Predictability of East Asian summer monsoon in seasonal climate forecast models

Abstract

The prediction skill and source of the predictability of the East Asian summer monsoon (EASM) system are examined in this work based on four state‐of‐the‐art seasonal climate forecast models including BCC_CSM1.1, ECMWF_SYS4, NCEP_CFS2 and TCC_CPS2. The prediction of the climatology and interannual EASM pattern and the impact on the prediction are further investigated. It is noted that the four models have some skill in predicting summer rainfall in the East Asia, however, the skill is low on average and also largely regional dependence. The interannual variation of EASM measured by monsoon circulation index is well reproduced, implying that the broad‐scale feature/pattern of EASM has higher predictability than the detailed spatial variation of EASM rainfall. The possible sources of predictability of the interannual variability of EASM are associated with the El Niño‐Southern Oscillation (ENSO) and the north Indian Ocean (NIO) sea surface temperature (SST) anomalies. The correlation pattern of rainfall with the NIO SST is characterized by a tripole pattern from south to north of East Asia, which is different from the correlation distribution of the southern‐northern dipole with ENSO, suggesting that NIO SST may exert influence on the EASM independently. The major biases in climatology of EASM in the models are the northward shift of the western Pacific subtropical high (WPSH) and weak monsoonal southerly over the coast of East Asia, which leads to the prediction bias of the Meiyu/Baiu/Changma (MBC) rainfall belt. The prediction of the interannual EASM pattern presents two deficiencies: too weak rainfall variability and northward shift of the dipole rainfall pattern (opposite variation between MBC and the northwestern Pacific), that may be caused by the biases of WPSH in the models.

Multiscale Variability of Meiyu and Its Prediction: A New Review

“…As shown in Figure 18, this sudden northward jump process occurred around the year 2000 but the model only predicted the gradual northward migration of rain belt. It should be pointed out, most coupled models could not predict the variation of Meiyu precipitation on decadal or interdecadal scale, as pointed out recently by Liu et al (2019).…”

“…Correspondingly, the Meiyu forecast in East Asia and China has also been significantly improved. The Meiyu climate conditions and related circulation patterns is also skillfully predicted by other operational climate prediction system like the NCEP Climate Forecast System with a lead time of one month (Gao et al, 2011; Liu et al, 2019). Based on verifications of high‐resolution models (Lau & Ploshay, 2009; Li et al, 2018; Lui et al, 2019), the increase of model resolution is emphasized to be an important contributor to the improvement of Meiyu simulation.…”

“…Beijing Climate Center is currently developing a multimodel ensemble forecast system (Liu et al, 2019). The results of the experiment are encouraging.…”

“…Prediction of summer (June–August) precipitation (shaded area, unit: mm/day) and 850 hPa wind vector (unit: m/s) of East Asian different modes in regression on orthogonalized observation of the East Asian summer monsoon index, (a) observations, (b) multimodal ensemble (MME), (c) BCC‐CSM, (d) ECMWF_SYS4, (e) NCEP_CSF2, and (f) TCC_CPS2. (copied from Liu et al, 2019). …”

East Asian summer rainfall projection and uncertainty under a global warming scenario

“…Figure 1 shows the simulated summer mean rainfall with the corresponding observations in the present-day period. In the observations, the monsoon rainfall belt in East Asia is largely controlled by the western Pacific subtropical high (WPSH), which is the anticyclone circulation over the western North Pacific (Song and Zhou, 2014;Liu et al, 2019a). Along the flank of WPSH, there are four rainfall centres ( Figure 1a): The Indochina peninsula, South China Sea (SCS), western North Pacific Ocean (WNP, along 10 N), and monsoon rainfall belt of MBC region (along 32 N, from Yangtze River basin in China to Japan).…”