variability of el nino southern oscillation activity at millennial timescales during the holocene epoch the variability of el nino southern oscillation enso during the holocene epoch in particular on millennial timescales is poorly understood palaeoclimate studies have documented enso variability for selected intervals in the holocene but most records are either too short or insufficiently resolved to investigate variability on millennial scales1 2 3 here we present a record of sedimentation in laguna pallcacocha southern ecuador which is strongly influenced by enso variability and covers the past 12 000 years continuously we find that changes on a timescale of 2 8 years which we attribute to warm enso events become more frequent over the holocene until about 1 200 years ago and then decline towards the present periods of relatively high and low enso activity alternating at a timescale of about 2 000 years are superimposed on this long term trend we attribute the long term trend to orbitally induced changes in insolation and suggest internal enso dynamics as a possible cause of the millennial variability however the millennial oscillation will need to be confirmed in other enso proxy records

coordinated hydrological regimes in the indo pacific region during the past two millennia instrumental data suggest that major shifts in tropical pacific atmospheric dynamics and hydrology have occurred within the past century potentially in response to anthropogenic warming to better understand these trends we use the hydrogen isotopic ratios of terrestrial higher plant leaf waxes delta d wax in marine sediments from southwest sulawesi indonesia to compile a detailed reconstruction of central indo pacific warm pool ipwp hydrologic variability spanning most of the last two millennia our paleodata are highly correlated with a monsoon reconstruction from southeast asia indicating that intervals of strong east asian summer monsoon easm activity are associated with a weaker indonesian monsoon im furthermore the centennial scale oscillations in our data follow known changes in northern hemisphere climate e g the little ice age and medieval warm period implying a dynamic link between northern hemisphere temperatures and ipwp hydrology the inverse relationship between the easm and im suggests that migrations of the intertropical convergence zone and associated changes in monsoon strength caused synoptic hydrologic shifts in the ipwp throughout most of the past two millennia

late holocene environmental changes as recorded in the sediments of high andean laguna chepical central chile 32 s 3050 m a s l abstract we present a reconstruction of environmental changes from sediments of high altitude laguna chepical in the subtropical andes of central chile 32 16 s 70 30 w 3050 m a s l for the past 3100 years based on subfossil pollen microscopic charcoal and diatoms we inferred changes in moisture related to precipitation and ice cover ice free season related to summer temperature at decadal to millennial scales sustained wetter and colder summer temperatures than today prevailed between 1100 bc and ca ad 1 afterward decreasing pollen accumulation rates and increased fire activity suggest drier conditions and possibly enhanced seasonality and or inter annual climate variability frequent changes between cold and warm summers were observed particularly for the last 1000 years about ad 1250 during the medieval climate anomaly wet years and early break up of ice cover occurred in central chile which is today typical for el nino like mean conditions conversely and with the exception of a few wet pulses a generally dry period with extended ice cover cool summers was observed between ad 1400 and ad 1850 little ice age this can be interpreted as a trend toward more la nina like mean conditions recent climate change and human disturbances during the last 100 years have prompted changes in diatom and plant communities that are unprecedented in the late holocene first planktonic diatoms increased as a result of hydraulic interventions in the lake during the late 19th century and secondly the andean vegetation shifted upward as result of recent warming and the frequency of arboreal taxa was significantly reduced at the same time peaks of fire activity were observed

moisture variations in lacustrine eolian sequence from the hunshandake sandy land associated with the east asian summer monsoon changes since the late pleistocene abstract paleoclimate records currently lack sufficient geographic detail to understand the spatiotemporal evolution of east asian summer monsoon easm rain belt since the late pleistocene in particular there is no consensus on whether the easm rain belt reached its modern northern limit by the early holocene here we present inferred moisture variations from a multi parameter absolute dated lacustrine eolian sequence from northern china that date back to the late pleistocene 14 ka bp or thousand years ago we observed a sharp transition towards wet conditions at the onset of the holocene epoch maximum wet climate occurred here during 11 3 8 5 ka the climate remained predominantly wet until 4 2 ka then it became progressively drier we observed alternating organic rich fine grained lake deposits and organic depleted coarse grained eolian sand layers during 14 7 ka these layers correspond to sedimentation associated with the allerod younger dryas yd post yd warming pre boreal oscillation pbo early holocene and 8 2 ka event we interpreted the orbital scale moisture variation at our study site to the changes in insolation assigning these abrupt and short lived changes during the late pleistocene holocene transition to a persistent teleconnection between the north atlantic and east asian climate zones

