field measurements of the flux and speed of wind blown sand a field experiment was conducted to measure the flux and speed of wind blown sand under known conditions in a natural setting the experiment run at pismo beach california involved a tract 100 m long parallel with the wind by 20 m wide the site was instrumented with four arrays of anemometers to obtain wind velocity profiles through the lower atmospheric boundary layer temperature probes to determine atmospheric stability and wind vanes to determine wind direction from these measurements wind friction speeds were derived for each experimental run in order to measure sand saltation flux a trench 3 m long by 10 m wide transverse to the wind direction by 0 5 m deep was placed at the downwind end of the tract and lined with 168 collector bins forming an egg box pattern the mass of particles collected in each bin was determined for four experimental runs in order to assess various sand trap systems used in previous experiments 12 leatherman traps one fryberger trap and one array of ames traps were deployed to collect particles concurrently with the trench collection particle velocities were determined from analysis of high speed 3000 and 5000 frames per second motion pictures and from a particle velocimeter sand samples were collected from the trench bins and the various sand traps and grain size distributions were determined fluxes for each run were calculated using various previously published expressions and then compared with the flux derived from the trench collection results show that bagnold s 1941 model and white s 1979 equation most closely agree with values derived from the trench comparison of the various collector systems shows that the leatherman and ames traps most closely agree with the flux derived from the trench although these systems tended to under collect particles particle speeds were measured from analysis of motion pictures for saltating particles in ascending and descending parts of their trajectories results show that particle velocities from the velocimeter are in the range 0 5 7 0 m s 1 compared to a wind friction velocity of 0 32 0 43 m s 1 and a wind velocity of 2 7 3 9 m s 1 at the height of the particle measurements descending particles tended to exceed the speeds of ascending particles by 0 5 m s 1

estimation of sampling efficiency of the big spring number eight bsne sampler at different heights based on sand particle size in the taklimakan desert abstract the big spring number eight bsne sampler is an important and widely used instrument in studies of aeolian sand transport its sampling efficiency is an important parameter and varies with particle size however little is known about the variations in sampling efficiency caused by the differences in particle size with height the variations in particle size with height from 10 to 200 cm were obtained from a field experiment at four sites in the taklimakan desert from may 2010 to april 2011 the variation in the sampling efficiency of the bsne sampler with particle size was estimated based on previous studies and a wind tunnel experiment it was found that the average particle size decreased with height above ground from 10 to 200 cm at three experimental sites while at the other site it decreased from 10 to 15 cm and then slightly increased the percentage distribution of particle sizes with height was similar for sizes below 63 m and between 125 and 200 m at all experimental sites but there were differences in the percentage of size classes between 63 and 125 m and above 200 m the sampling efficiencies ranged from 66 27 to 58 98 64 97 to 57 47 56 04 to 52 76 and 72 07 to 58 9 at the four sites respectively with an average of 64 84 to 57 03 at heights from 10 to 200 cm after correcting for sampling efficiency the amount of aeolian sand that passed through a section of 100 cm width 200 cm height increased by 44 5 52 1 78 8 and 26 4 at the four sites respectively with an average of 50 5 these results indicate that the sampling efficiency of the device needs to be considered when making observations across a gradient of particle sizes

grain size and transport characteristics of non uniform sand in aeolian saltation abstract size frequency distributions of sediment particles in a wind tunnel containing a bed of non uniform sand are investigated by re interpreting existing experimental data using particle size analysis each particle sample is classified into one of eight groups according to its size grading the analysis reveals that the modal shape of the particle size frequency distributions of the saltating sand at different elevations or longitudinal distances is similar to that of the mixed sand in the bed once the boundary layer is fully developed the standard deviation of the grain size frequency distribution increases with increasing elevation above the bed then stays constant whereas its skewness decreases the mean grain size decays exponentially with elevation the aeolian sand mass flux is determined for each size grading at different vertical and horizontal measurement locations the vertical profile of aeolian horizontal mass flux depends on the size grading the distribution of the sand transport rate according to the mean grain size in each grading fits the normal distribution a parameter w i is defined to reflect the likelihood of saltation for sand particles of the i th size grading and the mean sand size corresponding to the maximum value of w i is found to be 0 2 mm in addition wind velocity strongly influences the magnitudes of the particle size distribution and the sand mass flux distribution in both vertical and longitudinal directions

on the formation of ozone laminae at the edge of the arctic polar vortex ozone vertical profiles commonly display thin layered structures or laminae in the lower stratosphere of the extratropics predominantly during winter and spring the mechanism for their formation is still uncertain in this study high resolution isentropic transport of a passive tracer on synoptic time scales is performed with an off line transport model which is forced by winds derived from global meteorological analyses or forecasts the study focuses on a meteorological situation which occurred in late january 1992 on isentropic surfaces the tracer distribution initialized as the analysed potential vorticity is eroded into filamentary structures in the mid latitude surf zone repeated poleward intrusions of mid latitude air are shown to lead to the formation of convoluted filamentary structures at high latitudes by performing isentropic advection on many closely spaced independent levels the vertical structure of these tracer filaments can be studied they are shown to be part of tracer sheets which are vertically tilted in the shear zone in the vicinity of the polar jet thin laminar structures in the tracer vertical profiles appear as the result of isentropic wrapping and vertical shearing of such tracer sheets a comparison is made with ozone laminae found in balloon borne soundings during the european arctic stratospheric ozone experiment

local mixing events in the upper troposphere and lower stratosphere part i detection with the lyapunov diffusivity abstract a new diagnostic the lyapunov diffusivity is presented that has the ability to quantify isentropic mixing in diffusion units and detects local mixing events by describing latitude longitude variability it is a hybrid diagnostic combining the tracer based effective diffusivity with the particle based lyapunov exponent calculation isentropic mixing on the 350 k surface shows that there is significant longitudinal variation to the strength of mixing at the northern subtropical jet with a strong mixing barrier over asia and the western pacific a weaker mixing barrier over the western atlantic and active mixing regions at the jet exits over the eastern pacific and atlantic

differentiation of modern beach and coastal dune sands a logistic regression approach using the parameters of the hyperbolic function abstract particle size data have been obtained from sieved samples of sand from beach and coastal dune environments at ainsdale northwest england the four parameters of the hyperbolic distribution were calculated for each sample these together with additional derived parameters were the basis of a binomial logit regression model which sought to distinguish the two sand environments seventy five percent of the samples were correctly assigned by logistic equation containing a single independent variable which is a measure of the skewness of the hyperbolic distribution

3d ejection behavior of different sized particles in the grain bed collision process abstract the impact ejection process on a mixed grain size bed with granular packing was simulated with the discrete element method in order to understand the interaction between different sized grains in natural aeolian sand transport in this model the granular bed was formed by settling the randomly generated two sized particles under gravity and then a foreign particle was shot onto the granular bed at different speeds and angles the recorded speed direction and number of the ejected particles were then analyzed it was found that the probability distributions of the ejection speed and angle for different sized particles are all identical to those for the single size grain bed collision process the mean ejection speeds of different sized particles are nearly equal and the mean ejection angles of different sized particles are all equal to a constant of 60 the average number of each size of ejected particles grows linearly with the increasing impact speed but remains invariant for various impact angles moreover the smaller particles are preferentially ejected and the ratio between the mean numbers of different sized particles is independent of both the impact speed and angle additionally the ejected particles were found to move in a 3d space they become distributed symmetrically around the incident plane and jump not only forward but also backward these results are critical to understanding the grain size induced inhomogeneity in aeolian sand transport

poam iii measurements of dehydration in the antarctic lower stratosphere we present measurements of stratospheric water vapor and aerosols in the antarctic from the poam iii instrument during the period april through december 1998 the measured variations in water vapor enable us to study both descent in the vortex and the effect of dehydration that occurs in the lower stratosphere below 23 km when the temperature drops below the frost point in july there is a temporal correlation between the dehydration that occurs in july and an increase in high aerosol optical depth events in the lower stratosphere suggesting that these events are due to the presence of ice psc s when temperatures warm up there is some rehydration at the highest altitudes of the dehydrated region 20 23 km probably resulting from descent within the vortex at 12 km rehydration is probably the result of mixing in of air from outside the vortex the temperature increase in october produces little rehydration at 17 km and no clear rehydration at 14 km suggesting that the water has precipitated out of these layers

contribution of aeolian sand to backbarrier marsh sedimentation abstract the frequency of island overwash is commonly assumed to be the main factor regulating sand flux to backbarrier marshes however aeolian transport of sand across a barrier has received little attention in saltmarsh research the contribution of aeolian sand to backbarrier marshes is examined here with marsh cores and measurements of wind blown sediment transport across transgressive and regressive parts of a barrier island backbarrier marshes fronted by a wide washover fan or a high elevation dune ridge were supplied with aeolian sand that significantly contributed to vertical accretion especially near the marsh barrier island edge the percent volume of the marsh originating from aeolian sand based on the upper 1 cm of marsh sediment decreased by an order of magnitude only 20 m from the dune marsh boundary sandy beds sampled in every marsh core at depth are composed of aeolian sand and were likely emplaced over time after storms deposited a sandy washover fan near the marsh and or reduced vegetation cover across the island sand beds preserved within backbarrier marsh deposits are commonly thought to have been emplaced rapidly during a storm however post storm aeolian transport should also be considered as an important mechanism for forming sand beds over a longer period of time within saltmarsh strata the contribution of aeolian sand to backbarrier marsh accretion should increase as sea level continues to rise causing many barrier islands to narrow thereby reducing transport distances between the dune and marsh along developed coastlines however anthropogenic factors associated with increased development largely decrease the connectivity between the dunes and backbarrier marsh

