three eurasian teleconnection patterns spatial structures temporal variability and associated winter climate anomalies the eurasian eu pattern is a distinct teleconnection pattern observed in boreal winter since the eu pattern was first identified three types have been reported in the literature the conventional eu pattern the type 1 eu pattern or scandinavian scand pattern and the type 2 eu pattern or east atlantic west russia eatl wrus pattern based on several reanalysis and observational datasets the three eu patterns are extracted using the rotated empirical orthogonal function method in order to provide a further distinction and understanding of the three eu patterns a comprehensive side by side comparison is performed among them including their temporal variability horizontal and vertical structure related stationary rossby wave activity impact on climate and possible driving factors associated with external forcing the results reveal that all three eu patterns are characterised by a clear quasi barotropic wave train structure but each has a distinct source and centre of action accordingly their impacts on the precipitation and surface air temperature also differ from one other further evidence suggests that the conventional eu pattern is likely driven by anomalous sea surface temperatures sst over the north atlantic in which process the transient eddies are actively involved the scand pattern is partly maintained by the vorticity source over western europe which arises from the anomalous convergence divergence over the mediterranean and is efficiently driven by the tropical and southern indian ocean sst via divergent circulation the eatl wrus pattern shows some linkage to the north american snow cover and the involved process remains unclear and needs further investigation

effects of bi modal waves on overtopping application of uk and dutch prediction methods sometimes dike sections or seawalls are partially protected by low crested structures up to one kilometre in front of these coastal defences and more than one kilometre in length wave energy may be transmitted over these low crested structures or dams and waves can penetrate through various openings these waves have periods similar to the wave periods of the incident waves local wave growth of shorter period waves may become important if some fetch is present between dam and coastal defence wave spectra in front of the dike sections are often therefore bi modal also sea and swell and or irregularly shaped wave generation areas may give rise to these bi modal or double peaked spectra until now little was known about their influence on required dike heights a series of physical model studies conducted at a nominal scale of 1 20 were undertaken by hr wallingford for the flood and coastal defence with emergencies division of the uk ministry of agriculture fisheries and food maff the intention was to provide information on wave breaking behaviour and the impact of bi modal wave conditions on beaches and coastal structures this research was described by coates et al and by hawkes et al wave conditions and wave overtopping were measured for two or three water levels over different bed slopes of 1 50 1 20 and 1 10 during a project for the dutch public works department ijsselmeer district alkyon and infram studied wave structure behaviour over low crested dams and the effect of bi modal seas on required dike heights as a part of this project infram visited hr wallingford and used above research to establish a method for predicting wave overtopping with bi modal seas for dutch applications the research was described partly by van der meer et al at that time it was recognised that the wave and wave overtopping data measured by hr wallingford would be interesting to the dutch public works department for several reasons as they are responsible for establishment of wave boundary conditions and guidelines for safety assessment of the dutch coastal defences the actual work consisted of four parts and was described in full depth in van der meer et al 1 re analysis ot approximately 200 wave flume runs to obtain various time and frequency domain parameters this work was performed by hr wallingford 2 validation of the swan model and analysis of wave breaking formulations this work was performed by alkyon and delft hydraulics 3 validation ot a model on shallow wave height statistics by delft hydraulics and 4 further analysis on wave overtopping by uni and bi modal seas performed by infram in co operation with delft hydraulics only the latter part the wave overtopping analysis is the subject of this paper

exploring the combined effects of the arctic oscillation and enso on the wintertime climate over east asia using self organizing maps to examine the combined effects of the different spatial patterns of the arctic oscillation ao related sea level pressure slp anomalies and the el nino southern oscillation enso related sea surface temperature sst anomalies on the wintertime surface temperature anomalies over east asia a nonlinear method based on self organizing maps is employed investigation of identified regimes reveals that the ao can affect east asian temperature anomalies when there are significant slp anomalies over the arctic ocean and northern parts of eurasian continent analogously enso is found to affect east asian temperature anomalies when significant sst anomalies are present over the tropical central pacific the regimes with the warmest and coldest temperature anomalies over east asia are both associated with the negative phase of the ao the enso activated pacific east asian teleconnection pattern could affect the higher latitude continental regions when the impact of the ao is switched off when the spatial patterns of the ao and enso have significant but opposite impacts on the coastal winds no obvious temperature anomalies can be observed over south china further the circulation state with nearly the same ao and nino3 indices may drive rather different responses in surface temperature over east asia the well known continuous weakening recovery of the east asian winter monsoon that occurred around 1988 2009 can be attributed to the transitions of the spatial patterns of the slp anomalies over the arctic ocean and eurasian continent through their modulation on the occurrences of the ural and central siberian blocking events

eddy contributions at multiple timescales to the evolution of persistent anomalous east asian trough persistent strong and weak east asian trough eat cases during boreal winter are captured by projecting 12 utc geostrophic vorticity onto that of a seasonal strong eat the persistent cases are investigated in terms of seasonal intraseasonal and synoptic temporal scales the evolution of persistent strong and weak eat cases displays characteristics of intraseasonal temporal variation the onset and decay of strong weak cases is associated with the passage of an intraseasonal negative positive 500 hpa height anomaly from northeast asia to the midlatitude central pacific through the region of the eat the onset and decay stages of persistent strong weak eat cases occur in conjunction with a seasonal stronger than normal weaker than normal eat in addition it is noted that the difference between the number of strong and weak cases exhibits significant covariability with the strength of the seasonal eat meanwhile the seasonal eat also plays a role in the development and decay of persistent cases the contributions of dynamic and thermodynamic processes during the evolution of persistent strong and weak eat cases are investigated since the forcing of horizontal temperature advection and that of adiabatic and diabatic processes are likely to offset each other dynamic processes make a more important contribution to the evolution of the eat than do thermodynamic processes furthermore horizontal absolute vorticity advection is dominant in the dynamic processes and is caused mainly by the advection of synoptic and intraseasonal vorticity by seasonal wind the seasonal wind transports positive vorticity to away from the eat which results in a remarkable strengthening weakening of the eat during the onset decay stage for persistent strong eat cases

role of the east asian trough on the eastern mediterranean temperature variability in early spring and the extreme case of 2004 warm spell this study investigates the potential influence of the east asian trough eat on the eastern mediterranean temperature variability in early spring in connection with this it also examines the extreme case of the year 2004 when anomalous warming of the eastern anatolia resulted in unprecedented snowmelt runoff amounts in the euphrates and tigris basins in early march in the analyses we used reanalysis data gridded products of surface temperature and snow cover river discharge data and satellite imagery we employed an intensity index for the eat and a trough displacement index for the mediterranean trough medt to explore the relationship between the strength of the eat and the displacement of the medt at pentad resolution our analysis shows that there are statistically significant correlations at 99 confidence level between the strength of the eat and the zonal shift of the medt on some pentads e g 3rd 13th 37th and 59th but that the highest correlation occurs on the 13th pentad of the year corresponding to the early days of march it seems that on this pentad when the eat is strong the medt tends to be located in the west of its climatological position about 30 hbox 35 circ hbox e which causes warmer conditions over the eastern mediterranean in 2004 which appears to be an extreme year for this phenomenon the medt is positioned and deepened in the central mediterranean about 10 hbox 15 circ hbox e and extended towards central africa during the early days of march this synoptic pattern provided favorable conditions for the development of a tropical plume atmospheric river with a southwest northeast orientation carrying warm tropical african air towards the eastern mediterranean and anatolian highlands resulting in rapid melting of the snowpack as well as severe precipitation and thus flooding events in the eastern anatolia a key finding in our analysis is that the strengthening of the eat was instrumental to the increased amplitude of the ridge trough system over the euro mediterranean region in the early days of 2004 spring we highlight that the response of surface and upper level meteorological conditions to the amplitude of the ridge trough system enhanced by the strength of the eat might be crucial in the understanding of some of the extreme hydrometeorological events in the eastern mediterranean region

what leads to persisting surface air temperature anomalies from winter to following spring over mid to high latitude eurasia abstractsurface air temperature sat anomalies tend to persist from winter to following spring over the mid high latitudes of eurasia the present study compares two distinct cases of eurasian sat

