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

diatom responses to 20th century climate warming in lakes from the northern urals russia changes in diatom assemblages and spheroidal carbonaceous particle scp profiles during the last 200 years in 210pb dated sediment cores from five remote arctic and sub arctic lakes in the northern urals were analysed the study area covers a large territory from arctic tundra in the north to boreal forest on the western slopes of the ural mountains in the south ph was reconstructed using a diatom based model the degrees of compositional turn over and rates of change were estimated numerically the 20th century diatom floristic shifts the rise in diatom accumulation rates and the rates of diatom compositional change in the northern ural lakes correlate well with june temperature in the region and with the overall circum arctic temperature increase from the 1970s the main driving force behind diatom compositional shifts in the study lakes are the changes in the duration of ice free season timing of water turn over and stratification periods and habitat availability changes in spheroidal carbonaceous particles show no pronounced effect on diatom assemblages pollution is restricted to regional sources originating mainly from the vorkuta coal industry changes in diatom plankton are more pronounced than changes in diatom benthos there is no clear north south gradient in degree of compositional changes with greatest changes occurring in lake vankavad situated in northern boreal forest the degree of the 20th century diatom changes in lake vankavad is greater than in most circum arctic and sub arctic lakes from northern europe and canada

radar observations of a 3 day kelvin wave in the equatorial mesosphere mesospheric radars are used to investigate the characteristics of a kelvin wave from two equatorial sites jakarta indonesia in the western pacific and christmas island in the central pacific our study focuses on the time span from mid january through mid october 1993 a kelvin wave with a period near 3 days was detected throughout this 9 month duration although it underwent deep amplitude modulations on a 20 day timescale a fitting procedure is applied to study the phase amplitude behavior of the wave the vertical wavenumber was measured by the radars and found to be small wandering around zero with only a weak bias toward downward phase progression the long vertical wavelength suggests that the wave was predominantly zonal wavenumber 1 the amplitude of the wave measured by the jakarta meteor scatter radar was much larger than the amplitude measured by the mf partial reflection radar at christmas island the smaller wave amplitude at christmas island could at least partially be due to a measurement bias associated with mf radars the radar at jakarta is a vhf meteor scatter radar and is not susceptible to this bias however the mean velocities and the amplitudes of the tidal and quasi 2 day wave components were in good agreement at the two sites the estimated 9 month averaged zonal acceleration was 0 67 ms 1 day 1 over jakarta at 94 98 km and only about half as large over christmas island the magnitude of the zonal acceleration occasionally showed large enhancements which suggest the importance of refractive effects associated with vertical and temporal variations in the mean winds the larger 3 day wave amplitudes and inferred acceleration at jakarta may reflect its location in the western pacific a region of high convection and hence an excitation region for equatorial waves the relative phase of the wave between the two radar sites gradually shifted over a timescale of weeks these smooth variations in relative phase are suggestive of a superposition of waves with different zonal wavenumbers perhaps radiating preferentially from one longitude the phase of the wave as a function of altitude and time was much more disordered at jakarta than at christmas island the conjecture can be made that the more chaotic phase structure observed over jakarta is due to higher order zonal wavenumber components which weaken as they propagate eastward

remote sensing lower thermosphere wind profiles using non specular meteor echoes 1 this article describes a new method of measuring wind velocity profiles between 93 km and 110 km altitude by tracking non specular meteor echoes as neutral winds transport the plasma trails this requires a large vhf radar with interferometric capability able to point nearly perpendicular to the geomagnetic field a small data sample from the jicamarca radio observatory allows the measurement of horizontal wind speeds and directions with a range resolution of a few hundred meters these observations show speeds reaching 150 m s and sometimes changing by as much as 100 m s over a 6 km altitude range at the best times these measurements can be made with only a few minutes of data with some refinement of the data collection and analysis techniques this technique should produce high resolution images of lower thermospheric winds as they change in both altitude and time

vertical evolution of fluid venting structures in relation to gas flux in the neogene quaternary of the lower congo basin offshore angola abstract the processes preceding the genesis of pockmarks and their subsequent evolution has been rarely studied since pockmarks were discovered in 1970 a high resolution 3 d seismic survey from the continental slope of the lower congo basin allows us to study in detail the structures that developed before the formation of pockmarks as well as their subsequent geometric evolution this paper aims at reporting new type of fluid related structures that relate to pockmarks the objective of this research is to understand 1 the evolution of these structures and their genetic relationship with pockmarks and 2 how their morphologies may be influenced by changes in venting intensity over time pockmark and chimney structures in this survey are hosted within late miocene to quaternary hemipelagites above clastic reservoirs in a petroliferous basin they are all associated with positive high amplitude anomalies phaas on seismic data phaas are interpreted from their dramatically higher acoustic impedance relative to the background sedimentary values of the host units and by their association with seismic pull up effects from their planform and cross sectional geometry phaas are primarily interpreted as being due to the development of methane related carbonates but they may be associated with gas hydrates in one or two examples methanogenic carbonates form either by authigenic accumulation or by anaerobic methane oxidation amo once upwardly migrating methane enters the sulfate methane transition zone smtz typically within the first few tens of meters below the seabed therefore vertical accumulations of phaas are interpreted to reflect the temporal evolution of methane flux migrating upward to reach the paleo seabed or smtz timing of local scale fluid leakage can therefore be diagnosed by analyzing phaas at seep locations that occur in association with pockmark chimney structures a conceptual model for the evolution of different fluid venting structures is proposed here and is based on the analysis of venting structures that we expressed by 3 d seismic reflections in this model the main features are linked into a process based sequence culminating in the infill and termination of the pockmarks as fluid venting sites our model summarizes different rhythms of venting which are expressed by different types of phaas along with venting structures linear phaas and conduits inferred slow seeps they can be succeeded by sub circular phaas and shallow depressions which inferred slow to moderate seeps then the seep can become either a fast vent and terminated into a pockmark crater or it can become less active and be sealed afterwards subsurface sediment fluidizations and remobilizations are likely to happen in the last case and are probably caused by hydrate dissociations