identifying an asperity through 3 d mapping of the frequency magnitude distribution following the idea introduced by wiemer and wyss 1997 here is an attempt to map the seismic hazard in terms of the b value in the frequency magnitude distribution in a region with moderate seismic activity bearn region french pyrenees in this area the complexity of the geology makes it necessary to perform a 3 d mapping b values are computed within 5 km radius spherical volumes that contain an average of 140 events strong lateral variations between 0 45 and 1 8 are observed at short scales in the whole investigated volume the minimum of the b value is clearly correlated with a historically active zone which last ruptured in 1980 mb 5 1 interpretating low b values in terms of high stresses may lead us to consider this minimum b patch as a 5 km radius asperity this study allows to define its location and dimensions

a study of the dynamics of the equatorial lower stratosphere by use of ultra long duration balloons 2 gravity waves in the late southern winter of 1998 centre national d etudes spatiales cnes the french space agency released six 10 m diameter superpressure balloons from a location near quito ecuador three balloons collapsed soon after launching but the remaining three drifted westward for a few weeks at altitudes between 19 and 20 km two of those balloons crossed the pacific ocean before falling above the maritime continent while the other completed a revolution around the earth and crossed the pacific for a second time before its final fall despite the small number and the relatively short duration of the flights the balloons provided a unique in situ data set for the lower equatorial stratosphere this part 1 of a two part paper describes this data set and analyzes outstanding features in the planetary scales part 2 focuses on gravity wave scale it is argued that balloon trajectories over the pacific are primarily determined by the westward drift during the easterly phase of the equatorial quasi biennial oscillation qbo and the meridional velocity field of a mixed rossby gravity yanai wave with an apparent period of 4 days and zonal wave number 4 this wave appears to have two episodes of amplification during the balloon flights it is also argued that the balloons show evidence of oscillations with periods between 2 and 4 days and of a kelvin wave with an apparent period close to 10 days and zonal wave number 1 in this way the balloon behavior provided a pictorial view of air parcel trajectory in the equatorial lower stratosphere it is stated that larger balloon campaigns can provide excellent in situ data sets for studies on the dynamics and composition of the middle atmosphere

the pattern of grainfall deposition in the lee of aeolian dunes a simple model for the deposition pattern in the lee of aeolian dunes is presented that relies heavily upon a recently developed understanding of aeolian saltation grainfall deposition at any position on the lee face is the result of all saltation trajectories that leave any point on the surface of the dune upwind of the brink with sufficient initial velocity to travel the intervening distance the deposition rate at any position on the lee slope is obtained by integrating over all combinations of initial position and required velocity the velocity being weighted by its probability density the resulting calculated total deposition rate patterns show distinct maxima on the order of one to a few decimetres from the brink beyond which deposition rates fall off roughly exponentially an important length scale emerges that characterizes this decay with distance from the brink the length increasing with wind velocity and decreasing with grain diameter it is shown that this length scale is on the order of one metre for typical grain size and wind conditions that this is typically smaller than the length of the lee slope is what gives rise to the oversteepening and eventual avalanching of the lee sides of aeolian dunes the position of a pivot point on the lee slope may be predicted separating source regions from accumulation regions for grainflow avalanche deposits the calculated patterns provide not only a means for quantitative interpretation of active and fossil dune grainfall deposits but they provide the initial geometry for grainflow avalanches the initial failures should coincide with the steepest gradient in grainfall deposition slightly downslope from the grainfall maximum

ozone laminae inside the antarctic vortex produced by poleward filaments summary ozone soundings made inside the antarctic ozone hole exhibit localized ozone increases within thin layers in the lower stratosphere these structures called laminae are explained as poleward elaments emerging from the vortex edge and transporting relatively ozone rich air into levels above the geographical site where the sounding equipment has been launched it is shown that the interior of the antarctic vortex is not completely isolated with respect to the poleward air mixing filament development follows the occurrence of inward breaking near the vortex edge in a region where isentropes are locally uplifted it is shown that the circulation associated with such uplift may produce the poleward breaking the role of that circulation is supported by simple barotropic simulations where development of a poleward elament is reproduced in a realistic circular undisturbed vortex

the saltations of different sized particles in aeolian sand transport abstract wind tunnel experiments were performed in order to investigate the effect of mixing on the aeolian transport of sands with different grain sizes two types of sand with different grain size distributions and an equal mass binary mixture of these sands were used comparing the gradients of their measured mass flux profiles and some published profiles for mixed sand transport with those for nearly uniform sand transport it was found that for both of these types of sand bed the negative gradient of the mass flux profile on a log linear plot varies with the mass averaged grain size of the sand bed according to the same power law hence it can be deduced that during the aeolian transport of mixed sand beds the mean vertical ejection speeds of different sized grains are nearly identical to that for the transport of monospecific sized sand with the same mass averaged grain size theoretical analysis was undertaken to explore the characteristics of ejections of different sized grains during the aeolian transport of sand with mixed size grains it is proposed that the mean ejection angles and the mean ejection speeds for sand grains of different sizes are nearly identical and are equivalent to that for monospecific sized sand with the same mass averaged grain size it was also evident that the ratio between the transport rate of each grain size group expressed as the fraction in the whole transport rate and its mass fraction in the mixed size sand is a combined consequence of both the wind effect on the mean saltation distance of different sized grains and the effect of the mass fraction of each grain size group in the original mixture on its ejection potential responding to an impact of a saltating sand grain

assessment of space time hazard of large aftershocks of the 2008 mw7 9 wenchuan earthquake to adaptively forecast forthcoming large aftershocks of the 2008 mw7 9 wenchuan china earthquake we construct a new hazard model to describe the occurrence rate of aftershocks in a study region along the longmenshan fault the model is denoted by srj since it is a combination of the reasenberg jones rj model and a spatial hazard model that is obtained by taking a reference of previous earthquakes in the study region we employ the maximum likelihood ml method to estimate the srj model based on aftershocks that occurred within 1 or 2 days after the wenchuan earthquake the probabilities of m 5 0 aftershocks at each of the grids in the study region during next few days are then computed according to the estimated srj model and hence the corresponding relative aftershock hazard rah map is constructed finally according to a variety of criteria for evaluating the hazard maps on depicting possible rupture area of forthcoming large aftershocks the srj based rah map is demonstrated to be more efficient than the rah maps constructed based on the rj model incorporated with the gridding method using a fixed radius or varying radii

experimental investigation of mass flux and transport rate of different size particles in mixed sand transport by wind abstract sand transport by wind in arid regions is a geomorphic process affected by the grain size distribution knowledge of the transport behavior of each size group in mixed sand transport is important for understanding the saltation dynamics in dune migration this paper focuses on the characteristics of mass flux mass concentration horizontal velocity and transport rate of different particle size groups and the relation to their mass proportion in air experiments were carried out to analyze these relations in a wind tunnel by particle tracking velocimetry the mass flux of different size particles usually decays exponentially with height for larger size groups and deviates from exponential decay for smaller size groups the trend of mass concentration of different size groups with height is similar to the mass flux the mean horizontal velocity of different size groups generally increases with increasing height and decreases with the increase of particle size at the same height with increasing height the ratio of mass flux of each size group to the total mass flux increases for the smaller size group but decreases for the larger size group and the transition diameter of particles is about 0 14 mm for the 0 16 mm sand sample and about 0 21 0 27 mm for the 0 24 mm sand sample for the smaller size group the ratio of the mass weighted average horizontal velocity of each size group to that of all particle sizes is 1 0 and the ratio of the transport rate of each size group to the total transport rate is usually larger than its mass proportion in air this is the opposite for the larger size groups the maximum deviation of mass flux proportion of each size group from its mass proportion in air is about 15 which is determined by the mass weighted average horizontal velocity of each size group

dunes on the skeleton coast namibia south west africa geomorphology and grain size relationships simple and locally compound transverse and barchanoid dunes dominate the 2000 km2 skeleton coast dunefield in northwestern namibia south west africa dune height and spacing are closely correlated r 0 89 and decrease across the dunefield from southwest to northeast with an accompanying change from transverse to barchanoid ridges and ultimately barchans the dunes are aligned transverse to the dominant strong south and south southwest onshore winds alignment patterns indicate that surface roughness changes between coastal plain and dunes cause dune forming winds to swing to the right over the dunes but resume their original direction beyond grain size and sorting vary at three scales the dune the dune landscape and through the dunefield overall the sands derived from three localities by deflation from beaches supplied by vigorous longshore drift become progressively finer and better sorted across the dunefield paralleling changes in dune height and spacing a statistically significant relationship r 0 65 was established between dune spacing and the phi grain size of the coarser fraction of the dune sands demonstrating the importance of the protective effects of coarse grains and suggesting that the morphometry of simple transverse dunes may be controlled by the scale of turbulence associated with the threshold wind speed required to move the coarsest fraction of the dune sand

millimeter wave spectroscopic measurements over the south pole 1 a study of stratospheric dynamics using n2o observations millimeter wave measurements of n2o and o3 cheng et al 1995 along with several other trace gases have been made nearly continuously from february 1993 through early january 1994 at the amundsen scott station south pole in order to separate chemical and dynamical effects this paper uses the observations of the long lived tracer n2o to study stratospheric dynamics the main emphasis is on the synoptic evolution of the polar vortex over an entire winter period and quantitative results are given for various times and altitudes diabatic descent rates derived for different altitude levels showed the strongest descent in austral fall at high altitudes agreeing fairly well with model predictions by rosenfield et al 1994 subsidence was observed to continue until late october well after polar sunrise the breakdown of the vortex occurred first in the upper stratosphere marked in the intrusion of n2o rich air at these altitudes consistent with trajectory calculations our calculated descent rates are not consistent with the idea that the polar vortex is a flowing processor but instead should be viewed as an isolated system

