Zonal movement of the Mascarene High in austral summer

Abstract

Temporal variations in the Mascarene High (MH), defined by the sea level pressure (SLP) maximum within the region of [40°–120°E, 50°–10°S] in austral summer (November–January), were investigated using atmospheric reanalysis datasets. The MH longitudinal position has a dominant timescale at about 6 years, which appears to be independent of the MH intensity variation. The MH longitudinal movement is caused by a combination of SLP variations in the eastern South Indian Ocean (ESIO) and in the western South Indian Ocean (WSIO), as follows. (1) Pressure variations in the ESIO region are confined to the lower atmosphere up to the mid-troposphere, and are associated with the El Niño-Southern Oscillation events. (2) Pressure variations in the WSIO region, characterized by a quasi-barotropic structure throughout the troposphere, are related to the meridional movement of storm track. Sea surface temperature anomalies associated with the longitudinal movement of the MH show a southwest–northeast dipole structure, but this is shifted 10° westward in longitude compared with that associated with the MH intensity.