modes of climate variability and heat waves in victoria southeastern australia summertime heat waves in the southeastern state of victoria australia are associated with broad anticyclonic upper level potential vorticity pv anomalies the current research establishes the relationship between heat waves precipitation and three modes of climate variability of importance for rainfall in australia the el nino southern oscillation enso madden julian oscillation mjo and southern annular mode sam heat waves in victoria in summer are more common during phases 3 6 of the mjo when convection is enhanced over the eastern indian ocean maritime continent and western pacific ocean and la nina phases of enso the pv theta structure of the heat wave and pattern of convection varies with the phase of each mode of variability enhanced tropical convection results in a heat wave characterized by a monopole of anticyclonic pv whereas suppressed convection is associated with a dipole of anticyclonic and cyclonic pv

strike slip faulting and nested block rotations structural evidence from the cordillera de domeyko northern chile abstract based on a structural analysis tectonic rotations around vertical axes have been found affecting the sedimentary sequence of the purilactis group from the cordillera de domeyko of northern chile the affected rocks form the northern part of a pre existing syncline that was offset by two sets of strike slip faults during the upper eocene incaic orogeny uplift and shortening in the hangingwall of two main bounding thrusts initiated the strike slip faults which divided the purilactis group into several fault blocks further contraction of the enclosed block faulted area led to domino style anticlockwise rotation of the central main blocks and the bounding block faults with rotations up to 40 additionally eastward displacement of these blocks was accompanied by local indentation of the adjacent smaller blocks to the east giving rise to opposite rotation directions the block rotations may have been accommodated by a decollement located in the mudstone and evaporite of the basal part of the sequence tonel formation based on a reconstruction of the initial rock distribution different fault models are discussed and a model resembling pure shear deformation is proposed to explain the initiation of strike slip faults the occurrence of block rotations and the distortion of the block faulted domain

a preliminary study of satellite derived gravity and magnetic anomalies of india and contiguous regions abstract the residual satellite gravity anomaly map in and around the indian region has been prepared these residual anomalies are interpreted for crustal inhomogeneities using the magsat anomalies as one of the constraints while a strong correlation between these anomalies is observed over the dharwar aravalli marwar and singhbhum regions inverse correlation prevails over the eastern ghats and cambay basin the positive gravity and magnetisation strong correlation over the stable blocks of the peninsula is related to the alternating layers of basic and ultrabasic materials the positive gravity and low magnetisation poor correlation over the eastern ghats and cambay basin is interpreted as thinning of the crust the residual gravity map identifies the signatures of west central indian lineament and the submarine topographic features ridges in the indian ocean such as the chagos laccadive 85 e and ninety east ridges which are not so obvious in the unprocessed anomaly map at ground level an attempt is also made to explain the anomaly over the indo ganga brahmaputra basin using the ground and 400 km level satellite gravity anomaly maps

key dynamical features of the 2005 06 european winter abstract a three part study of the anomalously cold european winter of 2005 06 is undertaken climatological analysis indicates that the dominant pattern of climate variability in the euro atlantic sector during this winter was not a negative phase of the north atlantic oscillation nao but a pattern with a blocklike center located immediately upstream of the continent synoptic dynamical diagnosis of the winter indicates the frequent occurrence of long lasting blocks in this region and a lagrangian trajectory analysis points to the significant role of cloud diabatic effects in the dynamics of block inception a series of heuristic numerical simulations lend credence to the hypothesis that the occurrence of the blocks was sensitive to and significantly influenced by the warm surface temperature anomalies upstream over the western atlantic ocean and north america brief comments are made on the significance of the foregoing results for seasonal numerical weather prediction and also their relevance t

severe heat waves in southern australia synoptic climatology and large scale connections this paper brings a new perspective on the large scale dynamics of severe heat wave hw events that commonly affect southern australia through an automatic tracking scheme the cyclones and anticyclones associated with hws affecting melbourne adelaide and perth are tracked at both the surface and upper levels producing for the first time a synoptic climatology that reveals the broader connections associated with these extreme phenomena the results show that a couplet or pressure dipole formed by transient cyclones and anticyclones can reinforce the hw similarly to what is observed in cold surges cs with an obvious opposite polarity our results show that there is a large degree of mobility in the synoptic signature associated with the passage of the upper level ridges before they reach australia and the blocking is established with hw associated surface anticyclones often initiating over the west indian ocean and decaying in the eastern pacific in contrast to this result the 500 hpa anticyclone tracks show a very small degree of mobility responding to the dominance of the upper level blocking ridge an important feature of hws is that most of the cyclones are formed inland in association with heat troughs while in cs the cyclones are typically maritime often explosive associated with a strong cold front hence the influence of the cyclone is indirect contributing to reinforce the blocking ridge through hot and dry advection on the ridge s western flank additional insights are drawn for the record adelaide case of march 2008 with fifteen consecutive days above 35 c breaking the previous record by 7 days sea surface temperatures suggest a significant air sea interaction mechanism with a broad increase in the meridional temperature gradient over the indian ocean amplifying the upstream rossby waves that can trigger hw events a robust cooling of the waters close to the australian coast also contributes to the maintenance of the blocking highs locally which is a fundamental ingredient to sustain the hws

