Influences of IOD and ENSO on the snow cover in Tibet during early winter
University of Tokyo
Using reanalysis data and snow cover data derived from satellite observations, respective influences of Indian Ocean Dipole (IOD) and El Niņo/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 (no co-occurrences of El Niņo), negative geopotential height anomalies north of India are associated with warm and humid southwesterlies from the Bay of Bengal to enter the plateau 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 equivalent barotropic stationary Rossby waves in the South Asian wave guide. The waves may be generated by the downdraft over the Mediterranean region, which is caused by the IOD-related diabatic heating anomalies in the western/central Indian Ocean. In contrast, in pure El Niņo years (no co-occurrences of positive IOD), the anomalies of moisture supply and surface temperature over the plateau are insignificant, suggesting insignificant influences of ENSO on the early winter Tibetan snow cover.