East Asian Monsoon Region Research Articles

Characteristics of decadal-centennial-scale changes in East Asian summer monsoon circulation and precipitation during the Medieval Warm Period and Little Ice Age and in the present day

Using meteorological observations, proxies of precipitation and temperature, and climate simulation outputs, we synthetically analyzed the regularities of decadal-centennial-scale changes in the summer thermal contrast between land and ocean and summer precipitation over the East Asian monsoon region during the past millennium; compared the basic characteristics of the East Asian summer monsoon (EASM) circulation and precipitation in the present day, the Little Ice Age (LIA) and the Medieval Warm Period (MWP); and explored their links with solar irradiance and global climate change. The results indicate that over the last 150 years, the EASM circulation and precipitation, indicated by the temperature contrast between the East Asian mainland and adjacent oceans, had a significant decadal perturbation and have been weaker during the period of rapid global warming over the past 50 years. On the centennial time scale, the EASM in the MWP was strongest over the past 1000 years. Over the past 1000 years, the EASM was weakest in 1450–1570. When the EASM circulation was weaker, the monsoon rain belt over eastern China was generally located more southward, with there being less precipitation in North China and more precipitation in the Yangtze River valley; therefore, there was an anomalous pattern of southern flood/northern drought. From the 1900s to 1920s, precipitation had a pattern opposite to that of the southern flood/northern drought, with there being less precipitation in the Yangtze River valley and more precipitation in North China. Compared with the case for the MWP, there was a longer-time-scale southern flood/northern drought phenomenon in 1400–1600. Moreover, the EASM circulation and precipitation did not synchronously vary with the trend of global temperature. During the last 150 years, although the annual mean surface temperature around the world and in China has increased, the EASM circulation and precipitation did not have strengthening or weakening trends. Over the past 1000 years, the weakest EASM occurred ahead of the lowest Northern Hemispheric temperature and corresponded to the weakest solar irradiance.

Regionalization of Present-Day Precipitation in the Greater Monsoon Region of Asia*

Abstract The spatial domain of the Asian monsoon has been defined by the intensity, seasonal concentration, and annual range of precipitation. Monsoon subdomains, such as the Indian monsoon, East Asian monsoon, and western North Pacific monsoon, have also been identified based on seasonal wind reversals as well as the timing and source of monsoon moisture. However, precipitation across the Asian monsoon region is heterogeneous and spatially complex and may have influences farther north than commonly assumed, particularly if scientists consider records of past variability spanning the current interglacial period. This paper presents an additional means of identifying the Asian monsoon domain and monsoon subsystems using an empirical orthogonal function (EOF)-based regionalization of gridded precipitation values. Regions of unique precipitation variability for the Asian monsoon region are determined using monthly precipitation anomalies from the Climate Prediction Center Merged Analysis of Precipitation (CMAP) gridded precipitation dataset from 1979 to 2009. From these regions, an area of Asian monsoon influence extending from the Arabian Sea eastward to the western North Pacific Ocean is defined, similar to other studies. One key difference is that this region of monsoon influence penetrates farther north into the Tibetan Plateau and northern China. Thus, paleoclimate observations of wetter conditions in these northern arid regions may suggest an intensification of monsoon moisture, rather than a northward shift in the boundary of the monsoon. In contrast, the Arabian Peninsula, largely removed from monsoon precipitation today, likely saw a shift of monsoon influence inland earlier in the Holocene. Also identified are different subdomains of distinct precipitation variability in southeastern Asia, the western North Pacific, and the East Asian monsoon region of northeastern China that agree with previous studies. Not identified in the paper is a single Indian summer monsoon region. Instead, the Arabian Sea was found to have unique precipitation variability relative to the Indian subcontinent. Summers with enhanced precipitation over the Arabian Sea coincide with decreased summer precipitation in the western North Pacific. This relationship is likely a result of the El Niño–Southern Oscillation (ENSO)-induced development of the Philippine Sea anticyclone. Local and remote sea surface temperatures were generally found to covary with regional precipitation, but not all regions respond similarly to the remote climate variability associated with ENSO. There is some evidence that the EOF-defined regions were stable … through the Holocene, although additional regionalization analyses of paleorecords and model simulations of past precipitation variability are needed to reconstruct past regions of coherent precipitation variability.

