Comparative Analysis Of Impact Factors Of The Mascarene High Interannual Varibility Under Different Interdecadal Background

Based on the NCEP/NCAR and ERA-40 reanalysis dataset, interannual and interdecadal variations of the Mascarene High in four seasns are analyzed, specific attention is focused on changes in the factors affecting the interannual variability of the Mascarene High under different interdecadal background. Finally, changes in the factors affecting the interannual variability of the Mascarene High from June to August are further discussed under different interdecadal backgroung. Results show as follows:(1) Significantly changes of the Mascarene High are shown in different time scales. In the seasonal timescale, the intensity of the Mascarene High is biggest in summer, with its position in west, while the intensity is weakest in winter, with its position in east. In the long-term trend, the intensity of the Mascarene High in four seasons present a significant linear increase trend, with its trend strongest in spring, weakest in winter. In the interdecadal timescale, the intensity of the Mascarene High during four seasons experienced a marked interdecadal shift around 1976, characterized by a weaker Mascarene High before 1976 while a significantly strengthened one after 1976.(2) Further analysis shows that the factors affecting the interannual variability of the Mascarene High are different during these two periods. Prior to the year of 1976, El Nino/Southern Oscillation (ENSO) is closely related to the Mascarene High only in autumn, while in the other three seasons, there is no significant relationship; Antarctic Oscillation (AAO) is closely related to the Mascarene High only in summer, while in the other three seasons, there was no significant relationship; The relationship between the interannual variability of the Mascarene High and local sea surface temperature (SST) over the southern Indian Ocean is gradually increased from spring to summer, with its strongest relationship in summer. In the autumn, the relationship is weakened rapidly, and in winter there is no relationship between the Mascarene High and local SST over the middle latitude Indian Ocean. After 1976, the relationship between ENSO and the Mascarene High is increased from summer to autumn, and it is strongest in autumn. AAO is closely related to the Mascarene High in the four seasons, with its strongest in summer. Besides, compared with the relationship before 1976, it is significantly strengthened after 1976. The relationship between local SST over low latitude Indian Ocean and the Mascarene High is significantly weakened, while the thermal force of SST over middle latitude Indian Ocean on the Mascarene High is significantly strengthened, with its strongest force in summer.(3) In the every month of summer before 1976, local SST over middle and low latitude Indian Ocean is closely related with the Mascarene High from June to August, with the strongest forcing in July. There is no significant relationship between ENSO and the Mascarene High from June to August. After 1976, local SST over low latitude Indian Ocean shows no closely relationship with the Mascarene High from June to August, while the relationship between ENSO and the Mascarene High is gradually strengthened from June to August. The relationship between AAO and the Mascarene High is strongest in June and weakest in July both before and after 1976. Besides, compared with that before 1976, the relationship between AAO and the Mascarene High is significantly strengthened in every month in summer.