By: Liang Guo
The East Asian monsoon causes intense rainfall over China, Japan and the Koreas each summer season, and a chilly, dry season each winter. This is pushed by thermal and dynamical contrasts between the huge Pacific Ocean and the elevated Tibetan Plateau. Over 80% of East Asian rainfall is carried in from tropical oceans and mid-latitude land and oceans(Guo, Klingaman et al. 2018).
The power of the monsoon varies every year, with stronger monsoon seasons related to a better complete rainfall. However, the depth of particular person rainfall occasions is determined by smaller-scale perturbations within the climate, equivalent to a vortex shifting down from Tibet or a tropical cyclone from the Pacific.
As excessive rainfall occasions are damaging to each individuals and property, and occurring extra typically(Chevuturi, Klingaman et al. 2018), we wished to know the way a lot of the rainfall in East Asia is attributable to the imply monsoon move and the way a lot is attributable to perturbations within the climate.
To examine this, we used a moisture monitoring instrument: the Water Accounting Model (WAM). This deconvolves atmospheric circulation and moisture utilizing a spatial filter, and assumes that the ambiance maintains the identical hydrological stability at every grid level as occurred in actuality (i.e. evaporation and precipitation are unchanged) besides over East Asia.Figure 1: Annual cycles of rainfall over 5 East Asian subregions tracked utilizing decomposed moisture fluxes (colored traces). Sums of every parts (stable gray line) are in comparison with precipitation of ERA-Interim (dotted gray line).
Figure 1 reveals the outcomes of making use of this instrument to 5 totally different areas of East Asia: southeastern China (area 1), Tibetan Plateau (area 2), central jap China (area 3), northwestern China (area 4) and northeastern China (area 5). This reveals the quantity of rainfall which occurred as a result of imply move (black); the imply humidity gradient (crimson); the eddy move (yellow); the eddy humidity gradient (blue) over the course of a 12 months. The contributions from every of these parts added collectively present the overall rainfall for the area (stable gray line). This matches up nicely to the overall precipitation within the ERA-Intermin dataset (dotted gray line), which can be utilized as a reference.
We discovered that the imply monsoon move and imply monsoon gradient are the biggest causes of rainfall, notably in southeastern China and Tibet.
Chevuturi, A., et al. (2018). “Projected Changes in the Asian‐Australian Monsoon Region in 1.5°C and 2.0°C Global‐Warming Scenarios.” Earth’s Future 6(3): 339-358. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017EF000734
Guo, L., et al. (2018). “The contributions of local and remote atmospheric moisture fluxes to East Asian precipitation and its variability.” Climate Dynamics. https://journals.ametsoc.org/jhm/article/20/4/657/344214/Moisture-Sources-for-East-Asian-Precipitation-Mean