Southern Hemisphere westerly wind changes during the Last Glacial Maximum: model-data comparison
The Southern Hemisphere (SH) westerly winds are thought to be critical to global ocean circulation, productivity, and carbon storage. For example, an equatorward shift in the winds, though its affect on the Southern Ocean circulation, has been suggested as the leading cause for the reduction in atmospheric CO2 during the Last Glacial period. Despite the importance of the winds, it is currently not clear, from observations or model results, how they behave during the Last Glacial. Here, an atmospheric modelling study is performed to help determine likely changes in the SH westerly winds during the Last Glacial Maximum (LGM). Using LGM boundary conditions, the maximum in SH westerlies is strengthened by ∼+1 m s−1 and moved southward by ∼2° at the 850 hPa pressure level. Boundary layer stabilisation effects over equatorward extended LGM sea-ice can lead to a small apparent equatorward shift in the wind band at the surface. Further sensitivity analysis with individual boundary condition changes indicate that changes in sea surface temperatures are the strongest factor behind the wind change. The HadAM3 atmospheric simulations, along with published PMIP2 coupled climate model simulations, are then assessed against the newly synthesised database of moisture observations for the LGM. Although the moisture data is the most commonly cited evidence in support of a large equatorward shift in the SH winds during the LGM, none of the models that produce realistic LGM precipitation changes show such a large equatorward shift. In fact, the model which best simulates the moisture proxy data is the HadAM3 LGM simulation which shows a small poleward wind shift. While we cannot prove here that a large equatorward shift would not be able to reproduce the moisture data as well, we show that the moisture proxies do not provide an observational evidence base for it.
Details
Publication status:
Published
Author(s):
Authors: Sime, Louise C. ORCID record for Louise C. Sime, Kohfeld, Karen E., Le Quere, Corinne, Wolff, Eric, de Boer, Agatha M., Graham, Robert M., Bopp, Laurent
This website uses cookies to improve your experience. We'll assume you're okay with this, but you can opt-out if you wish.AcceptRead more
Privacy & Cookies Policy
Privacy Overview
This website uses cookies to improve your experience while you navigate through the website. Out of these, the cookies that are categorized as necessary are stored on your browser as they are essential for the working of basic functionalities of the website. We also use third-party cookies that help us analyze and understand how you use this website. These cookies will be stored in your browser only with your consent. You also have the option to opt-out of these cookies. But opting out of some of these cookies may affect your browsing experience.
Necessary cookies are absolutely essential for the website to function properly. This category only includes cookies that ensures basic functionalities and security features of the website. These cookies do not store any personal information.
Any cookies that may not be particularly necessary for the website to function and is used specifically to collect user personal data via analytics, ads, other embedded contents are termed as non-necessary cookies. It is mandatory to procure user consent prior to running these cookies on your website.