eof analysis and modeling of gps tec climatology over north america an empirical ionospheric model of the total electron content tec over north america 20 60 n 40 140 w is constructed using the gps tec data collected by massachusetts institute of technology mit haystack observatory during the years 2001 2012 this model is based on an analysis of quiet time monthly averages using the empirical orthogonal function eof decomposition technique allowing for separation of spatial and temporal variations the importance of different types of spatial temporal variations to the overall tec variability can be well represented by the characteristics of eof basis functions and associated principal components coefficients with various modes the mode one eof decomposition constitutes 97 5 of the total variance and therefore represents the essential feature of north america spatial and diurnal variation of the tec the mode two eof as reported in an earlier study reveals a large and significant symmetric longitudinal variation of the ionosphere organized with respect to magnetic declination the mode three eof decomposition shows midlatitude latitudinal structure that varies with season in a manner very similar to the so called winter anomaly because of the quick convergence of eof decomposition modes the first four eof modes are utilized for constructing a tec empirical model for each of the eof modes the temporal variations are expressed analytically in terms of local time season and solar activity and the spatial variations by cubic spline functions an analysis of accuracy and quality indicates that this regional empirical tec model can reflect the majority of the quiet time monthly means and represent characteristic temporal spatial variations in the north america

longitudinal variability of low latitude total electron content tidal influences 1 recently nighttime ultraviolet uv observations obtained by image fuv and timed guvi instruments have revealed a longitudinal wave number four pattern in the nighttime airglow intensity and in the position of the equatorial anomalies during equinox and high solar flux conditions in the present study we have extended this work and determined the longitudinal variability of the low latitude total electron content tec climatology during different geophysical conditions with a special emphasis on the longitudinal wave number four structure in the low latitude ionosphere we have used more than 5 million low latitude topex tec observations covering the entire 13 years of topex tec data from august 1992 until october 2005 this data set was used to determine the local time seasonal solar cycle and geomagnetic activity dependence of the longitudinal variability of tec at equatorial and low latitudes and in particular to address the existence and evolution of the wave number four longitudinal pattern under these conditions our study shows that the wave number four pattern is created during the daytime hours at equinox and june solstice but is absent or washed out by other processes during december solstice during equinox the wave number four pattern is created around noon with well defined longitudinal enhancements in the low latitude tec these enhancements which are symmetric about the geomagnetic equator during this season last for many hours and can be clearly seen past midnight the longitudinal patterns are found to be nearly identical between the vernal march april and autumnal september october equinoxes and largely independent of the solar cycle conditions the wave number four pattern is also observed during geomagnetically active conditions indicating that the processes that create this pattern are also present during active times the variations between the well defined longitudinal maxima and minima are of the order of 20 during june solstice the wave number four pattern is also observed in the afternoon hours but in contrast to the equinox cases it exhibits a strong hemispheric asymmetry and is not observed during the night the low latitude tec exhibits clear longitudinal variations during december solstice with large daytime enhancements over the east asian and pacific regions and a third enhancement emerging in the afternoon over the atlantic ocean but a clear wave number four pattern is not observed during this season although the equatorial and low latitude tec values exhibit clear longitudinal patterns during all seasons a significant amount of scatter remains in the tec data that is not accounted for by changes in the solar cycle the season or the local time or by the longitudinal variability this remaining scatter is largest near the poleward edges of the anomalies and is of the order of 40

statistical behavior of the longitudinal variations of daytime electron density in the topside ionosphere at middle latitudes electron density in the topside ionosphere has significant variations with latitude longitude altitude local time season and solar cycle this paper focuses on the global and seasonal features of longitudinal structures of daytime topside electron density ne at middle latitudes and their possible causes we used in situ ne measured by demeter and f2 layer peak height hmf2 and peak density nmf2 from cosmic the longitudinal variations of the daytime topside ne show a wave number 2 type structure in the northern hemisphere whereas those in the southern hemisphere are dominated by a wave number 1 structure and are much larger than those in the northern hemisphere the patterns around december solstice ds in the northern hemisphere winter are different from other seasons whereas the patterns in the southern hemisphere are similar in each season around march equinox me june solstice js and september equinox se in the northern hemisphere and around me se and ds in the southern hemisphere the longitudinal variations of topside ne have similar patterns to hmf2 around js in the southern hemisphere winter the topside ne has similar patterns to nmf2 and hmf2 does not change much with longitude thus the topside variations may be explained intuitively in terms of hmf2 and nmf2 this approach works reasonably well in most of the situations except in the northern winter in the topside not too far from the f2 peak in this sense understanding variations in hmf2 and nmf2 becomes an important and relevant subject for this topside ionospheric study

a total electron content space weather study of the nighttime weddell sea anomaly of 1996 1997 southern summer with topex poseidon radar altimetry this paper reports on a total electron content space weather study of the nighttime weddell sea anomaly overlooked by previously published topex poseidon climate studies and of the nighttime ionosphere during the 1996 1997 southern summer to ascertain the morphology of spatial tec distribution over the oceans in terms of hourly geomagnetic longitudinal and summer winter variations the topex tec magnetic and published neutral wind velocity data are utilized to understand the underlying physical processes the tec results are combined with inclination and declination data plus global magnetic field line maps to investigate spatial and temporal tec variations geographic magnetic latitudes and local times are computed as results show the nighttime weddell sea anomaly is a large 1 600 2 22 million km2 estimated for a steady ionosphere space weather feature extending between 200 e and 300 e geographic it is an ionization enhancement peaking at 50 s 60 s 250 e 270 e and continuing beyond 66 s it develops where the spacing between the magnetic field lines is wide medium easterly declination is large medium 20 50 and inclination is optimum 55 s its development and hourly variations are closely correlated with wind speed variations there is a noticeable 43 reduction in its average area during the high magnetic activity period investigated southern summer nighttime tecs follow closely the variations of declination and field line configuration and therefore introduce a longitudinal division of four indian western eastern pacific atlantic northern winter nighttime tecs measured over a limited area are rather uniform longitudinally because of the small declination variation topex maps depict the expected strong asymmetry in tec distribution about the magnetic dip equator

