holocene palaeoclimates from peat stratigraphy macrofossil proxy climate records from three oceanic raised bogs in england and ireland quantified analyses of plant macrofossil remains have been made from three profiles of peat from raised bogs spanning a distance of 425 km from western ireland to northern england the reconstructed vegetation of each profile is related to changing bog surface wetness bsw and since the bogs are ombrotrophic these bsw changes are interpreted in terms of changing climate using age depth models based on a total of 49 radiocarbon dates a number of wetter and drier phases are identified and phase shifts to wetter and or cooler climates are defined prominent coincident changes to wetter conditions are dated in at least two of the profiles to ca 4400 4000 1750 1400 and 1000 cal bp and in all three profiles at 3200 2750 2350 2250 and around 700 cal bp these phases are related to proxy climate changes in other terrestrial data sets from northwest europe and a broad degree of synchroneity is demonstrated

three dimensional modelling of a holocene tufa system in the lathkill valley north derbyshire using ground penetrating radar unlithified and partly lithified carbonate sequences are ideally suited to the application of ground penetrating radar gpr augmented by percussion augering and shallow seismic techniques all tied to present day topography using global positioning system gps methods this methodology provides the first clear information on the distribution and geometry of lithofacies within buried tufa complexes the approach has been applied to a thick succession of holocene tufas filling a gorge site along a 3 5 km length of the river lathkill north derbyshire earlier studies have demonstrated the presence of up to 16 m of tufas and sapropels associated with two transverse tufa dams barrages these strata have been accumulating throughout the holocene although tufa developments at present are of minor extent internal tufa morphologies are recorded by gpr as bright laterally continuous reflections for lithified concretionary and lithoclast rich horizons the brightest reflectors occur within well cemented barrages and delineate core areas and prograding buttress zones in contrast unlithified lime muds and sapropels produce low contrast reflections lithostratigraphic control and depth calibration of the gpr profiles was provided by percussion augering at selected sites six distinct lithofacies and four secondary barrages are identified in the study constructional and destructional events can be identified and correlated within the gpr profile network and the internal growth morphologies of the barrages are apparent gpr profiles also clearly define the evolution of the facies geometries three phases of tufa development can be recognized within the gpr data and greatly extend our understanding of holocene tufa forming processes in valley sites a early holocene barrage build ups but with limited paludal deposition b middle holocene ponding and sapropel accumulation under warm conditions and c late holocene barrage termination and valley levelling probably coincidental with anthropogenic activity this type of multidisciplinary approach should be considered as an essential prerequisite to all biostratigraphic and geochemical studies of holocene freshwater carbonate sites

holocene and modern sediments in the seine estuary france a synthesis this synthesis of numerous studies on the holocene and modern sediments in the macrotidal setting of the seine estuary demonstrates their overall evolution in common with a number of estuaries the lower seine was an incised valley during the weichselian glacio eustatic sea level fall and infilling occurred during the subsequent lowstand the holocene sea level rise and the late holocene stillstand in the upper estuary above the basal gravel bed fluvial freshwater deposits filled the valley next fine sand and silts invaded the estuary upstream to rouen the sequence ends in loam resulting from an increase in the supply of sediment to the fluvial system in the upper estuary anthropogenic deepening of the modern channel results in erosion of the holocene sediments the only bedforms are thin and narrow sand sheets and some rare megaripples in the lower estuary above the weichselian basal gravel the holocene wedge records the change from a transgressed fluvial setting i e gravel beds to an open estuarine environment i e tidal delta the modern seine estuary has been progressively infilled by marine sands and silts now silts and clays supplied during high river flows accumulate at the outlet and offshore sands and gravel of the eastern bay of the seine are temporarily covered with veneers of mud these freshly deposited muds i e mud patches are periodically partly reworked by waves and strong tidal currents but silting of the inner shelf is noticeable copyright 2003 john wiley sons ltd

kinematic and precipitation characteristics of convective systems observed by airborne doppler radar during the life cycle of a madden julian oscillation in the indian ocean abstractthis study presents characteristics of convective systems observed during the dynamics of the madden julian oscillation dynamo experiment by the instrumented noaa wp 3d aircraft nine separate missions with a focus on observing mesoscale convective systems mcss were executed to obtain data in the active and inactive phase of a madden julian oscillation mjo in the indian ocean doppler radar and in situ thermodynamic data are used to contrast the convective system characteristics during the evolution of the mjo isolated convection was prominent during the inactive phases of the mjo with deepening convection during the onset of the mjo during the mjo peak convection and stratiform precipitation became more widespread a larger population of deep convective elements led to a larger area of stratiform precipitation as the mjo decayed convective system top heights increased though the number of convective systems decreased eventually transitioning back to isolated convection a distinct

preservation potential for late quaternary river alluvium valley sequences of late quaternary alluvial units reflect alluvial preservation as well as alluvial production factors effects of lateral channel migration incision aggradation and channel stability on preservation potential are explored and then considered in the light of 14 available data sets cartographically dated and model data based on lateral channel migration well mapped and dated late quaternary valley unit surveys and composite age frequency plots for dated alluvial units and flood sediments despite much expectable variation between sites and the complex effects of river activity combinations a common characteristic of the data sets examined is the significance of preservation factors lateral migration tends to eliminate older units as it creates new alluvial deposits whereas incision may lead to the preferential preservation of older units beyond the incision slot aggradational environments are likely to preserve more complete records although simultaneous lateral migration may eliminate possibly repeatedly the upper parts of alluvial units the common pattern of inset and incised streams within pleistocene and early holocene fills or bedrock gives finite extent to later units within narrowing valleys so that development of new valley floor units is necessarily at the expense of reprocessing earlier ones floods associated with both slack water deposits and berms are also responsible for the removal of accessible earlier materials thus limiting the preserved record of earlier events in light of these censoring effects of river activities the sequence of preserved late quaternary units within uk sequences is reconsidered it is concluded that preservation potential factors have led to spatial and temporal bias in the alluvial record and that both here and elsewhere preservation potential needs to be considered systematically alongside variable sedimentation resulting from allogenic environmental factors when interpreting the alluvial archive copyright 2003 john wiley sons ltd journal of quaternary science

