environmental controls on the tl age of modern zero age proglacial outwash sediments abstract thermoluminescence tl signals from suspended sediment in an icelandic meltwater stream exhibit small scale random fluctuations over time but show sufficient consistency to indicate that larger scale fluctuations in tl are systematic rather than random it is concluded that diurnal tl fluctuations are related to changes in sediment source and ambient conditions during transport the results suggest young fluvioglacial sediments may prove difficult to date using standard tl techniques

images of transequatorial f region bubbles in 630 and 777 nm emissions compared with satellite measurements images of transequatorial f region bubbles were obtained from magnetic field aligned airglow observations from haleakala hawaii for 9 nights in august 1988 bubbles of scale size 10 100 km were recorded with an intensified ccd detector attached to a filter wheel imager and sequential images were made in the plasma recombination emissions at 630 nm and 777 nm and in the background emissions the observations also yield information on the large scale structure of the ionosphere in the northern appleton anomaly region particularly on the latitude variations of plasma concentration and layer height measurements from the dmsp f8 and f9 satellites extend this to include the southern anomaly region the dmsp satellites were near 830 km in altitude and in near polar orbits at about 1800 and 2120 hours local time a comparison of the bubble images and the dmsp results with plasma concentration and drift velocities obtained from the san marco satellite allows us to put the measurements along the san marco track into the larger ionospheric context one to one correspondence is found between the presence of the optical bubbles and the presence of plasma depletions measured from the san marco satellite allowing identification on consecutive orbits of the same depletions this extends for up to 5 hours of the satellite measured information for individual depletions that is their vertical and horizontal drift velocities and the plasma concentration variations the images show the shapes of the depletions in apex height and longitude and their evolution horizontal drift velocities of the bubbles were determined by a correlation analysis bubble occurrence is compared with day to day changes in the equatorial fountain electric fields and transequatorial asymmetries caused by neutral winds and with measurements of radar backscatter from centimeter scale irregularities associated with bubbles in the kwajalein sector the development of 10 100 km scale size bubbles at a given time and location is clearly a consequence of the presence of even larger wavelike corrugations in the f layer provided there is also at least a moderately strong equatorial fountain

threshold height h f c for the meridional wind to play a deterministic role in the bottom side equatorial spread f and its dependence on solar activity 1 detailed investigations have been carried out on the occurrence of bottom side equatorial spread f esf and the thermospheric meridional wind characteristics just before the former s initiation using ground based ionospheric data corresponding to the equinoctial periods of 1993 1998 from trivandrum 8 5 n 76 5 e dip 0 5 n and sriharikota 13 7 n 80 2 e dip 10 n in the indian longitudes critical analysis of the base height of the f region h f at the time of triggering of esf and the polarity of the meridional winds revealed that if the h f is above a certain level esf occurred under both equatorward and poleward wind conditions below that level esf occurred only when equatorward winds were present implying that the equatorward winds must somehow be able to offset the reduced growth rate of the plasma instability responsible for esf a plausible explanation linking equatorial ionization anomaly eia and the consequent equatorial temperature and wind anomaly etwa and the consequent neutral dynamics effectively enabling the instability even at lower height has been offered the threshold height h f c gleaned out on the basis of the polarity of the meridional winds has been shown to bear a linear relation to the solar activity and sheds light on the enigmatic short and long term variability of esf

timing of late quaternary glaciations in the himalayas of northern pakistan optically stimulated luminescence dating of late quaternary glaciogenic sediments was undertaken in critical areas of the himalayas of northern pakistan in order to examine the timing of glaciation the dates demonstrate that several glaciations occurred during the last glacial cycle in swat the grabral 2 stade and the kalam i stade were dated at ca 77 ka and ca 38 ka respectively the error on the former date is large and it is conceivable that the moraines may have formed during the early part of oxygen isotope stage 3 rather than during oxygen isotope stage 4 the kalam i stade however clearly represents a glaciation during oxygen isotope stage 3 the oldest moraines and those at the lowest altitude in the indus valley at shatial have an age of ca 60 ka these also relate to a major glacial advance during oxygen isotope stage 3 a younger series of moraines the jalipur tillite and glaciofluvial sands at liachar in the indus valley and moraines at rampur tarshing have ages of ca 27 ka ca 21 23 ka and ca 15 ka respectively these dates show that glaciers also occupied parts of the indus valley during oxygen isotope stage 2 these dates and the morphostratigraphy show that glaciation in the pakistani himalaya was more extensive during the early part of the last glacial cycle and that the local last glacial maximum in pakistan was asynchronous with the maximum extent of northern hemisphere ice sheets copyright 2000 john wiley sons ltd

osl dating of the massive landslide damming event in the jishixia gorge on the upper yellow river ne tibetan plateau frequent natural hazards cause huge damage to human life and society in the mountainous regions along the eastern rim of the tibetan plateau a massive landslide damming event has been reported in

onset conditions for equatorial spread f the problem of day to day variability in the occurrence of equatorial spread f esf is addressed using multidiagnostic observations and semiempirical modeling the observational results are derived from a two night case study of esf onset conditions observed at kwajalein atoll marshall islands using the altair incoherent scatter radar and all sky optical imaging techniques the major difference between nights when esf instabilities did not occur august 14 1988 and did occur august 15 1988 in the kwajalein sector was that the northern meridional gradient of 6300 a airglow was reduced on the night of limited esf activity modeling results suggest that this unusual airglow pattern is due to equatorward neutral winds previous researchers have shown that transequatorial thermospheric winds can exert a control over esf seasonal and longitudinal occurrence patterns by inhibiting rayleigh taylor instability growth rates we present evidence to suggest that this picture can be extended to far shorter time scales namely that surges in transequatorial winds acting over characteristic times of a few hours to a day can result in a stabilizing influence upon irregularity growth rates the seemingly capricious nature of esf onset may thus be controlled in part by the inherent variability of low latitude thermospheric winds

luminescence dating of proglacial sediments from the eastern alps the potential of optically stimulated luminescence osl for dating proglacial deposits is tested here at three last glacial key sites in the eastern alps this was undertaken using both sand sized feldspar and quartz grains as well as fine silt sized material the samples reveal rather poor luminescence intensities of the investigated quartz grains and it is also clearly demonstrated that several of the deposits were incompletely bleached prior to deposition bleaching experiments were carried out and different approaches for extracting the aliquots where the osl was completely bleached prior to burial were tested applying different osl measurement techniques and analytical procedures we investigated which approach was most appropriate for dating known age proglacial sediments best results were achieved using single aliquot regenerative dose methodology on coarse grain quartz and feldspar samples in combination with the approach of preusser et al 2007 luminescence dating of proglacial sediments from switzerland boreas in press for ed calculation

dating sediments using potassium feldspar single grain irsl initial methodological considerations abstract potassium feldspar shows good potential for luminescence dating of quaternary sediments in several locations assessed including california tibet mongolia spain egypt the uk and new zealand in many of these locations feldspar has particular importance owing to the low sensitivity of quartz osl optically stimulated luminescence signals observed potassium feldspar rich mineral fractions of sand sized grains from a range of fluvial alluvial lake shoreline and glacial contexts were separated and equivalent dose and fading determinations performed for single grains besides conventional multiple grain aliquots in some cases using a protocol modified from a post infra red irsl infra red stimulated luminescence procedure most samples but not all contain a significant proportion of grains that provide irsl signals sufficiently sensitive to determine equivalent dose values two main types of response have been observed one group of samples displays regular behavior with the majority of grains providing either a uniform equivalent dose de value for well bleached samples or a uniform minimum dose value with many higher values presumably caused by incomplete zeroing uniform de values or minimum values suggest that the magnitude of signal reduction by anomalous fading for grains of different sensitivity is the same for all grains a second common pattern of behavior is observed for these samples the minimum equivalent dose value is greater for grains with higher sensitivities a surprising feature of this behavior for a subset of samples is an apparent saturating stretched exponential relationship between minimum equivalent dose and irsl sensitivity samples in both groups contain rare grains with significantly lower de values interpreted as intrusive grains probably introduced by bioturbation this paper provides an initial survey of results and briefly explores single grain fading determination besides comparisons of age estimates between different methods an improved separation method to isolate the most sensitive grains referred to as super k is introduced resulting in significant enhancement of the number of grains with bright irsl signals

