observations of variability on synoptic timescales in the east pacific itcz abstract data obtained in the eastern pacific intertropical convergence zone itcz during the tropical eastern pacific process study tepps show a 3 6 day variability the noaa ship ronald h brown collected surface meteorological observations c band doppler radar volumes atmospheric soundings and rainfall data while on station at 7 8 n 125 w from 8 23 august 1997 the 3 6 day variability was a prominent timescale in the meridional wind and humidity data the maxima of the surface to 700 mb meridional wind anomalies were 5 12 m s 1 maxima of the moisture anomalies at the same levels were 1 3 g kg 1 in phase with the low level southerlies while upper level moisture lagged the southerlies by less than a day the radar indicated a close connection between precipitation in the vicinity of the ship and the meridional wind with the precipitation occurring when the surface southerlies were strongest the meridional and zonal wind components had a maximum of 850 450 mb wind shear during the southerly e

roles of synoptic to quasi biweekly disturbances in generating the summer 2003 heavy rainfall in east china abstractduring the mei yu season of the summer of 2003 the yangtze and huai river basin yhrb encountered anomalously heavy rainfall and the northern yhrb nyhrb suffered a severe flood because of five continuous extreme rainfall events a spectral analysis of daily rainfall data over yhrb reveals two dominant frequency modes one peak on day 14 and the other on day 4 i e the quasi biweekly and synoptic scale mode respectively results indicate that the two scales of disturbances contributed southwesterly and northeasterly anomalies respectively to the mei yu frontal convergence over the southern yhrb syhrb at the peak wet phase an analysis of bandpass filtered circulations shows that the lower and upper regions of the troposphere were fully coupled at the quasi biweekly scale and a lower level cyclonic anomaly over syhrb was phase locked with an anticyclonic anomaly over the philippines at the synoptic scale the strong northeasterly components of an anticyclonic anomaly with a deep cold

observations of rossby waves linked to convection over the eastern tropical pacific rossby wave activity propagating into the eastern tropical pacific from the midlatitudes during northern winter is examined in some detail these waves are associated with the intrusion of high potential vorticity air into low latitudes and they modulate cloudiness stability and vertical motion in the vicinity of the itcz in the upper troposphere and lower stratosphere the horizontal phase and group propagation of the wave activity are qualitatively like those of a nondivergent barotropic rossby wave as the waves move equatorward they become more shallow and propagate upward into the stratosphere the horizontal and vertical propagation is consistent with the tilts of the waves the large scale three dimensional background flow and with the signatures of momentum and heat fluxes associated with the wave activity in the lower troposphere paired cyclonic anomalies on either side of the equator accompany the upper level wave activity to the west of the itcz cloudiness signal these waves amplify following the peak in the itcz cloudiness and propagate westward along the equator this suggests that the upper level wave activity and possibly the associated convective heating can trigger the excitation of the equatorially trapped rossby modes the transient wave activity appears to be a crucial component of the momentum balance of the eastern tropical pacific circulation there is substantial interannual variability in the wave activity consistent with observed changes in the large scale basic state associated with the southern oscillation

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

influence of the monsoon trough on westward propagating tropical waves over the western north pacific part i observations abstractthe present study investigates the possible linkage between the monsoon trough and the interannual variability of the activity of westward propagating tropical waves wtw over the western north pacific wnp during july november for the period 1979 2007 it is shown that the interannual variability of wtw activity is closely related to the location of the monsoon trough during the years when the enhanced weakened monsoon trough extends eastward retreats westward the lower tropospheric wtw activity is above below normal within the southeastern quadrant of the wnp furthermore this study evaluates different wave structures and dynamics of two types of wtws equatorial rossby er waves and mixed rossby gravity mrg tropical depression td type waves in strong monsoon trough s mt and weak monsoon trough w mt years over the wnp there is a significant change in the three dimensional structure as those waves propagate westward to the east of the monsoon trough for the td mrg waves an

horizontal and vertical structure of easterly waves in the pacific itcz abstract outgoing longwave radiation olr and low level wind fields in the atlantic and pacific intertropical convergence zone itcz are dominated by variability on synoptic time scales primarily associated with easterly waves during boreal summer and fall this study uses spectral filtering of observed olr data to capture the convective variability coupled to pacific easterly waves filtered olr is then used as an independent variable to isolate easterly wave structure in wind temperature and humidity fields from open ocean buoys radiosondes and gridded reanalysis products the analysis shows that while some pacific easterly waves originate in the atlantic most of the waves appear to form and strengthen within the pacific pacific easterly waves have wavelengths of 4200 5900 km westward phase speeds of 11 3 13 6 m s 1 and maximum meridional wind anomalies at about 600 hpa a warm moist boundary layer is observed ahead of the waves with moisture lofted quickly through the troposphere by deep co

synoptic scale waves in sheared background flow over the western north pacific abstracttropical depression td type waves are the dominant mode of synoptic scale fluctuations over the western north pacific by applying spatiotemporal filters to the observed olr data and the ncep doe amip ii reanalysis data for 1979 2013 this study reveals the characteristics and energetics of convectively coupled td type waves under the effects of different circulation patterns in association with vertical wind shear results exhibit that different ambient sheared flows significantly affect the vertical structure of westward propagating td type waves with a lower tropospheric mode in an easterly sheared background and an upper tropospheric mode in a westerly sheared background energetic diagnoses demonstrate that when the disturbance is trapped in the lower upper level by easterly westerly shear the horizontal mean flow in the lower upper level favors wave growth by converting energy from the shear of the zonal mean flow from the convergence of the meridional mean flow during the penet

