a holocene north atlantic sst record and regional climate variability abstract by combined use of 210 pb dates identification of icelandic tephras of known age and wiggle matching of 14 c radiocarbon dates exceptional accurate chronologies have been established for two cores p1003mc and sc raised from the same location on the norwegian continental margin and that span the last 8 ka they are located directly under the core of the eastern branch of atlantic water entering the nordic seas comparing oxygen isotope measurements on the planktonic foraminiferal species neogloboquadrina pachyderma dex with nearby instrumental time series suggest that this parameter at this site primarily reflects summer temperature conditions of near surface c 50 m waters we argue that this proxy to some degree reflects north atlantic sea surface temperature variability through the holocene a detailed correlations of the oxygen isotope record with solar proxies for the last 1 ka was not apparent for the whole 8 ka record however a statistically significant 95 spectral peak at c 83 yr may represent the so called gleissberg solar cycle a relative high correlation r 0 53 between 14 c productivity and the ocean near surface temperature proxy was obtained on 800 1500 year band filtered data the latter lagging 180 year after the solar proxy multi channel singular spectrum analyses carried out on the p1003 time series the oxygen isotope record from the renland ice core from eastern greenland and on the tornetrask tree ring record from central scandinavia reveals a significant common frequency at 280 year the expression of this frequency in the different records shows variability in phase relationship and strength over time and does not appear to have any similarity to any known modes of climate variability in the area in order to predict future climate change in the region it is of utmost importance to develop a better understanding of the mechanisms behind multi decadal and multi centennial scale climate variability

source inversion of intensity patterns of earthquakes a destructive shock in 1936 in northeast italy 1 we demonstrate that it is possible to retrieve geometric and kinematic information about the source of a destructive past earthquake by inverting its regional macroseismic intensity patterns in fact in the case study the inversion results agree with the seismological instrumental measurements of the 1930s and with neotectonic evidence this leads to the hope that more knowledge about preinstrumental events can be obtained a key toward improving the calculation of seismic hazard mostly in the old world after validating our technique on the 1987 whittier narrows california earthquake pettenati and sirovich 2003 gentile et al 2004 we achieve the present results by investigating an earthquake that happened in 1936 in northeast italy the automatic inversions were performed by using a simplified formula for body waves that radiate from a linear source the inversion shows two minima on the hypersurface of the minimum residuals calculated observed intensity at all sites in the multiparameter model space these two minimum variance source models resemble the two auxiliary planes of the same theoretical fault plane solution similar to that given by the standard use of the first p wave arrivals the present result encourages us to treat more cases and to explore new inversion techniques for quantitatively treating the intensity patterns of earthquakes because at least in some cases they carry geometric and kinematic information about their source

the role of stationary waves in the maintenance of the northern annular mode as deduced from model experiments abstract the influence of stationary waves on the maintenance of the tropospheric annular mode am is examined in a simple global circulation model with perpetual january conditions the presented model experiments vary in the configurations of stationary wave forcing by orography and land sea heating contrasts all simulations display an am like pattern in the lower troposphere the zonal momentum budget shows that the feedback between eddies with periods less than 10 days and the zonal mean zonal wind is generally the dominating process that maintains the am the kinetic energy of the high frequency eddies depends on the stationary wave forcing where orographic forcing reduces and thermal forcing enhances it the ams in the model experiments differ in the superposed anomalous stationary waves and in the strength of the zonally symmetric component if only orographic stationary wave forcing is taken into account the mountain torque decelerates the barotropic wind anomaly and thus acts to weaken the a

interactions of synoptic and planetary waves scale dependent forcing of a gcm abstract in order to better understand planetary wave synoptic wave interactions in the atmosphere and to develop a tool for further studies the authors have applied a wavenumber dependent external forcing to a general circulation model gcm the forcing constrains various length scales of the gcm to be close to those in the evolving analyses of the european centre for medium range weather forecasts and the national centers for environmental prediction the forcing acts either on the planetary waves pw defined as zonal wavenumbers 0 5 the synoptic waves sw defined as zonal wavenumbers 6 20 the synoptic waves plus the zonal mean sw0 or the synoptic waves plus the zonal mean and wavenumber 1 sw01 the form of the forcing is a linear relaxation to the evolving analyses with a time constant of 8 h this forcing is applied only to the temperature and vorticity equations of the gcm which has a spectral truncation of t42 control integrations of length 30 days have been run starting on 15 dece

