the link between the north pacific climate variability and the north atlantic oscillation via downstream propagation of synoptic waves abstractthe north atlantic oscillation nao response to the northeast pacific climate variability is examined using the era 40 dataset the main objective is to validate a mechanism involving downstream wave propagation processes proposed in a recent idealized companion study a low frequency planetary scale ridge trough anomaly located in the eastern pacific north american sector induces more equatorward poleward propagation of synoptic scale wave packets on its downstream side which favors the occurrence of anticyclonic cyclonic wave breakings in the atlantic sector and the positive negative nao phase the mechanism first provides an interpretation of the canonical impact of the el nino southern oscillation on the nao in late winter the wintertime relationship between the pacific north american oscillation pna and the nao is also investigated for out of phase fluctuations between the pna and nao indices i e the most recurrent situation in late winter the eastern pacific pna ridge trou

understanding the contrasting north atlantic oscillation anomalies of the winters of 2010 and 2014 the present study investigates the two contrasting winters of 2010 and 2014 during which the north atlantic oscillation nao was mainly negative and positive respectively in the north pacific contrasting anomalies were also present with a straight zonal pacific jet in 2010 and a strong poleward deviation of the pacific jet in its exit region in 2014 using reanalysis data sets and adopting a nonlinear initial value approach with a quasi geostrophic model we show that the pacific north american anomalies are responsible for shaping synoptic wave trains propagating across north america this in turn largely determines the nature of wave breaking and the synoptic eddy feedback onto the mean flow in the north atlantic and finally the nao phase in such a proposed mechanism synoptic wave activity forms the cornerstone of the dynamical relationship between the north pacific and north atlantic large scale anomalies during the contrasting winters of 2010 and 2014

bolla bollana boulder beds a neoproterozoic trough mouth fan in south australia the bolla bollana formation is an exceptionally thick ca 1500 m rift related sedimentary succession cropping out in the northern flinders ranges south australia which was deposited during the sturtian mid cryogenian glaciation lithofacies analysis reveals three distinct facies associations which chart changing depositional styles on an ice sourced subaqueous fan system the diamictite facies association is dominant and comprises both massive and stratified varieties with a range of clast compositions and textures arranged into thick beds 1 to 20 m representing stacked ice proximal glaciogenic debris flow deposits a channel belt facies association most commonly consisting of normally graded conglomerates and sandstones displays scour and fill structure of ca 10 m width and 1 to 3 m depth these strata are interpreted as channelized turbidites rare mud filled channels in this facies association bear glacially striated lonestones finally a sheet heterolithics facies association contains a range of conglomerates through sandstones to silty shales arranged into clear normally graded cycles from the lamina to bed scale these record a variety of non channelized turbidites probably occupying distal and or inter channel locations on the subaqueous fan coarsening and thickening up cycles capped by dolomicrites or mudstones are indicative of lobe build out and abandonment potentially as a result of ice lobe advance and stagnation dropstones recognized by downwarped and punctured laminae beneath pebbles to boulders in shale or in delicate climbing ripple cross laminated siltstones are clearly indicative of ice rafting the co occurrence of ice rafted debris and striated lonestones strongly supports a glaciogenic sediment source for the diamictites comparison to pleistocene analogues enables an interpretation as a trough mouth fan most probably deposited leeward of a palaeo ice stream beyond emphasizing the highly dynamic nature of sturtian ice sheets these interpretations testify to the oldest trough mouth fan recorded to date

the role of synoptic waves in the formation and maintenance of the western hemisphere circulation pattern abstractprevious studies have demonstrated that the nao the leading mode of atmospheric low frequency variability over the north atlantic could be linked to northeast pacific climate variability via the downstream propagation of synoptic waves in those studies the nao and the northeast pacific climate variability are considered as two separate modes that explain the variance over the north atlantic sector and the east pacific north american sector respectively a newly identified low frequency atmospheric regime the western hemisphere wh circulation pattern provides a unique example of a mode of variability that accounts for variance over the whole north atlantic north american north pacific sector the role of synoptic waves in the formation and maintenance of the wh pattern is investigated using the ecmwf reanalysis datasets persistent wh events are characterized by the propagation of quasi stationary rossby waves across the north pacific north american north atlantic regions and by associated s