environmental factors contributing to tropical cyclone genesis over the western north pacific abstractthe flow environment associated with tropical cyclone genesis tcg over the western north pacific was assessed via categorization into five flow patterns monsoon shear line sl monsoon confluence region cr monsoon gyre gy easterly wave ew and preexisting tropical cyclone ptc using reanalysis data and an objective algorithm the authors defined contribution scores for the five flow patterns each score represents the contribution to tcg from each flow pattern and scores were calculated for 908 tcg cases from 1979 to 2008 30 yr of the major contribution flow patterns sl accounted for 42 of tcgs ew for 18 cr for 16 ptc for 11 and gy for 6 seasonal variations in the occurrence frequency of these five patterns were clear but interannual variations were not as apparent tropical cyclones often appear to be generated in conditions with multiple flow patterns thus relationships between multiple flow patterns were investigated by comparing contribution scores the sl and

the relationship between anomalous presummer extreme rainfall over south china and synoptic disturbances a spectral analysis of daily rainfall data has been performed to investigate extreme rainfall events in south china during the presummer rainy seasons between 1998 2015 excluding 1999 2006 2011 and 2014 the results reveal a dominant frequency mode at the synoptic scale with pronounced positive rainfall anomalies by analyzing the synoptic scale bandpass filtered anomalous circulations 24 extreme rainfall episodes defined as those with a daily rainfall amount in the top 5 are categorized into cyclone 15 and trough 8 types with the remaining events as an anticyclone type according to the the primary anomalous weather system contributing to each extreme rainfall episode the 15 cyclone type episodes are further separated into 11 lower and 4 upper tropospheric migratory anomalies an analysis of their anomalous fields shows that both types could be traced back to the generation of cyclonic anomalies downstream of the tibetan plateau except for two episodes of lower tropospheric migratory anomalies originating over the south china sea however a lower tropospheric cyclonic anomaly appears during all phases in the former type but only in the wettest phase in the latter type with its peak disturbance occurring immediately beneath an upper level warm anomaly the production of extreme rainfall in the trough type episodes is closely related to a deep trough anomaly extending from an intense cyclonic anomaly over north china which in turn could be traced back to a mid latitude rossby wave train passing by the tibetan plateau the results have important implications for understanding the origin structure and evolution of synoptic disturbances associated with the pre summer extreme rainfall in south china

the impact of the madden julian oscillation on high latitude winter blocking during el nino southern oscillation events abstractwintertime high latitude blocking is associated with persistent changes in temperature and precipitation over much of the northern hemisphere studies have shown that the madden julian oscillation mjo the primary form of intraseasonal tropical variability significantly modulates the frequency of high latitude blocking through large scale rossby waves that alter the global circulation however the characteristics of mjo teleconnections are altered by the el nino southern oscillation enso which modifies the global flow on interannual timescales suggesting that the mjo influence on blocking may depend on enso phase the characteristics of mjo rossby waves and blocking during enso events are examined using composite analysis and a nonlinear baroclinic model the enso phase dependent teleconnection patterns are found to significantly impact pacific and atlantic high latitude blocking during el nino a significant persistent increase in pacific and atlantic blocking follows mjo rmm phase 7 cha

mechanisms determining the winter atmospheric response to the atlantic overturning circulation abstractin climate models an intensification of the atlantic meridional overturning circulation amoc precedes a warming in the north atlantic subpolar basin by a few years in the ipsl cm5a lr model this warming may explain the atmospheric response to the amoc observed in winter which resembles a negative phase of the north atlantic oscillation nao to firmly establish the causality links between the ocean and the atmosphere and illustrate the underlying mechanisms in this model ensembles of atmosphere only simulations are conducted prescribing the sst and sea ice anomalies that follow an amoc intensification in late winter the north atlantic sst and sea ice anomalies drive atmospheric circulation anomalies similar to those found in the coupled model simulations only driven by the sst anomalies related to the amoc show that the largest oceanic influence is due to the warm subpolar sst anomaly which enhances the oceanic heat release and decreases the lower tropospheric baroclinicity in the reg

two paradigms of baroclinic wave life cycle behaviour two idealized baroclinic wave 6 life cycles examined here suggest a framework of opposite extremes a in which to view the behaviour of real synoptic scale disturbances in middle latitudes and b in which to interrelate the synoptic and wave theoretic viewpoints using the saturation propagation saturation sps picture of wave 6 life cycle behaviour the two life cycles dented by lc1 and lc2 are higher resolution versions of the simmons hoskins basic and anomalous cases showing strong and weak late decay of eddy kinetic energy eke they illustrate in varying degrees two extreme types of behaviour here disignated anticyclonic and cyclonic and epitomized by strongly contrasting upper air trough behaviour anticyclonic behaviour dominates the late stages of lc1 and is characterized by backward tilted thinning troughs being advected anticyclonically and equatorward as in the commoner cases of planetary scale mid stratospheric rossby wave breaking cyclonic behaviour dominates lc2 and is characterized by forward tilted broadening troughs wrapping themselves up cyclonically and poleward producing major cut off cyclones in high latitudes these morphologies are visualized by upper air maps of potential temperature on the nominal tropopause defined as a constant potential vorticity surface some atmospheric mid latitude disturbances examined here using the same visualization applied to operational analyses show the same two extreme types of trough behaviour together with intermediate cases the sps picture is re examined using eliassen palm and refractive index cross sections it is shown in particular by reference to a wave activity theorem of haynes that the late stages of lc2 can be looked upon as a remarkably clear and morphologically novel large amplitude counterpart of the nonlinear reflection scenario of rossby wave critical layer theory the late stages of lc1 by constrast look more akin to an nonlinear critical layer absorption scenario lc2 exhibits region of largely undular pv contours adjacent to a nonlinear of irreversiby deformen pv contous in the latter region pv rearrangement and hence absorption of rossby wave activity has largely ceased this accounts for the more persistent ekee in the lc2 case

