spectral analysis of gravity anomalies and the architecture of tectonic wedging ne venezuela and trinidad we have analyzed the spectral content of free air gravity anomalies in the caribbean south american plate boundary zone in order to determine better the near surface 0 120 km distribution of crustal and upper mantle elements which give rise to the unusual gravity field of this region the plate boundary zone in northeastern venezuela and trinidad is the site of the world s sea level continental minimum of bouguer gravity anomalies yet the region is also one of mild topography mean value 43 m maximum 1200 m we find the mean depths to interfaces of significant density contrast at a variety of depths for portions of the plate boundary zone we interpret interfaces at 30 35 km and 32 km beneath the guyana shield and the aves ridge respectively to be the moho other shallow interfaces 5 14 km are most likely sediment cover basement contacts in the maturin foreland basin and southern grenada basin deeper interfaces 54 63 km we associate with loaded and downwarped continental and oceanic south american lithosphere the deepest boundaries at depths of 89 120 km may be related to detached or detaching oceanic lithosphere overridden by continental south america we use our results to test the tectonic wedging model of the plate boundary zone recently published by russo and speed 1992 we find that the tectonic wedging model adequately describes many of the structural boundaries inferable from our analysis of gravity anomalies but that the model must be modified to include a thinner guyana shield crust

cenozoic collision of the lesser antilles arc and continental south america and the origin of the el pilar fault it is proposed that the cenozoic tectonic record of the southern lesser antilles arc and northeastern continental south america can be explained by ongoing right oblique collision between the arc and continent the collision has proceeded by the transport of the leading edge of the arc across the slope and outer shelf of a former north facing passive margin of the south american continent the overriding began in the study region near the gulf of cariaco in eastern venezuela in late eocene or oligocene time and has migrated with a generally se vector suturing has occurred between the arc and continent after the attainment of a critical distance of overlap today s point of suturing lies in the paria peninsula east of there overriding continues major tectonic elements engaged in or created by the collision are the southern lesser antilles magmatic arc forearc basin the araya tobago terrane a south american foreland thrust and fold belt and a foreland basin the araya tobago terrane is thought to consist of sediments of south american provenance that were accreted to the lesser antilles forearc during its transit of an ocean basin and the continental slope and outer shelf the emplacement of the magmatic arc and the araya tobago terrane caused tectonic imbrication of shelf strata to propagate ahead of the arc front as a foreland thrust and fold belt tectonic loading of the shelf also caused subsidence of a major foreland basin on the continentward side of the thrust belt it is proposed the el pilar fault exists between the gulf of cariaco and the paria peninsula as an active right slip fault but not east of paria it is not a throughgoing transform fault between the south american and caribbean plates the el pilar fault exists where the overlapping arc and the continent are sutured and takes up a suture parallel component of convergence between arc and continent the eastern tip of the fault propagates east with the point of suturing reconstructions of the cenozoic collision of the lesser antilles arc and the south american continent suggest that the arc lay somewhat north and west of its present position in the eocene this conclusion differs from that of plate reconstructions that assume that the arc was the leading edge of a caribbean plate that has moved east from pacific longitudes since the eocene

on the impact angle of hurricane sandy s new jersey landfall 1 hurricane sandy s track crossed the new jersey coastline at an angle closer to perpendicular than any previous hurricane in the historic record one of the factors contributing to record setting peak water levels in parts of new jersey and new york to estimate the occurrence rate of sandy like tracks we use a stochastic model built on historical hurricane data from the entire north atlantic to generate a large sample of synthetic hurricanes from this synthetic set we calculate that under long term average climate conditions a hurricane of sandy s intensity or greater category 1 makes nj landfall at an angle at least as close to perpendicular as sandy s at an average annual rate of 0 0014 yr 1 95 confidence range 0 0007 to 0 0023 i e a return period of 714 years 95 confidence range 435 to 1429

observational evidence for predictions of tropical cyclone propagation relative to environmental steering abstract theories of vortex motion due to the variations of the coriolis parameter and environmental vorticity are compared to observations of tropical cyclone motion relative to computed steering flows using previously published composite data the composite results are manipulated to obtain a vector quantity for the difference between tropical cyclone motion and steering and this vector difference is termed propagation the properties of these propagation vectors within various composite data stratifications provide tentative support for nonlinear numerical results such as i the general magnitude and direction of the induced propagation ii the dependence of such propagation on the outer wind strength of the tropical cyclone and iii the dependence of such propagation on the direction of the environmental vorticity gradient ambiguities in the composite data are discussed with respect to linear and nonlinear theories of tropical cyclone propagation and several new composite data stratific

