The southern westerlies: A preliminary survey; main characteristics and apparent associations

• Published in: Quarterly Journal of the Royal Meteorological Society
• Main Author: Lamb, H. H.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1959
• Subjects: Antarc*; Antarctic; Ross Sea; Southern Ocean
• Online Access: http://dx.doi.org/10.1002/qj.49708536302; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Fqj.49708536302; https://rmets.onlinelibrary.wiley.com/doi/pdf/10.1002/qj.49708536302

Abstract Provisional figures can now be given for the ratio of momentum in the southern circumpolar westerlies to the momentum of the better known northern system. This ratio appears to be 1·5, or rather more, over the year as a whole and rises to over 4 in the northern summer‐southern winter. The preponderance of the southern system is such that it may be regarded as the ‘flywheel’ of the general atmospheric circulation and there are indications that changes in the southern westerlies entail world‐wide adjustments. Preliminary survey at the 500 mb level shows the main trough south of 40°S centred about 100°–110°E at most seasons of the year and the principal ridge in the neighbourhood of the outer reaches of the Ross Sea. The mean troughs and ridges have notably smaller amplitude than in the northern hemisphere. Control of trough and ridge positions appears to be thermal rather than orographic, associated with the position of the broadest part of the Antarctic cooling surface. Little seasonal movement of the troughs and ridges in longitude is discerned and no very great change of circulation intensity, but there is an intensification of flow and increase of amplitude in the Indian Ocean trough from summer to late winter. The pattern of glaciation, as well as available data on depression tracks and anticyclone distribution over the Southern Ocean, support the pattern of ridges and troughs at 500 mb here described and throw light upon the occurrence of blocking in various sectors of the southern hemisphere. This study suggests that it may be the momentum and energy of the southern westerlies which are ultimately responsible for maintaining the meteorological equator on average north of the geographical equator, at least over the oceans. In any climatic epoch when the southern westerlies were (i) farther south than now, and/or (ii) weaker than now, the meteorological equator should under this proposition have been nearer the true equator than is now the case. The work of other investigators has suggested that the ...