statistical occurrence and mechanisms of the 2014 2016 delayed super el nino captured by a simple dynamical model the recent 2014 2016 period was marked by a failed el nino favoring a subsequent extreme el nino with dramatic worldwide impacts here this new type of major event so called the delayed super el nino is realistically captured by a simple dynamical model for the equatorial pacific with emphasis on the role of state dependent stochastic wind bursts we analyze qualitative analogues for this event compared and contrasted with the 1997 1998 super el nino in ensemble experiments based on the simple model in agreement with recent studies the timing and intensity of such an event is strongly controlled by atmospheric wind bursts both easterly and westerly in particular the early stalling by easterly wind bursts and subsequent development by westerly wind bursts as observed during 2014 2016 is consistently retrieved we show in addition that individual wind bursts may control the main characteristics of the event only during its early development while sequences of consecutive wind bursts have more important cumulative effects another important result from the present analysis is the significant statistical occurence of the delayed super el nino around 20 30 compared with the one of directly formed super events as that of 1997 1998 such a high occurence is directly linked to the random evolution of wind bursts and is retrieved here for all phases of the el nino southern oscillation used for the initiation of the ensemble experiments these results suggest that the delayed super el nino is not an unusual type of super event and could reoccur in the future

a momentum budget analysis of westerly wind events associated with the madden julian oscillation during dynamo abstractthe dynamics of the madden julian oscillation dynamo field campaign was conducted over the indian ocean io from october 2011 to february 2012 to investigate the initiation of the madden julian oscillation mjo three mjos accompanying westerly wind events wwes occurred in late october late november and late december 2011 momentum budget analysis is conducted to understand the contributions of the dynamical processes involved in the wind evolution associated with the mjo over the io during dynamo using european centre for medium range weather forecasts analysis this analysis shows that westerly acceleration at lower levels associated with the mjo active phase generally appears to be maintained by the pressure gradient force pgf which could be partly canceled by meridional advection of the zonal wind westerly acceleration in the midtroposphere tends to be mostly attributable to vertical advection the results herein imply that there is no simple linear dynamic model that can capture t

simulated annealing 2 d nonlinear inversion of geomagnetic deep sounding data near ujjain guna india an attempt has been made to use the global optimization technique of simulated annealing s a inversion to interpret the conductivity structure derived from the geomagnetic deep sounding data of n w india the present results supersede the earlier result obtained by 2 d conventional linearized inversion the earlier linearized inversion following an iterative gradient search technique on the same data set has been re evaluated and further constrained through an exhaustive search of the parameter space the conductive response of an hypothesized conductor located between ujjain and guna india has been modelled by this random search tool the location of the proposed model is now in agreement with the theory since the conductive bodies are centered exactly below the center of the response function in an earlier attempt by linearized inversion this was not feasible the central body is located at a depth of 19 km from the surface suggesting a thickness of 15 km and resistivity of 14 ohm m the resistivity contrast of this ensemble of conductive bodies with the background varies by a factor of 100 to 385 this low conductivity contrast with respect to the background is in conformity to the low temperature as inferred from the available heat flow data in the region a marginally different estimate of the conductivity normally mid crustal conductors are assigned conductivities of the order of 50 to 200 ohm m for the mid crustal conductor has been found existence of a mid crustal conductor is clearly indicated which was also not detected in the earlier study low geo temperature gradients existing in the region rule out the possibility of a thermal origin for this mid crustal conductor a likely explanation could be due to the presence of graphitic carbon at lower crustal depths however the role of electrolytic fluid present in the interconnected pore spaces of rocks may be another tangible explanation

relations of kinematics microphysics and electrification in an isolated mountain thunderstorm abstract this paper addresses aspects of the airflow microphysics and electrification in a mountain thunderstorm which occurred on 7 august 1979 over the langmuir laboratory new socorro new mexico site of the thunderstorm research international program trip single doppler observations are used to form a conceptual model of the essentially one dimensional storm updraft which is expressed in simple analytical form a one dimensional kinematic numerical cloud model is employed with the analytic updraft profile to diagnose the evolution of temperature war substance radar reflectivity space charge density and axial electric field in the main updraft region retrieved thermal microphysical and electrical variables are verified with in situ aircraft and balloon observations and measured radar reflectivity the calculated rate of noninductive charge transfer accompanying collision and separation of ice crystals and riming graupel particles is in direct proportion to cloud and precipitation content an

simulation of a supercellular storm using a three dimensional mesoscale model with an explicit lightning flash scheme 1 a complete lightning flash scheme is implemented in the three dimensional 3 d nonhydrostatic mesoscale model meso nh of the french community the scheme which is part of the electrical scheme follows a new approach with two steps first lightning flashes are modeled as bidirectional leaders to mimic the vertical propagation of the initial discharge channels along the electric field then a probabilistic branching algorithm is adapted from the dielectric breakdown concept to reinforce the flash propagation toward distant regions of high charge density but immersed in a weak electric field this results in a high increase of the total length of the lightning flash channel and also in a better capture of the morphology of intracloud lightning flashes the electrification and lightning schemes are tested for an ideal case of a supercellular storm the model succeeds in reproducing the general features of a storm and the electric charge cycle sensitivity analyses show that the implementation of a branching stage is necessary and efficient enough to relax the growth of the electric field the intracloud discharges generated by the model look realistic with a two layer horizontal structure extending over tens of kilometers from the triggering area the lightning flash length and the quantity of charge neutralized are ten times more important when the branching algorithm is taken into account the main conclusion drawn from this study is the feasibility and the benefit of an advanced treatment of lightning flashes in 3 d numerical simulations with an electrification scheme