an integrated view of the methane system in the pockmarks at vestnesa ridge 79 n accepted manuscript version published version available at https doi org 10 1016 j margeo 2017 06 006 accepted manuscript version licensed cc by nc nd 4 0

time gcm results for the quasi two day wave to understand how the quasi two day wave qtdw interacts with the mean flow and migrating tides we perturbed the lower boundary of the national center for atmospheric research thermosphere ionosphere mesosphere electrodynamics general circulation model time gcm to excite the qtdw results from our initial model runs computed for a perpetual january 15th show wave amplitudes in wind and temperature that are in qualitative agreement with previous model results and observations the wave period and amplitude change over the duration of the model run and it is expected that this results from changes in the zonal mean zonal winds evidence supporting nonlinear interactions between the qtdw and the migrating tides is presented

verification of large scale rapid transport in the lower thermosphere tracking the exhaust plume of sts 107 from launch to the antarctic 1 new analysis of the doppler shift of o2 airglow spectra recorded by the timed doppler interferometer tidi and the high resolution doppler imager hrdi have provided conclusive evidence that the shuttle main engine exhaust plume generated in the lower thermosphere by the launch of sts 107 and imaged by the global ultraviolet imager guvi instrument on timed was transported to the antarctic in 80 h supporting a key inference from the initial study by stevens et al 2005 these new results were aided by improved knowledge of the effects of instrumental and satellite artifacts imposed on the doppler spectra sts 107 launched on 16 january 2003 and the neutral wind near its launch trajectory and nearby volume was sampled within minutes by tidi these initial observations suggested that the northernmost end of the shuttle s exhaust plume would move northeast and that the southern end would move southeast motions that were identified in imagery acquired during the next orbit of timed the direction and magnitude of plume motion inferred from guvi images obtained 12 26 and 50 h after launch were again confirmed by tidi and hrdi the appearance of the plume over the antarctic 80 h after launch inferred from earlier work by the appearance of iron ablated from the shuttle s main engines was consistent with neutral winds measured by the satellite doppler instruments over the antarctic the transport of the plume from the coast of florida to the antarctic was aided by the favorable phase and strong amplitude of a 2 day planetary wave of wave number three in the southern hemisphere on 18 january 2003 the existence of the 2 day wave was deduced from zonally averaged and combined tidi and hrdi neutral wind observations we conclude that the existence of strong and sustained winds in the mlt significantly greater than expected from empirical and theoretical models is indisputable and provides compelling evidence supporting the global scale nature of thermospheric winds with magnitude greater than 100 m s observed by larsen 2002 from 40 years of sounding rocket chemical release experiments

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

temporal modulations of the longitudinal structure in f2 peak height in the equatorial ionosphere as observed by cosmic 1 this study investigates the temporal variability of longitudinal structure in f2 layer peak height hmf2 in the equatorial ionosphere for this study electron density profiles retrieved from the radio occultation measurements by the constellation observing system for meteorology ionosphere and climate cosmic are fitted with a two layer chapman function to determine hmf2 the hmf2 values in the magnetic equatorial region display a four peaked longitudinal structure that has been identified in other ionospheric observations the four peaked structure is likely the signature of the forcing by the eastward propagating nonmigrating diurnal tide with zonal wave number 3 de3 further analysis for the period of prominent four peaked structure over august september 2008 finds that this structure exhibits a 5 day periodicity coincidentally the all sky interferometric meteor radar s wind measurements at thumba 8 5 n 77 e in india for the mesosphere and lower thermosphere indicate strong 5 day planetary waves within that time period the observed temporal periodicity of the four peaked longitudinal structure in hmf2 could thus be attributed to the interaction of de3 with a 5 day planetary wave

climate changes lead pollution and soil erosion in south greenland over the past 700 years date of acceptance 05 06 2015 this research was made possible through funding provided by the leverhulme trust the spanish ministry of science and innovation project cgl2010 20672 and xunta de galicia grants r2014 001 and gpc2014 009 n silva sanchez is currently supported by a fpu pre doctoral grant ap2010 3264 funded by the spanish government kirsty golding andy mcmullen and ian simpson are thanked for their assistance with fieldwork alison sandison produced the maps pete langdon and two anonymous referees are thanked for comments that helped to improve the paper

quasi biennial variation of the 5 day wave in the stratosphere 1 interannual variability of the 5 day wave in the stratosphere is examined by the use of national center for environmental prediction reanalysis data quasi biennial variation of the 5 day wave amplitude is clearly seen in the stratosphere this quasi biennial variation is closely related to the zonal wind variation associated with the equatorial quasi biennial oscillation in the stratosphere we give a short description of the mechanism bringing about the relationship

five day mesospheric waves observed in solar mesosphere explorer ozone solar mesosphere explorer sme ozone data were analyzed for short term periodic oscillations in the altitude region from 50 to 90 km a 5 day oscillation was found to be a dominant feature at high southern latitudes near the december solstice in the altitude range from 50 to 80 km the wave feature appears to travel westward with a speed consistent with that of a wave number one planetary scale oscillation circling the globe in 5 days the amplitude also appears to be consistent with the temperature oscillations predicted by geisler and dickinson 1976 this oscillation was not found to be a dominant feature in sme ozone during northern hemisphere summer

