two views of the cold filament abstract two views of the cold filament first described by weatherly and kelley are presented the first is a local view near 40 n 62 w there its upslope edge is found to be a front which by benthic standards is large its downslope edge was not sampled what distinguishes this benthic front from others is that it is a permanent feature in the abyssal ocean above the cold filament relatively murky detached bottom layers were observed and tracked to where they separated from the bottom at the benthic front apparently these detached layers entrain overlying water a density jump at their base apparently restricts entrainment of underlying water primarily during the detachment process with comparably less entrainment thereafter the second view a regional one comes from examining historical hydrographic sections these indicate that the cold filament extends from the newfoundland ridge westward then southward to 24 n and possibly to 20 n along the base of the continental rise the cold filament i

evolution of mesoscale auroral cavities before substorm onset we have used density measurements made by the freja satellite to analyze the dynamical behavior of mesoscale auroral cavities at an altitude of 1700 km freja s orbital period of 109 min enabled a very large data set of cavity occurrences to be collected the occurrence distribution over 1 year was analyzed statistically and two case studies of individual events were used to provide additional information it was found that the data are consistent with persistence times of 2 or more hours for plasma cavities at this altitude the statistical distribution also showed a weak but demonstrable correlation between cavity occurrence times and substorm onsets this was also seen in the case studies which both happened prior to substorm onsets in the case studies the motions of the cavities could be tracked with the support of ground data it was found that the cavity followed the oval closely as the oval moved southward during the substorm growth phase the cavity also moved southward when the expansion phase began the data were consistent with the fact that the cavity expanded together with the oval this suggests that the region where the cavities are observed is embedded within the auroral oval and can follow the motions of the oval

late eocene and maastrichtian paleomagnetic poles for the pacific plate implications for the validity of seamount paleomagnetic data abstract mean paleomagnetic poles for the pacific plate have been calculated for the late eocene 39 ma and the maastrichtian 69 ma the former is located at 77 6 n 7 6 e the latter at 69 9 n 0 9 e although these pole positions are little changed from previous calculations they are better constrained with additional data slightly less than half of the data are derived from the inversion of seamount magnetic fields providing an excellent opportunity to compare such data with other paleomagnetic data of the same age as no significant systematic difference between the two types of data is evident it is inferred that most seamount paleomagnetic data are probably useful indicators of the paleomagnetic field direction

directivity and apparent velocity of the coseismic ionospheric disturbances observed with a dense gps array abstract coseismic disturbances in ionosphere have been observed after recent thrust earthquakes off the pacific coast of japan with a dense global positioning system array positive pulses in electron content as large as several times 10 15 electrons m 2 and as long as 4 5 min emerge 10 min after earthquakes and propagate horizontally with apparent velocity of 1 km s close to the sound velocity at the ionospheric height they may have been excited by coseismic uplifts of the sea surface initially as upward propagating compressive pulses of atmosphere which were gradually refracted to propagate horizontally in ionosphere the propagation has strong north south asymmetry and interaction between the movements of charged particles in acoustic waves and geomagnetic fields might have selectively attenuated the northward propagating disturbances

the vertical propagation of disturbances triggered by seismic waves of the 11 march 2011 m9 0 tohoku earthquake over taiwan in this paper concurrent colocated measurements of seismometers infrasonic systems magnetometers hf cw high frequency continuous wave doppler sounding systems and gps receivers are employed to detect disturbances triggered by seismic waves of the 11 march 2011 m9 0 tohoku earthquake no time delay between colocated infrasonic i e super long acoustic waves and seismic waves indicates that the triggered acoustic and or gravity waves in the atmosphere or seismo traveling atmospheric disturbances stads near the earth s surface can be immediately activated by vertical ground motions the circle method is used to find the origin and compute the observed horizontal traveling speed of the triggered infrasonic waves the speed of about 3 3 km s computed from the arrival time versus the epicentral distance suggests that the infrasonic waves i e stads are mainly induced by the rayleigh waves the agreements in the travel time at various heights between the observation and theoretical calculation suggest that the stads triggered by the vertical motion of ground surface caused by the tohoku earthquake traveled vertically from the ground to the ionosphere with speed of the sound in the atmosphere over taiwan

contribution of induced magnetization to magnetization of seamounts a fundamental assumption in modelling seamount magnetic anomalies is that the contribution of induced magnetization is negligible the general consistency of seamount and non seamount palaeopoles scarcity of poles skewed toward the present field direction and the high ratio of remanent to induced magnetization koenigsberger ratio of many oceanic basalts have been cited as evidence supporting this assumption1 2 recent discussions concerning the dominance of normally magnetized seamounts have focused attention on the possible role of viscous and induced magnetization in seamount anomalies3 6 here we determine natural remanent magnetization initial volume susceptibility and the koenigsberger ratio for more than 2 000 samples from a subaerially exposed seamount section on la palma canary islands table 1 by contrast to results from the oceanic crust and ophiolites these data indicate that a variety of rock types are potential magnetic sources the significant induced component of intrusives underscores the importance of the lithological distribution in determining the character of seamount magnetic anomalies the la palma data together with a plausible lithological distribution indicate that induced magnetization may account for one sixth of seamount magnetization

seasonal variations of the ionospheric total electron content in asian equatorial anomaly regions the ionospheric total electron contents tec in both northern and southern equatorial anomaly regions are examined by using the global positioning system gps in asian area the tec contour charts obtained at ymsm 25 2 n 121 6 e 14 0 n geomagnetic and dgar 7 3 s 72 4 e 16 2 s geomagnetic stations in 1997 solar minimum are investigated it is found that the ionospheric crests manifest remarkable seasonal variations the tec values on both northern and southern equatorial anomaly crests yield their maximum values during the vernal and autumnal months but the winter anomaly does not appear in the southern region results show that both crests are fully developed around midday in winter postnoon in equinoxes and late afternoon in summer and the two crests move significantly equatorward in winter but slightly poleward in summer and autumn these phenomena can be fully explained by a combined theory of the transequatorial netural wind the subsolar point and the auroral equatorward wind

concentric traveling ionosphere disturbances triggered by super typhoon meranti 2016 concentric traveling ionosphere disturbances ctids in total electron content tec triggered by super typhoon meranti on 13 september 2016 are detected using the ground based global navigation satellite system gnss network in taiwan the ctids emanated outwards before the typhoon landfall and lasted for more than 10 hours the characteristics of ctids agree with the gravity wave theory and exhibit spatial and temporal scales in wave periods of 8 30 minutes horizontal wavelengths of 160 200 km and horizontal phase velocities of 106 220 m s we also observe the ctids showing the stationary wave character broad spectra of ctids are excited after the rainbands of typhoon impinged on central mountain range cmr of taiwan the ray tracing technique confirms that the ctids were excited by convective clouds spiral rainbands and the eyewall of typhoon meranti this study provides new evidence of typhoon induced concentric gravity waves in the ionosphere

evolution of the walvis ridge rio grande rise hot spot system implications for african and south american plate motions over plumes crystallization ages of volcanic rocks dredged or drilled from the walvis ridge ten sites and the rio grande rise one site have been determined by the 40ar 39ar incremental heating technique the fundamentally age progressive distribution of these basement ages suggests a common hot spot source for volcanism on the island of tristan da cunha along the walvis ridge and rio grande rise and for the formation of the continental flood basalts located in namibia africa and brazil south america the walvis ridge rio grande rise volcanic system evolved along a section of the south atlantic spreading axis as the african and south american plates migrated apart astride or in close proximity to an upwelling plume reconstructions of the spatial relationship between the spreading axis the tristan hot spot and the evolving walvis ridge rio grande rise volcanic feature show that at about 70 ma the spreading axis began to migrate westward away from the hot spot the resulting transition to intraplate hot spot volcanism along the walvis ridge and associated termination of rio grande rise formation also involved a northward migration of previously formed african seafloor over the hot spot rotation parameters for african motion over fixed hot spots i e absolute motion have been recalculated such that the predicted trail of the tristan hot spot agrees with the distribution of radiometric and fossil basement ages along the walvis ridge african absolute motion has been extended to the south and north american plates by the addition of relative motion reconstruction poles

