changes in occurrence of cold surges over east asia in association with arctic oscillation 1 it has been newly found that the occurrence of cold surges in east asia is significantly influenced by the arctic oscillation ao in the present study the events of cold surge are objectively determined based on several synoptic criteria and the phase dependency of its occurrences in association with the ao has been revealed during the negative ao phase the frequency of cold surge occurrence is relatively increased than that of neutral and positive ao phases the variation of upper level trough and jet stream over east asia and the siberian high in association of ao are suggested to explain the change of cold surge occurrences

impacts of mjo convection over the maritime continent on eastern china cold temperatures abstractthe present study shows that winter cold events over eastern china can be induced by madden julian oscillation mjo associated anomalous convection over the maritime continent we conduct

isentropic analysis of polar cold airmass streams in the northern hemispheric winter abstractan analysis method is proposed for polar cold airmass streams from generation to disappearance it designates a threshold potential temperature t at around the turning point of the extratropical direct etd meridional circulation from downward to equatorward in the mass weighted isentropic zonal mean mim and clarifies the geographical distributions of the cold air mass the negative heat content nhc their horizontal fluxes and their diabatic change rates on the basis of conservation relations of the air mass and thermodynamic energy in the northern hemispheric winter the polar cold air mass below t 280 k has two main streams the east asian stream and the north american stream the former grows over the northern part of the eurasian continent flows eastward turns down southeastward toward east asia via siberia and disappears over the western north pacific ocean the latter grows over the arctic ocean flows toward the eastern coast of north america via hudson bay and disappears ov

genesis pathways and terminations of intense global water vapor transport in association with large scale climate patterns author s sellars sl kawzenuk b nguyen p ralph fm sorooshian s abstract 2017 the authors the connected object connect algorithm is applied to global integrated water vapor transport data from the nasa s modern era retrospective analysis for research and applications version 2 reanalysis product for the period of 1980 to 2016 the algorithm generates life cycle records in time and space evolving strong vapor transport events we show five regions located in the midlatitudes where events typically exist off the coast of the southeast united states eastern china eastern south america off the southern tip of south africa and in the southeastern pacific ocean global statistics show distinct genesis and termination regions and global seasonal peak frequency during northern hemisphere late fall winter and southern hemisphere winter in addition the event frequency and geographical location are shown to be modulated by the arctic oscillation pacific north american pattern and the quasi biennial oscillation moreover a positive linear trend in the annual number of objects is reported increasing by 3 58 objects year over year

precursory signals of east asian winter cold anomalies in stratospheric planetary wave pattern the impacts of the stratospheric polar vortex changes on the tropospheric climate variability have been emphasized in previous studies the present study presents evidence for precursory signals of cold anomalies over east asia in the stratospheric wave pattern during november through march the leading two empirical orthogonal function eof modes of daily 50 hpa geopotential height anomalies along 65 n correspond to changes in the amplitude and phase of the stratospheric planetary wavenumber 1 respectively composite analysis is performed to unravel the temporal evolution of anomalies during 8 phases of 34 events identified based on the second eof mode with a complete life cycle for the period 1979 2016 the surface cold anomalies over eastern china emerge in phase 3 corresponding to negative and positive 50 hpa height anomalies on the north atlantic and russian far east sector respectively and peak in phase 5 corresponding to positive 50 hpa height anomalies over eurasia when the siberian high extends southeastward and the east asian trough deepens with anomalous surface northerly winds downward propagation of stratospheric signal is detected over western europe and western siberia the former is a source region of the tropospheric rossby wave trains propagating along the polar front jet and subtropical jet the downward propagation of stratospheric signal is related to the reflection of stratospheric planetary wavenumber 1 pattern and contributes to the development of the tropospheric rossby wave train that in turn leads to the strengthening of the siberian high and the deepening of the east asian trough

relative contributions of synoptic and intraseasonal variations to strong cold events over eastern china the present study investigates the relative roles of intraseasonal oscillations isos and synoptic variations in strong cold events over eastern china during the boreal winter the isos and synoptic variations explain about 55 and 20 of the total area mean temperature anomaly in eastern china respectively the advection of synoptic winds on synoptic temperature gradients has a leading contribution to the temperature decrease before the cold events and thus the synoptic variations are important in determining the time of peak cold anomalies the isos have a larger role in sustaining the cold events the height anomalies associated with isos and synoptic variations are manifested as rossby wave trains propagating along the polar front jet over the eurasian continent before the cold events they both contribute to the deepening of the east asian trough and the development of cold events compared to the iso wave train the synoptic wave train has a smaller spatial scale and moves faster there are obvious intraseasonal signals in the stratosphere about 1 week before the cold events over eastern china large negative height anomalies associated with the weakening of the polar vortex are observed over the north atlantic these anomalies move eastwards and propagate downwards after reaching the west coast of europe the downward moving stratospheric signal triggers height anomalies in the troposphere over the entrance region of the polar front jet then the anomalies propagate towards east asia along the wave train contributing to the intensification of the siberian high and the east asian trough and the occurrence of cold events over eastern china

effects of vertical wind shear on the intensity and structure of numerically simulated hurricanes a series of numerical simulations of tropical cyclones in idealized large scale environments is performed to examine the effects of vertical wind shear on the structure and intensity of hurricanes the simulations are performed using the nonhydrostatic pennsylvania state university national center for atmospheric research fifth generation mesoscale model using a 5 km fine mesh and fully explicit representation of moist processes when large scale vertical shears are applied to mature tropical cyclones the storms quickly develop wavenumber one asymmetries with upward motion and rainfall concentrated on the left side of the shear vector looking downshear in agreement with earlier studies the asymmetries develop due to the storm s response to imbalances caused by the shear the storms in shear weaken with time and eventually reach an approximate steady state intensity that is well below their theoretical maximum potential intensity as expected the magnitude of the weakening increases with increasing shear all of the storms experience time lags between the imposition of the large scale shear and the resulting rise in the minimum central pressure while the lag is at most a few hours when the storm is placed in very strong 15 m s21 shear storms in weaker shears experience much longer lag times with th e5ms 21 shear case showing no signs of weakening until more than 36 h after the shear is applied these lags suggest that the storm intensity is to some degree predictable from observations of largescale shear changes in all cases both the development of the asymmetries in core structure and the subsequent weakening of the storm occur before any resolvable tilt of the storm s vertical axis occurs it is hypothesized that the weakening of the storm occurs via the following sequence of events first the shear causes the structure of the eyewall region to become highly asymmetric throughout the depth of the storm second the asymmetries in the upper troposphere where the storm circulation is weaker become sufficiently strong that air with high values of potential vorticity and equivalent potential temperature are mixed outward rather than into the eye this allows the shear to ventilate the eye resulting in a loss of the warm core at upper levels which causes the central pressure to rise weakening the entire storm the maximum potential vorticity becomes concentrated in saturated portions of the eyewall cloud aloft rather than in the eye third the asymmetric features at upper levels are advected by the shear causing the upper portions of the vortex to tilt approximately downshear the storm weakens from the top down reaching an approximate steady state intensity when the ventilated layer can descend no farther due to the increasing strength and stability of the vortex at lower levels

circumglobal teleconnections the jet stream waveguide and the north atlantic oscillation abstract monthly and seasonally averaged upper tropospheric northern hemisphere winter fields are examined to determine whether the waveguiding effect of the time averaged tropospheric jets on low frequency disturbances that is predicted by theory does affect the behavior of these disturbances it is found that indeed disturbances in the vicinity of the mean jets particularly the jet that stretches across south asia are fundamentally different from those that reside in regions where the mean winds have weaker meridional gradients like the mid pacific patterns of variability in the jets tend to be smaller scale and to consist of zonally oriented chains of anomalies while variability in the mid pacific is composed of patterns with distinct meridional orientation because they are meridionally trapped and zonally elongated patterns associated with the jet stream waveguide connect activity at points that are much farther apart than do patterns in other regions of the globe within the south asian waveg

