migrating and nonmigrating semidiurnal tides in the upper atmosphere excited by tropospheric latent heat release migrating and nonmigrating semidiurnal tides

the mesoscale and microscale structure and organization of clouds and precipitation in midlatitude cyclones viii a model for the seeder feeder process in warm frontal rainbands abstract previous field studies have indicated that warm frontal rainbands form when ice particles from a seeder cloud grow as they fall through a lower level feeder cloud in this paper we present results from a parameterized numerical model of the growth processes that can lead to the enhancement of precipitation in a seeder feeder type situation the model is applied to two types of warm frontal rainbands in the first type 1 situation the vertical air motions are typical of those associated with slow widespread lifting in the vicinity of warm fronts in the second type 2 situation the vertical air motions are stronger and more characteristic of the mesoscale the model simulations show that in the type 1 situations the growth of the seed ice crystals within the feeder zone is due to vapor deposition the feeder zone in this case is slightly sub saturated with respect to water due to the presence of the seed crystals in regions where the feeder zone is not seeded from aloft snow cryst

reduction in fully softened shear strength of natural clays with nacl leaching and its effect on slope stability abstractlandslides and slope failures in natural clay rich materials are frequently observed in coastal areas and other areas where these materials were deposited in a saline water environment high sodium chloride nacl concentration in the pore fluid results from deposition in this environment as shown by the results of this study subsequent reduction in the nacl concentration results in reduction in fully softened shear strength with potentially significant reduction in slope stability fourteen sample materials were collected from seven different landslide areas in niigata prefecture japan to evaluate the effect of saline water on fully softened shear strength fsss the sample materials were collected from the intact mudstones and the sliding surface materials pore waters from the powdered sliding surface materials exhibited low concentrations of nacl however the pore waters in the powdered intact rock samples exhibited a high concentration of nacl washing of nacl from the powdered intact

the impact of extratropical transition on the downstream flow an idealized modelling study with a straight jet the interaction of a tropical cyclone undergoing extratropical transition et with the midlatitude synoptic scale flow is investigated using full physics numerical experiments with idealized initial conditions the emphasis is on the impact on the midlatitude flow downstream of the et event the midlatitude flow is represented by a balanced straight jet stream as the tropical cyclone approaches the jet a ridge trough couplet and a distinct jet streak form in the upper level flow a midlatitude cyclone develops rapidly downstream of the et system and the further evolution is characterized by downstream baroclinic development based on hovmoller diagrams the upper level development is interpreted as the excitation and subsequent dispersion of a rossby wave train on the potential vorticity gradient associated with the jet the characteristics of this wave train are sensitive to the structure of the jet and to moist processes in the midlatitudes the tropical cyclone undergoing et acts as a sustained forcing for the wave train and the structure of the et system impacts the development most significantly one to two wavelengths downstream of et piecewise inversion of potential vorticity complemented by the partitioning of the flow into its rotational and divergent parts is applied to assess the impact of the et system quantitatively both the cyclonic circulation and the outflow of the tropical cyclone are important contributors to the formation and amplification of the ridge trough couplet the outflow anomaly reduces the eastward motion of the ridge trough couplet significantly and thus promotes phase locking between the tropical cyclone and the upper level pattern copyright 2008 royal meteorological society

variation in residual shear strength of the soil with the salinity of pore fluid slope stabilization procedures for seven landslides in the niigata prefecture of japan had provided an excellent and rare opportunity to examine the composition of ground water and residual shear strength of the sliding surface soil as well as unsheared mudstone ring shear tests were conducted on the soil samples collected from sliding surface soil revealed during the installation of 3 m diameter drainage galleries shear strength and index properties of the soil were measured by mixing the soil with distilled water and sea water and after leaching the nacl from the pore water the residual shear strength of the soil sample with distilled water was 3 5 lower than that with the sea water the residual shear strength of the intact rock powder after leaching the dissolved salt was close to that of the soil from sliding surface and the residual shear strength of the soil from sliding surface after mixing with sea water was close to that of the intact rock powder the increase in residual shear strength

groundwater surface waters interactions at slope and catchment scales implications for landsliding in clay rich slopes understanding water infiltration and transfer in soft clay shales slopes is an important scientific issue especially for landsliding geochemical investigations are carried out at the super sauze and draix laval landslides both developed in the callovo oxfordian black marls with the objective to define the origin of the groundwater in situ investigations soil leaching experiments and geochemical modeling are combined to identify the boundaries of the hydrological systems at super sauze the observations indicate that an external water flow occurs in the upper part of the landslide at the contact between the weathered black marls and the overlying formations or at the landslide basement through a fault network such external origin of water is not observed at the local scale of the draix laval landslide but is detected at the catchment scale with the influence of deep waters in the streamwater quality of low river flows hydrogeological conceptual models are proposed emphasizing the role of the interactions between local slope and regional catchment flow systems the observations suggest that this situation is a common case in the alpine area expected consequences of the regional flows on slope stability are discussed in term of rise of pore water pressures and physicochemical weathering of the clay shales

longitudinal variation of the lunar tide in the equatorial electrojet the atmospheric lunar tide is one known source of ionospheric variability the subject received renewed attention as recent studies found a link between stratospheric sudden warmings and amplified lunar tidal perturbations in the equatorial ionosphere there is increasing evidence from ground observations that the lunar tidal influence on the ionosphere depends on longitude we use magnetic field measurements from the champ satellite during july 2000 september 2010 and from the two swarm satellites during november 2013 february 2017 to determine for the first time the complete seasonal longitudinal climatology of the semidiurnal lunar tidal variation in the equatorial electrojet intensity significant longitudinal variability is found in the amplitude of the lunar tidal variation while the longitudinal variability in the phase is small the amplitude peaks in the peruvian sector 285 e during the northern hemisphere winter and equinoxes and in the brazilian sector 325 e during the northern hemisphere summer there are also local amplitude maxima at 55 e and 120 e the longitudinal variation is partly due to the modulation of ionospheric conductivities by the inhomogeneous geomagnetic field another possible cause of the longitudinal variability is neutral wind forcing by nonmigrating lunar tides a tidal spectrum analysis of the semidiurnal lunar tidal variation in the equatorial electrojet reveals the dominance of the westward propagating mode with zonal wavenumber 2 sw2 with secondary contributions by westward propagating modes with zonal wavenumber 3 sw3 and 4 sw4 eastward propagating waves are largely absent from the tidal spectrum further study will be required for the relative importance of ionopsheric conductivities and nonmigrating lunar tides

a chemo mechanical insight into the failure mechanism of frequently occurred landslides in the loess plateau gansu province china abstract thick loess deposits are considered problematic soils due to their susceptibility to collapse suddenly and in large volumes upon increase of water content in the past decades a large number of landslides occurred in the loess plateau in gansu province north western china triggered by the extensive irrigation the increase of water content has been identified as a key factor controlling the loess strength however the role of long term saturation and pore fluid chemistry changes has not been investigated systematically this paper reports on an experimental study on loess samples from heitai loess terrace yongjing gansu carried out through chemical analyses oedometer and ring shear tests the natural pore fluid was found to be a concentrated saline solution in unsaturated soil condition upon saturation the pore ion concentration drop can contribute to shear strength loss in the clay component and volume decrease a prolonged exposure to the irrigation water might facilitate cement dissolution which could result in further weakening

extratropical transition of tropical cyclones over the western north pacific part i evolution of structural characteristics during the transition process abstract the development of extratropical cyclone structural characteristics that resulted from the extratropical transition of typhoon ty david 1997 and ty opal 1997 over the western north pacific is examined david moved poleward ahead of a midlatitude trough that was moving eastward as the dominant midlatitude circulation feature over the western north pacific during the transition david coupled with the midlatitude trough which led to the evolution of an intense cyclone that became the primary circulation over the north pacific although opal also moved poleward ahead of a midlatitude trough the principal midlatitude feature over the western north pacific was a preexisting stationary cyclone over the kamchatka peninsula during transition opal weakened and became a secondary cyclone to the preexisting primary north pacific cyclone the structural characteristics of the evolving extratropical cyclone with respect to each case are examined in the context of the interaction between a vortex an