el nino variability off peru during the last 20 000 years here we present a high resolution marine sediment record from the el nino region off the coast of peru spanning the last 20 000 years sea surface temperature photosynthetic pigments and a lithic proxy for el nino flood events on the continent are used as paleo el nino southern oscillation proxy data the onset of stronger el nino activity in peru started around 17 000 calibrated years before the present which is later than modeling experiments show but contemporaneous with the heinrich event 1 maximum el nino activity occurred during the early and late holocene especially during the second and third millennium b p the recurrence period of very strong el nino events is 60 80 years el nino events were weak before and during the beginning of the younger dryas during the middle of the holocene and during medieval times the strength of el nino flood events during the last millennium has positive and negative relationships to global and northern hemisphere temperature reconstructions

linkages between climate fire and vegetation in southwest china during the last 18 5ka based on a sedimentary record of black carbon and its isotopic composition abstract fires are sensitive to climate changes and in addition they have a major influence on the global carbon cycle land surface properties and chemical composition of the atmosphere which in turn can affect the climate system projecting the impacts of future climate changes on fire mediated biogeochemical processes requires understanding of how various climatic factors influence regional fire regimes however long term variations in fire activity and their controls are poorly known in this study we report the concentration of black carbon bc and its isotopic composition 13cbc in an upland lake sediment core from southwest china in order to elucidate linkages between changes in fire regime climate and vegetation over the past 18 5 ka the results show that the sedimentary bc content recorded variations in fire activity and exhibits a close negative correlation with the amount of precipitation delivered by the indian summer monsoon ism during heinrich event 1 18 5 15 0 cal ka bp the younger dryas 12 8 11 1 cal ka bp and the mid to late holocene the weakening of the ism led to greatly increased fire activity in southwest china in the last 1 0 ka the bc record may have been affected by human activity in the catchment which may have caused an increased influx of minerogenic material to the lake thereby diluting the sedimentary bc concentration the general trend of changing vegetation compositions inferred from the 13cbc values also tracks the variations of the ism suggesting a change from mixed c3 c4 plant ecosystems during the last glacial maximum to c3 plant dominated forest during the holocene however the abundance of c4 plants may be overestimated during the bolling allerod warm interval and the early holocene due to the fact that fires were probably limited to the savanna ecosystem in the valleys and low lying basins

a 1500 year record of river discharge inferred from fluvial marine sediments in the australian subtropics abstract in australia there is a scarcity of high resolution hyrdoclimate reconstructions for the last several millennia fluvial marine sediments offer a potential avenue for examining trends in freshwater input to coastal settings and by inference past hydroclimates here major elemental geochemistry 13c and c n ratios of organic matter grain size and diatom species abundance measured in a 4 4 m long sediment core collected from moreton bay in east coast australia are used to infer the relative freshwater discharge of the adjacent catchment over the last 1500 years reduced freshwater discharge into the bay occurred from 630 to 1200 ce especially between 1100 and 1200 ce a broad increase in discharge is indicated after 1300 ce extending to the present the initial shift to the prolonged wet period coincides with both a decrease in the frequency of dry el nino events based on regional records from the austral pacific and a broad hemispheric scale cooling trend this record provides further insight into low amplitude climate variability in the australian subtropics over the last 1000 years supporting efforts in both forecasting current and future climates and managing regional water resources importantly instrumental records do not cover the full range of natural climate variability experienced in the region over the last 1000 years