zonal and vertical structure of the madden julian oscillation abstract a statistical study of the three dimensional structure of the madden julian oscillation mjo is carried out by projecting dynamical fields from reanalysis and radiosonde data onto space time filtered outgoing longwave radiation olr data mjo convection is generally preceded by low level convergence and upward motion in the lower troposphere while subsidence cooling and drying prevail aloft this leads to moistening of the boundary layer and the development of shallow convection followed by a gradual and then more rapid lofting of moisture into the middle troposphere at the onset of deep convection after the passage of the heaviest rainfall a westerly wind burst region is accompanied by stratiform precipitation where lower tropospheric subsidence and drying coincide with continuing upper tropospheric upward motion the evolution of the heating field leads to a temperature structure that favors the growth of the mjo the analysis also reveals distinct differences in the vertical structure

radar observed characteristics of precipitating systems during name 2004 abstract a multiradar network operated in the southern gulf of california goc region during the 2004 north american monsoon experiment is used to analyze the spatial and temporal variabilities of local precipitation based on the initial findings of this analysis it is found that terrain played a key role in this variability as the diurnal cycle was dominated by convective triggering during the afternoon over the peaks and foothills of the sierra madre occidental smo precipitating systems grew upscale and moved wnw toward the gulf distinct precipitation regimes within the monsoon are identified the first regime a corresponded to enhanced precipitation over the southern portions of the coast and goc typically during the overnight and early morning hours this was due to precipitating systems surviving the westward trip 7 m s 1 3 4 m s 1 in excess of steering winds from the smo after sunset likely because of enhanced environmental wind shear as diagnosed from local soundings the second

the precipitating cloud population of the madden julian oscillation over the indian and west pacific oceans 1 the variability of the precipitating cloud population of the madden julian oscillation mjo is represented by statistics of echo features seen by the tropical rainfall measuring mission s precipitation radar over the central indian and west pacific oceans echo features include isolated shallow echoes deep convective cores wide convective cores and broad stratiform regions isolated shallow echoes are ever present but most numerous during suppressed mjo phases broad stratiform regions dominate variability in areal coverage and maximize during active phases deep convective and wide convective cores are more common and variable in number than broad stratiform regions the magnitude of variability is similar in both regions in the central indian ocean active mjo phases have synchronous maximization of deep convective entities in the west pacific broad stratiform regions maximize prior to wide convective cores reanalysis indicates that isolated shallow echoes are most numerous in dry mid tropospheric conditions and strong low level 1000 750 hpa shear mid tropospheric moisture increases before deeper convective features increase in number maximizes as deep convective features maximize and decreases as wide convective cores and broad stratiform regions decline in population active stage deep and wide convective cores occur preferentially with moist mid tropospheric conditions and strong low level shear acute shear may favor downdraft momentum transport and consequently more robust gust front convective triggering broad stratiform regions maximize with a moist mid troposphere strong low level shear and moderate upper level 750 500 hpa shear that is not so strong that the stratiform region disconnects from its convective moisture source

diurnally modulated cumulus moistening in the preonset stage of the madden julian oscillation during dynamo abstractatmospheric soundings radar and air sea flux measurements collected during dynamics of the madden julian oscillation dynamo are employed to study mjo convective onset i e the transition from shallow to deep convection in the tropical indian ocean the findings indicate that moistening of the low midtroposphere during the preonset stage of the mjo is achieved by simultaneous changes in the convective cloud population and large scale circulation namely cumuliform clouds deepen and grow in areal coverage as the drying by large scale subsidence and horizontal westerly advection wane the reduction of large scale subsidence is tied to the reduction of column radiative cooling during the preonset stage which ultimately links back to the evolving cloud population while net column moistening in the preonset stage is tied to large scale circulation changes a new finding of this study is the high degree to which the locally driven diurnal cycle invigorates convective clouds and cumulus moiste

microphysical characterisation of west african mcs anvils deep convection in the tropics is the source of large tropospheric extended clouds usually called anvils these anvils may produce precipitation stratiform region of deep convective storms and also cirrus shields persisting from several hours to several days anvils impact the radiation budget they induce a storage term in the whole water budget which is still relatively poorly quantified and dynamical feedbacks may be induced in the upper troposphere the amma field campaign which was held over west africa during the 2006 wet season provided a unique opportunity to document the microphysics of these anvils from unprecedented airborne observations airborne in situ measurements of ice crystals and observations from a 95 ghz doppler radar are used to characterize the microphysical properties of tropical anvils the dataset is binned into stratiform and cirriform regions some data in the stratiform regions were likely obtained close enough to convective cores that the particles may have grown primarily within those cores the data obtained over the continent and over the ocean are also characterized separately particle habit and growth processes are inferred from an examination of the collected particle images from quantitative comparisons of 95 ghz reflectivities calculated from the in situ microphysical observations with the measured radar reflectivities and from a statistical analysis of the two dimensional particle images the predominant precipitation particles above the 0 c isotherm in the stratiform anvil region are rimed aggregates these rimed aggregates seem to get less dense and of smaller diameter when moving rearward of the system towards the cirriform region the retrieved density laws assumed to be power laws lie close to the relationship for rimed particles of locatelli and hobbs particle size distributions in tropical anvils are also studied the exponential shape seems to be a good approximation for these particle size distributions overall the decrease in concentration with diameter is also found to be faster for cirriform regions than for stratiform regions normalising these particle size distributions produces a relatively invariant shape in agreement with earlier studies with however an increased variability for the smallest and largest values of the normalised diameter the characterisation of the bulk microphysical properties using these in situ microphysical observations shows that the ice water content the effective radius and the reflectivity weighted fall velocity generally increase with air temperature in agreement with earlier studies these parameters are found to be systematically smaller on average in cirriform regions than in stratiform regions and this is true at all temperatures these values are then compared with statistical relationships used in cloud resolving models and general circulation models since a realistic representation of microphysics in models is very important to understand not only the processes at work but the dynamical feedbacks and effects on climate large differences are found the current parametrizations being unable to reproduce the large values of the considered microphysical parameters copyright c 2010 royal meteorological society