on the rossby wave source and the steady linear response to tropical forcing abstract a two level spectral model with a zonally homogeneous climate is used to study the steady response of a spherical atmosphere to tropical heating solutions are obtained by both averaging the time integration of the model and solving for the linear steady response it is found that the rossby wave source rws from a simple tropical heat source exhibits a relatively complicated horizontal structure that extends from the tropics into extratropical regions the strong extratropical component of the rws is important for the steady response in middle and high latitudes a decomposition of the solution using separately the components of the rws in tropical and extratropical regions shows that the responses to the tropical and extratropical rwss tend to cancel in middle and high latitudes the extratropical component of the rws may be understood by quasigeostrophic dynamics

on the maintenance and initiation of the intraseasonal oscillation in the ncep ncar reanalysis and in the gla and ukmo amip simulations in this study satellite derived outgoing longwave radiation olr and the reanalysis from the national centers for environmental prediction national center for atmospheric research are used as verification data in a study of intraseasonal variability in the goddard laboratory for atmospheres gla and the united kingdom meteorological office ukmo atmospheric general circulation models these models simulated the most realistic intraseasonal oscillations io of the 15 atmospheric model intercomparison project models previously analyzed during the active phase of the intraseasonal oscillation convection is observed to migrate from the indian ocean to the western central pacific ocean and into the south pacific convergence zone spcz the simulated convection particularly in the gla model is most realistic over the western central pacific ocean and the spcz in the reanalysis the baroclinic structure of the io is evident in the eddy stream function and eastward migration of the anticyclone cyclone pairs occurs in conjunction with the eastward development of convection both the gla and ukmo models exhibit a baroclinic structure on intraseasonal time scales the gla model is more realistic than the ukmo model at simulating the eastward migration of the anticyclone cyclone pairs when the convection is active over the western central pacific in the ukmo model the main heating is located off the equator which contributes to the irregular structures seen in this model on intraseasonal time scales the maintenance and initiation of the intraseasonal oscillation has also been investigated analysis of the latent heat flux indicates that evaporative wind feedback is not the dominant mechanism for promoting the eastward propagation of the intraseasonal oscillation since evaporation to the west of the convection dominants the data suggest a wave cisk conditional instability of the secondkind type mechanism although the contribution by frictional convergence is not apparent in the gla model enhanced evaporation tends to develop in place over the west pacific warm pool while in the ukmo simulation westward propagation of enhanced evaporation is evident it is suggested that lack of an interactive ocean may be associated with the models systematic failure to simulate the eastward transition of convection from the indian ocean into the western pacific ocean this hypothesis is based upon the examination of observed sea surface temperature sst and its relationship to the active phase of the intraseasonal oscillation which indicates that the io may evolve as a coupled ocean atmosphere mode the eastward propagation of convection appears to be related to the gradient of sst with above normal sst to the east of the convection maintaining the eastward evolution and decreasing sst near the western portion of the convective envelope being associated with the cessation of convection

impact of atmospheric blocking on south america in austral summer abstractthis study investigates atmospheric blocking over eastern south america in austral summer for the period of 1979 2014 the results show that blocking over this area is a consequence of propagating rossby waves that grow to large amplitudes and eventually break anticyclonically over subtropical south america ssa the ssa blocking can prevent the establishment of the south atlantic convergence zone sacz as such years with more blocking days coincide with years with fewer sacz days and reduced precipitation convection mainly over the indian ocean associated with madden julian oscillation mjo phases 1 and 2 can trigger the wave train that leads to ssa blocking whereas convection over the western central pacific associated with phases 6 and 7 is more likely to lead to sacz events it is found that the mjo is a key source of long term variability in ssa blocking frequency the wave packets associated with ssa blocking and sacz episodes differ not only in their origin but also in their phase and

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

effects of monsoon trough intraseasonal oscillation on tropical cyclogenesis over the western north pacific abstractthe effects of intraseasonal oscillation iso of the western north pacific wnp monsoon trough on tropical cyclone tc formation were investigated using the advanced research weather research and forecasting arw model a weak vortex was specified initially and inserted into the background fields containing climatological mean anomalies associated with active and inactive phases of monsoon trough isos the diagnosis of simulations showed that monsoon trough iso can modulate tc development through both dynamic and thermodynamic processes the dynamic impact is attributed to the lower midtropospheric large scale vorticity associated with monsoon trough iso interactions between cyclonic vorticity in the lower middle troposphere during the active iso phase and a vortex lead to the generation of vortex scale outflow at the midlevel which promotes the upward penetration of friction induced ascending motion and thus upward moisture transport in addition the low level convergence associated with ac