recent intensified impact of december arctic oscillation on subsequent january temperature in eurasia and north africa this study reveals an intensified influence of december arctic oscillation ao on the subsequent january surface air temperature sat over eurasia and north africa in recent decades the connection is statistically insignificant during 1957 58 1979 80 p1 which becomes statistically significant during 1989 90 2011 12 p2 the possible causes are further investigated associated with positive december ao during p2 significant anomalous anticyclone emerges over the central north atlantic which is accompanied with significant westerly and easterly anomalies along 45 65 n and 20 40 n respectively this favors the significant influence of december ao on the subsequent january sat and atmospheric circulation over eurasia and north africa via triggering the north atlantic tripole sea surface temperature sst anomaly that persists into the subsequent january by contrast the december ao related anomalous anticyclone during p1 is weak and is characterized by two separate centers located in the eastern and western north atlantic correspondingly the westerly and easterly anomalies over the north atlantic ocean are weak and the related tripole sst anomaly is not well formed unfavorable for the persistent impact of the december ao into the subsequent january further analyses indicate that the different anomalous anticyclone associated with the december ao over the north atlantic may be induced by the strengthened synoptic scale eddy feedbacks over the north atlantic which may be related to the interdecadal intensification of the storm track activity additionally the planetary stationary wave related to the december ao propagates from surface into upper stratosphere at mid latitudes during p2 which further propagates downward to the troposphere and causes anomalous atmospheric circulation in the subsequent january

distinct modes of the east asian winter monsoon two distinct modes of the east asian winter monsoon eawm have been identified and they correspond to real and imaginary parts of the leading mode of the eawm respectively analyses of these modes used the national centers for environment prediction ncep and national center for atmospheric research ncar monthly mean reanalysis datasets for the period 1968 2003 as well as the southern oscillation index soi north atlantic oscillation index and eastern equatorial pacific sea surface temperature sst data results were obtained by resolving a complex hermite matrix derived from 850 hpa anomalous wind fields and determining the resulting modes associations with several climate variables the first distinct mode m1 is characterized by an anomalous meridional wind pattern over east asia and the western north pacific mode m1 is closely related to several features of the atmospheric circulation including the siberian high east asian trough east asian upper tropospheric jet and local hadley circulation over east asia thus m1 reflects the traditional eawm pattern revealed in previous studies the second distinct eawm mode m2 which was not identified previously displays dominant zonal wind anomalies over the same area mode m2 exhibits a closer relation than m1 to sea level pressure anomalies over the northwestern pacific southeast of japan and with the soi and equatorial eastern pacific sst unlike m1 m2 does not show coherent relationships with the siberian high east asian trough and east asian upper tropospheric jet since atmospheric circulation anomalies relevant to m2 exhibit a quasibarotropic structure its existence cannot simply be attributed to differential land sea heating el nino events tend to occur in the negative phase of m1 and the positive phase of m2 both corresponding to a weakened eawm the arctic oscillation does not appear to impact the eawm on interannual time scales although the spatial patterns for the two modes are very different the two distinct modes are complementary with the leading eawm mode being a linear combination of the two the results herein therefore demonstrate that a single eawm index may be inappropriate for investigating and predicting the eawm

wave transmission spectral changes and its effects on run up and overtopping most research work on wave transmission over low crested structures has been concentrated on establishing the wave transmission coefficient i e the ratio between transmitted and incident significant wave height it is clear that such structures decrease the wave height but there is more goda tanimoto et al raichlen et al and van der meer all conclude that also the mean period reduces to 0 4 1 0 of the incident mean period the conclusion is that overtopping generates more waves further raichlen et al and lee give examples of measured spectra of transmitted waves both examples show the peak of the spectrum similar to the incident spectrum but with much more energy at the higher frequencies a good estimation of the wave height in front of a structure is required for design or assessment of such a structure but also wave period and sometimes spectral shape may have influence on the design wave run up for example depends largely on the wave period in order to establish the required dike height for acceptable run up both wave height and period should be known in situations where a low crested structure in front of such a dike gives some protection wave period and spectral changes should be studied a local situation in the netherlands was the reason for the research presented in this paper figure 1 gives a schematised layout a large lake is situated on the west side left side in the figure and nw wind may generate waves up to a significant wave height of over 2 m the dikes on the eastern side are partly protected by a system of various low crested structures or dams including some openings the figure shows the results of a calculation on wave penetration such calculations were performed by alkyon besides wave penetration wave transmission is generated over the low crested dams the area is about 1 km by 2 5 km this means that with a fetch of more than 1 km also locally generated short waves will be present during extreme conditions the wave climate in front of the dikes can be described as a combination of wave penetration wave transmission and locally generated wind waves this paper deals with wave transmission only but the effect on the total wave climate is discussed at the end

relationship between stationary planetary wave activity and the east asian winter monsoon 1 the variability of both the stationary planetary wave activity and the east asian winter monsoon is strongly associated with the thermal contrast between oceans and landmasses in this study we explore the interannual relationship between the monsoon and the wave activity defined by an index of the difference in the divergence of eliassenpalm flux between 50 n at 500 hpa and 40 n at 300 hpa it is found that compared to the winters of low wave activity the equatorward propagation of planetary waves in the middle and upper troposphere is stronger in the high wave activity winters during these high activity winters the upward wave propagation from the troposphere into the stratosphere becomes weaker this is accompanied by a smaller perturbation in the polar vortex which tends to be colder and stronger in the meantime the east asian westerly jet stream the east asian trough the siberian high and the aleutian low all become weaker apparently in particular the weakening of the siberian high and the aleutian low decreases the northeasterly wind over east asia leading to a warming condition in the region especially in northeastern asia a further analysis reveals that the zonal wavenumber 2 pattern of planetary waves contributes dominantly to the variability of the east asian winter monsoon

storm overwash of a gravel barrier field measurements and xbeach g modelling abstract gravel barriers provide a natural form of coastal protection and flood defence for many sites around the uk and worldwide predicting their vulnerability to different storm impact regimes that cause overtopping and overwash is crucial as these processes can lead to hazardous consequences such as inundation of the back of the barrier or breaching this paper presents the first field measurements of storm overwash events on a gravel beach loe bar cornwall england high frequency in situ observations 2 hz were performed using a 2d laser scanner and allowed a complete characterization of the overwash flows velocity and depth and morphological response along a cross shore section of the barrier these novel measurements are used to validate the numerical model xbeach g to forecast overwash discharge several simulations were performed with xbeach g to investigate the thresholds for the different storm impact regimes given a variety of water levels and wave heights wave period and wave spectral shape are found to significantly affect these thresholds while short period waves dissipate most of their energy by breaking before reaching the swash zone and produce short runup excursions long period waves due to their low steepness arrive at the swash zone unbroken with enhanced heights due to shoaling thus promoting large runup excursions when the offshore wave spectrum has a bimodal shape wave transformation in shallow water causes the long period peak to dominate the swash giving large runup excursions long period waves or strongly bimodal waves result in enhanced runup thereby reducing the thresholds for barrier overtopping or overwashing

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

cosmogenic effects in mbale l5 6 chondrite measurements of particle tracks cosmogenic radionuclides and rare gas isotopes in mbale indicate that the meteoroid had a simple one stage exposure for 30 2 ma in interplanetary space on the basis of the measured track production rates and 60co and 26al activities the meteoroid is estimated to be a sphere with a radius of 36 cm the activities of several cosmogenic radionuclides i e 57co 54mn 22na 44ti and 26al in two fragments having different shielding as estimated by their track density and 60co activity provide the depth variation in their production rates cobalt 57 54mn and 22na activities agree with the production that is expected around the maximum of the solar cycle 22 as calculated from the sunspot numbers the u th 4he and k 40ar ages are measured to be 0 54 ga indicating a late thermal event which is in agreement with the thermal history of some other l group chondrites the trapped n has 15n of 57 4 o which is much lighter than the average l group chondrite value this indicates the presence of an isotopically anomalous light n component

on the variability of cold wave episodes over northwest india using an ngfs retrospective analysis a retrospective analysis of 17 years of ncmrwf global forecast system ngfs data was conducted to understand the state and variability of cold wave episodes over northwest india during the 2000 2016 period a total of 21 cold wave episodes 202 cold nights were detected out of which 5 severe cold episodes 63 cold nights were registered the 10 6 episodes occurred during la nina el nino years suggesting that both phases of el nino southern oscillation provide a favourable background for the occurrence of cold waves the average duration of a cold wave episode was 9 6 days with the longest shortest episode seen in the year 2008 2006 lasting for 26 6 consecutive days the average duration of a severe cold wave episode is 4 days longer than that of a normal cold wave in the year 2005 both the earliest 11 december and latest 16 february onsets of cold waves were seen the omnipresence of intense siberian anticyclone and the presence of western disturbance brought cold winds to the study region also temperature advection and geo potential height anomalies play vital roles in the maintenance of cold waves the cold waves exhibit a significant intra annual variability over northwest india the intensity of cold waves has shown an increase of 0 11 c per cold episode

beni m hira a new chondritic l6 meteorite fall from tunisia the beni m hira meteorite fell on january 8 2001 in southeastern tunisia this is only the fifth observed fall from tunisia on the basis of mineralogical petrographic and geochemical data the stone can be classified as an l6 chondrite of shock stage s5

