climatology of mesopause region temperature zonal wind and meridional wind over fort collins colorado 41 n 105 w and comparison with model simulations 1 between may 2002 and april 2006 many continuous observations of mesopause region temperature and horizontal wind each lasting longer than 24 h termed full diurnal cycle observations were completed at the colorado state university na lidar facility in fort collins colorado 41 n 105 w the combined data set consists of 120 full diurnal cycle observations binned on a monthly basis with a minimum of 7 cycles in april and a maximum of 18 cycles in august each monthly data set was analyzed to deduce mean values and tidal period perturbations after removal of tidal signals monthly mean values are used for the study of seasonal variations in mesopause region temperature zonal and meridional winds the results are in qualitative agreement with our current understanding of mean temperature and wind structures in the midlatitude mesopause region with an observed summer mesopause of 167 k at 84 km summer peak eastward zonal wind of 48 m s at 94 km winter zonal wind reversal at 95 km and peak summer pole to winter pole meridional flow of 17 m s at 86 km the observed mean state in temperature zonal and meridional winds are compared with the predictions of three current general circulation models i e the whole atmosphere community climate model version 3 waccm3 with two different simulations of gravity wavefields the hamburg model of the neutral and ionized atmosphere hammonia and the 2003 simulation of the thermosphere ionosphere mesosphere electrodynamics general circulation model time gcm while general agreement is found between observation and model predictions there exist discrepancies between model prediction and observation as well as among predictions from different models specifically the predicted summer mesopause altitude is lower by 3 km 8 km 3 km and 1 km for waccm3 the two waccm runs hammonia and time gcm respectively and the corresponding temperatures are 169 k 170 k 158 k and 161 k the model predicted summer eastward zonal wind peaks to 71 m s at 102 km to 48 m s at 84 km to 75 m s at 93 km and to 29 m s at 94 km in the same order the altitude of the winter zonal wind reversal and seasonal asymmetry of the pole to pole meridional flow are also compared and the importance of full diurnal cycle observations for the determination of mean states is discussed

observations of the diurnal tide in the mesosphere and lower thermosphere over christmas island atmospheric tidal variations in the mesosphere wind field have been studied extensively using radars most of the climatological studies of the tide have been done at middle and high latitudes previous tropical observations of the diurnal oscillation derived from campaign studies have shown the dominance of the migrating diurnal tide in the mesosphere and lower thermosphere by using wind measurements obtained with a meteor radar system located at christmas island the diurnal tidal behavior in the upper atmosphere of the equatorial pacific has been characterized over several years the data collected from august 1988 to december 1993 are presented in this paper and compared to various model results our observations show the meridional wind component of the diurnal tide maximizes in april near 94 km the observed meridional vertical wavelengths are large and indicate upward propagating energy even though the vertical wavelengths for the zonal diurnal component are also large the phase progression is upward corresponding to downward propagating energy there is considerable interannual and intraseasonal variation in the diurnal amplitudes throughout the year

effects of biological crust coverage on soil hydraulic properties for the loess plateau of china biological soil crusts bscs are ubiquitous living covers that have been allowed to grow on abandoned farmlands over the loess plateau because the grain for green project was implemented in 1999 to control serious soil erosion however few studies have been conducted to quantify the effects of bsc coverage on soil hydraulic properties this study was performed to assess the effects of bsc coverage on soil hydraulic properties which are reflected by the soil sorptivity under an applied pressure of 0 s and 3 s cm saturated hydraulic conductivity k wetting front depth wfd and mean pore radius for the loess plateau of china five classes of bsc coverage i e 1 20 20 40 40 60 60 80 and 80 100 and a bare control were selected at both cyanobacteria and moss covered sites to measure soil hydraulic properties using a disc infiltrometer under 2 consecutive pressure heads of 0 and 3 cm allowing the direct calculation of s s k and the wfd was measured onsite using a ruler immediately after the experiments of infiltration the results indicated that both cyanobacteria and moss crusts were effective in changing the soil properties and impeding soil infiltration the effects of moss were greater than those of cyanobacteria compared to those of the control the s s k wfd and values of cyanobacteria covered soils were reduced by 13 7 11 0 13 3 10 6 and 12 6 on average and those of moss covered soils were reduced by 27 6 22 1 29 5 22 2 and 25 9 respectively the relative soil sorptivity under pressures of 0 rs and 3 rs cm the relative saturated hydraulic conductivity rk the relative wetting front depth rwfd and the relative mean pore radius r decreased exponentially with coverage for both cyanobacteria and moss covered soils the rates of decrease in rs rs rk rwfd and r of cyanobacteria were significantly slower than those of moss especially for the coverage of 0 40 with smaller ranges the variations of soil hydraulic properties with bsc coverage were closely related to the change in soil clay content driven by the bsc coverage on the loess plateau the results are useful for simulating the hydraulic parameters of bsc covered soils in arid and semiarid areas

oxide minerals in a layered kimberlite carbonate sill from benfontein south africa the lower sill at benfontein south africa shows a high degree of magmatic sedimentation to kimberlite oxide carbonate and carbonate layers the iron titanium oxide minerals are similar in the carbonate rich and silicate rich layers and are represented by titaniferous mg al chromite mg al titanomagnetite magnesian ilmenite rutile and perovskite the spinel crystallization trend was toward enrichment in mg and ti and depletion in cr this trend is similar to that observed in many kimberlites the ilmenite has mg and cr contents within the range observed in kimberlites and lacks the mn enrichment observed in ilmenites from carbonatites perovskite in silicate rich and carbonate rich layers shows similar total ree contents and lree enrichment and lacks the remarkable nb enrichment observed in perovskite from carbonatites these new data on the iron titanium oxide minerals in the lower benfontein sill do not support a genetic relationship between kimberlites and carbonatites

eliassen palm fluxes of the 2 day wave abstract high resolution doppler imager hrdi winds and temperatures are used to diagnose a 2 day wave event detected in the southern hemisphere during january 1994 a novel aspect of this study is the focus upon the wave fluxes throughout the 65 100 km range and their relationship to the background state a wave packet composed of zonal wavenumbers 2 3 and 4 propagates westward with a phase speed near 60 m s 1 the periods associated with zonal wavenumbers 2 3 and 4 are 3 5 2 1 and 1 7 days respectively the morphology of the 2 day temperature and wind fields is consistent with that of a developing baroclinic wave the divergence of the eliassen palm flux of zonal wavenumbers 2 4 is dominated by the vertical convergence of meridional heat flux the wave driving or eliassen palm flux divergence per unit mass is predominantly westward with magnitudes on the order of 5 m s 1 day 1 a steady state quasigeostrophic model of the mean meridionai circulation is used to estimate the mean wind respon

