global characteristics of occurrence of an additional layer in the ionosphere observed by cosmic formosat 3 global observations of electron density profile edp from the cosmic formosat 3 satellites were used to investigate for the first time the additional stratification of the f2 layer over the equatorial ionosphere on a global scale which is called f3 layer the f3 layer in edp was recognized through the altitude differential profile featured by two maxima existing from 220 km to the peak height of the electron density there were similar to 9 400 cases of f3 layer selected out of similar to 448 000 occultation events at low and equatorial areas during the period of april 2006 september 2010 statistical results show that the highest occurrence of f3 layer appears at dip latitude 7 similar to 8 degrees 7 similar to 8 degrees for northern southern hemisphere and is more pronounced during summer months at 10 00 14 00 lt the occurrence also has a clear longitude dependence during boreal summer with relatively higher occurrence at 80 similar to 100 degrees 20 similar to 20 degrees 80 similar to 120 degrees and 160 similar to 170 degrees longitudes that is possibly associated with the wavenumber 3 diurnal tide de3 the results support the principle of the f3 layer proposed by balan et al 1998 which in turn validate the accuracy of the retrieval of the cosmic edp data citation zhao b w wan x yue l liu z ren m he and j liu 2011 global characteristics of occurrence of an additional layer in the ionosphere observed by cosmic formosat 3 geophys res lett 38 l02101 doi 10 1029 2010gl045744

intra annual variation of wave number 4 structure of vertical e b drifts in the equatorial ionosphere seen from rocsat 1 1 this paper studies the intra annual variation of the wave number 4 structure in the equatorial vertical e b drifts at high solar flux level based on of the rocsat 1 observations during the interval from 1999 to 2004 it is found that the daytime longitudinal structure is significant in northern summer and early autumn but weak in northern winter this is consistent with the intra annual variations of the tidal mode de3 at night the intra annual variation of the wave number 4 structure shows some differences from that in daytime which may relate to different dynamo mechanisms operating in different local time we also found that the wave number 4 structure mainly shifts eastward during daytime in most of months which is coincident with the eastward propagation of the de3 tide however it is largely disturbed near sunrise and sunset we attribute this disturbance as the jumping of the main dynamo region between e and f layers as well as the different dynamo mechanisms in different dynamo regions

ostracod assemblages in late quaternary varved glaciomarine clay of the baltic sea yoldia stage in eastern middle sweden abstract four cored sites in eastern middle sweden have been analysed for their content of calcareous fossils the investigated sediments consist of late quaternary varved clay deposited during the baltic sea yoldia stage four regional palaeoecological units a d have been established unit a reflects ice proximal conditions unit b optimal conditions for the benthic fauna and unit c the termination of a saline phase in unit c oxygen deficiency might have occurred in the fourth unit d no fossils were found the fauna recorded is poor in taxa and indicates a weak marine influence the salinity was higher in the western part of the investigated area due to the proximity to the inlet of marine water the meltwater influx was high and the salinity probably fluctuated considerably the ostracod cytheromorpha macchesneyi brady and crosskey is reported for the first time in quaternary deposits from northwestern europe and indicates that a connection could have existed between the baltic and the white sea in late glacial times

an additional layer in the low latitude ionosphere in indian longitudes total electron content observations and modeling 1 the paper presents the observations and modeling of an additional layer in the low latitude ionosphere in indian longitudes the signatures of the additional layer are observed as ledges or humps between the equatorial ionization anomaly trough and crest eia in the latitudinal profiles of total electron content tec measured using a single ground based beacon receiver located at trivandrum 8 5 n 77 e dip 0 5 n in india the ground based ionograms also show the presence of the so called f 3 layer for a short duration corresponding to these signatures and the layer is found to drift upward to the topside ionosphere the study provides first observational evidence that the so called humps in the latitudinal variation of tec are nothing but the upward propagating f 3 layer this conclusion is supported by theoretical modeling using the sheffield university plasmasphere ionosphere model it is shown that upward exb drift and strong equatorward neutral wind perturbed by atmospheric waves can produce the humps in the latitudinal variation of tec through the reduction in the downward diffusion of ionization along geomagnetic field lines the model results also show that the f 3 layer drifts to the topside and forms topside ledges