comparison between vertical ozone soundings and reconstructed potential vorticity maps by contour advection with surgery sudden jumps and deep laminations observed on vertical stratospheric ozone profiles during the european arctic stratospheric ozone experiment easoe winter 1991 1992 are explained as resulting from transport on isentropic layers this is obtained by comparing the ozone profiles with high resolution reconstruction of the potential vorticity multilayer isentropic contour advection with surgery cas is performed using european center for medium range weather forecasts ecmwf analyzed winds the results presented in this work are based on analyzing the location of the edge of the polar vortex the horizontal and vertical extents of filamentary structures and intrusions within the polar vortex the results are consistent with the assumption of high ozone content within the polar vortex which is valid during normal winter conditions of the northern hemisphere the resolution required to carry out this study is much higher than that of current operational analysis by weather centers while it is achievable by cas reconstructions which provide a dynamical understanding of the ozone variations

statistical analysis of earthquakes after the 1999 mw 7 7 chi chi taiwan earthquake based on a modified reasenberg jones model abstract we investigated the temporal spatial hazard of the earthquakes after the 1999 september 21 m w 7 7 chi chi shock in a continental region of taiwan the reasenberg jones rj model reasenberg and jones 1989 1994 that combines the frequency magnitude distribution gutenberg and richter 1944 and time decaying occurrence rate utsu et al 1995 is conventionally employed for assessing the earthquake hazard after a large shock however it is found that the b values in the frequency magnitude distribution of the earthquakes in the study region dramatically decreased from background values after the chi chi shock and then gradually increased up the observation of a time dependent frequency magnitude distribution motivated us to propose a modified rj model mrj to assess the earthquake hazard to see how the models perform on assessing short term earthquake hazard the rj and mrj models were separately used to sequentially forecast earthquakes in the study region to depict the potential rupture area for future earthquakes we further constructed relative hazard rh maps based on the two models the receiver operating characteristics roc curves swets 1988 finally demonstrated that the rh map based on the mrj model was in general superior to the one based on the original rj model for exploring the spatial hazard of earthquakes in a short time after the chi chi shock

quantitative diagnostics of mixing in a shallow water model of the stratosphere two different approaches are applied to quantify mixing in a shallow water model of the stratosphere these are modified lagrangian mean mlm theory and a technique referred to as reverse domain filling with local gradient reversal rdf lgr the latter is similar to a previously existing technique using contour advection and contour surgery it is first proved that in an inviscid shallow water atmosphere subject to mass sources and sinks if the mass enclosed by a potential vorticity pv contour is steady in time then the integral of the mass source over the area enclosed by the contour must be zero next the mlm and rdf lgr approaches are used to diagnose the time averaged transport across pv contours in the model simulations the model includes a sixth order hyperdiffusion on the vorticity field except in a thin outer entrainment zone the hyperdiffusion term has only a very weak effect on the mlm mass budget of the polar vortex in the entrainment zone the hyperdiffusion term has a significant effect the rdf lgr results capture this behavior providing good quantitative estimates of the hyperdiffusion term which is equivalent to the degree of radiative disequilibrium at a pv contour this agreement shows that the main role of the hyperdiffusion is to mop up the filaments that are produced by the essentially inviscid large scale dynamics all calculations are repeated for two values of the hyperdiffusion coefficient that differ by a factor of 50 with little difference in the results this suggests that the amount of material entrained from the vortex edge into the surf zone does not depend on the details of the small scale dissipation as long as it is sufficiently weak and has some degree of scale selectivity

properties of aftershock sequences in southern california the temporal behavior of 39 aftershock sequences in southern california 1933 1988 was modeled by the modified omori relation minimum magnitudes for completeness of each sequence catalog were determined and the maximum likelihood estimates of the parameters k p and c with the standard errors on each were determined by the ogata algorithm the b value of each sequence was also calculated many of the active faults in the region both strike slip and thrust were sampled the p values were graded in terms of the size of the standard error relative to the p value itself most of the sequences were modeled well by the omori relation many of the sequences had p values close to the mean of the whole data set 1 11 0 25 but values significantly different from the mean as low as 0 7 and as high as 1 8 exist no correlation of p with either the b value of the sequence or the mainshock magnitude was found the results suggest a direct correlation of p values is with surface heat flow with high values in the salton trough high heat flow and one low value in the san bernardino mountains and on the edge of the ventura basin both low heat flow the large fraction of the sequences with p values near the mean are at locations where the heat flow is near the regional mean 74 mw m2 if the hypothesis that aftershock decay rate is controlled by temperature at depth is valid the effects of other factors such as heterogeneity of the fault zone properties are superimposed on the background rate determined by temperature surface heat flow is taken as an indicator of crustal temperature at hypocentral depths but the effects on heat flow of convective heat transport and variations in near surface thermal conductivity invalidate any simple association of local variations in heat flow with details of the subsurface temperature distribution the interpretation is that higher temperatures in the aftershock source volume caused shortened stress relaxation times in the fault zone materials leading to a faster decay rate higher p value in 1967 mogi proposed such a relation on the basis of japanese data seismic velocity distributions published for southern california generally support the hypothesis with low velocities higher temperatures corresponding to high p values and vice versa

height profile of particle concentration in an aeolian saltating cloud a wind tunnel investigation by piv msd 1 attempt is made to define the particle concentration in an aeolian saltating cloud and its variation with height using artificial spherical quartz sand in a wind tunnel the height profiles of the relative particle concentration in aeolian saltating cloud at three wind velocities were detected by the state of the art piv particle image velocimetry msd mie scattering diffusion technique and converted to actual concentration based on sand transport rate and the variation with height of velocity of the saltating cloud the particle concentration was found to decay exponentially with height and to increase with wind velocity it decayed more rapidly when the wind velocity decreased the volume volume concentration in the near surface layer was at the order of 10 4 the results obtained by piv msd technique were in good agreement with those derived from the sand flux and velocity profiles the former being about 15 greater than the later

settling velocity distributions and sorting processes on a longitudinal dune a case study the processes acting on a longitudinal dune are inferred from the response in the area size sorting characteristics of the sediment of the active layer the sediment size distributions are determined by settling and are best described by a log hyperbolic model which provides the most information on size sorting processes size sorting characteristics are markedly different across the low round crested part of the dune from cross sections of the high more sharp crested part this results in changes in textural parameters along the lee side consistent with changes in the lee side separation vortex this is the first time that the effect of wind speed up on the lee side is observed to be reflected in the sediment it can only be detected with the very sensitive log hyperbolic parameters

the harmonious character in equilibrium aeolian transport on mixed sand bed wind tunnel experiments were carried out to measure the spatial distribution in equilibrium transport of four types of mixed sand the flux profiles of each grain size group were calculated it is found that the vertical distribution of mean grain size has a close relation with the grain size distribution in the sand bed in a log linear plot the flux profiles of main grain size groups are all straight lines and their slopes are nearly equal it is also found that the ratio of transport rate of each size group to the whole transport rate is directly proportional to the mass ratio of each size group in the sand bed and the proportion value is only dependent on the grain size this harmonious law is applicable to all four types of mixed sand used in the experiment

changes in grain size of sand in transport over a foredune suspended sand is sampled at several heights and positions on a beach and foredune providing detailed insight into the vertical and horizontal variation in sand content in the air during landward transport grain size analysis is used to study the changes in grain size distribution during landward transport mean grain size and sorting decrease during transport changes in textural parameters follow a gradual and regular path when the sediment is transported into the foredune sediment trapped on the seaward slope at a height of 30 50 cm above the surface closely resembles the sediment trapped landward which implies that changes in the direction of transport are related to vertical changes within the sediment transport profiles the movement of sand over the vegetated foredunes is induced by turbulent forces created by the air flowing across the vegetation and the foredune leading to a change from saltation on the beach to modified saltation and suspension on the foredune small grains are lifted higher and fall more slowly than coarse grains and therefore are transported further landward resulting in a gradual decrease in grain size of the landward deposited sediment

experimental verification of aeolian saltation and lee side deposition models we report results of experiments intended to test the validity of a model for aeolian saltation and the resulting pattern of deposition on the lee side of aeolian dunes in steady sea breeze conditions on a 3 m tall dune at point ano nuevo california we measured simultaneously the near brink wind speed and the deposition on both horizontal and lee face collector platforms we then used the details of the deposition patterns to constrain approximate values of parameters in a numerical model of the deposition rate that incorporates the essence of the saltation process best fits to the data constrain a parameter that controls the probability distribution of liftoff speeds in addition the total vertical number flux of grains is constrained to roughly 107 108 grains m 2 s 1 at shear velocities of 0 33 0 40 m s 1 the lee side deposition pattern which shows the expected maximum in deposition rate at a distance of several decimetres from the brink is also well fit by the model in addition simultaneous collection of horizontal and lee deposition patterns along with the numerical simulation of these patterns strongly implies that the windfield in the lee of this particular dune is best described as a non recirculating wake grainflows on the lee face are caused by failure of grainfall depositional bumps our results suggest that the principal effect of increased wind speed is to increase the frequency of grainflows rather than to increase their size implying that very large thick grainflows require a different mechanism