The tropospheric biennial oscillation in the East Asian monsoon region and its influence on the precipitation in China and large‐scale atmospheric circulation in East Asia

AbstractThe precipitation in China manifests a remarkable quasi‐biennial signal. For interannual variability, about 70% stations over China indicate the dominance of a quasi‐2‐year period. The maximum precipitation variability associated with the quasi‐biennial oscillation is located over the Yangtze River valley (YRV) and Huaihe River valley (HRV) as well as South China. This paper attempts to reveal the spatial–temporal evolution of the precipitation in China and related large‐scale atmospheric circulation associated with the tropospheric biennial oscillation (TBO) in East Asia by using a season‐dependent empirical orthogonal function (S‐EOF) analysis approach.The leading two modes of the TBO of summer precipitation in China and associated large‐scale circulations are examined by the S‐EOF analysis and regression analyses based on the S‐EOF time coefficients. The first TBO mode is characterized by an elongated band of positive precipitation anomalies along the YRV and negative precipitation anomalies over both North and South China. The second TBO mode is characterized by an elongated band of positive precipitation anomalies along the HRV and negative precipitation anomalies to the north of the Yellow River and to the south of the Yangtze River, respectively. Meanwhile, the leading modes of the TBO in East Asia may be determined by the meridional teleconnection Rossby wave pattern extending from the WNP to the midlatitudes of East Asia that is forced by the heating source fluctuation over the WNP during boreal summer. And the cold air activity, which is associated with the East Asian winter monsoon, may further influence the leading modes of the TBO through a modulation of the large‐scale atmosphere circulation over East Asia during the following boreal summer.Also found is that the TBO in East Aisa depends on both the large‐scale air–sea coupling over the tropical Indo‐Pacific Ocean regions and the tropical–midlatitude interaction in the western North Pacific (WNP)‐East Asia region. A fundamental element for the TBO in East Asia is the WNP monsoon. It is not only an important component of the TBO cycle in the tropics but also serves as a major source of the TBO signal for the subtropical East Asia. The meridional teleconnection Rossby wave train over the WNP‐East Asia region acts as a conveyer belt that transports the tropical TBO signal to the midlatitudes of East Asia, and produces the TBO footprints in the large‐scale circulation and precipitation in East Asia. Furthermore, the cold air activity over the East Asia during boreal summer also services as an important link in the chain events of the tropical–midlatitude interaction, with enhancing the role of the TBO modes in East Asia. Copyright © 2011 Royal Meteorological Society

Simulation of direct radiative forcing of aerosols and their effects on East Asian climate using an interactive AGCM-aerosol coupled system

An interactive system coupling the Beijing Climate Center atmospheric general circulation model (BCC_AGCM2.0.1) and the Canadian Aerosol Module (CAM) with updated aerosol emission sources was developed to investigate the global distributions of optical properties and direct radiative forcing (DRF) of typical aerosols and their impacts on East Asian climate. The simulated total aerosol optical depth (AOD), single scattering albedo, and asymmetry parameter were generally consistent with the ground-based measurements. Under all-sky conditions, the simulated global annual mean DRF at the top of the atmosphere was −2.03 W m−2 for all aerosols including sulfate, organic carbon (OC), black carbon (BC), dust, and sea salt; the global annual mean DRF was −0.23 W m−2 for sulfate, BC, and OC aerosols. The sulfate, BC, and OC aerosols led to decreases of 0.58° and 0.14 mm day−1 in the JJA means of surface temperature and precipitation rate in East Asia. The differences of land-sea surface temperature and surface pressure were reduced in East Asian monsoon region due to these aerosols, thus leading to the weakening of East Asian summer monsoon. Atmospheric dynamic and thermodynamic were affected due to the three types of aerosol, and the southward motion between 15°N and 30°N in lower troposphere was increased, which slowed down the northward transport of moist air carried by the East Asian summer monsoon, and moreover decreased the summer monsoon precipitation in south and east China.