stratification of the f 2 layer observed in southeast asia this paper describes the latitudinal variation in f2 stratification balan and bailey 1995 as observed by a number of oblique and vertical ionosondes operating in southeast asia during 1997 stratification of the f2 layer was seen at dip latitudes from 4 s to 18 s on the southern side of the magnetic equator but did not occur at the closest reflection point to the magnetic equator dip latitude 2 3 n the observed transient cusp vertical ionosonde or additional nose oblique ionosonde was defined as an f3 layer or an f1 5 layer depending on whether it occurred above or below the layer which maintained continuity with the normal f2 layer peak within the zone of occurrence the transient layer was commonly seen as an f3 layer at reflection points closest to the magnetic equator but invariably as an f1 5 layer at reflection points farther from the magnetic equator these observations suggest that the distortion in the equatorial electron density profile associated with the phenomenon moved toward the base of the f2 layer as magnetic field lines descended with increasing latitude stratification of the f2 layer commenced at the same local time e g 0845 lt in november 1997 throughout the longitudinal range of coverage and was associated with a rapid rise in f2 layer height following sunrise the stratification ended at times varying from 1300 lt to sunset and was associated with a fall in the height of f2 peak electron density the region of maximum f2 layer stratification lay between the magnetic equator and the peak of the southern equatorial anomaly

diurnal nonmigrating tides from timed doppler interferometer wind data monthly climatologies and seasonal variations 1 timed doppler interferometer tidi measurements of zonal and meridional winds in the mesosphere lower thermosphere are analyzed for diurnal nonmigrating tides june 2002 to june 2005 climatologies of monthly mean amplitudes and phases for seven tidal components are presented at altitudes between 85 and 105 km and latitudes between 45 s and 45 n westward propagating wave numbers 2 3 and 4 the standing diurnal tide and eastward propagating wave numbers 1 2 and 3 the observed seasonal variations agree well with 1991 1994 uars results at 95 km comparisons between the tidi results and global scale wave model gswm and thermosphere ionosphere mesosphere electrodynamics general circulation model time gcm tidal predictions indicate that the large eastward propagating wave number 3 amplitude is driven by tropical tropospheric latent heat release alone in contrast latent heating and planetary wave migrating tidal interactions are equally important to westward 2 and standing diurnal tidal forcing there is good quantitative agreement between tidi and the model predictions during equinox but the latter tend to underestimate the westward 2 and standing diurnal tide during solstice neither model reproduces the observed seasonal variations of the eastward propagating components

direct observation of the f region dynamo currents and the spatial structure of the eej by champ 1 the satellite champ in its low altitude polar orbit and with its high resolution magnetic field measurements provides the opportunity to investigate ionospheric currents in great detail in this study we focus on average features of equatorial current systems during day time considering quiet time observations from the period aug 2000 to oct 2004 we determined the mean spatial structure of the eej current the existence of reverse currents at the flanks of the primary eastward current is confirmed more importantly average characteristics of the f region dynamo driven currents are observed for the first time throughout the daytime the meridional current system driven by westward thermospheric winds peaks around noon similar meridional currents but flowing in the opposite sense are observed at the dusk sector at champ altitudes we find over the dip equator in the f region a vertical sheet current of about 6 ma m oriented downward at noon and an upward current of 4 ma m around sunset

