idealized simulations of the effect of taiwan and philippines topographies on tropical cyclone tracks the effects of topography on tropical cyclone tc tracks are investigated using the weather research and forecasting model running on a beta plane with actual topography two sets of experiments are performed one focusing on taiwan topography and the other on the philippines in each set different parts of the terrain are set to be either present or absent and the tcs are inserted at a location southeast of the mountain so that landfall occurs at the central part of the mountain in the no terrain control cases relative to the control case a pair of terrain induced gyres is found in all with terrain experiments this pair of gyres rotates cyclonically around the tc and the gyre associated flow near the tc centre causes a northward deflection of the tc track prior to landfall an examination of the potential vorticity tendencies pvts suggests that in addition to the pvt produced by this flow the pvt from diabatic heating cannot be ignored in explaining the tc track during landfall the asymmetric diabatic heating is significant which tends to retard the fast displacement of the tc caused by horizontal advection this diabatic heating distribution results from three different mechanisms an incursion of dry air from the mountain low level convergence induced by the terrain altered wind field in the southwestern part of the tc and the development of convergence cyclonically inward from the eastern side of the mountain to the tc core however the first two mechanisms are apparently missing in the philippine experiments because of the lower height and the moister air over the mountains on luzon island

idealized simulations of the effect of local and remote topographies on tropical cyclone tracks this is the second part of a study on the effect of topography on tropical cyclone tc tracks in part i idealized simulations using the weather research and forecast wrf model were conducted with artificial tcs inserted at a location such that they make landfall on the central part of taiwan and the luzon in this second part the effects of local and remote topographies are studied by examining the tracks of several tcs approaching taiwan at different latitudes tropical cyclones approaching to the south of taiwan remote effect slow down and are first deflected southwestward and then northward moreover a sharp northward deflection occurs for a tc passing further south of taiwan but the deflection is small for a tc passing further north of taiwan in the presence of china s terrain an additional larger but weaker anticyclonic gyre is induced so that the tc is affected even when it is further away from the land the flow associated with this gyre reduces the northward deflection caused by the taiwan terrain but enhances the southwestward shift of the tc however no cyclonic gyre is found over inland china if the tc is far away from china s coast probably because of the irregular elevated topography for tcs making landfall on south china a westward shift is found just prior to landfall which is more significant if the height of china s terrain is doubled this westward shift can be explained by the horizontal advection vertical advection and diabatic heating terms in the potential vorticity tendency equation

an observational study of a coastal barrier jet induced by a landfalling typhoon abstractin this study the structure and evolution of a coastal barrier jet cbj along the east coast of taiwan is documented using operational doppler radars the formation of the cbj was control

tertiary sedimentary history and structure of the valencia trough western mediterranean abstract we present here main results of the common depth point cdp data acquired during the valsis 2 cruise in 1988 in the valencia trough the profiles are tied in with industrial well data and this correlation allows the sedimentary and structural history of the region to be deduced the valsis cruise seismic profiles have been supplemented by a very dense grid of industrial seismic lines and these data permit us to establish an accurate depth to basement map the formation of the initial grabens coeval with those of the gulf of lions is related to the early miocene opening of the northwestern mediterranean basin and the barcelona graben is filled by the same sedimentary layers including evaporites as that of the provencal region nevertheless the valencia catalan grabens have been reactivated by young extensional tectonics which could be a consequence of the convergence of africa relative to europe the valencia trough is segmented by transfer faults which trend nw se these faults which have a more accentuated structural expression than the valencia and catalonia grabens may act as transform faults separating the individual balearic islands the transfer faults are in strike with volcanic ridges which have been sampled during the dsdp leg 13 the dense seismic grid allows us to delineate several widespread volcanic features in the valencia trough which have been active from the early miocene to the pleistocene however we note that the volcanic features are mainly miocene in age whereas the recent volcanism is restricted to a narrow zone columbretes islands the compressional tectonics which deformed the balearic islands does not appear to extend far towards the north we delineate the compressional front north of ibiza but we failed to determine any thrust or fold north of mallorca whereas an extensional tectonics is evident

