The 30-70 day oscillations in the tropical Atlantic

Abstract

Evidence is presented for intraseasonal oscillations in the trade winds of the northern and southern tropical Atlantic. The pattern of intraseasonal oscillations in surface pressure and wind speed in the Northern Hemisphere resembles that of the North Atlantic Oscillation (NAO). Like the NAO, these oscillations have a strong seasonal cycle, with a maximum amplitude in boreal winter/spring. Winds in the southern tropical Atlantic are related to the Southern Hemisphere equivalent of the NAO, exhibiting a weaker seasonality with peak amplitudes in austral winter. The Madden-Julian Oscillation (MJO), which originates over the Indian Ocean, also exerts an influence on tropical Atlantic surface winds, particularly between about 10°N and 10°S. Where intraseasonal wind speed oscillations in the Atlantic are strong, they force changes in sea surface temperature (SST) through latent heat loss from the ocean, potentially affecting lower frequency climate variations. Copyright 2004 by the American Geophysical Union.