an empirical model of the earth s horizontal wind fields hwm07 1 the new horizontal wind model hwm07 provides a statistical representation of the horizontal wind fields of the earth s atmosphere from the ground to the exosphere 0 500 km it represents over 50 years of satellite rocket and ground based wind measurements via a compact fortran 90 subroutine the computer model is a function of geographic location altitude day of the year solar local time and geomagnetic activity it includes representations of the zonal mean circulation stationary planetary waves migrating tides and the seasonal modulation thereof hwm07 is composed of two components a quiet time component for the background state described in this paper and a geomagnetic storm time component dwm07 described in a companion paper

observations of altitudinal and latitudinal e region neutral wind gradients near sunset at the magnetic equator sounding rocket chemical release measurements of the e region neutral wind profiles were carried out at the magnetic equator at dusk on two consecutive days in september 1994 when a strong prereversal enhancement of the f region vertical plasma drift was present wind profiles were obtained at the equator and 450 480 km further north the profiles show wind speeds of 80 100 m s 1 in the lower e region and reversals of the wind direction over vertical scales of 10 15 km on both days the wind direction in the lower e region changed consistently between the northern and equatorial releases with a strong southward wind evident at the northern position and a stronger eastward wind at the equator

upper stratospheric circulations in the two hemispheres observed by satellites a global analysis is made of upper stratospheric circulations with the aid of nimbus 5 and tiros n satellite observations in order to make a comparison of characteristics between the northern hemisphere nh and the southern hemisphere sh it is shown that the reversal of north south gradient of the zonal mean temperature at the stratopause level is always observed in higher latitudes of the sh winter while the temperature gradient of the nh winter is variable because of the occurrence of sudden warmings consequently due to the thermal wind relation the polar night westerlies of the sh stratosphere are generally stronger than those of the nh stratosphere in association with this difference the activity of transient planetary waves of wavenumber 2 is striking in the sh in contrast to the predominance of steady waves in the nh finally the interrelation between the zonal mean field and planetary waves in the upper stratosphere is briefly discussed

intense winds and shears in the equatorial lower thermosphere measured by high resolution nonspecular meteor radar large horizontal winds and wind shears have been measured in the lower thermosphere by rockets lidars and nonspecular meteor radars this paper describes a detailed analysis of three multihour nonspecular meteor radar data sets collected at the jicamarca radio observatory this provides some of the highest resolution sustained measurements in this part of the atmosphere these show 1 intense wind speeds maintaining 180 m s for half an hour and 160 m s for another half an hour 2 winds structured in layers that move up or more commonly down in the predawn hours at rates of a few kilometers per hour 3 intense wind shears that typically persist at around 50 m s km but in one instance sustains values approaching 100 m s km for a few hours

two dimensional turbulence space shuttle plume transport in the thermosphere and a possible relation to the great siberian impact event 1 during two solstices stevens et al 2003 2005 presented satellite and ground based observations that indicated that the water vapor plume from the space shuttle s main engine rapidly expanded and moved quickly to the summer pole once there the water vapor plume condensed into large noctilucent cloud displays here we present a hypothesis for the plume s rapid transport and anomalous horizontal diffusion we argue that this system is two dimensionally turbulent which has the property of inverse cascade this energy transport to large scales explains the poleward transport and the well known system properties explain the anomalous diffusion additionally we apply these results to the aftermath of the 1908 great siberian impact event when extremely bright night skies were observed in great britain during the days following the impact the impacting object must have contained considerable ice and thus was very likely a comet

september 2019 antarctic sudden stratospheric warming quasi 6 day wave burst and ionospheric effects an exceptionally strong stationary planetary wave with zonal wavenumber 1 led to a sudden stratospheric warming ssw in the southern hemisphere in september 2019 ionospheric data from esa s swarm

seasonal interannual and short term variability of planetary waves in met office stratospheric assimilated fields met office stratospheric assimilated data have been used to study the variability of travelling planetary waves in the upper stratosphere during the last decade 1992 2001 to distinguish the various travelling and quasi standing waves a new space time filtering method has been developed the results of this analysis show that longer period planetary waves 10 t 20 days have significant amplitudes mainly during winter in both hemispheres westward propagating waves are dominant in the northern hemisphere but in the southern hemisphere eastward and westward propagating waves have comparable amplitudes and sometimes eastward propagating waves are dominant it is suggested that the main forcing of longer period travelling waves is an internal variability of the quasi stationary planetary waves in the tropo stratosphere and that the substantial activity of eastward propagating waves in the southern hemisphere is associated with seasonal changes of the general circulation of the middle atmosphere in the shorter period part of the wavelet spectra t 10 days westward propagating waves are dominant and the observed maxima in amplitude spectra can be identified with the first symmetric normal atmospheric modes the so called 5 and 4 day waves these waves present in the stratosphere during most of the year increase in amplitude during seasonal transitions analysis of the behaviour of wavelet amplitudes at different pressure levels shows that these normal mode waves propagate upward from the lower atmosphere and their amplitudes increase with altitude there exists also a substantial long period modulation of the 5 day wave amplitude with quasi period of about 30 days copyright 2004 royal meteorological society

observations of the 6 5 day wave in the mesosphere and lower thermosphere previous observations of atmospheric oscillations with zonal wave number 1 have consistently located waves of periods between 5 and 7 days this study presents a global and seasonal analysis of the 6 5 day wave in high resolution doppler imager daytime mesosphere and lower thermosphere horizontal winds temperatures and nighttime atomic oxygen at 95 km the horizontal structures of all these atmospheric variables are similar to the gravest symmetric wave number 1 rossby wave i e the 1 1 mode the seasonal and spatial analysis displays possible modification by the zonal mean wind finally the observed vertical structures of the 6 5 day wave indicate that it is an internal rossby wave not an external or lamb wave