late pleistocene and holocene sedimentary facies on the ebro continental shelf abstract late pleistocene holocene history of the ebro continental shelf of northeastern spain is recorded in two main sedimentary units 1 a lower transgressive unit that covers the shelf and is exposed on the outer shelf south of 40 40 n and 2 an upper progradational prodeltaic unit that borders the ebro delta and extends southward along the inner shelf the lower transgressive unit includes a large linear shoal found at a water depth of 90 m and hardground mounds at water depths of 70 80 m some patches of earlier pleistocene prodelta mud remain also exposed or covered by a thin veneer of transgressive sand on the northern outer shelf this relict sand sheet is 2 3 m thick and contains 9000 12 500 yr old oyster and other shells at water depths of 78 88 m the upper prodelta unit covers most of the inner shelf from water depths of 20 80 m and extends from the present ebro river delta to an area to the southwest where the unit progressively thins and narrows interpretation of high resolution seismic reflection data shows the following facies occurring progressively offshore 1 a thick stratified facies with thin progradational foresets beds 2 a faintly laminated facies with sparse reflectors of low continuity and 3 a thin transparent bottomset facies underlain by a prominent flat lying reflector deposition in the northern half of the prodelta began as soon as the shoreline transgressed over the mid shelf but progradation of the southern half did not begin until about 1000 3000 yrs after the transgression a classic deltaic progradational sequence is shown in the ebro prodelta mud by 1 gradation of seismic facies away from the delta 2 coarsening upward sequences near the delta and fining upward sequences in the distal mud belt deposits and 3 thin storm sand layers and shell lags in the nearshore stratified facies the boundaries of the prodeltaic unit are controlled by increased current speeds on the outer shelf where the shelf narrows and by development of the shoreface sand body resulting from shoaling waves on the inner shelf

influence of mesoscale topography on tropical cyclone tracks further examination of the channeling effect abstractobservations have documented typhoons experiencing pronounced track deflection before making landfall in taiwan in this study idealized full physics model experiments are conducted to assess the orographic influence on tropical cyclone tc track an intense and westward moving tc is simulated to approach the bell shaped terrain imitating the taiwan topography sensitivity numerical experiments are carried out to evaluate the topographic effect under different flow regimes and parameters such as tc intensity terrain height and incident angle of the tc movement toward the topography all the presented simulated storms experience southward track deflection prior to landfall different from the mechanism related to the channeling effect induced low level northerly jet as suggested in previous studies this study indicates the leading role of the northerly asymmetric flow in the midtroposphere in causing the southward deflection of the simulated tc tracks the midtropospheric northerly asymmetric

orographic influence on basic flow and cyclone circulation and their impacts on track deflection of an idealized tropical cyclone abstracta series of idealized numerical experiments and vorticity budget analyses is performed to examine several mechanisms proposed in previous studies to help understand the orographic influence on track deflection over a mesoscale mountain range when an idealized tropical cyclone tc is embedded in a uniform easterly flow and passes over a mountain with a moderate froude number it is deflected to the south upstream moves over the mountain anticyclonically and then resumes its westward movement the vorticity budget analysis indicates that the tc movement can be predicted by the maximum vorticity tendency vt the orographic effects on the above tc track deflection are explained by the following 1 upstream of the mountain the easterly basic flow is decelerated as a result of orographic blocking that causes the flow to become subgeostrophic which advects the tc to the southwest analogous to the advection of a point vortex embedded in a flow the vt is primarily dominated by the horizontal vo

sensitivity of typhoon track to asymmetric latent heating rainfall induced by taiwan topography a numerical study of typhoon fanapi 2010 1 typhoon fanapi 2010 traveled westward across the central mountain range of taiwan on 19 september and its rainfall shifted from a symmetric to an asymmetric pattern with convection mostly to the south and southeast meanwhile the storm slowed down from 22 to 14 km h 1 for 12 h upon leaving taiwan and led to heavy rainfall 800 mm and serious flooding over the low lying southwestern plains through simulation and sensitivity tests using the cloud resolving storm simulator at 3 km grid size this study shows that the sudden and temporary speed reduction was caused by the asymmetric latent heating lh not the environmental flow specifically over a 9 h period the model storm moved westward at 16 km h 1 in the control run but increasingly faster and more toward the northwest when the moisture and thus the lh effect and its asymmetry is gradually reduced steering flow analysis and estimation using model results suggest an eastward motion vector of about 8 km h 1 consistent with the observation is produced by the asymmetric lh effect when the effects from the vertical wind shear and beta drift are both taken into account this result is further supported by the diagnosis on storm motion based on potential vorticity tendency although important such feedback to typhoon track from rainfall asymmetry that is induced by the blocking effect of topography have not been reported or studied

