Defining the intensity of the East Asian summer monsoon (EASM) has been extremely controversial. This paper elaborates on the meanings of 25 existing EASM indices in terms of two observed major modes of interannual variation in the precipitation and circulation anomalies for the 1979-2006 period. The existing indices can be classified into five categories: the east-west thermal contrast, north-south thermal contrast, shear vorticity of zonal winds, southwesterly monsoon, and South China Sea monsoon. The last four types of indices reflect various aspects of the leading mode of interannual variability of the EASM rainfall and circulations, which correspond to the decaying El Niño, while the first category reflects the second mode that corresponds to the developing El Niño.The authors recommend that the EASM strength can be represented by the principal component of the leading mode of the interannual variability, which provides a unified index for the majority of the existing indices. This new index is extremely robust, captures a large portion (50%) of the total variance of the precipitation and three-dimensional circulation, and has unique advantages over all the existing indices. The authors also recommend a simple index, the reversed Wang and Fan index, which is nearly identical to the leading principal component of the EASM and greatly facilitates real-time monitoring.The proposed index highlights the significance of the mei-yu/baiu/changma rainfall in gauging the strength of the EASM. The mei-yu, which is produced in the primary rain-bearing system, the East Asian (EA) subtropical front, better represents the variability of the EASM circulation system. This new index reverses the traditional Chinese meaning of a strong EASM, which corresponds to a deficient mei-yu that is associated with an abnormal northward extension of southerly over northern China. The new definition is consistent with the meaning used in other monsoon regions worldwide, where abundant rainfall within the major local rain-bearing monsoon system is considered to be a strong monsoon.

[1] There are several monsoon regions in the world. Some monsoon indices have been proposed to describe their variability, but a unified monsoon index suitable for all known monsoon regions has not yet been found. Here we present a unified dynamical index of monsoon, the dynamical normalized seasonality (DNS), and carry out an analysis of observation data over the past 40 years. The analysis shows that the DNS index can characterize the seasonal cycle and interannual variability of monsoons over different areas very well. The South Asia summer monsoon (SASM) sector (5°-22.5°N, 35°-97.5°E) is composed of two independent components, SASM1 (2.5°-20°N, 35°-70°E) and SASM2 (2.5°-20°N, 70°-110°E), with quite different relations with the monsoon rainfall over the South Asia. The African summer monsoon (ASM) is dominated by variability on the decadal time-scale, and its decadal abrupt decrease in 1967 may be an important cause of the persistent drought over the Sahel region. It is also found that there is a remarkable global correlation pattern between the South China Sea summer monsoon index (SCSSMI) and global precipitation during boreal summer.

This paper introduces a new technique called species conservation for evolving paral-lel subpopulations. The technique is based on the concept of dividing the population into several species according to their similarity. Each of these species is built around a dominating individual called the species seed. Species seeds found in the current gen-eration are saved (conserved) by moving them into the next generation. Our technique has proved to be very effective in finding multiple solutions of multimodal optimiza-tion problems. We demonstrate this by applying it to a set of test problems, including some problems known to be deceptive to genetic algorithms.

[1] How to predict the year-to-year variation of the east Asian summer monsoon (EASM) is one of the most challenging and important tasks in climate prediction. It has been recognized that the EASM variations are intimately but not exclusively linked to the development and decay of El Niño or La Niña. Here we present observed evidence and numerical experiment results to show that anomalous North Atlantic Oscillation (NAO) in spring (April-May) can induce a tripole sea surface temperature pattern in the North Atlantic that persists into ensuing summer and excite downstream development of subpolar teleconnections across the northern Eurasia, which raises (or lowers) the pressure over the Ural Mountain and the Okhotsk Sea. The latter strengthens (or weakens) the east Asian subtropical front (Meiyu-Baiu-Changma), leading to a strong (or weak) EASM. An empirical model is established to predict the EASM strength by combination of the El Niño-Southern Oscillation (ENSO) and spring NAO. Hindcast is performed for the 1979-2006 period, which shows a hindcast prediction skill that is comparable to the 14 state-of-the-art multimodel ensemble hindcast. Since all these predictors can be readily monitored in real time, this empirical model provides a real time forecast tool.