a multiple profile approach to the palynological reconstruction of norse landscapes in greenland s eastern settlement acknowledgments the leverhulme trust is thanked for financial support gordon cook provided radiocarbon dates thanks are also due to andy mcmullen for botanical identifications and assistance in the field and to sikuu motzfeld for hospitality during fieldwork we are also grateful to emilie gauthier mike kaplan pete langdon and alan gillespie for their comments

observations of the quasi 2 day wave from the high resolution doppler imager on uars a strong westward traveling oscillation with a period of 2 days and zonal wave number 3 is observed in the mesospheric and lower thermospheric winds from the high resolution doppler imager on the upper atmosphere research satellite the important events happen in january july and september october of which the occurrence in january is the strongest with an amplitude over 60ms 1 detailed analyses for the periods of january 1992 and january 1993 reveal a cause and effect relationship in the wave developing process at 95km the global structures of the wave amplitude and phase are also presented

precursory effects in the subionospheric vlf signals for the kobe earthquake abstract the subionospheric vlf omega signal transmitted from tsushima japan geographic coordinates 34 37 n 129 27 e was continuously received at inubo 35 42 n 140 52 e this data was analyzed during an 8 month period centered on the great hyogo ken nambu kobe earthquake m g 7 2 on 17 january 1995 the epicenter located inside of fresnel zone of the vlf path to clarify the possible effect we developed the special tt terminator time method of data processing which was useful for our short vlf path distance 1000 km we discovered a statistically significant change of tt characteristics which began a few days before the main shock and probably continued a few weeks after it as a transient oscillation with period 10 days by simple modelling it was shown that tt changes could be caused by the decrease of the vlf reflection height by 2 km the possible underlying mechanisms of the effect are not defined however an increase of the regular electric field due to radon exhalation before the earthquake or an intensification of planetary waves by seismically influenced atmospheric turbulence might be considered

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

the 6 5 day wave and its seasonal variability in the middle and upper atmosphere 1 the zonal wave number 1 planetary wave of period near 6 5 days is a robust feature in the mesosphere and lower thermosphere mlt region with prominent seasonal variability as revealed by ground based and satellite observations this wave and its seasonal variability are well reproduced in a recent one model year run of the national center for atmospheric research thermosphere ionosphere mesosphere electrodynamics general circulation model time gcm with its lower boundary specified according to the national centers for environmental prediction analysis year 1993 wavelet analysis of the model output shows that in the mlt region the wave maximizes before and after the equinoxes and minimizes at solstices the wave amplitudes at the equinoxes are smaller than the peaks before and after but are still larger than the wave amplitudes at solstices however at the lower boundary near 30 km the wave peaks are predominantly between fall and the following spring by examining the episodes of maximum and minimum wave amplitude and by conducting additional control experiments using the time gcm the structure of this planetary wave and the factors determining the wave characteristics and seasonal variability are studied in detail it is found that the wave source mean wind structure instability and the critical layers of the wave can all affect the wave response in the mlt region and can have a strong seasonal dependence before and after equinox the wave follows the waveguide and propagates from the stratosphere to the summer mesosphere mesopause where it may amplify due to baroclinic barotropic instability such instability is usually absent from the equinoctial atmosphere so that there is no wave amplification at equinox at solstice the wave decays significantly when propagating away from its winter source due to the strong eastward winter stratospheric jet in the summer side the westward jet is also strong and the meridional and vertical extension of the critical layer of the wave is large enough to enclose the instability in the summer mesosphere mesopause at middle to high latitudes the wave is thus reflected away and prevented from reaching and amplifying at the unstable region the seasonal variation of the quasi two day wave which has zonal phase speed similar to the 6 5 day wave is also studied using similar diagnostics it is further shown that within certain seasonal window periods the variability in the mlt especially the summer mlt may closely track the lower atmospheric variability associated with these waves

seabed features caused by shallow gas in north sea abstract seepage of shallow gas mainly methane recently has been documented visually in the central section of the north sea at water depths of about 70 80 m the surface expressions caused by these seeps are not dramatic they mainly consist of small funnel shaped craters 20 cm across in the cover sand however in deeper parts of the north sea where the cover sediments consist of silt and clay the surface features are more dramatic here the craters pockmarks caused by shallow gas eruptions or seepages are up to 20 m deep and 100 m wide in some areas the pockmarks are paved with a crust of calcium carbonate cement which is believed to have formed as a result of gas efflux through the seabed furthermore the presence of these calcium carbonate reefs seems to have attr cted a wide variety of marine life the presence of shallow gas has caused an enrichment of marine life that seems to be significant beside the semicircular and composite pockmarks gas induced erosion also has caused elongate depressions these occur where the top sediment bedding has caused the gas to migrate along certain axes the mode and speed of formation of the gas induced erosion features are of major concern to oil exploration and development in the northern north sea research into these aspects recently has been stimulated by the discovery of one of the world s largest offshore gas reservoirs which coincidentally lies within a pockmarked area end of article last page 267

a 1400 year high resolution record of atmospheric circulation over the north atlantic and asia major ion series developed from new subannual scale sampling of an ice core from central greenland are calibrated with instrumental series of atmospheric sea level pressure recording major marine icelandic low and terrestrial siberian high atmospheric circulation systems to provide proxy records of atmospheric circulation over the past 1400 years examination of the proxy records reveals major changes in behaviour of these systems c ad 1400 multidecadal and centennial scale periodic components characterization of mean sea level pressure anomaly fields during the little ice age and the mediaeval warm period the potential role of solar forcing coupled ocean atmosphere associations and a perspective within which the characteristics of instrumental era climate can be assessed

