low-level, and it’s about 95-100% on mid-level. The huge relative moisture and moisture height on low-and mid-level are favorable to produce short-time strong rainfall.The high-level weather information observed by wind profile radar is obvious under the conditions of huge relative moisture on high-level or whole level, and it’s not obvious for the dry atmosphere on high-level. For the cause of abundant moisture, the short-time strong rainfall can be also produced even if the high-level weather information observed by wind profile radar isn’t obvious.The appropriate convective available potential energy (CAPE) and its addition are necessary to produce short-time rainfall. Although the values of convective available potential energy are different for the various strong rainfall events, it is necessary for the CAPE≥300J·kg-1 at Dali station, but the strength of rainfall is not always to correspond with the strength of CAPE, the huge CAPE sometimes is not favorable to produce short-time strong rainfall.The appropriate small lifting index (LI) and variation of LI with time and space are also necessary to produce short-time rainfall. The strong rainfall always emerges under the conditions of LI≤-1.5℃、△LI≥1.5℃. The smaller the lifting index is, the more the atmosphere stratiform becomes unstable, and the more the convective weather becomes possible. The smaller the variation of lifting index is, the more the short-time strong rainfall is favorable to be produced.The short-time strong rainfall always emerges among the area of upward movement. When the upward movement is strong, the information observed by wind profile radar is obvious, and it is an available sign for the short-time strong rainfall. But in contrast, the sign is not obvious. The downward movement on low-level is not favorable to the production of strong rainfall. |
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