论证了湿位涡物质的保守性,阐明强降水会造成湿位涡物质异常，异常高度主要出现在850～500 hPa之间。用NCEP/NCAR 11的分析资料对1999年6月下旬引起长江流域暴雨的对流系统进行了湿位涡物质的诊断分析，结果表明梅雨期间大气的湿位涡物质异常区域与降水带的位置和走向基本对应，主要位于梅雨锋及其南侧，与等 线的走向保持一致。依据湿位涡物质的保守性原理，等压面上等 线间的湿位涡物质异常区的移动示踪了暴雨区的移动，这可为暴雨预报提供一定的动力依据。

Based on the moist potential vorticity (MPV) equation containing both heat and mass forcing, the impermeability theorem of the MPV substance (MPVS) is proved. It is clarified that mass forcing induced by intensive precipitation can lead to the MPVS anomaly. The MPVS anomaly is mainly located between 850～500 hPa. With NCEP/NCAR 11 data in Meiyu period in 1999, we find that the MPVS anomaly region corresponds well with the rain belt (include the location and movement of the rainbelt), namely, the MPVS anomaly region is mainly located on the southern side of the Meiyu front, and keeps the same orientation with iso- . According to impermeability theorem of the MPVS, the movement of the MPVS anomaly region on the isobaric can indicate the movement of heavy rain region, which may provide a possible clue to forecast the orientation of the rainbelt.