the influence of tropical cyclones on heat waves in southeastern australia 1 heat waves in southeastern australia in summer are commonly associated with slow moving surface high pressure systems which result in warm northerly flow from the continental interior the underlying dynamical pattern of heat waves in this region is associated with propagating rossby waves which grow in amplitude and eventually overturn forming an upper level anticyclonic potential vorticity anomaly the influence of tropical cyclones on the development of these anomalies is investigated here tropical cyclones may affect heat waves in this region indirectly as the divergent outflow at upper levels perturbs the rossby wave guide leading to downstream development however the effect may also be direct through the advection of anomalously anticyclonic potential vorticity from regions of deep convection in the vicinity of tropical cyclones into the upper level anticyclone our research shows that this direct reinforcement of the anticyclone is likely to be more important in the formation of severe heat waves in southeastern australia

on utility of space borne vector magnetic measurements in crustal studies abstract the magsat data over india and contiguous regions for quiet periods kp 3 have been analysed to isolate components of crustal origin the main field contribution was removed with mgst 4 81 13th degree and order spherical harmonic expansion the external current contributions were estimated using the h and z components directly and assuming the potential to have p1 cos dependence a quadratic polynomial for each satellite pass had to be removed to make residuals from adjacent passes agree with each other these residuals over 2 2 blocks were averaged to prepare the anomaly maps the anomaly maps exhibit better resolution than langel et al features associated with the indian ocean geoid low clearly appear in the results a test on internal consistency of reduction techniques was made by synthesizing b map through the projection of three vector maps and comparing the same with the map obtained from direct measurements it is noticed that near the dip equator the features of z map are not reflected in the b map we conclude that in those regions where the main field direction is such that one or two of its components x y or z become zero or very small the crustal anomaly in that direction will not influence the b anomaly for it would have no projection in the direction of the main field

application of ridge regression in inversion of low latitude magnetic anomalies derived from space measurements abstract anomalies in total field horizontal and vertical components over the indian region derived from magsat measurements have been inverted through the ridge regression method basically to test 1 the application of the method in deriving a stable estimate of crustal magnetisation and 2 the relative amount of information on crustal magnetisation contained in scalar vis a vis vector data results show that the instabilities in magnetisation solution that appear when mayhew s conventional method is applied in low latitudes could be removed through the ridge regression technique it was also noticed that magnetisation distribution estimated through the inversion of the total field b does not relate well with the geological features in the equatorial region inversion of thez anomaly alone gives realistic results for the equatorial region but not over higher latitudes we conclude that a joint inversion ofx andz anomalies provides a magnetisation estimate consistent with known geological features both for equatorial and higher latitudes

the structure and evolution of heat waves in southeastern australia abstractthe underlying large scale dynamical processes responsible for the development of heat waves in victoria southeastern australia in summer are presented here heat waves are defined as periods of at least three days and two nights for which daily maximum and minimum temperatures exceed the 90th percentile for a particular location and month using a station daily temperature dataset composites of upper level potential vorticity anomalies from the interim ecmwf re analysis era interim reveal that heat waves in southeastern australia are associated with propagating rossby waves which grow in amplitude and eventually overturn the process of overturning generates an upper level anticyclone over southern australia and an upper level trough to the northeast with maximum amplitudes near the tropopause the northerly flow associated with the circulation around the surface anticyclone advects hot air from the continental interior over the southeast of australia leading to extreme surface temperatur