observations of internal wave reflection off sloping bottoms current and temperature spectra exhibit intensification and polarization near sloping bottoms over a band of frequencies centered at the local internal wave critical frequency examples are drawn from a variety of island seamount and continental slope observations waves propagating down from mid depth change energy density wave number and azimuth when they reflect off the bottom providing a natural perturbation to the deep ocean interior internal wave spectrum deviations from linear theory are interpreted as evidence for dissipation through subsequent shear instability and or nonlinear interaction topographic features appear likely to be energy sinks for internal wave energy

boundary layer intrusions from a sloping bottom a mechanism for generating intermediate nepheloid layers 1 laboratory experiments were used to investigate the growth of intrusions due to internal wave reflection from a sloping boundary when normalized by the incident energy density flux the average intrusion spreading velocity was found to be a linear function of the frequency ratio c where is the frequency of the incident wave and c is the critical frequency at which the wave characteristic has the same angle as the bottom slope evenly spaced layers indicating thin perturbations in the background density gradient developed within the mixing region and spread into the tank interior the vertical spacing of these layers also bore a linear relationship to c a linear model of internal wave reflection suggests that these layers may be related to an isopycnal displacement or overturn scale intrusion growth occurred at a range around the critical frequency and was strongest at slightly supercritical conditions a balance relating the spreading rate of intrusions to the divergence of energy density flux across the boundary layer is derived fitting the laboratory results to this theoretical prediction suggested a weak net buoyancy flux this balance might be of use in predicting spreading rates of intermediate nepheloid layers generated by internal wave mixing at oceanic margins

boundary flow on a lake slope during ekman layer arrest 1 the disruption of an arrested bottom ekman layer on a lake boundary slope is initiated when buoyancy enters the balance between the coriolis force and the pressure gradient this process is shown to behave in a lake in a qualitatively similar manner to the ocean a greater bottom slope and stronger stratification are found to dramatically shorten the shutdown timescale of the ekman flux compared to typical values on the continental shelf and slope convergence of the flow at the density front where the thermocline intersects the bottom leads to a detrainment of bottom boundary layer water into the interior of the lake and thus facilitates the transport of mass and heat independent of turbulence generation in the boundary layer by internal wave interactions internal waves complicate the flow structure the boundary water detrainment and gravitational instability due to ekman layer dynamics and the critical reflection and vertical overturns associated with the internal waves combine in effective boundary mixing

daytime e region field aligned irregularities observed during a solar eclipse the driving mechanism of the midlatitude field aligned irregularities fais has been in dispute for many years the experimental observations were carried out during the solar eclipse of 22 july 2009 in wuhan china to study the possibility of the wave driven irregularities a high frequency coherent scatter radar was used to detect the e region irregularities an ionosonde was applied to record the trace of gravity waves in ionosphere the e region fais occurred at the end of the solar eclipse with fluctuant doppler at the same time the oscillations on the fes maximum reflecting frequency of es curve and in the doppler velocity of the echoes from the es layer were also recorded the data analysis and comparison show that the gravity waves and the fais occurred at the same time with the in phase variations in amplitude and phase thus the solar eclipse and the gravity waves may play important roles in the occurrence of the irregularities a schematic diagram of one period gravity wave is used to explain the possible gravity wave driven mechanism and the doppler fluctuation in the irregularities the daytime fai in midlatitude is a rare phenomenon even in the condition of solar eclipse there are only four cases of the e region fais observed during a solar eclipse including our observations the unique feature of our observations is the synchronized oscillations in the irregularities and in the es layer which will help address the outstanding question of the source of the midlatitude e region fais

reply to comment by f masci and j n thomas on temporal and spatial precursors in ionospheric total electron content of the 16 october 1999 mw7 1 hector mine earthquake

short and long wavelength tids generated by the great american eclipse of 21 august 2017 on the 21 august 2017 the eclipse shadow drastically changed the state of the ionosphere over the united states this effect on the ionosphere is visible in the total electron content measured by global navigation satellite systems gnss the shadow moved with the supersonic speed of 1 000 m s over oregon to 650 m s over south carolina in order to exhaustively explore the ionospheric signature of the eclipse we use data of total electron content from 3 000 gnss stations seeing multiple global positioning system gps and global navigation satellite system glonass satellites to visualize the phenomena this tremendous dataset allows high resolution characterization of the frequency content and wavelengths using an omega k analysis based on 3 d fast fourier transform of the eclipse signature in the ionosphere in order to fully identify traveling ionospheric disturbances tids we confirm the generation of tids associated with the eclipse including tids interpreted as bow waves in previous studies additionally we reveal for the first time short 50 100 km and long 500 600 km wavelength tids with periods between 30 and 65 min the sources of the revealed short wavelength tids are co located with the regions of stronger gradient of the euv related to sunspots our work confirms and describes physical properties of the waves observable in the ionosphere during the great american eclipse

heat flow observations on the bermuda rise and thermal models of midplate swells the bermuda rise is a broad topographic swell which is apparent in both residual depth and geoid anomaly maps of the western north atlantic the magnitudes of the depth and geoid anomalies associated with the bermuda rise are similar to the anomalies associated with other swells surrounding recent volcanic islands e g hawaii suggesting that despite the lack of recent volcanism on bermuda the rise has a similar origin to other midplate swells results are reported from 171 new heat flow measurements at seven carefully selected sites on the bermuda rise and the surrounding seafloor off the bermuda rise the basement depths are generally shallower and the heat flow higher than either the plate or boundary layer models predict with the measured heat flow apparently reaching a uniform value of about 50 mw m 2 on 120 m y old crust on the bermuda rise the heat flow is significantly higher 57 4 2 6 mw m 2 than off the swell 49 5 1 7 mw m 2 the magnitude of the anomalous heat flux 8 10 mw m 2 is comparable to that previously found along the older portion of the hawaiian swell near midway the existence of higher heat flow on both the hawaiian swell and bermuda rise indicates that these features fundamentally have a thermal origin the differences in the shape uplift and subsidence histories of the hawaiian swell and bermuda rise can be quantitatively explained by the different absolute velocities of the pacific and north american plates moving across a distributed heat source in the underlying mantle two dimensional numerical convection models indicate that the observed depth geoid and heat flow anomalies are consistent with simple convection models in which the lower part of the thermally defined plate acts as the upper thermal boundary layer of the convection

ionospheric ripples excited by superimposed wave fronts associated with rayleigh waves in the thermosphere 1 coseismic ionospheric disturbances cids associated with the 2011 tohoku earthquake off the pacific coast mw 9 0 tohoku eq were examined using total electron content and seismic wave data a faster cid propagated at 3 0 km s only in the west southwest while a slower cid propagated concentrically at 1 2 km s or slower from the tsunami source area taking the propagation speed and oscillation cycle into account the faster cid was associated with a rayleigh wave but the slower cid was associated with an acoustic or gravity wave the north south asymmetry of the cid associated with the rayleigh wave suggests that the rayleigh wave did not act as a point source of the acoustic wave because a point source propagating in all directions must produce symmetric cid in all directions therefore a superimposed wave front of acoustic waves was excited by the rayleigh wave and produced the north south asymmetry of the faster cid due to the magnetic inclination effect which is different from a well known north south asymmetry of cid excited at the epicenter on the other hand above and south of the tsunami source area the cid with a period of 4 min was excited by a point source located at the tsunami source area because atmospheric waves propagating from a point source produce north south asymmetry in the resulting cid

mid cretaceous paleomagnetic reference field for north america restudy of 100 ma intrusive rocks from arkansas we have obtained new paleomagnetic data from three middle cretaceous alkalic intrusive complexes in central arkansas magnet cove and potash sulfur springs intrusions about 100 ma 20 sites and granite mountain stock about 88 ma 6 sites out of 254 specimens measured 147 from 20 sites were accepted the remainders have scattered magnetization directions which experiments indicate were caused by lightning occurring during frequent electrical storms in this region the geologic evidence indicates that the intrusions have not been tilted since emplacement the directions of magnetization calculated with respect to present day horizontal yield a mean paleopole at 192 5 e 74 1 n n 20 k 34 a95 5 7 this does not differ at 95 confidence from that determined previously by scharon and hsu but the error is diminished by half the angular dispersion sd of site virtual geomagnetic poles vgps is 13 6 similar to the value of sd about 15 predicted by current paleosecular variation models the revised arkansas paleopole is combined with four other cratonic north american paleopoles of mid cretaceous age to yield a revised middle cretaceous reference pole at 196 e 71 n a95 4 9 the mean of nine paleopoles derived from overprints in rock units from the craton and craton margin which range in age from proterozoic to jura cretaceous is 202 e 68 n a95 8 2 this is not different from the reference paleopole indicating that overprinting was very widespread across north america in mid cretaceous time

