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at the mid-lower of Yangtze Valley steadily with less movement during the
33rd-35th pentad, Yangtze Valley begin Meiyu period (Fig. 3(b)).
3.
EASM advance northward to Yangtze-Huaihe Valley
During the 36th-37th pentad, as West Pacific subtropical high moves
northward further, the front of monsoon advance northward to the Yangtze-
Huaihe Valley, Japan, Korea (Fig. 2(c)), these regions come into Huaihe
Meiyu period (Fig. 3(c)), Baiu, Changma, respectively.
4.
EASM jump northward to North China and then reach the northernmost
border
During the 38th-40th pentad, as the West Pacific subtropical high appears
the second time northward jump, the monsoon extend northward to North
China further (Fig. 2(d)). The rain belt also moves to North China and
the rainfall center stay at the lower of the Yellow River (Fig. 3(d)), but
the precipitation in South China and central China is decreases rapidly
and begin a dry period. During the 41st-42nd pentad, the West Pacific
subtropical high extends northward continuously, and southwesterly flows
move northeastward to Northeast China and the monsoon front reach the
northernmost border of EASM (Fig. 2(e)). The precipitation of North China
and Northeast China achieve maximum (Fig. 3(e)). In the 43rd pentad, the
EASM's front keeps on stay at Northeast China, but intensity was a little
weaker than that in the 41st-42nd pentad.
5.
EASM retreat southward rapid ly
During the 44th-45th pentad, the EASM's front begins to retreat southward
and the southwesterly flows begin to weaken visibly. The intensity of
precipitation over Northern China and Northeastern China also reduce
rapidly. As the monsoon retreats southward quickly from 46th pentad
(Fig. 2(f)), the EASM's front and the rain belt have moved southward
to near 20
◦
N and the summer rainfall in East China decrease rapidly at
the 47th pentad (Fig. 3(f)).
The advance and retreat of EASM behave in a stepwise way, but not in
a continuous way, it undergoes two abrupt northward shift at 33rd pentad
and 38th pentad and three standing stages during the 30th-32nd pentad,
33rd-35th pentad and 38th-43rd pentad. The process that EASM retreat
southward was much faster than when EASM moved northward. And the
transfer of rain belt over East China is consistent with the advance and
retreat of the EASM, that is, the EASM's front arrive at the region where
the rainy season will begin, therefore, the early or late arrival of EASM's