optical dating using infrared diodes young samples abstract ages are reported for unburnt sediment samples from 9 archaeological sites in england spanning 1000 5000 years samples from two modern contexts have also been measured

investigations of thermospheric ionospheric dynamics with 6300 a images from the arecibo observatory pilot observations were conducted at arecibo puerto rico using an all sky image intensified ccd camera system in conjunction with radar ionosonde and global positioning system gps diagnostic systems during the periods january 19 28 1993 and february 21 to august 22 1995 these represent the first use of campaign mode operations of an imager at arecibo for extended periods of f region observations the january 1993 period the so called 10 day run yielded a rich data set of gravity wave signatures perhaps the first case of direct imaging of thermospheric wave train properties in the f region the 6 month 1995 campaign revealed two additional optical signatures of f region dynamics a brightness wave in 6300 a passing rapidly through the field of view fov has been linked to meridional winds driven by the midnight temperature maximum mtm pressure bulge on may 3 1995 during a period of geomagnetic activity a 6300 a airglow depletion pattern entered the arecibo fov such effects represent the optical signatures of equatorial spread f instabilities that rise above the equator to heights near 2500 km thereby affecting arecibo s l 1 4 flux tube

scintillation producing fresnel scale irregularities associated with the regions of steepest tec gradients adjacent to the equatorial ionization anomaly 1 using ground based gps and digital ionosonde instruments we have built up at latitudes of the equatorial ionization anomaly eia in the brazilian sector a time evolving picture of total electron content tec l band amplitude scintillations and f region heights and we have investigated likely reasons for the occurrence or suppression of equatorial scintillations during the disturbed period of 18 23 november 2003 during the prestorm quiet nights scintillations are occurring postsunset as expected however during the storm time period their spatial temporal characteristics and intensity modify significantly owing to the dramatic changes in the ionospheric plasma density distribution and in the temporal evolution of tec the two dimensional maps showing both tec and amplitude scintillations revealed strong evidence of turbulences at the fresnel length causing scintillations concurrent with those regions of steepest tec gradients adjacent to the crests of the eia the largest density gradients have been found to occur in an environment of increased background electron density and their spatial distribution and location during the disturbed period may differ significantly from the magnetic quiet night pattern however in terms of magnitude the gradients at equatorial and low latitudes appear to not change during both magnetic quiet and disturbed conditions the scenarios for the formation or suppression of scintillation producing fresnel scale irregularities during the prestorm quiet nights and disturbed nights are discussed in view of different competing effects computed from numerical simulation techniques

an analysis of the quiet time day to day variability in the formation of postsunset equatorial plasma bubbles in the southeast asian region presented is an analysis of the occurrence of postsunset equatorial plasma bubbles epbs detected using a global positioning system gps receiver at vanimo the three year data set shows that the epb occurrence maximizes minimizes during the equinoxes solstices in good agreement with previous findings the vanimo ionosonde station is used with the gps receiver in an analysis of the day to day epb occurrence variability during the 2000 equinox period a superposed epoch analysis sea reveals that the altitude and the change in altitude of the f layer height is 1 standard deviation 1 larger on the days for which epbs were detected compared to non epb days these results are then compared to results from the thermosphere ionosphere electrodynamics general circulation model tiegcm which show strong similarities with the observations the tiegcm is used to calculate the flux tube integrated rayleigh taylor r t instability linear growth rate a sea reveals that the modeled r t growth rate is 1 higher on average for epb days compared to non epb days and that the upward plasma drift is the most dominant contributor it is further demonstrated that the tiegcm s success in describing the observed daily epb variability during the scintillation season resides in the variations caused by geomagnetic activity as parameterized by kp rather than solar euv flux as parameterized by f10 7 geomagnetic activity varies the modeled high latitude plasma convection and the associated joule heating that affects the low latitude f region dynamo and consequently the equatorial upward plasma drift key points day to day epb occurrence in southeast asia investigated using ground based gps tiegcm exhibits similiar daily variability to the epb observations small changes in kp strongly influence daily epb occurrence variability

optical dating of aeolian dynamism on the west african sahelian margin abstract the sahelian margin of west africa is widely recognised as an area of recent environmental catastrophe and human suffering arising from food shortage and land degradation associated with prolonged drought the propensity of this region to suffer drought has been related using environmental data collected during the period of instrumental records to a combination of low mean annual rainfall levels and a high degree of rainfall variability which relates to sea surface temperature anomalies in the adjacent tropical atlantic ocean despite the significant environmental and human consequences of such droughts there is a paucity of long term environmental data for the west african sahel aeolian dune reactivations in this area are a potentially highly useful environmental archive of past periods of extended drought conditions which may have resulted in localised or widespread dune reactivation here we describe the initial results from an ongoing programme of research which seeks to develop a detailed record of past dune reactivations in mali we find evidence for repeated holocene dune reactivation events and a significant number of reactivations which commenced at the time of onset of the last major drought cycle in the early 1970s we obtain ages as young as 20 30 years for some significant dune units thickness up to 1 m and describe the results of experiments which test the performance of our dating exercise we specifically test for the significance of preheat temperature on single aliquot regeneration sar equivalent dose determinations and recycling ratios neither are found vary significantly as a function of preheating optical dating of sand sized quartz could provide a useful tool for palaeogeographical mapping of ancient and historical dune reactivations in this region and elsewhere

on the generation and growth of equatorial backscatter plumes 2 structuring of the west walls of upwellings the west wall of large scale upwellings that develop in the bottomside of the nighttime equatorial f layer becomes structured by the wind driven gradient drift instability the same process that leads to the formation of striations in barium ion clouds upwellings are initiated by wavelike perturbations with long spatial wavelengths 400 km and are amplified by the collisional rayleigh taylor instability and sometimes assisted by the gradient drift instability in the case of an upward moving f layer the west wall structuring process is driven by an eastward neutral wind enhanced by reduced drag during the postsunset hours and a velocity shear in east west bulk plasma drift in the bottomside f layer west wall structures evolve in a manner analogous to primary plasma bubbles i e secondary plasma bubbles grow from the west wall their characteristics are compared with those of the primary bubbles and discussed in the light of existing theories

historical tsunami deposits in peru sedimentology inverse modeling and optically stimulated luminescence dating the entire coast of peru was surveyed to document deposits of historical tsunami evidence of four tsunami was found at puerto casma in northern peru a graded heavy mineral rich layer with shell and rock fragments was detected osl dating revealed an age of 0 37 0 03 ka 1615e1667 ad inverse modelling of tsunami onshore flow parameters indicates a flow depth of w 6ma nd aflow speed of w8 m s at a distance of w60 m from the shoreline for the chimbote earthquake of 1619 ad a tsunami was not listed in the historical tsunami catalogues although it is seen as a predecessor of the 1996 chimbote earthquake and tsunami hence this study may provide the first evidence of a local tsunami triggered by this event a graded shell rich event layer that contains cobbles with attached marine organisms was found at vila vila in southern peru this layer was dated to 0 17 0 04 ka 1797e1871 ad and is most probably the result of the 1868 arica tsunami two additional event layers found in boca del rio southern peru were dated 2 26 0 37 ka 615 bce119 ad and 1 98 0 23 ka 207 bce255 ad thus the layers record for the first time tsunami much older than the events listed in tsunami catalogues these two events exhibit similar parameters with flow speeds of 7e8 m s and depths of 6 m in a distance of 460 m from the present shoreline the time that passed between the events is similar to the recurrence interval of the two arica tsunami of 1604 and 1868 ad hence giving evidence of another prehistoric earthquake and tsunami couplet

