gravity data as a tool for landfill study this paper shows the potential of gravity data to map a buried landfill bottom topography to this end a gravity inversion method is presented for estimating the landfill s bottom depths at discrete points assuming a decrease of the density contrast with depth according to a hyperbolic law the method s efficiency was tested using synthetic data from simulated waste landfills producing estimated bottom topographies very close to the true ones the method s potentiality has been further evaluated in applying it to the gravity data from the abandoned thomas farm landfill site indiana usa whose bottom topography is known the estimated topography showed close agreement with the known thomas farm landfill s bottom topography

a snow transport model for complex terrain as part of the winter environment in middle and high latitude regions the interactions between wind vegetation topography and snowfall produce snow covers of non uniform depth and snow water equivalent distribution a physically based numerical snow transport model snowtran 3d is developed and used to simulate this three dimensional snow depth evolution over topographically variable terrain the mass transport model includes processes related to vegetation snow holding capacity topographic modification of wind speeds snow cover shear strength wind induced surface shear stress snow transport resulting from saltation and suspension snow accumulation and erosion and sublimation of the blowing and drifting snow the model simulates the cold season evolution of snow depth distribution when forced with inputs of vegetation type and topography and atmospheric foreings of air temperature humidity wind speed and direction and precipitation model outputs include the spatial and temporal evolution of snow depth resulting from variations in precipitation saltation and suspension transport and sublimation using 4 years of snow depth distribution observations from the foothills north of the brooks range in arctic alaska the model is found to simulate closely the observed snow depth distribution patterns and the interannual variability

automatic interpretation of gravity gradiometric data in two dimensions vertical gradient1 the magnetic and gravity field produced by a given homogeneous source are related through poisson s equation starting from this consideration it is shown that some 2d interpretation tools widely applied in the analysis of aeromagnetic data can also be used for the interpretation of gravity gradiometric data vertical gradient this paper deals specifically with the werner deconvolution analytic signal and euler s equation methods after a short outline of the mathematical development synthesized examples have been used to discuss the efficiency and limits of these interpretation methods these tools could be applied directly to airborne gravity gradiometric data as well as ground gravity surveys after transformation of the bouguer anomalies into vertical gradient anomalies an example is given of the application of the werner deconvolution and euler s equation methods to a microgravity survey

clustering of synoptic activity by indian summer monsoon intraseasonal oscillations 1 active and break phases of the indian summer monsoon are characterized by enhancement and decrease of precipitation over the monsoon trough region using genesis data of monsoon low pressure systems lps and circulation data for the period 1954 to 1993 it is shown that the frequency of occurrence of lps is nearly 3 5 times higher in the active phase of monsoon as compared to the break phase in addition the tracks of these synoptic systems are also strongly spatially clustered along the monsoon trough during the active phase of the monsoon the enhanced decreased frequency of occurrence of lps during active break phases is due to modulation of meridional shear of zonal winds and cyclonic vorticity along the monsoon trough by the intraseasonal oscillations iso

effects of zonal flows on equatorially trapped waves abstract linear shallow water equations are employed to study the effects of basic zonal flows on equatorially trapped waves analytical solutions are obtained for constant basic zonal flows it is shown that changes in the wave structures due to the non doppler effect of the basic zonal flow are considerable for the rossby wave moderate for the westward propagating mixed rossby gravity wave but negligible for the other equatorial waves the rossby wave and the westward propagating mixed rossby gravity wave possess greater eigenfrequencies and are less trapped in westerlies than in easterlies the dependence of the rossby wave structure upon the basic zonal flow is interpreted in terms of potential vorticity conservation in basic zonal flows with meridional shears the eigenfrequencies are found to be larger in equatorial easterlies than in equatorial westerlies for the westward propagating waves but smaller for the eastward propagating waves while the meridional structures of the eastward propagating

the indian monsoon and its variability for over 300 years the monsoon has been viewed as a gigantic land sea breeze it is shown in this paper that satellite and conventional observations support an alternative hypothesis which considers the monsoon as a manifestation of seasonal migration of the intertropical convergence zone itcz with the focus on the indian monsoon the mean seasonal pattern is described and why it is difficult to simulate it is discussed some facets of the intraseasonal variation such as active weak cycles break monsoon and a special feature of intraseasonal variation over the region namely poleward propagations of the itcz at intervals of 2 6 weeks are considered vertical moist stability is shown to be a key parameter in the variation of monthly convection over ocean and land as well as poleward propagations special features of the bay of bengal and the monsoon brought out by observations during a national observational experiment in 1999 are briefly described

coupling between northward propagating intraseasonal oscillations and sea surface temperature in the indian ocean using a hybrid atmosphere ocean coupled model it is shown that during the boreal summer northwardpropagating intraseasonal oscillations npisos are strongly coupled to the underlying sea surface temperature sst in the indian ocean sector on the one hand the intraseasonal atmospheric convection changes the sst through solar radiation latent heat flux and mixed layer entrainment on the other the induced sst fluctuations feed back to affect the intraseasonal convection the preferential northward rather than southward propagation of boreal summer isos in the indian ocean is partially explained by an interaction among the summer mean climate state the atmospheric disturbances and the ocean surface temperature a solution to an atmosphere only model forced with daily sst produces much stronger npisos than a similar solution forced with monthly mean sst amip type run the atmosphere only model however even when it is forced by daily sst from the coupled model with a small amount of noise in the initial and or boundary conditions is unable to reproduce the npisos in the coupled case in the coupled system intraseasonal sst anomalies are forced by intraseasonal atmospheric convection and hence are in quadrature with the convection in the stand alone atmospheric model however sst acts only as a boundary forcing and the resultant atmospheric convection has almost the same phase with the underlying sst one consequence is that the intensity of the sst forced intraseasonal convection in the stand alone atmospheric model is considerably weaker than in the coupled model finally solutions indicate that the northward movement of the off equatorial convection in the northern indian ocean is more closely related to local intraseasonal sst anomalies than to the equatorial eastward moving madden julian oscillation positive negative sst anomalies in the northern indian ocean lead the active break phases of the intraseasonal convection by about 2 pentads 10 days therefore intraseasonal sst anomalies in the northern indian ocean are potentially a useful index to forecast active break spells of the south asian summer monsoon

dependence of simulation of boreal summer tropical intraseasonal oscillations on the simulation of seasonal mean the link between realism in simulation of the seasonal mean precipitation and summer tropical intraseasonal oscillations and their dependence on cumulus parameterization schemes is investigated using the florida state university global spectral model fsugsm forty member model ensemble simulations of the northern summer season are generated for three different cumulus parameterization schemes namely arakawa schubert naval research laboratory nrl zhang and mcfarlane national center for atmospheric research ncar and emanuel massachusetts institute of technology mit the mit scheme simulates the regional pattern of seasonal mean precipitation over the indian monsoon region well but has large systematic bias in simulating the precipitation over the western pacific and the maritime continent although the simulation of details of regional distribution of precipitation over the indian monsoon region by the nrl and ncar schemes is not accurate they simulate the spatial pattern of precipitation over the tropical indo pacific domain closer to observation the nrl scheme seems to captures the observed northward and eastward propagation of intraseasonal precipitation anomalies realistically however the simulations of the ncar and mit schemes are dominated by a westward propagating component the westward propagating mode seen in the model as well as observations is indicated to be an equatorial rossby wave modified by the northern summer mean flow an examination of the relationship between simulation of the model climatology and eastward propagating character of monsoon intraseasonal oscillations isos in a limited sample shows that the scheme that simulates better seasonal mean pattern of rainfall over the tropical indo pacific domain also simulates better intraseasonal variance and more realistic eastward propagation of monsoon isos among the parameters known to be important for meridional propagation of the summer monsoon isos the meridional gradient of mean humidity in the lower atmosphere seems to be crucial in determining the northward propagation in the equatorial indian ocean between 10 s and 10 n for better prediction of the seasonal mean indian monsoon therefore the model climatology should have minimum bias not only over the indian monsoon region but also over the entire indo pacific basin