analysis of tec data from the topex poseidon mission 1 topex poseidon mission has provided an extensive database of vertical tec over the ocean since august 1992 data from nearly 10 years of topex tec observations were analyzed to study the tec climatology first tec data were binned by season geomagnetic activity and solar activity to create longitudinally averaged tec maps in magnetic latitude and local time these maps show the annual and semiannual anomalies well known from climatological studies of nmf2 but lack the seasonal anomaly because of the longitudinally averaged binning the equatorial anomaly is the most prominent feature in the maps and they show strong tec variations with solar activity but relatively weak variations with geomagnetic activity in our three kp bins compared with the low solar activity conditions f10 7 120 the tec values for f10 7 120 are much larger and the equatorial anomaly lasts longer into the night up to midnight during geomagnetically active periods the tec maps generally show a noticeable increase at low latitudes for f10 7 120 but this effect is barely detectable for f10 7 120 finally three longitudinal bins indian pacific and atlantic were added in order to see how the tec morphology varies with longitude the tec measurements display strong longitudinal variations that closely follow the longitudinal variation of the magnetic declination in the southern pacific where the declination is positive and large the diurnal tec variations significantly differ from those in the other longitude sectors where the magnetic declination is negative in the southern hemisphere also at noon the phase of the longitudinal tec variation is typically opposite to that at midnight

correlating paleomagnetic geochemical and petrographic evidence to date diagenetic and fluid flow events in the mississippian turner valley formation moose field alberta canada abstract petrographic geochemical and paleomagnetic analyses of the mississippian turner valley formation provide constraints on diagenesis and fluid flow events in the western canada sedimentary basin paleomagnetic plugs and companion geochemical samples were taken from two drillcores with fullbore microimage log orientations dolomite from both wells yielded two magnetization directions the low temperature low coercivity direction is a drilling induced remanence rather than a viscous remanent magnetization the high temperature high coercivity remanence direction is cretaceous and there is no sign of a primary mississippian direction geochemical analyses of matrix dolomite yield 18o values ranging from 0 65 to 3 34 vpdb standard and 13c values ranging from 1 77 to 3 05 vpdb the least depleted samples have stable isotope values consistent with or only slightly depleted from postulated mississippian dolomite values the remaining sample values exhibit a negative covariant trend consistent with either mixing with another diagenetic fluid or recrystallization during burial petrographic analysis reveals the presence of a recrystallization event that caused zoning and a gradual increase size of the dolomite crystals this event is thought to have caused both the cretaceous paleomagnetic remanence and the altered geochemical values the minor enrichment in sr radiogenic isotopes relative to coeval seawater values suggests that both an extrabasinal source for any fluid and large scale fluid flow are unlikely the results also indicate that magnetic remanences are very sensitive to visually minor changes in carbonate recrystallization from heat or pressure so that great care must be taken in correlating paleomagnetic and geochemical data

an investigation of motions of the equatorial anomaly crest using more than 350 ionospheric images reconstructed tomographically studies on the motion of the anomaly crest and its geophysical implications are carried out on an average day the crest forms at 09 00 lt and in the next two hours moves poleward with a speed of about 1 per hour as it intensifies this poleward motion is slowed as the crest reaches its highest latitude where it stays for several hours until early afternoon thereafter the crest starts to weaken as it recedes with a speed of about 0 5 per hour equatorward during 12 00 14 00 lt the crest latitude is found to correlate with the fountain strength and the total number of electrons in a cross sectional plane at the observational longitude of the whole equatorial ionosphere

eocene structural development of the valhalla complex southeastern british columbia the valhalla complex a cordilleran metamorphic core complex is a 100 km by 30 km structural culmination within the omineca belt of southeastern british columbia it comprises sheets of granitic orthogneiss ranging in age from 100 to 59 ma with intervening paragneiss of uncertain age and stratigraphic correlation the complex is roofed by the ductile valkyr shear zone and the ductile brittle slocan lake fault zone the upper plate comprises lower grade metasedimentary rocks intruded by middle jurassic plutons the valkyr shear zone and the slocan lake fault zone deform 62 and 59 ma granitic sheets in their footwalls the easterly directed valkyr shear zone is a 2 to 3 km thick zone of distributed ductile strain which is arched over the complex and is exposed around the periphery on the northern western and southern margins the shear zone was active between 59 and 54 ma under amphibolite facies conditions the juxtaposition of upper and lower plates with different structural and metamorphic histories indicates that the valkyr shear zone is a significant structure with large displacement there is evidence to support an easterly rooting direction consistent with an extensional origin its surface breakaway is suggested to be west of the valhalla complex the slocan lake fault zone on the eastern side of the complex is a gently 30 easterly dipping ductile brittle normal fault which roots to the east it was active between 54 and approximately 45 ma and truncates the valkyr shear zone timing and structural relationships indicate that the valkyr shear zone and the slocan lake fault zone are genetically related movement on the ductile valkyr shear zone arching of the complex and displacement on the slocan lake fault zone occurred as a continuum in early to middle eocene time this paper documents the presence of significant eocene ductile strain in the valhalla complex and suggests that the role of extension in this region is more profound than had been previously recognized