evolutionary phases of equatorial spread f including l band scintillations and plumes in the context of gps total electron content variability a case study 1 the evolution of large scale few kilometers medium scale few hundreds of meters and small scale meters size plasma density irregularities in the postsunset equatorial f region in the context of characteristic gps total electron content gtec variations are reported from indian longitudes the ionograms and gtec from a gps receiver installed as a part of the gps aided geo augmentation network gagan project for satellite based navigation are obtained from an equatorial station at trivandrum 8 5 n 76 91 e dip latitude 0 5 n the variations in the gtec with respect to tec are considered to represent the seed perturbations for the plasma instability that results in the equatorial spread f esf irregularities and are treated as a perturbation factor p the vhf radar at gadanki 13 5 n 79 17 e dip latitude 6 4 n provided the small scale structures of esf the background thermospheric conditions that affect the growth of the plasma instability through ion neutral collision frequency in are estimated using the f region base height h f and the representative scale height of the neutral atmosphere and are represented by a growth factor g the present case study reveals a close coupling between the background ionospheric conditions and the baseline perturbations in deciding the evolutionary phases of esf it has been shown that although large scale kilometer scale irregularities are formed without any constraints when the background ionospheric thermospheric conditions are favorable in the presence of fluctuations in gtec consistently the medium scale and small scale irregularities show remarkable similarity with the variations in the product of the perturbation and growth factors

optically stimulated luminescence dating of sediments over the past 200 000 years optical dating of sediment using optically stimulated luminescence has become important for studying earth surface processes and this technique continues to develop rapidly a group of closely linked luminescence methods can be used to estimate the time since grains of quartz and feldspar were last exposed to daylight by detecting their subsequent response to environmental ionizing radiation exposure the technique is well suited to the dating of deposits as young as one year to several hundred thousand years recent technical developments have established a dating protocol with improved precision a high degree of reliability and an in built means to detect incomplete signal removal during deposition this approach has been extended to age estimation for single grains opening up a wider range of potential environments and new possibilities for understanding postdepositional grain movement ongoing research offers the possibility of significant age range extension and novel applications including low t

the effect of thermal transfer on the zeroing of the luminescence of quartz from recent glaciofluvial sediments abstract the natural optically stimulated luminescence osl response of quartz grains extracted from a range of recent glaciofluvial and other glaciogenic sediments from western greenland is presented all samples were deposited within the last 10 years many only days or hours before collection consequently we would expect to measure zero or very small d e values had optical resetting of the osl signal been complete in the case of most samples d e values in the range 0 5 10 gy are observed while higher values are observed for a handful of samples however the regenerated osl growth curves constructed after daylight exposure of at least several hours also show large apparent d e values negative x axis intercepts corresponding samples from four different locations in the indian himalaya display similar osl characteristics the measurement of several regenerated osl growth curves omitting the preheat procedure which normally precedes osl measurement confirms that a significant degree of thermal transfer is occurring during the preheating it is this thermal transfer of charge during the preheat which is responsible for a significant contribution to the large apparent d e values observed for the regenerated osl growth in this paper we describe combined osl and tl measurements which have been used to monitor the charge transfer in detail for one sample an attempt is made to describe the charge transfer behaviour and we discuss methods appropriate to eliminating the unwanted effects of this phenomenon during osl dating preliminary results from the application of these techniques are presented and the implications of these observations for the osl dating of glaciogenic sediments are discussed

bunger hills east antarctica ice free at the last glacial maximum optically stimulated luminescence dating of glaciofluvial and glacial lake shoreline sediments indicates that the bunger hills area in coastal east antarctica was largely ice free by the last glacial maximum lgm deglaciation commenced as early as 30 ka and the southern hills were completely exposed by 20 ka the sediments do not record evidence of an lgm readvance previous reconstructions of lgm ice limits for the area are incompatible with this new evidence

luminescence dating of archaeometallurgical slag use of the sar technique for determination of the burial dose abstract the potential of using luminescence techniques to date metallurgical slag of archaeological origin has been investigated slag is an important residue from the metal smelting process and there is no technique currently available to directly date it an attempt has been made to apply an optically stimulated luminescence osl single aliquot technique using quartz extracted from the slag matrix a single aliquot regeneration technique was used and preliminary results are encouraging in spite of problems encountered in the determination of the equivalent dose d e and apparent underestimation of the preliminary dates obtained the results presented here were obtained from measurements on copper and iron slag from archaeological sites in britain and greece

luminescence dating of sand loess sequences and response of mu us and otindag sand fields north china to climatic changes the sand loess transition zone in north china is sensitive to climate change and is an ideal place to investigate past environmental changes however past climate change at millennial centennial timescales in this region has not been well reconstructed because of limited numerical dating alternations of sandy loam soils with aeolian sand layers in the mu us and otindag sand fields which lie along the sand loess transition zone indicate multiple intervals of dune activity and stability this change is probably a response to variations of the east asian monsoon climate during the late quaternary the single aliquot regeneration sar optically stimulated luminescence osl dating protocol which has been successfully applied to aeolian deposits worldwide is applied to these two sand fields in this study the osl ages provide reliable constraints for reconstruction of past climate changes at suborbital timescale sections in both sand fields contain aeolian sand beds recording millennial scale episodes of dry climate and widespread dune activation including episodes at about the same time as heinrich event 5 and the younger dryas in the north atlantic region these results demonstrate the potential of aeolian sediments in semi arid north china to record millennial scale climatic events and also suggest that dry wet climate variation at the desert margin in china may be linked to climatic change elsewhere in the northern hemisphere through atmospheric circulation this article was published online on 27 november 2008 an error was subsequently identified this notice is included in the online and print versions to indicate that both have been corrected 16 december 2008 copyright 2008 john wiley sons ltd

luminescence dating of quaternary sediments in the himalaya and high asia a practical guide to its use and limitations for constraining the timing of glaciation abstract knowledge of the glacial history of high asia is of critical importance for scientific understanding of the palaeoclimate of this region the lack of absolute age controls on glacial landforms of the himalaya and high asia region is arguably the greatest problem facing the construction of a history of quaternary glaciation in these areas a major reason for this lack of dates has been the absence of a suitable dating method this paper reviews the use of optically stimulated luminescence osl dating in the himalaya critical examination of existing data is used to suggest guidelines for the collection of suitable sediments for dating using osl in order to constrain the timing of glaciations osl has been shown to provide reproducible and apparently accurate ages which constrain glacial advances however the correct selection of sediments is of critical importance in spite of developments in the technique there remain limitations to its applicability reasons for this are considered as is the potential of osl for constraining the timing of glacial expansion

apparent osl ages of modern deposits from fabergstolsdalen norway implications for sampling glacial sediments the application of optically stimulated luminescence osl dating within glacial settings can be limited where sediments have not had their osl signal fully reset by sunlight exposure heterogeneous bleaching can result in age overestimations and although it is recognized that certain depositional settings are more likely to have experienced sufficient sunlight exposure to bleach the osl signal no comprehensive study has empirically investigated the processes of sediment bleaching or the variability in bleaching between deposits of the same type and within the same glacial catchment a suite of modern glacial and glaciofluvial sediments from fabergstolsda len southern norway have been analysed to explore the controls that sedimentary processes and depositional setting have on bleaching of the osl signal of quartz there is considerable variability in the residual osl ages of similar modern deposits which reflects high sensitivity of the osl signal to sediment source sedimentary process transport distance and depositional setting overdispersion values are greatest for the sediments which have been most heterogeneously bleached and these sediments have the lowest residual ages sampling strategies that incorporate sufficient consideration of the depositional framework of sample settings can minimize the effects of unbleached residuals on osl age determinations copyright 2013 the authors journal of quaternary science published by john wiley sons ltd on behalf of quaternary research association

holocene relative sea level change and deglaciation on alexander island antarctic peninsula from elevated lake deltas abstract field data constraining the rate and spatial pattern of deglaciation and relative sea level rsl change on the antarctic peninsula ap are relatively sparse but are needed to improve regional ice sheet and rsl change models and contribute to better model predictions of future sea level rise we investigated the geomorphology sedimentology and quartz fraction single aliquot regeneration optically stimulated luminescence sar osl geochronology of elevated deltas around two epishelf lakes ablation lake al and moutonnee lake ml alexander island antarctic peninsula al and ml are dammed by george vi ice shelf and maintain a direct hydraulic connection to the sea hence their water levels are controlled by changes in rsl our aim was to provide new terrestrial constraints on rsl and deglaciation for the southern ap by comparing the formation processes age and altitude of the al and ml deltas with 1 existing rsl curves for the ap 2 isostatically coupled ap ice sheet models and 3 existing ap deglaciation history and sar osl ages from elevated deltas around the nearby inland hodgson lake hl although there was insufficient quartz in the ml samples for sar osl dating the 4 6 0 4 ka sar osl age of the elevated delta at al represents the last time active deltas were forming higher than present day lake level and implies 1 a fall in rsl of up to 14 4 m since the mid holocene in this part of alexander island which is consistent with existing field based rsl chronologies for the ap 2 relatively smaller ice masses than suggested by some but not all isostatically coupled ice sheet models since the mid holocene and 3 significant mid holocene thinning of the ap ice sheets which is consistent with regional sediment core data and cosmogenic exposure ages and the 4 4 0 7 ka sar osl age of the lowermost hl delta