coral derived western pacific tropical sea surface temperatures during the last millennium reconstructions of ocean temperatures prior to the industrial era serve to constrain natural climate variability on decadal to centennial timescales yet relatively few such observations are available from the west pacific warm pool here we present multiple coral based sea surface temperature reconstructions from yongle atoll in the south china sea over the last 1 250 years 762 2013 common era ce reconstructed coral sr ca sea surface temperatures indicate that the little ice age 1711 1817 ce period was 0 7 c cooler than the medieval climate anomaly 913 1132 ce and that late 20th century warming of the western pacific is likely unprecedented over the past millennium our findings suggest that the western pacific warm pool may have expanded contracted during the medieval climate anomaly little ice age leading to a strengthening weakening of the asian summer monsoon as recorded in chinese stalagmites

persistent positive north atlantic oscillation mode dominated the medieval climate anomaly the medieval climate anomaly mca was the most recent pre industrial era warm interval of european climate yet its driving mechanisms remain uncertain we present here a 947 year long multidecadal north atlantic oscillation nao reconstruction and find a persistent positive nao during the mca supplementary reconstructions based on climate model results and proxy data indicate a clear shift to weaker nao conditions into the little ice age lia globally distributed proxy data suggest that this nao shift is one aspect of a global mca lia climate transition that probably was coupled to prevailing la nina like conditions amplified by an intensified atlantic meridional overturning circulation during the mca

high time resolution alkenone paleotemperature variations in tokyo bay during the meghalayan implications for cold climates and social unrest in japan abstract the regional paleoenvironmental record of tokyo central japan is required to enrich our understanding of climate change in east asia and its impact on japanese civilizations previous studies have generated paleotemperature records based on the analysis of shell mounds along the coast of tokyo bay and pollen from terrestrial borehole cores however a continuous high time resolution quantitative paleotemperature record does not exist a piston core was recovered from tokyo bay from which 22 mollusk shells were extracted an age model for the core determined via accelerator mass spectroscopy ams 14c dating of the shells and a scoria layer from the hoei eruption 1707 ce showed that the core contains continuous record from ca 2400 bce we analyzed the alkenone unsaturation ratios uk 37 to reconstruct the variations in the paleotemperature the temperature during the meghalayan was generally warmer than that at present exhibiting a declining trend which roughly matches the changes in the orbital forcing summer insolation and the millennial scale latitudinal shift of the subarctic front in the northeastern pacific ocean the largest cold period which occurred ca 2300 bce and had a minimum temperature of 19 5 c interrupted the warm conditions this cold period may correspond to the global cooling drying 4 2 ka bp event which marks the boundary between the northgrippian and meghalayan our results also revealed that several cold periods occurred which may have been caused by decreases in solar activity or large volcanic eruptions particularly large decadal to centennial scale cold periods were observed ca 440 bce and 100 ce during the yayoi era ca 900 bce 300 ce the coldest period after the establishment of a centralized system of government ca 300 ce present was recorded ca 1050 ce which may have been caused by the combination of a strong el nino mode and reduced solar activity these climate change events can all be linked and therefore may be the potential causes of significant periods of famine and civil war in japanese history which eventually led to major shifts in japanese social systems

southward movement of the pacific intertropical convergence zone ad 1400 1850 tropical rainfall patterns control the subsistence lifestyle of more than one billion people seasonal changes in these rainfall patterns are associated with changes in the position of the intertropical convergence zone which is characterized by deep convection causing heavy rainfall near 10 n in boreal summer and 3 n in boreal winter dynamic controls on the position of the intertropical convergence zone are debated but palaeoclimatic evidence from continental asia africa and the americas suggests that it has shifted substantially during the past millennium reaching its southernmost position some time during the little ice age ad1400 1850 however without records from the meteorological core of the intertropical convergence zone in the pacific ocean quantitative constraints on its position are lacking here we report microbiological molecular and hydrogen isotopic evidence from lake sediments in the northern line islands galapagos and palau indicating that the pacific intertropical convergence zone was south of its modern position for most of the past millennium by as much as 500km during the little ice age a colder northern hemisphere at that time possibly resulting from lower solar irradiance may have driven the intertropical convergence zone south we conclude that small changes in earth s radiation budget may profoundly affect tropical rainfall