east west differences in f region electron density at midlatitude evidence from the far east region the global configuration of the geomagnetic field shows that the maximum east west difference in geomagnetic declination of northern middle latitude lies in the us region similar to 32 degrees which produces the significant ionospheric east west coast difference in terms of total electron content first revealed by zhang et al 2011 for verification it is valuable to investigate this feature over the far east area which also shows significant geomagnetic declination east west gradient but smaller similar to 15 degrees than that of the us the current study provides evidence of the longitudinal change supporting the thermospheric zonal wind mechanism by examining the climatology of peak electron density nmf2 electron density ne of different altitudes in the far east regions with a longitude separation of up to 40 60 degrees based on ground ionosonde and space based measurements although the east west difference r ew over the far east area displays a clear diurnal variation similar to the us feature that is negative r ew west ne east ne in the noon and positive at evening night the observational results reveal more differences including 1 the noontime negative r ew is most pronounced in april june while in the us during february march thus for the late spring and summer period negative r ew over the far east region is more significant than that of the us 2 the positive r ew at night is much less evident than in the us especially without winter enhancement 3 the magnitude of negative r ew tends to enhance toward solar maximum while in the us showing anticorrelation with the solar activity the altitude distribution of pronounced negative difference 300 400 km moves upward as the solar flux increases and hence produces the different solar activity dependence at different altitude the result in the paper is not simply a comparison corresponding to the us results but raises some new features that are worth further studying and improve our current understanding of ionospheric longitude difference at midlatitude citation zhao b m wang y wang z ren x yue j zhu w wan b ning j liu and b xiong 2013 east west differences in f region electron density at midlatitude evidence from the far east region j geophys res space physics 118 542 553 doi 10 1029 2012ja018235

features of the f3 layer in the low latitude ionosphere at sunset the f 3 layer is a common feature within 10 degrees of the magnetic equatorial ionosphere in the daytime according to balan et al 1998 the f 3 layer occurs mainly during the morning noon period due to the combined effect of the upward e x b drift and the neutral wind that provides upward plasma drifts at and above the f 2 layer the f 3 layer occurrence rate is higher in summer and decreases with increasing solar activity in this study the characteristic of the sunset f 3 layer is first investigated using a solar cycle of ionosonde data 1995 2010 from the magnetic equatorial station at jicamarca and compared with the features derived from the four subtropical stations at sao luis fortaleza kwajalein and vanimo evidence shows that the local time distribution of the occurrence of the f 3 layer can extend to the postsunset time 1800 2100 local time the sunset f 3 layer has a strong seasonal dependence occurring mainly during the summertime unlike the daytime f 3 layer the occurrence of the sunset f 3 layer clearly increases and the virtual height of the bottom side of the f 3 layer statistically increases from 620 to 1000 km with increasing solar activity in addition the occurrence of the sunset f 3 layer at the other stations is much less than that at jicamarca these features of the dependence on the season solar activity and latitude are clearly related to the geomagnetic control of the evening prereversal enhancement of the equatorial zonal electric field and geomagnetic configuration

longitudinal variation of the e region electric fields caused by atmospheric tides 1 polarization electric fields created by the e and f region dynamos cause the uplift of f region plasma the subsequent redistribution of that plasma along the magnetic field lines creates the equatorial ionospheric anomaly eia observations of the post sunset eia made by the image and timed satellites are compared here with champ orsted and sac c observations of the noontime equatorial electrojet eej during magnetically quiet periods around equinox the eia and eej show a remarkably similar four peaked wave like longitudinal variation its structure is consistent with the longitudinal variation in the strength of diurnal tides that drive the e region dynamo this indicates a strong vertical coupling between the ionosphere and troposphere because the four peaked tidal structure is driven by tropospheric weather furthermore the dayside ionospheric conditions are found to perform the global scale longitudinal structure of the post sunset ionosphere at low latitudes

first simultaneous observations of f3 layer and e b drift in indian sector and modeling 1 although the basic mechanism of an additional stratification of the daytime equatorial f region called the f3 layer has been explained two observational aspects that remain not so clear are its summer winter differences and simultaneous occurrences on either side of the geomagnetic equator in this paper we address these two aspects using simultaneous observations of the f3 layer and vertical e b drift velocity made for the first time in an indian station gadanki 6 5 n mag lat during the low solar activity period 2008 2009 and making model computations using the sheffield university plasmasphere ionosphere model the observations confirm the frequent occurrence of the f3 layer in summer months compared to winter months the observations also reveal the occasional occurrence of clear and distinct f3 layer in winter although such a layer is frequent in summer in addition a threshold vertical plasma velocity involving the e b drift and neutral wind and its time integrated value are found to be important for the formation of the f3 layer the model results qualitatively reproduce the observations and show that irrespective of season the formation of the f3 layer is centered on that side of the equator where the equatorward neutral wind reduces the downward field aligned flow of plasma and the latitude band of the layer can extend to the opposite hemisphere especially when the vertical plasma velocity is large