gravity anomalies and flexure of the lithosphere at mountain ranges the bouguer gravity anomaly over the himalayan alpine and appalachian mountains is characterized by a generally asymmetric gravity low which spans the mountains and associated foreland basins the minimum of the gravity low is generally systematically displaced from the region of greatest topographic relief and shows no obvious relationship to surface geology in addition the alps and appalachians are associated with a generally symmetric gravity high that is unrelated to the topographic relief together the gravity low and high form a characteristic positive negative anomaly couple the steep gravity gradient between the positive and negative couple correlates with the insubric line and its equivalents in the alps and the brevard zone in the southern appalachians this gravity anomaly couple is interpreted as evidence for flexure of the continental lithosphere by subsurface buried and surface topographic loading the magnitude of the subsurface load is estimated from the integrated excess mass represented by the positive anomaly and the magnitude of the surface load from the topography by combining these loads the flexure of the lithosphere and the associated bouguer gravity anomaly are calculated for different assumed values of the elastic thickness te of continental lithosphere the best fitting value of te for the himalayas is 80 100 km for the alps 25 50 km and for the appalachians 80 130 km the model calculations suggest that the main contribution to the gravity couple in the alps and appalachians arises not from surface loads such as thrust sheets and nappes but from subsurface loads however in the case of the himalayas the topography appears to be a sufficient load to explain the observed asymmetric gravity low when subsurface loads do exist therefore we would not expect a close correlation between mountain topographic relief and depth to the m discontinuity as required by classical models of isostasy rather the m discontinuity is expected to relate to the center of mass of all the loads acting on the lithosphere the surface and subsurface loads inferred from the gravity anomaly play a major role in the development of mountains and foreland basins the emplacement of large subsurface loads represents the primary event in the alps and appalachians while in the himalayas the emplacement of the surface load is the primary event the emplacement of the subsurface load probably marks the initiation of foreland basin development the regional characteristics of the basin are controlled by the primary load while local variations are controlled by the secondary thrust sheet loads subsequent movement of either load will produce migration of the basin depocenter the origin of the subsurface load is not clear but its association with the insubric line in the alps and the brevard zone in the appalachians suggests that it may be related to the obduction of crustal blocks flakes onto the underlying plate during continental collision or possibly to the preloaded crustal structure of the underlying plate

tropical cyclone movement and surrounding flow relationships abstract this paper presents results of a comprehensive study of the relationship between the movement of tropical cyclones and the large scale circulation which surrounds them cyclones have been stratified by direction and speed of movement latitude intensity change and size as determined by the radius of the outermost closed surface isobar in three ocean basins the northwest pacific the west atlantic and the australian south pacific region twenty one different stratifications are available in the northwest pacific 13 in the west atlantic and 6 in the australian south pacific area cyclone movement and surrounding flow relationships were studied at different pressure levels and a variety of radii pressure weighted layer averages were also analyzed in search of such relationships results show an important relationship between surrounding large scale flow and tropical cyclone movement for all stratifications the winds in the mid troposphere 500 700 mb at 5 7 latitude radius from the cyclone

oceanic crust of the grenada basin in the southern lesser antilles arc platform seismic refraction data permit the southern lesser antilles arc and surrounding regions to be divided by the velocity of their basement we propose that high velocity basement of the arc platform beneath the grenadine islands and below a part of the tobago trough forearc basin is oceanic and continuous and was originally connected with oceanic crust of the grenada basin low velocity basements of the tobago terrane and the arc platform from st vincent north lie south and north respectively of the high velocity basement of the arc platform an oceanic origin of this high velocity crust in the grenadines is argued to be more plausible than an origin as unroofed lower arc crust the segment of probable oceanic crust in the arc platform was greatly uplifted during development of the present island arc mainly in late neogene time relative to the grenada basin and tobago trough accepting the proposition of shallow oceanic crust in the grenadines early middle eocene and possibly older pillow basalts of mayreau the oldest rock unit of the southern lesser antilles arc platform may be an exposure of such basement major and minor element compositions of mayreau basalt are indicative of a spreading rather than arc origin the stratigraphy of the pillow basalts indicates extrusion in an open marine environment distant or shielded from sources of arc or continental sediment followed by a period of pelagic sedimentation above the carbonate compensation depth the eocene basalt and pelagic cover formed a relatively deep floor of a marine basin in which arc derived turbidites and pelagic sediments accumulated over the succeeding 25 30 ma such basalts thus indicate a probable spreading origin of the grenada basin and an age of cessation of spreading in the region of mayreau in eocene time the configuration of the eocene basin and the direction of spreading however are unknowns regional structural relationships imply the spreading was probably backarc an origin also hinted at by ce zr ratios of mayreau basalt although the aves ridge probably was the remnant arc the existence and position of an early middle eocene frontal arc are unresolved the early paleogene tectonic architecture of the southeastern caribbean differed substantially from that of the neogene