unprecedented recent warming of surface temperatures in the eastern tropical pacific ocean climate variability in the tropical pacific ocean influences climate across much of the planet a diatom based record of sea surface temperatures from el junco lake galapagos reveals that the most recent half century is the warmest 50 year period in the past 1 200 years through its intimate connection with the el nino southern oscillation system climate variability in the tropical pacific ocean influences climate across much of the planet but the history of temperature change in the tropical pacific ocean during recent millennia is poorly known the available annually resolved records1 2 are discontinuous and rarely span more than a few centuries longer records at coarser temporal resolution suggest that significant oceanographic changes observed at multi year to multi century resolution have had important effects on global climate3 4 5 here we use a diatom record from el junco lake galapagos to produce a calibrated continuous record of sea surface temperature in the eastern tropical pacific ocean at subdecadal resolution spanning the past 1 200 years our reconstruction reveals that the most recent 50 years are the warmest 50 year period within the record because our diatom based sea surface temperature index resembles northern hemisphere temperature reconstructions we suggest that with continued anthropogenic warming the eastern tropical pacific ocean may continue to warm

modes of climate variability synthesis and review of proxy based reconstructions through the holocene abstract modes of climate variability affect global and regional climates on different spatio temporal scales and they have important impacts on human activities and ecosystems as these modes are a useful tool for simplifying the understanding of the climate system it is crucial that we gain improved knowledge of their long term past evolution and interactions over time to contextualise their present and future behaviour we review the literature focused on proxy based reconstructions of modes of climate variability during the holocene i e the last 11 7 thousand years with a special emphasis on i proxy based reconstruction methods ii available proxy based reconstructions of the main modes of variability i e el nino southern oscillation pacific decadal variability atlantic multidecadal variability the north atlantic oscillation the southern annular mode and the indian ocean dipole iii major interactions between these modes and iv external forcing mechanisms related to the evolution of these modes this review shows that modes of variability can be reconstructed using proxy based records from a wide range of natural archives but these reconstructions are scarce beyond the last millennium partly due to the lack of robust chronologies with reduced dating uncertainties technical issues related to proxy calibration and difficulty elucidating their stationary impact or not on regional climates over time while for each mode the available reconstructions tend to agree at mutidecadal timescales they show notable disagreement on shorter timescales beyond the instrumental period the reviewed evidence suggests that the intrinsic variability of modes can be modulated by external forcing such as orbital solar volcanic and anthropogenic forcing the review also highlights some modes experience higher variability over the instrumental period which is partly ascribed to anthropogenic forcing these features stress the paramount importance of further studying their past variations using long climate proxy records for the progress of climate science

persistent intensification of the kuroshio current during late holocene cool intervals abstract the kuroshio current kc which redistributes heat and moisture from the tropics toward mid latitudes considerably affects ocean atmosphere land interactions along its pathways however our knowledge about the kc strength and associated forcing based on investigations of instrumental data and model simulations is controversial impeding assessment of its possible change in the near future in this study we investigated kc strength over the past 4400 yr by analyzing alkenone u 37 k sea surface temperature sst signal in a sediment core under the influence of the yellow sea warm current yswc a branch of the kc in the western north pacific along with a coastal sst record over the last 1000 yr outside of the yswc effect our sst record in the warm current pathway opposite to the patterns of coastal sst and solar irradiance changes at multi centennial timescales effectively manifests variations of yswc strength in conjunction with published records we show a remarkably intensified yswc and probably the kc as well during the cool interval between 1400 1850 ad the little ice age lia we suggest that cold climate conditions perhaps in relation to strengthened east asian winter monsoon and pacific walker circulation were more favorable for kc enhancement