anomalies in geomagnetic variations on peninsular india near palk strait anomalies in transient geomagnetic variations have been previously studied using data from five permanent observatories in the peninsular india the results from the three observatories falling under the equatorial electrojet showed the presence of a strong current concentration between india and sri lanka island the currents seem to flow at the depth of the crust or upper mantle these findings have been confirmed hereby by collecting data from an array of magnetometers we associate the channelling to the presence of a geological conductor between india and sri lanka island

sst anomalies of enso and the madden julian oscillation in the equatorial pacific this study explores whether anomalies of sea surface temperature sst in the equatorial pacific during warm events of el nino southern oscillation enso are related to the madden julian oscillation mjo an index is derived from surface wind data of a global model reanalysis to measure forcing of oceanic kelvin waves by wind stress associated with the mjo this kelvin wave forcing index of the mjo is used to relate interannual anomalies in seasonal activity of the mjo to interannual anomalies in equatorial sst for the 1980 99 time period evidence is found showing that during enso warm events stronger kelvin wave forcing in the western pacific precedes greater sst anomalies in the eastern pacific by 6 12 months no such evidence however can be found for the period of 1950 79 the result suggests that during enso warm events amplitudes of sst anomalies in the eastern pacific can be affected by the mjo at least for the 1980 99 period through its seasonal activity of kelvin wave forcing a possible mechanism for such an mjo enso relationship is described how enso prediction can be benefited from the precursory signals of the mjo is discussed

thickness of the siwalik sediments in the mohand ramnagar region using magnetotelluric studies abstract magnetotelluric studies were conducted over a 150 km long linear profile between mohand and ramnagar covering the siwalik sediments in the foothills of the himalayas data were collected at 13 stations with an interstation spacing of 8 12 km in the frequency range 0 01 100 hz the response functions indicated a predominantly one dimensional substructure however two dimensional behaviour was observed at four stations in the low frequency range

westerly wind bursts and their relationship with intraseasonal variations and enso part ii energetics over the western and central pacific abstract the mechanism of synoptic scale eddy development in the generation of westerly wind bursts wwbs over the western central pacific and their relationship with the el nino southern oscillation enso and the madden julian oscillation mjo were examined in the wwb occurrences barotropic structures of equatorial eddy westerlies with cyclonic disturbances were found from the surface to the upper troposphere the dominant contributions to substantial eddy kinetic energy eke were the barotropic energy conversion kmke in the lower and middle tropospheres and the conversion from eddy available potential energy peke in the upper troposphere low frequency environmental westerlies centered near the equator preceded strong zonal convergence and meridional shear resulting in the substantial kmke the activation of synoptic convection also contributed to an increase in eke through peke these energies were redistributed to the lower equatorial troposphere through energy flux convergence gke the

geomagnetic induction and conductive structures in north west india summary magnetic disturbance events and quiet daily variation as recorded by the 1979 magnetometer array study in north west india are analysed for evidence of electrical conductivity structures in the region contour maps of fourier transform parameters are presented and the disturbance event data are also reduced to sets of real and quadrature parkinson arrows over a range of periods a variety of conductive structures in the area are mapped including some relatively shallow ones thought to be caused by sediments as in the ganga basin more information is obtained on a major conductivity structure which strikes perpendicular to the ganga basin into the foothills of the himalayas a second major conductivity structure is detected to lie to the west of the array area and may be associated there with some aspect of the suture zone of india and asia

magnetometer array study in north northeast brazil conductivity image building and functional induction modes magnetovariational fields recorded by an array of magnetometers in the equatorial region of north northeast brazil are analyzed to infer the configuration of internal induced currents in and around the extensive intracratonic parnaiba basin only nighttime magnetovariational fields were used because of the prevailing uniform source field conditions for periods exceeding 40 min the vertical fields at all inland sites are dominated by the effects of electric currents originating in the northeast in the deep atlantic ocean below this period although best developed in the 12 15 min period range the anomalous signatures are principally controlled by two distinct continental current paths the first is associated with a n60 e trending graben like structure in the southeastern part of the basin named the parnaiba basin conductivity anomaly pbca and the second appears as a subsurface sedimentary channel from the nw corner of the array to the central part of the basin this is named the link anomaly as it connects the northwestern marajo basin with the parnaiba basin while the pbca is shown to highlight the importance of basement tectonics in the geological evolution of the parnaiba basin the link anomaly provides strong geophysical evidence of the direction of the sea intrusion into the region of the basin and possibly indicates the connectivity of the parnaiba basin to the adjoining amazon basin through the marajo basin frequency and polarization dependence suggest that the induction response of individual structures is not determined by the local conductivity alone but also by their interconnectivity as well as by their linkage to the continental shelf and deep oceanic region

induction models of southern india and the effect of off shore geology abstract simple numerical tests based on thin sheet modelling are used to define the conductors most probably responsible for current channelling in the region including southern india a combination of crustal conductors located in the indo ceylon graben and underneath the comorin ridge best reproduces the observations at periods of 50 100 min in so far as channelling is concerned daytime variations do not help to define the location of conductors any better than night time data and may thus be ignored

