rear flank outflow dynamics and thermodynamics in the 10 june 2010 last chance colorado supercell abstracton 10 june 2010 the second verification of the origins of tornadoes experiment vortex2 armada observed a supercell thunderstorm near last chance colorado tempest unmanned aircraft system uas data collected in the rear flank outflow revealed what appeared to be an elevated outflow head turbulent wake and a cold rear flank internal surge rfis surface thermodynamic and kinematic data collected by the sticknet and mobile mesonet indicated that the outflow wake may have extended to or very near the surface perhaps modifying or outright replacing the leading edge of the outflow at times single doppler data collected by the noaa x pol mobile polarimetric doppler radar noxp were supportive of the possibility of a downdraft in the outflow wake associated with low level divergence a conceptual model of the hypothesized rear flank outflow structure in the nontornadic phase of the last chance supercell is presented the observed turbulent wake is consistent with mixing associated with the rel

vorticity evolution leading to tornadogenesis and tornadogenesis failure in simulated supercells abstracta three dimensional idealized cloud model was used to study the storm scale differences between simulated supercells that produce tornado like vortices and those that do not each simulation was initialized with a different rapid update cycle version 2 ruc 2 sounding that was associated with tornadic and nontornadic supercells in nature the focus is an analysis of vorticity along backward integrated trajectories leading up to tornadogenesis 19 simulations and tornadogenesis failure 14 simulations in so doing the differences between the nontornadic and tornadic cases can be explored in relation to their associated environmental sounding backward integrated trajectories seeded in the near surface circulation indicate that the largest differences in vertical vorticity production between the tornadic and nontornadic simulations occur in parcels that descend to the surface from aloft i e descending thus the results from this study support the hypothesis that descending air in the rear

the pretornadic phase of the goshen county wyoming supercell of 5 june 2009 intercepted by vortex2 part ii intensification of low level rotation abstractthe dynamical processes responsible for the intensification of low level rotation prior to tornadogenesis are investigated in the goshen county wyoming supercell of 5 june 2009 intercepted by the second verification of the origins of rotation in tornadoes experiment vortex2 the circulation of material circuits that converge upon the low level mesocyclone is principally acquired along the southern periphery of the forward flank precipitation region which is a corridor characterized by a horizontal buoyancy gradient thus much of the circulation appears to have been baroclinically generated the descending reflectivity core drc documented in part i of this paper has an important modulating influence on the circulation of the material circuits a circuit that converges upon the low level mesocyclone center prior to the drc s arrival at low levels approximately the arrival of the 55 dbz reflectivity isosurface in this case loses some of its previously acquired circulation during the final f

the dynamical structure of squall line type thunderstorms abstract the structure of squall line type thunderstorms is investigated with special emphasis on the upshear sloping updraft which is often observed in these storms to aid in the investigation a new version of the convective richardson number is formed which adds the negative buoyancy due to liquid water loading to the thermal buoyancy of the lifted parcel in the calculation of the buoyant energy this modified convective richardson number is easily calculated using a pre storm sounding and has predictive value for thunderstorm type while it is widely accepted that the updraft s upshear slope is caused by the ascending parcels partially conserving their horizontal momentum toward the rear of the storm this paper presents a new theory for the production of this slope in this theory the vorticity production due to the liquid water distribution leads to an upshear slope of the updraft downdraft interface a stable slope is reached when the loading mechanism is balanced by the forces exerted by the env

land subsidence due to groundwater withdrawal potential damage of subsidence and sea level rise in southern new jersey usa land subsidence due to groundwater withdrawal combined with a global sea level rise creates a serious environmental problem in the coastal region groundwater withdrawal results in fluid pressure change in the layers the pressure change in the layers induces both elastic and inelastic land compaction the elastic compaction can be recovered if the water level rises again and inelastic compaction becomes permanent groundwater response to barometric pressure change is used to estimate the elastic compaction in this study the storativity specific storage and other layer and hydrological information are used to estimate the inelastic compaction of the layers due to fluid withdrawal the discussed methods are applied to estimate and predict the subsidence potentials resulting from overdrafting of the groundwater in the southern new jersey the estimated subsidence is about 2 3 cm near the location of monitoring wells in atlantic camden cumberland and cape may counties over the past 20 years if the current trend of water level drop continues the average subsidence in southern new jersey in the vicinity of some monitoring wells will be about 3 cm in the next 20 years the rise of global sea level is about 2 mm year on average because of the very gentle slope in southern nj the combination of subsidence and sea level rise will translate into a potentially substantial amount of land loss in the coastal region in each 20 year period this combination will also accelerate the coastal flooding frequency and the erosion rate of the new jersey coastal plain and pose a serious threat to the coastal economy