hurricane juan 2003 part ii forecasting and numerical simulation abstract the landfall of hurricane juan september 2003 in the canadian maritimes represents an ideal case in which to study the performance of operational forecasting of an intense predominantly tropical feature entering the midlatitudes a hybrid cyclone during its genesis phase juan underwent a tropical transition as it drifted slowly northward 1500 km from the east coast of the united states shortly after reaching its peak intensity as a category 2 hurricane the storm accelerated rapidly northward and made landfall near halifax nova scotia canada with maximum sustained winds of 44 m s 1 although the forecasts and warnings produced by the u s national hurricane center and the canadian hurricane centre were of high quality throughout hurricane juan s life cycle guidance from numerical weather prediction models became unreliable as the storm accelerated toward the coast the short range near surface forecasts from eight operational models during the crucial prelandfall portion of juan s track

extratropical transition of southwest pacific tropical cyclones part ii midlatitude circulation characteristics abstract this second of two papers on extratropical transition et over the southwest pacific ocean focuses on the variability of et a climatology of et onset based on a previously described objective technique shows that et commences 15 of latitude nearer the equator on average than similar cases from the northern hemisphere characteristic midlatitude circulation patterns accompanying et near 30 s are identified by means of empirical orthogonal function eof analysis of 50 storms the first eigenvector pattern explaining nearly half the circulation variability expresses relaxed and enhanced pressure gradients south of the storm that define composites similar to cradled and captured classifications previously described for the southeast indian ocean the second eof distinguishes redeveloping from weakening storms reintensifying storms were located beneath strong cyclonic vorticity advection cva near the equatorward entrance region of an upper jet whereas the upper jet was well to the west of

determination of a consistent time for the extratropical transition of tropical cyclones part i examination of existing methods for finding et time abstract as a tropical cyclone moves poleward and interacts with the midlatitude circulation the question of whether it will undergo extratropical transition et and if it does whether it will reintensify or dissipate is a complex problem several quantities have been proposed in previous studies to describe extratropical transition including frontogenesis 500 hpa geopotential heights and cyclone phase space parameters in this study these parameters are explored for their utility in defining an et time using the navy s operational global assimilation and prediction system gridded analyses the 500 hpa geopotential heights and frontogenesis currently do not have objective numerical definitions therefore this study attempts to establish and examine threshold values that may be used to objectively define the et time cyclone phase space already has numerical threshold values that can be examined results show that the 500 hpa geopotential height open wave distinguishes 81 of 82 cases but it fails

the effect of large scale flow on low level frontal structure and evolution in midlatitude cyclones abstract observational and modeling studies documented in the literature indicate that the large scale flow has an important effect on the structure and evolution of low level fronts in midlatitude cyclones the purpose of this paper is to address the role of the large scale flow on low level cyclone frontal structure and evolution through a combined observational and idealized modeling approach analyses of two observed cyclone cases embedded in large scale diffluence and confluence respectively are presented to illustrate two possible cyclone frontal structures and evolutions specifically the cyclone moving into a diffluent high amplitude ridge becomes meridionally elongated and possesses a strong meridionally oriented cold front and a weak warm front the cold front rotates into the warm front forming an occluded front in the manner of the norwegian cyclone model as indicated by the narrowing of the thermal ridge connecting the warm sector to the cyclone center in contrast the cyclone moving i

tidal variability in the ionospheric dynamo region 1 the seasonal and interannual variability of migrating sun synchronous and nonmigrating solar atmospheric tides at altitudes between 100 and 116 km are investigated using temperature measurements made with the saber instrument on the timed spacecraft during 2002 2006 quasi biennial variations of order 10 15 in migrating diurnal and semidiurnal tidal amplitudes are found presumably due to modulation by the quasi biennial oscillation qbo as the tides propagate from their troposphere and stratospheric sources to the lower thermosphere a number of nonmigrating tidal components are found that have the potential to produce significant longitudinal variability of the total tidal fields the most prominent of these i e those that appear at amplitudes of order 5 10 k in a 5 year mean climatology include the zonally symmetric s 0 diurnal tide d0 the eastward propagating diurnal and semidiurnal tides with zonal wave numbers s 2 de2 and se2 and s 3 de3 and se3 and the following westward propagating waves diurnal s 2 dw2 semidiurnal s 1 sw1 s 3 sw3 and s 4 sw4 and terdiurnal s 5 tw5 these waves can be plausibly accounted for by nonlinear interaction between migrating tidal components and stationary planetary waves with s 1 or s 2 or by longitudinal variations of tropospheric thermal forcing additional waves that occur during some years or undergo phase cancellation within construction of a 5 year climatology include dw5 se1 se4 sw6 te1 tw1 and tw7 it is anticipated that the winds that accompany all of these waves in the 100 170 km region will impose longitudinal variability in the electric fields produced through the ionospheric dynamo mechanism thereby modulating vertical motion of the equatorial ionosphere and the concomitant plasma densities in addition to the wave 4 modulation of the equatorial ionosphere that has recently been discovered and replicated in modeling studies the waves revealed here will generate wave 1 sw1 sw3 d0 dw2 wave 2 sw4 tw1 wave 3 de2 se1 wave 4 de3 se2 dw5 sw6 te1 tw7 wave 5 se3 and wave 6 se4 components of this ionospheric variability depending on year and time of year however the absolute and relative efficiencies with which these waves produce electric fields remains to be determined

hydrogeological assessment of a deep seated coastal landslide based on a multi disciplinary approach abstract this study focuses on the understanding of the hydrogeological functioning of a complex landslide affecting the coastal municipality of villerville normandy france we wish to provide a conceptual model of functioning using a multi disciplinary approach a set of geomorphological geological and hydrological data as well as in situ observations were first used to understand the main landslides processes new acquisitions were then carried out to strengthen our hypotheses thanks to passive geophysics sp and the characterization of physicochemical parameters of surface waters the joint analysis of former ert surveys and sp results is of significant interest for correlating hydrokinetic information measured at the surface with resistivity tomograms which provide internal information this study highlights 1 a division of the behaviour into three parts from east to west 2 variable internal dynamics highlighted by geology and electric fields 3 a preferential discharge of the continental water table upstream of the central area of the landslide this work tends to demonstrate that on the basis of initial in situ knowledge available on many study areas the understanding of the hydrogeological functioning can be substantially improved by implementing light and inexpensive surveys also suitable for large and complex landslides

lunar tidal winds between 80 and 110 km from uars hrdi wind measurements 1 recent observations and models show the considerable effects of upward propagating lunar atmospheric tides on many aspects of the ionosphere thermosphere system a key aspect of atmosphere ionosphere coupling is the wind field in the ionospheric e region circa 100 150 km where the dynamo generation of electric fields occurs yet global specifications of lunar tidal winds exist only in theoretical predictions although years of satellite observations on atmospheric winds exist with almost global coverage in the present paper we report on quasi global semidiurnal lunar tidal winds up to 115 km from data gathered by the high resolution doppler imager hrdi on board the upper atmosphere research satellite during the early years from 1991 to 1999 the observed lunar semidiurnal tidal winds are consistent with global scale wave model gswm simulations in both amplitude and phase with maximum amplitudes located between about 40 n 60 n around the solstices the peak amplitudes of the lunar tidal winds lie in the 10 15 ms 1range whereas those simulated by gswm lie between 15 and 25 ms 1 the smaller hrdi amplitudes are likely due in part to amplitude suppression in construction of the climatological mean resulting from year to year phase variability in the lunar tide it is also possible that wave dissipation is underestimated to some degree in the gswm

