planetary scale wave observations over a low latitude e region using simultaneous observations of vhf radar and ionosonde over sanya 18 34 n 109 62 e 1 the planetary scale oscillations of the field aligned irregularities fai and the sporadic e es layers in the low latitude e region were studied in terms of the observations from 8 june to 22 august 2009 using coherent backscatter radar and a digital ionosonde installed at sanya 18 34 n 109 62 e hainan island china quasi 2 day waves were observed both in the meridional wind and in daytime backscatter echo occurrence simultaneous observations on sporadic e layers in daytime showed a planetary scale wave signature in the low latitude region for the first time close correlation between echo occurrence and the mean critical frequency foes was found when the quasi 2 day planetary wave qtpw existed these results suggest that the es plays an important role in determining the long term variability of the low latitude e region fai to test the nonlinear interactions between tides and qtpw the hourly meridional and zonal winds are analyzed the subsidiary waves with anticipated frequencies and their height evolutions provide evidence of tide qtpw interactions bispectral analysis on the winds further validates the strong nonlinear interactions between tides and the qtpw in the meridional wind our results suggest that the mechanism proposed by pancheva et al 2003 is a reasonable explanation for the planetary scale variability of the low latitude e region fai and es the different responses of the es layers and the e region fais on the qtpw between day and night can be attributed to diurnal variations in ion densities in the region between 100 and 160 km

planetary and tidal wave type oscillations in the ionospheric sporadic e layers over tehran region 1 it is believed that in the lower ionosphere particularly in the ionospheric sporadic e es layers 90 130 km the planetary and tidal wave type oscillations in the ionized component indicate the planetary and tidal waves in the neutral atmosphere in the present work the presence of wave type oscillations including planetary and tidal waves in the ionospheric sporadic e layers over tehran region is examined data measured by a digital ionosonde at the ionospheric station of the institute of geophysics university of tehran from july 2006 to june 2007 are used to investigate seasonal variations of planetary and tidal waves activities for the purpose of accurate comparison between different seasons wavelet transform is applied to time series of foes and h es namely the critical frequency and virtual height of es layers respectively the results show that the sporadic e layers over tehran region are strongly under the influence of upward propagation of waves from below more specifically among diverse range of periodicities in the sporadic e layers we found that diurnal 24 hours and semidiurnal 12 hours oscillations in all seasons for both parameters moreover terdiurnal 8 hours tide like variation is observed during spring and summer for foes parameter and summer and winter for h es furthermore the results show that diurnal tidal waves obtain their maximum activities during autumn and winter seasons and their activities decrease during the late spring and summer in addition periods of about 2 4 6 10 14 and 16 days in our observation verifies the hypothesis of upward propagation of planetary waves from lower atmosphere to the ionosphere moreover planetary waves have their maximum activities during equinox

an 1800 year archeological experiment in remagnetization limestone masonry from monuments dating from 300ad to 1940 remagnetized partly and progressively with age parallel to the present earth s magnetic field the remagnetization was probably due to viscous remanent magnetization vrm neel s theory predicts that natural vrm acquired at low temperature ta over a long time ta disappears at a higher temperature td in a short period td in the laboratory i calibrated td for the postconstruction remagnetization against the ages td of masonry used in well dated historic buildings in eastern england empirically ta m td b relates acquisition age tayears to demagnetization temperature td c lincoln limestone remagnetizes more quickly m 1 298 10 6 and b 3 598 over 1800 years than speeton chalk m 4298 10 6 and b 1 973 over 350 years magnetite with an effective pseudo single domain or small multidomain size carries the remanence

thermal demagnetization of vrm and ptrm of single domain magnetite no evidence for anomalously high unblocking temperatures stepwise thermal demagnetization of viscous remanent magnetization vrm and partial thermoremanent magnetization ptrm of single domain magnetite with mean grain size 37 nm reveals only minor deviations from the predictions of neel theory three different initial states were used following 1 alternating field demagnetization to 100 mt 2 thermal demagnetization to 610 c and 3 modified thermal demagnetization consisting of zero field heating to 610 c followed by zero field cooling to the vrm or ptrm acquisition or blocking temperature tb vrms were produced by applying a 0 1 mt field for 3 5 hr starting from initial states 2 3 and 1 in that order at tb 283 c and from states 3 2 and 1 at tb 404 c in a final experiment ptrm was produced by applying 0 1 mt during cooling from tb1 414 c to tb2 404 c starting from state 3 in all but one case vrm began to unblock significantly 90 of initial intensity 15 c below tb dropped to 50 at tb and then tailed off dropping below 10 40 c above tb 283 c or 25 c above tb 404 c partial trm behaved in the same way except that demagnetization was essentially complete by tb1 414 c the maximum unblocking temperatures tub observed are exactly as predicted by the theory of pullaiah et al 1975 although very long acquisition times cannot be tested we find no evidence for anomalously high tubs of vrm in single domain grains in previously reported cases of rocks with unexpectedly high tubs the vrm was probably carried by multidomain grains

planetary scale variability in the low latitude e region field aligned irregularities first results from gadanki observations 1 in this paper we present for the first time planetary scale wave signatures in the low latitude e region field aligned irregularities fai observed during june 2004 to may 2005 using the gadanki mesosphere stratosphere troposphere radar we have observed a clear signature of 5 8 day variability in echo occurrence in snr and also in doppler velocity observed above 100 km concurrent temperature observations made using the sounding of the atmosphere using broadband emission radiometry saber on board the thermosphere ionosphere mesosphere energetic and dynamics timed satellite have also clearly shown the presence of 5 8 day variability similar to that of fai the temperature variations have been characterized with zonal wave numbers of 3 and 4 and vertical wavelength of 15 20 km these waves are found to have increasing amplitude with increasing height and phase progressing downward suggesting that they were of lower atmospheric origin it is emphasized that the planetary scale characteristics of neutral atmosphere in the fai observations are important in understanding the vertical coupling of the low latitude ionosphere atmosphere system these observations and the pertinent issues are discussed in the light of current understanding of the planetary scale role on the fai variability

first measurements of tidal modes in the lower thermosphere by the eiscat svalbard radar first measurements by the eiscat svalbard radar of ion velocities in the lower thermosphere show the presence of strong tidal or quasi tidal modes with periods of 24 12 and 8 hours the diurnal mode shows no variation of phase with height above 100 km in contrast the semidiurnal and terdiurnal modes show a steady variation of phase with height corresponding to vertical wavelengths of about 40 km and 30 km respectively in addition there is evidence at 93 km the lowest height measured of a planetary wave with a period of 2 3 days

tsunami recurrence revealed by porites coral boulders in the southern ryukyu islands japan information about past tsunami hazards such as their recurrence interval and magnitude is needed for future disaster prediction and mitigation we examined radiocarbon ages of the surfaces of massive coral boulders cast ashore by past tsunamis in the southern ryukyu islands japan where few historical and geological records of past tsunamis are available we selected only non eroded porites coral boulders along the shoreline because their characteristics make it possible to determine the probable timing of their deposition by tsunamis and we applied a dating method that uses the cumulative probability distributions of large numbers of radiocarbon measurements of those boulders to determine the timing of past tsunamis the results demonstrate that the southern ryukyu islands have repeatedly experienced tsunami events since at least 2400 yr ago with a recurrence interval of 150 400 yr the largest porites tsunami boulder that we studied long axis 9 m which is probably the largest single colony tsunami boulder in the world was displaced by the a d 1771 meiwa tsunami although the 1771 meiwa tsunami was likely the largest event in at least the past 700 yr calculations of current velocity show that all identified tsunamis occurring before 1771 were probably large enough to cause considerable damage to human built structures and loss of life this study demonstrates that by reliably dating large numbers of selected coastal boulders it is possible to ascertain the timing recurrence interval and magnitude of past tsunamis in a location where few adequate survey sites of sandy tsunami deposits exist