climate modulation of north atlantic hurricane tracks the variability of north atlantic tropical storm and hurricane tracks and its relationship to climate variability is explored tracks from the north atlantic hurricane database for the period 1950 2007 are objectively separated into four groups using a cluster technique that has been previously applied to tropical cyclones in other ocean basins the four clusters form zonal and meridional separations of the tracks the meridional separation largely captures the separation between tropical and more baroclinic systems while the zonal separation segregates gulf of mexico and cape verde storms general climatologies of the seasonality intensity landfall probability and historical destructiveness of each cluster are documented and relationships between cluster membership and climate variability across a broad spectrum of time scales are identified composites with respect to cluster membership of sea surface temperature and other environmental fields show that regional and remote modes of climate variability modulate the cluster members in substantially

modulation of eastern north pacific hurricanes by the madden julian oscillation abstract hurricane and tropical storm statistics verify the modulation of eastern pacific tropical systems by the madden julian oscillation mjo as hypothesized by maloney and hartmann over twice as many named tropical systems hurricanes and tropical storms accompany equatorial 850 mb westerly anomalies than accompany equatorial easterly anomalies and the systems that do exist are stronger hurricanes are over four times more numerous during westerly phases of the mjo than during easterly phases the current study constructs a composite life cycle of the mjo during may november 1979 95 using an index based on the 850 mb equatorial zonal wind equatorial kelvin waves propagating eastward from convective regions of the western pacific ocean alter dynamical conditions over the eastern pacific ocean westerly easterly equatorial 850 mb wind anomalies are accompanied by enhanced suppressed convection over the eastern pacific hurricane region convection locally amplifies the wind anomalies over the ea

role of extensional tectonics in exhumation of eclogites and blueschists in an oblique subduction setting northeastern venezuela eclogites and blueschists in northeastern venezuela belong to a mid to late cretaceous subduction complex fore arc terrane related to right oblique subduction of the proto caribbean plate beneath the farallon plate along the leeward antilles volcanic island arc these rocks were metamorphosed at high pressures and subsequently underwent retrogradation at decreasing pressures but at constant or slightly increasing temperatures they underwent five phases of deformation three synmetamorphic and two postmetamorphic the major principal extensions x axes of each of the three synmetamorphic deformations are subparallel to the volcanic arc the extension parallel to the arc and the associated exhumation and uplift of the subduction complex fore arc terrane may have resulted primarily from an increase of the arc parallel displacement rate of this terrane caused by an increase of obliquity of plate convergence

effect of enso and the mjo on western north pacific tropical cyclones prior work has suggested that rossby wave accumulation in the lower troposphere may be an important mechanism for the development of synoptic scale disturbances in the western north pacific in northern summer this work examines the intraseasonal and interannual variability of wave accumulation by computing the barotropic wave activity flux divergence at 850 hpa for different phases of the madden julian oscillation mjo and el nino southern oscillation enso indirectly and without ruling out other influences the results suggest a physical mechanism behind previously identified relationships between tropical cyclogenesis statistics and these two modes of variability mjo and enso

the global atmospheric circulation response to tropical diabatic heating associated with the madden julian oscillation during northern winter abstractthe detailed dynamical mechanisms of the upper tropospheric circulation response to the madden julian oscillation mjo convection are examined by integrating a primitive equation model a series of initial value calculations with the climatological boreal winter background flow forced by the mjo like thermal forcing successfully capture the key aspects of the observed circulation response to the mjo convection this suggests that a large fraction of mjo related circulation anomalies are direct responses to tropical heating in both the tropics and extratropics and can be largely explained by linear dynamics it is found that mjo like dipole heatings not only intensify tropical upper tropospheric anomalies but also weaken them at certain regions because of the interaction between equatorial kelvin and rossby waves the rossby wave train primarily excited by horizontal divergence of upper level perturbation flow propagates northeastward and then heads back to the equator in this way rossby wave act

