Remote Connection of the Northeast Asian Summer Rainfall Variation Revealed by a Newly Defined Monsoon Index

Abstract

A new northeast Asian summer monsoon index is introduced to investigate the characteristics of the northeast Asian summer rainfall variation, including Korea, Japan, and northeast China, and its possible connection to the tropical and midlatitude circulations. The summer precipitation over northeast Asia is separated into two components associated with tropical forcing and midlatitude dynamics using this monsoon index. The connection between the northeast Asian summer rainfall and ENSO is clearly identified by separating the Tropics-related component from the northeast Asian summer rainfall. That is, the Tropicsrelated precipitation over northeast Asia tends to be enhanced after the mature phase of El Niño. On the other hand, it is revealed that the extratropics-related component of summer precipitation is connected to the Eurasian wave pattern with no significant lag correlation.The intensity of the western North Pacific anticyclone modulated by ENSO is a key factor in the variation of the northeast Asian summer precipitation. It is found that the warm SST over the tropical eastern Pacific plays an important role in establishing the western North Pacific anticyclone during the preceding winter of strong northeast Asian summer monsoon years, whereas convective activities over the Bay of Bengal are contributed to the modulation of the anticyclonic circulation in the summer. The warming over the Indian Ocean in the summer of strong monsoon years induces the development of the anticyclone over the western North Pacific and the suppressed convection over the western Pacific tends to enhance the northeast Asian summer rainfall through the Pacific-Japan or East Asia-Pacific teleconnections.

Seasonal forecasting of East Asian summer monsoon based on oceanic heat sources

“…NEASM precipitation is significantly correlated with the principal component 1 (PC 1) NEASM index obtained from the first leading empirical orthogonal function (EOF 1) of JJA precipitation over the 20°∼ 50°N and 100°∼ 180°E (r = 0.70). The PC 1 NEASM index is defined as the PC 1 time series multiplied by area-averaged value of the first eigenvector over the NEASM region (Lee et al, 2005). NEASM and SEASM precipitation are also significantly correlated with area-averaged divergences at 150 hPa over the NEASM and SEASM regions, as mentioned in Section 3, thus we use them as an index of each sub-EASM.…”

“…The PEA teleconnection is a vorticity wave that emanates from tropical central Pacific convection anomalies and propagates westward and poleward against the westerly jet stream (Wang et al, 2000). During the mature phase of an El Niño/Southern Oscillation (ENSO), the PEA pattern consists of an anomalous anticyclonic circulation over the WNP and anomalous cyclonic circulations over both the eastern North Pacific and East Asia (Lee et al, 2005). Thus, this WNP anticyclone plays an important role in the connection between the East Asian monsoon and the 668 E. LEE ET AL.…”

A Source of AGCM Bias in Simulating the Western Pacific Subtropical High: Different Sensitivities to the Two Types of ENSO

“…The western flank of the subtropical high is referred to as the western Pacific subtropical high (WPSH) and is known to have profound impacts on Asian-Pacific climate. Variations in the location and intensity of the WPSH, for example, are known to affect the East Asian summer monsoon strength (e.g., Chang et al 2000;Wang et al 2000;Lee et al 2005) and the western Pacific typhoon track (e.g., Ho et al 2004;Wu et al 2005). Therefore, it is important for a general circulation model (GCM) to realistically simulate the WPSH variability to be useful for weather forecasts and climate projections for the Asian-Pacific region.…”

The fluctuation of the beginning time of flood season in North China during AD1766–1911

“…In the years of strong summer monsoon, the rainbelt rushes quickly over northern China and causes drought in the Yangtze River Valley and wetness along the northern boundary of the EASM (Tao and Chen, 1987). As the intensity of the EASM is significant in determining the northern extension of the summer monsoon, it is reasonable to conclude that the intensity of the monsoon is related to the beginning of the flood season in this (Guo, 1983;Tao et al,1987;Zhao and Zhang, 1996;Shi andZhu, 1996 Lu andChan, 1999;Sun et al, 2001;Wang, 2001;Zhang and Liu, 2003;Zhang et al, 2003a, b;Guo et al, 2004;Huang, 2004;Lian et al, 2004;Lee et al, 2005;Zhao and Zhou, 2005;Zhu et al, 2005). Guo et al (2004) reconstructed the index of summer monsoon (Ism) on the basis of the sea level pressure record (SLP) from 1873 to 2000.…”