high resolution simulation of the boreal summer intraseasonal oscillation in met office unified model the present study investigates the fidelity and resolution sensitivity of met office unified model global atmosphere 3 0 in simulating the intra seasonal oscillation iso of the east asia and western north pacific summer monsoon two sets of model simulations at horizontal resolutions of n216 60km and n96 130km forced by observed daily high resolution sea surface temperature are examined and compared with the observations diagnostic results show that the model can well reproduce the gross spatio temporal features of observed summer iso over the east asia and western north pacific in terms of period dominant reof mode variance northward propagation cycle evolution and vertical structure the intra seasonal change in intensity and position of western north pacific subtropical high and upper troposphere westerly jet associated with the northward propagating isos are also reasonably captured in the model moreover increasing horizontal resolution improves most aspects of the iso simulation especially the intensity and northward propagation of the iso related convection and circulation systems further analysis indicates that the improvement as resolution increases is related to the weakening in background state of east asian summer monsoon which is due to the realistic simulation of land sea thermal contrast at higher resolution model this study suggests that enhanced model resolution can have some beneficial impacts on the iso simulation

quasi periodic oscillations in a symmetric general circulation model abstract long lime integrations with a symmetric version of the clas climate model with hydrology have shown that the hadley circulation has well defined strong and weak episodes this oscillation of the hadley circulation seems to occur in two dominant range of periodicities one with periods between 10 and 15 days and another with periods between 20 and 40 days this quasi periodic behavior of the hadley circulation is seen only when the moist convective heating is determined by dynamics if the latent beating in the atmosphere is prescribed and kept artificially fixed this oscillation of the hadley circulation disappears thus this oscillation of the hadley circulation appears as a result of interactions between moist convective and dynamical processes a wave phenomenon is seen in the lower atmosphere that propagates toward the position of maximum radiative beating this wave perturbation has a length scale of about 15 20 degrees latitude in the north south direction this phenomenon has large ampli

the 10 20 day mode of the 1979 indian monsoon its relation with the time variation of monsoon rainfall abstract the synoptic structure of the 10 20 day monsoon mode and this intraseasonal monsoon mode s relationship with the indian monsoon rainfall are examined with the 1979 summer first garp global experiment iiib data of the european centre for medium range weather forecasts and the daily 1 1 rainfall estimates retrieved from the satellite data by the goddard laboratory for atmospheres the major findings of this study are as follows 1 the 10 20 day monsoon mode exhibits a double cell either double high or double low structure one cell is centered at about 15 20 n and the other at the equator 2 both cells of the 10 20 day monsoon mode propagate coherently westward along the indian monsoon trough and along the equator respectively 3 based upon the zonal wind and local hadley circulation the vertical structure of the 10 20 day monsoon mode does not exhibit a phase change 4 a significant rainfall occurs around low centers of the 10 20 day monsoon mode through the modulation of this monsoon

understanding the gravity response variability of sedimentary basins using forward stratigraphic modelling abstract it is accepted that gravity inversions are non unique and that multiple models will fit the data equally well over sedimentary basins this implies that gravity anomalies can be equally well explained by sedimentary strata with constant densities over a highly heterogeneous basement or by highly heterogeneous sedimentary strata over a constant density basement while both scenarios minimise the difference between the predicted and observed gravity signal neither are geologically plausible in this work we explore stratigraphic modelling as a new parameterisation for gravity models by using a process based numerical simulation to generate the sedimentary basins density models we seek to focus only on geologically plausible models we then study the variability of the sedimentary strata s gravity response i e the range of possible geophysical signatures to stratigraphic parameter changes results from a study of a 2d section in the northern carnarvon basin the northwest shelf of australia emphasize that even when the stratigraphic models are trialled using a wide range of input parameters the simulated gravity response still has a limited variability when compared to model results generated using other parameterisations lastly our results provide insights into the global sensitivity of the gravity response highlighting the sedimentary and stratigraphic parameters that most affect the geophysical signal allowing for a discussion of the geologic and stratigraphic controls of the sedimentary basin s gravity response

horizontal and vertical structure of observed tropospheric equatorial rossby waves equatorial rossby er waves are identified in an 8 year data set of national meteorological center operational analyses the westward moving waves have symmetric circulations about the equator and eastward energy dispersion with maximum zonal wind perturbations along the equator and meridional wind maxima roughly 10 15 off the equator they have maximum amplitude in the lower troposphere and are associated with convective signals at roughly the mean latitude of the tropical convergence zones the circulations thus possess many of the features of the equatorially trapped n 1 rossby modes derived by matsuno 1966 they are generally around zonal planetary wavenumber 6 scale and have a deep nearly equivalent barotropic structure up to 100 mbar this is in contrast with the madden julian oscillation and mixed rossby gravity waves which generally have a first baroclinic mode vertical structure during the intensive observing period iop of the tropical ocean global atmosphere toga coupled ocean atmosphere response experiment coare and in other years westward propagating er disturbances along the equator are observed by using 6 to 30 day filtered circulation data at 850 mbar zonal wind anomalies at 850 mbar are preferentially associated with like signed anomalies in a deep layer at this frequency as was observed during coare the er waves are most common during northern winter in the central pacific although they can be detected sporadically over the other ocean basins and in other seasons as well one source for the equatorial rossby waves appears to be upper level extratropical rossby wave activity propagating into the eastern pacific although the equatorial waves are sometimes present during the northern summer when the extratropical source is absent we cite evidence that propagation of er wave activity from the central into the western pacific is related to occurrences of westerly wind bursts

simultaneous 3d depth to basement and density contrast estimates using gravity data and depth control at few points we have developed a gravity inversion method for simultaneouslyestimatingthe3dbasementreliefofasedimentary basin and the parameters defining a presumed parabolic decay of the density contrast with depth in a sedimentary pack assumingpriorknowledgeaboutthebasementdepthatafew points thesedimentarypackisapproximatedbyagridof3d vertical prisms juxtaposed in both horizontal directions of a right handed coordinate system the prisms thicknesses representthedepthstothebasementandaretheparametersto be estimated from the gravity data to estimate the parameters defining the parabolic decay of the density contrast with depthandtoproducestabledepth to basementestimates we imposed smoothness on the basement depths and proximity between estimated and known depths at boreholes we applied our method to synthetic data from a simulated complex 3d basement relief with two sedimentary sections having distinct parabolic laws describing the density contrast variationwithdepth theresultsprovidegoodestimatesofthetrue parameters of the parabolic law of density contrast decay with depth and of the basement relief inverting the gravity data from the onshore and part of the shallow offshore almadabasinonbrazil snortheasterncoastshowsgoodcorrelationwithknownstructuralfeatures

diabatic heating profiles over the continental convergence zone during the monsoon active spells the present paper aims to bring out the robust common aspects of spatio temporal evolution of diabatic heating during the monsoon intraseasonal active phases over the continental tropical convergence zone ctcz the robustness of spatio temporal features is determined by comparing the two state of the art reanalyses ncep climate forecast system reanalysis and modern era retrospective analysis the inter comparison is based on a study period of 26 years 1984 2009 the study confirms the development of deep heating over the ctcz region during the active phase and is consistent between the two datasets however the detailed temporal evolution of the vertical structure e g vertical tilts of heating differs at times the most important common feature from both the datasets is the significant vertical redistribution of heating with the development of shallow low level heating and circulation over the ctcz region 3 7 days after the peak active phase the shallow circulation is found to be associated with increased vertical shear and relative vorticity over certain regions in the subcontinent this increased vertical shear and relative vorticity in the lower levels could be crucial in the sustenance of rainfall after the peak active phase model experiments with linear dynamics affirm the role of shallow convection in increasing the lower level circulation as observed

deep pass an aeromagnetic data filter to enhance deep features in marginal basins abstractan aeromagnetic data filter was tested as a tool in enhancing the magnetic responses of deep sources associated with marginal basins our approach consists in amplifying the responses of magnetic sources which extend through the continental slope and continental rise this amplification compensates for the magnetic response attenuation over the continental slope as a result of 1 the seaward increase of the distance between the source and the magnetometer and 2 the seaward decrease in the volume of sources within the continental crust to amplify the source response we multiply the total field anomaly at a given location by the exponential of the bathymetric depth at the same point tests on synthetic and real data showed that the filter was able to recover the locations of linear magnetic responses not clearly seen in the total field anomaly map when compared with the analytic signal amplitude and the total horizontal derivative filters the proposed filter proved to be complementary in enha

