hydrometeorological controls and erosive response of an extreme alpine debris flow on 29 august 2003 an intense convective storm system affected the fella river basin in the eastern italian alps producing rainfall peaks of approximately 390 mm in 12 h the storm triggered an unusually large debris flow in the ungauged rio cucco basin 0 65 km2 with a volume of approximately 78 000 m3 the analysis of the time evolution of the rainstorm over the basin has been based on rainfall estimates from radar observations and data recorded by a raingauge network detailed geomorphological field surveys carried out both before and after the flood of august 2003 and the application of a distributed hydrological model have enabled assessment of flood response estimation of erosion volumes and sediment supply to the channel network the accounts of two eyewitnesses have provided useful elements for reconstructing the time evolution and the flow processes involved in the event liquid peak discharge estimates cluster around 20 m3 s 1 km 2 placing this event on the flood envelope curve for the eastern italian alps the hydrological analysis has shown that the major controls of the flood response were the exceptional cumulated rainfall amount required to exceed the large initial losses and the large rainfall intensities at hourly temporal scales required to generate high flood response at the considered basin scale observations on the deposits accumulated on the alluvial fan indicate that although the dominant flow process was a debris flow sheetflood also contributed to fan aggradation and fluvial reworking had an important role in winnowing debris flow lobes and redistributing sediment on the fan surface this points out to the large discharge values during the recession phase of the flood implying an important role for subsurface flow on runoff generation of this extreme flash flood event copyright 2009 john wiley sons ltd

extreme rainfall and flooding from orographic thunderstorms in the central appalachians 1 the central appalachian region has experienced some of the largest rainfall accumulations in the world at time intervals less than 6 h including the 18 july 1942 smethport pennsylvania storm that produced 780 mm in less than 5 h the envelope curve of central appalachian flood peaks at small drainage areas less than 1000 km2 is dominated by orographic thunderstorm systems like the smethport storm orographic thunderstorm systems that have produced catastrophic flooding in the central appalachians are examined through observational and numerical model analyses using the weather research and forecasting wrf model analyses suggest that the frequency of catastrophic flooding varies over the central appalachian region and that small scale variation may be linked to the role of complex terrain in altering thunderstorm dynamics catastrophic flooding along the western margin of the central appalachians is dominated by four storms that occurred on 18 19 july 1889 1942 1977 and 1996 which were associated with warm season extratropical systems and were characterized by rapidly moving storm elements in complex terrain along the eastern margin and interior of the central appalachians catastrophic flooding is linked to four terrain locked orographic convective systems that occurred 17 18 june 1949 18 19 august 1969 27 june 1995 and 11 august 2003 wrf model simulations of the little river storm june 1949 rapidan storm june 1995 smethport storm 18 july 1942 and redbank storm 18 19 july 1996 are used to characterize ingredients of catastrophic rainstorms in the central appalachians

evolution of channel morphology and hydrologic response in an urbanizing drainage basin the dead run catchment in baltimore county maryland has undergone intense urbanization since the late 1950s reconstruction of the channel planform from topographic maps dating back to the 1890s and aerial photographs dating back to the 1930s indicates that the channel has remained stable in planform since at least the 1930s the relative stability of dead run contrasts with the alterations in channel morphology reported for other urbanizing streams in the piedmont physiographic province of the eastern united states trend analyses of discharge records in dead run show that urban development and stormwater control measures have had significant impacts on the hydrologic response of the catchment the flood hydraulics of the dead run catchment are examined for the event that occurred on 22 june 1972 in association with hurricane agnes a two dimensional hydraulic model telemac 2d was used with a finite element mesh constructed from a combination of high resolution lidar topographic data and detailed field survey data to analyse the distribution of boundary shear stress and unit stream power along the channel and floodplain during flooding from hurricane agnes the spatial and temporal distributions of these parameters relative to channel gradient and channel valley bottom geometry provide valuable insights on the stability of the dean run channel the stability of dead run s channel planform in spite of extreme flooding and decades of urban development is most likely linked to geological controls of channel and floodplain morphology copyright 2006 john wiley sons ltd

boundary layer cloud and drizzle variability in the southeast pacific stratocumulus regime abstract the southeast pacific stratocumulus regime is an important component of the earth s climate system because of its substantial impact on albedo observational studies of this cloud regime have been limited but during the past 5 yr a series of cruises with research vessels equipped with in situ and remote sensing systems have provided unprecedented observations of boundary layer cloud and drizzle structures these cruises started with the east pacific investigation of climate epic 2001 field experiment followed by cruises in a similar area in 2003 and 2004 pan american climate studies pacs stratus cruises the sampling from these three cruises provides a sufficient dataset to study the variability occurring over this region this study compares observations from the 2004 cruise with those obtained during the previous two cruises observations from the ship provide information about boundary layer structure fractional cloudiness cloud depth and drizzle characteristics this study indicat

kinematic dispersion in stream networks 2 scale issues and self similar network organization 1 when the flow parameters such as celerity and hydrodynamic dispersion coefficient are allowed to vary spatially within a basin three mechanisms namely geomorphologic kinematic and hydrodynamic dispersion contribute to the variance of the instantaneous response function the relative contributions of the three dispersion mechanisms as a function of scale or strahler order of the basin are studied this analysis is performed for two study basins the vermilion and the mackinaw river basins in central illinois log linear trends for all the dispersion coefficients as a function of scale are observed these trends can be cast in the form of horton law type of relations the asymptotic behavior of the dispersion coefficients of basins with self similar network structure is consistent with the observations