a new dynamical index for classification of cold surge types over east asia the cold surges over east asia can be classified into wave train type and blocking type according to their dynamic origins in the present study two dynamic indices are proposed to objectively identify cold surge types using potential temperature on the dynamic tropopause at 2 potential vorticity units 2 pvu surface the two indices are designed to represent primary characteristics of the two types of cold surge the wave train index wi is defined as a difference of anomalous on the 2 pvu surface between the western north pacific and northeast china which captures a southward northward intrusion of cold warm air mass related to the trough ridge pattern the blocking index bi is defined as a difference of anomalous between the subarctic region and northeast china which indicates air mass overturning related to a reversal of the usual meridional gradient commonly observed in the occurrence of blocking type cold surge composite analyses based on the distribution of the wi and bi clearly demonstrate the dynamic evolutions of corresponding cold surge types the wave train cold surge is associated with a southeastward expansion of the siberian high and northerly wind near surface which is caused by growing baroclinic waves during the blocking cold surge a geopotential height dipole indicating the subarctic blocking and deepening of east asian coastal trough induces a southward expansion of the siberian high and northeasterly wind compared to the wave train type the blocking cold surge exhibits a longer duration and stronger intensity in the new framework of these dynamic indices we can detect a third type of cold surge when both the wave train and the blocking occur together in addition we can exclude the events that do not have the essential features of the upper tropospheric disturbances or the subarctic anticyclonic circulation which are responsible for cold surge occurrence using the new indices

westward shift of western north pacific tropical cyclogenesis tropical cyclones tcs in the western north pacific or typhoons account for one third of all tcs in the world and the change of the mean tc genesis location can affect billions of people in pacific islands and asian countries the annual mean tc genesis longitude is generally controlled by the east west shift of the tropical upper tropospheric trough tutt a pronounced westward shift in the tutt is found in all of the available reanalysis data sets during 1979 2012 suppressing tc genesis in the eastern portion east of 145 e of the western north pacific basin due to the enhanced vertical wind shear associated with the tutt shift as a result the annual mean tc genesis longitude has significantly shifted westward since 1979 the westward shifting trends in the tutt and tc genesis are associated with the enhanced tropical tropospheric warming which is consistent with the response of the tropospheric temperature to global warming

processes for occurrence of strong cold events over eastern china abstracta strong cold event hit eastern china around 24 january 2016 with surface air temperature reaching more than 10 c below the climatological mean in most regions of eastern china south of 40 n a total of 37 strong cold events similar to the january 2016 event with temperature anomalies over eastern china exceeding 5 c have been identified during the winters from 1979 80 to 2015 16 a comparative analysis of events with surface temperature anomalies of the same intensity but limited to north of 40 n indicates that the southward invasion of cold air to eastern china south of 40 n is related to two factors one is the latitudinal location of the upper level wave train the surface siberian high and the midtropospheric east asian trough over the mid to high latitude eurasian continent the other is a subtropical upper level wave train emanating from the midlatitude north atlantic the emergence of the subtropical wave train is related to the positive phase of the north atlantic oscillation nao wh

performance of the cmip5 models in simulating the arctic oscillation during boreal spring this study evaluates the performance of thirty coupled models from the coupled model intercomparison project phase 5 cmip5 in capturing the arctic oscillation ao during boreal spring we focus on model s ability in simulating spring ao s spatial structure dominant temporal frequencies and climatic impacts the anomalous anticyclone over the north pacific and the north atlantic in the positive spring ao phase is much stronger in most of the models than in the observations this may be due to that most models simulate a stronger interannual variability of atmospheric anomalies over the north pacific and north atlantic in addition the center of the anomalous anticyclone over the north pacific in the mme shifts obviously southeastward and that over the north atlantic shift northeastward compared to the observations inter model longitudinal spread is larger than the latitudinal spread in the anomalous anticyclone center over both the north pacific and north atlantic most of the models produce periods longer than the observed 4 year spectral peak in spring ao index in addition the model s ability in reproducing the vertical structure of zonal wind tends to have a close relation with the model s performance in capturing the vertical structure of air temperature related to the spring ao furthermore there exist larger spreads among the models in simulating the spring ao related surface air temperature over the russian far east and the west coast of north america these spreads were partly related to the biases of the models in capturing the atmospheric circulation anomalies related to the pacific center of the spring ao

annular modes in the extratropical circulation part i month to month variability the leading modes of variability of the extratropical circulation in both hemispheres are characterized by deep zonally symmetric or annular structures with geopotential height perturbations of opposing signs in the polar cap region and in the surrounding zonal ring centered near 458 latitude the structure and dynamics of the southern hemisphere sh annular mode have been extensively documented whereas the existence of a northern hemisphere nh mode herein referred to as the arctic oscillation ao has only recently been recognized like the sh mode the ao can be defined as the leading empirical orthogonal function of the sea level pressure field or of the zonally symmetric geopotential height or zonal wind fields in this paper the structure and seasonality of the nh and sh modes are compared based on data from the national centers for environmental prediction national center for atmospheric research reanalysis and supplementary datasets the structures of the nh and sh annular modes are shown to be remarkably similar not only in the zonally averaged geopotential height and zonal wind fields but in the mean meridional circulations as well both exist year round in the troposphere but they amplify with height upward into the stratosphere during those seasons in which the strength of the zonal flow is conducive to strong planetary wave mean flow interaction midwinter in the nh and late spring in the sh during these active seasons the annular modes modulate the strength of the lagrangian mean circulation in the lower stratosphere total column ozone and tropopause height over mid and high latitudes and the strength of the trade winds of their respective hemispheres the nh mode also contains an embedded planetary wave signature with expressions in surface air temperature precipitation total column ozone and tropopause height it is argued that the horizontal temperature advection by the perturbed zonal mean zonal wind field in the lower troposphere is instrumental in forcing this pattern a companion paper documents the striking resemblance between the structure of the annular modes and observed climate trends over the past few decades

an east asian cold surge case study abstract since a cold surge is a hazardous weather phenomenon in east asia the rapid population increase and economic growth over the past two decades require improvement in forecasting cold surges and their related weather events over this region however without a better understanding of these events this task cannot be accomplished a cold surge with a well defined cold front passing through taiwan was selected to illustrate its impact on the east asian weather system this case is typical of a large portion of surges occurring in the region major findings of this study are as follows coupling with the upper ridge trough structures of the wave train straddling the eastern seaboard of northeast asia cold surges occur sequentially a cold front with a prefront high pressure zone is formed by the new surge outflow interacting with the anticyclone of the aging surge the warm moist air advected northeastward along the cold front assists the development of the new surge s low center while the prefron