rapid descent of mesospheric air into the stratospheric polar vortex this paper describes simulations carried out to calculate the lagrangian trajectories of greater than 40 000 air parcels in the middle atmospheric region of the southern polar vortex the purpose was to see if model calculations would support recent observations which indicate that there is rapid vertical transport of air masses downward from the mesosphere into the stratospheric polar vortex this conclusion was drawn from looking at the spatial distribution of long lived trace gases such as methane in the middle atmosphere looking at the lagrangian fields provides a graphic picture of any mass motion and does so in a fairly averaged manner

fine scale study of a thick stratospheric ozone lamina at the edge of the southern subtropical barrier a large scale transport event resulting in a thick ozone lamina originating from midlatitudes is observed in the tropical stratosphere over reunion island 55 e 21 s this isentropic transport was detected from stratospheric balloon borne ozone measurements that showed the occurrence of the lamina and was investigated using different tools based on ertel s potential vorticity epv analyses an original software dybal using surface coordinate and the equivalent length of epv contours as diagnostic tools in conjunction with high resolution outputs from an epv advection model mimosa allows us to specify the origin of the lamina the results indicate that a broad layer of stratospheric air was isentropically advected from midlatitudes across the southern edge of tropical reservoir and reached reunion island on 12 july 2000 in addition eliassen palm s flux vectors calculated from ecmwf analysis show that planetary wave activity was quite large during that time period with wave breaking occurring around 30 km and could have driven that exchange in contrast with analyses of filamentation events based on model and satellite data the present study focuses on a fine scale vertical survey from in situ measurements the filament reported in this paper is characterized by a large vertical extension and is located around the maximum of ozone concentration in the tropical stratosphere 600 k the analysis of such events poorly documented in the tropics could complement satellite studies and contribute to a better determination of the transport between the tropics and the midlatitudes

vertical displacements induced by quasi stationary waves in the southern hemisphere stratosphere during spring abstract vertical displacements induced by the quasi stationary wave with wavenumber 1 qsw1 in the southern hemisphere stratosphere during spring are studied the displacement exhibits two amplitude maxima located in the upper and lower stratosphere with a phase change of 180 between the two regions ozone mixing ratio and temperature wave signatures are explained by the wave induced displacement in the presence of mean vertical gradients the qsw1 induces radiative diabatic forcing in the upper stratosphere that results in a cross isentropic ozone transport correlation between vertical displacement at different levels and total ozone indicates that total ozone is directly connected to the displacement in the lower stratosphere the displacement extends to the tropopause and results in a correlation between total ozone and the tropopause height but with smaller values relative deviation between reconstructed potential vorticity pv by using a high resolution model and pv from observations indicates

variation in particle size distribution over a small dune the variation in particle size distribution for a sequence of sand samples collected from the surface of a small barchanoid dune along a sampling line parallel to the windflow is studied by means of the hyperbolic distribution the modal or typical value of the log size increases linearly with distance from the windward foot to the crest of the dune and falls off steeply on the lee side the spread of the log size distribution locally near the modal value is roughly constant on the windward side but decreases significantly down the slip face two other parameters of the four parameter hyperbolic distribution can be considered largely constant a comparison of the log size distributions for heavy and light mineral grains based on a selected set of the samples showed that heavy and light minerals follow different hyperbolic patterns however the difference in modal size of the distributions for the two types of minerals was virtually constant among the samples

toggling of seismicity by the 1997 kagoshima earthquake couplet a demonstration of time dependent stress transfer 1 two m 6 well recorded strike slip earthquakes struck just 4 km and 48 days apart in kagoshima prefecture japan in 1997 providing an opportunity to study earthquake interaction aftershocks are abundant where the coulomb stress is calculated to have been increased by the first event and they abruptly stop where the stress is dropped by the second event this ability of the main shocks to toggle seismicity on and off argues that static stress changes play a major role in exciting aftershocks whereas the dynamic coulomb stresses which should only promote seismicity appear to play a secondary role if true the net stress changes from a sequence of earthquakes might be expected to govern the subsequent seismicity distribution however adding the stress changes from the two kagoshima events does not fully capture the ensuing seismicity such as its rate change temporal decay or migration away from the ends of the ruptures we therefore implement a stress transfer model that incorporates rate state friction in which seismicity is treated as a sequence of independent nucleation events that are dependent on the fault slip slip rate and elapsed time since the last event the model reproduces the temporal response of seismicity to successive stress changes including toggling decay and aftershock migration nevertheless the match of observed to predicted seismicity is quite imperfect due perhaps to inadequate knowledge of several model parameters however to demonstrate the potential of this approach we build a probabilistic forecast of larger earthquakes on the expected rate of small aftershocks taking advantage of the large statistical sample the small shocks afford not surprisingly such probabilities are highly time and location dependent during the first decade after the main shocks the seismicity rate and the chance of successive large shocks are about an order of magnitude higher than the background rate and are concentrated exclusively in the stress triggering zones

stress evolution following the 1999 chi chi taiwan earthquake consequences for afterslip relaxation aftershocks and departures from omori decay summary we explore how coulomb stress transfer and viscoelastic relaxation control afterslip and aftershocks in a continental thrust fault system the 1999 september 21 m w 7 6 chi chi shock is typical of continental ramp dsystems throughout the world and so inferences drawn from this uniquely well recorded event may be widely applicable first we find that the spatial and depth distribution of aftershocks and their focal mechanisms are consistent with the calculated coulomb stress changes imparted by the coseismic rupture some 61 per cent of the m 2 aftershocks and 83 per cent of the m 4 aftershocks lie in regions for which the coulomb stress increased by 0 1 bars and there is a 11 12 per cent gain in the percentage of aftershocks nodal planes on which the shear stress increased over the pre chi chi control period second we find that afterslip occurred where the calculated coseismic stress increased on the fault ramp and dsubject to the condition that friction is high on the ramp and low on the d ecollement third viscoelastic relaxation is evident from the fit of the post seismic gps data on the footwall fourth we find that the rate of seismicity began to increase during the post seismic period in an annulus extending east of the main rupture the spatial extent of the seismicity annulus resembles the calculated 0 05 bar coulomb stress increase caused by viscoelastic relaxation and afterslip and we find a 9 12 per cent gain in the percentage of focal mechanisms with 0 01 bar shear stress increases imparted by the post seismic afterslip and relaxation in comparison to the control period thus we argue that post seismic stress changes can for the first time be shown to alter the production of aftershocks as judged by their rate spatial distribution and focal mechanisms

spatial variability of seismicity parameters in aftershock zones the spatial variability of the b value of the frequency magnitude relationship and the decay rate of aftershocks as described by the p value of the modified omori law is investigated by using dense spatial grids we map out the distribution of b and p values within the landers northridge morgan hill and kobe aftershock sequences considerable spatial variability is found with b values of independent subvolumes ranging from 0 6 to 1 4 and p values ranging from 0 6 to 1 8 these systematic and statistically highly significant differences argue that it is an oversimplification to assign one single p and b value to an aftershock sequence that extends up to 100 km the spatial distribution of these two parameters is compared with the slip distribution during the mainshock suggesting that the areas of largest slip release correlate with high b value regions we hypothesize that the frictional heat created during the event may influence the p value distribution within an aftershock zone while applied shear stress crack density and pore pressure govern the frequency magnitude distribution by investigating the frequency magnitude distribution separately for preseismic and postseismic periods for the morgan hill mainshock we find that only the volume in the vicinity of the highest slip release shows a significant increase in the b value which decays to premainshock values within a year surrounding areas of the aftershock zone show an approximately constant b value with time because the aftershock hazard after a mainshock depends strongly on both the b and p value we propose that aftershock hazard assessment can be improved by taking into account the spatial distribution of the parameters

flow and sediment transport dynamics in a slot and cauldron blowout and over a foredune mason bay stewart island rakiura nz abstract this study is the first to simultaneously compare flow and sediment transport through a blowout and over an adjacent foredune and the first study of flow within a highly sinuous slot and cauldron blowout flow across the foredune transect is similar to that observed in other studies and is primarily modulated by across dune vegetation density differences flow within the blowout is highly complex and exhibits pronounced accelerations and jet flow it is characterised by marked helicoidal coherent vortices in the mid regions and topographically vertically forced flow out of the cauldron portion of the blowout instantaneous sediment transport within the blowout is significant compared to transport onto and or over the adjacent foredune stoss slope and ridge with the blowout providing a conduit for suspended sediment to reach the downwind foredune upper stoss slope and crest medium term 4 months aeolian sedimentation data indicates sand is accumulating in the blowout entrance while erosion is taking place throughout the majority of the slot and deposition is occurring downwind of the cauldron on the foredune ridge the adjacent lower stoss slope of the foredune is accreting while the upper stoss slope is slightly erosional longer term 16 months pot trap data shows that the majority of foredune upper stoss slope and crest accretion occurs via suspended sediment delivery from the blowout whereas the majority of the suspended sediment arriving to the well vegetated foredune stoss slope is deposited on the mid stoss slope the results of this study indicate one mechanism of how marked alongshore foredune morphological variability evolves due to the role of blowouts in topographically accelerating flow and delivering significant aeolian sediment downwind to relatively discrete sections of the foredune