palaeomagnetism of cretaceous pacific seamounts summary the palaeomagnetism of cretaceous pacific seamounts as deduced from their magnetic anomalies is reviewed results from 35 seamounts are reported here for the first time of these 35 results 15 are of high enough quality to be useful this has resulted in a considerable increase in the available information concerning the palaeomagnetism of the pacific plate using only the most reliable results we calculate a palaeomagnetic pole for the upper cretaceous at 58 north 350 east with a 95 per cent cone of confidence of only 5 this pole is considerably more accurate than the one previously reported and is farther to the west the previously reported difference between the mean pole position from seamounts close to japan and the mean pole position from seamounts close to hawaii is not real although one group of seamounts close to japan gives an anomalous pole position several mechanisms have been suggested whereby errors might be introduced in the determinations of pole positions from seamounts no error is introduced in the pole position because of the restricted extent of surveys and the consequent inaccuracy in the determination of the regional field the demagnetization effect which can produce differences between the observed direction of magnetization and the direction of the magnetizing field in an elongated body is unimportant for seamounts the new pole position is sufficiently accurate for use in many types of calculations in which it is desired to locate the pacific plate with respect to the earth s spin axis

a new geomagnetic polarity time scale for the late cretaceous and cenozoic we have constructed a magnetic polarity time scale for the late cretaceous and cenozoic based on an analysis of marine magnetic profiles from the world s ocean basins this is the first time since heirtzler et al 1968 published their time scale that the relative widths of the magnetic polarity intervals for the entire late cretaceous and cenozoic have been systematically determined from magnetic profiles a composite geomagnetic polarity sequence was derived based primarily on data from the south atlantic anomaly spacings in the south atlantic were constrained by a combination of finite rotation poles and averages of stacked profiles fine scale information was derived from magnetic profiles on faster spreading ridges in the pacific and indian oceans and inserted into the south ariantic sequence based on the assumption that spreading rates in the south atlantic were smoothly varying but not necessarily constant a time scale was generated by using a spline function to fit a set of nine age calibration points

fate of mantle plume material trapped within a lithospheric catchment with reference to brazil 1 local regions of thin lithosphere act as catchments of hot buoyant plume material unless replenished the trapped plume material cools by convection to the mantle adiabat by several tens of million years in particular currently hot material from the 130 ma parana starting plume head is unlikely to supply 85 ma to recent volcanism on the mainland of brazil and the martin vaz and fernando hot spots rather a plume tail may now underlie southern brazil where tomographic studies detect conduit shaped velocity anomaly through the upper mantle if the tomographic study in fact found a plume tail the track crossed the amazon rift at 85 ma and since then lateral flow along thin regions of the lithosphere from the tail fed widespread feeble volcanism including the flow line hot spots of martin vaz and fernando

a study of tomographically reconstructed ionospheric images during a solar eclipse the low latitude ionospheric tomography network litn consists of a chain of six naval navigation satellite system nnss receiving stations established along 121 e longitude from a geographic latitude of 14 6 n to 31 n it is specifically designed to observe large scale ionospheric variations over the equatorial anomaly region by using tomographic imaging techniques recently the network litn was applied to observations of the october 24 1995 solar eclipse two dimensional images of ionospheric electron density during the eclipse period were reconstructed these images and the corresponding results from a nearby ionosonde were compared with those for a reference day it is shown that during the eclipse day the ionosphere experienced some large scale changes in particular four episodes of electron density enhancement or depression have been identified 1 the maximum enhancement occurred before the maximum phase of the solar eclipse at approximately 7 10 n geomagnetic latitude at the 275 300 km ionospheric height 2 the second enhancement appeared roughly 3 1 2 hours after the maximum obscuration at 15 22 n geomagnetic latitude and 300 325 km ionospheric height 3 the largest electron density depression occurred roughly 2 hours after the maximum obscuration at approximately 9 15 n geomagnetic latitude and on both the bottom and topside ionosphere 4 the second depression occurred about 4 hours after the maximum obscuration at approximately 5 5 n geomagnetic latitude and mainly on the topside ionosphere more detailed study suggests that the two enhancements have their origins in the ionospheric day to day variations the first depression is related to the combined photochemical and the equatorial fountain effects and the second depression may have its origin in geomagnetic coupling between conjugate ionospheres these observations are interpreted within the framework of ionospheric dynamics in the equatorial anomaly region

observations of high frequency internal waves in the coastal ocean dynamics region current meter data from the second coastal ocean dynamics experiment code ii for july 1982 are analyzed for internal waves in the 6 to 40 cycles per day cpd frequency band it is found that the wave field is anisotropic and that the current ellipses are oriented in approximately the cross isobath direction the squares of the ratio of the major to minor axes of the current ellipses the ellipticity are consistent with a continuum of internal waves propagating onshore but are not consistent with a single wave propagating onshore the reduction of internal wave energy across the shelf is consistent with propagation from the deep ocean or shelf break as is the correlation between vertical velocities and velocities parallel to the minor axis however there is evidence for the generation of additional internal wave energy on the shelf in the evolution of the current ellipses across the shelf and in the bluing of the internal wave spectra across the shelf internal wave energy levels are elevated by a factor of 1 5 to 5 above garrett and munk 1972 levels at the moorings on the 130 and 365 m isobaths the first vertical mode dominates at the 130 m isobath the only mooring for which the vertical modal analysis was done

the bathymetry and distribution of the bahia seamounts brazil basin abstract geophysical measurements taken aboard r v conrad in march 1988 and february march 1989 revealed the subtle morphology and structure of the bahia seamount group three distrinct seamount chains comprise the seamount group two of which are remarkably parallel and linear radiometric dates were obtained from the analysis of dredge samples from two of the seamounts and display dates of origin of approximately 78 m y b p late cretaceous which is only slightly younger than the underlying crust i e middle to the late cretaceous the chains are completely separated by thickly sedimented only slightly disturbed sedimentary basis indicating a long period of stable existence the peaks appear to fall into three distinct classes a round steep peaked volcanoes b flat topped small to medium sized guyots and c elongated peaks most of the peaks appear to have been eroded or altered either by mass wasting or by later episodes of volcanism samples from all the seamounts that have been dredged contain complex mineral crusts indicatng low temperature hydrothermal activity pernambuco channel flows through the region and is a fully incised bottom meandering river like channel whose generally nortierly course is partly controlled by the positions of the seamounts it is believed that the channel reflects erosion by northward flowing antarctic bottom water which travers the argentine and brazil basins and is funnelled through existing topographic gaps causing increased flow and transport of marine sediments prior to terminating in the open parts of the northern brazil basin

bow and stern waves triggered by the moon s shadow boat 1 it has been predicted that the moon s shadow the cooling region sweeping over the earth s atmosphere with a supersonic speed could trigger bow waves since 1970 the longest total solar eclipse within next hundred years occurring on 22 july 2009 sweeps over the eastern asia region during the noontime period an analysis of the hilbert huang transform hht is applied to study ionospheric tec total electron content derived from ground based gps receivers in taiwan and japan we not only find the feature of the predicted bow wave but also the stern wave on the equator side of the eclipse path as well as the stern wake right behind the moon s shadow boat the bow and stern waves are formed by acoustic gravity waves of periods about 3 and or 5 minutes traveling equatorward with a phase speed of about 100 m s in the ionosphere

