A new global coupled atmosphere-ocean wavenumber-4 pattern in Southern mid–latitudes during austral summer and its climate linkage

Abstract

A new pattern referred to as the coupled ocean-atmosphere wavenumber-4 (COAW4) pattern has been identified in the Southern mid-latitudes during austral summer. This pattern consists of a wavenumber-4 pattern in the anomalous 200-hPa meridional wind and a wavenumber-4 pattern of the anomalous sea surface temperature (SST). The SST component of the COAW4 pattern, which includes the Indian Ocean Subtropical Dipole (IOSD), the South Atlantic Subtropical Dipole (SASD) and the South Pacific Subtropical Dipole (SPSD), develops through air-sea interactions involving surface turbulent heat flux, surface wind, and ocean mixed-layer depth. The atmospheric component displays a barotropic structure. The sources for COAW4 pattern include not only the wavenumber-4 pattern of the anomalous SST over Southern oceans, but also the anomalous convective activities over Southern land areas. The COAW4 pattern is associated with increased precipitation over land in southern mid-latitudes, particularly in central Australia. Furthermore, the COAW4 pattern is linked to Antarctic sea ice cover in the Weddell, Amundsen, and northern Ross Seas. Plain language summary In the southern mid-latitudes, there exists a wavenumber 4 pattern in the anomalous 200-hPa meridional wind and a wavenumber-4 pattern of the anomalous sea surface temperature (SST). Previous studies have examined the two wavenumber-4 patterns separately, but their potential linkage remains largely unknown. Through statistical analyses of SST and atmospheric global data, we demonstrated that the two wavenumber 4 patterns could be integrated into a coupled ocean-atmosphere wavenumber-4 (COAW4) pattern in Southern mid-latitudes in austral summer. Additionally, we have investigated the sources of this pattern as well as its effect on precipitation over southern lands and on Antarctic sea ice.

Keywords

• global atmosphere-ocean wavenumber-4
• the Indian Ocean subtropical dipole (IOSD)
• the South Atlantic subtropical dipole (SASD)
• the South Pacific subtropical dipole (SPSD)