a non uniform thin sheet model for geomagnetic induction anomalies in central india abstract a non uniform thin sheet model has been developed to account for the geomagnetic induction anomalies revealed by a magnetometer array study over central india the conductance distribution map indicates three conductive zones the first beneath the satpura the second appearing as a nw se continuation of the godavari graben and the third an arcuate conductivity zone in the vicinity of sehore the surface and near surface sedimentary basins known from earlier gravity and deep seismic sounding studies cannot provide the estimated conductance for the different conductors collation of a variety of geographical data including heat flow suggests that heat fluxes characterizing the region are sufficient to cause partial melting at the crust mantle interface and to initiate metamorphic dehydration leading to a release of fluids at mid crustal levels the characteristics of the regional gravity anomaly absence of a low velocity zone at the base of crust as against the presence of the large number of a discontinuous reflectors in the mid crust favour a fluid phase as the likely mechanism for the mapped high conductivity zones

geomagnetic variation anomalies in peninsular india summary geomagnetic substorms recorded by an array of magnetometers over peninsular india have been analysed to investigate the subsurface electric configuration of the area the study considered only night time events when the external inducing field is uniform over the indian peninsula and the conventional interpretational techniques of geomagnetic deep sounding can be readily applied contour maps of fourier transform amplitudes and phases along with real and quadrature parkinson arrows are presented their features reveal a complex anomaly pattern the observed anomalies can be classified into i southern peninsular anomalies ii palk sirait anomalies iii pondicherry rift anomalies and iv anomalies in the central region a large scale induction process seems to be disturbed by localized perturbations the prominent anomaly observed over the southern tip seems to have a direct relevance to the tectonic setting of the indian ocean and adjoining areas

westerly wind bursts and their relationship with enso in cmip3 models 1 equatorial westerly wind bursts wwbs and their relationship with el nino southern oscillation enso in the 18 climate models presented in the world climate research programme s coupled model intercomparison project phase 3 cmip3 are examined some models depict a realistic eastward shift of collective occurrences of wwbs over the pacific as the warm pool expands eastward these models that depict the frequent western pacific wwbs preceding el nino peak known to trigger or enhance el nino tend to reproduce westerly background states and enso more accurately thus the reproducibility of the westerly background states is suggested to be fundamental for wwb occurrences as well as the following el nino although wwbs generate with active convection in most of the models as observations various kinds of intraseasonal disturbances that cause the active convection are found it is suggested that organized convection is essential for the wwb generation but is prepared by each model s own dominant mode in the tropics under global warming wwbs tend to increase over the eastern pacific and decrease over the indian ocean whereas the total number of wwbs does not change consistently this might arise from an increase of short period convective disturbances over the eastern pacific due to a sea surface temperature increase although there is a weak relationship between changes in the enso amplitude and the eastern pacific wwbs in general good models reproducing the wwb enso relationship in the current climate tend to show consistent changes suggesting the possibility of the eastern pacific wwbs to intensify enso

a transverse conductive structure in the northwest himalaya abstract data from a linear profile of magnetometers running parallel to the strike of the northwest himalaya are analysed to bring out more information on the major conductivity structure delineated through the 1979 magnetometer array examination of data in the form of induction arrows and pseudosection of z h has permitted a precise estimate of the position and orientation of the conductor numerical modelling of the data suggests that a 45 km wide ridge rising from asthenospheric depths to a depth of 15 km and having an electrical resistivity of 2 m accounts for the observations fairly well the coincidence of the conductivity anomaly with a zone of high seismicity suggests that stresses associated with underthrusting of the indian plate at its collision with the eurasian plate may cause fracture in the indian shield resulting in the upflow of asthenospheric material in the form of a ridge certain signatures indicative of an electrical discontinuity at the main boundary thrust are also identified

an inversion of geomagnetic deep sounding data using simulated annealing abstract a maiden attempt on the use of the global optimization technique of simulated annealing s a inversion to model the conductivity structure derived from the geomagnetic deep sounding data of nw india is reported here the location of the proposed model is now in agreement with the theory since the conductive bodies are centered exactly below the center of the response function which was not feasible by the earlier linearized inversion the central body is located at a depth of 19 km from the surface suggesting thickness of 15 km and resistivity of 14 m the resistivity contrast of this ensemble of conductive bodies with the background is varying by a factor of 100 to 385 existence of mid crustal conductor the conductivity estimate is marginally different is clearly indicated which was also not detected in the earlier study a likely explanation could be due to the presence of graphitic carbon at lower crustal depths however the role of electrolytic fluid present in the interconnected pore spaces of rocks may be another explanation

an explanation of induced magnetic variations at sabhawala india abstract induction vectors calculated for short period events such as bays and storm sudden commencements sscs indicate that the conductor causing the anomaly lies to the south of sabhawala the nature of vertical transfer functions obtained from spectral analysis of storm time variations further confirms the presence of such a conductor the nature of maximum g p and minimum g 1 response functions suggests that a two dimensional conductor south of sabhawala is responsible for anomalies in z invoking a structural model of the earth s crust beneath the himalayas in keeping with accepted orogenic theories we propose that one structure capable of producing the desired conducting path is a rise of the asthenosphere south of the himalayan range another important factor contributing to the induced variations at sabhawala is due to a sedimentary trough running parallel to the himalayas again to the south these views are confirmed by a two dimensional model calculation it is found that the undulation of the asthenosphere alone does not reproduce the nature of the anomalies in h and z

