on the role of inertial instability in stratosphere troposphere exchange near midlatitude cyclones abstractin simulations of midlatitude cyclones with the university of wisconsin nonhydrostatic modeling system uwnms mesoscale regions with large negative absolute vorticity commonly occur in the upper troposphere and lower stratosphere utls overlying thin layers of air with stratospheric values of ozone and potential vorticity pv these locally enhanced stratosphere troposphere exchange ste events are related to upstream convection by tracing negative equivalent potential vorticity epv anomalies along back trajectories detailed agreement between the patterns of negative absolute vorticity pv and epv each indicators of inertial instability in the utls is shown to occur in association with enhanced ste signatures results are presented for two midlatitude cyclones in the upper midwest where convection develops between the subpolar and subtropical jets mesoscale regions of negative epv air originate upstream in the boundary layer as they are transported through convection epv becomes incre

a seasonal climatology of rossby wave breaking in the 320 2000 k layer abstract differential advection in rossby waves can lead to potential vorticity pv p contours on isentropic surfaces folding over in latitude py 0 in a process called rossby wave breaking rwb exploring the properties of rwb may shed light on underlying dynamics and enable quantification of irreversible transport a seasonal climatology of py and rwb statistics is presented for the 320 850 k layer using ncep reanalysis data during 1979 2005 and for the 320 2000 k layer using the met office ukmo data during 1991 2003 a primary goal is to depict the spatial extent and seasonality of rwb maxima this analysis shows seven distinct rwb regimes poleward and equatorward of the subtropical westerly jets poleward and equatorward of the stratospheric polar night jets flanking the equator in the stratosphere and mesosphere equatorward of subtropical monsoon anticyclones and the summertime polar stratosphere a striking pv gradient maximum exists at the equator throughout the layer 360 2000 k flanke

progressive mitigation method of rock bursts under complicated geological conditions abstract jingxi coalfield which is called china s geological encyclopedia has a complicated geological condition as one its representative mines muchengjian mine has witnessed nearly thirty rock bursts in the past decade considering geological structures the in situ stress state and the burst proneness of coal one typical mining area in muchengjian mine is selected for analysis where nearly one third of rock bursts occurred this analysis lays the foundation for selecting mitigation strategies results indicate that the blasting disturbance plays an important role in the intensity and the scale of these rock bursts jingxi coalfield has three types of rock burst mechanisms i high in situ stress rock burst ii high mining induced stress rock burst and iii high in situ stress plus high mining induced stress rock burst therefore we follow two guidelines for rock burst control one is to mitigate the high stress concentration and the second is to control the disturbance stress on the basis of these two guidelines we designed a progressive mitigation method of rock bursts pmmrb first the weak disturbance destress techniques e g large diameter drilling water infusion are applied to weaken the strength and the burst proneness of coal and to expand crack zones to reduce the stress concentration and second the strong disturbance destress blasting is applied if the release of stress concentration is not sufficient pmmrb is adopted in a similar mining area with a higher in situ stress which indicates that pmmrb is applicable to the control of rock bursts and the reduction of rock burst intensity

the miwah high sulphidation epithermal au ag deposit aceh indonesia geology and spatial relationships of gold with associated metals and structures abstract geological mineralogical and whole rock geochemical studies of the plio pleistocene miwah high sulphidation au ag deposit in aceh indonesia revealed evidence of a complex and dynamic interplay between structural development and mineralisation the mineralisation occurs in a zone of predominantly phreatic breccias measuring 1 1 km long by 400 m wide and 200 350 m deep within a fault bounded calc alkaline andesite ridge within this zone low grade disseminated au ag has superimposed narrow high grade au ag zones hydrothermal alteration and mineralisation in three mineralised centres the miwah bluff in the west and the west block m and east block m in the east are controlled by steeply dipping 60 and northerly trending pre to syn mineral feeders this alteration displays an outward sequence of vuggy silica i alunite silica advanced argillic and kaolinite illite argillic a distal chlorite smectite propylitic zone may precede or constitute the end product of the above alteration late silica flooding converted parts of the vuggy silica i and the alunite quartz zone into variably sulphide rich massive silica and vuggy silica ii containing pyrophyllite alunite respectively penecontemporaneous with the massive silicification main stage mineralisation initially deposited intergrowths of pyrite enargite quartz followed by scattered enargite and pyrite and finally rapidly precipitated ag bearing native gold dendrites in vugs with lesser amounts of sulphides the crack seal texture of the host rocks paragenetic variation in precious and base metal mineral species and selective dissolution fracturing and shearing of most of the metallic and gangue minerals are interpreted to reflect transient pulses of fluid flows and mineralisation within zones of structural deformation high grade au zones and associated metals formed clusters along the feeders whereas low grade disseminations of the same metals were spread across the deposit these metals are zoned along the feeders from apical au ag to deep cu as sb te and sn are variably distributed laterally the zonation is from au ag in the feeders through cu as sb bi te and sn and finally to pb or zn in the periphery while these bulk rock metal abundances indicate the efficacy of certain physico chemical conditions of the fluids to accumulate the metals their ratios point to an upward paleo flow path of the fluids along the northerly striking faults and related fractures combining all of the above data we propose that miwah developed in fault fracture networks beneath paleo solfataras in a volcanic crater where the ascending acidic magmatic gas or gas fluids vapours transformed the phreatic breccia host rocks first into vuggy silica and advanced argillic rocks which were subsequently resilicified and mineralised into au and base metal rich massive silica during the depressurisation and condensation of the gas fluid phases mineralisation processes terminated with limited ag enrichment by late stage fluids in the upper segment of the deposit and in deep fractures

