Resolution of Summertime East Asian Pressure Pattern and Southerly Monsoon Wind in CMIP5 Multi-model Future Projections

Abstract

The southerly surface wind index over the summertime East Asia (SWI) is strengthened in the future in the fifth phase of the Coupled Model Intercomparison Project (CMIP5). However, the differences among the models are much larger than the ensemble average. The empirical orthogonal function (EOF) analysis is applied to the future changes in the East Asian surface pressure pattern responsible for the SWI. The ensemble average and five EOF modes for the pressure patterns and the associated precipitation changes are identified, and their possible sources are examined.The CMIP5 ensemble mean change in the summertime Asia Pacific surface pressure pattern possesses the characteristics of the first to third modes. The first and second mode components contribute to the positive SWI in the future, but are cancelled mostly by the third mode component. The first mode is high surface pressure anomalies over low Asia Pacific sea surface temperature. The second mode is related to warm temperature anomalies over the Northern Hemisphere continents and the increased equatorial Pacific precipitation. The large model dependence of the SWI is created by the third mode, which represents the weak Pacific High in northern East Asia and is characterized with suppressed vertical motions over the northern Indian and Pacific oceans. The fourth mode is the Okhotsk High. The fifth mode represents the east-west contrast of the southern East Asian surface pressure anomalies and is associated with the Northern Hemisphere ocean temperatures. The fourth and fifth modes feature the mean projection using the 10 models reproducing an accurate present-day summertime East Asian climatology.The mode-related suppressed vertical motions in global warming reflect the present-day vertical motion (i.e., precipitation) climatology; hence, the future increase/decrease in the SWI tends to be projected by models simulating the relatively small/large Asia Pacific monsoon precipitation over the tropical oceans, except near the mountains, in the present-day model climatology.

Inter‐model Spread of the Changes in the East Asian Summer Monsoon System in CMIP5/6 Models

“…Therefore, the decreased meridional temperature gradient leads to a weakened EAJ (Figure 14). The MV‐EOF2 is somewhat similar to the second EOF mode of the future changes in sea‐level pressure over the East Asia revealed by a recent study (Ose et al., 2020). In CMIP5, the greater surface warming is mainly located over the continental margins (Figure 15a), while it moves to the Arctic in CMIP6 (Figure 15c).…”

Seasonal characteristics of future climate change over Japan and the associated atmospheric circulation anomalies in global model experiments

“…In JJA, ΔSLP corresponds to the weakening of the present-day northward expansion of the summer Pacific High over JPN; that is, the negative ΔSLP in the north of JPN ( Figure 4c) and a more westerly wind over JPN. This ΔSLP pattern is similar to the primary mode in Ose et al (2020). The increase in precipitation is clear over all of the JPN area.…”