sea surface height determination in the arctic ocean from ers altimetry 1 accurate sea surface height measurements have been extracted from ers altimeter data in sea ice covered regions for the first time the data have been used to construct a mean sea surface of the arctic ocean between the latitudes of 60 degreesn and 81 5 degreesn based on 4 years of ers 2 data an rms value for the crossover differences of mean sea surface profiles of 4 2 cm was observed in the ice covered canada basin compared with 3 8 cm in the ice free greenland iceland norwegian seas comparisons are made with an existing global mean sea surface osumss95 highlighting significant differences between the two surfaces in permanently ice covered seas in addition we present the first altimeter derived sea surface height variability map of the arctic ocean comparisons with a high resolution coupled ocean sea ice general circulation model reveal a good qualitative agreement in the spatial distribution of variability quantitatively we found that the observed variability was on average a factor of 3 4 greater than model predictions

seamount statistics in the pacific ocean we apply the wide beam sampling technique of jordan et al 1983 to approximately 157 000 km of wide beam profiles to obtain seamount population statistics for eight regions in the eastern and southern pacific ocean population statistics derived from wide beam echograms are compared with seamount counts from sea beam swaths and with counts from bathymetric maps we find that the average number of seamounts with summit heights h h is well approximated by the exponential frequency size distribution h oe h the exponential model for seamount sizes characterized by the single scale parameter 1 is found to be superior to a power law self similar model which has no intrinsic scale in describing the average distribution of pacific seamounts and it appears to be valid over a size spectrum spanning 5 orders of magnitude in abundance large scale regional variations in seamount populations are documented we observe significant differences in seamount densities across the murray fracture zone in the north pacific and the eltanin fracture zone system in the south pacific the eltanin discontinuity is equally evident on both sides of the pacific antarctic ridge in the south pacific regions symmetrically disposed about the ridge axis have very similar seamount densities despite the large difference between pacific plate and antarctic plate absolute velocities evidently any differences in the shear flows at the base of the pacific and antarctic plates do not affect seamount emplacement systematic variations in o and are observed as a function of lithospheric age with the number of large seamounts increasing more rapidly than small seamounts these observations have been used to develop a simple model for seamount production under the assumptions that 1 an exponential size frequency distribution is maintained 2 production is steady state and 3 most small seamounts are formed on or near the ridge axis the limited data available from this study appear to be consistent with the model but they are insufficient to provide a rigorous test of the assumptions or determine accurately the model parameters however the data from the south pacific indicate that the off axis production of large seamounts probably accounts for the majority of seamounts with summit heights greater than 1000 m

seismic interpretation of pelagic sedimentation regimes in the 18 53 ma eastern equatorial pacific basin scale sedimentation and infilling of abyssal valleys understanding how pelagic sediment has been eroded transported and deposited is critical to evaluating pelagic sediment records for paleoceanography we use digital seismic reflection data from an integrated ocean drilling program site survey amat03 to investigate pelagic sedimentation across the eastern central equatorial pacific which represents the first comprehensive record published covering the 18 53 ma eastern equatorial pacific our goals are to quantify 1 basin hill scale primary deposition regimes and 2 the extent to which seafloor topography has been subdued by abyssal valley filling sediments the eastern pacific seafloor consists of a series of abyssal hills and basins with minor late stage faulting in the basement ocean crust rarely outcrops at the seafloor away from the rise crest both hills and basins are sediment covered the carbonate compensation depth is identified at 4440 m by the appearance of acoustically transparent clay intervals in the seismic data overall we recognized three different sedimentation regimes depositional high sedimentation rate transitional and minimal sedimentation low sedimentation rate regimes in all areas the sedimented seafloor mimics the underlying basement topography although the degree to which topography becomes subdued varies depositional regimes result in symmetric sedimentation within basins and subdued topography whereas minimal sedimentation regimes have more asymmetric distribution of sediments within topographic lows and higher seafloor relief regardless of sedimentation regime enhanced sediment deposition occurs within basins however we observe that basin infill is rarely more than twice as thick as sediment cover over abyssal hills if this variation is due to sediment focusing the focusing factor in the basins as measured by 230th is no more than a factor of 1 3 of the total vertical particulate rain

julia radar studies of equatorial spread f this paper presents coherent scatter radar observations of plasma irregularities in the equatorial f region ionosphere made with the julia jicamarca unattended long term studies of the ionosphere and atmosphere radar and discusses model equations and simulations pertinent to their interpretation the data set shows that bottom type and bottomside scattering layers are prevalent throughout solar minimum equinox bottom type layers are undifferentiated and relatively weak layers confined to a narrow range of altitudes falling within regions of the ionosphere driven by the e region dynamo these layers are often precursors to large scale radar plumes as well as to bottomside layers which are broader more structured and more intense layers than the bottom type variety bottomside layers are the source of intermediate scale plasma depletions that can ascend and penetrate through to the topside fluid simulations of the collisional interchange instability suggest that dynamo theory explains why one kind of layer emerges at a given time and altitude

high resolution swath sonar investigation of sand ridge dune and ribbon morphology in the offshore environment of the new jersey margin abstract sand ridges on the northeast us atlantic shelf form in the near shore environment most likely in response to storm driven flows as the holocene transgression has continued the ridges have been transferred to an offshore hydrodynamic regime where currents are not constrained by the coast and storms do not influence bottom currents as frequently or as strongly here we qualitatively and quantitatively investigate the morphology of offshore sand ridges and smaller scale features in an effort to place constraints on bedform development in these deeper waters a recent high resolution swath sonar survey mapped a portion of the new jersey shelf from 20 m water depth to the shelf break 120 m imaging both sand ridges and smaller scaled dunes and ribbons in far greater detail than has been previously possible using a robust statistical analysis we find that the gross morphology of ridges height width length does not change with depth beyond 20 m water depth and changes in ridge orientation generally mirror changes in regional contour orientation hence ridges have not continued to grow since transgression has brought them into the offshore hydrodynamic regime however on the inner shelf 20 m water depth to the mid shelf shore we do find evidence in the ridge shape which has an asymmetry opposite to that seen near shore and in the complex backscatter response that some important modifications to ridges are taking place at these water depths in contrast on the mid shelf from the mid shelf shore to the franklin shore ridges tend to have higher backscatter at the crests implying that these are largely winnowed relict features lineated smaller scale 100 500 m wavelength