3 d seismic attributes using a semblance based coherency algorithm seismic coherency is a measure of lateral changes in the seismic response caused by variation in structure stratigraphy lithology porosity and the presence of hydrocarbons unlike shaded relief maps that allow 3 d visualization of faults and channels from horizon picks seismic coherency operates on the seismic data itself and is therefore unencumbered by interpreter or automatic picker biases we present a more robust multitrace semblance based coherency algorithm that allows us to analyze data of lesser quality than our original three trace cross correlation based algorithm this second generation semblance based coherency algorithm provides improved vertical resolution over our original zero mean crosscorrelation algorithm resulting in reduced mixing of overlying or underlying stratigraphic features in general we analyze stratigraphic features using as narrow a temporal analysis window as possible typically determined by the highest usable frequency in the input seismic data in the limit one may confidently apply our new semblance based algorithm to a one sample thick seismic volume extracted along a conventionally picked stratigraphic horizon corresponding to a peak or trough whose amplitudes lie sufficiently above the ambient seismic noise in contrast near vertical structural features such as faults are better enhanced when using a longer temporal analysis window corresponding to the lowest usable frequency in the input data the calculation of reflector dip azimuth throughout the data volume allows us to generalize the calculation of conventional complex trace attributes including envelope phase frequency and bandwidth to the calculation of complex reflector attributes generated by slant stacking the input data along the reflector dip within the coherency analysis window these more robust complex reflector attribute cubes can be combined with coherency and dip azimuth cubes using conventional geostatistical clustering and segmentation algorithms to provide an integrated multiattribute analysis

influence of indian ocean dipole on poleward propagation of boreal summer intraseasonal oscillations abstract the influence of the indian ocean dipole iod on the poleward propagation of boreal summer intraseasonal oscillations bsisos is examined using observed datasets this study finds that coherent incoherent poleward propagation of precipitation anomalies from 5 s to 25 n are observed during negative positive iod years disorganized poleward propagation of bsiso in the south equatorial indian ocean is observed during positive iod years the rationale behind such an anomaly in the poleward propagation of bsiso in contrasting iod years is identified based on the theory of northward propagating bsiso which suggests the influential role of air sea interaction on the genesis and propagation of bsiso it is found that the mean structure of moisture convergence and meridional specific humidity distribution undergoes radical changes in contrasting iod years which in turn influences the meridional propagation of bsiso this study assumes significance considering the critical role of bsiso in modulat

remote influences on the indian monsoon low level jet intraseasonal variations a strong low level jet llj also known as the findlater jet develops over the arabian sea during the indian summer monsoon this jet is an essential source of moisture for monsoonal rainfall over the densely populated indian subcontinent and is a key contributor to the indian ocean oceanic productivity by sustaining the western arabian sea upwelling systems the llj intensity fluctuates intraseasonally within the 20 to 90 day band in relation with the northward propagating active and break phases of the indian summer monsoon our observational analyses reveal that these large scale regional convective perturbations only explain about half of the intraseasonal llj variance the other half being unrelated to large scale convective perturbations over the indian ocean we show that convective fluctuations in two regions outside the indian ocean can remotely force a llj intensification four days later enhanced atmospheric deep convection over the northwestern tropical pacific yields westerly wind anomalies that propagate westward to the arabian sea as baroclinic atmospheric rossby waves suppressed convection over the eastern pacific north american monsoon region yields westerly wind anomalies that propagate eastward to the indian ocean as dry baroclinic equatorial kelvin waves those largely independent remote influences jointly explain 40 of the intraseasonal llj variance that is not related to convective perturbations over the indian ocean i e 20 of the total with the northwestern pacific contributing twice as much as the eastern pacific taking into account these two remote influences should thus enhance the ability to predict the llj

a mechanism of scale selection in tropical circulation at observed intraseasonal frequencies abstract it is shown in this work that two prominent intraseasonal oscillations of the tropical atmosphere namely the 3 4 day westward propagating wave observed over the equatorial atlantic and pacific oceans and the quasibiweekly or 10 20 day oscillation observed over the indian ocean summer monsoon region can be understood as arising from selective excitation of the tropical normal modes in the presence of moist feedbacks and a moisture relaxation timescale unlike in earlier studies of a similar nature the central theme of the present work is that the dynamics of the moisture variable is governed by a moisture relaxation timescale in other words the large scale flow is not in exact quasi equilibrium with the precipitational heating the implications of this hypothesis are investigated by using a shallow water model of the tropical atmosphere on an equatorial plane with a fixed vertical structure the two major findings of the present work are 1 both the 3 4 day wave and the 10 20 day wave

structure and characteristics of submonthly scale waves along the indian ocean itcz this study examines wave disturbances on submonthly 6 30 day timescales over the tropical indian ocean during southern hemisphere summer using japanese reanalysis jra25 jcdas products and national oceanic and atmospheric administration outgoing longwave radiation data the analysis period is december february for the 29 years from 1979 1980 through 2007 2008 an extended empirical orthogonal function eeof analysis of daily 850 hpa meridional wind anomalies reveals a well organized wave train pattern as a dominant mode of variability over the tropical indian ocean daily lagged composite analyses for various atmospheric variables based on the eeof result show the structure and evolution of a wave train consisting of meridionally elongated troughs and ridges along the indian ocean intertropical convergence zone itcz the wave train is oriented in a northeast southwest direction from sumatra toward madagascar the waves have zonal wavelengths of about 3 000 5 000 km and exhibit westward and southwestward phase propagation individual troughs and ridges as part of the wave train sequentially travel westward and southwestward from the west of sumatra into madagascar meanwhile eastward and northeastward amplification of the wave train occurs associated with the successive growth of new troughs and ridges over the equatorial eastern indian ocean this could be induced by eastward and northeastward wave energy dispersion from the southwestern to eastern indian ocean along the mean monsoon westerly flow in addition the waves modulate the itcz convection correlation statistics show the average behavior of the wave disturbances over the tropical indian ocean these statistics and other diagnostic measures are used to characterize the waves obtained from the composite analysis the waves appear to be connected to the monsoon westerly flow the waves tend to propagate through a band of the large meridional gradient of absolute vorticity produced by the mean monsoon westerly flow this suggests that the monsoon westerly flow provides favorable background conditions for the propagation and maintenance of the waves and acts as a waveguide over the tropical indian ocean the horizontal structure of the wave train may be interpreted as that of a mixture of equatorial rossby waves and mixed rossby gravity wavelike gyres

low frequency equatorial waves in vertically sheared zonal flow part i stable waves abstract the mechanism by which a vertically sheared zonal flow affects large scale low frequency equatorial waves is investigated with two level equatorial plane and spherical coordinates models vertical shears couple barolinic and barotropic components of equatorial wave motion affecting significantly the rossby wave and westward propagating yanai wave but not the kelvin wave this difference results from the fact that the barotropic component is a modified rossby mode and can be resonantly excited only by westward propagating internal waves the barotropic components emanate poleward into the extratropics with a pronounced amplitude while the baroclinic components remain equatorially trapped a westerly vertical shear favors the trapping of rossby and yanai waves in the upper troposphere whereas an easterly shear tends to confine them in the lower troposphere as such their westward propagation is slowed down by both westerly and easterly shears when the strength of the vertical shear varies w

detection of subtle basement faults with gravity and magnetic data in the alberta basin canada a data use tutorial editor s note this paper is based on a presentation at the 2003 canadian society of petroleum geologists canadian society of exploration geophysicists joint convention in calgary exploration for a wide range of mineral deposits is critically dependent on knowledge of the location and age of fractures and faults oil and gas fields in many sedimentary basins are distributed along fault controlled linear trends and fault identification is often used effectively for target area selection in hydrocarbon exploration similarly mineral deposits in various geologic settings are commonly associated with fluid conducting faults in the platformal phanerozoic alberta sedimentary basin in western canada figure 1 two fundamentally different types of crystalline basement structure formed in different tectonic conditions are recognized lyatsky et al 1999 figure 1 location of the northern alberta study area in relation to main regional geologic features 1 archean and early proterozoic hudsonian and older ductile orogenic structures and 2 middle proterozoic to recent cratonic ones the influence of ancient ductile structures on the alberta basin seems largely confined to the control on early paleozoic depositional and drape patterns by the precambrian erosional basement relief which may to some extent be related to the basement lithology distribution controlled by ductile ancient structures these structures were mostly healed and innactive during the phanerozoic development and evolution of the alberta basin and thus of limited significance to fluid migration their geophysical expression typically consists of large magnetic and gravity anomalies which often obscure the potential field signatures of the desirable brittle faults the steep brittle basement faults in the western canadian platforms and cordilleran foreland although much more subtle than their spectacular counterparts in western united states exerted considerable syn and postdepositional influence on the phanerozoic sedimentary cover occasionally brittle faults and fractures follow the older orogenic basement structures but commonly cut across them even when subresolution seismically many