characteristics of size change of tropical cyclones traversing the philippines abstractthis study investigates the size changes of tropical cyclones tcs traversing the philippines based on a 37 yr statistical analysis tc size is defined by the radius of 30 kt 15 4 m s 1

on typhoon track deflections near the east coast of taiwan abstracttyphoons with deflection tracks dts within a 200 km distance of the mountainous island of taiwan are examined we analyze 84 landfalling typhoons that compose 49 dt cases turning to the left hand side including 18 with very large deflection angles da 20 and another 7 having looped tracks lts most of the large da and lt cases are northern landfall type reaching taiwan s east coast poleward of 24 n and originally possessing relatively slow translation speeds 4 m s 1 their average translation speeds however increase by 50 in the 3 h prior to landfall the wrf model is used to simulate dt cases and potential vorticity pv tendency diagnosis is used to interpret the contributions of the horizontal advection ha vertical advection va and diabatic heating dh terms the northern landfall tropical cyclones tcs possess significant cross mountain flow to the south of the storm near the coast resulting in vorticity stretching the va effect and subsidence warming the subsi

characterisation of the recent big 95 debris flow deposit on the ebro margin western mediterranean sea after a variety of seismic reflection data swath bathymetry and backscatter data side scan sonographs high resolution hr and very high resolution vhr reflection seismic profiles and sediment cores reveal the complexity of the seafloor and subseafloor features resulting from a large debris flow event that affected the ebro continental slope and base of slope at the beginning of the holocene the big 95 debris flow as it has been named disturbed more than 2200 km2 including a 26 km3 deposit of remobilised sediment covering 2000 km2 swath bathymetry and backscatter imagery allow to distinguish four main areas within the debris flow the source area the proximal depositional area the intermediate blocky depositional area and the distal depositional area in the source area a sinuous headwall scar 20 km long and up to 200 m high and several other secondary scars have been identified sediment released from the source area flowed southeastwards to the proximal depositional area which is the main depocentre of the big 95 debris flow deposit with accumulations over 90 m thick large slabs of sediment detached from this area and from the headwall scar and moved southeastwards embedded in a more mobile matrix thus forming the intermediate blocky depositional area only the looser matrix reached the distal depositional area finally freezing in and partially burying the valencia channel a mid ocean type channel digitisation of vhr seismic reflection profiles where the debris flow deposit is shown as a body of mainly transparent seismic facies has allowed the construction of isobath and isopach maps showing the thickness distribution of the deposit and its interplay with preexisting canyons and channels dating of two sediment cores gives a minimum age of 11 000 calendar years bp for the big 95 debris flow a set of triggering mechanisms including seismicity and oversteepening of the slope due to the existence of a volcanic structure underneath the main headwall is invoked

the effect of hawai i s big island on track and structure of tropical cyclones passing to the south and west abstractthe effect of the big island of hawai i on tropical cyclone tc track and structure is investigated using the weather research and forecasting wrf model the high 4000 m mountains of the big island modulate lower tropospheric flow in such a way that it can influence tcs hundreds of kilometers away from the island when a tc approaches from the east the blocking of lower tropospheric flow leads to a slowing of the tc s movement as a tc passes close to the south side of the big island it deviates southward the tc core convection and winds can become axisymmetric because of the blocking of the stronger northeasterly flow to the north of the storm the authors hypothesize that this axisymmetrization led to the unexpected eye formation of hurricane flossie 2007 just southeast of the big island as a tc moves into the lee southwest side of the big island the flow associated with the island wake leads to a track deviated to the right the hurricane dot 1959 simulations suggest that this