impact of the winter north atlantic oscillation nao on the western pacific wp pattern in the following winter through arctic sea ice and enso part ii multi model evaluation of the nao enso linkage a 1 year lagged relationship between the north atlantic oscillation nao in winter and el nino southern oscillation enso in the following year was examined with a multi model ensemble analysis using coupled model intercomparison project phase 3 models a coherency index was developed as a measure of the coherence between the nao and enso in each model and used as a weighting factor in the ensemble model weighted multi model ensemble means of the regressed field on the maximum covariance analysis coefficients between the surface pressure field in the north atlantic nao field and the sea surface temperature field in the equatorial pacific enso field were explored the results indicated that when the wintertime nao was in its negative positive phase anomalous atmospheric circulation associated with a large small eurasian snow mass anomaly intensified weakened the asian cold surge and the westerly wind burst wwb in the warm pool region intensification of the wwb initiates el nino a sensitivity experiment using an idealized dry general circulation model revealed that the atmospheric response to anomalous near surface cooling associated with an anomalous eurasian snow mass induced higher surface pressure near the tibetan plateau and thus intensified the asian cold surge and wwb linear regression analyses applied to the reanalysis data strongly supported the model results our results therefore suggest an influence of the nao on the initiation of el nino via a process that involves eurasian snow anomalies associated with the nao phase

equatorially forced intraseasonal propagations along the peru chile coast and their relation with the nearshore eddy activity in 1992 2000 a modeling study 1 a regional eddy resolving oceanic model spanning the 1992 2000 period is used to study the influence of 50 to 80 day intraseasonal equatorial kelvin waves iekw on mesoscale eddy activity off the west coast of peru and northern and central chile the model is shown to realistically simulate nearshore intraseasonal sea level variability poleward propagation of equatorially forced coastal trapped waves along the coastal waveguide and offshore variability related to mesoscale eddies and rossby waves rw in agreement with linear theory rw are confined equatorward of 12 s in the 50 80 days period range south of that critical latitude westward propagation is dominated by energetic mesoscale signals resulting mainly from coastal flow instability sensitivity experiments to the open boundary conditions are then used to estimate to what extent eddy activity is impacted by the remote equatorial forcing a coastal increase in eddy kinetic energy related to the energetic 60 day iekw activity present in the open boundary forcing is evidenced and is largest off northern peru whereas no major changes are observed offshore additional regional simulations with different open boundary conditions corroborate our findings and suggest that this limited effect of iekw on the offshore eddy kinetic energy may be a robust feature citation belmadani a v echevin b dewitte and f colas 2012 equatorially forced intraseasonal propagations along the peru chile coast and their relation with the nearshore eddy activity in 1992 2000 a modeling study j geophys res 117 c04025 doi 10 1029 2011jc007848

crustal block of the western ganga basin a fragment of oceanic affinity abstract three component long period new delhi records of two earthquakes occurring near multan central pakistan are used to determine group velocities of multimode surface waves in the period range of 5 to 57 sec inversion of these data has provided insight regarding the crustal shear velocity structure in the western ganga basin in the northwestern wedge of the indian subcontinent the shear velocity is less than 3 10 km sec within the topmost 10 km of its 40 km thick crust the estimated velocity in the 10 to 20 km depth range is 3 80 0 09 km sec in the lower half crust the velocity is as high as 3 98 0 08 km sec unlike the continental shield crust in the new delhi shillong region the crustal structure in this western part of the ganga basin is strongly reminiscent of certain oceanic plateaus this suggests that the crustal block underlying the sediments is not part of the stable core or the craton of the indian shield the available data do not allow the determination of fine velocity structure in the upper mantle the average velocity in the uppermost 80 km of the mantle is 4 52 km sec this value appears to be characteristic of the entire northern indian subcontinent and may be indicative of active tectonism in the mantle south of the himalayas

magnetometer array studies earth structure and tectonic processes this review presents results from magnetovariation fields recorded by two dimensional arrays of magnetometers the emphasis is on the conductive structures mapped and studied and their tectonic implications eleven arrays were operated in north america between 1967 and 1985 a region of highly conductive uppermost mantle and or lower crust extending at least from 33 n to 54 n has been shown to extend beneath much of the continent west of the rocky mountains two recent investigations are discussed in more detail those of conductive structures under the canadian rockies and emslab electromagnetic sounding of the lithosphere and beyond array results for washington and oregon including a conductive strip beneath the cascades volcanoes correlations with high heat flow and seismic parameters make it reasonable to attribute these regional conductors to partial melting and or hot saline water within the craton the north american central plains conductor is discussed this narrow crustal feature is associated with a major fracture zone and age boundary which may be a plate boundary of proterozoic time an array beneath the auroral electrojet for study of the external currents is noted results from four array studies in southern africa are considered two of these relate to the southern cape conductive belt which correlates not with high heat flow but with a large static magnetic anomaly the magnetovariation magnetic and gravity anomalies and geological data can be accounted for if an accumulation of ophiolitic rocks including serpentine is present in the lower crust such an accumulation may have formed at a subduction in proterozoic time two other arrays delineated a conductive belt associated with the southwestern end of the african rift system in namibia subsequent resistivity soundings located a conductor of resistivity 10 ohm m at less than 4 km depth two array studies in india follow one in the north and one in the south the array in the himalayan foothills and indo gangetic plain mapped a conductor transverse to the regional strike this may be a fracture zone produced in the interplate collision with a rise of asthenospheric material such as fluids into the fractures the southern indian array reveals crustal conductors under the indo sri lankan graben and another under the comorin ridge southwest of the tip of the subcontinent array studies in central and southeastern australia and in fennoscandia in regions without large local conductivity anomalies have been used to study conductivity variation with depth a note on the carpathian crustal anomaly is included as an example of combination of response parameters secured at different times to form a virtual array

