a 2 14 myr astronomically tuned record of relative geomagnetic paleointensity from the western philippine sea 1 we present a 2 14 myr astronomically tuned relative geomagnetic paleointensity record from the western philippine sea pseudosingle domain titanomagnetite is the only magnetic mineral identified and variations in titanomagnetite concentration fall well within the accepted limits for relative paleointensity variations no significant temporally persistent periodicities are observed in wavelet analyses of the paleointensity time series or in the rock magnetic parameters used for relative paleointensity normalization this suggests that our paleointensity record is largely free of rock magnetic or lithological artefacts and that it represents a reliable record of geomagnetic behavior with no evidence for modulation of the field at earth orbital periods the paleointensity record is highly coherent with the sint 800 global paleointensity stack for the last 800 kyr and with a coeval record from the west caroline basin our record confirms that it is normal for the geomagnetic field to undergo dynamic changes within polarity intervals with relatively frequent collapses of the field to low paleointensities and concomitant deviations away from the stable field direction we do not observe an asymmetrical sawtooth form in our paleointensity record which might suggest that previously observed asymmetrical sawtooth paleointensities result from rock magnetic artefacts also we do not observe a persistent 100 kyr inclination periodicity in contrast to the suggestion that geomagnetic field directions are modulated by orbital eccentricity good agreement between our paleointensity record and the coeval west caroline basin record provides the beginning of a detailed view of geomagnetic field behavior between 0 8 and 2 14 ma

geomagnetic reversal spurts and episodes of extraterrestrial catastrophism the possibility that the observed 26 32 myr periodicity in the records of extinction events1 and astrobleme ages2 was caused by periodic episodes of physical bombardment of the planetary surface has raised the likelihood that such an astronomical clock also affects geomagnetic reversals3 4 however the detection5 of a comparable 30 myr harmonic in the geomagnetic reversal record has now been found6 to be an accident of data length while the earlier reported7 32 34 myr harmonic of the reversal record may well be an artefact of the data base here we examine the temporal relation between geomagnetic reversals and those catastrophic episodes which occurred during periods of frequent reversals as geomagnetic history comprises long intervals of frequent reversals alternating with intervals of fixed polarity our rationale is that the geomagnetic field should be most susceptible to catastrophism during its relatively unstable periods of frequent reversals we find spurts in the frequency of geomagnetic reversals at approximately 30 myr intervals correlated with catastrophic episodes these spurts can be seen as the geomagnetic signatures of terrestrial catastrophism and we tentatively ascribe them to enhanced core turbulence during episodes of bombardment the absence of reversal spurts during long intervals of fixed polarity is attributed to the failure during these intervals of the geomagnetic dynamo s bi stable oscillations

global gravity wave variances from aura mls characteristics and interpretation abstract the gravity wave gw resolving capabilities of 118 ghz saturated thermal radiances acquired throughout the stratosphere by the microwave limb sounder mls on the aura satellite are investigated and initial results presented because the saturated optically thick radiances resolve gw perturbations from a given altitude at different horizontal locations variances are evaluated at 12 pressure altitudes between 21 and 51 km using the 40 saturated radiances found at the bottom of each limb scan forward modeling simulations show that these variances are controlled mostly by gws with vertical wavelengths z 5 km and horizontal along track wavelengths of y 100 200 km the tilted cigar shaped three dimensional weighting functions yield highly selective responses to gws of high intrinsic frequency that propagate toward the instrument the latter property is used to infer the net meridional component of gw propagation by differencing the variances acquired from ascending a and descending d o

latitudinal and seasonal variations of inertial gravity wave activity in the lower atmosphere over central china 1 gravity wave activities and background dynamical structure in the troposphere and lower stratosphere tls over five stations at latitudes from 10 n to 40 n were statistically studied by using the data from radiosonde observation on a twice daily basis at 0800 and 2000 lt the background dynamical structure exhibits evident latitudinal and seasonal variations and has a profound influence on inertial gravity waves in the tls in the analyses of inertial gravity waves according to the background structures the observation height coverage is divided into two segments which are the tropospheric 0 10 km and lower stratospheric segments 18 25 km the observational results indicate that the tropospheric jet is the most important excitation source for gravity waves both in the troposphere and lower stratosphere and it plays different roles in determining the morphology of gravity waves in these two segments the jet excited gravity waves in the troposphere can propagate both upward and downward and only part of the upward propagating waves can penetrate into the stratosphere because of the doppler shifting by the jet while in the lower stratosphere gravity waves excited by the tropospheric jet propagate upward most differences between the tropospheric and lower stratospheric results can be explained from the linear dispersion relations of gravity waves and the doppler shifting by the strong tropospheric jet however such an explanation is qualitative rather than quantitative generally the observations reveal that the tropospheric gravity waves are mainly controlled by their excitation sources implying the wave characteristics may be regarded as at least an indicator of the wave excitation source characteristics these results suggest that in order to attain a more realistic source parameterization for gravity waves propagating in the middle and upper atmosphere more attention should be paid to the gravity waves in the troposphere moreover the causes of the pronounced peak of lower stratospheric gravity wave intensity at tropical latitudes revealed by previous observations are also discussed

polarity transitions and excursions of the geomagnetic field the nature of geomagnetic field behavior during polarity transitions is one of the most hotly debated issues in modern geophysics dynamo action in the earth s fluid outer core is known to be responsible for generating the earth s main magnetic field however the mechanism for polarity transition is still unknown polarity transitions are a fundamentally important property of the geomagnetic field but because they have not taken place in historic time it is necessary to turn to the paleomagnetic record to understand the mechanism by which they occur

