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The Amundsen-Bellingshausen Seas Low in CMIP5 Climate Models
Hosking, J.S., Orr, A., Marshall, G.J., Turner, J. and Phillips, T. 2013. The influence of the Amundsen-Bellingshausen Seas Low on the Climate of West Antarctica and it representation in coupled climate model simulations. Journal of Climate 26: 6633-6648.

The authors write that "the Amundsen-Bellingshausen Seas low (ABSL) is a quasi-stationary area of climatological low pressure that exists over the South Pacific sector of the Southern Ocean between the Antarctic Peninsula and the Ross Sea," and they note that "the minimum mean sea level pressure (MSLP) associated with the ABSL is characterized by large seasonal variability in both location and central pressure," which variability, in their words, "strongly influences the climate of West Antarctica by controlling the meridional component of the large-scale atmospheric circulation, with consequences for 10-m meridional wind velocity, near-surface (2-m) air temperature, precipitation, and sea ice concentration," citing Turner et al. (2009) and Kuttel et al. (2012).

What was done
Hosking et al. investigated "the representation of ABSL variability (as well as the associated representation of West Antarctic climate) in the set of climate models participating in phase 5 of the Coupled Model Intercomparison Project (CMIP5; Taylor et al. 2012), as used in the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5)."

What was learned
The five UK researchers with the British Antarctic Survey report that (1) "investigation of 17 CMIP5 climate models run with historical forcing showed that the majority of the models have statistically significant and systematic biases," that (2) "a few of the models even simulate an ABSL longitudinal migration that is the reverse of reality," and that (3) "the majority of them show a significant bias in at least one winter month" that "is more or less evenly split in terms of negative and positive biases."

What it means
"The implications of this," in the words of Hosking et al., are that "the majority of CMIP5 models will have a correspondingly poor representation of West Antarctic climate due to difficulties in representing the ABSL annual cycle, particularly its longitudinal position." In addition, they note that "Turner et al. (2013) showed that the majority of the CMIP5 models have a seasonal cycle of sea ice extent that differs markedly from the observations," and that Zunz et al. (2012) showed that the CMIP5 multi-model mean underestimates (overestimates) the sea ice extent in the ABS and Ross Sea sectors over the period from 1979 to 2005 in February (September), which are the months where the sea ice cover reaches its minimum (maximum)."

Kuttel, M., Steig, E.J., Din, Q., Monaghan, A.J. and Battisti, D.S. 2012. Seasonal climate information preserved in West Antarctic ice core water isotopes: Relationships to temperature, large-scale circulation, and sea ice. Climate Dynamics 39: 1841-1857.

Taylor, K.E., Stouffer, R.J. and Meehl, G.A. 2012. An overview of CMIP5 and the experiment design. Bulletin of the American Meteorological Society 93: 485-498.

Turner, J., Bracegirdle, T.J., Phillips, T., Marshall, G.J. and Hosking, J.S. 2013. An initial assessment of Antarctic sea ice extent in the CMIP5 models. Journal of Climate 26: 1473-1484.

Turner, J., Comiso, J.C., Marshall, G.J., Lachlan-Cope, T.A., Bracegirdle, T., Maksym, T., Meredith, M.P., Wang, Z. and Orr, A. 2009. Non-annular atmospheric circulation change induced by stratospheric ozone depletion and its role in the recent increase of Antarctic sea ice extent. Geophysical Research Letters 36: 10.1029/2009GL037524.

Zunz, V., Goosse, H. and Massonnet, F. 2012. How does internal variability influence the ability of CMIP5 models to reproduce the recent trend in Southern Ocean sea ice extent? Cryosphere Discussions 6: 3539-3573.

Reviewed 20 November 2013