growth by extension and reworking of a south western kalahari linear dune optically stimulated luminescence osl dating studies of linear longitudinal dunes have been used extensively to elucidate late quaternary environments and climates in arid or formerly arid regions yet understanding of the development of such dunes is incomplete in particular conflicting opinions have been presented regarding the propensity of linear dunes to migrate laterally the degree to which they rework their own sediment during accumulation and whether they form primarily by extension as opposed to lateral sand movement from adjacent interdunes this study focuses on this last point although the importance of the other controversies is discussed in context a simple linear dune in the south western kalahari which has a prominent termination on a pan playa surface provides an opportunity to directly test hypotheses of dune extension chronostratigraphy along a 600 m transect along the crest of the dune constrained by 42 osl ages reveals that the dune grew by extension on occasions in the late pleistocene and early holocene but has also been subject to reworking along its length which has continued until recent times dune development by extensional growth is suggested to operate under environmental conditions more conducive to net accumulation whereas reworking is largely independent of conditions throughout the last 18 ka and may represent seasonal fluctuations in the position of the dune crest the relative significance of these two modes of development is suggested to be a key control on the efficacy of linear dunes as archives of environmental and climatic change copyright 2011 john wiley sons ltd

holocene aeolian activity in the southwestern kalahari desert southern africa significance and relationships to late pleistocene dune building events little is known about the timing of dune building episodes in the southwestern kalahari desert previously arid phases when dune activity occurred have been inferred from gaps in chronologies derived from information that attests to former humid periods to redress this optically stimulated luminescence osl dating was applied to sediment samples taken from a range of aeolian landforms in the sw kalahari four periods of dune building are identified in the late pleistocene and holocene holocene aeolian activity at 6 ka and 1 2 ka led to the construction of localised dune forms in contrast to late pleistocene times when the extensive field of linear dunes that dominates the region was emplaced late holocene aridity was however sufficient to allow rapid emplacement of the lunette dune at witpan the record of aeolian activity is evaluated in the context of humid chronologies and an ocean atmosphere model of holocene climate change with good agreement obtained it is concluded that the application of

frequency and magnitude biases in the fryberger model with implications for characterizing geomorphically effective winds abstract the fryberger model uses standardized wind data to estimate regional aeolian sediment drift potential dp which allows for interpretation and classification of aeolian dune landscapes this paper identifies systematic frequency and magnitude biases in the model that result from i variations in wind direction sector range which affects frequency bin size for determining percent occurrence of transporting winds and ii use of wind speed class mid point values over more statistically representative values e g mean median or minimally classified whole knot wind speeds in the magnitude weighting factor for dp calculations the significance of these biases is tested using unclassified data from stanhope prince edward island canada frequency bias resulting from wind data aggregation into direction sectors of varying size produces statistically significant discrepancies in dp and rdp estimates for this dataset when 36 point 10 s of degree data are reduced to 16 sectors cardinal directions receive one extra direction class and the magnitude of dp and rdp values decreases by 1 4 and 2 8 respectively compared to 16 equal 22 5 sectors derived from original data this results from under representation of intermediate direction classes for this dataset the effects on rdd less than 1 and directional variability ratio rdp dp are insignificant magnitude biases result from the use of the wind speed class mid point values instead of other statistically representative measures of wind speed in dp calculations in that wind speed distributions are often positively skewed mid point values yield an over estimate of total dp by as much as 34 and rdp by up to 22 for this dataset over those derived using mean median and whole knot minimally classified values this difference is statistically significantly at both the individual wind speed direction category level and at the aggregate directionally summed level and causes rdp vectors to shift 3 5 to the south though the impacts of these frequency magnitude biases are site specific and modest the effects on rdp estimation may be more significant in complex i e multi modal wind regimes and or in environments with more frequent high magnitude winds from the cardinal directions given the increased availability of more precise unclassified wind data most of these systematic frequency magnitude biases can be avoided recommendations on reducing inaccuracies imposed by these biases include i using to the degree wind data where available and categorizing into 16 equal 22 5 direction sectors ii using either wind speed class statistical mean values or minimally classified whole knot values in dp calculations and iii recognizing that converting 36 point 10 s of degrees data to 16 direction classes may introduce a frequency bias toward the cardinal directions and will cause inaccuracies in dp and rdp estimates of an amount that depends on the wind regime further research is needed to assess the implications of such biases in different wind regimes and into the influence of localized supply and transport limiting factors on regional scale assessments of dune morphodynamics and mobility these findings are also relevant for other applications that use categorized wind speed direction data such as dust or contaminant plume dispersion modelling

an evaluation of volcanic cloud detection techniques during recent significant eruptions in the western ring of fire we examined recent volcanic cloud events in the western pacific and indonesian area to validate the performance of remote sensing techniques used to support the international airways volcano watch iavw five events were considered during which eruptions from eight volcanoes injected ash into the upper troposphere or lower stratosphere for one of the eruptions at miyakejima japan at least five aircraft encountered volcanic ash clouds and the cost to three operators alone exceeded us 12 000 000 in aircraft repairs diversions and lost operating time we performed reverse absorption and pattern analysis using gms 5 vissr modis and avhrr data and we examined toms so2 and aerosol index data surface based observations pilot reports and dispersion model output our results verify that the introduction of reverse absorption using the geostationary gms 5 platform significantly enhanced our capacity to monitor volcanic ash clouds in the region in one case we tracked an eruption cloud for approximately 80 h the primary impediment to remote monitoring is the presence of overlying cloud or substantial amounts of ice within the volcanic clouds toms data showed success in identifying volcanic clouds during these conditions but was limited by the infrequency of observations more effective future operation of the iavw relies on developing complementary methods of volcanic cloud remote sensing and greatly increasing the amount and quality of available surface and air observations including observations of precursor activity an understanding of the likely future limitations of remote sensing techniques will aid in the refining of iavw procedures

morphological characteristics and development of coastal nabkhas north east kuwait the coastal aeolian nabkhas in kuwait are mostly elongated with an average length of about 10 m an average width of 3 7 m and an average height of 0 65 m the horizontal component of the nabkha dune hc the mean of the length and width of nabkha dune developed around nitraria retusa was measured and compared with the height of the shrub a second polynomial function was found to best fit the set of data the fitting identified three trends of the development of the nabkhas initially as the height of shrubs h increases the hc increases linearly until it reaches approximately 10 m when h exceeds 2 m the effect of shrub height becomes ineffective in trapping more sediments that is reaching an equilibrium condition before a decrease in shrub height effectiveness occurs sediments of the nabkha crest and wings left and right sides are subjected to high energy winds and therefore they are generally coarser and better sorted than those of the tail or the nose minor differences are noted in the textural characteristics and the mineral composition of nabkha sediments and those of other aeolian landforms found in upwind nabkha field this indicates that the sediments were derived from the nearby sources

structure and composition of organic reefs and carbonate mud mounds concepts and categories defined here as essentially in place calcareous deposits created by sessile organisms organic reefs are diverse and complex structures with a long geological history their classification has been the subject of fierce debate often characterized by reliance on subjective features such as wave resistance and qualitative attempts to discriminate between first and second class reefs in contrast emphasis is here placed on the objective characteristic of the type of sedimentary support which largely determines the sedimentary composition of the deposit constructional and depositional processes result in three principal sedimentary components matrix m essentially in place skeletons s and cavity cement c whose proportions can be represented on msc triangular plots separately or together these components also provide the structural support for the reef on these compositional and structural bases three main categories of organic reef are recognized 1 matrix supported reefs agglutinated microbial reefs cluster reefs segment reefs 2 skeleton supported reefs frame reefs 3 cement supported reefs cement reefs agglutinated microbial reefs possess laminated clotted or aphanitic fabrics created by microbial trapping of particulate sediment in place skeletons and large primary cavities are rare early cementation may provide added support topographic relief is limited by the need for currents to provide sediment to accreting surfaces cluster reefs skeletal reefs in which essentially in place skeletons are adjacent but not in contact resulting in matrix support characterized by relatively high matrix skeleton ratios and low volumes of extra skeletal early cement sediment trapping is an important corollary of skeletal growth and cluster reef organisms are tolerant of loose sediment absence of framework limits the topographic relief that cluster reefs can attain relative to spatial extent and may permit bedding to develop within the reef close cluster reefs have skeletons up to 1 unit distance apart spaced cluster reefs have skeletons more than 1 and up to 2 unit distances apart with increasing separation of skeletons they grade to level bottom communities segment reefs matrix supported reefs in which skeletons are adjacent and may be in contact but are mostly disarticulated and mainly parauthochtonous matrix abundance is high and early cement relatively low moderate relief can develop in response to intense on reef sediment production frame reefs skeletal reefs in which essentially in place skeletons including calcified microbes are in contact characterized by relatively high skeleton matrix ratio skeletal support enables them to raise themselves above the substrate independently of cementation and particulate sedimentation simultaneously by creating partly open shelter cavities skeletal support may facilitate early cementation both relief and early lithification promote marginal talus formation skeletal shape and orientation distinguish conical stick like dendritic domical and laminar frames each of these may be open or filled open frame reefs