trace gas transport in the arctic vortex inferred from atmos atlas 2 observations during april 1993 measurements of the long lived tracers ch4 n2o and hf from the atmospheric trace molecule spectroscopy atmos instrument during the atmospheric laboratory for science and applications 2 atlas 2 space shuttle mission in april 1993 are used to infer average winter descent rates ranging from 0 8 km month at 20 km to 3 2 km month at 40 km in the arctic polar vortex during the 1992 93 winter descent rates in the mid stratosphere are similar to those deduced for the antarctic vortex using atmos atlas 3 measurements in november 1994 but the shorter time period of descent in the arctic leads to smaller total distances of descent strong horizontal gradients observed along the vortex edge indicate that the arctic vortex remains a significant barrier to transport at least until mid april in the lower to middle stratosphere

earthquake hazard after a mainshock in california after a strong earthquake the possibility of the occurrence of either significant aftershocks or an even stronger mainshock is a continuing hazard that threatens the resumption of critical services and reoccupation of essential but partially damaged structures a stochastic parametric model allows determination of probabilities for aftershocks and larger mainshocks during intervals following the mainshock the probabilities depend strongly on the model parameters which are estimated with bayesian statistics from both the ongoing aftershock sequence and from a suite of historic california aftershock sequences probabilities for damaging aftershocks and greater mainshocks are typically well constrained after the first day of the sequence with accuracy increasing with time

constructing notches in foredunes effect on sediment dynamics in the dune hinterland measurements were carried out on the island of ameland the netherlands to determine whether notches cut into foredunes stimulated the supply of fresh calcareous beach and dune sand into the white and grey dune habitats behind the dunes increasing these habitats biological quality sediment characteristics and dynamics deposition flux and grain size properties as well as aspects of the vegetation occurrence composition and cover density were studied along six transects three behind an intact foredune and three behind a foredune with a notch cut into it compared to an intact foredune the notched foredune exhibited higher deposition and accumulation behind the dune the extra supply of sand was small however and for the notches studied limited to the zone within approximately 50 60 m of the foredune s crest farther away from the dune the effect of the notches became negligible the presence of a notch did affect the grain size composition of sediment deposited behind the foredune for intact foredunes the grain size composition behind the dune was similar to that on the dune itself when a notch had been cut the sediment was finer behind the foredune gradually coarsening away from the dune sand spray deposition of sand eroded from the dune and transported in modified saltation during heavy winds explains these granulometric results the effect of the notches on the vegetation in the grey dune habitat behind the foredune was small and for the notches studied limited to the first approximately 35 m of the grey dune area between 30 and 65 m from the foredune s crest the notches had a greater effect on the white dune habitat but in the opinion of the authors this remained disproportionately small relative to the effort required for notch excavation and maintenance

minimum magnitude of completeness in earthquake catalogs examples from alaska the western united states and japan we mapped the minimum magnitude of complete reporting m c for alaska the western united states and for the junec earthquake catalog of japan mc was estimated based on its departure from the linear frequency magnitude relation of the 250 closest earthquakes to grid nodes spaced 10 km apart in all catalogs studied mc was strongly heterogeneous in offshore areas the mc was typically one unit of magnitude higher than onshore on land also mc can vary by one order of magnitude over distance less than 50 km we recommend that seismicity studies that depend on complete sets of small earthquakes should be limited to areas with similar mc or the minimum magnitude for the analysis has to be raised to the highest com mon value of mc we believe that the data quality as reflected by the mc level should be used to define the spatial extent of seismicity studies where mc plays a role the method we use calculates the goodness of fit between a power law fit to the data and the observed frequency magnitude distribution as a function of a lower cutoff of the magnitude data mc is defined as the magnitude at which 90 of the data can be modeled by a power law fit mc in the 1990s is approximately 1 2 0 4 in most parts of california 1 8 0 4 in most of alaska aleutians and panhandle excluded and at a higher level in the junec catalog for japan various sources such as ex plosions and earthquake families beneath volcanoes can lead to distributions that cannot be fit well by power laws for the hokkaido region we demonstrate how neglecting the spatial variability of m c can lead to erroneous assumptions about deviations from self similarity of earthquake scaling

on the maintenance of potential vorticity in isentropic coordinates we present a diagnostic study of the maintenance of the potential vorticity pv on isentropic surfaces in the troposphere to the lower stratosphere using ten years of analyses produced by the european centre for medium range weather forecasts after a brief three dimensional description of the general circulation in isentropic coordinates we examine the budgets of the pv evolution equation by decomposing the flow into its mean high frequency transient and low frequency transient parts we assess the role of these various scales of motion in the maintenance of the mean pv distribution the contribution of vortical and thickness fluxes is also investigated one interesting result is the key role of the divergent part of the transient flow along the tropopause in the midlatitudes which creates a large pv sink region we give here a tentative explanation the pv maps are also used to generate a climatology of a wave activity called pseudomomentum that indicates four centres of wave activity over the atlantic and pacific the first two are located in the northern hemisphere storm tracks and the two others in the upper tropospheric subtropical areas between the 310 k and the 350 k levels

negatively skewed aeolian sands from a humid tropical coastal dunefield northern australia abstract this paper describes the nature and environmental significance of variations in textural parameters within a large coastal dunefield in tropical northern australia grain size parameters of modern beaches and foredunes are very similar but are distinct from those of parabolic dune and sandplain environments on average beach and foredune sands have a normal grain size distribution but parabolic dune sands are predominantly negatively skewed negative skewness is interpreted as primarily reflecting sorting of dune sediments by winnowing at dune crests and by avalanching on slip faces a general relationship between mean size and skewness is supported with finer sediments showing increased negative skewness positive skewness can therefore not be used as a diagnostic property of aeolian sediments

longitudinally dependent ozone increase in the antarctic polar vortex revealed by balloon and satellite observations the horizontal structure of processes causing increases in ozone in the antarctic polar vortex was examined using data measured in 2003 from an ozonesonde observation campaign at syowa station 39 68e 69 08s and from the improved limb atmospheric spectrometer ii ilas ii onboard the advanced earth observing satellite ii the ilas ii data are daily and distributed uniformly at 14 points in the zonal direction mostly at polar latitudes the antarctic ozone hole that developed in 2003 was one of the largest recorded the period of focus in this study is 26 september through 24 october when a strong polar vortex was situated in the stratosphere an ozone mixing ratio contour 1 0 ppmv moved downward near a height of 20 km during the period of focus this increase in ozone is likely to result from downward transport of ozone rich air originating from lower latitudes by brewer dobson circulation first the descent rate of the mixing ratio contour was estimated by taking the geometric height as the vertical coordinate for the deep vortex interior around 20 km a significant longitudinal dependence was observed an analysis using ecmwf operational data shows that this dependence can be approximately explained by longitudinally dependent vertical movements of the isentropes caused by a zonal wavenumber 1 quasi stationary planetary wave with amplitude and phases varying on a seasonal time scale next the descent rate was calculated around 500 k around 20 km by taking the potential temperature isentrope as the vertical coordinate the longitudinal dependence was still present using this coordinate meaning that the ozone mixing ratio and its increase are not constant on the isentropic layer even in the interior of the polar vortex a backward trajectory analysis showed that air parcels with large ozone mixing ratios were mostly transported from the polar vortex boundary region this result suggests that lateral transport mixing is important even before the breakup of the polar vortex results from a tracer tracer correlation analysis of o3 and long lived constituent n2o were also consistent with this inference the contribution of lateral mixing to the increase in ozone was estimated at about 17 6 4 that of the brewer dobson circulation around 20 km using the calculated descent rates the results of this study also imply that lagrangian downward motions in the vortex interior are not correctly estimated without accounting for lateral mixing even if the polar vortex is dynamically stable

properties of the aftershock sequence of the 1999 mw 7 1 hector mine earthquake implications for aftershock hazard we investigate the spatial and temporal seismicity parameters and the related probabilistic aftershock hazard for the aftershock sequence of the 1999 m w 7 1 hector mine mainshock and compare it with the neighboring 1992 m w 7 3 landers sequence using a catalog of 11 000 earthquakes we determine the earthquake size distribution b value the aftershock decay rate p value and the seismic activity rate a value the b values are high b 1 2 within the rupture area significantly lower b 0 7 north of the rupture area and increase with time since the mainshock probabilistic aftershock hazard maps computed automatically as early as 4 days after the mainshock identified the northernmost part of the sequence as the highest hazard region these maps show a good agreement between the forecasts and the recorded large aftershocks based on the asymmetrical b value and hazard patterns for both the hector mine and landers sequences we hypothesize that the mainshock rupture directivity and slip distribution influence aftershock hazard current static or dynamic stress triggering models cannot resolve this spatial and temporal evolution of the hazard stress tensor inversions of 1400 relocated first motion focal mechanisms show predominantly a strike slip stress state with a sw ne trend of the greatest principal stress the heterogeneity of the stress field is unusually high near the hector mine and landers mainshock ruptures particularly near patches of large slip

mobility of a remobilised parabolic dune in kennemerland the netherlands abstract a parabolic dune in the netherlands was remobilised in december 1998 by removing vegetation and soil the main aim of the experiment was ecological to investigate whether permanent rejuvenation at the landscape scale is possible by restoration of natural processes if processes can be reactivated at coarse scale periodic rejuvenation of the landscape over the long term is possible without the need for managers to interfere further the experiment provides the opportunity to address another important question can large parabolic dunes in the netherlands be mobile in the present climate mobility of the dune is investigated by means of erosion pins aerial photography and measurement of cross sections activity indices are derived from erosion pin recordings and correlated to weather conditions from 1999 to 2001 displacement of the dune ranged from 0 to 12 m in east northeasterly direction activity of the dune is related to wind conditions but the relationship is strongly influenced by precipitation and therefore differs for wet and dry periods periods with extreme wind speeds resulted in much less geomorphic change than expected