relationship between the track and structural evolution of hurricane sandy 2012 using a regional ensemble abstractan ensemble of 72 weather research and forecasting wrf model simulations is evaluated to examine the relationship between the track of hurricane sandy 2012 and its structural evolution

magnetic storm response of lower thermosphere density measurements of atmospheric density near 200 km from the satellite electrostatic triaxial accelerometer seta experiment are used to delineate the temporal seasonal latitudinal and day night dependences of the response to magnetic storm related perturbations in high latitude energetic inputs five periods of geomagnetic activity are analyzed and yield consistent results which can be interpreted within the framework of recent thermosphere ionosphere simulations by fuller rowell et al 1995 in response to a change in magnetic activity level from quiet kp 1 2 to active kp 4 7 conditions an increase in daytime 1030 lt density of order 50 70 occurs between 60 and 80 geographic latitude in the summer hemisphere with about half the maximum response in the winter hemisphere this difference is mainly due to the difference in ionization conductivity levels and hence joule heating rates between the hemispheres on the dayside penetration of the disturbance at about the 50 intensity level is realized at the equator whereas in the winter hemisphere equatorward penetration is much weaker these effects are connected with the prevailing solar driven circulation the net summer to winter meridional flow facilitates equatorward advection of the disturbance bulge in the summer hemisphere but hinders advection in the winter hemisphere in both hemispheres the daytime component of the solar driven diurnal circulation tends to oppose equatorward penetration to the same degree however on the nightside 2230 lt penetration at nearly the 100 level of both summer and winter disturbance bulges are realized to within 20 of the geographic equator this behavior is associated with the equatorward advection in both hemispheres consistent with the nighttime component of the solar driven circulation comparisons with the msise90 model hedin 1991 show it to capture the salient features of the daytime behavior but exhibits little day night asymmetry in contrast to the experimental results

precipitation over greenland retrieved by a dynamic method and its relation to cyclonic activity abstract in order to calculate the vertical motion over some high mountain regions such as greenland an equation without the quasigeostrophic approximation in coordinates has been developed a dynamic method for retrieving precipitation over greenland is based on this equation the retrieved annual mean precipitation distribution for 1987 and 1988 is in very good agreement with the observed annual accumulation pattern over the greenland ice sheet the major weather system producing precipitation over greenland is the frontal cyclone based on the precipitation characteristics greenland can be divided into five subregions precipitation over the north coastal and central interior regions primarily occurs in summer for the three other subregions if the composite monthly mean sea level pressure charts for high and low monthly precipitation amounts are constructed a clear relationship between precipitation and cyclonic activity emerges if a mean cyclone exists in the labrador sea heavy precipita

orographic precipitation and air mass transformation an alpine example a case of orographic precipitation in the alps on 20 september 1999 was studied using several models along with rain gauge and radar data the objective of the study is to describe the orographic transformation of an air mass including multi scale aspects several new and some conventional diagnostic quantities are estimated including drying ratio precipitation efficiency buoyancy work condensed water residence time parcel changes in heat moisture and altitude and dominant space and time scales for the case considered the drying ratio was about 35 precipitation efficiency values are ambiguous due to repeated ascent and descent over small scale terrain the sign of buoyancy work changed during the event indicating a shift from stratiform orographic to weak convective clouds cloud water residence times are different for the two mesoscale models 400 compared to 1000 s due to different cloud physical formulations the two mesoscale models agree that the dominant spatial scale of lifting and precipitation is about 10 km smaller than the scale of the main alpine massif trajectory analysis of air crossing the alps casts doubt on the classic model of fohn few parcels exhibit classic pattern of moist ascent followed by dry descent parcels that gain latent heat descend only briefly before rising into the middle troposphere parcels that descend along the lee slope originate in the middle troposphere and gain little or even lose latent heat during the transit as parcels seek their proper buoyancy level downstream a surprising scrambling of the air mass occurs radar data confirm the model prediction that the rainfall field is tightly controlled by local terrain on scales as small as 10 km rather than the full 100 km cross alpine scale a curious pulsing of the precipitation is seen indicating either drifting moisture anomalies or weak convection copyright 2003 royal meteorological society

simulations of the extratropical transition of tropical cyclones contributions by the midlatitude upper level trough to reintensification abstract the extratropical cyclone development processes during the reintensification stage of an extratropical transition from a tropical cyclone tc are described using numerical simulations three control simulations without a tropical cyclone present examine the extratropical cyclogenesis associated with upper level troughs that are characterized as weak moderate and strong when no tropical cyclone is included in the simulation the minimum surface pressures attained with the weak moderate and strong troughs are 1003 991 and 977 mb respectively in all three cases the low tilts northwestward with height during intensification and the rainfall pattern and eventual occlusion are representative of classic extratropical cyclone development the interactions of a tropical cyclone with each of the three midlatitude circulation patterns are compared with the control simulations to illustrate the contributions to the extratropical transition of the tropical cyclone in the three trough with tc case

effect of sudden stratospheric warming on lunar tidal modulation of the equatorial electrojet 1 using the equatorial electrojet eej peak current intensity as deduced from champ magnetic observations from the years 2001 through 2009 we investigated the relationship between sudden stratospheric warming ssw and lunitidal signatures in the tropical ionosphere there is a practically one to one correspondence between midwinter ssw periods and the strongest 13 day modulation of the eej strength as observed by champ that is all the midwinter ssw periods from december 2001 to august 2009 were accompanied by an enhanced 13 day modulation of the eej strength no other geophysical phenomenon brought about as strong a 13 day modulation as those of the midwinter ssw periods during each midwinter ssw period the amplified 13 day modulation of the eej strengths starts roughly within 1 week around the first peak in stratospheric temperature difference an oscillation with a period of 13 26 days is predicted by the lunitidal equation when considering the precession of the champ orbit when fitting the lunitidal equation to the eej modulations during the midwinter ssw periods consistent phase delays of 4 4 0 3 days of the tidal signal emerge for all the cases the results suggest that the pronounced 13 day modulation of the eej strength is related to an enhancement of the lunar tide in the ionosphere by the ssw effect

on modeling migrating solar tides recent updates and extensions to a steady state two dimensional linearized model of global scale atmospheric waves have facilitated improved calculations of the subset of those waves which are subharmonics of a solar day and propagate with the apparent motion of the sun the model improvements are briefly described and some updated predictions of the migrating solar diurnal component are highlighted the latter represent the first numerical modeling effort to examine the seasonal variability of the migrating diurnal harmonic as it propagates into the mesosphere and lower thermosphere

temperature dependent residual shear strength characteristics of smectite bearing landslide soils this paper presents experimental investigations regarding the effect of temperature on the residual strength of landslide soils at slow to moderate shearing velocities we performed ring shear tests on 23 soil samples at temperatures of 6 29 c the test results show that the shear strength of smectite rich soils decreased when temperatures were relatively low these positive temperature effects strength losses at lower temperatures observed for smectite bearing soils are typical under relatively slow shearing rates in contrast under relatively high shearing rates strength was gained as temperature decreased as rheological properties of smectite suspensions are sensitive to environmental factors such as temperature ph and dissolved ions we inferred that temperature dependent residual strengths of smectitic soils are also attributed to their specific rheological properties visual and sem observations of ca bentonite suggest that slickensided shear surfaces at slow shearing rates are very shiny and smooth whereas those at moderate shearing rates are not glossy and are slightly turbulent indicating that platy smectite particles are strongly orientated at slow velocities the positive temperature effect is probably due to temperature dependent micro friction that is mobilized in the parallel directions of the sheet structure of hydrous smectite particles on the contrary the influence of micro viscous resistance which appears in the vertical directions of the lamination is assumed to increase at faster velocities our results imply that if slip surface soils contain high fractions of smectite decreases in ground temperature can lead to lowered shear resistance of the slip surface and trigger slow landslide movement