active break cycles diagnosis of the intraseasonal variability of the asian summer monsoon in this study various diagnostics have been applied to daily observed outgoing longwave radiation olr and ecmwf reanalysis era products to provide a comprehensive description of the active break cycles associated with the asian summer monsoon and to address the differing behaviour of the two dominant time scales of intraseasonal variability 10 20 days and 30 60 days composite analysis of olr based on filtered daily all india rainfall air for the 40 day 30 60 days intraseasonal mode indicates that during active phases convection is significantly enhanced over the indian continent extending over the bay of bengal maritime continent and equatorial west pacific while convection is suppressed over the equatorial indian ocean and northwest tropical pacific resulting in a quadrapole structure over the asian monsoon domain in response to this heating pattern the large scale hadley lateral and the two east west transverse tropical circulations are enhanced there is also a significant impact on the extra tropical circulation through excitation and propagation of rossby waves in contrast the 15 day mode is more regional to the monsoon domain and has a prominent east west orientation in convection only the local hadley circulation over the monsoon region is modulated by this mode the evolution of these two modes as revealed by pop principal oscillation pattern analysis shows that the 40 day mode originates over the equatorial indian ocean once formed it has poleward propagation on either side of the equator and eastward propagation into the equatorial west pacific from the equatorial west pacific northward propagation over the west pacific and westward propagation into the indian longitudes are prominent the propagative features are complex and interactive and are responsible for the quadrapole structure in convection seen from the composites the interannual variability assessed from the pop coefficient time series indicates that the 40 day mode is strong during the onset phase of the monsoon in all the years but systematic propagation over the entire season depends crucially on the activity of the oceanic tcz tropical convergence zone the pop analysis of the 15 day mode indicates that this event originates over the equatorial west pacific associated with westward propagating rossby waves amplifies over the northwest tropical pacific and modulates both the continental and oceanic tczs over indian longitudes simultaneously this mode is pronounced during the established phase of the monsoon due to the complexity in the propagational features of both the intraseasonal modes it is concluded that understanding the subseasonal variability of one regional component of the asian summer monsoon asm requires understanding the entire asm system

interaction between the summer monsoons in east asia and the south china sea intraseasonal monsoon modes abstract the summer monsoons in east and southeast asia are characterized respectively by the mei yu in eastern china baiu in japan front mbf and by the monsoon trough stretching from northern indochina to the philippine sea these two major monsoon elements are separated by the north pacific anticyclone as indicated by the 850 mb zonal wind and cumulus convection over some key areas a distinct opposite phase intraseasonal variation exists between the two monsoon elements two approaches are adopted to explore the cause of this opposite phase variation which reflects the coupling between the two monsoon components 1 the correlation coefficient patterns between the 850 mb zonal wind monsoon index and the 850 mb streamfunction field and 2 the composite 850 mb streamline charts and the 120 e zonal wind cross sections it is shown that the opposite phase variation between the two monsoon elements is caused by the anomalous circulation associated with the northward migrating 30 60 day monsoon tr

causes of intraseasonal diabatic heating variability over and near the tibetan plateau in boreal summer the structure and evolution features of the first two leading modes of the intraseasonal diabatic heating variability over the tibetan plateau tp during northern summer are investigated using reanalysis and observational data both of the leading modes present a dominant 10 30 day intraseasonal oscillation iso the first mode is characterized by a perturbation center over the southern tp stp which remains quasi stationary and is closely related to the low latitude iso the associated low latitude iso is originated from the tropical western pacific wp and propagates westward northwestward toward northwestern india along the mean monsoon trough the westward propagation near the south china sea is mainly attributed to anomalous meridional vorticity advection and the advection of the planetary vorticity by iso flow the stationary feature of the perturbation over the stp is ascribed to the topographical features around the stp the intraseasonal heating variability over the stp is attributed to the alternation of anticyclonic and cyclonic flow associated with the westward propagating iso perturbation originated from the tropical wp the second leading mode is characterized by an east west asymmetric structure over the tp the intraseasonal diabatic heating anomaly propagates clockwise from the northwestern to eastern tp while a heating anomaly with an opposite sign propagates from the southeastern to western tp the mid latitude rossby wave trains play an essential role in forming the dipole structure the wave trains propagate southeastward before reaching the tp and then eastward as they cross the tp the source of anomalous water vapor over the tp is originated from lower latitudes the upper and lower level wave trains are well coupled over the tp exhibiting a baroclinic structure

an analysis of convectively coupled kelvin waves in 20 wcrp cmip3 global coupled climate models abstract output from 20 coupled global climate models is analyzed to determine whether convectively coupled kelvin waves exist in the models and if so how their horizontal and vertical structures compare to observations model data are obtained from the world climate research program s wcrp s coupled model intercomparison project phase 3 cmip3 multimodel dataset ten of the 20 models contain spectral peaks in precipitation in the kelvin wave band and of these 10 only 5 contain wave activity distributions and three dimensional wave structures that resemble the observations thus the majority 75 of the global climate models surveyed do not accurately represent convectively coupled kelvin waves one of the primary sources of submonthly zonally propagating variability in the tropics the primary feature common to the five successful models is the convective parameterization three of the five models use the tiedtke nordeng convective scheme while the other two utilize the pan and randall scheme

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

mesozoic break up of sw gondwana implications for regional hydrocarbon potential of the southern south atlantic abstract this work provides new palinspastic palaeofacies reconstructions of sw gondwana incorporating rotation of a falkland malvinas microplate we discuss the implications of this for the tectonic evolution of the southern south atlantic and hence for the regional hydrocarbon potential existing gondwana reconstructions display good fits of major continents but poorly constrained fits of microcontinents in most continental reconstructions the falkland malvinas plateau was assumed to be a rigid fragment of pre permian south american crust however it has been suggested on the basis of palaeomagnetic data that the falkland malvinas islands were rotated by 180 after 190 ma this rotation hypothesis has been successfully tested on the basis of devonian stratigraphy and palaeontology permian stratigraphy and sedimentology and late palaeozoic and early mesozoic structure making it unlikely that the plateau behaved as a rigid structure during breakup we have explored the consequences of accepting this hypothesis for the tectonic evolution of sw gondwana by compiling new palaeogeographic maps for the permian cretaceous of the southern atlantic area to achieve a realistic close fit we have devised a pre rift proxy for the ocean continent boundary for the south atlantic in order to produce the best fit it is necessary to subdivide south america into four plates the consequences of this are far reaching our work suggests that although sedimentary basins were initiated at different times three major tectonic phases can be recognised in regional terms these can be thought of as pre syn and post rift during the pre rift time until the late triassic the area was dominated by compressional tectonism and formed part of the gondwana foreland the falkland malvinas islands lay east of africa the falkland malvinas plateau was 33 shorter and patagonia was displaced east with respect to the rest of south america in part along the line of the gastre fault system potential source facies are dominantly post glacial black shales of late permian age deposited in lacustrine or hyposaline marine environments these rocks would also be an effective regional seal sandstones deposited in the late permian would be dominantly volcaniclastic with poor reservoir qualities triassic sandstones tend to be more mature there was significant extension from about 210 ma end triassic until the south atlantic opened at about 130 ma early cretaceous in the early syn rift phase extension was accompanied by strike slip faulting and block rotation later extension was accompanied by extrusion of large volumes of lava early opening of the south atlantic was oblique which created basins at high angle to the trend of the ocean on the argentine margin and resulted in microplate rotation in ne brazil intermittent physical barriers controlled deposition of upper jurassic cretaceous anoxic sediments during breakup some of these mudrock units are effective seals with likely regional extent during crustal reorganisation clastic sediments changed from a uniform volcaniclastic provenance to local derivation with variable reservoir quality in the late rift and early post rift phase continental extension changed from oblique to normal and basins developed parallel to the continental margins of the south atlantic this change coincides with the main rifting in the equatorial basins of brazil and the early impact of the santa helena plume it resulted in widespread development of unconformities the abandonment of the reconcavo tucano jatoba rift and the end of ne brazil plate rotation which remained attached to south america there was extensive deposition of evaporites concentrated in but not restricted to the area north of the rio grande rise walvis ridge widespread deposits can be used to define potential regional elements of hydrocarbon systems and to provide a framework for relating more local elements our main conclusion is that the regional hydrocarbon potential of the southern south atlantic has been constrained by the tectonic evolution