a new perspective toward cataloging northern hemisphere rossby wave breaking on the dynamic tropopause abstractrossby wave breaking rwb events are a common feature on the dynamic tropopause and act to modulate synoptic scale jet dynamics these events are characterized on the dynamic tropopause by

dynamical evolution of north atlantic ridges and poleward jet stream displacements the development of a particular wintertime atmospheric circulation regime over the north atlantic comprising a northward shift of the north atlantic eddy driven jet stream and an associated strong and persistent ridge in the subtropics is investigated several different methods of analysis are combined to describe the temporal evolution of the events and relate it to shifts in the phase of the north atlantic oscillation and east atlantic pattern first the authors identify a close relationship between northward shifts of the eddydriven jet the establishment and maintenance of strong and persistent ridges in the subtropics and the occurrence of upper tropospheric anticyclonic rossby wave breaking over iberia clear tropospheric precursors are evident prior to the development of the regime suggesting a preconditioning of the atlantic jet stream and an upstream influence via a large scale rossby wave train from the north pacific transient 2 6 days eddy forcing plays a dual role contributing to both the initiation and then the maintenance of the circulation anomalies during the regime there is enhanced occurrence of anticyclonic rossby wave breaking which may be described as low latitude blocking like events over the southeastern north atlantic a strong ridge is already established at the time of wave breaking onset suggesting that the role of wave breaking events is to amplify the circulation anomalies rather than to initiate them wave breaking also seems to enhance the persistence since it is unlikely that a persistent ridge event occurs without being also accompanied by wave breaking

tropospheric rossby wave breaking and the nao nam objective analysis of several hundred thousand anticyclonic and cyclonic breaking rossby waves is performed for the northern hemisphere nh winters of 1958 2006 a winter climatology of both anticyclonic and cyclonic rossby wave breaking rwb frequency and size zonal extent is presented for the 350 k isentropic surface over the nh and the spatial distribution of rwb is shown to agree with theoretical ideas of rwb in shear flow composites of the two types of rwb reveal their characteristic sea level pressure anomalies upper and lower tropospheric velocity fields and forcing of the upper tropospheric zonal flow it is shown how these signatures project onto the centers of action and force the velocity patterns associated with the north atlantic oscillation nao and northern hemisphere annular mode nam previous studies have presented evidence that anticyclonic cyclonic breaking leads to the positive negative polarity of the nao and this relationship is confirmed for rwb over the midlatitudes centered near 50 n however an opposite and statistically significant relationship in which cyclonic rwb forces the positive nao and anticyclonic rwb forces the negative nao is shown over regions 20 to the north and south centered at 70 and 30 n respectively on a winter mean basis the frequency of rwb over objectively defined regions covering 12 of the area of the nh accounts for 95 of the nao index and 92 of the nam index a 6 hourly analysis of all the winters indicates that rwb over the objectively defined regions affects the nao nam without a time lag details of the objective wave breaking analysis method are provided in the appendix

on double rossby wave breaking in the north atlantic we discuss the dynamical features associated with double rossby wave breaking dwb concurrent cyclonic and anticyclonic breakings over the north atlantic with a focus on the north atlantic oscil

the north atlantic oscillation response to large scale atmospheric anomalies in the northeastern pacific abstractingredients in the north pacific flow influencing rossby wave breakings in the north atlantic and the intraseasonal variations of the north atlantic oscillation nao are investigated using both reanalysis data and a three level quasigeostrophic model on the sphere first a long term run is shown to reproduce the observed relationship between the nature of the synoptic wave breaking and the phase of the nao furthermore a large scale low frequency ridge anomaly is identified in the northeastern pacific in the days prior to the maximum of the positive nao phase both in the reanalysis and in the model a large scale northeastern pacific trough anomaly is observed during the negative nao phase but does not systematically precede it then short term linear and nonlinear simulations are performed to understand how the large scale ridge anomaly can act as a precursor of the positive nao phase the numerical setup allows for analysis of the propagation of synoptic waves in the eastern pacific in the p