tornado like vortexgenesis in a simplified numerical model abstract a novel approach to the modeling of tornado like vortexgenesis has been developed and is used to articulate the sequence of events that leads to tornadogenesis the pseudostorm is an idealized thunderstorm representation and emulates the storm relative flow into an updraft of the horizontal streamwise vorticity that is baroclinically generated in cold air outflow by not explicitly simulating the morphology of a tornadic thunderstorm but instead concentrating on the development of low level rotation and tornado scale vortices the authors are able to transcend many of the experimental limitations encountered by cloud modelers intense near ground cyclonic vortices which are classified herein as tornado like evolve solely from horizontal streamwise vorticity due to buoyancy gradients and friction if present at the lower boundary regardless of the lower boundary condition none of the vortices exceed the thermodynamic speed limit based on the vertically integrated buoyancy or convect

subsurface characterization and prediction of land subsidence for hcm city vietnam abstract the demands of domestic and industrial water supply in ho chi minh city hcm city have surged rapidly since 1990s with the opening up of vietnam s economy in the same time groundwater extraction has continuously increased and is suspected to have caused land subsidence which in turn would affect the growing infrastructure of the city by now only a few monitoring stations have been installed and both pore pressure and settlement observation data are not yet available as an alternative we proposed an approach to estimate land subsidence based on the available data of groundwater drawdown in the pumped aquifer and geotechnical properties of the adjacent clay layers in this study a large amount of borehole data was collected to construct a computer based subsoil database as a result a complete characterization of a six aquifer system up to 360 m deep and that of the shallower subsoil profile up to 140 m deep was done based on data from more than 3000 boreholes examples of land subsidence prediction were done for three cases i e i at a borehole location that has sign of well protrusion ii along the new mrt line no 1 and iii over a profile crossing the city from nw to se the first two cases were to show the procedure of land subsidence prediction while the third case was to compare the fem analysis results with those estimated by satellite image analysis the results of this study showed that the subsoil in hcm city with thick soft clay layers is vulnerable to the groundwater extraction it is expected that the maps of drawdown and the subsoil database developed by this study in combination with a 1d fem consolidation program will provide a useful tool to estimate land subsidence of hcm city while the pore pressure and settlement data are not yet available

simulated supercells in nontornadic and tornadic vortex2 environments abstractthe composite near storm environments of nontornadic and tornadic supercells sampled during the second verification of the origins of rotation in tornadoes experiment vortex2 both appear to be generally favorable for supercells and tornadoes it has not been clear whether small differences between the two environments e g more streamwise horizontal vorticity in the lowest few hundred meters above the ground in the tornadic composite are actually determinative of storms tornadic potential from the vortex2 composite environments simulations of a nontornadic and a tornadic supercell are used to investigate storm scale differences that ultimately favor tornadogenesis or tornadogenesis failure both environments produce strong supercells with robust midlevel mesocyclones and hook echoes though the tornadic supercell has a more intense low level updraft and develops a tornado like vortex exceeding the ef3 wind speed threshold in contrast the nontornadic supercell only produces shallow vortic

vortex lines within low level mesocyclones obtained from pseudo dual doppler radar observations abstract vortex lines passing through the low level mesocyclone regions of six supercell thunderstorms three nontornadic three tornadic are computed from pseudo dual doppler airborne radar observations obtained during the verification of the origins of rotation in tornadoes experiment vortex in every case at least some of the vortex lines emanating from the low level mesocyclones form arches that is they extend vertically from the cyclonic vorticity maximum then turn horizontally usually toward the south or southwest and descend into a broad region of anticyclonic vertical vorticity this region of anticyclonic vorticity is the same one that has been observed almost invariably to accompany the cyclonic vorticity maximum associated with the low level mesocyclone the vorticity couplet straddles the hook echo of the supercell thunderstorm the arching of the vortex lines and the orientation of the vorticity vector along the vortex line arches compared to the orientation of the ambient barotrop