tracer interrelationships in the stratosphere 1 relationships between long lived stratospheric tracers manifested in similar spatial structures on scales ranging from a few to several thousand kilometers are displayed most strikingly if the mixing ratio of one is plotted against another when the data collapse onto remarkably compact curves distinct curves form in the polar vortex the midlatitude surf zones and the tropics theory predicts such relationships for sufficiently rapid mixing along isentropic surfaces model results are used to illustrate the formation and seasonal evolution of distinct tracer relationships in the different regions using such relationships to associate departures from canonical forms with anomalous chemical or microphysical behavior must be done with care and with full awareness of the meteorological context of the data although the theory has been developed in the context of stratospheric tracers the key requirement is that transport is predominantly two dimensional while the theory is thus inappropriate in the troposphere it should be applicable to transport in the ocean interior

determinants of sediment properties and organic matter in beach and dune environments based on boosted regression trees grain size properties and the variation of organic matter in coastal beach and dune environments are assumed to be controlled by the intensity of aeolian processes time and the sediment source however assumptions are based on relatively limited empirical studies in this study we examined which environmental variables are the main predictors of multiple topsoil properties to achieve this we analysed an extensive dataset systematically collected across all beach zones and a large geographical area at the finnish baltic sea coast characterized by post glacial land uplift we included a comprehensive set of predictors in the analysis and applied boosted regression trees a modern modelling technique particularly suited for analysis without prior assumptions of the data model the results suggest that mean grain size and sorting are mainly determined by northing and fetch northing disturbance and fetch predicted the variation of soil organic matter while litter cover was strongly related to disturbance based on the analyses we were able to identify the main drivers of multiple topsoil properties on land uplift beaches parent material is suggested to determine sediment textural properties which largely masks the effects of transient processes mean grain size and sorting are highly interdependent grains become finer and sorting improves with increasing shore exposure the intensity of momentary geomorphic processes controls the accumulation of litter whereas the slower accumulation of organic matter in the soil is influenced also by the static exposure setting skewness and kurtosis of the grain size distribution are mainly influenced by unmeasured processes potentially relating to the geomorphological origin of the sediment copyright 2014 john wiley sons ltd

meteorological conditions of the stratosphere for the crista 2 campaign august 1997 1 during the crista 2 campaign in august 1997 the antarctic polar vortex according to uk met office ukmo data was strong but temporarily disturbed by planetary waves this winter was in general warmer than the five previous winters nevertheless temperatures cold enough to allow the formation of nitric acid trihydrate nat and ice particles occurred throughout the period from mid june to the end of august the cold vortex core developed in the potential temperature range from 400 to 700 k at the beginning of the winter initially centered at 600 k but slowly progressing downward to 450 k in the subsequent months the vortex disturbances showed a clear zonal wave number 1 and 2 pattern this planetary wave activity caused a strong day to day fluctuation of the vortex shape during august when the second cryogenic infrared spectrometers and telescopes for the atmosphere crista 2 mission took place the vortex was elongated toward the southern atlantic ocean processing slowly eastward the perturbation of the vortex was associated with air masses transported from middle and low latitudes into the polar region in small scale streamers similarly tongues of vortex air peeled off the vortex edge and moved equatorward enhancing the exchange between polar regions and the tropics in addition the disturbance of the vortex led to the generation of filaments at the inner side of the vortex edge thus covering the vortex interior with small scale structures a comparison between crista observations and potential vorticity derived from ukmo data shows discrepancies concerning small scale structures high resolution potential vorticity fields calculated from reverse domain filling trajectory simulations on isentropic surfaces based on horizontal winds from ukmo analyses and vertical motion from diabatic calculations are much more consistent with the measurements both observation and reverse domain filling rdf simulations show the strong atmospheric variability of this period of unusual enhanced planetary wave activity in the southern hemisphere

introducing probabilistic aftershock hazard mapping aftershocks to large earthquakes pose a significant hazard a fact that was highlighted by damaging aftershocks to the 1999 turkey and taiwan mainshocks a new approach is introduced to quantify this hazard in terms of physical parameter maps that forecast the probabilistic aftershock hazard based on the observed spatially varying aftershock activity for two case studies the landers and northridge mainshocks probabilistic aftershock hazard maps are shown to improve conventional aftershock hazard assessment

wave breaking and critical levels for propagating inertio gravity waves in the lower stratosphere this paper analyses and interprets the formation of mixed layers due to propagating inertio gravity waves observed during the fronts and atlantic storm track experiment the data used are high vertical resolution soundings launched from different sites located in the north atlantic sector in agreement with other studies attributing the origin of the inertio gravity waves to the adjustment of the jet stream near fronts the largest waves observed are often located in the vicinity of and above frontal bands the amplitude of these waves is large enough that they give rise to narrow mixed layers by a detailed analysis of the waves characteristics we can distinguish whether such a mixing is favoured by the presence of an inertia critical level where f or results from wave induced convective instability occurring far from critical levels here is the wave intrinsic frequency and f is the coriolis parameter these observations highlight the importance of inertio gravity waves in the vertical exchanges that occur in the stratosphere copyright 2002 royal meteorological society

a process based model for aeolian sediment transport and spatiotemporal varying sediment availability aeolian sediment transport is influenced by a variety of bed surface properties like moisture shells vegetation and nonerodible elements the bed surface properties influence aeolian sediment transport by changing the sediment transport capacity and or the sediment availability the effect of bed surface properties on the transport capacity and sediment availability is typically incorporated through the velocity threshold this approach appears to be a critical limitation in existing aeolian sediment transport models for simulation of real world cases with spatiotemporal variations in bed surface properties this paper presents a new model approach for multifraction aeolian sediment transport in which sediment availability is simulated rather than parameterized through the velocity threshold the model can cope with arbitrary spatiotemporal configurations of bed surface properties that either limit or enhance the sediment availability or sediment transport capacity the performance of the model is illustrated using four prototype cases the simulation of two wind tunnel experiments from literature and a sensitivity analysis of newly introduced parameters

antarctic polar descent and planetary wave activity observed in isams co from april to july 1992 antarctic polar descent and planetary wave activity in the upper stratosphere and lower mesosphere are observed in isams co data from april to july 1992 co derived mean april to may upper stratosphere descent rates of 15 k day 0 25 km day at 60 s and 20 k day 0 33 km day at 80 s are compared with descent rates from diabatic trajectory analyses at 60 s there is excellent agreement while at 80 s the trajectory derived descent is significantly larger in early april zonal wavenumber 1 enhancement of co is observed on 9 and 28 may coincident with enhanced wave 1 in ukmo geopotential height the 9 may event extends from 40 to 70 km and shows westward phase tilt with height while the 28 may event extends from 40 to 50 km and shows virtually no phase tilt with height

atmos atlas 3 observations of long lived tracers and descent in the antarctic vortex in november 1994 observations of the long lived tracers n2o ch4 and hf obtained by the atmospheric trace molecule spectroscopy atmos instrument in early november 1994 are used to estimate average descent rates during winter in the antarctic polar vortex of 0 5 to 1 5 km month in the lower stratosphere and 2 5 to 3 5 km month in the middle and upper stratosphere descent rates inferred from atmos tracer observations agree well with theoretical estimates obtained using radiative heating calculations air of mesospheric origin n2o 5 ppbv was observed at altitudes above about 25 km within the vortex strong horizontal gradients of tracer mixing ratios the presence of mesospheric air in the vortex in early spring and the variation with altitude of inferred descent rates indicate that the antarctic vortex is highly isolated from midlatitudes throughout the winter from approximately 20 km to the stratopause the 1994 antarctic vortex remained well isolated between 20 and 30 km through at least mid november

accuracy of the isentropic trajectories calculated for the easoe campaign during easoe 10 day backward trajectories ending on most measurement sites were calculated on 6 isentropic levels every day the temporal and spatial coarseness of the ecmwf analyses used cause significant errors in the trajectories these interpolation errors are largest in the direction along the trajectories the difference between two trajectories of the polar vortex balloon experiment and calculated trajectories is 8 and 12 of the trajectory length after 1 83 and 2 14 days this discrepancy is not explainable by interpolation errors alone

air flow over foredunes and implications for sand transport more than 4000 hourly wind profiles measured on three topographically different foredunes are analysed and discussed wind flow over the foredunes is studied by means of the relative wind speed the ratio between wind speed at a certain location and the reference wind speed at the same height relative wind speeds appear to be independent of general wind speed but dependent on wind direction for perpendicular onshore winds the flow over the foredune is accelerated due to topographic changes and decelerated due to changes in surface roughness accelerations dominate over decelerations on the seaward slope the pattern of acceleration and deceleration in relation to wind direction is more or less comparable for different foredunes but the magnitudes differ an increase in foredune height from 6 to 10m leads to an increase in speed up near the top of the seaward slope from 110 to 150 per cent during onshore wind but further increase of foredune height from 10 to 23 m appears to have little effect due to increased roughness and deflection of flow topography also influences the direction of the flow between beach and top the flow deflects in the direction of the normal during onshore winds during offshore winds the flow is deflected to the parallel near the dunefoot deflection is always in the direction of the parallel and increases with steeper topography the maximum deflection near the dunefoot was 90 over a 23 m high dune observed during offshore winds patterns of erosion and sedimentation resulting from winds from different directions can be explained by the observed accelerations and decelerations owing to speed up on the seaward front of the foredune sand transport capacity of the wind increases which results in erosion if vegetation is absent during strong onshore wind sand is lifted near the dunefoot and moves over the foredune in suspension during weaker winds vertical wind velocities do not exceed fall velocities of the sand grains and most of the sand is deposited near the dunefoot

