Using a low-order spectral model derived from the equatorial equilibrium model, possible physical mechanisms are interpreted by the theory of multiple equilibria states for the active and break phases of the South Asi...Using a low-order spectral model derived from the equatorial equilibrium model, possible physical mechanisms are interpreted by the theory of multiple equilibria states for the active and break phases of the South Asian Monsoon, with consideration of the effects of heating by cumulus heating and cooling by radiation. The result shows that the South Asian Monsoon is active when the cumulus convection intensifies (or the radiation cooling weakens). the monsoon breaks when the convection weakens (or the cooling intensifies). It is consistent with the hypothesis of cloud-radiation by Krishnamurti et al.展开更多
The future changes in the relationship between the South Asian summer monsoon(SASM)and the East Asian summer monsoon(EASM)are investigated by using the high-emissions Shared Socioeconomic Pathway 5-8.5(SSP5-8.5)experi...The future changes in the relationship between the South Asian summer monsoon(SASM)and the East Asian summer monsoon(EASM)are investigated by using the high-emissions Shared Socioeconomic Pathway 5-8.5(SSP5-8.5)experiments from 26 coupled models that participated in the phase 6 of the Coupled Model Intercomparison Project(CMIP6).Six models,selected based on their best performance in simulating the upper-and lower-level pathways related to the SASM-EASM teleconnection in the historical run,can capture the positive relationship between the SASM and the rainfall over northern China.In the future scenario,the upper-level teleconnection wave pattern connecting the SASM and the EASM exhibits a significant weakening trend,due to the rainfall anomalies decrease over the northern Indian Peninsula in the future.At the lower level,the western North Pacific anticyclone is projected to strengthen in the warming climate.The positive(negative)rainfall anomalies associated with positive(negative)SASM rainfall anomalies are anticipated to extend southward from northern China to the Yangtze-Huai River valley,the Korea Peninsula,and southern Japan.The connection in the lower-level pathway may be strengthened in the future.展开更多
The long-term trend of the Arabian Sea surface temperature(ASST)during the formation of the South Asian summer monsoon(SASM)is discussed in this manuscript.From April to June,ASST changed from a meridional gradual dis...The long-term trend of the Arabian Sea surface temperature(ASST)during the formation of the South Asian summer monsoon(SASM)is discussed in this manuscript.From April to June,ASST changed from a meridional gradual distribution to a spatially uniform distribution and then to a zonal gradual distribution.The South Asian summer monsoon intensity(SASMI)and South Asian summer monsoon direction(SASMD)indicate that the variation of the ASST is highly related to the formation of the SASM during the summer monsoon period and can contribute to the spread of the SASM from the Southwest Arabian Sea throughout all of South Asia.Results of the correlation between the ASST and SASMI for the same month and its adjacent months were the same,and the areas of the positive correlation between the ASST and SASMI significantly increased from May–June as compared to April–May.The maximum correlation coefficient was 0.86.The results of the ASST and SASMD for the same month and its adjacent months were substantially different.However,the ASST and SASMD for May and April also showed a high positive correlation with a maximum correlation coefficient of 0.61 in the southwestern Arabian Sea.Existence of the ASST had a spatially consistent and significant upward trend with a mean increase of 0.6℃during the summer monsoon period from 1980 to 2020(between April and September),whereas the SASMI had a strengthening trend along the western and southwestern regions of the Arabian Sea and the southeastern region of the Arabian Peninsula.Meanwhile,the rest of the study regions showed a declining trend.Overall,the entire study region showed a slight downward trend,and the average value decreased by 0.02ms^(−1).展开更多
The e?ect of anomalous snow cover over the Tibetan Plateau upon the South Asian summer monsoon is investigated by numerical simulations using the NCAR regional climate model (RegCM2) into which gravity wave ...The e?ect of anomalous snow cover over the Tibetan Plateau upon the South Asian summer monsoon is investigated by numerical simulations using the NCAR regional climate model (RegCM2) into which gravity wave drag has been introduced. The simulations adopt relatively realistic snow mass forcings based on Scanning Multi-channel Microwave Radiometer (SMMR) pentad snow depth data. The physical mechanism and spatial structure of the sensitivity of the South Asian early summer monsoon to snow cover anomaly over the Tibetan Plateau are revealed. The main results are summarized as follows. The heavier than normal snow cover over the Plateau can obviously reduce the shortwave radiation absorbed by surface through the albedo e?ect, which is compensated by weaker upward sensible heat ?ux associated with colder surface temperature, whereas the e?ects of snow melting and evaporation are relatively smaller. The anomalies of surface heat ?uxes can last until June and become unobvious in July. The decrease of the Plateau surface temperature caused by heavier snow cover reaches its maximum value from late April to early May. The atmospheric cooling in the mid-upper troposphere over the Plateau and its surrounding areas is most obvious in May and can keep a fairly strong intensity in June. In contrast, there is warming to the south of the Plateau in the mid-lower troposphere from April to June with a maximum value in May. The heavier snow cover over the Plateau can reduce the intensity of the South Asian summer monsoon and rainfall to some extent, but this in?uence is only obvious in early summer and almost disappears in later stages.展开更多
High-resolution pollen records from 6 small lakes in the Tibetan Plateau provided the details of evolution of South Asian monsoon since the Last Glacial Maximum. Prior to 16 kaBP, the region was a desert-steppe charac...High-resolution pollen records from 6 small lakes in the Tibetan Plateau provided the details of evolution of South Asian monsoon since the Last Glacial Maximum. Prior to 16 kaBP, the region was a desert-steppe characterized by cold and dry climates, the January temperature was 7 -10℃lower than that of present and the annual precipitation only accounted for 40% of the present. The temperature and precipitation increased gradually and trees began to live in the region after 12 kaBP, but during the interval from 9.2 to 6.3 kaBP, forest and forest-meadow appeared occasionally. From 8 to 5 kaBP, both January and July temperature was 2-3℃ higher and annual precipitation was also about 200 mm higher than that of the present. After 5 kaBP, temperature and precipitation decreased linearly and steppe vegetation began to degenerate.展开更多
In this paper, results from a pilot study for the South China Sea Monsoon Experiment are reported. Based on analyses of 9 years of pentad and monthly mean data, the climatology of subseasonal features and interannual ...In this paper, results from a pilot study for the South China Sea Monsoon Experiment are reported. Based on analyses of 9 years of pentad and monthly mean data, the climatology of subseasonal features and interannual variability of the Southeast Asian monsoon (SEAM) are documented. The present analysis is focused on the sudden onset of the South China Sea monsoon and its relation to the atmospheric and oceanic processes on the entire Asian monsoon region. \ \ It is found that the onset of the SEAM occurs around mid-May, signaling the earliest stage of the entire Asian summer monsoon system. The establishment of monsoon rainfall over the South China Sea is abrupt, being accompanied by substantial changes in the large scale atmospheric circulation and sea surface temperature in the adjacent oceans. The onset and fluctuations of SEAM involve the interaction and metamorphosis of the large scale convection over the Indo-China, the South China Sea and the southern Bay of Bengal. Results show that the onset time of the SEAM differs greatly from one year to another. The delayed (advanced) onset of the monsoon may be related to basin-wide warm (cold) events of the Pacific and Indian Oceans. We also present evidence showing that the SEAM fluctuations in May may foreshadow the development of the full-scale Asian summer monsoon during the subsequent months.展开更多