15 myr periodicity in the frequency of geomagnetic reversals since 100 myr the statistical properties of the magnetic polarity time scale have been examined recently1 2 for several time scales for some of these scales the time evolution of the frequency of reversals as seen through an 8 myr moving rectangular window have been determined in particular over the past 100 myr the mean reversal frequency appears to be dominated by a linearly increasing trend on which is superimposed a rhythmic fluctuation we have attempted to analyse the mathematical structure of the reversal frequency curve in detail and to determine whether the rhythmic fluctuation was indeed periodic by modelling the time evolution of the reversal frequency we find a dominant frequency corresponding to a period of 15 myr this result represents one of the most persistent long term periodicities ever reported for a geophysical phenomenon

a statistical study of gravity waves in the polar regions based on operational radiosonde data gravity waves in the lower polar stratosphere are examined using operational radiosonde observations gathered from 33 stations over a period of 10 years both the potential and kinetic energies of the gravity waves vary annually and reach maxima in winter in the arctic and in spring in the antarctic in the antarctic spring a region of large gravity wave energy propagates downward following the movement of a zone of high static stability associated with southern hemispheric warming moreover the enhanced energy region and the high stability zone coincide in the horizontal plane and move gradually from 135 e 50 s to 45 w 70 s over the south pole the vertical and horizontal directions of wave propagation are examined using hodograph analysis in the vertical most gravity waves transfer energy upward in the arctic while the percentage of downward energy propagation is relatively high in winter and spring in the antarctic horizontally gravity waves propagate westward relative to the mean wind in the arctic while in the antarctic the dominant direction varies from station to station the correlation between gravity wave energy in the lower stratosphere and the mean wind is also examined in the arctic gravity wave energy is highly correlated with the surface wind though in the antarctic it correlates with the stratospheric wind these results suggest that gravity waves observed in the arctic are forced by topography whereas in antarctica some sources may exist in the stratosphere one such source candidate is likely to be the polar night jet

radiosonde observations of gravity waves in the lower stratosphere over davis antarctica radiosonde observations made from davis station antarctica 68 6 s 78 0 e between 2001 and 2012 are used to compile a climatology of lower stratosphere inertial gravity wave characteristics wavelet analysis extracts single wave packets from the wind and temperature perturbations wavelet parameters combined with linear gravity wave theory allow for the derivation of a wide range of wave characteristics observational filtering associated with this analysis preferentially selects inertial gravity waves with vertical wavelengths less than 2 3 km the vertical propagation statistics show strong temporal and height variations the waves propagate close to the horizontal and are strongly advected by the background wind in the wintertime notably around half of the waves observed in the stratosphere above davis between early may and mid october propagate downward this feature is distributed over the observed stratospheric height range based on the similarity between the upward and downward propagating waves and on the vertical structure of the nonlinear balance residual in the polar winter stratosphere it is concluded that a source due to imbalanced flow that is distributed across the winter lower stratosphere best explains the observations calculations of kinetic and potential energies and momentum fluxes highlight the potential for variations in results due to different analysis techniques

missing reversals in the geomagnetic polarity timescale their influence on the analysis and in constraining the process that generates geomagnetic reversals a major problem in defining the chronology of geomagnetic reversals is linked to the detection of short 30 kyr time intervals between reversals tibr published polarity timescales do not usually include the shortest tibr therefore the timescales are inherently incomplete the purpose of this paper is to investigate the effects of this incompleteness on the analysis of the geomagnetic polarity timescale the ultimate goal is to provide constraints on the earth s core processes the effects of inclusion exclusion of the shortest tibr are verified by comparing the results obtained by statistical analysis of real and synthetic series of events for the real sequence two basic cases are considered in which the tiny wiggles are attributed either to short tibr or to paleointensity fluctuations particular attention is paid to the influence of measurement errors estimated for the most recently published cenozoic timescale by following the minimalist philosophy of occam s razor which is particularly suitable for studying poorly known processes the reliability of the simplest model i e the poisson process which is symmetric in polarity can be checked the results indicate the plausibility of a generalized renewal process the only regularity is relative to the long term trend which is probably linked to core mantle coupling in detail a uniform exponential trend in the last 80 myr is found for the timescale it is not presently possible to estimate the influence of the inclusion of tiny wiggles because they are well resolved only in the last 30 myr a period in which both series are stationary the sequences with and without tiny wiggles are symmetric in polarity with no evidence of low dimensional chaos and memory of past configurations the empirical statistical distribution of the tibr departs slightly from a theoretical exponential distribution i e from a poisson process which can be explained by a lack of short anomalies and or by a generating process with wear out properties a more general renewal process a real exponential distribution is sustainable only if the number of missing short tibr in the last 30 myr is larger than the number of tiny wiggles observed in the same period

gravity wave generation around the polar vortex in the stratosphere revealed by 3 hourly radiosonde observations at syowa station intensive radiosonde observations were performed at syowa station 69 0 s 39 6 e over about 10 days in each of march june october and december 2002 to examine inertia gravity wave characteristics in the antarctic lower stratosphere based on the 3 hourly observation data two dimensional i e vertical wavenumber versus frequency spectra of wind fluctuations were examined utilizing a double fourier transform method clear signals of gravity waves whose phases propagate upward suggesting downward energy propagation are detected in june and october when the polar night jet pnj was present on the other hand downward phase propagation i e upward energy propagation components are dominant in all months there is a spectral peak around the inertial frequency in a wide range of vertical wavenumbers in december when the background wind was weak whereas large spectral densities are distributed over lower frequency regions in june and october these spectral characteristics are consistent with the results obtained using a gravity wave resolving global circulation model gcm by sato et al dynamical characteristics are examined separately for upward and downward propagating gravity waves in june using a hodograph analysis method as a result it is found that upward and downward propagating wave packets observed simultaneously in the same height regions have similar horizontal wavelengths and phase velocities this fact suggests that these gravity waves are generated from the same source with a similar mechanism when the wave packets were observed both the local rossby number and the residual in the nonlinear balance equation estimated using ncep ncar reanalysis data are large around the pnj situated slightly to the lower latitudes of syowa station therefore it is likely that the observed inertia gravity waves are generated by a spontaneous adjustment around the geostrophically unbalanced pnj and propagate toward syowa station the possibility of spontaneous gravity wave generation around the pnj is confirmed by comparison with the gcm simulation by sato et al