precipitation hydrometeor type relative to the mesoscale airflow in mature oceanic deep convection of the madden julian oscillation composite analysis of mature near equatorial oceanic mesoscale convective systems mcss during the active stage of the madden julian oscillation mjo shows where different hydrometeor types occur relative to convective updraft and stratiform midlevel inflow layers the national center for atmospheric research ncar s polka radar observed these mcss during the dynamics of the madden julian oscillation atmospheric radiation measurement mjo investigation experiment dynamo amie ncar s particle identification algorithm pid is applied to s polka s polarimetric data to identify the dominant hydrometeor type in each radar sample volume combining s polka s doppler velocity data with the pid demonstrates that hydrometeors have a systematic relationship to the airflow within mature mcss in the convective region moderate rain occurs within the updraft core the heaviest rain occurs just downwind of the core wet aggregates occur immediately below the melting layer narrow zones containing graupel rimed aggregates occur just downstream of the updraft core at midlevels dry aggregates dominate above the melting level and smaller ice particles occur along the edges of the convective zone in the stratiform region rain intensity decreases toward the anvil melting aggregates occur in horizontally extensive but vertically thin regions at the melting layer intermittent pockets of graupel rimed aggregates occur atop the melting layer dry aggregates and small ice particles occur sequentially above the melting level and horizontally oriented ice crystals occur between 10 c and 20 c in turbulent air above the descending midlevel inflow suggesting enhanced depositional growth of dendrites the organization of hydrometeors within the midlevel inflow layer is insensitive to the presence or absence of a leading convective line

investigation of microphysical processes occurring in isolated convection during name abstracta major objective of the north american monsoon experiment name was to quantify microphysical processes within convection occurring near the steep topography of northwestern mexico a previous study compared examples of isolated convection using polarimetric radar data and noted a dependence on mixed phase processes via drop freezing and subsequent riming growth along the coastal plain and western slopes with an even greater role of melting ice in rainfall production over the highest terrain despite the higher frequency of these isolated cells compared to organized convective systems the latter were responsible for 75 of rainfall therefore this study seeks to evaluate the role of mesoscale organization on microphysical processes and describes the evolution of these systems as a function of topography similar to isolated convection both warm rain and ice based processes played important roles in producing intense rainfall in organized convection although similarities existed between cell

coarse sediment connectivity in river channel systems a conceptual framework and methodology identification of coarse sediment connectivity down river channel systems is important for understanding the linkages between river reaches the influence of sediment sources on channel morphology and the mechanisms and liability to propagation of morphological change a conceptual framework is developed in which several types and degrees of connectivity are proposed it is hypothesised that sediment connectivity varies with sediment sources and with stream competence to transport the coarse fractions a method of identifying the status of reaches is developed based on field mapping of morphology and sedimentology the analysis is exemplified by two channels one an ephemeral channel in se spain the other a perennial channel in nw england questions arise over whether reaches that lack channel stores transfer coarse sediment three scenarios are suggested 1 lack of flux due to lack of competence of the reach 2 flushing through of sediment due to high competence and 3 potential transport of coarse sediment but exhaustion or lack of availability changes in connectivity will take place over different time scales depending on the nature of exchange and time scales of storage short term variations in connectivity can be identified by repeated mapping

vertical diabatic heating structure of the mjo intercomparison between recent reanalyses and trmm estimates abstractcapitalizing on recently released reanalysis datasets and diabatic heating estimates based on tropical rainfall measuring mission trmm the authors have conducted a composite analysis of vertical anomalous heating structures associated with the madden julian oscillation mjo because diabatic heating lies at the heart of prevailing mjo theories the intention of this effort is to provide new insights into the fundamental physics of the mjo however some discrepancies in the composite vertical mjo heating profiles are noted among the datasets particularly between three reanalyses and three trmm estimates a westward tilting with altitude in the vertical heating structure of the mjo is clearly evident during its eastward propagation based on three reanalysis datasets which is particularly pronounced when the mjo migrates from the equatorial eastern indian ocean eeio to the western pacific wp in contrast this vertical tilt in heating structure is not readily seen in the three trmm product

the statistical characteristics of convective cells in a monsoon regime darwin northern australia abstract a season of operational cell and track data from darwin australia has been analyzed to explore the statistical characteristics of the convective cell heights the statistics for the monsoon and break regimes are significantly different with the break season cells being higher for a given reflectivity threshold the monsoon cells produce more rain but there are fewer intense cells and there is a much larger contribution from stratiform rain the monsoon cells are also slightly larger but shorter lived than the breaks the shorter lifetime may reflect a more rapid transition to a longer lived stratiform character the monsoon regime is shown to be associated with large scale ascent and higher humidity that may lead to more frequent but weaker cells within regimes the subset of intense cells generally reach near the tropopause or overshoot however there is little evidence in the data for a multimodal distribution of cell heights except perhaps for the intense monsoon cases instead the pi

climate and related controls on interglacial fluvial sedimentation in lowland britain lewin john gibbard p l 2002 climate and related controls on interglacial fluvial sedimentation in lowland britain sedimentary geology 151 3 4 pp 187 210 rae2008

structural evolution in heating profiles of the mjo in global reanalyses and trmm retrievals abstract diabatic and latent heating profiles from four global reanalyses and three tropical rainfall measuring mission trmm algorithms were compared first generally for the tropics and then in the context of the madden julian oscillation mjo most of them exhibit three heating maxima corresponding to known convection centers over south america africa and the indian western pacific warm pool but they still differ substantially in many ways most noticeably a double peak vertical structure with one peak in the upper and the other in the lower troposphere and relative weak heating over the maritime continent in comparison to heating over the indian and western pacific oceans are clearly seen in some heating data but absent in others heating profiles associated with the mjo were diagnosed through composites and case studies the composites were constructed as functions of mjo phases at three longitudes representing the indian ocean maritime continent and western pacific respectively four mjo ev