scale effect on geomorphologic and kinematic dispersion geomorphologic dispersion relates to the fraction of the variance of residence time distributions that can be directly linked to the heterogeneity of the paths available to hydrologic runoff of a river basin in response to suitable rainfall pulses it thus defines the dispersive characters of geomorphological origin hillslope transport processes and systematic variations of advective processes in the channel network define a kinematic component of dispersion here we suggest that channel borne kinematic effects are likely to be clouded by hillslope dispersion in a surprisingly wide spectrum of basin scales we find that the signatures of hillslope transport on travel time distributions do not fade away rapidly with the size of the catchment i e when the basin scale becomes much greater than the mean hillslope size in particular because of their major impact on the skewness of the travel time distribution we suggest that an appropriate description of hillslope channel transitions entails a combination of geomorphic and kinematic effects which plays a decisive role in shaping the main characters of the hydrologic response in cases of practical interest

kinematic dispersion effects of hillslope velocities 1 when the flow parameters such as celerity and hydrodynamic coefficient are allowed to vary spatially within a basin three mechanisms namely geomorphologic kinematic and hydrodynamic dispersion contribute to the variance of the instantaneous response function the relative contributions of the three dispersion mechanisms as a function of scale or strahler order of the basin were studied earlier by saco and kumar 2002a 2002b in this study we investigate the main mechanisms that are responsible for the variance when we take into account the hillslope dynamics we use an approach similar to that derived by saco and kumar 2002a 2002b but for width functions to compute the relative contributions of geomorphologic and kinematic dispersion due to hillslope celerities we find that the kinematic dispersion due to hillslopes does not tend to reinforce the effect of geomorphologic dispersion rather it tends to counteract it this means that the effect of hillslopes tends to decrease the variance induced by the geomorphology of the network for hillslope celerities that are very small compared with channel celerities the travel times in the hillslopes begin to be of the same order of magnitude as those in the network if the celerity continues to decrease all the variance is induced by the travel times at the hillslopes and the impact of geomorphologic dispersion becomes negligible

hillslope and channel contributions to the hydrologic response 1 this paper develops a new framework to analyze the relevance of hillslope with respect to channel processes in the generation of the hydrologic response at different scales the dependence between basin response and geomorphic features of channels and hillslopes is analyzed through the mean and variance of travel times under simple but realistic dynamical hypotheses and within the framework of the rescaled width function the distribution of travel times is also studied in association with variations of the fraction of saturated areas with small values of the saturated fraction the channel network controls most of the mean and variance of travel time distribution vice versa when the basin is saturated the properties of this distribution may be significantly affected by hillslope processes these properties depend also on the basin size with the role of hillslope processes becoming more important in the smaller basins furthermore the average residence time is related to contributing area and drainage density through a simple expression which is shown to be consistent with previous empirical laws

a tem study of particles carried by ascending gas flows from the bairendaba lead zinc deposit inner mongolia china abstract in order to find deep seated deposit there is a need to develop non traditional surface geochemistry geogas is of particular interest particles transported by geogas from the deeply concealed deposits potentially hold great information this study investigates particles carried by ascending gas flows from the bairendaba lead zinc deposit this deposit is covered by a thick exotic substance which hinders probing the ore body directly the samples were collected using a static sampling method and were analysed by transmission electron microscopy tem to observe particle features such as shape component size structure and form of polymerization these particles contain information on buried deposits numerous pb zn and cu bearing particles as well as particles containing other metal compounds occur as individuals or aggregates in the ascending gas flows most particles have a large oxygen o content this is likely caused by the course of gas flows ascending from the deep ore body to the ground surface sulphur s is commonly associated with pb cu as fe and sb and occurs as sulphate in this deposit most metallic elements occur as sulphate oxide and carbonate in the detected particles in contrast to the samples collected in the peripheral area samples collected from the concealed deposit include numerous particles containing metallogenic elements although particles containing major elements can be found in both areas moreover the trend of each pb or zn bearing particle along a unique sampling line is directly related to the distribution of the corresponding ore bodies this indicates that the particles were generated at a certain depth carried by the ascending gas flow and directly provide important information regarding the concealed ore bodies the anomalous area can be used as a basis for further prospect analysis and improve the prospecting success rate