high latitude mesospheric mean winds a comparison between tromso 69 n and svalbard 78 n 1 daily mean winds in the upper mesosphere regions above tromso 69 n 19 e and svalbard 78 n 16 e are presented these having been obtained from 6 years operation of the middle frequency radar at tromso and almost 2 years operation of the svalbard meteor radar the findings depart somewhat from the predictions of current modeling particularly in that outflow from the pole occurs almost all year round this picture is in accordance with a ferrell cell circulation in summer but not in winter gravity wave drag parameterized by the rayleigh drag coefficient is suggested as a likely cause of the widespread ageostrophic motion characterizing the winter dynamics

latitude and seasonal dependence of the semidiurnal tide observed by the high resolution doppler imager the high resolution doppler imager hrdi on the upper atmosphere research satellite uars has provided measurements of the horizontal wind field in the mesosphere and lower thermosphere mlt since november 1991 the observed dynamical patterns are dominated by the 1 1 diurnal tide but semidiurnal perturbations are also very prominent in the hrdi data particularly at latitudes greater than 40 this paper presents a preliminary study of the semidiurnal tide and discusses latitudinal and seasonal variations in the phenomenon regular seasonal changes are clearly detected and significant interhemispheric asymmetries have been identified in general the observed features are consistent with previous measurements and model results but some discrepancies have been found this new technique which brings a global perspective to the observation of mlt dynamics is complementary to the very detailed but localized radar data sets currently available and should provide important constraints for numerical models

zonal mean winds in the equatorial mesosphere and lower thermosphere observed by the high resolution doppler imager this paper presents analyses of mesospheric and lower thermospheric zonal mean winds observed by the high resolution doppler imager hrdi on the upper atmosphere research satellite uars monthly averages of the equatorial zonal mean zonal winds are presented for january 1992 through june 1993 equatorial zonal winds in the 70 90 km region are dominated by a semiannual oscillation sao ranging from 30 m s 1 westerly to 100 m s 1 easterly at high latitudes the zonal wind variations are predominantly annual above 90 km the low latitude flow is easterly at all times punctuated by a small semiannual variation this behavior may be related to the deposition of momentum by the diurnal tides

characteristics of gravity waves 10 min 6 hours at saskatoon 52 n 107 w observations by the phase coherent medium frequency radar height time cross sections of the power spectral density in two bands 10 100 min 2 6 hours for gravity waves igw are formed from horizontal u v and vertical w wind measurements made during 1989 and 1990 using the saskatoon mf radar 52n 107w these climatologies are compared with the seasonally varying mean winds and are consistent with data from previous years 1979 1984 which demonstrated semiannual variations solstitial maxima below 90 km and annual winter maximum above 90 km directions of preferred propagation are inferred by forming the wind perturbation u v covariances and fitting ellipses to the perturbation velocities the preferred orientations are closer to meridional ns than to zonal ew especially for the shorter periods finally the u w v w products which are the vertical fluxes of horizontal momenta are formed in cross section and time series formats for the longer periods the zonal momenta u w have a seasonal variation below 85 km apparently modulated by the zonal mean winds with mainly westward eastward momenta in winter summer months the divergences of the flux provide accelerations of 10 m s 1 d 1 in summer 65 80 km and 15 ms 1 d l in winter 75 90 km which are somewhat less than but often opposite in sign to the coriolis torque on the meridional flow such comparisons suggest that shorter period waves must also contribute important fluxes of momentum the fluctuations in igw intensities and covariances over time scales of several days may be considerable and will affect the sampling needed to obtain seasonal means fluctuations due to planetary waves and stratwarms are observed

first observations of mesospheric dynamics with a partial reflection radar in hawaii 22 n 160 w we present here an overview of the wind measurements made during the first year of operation of a partial reflection radar system in hawaii the system operates at 1 98 mhz and provides wind estimates between 60 and 100 km at 2 km intervals our wind observations reveal a zonal mean motion that has several features in common with the mesopause semiannual oscillation msao seen at more equatorial latitudes but which is influenced as well by the seasonal variations of the mesospheric jet structure at higher latitudes major features of the zonal mean wind structure include a downward progression of strong eastward and westward phases of the msao from january to july coinciding with the period during which the msao and the annual cycle of the zonal mean wind at higher latitudes are in phase this results in an eastward maximum of 60 ms 1 near 80 km during january and february which descends rapidly and a westward maximum of 50 ms near 85 km during march and april which descends much more slowly the second msao cycle is greatly suppressed relative to the first due to the reversal of the correlation between this and the annual cycle at higher latitudes from july to december mean eastward motions occur primarily above 85 km early in this cycle and throughout the height range at later times planetary wave activity is seen to contribute substantial variability during times of eastward mean flow and to have a smaller role when zonal mean motions are westward tidal and 2 day motions are found to be large and variable with the maximum 2 day amplitudes occurring during february and august the largest diurnal tides were observed during october and november march and april and july and august while the semi diurnal amplitudes exhibited a minimum from april to june

study of mesosphere lower thermosphere mlt mean winds over yamagawa 31 2 n 130 6 e during 1996 1998 the mean motions in the mesosphere and lower thermosphere from 70 to 98 km were observed with the recently installed mf radar at yamagawa 31 2 n 130 6 e we have utilized the continuous wind data collected during the 3 year period 1996 1998 seasonal variations of mean winds over the site are constructed and the climatologies are then compared with observations from similar latitudes and the latest empirical model results the mean zonal circulation in the mesosphere is characterized by a clear annual variation with summer westward easterly flow and winter eastward westerly flow the summer westward jet closes at a height in between 80 and 85 km southward motion exhibits its dominance at 90 98 km during all times of the year and at lower heights 70 90 km southward northward motions predominate during summer winter season the annual mean zonal wind has an eastward motion in the 70 98 km it maximizes at around 90 km with a strength of 15 17 m s the annual mean meridional circulation shows both poleward and equatorward motions harmonic analysis of mean zonal winds clearly demonstrates the dominance of annual oscillation over the other periods comparison of mean winds over yamagawa japan and london ontario canada demonstrates that the zonal circulation over these two sites has some similar features similarly the results compared for yamagawa and urbana show some consistency in mean wind circulation the paper also presents the results of the comparison of mf radar derived winds and the hwm93 model outputs there is reasonable agreement between the observation and the model values