cloud to ground lightning observations from toga coare selected results and lightning location algorithms abstract recently observations of electrified oceanic convection and associated cloud to ground cg lightning were obtained over the tropical western pacific ocean during toga coare tropical ocean global atmosphere coupled ocean atmosphere response experiment during coare observations of convection were made using a variety of instrument platforms including ship and airborne doppler radars an advanced lightning direction finder aldf network and a shipborne inverted electric field mill this study focuses on data collected by the coare aldf network fusion of those data with observations and the methods used to calculate accurate cg return stroke locations analysis of cg lightning data and doppler radar data indicates that lightning producing oceanic convection is characterized by deep vertically developed convective cells with radar reflectivities exceeding 30 dbz above the height of the 10 c level in several cases a peak in cg frequency occurred coincident with the descent of precipitation

fluvial system evolution and environmental changes during the holocene in the mue valley western france geomorphological and palaeoenvironmental research on holocene sedimentation in the mue valley provides evidence for fluvial system changes related to climate and human activities in normandy a poorly studied area of the paris basin the 24 km long valley bottom has been investigated through a systematic survey it shows an original longitudinal sedimentary pattern in relation with valley morphology and local geological controls minerogenic tufaceous and peaty deposits provide opportunities for multi proxy analyses and radiocarbon dating control sedimentation began around 9500 14c bp with silt deposition in a meandering system the boreal and the lower atlantic periods 8500 6000 14c bp were mainly characterized by unlithified calcareous tufa locally these deposits are very thick 7 to 13 m the tufa formed barrages across the valley bottom providing an autogenic control on upstream sedimentation during the upper atlantic period 6000 4700 14c bp the valley experienced a decrease in calcareous sedimentation and the development of organic deposits at the beginning of the subboreal 4700 3500 14c bp peat deposits expanded especially behind the tufa barrages the valley bottom was characterized by large marshy areas whereas the regional vegetation was progressively modified by human activities at the end of the subboreal 3300 3000 14c bp the infilling of the valley by calcareous silt was caused by an increase of river activity related to climatic and land use changes from the iron age and gallo roman periods 2800 1700 14c bp the valley bottom was filled by silty overbank deposits related to an increase of soil erosion the slopes and river system were once again coupled and the fluvial system functioned as a continuum from upstream to downstream the alluvial record of the mue valley reflects a broad regional pattern of environmental changes but presents particular features which highlight the need of longitudinal studies to take into account spatial and temporal discontinuities of holocene hydro sedimentary systems even in small order valleys

the late holocene tufa decline in europe over much of europe it has been postulated that in the late holocene since c 2500 bp there was a marked decline in the deposition of tufa there has been considerable debate about the causes of this phenomenon with some authors postulating the importance of natural climatic changes and others asserting that miscellaneous human influences have been crucial this article discusses the role that various changes both natural and anthropogenic may have played and suggests ways in which the large number of possible hypotheses can be tested

three dimensional kinematic and microphysical evolution of florida cumulonimbus part ii frequency distributions of vertical velocity reflectivity and differential reflectivity abstract high resolution radar data collected in florida during the convection and precipitation electrification experiment are used to elucidate the microphysical and kinematic processes occurring during the transition of a multicellular storm from convective to stratiform stages a statistical technique is employed to examine the evolving properties of the ensemble small scale variability of radar reflectivity vertical velocity and differential reflectivity over the entire storm differential radar reflectivity data indicate that the precipitation at upper levels was nearly glaciated early in the storm s lifetime dual doppler radar data show that throughout the storm s lifetime both updrafts and down drafts were present at all altitudes and that most of the volume of the radar echo contained vertical velocities incapable of supporting precipitation size particles thus the ensemble microphysical properties of the storm were increasingly dominated by particles falling in an environment of weak vertic

interpreting alluvial archives sedimentological factors in the british holocene fluvial record abstract a holocene alluvial archive of 506 dated units for great britain is analysed in terms of the sedimentation styles involved the database is classified by sedimentation unit channel sediments palaeochannel fills floodplain surface sediments floodbasins and colluvial deposits and alluvial ensemble fans and cones upland gullies and streams braided systems and active inactive meandering and anastomosing systems floodplain palaeochannel and floodbasin sediments dominate the record mostly from meandering anastomosing systems different sediment units show varied potential for recording environmental change some are relatively poorly dated with respect to the volumes of material involved whilst many dates float in periods of depositional activity which lasted for extended time periods much dated activity is autogenic and of relatively little value in interpreting external environmental influence ensembles and units are similar in age patterns in some respects commonly they exhibit sets of short term peaks in sedimentation activity but differ in others floodbasins and to an extent braided systems feature in the earlier holocene whilst dated fan deposition is more evident in the late holocene there is a general bias towards sediment units of late holocene age which probably reflects preservation factors previous british holocene alluviation models are reviewed it is suggested that the majority of earlier models reflect partial views imposed by limited regional coverage and available dating

molluscan successions from the holocene tufa of st germain le vasson normandy france and their biogeographical significance a detailed molluscan succession from a 10 m thick deposit of holocene tufa at st germain le vasson normandy provides the most complete record from northern france and has shed new light on the historical biogeography of several species of land snail the succession has been reconstructed from four profiles and a chronology provided by accelerator mass spectrometry radiocarbon dating of charcoal wood and shell the onset of tufa formation occurred after 9700 90 yr bp and persisted until 4213 77 yr bp the tufa appears to have accumulated at a remarkably constant rate 14 4 16 5 cm 100 yr 1 except for the upper levels where the rate increases fourfold the succession has been divided into six local molluscan zones an early assemblage consisting of ecologically tolerant species and those indicative of marshy grassland is replaced by a sequence of shade demanding taxa reflecting the encroachment of woodland shaded conditions persist until the end of the sequence but the most hygrophilous elements decline after 5422 60 yr bp zone 5 a change also reflected in the tufa lithology by the development of silty grey horizons notable species recovered from the tufa include acicula fusca vertigo substriata v alpestris v moulinsiana all rare or unknown living in northern france hygromia limbata a twentieth century introduction to britain was previously thought to be a relatively recent arrival in northern france but its record at st germain shows that it has been present in normandy since 6500 yr bp azeca goodalli another shade demanding species appeared at st germain much later just after 4420 65 yr bp several other species present in the tufa such as pomatias elegans no longer live on the site adding to the evidence for a distributional decline in normandy and elsewhere perhaps the most noteworthy record is that of leiostyla anglica between about 8500 yr bp and 5000 yr bp because this constitutes its only holocene occurrence from mainland europe following this discovery it seems likely that further holocene sites with l anglica may be found along the western seaboard of europe connecting populations in iberia with those of the british isles copyright 2004 john wiley sons ltd