synfolding remagnetization and deformation results from palaeozoic sedimentary rocks in west virginia summary palaeomagnetic analysis was conducted at 27 sites from two stratigraphically adjacent palaeozoic units along two transects meldey and rig of the patterson creek anticline in the appalachian orogen of west virginia to better understand the relationship between deformation and remagnetization while no primary directions were observed we isolated identical well defined secondary late palaeozoic magnetizations in carbonates from the late silurian tonoloway formation and the early devonian helderberg group standard application of conventional palaeomagnetic fold tests suggests that the magnetizations are synfolding in the helderberg group and pre folding to early synfolding in the tonoloway formation a fold test on all data combined indicates a synfolding magnetization best grouping at 60 65 per cent unfolding but the resulting distributions are not circular an alternative interpretation based on optimal differential unfolding at the site mean level yields one group with a nearly pre folding or early synfolding magnetization 70 per cent unfolding that is both circular and concordant with north america s apparent polar wander path the second group has a variable synfolding magnetization that is elliptical at the optimum unfolding level and falls off the path differences in either the age of remagnetization or viscous partial thermoremanent magnetization contamination cannot account for this result the sites falling into the pre folding group are biased towards the tonoloway formation the medley transect the northwest limb away from small folds and lower dip angle relative to the sites in the synfolding group the two groups defined by the fold test results also have a relationship with both total strain and strain partitioning the rocks containing the early synfolding remanence exhibit less total strain and in particular less pressure solution strain relative to grain boundary sliding and calcite twinning it is likely that the remagnetization in the entire area was coincident and occurred prior to folding even though some sites reveal synfolding directions the variation in the behaviour of the remagnetization relative to folding is unclear at present but it indicates that pressure solution and stylolite formation are important processes in remagnetization in any event the relationship between deformation and magnetization is not simple apparently identical magnetizations from adjacent sites may have very different histories and or responses to deformation while the exact relationship between remagnetization and deformation remains elusive this study demonstrates that significant variation in behaviour can exist at a very local scale

a statistical study of large scale traveling ionospheric disturbances observed by gps tec during major magnetic storms over the years 2003 2005 1 in this paper we plot two dimensional total electron content tec perturbation maps and investigate the statistical characteristics of large scale traveling ionospheric disturbances lstids during major magnetic storms from 2003 to 2005 the tec data were obtained from more than 600 gps receivers in north america within the geographical latitudes of 25 n 55 n we found a total of 135 cases of lstids with amplitudes of up to 3 5 tecu and a maximum front width of 4000 km the mean value of periods horizontal velocities and azimuths are 1 8 h 300 m s and 187 7 west of south respectively the mean velocity is obviously slower than that observed at lower latitudes such as japan of all the 135 lstid events 35 cases 26 occurred in the nighttime with their possible source within the region of north america according to the variation of magnetic h component observed in this region in addition the occurrence of lstids peaks at 1200 lt and at 1900 lt it is also pointed out that the ut dependence of the occurrence of auroral geomagnetic disturbances plays a major role in the forming of ut and lt dependence of the occurrence of lstids observed at midlatitudes

paleomagnetic constraints on the tectonic history of the foreland belt southern canadian cordillera preliminary results in the southern canadian cordillera the paleomagnetic memory of paleozoic carbonate strata in the front ranges and inner foothills of the foreland thrust and fold belt retains no record of their known deposition at low latitudes instead each folded structure exhibits a similar but asynchronous sequence of events including an eastwardly progressing predeformational chemical remagnetization during the cordilleran orogeny the remagnetization of a western front ranges structure occurs during a period of normal polarity before 130 ma the paleomagnetic pole requires that the subsequent deformation of the western front ranges is jurassic or younger the remagnetization of a front ranges structure in the lewis thrust sheet occurs during a period of normal polarity after 130 ma but before deformation which from other evidence occurred around 75 ma the predeformational remagnetization of an inner foothills structure occurs during a reversed magnetic period that we interpret to be after 75 ma an early cretaceous sill in the lewis thrust sheet was remagnetized during a reverse polarity chron prior to the end of lewis thrust deformation when about 70 of the present dip of the sill was acquired remagnetization consistently predates deformation whereas it occurs later at more easterly localities there are also similarities in character and style of the remagnetizations among localities when coupled with the eastward progression of the deformation our observations suggest that an important and pervasive but hitherto unrecognized and unappreciated orogenic chemical process affected paleozoic carbonate strata in the van of the deforming cordilleran tectonic wedge

the altitude extension of the mid latitude trough and its correlation with plasmapause position 1 tomographic imaging provides a powerful technique for obtaining images of the spatial distribution of ionospheric electron density in an altitude versus geographic latitude grid at a specified longitudinal sector the method which involves monitoring the total electron content tec of the ionosphere using signals transmitted from the global positioning system gps has the ability to reveal the detailed structure of the ionosphere including the mid latitude trough the tomographic reconstruction of ionospheric electron density structures are performed at different specific longitudinal sectors both in the northern and southern hemisphere at the same time the plasmapause position is estimated from image euv images and mapped onto tomographic images the simultaneous location of the altitude extension of the mid latitude trough and the plasmapause position are essentially co located