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

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

shock metamorphism of ordinary chondrites a revised petrographic classification of progressive stages of shock metamorphism of ordinary chondrites is proposed six stages of shock s1 to s6 are defined based on shock effects in olivine and plagioclase as recognized by thin section microscopy the characteristic shock effects of each shock stage are s1 unshocked sharp optical extinction of olivine s2 very weakly shocked undulatory extinction of olivine s3 weakly shocked planar fractures in olivine s4 moderately shocked mosaicism in olivine s5 strongly shocked isotropization of plagioclase maskelynite and planar deformation features in olivine and s6 very strongly shocked recrystallization of olivine sometimes combined with phase transformations ringwoodite and or phases produced by dissociation reactions s6 effects are always restricted to regions adjacent to melted portions of a sample which is otherwise only strongly shocked in stages s3 to s6 localized melting results from stress and temperature peaks which locally deviate from the equilibration shock pressure due to differences in shock impedance these melting effects are a opaque melt veins shock veins b melt pockets with interconnecting melt veins c melt dikes and d troilite metal deposits in fractures based on a critical evaluation of data from shock recovery experiments a shock pressure calibration for the six shock stages is proposed which defines the s1 s2 s2 s3 s3 s4 s4 s5 and s5 s6 transitions at 5 5 10 15 20 30 35 and 45 55 gpa respectively whole rock melting and formation of impact melt rocks or melt breccias occurs at about 75 90 gpa the symbol for the shock stage may be used in combination with the symbol for the petrologic type to abbreviate the complete classification of a chondrite e g h5 s3 we propose this new shock classification and pressure calibration system to replace previous systems which are out of date with respect to the pressure calibration nominally restricted to l chondrites and based on incomplete and in part illdefined sets of shock effects we have classified seventy six ordinary chondrites using the new classification system and conclude the following 1 1 shock effects and the sequence of progressively increasing degrees of shock metamorphism are very similar in h l and ll groups differences in the frequency distribution of shock stages are relatively minor e g l chondrites appear to have the largest fraction with stages s5 and s6 this suggests that the collisional histories of the h l and ll parent bodies were similar 2 2 petrologic type 3 chondrites are deficient in stages s4 to s6 and with increasing petrologic type the frequency of stages s4 to s6 increases we suggest that the more porous and volatile rich type 3 chondrites are subject to melting at a lower shock pressure than the nonporous chondrites of higher petrologic type volatiles trapped in pores cause shock induced dispersal of the shocked and melted material into small particles which are not expected to survive as meteorites 3 3 stage s3 is the most abundant in nearly all petrologic types 4 4 at shock pressures in excess of about 35 gpa s5 and s6 4he and 40ar are almost completely lost pressures below 10 gpa s1 and s2 do not cause noble gas losses

variation of circulation and east asian climate associated with anomalous strength and displacement of the east asian trough variations of the east asian trough eat and its relationship with the east asian climate are documented in this study the variations investigated include the trough s strength and its meridional and zonal displacements anomalous cold warmth in southeast asia is concurrent with the southward northward displacement of the eat the southward displacement of the eat is likely associated with an anomalous strong siberian high and aleutian low which manipulate anomalous northerly wind between them on the other hand the temperature in northeast asia is influenced by both the strength and the zonal displacement of the trough these properties of the eat are closely linked to temperatures in the northern and southern portions of east asia the relation between variations of the eat and the east asian winter monsoon is also examined in addition the relation between the eat and transient eddies is studied anomalous transient eddies concurrent with variations of the eat are contributed by a localized anomalous meridional gradient due to the variation of stationary eddies and zonal symmetric structure variations in the polar vortex are significant for variations in the strength of the eat to investigate the role of eddies in the anomalous evolution of the eat we also study stationary and transient eddy forcing on the evolution of anomalous eat and zonal symmetric structures using wave activity flux and extended e vectors

itawa bhopji l3 5 chondrite regolith breccia fall classification and cosmogenic records a stony meteorite fell at itawa bhopji rajasthan india on 2000 may 30 this is the fifth recorded fall in a small area of rajasthan during the past decade the meteorite is an ordinary chondrite with light clasts in a dark matrix consisting of a mixture of equilibrated mainly type 5 and unequilibrated components olivine is fa24 26 and pyroxene fs20 22 but within the unequilibrated components olivine fa5 29 and low calcium pyroxene fs5 37 are highly variable based on petrographic studies and chemical analyses it is classified as l 3 5 regolith breccia studies of various cosmogenic records including several gamma emitting radionuclides varying in half life from 5 6 day 52mn to 0 73 ma 26al tracks and rare gases have been carried out the exposure age of the meteorite is estimated from cosmogenic components of rare gases to be 19 6 ma the track density varies by a factor of 3 from 4 to 12 x 10 6 cm 2 within the meteorite indicating a preatmospheric body of 9 cm radius corresponding to a meteoroid mass of 11 kg and small ablation 1 5 to 3 6 cm trapped components in various rare gases are high and the solar component is present in the dark portion of the meteorite large excess of neutron produced 82kr and 128xe in both the light and the dark lithology but very low 60co indicating low neutron fluxes received by the meteoroid in the interplanetary space are clear signatures of an additional irradiation on the parent body

a strong phase reversal of the arctic oscillation in midwinter 2015 2016 role of the stratospheric polar vortex and tropospheric blocking in january 2016 asia and north america experienced unusual cold temperatures although the global average of surface air temperature broke the warmest record during a strong el nino event this was closely related to the remarkable phase transition of the arctic oscillation ao which can be explained by stratosphere troposphere interactions first the quasi biennial oscillation changed to its westerly phase in summer 2015 and the stratospheric polar vortex was stronger in early to midwinter 2015 2016 as blocking did not occur in december the associated downward propagation signal resulted in a strongly positive ao in late december 2015 second after late december the positive phase of pacific north america pattern became apparent in el nino event which strengthened the aleutian anticyclone in the stratosphere in addition an equivalent barotropic blocking anticyclone was established in the troposphere over asia the coexistence of blocking over asia and north america characterized the negative ao and a strong zonal wave number 2 pattern due to stronger zonal wave number 2 signals from the troposphere the stronger stratospheric polar vortex was elongated with two cyclonic centers over asia and the north atlantic in january the resultant southward displacement of polar vortices was followed by rare snowfall in the subtropical region of east asia and a heavy snowstorm on the east coast of the united states

shrinkage of east asia winter monsoon associated with increased enso events since the mid holocene instrumental records indicate a close relationship between the el nino southern oscillation and the east asian winter monsoon eawm on interannual to decadal time scales however few studies have examined possible links between them on centennial millennial time scales in northeast china modern observations show that the immigration of temperate forest trees such as pinus pine and quercus oak into cold temperate boreal forest is sensitive to changes in winter temperature here we present a continuous high resolution pollen record from lake moon in the central part of the great khingan mountain range northeast china the record reveals increasing contents of pinus and quercus pollen after similar to 6 0 ka cal bp which may indicate a gradual weakening of the eawm it is broadly coupled with an increasing el nino frequency since the middle holocene and we observe a statistically significant correlation between the percentages of pinus and quercus and a time series of el nino events on the centennial to millennial time scale the results of wavelet analysis and band pass filtering show that the occurrence and development of el nino have also promoted a weaker eawm after similar to 6 0 ka cal bp which is inversely correlated with the variation of the ca 500 year cycle originated from changes in solar output these results imply that the climate transition in the mid holocene is caused by the change of variations in solar activity and amplified by ocean circulation el nino southern oscillation to influence the east asian monsoon system especially the eawm and finally change the vegetation in great khingan mountain range