the influence of island topography on typhoon track deflection abstracthigh resolution simulations for typhoon krosa 2007 and a set of idealized experiments are conducted using a full physics model to investigate the eminent deflection of typhoon track prior to its landfall over mountainous island topography the terrain height of taiwan plays the most important role in typhoon krosa s looping motion at its landfall while the surface properties details in the topographic shape of taiwan and the cloud microphysics are shown to be secondary to the track deflection a simulation with 3 km resolution and realistic model settings reproduces the observed krosa s track while that with 9 km resolution fails suggesting that high resolution to better resolve the typhoon terrain interactions is important for the prediction and simulation of typhoon track deflection prior to landfall results from idealized experiments with model configurations mimicking those of supertyphoon krosa show that vortices approaching the northern and central topography are significantly deflec

a numerical study of the track deflection of supertyphoon haitang 2005 prior to its landfall in taiwan abstract a series of numerical simulations are conducted using the advanced research version of the weather research and forecasting model with a 4 km fine mesh to examine the physical processes responsible for the significant track deflection and looping motion before the landfall of supertyphoon haitang 2005 in taiwan which poses a unique scientific and forecasting issue in the control experiment a low level northerly jet induced by the channeling effect forms in the western quadrant of the approaching storm where the inner core circulation is constrained by the presence of taiwan s terrain because of the channeling effect the strongest winds of the storm are shifted to the western portion of the eyewall the northerly advection flow averaged asymmetric winds within 100 km radius results in a sharp southward turn of the westward moving storm the time series of the advection flow shows that the advection wind vectors rotate cyclonically in time and well match the motion of the simulated vortex

on the geographic asymmetry of typhoon translation speed across the mountainous island of taiwan abstractthis paper examines the effect of topographically phase locked convection on the motion of typhoons across the island of taiwan data for 84 typhoons that reached taiwan s eastern coast from 1960 to 2010 are analyzed with motions compared to the long term average overland translation speed for 61 continuous track typhoons among all cases 77 of the slow moving tropical cyclones tcs made landfall on the northern end of taiwan s eastern coast while 60 of the fast storms had southeastern coastal landfalls this geographic asymmetry with respect to typhoon translation speeds widened after landfall as the slow movers typically decelerated during the overland period whereas the faster tcs sped up in particular the average overland duration was 16 h for the slow class compared to only 3 h for the fast moving typhoons the combination of slower translation with longer duration for the northern class of tcs led to large rainfall on the southwestern slope of the island s central mountain range we

interaction of typhoons with the taiwan orography part ii continuous and discontinuous tracks across the island abstract numerical model simulations of west moving tropical cyclones approaching and crossing the taiwan orography are shown to contain many of the observed surface features vortices tend to track continuously around the northern end of the island due to the deflection of the deep layer mean flow and the vortex circulation is modified less because the higher winds to the right of the center do not have a strong interaction with the barrier discontinuous tracks predominate for vortices approaching the central southern portions of the taiwan orography severe distortions of the inner core circulation occur and the surface pressure and surface wind centers become decoupled and may be dissipated at different rates numerical sensitivity studies demonstrate that more intense and rapidly moving vortices are more like to cross directly over the barrier and thus maintain a continuous track in one special case of a weak but fast moving vortex approaching the southern end the model simulates the existence of

interaction of typhoons with the taiwan orography part i upstream track deflections abstract a combined observational and numerical modeling approach is used to study the upstream track deflections of westward moving tropical cyclones approaching the mountainous terrain of taiwan although the standard deviations are large the mean track deflections are larger and have a different orientation for storms approaching the southern end of the island from those approaching the northern end the deflections tend to be larger for weaker and slower moving storms two distinct regions of upstream track deflections that are detected in the observations are explored in a sensitivity study with a 45 km horizontal resolution and 16 layer numerical model as the outer circulation of the tropical cyclone begins to interact with the mountain barrier the zonal decelerations and southward track deflections are explained by an enhanced blocking and deflection of the environmental flow advecting the cyclone the larger effect for southern approaching storms compared to northern storms is because the stron

