Forced and internal modes of variability of the East Asian summer monsoon

Abstract

Abstract. The modern instrumental record is analyzed in an attempt to reveal the dynamical structure and origins of the major modes of interannual variability of East Asian summer monsoon (EASM) and to elucidate their fundamental differences with the major modes of seasonal variability. These differences are instrumental in understanding of the forced (say orbital) and internal (say interannual) modes of variability in EASM. We show that the leading mode of interannual variation, which accounts for about 39% of the total variance, is primarily associated with decaying phases of major El Nino, whereas the second mode, which accounts for 11.3% of the total variance, is associated with the developing phase of El Nino/La Nina. The EASM responds to ENSO in a nonlinear fashion with regard to the developing and decay phases of El Nino. The two modes are determined by El Nino/La Nina forcing and monsoon-warm ocean interaction, or essentially driven by internal feedback processes within the coupled climate system. For this internal mode, the intertropical convergence zone (ITCZ) and subtropical EASM precipitations exhibit an out-of-phase variations; further, the Meiyu in Yangtze River Valley is also out-of-phase with the precipitation in the central North China.In contrast, the annual cycle forced by the solar radiation shows an in-phase variation between the ITCZ and the subtropical EASM precipitation. Further, the seasonal march of precipitation displays a continental-scale northward advance of a southwest-northeastward tilted rainband from mid-May toward the end of July. This coherent seasonal advance between Indian and East Asian monsoons suggests that the position of the northern edge of the summer monsoon over the Correspondence to: J. Liu (jianliu@niglas.ac.cn) central North China may be an adequate measure of the monsoon intensity for the forced mode. Given the fact that the annual modes share the similar external forcing with orbital variability, the difference between the annual cycle and interannual variation may help to understand the differences in the EASM variability on the orbital time scale and in the modern records.

A Linear Markov Model for East Asian Monsoon Seasonal Forecast

“…Thus, reduced precipitation is seen along the East Asia subtropical front. Note that Liu et al (2008) found a sandwich precipitation pattern in the second MEOF mode of EASM, which is probably associated with the developing phase of ENSO (Wang et al 2008b;Huang and Wu 1989). However, such a pattern is not present in our analysis of the full EAM.…”

Influence of climate change on saline lakes of the Tibet Plateau, 1973–2010

“…In summer, the climate is influenced by the currents of tropospheric tropical easterlies, subtropical westerlies, stratospheric easterlies, and the southwestern monsoon from the Indian Ocean (Liu et al, 2008), which results in precipitation being concentrated in June to September. In winter, the climate is dominated by cold and dry westerlies.…”

Performance of the New NCAR CAM3.5 in East Asian Summer Monsoon Simulations: Sensitivity to Modifications of the Convection Scheme

“…The generally recognized EASM system consists of three main components, namely, the East Asian mei-yu/baiu/ changma front (a major rain-bearing system in the subtropics and midlatitudes), the western Pacific subtropical high (WPSH), and the tropical western Pacific monsoon trough or the western Pacific intertropical convergence zone (ITCZ). These three components are intimately coupled (Nitta 1987;Huang and Wu 1989;Liu et al 2008).…”