tropical cyclogenesis associated with rossby wave energy dispersion of a preexisting typhoon part i satellite data analyses abstract the structure and evolution characteristics of rossby wave trains induced by tropical cyclone tc energy dispersion are revealed based on the quick scatterometer quikscat and tropical rainfall measuring mission trmm microwave imager tmi data among 34 cyclogenesis cases analyzed in the western north pacific during 2000 01 typhoon seasons six cases are associated with the rossby wave energy dispersion of a preexisting tc the wave trains are oriented in a northwest southeast direction with alternating cyclonic and anticyclonic vorticity circulation a typical wavelength of the wave train is about 2500 km the tc genesis is observed in the cyclonic circulation region of the wave train possibly through a scale contraction process the satellite data analyses reveal that not all tcs have a rossby wave train in their wakes the occurrence of the rossby wave train depends to a certain extent on the tc intensity and the background flow whether or not a rossby wave train can finally lead to cy

interactions between typhoon megi 2010 and a low frequency monsoon gyre abstractthe arw model is used to investigate the sharp northward turn of super typhoon megi 2010 after it moved westward and crossed the philippines the ncep analyzed fields during this period are separated into a slowly varying background flow component a 10 60 day low frequency component representing the monsoon gyre and a 10 day high pass filtered component representing megi and other synoptic scale motion it appears that the low frequency 10 60 day monsoon gyre interacted with megi and affected its track to investigate the effect of the low frequency mode on megi numerical experiments were designed in the control experiment the total fields of the analysis are retained in the initial and boundary conditions and the model is able to simulate megi s sharp northward turn in the second experiment the 10 60 day monsoon gyre mode is removed from the initial and lateral boundary fields and megi moves westward and slightly northwestward without turning north tracks of the relative positions b

structures and mechanisms of the northward propagating boreal summer intraseasonal oscillation abstract the spatial and temporal structures of the northward propagating boreal summer intraseasonal oscillation bsiso are revealed based on the analysis of both the echam4 model simulation and the ncep ncar reanalysis the bsiso structure and evolution characteristics simulated by the model bear many similarities to those derived from the ncep ncar reanalysis the most notable features are the remarkable meridional asymmetries relative to the bsiso convection in the vorticity and specific humidity fields a positive vorticity perturbation with an equivalent barotropic structure appears a few latitude degrees north of the convection center the maximum specific humidity also shows a clear northward shift in the lower troposphere two internal atmospheric dynamics mechanisms are proposed to understand the cause of the northward propagation of the bsiso the first is the vertical shear mechanism the key process associated with this mechanism is the generation of barotropic vorticity due to the couplin

links between tropical cyclone activity and madden julian oscillation phase in the north atlantic and northeast pacific basins abstract the leading intraseasonal mode of atmospheric and oceanic variability the madden julian oscillation mjo influences tropical and extratropical sea level pressure temperature divergent and rotational wind components moisture and deep convection as a 40 to 50 day oscillation the mjo is also known to influence tropical phenomena including tropical cyclone tc activity in various tc basins the links between the mjo and multiple measures of tc activity including genesis landfall and an integrative accumulated cyclone energy ace index were quantified for multiple tc formation basins across the western hemisphere including the north atlantic and northeast pacific ocean and subbasins for the period 1978 2006 using this relatively long 29 yr tc dataset and employing an upper tropospheric mjo diagnostic that is physically meaningful over the entire western hemisphere this study extends existing research on the relationships between the mjo and tcs the noaa climate prediction cente

fundamental causes of propagating and nonpropagating mjos in mjotf gass models abstractthis study investigates the fundamental causes of differences in the madden julian oscillation mjo eastward propagation among models that participated in a recent model intercomparison project these models are categorized into good and poor groups characterized by prominent eastward propagation and nonpropagation respectively column integrated moist static energy mse budgets are diagnosed for the good and the poor models it is found that a zonal asymmetry in the mse tendency characteristic of eastward mjo propagation occurs in the good group whereas such an asymmetry does not exist in the poor group the difference arises mainly from anomalous vertical and horizontal mse advection the former is attributed to the zonal asymmetry of upper midtropospheric vertical velocity anomalies acting on background mse vertical gradient the latter is mainly attributed to the asymmetric zonal distribution of low tropospheric meridional wind anomalies advecting background mse and moisture fields base