extratropical transition of southwest pacific tropical cyclones part i climatology and mean structure changes a database of tropical cyclone best track and intensity information for the southwest pacific ocean basin is used to construct a 28 year climatology for tropical cyclones that move into middle latitudes of the nine or so tropical cyclones that form each year an average of about three can be expected to migrate south of 358s with the greatest fraction in march storms entering the tasman sea west of new zealand nz move almost due south on average and retain greater intensity than those to the east of nz where storms decay quickly while moving rapidly away to the southeast storms east of nz are embedded in a stronger more zonal flow than those to the west which move poleward ahead of a larger amplitude trough during el nino years tropical cyclones that move into middle latitudes exhibit stronger zonal motion and occur over a wider range of longitudes than during la nina years storm intensity is only weakly correlated with concurrent sst anomalies suggesting that atmospheric circulation is the dominant influence on storm properties average structure changes during extratropical transition et are identified using the ncep ncar reanalysis dataset for a subset of 33 transitioning storms during 1980 97 composites are used to construct a three dimensional conceptual model of the transformation from a mature hurricane to an asymmetric baroclinic midlatitude cyclone southwest pacific tropical cyclones encounter the baroclinic westerlies early in their lives accounting for their average eastward and poleward motion at maximum average intensity near 208s baroclinic effects are already important with warm frontogenesis appearing in the southeast quadrant and outflow aloft into a downstream subtropical wind maximum that moves poleward with the storm by 258s the average tc has lost the characteristic symmetric anticyclonic outflow aloft and acquired the characteristics of a baroclinic midlatitude storm including regions of warm and cold frontogenesis a vertical motion dipole and a westward tilt with height from about 308s poleward a second upper tropospheric wind maximum appears west of the storm with strengthening cyclonic vorticity advection aloft below about 400 hpa the storm retains the vertical warm cyclonic core as it migrates poleward

the role of diabatic heating in maintaining the upper tropospheric baroclinic zone in the south pacific a modified set of ecmwf fgge level iii b analyses is used to examine the four dimensional structure of the region containing the south pacific convergence zone spcz during a period when two cyclones form in the tropics and propagate south eastward along the spcz into middle latitudes during this period 10 18 january 1979 the atmosphere is characterized by a highly baroclinic state which together with the existence of an upper tropospheric subtropical jet supports the growth and development of the observed cyclone activity in a previous study it was found that convective activity was prominent during the life cycle of each cyclone the goal of the present study is to examine the significance of kinematic and thermodynamic processes in maintaining the upper baroclinic region coincident with the subtropical jet this baroclinic zone lies just poleward of the warm core associated with the convectively active spcz a partitioned form of the fronto genetical function is used to diagnose the adiabatic and diabatic contributions to the maintenance of baroclinicity in the vicinity of the spcz a major balance is found between the frontogenetical contribution by differential diabatic heating and the opposing diabatic tilting processes in contrast to the results of most mid latitude cyclone studies the adiabatic contributions from the deformation and tilting terms appear to be of lesser importance also the contribution from the deformation associated with the horizontal branch of the diabatically forced circulation is found to be relatively unimportant the latter finding is in disagreement with some previously reported numerical results concerned with middle latitude moist frontogenesis possible reasons for these differences are discussed

a phase locking perspective on rossby wave amplification and atmospheric blocking downstream of recurving western north pacific tropical cyclones abstractthe extratropical transition et of tropical cyclones tcs can significantly influence the evolution of the midlatitude flow however the interaction between recurving tcs and upstream u

evidence for stratosphere sudden warming ionosphere coupling due to vertically propagating tides 1 observations of the global positioning system gps total electron content tec are used to study the coupling between the 2009 sudden stratospheric warming ssw and ionospheric perturbations the observations reveal both migrating and nonmigrating perturbations to the semidiurnal tide in the equatorial ionization anomaly crest region that are associated with changes in electric fields induced by the tidal dynamo in particular a significant enhancement is observed in the nonmigrating semidiurnal westward propagating tide with zonal wavenumber 1 sw1 in gps tec during the ssw the sw1 perturbations in the low latitude ionosphere are found to oscillate with a similar period as planetary wave 1 activity in the northern hemisphere stratosphere this connection is attributed to the nonlinear interaction between tides and planetary waves and strongly supports the theory that planetary wave tide interaction is the primary mechanism coupling ssws to ionospheric variability enhancements are also observed in the nonmigrating semidiurnal tide with zonal wavenumber 0 s0 during this time period and may be related to the nonlinear interaction between the migrating semidiurnal tide and planetary wave 2 the connection between planetary wave 2 and s0 is however less clear which may be attributed to differences in the zonal mean zonal winds in the mesosphere and lower thermosphere during the times of peak planetary wave 1 and planetary wave 2 activity we conclude that the changing zonal winds during ssws play an important role in the coupling between ionospheric variability and the forcing from planetary waves of lower atmospheric origin during ssws

weathering of submerged stressed calcarenites chemo mechanical coupling mechanisms long portions of the apulian coast are steep cliffs in carbonate soft rocks these especially the calcarenite are affected by weathering processes that markedly alter their mechanical properties with time potentially leading to instability of coastal geomorphological structures such alterations are mainly due to chemical reactions between the solid and fluid phases and are driven by chemical variables which are internal variables and hence uncontrollable in a search for the variables that drive the process of rock weakening recourse is made to the micro scale at which most of the chemical processes are observed and quantified observations using scanning electron microsope thin sections and x ray computed tomography analyses appear to be crucial for the understanding interpretation and definition of the degradation mechanisms of the material a chemo mechanical coupled model at the meso scale of the chemically reactive stressed porous system is presented and framed in the context of a multi sca

lunar tide in the equatorial electrojet in relation to stratospheric warmings 1 the relationship between sudden stratospheric warmings ssws and large amplitude lunar tides in the equatorial electrojet eej is studied analysis of ground magnetometer data shows that the lunar tide in the eej is maximum during the northern winter season except in the pacific ocean region since ssws are also a northern winter phenomenon it is suggested that the relation between the large lunar tide in the eej and the ssw may possibly be coincidental the lunar tide in the geomagnetic variations at huancayo is anomalously large compared with other eej stations an examination of geomagnetic variations at eej stations during ssw events shows that afternoon counter electrojets are frequently present at new moon and full moon though the relationship is sometimes broken the observation of large lunar eejs when no ssw is present and of various different delay times suggests that other atmospheric processes are likely to be in play

hurricane juan 2003 part i a diagnostic and compositing life cycle study abstract a detailed analysis of the complex life cycle of hurricane juan in 2003 is undertaken to elucidate the structures and forcings that prevailed over the period leading up to the hurricane s landfall in halifax nova scotia canada despite the presence of easterly wave precursors hurricane juan s initial development is shown to occur in a baroclinic environment beneath a low latitude potential vorticity streamer this feature interacts with a lower level shear line as the incipient vortex begins to effectively focus ascent and convection the system undergoes a slow tropical transition over a period of several days as the deep layer shear over the developing storm decreases the hurricane is repeatedly perturbed by subsynoptic scale waves traveling along the leading edge of a large upstream trough however hurricane juan maintains its tropical structure despite its relatively high formation latitude 28 n and its northward trajectory the unusual persistence of the storm s tropical nature as i