modelling temporal variation of surface creep on the chihshang fault in eastern taiwan with velocity strengthening friction summary the active chihshang fault at the boundary between the eurasian and the philippine sea plates along the longitudinal valley in eastern taiwan is creeping near the surface but has also produced large earthquakes at mid crustal depth such as the 2003 m w 6 5 chengkung earthquake the creep rate measured at the surface shows strong seasonal fluctuations before the chengkung earthquake correlated with groundwater pressure variations measured at nearby wells the chengkung earthquake did not rupture the fault near the surface but induced a sudden increase of creep rate that decayed with time during the postseismic period these observations suggest that the near surface fault obeys a rate strengthening friction law we conduct numerical simulations based upon the observed variations of creep rate with regard to a velocity strengthening friction law and 1 d groundwater diffusion model to investigate the fault rheology behind this phenomenon the model which assumes a creeping fault segment extending from the surface to a depth of 5 km yields a good fit to the creep data when the friction parameters are assumed to vary with depth or to have changed at the time of the chengkung earthquake our best model suggests that the creeping zone is characterized by a rate parameter a log v o f 1 3 10 2 and a friction coefficient of 0 84 and a long term slip rate of 25 9 mm yr 1 at depths less than 87 m by contrast the lower segment of the creeping zone exhibits a much lower friction coefficient of 0 19 a smaller a of 6 6 10 3 and a higher long term slip rate of 38 1 mm yr 1 at depths between 0 087 and 5 0 km this change in rate parameters implies that the lithologies or physical properties of the fault rocks may vary with depth alternatively a model assuming a dramatic increase in rate parameter from 5 6 10 4 to 6 2 10 3 by the strong ground shaking of the chengkung earthquake can also yield a fair agreement with the observed data the lack of a notable deceleration in fault creep rate during the dry period from 2002 to mid 2003 suggests that the real recharging system for the fault zone may be more complicated than what we assumed in this study

reconstructing sea level pressure variability via a feature tracking approach abstractthe aim of this paper is to quantify the contribution of synoptic transients to the full spectrum of space time variability of sea level pressure slp in middle latitudes in previous work by the authors it was shown that tracking cyclones and anticyclones in an idealized atmospheric model allows one to reconstruct a surprisingly large fraction of the model s variability including not only synoptic components but also its large scale low frequency component motivated by this result the authors performed tracking of cyclones and anticyclones and estimated cyclone and anticyclone size and geometry characteristics in the observed slp field using the 1948 2008 ncep ncar reanalysis dataset the reconstructed synoptic field was then produced via superimposing radially symmetrized eddies moving along their actual observed trajectories it was found that similar to earlier results for an idealized model the synoptic reconstruction so obtained accounts for a major fraction of the full observed slp v

how rossby wave breaking over the pacific forces the north atlantic oscillation 1 anticyclonic rossby wave breaking rwb over a well defined limited area region of the east pacific leads to the positive polarity of the north atlantic oscillation nao by locally piling up wave activity where it may be advected downstream resulting in increased wave activity flux and anticyclonic rwb over the subtropical atlantic a composite time series shows that pacific rwb occurs several days prior to the atlantic rwb and the peak of the nao index following pacific rwb a channel of increased pseudomomentum flux extends from the pacific wave breaking region northeastward toward midlatitudes of eastern north america where pseudomomentum density accumulates for several days prior to moving eastward and leading to anticyclonic rwb over the atlantic

anatomy of synoptic eddy nao interaction through eddy structure decomposition abstracta method of eddy structure decomposition is proposed to detect how low frequency flow associated with the north atlantic oscillation nao organizes systematically synoptic eddy se activity to generate in phase and upstream feedbacks in this method a statistical eddy streamfunction ses field defined by the three point covariance of synoptic scale streamfunction is introduced to characterize spatiotemporal se flow structures the ses field is decomposed into basic and anomalous parts to represent the climatological se flow structure and its departure these two parts are used to calculate the basic and anomalous eddy velocity eddy vorticity and thus eddy vorticity flux fields in order to elucidate those two se feedbacks onto the nao this method is validated by the fact that the observed anomalous eddy vorticity flux field can be reproduced well by two linear terms the basic eddy velocity field multiplied by anomalous eddy vorticity field and the anomalous eddy velocity field multiplied