tropical cyclone motion in response to land surface friction abstract numerical experiments are performed with the fifth generation pennsylvania state university national center for atmospheric research mesoscale model mm5 to study the effects of surface moisture flux and friction over land on the movement of tropical cyclones tcs on an f plane the tcs are initially placed 150 km due east of a north south oriented coastline in an atmosphere at rest it is found that a tc could drift toward land when the roughness length is 0 5 m over land with an average drift speed of 1 m s 1 friction but not surface moisture flux over land is apparently essential for the movement toward land the friction induced asymmetry in the large scale flow is the primary mechanism responsible for causing the tc drift the mechanism responsible for the development of the large scale asymmetric flow over the lower to midtroposphere 900 600 hpa appears to be the creation of asymmetric vorticity by the divergence term in the vorticity equation horizontal advection then rotates t

idealized simulations of the effect of taiwan topography on the tracks of tropical cyclones with different steering flow strengths this is the fourth part of a study on the effect of topography on tropical cyclone tc tracks in previous parts idealized simulations were conducted using the weather research and forecasting model to investigate the underlying mechanisms for the upstream deflection and the local and remote topography effect on tcs with different sizes none of these simulations included any background flow in this part uniform easterly steering flows of 5 and 10 m s 1 are introduced to study the track changes under such conditions lee vortices are generated downstream of the taiwan topography by the steering flow the tc terrain induced gyres found in the previous parts also develop when the tc circulation begins to interact with the topography and subsequently dominate over taiwan the cyclonic gyre merges with the cyclonic lee vortex induced by the steering flow and the anticyclonic gyre is advected cyclonically around the tc centre which later deflects the tc because the circulation at the outer radii of a tc competes with the steering flow a smaller tc under a stronger steering flow has to move closer to taiwan in order to generate such gyres this delayed generation of the gyres then leads to the delayed onset of the northward deflection for such a tc for a large tc the circulation at its southern part is weakened by the steering flow so that the track of the anticyclonic terrain induced gyre is changed which results in a larger track deflection of the tc

late quaternary sedimentation patterns of the ebro turbidite systems northwestern mediterranean two styles of deep sea deposition abstract seven sediment types are identified from the analysis of 60 piston cores in the ebro turbidite systems 1200 1800 m deep between the ebro shelf and the valencia trough in the northwestern mediterranean sea these sediments are grouped into five facies associations channel floor of erosive depositional channel levee complex levee of erosive depositional channel levee complex depositional channel levee complex interchannel and apron facies unconfined slides debris flows channeled turbidity currents and differential hemipelagic settling are the main depositional processes which develop these facies deposition in the ebro turbidite systems occurred primarily during the pleistocene when turbidity currents funneled coarsegrained sediments through canyon channel systems during the holocene most sediment was trapped in deltaic and nearshore environments and turbidite deposition was replaced by hemipelagic settling in the hemipelagic sequence thus created grain size terrigenous components and chlorite kaolinite and illite kaolinite ratios decrease upwards while planktonic and calcite quartz ratios increase two styles of growth patterns are present during periods of low sea level most common are base of slope channel levee complexes each of which is developed alongside an older complex the complexes were formed by sediment supplied from different canyons as the systems migrated from north to south with time in addition in the central sector base of slope aprons have been formed in gullied slope terrains by unconfined slides and less commonly by unconfined turbidity currents the major differences between the ebro and other base of slope systems are a the incomplete development of channel levee complexes as compared to typical deep sea fans b the coexisting growth of aprons and c multiple canyon sources low slope stability resulting in many sediment supply point sources is one of the primary factors which encourages development of base of slope aprons

track deflection of typhoon nesat 2017 as realized by multiresolution simulations of a global model abstracttyphoon nesat 2017 headed west northwestward toward taiwan but took a relatively larger northward deflection about 300 km away and then a leftward deflection after landfall at northern ta

the effect of a river delta and coastal roughness variation on a landfalling tropical cyclone 1 numerical simulations on an f plane are performed using the weather research forecasting wrf model to study how the presence of a river delta and variations in coastal roughness might affect the motion and the structure of a tropical cyclone tc near landfall in each delta experiment an idealized triangular shaped delta pointing to the west with length 150 km and a river mouth size of 100 km is inserted along the coastline the surface roughness and the moisture availability of the delta vary among the delta experiments and the surface properties are uniform in the rest of the land area in another set of experiments where there is no delta the roughness of a whole land area has different values along the north south oriented coast results suggest that the tc in the control experiment ctrl with no delta or roughness variation along the coast is weaker than all the delta cases during a certain period before landfall moisture supply from the delta appears to have an effect on sustaining the approaching tc despite the relatively small scale of the delta tracks of the tcs in the roughness variation experiments deviate from that of the ctrl the roughness variation along the coast apparently affects the convergence patterns higher roughness induces stronger convergence and hence increases the vertical advection term in the potential vorticity tendency distribution over the rougher area hence a tc tends to move toward a region with higher roughness

