Improved Simulation of East Asian Summer Monsoon in the High-resolution CESM1 and Its Causes
0
Citation
66
Reference
10
Related Paper
Keywords:
East Asian Monsoon
This study provides a detailed analysis of the mid-Holocene to present-day precipitation change in the Asian monsoon region. We compare for the first time results of high resolution climate model simulations with a standardised set of mid-Holocene moisture reconstructions. Changes in the simulated summer monsoon characteristics (onset, withdrawal, length and associated rainfall) and the mechanisms causing the Holocene precipitation changes are investigated. According to the model, most parts of the Indian subcontinent received more precipitation (up to 5 mm/day) at mid-Holocene than at present-day. This is related to a stronger Indian summer monsoon accompanied by an intensified vertically integrated moisture flux convergence. The East Asian monsoon region exhibits local inhomogeneities in the simulated annual precipitation signal. The sign of this signal depends on the balance of decreased pre-monsoon and increased monsoon precipitation at mid-Holocene compared to present-day. Hence, rainfall changes in the East Asian monsoon domain are not solely associated with modifications in the summer monsoon circulation but also depend on changes in the mid-latitudinal westerly wind system that dominates the circulation during the pre-monsoon season. The proxy-based climate reconstructions confirm the regional dissimilarities in the annual precipitation signal and agree well with the model results. Our results highlight the importance of including the pre-monsoon season in climate studies of the Asian monsoon system and point out the complex response of this system to the Holocene insolation forcing. The comparison with a coarse climate model simulation reveals that this complex response can only be resolved in high resolution simulations.
East Asian Monsoon
Intertropical Convergence Zone
Cite
Citations (47)
This paper is the first of a two-part study to investigate the possible relationships between summer and winter monsoons over East Asia during the period 1958 to 1999. It documents the approach employed in the study. Assuming the existence of relationships, the central theme of the study is to answer the questions: Is there evidence for the relationships and, if so, what are the relationships? In particular, the approach used to interpret the available evidence to make inferences about the conditions of the summer monsoon is described. Six winter monsoon categories are defined in terms of the monsoon strength and the conditions of the El Niño–southern oscillation. The conditions of the summer monsoons preceding and following each winter monsoon category are assessed to identify the possible summer-to-winter monsoon and winter-to-summer monsoon relationships respectively. Summer monsoons are classified into unlikely strong (notS) or unlikely weak (notW) according to the bias in the relative occurrence of positive and negative anomalies of several summer monsoon indices. The rainfall condition over China and the characteristics of the subtropical high are also used to provide supplementary evidence for the summer monsoon strength and to describe the accompanying synoptic situations. Copyright © 2005 Royal Meteorological Society.
Subtropical ridge
East Asian Monsoon
Tropical monsoon climate
Cite
Citations (10)
East Asian Monsoon
Precipitable water
Tropical monsoon climate
Cite
Citations (48)
Indian Monsoon and East Asian Monsoon are two sub-systems of Asian Monsoon.A common pattern between the two monsoons at the seasonal and orbital time scales was formulated from the meteorological data and geological records.However,the relationship of the two sub-systems on the inter-annual and inter-decadal scales remains quite obscure.In this study,high-resolution oxygen isotope compositions of two laminated speoleothems from the Defore Cave of Oman and the Heshang Cave of China were compared with each other to detect the link between the Indian Monsoon and the East Asian Monsoon.δ18O of Defore stalagmite is characteristic of the Indian Monsoon while δ18O of Heshang stalagmite is an indicator of the East Asian Monsoon.Two stalagmite records show similar structures for the last 780 years on the decadal scale,implying the asynchronous variation of the Indian Monsoon and the East Asian Monsoon.
Stalagmite
East Asian Monsoon
δ18O
Cite
Citations (1)
To simulate the onset and intraseasonal variability of summer monsoons, the National Centers for Environmental Prediction Eta Model (80 km, L38) is nested in the Center for Ocean–Land–Atmosphere Studies GCM (R40, L18). The region of the Eta Model is (30°S–50°N and 30°–140°E), which includes the Indian, Chinese, and Southeast Asian monsoons. The summer monsoons of 1987 and 1988 are simulated by integrating the nested model from mid-April to the end of September, prescribing the seasonal variations of SST of the respective years. The summer monsoons of 1987 and 1988 were extreme. In 1987, an El Niño year, the Indian monsoon rainfall was far below normal but over southeast China the rainfall exceeded normal. In contrast, in 1988, a La Niña year, Indian monsoon rainfall was far above normal but the rainfall over southeast China was below normal. The Eta Model was able to simulate the typical observed features of the monsoon onset, that is, an abrupt increase in the precipitation rate as well as in the strength of the circulation. The simulated onset dates for 1987 and 1988 were in good agreement with observations. The Eta Model was also able to simulate the observed circulation features of the break and active periods during these two years. To investigate the contrasting characteristics of the Indian and the Chinese monsoons, for these two years the following hypothesis, largely based on observational evidence, is verified. There are two preferred locations of ITCZ: one over the warm waters of the equatorial Indian Ocean and the other over the heated continent in the vicinity of the seasonal monsoon trough. There is a northward migration of the convective precipitation bands from the equatorial ITCZ to the continental ITCZ with the timescale of a few weeks. There exists an inverse relationship between the strength of the two ITCZs. During an El Niño year, sea level pressure over the Indian subcontinent and over the Maritime Continent increases. Consequently, the ITCZ over the Indian subcontinent and over the Maritime Continent weakens and the ITCZ over the equatorial Indian Ocean, Southeast Asia, and southeast China strengthens. The Eta Model simulated circulations are in support of the hypothesis. The simulations also show that there is a northward migration of convective precipitation bands from the equatorial ITCZ to the continental ITCZ.
Intertropical Convergence Zone
East Asian Monsoon
Atmospheric Circulation
Cite
Citations (37)
Abstract. Based on the simulations with fifteen climate models in the Pliocene Model Intercomparison Project (PlioMIP), the regional climate of East Asia (focusing on China) during the mid-Pliocene is investigated in this study. Compared to the pre-industrial, the multi-model ensemble mean (MMM) of all models shows the East Asian summer wind (EASW) largely strengthens in monsoon China, and the East Asian winter wind (EAWW) strengthens in south monsoon China but slightly weakens in north monsoon China in mid-Pliocene. The MMM of all models also illustrates a warmer and wetter mid-Pliocene climate in China. The simulated weakened mid-Pliocene EAWW in north monsoon China and intensified EASW in monsoon China agree well with geological reconstructions. However, the model-model discrepancy in simulating mid-Pliocene East Asian monsoon climate, in particular EAWW, should be further addressed in the future work of PlioMIP.
East Asian Monsoon
Tropical monsoon climate
Cite
Citations (12)
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
Cite
Citations (36)