lake sediments erosion and landscape change during the holocene in britain and ireland abstract lakes are excellent repositories of air borne and especially stream borne materials it has long been recognised that lake sediments contain a strong record of catchment soils via the inputs of minerogenic and chemical erosional products to these may be added a variety of palaeoecological indicators including pollen fungi sphagnum leaves and faunal remains pollen analysis in particular enables land use change to be assessed over many millennia and demonstrates the landscape impacts of woodland clearance grazing and crop cultivation radiocarbon dating provides a chronology for environmental and agricultural change and acts as an indicator of erosion in its own right the use of such indicators to reconstruct past instances and patterns of erosion is demonstrated with reference mainly to 50 british and irish lake sites and especially those which have produced signals of erosion in the form of accelerated sediment accumulation and inversed or reversed sequences of radiocarbon dates during the mid and late holocene sites displaying even or decreased sedimentation through time are concentrated in northern and northwestern scotland and have either no clear signs of human impact or only so towards the latter part of the holocene this pattern probably reflects a combination of factors including low population densities thin soils and the sealing effect of blanket peat in contrast all sites with accelerated erosion have indications of anthropogenic impact this is often prior to levels of increased sedimentation showing a delay in system response while the spread of dates for the start of the rise in sediment accumulation spans 6200 940 bp three clusters are evident at 5295 4970 4530 4235 and 2980 2810 bp radiocarbon inversions mostly reversals are evident for 18 sites no obvious causal patterning is indicated and they probably demonstrate no more than the fact that catchment soils including peats around a particular site were pushed beyond an erosional threshold sufficient to age the sediments deposited within the lakes it is hoped that improvements in data quality will allow the refinement of such exercises in the future and that lakes will be valued as repositories of long term landscape sensitivity

oh layer characteristics during unusual boreal winters of 2004 and 2006 1 we report observations of unusual mesospheric oh airglow made by the saber instrument on the timed satellite during portions of the boreal winters of 2004 and 2006 and over much of the region poleward of 60 n the oh layer was 5 8 km lower than normal and twice as bright using retrieved volume emission rates vers in two saber channels we document the characteristics spatial extent and temporal variability of the anomalous behavior we show that it is correlated with unusual mesospheric and upper stratospheric temperature patterns that have been reported and other observations the unusual layer properties are likely produced by enhanced downward transport of atomic oxygen a circumstance consistent with the planetary wave dynamics thought to be responsible for the other changes these observations raise the possibility of using easily observed oh airglow as a proxy for perturbed meteorological conditions

mesosphere inversion layers and stratosphere temperature enhancements 1 it has been known for at least 30 years that vertically narrow thermal layers form within the middle atmosphere two types of temperature enhancements the low latitude to midlatitude mesosphere inversion layer mil and the high latitude winter stratosphere temperature enhancement ste have both received much attention within the atmospheric science community because of their unexplained formation mechanisms and potential impacts on the middle atmosphere global circulation numerous experimental numerical and theoretical studies have attempted to explain certain aspects of these respective thermal layers but no one theory consistently and satisfactorily describes all the features observed we present a review of the literature and explicitly propose a classification scheme based on the different formation mechanisms suspected to cause these events for the mil we demonstrate that there are two subtypes the first one is tidally driven and tends to occur above 85 km this mil originates from large amplitude tidal waves propagating into the mesosphere and their subsequent nonlinear interactions with gravity waves which can often create the appearance of a double mil separated by approximately one vertical tidal wavelength 25 km the other subtype of mil is formed by a climatological planetary wave dissipation mechanism that occurs at a zero wind line the dissipation of the planetary wave tends to generate a mesoscale 1000 km inversion layer in the range of 65 80 km these two formation mechanisms explain a host of observed characteristics including the reason behind the downward progression of some mils and not others the different climatological nature of the two forms of mil events and the relative scarcity of mil observations at high latitudes the ste is believed to be generated by an altogether different process namely the nonlinear interaction between the polar vortex and planetary waves aleutian high the induced temperatures typically peak around 40 km and often exceed 300 k generating what appears to be a low hot stratopause when vertical temperature profiles are combined with synoptic analyses one observes that the ste is the consequence of high latitude vortex interactions creating a baroclinic atmosphere i e a downward adiabatic compression induced by an ageostropic flow we summarize the details of the relationship between this feature and sudden stratospheric warmings as well as the potential for in situ gravity wave generation we close with a review of currently unexplained mil ste features and offer new directions for future middle atmosphere thermal layer research

palaeoecological and historical evidence for manuring and irrigation at garðar igaliku norse eastern settlement greenland palaeoenvironmental data are presented from the site of gar ar modern igaliku the location of the cathedral and the bishop s farm in the norse eastern settlement of greenland the latter was founded from c ad 985 and abandoned some time during the fifteenth century inspection of drainage ditches located in close proximity to the settlement ruins revealed inter alia an organic rich unit containing cultural debris worked wood animal bone stone and charcoal dated by ams radiocarbon dates on seeds to the period c ad 1110 1370 fossil insect and pollen assemblages contained within the deposit appear representative of natural environments primarily wet eutrophic meadows but are mixed with high frequencies of a range of synanthropic insects including human and animal ectoparasites that could only derive from indoor habitats this is strongly indicative of the manuring of fields with waste from houses and byres in order to increase yields of hay large amounts of hay would have been necessary to prov

subionospheric vlf signal perturbations possibly related to earthquakes a likely vlf subionospheric signal effect related to seismic activity was first reported by hayakawa et al 1996a b in association with the great kobe earthquake we have analyzed similar data during periods around 10 other great earthquakes magnitude m 6 in order to understand the main features of such an effect the following characteristics emerged from our analysis the effect appears as a transient oscillation with a 5 to 10 day period which is initiated a few days before a large earthquake and decays over a few days to weeks after it it is mainly related to crustal earthquakes it appears when resonant atmospheric oscillations with periods in a range of 5 11 days exist before the earthquake the seismic influence on the vlf signal is probably explained by the generation of long period gravity waves during the earthquake process and their intensification at heights of 70 90 km