field aligned neutral wind bias correction scheme for global ionospheric modeling at midlatitudes by assimilating formosat 3 cosmic hmf2 data under geomagnetically quiet conditions this study demonstrates the usage of a data assimilation procedure which ingests the formosat 3 cosmic f3 c hmf2 observations to correct the model wind biases to enhance the capability of the new global ionosphere plasmasphere electrodynamics ipe model under geomagnetically quiet conditions the ipe model is built upon the field line interhemispheric plasma model with a realistic geomagnetic field model and empirical model drivers the hmf2 observed by the f3 c radio occultation technique is utilized to adjust global thermospheric field aligned neutral winds i e a component of the thermospheric neutral wind parallel to the magnetic field at midlatitudes according to a linear relationship between time differentials of the field aligned wind and hmf2 the adjusted winds are further applied to drive the ipe model the comparison of the modeled electron density with the observations of f3 c and ground based gps receivers at the 2012 march equinox suggests that the modeled electron density can be significantly improved in the midlatitude regions of the southern hemisphere if the wind correction scheme is applied moreover the f3 c observation the ipe model and the wind bias correction scheme are applied to study the 2012 southern hemisphere midlatitude summer nighttime anomaly southern msna weddell sea anomaly wsa event at december solstice for examining the role of the neutral winds in controlling the longitudinal variation of the southern msna wsa behavior with the help of the wind bias correction scheme the ipe model better tracks the f3 c observed eastward movement of the southern msna wsa feature the apparent eastward movement of the southern msna wsa features in the local time coordinate is primarily caused by the longitudinal variation in the declination angle of the geomagnetic field that controls the field aligned projection of both geographic meridional and zonal components of the neutral wind both the ipe simulations and the f3 c observations show the significant longitudinal variation in the speed of the eastward movement of the southern msna wsa

high frequency internal waves in lake geneva trains of high frequency internal waves have been observed in the thermocline of lake geneva within a few hours after the passing of disturbances which cause a rapid increase or jump in the depth of the thermocline three possible mechanisms for the source of the internal waves are proposed and compared with available data i that the waves are a soliton packet following the jump ii that the waves are generated as the jump passes over or around a local region of rough topography and iii that the jump produces a moving disturbance near the shoreline with internal waves forming a wake behind it the investigation of the last possibility involves the solution of the problem of the form of an internal wave wake in the presence of mean currents which vary in depth both in their strength and direction the wave pattern of the wake in the observed current distribution and stratification of the lake is described and compared with that in the absence of shear an expression for the energy of internal waves propagating in a shear flow is also derived and it is found that the rate of energy loss from the jump to the waves is small the minimum richardson number resulting from the co existence of the mean shear and the internal waves is marginally greater than 1 4 suggesting that the waves may be limited by shear flow instability however none of the mechanisms for their generation and propagation is fully compatible with the available data

ionospheric f2 region perturbed by the 25 april 2015 nepal earthquake seismic waves can be detected in the earth s atmosphere and ionosphere however their impacts on ionospheric electron density ne structures near the altitude of peak ne hmf2 have not yet been fully determined due to the lack of sufficient observations sampled in the vertical direction here we apply a ground based global positioning system gps receiving network in asia as well as the space based gps occultation experiment on board the formosat 3 cosmic f3 c satellite to vertically scan the ionospheric ne structures which were perturbed by the magnitude mw7 8 nepal earthquake that occurred on 25 april 2015 the f3 c altitudinal ne profiles show that the nepal earthquake induced air perturbations penetrate into the ionosphere at supersonic speeds of approximately 800 m s and change the ne structure by 10 near hmf2 the vertical scale of the ne perturbation is 150 km while the hmf2 is uplifted by more than 30 km within 1 min those results reveal that the earthquake induced ground displacement should be considered as a significant force that perturbs the vertical ne structure of the ionosphere

variations of ionospheric total electron content during the chi chi earthquake on 20 september1999 ut 21 septemberin local time lt a large earthquake mw 7 7 struck central taiwan nearthe small town of chi chi the greatest plasma frequency in the ionosphere fof2 observed by the chung li ionosonde 25 0 n 121 2 e reveals three clear precur sors at 1 3 and 4 days prior to the earthquake this paper examines the ionospheric total electron content tec ob served by a network of the global positioning system gps receivers in taiwan area it is found that variations in fof2 and overhead tec recorded at chung li have a similar ten dency combining the data of the network of 13 gps re ceivers time and spatial variations of tec prior to the chi chi earthquake are examined results show that the equa torial anomaly crest moves equatorward and its tec value significantly decreases 1 3 and 4 days before the earth quake a comparison between the disturbed and reference previous 15 day median days confirms that tec decreases significantly around the epicenter in the afternoons of these days finally possible mechanisms are proposed and dis cussed

nonuniform magnetization of seamounts a least squares approach residual total magnetic field anomalies relative to the best fitting uniform magnetization models are large and spatially coherent over three small tertiary seamounts on the cocos plate furthermore the paleomagnetic parameters determined from the uniform magnetization models in some cases disagree significantly with those predicted from models of absolute motion for the cocos plate inversion of the sea surface magnetic anomaly using a least squares procedure which allows magnetization to vary among different sections of each seamount shows clear polarity reversals in two of the seamounts studied the reversed zones constitute about 10 of the seamount volume for the third seamount the nonuniform magnetization solution more correctly determines the paleomagnetic inclination and declination for the only section of the dipolar anomaly not obscured by a magnetic lineation traversing the area the polarities indicated in the least squares solutions were confirmed by magnetic gradiometer measurements from the submersible alvin for all three seamounts the paleomagnetic latitudes and or rotation angles in the nonuniform magnetization solutions changed appreciably by as much as 20 to agree better with plate motion models the nonuniform magnetization models reveal that growth rates for such volcanoes approach 1000 km3 ma with the final phase of volcanism consisting of summit as opposed to flank eruptions the largest of the three volcanoes formed off ridge on lithosphere at least 0 5 ma old and may have remained active for 1 ma hydrothermal activity apparently persists at least 0 7 ma after the last major phase of volcanism

numerical simulations of buoyant ekman layers in the presence of variable stratification part i constant interior forcing abstract two dimensional numerical simulations of the turbulent buoyant ekman layer in the presence of variable stratification help explain a transport mechanism for the detachment of the boundary layer flow around the front initially a constant spatially uniform along the isobaths interior current and constant interior stratification are assumed buoyant inhibition of the boundary layer ekman flow in the stratified region leads to shut down processes that are absent in the unstratified region depending on the direction of the interior flow two dynamically distinct possibilities exist i convergence around the front and subsequent export detrainment of boundary fluid toward the interior southward forcing current i e with shallow water on the right and ii divergence around the front and subsequent import entrainment of interior fluid northward interior forcing i e with shallow water on the left or y positive the position and strength of the convergence divergence are controlled by

short wavelength geoid bathymetry and the convective pattern beneath the pacific ocean summary the geoid and bathymetry data in the pacific ocean are used to shed new light on the structure of upper mantle convection at short wavelengths 200 km the geoid pattern is characterized by parallel lineations lineations however appear less clearly at larger wavelengths 400 or 600 km where the signal due to convective thermal anomalies might be expected the most prominent features among the short wavelength lineations are associated with the well known chains of seamounts and islands other lineations observed in the geoid coincide with computed tracks of other volcanic centres although these tracks are not continuous this suggests that long lived plumes are at the origin of the apparently short chains of seamounts apart from the lineations corresponding to the tracks of classical hotspots there are numerous similar lineations visible on the filtered geoid maps which have the same directions as hotspot tracks these preferential directions and the gravity to bathymetry ratios seem to indicate that the lineations are due to magmas implaced just above or within the lithosphere convective plumes fixed with respect to each other and much more numerous than the classical hotspots could be the source of these magmas a geometrical test of this hypothesis is performed by comparing the lineation pattern with the computed tracks for a set of tentative new hotspots in this way numerous plumes long lived and fixed with respect to each other are found to provide an explanation of the observed small wavelength geoid features

deceleration of a finite width stratified current over a sloping bottom frictional spindown or buoyancy shutdown abstract the deceleration of an unforced two dimensional finite width current over a sloping bottom in a stratified fluid is studied to quantify the relative importance of frictional spindown and buoyancy shutdown when both act simultaneously frictional spindown decelerates the current through ekman suction and pumping at the current edges which transmit stresses into the interior fluid buoyancy shutdown is the process by which lateral advection of density in the bottom boundary layer generates thermal wind shears that reduce the bottom stress thereby halting deceleration a theoretical model of a downwelling current suggests that buoyancy shutdown always reduces the deceleration timescale from that for frictional spindown alone and produces a nonzero steady along isobath current overlying an arrested bottom mixed layer the model is most sensitive to the burger number s n f where n is the buoyancy frequency the bottom slope and f the coriolis parameter larger s produces a stronger steady cu