a north pacific short wave train during the extreme phases of enso abstract sea surface temperatures ssts exhibit an interannual seesaw between the eastern and western tropical pacific in concert with the el nino southern oscillation enso cycle evidence accumulated from previous studies suggests that a teleconnection link may exist between enhanced rainfall convection in the western pacific and precipitation severe weather over north america the aforementioned link could possibly be established by a teleconnection wave pattern induced by the anomalously warm cold sst anomalies in the western tropical pacific to demonstrate this possibility a fourier scale separation was introduced to divide the enso anomalous circulation into two wave regimes long wave waves 1 3 and short wave waves 4 15 the classic pacific north american teleconnection pattern is formed by the long wave regime in contrast emerging in the short wave regime is a well organized wave train that propagates from the western subtropical pacific along the north pacific rim into north america in

north atlantic cloud cover response to the north atlantic oscillation and relationship to surface temperature changes 1 cloud cover changes over the high latitude north atlantic during january associated with the north atlantic oscillation nao are studied using the polar mm5 regional climate model the cloud response to the nao is marked by an increase in cloudiness during the high phase over much of the north atlantic east of greenland and an overall decrease in cloudiness west of greenland these cloud changes are accompanied by surface cloud radiative forcing anomalies that are of the same sign as the model simulated surface air temperature sat anomalies in most areas nao related cloud cover changes in january are therefore likely to represent a positive feedback on the sat changes induced by anomalous atmospheric advection

formation and exhumation of ultra high pressure rocks during continental collision role of detachment in the subduction channel 1 uhp rocks commonly form and exhume during the transition from oceanic subduction to continental collision their exhumation in subduction channels depends on the balance between down channel shear traction and up channel buoyancy thermal mechanical upper mantle scale numerical models are used to investigate how variations in material properties of the subducting continental margin affect this balance changes in shear traction leading to crustal decoupling detachment are investigated by varying the onset of strain weakening thermal parameters and convergence velocity variations in buoyancy force are investigated by modifying subducted material density and volume the model results are interpreted in terms of the exhumation number e which expresses the role of the pressure gradient channel thickness effective viscosity and subduction velocity peak metamorphic conditions exhumation velocity and timing of exhumation are temporally and spatially variable and are sensitive to the evolution of e the models reproduce natural ptt constraints and indicate that neither slab breakoff nor surface erosion is required for uhp exhumation

role of storm track activity in the interannual seesaw of summer precipitation over northern eurasia 1 oscillation between relatively dry and wet extremes is a noteworthy characteristic of the interannual variability in summer precipitation over siberia recently we identified an out of phase relationship in the temporal signature of basin scale precipitation between eastern and western siberia es and ws this east west seesaw has been especially pronounced during the past 30 years the spatial structure of large scale precipitation and circulation anomalies associated with this east west seesaw is characterized by an east west dipole across northern eurasia we extended our work to investigate the important atmospheric processes involved in the dipole patterns of precipitation and large scale circulation anomalies for the northern summers june august of 1972 2001 in particular this work focuses on the role of storm track activities associated with synoptic scale 10 days eddies in producing the stationary waves that correspond to the precipitation anomaly dipoles linear regression and composite analyses of various eddy statistics are performed for two contrasting extremes in the siberian summer precipitation seesaw these two extreme phases are denoted es wet ws dry and ws wet es dry the summer mean atmospheric anomalies related to the precipitation seesaw show stationary wavetrain patterns in conjunction with the precipitation dipole anomalies the cold trough warm ridge dipole corresponds to the relative wet and dry region analysis of storm track activity reveals similar east west contrasting structures meaning that the displacements associated with the anomalous storm tracks are accompanied by a phase reversal between the two extreme phases an anomalous stationary trough ridge corresponds to the anomalous high low synoptic scale eddy activity region in both es and ws the forcing by synoptic scale eddies is examined to confirm the storm track feedback on the eurasian stationary waves the results show that barotropic feedback induced by synoptic scale eddy vorticity fluxes is in phase with the eurasian wave field cyclonic anticyclonic circulation forcing is collocated with the anomalous stationary trough ridge these spatially coherent relationships suggest that storm track feedback due to eddy vorticity fluxes helps to reinforce and maintain the eurasian wave structure coupled with the precipitation dipole pattern of each phase consequently the interannual variability of the eurasian storm track intensity and location is a crucial factor in forcing the mean precipitation and circulation patterns between the two extreme phases