Both evolution of the Asian monsoon system and the Cenozoic global cooling are thought to be closely linked to the Himalayan—Tibetan orogen. The South China Sea (SCS) with its high sedimentation rates of carbonate\|r...Both evolution of the Asian monsoon system and the Cenozoic global cooling are thought to be closely linked to the Himalayan—Tibetan orogen. The South China Sea (SCS) with its high sedimentation rates of carbonate\|rich hemipelagic sediments offers a unique opportunity to study the variability of the East Asian monsoon, the erosion and weathering of tectonic orogens as well as its possible impact on global and regional climate.Leg 184, the first deep\|sea drilling leg to the seas off China, cored 17 holes at 6 sites in the northern and southern parts of the SCS and recovered 5463m of sediment. The drilling of hemipelagic sediments was exceptionally successful, with core recovery averaging 83%~101%. The 32Ma sequence of deep\|sea sediments recovered during Leg 184 covers almost the entire environmental history of the SCS since its opening. The abnormally high sediment accumulation rates in the Oligocene section are correlative with the incipient sea floor spreading. The bathyal nature of the Oligocenefauna implies that rifting occurred in the Eocene or earlier. Faunal changesfrom the early to late Oligocene are indicative of basin deepening, a trend thatis even more evident in the Miocene section. Sediment deformation, abruptlithologic changes, and a hiatus occur near the Oligocene/Miocene boundary,representing one of the most significant events in the tectonic andenvironmental history of the SCS.展开更多
Based on best-track,outgoing longwave radiation,sea surface temperature,and reanalysis data during 1979-2018,statistical and composite analyses were performed to investigate characteristics of the southwesterly water ...Based on best-track,outgoing longwave radiation,sea surface temperature,and reanalysis data during 1979-2018,statistical and composite analyses were performed to investigate characteristics of the southwesterly water vapor transport(WVT)induced by Bay of Bengal(BoB)tropical cyclones(TCs)during the South Asian summer monsoon(SASM)transition period.The results show that the BoB TCs mainly occur several days before/after the date of SASM onset(retreat)in May(October-November),thereby imposing an important impact on southwesterly WVT to China in those two periods.The WVT is significant in the middle and lower troposphere during the bimodal peak periods of BoB TCs,with large values over the east-central BoB,southeastern Tibetan Plateau,and Southwest and South China.The WVT is located more northward at 500 hPa than at 700 hPa,reaching close to 35°N and covering the southeastern Tibetan Plateau owing to weakening of the plateau’s blocking effect at upper levels.The BoB TCs mainly increase the northward and eastward WVT anomalies compared to the climatological mean.Furthermore,the large southerly WVT anomalies are located in the lower troposphere in low-latitude areas,while the large westerly WVT anomalies appear mainly in the middle troposphere in high-latitude areas.This indicates an enhanced WVT channel where the southwesterly moisture jet first climbs northwards to the southeastern Tibetan Plateau and then turns eastwards to East China under the influence of the BoB TCs.Besides,the southwesterly WVT during the TC period in May is stronger and more widespread than that in October-November,being about twice the latter in value.However,their maximum contributions to the climatological average do not differ much,with maximums of 12%and19%occurring in Southwest China during the bimodal periods,respectively,implying an important role played by the BoB TCs in the WVT.展开更多
This paper analyzes the differences in the characteristics and spatio–temporal variabilities of summertime rainfall and water vapor transport between the East Asian summer monsoon(EASM) and South Asian summer mons...This paper analyzes the differences in the characteristics and spatio–temporal variabilities of summertime rainfall and water vapor transport between the East Asian summer monsoon(EASM) and South Asian summer monsoon(SASM) systems. The results show obvious differences in summertime rainfall characteristics between these two monsoon systems. The summertime rainfall cloud systems of the EASM show a mixed stratiform and cumulus cloud system, while cumulus cloud dominates the SASM. These differences may be caused by differences in the vertical shear of zonal and meridional circulations and the convergence of water vapor transport fluxes. Moreover, the leading modes of the two systems' summertime rainfall anomalies also differ in terms of their spatiotemporal features on the interannual and interdecadal timescales. Nevertheless, several close links with respect to the spatiotemporal variabilities of summertime rainfall and water vapor transport exist between the two monsoon systems. The first modes of summertime rainfall in the SASM and EASM regions reveal a significant negative correlation on the interannual and the interdecadal timescales. This close relationship may be linked by a meridional teleconnection in the regressed summertime rainfall anomalies from India to North China through the southeastern part over the Tibetan Plateau, which we refer to as the South Asia/East Asia teleconnection pattern of Asian summer monsoon rainfall. The authors wish to dedicate this paper to Prof. Duzheng YE, and commemorate his 100 thanniversary and his great contributions to the development of atmospheric dynamics.展开更多
This study investigates the projected changes in interannual variability of South Asian summer monsoon and changes of ENSO–monsoon relationships in the 21st century under the Intergovernmental Panel on Climate Change...This study investigates the projected changes in interannual variability of South Asian summer monsoon and changes of ENSO–monsoon relationships in the 21st century under the Intergovernmental Panel on Climate Change (IPCC) scenarios A1B and A2, respectively, by analyzing the simulated results of twelve Coupled Model Intercomparison Project Phase 3 (CMIP3) coupled models. The dynamical monsoon index (DMI) was adopted to describe the interannual variability of South Asian summer monsoon, and the standard deviation (SD) was used to illustrate the intensity of interannual variability. It was found that most models could project enhanced interannual variability of monsoon in the 21st century. The multi-model ensemble (MME) results showed increases in the interannual variability of DMI: 14.3% and 20.0% under scenarios A1B and A2, respectively. The MME result also showed increases in the rainfall variability are of about 10.2% and 22.0% under scenarios A1B and A2. The intensification of interannual variability tended to occur over the regions that have larger variability currently; that is, "the strong get stronger". Another finding was that ENSO–monsoon relationships are likely to be enhanced in the 21st century. The dynamical component of the monsoon will be more closely correlated to ENSO in the future under global warming, although the ENSO–summer rainfall relationship cannot be reasonably projected by current models. This suggests that the South Asian summer monsoon is more predictable in the future, at least dynamically.展开更多