the magnetic reversal record is not periodic statistical analysis of one version of the magnetic reversal record suggests that the frequency of reversals has changed cyclically with a period of 30 myr starting at least 165 myr ago but factors other than periodicity affect the analysis used and here i show that there is no compelling evidence for periodicity in the reversal record the results of essentially identical analyses that have been applied to other geolocial data should also be re evaluated

lower mantle convection and geomagnetism the statistical properties of recent marine magnetic anomaly time scales covering the period from 165 ma to the present are analyzed via the methods presented in the companion paper mcfadden this issue the data no longer support the hypothesis that during the last 86 ma there were two periods separated by a discontinuity at about 45 ma when the properties were stationary instead there is strong evidence that the rate of reversals decreased in an approximately linear manner with time from 165 ma until it reached zero resulting in the cretaceous normal polarity interval at about 86 ma ago the process of reversals began again and the rate of reversals increased linearly with time there is a slight indication that the rate of reversals reached a maximum about 10 ma ago and is again decreasing analysis of the reversal sequences shows there is no good evidence for the concept of differences in the relative stabilities of the two polarity states nor need such a concept be invoked to explain long intervals without reversals such as the cretaceous normal polarity interval quite clearly there has been some form of thermal perturbation at the base of the mantle with a characteristic time of the order of 108 years our interpretations require convection deep within the mantle and suggest that the temperature at the base of the mantle attains a maximum during long magnetic quiet intervals

mls observations of atmospheric gravity waves over antarctica 1 stratospheric gravity waves over antarctica are studied with the radiance variances observed by upper atmosphere research satellite microwave limb sounder uars mls strong wave activities are found during august and september in 1992 1994 over the drake passage region 290 315 longitude and 50 s 70 s latitude where the enhancement seems associated with the topography of both south america and antarctic peninsula tips during the same period significant gravity wave activities are also evident along the antarctic coastal region the vertical growth of the wave variance shows a scale height of 14 km at low altitudes for both drake passage and the coastal regions but reduces substantially at high altitudes the growth rate transition occurs at a lower altitude in the drake passage region where the variance is larger the gravity wave activities observed near the antarctic may contribute significantly to the formation of polar stratospheric clouds psc because of the overlapping with the vortex edge and with the psc activities as observed by claes cryogenic limb array etalon spectrometer

high resolution temperature profiles measured with stratospheric balloons near the andes mountains a spectral analysis of two balloon soundings of temperature performed in the troposphere and lower stratosphere over the andes mountains in argentina with a vertical resolution of 10 m has been performed the first and second soundings launched at the same location were performed during unusually calm and disturbed atmospheric conditions respectively considerable deviations from the 3 value predicted for the spectral slopes in the power law range by current saturation theories are found these departures are reduced if the data resolution at disposal is diminished thereby eliminating the highest wavelength harmonics slopes do not clearly steepen with increasing height as suggested by other authors and topography seems to be responsible for this fact at low altitudes the spectral amplitude increase with height detected from recent lidar data is corroborated only in the sounding with calm atmospheric conditions spectra are found to scale with the buoyancy frequency not as simply as suggested by the saturation models

energy enhancements of gravity waves in the antarctic lower stratosphere associated with variations in the polar vortex and tropospheric disturbances 1 gravity waves in the antarctic lower stratosphere are examined using original operational radiosonde data obtained at syowa station 69 0 s 39 6 e with fine vertical resolution in the lower stratosphere the temporal variation in gravity wave energy depends on height in the height region of 13 15 km just above the tropopause the seasonal variation in gravity wave energy is not evident the wave energy is rather enhanced when the absolute value of potential vorticity in the upper troposphere becomes small over syowa station this fact implies that tropospheric disturbances affect the dynamical processes of gravity waves there however the gravity wave energy in the height region of 15 25 km shows clear seasonal variation having a maximum in spring the time variation in gravity wave energy is examined in detail in terms of the polar vortex by using the equivalent latitude coordinate energy enhancements occur when the edge of the polar vortex approaches syowa station and the enhancements are especially large when the polar vortex breaks down in spring these results suggest that height variation in the background atmosphere leads to the difference of wave characteristics between the two height regions the enhancements of wave energy are partly explained as modification of the wave structure by the background wind speed and the static stability but it is also likely that enhancements of wave activity contribute to the energy enhancement at the edge of the polar vortex in spring

geomagnetic reversal frequency since the late cretaceous models of geomagnetic reversals as a stochastic or gamma renewal process have generally been tested for the heirtzler et al 1 magnetic polarity time scale which has subsequently been superseded examination of newer time scales shows that the mean reversal frequency is dominated in the cenozoic and late cretaceous by a linearly increasing trend on which a rhythmic fluctuation is superposed subdivision into two periods of stationary behavior is no longer warranted the distribution of polarity intervals is visibly not poissonian but lacks short intervals the labrecque et al 2 polarity time scale shows the positions of 57 small wavelength marine magnetic anomalies which may represent short polarity chrons after adding these short events the distribution of all polarity intervals in the age range 0 40 myr is stationary and does not differ significantly from a poisson distribution a strong asymmetry develops in which normal polarity chrons are poisson distributed but reversed polarity chrons are gamma distributed with indexk 2 this asymmetry is of opposite sense to previous suggestions and results from the unequal distribution of the short polarity chrons which are predominantly of positive polarity and concentrated in the late cenozoic if short wavelength anomalies arise from polarity chrons the geomagnetic field may be more stable in one polarity than the other alternative explanations of the origin of short wavelength marine magnetic anomalies cast doubt on the inclusion of them as polarity chrons however the observed behavior of reversal frequency suggests that core processes governing geomagnetic reversals possess a long term memory