a strengthened impact of november arctic oscillation on subsequent tropical pacific sea surface temperature variation since the late 1970s the connection between november arctic oscillation ao and the following spring summer tropical pacific sea surface temperature sst experienced a pronounced enhancement around the late 1970s the connection was weak before but strong after the late 1970s the present study investigates the plausible reasons for the connection change after the late 1970s significant anomalous cyclone appears over subtropical north pacific and pronounced anomalous westerly winds occur over tropical western pacific in the positive phase of november ao as such november ao could exert a significant influence on the subsequent spring summer tropical pacific sst variation by contrast before the late 1970s anomalous cyclone and associated anomalous westerly winds to its south are weak and shift northward thereby the connection between november ao and tropical pacific sst is weak further analyses suggest that the interdecadal change in the anomalous cyclone over the subtropical north pacific may be related to the change in the november ao s pacific component and the strength of feedback of synoptic scale eddy to mean flow specifically after the late 1970s november ao s pacific component displays a zonally elongated structure which is favorable for the formation of easterly wind anomalies over the mid latitude north pacific and related wave mean flow interaction in addition feedback of synoptic eddy to mean flow is enhanced after the late 1970s which is partly related to the intensification of the north pacific storm track this may also contribute to enhancement of the anomalous cyclone over the subtropical pacific

interdecadal variations in the relationship between the winter north atlantic oscillation and temperature in south central china abstractinterdecadal variations in the relationship between the winter north atlantic oscillation nao and surface air temperature in china are investigated using observational and reanalysis data focus is on south central china in which temperature variability is strongly related to the nao it is revealed that the relationship shows clear interdecadal variations in midwinter during 1951 2015 a relatively weak in phase relationship occurs before the early 1970s p1 but a significant out of phase relationship dominates in the last two decades of the twentieth century p2 though it is clearly weaker from the late 1990s onward observational evidence shows that such interdecadal variations are related mainly to variations in the spatial pattern and amplitude of the nao the northern center of the nao shifted eastward over the second half of the twentieth century in addition the amplitude of the center strengthened from p1 to p2 resulting in a perturbation in the atmospheric circulation response p

asian jet waveguide and a downstream extension of the north atlantic oscillation abstract anomalous atmospheric fields associated with the north atlantic oscillation nao are analyzed on interannual and intraseasonal time scales in order to examine the extent to which the nao is a regional phenomenon analyses on the interannual time scale reveal that the nao signal is relatively confined to the euro atlantic sector in december while it extends toward east asia and the north pacific in february the difference is most clearly seen in the meridional wind anomaly which shows a wave train along the asian jet collocated with an anomalous vorticity source near the jet entrance diagnoses using a linear barotropic model indicate that this wave train is interpreted as quasi stationary rossby waves trapped on the asian jet waveguide and effectively excited by the anomalous upper level convergence over the mediterranean sea it is found that when the nao accompanies the mediterranean convergence mc anomaly most frequently seen in february the nao indeed has a much wider horizontal str

decadal oscillation of spring rain in northern taiwan 1 this study found that the spring february april rainfall in northern taiwan has fluctuated concurrently with the pacific decadal oscillation pdo since the early 20th century it is proposed that this fluctuation in spring rain is induced by the tropical sea surface temperature sst anomaly embedded in the pdo which has been known to oscillate in opposite phase to the sst in the extra tropical north pacific when the pdo index is positive negative the sst over the tropical central eastern pacific is warmer colder than normal and a low level anti cyclonic cyclonic anomalous flow is induced over the philippine sea this anomalous anti cyclonic cyclonic flow results in southwesterly northeasterly anomalous winds to the east of taiwan and enhances reduces the trough extending southwestward from southern japan to northern taiwan as a consequence more less spring rain occurs in northern taiwan during the positive negative pdo phases

is the poleward migration of tropical cyclone maximum intensity associated with a poleward migration of tropical cyclone genesis a recent study showed that the global average latitude where tropical cyclones achieve their lifetime maximum intensity has been migrating poleward at a rate of about one half degree of latitude per decade over the last 30 years in each hemisphere however it does not answer a critical question is the poleward migration of tropical cyclone lifetime maximum intensity associated with a poleward migration of tropical cyclone genesis in this study we will examine this question first we analyze changes in the environmental variables associated with tropical cyclone genesis namely entropy deficit potential intensity vertical wind shear vorticity skin temperature and specific humidity at 500 hpa in reanalysis datasets between 1980 and 2013 then a selection of these variables is combined into two tropical cyclone genesis indices that empirically relate tropical cyclone genesis to large scale variables we find a shift toward greater smaller average potential number of genesis at higher lower latitudes over most regions of the pacific ocean which is consistent with a migration of tropical cyclone genesis towards higher latitudes we then examine the global best track archive and find coherent and significant poleward shifts in mean genesis position over the pacific ocean basins

phase asymmetric downstream development of the north atlantic oscillation and its impact on the east asian winter monsoon 1 the phase asymmetry in a downstream pattern of the north atlantic oscillation nao is examined during boreal winter time we compared the downstream anomaly patterns associated with the positive and negative persistent nao events over several days both phases of the persistent nao events accompany quasi stationary wave trains in downstream upper levels however a distinct low level anomaly appears only for the negative persistent nao events the low level anomaly migrates eastward as a surface anticyclone that is confined to the low troposphere a few days later the surface anticyclone reaches central siberia and induces cold advection over east asia therefore the phase dependent downstream development of the nao expands the impact of the nao to the east asian region we also discuss the possible interaction between the upper and lower level anomalies a necessary condition for the amplification of the siberian high

the effects of deep water cycling on planetary thermal evolution 1 we use a parameterized convection model to investigate the effects of deep water cycling on the thermal evolution of an earth like planet the model incorporates two water reservoirs a surface and an interior mantle reservoir exchange between the two is calculated using a mantle convection parameterization that allows for temperature and water dependent mantle viscosity together with internally self consistent degassing and regassing parameterizations the balance between degassing and regassing depends on the average spreading rate of tectonic plates the amount of water partitioned into melt the thickness of a mantle melt zone and of a hydrated layer at the top of subducting plates degassing scales with melt zone thickness such that an early period of extensive melting would create a drier and more viscous mantle shifting the solidus line in a direction that would reduce the melt zone thickness and the rate of mantle heat loss coupling a hydrated zone thickness dependent regassing factor to the model to mimic water delivery to the mantle via a serpentinized layer allows for the potential of a reversing point where the overall water flow direction switches from degassing to regassing as the mantle cools the water effect on viscosity creates a negative feedback that tends to regulate the final amount of water in the mantle so it is not strongly dependent on the initial amount of planetary water the final amount of water in the surface reservoir is then determined by this feedback effect together with the initial water budget of the entire planet this implies that if the initial water budget of a planet can be estimated from planetary formation models then the volume of surface water can be used to estimate the volume of water in the mantle of an earth like planet applying this methodology to the earth leads to predictions for water concentration in the earth s mantle that are in line with geochemical and petrological constraints

relationship between the arctic oscillation and cold surges over east asia abstract the present study reveals the changes in the characteristics of cold surges over east asia associated with the arctic oscillation ao based on circulation features cold surges are grouped into two general types wave train and blocking types the blocking type of cold surge tends to occur during negative ao periods that is the ao related polarity of the blocking type however the wave train type is observed during both positive and negative ao periods although the wave train features associated with negative ao are relatively weaker the cold surges during negative ao are stronger than those during positive ao in terms of both amplitude and duration the cold surges during positive ao in which the extent of effect is confined to inland china passes through east asia quickly because of weaker siberian high and aleutian low leading to short duration of these cold surges in contrast the cold surge during negative ao characterized by a well organized anticyclone cyclone couplet with high p

stratospheric origin of cold surge occurrence in east asia 1 in the present study we have found a precursory signal in the stratospheric circulation prior to the cold surge occurrence in east asia over northern eurasia about one week before the cold surge occurrence strong stratospheric negative potential vorticity anomalies and rising of geopotential height are observed the dynamic linkage between the stratospheric perturbations and the tropospheric adjustment along with initial disturbances for a cold surge occurrence are discussed