polar mesosphere and lower thermosphere dynamics 1 mean wind and gravity wave climatologies 1 mean wind and gravity wave climatologies are presented for the polar mesosphere and lower thermosphere mlt the data were derived using mf radars at davis 69 s 78 e and syowa 69 s 40 e in the antarctic and poker flat 65 n 147 w and andenes 69 n 16 e in the arctic the dynamics of the antarctic mlt are found to be significantly different from the arctic mlt summer maxima in both the westward and equatorward winds occur closer to the solstice in the antarctic than in the arctic the greater symmetry around the solstice suggests radiative effects may play a greater role in controlling the state of the antarctic mlt than in the arctic where dynamical effects appear to be more important gravity wave observations also suggest that wave drag may be greater in the arctic than in the antarctic the equatorward flow near the mesopause persists later in summer in the arctic than in the antarctic as do observations of polar mesospheric clouds and polar mesospheric summer echoes all three phenomena begin at about the same time in each hemisphere but end later in the arctic than in the antarctic it is proposed that the magnitude of the meridional winds can be used as a proxy for gravity wave driving and the consequent adiabatic cooling in the mlt seasonal variations in gravity wave activity are predominately combinations of annual and semiannual components significant hemispheric differences are observed for both the timing and magnitude of these seasonal variations

mean winds and tides in the upper middle atmosphere at urbana 40 n 88 w during 1991 1992 a summary of the first 18 months of continuous wind observations using the urbana medium frequency mf radar is presented emphasis is placed on height time contours of monthly mean winds and on amplitudes and phases of 24 hour and 12 hour tides results are compared with data from other midlatitude stations and models below 85 km monthly mean winds are shown to agree closely with the zonal mean geostrophic wind model cira86 significant discrepancies above 85 km have been noted in comparisons between cira86 and the other mesosphere lower thermosphere mlt radar stations including mf meteor and low frequency lf radars and are also sustained in the observations reported here tidal characteristics are generally consistent with other midlatitude observations although significant differences are noted between urbana and its closest mlt network neighbor station durham 43 n 71 w the mean wind observations provide a context for the gravity wave climatology derived from na lidar observations at urbana and promise to contribute toward improvements of middle atmosphere wind and tidal models

climatology and modeling of quasi monochromatic atmospheric gravity waves observed over urbana illinois from analyzing nine months of airglow imaging observations of atmospheric gravity waves agws over adelaide australia 35 s walterscheid et al 1999 have proposed that many of the quasi monochromatic waves seen in the images were primarily thermally ducted here are presented 15 months of observations from february 1996 to may 1997 for agw frequency and propagation direction from a northern latitude site urbana illinois 40 n as adelaide urbana is geographically distant from large orographic features similar to what was found in adelaide the agws seem to originate from a preferred location during the time period around summer solstice in conjunction with these airglow data there exists mf radar data to provide winds in the 90 km region and near simultaneous lidar data which provide a temperature climatology the temperature data have previously been analyzed by states and gardner 2000 the temperature and wind data are used here in a full wave model analysis to determine the characteristics of the wave ducting and wave reflection during the 15 month observation period this model analysis is applied to this and another existing data set recently described by nakamura et al 1999 it is shown that the existence of a thermal duct around summer solstice can plausibly account for our observations however the characteristics of the thermal duct and the ability of waves to be ducted is also greatly dependent on the characteristics of the background wind a simple model is constructed to simulate the trapping of these waves by such a duct it is suggested that the waves seen over urbana originate no more than a few thousand kilometers from the observation site

empirical models for predicting the erosion reducing effects of plant roots during concentrated flow erosion recent research indicates that plant roots can reduce soil erosion rates during concentrated flow significantly earlier studies revealed the erosion reducing effects of plant roots under controlled laboratory conditions and presented some equations applicable to the tested soil and flow conditions only although an attempt was made to unravel the impact of different environmental plant and flow properties on the erosion reducing potential of plant roots during concentrated runoff significant effects were hard to demonstrate because of the small number of data therefore the objective of this study is to pool different datasets 384 data collected under standardized experimental conditions in total together for constructing empirically based models predicting 1 soil detachment rates for both bare and root permeated topsoils and 2 the erosion reducing potential of plant roots during concentrated flow erosion the model that best predicts absolute soil detachment rates from bare and root permeated silt or sandy loam topsoils asd requires information on root density topsoil moisture content prior to concentrated flow erosion bulk density and mean bottom flow shear stress although all these variables contribute significantly to the prediction of asd the validation results indicate that there is still a large scatter on the data especially for small detachment rates the model tends to overestimate the observed values another model predicting the reduction in detachment rates of root permeated topsoils compared to bare ones rsd does not show good validation results either however the model for fibrous root systems was found to be very promising this model explains 79 of the variation using only root density and soil texture information and the validation results show that 69 of the variation in the validation dataset is accounted for by the model for topsoils permeated with tap root systems however the model results were not satisfactory only 10 of the variation in the validation dataset could be explained by a model using root density and mean root diameter as input variables we conclude that the erosion reducing effect of topsoils permeated with fibrous roots can be predicted very well whereas relative erosion rates for tap root permeated topsoils still remain difficult to predict with the studied variables only more process based knowledge is needed to distinguish erosion reducing effects from erosion accelerating effects for tap root permeated topsoils

assimilation of felsic crust by basaltic magma thermal limits and extents of crustal contamination of mantle derived magmas basaltic magma is the most widely used probe of mantle chemistry and structure chemical characterization of the sources for mantle derived magma is possible only after quantitative evaluation of possible contamination by crustal wall rocks the most commonly invoked contamination mechanisms are the combined processes of crustal assimilation and magmatic fractional crystallization afc because of the energetic link between these processes predicting assimilation and crystallization progress requires modeling both heat and mass transfer in the magma country rock system using the melts software package we modeled isenthalpic heat balanced afc between two common types of basaltic magma and several types of felsic crust at 1 kbar our simulations show that during the early stages of isenthalpic afc the ratio of rates of assimilation to crystallization r may be substantially greater than one 2 0 2 7 allowing assimilation of a mass of country rock up to 5 18 of the initial magma mass with only 3 7 crystallization the second stage of afc beginning with plagioclase and or pyroxene saturation is characterized by lower r 0 5 1 0 the initial high r stage results from suppression of crystallization associated with the change in magma composition as assimilation progresses under certain conditions even small degrees of crystallization of olivine alone coupled with cooling of the magma can accommodate relatively large amounts of crustal assimilation and cause large shifts in isotopic and trace element geochemical indices with little differentiation