areal subsidence under pumping well curtain interaction in subway foundation pit dewatering conceptual model and numerical simulations subway foundation pit dewatering may contribute to the regional land subsidence in a built up area when aquifers are too thick to be cut off by a curtain the land subsidence induced by subway foundation pit dewatering was divided into local subsidence and areal subsidence the former was managed by construction organizations while the latter was managed by a land resource urban management and hazard prevention department the areal subsidence could not be recovered after dewatering because of its vast influence area and contribution to regional land subsidence the boundary between local subsidence and areal subsidence was defined as the location of three times the foundation pit depth to the foundation pit boundary the subsidence within the boundary belonged to local subsidence whereas the subsidence outside the boundary belonged to areal subsidence with shanghai as background the conceptual and mathematical models that considered hydrogeological conditions curtain depth and pumping well screens were established and numerical simulations were performed when the pumping well screens were enveloped by a diaphragm wall the best vertical distance of about 1 0 4 0 m was obtained between the screen bottoms and curtain bottom the decreasing rate of areal subsidence was the highest under the interaction of diaphragm wall and pumping well screens further increasing the penetration depth of the diaphragm wall and shortening the length of the pumping well screen were both less efficient

a numerical simulation of cyclic mesocyclogenesis abstract a three dimensional nonhydrostatic numerical model the advanced regional prediction system is used to study the process of cyclic mesocyclogenesis in a classic supercell thunderstorm during the 4 h simulation the storm s mesocyclone undergoes two distinct occlusions with the beginning of a third indicated at the end of the simulation the occlusion process exhibits a period of approximately 60 min and is qualitatively similar in each case initial midlevel 3 7 km mesocyclogenesis proceeds according to the classic picture that is via tilting of streamwise environmental vorticity the development of an evaporatively driven rear flank downdraft rfd signals the beginning of the occlusion process the developing rfd wraps cyclonically around the mesocyclone causing the gust front to surge outward simultaneously the occluding mesocyclone rapidly intensifies near the surface trajectory analyses demonstrate that this intensification follows from the tilting and stretching of near ground

impacts of lapse rates on low level rotation in idealized storms abstractadiabatic lapse rates appear to be a common feature in the lower troposphere on tornado days this article reviews physical reasons why lapse rates may influence surface vortex intensification and reports on numerical simulations designed to study the key processes in the idealized numerical model an initial mesocyclone like vortex and nonvarying convection like heat source are used in different environmental stability profiles the scales of interest in these simulations typify those of a parent supercell and the developing circulations constitute direct responses to the imposed heating downward parcel displacements are needed for surface vortex development in environments with no preexisting surface vorticity in the simulations under neutral stratification there is strong heating induced subsidence anchored near the storm edge whereas under stable stratification there are instead gravity waves that propagate away to the far field in addition under weak or neutral low level stratification

linear and nonlinear propagation of supercell storms abstract a nonlinear formula for updraft motion in supercell storms is derived from petterssen s formula for the motion of systems and the vertical equation of motion and tested on form preserving disturbances at each level continuous propagation of an updraft maximum is determined largely by the horizontal gradient of the nonhydrostatic vertical pressure gradient force nhvpgf at the updraft center the nhvpgf is deduced from the formal solution of the poisson equation for nonhydrostatic pressure in anelastic flow subject to homogeneous neumann boundary conditions at the ground and top boundary recourse also is made to published fields of partitioned vertical pressure gradient force updraft motion is partitioned into parts forced by horizontal gradients of hydrostatic pressure linear interaction between the environmental shear and updraft and nonlinear dynamical effects the dynamics of supercell storms for nearly straight and highly curved hodographs are found to be different nonlinear rotation

the effects of pulsed pumping on land subsidence in the santa clara valley california abstract land subsidence caused by pulsed and constant pumping schemes was calculated and the results were compared to determine the possible advantages of pulsed pumping in reducing land subsidence pulsed pumping refers to pumping strategies involving alternation between periods of pumping and recovery in a well subsidence was calculated using a numerical model based on the santa clara valley ca the model accounts for delay in the release of water from storage in compressible interbeds as well as flow within aquifers for these tests the ratio of pumping period length to recovery period length was either 1 1 or 1 3 pulsing interval length length of one pumping period plus one recovery period ranged from 4 to 90 days pumping rates were adjusted so that pulsed pumping and constant pumping removed the same volume of water over the period under consideration pulsed pumping has the potential to concentrate subsidence around the pumping well for all simulations pulsed pumping caused greater subsidence near the test well than constant pumping under some conditions a transition point was reached beyond which pulsed pumping caused less subsidence than steady pumping the distance from the test well to the transition point decreases for a decreasing aquifer transmissivity b decreasing ratio of pumping period to recovery period and c increasing pulsing interval length the concentration of subsidence was reduced considerably when delay in release of water from storage in compressible aquitards was neglected indicating the importance of including delay effects in subsidence studies all pulsed pumping strategies caused a greater total volume of subsidence than steady pumping