grenville age a type and related magmatism in southern laurentia texas and new mexico u s a abstract large grenville age plutons are known to be present in the 1340 1370 ma basement in texas and eastern new mexico but their distribution and compositional ranges are poorly known new u pb zircon dates shrimp rg stanford university on subsurface samples have identified widespread presence of compositionally diverse grenville age 1070 1110 ma plutonic rocks in the texas panhandle core from a 175 m thick sill like gabbroic intrusion yielded a date of 1081 8 3 ma in situ differentiation of this tholeiitic magma led to a 7 fold increase in incompatible element concentrations as ree patterns remained essentially flat trace element data suggest an e morb like source to the south alkali feldspar granite with a type affinities was recovered from drill core from the abilene gravity minimum near albany texas it yielded a date of 1078 23 ma similar to undeformed post orogenic granites in the llano uplift further west an anorthosite xenolith from the eocene three sisters intrusion in el paso texas yielded a date of 1068 30 ma which is within error of the 1110 19 ma age determined for the main stage of the nearby a type red bluff granitic suite xenoliths from potrillo maar volcano in the center of the southern rio grande rift include monzonitic xenoliths with granulitic texture which yielded dates of 1072 ma in contrast potrillo maar xenoliths with igneous textures yielded u pb dates of 27 ma development of the granulitic texture is interpreted to reflect granulite facies metamorphism during tertiary time 26 27 ma on the basis of age zoning and u concentrations in the zircon crystals our results show that grenville age magmatism in the texas and new mexico subsurface was widespread and was coeval with syn and post deformation granites in the llano uplift of central texas the compositions of dated samples suggest that mafic magmas were broadly tholeiitic in character and that granitic magmas were a type these magmatic affinities are thought to be associated with crustal extension rather than with subduction moreover the presence of anorthosite xenoliths in the el paso kilbourne hole region the broadly tholeiitic character of mafic rocks and the a type nature of the granitic rocks are broadly similar to amcg anorthosite mangerite charnockite granite suites present in the grenville province of eastern laurentia

magnetic conjugate observation of the f3 layer using the sealion ionosonde network 1 results from the meridional ionosonde network located in southeast asia sealion demonstrate the interesting nature of the f3 layer showing its generation mechanism ionograms obtained on 16 november 2004 and 31 march 2005 at chiang mai cmu geographic latitude 18 8 n geographic longitude 98 9 e and magnetic latitude 13 2 n chumphon cpn 10 7 n 99 4 e and 3 2 n and kototabang ktb 0 2 s 100 3 e and 10 1 s showed significant differences between cpn near the magnetic equator and cmu and ktb in the magnetic low latitude region the simultaneous magnetic conjugate observations of the f3 layer achieved using the sealion ionosonde network data showed clear dependences of the f3 layer on the magnetic latitude it is suggested that these magnetic latitude dependences of the f3 layer can be explained by considering the plasma diffusion effects along the magnetic field lines in the magnetic low latitude region