estimates of the precision of gps radio occultations from the cosmic formosat 3 mission 1 the constellation observing system for meteorology ionosphere and climate cosmic formosa satellite 3 formosat 3 is a six satellite radio occultation mission that was launched in mid april 2006 the close proximity of the cosmic satellites provides a unique opportunity to estimate the precision of the radio occultation remote sensing technique from closely collocated occultations 10 km separation of tangent points the rms difference of refractivity between 10 and 20 km altitude is less than 0 2 which is approximately twice better than previous estimates obtained from champ and sac c collocated occultations apparently due to smaller separation of the occultation pairs and due to parallel occultation planes in the lower troposphere the maximal rms is 0 8 at 2 km altitude and decreases abruptly to 0 2 between 6 and 8 km altitude the rms difference of electron density in the ionosphere between 150 and 500 km altitude for collocated occultations is about 103 cm 3

assessment of gps global ionosphere maps gim by comparison between code gim and topex jason tec data ionospheric perspective 1 we performed a comprehensive comparison between gps global ionosphere map gim and topex jason t j total electron content tec data for the periods of 1998 2009 in order to assess the performance of gim over the global ocean where the gps ground stations are very sparse using the gim model constructed by the center for orbit determination in europe at the university of bern the gim tec values were obtained along the t j satellite orbit at specific locations and times of measurements and then binned into various geophysical conditions for direct comparison with the t j tec on the whole the gim model was able to reproduce the spatial and temporal variations of the global ionosphere as well as the seasonal variations however the gim model was not accurate enough to represent the well known ionospheric structures such as the equatorial anomaly the weddell sea anomaly and the longitudinal wave structure furthermore a fundamental limitation of the model seems to be evident in the unexpected negative differences i e gps t j at night represent the plasmaspheric contribution to gps tec which is maximized reaching up to 100 of the corresponding t j tec values in the early morning sector in particular the relative differences decreased with increasing solar activity and this may indicate that the plasmaspheric contribution to the maintenance of the nighttime ionosphere does not increase with solar activity which is different from what we normally anticipate

geomagnetic conjugate observations of equatorial airglow depletions 1 we report for the first time large scale equatorial f region airglow depletions extending to low midlatitudes in both hemispheres the observational sites were located at low midlatitude geomagnetic conjugate points clear depletions of 630 0 nm airglow intensity due to equatorial plasma bubbles were simultaneously observed with two all sky imagers at sata japan magnetic latitude 24 n and its geomagnetic conjugate point darwin australia magnetic latitude 22 s on the night of november 12 2001 airglow depletion regions with east west scale sizes of 40 100 km extend poleward the maximum apex altitude of the plasma bubbles is about 1 700 km over the geomagnetic equator the depletions move eastward at about 100 m s without changing their structures the darwin depletion structures mapped onto the northern hemisphere along the geomagnetic field coincide closely with structures in the sata images even for the 40 km structure these observations indicate that plasma depletions in the equatorial ionosphere elongate along the geomagnetic field lines

local time dependent response of postsunset esf during geomagnetic storms 1 development or inhibition of esf during magnetically active periods has been an important space weather topic of interest during the recent past in view of its applications in the satellite based navigational systems particularly the postsunset period exhibits significant variability for storm time development of esf versus longitude in this paper we report the results of a multi instrumental ground based and space borne and multistation study on the development inhibition of postsunset esf during five moderate to intense geomagnetic storms occurred during the low and descending phase of the solar activity period 2004 2006 it has been observed that the prompt penetration of eastward electric fields into low latitudes and subsequent development of esf occurred in all longitudinal sectors where the local time corresponds to postsunset hours during the entire main phase of the storm in this paper we show the development of plasma bubble irregularities over a wide longitudinal extent of 92 owing to the dusk time penetration of eastward electric fields into low latitudes either the sudden increase in ae index and or a marked decrease in sym h index may be used as proxies to determine the occurrence as well as the time of penetration of electric fields into equatorial and low latitudes however in such cases where the ae index does not represent any sudden increase the dsymh dt seems to be the better index to determine the time of penetration in this paper is also presented an interesting case where the prompt penetration eastward electric fields dominated the existing strong westward electric fields and subsequently caused the onset of spread f and scintillations at both vhf 244 mhz as well as l band 1 5 ghz frequencies

total electron content behavior over japan during geomagnetic storms 1 the total electron content tec obtained from gps signals is used to study ionospheric dynamics over japan during geomagnetically disturbed conditions the numerous tec measurements are averaged in cells with a size 1 5 1 5 geographic scale and formatted as time series within the years 2000 2002 to extract the storm time changes of tec the diurnal and 27 day periodicities are subsequently removed diurnal variations are removed by replacing absolute tec values in each cell with their relative deviations rtec from medians the hourly rtec values from all cells within the central 4 wide band over japan area are then approximated by a plane surface this surface is represented by two parameters its value at the center rt and the slope b along the main axis taken as constants of the linear regression the 27 day periodicity was approximated by fourier waves with main period of 640 hours and two harmonics separately for rt and b and subtracted from them the analysis of rt and b behavior during a number of geomagnetic storms allowed us to reveal several repeatable features of average tec behavior it was found that tec behavior during the storms is similar to that of fof2 at the f region and was local time dependent a marked poleward expansion of the equatorial ionosphere crest region at the end of recovery phase is persistently observed feature produced probably by intensified eastward zonal winds such an expansion of equatorial ionosphere is observed also during isolated substorms outside main geomagnetic storms an oscillation like change of positive and negative disturbances with period of 24 hours is observed during a 4 day period following a moderate storm in the absence of geomagnetic activity driver that effect is probably caused by the alternative expansion and contraction of equatorial ionosphere