geographical dependence of upper level blocking formation associated with intraseasonal amplification of the siberian high abstract intraseasonal amplification events of the surface siberian high in winter are generally associated with blocking ridge formation in the upper troposphere composite analysis applied to the 20 strongest intraseasonal events of upper level anticyclonic anomalies at every grid point over siberia reveals that the blocking formation differs fundamentally between the east and west of the climatological upper level trough over the far east to the west what can be called wave train atlantic origin type is common where a blocking ridge develops from anomalies as a component of a quasi stationary rossby wave train propagating across the eurasian continent under modest feedback forcing from transient eddies to the east of the trough what can be called pacific origin type dominates where a blocking ridge forms in association with westward development of anticyclonic anomalies from the north pacific under stronger feedback forcing from the pacific storm track regardless of a particular type of bl

interannual variations of the dominant modes of east asian winter monsoon and possible links to arctic sea ice two dominant modes of the winter temperature over east asia a northern mode and a southern mode and their links with arctic climate conditions are analyzed the relationships of the two modes with arctic sea ice are different the northern mode is closely linked to variations in sea ice of the arctic barents laptev sea in previous autumn and most of the arctic in concurrent winter the southern mode seems independent from the arctic sea ice variations but is associated with sea surface temperature sst anomalies in the equatorial central eastern pacific results suggest an effect of arctic sea ice variation on the northern mode and an influence of tropical sst anomalies on the southern mode reduced sea ice over the arctic increases 1000 500 hpa thickness over the high latitudes of eurasian continent which reduces the meridional thickness gradient between the middle and high latitudes and thus weakens the extratropical upper level zonal wind the weakened zonal wind provides a favorable dynamic condition for the development of a high latitude ridge around the ural mountain reduced arctic sea ice also tends to enhance the siberian high through both thermodynamic and dynamic processes the above atmospheric circulation patterns provide a favorable condition for the intrusion of cold air to northern east asia

influence of the madden julian oscillation on wintertime surface air temperature and cold surges in east asia 1 the variations of wintertime surface air temperature sat and the occurrences of cold surges over east asia in association with the madden and julian oscillation mjo are examined the mjo is defined as a combination of the two leading empirical orthogonal function modes of 850 and 200 hpa zonal winds and outgoing longwave radiation in the tropics the spatial pattern and magnitude of sat anomalies over east asia significantly change with respect to mjo phases composite analysis reveals that the mjo sat relationship is mainly affected by strong temperature advection in the lower troposphere in addition occurrences of cold surges are identified using objectively determined synoptic criteria and their relation to the mjo is analyzed most extreme cold surges occur when the mjo convection center is located over the indian ocean and it is suggested that mjo induced circulation anomalies may reinforce the amplification of normal cold surges to extreme cold surges

combined effects of the mjo and the arctic oscillation on the intraseasonal eastern china winter temperature variations abstractthe present study reveals that the madden julian oscillation mjo related temperature anomalies over east asia have notable differences among positive neutral and negative arctic oscilla

downstream development of the summertime tropical cyclone submonthly wave pattern in the extratropical north pacific abstract the impact of tropical perturbation on the extratropical wave activity in the north pacific in the submonthly time scale is demonstrated here previous studies identified a tropical cyclone tc submonthly wave pattern which propagated north northwestward in the philippine sea and recurved in the oceanic region between japan and taiwan this study found that after the arrival of the tc submonthly wave pattern at the recurving region the eastward propagating wave activity in the extratropical north pacific was significantly enhanced it is suggested that the tc submonthly wave pattern which is originated in the tropical western north pacific enhances the eastward energy propagation of rossby wave like perturbation in the extratropical north pacific and may have an impact on the long range weather predictability in the eastern north pacific and western north america

the association between stratospheric weak polar vortex events and cold air outbreaks in the northern hemisphere previous studies have identified an association between temperature anomalies in the northern hemisphere and the strength of stratospheric polar westerlies large regions in northern asia europe and north america have been found to cool during the mature and late stages of weak vortex events in the stratosphere a substantial part of the temperature changes are associated with changes in the northern annular mode nam and north atlantic oscillation nao pressure patterns in the troposphere the apparent coupling between the stratosphere and the troposphere may be of relevance for weather forecasting but only if the temporal and spatial nature of the coupling is known using 51 winters of re analysis data we show that the development of the lower tropospheric temperature relative to stratospheric weak polar vortex events goes through a series of well defined stages including the formation of geographically distinct cold air outbreaks at the inception of weak vortex events a precursor signal in the form of a strong high pressure anomaly over northwest eurasia is associated with long lived and robust cold anomalies over asia and europe a few weeks later near the mature stage of the weak vortex events a shorter lived cold anomaly emerges off the east coast of north america the probability of cold air outbreaks increases by more than 50 in one or more of these regions during all phases of the weak vortex events this shows that the stratospheric polar vortex contains information that can be used to enhance forecasts of cold air outbreaks as large changes in the frequency of extremes are involved this process is important for the medium range and seasonal prediction of extreme cold winter days three hundred year pre industrial control simulations by 13 coupled climate models corroborate our results copyright 2010 royal meteorological society and crown copyright

contrasting impacts of the arctic oscillation on surface air temperature anomalies in southern china between early and middle to late winter abstractin the boreal winter the arctic oscillation ao evidently acts to influence surface air temperature sat anomalies in china this study reveals a large intraseasonal variation in the relationship between the winter ao and southern china sat anomalies specifically a weak in phase relationship occurs in december but a significant out of phase relationship occurs in january and february the authors show that the linkage between the ao and southern china sat anomalies strongly depends on the ao associated changes in the middle east jet stream mejs and that such an ao mejs relationship is characterized by a significant difference between early and middle to late winter in middle to late winter the azores center of high pressure anomalies in the positive ao phase usually extends eastward and yields a significantly anomalous upper level convergence over the mediterranean sea which can excite a rossby wave train spanning the arabian sea and intensify the mejs in early winter however the azo

global view of the intraseasonal oscillation during northern winter abstract in this study svd analysis is applied to a normalized 200 mb streamfunction olr covariance matrix to extract the most recurrent coupled pattern in the northern winter after the removal of the climatological seasonal cycle and seasonal means for each winter the first two singular vectors are on an intraseasonal timescale and the combination of the two forms an oscillation it is characterized by eastward propagation in the indian ocean and the western pacific standing oscillations in both the tropics and the extratropics and the poleward propagation of a zonally symmetric structure although there exists an eastwardly propagating pattern the phase relationship between geopotential wind and streamfunction fields is inconsistent with that of equatorial kelvin waves eastward propagation is most evident in the tropics of the southern hemisphere while the signals in the northern hemisphere are characterized by standing oscillations the distinct characteristics of the northern and southern he

global teleconnections in the 250 mb streamfunction field during the northern hemisphere winter abstract teleconnections of the streamfunction in the global domain based on ecmwf 250 mb winds for the 11 northern winters from 1978 79 through 1988 89 are documented in this study a zonal structure with a node near the equator indicating an out of phase relationship between the streamfunctions in the northern and southern hemisphere appears to mask the fluctuations of the asymmetric components of streamfunction after removing zonal means a global pattern emerges as the dominant structure in the low frequency band this pattern consists of several dipoles straddling either the exit region of midlatitude jets or the equator indicating the existence of teleconnections not only between the midlatitudes and the tropics but also between the northern and southern hemispheres teleconnection patterns in the intermediate frequency band are predominantly wavelike seven waveguides are identified based on the one point lag correlation maps for base points near the maximum teleconnectivity among them are thr