impact of meridional winds on equatorial spread f revisited 1 the impact of meridional winds on the onset and evolution of equatorial spread f esf is studied using the nrl ionosphere model sami3 esf the prevailing belief is that meridional winds have a stabilizing effect on the onset of esf in this letter it is shown that this is not necessarily the case and that meridional winds can be destabilizing we find that a wind profile with a positive gradient as a function of latitude v m 0 is a stabilizing influence on the generalized rayleigh taylor instability a wind profile with a negative gradient v m 0 is a destabilizing influence here a northward wind is positive and increases in the northward direction it is suggested that meridional wind profiles may account for in part the longitudinal and day to day variability of esf

the storage of bed material in mountain stream channels as assessed using optically stimulated luminescence dating abstract a detailed understanding of channel forming and maintenance processes in mountain streams requires some measurement and or prediction of bed load transport and sediment mobility traditional field based measurements of such processes are problematic because of the high formative discharges characteristic of such streams the application of optically stimulated luminescence osl dating is proposed here as a new way of determining actual residency times of fine sediments and consequently validating selected predictions for the entrainment of sediment in these streams model predictions of sediment mobility for selected step pool and plane bed channels in a mountain catchment in south eastern australia are initially calculated using equations of hydraulic competence and the one dimensional hec ras model results indicate that floods exceeding bankfull with recurrence intervals up to 13 years are competent to mobilise the maximum overlying surface grain sizes at both sites osl minimum age model results from 7 samples of well bleached quartz in the fine matrix particles indicate general agreement with selected competence equations the apparent long 100 1400 y burial age of most of the mineral quartz however suggests that competent flows are not able to flush all subsurface fine bed material the depth of maximum bed load exchange flushing was limited to twice the depth of the overlying d 90 grain size application of osl in this study provides important insight into the nature of storage and flushing of matrix material in mountain streams

the last deglacial history of lutzow holm bay east antarctica past fluctuations of the antarctic ice sheet are poorly understood because of a lack of datable materials radiocarbon reservoir ages and severe environments direct evidence of the timing of ice retreat is important in order to understand the antarctic contribution to global sea level rise since the last glacial maximum here we report the first exposure ages constraining the timing of the last deglaciation from lutzow holm bay east antarctica our data suggest that the final retreat of the ice sheet in the region occurred rapidly in the early holocene and the reduction of the ice thickness in the region was at least 350 m this occurred after the major northern hemisphere deglaciation copyright 2011 john wiley sons ltd

dating fluvial sediments by optically stimulated luminescence selection of equivalent doses for age calculation fluvial sediments are not an ideal material for optical dating because of insufficient or and uneven exposure to daylight prior to burial the equivalent doses for a sample obtained using the single aliquot regenerative dose method usually show a large scatter which may be attributed to many factors here we developed a technique to evaluate the contributions from each factor using this technique relatively well bleached aliquots were identified and the average of their equivalent doses was taken for age calculation

timing of late quaternary glaciations south of mount everest in the khumbu himal nepal moraines south of mount everest in the khumbu himal were dated using optically stimulated luminescence clustering of ages and morphostratigraphy allowed three advances to be dated 1 the periche glacial stage ca 18 25 ka 2 the chhukung glacial stage ca 10 ka and 3 the lobuche stage ca 1 2 ka the periche stage is coincident with oxygen isotope stage 2 the chhukung stage represents a late glacial or early holocene glacial advance and the lobuche stage is a late holocene glacial advance that predates the little ice age

luminescence dating and its application to key pre late devensian sites in scotland abstract relatively few sites have been identified in scotland that contain records that predate the peak of the late devensian glaciation ca 18 ka bp where such records have been identified they have assumed a key role in developing our understanding of climate change in scotland radiocarbon dating has been the primary chronological tool applied to these sites but the reliability of age determinations in excess of 30 ka is questionable in this paper we describe the results of a programme which applies luminescence dating methods to eight key pre late devensian sites in scotland methods were developed and tested to enable the identification of samples for which luminescence dating was only able to provide an upper limit on the age because of the limited light exposure that the sample experienced at deposition these new approaches were applied to four sites where independent age control was available this meant that the choice of sediments from test sites was restricted to those sediments which were formed in the last 40 000 years and hence were amenable to radiocarbon dating the luminescence age estimates for the control sites and the pre late devensian sites are discussed within the context of any existing chronological control on a site by site basis

equatorial ionospheric zonal drift by monitoring local gps reference networks 1 the propagation of electromagnetic waves through the turbulent ionosphere produces scintillations through diffraction and understanding the physical nature of scintillations is important for engineers and technologists as well as for scientists in recent years the establishment of the global positioning system gps provided a new technique that can be used to study ionospheric scintillations the usual way of doing that is the deployment of gps receivers closely spaced in east west magnetic direction and then estimating the zonal drift velocities based on the signal power observations one of the weaknesses of this method is that high rate sampling such as 20 hz is required for close spaced stations and generally no such data are available for studying ionospheric scintillation in the past years in this research work a scintillation monitoring method based on slant tec stec observations of local gps continuously operating reference station cors network is proposed first the past research works on the equatorial ionospheric drift velocities are summarized then by comparing the scintillation pattern of the signal power and stec observations of california local gps reference network we find that the stec is a good choice for estimating the ionospheric zonal drift velocity then it is illustrated how to calculate the ionospheric scintillation velocity based on stec finally the proposed method is applied to hong kong gps reference network and several cases of the calculated ionospheric zonal velocities are given

relic permafrost structures in the gobi of mongolia age and significance relict permafrost structures ice wedge casts and cryoturbation structures are present in the gobi of southern mongolia luminescence dates of sediments are presented to constrain the age of formation of permafrost structures these data show that there was a phase of permafrost development during the latter part of the last glacial after about 22 to 15 ka that resulted in cryoturbated sediments and ice wedge casts furthermore permafrost degradation occurred during late pleistocene times 13 10 ka and was absent during the early holocene these permafrost structures mark the southernmost evidence of permafrost in northern asia during late quaternary times and indicate that the mean annual air temperature was below approximately 6 c during their formation 1998 john wiley sons ltd

timing of formation of forebergs in the northeastern gobi altai mongolia implications for estimating mountain uplift rates and earthquake recurrence intervals bedrock and quaternary alluvial fans in the forelands of the northern gobi altai have been faulted and warped by foreland propagating thrust faults to form elongate hills known as forebergs forebergs near bogd town north of arsta bogd and at ih hetsuu north of baga bogd were mapped and their formation constrained using luminescence dating of lacustrine and fanglomerates sediments to give localized uplift rates of c 0 05 m ka 1 and between c 1 6 and 4 1 m ka 1 respectively comparisons between vertical surface rupture during the 1957 gobi altai earthquake with the age and amount of uplift of lacustrine sediments provide a tentative estimate of between 1288 382 to 497 120 years for the average recurrence interval of great earthquakes in the baga bogd region these localized uplifts rates support the view that the gobi altai mountains probably took between 50 and 25 million years to form and were therefore coeval with the uplift of the himalayas and the tibetan plateau