gps measured land subsidence in ojiya city niigata prefecture japan abstract land subsidence caused by compression of clay layers in ojiya city japan was measured by global positioning system gps between 1 april 1996 and 31 december 1998 three baselines were selected in and around the city and height difference on a wgs 84 ellipsoid was measured by gps on each baseline the ground at the gps station in the city subsides and rebounds 7 cm every winter and spring respectively measurement accuracy was 9 5 mm standard deviation ground water level was observed at a well near the gps station regression analysis between total strain calculated as ratio of the height difference displacement to the total thickness of the clay layers and the layers effective stress change with ground water level change gave good correlation the slope of regression line 7 0 10 11 m2 n was obtained as an average apparent coefficient of volume compressibility of the layers

groundwater derived land subsidence in the north china plain land subsidence usually bears strong relationship to abstraction of underground fluid land subsidence occurs commonly in the north china plain ncp and has become a major environmental factor hindering regional sustainable development this paper focuses on issues associated with mechanism of land subsidence in the ncp the analysis shows that multi layer aquifer systems with deep confined aquifers and the thick normally consolidated or unconsolidated compressible clay layers are the key of geological and hydrogeological conditions favorable for the development of land subsidence in the ncp groundwater withdrawal results in an increase in the distribution of effective stress within the strata and the compression of the aquifers and the confining layers and then triggers land subsidence in the middle east plain of the ncp the land subsidence volume approximately represents the amount of water released from compression of deep aquifers and aquitards in that land subsidence is primarily caused by excessive groundwater withdrawal in deep aquifer system the percentage of water released from compression of aquifers and aquitards in deep groundwater abstraction is significant but distinct in cangzhou city and in the whole middle east plain this is due to the difference in local lithological structure and recharge and discharge conditions of deep groundwater system the hysteresis of land subsidence is also discussed in typical areas and the results reveal that the time for completing the primary consolidation ranges from less than one year to tens of years and that the rate of secondary compression tends to increase with the moisture content

storm relative helicity revealed from polarimetric radar measurements the dual polarization radar variables are especially sensitive to the microphysical processes of melting and size sorting of precipitation particles in deep convective storms polarimetric measurements of such processes can provide information about the airflow in and around the storm that may be used to elucidate storm behavior and evolution size sorting mechanisms include differential sedimentation vertical transport strong rotation and wind shear in particular winds that veer with increasing height typical of supercell environments cause size sorting that is manifested as an enhancement of differential reflectivity zdr along the right or inflow edge of the forward flank downdraft precipitation echo which has been called the zdr arc signature in some cases this shear profile can be augmented by the storm inflow it is argued that the magnitude of this enhancement is related to the low level storm relative environmental helicity srh in the storm inflow to test this hypothesis a simple numerical model is constructed that calculates trajectories for raindrops based on their individual sizes which allows size sorting to occur the modeling results indicate a strong positive correlation between the maximum zdr in the arc signature and the low level srh regardless of the initial drop size distribution aloft additional observational evidence in support of the conceptual model is presented potential changes in the zdr arc signature as the supercell evolves and the low level mesocyclone occludes are described

near surface intensification of tornado vortices abstract an idealized analytical model and numerical large eddy simulations are used to explore fluid dynamic mechanisms by which tornadoes may be intensified near the surface relative to conditions aloft the analytical model generalizes a simple model of barcilon and fiedler and rotunno for a steady supercritical end wall vortex to more general vortex corner flows angular momentum distributions and time dependence the model illustrates the role played by the corner flow swirl ratio in determining corner flow structure and intensification predicts an intensification of near surface swirl velocities relative to conditions aloft of i 2 for supercritical end wall vortices in agreement with earlier analytical numerical and laboratory results and suggests how larger intensification factors might be achieved in some more general corner flows examples of the latter are presented using large eddy simulations by tuning the lateral inflow boundary conditions near the surface quasi steady vortices exhi

velocity field of gps stations in the taiwan area abstract the 131 stations of the taiwan gps network were surveyed 4 6 times from 1990 to 1995 with dual frequency geodetic receivers the standard deviation of an observed baseline length with its linear trend removed is in the range of 6 10 mm for a 3 120 km long baseline the average rates of length change for all baselines of the network and those from nine continuously monitoring permanent stations are used in a least squares adjustment to estimate the velocities of the gps stations relative to paisha penghu situated at the chinese continental margin to the south of fengping in the northern coastal range the velocity vectors of stations in lanhsu lutao and the coastal range trend in the directions of 306 322 with rates of 56 82 mm yr in contrast there is a dramatic decrease in the rates to the north of fengping this may be caused by the motion along the ne sw trending thrusts which obliquely cut the northern coastal range a discontinuity of about 30 mm yr in the rates along with a remarkable change in the directions of station velocity is observed across the longitudinal valley then the moving directions gradually shift to the west for the stations in the western foothills in the kaohsiung pingtung coastal area the station velocities are even directed toward the southwest to the north of the peikang high the velocity vectors of the stations change direction from the west gradually to the north and finally to the east and southeast significant nw se extensional deformation is found in the ilan plain and northern taiwan in general the pattern of the velocity field for gps stations in the taiwan area is quite consistent with the directions of present day tectonic stress