petrology of hypabyssal kimberlites relevance to primary magma compositions abstract hypabyssal kimberlites are similar in their mineralogy and geochemistry across the world and thus form a distinct magma type that is produced repeatedly in time and space this small volume magma is derived from the asthenosphere 200 650 km and as it nears the surface consists of olivine macrocrysts i e xenocrysts 25 vol olivine phenocrysts 25 vol entrained in a ba ti mg rich al poor carbonate silicate liquid containing high but unknown amounts of dissolved co2 ch4 and h2o hypabyssal kimberlites are shown to be hybrid rocks formed by mixing with and assimilation of mantle derived lherzolite and harzburgite orthopyroxene is not stable in these magmas and its resorption leads the precipitation of primary liquidus olivine the magma crystallizes rapidly at crustal levels to uniform holocrystalline rocks that do not contain glass in addition to spinel perovskite monticellite apatite and phlogopite kinoshitalite primary carbonates are typically present as low pressure liquidus phases serpentines primary polygonal serpentine and chrysotile and carbonate commonly crystallize together from volatile rich co2 h2o deuteric residua as a polycrystalline mesostasis or discrete segregations the latter are not in filled vesicles kimberlite magmas have a very long crystallization interval ranging from 1200 to 300 c and there is a continuum from the magmatic crystallization of silicate and oxide minerals to carbo hydrothermal residua forming the calcite serpentine mesostasis it is concluded that there are no hypabyssal kimberlites which are representatives of the initial primary magma all kimberlites are hybrid and contaminated magmas which have undergone crystallization in the mantle prior to crystallization of the groundmass mesostasis assemblages

degassing in kimberlite oxygen isotope ratios in perovskites from explosive and hypabyssal kimberlites interest in the radiogenic and trace element characteristics of uncontaminated kimberlitic magma has been rekindled by recent isotope studies on groundmass perovskite which is a major sink of most of the trace elements including rare earth elements ree in kimberlite magma perovskite is also quite resistant to sub aerial weathering in situ trace element oxygen isotope ratios and conventional tims sr isotopic analyses of perovskites are presented for two kimberlites one from orapa a crater facies group i kimberlite from botswana and the other from wesselton a hypabyssal facies group i kimberlite from south africa the perovskites from orapa exhibit greater ranges in trace element abundances and 87sr 86sr ratios than those from wesselton la 7000 13 600 times primitive mantle and 87sr 86sr 0 70310 0 70541 in orapa perovskites and la 4000 7000 times primitive mantle and 87sr 86sr 0 70441 0 70558 in wesselton the 18o values from orapa perovskites have two distinct peaks around 3 6 and 0 6 which are unlikely to reflect crustal assimilation processes wesselton perovskites in contrast are clustered around 18o values of 4 perovskite in equilibrium with the mantle has lower 18o than other common upper mantle minerals olivine orthopyroxene the group of orapa perovskites with 18o clustering around 3 6 and the wesselton perovskites are interpreted to have 18o values 4 2 that reflect the 18o of uncontaminated kimberlite magma of an upper mantle origin 5 2 the negative 18o values from the second group of orapa perovskites are attributed to crystallisation of perovskite after magma degassing that depleted 18o in the residual magma abundance of magmatic carbonate in the wesselton sill together with the absence of any perovskite with very low 18o indicates a lack of significant degassing for the wesselton kimberlite

effects of microbiotic crusts under cropland in temperate environments on soil erodibility during concentrated flow several studies illustrate the wind and water erosion reducing potential of semi permanent microbiotic soil crusts in arid and semi arid desert environments in contrast little is hitherto known on these biological crusts on cropland soils in temperate environments where they are annually destroyed by tillage and quickly regenerate thereafter this study attempts to fill the research gap through a a field survey assessing the occurrence of biological soil crusts on loess derived soils in central belgium in space and time and b laboratory flume 2 m long experiments simulating concentrated runoff on undisturbed topsoil samples 0 4 0 1 m2 quantifying the microbiotic crust effect on soil erosion rates three stages of microbiotic crust development on cropland soils are distinguished 1 development of a non biological surface seal by raindrop impact 2 colonization of the soil by algae and gradual development of a continuous algal mat and 3 establishment of a well developed microbiotic crust with moss plants as the dominant life form as the silt loam soils in the study area seal quickly after tillage microbiotic soil crusts are more or less present during a large part of the year under maize sugar beet and wheat representing the main cropland area on average the early successional algae dominated crusts of stage 2 reduce soil detachment rates by 37 whereas the well developed moss mat of stage 3 causes an average reduction of 79 relative soil detachment rates of soil surfaces with microbiotic crusts compared with bare sealed soil surfaces are shown to decrease exponentially with increasing microbiotic cover b 0 024 for moss dominated and b 0 006 for algae dominated crusts in addition to ground surface cover by vegetation and crop residues microbiotic crust occurrence can therefore not be neglected when modelling small scale spatial and temporal variations in soil loss by concentrated flow erosion on cropland soils in temperate environments copyright 2007 john wiley sons ltd

further evidence of hemispheric differences in the mlt mean wind climatology simultaneous mf radar observations at poker flat 65 n 147 w and davis 69 s 78 e 1 results of a comparative study of the wind fields in the mesosphere and lower thermosphere over poker flat 65 n 147 w and davis 69 s 78 e are presented the study utilized the mf radar wind data collected simultaneously during the period 1999 2000 mean winds during this period are examined to study the hemispheric features emphasis has been given to the climatological variations over these two high latitude stations the results suggest large hemispheric differences in the mean circulation further the observed mean wind characteristics are compared with results obtained from other high latitude stations

biological soil crust development and its topsoil properties in the process of dune stabilization inner mongolia china this study was undertaken at horqin sand land inner mongolia northern china field samples of biological soil crusts bscs and underlying topsoil 0 5 cm under bsc were taken in areas of different dune stabilization stages and their physicochemical properties were analyzed including particle size distribution bulk density organic matter nitrogen phosphorus electrical conductivity ec ph and caco3 content the results revealed that semi mobile dunes semi fixed dunes and fixed dunes had developed a physical crust algae crust and moss crust respectively the thickness hardness water content fine fraction and nutrient contents of bscs were gradually increasing along the dune stabilization gradient meanwhile bsc establishment and development enhanced the bulk density silt and clay content and nutrients of the topsoil under it in an increasing tend from semi mobile dune to fixed dune organic matter concentrations and other nutrients in the 0 5 cm topsoil layer under bscs were significantly higher compared to unconsolidated soil control moreover there were strong significant positive correlations between topsoil and bscs organic matter total nitrogen available nitrogen available phosphorus caco3 and 0 05 mm particle content suggesting that bscs have an influence on some of the properties of the underlying topsoil

a long term comparison of middle atmosphere winds measured at saskatoon 52 n 107 w by a medium frequency radar and a fabry perot interferometer since late 1988 a medium frequency radar mfr and an imaging fabry perot interferometer fpi have been operating continuously at saskatoon measuring winds and waves in the upper mesosphere and lower thermosphere when weather and auroral conditions permit the fpi measures doppler winds from the atomic oxygen oi 557 7 nm airglow layer centered at an altitude of about 97 km this study is similar to earlier comparisons between the mfr fpi systems except that it draws on 4 years of simultaneous observations because the mfr and fpi are somewhat mutually exclusive in their data acquisition rate real time comparisons of winds are often poor however with the much larger fpi data set now available rather better long term comparisons between the two systems can be made once again strong similarities in the mf radar and fpi doppler wind fields are observed although there are some differences these differences and the causes are discussed