response and recovery of a subalpine stream following a catastrophic flood the july 15 1982 lawn lake flood in rocky mountain national park colorado was caused by the failure of a 79 yr old earthen dam peak discharges of the flood far exceeded naturally occurring flows and it caused severe channel disturbance along most of roaring river and some parts of fall river this study documents the geomorphic response of a 5 km reach of fall river in the 5 yr following the flood in 1983 the first year after the lawn lake flood snowmelt flows were well above average these high flows together with very high sediment yields from roaring river resulted in significant geomorphic changes on reaches of fall river downstream during the 1983 snowmelt runoff 15 5 x 106 kg of bed load sediment was eroded from the upper part of the study area these loads were at least 1 000 times higher than before the lawn lake flood most of this sediment was then deposited in a highly sinuous reach of fall river in the lower part of the study area this reach had not been much affected by the lawn lake flood but sedimentation during the period of high flow in 1983 completely filled in the channel resulting in the formation of a continuous 2 3 km long depositional zone in 1984 sediment yield from roaring river declined dramatically and this trend continued for the next 3 yr by 1987 the bed load sediment yield in the upper reaches of fall river was only about 0 4 x 106 kg yr the decline in sediment loads resulted in progressive erosion and recovery of the original channel of fall river in the depositional zone reach recovery in the upstream part of the depositional zone was complete by 1985 recovery in the downstream part of the depositional zone took longer because of the continued supply of sediment and because the sediment was mobile less of the time as of 1987 about 80 of the material initially stored in the sedimentation zone had been eroded bed load sediment yields at a sampling site 1 km downstream of the terminus of the depositional zone ranged from 5 x 106 to 11 x 106 kg yr but showed no significant decline over the 5 yr study period the average rate of bed load transport through this reach was at least 100 times greater than before the lawn lake flood but few discernible channel changes resulted from the higher loads

hydraulic causes for basin hydrograph skewness it has been suggested that hydrograph skewness depends on the relative dominance between hillslope and channel network transport processes where the former ones make the hydrograph positively skewed while the latter tends to make it negatively skewed more recently however the role of river hydraulics in shaping the hydrograph has been highlighted we present a set of numerical modelling experiments using a hydrodynamic model of river networks in which we investigate how channel hydraulics influence the shape of the hydrograph particularly its skewness we further investigate the influence of baseflow rainfall intensity cross section geometry and basin scale on unit hydrograph response we show that river hydraulics has a decisive role because positively skewed hydrographs may occur even when water inputs to the river network are negatively skewed and in catchments whose width function is also negatively skewed we show additional results related to the effect of the degree of non linearity in the relationship between celerity and discharge the effects of baseflow and rainfall intensity these further confirm that hydraulic factors may be decisive in determining hydrograph shape

catastrophic flooding from an orographic thunderstorm in the central appalachians 1 an orographic thunderstorm system in pendleton county west virginia produced 125 150 mm of rainfall in less than 1 hour on 9 august 2003 rainfall and fluvial impacts were concentrated in the ungauged 2 1 km2 saul s run watershed despite the short duration of the event the flood produced significant fluvial impacts and abrupt changes in the extent of incision and channel widening hydrometeorological analyses of the storm are based on wsr 88d radar reflectivity observations and rain gauge observations the small multicell thunderstorms that produced the saul s run flood were not markedly different from other storms in the central appalachian region on 9 august 2003 detailed surveys of high watermarks and channel floodplain geometry are used for hydraulic analyses of the saul s run flood including estimation of peak discharge at four locations peak discharge estimates at the 1 km2 scale cluster around 18 m3 s 1 placing this event on the flood envelope curve for the mid atlantic region observed rainfall estimated peak discharge and observer notes on timing of peak discharge are used along with a distributed hydrologic model to reconstruct hydrographs at multiple locations hydrologic modeling indicates that land use effects may have significantly influenced extreme flood response in saul s run the wide range of fluvial impacts is consistent with patterns of boundary shear stress and unit stream power derived from a simulation of the saul s run flood using a 2 d depth averaged hydraulic model

effect of sediment transport boundary conditions on the numerical modeling of bed morphodynamics abstractexperimental sediment transport and river morphologic studies in laboratory flumes can use two sediment supply methods an imposed feed at the upstream end or a recirculation of sediment f

geomorphic impacts of flash flooding in a forested headwater basin abstract geomorphic impacts of a july 2001 flood in the hungry mother basin near marion virginia were examined to shed light on the relationships between channel characteristics and the frequency of channel modifying discharges creeks in the study area have been observed for many years with no significant channel changes since at least 1985 the 2001 flood had a recurrence interval of 200 years and caused the only channel change bank erosion and transport of coarse channel material observed in recent decades the paucity of fines in channels before or after the flood and the absence of sub sand sized material in the flood deposits indicates that normal frequent well below bankfull flows are sufficient to transport the apparently limited supply of fines the large particles transported during the 2001 flood after years of inactivity indicate that relatively rare floods are necessary to mobilize this material this suggests the notion of a bimodal dominant discharge on the one hand frequent flows considerably below bankfull levels are sufficient to maintain the channel and prevent significant accumulation of fine sediments and organic matter on the other hand rare floods are necessary to transport the coarser bed material and erode channel banks in the hungry mother area bed material has no relationship to normal flows or to flows with recurrence intervals on the order of 1 3 years bankfull discharge is apparently not related to either the maintenance or channel changing dominant discharges these results suggest that the use of channel dimensions and or bed material as surrogate indicators of hydrologic regimes can be quite complicated and that in some streams bankfull flow has no particular significance in terms of sediment transport and channel modifications

spatial variability of atmospheric boundary layer structure over the eastern equatorial pacific abstract variations in the atmospheric boundary layer structure over the eastern equatorial pacific are analyzed using 916 soundings collected during the first global atmospheric research program global experiment unstable boundary layer structures are observed much more frequently in soundings north of the ocean front located near 2 5 n in the eastern equatorial pacific than in soundings south of the front an objective criterion is applied to identify the presence of the transition layer a weak stable layer near cloud base in the soundings the transition is observed in about 45 of the soundings in both the unstable and the inversion categories a comparison of soundings over the cold tongue with those over the itcz indicates that differences in static stability between these regions are limited to the layer from the surface to about 850 mb which is the mean height of the inversions capping the cloud layer over the cold tongue the cold tongue soundings on average are found to be drier from the sur