a climatology of gravity wave motions in the mesopause region at adelaide australia abstract a statistical study of gravity wave motions in the mesosphere and lower thermosphere measured with a mf partial reflection radar located at buckland park new adelaide 35 s 138 e in the period november 1933 to december 1984 is presented the analyses am confined to waves with ground based periods between 1 and 24 h time height cross sections show that the mean square amplitudes u 2 and v 2 of the zonal and meridional perturbation velocities respectively vary in a predominantly semiannual manner such that the minima in wave activity coincide with the reversals in the zonal circulation in the middle atmosphere in most instances v 2 is greater than u 2 which together with the small but nonzero u v fluxes shows that the gravity wave field is partially polarized a technique similar to that used to analyse partially polarized electromagnetic waves suggests that on a seasonal basis the wave field is polarized by about 10 to 20 but for shorter periods the degree of polarization may be signi

falling sphere observations of anisotropic gravity wave motions in the upper stratosphere over australia a study of inertial scale gravity wave motions in the region of the atmosphere between 30 and 60 km has been undertaken using wind and temperature data derived from rocket borne falling sphere density experiments performed over woomera australia between 1962 nad 1976 the gross features of the wave field compare favorably with those found in similar northern hemispheric studies wave propagation is found to be both vertically and horizontally anisotropic a rotary spectral analysis indicates predominately upgoing wave energy suggesting that the majority of sources of these waves lie below 30 km a detailed statistical investigation of the waves made using the stokes parameters technique reveals that phase progression is also highly directional in the horizontal with a significant zonal component in summer but with a strong meridional component in winter propagation towards the southeast is inferred in summer with the waves possibly emanating from tropospheric sources in equatorial regions to the north of australia the technique also shows that on average the waves appear to have mean ellipse eccentricities f around 0 4 0 45 indirect estimates of a number of important wave parameters are made in particular v andw flux estimates are made over several height intervals the vertical gradient of density weighted flux implies wave induced mean flow accelerations of the order 0 1 1 ms 1day 1 this suggests that dissipating gravity waves are a significant source of the momentum residuals that are encountered in studies of satellite data from this region

sources of gravity waves in the lower stratosphere above south pole 1 five year 2001 2005 high resolution radiosonde data were processed to obtain the gravity wave gw variabilities in the lower stratosphere over south pole sp our results show that gw activities in the lowermost section 10 15 km are strongest in may and september and weakest in the austral summer whereas in the altitude range of 15 25 km strongest weakest gw kinetic energy is observed around september january we also explored the relationships of gws to the synoptic scale variations in the troposphere and the ageostrophic motions in the upper troposphere over the antarctic which are expected to be significant mechanisms for gw generation a ray tracing model grograt was used to explore the relationship between gw propagation and the background field in the altitude of 15 25 km the annual cycle of gw activity resembles that of adjustment process below 15 km the annual cycle of gw activity has two peaks in may and september our analysis suggests that these two peaks are due to the variation of topographic gw generation and filtering of background atmosphere due to critical level filtering in the lowermost section topographic gws cannot propagate upward which makes the shape of gw annual cycle at higher altitudes closer to the annual cycle of adjustment processes the analysis suggests that the minimum of gw activity at sp during the austral summer may be due to the combination of weaker wave generation from adjustment processes associated with synoptic scale systems flow over topography and unfavorable background field for gw propagation

paleomagnetic tomography of the core mantle boundary abstract analysis of updated global paleomagnetic data indicates that over the last 5 million years the normal and reverse polarity states are discernibly different this difference which can be characterized by a higher ratio of the axial quadrupole to dipole field for the reverse polarity relative to the normal polarity is attributed to lateral variations in temperature or composition at or near the core mantle boundary although several mechanisms are considered thermal electric effects associated with core mantle topography and or with chemical variations in d the seismic layer approximately 150 km thick at the base of the mantle are judged to be the most likely sources of the observed polarity asymmetry this asymmetry should not necessarily be expected to give rise to systematic trends in polarity transitions

cambrian palaeomagnetic data confirm a natal embayment location for the ellsworth whitmore mountains antarctica in gondwana reconstructions summary the ellsworth whitmore mountains ewm are one of five terranes that form west antarctica constraining the positions of these terranes in pre break up gondwana is crucial to understanding the history of the palaeo pacific gondwana margin we report the results of a detailed palaeomagnetic investigation of the ewm which comprises some 150 sites in six formations ranging in age from cambrian to permian five of the studied units yield only viscous remnant magnetizations of recent age or unstable natural remanent magnetizations the remaining unit the mid late cambrian frazier ridge formation yielded stable magnetizations at 16 of 35 sites this component passes a fold test at the 95 per cent confidence level indicating that it pre dates permian deformation and we argue that it is of primary origin the resulting palaeopole 9 n 293 e a95 5 1 is in good agreement with two previously published palaeopoles from similarly aged rocks in the ewm collectively these data indicate that the ewm were located in the natal embayment prior to gondwana break up and underwent 90 of anticlockwise rotation during break up all three studies however yield inclinations

paleomagnetism and the nature of the geodynamo records of direct observations of the earth s magnetic field cover less than a ten millionth ofthe known lifetime of the field thus our knowledge of several geomagnetic phenomena critical to our understanding of the geodynamo must come firom the paleomagnetic record a combination of substantial advances during the past decade or so both in dynamo theory previously the domain of the mathematician and in paleomagnetism previously the domain of the geologist has led to provocative models of the earth s magnetic field and a better understanding of the geodynamo

