Climate Change Research Spotlight

Air-Sea Interactions Influence Major Southern Wind Belt

Ocean and atmospheric data provide evidence for how sea surface temperatures affect the Southern Annular Mode.

Source: Geophysical Research Letters

By

A wide band of westerly winds encircles Antarctica and influences Southern Hemisphere weather patterns throughout the middle and high latitudes. This belt undergoes periodic tightening, in which it shifts farther south, or expansion, when it shifts north. Such movement is known as the Southern Annular Mode (SAM), or the Antarctic Oscillation.

Previous computer modeling studies have suggested that SAM can cause anomalies in sea surface temperatures, which can, in turn, enhance SAM behavior. However, the details of this feedback are largely unknown. In a new study, Xiao et al. provide support for a mechanism by which sea temperature anomalies caused by SAM feed back to the atmosphere.

To examine interactions between the sea and atmosphere in SAM, the researchers analyzed daily weather data from the European Centre for Medium-Range Weather Forecasts, sea surface temperature data from the National Oceanic and Atmospheric Administration, and ocean current data from the Global Ocean Data Assimilation System.

The data support the findings of previous modeling studies that suggested air-sea interactions enhance the persistence of SAM behavior. The results also support a previously proposed mechanism for this positive feedback effect: Sea surface temperature anomalies caused by SAM help maintain temperature anomalies in the lower atmosphere, which cause air eddy behavior that enhances the persistence of SAM movements.

Further analysis also found that this eddy feedback operates by a barotropic mechanism (involving propagation and deformation of air eddy) at midlatitudes and a baroclinic mechanism (involving generation of air eddy) at high latitudes.

On the basis of their results, the authors suggest that air-sea interactions may significantly affect SAM variability at timescales of 70 to 80 days or longer. The findings could help improve predictions of SAM behavior between seasons or within a single season. (Geophysical Research Letters, doi:10.1002/2016GL070255, 2016)

—Sarah Stanley, Freelance Writer

Citation: Stanley, S. (2016), Air-sea interactions Influence major southern wind belt, Eos, 97, doi:10.1029/2016EO059181. Published on 13 September 2016.
© 2016. The authors. CC BY-NC-ND 3.0
  • davidlaing

    As with all modeling studies, this one should be backed up with actual, on-the-water and in-the-air observations, i.e., hard data, before it is taken as a representation of actual truth. This critical step is all to often discounted in modern, model-happy science.

    • Bill Carson

      As far as I know, at least the ocean data used here ARE actual “on-the-water” data, i.e. retrieved from ARGO observations. Atmospheric datasets are reanalysis data but the variables concerned are generally considered of having descent quality, e.g. wind, pressure. It is “physics” data, e.g. precipitation, sensible heat flux, or cloud covering, that are not accurate and relying much on assimilation model details.

      • davidlaing

        Good.