a statistical study of gravity waves in the polar regions based on operational radiosonde data gravity waves in the lower polar stratosphere are examined using operational radiosonde observations gathered from 33 stations over a period of 10 years both the potential and kinetic energies of the gravity waves vary annually and reach maxima in winter in the arctic and in spring in the antarctic in the antarctic spring a region of large gravity wave energy propagates downward following the movement of a zone of high static stability associated with southern hemispheric warming moreover the enhanced energy region and the high stability zone coincide in the horizontal plane and move gradually from 135 e 50 s to 45 w 70 s over the south pole the vertical and horizontal directions of wave propagation are examined using hodograph analysis in the vertical most gravity waves transfer energy upward in the arctic while the percentage of downward energy propagation is relatively high in winter and spring in the antarctic horizontally gravity waves propagate westward relative to the mean wind in the arctic while in the antarctic the dominant direction varies from station to station the correlation between gravity wave energy in the lower stratosphere and the mean wind is also examined in the arctic gravity wave energy is highly correlated with the surface wind though in the antarctic it correlates with the stratospheric wind these results suggest that gravity waves observed in the arctic are forced by topography whereas in antarctica some sources may exist in the stratosphere one such source candidate is likely to be the polar night jet

symmetric instability in the outflow layer of a major hurricane abstracta set of 327 dropsondes from the noaa g iv aircraft was used to create a composite analysis of the azimuthally averaged absolute angular momentum in the outflow layer of major hurricane ivan 2004 inertial instability existed over a narrow layer in the upper troposphere between the 350 and 450 km radii isolines of potential and equivalent potential temperature showed that the conditions for both dry and moist symmetric instability were satisfied in the same region but over a deeper layer from 9 to 12 km the radial flow maximized at the outer edge of the unstable region the symmetrically unstable state existed above a region of outward decrease of temperature between the cirrus overcast of the storm and clear air outside it is hypothesized that the temperature gradient was created as a result of longwave heating within the cirrus overcast and longwave cooling outside the cloudy region this produced isentropes that sloped upward with radius in the same region that absolute momentum surfaces

numerical investigation of load shedding and rockburst reduction effects of top coal caving mining in thick coal seams abstract by comparing the overburden structure characteristics and the distribution of stresses around roadways and coalfaces in slice mining and top coal caving mining in thick coal seams this study analysed the effects of the two mining methods on rockburst prevention furthermore by using flac3d numerical simulation this research studied the distribution of surrounding rock stress in the first mining panels subsequent panels solid coal roadways and gob side roadways and the influence of parameters including mining height bottom coal and coal seam thickness on stresses in the surrounding rocks on this basis the effects of load shedding and rockburst reduction of top coal caving mining of thick coal seams were summarised and verified through field investigation the results show that compared with slice mining overburden structures in top coal caving mining of thick coal seams weakened the stress concentration in surrounding rocks resulting in lower peak values but wider ranges of advanced abutment stress and side abutment stress in panels the point of peak stress was observed deeper into the coal masses with the increase of mining height and the decrease of bottom coal thickness the stress concentration around roadways and coalfaces decreased rapidly and then tended to be stable therefore top coal caving mining can reduce the stress concentration around roadways and coalfaces to decrease rockburst risk while mining thick coal seams top coal caving mining needs to be conducted preferentially over a reasonable range of mining heights field practice in xing an and junde mines revealed that the top coal caving mining induced a lower rockburst frequency over a smaller range and with lower intensity which validated the effects of load shedding and rockburst reduction of the proposed mining method