induction anomalies in geomagnetic sq in peninsular india anomalies in geomagnetic sq h sq z and sq d as recorded at an array of 21 magnetometers and 5 permanent observatories in peninsular india during 1979 1980 are analyzed and discussed in relation to geology signatures of the kodaikanal batholith the dharwar series of rocks and a graben structure in the palk strait on the geomagnetic records of nearby stations are unmistakably identified and associated with internal induction effect the extent and influence of the ionospheric equatorial electrojet and oceanic induced currents observed on the ground in this complex region are also mapped

crustal structure and lateral variations in moho beneath the delhi fold belt nw india insight from gravity data modeling and inversion abstract the proterozoic delhi fold belt dfb in nw india shows a prominent nne ssw trending gravity high but its northward extension beneath gangetic alluvium lack understanding we model the gravity anomaly using radially averaged power spectrum depth from extreme points dexp method wavelength filtering 3d structural inversion to constrain crustal structure of the dfb the radially averaged power spectrum analysis suggests three interfaces and the dexp method indicates presence of a horizontal cylindrical source below the dfb the 3d structural inversion shows depth variation from 39 to 46 km in the study region and presence of an upwarp below the dfb and sandmata complex our modeling suggests that an underplated mafic material possibly a residual plume head produces gravity high the transverse structure of dfb is absent beneath gangetic alluvium and show notable westward deflection in line with the nw se trending delhi sargodha ridge the transverse dfb attains westward deflection possibly due to nw indentation and counterclockwise rotation of indian plate after himalayan collision in eocene with continued convergence this dfb structural element at the leading edge of indian peninsula got involved in flexural upwarp of underthrusting indian plate beneath the himalaya

cloud to ground lightning associated with the evolution of a multicell storm 1 the relationship of cloud to ground cg lightning strikes to the stages of updraft downdraft evolution is investigated in a multicell thunderstorm that occurred on 11 july 1989 during the north dakota thunderstorm project with only single doppler radar data available for this storm reflectivity and single doppler velocity signatures are used to identify individual cells within the storm and to deduce the stage of evolution within each cell cell evolution appeared to follow the thunderstorm project model of the late 1940s updraft growth and vertical development during the growing cumulus stage updraft peaking in the upper portion of the cell and rainy downdraft descending from the middle portion during the mature stage and lighter precipitation settling out during the dissipating stage on 11 july cells tended to occur in clusters each cluster consisting of growing mature and dissipating cells close together in both time and space no cg strikes were detected when the convective region of the storm contained only one cluster of cells all strikes occurred when there were two or more clusters of cells with only two exceptions strikes occurred in the convective region of the storm typically closer to growing mature cells than to dissipating cells these observations support the hypothesis that descending precipitation creates electrical conditions conducive to flashes reaching ground however these observations also suggest that the greater complexity of electrical structure due to the juxtaposition of several cells is especially conducive to cg flashes and can cause cg flashes to occur earlier in a new cell s life cycle than would otherwise be the case

structural control on along strike variation in the seismicity of the northwest himalaya an overview of seismicity along the northwest himalaya exhibit along strike segmentation intricately controlled by the subsurface topographic ridges on the underthrusting indian plate as well by rift and nappe structures in the overriding wedge of the himalaya the segmentation exists for thrust dominated large magnitude earthquakes m 6 seated on the active detachment beneath the outer and lesser himalaya segmentation also prevails for moderate and small magnitude earthquakes concentrated in a narrow himalaya seismic belt hsb straddling northern lesser himalaya and southern higher himalaya numerical calculations of stress distribution favour that the degree of seismicity in the hsb is a good proxy to the presence of mid crustal ramp connecting the locked section of active detachment to aseismically slipping detachment beneath higher himalaya further gap or diffused pattern in the concentrated seismicity in the hsb in agreement with mapped high electrical conductive structure suggests ramp structure may be absent where underthrusting delhi hardwar ridge interacts with the himalaya arc in the nappe dominated tectonics the accommodation of the accumulating strains on the listric thrust faults produces increased frequency of moderate magnitude earthquakes and thereby possibly influences stress level on the detachment this may explain relatively less frequent occurrences of large earthquake in the kangra chamba region compared to that in the garhwal himalaya the low level seismicity in the simla region may also be influenced by the active kaurik chango rift in the higher himalaya as the former casts a stress shadow on the latter