the record of cosmogenic radiogenic fissiogenic and trapped noble gases in recently recovered chinese and other chondrites abstract we performed a comprehensive study of the noble gas isotopic abundances in thirty six chondrites including twenty seven chondrites recovered in china the large data base allows us to recognize some new characteristics of the nuclear record in chondritic matter the comparison of the trapped noble gas release pattern for ordinary and carbonaceous chondrites shows that the planetary trapped noble gases in ordinary chondrites are released mainly above 1200 c whereas 85 of these gases in carbonaceous chondrites are degassed at 200 c there exists a clear correlation of the fraction of trapped xe released at 1200 c and petrologic type of chondrites it thus appears that the carrier phases of the trapped noble gases in ordinary and in carbonaceous chondrites may not be the same the ngawi ll3 chondrite is solar gas rich the solar gases in meteorites and lunar surface material are mixtures of solar wind sw and solar energetic particles sep we show that the variations of the 3 he 4 he and 20 ne 22 ne ratios for solar gas rich meteorites and lunar surface material could be either due to preferential diffusive losses of the lighter isotopes of he and ne or due to a change of the sw sep flux ratio with time furthermore we demonstrate that the 81kr concentration is a function of the shielding depth of a sample within the meteoroid deviations from this depth dependency curve are observed for jilin h5 lishui l5 suizhou l6 and dongtai ll6 a complex exposure history for jilin is thus confirmed and is possible for the other three chondrites cosmic ray exposure ages are calculated based on six different nuclides 3he 21ne 38ar 83kr 126xe and 81kr kr in most cases good agreement is observed for the ages derived from the different methods quality classes are assigned to the exposure ages and the age distributions are discussed in some meteorites we observe effects induced by secondary cosmicray produced neutrons epithermal neutron fluxes jn 30 300 ev and fast neutron fluxes jn 5 mev are derived based on the reactions 79br n 80kr and 24mg n 21ne respectively and preatmospheric masses of the meteoroids are estimated we show that the ratio j n 30 300 ev j n 5 mev increases with increasing preatmospheric mass we introduce a 3he exposure age 21ne exposure age vs 4he gas retention age 40ar gas retention age diagram that is a powerful tool for distinguishing different thermal histories of meteoroids finally in some chondrites we observe xe produced by 244pu fission and calculate the time span between fission xe retention in these chondrites and that of the angra dos reis achondrite we find that the ordinary chondrites started to retain fission xe 48 30 ma earlier than angra dos reis we do not observe systematic differences between h l and ll or type 5 and 6 chondrites with respect to the time of fission xe retention

interannual variations of east asian trough axis at 500 hpa and its association with the east asian winter monsoon pathway interannual variations of the east asian trough eat axis at 500 hpa are studied with the european centre for medium range weather forecasts 40 yr reanalysis data the associated circulation pattern and pathway of the east asian winter monsoon eawm with the eat axis tilt are specially investigated with a trough axis index which is closely related to the midlatitude baroclinic process and mainly represents the intensity of the eddy driven jet over the east asia north pacific sector when the tilt of eat is smaller than normal the eawm prefers to take the southern pathway and less cold air moves to the central north pacific however the eawm prefers the eastern pathway and brings more cold air to the north pacific when the tilt of eat is larger than normal these differences induce pronounced changes in both the precipitation and the surface air temperature over east and southeast asia furthermore the tilt status of the eat has a significant modulation effect on the regional climate anomalies related to the intensity of the eawm the findings suggest an increase in the temperature anomaly associated with the eawm intensity and a clear northward southward shift in its pattern in anomalous tilt phase of the eat in addition the modulation tends to be confined mainly to east asia and expanded to a larger area during the weak and the strong eawm winters respectively the possible reasons for interannual variations of the eat tilt are discussed and it is speculated that the midlatitude air sea interaction in the north pacific plays a dominant role this study on the eat tilt may enrich knowledge of the east asian winter monsoon beyond the conventional intensity index and may be helpful to improve regional climate prediction in east asia

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

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

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

transient eddy forcing of blocking flows abstract the net forcing of blocking flows by transient eddies having synoptic time scales is examined within the framework of quasi geostrophic theory temporal filtering is used to distinguish the effects of transients having synoptic lime scales i e periods less than approximately seven days from those having longer time scales convergences of transient eddy transports of heat and vorticity during blocking conditions are computed from highpass filtered time series the eddy flux convergences for individual blocking events are then composited according to the locations of the blocks the quasi geostrophic potential vorticity equation relating geopotential tendency and the eddy flux convergences of heat and vorticity is solved for composite blocking conditions the diagnosis is performed for both observed blocks and blocks simulated by a general circulation model the net quasi geostrophic geopotential tendencies due to transports by the synoptic scale transient eddies exhibit a quadrature relations

the seasonally varying effect of the tibetan plateau on northern hemispheric blocking frequency and amplitude the northern hemisphere atmospheric blocking is a primary weather and climate system that accompanies extreme cold spells and heat waves this study assesses effects of the tibetan plateau tp the largest continental mountain belt on the blocking frequency bf and amplitude ba with progressive tp uplift experiments from 0 to 100 using a coupled atmosphere ocean general circulation model the tp uplift increases the annual mean bf by 3 and 21 over the pacific and atlantic basins respectively a particular focus is placed on the seasonally distinct mechanism in the effects of tp uplift on the boreal winter and summer blockings during winter the tp uplift increases the bf over the active centers of both ocean basins via amplifying the eddy kinetic energy of stationary waves on the other hand in summer the tp uplift tends to shift the location of bf northward due to notable poleward displacement of the jet stream and transient eddy activities particularly over the atlantic compared to the considerable bf increase in both seasons the amplification of ba due to the tp uplift is much stronger in winter than in summer reaffirming the seasonally varying tp effect on the blocking further analyses reveal that in summer the tp uplift modulates more effectively the jet displacement than its strength leading more linear northward shift of jet and bf especially over the atlantic this study will contribute to advances in simulation and prediction of atmospheric blocking events

conditions of the cosmic ray exposure of the jilin chondrite abstract nine documented samples from the main mass jilin 1 and three samples from different locations of the strewn field have been analyzed for cosmogenic 26 al t 1 2 0 716 myr 60 co t 1 2 5 27 yr and 22 na t 1 2 2 6 yr 53 mn t 1 2 3 7 myr has been determined in seven of the same documented samples and in two further documented samples the pre atmospheric size of jilin was reconstructed from the documented sample positions and from the measured 60 co activities jilin was almost spherical and had a pre atmospheric radius of about 85 cm the cosmogenic nuclides in jilin can be explained by a two stage exposure history the first stage occurred near the surface of the parent body in 2 geometry and lasted about 10 myr jilin was then expelled from its parent body and exposed to cosmic rays in a second 4 stage lasting approximately 0 4 myr the measured concentration profiles of spallogenic nuclides are compared to calculated production rates

propagation of the arctic oscillation from the stratosphere to the troposphere geopotential anomalies ranging from the earth s surface to the middle stratosphere in the northern hemisphere are dominated by a mode of variability known as the arctic oscillation ao the ao is represented herein by the leading mode the first empirical orthogonal function of low frequency variability of wintertime geopotential between 1000 and 10 hpa in the middle stratosphere the signature of the ao is a nearly zonally symmetric pattern representing a strong or weak polar vortex at 1000 hpa the ao is similar to the north atlantic oscillation but with more zonal symmetry especially at high latitudes in zonal mean zonal wind the ao is seen as a north south dipole centered on 40 45 n in zonal mean temperature it is seen as a deep warm or cold polar anomaly from the upper troposphere to 10 hpa the association of the ao pattern in the troposphere with modulation of the strength of the stratospheric polar vortex provides perhaps the best measure of coupling between the stratosphere and the troposphere by examining separately time series of ao signatures at tropospheric and stratospheric levels it is shown that ao anomalies typically appear first in the stratosphere and propagate downward the midwinter correlation between the 90 day low pass filtered 10 hpa anomaly and the 1000 hpa anomaly exceeds 0 65 when the surface anomaly time series is lagged by about three weeks the tropospheric signature of the ao anomaly is characterized by substantial changes to the storm tracks and strength of the midtropospheric flow especially over the north atlantic and europe the implications of large stratospheric anomalies as precursors to changes in tropospheric weather patterns are discussed