large midlatitude stratospheric temperature variability caused by inertial instability a potential source of bias for gravity wave climatologies stratospheric temperature perturbations tp that have previously been misinterpreted as due to gravity waves are revisited the perturbations observed by radio occultations during december 2015 had peak to peak amplitudes of 10 k extending from the equator to midlatitudes the vertically stacked and horizontally flat structures had a vertical wavelength of 12 km the signs of the tp were 180 degrees phase shifted between equatorial and midlatitudes at fixed altitude levels high resolution operational analyses reveal that these shallow temperature structures were caused by inertial instability due to the large meridional shear of the polar night jet at its equatorward flank in combination with rossby wave breaking large stratospheric tp owing to inertial instability do frequently occur in the northern hemisphere southern hemisphere from october to april april to october in the 39 years of ecmwf re analysis interim data during 10 of the days tp exceed 5 k peak to peak plain language summary the stratosphere is the part of the atmosphere between altitudes of similar to 15 50 km which contains the ozone layer that shields life from hazardous radiation we use global stratospheric temperature measurements to learn about the variability of temperatures on vertical scales 15 km usually it is thought that such variations are caused by waves that are excited by the displacement of air when being lofted upward when for example the wind blows over mountains the air then starts oscillating around its original height level because of gravity gravity waves are an important driver of stratospheric winds which for example determine the distribution of ozone we present observations of large stratospheric temperature perturbations which could easily be misinterpreted as gravity waves combining the measurements with output of a numerical weather prediction model we show that the observations are caused by a large scale atmospheric instability called inertial instability using meteorological data spanning the past 40 years we quantify when and how often such temperature perturbations of a certain size occur our results are important for properly constructing gravity wave climatologies where inertial instability events must be excluded which are in turn an important input for the correct formulation of climate models

model experimentation of the effect of gravity on tectonic processes summary it seems likely that many of the tectonic phenomena in the earth s crust are generated by processes within the mantle our view of such a large scale tectonic phenomenon as the evolution of orogenic belts consequently ought to reflect on the theorizing of the behaviour of the mantle the author finds it therefore appropriate to present in this symposium some results from experimental model studies related to the origin of geosynclines and orogens some models simulating convection currents in the mantle are also discussed

a fault and stress field analysis in a coal mine gardanne bouches du rhone france abstract this paper develops an interpretation of faulting in the mining district of the arc basin where research has been conducted since 1978 in the underground workings coal winning is carried out by the houilleres de bassin du centre et du midi h b c m mining takes place in an upper cretaceous series lying ahead of an overthrust sheet etoile sheet forming the southern limit of the arc basin with a few exceptions the observations and measurements have been taken in the seam named grande mine which is the only bed being worked at present a chronological account of faulting is put forward normal faulting occurred prior to the overthrusting which brought about reverse faulting continued compression nne ssw led to strike slip faulting the last compressive phase again induced strike slip faulting along a few major faults this was a nearly e w trending compression the stress field pertaining to each period is investigated and an attempt is made to calculate the values of the principal stresses these findings on the stress history fit what is already known about the sequence of geological events in the region the present day stress field determined through in situ measurements can be at least in one part of the coal field said to result directly from the tectonic conditions it is a major cause of rock bursts in the mine workings

layered structure associated with low potential vorticity near the tropopause seen in high resolution radiosondes over japan horizontal wind and temperature data obtained from operational radiosondes over japan have recently been available with high vertical resolution analyzing these data over 4 yr has indicated horizontal velocity layers with vertical scales of about 5 km lasting for a week or more the layers appear frequently in winter at several stations simultaneously and are dominant in the height range of 8 16 km an empirical orthogonal function eof analysis for the time series of layered disturbance amplitude in winter indicates that there are two dominant principal components the first component eof1 describes layered disturbances in the middle of japan 308 378n and the second one eof2 describes disturbances in the south of japan 238 308n using global analysis data the background field of the layered disturbances was examined an interesting result is that the background potential vorticity pv is approximately zero or negative for eof2 disturbances even though located in a relatively high latitude region this fact suggests that the eof2 disturbances are due to inertial instability it is also shown that negative pv occurs more than 30 of the time in winter in a zonally elongated region of 238 298n in the western pacific on an isentropic surface of 345 k 10 km altitude such a high frequency of negative pv is not observed at other longitudes in this latitude band to determine the origin of the anomalous pv backward trajectories were analyzed for eof2 disturbances air parcels having mostly negative pv are traced back to the equatorial region in the longitude band 208w 1408e within a few days this is due to a strong northward branch of the hadley circulation associated with deep convection over the maritime continent and a strong northeastward subtropical jet stream on the other hand the background pv is low but scarcely negative for eof1 disturbances air parcels at eof1 stations are traced back to the far west because they are advected mostly by a strong eastward jet stream thus it is inferred that the eof1 disturbances may be due to inertia gravity waves trapped in a duct of the westerly jet core

inertial instability and rossby wave breaking in a numerical model abstract a mechanistic model of the middle atmosphere is used to study the interaction between rossby waves forced at the extratropical tropopause and inertial instability in the equatorial lower mesosphere the impact of cross equatorial shear strength and rossby wave forcing amplitude is explored model results support the hypothesis based on satellite temperature observations that rossby waves organize regions of equatorial inertial instability into coherent large scale circulations horizontal convergence and divergence maxima are found stacked over the boundaries of regions of anomalous potential vorticity pv this supports observational diagnoses and theoretical expectations that parcel inertial accelerations arise in regions of anomalous pv with divergence and convergence occurring at the boundaries although cross equatorial shear determines the initial volume of inertially unstable air rossby waves arriving from the winter hemisphere deform pv contours such that zonally confined regions of