the characterization of viscous remanent magnetization in large and small magnetite particles previous work on the properties of viscous remanent magnetization vrm have shown that it can play an important role in some paleomagnetic investigations the results of this study on the properties of vrm of very fine single domain sd and coarse multidomain md magnetite particles ranging in size from 0 02 to 60 m indicate that the md samples are very sensitive to the previous magnetic history of the samples the af demagnetization causes a dramatic decrease in the ability of md samples to acquire vrm compared to the same sample with an undemagnetized thermal remanent magnetization trm thermal demagnetization of the same md samples causes an increase in the ability to acquire vrm components submicron sd samples show vrm acquisition and decay curves that are independent of previous magnetic treatment both md and sd samples are extremely sensitive to the length of time of zero and weak field storage that occurs prior to the application of the external vrm field a model using the total energy of the system is used to describe the above results

an explanation for the seasonal dependence of midlatitude sporadic e layers 1 the midlatitude sporadic e layers form when metallic ions of meteoric origin in the lower thermosphere are converged vertically in a wind shear the occurrence and strength of sporadic e follow a pronounced seasonal dependence marked by a conspicuous summer maximum although this is known since the early years of ionosonde studies its cause has remained a mystery as it cannot be accounted for by the windshear theory of e s formation we show here that the marked seasonal dependence of sporadic e correlates well with the annual variation of sporadic meteor deposition in the upper atmosphere the later has been established recently from long term measurements using meteor radar interferometers in the northern and southern hemispheres knowing that the occurrence and strength of sporadic e layers depends directly on the metal ion content which apparently is determined primarily by the meteoric deposition the present study offers a cause and effect explanation for the long going mystery of sporadic e layer seasonal dependence

evidence for planetary wave effects on midlatitude backscatter and sporadic e layer occurrence in this paper a large database of midlatitude e region coherent backscatter obtained with a 50 mhz doppler system is used to investigate the long term variability in echo occurrence the backscatter is found to be dominated by pronounced quasi periodic variations with periods in the range from about 2 to 9 days that persist for time intervals from about 10 to maybe more than 20 days and have no relation to geomagnetic activity the most commonly observed periods appear in two preferential bands that is the 2 to 3 day and the 4 to 6 day band using concurrent ionosonde data we find the variations in backscatter to be exactly in phase with similar periodicities in the occurrence of relatively strong sporadic e layers the present findings support the possibility that planetary waves are responsible for the observed long term periodicities which indicates also a close relation between planetary waves and the well known but not well understood seasonal es dependence we suggest the planetary wave option constitutes a new component into the research of midlatitude sporadic e layer formation and occurrence that needs to be considered and closely investigated

separating multidomain and single domain like remanences in pseudo single domain magnetites 215 540 nm by low temperature demagnetization it has long been hypothesized that the pseudo single domain properties of submicron magnetites are a result of coexisting multidomain and single domain like remanences we have separated these two types of remanence by low temperature demagnetization ltd in which samples are cooled through the low temperature magnetite isotropic point and rewarmed to room temperature all in zero field at the isotropic point the first crystalline anisotropy constant vanishes and multidomain remanence due to displaced domain walls will be unpinned we measured stepwise alternating field af and thermal demagnetization curves of weak field thermoremanent magnetization trm and anhysteretic remanent magnetization and of saturation isothermal remanent magnetization irms both with and without prior ltd for magnetites with mean particle sizes of 215 390 and 540 nm the memory fraction of remanence recovered after ltd which represents the single domain like component decreased from 44 for 215 nm grains to 23 for 540 nm grains in the case of irms memory of trm was approximately twice as large af decay curves were soft and multidomain like before ltd but became harder and single domain like in shape after ltd ltd removed most low unblocking temperature trm and irms distributed low unblocking temperatures are therefore a multidomain phenomenon probably resulting from successive adjustments of domain walls to changing internal fields and pinning strengths during heating

evidence of a role for modulated atmospheric tides in the dependence of sporadic e layers on planetary waves 1 a large amplitude 7 day period westward propagating s 1 planetary wave pw of global response has been reported from ground radar and satellite wind measurements in the mesosphere lower thermosphere mlt during the second half of august and well into september 1993 following recent suggestions that pw might play a role in the formation of midlatitude sporadic e layers es haldoupis and pancheva 2002 found a strong 7 day periodicity present in all stations concurrently with the 7 day planetary wave reported elsewhere by analyzing sporadic e critical frequency foes time series from eight midlatitude ionosonde stations covering a longitudinal zone from about 58 e to 157 w this study provided the first direct proof in favor of a pw role on es formation in the present paper we further investigate this role by considering the same pw event and correlating the 7 day periodicity in foes directly with concurrent variations in the mesospheric neutral wind measured with atmospheric radars in saskatoon canada and in sheffield united kingdom although our analysis cannot exclude a direct pw role on es formation it shows clearly that es is affected indirectly by the pw through the action of the diurnal and semidiurnal tides which are strongly modulated by the same pw apparently through a nonlinear interaction process at altitudes below 100 km this 7 day pw modulation was found to be clearly present simultaneously in the amplitude of the zonal 12 hour tidal wind the meridional 24 hour tidal wind and in both the 12 hour and 24 hour periodicities which existed in the foes time series the results here provide a new physical explanation for the observed relation between sporadic e layers and planetary waves

dating of tsunami boulders from ishigaki island japan with a modified viscous remanent magnetization approach abstract reworked boulders are expected to acquire a viscous remanent magnetization vrm approximately parallel to earth s modern magnetic field the magnitude of such a vrm depends on several factors including the time since reworking and ambient temperature for which there are well known theoretical relationships vrm unblocking temperature can therefore be a powerful tool for determining the reworking age of boulders and can be used to assess the timing of geological hazards such as landslides and tsunami events in this study vrm unblocking temperatures for twenty seven samples from four coral tsunami boulders on ishigaki island japan are compared with three candidate time temperature relationships for vrm acquisition for the pullaiah nomogram which is applicable to single domain magnetite particle assemblages nineteen samples from four boulders agree well with the expected unblocking temperature derived from previously reported 14c ages two samples have low unblocking temperatures and six samples appear to have anomalously high vrm unblocking the walton nomogram which is used for lognormal grain size distributions relates acquisition temperatures required to produce equal magnetic paleo intensities and cannot explain the high unblocking temperatures it produces younger predicted ages than the youngest boulder 14c age we find that an alternative time temperature relationship defined by a stretched exponential law has the potential to yield reworking ages for the anomalous boulders that are consistent with the 14c ages we suggest that future vrm dating can be undertaken using a combination of the pullaiah nomogram and the stretched exponential law

vertical coupling from the lower atmosphere to the ionosphere observations inferred from indian mst radar gps radiosonde ionosonde magnetometer olr noaa and saber timed instrument over gadanki

calibrating the devonian time scale a synthesis of u pb id tims ages and conodont stratigraphy the recalibrated devonian time scale represents an important improvement of devonian chronology regarding two aspects firstly a data set of 13 biostratigraphically well bracketed u pb id tims zircon and monazite ages constitutes the framework of the scale secondly approximately time linear biostratigraphic scales have been used for the interpolation between the isotopic ages the new construction thus represents a biochronometric time scale which allows the assignment of numeric ages not only to stage boundaries but also to each biozone boundary the method of interpolation applied also enables the projection of the geochronological error onto the time scale according to the newly calibrated scale the devonian lasted 57 4 5 7 ma from 418 1 3 0 to 360 7 2 7 ma this is compared to previously published time scales the longest time span ever calculated for this period the age interpolations for the eight stage boundaries are famennian tournaisian devonian carboniferous 360 7 2 7 ma frasnian famennian 376 1 3 6 ma givetian frasnian 383 7 3 1 ma eifelian givetian 388 1 2 6 ma emsian eifelian 391 9 3 4 ma pragian emsian 409 1 3 8 ma lochkovian pragian 412 3 3 5 ma pridolian lochkovian silurian devonian 418 1 3 0 ma full size table table options view in workspace download as csv the duration of the middle devonian is calibrated here as quite short with 8 2 ma and the emsian and the famennian are the longest stages with interpolated durations of 17 2 and 15 4 ma respectively together all devonian stages contain 57 conodont zones including subzones according to the standard conodont zonation giving a mean duration of about 1 ma in the highly resolved part of the time scale mid eifelian to the devonian carboniferous boundary zonal resolution averages 0 6 ma in contrast the lowest resolution is shown in the early emsian to mid eifelian interval with zonal durations of up to 5 5 ma serotinus zone

