Comparision between NCEP and NASA Reanalysis Data in Activities of South Asia High

Through the bilinear interpolation, correlation analysis and Morlet wavelet analysis methods, surrounding on the usability of new high resolution seismic reanalysis data MERRA, we compare system characteristics (particularly in South Asia High) between MERRA and NCEP- 2 reanalysis data. The main results are as follows: At 100hPa, value of South Asia High (SAH) characteristic line in MERRA is smaller than value in NCEP-2 and its value is 1676 dgpm, but the scope of SAH in MERRA data is significantly bigger than the scope in NCEP- 2 data. In addition to SAH eastward index, their interannual variability trends of the same SAH characteristic index are also similar, especially in two data, interannual variabilities of the SAH ridge line index curve coincide. Prior to the early 1990s, SAH eastward index, area index and intensity index in NCEP- 2 data show positive anomalies; the same indices in MERRA data show negative anomalies; corresponding to the indices in NCEP- 2 data, the index value in MERRA data is smaller; after the early 1990s, and vice versa. There is no significant difference between means of SAH eastward and ridge line index in two data. Only variances of SAH intensity index between NCEP- 2 and MERRA data have significant differences, and NCEP- 2 greater than MERRA. The wavelet variance verification indicates that the same SAH characteristic index of NCEP- 2 and MERRA data during 1979 and 2009 in summer are in good agreement: both have the same significant oscillation periods, and their phases are also consistent, but there are some differences between their predominant period: in MERRA data SAH area and intensity index performance quasi- 4 years oscillation as the predominant period; in NCEP- 2 data SAH area and intensity index performance quasi- 4 years and 8 to 9 years oscillation at the same time.