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Amundsen-Bellingshausen Seas Low (ABSL) Index

The Amundsen-Bellingshausen Seas Low (ABSL) is a non-stationary climatological low pressure system situtated within the Pacific Sector of the Southern Ocean. The ABSL is an important feature of regional atmospheric circulation and winds and thus a key driver of the climate of West Antarctica, the Antarctica Peninsula and the Southern Ocean Pacific sector.

The data for indices which characterise the location and strength of the ABSL are made available below.

Methodology

The ABSL Relative Central Pressure Index is calculated as follows: [1] the representative background pressure is calculated by area-averaging the mean sea level pressure (MSLP) field over the ABSL sector†; [2] This value is then subtracted from the actual MSLP field to give the regional pressure anomaly; [3] the relative central pressure is then taken as the minimum value within this regional pressure anomaly field. By calculating the depth of the ABSL relative to the background pressure field we remove much of the large-scale variability which strongly modulates the ABSL Actual Central Pressure Index (see below). Indicies which describe the monthly and seasonal variability of the ABSL relative central pressure, and its location are constructed from ERA-Interim Reanalyses (between January 1979 — December 2012 inclusive) and can be found within the ascii files within the secton below.

The ABSL Actual Central Pressure Index is taken as the minimum value within the MSLP field within the ABSL sector†. This index is also provided within the ascii files below. Note that this index is strongly modulated by the Southern-Hemisphere Annual Mode across all seasons, with time series correlations significant at p < 0.01.

The ABSL latitude and longitude is taken as the geographical location of the minimum MSLP in the ABSL sector†. The longitudinal location has been shown to be the primary driver of climate variability over West Antarctica (Hosking et al., 2013) (see time series plot).

  † The ABSL sector is defined as 170°—290° E and 60°—75° S (indicated by the boxes in Fig. 2e-h in Hosking et al. (2013))

Also known as: Amundsen Sea Low (ASL)

For more information please contact: Dr Scott Hosking

Download Data

  • The monthly ABSL index calculated from ERA-Interim Reanalysis can be found here
  • The seasonal ABSL index calculated from ERA-Interim Reanalysis can be found here
  • The monthly ABSL index calculated from seventeen CMIP5 coupled-climate models run as part of the Historical experiment (1979-2005) can be found here
  • Python script to plot monthly relative central pressure timeseries can be obtained from here

References

When using the data set in a paper, the following is the correct citation to use:

J. S. Hosking, A. Orr, G. J. Marshall, J. Turner, and T. Phillips: The influence of the Amundsen-Bellingshausen Seas Low on the climate of West Antarctica and its representation in coupled climate model simulations, Journal of Climate, 2013. [ http ]