aquatic ecosystem responses to holocene climate change and biome development in boreal central asia boreal ecosystems are highly vulnerable to climate change and severe ecological impacts in the near future are virtually certain to occur we undertook a multiproxy study on an alpine lake esm 1 at the modern tree line in boreal southern siberia steppe and tundra biomes were extensive in eastern sayan landscapes during the early holocene boreal forest quickly expanded by 9 1 ka bp and dominated the landscape until c 0 7 ka bp when the greatest period of compositional turnover occurred at this time alpine meadow landscape expanded and picea obovata colonised new habitats along river valleys and lake shorelines because of prevailing cool moist conditions during the early holocene chironomid assemblages were dominated by cold stenotherms diatoms for much of the holocene were dominated by alkaliphilous fragilarioid taxa up until 0 2 ka bp when epiphytic species expanded indicative of increased habitat availability c n mass ratios ranged between 9 5 and 13 5 11 1 15 8 c n atomic ratios indicative of algal communities dominating organic matter contributions to bottom sediments with small persistent contributions from vascular plants however 13c values increased steadily from 34 9 during the early holocene 9 3 ka bp to 24 8 by 0 6 ka bp this large shift in magnitude may be due to a number of factors including increasing within lake productivity increasing disequilibrium between the isotopic balance of the lake with the atmosphere as the lake became isotopically mature and declining soil respiration linked to small but distinct retreat in forest biomes the influence of climatic variables on landscape vegetation was assessed using redundancy analysis rda a linear direct ordination technique changes in july insolation at 60 n significantly explained over one fifth of the variation in species composition while changes in estimates of northern hemisphere temperature and ice rafted debris events in the north atlantic were also significant but considerably less important the potential importance of climate and biome development tundra steppe cold deciduous forest and taiga on different trophic levels i e chironomid and diatom communities in lake esm 1 was also assessed using rda climate predictors had a more significant influence on holocene chironomid assemblages especially july insolation at 60 n estimates of regional precipitation and estimates of northern hemisphere temperature while only the development of the taiga biome had a significant impact on these primary consumers diatom communities also had a small but significant influence on holocene chironomid populations perhaps linked to variation in faunal feeding strategies in contrast climatic and biome predictors explained similar amounts of variation in the holocene diatom assemblage approximately 20 each while chironomids themselves as predictors explained just under 7 of diatom variation lake acidity was inferred using a diatom inference model results suggest that after deglaciation the lake did not undergo a process of gradual acidification most likely due to the presence of continuous permafrost and low levels of precipitation preventing base cations and dissolved organic carbon entering the lake except for the period between 1 7 and 0 7 ka bp we conclude that lakes in continental boreal regions undergo different models of lake ontogeny than oceanic boreal regions unlike other regions discussed climate is a more important driver of ecosystem change than catchment changes we also demonstrate that the start of the period coincident with the onset of the little ice age resulted in important thresholds crossed in catchment vegetation and aquatic communities

deglaciation shore displacement and early holocene vegetation history in eastern middle sweden the sedimentary record at lake vibysjo lake basin is situated close to the narke strait where the main water exchange occurred between the vanern basin and baltic basin during the middle and late phases of the yoldia sea stage of the baltic sea c 10 000 9500 14c years bp the area was deglaciated in a glaciomarine environment as reflected by the occurrence of benthic calcareous fossils foraminifera ostracods and the mollusc portlandia arctica gray in the lower most clay units the estimated date of deglaciation 10 440 clay varve years bp suggests that a saline bottom water current entered the baltic basin shortly after the high areas south of lake vibysjon became free of ice the brackish water fauna occurs during a regional betula empetrum hippophae pollen zone which in southern sweden is correlated with the early preboreal the isolation of the lake vibysjon basin is dated to 8100 14c years bp and occurred during the last part of the ancylus lake stage based on investigations of other bas

ignimbrites trachytes and sedimentary rocks of the precambrian thunderbird group franklin mountains el paso texas metamorphosed trachytes ignimbrites of rhyolitic composition and volcaniclastic rocks are recognized in the precambrian thunderbird group franklin mountains near el paso texas chemically both the trachytes and pyroclastic rocks are alkalic contact metamorphism due to intrusion of the red bluff granite recrystallized the thunderbird group to the albite epidote hornfels facies however primary igneous and sedimentary structures are well preserved as seen both in outcrops and thin sections throughout most of the thunderbird group

palaeoenvironment during preboreal boreal in narke south central sweden abstract four sites have been investigated to illustrate the shore displacement and vegetation history during the yoldia sea stage in an area east of the narke strait diatom analysis shows that two of the localities at 165 170 m and 147 m altitude were located above the highest shore line formed during the yoldia sea stage and that only freshwater diatom assemblages were registered in the sediments deposited during the preboreal and boreal chronozones acidification of the water seems to have taken place rather early according to the composition of the diatom flora the basin ladfallet at 142 m was situated slightly above or at the yoldia limit and might have been temporarily influenced by the yoldia sea as the diatom flora contains the slightly brackish littoral taxon mastogloia smithi v lacustris grunow the basin skelnabackakarret at 127 m was isolated from a bay of the yoldia sea which is clearly reflected by the brackish marine diatom flora the composition of the pollen flora illustrates that the isolation occurred during the betula empetrum pollen assemblage zone radiocarbon datings of the sediments deposited at the isolation gave too high ages but the spread of corylus and alnus were dated approximately 9400 and 8500 bp respectively the pollen flora at the four sites studied indicates a vegetational succession from open herb and shrub communities with betula nana and empetrum followed by a phase of open birch forests with juniperus before the immigration of pinus corylus and alnus