the relationship between the north atlantic jet and tropical convection over the indian and western pacific oceans abstractboreal winter jet variability over the north atlantic is investigated using 40 yr european centre for medium range weather forecasts re analysis era 40 data where the variability is defined by the first eof of the zonal wind on seven vertical levels the principal component time series of this eof is referred to as the jet index a pattern correlation analysis indicates that the jet index more accurately describes intraseasonal north atlantic zonal wind variability than does the north atlantic oscillation nao a series of composite calculations of the jet index based on events of intraseasonal convective precipitation over the tropical indian and western pacific oceans reveals the following statistically significant relationships 1 negative jet events lead enhanced indian ocean precipitation 2 positive jet events lag enhanced indian ocean precipitation 3 positive jet events lead enhanced western pacific ocean precipitation and 4 negative jet events lag enhanced western pacific ocean p

the melting arctic and midlatitude weather patterns are they connected abstractthe potential of recent arctic changes to influence hemispheric weather is a complex and controversial topic with considerable uncertainty as time series of potential linkages are short 10 yr and understanding involves the relative contribution of direct forcing by arctic changes on a chaotic climatic system a way forward is through further investigation of atmospheric dynamic mechanisms during several exceptionally warm arctic winters since 2007 sea ice loss in the barents and kara seas initiated eastward propagating wave trains of high and low pressure anomalous high pressure east of the ural mountains advected arctic air over central and eastern asia resulting in persistent cold spells blocking near greenland related to low level temperature anomalies led to northerly flow into eastern north america inducing persistent cold periods potential arctic connections in europe are less clear variability in the north pacific can reinforce downstream arctic changes and arctic amplification

the influence of boreal spring arctic oscillation on the subsequent winter enso in cmip5 models this study examines the influence of boreal spring arctic oscillation ao on the subsequent winter el nino southern oscillation enso using 15 climate model outputs from the coupled model intercomparison project phase 5 cmip5 results show that out of the 15 cmip5 models ccsm4 and cnrm cm5 can well reproduce the significant ao enso connection these two models capture the observed spring ao related anomalous cyclone anticyclone over the subtropical western central north pacific and westerly easterly winds over the tropical western central pacific in contrast the spring ao related anomalous circulation over the subtropical north pacific is insignificant in the other 13 models and the simulations in these models cannot capture the significant influence of the spring ao on enso further analyses indicate that the performance of the cmip5 simulations in reproducing the ao enso connection is related to the ability in simulating the spring north pacific synoptic eddy intensity and the spring ao s pacific component strong synoptic scale eddy intensity results in a strong synoptic eddy feedback on the mean flow leading to strong cyclonic circulation anomalies over the subtropical north pacific which contributes to a significant ao enso connection in addition a strong spring ao s pacific component and associated easterly wind anomalies to its south may provide more favorable conditions for the development of spring ao related cyclonic circulation anomalies over the subtropical north pacific

relationship between ural siberian blocking and the east asian winter monsoon in relation to the arctic oscillation and the el nino southern oscillation this study attempts to assess the possible linkage between ural siberian blocking and the east asian winter monsoon eawm during the boreal winter the dominance of blocking thermally enhances cold advection downstream the frequent occurrence of ural siberian blocking potentially promotes a cold eawm and vice versa the seasonal blocking activity can be regarded as the combined effect of the arctic oscillation ao and the el nino southern oscillation enso weakened strengthened meridional flow in the positive negative phase of the ao is unfavorable favorable for the formation of blocking highs because the ao shows a close relationship with the north atlantic oscillation nao its teleconnection with ural siberian blocking may exist in the form of an eastward propagating wave train be that as it may the wave train signal across east asia may be disturbed by the external effect of a strong enso event which probably enhances weakens the westerlies near siberia in its warm cold phase consequently the blocking eawm relationship is stronger weaker when the ao and enso are in phase out of phase if both ao and enso attain the positive negative phase the siberian high tends to be weaker stronger and the temperature tends to be higher lower in east asia with less more ural siberian blocking on the other hand if they are out of phase they are not strongly linked to the intensity of the siberian high and the blocking activity over ural siberia is unclear

decadal relationship between the north atlantic oscillation and cold surge frequency in taiwan 1 the close decadal relationship between the north atlantic oscillation nao and the cold surge frequency in northern taiwan is identified the cold surge frequency was higher lower in 1957 1977 1981 2001 which corresponded to the negative positive phase of the nao the teleconnection pattern associated with the nao suggests that the siberian high the ridge upstream of lake baikal and the east asian trough which are well known circulation characteristics favorable for cold surge occurrences were enhanced in the negative nao phase a weakened upper level convergence over the mediterranean sahara occurring in the negative nao phase was associated with a wave like pattern spreading toward east asia along the subtropical jet stream barotropic modeling results suggest that the suppressed upper level convergence in the mediterranean sahara region may force a wave train emanating toward east asia along the subtropical jet stream which acts as a rossby waveguide the barotropic wave pattern may result in a stronger low level northerly over subtropical east asia and create a favorable background for the further southward penetration of cold air and therefore more frequent cold surge occurrence the same process may be applied to the period when the nao is in the positive phase

a synoptic and dynamical characterization of wave train and blocking cold surge over east asia through an agglomerative hierarchical clustering method cold surges over east asia are classified into two distinct types based on the spatial pattern of the geopotential height anomalies at 300 hpa one is the wave train type that is associated with developing large scale waves across the eurasian continent the other is the blocking type whose occurrence accompanies subarctic blocking during the wave train cold surge growing baroclinic waves induce a southeastward expansion of the siberian high and strong northerly winds over east asia blocking cold surge on the other hand is associated with a southward expansion of the siberian high and northeasterly winds inherent to a height dipole consisting of the subarctic blocking and the east asian coastal trough the blocking cold surge tends to be more intense and last longer compared to the wave train type the wave train cold surge is associated with the formation of a negative upper tropospheric height anomaly southeast of greenland approximately 12 days before the surge occurrence further analysis of isentropic potential vorticity reveals that this height anomaly could originate from the lower stratosphere over the north atlantic cold surge of the blocking type occurs with an amplifying positive geopotential and a negative potential vorticity anomaly over the arctic and the northern eurasia in stratosphere these anomalies resemble the stratospheric signature of a negative phase of the arctic oscillation this stratospheric feature is further demonstrated by the observation that the blocking type cold surge occurs more often when the arctic oscillation is in its negative phase

global extratropical response to diabatic heating variability of the asian summer monsoon abstract global teleconnections associated with the asian summer monsoon convective activities are investigated based on monthly data of 29 northern hemisphere summers defined as june september jjas two distinct teleconnection patterns are identified that are associated respectively with variabilities of the indian summer monsoon and the western north pacific summer monsoon the indian summer monsoon convective activity is associated with a global pattern that has a far reaching connection in both hemispheres whereas the western north pacific summer monsoon convective activity is connected to a southern hemisphere wave train that influences the high latitude south pacific and south america a global primitive equation model is utilized to assess the cause of the global circulation anomalies the model responses to anomalous heatings of both monsoon systems match the general features of the observed circulation anomalies well and they are mainly controlled by linear processes the response patterns ar

interannual variation of the east asian cold surge activity abstract the occurrence frequency of the east asian cold surge exhibits an interannual variation in concert with the el nino southern oscillation enso cycle that is the cold surge occurs more less frequently during warm cold enso winters because the cold surge high low dipoles are coupled with the upper level synoptic short waves any mechanism modulating the activity of these waves would affect the cold surge activity the streamfunction budget analysis in the short wave regime indicates that the development of the cold surge short wave train over east asia and the northwest pacific is modulated by the north pacific enso short wave train due to the coupling between the upper level cold surge short wave train and the surface cold surge dipole it is inferred from this streamfunction budget analysis that the interannual variation of the cold surge occurrence frequency is a result of this modulation