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

late cretaceous to early tertiary magnetostratigraphy of a continental sequence red deer valley alberta canada the red deer valley exposes a conformable 350 m thick late campanian to early paleocene fluvial deltaic coal bearing sequence named the edmonton group systematic sampling and paleomagnetic analysis of the dominant lithologies mudstones sandstones and shales were carried out over five sections correlated by coal seams to provide some 500 sites stratigraphic levels primary detrital remanent magnetization directions after alternating field cleaning produce a polarity reversal pattern correlatable to sea floor magnetic anomalies 29 33 the campanian maastrichtian boundary based upon the first appearance of wodehouseia and the maastrichtian paleocene cretaceous tertiary boundary based upon an ir anomaly associated with dinosaur and cretaceous palynofloral extinctions correlate closely magnetostratigraphically with the marine foraminiferal section at gubbio italy radiometric dating of bentonites has indicated the ages of these boundaries to be approximately 71 and 64 ma respectively

the winter anomaly in the middle latitude f region during the solar minimum period observed by the constellation observing system for meteorology ionosphere and climate 1 the winter anomaly or seasonal anomaly at middle latitudes is a phenomenon during which the daytime plasma density at the f peak height nmf2 is greater in winter than in summer radio occultation measurements from the constellation observing system for meteorology ionosphere and climate cosmic satellites provide a new data source for study of the winter anomaly on a global scale in this study we investigate the altitude local time latitude longitude and hemispheric variations of the electron density in the middle latitude ionosphere by analyzing the cosmic data measured in 2007 during a magnetically quiet period kp 3 the seasonal mean behavior of the nmf2 obtained from cosmic data shows the occurrence of the winter anomaly feature during 0800 1600 lt in the northern hemisphere but not in the southern hemisphere the intensity of the winter anomaly is variable with longitude and a more intense winter anomaly is likely to occur at longitudes closer to the magnetic pole at northern middle latitudes a greater electron density in the winter than in the summer occurs in the narrow altitude range near the f peak height except for the winter anomaly feature at northern middle latitudes the electron density at middle latitudes is greater during the summer than during the winter in both hemispheres

late laramide dolomite recrystallization of the husky rainbow a hydrocarbon devonian reservoir northwestern alberta canada paleomagnetic and geochemical evidence the rainbow field is in reefal carbonates of the middle devonian keg river formation in the western canada sedimentary basin alternating field and thermal step demagnetization was done on specimens from unoriented core from a vertical an inclined and a horizontal well core in the dolomite reservoir although they had no viscous remanent magnetization component to use for orientation most specimens had a well defined characteristic remanent magnetization chrm that resides in single to pseudosingle domain magnetite by rotating the mean chrm direction around its core axis a small circle can be generated for each core and the small circles intersect in the true chrm direction of d 168 i 73 5o 95 5 8 k 32 2 its paleopole of 164 e 83 n a95 10 defines a tertiary age with one sigma limits of middle eocene to middle miocene age petrographic examination defines four generations of dolomite matrix dolomite has 60 100 m diameter crystals that were later recrystallized to 200 400 m

equatorial plasma fountain and its effects over three locations evidence for an additional layer the f 3 layer the equatorial plasma fountain and equatorial anomaly in the ionospheres over jicamarca 77 w trivandrum 77 e and fortaleza 38 w are presented using the sheffield university plasmasphere ionosphere model under magnetically quiet equinoctial conditions at high solar activity the daytime plasma fountain and its effects in the regions outside the fountain lead to the formation of an additional layer the f3 layer at latitudes within about plus or minus 10 of the magnetic equator in each ionosphere the maximum plasma concentration of the f3 layer which occurs at about 550 km altitude becomes greater than that of the f2 layer for a short period of time before noon when the vertical e b drift is large within the f3 layer the plasma temperature decreases by as much as 100 k the ionograms recorded at fortaleza on january 15 1995 provide observational evidence for the development and decay of an f3 layer before noon the neutral wind which causes large north south asymmetries in the plasma fountain in each ionosphere during both daytime and nighttime becomes least effective during the prereversal strengthening of the upward drift during this time the plasma fountain is symmetrical with respect to the magnetic equator and rises to over 1200 km altitude at the equator with accompanying plasma density depletions in the bottomside of the underlying f region the north south asymmetries of the equatorial plasma fountain and equatorial anomaly are more strongly dependent upon the displacement of the geomagnetic and geographic equators jicamarca and trivandrum than on the magnetic declination angle fortaleza