critical flow constrains flow hydraulics in mobile bed streams a new hypothesis a new hypothesis predicts that in mobile bed river channels interactions between the channel hydraulics and bed configuration prevent the froude number fr from exceeding 1 for more than short distances or periods of time flow conditions in many steep competent streams appear to be close to critical froude numbers of steep slope 0 01 sand bed streams with considerable freedom to adjust boundaries oscillate between 0 7 and 1 3 over 20 to 30 s cycles with an average of 1 0 at the channel thalweg criticalflow in these streams is maintained by the interaction between the mobile bed and free water surface at highfr which results in a cyclical pattern of creation and destruction of bed forms field observations support that a similar mechanism offlow bed form interaction constrains fr 1 in active bed braided gravel rivers step pool streams laboratory rills lahar runout channels and even some bedrock channels empirical and analytical results show that as slope increases competentflows tend to asymptotically approach criticalflow an assumption of criticalflow would dramatically simplify paleohydraulicflow reconstructions and modeling offlow hydraulics in high gradient streams

a new boundary layer mixing scheme part i scheme description and single column model tests a new boundary layer turbulent mixing scheme has been developed for use in the ukmo weather forecasting and climate prediction models this includes a representation of nonlocal mixing driven by both surface fluxes and cloud top processes in unstable layers either coupled to or decoupled from the surface and an explicit entrainment parameterization the scheme is formulated in moist conserved variables so that it can treat both dry and cloudy layers details of the scheme and examples of its performance in single column model tests are presented

pub in quebec a robust geomorphology based deconvolution reconvolution framework for the spatial transposition of hydrographs abstract the flexibility and parsimony of transpositioning hydrographs using geomorphology based deconvolution reconvolution frameworks is particularly adapted to prediction in ungauged basins although already tested in semi arid and oceanic temperate hydro climates its predictions must be reproducible in a variety of hydrological contexts the present study explores the nivo pluvial hydrological regime using geomorphology based hydrograph transposition between 21 gauged catchments ranging from 1 1 to 4466 4 km2 in quebec canada and constitutes a case study in prediction in ungauged basins three metrics were used to assess model performance for each donor target pair nash sutcliffe efficiency nse nse calculated for the square root of discharge nsesqrt and volumetric efficiency ve the classic transposition of hydrographs using the specific discharge ratio used as a reference was almost always outperformed by the geomorphology based approach good but seasonally variable performance values were obtained for several pairs of catchments revealing simultaneous structural and circumstancial effects the difference in size the physical distance between the gauged donor and its target ungauged catchment and the season influenced the performance of the geomorphology based transposition

vertical velocity structure of nonprecipitating continental boundary layer stratocumulus clouds 1 continental boundary layer bl stratocumulus clouds affect the local weather by modulating the surface energy and moisture budgets and are also intimately tied to the diurnal cycle of the turbulence in the bl vertical velocity structure of these clouds is studied using data from the atmospheric radiation measurement program s southern great plains observing facility located near lamont oklahoma data from vertically pointing cloud radar from eleven cases of nonprecipitating bl stratocumulus clouds are used to obtain half hourly values of in cloud vertical velocity variance skewness updraft fraction downdraft fraction and mass flux the variance showed a general decrease with height while the skewness was weakly positive in the cloud layer and negative near cloud top on half hourly time scales vertically coherent structures spanning through the entire cloud layer were responsible for 40 of the observed vertical velocity variance while horizontally temporally coherent structures lasting at least 20 s were responsible for 77 of the vertical velocity variance the half hour periods were then classified on the basis of the surface buoyancy flux b as small b periods b 60wm 2 small b periods exhibited lower variance near cloud base compared to large b periods with the differences being reversed near cloud top the skewness was positive in the cloud layer during large b periods and negative during small b periods while the skewness was negative near cloud top in both scenarios the small b periods had about ten times more updrafts greater than 1 m s 1 near cloud top compared to large b periods

on geomorphological dispersion in natural catchments and the geomorphological unit hydrograph since the introduction of the geomorphological instantaneous unit hydrograph giuh by rodriguez iturbe and valdes 1979 there have been a number of different approaches to expressing the geomorphology of a catchment for determining the hydrological response of the catchment we examine three approaches by which geomorphology can be introduced through the probabilities and lengths of the pathways available within a network 1 using the horton order ratios to derive analytical expressions for these pathway parameters 2 extracting these probabilities and lengths directly from a strahler ordered network without using the horton order ratios and 3 using a contributing area flow distance function extracted directly from the digital elevation model dem of a catchment without the assumptions of strahler stream ordering we use these techniques to derive the giuh and the geomorphological dispersion coefficient as defined by rinaldo et al 1991 for two catchments in the southwestern region of australia the geomorphological dispersion coefficient derived from the area distance function expresses the natural dispersion within the catchment in a more fundamental manner than the other methods and the giuhs derived from this function exhibit an underlying dispersion of an order of magnitude greater than either of the approaches based on strahler ordering we look at the concept of the completeness of a network from which we derive catchment parameters and how this concept is related to the threshold area supporting a network derived from a catchment dem