fluid ascent and magma storage beneath gunung merapi revealed by multi scale seismic imaging abstract magma is fed to a volcano through a complex plumbing system that involves not only shallow structures beneath the volcano edifice but also deep structures and processes within the underlying crust and upper mantle this paper summarizes seismic experiments carried out over many years at gunung merapi in central java these have resolved the 3d seismic velocity structure of the merapi edifice and provided a 3d structural image of the lithosphere and subduction zone beneath central java earthquake locations reveal that with distance from the trench the dip of the subducting slab steepens from nearly horizontal 0 150 km through 45 150 250 km to 70 250 km the slab appears as a 30 km thick double layer of seismicity in a depth range of 80 km to 150 km and it can be identified seismically to a depth of more than 600 km the active volcanoes of merapi sumbing and lawu are located at the edge of a large low velocity body that extends from the upper crust to the upper mantle beneath central java shear wave signals recorded above this anomaly are strongly attenuated compared to neighboring areas the anomalous body has a detected volume of 50 000 km3 and a decrease in p and s velocities relative to adjacent regions of up to 30 the resulting vp vs ratio of up to 1 9 is unusually high for lower crust additionally the anomaly extends along a 45 degree slope downward from beneath the volcanic arc and meets the slab at 100 km depth we interpret this sloping anomaly as a pathway for fluids and partial melts increased seismicity is observed at depths of 100 km possibly as a result of dehydration of the subducting slab with related fluid releases causing partial melting of overlying mantle material the large velocity reduction and high vp vs ratio in the region are consistent with an increase in temperature a reduction of shear strength and the presence of fluids or melts of 13 to 25 vol the detected strong anomaly beneath central java is unique in size and amplitude compared to other subduction zones the geophysical evidence suggests that this segment of the arc has a high magma flux and is thus capable of developing even larger shallow crustal reservoirs and more voluminous explosive eruptions in the future

a linkage between the north atlantic oscillation and its downstream development due to the existence of a blocking ridge 1 in this work the spatial growth of the north atlantic oscillation nao and its relationship to downstream development are examined in contrast to positive nao events which are primarily initiated over the western north atlantic negative persistent nao events tend to be preceded by a blocking ridge in the vicinity of northern europe this blocking ridge contributes to the growth of negative nao events through a low frequency eddy interaction it is also shown that a noticeable downstream development is dominant only for negative persistent nao events that are preceded by the blocking ridge while the blocking ridge exists over inland eurasia it induces anticyclonic circulation near the surface over siberia as the nao grows a stationary wave train that originates from the north atlantic transfers wave energy downstream toward siberia the surface anticyclone is then reinforced by the wave train and begins to migrate eastward this process explains the distinct impact of the negative nao on the downstream eurasian region

tropical upper tropospheric potential vorticity intrusions during sudden stratospheric warmings abstractthe intrusion of lower stratospheric extratropical potential vorticity into the tropical upper troposphere in the weeks surrounding the occurrence of sudden stratospheric warmings ssws is examined the analysis reveals that ssw related pv intrusions are significantly stronger penetrate more deeply into the tropics and exhibit distinct geographic distributions compared to their climatological counterparts while climatological upper tropospheric and lower stratospheric utls pv intrusions are generally attributed to synoptic scale rossby wave breaking it is found that ssw related pv intrusions are governed by planetary scale wave disturbances that deform the extratropical meridional pv gradient maximum equatorward as these deformations unfold planetary scale wave breaking along the edge of the polar vortex extends deeply into the subtropical and tropical utls in addition the material pv deformations also reorganize the geographic structure of the utls waveguide which alters where synopti

an analysis of the large scale climate anomalies associated with the snowstorms affecting china in january 2008 abstract extraordinarily frequent and long lasting snowstorms affected china in january 2008 causing above normal precipitation below normal temperature and severe icing conditions over central southern china these snowstorms were closely linked to the change in the middle east jet stream mejs which intensified and shifted southeastward the change in mejs was accompanied by southeastward shifts of the ridge and the trough over europe and western asia the intensified mejs also strengthened the trough embedded in the southern branch of the subtropical westerlies over the southern tibetan plateau enhancing the water vapor transport from western asia and the bay of bengal to china in the meantime the subtropical western pacific high swph was stronger and its ridgeline was farther north than normal the anomalous high slowed down the eastward propagation of weather systems to the pacific and favored convergence of water vapor over central southern china the mejs is usually strong when the arctic

another look at interannual to interdecadal variations of the east asian winter monsoon the northern and southern temperature modes abstract this study investigates the causes of interannual to interdecadal variability of the east asian ea 0 60 n 100 140 e winter monsoon eawm over the past 50 yr 1957 2006 the winter mean surface air temperature variations are dominated by two distinct principal modes that together account for 74 of the total temperature variance the two modes have notably different circulation structures and sources of variability the northern mode characterized by a westward shift of the ea major trough and enhanced surface pressure over central siberia represents a cold winter in the northern ea resulting from cold air intrusion from central siberia the southern mode on the other hand features a deepening ea trough and increased surface pressure over mongolia representing a cold winter south of 40 n resulting from cold air intrusion from western mongolia the cold northern mode is preceded by excessive autumn snow covers over southern siberia mongolia whereas the cold southern mode is preceded b

decadal to bi decadal rainfall variation in the western pacific a footprint of south pacific decadal variability 1 decadal to bi decadal rainfall variation in the western pacific during july october in the second half of the 20th century was identified in this study this 10 20 year quasi periodic oscillation was found associated with the leading sea surface temperature sst pattern in the south pacific which is called the 10 20 year south pacific inter decadal oscillation spdo it is suggested that the 10 20 year fluctuation of the spdo resulted in significant decadal to bi decadal rainfall variation along the western pacific coast the anomalous divergent circulations were likely driven by the ssta sst anomaly and resulted in the anomalous rainfall in eastern australia and the maritime continent it is conjectured that the ssta in the western south pacific led to an anomalous hadley like circulation in the western pacific and indirectly affected the convection activity in the philippine sea which in turn impacted the rainfall in the philippines taiwan and korea

a joint interpretation of electromagnetic and seismic tomography models suggests the mantle transition zone below europe is dry abstract the three dimensional 3d electrical conductivity distribution in the mantle transition zone mtz below europe is resolved by directly inverting geomagnetic response functions from 12 selected european observatories comparison of the conductivity image with the results of global seismic tomography reveals a good correlation between low conductivity and high velocity anomalies at depths of 400 700 km beneath the mediterranean subduction zone in central europe interpretation of the 3d conductivity model combined with seismic tomography indicates that the european mtz is drier than the mtz beneath the western pacific subduction zone even though the subducted slab material is stagnating similarly in both regions

the leading interannual variability modes of winter surface air temperature over southeast asia the present study analyzes the leading interannual variability modes of southeast asian surface air temperature sat during boreal winter the first empirical orthogonal function eof1 mode displays same sign sat anomalies over southeast asia with a center around the north indo china peninsula and south china the second eof eof2 shows a dipole sat anomaly pattern between the indo china peninsula and south china surface heat flux change may not be able to explain sat variation related to the eof1 but explain partly the sat change associated with the eof2 atmospheric anomalies play a crucial role in the sat variations via wind induced temperature advection specifically for the eof1 marked northerly anomalies appear over the southeast asia which bring colder air from higher latitude and contribute to negative sat anomalies change in the intensity of arctic oscillation siberian high and la nina like sea surface temperature sst anomalies over the tropical central eastern pacific play a key role in forming the northerly anomalies related to the eof1 for the eof2 at the lower troposphere a pair of anomalous cyclones appears over the tropical north and south indian ocean together with southwesterly wind anomalies extending from the indian ocean to the indo china peninsula which favor positive sat anomalies there formation of the twin cyclones is likely to be a gill type rossby wave response of the tropical indian ocean sst warming at the upper troposphere two wave trains one originated from the arctic region and another from the mediterranean sea contribute collectively to the atmospheric circulation anomalies over southeast asia related to the eof2