synoptic view of the north atlantic oscillation abstract this article investigates the synoptic characteristics of individual north atlantic oscillation nao events by examining the daily evolution of the potential temperature field on the nominal tropopause the 2 pvu surface this quantity is obtained from the national centers for environmental prediction national center for atmospheric research ncep ncar reanalysis dataset for the winter season for both phases the nao is found to originate from synoptic scale waves as these waves evolve into the low frequency nao pattern they break anticyclonically for the positive phase and cyclonically for the negative phase the results of this analysis suggest that it is the remnants of these breaking waves that form the physical entity of the nao throughout the nao events for both phases the nao is maintained by the successive breaking of upstream synoptic scale waves when synoptic scale disturbances are no longer present mixing processes play an important role in the nao decay as in other recent

tropical and subtropical north atlantic vertical wind shear and seasonal tropical cyclone activity abstractgiven recent insights into the role of anticyclonic rossby wave breaking awb in driving subseasonal and seasonal north atlantic tropical cyclone tc activity this study further examines

impact of midlatitude stationary waves on regional hadley cells and enso 1 stationary planetary waves are excited in the midlatitudes propagate equatorward and are absorbed in the subtropics the impact these waves have on the tropical climate has yet to be fully unraveled previous work has shown that interannual variability of zonal mean stationary eddy stress is well correlated with interannual variability in hadley cell strength a separate line of research has shown that changes in midlatitude planetary waves local to the pacific strongly affect enso variability here we show that the two phenomena are in fact closely connected interannual variability of wave activity flux impinging on the subtropical central pacific affects the local hadley cell the associated changes in subtropical subsidence affect the surface pressure field and wind stresses which in turn affect enso as a result a winter with an anomalously weak hadley cell tends to be followed a year later by an el nino event

the role of dynamic tropopause rossby wave breaking for synoptic scale buildups in northern hemisphere zonal available potential energy abstractzonal available potential energy az measures the magnitude of meridional temperature gradients and static stability of a domain here the role of northern hemisphere dynamic tropopause 2

linking atmospheric river hydrological impacts on the u s west coast to rossby wave breaking abstractatmospheric rivers ars have significant hydrometeorological impacts on the u s west coast this study presents the connection between the characteristics of large scale rossby wave breaking rwb over the eastern north pacific and the regional scale hydrological impacts associated with landfalling ars on the u s west coast 36 49 n ars associated with rwb account for two thirds of the landfalling ar events and 70 of total ar precipitation in the winter season the two regimes of rwb anticyclonic wave breaking awb and cyclonic wave breaking cwb are associated with different directions of the vertically integrated water vapor transport ivt awb ars impinge in a more westerly direction on the coast whereas cwb ars impinge in a more southwesterly direction most of the landfalling ars along the northwestern coast of the united states states of washington and oregon are awb ars because of their westerly impinging angles when compared to cwb ars awb ars arrive more orthogonally to the

characteristics of the atlantic storm track eddy activity and its relation with the north atlantic oscillation abstract this study focuses on feedbacks of the high frequency eddy activity onto the quasi stationary circulation particularly with regard to the north atlantic oscillation nao the methodology consists of analyzing ncep ncar reanalysis data and sensitivity runs from a high resolution nonhydrostatic regional model consistent with recent studies results show that the jet displacement characteristic of the nao phenomenon depends strongly on the dynamics of the synoptic scale waves and the way they break positive and negative phases of the nao are closely related to anticyclonic and cyclonic wave breaking respectively indeed the high frequency momentum flux whose sign is directly related to the type of wave breaking is correlated with the nao index over the atlantic the peak of the momentum flux signal precedes that of the nao by a few days suggesting that wave breaking is triggering nao events two examples illustrate the significant impact of single storms in particular those occurring in the e