on the large wind shear and fast meridional transport above the mesopause 1 unexpectedly strong winds shears and fast meridional transport above the mesopause have been revealed from previous rocket and satellite observations using richardson number criteria for dynamic stability we estimate the maximum wind shears allowable by the background static stability which peaks above the mesopause these maximum shears are in general agreement with the large wind shears inferred from the rocket measurements at low and mid latitudes indicating the close relationship between the latter and the stability constraint set by the background atmosphere diagnostic calculations also indicate that the meridional transport in this region may not be well understood solely by examining the mean meridional circulation and large amplitude tides planetary waves can play an important role in the bulk transport of tracers strong stochastic winds presumably due to gravity waves do not seem to significantly change the large scale pattern of the transport but may extend the range of the tracer movement

problematic but promising ponds palaeoenvironmental evidence from the norse eastern settlement of greenland pollen and related proxy based studies of human environment interactions during the norse and later periods within greenland have primarily involved the investigation of peat lake and soil deposits all of which have taphonomic and sampling problems many small ponds exist but they seem to have been relatively ignored in investigations of palaeoecologically based environmental history to evaluate their usefulness for studies of ecologically related cultural history especially where sites are in intimate association with the archaeology a pond in the norse eastern settlement has been examined to investigate three principal questions i does such a site contain a useful record of environmental history ii does it offer a record of sufficient resolution and sensitivity for the study of anthropogenic landscape impacts iii are there any apparent drawbacks to these sequences using data obtained from palynological diatom sedimentological and radiocarbon analyses it is concluded that environmental data for each proxy aside from 14c dating are clearly capable of being explained in a reasonably straightforward and compatible manner and fulfil the hopes for the sampling medium copyright 2011 john wiley sons ltd

two day wave coupling of the low latitude atmosphere ionosphere system 1 vertical coupling in the low latitude atmosphere ionosphere system driven by the 2 day wave in the tropical mlt region has been investigated the problem is studied from an observational point of view three different types of data were analyzed in order to detect and extract the 2 day wave signals the 2 day wave event during the period from 1 december 2002 to 28 february 2003 was identified in the neutral winds by radar measurements located at four tropical stations the 2 day variations in the ionospheric electric currents registered by perturbations in the geomagnetic field and in the f region electron densities were detected in the data from 23 magnetometer and seven ionosonde stations situated at low latitudes two features for each kind of wave were investigated in detail the variation with time of the wave amplitude and the zonal wave number the results show that the westward propagating global 2 day wave with zonal wave number 2 seen in the ionospheric currents and in f region plasma is forced by the simultaneous 2 day wave activity in the mlt region the main forcing agent in this atmosphere ionosphere coupling seems to be the modulated tides particularly the semidiurnal tide this tide has a larger vertical wavelength than the diurnal tide and propagates well into the thermosphere the parameter that appears to be affected and thus drives the observed 2 day wave response of the ionosphere is the dynamo electric field

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

global distribution and variability of quasi 2 day waves based on the nogaps alpha reanalysis model this study presents the analysis of 14 months january 2009 february 2010 of continuous hourly nogaps alpha reanalysis data used for examining the quasi 2 day wave otdw the global structure and seasonal variability of the eastward and westward traveling qtdws in all meteorological fields geopotential height zonal and meridional wind and temperature have been studied the use of hourly reanalysis data allows a comprehensive understanding of the global spatial temporal qtdw distribution by simultaneous separations of all tides and planetary waves the wave characteristics amplitudes and phases are presented in latitude range 80 and altitudes from 15 to 95 km two different types of eastward traveling waves are identified i waves at middle and high latitudes with zonal wave numbers 2 and 3 which are observed in the local winters and ii waves observed predominantly over the equator with zonal wave number 2 which do not have a well defined seasonal variability but show some enhancement between june and august while the first type waves are seen in all meteorological fields the second ones are not seen in the meridional wind and belong to the ultra fast kelvin waves two different types of westward traveling waves have been identified as well i waves at middle and high latitudes with zonal wave numbers 2 3 and 4 which are observed mainly in summer hemisphere and ii waves observed predominantly over the equator with zonal wave numbers 1 2 and 3 enhanced predominantly at both solstices but are seen in other seasons as well while the first type waves are seen in all meteorological fields the second ones are observed in the meridional wind and are rossby gravity normal modes

environmental impacts around the time of norse landnam in the qorlortoq valley eastern settlement greenland abstract palynology radiocarbon dating and open section stratigraphies from archaeological trenches are used to examine the impact of human activity around the time of norse landnam on vegetation and landscape associated with a small farm o34 in the qorlortoq valley eastern settlement greenland 61 n 45 w peat deposits from a mire abutting the norse ruins revealed a discontinuous palaeoenvironmental record containing a possible hiatus from ca ad 410 1020 palaeovegetational data were recovered either side of this period pollen assemblages suggest that open salix scrub dominated the landscape during the pre settlement phase the later phases of landnam resulted in the creation of hay fields and heavily grazed grassy heath site abandonment is reflected by a re expansion of salix this occurs shortly before the onset of deposition of a sphagnum peat dated to cal ad 1420 1630 2 and reflecting an increase in mire surface wetness probably in response to a deteriorating climate radiocarbon dates were obtained on peat and plant macrofossils sampled from either side of the proposed hiatus at two different but closely spaced landnam period cal bc 2130 1770 and cal ad 240 410 respectively but near synchronous dates for the recommencement of peat growth cal ad 890 1150 for peat and a probably more reliable interval of cal ad 1020 1190 based on plant macrofossils it is suggested that this hiatus may represent the first direct evidence for peat cutting in norse greenland