deep subduction and rapid exhumation role of crustal strength and strain weakening in continental subduction and ultrahigh pressure rock exhumation 1 the exhumation of crustal ultra high pressure uhp material depends on temporal and spatial variations in its detachment within the subduction channel this dependence is investigated using numerical models with variable initial crustal strengths representing a range of initial crustal compositions and parameterized strain weakening representing a range of processes that reduce effective crustal viscosity during deformation competition between down channel shear traction favoring subduction and up channel buoyancy favoring exhumation is expressed as the exhumation number e which can vary with time and position along the channel exhumed lower strength crust which resists subduction owing to weak down channel traction records peak conditions 38 kbar given sufficient strain weakening exhumation proceeds at 60 km ma 1 indicating that buoyancy e 1 drives exhumation in these models in all models exhuming uhp material forms a deforming ductile plume with a range of possible structural relationships predicted between exhumed uhp and hp materials

northern hemisphere winter circulation associated with the north atlantic oscillation and stratospheric polar night jet the interannual variability of the atmospheric winter circulation as characterized by the geopotential height at 500 hpa and temperature at 850 hpa associated with the north atlantic oscillation nao and stratospheric polar night jet pnj is examined it is suggested that the wintertime atmospheric circulation related to the nao index can be separated into two different modes of variability one is a regional mode characterized by a meridional dipole type pattern in the 500 hpa geopotential height anomaly field over the atlantic region the other having more zonal structure extends over wider region of the northern hemisphere this is also related to the lower stratospheric polar night jet air temperature near the surface over the eastern part of the eurasian continent is more closely correlated with the above mentioned hemispheric mode of variability than the regional nao

influence of the north atlantic oscillation on the canary islands precipitation abstract the aim of this paper is to investigate the relationship between the canary island rainfall and the atlantic large scale circulation characterized by the north atlantic oscillation nao index the canary islands are located in the atlantic subtropical belt under the direct influence of the azores high and the trade winds their steep orography makes the islands very sensitive to small variations in a synoptic situation thus providing an excellent natural observatory for the north atlantic variability associated with changes in pressure patterns a significant relationship between rainfall and the nao is found for five of the seven canary islands in order to characterize the physical mechanisms involved a set of automatic objective techniques for identification and detection of disturbances is applied to the 1000 and 500 hpa geopotential from the ncep ncar reanalysis for the period from 1955 to 1998 this method allows for the identification and detection of four main synoptic systems either

coastal storm characterization and morphological impacts on sandy coasts the present work deals with storm classification using the storm power index and beach morphological response to storm events in the gulf of cadiz sw spain over the 1958 2001 period 377 events divided into five classes ranging from weak to extreme were characterized classes i weak and ii moderate accounted for 60 and 23 of events respectively class iii significant were 9 of the recorded events and classes iv severe and v extreme accounted for 5 and 2 respectively the probability of storm occurrence per year ranged from 93 for class i to 15 for class v in order to characterize beach response to storm events 214 beach profiles carried out with a monthly periodicity over the 1996 1998 period along the chipiona rota littoral were analysed as well as published data different beach types were observed i intermediate beaches underwent important vertical relief changes ranging from 0 3 m to 1 33 m associated with average slope changes from tan 0 06 to tan 0 03 ii the dissipative beaches were characterized by smaller and homogeneous foreshore vertical changes from c 0 36 m to 0 65 m according to the parallel retreat mechanism characterized by small slope variations from tan 0 025 to tan 0 035 and iii intermediate with rock shore platform experienced small morphological and foreshore slope variations related to both beach pivoting and parallel retreat mechanisms the most important morphological changes were due to the impact of usually weak and moderate events during october and november that produced berm erosion and upper foreshore lowering and the impact of severe significant and extreme events in december and january which produced dune escarpment overwash and or damage to coastal structures copyright 2011 john wiley sons ltd

