Journal Article

Role of Tropical SST Variability on the Formation of Subtropical Dipoles

Masumoto, Yukio, Masson, Sébastien, Prodhomme, Chloé, Terray, Pascal, Morioka, Yushi, Behera, Swadhin K.

2014

Overview

Interannual variations of sea surface temperature (SST) in the midlatitudes of the Southern Hemisphere play an important role in the rainfall variability over the surrounding countries by modulating synoptic-scale atmospheric disturbances. These are frequently associated with a northeast–southwest-oriented dipole of positive and negative SST anomalies in each oceanic basin, referred to as a subtropical dipole. This study investigates the role of tropical SST variability on the generation of subtropical dipoles by conducting SST-nudging experiments using a coupled general circulation model. In the experiments where the simulated SST in each tropical basin is nudged to the climatology of the observed SST, the subtropical dipoles tend to occur as frequently as the case in which the simulated SST is allowed to freely interact with the atmosphere. It is found that without the tropical SST variability, the zonally elongated atmospheric mode in the mid- to high latitudes, called the Antarctic Oscillation (AAO), becomes dominant and the stationary Rossby waves related to the AAO induce the sea level pressure (SLP) anomalies in the midlatitudes, which, in turn, generate the subtropical dipoles. These results suggest that the tropical SST variability may not be necessary for generating the subtropical dipoles, and hence provide a useful insight into the important role of the AAO in the midlatitude climate variability.

• Publisher: American Meteorological Society
• Subject: Annual variations / Anomalies / Antarctic Oscillation / Atmosphere / Atmospheric disturbances / Atmospherics / Climate / Climate models / Climate variability / Climatology / Climatology. Bioclimatology. Climate change / Dipoles / Earth, ocean, space / El Nino / Exact sciences and technology / Experiments / External geophysics / Feedback / FTP / General circulation models / Geophysics / Heat / Interannual variations / Latitude / Marine / Meteorology / Ocean basins / Ocean, Atmosphere / Oceanic climates / Oceans / Physics / Physics of the oceans / Planetary waves / Radiation / Rain / Rainfall / Rainfall variability / Rossby waves / Sciences of the Universe / Sea level / Sea level anomalies / Sea level pressure / Sea surface / Sea surface temperature / Sea surface temperature anomalies / Sea-air exchange processes / Southern Hemisphere / Studies / Surface temperature / Temperate regions / Tropical climates / Variability