palaeoenvironmental conditions during the baltic yoldia stage in the tallinn area northern estonia abstract this paper reviews both the current and previous studies of the baltic yoldia stage along with their alternative interpretations of the results and events focus is placed on the tallinn area in northern estonia on the basis of palaeogeographical and diatom stratigraphical studies the changes in the palaeoenvironment during the transition from late glacial to early holocene preboreal conditions are described the tondi and sojamae mires at altitudes just around the yoldia level of the area ca 40 m a s l show only very slight influence of the brackish yoldia sea in their supralittoral to littoral environment the two sites at lower altitudes with a yoldia water depth of approx 40 m at pirita and approx 60 m at harku register pronounced brackish water conditions in their diatom assemblages characteristic of the littoral to sublittoral environment of the yoldia sea the litho and biostratigraphical data cannot confirm a transgressive nature of the baltic during the brackish yoldia stage but are rather suggesting a regressive development of shoreline according to the present study the diatom composition of the yoldia sediments was dependent on the depositional environment and the abundance of saline water diatoms increased with water depth the influx of older redeposited marine diatoms was here of minor importance

geochemical and sr and nd isotopic constraints on the origin of late proterozoic volcanics and associated tin bearing granites from the franklin mountains west texas late proterozoic volcanic and granitic rocks from the franklin mountains in west texas define a continuous tholeiitic trend from rhyolite granite to trachyte with a small compositional gap betwee

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

the earth s thermospheric superrotation from dynamics explorer 2 neutral thermospheric zonal winds measured from the wind and temperature experiment on dynamics explorer 2 have been analyzed to provide a measure of the superrotation of the neutral thermosphere the data were averaged in local time in 10 degree bands from the equator to 40 degrees latitude the results show an average wind velocity on the order of 18 m s to the east at the equator and a westward wind of the same magnitude at mid latitudes within the range of altitudes of the data base 200 to 700 km no evidence of any significant altitude dependence was found averaging our data over the latitude bands studied indicates a net corotation of the thermosphere this result is not in agreement with the superrotation value reported by king hele and walker on the basis of satellite drag analysis

features of additional stratification in ionospheric f2 layer observed for half a solar cycle over indian low latitudes 1 the features of the additional stratification in the ionospheric f2 layer often referred to as the f3 layer observed over an indian low latitude station waltair 17 7 n 83 3 e magnetic latitude mag lat 8 2 n during the period 1997 2003 are presented along with the data from two other indian stations the observations grossly confirm those reported earlier in the occurrence and seasonal variability of the f3 layer from an analysis of half a solar cycle ionosonde data 1997 2003 it is observed that the layer appeared more frequently during the summer solstice months of low solar activity period and persisted for longer durations during this season compared with equinox and winter solstice the best stratification is seen between 10 12 hours ist the occurrence of the f3 layer does not seem to depend on magnetic activity but the percentage of occurrence decreased with increasing solar activity the solar activity dependence over waltair confirms the model predictions of balan et al 1998 that the layer becomes less distinct and less frequent as solar activity increases the ionosonde data for the same period 1997 2003 from an equatorial station trivandrum 8 4 n 76 9 e mag lat 0 47 n and another low latitude station shar 14 n 80 e mag lat 6 8 n are also analyzed with a view to examine the effect of the equatorial plasma dynamics on the occurrence of such events

an event stratigraphy for the last glacial holocene transition in eastern middle sweden results from investigations of varved clay and terrestrial sequences this paper presents an event stratigraphy for the last glacial holocene transition in eastern middle sweden the event stratigraphy for eastern middle sweden comprises ten events and covers the tim

