Respective influences of IOD and ENSO on the Tibetan snow cover in early winter
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Using reanalysis data and snow cover data derived from satellite observations, respective influences of Indian Ocean Dipole (IOD) and El Niño/Southern Oscillation (ENSO) on the Tibetan snow cover in early winter are investigated. It is found that the snow cover shows a significant positive partial correlation with IOD. In the pure positive IOD years with no co-occurrences of El Niño, negative geopotential height anomalies north of India are associated with warm and humid southwesterlies to enter the plateau from the Bay of Bengal after rounding cyclonically and supply more moisture. This leads to more precipitation, more snow cover, and resultant lower surface temperature over the plateau. These negative geopotential height anomalies north of India are related to the equivalent barotropic stationary Rossby waves in the South Asian wave guide. The waves can be generated by the IOD-related convection anomalies over the western/central Indian Ocean. In contrast, in the pure El Niño years with no co-occurrences of the positive IOD, the anomalies of moisture supply and surface temperature over the plateau are insignificant, suggesting negligible influences of ENSO on the early winter Tibetan snow cover. Further analyses show that ENSO is irrelevant to the spring/early summer Tibetan snow cover either, whereas the IOD-induced snow cover anomalies can persist long from the early winter to the subsequent early summer.
KeywordsTibetan snow cover Indian Ocean Dipole El Niño/Southern Oscillation Wave-activity flux
We thank Drs. H. Nakamura, Y. Masumoto, P. Chang, F.-F. Jin, S.-P. Xie and S. K. Behera for fruitful discussions. The present research is supported by the Japan Society for Promotion of Science through Grant-in-Aid for Scientific Research (B) 20340125 and Sumitomo Foundation. The first author has been supported by the scholarship for foreign students offered by Ministry of Education, Culture, Sports, Science and Technology, Japan.
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