explicit characteristics of evolutionary type plasma bubbles observed from equatorial atmosphere radar during the low to moderate solar activity years 2010 2012 using the fan sector backscatter maps of 47 mhz equatorial atmosphere radar ear at kototabang 0 2 s geographic latitude 100 3 e geographic longitude and 10 4 s geomagnetic latitude indonesia the spatial and temporal evolution of equatorial plasma bubbles epbs were examined to classify the evolutionary type epbs from those which formed elsewhere and drifted into the field of view of radar a total of 535 epbs were observed during the low to moderate solar activity years 2010 2012 out of which about 210 39 are of evolving type and the remaining 325 61 are drifting in epbs in general both the evolving type and drifting in epbs exhibit predominance during the postsunset hours of equinoxes and december solstices interestingly a large number of epbs were found to develop even a few minutes prior to the apex sunset during equinoxes further the occurrence of evolving type epbs exhibits a clear secondary peak around midnight 2300 0100 lt primarily due to higher rate of occurrence during the postmidnight hours of june solstices a significant number 33 of postmidnight epbs generated during june solstices did not exhibited any clear zonal drift while about 14 of epbs drifted westward also the westward drifting epbs are confined only to june solstices the responsible mechanisms for the genesis of fresh epbs during postmidnight hours were discussed in light of equatorward meridional winds in the presence of weak westward electric fields

geochronology and geomorphology of the jones point glacial landform in lower hudson valley new york insight into deglaciation processes since the last glacial maximum abstract the glacial deposits at jones point located on the western side of the lower hudson river new york were investigated with geologic geophysical remote sensing and optically stimulated luminescence osl dating methods to build an interpretation of landform origin formation and timing osl dates on eight samples of quartz sand seven single aliquot and one single grain of quartz yield an age range of 14 27 ka for the proglacial and glaciofluvial deposits at jones point optical age results suggest that jones point deposits largely predate the glacial lake albany drainage erosional flood episode in the hudson river valley ca 15 13 ka based on this data we conclude that this major erosional event mostly removed valley fill deposits leaving elevated terraces during deglaciation at the end of the last glacial maximum lgm our analysis supports the earlier 15 ka date for the flood occurrence and suggests that more recent overlying glaciofluvial deposits formed in the lee side of the jones point promontory

relationship of the onset of equatorial f region irregularities with the sunset terminator observed with the equatorial atmosphere radar 1 the relationship between sunset terminators and the onset of radar backscatter plumes associated with equatorial spread f esf observed with the 47 mhz equatorial atmosphere radar from october 2002 to april 2004 is discussed almost all irregularity echoes began to appear at or before sunset time at the altitude of the apex of the geomagnetic field line connected with the observed area and the onset time of more than half of the events corresponded exactly to apex sunset time this tendency should be due to two causes 1 the rapid change of the evening zonal electric field and 2 damping of 3 m scale irregularities by the solar radiation before the apex sunset

on the generation and growth of equatorial backscatter plumes 1 wave structure in the bottomside f layer we examine the initial conditions that lead to backscatter plume development in the equatorial f region ionosphere by analyzing altair radar data we obtained the following principal results 1 prior to plume development an altitude modulation of electron density contours exists in the bottomside f layer these quasi periodic variations were mapped spatially over a 1200 km east west distance by using incoherent scatter measurements and found to consist of three cycles with an average spatial wavelength of 400 km 2 the wave structure observed in the bottomside electron density contours grew in amplitude at a rate consistent with that predicted by the generalized gradient drift instability 3 bottomside backscatter developed on the west walls of all three altitude modulated regions followed by plume development from near the crests of these regions

quartz as a natural luminescence dosimeter abstract luminescence from quartz is commonly used in retrospective dosimetry in particular for the dating of archaeological materials and sediments from the quaternary period the phenomenon of luminescence is related to the interaction of natural radiation with mineral grains by the activation of and subsequent trapping of electrons at defects within the quartz lattice the latent luminescence signal i e the trapped electrons is released when the grains are exposed to stimulation energy in the form of light or heat despite the fact that quartz is most nominally pure sio2 the mineral forms in several different geological settings i e under different pressure and temperature conditions the luminescence emitted from quartz is complex and shows a variety of different components with diverse physical properties this complexity is explained by the variety of defects in quartz that are either intrinsic e g si and o vacancies or related to impurity atoms e g al or ti the concentration of impurity related defects is dependent on the conditions of mineral formation or subsequent alteration experimental data have shown that the luminescence properties of quartz are highly variable with geological source and vary even at a grain to grain level within a sediment as a consequence caution is needed when making any general statements about the luminescence properties of quartz when using luminescence measurements as a dating technique it is necessary to adjust the measurement procedures for each geological provenance furthermore some quartz has luminescence properties that make it problematic or even unsuitable for certain applications these problems can arise from low and changing luminescence sensitivity thermal transfer of trapped electrons thermal instability of the trapped electrons and low saturation dose reviewing the present knowledge reveals that insufficient information is available either to unambiguously link distinctive lattice defects with characteristic luminescence components or even to explain problems observed in application studies by potential dynamics of the defects within the crystal this paper gives some ideas on how future research could utilise innovative analytical tools to identify or map the distribution of lattice defects and how practitioners could relate lattice defects to measured luminescence properties of quartz

can glacial shearing of sediment reset the signal used for luminescence dating abstract understanding the geomorphology left by waxing and waning of former glaciers and ice sheets during the late quaternary has been the focus of much research this has been hampered by the difficulty in dating such features luminescence has the potential to be applied to glacial sediments but requires signal resetting prior to burial in order to provide accurate ages this paper explores the possibility that rather than relying on light to reset the luminescence signal glacial processes underneath ice might cause resetting experiments were conducted on a ring shear machine set up to replicate subglacial conditions and simulate the shearing that can occur within subglacial sediments luminescence measurement at the single grain level indicates that a number albeit small of zero dosed grains were produced and that these increased in abundance with distance travelled within the shearing zone observed changes in grain shape characteristics with increasing shear distance indicate the presence of localised high pressure grain to grain stresses caused by grain bridges this appears to explain why some grains became zeroed whilst others retained their palaeodose based on the observed experimental trend it is thought that localised grain stress is a viable luminescence resetting mechanism as such relatively short shearing distances might be sufficient to reset a small proportion of the luminescence signal within subglacial sediments dating of previously avoided subglacial sediments may therefore be possible

luminescence dating of glaciofluvial deposits a review abstract for glacigenic sediments optically stimulated luminescence osl dating offers an opportunity to date the time of deposition of quartz and feldspar minerals that are ubiquitous within the sediment matrix rather than relying upon the chance occurrence of organic material for radiocarbon dating the osl dating signal or charge accumulates in crystal defects of individual quartz and feldspar minerals through exposure to environmental radiation within their depositional setting the osl signal within individual grains can be reset or bleached through exposure to daylight during transportation processes thus osl dating of sediments attempts to determine the time elapsed since burial glacigenic sediments present considerable challenges for osl dating not only in terms of poor bleaching of the osl signal during the transport and deposition cycle but also poor quartz luminescence characteristics which are often related to sediment provenance the nature of the bedrock or source material and the freshly eroded nature of many such deposits this paper reviews luminescence dating techniques as applied to glaciofluvial sediments and explores the challenges that such deposits present to the technique successful application of osl techniques can be judged in a number of ways comparison with the independent chronologies is prevalent in the literature but recently the movement towards measurement of large numbers of small aliquots and single grains allows a more robust assessment of luminescence properties and behaviour for individual samples and ultimately more precise luminescence ages to be determined for glaciofluvial sediments in particular it is important to investigate the depositional sub environment of each sample in relation to the chance of sufficient bleaching during transport and deposition a lithofacies based approach to sampling for optically stimulated luminescence dating of these sediments is suggested whereby hypothetically well bleached deposits are targeted after a detailed investigation into possible environments of deposition this approach together with small aliquot single grain analysis methodologies should further enhance the likelihood of obtaining a sufficiently bleached sample for osl dating