modulation of the interannual variation of the india burma trough on the winter moisture supply over southwest china anomalous moisture circulation associated with the interannual variation of the india burma trough was investigated to examine how the trough affects the moisture supply to southwest china in winter when the india burma trough is strong abnormal moisture is transported to southwest china mainly via the southern boundary in the 750 650 hpa layer instead of via the western boundary in contrast to the climatological situation the abnormal moisture convergence is constrained in a thin layer along the windward side of the tibetan plateau the moisture circulation response to the variation of the india burma trough shows great baroclinicity over the bay of bengal bob northwesterly transport behind and southwesterly transport ahead of the trough appear only between 850 and 650 hpa with anticyclonic moisture circulation underneath and cyclonic moisture circulation on top beyond the bob the moisture circulation response can be traced upstream with abnormal anticyclonic cyclonic moisture circulations over the mediterranean sea and arabian sea red sea above 850 hpa and downstream with anticyclonic moisture circulation over the philippine sea near the surface the activity of the india burma trough is not a local phenomenon but a part of the south asian jet wave trains and is modulated by the enso via the philippine sea anticyclone further investigation of the separate role of wind and moisture disturbances shows that the abnormal moisture flux is dominated by the wind disturbance as is the abnormal moisture divergence in the lower level while that in the upper level is dominated by both the wind and moisture disturbances

pacific east asian teleconnection how does enso affect east asian climate observational evidence is presented to show a teleconnection between the central pacific and east asia during the extreme phases of enso cycles this pacific east asian teleconnection is confined to the lower troposphere the key system that bridges the warm cold events in the eastern pacific and the weak strong east asian winter monsoons is an anomalous lower tropospheric anticyclone cyclone located in the western north pacific the western north pacific wind anomalies develop rapidly in late fall of the year when a strong warm or cold event matures the anomalies persist until the following spring or early summer causing anomalously wet dry conditions along the east asian polar front stretching from southern china northeastward to the east of japan kuroshio extension using atmospheric general circulation and intermediate models the authors show that the anomalous philippine sea anticyclone results from a rossby wave response to suppressed convective heating which is induced by both the in situ ocean surface cooling and the subsidence forced remotely by the central pacific warming the development of the anticyclone is nearly concurrent with the enhancement of the local sea surface cooling both the anticyclone and the cooling region propagate slowly eastward the development and persistence of the teleconnection is primarily attributed to a positive thermodynamic feedback between the anticyclone and the sea surface cooling in the presence of mean northeasterly trades the rapid establishment of the philippine sea wind and sst anomalies implies the occurrence of extratropical tropical interactions through cold surge induced exchanges of surface buoyancy flux the central pacific warming plays an essential role in the development of the western pacific cooling and the wind anomalies by setting up a favorable environment for the anticyclone sst interaction and midlatitude tropical interaction in the western north pacific

solar and galactic cosmic ray records of the fermo h chondrite regolith breccia we demonstrate the presence of solar flare as well as neutron capture effects in the isotopic composition of rare gases in the fermo regolith breccia acquired on its parent body based on the measurements of tracks rare gases and radionuclides the track density along a 3 2 cm long core decreases by a factor of about 6 and by more than a factor of 13 within the meteorite indicating small 2 9 cm and asymmetrical ablation rare gases show a large trapped component the isotopic ratios particularly 20 ne 22 ne 11 and 20 ne 36 ar 10 are indicative of a solar component the galactic cosmic ray exposure age is determined to be 8 8 ma activities of a dozen radionuclides ranging in half life from 16 day 48 v to 0 73 ma 26 al are consistent with their expected production rates track rare gas and radionuclide data show that the meteoroid was a small body 120 kg and had a simple one stage exposure history to cosmic rays in the interplanetary space however 82 kr and 128 xe show an excess due to neutron irradiation on the parent body of the meteorite the presence of solar gases and the neutron capture effects indicate several stages of irradiation on the parent asteroid the chemical composition of fermo confirms that it belongs to the h group of ordinary chondrites with lithic clasts having varying compositions 15 n is found to be 8 3 1 2 0 close to the typical values observed in h chondrites

impacts of early autumn arctic sea ice concentration on subsequent spring eurasian surface air temperature variations this study reveals a close relation between autumn arctic sea ice change sic in the laptev sea eastern siberian sea beaufort sea and subsequent spring eurasian surface air temperature sat variation specifically more less sic over the above regions in early autumn generally correspond to sat warming cooling over the mid high latitudes of eurasia during subsequent spring early autumn arctic sic affects spring eurasian sat via modulating spring arctic oscillation ao associated atmospheric changes the meridional temperature gradient over the mid high latitudes decreases following the arctic sea ice loss this results in deceleration of prevailing westerly winds over the mid latitudes of the troposphere which leads to increase in the upward propagation of planetary waves and associated eliassen palm flux convergence in the stratosphere over the mid high latitudes thereby westerly winds in the stratosphere are reduced and the polar vortex is weakened through the wave mean flow interaction and downward propagation of zonal wind anomalies a negative spring ao pattern is formed in the troposphere which favors sat cooling over eurasia the observed autumn arctic sic spring eurasian sat connection is reproduced in the historical simulation 1850 2005 of the flexible global ocean atmosphere land system model spectral version 2 fgoals s2 the fgoals s2 also simulates the close connection between autumn sic and subsequent spring ao further analysis suggests that the prediction skill of the spring eurasian sat was enhanced when taking the autumn arctic sic signal into account

modulation of aleutian low and antarctic oscillation co variability by enso we use both the national centers for environmental prediction ncep national center for atmospheric research ncar reanalysis data 1979 2013 and the community atmospheric model version 3 to explore the modulation of el nino southern oscillation enso on the co variability of the aleutian low al and the antarctic oscillation aao the empirical orthogonal function analysis on the ncep ncar reanalysis data indicates that after the late 1990s the global sea level pressure slp and 300 hpa geopotential height z300 in boreal january are characterized by the concurrence of the al and the negative phase of the aao aao associated with this al aao co variation is a sea surface temperature anomaly that resembles the enso cycle further analyses reveal that the interdecadal change in enso signal westward extension and more la nina events is responsible for the co variability of al and aao after the late 1990s correspondingly the el nino related anomalous heating and upward motion over the eastern central equatorial pacific can lead to the upper tropospheric divergence in the western central pacific this upper tropospheric divergence plays an essential role in coupling the equatorial heat anomalies with the variation of the subtropical westerly jet of both hemispheres and therefore results in the enhanced meridional circulation of the three cells it thus implies that enso might act as a bridge linking al and aao after the late 1990s causing their consistent co variability the numerical experiment also supports this hypothesis

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

on the cooccurrence of wintertime temperature anomalies over eastern asia and eastern north america the co occurrence of wintertime temperature anomalies over eastern asia and eastern north america is examined the winter days during 1948 2014 are assigned to nine regimes by applying the self organizing map clustering method to the area averaged land surface temperature anomalies over these two regions about half of the winter days are associated with concurrent temperature anomalies the occurrence of the concurrent non concurrent regimes is closely related to the large scale circulation conditions the eurasian teleconnection pattern and the pacific north american teleconnection pattern are two dominant large scale circulation modes associated with the co occurrence of the temperature anomalies through their impacts on the intensities of the corresponding troughs the precursor analysis reveals that the lead time of the early signals for the concurrent cold anomalies is about four days longer than that for the concurrent warm anomalies in addition the average lead time of the precursor signals for the wintertime temperature anomalies over eastern asia is longer than that is over eastern north america

