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University of Mie (2008)

The recent increasing trend of the precipitation in Sahel and its associated interhemispheric dipole of the global SST

宗本 政紀

Titre : The recent increasing trend of the precipitation in Sahel and its associated interhemispheric dipole of the global SST

Auteur : 宗本 政紀

Université de soutenance : University of Mie

Grade : Master 2008

Résumé
The Sahel region, located in the southem of the Sahara desert underwent an unprecedented severe drought involved with the decrease of the precipitation in 1970sand 1980s. However, since the middle of 1980s the annual mean precipitation in Sahel has gradually increased. This trend shift slgnifies the occurrence of a global climate shift. This study diagnoses the relation of the trend shift in Sahel with global atmospheric flelds and Sea Surface Temperature (SST). The present study clarifleS that the shift of the precipitation trend occurred not only within Sahel but also all over the world. SigniflCant Precipitation-shifted areas are in South America, northem Eurasia and Australia. The precipitation variability in Sahel is remarkably similar to the north-south SST polarity that is 也e SST contrast between the area-averaged SST in the Soutbem Hemisphere and in也e Northem Hemisphere. When the SST in the Sou血em Hemisphere was colder than that of the Nor血em Hemisphere, the precipitation in Sahel was larger than normal. In addition, this north-south interhemispheric contrast of the global SST has remarkably similar trend to that of Sahel precipitation. The trend of the SST contrast is also in association with the trends of globaトscale meridional and zonal atmospheric circulations. In years of the increaslng trend of the Sahel precipitation, an up draft strengthened over North A丘ica along with the increase of the specific humidity These results suggest that the SST contrast detemined the precipitation trends on the earth through the change of the global atmospheric circulations.

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