Relationships amongs the Indian monsoon, the South China Sea monsoon, and the Western North Pacific precipitation
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It is hypothesized that the South China Sea (SCS) monsoon and the Indian monsoon intensify each other in the boreal summer. The Indian monsoon westerlies strengthen the SCS monsoon through the WE (Wind- Evaporation feedback) mechanism, but weaken it through the reduction in SCS SST. The SCS monsoon may have a positive feedback to enhance the Indian monsoon westerlies through the Walker circulation. Further question is how the convective activity over the Western North Pacific (WNP) interacts the Indian monsoon westerlies. The WNP SST may affect the Indian monsoon through the WNP precipitation. In this study, we investigate the relationships among the Indian monsoon, SCS monsoon and WNP activities from various observational data. The regression coefficient analyses are made. The data are NCEP reanalysis data, the CMAP precipitation data and ICOADS SST data averaging over June-July-August (JJA) for 21 years (1982-2002). First, the precipitation anomalies are regressed to the Indian monsoon westerly anomaly. The result shows that the Indian monsoon westerlies are positively correlated with the SCS precipitation. It indicates that the surface heating exchange over the SCS region is largely induced by the Indian monsoon westerlies and/or the SCS monsoon enhances the Indian monsoon westerlies. Another map of the regression of the 850hPa wind field anomalies to the WNP precipitation anomaly also shows that the Indian monsoon westerlies are positively correlated with the WNP precipitation. Completing this result, we confirm that the WNP precipitation and WNP SST have a positive correlation. Thus, the strengthening of the Indian monsoon westerlies and SCS westerlies may be also induced by the precipitation increase on the WNP region through the stronger east-west circulation associated with the warmer WNP SST. From the above results, it is found that the Indian monsoon westerlies are strongly correlated with the SCS monsoon activity and the WNP precipitation. Probably, the SCS monsoon is affected by the Indian monsoon through the WE, and affects the Indian monsoon through the diabatic heating. Further link is found to the precipitation over the WNP. To confirm the mechanism of correlation, the model study is underway.Keywords:
Westerlies
East Asian Monsoon
Westerlies
Atmospheric Circulation
East Asian Monsoon
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East Asian Monsoon
Forcing (mathematics)
Orbital forcing
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Abstract The Asian monsoon variations under global temperature changes during the Pliocene are still debated. Here we use a sedimentary record of phytoliths (plant silica) from the Weihe Basin, central China, to explore the history of C 4 grasses and quantitatively reconstruct the Asian monsoon climate since the late Miocene. Our results show that C 4 grasses have been a dominant grassland component since ~11.0 Ma. A subsequent marked decrease in warm- and humid-adapted C 4 grasses and an increase in cool- and dry-adapted C 3 grasses occurred in the Pliocene, ~4.0 Ma; the phytolith-based quantitative reconstruction of mean annual precipitation marked a decrease from 800~1673 mm to 443~900 mm, indicating a reduction in Asian monsoon rainfall in the Pliocene. Our newly obtained records conflict with the hypothesis that the growth of the Tibetan Plateau strengthened the Asian monsoon rainfall. Nevertheless, they emphasize the importance of global temperature as a determinant of Pliocene Asian monsoon variations.
East Asian Monsoon
Phytolith
Paleoclimatology
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DOI = 10.3126/hjs.v5i7.1260 Himalayan Journal of Sciences Vol.5(7) (Special Issue) 2008 p.58
Neogene
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The Asian monsoon is the most significant component of the global climate system. During recent two decades, a more and more efforts have been made to study the Asian monsoon. A substantial achievement has been made in basic physical processes, predictability and prediction since the MONEX of 1978-1979. The major advance in our new understanding of the variability of the Asian summer monsoon has been highlighted in this paper. The present paper is structured with four parts. The first part is the introduction, indicating the new regional division of the Asian monsoon system and significant events of the history of the Asian monsoon research. The second part discusses the annual cycle and seasonal march of the Asian monsoon as the mean state, with a special emphasis on the onset, propagation, active-break cycle and withdrawal of the Asian summer monsoon. The process and mechanism of the earliest onset of the Asian summer monsoon which takes place in the near-equatorial East Indian ocean-central and southern Indochina Peninsula have been well documented. The third part deals with the multiple scale variability of the Asian summer monsoon, including the intraseasonal, interannual and inter-decadal variability. Their dominant modes such as 10-20 day and 30-60 day oscillations for the intraseasonal variability, the Tropospheric Biennial Oscillation (TBO), the Indian Ocean Dippole Mode (IODM) and teleconnection patterns for interannual variability and the 60-year oscillation for the inter-decadal variability, as well as related SST-monsoon relationship and land-monsoon relationship have been discussed in more details. The fourth part is the conclusion, summarizing the major findings and proposing future work.
Teleconnection
East Asian Monsoon
Predictability
Annual cycle
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The monsoon rainfall contributes about 30% of the total global rainfall. The Asian monsoon system (ASM) is one of the largest systems and is of great significance in the global climate system. It consists of two subsystems, namely Indian summer monsoon (ISM)/southwest (SW) monsoon/South Asia summer monsoon (SASM) and East Asia monsoon (EAM).
East Asian Monsoon
Tropical monsoon climate
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Abstract. The recently proposed global monsoon hypothesis interprets monsoon systems as part of one global-scale atmospheric overturning circulation, implying a connection between the regional monsoon systems and an in-phase behaviour of all northern hemispheric monsoons on annual timescales (Trenberth et al., 2000). Whether this concept can be applied to past climates and variability on longer timescales is still under debate, because the monsoon systems exhibit different regional characteristics such as different seasonality (i.e. onset, peak and withdrawal). To investigate the interconnection of different monsoon systems during the pre-industrial Holocene, five transient global climate model simulations have been analysed with respect to the rainfall trend and variability in different sub-domains of the Afro-Asian monsoon region. Our analysis suggests that on millennial timescales with varying orbital forcing, the monsoons do not behave as a tightly connected global system. According to the models, the Indian and North African monsoons are coupled, showing similar rainfall trend and moderate correlation in centennial rainfall variability in all models. The East Asian monsoon changes independently during the Holocene. The dissimilarities in the seasonality of the monsoon sub-systems lead to a stronger response of the North African and Indian monsoon systems to the Holocene insolation forcing than of the East Asian monsoon and affect the seasonal distribution of Holocene rainfall variations. Within the Indian and North African monsoon domain, precipitation solely changes during the summer months, showing a decreasing Holocene precipitation trend. In the East Asian monsoon region, the precipitation signal is determined by an increasing precipitation trend during spring and a decreasing precipitation change during summer, partly balancing each other. A synthesis of reconstructions and the model results do not reveal an impact of the different seasonality on the timing of the Holocene rainfall optimum in the different sub-monsoon systems. Rather they indicate locally inhomogeneous rainfall changes and show that single palaeo-records should not be used to characterise the rainfall change and monsoon evolution for entire monsoon sub-systems.
East Asian Monsoon
Orbital forcing
Forcing (mathematics)
Tropical monsoon climate
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