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

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

the global response to tropical heating in the madden julian oscillation during the northern winter a life cycle of the madden julian oscillation mjo was constructed based on 21 years of outgoing long wave radiation data regression maps of ncep ncar reanalysis data for the northern winter show statistically significant upper tropospheric equatorial wave patterns linked to the tropical convection anomalies and extratropical wave patterns over the north pacific north america the atlantic the southern ocean and south america to assess the cause of the circulation anomalies a global primitive equation model was initialized with the observed three dimensional 3d winter climatological mean flow and forced with a time dependent heat source derived from the observed mjo anomalies a model mjo cycle was constructed from the global response to the heating and both the tropical and extratropical circulation anomalies generally matched the observations well the equatorial wave patterns are established in a few days while it takes approximately two weeks for the extratropical patterns to appear the model response is robust and insensitive to realistic changes in damping and basic state the model tropical anomalies are consistent with a forced equatorial rossby kelvin wave response to the tropical mjo heating although it is shifted westward by approximately 20 longitude relative to observations this may be due to a lack of damping processes cumulus friction in the regions of convective heating once this shift is accounted for the extratropical response is consistent with theories of rossby wave forcing and dispersion on the climatological flow and the pattern correlation between the observed and modelled extratropical flow is up to 0 85 the observed tropical and extratropical wave patterns account for a significant fraction of the intraseasonal circulation variance and this reproducibility as a response to tropical mjo convection has implications for global medium range weather prediction copyright 2004 royal meteorological society

modulation of hurricane activity in the gulf of mexico by the madden julian oscillation the madden julian oscillation mjo is a large scale episodic modulation of tropical winds and precipitation that travels eastward from asia to america with a characteristic repeat time of 30 to 60 days here it is shown that when mjo wind anomalies in the lower troposphere of the eastern pacific are westerly gulf of mexico and western caribbean hurricane genesis is four times more likely than when the mjo winds are easterly accurate predictions of the mjo may lead to improved long range forecasts of tropical cyclone activity

the madden julian oscillation barotropic dynamics and north pacific tropical cyclone formation part ii stochastic barotropic modeling abstract a stochastic barotropic model linearized about the 850 mb flow is used to investigate the relationship between wind variations associated with the madden julian oscillation mjo and eddy kinetic energy variations in the tropics such a model is successful in predicting the observed location of eddy kinetic energy maxima during the westerly phase of the mjo and the suppression of eddy activity during the easterly phase of the mjo the concentration of eddy energy during the westerly phase results from the strong east west and north south gradients of the large scale wind fields the model shows that barotropic wave propagation and wave mean flow interaction tend to concentrate small scale rossby wave energy in regions of convergence which may be an important mechanism for organizing convection into tropical cyclones the structure and barotropic energetics of the wave activity are similar to those observed but the modeled eddies are smaller in scale and do not move westward as do the observed e

the origin of the subtropical anticyclones abstract the origin of the northern hemisphere summer subtropical anticyclones is investigated using a linear quasigeostrophic model it is found that the broad features in the model solutions forced by realistic heating fields acting on observed zonal flows agree well with those in the observations the realistic features of the model solutions include the subtropical continental lows and oceanic highs in the lower troposphere and continental ridges and midoceanic troughs in the upper troposphere the forced responses are largest near the surface and the tropopause with a vertical node around 500 hpa as observed the results indicate that the model stationary waves owe their existence largely to the asian heat source the authors thus propose that the observed low level subtropical anticyclones over the north pacific and north atlantic oceans be interpreted as a remote response of rossby waves forced by the large scale heat sources over asia the results support the existing theory that the observed low

oblique collision and tectonic wedging of the south american continent and caribbean terranes our studies of the surface structures seismicity and gravity anomalies of the caribbean south american plate boundary zone of northeast venezuela and trinidad show that the crustal and upper lithospheric structure and kinematics of this zone are complex and differ markedly along strike we propose a model of the zone9s lateral transition from near trinidad west to caracas emphasizing three concepts 1 the steepening detachment and then sinking away of atlantic oceanic lithosphere that is was attached to the northern edge of continental south america 2 the wedging seaward and imbricate thickening of the northern margin of the continent in the region of the detaching atlantic slab the continental wedge overrides the slab and is overridden by terranes attached to the caribbean plate and 3 that the structural and kinematic transitions are a consequence of the progressive oblique collision between continental south america and the overriding caribbean terranes

an observed connection between the north atlantic oscillation and the madden julian oscillation abstract based on the bivariate madden julian oscillation mjo index defined by wheeler and hendon and 25 yr 1979 2004 of pentad data the association between the north atlantic oscillation nao and the mjo on the intraseasonal time scale during the northern hemisphere winter season is analyzed time lagged composites and probability analysis of the nao index for different phases of the mjo reveal a statistically significant two way connection between the nao and the tropical convection of the mjo a significant increase of the nao amplitude happens about 5 15 days after the mjo related convection anomaly reaches the tropical indian ocean and western pacific region the development of the nao is associated with a rossby wave train in the upstream pacific and north american region in the atlantic and african sector there is an extratropical influence on the tropical intraseasonal variability certain phases of the mjo are preceded by the occurrence of strong naos a significant change of upper zonal