determining palaeomagnetic poles and anomalous skewness from marine magnetic anomaly skewness data from a single plate summary we present a method for simultaneously determining palaeomagnetic poles and anomalous skewness from the observed skewness of marine magnetic anomalies from a single plate skewness is esimated by visual comparison of phase shifted observed anomaly profiles with an ideal zero phase synthetic anomaly calculated for sea floor formed and observed in a vertical magnetic field we assume that each crossing of the same anomaly or anomalies is anomalously skewed by an identical amount this assumption is supported by the great reduction in squared error i e x obtained by adding just this one adjustable parameter our inversion procedure determines the palaeomagnetic pole and anomalous skewness that give a maximum likelihood best fit in a least squares sense to the observed effective remanent inclinations which are inferred by simple calculation from the observed phase shift our method determines 95 per cent confidence limits both from a constant chisquare boundary and by linear propagation of errors and also estimates the information distribution of the data the anomalous skewness values we determine agree with values estimated from comparison of anomalies across a spreading centre these encouraging results suggest that further skewness studies may permit variations in anomalous skewness with age to be quantified provide constraints for models that describe the processes affecting the magnetic source layer during its creation and evolution and permit oceanic plate apparent polar wander paths to be determined with a fine age resolution

the bahia seamounts test of a hotspot model and a preliminary south american late cretaceous to tertiary apparent polar wander path abstract detailed bathymetric and magnetic data collected over the bahia seamounts in the western south atlantic brazil basin are analyzed six paleomagnetic poles are determined one from three seamounts sharing a ridge and five from isolated seamounts two poles fall near a continental late cretaceous south american pole and are assumed to be of late cretaceous age another seamount has a preliminary 40 ar 39 ar age of 62 4 ma we check this age and estimate the ages of other seamounts by rotating their poles into north american coordinates and comparing them with north american paleomagnetic reference poles these ages and the characteristic magnetic polarities of all bahia seamounts are used to test hotspot models of formation of the seamount group the northern and central bahia seamount chains could have formed from a single hotspot the southern bahia chain may require a second hotspot the two postulated hotspots were probably concurrent and separated by 150 to 200 km the paleomagnetic poles trace out a smooth curve from the late cretaceous poles to a pole that is indistinguishable from the spin axis which we estimate as having an early eocene age the pole ages remain preliminary until better age dates are found and rocks are recovered from more seamounts

ionospheric bow waves and perturbations induced by the 21 august 2017 solar eclipse u s national science foundation grant ags 1242204 nasa grant nnx17ah71g nasa lws muri grant onr15 foa 0011 onr n00014 17 1 2186

paleomagnetism of abbott seamount and implications for the latitudinal drift of the hawaiian hot spot the magnetic anomaly of abbott seamount located near the hawaiian emperor bend has been analyzed for its paleomagnetic information short wavelength noise components of the anomaly assumed to result from small magnetization inhomogeneities or reversals in the upper layers of the volcano were filtered out by upward continuation the polarity of the bulk of the seamount is reversed and its virtual geomagnetic pole is located at 75 5 n 4 6 e this pole lies close to pacific paleomagnetic poles of late eocene age and is consistent with the age of the edifice to be expected from its position in the hawaiian chain the paleolatitude of the seamount 17 5 n 4 4 is not significantly different from the present latitude of the hawaiian hot spot approximately 19 5 n this finding implies that the hawaiian hot spot and by inference other hot spots has remained relatively fixed with respect to the spin axis since the eocene however other paleolatitudes from the hawaiian emperor chain suggest that systematic variation of the hot spot s latitude may have occurred comparison of the hawaiian emperor paleolatitude data with paleomagnetic data from central pacific piston cores and with north pacific paleoequator data from deep sea drilling project cores indicates that the apparent latitude drift since the eocene has been largely the result of long term nondipole components in the geomagnetic field rather than relative motion between the hot spot and the spin axis conversely the variation that occurred prior to the eocene appears to contain a significant amount of such motion coupled with an indeterminate amount of nondipole effect

dynamics of the bottom boundary layer on the northern california shelf abstract time series measurements of velocity temperature and conductivity on the northern california shelf during two winter seasons permit an observational test in vertically integrated form of a simple set of subinertial momentum and heat balances for the bottom boundary layer which have resulted from recent theoretical work these are 1 an along isobath momentum equation that reduces to a classic ekman balance 2 a cross isobath momentum equation in which the ekman balance is modified by a buoyancy force caused by distortion of the isopycnal surfaces within the boundary layer and 3 a heat balance in which variability of temperature is produced by cross isobath advection the measurements confirm the importance of buoyancy in the cross isobath momentum equation and as has recently been predicted theoretically they indicate that buoyancy is a dominant effect when the boundary layer is thick which typically occurs during downwelling favorable flows an ekman balance describes subinertial flu

gps tec response to the 22 july 2009 total solar eclipse in east asia 1 the longest total solar eclipse of this century occurred in east and south asia on 22 july 2009 the eclipse was accompanied with a medium magnetic storm whose main phase onset occurred 27 min after the passage of the moon s umbral shadow using tec data from 60 gps stations we construct differential tec maps to investigate the ionosphere response to the solar eclipse in central china in the range of 26 n 36 n 108 e 118 e i e the magnetic latitude 15 n 25 n during the eclipse s totality a shadow in the ionosphere shown as tec depletion area was formed 100 km south of the moon s umbral path with a maximum decrease of 5 tecu the tec depletion area moved eastward following the movement of the totality area with a time lag of 10 min enhancements of tec due to the storm are observed after the main phase onset the relative drop of tec due to the solar eclipse is evidently larger at lower latitudes than that at higher ones and around noontime than that in the morning by modeling work we find that the latitudinal dependence of the tec response may result from latitudinal variation of magnetic inclination which influences the diffusion of ionization among different layers besides the local time dependence of tec response is closely related to the local time variation of background atmosphere density which affects the electron loss efficiency in the ionosphere

coseismic ionospheric disturbances triggered by the chi chi earthquake 1 at 17 47 ut on 20 september 1999 a large earthquake of magnitude mw 7 6 struck the central taiwan near a small town of chi chi the ground based receivers of the global positioning system gps in the taiwan area detected coseismic ionospheric disturbances cids in the total electron content tec triggered by the chi chi earthquake when the cids travel away from the origin on the earth surface and then propagate into the ionosphere their amplitudes and periods generally become smaller and longer respectively moreover two global grid searches adapting the ray tracing and the beam forming techniques have been used to analyze the observed gps tec we have not only estimated the average speed of the cids propagating in the atmosphere and ionosphere but also determined the location of cid origin on the earth surface by using the two techniques the results show that the observed cids result from shock acoustic waves triggered by sudden and large vertical motions of the chi chi earthquake

magnetization of the la palma seamount series implications for seamount paleopoles paleopoles determined from seamount magnetic anomalies constitute the major data source for the pacific apparent polar wander path but relatively little is known about the processes of remanence acquisition in seamounts since magnetic anomalies reflect both natural remanence nrm and the induced field it is important first to assess whether the nrm is likely to represent an original field direction and second to constrain the magnitude of the induced component to this end we present paleomagnetic data from an uplifted subaerially exposed section through a seamount on la palma canary islands the pliocene seamount series of la palma comprises a 6 km sequence of alkalic extrusives and intrusives which includes all lithologies likely to be volumetrically important in seamounts the structural tilt of the seamount series allows separation of early thermal or chemical remanence from magnetization components acquired after tilting e g viscous remanence the nrm provides a poor indication of the original magnetization direction although the characteristic magnetization of many la palma samples is compatible with the original pretilt direction hydrothermal alteration has resulted in the production of ti poor magnetite and an increasing contribution of hematite with increasing degree of alteration more importantly well defined magnetization directions which deviate from any reasonable geomagnetic direction at la palma can be attributed to hydrothermal alteration in a different polarity than prevalent during the original magnetization based on a comparison of the magnitude of low stability components of magnetization and laboratory acquisition of viscous remanence and previous estimates of the induced magnetization we conclude that viscous and induced magnetization probably account for 15 25 of the total magnetization of seamounts the resulting paleopole bias is a function of the polarity and paleolatitude of the seamount and ranges from 4o to 16 o for cretaceous seamounts in the pacific

