Twice Northward Jumps Of WPSH And Its Relationship With Summer Rainfall In Eastern China Under Global Warming

Western Pacific subtropical high (WPSH for short) is one of the main members of the east Asian summer monsoon system, its north-south position movement possess the characteristic of slowly or suddenly, and it is a global phenomenon.The time of twice northward jumps of WPSH (West Pacific Subtropical High) has an important impact on summer rainfall anomalies in eastern China. Especially in the context of global warming, the variability of WPSH belonging to East Asian monsoon is worthy of concerning. It is necessary to have an objective and quantitative definition of WPSH northward jump in order to study its response to Global warming. After having the time series of two northward jump time, we can provide support for the research of summer rainfall anomalies in eastern China.Base on the above understandings, this paper performs three works base on the pentad-scale ridge data in 1951-2014. First on the basis of others’ researches, we proposes a new objective and quantitative definition of WPSH two northward jump time. After comparing with the monitoring data of Meiyu, we find that the definition presented in this article can accurately describe the coming of two northward jump time, which is more objective. Second we discuss the interdecadel, interannual and intraseasonal evolution and the relationship with summer precipitation in eastern China using the time series of two northward jump time under Global warming. The results show that:(1)The occurrence of the first time of northward jump shows "sustained early-sustained late" interdecadal transition with the transition time of 1980, which is consistent with global warming. And it is the latest decadel from the 21th century to present. The occurrence of second noccurrence orthward jump shows "sustained late-sustained early-sustained late" decadal transition with the transition time of 1954 and 1978 respectively and it is the second latest decadel from thel9th century. Form the above we can see there is a from thel9th century happens in the ’80s, which changes the summer rainfall anomalies in eastern China form "north-abundant-south-below average" to "south-abundant-north-below average". (2) The early years of two northward jumps are more happen in early stage then late stage, and the late years of two northward jumps are more happen in late stage then early stage. It shows the interannual anomaly of northward jump time has a characteristic of cluster. The difference of interannual variation of northward jump time has a great influence on summer precipitation. When the first northward jump time occurs abnormal, the location of main rain belt is different in Yangtze River which lies in 30°N. When it comes to the second northward jump time, the boundary will comes in two, one is 25°N and the other is 35°N. In nine cases when abnormalities occur to twice northward jumps simultaneously, the position of main rain belt can be considered as a superposition of isolated abnormal effects of twice northward jumps. (3)We divide an integrated 10-30days intraseasonal oscillation into 6 phases, the composite of summer rainfall results show that in the 1st phase, which the WPSH ridge line is in the south, the rain belt is located in south China, and it will move northward with the development of phases, at 6th phase the rain belt is moving to the north of northeast China. And then the rain belt will lies in south China which means comes to the next oscillation.At last we make a brief analysis of the general atmospheric circulation and external force of SST which have a influence on multi-scale evolution of northward jump time. It shows that, (1) Although PDO and ENSO both have a great influence on two northward jumps time, the PDO’s effect is more pronounce than ENSO’s on the scale of interdecadel, and ENSO’s effect is more reflect on the scale of nterannual. After canceling the interference of ENSO, the vertical atmospheric circulation is composited in different phases of PDO.The results show that during the cold(warm) phase of PDO, the atmospheric circulation on 200hPa,500hPa and 850hPa is all contribute to earlier(later) northward jump of WPSH. The results show that during the cold(warm) phase of PDO, the atmospheric circulation on 200hPa,500hPa and 850hPa is all contribute to earlier(later) northward jump of WPSH. (2) On interannual scales, when the La Nina evolves from strong in winter to weak in summer, the first northward jumps usually early, when the La Nina evolves from weak in winter to strong in summer,the second northward jumps usually early, when El Nino evolves from strong in winter to weak in summer, the 1st northward jump usually late, and when El Nino evolves from weak in winter to strong in summer, the 1st northward jump usually early. (3) In this paper, the reason why intraseasonal oscillation will happen is analyzed by two cases. Our study shows that the low frequency oscillation of WPSH closely associate with the EAP (East Asian-Pacific) pattern teleconnetion-like wave. When the low-frequency potential wave firstly transport south from high latitude in 40～60°E to 40～50°N, and then transport east form 40～60°E to 100～120°E, the northward jump is more likely to happen. But when the low-frequency potential wave can not transport to 100～120°E, the northward jump is less likely to happen.