effectiveness of exceptional rainstorms on a small mediterranean basin abstract a comprehensive investigation of rainstorms and their consequent impacts on landscape evolution is geomorphologically important but only scant information may be available on exceptional events because parameters on synoptic conditions rainstorm landforms and hydrology for such events may be incomparable with previous knowledge we studied an exceptional storm on april 2 2006 in the ramot menashe region israel our investigation of rainfall landslides debris flows and channel suggests the effectiveness of such an event on the development of basin scale morphology the storm caused damage and casualties although it covered relatively narrow strips neither direct rainfall nor runoff measurements exist for the most severely affected area of ramot menashe but the geomorphologic evidence combined with high resolution meteorological radar data provides the basic understanding of the processes and hazardous conditions which prevailed at the time in the storm core based on estimation from meteorological radar data 263 mm of rain fell within 3 h with a maximum intensity of 220 mm h 1 for 10 min triggering both sporadic landslides at the soil bedrock contact on the upper slopes and widespread landslides at the fractured massive bedrock contact on the lower slopes the 1st order channels on the alternation of chalk and marl also underwent erosion and the produced sediment deposited on alluvial fans at the confluence with the main channel the specific peak discharges for catchment size of 0 3 10 km2 were 11 to 73 m3 s 1 km 2 higher than any recorded floods in the mediterranean climatic region of israel the effectiveness of the flood for geomorphic work represented by shear stress and stream power per unit boundary area reached 87 398 n m 2 and 212 2134 w m 2 respectively this kind of analysis can be applied to hazard prediction in other areas under similar geomorphological conditions

role of tree dams in the construction of pseudo terraces and variable geomorphic response to floods in little river valley virginia geomorphic response to a 1985 flood in little river valley northern virginia was different in magnitude and style from the largest historic flood in the same valley in 1949 the primary geomorphic activity during the 1985 flood was severe bank erosion and channel gravel deposition rather than the debris flow and avalanching of the 1949 event an unusual and widespread phenomenon of the recent flood was that large trees eroded and transported by the floodwater were aligned parallel to the river banks and at isolated sites were braced and stacked against trees still standing on the floodplain lateral barriers or dams created from these displaced trees allowed the channel to be locally aggraded above the level of the flood plain in these reaches little if any river gravel was deposited on the floodplain even though the adjacent channel floor was raised well above that surface the river has now shifted around the filled segments leaving flat isolated surfaces underlain by channel gravel standing above the level of the modern floodplain these features may be mistaken for terraces alter they become vegetated and the trees bracing the gravels decay interpreting these surfaces to be terrace remnants would lead to a faulty reconstruction of geomorphic history in the little river valley and other valleys where floodplain morphology is controlled by infrequent flood events

role of debris flows in long term landscape denudation in the central appalachians of virginia four major storms that triggered debris flows in the virginia west virginia appalachians provide new insights into the role of high magnitude low frequency floods in longterm denudation and landscape evolution in mountainous terrain storm denudation in the blue ridge mountain drainage basins is approximately an order of magnitude greater compared to basins located in the mountains of the valley and ridge province this difference is probably the result of higher storm rainfall from the blue ridge storms radiocarbon dating of debris flow deposits in the blue ridge indicates a debris flow return interval of not more than 2 4 k y in mountainous river basins this finding combined with measurements of basin denudation suggests that approximately half of the long term denudation from mechanical load occurs episodically by debris flow processes although floods of moderate magnitude are largely responsible for mobilizing sediment in lowgradient streams our data suggest that high magnitude low frequency events are the most significant component in delivering coarse grained regolith from mountainous hollows and channels to the lowland floodplains

thermodynamic and radiative structure of stratocumulus topped boundary layers abstractstratocumulus topped boundary layers stbls observed in three different regions are described in the context of their thermodynamic and radiative properties the primary dataset consists of 131 soundings from the southeastern pacific sep 90 soundings from the island of graciosa grw in the north atlantic and 83 soundings from the u s southern great plains sgp a new technique that makes an attempt to preserve the depths of the sublayers within an stbl is proposed for averaging the profiles of thermodynamic and radiative variables a one dimensional radiative transfer model known as the rapid radiative transfer model was used to compute the radiative fluxes within the stbl the sep stbls were characterized by a stronger and deeper inversion together with thicker clouds lower free tropospheric moisture and higher radiative flux divergence across the cloud layer as compared to the grw stbls compared to the stbls over the marine locations the stbls over sgp had higher wind shear and a n

conserved variable analysis of the convective boundary layer thermodynamic structure over the tropical oceans abstract an analysis of fgge dropwindsonde data using conserved thermodynamic variables shows mixing line structures for the convective boundary layer over the equatorial pacific deeper boundary layers show a double structure reversals of the gradients of mixing ratio and equivalent potential temperature above the boundary layer top are present in all the averages and suggest that the origin of the air sinking into the boundary layer needs further study

incorporating hillslope effects into the geomorphologic instantaneous unit hydrograph use of gamma distributions of stream holding times rather than the traditional exponential distributions results in geomorphologic instantaneous unit hydrographs giuhs that better fit data based iuhs in this paper hillslope effects are incorporated into the gamma giuh ggiuh model by assuming that the hillslope travel distance in an area of a given order is approximated by the inverse of twice the local drainage density and introducing a hillslope velocity term a method of moments fitting procedure is developed to estimate the channel and hillslope velocity terms in the ggiuh model from the moments of rainfall input and basin discharge output it was found that hillslope velocities are 2 orders of magnitude smaller than channel velocities the values found for the latter are reasonable given the range of values given in the literature for channel velocities similarly the hillslope velocity term found by the method of moments procedure matches macropore velocities reported in the literature