quasi periodic radar echoes from midlatitude sporadic e and role of the 5 day planetary wave using measurements of magnetic aspect sensitive radar echoes from midlatitude sporadic e collected over a two month period from tanegashima japan we show that while their occurrence duration from night to night did not exhibit any systematic variation that of the so called quasi periodic qp echoes varied sinusoidally with a period of 5 days we have interpreted this behavior in terms of effects produced by a planetary wave and identified its presence through neutral wind measurements made with a partial reflection drift radar located nearby at yamagawa we propose that the occurrence of qp echoes is affected both by a contribution of the wind to the dynamo electric field and by the direction of the neutral wind we argue that because the wind vector of the planetary wave is elliptically polarized at midlatitudes a preferred wind direction conducive to the generation of qp echoes occurs once every 5 days on the other hand this wave is linearly polarized and directed zonally over the geographic equator the fact that qp echoes are most fully developed at midlatitudes and less so at lower latitudes suggests that zonal flow is not particularly favorable for qp echo production

the 8 hour tide in the arctic mesosphere and lower thermosphere an all sky vhf meteor radar at esrange 68 n 21 e near kiruna in northern sweden has been used to investigate the 8 hour tide in the arctic mesosphere and lower thermosphere we present a climatology of the 8 hour tide over the period october 1999 to april 2001 the tide appears to be a persistent feature of the arctic atmosphere although a large day to day variability of the tidal amplitude is observed at times the 8 hour tide reaches amplitudes over 30 m s 1 the amplitude of the tide increases with height across the observed height range of 80 100 km monthly mean tidal amplitudes range from 2 m s 1 to values as large as 10 m s 1 a clear seasonal behavior is apparent with maximum amplitudes observed in the autumn vertical wavelengths are shortest in winter and spring 25 35 km and longest in summer and autumn 50 90 km at least on some occasions the vertical wave number relationships between the 8 12 and 24 hour tides suggest that the 8 hour tide is being generated by nonlinear interaction between the 12 and 24 hour tides

thermoviscous remagnetization in some appalachian limestones experimental evidence shows that blocking temperature relaxation time theory for single domain magnetite can grossly underestimate laboratory thermal demagnetization temperatures of a present day viscous remanence in devonian limestones of new york state thermoviscous remagnetization at moderately elevated burial temperatures during the late paleozoic cannot therefore be readily excluded for the origin of the stable secondary component in these rocks more generally these results emphasize that single domain thermal activation theory cannot be assumed a priori to correctly predict temperature of thermoviscous remanence acquisition in all magnetite bearing rocks the prob leto

mean winds and tides in the arctic mesosphere and lower thermosphere 1 a new meteor radar has been deployed at esrange 68 n 21 e near kiruna in sweden the radar has been used to measure winds and tides in the arctic mesosphere lower thermosphere region over the interval august 1999 to july 2000 conspicuous features of the measured mean winds include a strong shear of up to 5 m s 1 km 1 in the summer zonal flow resulting in eastward flows of in excess of 30 m s 1 at the upper heights observed 97 km an equatorward meridional flow is observed in summer and winter which reaches maximum values of 13 m s 1 in a summer jet poleward flow in comparison is weak and only occurs at the equinoxes the monthly mean and seasonal mean behaviors of the amplitudes and phases of the 12 and 24 hour tides are examined and compared to the global scale wave model 98 the observations are generally very close to the model predictions for the 24 hour tide and for the 12 hour tide in winter in other seasons particularly summer the observed 12 hour tidal amplitudes are significantly larger than those predicted in spring and summer the wavelength of the 12 hour tide is significantly larger than that predicted

measurements and modelling of intermediate descending and sporadic layers in the lower ionosphere results and implications for global scale ionospheric thermospheric studies we demonstrate that conventional ionosondes can provide long term observations of intermediate descending and transitional layers in the 100 200 km altitude region of the ionosphere using 15 consecutive days of observations at townsville australia during the sundial campaign of september 1989 we tracked the birth of the layers at altitudes above 150 km and their systematic downward motion to the 110 km region at rates between 4 and 5 km hr the observations are compared with ncar tigcm simulations and the results show i that the layering process is identifiable with meridional wind shear node convergence of ions ii that zonal wind controls of the layers are insignificant under the prevailing conditions and iii that electric fields play an important role in the effectiveness of the ion convergence and downward transport processes at altitudes above 125 km the measurement and modelling comparisons are the first of a kind providing insight into the relative roles of winds and electric fields and opening possibilities for determining the global characteristics of the layers and their cause effect roles in the dynamics of the lower ionospheric thermospheric domain

terdiurnal migrating tide signature in ionospheric total electron content we report the latitudinal seasonal and solar cycle variations of terdiurnal migrating tide i e terdiurnal westward wave number 3 tw3 signature in ionospheric total electron content tec our investigations are based on the jpl global ionospheric maps gims during 1999 2011 the absolute amplitude of tw3 exhibits maximum values in the magnetic equatorial region which reaches about 8 tecu under high solar activity and 1 5 tecu under low solar activity the relative amplitude of zonal mean tec in equatorial region however shows persistent patterns from 1999 to 2011 with little solar activity dependence the relative amplitude of tw3 has a peak of similar to 10 in the magnetic equatorial region and a second one of similar to 7 at magnetic middle latitudes 30 degrees 50 degrees at high latitudes in local winter seasons the maximum relative amplitude occurs which varies between 8 and 15 with slightly larger amplitudes in the northern hemisphere the global structure of tw3 signature in tec should shed some light on the coupling between the ionosphere thermosphere and the lower atmosphere

insights into a million year scale rhenohercynian carbonate platform evolution through a multi disciplinary approach example of a givetian carbonate record from belgium in this paper we formulate answers to three important questions related to givetian carbonate records and their use for reconstructing million year scale past palaeoenvironmental changes first we provide detailed illustrations of the fascinating diversity that shaped a significant shallow reefal platform during early to late givetian time in the rhenohercynian ocean secondly we improve the sedimentological model of the extensive givetian carbonate platform in the dinant basin and thirdly we evaluate the application of magnetic susceptibility as a tool for long term trend correlations and palaeoenvironmental reconstructions these goals are reached by making a sedimentological geophysical and geochemical study of the la thure section through the early late givetian interval we discerned 18 microfacies ranging from a homoclinal ramp to a discontinuously rimmed shelf and then a drowning shelf the comparison of these sedimentological results with those published for the south of the dinant syncline allowed us to provide an up to date model of the vertical and lateral environmental development of one of the largest givetian carbonate platforms in europe this comparison also increased the knowledge on the distribution of facies belts in the dinant basin and allowed us to highlight the taghanic event palaeoredox proxies reveal a substantial change in the oxygenation level from oxygen depleted to more oxic conditions between middle and late givetian time we demonstrated the relationship between variation in magnetic susceptibility values and proxies for siliciclastic input such as si al the la thure section is considered a key section for the understanding of internal shelf settings bordering laurussia9s southeastern margin