The relationship between June precipitation over mid-lower reaches of the Yangtze River basin and spring soil moisture over the East Asian monsoon region

Using the US Climate Prediction Center (CPC) soil moisture dataset and the observed precipitation over China together with the NCEP/NCAR reanalysis wind and air temperature, the relationship between June precipitation over mid-lower reaches of the Yangtze River basin (MLR-YRB) and spring soil moisture over the East Asian monsoon region was explored, with the signal of the ENSO effect on precipitation removed. A significant positive correlation was found between the mean June precipitation and the preceding soil moisture over the MRL-YRB. The possible response mechanism for this relationship was also investigated. It is found that when the soil over the MRL-YRB is wetter (drier) than normal in April and May, the air temperature in the lower troposphere over this region in May is lower (higher) than normal, and this temperature effect leads to a decrease (increase) in the temperature contrast between the land and the sea. Generally, a decrease (increase) in the land-sea temperature contrast leads to weaker (stronger) East Asian summer monsoon in June. Southerly (northerly) wind anomalies at 850 hPa then show up in the south of the Yangtze River basin while northerly (southerly) wind anomalies dominate in the north. These anomalies lead to the convergence (divergence) of wind and water vapor and hence gives rise to more (less) precipitation in June over the MLR-YRB.

High-resolution climate change in mid-late Holocene on Tianchi Lake, Liupan Mountain in the Loess Plateau in central China and its significance

Tianchi Lake, Liupan Mountain in Loess Plateau sediment, fossil pollen assemblages, magnetic susceptibility (MS) and color scale were measured based on reliable Abies leaf macrofossils radiocarbon chronology. We recovered a very good high-resolution mid-late Holocene climate change achieve for the transition area of the East Asia monsoon region and northwest arid region. The results show that the basic climate background was in agreement with the records from cave records in monsoon regions in eastern China. Besides, it shows more detailed records in abrupt climate change.

A study of the impact of climate change on local precipitation using statistical downscaling

This study investigates the potential of projecting regional precipitation over Yunlin County using a singular‐value‐decomposition (SVD) based statistical downscaling scheme to cope with climate change; the change rate of local precipitation and its connection with the variability of large‐scale circulation are also discussed. It is found that rainfall over Yunlin County is closely tied to the large‐scale circulation over the East Asian monsoon region, and that general circulation models (GCMs) perform reasonably in simulating the mean states of sea level pressure (SLP) and meridional wind field at 850 hPa (V850) over this region. Consequently, the two large‐scale variables, SLP and V850, both of which are taken from seven GCMs involving the 20C3M, A1B, and B1 scenarios, are used as predictors for downscaling. The result shows that the downscaling schemes based on these predictors show a skillful and stable performance in reproducing historical seasonal rainfall anomalies over Yunlin County, especially when the strategies of using two predictors and multiple model ensemble (MME) are considered. It also shows that comparing the mean states of 20C3M‐downscaled and scenario‐projected seasonal local rainfall in the coming 36 years with respect to the period of 1975–2000 reveals a suppressive pattern in the wet season and an increasing pattern in the dry season; the finding may be associated with the strength of large‐scale circulation under different scenarios. Overall, this study demonstrates that useful information concerning the impact of climate change on regional precipitation can be obtained by downscaling schemes using outputs of GCMs as predictors.

