Can coupled models perform better in the simulation of sub‐seasonal evolution of the western North Pacific subtropical high than atmospheric models in boreal summer?

Abstract

This study examines the climatological sub‐seasonal evolution of the western North Pacific subtropical high (WNPSH) in boreal summer using observation and multiple state‐of‐the‐art climate models, which has not been focused by previous research. The two sub‐seasonal shifts in boreal summer are analyzed, one from June to July (J–J) and another from July to August (J–A). In observation, the WNPSH consistently retreats eastward and jumps northward (weakens) from June to August. Driven by observed sea surface temperature (SST), the multi‐models ensemble (MME) of atmospheric general circulation models (AGCMs) that participated in the Coupled Model Intercomparison Project Phase 5 (CMIP5) can reproduce the weakening of WNPSH from June to July, but fail to simulate the weakening from July to August. This may be due to the sub‐seasonal variation of local SST increasing from June to July but decreasing from July to August. Compared with AGCMs simulation, CMIP5 coupled models MME largely improve the sub‐seasonal variation of the WNPSH and associated precipitation change. Thus, it is argued that coupled models should be adopted in studies of the WNPSH on sub‐seasonal timescales.

Zonal displacement of the Western North Pacific subtropical high from early to late summer

“…This relation between the local SST anomaly and circulation indicated that it was the shift in the circulation that induced the relative warming/ cooling of the local SST from early to late summer, which further confirmed the importance of the local air-sea interactions in this region. In our previous work, we found that compared with the atmosphere-only models, the air-sea coupled models could perform much better in simulating the month-to-month variation in the WNPSH in the boreal summer (Dong et al, 2017a(Dong et al, , 2017bLin et al, 2018). Similar results can be derived from the composite of the ERA-Interim and NCEP1 datasets (Figures 10 and 11).…”

Climatological Increased Precipitation from July to August in the Western North Pacific Region Simulated by CMIP6 Models

“…The water vapor budget analysis confirmed that the precipitation increase can be mainly attributed to the vertical motion change from July to August. In a previous study [30], CMIP5 AMIP simulations were examined and the results show that they cannot reasonably reproduce the precipitation increase from July to August, which is associated with the local SST change, as discussed in the previous subsection. The eastward retreat of the WPSH cannot be reproduced by AMIP experiments [29].…”

“…The climatological precipitation change from June to July and from July to August, along with the simulation performances in the uncoupled Atmospheric General Circulation Model (AGCM) and coupled CMIP5 models, have been examined in a previous study [30]. The author found that from June to July, the local SST increases, thus in AGCMs the positive precipitation center can be reproduced very well.…”

“…Figure 5 shows the spatial pattern of each item in the water vapor budget equation, including vertical transport by the anomalous vertical motion, horizontal transport, and evaporation. It is obvious that the precipitation increase is The climatological precipitation change from June to July and from July to August, along with the simulation performances in the uncoupled Atmospheric General Circulation Model (AGCM) and coupled CMIP5 models, have been examined in a previous study [30]. The author found that from June to July, the local SST increases, thus in AGCMs the positive precipitation center can be reproduced very well.…”

“…For the subseasonal scale, previous studies have shown that the month-to-month northward shifts of the WPSH can be reasonably reproduced, while it is a great challenge for large amounts of CMIP Phase 5 (CMIP5) models to simulate the zonal shifts of the WPSH from early to late summer [29]. Moreover, compared with atmospheric models driven by the prescribed sea surface temperature (SST, the so-called Atmospheric Model Intercomparison Project (AMIP) type simulation), air-sea coupled climate models have shown better performances in reproducing the sub-seasonal variation in WPSH and associated precipitation [30]. Although these preliminary conclusions can be drawn concerning the sub-seasonal scale, the sub-seasonal variation in the WPSH and associated precipitation in the WNP and East Asia are relatively lower than the summer mean and deserve further research.…”