seismic imaging in hardrock environments the role of heterogeneity abstract we investigate the effect of petrophysical scale parameters and structural dips on wave propagation and imaging in heterogeneous media seismic wave propagation effects within the heterogeneous media are studied for different velocity models with scale lengths determined via stochastic analysis of petrophysical logs from the matagami mine quebec canada the elastic modeling study reveals that provided certain conditions of the velocity fluctuations are met strong local distortions of amplitude and arrival times of propagating waves are observed as the degree of scale length anisotropy in the p wave velocity increases the location of these local amplitude anomalies is related to the dips characterizing the fabric of the host rocks this result is different from the elliptical shape of direct waves often defined by effective anisotropic parameters used for layered media although estimates of anisotropic parameters suggest weak anisotropy in the investigated models these effective anisotropic parameters often used in vti tti do not sufficiently describe the effects of scale length anisotropy in heterogeneous media that show such local amplitude travel time and phase distortions in the wavefields numerical investigations on the implications for reverse time migration rtm routines corroborate that mean p wave velocity of the host rocks produces reliable imaging results based on the rtm results we postulate the following weak anisotropy in hardrock environments is a sufficient assumption for processing seismic data and seismic scattering effects due to velocity heterogeneity with a dip component is not sufficient to cause mislocation errors of target structures as observed in the discrepancy between the location of the strong seismic reflections associated to the matagami sulfide orebody and its true location future work will investigate other factors that may provide plausible explanations for these mislocation problems with the objective of providing a mitigation strategy for incorporation into the seismic data processing sequence when imaging in hardrock settings

bathymetric artifacts in sea beam data how to recognize them and what causes them sea beam multibeam bathymetric data have greatly advanced understanding of the deep seafloor however several types of bathymetric artifacts have been identified in sea beam s contoured output surveys with many overlapping swaths and digital recording on magnetic tape of sea beam s 16 acoustic returns made it possible to evaluate actual system performance the artifacts are not due to the contouring algorithm used rather they result from errors in echo detection and processing these errors are due to internal factors such as side lobe interference bottom tracking gate malfunctions or external interference from other sound sources e g 3 5 khz echo sounders or seismic sound sources although many artifacts are obviously spurious and would be disregarded some particularly the omega effects described in this paper are more subtle and could mislead the unwary observer artifacts observed could be mistaken for volcanic constructs abyssal hill trends hydrothermal mounds slump blocks or channels and could seriously affect volcanic tectonic or sedimentological interpretations misinterpretation of these artifacts may result in positioning errors when seafloor bathymetry is used to navigate the ship considering these possible geological misinterpretations a clear understanding of the sea beam system s capabilities and limitations is deemed essential

effects of interplanetary electric field on the development of an equatorial spread f event 1 on a geomagnetically disturbed night 7 january 2005 an equatorial spread f esf event was captured during premidnight hours by the indian mst radar operated in ionospheric mode at gadanki 13 5 n 79 2 e dip angle 12 5 n the base height of the ionospheric f region over dip equator and a low latitude station showed similar variation during most of the esf interval except mainly during 2145 2200 ist indian standard time ist universal time ut 5 5 hours the zonal electric field variation over dip equator responded to a prompt penetration event at 2000 ist by gradually changing its polarity from westward to eastward after 2015 ist leading to the initiation of esf at 2035 ist the linear growth rate analysis supports the generation of irregularities only when the eastward electric field owing to the prompt penetration effect is taken into account the zonal electric field became westward again after 2100 ist however it ephemerally turned eastward shortly after 2145 ist 1615 ut that is believed to be associated with an overshielding condition a plasma plume got resurrected after 30 min indicating the association of the development of this plume structure with the overshielding electric field the oi 630 0 nm airglow intensity variations observed by a collocated airglow photometer simultaneously operated in a bidirectional zenith and east mode corroborated well with the esf structure and dynamics during the disturbed period these observations evince the active role of interplanetary electric field ief in the development of esf in the premidnight hours

a method for determining the average height of a large topographic ice sheet from observations of the echo received by a satellite altimeter ice sheet surfaces have scales of fluctuation that are similar to the diameter of the area illuminated by a satellite radar altimeter the present theory of altimetry developed to describe scattering from the ocean surface does not deal properly with the geometry of ice sheet surfaces in this paper the theory of altimetry is extended to cover this geometry a general relation for the altimeter echo from a surface of unknown geometry is developed including the effects of the penetration of the surface by the radar waves this expression is linearized using the characteristic operating geometry of satellite altimeters and the gentle nature of ice sheet gradients from this expression an integral equation is derived from whose solution the spatial average of the height of the surface relative to a spherical datum can be determined the integral equation is of a volterra type which permits the uniqueness of the solution for the average height to be investigated simply the method is extended to provide a solution for the spatial average of the height of a local region of the ice sheet provided the region remains large in comparison with the area illuminated by the altimeter and to deal with variations in the antenna boresight alignment the results have a number of implications for the collection and reduction of echoes in an experiment to determine the average height of an ice sheet the unique determination of the average height requires the echo to be known over a time interval that depends on the extrema of the surface which therefore must be known a priori the average height itself can be determined by the operation on the echo of a linear operator whose kernel is derived from the solution of the volterra type equation this marks a change from the procedures currently used in practice to reduce echoes from ice sheets

equatorial ionospheric plasma bubble irregularity occurrence and zonal velocities under quiet and disturbed conditions from polarimeter observations amplitude scintillation and faraday rotation angle fluctuations of satellite vhf beacons registered by electronic polarimeters operated at two stations spaced 110 km apart in the magnetic east west direction namely cachoeira paulista 22 41 s 45 w dip angle of 26 and sao jose dos campos 23 12 s 45 51 w dip angle of 26 in brazil are analyzed for equinoctial and summer months of 1982 1983 to determine the irregularity patch occurrence characteristics and their zonal velocities under varying levels of magnetic disturbances the scintillation patch occurrences and total electron content fluctuations representing plasma depletion structures decrease during premidnight hours and are enhanced in the postmidnight period the occurrences often extend to morning hours with increasing magnetic activity index while the night events are associated with eastward irregularity patch motion the morning events have westward velocities the reversal occurring around 0400 lt reflecting the morning velocity reversal in the f region bulk plasma motion reported earlier from jicamarca radar measurements the westward plasma bubble motions reported here represent the first observation of this kind another important finding from the present investigation is a clear tendency for the zonal plasma motion namely the equatorial meridional electric field to become enhanced mainly in the premidnight hours immediately following strong magnetic activity