A warming interval during the MIS 5a/4 transition in two high-resolution loess sections from China

An abrupt climatic change during the MIS 5a/4 transition is evident in the loess records of China (S1/L1). Proxies including geochemical elements, grain size, soil color, magnetic susceptibility and carbonate (CaCO3) content indicate a warming interval, which lasted approximately 3 ka, during the MIS 5a/4 transition in both the Wangguan and Shagou loess sections, located in Sanmenxia (Henan Province) and Wuwei (Gansu Province), respectively. Both the winter and summer monsoon proxies demonstrate that this warming interval occurred at the same time in both sections (nearly 70.5–73.6 ka BP), with maximum warming from 71.4 to 72.0 ka BP. This study suggests a universal abrupt warming interval in the East Asia monsoon region at this time. Comparisons with marine, terrestrial and ice-core records indicate this event was very likely an abrupt global warming interval during the last glacial–interglacial transition.

Interdecadal variability of East Asian summer monsoon precipitation over 220 years (1777–1997)

In this study, long-term (1777–1997) precipitation data for Seoul, Korea, wetness indices from eastern China, and modern observations are used to identify the interdecadal variability in East Asian summer monsoon precipitation over the last 220 years. In the East Asian monsoon region, two long-term timescales of dry-wet transitions for the interdecadal variability and quasi-40- and quasi-60-year timescales are dominant in the 220-year precipitation data of Seoul, as well as in the wetness indices over China. The wet and dry spells between Seoul (southern China) and northern China are out-of-phase (out-of-phase) at the quasi-60-year timescale, and in-phase (out-of-phase by approximately 90° before 1900 and in-phase after 1900) at the quasi-40-year timescale. In particular, during the last century, the dominant long-term timescales over East Asia tend to decrease from the quasi-60-year to the quasi-40-year with increasing time. The dominant quasi-40-year and quasi-60-year timescales of the Seoul precipitation in Korea are strongly correlated with these timescales of the northern Pacific Ocean.

Colder Subarctic Pacific with larger sea ice caused by closure of the Central American Seaway and its influence on the East Asian monsoon: a climate model study

Abstract The changes in the sea-ice conditions and sea surface temperatures in the Subarctic Pacific caused by the closure of the Central American Seaway and their influence on the East Asian monsoon are investigated by a series of closed (CE), open (OE) and re-closed (RCE) seaway experiments with a climate model. It is found that a permanent halocline forms in the Subarctic Pacific because of the termination of saline water transport through the seaway in CE and RCE. Efficient cooling by shallow convection in the stratified permanent halocline causes thicker and more extensive sea ice in winter, and leads to colder surface water in summer in the Subarctic Pacific. Colder air, over more extensive sea ice cover in winter and over the colder water in summer, produces higher surface air pressure with anticyclonic wind anomalies in both seasons. Southeasterly and southerly wind anomalies develop around the Japanese archipelago in the East Asian monsoon region and induce warm and humid surface air with increased precipitation over the East Asian continent. These results indicate that the East Asian monsoon is weakened in winter and strengthened in summer as a result of closing the Central American Seaway.

How Much Do Tropical Cyclones Affect Seasonal and Interannual Rainfall Variability over the Western North Pacific?