microseismic monitoring and stability analysis of the left bank slope in jinping first stage hydropower station in southwestern china risks associated with the left bank slope of jinping first hydropower station in southwestern china are growing as a result of excavation of the dam foundation ditch and various tunnels as well as grouting to soft strata to improve our understanding of the slope instability and resolve the complex subsurface conditions of the highly fractured rock mass a microseismic monitoring system was installed in june 2009 which is the first time such a technique has been introduced into stability analysis of a high steep rock slope in china the microseismic monitoring system consists of a data acquisition unit a data processing unit and a three dimensional array of uniaxial accelerometers in order to analyze the correlation between seismicity and potential slip surface of the slope a numerical model was implemented to analyze the failure processes and stability of the slope the monitoring results illustrate that microseismic events mainly occur as a strip along the spandrel groove of the dam which coincides with the potential slip surface obtained from numerical analysis especially at the bottom of the slope therefore the comprehensive method incorporating microseismic monitoring and numerical analysis has been proven to be very promising in instability prediction of rock slope subject to identification and delineation of potential slip surface and failure regions

vertical wind disturbances in the troposphere and lower stratosphere observed by the mu radar abstract an analysis is made of vertical wind disturbances vwds observed by the mu radar shigaraki shiga japan in terms of the wave structures sources and vertical momentum flux first it is shown through spectral and lag correlation analyses that there are several common features in three observation periods when the vwds appeared large power in the vertical wind fluctuations exists below a height of 20 km and is distributed largely at lower frequencies the decrease in power near 20 km is sharp and the correlation between vertical winds above and below the level is very small suggesting that the height of 20 km is a special level for the vwds such as a critical level the disturbances below 20 km consist of several modes in a height frequency space some of which oscillate almost in phase in a wide height range spanning 8 km at the maximum second using eight sets of the mu radar data the relationship between vertical wind activity and horizontal wind near the surface is examined in order

comparison of rockburst occurrence during extraction of thick coal seams using top coal caving versus slicing mining methods in recent years rockbursts have occurred frequently during the mining of thick coal seams in china use of the top coal caving or slicing mining method to extract these thick seams may result in d

observational evidence for asymmetric inertial instability abstract we present a detailed analysis of a mesoscale circulation phenomenon that appeared on satellite images as a group of propagating cloud wavelets these wavelets developed on the anticyclonic side of a strong upper level subtropical jet in a region of negative potential vorticity p during their lifetime the wavelets were located over the north american synoptic sounding network the meteorological conditions surrounding their occurrence are examined we investigate the various physical mechanisms that may have been responsible for generating the observed cloud wavelets in consideration of the time scale of the wavelets and their proximity to the region where p 0 inertial instability appears to be the most likely dynamical mechanism for explaining their existence using hourly satellite images we determined that the wavelets propagated downstream at a phase speed 25 m s 1 slower than the maximum wind speed of the jet with life cycles of 4 5 h horizontal wavelengths of 400 km and periods

microseismic investigation of mining induced brittle fault activation in a chinese coal mine abstract the process whereby a brittle fault was activated by mining is not only significant for disaster prediction but also for earthquake prediction thus it was necessary to study their activation process in this study stress state ae acoustic emission ms microseismic activities during brittle fault activation stages of brittle fault activation and the relation between ae ms activities and brittle fault parameters were analysed and it was feasible to identify buried brittle faults determine their parameters and activation process based on ms monitoring the no 22517 working face in the dongjiahe coalmine was taken as an example firstly a buried brittle fault was identified in no 22517 working face by the ms monitoring method secondly the buried brittle fault parameters were determined its azimuth angle was 307 5 in the orbital roadway and 357 5 on the haulage roadway its dip angle was 73 and it was a reverse fault thirdly the activation process of the buried brittle fault was determined the buried brittle fault was not affected by the mining activities when the distance from mining activities to the buried brittle fault was over 300 m the disturbance stage was from 300 m to 80 m and the local activation stage from 100 m to 30 m and the whole activation stage around 30 m the b value decreased during the process of brittle fault activation and reached a minimum value at the whole activation stage it was concluded that these changes are related to the stress distribution around the brittle fault the results demonstrated that ms monitoring technology can detect small buried brittle faults ahead of the working face and is also an effective method to study the process and mechanism of brittle fault activation

