Forecasting the June Ridge Line of the Western Pacific Subtropical High with a Machine Learning Method

Abstract

The ridge line of the western Pacific subtropical high (WPSHRL) plays an important role in determining the shift in the summer rain belt in eastern China. In this study, we developed a forecast system for the June WPSHRL index based on the latest autumn and winter sea surface temperature (SST). Considering the adverse condition created by the small observed sample size, a very simple neural network (NN) model was selected to extract the non-linear relationship between input predictors (SST) and target predictands (WPSHRL) in the forecast system. In addition, some techniques were used to deal with the small sample size, enhance the stabilization of the forecast skills, and analyze the interpretability of the forecast system. The forecast experiments showed that the linear correlation coefficient between the predictions from the forecast system and their corresponding observations was around 0.6, and about three-fifths of the observed abnormal years (the years with an obviously high or low WPSHRL index) were successfully predicted. Furthermore, sensitivity experiments showed that the forecast system is relatively stable in terms of forecast skill. The above results suggest that the forecast system would be valuable in real-life applications.

Predicting the interannual variability of the subtropical high over the western Pacific Ocean based on the improved information diffusion model

“…In recent years, meteorologists (Sui et al, 2007;Wu and Zhou, 2008) have paid more attention to the formation and IAV of the WPSH by studying its characteristic structure and variation. In particular, the physical mechanisms behind the abrupt changes and morphological variability of the WPSH, such as its northward, southward, and sustained westward extension, have become the focus of atmospheric-circulation and medium-and long-term forecasts (Xiang et al, 2013;Sun et al, 2022), despite being difficult issues to solve.…”

The north–south shift of the ridge location of the western Pacific subtropical high and its influence on the July precipitation in the Jianghuai region from 1978 to 2021

“…The WPSH center is weak and gradually moves westward toward the mainland in spring from the ocean, and the WPSH strengthens and the center moves close to the East Asian continent in summer, with a northward shift of the WPSH ridge and the rain belt. The north-south shift of the WPSH ridge location controls the movement of the rain belt in eastern Asia (Ren et al, 2005;Tao and Wei, 2006;Liu et al, 2013;Wu and Guo, 2019;Sun et al, 2022). For example, the summer precipitation in eastern China is mainly driven by the EASM and shows a zonal distribution (Zhou and R, 2005;Zhu et al, 2011), but the strength of the EASM is mainly affected by the WPSH (Huang and Sun, 1992;Lin and Wang, 2016).…”