correlation between groundwater level and altitude variations in land subsidence area of the choshuichi alluvial fan taiwan one of the prominent features observed in the groundwater overdraft area is the land subsidence that creates a permanent damage to the land surface severe land subsidence has occurred in the western taiwan due to excessive extraction of groundwater in the past decades the areas of land subsidence have been gradually expanded and caused many problems such as flooding and building damage this study examines the elevation changes on surface which is the vertical component from the global positioning system in the choshuichi alluvial fan of central taiwan and describes the land subsidence phenomena quantitatively the choshuichi alluvial fan has a high density array of wells monitoring the groundwater level variations of various aquifers automatically in an hourly basis through an assumed linear relationship the inferred results show that the global positioning system data are closely correlated to the groundwater level variations of deep aquifers the highest correlations between elevation changes and groundwater level variations have been found in the land subsidence area even if a drought period is present the responses on the surface vertical displacements from the groundwater level changes of deep aquifers can be quantitatively estimated furthermore the long term subsidence trends can be derived and be used as useful reference for land and water resources management

mapping the upper mantle three dimensional modeling of earth structure by inversion of seismic waveforms a method is presented for the inversion of waveform data for the three dimensional distribution of seismic wave velocities the method is applied to data from the global digital networks international deployment of accelerometers global digital seismograph network the selected data set consists of some 2000 seismograms corresponding to 53 events and 870 paths the moment tensors of the earthquakes are determined through an iterative procedure which minimizes the corrupting influence of lateral heterogeneity a global model is constructed for shear wave velocity expanded up to degree and order 8 in spherical harmonics and described by a cubic polynomial in depth for the upper 670 km of the earth s mantle although no a priori information is incorporated the model predictions reproduce much of what is known about the dispersion of mantle waves for example high phase velocities for shields low velocities at ridges and a strong degree 2 pattern for rayleigh waves since the method makes use of complete waveforms overtone data are also included it is shown that the model is reproducible in that substantially the same model can be constructed from each half of the total data set considered independently the model shows that shields and ridges are major features in the depth interval 25 250 km the ridges of the southern pacific and the larger shields persist to 350 km but the southeast indian rise is underlain by a high velocity anomaly at this depth as is much of the mid atlantic ridge at 450 650 km the major features are a broad region of high velocities incorporating south america much of the south atlantic and parts of west africa a broad region of low velocities in the central and eastern pacific high velocities in the western pacific and a low velocity anomaly beneath the red sea and the gulf of aden in the absence of a crustal correction degrees 2 and 3 show a high positive correlation with the geoid paradoxically this is largely destroyed when the distribution in crustal thickness is taken into account spherical harmonic degrees 4 7 show a significant negative correlation

three dimensional surface displacements and rotations from differencing pre and post earthquake lidar point clouds 1 the recent explosion in sub meter resolution airborne lidar data raises the possibility of mapping detailed changes to earth s topography we present a new method that determines three dimensional 3 d coseismic surface displacements and rotations from differencing pre and post earthquake airborne lidar point clouds using the iterative closest point icp algorithm tested on simulated earthquake displacements added to real lidar data along the san andreas fault the method reproduces the input deformation for a grid size of 50 m with horizontal and vertical accuracies of 20 cm and 4 cm values that mimic errors in the original spot height measurements the technique also measures rotations directly resolving the detailed kinematics of distributed zones of faulting where block rotations are common by capturing near fault deformation in 3 d the method offers new constraints on shallow fault slip and rupture zone deformation in turn aiding research into fault zone rheology and long term earthquake repeatability

genesis of the goshen county wyoming tornado on 5 june 2009 during vortex2 abstractthe genesis of a strong and long lived tornado observed during the second verification of the origins of rotation in tornadoes experiment vortex2 in goshen county wyoming on 5 june 2009 is studied mobile radar mobile mesonet rawinsonde and photographic data are used to produce an integrated analysis of the evolution of the wind precipitation and thermodynamic fields in the parent supercell to deduce the processes that resulted in tornadogenesis several minutes prior to tornadogenesis the rear flank downdraft intensifies and a secondary rear flank downdraft forms and cyclonically wraps around the developing tornado kinematic and thermodynamic analyses suggest that horizontal vorticity created in the forward flank and hook echo is tilted and then stretched near the developing tornado tilting and stretching are enhanced in the developing low level circulation as the secondary rear flank downdraft develops intensifies and wraps around the circulation center shortly thereafter the to