entrainment rayleigh friction and boundary layer winds over the tropical pacific abstract winds over the tropical pacific are interpreted using mixed layer theory the theory which posits that the surface winds can be derived in terms of a force balance among surface drag pressure gradients coriolis forces and the vertical mixing of momentum into the boundary layer entrainment is very successful in predicting the seasonal climatology of the surface winds the model is also used as a basis for interpreting previous results in particular the model illustrates why studies that model the momentum flux divergence as a rayleigh damping find optimal damping coefficients that are anisotropic a linear variant of the model which also incorporates entrainment but neglects the quadratic relation between the wind speed and the surface stress is also found to predict the surface winds skillfully in addition to improving the representation of the winds it leads to realistic representations of the divergence of the vector wind if the key parameters of the model the entrainment rate and t

total variation regularization for depth to basement estimate part 1 mathematical details and applications we have developed an inversion approach that estimates the basement relief of a fault bounded sedimentary basin the sedimentary pack is approximated by a grid of 3d or 2d vertical prisms juxtaposed in the horizontal directions of a right handed coordinate system the prisms thicknesses represent the depths to the basement and are the parameters to be estimated from the gravity data to obtain depth to basement estimates we introduce the total variation tv regularization as a stabilizing function this approach lets us estimate a nonsmooth basement relief because it does not penalize sharp features of the solution we have deduced a compact matrix form of the gradient vector and the hessian matrix of the approximation to the tv function that allows a regularized gauss newton minimization approach because the hessian matrix of the approximation to the tv function is ill conditioned we have modified this hessian matrix to improve its condition and to accelerate the convergence of the gauss newton algorithm tests conducted with synthetic data show that the inversion method can delineate discontinuous basements presenting large slips or sequences of small slip step faults tests on field data from the almada basin brazil and from the san jacinto graben california u s a confirm the potential of the method in detecting and locating in depth normal faults in the basement relief of a sedimentary basin

the role of inertial instability in determining the location and strength of near equatorial convection there are two major organized cloud configurations in the vicinity of the equator where there is a small cross equatorial surface pressure gradient convection is close to the equator and is generally tied to the location of the lowest sea level pressure slp and warmest sea surface temperature sst in agreement with arguments based upon simple thermodynamical considerations however when there is a substantial cross equatorial pressure gradient such as occurs in the monsoon regions organized convection appears off the equator in the summer hemisphere equatorward of the slp minimum and not necessarily collocated with the warmest ssts thus in this instance simple thermodynamical considerations alone cannot explain 2he location of the convection in this situation the zero absolute vorticity contour 0 also lies in the summer hemisphere therefore between the equator and the 0 contour is a region of locally anticyclonic absolute vorticity and an inertially unstable regime it is argued that the convection results from the low level divergence convergence doublet centred about the 0 contour which is the mitigating response to the inertial instability the associated latitude height secondary circulation should provide subsidence suppressed convection over the equator and rising motion enhanced convection to the north of the zero absolute vorticity contour signatures of the inertial instability predicted by theory are found in observations supporting the hypothesis wherever a strong cross equatorial pressure gradient exists the 0 contour bisects a maximum in the divergent wind field divergence is found equatorward of the zero contour and convergence on the poleward side latitude height cross sections show strong local meridional circulations with maximum rising motion on the poleward side of 0 as the regions where the rising motions occur are conditionally unstable there is deep convection and the vertical circulations extend throughout the troposphere it is noted that the intensity of the off equator convection is deeper and probably stronger than convection located at the equator this is probably because the convection associated with the inertial instability is more efficient necessary conditions for the location of near equatorial convection are listed arguments are presented whereby inertial instability is established as the cause rather than an effect of off equatorial convection these include an outline of the sequence of processes leading up to the convection the factors that limit the encroachment of the 0 contour into the summer hemisphere are discussed and an explanation for the existence of the low level westerly monsoon wind maximum is suggested the possible role played by the instability mechanism or the lack of it in coupled model simulations that produce seasonally migrating and or double itczs in the eastern pacific ocean is discussed finally it is proposed that the instability mechanism is important in the initiation of westward moving disturbances found in the eastern pacific and in determining active and break periods in the summer indian monsoon

simulation of monsoon intraseasonal oscillations in a coarse resolution aquaplanet gcm the skill of the global climate models gcms to realistically simulate the monsoon intraseasonal oscillations misos is related to the sensitivity of their convective parameterization schemes here we show that by coupling a simple multicloud parameterization to a coarse resolution aquaplanet gcm realistic misos can be simulated we conduct three different simulations with a fixed nonhomogeneous sea surface temperature mimicking the indian ocean western pacific warm pool wp centered at the three latitudes 5 n 10 n and 15 n respectively to replicate the seasonal migration of the tropical convergence zone tcz this results in the generation of mean circulation resembling the monsoonal flow pattern in boreal summer succession of eastward propagating madden julian oscillation mjo disturbances with phase speed amplitude and structure similar to summer mjos are simulated when the wp is at 5 n when the wp is located over 10 n northward and eastward propagating misos are simulated this case captures the meridional seesaw of convection between continental and oceanic tcz observed during boreal summer over south asia westward propagating rossby wave like disturbances are simulated when the wp is over 15 n congruous with the synoptic disturbances seen over the monsoon trough the initiation of intraseasonal oscillations in the model can occur internally through organization of convective events above the wp associated with internal dynamics

instruments and methods simulating complex snow distributions in windy environments using snowtran 3d we present a generalized version of snowtran 3d version 2 0 that simulates wind related snow distributions over the range of topographic and climatic environments found globally this version includes three primary enhancements to the original liston and sturm 1998 model 1 an improved wind sub model 2 a two layer sub model describing the spatial and temporal evolution of friction velocity that must be exceeded to transport snow the threshold friction velocity and 3 implementation of a three dimensional equilibrium drift profile sub model that forces snowtran 3d snow accumulations to duplicate observed drift profiles these three sub models allow snowtran 3d to simulate snow transport processes in variable topography and different snow climates in addition snowtran 3d has been coupled to a high resolution spatially distributed meteorological model micromet to provide more realistic atmospheric forcing data micromet distributes data precipi tation wind speed and direction air temperature and relative humidity obtained from meteorological stations and or atmospheric models located within or near the simulation domain snowtran 3d has also been coupled to a spatially distributed energy and mass balance snow evolution modeling system snowmodel designed for application in any landscape and climate where snow is found snowtran 3d is typically run using temporal increments ranging from 1 hour to 1 day horizontal grid increments ranging from 1 to 100 m and time spans ranging from individual storms to entire snow seasons

role of the atmospheric mean state on the initiation of the madden julian oscillation in a tropical channel model tropical channel models defined as models that are global in the zonal direction but bounded in the meridional direction are particularly useful for simulating the madden julian oscillation mjo and understanding its physical and dynamical basis influences from the extratropics through the lateral boundaries have been found to be essential to the reproduction of the initiation of certain mjo events this led to a hypothesis that multi year simulations using a tropical channel model would reproduce reasonable mjo statistics under the influence of prescribed lateral boundary conditions derived from global reanalyses interestingly the mjo statistics in such a multi year simulation by a high resolution tropical channel model are not better than those from global climate models the error in the atmospheric mean state is found to be a possible reason for the poor mjo statistics in the simulation nevertheless even with a large error in the mean state the multi year simulation captures two mjo events previously found to be initiated by extratropical influences however the model does not reproduce a third event whose initiation is not directly influenced by the extratropics this implies that in the absence of dynamical interactions between the mjo and the lateral boundary conditions the error in the mean state could be sufficient to prevent the mjo initiation to explore this third mjo event further a series of sensitivity tests are conducted these tests show that the simulation of this event is neither critically influenced by the cumulus parameterization employed nor the initial conditions when the model is integrated 2 weeks prior to the mjo initiation the model captures this event when the mjo signal is already present in the initial conditions the use of high resolution sea surface temperature does not improve the simulation of the third mjo event a higher resolution nested domain covering the indo pacific warm pool region and including a cloud system resolving domain over the indonesian maritime continent has little effect on the mjo initiation over the indian ocean in 2 weeks the error in the simulation is comparable to the climate error the role of the simulated mjo on the mean state is also explored implications and limitations of these results are discussed