global climatology of inertial instability and rossby wave breaking in the stratosphere 1 climatologies using united kingdom met office assimilated analyses from november 1991 through march 2004 are used to juxtapose the evolution of inertial instability and rossby wave breaking in longitude latitude altitude and time the results for the upper and middle stratosphere indicate deep poleward and eastward channels of higher inertial instability frequency extending from the central equatorial pacific in both winter hemispheres these corridors of enhanced inertial instability frequency are generally found just poleward of regions of frequent rossby wave breaking a result confirmed with a case study drawn from the period of the climatology both of these patterns are evident from the stratopause downward into the middle stratosphere with the frequency of events diminishing with decreasing altitude analysis of interannual variability of rossby wave breaking and inertial instability in the middle stratosphere channels confirms a correlation between them as well as a possible quasi biennial oscillation signal in the early years of the climatology in the lower stratosphere a channel of enhanced inertial instability frequency exists near east asia in northern hemisphere winter again just poleward of a rossby wave breaking maximum these results generally agree closely in space and time with and significantly extend the relatively few previously published climatologies and case studies of episodes of rossby wave triggered inertial instability for the stratosphere

the nature of a deformation zone and fault rock related to a recent rockburst at western deep levels gold mine witwatersrand basin south africa abstract in august 1998 a major deformation zone was exposed over several metres during mining operations on 87 level 2463 m below surface at western deep levels gold mine southwest of johannesburg providing a unique opportunity to study the products of a recent rockburst this zone consists of three shear zones with dip slip displacements of up to 15 cm that are oriented near parallel to the advancing stope face jogs and a highly pulverised cataclastic rock flour are developed on the displacement surfaces and several sets of secondary extensional fractures occur on either side of the shear zones a set of pinnate feather joints intersects the fault surfaces perpendicular to the slip vector microscopically the shear zones consist of two pinnate joint sets that exhibit cataclastic joint fillings quartz grains display intense intragranular fracturing secondary intergranular extension fractures are associated with the pinnate joints extensional deformation is also the cause of the breccia fill of the pinnate joints the initial deformation experienced by this zone is brittle and tensile and is related to stresses induced by mining this deformation has been masked by later changes in the stress field which resulted in shearing this deformation zone does not appear to be controlled by pre existing geological features and thus represents a burst fracture which is believed to be related to a seismic event of magnitude ml 2 1 recorded in july 1998 the epicentre of which was located to within 50 m of the study locality

reply to comment by j wickham on basin inversion and fault reactivation in laboratory experiments 1 introductionthe comments by wickham 2007 raise a number ofquestions about the reliability of the experimental resultsreported in our paper del ventisette et al 2006 dealingwith basin inversion and fault reactivation processes we wel come his comments and appreciate the opportunity to clarifyour interpretations and starting points of the modelling it iswell know that experimental models must necessarily includesome simpli cations on the other hand such models are use ful for visualizing complex geological settings whereas full 3dnumerical experiments are still dif cult wickham 2007 presents various combinations ofdimensionless ratios of length l viscosity h density r gravity g and time t reported in del ventisette et al 2006 to calculate the dimensionless ratios of fundamentalunits of mass m time t and length l we agree thatthe various combinations show different magnitudes of m l and t bringing wickham 2007 to argue that the modelsfail to simulate natural deformation more speci cally wick ham 2007 states in his conclusion section that in the basininversion system modelled by del ventisette et al 2006 vis cous materials with horizontal density gradients seem to bea central feature in the deformation so gravity must be includedin the scaling parameters 2 basic simpli cation principlesscalingofgravityisachiefissueinphysicalmodelling inhispioneerwork hubbert 1937 addressedthistopic showingthatsince aphysicalmodelanditsprototypeboth format theearth ssurface they obey the same gravity acceleration so that we areforced to set the gravity acceleration rate l t

pre existing cross structures and active fault segmentation in the northern central apennines italy abstract the multideformed axial zone of the apennines provides a great opportunity to explore the influence of pre existing cross structures inherited from pre quaternary tectonic phases on the segmentation of quaternary active seismogenic extensional faults detailed geological and structural data and their comparison with seismological data show that although the attitudes strike and dip of oblique pre existing faults are certainly an important factor in determining a segment boundary the size of the inherited oblique structures seems to be more crucial pre existing cross structures with lengths ranging from several kilometers to a few tens of kilometers show a twofold behavior they can act as segment barriers during the rupture of a single fault segment or they can be reactivated as transfer zones inducing the activation of two adjacent segments that belong to the same fault system regional basement crustal oblique pre existing cross structures with lengths ranging from several tens of kilometers to hundreds of kilometers commonly nne striking may act as persistent structural barriers that halt both fault segment and fault system propagation thus determining their terminations and maximum sizes in the northern central apennines the nne striking ancona anzio valnerina and ortona roccamonfina tectonic lineaments although having been repeatedly reactivated since the mesozoic represent the most important examples of these structures moreover probably due to their misorientation with respect to the present extensional stress field regional nne striking pre existing structures appear to be less likely to produce strong magnitude events no surface evidence for quaternary faulting has been found thus far and historical and instrumental seismicity shows only m m 7 event on the other hand is more likely to occur along the n nw s se trending normal fault systems lastly we propose a model that can explain the different sizes of fault segments and fault systems on the basis of their location with respect to the persistent structural barriers and their spacing in this view our results may contribute to a more reasonable assessment of the nature and size of future surface ruptures in the northern central apennines which are of critical importance to estimating seismic hazard