thirty year land elevation change from subsidence to uplift following the termination of groundwater pumping and its geological implications in the metropolitan taipei basin northern taiwan several levelling routes in the metropolitan taipei basin have been repeatedly conducted during the past decades mainly in order to monitor the anthropogenic ground subsidence due to massive pumping of groundwater we analysed the levelling data released from government and investigated the rate of ground level change from 1975 to 2003 which postdate the massive groundwater exploitation in taipei area based on the contour maps created from the levelling data of 406 benchmarks the overall subsidence rate in the taipei basin gradually decreased since 1975 and around 1989 the basin switched to slight uplift throughout a large part of the basin three mechanisms are proposed to be responsible for the observed land elevation changes including shallow soil compaction deformation within aquifer and tectonic subsidence the trend of the ground level change in 1975 2003 essentially demonstrated the effects of natural recharge to previously depleted aquifers and is explained by the hydro mechanical coupling of aquifer materials i e elastic rebound to the rising piezometric level the rate of shallow soil compaction is estimated about 1 8 mm yr throughout the basin according primarily to the shallow clay thickness asymmetric tectonic subsidence related to the shanchiao fault was estimated to be 1 75 mm yr and 0 9 mm yr in the western part and the central part of the basin respectively by subtracting the components of the soil compaction and tectonic subsidence from the surface land elevation change the rebound of aquifer strata was estimated to be about 6 7 cm and 16 cm in western margin and central taipei respectively the amount of rebound is approximately 10 in magnitude comparing to the amount of previous anthropogenic subsidence due to massive groundwater pumping totally about 2 m 2007 elsevier b v all rights reserved

the influence of a local swirl ratio on tornado intensification near the surface abstract the results of high resolution fully three dimensional unsteady simulations of the interaction of a tornado with the surface are presented the goal is to explore some of the range of structures that should be expected to occur in nature within the tornadic corner flow that region where the central vortex meets the surface the most important physical variables considered are the tornado scale circulation and horizontal convergence the effective surface roughness the tornado translation speed the low level inflow structure and the upper core structure a key ingredient of the corner flow dynamics is the radial influx of fluid in the surface layer with low angular momentum relative to that of the fluid in the main vortex above it this low swirl fluid arises initially from outside or below the larger scale vortex or through frictional loss of angular momentum to the surface and forms much of the vortex core flow after it exits the corner flow region changes in the surface layer inflow or

processes governing natural land subsidence in the shallow coastal aquifer of the ravenna coast italy abstract we identified the processes governing natural land subsidence in a shallow coastal aquifer near ravenna north eastern italy by analysing the relationships among different data set time series water table level rainfall drainage sea level etc and establishing the correlations with vertical ground motion observed at a high resolution settlement gauge for the first time we establish the relationships between water table fluctuations and vertical displacement in a real field dataset as well as demonstrate the important contribution of primary consolidation and aquifer stratigraphy to natural land subsidence our study highlights the presence of three deformation components related to different processes controlling land subsidence elastic delayed elastic and irreversible plastic components the elastic and delayed elastic components are closely related to water table fluctuations that change the effective stress in two portions of the coastal aquifer at a daily in the sandy unconfined portion and seasonal time scales in the finely layered clay rich semiconfined prodelta portion respectively the irreversible component represents the trend in the land subsidence time series and is due to primary consolidation pore water pressure dissipation of the fine grained prodelta levels above where the settlement gauge is located the amplitudes of the elastic component can be up to 0 2 0 3 mm whereas the amplitude of the delayed elastic component reaches 0 89 mm the primary consolidation rate of deformation is 0 9 mm year and constrains the likely age of prodelta sediments deposition to 1300 2800 years before present the average degree of consolidation for the prodelta sediments varies from 0 8 to 0 99 according to consolidation coefficients varying from 1 58 to 3 15 m2 year which are accepted values in the literature our analysis point out that primary consolidation in the shallow fine grained sediments of the shallow coastal aquifer is still ongoing the delayed elastic land subsidence rate has similar magnitude to that due to primary consolidation and is likely connected to poroelastic effects in the prodelta sequence following seasonal variations in water table our findings are important for planning land subsidence management and monitoring strategies especially where the surface aquifer structure is heterogeneous due to different depositional settings