observations of tidal temperature and wind perturbations in the mesopause region above urbana il 40 n 88 w na lidar and mf radar measurements of temperature and horizontal winds were conducted simultaneously during several continuous 24 h periods in march and april 1996 at the urbana atmospheric observatory the data are used to determine the amplitude and phase profiles of the 24 and 12 h tides in the mesopause region between about 82 and 100 km the measured amplitudes and phases of the tidal components of the horizontal winds are generally consistent with the predictions of the global scale wave model gswm the measured 24 h temperature amplitude is comparable to the gswm predictions between 85 and 96 km but is significantly larger than gswm above 96 km the measured phase progression is downward below 94 km with an inferred vertical wavelength of 14 1 km above 94 km the temperature phase progression is upward with a vertical wavelength of 12 1 km the measurements suggest the presence of a diurnal heat source in the lower thermosphere which is generating a strong downwardly propagating 24 h wave

a comparison study of the auroral lower thermospheric neutral winds derived by the eiscat uhf radar and the tromso medium frequency radar 1 a comparative study of the neutral wind in the polar upper mesosphere lower thermosphere is conducted using two radars the european incoherent scatter eiscat uhf radar 931 mhz and the tromso mf radar 2 8 mhz colocated in northern scandinavia comparisons of winds are made in case studies as well as on a statistical basis on the basis of simultaneous observations obtained by the two radars comparisons over a height range from 90 to 100 km are made for about 20 days between february and october 1999 in these comparisons we directly compare temporal wind variations on the other hand mean winds as well as diurnal and semidiurnal components are derived using 1 month averaged wind data obtained by the medium frequency mf radar for 1999 they are compared with those derived from 56 days of eiscat data studied by nozawa and brekke 1999a 1999b in the case studies we have also utilized altitude profiles of electron density obtained by the eiscat radar at and above 62 km height to determine the total reflection height as well as to estimate the effect of group retardation for 2 8 mhz radio wave it can be seen that the effect of particle precipitation sometimes penetrates into the d region down to 84 km generally wind velocities derived by eiscat with the monostatic method exhibit significant scatter with time below 100 km while the number of the mf radar wind data sharply decreases above 90 km except for summer these facts make the comparison difficult but no significant departures between different radar winds are identified on an instantaneous basis in the statistical studies generally both altitude profiles are well connected or continuous but significant disagreements are observed for the mean wind and the tidal components for summer on the basis of these comparisons we raise strong concerns regarding the use of summer wind data above 91 km obtained by mf radar located at high latitude under high solar activity conditions the wind values during the winter and equinox observed by the two radars are complementary thus here is a good opportunity to utilize wind data from the two different radars through a year which then enables us to cover a wide height range approximately 70 120 km this wide range gives us good opportunities to examine the mesosphere lower thermosphere coupling processes based on observational data

using perovskite to determine the pre shallow level contamination magma characteristics of kimberlite abstract it remains difficult to obtain reliable geochemical signatures of uncontaminated kimberlite magma from bulk rock studies due to the combined effects of crustal assimilation and element mobility during post emplacement alteration processes groundmass perovskite catio 3 a typical accessory phase from orapa botswana and wesselton south africa kimberlites has been used to evaluate the isotope and trace element composition of the pre contamination magmas and the effects of shallow level contamination in situ trace element signatures of orapa and wesselton perovskite grains are broadly similar and unaffected by crustal contamination single grain 87 sr 86 sr isotope ratios of perovskite from orapa 0 7030 0 7036 are less scattered than bulk rock analyses 0 7063 0 7156 which are variably affected by contamination and late stage alteration initial 87 sr 86 sr isotope ratios of perovskite 0 7044 0 7049 from wesselton overlap with published whole rock studies on fresh hypabyssal kimberlites 0 7042 0 7047 the limited intra kimberlite variation in sr isotope ratios recorded by the perovskite are unlikely to be due to crustal contamination as the calculated liquid compositions in equilibrium with the perovskite analysed typically have 1500 ppm sr and most common crustal lithologies underlying these kimberlites have relatively low sr contents and are not highly radiogenic calculated pre shallow level contamination magma compositions for orapa and wesselton have significantly fractionated lree and highly variable non smooth trace element patterns initial sr and nd isotope ratios of both kimberlites fall on the mantle nd sr array with enriched sr and slightly depleted nd signatures similar to group i kimberlites overall the trace element and isotopic composition of orapa and wesselton kimberlites are similar to the reported group i kimberlites from southern africa which are derived by very low degrees of partial melting from a lree depleted metasomatised sub continental lithospheric mantle sclm source

the potential roles of biological soil crusts in dryland hydrologic cycles biological soil crusts bscs are the dominant living cover in many drylands of the world they possess many features that can influence different aspects of local hydrologic cycles including soil porosity absorptivity roughness aggregate stability texture pore formation and water retention the influence of biological soil crusts on these factors depends on their internal and external structure which varies with climate soil and disturbance history this paper presents the different types of biological soil crusts discusses how crust type likely influences various aspects of the hydrologic cycle and reviews what is known and not known about the influence of biological crusts on sediment production and water infiltration versus runoff in various drylands around the world most studies examining the effect of biological soil crusts on local hydrology are done by comparing undisturbed sites with those recently disturbed by the researchers unfortunately this greatly complicates interpretation of the results applied disturbances alter many soil features such as soil texture roughness aggregate stability physical crusting porosity and bulk density in ways that would not necessarily be the same if crusts were not naturally present combined these studies show little agreement on how biological crusts affect water infiltration or runoff however when studies are separated by biological crust type and utilize naturally occurring differences among these types results indicate that biological crusts in hyperarid regions reduce infiltration and increase runoff have mixed effects in arid regions and increase infiltration and reduce runoff in semiarid cool and cold drylands however more studies are needed before broad generalizations can be made on how biological crusts affect infiltration and runoff we especially need studies that control for sub surface soil features such as bulk density micro and macropores and biological crust structure unlike the mixed effects of biological crusts on infiltration and runoff among regions almost all studies show that biological crusts reduce sediment production regardless of crust or dryland type copyright 2006 john wiley sons ltd

dynamics of the equatorial mesosphere first results with a new generation partial reflection radar the first observations of mesospheric winds made between january august 1990 with an mf partial reflection radar located on christmas island 2 n 157 w in the central pacific are described the mean zonal winds are in general westward but show clear evidence for a wave driven circulation power spectral studies indicate that waves are present over a wide range of periods ultra fast kelvin waves are especially evident in january march with peak amplitudes 20 ms 1 and intrinsic phase speeds of 150 ms 1 indicated the kelvin waves are estimated to contribute an eastward acceleration of up to 10 ms 1 day 1 gravity wave amplitudes are also found to be almost as large as those observed at mid latitude sites which suggests that convection is a major source of gravity wave activity