origin and transport of tropical cirrus clouds observed over paramaribo suriname 5 8 n 55 2 w 1 the intertropical convergence zone itcz passes twice a year over tropical suriname bringing two wet and two dry seasons during a pilot study campaign in suriname cirrus clouds were observed with a mobile aerosol raman lidar marl and with balloon sondes containing a frost point hygrometer called snow white over the period october november 2004 these observations are used to study the origin of cirrus clouds and the dynamical processes that determine their transport using european centre for medium range weather forecasts ecmwf operational analyses the height of cirrus occurrence is in phase with the height of the cold point tropopause with maximum heights occurring during northern hemisphere winter that are about 2 km above the minimum values in summertime the occurrence of cirrus often corresponds with a northerly meridional wind flow in a layer underneath the tropopause also when the itcz lies to the south in the period january may ecmwf analyses point out that inertial instability flow in the form of vertically stacked meridional circulation cells in the upper troposphere ut can explain the transport of these cirrus events also evident is that radiative cooling of a moist layer transported in the ut leads to a thermal wind in the form of an easterly westerly jet associated with the southward northward transport of moist air an interactive play between the inertial instability and thermal wind mechanisms explains many of the observed features of cirrus occurrence over suriname the observed cirrus mostly originates from the itcz or from deep convective centers to the south that form during the early summer monsoon

fault zone migration by footwall shortcut and recumbent folding along an inverted fault example from the mosha fault central alborz northern iran the mosha fault is a multiply inverted fault in the central alborz field observations and structural data from this fault show that a footwall shortcut is the major mode of response of this fault to contractional deformation although the mosha fault is a basement involved fault there is no evidence of involvement of basement along its footwall shortcuts at least in the study area footwall shortcuts along this fault vary in size from several hundreds of metres to tens of kilometres suggesting that a footwall shortcut can be scale independent it is proposed that footwall shortcuts can also occur as blind thrusts under fault related folds in the terrains near the major inverted faults similar cases also exist in other regions such as japan some large footwall shortcuts may be the causative fault of devastating earthquakes in the active inverted terrains such as the south central alborz incompetent layers acting as detachments may play an important role in the development of footwall shortcuts recu

high resolution observations with mu radar of a kh instability triggered by an inertia gravity wave in the upper part of a jet stream kelvin helmholtz kh instability is likely one of the most important sources of clear air turbulence in the lower atmosphere it produces billows which mix and transport heat and materials vertically in the stably stratified atmosphere billows can also dissipate energy therefore they can affect the larger scale dynamics while only a few direct observations have been reported in the tropopause region in this work the authors report very detailed observations of billow structures around 16 km altitude in the upper part of the jet stream observations were made with very high frequency vhf band mid and upperatmosphere mu radar shigaraki japan 34 85 n 136 10 e whose height resolution was improved with a range imaging technique kh billow structures were observed for at least 2 h and were found to have horizontal wavelengths of about 5 3 km and vertical extents between 0 5 and 1 0 km analysis of wind and temperature profiles measured by radiosondes launched from nearby meteorological stations indicated the presence of nearly monochromatic disturbances likely due to a dominant inertia gravity wave igw superimposed on the background wind field the presence of the igw was also confirmed by analysis of wind profiles measured by the mu radar just before the kh billows were detected by the observations in range imaging mode the igw with vertical and horizontal wavelengths of about 3 5 and 600 km respectively may have been a direct radiation from the jet stream as suggested by recent works and likely played a major role in the onset of the observed kh instability

comment on basin inversion and fault reactivation in laboratory experiments a recent paper describing laboratory experiments on fault reactivation misinterprets the principles of scale models of physical systems by using inconsistent dimensionless ratios that determine the correspondence between model and nature for example the dimensionless stress ratio is not consistent with the dimensionless time ratio moreover consistent independent fundamental ratios of mass length and time cannot be derived from the values of the variables and constants known in both the model and nature consequently little information about the natural system can be derived from the model

observation of 3 6 day meridional wind oscillations over the tropical pacific 1973 1992 horizontal structure and propagation abstract twenty years of rawinsonde data 1973 1992 were examined in conjunction with european centre for medium range weather forecasts ecmwf analyses and outgoing longwave radiation olr in 1980 1989 to determine the horizontal structure propagation and convective coupling of 3 6 day meridional wind oscillations over the tropical pacific wave properties from ecmwf data determined by lag correlation with respect to rawinsonde or ecmwf principal components were consistent with what could be determined from the sparse rawinsonde network alone gridded analyses allowed a clearer distinction between equatorially trapped rossby gravity waves rgw and off equatorial tropical depression td disturbances so that the contrasting properties of these waves including their seasonal and interannual variation could be studied in better detail significant correlations with olr were found increasing in magnitude from eastern to western pacific the apparent group propagation of disturbances was equator