the extratropical transition of hurricane irene 1999 a potential vorticity perspective extratropical transition et of tropical cyclones is common in all ocean basins where tropical cyclones recurve polewards after the tropical cyclone experiences et a rapid deepening can take place resulting in the development of a very large and deep extratropical cyclone the et of hurricane irene 1999 was an example of such an explosive et irene formed in the caribbean and experienced et as it moved poleward resulting in a low pressure system which deepened 39 hpa in 24 hours according to the met office analyses the extent to which the hurricane was responsible for the explosive extratropical development has been determined by performing met office unified model forecasts from initial states with and without the hurricane the circulation and temperature anomalies associated with the hurricane were removed from the initial state using potential vorticity inversion the moisture anomaly co located with the hurricane core was also removed the results show that an extratropical cyclogenesis event takes place regardless of the presence of the hurricane in the initial conditions however the hurricane makes a significant difference to the track and central mean sea level pressure evolution of the resulting extratropical cyclone when irene was present the track of the extratropical cyclone was more zonal and the cyclone deepening rate was twice as fast as when irene was not present these effects appear to be particularly associated with a negative potential vorticity anomaly and enhanced divergent flow in the region of the upper level outflow of the transforming hurricane rather than with the hurricane vortex results also show that the presence of the hurricane resulted in a significant downstream surface low development in the eastern atlantic copyright 2004 royal meteorological society

on the day to day variation of the equatorial electrojet during quiet periods it has been known for a long time that the equatorial electrojet varies from day to day even when solar and geomagnetic activities are very low the quiet time day to day variation is considered to be due to irregular variability of the neutral wind but little is known about how variable winds drive the electrojet variability we employ a numerical model introduced by liu et al 2013 which takes into account weather changes in the lower atmosphere and thus can reproduce ionospheric variability due to forcing from below the simulation is run for may and june 2009 constant solar and magnetospheric energy inputs are used so that day to day changes will arise only from lower atmospheric forcing the simulated electrojet current shows day to day variability of 25 which produces day to day variations in ground level geomagnetic perturbations near the magnetic equator the current system associated with the day to day variation of the equatorial electrojet is traced based on a covariance analysis the current pattern reveals return flow at both sides of the electrojet in agreement with those inferred from ground based magnetometer data in previous studies the day to day variation in the electrojet current is compared with those in the neutral wind at various altitudes latitudes and longitudes it is found that the electrojet variability is dominated by the zonal wind at 100 120 km altitudes near the magnetic equator these results suggest that the response of the zonal polarization electric field to variable zonal winds is the main source of the day to day variation of the equatorial electrojet during quiet periods

the extratropical transition of tropical cyclones part i cyclone evolution and direct impacts abstractextratropical transition et is the process by which a tropical cyclone upon encountering a baroclinic environment and reduced sea surface temperature at higher latitudes transforms into an extratropical cyclone this process is influenced by and influences phenomena from the tropics to the midlatitudes and from the meso to the planetary scales to extents that vary between individual events motivated in part by recent high impact and or extensively observed events such as north atlantic hurricane sandy in 2012 and western north pacific typhoon sinlaku in 2008 this review details advances in understanding and predicting et since the publication of an earlier review in 2003 methods for diagnosing et in reanalysis observational and model forecast datasets are discussed new climatologies for the eastern north pacific and southwest indian oceans are presented alongside updates to western north pacific and north atlantic ocean climatologies advances in understanding and in some cases mode

life cycle study of a diabatic rossby wave as a precursor to rapid cyclogenesis in the north atlantic dynamics and forecast performance abstractthe life cycle of a north atlantic cyclone in december 2005 that included a rapid propagation phase as a diabatic rossby wave drw is investigated by means of operational analyses and deterministic forecasts from the ecmwf a quasigeostrophic omega diagnostic has been applied to assess the impact of upper level forcing during the genesis propagation and intensification phase respectively the system was generated in the gulf of mexico as a mesoscale convective vortex mcv influenced by vertical motion forcing from a nearby upper level trough the drw propagation phase was characterized by a shallow low level diabatically produced potential vorticity pv anomaly that rapidly propagated along the southern border of an intense baroclinic zone no significant upper level forcing could be identified during this phase of the development eventually explosive intensification occurred as the region of vertical motion forced by an approaching upper level trough reached the position of the drw the

the impact of tropical remnants on extratropical cyclogenesis case study of hurricanes danielle and earl 1998 abstract the importance of remnant tropical cyclone tc circulation and moisture structures is investigated for a simultaneous extratropical transition et event involving ex hurricanes danielle and earl september 1998 although both storms undergo prolonged periods of reintensification following et the forcings involved in each of their redevelopment processes differ fundamentally a review of the tropical and baroclinic et modes in the north atlantic stresses the importance of jet front structures to the nature of the reintensification process ex hurricane danielle begins to redevelop in the eastern half of the basin in the downstream poleward sector of an intensifying polar jet the system undergoes a tropical mode of reintensification resulting in a troposphere deep warm environment surrounding the storm devoid of near surface fronts and maintained by strong tropopause folds at its periphery ex hurricane earl reintensifies near the eastern seaboard according to a baroclinic mode under the i

the role of cloud top generating cells and boundary layer circulations in the finescale radar structure of a winter cyclone over the great lakes abstractdata from airborne w band radar are used in conjunction with thermodynamic fields from the weather research and forecasting model and air parcel back trajectories from the hysplit model to investigate the finescale reflectivity vertical motion and airmass structure of the comma head of a winter cyclone in the vicinity of the great lakes cloud top generating cells formed along an upper level frontal boundary vertically separating dry air which 48 h earlier was located in the upper troposphere over south central canada from moist air which was located in the lower troposphere over the southeast united states the stronger updrafts within the generating cells had vertical velocities ranging from 1 to 3 m s 1 the generating cells were important to precipitation production within the comma head precipitation trails formed within the generating cells could sometimes be followed to the boundary layer before merging boundary layer air beneath the cyclone s comma head exhibited convective circulati

physical and mechanical properties of loess discharged from the yellow river into the bohai sea china abstract chinese loess is unique in having great scientific value whilst also playing an important role in societal development large volumes of loess are continually carried by the yellow river from the chinese loess plateau to the bohai sea northeast china forming the yellow river delta the physical and mechanical properties of this loess vary during transportation and these characteristics have been investigated in detail using several samples of estuarine loess collected from tidal flats with different depositional ages the wet densities natural moisture contents specific gravities atterberg limits grain size distributions microstructures and mineral compositions of these samples have been determined our results show that the estuarine loess is classified as silty loess and that its specific gravity plasticity and grain size characteristics were very similar to land derived loess its unit weight and water content increasd during discharge into the sea and its plastic index decreased the estuarine loess also had fewer large pores that were more closely connected than those in land loess as a result of these changes in index properties and pore water chemistry estuarine loess is less susceptible to liquefaction than land derived loess in addition these physical and mechanical properties show strong correlations to the long term depositional history of the delta with older deposits typically having a lower dry density and higher void ratio than younger deposits the results of this study have implications for hazard mitigation and improving our understanding of the mechanisms responsible for loess related geological disasters

downstream development associated with the extratropical transition of tropical cyclones over the western north pacific abstract the movement of a tropical cyclone into the midlatitudes involves interactions among many complex physical processes over a variety of space and time scales furthermore the extratropical transition et of a tropical cyclone may also result in a high amplitude rossby wave response that can extend to near hemispheric scales after an et event occurs over the western portion of a northern hemisphere ocean basin the high amplitude downstream response often forces anomalous midlatitude circulations for periods of days to a week these circulations may then be related to high impact weather events far downstream of the forcing by the et event in this study downstream development following et events over the western north pacific ocean is examined local eddy kinetic energy analyses are conducted on four cases of north pacific tropical cyclones of varying characteristics during et into varying midlatitude flow characteristics during 15 july 30 september 2005 the goal is to examine the impact of e

the transformation of tropical storm agnes into an extratropical cyclone part i the observed fields and vertical motion computations abstract this is the first of two papers dealing with the transformation of tropical storm agnes june 1972 into an extratropical cyclone synoptic analyses and vertical motion patterns are used to describe the behavior of agnes over a five day period subsequent to initial landfall during which time agnes regained tropical storm strength prior to transforming into an extratropical cyclone and dissipating input data for all calculations are obtained from optimum interpolation objective analyses with a resolution of 1 latitude longitude in the horizontal and 100 mb in the vertical a modified 9 level version of krishnamurti s 1968a diagnostic balance model is discussed and applied to the data set to determine the fields of vertical motion redevelopment of agnes subsequent to initial landfall is the result of the spread of an area of appreciable cyclonic vorticity advection aloft over the periphery of the low level circulation devoid of significant baroclinicity unlike a corresponding midlatitude sto

