CLIMATE OF THE WEST COAST OF SOUTH AMERICA AND ITS CHANGE
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概要
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From July 1971 to November 1971 I made a field survey along the west coast of South America as a member of the Scientific Expedition to South America, University of Tokyo. The main theme of my research was to find field evidences of the northward displace-ment of the ITC and the Polar front of the Southern Hemisphere during the Warm Glacial Age, which I had previously inferred from literatures (See footnote 4). If the displacement was real, traces of dry climate must be found out in Ecuador, and those of humid climate in the Atacama desert. In the present survey the former was identified by the landform due to sheetflood, which is something between alluvial cone and sedimentary pediment and, therefore, might be called peripediment. This landform exists in the Peruvian coastal desert and extends continuously southward to just short of Chala, Peru. This distribution is just the same with distribution of the past heavy rains still remembered by fishermen along the coast. For this reason and from other field observations, I believe that this landform is not fossil, but . is now being formed. The same type of landform is traced further northward and found out as fossil in the Ecuadorian savanna and forest. Thus, the ITC is believed to have been displaced northward one geomorphological period previously. This conclusion is against some other studies which maintain that the ITC was displaced southward and El Niño was more frequent in the Worm Glacial Age. I have made a review of the concept of El Niño in literature and in the practice among the fishermen and defined it tentatively as the anomalous rain on the west coast of northern Peru caused by the unusual displacement of the ITC on the westside of the Andes, and therefore accompanied by W-N winds. According to this definition, there is a group of anomalous rainfalls on the west coast of Peru which does not belong to El Nifo rains. The latest example is the rain of Jan. 15, 1970. I made a detailed analysis of this rain and concluded that it was caused by a cold front which had come down from the North American Continent. The ITC was displaced southward during this rain, but only on the east side of the Andes. The ITC, with its taxes structure, is traced to move regularly to the latitude of about 20°S, which is against many recent analysis. As for the humid imprints in the Atacama Desert I found the northernmost relic of them at latitude 21°45'S. This latitude being equivalent to 30°S of today, there was a northward displacement of the middle-latitude Westerlies by 8° in latitude in the last Glacial Age. An extremely high precipitation peak with more than 1, 000 mm monthly amount is found around 40°S today. A displacement of 8° of this peak satisfactorily explains the sudden appearance of a wide fossil river terrace at Rio Huasco and the 2-cyclic landf orms near Santiago which indicate the recent desiccation. A full translation of this paper is soon to appear in the Bulletin of the Department of Geography, University of Tokyo.
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The Association of Japanese Geographers | 論文
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