widespread fog over the indo gangetic plains and possible links to boreal winter teleconnections boreal wintertime planetary scale atmospheric circulations and their possible consequences to widespread fog occurrences over the indo gangetic plains igp region of the himalayan valley are investigated in this study among the different fog types radiation fog type seen at night or early morning hours favored by large scale subsidence aloft and strong near surface inversion is focused in this study a composite analysis reveals that upper air circulation associated with 105 fog days over the igp region show a trail linked to circulation anomalies over the eurasian continents and the arctic circle the findings suggest that there is a footprint of the arctic oscillation ao and conventional eurasian eu circulation patterns linked to anticyclonic circulation aloft over the igp region although widespread igp fog occurrences under the large scale subsidence environment are seen to occur during both phases of ao the negative ao phase high pressure environment over the arctic circle portends a greater likelihood for fog occurrences in the igp region a coupling of positive mid tropospheric height anomalies over western eurasia and the anticyclonic circulation anomalies over the igp region is evident during the igp fog periods concomitant with eu positive height excess over siberia phase further anomalous circulation over the igp region during the fog periods appears to rely more on the strength of the ao negative phase than the circulation strengths over eurasia on the contrary the eurasian circulation largely appears to influence the subsidence aloft over the igp region irrespective of the strength of the ao positive phase it is also noted that upper air circulation during non foggy periods over the igp region has conformity with positive ao phase and rapidly progressing eu pattern these planetary scale teleconnection pathways offer new dynamical insights into comprehending widespread igp fog scenario which have been hitherto perceived mostly from a regional context

modulation of the qbo on the mjo related surface air temperature anomalies over eurasia during boreal winter previous studies have indicated the modulation of the madden julian oscillation mjo by the quasi biennial oscillation qbo and the influence of the mjo on surface temperature over eurasia during boreal winter the present study reveals that the mjo related circulation anomalies are different in easterly and westerly qbo years leading to distinct surface temperature anomaly patterns over eurasia during the easterly qbo years the surface air temperature anomalies over eurasia display a meridional dipole pattern in mjo phase 2 associated with the mid latitude surface anticyclonic anomalies the development of surface anomalous anticyclone is attributed to a combined effect of negative north atlantic oscillation nao related mid latitude wave train and stronger mjo convection triggered poleward propagation of rossby wave train the negative nao is related to the easterly qbo through the holton tan relationship the anomalous overturning circulation excited by the stronger mjo convection in easterly qbo years also contributes to the development and eastward extension of anomalous anticyclone the anticyclonic anomalies induce the meridional temperature anomaly pattern by horizontal advection during the westerly qbo years the surface air temperature anomalies over eurasia show a zonal alternating pattern in mjo phase 3 which corresponds to the development of mid latitude rossby wave train associated with positive nao with a stronger mjo nao connection in westerly qbo years the mjo convection induces upper level divergent wind anomalies contributing partially to the development of the rossby wave source and helping the building of the mid latitude wave train the zonal temperature anomalies over eurasia are also contributed by the horizontal advection associated with surface cyclonic anomalies

asymmetric influence of boreal spring arctic oscillation on subsequent enso previous studies have suggested that the boreal spring arctic oscillation ao could exert a significant influence on the outbreak of el nino southern oscillation enso during the following winter this study further reveals that the influence of the spring ao on the subsequent enso is asymmetric when the spring ao is in its high phase significant el nino like sea surface temperature sst warming anomalies are observed over the tropical central eastern pacific in the following winter however when the spring ao is in its low phase negative sst anomalies over the tropical central eastern pacific are weak and statistically insignificant this asymmetric influence is attributed to the asymmetric features of both the atmospheric circulation anomalies in spring and atmospheric heating anomalies over the subtropical north pacific from spring to summer for the high ao phase composite the anomalous cyclonic circulation over the subtropical western north pacific and the related westerly wind anomalies to its south over the tropical western pacific are strong and significant in spring the tropical zonal wind anomalies would trigger enso events via the excitation of an eastward propagating kelvin wave meanwhile the atmospheric heating anomalies over the subtropical north pacific play an important role in sustaining the westerly wind over the tropical western pacific from spring to summer in contrast the counterparts in the low ao phase composite are weak and statistically insignificant our results indicate that the phase of spring ao should be taken into account when using spring ao as a predictor for enso

the fate of water within earth and super earths and implications for plate tectonics the earth is likely to have acquired most of its water during accretion internal heat of planetesimals by short lived radioisotopes would have caused some water loss but impacts into planetesimals were insufficiently energetic to produce further drying water is thought to be critical for the development of plate tectonics because it lowers viscosities in the asthenosphere enabling subduction the following issue persists if water is necessary for plate tectonics but subduction itself hydrates the upper mantle how is the upper mantle initially hydrated the giant impacts of late accretion created magma lakes and oceans which degassed during solidification to produce a heavy atmosphere however some water would have remained in the mantle trapped within crystallographic defects in nominally anhydrous minerals in this paper we present models demonstrating that processes associated with magma ocean solidification and overturn may segregate sufficient quantities of water within the upper mantle to induce partial melting and produce a damp asthenosphere thereby facilitating plate tectonics and in turn the habitability of earth like extrasolar planets this article is part of the themed issue the origin history and role of water in the evolution of the inner solar system

persistent severe drought in southern china during winter spring 2011 large scale circulation patterns and possible impacting factors 1 severe drought persisted in southern china from january to may in 2011 in this study a statistical analysis is carried out to discuss the multiple possible impacting factors including la nina the north atlantic oscillation nao and the thermal condition of the tibetan plateau tp the la nina event in 2010 11 excited a lower tropospheric anomalous cyclone over the northwestern pacific weakening the northwestern pacific subtropical high and caused an eastward shift of the high as a result transportation of wet and warm moisture from tropical oceans to southern china decreased the la nina event also strengthened the upper tropospheric east asian jet stream and deepened the east asian trough favoring a southward intrusion of dry northerly flow from the siberia the la nina condition in the previous two seasons also seemed to provide precursory signals for the drought moreover in january may 2011 the nao was in a positive phase and it tended to excite stationary rossby waves that were distributed along the sub polar and subtropical waveguides respectively the sub polar one induced an anomalous anticyclone over the siberia favoring a southward intrusion of high latitude northerly flow to southern china the subtropical one associated possibly with the enhanced convection over the broad region from the mediterranean to sahara was favorable for an influence of upper tropospheric flow on southern china the tp might also exert an influence on the drought by weakening the westerly flow to the southern flank of tp and reducing water vapor transport from the bay of bengal to southern china

