Abstract:
Using the blocking high objective identification method, the identification results based on daily reanalysis data of the NCEP/NCAR-Ⅰ, NCEP-Ⅱ and ERA-interim at 6 h intervals in the summer (June to August) for the period 1979-2016 are compared. Taking the type D blocking high as an example, we discuss its possible impacts on the climate in Northeast China during June. Results suggest that the reanalysis data of NCEP-Ⅰ and NCEP-Ⅱ show little difference in the identified number of days, frequency of occurrence and interdecadal variation of blocking high, while results from the ERA-interim reanalysis data are greatly different with results from the former two datasets. The three reanalysis datasets all indicate that there are areas where the number of various types of blocking high activity days is highly correlated with the height field of 500 hPa in the summer, and the patterns are similar between the three datasets. However, the characteristics of the results from the first two datasets for various types of blocking high are relatively consistent, while the characteristic area and range of blocking high from the ERA-interim reanalysis dataset is relatively small. The cumulative days of type D blocking high in June are closely related to temperature and precipitation in Northeast China. In the active years of type D blocking high, the atmospheric circulation is dominated by a meridional type. Low temperature and warm advection in the lower troposphere as well as high temperature and cold advection in the upper troposphere indicate an unstable atmospheric stratification. At the same time, abnormal low pressure circulation prevails over Northeast China, and the strong updraft is favorable for the formation of low temperature and rainy weather in Northeast China during June. The Okhotsk Sea area is an important source of Rossby wave in June, and the formation of type D blocking high in June may be related to the temperature difference between the sea and the land.