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

vegetation change on papa stour shetland scotland a response to coastal evolution and human interference the first palynological and related sedimentological studies from papa stour shetland are presented and supplement the limited data available for the study of holocene vegetation change from the northern isles of scotland two pollen sites were located on an isthmus which has experienced the marked influences of waterlevel changes inundation by blown shell sand and probable grazing and arable activity in spite of the unpromising calcareous nature of the mineral materials at the sites very rich suites of pollen and spore taxa were recovered including those of taxa now absent from or rare in the islands the assemblages indicate a strong interplay between two major habitat types maritime heath and grassland in addition the sites demonstrate the effects of intermittent pool formation the study shows that the vegetational and geomorphological landscapes of the study area are both dynamic and closely linked

departures from the local inverse barometer model at periods of 5 days in the central south atlantic tide gauge data from ascension and st helena in the central south atlantic supplemented by altimeter data from the topex poseidon mission suggest that the local inverse barometer lib model for the forcing of sea level variability by means of air pressure changes is not applicable within a narrow band of the variability spectrum with periods of approximately 5 days this is in contrast to other sections of the wider frequency band spanning approximately 0 05 to 0 5 cycles d wherein the data are either consistent with approximate lib response or at least suggest no departures from the lib model of similar magnitude these results have similarities to findings from pacific gauges obtained over a decade ago but so far no comparisons have been to data from other ocean areas they are also qualitatively similar to predictions for the region from a recent global barotropic numerical model the anomalous part of the spectrum coincides in frequency with the madden and julian 1972 1973 5 day pressure wave in the atmosphere if that global scale forcing is responsible for both the atlantic and pacific departures from the lib model around 5 days then similar features should be observable in tide gauge data from other tropical areas

radiocarbon geochemistry of modern and ancient arctic lake systems baffin island canada the accuracy of arctic lake chronologies has been assessed by measuring the14c activities of modern carbon sources and applying these isotopic mass balances to dating fossil lake materials small 1 km2 shallow 25 m arctic lakes with watersheds 12 km2have soil and peat stratigraphic sections with14c activities ranging from 98 to 51 modern the14c activity of particulate organic carbon dissolved organic carbon and dissolved inorganic carbon from lake and stream waters ranges from 121 to 95 modern the sediment water interface of the studied lakes shows consistent14c ages of 100014c yr although the14c activity of living aquatic vegetation is 115 modern radiocarbon measurements of components of the lacustrine carbon pool imply that the 100014c yr age of the sediment water interface results from deposition of14c depleted organic matter derived from the watershed

revised global model of thermosphere winds using satellite and ground based observations thermospheric wind data obtained from the atmosphere explorer e and dynamics explorer 2 satellites have been combined with wind data for the lower and upper thermosphere from ground based incoherent scatter radar and fabry perot optical interferometers to generate a revision hwm90 of the hwm87 empirical model and extend its applicability to 100 km comparison of the various data sets with the aid of the model shows in general remarkable agreement particularly at mid and low latitudes the ground based data allow modeling of seasonal diurnal variations which are most distinct at mid latitudes while solar activity variations are now included they are found to be small and not always very clearly delineated by the current data they are most obvious at the higher latitudes the model describes the transition from predominately diurnal variations in the upper thermosphere to semidiurnal variations in the lower thermosphere and a transition from summer to winter flow above 140 km to winter to summer flow below significant altitude gradients in the wind are found to extend to 300 km at some local times and pose complications for interpretation of fabry perot observations

large scale rossby normal modes during some recent northern hemisphere winters abstractlarge scale rossby normal modes are studied for the northern hemisphere winters of 2005 2006 2008 and 2009 using global observational meteorological analyses spanning the 0 92 km altitude range spectral analysis of geopotential height fields shows pronounced peaks at westward propagating zonal wavenumber 1 near the theoretical locations of the free rossby waves at 25 16 10 and 5 days that in some cases have amplitudes significantly larger than the estimated background spectrum evidence is also found for a wavenumber 2 free mode near 4 days a coherence analysis is used to extract the amplitude and phase of the waves and to isolate those regions of the latitude altitude plane where the signals are statistically significant although the spectral location temporal evolution and vertical structure of several of these waves are suggestive of the presence of rossby normal modes this study shows that in the real atmosphere the waves only occasionally have the global properties of classical

amplification of the quasi two day wave through nonlinear interaction with the migrating diurnal tide 1 we present a case study of the non linear interaction between the quasi two day wave q2dw and the migrating diurnal tide based on global synoptic meridional wind fields for january 2006 and january 2008 from a high altitude data assimilation forecast system we find large quasi two day wave amplitudes small diurnal tide amplitudes and phase locking of the q2dw with the diurnal cycle during january 2006 in january 2008 the amplitudes of the q2dw were much smaller with no evidence of phase locking while the tidal amplitudes were larger than in the 2006 case space time spectral analysis reveals an enhancement in a diurnal zonal wavenumber 6 feature in the january 2006 case which can be attributed to a non linear interaction between the q2dw and migrating diurnal tide the relatively strong summer easterly jet in the extratropical upper mesosphere during early january 2006 appears to have created conditions favoring this interaction