evidence for extreme floods in arid subtropical northwest australia during the little ice age chronozone ce 1400 1850 abstract here we report a 2000 year sediment sequence from the fortescue marsh martuyitha in the eastern pilbara region which we have used to investigate changing hydroclimatic conditions in the arid subtropics of northwest australia the pilbara is located at the intersection of the tropical indian and pacific oceans and its modern rainfall regime is strongly influenced by tropical cyclones the intertropical convergence zone itcz and the indo pacific warm pool we identified four distinct periods within the record the most recent period p1 ce 1990 present reveals hydroclimatic conditions over recent decades that are the most persistently wet of potentially the last 2000 years during the previous centuries p2 ce 1600 1990 the fortescue marsh was overall drier but likely punctuated by a number of extreme floods which are defined here as extraordinary strongly episodic floods in drylands generated by rainfall events of high volume and intensity the occurrence of extreme floods during this period which encompasses the little ice age lia ce 1400 1850 is coherent with other southern tropical datasets along the itcz over the last 2000 years suggesting synchronous hydroclimatic changes across the region this extreme flood period was preceded by several hundred years p3 ce 700 1600 of less vigorous but more regular flows the earliest period of the sediment record p4 ce 100 700 was the most arid with sedimentary and preservation processes driven by prolonged drought our results highlight the importance of developing paleoclimate records from the tropical and sub tropical arid zone providing a long term baseline of hydrological conditions in areas with limited historical observations

a record of the southern oscillation index for the past 2 000 years from precipitation proxies the el nino southern oscillation enso is a coupled ocean atmosphere climate phenomenon in the tropical pacific ocean the interannual climate variations have been shown to modify both the hadley and walker meridional and zonal atmospheric circulations with strong impacts on global climate 1 3 proxy based reconstructions of the southern oscillation index on a multi decadal scale have shown that the strength and frequency of el nino occurrences have varied over the past millennium 4 7 here we compile reconstructions of precipitation 8 15 from regions that experience substantial enso variability to extend the multidecadal scale southern oscillation index to include the past 2 000 years we find that the medieval warm period similar to ad 800 1300 was characterized by a negative index which indicates more el nino dominated conditions whereas during the little ice age similar to ad 1400 1850 more la nina dominated conditions prevailed the southern oscillation index we derive is significantly correlated with reconstructions of solar irradiance and mean northern hemisphere temperature fluctuations

east african rift system offset age and tectonic significance of the tanganyika rukwa malawi intracontinental transcurrent fault zone abstract the 1000 200 km tanganyika rukwa malawi fractures area is shown to be a right lateral intracontinental transform zone belonging to the east african rift system using the results carried out from complementary techniques remote sensing field structural analysis and k ar isotopic dating it appears that tectonics in this area have acted at different times the oldest being at 2000 1400 m y the youngest being still active today and are mainly due to the reactivation of nw se structures the area consists mainly of large nw se en echelon dextral transcurrent faults along which the southern tanganyika rukwa and northern malawi troughs are opening ne sw transverse faults showing a curved horizontal shape end these troughs axially eocene to recent volcanic activity is associated with the intersection of the northeastern main nw se transcurrent fracture the livingstone fault

a multiproxy index of the el nino southern oscillation a d 1525 1982 1 an understanding of past variability in the el nino southern oscillation enso on interannual interdecadal and longer time scales would be useful in assessing recent observed changes to enso and in determining the realism of climate model simulations using tree ring coral and ice core data we reconstruct a proxy based enso index between a d 1525 and 1982 unlike most previous studies which have drawn climate proxies from limited geographic regions our network is pacific basin wide using enso sensitive proxies from the western equatorial pacific new zealand the central pacific and subtropical north america by considering multiple teleconnection regions this network provides a more robust proxy enso signal the common signal recorded in the multiproxy network has a high correlation with the southern oscillation index soi nino 3 4 sea surface temperature nino3 4 sst and a combined ocean atmosphere enso index cei the proportion of instrumental variance explained is 47 for the soi 48 for nino3 4 sst and 52 for the cei the proxy enso index also displays skill in reproducing warm and cold extremes of the soi the proxy enso index over the last 450 years shows considerable amplitude and frequency modulation in the 3 10 year band on multidecadal time scales there is a relative reduction in the amplitude of high frequency variability during the sixteenth early seventeenth and mid eighteenth centuries in contrast high frequency enso variability has increased over the last 200 years variability during the first half of the twentieth century is similar to that evident in the nineteenth century