Clay mineral assemblages, crystallinity, chemistry, and micromorphology of clay particles in sediments from ODP Site 1146 in the northern South China Sea (SCS) were analyzed, and used to trace sediment sources and o...Clay mineral assemblages, crystallinity, chemistry, and micromorphology of clay particles in sediments from ODP Site 1146 in the northern South China Sea (SCS) were analyzed, and used to trace sediment sources and obtain proxy records of the past changes in the East Asian monsoon climate since the Miocene, based on a multi-approach, including X-ray diffraction (XRD) and scanning electron microscopy combined with energy dispersive X-ray spectrometry (SEM-EDS). Clay minerals consist mainly of illite and smectite, with associated chlorite and kaolinite. The illite at ODP Site 1146 has very well-to-well crystallinity, and smectite has moderate-to-poor crystallinity. In SEM the smectite particles at ODP Site 1146 often appear cauliflower-like, a typical micromorphology of volcanic smecites. The smectite at ODP Site 1146 is relatively rich in Si element, but poor in Fe, very similar to the smectite from the West Philippine Sea. In contrast, the chemical composition of illite at ODP Site 1146 has no obvious differences from those of the Loess plateau, Yellow River, Yangtze River, and Pearl River. A further study on sediment source indicates that smectite originates mainly from Luzon, kaolinite from the Pearl River, and illite and chlorite from the Pearl River, Taiwan and/or the Yangtze River. The clay mineral assemblages at ODP Site 1146 were not only controlled by continental eathering regimes surrounding the SCS, but also by the changing strength of the transport processes. The ratios of (illite+chlorite)/smectite at ODP Site 1146 were adopted as proxies for the East Asian monsoon evolution. Relatively higher ratios reflect strongly intensified winter monsoon relative to summer monsoon, in contrast, lower ratios indicate a strengthened summer monsoon relative to winter monsoon. The consistent variation of this clay proxy from those of Loess plateau, eolian deposition in the North Pacific, planktonic, benthic foraminifera, and black carbon in the SCS since 20 Ma shows that three profound shifts of the East Asian winter monsoon intensity, and aridity in the Asian inland and the intensity of winter monsoon relative to summer monsoon, occurred at about 15 Ma, 8 Ma, and the younger at about 3 Ma. The phased uplift of the Himalaya-Tibetan plateau may have played a significant role in strengthening the Asian monsoon at 15 Ma, 8 Ma, and 3 Ma.展开更多
Based on observational and reanalysis data,the relationships between the eastern Pacific(EP)and central Pacific(CP)types of El Niño−Southern Oscillation(ENSO)during the developing summer and the South Asian summe...Based on observational and reanalysis data,the relationships between the eastern Pacific(EP)and central Pacific(CP)types of El Niño−Southern Oscillation(ENSO)during the developing summer and the South Asian summer monsoon(SASM)are examined.The roles of these two types of ENSO on the SASM experienced notable multidecadal modulation in the late 1970s.While the inverse relationship between the EP type of ENSO and the SASM has weakened dramatically,the CP type of ENSO plays a far more prominent role in producing anomalous Indian monsoon rainfall after the late 1970s.The drought-producing El Niño warming of both the EP and CP types can excite anomalous rising motion of the Walker circulation concentrated in the equatorial central Pacific around 160°W to the date line.Accordingly,compensatory subsidence anomalies are evident from the Maritime Continent to the Indian subcontinent,leading to suppressed convection and decreased precipitation over these regions.Moreover,anomalously less moisture flux into South Asia associated with developing EP El Niño and significant northwesterly anomalies dominating over southern India accompanied by developing CP El Niño,may also have been responsible for the Indian monsoon droughts during the pre-1979 and post-1979 sub-periods,respectively.El Niño events with the same“flavor”may not necessarily produce consistent Indian monsoon rainfall anomalies,while similar Indian monsoon droughts may be induced by different types of El Niño,implying high sensitivity of monsoonal precipitation to the detailed configuration of ENSO forcing imposed on the tropical Pacific.展开更多
Based on the wavelet packet decomposition/reconstruction method and the NCEP/NCAR daily reanalysis data set, the relation between the south Asian summer monsoon and the west Pacific subtropical high seasonal variation...Based on the wavelet packet decomposition/reconstruction method and the NCEP/NCAR daily reanalysis data set, the relation between the south Asian summer monsoon and the west Pacific subtropical high seasonal variation was discussed, and a corresponding summer monsoon frequency-band energy criterion was defined and introduced for diagnosing the west Pacific subtropical high. Besides, some existing characteristics and rules about the west Pacific subtropical high were further argued and proofed, a few new phenomena and correlation between the south Asian summer monsoon and the west Pacific subtropical high were also revealed and presented.展开更多
The East Asian monsoon system influences the sedimentation and transport of organic matter in East Asian marginal seas that is derived from both terrestrial and marine sources. In this study, we determined organic car...The East Asian monsoon system influences the sedimentation and transport of organic matter in East Asian marginal seas that is derived from both terrestrial and marine sources. In this study, we determined organic carbon(OC) isotope values, concentrations of marine biomarkers, and levels of OC and total nitrogen(TN) in core YSC-1 from the central South Yellow Sea(SYS). Our objectives were to trace the sources of OC and variations in palaeoproductivity since the middle Holocene, and their relationships with the East Asian monsoon system. The relative contributions of terrestrial versus marine organic matter in core sediments were estimated using a two-end-member mixing model of OC isotopes. Results show that marine organic matter has been the main sediment constituent since the middle Holocene. The variation of terrestrial organic carbon concentration(OCter) is similar to the EASM history. However, the variation of marine organic carbon concentration(OCmar) is opposite to that of the EASM curve, suggesting OCmar is distinctly influenced by terrestrial material input. Inputs of terrestrial nutrients into the SYS occur in the form of fluvial and aeolian dust, while concentrations of nutrients in surface water are derived mainly from bottom water via the Yellow Sea circulation system, which is controlled by the East Asian winter monsoon(EAWM). Variations in palaeoproductivity represented by marine organic matter and biomarker records are, in general, consistent with the recent EAWM intensity studies, thus, compared with EASM, EAWM may play the main role to control the marine productivity variations in the SYS.展开更多
The siliciclastic sediments of the uppermost section of 185 mcd (meters composite depth) from ODP Site 1146 on the northern continental slope of the South China Sea (SCS) were partitioned according to their source...The siliciclastic sediments of the uppermost section of 185 mcd (meters composite depth) from ODP Site 1146 on the northern continental slope of the South China Sea (SCS) were partitioned according to their sources using end-member modeling on grain-size data.The goal was to evaluate the evolution of the East Asian monsoon over the past 2 million years.The siliciclastic sediments were described as hybrids of four end-members,EM1,EM2,EM3,and EM4,with modal grain sizes of 8-22 μm,2-8 μm,31-125 μm,and 4-11 μm,respectively.EM1 and EM3 are interpreted as eolian dust and EM2 and EM4 as fluvial mud.The ratio of eolian dust to fluvial mud ((EM1+EM3)/(EM2+EM4)) is regarded as an indicator of the East Asian monsoon.The variation in this ratio not only shows periodical oscillations consistent with oxygen isotope stages,but also exhibits a phased increasing trend corresponding with the phased uplifts of the Tibetan Plateau,indicating that the evolution of the East Asian Monsoon was controlled not only by glacial-interglacial cycles,but also by the phased uplifts of the Tibetan Plateau during the Quaternary.展开更多
Results of the definition of South China Sea summer monsoon onset date and East Asian summermonsoon index in recent years are summarized in this paper. And more questions to be resolved are introducedlater.