ionospheric plasma blobs observed by oi 630 nm all sky imaging in the brazilian tropical sector during the major geomagnetic storm of april 6 7 2000 1 this paper presents first observations of plasma blobs localized plasma density enhancements associated with large scale plasma density depletions plasma bubbles in the nighttime low latitude f region during a major geomagnetic disturbance ground based observations of the oi 630 nm all sky images obtained at cachoeira paulista 22 7 s 45 0 w brazil in the appleton anomaly region showed the presence of plasma blobs during the major geomagnetic storm of april 6 7 2000 kp 38 40 dst max 288 nt the oi 630 nm emission images were used to map the spatial and temporal locations of plasma blobs and bubbles in the bottomside of the f region the f region parameters presented in this work were obtained from ionosondes operating near the same site and also at sao luis 2 6 s 44 4 w brazil ionospheric plasma blobs and bubbles zonal drift velocities measured by the all sky imaging system showed that both the plasma blobs and the bubbles moved westward normally the plasma drift is eastward during nighttime on this magnetically disturbed night furthermore the plasma blobs showed typically east west and north south extensions in the range of 110 160 km and 200 450 km respectively it appears that the dmsp 15 satellite orbiting at about 850 km altitude passed through one of the blobs detected by the ground based observations on this night while crossing the brazilian sector this indicates the enormous altitude extent from about 275 km oi 630 0 nm emission to 850 km dmsp satellite altitude of the localized plasma density enhanced regions in this work we present and discuss several features related to the dynamics of the localized plasma density enhancements and large scale plasma density depletions during this major geomagnetic disturbance

glacial cycles drive variations in the production of oceanic crust glacial cycles redistribute water between oceans and continents causing pressure changes in the upper mantle with consequences for the melting of earth s interior using plio pleistocene sea level variations as a forcing function theoretical models of mid ocean ridge dynamics that include melt transport predict temporal variations in crustal thickness of hundreds of meters new bathymetry from the australian antarctic ridge shows statistically significant spectral energy near the milankovitch periods of 23 41 and 100 thousand years which is consistent with model predictions these results suggest that abyssal hills one of the most common bathymetric features on earth record the magmatic response to changes in sea level the models and data support a link between glacial cycles at the surface and mantle melting at depth recorded in the bathymetric fabric of the sea floor

altitude extended equatorial spread f observed near sunrise terminator over indonesia 1 spatial structure of a post sunrise backscatter plume associated with a plasma bubble has been observed for the first time with the 47 mhz equatorial atmosphere radar ear in west sumatra indonesia 0 20 s 100 32 e dip latitude 10 36 n this plume is likely associated with a geomagnetic storm it extended from what appears to be the base of the f layer into the topside ionosphere and differed from all plumes previously observed it was also extended in longitude i e in the east west direction and appeared to involve two spatially separated regions the plume was first observed around sunrise close to 200 250 km altitude but at a time when the e region was not yet sunlit spatial maps of the line of sight doppler velocity show that there was upward development and westward drift of backscatter regions indicative of daytime drift conditions the observations remain puzzling because the plume continued for approximately two hours after e region sunrise

toward a synthesis of equatorial spread f onset and suppression during geomagnetic storms 1 we present initial steps toward unifying our understanding of storm time equatorial spread f esf by searching for the common elements in past case studies and statistical occurrence patterns we show that the development or inhibition of equatorial irregularities during magnetically active periods can be understood using the ae parameterized fejer scherliess model for disturbance vertical drifts versus storm time and local time this model takes into account the different sources of perturbation electric fields magnetospheric and ionospheric dynamos that ultimately drive the equatorial vertical drifts showing prompt and delayed effects in the premidnight sector where both generation and suppression can occur as well as in the postmidnight period where generation dominates the postsunset period exhibits the greatest variability for storm time esf versus longitude and thus we demonstrate the fejer scherliess model s applicability in a test case 6 april 2000 that had an ae pattern compatible with their parameterization scheme the model successfully accounts for the pronounced longitude confinement in the observed postsunset esf patterns finally we move beyond the empirically derived relationships between geomagnetic indices and the occurrence of esf aarons 1991 into a framework of true solar terrestrial parameters that drive such effects additional case studies taken from the published literature are then used to show a consistent linkage between postsunset esf onset and the interplanetary electric field ief esw while ae dst kp and dst dt indices were used in earlier studies to determine the dusk longitude sector of disturbance electric fields here we attribute to the ief the main role in the determination of this longitude sector

tidal conversion by supercritical topography calculations are presented of the rate of energy conversion of the barotropic tide into internal gravity waves above topography on the ocean floor the ocean is treated as infinitely deep and the topography consists of periodic obstructions a green function method is used to construct the scattered wavefield the calculations extend the previous results of balmforth et al for subcritical topography wherein waves propagate along rays whose slopes exceed that of the topography everywhere by allowing the obstacles to be arbitrarily steep or supercritical so waves propagate at shallower angles than the topographic slopes and are scattered both up and down a complicated pattern is found for the dependence of energy conversion on e the ratio of maximum topographic slope to wave slope and the ratio of obstacle amplitude and separation this results from a sequence of constructive and destructive interferences between scattered waves that has implications for computing tidal conversion rates for the global ocean