secondary flow deflection in the lee of transverse dunes with implications for dune morphodynamics and migration measurements of lee side airflow response from an extensive array of meteorological instruments combined with smoke and flow streamer visualization is used to examine the development and morphodynamic significance of the lee side separation vortex over closely spaced transverse dune ridges a differential deflection mechanism is presented that explains the three dimensional pattern of lee side airflow structure for a variety of incident flow angles these flow patterns produce reversed along dune and deflected surface flow vectors in the lee that are inferred to result in net lateral diversion of sand transport over one dune wavelength for incident angles as small as 10 from crest transverse i e 80 from the crest line this lateral displacement increases markedly with incident flow angle when expressed as the absolute value of the total deflection in degrees reversed and multi directional flow occurs for incident angles between 90 and 50 these results document the three dimensional nature of flow and sand transport over transverse dunes and provide empirical evidence for an oblique migration model copyright 2013 john wiley sons ltd

a quantitative approach to understanding dated dune stratigraphies attempts to reconstruct past changes in climate related forcing of dryland landscapes are hampered by the lack of an adequate quantitative framework for understanding the production and interpretation of dated sedimentary records in drylands as in other environments information on past forcing conditions is progressively modified degraded and removed from the available stratigraphic record by a series of filters involving changes in the primary forcing factors themselves geomorphological processes and the sampling dating procedures in this paper we describe a quantitative model that includes these effects and use the model to examine the nature of preserved dryland sedimentary records and their relationships to primary forcing conditions thicker preserved sedimentary records reflect periods of more intense aeolian activity localized switching between erosion and deposition results in discontinuous and highly variable stratigraphic sequences a preservation bias towards younger deposits is observed potentially leading to a continuum of accumulation that decays approximately in proportion to time periods not represented by deposition can in some cases be interpreted as periods of higher precipitation and or lower wind energy an asymmetry exists between the efficiency with which past drier and wetter episodes can be identified which relates to the time separation of depositional periods and the correct distinction between hiatuses due to forcing conditions and those due to under sampling relevant to this is the effect of random dating errors statistical uncertainty which increasingly with age filter out higher frequency events from the record a new data treatment method termed accumulation rate variability provides an efficient proxy for accumulation rates and therefore the intensity of aeolian activity with significant improvements over existing date frequency methods the filtering problem discussed applies to all attempts at understanding the timing and nature of past events independent of the proxies and dating methods employed further explicit analysis of these issues would be beneficial copyright 2013 john wiley sons ltd

evidence for semi sessile early juvenile life history in cretaceous ammonites abstract here we present evidence for a semi sessile early juvenile stage of ammonites our hypothesis is based on fossil evidence in early diagenetic limestone concretions discovered in platy limestone deposits of cenomanian age in the northern state of coahuila mexico in these locations densely packed post embryonic shell assemblages were attached to fossilized algal or bacterial mats and preserved in sediments deposited under permanently anoxic bottom conditions tiny ammonites as well as gastropods and byssate pectinid bivalves are abundant and restricted to these mats they do not occur elsewhere in the sediment the ammonite hatchlings were apparently unable to escape from mats sinking to the hostile sea floor and must thus have been semi sessile similar to the associated gastropods and bivalves

analysis of linear sand dune morphological variability southwestern kalahari desert abstract linear dunes are the most common desert dune form usually occurring in extensive dunefields rather than as isolated individuals as part of a wider project investigating the dynamics and environmental significance of linear dunes the extensive linear dunefield of the southwestern kalahari desert southern africa was investigated for planimetric pattern variability considerable intradunefield variability was identified through aerial photograph analysis of a 4000 km 2 area leading to the development of a five class classification scheme this scheme was validated statistically utilising data for key planimetric pattern variables y junctions termini orientation range and wavelength the application of the classification scheme thoughout the dunefield permits the identification of trends in planimetric patterns this provides a basis for first attempts to explain aspects of planimetric variability in terms of the behaviour of linear dunes and their responses to key environmental variables

microbial carbonates the geological record of the calcified bacterial algal mats and biofilms summary deposits produced by microbial growth and metabolism have been important components of carbonate sediments since the archaean geologically best known in seas and lakes microbial carbonates are also important at the present day in fluviatile spring cave and soil environments the principal organisms involved are bacteria particularly cyanobacteria small algae and fungi that participate in the growth of microbial biofilms and mats grain trapping is locally important but the key process is precipitation producing reefal accumulations of calcified microbes and enhancing mat accretion and preservation various metabolic processes such as photosynthetic uptake of co2 and or hco3 by cyanobacteria and ammonification denitrification and sulphate reduction by other bacteria can increase alkalinity and stimulate carbonate precipitation extracellular polymeric substances widely produced by microbes for attachment and protection are important in providing nucleation sites and facilitating sediment trapping microbial carbonate microfabrics are heterogeneous they commonly incorporate trapped particles and in situ algae and invertebrates and crystals form around bacterial cells but the main component is dense clotted or peloidal micrite resulting from calcification of bacterial cells sheaths and biofilm and from phytoplankton stimulated whiting nucleation interpretation of these texturally convergent and often inscrutable fabrics is a challenge conspicuous accumulations are large domes and columns with laminated stromatolite clotted thrombolite and other macrofabrics which may be either agglutinated or mainly composed of calcified or spar encrusted microbes stromatolite lamination appears to be primary but clotted thrombolite fabrics can be primary or secondary microbial precipitation also contributes to hot spring travertine cold spring mound calcrete cave crust and coated grain deposits as well as influencing carbonate cementation recrystallization and replacement microbial carbonate is biologically stimulated but also requires favourable saturation state in ambient water and thus relies uniquely on a combination of biotic and abiotic factors this overriding environmental control is seen at the present day by the localization of microbial carbonates in calcareous streams and springs and in shallow tropical seas and in the past by temporal variation in abundance of marine microbial carbonates patterns of cyanobacterial calcification and microbial dome formation through time appear to reflect fluctuations in seawater chemistry stromatolites appeared at 3450 ma and were generally diverse and abundant from 2800 to 1000 ma inception of a proterozoic decline variously identified at 2000 1000 and 675 ma has been attributed to eukaryote competition and or reduced lithification thrombolites and dendrolites mainly formed by calcified cyanobacteria became important early in the palaeozoic and reappeared in the late devonian microbial carbonates retained importance through much of the mesozoic became scarcer in marine environments in the cenozoic but locally re emerged as large agglutinated domes possibly reflecting increased algal involvement and thick micritic reef crusts in the late neogene famous modern examples at shark bay and lee stocking island are composite coarse agglutinated domes and columns with complex bacterial algal mats occurring in environments that are both stressed and current swept products of mat evolution ecological refugia sites of enhanced early lithification or all three