The timing of the South Asian High(SAH) establishment over the Indochina Peninsula(IP) from April to May and its relations to the setup of the subsequent tropical Asian summer monsoon and precipitation over eastern-ce...The timing of the South Asian High(SAH) establishment over the Indochina Peninsula(IP) from April to May and its relations to the setup of the subsequent tropical Asian summer monsoon and precipitation over eastern-central China in summer are investigated by using NCEP/NCAR daily reanalysis data,outgoing longwave radiation(OLR)data and the daily precipitation data from 753 weather stations in China.It is found that the transitions of the zonal wind vertical shear and convection establishment over tropical Asia are earlier(later) in the years of early(late) establishment of SAH.In the lower troposphere,anti-cyclonic(cyclonic) anomaly circulation dominates the equatorial Indian Ocean.Correspondingly,the tropical Asian summer monsoon establishes earlier(later).Furthermore,the atmospheric circulation and the water vapor transport in the years of advanced SAH establishment are significantly different from the delayed years in Asia in summer.Out-of-phase distribution of precipitation in eastern-central China will appear with a weak(strong) SAH and western Pacific subtropical high,strong(weak) ascending motion in the area south of Yangtze River but weak(strong) ascending motion in the area north of it,and cyclonic(anti-cyclonic) water vapor flux anomaly circulation from the eastern-central China to western Pacific.Accordingly,the timing of the SAH establishment at the upper levels of IP is indicative of the subsequent onset of the tropical Asian summer monsoon and the flood-drought pattern over eastern-central China in summer.展开更多
The study has shown that the shear component of the vertical integrated kinetic energy(Ks)over the box(40oE-100oE,0-20oN)can be used to measure the intensity of the South Asian summer monsoon(SASM).Based on its value ...The study has shown that the shear component of the vertical integrated kinetic energy(Ks)over the box(40oE-100oE,0-20oN)can be used to measure the intensity of the South Asian summer monsoon(SASM).Based on its value averaged between June and August,the SASM can be divided into strong and weak monsoon episodes.Between1958 and 2018,there existed 16(16)strong(weak)monsoon episodes.Based on the calendar year,the relationship between the SASM and ENSO episodes can be grouped into six patterns:weak monsoon-El Ni?o(WM-EN),normal monsoon-El Ni?o(NM-EN),weak monsoon-non ENSO(WM-NE),strong monsoon-La Ni?a(SM-LN),normal monsoon-La Ni?a(NM-LN)and strong monsoon-non ENSO(SM-NE).Previous studies suggest that the WM-EN and SM-LN patterns reflect the correlated relationship between the SASM and El Ni?o/Southern Oscillation(ENSO)events.Therefore,we name these two strongly coupled categories WM-EN and SM-LN as the resonance effect.Two important circulations,i.e.,Walker circulation(WC)and zonal Asian monsoon circulation(MC),in the vertical plane are found to be not always correlated.The MC is controlled by thermal gradients between the Asian landmass and the tropical Indian Ocean,while the WC associated with ENSO events is primarily the east-west thermal gradient between the tropical South Pacific and the tropical Indian Ocean.Furthermore,the gradient directions caused by different surface thermal conditions are different.The main factor for the resonance effect is the phenomenon that the symbols of SSTA in the tropical Indian Ocean and the equatorial eastern Pacific are the same,but are opposite to that of the SSTA near the maritime continent.展开更多
Monthly ocean temperature from ORAS4 datasets and atmospheric data from NCEP/NCAR Reanalysis I/II were used to analyze the relationship between the intensity of the South Asian summer monsoon(SASM) and upper ocean hea...Monthly ocean temperature from ORAS4 datasets and atmospheric data from NCEP/NCAR Reanalysis I/II were used to analyze the relationship between the intensity of the South Asian summer monsoon(SASM) and upper ocean heat content(HC) in the tropical Indo-Pacific Ocean.The monsoon was differentiated into a Southwest Asian Summer Monsoon(SWASM)(2.5°–20°N,35°–70°E) and Southeast Asian Summer Monsoon(SEASM)(2.5°–20°N,70°–110°E).Results show that before the 1976/77 climate shift,the SWASM was strongly related to HC in the southern Indian Ocean and tropical Pacific Ocean.The southern Indian Ocean affected SWASM by altering the pressure gradient between southern Africa and the northern Indian Ocean and by enhancing the Somali cross-equatorial flow.The tropical Pacific impacted the SWASM through the remote forcing of ENSO.After the 1976/77 shift,there was a close relationship between equatorial central Pacific HC and the SEASM.However,before that shift,their relationship was weak.展开更多
The seasonal forecasting skill with respect to the South Asian summer monsoon(SASM) was compared between the European Commission FP7 project(ENSEMBLES) and the Development of a European Multimodel Ensemble System for ...The seasonal forecasting skill with respect to the South Asian summer monsoon(SASM) was compared between the European Commission FP7 project(ENSEMBLES) and the Development of a European Multimodel Ensemble System for Seasonal to Interannual Prediction project(DEMETER). The Webster-Yang index(WYI) was chosen to represent the intensity of the SASM. First, the authors compared the ability to forecast the zonal wind at 850 h Pa(U850) and 200 h Pa(U200) between ENSEMBLES and DEMETER models. The results indicated that the models from the European Centre for Medium-Range Weather Forecasts, International Organization(ECMWF) and UK Met Office(UKMO) in ENSEMBLES possess greater skill in seasonally forecasting the JJA(June, July, and August) U850, U200, and U850 minus U200 than in DEMETER. Compared to in DEMETER, the JJA U200 and U850 minus U200 forecasting skill was greater for the model from MétéoFrance(MF) in ENSEMBLES over most of the SASM region. The three coupled models(ECMWF, MF, and UKMO), especially the UKMO model in ENSEMBLES, all demonstrated improved skill in their seasonal forecasts compared to in DEMETER with respect to the interannual variability of the SASM. The three ENSEMBLES models also showed better ability in forecasting the sea surface temperature anomalies(SSTAs) over the eastern equatorial Pacific and North Indian Ocean, and more accurately reproduced the large-scale atmospheric circulation and precipitation over northern India, which are related to the SASM. It seems that the couple between the atmospheric system and external forcing of ENSMBLES over Indian Ocean and Pacific is better than that of DEMETER.展开更多
文摘Using a low-order spectral model derived from the equatorial equilibrium model, possible physical mechanisms are interpreted by the theory of multiple equilibria states for the active and break phases of the South Asian Monsoon, with consideration of the effects of heating by cumulus heating and cooling by radiation. The result shows that the South Asian Monsoon is active when the cumulus convection intensifies (or the radiation cooling weakens). the monsoon breaks when the convection weakens (or the cooling intensifies). It is consistent with the hypothesis of cloud-radiation by Krishnamurti et al.