stretched exponential relaxation of viscous remanence and magnetic dating of erratic boulders viscous remanence continuously increases with the duration of reorientation of rocks and the remanence gets partially overprinted in rocks parallel to the earth s magnetic field this overprinted viscous remanence is unblocked at a certain temperature that enables the estimation of the time required for the rock to acquire the magnetism by assuming the exponential law of neel s single domain theory however previous results of dating the rocks by the exponential law have shown older ages than radiometric or cosmogenic exposure ages neel s exponential decay law is applicable to a system whose magnetic grains have an identical relaxation time however in real systems the expected behavior is not usually observed because relaxation times vary for individual grains moreover the variation of viscous remanence with the logarithmic law for a distribution of relaxation times is predicted to be concave downwards here we found that the stretched exponential law exp t 1 n with 0 n 1 explains previously published data on viscous decay the observed stretched exponential relaxation can be interpreted in terms of the global relaxation of a system containing many relaxing species each of which decays exponentially in time with a specific fixed relaxation rate using this law we derived an extended time temperature relationship of magnetite involving the neel s exponential decay law with n 0 and a system containing many relaxing times with variable n the extended time temperature relationship shows that the age of a coral tsunami boulder with high anomalous unblocking temperatures can be fitted with an assigned radiometric age

devonian climate sea level and evolutionary events an introduction the face of planet earth has changed significantly through geological time dynamic processes active today such as plate tectonics and climate change have shaped the earth s surface and impacted biodiversity patterns from the beginning organisms on the other hand have the capacity to significantly alter earth s hydrological and geochemical cycles its atmosphere and climate sediments and even hard rocks deep down under the surface abiotic biotic interactions characterize earth s system history and together with biotic competition and food webs were the main trigger of evolutionary change innovations and biodiversity fluctuations within the palaeozoic the devonian was an especially interesting time interval as it was characterized by the mid paleozoic predator revolution signor brett 1984 brett 2003 and the related nekton revolution klug et al 2010 characterized by the blooms of free swimming cephalopods including the oldest ammonoids and fish groups e g toothed sharks and giant placoderms the rise of more advanced vertebrates including the oldest tetrapods e g blieck et al 2007 2010 niedzwiedzki et al 2010 the most extensive reef complexes of the phanerozoic e g kiessling 2008 and the greening of land by the diversification and spread of land plants including the oldest forests e g stein et al 2012 giesen berry 2013 which resulted in new soil types and changing weathering these major evolutionary trends did not unfold in a long interval of environmental stability but in times of numerous and repeated geologically brief global events that punctuated prolonged periods up to several million years in duration of relative stability termed ecological evolutionary subunits ee subunits boucot 1990 brett baird 1995 brett et al 2009 the bounding events even those of lesser intensity produced major re structuring in local to global ecosystems and are seen as critical drivers of long term evolutionary patterns brett 2012 these linked abiotic and biotic events and extinctions of different magnitude have been summarized by house 1983 1985 2002 walliser 1984 1996 and more recently by becker et al 2012 the devonian event succession is summarized in figure 1 two first order mass extinctions at the frasnian famennian boundary kellwasser crisis and at the end of the devonian hangenberg crisis characterized by the loss of major fossil groups classes and orders and complete ecosystems e g metazoan reefs early forests have to be viewed in the context of a complex global event sequence there are important similarities between discrete pulses phases of the major biotic crises and individual smaller scale events in our understanding second order global events are characterized by sudden extinctions in many groups and ecosystems including the complete disappearance of several widespread and diverse organism groups orders and families examples are the basal emsian atopus event where the planktonic graptolites finally died out the taghanic crisis frasnes events and lower kellwasser event third order global events show globally elevated extinction rates often at lower taxonomic level genera and species but within many clades and in several ecosystems examples are the silurian devonian boundary klonk event and the daleje chot c kacak condroz and annulata events fourth order global extinctions refer to the sudden disappearance of relatively fewer but widespread groups which implies a global not regional trigger this category may include the lochkovian pragian boundary

a 6 5 day westward propagating planetary wave origin and characteristics a large 10 30 m s 1 6 7 day period westward propagating planetary wave was seen in both ground radar and satellite data within the 80 100 km height regime during august and september 1993 previous analyses of these data argue that it was most likely a manifestation of the 1 2 rossby planetary wave commonly referred to as the 5 day wave perhaps shifted to longer periods by interaction with the mean zonal winds in this study the global scale wave model gswm hagan et al 1993 is used to analyze the characteristics of this westward propagating wave we propose that the observed wave is not a doppler shifted 5 day wave but rather an unstable mode drawing energy from unstable regions in the upper mesosphere whose realization is global in scale the concept of atmospheric instability is used to determine a likely source region and the model is used determine the characteristic period growth rate and perturbation fields of the instability driven wave

conodont biofacies patterns in the kellwasser facies upper frasnian lower famennian of the eastern anti atlas morocco abstract the abundant conodont fauna of a black limestone and shale lithology kellwasser facies of late frasnian early famennian age provides a significant example of environmental control on conodont distribution and abundance conodont collections from the upper gigas and upper crepida zones of the eastern anti atlas were examined biofacies maps for the conodont genera palmatolepis polygnathus icriodus ancyrodella and ancyrognathus were constructed and their facies distribution patterns analysed no significant restriction in conodont distribution was observed to be caused by the rise and extension of oxygen depleted water over the platform during the late frasnian early famennian the abundance of conodonts however appears to have been related to optimal food supply in the oxygenated portion of the water column conodont biofacies patterns observed in the upper devonian of the eastern anti atlas do not fit a simple ecological model involving distance from shore and depth of water the faunas of two intervals investigated exhibit a similar level of species diversity the pattern of which evidently follows the platform basin configuration but the majority of species shows a more or less random distribution the onset of black sediment deposition was characterized by the dominance of polygnathus and icriodus whereas towards its termination during the upper crepida zone time interval the genus palmatolepis clearly predominated this difference is a consequence of both a rise of sea level and of evolutionary changes in the composition of the conodont fauna during the early famennian

the terdiurnal tide in the mesosphere and lower thermosphere over london canada 43 n 81 w radars have been used successfully for many years to measure atmospheric diurnal and semidiurnal tides but studies of the atmospheric terdiurnal tide have only rarely been reported to date in the literature in this paper we investigate the amplitude phase and vertical wavelength for the terdiurnal tide using the university of western ontario uwo 2 mhz radar near london canada emphasis is placed on short term monthly seasonal and annual variations of the terdiurnal tide the results of the present study bring out certain new aspects of the terdiurnal tide at midlatitudes in the northern hemisphere we show that terdiurnal tides have significant amplitudes in the mesosphere and lower thermosphere indeed the terdiurnal amplitudes are often comparable to the diurnal ones we also draw attention to the annual variability and especially highlight the occurrence of the terdiurnal tide in non winter months for example the occurrence of the terdiurnal tide in spring months is not uncommon thus it seems that the 8 hour component observed over london canada cannot be explained by the terdiurnal tide being due to solar heating alone particular cases of the terdiurnal tide are examined and the observed amplitude and phase profiles of the terdiurnal tide at certain times of the year are discussed in terms of nonlinear interaction between the diurnal and semidiurnal tides we suspect that this effect may also explain the fact that diurnal and semidiurnal tides at our station often seem suppressed relative to other sites thayaparan et al 1995a on the basis of our previous and present observations it is also possible that large terdiurnal amplitudes observed at certain times of the year may be partly explained in terms of tidal gravity wave interactions however this possibility needs to be further investigated in the future

