distribution characteristics of topside ionospheric density irregularities equatorial versus midlatitude regions 1 the global distribution of the occurrence rate for density irregularities at 600 km topside ionosphere between 35 geographic latitudes has been studied with the rocsat data during moderate to high solar activity years of 1999 to 2004 the result indicates that the global occurrence distribution of the intermediate scale 0 1 to 50 km density irregularities can be grouped into two different populations one in the equatorial region and the other in the middle to subauroral latitude region the global seasonal longitudinal s l distribution of equatorial irregularities in the current report reproduces the result of mcclure et al 1998 obtained with the ae e observations of the mesoscale 50 to 1000 km plasma bubble structures during high solar activity years of 1978 to 1980 two solar cycles ago this implies that the density irregularities of different scales from multistage cascading process of the large scale 1000 km gravitational rayleigh taylor instability have manifested in same global s l distribution pattern furthermore global variation in seeding mechanism and growth condition of the instability process that results in major features in global irregularity pattern seems to persist for past 25 years in addition the current result further indicates that an upper latitudinal limit of the equatorial irregularity distribution is located at about 30 a different kind of midlatitude irregularity distribution starts to fill in from this dip latitude in other words the equatorial density irregularity inside a depleted flux tube can only rise on statistical average to an apex height of 2000 km different magnetic and solar variability effects as well as the local time dependence are noted for the occurrences of density irregularities in the equatorial region versus that at midlatitudes the occurrence frequency of equatorial density irregularities increases with solar flux intensity whereas the midlatitude density irregularity is more likely to occur during low solar activity period the equatorial density irregularities are more likely to occur during periods of low magnetic activity than during magnetic disturbed times on the other hand the occurrence of midlatitude density irregularities indicates little dependence on geomagnetic activity the local time distribution of equatorial irregularity peaks before midnight while the midlatitude irregularity indicates a plateau of high occurrence rate after midnight such opposite characteristics in the occurrence pattern between these two spatially separated distributions suggest that different instability mechanisms are operated in two different latitude regions for the occurrence of intermediate scale density irregularities

magnetic fabric of the barrington passage pluton meguma terrane nova scotia a two stage fabric history of syntectonic emplacement abstract structural analysis and the anisotropy of magnetic susceptibility ams are used to document the internal magmatic to high temperature subsolidus fabrics of the tonalitic late devonian barrington passage pluton the ams fabric orientations compare favorably with mesoscopic scale fabrics in general the k1 k2 principal plane of the ams is close to the observed mineral foliation defined by biotite and plagioclase and the k1 axis is aligned parallel to a mineral lineation defined by the same minerals and to a locally developed weak extension lineation defined by quartz measurement of the anisotropy of anhysteretic remanence aar and image analysis of biotite preferred orientations confirm that the orientation of the ams is principally controlled by biotite locally anomalous ams orientations are attributed to the influence of fine grained magnetite crystals the presence of which is revealed by measurements of hysteresis and coercivity properties a two stage fabric history is revealed first horizontal fabrics were formed foliation compositional banding during emplacement of a laccolith like pluton the second stage involved synmagmatic folding of the horizontal foliation and banding in response to regional contraction associated with the acadian orogeny with development of a lineation that records stretching parallel to the fold axis the results demonstrate that the barrington passage pluton was emplaced during the main phase of the acadian orogeny a model is proposed that depicts the barrington passage pluton as the folded base of a larger syntectonic pluton that is now largely eroded off

