The semiannual oscillation and Antarctic climate, part 5: impact on the annual temperature cycle as derived from NCEP/NCAR re-analysis |
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| Authors: | M R Van den Broeke |
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| Institution: | (1) Institute for Marine and Atmospheric Research Utrecht (IMAU) Utrecht University, PO Box 8005, 3508 TA Utrecht, The Netherlands E-mail: broeke@phys.uu.nl, NL |
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| Abstract: | We use NCEP/NCAR reanalysis data to study the impact of the semiannual oscillation (SAO) on the annual cycle of Antarctic
near-surface temperature. When the SAO is weak, the contracted phases (March/April and September/October) are warm and the
expanded phases (December/January and June/July) cold. This pattern is explained in terms of the changing meridional fetch
of the circumpolar pressure trough. Because of the wave number three character of the SAO, large regional deviations are found.
For instance, enhanced north-westerly flow in the second expansion phase (June/July) of weak SAO years limits the growth of
the sea ice in the Amundsen and Bellingshausen seas, leading to anomalously high temperatures in the Antarctic Peninsula region.
The short (<50 year) temperature records at Antarctic stations still carry the fingerprint of decadal SAO variability. By
matching the observed monthly temperature trends to the patterns derived from the gridded re-analysis, we propose a background
Antarctic warming trend for the second expansion phase (June/July) of 4.62 ± 1.02 °C per century, four times the annual value.
Received: 23 August 1999 / Accepted: 28 October 1999 |
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