satellite observations of polar ice fields this paper outlines the research needed to advance the knowledge of polar ice masses that could be or has been provided by satellite techniques inland ice sheets ice shelves and pack ice on polar oceans are discussed in separate sections because a satellite radar altimeter can cover wide areas of polar ice economically and rapidly the interpretation of altimeter results is discussed in detail theoretical considerations are used to explain various characteristics of pulse shapes recorded over antarctica by seasat over inland ice surface undulations cause the pulse shape to change rapidly with location and the leading edge to migrate rapidly altimetry over ice shelves should be accurate to better than 1 m and provide new methods for studying their mass balance nearly all sea ice returns that have been studied show a characteristic glistening quite distinct from returns from the open ocean inland ice or ice shelves reasons for glistening are presented and the need for ground truth stressed because pulse shapes should provide an additional source of data to define pack ice characteristics from satellite observations ice sheets in greenland and antarctica constitute 10 of the surface land area of the earth their accumulated 36 x 106 km3 of ice comprises 90 of global freshwater reserves sea ice covers a maximum global surface area of 24 x 106 km2 during the northern summer ca 7 of the world ocean surface these ice masses are coupled closely with other aspects of the natural environment through complex exchanges of energy and mass radok 1978 sergin i979 an understanding of their dynamics and thermodynamics is fundamental to realistic global modelling of climatic oceanographic and lithospheric processes the investigation of ice masses principally in polar areas is hampered by extreme cold long periods of darkness and persistent cloud cover in some areas remote sensing has and will play a critical role in the gathering of data and their routine surveillance this paper briefly reviews the most important research needs for the study of polar ice and points out where research can benefit from satellite techniques table 1 lists these needs for ice sheets and ice shelves and the contributions that have been made by satellite missions or those being planned table of gudmandsen this symposium lists similar requirements for the study of sea ice these cover two types of data sets one acquired within a time domain to study timedependent changes such as sea ice distribution and glacier dimensions the other within a spatial domain where very detailed geographic coverage is required because of their importance to both types of study techniques of radio altimetry from satellites are discussed in some detail

quantitative methods for analyzing the roughness of the seafloor the bathymetry of the world ocean has been mapped using a variety of acoustic sounding instruments and traditional contouring methods prior to this study relatively few quantitative studies have been focused on the detailed morphology of the seafloor the work of most investigators has generally dealt with the analysis of seafloor relief without regard to spatial frequency or concern for obvious morphologic anisotropies a brief review of previous work is presented and is accompanied by an identification of the specific applications and limitations of those approaches the availability of more precise digital sounding data coupled with the development of higher resolution sonar mapping instruments e g deeptow seamarc now make it possible to investigate quantitatively many important aspects of seafloor relief and the geological processes responsible for its formation typical bathymetric contour maps represent a low frequency deterministic model of the seafloor to describe the higher frequency variability or roughness of the seafloor requires the development of an appropriate statistical method for generating a valid stochastic model new methods are developed herein which allow valid statistical models of the variability of oceanic depths to be derived from existing digital bathymetric soundings the smooth contoured surface often preserved as a geographic grid of depths when supplemented by such a roughness model can provide an essentially complete statistical description of the relief statistical models of seafloor roughness are also valuable tools for predicting acoustic scattering and bottom loss and in addition contain a wealth of information for more comprehensive interpretations of deep sea relief forming geological processes to allow the variability of depths to be described as a function of scale spatial frequency the amplitude spectrum is employed as the fundamental statistic underlying the model since the validity of the amplitude spectrum depends upon the assumption of a statistically stationary sample space a computer algorithm operating in the spatial domain was developed which delineates geographic provinces of limited statistical heterogeneity within each of these provinces a spectral model is derived by fitting the amplitude estimates with one or two two parameter power law functions using specialized regression techniques the distribution of resultant model parameters is examined for a large test area adjacent to the coast of oregon 42 45 n 130 124 w which includes several contrasting geologic environments the distribution of roughness corresponds generally with the various physiographic provinces observed in the region within some provinces additional complexities are apparent in the roughness model which cannot be inferred by simply studying the bathymetry these patterns are related to a variety of geological processes operating in the region such as the convergence of the continental margin and the presence of a propagating rift on the northern gorda rise in contrast a very large area of the continental margin off the east coast of the united states was found to have in common a single distinct amplitude spectrum this amplitude spectrum is almost identical to that found from the tufts abyssal plain region off the west coast of the united states spectra from both of these areas can be clearly separated into two straight line segments of different slope the two segments of these spectra are interpreted as reflecting two dominant relief forming processes the higher frequency band representing a sedimentary regime and the lower frequency band representing an underlying tectonic volcanogenic regime in many cases the calculated roughness statistics are not constant for data collected along different ship track directions this is due to the anisotropic nature of the seafloor relief a simple model is developed which describes the roughness statistics as a function of azimuth the parameters of this model quantify the anistropy of the seafloor allowing insight into the directionality of the corresponding relief forming processes and the physical meaning of the derived model statistical parameters finally the model is used to successfully predict the roughness of a surface at scales much smaller than those resolvable by surface sonar systems the model regression line derived from a hull mounted sonar is compared to data from deep towed sonars and bottom photographs the amplitude of roughness is predicted to within half an order of magnitude over five decades of spatial frequency and this prediction capability can probably be improved even further the stochastic models presented also demonstrate the potential for closely approximating the full two dimensional nature of some areas of the seafloor with only four statistical parameters these parameters can be estimated from random ship track data given a sufficient number of tracks and range of headings

changes in fe oxidation rate in hydrothermal plumes as a potential driver of enhanced hydrothermal input to near ridge sediments during glacial terminations j t c and l a c were supported by the natural sciences and engineering research council of canada

highly localized unique electrodynamics and plasma irregularities linked with the 17 march 2015 severe magnetic storm observed using multitechnique common volume observations from gadanki india in this paper we study equatorial electrodynamics and plasma irregularities linked with the 17 march 2015 severe magnetic storm in the indian sector using common volume observations made by the gadanki ionospheric radar interferometer airglow imager digisonde and gps receiver established at gadanki 13 5o n 79 2o e observations show that with the initiation of the storm at 6 ut on 17 march which happened to be midday in the indian sector the low latitude ionosphere responded in tune with the storm induced electric field and by the sunset time the base of the f layer ascended to an altitude of 470 km with a peak upward velocity of 50 m s 1 eventually manifesting equatorial plasma bubble and irregularities causing strong gps scintillation the most important finding found in this study is the confinement of plasma bubble and irregularities in a narrow longitude zone of 69o 98o e results also show reversal of zonal drift of the irregularities from 120 m s 1 eastward drift to 120 m s 1 westward drift in a time span of 30 min both observations are shown to be linked with very special electrodynamical conditions induced by the magnetic storm related electric field in the dusk sector intriguing details of the longitudinally localized electrodynamics and plasma irregularities are discussed in terms of prompt penetration and disturbed dynamo electric field effects