magmatic fabric acquisition mechanisms in a syenite results of a combined anisotropy of magnetic susceptibility and image analysis study the structural significance of the anisotropy of magnetic susceptibility ams and acquisition mechanisms of silicate and ferrimagnetic mineral fabrics are investigated in the archean lebel syenite intrusion ontario canada bulk mineral subfabrics are determined by intercept counting of mineral phases in classified digital images of thin sections cut parallel to the principal planes of the magnetic fabric ellipsoids of the samples intensities shapes and principal direction orientations of the resulting intercept ellipsoids are generally similar to the corresponding ams ellipsoids differences are due mainly to bimodal distribution of mineral fabrics observed on foliation planes of some samples showing pre full crystallization textures and structural overprinting in samples deformed after crystallization subfabrics of clinopyroxene and magnetite in samples showing pre full crystallization microstructure are investigated by measuring inertia tensors of individual grain shapes the resulting inertia tensor ellipsoids indicate that magnetic fabrics in these rocks are strongly correlated to the shape preferred orientation of magnetite which is similar to the overall petrofabric of the samples crystal size distributions of clinopyroxene and magnetite indicate that they formed during in situ crystallization and that magnetite probably appeared late in the crystallization and flow history of the magma analysis of preferred orientations of these grains suggests that the petrofabrics of the samples were acquired during flow with strongly interacting grains analogous to a logjam in a river the final characteristics of the ams and silicate petrofabric are the end points of a continuous crystallization and flow history in the magma rather than transient late features

on the relationship between the postmidnight thermospheric equatorial mass anomaly and equatorial ionization anomaly under geomagnetic quiet conditions the equatorial mass anomaly ema in the thermosphere and equatorial ionization anomaly eia in the ionosphere are two interesting phenomena in low equatorial latitude regions previous studies have shown that the ema appears between 1000 and 2000 local time lt and its location of trough is aligned with dip equator indicating the plausible role of the eia structure in the development of ema in this report we conducted a statistical study of the occurrence of postmidnight ema and eia on the basis of the champ in situ measurements during 2002 2008 our results revealed that clear ema and eia structures are sometimes visible in the postmidnight sector 0100 0600 lt during geomagnetic quiet periods kp 3 the postmidnight ema is not necessarily accompanied by the eia signature in both case study and statistics sense being distinct from the daytime situation in addition the occurrence rates of postmidnight ema and eia display contrasting behavior with respect to their local time longitudinal and solar activity dependences the highest occurrence rate for ema is 8 at around 0300 lt while the occurrence rate of the eia decreases gradually from about 30 at around 2300 lt to similar to 5 at 0600 lt longitudinal occurrence of postmidnight eia presents a wave like pattern however no salient feature appears for the longitudinal occurrence of ema postmidnight ema is more likely to occur at lower solar activity whereas an opposite trend presents in the eia on the basis of above results our findings imply that a simple eia ema cause effect relationship does not hold in the postmidnight sector

the main variscan deformation event in the pyrenees new data from the structural study of the bielsa granite abstract a structural and magnetic fabric study of the bielsa granite axial zone of the pyrenees provides new data indicating that this pluton was emplaced during the main variscan event recognized in the pyrenees we argue that the later post triassic deformation was localized along mylonitic bands reactivating earlier variscan shear bands the bielsa granite intrudes cambro ordovician metasediments at its northern border and the pluton is unconformably overlain by sediments triassic in age to the south and east the main structures in the igneous body are magmatic foliations and lineations defined by feldspar phenocrysts and biotite and dextral shear bands with dominant wnw ese trends the wnw ese striking magmatic foliations have variable dips and the magmatic lineation a subhorizontal wnw ese trend the zonation of low field magnetic susceptibility coarsely related to mineral content indicates a layer arrangement of rock types with more basic compositions at the northern border the magnetic ellipsoids are prolate along a wnw ese central band and oblate at the pluton borders where flattening is more important all these data allow us to interpret the bielsa intrusion as being caused by coeval nne shortening and dextral shear the presence of shear bands indicates that strain localization under dextral transpression continued during late variscan times

characterization of the magnetic fabric of rocks abstract an inextensive system of magnetic susceptibility anisotropy factors is suggested which is sufficient in the majority of practical applications for characterizing the magnetic fabric of rocks the system involves three newly devised factors the corrected anisotropy degree the shape factor and the difference shape factor the first of these characterizes the quantity of anisotropy somewhat better than the commonly used anisotropy degree the shape factor characterizes the quality of anisotropy i e the shape of the susceptibility ellipsoid in a convenient way its definition is based on a certain analogy between the anisotropy ellipsoid and the strain ellipsoid the difference shape factor can replace the shape factor when only the differences between the principal susceptibilities are given while the mean susceptibility is unknown