physical processes controlling earlier and later onset of a typhoon season in the western north pacific the interannual variability of typhoon onset date in western north pacific wnp during 1979 2015 is investigated the average date in the earlier later onset group is early april late july a diagnosis of the genesis potential index shows that the key factor affecting the earlier and later onset lies in the background moisture field according to their evolution feature the earlier onset cases are further divided into two sub groups in the first sub group positive specific humidity anomalies were confined in the western wnp and caused primarily by circulation anomalies associated with a la nina in the equatorial eastern pacific in the second sub group positive specific humidity anomalies were confined in the eastern wnp and caused by anomalous convection associated with the pacific meridional mode pmm in the tropical and subtropical eastern pacific in the later onset composite negative specific humidity anomalies appear in the wnp and were accompanied by an anomalous anticyclone in situ and a v shape negative ssta pattern in the western pacific in addition the change of background vertical wind shear vws also influences the tc onset date a decrease increase in the vws magnitude and an easterly westerly shear anomaly occur in the earlier later onset composite physically it is argued that both the magnitude of the vws and the sign of anomalous zonal wind shear may affect tc formation in the wnp

rossby waves in zonally opposing mean flow behavior in northwest pacific summer monsoon abstract the interactions between monsoon circulations and tropical disturbances in the northwest pacific where the low level mean flow is westerly in the west and easterly in the east are studied with a barotropic model the authors model results suggest that the scale contraction by the confluent background flow the nonlinear dynamics the effect and the large scale convergence are important for the energy and enstrophy accumulation near the region where the zonal flow reverses the energy enstrophy accumulation can be maintained with a continuous rossby wave emanation upstream the largest accumulation occurs when the emanating zonal wavelength is around 2000 km longer rossby waves experience less scale contraction and nonlinear effects while shorter rossby waves cannot hold a coherent structure against dispersive effects the nonlinear energy enstrophy accumulation mechanism is significantly different from previous linear energy accumulation theories in the linear theories this is primarily a

the origin and dispersion characteristics of the observed tropical summertime synoptic scale waves over the western pacific abstract the origin initiation and dispersion behavior of the observed summertime synoptic scale disturbances in the tropical western pacific are studied these westward propagating disturbances have the strongest growth rate over the region of 130 160 e off the equator the three dimensional wave activity flux associated with a wave packet in the vicinity of this region is computed in general wave activity is directed westward there is accumulation of activity flux which gives rise to the amplification of waves in the low levels such accumulation can be attributed to the convergence of both the mean flow and the intrinsic group velocity diabatic forcing also contributes to the growth of disturbances and is most important in the 500 600 hpa layer along the east west oriented storm tracks of the synoptic scale disturbances there are two different dynamical regimes west of 150 e enhanced convection is associated with increased specific humidity at the top of the planetary boundary layer an

abrupt variation in channel width along part of the river severn near shrewsbury shropshire england the river severn near shrewsbury shropshire england is formed by the union of the uppermost severn with the vyrnwy both of these major headstreams drain from the welsh upland that part of the trunk severn here under consideration has been under investigation for some years as exemplifying osage type underfitness in the course of the investigation a census was made of width between banktops on two reaches and of water surface width on one of these reaches the difference between the two types of width gives the value of a third type the width of batter all three width types produce poisson distributions of frequency width particularly width between banktops varies rapidly in the downstream direction in view of the observed poisson distributions transform rather than arithmetic values have been used in difference of means tests applied to variation along the channel cube root transforms are the type selected although there is little to choose on the study reaches between arithmetic means and poisson modes the results obtained do suggest a query about the selection of the most appropriate width values for instance for the purposes of channel morphology all types of width are found to vary along the channel far more rapidly than would be expected from mere randomness variation in bank strength appears to account for about half the variation in width between banktops the results obtained for batter width could be applied in the design of a sampling programme designed to identify local difference in bank strength

origin of the intraseasonal variability over the north pacific in boreal summer abstractthe spatial structure and temporal evolution of the intraseasonal oscillation iso in boreal summer over the midlatitude north pacific ocean are investigated through the diagnosis of ncep reanalysis data it is found that the midlatitude iso has an equivalent barotropic structure with maximum amplitude at 250 hpa initiated near 120 w the iso perturbation propagates westward at a phase speed of about 2 4 m s 1 and reaches a maximum amplitude at 150 w a diagnosis of barotropic energy conversion shows that the iso gains energy from the summer mean flow in the iso activity region a center followed column averaged vorticity budget analysis shows that the nonlinear eddy meridional vorticity transport plays a major role in the growth of the iso perturbation there is a two way interaction between iso flows and synoptic eddies while a cyclonic anticyclonic iso flow causes synoptic scale eddies to tilt toward the northwest southeast northeast southwest direction the tilted synoptic eddies then

