Identification of the atmospheric water sources and pathways responsible for the East Asian summer monsoon rainfall

• The East Asian summer monsoon rainfall provides water security and socio-economic benefit for over 20% of the global population. However, the sources of this rainfall and how it is carried to the East Asian landmass are still uncertain. To address this, atmospheric water sources and pathways associated with the East Asian summer rainfall are identified and quantified in this study using atmospheric water trajectories, calculated with a novel Lagrangian framework. Evaporated water from the East Asian landmass is found to be the major contributor to East Asian rainfall, amounting to local recycling. The results further indicated that the south Indian Ocean is a major non-local source for rainfall over southern East Asia during June to August. The role of the south Indian Ocean as a source of atmospheric water is one of the major findings of the study and would help in better understanding and predicting the East Asian summer rainfall. Evaporated waters from the Pacific Ocean (particularly the far-west Pacific Ocean) dominate the non-local contribution to precipitation over northern East Asia during June to September and over southern East Asian rainfall during September. The spatial structure of the East Asian rainfall is reported to be determined by the atmospheric waters that are evaporated and transported from the non-local sources. The role of the north Indian Ocean and the South Asian landmass as a source of water for East Asian precipitation is minimal and restricted to southern East Asia. The cross-equatorial Somali jet and equatorial trade winds associated with the western North Pacific subtropical high are important pathways for East Asian precipitation sourced over the south Indian Ocean and the Pacific Ocean respectively. In contrast, minor roles are attributed to the Bay of Bengal as a source, and midlatitude westerlies as a transport pathway, for East Asian precipitation. Randomly chosen atmospheric water trajectories were obtained from the backward tracing of the East Asian summer rainfall. These trajectories are a small subset of a total of 5 million trajectories. The green dots are the starting (net precipitation) positions and the blue dots indicate the ending locations (net evaporation) of the trajectories. Basins were defined as the south Indian Ocean (SIO), north Indian Ocean (NIO), South Asia (SA), East Asia (EA), Pacific Ocean (PAC), Atlantic Ocean (ATL). Atmospheric water sources and pathways associated with the East Asian summer rainfall are identified and quantified in this study using a novel Lagrangian framework. The results show the following: (1) Evaporated water from the East Asian landmass is found to be the major contributor to East Asian rainfall, amounting to local recycling. (2) The south Indian Ocean is a major non-local source for rainfall over southern East Asia during June-August. Evaporated waters from the Pacific Ocean dominate the non-local contribution to precipitation over northern East Asia during June-September. (3) The spatial structure of the East Asian rainfall is reported to be determined by the atmospheric waters that are evaporated and transported from the non-local sources. Minor roles are attributed to the Bay of Bengal as a source, and midlatitude westerlies as a transport pathway, for East Asian precipitation.image

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Miljövetenskap (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Environmental Sciences (hsv//eng)

Nyckelord

atmospheric water source

East Asian summer monsoon

evaporation

Lagrangian water tracing

rainfall

water transport pathways

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