coeval blueschist exhumation along thousands of kilometers implications for subduction channel processes we herein focus on understanding what controls the detachment and migration of oceanic crustal slices along subduction zones we provide evidence for the coeval middle to late cretaceous exhumation of oceanic blueschists in the same neotethyan subduction zone across more than 3000 km from depths around 30 40 km over a short time interval similar to 25 ma compared to the duration of subduction 100 ma we stress the importance of such a geodynamic process and suggest that this exhumation was promoted by a regional scale change in the long term interplate mechanical coupling on the basis of geological and geophysical evidence we propose that the upward migration of oceanic fragments in subduction zones is normally inhibited and only occurs discontinuously as the subduction channel opens up in response to a major change in plate geodynamics slab geometry and dynamics mantle wedge and slab hydration or a combination of these

thermally driven and eddy driven jet variability in reanalysis two important dynamical processes influence the extratropical zonal wind field angular momentum transport by the thermally direct hadley circulation thermal driving t and momentum flux convergence by atmospheric waves eddies that develop in regions of enhanced baroclinicity eddy driving e the relationship between extratropical zonal wind variability and these driving processes is investigated using 40 yr european centre for medium range weather forecasts re analysis era 40 data indices representing the processes it and ie are defined based on vertically integrated diabatic heating and meridional convergence of the meridionalflux of zonal momentum by eddies respectively zonal wind signatures associated with these indices are identified via composite analysis in the atlantic sector zonal wind variability is mainly associated with momentum flux convergence by baroclinic eddies supporting the established view that the atlanticjetis primarilyeddydriven inthe pacificsector zonal windvariability isassociatedwith bothdriving processes evidence that the pacific jet is both thermally driven and eddy driven the thermally driven pacific signature reflects changes in jet strength intensity and longitudinal extent with some resemblance to the zonal wind anomalies of the pacific north america pna pattern the eddy driven signature reflects a latitudinal shift of the jet exit region in both sectors that resembles the zonal wind anomalies of the north atlantic oscillation nao or west pacific wp patterns

influences of enso on stratospheric variability and the descent of stratospheric perturbations into the lower troposphere abstractthe linkage between el nino southern oscillation enso and north atlantic oscillation nao through the stratospheric pathway is examined using a global coupled climate model gfdl climate model version 3 cm3 with increased vertical resolution and extent in the stratosphere as compared to an earlier model gfdl climate model version 2 cm2 it is demonstrated that the relationship between enso and nao is stronger in cm3 than in cm2 it is found that enso plays an important role in modulating the frequency of occurrence of the stratospheric polar vortex anomalies through enhancement attenuation of the amplitudes of zonal wavenumbers 1 and 2 especially in late winter a higher frequency of weak strong stratospheric vortex events is simulated in cm3 during el nino la nina episodes the weak vortex events during el nino winters are preceded by enhancement of the zonal wave 1 pattern and weakening of zonal wave 2 pattern these modified tropospheric planetary waves propagate upward and then w

decadal relationship between european blocking and the north atlantic oscillation during 1978 2011 part ii a theoretical model study abstractin part i of this study it is revealed that decadal variations of european blocking in its intensity duration and position during 1978 2011 are modulated by decadal changes in the frequency of north atlantic oscillation nao events associated with background atlantic conditions in part ii reanalysis data are analyzed to first show that a t bone type structure of the climatological mean blocking frequency in the euro atlantic sector roughly results from a combination of the blocking frequency distributions along the southeast northwest se nw direction associated with negative phase nao nao events and along the southwest northeast sw ne direction associated with positive phase nao nao events a nonlinear multiscale interaction nmi model is then used to examine the physical processes behind the blocking frequency distributions this model shows that the combination of eastward and westward displaced blocking frequency patterns along the sw ne and se nw directions associated with n

impact of enso on the atmospheric variability over the north atlantic in late winter role of transient eddies abstractthe dynamical mechanism for the late winter teleconnection between el nino southern oscillation enso and the north atlantic oscillation nao is examined using the output from a 2000 yr integration of a coupled general circulation model gcm the coupled model captures many salient features of the observed behavior of both enso and nao as well as their impact on the surface climate in late winter both the observational and model data indicate more occurrences of negative phase of nao in late winter during el nino events and positive nao in la nina episodes the potential role of high frequency transient eddies in the above teleconnection is diagnosed during el nino winters the intensified transient disturbances along the equatorward shifted north pacific storm track extend their influences farther downstream the eddy induced negative height tendencies are found to be more coherent and stronger over north atlantic than that over north pacific these negative height tendencies over the north