peculiar features of ionospheric f 3 layer during prolonged solar minimum 2007 2009 we present the seasonal and local time occurrence of ionospheric f 3 layer over tirunelveli geographic longitude 77 8 e geographic latitude 8 7 n dip 0 7 during extremely low and prolonged solar activity period 2007 2009 canadian advanced digital ionosonde observations from this station are used in the present study we find that the occurrence of f 3 layer is nearly 3 times higher during 2009 48 as compared to that during 2007 16 the increase of this order just within the low solar activity period is unusual in earlier studies similar increase in f3 occurrence has been reported when solar activity changes from high f10 7 182 t o low f10 7 72 the other important feature is the presence of postnoon f3 layers which are observed dominantly during summer solstice of 2009 such occurrence of postnoon f3 layers was nearly absent during summer solstice of the previous solar minimum 1996 over nearby dip equatorial station trivandrum we take equatorial electrojet eej as a proxy for eastward electric field it is noticed that the eej strength and the maximum rate of change of eej are higher for f3 days as compared to those on non f3 days we find that the peak occurrence of prenoon f3 layer closely coincides with the time of maximum rate of change of eej it is in general accordance with the theory proposed by balan et al 1998 that suggests the formation of f3 through vertically upward e b drift in presence of equatorward neutral wind the present study reveals that the rate of change of eastward electric field de dt as well plays an important role in the formation of f3 layer

longitudinal variation of f region electron density and thermospheric zonal wind caused by atmospheric tides 1 simultaneous observations of the electron density and the zonal wind obtained by the champ satellite at 400 km are used to study systematic longitudinal variations the time period selected is august september 2004 allowing observations at pre noon and post sunset hours the equatorial ionization anomaly eia and the zonal delta wind deviation from zonal average show a persistent and dominant 4 peaked longitudinal variation we interpret this structure as caused by the wavenumber 3 nonmigrating diurnal tide de3 the eia and the zonal delta wind exhibit extrema at about the same longitudes but while the intensifications of the eia and the delta wind are in phase during the evening hours they are out of phase in the morning possible coupling mechanisms are investigated

physical mechanism and statistics of occurrence of an additional layer in the equatorial ionosphere a physical mechanism and the location and latitudinal extent of an additional layer called the f3 layer that exists in the equatorial ionosphere are presented a statistical analysis of the occurrence of the layer recorded at the equatorial station fortaleza 4 s 38 w dip 9 s in brazil is also presented the f3 layer forms during the morning noon period in that equatorial region where the combined effect of the upward e b drift and neutral wind provides a vertically upward plasma drift velocity at altitudes near and above the f2 peak this velocity causes the f2 peak to drift upward and form the f3 layer while the normal f2 layer develops at lower altitudes through the usual photochemical and dynamical effects of the equatorial region the peak electron density of the f3 layer can exceed that of the f2 layer the f3 layer is predicted to be distinct on the summer side of the geomagnetic equator during periods of low solar activity and to become less distinct as the solar activity increases ionograms recorded at fortaleza in 1995 show the existence of an f3 layer on 49 of the days with the occurrence being most frequent 75 and distinct in summer as expected during summer the layer occurs earlier and lasts longer compared to the other seasons on the average the layer occurs at around 0930 lt and lasts for about 3 hours the altitude of the layer is also high in summer with the mean peak virtual height being about 570 km however the critical frequency of the layer f0f3 exceeds that of the f2 layer f0f2 by the largest amounts in winter and equinox f0f3 exceeds f0f2 by a yearly average of about 1 3 mhz

correlation of swedish glacial varves with the greenland grip oxygen isotope record a mean varve thickness curve has been constructed for a part of the swedish varve chronology from the northwestern baltic proper the mean varve thickness curve has been correlated with the delta 1