coordinated investigation of summer time mid latitude descending e layer es perturbations using na lidar ionosonde and meteor wind radar observations over logan utah 41 7 n 111 8 w 1 it is well known that there is a strong correlation between the formation of a descending sporadic e layer es and the occurrence of large upper atmospheric zonal wind shears most likely driven by solar thermal tides and or gravity waves we present new results of es perturbation events captured between 13 and 17 july 2011 ut days 194 198 as part of a coordinated campaign using a wind temperature na lidar at utah state university 41 7on 111 8 w and a canadian advanced digital ionosonde cadi scientific instrumentation ltd saskatoon saskatchewan canada and skiymet meteor wind radar both located at nearby bear lake observatory 41 9 n 111 4 w during this period the cadi detected strong descending es on 2 days 195 and 197 when large modulations of the top side mesospheric na layer occurred in synchronism with strong oscillations in the ionosonde e region echoes a weakening in the descending e layer echoes was observed on the other 2 days 196 and 198 coincident with a large reduction in the zonal diurnal and semidiurnal amplitudes above 95 km both tidal components were found to have comparable contributions to the total zonal wind shear that was critical for es formation and its downward propagation further investigation indicates that the weakening tidal amplitudes and the occurrence of the es events were also influenced by a strong quasi two day period modulation suggesting significant quasi two day wave qtdw interactions with the tides indeed a nonlinear wave wave interaction induced 16 hour period child wave was also detected with amplitude comparable to that of the prevailing tides these interaction processes and their associated effects are consistent with earlier thermosphere ionosphere mesosphere electrodynamics general circulation model studies of nonlinear interactions between the migrating tidal waves and the qtdw and were probably responsible for the observed damping of the tidal amplitudes resulting in the disruption of the es

effect of grain size and domain state on thermal demagnetization tails thermal demagnetization of viscous remanence vrm and partial thermoremanence ptrm of 20 and 135 m natural magnetites reveals a broad spectrum f tub of unblocking temperatures tub both and tb the blocking temperature in contrast 0 04 m single domain sd grains demagnetize sharply at tub tb high and low tub tails of f tub were wider for 135 m multidomain md grains than for 20 m psd grains 10 mt alternating field demagnetization rendered the vrm of the 20 m magnetite more sd like in subsequent thermal cleaning selectively erasing both low and high tub tails of f tub primary and secondary remanences are then cleanly separated and non linear thellier paleointensity determination becomes linear our results agree well with tb tub data for 105 year thermoviscous overprints in the milton monzonite over the range of log time common to the two studies because tub av tb for psd and md as well as sd grains the pullaiah et al paleothermometry method will work if tub av values are used instead of tub max values

terdiurnal tidelike variability in sporadic e layers 1 time series analysis was performed on a large database of ionosonde recordings taken over 12 years for the 6 month period from the beginning of may to the end of october when sporadic e layer occurrence is frequent the results show that in addition to the well known 24 and 12 hour tidal variations there is also a weaker but regular 8 hour periodicity in midlatitude sporadic e layers es statistically this terdiurnal periodicity is significant and occurs in both the sporadic e layer critical frequency foes and the layer virtual height h es becoming strongest around summer solstice and later in october after a minimum in september at times a weak 6 hour periodicity can also be present in es but its effects are much less significant than those of the 8 hour oscillation the 8 hour periodicity in es is attributed to the terdiurnal tide presumably acting through its vertical wind shear forcing of the metallic ions in the lower thermosphere the relation to the terdiurnal tide was inferred from simultaneous ionosonde recordings from three widely spaced stations in the same midlatitude zone showing the 8 hour oscillation to be present simultaneously in all ionosonde stations and have phases which are consistent with a westward propagating terdiurnal wave of zonal wave number 3 the present study establishes the regular occurrence of a terdiurnal tidelike oscillation in es which needs to be incorporated into the physics and modeling of sporadic e layer formation and dynamics

an analysis of tidal and planetary waves in the neutral winds and temperature observed at low latitude e region heights we present an extensive analysis of tidal and planetary waves in the altitude range of 94 to 144 km for the january 20 30 1993 period using the temperature and winds measured by the arecibo incoherent scatter radar isr this is the first time that simultaneous observational results for the 6 8 12 24 hour tides and a quasi 2 day planetary wave at e region heights have been reported at tropical latitudes in order to derive the major oscillations from the mainly daytime data we fill in the nighttime periods with assumed data values and large error bars when valid measurements are not obtainable and then fit the data using the measured and assumed errors as weight simulated results show that such a method is demonstratively better than leaving the nighttime as a gap the salient features of the tidal analysis results include the following 1 despite their large day to day variabilities in amplitude the 6 8 hour oscillations are shown to be upward propagating tides 2 the vertical wavelength of the semidiurnal tide in the zonal wind lengthens from 25 to 110 km for the altitude range from 94 to 135 km while the vertical wavelength of the meridional wind remains constant the semidiurnal component of the meridional wind experiences little dissipation above 106 km which is indicative of the turbopause height 3 the diurnal tide which has often been assumed to be negligible in earlier observations can be quite substantial above 110 km 4 a 2 day planetary wave dominates the diurnal and semidiurnal tides in the meridional wind between 97 and 108 km continuous isr operation during the january 20 30 1993 campaign also provides an opportunity to examine the tidal variability both in phase and amplitude

mesospheric planetary wave signatures in the equatorial electrojet 1 using five years 1994 1998 of simultaneous and collocated measurements of horizontal winds associated with mesosphere and lower thermosphere mlt region and geomagnetic field measurements in the indian geomagnetic dip equatorial region an extensive experimental study has been made on the influences of mesospheric planetary waves on the equatorial electrojet eej the winds are measured using medium frequency mf radar 1 98 mhz located at tirunelveli the eej strength is determined by measuring the geomagnetic field strength at both the geomagnetic dip and off dip equatorial stations trivandrum and alibag india by noting the simultaneous time evolution of spectral signal morlet wavelet analysis in both the eej strength and mesospheric winds at 88 km it is found that mesospheric planetary waves with periodicities of 2 25 days often do propagate up to the ionospheric dynamo region and have their influences on eej strength sometimes only one of the parameters shows strong spectral signal in this periodicity range it is also observed that often the diurnal oscillation in eej strength and mesospheric winds exhibits coherent variations in amplitude when the signature of mesospheric planetary scale oscillations is found in the eej strength also it is found that variations in high energy solar radiations f10 7 is used as a proxy can influence the eej strength at planetary timescales this leads to an interesting question what actually causes the vertical coupling between ionosphere and atmosphere through upward propagating planetary waves to be operative only during some and not all of the episodes

conodont biofacies of the taghanic transgressive interval middle givetian polish record and global comparisons conodont biofacies of the lublin and eysogory radom basins in se poland have been analysed in five cored borehole sections in a narrow interval of the middle givetian polygnathus ansatus zone corresponding to the global taghanic transgression assemblages exhibiting various proportions of dominant genera icriodus i and polygnathus p as well as particular p species and a few accessory taxa reflect both temporal transgression dynamics and lateral facies changes the latter comprise transition from a brackish lagoon with intermittent open marine influ ence to a carbonate shoal and offshore marly shelf generally characterized by p i biofacies but with a varying proportion of constituent genera and polygnathid species comparison of the polish record with stratigraphically well constrained quantitative biofacies evidence worldwide allowed the construction of a 2d nearshore offshore model for the euramerican epicontinental faunas con nected with taghanic transgressive facies the i p ratio has a diagnostic value for specific sub environments very nearshore shallow water and drowned platform but for other settings the polygnathus ansatus to polygnathus linguiformis ratio appears more useful the moroccan faunas display specific biofacies patterns tentatively explained by different climatic conditions the conodont biofacies concept has a limited application for palaeogeographically isolated set tings including pelagic oceanic areas of microcontinents or submarine rises in other cases eastern australia palaeobiogeographical bias precludes direct comparisons with the euramerican model

a statistical analysis of sporadic e layer occurrence in the midlatitude china region a statistical analysis of sporadic e layer recorded from september 2011 to september 2015 at four chinese ionospheric sounding stations of mohe 122 37 e 53 50 n beijing 116 25 e 40 25 n wuhan 114 61 e 30 53 n and hainan 109 13 e 19 52 n are presented to investigate the characteristics of sporadic e layer at the middle latitudes over china the occurrence of the sporadic e layer in mid latitude china region shows strong dependence on local time and season consistent with previous studies the occurrence of the mid latitude sporadic e layer is prominent at local daytime in summer season the results also reveal that the post sunset sporadic e layer is statistically pronounced in mid latitude china region possibly related to the nighttime mid latitude e region irregularities the mid latitude sporadic e layer is modulated by atmospheric tidal waves and planetary waves at different latitudes the occurrence of the mid latitude sporadic e layer also tends to increase with the level of geomagnetic activity on basis of both the statistical analysis and case study

