Characteristics of Future Changes in Summertime East Asian Monthly Precipitation in MRI-AGCM Global Warming Experiments

Abstract

Global warming experiments using three different 60 km mesh atmospheric global circulation models are studied to characterize ensemble mean future changes in monthly East Asian precipitation for June to August. During the summer, wetting and drying effects due to changes in the mean vertical motion play a key role in future precipitation changes, as does the "wet-get-wetter" effect due to increased moisture. The former processes are related adiabatically to the projected modification of 500 hPa horizontal atmospheric circulation, which is characterized by two cyclonic circulation anomalies extending over the eastern Eurasian Continent (C1) and the western North Pacific Ocean (C2) for each month. Over Japan, the western edge of C2 shifts from a region south of the Japanese Islands to northern Japan during June to August, representing a delayed northward movement or southward shift of the westerly jet over the western North Pacific in the future compared with the present-day climatology. Most regions of Japan lie within the northeasterly wind and associated downward-motion zones of C2, leading to significant uncertainties in future precipitation over Japan by the offset against the "wet-get-wetter" effect and possibly even a future decrease in precipitation. A wetter future climate is anticipated under weak subsidence or upward vertical motion zone of C2, such as western Japan in August away from C2, and the Southwest Islands of Japan in June in the C2 southwesterly wind zone. Over the eastern Eurasian Continent, C1 is distributed mainly over northeastern China in June and over central and southern China in July and August, respectively. During these months, most of the eastern regions are located within the southwesterly to southeasterly wind zone of C1, indicating wet future conditions due to enhanced upward motion. This tendency drives a further increase in precipitation in future wetter East Asian climate via the "wet-get-wetter" effect and the increased evaporation.

Future Changes in Summertime East Asian Monthly Precipitation in CMIP5 and Their Dependence on Present-Day Model Climatology

“…However, the magnitudes of the future changes in the adiabatically diagnosed vertical velocity are comparable with those of the actually simulated vertical velocity or even greater. This contrasts with the reasonable results obtained in previous studies (Sampe and Xie 2010;Ose 2019) in which the former is onehalf to one-third of the latter. This cannot be attributed to the careless use of the 25-year mean climatology in the diagnostics.…”

“…The 36-model average of each model's corresponding COR for JJA is 0.424 (0.422). These relationships are qualitatively consistent with the results of the study on the Baiu rainband formation by Sampe and Xie (2010) and its application by Ose (2019). However, the magnitude of the future change in adiabatically diagnosed vertical velocity is comparable to that of the simulated vertical velocity, which is in contrast to those two previous studies that found the former to be a half to one-third of the latter.…”

“…This study was initiated to address two questions that arose from a preceding study by Ose (2019), who analyzed future changes in summertime East Asian the fifth phase of the Coupled Model Intercomparison Project (CMIP5: Taylor et al 2012). Although 60 km resolution MRI-AGCMs display high skill with respect to present-day climatological simulations, MRI-AGCMs represent a small model diversity of three different cumulus schemes available when compared with the CMIP5 model ensemble.…”

“…Future circulation changes are sometimes formed by atmospheric wave propagation from remote sources. Therefore, significant uncertainties can be entered into projections for the future distribution of the East Asian summer precipitation (Zhou et al 2017;Ose 2019). The dynamical components of moisture transportation are changed by various characteristic sources related to the global warming.…”

Comparison of regional characteristics of land precipitation climatology projected by an MRI-AGCM multi-cumulus scheme and multi-SST ensemble with CMIP5 multi-model ensemble projections

“…Kitoh and Endo (2016) and Mizuta et al (2017) assessed global precipitation, including extreme weather events, using MRI-AGCM3.2S and MRI-AGCM3.2H, respectively. The high resolution of MRI-AGCM3.2 has allowed realistic simulations of regional precipitation (e.g., Endo et al 2012Endo et al , 2017Kusunoki and Mizuta 2013;Ose 2017Ose , 2019Surendran et al 2019). For instance, Endo et al (2012) reported that MRI-AGCM3.2 at both resolutions realistically simulates the present-day precipitation over several areas in Asia, and discussed the contributions of SST changes and model physics to the uncertainty in future changes of regional precipitation using MRI-AGCM3.2H.…”