comparison of the synoptic conditions in midlatitudes accompanying cold surges over eastern asia for the months of december 1974 and 1978 part i monthly mean fields and individual events abstract east asian cold surges during two periods of contrasting intensity december 1974 strong and december 1978 weak are studied it is shown that the midlatitude mechanisms initiating cold surges during both months are quite similar in nature synoptic scale short waves passing through the long wave trough position near the east asian coast act to release the cold air southward from the main reservoir over eastern siberia dynamic descent is initiated by these synoptic scale waves entering the northwesterly flow on the western side of the long wave trough anchored on the coast this is the descent center in the local direct circulation in the entrance region of the east asian jet maximum at 200 mb the frequency and intensity of the cold air surges for a given month depend on the large scale circulation pattern the average flow over asia for december 1974 and 1978 presents a contrast with respect to ridging over the midcontinent in december 1978 the flow was characterized by a low zonal inde

interdecadal variation of winter cold surge path in east asia and its relationship with arctic sea ice abstractthe paths of winter cold surge cs events in east asia ea from 1979 to 2017 are tracked by the flexible particle flexpart model using era interim daily datasets and the probability de

on the link between the subseasonal evolution of the north atlantic oscillation and east asian climate we analyse the impact of the north atlantic oscillation nao on the climate of east asia at subseasonal time scales during both winter and summer these teleconections have mainly been investigated at seasonal and longer time scales while higher frequency links are largely unexplored the nao is defined using extended empirical orthogonal functions on pentad mean observations which allows to elucidate the oscillation s spatial and temporal evolution and clearly separate the development and decay phases the downstream dynamical imprint and associated temperature and precipitation anomalies are quantified by means of a linear regression analysis it is shown that the nao generates a significant climate response over east asia during both the dry and wet seasons whose spatial pattern is highly dependent on the phase of the nao s life cycle temperature and precipitation anomalies develop concurrently with the nao mature phase and reach maximum amplitude 5 10 days later these are shown to be systematically related to mid and high latitude teleconnections across the eurasian continent via eastward propagating quasi stationary rossby waves instigated over the atlantic and terminating in the northeastern pacific these findings underscore the importance of rapidly evolving dynamical processes in governing the nao s downstream impacts and teleconnections with east asia

possible mechanisms for four regimes associated with cold events over east asia circulation patterns associated with cold events over east asia during the winter months of 1948 2014 are classified into four regimes by applying a k means clustering method based on the area weighted pattern correlation the earliest precursor signals for two regimes are anticyclonic anomalies which evolve into ural and central siberian blocking like circulation patterns the earliest precursor signals for the other two regimes are cyclonic anomalies both of which evolve to amplify the east asian trough eat both the blocking like circulation patterns and amplified eat favor the initialization of cold events on average the blocking related regimes tend to last longer the lead time of the earliest precursor signal for the central siberian blocking related regime is only 4 days while those for the other regimes range from 16 to 18 days the north atlantic oscillation plays essential roles both in triggering the precursor for the ural blocking related regime and in amplifying the precursors for all regimes all regimes preferentially occur during the positive phase of the eurasian teleconnection pattern and the negative phase of the el nino southern oscillation for three regimes surface cooling is primarily due to reduced downward infrared radiation and enhanced cold advection for the remaining regime which is associated with the southernmost cooling center sensible and latent heat release and horizontal cold advection dominate the east asian cooling

the arctic oscillation signature in the wintertime geopotential height and temperature fields the leading empirical orthogonal function of the wintertime sea level pressure field is more strongly coupled to surface air temperature fluctuations over the eurasian continent than the north atlantic oscillation nao it resembles the nao in many respects but its primary center of action covers more of the arctic giving it a more zonally symmetric appearance coupled to strong fluctuations at the 50 hpa level on the intraseasonal interannual and interdecadal time scales this arctic oscillation ao can be interpreted as the surface signature of modulations in the strength of the polar vortex aloft it is proposed that the zonally asymmetric surface air temperature and mid tropospheric circulation anomalies observed in association with the ao may be secondary baroclinic features induced by the land sea contrasts the same modal structure is mirrored in the pronounced trends in winter and springtime surface air temperature sea level pressure and 50 hpa height over the past 30 years parts of eurasia have warmed by as much as several k sea level pressure over parts of the arctic has fallen by 4 hpa and the core of the lower stratospheric polar vortex has cooled by several k these trends can be interpreted as the development of a systematic bias in one of the atmosphere s dominant naturally occurring modes of variability

interannual variability of the east asian winter monsoon and related modulations of the planetary waves abstractinterannual variability of the east asian winter monsoon is investigated through composite analysis applied to observational data for 50 recent years although the monsoon activity itself is confined into the lower troposphere its midwinter variability tends to accompany upper tropospheric geopotential height anomalies similar to the eurasian eu and western pacific wp teleconnection patterns the eu like pattern is characterized by a wavy signature over the eurasian continent and the north atlantic with surface temperature anomalies over the far east and north america in the wp like pattern a meridional dipole of upper level height anomalies is evident over the far east these anomaly patterns related to the anomalous winter monsoon activity are found to accompany marked modulations of the climatological development of the upper tropospheric planetary waves from late autumn to midwinter enhanced monsoon activity in january associated with the wp like pattern involves anomalous seasonal

influence of track changes on the poleward shift of lmi location of western north pacific tropical cyclones abstractthe annual mean latitude at which tropical cyclones tcs reach their lifetime maximum intensity lmi over the western north pacific ocean basin has shifted northward since the early 1980s

the generation of global rotational flow by steady idealized tropical divergence abstract tropical convective heating is balanced on the large scale by the adiabatic cooling of ascent the horizontal divergence of the wind above this heating may be viewed as driving the upper tropospheric rotational wind field a vorticity equation model is used to diagnose this relationship it is shown that because of the advection of vorticity by the divergent component of the flow the rossby wave source can be very different from the simple fd source often used in particular an equatorial region of divergence situated in easterly winds can lead to a rossby wave source in the subtropical westerlies where it is extremely effective this part of the source can be relatively insensitive to the longitudinal position of the equatorial divergence a divergence field which is asymmetric about the equator can lead to a quite symmetric rossby wave source for a steady frictionless flow the rossby wave source averaged over regions within closed streamfunction or absolute vorticity contours is under cert

meridional displacement of the east asian trough and its response to the enso forcing this paper examined the underlying dynamic mechanisms associated with the meridional displacement of the east asian trough eat which is closely related to the temperature variability in the southern part of east asian winter monsoon eawm during the southward displacement of the eat the siberian high is stronger and the aleutian low is displaced southward this is due mainly to the anomalous cyclonic flow associated with seasonal eddies over the midlatitude central pacific which enhances the horizontal advection of cold warm air to the southern northern part of the eat in the lower troposphere the cold warm advection narrows thickens the height thickness and results in negative positive temperature anomalies in the southern northern part of the eat these anomalous circulation features can be reasonably explained by the phase of the el nino southern oscillation enso the results are also verified by the numerical experiments with prescribing enso like heat source anomalies over the tropical eastern and western pacific in an anomaly atmospheric general circulation model all of these results advance our understanding for the linkage between the enso and the eawm via its modulation of the eat

impact of subgrid scale orography on equatorial angular momentum budget and the cold surges in a general circulation model abstractthe dynamical relations between equatorial atmospheric angular momentum eaam equatorial mountain torques and cold surges are analyzed in a general circulation model gcm first the authors show that the global eaam budget is well closed in the gcm much better than in the ncep ncar reanalysis they then confirm that the equatorial torques due to the tibetan plateau the rockies and the andes are well related to the cold surges developing over east asia north america and south america respectively for all these mountains a peak in the equatorial mountain torque components precedes by few days the development of a cold surge confirming that the cold surge s preconditioning is dynamically driven by large scale mountains the authors also analyze the contribution of the subgrid scale orography sso parameterizations and find that they contribute substantially to the torques in experiments where these parameterizations are almost entirely reduced over a given massif the authors find th