coriolis effects in mesoscale flows with sharp changes in surface conditions a general linearized shallow layer perturbation model where the approximately neutral lower layer of thickness h0 is situated below a stable upper layer i e an inversion with temperature change t is developed for steady mesoscale atmospheric flows over low lying topography whose height is less than h0 with the coriolis parameter f sharp changes in surface conditions surface roughness terrain elevation heat flux are modelled as a distributed body force through the lower layer the froude number of this layer is small typical cases of mesoscale discontinuities are examined the results are compared with those of a continuously stratified model and observations and with numerical mesoscale model results for a meteorological case study over the dover straits region of the english channel the main results are i if the wind direction is parallel to the edge line separating the change in surface roughness there are marked increases and decreases in these coastal winds whose maxima can occur over the sea within a distance of order h0 1 km of a coast the strength of these wind jets which do not occur in the absence of coriolis force decrease away from the edge line gradually over transverse length scales of the order of the rossby deformation radius changes to surface roughness lead to an increase in the wind speed perturbation in the downwind direction until limited by non linear effects when the wind is at an angle to a roughness change or coast the maxima occur at the coastline ii where there are sharp changes in the orientation of contours of constant roughness length e g at capes or bays on the coastline or wakes of high drag areas detached jets are formed in the downwind direction iii changes in surface elevation at a coast produce effects different from those of roughness a positive wind jet forms parallel to the coast in the direction of the wind when the coast is on the right looking downwind and a negative jet when the coast is on the left these jets do not increase in strength along the flow and do not persist downwind iv coriolis effects also determine how the inversion height varies near coastlines and surface roughness changes for example increasing decreasing inland over a distance lr when stable airflow approaches from the sea and the coast is on the right left of an observer looking downwind opposite in the southern hemisphere this mechanism is consistent with observed increasing decreasing cloudiness inland from a coast v other effects occur where the surface elevation changes gradually over a distance of order lr e g a wide shallow valley frictional effects are comparable with buoyancy and coriolis forces and flows perpendicular to the elevation change are deflected to the left in the northern hemisphere as observed in the rhine valley vi the shallow layer model simulates the major features of the low level flow field computed using the numerical mesoscale model with a horizontal resolution of 2 km i e of order h0 broad features were captured using a coarser resolution of 12 km vii the analysis provides a method of estimating errors associated with finite grid size in numerical mesoscale models copyright 2004 royal meteorological society

orographic influence on a drifting cyclone abstract in this study a primitive equation numerical model is adopted to investigate the orographic influence on a drifting cyclone over an idealized topography similar to that of taiwan for a cyclone propagating from the east and impinging on the central portion of the mountain a northerly surface jet tends to form upstream of the mountain between the primary cyclone and the mountain due to blocking and channeling effects two pressure ridges and one trough are also produced when the cyclone approaches the mountain the low level vorticity and low pressure centers decelerate and turn southward upstream of the mountain due to orographic blocking at the same time the upstream low level vorticity is blocked by the mountain the abrupt increase of surface vorticity and the contraction of cyclone scale on the lee side are explained by the generation of new potential vorticity pv due to wave breaking associated with the severe downslope wind and hydraulic jump the generation of this new pv is evidenc

the impact of idealized terrain on upstream tropical cyclone track abstracttropical cyclones tcs encountering the terrain of taiwan usually experience prominent track deflection resulting in uncertainty in tc track forecasts the underlying mechanisms of tc def