response of the equatorial ionosphere in the south atlantic region to the great magnetic storm of july 15 2000 the effects of the great magnetic storm of july 15 2000 on the equatorial ionosphere have been studied by ground based and satellite in situ measurements a large westward plasma drift in the evening equatorial ionosphere was observed as a result of the ionospheric disturbance dynamo in that environment the imf bz turned southward and presumably caused penetration of e fields to low latitudes this e field initiated the onset of 250 mhz and l band scintillations at ascension island 15 w and precipitous tec decrease at fortaleza brazil 38 w bounding the narrow longitude region in the south atlantic these impulsive ionospheric effects were extremely well correlated with abrupt decreases of sym h 1 min resolution dst the dmsp in situ measurements showed the presence of severe ion density bite outs extending over 30 latitude in the south atlantic magnetic anomaly region the rocsat 1 satellite measured upward and large southward ion drifts in the same sector

elevation change of the greenland ice sheet and its measurement with satellite radar altimetry satellite radar altimetry is presently the only method that has provided the spatial coverage and density of observations needed to reduce the present uncertainty in the mass balance of the greenland ice sheet and its contribution to change in eustatic sea level the only such measurement reported however estimated that southern greenland was thickening at 23 6 cm a 1 which is larger than was thought hitherto this value is reconsidered given more recent information concerning the errors in the measurement a survey of measurements of specific mass balance of the greenland ice sheet is given together with estimates of its sensitivity to temperature change the expected behaviour is described of errors in the satellite position and errors in the range measurement to the ice sheet surface the treatment of biases and the number of independent observations of random errors is described it is found in particular that a higher degree of independence was given to the random errors than should have been the case the total error is recalculated with this accounted for and is found to remain dominated by the bias estimate and therefore largely unaffected by this change the estimate is 23 7 cm a 1 it is concluded that the observation does support a recent thickening of the southern greenland ice sheet

response to comment on glacial cycles drive variations in the production of oceanic crust goff comments that faulting is important for creation of abyssal hills and is the dominant process at slow spreading ridges we respond that faulting is indeed important but cannot alone explain the bathymetric signal predicted by our models and observed at the australian antarctic ridge we show that for intermediate to fast spreading ridges abyssal hill spacing is consistent with the periodicity of the obliquity cycle

a ridgelet transform method for constraining tectonic models via abyssal hill morphology abyssal hill shape and orientation are related to the direction and spreading rate of paleo spreading centers therefore analyzing abyssal hill shape and trend is useful for constraining tectonic models of regions devoid of magnetic reversal anomalies detecting systematic changes of abyssal hill shapes or trends due to changes in spreading rate or direction is not straightforward which makes it difficult to determine appropriate regions over which to average abyssal hill parameters often however detecting these systematic changes where they occur and the scale over which they occur is of primary importance for tectonic reconstructions we present a new method of abyssal hill analysis that is based on the ridgelet transform a relative of the two dimensional wavelet transform our method is capable of locally estimating the width azimuth and root mean square rms amplitude of abyssal hill fabric and highlights changes in these parameters across a survey area making it possible to identify regions created with a constant spreading rate and direction we use three multibeam swaths one crossing the osbourn trough in the southwest pacific basin one crossing the east pacific rise and one crossing the mid atlantic ridge to demonstrate the utility and performance of our method

stochastic characterization of mesoscale seismic velocity heterogeneity in long beach california s u m m a r y earth s seismic velocity structure is heterogeneous at all scales andmapping that heterogeneity provides insight into the processes that create it at large scale lengths seismic tomography is used to map earth structure deterministically at small scale lengths structure can be imaged deterministically but because it is impractical to image short wavelength heterogeneity everywhere we often resort to statistical methods to depict its variability in this study we develop random field model representations of a 3 d p wave velocity model at long beach california estimated from dense array recordings of the ambient seismic wavefield we focus on heterogeneity at the mesoscale which is smaller than 10 km scale of regional tomography but larger than the micro scale of borehole measurements we explore four ellipsoidally anisotropic heterogeneity models including von karman gaussian self affine and kummer models based on their autocorrelation functions we find that the von karman model fits the imaged velocity model best among these options with a correlation length in the horizontal direction about five times greater than in the vertical direction and with strong small scale length variations we validate our results by showing that our model accurately predicts the observed decay of scattered waves in the coda of a nearby earthquake suggesting that quantitative measures of velocity variability will be useful for predicting high frequency ground motion in earthquakes

magmatic and tectonic extension at mid ocean ridges 2 origin of axial morphology 1 we investigate the origin of mid ocean ridge morphology with numerical models that successfully predict axial topographic highs axial valleys and the transition between the two the models are time dependent simulating alternating tectonic and magmatic periods where far field extension is accommodated by faulting and by magmatism respectively during tectonic phases models predict faults to grow on either side of the ridge axis and axial height to decrease during magmatic phases models simulate magmatic extension by allowing the axial lithosphere to open freely in response to extension results show that fault size and spacing decreases with increasing time fraction spent in the magmatic phase fm magmatic phases also simulate the growth of topography in response to local buoyancy forces the fundamental variable that controls the transition between axial highs and valleys is the rise sink ratio fm ft t m where fm ft is the ratio of the time spent in the magmatic and tectonic periods and t m is the ratio of the characteristic rates for growing topography during magmatic phases 1 m and for reducing topography during tectonic phases 1 t models predict the tallest axial highs when fm ft t m 1 faulted topography without a high or valley when fm ft t m 1 and the deepest median valleys when fm ft m t 1 new scaling laws explain a global negative correlation between axial topography and lithosphere thickness as measured by the depths of axial magma lenses and microearthquakes exceptions to this trend reveal the importance of other behaviors such as a predicted inverse relation between axial topography and spreading rate as evident along the lau spreading center still other factors related to the frequency and spatial pervasiveness of magmatic intrusions and eruptions as evident at the mid atlantic and juan de fuca ridges influence the rise sink ratio fm ft t m and thus axial morphology