linear dune pattern variability in the vicinity of dry valleys in the southwest kalahari linear sand dunes in the southwest kalahari dunefield have been widely observed to change pattern size and orientation in the vicinity of river valleys yet few explanations for this change have been put forward this paper identifies and describes four main associations between dunes and valleys which occur in the southwest kalahari i dunes which adjoin the valley on both sides with no discernible change in pattern or orientation ii dunes which adjoin the valley and change pattern iii dunes which adjoin the upwind valley flank but not the downwind side iv dune free zones on both sides of the valley the two main factors which influence the evolution of these associations are identified as the effect of the valley upon sediment supply and the effect of the valley upon wind regime our current state of knowledge about the potential geomorphological effects of these two variables is evaluated with reference to each association described

preliminary analysis of observations of the pinatubo volcanic plume with a polarization sensitive lidar a dual polarization lidar aboard the nasa electra aircraft was used in july 1991 to survey the stratospheric plume from the recent mt pinatubo eruption both depolarizing and non depolarizing volcanic layers were observed ranging from 17 to 26 km in altitude differences in the depolarization signatures of the layers indicates differences in the composition or physical state of the particles in the layers

complex holocene lunette dune development south africa implications for paleoclimate and models of pan development in arid regions closed depressions pan or playa basins are very common landscape features in arid or formerly arid regions many have associated downwind dune assemblages lunettes that have been explained in terms of deflation of sediments from the basin these widespread features have also been used as proxies of late quaternary rainfall and atmospheric circulation change we use a detailed program of optically stimulated luminescence dating at witpan south africa to show that lunette construction may be rapid and spatially complex this study presents 33 ages from 9 sample sites on the dune that show how accumulation of the present dune largely occurred over the past 2 k y but with marked sectoral variability in accumulation rates and timing variability is attributed largely to local sediment supply factors geochemical analysis shows that primary deflation from the pan has not contributed significantly to the construction of much of the current lunette most sand is derived from recycling of older lunette sediments preserved today at only a few locations and from neighboring linear dunes these findings if representative of lunettes in other localities have marked implications for the types of paleoclimatic information that these features may yield

calipso lidar observations of the optical properties of saharan dust a case study of long range transport 1 an extensive dust storm originating on 17 august 2006 in north africa was observed and tracked by the cloud aerosol lidar and infrared pathfinder satellite observations calipso lidar over the next several days the dust layer moved westward across the atlantic ocean and into the gulf of mexico the initial stages of the event were examined using a sequence of calipso measurements the first of these was acquired very near the source on 18 august successive measurements were made over the atlantic ocean on 19 and 20 august at respective locations approximately 1300 km and 2400 km from the source region the later stages of the event were assessed using measurements acquired by the nasa langley research center airborne hsrl over the gulf of mexico on 28 august within the free troposphere the intrinsic optical properties of the dust remain relatively unchanged for the first 3 d of transport over the atlantic ocean this is consistent with previous in situ measurements that have shown that there is little change in the size distribution of dust as it crosses the atlantic after the 10 d journey to the gulf of mexico some changes are seen in the lidar ratios the backscatter color ratio and the optical depth ratio the linear depolarization ratio appears to remain essentially constant 0 32 at all four locations mentioned above demonstrating a notable consistency in the dust particle nonsphericity the measured 532 nm lidar ratios are 41 3 41 4 41 6 and 45 8 0 8 sr respectively at locations near the source over the atlantic ocean and in the gulf of mexico the corresponding 1064 nm lidar ratios are 52 5 55 5 54 13 and 44 8 3 sr the 532 nm lidar ratios are consistent with previous measurements and with calipso s prelaunch models the lidar ratios retrieved at 1064 nm are somewhat larger than would be expected on the basis of existing modeling studies the backscatter color ratios are 0 74 0 07 0 75 0 08 0 72 0 04 and 0 62 0 01 and the optical depth ratios are 0 97 0 02 1 01 0 05 0 93 0 17 and 0 62 0 13 respectively

multi decadal satellite measurements of global volcanic degassing abstract satellite instruments have been providing measurements of global volcanic emissions of sulfur dioxide so 2 since 1978 based on observations in the ultraviolet uv infrared ir and microwave spectral bands we review recent advances in satellite remote sensing of volcanic gases focusing on increased instrument sensitivity to tropospheric so 2 emissions and techniques to determine volcanic plume altitude a synthesis of 36 years of global uv ir and microwave satellite measurements yields an updated assessment of the volcanic so 2 flux to the upper troposphere and lower stratosphere utls between 1978 and 2014 1 2 tg yr the present availability of multiple uv and ir satellite so 2 products provides increased confidence in calculated so 2 loadings for many eruptions we examine the temporal and latitudinal distribution of volcanic so 2 emissions and reassess the relationship between eruptive so 2 discharge and eruption magnitude finding a first order correlation between so 2 emission and volcanic explosivity index vei but with significant scatter based on the observed so 2 vei relation we estimate the fraction of eruptive so 2 emissions released by the smallest eruptions 0 48 tg yr which is not recorded by satellite observations a detailed breakdown of the sources of measured so 2 emissions reveals intuitively expected correlations between eruption frequency so 2 loading and volcanic degassing style we discuss new constraints on e folding times for so 2 removal in volcanic plumes and highlight recent measurements of volcanic hydrogen chloride hcl injections into the utls an analysis of passive volcanic emissions of so 2 detected in ozone monitoring instrument omi so 2 data since 2004 provides new insight into the location and stability of the dominant sources of volcanic so 2 over the past decade since volcanic so 2 emissions constitute a random highly variable perturbation to the atmosphere climate system continued monitoring of volcanic so 2 emissions from space by multiple uv and ir instruments to extend the current multi decadal record is essential and near global geostationary measurements of so 2 may be available by the end of the current decade

volcanic plume elevation model and its velocity derived from landsat 8 abstract in this paper we present a method to restitute the volcanic gas ash plume elevation model pem from optical satellite imagery as the volcanic plume is moving rapidly conventional satellite based photogrammetric height restitution methods do not apply as the epipolar offset due to plume motion adds up to the one generated by the stereoscopic view this is because there are time lags of tens of seconds between conventional satellite stereoscopic acquisitions depending on the stereo acquisition mode our method is based on a single satellite pass we exploit the short time lag and resulting baseline that exist between the multispectral ms and the panchromatic pan bands to jointly measure the epipolar offsets and the perpendicular to the epipolar p2e offsets the first are proportional to plume height plus the offsets due to plume velocity in the epipolar direction the second are proportional to plume velocity in the p2e direction only the latter is used to compensate the effect of plume velocity in the stereoscopic offsets by projecting it on the epipolar direction assuming a known plume direction thus improving the height measurement precision we apply the method to landsat 8 data taking into account the specificities of the focal plane modules we focus on the holuhraun 2014 fissure eruption iceland we validate our measurements against ground based measurements the method has potential for detailed high resolution routine measurements of volcanic plume height velocity the method can be applied both to other multifocal plane modules push broom sensors such as the esa sentinel 2 and potentially to other push broom systems such as the cnes spot family and pleiades

estimation of ash injection in the atmosphere by basaltic volcanic plumes the case of the eyjafjallajokull 2010 eruption 1 during explosive eruptions volcanic plumes inject ash into the atmosphere and may severely affect air traffic as illustrated by the 2010 eyjafjallajokull eruption quantitative estimates of ash injection can be deduced from the height reached by the volcanic plume on the basis of scaling laws inferred from models of powerful plinian plumes in less explosive basaltic eruptions there is a partitioning of the magma influx between the atmospheric plume and an effusive lava flow on the ground we link the height reached by the volcanic plume with the rate of ash injection in the atmosphere via a refined plume model that 1 includes a recently developed variable entrainment law and 2 accounts for mass partitioning between ground flow and plume we compute the time evolution of the rate of injection of ash into the atmosphere for the eyjafjallajokull eruption on the basis of satellite thermal images and plume heights and use the dispersion model of the volcanic ash advisory center of toulouse to translate these numbers into hazard maps the classical plinian model would have overestimated ash injection by about 20 relative to the refined estimate which does not jeopardize risk assessment this small error was linked to effective fragmentation by intense interactions of magma with water derived from melting of ice and hence strong mass partitioning into the plume for a less well fragmented basaltic dry eruption the error may reach 1 order of magnitude and hence undermine the prediction of ash dispersion which demonstrates the need to monitor both plume heights and ground flows during an explosive eruption