electromagnetic evidence for lateral inhomogeneities within the earth s upper mantle abstract the composition of the upper mantle is of great significance to our understanding of plate tectonics and global evolution information about the physical properties of the earth at upper mantle depths including lateral variations in electrical conductivity can be deduced from measurements of the electric and magnetic fields at the earth s surface electromagnetic methods appear to give poorer resolution than do some other methods for example seismics but as they are sensitive to quite different properties of a medium they provide a different and complementary class of information the basic theory of electromagnetic sounding methods is briefly reviewed below and evidence regarding lateral conductivity inhomogeneities in the earth s upper mantle is examined while lateral electrical conductivity inhomogeneities appear to be the rule rather than the exception the interpretation of electromagnetic data still presents difficulties and the results from many regions are not as yet unambiguous where the data are of sufficient resolution a rapid increase in electrical conductivity can usually be identified within the upper mantle the depth to this highly conductive zone is different in different tectonic environments but is broadly consistent between analogous but widely separated tectonic environments a comparatively shallow conducting region is found beneath the ocean lithosphere the depth of this region is dependent on lithospheric age many of the more shallow conducting regions in both continental and oceanic environments are associated with high heat flow values and seismic low velocity zones these highly conducting regions may be zones of partial melt

fluid genesis through serpentinites and the origin of subsurface electrical conductors in northwest india and adjoining regions abstract large scale conductivity anomalies have been detected and subsequently modelled inverted based on the data of geomagnetic deep sounding in northwest india by various researchers in this study by analytical dissection of several other geophysical parameters in conjunction with the constrained modelling of electrical parameters of the conductors we believe that we have resolved the origin of three northwest indian conductors this issue had remained so far either speculative or an explanation was given without taking due analytical support from other geophysical data moreover a unique relationship has been found and the same advocated amongst the high values of poisson s ratio and the electrical parameters of conductors these high values of poisson s ratio conform to the presence of serpentinites in the region at appropriate depths under the present geotectonic setting the upward migration of serpentine from mantle to subcrustal level and its consequent dehydration leading to fluid genesis seems to be the appropriate cause for the conductivity anomalies in the northwest indian region including lesser himalaya however the exact mechanism for upward migration a fact established elsewhere may at present remain tentative some indirect inferences have been drawn through a hypothesized model cartoon to shed light on the possible mode of fluid transport resulting in conductivity anomalies of the region the presence of fluids has also been cited in literature in higher himalayan regions resulting due to under thrusting of the indian basement elsewhere in the northwest himalayan region the presence of serpentinite in close association of eclogite has been found these serpentinites are formed by hydration of the mantle wedge resulting due to de watering of the subducted slab these facts strengthen the belief of the continuation of fluid body in himalayan and adjacent northwest region in the crust

model study for the proposed magnetotelluric mt traverse in north india abstract in anticipation of an mt traverse into the himalayas extensive modelling was done to determine survey specifications this was based on a combination of geologic seismic and low frequency electromagnetic induction data available in the literature the modelling technique used is one which is now fairly standard involving the numerical solution of maxwell s equations for a two dimensional geoelectrical structure the models included most known features of the surface and subsurface including the ganges basin the topography of the mountains and the main boundary thrust proposed high temperature zones were also modelled in the course of the modelling some constraints were found for the source of the aravalli anomaly observed by lilley et al 1981

on the interpretation of the distinctive pattern of geomagnetic induction observed in northwest india the geomagnetic variation data from the 1979 indian array experiment have been reanalyzed and reexamined using the hypothetical event analysis technique the contour map of the z h ratio replicates distinctive anomaly in northwest india previously delineated in maps of the fourier coefficients the anomaly reveals the presence of a significant conductor under the ganga basin the contour map has been used to derive a response profile perpendicular to the strike of the anomaly for comparison with 2 d numerical models an excellent fit was found for a conductor at a depth of 32 km with a width of 110 km and a conductivity contrast of 1000 this result places the conductor deep within the lithosphere in the absence of supporting data the origin of the conductor is difficult to resolve however it is thought to be related to pressure released partial melting caused by fracturing of the indian crust during the collision of india with asia

assessing the relationship between mjo and equatorial pacific wwbs in observations and cmip5 models abstractthis study evaluates the relationship between the madden julian oscillation mjo and the occurrence of equatorial pacific westerly wind bursts wwbs during the convective mjo phase anom

a magnetometer array study in northwest india abstract a magnetometer array study has been carried out in northwest india from rajasthan across the indo gangetic plain into the himalayan foothills over the three months of operation a wide variety of natural geomagnetic events has been recorded the analysis of a simple substorm polarized just west of north shows a strong anomaly in the form of a reversal of the vertical component of the fluctuation both in the himalayan foothills and on the ganga plain the magnetic fluctuations pattern observed is most directly interpreted in terms of a path of concentrated current flow in the earth striking across the himalaya it is evidently aligned with the aravalli belt which outcrops further south and may indicate that some geological structure in the sub basement is of abnormally high electrical conductivity the path of such a current concentration across the foothills raises the question whether some transverse structure in the himalaya is not acting as a bridge to peninsular india for current induced in the tibetan plateau to the northeast