numerical models of the geodynamo and observational constraints 1 the past few years have seen the emergence of a large number of numerical simulations of the geodynamo in parallel both new and old geomagnetic archeomagnetic and paleomagnetic observations have been interpreted as actual geomagnetic features and used as constraints for dynamo models naturally model predictions should be tested against actual characteristics of the geomagnetic field despite huge differences sometimes in excess of a billion between the values of parameters used in the simulations and those estimated for the earth it is intriguing that many available simulations succeed in producing largely axial dipolar magnetic fields with weaker nondipolar structures in agreement with the first order characteristics of the geomagnetic field yet when considering finer characteristics there are significant differences and failures to actually produce a number of fundamental characteristic features in this presentation we first review numerical results obtained to date then we attempt to summarize which field characteristics derived from observational data sets can be considered robust on the basis of simple criteria used to evaluate the degree of confidence that can be placed in each datum we sort presumably characteristic geomagnetic features into three categories robust controversial and unlikely we conclude that numerical models should be illustrated with a number of key predictions averaged over at least 10 dipole diffusion times these predictions should be tested against the subset of robust observations only controversial observations should await additional confirmation

the parana etendeka continental flood basalt province a historical perspective of current knowledge and future research trends abstract the development of ideas concerning continental flood basalt provinces is not new and many studies were completed on specific provinces before the advent of plate tectonics the parana etendeka province is not an exception and actually is an example of a province that has been thoroughly studied for 100 years in this work i present a brief summary of various aspects of this province from a rather general point of view including many references of difficult access to a reader not versed on the portuguese language key features include the presence of alkaline volcanism along the edges of the main basin before and after a markedly tholeiitic event the uneven spatial distribution of eruptive products relative to the location of continental rupture the apparent lack of a pattern of temporal activity across the whole province and the close relationship between the structure of the underlying sedimentary basin and the distribution of volcanic rocks by bringing together information relevant to all of those key features an evolutionary model emphasizing the role played by the changing local structure is outlined this model is an example of how key observations many of which were overlooked for 50 years provide the required impetus for the completion of future research that has the potential to substantially change the form in which this province has been visualized for at least the past 30 years

the separated polar winter stratopause a gravity wave driven climatological feature abstract an examination of satellite derived temperatures reveals that the winter polar stratopause is usually elevated and warmer than the adjacent midlatitude stratopause this separated stratopause occurs in both hemispheres but is more pronounced and persistent in the southern winter it descends with time towards spring and exhibits week to week variability observational diagnostics and results from a two dimensional 2 d model suggest that gravity wave driving can account for this separated polar stratopause by driving a meridional circulation with downwelling over the winter pole in the model the solar heating pattern induces stronger winter westerlies than summer easterlies which leads to a stronger gravity wave driven circulation in the winter hemisphere spherical geometry and the high latitude location of the winter westerly jet combine to yield a concentrated region of downwelling model results suggest that descent of the temperature maximum with time is probably caused by wave mean f

development of kinematic partitioning within a pure shear dominated dextral transpression zone the southern ellsworth mountains antarctica the heritage range of the southern ellsworth mountains west antarctica is composed of cambrian to permian sedimentary and volcanic rocks which were deformed during the permo triassic gondwanian orogeny the structural grain of the heritage range exhibits a previously unrecognized 18 swing from 333 153 in the north to 315 135 in the south a change in structural and kinematic style accompanies this strike swing with a structure consistent with near orthogonal shortening present in the south and a structural style consistent with dextral transpression within the central and northern heritage range kinematic partitioning is present within the central heritage range where strikeparallel contemporaneous domains of dextral and reverse shear have developed simultaneously with the regional cleavage comparison of the structure and kinematics within both structural domains suggests that the central and northern heritage range experienced pure shear dominated dextral transpression with an approximate angle of relative shortening of 65 70 results derived by integrating field data into a published kinematic partitioning model suggest relatively efficient kinematic partitioning has occurred however such efficient partitioning cannot be explained by strain partitioning models based purely on plate boundary conditions therefore it is proposed that pre existing weak structures were present within the unexposed basement facilitating the apparent high percentage of kinematic partitioning

longitudinally dependent ozone increase in the antarctic polar vortex revealed by balloon and satellite observations the horizontal structure of processes causing increases in ozone in the antarctic polar vortex was examined using data measured in 2003 from an ozonesonde observation campaign at syowa station 39 68e 69 08s and from the improved limb atmospheric spectrometer ii ilas ii onboard the advanced earth observing satellite ii the ilas ii data are daily and distributed uniformly at 14 points in the zonal direction mostly at polar latitudes the antarctic ozone hole that developed in 2003 was one of the largest recorded the period of focus in this study is 26 september through 24 october when a strong polar vortex was situated in the stratosphere an ozone mixing ratio contour 1 0 ppmv moved downward near a height of 20 km during the period of focus this increase in ozone is likely to result from downward transport of ozone rich air originating from lower latitudes by brewer dobson circulation first the descent rate of the mixing ratio contour was estimated by taking the geometric height as the vertical coordinate for the deep vortex interior around 20 km a significant longitudinal dependence was observed an analysis using ecmwf operational data shows that this dependence can be approximately explained by longitudinally dependent vertical movements of the isentropes caused by a zonal wavenumber 1 quasi stationary planetary wave with amplitude and phases varying on a seasonal time scale next the descent rate was calculated around 500 k around 20 km by taking the potential temperature isentrope as the vertical coordinate the longitudinal dependence was still present using this coordinate meaning that the ozone mixing ratio and its increase are not constant on the isentropic layer even in the interior of the polar vortex a backward trajectory analysis showed that air parcels with large ozone mixing ratios were mostly transported from the polar vortex boundary region this result suggests that lateral transport mixing is important even before the breakup of the polar vortex results from a tracer tracer correlation analysis of o3 and long lived constituent n2o were also consistent with this inference the contribution of lateral mixing to the increase in ozone was estimated at about 17 6 4 that of the brewer dobson circulation around 20 km using the calculated descent rates the results of this study also imply that lagrangian downward motions in the vortex interior are not correctly estimated without accounting for lateral mixing even if the polar vortex is dynamically stable