continental uplift compensation and shunting during trench spreading center collision abstract a model for continental uplift at a convergent margin damon 1979 is further developed the model assumes the necessity of isostatic compensation of the subducted lithospheric plate it predicts a continental declivity that reaches its maximum uplift and extent at the time of trench spreading center collision as a result of the passage of the subducted plate eastward the region of maximum uplift increases and migrates eastward behind the eastward migrating declivity the gang plank from the front range to the mississippi river is the most obvious modern expression of the continental declivity whereas the great basin is an expression of the area of maximum uplift lowered somewhat by extension and crustal thinning compensation takes place by transfer of asthenosphere to the base of continental lithosphere at the time of trench spreading center collision a pressure gradient shunts the asthenospheric current from the quenched spreading center to the channel between the continental lithosphere and the subducted plate sinking of the subducted plate causes upwelling of asthenosphere feeding the laminar flow between the two plates the model is in accord with the physiography of north america and the geologic record

roles of the synoptic scale wave train the intraseasonal oscillation and high frequency eddies in the genesis of typhoon manyi 2001 abstractexperiments using the weather research and forecasting wrf model were conducted to investigate the effects of multiscale motions on the genesis of typhoon manyi 2001 in the western north pacific the precursor signal associated with this typhoon genesis was identified as a northwest southeast oriented synoptic scale wave train swt the model successfully simulated the genesis of the typhoon in the wake of the swt further experiments were conducted to isolate the effects of the swt the intraseasonal oscillation iso and high frequency shorter than 3 days eddies in the typhoon formation removing the swt in the initial and boundary conditions eliminates the typhoon genesis this points out the importance of the swt in the typhoon genesis it was noted that the swt strengthened the wake cyclone through southeastward energy dispersion the strengthening wake cyclone triggered multiple episodes of strong sustained convective updrafts leading to aggregation of vertical vorticity and formatio

evaluation of a linear bank erosion equation field surveys and aerial photographs were used to measure the rate of migration of a bend of the brandywine creek near chadds ford pennsylvania velocities near the bank were measured in the field during high flows and also estimated by solving a form of the st venant equations engineering properties of the bank soils and the spatial density of trees growing along the bank were also measured the data indicate that rates of bank migration are linearly related to the magnitude of the near bank velocity if the st venant equations are used to estimate the near bank velocity the data also suggest that erosion rates are proportional to ub u where ub is the near bank velocity and u is the reach averaged velocity in addition rates of bank migration are reduced where the density of silver maples acer saccharinum is high boxelder acer negundo and white ash fraxinus americana are also found along the bend but these species do not noticeably influence rates of bank migration

an assessment of the impact of transient eddies on the zonal flow during a blocking episode using localized eliassen palm flux diagnostics abstract the eliassen palm e p flux applied to zonal men flows is an indicator of both the flux of eddy activity and the eddy forcing of the zonal mean flow for time mean flows a localized e p flux is derived and used diagnostically to assess the impact of transient eddies on a major blocking episode that occurred over the south pacific during the southern hemisphere winter of 1979 in contrast to previous studies that have focused on the mean quasi geostrophic potential vorticity equation the focus here is on the mean momentum equations eddy transports and the associated induced meridional circulation and other internal adjustments necessary to maintain the thermal wind balance are gathered together allowing the residual circulation and the effects of the eddies to be determined the time mean equations of motion are thus transformed to consist of mean terms the residual circulation and the divergence of a localized e p flux vector the latter is a measure of the eddy forcing of the mean flow

mixed rossby gravity waves and western pacific tropical cyclogenesis part i synoptic evolution abstract a large amplitude mixed rossby gravity wave packet is identified in the western pacific using 6 10 day bandpass filtered winds individual disturbances of 2300 3000 km wavelength propagated westward as the packet moved slowly eastward the packet first appeared and subsequently amplified within a region of active convection associated with the madden julian oscillation mjo which was isolated by low pass filtered outgoing longwave radiation the packet lasted about 5 weeks then rapidly dispersed as the active mjo moved away from it to the east west of 150 e individual disturbances within the packet turned northwestward away from the equator indicating an apparent transition from mixed rossby gravity waves to off equatorial tropical depression td type disturbances cyclones filled with cloud and anticyclones cleared during the transition nevertheless convective structure consistent with mixed rossby gravity waves remained outside the circulation centers and three tropical cyclones for

rossby wave energy dispersion from tropical cyclone in zonal basic flows this study investigates tropical cyclone energy dispersion under horizontally sheared flows using a nonlinear barotropic model in addition to common patterns unusual features of rossby wave trains are also found in flows with constant vorticity and vorticity gradients in terms of the direction of the energy dispersion the wave train can rotate clockwise and elongate southwestward under anticyclonic circulation ash which contributes to the reenhancement of the tropical cyclone tc the wave train even splits into two obvious wavelike trains in flows with a southward vorticity gradient wsh energy dispersed from tcs varies over time and variations in the intensity of the wave train components typically occur in two stages wave activity flux diagnosis and ray tracing calculations are extended to the frame that moves along with the tc to reveal the concrete progress of wave propagation the direction of the wave activity flux is primarily determined by the combination of the basic flow and the tc velocity along the flux the distribution of pseudomomentum effectively illustrates the development of wave trains particularly the rotation and split of wave propagation ray tracing involves the quantitative tracing of wave features along rays which effectively coincide with the wave train regimes flows of a constant shear parabolic meridional variation produce linear nonlinear wave number variations for the split wave trains the real and complex wave number waves move along divergent trajectories and are responsible for different energy dispersion ducts