基金Guangdong Major Project of Basic and Applied Basic Research Foundation(2020B0301030004)National Natural Science Foundation of China(41975074)+2 种基金Guangdong Basic and Applied Basic Research Foundation(2023A1515010908)Guangdong Province Key Laboratory for Climate Change and Natural Disaster Studies(2020B1212060025)Innovation Group Project of Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai)(311021001)。
文摘The future changes in the relationship between the South Asian summer monsoon(SASM)and the East Asian summer monsoon(EASM)are investigated by using the high-emissions Shared Socioeconomic Pathway 5-8.5(SSP5-8.5)experiments from 26 coupled models that participated in the phase 6 of the Coupled Model Intercomparison Project(CMIP6).Six models,selected based on their best performance in simulating the upper-and lower-level pathways related to the SASM-EASM teleconnection in the historical run,can capture the positive relationship between the SASM and the rainfall over northern China.In the future scenario,the upper-level teleconnection wave pattern connecting the SASM and the EASM exhibits a significant weakening trend,due to the rainfall anomalies decrease over the northern Indian Peninsula in the future.At the lower level,the western North Pacific anticyclone is projected to strengthen in the warming climate.The positive(negative)rainfall anomalies associated with positive(negative)SASM rainfall anomalies are anticipated to extend southward from northern China to the Yangtze-Huai River valley,the Korea Peninsula,and southern Japan.The connection in the lower-level pathway may be strengthened in the future.
基金supported by the Global Change and Airsea Interaction Project,the Research and Development of Marine Electromagnetic Field Sensors and Demonstration of Electromagnetic Detection Applications(No.2022YFC 3104000)the Special Project.
文摘The long-term trend of the Arabian Sea surface temperature(ASST)during the formation of the South Asian summer monsoon(SASM)is discussed in this manuscript.From April to June,ASST changed from a meridional gradual distribution to a spatially uniform distribution and then to a zonal gradual distribution.The South Asian summer monsoon intensity(SASMI)and South Asian summer monsoon direction(SASMD)indicate that the variation of the ASST is highly related to the formation of the SASM during the summer monsoon period and can contribute to the spread of the SASM from the Southwest Arabian Sea throughout all of South Asia.Results of the correlation between the ASST and SASMI for the same month and its adjacent months were the same,and the areas of the positive correlation between the ASST and SASMI significantly increased from May–June as compared to April–May.The maximum correlation coefficient was 0.86.The results of the ASST and SASMD for the same month and its adjacent months were substantially different.However,the ASST and SASMD for May and April also showed a high positive correlation with a maximum correlation coefficient of 0.61 in the southwestern Arabian Sea.Existence of the ASST had a spatially consistent and significant upward trend with a mean increase of 0.6℃during the summer monsoon period from 1980 to 2020(between April and September),whereas the SASMI had a strengthening trend along the western and southwestern regions of the Arabian Sea and the southeastern region of the Arabian Peninsula.Meanwhile,the rest of the study regions showed a declining trend.Overall,the entire study region showed a slight downward trend,and the average value decreased by 0.02ms^(−1).
基金the National Natural Science foundation of China(Grant No.40375027) opening item of the Key Laboratory for Mleteorological Disasters and Environmental Change of Nanjing Institute of Mleteorology(No.K2107).
文摘The e?ect of anomalous snow cover over the Tibetan Plateau upon the South Asian summer monsoon is investigated by numerical simulations using the NCAR regional climate model (RegCM2) into which gravity wave drag has been introduced. The simulations adopt relatively realistic snow mass forcings based on Scanning Multi-channel Microwave Radiometer (SMMR) pentad snow depth data. The physical mechanism and spatial structure of the sensitivity of the South Asian early summer monsoon to snow cover anomaly over the Tibetan Plateau are revealed. The main results are summarized as follows. The heavier than normal snow cover over the Plateau can obviously reduce the shortwave radiation absorbed by surface through the albedo e?ect, which is compensated by weaker upward sensible heat ?ux associated with colder surface temperature, whereas the e?ects of snow melting and evaporation are relatively smaller. The anomalies of surface heat ?uxes can last until June and become unobvious in July. The decrease of the Plateau surface temperature caused by heavier snow cover reaches its maximum value from late April to early May. The atmospheric cooling in the mid-upper troposphere over the Plateau and its surrounding areas is most obvious in May and can keep a fairly strong intensity in June. In contrast, there is warming to the south of the Plateau in the mid-lower troposphere from April to June with a maximum value in May. The heavier snow cover over the Plateau can reduce the intensity of the South Asian summer monsoon and rainfall to some extent, but this in?uence is only obvious in early summer and almost disappears in later stages.
文摘High-resolution pollen records from 6 small lakes in the Tibetan Plateau provided the details of evolution of South Asian monsoon since the Last Glacial Maximum. Prior to 16 kaBP, the region was a desert-steppe characterized by cold and dry climates, the January temperature was 7 -10℃lower than that of present and the annual precipitation only accounted for 40% of the present. The temperature and precipitation increased gradually and trees began to live in the region after 12 kaBP, but during the interval from 9.2 to 6.3 kaBP, forest and forest-meadow appeared occasionally. From 8 to 5 kaBP, both January and July temperature was 2-3℃ higher and annual precipitation was also about 200 mm higher than that of the present. After 5 kaBP, temperature and precipitation decreased linearly and steppe vegetation began to degenerate.
文摘In this paper, results from a pilot study for the South China Sea Monsoon Experiment are reported. Based on analyses of 9 years of pentad and monthly mean data, the climatology of subseasonal features and interannual variability of the Southeast Asian monsoon (SEAM) are documented. The present analysis is focused on the sudden onset of the South China Sea monsoon and its relation to the atmospheric and oceanic processes on the entire Asian monsoon region. \ \ It is found that the onset of the SEAM occurs around mid-May, signaling the earliest stage of the entire Asian summer monsoon system. The establishment of monsoon rainfall over the South China Sea is abrupt, being accompanied by substantial changes in the large scale atmospheric circulation and sea surface temperature in the adjacent oceans. The onset and fluctuations of SEAM involve the interaction and metamorphosis of the large scale convection over the Indo-China, the South China Sea and the southern Bay of Bengal. Results show that the onset time of the SEAM differs greatly from one year to another. The delayed (advanced) onset of the monsoon may be related to basin-wide warm (cold) events of the Pacific and Indian Oceans. We also present evidence showing that the SEAM fluctuations in May may foreshadow the development of the full-scale Asian summer monsoon during the subsequent months.