a modeling study of typhoon nari 2001 at landfall part i topographic effects abstract although there have been many observational and modeling studies of tropical cyclones understanding of their intensity and structural changes after landfall is rather limited in this study several 84 h cloud resolving simulations of typhoon nari 2001 a typhoon that produced torrential rainfall of more than 1400 mm over taiwan are carried out using a quadruply nested grid mesoscale model whose finest grid size was 2 km it is shown that the model reproduces reasonably well nari s kinematic and precipitation features as well as structural changes as verified against radar and rain gauge observations these include the storm track the contraction and sizes of the eye and eyewall the spiral rainbands the rapid pressure rise 1 67 hpa h 1 during landfall and the nearly constant intensity after landfall in addition the model captures the horizontal rainfall distribution and some local rainfall maxima associated with taiwan s orography a series of sensitivity experiments are performed i

coriolis effects on orographic and mesoscale flows a perturbation theory is developed for the effects of rotation on stably stratified flow over mountains at low froude number f u0 nh where n is the buoyancy frequency u0 is the wind speed and h is the mountain height the rossby number r0 u0 f d where f is the coriolis parameter and d the along wind length of the mountain is assumed to be a large number the mountain width d is assumed to be larger than d typically r0 is found to lie in the range 3 10 the results are compared with the recent numerical simulations it is found that as the flow impacts on the mountain in the northern hemisphere it turns to the left with your back to the wind also wave activity over the top of the mountain is greatest on the left side but the pressure drop is greatest on the right in the northern hemisphere over the rossby deformation distance lr of the order of hn f e g 150 km for the pyrenees a new wake structure develops that can extend downwind over 1000 km or a spin down distance there is a momentum defect within the wake but the wind speed increases either side of the wake coriolis forces induce a deflection upwards of the isopycnals and hence more precipitation on the left and downwards on the right this is consistent with some of the differences in mesoscale weather and climate phenomena that are observed on the different flanks of elongated mountains and between the different side of wide valleys and also in the wakes downwind of mesoscale convection cells the large perturbation pressure change predicted by the theory is of the order of pu20 f where p is the density which is consistent with the magnitude of the terms introduced into the recent european centre for medium range weather forecasts orographic parametrizations but it should be noted that these large rossby froude orographic effects on drag and wave flux are asymmetric with respect to the mountain s centre line the theory shows how lift forces on the mountain are caused and how these are related to circulation in horizontal planes around the mountains

an investigation on how inner core structures obtained through radar data assimilation affect track forecasting of typhoon jangmi 2008 near taiwan island the impacts of radar data assimilation da on the westward track deflection of typhoon jangmi 2008 near taiwan island and the deflection mechanism are investigated initial conditions from two data assimilation experiments with significant track forecast differences are analyzed and compared the environmental axisymmetric wavenumber 1 to 3 asymmetric fields of the typhoon are decomposed using vortex separation and fourier decomposition methods the components are selectively recomposed into new initial conditions that include different vortex scale components to examine the impact of individual components on the track prediction the wavenumber 1 asymmetric structure is found to play a dominant role in the westward deflection of typhoon jangmi and the accurate analysis of this component with radar da helps to improve the track forecast the wavenumber 1 asymmetric circulation is manifested as a pair of cyclonic and anticyclonic gyres with well defined ventilation flows through the inner core region which provides additional steering of the typhoon vortex the layer mean environmental steering flow and ventilation flow associated with the wavenumber 1 gyres are further calculated to quantitatively evaluate the impact of ventilation flow the ventilation flow is shown to be responsible for most of the westward motion component suggesting again its role in causing the westward track deflection of typhoon jangmi the results also suggest the importance of analyzing vortex scale asymmetric structures for accurate tropical cyclone track forecasting especially when there is a significant track deflection

idealized simulations of the effect of taiwan topography on the tracks of tropical cyclones with different sizes this is the third part of a study of the effect of topography on tropical cyclone tc tracks in previous parts idealized simulations were conducted using the weather research and forecasting model to study the underlying mechanisms for the upstream northward deflection of a tc and the effects of local and remote topography the initial tc size was the same in all these simulations in this third part the track deflections of tcs with different sizes are investigated as in the two earlier parts the simulations are made on a beta plane with no background flow for a tc approaching taiwan there is an apparent optimal tc size with the largest northward deflection however an appreciable track deflection is only found for smaller tcs approaching taiwan directly in addition as might be expected the onset location of the northward deflection is closer to taiwan for smaller tcs moreover the contribution from diabatic heating is opposite to that from horizontal advection ha in the potential vorticity tendency pvt calculation due to the vertical wind shear induced by the terrain induced gyres although ha is still the dominant term in the pvt equation a southward deflection on the eastern side of taiwan is found in some smaller tc cases a looping track occurs for a medium size tc approaching central taiwan and a v shape track is found for a small size tc approaching northern taiwan among the cases some similarities can be found first the gyre flow becomes weak so that the tc is slowed down second an individual cyclonic gyre is found on the southeastern side of taiwan so that the tc is deflected westward and then southward third another newly generated gyre pair pushes the tc northward after the southward deflection