hook echoes and rear flank downdrafts a review abstract nearly 50 years of observations of hook echoes and their associated rear flank downdrafts rfds are reviewed relevant theoretical and numerical simulation results also are discussed for over 20 years the hook echo and rfd have been hypothesized to be critical in the tornadogenesis process yet direct observations within hook echoes and rfds have been relatively scarce furthermore the role of the hook echo and rfd in tornadogenesis remains poorly understood despite many strong similarities between simulated and observed storms some possibly important observations within hook echoes and rfds have not been reproduced in three dimensional numerical models

direct surface thermodynamic observations within the rear flank downdrafts of nontornadic and tornadic supercells abstract despite the long surmised importance of the hook echo and rear flank downdraft rfd in tornadogenesis only a paucity of direct observations have been obtained at the surface within hook echoes and rfds in this paper in situ surface observations within hook echoes and rfds are analyzed these mobile mesonet data have unprecedented horizontal spatial resolution and were obtained from the verifications of the origins of rotation in tornadoes experiment vortex and additional field experiments conducted since the conclusion of vortex the surface thermodynamic characteristics of hook echoes and rfds associated with tornadic and nontornadic supercells are investigated to address whether certain types of hook echoes and rfds are favorable or unfavorable for tornadogenesis tornadogenesis is more likely and tornado intensity and longevity increase as the surface buoyancy potential buoyancy as measured by the convective available potential energy and equivalent potential temperature in the r

preseismic deformation and coseismic displacements associated with the 1999 chi chi taiwan earthquake the destructive 1999 chi chi taiwan earthquake m w 7 5 produced an approximately 100 km long surface rupture mostly along the previously recognized north south trending chelungpu fault preseismic deformation in central taiwan is realized from annually repeated global positioning system gps data acquired during the 1992 1999 period the total wnw ese shortening rate in the vicinity of the epicentral region that is from the west coast to the western boundary of the central range is up to 25 mm yr the crustal deformation before the chi chi earthquake was essentially a uniaxial compressional strain of 0 36 strain yr in the direction of 114 the gps measurements taken 0 2 2 7 yr before and within 3 months after the mainshock were utilized to estimate the coseismic displacements horizontal movements of 1 1 9 1 m in the nw nnw directions are observed on the hanging wall eastern side of the fault there is a northward increasing trend in the magnitude of the displacement vectors and a dramatic change in the direction of about 50 toward the east along the fault strike in contrast much smaller se see movements of 0 1 1 5 m are found on the footwall western side of the fault the gps data show 2 4 10 1 m of total horizontal offsets across the chelungpu fault vertical offsets of 1 2 4 4 m with the eastern side up are also observed along the surface rupture the uplift on the hanging wall decreases rapidly toward the east it becomes subsidence at sun moon lake and in the puli wushe area the stations on the footwall show subsidence of 0 02 0 26 m the width of the uplift zone increases from about 10 km in the south to approximately 30 km in the north manuscript received 13 october 2000

plausibility of substantial dry adiabatic subsidence in a tornado core abstract the question of whether or not the cores of some tornadoes are significantly warmed above the moist adiabatic temperature of their parent cb by dry adiabatic subsidence is discussed in terms of limited supporting evidence and scientific arguments both for and against further supporting evidence is provided by axisymmetric numerical simulations described here in which a background field of vertical vorticity is spun up at low levels by a moist convective updraft in a potentially unstable thermal environment typical for tornado events substantial axial subsidence heating develops in the simulations provided the vortex swirl is comparable to or larger than the maximum values observed in tornadoes the significant axial forces including buoyancy vertical acceleration and momentum diffusion are examined in detail for their effect on the surface pressure deficit and the maximum low level windspeed

on the reliability of hook echoes as tornado indicators abstract a study of radar echoes associated with the tornadoes of the 3 april 1974 outbreak was performed to evaluate the usefulness of echo shape as an indicator of tornadic thunderstorms the hook shape was usually successful in characterizing an echo as tornadic with a false alarm rate of 169 because hook echoes were relatively rare however a less restrictive shape called distinctive was more successful at detecting tornadic thunderstorms identifying 65 of the tornadic echoes an echo had a distinctive shape if it possessed a marked appendage on its right rear flank or was in the shape of a spiral comma or line echo wave pattern lewp characteristics of the distinctive echo are given