tidal signatures in temperature data from crista 1 mission temperature measurements in the stratosphere and mesosphere were taken during the first cryogenic infrared spectrometers and telescopes for the atmosphere crista 1 mission using co2 emissions these measurements range from 13 to close to 100 km and individual temperature measurements have a precision of 1 k the crista orbit was circular at an inclination of 57 so local time variations during the 7 day mission were small for a given latitude and orbit leg zonal averages of the data show significant structure in the vertical and as a function of latitude temperature differences between the zonal mean data from the ascending and descending portions of the orbit are of the form expected from the diurnal tide the maximum zonal mean difference is 20 k and occurs over the equator at an altitude of 75 km zonal variations in the temperature difference indicate that the tidal amplitude is not uniform at all longitudes at the equator the maximum amplitude 30 k appears over the african sector and the minimum 10 k over the pacific sector this variation is most likely a nonmigrating wavenumber 2 diurnal tide although other less plausible possibilities exist to facilitate comparisons with model results the temperature variations are converted to equivalent vertical displacements assuming the tidal motions are adiabatic such an approach is appropriate in the mesosphere where diurnal variations due to radiative effects are small and reduces the dependence of the measured temperature amplitude on the background temperature profile equivalent vertical displacements are also calculated using results from the global scale wave model for the most part the model results and observations are in excellent qualitative and good quantitative agreement from the tropopause to the mesopause however the observed vertical wavelength is smaller and its amplitude in terms of equivalent displacement is smaller in the upper mesosphere than that in the model the decrease in amplitude is consistent with that expected from the transition from equinox to solstice conditions

effect of natural restoration time of abandoned farmland on soil detachment by overland flow in the loess plateau of china vegetation restoration has significant effects on soil properties and vegetation cover and thus affects soil detachment by overland flow few studies have been conducted to evaluate this effect in the loess plateau where a great green project was implemented in the past decade this study was carried out to quantify the effects of age of abandoned farmland under natural vegetation restoration on soil detachment by overland flow and soil resistance to erosion as reflected by soil erodibility and critical shear stress the undisturbed soil samples were collected from five abandoned farmlands with natural restoration age varying from 3 to 37 years the samples were subjected to flow scouring in a 4 0 m long by 0 35 m wide hydraulic flume under six different shear stresses ranging from 5 60 to 18 15 pa the results showed that the measured soil detachment capacities in currently cultivated farmland were 24 1 to 35 4 times greater than those of the abandoned farmlands for the abandoned farmlands soil detachment capacities fluctuated greatly due to the complex effects of root density and biological crust thickness and could be simulated well by flow shear stress and biological crust thickness with a power function nse 0 851 soil erodibility of abandoned farmlands decreased gradually with restoration age and reached a steady stage when restoration age was greater than 28 years the critical shear stress of the natural abandoned farmlands declined when restoration age was less than 18 years and then increased due to the episodic influences of vegetation recovery and biological crust development more studies in the loess plateau are necessary to quantify the relationship between soil detachment capacity and biological crust thickness for better understanding the mechanism of soil detachment under natural vegetation restoration copyright 2013 john wiley sons ltd

winds and waves from the canadian prairies cnsr triple mf radar system two medium frequency radars have been developed 500 km from the saskatoon mf radar 52 2n 107 1w to form a triangle within the canadian prairies the western system is at sylvan lake 52 4n 114 1w in the lee of the rockies and the southern system is at robsart 49 2n 109 3w in this preliminary assessment of winds data daily mean winds and solar tides 24 12 hour are shown to be very similar with short term variations of several days being seen at all three radars this shows that such short term changes are of larger scale than 500 km variations of the wind field with periods ranging from minutes to several hours are seen at all radars presumably associated with internal gravity waves of these only the longer periods appear to be correlated over this spatial scale spectral analysis techniques developed for the smaller gravnet system are applied to these oscillations as are hodograph techniques to determine the igw characteristics

penetration resistance of biological soil crusts and its dynamics after crust removal relationships with runoff and soil detachment abstract soil sealing and crusting are common widespread processes in arid and semiarid soils that strongly affect runoff and erosion in these soils biological soil crusts bscs are an essential surface component known to have an important role in water processes and are also strong erosion protection agents however these crusts are also highly vulnerable to disturbances which seriously affect their pedological and ecological roles the aims of this study were to examine whether penetration resistance pr depends on bsc developmental stage and how removal of bscs affects pr under dry and wet soil conditions and to analyse the relationship between pr and runoff and soil detachment in these soils this research was conducted in two semiarid ecosystems representative of crusting processes in se spain el cautivo and las amoladeras almeria province four pairs of plots containing the main bsc types identified at both sites were selected and two treatments were considered one in each plot in the pair i unaltered bsc and ii bsc removal by scraping two intense rainfall simulation experiments were performed one after another in these plots runoff was measured during both and water samples were collected for further determination of sediment yield pr was measured in undisturbed bsc and scalped soil on dry soil prior to rainfall on wet soil after the first and second rainfalls and on dry soil seven months after bsc removal crust pr was higher at las amoladeras 3 13 0 54 kg cm 2 than at el cautivo 1 52 0 74 kg cm 2 due to soil compaction from trampling by livestock in the former pr varied with bsc development with less developed cyanobacteria bscs showing higher resistance under dry and wet conditions than more developed lichen bscs bsc removal was followed by the formation of a new seal physical crust upon raining which however did not result in increased pr no significant relationship was found between pr and runoff but there was a weak negative relationship between pr and soil detachment because in bscs which had higher prs soil detachment rates were much lower than in recently scalped soils seven months after bsc removal pr was significantly higher in scalped soils than for undisturbed bscs our results show that pr was not a good indicator of hydrological and soil detachment response of bscs or the soil sealing during rain immediately after bsc removal but it was a good indicator of physical soil crust formation in scalped soils over time

climatology of mesospheric gravity wave activity over urbana illinois 40 n 88 w a 5 year 1991 1995 climatology of mesospheric gravity wave activity observed with the urbana medium frequency mf radar is presented we focus on the monthly mean horizontal wind variances associated with gravity waves with observed periods between 10 min and 8 hours these results are compared with the seasonal characteristics from other gravity wave observations the total wave variance displays a dominant semiannual variation maxima summer winter minima spring fall below 87 km with little seasonal variation above 87 km the zonal wave variance exceeds the meridional wave variance except around regions of zonal wind reversal in all seasons the observed variance scale height is greater than that of a nondissipating wave field a simple zero mean wind model based on linear saturation theory is found to be inadequate in reproducing the seasonal characteristics of the observed wave variances an alternative model based on critical layer filtering by a height dependent wind field can reproduce the observed semiannual oscillation in the wave variance given a specific source input