control parameters for the influence of a mesoscale mountain range on cyclone track continuity and deflection abstract in this study prospective control parameters are identified for diagnosing the continuity and deflection of cyclone tracks across a mesoscale mountain range based on idealized simulations of a westward moving cyclone it was found that the cyclone track becomes a discontinuous continuous track and the cyclone experiences more less deflection with a combination of small large values of vmax nh u nh r ly u flx and vmax fr and large small value of h lx the symbols are defined as follows vmax the maximum tangential wind n the brunt vaisala frequency h the mountain height u the basic wind speed r the radius of vmax f the coriolis parameter and lx and ly the horizontal scales of the mountain in x and y directions respectively a conceptual model is proposed to explain track deflection and continuity for a westward moving cyclone encountering idealized topography representative of the central mountain range of taiwan with weak orographic blocking a cyclone crosses over the mount

tsunamigenic sea floor deformations in addition to the primary damage they do earthquakes can cause tsunamis massive ocean swells that can inundate coastal regions in their perspective synolakis et al describe results presented at a workshop on the interface between seismology and tsunami hydrodynamics held in santa monica in may 1997 the authors discuss the highlights of the meeting and summarize future directions for research

low sea level emplacement of a very large late pleistocene megaturbidite in the western mediterranean sea large volume turbidites termed megaturbidites or megabeds result from catastrophic slope failures and the associated downslope transport of enormous quantities of sediment from continental margins to the deep sea such large sediment failures can generate tsunamis and in terrains underlain by gas hydrates clathrates may be associated with the release of substantial amounts of the greenhouse gas methane it has been proposed that the megaturbidite events may be triggered by seismic activity or may result from gas hydrate release itself caused by a lowering of hydrostatic pressure on clathrates as a result of low sea level previous conclusions on the significance of sea level change however have been conditional because of the lack of absolute times of turbidite emplacement here we use accelerator mass spectrometry radiocarbon dating in five widely spaced cores to constrain the date of emplacement of a large volume 500 km3 bed in the balearic basin of the western mediterranean this turbidite is exceptional in its magnitude and represents the main sedimentation event in the balearic basin over the past 100 kyr our data provide an estimate of 22 000 calendar years before present for emplacement of the megabed a time when sea level stood at its lowest level during the last glacial maximum the coincidence of these dates is consistent with emplacement due to clathrate destabilization caused by low sea level although other triggering mechanisms such as seismic shock cannot be ruled out

new moscovian palaeomagnetic pole from the edjeleh fold saharan craton algeria summary a palaeomagnetic study was carried out in the moscovian y305 ma formation in the edjeleh anticline the only area where important dips can be observed in the upper palaeozoic series of the illizi basin algeria this study shows the existence of three magnetization components two of them are interpreted as cenozoic and permian remagnetizations their poles are 88 8un 164 0ue k 262 a95 3 3u and 43 4us 61 7ue k 93 a95 5 9u respectively the third component is determined by both welldefined chrms and remagnetization circles analysis its associated fold test is positive and significant because the folding started before or during the autunian this third component was acquired very early and is very probably the primary magnetization its corresponding palaeomagnetic pole 28 3us 58 9ue k 157 a95 4 2u is close to the poles from the saharan platform obtained from neighbouring periods the positive fold test of this study thus validates these previous upper palaeozoic poles this new result is in agreement with the geodynamical model matte 1986 henry et al 1992 which proposed the occurrence of a large clockwise rotation of africa during the carboniferous such a motion agrees with the permian pangaea a2 reconstruction