near surface vortex intensification through corner flow collapse abstract results are presented from a large set of large eddy simulations of a class of unsteady vortex evolution that may sometimes play a role in tornadogenesis or tornado variability beginning with a high swirl parent vortex with an excess of low swirl flow through the surface corner core region perturbation of the low swirl near surface inflow at a large radius can trigger a subsequent dynamic corner flow collapse producing dramatic near surface intensification relative to conditions aloft of an order of magnitude or more in velocity scale this paper presents a more detailed treatment of the physics and simulation of corner flow collapse expanding upon the presentation given in a companion paper treating near surface vortex intensification more generally for both steady and unsteady conditions the basic scaling of the onset intensification structure and duration of the phenomenon is explored as a function of some of the dominant physical parameters involved a dimensionless rate of change of

numerical simulations of an isolated microburst i dynamics and structure abstract isolated and stationary microbursts are simulated using a time dependent high resolution axisymmetric numerical model a microburst downdraft is initiated by specifying a distribution of precipitation at the top boundary of the model and allowing it to fall into the domain part i of this two part series focuses on two case studies of a hazardous wet high reflectivity microburst the first case assumes the environmental conditions that were observed on 30 june 1982 during the jaws field experiment the simulated microburst produced mean horizontal wind shears in excess of 10 2 s 1 for several minutes and was of an intensity similar to the observed microbursts on that date the second case attempts to simulate the isolated microburst which occurred near the dallas fort worth airport on 2 august 1985 a comparison of the results to actual flight recorder data showed good agreement based on these case studies the evolution and structure of the microbursts are discussed the simulated microburs

precipitation and evolution sensitivity in simulated deep convective storms comparisons between liquid only and simple ice and liquid phase microphysics abstract weisman and klemp suggested that their liquid only deep convective storm experiments should be repeated with a liquid ice microphysics scheme to determine if the solutions are qualitatively the same using a three dimensional nonhydrostatic cloud model such results are compared between three microphysics schemes the kessler liquid only scheme used by weisman and klemp a lin farley orville like scheme with liquid and ice parameterization li and the same lin farley orville like microphysics scheme but with only liquid processes turned on lr convection is simulated using a single thermodynamic profile and a variety of shear profiles the shear profiles are represented by five idealized half circle wind hodographs with arc lengths us of 20 25 30 40 and 50 m s 1 the precipitation cold pool characteristics and storm evolution produced by the different schemes are compared the kessler scheme produces similar accumulated precipitation over 2 h compared to lr for all shear regimes

can a descending rain curtain in a supercell instigate tornadogenesis barotropically abstract this paper investigates whether the descending rain curtain associated with the hook echo of a supercell can instigate a tornado through a purely barotropic mechanism a simple numerical model of a mesocyclone is constructed in order to rule out other tornadogenesis mechanisms in the simulations the flow is axisymmetric and boussinesq with constant eddy viscosity in a neutrally stratified environment the domain is closed to avoid artificial decoupling of a vortex from the storm scale circulation in the principal simulation the initial condition is a balanced slowly decaying beltrami flow describing an updraft that is rotating cyclonically at midlevels around a low pressure center surrounded by a concentric downdraft that revolves cyclonically but has anticyclonic vorticity the boundary conditions are no slip on the tangential wind and free slip on the radial or vertical wind to accommodate this initial condition and to allow strong interaction of a vortex with the ground precipitation is

geomorphological controls on soil fertility of semi arid alluvial fans a case study of the joghatay mountains northeast iran abstract alluvial fans are ideal locations to examine the effect of geomorphic processes and landforms on the soil characteristics the rate of soil development and fertility differs between active surfaces exposed to aggradation and old or relict surfaces subject to degradation the aim of this research is to evaluate the effect of landforms and processes on soil fertility based on the studies on three alluvial fans of different ages relict old and young a total of 36 soil samples were collected from these three alluvial fan surfaces the samples were gathered from different locations of fans apex and toe and landforms gully beds interfluves swales and bars and for each sample nine variables including soil texture acidity ph electrical conductivity ec total neutralizing value tnv available phosphorus ap available potassium ak total nitrogen tn total organic carbon toc and hydraulic conductivity k were measured the results show that the values of tnv ap ak tn and toc increase as clay increases in the relict and old fans the values of tnv toc tn ap ak clay and silt are higher in the interfluves than in the gully beds also in the relict and old fans the rates of clay silt toc tn and ap are higher in the apexes than in the toes in the young fan the values of most variables are higher in the toe compared to the apex the wide and relatively flat interfluves of the apex of old and relict fans have soils that are more fertile compared to the extensively entrenched surfaces of relict and old fan toes with relatively steep sloped interfluves the less fertile soils in the apex of young fan can be attributed to its coarse textured soils and also to repeated flooding and depositional processes overall this study reveals that geomorphological landforms and processes such as aggradation and degradation play an important role in the spatial variation of soil fertility