in situ and space based observations of the kelud volcanic plume the persistence of ash in the lower stratosphere volcanic eruptions are important causes of natural variability in the climate system at all time scales assessments of the climate impact of volcanic eruptions by climate models almost universally assume that sulfate aerosol is the only radiatively active volcanic material we report satellite observations from the cloud aerosol lidar with orthogonal polarization caliop on board the cloud aerosol lidar and infrared pathfinder satellite observations calipso satellite after the eruption of mount kelud indonesia on 13 february 2014 of volcanic materials in the lower stratosphere using these observations along with in situ measurements with the compact optical backscatter aerosol detector cobald backscatter sondes and optical particle counters opcs made during a balloon field campaign in northern australia we find that fine ash particles with a radius below 0 3 m likely represented between 20 and 28 of the total volcanic cloud aerosol optical depth 3 months after the eruption a separation of 1 5 2 km between the ash and sulfate plumes is observed in the caliop extinction profiles as well as in the aerosol number concentration measurements of the opc after 3 months the settling velocity of fine ash with a radius of 0 3 m in the tropical lower stratosphere is reduced by 50 due to the upward motion of the brewer dobson circulation resulting a doubling of its lifetime three months after the eruption we find a mean tropical clear sky radiative forcing at the top of the atmosphere from the kelud plume near 0 08 w m2 after including the presence of ash a value 20 higher than if sulfate alone is considered thus surface cooling following volcanic eruptions could be affected by the persistence of ash and should be considered in climate simulations

variations in wind velocity and sand transport on the windward flanks of desert sand dunes the magnitudes of increases in wind velocity or speed up factors have been measured on the windward flanks of transverse and linear dunes of varying height on transverse dunes velocity speed up varied with dune shape and height for linear dunes speed up factors varied principally with wind direction relative to the dune with dune shape and dune height the main effect of velocity speed up on the windward flanks of dunes is to increase potential sand transport rates considerably in crestal areas this is greatest for large dunes with winds of moderate velocity blowing at a large angle to the dune changing ratios of base to crest sand transport rates on transverse dunes tend to reduce dune steepness as overall wind velocities increase on linear dunes the tendency for crestal lowering is counteracted by deposition in this area when winds reverse in a bi directional wind regime

new chronological evidence for the nature and timing of linear dune development in the southwest kalahari desert abstract the age of the linear dunes in the southwest kalahari desert has not previously been directly established by applying the optical dating method to samples from the dunefield a number of questions relating to the timing and nature of linear dune development are addressed the last major period of simple linear dune development occurred 17 000 10 000 years ago probably from the reworking of earlier aeolian sediments dune emplacement occurred under more arid probably windier conditions than those prevailing today which are only responsible for episodic surficial dune sand movement as well as simple linear dunes the dunefield also contains more complex linear dune patterns samples from one area in the eastern dunefield demonstrate that multi phase development is more probable for complex dune patterns as opposed to single phase evolution under a complex wind regime

dune sand transport as influenced by wind directions speed and frequencies in the ordos plateau china the ordos plateau in china is a region with extensive wind erosion severe desertification and various aeolian sand hazards in order to determine aeolian sand transport in this region the relationship between the sand transport rate and wind speed at 10 min frequencies was established by field observation in both the qubqi sand desert and the mu us sandy land threshold wind speeds 2 m above the ground for mobile semi fixed and fixed dune surfaces were estimated by field observations the sand transport rate increased with the increase of the bare land ratio and near bed wind speed high resolution meteorological 10 min average wind velocity data at 10 m above the ground were converted into velocity values at a height of 2 m to calculate sand transport potential based on three specific parameters decisive for sand transport wind speed duration and direction the quantity of aeolian sand transported was calculated for various wind speed levels and directions and the overall characteristics of sand transport on different dune surface types were determined by vector operation techniques sand transporting winds took place mainly in springtime the prevailing wind directions were w wnw and nw with a frequency of more than 60 in total and sand transport in these directions made up more than 70 of the total transport corresponding to a general southeastward encroachment of aeolian sand in the study area the relationship between wind frequency and speed can be expressed by a power function high magnitude strong winds had a low frequency but they played a dominant role in aeolian sand transport

late quaternary linear dune accumulation and chronostratigraphy of the southwestern kalahari implications for aeolian palaeoclimatic reconstructions and predictions of future dynamics abstract the linear dunes of the kalahari now largely inactive have long been identified as having potential palaeoenvironmental significance the application of optically stimulated luminescence osl dating to these dunes in the 1990s provided the first chronology of aeolian accumulation in this region though field methodologies and time consuming multiple aliquot laboratory protocols limited both the depth of sampling in dune bodies and the total number of samples dated in order to permit a more thorough investigation of the potential of these dunes to preserve long chronological records this intensive study presents 71 osl ages from the linear dunes of the southwestern kalahari at witpan south africa sampled with coring equipment at regular and frequent intervals down to bedrock the earliest sand accumulation recorded at witpan is at 104 ka and in spatially discrete locations other evidence of dune activity is recorded at 77 76 57 52 and 35 27 ka although an inherently discontinuous archive the linear dunes of the southwestern kalahari have the potential to record multiple phases of dune construction following the last glacial maximum there is near continuous evidence of dune building with a peak of accumulation recorded from 15 to 9 ka at five individual sites this latter period is generally recognised from other proxy evidence as being unusually arid in this region and such periods of dune activity are likely to be related to intensification of the continental anticyclone during the holocene accumulation has continued at most sites sampled albeit at a lesser intensity this may imply that these dunes are presently not far from thresholds of activation

paleoenvironmental implications of fixed dune systems in southern africa extensive systems of fixed linear dunes occur in the kalahari region of southern africa from 28 s to 16 30 s they provide evidence for large scale expansion of arid climates in the subcontinent during the quaternary on the basis of differing dune morphologies and alignments three periods of upper pleistocene aridity are recognised patterns of dune alignments reflect paleosand flow regimes and permit deduction of past winds and circulation patterns leading to the conclusion that arid episodes were associated with and probably caused by greater strength and persistence of the south african anticyclone a tentative chronology of the arid periods tends to support the hypothesis that subtropical aridity was contemporaneous with glacial conditions in high latitudes

caliop observations of the transport of ash from the eyjafjallajokull volcano in april 2010 1 the cloud aerosol lidar with orthogonal polarization caliop is an elastic backscatter lidar carried on the calipso satellite caliop observations between 15 and 20 april 2010 of volcanic ash plumes following the eruption of the icelandic eyjafjallajokull volcano are reported here while caliop has limited spatial coverage due to nadir only sampling ash plumes were observed by caliop over a wide region from the north atlantic ocean to eastern europe during both day and night due to its nadir only view however caliop did not sample the densest ash plumes which were observed by passive satellite sensors and ground based lidar lidar depolarization and spectral backscatter signatures are used to discriminate ash layers from clouds most ash was observed in thin layers of laminar appearance with thicknesses ranging from 0 4 km to a little more than 1 km and at relatively low altitudes between 1 and 7 km most layers reported here produced strong lidar depolarization indicating a predominance of ash over sulfate aerosol in the plumes estimates of lidar extinction to backscatter ratio allow the retrieval of profiles of ash optical properties layers were observed with mean optical extinction ranging from 0 03 km 1 to nearly 1 km 1 combined with an estimate of mass extinction efficiency mass concentration profiles can also be estimated these observations of the three dimensional dispersion of the plume are complementary to observations from passive satellite instruments and ground based lidars and can be useful for verification of dispersion models such as those used by the volcanic ash advisory centers

wind energy environments and dunefield activity in the chinese deserts there are few detailed analyses of the wind energy environments and dunefield activity in the chinese deserts on the basis of wind data and other climatic parameters collected at meteorological stations in and around the deserts this paper considers wind environments and dunefield activity in the chinese deserts in the 1990s the results show that dunes in most of the deserts were developed and controlled by low energy wind regimes although most dunes had the morphology of transverse and linear types which is consistent with wind regimes some deserts did not show close relations between dune morphology and regional wind directional distributions due to other controls although sand transport mainly occurs in spring and early summer there is strong sand transport activity in winter in some deserts dune activity in the chinese deserts has great spatial variations the regions with low dune activity are located in the chaidm mu us hobq horqin and nenjiang deserts due to much higher annual precipitation in these regions the areas with strong dune activity are located in the eastern taklimakan and northern badain jaran deserts due to arid conditions and much stronger winds