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

nitrogen isotopes in bulk ordinary chondrites nitrogen isotopic compositions of twenty one ordinary chondrites were measured using a stepwise combustion technique we observed a good correlation between the abundances of cosmogenic15n and cosmogenic 38ar we obtained a relationship between the abundances of these two cosmogenic nuclides as follows 15nc atoms g 16 0 3 7 38arc atoms g using this relationship the cosmogenic nitrogen production rate in l chondrites is calculated to be 5 0 1 2 10 12 g 15n g myr assuming the cosmogenic38ar production rate given by eugster 1988 this value is consistent with the production rate on the lunar surface estimated by becker et al 1976 isotopic ratios of trapped nitrogen in ordinary chondrites seem to be heterogeneous among both unequilibrated and equilibrated meteorites heterogeneity among the latter are well observed in this study the isotopic ratios of the trapped components seem to differ by more than 110 ranging from 18 observed in guaren a h6 to 95 observed in jilin h5 a lack of correlation between nitrogen abundances and isotopic ratios indicates that differences in nitrogen isotopic ratios are not produced by mass dependent isotopic fractionation an inverse correlation between nitrogen abundances and the degree of thermal metamorphism is observed among most of the unequilibrated chondrites nitrogen abundances decrease from 8 25 p p m to 1 p p m with increasing petrographic subtype from 3 4 3 9 the nitrogen abundance in equilibrated chondrites is generally higher than the amount expected by extending the trend observed among unequilibrated ones this is probably because contaminating nitrogen masked the trend at small amounts of trapped nitrogen

devgaon h3 chondrite classification and complex cosmic ray exposure history the devgaon meteorite fell in india on february 12 2001 and was immediately collected it is an ordinary chondrite having a number of sio2 rich objects and some ca al rich inclusions olivines fa17 19 are fairly equilibrated while pyroxenes fs4 20 are unequilibrated occasionally shock veins are visible but the bulk rock sample is very weakly shocked s2 chondrules and chondrule fragments are abundant based on chemical and petrological features devgaon is classified as an h3 8 group chondrite several cosmogenic radionuclides ranging in half lives from 5 6 d 52mn to 7 3 x 10 5 yr 26al noble gases he ne ar kr and xe and particle track density have been measured the track density in olivines from five spot samples varies between 4 6 to 9 x 10 6 cm 2 showing a small gradient within the meteorite the light noble gases are dominated by cosmogenic and radiogenic components large amounts of trapped gases ar kr and xe are present in addition n products from br and i are found in kr and xe respectively the average cosmic ray exposure age of 101 8 ma is derived based on cosmogenic 38ar 83kr and 126xe the track production rates correspond to shielding depths of about 4 9 to 7 8 cm indicating that the stone suffered type iv ablation low 60co high 22ne 21ne c and large neutron produced excesses at 80kr 82kr and 128xe indicate a complex exposure history of the meteoroid in the first stage a meter sized body was exposed for nearly 108 yr in the interplanetary space that broke up in 50 cm sized fragments about a million years ago stage 2 before it was captured by the earth

mechanisms of intraseasonal amplification of the cold siberian high mechanisms of intraseasonal amplification of the siberian high are investigated on the basis of composite anomaly evolution for its strongest events at each of the grid points over siberia at each location the amplification of the surface high is associated with formation of a blocking ridge in the upper troposphere over central and western siberia what may be called wave train atlantic origin type is common where a blocking ridge forms as a component of a quasi stationary rossby wave train propagating across the eurasian continent a cold air outbreak follows once anomalous surface cold air reaches the northeastern slope of the tibetan plateau it is found through the potential vorticity pv inversion technique that interaction between the upperlevel stationary rossby wave train and preexisting surface cold anomalies is essential for the strong amplification of the surface high upper level pv anomalies associated with the wave train reinforce the cold anticyclonic anomalies at the surface by inducing anomalous cold advection that counteracts the tendency of the thermal anomalies themselves to migrate eastward as surface thermal rossby waves the surface cold anomalies thus intensified in turn act to induce anomalous vorticity advection aloft that reinforces the blocking ridge and cyclonic anomalies downstream of it that constitute the propagating wave train the baroclinic development of the anomalies through this vertical coupling is manifested as a significant upward flux of wave activity emanating from the surface cold anomalies which may be interpreted as dissipative destabilization of the incoming external rossby waves

vertical structure physical properties and energy exchange of the east asian trough in boreal winter the relation between the intensity of the east asian trough and the strength of the east asian winter monsoon is documented a prominent dipole of the available potential energy of the zonal mean flow can be observed over the midlatitudes and polar regions and is related to temperature anomalies variation in the intensity of the east asian trough is caused by variation in the energy conversion from the available potential energy of the zonal mean flow to the east asian trough the in phase relation between the intensities of the east asian jet and east asian trough is illustrated by the relation between the potential energy and kinetic energy of stationary eddies the dipole of height anomalies over the midlatitude and polar regions develops in late autumn and decays in early spring we investigate the effect of both stationary and transient eddy forcing on the evolution of the dipole the combined forcing of the two types of eddy makes an important contribution to the development maintenance and decay of the dipole

fall classification and cosmogenic records of the sabrum ll6 chondrite the petrographic and chemical characteristics of a fresh indian meteorite fall at sabrum are described its mean mineral composition is defined by olivine fa31 4 orthopyroxene fs25 1 wo2 0 clinopyroxene wo45en45 6fs9 4 and plagioclase an10 6ab83 6or5 8 the meteorite shows moderate shock features which indicate that it belong to the s4 category based on mineralogical and chemical criteria the meteorite is classified as ll6 brecciated veined chondrite several cosmogenic radioisotopes 46sc 7be 54mn 22na and 26al noble gas he ne ar kr and xe nitrogen isotopes and particle tracks density have been measured concentrations of cosmogenic 21ne and 38ar indicate that its cosmic ray exposure is 24 8 ma small amounts of trapped kr and xe consistent with petrologic class 5 6 are present the track density in olivines is found to be 1 3 0 3 x 10 6 cm 2 activities of most of the short lived isotopes are lower than those expected from solar cycle variation 22na 26al 1 12 0 02 is found to be significantly anomalous being approximately 25 lower than expected from the climax neutron monitor data these results indicate that the cosmic ray flux during the terminal segment of the meteoroid orbit was low the activities of 26al and 60co and the track density indicate small meteoroid size with radius 15 cm

interannual variations of stationary planetary wave activity in the northern winter troposphere and stratosphere and their relations to nam and sst 1 with the national centers for environmental prediction national center for atmospheric research ncep ncar reanalysis data from 1958 to 1998 two teleconnection patterns in the eliassen palm ep flux divergence field due to stationary planetary waves with wavenumbers wns 1 to 3 are studied in the northern hemisphere winter both patterns appear as dipole structures with divergence of ep flux in the north and convergence in the south or vice versa one dipole evolves mainly in the stratosphere and is referred to as the stratospheric interannual oscillation sio the other evolves mostly in the troposphere and is referred to as the tropospheric interannual oscillation tio the tio and the sio are shown to be associated with anomalous meridional planetary wave propagation in the troposphere and stratosphere respectively the upward and poleward refraction of planetary waves into the polar waveguide across the tropopause is closely linked to the tio examination of individual waves indicates that the tropospheric dipole ofep flux divergence comes basically from wn 3 whereas the stratospheric one comes totally from wns 1 and 2 the reduced refraction of planetary waves into the polar waveguide across the tropopause associated with positive tio index is dominantly contributed from both wns 1 and 2 regression and correlation analyses suggest that the tio is closely related to the northern annular mode nam its relation to the sea surface temperature sst is consistent with previous studies on the relation of nam to sst on the other hand the sio is shown to be closely associated with anomalous zonal mean winds in the subtropics of the midstratosphere and has a moderate correlation with an augmented pacific north american pna pattern in 500 hpa geopotential height for the leading eof of stratospheric u variability the sio accounts for a smaller fraction than the tio however with the teleconnectivity in stratospheric ep flux divergence one can distinguish a stratospheric variation of anomalous north south planetary wave propagation from the total amount of wave activity entering the stratosphere which may help us to understand the variability of transport circulation in the stratosphere significant correlation of sio with tropical sst reveals that tropical sst is leading the sio by up to around 9 months which suggests a strong impact of el nino southern oscillation enso on the sio planetary waves tend to be bent poleward in the midstratosphere when there is a warm event the situation tends to be reverse during a cold event

structure and dynamics of a springtime atmospheric wave train over the north atlantic and eurasia the leading pattern of boreal spring 250 hpa meridional wind anomalies over the north atlantic and mid high latitude eurasia displays an obvious wave train the present study documents the structure energy source relation to the north atlantic sea surface temperature sst and impacts on eurasian climate of this wave train during 1948 2018 this atmospheric wave train has a barotropic vertical structure with five major centers of action lying over subtropics and mid latitudes of the north atlantic northern europe central eurasia and east asia respectively this spring wave train can efficiently extract available potential energy from the basic mean flow the baroclinic energy conversion process and positive interaction between synoptic scale eddies and the mean flow both play important roles in generating and maintaining this wave train the north atlantic horseshoe like nah sst anomaly contributes to the persistence of the wave train via a positive air sea interaction specifically the nah sst anomaly induces a rossby wave type atmospheric response which in turn maintains the nah sst anomaly pattern via modulating surface heat fluxes this spring atmospheric wave train has significant impacts on eurasian surface air temperature sat and rainfall during the positive phase of the wave train pronounced sat warming appears over central eurasia and cooling occurs over west europe and eastern eurasia in addition above normal rainfall appears over most parts of europe and around the lake baikal accompanied by below normal rainfall to east of the caspian sea and over central asia

piplia kalan eucrite fall petrography and chemical characteristics two stones that fell near piplia kalan on 1996 june 20 are identified as ca rich achondrites belonging to the eucrite group the conditions of their fall are described the petrographic description texture and chemical composition the elemental ratios particularly k la and yb sc and relatively flat rare earth element ree patterns 6 8 chondrite of bulk samples without any significant eu anomaly all agree with the characteristic values found in eucrites a feldspar rich fraction shows a significant positive eu anomaly the presence of several different lithologies and clasts indicates that it is a texturally diverse breccia and the chemical analysis suggests that it belongs to the noncumulate group of eucrites falling in the nuevo laredo trend