sea surface temperature variability in southern okinawa trough during last 2700 years 1 most of the temperature reconstructions for the past two millennia are based on proxy data from various sites on land here we present a bidecadal resolution record of sea surface temperature sst in southern okinawa trough for the past ca 2700 years by analyzing tetraether lipids of planktonic archaea in the odp hole 1202b a site under the strong influence of kuroshio current and east asian monsoon the reconstructed sst anomalies generally coincided with previously reported late holocene climate events including the roman warm period sui tang dynasty warm period medieval warm period current warm period dark age cold period and little ice age however the medieval warm period usually thought to be a historical analogue for the current warm period has a mean sst of 0 6 0 8 c lower than that of the roman warm period and sui tang dynasty warm period despite an increase since 1850 ad the mean sst in the 20th century is still within the range of natural variability during the past 2700 years a close correlation of sst in southern okinawa trough with air temperature in east china intensity of east asian monsoon and the el nino southern oscillation index has been attributed to the fluctuations in solar output and oceanic atmospheric circulation

summer monsoon induced upwelling dominated coastal sea surface temperature variations in the northern south china sea over the last two millennia the south china sea scs situated to the north of the indo pacific warm pool ipwp is under the strong influence of the asian monsoon system however coastal sea surface temperature sst reco

holocene changes in eastern tropical pacific climate inferred from a galapagos lake sediment record abstract paleoclimate records from the tropical pacific suggest the early to mid holocene was a period of reduced el nino southern oscillation enso variability with a transition to modern increased enso frequency occurring some time in the last few thousand years however the nature and timing of this shift remains uncertain due to the discontinuous nature and or coarse resolution of many enso proxies as well as a lack of agreement between previously published records a new continuous climate record from el junco crater lake in the galapagos islands reveals several abrupt changes in lake level and precipitation through the holocene hydroclimatic model simulations suggest that el junco lake level responds sensitively to increases in precipitation associated with el nino events rising during wet el nino events and falling during the intervening dry periods grain size data from el junco sediment cores indicate past lake level variability likely associated with changing seasonal precipitation and enso frequency the grain size data suggest increased precipitation intensity prior to 9000 120 cal years bp and after 4200 130 cal years bp as well as a two step increase in precipitation at 3200 160 and 2000 100 cal years bp maximum holocene precipitation and inferred enso variability occurred between 2000 100 and 1500 70 cal years bp during the same period that six other independent proxy records suggest higher enso frequency and longer stronger el nino events decreasing sediment carbon nitrogen c n ratios in el junco sediments indicate rising lake levels from the early holocene to present corroborating the grain size data the inferred increase in precipitation at 4200 130 cal years bp and at 2000 100 cal years bp coincides with decreasing southwest asian and east asian monsoon intensity suggesting tropical pacific climate and the asian monsoon were interconnected systems at centennial to millennial timescales during the holocene a weakening trend in the asian monsoon and the trend toward wetter conditions at el junco also coincide with a trend toward cooler and drier conditions inferred from cariaco basin sediment proxies from the mid holocene to present suggesting the migration of the intertropical convergence zone itcz likely influenced hydrological changes in both the eastern tropical pacific and the asian monsoon region during the holocene

climate and hydrographic variability in the indo pacific warm pool during the last millennium planktonic foraminiferal mg ca and delta o 18 derived sea surface temperature and salinity records from the makassar strait indonesia show a long term cooling and freshening trend as well as considerable centennial scale variability during the last millennium the warmest temperatures and highest salinities occurred during the medieval warm period mwp while the coolest temperatures and lowest salinities occurred during the little ice age lia these changes in the western pacific along with observations from other high resolution records indicate a regionally coherent southern displacement of the inter tropical convergence zone during the lia with more arid conditions in the northern tropics and wetter conditions in the southern tropics