revised and synthetic apparent polar wander paths of the african eurasian north american and indian plates and true polar wander since 200 ma we have reviewed paleomagnetic data available for the eurasian african north american and indian plates over the last 200 ma selection criteria are those generally accepted with an emphasis on evidence for lack of remagnetization accurate dating and proper structural analysis this results in 23 35 51 and 2 poles for eurasia africa north america and india respectively we believe that this limited set of higher quality data is more likely to reveal key features of apparent polar wander apw paths than averaging of larger data sets involving less stringent selection criteria we propose and describe revised apw paths but more importantly we next use relative motion models to transfer all data in a common reference frame we find good agreement between transferred data when they are averaged separately for each plate in independent 20 ma windows this is a check on consistency of paleomagnetic data kinematic models and of the geocentric dipole hypothesis transferred data from all plates are averaged in 20 ma windows to generate synthetic apw paths for all plates studied these synthetic paths are in agreement with the original revised apw paths that use only data from a single plate moreover both geographic and time resolution are improved spatial confidence intervals are of the order of 5 the synthetic paths display interesting features such as a previously ill recognized apw loop for eurasia paleomagnetic and hotspot apw are next compared and a determination of true polar wander tpw is derived we find significant tpw amounting to over 20 in the last 200 ma tpw appears to be episodic with a standstill between 180 and 110 ma there is general agreement with a previous study of livermore et al 1984 the tpw standstill appears to correlate with a time of decreasing reversal frequency ending with the cretaceous long normal superchron other periods of fast tpw would seem to correspond to increasing reversal frequency however it is suggested that the major tpw hairpin at 50 ma might correspond to the collision of india with eurasia tentative correlations with core or mantle indicators can be understood as a result of couplings between the core mantle and lithosphere we believe primarily related to episodic evolution of the d layer

simultaneous global positioning system and radar observations of equatorial spread f at kwajalein gps satellites broadcast at two frequencies ll of 1575 42 mhz and l2 of 1227 6 mhz the dispersive property of the ionosphere is frequently used to correct positional measurements for ionospheric effects independent measurements at the two frequencies can also be combined to form a relative ionospheric delay and a measure of the total electron content tec which is uncertain by an additive constant in a previous paper musman et al 1990 estimates of this offset were utilized in constructing models of the time history of the equivalent zenith delay at westford massachusetts an ionospheric model composed of uniform shells whose electron density changes slowly in a typical diurnal pattern would produce relative ionospheric delays with a simple u shaped or j shaped curve most of the change in delay would be a result of changes in geometry between the observer and the satellite departures from a simple pattern are indicative of ionospheric disturbances and the influence of the protonosphere from gps data alone it is ambiguous whether these disturbances are due to spatial structures temporal changes or some combination of the two equatorial spread f esf refers to a variety of equatorial ionospheric disturbances some of which are associated with rising plasma plumes having low electron density and a high degree of turbulence this phenomenon occurs primarily between local sunset and local midnight at sites within about 15 of the magnetic equator in some seasons disturbances can occur during two out of three evenings while at other times it can be much quieter gps observations at kwajalein 9 n latitude reported here for august 14 1990 show severe ionospheric disruption two independent and simultaneous sets of radar observations confirm the presence of esf and reveal quite a bit about the spatial and temporal conditions which affect the system gps observations on august 15 1990 when no esf was present are much quieter we find that tens of minute variations in the tec correspond to the motion of large scale features across the gps field of view more severe gps effects are seen to be collocated with turbulent low density plumes which rise rapidly to high altitudes and drift west to east across the gps line of sight severe disruption can occur in moderately sophisticated gps systems during such events at least near solar maximum

thrust loads and foreland basin evolution cretaceous western united states two dimensional modeling of loading during the formation of the idaho wyoming thrust belt shows that regional isostatic compensation by flexure of an elastic lithosphere is sufficient to control the formation of a foreland basin the flexural rigidity of the lithosphere is inferred to have been approximately 1023 nm 1030 dyne cm on the basis of palinspastic comparison of predicted downwarping due to the thrust plate loads to the shape of the sedimentary wedge on the west side of the cretaceous western interior seaway erosion of part of the uplifted thrust plates redistributed the load depositing it farther to the east thereby causing subsidence over a much wider area than could have been accomplished only by the loading by thrust plates paleotopography after major cretaceous thrust events was calculated the resulting mountainous terrain gentle alluvial plain and flat sea floor correspond well with the topography of the modern foreland thrust belt and basin system in the andes of south america and to paleogeographic reconstructions in the western united states thrust belt topography is controlled by the subsurface geometry of the thrust faults particularly the positions of ramp zones and by isostatic subsidence

the occurrence and origin of late paleozoic remagnetization in the sedimentary rocks of north america although it has been known for 25 years that some paleozoic sedimentary rock units in europe and north america were remagnetized during pennsylvanian or permian time it is only very recently that the complex and widespread nature of the late paleozoic remagnetization phenomenon has been generally acknowledged it is now recognized that many paleozoic paleomagnetic poles for north america that were once considered reliable are in fact the result of remagnetization and as a consequence the paleomagnetic data base for the paleozoic is undergoing rapid and drastic revision the causes of late paleozoic remagnetization in north america are currently the focus of much interest and active research the remagnetization can reside in either hematite or magnetite and different remagnetization mechanisms have been important in different settings chemical remagnetization processes some related to specific diagenetic events are dominant in hematite bearing sandstones and carbonates in magnetite bearing carbonates both chemical and thermoviscous remagnetization processes appear to have been important but it is difficult to determine which process is the dominant one in some settings some of the observed remagnetizations can be linked to the migration of chemically active and perhaps hot fluids during the mountain building events that affected much of the continent during the late paleozoic paleomagnetic studies promise to be important in assessing the role of orogeny in driving fluid migrations within sedimentary basins and in constraining the age of the migrations and the nature of the fluids