an equivalent layer magnetization model for the united states derived from satellite altitude magnetic anomalies long wavelength 500 km magnetic anomalies measured by the pogo series satellites at altitudes 400 700 km over the united states and adjacent areas are inverted to an equivalent layer magnetization model based on an equal area dipole source array at the earth s surface minimum source spacing giving a stable solution and a physically meaningful magnetization distribution is 300 km but a scheme is presented for effectively sampling the distribution on a grid twice as fine the model in effect expresses lateral variation in the vertical integral of magnetization and is a starting point for models of lateral variation in the form of the magnetization depth curve in the magnetic crust the magnetization model contours correlate with large scale tectonic features and in the western part of the country probably reflect curie isotherm undulations

spatial variability of sea level pressure and 500 mb height anomalies over the southern hemisphere abstract the spatial variability of mean sea level pressure slp and 500 mb height anomalies over the southern hemisphere during summer djf and winter jja is determined using eigenvector analysis based on daily synoptic maps from 1972 to 1979 the patterns of spatial distribution of pressure and height anomalies are further verified and examined by means of station data and the eigenvectors are compared between the seasons and to those found for the northern hemisphere the first eigenvector shows that midlatitude anomalies of slp and 500 mb height are of an opposite sign to those found over and around antarctica the pattern is highly barotropic and suggests strengthening and weakening of the zonal wind in alternating latitude belts the 500 mb height differences are calculated for five midlatitude to antarctic station pairs using data from the late 1950 s onward these latitudinal height differences are also used to describe the association between the hemispheric westerlies and the southern oscil

southeastern australian heat waves from a trajectory viewpoint abstractalthough heat waves account for more premature deaths in the australian region than any other natural disaster an understanding of their dynamics is still incomplete the present study identifies the dynamical mechanisms responsible for heat waves in southeastern australia using 10 day backward trajectories computed from the era interim reanalyses prior to the formation of a heat wave trajectories located over the south indian ocean and over australia in the lower and midtroposphere ascend diabatically ahead of an upper level trough and over a baroclinic zone to the south of the continent these trajectories account for 44 of all trajectories forming the anticyclonic upper level potential vorticity anomalies that characterize heat waves in the region at the same time trajectories located over the south indian ocean in the lower part of the troposphere descend and aggregate over the tasman sea this descent is accompanied by a strong adiabatic warming a key finding is that the temperatures a

a study of frontal dynamics with application to the australian summertime cool change abstract the dynamics of frontal evolution is investigated in the context of the australian summertime cool change using a two dimensional numerical model the model is essentially the same as that used by reeder and smith but with different initial conditions and with an open rather than periodic flow domain the initial conditions are an idealization of cross sections through a typical preexisting finite amplitude disturbance prior to its amplification to an intense front trough system basically they consist of a warm prefrontal northerly airstream embedded in a zonal shear flow in thermal wind balance the model develops a quasi steady surface cold front during the 24 hours real time of integration and this front is shown to have many features in common with a kinematic model of the australian summertime cool change the latter model was synthesized from observational data on surface cold fronts obtained during the phase i and ii field experiments of the australian cold fronts research program

some structural features of the bay of bengal abstract continuous bathymetric magnetic and gravity data covering the bay of bengal from 10 n to 19 30 n and between the east coast of india and the western margins of the andaman islands and bangladesh were collected on board r v chain in 1973 these data have brought out several features that show correspondence from profile to profile in topography and in magnetic and gravity values the magnetic basement computed from the magnetic anomalies and the crustal structure models deduced to fit the observed free air gravity anomalies have revealed that the sediment thickness ranges from about 4 5 km to more than 10 km between 10 n and 19 30 n five major structural zones trending nearly n s have been delineated in the bay of bengal these are the marginal high that extends along all the east coast of india the marginal basin identified only on the southern margins of the east coast of india the graben abutting the continental slope and shelf near visakhapatnam the central basin in the central bay of bengal and the extension of ninetyeast ridge as a subsurface feature up to 17 n

the crustal evolution and uplift mechanism of the qinghai tibet plateau abstract the qinghai tibet plateau covers part of each of the following four plates the tarim qaidam the qiangtang yangtze the gandise and the indian plates containing four crustal suture zones the northern qilian the east kunlun the karakorum lancang and the yarlung zangbo tsangpo suture zones the tarim qaidam and qiangtang yangtze plates belong to part of the paleo eurasian continent and the gandise and indian plates are component parts of the old gondwana land a typical ancient trench arc basin system and ophiolite belt are developed in both the qilian mountains and the area of the yarlung zangbo river the crust of this particular plateau has an obvious layered structure and comprises three structural layers the upper sialic the middle simatic and the lower mixed crust mantle layers the crustal shortening and thickening since the late eocene has been brought about by deformations of these three structural layers in different ways the uplifting process of the qinghai tibet plateau probably experienced two stages a stage of thickening by compression and a stage of isostatic uplift from the late eocene to pliocene the deformation was mainly of a compressional nature resulting in a large scale crustal shortening and thickening a considerable depression of the upper mantle and formation of a broad and deep plateau mountain root from the early pleistocene to the present time along with the weakening of compression stress relaxation has occurred and with the operation of the mountain root a strong isostatic adjustment has taken place causing the plateau to uplift both rapidly and remarkably