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

seismicity and tectonics of the southeastern caribbean we present 33 new focal mechanisms for se caribbean earthquakes 1963 1988 we use these mechanisms in conjunction with 28 previously available mechanisms to distinguish between two models of plate boundary zone interaction in the se caribbean the trench trench transform and hinge faulting model and the right oblique collision model shallow 0 70 km and intermediate 70 200 km depth earthquakes occur in the study region we focus on the tectonic causes of these events and the motions they delineate the shallow earthquakes are in a broad linear zone which trends ne from the paria peninsula of venezuela towards barbados intermediate depth earthquakes cluster beneath and nw of the peninsula and deepen to the nw perpendicular to the ne trending shallow events the vertical distribution of the earthquakes suggests a slab with steep nw dip shallow dextral strike slip on e striking faults is restricted to a 60 km wide linear zone between the gulf of cariaco and the western margin of the gulf of paria dextral strike slip is active only as far east as the gulf of paria and not within or east of trinidad shallow thrust events with ene striking planes distributed between the araya peninsula and the gulf of paria indicate collision at crustal levels between south america and caribbean and that folding and thrusting are still active over a 60 km interval south of the araya paria isthmus active thrusting in venezuela corroborates predictions of transpression between caribbean and south america and discounts transtensional motions between the two plates in the se caribbean the conjunction of shallow thrust strike slip and normal earthquakes in the gulf of paria at around 62 3 may be the expression of unpartitioned oblique compressive deformation in the plate boundary zone intermediate 165 km h 70 km depth thrust and dip slip events within the nw dipping slab indicate that oceanic lithosphere probably originally attached to south america subducts to the nw beneath the caribbean plate shallow normal faulting events e and ne of trinidad are expressions of plate bending about near horizontal axes parallel to the lesser antilles subduction zone we conclude that the earthquake mechanisms provide strong support for the right oblique collision model of caribbean south american plate interaction

monsoonal interactions leading to sudden tropical cyclone track changes abstract sudden poleward track changes of tropical cyclones embedded in monsoon gyres in the western north pacific are documented during these track changes which are generally not well forecast the cyclones are often accompanied by a separate comma shaped area of gale force winds and deep convection along the eastern periphery this monsoon surge is distinct from the tropical cyclone synoptic analyses often reveal a building anticyclone to the east or southeast of the monsoon gyre the hypothesis that the sudden track change is initiated by a binary interaction of the tropical cyclone and monsoon gyre is tested with a nondivergent barotropic model tropical cyclone scale vortices with initial positions within the eastern semicircle of a larger monsoon gyre scale vortex initially coalesce with the monsoon gyre and then exhibit sudden poleward track changes that are similar to the observations during the coalescence phase the large and relatively weak monsoon gyre undergoes a induced dispersion in

on the madden julian oscillation atlantic hurricane relationship abstract the large scale equatorial circulation known as the madden julian oscillation mjo has been shown to impact tropical cyclone activity in several basins around the globe in this paper the author utilizes an mjo index created by wheeler and hendon to examine its impacts on tropical genesis and intensification in the atlantic large differences in frequency and intensity of tropical cyclone activity are seen both in the tropical atlantic as well as in the northwest caribbean and gulf of mexico depending on the mjo phase coherent changes in upper and lower level winds and relative humidity are likely responsible for these differences since the mjo shows potential predictability out to about two weeks the relationships discussed in this paper may be useful for short term predictions of the probability of tropical cyclone activity in the atlantic as a complement to the already available longer term seasonal predictions

the association between intraseasonal oscillations and tropical storms in the atlantic basin abstract tropical intraseasonal variations in the pacific are related to the tropical storm activity in the atlantic basin using outgoing longwave radiation anomalies olras and circulation anomalies from the ncep ncar reanalysis tropical storms are most likely to develop and maintain in the atlantic when enhanced convection associated with the tropical intraseasonal oscillations tios is located over the indian ocean and convection in the pacific is suppressed tropical storm activity decreases when the tio shifts to the opposite phase the dominant signal associated with the tio is the madden julian oscillation the atmospheric response in the tropics is a dipole pattern in the 200 hpa streamfunction anomalies just north of the equator positive olra propagates eastward from the indian ocean to the central pacific the dipole moves eastward in concert with olras when enhanced convection is located in the indian ocean and convection in the pacific is suppressed positive 200 hpa streamfunction anoma