k u band airborne radar altimeter observations of marginal sea ice during the 1984 marginal ice zone experiment pulse limited airborne radar data taken in june and july 1984 with a 13 8 ghz altimeter over the fram strait marginal ice zone are analyzed with the aid of large format aerial photography airborne synthetic aperture radar data and surface observations variations in the radar return pulse waveforms are quantified and correlated with ice properties recorded during the marginal ice zone experiment results indicate that the wide beam altimeter is a flexible instrument capable of identifying the ice edge with a high degree of accuracy calculating the ice concentration and discriminating a number of different ice classes this suggests that microwave radar altimeters have a sensitivity to sea ice which has not yet been fully exploited when fused with ssm i avhrr and ers 1 synthetic aperture radar imagery future ers 1 altimeter data are expected to provide some missing pieces to the sea ice geophysics puzzle

role of imf b y in the prompt electric field disturbances over equatorial ionosphere during a space weather event on 7 january 2005 a p 40 prompt penetration electric field perturbations of opposite polarities were observed over thumba and jicamarca on a few occasions during 13 45 16 30 ut however the electric field was found to be eastward during 14 45 15 30 ut over both thumba and jicamarca contrary to the general expectation wherein opposite polarities are expected at nearly antipodal points on closer scrutiny three important observational features are noticed during 14 10 15 15 ut first during 14 10 14 45 ut despite increasing southward interplanetary magnetic field imf b z condition the already westward electric field over thumba weakened less westward while the eastward electric field over jicamarca intensified more eastward second the electric field not only became anomalously eastward over thumba but also got intensified further during 14 45 15 00 ut similar to jicamarca third during 15 00 15 15 ut despite imf b z remaining steadily southward the eastward electric field continued to intensify over thumba but weakened over jicamarca it is suggested that the changes in imf b y component under southward imf b z condition are responsible for skewing the ionospheric equipotential patterns over the dip equator in such a way that thumba came into the same dp2 cell as that of jicamarca leading to anomalous electric field variations magnetic field measurements along the indian and jicamarca longitude sectors and changes in high latitude ionospheric convection patterns provide credence to this proposition thus the present investigation shows that the variations in imf b y are fundamentally important to understand the prompt penetration effects over low latitudes

azimuthal offset dependent attributes applied to fracture detection in a carbonate reservoir offset dependent attributes amplitude versus offset avo and frequency versus offset are extracted from 2 d p wave seismic data using the multiple signal classification technique these attributes are used to detect fracture orientation in a carbonate reservoir located in the maporal field in the barinas basin of southwestern venezuela in the fracture normal direction p wave reflectivity is characterized by a large increase of amplitude with offset large positive avo gradient and a large decrease of frequency with offset large negative frequency versus offset gradient in the fracture strike direction p wave reflectivity shows a scattered variation in avo but a small variation in frequency with offset our results also show that the reservoir heterogeneity can lead to large variations of avo signatures and that using azimuthal offset dependent frequency attributes can help lessen the ambiguity when detecting fracture orientation

first observations of the interaction of ocean swell with sea ice using satellite radar altimeter data the action of ocean waves and swell on sea ice in the marginal ice zone miz controls the size distribution of ice floes and thus affects ice dynamics and the thermodynamics of ice growth and decay an understanding of ice processes is important because of the influence of the sea ice cover on high latitude weather and global climate1 also long term changes in average sea ice extent could provide a sensitive indication of climatic change if the degree of shorter term variability were better understood2 previous observations of the propagation of swell within the ice pack have been limited in spatial and temporal extent3 6 here we present new results from the us seasat satellite which suggest that radar altimetry can provide a powerful means of global synoptic monitoring of the interaction between ocean and ice

incorporating sinuous connectivity into stochastic models of crustal heterogeneity examples from the lewisian gneiss complex scotland the franciscan formation california and the hafafit gneiss complex egypt stochastic models are valuable and sometimes essential tools for investigating the behavior of complex phenomena in seismology stochastic models can be used to describe velocity heterogeneities that are too small or too numerous to be described deterministically where analytic approaches are often infeasible synthetic realizations of such models can be used in conjunction with finite difference algorithms to systematically investigate the response of the seismic wave field to complex heterogeneity this paper represents a continuing effort at formulating a complete and robust stochastic model of lithologic heterogeneity within the crust and the means of generating synthetic realizations complete implies that the model is flexible enough to describe all types of random heterogeneity within the crust while robust implies sufficiently constrained parameterization that an inversion problem may be well posed as a basis for investigation we use geologic maps of crustal exposures and petrophysically inferred velocities earlier efforts at stochastic modeling have focused on characterization of the univariate probability density function which is typically modal i e binary ternary etc and the covariance function which is typically fit with a von karman function here we provide a means of characterizing the property of sinuous connectivity and for generating realizations that possess this property sinuous connectivity is the tendency for individual lithologic units to be continuous over long and highly contorted paths there is no means in the earlier modeling of either characterizing or synthesizing this property we generate sinuously connective realizations by mapping regions encompassed by two contours in a gaussian distributed surface into the two values of the binary field this operation is nonunique as one can choose in many ways the values for the contours