文摘Both evolution of the Asian monsoon system and the Cenozoic global cooling are thought to be closely linked to the Himalayan—Tibetan orogen. The South China Sea (SCS) with its high sedimentation rates of carbonate\|rich hemipelagic sediments offers a unique opportunity to study the variability of the East Asian monsoon, the erosion and weathering of tectonic orogens as well as its possible impact on global and regional climate.Leg 184, the first deep\|sea drilling leg to the seas off China, cored 17 holes at 6 sites in the northern and southern parts of the SCS and recovered 5463m of sediment. The drilling of hemipelagic sediments was exceptionally successful, with core recovery averaging 83%~101%. The 32Ma sequence of deep\|sea sediments recovered during Leg 184 covers almost the entire environmental history of the SCS since its opening. The abnormally high sediment accumulation rates in the Oligocene section are correlative with the incipient sea floor spreading. The bathyal nature of the Oligocenefauna implies that rifting occurred in the Eocene or earlier. Faunal changesfrom the early to late Oligocene are indicative of basin deepening, a trend thatis even more evident in the Miocene section. Sediment deformation, abruptlithologic changes, and a hiatus occur near the Oligocene/Miocene boundary,representing one of the most significant events in the tectonic andenvironmental history of the SCS.
基金Supported by the National Natural Science Foundation of China(41930972,41775055,51778617,and 42005141)Science and Technology Development Funds of the Chinese Academy of Meteorological Sciences(2020KJ019)。
文摘Based on best-track,outgoing longwave radiation,sea surface temperature,and reanalysis data during 1979-2018,statistical and composite analyses were performed to investigate characteristics of the southwesterly water vapor transport(WVT)induced by Bay of Bengal(BoB)tropical cyclones(TCs)during the South Asian summer monsoon(SASM)transition period.The results show that the BoB TCs mainly occur several days before/after the date of SASM onset(retreat)in May(October-November),thereby imposing an important impact on southwesterly WVT to China in those two periods.The WVT is significant in the middle and lower troposphere during the bimodal peak periods of BoB TCs,with large values over the east-central BoB,southeastern Tibetan Plateau,and Southwest and South China.The WVT is located more northward at 500 hPa than at 700 hPa,reaching close to 35°N and covering the southeastern Tibetan Plateau owing to weakening of the plateau’s blocking effect at upper levels.The BoB TCs mainly increase the northward and eastward WVT anomalies compared to the climatological mean.Furthermore,the large southerly WVT anomalies are located in the lower troposphere in low-latitude areas,while the large westerly WVT anomalies appear mainly in the middle troposphere in high-latitude areas.This indicates an enhanced WVT channel where the southwesterly moisture jet first climbs northwards to the southeastern Tibetan Plateau and then turns eastwards to East China under the influence of the BoB TCs.Besides,the southwesterly WVT during the TC period in May is stronger and more widespread than that in October-November,being about twice the latter in value.However,their maximum contributions to the climatological average do not differ much,with maximums of 12%and19%occurring in Southwest China during the bimodal periods,respectively,implying an important role played by the BoB TCs in the WVT.
基金supported jointly by the National Key Research and Development Program(Grant No.2016YFA0600603)the National Basic Research of China(Grant No.2013CB430201)the National Natural Science Foundation of China(Grant Nos.41605058,41375065,41461164005,41230527,and 41375082)
文摘This paper analyzes the differences in the characteristics and spatio–temporal variabilities of summertime rainfall and water vapor transport between the East Asian summer monsoon(EASM) and South Asian summer monsoon(SASM) systems. The results show obvious differences in summertime rainfall characteristics between these two monsoon systems. The summertime rainfall cloud systems of the EASM show a mixed stratiform and cumulus cloud system, while cumulus cloud dominates the SASM. These differences may be caused by differences in the vertical shear of zonal and meridional circulations and the convergence of water vapor transport fluxes. Moreover, the leading modes of the two systems' summertime rainfall anomalies also differ in terms of their spatiotemporal features on the interannual and interdecadal timescales. Nevertheless, several close links with respect to the spatiotemporal variabilities of summertime rainfall and water vapor transport exist between the two monsoon systems. The first modes of summertime rainfall in the SASM and EASM regions reveal a significant negative correlation on the interannual and the interdecadal timescales. This close relationship may be linked by a meridional teleconnection in the regressed summertime rainfall anomalies from India to North China through the southeastern part over the Tibetan Plateau, which we refer to as the South Asia/East Asia teleconnection pattern of Asian summer monsoon rainfall. The authors wish to dedicate this paper to Prof. Duzheng YE, and commemorate his 100 thanniversary and his great contributions to the development of atmospheric dynamics.
基金supported bythe National Natural Science Foundation of China (Grant No. 40725016) the National Basic Research Pro-gram of China (Grant No. 2009CB421405)
文摘This study investigates the projected changes in interannual variability of South Asian summer monsoon and changes of ENSO–monsoon relationships in the 21st century under the Intergovernmental Panel on Climate Change (IPCC) scenarios A1B and A2, respectively, by analyzing the simulated results of twelve Coupled Model Intercomparison Project Phase 3 (CMIP3) coupled models. The dynamical monsoon index (DMI) was adopted to describe the interannual variability of South Asian summer monsoon, and the standard deviation (SD) was used to illustrate the intensity of interannual variability. It was found that most models could project enhanced interannual variability of monsoon in the 21st century. The multi-model ensemble (MME) results showed increases in the interannual variability of DMI: 14.3% and 20.0% under scenarios A1B and A2, respectively. The MME result also showed increases in the rainfall variability are of about 10.2% and 22.0% under scenarios A1B and A2. The intensification of interannual variability tended to occur over the regions that have larger variability currently; that is, "the strong get stronger". Another finding was that ENSO–monsoon relationships are likely to be enhanced in the 21st century. The dynamical component of the monsoon will be more closely correlated to ENSO in the future under global warming, although the ENSO–summer rainfall relationship cannot be reasonably projected by current models. This suggests that the South Asian summer monsoon is more predictable in the future, at least dynamically.