evolution properties and spatial variability of mjo convection near and off the equator during dynamo abstractthis study investigates the evolution structure and spatial variability of madden julian oscillation mjo convection observed during the 2011 12 dynamics of the mjo dynamo field campaign generally the c band radars located in the near equatorial indian ocean shared mobile atmospheric research and teaching radar smart r on addu atoll gan and nasa toga on the r v roger revelle revelle observed similar trends in echo top heights stratiform rain fraction and precipitation feature size across the mjo life cycle these trends are closely related to changes in mid to upper tropospheric moisture sea surface temperature sst zonal wind and diagnosed vertical air motions however the evolution of convection moisture and vertical air motion at the r v mirai mirai located in the intertropical convergence zone itcz at 8 s exhibited a pattern nearly opposite to gan and revelle when the mjo was active over the equator convection was suppressed around mirai owing to induced subsiden

drop size distributions and radar observations of convective and stratiform rain over the equatorial indian and west pacific oceans abstracttwo dimensional video disdrometer 2dvd data were analyzed from two equatorial indian gan and west pacific ocean manus islands where precipitation is primarily organized by the intertropical convergence zone and the madden julian oscillation mjo the 18 3 5 months of 2dvd data from manus gan island show that 1 the two sites have similar drop size distribution dsd spectra of liquid water content median diameter rain rate r radar reflectivity z normalized gamma number concentration nw and other integral rain parameters 2 there is a robust nw based separation between convective c and stratiform s dsds at both sites that produces consistent separation in other parameter spaces the 2dvd data indicate an equatorial maritime average c s rainfall accumulation fraction frequency of 81 19 41 59 at these locations it is hypothesized that convective fraction and frequency estimates are slightly higher than previous radar based studies because the ubiquitous weak shallow convec

the relationship between precipitation and lightning in tropical island convection a c band polarimetric radar study one of the primary scientific objectives of the maritime continent thunderstorm experiment was to study cloud electrification processes in tropical island convection in particular the coupling between ice phase precipitation and lightning production to accomplish this goal a c band polarimetric radar was deployed in the tropics 11 68s 130 88e for the first time accompanied by a suite of lightning measurements using observations of the propagation corrected horizontal reflectivity and differential reflectivity along with specific differential phase rain and ice masses were estimated during the entire life cycle of an electrically active tropical convective complex known locally as hector over the tiwi islands on 28 november 1995 hector s precipitation structure as inferred from these raw and derived radar fields was then compared in time and space to the measured surface electric field cloud to ground cg and total lightning flash rates and ground strike locations during hector s developing stage precipitating convective cells along island sea breezes were dominated by warm rain processes no significant electric fields or lightning were associated with this stage of hector despite substantial rainfall rates aided by gust front forcing a cumulus merger process resulted in larger taller and more intense convective complexes that were dominated by mixed phase precipitation processes during the mature phase of hector lightning and the surface electric field were strongly correlated to the mixed phase ice mass and rainfall merged convective complexes produced 97 of the rainfall and mixed phase ice mass and 100 of the cg lightning as hector dissipated lightning activity rapidly ceased as evidenced from the multiparameter radar observations the multicell nature of hector resulted in the continuous lofting of supercooled drops to temperatures between 2108 and 2208c in discrete updraft cores during both the early and mature phases the freezing of these drops provided instantaneous precipitation sized ice particles that may have subsequently rimed and participated in thunderstorm electrification via the noninductive charging mechanism

evolution of the population of precipitating convective systems over the equatorial indian ocean in active phases of the madden julian oscillation three dimensional radar reflectivity fields from a dual wavelength doppler polarimetric radar s polka deployed in the equatorialindian ocean are used to evaluate the composition of the populationof convective cloud elements during active phases of the mjo rainfall in active periods was intermittent occurring in 11 episodesofabout 2 4days separated byseveralnonrainydays dataforthese 2 dayperiodswerecomposited relative to the time of maximum rainfall analysis of the s polka data shows the makeup of the convective population during the rainfall episodes four types of echo structures were analyzed statistically for the 11 rainfallepisodes shallowconvectiveechoes sce deepconvectivecores dcc wideconvectiveechocores wcc and broad stratiform bsr echo regions sce and dcc events were most frequent before the maximum rainfall with the peak frequency of sce leading that of dccs wccs were most frequent during therainfallmaximum and bsr regionswere most frequentinthe later part oftherainfallepisode composited ecmwf interim re analysis era interim data and 3 hourly atmospheric soundings indicate that the 2 4 day episodes were related to the passage of equatorial waves in the early part of a rainfall episode the wave passageconditionswereunstable favoringdeeppenetratingconvectiveelements whileinthelaterperiod the wave divergence profile was commensurate with convective systems in late anvil producing stages these results support the stretched building block notion of the life cycle of tropical convection and confirm satellitebased interpretations of sce dcc wcc and bsr statistics in the composition of the convective population

characteristics of precipitation cloud and latent heating associated with the madden julian oscillation abstract this study investigates the evolution of cloud and rainfall structures associated with madden julian oscillation mjo using tropical rainfall measuring mission trmm data two complementary indices are used to define mjo phases joint probability distribution functions pdfs of cloud top temperature and radar echo top height are constructed for each of the eight mjo phases the genesis stage of mjo convection over the western pacific phases 1 and 2 features a bottom heavy pdf characterized by abundant warm rain low clouds suppressed deep convection and higher sea surface temperature sst as mjo convection develops phases 3 and 4 a transition from the bottom heavy to top heavy pdf occurs the latter is associated with the development of mixed phase rain and middle to high clouds coupled with rapid sst cooling at the mjo convection peak phase 5 a top heavy pdf contributed by deep convection with mixed phase and ice phase rain and high echo top heights 5 km dominates the decay