the extratropical transition and precipitation distribution of hurricane floyd 1999 abstract several recent landfalling tropical cyclones e g dennis floyd and irene 1999 have highlighted a need for a refinement in the forecasting paradigms and techniques in the area of quantitative precipitation forecasting floyd proved to be a particularly challenging forecast problem as it was accompanied by catastrophic flooding over large regions of the east coast in spite of its relatively quick northward movement the extent and intensity of the precipitation distribution was strongly modulated by the storm s interaction with a midlatitude trough in an attempt to better understand and quantify the relevant dynamics during this interaction potential vorticity pv and quasigeostrophic perspectives are utilized as floyd approached the east coast precipitation shifted to the left of the storm track due to the presence of a deep midlatitude trough in the ohio valley the juxtaposition of a cold core pv anomaly associated with the midlatitude trough and a warm core pv anomaly associated with

a 10 yr climatology of diabatic rossby waves in the northern hemisphere abstractdiabatic rossby waves drws are low tropospheric positive potential vorticity pv anomalies in moist and sufficiently baroclinic regions they regenerate continuously by moist diabatic processes and potentially develop into explosively intensifying cyclones in this study a specific drw tracking algorithm is developed and applied to operational ecmwf analyses to compile a first climatology of drws in the northern hemisphere for the years 2001 10 drws are more frequent over the north pacific than over the north atlantic with on average 81 and 43 systems per year respectively less than 15 of these systems intensify explosively on average 12 per year over the pacific and 5 over the atlantic drws are most frequent in summer but most of the explosively intensifying drws occur in autumn and winter drws are generated typically between 30 50 n over the eastern parts of the continents and the western central parts of the oceans they propagate fairly zonally along the midlatitude baroclinic zone

the extratropical transitions of hurricanes felix and iris in 1995 abstract the extratropical transitions of hurricanes felix and iris in 1995 are examined and compared both systems affected northwest europe but only iris developed significantly as an extratropical system in both cases the hurricane interacts with a preexisting extratropical system over the western atlantic the remnants of the exhurricanes can be identified and tracked across the atlantic as separate low level potential vorticity pv anomalies the nature of the baroclinic wave involved in the extratropical transition is described from a pv perspective and shown to differ significantly between the two cases the role of vertical shear in modifying the hurricane structure during the early phase of the transition is investigated iris moved into a region of strong shear the high pv tower of iris developed a marked downshear tilt felix moved into a vertically sheared environment also but the shear was weaker than for iris and the pv tower of felix did not tilt much iris maintained its warm core struc

an early autumn polar low formation over the norwegian sea around october 15 1993 an unusual polar low formation took place over the norwegian sea the evolution is studied by means of the hirlam forecasting model at the danish meteorological institute satellite imagery and observations the investigation to some extent based on generalized forms of the equations for omega and geopotential tendency reveals that the disturbance forms initially by baroclinic instability along a frontal zone within a maritime polar air mass and in close proximity of an intense extratropical cyclone during its growth to a polar low air sea interaction seems to work in conjunction with the baroclinic process a parallel forecast with the latent heat set to zero shows that heating of the atmosphere associated with precipitation is necessary for the polar low formation

atmospheric tide 2 the solar and lunar semidiurnal components solar and lunar semidiurnal wind and temperature oscillations from the surface to 400 km are simulated for average solar activity conditions utilizing the numerical tidal model described in part 1 hough mode decomposition of the solstitial solar semidiurnal tide excited by h2o and o3 insolation absorption below 80 km indicates that it is characterized by a predominance of 2 2 below 60 km about equal contributions of 2 2 2 3 and 2 4 between 70 and 90 km mostly 2 4 with some 2 5 and 2 2 between 90 and 120 km and a predominance of 2 2 above 140 km with secondary contributions from 2 3 and 2 5 the solstitial lunar semidiurnal tide is characterized by a predominance of 2 2 below 70 km 2 4 with secondary contributions from 2 2 2 3 and 2 5 between 80 and 110 km and by 2 2 with a fairly strong secondary contribution from 2 3 above 120 km similar descriptions for both the solar and lunar oscillations apply at equinox except that the asymmetric 2 3 and 2 5 modes are absent relative to the solar component lunar temperature and wind amplitudes are sufficiently large 20 in the lower and upper thermosphere to account for some of the observed variability previously attributed to the solar tide amplitudes of the 2 4 and 2 5 modes above 100 km are significantly affected by mesospheric eddy diffusion coefficients in excess of 2 106 cm s 1 the total solar semidiurnal exospheric temperature oscillation for average solar conditions ranges from 10 20 k poleward of 40 n to 40 60 k equatorward of 30 n and has its origin in three sources of excitation all of comparable importance 1 euv solar radiation absorption in the lower thermosphere 100 200 km 2 in situ momentum coupling due to the interaction of diurnal winds and diurnally varying ion drag and 3 tides propagating upwards from below 100 km in addition the calculations are compared with rocket meteor radar partial reflection thomson scatter and satellite data to evaluate the consistency of the model with observations

the present day simulation and twenty first century projection of the climatology of extratropical transition in the north atlantic abstractthis study explores the simulations and twenty first century projections of extratropical transition et of tropical cyclones tcs in the north atlantic with a newly developed global climate model the forecast oriented low ocean resolution flor version of the geophysical fluid dynamics laboratory gfdl coupled model version 2 5 cm2 5 flor exhibits good skill in simulating present day et properties e g cyclone phase space parameters a version of flor in which sea surface temperature sst biases are artificially corrected through flux adjustment flor fa shows much improved simulation of et activity e g annual et number this result is largely attributable to better simulation of basinwide tc activity which is strongly dependent on larger scale climate simulation flor fa is also used to explore changes of et activity in the twenty first century under the representative concentration pathway rcp 4 5 scenario a contrasting pattern is found in which regional tc density increas

the key role of diabatic outflow in amplifying the midlatitude flow a representative case study of weather systems surrounding western north pacific extratropical transition abstractrecurving tropical cyclones tcs undergoing extratropical transition et may substantially modify the large scale midlatitude flow pattern this study highlights the role of diabatic outflow in midlatitude flow amplification within the context of a review of the physical and dynamical processes involved in et composite fields of 12 western north pacific et cases are used as initial and boundary conditions for high resolution numerical simulations of the north pacific north american sector with and without the tc present it is demonstrated that a three stage sequence of diabatic outflow associated with different weather systems is involved in triggering a highly amplified midlatitude flow pattern 1 preconditioning by a predecessor rain event pre 2 tc extratropical flow interaction and 3 downstream flow amplification by a downstream warm conveyor belt wcb an ensemble of perturbed simulations demonstrates the robustness of these stages beyond earlier studies investigating pres recurv

synoptic scale diagnosis of the extratropical transition of a southwest pacific tropical cyclone abstract this is the first of two case studies on the transformation of tropical storms in the southwest pacific this study uses ecmwf analyses and observations to examine the behavior of tropical cyclone patsy in december 1986 prior to and during its transit to midlatitudes these analyses adequately depicted synoptic scale features during the extratropical phase but underestimated the inner core of strong wind during the hurricane phase interactions with troughs in the subtropical westerlies provided the impetus for the major motion and structure changes during patsy s life during the hurricane phase patsy was steered by the flow above 400 hpa the passage of a first trough to poleward led to disintegration of the characteristic tropical cyclone structure decay was due to shearing effects loss of upper level outflow and the transient incorporation of cooler air into the low level circulation a few days later patsy commenced moving rapidly south as a single center as ascent redeveloped in the p