dunefield activity response to climate variability in the southwest kalahari abstract aeolian activity on the crests of linear dunes in the arid southwest kalahari desert is primarily controlled by vegetation cover cover is temporally variable in response to rainfall with mobility index mi values and field based studies demonstrating the dynamic nature of aeolian processes in this dunefield landsat tm data for a drought 1984 and wetter 1993 year were analysed for two subscenes in the dune field one for a pastoral landscape and one for a conservation area to investigate the spatial dynamics of dune activity using the empirically determined 14 cover threshold as the limit to crestal aeolian activity tm band 3 data were found to best represent vegetation cover including senesced material at the end of the dry season the period when the potential for aeolian activity is normally high due to the wind strength at this time the extent of 0 14 cover areas ranged from 10 1984 to 3 1993 for the pastoral area and 16 1984 to 6 1993 for the conservation landscape the wetter 1993 image residuals have different spatial characteristics in the two subscenes with bare active dunes in the pastoral lands associated with locations of livestock pressure and those in the conservation area related to natural fire events the study demonstrates the spatial dynamics of temporally variable linear dune activity in the southwest kalahari and also shows that areas devegetated by drought can recover sufficient vegetation in wet years to limit the spatial extent of aeolian transport on dune crests

late quaternary environmental change in central southern africa new data synthesis issues and prospects much of the interior of central southern africa is a sand sea within which aeolian and lacustrine landforms and sediments of local and regional extent are preserved closed cave sites are restricted to very few locations while fluvial systems traverse the margins of the interior until the early 1990s chronologies of late quaternary environmental and climatic changes developed for this region were based on only a limited number of proxy data sets derived largely from lacustrine deposits and precipitates in particular directly determined ages from aeolian deposits the most extensive suite of features in the region were absent the application of luminescence dating techniques to dune sediments and the development of further detailed chronologies from cave precipitates is now providing a more comprehensive record for the last 50 ka with some chronologies extending back a further 100 ka we present and review these data assess their contribution to enhanced understanding of late quaternary environmental changes in the region and for the first time assess them against corrected radiocarbon ages from lacustrine sites it is concluded that there is now an enhanced understanding of the spatial and temporal complexity of climate changes affecting the region in the last glacial cycle including a complex record of punctuated aridity but that many issues including data set integration and forcing mechanism controls are imperfectly understood

two types of longitudinal dune fields and possible mechanisms for their development longitudinal dune fields characterized by nearly uniform interdune spacing are distinguished from longitudinal dune fields characterized by fairly variable interdune spacing and high frequencies of dune coalescence the empirical and theoretical evidence indicating that the former may be due to helical air currents aligned with the dunes is reviewed hypotheses arguing that the latter may arise indirectly from horizontal pressure gradients or bidirectional wind regimes are discussed evenly spaced linear sand banks aligned with tidal currents may be shown mathematically to result from energy optimalization within two dimensional sand transporting flow regimes and a similar simple or non rotational flow model is considered for the problem of desert longitudinal dunes an initial complex or rotational flow analysis is undertaken to discern the likely significance of roll vortices in desert sediment transport an evolutionary timescale is estimated for the formation of desert longitudinal dune fields a simple analysis is performed for the effect of regional sand mass change on longitudinal dune field ordering recommendations are made for future empirical and theoretical research

the australian desert dunefields formation and evolution in an old flat dry continent a new map the first based on interpretation of satellite imagery reveals both the complexityofaustralia sdunefieldsandtheirrelationshipswithtopography climateandsubstrate of the five main sand seas the mallee strzelecki and simpson in eastern australia cover quaternary sedimentary basins whereas the great victoria and great sandy dunefields in the west are formed by reworking of valley and piedmont sediments in a non basinal landscape of low relief ridge and valley topography these dunefields cover large areas of the arid zone and semi arid zone and small areas of dunes in sub humid areas around the margins of the continent reflecting past expansion of arid climates during glacial stages of the last several glacial cycles several areas of low relief stand out as being largely dune free the limestone nullarbor plain clay plains of the georgina basin and floodplains of rivers in the carpentaria lake eyre and murray darling drainage basins where sand is rare or not transported by diminished late quaternary rivers the yilgarn block of southwestern australia is also surprisingly free of dunes possibly as a result of long deep weathering everywhere the history of climate change is evident in dune morphology and distribution including large areas where the sand dune orientations are markedly divergent from modern sand moving wind directions

ontogeny and habitat change in mesozoic cephalopods revealed by stable isotopes δ18o δ13c abstract stable isotope 18 o and 13 c ratios were measured in successive aragonitic shell sequences of ammonoids class cephalopoda to determine whether their depth distributions changed within ontogeny and whether stable isotope values differ in various morphological groups e g leiostraca vs trachyostraca we concentrate mainly on 18 o for temperature results and added 13 c data to obtain information on the ontogenetic history for which full spiral measurements were undertaken for the first time to obtain valid stable isotope data from ammonoid shells we measured ontogenetic sequences full shell within different genera data sets from the jurassic cadoceras and cretaceous hypacanthoplite s nowakites were chosen due to the pure primary aragonitic shell preservation the study was designed to extract better information on the habitat and life cycle of fossil cephalopods e g ammonoids in comparison with recent cephalopods e g nautilus spirula sepia possessing equivalent or comparable hard parts the data from three genera suggest different modes of life in at least two morphological groups we detected and established two main groups with different ontogenetic strategies based on the 18 o data the wcw type warm cool warm type of cadoceras resembles strategies in nautilus and sepia which migrate from shallow into deeper environments and back in ontogeny wc type warm cool type and the cw type cool warm type of hypacanthoplites resembling the first two migration phases of spirula cwc type which migrates from deeper into shallower and back again into deeper habitats the main three phases revealed by both 18 o and 13 c data sets most probably reflect diet changes in juvenile to mid aged individuals followed by a habitat change for spawning adults in cadoceras the temperatures range from 21 2 c for juveniles down to 12 1 c for mid aged individuals and back up 16 9 c in adults the cw type strategy of hypacanthoplites involves a temperature range of 22 8 c to 28 9 c the respective mean values are 24 2 c juveniles 25 8 c middle phase and 27 8 c adults the 13 c values also revealed three ontogenetic stages in cadoceras and hypacanthoplites including two major shifts from positive to negative and from negative to positive values which probably correspond to sexual maturation the initiation of reproduction and concomitant changes in diet the presented data combined with previous ontogenetic studies e g stable isotopes on spirula nautilus and sepia can be used as proxies to directly correlate the habitats and ontogeny of recent and fossil cephalopods

volcanic ash over scandinavia originating from the grimsvotn eruptions in may 2011 a volcanic ash plume that originated from the eruptions of iceland s grimsvotn volcano in may 2011 was observed over the nordic countries using a combination of satellite observations and ground based measurements the dispersion of the plume was investigated using london vaac ash forecasts and modis observations hourly pm10 concentrations at air quality monitoring stations in the southern parts of norway sweden and finland exceeded 100 mu g m 3 for several hours the flexpart dispersion model has been used to confirm the icelandic origin of the sampled air masses column integrated quantities from a sun photometer and vertical profiles from a raman lidar were used to estimate the ash concentration within an elevated layer over stockholm a lofted layer with an optical thickness of 0 3 at 532 nm passed stockholm in the morning hours of 25 may 2011 considering a realistic range of coarse mode fractions and specific ash extinctions from the literature an estimated range of maximum ash mass concentration of 150 340 mu g m 3 was derived from the lidar measurements at an altitude of 2 8 km the lower estimate of the lidar derived ash mass concentrations within the planetary boundary layer was found to be in good agreement with surface observations of pm10