a radar study of convective cells in mesoscale systems in gate part i vertical profile statistics and comparison with hurricanes abstract this is part i of a two paper describing the structure of the vertical profile of radar reflectivity in convective cells which are of part of mesoscale convective systems in gate earlier work has established that characteristic mean vertical velocities in such convective clouds in gate were rather weak 3 5 m s 1 the microphysical implications of the weak updrafts have been proposed to include the rarity of large particles above the freezing level as a working hypothesis for these papers it is proposed that cells with weak updrafts have characteristic vertical reflectivity profiles exhibiting modest reflectivities at low levels and decreasing rapidly with height above the freezing level vertical radar reflectivity profiles are compiled from 296 convective cells having at least 40 dbz surface reflectivity and it is found that the profiles are consistent with the above reasoning the mean profile is of modest strength 45 dbz echo at the surface and a 20 dbz echo top of 8 2 km and the refle

small valley bottom deposits in the sandy districts of the sarthe basin france climatic and or human origin the study of the small valley bottom deposits in a sandy district where several recent erosional events have occurred makes it possible to distinguish deposits which are caused by climatic oscillations from those induced by both climate and human activities the coarse alluvium with flints which reached the main valleys prior to the subboreal was transported by greater flows than those which resulted from later human induced flood discharges where flints were not evacuated from the small valleys radiocarbon dates of peat set those deposits in the iron age in the transition from antiquity to the medieval period at the end of the optimum climatique de l an mil and during the little ice age at the present time human induced flood discharges reach again the main valleys d 2002 elsevier science b v all rights reserved

holocene floodplain diachronism and inherited downstream variations in fluvial processes a study of the river perry shropshire england this paper attempts to explain downstream variations in the rates and processes of holocene floodplain formation in a small to medium sized lowland catchment in central england four macro reaches were identified and horizons from at least one stratigraphic cross section from each were radiocarbon dated considerable diachronism was revealed with the basal age and hence minimum residence time of the top two metres varying from 1000 9000yrs the trend a decrease in minimum residence time downstream is explained by the basin and gorge bedrock long profile inherited from the devensian glaciation of the area this is illustrated by a positive relationship between the mean floodplain accumulation rate and the sl index slope stream length product pollen analysis of the organic sediments shows that floodplain clearance took place around 1 300 bp but probably locally pre dated and post dated accelerated alluviation associated with agricultural expansion in the catchment this study concludes that a different macro reaches in this small to medium sized catchment have adjusted in different ways to long term catchment changes as part of autogenic floodplain evolution b this has involved a change in the catchment s sediment conveyance characteristics during the holocene and c an important control on channel behaviour and floodplain sedimentation throughout the holocene as well as at present has been the valley slopes inherited from the quaternary glaciation of the area

response of the selle river to climatic modifications during the lateglacial and early holocene somme basin northern france abstract research on lateglacial sequences from the selle valley leads to an overview of its evolution in relation to climatic variations between the end of the weichselian upper pleniglacial and the beginning of the holocene the first major modification of the fluvial morphology is dated at the upper pleniglacial lateglacial transition 13 000 14 c yr bp at that time the response to climatic improvement and environmental modifications is marked by downcutting and evolution from a braided river to a transitional river pattern bolling infilling in the newly created channels after a short cold phase recorded in a thin calcareous bed at the top of the bolling peat attributed to the older dryas dr ii the allerod is characterized by the deposition of organic overbank silts within a large single channel meandering system in lower slope environments this period is also marked by slow rates of colluvial accumulation and by the development of upbuilding soils allerod soil on the other hand the end of the lateglacial is characterised by the infilling of the whole valley by fine calcareous overbank silts during the younger dryas cold phase overflow of a large single channel and lateral input of chalk mud a second major downcutting phase occurs at the beginning of the holocene at around 10 000 bp in parallel with another rapid climatic improvement and the renewed spread of vegetation from a general point of view the evolution of fluvial environments in the selle valley is comparable with many other river valleys in nw europe showing that fluvial systems react very quickly to climatic variations of short duration 1000 to 100 years finally in the upper selle river incision events occur clearly before the main modifications of the vegetal cover they are most likely linked to a rapid shift in the balance between water discharge and sediment supply caused by climate modifications shift to more temperate and oceanic conditions and the resulting environmental changes cessation in aeolian sedimentation strong reduction of slope processes permafrost disappearance and soil development

tropospheric turbulence over the tropical open ocean role of gravity waves a large set of soundings obtained in the indian ocean during 3 field campaigns is used to provide statistical characteristics of tropospheric turbulence and its link with gravity wave gw activity the thorpe method is used to diagnose turbulent regions of a few hundred meters depth above the mixed layer turbulence frequency varies from 10 in the lower troposphere up to 30 around 12km heights gw are captured by their signature in horizontal wind normalized temperature and balloon vertical ascent rate these parameters emphasize different parts of the wave spectrum from longer to shorter vertical wavelengths respectively composites are constructed in order to reveal the vertical structure of the waves and their link with turbulence the relatively longer wavelength gw described by their signature in temperature gwt are more active in the lower troposphere where they are associated with clear variations in moisture turbulence is then associated with minimum static stability and vertical shear stressing the importance of the former and the possibility of convective instability conversely the short waves described by their signature in balloon ascent rate gww are detected primarily in the upper troposphere and their turbulence is associated with a vertical shear maximum suggesting the importance of dynamic instability furthermore gww appear to be linked with local convection whereas gwt are more active in suppressed and dry phases in particular of the madden julian oscillation these waves maybe associated with remote sources such as organized convection or local fronts such as those associated with dry air intrusions