ground based gps observation of sed associated irregularities over conus 1 it has been known that steep total electron content tec gradients observed at the boundary between the storm enhanced plasma density sed and the low tec region at subauroral and midlatitude regions are associated with ionospheric irregularities that impact communication and navigation systems however the relationship between the sed associated irregularities and tec gradients is still not well understood partly because of the difficulties of resolving small scale tec gradients from sparsely distributed tec observations in this study we examine the relationship between the sed associated irregularities and tec gradients during the intense geomagnetic storms of 31 march 2001 and 30 october 2003 to explore this relationship tec maps over the continental united states conus were constructed from ground based gps tec observations using kalman filter update formulae with a recently developed nonstationary wavelet based covariance model that enables resolution of tec structures on both large and finer scales our results show that intense tec gradients and ion drifts are thought to be required conditions for the formation of irregularities on the northeast side of the sed additionally our methodology identified the narrow east west stretch of tec enhancement within the midlatitude low tec region on 30 october 2003 and this tec enhancement is most likely to be caused by auroral precipitation

a directional analysis of the small wavelength geoid in the pacific ocean the geoid over the pacific ocean has been filtered in order to enhance wavelengths of the order of 200 km as noticed by previous authors lineations elongated in the direction of present plate motion are observed in the east central pacific elongated features as clearly visible with a larger amplitude and a totally different direction are also present south of the hawaiian chain and west of baja california the dominant directions visible on the filtered geoid map have been confirmed by spectral analyses near the californian coast the ne sw lineations seem to be related to extensional tectonics south of hawaii the nw se directions correspond to the various directions of the pacific plate prior to 40 ma magmas implaced in the lithosphere over fixed convective plumes may be the source of these geoid lineations

evidence for small scale mantle convection from seasat altimeter data evidence for the early development of convective instability in the thermal boundary layer associated with cooling plates has been found from gravity anomalies and residual sea surface heights derived from seasat altimeter data subtle lineated patterns trending in the direction of plate motion in the hot spot reference frame are observed over the younger portions of the fast moving pacific and indo australian plates in particular for the east central pacific ocean the seasat derived data sets reveal lineations with 1 wavelengths in the range 150 500 km perhaps increasing with plate age and 2 peak to trough amplitudes of 5 20 mgal for gravity anomalies the lineated pattern over the pacific plate which first becomes discernable over seafloor 5 to 10 m y old west of the east pacific rise is clearly oblique to the trends of the prominent pacific farallon fracture zones onset of convective instability at such early ages can be understood if young oceanic lithosphere is underlain by a layer having a viscosity of about 1018 pa s 1019 p which is about 3 orders of magnitude less than mantle viscosity inferred from postglacial rebound studies recent numerical studies of convection in fluids with a temperature and pressuredependent viscosity support an early onset time for convective instability and low viscosity zones in the upper mantle beneath young lithosphere such low viscosity zones may correspond to similarly located regions of low shear wave velocities resolved through studies of surface waves

signature of the 29 march 2006 eclipse on the ionosphere over an equatorial station 1 this study documents some results of the effect of the 29 march 2006 eclipse on the ionosphere over ilorin nigeria longitude 4 57 e latitude 8 53 n dip 4 1 s an equatorial station in the west african region the maximum obscuration of the eclipse at this station was 99 percent and it occurred before midday true height electron density profile analysis below the f2 peak was employed in the study the effect on the e and f1 layers was a drastic decrease in electron density with maximum decrease percentages of 60 and 68 for the e and f1 layers respectively a decrease in fof2 began at about 1 hour 20 min after those in the lower layers had started variation of electron density with height showed that the decrease in the electron density occurred through out the e and f1 heights at about the same time while that of the f2 region began at lower heights and extended progressively toward the peak of electron density height of the layer the recovery in the e and f1 layers has already reached an advanced stage before the effect of the eclipse got to the maximum in the f2 region a major departure of hmf2 from the normal variation was observed and discussed

flexural isostasy and loading sequence of the dokdo seamounts on the ulleung basin in the east sea sea of japan abstract the isostatic compensation and loading sequence of the dokdo seamounts on the ulleung basin in the east sea are studied by a flexure model using gravity and bathymetric data the dokdo seamounts comprise dokdo dok island lying as a cluster of emerged small islets surmounting a large submerged volcanic edifice and two voluminous tablemounts simheungtaek and isabu in spite of their similarity in topographic expression a large difference of about 50 mgal between the observed gravity anomaly peaks over dokdo and the isabu tablemount implies different amounts of compensation a comparison between the observed and calculated gravity anomalies of the seamounts shows that the flexural compensation investigated in this study predicts well the observed data the flexure model suggests that the dokdo seamounts might be composed of high density volcanic rocks modeling results show that the flexural rigidity or effective elastic thickness of the lithosphere under dokdo is stronger or thicker than that under the isabu tablemount it implies that the age of lithosphere at the time of loading for isabu was younger than that for dokdo the effective elastic thicknesses associated with the dokdo seamounts approximately follow 200 400 c isotherms in the cooling plate model the results of this study and the former age dating of dokdo suggest that the isabu tablemount was formed first followed by dokdo after the opening of the east sea ceased

the history of intrusive activity on the island of la palma canary islands abstract the island of la palma located in the northwest of the canary archipelago consists of two main geological units 1 the subaerial extrusive coberta series covers most of the island and consists of alkali basaltic lavas phonolitic plugs and pyroclastic rocks erupted between 1 61 ma and the recent 2 the basement complex is exposed in the barranco de las angustias and the caldera de taburiente and consists of the submarine intrusive and extrusive seamount series and a basal plutonic complex alkali basaltic dikes of different ages and orientations intruded in both units three groups of dikes and sills can be distinguished based on their field relationships petrography geochemistry and ages the oldest group i represent the feeder dikes to the seamount series intruded between 2 9 and 4 0 ma b p they were originally steep with a n05 w strike and perpendicular to the originally nearly flat bedding of the layered seamount series subsequent to emplacement group i dikes and the extrusives of the seamount series were rotated into their present orientation group ii sills intruded parallel to the bedding of the seamount series 45 230 are coeval with or younger than group i but older than the erosional unconformity separating the coberta and the basement complex i e 1 6 ma 50 vol of the volcanic edifice of the la palma seamount and highlight the importance of intrusive processes for island growth intrusions into central oceanic volcanoes like la palma may result in an uplift and rotation of more than 30 km 3 by up to 45

the prereversal enhancement of the zonal electric field in the equatorial ionosphere the electric fields in the ionospheric e and f regions near the magnetic equator often show a strong eastward enhancement shortly after sunset and before the eastward normally daytime field reverses to westward several theoretical models of the low latitude fields suggest that this enhancement is caused mainly or entirely by f region winds the f region dynamo but some authors have suggested that it could be produced solely by e region tidal winds we give here additional calculations and arguments in support of the f region source the enhancement of the eastward field for an eastward f region wind turns out to be a simple direct consequence of the fact that after sunset the ionospheric conductivity decreases far more rapidly in the e region than in the f region

paleomagnetism of the patagonian plateau basalts southern chile and argentina a total of 505 paleomagnetic samples were collected from 65 sites volcanic flows of the patagonian plateau basalts at four locations in southern chile and argentina k ar analyses indicate that 38 flows from two locations form a late cretaceous group 64 79 ma while the remaining 27 flows are eocene in age 42 56 ma progressive demagnetization indicates that a characteristic remanent magnetization chrm has been successfully isolated from 59 flows rock magnetic properties and analysis of chrm directions within and between sites allow the secure inference that the chrm is a thermoremanent magnetization acquired during original cooling the eocene flows yield 15 independent samplings of the paleomagnetic field however these data fail the reversals test and probably do not adequately average geomagnetic secular variation the late cretaceous flows yield 18 independent samplings of the paleomagnetic field six of normal polarity and 12 of reversed polarity these data pass the reversals test and have angular dispersion of virtual geomagnetic poles vgps consistent with adequate sampling of geomagnetic secular variation the mean of these 18 vgps yields a late cretaceous paleomagnetic pole for south america latitude 78 7 s longitude 358 4 e a95 6 3 k 31 6 s 14 5 this pole is consistent with similar age poles from north america and africa when the atlantic is reconstructed to 70 ma contrary to previous indications the south american apparent polar wander path does not reach the present rotation axis until after late cretaceous time