doppler imager wind measurements with simulations from the ncar thermosphere ionosphere mesosphere electrodynamics circulation model in this paper a comparison is presented between simulations of the diurnal and semidiurnal tides in the middle and upper atmosphere from the thermosphere ionosphere mesosphere electrodynamics general circulation model timegcm and satellite observations from the upper atmosphere research satellite uars high resolution doppler imager hrdi reasonable agreement is found between the model and observations for a march condition when a strong diurnal tide was observed the model is able to reproduce many tidal features at altitudes between 65 and 110 km as observed in the hrdi wind measurements of interest in these features is the shortening vertical wavelength of the 1 1 tide in the upper mesosphere and lower thermosphere which appears in both model simulations and the wind observations the hrdi data also show large longitudinal variations in the diurnal tide of which the amplitude can be as high as 50 of the migrating tide the wavelike structures in latitude and altitude dimensions suggest that the longitudinal variations are likely due to the presence of propagating nonmigrating tides in the upper mesosphere and lower thermosphere for further investigations of the observed tidal variability the model demonstrates great potential with the use of more realistic heating cooling and wave forcing schemes

quantifying the surface covering binding and bonding effects of biological soil crusts on soil detachment by overland flow biological soil crusts bscs have impacts on soil detachment process through surface covering and binding and bonding b b mechanisms which might vary with successional stages of bscs this study was conducted to quantify the effects of surface covering binding and bonding of bscs on soil detachment capacity by overland flow in a 4 m long hydraulic flume with fixed bed two dominant bsc types developed well in the loess plateau the early successional cyanobacteria and the later successional moss were tested using natural undisturbed soil samples collected from the abandoned farmlands two treatments of undisturbed crusts and one treatment of removing the above ground tissue of bscs were designed for each bsc type for comparison bare loess soil was used as the baseline the collected soil samples were subjected to flow scouring under six different shear stresses ranging from 6 7 to 21 2 pa the results showed that soil detachment capacity dc and rill erodibility kr decrease with bsc succession and the presence of bscs obviously increased the critical shear stress especially for the later successional moss crust for the early successional cyanobacteria crust dc was reduced by 69 2 compared to the bare loess soil where 37 7 and 31 5 are attributed to the surface covering and b b respectively for the later successional moss crust dc decreased by 89 8 compared to the bare loess soil where 68 9 and 20 9 contributed to the surface covering and b b respectively these results are helpful in understanding the influencing mechanism of bscs on soil erosion and in developing the process based erosion models for grassland and forestland copyright 2017 john wiley sons ltd

mesospheric gravity waves at saskatoon 52 n kyoto 35 n and adelaide 35 s the gravity waves with periods of 10 min to 8 hours in the mesosphere 67 80 km are studied using observations from the adelaide mf radar 35 s saskatoon mf radar 52 n and the middle and upper atmosphere mu radar at shigaraki near kyoto 35 n the seasonal variations of the gravity wave intensity deduced from the horizontal wind velocities showed semiannual variations with solstitial maxima and equinoctial minima at all three locations but the month of maximum intensity in the year depends on the locations and wave frequency the kinetic energy due to gravity waves showed similar amplitude between kyoto and adelaide but smaller at saskatoon which agrees well with the results of the preliminary comparison using a limited frequency range and limited observation periods by nakamura et al 1993a b the horizontal propagation direction of these gravity waves showed small seasonal variations and significant dependency with wave periods at saskatoon but showed more frequent variation without a large frequency dependency at kyoto and adelaide these characteristics indicate that at the lower latitudes gravity wave activity is larger as pointed out by tsuda et al 1994 from various observational techniques also the frequent changes of the gravity wave intensities at the lower latitudes suggest that there are strong influences of the background wind variation in the middle atmosphere such as semiannual oscillation mesospheric semiannual oscillation and other wind variations in the low latitudes

in situ u pb age determination and nd isotopic analysis of perovskites from kimberlites in southern africa and somerset island canada abstract determination of the emplacement ages and initial isotopic composition of kimberlite by conventional isotopic methods using bulk rock samples is unreliable as these rocks usually contain diverse clasts of crustal and mantle derived materials and can be subject to post intrusion sub aerial alteration in this study 8 samples from 5 kimberlites in southern africa and twelve samples from 7 kimberlites from somerset island canada have been selected for in situ perovskite u pb isotopic age determination and nd isotopic analysis by laser ablation using thin sections and mineral separates these fresh perovskites occur as primary groundmass minerals with grain sizes of 10 100 m they were formed during the early stage of magmatic crystallization and record data for the least contaminated or contamination free kimberlitic magma u pb isotopic data indicate that the majority of the southern africa kimberlites investigated were emplaced during the cretaceous with ages of 88 3 to 97 6 ma although one sample yielded an early paleozoic age of 515 6 ma twelve samples from somerset island yielded ages ranging from 93 4 ma to 108 5 ma and are contemporaneous with other cretaceous kimberlite magmatism in central canada 103 94 ma although whole rock compositions of the kimberlites from southern africa have a large range of end t values 0 5 to 5 1 the analysed perovskites show a more limited range of 1 2 to 3 1 perovskites from somerset island have end t values of 0 2 to 1 4 these values are lower than that of depleted asthenospheric mantle suggesting that kimberlites might be derived from the lower mantle this study shows that in situ u pb and nd isotopic analysis of perovskite by laser ablation is both rapid and economic and serves as a powerful tool for the determination of the emplacement age and potential source of kimberlite magmas

tides in the mesopause region over fort collins colorado 41 n 105 w based on lidar temperature observations covering full diurnal cycles 1 eighteen sets of 24 hour continuous lidar temperature observation well distributed throughout the year have been analyzed to reveal the mean amplitude and phase of oscillations with 24 12 8 and 6 hour periods for four seasons the amplitude and phase of both 24 and 12 hour components are compared to the prediction of the most recent global scale wave model gswm 00 the variability of diurnal and semidiurnal oscillations is examined by comparing the amplitude and phases of each observed day in autumn winter and spring even with the limited data sets reported here surprisingly good general agreement between the observed and model tidal phases can be established implicating the prevalence of migrating diurnal and semidiurnal tides compared to the diurnal and semidiurnal phases which typically show clear downward phase progression the 8 and 6 hour components exhibit small amplitude and show unorganized phase propagation as a function of altitude the advantage of having coverage over complete diurnal cycle and entire mesopause altitudes as demonstrated here would hopefully stimulate future tidal studies with lidar temperature and zonal and meridional wind observations

