Geoscience Reference
In-Depth Information
Huang
et al.
11
,
12
pointed that the summer rainfall in China exhibits two
abrupt changes of climate which occurred in 1965 and 1976 respectively,
the summer precipitation over North China begins to decrease obviously
from 1965, but the rainfall in the middle-lower Yangtze River — the Huai
River Valley keeps increasing since the later 1970s, while the precipitations
in South and North China in the period from 1980s to the early 1990s were
obviously less than those in the 1970s and drought trend was more and
more severe there. However, from the mid-1990s, there was an increasing
trend in the precipitation in the northern part of North China. Xu and
Wei
13
showed that there are four periods in the precipitation of North
China. The plenitude of precipitation appears from 1880 to 1898 and 1949
to 1964 and the low rain water appears from 1899 to 1947 and from 1965 to
1999. Shi and Xu
14
showed that the precipitation over China exhibits the
transition of interdecadal trend occurs in 1980s by using mode of the trend
discretion, the rainfall in south of China increases after the transition, but
rainfall in north of china begins to decrease.
From the above analysis, we know that the EASM exhibits distinct
interdecadal variability. The before study mainly bases on two methods.
The first method of EASM index is used by Zhang Zhixiu, Guo Qiyun
and so on. They showed that EASM experiences interdecadal variability
by the analyses of time series of EASM's index. But these indices were
developed for EASM as a whole on a monthly or seasonal basis. In
addition, Wu Changgang, Hu Haoran, Qian Weihong
et al.
used the
variations of EASM's north edge to discuss the interdecadal variability.
In fact, EASM moves northward from low to middle and high latitudes
or retreat southward as the EASM develop and it do not stay at only
one region with less movement. Therefore, it brings different influence to
different regions. A single index or the north edges fail to describe the
condition during EASM's advance/retreat and its vigor locally. The study
about how the advance and retreat of the EASM influence the drought
and flood is much less, especially in interdecadal timescales. In addition,
we know that the precipitation over East China also has interdecadal
variability and the spatial distribution pattern of the summer fall in East
China has distinct transition. Whether the EASM's movement also exhibits
interdecadal variability? How is the relationship between the interdecadal
variability of EASM's movement and the spatial distribution pattern of the
rainfall in East China?
In order to answer above questions, by using ECMWF 2
5
◦
upper air reanalysis daily data and 740 stations rainfall data compiled by
5
◦
×
.
2
.