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

characteristics of the recent eastward shift of interannual nao variability recent observational studies have shown that the centers of action of interannual variability of the north atlantic oscillation nao were located farther eastward during winters of the period 1978 97 compared to previous decades of the twentieth century in this study which focuses on the winter season december march new diagnostics characterizing this shift are presented further the importance of this shift for nao related interannual climate variability in the north atlantic region is discussed it is shown that an nao related eastward shift in variability can be found for a wide range of different parameters like the number of deep cyclones near surface air temperature and turbulent surface heat flux throughout the north atlantic region by using a near surface air temperature dataset that is homogenous with respect to the kind of observations used it is shown that the eastward shift is not an artifact of changes in observational practices that took place around the late 1970s finally an eof based monte carlo test is developed to quantify the probability of changes in the spatial structure of interannual nao variability for a relatively short 20 yr time series given multivariate white noise it is estimated that the likelihood for differences in the spatial structure of the nao between two independent 20 yr periods which are similar as measured by the angle and pattern correlation between two nao patterns to the observed differences to occur just by chance is about 18 from the above results it is argued that care has to be taken when conclusions about long term properties of nao related climate variability are being drawn from relatively short recent observational data e g 1978 97

nd isotope signature of holocene baltic mn fe precipitates as monitor of climate change during the little ice age neodymium nd isotope profiles were analyzed on two baltic mn fe precipitates 99 2 and tl1 from shallow water 20 m of the mecklenburg bay the age range of these mn fe precipitates determined by 226raex ba dating reaches from recent growth back to 4300 and 1000 yr bp respectively over this time range the nd isotope composition varies from end 0 13 1 to 17 5 in the selected baltic precipitates indicating substantial changes in the nd isotope composition of the baltic sea the lowest end values were recorded during the time interval of the little ice age lia ad 1350 to 1850 these minimum values indicate either an increase of the input of less radiogenic nd from scandinavian archean proterozoic sources end about 22 to the baltic sea or a decrease of the input of more radiogenic nd from continental european sources end about 12 and or north sea water end about 10 variations of both erosive continental input and north sea inflow may indicate a direct response of the nd isotope signal in the baltic sea to climate changes during the lia and be related to cyclic shifts in the atmospheric circulation triggered by the north atlantic oscillation nao another aspect that possibly influenced the input of trace elements and nd isotopes into the baltic sea is the population development in the circum baltic area during the lia the lowest end values also correspond to the medieval demographic crises that led to a significant decrease of agricultural activity and farmland the reduction of soil erosion and enhanced regrowth of natural vegetation may have changed the amount and proportions of dissolved and suspended particulate matter transported into the baltic sea by rivers which in turn may have resulted in a change of the nd isotope composition of baltic sea water

spatial pattern and zonal shift of the north atlantic oscillation part i a dynamical interpretation abstract this paper presents a possible dynamical explanation for why the north atlantic oscillation nao pattern exhibits an eastward shift from the period 1958 77 p1 to the period 1978 97 p2 or 1998 2007 p3 first the empirical orthogonal function analysis of winter mean geopotential heights during p1 p2 and p3 reveals that the nao dipole anomaly exhibits a northwest southeast nw se tilting during p1 but a northeast southwest ne sw tilting during p2 and p3 the nao pattern especially its northern center undergoes a more pronounced eastward shift from p1 to p2 the composite calculation of nao events during p1 and p2 also indicates that the negative positive nao phase dipole anomaly can indeed exhibit such a nw se ne sw tilting second a linear rossby wave formula derived in a slowly varying basic flow with a meridional shear is used to qualitatively show that the zonal phase speed of the nao dipole anomaly is larger smaller in higher latitudes and smaller larger in lower latitud