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

on the teleconnectivity of the arctic oscillation the term arctic oscillation ao has recently been introduced to describe the leading structure of slp variability over the northern hemisphere a key feature of the ao is its zonally symmetric appearance with a primary center of action over the arctic and opposing anomalies in midlatitudes does the ao s annular appearance result from significant temporal correlations between slp anomalies at distant longitudes the results presented indicate that the temporal coherence between the arctic and midlatitudes is strongest over the atlantic sector with weak correlations between the atlantic and pacific midlatitudes both on intraseasonal and interannual time scales during the past 50 yrs hence the annular character of the ao is more a reflection of the dominance of its arctic center of action than any coordinated behavior of the atlantic and pacific centers of action in the slp field the ao is nearly indistinguishable from the leading structure of variability in the atlantic sector e g the north atlantic oscillation their temporal correlation is 0 95 for monthly data

a unified three dimensional instability theory of the onset of blocking and cyclogenesis abstract the instability characteristics of three dimensional flow typical of the northern hemisphere average winter troposphere are examined in a two layer spherical quasigeostrophic model the properties of the four fastest growing small amplitude disturbances that develop on the basic state have been analyzed for three cases case 1 2a and 3 having increasingly larger static stability parameters for case 1 the fastest growing disturbance mode which is propagating eastward rather rapidly has a monopole cyclogenesis structure with maximum amplitudes slightly downstream of the jetstream maxima in the pacific ocean and off the cast coast of north america comparisons of streamfunctions squared and momentum and heat fluxes with bandpass filtered observations for transient eddies which pick out the developing storms are quite reasonable considering that a two layer model is used and the contributions from individual linear modes are considered for case 2a the fastest growing mode has large scale hi

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

on the role of successive downstream development in east asian polar air outbreaks abstract a composite of 16 strong east asian polar outbreak occurrences widely separated in time reveals a clear sequence of events beginning over the western north atlantic six or seven days in advance of the key day as defined by the cold frontal passage over korea troughs and ridges are seen to form develop and decay successively downstream of one another across the eurasian continent until the polar outbreak occurs these troughs and ridges reach their maximum amplitude in much the same location and at the same time relative to the key day in the majority of the 16 cases the center of the wave packet moves along a curved trajectory approximating the mean 300 mb flow at a nearly constant rate of 30 longitude per day the perturbation moves as an essentially barotropic dispersive wave across most of eurasia but its evolution becomes highly baroclinic as it approaches the east asian coast the wavetrain nature of this perturbation breaks down as it propagates out over the pacific ocean this bre

interannual variability of surface air temperature over mid high latitudes of eurasia during boreal autumn this study analyzes the dominant modes of interannual variability of surface air temperature sat during boreal autumn over the mid high latitudes of eurasia and investigates their associations with snow cover atmospheric circulation and sea surface temperature sst the first second and third empirical orthogonal function eof mode of autumn sat anomalies displays same sign distribution an east west dipole pattern and a south north dipole pattern respectively analysis of surface heat fluxes indicates that snow changes explain only small patches of sat anomalies related to the first two eofs via altering surface shortwave radiation atmospheric circulation anomalies have important contributions to the formation of sat anomalies southerly northerly wind anomalies generally favor positive negative sat anomalies via bringing warmer colder air from lower higher latitudes the atmospheric circulation anomalies related to the first eof mode are attributed to a combination of the arctic oscillation ao and the scandinavia pattern and those related to the second eof mode have a close relation with the east atlantic west russian eawr and circumglobal teleconnection cgt patterns formation of the atmospheric circulation anomalies related to the third eof mode is partly related to the arctic sea ice change around the barents kara seas sst anomalies have little contribution to the atmospheric circulation anomalies associated with the first three eof modes of eurasian autumn sat interannual variations hindcast skill of the sat anomalies related to the first second eof mode is improved when taking both the ao and scandinavia eawr and cgt patterns into account

observational climatology and characteristics of wintertime atmospheric blocking over ural siberia this study investigates the climatological aspects and temporal characteristics of wintertime ural siberian blocking usb centered over 30 100 e for the period 1980 1981 2009 2010 sixty eight events are identified and their physical structure is diagnosed using thermodynamic and geostrophic vorticity tendency equations in climatology horizontal advections play a fundamental role in constructing a usb event in which the anticyclonic center is a warm core in the troposphere and a cold core in the lower stratosphere the decay of the thermal structure is related to diabatic cooling along the vertical structure and warm advection in the lower stratosphere meanwhile the collapse of the height structure is caused primarily by cyclonic vorticity advection a strong interrelationship exists between the intensity and extension of usb events the temporal characteristics of usb events are analyzed by examining strong and weak events which are of high and low intensity the strong events are probably preceded by an open ridge over europe and a cyclogenesis over the mediterranean sea and their formation is followed by the stronger amplification of a rossby wave packet across eurasia on the other hand the weak events are likely to be triggered by surface cold anomalies over siberia overall the evolution of a usb event forms a dynamic linkage with the siberian high in which the decay stage of the usb event is accompanied by a southeastward migration of the siberian high and a subsequent cold air outbreak in east asia these results advance our understanding of usb and its relationship with east asian winter monsoon activities

the fall of the st robert meteorite the st robert quebec canada meteorite shower occurred on 1994 june 15 at 0h02m ut accompanied by detonations audible for 200 km from the fireball endpoint the fireball was recorded by visual observers in vermont new york state new hampshire quebec and ontario as well as by optical and infrared sensors in earth orbit penetration to an altitude of 36 km occurred 60 km to the northeast of montreal where the bolide experienced several episodes of fragmentation a total of 20 fragments of this h5 chondrite comprising a total mass of 25 4 kg were recovered in an ellipse measuring 8 3 5 km one fragment of the shower partially penetrated the aluminum roof of a shed interpretation of the visual and satellite data suggests that the fireball traveled from south southwest to north northeast with a slope from the horizontal of 55 61 a statistical evaluation of the likely heliocentric orbits for the body prior to collision with the earth coupled with theoretical modeling of the entry suggests an entry velocity in the range of 12 7 13 3 km s the meteoroid had moved in a low inclination orbit with orbital perihelion located extremely close to the earth s orbit from satellite optical data it is found that the photometric mass consumed during the largest detonation is 1200 kg estimation of the amplitude of the acoustic signal detected by the most distant observer yields a source energy near 0 5 kt tnt equivalent energy which corresponds to a mass of order 10 metric tonnes this measure is uncertain to approximately one order of magnitude theoretical modeling of the entry of the object suggests a mass near 1600 kg cosmogenic radionuclide activities constrain the lower initial mass to be 700 kg with an upper limit near 4000 kg seismic data possibly associated with the fireball suggest extremely poor coupling between the airwave and the ground the total mass estimated to have reached the ground is 100 kg in material comprising 55 g fragments while the preatmospheric mass is found to be most probably in the range of 1200 2000 kg

interdecadal changes in the relationship between interannual variations of spring north atlantic sst and eurasian surface air temperature abstractthis study investigates interdecadal changes in the relationship between interannual variations of boreal spring sea surface temperature sst in the north atlantic and surface air temperature sat over the mid to high latitudes of eurasia during 1948 2014 analyses show that the connection between the spring north atlantic tripole sst anomaly pattern and the eurasian sat anomalies has experienced marked interdecadal shifts around the early 1970s and mid 1990s the connection is strong during 1954 72 and 1996 2014 but weak during 1973 91 a diagnosis indicates that interdecadal changes in the connection between the north atlantic sst and eurasian sat variations are associated with changes in atmospheric circulation anomalies over eurasia induced by the north atlantic tripole sst anomaly pattern further analyses suggest that changes in atmospheric circulation anomalies over eurasia are related to changes in the position of atmospheric heating anomalies over the north atlantic which may be due to