microphysical characteristics of mjo convection over the indian ocean during dynamo the microphysical characteristics of precipitating convection occurring in various stages of the madden julian oscillation mjo over the indian ocean are determined from data obtained from the national center for atmospheric research dual polarimetric doppler s band radar s polka deployed as part of the dynamics of the mjo dynamo field experiment active mjo events with increased rainfall occurred in october november and december 2011 during each of these active mjo phases in addition to enhanced rainfall convection became deeper and ice phase microphysics played a greater role s polka consistently showed nonoriented small ice particles dominating the radar echoes at altitudes of 9 10 km dry aggregates concentrated between 7 and 9 km and wet aggregates and graupel near the melting level 5 km graupel occurred mainly in actively convective towers while the wet aggregates occurred almost exclusively in the stratiform regions of mesoscale convective systems mcss during each of the three multiweek mjo active phases the maximum rainfall occurred in short bursts lasting a few days each multiday rainy period began with deepening convective elements and a concurrent increase in occurrence of dry aggregates which maximized just prior to organization into mcss the peak rainfall occurrence coincided with the maximum coverage of the radar domain by mcss reflecting large stratiform regions that exhibited the most frequent occurrence of wet aggregates during the december active mjo phase however the mcss were shallower and had a slightly lower tendency for wet aggregates in the stratiform regions and therefore generally weaker brightbands

frictional moisture convergence in a composite life cycle of the madden julian oscillation abstract a composite life cycle of the madden julian oscillation mjo is constructed using an index based on the first two eofs of the bandpass filtered 20 80 days 850 mb zonal wind averaged from 5 n to 5 s every 2 5 around the equator precipitation 1000 mb convergence 850 mb wind and 200 mb wind are composited for the period 1979 95 water vapor integrated from the surface to 300 mb is composited for the period 1988 92 frictional moisture convergence at the equator is shown to play an important role in the life cycle of the madden julian oscillation mjo regions of boundary layer convergence foster growth of positive water vapor anomalies to the east of convection this convergence coincides with 850 mb easterly wind anomalies as is consistent with kelvin wave dynamics drying of the atmosphere occurs rapidly after the passage of convection with the onset of 850 mb westerly perturbations possible mechanisms for this drying include boundary layer divergence and subsidence or horizontal advect

active tectonics seismicity and geomorphology with special reference to normandy france integrated studies based on tectonic seismotectonic and geomorphological analyses indicate that normandy northwest france has been an active area during the quaternary topography and landform discontinuities reflect the dislocation and differential uplift of a late cenozoic platform the tectonic activity is represented by i active faults indicated by linear scarps and seismic activity ii offsetting of pre existing surfaces iii plio pleistocene sedimen tation restricted within narrow subsiding zones and iv morphometric properties of drainage basins that indicate zones of differential uplift the inferred strain pattern involves i a shortening direction that strikes nw se as expected in the european context of alpine compression and ii a ne sw trending extension accommodated by nw se normal faults the geomorphological systems encountered in normandy preferentially record differential vertical displacements copy right 2000 john wiley sons ltd

vertical velocity in oceanic convection off tropical australia abstract time series of 1 hz vertical velocity data collected during aircraft penetrations of oceanic cumulonimbus clouds over the western pacific warm pool as part of the equatorial mesoscale experiment emex are analyzed for updraft and downdraft events called cores an updraft core is defined as occurring whenever the vertical velocity exceeds 1 m s 1 for at least 500 m a downdraft core is defined analogously over 19 000 km of straight and level flight legs are used in the analysis five hundred eleven updraft cores and 253 downdraft cores are included in the dataset core properties are summarized as distributions of average and maximum vertical velocity diameter and mass flux in four altitude intervals between 0 2 and 5 8 km distributions are approximately lognormal at all levels examination of the variation of the statistics with height suggests a maximum in vertical velocity between 2 and 3 km slightly lower or equal vertical velocity is indicated at 5 km near the freezing level virtual t

impacts of land use change on patterns of sediment flux in weraamaia catchment new zealand forest clearance between the 1890s and the early 1920s subsequent scrub growth and commencement of an afforestation program in 1979 modified the pattern and rate of sediment delivery to valley floors via shallow landslides and gully complexes in a steep headwater catchment 4 8 km2 in new zealand analysis of the historical record air photograph interpretation and field survey indicates that both erosion types occurred across the catchment in the 1938 storm aggrading channel beds and widening the active channel zone in contrast a 1 in 100 year event in 1988 cyclone bola induced numerous shallow landslides but erosion of gully complexes was largely restricted to subcatchments that retained pasture and the geomorphic impact of this event on channels was small the changing volume and calibre of materials delivered to the valley floor and the distribution of gully complexes altered patterns and rates of channel adjustment after the events and the resulting sediment flux development of gully complexes maintained coupling processes with channels for periods up to 102 years forming wide channels in downstream reaches upstream downstream connectivity along the trunk stream was altered by the formation of a large debris fan at the confluence with a tributary subjected to gully complex erosion in contrast slopes subjected to shallow landslides became decoupled from channels within 10 years accelerating channel degradation and narrowing effective conveyance of a large volume of fine grained materials promoted immediate aggradation of gentle gradient channels downstream as gully complex areas stabilized following an increase in forest and scrub cover channel courses became significant sediment sources although shallow landslide activity will continue to induce intermittent aggradation in the future it is inferred that average sediment yield will continue to diminish to levels approaching those experienced prior to clearcutting and the pattern of sediment flux will recover by 2030

effective timescales of coupling within fluvial systems this paper presents a review of the coupling concept in fluvial geomorphology based mainly on previously published work coupling mechanisms link the components of the fluvial system controlling sediment transport down the system and the propagation of the effects of base level change up the system they can be viewed at several scales at the local scale involving within hillslope coupling hillslope to channel coupling and within channels tributary junction and reach to reach coupling at larger scales coupling can be considered as zonal coupling between major zones of the system or as regional coupling relating to complete drainage basins these trends are illustrated particularly by the examples of hillslope to channel coupling in the howgill fells northwest england badland systems in southeast spain alluvial fans in spain usa and uae and base level induced dissection of neogene sedimentary basins in southeast spain as the spatial scales increase so do the timescales involved effective temporal scales relate to magnitude and frequency characteristics recovery time and propagation time the relative importance changing with the spatial scale for downsystem coupling at the local scale the first two are important with propagation time increasing in importance in larger systems especially in those involving upsystem coupling related to base level change the effective timescales range from the individual event with a return period of decades through decadal to century timescales for downsystem coupling to tens to hundreds of thousands of years for the basinwide response to base level change the effective timescales influence the relative importance of factors controlling landform development

