Year-to-year Variations of Rainfall over the India-Equatorial Pacific Region and of Low and Middle Latitude Circulations in the Southern Hemisphere

Abstract

It is well known that year-to-year variations of rainfall are very peculiar over the so called equatorial Pacific dry zone which extends from the Peru coast to 180° or further west along the equator. As a result of investigating the world precipitation and precipitation anomaly distribution maps which are included in "Die Witterung in Ubersee (1953— )" by Hamburg Seewetteramt, the author recognized that there are very scanty rainfalls in the India—Indonesia region when there are anomalous plentiful rainfalls in the dry zone islands. These events occurred in 1957, 1958, 1965 and 1966. And in 1955, 1956 and 1962, reverse types are recognizable. Further investigations of the long-period Indian flood and drought data and the rainfall data of Ocean Island and Fanning Island in the dry zone have shown that the above mentioned reverse phase rainfall variations between India and the equatorial Pacific had occurred in earlier years. In addition to the relationships between these peculiar rainfall fluctuations and the influences of the southeast trades, we should. recognize the effect of mid-latitude westerlies in the Southern Hemisphere because anomalous rainfall distributions that occurred in 1957-58 and 1965-66, when the southern westerlies were very weak, especially in a winter month (July). Recently Walker's southern oscillation advanced to the new zonal and tropospheric circulation model in tropical and sub-tropical latitudes, which is named the Walker circulation by BJERKNES (1969). It * This work was performed as part of the group studies on "Water Balance of Monsoon Asia" with the support of the Department of Education in Japan (Hydrology 1969—No. 91012). is possible to say that the variations of southern westerlies play an important role in the weakening or strengthening of the Walker circulation through the variations of sea-surface temperature under the southeast trades.