the blake geomagnetic event transition geometry dynamical characteristics and geomagnetic significance abstract two records of the blake geomagnetic event have been obtained from marine cores in the mediterranean the upper bound for duration of the event calculated from accurate oxygen isotope stratigraphy and or tephrochronology is 4000 years one record is very detailed with 70 transitional directions and allows some characteristics of the event to be precisely retrieved the directional changes do not occur at constant speed rather a stop and go behaviour is observed as in detailed records of reversals the virtual geomagnetic pole vgp path confined to two bands of longitude over the americas and antipodal to them is virtually identical to the only other path of this event obtained from lacustrine sediments in the western usa suggesting that a dipolar component may be present in the transitional field during the blake event the two bands of longitude coincide with those of many recent reversals suggesting that the physical processes leading to reversals or events are basically the same and that the same mechanism is statistically observed over long periods of time

relative geomagnetic paleointensity across the jaramillo subchron and the matuyama brunhes boundary analysis of old paleomagnetic data and new mineral magnetic data from a sediment core from the central equatorial pacific ocean indicates that this core can be used for determination of relative geomagnetic paleointensity these data indicate that during the jaramillo subchron there was a gradual decrease in paleointensity from the onset of the subchron to its termination the data from the subchron also display high amplitude fine scale features that may be coherent over the scale of an ocean basin furthermore there was a rapid rise in paleointensity immediately after the termination of the matuyama brunhes polarity transition these observations support the hypothesis that an asymmetrical saw tooth pattern in paleointensity may be a common characteristic of polarity transitions however a better understanding of the high amplitude features is needed before definitive conclusions can be drawn about the overall behavior of the field the coherence of fine scale features across such large distances does not support the suggestion that the asymmetrical sawtooth pattern is an artifact of viscous remanent remagnetization

nonorographic generation of arctic polar stratospheric clouds during december 1999 1 during december 1999 polar stratospheric clouds pscs were observed in the absence of conditions conducive to generation by topographic gravity waves the possibility is explored that pscs can be generated by inertia gravity waves igw radiating from breaking synoptic scale rossby waves on the polar front jet the aerosol features on 7 and 12 december are selected for comparison with theory and with simulations using the university of wisconsin nonhydrostatic modeling system uwnms consistent with rossby adjustment theory a common feature in the uwnms simulations is radiation of igw from the tropopause polar front jet especially from sectors which are evolving rapidly in the rossby wave breaking process packets of gravity wave energy radiate upward and poleward into the cold pool while individual wave crests propagate poleward and downward causing mesoscale variations in vertical motion and temperature on 12 december the eastbound dc 8 lidar observations exhibited a fairly uniform field of six waves in aerosol enhancement in the 14 20 km layer consistent with vertical displacement by a field of igw propagating antiparallel to the flow with characteristic horizontal and vertical wavelengths of 300 and 10 km uwnms simulations show emanation of a field of igw upward and southwestward from a northward incursion of the polar front jet the orientation and evolution of the aerosol features on 7 december are consistent with a single psc induced by an igw packet propagating from a breaking rossby wave over western russia toward the northeast into the coldest part of the base of the polar vortex with characteristic period 9 hours vertical wavelength 12 km and horizontal wavelength 1000 km linear theory shows that for both of these cases igw energy propagates upward at 1 km hour and horizontally at 100 km hour with characteristic trace speed 30 m s the spatial orientation of the psc along igw phase lines is contrasted with the nearly horizontal filamentary structures in the psc which are indicative of flow streamlines it is suggested that vertical displacement is a crucial factor in determining whether a psc will form and that most pscs are relatable to specific synoptic and mesoscale motions

the characteristics of the lower stratospheric gravity wavefield above halley 75 s 26 w antarctica from radiosonde observations daily radiosonde observations between 2003 and 2013 from halley research station antarctica 75 s 26 w are used to determine climatologies of gravity wave properties in the lower stratosphere between 15 km and 22 km altitude individual waves are extracted from the radiosonde profile using wavelet analysis and separated into upward and downward propagating waves an increase in the percentage of downward propagating waves 30 of the waves is seen during the winter months for the upward and downward propagating waves their horizontal and vertical wavelength intrinsic frequency energy density pseudo momentum flux and direction of propagation are determined the upward propagating wave field is found to be dominated by waves with short vertical wavelength 1 km and low intrinsic frequency f the downward propagating wave field is composed of a wider distribution of vertical wavelength waves and has a larger proportion of higher frequency waves present the upward propagating waves show an increase in total energy density in autumn and spring the larger increase occurs during spring up to 1 7 j kg 1 in september the downward propagating waves increase in total energy density occurs during wintertime up to 0 7 j kg 1 in june during winter the contributions of the upward and downward propagating waves to the total energy density and pseudo momentum flux are almost equal this paper details the first study of individual gravity wave properties combined into upward and downward propagating wave climatologies in the lower stratosphere above halley

estimation of gravity wave momentum flux and phase speeds from quasi lagrangian stratospheric balloon flights part ii results from the vorcore campaign in antarctica the stratospheric gravity wave field in the southern hemisphere is investigated by analyzing observations collected by 27 long duration balloons that flew between september 2005 and february 2006 over antarctica and the southern ocean the analysis is based on the methods introduced by boccara et al in a companion paper special attention is given to deriving information useful to gravity wave drag parameterizations employed in atmospheric general circulation models the balloon dataset is used to map the geographic variability of gravity wave momentum fluxes in the lower stratosphere this flux distribution is found to be very heterogeneous with the largest time averaged value 28 mpa observed above the antarctic peninsula this value exceeds by a factor of 10 the overall mean momentum flux measured during the balloon campaign zonal momentum fluxes were predominantly westward whereas meridional momentum fluxes were equally northward and southward a local enhancement of southward flux is nevertheless observed above adelie land and is attributed to waves generated by katabatic winds for which the signature is otherwise rather small in the balloon observations when zonal averages are performed oceanic momentum fluxes are found to be of similar magnitude to continental values 2 5 3 mpa stressing the importance of nonorographic gravity waves over oceans last gravity wave intermittency is investigated mountain waves appear to be significantly more sporadic than waves observed above the ocean