stretching lineations in transpressional shear zones an example from the sierra nevada batholith california abstract ductile shear zones and associated stretching lineations are generally considered to be the result of two dimensional simple shear deformations with stretching lineations interpreted to rotate into parallelism with the direction of tectonic transport with increasing deformation however stretching lineations perpendicular to the inferred tectonic transport direction are displayed by some shear zones field studies in the sierra nevada batholith have revealed a single shear zone the rosy finch gem lake shear zone that contains both steeply plunging stretching lineations in older metamorphosed sedimentary and granitic rocks and shallowly plunging stretching lineations in syntectonic granitoids dextral sense of shear indicators are found in all these units and deformation occurred simultaneously along the length of the shear zone theoretical strain modeling indicates that stretching lineations can be either horizontal or vertical within transpressional shear zones to investigate the kinematics of three dimensional deformation we examine the role of stretching lineations which form as a result of finite strain including the possibility of partitioning a component of the strike slip movement onto shear bands comparing the field data with the strain modeling we interpret the along strike variation in lineation behavior within the rosy finch gem lake shear zone to be a result of the differences in finite strain recorded by different units the older units showing steeply plunging lineation have recorded more finite strain across a narrower shear zone than the syntectonic granites which record shallowly plunging lineations we conclude that the orientation of the lineation within transpressional shear zones does not necessarily correlate with the transport direction but may reflect along strike variations in finite strain and or strain partitioning

deformation mechanisms in granitic rocks at shallow crustal levels abstract microstructural observations of naturally faulted granitic gneisses show that feldspar grains are weaker than quartz grains at temperatures below 325 c and at depths of less than 8 10 km feldspar grains sustained most of the deformation by grain scale faulting slip along cleavage controlled fractures and cataclasis fracture of feldspar grains within fault zones promoted their alteration to kaolinite quartz grains also deformed by fracturing and often healed to form quartz porphyroclasts and mosaics in a comminuted matrix of feldspar and kaolinite syntectonic alteration of the feldspar grains may have weakened the fault zones over time and resulted in foliated textures within the fault zones this study of naturally deformed rocks confirms published experimental results on the behavior of granitic rocks at low temperatures and pressures and taken together these data show that the theology of the upper 10 km of the crust is greatly influenced by cataclastic processes in feldspar

u pb age and lead isotopic characterization of au bearing skarn related to the andorra granite central pyrenees spain auriferous skarns are associated with post and late kinematic hercynian granites that intruded into cambro ordovician to devonian sediments of the central pyrenees we determined the age of the andorra granite and the associated skarn at 305 3 ma by u pb dating titanite from the endo skarn the sulfur isotopic composition from sulfides in the skarn cardellach et al 1992 shows a significant variation with isotopically light sulfur 34s 3 in the barren skarns and heavy sulfur 34s 11 in the gold bearing skarns outwards it increasingly resembles sulfur from arsenopyrite disseminations in the cambro ordovician sediments the lead isotopic composition from sulfides of the skarns is very homogeneous 206pb 204pb 18 410 207pb 204pb 15 699 208pb 204pb 38 574 in contrast to the one in gold bearing arsenopyrite veins and in arsenopyrite disseminations in the sediments e g 206pb 204pb varies from 18 54 to 30 36 combined sulfur and lead isotope data indicate that the lead in the skarn is dominantly derived from the granite whereas the sulfur is derived at variable portions from both the granite and the sediments

variscan dextral transpression in the french pyrenees new data from the pic des trois seigneurs granodiorite and its country rocks abstract new structural data from both the trois seigneurs granodiorite and its country rock lead to new conclusions about the variscan tectonic history of this part of the pyrenees sedimentary rocks of the massif that increase in metamorphic grade from north to south are imprinted by a single major deformation responsible for both the tight upright e w trending folds with vertical to steeply n dipping foliations and the gently w plunging stretching lineations syntectonic emplacement of the pic des trois seigneurs granodiorite is demonstrated by the parallelism between structures of the pluton as determined by magnetic fabric measurements and the foliations and lineations imprinted in the country rocks large deformation of the granodiorite magma during emplacement is indicated by strong anisotropy and ubiquitous magmatic microstructures the high thermal gradients of regional metamorphism which is also syntectonic are attributed to a large thermal aureole provided by deep seated magma reservoirs shear sense criteria in xz thin sections of the metasedimentary country rocks indicate a dextral sense of the non coaxial component of strain throughout the massif and regardless of metamorphic grade the overall structure of the massif is concluded to have derived from a major shearing event that is equated with the d 2 main phase observed in the entire variscan pyrenees as the e w oriented stretch and dextral shear cannot be separated from compressive structures generally considered to be characteristic of d 2 this phase is concluded as representing regional transpression