northeastern brazilian margin regional tectonic evolution based on integrated analysis of seismic reflection and potential field data and modelling abstract integration of regional seismic reflection and potential field data along the northeastern brazilian margin complemented by crustal scale gravity modelling is used to reveal and illustrate onshore offshore crustal structure correlation the character of the continent ocean boundary and the relationship of crustal structure to regional variation of potential field anomalies the study reveals distinct along margin structural and magmatic changes that are spatially related to a number of conjugate brazil west africa transfer systems governing the margin segmentation and evolution several conceptual tectonic models are invoked to explain the structural evolution of the different margin segments in a conjugate margin context furthermore the constructed transects the observed and modelled moho relief and the potential field anomalies indicate that the reconcavo tucano and jatoba rift system may reflect a polyphase deformation rifting mode associated with a complex time dependent thermal structure of the lithosphere the constructed transects and available seismic reflection profiles indicate that the northern part of the study area lacks major breakup related magmatic activity suggesting a rifted non volcanic margin affinity in contrast the southern part of the study area is characterized by abrupt crustal thinning and evidence for breakup magmatic activity suggesting that this region evolved partially with a rifted volcanic margin affinity and character

dynamically supported geoid highs over hotspots observation and theory hotspots are associated with long wavelength geoid highs an association that is even stronger when the geoid highs associated with subduction zones are removed we quantify these associations by expanding the hotspot distribution in spherical harmonics and calculating correlation coefficients as a function of harmonic degree the hotspot distribution spectrum is nearly white except for peaks at degrees 2 and 6 it is correlated positively with the slab residual geoid for degrees 2 6 with low seismic velocity in the lower mantle at degree 2 and with low seismic velocity in the upper mantle at degree 6 we test fluid mechanical models for hotspots including lithospheric delamination and hot plumes by calculating their predicted dynamic geoid responses and comparing them to the observations these models include the effects of temperature dependent rheology our preferred hotspot model based on observations of the geoid and seismic tomography has plumes preferentially occurring in regions of large scale background temperature highs in a mantle which has a substantial viscosity increase with depth although other models are possible alternatively strong plumes in the lower mantle may neck down and attenuate in the upper mantle due to changes in plume viscosity the major low density anomalies causing the geoid highs associated with plumes appear to be in the lower mantle we hypothesize that cold lower mantle underlying the complementary geoid lows is due to deeply subducted oceanic lithosphere and that hotspot plumes tend to be excluded from these cold regions of the mantle

the midlatitude f2 layer during solar eclipses observations and modeling national natural science foundation of china 40725014 40674090 40636032 national important basic research project 2006cb806306

a paleocene north american paleomagnetic pole incorporating declination only data a problem in determining apparent polar wander paths for the continents is how to incorporate the valid declinations from paleomagnetic studies that have measured shallowly biased inclinations i e inclination error it is proposed that in such cases pole positions and confidence limits be determined using a method previously applied only to paleomagnetic data from oceanic plates applying this method to paleomagnetic data from 67 55 ma rocks of north america a paleomagnetic pole 78 7 n 185 1 e and 95 confidence ellipse 6 0 major semiaxis striking 105 clockwise from north and minor semiaxis of 3 7 were determined an analysis of the information content of the data shows that the single declination only datum from the nacimiento formation new mexico contains 31 of the information which would have been wasted by conventional paleomagnetic analysis if excluded or caused a bias if the inclination had also been included

paleomagnetism of the late cretaceous early tertiary north central montana alkalic province paleomagnetic results have been obtained from the late cretaceous early tertiary igneous complexes of the north central montana alkalic province data from 94 sites in eocene volcanic and intrusive rocks give a paleomagnetic pole located at 82 0 n 170 2 e a95 3 5 k 18 6 while 36 sites in paleocene intrusions yield a paleomagnetic pole at 81 8 n 181 4 e a95 5 4 k 20 2 these poles differ by only 1 6 and are not significantly different statistically the 130 site virtual geomagnetic poles show no significant elongation and suggest no significant apparent polar wander apw during the period of magnetization of the igneous centers postmagnetization structural complications in these rocks are minimal the presence of a single predominant polarity in these intrusive complexes reinforces the radiometric age data that suggest that igneous activity within individual centers was of short duration the northcentral montana data together with other early tertiary cretaceous and mid tertiary paleomagnetic results require modification of our earlier apw chronology diehl et al 1980 it now appears that apw relative to north america since the early cretaceous consists of a polar still stand during much of the cretaceous 120 75 m y b p a period of rapid movement in latest cretaceous time 75 65 m y b p and a period of slow polar movement thereafter the onset of this period of rapid apw correlates well with a major change in plate motions at 80 m y and the beginning of the laramide orogeny

ionospheric total electron content response to solar eclipses on october 24 1995 and march 9 1997 two solar eclipse events occur it is therefore of interest to investigate how the ionosphere responded to the eclipses five global positioning system gps ground based receivers are specifically designed to observe large scale ionospheric variations over the geomagnetic equatorial equatorial anomaly crest and midlatitude regions two dimensional images of ionospheric total electron content tec during the two eclipse periods are constructed the deviations in the tec images on eclipse days from those on reference days show that during the eclipse days the ionosphere experienced some large scale changes four features of the tec deviations pre ascension pa major depression md sunset ascension sa and secondary depression sd have been observed a detailed study shows that in geomagnetic low latitudes pas are possibly related to the locations of the equatorial anomaly crest the latitudinal location amplitude and occurrence time of mds suggest that the fountain effect is essential sas and sds occurring in geomagnetic equatorial and low latitudes and appearing respectively before around and after local sunset indicate that the prereversal enhancement plays an important role

paleomagnetic results from the mogollon datil volcanic field southwestern new mexico and a refined mid tertiary reference pole for north america miocene oligocene rocks of the mogollon datil volcanic field in southwestern new mexico have yielded paleomagnetic data giving 61 site mean unit vgps and a paleomagnetic pole located at 81 9 n 143 6 e a95 4 5 k 17 6 this pole is indistinguishable from other mid tertiary reference poles for north america combining the mogollon datil data with vgp data from other studies of mid tertiary 20 40 ma rocks yields a paleomagnetic pole at 81 5 n 147 3 e n 239 a95 2 4 k 15 4 when divided into normal and reversed polarity subsets the data yield paleomagnetic poles that are statistically different at the 95 confidence level mcfadden and lowes 1981 the paleopole determined from reversely magnetized units located at 78 6 n 138 5 e n 125 a95 3 4 k 14 5 is 6 8 on the far side of the paleopole determined from normally magnetized units positioned at 84 2 n 166 4 e n 114 a95 3 3 k 17 0 when viewed from a common site location i e the western united states similar pole positions an differences are also seen in 10 ma subsets of this data set incomplete removal of a normal overprint on the reversely magnetized units appears unlikely to explain these results rather we suggest that the differences are consistent with the concept that differing harmonics may be associated with the two polarity states over the long term merrill and mcelhinny 1977 merrill et al 1979