the influence of wave trains in mid high latitudes on persistent heavy rain during the first rainy season over south china based on daily precipitation data from the chinese meteorological administration and reanalysis data from the national centers for environmental prediction department of energy the character of low frequency precipitation variability during the first rainy season april june over south china and its corresponding atmospheric circulations in the mid high latitudes are investigated the results show that the precipitation anomalies during this period exhibit obvious quasi biweekly oscillation qbwo features with a period of 8 24 days the influence of wave trains in the mid high latitudes to low frequency persistent heavy rain event phr lf event the 8 24 day filtered precipitation larger than one standard deviation of filtered time series and persisting at least three days over south china is further discussed during the first rainy season over south china there are two low frequency wave trains in the mid high latitudes associated with the phr lf event the wave train crossing the eurasian continent and the wave train along the subtropical westerly jet analysis of wave activity flux indicates that the wave energy disperses toward eastern china along these two low frequency wave trains from north to south and from west to east and then propagates downward over south china accordingly the disturbance of the relative vorticity of the cyclonic anomalies over eastern china is strengthened which enhances the meridional gradient of relative vorticity owing to the transport of low frequency relative vorticity and geostrophic vorticity by meridional wind the ascending motion over south china intensifies and lasts for a long time triggering a phr lf event in addition the tropical system is also a key factor to phr lf event the qbwo of the convection over the south china sea provide moisture for phr lf events maintaining persistent rainfall and vertical ascending motion over south china

an appraisal of the velocity reversal hypothesis for stable pool riffle sequences in the river severn england the velocity reversal hypothesis is the linchpin for a number of recent conceptual models pertaining to sediment sorting and the maintenance of pool riffle sequences in gravel bedded streams the literature in support of the hypothesis together with published adverse criticism is reviewed it is concluded that convincing evidence for the ubiquitous occurrence of such a reversal in a range of channel geometries is currently unavailable continuity considerations indicate that riffles need to be considerably wider than pools for a reversal in the mean velocity to occur under conditions of subcritical flow high stage and stable morphology these observations are substantiated by a detailed study of the hydraulic geometry of stable pool riffle sequences in the river severn england neither the sectionally averaged velocity nor the near bed shear velocity is sensibly greater in the pools than over the riffles during bankfull or near bankfull flow instead a tendency towards equalization of the values of average hydraulic variables is noted as discharge increases a detailed investigation of the three dimensional character of the flow is required to demonstrate whether the entrainment forces within pools can locally exceed those over neighbouring riffles unusual behaviour of the energy gradient over riffles during moderate discharges is related to backwater effects as mediated by the spacing of the riffles the hydraulic data are used to comment on the stability of the test reaches in the context of the development of the river severn in the vicinity of shrewsbury

origin of the summertime synoptic scale wave train in the western north pacific abstract the origin of the summertime synoptic wave train in the western north pacific is investigated with a multilevel nonlinear baroclinic model a realistic three dimensional summer mean state is specified and eigenvectors are calculated by introducing small perturbation initially to the model numerical experiments indicate that the origin of the synoptic wave train may arise from instability of the summer mean flow in the presence of a convection frictional convergence cfc feedback in the lack of the cfc feedback the summer mean flow supports only a least damped mode characterized by a northwest southeast oriented wave train pattern with a zonal wavelength of 2500 km in the presence of both the realistic summer mean flow and the cfc feedback the model reproduces a fast growing mode whose structure and propagation characters are similar to the observed sensitivity experiments with different initial perturbation patterns indicate that the model solution is not sensitive to initial conditions

convectively coupled equatorial waves 1 convectively coupled equatorial waves ccews control a substantial fraction of tropical rainfall variability their horizontal structures and dispersion characteristics correspond to matsuno s 1966 solutions of the shallow water equations on an equatorial beta plane namely kelvin equatorial rossby mixed rossby gravity and inertio gravity waves because of moist processes the tilted vertical structures of ccews are complex and their scales do not correspond to that expected from the linear theory of dry waves the dynamical structures and cloud morphology of ccews display a large degree of self similarity over a surprisingly wide range of scales with shallow convection at their leading edge followed by deep convection and then stratiform precipitation mirroring that of individual mesoscale convective complexes ccews have broad impacts within the tropics and their simulation in general circulation models is still problematic although progress has been made using simpler models a complete understanding of ccews remains a challenge in tropical meteorology

on the westward turning of hurricane sandy 2012 effect of atmospheric intraseasonal oscillations abstracthurricane sandy 2012 experienced an unusual westward turning and made landfall in new jersey after its northward movement over the atlantic ocean the landfall caused severe casualties an

dispersion characteristics and circulation associated with boreal summer westward traveling mixed rossby gravity wave like disturbances abstractan algorithm has been developed to track synoptic scale westward traveling mixed rossby gravity mrg wave like disturbances with a cross equatorial component applied to space time filtered meridional wind data this algorithm finds locations with gaussian shaped wind structures stated in the solutions of shallow water equations swes based on 850 hpa meridional wind from the global national centers for environmental prediction ncep climate forecast system reanalysis cfsr dataset local and instantaneous wave properties including the occurrence time wavenumber intrinsic frequency and magnitude were examined it was found that these low level mrg wave like disturbances can be classified into a longer wavelength group and a shorter wavelength group while most waves identified in the eastern pacific give longer wavelengths disturbances in the western pacific tend to have a wider range of wavenumbers composite analysis revealed that east of 140 e low level disturbances are characterize