magnetometer array studies in india and the lithosphere abstract two magnetometer array experiments were conducted in india during 1978 1980 under an indo australian collaboration project using 21 australian three component magnetometers of the gough reitzel type the first array study was made in the northwestern region covering the aravallis the punjab and the lesser himalaya while the second experiment was carried out in the southern peninsular shield area both these sets of geomagnetic deep sounding gds observations yielded valuable results on the crustal and upper mantle structure in the two geologically and geophysically important regions of india geomagnetic induction patterns observed in northwest india have revealed a variety of electrical conductivity structures the primary conductivity structure providing paths for induced currents is found to be striking at right angles to the himalayan mountains the conductivity structure is indicated to be a northward continuation of the aravalli belt and thus suggesting the continuation of the indian shield at depth into the base of the himalayan foothills under the ganga basin the induction effects observed in the southern tip of peninsular india are by far the most complex geophysical phenomenon due to the simultaneous occurrence of the sea coast the crustal and upper mantle conductivity anomalies between india and sri lanka under the sea and the day time equatorial electrojet as part of the external heterogeneous inducing field it is further complicated by the existence of a conductive step structure along the coastline at the moho boundary and a graben structure in the palk strait as revealed by the array observations

earthquakes in the garhwal himalaya of the central seismic gap a study of historical and present seismicity and their implications to the seismotectonics the historical and the present seismicity catalogues of the garhwal himalaya have been studied for their spatio temporal variations and their implications on the seismotectonics of the region the micro seismicity fractal dimensions dc and frequency magnitude distribution b value coupled with the available literature on geology geomorphology and geophysics have been used to derive the seismotectonics and stress level changes in the region the seismic cross sections for the relocated micro seismicity focal mechanisms and the swath profiles for the presence of physiographic transition 2 pt2 at the foothill of the higher himalaya indicate the constant presence of the mid crustal ramp mcr in the detachment plane and its active seismogenic nature the comparison of this scenario suggests the constant presence of seismogenically active mcr structure throughout the central seismic gap the seismic cross sections further reveal that the sensu stricto main central thrust munsiari thrust is also a site of generation of the micro seismicity in few segments due to its reactivation by thrusting along the mcr the high fractal dimension value dc 1 47 suggests the heterogeneous nature of the region owing to the presence of local faults and transverse tectonics the high stress accumulation in the garhwal himalaya with low b value b 0 70 suggests the high probability of occurrence of a larger or greater earthquake in the near future further the study also reveals that the 2011 chamoli earthquake of m 5 0 preceded by a quiescence period of nearly a year shows different stress levels before and after its occurrence which is well constrained with the increased moderate earthquake activity around the chamoli region this increased seismic activity and stress conditions in the chamoli region suggest the high possibility of the occurrence of major earthquakes hence the study recommend for a detailed seismic hazard evaluation of the region

possible influence of subducting ridges on the himalayan arc and on the ruptures of great and major himalayan earthquakes abstract subduction of bathymetric features such as ridges seamounts fractures etc on the subducting plate influences the arc morphology and earthquake ruptures we analyse their effect on the development of the arcuate shape of the himalayan arc and on the ruptures of great and major himalayan earthquakes besides the two most prominent ridges in the indian ocean namely the chagos laccadive deccan ridge and the 90 e ridge which are assumed to extend up to the himalayan arc at least three major subsurface ridges have been mapped on the underthrusting indian plate under the indo gangetic plains it appears that the subduction of the two most prominent ridges contributed to the development of the arcuate shape of the himalayan arc the interaction and subduction of the other subsurface ridges probably influenced the himalayan arc morphology by causing a localised cusp in the frontal topography also these ridges probably acted as barriers to the ruptures of the major and great himalayan earthquakes

electrification of stratiform regions in mesoscale convective systems part ii two dimensional numerical model simulations of a symmetric mcs abstract model simulations of a symmetric mesoscale convective system mcs observations discussed in part i were conducted using a 2d time dependent numerical model with bulk microphysics a number of charging mechanisms were considered based on various laboratory studies the simulations suggest that noninductive ice ice charge transfer in the low liquid water content regime characteristic of mcs stratiform regions is sufficient to account for observed charge density magnitudes and as much as 70 of the total charge in the stratiform region the remaining 30 is contributed by charge advection from the convective region the strong role of in situ charging is consistent with previous water budget studies which indicate that roughly 70 of the stratiform precipitation results from condensation in the mesoscale updraft thus both in situ charging and charge advection the two previously identified hypotheses appear to be important contributors to the electrical budget of the stratiform region the

westerly wind bursts enso s tail rather than the dog westerly wind bursts wwbs in the equatorial pacific occur during the development of most el nino events and are believed to be a major factor in enso s dynamics because of their short time scale wwbs are normally considered part of a stochastic forcing of enso completely external to the interannual enso variability recent observational studies however suggest that the occurrence and characteristics of wwbs may depend to some extent on the state of enso components implying that wwbs which force enso are modulated by enso itself satellite and in situ observations are used here to show that wwbs are significantly more likely to occur when the warm pool is extended eastward based on these observations wwbs are added to an intermediate complexity coupled ocean atmosphere enso model the representation of wwbs is idealized such that their occurrence is modulated by the warm pool extent the resulting model run is compared with a run in which the wwbs are stochastically applied the modulation of wwbs by enso results in an enhancement of the slow frequency component of the wwbs this causes the amplitude of enso events forced by modulated wwbs to be twice as large as the amplitude of enso events forced by stochastic wwbs with the same amplitude and average frequency based on this result it is suggested that the modulation of wwbs by the equatorial pacific sst is a critical element of enso s dynamics and that wwbs should not be regarded as purely stochastic forcing in the paradigm proposed here wwbs are still an important aspect of enso s dynamics but they are treated as being partially stochastic and partially affected by the large scale enso dynamics rather than being completely external to enso it is further shown that wwb modulation by the large scale equatorial sst field is roughly equivalent to an increase in the ocean atmosphere coupling strength making the coupled equatorial pacific effectively self sustained