an assessment of the performance of the geophysical methods as a tool for the detection of zones of potential subsidence in the area southwest of nakuru town kenya the area to the southwest of nakuru town in kenya located within the kenya rift valley is prone to incidences of ground subsidence especially toward the end of the heavy rain season the zones affected by subsidence are typically linear trending approximately north south conforming to the structural trend of the kenya rift valley these ground subsidence incidences have in the past led to collapse of houses and damage to roads that happen to be located above the affected linear zones this study set out to investigate the potential of geophysical methods to delineate these linear zones two profiles of lengths 2 430 and 2 850 m respectively were selected for this purpose the study was conducted immediately after one major incidence of subsidence when the zones affected were still fresh and observable magnetics very low frequency electromagnetics vlf em and gravity methods were used in the study the choice of these methods was dictated by their widely known applicability in the detection of linear structures especially faults the results of the study have shown that the linear zones affected yield good response to magnetic and vlf em methods anomalies similar to those detected across fresh subsidence zones were also detected at locations where there was no surface expression of subsidence suggesting that the latter locations are potential zones of future subsidence further there were locations along the profile that were without any anomalies the relatively low sensitivity of the zones to the gravity method is attributed to the very narrow nature of these zone and hence limited low density material to generate appreciable negative gravity anomalies it is concluded from this study that geophysics permits identifying the potential areas to develop surficial collapse and to identify sectors that are potentially dangerous because they present similar signatures as the sectors with surficial evidence and sectors without anomalies the sectors without anomalies are interpreted as having a different subsoil structure to that with sinkholes

organic and isotope geochemistry of the early cretaceous rift sequence in the camamu basin brazil paleolimnological inferences and source rock models abstract the camamu basin located at the eastern brazilian continental margin is characterized by a thick early cretaceous organic rich rift sequence the integration of bulk geochemical isotopic and biomarker data with paleontological and geological information provided the basis for a better assessment of rift lake evolution hydrological regime redox potential salinity etc and its impact on source rock development pyrolysis and visual kerogen analyses reveal the dominance of lipid rich algal bacterial type i kerogen through the entire rift sequence paleolimnological reconstruction suggests that the lower rift sequence morro do barro formation neocomian was deposited in a fault bounded deep lake with fresh to brackish water stable water column stratification and water bottom anoxia high hydrogen indices 700 900 mg hc gtoc and 13c depleted carbon isotopic composition of the organic matter 13c values around 30 might reflect enhanced organic preservation the recycling of light ch4 generated by methanogenesis and the incorporation of isotopically light lipid rich bacterial biomass on the other hand the upper rift sequence rio de contas formation barremian was probably deposited within a broader shallower lake with a higher frequency of water column overturn and a deeper thermocline high organic carbon contents and strong 13c enrichment of the organic matter 13c excursions of up to 23 are interpreted to have resulted from enhanced primary productivity triggered by an increased input recycling of nutrients favored by lake morphology and humid climate

poleward propagating intraseasonal monsoon disturbances in an intermediate complexity axisymmetric model abstract a model of intermediate complexity based on quasi equilibrium theory a version of the quasi equilibrium tropical circulation model with a prognostic atmospheric boundary layer as well as two free tropospheric modes in momentum and one each in moisture and temperature is used in a zonally symmetric aquaplanet configuration to simulate aspects of the south asian monsoon and its variability key qualitative features of both the mean state and the 30 60 day mode of the intraseasonal variability are simulated satisfactorily the model has two limit cycles of similar period and structure that can account for this mode both feature northward propagation of the tropical convergence zone from 5 s to 25 n with a period of about 50 days the dynamics of the oscillations are investigated the system reaches a hopf bifurcation when the asymmetry of the sea surface temperature sst forcing is increased beyond the bifurcation the mean flow is linearly unstable and the one linearly unstable mode is simila

selective response of the south china sea circulation to summer monsoon abstractthe response of the south china sea scs circulation to intraseasonal variability of the summer monsoon is studied with both observations and a 1 5 layer reduced gravity model intraseasonal variability of the scs summer monsoon is characterized by evolution of the wind jet intensity in the midbasin with typical amplitude of 6 m s 1 and several peaks on its power spectrum between 10 and 60 days however this study finds that intraseasonal variability of the sea surface height ssh in the scs presents significant variability to the southeast of vietnam with amplitude of 6 cm and a period only between 40 and 60 days this implicates the frequency selectivity of oceanic response to wind forcing numerical experiments suggest that the intrinsic variability of the scs circulation accounts for this phenomenon based on the rossby basin mode theory this is explained by the interaction between the long westward propagating rossby waves and the short eastward propagating rossby waves

cross equatorial influences of submonthly scale southerly surges over the eastern indian ocean during southern hemisphere winter 1 lower tropospheric southerly surges occurring at submonthly timescales over the eastern indian ocean eio during southern hemisphere sh winter are extratropical tropical interaction phenomena involving various processes this study examined the physical mechanism driving equatorial wave disturbances associated with surge induced cross equatorial flow over the eio japanese 25 year reanalysis jra25 and tropical rainfall measuring mission satellite trmm 3b42 data products from june to august for the 7 years from 1998 to 2004 were analyzed composite analyses of low level wind and vorticity fields reveal that an equatorial clockwise gyre develops just after cross equatorial penetration of southerly surge winds this gyre is interpreted as an equatorially trapped rossby wave that develops asymmetrically around the equator in response to surge induced cross equatorial flow eddy vorticity budget analysis demonstrates the dynamic role of the southerly surge in the genesis of the equatorial clockwise gyre the result indicates that an injection of negative absolute vorticity into the equatorial tropics due to both advective and convergent processes associated with the surge winds is primarily responsible for the gyre genesis cross equatorial advection of basic state absolute vorticity by the surge eddy winds and vortex stretching by surge wind convergence are most effective in spinning up the equatorial clockwise gyre wave activity flux analysis further emphasizes that rossby wave energy propagation from the sh extratropics into the equatorial eio region is caused by the southerly surge these dynamic diagnostics suggest that the southerly surge plays a lateral forcing role in exciting the equatorial wave disturbance over the eio composite analyses of moisture flux and precipitation anomalies characterize the equatorial clockwise gyre as a convectively coupled equatorial rossby wave enhanced cross equatorial moisture transport due to the southerly surge appears to be linked to precipitation along the west coast of the southern indo china peninsula a case study of the southerly surge event during august 2000 illustrates the formation of the equatorial clockwise gyre and its convectively coupled equatorial rossby wave signature

dynamics of breaks in the indian summer monsoon abstract in this paper the authors present results of diagnostic analysis of observations and complementary experiments with a simple numerical model that enable them to synthesize the morphology and dynamics of breaks in the indian summer monsoon ism almost one week ahead of the onset of a break spell over india a monotonically decreasing trend in convective activity is found to occur over the bay of bengal in response to a steady eastward spreading of dry convectively stable anomalies from the equatorial indian ocean a major intensification of the convectively stable anomalies over the bay of bengal is seen about 2 3 days prior to commencement of a monsoon break both observations and modeling experiments reveal that rapid northwest propagating rossby waves are triggered in response to such a large strengthening of the convectively stable anomalies it is shown that an abrupt movement of anomalous rossby waves from the bay of bengal into northwest and central india marks the initiation of a break

quasi biweekly oscillations of the south asian monsoon and its co evolution in the upper and lower troposphere the upper tropospheric quasi biweekly oscillation uqbw of the south asian monsoon is studied using the potential vorticity field on the 370 k isentrope the uqbw is shown to be a common occurrence in the upper troposphere during the monsoon and its typical evolution is described we suggest that the uqbw is a phenomenon of both the middle and tropical latitudes owing its existence to the presence of the planetary scale upper tropospheric monsoon anticyclone the uqbw is first identified as rossby waves originating in the northern flank of the monsoon anticyclone these rossby waves break when reaching the pacific ocean and their associated cyclonic pv anomalies move southward to the east of asia and then westward across the indian ocean and africa advected by the monsoon anticyclone a strong correlation or co evolution between the uqbw and quasi biweekly oscillations in the lower troposphere qbw is also found in particular analysis of vertically integrated horizontal moisture transport 850 hpa geopotential and outgoing long wave radiation show that the uqbw is usually observed at the same time as and co evolves with the lower tropospheric qbw over south asia we discuss the nature of the uqbw and its possible physical link with the qbw

gravity data as a tool for detecting faults in depth enhancement of subtle almada s basement faults brazil we demonstrate the potential of gravity data to detect and to locate in depth subtle normal faults in the basement relief of a sedimentary basin this demonstration is accomplished by inverting the gravity data with the constraint that the estimated basement relief presents local abrupt faults and is smooth elsewhere we inverted the gravity data from the onshore almada basin in northeastern brazil and we mapped several normal faults whose locations and plane geometries were already known from seismic imaging the inversion methoddelineatedwellboththediscontinuitieswithsmallor largeslipsandasequenceofstepfaults usingsyntheticdata weperformedasystematicsearchofnormalfaultslipsversus fault displacement depths to map the fault detectable region inthisspace thismappinghelpstoassesstheabilityofgravityinversiontodetectnormalfaults mappingshowsthatnormalfaultswithsmall0 5 km mediumabout1 km and large about 2 km vertical slips can be detected if the maximummidpointdepthsofthefaultplanesaresmallerthan1 8 3 8 and6 8 km respectively