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

a diagnostic study of the potential vorticity in a warm blocking anticyclone abstract dynamical features of the warm blocking anticyclone which persisted over europe during the summer of 1976 are studied using national meteorological centre analyses the dynamics am presented from the perspective of quasi geostrophic potential vorticity q the block is shown to be a region of anomalously low almost uniform q computed balances in the 300 mb monthly mean quasi geostrophic potential vorticity equation show that the mean flow advection v q and the eddy forciv q of q are of comparable magnitude and have the tendency to balance one another it is suggested that transfer by synoptic scale systems acts to maintain the q anomaly against its advection downstream

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

interdecadal variations of the east asian winter monsoon and their association with quasi stationary planetary wave activity abstract interdecadal variations of the east asian winter monsoon eawm and their association with the quasi stationary planetary wave activity are analyzed by using the 40 yr european centre for medium range weather forecasts re analysis dataset and the national centers for environmental prediction national center for atmospheric research reanalysis dataset it is found that the eawm experienced a significant weakening around the late 1980s that is the eawm was strong during 1976 87 and became weak after 1988 this leads to an obvious increase in the wintertime surface air temperature as well as a decrease in the frequency of occurrence of cold waves over east asia the dynamical process through which the eawm is weakened is investigated from the perspective of quasi stationary planetary waves it is found that both the propagation and amplitude of quasi stationary planetary waves have experienced obvious interdecadal variations which are well related to those of the eawm compared to the period 1976

oscillating relationship between the east asian winter monsoon and enso abstractthis work investigates the interdecadal variations of the relationship between the el nino southern oscillation enso and the east asian winter monsoon eawm further explores possible mechanisms and finally considers a recent switch in the enso eawm relationship the 23 yr sliding correlation between the nino 3 4 index and the eawm index reveals an obvious low frequency oscillation with a period of about 50 yr in the enso eawm relationship warm enso events during high correlation periods are associated with an unusually weak east asian trough a positive phase of the north pacific oscillation npo significant southerly wind anomalies along coastal east asia and warmer east asian continent and adjacent oceans however there are no robust and significant anomalies in the eawm related circulation during low correlation periods because of the southeastward shift of the walker circulation the area of anomalously high pressure in the western pacific retreats south of 25 n confining it to the

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

explosive cyclogenesis and large scale circulation changes implications for atmospheric blocking abstract large scale circulation changes attending explosive surface cyclogenesis are quantitatively examined in two cases selected from recent winter seasons both cases feature a rapidly deepening surface cyclone over the western atlantic ocean but changes in the 500 mb geopotential height field near the cyclone differ in each case one event during january 1977 is characterized by the retrogression of an anticyclonic vortex blocking high in the 500 mb height field downstream of the surface cyclone the second case in february 1978 is distinguished by the formation of a 500 mb cyclonic vortex cutoff low upstream of the surface cyclone but no downstream anticyclonic vortex is observed the retrogression of the january 1977 block over the atlantic ocean coincides with the migration of a 500 mb synoptic scale perturbation associated with the surface cyclone from a planetary scale trough over north america toward a planetary scale ridge over europe in the february 1978 case the blocking cyclo

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

contrasting relationship between wintertime blocking highs over europe siberia and temperature anomalies in the yangtze river basin abstractbased on the japanese 55 year reanalysis dataset this study identifies 92 europe siberia blocking high events esbs over the 60 winters november to march from 1958 1959 to 2017 2018 ac

duplex equilibria of ural circulation anomalies atmospheric circulation anomalies over the ural mountains are crucial indicators of the anomalous downstream weather and climate over east asia here we provide a new perspective on the mechanism of ural circulation anomalies we use a simple theoretical model to determine that the relationship between the solar forcing and three ural circulation patterns namely neutral type trough anomaly and ridge anomaly is a nonlinear relationship following the supercritical pitchfork bifurcation theory the theory predicts that when the total solar irradiance tsi is below a critical value trough and ridge anomalies represent duplex equilibria and are equally likely to occur at the same tsi based on 180 winter months record we have estimated the bidimensional probability density of tsi and the monthly mean geopotential height at 500 hpa or zonal wind at 850 hpa over the ural mountains results show that sc 1360 9 w m 2 is a critical value of tsi the neutral type pattern is the single circulation regime when tsi sc whereas trough and ridge anomaly patterns are duplex circulation regimes when tsi sc besides when tsi sc during the same tsi range trough and ridge anomaly events occur at nearly the same frequencies these results generally agree with the theoretical model we demonstrate that trough and ridge anomalies as duplex equilibria result from the large scale zonal flow interacting with the ural mountains low tsi tends to strengthen the large scale zonal flow over the ural mountains hence inducing either a trough anomaly or ridge anomaly

the vissannapeta eucrite a wholly encrusted single stone that fell in vissannapeta andhra pradesh india has been identified as a cumulate eucrite based on its primary texture and mineral composition anorthite an 92 4 94 6 orthopyroxene en 49 1 51 8 fs 44 2 49 7 wo 1 2 4 0 and clinopyroxene en 38 8 46 8 fs 14 8 33 6 wo 19 6 46 4 the stone is pyramidal in shape and the crust shows rib like flow features indicating that it had an oriented passage through the atmosphere towards the terminal stage of its flight conditions of its fall mineralogical characteristics and results of measurements of cosmogenic radioactivity 26 al 22 na and 54 mn and track density are described aluminum 26 and 22 na in vissannapeta are 75 of the expected values and also lower by a similar factor compared to the activities measured in piplia kalan another eucrite which fell 18 months before vissannapeta because higher activity of 22 na and 54 mn would be expected from solar cycle modulation of galactic cosmic rays these results as well as the track density gradient indicate that vissannapeta was a small body 120 kg in the interplanetary space wherein the nuclear cascade due to galactic cosmic rays did not develop fully tracks surface morphology and crustal features indicate at least two fragmentation events in the atmosphere

weakening of the winter monsoon and abrupt increase of winter rainfalls over northern taiwan and southern china in the early 1980s abstract the rainfall characteristic of the east asian winter monsoon eawm is less emphasized in previous works this study reveals that the circulation of the eawm weakened in recent decades which results in a decrease of winter rainfall over several windward coastal areas over east asia including the hills in northern taiwan in contrast there is an abrupt increase of rainfall in southern china and the plains of northern taiwan during the early 1980s this is due to the increase in sea surface temperature and lower troposphere moisture over the south china sea and the anomalous northward flow that enhances the moisture transport to southern china because more moisture is provided for the frontal system that moves eastward the fronts frequently come with abundant moisture and a well developed rainband in winter therefore the plains of northern taiwan receive more rainfall after the 1980s

recent weakening of the linkage between the spring arctic oscillation and the following winter el nino southern oscillation previous studies indicated that the spring arctic oscillation ao is an important extratropical forcing of the occurrence of el nino southern oscillation enso in the following winter this study reveals an interdecadal weakening in the spring ao winter enso connection around the early 1990s and investigates the reason of this change before the early 1990s in association with the positive phase of the spring ao an anomalous anticyclone appears over the mid latitude north pacific accompanied by an anomalous cyclone over the subtropical north pacific that is supported by the wave mean flow interaction correspondingly the sea surface temperature sst warming and its associated positive precipitation anomalies develop over the subtropical north pacific which play a crucial role in forming and maintaining the westerly wind anomalies over the tropical western pacific twp from spring to the following summer the twp westerly wind anomalies would induce the el nino event in the following winter after the early 1990s by contrast the pacific component of the circulation anomalies related to the spring ao is weak and shifts northward this is followed by weak anomalies of sst and precipitation over the subtropical north pacific as well as weak twp westerly wind anomalies from spring to the following summer hence the spring ao winter enso connection is weak after the early 1990s the change of the spring ao associated circulation anomalies over the north pacific around the early 1990s tends to be related to the interdecadal change in the intensity of the aleutian low