lightning location relative to storm structure in a supercell storm and a multicell storm relationships between lightning location and storm structure are examined for one radar volume scan in each of two mature severe storms one of these storms had characteristics of a supercell storm and the other was a multicell storm data were analyzed from dual doppler radar and dual vhf lightning mapping systems the distributions of vhf impulse sources were compared with radar reflectivity vertical air velocity and their respective gradients in the supercell storm lightning tended to occur along streamlines above and downshear of the updraft and reflectivity cores vhf impulse sources were most concentrated in reflectivities between 30 and 40 dbz and were distributed uniformly with respect to updraft speed in the multicell storm on the other hand lightning tended to coincide with the vertical reflectivity and updraft core and with the diverging streamlines near the top of the storm the results suggest to us that the location of lightning in these severe storms was most directly associated with the wind field structure relative to updraft and reflectivity cores since the magnitude and vertical shear of the environmental wind are fundamental in determining the reflectivity and wind field structure of a storm we suggest that these environmental parameters are also fundamental in determining lightning location

evidence for the neoproterozoic phulad suture zone and genesis of malani magmatism in the nw india from deep seismic images implications for assembly and breakup of the rodinia abstract deep seismic reflection images across the late mesoproterozoic south delhi fold belt sdfb nw india provide evidence for crustal scale tectonic imbrication and collisional tectonism an andean type margin with eastward subduction of oceanic lithosphere and subsequent collision of volcanic arc with mewar craton is responsible for the evolution of the sdfb contrasting geophysical particularly the deep seismic and gravity models and geological signatures found across the sdfb suggest this as a suture the phulad suture zone psz with its extension into the himalaya post collisional delamination and orogenic collapse are responsible for the equilibrated younger moho and evolution of malani magmatism in the region the present study envisages an evolutionary model for the malani volcanics unambiguously identifying for the first time the sdfb rocks as their basement this model successfully resolves the ambiguity by correlating the marwar terrain with the rodinia assembly rather than later pan african orogeny located further west evolution of the sdfb and malani magmatism are coeval with the rodinia assembly and breakup the south delhi orogeny located between the east and the west gondwana fragments plays an important role for reconstruction of the gondwana

2 d inversion of geomagnetic deep sounding data near ujjain guna india summary the inductive response of a hypothesized conductor located between ujjain and guna india has been modelled in the absence of a satisfactory fit from forward numerical modelling 2 d inversion of the anomaly profile of z h ratio has revealed the main conductor to be situated below ujjain guna with an offset and another secondary conductor in the form of a jointed body the main conductor is at a depth of 23 km from the surface thickness being 20 km and the resistivity 3 m the jointed secondary conductors are at depths of 31 km and 28 km with thicknesses of 14 km and 21 km and resistivities 3 m and 5 m respectively the resistivity contrast with the background is a factor of 1600 or even slightly more the possibility of mineralization on the flanks of the subsurface granitic intrusion cannot be ruled out however partial melting of the subsurface granites seems to be another plausible explanation for the high conductivity contrast

a comprehensive mass flux scheme for cumulus parameterization in large scale models abstract observational studies indicate that a mass flux approach may provide a realistic framework for cumulus parameterization in large scale models but this approach through the introduction of a spectral cloud ensemble leads normally to rather complex schemes in this paper the question is addressed whether much simpler schemes can already provide realistic values of the thermal forcing by convection under various synoptic conditions this is done through verifying such a scheme first on data from field experiments for periods of tropical penetrative convection gate marshall islands tradewind cumuli atex bomex and extratropical organized convection sesame 79 and then in a nwp model the scheme considers a population of clouds where the cloud ensemble is described by a one dimensional bulk model as earlier applied by yanai et al in a diagnostic study of tropical convection cumulus scale downdrafts are included various types of convection are represented i e penetrative convection in c

topographic constraints on deviatoric stress field in the indo eurasian collision region seismo tectonic implications the deviatoric stress field are computed from the inversion of gravitational potential energy gpe for the indo eurasian plate collision region including the himalaya and the tibet plateau the resulting stress pattern in combination with stress and strain rates obtained by inverting respectively the focal mechanism solution of large earthquakes and gps derived plate motions are used to study the nature of the present day deformations a narrow belt bordering the himalayan collision zone from the south is characterized by strong compressive stresses the variations in stress pattern along this belt coincide with arc normal ridges extending into the himalaya and are able to explain arc parallel segmentation of seismicity gravitational collapse seems to play an important role in the southeastern tibet plateau depth sensitivity of the seismic derived stresses and gps derived surface strain rates coupled with evidence of arcuate shaped high electrical conductivity favour strong ductile flow around the eastern himalaya syntaxis ehs at mid crustal depth the deflection of crustal flow indicted by the viscous resistance offered by the rigid sichuan basin adds to the traction stresses to cause clockwise rotation of the block around ehs