orogenic remagnetizations in the front ranges and inner foothills of the southern canadian cordillera chemical harbinger and thermal handmaiden of cordilleran deformation abstract paleomagnetic studies of carbonate rocks in mountain belts have been helpful to the understanding of orogenic mational origin with only one exception the a component has normal polarity in the front ranges and reverse processes the timing of deformation and the nature of fluid flow in actively deforming foreland basins most studies on shallow water carbonates indicate that their remanence is not primary but rather they record remagnetization events contemporaneous with orogeny by considering the remanent directions fold test results and rock magnetic properties and tying these results to complementary structural geochronological and geochemical studies we are able to interpret deformation history hydrological environment and orogenic diagenesis we study the relationship between remagnetization and deformation of paleozoic carbonates of the front ranges and inner foothills of the southern canadian rockies the magnetic properties are remarkably constant along 500 km strike length as sampled at 124 sites through 4 transects primary paleozoic remanent directions which would have shallow inclination are never observed rather the paleomagnetic signal is dominated by geographically persistent remagnetizations characterized by steep inclination as well as a soft present field overprint we observed two distinctive secondary magnetizations named the a and b components carried by fine grained magnetite pervasive diagenesis induced the a component a total chemical remanent remagnetization poles for the a component are better concentrated after bedding correction indicating a pre or early syndefor polarity in the inner foothills pole positions polarity and geological and thermal constraints indicate that the a component was acquired diachronously in advance of the eastward migrating cordilleran tectonic wedge subsequently an intermediate temperature partial thermo remanent remagnetization the b component was superimposed on large regions of the front ranges and inner foothills b component directions are brought into optimal concentration by differential untilting of 0 to 50 indicating that the component was acquired after the rocks were incorporated into the orogenic wedge but before the end of contractional deformation the b component is strongest within a couple of kilometers of the frontal thrust of the front ranges the relative magnitude of the b to a components and the maximum unblocking temperature of the b component decrease away from the frontal thrust over about 30 km both to the west and to the east the b component thermal overprint was attained by 250 c heating in response to tectonic or possibly sedimentary loading it was preserved by a rapid cooling accompanying a differential uplift and erosion of up to 8 km in the vicinity of the frontal thrust late in or post dating its local tilting history the likely cause was uplift of the exposed structural panel by contraction of younger underlying thrust structures

paleomagnetism and age of three canadian rocky mountain diatremes paleomagnetic results and age estimates derived from them arc presented for three diatremes using as a basis of comparison the combined apparent polar wander apw path for north america and europe of van der voo the cross diatreme of the front ranges of the canadian rocky mountains has yielded a radiometric age of 241 ma earliest triassic and is hosted by the flat lying pennsylvanian tunnel mountain formation it has normal polarity magnetization and yields a paleopole correctly placed according to its radiometric age on the apw path the blackpool diatreme for which no radiometric age is available which is located in the main ranges of the rocky mountains is known to be post late ordovician because it is hosted by rocks of that age it also has magnetization of normal polarity and yields a paleopole that when calculated with respect to present horizontal is coincident with the latest cretaceous to paleocene paleopole for north america the paleopole when calculated with respect to bedding

airglow characteristics of equatorial plasma depletions a new low light level all sky 6300 a airglow imaging system has been developed for ground based studies of the optical signatures of equatorial plasma depletions the system was designed for narrowband interference filters 6 a full width at half power with interchangeable all sky 180 and narrow field 60 lenses and records images photographically by using a standard 35 mm camera a field test of the apparatus was conducted on ascension island 8 0 s 14 4 w from january 24 to february 10 1981 the photographs were analyzed for broad morphological characteristics by using simple overlay techniques augmented by digital image processing methods to extract more quantitative detail the initial results to come from these observations show that airglow depletions occur most often during the 2030 2330 lt period often covering one fourth of the visible sky they extend from the magnetic equator to beyond the crest of the equatorial anomaly with east west cross sections of 100 km to several hundred kilometers they are usually not aligned with magnetic meridians showing a progressive skewness to the west at further distances from the equator several cases of apparently twisting overlapping and bifurcating depletions were observed the depletions drifted to the east with speeds that decreased from 190 m s at 2100 lt to 80 m s at 0100 lt the airglow intensities within depletions were typically 40 50 of the background levels and the western walls of the depletions usually had a steeper gradient than the corresponding eastern walls

paleomagnetic reconnaissance of early mesozoic carbonates from williston lake northeastern british columbia canada evidence for late mesozoic remagnetization three classic sections of middle and late triassic fossiliferous limestones cropping out around williston lake in british columbia canada were sampled for paleomagnetic study the objective was to test the suitability of these units for detailed magnetobiostratigraphic study with the aim of improving the reference triassic geomagnetic polarity time scale the williston lake characteristic magnetizations differ however from any triassic north america cratonic reference directions a satisfactory agreement is found instead with cretaceous early cenozoic north america cratonic reference directions the exclusive occurrence of normal polarity suggests that remagnetization likely occurred during the cretaceous long normal superchron remagnetizations may have been triggered by connate brines which moved along aquifers of porous sandstones and carbonates in the early stages of laramide folding resume trois sections fossiliferes classiques de calcaires trias moyen et tardif affleurant autour du lac williston en colombie britannique ont ete echantillonnees pour une etude paleomagnetique l objectif etait de s assurer de la pertinence de ces unites pour une etude magneto bio stratigraphique detaillee visant a ameliorer l echelle referentielle de temps de la polarite geomagnetique au trias les magnetisations caracteristiques du lac williston different toutefois de toute direction cratonique referentielle au trias en amerique du nord toutefois une correlation satisfaisante est etablie avec les directions cratoniques referentielles du cretace cenozoique precoce en amerique du nord l occurrence exclusive d une polarite normale suggere qu il y eut probablement une remagnetisation au cours du long superchron normal du cretace les remagnetisations peuvent avoir ete declenchees par des saumures connees qui se sont deplacees le long d aquiferes de gres et de carbonates poreux dans les premieres phases du plissement laramide

