Geoscience Reference
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August every year, the transfer of rain belt and the most of drought and
floods in China, especially in the East China. After the onset of EASM,
Pre-flood Season Precipitation reaches to be strongest period, and then
the major seasonal rain belt over China extend northward to the Yangtze-
Huaihe River Valley, North China, and Northeast China, respectively. 1 , 2
The stay duration and the strength of EASM in its journey to the north
determine directly local rainfall amount on its way, however, as the intensity
of monsoon and the process of advance and retreat of EASM are different
every year, so the precipitation of different regions in East China has the
visible inter-annual variability, and this is also the important natural cause
of the high-frequency and fierce disaster, such as the drought, flood, clod,
and hot. Therefore, describing and monitoring the movement of EASM is
important value to the prediction of the rain belt.
Huang and Zhou 3 showed that the interdecadal variability of EASM is
very obvious during the recent 50 years. EASM is stronger than normal from
1950 to mid-1960s, while it turns to be weaker since mid-1960s. Based on
Shi Neng's summer monsoon index (SMI), Zhang et al. 4 also indicated that
EASM is continually stronger from 1950 to mid-1960s and it became weaker
from mid-1960s, especially since 1980 EASM became weaker and weaker.
Guo et al. 5 pointed out that there is a systematic reduction of EASM during
the period of 1951-2000 and EASM have obvious interdecadal variability.
Strong monsoon (SMI = 1.0) was predominated during the period of 1951-
1975; SMI was less than 1.0 since 1976. Wu et al. 6 calculated the location
of northward shift of EASM by using NCEP/NCAR air temperature and
specific humidity reanalysis data in recent 50 years. They found that there
is obvious interdecadal change in the north boundary of EASM, and the
years with the far north boundary centralize in 1950s and 1960s, with the far
south in 1980s and 1990s. Wu and Qian 7 defined the north edge of EASM
based on precipitation, wind and pseudo-equivalent potential temperature,
basing the northernmost location that the EASM can reach from 1961 to
2001. They pointed out that the northernmost location that the EASM
can reach have dominant interdecadal shift during the period of 1977-1979.
Kwon et al. 8 showed that the general circulation over East Asia has a shift
during mid-1990s.
Wang et al. 9 showed that the rainfall in East China exhibits obvious
interdecadal variability. The temporal and spatial distribution of the
summer precipitation in East China has some regularity. Zhao 10 divided
the distribution of summer precipitation in East China into three different
patterns: the northern type, the middle type, and the southern type.
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