a holocene late pleistocene aeolian record from lunette dunes of the western free state panfield south africa the greatest concentration of pans in southern africa occurs in the western free state province south africa a feature of many free state pans is their fringing lunettes located on the southern

airflow and roughness characteristics over partially vegetated linear dunes in the southwest kalahari desert there is little understanding of the flow field surrounding semi vegetated linear dunes and predictions of dune mobility are hampered by a lack of empirical data concerning windflow in an attempt to characterize the near surface airflow upwind of and over partially vegetated linear dunes in the southwest kalahari desert this study presents measurements of vertical and horizontal wind velocity profiles across cross sectional transects of seven partially vegetated linear dunes vegetation surveys combined with velocity measurements from vertical arrays of cup anemometers placed up to 2 3 m above the ground surface were used to gain information concerning the modification of airflow structure caused by the intrusion of the dunes into the atmospheric boundary layer and to predict the variability of aerodynamic roughness z0 from interdune to crest the results suggest an acceleration of flow up the windward slopes of the dunes and as such the data correspond to classical theory concerning flow over low hills essentially jackson and hunt 1975 principles where the theory is incapable of explaining the airflow structure and acceleration characteristics this is explained in part by the presence of a spatially variable vegetation cover over the dunes the vegetation is important both in terms of the varying aerodynamic roughness z0 and problems concerning the definition of a zero plane displacement d it is considered that any attempts to characterize surface shear stress over the kalahari linear dunes in order to predict sand transport and dune mobility will be hampered by two problems these are the progressively non log linear nature of the velocity profiles over the dunes caused by flow acceleration and the production of thin near surface boundary layers caused by areally variable aerodynamic roughness as a result of the partially vegetated nature of the dunes

environmental oxygen fluctuations and the adaptive response of marine benthic organisms oxygen depletion is widespread in modern and ancient benthic environments most modern examples exhibit a significant cyclic fluctuation in o 2 availability ranging from tidal to seasonal cycles and longer term periods e g el nino in contrast only long term changes have been generally recognized in ancient environments benthic organisms adapt along two pathways 1 to low o 2 values and free h 2 s including chemosymbiosis 2 synchronization of individual life cycles to the o 2 fluctuation cycle by living as planktonic larvae in oxygenated surface waters using oxygenated periods in bottom waters during the adult stage examples of both adaptive pathways can be recognized in the benthic faunas of fossil oxygen controlled environments thus recording short and longer term fluctuations

so2 as a possible proxy for volcanic ash in aviation hazard avoidance 1 airborne volcanic ash poses a significant danger to aircraft but is difficult to quantify accurately using satellite data while sulphur dioxide is much easier to detect accurately but is much less of a direct hazard to aviation this paper investigates the reliability of using so2 as a proxy for the location of volcanic ash using an so2 retrieval from the infrared atmospheric sounding interferometer iasi and ash detections from iasi and the advanced along track scanning radiometer aatsr using a numerical missed ash fraction applied to the eruptions of eyjafjallajokull in 2010 and puyehue cordon caulle in 2011 reveals that the so2 flag typically misses 30 of the detectable ash furthermore the missed ash fraction is found to be highly variable both between the two eruptions and over the course of each eruption with values of over 80 found on some days the detection threshold of the aatsr ash flag is also investigated using radiative transfer calculations allowing the threshold of the iasi flag to be inferred and these are related to the ash contamination levels

satellite observations and interpretation of the 1991 mount pinatubo eruption plumes we demonstrate the use of hourly geostationary meteorological satellite gms and noaa polar orbiting advanced very high resolution radiometer avhrr satellite images of the june 1991 mount pinatubo volcanic eruption plumes in providing details of the timing changing eruptive style and umbrella plume movement and dynamics a chronology of explosive events which culminated in a 9 hour long climactic phase on june 15 has been determined from satellite data and favorably compared to ground based and other ancillary information maximum eruption column altitudes of 40 km and column top undercooling in excess of 55 c below the ambient atmosphere occurred during the climactic phase phases dominated by plinian versus coignimbrite eruptive plumes can be distinguished on the images analysis of the spreading umbrella plume during the climactic phase suggests that over the first 4 5 hours the plume spread laterally as a gravitational intrusion before becoming advected in the ambient winds we compare the rate of plume growth to a model of a radially symmetric continuously fed intrusion to describe the motion the rate of plume growth shows good agreement with this simple model for the first 4 5 hours from column top heights we determine eruption rates and obtain an independent estimate of the total volume of magma erupted from june 12 16 of 5 5 km3 dense rock equivalent dre in good agreement with an independent estimate of the total eruptive volume made from deposits on land and submarine ash fall of up to 5 3 km3 dre we also show that secondary explosions in the pinatubo ignimbrite deposits produced ash plumes reaching altitudes as high as 19 km in september 1991 this study indicates that realistic interpretation and monitoring of major eruption plumes can be accomplished by analysis of high temporal resolution satellite data

mixing processes within the polar night jet abstract lagrangian material line simulations are performed using u k meteorological office assimilated winds and temperatures to examine mixing processes in the middle and lower stratospheric polar night jet during the 1992 southern hemisphere spring and northern hemisphere winter the lagrangian simulations are undertaken to provide insight into the effects of mixing within the polar night jet on observations of the polar vortex made by instruments onboard the upper atmosphere research satellite during these periods a moderate to strong kinematic barrier to large scale isentropic exchange similar to the barrier identified in gcm simulations is identified during both of these periods characteristic timescales for mixing by large scale isentropic motions within the polar night jet range from 20 days in the southern hemisphere lower stratosphere to years in the northern hemisphere middle stratosphere the long mixing timescales found in the northern hemisphere polar night jet do not persist instead

comparative lidar study of the optical geometrical and dynamical properties of stratospheric post volcanic aerosols following the eruptions of el chichon and mount pinatubo the spatiotemporal evolution of aerosols formed from precursors injected into the stratosphere by major volcanic eruptions such as those of el chichon in 1982 and mount pinatubo in 1991 has been studied using a ground based lidar system located at the observatoire de haute provence ohp in southern france 44 n 5 e from the inversion of the lidar signals the optical geometrical and dynamical properties of the particles have been determined as a function of time after the eruption in immediate post volcanic conditions when the optical thickness of particles in the stratosphere is largely enhanced an estimate of the aerosols backscatter phase function has been evaluated directly from the lidar measurements using a size distribution model adjusted to in situ balloon measurements the precision of this determination lies in the 15 range values of the mean radius of the particles of their integrated content surface areas and sedimentation velocities are then derived from the systematic lidar measurements performed at ohp these values are compared for the two major volcanic eruptions which have occurred over the last decade although the injection of sulphur dioxide was twice as large for the mount pinatubo eruption as compared to the el chichon case the diffusion of the cloud in the two hemispheres due to the interaction of the particular phase of the quasi biennal oscillation with several other dynamical processes at the time of the eruption led to the observation of similar values for the aerosol content over the observatoire de haute provence in the months just following the two events however the residence time of the particles in atmospheric layers below 20 km are 4 months longer after the mount pinatubo eruption caused by the observed difference in the initial vertical distribution of the aerosol cloud

identifying eruptive sources of drifting volcanic ash clouds using back trajectory modeling of spaceborne thermal infrared data a new approach is presented for determining the source region of disconnected volcanic ash clouds using a combination of orbital thermal infrared tir image data hysplit generated backward trajectories and spatial geostatistics interpolated surfaces derived from the tir data are created to find the most likely ash cloud travel path and the potential source volcanoes identified from that path the ability to use backward trajectories to determine the ash cloud source region will become an important triggering tool to target high spatial resolution orbital sensors which normally rely on thermal anomalies for new targeting during cases where thermal anomalies are not present or masked by meteorological cloud ash cloud detection and predicted source location become more important image data from several well documented past eruptions are presented to validate and determine the overall accuracy of this technique because this is seen as a limited range source region validation tool the ash clouds examined were 1000 km from their source vent the approach and analysis are deemed successful if 80 of the model results produce one or more trajectories that pass within 60 km of the source volcano this methodology could be improved further with the ability to determine the cloud location more accurately using higher image data frequency and most importantly greater accuracy in determining the cloud height in the atmosphere

