KEYWORDS: Temperature metrology, Climate change, Meteorology, Data modeling, Climatology, Information science, Information technology, Analytical research, Systems modeling, Environmental sensing
Variation of winter and summer temperature in China were discussed in detail by using EOF analysis and
differences between the datasets derived from in situ stations of china meteorological data sharing service system and
NECP/NCAR reanalysis, ERA40 reanalysis were compared in winter and summer temperature in China. Results showed
that: 1) Winter temperature increases linearly with identical signs all over china except the Tibetan plateau. It is colder
than the normal before the late 1970s and warmer since then, especially in 1990s.2) Variation of summer temperature is
complicated that it increases in north China but decreases in south to mid-lower reaches of Huanghe and the north of
Jiangnan district; 3) The values of NCEP/NCAR and ERA40 reanalysis data are commonly lower than the observations
in winter and higher in summer; meanwhile, the change ranges of the reanalysis are closer to the observations'. The
spatial and temporal features of winter temperature obtained from the reanalysis data are consistent with that of the
observations, but for summer temperature, the spatial and temporal features derived from the ERA40 are better than that
of NCEP/NCAR. ERA40 can represent main variations of the summer temperature as the spatial distributions, linear
trend and inter-decadal characteristics, but the NCEP/NCAR dataset shows significant differences from the observations
for the spatial/temporal variations, the remarkable abrupt change around mid-1970s in NCEP/NCAR can not be seen in
observations and in ERA40.
Since the summer rainfall over Yangtze River and Huaihe River often leads to the occurrence of floods, with inconsistent distribution among those years, it is important to investigate the characteristics and the causes of rainfall anomalies. Therefore, REOF analysis is performed on 1951-1998 monthly mean precipitation from both CMA (China Meteorological Administration)-provided 160 weather stations and NCEP/NCAR re-analyses. Results show that: 1) summer rainfall over the mid-lower reaches of Yangtze River (MLRYR) can be divided into two rain belts in the south and north of the study region, called as the southern and northern branch of rain belt, respectively. In detail, the southern belt is located in south of the MLRYR, i.e. regions of Jiangxi, Hunan and Zhejiang, and the other is located in regions of Chongqing, southeast Shaanxi, Hubei, south Henan and Anhui, with east-west zonal distributions for the both; 2) both the rain belts are marked by conspicuous intra-annual and inter-decadal oscillations, with remarkable 14-/8-yr periods on the inter-decadal scale for the southern/northern belt. Besides, two belts are different in the amount of precipitation during the same stage, which is closely related to the large-scale circulation, especially the strength of summer monsoon and subtropical high, both impacting greatly on amount and distribution of the precipitation in two belts.
Interdecadal features of summer rainfall in North China, East Asia summer monsoon (EASM) and the anomaly of
general circulation were explored by using NCEP/NCAR reanalysis data and summer rainfall collected from 20 stations
over North China. Results showed that the periods of summer rainfall in North China are not in agreement with those of
EASM, interdecadal features are obvious, the former with notable periods of 8a and18a, with an abrupt change occurred
in 1960s, the latter 18a and 28a, with abrupt change in 1970s. There is marked correlation between the summer
precipitation of North China and EASM, strong/weak summer monsoon with more/less precipitation in North
China .Weak EASM is an important factor of the rainfall decreasing, but not the only one, for general circulation
anomaly is close related to the rainfall decrease. The decline of air temperature in Tibetan tableland and North China
results in less low pressure here; lack of water vapor is another factor for the rainfall decreasing. The weakened
southwest monsoon in East Asia leads to the fact that water vapor can't arrive in the region to the north of 30°N. As
opposite to the 1950s', the EU teleconnection pattern of 1980s is of the character with Europe(+),Ural(-),and mid-Asia(+)
at 500hPa, which means the Ural ridge and Baikal trough weakening, zonal circulation is not good for exchanging cold
and warm air. As a result, the activity of cold and warm air and precipitation over North China reduced.
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