基金the National Fundamental Research and Development Planning Project (No. 2007CB411703)the National Natural Science Foundation of China (No. 40706025)
文摘Clay mineral assemblages, crystallinity, chemistry, and micromorphology of clay particles in sediments from ODP Site 1146 in the northern South China Sea (SCS) were analyzed, and used to trace sediment sources and obtain proxy records of the past changes in the East Asian monsoon climate since the Miocene, based on a multi-approach, including X-ray diffraction (XRD) and scanning electron microscopy combined with energy dispersive X-ray spectrometry (SEM-EDS). Clay minerals consist mainly of illite and smectite, with associated chlorite and kaolinite. The illite at ODP Site 1146 has very well-to-well crystallinity, and smectite has moderate-to-poor crystallinity. In SEM the smectite particles at ODP Site 1146 often appear cauliflower-like, a typical micromorphology of volcanic smecites. The smectite at ODP Site 1146 is relatively rich in Si element, but poor in Fe, very similar to the smectite from the West Philippine Sea. In contrast, the chemical composition of illite at ODP Site 1146 has no obvious differences from those of the Loess plateau, Yellow River, Yangtze River, and Pearl River. A further study on sediment source indicates that smectite originates mainly from Luzon, kaolinite from the Pearl River, and illite and chlorite from the Pearl River, Taiwan and/or the Yangtze River. The clay mineral assemblages at ODP Site 1146 were not only controlled by continental eathering regimes surrounding the SCS, but also by the changing strength of the transport processes. The ratios of (illite+chlorite)/smectite at ODP Site 1146 were adopted as proxies for the East Asian monsoon evolution. Relatively higher ratios reflect strongly intensified winter monsoon relative to summer monsoon, in contrast, lower ratios indicate a strengthened summer monsoon relative to winter monsoon. The consistent variation of this clay proxy from those of Loess plateau, eolian deposition in the North Pacific, planktonic, benthic foraminifera, and black carbon in the SCS since 20 Ma shows that three profound shifts of the East Asian winter monsoon intensity, and aridity in the Asian inland and the intensity of winter monsoon relative to summer monsoon, occurred at about 15 Ma, 8 Ma, and the younger at about 3 Ma. The phased uplift of the Himalaya-Tibetan plateau may have played a significant role in strengthening the Asian monsoon at 15 Ma, 8 Ma, and 3 Ma.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.41405058 and 41861144015)the National Key R&D Program of China(2017YFA0603201).
文摘Based on observational and reanalysis data,the relationships between the eastern Pacific(EP)and central Pacific(CP)types of El Niño−Southern Oscillation(ENSO)during the developing summer and the South Asian summer monsoon(SASM)are examined.The roles of these two types of ENSO on the SASM experienced notable multidecadal modulation in the late 1970s.While the inverse relationship between the EP type of ENSO and the SASM has weakened dramatically,the CP type of ENSO plays a far more prominent role in producing anomalous Indian monsoon rainfall after the late 1970s.The drought-producing El Niño warming of both the EP and CP types can excite anomalous rising motion of the Walker circulation concentrated in the equatorial central Pacific around 160°W to the date line.Accordingly,compensatory subsidence anomalies are evident from the Maritime Continent to the Indian subcontinent,leading to suppressed convection and decreased precipitation over these regions.Moreover,anomalously less moisture flux into South Asia associated with developing EP El Niño and significant northwesterly anomalies dominating over southern India accompanied by developing CP El Niño,may also have been responsible for the Indian monsoon droughts during the pre-1979 and post-1979 sub-periods,respectively.El Niño events with the same“flavor”may not necessarily produce consistent Indian monsoon rainfall anomalies,while similar Indian monsoon droughts may be induced by different types of El Niño,implying high sensitivity of monsoonal precipitation to the detailed configuration of ENSO forcing imposed on the tropical Pacific.
基金A project in the Natural Science Foundation of China (40375019) a key project in the Natural Science Foundation of China (40135020)
文摘Based on the wavelet packet decomposition/reconstruction method and the NCEP/NCAR daily reanalysis data set, the relation between the south Asian summer monsoon and the west Pacific subtropical high seasonal variation was discussed, and a corresponding summer monsoon frequency-band energy criterion was defined and introduced for diagnosing the west Pacific subtropical high. Besides, some existing characteristics and rules about the west Pacific subtropical high were further argued and proofed, a few new phenomena and correlation between the south Asian summer monsoon and the west Pacific subtropical high were also revealed and presented.
基金supported by funds from the National Natural Science Foundation of China(Nos.41576058,41476052 and 41306066)the Geological Survey Project(No.DD20189836)the Open Foundation of the State Key Laboratory of Loess and Quaternary Geology(No.SKLLQG1707)
文摘The East Asian monsoon system influences the sedimentation and transport of organic matter in East Asian marginal seas that is derived from both terrestrial and marine sources. In this study, we determined organic carbon(OC) isotope values, concentrations of marine biomarkers, and levels of OC and total nitrogen(TN) in core YSC-1 from the central South Yellow Sea(SYS). Our objectives were to trace the sources of OC and variations in palaeoproductivity since the middle Holocene, and their relationships with the East Asian monsoon system. The relative contributions of terrestrial versus marine organic matter in core sediments were estimated using a two-end-member mixing model of OC isotopes. Results show that marine organic matter has been the main sediment constituent since the middle Holocene. The variation of terrestrial organic carbon concentration(OCter) is similar to the EASM history. However, the variation of marine organic carbon concentration(OCmar) is opposite to that of the EASM curve, suggesting OCmar is distinctly influenced by terrestrial material input. Inputs of terrestrial nutrients into the SYS occur in the form of fluvial and aeolian dust, while concentrations of nutrients in surface water are derived mainly from bottom water via the Yellow Sea circulation system, which is controlled by the East Asian winter monsoon(EAWM). Variations in palaeoproductivity represented by marine organic matter and biomarker records are, in general, consistent with the recent EAWM intensity studies, thus, compared with EASM, EAWM may play the main role to control the marine productivity variations in the SYS.
基金Funding for this research was provided by the National Natural Science Foundation of China (NSFC), grant number 40576034
文摘The siliciclastic sediments of the uppermost section of 185 mcd (meters composite depth) from ODP Site 1146 on the northern continental slope of the South China Sea (SCS) were partitioned according to their sources using end-member modeling on grain-size data.The goal was to evaluate the evolution of the East Asian monsoon over the past 2 million years.The siliciclastic sediments were described as hybrids of four end-members,EM1,EM2,EM3,and EM4,with modal grain sizes of 8-22 μm,2-8 μm,31-125 μm,and 4-11 μm,respectively.EM1 and EM3 are interpreted as eolian dust and EM2 and EM4 as fluvial mud.The ratio of eolian dust to fluvial mud ((EM1+EM3)/(EM2+EM4)) is regarded as an indicator of the East Asian monsoon.The variation in this ratio not only shows periodical oscillations consistent with oxygen isotope stages,but also exhibits a phased increasing trend corresponding with the phased uplifts of the Tibetan Plateau,indicating that the evolution of the East Asian Monsoon was controlled not only by glacial-interglacial cycles,but also by the phased uplifts of the Tibetan Plateau during the Quaternary.
基金Natural Science Foundation of China (grant No.40233027)Natural Science Foundation ofChina (Project 90211010)"Research on the monitoring and service of South China Sea monsoons", ResearchFund for Tropical Marine Meteorology
文摘Results of the definition of South China Sea summer monsoon onset date and East Asian summermonsoon index in recent years are summarized in this paper. And more questions to be resolved are introducedlater.
