Deuterium Content in the Himalayan Precipitation at Khumbu District, Observed in 1974/1975

A total of 129 water samples of daily precipitations were collected at Lhajung (4420 m) from April 1974 to March 1975. Samples were collected for 124 days within 127 wet days. The deuterium content of each sample was measured by mass spectrometry. Specially high deuterium content was found in the pre-monsoon precipitations, while lowest content in the middle of the monsoon. Annual changes of deuterium content, air temperature, and precipitation amount are clearly divided into four stages. Analyzing the long term trend of daily deuterium content, deuterium rich precipitations in pre-monsoon are attributed to the direct transport of water vapour from the Indian Ocean to the Himalayas without much rainfall on the way. The history of isotopic depletion caused by rainfall at the Indian coast is analyzed, showing the travelling time from the coast near Calcutta to the Mt. Sagarmatha region to be about four days in the wet season.