partial anhysteretic remanent magnetization in magnetite 1 additivity 1 we have tested the additivity of partial anhysteretic remanent magnetization parm for suites of eight synthetic magnetites with mean grain sizes from 65 nm to 18 m and 18 natural samples including lake sediments oceanic and continental volcanic rocks gabbros and granites in both synthetic and natural sample suites domain states inferred from hysteresis and other magnetic properties vary from single domain sd through pseudosingle domain psd to multidomain md for each sample total arm intensity was compared with sums of partial arms of three different types four conjugate pairs of parallel parms four pairs of perpendicular parms and one set of five neighboring parallel parms in each case the intervals of alternating field af over which a steady field h was applied to produce the partial arms are nonoverlapping and cover the entire af range 0 100 mt used to produce the total arm additivity of partial arms was verified to better than 3 for all the samples whatever the domain state sd psd and md or composition ranging from pure magnetite to x 0 6 titanomagnetite the universality of parm additivity is unexpected because its analog partial thermoremanent magnetization ptrm deviates from ideal behavior as the grain size increases and the domain structure becomes md the different behaviors probably result from the fact that parm is produced at ordinary temperatures over short times whereas the most intense ptrm is produced at temperatures approaching the curie point with significant dwell times promoting such processes as isothermal remanence acquisition domain nucleation and domain wall reequilibration verification of the law of additivity of parms is an encouraging first step toward validating pseudo thellier and other methods of paleointensity determination that use arm in place of or in addition to trm

planetary waves and midlatitude sporadic e layers strong experimental evidence for a close relationship 1 a large amplitude 7 day period westward propagating s 1 planetary wave has been reported from ground radar and satellite wind measurements in the mesosphere lower thermosphere mlt during the second half of august and well into september 1993 following recent suggestions that planetary waves might play a role in the formation of midlatitude sporadic e layers es we have obtained and analyzed for the period from august 1 to september 30 1993 the sporadic e critical frequency foes time series from eight midlatitude ionosonde stations covering a large longitudinal zone from 58 e to 157 w the analysis revealed that all eight station foes data showed a strong 7 day periodicity occurring concurrently with the 7 day planetary wave reported elsewhere using independent methods for the analysis of the foes time series we computed identical estimates for the propagation direction zonal wave number and phase velocity of the 7 day wave which are in agreement with those reported from radar and satellite neutral wind mlt measurements the present findings provide the first direct evidence proving that planetary waves play an important role in the physics of midlatitude sporadic e region layers in addition our results include an important implication that the es parameters measured routinely and rather reliably with a dense global network of digital ionosondes as well as the enormous ionogram databases existing in world data centers may be used as an alternative means of studying large scale neutral atmospheric dynamics in the mlt region

the global taghanic biocrisis givetian in the eastern anti atlas morocco abstract in the tafilalt of the eastern anti atlas morocco the impact of the polyphase global taghanic crisis upper part of middle givetian on facies and faunas was studied in more than twenty successions of a strongly condensed hemipelagic platform northern and central tafilalt of a more neritic to biostromal area with interspersed shale basins southern tafilalt amessoui syncline and in a predominantly hypoxic basin southeastern tafilalt in the pre crisis interval a deepening depophase if win and increased nutrient supply allowed faunal blooms of macrofauna especially of goniatites maenioceras resulting in the deposition of the fossiliferous maenioceras marls middle part of ansatus zone on the platform and of correlative dark goniatite shales in the se in the amessoui syncline shales alternate with small sized but widespread coral stromatoporoid biostromes in the western tafilalt thin styliolinites indicate eutrophic peaks at the top a significant pre taghanic regressive trend top of depophase if is recorded by disconformity bound shallowing upwards cycles at the base within and at the top of the upper sellagoniatites bed higher part of ansatus zone with polygnathus ovatinodosus and by corresponding biostromes and calcareous sandstones in the s and se the regressive episode allowed the local re appearance of shallow water conodonts youngest known bipennatus culminated in an iron encrusted hardground or intraclastic reworked unit and caused local extinctions of ammonoids and of reefal fauna the initial taghanic onlap base of depophase iia tagh upper part of ansatus zone with rare po alveoliposticus led to the return of marls and styliolinid rich nodular limestones or of hypoxic shales in the s and se equivalents of the lower and middle tully limestones of the north american taghanic type area can be recognized may display subcycles and are separated by a minor regressive phase a disconformity or distinctive sea level fall associated with the final extinction of sobolewiidae and other goniatites separates equivalents of the upper tully limestone the subsequent aff amplexum bed base of depophase iia ut is characterized by an initial radiation of pharciceratidae and of some conodonts oz semialternans zone by blooms in branching tabulate corals youngest known bainbridgia and phacopid trilobites and by a positive carbon isotope excursion the final extinction of maenioceratidae and agoniatitina sellagoniatites coincided with a minor regression at the top of the taghanic crisis interval uniquely in the eastern tafilalt with the most complete sedimentary record a thin bioclastic conodont lag is preserved at the base of the upper givetian and below the deepening of depophase iia gen the post taghanic radiation of ammonoids and especially of conodonts falls in the nodular mzerrebites erraticus beds hermanni zone of the platform and in correlative hypoxic goniatite shales and marls of the s and se radiation continued in the subsequent haematite rich lunupharciceras nodules of the platform and in the widespread lower marker bed both cristatus ectypus zone that are separated by disconformities the tafilalt record confirms that the taghanic crisis was a second order global overturn of pelagic and reefal biota that progressed in at least three distinctive steps over several hundred thousand years the detailed event stratigraphy allows global correlations and comparisons with other regions new york type area dra valley france germany that have been investigated in similar detail it is assumed that the taghanic crisis was primarily driven by repeated and fast eustatic fluctuations and climate change greenhouse overheating pulses which were probably linked hypoxia anoxia played only a local role in extinctions the crisis can be recognized globally but it had very different effects regionally leading variably to faunal migrations blooms and extinctions

seasonal variations of the terdiurnal tide in the mesosphere and lower thermosphere a model study observations of the terdiurnal 8 hour tidal wind oscillations in the mesosphere and lower thermosphere mlt reveal strong seasonal and latitudinal variations the tidal amplitudes reach a maximum of about 15 20 m s 1 at midlatitudes in winter the vertical phase progression corresponds to very long vertical wavelengths during summer the amplitudes are typically weaker and the phases are less regular first simulations of the terdiurnal tide with the spectral mesosphere lower thermosphere model are presented the model explicitly accounts for the solar thermal excitation in the middle and upper atmosphere and reproduces the salient features of the terdiurnal wind oscillations well the preferential solar excitation of antisymmetric terdiurnal modes capable of propagating into the mlt combined with an asymmetric atmospheric response appears to be primarily responsible for the observed seasonal variations nonlinear interactions of the diurnal and semidiurnal tides are demonstrated to make a noticeable in situ contribution to the excitation of the terdiurnal tide at 95 100 km especially during equinox

elevated temperature viscous remanent magnetization of natural and synthetic multidomain magnetite abstract the time temperature relationship of magnetization is a subject of much interest and debate by paleomagnetists rock magnetists and magnetic anomaly modellers we have investigated this relationship by studying the viscous remanent magnetization vrm of coarse grained multidomain md magnetite our experiments covered the temperature range from 22 to 400 c times from minutes to months and included both australian granulite samples and multidomain magnetite samples synthesized by the glass ceramic method vrm acquisition was found to generally increase with temperature but not always at the rate predicted from classical thermal fluctuation theories thermal cycling between room temperature at which the measurements were made and the vrm acquisition temperature sharply decreased the temperature dependence of the vrm room temperature vrm acquisition accelerates with time when plotted on a semilog plot whereas at elevated temperature the curves are quasilinear against log time for both the natural and synthetic samples this change in behavior may suggest a variation in the vrm acquisition mechanism as a function of temperature for md magnetite the granulites have a nearly linear increase in vrm acquisition rate with temperature whereas the glass ceramics display little change in the acquisition rate between 22 and 200 c but increase by nearly a factor of 3 by 400 c the increase in vrm of the glass ceramics between 200 and 400 c is in general qualitative agreement with thermal fluctuation theory there was no systematic change in the rate of vrm acquisition with grain size for the multidomain magnetites used in this study elevated temperature e g 400 c vrm acquisition by the deep crustal granulites if extrapolated over the brunhes chron would produce a magnetization of several a m which if true is of the order required by models for the source of long wavelength magnetic anomalies