river system evolution and environmental changes during the lateglacial in the paris basin france abstract lateglacial sequences from the paris basin floodplains provide a general overview of the valley s evolution related to climatic changes from the weichselian upper pleniglacial to the beginning of the holocene comparison between morphostratigraphical and palaeobiological data allows discussion of fluvial dynamics and related palaeoenvironmental conditions the upper pleniglacial oldest dryas transition remains poorly documented it is represented by sands and silts deposited by a braided channel network the bolling begins with a significant incision related to a meandering system which is followed by local organic and minerogenic deposition contemporaneous with vegetation development the older dryas is evident in several sequences the allerod appears more stable and the forest extension is accompanied by a thin soil formation on the banks the younger dryas is characterised by a strong infilling of the valleys by calcareous silts this last sharp event precedes a second major downcutting phase which takes place in the early postglacial and is followed by a decline in river flow and sediment supply this evolution reflects a broad regional pattern of fluvial response which illustrates its sensitivity to climatic change the study of various morphosedimentary contexts shows their influence on the fluvio dynamic record and bio proxies which complicates the detection of minor phases

roles of deep and shallow convection and microphysics in the mjo simulated by the model for prediction across scales the november event of the madden julian oscillation mjo during the dynamo field campaign was simulated using the global compressible nonhydrostatic model for prediction across scales mpas with global coarse 60 and 15 km and regional the indian ocean cloud permitting 3 km meshes the purpose of this study is to compare roles of parameterized deep and shallow cumulus and microphysics in mjo simulations two cumulus schemes were used tiedtke and grell freitas the deep and shallow components of tiedtke scheme can be turned on and off individually the results reveal that microphysics alone without cumulus parameterization is able to produce strong signals of the mjo in precipitation with 3 km mesh and weak mjo signals with 15 km mesh a shallow scheme tiedtke along with microphysics strengthens the mjo signals but makes them less well organized on large scales a deep cumulus scheme can either improve the large scale organization of mjo precipitation produced by microphysics and shallow convection tiedtke or impair them grell freitas the deep scheme of tiedtke cannot reproduce the mjo well without its shallow counterpart the main role of shallow convection in the model is to transport moisture upward to the lower mid troposphere by doing so it removes dry biases in the lower mid troposphere a distinct feature in simulations with weak or no mjo signals and enhances total precipitation and diabatic heating produced by microphysics and deep cumulus schemes changing model grid spacing from 60 to 15 km makes a little difference in the model fidelity of reproducing the mjo all roles of shallow convection in 15 km simulations with parameterized deep convection cannot be reproduced in 3 km simulations without parameterized deep convection results from this study suggest that we should pay more attention to the treatment of shallow convection and its connection to other parameterized processes for improving mjo simulations in other words a holistic approach should be taken that consider parameterization of shallow cumulus microphysics boundary layer as well as deep cumulus as a whole for model improvement

vertical mode decompositions of 2 day waves and the madden julian oscillation abstract vertical structures of 2 day waves and the madden julian oscillation mjo are projected onto vertical normal modes for a quiescent tropical troposphere three modes capture the gross tropospheric structure of 2 day waves while only two modes are needed to represent most of the baroclinic structure of the mjo deep circulations that project onto the first baroclinic mode are associated with deep cumulonimbus and stratiform rainfall shallow circulations that project onto higher wavenumber modes are associated with precipitating shallow cumulus and congestus and stratiform rainfall for both disturbances the horizontal divergence contributed by shallow modes is an important factor in the column integrated moist enthalpy budget these modes converge moist static energy for a time prior to when deep circulations export moist static energy these results highlight the importance of properly representing the effects of shallow cumulus congestus and stratiform precipitation in theories of convective

floodplain environmental change during the younger dryas and holocene in northwest europe insights from the lower kennet valley south central england abstract many lowland rivers across northwest europe exhibit broadly similar behavioural responses to glacial interglacial transitions and landscape development difficulties exist in assessing these largely because the evidence from many rivers remains limited and fragmentary here we address this issue in the context of the river kennet a tributary of the thames since c 13 000 cal bp some similarities with other rivers are present suggesting that regional climatic shifts are important controls the kennet differs from the regional pattern in a number of ways the rate of response to sudden climatic change particularly at the start of the holocene and also mid holocene forest clearance appears very high this may reflect abrupt shifts between two catchment scale hydrological states arising from contemporary climates land use change and geology stadial hydrology is dominated by nival regimes with limited winter infiltration and high spring and summer runoff under an interglacial climate infiltration is more significant the probable absence of permafrost in the catchment means that a lag between the two states due to its gradual decay is unlikely palaeoecology supported by radiocarbon dates suggests that at the very start of the holocene a dramatic episode of fine sediment deposition across most of the valley floor occurred lasting 500 1000 years a phase of peat accumulation followed as mineral sediment supply declined a further shift led to tufa deposition initially in small pools then across the whole floodplain area with the river flowing through channels cut in tufa and experiencing repeated avulsion major floods leaving large gravel bars that still form positive relief features on the floodplain followed mid holocene floodplain stability prehistoric deforestation is likely to be the cause of this flooding inducing a major environmental shift with significantly increased surface runoff since the bronze age predominantly fine sediments were deposited along the valley with apparently stable channels and vertical floodplain accretion associated with soil erosion and less catastrophic flooding the kennet demonstrates that while a general pattern of river behaviour over time within a region may be identifiable individual rivers are likely to diverge from this consequently it is essential to understand catchment controls particularly the relative significance of surface and subsurface hydrology

kinematics and microphysics of convection in the outer rainband of typhoon nida 2016 revealed by polarimetric radar abstractthis study analyzes the microphysics of convective cells in an outer rainband of typhoon nida 2016 using data collected by a newly upgraded operational polarimetric radar in china the li