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

twelve hour tides in the winter northern polar mesosphere and lower thermosphere 1 an investigation of the tidal oscillations near the winter northern polar mesopause has been carried out at resolute bay canada 74 9 n 94 9 w the daily monthly and annual variations of the tidal field were studied using the 1995 1996 and 1996 1997 data ground based measurements were obtained using a fabry perot interferometer with a circle to line interferometric optical system fpi clio and the e region wind interferometer erwin the fpi clio observed the doppler winds of the oh emission near 86 km altitude the erwin provided simultaneous oh near 86 km and oi near 97 km wind measurements monthly data were compared to the global scale wave model gswm and the forbes vial solar semidiurnal tidal model predictions analysis of the 12 hour oscillation near 86 and 97 km altitudes indicates that it is persistent and characteristic of a semidiurnal propagating tide the semidiurnal tide was found to be highly variable in amplitude and phase from day to day the observations presented provide a continuous and extensive data set for the winter season index terms 3332 meteorology and atmospheric dynamics mesospheric dynamics 3334 meteorology and atmospheric dynamics middle atmosphere dynamics 0341 0342 3384 meteorology and atmospheric dynamics waves and tides keywords semidiurnal tide polar mesosphere polar thermosphere fabry perot interferometer resolute bay mesopause

case studies of the mesospheric response to recent minor major and extended stratospheric warmings 1 we have studied the mesospheric response to two recent stratospheric warmings by performing short term forecasts at medium 1 5 and high 0 5 spatial resolution under different gravity wave drag gwd scenarios we validated our models with our high altitude analysis that extends from 0 to 90 km for the minor warming of january 2008 reduced upper level orographic gwd weakened the downward residual circulation and cooled the mesosphere parameterized nonorographic gwd increased the simulated mesospheric cooling for the prolonged major warming of 2006 heavily attenuated orographic gwd led to pronounced cooling near 50 km during the extended phase of this event an unusually strong westerly polar vortex reformed in the lower mesosphere which allowed westward propagating nonorographic gravity waves to reach the mesosphere and break with net westward accelerations of over 50 m s 1 d 1 this in turn forced a strong residual circulation yielding descent velocities over 2 cm s 1 between 65 n and 85 n consistent with previous reports of enhanced downward transport of trace constituents the resulting adiabatic heating as evidenced by the unusually vertically displaced stratopause at 80 km is likely a direct consequence of this enhanced gravity wave driven descent high resolution simulations without parameterized gwd were closer to the analysis than medium resolution simulations with parameterized orographic gwd only but still did not fully simulate the mesospheric thermal response specifically the 80 km temperature enhancement was still underestimated in these simulations this suggests that higher spatial resolution is needed to adequately resolve extratropical gravity wave momentum fluxes

the 6 5 day wave in the tropical stratosphere and mesosphere 1 the 6 5 day wave is a westward propagating zonal wave number 1 s 1 planetary wave that is prominent near equinox the spatial temporal structure of the 6 5 day wave seen in the united kingdom meteorological office ukmo data in the stratosphere is found to be consistent with that obtained from upper atmosphere research satellite high resolution doppler imager hrdi measurements of horizontal winds and temperatures in the mesosphere lower thermosphere mlt two wave events are commonly observed before and after equinox at low latitudes in both ukmo and hrdi data this paper focuses on a pair of such events in late 1994 the amplitude growth and phase decrease with altitude of the zonal wind 6 5 day wave appear to be continuous between the two data sets for the period analyzed both wave events appear to grow from the stratosphere to the upper atmosphere at a rate consistent with the suggested vertical phase velocity such consistency between the two data sets establishes that the wave previously observed in the mlt is propagating from the stratosphere further analyses of the ukmo data shows the presence of the 10 day s 1 and 4 day s 2 waves that appear to be either nonlinearly coupled with the 6 5 day wave or related through a common sourcing mechanism

an integrated geochemical and palynological study of human impacts soil erosion and storminess from southern greenland since c ad 1000 abstract an integrated pollen analytical and geochemical study is presented from qinngua kangilleq southwest greenland this site was formerly one of the largest farms in the eastern settlement of norse greenland the study is the first to determine what link if any exists between norse landnam early settlement vegetation change soil erosion climate change and peat geochemistry the data suggest that fluxes in lithogenic elements supplied to a peat column by terrestrial sources and atmospheric deposition were coupled to the pattern of local norse settlement beginning cal ad 1020 a severe phase of soil erosion is indicated which is coincident with the landnam horizon this may represent proxy evidence for the stripping of turf for the construction of turf and stone buildings at the farm radiocarbon dates suggest the presence of a hiatus in the sediment column spanning cal ad 1380 1950 following the recommencement of sediment accumulation the geochemical data indicate a critical change in site conditions which may be consistent with the well known change in northern hemisphere atmospheric circulation that started between c ad 1400 and 1420 bromine br and chlorine cl concentrations are demonstrably higher in the sediments dating to the 20th century relative to the pre 15th century deposits rising halogen concentrations at qinngua appear to be correlated with increased levels of na sea salt sodium precipitation in the gisp2 ice core which earlier studies have interpreted as indicative of increased north atlantic storminess

high resolution paleoenvironmental and chronological investigations of norse landnam at tasiusaq eastern settlement greenland abstract high resolution paleoenvironmental data from a peat profile with a small pollen source area are used to reconstruct the impacts of landnam on vegetation and soils at a norse farm complex 2 at tasiusaq comprising two farms in the eastern settlement of greenland analyses include the ams 14c dating of plant macrofossil samples and the use of bayesian radiocarbon calibration to construct improved age depth models for norse cultural horizons the onset of a regional landnam may be indicated by the clearance of betula pubescens woodland immediately prior to local settlement the latter is dated to ad 950 1020 2 and is characterised by possible burning of betula glandulosa scrub to provide grassland pasture for domestic stock clearance and grazing resulted in accelerated levels of soil erosion at a westerly farm this was followed by an easterly migration of settlement and agriculture site constraints prevent an assessment of the demise of the easterly farm but pressures of overgrazing and land degradation may have been the major factors responsible for the abandonment of the earlier farm