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

intraseasonal teleconnection between the summer eurasian wave train and the indian monsoon this study investigated the most recurrent coupled pattern of intraseasonal variability between midlatitude circulation and the indian summer monsoon ism the leading singular vector decomposition svd pattern reveals a significant coupled intraseasonal variation between a rossby wave train across the eurasian continent and the summer monsoon convection in northwestern india and pakistan hereafter referred to as nism the wave train associated with an active phase of nism rainfall displays two high pressure anomalies one located over central asia and the other over northeastern asia they are accompanied by increased rainfall over the western siberia plain and northern china and decreased rainfall over the eastern mediterranean sea and southern japan the circulation of the wave train shows a barotropic structure everywhere except the anomalous central asian high located to the northwest of india where a heat induced baroclinic circulation structure dominates the time lagged svd analysis shows that the midlatitude wave train originates from the northeastern atlantic and traverses europe to central asia the wave train enhances the upper level high pressure and reinforces the convection over the nism region meanwhile it propagates farther toward east asia along the waveguide provided by the westerly jet after an outbreak of nism convection the anomalous central asian high retreats westward composite analysis suggests a coupling between the central asian high and the convective fluctuation in the nism the significance of the midlatitude ism interaction is also revealed by the close resemblance between the individual empirical orthogonal functions and the coupled svd modes of the midlatitude circulation and the ism it is hypothesized that the eastward and southward propagation of the wave train originating from the northeastern atlantic contributes to the intraseasonal variability in the nism by changing the intensity of the monsoonal easterly vertical shear and its associated moist dynamic instability on the other hand the rainfall variations over the nism reinforce the variations of the central asian high through the monsoon desert mechanism thus reenergizing the downstream propagation of the wave train the coupling between the eurasian wave train and nism may be instrumental for understanding their interaction and can provide a way to predict the intraseasonal variations of the indian summer monsoon and east asian summer monsoon

the role of tropical waves in tropical cyclogenesis abstract this paper analyzes relationships between tropical wave activity and tropical cyclogenesis in all of the earth s major tropical cyclone basins twenty nine years of outgoing longwave radiation data and global reanalysis winds are filtered and analyzed to determine statistical relationships between wave activity in each basin and the corresponding cyclogenesis composite analyses relative to the storm genesis locations show the structures of the waves and their preferred phase relationships with genesis five wave types are examined in this study including mixed rossby gravity waves tropical depression type or easterly waves equatorial rossby waves kelvin waves and the madden julian oscillation the latter is not one of the classical tropical wave types but is a wavelike phenomenon known to have a strong impact on tropical cyclogenesis tropical cyclone formation is strongly related to enhanced activity in all of the wave filter bands except for the kelvin band in each basin the structure o

mini rf and lroc observations of mare crater layering relationships abstract the lunar maria cover approximately 17 of the moon s surface discerning discrete subsurface layers in the mare provides some constraints on thickness and volume estimates of mare volcanism multiple types of data and measurement techniques allow probing the subsurface and provide insights into these layers including detailed examination of impact craters mare pits and sinuous rilles and radar sounders unfortunately radar sounding includes many uncertainties about the material properties of the lunar surface that may influence estimates of layer depth and thickness because they distribute material from depth onto the surface detailed examination of impact ejecta blankets provides a reliable way to examine deeper material using orbital instruments such as cameras spectrometers or imaging radars here we utilize miniature radio frequency mini rf data to investigate the scattering characteristics of ejecta blankets of young lunar craters we use circular polarization ratio cpr information from twenty two young fresh lunar craters to examine how the scattering behavior changes as a function of radius from the crater rim observations across a range of crater size and relative ages exhibit significant diversity within mare regions five of the examined craters exhibit profiles with no shelf of constant cpr near the crater rim comparing these cpr profiles with lroc imagery shows that the magnitude of the cpr may be an indication of crater degradation state this may manifest differently at radar compared to optical wavelengths comparisons of radar and optical data also suggest relationships between subsurface stratigraphy and structure in the mare and the block size of the material found within the ejecta blanket of the examined craters twelve have shelves of approximately constant cpr as well as discrete layers outcropping in the subsurface and nine fall along a trend line when comparing shelf width with thickness of subsurface layers these observations suggest that surface cpr measurements may be used to identify near surface layering here we use ejected material to probe the subsurface allowing observations of near surface stratigraphy that may be otherwise hidden by layers higher from remote observations