[A-CG32] Land-Atmosphere interactions and Asian monsoon precipitation (LAMos)

[ACG32-01] Different future changes between early and late summer monsoon precipitation in East Asia

*Hirokazu Endo¹, Akio Kitoh^1,2, Ryo Mizuta¹, Tomoaki Ose¹ (1.Meteorological Research Institute, Japan Meteorological Agency, 2.Japan Meteorological Business Support Center)

Keywords:Summer monsoon, East Asia, Global warming, Baiu, MRI-AGCM

Future changes in the East Asian summer monsoon (EASM) precipitation and associated atmospheric circulation changes are investigated based on ensemble projections with a 60-km mesh Meteorological Research Institute atmospheric general circulation model (MRI-AGCM60). The projections at the end of the twenty-first century under the RCP8.5 scenario indicate an overall increase in EASM precipitation but with sub-seasonal and regional variations. On monthly basis, the Meiyu-Baiu rainband is projected to strengthen with its eastern part (i.e., Baiu rainband) shifted southward relative to the present-day position in June. These are highly consistent among the simulations, suggesting robustness of the result. In July and August, the simulations consistently project a significant increase in precipitation over the northern East Asian continent and the neighbor seas; however, there is a lack of consensus in the projection of the Meiyu-Baiu rainband in July, and precipitation change is small over the Pacific in August.
Sensitivity experiments with the MRI-AGCM60 reveal that the precipitation change in early summer is dominated by the effects of the globally uniform sea surface temperature (SST) warming and tropical SST pattern change that induce a strengthening and southward shift of the East Asian westerly jet (EAJ) especially over the Pacific as well as an increase in atmospheric moisture content. On the other hand, the late summer precipitation change is largely influenced by the effects of the greenhouse-gas-induced land warming and successive large SST warming in the extratropics, which act to oppose the early summer effects. The late summer effects induce the weakened and northward-shifted EAJ, together with an intensification of lower-level southerly monsoon winds over the East Asian continent. The results suggest that the large cancelation between the effects of early and late summer leads to a weaker response of the Meiyu-Baiu rainband in July compared to in June.