dynamic loading induced by the instability of voussoir beam structure during mining below the slope abstract dynamic loading events in the longwall faces under slopes in the shendong coalfield china seriously limit the safety and efficiency of mining the slope characteristics such as direction height and angle determine the load type and the stability of the voussoir beam structure vbs formed by fractured blocks of the primary key stratum pks whether or not dynamic loading events will occur can be directly determined based on the presence or absence of a stable vbs in the pks based on this relationship six structural mechanical vbs models for different load distributions were established and then the effects of the slope direction height and angle on the stability of vbs was analysed changes of load type intensified the compression force between the hinged blocks when the compression force between blocks exceeded the strength of the rock vbs instability and dynamic loading events occurred the compression force in the vbs increased with increasing slope angle and height when the slope directions were similar becoming more pronounced for mining under the uphill sections of the slopes therefore a method of determining the critical slope parameter values indicating a risk of dynamic loading was proposed enabling such slopes to be recognised in advance measures such as slope top cutting or backfilling can then be applied to prevent potential dynamic loading accidents this study can provide guidelines for safe mining under geological conditions involving widespread slopes and gullies

dynamic behaviour of mining induced fault slip abstract fault slip bursts induced by mining activities could inflict severe damage to nearby mine developments considering a variety of factors that might exert an influence on the fault slip dynamic numerical analyses are conducted for models having a fault parallel to a tabular ore deposit the results obtained from the analyses show that the maximum dynamic shear displacement increment induced by stope extraction is significantly affected by the friction angle of the fault as well as mining depth and position of fault with respect to the orebody while the stiffness and the dilation angle of the fault do not have as much influence seismic source parameters are computed based on the numerical results and as is the case with the maximum relative shear displacements the position and friction angle of the fault appear to have the strongest influence on seismic moment and energy released by fault slip the limitations of mohr coulomb criterion as applied to the dynamic analysis of fault slip bursts are discussed in light of the results obtained lastly slip rates and rupture velocity are investigated the results show that the maximum slip rates are associated with the maximum increments of relative dynamic shear displacement it is shown that extremely high rupture velocity could be induced by stope extraction this could be the cause for a severe seismic event

basin inversion and fault reactivation in laboratory experiments abstract a series of analogue models have been performed to get insights into the relationships between the reactivation of pre existing normal faults and the orientation of a successive compressive stress field the models were deformed in two phases 1 a first extension phase h 3 generating a graben and 2 a successive compressive phase with the orientation of the shortening direction h 1 trending between 0 and 90 obliquity angle to the faults bounding the graben the deepening of this graben was accompanied by syn tectonic sedimentation that included a basal ductile layer simulating salt in nature overlain by a brittle sand pack the experimental results suggest that the development of compressive structures is strongly controlled by the pre existing normal faults and by the obliquity angle the experiments have invariably shown that the extensional faults were reactivated during shortening whatever the value of the angle whereas strike slip reactivation of major normal faults is favoured by low obliquity angles mostly dip slip reactivation of pre existing structures is instead promoted for high obliquity angles the analysis of model results highlights the important role played by a ductile layer at the base of the basin fill and the obliquity angle in controlling both strain partitioning and brittle ductile decoupling

global characteristics of medium scale tropopausal waves observed in ecmwf operational data global characteristics and seasonal variation of medium scale zonal wavelengths of 2000 3000 km waves observed around the midlatitude tropopause are examined using 6 hourly european centre for medium range weather forecasts operational data over four years 1990 93 covering both hemispheres medium scale waves and synoptic scale waves are extracted using time filters and their characteristics are compared hovmoller diagrams indicate the existence of medium scale waves in the southern hemisphere as well as in the northern hemisphere the zonal wavelengths of medium scale waves are slightly larger in the southern hemisphere than in the northern hemisphere medium scale waves are mostly active in three regions the north atlantic in winter dec jan feb the north pacific in spring mar apr may mam and the south indian ocean in autumn mam these regions are roughly corresponding to and slightly downstream of storm tracks where synoptic waves are dominant significant differences in seasonal variation of the intensity between the two kinds of waves are also found the maximum of wave amplitudes is seen around the tropopause at latitudes slightly higher than the jet stream axis where the meridional gradient of the quasigeostrophic potential vorticity qpv is maximized the positive large qpv gradient is attributed to the atmospheric structure around the midlatitude tropopause that is located in vertical westerly shear of the jet stream this fact suggests that the medium scale waves are waves trapped around the midlatitude tropopause