seasonal variation of diurnal perturbations in mesopause region temperature zonal and meridional winds above fort collins colorado 40 6 n 105 w 1 on the basis of lidar observations from may 2002 through april 2003 covering both day and night we performed a harmonic analysis to extract the diurnal perturbations in mesopause region temperature zonal and meridional winds over fort collins colorado 40 6 n 105 w binned every 2 months the results were compared to predictions of the 2000 and 2002 versions of global scale wave model gswm00 and gswm02 the diurnal tidal period oscillations showed a mixture of propagating and evanescent trapped modes but the propagating modes dominated for most of the year the agreement in temperature diurnal phases between observation and gswm prediction is marginal on the other hand other than july august meridional winds the observed diurnal phases in both wind components are in good agreement with gswm predictions for most of the altitude range reported the diurnal amplitude predictions of gswm00 were reasonably close to lidar observations while other than january february the gswm02 amplitude prediction overestimated the observations typically by a factor of two we also conducted comparisons on tidal perturbations in zonal wind between radar campaigns and our lidar observations the lidar data agreed reasonably well with the mf radar data from 2000 to 2001 at nearby platteville colorado 40 2 n 104 7 w but showed considerable differences with the data from other midlatitude stations from 1992 to 1993 the dominance of the evanescent mode in the temperature diurnal tidal oscillation during the early winter november and december which reached a peak value at midnight was interesting and anomalous by invoking the more recent data november and december in 2003 as well as the diurnal temperature observations from december 1998 we report that the evanescent trapped diurnal tidal perturbations were robust and persisted from one year to the next

medium frequency radar studies of gravity wave seasonal variations over hawaii 22 n 160 w 1 using simple numerical filters estimates of wind variances with period bands of 0 1 to 1 hour and 1 to 5 hours have been derived from data taken with the medium frequency radar on the island of kauai hawaii 22 n 160 w the observations cover altitudes of 70 to 90 km and extend over the years 1990 2000 the results show seasonal and interannual variations of the wind variances which can be attributed to atmospheric gravity waves the mean zonal wind has mainly an annual variation below an altitude of 83 km and a semiannual variation above the gravity waves have maximum intensity at the solstices below 83 km but at higher altitudes the times of the maxima shift to the equinoxes numerical simulations suggest this behavior results from the dependence of gravity wave generation and propagation on the background wind and temperature

comparisons between satellite derived gradient winds and radar derived winds from the cira 86 abstract satellite radiance data nimbus 5 6 80 km and the msis 83 model have been used to prepare global zonal mean gradient winds 30 120 km for the new cira 1986 here these are supplemented by planetary wave morphology from the same nimbus data to provide local gradient winds the zonal wind and the eddy portion of the meridional wind are calculated by this method these data are then compared with radar derived wind contours 60 110 km extending the comparisons done earlier manson et al for heights below 80 km overall the agreement for the zonal winds is good especially below 80 km differences are shown so the user can evaluate each product the comparison of meridional winds is particularly valuable and unique as it reveals considerable ageostrophy particularly in summer months near the height of the zonal wind s reversal from west to eastward flow coriolis torques due to this meridional flow are available from saskatoon 52 poker flat 65 and tromso 70 in the northern hemis

duration and periodicity of kimberlite volcanic activity in the lac de gras kimberlite field canada and some recommendations for kimberlite geochronology abstract establishing the emplacement ages and distribution pattern of central slave kimberlites has played a key role in diamond exploration within the lac de gras kimberlite field nonetheless emplacement age information is lacking for approximately 80 of the known kimberlites in this field making the assessment of emplacement age patterns difficult this study expands the number and geographic coverage of kimberlite emplacement ages within the lac de gras field to re assess the absolute timing duration and possible number of pulses of kimberlite eruption u pb perovskite ages for eight previously undated kimberlites and an additional thirteen kimberlites which were previously dated by either the rb sr or u pb methods fall within the age range of 75 45 ma as previously suggested for kimberlite magmatism in this area we report the first carboniferous age kimberlite in the central lac de gras field the eddie kimberlite with a u pb perovskite age of 321 0 3 0 ma a compilation of 57 kimberlite emplacement ages from the central lac de gras field was evaluated using probability density and mixture modeling methods five short duration 4 5 ma periods of kimberlite magmatism are recognized at 48 54 61 66 and 72 ma the three younger pulses have been previously recognized and remain relatively unchanged the 54 ma pulse represents the major kimberlite eruption event containing 40 of the currently dated kimberlites in lac de gras field a detailed evaluation of the temporal spatial evolution of lac de gras kimberlites reveals that the oldest diamond poor kimberlites 75 60 ma were emplaced in the northern and eastern parts of the field whereas the younger 55 48 ma economic kimberlites are concentrated in the center of the field

seasonal variations of semidiurnal tidal perturbations in mesopause region temperature and zonal and meridional winds above fort collins colorado 40 6 n 105 1 w 1 on the basis of colorado state university csu na lidar observations over full diurnal cycles from may 2002 to april 2006 a harmonic analysis was performed to extract semidiurnal perturbations in mesopause region temperature and zonal and meridional winds over fort collins colorado 40 6 n 105 1 w the observed monthly results are in good agreement with mf radar tidal climatology for urbana illinois and with predictions of the hamburg model of the neutral and ionized atmosphere hammonia sampled at the csu na lidar coordinates the observed semidiurnal tidal period perturbation within the mesopause region is found to be dominated by propagating modes in winter and equinoctial months with a combined vertical wavelength varying from 50 km to almost 90 km and by a mode with evanescent behavior and longer vertical wavelength 100 150 km in summer months most likely due to dominance of 2 2 and 2 3 tidal hough modes the observed semidiurnal tidal amplitude shows strong seasonal variation with a large amplitude during the winter months with a higher growth rate above 85 90 km and minimal amplitudes during the summer months maximum tidal amplitudes over 50 m s for wind and 12 k for temperature occur during fall equinox a detailed comparison with hammonia predictions shows excellent agreement in semidiurnal phases hammonia predicted semidiurnal amplitudes generally agree well with observations however hommonia underestimates temperature amplitudes in some of the nonsummer months as well as zonal wind and meridional wind amplitudes in april and september but overestimates them in february to reveal the effects of the atmospheric background on vertical propagation of tidal modes and their relative importance in the composite semidiurnal tide during different seasons we use the lidar observed monthly mean temperature and zonal wind from the same data set as well as hammonia output to calculate the vertical wave number seasonal variations of the major tidal modes of the migrating semidiurnal tide this leads to a qualitative understanding of the lidar observed and hammonia predicted seasonal variation of the semidiurnal tidal perturbation