stochastic modeling of seafloor morphology inversion of sea beam data for second order statistics at scale lengths less than 100 km or so statistical descriptions of seafloor morphology can be usefully employed to characterize ridge crest processes off ridge tectonics and vulcanism sedimentation and postdepositional transport we seek to develop methods for the estimation of seafloor statistics that take into account the finite precision resolution and sampling obtained by actual echo sounding systems in this initial paper we restrict our attention to the problem of recovering second order statistics from data sets collected by multibeam devices such as sea beam the seafloor is modeled as a stationary zero mean gaussian random field completely specified by its two point covariance function we introduce an anisotropic two point covariance function that has five free parameters describing the amplitude orientation characteristic wave numbers and hausdorff fractal dimension of seafloor topography we formulate the general forward problem relating this model to the statistics of an ideal multibeam echo sounder in particular the along track autocovariance functions of individual beams and the cross covariance functions between beams of arbitrary separation using these second moments as data functionals we then pose the inverse problem of estimating the seafloor parameters from realistic noisy data sets with finite sampling and beamwidth and we solve this inverse problem by an iterative linearized least squares method the inversion method is applied to sea beam transit data from both the pacific and atlantic oceans sea beam system noise stands out as a sharp spike on the along track autocovariance function and can be modeled as a white noise process whose amplitude generally increases with beam angle the five parameters in our second order model can be estimated from the inversion of data sets comprising 100 200 km of track length in general the cross track wave number is the most poorly determined although uncertainties in the assumed sea beam response may bias the values of the fractal dimension using the assumed beamwidth the measured noise values and the seafloor parameters recovered from the inversion we generate sea beam synthetics whose statistical character can be directly compared with raw sea beam data for most of the track segments we have processed thus far the synthetics are similar to the data in the case of one atlantic profile however the comparison clearly indicates the necessity of incorporating higher order statistics the space domain procedures described in this paper can be extended for this purpose

density and size distribution of seamounts in the eastern pacific inferred from wide beam sounding data theoretical expressions relating the distribution of apparent seamount heights per unit length of ship track to the distribution of actual seamount heights per unit area of seafloor are derived for both narrow beam and wide beam echo sounders the shapes of seamounts are approximated as truncated right circular cones of constant slope e height to radius ratio and flatness f i e a seamount of basal radius r has a height h r a flat top of radius fr and a slope angle of arctan e the set of all seamounts in a given physiographic province is assumed to be a poissonian ensemble specified by a function v r the average number of seamounts per unit area for which r r a simple choice for the size distribution of seamounts and one shown to be consistent with data in the eastern pacific is to specify that it decays exponentially with r v r vo exp r in the case of a profile of length l taken in water of depth d with a wide beam echo sounder half beam width the shallow slope deep water approximation e 1 e d yields that the expected number of seamounts with apparent heights h h is n h l 2 1 ed 2 fh lv0e h we apply this sampling theory to apparent height data measured from 44 020 km of wide beam profiles on pacific crust of post mesozoic age although the spatial distribution of seamounts in the eastern pacific is certainly not poissonian the abundance statistics do not involve spatial correlations and we show they are robust with respect to deviations from the poisson model provided the statistics are interpreted as averages over the area actually sampled by the track lines the observed falloff of apparent heights in the eastern pacific is very nearly exponential justifying our use of an exponential model of seamount size distribution the shape parameters are estimated from multibeam surveys of pacific seamounts an analysis of 30 features in the height range 200 4000 m yields 0 21 0 011 and f 0 21 0 028 using these parameters we obtain vo 4 0 1 1 10 9 m 2 and 6 3 0 8 10 4 m 1 these values imply that per 106 km2 in the eastern pacific there are 1600 400 seamounts with summit heights greater than 300 m and 200 60 greater than 1000 m integrated over the entire size distribution seamounts occupy about 6 of the seafloor area and constitute about 0 4 of the oceanic crustal volume our estimates of seamount abundance are appreciably greater than those of most other authors a discrepancy we attribute primarily to the sampling bias of previous studies which generally used uncorrected map counts this hypothesis is corroborated by a comparison of our statistics with map count data for seamounts of heights exceeding 2000 m compiled for the eastern central pacific from the scripps charts above 3000 m the map counts are consistent with the predictions of the exponential model but below this height they are biased to low values

characteristics of the equatorial plasma drifts as obtained by using canadian doppler ionosonde over southern tip of india we present here characteristics of the doppler drift measurements over tirunelveli 8 73 n 77 70 e dip 0 5 n an equatorial site over southern india using doppler interferometry technique of canadian ionosonde three dimensional bulk motions of the scatterers as reflected from the ionosphere are derived by using doppler interferometry technique at selected frequencies using spaced receivers arranged in magnetic e w and n s directions after having compared with lowell s digisonde drifts at trivandrum we studied the temporal and seasonal variabilities of quiet time drifts for the year 2012 the observations showed higher vertical drifts during post sunset in the equinox followed by winter and summer seasons the comparison of doppler vertical drifts with the drifts obtained from a virtual height and b fejer drift model suggests that doppler vertical drifts are relatively higher as compared to the drifts obtained from model and virtual height methods further it is seen that vertical drifts exhibited equinoctial asymmetry in prereversal enhancement quite similar to such asymmetry observed in the spread f in the ionograms and gps l band scintillations the zonal drifts on the other hand showed westward during daytime with mean drifts of 150 200 m s and correlated well with equatorial electrojet strength indicating the role of e region dynamo during daytime while they are eastward during nighttime with mean drifts of 100 m s resembling f region dynamo process also zonal drifts showed large westward prior to the spread f onset during autumn equinox than vernal equinox suggesting strong zonal shears which might cause equinoctial asymmetry in spread f

comment on glacial cycles drive variations in the production of oceanic crust crowley et al reports 13 march 2015 p 1237 propose that abyssal hill topography can be generated by variations in volcanism at mid ocean ridges modulated by milankovitch cycle driven changes in sea level published values for abyssal hill characteristic widths versus spreading rate do not generally support this hypothesis i argue that abyssal hills are primarily fault generated rather than volcanically generated features

