Modes of Meiyu Frontal Cloud Systems. Part Ⅱ：Frequencies and Transitional Characteristics

On the basis of the leading modes of the Meiyu frontal cloud system extracted by the empirical orthogonal function (EOF) from the black body temperatures (TBBs) in the active periods of Meiyu during 1998 to 2008, the frequency of occurrence, persistence time, and transitional characteristics are investigated. There are seven independent leading modes for TBB anomalies (EOF1 to EOF7). The statistics show that the positive phase of EOF1 has the highest frequency of occurrence and can explain the first appearance mode in 25% of the total Meiyu processes. The positive phase of EOF5 has the lowest frequency of occurrence of all of these leading modes and is often mixed with other modes as a transition mode. In addition, the longest persistence time of the negative EOF2 is 81 h and is longer than that of the other leading modes, whereas the longest duration time of the positive EOF5 is only 18 h, which is shorter than that of the other leading modes. The negative phase of EOF6 has the longest mean duration time. The conversions between the leading modes are random, whereas only the negative EOF5 and EOF6 show better directionality. Among them, the probability for the transition from the negative phase of EOF6 to the negative phase of EOF5 is 66.67%, whereas the negative phase of EOF5 often transites to the positive phase of EOF3 and the negative phase of EOF1.