Evaluation of the Antarctic Circumpolar Wave Simulated by CMIP5 and CMIP6 Models

As a coupled large-scale oceanic and atmospheric pattern in the Southern Ocean, the Antarctic circumpolar wave (ACW) has substantial impacts on the global climate. In this study, using the European Centre for Medium-Range Weather Forecasts ERA5 dataset and historical experiment outputs from 24 models of the Coupled Model Intercomparison Project Phase 5 and Phase 6 (CMIP5/CMIP6) spanning the 1980s and 1990s, the simulation capability of models for sea-level pressure (SLP) and sea surface temperature (SST) variability of the ACW is evaluated. It is shown that most models can capture well the 50-month period of the ACW. However, many simulations show a weak amplitude, but with various phase differences. Selected models can simulate SLP better than SST, and CMIP6 models generally perform better than the CMIP5 models. The best model for SLP simulation is the CanESM5 model from CMIP6, whereas the best model for SST simulation is the ACCESS1.3 model from CMIP5. It seems that the SST simulation benefits from the inclusion of both a carbon cycle process and a chemistry module, while the SLP simulation benefits from only the chemistry module. When both SLP and SST are taken into consideration, the CanESM5 model performs the best among all the selected models.

The Antarctic Circumpolar Wave: Its Presence and Interdecadal Changes during the Last 142 Years

The Southern Ocean (SO) is the region of the World Ocean bordering on Antarctica over which significant exchanges between the atmosphere, the ocean, and the sea ice take place. Here, the strong and nearly unhindered eastward flow of the Antarctic Circumpolar Current plays an important role in mean global climate as it transmits climate anomalies around the hemisphere. Features of interannual variability have been observed to propagate eastward around the SO with the circumpolar flow in the form of a system of coupled anomalies, known as the Antarctic circumpolar wave (ACW). In the present study, the 142-yr series of the Twentieth Century Reanalysis, version 2, dataset (850-hPa geopotential height, sea level pressure, sea surface temperature, surface meridional wind, and surface air temperature) spanning from 1871 to 2012 is used to investigate the presence and variability of ACWs. This examination shows, for the first time, the presence of the ACW before the mid-1950s and interdecadal changes in its characteristics. Modifications in the strength and speed of the circumpolar wave are shown to be linked with large-scale climate changes. Complex empirical orthogonal function analyses confirm that the ACW becomes apparent when the tropical El Niño–Southern Oscillation (ENSO) signal gives rise to the Pacific–South American (PSA) pattern and is a consequence of the constructive combination of the PSA and the subantarctic zonal wavenumber 3. Correlation analyses are also performed to quantify the role played by ENSO teleconnections for the appearance of the ACW, and the impact on the presence of ACWs of three super–El Niño events is investigated.

Multiscale Analysis of Antarctic Surface Temperature Series by Empirical Mode Decomposition

This article illustrates the multiscale nature of the Antarctica climatology. Its variability is analyzed from coastal weather stations climate recordings of the continent, supplying temperature data since 1955. Using empirical mode decomposition, coupled to wavelet analysis, climatological signals are detected of a weak near-8-yr rotating wave that could be the so-called Antarctic Circumpolar Wave.