towards successful osl sampling strategies in glacial environments deciphering the influence of depositional processes on bleaching of modern glacial sediments from jostedalen southern norway the optically stimulated luminescence osl signals of quartz and k feldspar are known to bleach poorly within some glacial settings and can present a major challenge to dating applications however because the osl signal is extremely sensitive to sunlight exposure history the residual luminescence signals of modern glacial sediments also encode information about transport and depositional processes through examination of the residual luminescence properties equivalent dose de and overdispersion values of a suite of modern glacial sediments from different depositional settings sandar proglacial delta and main meltwater channel this study provides insights not only into which sediments are likely to be fully bleached within glacial settings but also into how osl can be used to trace different depositional processes across sedimentary landforms improved understanding of the processes of sediment bleaching will enable better sample selection and may improve the accuracy and precision of osl dating of glacial sediments the luminescence signals of both coarse grained quartz and k feldspar with similar sediment sources are found to be sensitive to both depositional process and specific depositional setting whereas modern braid bar head deposits from the nigardsdalen ice proximal proglacial delta typically have ages of 3 ka similar depositional features from the fabergstolsgrandane sandur have residual ages of 26 ka exploration of changing residual luminescence signals across individual sandur and proglacial delta braid bar features shows that braid bar head deposits can retain large residual d e values while the partner braid bar tail deposits are almost completely bleached the quartz osl signal and k feldspar irsl50 and post ir irsl250 signals are shown to bleach at the same rate across the same bar feature and the irsl50 k feldspar signal is also shown to be completely bleached for bar tail deposits in nigardsdalen therefore the irsl50 k feldspar signal is suitable for dating some glacial deposits circumventing the challenges associated with dim quartz signals 2014 the authors published by elsevier ltd this is an open access article under the cc by license

spread f and the structure of equatorial ionization depletions in the southern anomaly region combined optical and radio sensors provide a unique characterization of the structure of equatorial emission depletion regions connected to rising bubbles over the magnetic equator in chile as part of the miseta campaign in fall 1994 a ccd enhanced all sky imaging photometer provided optical images of the postsunset appearance and motions of the depletion bands at a magnetic dip latitude of 11 s concurrently a digisonde collocated with the photometer monitored the appearance of spread f in between the ionograms the sounder operated as a doppler interferometer identifying the locations of f layer irregularities associated with the spread f they were found to lie inside the emission depletion regions the hf sounder requiring orthogonality with the field aligned f layer irregularities to generate the spread structure tracked these irregularities inside the emission depletion bands as they drifted eastward ray tracing simulations show that the radio waves become trapped within the depletion regions when the depletions are within 300 km of the sounder site model calculations indicate that the sounder rays encounter orthogonality with the earth s magnetic field within the depletion bubble southward from the site consistent with the local dip angle the combination of optical images with hf radio sounding demonstrated that radio imaging in the equatorial ionosphere can be done with a digital ionosonde that operates as a doppler interferometer the digisonde measurements and ray tracing show for the first time that the spread f signatures on ionograms are the result of coherent scatter from irregularities primarily within the walls of the depletion

luminescence chronology of late quaternary moraines and last glacial maximum equilibrium line altitude reconstruction from parlung zangbo valley south eastern tibetan plateau optically stimulated luminescence dating was applied to samples from glacial sediments in the parlung zangbo valleys daba and charao of the south eastern tibetan plateau to better constrain the timing of late quaternary glaciation which is thought to have been linked to the indian monsoon the single aliquot regenerative dose protocol on quartz was used for equivalent dose d e determination using small aliquots for samples from the daba valley the comparison of ages using two grain size fractions middle 38 63 mu m and coarse 90 250 mu m were conducted the coarse grain ages in the daba valley p3 and charao valley p7 range from 16 4 to 26 0 ka and are consistent with previously published cosmogenic radionuclide exposure ages in the baiyu valley pb1 our dating results reveal that these moraines were formed during the last glacial maximum lgm we then reconstruct the past equilibrium line altitudes elas during the lgm for five glacial valleys in the study area which range from 3286 to 4014 m with an average value of 3730 m while the contemporary average ela is 4655 m after correction for terrain uplift about 8 m since the lgm the difference in the ela values between the lgm and today is 917 m according to these data the estimated temperature during the lgm is 6 3 degrees c lower than present for the parlung zangbo river valley copyright c 2014 john wiley sons ltd

characteristics of large scale wave structure observed from african and southeast asian longitudinal sectors the spatial large scale wave structure lsws at the base of f layer is the earliest manifestation of seed perturbation for rayleigh taylor instability hence found to play a deterministic role in the development of equatorial plasma bubbles epbs except for a few case studies a comprehensive investigation has not been conducted on the characteristics of lsws because of the complexity involved in detecting the lsws particularly in spatial domain in this scenario a comprehensive study is carried out for the first time on the spatial and temporal characteristics of lsws observed in spatial domain over african and southeast asian longitudinal sectors during the year 2011 the observations indicate that these wave structures can be detected a few degrees west of e region sunset terminator and found to grow significantly at longitudes past the sunset terminator the phase fronts of these spatial structures are found to align with the geomagnetic field b lines over a latitudinal belt for at least 5 6 500 600 km centered on dip equator the zonal wavelengths of these structures are found to vary from 100 to 700 km which is consistent with the earlier reports and the epbs were consistently observed when the amplitudes of lsws were grown to sufficient strengths these results would provide better insights on the underlying physical processes involved in excitation of lsws in terms of important roles being played by e region electrical loading and polarization electric fields induced via spatially varying dynamo current due to neutral wind perturbations associated with atmospheric gravity waves

the condor equatorial spread f campaign overview and results of the large scale measurements during the condor campaign a number of instruments were set up in peru to support the rocket experiments in this series of papers we report on the results of the experiments designed to study the equatorial f region in this overview paper we summarize the main results as well as report upon the macroscopic developments of spread f as evidenced by data from backscatter radas from scintillation observations and from digital ionosonde meaurements in this latter regard we argue here that at least two factors other than the classical gravitational rayleigh taylor plasma instability process must operate to yield the longest scale horizontal organization of spread f structures the horizontal scale typical of plume separation distances can be explained by invoking the effect of a shear in the plasma flow although detailed comparison with theory seems to require shear frequencies a bit higher than observa tions indicate on the other hand the largest scale organization or modulation of the scattering layer cannot be explained by the shear theory and must be due to local time variations in the ionospheric drift or to gravity wave induced vertical motions using simultaneous rocket and radar data we were also able to confirm the oft quoted hypothesis that rapid overhead height variations in the scattering region over jicamarca are primarily spatial structures advecting overhead the detailed rocket radar compari son verified several other earlier results and speculations particularly those made in the plumex experiments in particular companion papers discuss and extend some of the plumex results to include the role of anomalous diffusion labelle et al this issue in the theory of equatorial spread f and to shed light upon the shallow spectral form often observed in the intermediate scale regime labelle and kelley this issue

global distribution of density irregularities in the equatorial ionosphere we analyzed measurements of ion number density made by the retarding potential analyzer aboard the atmosphere explorer e ae e satellite which was in an approximately circular orbit at an altitude near 300 km in 1977 and later at an altitude near 400 km large scale 60 km density measurements in the high altitude regions show large depletions of bubble like structures which are confined to narrow local time longitude and magnetic latitude ranges while those in the low altitude regions show relatively small depletions which are broadly distributed in space for this reason we considered the altitude regions below 300 km and above 350 km and investigated the global distribution of irregularities using the rms deviation n n over a path length of 18 km as an indicator of overall irregularity intensity seasonal variations of irregularity occurrence probability are significant in the pacific regions while the occurrence probability is always high in the atlantic african regions and is always low in the indian regions we find that the high occurrence probability in the pacific regions is associated with isolated bubble structures while that near 0 longitude is produced by large depletions with bubble structures which are superimposed on a large scale wave like background considerations of longitude variations due to seeding mechanisms and due to f region winds and drifts are necessary to adequately explain the observations at low and high altitudes seeding effects are most obvious near 0 longitude while the most easily observed effect of the f region is the suppression of irregularity growth by interhemispheric neutral winds

longitudinal variability of annual changes in activity of equatorial spread f and plasma bubbles global distribution maps of equatorial spread f esf activity for various annual periods were derived from the topside soundings by the ionosphere sounding satellite b iss b in 1978 1980 the esf activity during the northern winter period reveals maximum enhancement at the atlantic longitudes of large westward geomagnetic declination and during the northern summer at the pacific longitudes of large eastward declination on several orbits passing over the region of the esf activity enhancement abrupt depletions of the electron density or equatorial plasma bubbles were observed at the satellite altitude of about 1100 km it has also been found that the background electron density distributions tend to be symmetric with respect to the magnetic equator in the region of the enhanced esf activity and asymmetric in the region of the suppressed esf activity these observations are taken account of by the influence of a transequatorial thermospheric wind upon the suppression of the rayleigh taylor type plasma instability