36cl dating of the classic pleistocene glacial record in the northeastern cascade range washington and are more degraded seventy six 36 cl dates for the moraines cluster in groups having mean ages 1 of 12 500 500 13 300 800 16 100 1100 19 100 3000 70 900 1500 93 100 2600 and 105 400 2200 years a still older highly weathered and eroded moraine is undated but likely is at least 165 000 years old the moraine ages and relative extent of the icicle creek glacier correspond closely to the ages and relative amplitude of july insolation minima at 47 5 n latitude they also are in accord with ages for glaciations in the european alps that were inferred by milutin milankovitch and colleagues in the 1920s based on calculations of summer insolation evidence that the greatest late pleistocene glacier advance occurred at the onset of the last glaciation during marine isotope substage 5d is consistent with a cooling climate and major glacier advances at that time elsewhere in north america and the eurasian arctic with a dramatic increase in global ice volume and with the shifting track of the jet stream over northwestern united states

magnetic viscosity of some doleritic basalts in relation to the interpretation of the oceanic magnetic anomalies the growth of induced magnetization vim with time t in a 5 oe acquisition field followed by subsequent decrease in zero field of the viscous remanent magnetization vrm with time t was investigated at room temperature for 5 oceanic doleritic basalts and at temperature up to 105 c for 1 dike sample both vim acquisition and vrm decay are enhanced by increasing temperature and time however the growth and decay do not uniformly obey a log t law on an experimental time of 2 hours the results show that far from the ridge axes at the bottom of oceanic pillow layer 2a and in the upper part of the dike layer 2b the induced magnetization might largely dominate the remanent one while only a small fraction of the primary trm corresponding to the highest blocking temperatures tb would be preserved the partial trm corresponding to the lowest tb having been replaced by a viscous magnetization consequently the doleritic basalts would rarely if ever contribute to oceanic magnetic anomalies

gravitational settling of conodont elements implications for paleoecologic interpretations of conodont assemblages gravitational settling experiments show that conodont elements settle with a wide spectrum of velocities ranging from 0 5 to 5 5 cm s in synthetic seawater significant differences in settling velocity exhibited by representatives of the three major shape classes of conodonts pectiniform coniform and ramiform elements are due to differences in grain mass and cross sectional area exposed to fluid shear and normal forces during settling settling trajectory is a spiral or helical pattern that is less variable than settling velocity but differs from models that characterize most skeletal carbonate grains conodont elements exhibit viscosity dominated stokesian settling and are hydraulically equivalent to phosphate spheres of coarse silt to fine sand size thus even under conditions of modest net horizontal currents lateral separation and sorting due to differences in size and shape of conodont elements belonging to a single animal will occur during gravitational settling differential sorting related to gravitational settling probably influenced the formation of most preserved conodont assemblages the disparity between observed element types forms and sizes compared to known or proposed species apparatus compositions can be used both as an indication of taphonomic disruption and as a useful factor in interpreting sedimentary environment

the dynamic ionosphere over arecibo a theoretical investigation numerical simulations of the f region ionosphere over arecibo puerto rico are presented we deduce from these simulations that the dynamic behavior of the arecibo ionosphere particularly the so called midnight collapse phenomenon is strongly influenced by the upward propagating semidiurnal tidal component of the neutral meridional wind excited below thermospheric levels presence of a terdiurnal component in the wind field improves the agreement with experiment and could result from nonlinear interactive coupling between the neutral wind and ion drag the steep underside density gradients occurring in conjunction with the collapse are due to vertical shear in the meridional wind field associated with the propagating semidiurnal tide these gradients are capable of triggering the gradient drift instability thus accounting for plasma irregularity formation and observations of vhf scintillations associated with the collapse phenomenon

observations of the 5 day wave in the mesosphere and lower thermosphere the 5 day planetary wave has been detected in the winds measured by the high resolution doppler imager hrdi on the upper atmosphere research satellite uars in the mesosphere and lower thermosphere 50 110 kin the appearances of the 5 day wave are transient with a lifetime of 10 20 days in the two year data set the structures of selected 5 day wave events are in generally good agreement with the 1 1 rossby normal mode for both zonal and meridional components a climatology of the 5 day wave is presented for an altitude of 95 km and latitudes mainly between 40os and 40on

quasi 16 day oscillation in the mesosphere and lower thermosphere a quasi 16 day wave in the mesosphere and lower thermosphere is investigated through analyses of radar data during january february 1979 and through numerical simulations for various background wind conditions previous workers have examined about 19 days of tropospheric and stratospheric data during january 10 28 1979 and present conflicting evidence as to whether a large westward propagating wavenumber 1 oscillation observed during this period can be identified in terms of the second symmetric rossby normal mode of zonal wavenumber 1 commonly referred to as the 16 day wave in the present work we have applied spectral analysis techniques to meridional and zonal winds near 95 km altitude obtained from radar measurements over obninsk russia 54 n 38 e and saskatoon canada 52 n 107 w these data reveal oscillations of the order of 10 m s 1 with a period near 16 days as well as waves with periods near 5 and 10 days these periodicities all correspond to expected resonant frequencies of atmospheric disturbances associated with westward propagating free rossby modes of zonal wavenumber 1 numerical simulations are performed which demonstrate that the 95 km measurements of the 16 day wave are consistent with upward extension of the oscillation determined from the tropospheric and stratospheric data noteworthy features of the model in terms of its applicability in the mesosphere lower thermosphere regime are explicit inclusion of eddy and molecular diffusion of heat and momentum and realistic distributions of mean winds especially between 80 and 100 km the latter include a westerly wind regime above the summer easterly mesospheric jet thus providing a ducting channel enabling interhemispheric penetration of the winter planetary wave disturbance this serves to explain the appearance of a quasi 16 day wave recently reported in the high latitude summer mesopause williams and avery 1992 however the efficiency of this interhemispheric coupling may be reduced by gravity wave stress no significant penetration of the 16 day oscillation above about 100 km is predicted by the model reported signatures of a 16 day periodicity in ionospheric data therefore require modulation of tidal or gravity wave accessibility to the thermosphere or perhaps in situ excitation

paleomagnetism reveals the emplacement age of tsunamigenic coral boulders on ishigaki island japan abstractwe use temperature dependent viscous remanent magnetization to estimate the emplace ment age of tsunamigenic coral boulders along the shorelines of ishigaki island japan the boulders consist of the hermatypic coral porites and the time of their deposition by tsuna mis has been established using radiocarbon dating recently deceased corals at reef edges around ishigaki island record the earth s current magnetic field present earth field pef as a remanence parallel to the field in the skeleton since the time when the coral skeletons were emplaced on the shorelines as boulders by destructive tsunami waves a new viscous magne tization was partially overprinted in the boulder parallel to the pef the results of thermal demagnetization indicated that the boulders were rotated at least once and their emplace ment ages determined from l neel s relaxation theory for single domain magnetite agree well with the radiocarbon ages although there are traces of multidomain magnetites new applica tion of neel s theory to tsunamigenic coral boulders gives us an opportunity to ascertain the age and transportation mode of individual tsunamigenic coral boulders in this area