vegetation and sedimentation on coastal foredunes on a timescale of years to decades vegetated foredunes may show various modes of morphological development vegetation is one of the factors that determine the sedimentation pattern and thus morphology on the foredune in turn the vegetation pattern may be controlled by the sedimentation pattern although these effects have been quantified for short timescales there is relatively little information on the interaction between vegetation and sedimentation for timescales of over a year for the island of ameland the netherlands elevation measurements and aerial photographs between 2002 and 2012 were used to derive changes in elevation and vegetation patterns on a year to year basis this was done for a range of stable to accreting foredunes sedimentation increases from the beach to a maximum halfway up the seaward slope of the foredune and then decreases again when going landward this trend is further modified by the vegetation s spatial pattern on a timescale of years there is no correlation between the density of vegetation cover and the amount of accretion however by accounting for the gradual depletion of the sand load over the foredune a relationship can be defined between vegetation cover and its trapping efficiency foredune vegetation spreads mainly by lateral expansion of existing patches no strong effect was found of the sedimentation balance on the expansion of vegetation it is suggested that other growth limiting factors are of similar importance masking any possible dependency of vegetation growth on sand accretion

intrusions into the lower stratospheric arctic vortex during the winter of 1991 1992 investigations of the kinematics of the lower stratospheric arctic vortex during the winter of 1991 1992 using the contour advection with surgery technique reveal three distinct events in which there was substantial intrusion of midlatitude air into the vortex in apparent contradiction of the view that the polar vortex constitutes an isolated air mass two of these events in late january and mid february were well documented they were predicted in high resolution forecasts by the european centre for medium range weather forecasts most clearly in experimental forecasts with reduced diffusion direct confirmation of the presence of the intrusions and of their calculated locations was provided by aerosol observations from the airborne differential absorption laser lidar aboard the nasa dc 8 taken as part of the second airborne arctic stratospheric expedition campaign aerosol rich air of midlatitude origin was seen in the expected position of the intrusions the reality of the february event was also confirmed by in situ measurements from the nasa er 2 such events may be significant for the chemical processes taking place within the winter vortex the intrusions were evidently related to the meteorology of the northern stratosphereduring this winter and in particular to persistent tropospheric blocking over the northeastern atlantic ocean and western europe and concomitant ridging into the lower stratospheric vortex in this region nevertheless preliminary investigations have indicated that such events are not uncommon in other northern hemisphere winters although no such events were found in the southern hemisphere during the antarctic winter of 1987

the b value as an earthquake precursor a systematic study of b values in new zealand has shown that within the vicinity of forthcoming large earthquakes there is initially an increase in b and then a return to normal the caracas and san fernando earthquakes show the same phenomenon which is related to that of seismic gaps

interannual variability of the vertical descent rate in the antarctic polar vortex to investigate a descent rate in the antarctic polar vortex we analyzed the long lived trace gas data derived from the halogen occultation experiment on board the upper atmosphere research satellite during the 6 year period from 1992 to 1997 by comparing the antarctic fall february and march and spring september and october methane profiles we estimated the middle stratospheric descent for each of the six winters large year to year variations are seen 1 2 1 8 km month 1 at 0 6 ppmv which consist of a biennial oscillation and a decreasing trend for the period analyzed the descent rate is larger in the even years 1992 1994 and 1996 than in the odd years 1993 1995 and 1997 dynamical fields for the 6 years are also analyzed using the united kingdom meteorological office assimilation data the differences between the even and odd years are clear in the midwinter in the even years the downward and poleward movement of the westerly jet occurs earlier the thermal wind relation infers that this event is associated with the development of a warm pool around the antarctic stratopause resulting from adiabatic heating due to the downward motion of air planetary wave activity over the winter season is more vigorous in the even years than in the odd years suggesting a close relationship between the mean flow and planetary waves

spatial and temporal patterns of aeolian sediment transport on an inland parabolic dune bigstick sand hills saskatchewan canada abstract topographic changes from erosion pins and on site meteorological data document the spatial and temporal patterns of aeolian sediment transport at monthly to annual timescales across an active parabolic dune within a vegetation stabilized inland prairie dune field over two years the sediment budget calculated from digital elevation models shows that the total volume of erosion 9890 m 3 is greater than the amount of deposition 6990 m 3 indicating a net loss of 2900 m 3 of sediment or 29 of eroded sediment from the dune sediment erosion occurred mainly on the stoss slope 3600 m 3 36 of eroded sediment but also on the south 2100 m 3 21 and north sides of the dune head 1700 m 3 17 the blowouts along the arms 1740 m 3 18 and the crest 650 m 3 7 erosion from the deflation basin is limited by surface roughness and armoring effects of a gravel lag deposit 100 m 3 1 thus the blowouts currently contribute to maintaining dune mobility because no other sediment input occurs from upwind sediment deposition onto the dune occurred primarily beyond the brink on the south and southeast lee slopes 5500 m 3 80 coinciding with the southeasterly resultant transport direction for november 2004 05 the net loss of about 2900 m 3 29 may be attributed to sediment carried in suspension over and beyond the dune correlation analysis between sediment transport and meteorological variables suggests that monthly to seasonal changes of surface conditions e g vegetation cover ground freezing moisture buffer the relative importance of temperature and precipitation on rates of sediment transport conversely wind correlates well on a monthly to seasonal basis because it is a driver of transport under all types of surface conditions seasonal effects produce a complex interaction between wind climate and surface conditions this leads to a dynamic range of threshold velocities which in turn causes spatial and temporal variations in transport limiting and supply limiting conditions collectively these findings have implications for modeling parabolic dune morphodynamics and sediment transport in mid to high latitude inland settings

lamination and polar vortex development in fall from atmos long lived trace gases observed during november 1994 long lived trace gas profiles observed by the atmospheric trace molecule spectroscopy atmos instrument around the developing polar vortex the protovortex during early november 1994 show distinctive inversions laminae high resolution profiles calculated using a reverse trajectory rt model reproduce the majority of these laminae demonstrating that most of these features arise from advection by the large scale winds the relationship between ch 4 and n 2 o sampled in filaments of low latitude air changes from the canonical midlatitude correlation to one typical of tropical air confirming the identification of tropical laminae n 2 o ch 4 correlations for laminae in vortex filaments indicate that enough confined descent and mixing has already occurred in the middle and upper stratosphere by early november to alter the tracer relationship in the protovortex from that in midlatitudes distributions of laminae in atmos observations agree with regions of greater or less filamentation seen in high resolution rt maps there is a deep minimum in laminae occurrence between 30 and 90 e at all levels extending to about 150 e above 35 km maxima in lamination in the lower stratosphere near 90 150 e and 210 270 e are associated with the main regions where tropical air is drawn up around the developing vortex continuous filamentation associated with the developing vortex and anticyclone in early november 1994 shows that transport and mixing processes previously reported during winter are already important during fall

formation of an ozone lamina due to differential advection revealed by intensive observations 1 an intensive observation with ozonesondes radiosondes and the middle and upper atmosphere mu radar was conducted at shigaraki 34 9 n 136 1 e japan from 16 through 24 april 1998 to investigate the formation mechanism of ozone laminae in the midlatitude lower stratosphere in these observations the temporal variation of an ozone lamina at shigaraki was continuously observed through a short time interval of 8 hours during the observation period an ozone lamina with a thickness of 2 3 km appeared and ascended with a speed of 1 km day 1 in the height region of 18 21 km it is deduced that inertia gravity waves existing in this height region did not contribute to formation of the ozone lamina because their amplitudes were too small and their vertical phase propagation was in the opposite direction the reverse domain filling method was used to reconstruct the high resolution modified potential vorticity field using backward trajectory calculations the results indicate that this ozone lamina was caused by differential advection due to the vertical shear associated with the subtropical westerly jet and embedded stationary rossby wave therein this means that large scale motions concurrent with vertical wind shear can produce much smaller scale structures in material fields than those of the large scale motions themselves

measurements of polar vortex air in the midlatitudes the stratospheric photochemistry aerosols and dynamics expedition spade was conducted in the spring of 1993 from moffett field california nasa ames research center utilizing the nasa high altitude er 2 aircraft these northern midlatitude aircraft flights showed laminae containing high ozone concentrations traceable to the april 1993 polar vortex breakup and corroborated by laminae of other trace gases such as cfcs ch4 n2o and co2 these laminae are clearly traceable as polar vortex breakup fragments using rossby ertel s potential vorticity and isentropic trajectory calculations laminae in stratospheric ozone profiles are commonly observed in the northern hemisphere from fall to spring and are hypothesized to originate from very low frequency transverse waves and or via rossby wave breaking on the basis of these results the ozone laminae observed during spade were a result of rossby wave breaking during the breakdown of the polar vortex in addition it is shown that conventional once per day meteorological analyses were adequate for representing the transport of this material into the lower stratosphere midlatitudes over the course of the spring vortex breakup