hemispheric asymmetries in the longitudinal structure of the low latitude nighttime ionosphere 1 observations performed with the low resolution airglow and aurora spectrograph loraas which flew aboard the advanced research and global observation satellite argos show evidence of wave number four longitudinal variations in the nighttime equatorial anomaly during march 2001 and march 2002 loraas limb scans of o i 135 6 nm emission features are used to reconstruct electron density profiles from which maps of the monthly average peak f region electron densities and heights at 0230 lt are generated the longitudinal structure is nearly identical in both years the locations of the longitudinal maxima in the northern hemisphere match that of previous studies but the loraas data show a pronounced hemispheric asymmetry in the locations of the maxima in the southern hemisphere the loraas results are compared with the international reference ionosphere iri 90 to show the derived electron densities and peak altitudes are consistent with the climatology but that the observed longitudinal structure is not a physics based model of the ionosphere sami is another model of the ionosphere sami2 is used to study the role of thermospheric neutral winds in generating the observed longitudinal pattern it is demonstrated that longitudinally varying f region winds along with effects due to the offset of the geographic and magnetic equator are the plausible cause of the hemispheric asymmetry together the effects enhance the observed wave number four pattern in the nighttime ionosphere

magnetic susceptibility of the mont louis andorra ilmenite type granite pyrenees a new tool for the petrographic characterization and regional mapping of zoned granite plutons we have observed remarkably consistent patterns of concentric zonation in the values of low field magnetic susceptibility measurements over the variscan age mont louis andorra granite pluton of the eastern pyrenees of andorra spain and france this zonation is a function of the rock petrology since a close correlation is shown between the petrographic nature as defined by chemical analysis and the magnetic susceptibility magnitude of the rocks it reflects the dominantly paramagnetic nature of the granite carried by fe bearing silicates and this is demonstrated by the fact that low field susceptibilities of representative specimens are almost equal to 1 their high field susceptibilities and 2 their calculated susceptibilities using fe contents assuming a null ferromagnetic contribution we conclude that this technique accurately reflects the modal abundances of ferromagnesian phases in rocks of the ilmenite series and that it represents a powerful and efficient tool for the reconnaissance surveying of petrological variations in granitoid plutons

thrust tectonics in the south central pyrenees abstract surface structural data and published stratigraphies are combined to construct two balanced and restored sections through the nogueras zone of the south central pyrenees the allochthonous nogueras zone units are interpreted as the foreland dipping margin of a major antiformal stack in the palaeozoic rocks of the pyrenean axial zone their structural evolution is summarized in a hangingwall sequence diagram this reinterpretation of the nogueras zone is incorporated into a new n s balanced and restored section from the centre of the pyrenean axial zone to the ebro basin a classical rocky mountains piggy back thrust model is employed and the resulting section is a significant departure from those previously published it is argued that gravity gliding has never been an important mechanism in the alpine pyrenees section restoration casts doubt on the correlation of the surface expression of the north pyrenean fault and the seismically detected moho step beneath it

unusual early morning development of the equatorial anomaly in the brazilian sector during the halloween magnetic storm 1 the solar events that occurred at the end of october 2003 gave rise to very strong geomagnetic disturbances that peaked twice with dst values reaching 345 nt around 0000 ut on 30 october and 400 nt around 2300 ut on the same day disturbances in several ionospheric parameters were observed over brazil this work will focus on the ionospheric response to the initial westward prompt penetration electric field and on the strong intensification of the equatorial ionization anomaly that occurred because of the electric field polarity reversal that followed in the early morning hours of 29 october the f layer peak height over the equator first decreased under the strong prompt penetration westward electric field which was followed by significant height increase under eastward electric field we have used sheffield university plasmasphere ionosphere model supim with an intensified westward disturbed electric field in the presunrise hours presumably due to prompt penetration from the magnetosphere in order to study the effect of such a field in the ionosphere the simulation results showed that prompt penetration of magnetospheric electric fields of westward polarity to the nightside equatorial region seems to be the most probable cause of the initial f layer height decreases the intensification of the equatorial ionization anomaly and the unusual enhancement on f layer peak density which was not modeled by the supim are explained as caused by the strong eastward electric field that followed the initial phase in combination with a highly variable disturbed meridional transequatorial wind system as inferred from the f2 layer peak height variations the highly dynamic wind pattern with a short term response 2 4 hours is compatible with the predictions of some previous theoretical model calculations reported in the literature