investigation and analysis of the rock burst mechanism induced within fault pillars abstract an investigation is made of the characteristic strata movement and mechanism underlying fault pillar induced rock bursts fpirbs in order to mitigate rock burst damage in fault areas a mechanical analysis of the fault pillar model is established and roof rotation criteria is obtained a formula is derived for the average static stress in the pillar through theoretical analysis physical simulations and engineering practice the results show that when a coalface approaches a fault area two or more roof strata simultaneously fracture in the fault area leading to an increase in the dynamic and static stresses in the pillar the most important factors affecting fpirb are the static stress in the pillar and the dynamic stress induced by fault slides the roof block rotates more easily when the pillar width is smaller the roof thickness larger and the roof subsidence smaller the average static stress in the pillar increases with decreasing pillar width and or increasing roof fracture length the stress is greater if there is a voussoir beam structure in which case the stress is directly proportional to the squared length of the fractured roof and inversely proportional to the squared width of the pillar just before rotation occurs after rotation it is directly proportional to the roof fracture length and inversely proportional to the pillar width based on the fpirb mechanism and analysis of the mechanical model six methods of fpirb prevention are proposed also we find that fpirb occurrence can be effectively reduced by the use of de stress blasting and large diameter drilling

observation of 3 6 day meridional wind oscillations over the tropical pacific 1973 1992 vertical structure and interannual variability abstract rawinsonde data from tropical pacific stations were examined for westward propagating 3 6 day meridional wind oscillations in the troposphere and lower stratosphere 1973 1992 four types were identified from cross spectrum and principal component analysis 1 the dominant oscillation near 250 mb had a period slightly greater than 5 days zonal wavenumber 4 6 and modified rossby gravity structure near the date line 2 in the western pacific lower troposphere there was broadband activity with short zonal scale coupled to upper tropospheric waves in nh summer 3 in the central pacific during nh autumn there was a well defined 4 day oscillation with maximum amplitude in the lower troposphere and baroclinic phase tilt above the vertical structure suggested coupling to deep tropical convection this interpretation was supported by correlation of meridional wind with antisymmetric outgoing longwave radiation 4 in the stratosphere rossby gravity waves had periods 4 days and zonal wavenu

radiosonde observations of equatorial atmosphere dynamics over indonesia 1 equatorial waves and diurnal tides this paper describes the characteristics of the mean winds equatorial waves with periods ranging from 4 to 20 days and diurnal tides determined by analyzing the profiles of wind velocity temperature and humidity obtained every 5 7 hours in the height range up to about 35 km with a height resolution of 150 m during an observation campaign conducted february 27 to march 22 1990 in east java indonesia the structures of the mean winds in the troposphere and lower stratosphere seemed to be affected by the australian monsoon and the quasi biennial oscillation respectively frequency spectra indicated that the equatorial waves as well as the diurnal tides were dominant below about 25 km while gravity waves with periods shorter than 4 days became more significant above 25 km a 7 day oscillation showing an antiphase relation between the eastward and northward components and exhibiting large amplitudes was observed in the lower troposphere the time height variations of the activity of this 7 day oscillation were clearly correlated with a region of high relative humidity perturbations in the zonal wind and temperature with wave periods varying from 15 to 17 days were also enhanced in the troposphere while kelvin waves with periods of about 7 and 20 days were detected in the lower stratosphere and activity near the tropopause was conspicuously enhanced we found that the 20 day kelvin wave greatly modified the structure of the tropopause such as the minimum temperature the tropopause height and the values of the brunt vaisala frequency squared n2 which further suggests the effects of kelvin waves on the transportation of tropospheric water vapor into the stratosphere and on the downward mixing of stratospheric minor constituents into the troposphere the observed profiles of the diurnal oscillation were compared with those of a numerical model assuming only migrating tides which reasonably agreed above about 25 km below 25 km however the observed amplitudes were 1 1 5 m s exceeding those of the model about 10 times moreover the phase profiles involved fluctuations with small vertical scales suggesting interference by many nonmigrating tides with short vertical wavelengths

vertically stacked temperature disturbances near the equatorial stratopause as seen in cryogenic limb array etalon spectrometer data temperature data derived from the cryogenic limb array etalon spectrometer claes on board the upper atmosphere research satellite uars are used to investigate planetary scale temperature disturbances near the equatorial stratopause for january 1992 to may 1993 the disturbances are characterized by vertically stacked temperature extrema of alternating sign with a vertical scale of about 10 km and have a localized and stationary nature in the longitudinal direction with persistence of about 1 week these are nearly identical to so called pancake structures first identified by hitchman et al 1987 using data from the limb infrared monitor of the stratosphere lims their analysis suggested that pancake structures are consistent with those predicted by inertial instability theory and that their appearance is synchronized with strong planetary waves in the winter midlatitude though the lims observations were made only during the northern winter using the claes data for about 14 months this study shows that pancake structures occur not only during the northern winter but also during the southern winter in addition it is found that an equatorial pancake structure has its counterpart with reversed phase in the winter midlatitude suggesting clear evidence for inertial instability further analyses on the basis of ertel s potential vorticity show that inertially unstable regions intrude locally far into the winter hemisphere around pancake structures that appear when planetary wave breaking is going on this implies a mechanism of localized inertial instability and resulting pancake structures caused by midlatitude planetary waves in the winter hemisphere as some numerical studies have inferred