Abstract The authors investigate the effects of tropical cyclones (TCs) on seasonal and interannual rainfall variability over the western North Pacific (WNP) by using rainfall data at 22 stations. The TC-induced rainfall at each station is estimated by using station data when a TC is located within the influential radius (1000 km) from the station. The spatial–temporal variability of the proportion of TC rainfall is examined primarily along the east–west island chain near 10°N (between 7° and 13°N) and the north–south island chain near 125°E (between 120° and 130°E). Along 10°N the seasonality of total rainfall is mainly determined by non-TC rainfall that is influenced by the WNP monsoon trough. The proportion of the TC rain is relatively low. During the high TC season from July to December, TC rainfall accounts for 30% of the total rainfall in Guam, 15%–23% in Koror and Yap, and less than 10% at other stations. In contrast, along 125°E where the WNP subtropical high is located, the TC rainfall accounts for 50%–60% of the total rainfall between 18° and 26°N during the peak TC season from July to October. In Hualien of Taiwan, TC rainfall exceeds 60% of the total rainfall. The interannual variability of the TC rainfall and total rainfall is primarily modulated by El Niño–Southern Oscillation (ENSO). Along 10°N, the ratio of TC rainfall versus total rainfall is higher than the climatology during developing and mature phases of El Niño (from March to the following January), whereas the ratio is below the climatology during the decaying phase of El Niño. The opposite is true for La Niña, except that the impact of La Niña is shorter in duration. Furthermore, in summer of El Niño developing years, the total seasonal rainfall increases primarily because of the increase of TC rainfall. In the ensuing autumn, an anticyclonic anomaly develops over the Philippine Sea and TC rainfall shifts eastward; as a result, the total rainfall over the Philippines and Taiwan decreases. The total rainfall to the east of 140°E, however, changes little, because the westward passage of TCs enhances TC rainfall, which offsets the decrease of non-TC rainfall. Along the meridional island chain between 120° and 130°E, the total rainfall anomaly is affected by ENSO starting from the autumn to the following spring, and the variation in TC rainfall dominates the total rainfall variation only in autumn (August–November) of ENSO years. The results from this study suggest that in the tropical WNP and subtropical East Asian monsoon regions (east of 120°E), the seasonal and interannual variations of rainfall are controlled by changes in nonlocal circulations. These changes outside the monsoon domain may substantially affect summer monsoon rainfall by changing TC genesis and tracks.

Empirical evidence of monsoon influences on Asian Lakes

Limited information is available on how the Asian monsoon influences contemporary lake processes, seasonal patterns and interannual variation. Data sets from Nepal (Indian monsoon region) and South Korea (East Asian monsoon region) along with published literature show a wide range in the response of Asian lakes to the seasonal monsoon. Cross-system patterns show nutrients and algal biomass peak in most lakes in response to monsoon inflow, which suggests nonpoint sources dominate external loading. This seasonal increase may be the general phenological model for nutrients and phytoplankton in lakes in monsoon regions. Major ions show dilution by surface runoff during the monsoon and post-monsoon increases. Dilution of nutrients in fertile systems during the monsoon suggests point source inputs dominate peak loads during the non-monsoon period. Peak monsoon runoff can enter the water column of large stratified lakes as a density-dependent interflow at depth in the water column with little direct influence on the mixed layer. In these water bodies nutrients in surface water can be lower during strong monsoon seasons because of sub-surface loading. Short-interval data from individual lakes show the linkage between nutrients and phytoplankton biomass can be uncoupled by physical processes and light limitation, resulting in considerable temporal variation. Collectively these mixed responses limit our ability to generalize patterns or predict conditions in individual lakes during the monsoon.

Record of environmental change by α-cellulose δ 13C of sphagnum peat at Shennongjia, 4000–1000 aBP

The Dajiuhu Basin at Shennongjia, located within typical East Asian Monsoon region, preserves a sub-alpine sphagnum peat deposition in its central area. The topmost 120 cm of the peat covers the last 4000 years according to AMS 14C dating of pollen concentration. Carbon isotope of α-cellulose, extracted from sphagnum peat, provides a quantitative reconstruction of atmospheric relative humidity, based on transfer functions of C3 plants carbon isotopic fractionation equation and the bryophyte photosynthesis CO2 absorption rate equation. δ13C, TOC and C/N variations reveal that the Dajiuhu area has experienced a long-term tendency to dry during 4000–1000 aBP, with a major transition happening around 3000 aBP. Four relative dry events are identified at 3400–3200, 3000–2600, 2200–2000 and 1600–1400 aBP, respectively, corresponding to those climate events documented in many global records. Three periodicities, 664 a, 302 a and 277 a enclosed in the atmospheric humidity of Dajiuhu are correlated to the cycles of solar activities. The weakening of East Asia summer monsoon during this period registered in the Dajiuhu peat is consistent with the synchronous weakening of Indian Monsoon. This trend may be attributed to gradual decrease of Northern Hemispheric summer solar insolation and the consequently southward migration of Intertropical Convergent Zone (ITCZ).