the variscan geology of the pyrenees abstract the main outlines of the geology of the variscan part of the pyrenees are discussed rocks involved in this cycle are high grade basement gneisses palaeozoic sediments and their metamorphic equivalents late intrusive granodiorites and early pre variscan granites the main features of the stratigraphy of the palaeozoic are given structures fall into two domains a low grade suprastructure essentially with steep folds and cleavages and a high grade infrastructure with dominantly low dipping foliations an important phase of early pre cleavage folding occurs in low grade rocks mainly along the southern border of the axial zone in high grade rocks most structures and the metamorphism postdate the main cleavage phase in low grade rocks the influence of the alpine orogeny on the variscan structures consists mainly of faults steep reverse faults in the northern and south directed thrusts in the southern part of the pyrenees metamorphism took place under high geothermal gradients and low pressures as indicated by the abundant occurrence of andalusite and cordierite

paleomagnetism of the north patagonian batholith southern chile an exercise in shape analysis abstract over 100 sites in granitic country rock mafic inclusions within granitic rock and mafic dikes were sampled in the northernmost 550 km of the patagonian batholith after magnetic cleaning some sites were rejected as magnetically unstable and others were combined because they were contiguous and carried similar directions hence probably representing duplicate samplings of the same direction of the geomagnetic field a total of 42 well determined directions 29 from granitic country rock and inclusions and 13 from dikes survived to be included in the interpretation most of these had a normal magnetic polarity probably indicating that a disproportionate fraction of the north patagonan batholith formed during the mid cretaceous long normal interval tectonic interpretation of paleomagnetic directions from intrusive rocks often is difficult because paleohorizontal indicators in such rocks are usually lacking rather than struggle against this limitation we yielded to it and elected to concentrate on the shapes of our various data sets the method used is simple and straightforward involving bingham statistics and small circle fitting from this analysis it appears that the main structural feature within the north patagonian batholith npb the liquine ofqui fault zone is a site of crustal detachment a sliver of south america west of the fault is detached from the rest of the continent and has moved relatively northward because the main strands of the liquine ofqui fault are curved and concave to the west northward movement was accompanied by counterclockwise rotation east of the fault the npb appears to have been the locus of distributed shear mainly dextral the principal period of deformation of the batholith appears to have been mid or late cenozoic and may have been initiated by the arrival of the south america nazca farallon phoenix aluk triple junction

magnetic anisotropy of some phyllosilicates magnetic susceptibility anisotropy of susceptibility and hysteresis of single microcrystals of chlorite biotite phlogopite muscovite zinnwaldite and fuchsite were measured in low and high magnetic fields with an alternating gradient force magnetometer micromag their properties are sufficient to account for the low field susceptibility ams of most micaceous rocks nearly all samples show some ferromagnetic contribution at low fields due to inclusions of pseudosingle domain and multidomain magnetite the paramagnetic contribution isolated at high fields usually exceeds the ferromagnetic contribution the paramagnetic susceptibility is intrinsic to the silicate lattice and agrees with values predicted from chemical composition within the limits of error the minimum susceptibility is nearly parallel to c another axis is parallel to b and the third susceptibility usually the maximum is close to a the paramagnetic susceptibility has a disk shaped magnitude ellipsoid with strong anisotropy p 2 the ferromagnetic contributions at low fields have more variably shaped ellipsoids with greater eccentricity p 5 the silicate lattice does not constrain their orientation our technique cannot determine the principal axes of the ferromagnetic component however its principal values usually correspond with the paramagnetic principal susceptibilities in order of magnitude thus the combined paramagnetic ferromagnetic anisotropy recognised in routine studies of ams should faithfully represent the petrofabric of most micaceous rocks nevertheless nearly 10 of our samples have incompatible anisotropy ellipsoids for the silicate host and magnetite inclusions these yield a net inverse ams that does not correctly represent the orientation of the silicate lattice therefore some caution is necessary in petrofabric ams studies of micaceous rocks