minimal crustal magnetizations from satellite data abstract the minimum amplitude crustal magnetization needed to explain magsat vector anomaly data is found using harmonic splines as basis functions shure et al 1982 phys earth planet inter 28 215 229 and choosing a subset of the original basis parker and shure 1982 geophys res lett 9 812 815 to represent magnetization we suggest the optimum model of this type is obtained by associating representers only with north and vertically downwards data points given the larger uncertainties associated with east component magsat data following parker et al 1987 rev geophys 25 17 40 we find a model minimizing the r m s volume integral of magnetization over the magnetized lithosphere the numerical effort involved in producing a regional or continental scale model with given horizontal spatial detail with our method is less than that for an equivalent source dipole model when the magnetization is not assumed induced approximately equal to that for an induced magnetization equivalent dipole model and considerably less than that for a spherical harmonic apparent susceptibility model the method is demonstrated by producing a solution for two regions the contiguous usa for comparison with previously published models and africa and its continental margins magnetization models fit the data slightly worse than those of the downward continued anomaly field at the earth s surface comparison of our component of magnetization for the usa in the direction of the core field with the induced magnetization equivalent dipole model of mayhew 1984 earth planet sci lett 71 290 296 is very good as expected for magnetization either induced by or frozen remanently in an approximately dipole field either parallel or antiparallel to the current rotation axis the east component of magnetization is much smaller than the north and vertically downwards components we make no assumptions about the relative contributions of remanent and induced magnetization and the resulting models have a substantial remanent component however our models suffer from the severe non uniqueness common to all magnetization models whereby magnetization in a uniform susceptibility and thickness shell concentric with the earth s centre owing to any internal magnetic field that is then switched off generates no external magnetic field

a three dimensional numerical model study of electromagnetic induction around the indian peninsula and sri lanka island abstract magnetic field variations recorded using an array of magnetometers have shown earlier significant anomalies at some southern stations of india e g annamalainagar adiramapatnam and trivandrum the nature of anomalous horizontal and vertical fields and their persistence to periods of the order of hours cannot be explained in terms of the usual coast effect alone some authors have suggested that these anomalies could be caused by the electric currents induced in the deep ocean but channelled through a good conductor situated below the palk strait and gulf of manowar between india and sri lanka to investigate the effect of such a deep conductor possibly in the lower crust or upper mantle a three dimensional model of india sri lanka and the surrounding coast lines has been studied using a numerical technique with the aid of the well known finite difference numerical method for partial differential equations solutions of the magnetic fields have been computed for two different models 1 without conductor and 2 with a conductor in the palk strait gulf of manowar region below the ocean floor the results are presented in the form of contour plots and spatial behaviour of the amplitudes of three magnetic field components h d z at the surface of the earth contour plots clearly reveal that when a highly conducting sub surface structure is introduced in the palk strait region the currents tend to flow along the direction of the conductor and contribute to enhancement of the magnetic field amplitudes along the east coast of the indian peninsula and west coast of sri lanka island the amplitude plots show that in general the numerical results for the model with the sub surface conductor tend to agree with the results of the magnetometer observations thereby supporting the hypothesis of a sub surface conducting structure between india and sri lanka

definition of the continent ocean boundary of india and the surrounding oceanic regions from magsat data abstract magsat studies over the indian region and adjoining areas show that the continental oceanic contrasts appear more distinctly in the equivalent magnetization solution than in the anomaly maps the vertical component z is found to be more useful for the equatorial regions it is also noted that in general the continental crust has a higher magnetization than the oceanic crust further the continental crust seems to extend into the arabian sea across a part of the west coast a similar continuation is seen in the northern part of the bay of bengal the west coast result is corroborated using land and marine bouguer gravity anomalies