conjugate studies of an isolated equatorial irregularity region coordinated ground and airborne measurements were conducted at three points along the ascension island magnetic meridian to investigate the distribution of scintillation producing km scale ionospheric irregularities within an isolated equatorial plasma depletion airglow measurements near the northern appleton anomaly show that irregularities are confined to the region within a 6300 a airglow depletion the airglow measurements are then used to map the depletion region along magnetic field lines for comparison with scintillation measurements near the magnetic equator and near the conjugate point at ascension island results show that the irregularity region is magnetic flux tube aligned and conjugate over north south distances of 3000 km

widespread cretaceous secondary magnetization in the high atlas morocco a common origin for the cretaceous remagnetizations in the western tethys in this paper we present the first palaeomagnetic data 51 sites for mesozoic lower middle jurassic sediments of the moroccan central high atlas and address the study of a widespread remagnetization the remagnetization is characterized by a very stable component with systematic normal polarity carried by magnetite the relationship between the magnetic properties and location within the basin suggests that the acquisition of the remagnetization is controlled by basin geometry fold tests indicate that the overprint acquisition is syn folding in some structures but clearly predates the tertiary compressional stage using the small circle intersection method we have calculated the remagnetization direction d 336 4 i 29 2 comparison with the global apparent polar wander path indicates that the remagnetization was acquired during the late cretaceous probably cenomanian considering both the basinal confinement of remagnetization and the connection with other remagnetization events in the western tethys we propose a scenario explaining widespread remagnetizations in the region concerning both basin scale conditions mainly related to sediment thickness and a regional scale thermal event acting as catalyst of remagnetizations in those sedimentary basins that satisfy the basin scale conditions

radar and satellite global equatorial f region vertical drift model we present the first global empirical model for the quiet time f region equatorial vertical drifts based on combined incoherent scatter radar observations at jicamarca and ion drift meter observations on board the atmospheric explorer e satellite this analytical model based on products of cubic b splines and with nearly conservative electric fields describes the diurnal and seasonal variations of the equatorial vertical drifts for a continuous range of all longitudes and solar flux values our results indicate that during solar minimum the evening prereversal velocity enhancement exhibits only small longitudinal variations during equinox with amplitudes of about 15 20 m s is observed only in the american sector during december solstice with amplitudes of about 5 10 m s and is absent at all longitudes during june solstice the solar minimum evening reversal times are fairly independent of longitude except during december solstice during solar maximum the evening upward vertical drifts and reversal times exhibit large longitudinal variations particularly during the solstices in this case for a solar flux index of 180 the june solstice evening peak drifts maximize in the pacific region with drift amplitudes of up to 35 m s whereas the december solstice velocities maximize in the american sector with comparable magnitudes the equinoctial peak velocities vary between about 35 and 45 m s the morning reversal times and the daytime drifts exhibit only small variations with the phase of the solar cycle the daytime drifts have largest amplitudes between about 0900 and 1100 lt with typical values of 25 30 m s we also show that our model results are in good agreement with other equatorial ground based observations over india brazil and kwajalein

motions of the equatorial ionization anomaly crests imaged by formosat 3 cosmic 1 the equatorial ionization anomaly eia structures and evolutions are imaged using radio occultation observation of the newly launched formosat 3 cosmic f3 c satellite constellation three dimensional ionospheric images provide unprecedented detail of the eia structure globally this paper presents images of the eia structures during july august 2006 and discusses the development and subsidence of the eia clear seasonal asymmetries in both ionospheric electron density and layer height are observed two dimensional cross section maps at a meridian provide dynamic variations and motions of the northern and southern eia crests results suggest that in addition to the asymmetric neutral composition effect interactions between the summer to winter transequatorial neutral winds and strength of the equatorial plasma fountain effect play important roles in producing asymmetric development of the eia crests as imaged by the f3 c

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

first observation of interhemispheric asymmetry in the epbs during the st patrick s day geomagnetic storm of 2015 in this work we have studied the characteristics of epbs such as their zonal drift and tilt from the low latitude and dip equatorial region in the indian longitude sector during the main phase of the 17 march 2015 storm all sky airglow imaging observations from tirunelveli 8 7on 77 8oe geographic 1 7on dip latitude and kolhapur 16 7on 74 3oe geographic 11 5on dip latitude are utilized here on 17 march 2015 epbs were observed to drift eastward during 14 30 16 30 ut between 3os and 15on dip latitudes a westward drift presumably under the influence of the disturbance dynamo electric field ddef initially appeared at higher dip latitudes almost 10 hours after the storm onset and subsequently the same was observed at lower dip latitudes the epbs attained a peak westward drift at 17 00 ut followed by a gradual decrease in their speed till 18 30 ut after regaining their westward speed the epbs continued to drift westward till 22 00 ut moreover a latitudinal gradient in the drift motion of the epbs was also observed on this night another interesting observation made from the images obtained from tirunelveli was the presence of a large westward tilt of the epbs the most intriguing finding of this study however was the asymmetry in the tilt of the epbs at conjugate points during the pre midnight hours on 17 march 2015 in this study the possible mechanisms that can explain these observations are discussed in the light of the current understanding of the equatorial electrodynamics and epbs