influence of indian ocean dipole on boreal summer intraseasonal oscillations in a coupled general circulation model 1 the role of indian ocean dipole iod on poleward propagation of boreal summer intraseasonal oscillations bsiso is examined using long simulation of a coupled ocean atmosphere general circulation model the model sintex f1 simulates the salient features of bsiso realistically it is found that coherent incoherent poleward propagation of precipitation anomalies from 5 s to 25 n are observed during negative positive iod years the probable mechanisms behind such an anomaly in poleward propagation of bsiso in contrasting iod years are identified we find that the mean structure of meridional specific humidity distribution undergoes cardinal changes in contrasting iod years which in turn influences the meridional propagation of bsiso enhanced decreased air sea interaction in negative positive iod years also supports coherent incoherent poleward propagation of bsiso anomalies this study has important implications considering the critical role of bsiso in modulating the seasonal mean summer monsoon rainfall

mechanisms of monsoon low frequency variability surface hydrological effects abstract observations indicate that monsoon systems are characterized by orderly large scale and low frequency variations with a time scale of two weeks and sometimes longer regions of ascending motion are observed to form to the north of the equator and propagate slowly northward across southeast asia the propagation appears to be associated with the active break sequence of the summer monsoon which acts as a modulator on the activity of the synoptic scale disturbances a zonally symmetric non linear two layer model containing an interactive ocean and a continent poleward of 18 n is used to investigate the mechanisms which produce the observed low frequency variability only when a full hydrology cycle is considered does the model product variations which resemble the observed structures mechanisms are traced to include the interaction of the components of the total heating function the sensible heat input in the boundary layer although considerably smaller than the other heating components de

the 30 50 day mode at 850 mb during monex abstract the analyzed wind field at 850 mb during the summer monsoon experiment monex is subjected to a time series analysis to confirm the existence of a peak in the time range of 30 50 days having established that this study presents a mapping of the motion field for this time scale in this short paper we illustrate the steady meridional propagation of a train of troughs and ridges that seem to form near the equator and dissipate near the himalayas the meridional scale of this mode is around 300 km and its meridional speed of propagation is 0 75 latitude per day the amplitude of the wind for this mode is around 3 6 m s 1 the salient contributions here are the mapping and the demonstration of a very regular behavior of this mode its existence is here noted from a period well before the onset of monsoon i e from early may to late july three major storms during monex were noted to form within the trough line of this system and the period of major cessation of rains over the indian subconti

large scale vapor transport of remotely evaporated seawater by a rossby wave response to typhoon forcing during the baiu meiyu season as revealed by the jra 55 reanalysis the modulation of large scale moisture transport from the tropics into east asia in response to typhoon induced heating during the mature stage of the baiu meiyu season is investigated using the japanese 55 year reanalysis jra 55 aided by a rayleigh type global isotope circulation model icm we highlighted the typhoons that migrate northward along the western periphery of the north pacific subtropical high and approach the vicinity of japan anomalous anticyclonic circulations to the northeast and southeast of typhoons and cyclonic circulation to their west become evident as they migrate toward japan which could be interpreted as a rossby wave response to typhoon heating these resultant anomalous circulation patterns form moisture conveyor belt mcb stretching from the south asian monsoon region to east asia via the confluence region between the monsoon westerlies and central pacific easterlies the icm results confirm that the well defined nature of the mcb leads to penetration of the indian ocean south china sea philippine sea and pacific ocean water vapors into western japan the typhoons have the potential to accumulate large amounts of moisture from distant tropical oceans through the interaction of their rossby wave response with the background flow in the case of a typical typhoon the total precipitable water around the typhoon center as it approaches japan is maintained by the moisture supply from distant oceans rather than from the underlying ocean which indirectly leads to the occurrence of heavy rainfall over western japan

origin of intraseasonal variability of circulation in the tropical central indian ocean observed upper ocean currents south of sri lanka exhibit large irregular fluctuations with periods of days to weeks an ocean model driven by daily surface winds is able to reproduce the observed fluctuations we find from model experiments that low frequency 30 50 day intraseasonal variability isv arises when rossby waves radiated from the eastern boundary are amplified by hydrodynamic instability in the eastern and central indian ocean high frequency 10 15 day isv is forced directly by isv of the wind field in the eastern indian ocean in spite of the contribution from instability the ocean circulation south of sri lanka is a deterministic response to wind forcing

an eulerian equation for snow accumulation downstream of an object this study investigated the form of the governing equation for the particle distribution by focusing on the particle motion processes rather than flow regime and particle characteristics a linear erosion term for a fetch eddy effect was introduced to the advection dispersion equation the equation formulated in this paper described most of the particle deposit patterns behind an object including porous and solid snow fences and a tree this theory may enable us to estimate particle motion parameters such as diffusion drift and erosion coefficients from field observed particle distributions snow stratigraphy observed by ground penetrating radar gpr was used verify to result of the modeled theoretical snow redistribution these analyses confirmed the effectiveness of the linear erosion term at explaining the particle deposition patterns due to eddys around a porous snow fence this article is protected by copyright all rights reserved

back analysis of drifting snow measurements over an instrumented mountainous site the nemo numerical model of drifting snow whose general outlines are presented in this paper is based on a physical model for saltation and turbulent diffusion the model needs a set of input parameters including fall velocity threshold shear velocity shear velocity mass concentration and roughness which are obtained from empirical formulae and wind speed measured at a given height to better determine the required field data in an alpine context our experimental site col du lac blanc 2700 m a s l french alps was first equipped with one anemometer and blowing snow acoustic sensors which proved not to be accurate enough for research purposes in the current state of development even though a new calibration curve was used we therefore set up a snow particle counter and we returned to the traditional robust mechanical traps and a 10 m mast with six anemometers two temperature sensors and a depth sensor to better determine friction velocity and aerodynamic roughness based on the studied drifting snow events we conclude 1 the proportionality of the aerodynamic roughness to the square of the friction velocity was confirmed but with a varying proportionality ratio depending on the snowdrift event 2 values of s u f were relatively well approximated by empirical formulae from data originating from antarctica and 3 snowdrift concentration profiles obtained by pomeroy s semi empirical formulae for the saltation layer coupled with a theoretical approach for the diffusion layer overestimated the concentration profiles for the studied blowing snow event

gravity inversion of basement relief using approximate equality constraints on depths we present a gravity interpretation method for estimating the relief of an arbitrary interface separating two homogeneous media the upper medium is discretized into rectangular juxtaposed prisms whose thicknesses represent the depths to the interface and are the parameters to be estimated from the gravity anomaly the density contrast of each prism is assumed to be constant and known to stabilize the inversion we introduce two kinds of constraints on the depths the first one requires proximity between the observed and computed depths at isolated points such as those obtained from boreholes absolute equality constraint the second one requires that groups of depths approximately follow an established linear relationship among the depths relative equality constraint both kinds of constraints are imposed in the least squares sense we illustrate the method performance by applying it to a synthetic anomaly produced by a simulated basement relief consisting of four narrow and adjacent structural lows

interactions between synoptic intraseasonal and interannual convective variability over southern africa after removing the annual cycle a principal component analysis is applied to the daily outgoing longwave radiation anomaly field used here as a proxy for atmospheric convection the analysis is carried out over the southern african region 7 5 e 70 e 10 s 40 s for austral summer november through february for the period 1979 1980 to 2006 2007 the first five principal components pc are retained the first two pcs describe spatial patterns oriented north west to south east from tropical southern africa sa to the mid latitudes they are interpreted to be different possible locations for synoptic scale tropical temperate troughs ttt one dominant rainfall producing synoptic system in the region the phase relationship between these two pcs describes a tendency for these ttt to propagate eastwards from sa to the mozambique channel and southern madagascar the next three pcs describe convective fluctuations respectively located over the north west the south and the centre of sa their time series are significantly associated with madden julian oscillation mjo activity in the tropics however we find that ttt systems are statistically independent of the mjo i e they are equally liable to occur during any phase of the mjo three pcs out of five also show a significant association with el nino southern oscillation confirming that el nino years mostly coincide with suppressed convection at the intraseasonal time scales a result consistent with its impact on seasonal averages diagnosed in previous studies