Anomalous Propagation of the Quasi-stationary Planetary Waves in the Atmosphere and Its Roles in the Impact of the Stratosphere on the East Asian Winter Climate

East Asian monsoon region is influenced by both the vast ocean and continent in the world.Strong disturbances with planetary scale are forced by this thermal contrast between ocean and continent and the topography of Tibetan Plateau.And these planetary scale disturbances are quasi-stationary.By using the reanalysis dataset the influences of anomalous planetary wave activities on the East Asian winter climate are studied mainly on the interannual and intraseasonal timescales.On the interannual timescale,two waveguides of planetary waves in the northern winter have anti-phase oscillation.On the one hand,this interannual oscillation has an interaction with the Northern Annular Mode.On the other hand,it exerts influence on the climate anomalies over East Asia.During the strong low-latitude waveguide winters,the Siberian high tends to wea and the temperature tends to increase over Northeast China and North China.The situation tends to be reverse during the weak low-latitude waveguide winters.The results also indicate that the relationship between the planetary wave activity and the East Asian winter climate on interannual timescale is strongly modulated by the tropical quasi-biennial oscillation(QBO) of zonal wind in the stratosphere.Only in the QBO easterly phase,the interannual oscillation of planetary wave propagation is closely related to the climate anomalies over East Asia.On the intraseasonal timescale,the variability in the quasi-stationary planetary wave activity is closely associated with the low frequency variation of stratospheric polar vortex.The results indicate that the anomalous polar vortex in the stratosphere may have a downward influence on the short-term climate in the troposphere via the interaction with the planetary waves.This downward propagation of stratospheric anomalies associated with polar vortex has an evident influence on the general circulation in the troposphere,and the influence is particularly significant over East Asia.Since the stratospheric variability generally has longer timescales and this downward propagation leads the variations in the troposphere,our research provides a new predictor for the East Asian winter short-term climate anomalies.

Quartz OSL dating of sand dunes of Late Pleistocene in the Mu Us Desert in northern China

The Mu Us Desert, located in the northwestern fringe of the East Asian monsoon region, is sensitive to climate variability. The desert is characterized by mobile, semi-fixed and fixed sand dunes. Alternating units of dune sands and sandy palaeosols in the Mu Us Desert imply multiple episodes of dune building and stabilization, in response to the ebb and flow of the East Asian monsoon. Desert evolution and climatic change of high-resolution in the Mu Us Desert are still poorly understood due to limited numerical dating results. In the present study, 19 samples collected from five sand dune sections along a northwest–southeast transect in the Mu Us Desert were dated using quartz optically stimulated luminescence (OSL) and single aliquot regenerative-dose (SAR) protocol. Internal checks of the OSL dating indicate that the SAR protocol is appropriate for equivalent dose ( D e) determination for the samples under study. Combined with the lithologic stratigraphy and the luminescence chronology, the sand dune development in the Mu Us Desert during the Late Pleistocene is discussed. Our results indicate that the sand was mobilized approximately at 91 ka, 71 ka, 48–22 ka, 5 ka, 1 ka, and 0.44 ka; the sand was fixed approximately at 65 ka and Holocene Optimum period in the interior Mu Us Desert. The Mu Us Desert formed at least before ∼144 ka, and has shown increasing aridity in the Late Pleistocene.