scilly isles uk optical dating of a possible tsunami deposit from the 1755 lisbon earthquake abstract we present the results of optical dating of quartz from marine and aeolian deposits on st agnes island scilly isles uk the single aliquot regenerative dose protocol was used to estimate the equivalent dose in these samples proposed tsunami laid deposits at big pool provided ages of 230 40 and 380 60 years both are consistent with an expected age of 244 years an osl age of 6 3 years was obtained on a modern sub aqueous beach deposit these results suggest that the osl signal in the tsunami laid quartz was completely reset before deposition and that these sediments can be dated accurately by optical dating techniques sand dunes at bergecooth 250 m south of big pool were also dated using osl these ages indicate phases of aeolian activity at 300 a and 1000 a in the scilly isles

effects of the vertical plasma drift velocity on the generation and evolution of equatorial spread f we use radar observations from the jicamarca observatory from 1968 to 1992 to study the effects of the f region vertical plasma drift velocity on the generation and evolution of equatorial spread f the dependence of these irregularities on season solar cycle and magnetic activity can be explained as resulting from the corresponding effects on the evening and nighttime vertical drifts in the early night sector the bottomside of the f layer is almost always unstable the evolution of the unstable layer is controlled by the history of the vertical drift velocity when the drift velocities are large enough the necessary seeding mechanisms for the generation of strong spread f always appear to be present the threshold drift velocity for the generation of strong early night irregularities increases linearly with solar flux the geomagnetic control on the generation of spread f is season solar cycle and longitude dependent these effects can be explained by the response of the equatorial vertical drift velocities to magnetospheric and ionospheric disturbance dynamo electric fields the occurrence of early night spread f decreases significantly during equinox solar maximum magnetically disturbed conditions due to disturbance dynamo electric fields which decrease the upward drift velocities near sunset the generation of late night spread f requires the reversal of the vertical velocity from downward to upward for periods longer than about half an hour these irregularities occur most often at 0400 local time when the prompt penetration and disturbance dynamo vertical drifts have largest amplitudes the occurrence of late night spread f is highest near solar minimum and decreases with increasing solar activity probably due to the large increase of the nighttime downward drifts with increasing solar flux

a statistical analysis of equatorial plasma bubble structures based on an all sky airglow imager network in china this paper investigates the statistical features of equatorial plasma bubbles epbs using airglow images from 2012 to 2014 from a ground based network of four imagers in the equatorial region of china it is found that 1 epbs mainly occur during 21 00 00 00 local time lt in equinoxes there is an asymmetry in occurrence rates between march june and september equinoxes december solstices 2 most epbs occur in groups of two to six depletions the distance between adjacent epb depletions is 100 700 km and the average is 200 300 km the zonal extension of an epb group is usually less than 1500 km but can reach 3000 km 3 epbs usually have a maximum drift velocity near 100 m s at 21 00 22 00 lt in 9 5 1 5 geomagnetic latitude and then decrease to 50 70 m s toward sunrise 4 the averaged westward tilt angle of most epbs with respect to the geographic north south increased from 5 10 to 23 30 with lt between 20 00 and 03 00 lt then decreasing to 10 20 toward sunrise 5 when 90 140 the maximum pmle increases by 3 4 5 5 when f10 7 changes from 90 to 190 6 the epb occurrence patterns and zonal drift velocities are significantly different from those at kolhapur india which locates west to our stations by 20 0 32 0 in longitude

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

optical dating using inclusions within quartz grains a sequence of stranded beach dunes in the southeast of south australia which resulted from the advance and retreat of the sea over a tectonically rising land surface during the past 800 ka has been securely dated by geological means and successfully used to test thermoluminescence dating based on quartz we have now obtained a series of promising results from the same sequence with a test of optical dating on inclusions within the quartz grains the innovative aspect of the measurements is the use of infrared irradiation to stimulate emission from the inclusions rather than conventional stimulation of the quartz itself by light of shorter wavelength satisfactory ages were found for seven dunes covering the time span 0 400 ka

optically stimulated luminescence dating of the city wall system of ancient tayma nw saudi arabia abstract in addition to a series of chronological markers artefacts pottery in the archaeological contexts of ancient tayma nw saudi arabia optically stimulated luminescence osl and radiocarbon dating techniques were applied to generate reliable ages for the city wall system of the oasis a massive aeolian sand deposit burying the oldest part of the outer wall of tayma was sampled to obtain a minimum age for the construction of this wall the sequence of osl ages from the inactive dune id 4900 300 a 5100 400 a 4400 300 a 3900 200 a 4000 200 a is in full accordance with 14 c ams ages of charcoal embedded into the same dune 4190 4420 cal bp 3870 4080 cal bp underlying alluvial samples from the inactive gravel sheet igs in contrast give maximum ages for the construction which scatter between 6600 300 a and 4900 400 a the new dating sequence provides evidence that the oldest part of the ancient city wall system already existed in the 2nd half of the 3rd mill bc which is earlier than expected thus far from archaeological and architectural interpretation

optically stimulated luminescence dating of young sediments a review optically stimulated luminescence osl dating of young 1000 years sediments is used increasingly in a wide variety of late holocene studies as a mean of establishing contemporary sedimentation rates or the timing of sediment deposition this paper provides a summary of the basic principles of osl dating outlines the problems specific to the dating of young material and then uses recent applications to young sediments to illustrate the greatly increased scope and potential of the method in geomorphology and the geology of recent deposits the overall reliability of this new generation of osl ages is examined by comparing where possible osl ages with independent age control it is concluded that the osl ages are accurate in that there is no evidence for systematic over or under estimation it is our conclusion that osl dating should be regarded as a reliable chronological tool for determining the time of deposition of water lain sediments from the coastal zone and aeolian deposits from both coastal and inland environments our conclusion is supported by the growing popularity of osl dating in geomorphology and geology

the potential of using thermoluminescence to date buried soils developed on colluvial and fluvial sediments from utah and colorado u s a preliminary results the natural tl intensity for surface and buried holocene and pleistocene a horizons developed on flood plain silts near denver colorado exponentially decreases with time this signal is approaching saturation by ca 130 ka the a horizon of the modern flood plain soil is not fully light bleached the tl properties and age estimates are presented for radiocarbon dated eolian enriched buried a horizons developed on fault derived colluvium from the american fork segment of the wasatch fault zone utah dating of these buried soils provide a close age estimate on paleoearthquake events mean tl age estimates by regeneration and total bleach techniques for buried a horizons are 0 5 0 1 ka and 2 7 0 4 ka which are in agreement with corresponding radiocarbon dates of 980 70 years bp and 2620 70 years bp a surface sag pond mud formed within an antithetic grabben is well light bleached and yielded a tl age estimate by the total bleach method of 240 60 years bp in agreement with its known age of 300 years bp this study indicates that relatively brief periods of pedogenesis are not sufficient to light bleach sediment and that eolian additions enhance the reduction of tl in soils

unravelling the evolution of an alpine to post glacially active fault in the swiss alps abstract the gemmi fault is a prominent nw se striking lineament that crosses the gemmi pass in the central swiss alps a multidisciplinary investigation of this structure that included geological mapping joint profiling cathodoluminescence and scanning electron microscopy stable isotope measurements luminescence and u th dating 3d ground penetrating radar gpr surveying and trenching reveals a history of fault movements from the miocene to the holocene the main fault zone comprises a 0 5 3 m thick calcite cataclasite formed during several cycles of veining and brittle deformation displaced cretaceous rock layers show an apparent dextral slip of 10 m along the fault a detailed study of a small sediment filled depression that crosses the fault provides evidence for a post glacial reactivation of the fault a trench excavated across the fault exposed a late glacial age loess layer and late holocene colluvial like slope wash deposits that showed evidence for fault displacement of a few centimeters indicating a recent strike slip reactivation of the fault focal mechanisms of recent instrumentally recorded earthquakes are consistent with our findings that show that the fault at the gemmi pass together with other parallel faults in this area may be reactivated in today s stress field taking together all the observations of its ancient and recent activity the gemmi fault can be viewed as a window through geological space and time