the comparative importance of de3 se2 and spw4 on the generation of wavenumber 4 longitude structures in the low latitude ionosphere during september equinox 1 numerical simulations are performed to investigate the generation of the wave 4 longitude variation in the low latitude ionosphere due to the diurnal eastward propagating nonmigrating tide with zonal wavenumber 3 de3 semidiurnal eastward propagating nonmigrating tide with zonal wavenumber 2 se2 and stationary planetary wave 4 spw4 from a fixed local time perspective the de3 se2 and spw4 all appear as wave 4 structures in longitude and thus each of these waves must be considered as a potential source of the wave 4 variation in the ionosphere both thede3 and spw4 are found to produce significant wave 4 variations in the equatorial verticale bdrift velocity and in the ionospheric peak density nmf2 at 15 n magnetic latitude the daytime wave 4 variation in nmf2 is driven by the combination of verticale bdrift variability and in situ effects due largely to meridional neutral winds the simulation results indicate that these2 is not a contributor to the wave 4 longitude variation our results further demonstrate that the actual wave 4 longitude variation is due to a combination of thede3 and spw4 we therefore conclude that in addition to the de3 the spw4 also needs to be considered as an important driver of the wave 4 longitude variation in the low latitude ionosphere we additionally present evidence for the generation of thespw4 due to the nonlinear interaction between the migrating diurnal tide and the de3 and demonstrate the impact of de3 variability on the amplitude of the spw4

structure and origins of the weddell sea anomaly from tidal and planetary wave signatures in formosat 3 cosmic observations and gaia gcm simulations the weddell sea anomaly wsa is a recurrent feature of the austral summer midlatitude ionosphere where electron densities are observed to maximize during the local nighttime in this study tidal decomposition is applied to formosat 3 formosa satellite constellation observing system for meteorology ionosphere and climate cosmic total electron content tec and electron density observations between 2007 and 2012 to quantify the components dominating local time and spatial variation in the wsa region our results present some of the first three dimensional spaceborne analyses of the wsa from a tidal perspective over multiple years we find that the features of the wsa can be reconstructed as the result of superposition between the dominant diurnal standing d0 eastward wave number 1 de1 westward wave number 2 dw2 and stationary planetary wave 1 spw1 components in tecs producing the characteristic midnight wsa peak the d0 de1 dw2 and spw1 components are found to be an interannually recurring feature of the southern midlatitude to high latitude ionosphere during the summer manifesting as enhancements in electron density around 300 km altitude of the summer middle to high magnetic latitudes the phases of the aforementioned nonmigrating diurnal signatures in electron density in this region are near evanescent suggesting in situ generation rather than upward propagation from below however the spw1 signature shows some signs of an eastward tilt with altitude suggesting possible downward propagation the relation of these components to possible generation via in situ photoionization or plasma transport along magnetic field lines is also discussed using results from the ground to topside model of atmosphere and ionosphere for aeronomy gaia general circulation model gcm connecting the tidal interpretation of the wsa to previously examined generation mechanisms

scaling and geometric properties of extensional fracture systems in the proterozoic basement of yemen tectonic interpretation and fluid flow implications abstract multi scale mappings of fracture systems in the crystalline basement of yemen are presented fracture datasets are described through statistical analyses of direction length spacing density and spatial distribution results are combined with field observations and can be directly used to model the geometry of the fracture networks in analog basement rocks from multi kilometric to decametric scales the fractured reservoir analog is defined with a dual porosity model in which tectonic and joint systems correspond to the basement reservoir backbone and matrix respectively these two end members reveal contrasting geometrical reservoir and scaling properties in tectonic systems multi scale geometries are self similar the fracture network shows fractal behavior power law length distribution and clustered spacing and fault zones show hierarchical organization of geometrical parameters such as length thickness and spacing in joint systems the fracture network is scale dependent with exponential length distribution and shows anti clustered spacing however these two end members have both well connected properties with fault zones acting as main drain and joint systems acting as the fluid supply

