The state of climate over the tropical Indian Ocean and India from the late nineteenth century throughout the twentieth century.

摘要

Observational datasets from the late 19th century throughout the 20th century are statistically analyzed to reveal the state of climate over India and Indian Ocean during this period.; When the Indian summer monsoon rainfall is normal or above normal despite the occurrence of an El Nino event of boreal summer, the zonal wind over the equatorial Indian Ocean tends to be anomalously negative during four summer monsoon months.; Timing of El Nino-related warming over the Indo-Pacific Oceans also significantly impacts the interannual variability of Indian summer monsoon rainfall. Unlike the "canonical" El Nino evolution, an El Nino event tends to start from boreal winter and persist to boreal summer such that the western central Pacific and northern central Indian Ocean are warmer than normal during the summer monsoon season when the Indian summer monsoon rainfall is normal or above normal.; Severe drought in July over the Homogeneous Indian Monsoon region is more linked to the SST based Indian Ocean dipole mode index prior to July than to the strength of El Ninos of the summer monsoon season. When, during El Nino years the Homogeneous India experiences an extremely dry July, the development of the positive dipole mode that usually begins around May-June does not start until the second half of the summer monsoon season.; The occurrences of positive and negative Indian Ocean dipole events are irregular during the late 19th century throughout the 20 th century. The negative events that tend to co-occur with La Nina events dominates over the positive events during the period from the late 19th century to the early 20th century, which was followed by the period of weak dipole events. After 1960, the strong positive events with significant anomalous warming over the western pole and cooling over the eastern pole that are not observed in the earlier periods show, tending to co-occur with El Nino events.