on african easterly waves that impacted two tropical cyclones in 2004 1 the u s navy operational global atmospheric prediction system nogaps daily analysis fields are used to study the african easterly waves to show how they impacted two tropical cyclones danielle and earl 2004 formed approximately at the same time in the atlantic a three to eight day band pass filter is applied to the daily global analysis fields to reveal the characteristics of the african easterly waves related to the two cyclones the time filtered 850 mb vorticity shows that african easterly waves reaching the formation locations of danielle and earl on and about 14 august 2004 bear similar structures indicating a unique situation in which one train of the easterly wave is responsible for the genesis of two tropical cyclones located one wavelength apart in addition using piecewise time filtered analysis for different latitude bands it is demonstrated that the movements of both cyclones are significantly modulated by the propagation of the easterly waves even during danielle s poleward movement for more than ten degrees latitude

enso phase dependent td and mrg wave activity in the western north pacific the three dimensional structure and evolution characteristics of tropical depression td and mixed rossby gravity wave mrg type disturbances in the tropical western north pacific during el nino and la nina summers are investigated based on observational and reanalysis data a clear mrg to td transition was observed during el nino summers while such a transition is unclear during la nina summers the vertical structure of the td mrg waves appears equivalent barotropic during el nino but becomes tilted eastward with height during la nina the diagnosis of barotropic energy conversion shows that both the rotational and divergent components of the background flow change associated with e1 nino southern oscillation enso are responsible for energy conversion from the mean flow to the td mrg perturbations a further examination of the pure mrg mode shows that its intensity does not vary between el nino and la nina while its phase speed does a faster slower westward propagation speed during la nina el nina is attributed to enhanced reduced mean easterlies in the western equatorial pacific the heating associated with the mrg wave appears more anti symmetric during la nina than during el nino in contrast to the mrg waves the amplitude of the td waves depends greatly on the enso phase the enhanced suppressed td disturbances during el nino la nina is attributed to greater less barotropic energy conversion associated with the background flow change the vertical structure of the td waves appears quasi barotropic in the geopotential height field but baroclinic in the divergence field

multi scale interactions of equatorial waves associated with tropical cyclogenesis over the western north pacific the tropical cyclone tc centric approach developed in previous studies tends to overemphasize the direct impact of tropical waves and underestimates their large scale modulation of western north pacific wnp tropical cyclogenesis tcg to overcome these limitations this study proposes a new approach based on empirical orthogonal function analyses to re examine associations of multiple waves including the madden julian oscillation mjo quasi biweekly oscillation qbwo convective equatorial rossby er waves and synoptic scale waves ssws with wnp tcg events there is a close association between wnp tcg events total of 273 tcs in this study and ssws 64 mjo 68 qbwo 64 and er 65 waves these suggest that ssw is critical for many tcg events and all of these intra seasonal waves significantly modulate tcg events a majority of tcs 79 were found to be related to more than one wave type indicating an important role for a combination of dynamic and thermodynamic conditions associated with multiple waves in tcg events further analyses show that ssw activity is strongly modulated by the mjo and er waves while the qbwo has no significant impact on ssws during convectively active mjo and er phases stronger ssw trains with more distinct southeast northwestward aligned structures can be found compared to convectively inactive phases similar intra seasonal modulation of the transition from the mixed rossby gravity waves from the equatorial central pacific to the ssw trains over the wnp by the three waves is noted with such transitions largely favored during convectively active mjo and er phases

the shape propagation and mean flow interaction of large scale weather systems abstract for a zonal average operator the eliassen palm flux provides a diagnostic of both eddy behavior and the feedback of the eddies onto the mean flow this paper addresses the diagnosis problem for other averaging operators and in particular for time averaging which has proved in recent years such a powerful means of viewing the three dimensional tropospheric flow the horizontal velocity correlation tensor gives a measure of the characteristic horizontal eddy shape at a point it also implies the direction of the group velocity relative to the mean flow in cases where such a concept is valid however the major emphasis here is on the mean flow feedback of eddies in this respect the eddy vorticity flux is determined by derivatives of the components of the anisotropic part of the tensor making a reasonable approximation allows the eddy vorticity flux convergence to be written in terms of e v 2 u 2 u v a simple interpretation of the mean flow feedback of eddies is then possible a sligh

a subtropical cyclonic gyre associated with interactions of the mjo and the midlatitude jet abstractthis paper describes a large cyclonic gyre that lasted several days in the northwest pacific during july 1988 cyclonic winds at 850 hpa extended beyond the 2000 km radius with a radius of maximum winds of 700 800 km the gyre exhibited clear skies within and north of its center active convection extended 4000 km in longitude to its south the madden julian oscillation mjo was in its active phase in the indian ocean prior to gyre formation consistent with earlier studies diabatic heating in the mjo was associated with an anomalous upper tropospheric westerly jet over the northeast asian coast and a jet exit region over the northwest pacific repeated equatorward wave breaking events developed downwind of the jet exit region one such event left behind a region of lower tropospheric cyclonic vorticity and convection in the subtropics that played a key role in the gyre formation a second wave breaking event produced strong subsidence north of the mature gyre that contributed to its convective a