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

syntectonic emplacement of the maladeta granite pyrenees deduced from relationships between hercynian deformation and contact metamorphism the relationships between hercynian deformation and contact metamorphism in the aureole of the aneto unit a constituent pluton of the maladeta granite complex spanish pyrenees provide new data relevant to the controversy between the syn and post tectonic models of emplacement for the pyrenean granites the deformation in the aneto aureole is related to two superimposed hercynian episodes the first was a top to the sw thrusting which induced sw verging recumbent folds the second which was essentially compressive in the aneto area is represented by e w trending subvertical cleavage and folds with subhorizontal axes this second episode can be assigned to the d2 main hercynian tectonic event of the pyrenees the contact metamorphic assemblages grew during the d2 event and were deformed by it close to the contact the conclusion that the pluton was emplaced during d2 is strengthened by the structural and kinematic similarities between the magmatic deformation in the southern rim of the pluton and the d2 deformation in the country rocks this syntectonic timing is supported by new geochronological data that conflict with an existing rb sr post tectonic permian whole rock age for the maladeta granite more generally in accordance with some very recent structural and u pb zircon studies our results contradict the geodynamical models of the pyrenees which relate the granite intrusions to a late extensional event

effect of atmospheric tides on the morphology of the quiet time postsunset equatorial ionospheric anomaly longitudinal wave number four pattern in the magnetic latitude and concentration of the f region peak ion density when measured at a fixed local time in a new comparison of two data sets with observations made by the ogo 4 satellite this pattern is seen to be persistent over many days around equinox during magnetically quiet conditions close to solar maximum but can be dominated by other processes such as cross equator winds during other periods it is found that the longitudinal variability is created by a processes occurring in the dayside ionosphere a longitudinal modulation of the dayside equatorial fountainisthemostlikelydrivingmechanism throughcomparisonwithgwsm 02model it isshownthatthepredictedmodulationofthedaysidethermosphericwindsandtemperaturesat e region altitudes created by non migrating diurnal tides can explain the modulation in the dayside equatorial fountain this result highlights the importance of understanding the temporal variability of tropospheric weather systems on our understanding and possible predictability of the development of the f region ionosphere it may also provide a possible further means of testing our understanding of atmospheric tides on a global scale

attribution of ionospheric vertical plasma drift perturbations to large scale waves and the dependence on solar activity 1 in this study we quantify the contribution of individual large scale waves to ionospheric electrodynamics and examine the dependence of the ionospheric perturbations on solar activity we focus on migrating diurnal tide dw1 plus mean winds migrating semidiurnal tide sw2 quasi stationary planetary wave one qspw1 and nonmigrating semidiurnal westward wave one sw1 under northern winter conditions when qspw1 and sw1 are climatologically strong from thermosphere ionosphere mesosphere electrodynamics general circulation model simulations under solar minimum conditions it is found that the mean winds and dw1 produce a wave two pattern in equatorial vertical e bdrift that is upward in the morning and around dusk the modeled sw2 also produces a wave two pattern in the ionospheric vertical drift that is nearly a half wave cycle out of phase with that due to mean winds and dw1 sw1 can cause large vertical drifts around dawn while qspw1 does not have any direct impact on the vertical drift wind components of both sw2 and sw1 become large at middle to high latitudes in the e region and kernel functions obtained from numerical experiments reveal that they can significantly affect the equatorial ion drift likely through modulating the e region wind dynamo the most evident changes of total ionospheric vertical drift when solar activity is increased are seen around dawn and dusk reflecting the more dominant role of large f region pedersen conductivity and of the f region dynamo under high solar activity therefore the lower atmosphere driving of the ionospheric variability is more evident under solar minimum conditions not only because variability is more identifiable in a quieter background but also because the e region wind dynamo is more significant these numerical experiments also demonstrate that the amplitudes phases and latitudinal and vertical structures of large scale waves are important in quantifying the ionospheric responses