enso like modulated tropical pacific climate changes since 2 36 myr and its implication for the middle pleistocene transition el nino southern oscillation enso activity and the pacific walker circulation are controlled by the zonal sea surface temperature sst gradient between the western and eastern equatorial pacific eep and the corresponding barometric difference variations in the zonal sst gradient since the early pleistocene have primarily been triggered by changes in the sst in the eastern equatorial pacific however the response of the enso like long term state to the cooling of the eep and its coupling role with tropical pacific climate changes are still not well established here we present a high resolution grain size record spanning the last 2 36 myr obtained from marine core sediment located in the west philippine sea in order to decipher the tropical pacific climate changes and reveal its controlling mechanism by combining our data with other long term climatic records from the equatorial pacific we demonstrate that the cooling of sst and enhanced upwelling in the eep resulted in the development of the walker circulation and increased monsoon precipitation in luzon from 2 2 to 1 6 myr from 1 2 to 0 8 myr and since 0 2 myr ago the progressive cooling of the high latitudes in the quaternary may be responsible for our observation here a newly identified 100 kyr dominant period between 2 2 and 1 6 myr in the enso like modulated pacific climate records indicates that the enso like system may play a key role in facilitating or responding to the global climate changes

magma fragmentation in highly explosive basaltic eruptions induced by rapid crystallization basaltic eruptions are the most common form of volcanism on earth and planetary bodies the low viscosity of basaltic magmas inhibits fragmentation which favours effusive and lava fountaining activity yet highly explosive hazardous basaltic eruptions occur the processes that promote fragmentation of basaltic magma remain unclear and are subject to debate here we used a numerical conduit model to show that a rapid magma ascent during explosive eruptions produces a large undercooling in situ experiments revealed that undercooling drives exceptionally rapid in minutes crystallization which induces a step change in viscosity that triggers magma fragmentation the experimentally produced textures are consistent with basaltic plinian eruption products we applied a numerical model to investigate basaltic magma fragmentation over a wide parameter space and found that all basaltic volcanoes have the potential to produce highly explosive eruptions the critical requirements are initial magma temperatures lower than 1 100 c to reach a syn eruptive crystal content of over 30 vol and thus a magma viscosity around 105 pa s which our results suggest is the minimum viscosity required for the fragmentation of fast ascending basaltic magmas these temperature crystal content and viscosity requirements reveal how typically effusive basaltic volcanoes can produce unexpected highly explosive and hazardous eruptions volcanoes that typically erupt effusively can generate highly explosive eruptions of basaltic lava under specific temperature and viscosity conditions suggest crystallization experiments combined with numerical models of magma fragmentation

variation of the summer asian westerly jet over the last millennium based on the pmip3 simulations investigation of the evolution of summer asian westerly jet awj in earth history may deepen our understanding of the behavior of awj in the present and future here the variation of summer weste

atmospheric circulation cells associated with the el nino southern oscillation abstract atmospheric circulation cells associated with the el nino southern oscillation enso are described and examined using the ncep ncar reanalysis field and the ncep sea surface temperature sst from january 1950 to december 1999 the divergent wind and pressure vertical velocity are employed for the identification of atmospheric circulation cells the warm phase of enso shows positive sst anomalies in the equatorial eastern pacific and along the east coast of asia and the west coast of north america and negative sst anomalies in the off equatorial western pacific and in the central north pacific associated with this sst anomaly distribution are variations of atmospheric zonal and meridional circulation cells over the pacific the equatorial zonal walker circulation cell is weakened consistent with previous schematic diagrams the anomalous meridional hadley circulation cell in the eastern pacific shows the air rising in the tropics flowing poleward in the upper troposphere sinking in the subt