airflow and sand transport variations within a backshore parabolic dune plain complex ne graham island british columbia canada onshore aeolian sand transport beyond the beach and foredune is often overlooked in the morphodynamics and sediment budgets of sandy coastal systems this study provides detailed measurements of airflow sand transport via saltation and modified suspension vegetation density and surface elevation changes over an extensive 325 30 m swath of a backshore foredune parabolic dune plain complex near surface 30 cm wind speeds on the backshore ranged from 4 3 to 7 3 m s 1 gusting to 14 0 m s 1 oblique onshore flow is steered alongshore near the incipient foredune then landward into a trough blowout where streamline compression flow acceleration to 1 8 times the incident speed and increasing steadiness occur highest saltation rates occur in steady topographically accelerated flow within the blowout as such the blowout acts as a conduit to channel flow and sand through the foredune into the foredune plain beyond the blowout flow expands vegetation roughness increases and flow decelerates over the foredune plain localized flow steering and acceleration to 1 6 times the incident speed occurs followed by a drop to 40 of incident flow speed in a densely vegetated zone upwind of an active parabolic dune at 250 m from the foredune sediment properties reflect variations in near surface flow and transport processes well sorted fine skewed backshore sands become more poorly sorted and coarse skewed in the blowout due to winnowing of fines sorting improves and sands become fine skewed over the foredune plain toward the parabolic dune due to grainfall of finer sands winnowed from the beach and foredune during the fall winter season significant amounts of sand up to 110 kg m 2 are transported via modified suspension and deposited as grainfall up to 300 m landward of the foredune no distinct trend in grainfall was found although most fell on the depositional lobe of the blowout and at 200 m near an isolated active parabolic dune grainfall amounts may reflect several transporting events over the measurement period and the transport process is likely via localized modified suspension from the crest of the foredune and other compound dune features in the foredune plain this evidence suggests that the process of grainfall delivery though often overlooked in coastal research may be a key process in maintaining active dunes hundreds of metres from the shoreline in a densely vegetated foredune plain the effectiveness of this process is controlled by seasonal changes in vegetation cover and wind strength as well as shorter term e g tidally controlled variations in sand availability from the beach

mapping the frequency magnitude distribution in asperities an improved technique to calculate recurrence times we hypothesize that highly stressed asperities may be defined by mapping anomalously low b values along the san andreas fault near parkfield the asperity under middle mountain with its b 0 46 can be distinguished from all other parts of the fault surface likewise along the calaveras fault the northern asperity of the morgan hill 1984 m6 2 rupture can be identified by its low b of 0 5 as a high stress patch along the fault we add further evidence to the observations that the b value of the frequency magnitude relationship of earthquakes is inversely proportional to stress by showing that it decreases with depth in the parkfield segment of the san andreas and along the calaveras fault in both of these areas b values above and below 5 km depth are 1 2 and 0 8 respectively we propose that probabilistic recurrence times tr based on the seismicity parameters a and b should be calculated from their values within asperities only instead of from the values of the entire rupture area of the maximum expected earthquake the strong patches on faults control the time of rupture because they are capable of accumulating larger stresses than the rest of the fault zone which slips along passively when an asperity breaks therefore no information on tr is contained in the passive fault segments only in the asperities at parkfield the probabilistic estimates of tr derived from the data in the whole rupture and in the asperity only are 72 18 24 and 23 12 18 years respectively compared to the historically observed repeat time of 22 years at morgan hill the tr estimates are 122 46 76 and 78 47 110 years respectively compared to the observed repeat time of 72 years

transport out of the lower stratospheric arctic vortex by rossby wave breaking the fine scale structure in lower stratospheric tracer transport during the period of the two arctic airborne stratospheric expeditions january and february 1989 december 1991 to march 1992 is investigated using contour advection with surgery calculations these calculations show that rossby wave breaking is an ongoing occurrence during these periods and that air is ejected from the polar vortex in the form of long filamentary structures there is good qualitative agreement between these filaments and measurements of chemical tracers taken aboard the nasa er 2 aircraft the ejected air generally remains filamentary and is stretched and mixed with midlatitude air as it is wrapped around the vortex this process transfers vortex air into midlatitudes and also produces a narrow region of fine scale filaments surrounding the polar vortex among other things this makes it difficult to define a vortex edge the calculations also show that strong stirring can occur inside as well as outside the vortex

grain size characteristics of linear dunes in the southwestern kalahari abstract linear dunes in the southwestern kalahari sand sea exhibit characteristic grain size and sorting patterns in which sands become coarser better sorted and more finely skewed from interdune to crest in addition at a regional scale sands tend to become finer and better sorted in the direction of transport these patterns can best be explained in terms of the differential movement of sand in creep and saltation populations whereby the saltating population moves more rapidly and is concentrated downwind and in dunes slower moving creep populations remain close to source areas and in interdunes the fines will tend to be concentrated in interdunes because they can penetrate between coarse grains where they are protected from further movement this type of model probably explains most grain size and sorting relationships in desert sand seas

the structure of the polar vortex reconstruction of the airborne antarctic ozone experiment and airborne arctic stratosphere expedition aircraft constituent observations radiative heating rate computations and trajectory calculations are used to generate comparative pictures of the 1987 southern hemisphere sh late winter and 1989 northern hemisphere nh mid winter lower stratospheric polar vortices overall both polar vortices define a region of highly isolated air where the exchange of trace gases occurs principally at the vortex edge through erosional wave activity aircraft measurement showed that 1 between 50 and 100 mbar horizontally stratified long lived tracers such as n20 are displaced downward 2 3 km on the cyclonic poleward side of the jet with the meridional tracer gradient sharpest at the jet core 2 eddy mixing rates computed using parcel ensemble statistics are an order of magnitude or more lower on the cyclonic side of the jet compared to those on the anticyclonic side 3 poleward zonal mean meridional flow on the anticyclonic side of the jet terminates in a descent zone at the jet core despite the similarities between the sh and nh winter vortices there are important differences during the aircraft campaign periods the sh vortex jet core was located roughly 8 o 10 o equatorward of its nh counterpart after pole centering as a result of the arger size of the sh vortex the dynamical heating associated with the jet core descent zone is displaced further from the pole the sh polar vortex can therefore approach radiative equilibrium temperatures over a comparatively larger area than the nh vortex the subsequent widespread formation of polar stratospheric clouds within the much colder sh vortex core gives rise to the interhemispheric differences in the reconstructed h20 noy c10 and 03 species which are affected by polar stratospheric clouds

grain size characteristics of namib desert linear dunes the results of a systematic sampling of linear dunes in the northern namib sand sea show that they are composed of two distinct groups of sands a fine well sorted near symmetrical crest and slip face population and a coarse moderately sorted positively skewed plinth population these may be explained in terms of the aeolian sorting processes operative on the dunes which involve differential rates of movement of creep and saltation load on windward flanks and avalanching on leeward slopes leading to the concentration of coarse sands towards the dune base

patterns of sand transport on vegetated foredunes the aeolian development of coastal foredunes is studied at two sites along the dutch coast amounts of sand transport are measured in cross sections over the foredunes and changes in surface height are monitored sand transport decreases rapidly landward of the vegetation boundary near the dunefoot changes in surface roughness and topography generate turbulence and upward flow causing a small part of the sand to be transported in suspension patterns of transport are found to be closely related to air flow which in turn is related to topography and vegetation density with steeper topography the amounts of sand transported landward from the dunefoot increase if vegetation density is low during oblique onshore winds most of the sand accumulates at the dune front during perpendicular onshore winds a large proportion of the sand is deposited landward of the slope when deflection of flow occurs landward transport of sand is interrupted

computations of diabatic descent in the stratospheric polar vortex a radiation model together with national meteorological center temperature observations was used to compute daily net heating rates in the northern hemisphere nh for the arctic late fall and winter periods of both 1988 1989 and 1991 1992 and in the southern hemisphere sh for the antarctic fall and winters of 1987 and 1992 the heating rates were interpolated to potential temperature surfaces between 400 k and 2000 k and averaged within the polar vortex the boundary of which was determined by the maximum gradient in potential vorticity the averaged heating rates were used in a one dimensional vortex interior descent model to compute the change in potential temperature with time of air parcels initialized at various values as well as to compute the descent in log pressure coordinates in the nh vortex air parcels which were initialized at 18 km on november 1 descended about 6 km by march 21 while air initially at 25 km descended 9 km in the same time period this represents an average descent rate in the lower stratosphere of 1 3 to 2 km per month air initialized at 50 km descended 27 km between november 1 and march 21 in the sh vortex parcels initialized at 18 km on march 1 descended 3 km while air at 25 km descended 5 7 km by the end of october this is equivalent to an average descent in the lower stratosphere of 0 4 to 0 9 km per month during this 8 month period air initialized at 52 km descended 26 29 km between march 1 and october 31 in both the nh and the sh computed descent rates increased markedly with height the descent for the nh winter of 1992 1993 and the sh winter of 1992 computed with a three dimensional trajectory model using the same radiation code was within 1 to 2 km of that calculated by the one dimensional model thus validating the vortex averaging procedure the computed descent rates generally agree well with observations of long lived tracers thus validating the radiative transfer model

vertical diffusivity in the lower stratosphere from lagrangian back trajectory reconstructions of ozone profiles 1 we present a simple stochastic dynamical approach to estimate the turbulent vertical diffusivity d in the lower stratosphere from routinely observed ozone profiles first an observed ozone profile is reconstructed using three dimensional back trajectories obtained from analyzed winds and initializing the trajectories with ozone values from the output of a chemistry transport model assuming that diffusion in the vertical follows a simple random walk leading to a gaussian probability distribution for the particle displacements we perform monte carlo simulations with ensembles of particles originating along each point in the vertical profile by choosing different values of d as input in the calculations we generate different profiles that are smoothed through diffusion comparing with the observed profile we can identify that value of d which is in best agreement at an intermediate range of vertical length scales as an upper bound of the actual d for northern midlatitude lower stratospheric conditions during winter over a period of 12 days the best estimate is d 0 1 m2 s 1 or slightly larger the present results are discussed in the context of comparable estimations of vertical diffusivity in the literature