an overview of the early november 1993 geomagnetic storm this paper describes the development of a major space storm during november 2 11 1993 we discuss the history of the contributing high speed stream the powerful combination of solar wind transients and a corotating interaction region which initiated the storm the high speed flow which prolonged the storm and the near earth manifestations of the storm the 8 day storm period was unusually long the result of a high speed stream maximum speed 800 km s emanating from a distended coronal hole storm onset was accompanied by a compression of the entire dayside magnetopause to within geosynchronous earth orbit geo for nearly 12 hours the near earth environment was in a state of tumult a super dense plasma sheet was observed at geo and severe spacecraft charging was reported the effects of electrons precipitating into the atmosphere penetrated into the stratosphere subauroral electron content varied by 100 and f layer heights oscillated by 200 km equatorial plasma irregularities extended in plumes to heights of 1400 km later energetic particle fluxes at geo recovered and rose by more than an order of magnitude a satellite anomaly was reported during the interval of high energetic electron flux model results indicate an upper atmospheric temperature increase of 200 k within 24 hours of storm onset joule heating for the first 24 hours of the storm was more than 3 times that for typical active geomagnetic conditions we estimate that total global ionospheric heating for the full storm interval was 190 pj with 30 of that generated within 24 hours of storm onset

asynchronous glaciation at nanga parbat northwestern himalaya mountains pakistan comment we welcome phillips et al s 2000 1 study which substantiates previous evidence for glaciation during global interstadials in the himalaya sharma and owen 1996 2 richards et al 2000 3 we were surprised however to read their criticism of the optically stimulated luminescence osl

scintillations plasma drifts and neutral winds in the equatorial ionosphere after sunset an equatorial campaign was conducted during september 25 to october 7 1994 to investigate the neutral and plasma dynamics in the equatorial ionosphere after sunset in relation to the day to day variability of the occurrence of equatorial spread f esf the campaign was organized under the auspices of national science foundation s multi instrumented studies of the equatorial thermosphere aeronomy program miseta which included the jicamarca radar spaced antenna satellite scintillation digisonde all sky imager and fabry perot interferometer fpi measurements near the magnetic equator in peru during a part of the period september 27 to october 3 the geophysics directorate of phillips laboratory performed measurements away from the magnetic equator at aguaverde chile magnetic latitude 11 s located 800 km to the east of the jicamarca meridian using geostationary and gps satellite scintillation digisonde and all sky imager systems the incoherent scatter radar results indicate that the postsunset enhancement of upward plasma drift even though of the order of only 20 m s 1 during the solar minimum period is a necessary condition for the generation of esf in view of the extreme difficulty of determining the neutral wind speed during the early evening hours by the fpi due to low airglow intensity it was not possible to unequivocally associate the observed postsunset enhancements with strong eastward neutral winds however considering a few observations contiguous to the campaign period it appears that such a causal relationship may exist the scintillation drift measurements in peru and chile indicated that the zonal irregularity drift was smaller away from the magnetic equator implying a variation of neutral wind with latitude this is reproduced in the altitude variation of zonal drift observed by the jicamarca radar during a magnetic storm scintillation measurements indicated that eastward drifts near the magnetic equator are accompanied by westward drifts near the anomaly peak which is consistent with the effects of a disturbance dynamo the campaign results indicate that in order to resolve the variability of esf a careful probing of neutral dynamics as a function of latitude needs to be undertaken during the postsunset period

reconstruction of holocene glacier history from distal sources glaciofluvial stream bank mires and a glaciolacustrine sediment core near sota saeter breheimen southern norway this study attempts to reconstruct the holocene glacier history of breheimen southern norway from four stream bank mire sites and a downstream lake sediment core near sota saeter based on lithostr

an equatorial bubble its evolution observed in relation to bottomside spread f and to the appleton anomaly this is a case study that undertakes the first comprehensive description of the concurrent evolutions of an isolated equatorial bubble bottomside spread f bssf and the enhanced appleton anomaly a principal focus is the dynamics of the intersection of the bubble with the anomaly crest which is the source of maximum scintillation on transionospheric rf propagation conditions are equinox at solar maximum measurements were by an array of eight ionospheric sounders in the western hemisphere with a collective field of view extending along the dip equator for about 1600 km and to 40 north dip latitude that resolved rapid changes in the phenomena yet encompassed their extent and duration viewed locally the bubble was triggered by an upwelling of the bottomside f layer during e b upward drift that accelerated upward for 15 20 min before the onset of irregularities seen as range spread f rsf viewed macroscopically this onset was part of continuous front of rsf onset that coincided with e b reversal and moved westward at the velocity of the terminator so as to remain at 1920 lt to the east of the bubble as bssf within the bubble during the upwelling of the bottomside crest at the west wall of the bubble at the onset of its eastward drift and west of the bubble as bssf the bubble drifted eastward at 185 m s and rose upward at 190 m s intersecting the maximum of the anomaly crest at 2100 lt 95 min after bubble onset during this entire period the bubble was in continuous contact with the anomaly profile which was simultaneously increasing but as a function of lt thus the intersection was a function of the upward and eastward velocities of the bubble and the westward motion of the anomaly at the velocity of the terminator the time and place of the intersection is thus dependent on the entire sequence of events and on the differing dependences on ut and lt and since each can vary the time and place of maximum scintillation is highly variable in light of this variability observations at least as comprehensive as those reported here appear to be necessary to describe the region adequately and therefore to study it further

methodological considerations in the optical dating of quartz abstract the optically stimulated luminescence from quartz grains extracted from sediments at two archaeological sites has been studied the sites were the upper palaeolithic site at hengistbury head dorset u k and the upper aterian site at chaperon rouge morocco problems associated with the technique of optical dating are discussed particularly the thermal treatment that is necessary to remove thermally unstable charge following artificial irradiation and the extrapolation of growth curves to estimate the equivalent dose the technique used is described and some preliminary dates are presented

time evolution and dynamics of equatorial backscatter plumes 1 growth phase much of our understanding of equatorial spread f phenomena has resulted from vhf radar studies of backscatter plumes i e patterns of backscatter that appear to extend from the bottomside into the topside of the f layer by using altair a fully steerable backscatter radar to map selected plumes repeatedly it was found that the dynamic behavior of plumes can be characterized by a growth and a decay phase the growth phase characteristics described in this paper are found to be generally consistent with equatorial irregularity generation as predicted by the rayleigh taylor and gradient drift instabilities in particular 1 plumes are generated primarily in the local time around f layer sunset 2 plumes develop from local perturbations in plasma density in the bottomside of the f layer 3 plumes develop upward with growth velocities ranging from 125 to 350 m s and 4 backscatter strength increases during upward plume development and decreases when upward plume growth slows or ceases however certain characteristics namely an east west asymmetry in backscatter strength found in the bottomside f layer have been found that suggest key roles played by the eastward neutral wind and by altitude modulation of the bottomside f layer in establishing the initial conditions for plume growth

optical dating of sediments a new method for dating sediments is proposed which determines the time since the sediment was last exposed to sunlight an argon ion laser is used to excite electrons from thermally stable light sensitive traps and the subsequent luminescence used as a measure of the past radiation dose two sample sequences spanning the periods 0 700 kyr and 0 6 kyr show steadily increasing luminescence with age an age of 62 8 kyr is obtained for a silt radiocarbon dated at 58 8 0 3 kyr problems were found with two much younger samples

optical dating of young glacial sediments from the source area of the urumqi river in tianshan mountians northwestern china abstract incomplete bleaching which will lead to overestimation of age still remains one of the most significant problems in luminescence dating on glacial sediments in order to test the bleachability of luminescence signals of mountain glacial sediments nineteen young samples from different geomorphological positions and different sediment settings in the source area of the urumqi river in tianshan mountains a key area of quaternary glaciation study in china were collected and dated using optically stimulated luminescence osl dating methods equivalent dose d e was determined by quartz sar sgc procedures results show that most of the samples suffer from varying degrees of overestimation in general glaciofluvial and lateral moraine till samples show relatively low residual doses 0 20 5 gy while subglacial tills tills from terminal moraines ground moraines and hummocky moraines show higher residual doses 22 4 205 6 gy reworked loessic sediments exhibit surprisingly high residual doses 24 1 and 46 5 gy glaciofluvial and materials from lateral moraine upper part are recommended when sampling whereas those from subglacial tills terminal moraines ground moraines and hummocky moraines should be avoided