Intercomparison of the summertime subtropical high from the ERA-40 and NCEP/NCAR reanalysis over East Eurasia and the western North Pacific

An intercomparison of summertime (JJA) subtropical geopotential heights from the ERA-40 and NCEP/NCAR reanalysis is specifically conducted over East Eurasia and the western North Pacific. The NCEP/NCAR is obviously lower than the ERA-40 in the mid-to-lower troposphere in most regions of East Eurasia before the mid-1970s, but becomes higher than the ERA-40 after the mid-1970s and thus demonstrates stronger increased trends during the period of 1958–2001. Both reanalyses are lower than the observations in most regions of China. The NCEP/NCAR especially shows tremendously systematic lower values before the mid-1960s and displays abrupt changes before the 1970s. Several indices of the western North Pacific subtropical high (WNPSH), calculated from both reanalyzed summer geopotential heights, also reveal that the variation trend of the NCEP/NCAR is stronger than that of the ERA-40 in the mid-to-lower troposphere from 1958 to 2001. Through singular value decomposition (SVD) analysis, the summer geopotential heights at 500 hPa from the ERA-40 are better than the NCEP/NCAR counterparts at interacting with the precipitation over the East Asian monsoon region. The results indicate that the NCEP/NCAR in the mid-and-lower troposphere may overestimate interdecadal changes and should be used cautiously to study the relationship between the WNPSH and precipitation ove ther East Asia Monsoon region before the mid-1970s.

On the atmospheric dynamical responses to land-use change in East Asian monsoon region

This study aims at (1) exploring dominant atmospheric dynamical processes which are responsible for climate model-simulated land-use impacts on Asian monsoon; and (2) assessing uncertainty in such model simulations due to their skills in simulating detailed monsoon circulations in the region. Firstly, results from a series of the Australian Bureau of Meteorology Research Centre (BMRC) global model simulations of land-use vegetation changes (LUC) in China are analysed. The model showed consistent signals of changes in atmospheric low-level vertical profile and regional circulations responding to LUC. In northern winter, the model-simulated rainfall reduction and surface cooling are associated with an enhanced southward penetration of dry and cold air mass, which impedes warm and humid air reaching the region for generating cold-front rainfall. In its summer, an enhanced cyclonic circulation responding to LUC further blocks the northeast penetration of southwestly summer monsoon flow into the region and results in rainfall decreases and a surface warming. Secondly, we have explored uncertainties in the proposed mechanism operating in the global model. By comparing its results with a set of high-resolution regional model simulations using the same vegetation datasets, it reveals similar changes in winter rainfall but opposite features in summer rainfall responses. In the global model, there is a cyclonic low-level circulation pattern over the South China Sea and adjacent region, an unsatisfactory feature commonly seen in other global climate models. With the reduction in surface roughness following LUC, such a deficiency becomes more prominent which further results in a weakened south/southwestly summer monsoon flow and rainfall reduction. In contrast, in the regional model, its southwestly summer monsoon flow is further enhanced due to the same process as reduced surface roughness. The enhanced monsoon flow further pushes the East Asian monsoon rainfall belt more northward and increases summer rainfall in the Yangtze River region. This study highlights the need for better monsoon simulations in climate models to produce reliable climate change projections in the region.

Statistical downscaling for multi-model ensemble prediction of summer monsoon rainfall in the Asia-Pacific region using geopotential height field

The 21-yr ensemble predictions of model precipitation and circulation in the East Asian and western North Pacific (Asia-Pacific) summer monsoon region (0°–50°N, 100°–150°E) were evaluated in nine different AGCM, used in the Asia-Pacific Economic Cooperation Climate Center (APCC) multi-model ensemble seasonal prediction system. The analysis indicates that the precipitation anomaly patterns of model ensemble predictions are substantially different from the observed counterparts in this region, but the summer monsoon circulations are reasonably predicted. For example, all models can well produce the interannual variability of the western North Pacific monsoon index (WNPMI) defined by 850 hPa winds, but they failed to predict the relationship between WNPMI and precipitation anomalies. The interannual variability of the 500 hPa geopotential height (GPH) can be well predicted by the models in contrast to precipitation anomalies. On the basis of such model performances and the relationship between the interannual variations of 500 hPa GPH and precipitation anomalies, we developed a statistical scheme used to downscale the summer monsoon precipitation anomaly on the basis of EOF and singular value decomposition (SVD). In this scheme, the three leading EOF modes of 500 hPa GPH anomaly fields predicted by the models are firstly corrected by the linear regression between the principal components in each model and observation, respectively. Then, the corrected model GPH is chosen as the predictor to downscale the precipitation anomaly field, which is assembled by the forecasted expansion coefficients of model 500 hPa GPH and the three leading SVD modes of observed precipitation anomaly corresponding to the prediction of model 500 hPa GPH during a 19-year training period. The cross-validated forecasts suggest that this downscaling scheme may have a potential to improve the forecast skill of the precipitation anomaly in the South China Sea, western North Pacific and the East Asia Pacific regions, where the anomaly correlation coefficient (ACC) has been improved by 0.14, corresponding to the reduced RMSE of 10.4% in the conventional multi-model ensemble (MME) forecast.