first continuous gps soundings of temperature structure over antarctic winter from formosat 3 cosmic constellation 1 the formosat 3 cosmic mission provides unprecedented spatial coverage of daily sounding profiles of the antarctic atmosphere our analysis shows that temperature profiles from these global positioning system gps soundings agree well with the radiosondes over the south pole and neumayer stations during the 2006 southern hemisphere sh winter season these gps soundings reveal a vertical domain of low temperature e g t 78 c at 28 km altitude that is not clearly defined by the antarctic radiosondes latitudinal analysis of the gps soundings shows that regions with t 78 c occur from about 10 km to 28 km altitudes indicating an 18 km thick of the cold vertical layer the extremely cold regions are found at latitudes between 71 s and 87 s and in altitudes between 15 and 25 km not coinciding with the geographical south pole these results demonstrate the potential of the formosat 3 cosmic data for polar studies

periodicity of the earth s magnetic reversals reversals of the earth s magnetic field may occur with a certain regularity using observed percentages of normal and reversed polarity during different time intervals negi and tiwari1 detected several significant periodicities notably one of 32 34 myr raup2 used the dates of individual reversals to propose a 30 myr period in the frequency of reversals although mazaud et al 3 obtained a periodicity of only 15 myr like negi and tiwari s1 other detected short periods the 15 myr period may be harmonically related to a basic 30 myr period4 it has also been suggested that these are accidental periodicities arising in a short record5 6 or are harmonics of the record length itself7 in fact all of the cited studies have used different data different record lengths and different methods of time series analysis raup8 has consequently retracted his original claim here i present a much fuller analyis of the reversal record and show that a statistically significant period of 30 myr does formally exist in spite of the cited differences

the relative stabilities of the reverse and normal polarity states of the earth s magnetic field recent analyses of the geomagnetic reversal sequence have led to different conclusions regarding the important question of whether there is a discernible difference between the properties of the two polarity states the main differences between the two most recent studies are the statistical analyses and the possibility of an additional 57 reversal events in the cenozoic these additional events occur predominantly during reverse polarity time but it is unlikely that all of them represent true reversal events nevertheless the question of the relative stabilities of the polarity states is examined in detail both for the case when all 57 events are included in the reversal chronology and when they are all excluded it is found that there is not a discernible difference between the stabilities of the two polarity states in either case inclusion of these short events does however change the structure of the non stationarity in reversal rate but still allows a smooth non stationarity only 7 of the 57 short events are pre 38 ma but the evidence suggests that this is a real geomagnetic phenomenon rather than degradation of the magnetic recording or a bias in observation this could be tested by detailed magnetostratigraphic and oceanic magnetic surveys of the paleogene and late cretaceous overall it would appear that the present geomagnetic polarity timescale for 0 160 ma is probably a very good representation of the actual history and that different timescales and additional events now represent only changes in detail

geomagnetic reversal history the history of geomagnetic polarity reversals in the cenozoic and late mesozoic is well known since the late jurassic oxfordian a continuous record of polarity has been derived for this time interval from the interpretation of oceanic magnetic anomalies most of the polarity chrons in this oceanic record have been verified and dated in coordinated magnetostratigraphic and biostratigraphic studies this has led to the generation of progressively refined and improved geomagnetic reversal time scales that provide a framework for absolute dating of palaeontological zonations by serving as a basis for statistical analysis of reversal frequency they provide information relevant to processes in the earth s core the rate of reversals since the late cretaceous shows a steady increase on which a cyclical variation appears to be superposed a stochastic model for reversals predicts a poisson distribution of polarity interval lengths the polarity time scales contain many fewer short 50 kyr polarity chrons than a poisson distribution and it has been suggested that a gamma renewal process with index greater than unity is a more appropriate statistical model the statistical arguments give no convincing reason for abandoning the model and other physical reasons must be sought to explain the incompleteness of the reversal record the discovery and verification of short chrons in the oceanic record may best be investigated by deep tow magnetometer surveys the reversal history before the late jurassic is not well known magnetostratigraphy in coeval early jurassic sections has not given correlatable records and it has not been possible to compile a definitive polarity sequence evaluation of geomagnetic polarity history for the early mesozoic and the palaeozoic will require unambiguous magnetostratigraphy in well dated sections where verification of the polarity pattern is possible at the fossil zone or stage level

paleogene magnetic stratigraphy in umbrian pelagic carbonate rocks the contessa sections gubbio the umbrian sequence of pelagic carbonate rocks provides an opportunity for precise correlation between paleogene biostratigraphy and geomagnetic polarity history the red to pink paleocene to middle eocene scaglia rossa limestone the varicolored upper eocene scaglia variegata limestone and the gray green oligocene scaglia cinerea marlstone form a 250 m thick continuous exposure in the contessa valley near gubbio italy magnetostratigraphic lithostratigraphic and biostratigraphic investigations in three sections covering the entire paleogene have confirmed and dated the geomagnetic reversal sequence for most of this period the ferromagnetic mineral in the scaglia cinerea is magnetite and af demagnetization to peak fields of 20 mt is sufficient to define the characteristic remanent magnetization the scaglia variegata and pink scaglia rossa samples contain an additional hematite component which is very pronounced in dark red paleocene scaglia rossa samples changes of magnetic mineralogy take place in these limestones during heating especially above 500 c however thermal demagnetization is effective in isolating the characteristic remanence vectors which form almost antipodal clusters of directions representing normal and reversed polarities the directions are rotated counterclockwise partly due to post oligocene tectonism paleontological zonations of planktic foraminifera and calcareous nannofossils were hampered by poor preservation but the major epoch and stage 29 as in the gubbio bottaccione section paleocene eocene just above anomaly 25 eocene oligocene between anomalies 13 and 15 oligocene miocene just below anomaly 6c these correlations require slight modifications to previous conclusions on paleogene sea floor spreading rates