analysis of thermal inversions in the khareef salalah region in the sultanate of oman 1 meteorology and topography shape of the land are two of the most important environmental factors that control the movement of pollutants in the atmosphere a well known example of the importance of topography and meteorology is the so called monsoon season in salalah khareef salalah in the sultanate of oman the purpose of this paper is to investigate the role of the elevated stable layer particularly during monsoon season in salalah the study addresses the statistical analysis of inversion parameters it will also improve our common understanding of the monsoon and how it is dominated by inversions in this work the monthly characteristics of inversions are investigated using the daily radiosonde measurements to a height of 2 km over a period of 1 year both surface based and elevated inversions are investigated based on the analysis of data recovered from weather balloons the study shows a strong monthly change in inversion frequency depth and strength overall inversions are less common in summer 55 4 in may than in winter 82 8 in january the surface based inversion frequency is at a minimum in summer and at a maximum in winter the surface based inversions reach a maximum depth in winter and are almost absent during summer an opposite trend in elevated inversion is seen most summer inversions are elevated and a maximum in their frequencies is found during may to september the elevated inversions are generally deeper and stronger than the surface based inversions the correlation coefficient for the relationships between the inversion depth and temperature difference across the inversion was determined for both the surface based and elevated inversions it was 0 82 for the surface based inversion whereas it was appreciably lower 0 39 for the elevated inversion moreover the correlation coefficient between the log inversion depth and the log temperature difference across the elevated inversion was high i e 0 75

microflow of geogas a possible formation mechanism for deep sea nodules reply abstract a formation model for deep sea manganese nodules based on ascending bubble trains of geogas is proposed the bubble train forces material in the sediments and particles adsorbed by the bubbles to the sediment water interface where precipitation reactions occur in the presence of a nucleating agent a nodule is formed such a model might explain a number of observations concerning nodular structure genesis and distribution

structural patterns in river network organization at both infra and supra basin levels the case of a granitic relief within a landform the channelized water path from any point to the corresponding outlet is split into successive components within the strahler ordering scheme the probability density functions pdf of the length l of the whole channelized path and of the lengths of the components are studied as multi level structural functions we have considered a granitic area and studied both its main basin and the set of its 48 constituent basins with respect to the main basin the pdf of the component lengths exhibit a strong scaling property except for the highest orders due to a hierarchical constraint hence the pdf of sum l has no particular shape we have nevertheless identified an underlying structural pattern at particular infra and supra basin levels where the hierarchical constraint is weaker this identification process entails noting structurally emerging patterns based on multi level variables and distributions which satisfy the general self similarity of networks the fairly good fit of an analytical gamma law with most of these emerging patterns can prove to be a positive step towards both a general modelling approach to the geomorphometric functions and a stronger geomorphological basement of hydrological transfer functions copyright 2005 john wiley sons ltd

surface based observations of mesoscale cumulus stratocumulus interaction during astex abstract data obtained from the island of santa maria in the azores during the atlantic stratocumulus transition experiment astex are used to describe cloud and boundary layer structure for a 24 h period on 15 june 1992 over the east central atlantic 37 n 25 10 w the evolution of the mesoscale cloud structure during a 24 h period in the vertical column above the surface site was characterized using a 94 ghz radar a laser ceilometer 3 h radiosonde ascents and surface micrometeorological instrumentation mesoscale circulations and drizzle were found to be key elements of the boundary layer clouds observed in this region during the late night and predawn hours of the study period a single layer of stratocumulus that averaged 200 m in thickness topped a well mixed marine boundary layer mesoscale cellular convection mcc which had ascending regions with horizontal dimensions of 7 km was observed during this period at sunrise decoupling was imposed on this mcc and extreme mesoscale variatio

sediment supply and the development of the coarse surface layer in gravel bedded rivers the bed surface of most gravel rivers is considerably coarser than the sub surface or the gravel load transported over it a phenomenon affecting river dynamics morphology and ecology the coarse surface layer often called an armour or pavement has been attributed to an inherent tendency for small grains to settle between larger ones during active transport of all sizes1 2 and to selective erosion or trapping of finer particles when the coarse grains are relatively immobile3 4 where bedload supply is cut off below dams selective erosion causes coarsening5 6 using a simple quantitative model we propose that surface coarsening develops in gravel bedded rivers when local bedload supply from upstream is less than the ability of the flow to transport that load we present laboratory results which support this hypothesis and show that supply reduction causes changes in bedforms and progressive confinement of active bedload transport to a narrow band of finer bed surface bordered by a coarse less active bed it may therefore be possible to relate the degree of river bed surface coarsening to sediment supply resulting from land use