understanding linear dune chronologies insights from a simple accumulation model abstract dunefields are today often found in regions where environmental conditions are no longer conducive to widespread aeolian transport and deposition and are thus seen as potential archives of palaeoenvironmental information some dune types are more suitable for this purpose than others and linear dunes used here synonymously with longitudinal dunes have been most frequently employed they are commonly found in dryland and dryland marginal regions and they are apparently less migratory than some other dune forms thereby offering the potential for longer environmental histories most recent studies have employed optical osl dating surveys which directly date the emplacement of dune sands to attempt to produce a representative history of aeolian accumulation at a dunefield scale yet such studies have not always given due consideration to the geomorphology of linear dune accumulation although linear dunes do not rework their sand as readily as say barchans dunes it is clear that sand deposited during an aeolian event is likely to have been removed from elsewhere on the dunefield s surface for this reason all dune archives must be assumed to be discontinuous over long timescales the effect of sediment redistribution on dune preservation and thus palaeoenvironmental interpretation is difficult to observe and poorly understood we present a simplified probabilistic model to replicate deposition erosion of sand at a linear dune crest thus simulating the type of profile sampled in many field studies in order to produce a local accumulation history the modelled sand flux incorporates various feedbacks and the simulations are run with varying boundary conditions in which the simulated surface is assumed to be in equilibrium over the multi millennial timescales of the model s duration periodic instabilities in the landscape are generally well recorded by the modelled dune accumulation history particularly when the events involve the system as a whole briefly functioning out of an equilibrium state i e the probabilities of deposition and reworking are not equal however under forcing conditions where the probabilities are unchanged throughout the duration of the model run the results can show apparent structure within the data when sample sizes are low although at large sample sizes the preservation potential decays with burial age according to a power law the model confirms the importance of rigorous sampling strategies for such studies but also suggests that if such precautions are taken the reworking inherent to linear dune aeolian systems does not preclude their use as a quaternary palaeoenvironmental archive of environmental change

the history and nature of wind erosion in deserts recently the importance of wind erosion has been reevaluated many low angle surfaces developed on susceptible materials possess closed depressions pans and these often have a distinctive morphology and lunette dunes on their lee sides it has also become apparent that in drylands there are extensive areas of stone pavements some of which have been molded by deflation however it is now recognized that other horizontal sorting processes have played a role especially movement of fines by overland flow vertical sorting associated with wetting and drying salt heave bioturbation frost action and dust accretion have also played a role in hyperarid areas especially with unidirectional winds bedrock outcrops and old lake beds have been molded to give aerodynamic forms called yardangs the study of dust storms by analysis of climatological data and remote sensing has revealed the importance of deflation especially in hyperarid areas with centripetal drainage deflation hot spots such as the bo

intrusion triggering of the 2010 eyjafjallajokull explosive eruption the ash cloud that brought chaos to european air traffic in april this year was the result of emissions from an icelandic volcano that had been intermittently active for about 18 years a combination of detailed space based geodetic measurements and seismic monitoring of the eyjafjallajkull volcano in the run up to the ash producing explosive summit eruption reveals an unusual deformation pattern that may be attributed to its off rift setting with relatively cool subsurface structure and limited magma at shallow depth as to the predictability of such a dramatic reawakening the immediate precursors to the initial eruption of the volcano in 2010 were subtle and difficult to detect but the clear signs of volcanic unrest during the weeks months and years preceding it may provide better clues to the catastrophic explosion

cloud top height determination using atsr data abstract a method for computing cloud top heights using multiangle satellite data has been developed by exploiting the dual angle capability of the ers 1 along track scanning radiometer atsr cloud top heights can be determined to a nominal accuracy of 1 km the method uses a spatial correlation function to determine the best fit between the nadir and forward images of any channel the resulting horizontal shifts are then converted to cloud top heights using a simple but accurate approximation to the atsr view geometry the technique is presented and some examples of cloud top height determination are given the possibility of determining cloud top winds using this technique is explored

quantification of volcanic cloud top heights and thicknesses using a train observations for the 2008 chaiten eruption new evidence of vertically thin 10 km ash clouds from the may 2008 chaiten eruption in southern chile is presented a train remote sensors were used to measure high resolution volcanic cloud top heights vcths during the explosive phase 2 10 may 2008 of the eruption ash clouds were identified using a reverse absorption technique applied to hyperspectral measurements taken by the atmospheric infrared sounder once identified heights and thicknesses were derived from the cloud aerosol lidar with orthogonal polarization caliop instrument as these two instruments are part of the same constellation of satellites coincident retrievals are routinely possible collocation of the data allowed for detection of volcanic ash within caliop profiles using a simple thresholding algorithm vcth and thickness were derived from the caliop profiles a total of 12 vcth measurements ranging from 3 7 to 16 6 km have been derived back trajectories from the hybrid single particle lagrangian integrated trajectory dispersion model were used as a check on volcanic origin of the detected ash clouds ensemble forward trajectories were generated to demonstrate how the new data could be used to improve volcanic ash advisory center operations the findings reported here demonstrate several cases where low level ash was not recorded previously and include observations of thin ash clouds at large distances 4000 km from the volcano

wind regimes and aeolian transport in the great basin u s a abstract the modern great basin of the interior western united states is characterized by surface winds with considerable spatial and temporal variabilities wind records from the second half of the 20th century for 12 great basin localities analyzed with standard aeolian sediment transport methods developed elsewhere in the world reflect this complexity the drift potential dp for aeolian deposits is generally moderate dp 200 400 in the western great basin and weak dp 300 at the eastern edge of the great basin where the dominant prevailing wind direction is south southwesterly both dp and resultant drift direction rdd are consistent with synoptic meteorological observations of the evolution of cold fronts in the great basin meteorological observations show that effective winds to produce dunes are most commonly the result of late winter early spring cyclogenesis there has been considerable temporal variability of dp in the latter half of the 20th century most of the great basin has experienced decreasing wind strength since 1973 consistent with recent studies of wind strength in north america and elsewhere dune morphology matches both localized rdd and temporal variations in dp reasonably well in the great basin the results demonstrate that local topography can have an important influence on wind directionality thus providing a cautionary note on the interpretation of dune morphology in the paleoclimatic and stratigraphic record

fluctuations of the oxygen minimum zone at the end of oceanic anoxic event 2 reflected by benthic and planktic fossils the latest cenomanian to early turonian late cretaceous section at vallecillo mexico contains a continuous and highly fossiliferous sedimentary record across the late oceanic anoxic event oae 2 and shows similar distributions of benthic inoceramids and planktic foraminifers during this period of an expanded oxygen minimum zone omz we suggest that these synchronous abundance changes result from similar environmental vulnerability of planktotrophic larval stages of inoceramids and deeper dwelling planktic foraminifers and that these synchronous changes reflect the expansion of the omz the abundances of ammonites and fishes used as independent control groups do not correlate and rule out a preservational bias ammonites fishes and their hatchlings thus populated shallower water depths than inoceramid gametes and planktic foramininifers the improving conditions at the end of oae 2 resulted in the dispersal of new inoceramid and foraminiferal morphotypes

aggregation dominated ash settling from the eyjafjallajokull volcanic cloud illuminated by field and laboratory high speed imaging the recent eyjafjallajokull iceland eruption strikingly underlined the vulnerability of a globalized society to the atmospheric dispersal of volcanic clouds from even moderate size eruptions ash aggregation controls volcanic clouds dispersal by prematurely removing fine particles from the cloud and depositing them more proximally physical parameters of ash aggregates have been modeled and derived from ash fallout deposits of past eruptions yet aggregate sedimentation has eluded direct measurement limiting our ability to predict the dispersal of volcanic clouds here we use field based high speed video analysis together with laboratory experiments to provide the first in situ investigation and parameterization of the physical features and settling dynamics of ash aggregates from a volcanic cloud in may 2010 high speed video footage was obtained of both ash particles and aggregates settling from the eyjafjallajokull volcano eruption cloud at a distance of 7 km from the vent fallout samples were collected simultaneously experimental laboratory determinations of the density morphology and settling velocity of individual ash particles enable their distinction from aggregates the combination of field and experimental analyses allows a full characterization of the size settling velocity drag coefficient and density distributions of ash aggregates as well as the size distribution of their component particles we conclude that ash aggregation resulted in a tenfold increase in mass sedimentation rate from the cloud aggravating the ash hazard locally and modifying cloud dispersal regionally this study provides a valuable tool for monitoring explosive eruptions capable of providing robust input parameters for models of cloud dispersal and consequent hazard forecast

