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几种再分析地表气压资料在中国区域的适用性评估
Applicability Evaluation of Surface Pressure for Several Reanalysis Datasets over China
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摘要: 应用台站观测资料对ERA-40, NCEP/NCAR以及NCEP/DOE再分析地表气压产品在中国不同区域、不同年代和不同季节的适用性进行了评估。分析发现, 几种再分析产品虽然能在一定程度上反映出观测资料所具有的时空分布特征, 但它们之间的差异却具有明显的区域和季节变化特征, 即冬季小而夏季大、东部地区小而西部地区大; 同时还发现ERA-40和NCEP/NCAR再分析产品在20世纪70年代以前均与观测资料有相对较大的差别, 特别是NCEP/NCAR在70年代以前的夏季气压值过于偏低, 从而夸大了很多地区的年代际变化特征。相比而言, ERA-40地表气压的长期变化趋势以及时空演变规律在中国大多数地区要优于NCEP/NCAR再分析产品, 特别是在中国西部地区。分析还表明, NCEP/DOE虽与观测资料存在一定的系统性偏差, 却与另外两种再分析产品有着较为相似的年际变化特征及趋势。Abstract: The evaluation of applicability of the reanalysis datasets is crucial to their application. The reliability of surface pressure in China obtained respectively from the reanalysis datasets is focused on, i. e. , ERA-40, NCEP/NCAR and NCEP/DOE. The analysis is carried out in different regions, different seasons and different periods with compared to the station observations over China.The results indicate that mean values of the three reanalysis products could basically display spatio-temporal consistence with observation. However, the differences found among them are more obvious in the western China than in the eastern China, and is more significant in summer than in winter. At the same time, the differences among the ERA-40, NCEP/NCAR and the observations are stronger before 1970s, and the significant systematic bias could be detected from the mean value of NCEP/DOE and the observations, but the ERA-40 is closer than the NCEP/NCAR and NCEP/DOE to the observations over most parts of China, especially in the west of China.The results also indicate that three reanalysis products all can represent the interannual variations and the linear climate trends displayed by the observations in most regions of China to a certain extent, but the discrepancies among them still has a certain regional and seasonal dependency. The most obvious differences among them can be detected in the west areas, especially the Tibet Plateau and the surrounding regions in sumer. In terms of the agreement with the observations, the ERA-40 is more consistent with observations, but the NCEP/NCAR overestimate interdecadal variations for most areas of China in summer due to the tremendously "low" value before 1970s.In conclusion, the reliability and applicability the surface pressure of ERA-40 are better than those of NCEP/NCAR and NCEP/DOE in most areas of China. The possible causes may be that more observing data, such as surface air temperature, surface pressure and so on, have been used in the ERA-40 assimilation systems, while the data used by the NCEP assimilation systems only include the observed wind field.
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Key words:
- surface pressure;
- reanalysis;
- observations;
- applicability evaluation
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图 1 台站分布与地形 (阴影区, 单位:m) 及分区
Fig. 1 The distribution of observation stations with topography (shaded areas, unit:m) and sub-regions over China
图 2 冬季和夏季再分析资料与观测地表气压偏差的空间分布 (单位:hPa)
Fig. 2 The spatial distributions of surface pressure differences (unit:hPa) between the reanalysis and the observations in the winter and summer
图 3 冬季和夏季中国9个分区1958—2001年观测及再分析 (NCEP-2, 1979—2001年) 地表气压相对于1979—2001年气候平均值的距平序列
Fig. 3 The surface pressure anomaly, relative to the 1979—2001 base period, for the reanalysis and observations across 9 regions of China in the winter and summer
图 4 夏季地表气压距平线性变化趋势的空间分布 (单位:hPa/10a)
Fig. 4 The spatial distributions of linear trends of the surface pressure anomalies (unit:hPa/10a) for reanalysis and observations
图 5 夏季地表气压距平EOF分解前两模态及其时间系数
(R1为ERA-40与观测结果PC的相关系数, R2为NCEP-1与观测结果PC的相关系数)
Fig. 5 The first leading EOF eigenvectors and associated time series of the summer surface pressure (unit:hPa) anomaly
(coefficients R1 and R2 are correlation coefficients of the PCs of ERA-40 and NCEP-1 with that of observations, respectively)
表 1 中国9个分区再分析与观测地表气压偏差 (单位:hPa)
Table 1 The differences of surface pressure between reanalysis and observations in 9 regions of China (unit:hPa)
表 2 前二主分量解释方差 (单位:%)
Table 2 The percentage variances explained by the first two leading eigenvectors (unit:%)
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