understanding the sam influence on the south pacific enso teleconnection the relationship between the el nino southern oscillation enso and the southern hemisphere annular mode sam is examined with the goal of understanding how various strong sam events modulate the enso teleconnection to the south pacific 45 70 s 150 70 w the focus is on multi month multi event variations during the last 50 years a significant p 0 10 relationship is observed most marked during the austral summer and in the 1970s and 1990s in most cases the significant relationship is brought about by la nina el nino events occurring with positive negative phases of the sam more often than expected by chance the south pacific teleconnection magnitude is found to be strongly dependent on the sam phase only when enso events occur with a weak sam or when a la nina el nino occurs with a positive negative sam phase are significant south pacific teleconnections found this modulation in the south pacific enso teleconnection is directly tied to the interaction of the anomalous enso and sam transient eddy momentum fluxes during la nina sam and el nino sam combinations the anomalous transient momentum fluxes in the pacific act to reinforce the circulation anomalies in the midlatitudes altering the circulation in such a way to maintain the enso teleconnections in la nina sam and el nino sam cases the anomalous transient eddies oppose each other in the midlatitudes overall acting to reduce the magnitude of the high latitude enso teleconnection

characterizing two types of transient intraseasonal oscillations in the eastern tibetan plateau summer rainfall during summer the intraseasonal disturbances over the eastern tibetan plateau etp can initiate development of severe weather system downstream previous studies yielded inconsistent results on the intraseasonal variability isv of summer rainfall in terms of periodicity genesis process and propagation pathway over the ept based on small samples in this study we detected two dominant peaks of transient isv centered on quasi biweekly 12 24 days qbw and quasi 9 8 11 days using daily rainfall data over the etp during the period of 1992 2012 composite analysis revealed that the two isvs were predominantly associated with the non stationary wave trains which traveled along different pathways for the qbw its mid latitude wave train featured a upper level southeastward migration originating in northern europe and traveling via the east european plain the ural mountains lake balkhash lake baikal the mongolian plateau and then continued southward to the etp and south asia and its tropical wave train was characterized with a northwestward northward migration in low level starting from the philippine sea ps south china sea scs region moving over northern bay of bengal scs region and arriving over the southern fridge of tp and southern china in contrast for quasi 9 day the most significant mid latitudes variability featured an eastward propagating upper level wave train originating from western europe passing across the mediterranean the black and caspian seas arriving over the tp and moving towards east asia and the most evident tropical variability exhibited a clear northwestward westward migration of a low level wave train originating from ps passing over taiwan and subsequently moving towards southeastern china their different spatiotemporal features of associated wave trains caused their distinct linkages with eastern china rainfall anomalies a meridional pattern with a giant ural mountain ridge was the most remarkable precursory signals in upstream region before the qbw wet phase occurrence which was different from the quasi 9 day the major processes generating the local wet spells for the two modes were commonly linked to the preceding boundary warming the upper level negative vorticity and low level prevalent winds which triggered the ascending anomaly and lower tropospheric pre moistening we also discussed the co variation of the wave trains between mid latitudes and low latitudes the distinct evolution related with the two isvs over the etp described here may provide a useful guidance for 2 3 weeks extended range forecasts over the etp and its downstream regions

development of synoptic scale disturbances over the summertime tropical northwest pacific abstract this study addresses the origin of the synoptic scale disturbances that occur in the tropical western north pacific ocean wp region in northern hemisphere summer these have been called easterly waves and tropical depression type td disturbances this analysis uses the national center for environmental prediction national center for atmospheric research reanalysis dataset by performing a regression analysis on several terms in the vorticity equation at 850 hpa it is shown that the td disturbances propagate approximately as barotropic rossby waves at 850 hpa given this ray tracing calculations and the wave activity diagnostic introduced by plumb are used to show that wave accumulation is a promising candidate for the initial development mechanism of the td disturbances the expected local growth rate from this mechanism is simply the convergence of the group velocity which reaches values corresponding to a growth timescale of 3 days this convergence is dominated by but somewhat lar

laramide crustal thickening event in the rocky mountain foreland and great plains the rocky mountain foreland and great plains of the western united states were formerly part of a continental platform adjusted by erosion and deposition in cambrian through jurassic time to near mean sea level and therefore to a near uniform crustal thickness of approximately 33 km today the region stands at regional elevations up to 2 km isostatically supported by a crust exceeding 50 km in thickness reasonable estimates of tertiary sedimentation and laramide strain do not account for more than 15 of the implied thickening however from approximately 70 40 m y b p this region was underlain by a horizontally subducting slab of farallon plate lithosphere moving northeast this slab could have been the cause of the thickening finite difference thermal models with specified kinematics show only a temporary cooling of the base of the north american lithosphere by this slab the excess weight of the slab would have depressed the region plate bending calculations show a quantitative agreement of predicted depression with upper cretaceous isopachs since depression by this slab lasted until the eocene at least the latest cretaceous regression was probably caused by a laramide crustal thickening event the farallon slab might have caused crustal thickening in two ways its excess weight would have drawn in ductile lower crust from surrounding regions however calculations show that this effect is too slow too local and too reversible to explain most of the crustal thickening therefore it seems likely that ductile lower crust was transported from sw to ne by shear stresses which the farallon plate exerted on the base of the north american lithosphere a preliminary finite element calculation based on this hypothesis shows the correct general pattern of crustal thickening an unexpected but encouraging result is that predicted principal compression directions are orthogonal to many laramide basement uplifts