multisatellite multisensor observations of a sub plinian volcanic eruption the 2015 calbuco explosive event in chile a train satellite data acquired during the calbuco volcano chile sub plinian eruption in april 2015 are discussed to explore the complementarity of spaceborne observations in the microwave mw thermal infrared tir and visible wavelengths for both near source plume and distal ash clouds the analysis shows that tir based detection techniques are not suitable near the volcanic vent where rising convective columns are associated with large optical depths detection and parametric estimates of near source tephra mass loading and plume height from mw radiometric data available 69 min after the eruption onset are proposed results indicate a maximum plume altitude of about 21 km above the sea level and an ash mass of 3 65 times 10 10 kg in agreement with mass values obtained from empirical formulas but less than proximal distal mass deposit of 1 86 times 10 11 kg this discrepancy may be explained by extrapolating advanced technology microwave sounder based estimates to 6 h thus obtaining a total mass of about 1 90 times 10 11 kg distal volcanic cloud retrievals are derived from tir imagery and results show a good agreement between moderate resolution imaging spectroradiometer modis and visible infrared imaging radiometer suite viirs retrievals of total mass taking into account the overpass time shift if only the overlapping pixels between modis and viirs are considered the respective estimates are 1 90 times 10 9 kg and 1 80 times 10 9 kg tir radiometric estimates of distal ash cloud height and mass loadings are also compared with cloud aerosol lidar and infrared pathfinder satellite observations lidar retrievals for low to medium optically thick ash cloud average cloud aerosol lidar with orthogonal polarization derived mass loading is about 0 8 g m2 against 0 4 g m2 from viirs and 1 4 g m2 from modis

chaotic advection in the stratosphere implications for the dispersal of chemically perturbed air from the polar vortex the lagrangian evolution of material lines within the northern hemisphere winter stratospheric vortex is determined using isentropic winds and diabatic heating rates obtained from the nasa langley research center larc atmospheric circulation model transient subtropical anticyclones lead to deformation of the material lines near the edge of the polar vortex which then rapidly evolve into elongated filaments as material is drawn around the anticyclones the rate of stretching of the material lines is shown to be exponential with typical e folding times of the order of 4 to 8 days these results provide evidence for chaotic advection near the edge of the stratospheric polar vortex which leads to rapid mixing of vortex air with tropical and midlatitude air the characteristic timescales of these mixing processes and the extent to which the mixing penetrates the polar vortex have important implications for the dispersal of chemically perturbed air from the polar vortex throughout the northern hemisphere and attendant ozone depletion

significance of variations in the wind energy environment over the past 50 years with respect to dune activity and desertification in arid and semiarid northern china climate data from 339 meteorological stations collected from the 1950s to the early 2000s was employed to discuss aeolian activity in arid and semiarid northern china the results show that at decadal time scales erosivity varied greatly in this region most of arid and semiarid northern china was characterised by environments with moderate to low wind energy after the 1980s the erosivity was only 20 to 50 of that beforehand and this difference had a significant impact on the environmental changes observed during the two periods the dune mobility index was consistent with the observed dune activity after the 1980s dune activity decreased and in some deserts with vegetated dune systems during the 1970s most of the dune plinths were active until the 1980s after which only the crests were active some mobile dunes that had developed at the margins of mobile deserts were replaced by semi anchored or anchored dunes because most desert areas with vegetated dune systems in arid and semiarid northern china are used for farming or grazing the results of our monitoring show that the desertification trends were consistent with the trends in erosivity and dune activity in this region desertification was controlled much more by climatic changes than has previously been acknowledged and especially by fluctuations in wind energy

the 7 8 august 2008 eruption of kasatochi volcano central aleutian islands alaska 1 kasatochi volcano in the central aleutian islands erupted unexpectedly on 7 8 august 2008 kasatochi has received little study by volcanologists and has had no confirmed historical eruptions the island is an important nesting area for seabirds and a long term biological study site of the u s fish and wildlife service after a notably energetic preeruptive earthquake swarm the volcano erupted violently in a series of explosive events beginning in the early afternoon of 7 august each event produced ash gas plumes that reached 14 18 km above sea level the volcanic plume contained large amounts of so2 and was tracked around the globe by satellite observations the cumulative volcanic cloud interfered with air travel across the north pacific causing many flight cancelations that affected thousands of travelers visits to the volcano in 2008 2009 indicated that the eruption generated pyroclastic flows and surges that swept all flanks of the island accumulated several tens of meters of pyroclastic debris and increased the diameter of the island by about 800 m pyroclastic flow deposits contain abundant accidental lithic debris derived from the inner walls of the kasatochi crater juvenile material is crystal rich silicic andesite that ranges from slightly pumiceous to frothy pumice fine grained pyroclastic surge and fall deposits with accretionary lapilli cover the lithic rich pyroclastic flow deposits and mark a change in eruptive style from episodic explosive activity to more continuous ash emission with smaller intermittent explosions pyroclastic deposits completely cover the island but wave erosion and gully development on the flanks have begun to modify the surface mantle of volcanic deposits

wind energy variations in the southwestern kalahari desert and implications for linear dunefield activity the southwestern kalahari linear dunefield which displays marked morphological variability possesses a partial but temporally and spatially variable vegetation cover and has frequently been described as a palaeodunefield palaeo status has been ascribed on the basis of several criteria including the presence of vegetation but also because dunes are thought to be out of alignment with modern resultant potential sand moving wind directions and because present day wind energy is regarded as low for the period 1960 1992 wind data from eight dunefield meteorological stations are analysed in detail to examine these assertions potential sand transport directions including spatial and temporal variations and potential drift directions for the windiest three month periods are calculated and explained it is concluded that the present day potential sand transport environment is markedly variable from year to year and from place to place while periods of low sand transport energy do occur it is also noted that the 1980s possessed considerable potential for sand transport in the dunefield directional variability is also relatively high perhaps exceeding that under which linear dunes can be expected to form because linear dune aeolian activity has a number of states however the present day wind environment may allow dune surface aeolian activity to occur which does not alter the overall pattern of the dunes

dune mobility and vegetation cover in the southwest kalahari desert as part of a wider project investigating the palaeoenvironmental significance of partially vegetated linear dunes in the southwest kalahari data collected in the latter part of 1992 concerning dune movement and vegetation cover suggest that sediment transport is occurring on some dune surfaces and that the majority of surface activity occurs on the crests and upper slopes of the dunes the data suggest that the limiting variables on surface sediment movement vary on different parts of a dune on interdunes and lower dune slopes the primary limiting variable is available wind energy while on dune crests and upper slopes it is vegetation cover ground cover by litter has much greater importance in protecting the surface sediment from erosion than rooted vegetation from individual data points no evidence is found to support a threshold vegetation cover below which sediment movement occurs rather a gradient of activity is suggested whereby a reduction in vegetation cover increases the potential for sediment movement and surface change however dunes with differing amounts of mean vegetation cover display differing degrees of surface activity and at this scale a vegetation cover threshold in the region of 14 per cent may be recognized

dunes of the gran desierto sand sea sonora mexico the gran desierto sand sea contains dunes of crescentic and star form in simple compound and complex varieties the dunes have developed in bimodal to complex wind regimes of intermediate energy transitions from simple through compound to complex crescentic dunes are associated with regional changes in wind regimes growth of large star dunes takes place by merging of smaller crescentic and reversing dunes from southerly directions and reworking of sand by northerly and westerly winds although wind regimes appear to be the major control of dune morphology in this sand sea there is a close correlation between the spacing of simple crescentic dunes and the grain size of the coarse 20th percentile