thermal consequences of a subduction boundary jump a numerical model for generating subduction related clockwise pressure temperature paths 1 clockwise pressure temperature p t paths with a temperature increase after peak p have been reported from a number of subduction related metamorphic belts around the world however an adequate tectonic interpretation of these paths has been lacking one of the principal difficulties is the lack of a sufficient heat source to account for the post peak p temperature rise however two dimensional thermal calculations incorporating accretion of a thick metamorphic unit in a subduction zone reveal that in general an accreted sheet with a width of several kilometers experiences a post accretion heating without having to appeal to any special internal heat source the heating effect is due to the spatial shift of the subduction boundary or subduction boundary jump this heating can account for the generation of subduction related clockwise p t paths within thick metamorphic units for such units the styles of clockwise p t paths vary considerably and can be used as a general indicator of the exhumation rate by considering the balance between conduction and advection during exhumation in contrast a thin unit with a width of 1 km tends to record a nonclockwise p t path regardless of its exhumation rate this is because the thinness decreases the potential both for post accretion heating and for maintaining the higher achieved temperature during exhumation in addition a subduction boundary jump can cause a post accretion transition of metamorphic p t conditions from high to low p t ratios and it may therefore be incorrect to use peak t metamorphic conditions as an indicator of the geotherm along the coeval subduction boundary

solar cycle modulation of the north atlantic oscillation implication in the spatial structure of the nao 1 the spatial extent of the north atlantic oscillation nao is investigated the results suggest that the spatial structure of the nao differs significantly according to the phase of the solar cycle during the solar maximum phases the nao has a hemispherical structure extending into the stratosphere which is similar to the arctic oscillation ao except for the pacific sector however during the minimum phase the nao is confined to the eastern atlantic sector in the troposphere whether or not the nao is modulated by the solar cycle these results may shed new light on the controversy of the physical reality of the two modes of variability the nao and the ao

two teleconnection patterns involved in the north atlantic arctic oscillation 1 the north atlantic oscillation nao and arctic oscillation ao are known as phenomena influencing the weather and climate of the euro atlantic region often however they are treated together in this study two indices representing two independent teleconnection patterns in the sea level pressure are introduced to characterize their differences one is a seesaw between the azores and iceland ai and the other is that between the polar and mediterranean pm regions the result of our study shows that differences in the nao ao indices mainly arise from the inclusion of different portions of the ai and pm and the nao ao indices can be reproduced by a linear combination of the ai and pm indices

ordovician continental margin terranes in the lachlan orogen australia implications for tectonics in an accretionary orogen along the east gondwana margin 1 four continental margin turbidite black shale terranes of the lachlan orogen in the southern tasmanides of eastern australia formed in two major systems along the east gondwana margin and constrain the ordovician assembly of this accretionary orogen key features are the dissimilar stratigraphies of the adjacent bendigo and melbourne terranes in the western system the dissimilar stratigraphies of the adjacent melbourne and albury bega terranes that reflect juxtaposition of the two systems during the middle devonian and the presence of the albury bega terrane both west and east of the macquarie arc in the eastern system that also includes the ocean floor narooma terrane and igneous ocean crust terrane s repetition of the albury bega terrane either side of the arc requires either rifting or orogen parallel strike slip duplication of a once contiguous package terrane interactions began in the earliest gisbornian with early docking uplift deformation and exchange of detritus amalgamation occurred in the earliest silurian benambran orogeny with accretion in the middle devonian over 40 myr discrete turbidite terranes aligned along the gondwana margin in two systems were converted into a very wide orogen characterized by the along strike juxtaposition of superficially similar terranes

paired metamorphic belts revisited abstract the modern plate tectonics regime is characterized by a duality of thermal environments one representing the subduction zone and the other representing the arc backarc or orogenic hinterland this duality is the hallmark of one sided asymmetric subduction and the characteristic imprint of one sided subduction in the geological record is predicted to be the broadly contemporaneous occurrence of two contrasting types of metamorphic belt one of high dt dp type and the other low dt dp type the broadly contemporaneous occurrence of granulite and ultrahigh temperature metamorphism with eclogite high pressure granulite metamorphism in the geological record since the neoarchean era is evidence of dual thermal environments and indicates that subduction has operated on earth since that time classic paired metamorphic belts in which an inboard high dt dp metamorphic belt is juxtaposed against an outboard low dt dp metamorphic belt along a tectonic contact such as the ryoke and sanbagawa belts in japan are found in phanerozoic accretionary orogens of the circum pacific generally they appear to result from juxtaposition of terranes with different metamorphic facies series that may or may not be exactly contemporaneous and that may or may not be far traveled this is a consequence of the difference between globally continuous subduction generating a low to intermediate dt dp environment in the subduction zone and a high dt dp environment in the arc backarc system and metamorphic imprints in the geological record that represent discrete events due to changes in plate kinematics or subduction boundary dynamics or as a result of collision of ridges arcs or continents with the upper plate at the trench the concept of paired metamorphic belts may be generalized and extended more widely than in the original proposition to subduction to collision orogenic systems in addition to accretionary orogenic systems in this wider application the term paired metamorphic belts may be used for penecontemporaneous belts of contrasting type of metamorphism that record different apparent thermal gradients one warmer and the other colder juxtaposed by plate tectonics processes brown 2009 this extends the original concept of miyashiro 1961 beyond the simple pairing of high dt dp and low dt dp metamorphic belts in circum pacific accretionary orogens and makes it more useful in the context of our better understanding of the relationship between thermal regimes and tectonic settings this is particularly useful in subduction to collision orogenic systems where the suture and lower plate materials will register the imprint of low to intermediate dt dp and the upper plate will register penecontemporaneous high dt dp metamorphism commonly manifested at shallow crustal levels by the occurrence of granites in the rock record