surface subsurface flow modeling with path based runoff routing boundary condition based coupling and assimilation of multisource observation data received 21 october 2008 revised 2 september 2009 accepted 16 september 2009 published 13 february 2010 1 a distributed physically based model incorporating novel approaches for the representation of surface subsurface processes and interactions is presented a path based description of surface flow across the drainage basin is used with several options for identifying flow directions for separating channel cells from hillslope cells and for representing stream channel hydraulic geometry lakes and other topographic depressions are identified and specially treated as part of the preprocessing procedures applied to the digital elevation data for the catchment threshold based boundary condition switching is used to partition potential atmospheric fluxes into actual fluxes across the land surface and changes in surface storage thus resolving the exchange fluxes or coupling between the surface and subsurface modules nested time stepping allows smaller steps to be taken for typically faster and explicitly solved surface runoff routing while a mesh coarsening option allows larger grid elements to be used for typically slower and more compute intensive subsurface flow sequential data assimilation schemes allow the model predictions to be updated with spatiotemporal observation data of surface and subsurface variables these approaches are discussed in detail and the physical and numerical behavior of the model is illustrated over catchment scales ranging from 0 0027 to 356 km 2 addressing different hydrological processes and highlighting the importance of describing coupled surfacesubsurface flow

runoff of small rocky headwater catchments field observations and hydrological modeling in dolomitic headwater catchments intense rainstorms of short duration produce runoff discharges that often trigger debris flows on the scree slopes at the base of rock cliffs in order to measure these discharges we placed a measuring facility at the outlet elevation 1770 m a s l of a small rocky headwater catchment area 0 032 km2 average slope 320 located in the venetian dolomites north eastern italian alps the facility consists of an approximately rectangular basin ending with a sharp crested weir six runoff events were recorded in the period 2011 2014 providing a unique opportunity for characterizing the hydrological response of the catchment the measured hydrographs display impulsive shapes with an abrupt raise up to the peak followed by a rapidly decreasing tail until a nearly constant plateau is eventually reached this behavior can be simulated by means of a distributed hydrological model if the excess rainfall is determined accurately we show that using the soil conservation service curve number scs cn method and assuming a constant routing velocity invariably results in an underestimated peak flow and a delayed peak time a satisfactory prediction of the impulsive hydrograph shape including peak value and timing is obtained only by combining the scs cn procedure with a simplified version of the horton equation and simulating runoff routing along the channel network through a matched diffusivity kinematic wave model the robustness of the proposed methodology is tested through a comparison between simulated and observed timings of runoff or debris flow occurrence in two neighboring alpine basins this article is protected by copyright all rights reserved

a hybrid 3d hillslope hydrological model for use in earth system models hillslope scale rainfall runoff processes leading to a fast catchment response are not explicitly included in land surface models lsms for use in earth system models esms due to computational constraints this study presents a hybrid 3d hillslope hydrological model h3d that couples a 1 d vertical soil column model with a lateral pseudo 2d saturated zone and overland flow model for use in esms by representing vertical and lateral responses separately at different spatial resolutions h3d is computationally efficient the h3d model was first tested for three different hillslope planforms uniform convergent and divergent we then compared h3d with single and multiple soil columns with a complex physically based 3 d model and a simple 1 d soil moisture model coupled with an unconfined aquifer as typically used in lsms it is found that simulations obtained by the simple 1 d model vary considerably from the complex 3 d model and are not able to represent hillslope scale variations in the lateral flow response in contrast the single soil column h3d model shows a much better performance and saves computational time by 2 3 orders of magnitude compared with the complex 3 d model when multiple vertical soil columns are implemented the resulting hydrological responses soil moisture water table depth and base flow along the hillslope from h3d are nearly identical to those predicted by the complex 3 d model but still saves computational time as such the computational efficiency of the h3d model provides a valuable and promising approach to incorporating hillslope scale hydrological processes into continental and global scale esms

wood mediated geomorphic effects of a jokulhlaup in the wind river mountains wyoming a jokulhlaup burst from the head of grasshopper glacier in wyoming s wind river mountains during early september 2003 five reaches with distinct sedimentation patterns were delineated along the dinwoody creek drainage this paper focuses on a portion of the jokulhlaup route where erosion of the forested banks created 16 large logjams spaced at longitudinal intervals of tens to hundreds of meters aggradation within the main channel upstream from each logjam created local sediment wedges and the jams facilitated overbank deposition during the jokulhlaup field surveys during 2004 and 2006 documented logjam characteristics and associated erosional and depositional features as well as initial modification of the logjams and flood deposits within the normal seasonal high flow channel overbank deposits have not been altered by flows occurring since 2003 field measurements supported three hypotheses that i logjams present along the forested portions of the jokulhlaup route are larger and more closely spaced than those along adjacent otherwise comparable stream channels that have not recently experienced a jokulhlaup ii logjams are not randomly located along the jokulhlaup route but instead reflect specific conditions of channel and valley geometry and flood hydraulics and iii the presence of logjams facilitated significant erosional and depositional effects this paper documents a sequence of events in which outburst floodwaters enhance bank erosion and recruitment of wood into the channel and thus the formation of large logjams these logjams sufficiently deflect flow to create substantial overbank deposition in areas of the valley bottom not commonly accessed by normal snowmelt peak discharges and through this process promote valley bottom aggradation and sediment storage changes in the occurrence of glacier outburst floods thus have the potential to alter the rate and magnitude of valley bottom dynamics in these environments which is particularly relevant given predictions of worldwide global warming and glacial retreat processes observed at this field site likely occur in other forested catchments with headwater glaciers