an empirical model of the occurrence of an additional layer in the ionosphere from the occultation technique preliminary results about 8 year electron density profile edp data from the cosmic formosat 3 satellites radio occultation technique were used to investigate the additional stratification of the f2 the so called f3 layer layer over the equatorial and low latitude ionosphere on a global scale for both the bottomside and topside ionosphere the f3 layer was recognized through the altitude differential profile featured by two maxima existing from the selected edp profile there were 37 000 bottomside and 25 000 topside cases of f3 layer selected out of 1 27 million occultation events at equatorial and low latitude areas during the period of april 2006 to august 2014 the statistical results for the bottomside ionosphere resemble that reported in zhao et al 2011a while in the topside the highest occurrence of f3 layer shows a 3 4 h delay depending on the altitude range of the stratification the magnetic latitude distribution shows different dependence with a tendency to form a single crest toward high altitude also the seasonal variation is weaker in the topside ionosphere compared to the bottomside one especially in the high altitude then we build up an empirical model of the f3 layer occurrence using the bottomside statistics based on empirical orthogonal function eof decomposition as it gets the inherent characters inside the data set and converges quickly the model well grasps the main features of the f3 occurrence e g the f3 occurrence s sensitivity on the magnetic latitude further in order to accommodate the ground observation a corrected factor was introduced as f3 layer is an important phenomenon in the low latitude ionosphere we have made an attempt to describe its feature with a consecutive function although future work needs to be done for an overall expression of this structure

strong evidence for the tidal control on the longitudinal structure of the ionospheric f region this paper presents for the first time the global latitude structure and seasonal variability of the ionospheric response to the forced from below de3 and de2 tides during the period of time january 2008 march 2009 the cosmic hmf2 and saber temperature data have been utilized in order to define the ionospheric de3 and de2 tidal response to the de3 and de2 temperature tides propagating from below the cosmic de3 and de2 hmf2 tidal oscillations are derived by the same method as the tides seen the saber temperatures it has been shown that the longitude wave 4 and wave 3 hmf2 structures observed respectively in september and may 2008 are forced mainly by de3 wave 4 and de2 wave 3 temperature tides coming from below the longitude wave 3 hmf2 structure observed in january 2008 however is forced by the combined action of the de2 temperature tide coming from below and the spw3 probably generated in situ

relative importance of hydrological and climatic controls on holocene paleoenvironments inferred using diatom and pollen records from a lake in the central hudson bay lowlands canada postglacial paleoenvironmental changes and landscape development in the hudson bay lowlands in subarctic canada were inferred using sediment properties and diatom and pollen assemblages in the sediments of a lake raised above the surrounding peatlands in an ice marginal landform coarse grained inorganic sediments at the base of the lake at01 core suggest a high energy periglacial environment following isostatic emergence from hudson bay around 6840 cal bp initial diatom assemblages dominated by fragilaria spp and pollen of shepherdia canadensis indicate early successional conditions in a recently deglaciated environment around 6200 cal bp tychoplanktonic fragilarioid diatoms are replaced by large benthics coincident increases in equisetum spores cyperaceae pollen and sediment organic matter suggest the establishment of a more productive macrophyte rich shallow lake while the holocene thermal maximum and subsequent neoglacial may have contributed to these shifts pollen and diatom records sug

quiet time equatorial f region vertical plasma drift model derived from rocsat 1 observations 1 we have used five years of measurements on board the rocsat 1 satellite to develop a detailed quiet time global empirical model for equatorial f region vertical plasma drifts this model describes the local time seasonal and longitudinal dependence of the vertical drifts for an altitude of 600 km under moderate and high solar flux conditions the model results are in excellent agreement with measurements from the jicamarca radar and also from other ground based and in situ probes we show that the longitudinal dependence of the daytime and nighttime vertical drifts is much stronger than reported earlier especially during december and june solstice the late night downward drift velocities are larger in the eastern than in the western hemisphere at all seasons the morning and afternoon december solstice drifts have significantly different longitudinal dependence and the daytime upward drifts have strong wave number four signatures during equinox and june solstice the largest evening upward drifts occur during equinox and december solstice near the american sector the longitudinal variations of the evening prereversal velocity peaks during december and june solstice are anti correlated which further indicates the importance of conductivity effects on the electrodynamics of the equatorial ionosphere

grenville magmatism in west texas petrology and geochemistry of the red bluff granitic suite zone of regional extension as suggested by recent geophysical and the red bluff granitic suite rbgs underlies part of the franklin petrological studies mountains in west texas it was emplaced into a middle proterozoic shelf sequence at 1120 35 ma the suite is predominantly metaluminous it consists of early granitic to quartz syenitic sills a main mass of alkali feldspar granite small bodies of alkali feldspar syenite leucogranitic dikes and late stage peralkaline