thermal model for approach of a spreading ridge to subduction zones and its implications for high p high t metamorphism importance of subduction versus ridge approach ratio 1 the approach of oceanic ridges to subduction zones finally resulting in ridge subduction is observed on the present earth s surface the thermal effects of the ridge approach event are studied using a two dimensional numerical model around subduction zones with particular emphasis on the implications for the associated high p high t metamorphism the ridge approach occurs when the subduction rate v is larger than the half spreading rate at the ridge the difference between the two rates represents the ridge approach rate to the trench u which is newly incorporated in the present thermal model the calculated thermal structure along the slab surface when a ridge reaches the trench generally depends only on u v when shear heating or mantle flow is not taken into account if u v is small or the ridge approach is slow compared to the subduction rate the thermal effect of the ridge approach is large enough to explain the hot general p t conditions of high p high t metamorphism relative to the steady state conditions predicted by numerical simulations in addition when the ridge is close to the trench the subduction stage p t paths experienced by high p high t metamorphic rocks show a strongly curved trajectory with the dp dt progressively increasing with pressure this suggests that the slope of petrologically determined subduction p t paths may indicate if ridge approach contributed to the formation of the metamorphic rocks

transient eddy forcing of the rotational flow during northern winter abstract the total direct transient eddy forcing of the vorticity balance in the upper troposphere during northern winter is examined using 11 years of 2 to 8 day bandpassed global analyses most examinations of the importance of high frequency eddy vorticity fluxes to the maintenance of either the climatological standing waves or low frequency anomalous flows have focused on only the horizontal blow or the rotational component of the horizontal transient flow the latter simplification has been shown to be questionable for planetary scales the vorticity flux by the transient divergent flow produces a forcing of the mean streamfunction that is of comparable magnitude with the equivalent rotational term however the streamfunction forcing by the sum of the transient vertical advection and twisting terms largely balances the fearing by the vorticity flux convergence associated with the divergent flow the result is that the convergence of the eddy vorticity flux by the total transient flow is not a good a

imprints of the north atlantic oscillation on four unusual atmospheric parameters abstract using data for 41 yr 1958 1998 from the national center for environmental prediction national center for atmospheric research reanalysis the authors study the impact of the north atlantic oscillation nao on four atmospheric parameters these four parameters have three common characteristics their previous limited use as climate diagnosis tools their high dependence on changes in atmospheric circulation and their relationship with variables associated with the development of synoptic perturbances they are 1 relative angular momentum from 500 hpa to 200 hpa and from 55 n to 90 n 2 advection of temperature at 500 hpa 3 equivalent temperature at 850 hpa and 4 distribution of upper level low systems ull the most significant results are 1 a significant positive correlation between the relative angular momentum from 500 hpa to 200 hpa and from 55 n to 90 n with the nao index computed as the normalized pressure difference between ponta delgada azores and reykjavik iceland 2 the nao affects 500 hpa temperature advection from 45 n to 70 n and a positive nao index is alternatively related to positive or negative anomalies of advection the relationship is positive over the atlantic asia and western america and negative over europe the pacific and eastern america 3 the correlation pattern between nao index and the equivalent temperature at 850 hpa shows a semiannular structure with negative correlations over the arctic and positive correlations over midlatitudes with the exception of the pacific area and 4 the distribution of ull systems is only influenced by nao over both sides of the atlantic ocean and for the latitude belt from 20 n to 50 n