floods in mountain environments a synthesis floods are a crucial agent of geomorphic change in the channels and valley floors of mountains watercourses at the same time they can be highly damaging to property infrastructure and life because of their high energy mountain watercourses are highly vulnerable to environmental changes affecting their catchments and channels many factors have modified and frequently still tend to modify the environmental conditions in mountain areas with impacts on geomorphic processes and the frequency magnitude and timing of floods in mountain watercourses the ongoing climate changes vary between regions but may affect floods in mountain areas in many ways in many mountain regions of europe widespread afforestation took place over the twentieth century considerably increasing the amounts of large wood delivered to the channels and the likelihood of jamming bridges at the same time deforestation continues in other mountain areas accelerating runoff and amplifying the magnitude and frequency of floods in foreland areas in many countries in channel gravel mining has been a common practice during recent decades the resultant deficit of bed material in the affected channels may suddenly manifest during flood events resulting in the failure of scoured bridges or catastrophic channel widening during the past century many rivers in mountain and foreland areas incised deeply the resultant loss of floodplain water storage has decreased attenuation of flood waves hence increasing flood hazard to downstream river reaches on the other hand a large amount of recent river restoration activities worldwide may provide examples of beneficial changes to flood risk attained as a result of increased channel storage or reestablished floodplain water storage relations between geomorphic processes and floods operate in both directions which means that changes in flood probability or the character of floods e g increased wood load may significantly modify the morphology of mountain rivers but morphological changes of rivers can also affect hydrological properties of floods and the associated risk for societies this paper provides a review of research in the field of floods in mountain environments and puts the papers of this special issue dedicated to the same topic into context it also provides insight into innovative studies methods or emerging aspects of the relations between environmental changes geomorphic processes and the occurrence of floods in mountain rivers

coherent structures in large eddy simulations of a nonprecipitating stratocumulus topped boundary layer abstractthe properties of coherent convective structures are analyzed in a nonprecipitating marine nocturnal stratocumulus topped boundary layer stbl with a series of high resolution large eddy simulations less a new classification method based on octant analysis using vertical velocity and two passive scalars is introduced to systematically define convective structures in both the cloudy and the cloud free regions it is therefore possible to detect and track updrafts downdrafts and their turbulent shells both ascending and subsiding together with the entraining air from the inversion layer or the free troposphere the geometrical and thermodynamical characteristics e g areal fraction temperature liquid and total water mixing ratio buoyancy of those structures are then accurately described and particular attention is given to their respective contributions to the turbulent transport of mass heat and moisture it is shown that updrafts downdrafts and entrainment are equally important

upper limits of flash flood stream power in europe abstract flash floods are characterized by strong spatial gradients of rainfall inputs that hit different parts of a river basin with different intensity stream power values associated with flash floods therefore show spatial variations that depend on geological controls on channel geometry and sediment characteristics as well as on the variations of flood intensity this stresses the need for a field approach that takes into account the variability of the controlling factors post flood assessment of peak discharge after major floods makes it possible to analyse stream power in fluvial systems affected by flash floods this study analyses the stream power of seven intense return period of rainfall 100 years at least in some sectors of the river basin flash floods that occurred in mountainous basins of central and southern europe from 2007 to 2014 in most of the analysed cross sections high values of unit stream power were observed this is consistent with the high severity of the studied floods the highest values of cross sectional stream power and unit stream power usually occur in mediterranean regions this is mainly ascribed to the larger peak discharges that characterize flash floods in these regions the variability of unit stream power with catchment area is clearly nonlinear and has been represented by log quadratic relations the values of catchment area at which maximum values of unit stream power occur show relevant differences among the studied floods and are linked to the spatial scale of the events values of stream power are generally consistent with observed geomorphic changes in the studied cross sections bedrock channels show the highest values of unit stream power but no visible erosion whereas major erosion has been observed in alluvial channels exceptions to this general pattern which mostly occur in semi alluvial cross sections urge the recognition of local or event specific conditions that increase the resistance of channel bed and banks to erosion or like short flow duration reduce the geomorphic effectiveness of the flood

factors influencing cloud area at the capping inversion for shallow cumulus clouds large eddy simulations of marine cumulus clouds are performed aspects of the simulations are varied in order to identify those parameters that play a role in determining when the cumulus clouds spread out under the capping inversion into stratocumulus these include the strength of the surface fluxes which also affects the strength of the cumulus mass transport the strength of the capping inversion the moisture content of the free atmosphere the strength of cloud top radiative cooling and whether there is significant precipitation or sedimentation of cloud drops tests are also performed to evaluate sensitivity to the model resolution as in previous studies having sufficient resolution at the capping inversion is found to be important for robust simulation of any stratiform cloud that forms there in addition the cloud cover is found to be sensitive to many of the physical processes investigated in the end though a clear and robust dependence emerges on the cloud top entrainment instability parameter for large a typical small shallow cumulus cloud cover is seen for below the threshold for buoyancy reversal the cumulus spreads into a solid sheet of stratocumulus beneath the inversion consistent with previous studies there is no abrupt transition and the cloud cover decreases smoothly as increases the conclusion is reached that varying other parameters in the simulations affects the cloud cover through their impact on the size of the jumps across the inversion and thence the implications for turbulent mixing parametrizations in general circulation models are discussed crown copyright 2009 reproduced with the permission of hmso published by john wiley sons ltd