observed temperature structure of the atmosphere above syowa station antarctica 69 s 39 e 1 by combining balloonsonde and na rayleigh temperature lidar observations made at syowa station 69 s 39 e during 2000 and 2001 a total of 176 observations 5 9 observations per week the winter temperature structure from 0 to 110 km is characterized from march to october the data are also compared with the temperature model of south pole from pan and gardner 2003 which was derived from observations made during the same period as the measurements at syowa although syowa and south pole are separated more than 2300 km the temperature structure is quite similar through the year below 30 km the annual temperature amplitude at syowa is about 6 7 k smaller than the south pole data because of the difference in seasonal solar flux variations between the two sites in spring when the polar vortex weakens and dissipates the stratospheric temperatures at syowa increase rapidly as a result of the inflow of warmer air from lower latitudes in the mesosphere the annual temperature amplitude is anticorrelated with the solar heating because of the strong adiabatic heating and cooling effects associated with the meridional circulation system the annual temperature amplitude at syowa is 5 k smaller than at south pole which is consistent with the smaller adiabatic heating and cooling expected at lower latitudes the semiannual amplitude at syowa is 5 7 k larger than at south pole between 30 and 60 km and it is 15 k smaller than at south pole between 80 and 100 km

geodynamo energy source constraints from palaeomagnetic data abstract analyses of palaeo geomagnetic data can provide surprisingly strong constraints upon models of the geodynamo in particular it is shown here from an analysis of the geomagnetic reversal sequence that long term variation in reversal rate does not occur as a result of change in any inherent inhibition or encouragement in the reversal process instead there must be some physical process that actually triggers reversals and this process must derive from an energy source effectively independent of the energy source powering the main geomagnetic field from this two very simple generalised models referred to as the hot blob and cold blob models are suggested data from individual reversal transitions are used to discriminate between these two models the preferred model is that the geodynamo is driven primarily by convection related to freezing of the outer core at the inner core outer core boundary cold blobs descending from the core mantle interface are identified as the instabilities that trigger reversals

rayleigh lidar observations of gravity wave activity in the winter upper stratosphere and lower mesosphere above davis antarctica 69 s 78 e 1 gravity wave activity in the upper stratosphere and lower mesosphere uslm is investigated using temperature data retrieved from a rayleigh lidar at davis antarctica 69 s 78 e during the 2007 and 2008 winters the temporal and height variabilities of waves with ground based periods greater than 2 h and vertical wavelengths between 4 km and 20 km are analyzed stratospheric gravity wave potential energy per unit mass shows a weaker correlation with stratospheric winds at davis than that reported in the arctic gravity waves dissipate above 40 km during winter while there is no dissipation in the autumn mesosphere a separate analysis of gravity waves with ground based periods of 2 6 h revealed lower dissipation in the winter mesosphere the seasonal cycle of gravity wave activity is evident throughout the uslm with peak activity observed during winter the gravity wave potential energy and vertical wavenumber power spectral density at davis are similar to that recorded at other high latitude sites

geomagnetic field stability reversal events and excursions abstract it has been suggested that there are several reverse subchrons in the brunhes and this suggestion is gaining some acceptance however such a suggestion has fundanmental implications for the reversal process because it implies that the reverse polarity state has been substantially less stable than the normal polarity state during the brunhes chron analysis of the latest polarity reversal timescale confirms that there is no reason to reject the hypothesis of a common stability for the two polarity states the cretaceous superchron appears to be a time when the reversal rate slowed to the point where the reversal process actually halted so does not indicate any difference in the stability of the two polarity states after examining the data we found no convincing evidence for even a single reversal event during the brunhes and we conclude that the only reversal excursions that are sufficiently well documented for the brunhes are the laschamp and the blake further we note that the question of whether of large excursions represent aborted reversals is unresolved so excursion data should not at this stage be grouped with transition polarity data finally we note that most of the time the nearly axially symmetric normal and reverse polarity states appear to be remarkably stable

gravity wave characteristics in the lower atmosphere at south pole a 4 year 1993 1996 temperature and wind data set obtained from over 2000 high resolution balloon soundings at south pole is used to study gravity wave characteristics in the troposphere and lower stratosphere extensive analyses of energy density spectra and static stability are performed to present a comprehensive view of the gravity wave characteristics in the lower atmosphere at south pole our results show that the gravity waves are ubiquitous and often fairly strong at south pole even though the generation mechanisms are not clear gravity wave characteristics are in general similar to those obtained at other high latitude southern hemisphere stations potential energies vary between about 0 5 j kg and 5 j kg with season and altitude variations in kinetic energies are not well correlated with potential energy variations and range from 1 j kg to 11 j kg we observe significant seasonal variations of the slope and magnitude of the vertical wavenumber spectrum of temperature fluctuations especially in the stratosphere in general the gravity waves in the stratosphere are stronger weaker in austral spring fall wave activity in the troposphere has little seasonal dependence stability analysis shows that instabilities are more likely to occur in the troposphere than in the stratosphere the probability of wave instability is 13 7 in the troposphere and 5 4 in the stratosphere this is due to the less stable stratification in the troposphere where the buoyancy period averages 8 3 min compared to 4 9 min in the stratosphere dynamic shear instability is more likely to occur than convective instability 11 versus 2 6 in the troposphere and 4 7 versus 0 7 in the stratosphere due to the prevailing strong wind shear the instability probabilities vary seasonally with the austral winter exhibiting the highest probability of instabilities dynamic and convective instabilities combined in both the troposphere and stratosphere