High-resolution geochemistry records of climate changes since late-glacial from Dajiuhu peat in Shennongjia Mountains, Central China

A peat core with depths of 297 cm was obtained from the Dajiuhu Basin (31°29′27″N, 109°59′45″E, 1760 m) in Hubei Province, Central China. 10 AMS ages provide a time control and reveal that this core spans the past about 16.0 kaBP (calibrated age) (14C age: 13.3 kaBP). Multi-proxy indexes analysis of geochemistry shows the following character of climate and environmental changes since about 16 kaBP: (1) The climate during the late-glacial period was cold and wet as a whole, but fluctuated continually. 11.4–12.6 cal. kaBP, 12.6–15.2 cal. kaBP and 15.2–16 kaBP were corresponding respectively to the Younger Drays, Bolling-Allerod Warm Period and the Oldest Drays. (2) Inheriting the some climate characteristics of the late-glacial, the climate during the early-Holocene was wet and temperature increased gradually, during which an obvious dry event around 10.6 cal. kaB appeared. (3) The climate during the mid-Holocene was genarally warm and wet.During 9.2–7.5 kaBP, temperature increased gradually, precipitation was less comparatively and the 8.2 kaBP cold event which might be representative in the globe was reflected markedly. Then, multi-proxy records were relatively stable during 6.7–4.2 kaBP, which shows the best water and thermal condition in the Holocene Optimum. (4) Around 4.2 kaBP, the climate and environment transform from warm and wet to cool and dry, which may result in the collapse of the Neolithic Culture and midwifery the civilization of Xia Dynasty in this region. After 0.9 kaBP, the climate turned cool and wet. Climate and environmental changes archived in Dajiuhu peat respond to the global changes since the late-glacial period and can be contrasted to the changes recorded in other high-resolution archives from the East Asia Monsoon region, which take on the variety model that the monsoon strengthened abruptly after the late-glacial, was strong during the early Holocene, subsequently declined and became weak after the middle Holocene with dry climate. According to our analysis, the driving mechanism should be the response of solar radiation changes in the East Asia Monsoon region at middle latitudes.

The SST‐forced predictability of the sub‐seasonal mode over East Asia with an atmospheric general circulation model

AbstractThe sea surface temperature (SST)‐forced predictability in precipitation is investigated in terms of the seasonal mean modes (SMMs) for June–July (JJ) and the sub‐seasonal mode (SSM) using the 24‐year six‐member ensembles simulation with an atmospheric general circulation model (AGCM). The SSM was defined as a 20‐day window length by an extended empirical orthogonal function (EOF) over the East Asian monsoon region. For the JJ mean rainfall, the first EOF of the model ensemble is considered to be the forced SST mode, with being an El Niño Southern Oscillation (ENSO) related pattern from the regressed SST field. The first mode of model was well correlated with the second mode of the observation in the spatial and temporal variation.In the potential predictability, the analysis of variance (ANOVA) was used for the mean mode and the SSM. The potential predictability for the SMM is improved over the north of the 30°N. Compared with JJ mean mode, the SSM has more SST‐forced variance and less internal variability. Copyright © 2008 Royal Meteorological Society