基金Major Program of the Natural Science Researches for Colleges and Universities in Jiangsu Province(14KJA170004)Natural Science Foundation of Jiangsu Province(BK20131432)+1 种基金"Qing Lan"Project of Jiangsu Province"333"Project of Jiangsu Province
文摘The timing of the South Asian High(SAH) establishment over the Indochina Peninsula(IP) from April to May and its relations to the setup of the subsequent tropical Asian summer monsoon and precipitation over eastern-central China in summer are investigated by using NCEP/NCAR daily reanalysis data,outgoing longwave radiation(OLR)data and the daily precipitation data from 753 weather stations in China.It is found that the transitions of the zonal wind vertical shear and convection establishment over tropical Asia are earlier(later) in the years of early(late) establishment of SAH.In the lower troposphere,anti-cyclonic(cyclonic) anomaly circulation dominates the equatorial Indian Ocean.Correspondingly,the tropical Asian summer monsoon establishes earlier(later).Furthermore,the atmospheric circulation and the water vapor transport in the years of advanced SAH establishment are significantly different from the delayed years in Asia in summer.Out-of-phase distribution of precipitation in eastern-central China will appear with a weak(strong) SAH and western Pacific subtropical high,strong(weak) ascending motion in the area south of Yangtze River but weak(strong) ascending motion in the area north of it,and cyclonic(anti-cyclonic) water vapor flux anomaly circulation from the eastern-central China to western Pacific.Accordingly,the timing of the SAH establishment at the upper levels of IP is indicative of the subsequent onset of the tropical Asian summer monsoon and the flood-drought pattern over eastern-central China in summer.
基金Strategic Priority Research Program of the Chinese Academy of Sciences(XDA20060503)Fund of Southern Marine Science and Engineering Guangdong Laboratory(ZJW-2019-08)+2 种基金National Key R&D Program of China(2017YFC1501802,2018YFA0605604)Project of Enhancing School with Innovation of Guangdong Ocean University(230419053)Projects(Platforms)for Construction of Topranking Disciplines of Guangdong Ocean University(231419022)
文摘The study has shown that the shear component of the vertical integrated kinetic energy(Ks)over the box(40oE-100oE,0-20oN)can be used to measure the intensity of the South Asian summer monsoon(SASM).Based on its value averaged between June and August,the SASM can be divided into strong and weak monsoon episodes.Between1958 and 2018,there existed 16(16)strong(weak)monsoon episodes.Based on the calendar year,the relationship between the SASM and ENSO episodes can be grouped into six patterns:weak monsoon-El Ni?o(WM-EN),normal monsoon-El Ni?o(NM-EN),weak monsoon-non ENSO(WM-NE),strong monsoon-La Ni?a(SM-LN),normal monsoon-La Ni?a(NM-LN)and strong monsoon-non ENSO(SM-NE).Previous studies suggest that the WM-EN and SM-LN patterns reflect the correlated relationship between the SASM and El Ni?o/Southern Oscillation(ENSO)events.Therefore,we name these two strongly coupled categories WM-EN and SM-LN as the resonance effect.Two important circulations,i.e.,Walker circulation(WC)and zonal Asian monsoon circulation(MC),in the vertical plane are found to be not always correlated.The MC is controlled by thermal gradients between the Asian landmass and the tropical Indian Ocean,while the WC associated with ENSO events is primarily the east-west thermal gradient between the tropical South Pacific and the tropical Indian Ocean.Furthermore,the gradient directions caused by different surface thermal conditions are different.The main factor for the resonance effect is the phenomenon that the symbols of SSTA in the tropical Indian Ocean and the equatorial eastern Pacific are the same,but are opposite to that of the SSTA near the maritime continent.
基金Supported by the Key Program of National Natural Science Foundation of China(NSFC)(No.41330963)the Strategic Priority Research Program of Chinese Academy of Sciences(No.XDA01010101)+1 种基金the NSFC-Shandong Joint Fund for Marine Science Research Centers(No.U1406401)the Fund for Innovative Research Groups of the NSFC(No.41421005)
文摘Monthly ocean temperature from ORAS4 datasets and atmospheric data from NCEP/NCAR Reanalysis I/II were used to analyze the relationship between the intensity of the South Asian summer monsoon(SASM) and upper ocean heat content(HC) in the tropical Indo-Pacific Ocean.The monsoon was differentiated into a Southwest Asian Summer Monsoon(SWASM)(2.5°–20°N,35°–70°E) and Southeast Asian Summer Monsoon(SEASM)(2.5°–20°N,70°–110°E).Results show that before the 1976/77 climate shift,the SWASM was strongly related to HC in the southern Indian Ocean and tropical Pacific Ocean.The southern Indian Ocean affected SWASM by altering the pressure gradient between southern Africa and the northern Indian Ocean and by enhancing the Somali cross-equatorial flow.The tropical Pacific impacted the SWASM through the remote forcing of ENSO.After the 1976/77 shift,there was a close relationship between equatorial central Pacific HC and the SEASM.However,before that shift,their relationship was weak.
基金jointly supported by the National Science Fund for Distinguished Young Scholars(41325018)the National Natural Science Foundation of China(General Program,41175071)National Science Fund for Innovation Research Groups(41421004)
文摘The seasonal forecasting skill with respect to the South Asian summer monsoon(SASM) was compared between the European Commission FP7 project(ENSEMBLES) and the Development of a European Multimodel Ensemble System for Seasonal to Interannual Prediction project(DEMETER). The Webster-Yang index(WYI) was chosen to represent the intensity of the SASM. First, the authors compared the ability to forecast the zonal wind at 850 h Pa(U850) and 200 h Pa(U200) between ENSEMBLES and DEMETER models. The results indicated that the models from the European Centre for Medium-Range Weather Forecasts, International Organization(ECMWF) and UK Met Office(UKMO) in ENSEMBLES possess greater skill in seasonally forecasting the JJA(June, July, and August) U850, U200, and U850 minus U200 than in DEMETER. Compared to in DEMETER, the JJA U200 and U850 minus U200 forecasting skill was greater for the model from MétéoFrance(MF) in ENSEMBLES over most of the SASM region. The three coupled models(ECMWF, MF, and UKMO), especially the UKMO model in ENSEMBLES, all demonstrated improved skill in their seasonal forecasts compared to in DEMETER with respect to the interannual variability of the SASM. The three ENSEMBLES models also showed better ability in forecasting the sea surface temperature anomalies(SSTAs) over the eastern equatorial Pacific and North Indian Ocean, and more accurately reproduced the large-scale atmospheric circulation and precipitation over northern India, which are related to the SASM. It seems that the couple between the atmospheric system and external forcing of ENSMBLES over Indian Ocean and Pacific is better than that of DEMETER.