early precambrian crustal development changing styles of mafic magmatism the work of sutton watson 1951 was one of the cornerstones in the interpretation of the evolution of early precambrian archaean and early proterozoic gneiss complexes and in the documentation of mafic dyke swarms that intruded recently accreted archaean cratons since then the concept of geological terranes and terrane accretion has been extended back to the archaean and different events can be distinguished by increasingly precise isotopic dating techniques there is growing evidence that with certain clear provisos the principle of uniformitarianism can be applied as equally to the early precambrian as it can through the rest of the geological record in terms of mafic magmatism there are similarities between some ancient and modern suites both intrusive and extrusive but there are also some major differences such as the presence of komatiites in the archaean and the formation of large scale layered intrusions and extensive dyke swarms at the end of the late archaean and in the early proterozoic the mantle has evolved continuously with the progressive extraction of mafic magmas but allowing for this continental tholeiites appear to have changed little with time ancient mid ocean ridge basalts are elusive because of their poor preservation record the geochemistry of mafic volcanics occurring in many greenstone belts commonly suggests a continental contamination component and that these volcanic rocks are most closely akin to those from present day arc systems the relative abundance of early precambrian intrusive mafic suites parallels the crustal growth curve reflecting the global crustal accretion differentiation superevent towards the close of the archaean bimodal tholeiitic noritic mafic magmatism associated with many of these intrusive suites stems from this rapid turnover in the mantle mafic crust continental crust system this in turn gives a possible link between the respective evolutions of archaean to recent komatiitic noritic and boninitic suites

opposing effects of reflective and nonreflective planetary wave breaking on the nao planetary wave breaking pwb over the subtropical north atlantic is observed over 45 winters december 1958 arch 2003 using ncep ncar reanalysis data pwb is manifested in the rapid large scale and irreversible overturning of potential vorticity pv contours on isentropic surfaces in the subtropical upper troposphere as breaking occurs over the subtropical north atlantic an upper tropospheric pv tripole anomaly forms with nodes over the subtropical midlatitude and subpolar north atlantic the northern two nodes of this tripole are quite similar to the spatial structure of the north atlantic oscillation nao with positive polarity nonlinear reflection is identified in approximately a quarter of all pwb events following breaking two distinct circulation regimes arise one in response to reflective events and the other in response to nonreflective events for reflective events anomalies over the north atlantic rapidly propagate away from the breaking region along a poleward arching wave train over the eurasian continent the quasi stationary wave activity flux indicates that wave activity is exported out of the atlantic basin at the same time the regional poleward eddy momentum flux goes through a sign reversal as does the polarity of the nao for nonreflective events the dipole anomaly over the north atlantic amplifies diagnostics for nonreflective events suggest that wave activity over the azores gets absorbed allowing continued enhancement of both the regional poleward eddy momentum flux and the positive nao

a mechanism for the poleward propagation of zonal mean flow anomalies abstract observational studies have shown that tropospheric zonal mean flow anomalies frequently undergo quasi periodic poleward propagation a set of idealized numerical model runs is examined to investigate the physical mechanism behind this poleward propagation this study finds that the initiation of the poleward propagation is marked by the formation of negative zonal wind anomalies in the tropics these negative anomalies arise from meridional overturning breaking of waves that originate in midlatitudes this wave breaking homogenizes the potential vorticity pv within the region of negative zonal wind anomalies and also leads to the formation of positive zonal wind anomalies in the subtropics subsequent equatorward radiation of midlatitude waves is halted which results in wave breaking at the poleward end of the homogenized pv region this in turn generates new positive and negative zonal wind anomalies which enables a continuation of the poleward propagation the shielding of the homogenized

satellite data analysis and numerical simulation of tropical cyclone formation 1 forecast of tropical cyclone tc formation has long been a great challenge owing to lack of reliable observations over vast open oceans recent satellite products provide a unique opportunity to reveal detailed atmospheric wave structures prior to tc formation using the quikscat surface wind and the tropical rainfall measurement mission microwave image data we document temporal and spatial structures of rossby wave trains induced by energy dispersion from a pre existing tc and easterly wave propagation characteristics prior to cyclogenesis in the western north pacific using a baroclinic model we further simulate cyclogenesis processes associated with the tc energy dispersion and easterly waves

a climatology of rossby wave breaking along the subtropical tropopause ten years 1986 95 of global analyses from the european centre for medium range weather forecasts are used to investigate the temporal and spatial distributions of rossby wave breaking rwb at 350 k along the tropopause herein defined by the 61 5 potential vorticity pv unit 10 26 km 2 s21 kg21 contours though many studies acknowledge rwb as an important contributor to the complex of mixing processes in the atmosphere there exists no prior climatological study of its distribution near the tropopause as in previous studies rwb is identified in the global analyses by southward directed pv gradients at 350 k rwb along the tropopause occurs preferentially during summer over the midoceans in relative proximity to the planetary scale high pressure systems in the subtropics isentropic trajectories at 350 k show that outflow from the tops of these subtropical highs directly participates in rwb over the adjacent downstream oceanic regions two regions are highlighted in this study the north pacific during boreal summer and the south atlantic during austral summer synoptic maps of breaking rossby waves in these regions are provided to reveal the acute tropopause folding in the meridional plane which characteristically accompanies rwb the rich interaction between the tropical flow and the extratropical westerly current exhibited by these cases suggests that the subtropical highs serve as important agents in the coupling between the tropical troposphere and the extratropical stratosphere as expected from theoretical considerations the locations where rwb occurs most frequently known as surf zones are shown to coexist with regionally weak time mean wind speeds and horizontal gradients of pv at 350 k