A SOURCE OF VARIABILITY IN DRAKE PASSAGE

The pressure records from the north side of Drake Passage between 1975 and 1980 are used with sea level data along the west coast of South America to demonstrate sea level propagation poleward from 12 to 56°S. This signal is coherent between stations above the 90% level. The phase difference between stations suggests a propagation speed of 0.8 m s-1 for the data comprised of monthly means, and a slightly slower speed of 0.6 m s-1 for the data with monthly means removed. Computations of phase speed for the first four modes using hydrographic data from Drake Passage and along the west coast of South America indicate that the poleward propagation speeds found in the data are too slow for the first mode but are comparable to the mode 3 and 4 phase speeds. The large-scale atmosphere may force the coastal motions found here, but for the semi-annual period it has been shown that such signals do not influence the sea surface slope across Drake Passage. The results presented here suggest that future monitoring of Drake Passage to estimate volume transport should take into account coastal variability induced by poleward-propagating signals. © 1990.