ocean atmosphere coupling in the monsoon intraseasonal oscillation a simple model study a simple coupled model is used in a zonally symmetric aquaplanet configuration to investigate the effect of ocean atmosphere coupling on the asian monsoon intraseasonal oscillation the model consists of a linear atmospheric model of intermediate complexity based on quasi equilibrium theory coupled to a simple linear model of the upper ocean this model has one unstable eigenmode with a period in the 30 60 day range and a structure similar to the observed northward propagating intraseasonal oscillation in the bay of bengal west pacific sector the ocean atmosphere coupling is shown to have little impact on either the growth rate or latitudinal structure of the atmospheric oscillation but it reduces the oscillation s period by a quarter at latitudes corresponding to the north of the indian ocean the sea surface temperature sst anomalies lead the precipitation anomalies by a quarter of a period similarly to what has been observed in the bay of bengal the mixed layer depth is in phase opposition to the sst a monsoon break corresponds to both a warming and a shoaling of the mixed layer this behavior results from the similarity between the patterns of the predominant processes wind induced surface heat flux and wind stirring the instability of the seasonal monsoon flow is sensitive to the seasonal mixed layer depth the oscillation is damped when the oceanic mixed layer is thin about 10 m deep or thinner as in previous experiments with several models aimed at addressing the boreal winter madden julian oscillation this suggests that the weak thermal inertia of land might explain the minima of intraseasonal variance observed over the asian continent

anomalous intraseasonal events in the thermocline ridge region of southern tropical indian ocean and their regional impacts 1 the present study explores the mechanisms responsible for the strong intraseasonal cooling events in the thermocline ridge region of the southwestern indian ocean air sea interface and oceanic processes associated with madden julian oscillation are studied using an ocean general circulation model and satellite observations sensitivity experiments are designed to understand the ocean response to intraseasonal forcing with a special emphasis on 2002 cooling events which recorded the strongest intraseasonal perturbations during the last well observed decade this event is characterized by anomalous walker circulation over the tropical indian ocean and persistent intraseasonal heat flux anomaly for a longer duration than is typical for similar events but without any favorable preconditioning of ocean basic state at the interannual timescale the model heat budget analysis during 1996 to 2007 revealed an in phase relationship between atmospheric fluxes associated with madden julian oscillation and the subsurface oceanic processes during the intense cooling events of 2002 the strong convection reduced shortwave radiation and increased evaporation have contributed to the upper ocean heat loss in addition to the slower propagation of active phase of convection which supported the integration of longer duration of forcing the sensitivity experiments revealed that dynamic response of ocean through entrainment at the intraseasonal timescale primarily controls the biological response during the event with oceanic interannual variability playing a secondary role this study further speculates the role of oceanic intraseasonal variability in the 2002 droughts over indian subcontinent

gravity inversion of basement relief constrained by the knowledge of depth at isolated points we present an interpretation method for the gravity anomaly of an arbitrary interface separating two homogeneous media it consists essentially of a downward continuation of the observed anomaly and the division of the continued anomaly by a scale factor involving the density contrast between the media the knowledge of the interface depth at isolated points is used to estimate the depth d1 of the shallowest point of the interface the density contrast between the two media and the coefficients c1 and c2 of a first order polynomial representing a linear trend to be removed from data the solutions are stabilized by introducing a damping parameter in the computation of the downward continued anomaly by the equivalent layer method different from other interface mapping methods using gravity data the proposed method 1 takes into account the presence of an undesirable linear trend in data 2 requires just intervals for both rather than the knowledge of its true value and coefficients c1 and c2

deglaciation in the tropical indian ocean driven by interplay between the regional monsoon and global teleconnections abstract high resolution climate records of the ice age terminations from monsoon dominated regions reveal the interplay of regional and global driving forces speleothem records from chinese caves indicate that glacial terminations were interrupted by prominent weak monsoon intervals wmi lasting a few thousand years deglacial wmis are interpreted as the result of cold temperature anomalies generated by sea ice feedbacks in the north atlantic most prominently during heinrich events recent modeling results suggest however that wmis reflect changes in the intensity of the indian rather than the east asian monsoon here we use foraminiferal trace element mg ca and ba ca and stable isotope records from a sediment core off the malabar coast in the southeastern arabian sea with centennial scale resolution to test this hypothesis and to constrain the nature and timing of deglacial climate change in the tropical indian ocean the malabar deglacial sst record is unique in character and different from other tropical climate records sst at the last glacial maximum was 2 7 0 5 c colder than pre industrial sst deglacial warming started at 18 6 95 ci range 18 8 18 1 kyr bp within error of the onset of warming at other tropical sites as well as in antarctica and the southern ocean and either coeval with or up to 1 kyr before the atmospheric co 2 rise warming took place in two steps separated by an interval of stable sst between 15 7 16 2 14 9 and 13 2 13 9 12 0 kyr bp the 18 o water record and the ba ca record which is a measure of indian sub continent riverine runoff indicate that the last ice age termination was marked by a prominent weak indian monsoon interval interrupted by an intense monsoon phase as seen in speleothem records and predicted by modeling a strong correspondence between the timing of the malabar 18 o sw record and the hulu cave monsoon record suggests that deglacial 18 o changes in both localities dominantly reflect compositional changes in precipitation likely driven by changes in the north atlantic

study of the periodicities of lightning activity in three main thunderstorm centers based on schumann resonance measurements abstract time variations of lightning activity in the three main tropical thunderstorm centers located in the maritime continent pakistan india southeast asia indonesia and australia africa and the americas are analyzed using a lightning activity index irs which is calculated from the resonances of magnetic field in the extremely low frequency range the schumann resonances which were observed at hylaty station poland in the time interval july 2005 may 2006 power spectrum analysis of the irs series is carried out for this time interval the annual and semiannual variations are shown in all of the series together with the following characteristic periodicities 45 madden julian oscillation 17 6 13 5 and 4 8 days seen mainly in the series describing the lightning activity of the maritime continent in addition maps of the dynamical power spectrum are constructed they present variability both in the values of characteristic periods 26 30 17 22 12 14 9 10 and 5 7 days and in their durat

structure genesis and scale selection of the tropical quasi biweekly mode the quasi biweekly mode qbm and the 30 60 day mode are two major intraseasonal oscillations isos in the tropics the qbm is known to have a major influence in determining the active and break conditions of the indian monsoon during the northern summer a westward propagating equatorial rossby wave with quasi biweekly period influences the australian monsoon during the northern winter universality between the summer and winter qbm is established through analysis of daily circulation and convection data for 10 years it is shown that the mean spatial structure of the qbm in circulation and convection resembles that of a gravest meridional mode equatorial rossby wave with wavelength of about 6000 km and westward phase speed of approximately 4 5 m s 1 however the maximum zonal wind occurs at around 5 n 5 s during the northern summer winter the wave structure appears to be translated northward southward by about 5 during the northern summer winter the relationship between outgoing long wave radiation and circulation data indicates that the mode is driven unstable by coupling with moist convection similarity in temporal and spatial characteristics of the mode during the two seasons leads us to propose that the same mechanism governs the genesis and scale selection of the mode in both the seasons an acceptable mechanism for genesis and scale selection of the qbm has been lacking in the present study a mechanism for genesis and scale selection of the observed qbm is proposed a simple 2 layer model that includes a steady ekman boundary layer bl formulation incorporating effect of entrainment mixing is constructed for the convectively coupled equatorial waves without influence of the background mean flow moist feedback in the presence of frictional bl convergence drives the gravest meridional mode equatorial rossby wave unstable with observed wavelength and period but with zonal winds symmetric about the equator potential temperature perturbation associated with the rossby wave is in phase with relative vorticity perturbation at low level the bl drives moisture convergence in phase with the relative vorticity at the top of the bl release of latent heat associated with the bl convergence enhances the potential temperature leading to a positive feedback the mean flow over the indian ocean and western pacific at low levels is such that the zero ambient absolute vorticity or the dynamic equator shifts to around 5 n 5 s during summer winter and results in a shift of the unstable rossby waves towards the north south by about 5 the resulting structure of the unstable rossby mode resembles the observed structure of the biweekly mode it is shown that neither evaporation wind feedback nor vertical shear of the mean flow is crucial for the existence of the mode however these processes marginally modify the growth rate and make the structure of the unstable wave more realistic