paleomagnetism of line islands seamounts evidence for late cretaceous and early tertiary volcanism seamount magnetic anomaly studies have been conducted on eight volcanoes in the line islands seamount chain the magnetic anomalies of these seamounts were inverted to obtain paleomagnetic information four of these gave paleomagnetic pole positions consistent with other pacific cretaceous pole positions of these three have reliable radiometric ages ranging from 72 to 85 ma the remaining four seamounts gave geomagnetic poles that agree with other eocene early oligocene pacific paleomagnetic data and one has a reliable radiometric age of 39 ma all of the apparently eocene volcanoes occur in the central line islands between 8 n and 3 s we suggest that the eocene volcanic event was approximately coincident with the profound change in pacific plate motion recorded by the bend in the hawaiian emperor seamount chain that occurred at approximately 43 ma this volcanism may have resulted from the large change in intraplate stress accompanying the change of plate motion the change in stress might have pulled apart a zone of weakness caused by the original formation of the line islands detailed paleomagnetic modeling of the line islands seamounts was necessary to obtain good results as seven of the eight seamounts appear to be inhomogeneously magnetized to some extent despite these inhomogeneities the high goodness of fit parameters and the excellent agreement of these results with other pacific paleomagnetic data suggest that the paleopoles derived from these seamounts are reliably determined

plate motions and the geomagnetic field ii jurassic to tertiary summary the analysis of the time averaged geomagnetic field is extended back to 200ma palaeomagnetic poles from the major plates have been carefully selected from recent compilations of reliable results for each region these were returned with their corresponding sampling sites to their locations at the estimated dates of magnetization in a fixed hotspots framework the corrected results were then grouped into 20ma windows at intervals of 10ma representing the past 100ma and 40ma windows at 30ma intervals for the more sparse 100 200ma data global means and fisher statistics were calculated for each window having included the axial quadrupole in the calculation the value of this coefficient which gave the maximum value for the fisher precision parameter tightest grouping of poles was taken as representative of each interval the results indicate that a small axial quadrupole of the same sign as the axial dipole may have persisted throughout the cenozoic this is equivalent to a northward offset axial dipole field far sided effect during the late cretaceous this component appears to have changed sign with respect to the dipole negative values seem to have obtained throughout the cretaceous long normal polarity interval corresponding to a southward offset dipole near sided effect the data distribution is inadequate for the resolution of the quadrupole at earlier times and zero values cannot be discounted little relative motion is implied between the hotspots and the geomagnetic axis for the past 90 ma the global mean polar path curving around the predicted fixed hotspots pole at a distance of typically 5 latitude with little sign of rapid tertiary polar wander as implied by studies of pacific data alone between 100 and 200 ma however there is a clear difference between the two reference frames amounting to 17 19 in the jurassic this may reflect motion of the mantle relative to the geomagnetic axis but may also include errors due to inaccurate determination of hotspot tracks and inter hotspot motion

a statistical theory of seamount magnetism the standard least squares estimation of the average magnetization of a seamount is generally regarded as unsatisfactory the reason for its poor performance is i assert due to the strong correlation and uneven magnitudes of the unfitted noise component of the magnetic anomaly least squares estimation depends for its efficiency and freedom from bias upon the statistical independence and common distribution of the random contamination the primary contributor to the unfitted field is the part due to nonuniformity of the magnetic material within the seamount if the magnetic heterogeneities are modeled as a random stationary vector field of known functional form it is possible to calculate the covariance matrix of the magnetic field noise then to the extent that the statistical description of the magnetic sources is valid the correlation can be properly accounted for in the least squares procedure by weighting the observations to form an equilibrated set with random components that are independent and identically distributed the main use of the average magnetization vector is in the determination of the associated paleopole position i show how the least squares estimates of the magnetization vector and its uncertainty are mapped into a confidence region for the pole position application of this theory to a young seamount in the south pacific is highly satisfactory the model stationary vector field chosen for the magnetization is one with isotropic directional behavior and a very short length scale of correlation it is found that the equilibrated residuals are far less correlated than those of the conventional procedure and the misfits are uniformly distributed throughout the equilibrated data the estimated paleopole position is within a few degrees of the north geographic pole which is the expected location because the seamount is geologically young traditional least squares fitting gave a pole at latitude 60 n the 95 confidence zone associated with the paleopole position has semiaxes measuring 16 by 13 and thus the uncertainty is not much larger than those of standard paleomagnetic work

mid cretaceous to early tertiary apparent polar wander path of the pacific plate pacific apparent polar wander was delineated for mid cretaceous to early tertiary time using 22 seamount paleomagnetic poles 11 paleocolatitudes from azimuthally unoriented cores five effective inclinations from two dimensional magnetic anomaly inversions and one magnetic lineation relative amplitude datum three of the seamount paleomagnetic poles were new data calculated in this study the apparent polar wander path was defined with six mean poles having ages of 39 66 76 82 85 and 94 ma an alternate path was constructed combining data from two pairs of mean poles 66 and 76 ma 85 and 94 ma that were statistically indistinguishable the apparent polar wander path is hook shaped with a nearly right angle bend at 82 ma its post 82 ma section trends north south the pre 82 ma part east west the path indicates uneven polar wander unresolvable polar motion occurred between 66 76 ma and 85 94 ma suggesting stillstands however the large distances between the 85 and 82 ma poles 15 2 3 8 and 82 and 76 ma poles 11 3 2 8 imply rapid polar wander at rates of 5 1 1 3 m y and 1 9 0 5 m y respectively both the sharp bend and rapid polar wander occurred at the end of the cretaceous normal polarity superchron the mid cretaceous paleomagnetic data show a trend suggestive of southward motion of the pacific plate that may be the end of a period of southward drift postulated by others to have begun in the jurassic the evolution of various features of the apparent polar wander path are discussed in terms of plate motion true polar wander and time varying non dipole geomagnetic fields we argue that the overall shape of the polar wander path resulted from the change of pacific plate motion from southward to northward perhaps brought about by the beginning of the subduction of the plate beneath asia

contribution of global potential field data to the tectonic reconstruction of the rio grande rise in the south atlantic abstract the application of advanced enhancement techniques for geophysical anomalies to global gravity wgm2012 and magnetic emag2 models sheds light on the complex tectonic evolution of the rio grande rise rgr in the southern south atlantic long wavelength bouguer gravity lows indicate a thicker crust beneath of the ridge whose nature can be related to a microcontinent or an excess of volcanism within the oceanic realm recently dredged continental rocks reinforce the hypothesis of a microcontinent or at least slivers of continental crust however the reserval magnetic pattern of the processed magnetic anomalies provide no evidence of aborted spreading center similar to the well studied jan mayen microcontinent and the surrounding inactive aegir and active kolbeinsey ridges in the north atlantic ocean the reversal magnetic anomalies show a series n s trending parallel stripes roughly follow the current south american coastline and segmented by e w oriented oceanic fracture zones fzs the magnetic stripes are bended eastwards at the rgr showing a more complex magnetic pattern similar to that in the iceland the aborted cruzeiro do sul rift csr and the jean charcot chain jcc are structures that cross the rgr and contribute to the understanding of the tectonic evolution of the south atlantic ocean nw se oriented extensive gravity lows and bathymetric valleys which mark the csr are segmented by e w trending magnetic lineaments related to fzs this structural configuration suggests that the extensional event which formed the rift and the seamounts chain was replaced by strike slip movements along the fzs in addition we constructed a plate kinematic model for the evolution of the rgr based on bathymetric free air and bouguer gravity and magnetic data our model comprises five main stages of the rgr formation and evolution between late cretaceous and paleocene ca 95 60 ma separated by published seafloor isochrones the proposed model suggests that the rgr was built at the mid atlantic ridge by increased magmatism probably related to the tristan da cunha hotspot

ionospheric disturbances induced by a missile launched from north korea on 12 december 2012 1 ionospheric disturbances caused by a missile launched from north korea on 12 december 2012 were investigated by using the gps total electron content tec the spatial characteristic of the front edge of v shaped disturbances produced by missiles and rockets was first determined considering the launch direction and the height of estimated ionospheric points at which gps radio signal pierces the ionosphere the missile passed through the ionosphere at heights of 391 425 and 435 km at 0056 30 0057 00 and 0057 30 ut respectively the observed velocities of the missile were 2 8 and 3 2 km s at that time which was estimated from the traveling speed of the front edge of v shaped disturbances westward and eastward v shaped disturbances propagated at 1 8 2 6 km s the phase velocities of the westward and eastward v shaped disturbances were much faster than the speed of acoustic waves reported in previous studies suggesting that sources other than acoustic waves may have played an important role furthermore the plasma density depletion that is often observed following missile and rocket launches was not found this suggests that the depletion resulting from the missile s exhaust was not strong enough to be observed in the tec distribution in the topside ionosphere