identifying the origin of groundwater and ﬂow processes in complex landslides affecting black marls insights from a hydrochemical survey the super sauze mudslide is a persistently active slow moving landslide occurring in the black marl outcrops of the french south alps it has been intensively studied since the early 1990s geotechnical geomorphological geophysical and hydrological investigations have led to a better understanding of the processes governing the landslide motion water ows inside the system have been proven to have a major impact to look closer at the processes involved and especially to gain a better idea of the origin and pathways of the waters a hydrochemical study was carried out from may 2003 to may 2004 the groundwater was sampled during ve eld campaigns spread uniformly over the year groundwater from a network of boreholes was collected as well as spring waters from the fractured bedrock in situ black marl and from the moraine aquifer above the landslide results showed that the groundwater chemistry could not be fully explained by rainfall recharge or simple water matrix equilibrium a contribution of saline waters coming from the bottom of a thrust sheet overhanging the landslide was required to get the observed high mineralization on a ow line the hydrochemical evolution was related to both soil matrix equilibrium and deep water sources coming up to the surface by means of major faults the bedding planes and the schistosity hydrochemical anomalies made it possible to point out such contributions locally it was shown that water chemistry and landslide activity were closely related this hydrochemical investigation also enabled us to better de ne the hydrosystem limits copyright 2006 john wiley sons ltd

modeling of upwelling relaxation events with the navy coastal ocean model prediction system coamps tm coamps is a registered trademark of the naval research laboratory issues investigated in this study are ncom based model simulations of upwelling and relaxation events coupling to coamps use of sigma versus hybrid sigma z vertical grids and coupling with a larger scale model on the open boundaries the ncom simulations were able to reproduce the observed sequence of the upwelling and relaxation events which can be attributed in part to the good agreement between the observed and coamps winds comparisons with the mooring observations show that coamps overestimates shortwave radiation values which makes the ncom modeled ssts too warm in comparison with observations the ncom runs forced with different resolution atmospheric forcing 3 versus 9 km do not show significant differences in the predicted ssts and mixed layer depths at the mooring locations at the same time during the extended upwelling event the model runs forced with 3 and 9 km resolution coamps fields show differences in the surface circulation patterns which are the most distinct in the southern portion of the model domain the model run with 9 km forcing develops a northward flow along the coast which is not present in the run with 3 km forcing and in observations for example hf radar derived radials comparison of the wind patterns of the 3 and 9 km products shows a weakening of the 9 km wind stress along the southern coast of the ncom model domain which is responsible for the development of the artificial northward flow in the ncom run with 9 km forcing

the intense lee wave rotor event of sierra rotors iop 8 abstract a large amplitude lee wave rotor event observationally documented during sierra rotors project intensive observing period iop 8 on 24 26 march 2004 in the lee of the southern sierra nevada is examined mountain waves and rotors occurred over owens valley in a pre cold frontal environment in this study the evolution and structure of the observed and numerically simulated mountain waves and rotors during the event on 25 march in which the horizontal circulation associated with the rotor was observed as an opposing easterly flow by the mesonetwork of surface stations in owens valley are analyzed the high resolution numerical simulations of this case performed with the coupled ocean atmosphere mesoscale prediction system coamps run with multiple nested grid domains the finest grid having 333 m horizontal spacing reproduced many of the observed features of this event these include small amplitude waves above the sierra ridge decoupled from thermally forced flow within the valley and a l

dynamic earth system and ecological controls of rainfall initiated landslides abstract rainfall initiated landslides continue to inflict damages and loss of life throughout the world processes and mechanisms revealed from hydrological geomorphic geotechnical pedological geological hydrochemical and biological investigations have advanced our understanding of these effects on slope stability however the interactions amongst these processes and attributes as they affect the initiation and propagation of landslides are not as well understood too often landslide studies are conducted from only one or at most two of these perspectives moreover while precipitation and hydrology are recognized as dynamic influences the earth system and ecological effects are often assumed to be static we assess the interplay of these processes related to landslides triggered by positive pore water accretion and loss of soil suction each of these conditions arguably requires a different view on the processes that cause slope failure and predictive approaches this review starts from the perspective of dynamic adapting earth and ecological systems and discusses how these attributes relate to landslide initiation mode location and timing specifically the role that large and small scale preferential flow plays in both contributing to and mitigating instability is elucidated including effects of bedrock exfiltration we also examine how and under what conditions these pathways manifest in different soils lithology and landforms the multiple effects of rhizosphere processes on slope stability are discussed including root reinforcement evaporation from canopies and litter layers transpiration and the role of root structure affecting preferential flow paths rainfall initiated landslides involve highly dynamic hydrologic earth surface and ecological processes that persist over a range of spatial and temporal scales however guidance for overcoming these challenges has been elusive a conceptual framework is presented to shed light on these dynamic and interactive processes that should lend insights into why and when certain slopes fail during storms while other seemingly similar slopes do not fail such advances will benefit landslide hazard assessments and disaster responsiveness protocols

the influence of the downstream state on extratropical transition hurricane earl 1998 case study abstract the multitude of tropical extratropical interactions that occur during an extratropical transition et complicate the prediction and diagnosis of these extreme events this study focuses on the analysis of a double et and reintensification event that took place between 5 and 7 september 1998 ex hurricanes earl and danielle reintensified rapidly over the western and eastern north atlantic respectively a set of simulations designed to test the sensitivity of earl s et to features in the downstream state was run using a set of idealizations for a numerical model s initial and boundary conditions downstream of ex hurricane earl dynamic tropopause analyses and the pv thinking paradigm applied under the eady model highlight important developmental and structural differences between the tests in fact two distinct solution modes are diagnosed both in the control and in the sensitivity tests earl s et proceeds according to a baroclinic mode of redevelopment whereas danielle displays distinct

some geomorphological considerations for the future development of landslide models this paper reviews the commonly available models used to model landslides the main purpose is then to examine some of the wider issues associated with the developments that are required if we are to develop 3 d applications and to extrapolate their use to long time scales the paper does not discuss landslide hazard mapping models but concentrates on the 3 d and temporal problems associated with the modelling of single slides

ice crystal habits and growth processes in stratiform clouds with embedded convection examined through aircraft observation in northern china abstractice crystal habits and growth processes in two cases of stratiform clouds with embedded convection are investigated using data observed simultaneously from three aircraft on 18 april 2009 and 1 may 2009 as part of the beijing cloud experiment bce the results show that the majority of ice crystal habits found in the two cases at temperatures between 0 and 16 c included platelike needle column capped column dendrite and irregular a mixture of several ice crystal habits was identified in all of the clouds studied however the ice crystals recorded in the embedded convection regions contained more dendrites and possessed heavier riming degrees and the ice crystals identified in the stratiform clouds contained more hexagonal plate crystals both riming and aggregation processes played central roles in the broadening of particle size distributions psds and these processes were more active in embedded convection regions than in stratiform regions however riming was more prevalent in the

influence of lixiviation by irrigation water on residual shear strength of weathered red mudstone in northwest china implication for its role in landslides reactivation abstract irrigation in loess tableland areas of northwest china has induced a large number of landslides around their edges of which loess red mudstone landslide is one of the most frequent types salt sinters commonly observed at the toes of these landslides where the weathered red mudstone wrm outcrops have raised the possibility that removal of soluble salts in the wrm by irrigation water could be crucial in the reduction of its shear strength and thus in the occurrence of these landslides in order to investigate the effects of lixiviation by irrigation water on residual shear strength of the wrm samples of the wrm close to two landslides in lanzhou city one of the largest cities in northwest china were tested after being treated under different conditions these included 1 saturation with the yellow river water the only source of irrigation 2 saturation with groundwater and 3 saturation and leaching with deionized water based on the results of these tests specific mechanisms of residual shear strength reduction of the wrm due to lixiviation by irrigation water were discussed in terms of physico chemical interactions between the wrm and water it was found that lixiviation reduced residual shear strength and residual friction angle r of the wrm by up to 65 and 62 respectively after being leached 6 times this coincided with a dramatic dissolution and leaching of soluble salts from the wrm particle size distribution showed that the more the wrm was leached the more the clay fraction and the lesser coarser fractions this suggested that reduction in residual shear strength of the wrm could be attributed to mainly disaggregation of particles coarser than clay and to a lesser degree to weakening of interparticle forces among individual clays it was further postulated that variation in clay mineralogy may influence performance of particle disaggregation

