Analysis of weather data for the summer of 1979 shows that. when one or more low pressure systems are found over the western North Pacific with a wide stretch of tropical westerlies to the south of 10°N.large negative values of -(Δu/Δy) may appear in the area between 0° and 10°N. south of the low pressure belt. even though there is no cold outbreak in the Southern Hemisphere nor notable increase of easterlies along the equator. This favors the development of the equatorial buffer zone or the equatorial anticyclone. On the contrary. when the tropical and subtropical area of the Northern Hemisphere is under the domination of the high pressure belt and easterlies prevail on both sides of the equator.the value of -(Δu/Δy) would be quite small and no buffer zone or tropical anticyclone would form regardless of cold outbreaks in the Southern Hemisphere.