magnetospheric disturbance induced equatorial plasma bubble development and dynamics a case study in brazilian sector 1 equatorial ionospheric plasma bubble irregularity development and dynamics during the major magnetospheric storm of 26 august 1998 are investigated using the data collected by a multistation and multi instrument diagnostic network operated at equatorial and low latitude sites in brazil and auroral electrojet activity au al imf and dst indices a magnetospheric disturbance onset in the morning of 26 august 1998 was initiated by a solar wind shock and associated imf bz polarity reversals and ssc that were soon followed by a succession of substorm like auroral electrojet ae intensifications and dst development an imf bz southward turning and associated ae intensifications in the brazilian dusk sector produced intense prompt penetration eastward electric field that caused large f region vertical drift and consequently the developments of intense postsunset equatorial anomaly and a series of intense plasma bubbles the latter event lasting the entire night as observed by digital ionosondes at sao luis 2 33 s 315 8 e dip angle 5 and fortaleza 3 9 s 321 55 w dip angle 9 and an all sky imager two scanning photometers and a digisonde at the low latitude site cachoeira paulista 22 6 s 315 e dip angle 28 a notable aspect of the dynamics of the bubbles was their initially very low eastward drift velocity which turned into steadily increasing westward velocity that lasted till early morning hours the results show for the first time a relationship between the zonal drift velocities of optically observed large scale bubbles tens to hundreds of kilometers and that of the smaller scale kilometer sizes structures as observed by a digital ionosonde the results point to the dominant role of a disturbance dynamo associated westward thermospheric wind to maintain the plasma irregularity drift increasingly westward going into postmidnight hours as an important finding the results further show that significant contribution to the westward plasma bubble irregularity drift normally attributed to disturbance dynamo effect could arise from prompt penetration disturbance zonal electric field in the course of a disturbance sequence lasting several hours such effect is attributed to hall electric field arising from the primary disturbance zonal electric field under enhanced nighttime ionospheric conductivities produced possibly by storm associated particle precipitation in the brazilian longitude sector in agreement with recent evidences abdu et al 1998b

seasonal and inter annual variations in antarctic sea ice extent as mapped by radar altimetry previous work has shown that inter annual variations in total sea ice extent may provide a sensitive indicator of global climate change data from passive microwave instruments have allowed mapping of global sea ice extents from 1973 76 and from 1978 up to september 1987 gloerson and campbell 1988 in this paper data from another microwave instrument the geosat radar altimeter have been used to map the antarctic sea ice extent for the period november 1986 to january 1989 comparison with total antarctic sea ice extents derived from the scanning multichannel microwave radiometer smmr show excellent agreement during the freeze up period but show significant differences during the late part of the melt period

the size distribution of pacific seamounts an analysis of wide beam sea beam and map count data in the eastern and southern pacific confirms the hypothesis that the average number of ordinary seamounts with summit heights h h can be approximated by the exponential frequency size distribution v h vo e h the exponential model characterized by the single scale parameter 1 is found to be superior to a power law self similar model the exponential model provides a good first order description of the summit height distribution over a very broad spectrum of seamount sizes from small cones h 3500 m the distribution parameters obtained from 157 000 km of wide beam profiles in the eastern and southern pacific ocean are vo 5 4 0 65 10 9m 2 and 3 5 0 21 10 3 m 1 yielding an average of 5400 650 seamounts per million square kilometers of which 170 17 are greater than one kilometer in height the exponential distribution provides a reference for investigating the populations of not so ordinary seamounts such as those on hotspot swells and near fracture zones and seamounts in other ocean basins if we assume that volcano height is determined by a hydraulic head proportional to the source depth of the magma column then our observations imply an approximately exponential distribution of source depths for reasonable values of magma and crustal densities a volcano with the characteristic height 1 285 m has an apparent source depth on the order of the crustal thickness

a stochastic view of lower crustal fabric based on evidence from the ivrea zone despite its complicated history the ivrea zone is considered to be a representative surface exposure of extended continental crust we have digitized two standard 1 25 000 geological maps from this area and evaluated their structural statistics because of the subvertical orientation of the ivrea zone these maps can be considered as small scale cross sections through the lower continental crust the autocorrelation functions of the digitized lithologies measured from these maps show a clear self similar or fractal rather than a gaussian or deterministic trend we found that an anisotropic von karman correlation function with an aspect ratio around 4 and a hurst number of 0 3 corresponding to a fractal dimension of 2 7 matches the observed data our results represent an explicit confirmation of previous indirect evidence for the fractal nature of lithospheric heterogeneities and provide the means to construct realistic crustal scale seismic models of ivrea type lower continental crust

low latitude ionosphere response to super geomagnetic storm of 17 18 march 2015 results from a chain of ground based observations over indian sector in this paper we present unique results of equatorial and low latitude ionosphere response to one of the major geomagnetic storms of the current solar cycle that occurred during 17 18 march 2015 where dst reached its minimum of 228 nt here we utilized data from magnetometers chain of ionosondes located at tirunelveli 8 73 n 77 70 e geometry 0 32 n hyderabad 17 36 n 78 47 e geometry 8 76 n and allahabad 25 45 n 81 85 e geometry 16 5 n along with multistation gps receivers over indian sector the observations showed a remarkable increase of h f to as high as 560 km over tirunelveli magnetic equator with vertical drift of 70 m s at 13 30 ut due to direct penetration of storm time eastward electric fields which exactly coincided with the local time of pre reversal enhancement pre and caused intense equatorial spread f irregularities in ionosondes and scintillations in gps receivers at wide latitudes plasma irregularities are so intense that their signatures are seen in allahabad lucknow storm time thermospheric meridional winds as estimated using two ionosondes suggest the equatorward surge of gravity waves with period of 2 h suppression of anomaly crest on the subsequent day of the storm suggests the complex role of disturbance dynamo electric fields and disturbance wind effects our results also show an interesting feature of traveling ionospheric disturbances possibly associated with disturbance meridional wind surge during recovery phase in addition noteworthy observations are nighttime westward zonal drifts and pre related total electron content enhancements at anomaly crests during main phase and counter electrojet signatures during recovery phase

quiet time equatorial f region vertical plasma drift model derived from rocsat 1 observations 1 we have used five years of measurements on board the rocsat 1 satellite to develop a detailed quiet time global empirical model for equatorial f region vertical plasma drifts this model describes the local time seasonal and longitudinal dependence of the vertical drifts for an altitude of 600 km under moderate and high solar flux conditions the model results are in excellent agreement with measurements from the jicamarca radar and also from other ground based and in situ probes we show that the longitudinal dependence of the daytime and nighttime vertical drifts is much stronger than reported earlier especially during december and june solstice the late night downward drift velocities are larger in the eastern than in the western hemisphere at all seasons the morning and afternoon december solstice drifts have significantly different longitudinal dependence and the daytime upward drifts have strong wave number four signatures during equinox and june solstice the largest evening upward drifts occur during equinox and december solstice near the american sector the longitudinal variations of the evening prereversal velocity peaks during december and june solstice are anti correlated which further indicates the importance of conductivity effects on the electrodynamics of the equatorial ionosphere