a cyclone phase space derived from thermal wind and thermal asymmetry abstract an objectively defined three dimensional cyclone phase space is proposed and explored cyclone phase is described using the parameters of storm motion relative thickness asymmetry symmetric nonfrontal versus asymmetric frontal and vertical derivative of horizontal height gradient cold versus warm core structure via the thermal wind relationship a cyclone s life cycle can be analyzed within this phase space providing substantial insight into the cyclone structural evolution an objective classification of cyclone phase is possible unifying the basic structural description of tropical extratropical and hybrid cyclones into a continuum stereotypical symmetric warm core tropical cyclone and asymmetric cold core extratropical cyclone life cycles are illustrated using 1 navy operational global atmospheric prediction system nogaps operational analyses and 2 5 ncep ncar reanalyses the transitions between cyclone phases are clearly illustrated within the phase space including extratro

experimental evidence for shallow slow moving landslides activated by a decrease in ground temperature in order to understand the trigger mechanism of slow moving landslides occurring in the early cold season from late autumn to winter we investigated the effect of temperature on the shear strength of slip surface soils displacement controlled and shear stress controlled box shear experiments were performed on undisturbed slip zone soils under residual strength conditions test results conducted at temperatures from 9 to 25 c showed remarkable shear strength reductions with decreasing temperature creep like slow shear displacements were induced by a decrease in temperature these temperature dependent shear behaviors are attributed to the rheological properties of hydrous smectite that dominantly compose the soil material along the failure surface our experimental results imply that ground temperature conditions influence slope instability especially for shallow landslides occurring in smectite bearing rock areas

extratropical transition of tropical cyclones over the western north pacific part ii the impact of midlatitude circulation characteristics abstract two characteristic midlatitude circulation patterns labeled northwest and northeast are found to be associated with extratropical transition et of tropical cyclones over the western north pacific ocean although in both cases the tropical cyclone moves poleward ahead of a midlatitude trough the primary midlatitude circulation is either that trough or is a large quasi stationary cyclone to the northeast of the poleward moving tropical cyclone transition into a northwest pattern typically results in the development within 36 h of an intense extratropical cyclone that moves north northeast a tropical cyclone that moves into a northeast pattern enters into strong zonal flow between the primary midlatitude circulation and the subtropical ridge to the southeast these systems move rapidly eastward and do not intensify significantly during the 36 h following transition in part i of this study the et of typhoon ty david 1997 and the et of ty opal 1997 were investigated in terms of the form

numerical simulations of the extratropical transition of floyd 1999 structural evolution and responsible mechanisms for the heavy rainfall over the northeast united states abstract this paper examines the extratropical transition et of hurricane floyd along the u s east coast on 16 17 september 1999 using the fifth generation pennsylvania state university ncar mesoscale model mm5 down to 1 33 km horizontal grid spacing the 36 h mm5 simulation reproduced the basic features of the et event such as the track of floyd the development of a deep and intense baroclinic zone along the coast and its associated precipitation evolution and the tendency for the heavy 30 cm precipitation to fall in a relatively narrow 30 40 km wide band just inland of the coast however the mm5 overpredicted the moderate 10 20 cm precipitation amounts near the coast by 40 50 as the horizontal grid spacing was reduced to 1 33 km the mm5 was used to diagnose the evolution of the enhanced baroclinic zone and associated heavy precipitation to the north of floyd a deep layer of deformation frontogenesis extended from the surface to 400 mb as a result of confluence between the southeasterl

residual shear strength measured by laboratory tests and mobilized in landslides drained residual shear strength measured by multiple reversal direct shear or ring shear tests has been successfully used for over four decades for stability analyses of reactivated landslides in stiff clays and clay shales a body of literature has accumulated in recent decades claiming that healing or strength regain is realized in time on preexisting slip surfaces already at residual condition in other words the shear stress required to reactivate a landslide is claimed to be larger than the drained residual shear strength determined using laboratory tests this article presents 1 a comparison of secant residual friction angle determined from laboratory tests and secant mobilized friction angle back calculated for reactivated landslides 2 explanations that field evidence used to claim healing can be attributed to alternative factors and the laboratory evidence on strength regain upon reshearing is the result of either the testing apparatus or testing procedure or is inapplicable to stiff clays and shales and 3 laboratory aging test results which show no strength regain on preexisting shear surfaces at residual condition doi 10 1061 asce gt 1943 5606 0000624 2012 american society of civil engineers ce database subject headings clays shale residual strength landslides slope stability laboratory tests author keywords clays shales residual strength landslides slope stability

detecting slope deformation using two pass differential interferometry implications for landslide studies on earth and other planetary bodies landslide features have been identified on earth and the moon mars venus as well on the jovian moons by focusing on a terrestrial landslide complex we test the operational parameters of radarsat 1 and the use of two pass differential interferometry to detect change to map its extent and to measure the amount of movement over a given time period radarsat 1 was chosen because of its variable imaging modes and geometry for investigations of landslide motions using remote sensing techniques repeat pass data are required synthetic aperture radar sar interferometry insar can ideally monitor movements across the whole surface of a landslide to a millimeteric precision yielding a coverage significantly better than that obtained by ground instrumentation obtaining optimal data for insar analysis requires controlled orbital characteristics and imaging geometries an understanding of the landslide characteristics and behavior a cooperative surface and mitigation of the factors that can affect phase using two pass differential interferometry a slope deformation map has been generated from radarsat 1 data for part of the black ven landslide 2 52 w 50 40 n on the south coast of england four months separate the insar pair during which time 0 03 m of subsidence was measured from this a movement rate of 0 09 m yr can be calculated this agrees well with ground observations and an in situ record of movement thus demonstrating that the technique can be used to investigate landslides with further refinement it can provide more direct measurements of landslide deformation on earth and other planetary bodies than are currently available

physico chemical effects on the behaviour of a coastal mudslide previous work has shown that the type of clay mineral the valency state of adsorbed cations and the salt concentration of pore water influences the residual strength of clays residual strength can therefore be modified through weathering reactions clay mineral alterations and fluctuations in groundwater chemistry this has implications for studies of the seasonal and long term behaviour of clay slopes the paper presents results from an investigation of a shallow coastal mudslide on the south coast of england which attempts to isolate the influence of physico chemical processes on mudslide behaviour fluctuations in groundwater chemistry coincided with temporal movement patterns low pore water ion concentrations were apparent immediately before seasonal mudslide reactivation or periods of high activity laboratory tests showed that low pore water ion concentrations resulted in low residual shear strength higher concentrations observed after movement events led to increases in residual strength

the extratropical transition of tropical cyclone edisoana 1990 abstractdocumentation of southwest indian ocean swio tropical cyclones tcs and extratropical transition et events is sparse in the refereed literature the authors present a climatology of swio tc and et events for 1989 2013 the swio averages 9 tropical cyclones tcs per year in this modern era of these tcs 44 undergo extratropical transition et or four per year a case study of tc edisoana 1990 the most rapidly intensifying swio post et tc between 1989 and 2013 shows that extratropical interactions began when an approaching trough embedded in the subtropical jet stream stj induced et on 7 march as edisoana underwent et a subtropical ridge downstream amplified in response to poleward directed positive potential vorticity pv advection associated with diabatically convectively driven upper level outflow from tc edisoana this amplifying lower latitude ridge phased with a lower amplitude higher latitude ridge embedded in the polar front jet pfj resulting in the merger of the t