continent like crustal thickness beneath the bay of bengal sediments observed dispersion of fundamental mode rayleigh and love waves across the bay of bengal to wwssn and indian seismograph stations suggests increasing crustal thickness northward from an approximate 15 km thick oceanic crust south of the latitude of the southern tip of india to a more continent like thickness of approximately 25 km at 20 n and over 35 km at the northernmost part of the bengal fan the dispersion data are not consistent with models which simply add the increasing sedimentary thickness on top of a normal oceanic crust the sediment thicknesses and crust velocities are controlled by extensive seismic refraction results and are in agreement with clearly observed sedimentary higher mode waves recorded at the indian seismograph stations madras and vishakapatnam several hypotheses might explain this surprising result 1 1 the blanketing effect of the sediments with consequent temperature rise has brought about differentiation of basalt to increase the crustal thickness r n singh personal communication 2 2 the change in moho depth represents dynamic isostatic adjustment such as a phase change boundary which is lowered because of temperature or pressure perturbations from the sedimentary blanket or from pressure perturbations of plate collision 3 3 the collision has underthrust a wedge of low velocity material beneath the oceanic crust 4 4 the northern bay of bengal is actually fortuitiously continental or continent like possibly as a result of the influence of the 90 ridge especially in the northern part if the explanation is 1 2 or 3 the result is important to our understanding of crust and upper mantle dynamics it is suggested that further controlled studies be performed to verify the result

magsat scalar anomaly map of india and a part of indian ocean magnetic crust and tectonic correlation magnetic scalar anomaly maps over india and a part of the indian ocean are prepared from the magsat data using an average of the observed field in a grid of 1 1 the magsat scalar anomaly map thus obtained is characterised by highs over the indian shield and large lows over the himalayas centered over tibet plateau a ne sw magnetic trend emanating from ne india and spreading almost over the entire peninsular shield is the single most prominent feature of the map which might be related to the stress system or deepseated structural trends associated with plate motion the deccan traps are reflected by nosing of the magnetic contours the shillong massif is characterised by a separate anomaly which deflects the ne sw magnetic trend referred to above a magnetic crustal map prepared from this magsat scalar anomaly using the principles of harmonic inversion yields a thickness of 30 km under the cambay basin and the western part of the narmada son lineament for a magnetization of 2a m suggesting a higher subsurface thermal gradient in this area and therefore a tectonically active region a maximum thickness of 40 42 km is found under the regions of aravallis singhbhum and south of the narmada son lineament which are precambrian stable cratons major lineaments and faults are reflected as variations in the thickness of the magnetic crust along these lines the himalayas are chaaracterised by an average thickness of 35 36 km with a thickening of 2 4 km under the tibet plateau and shillong massif the magsat anomaly in the northern part of the indian ocean can be accounted for by a thickening of 8 km in the magnetic crust the center of this crustal thickening derived from the magsat anomaly after appropriate correction for the inclination of the earth s magnetic field in this region coincides with the wellknown indian ocean gravity and geoid lows

crustal magnetisation model of the indian subcontinent through inversion of satellite data abstract an apparent magnetisation model of the indian subcontinent and the adjoining regions has been obtained through the inversion of magsat total field scalar and vertical field data a staggered 4 4 grid pattern with a constant continental crustal thickness of 40 km yielded magnetisation values over a 2 2 grid over the major part of the indian subcontinent the magnetisation picture brings out a prominent high sandwiched between the eastern ghats and the main boundary fault of the himalayas in contrast the identity of the western ghats comprising mainly deccan traps is missing while a distinct magnetisation low is observed over the known hot spot region of the saurashtra peninsula two magnetisation highs one over the shillong massif and the other over the central part of india covering aravallis and the bundelkhand massif are obtained interestingly even at a height of 400 km the well known narmada son lineament is clearly reflected in the total intensity map as well as in the corresponding magnetisation map the bay of bengal and the himalayas ara characterised by magnetisation lows

structure and evolution of the pamir hindu kush region lithosphere abstract the deep structure of the pamirs hindu kush region is considered using the geological and tectonic data a conclusion is reached on the sliding of the 30 km uppercrustal layer and its disharmony relative to the upper crust on the basis of the methods of the three dimensional wave velocity model of the lithosphere obtained by the seismic tomography algorithm and of the investigations of the recurrency law of the earthquakes in the pamirs hindu kush mantle focal zone developed by the author s a considerable horizontal inhomogeneity is recognized in the structure of the region up to a depth of 300 km all these data indicate that the movement of the lithosphere plates is brought about not by simple subduction but by their twisting differentiated at various levels occurring in the upper mantle notless but perhaps even more intensively than in the earth s crust the mixing of the crustal and mantle materials accompanying this process can account for the decrease in the upper mantle average density in certain parts of the region