In this study, climatological characteristics and trends of East Asian upper jet (EAUJ) streams were analyzed based on the three definition methods(Isobaric surface method, Mass weighted method, Vertical section method) for the selected common conditions (data sets, resolution, analysis region and period) using the recent four reanalyses data sets(CFSR, ERA-Int., JRA-55, MERRA). And evaluation on the simulation skills of the selected 10 CMIP5 models for the characteristics of EAUJ was carried out. The EAUJ streams shows a very strong seasonal variations in terms of intensity, three dimensional location of Jet core regardless of the analysis methods and data sets. The 30-year average of wind speed at jet core is the lowest (～30ms-1) and highest (～75ms-1) in summer and winter, respectively. And the core locations of EAUJ for summer and winter are around 40°N, 90°E and around 30°N, 140°E. Also the average altitude of jet core shows a strong seasonal variation with the maximum in summer and minimum in winter. In general, the differences on the properties of EAUJ streams among the reanalyses data sets are relatively small irrespective of the season. However, there are substantial differences in the properties of EAUJ among the three definition methods, in particular, the intensity and height of EAUJ, minimum intensity (less than 10ms-1) and lowest altitude (less than 50 hPa other methods) in MWM. The reason for the large differences is that the properties of EAUJ are normalized using the mass weighted process for the layer of 400 and 100 hPa.
The intensity of EAUJ for the 30 years(1979-2008) shows a contrasting trend, an increasing trend in the southern area including the jet core but a decreasing trend in the northern area of Jet core during spring.
It indicates that the core of EAUJ is slightly shifted to the south during spring. However, the wind speed shows a decreasing trend in most of the analysis area in summer. And it shows a contrasting trend, strong decreasing trend in the southern area including the jet core and an increasing trend in the northern area both in autumn and winter. In general, the altitude of jet core shows a increasing trend irrespective of the season, analysis methods and data sets. Although it depends on the data sets and analysis methods, the location of EAUJ is significantly shifted to southward in spring but slightly shifted to northward in summer. However, there is no significant trend in autumn and winter. This results are not consistent with the results of previous studies, consistent northward trend due to the expansion of Hadley cell. Also, the EAUJ is shifted to westward irrespective of data sets and analysis methods except autumn.
Compared to the ensemble of four reanalysis data sets, the 10 CMIP5 models relatively well simulate the seasonal average intensity and the location of the EAUJ including seasonal variations but simulate the interannual variation of EAUJ too weakly. Also the simulation skills of 10 CMIP5 models for the properties of EAUJ are significantly different among models irrespective of season, intensity and three dimensional location. In general, the simulated latitude of jet core is shifted to the southward compared to that of the reanalysis data except the winter. Also the simulations skills for the longitude of EAUJ depend on the season with a large difference of about 40° among models in summer.
The CMIP5 models show an increasing and decreasing trend of mean wind speed in spring and summer, respectively, as shown in the four reanalysis data sets. However, they show an increasing trend in the wind speed contrary to that of reanalysis data during autumn and winter. And the CMIP5 models show a consistent increasing trend of the mean altitude of EAUJ as shown in the reanalyses data sets in all seasons.
The results show that the characteristics of EAUJ are strongly affected by the complex combination of the global scale environments and regional environments. So, more works are needed to identify the main reasons for the different changing patterns of EAUJ compared to that of other regions.