evidence for nonlinear coupling of planetary waves and tides in the antarctic mesopause analyses of hourly mean meridional and zonal winds near 95 km observed with the meteor radar system at molodezhnaya station 68 s 45 e during 1990 reveal the presence of long period 2 18 day waves with dominant periods corresponding to those of rossby normal modes modified by mean zonal winds time varying analyses indicate that although significant contributions at planetary wave periods persist with nearly constant periods for intervals of days to weeks temporal variability of these periods is observed over longer intervals tidal motions which mainly consist of the semidiurnal and the diurnal periods demonstrate considerable modulation of their amplitudes that vary with time the observed tidal amplitude modulations are investigated through bispectral analyses the results of these analyses suggest nonlinear interactions of quadratic form between oscillations with periods in the range of 2 to 19 days and the diurnal and semidiurnal tides at various intervals during 1990

sequence stratigraphy and a revised sea level curve for the middle devonian of eastern north america abstract the well exposed middle devonian rocks of the appalachian foreland basin onondaga formation hamilton group tully formation and the genesee group of new york state preserve one of the most detailed records of high order sea level oscillation cycles for this time period in the world detailed examination of coeval units in distal areas of the appalachian basin as well as portions of the michigan and illinois basins has revealed that the pattern of high order sea level oscillations documented in the new york pennsylvania section can be positively identified in all areas of eastern north america where coeval units are preserved the persistence of the pattern of high order sea level cycles across such a wide geographic area suggests that these cycles are allocyclic in nature with primary control on deposition being eustatic sea level oscillation as opposed to autocylic controls such as sediment supply which would be more local in their manifestation there is strong evidence from studies of cyclicity and spectral analysis that these cycles are also related to milankovitch orbital variations with the short and long term eccentricity cycles 100 kyr and 405 kyr being the dominant oscillations in many settings relative sea level oscillations of tens of meters are likely and raise considerable issues about the driving mechanism given that the middle devonian appears to record a greenhouse phase of phanerozoic history these new correlations lend strong support to a revised high resolution sea level oscillation curve for the middle devonian for the eastern portion of north america recognized third order sequences are eif 1 lower onondaga formation eif 2 upper onondaga and union springs formations eif giv oatka creek formation giv 1 skaneateles giv 2 ludlowville giv 3 lower moscow giv 4 upper moscow lower tully and giv 5 middle tully geneseo formations thus in contrast with the widely cited eustatic curve of johnson et al 1985 which recognizes just one major transgressive regressive t r cycle in the early mid givetian if prior to the major late givetian taghanic unconformity iia upper tully geneseo shale we recognize four t r cycles if restricted ig ih and ii we surmise that third order sequences record eustatic sea level fluctuations of tens of meters with periodicities of 0 8 2 myr while their medial scale fourth order subdivisions record lesser variations primarily of 405 kyr duration long term eccentricity this high resolution record of sea level change provides strong evidence for high order eustatic cycles with probable milankovitch periodicities despite the fact that no direct evidence for middle devonian glacial sediments has been found to date

paleothermometry of the sydney basin evidence from overprinting of magnetizations of late permian and mesozoic rocks and from the rank of permian coals and mesozoic phytoclasts coal particles suggests that surface rocks in the sydney basin eastern australia have been raised to temperatures of the order of 200 sup 0 c or higher as vitrinite reflectance an index of coal rank or coalification is postulated to vary predictably with temperature and time estimates of the paleotemperatures in the sydney basin based on observed vitrinite reflectance measurements can be made in conjunction with reasonable assumptions about the tectonic and thermal histories of the basin these estimates give maximum paleotemperatures of present day surface rocks in the range 60 249 sup 0 c depending on factors such as location in the basin the thickness of the sediment eroded and the maximum paleogeothermal gradient higher coal rank and consequently larger eroded thicknesses and paleogeothermal gradients occur along the eastern edge of the basin and may be related to seafloor spreading in the tasman sea on the basin s eastern margin a theory of thermal activation of magnetization entailing the dependence of magnetic viscosity on the size distribution of the magnetic grains is used to obtain an independent estimate of the maximum paleotemperaturesmore in the sydney basin this estimate places the maximum paleotemperature in the range 250 300 sup 0 c along the coastal region both coalification and thermal activation of magnetization models provide strong evidence of elevated paleotemperatures which in places exceed 200 sup 0 c and the loss of sediment thicknesses in excess of 1 km due to erosion less

an upper e region quarterdiurnal tide at arecibo studies of the time height trajectories of ionosphere e region layers at arecibo have revealed not only the usual diurnal sporadic e and semidiurnal intermediate layer structures but also that on occasion extra layers form and descend through the e region in particular during january 1981 four layers per day were observed to descend through the upper e region this four per day layer system was remarkably coherent over the 3 days of observation and suggests the existence of a 6 hour period or quarterdiurnal tidal wind system in the upper e region numerical simulations of ion trajectories in a realistic model atmosphere with diurnal semidiurnal and quarterdiurnal tidal wind systems of appropriate amplitude and phase structures confirm that the presence of a quarterdiurnal tide is sufficient to explain the observations

a study of tidal and planetary wave periodicities present in midlatitude sporadic e layers the diurnal and semidiurnal atmospheric tides are known to be of fundamental importance in the formation of midlatitude sporadic e layers acting through their vertical windshear forcing of the long living metallic ions in the lower thermosphere also recent studies suggested that planetary waves play a role on sporadic e generation as well a fact that went unnoticed in the long going research of sporadic layers in this paper a methodology is employed to investigate the tidal and planetary wave periodicities imprinted onto sporadic e critical frequencies foes in this approach standard analysis techniques used in neutral atmospheric dynamics are applied on foes time series obtained during summertime when sporadic e occurrence is nearly continuous it is shown that besides the dominant and known 24 hour and 12 hour tidal periodicities in foes there is often a weaker terdiurnal 8 hour oscillation present as well in addition there are planetary wave periodicites in foes with periods near the normal rossby modes that is 2 5 10 and 16 days it is also found that the tidal oscillations in foes undergo a strong amplitude modulation with periods comparable to the dominant planetary wave periodicities present in the data our results are in line with recent findings based on a single event study which suggested that sporadic e layers are affected indirectly by planetary waves through their nonlinear interaction and modulation of the atmospheric tides at lower altitudes the close relationship between neutral wave dynamics and midlatitude sporadic e periodicities suggests that the ionosonde data can be used as an alternative means of studying tidal and planetary wave characteristics and their climatology in the lower thermosphere

structure of the terdiurnal tide at 95 km satellite wind observations from the high resolution doppler interferometer hrdi instrument on the upper atmosphere research satellite uars are used to describe the latitudinal structure and seasonal variation of the terdiurnal 8 hour atmospheric tide at 95 km the amplitude of the annual average tide is 5 m s meridional and 15 m s zonal within the range observed 60 s to 60 n the maximum amplitudes are found during fall and winter at midlatitudes only weak temporal correlations with the diurnal and semidiurnal tides are seen on the monthly time scales resolved

thermoviscous remanent magnetism of columbia river basalt blocks in the cascade landslide we studied sixteen basalt samples from a landslide in the columbia river gorge to determine if they had acquired a thermoviscous remanent magnetism tvrm since the slide was emplaced about 800 years ago all samples were thermally demagnetized at 20 heating steps until 360 c where a large change in susceptibilit y was noted analysis of the directional changes during demagnetization indicates that the samples contain up to four tvrm components in addition to an nrm component the tvrm components with the lowest blocking temperatures are tightly clustered around the present field direction while the nrm directions are consistent with a random distribution as expected for a landslide deposit measurements of hysteresis parameters and thermomagnetic analyses of the samples demonstrate that the dominant magnetic mineral in the basalt is single domain magnetite the temperature at which the first tvrm component was removed ranges from 70 c to 100 c this result can be compared to nomographs that relate the time and temperature used to demagnetize a tvrm with the time and temperature at which the tvrm was acquired our results are more consistent with the nomograph of pullaiah et al 1975 than with the nomograph of middleton schmidt 1982