characteristics of the antarctic surface mass balance 1958 2002 using a regional atmospheric climate model temporal and spatial characteristics of the antarctic specific surface mass balance ssmb are presented including its components solid precipitation sublimation deposition and melt for this purpose we use the output of a regional atmospheric climate model racmo2 ant horizontal resolution of 55 km for the period 1958 2002 racmo2 ant uses european centre for medium range weather forecasts ecmwf 40 year re analysis era 40 fields as forcing at the lateral boundaries racmo2 ant underestimates ssmb in the high interior of east and west antarctica and overestimates ssmb on the steep coastal slopes otherwise the modeled spatial pattern of ssmb is in good qualitative agreement with recent compilations of in situ observations large scale patterns like the precipitation shadow effect of the antarctic peninsula are well reproduced and mesoscale ssmb patterns such as the strong precipitation gradients on law dome are well represented in the model the integrated ssmb over the grounded ice sheet is 153mmw e a 1 for the period 1958 2002 which agrees within 5 with the latest measurement compilations sublimation and melt remove 7 and

atmospheric processes and climatological characteristics of the 79n glacier northeast greenland abstractthe nioghalvfjerdsfjorden glacier the 79 fjord henceforth referred to as 79n has been thinning and accelerating since the early 2000s as a result of calving episodes at the front of the

seasonal cycles of antarctic surface energy balance from automatic weather stations we present the seasonal cycle of the antarctic surface energy balance seb using 4 years 1998 2001 of automatic weather station aws data the four awss are situated on an ice shelf in the coastal and inland katabatic wind zone and the interior plateau of dronning maud land to calculate surface temperature we use a seb closure assumption for a surface skin layer modelled and observed surface have a root mean square difference of 1 8 k at the plateau aws corresponding to an uncertainty in the seb of 5 w m 2 and 1 k 3 w m 2 at the other sites the effect of wind speed sensor freezing on the calculated seb is discussed at all sites the annual mean net radiation is negative and the near surface air is on average stably stratified differences in the seasonal cycle of the seb are mainly caused by the different wind climates at the aws sites in the katabatic wind zone a combination of clear skies and strong winds forces a large wintertime turbulent transport of sensible heat towards the surface which in turn enhances the longwave radiative heat loss on the coastal ice shelf and on the plateau strong winds are associated with overcast conditions limiting the radiative heat loss and sensible heat exchange during the short antarctic summer the net radiation becomes slightly positive at all sites away from the cold interior the main compensating heat loss at the surface is sublimation in the interior summer temperatures are too low to allow significant sublimation to occur here surface heat loss is mainly due to convection

atmosphere ocean mechanisms of climate anomalies in the angola tropical atlantic sector abstract interannual variations in the large scale atmospheric and oceanic fields over the tropical atlantic are studied in relation to rainfall anomalies on the angola coast departure patterns are constructed by stratification with respect to extremely dry and wet years and by correlation with rainfall in angola which is concentrated in march april the analysis suggests a causality chain of atmospheric oceanic anomalies variations of westward wind stress on the western equatorial atlantic constitute an early link in this chain the annual cycle is characterized by a relaxation of the wind stress from september november to february march anomalous seasonal relaxation of easterly wind stress over the western equatorial atlantic remotely forces the sea surface temperature sst departures in the eastern south atlantic a large relaxation being followed by positive sst departures sea surface temperature modulates the rainfall over downstream angola by controlling the atmospheric moisture and stability

the source of benguela ninos in the south atlantic ocean 1 the intermittent occurrence of anomalous warm events in the upwelling regions of the pacific el ninos has been intensively studied pacific ninos have striking effects on the local ecosystem hence on the fisheries and on rainfall similar dramatic events have been observed in the south atlantic off the coasts of angola and namibia and named benguela ninos they tend not to occur in unison with their pacific counterpart and may thus have unrelated forcing mechanisms using an ocean general circulation model forced by real winds and verified with satellite data it is shown that benguela ninos are generated by specific wind stress events in the west central equatorial atlantic and progress from there as subsurface temperature anomalies that eventually outcropped only at the south west african coast these results suggest that it now may be possible to predict the occurrence of these disruptive events with a lead time of 2 months

power series solution for ponded infiltration on sloping surfaces summary recently it has been shown that the philip power series solution can also be applied for falling head ponded infiltration mollerup and hansen 2007 or more generally for variable head vh ponded infiltration on flat surfaces mollerup 2007 in this study it is shown that the power series solution can also be applied for vh ponded infiltration on sloping surfaces numerical simulations have been made for a guelph loam for a vh scenario the power series solution was compared with a 2d fem solution of richards equation with good agreement using the developed series solutions a vh scenario was compared with constant head ch simulations with both a ponding depth of zero and the average ponding depth as used in the vh simulations especially the latter gave small differences in the cumulative infiltration compared with the vh results simulations showed that cumulative infiltration normal to the slope as function of time is decreasing with increasing slope angles for similar vertical ponding depths corresponding to equal amount of surface water on a given horizontal slope section in contrast the infiltration on a given projected horizontal area increases with the slope angle

the west african monsoon dynamics part ii the preonset and onset of the summer monsoon the arrival of the summer monsoon over west africa has been documented by using daily gridded rainfall data and ncep ncar reanalyses during the period 1968 90 and olr data over the period 1979 90 two steps have been characterized through a composite approach the preonset and the onset of the summer monsoon the preonset stage corresponds to the arrival in the intertropical front itf at 15 8n that is the confluence line between moist southwesterly monsoon winds and dry northeasterly harmattan bringing sufficient moisture for isolated convective systems to develop in the sudano sahelian zone while the intertropical convergence zone itcz is centered at 58n the mean date for the preonset occurrence is 14 may and its standard deviation is 9 5 days during the period 1968 90 this leads to a first clear increase of the positive rainfall slope corresponding to the beginning of the rainy season over this sudano sahelian area the onset stage of the summer monsoon over west africa is linked to an abrupt latitudinal shift of the itcz from a quasi stationary location at 58n in may june to another quasi stationary location at 108n in july august the mean date for the onset occurrence is 24 june and its standard deviation is 8 days during the period 1968 90 this leads to a second increase of the positive rainfall slope over the sudano sahelian zone signing the northernmost location of the itcz and the beginning of the monsoon season this abrupt shift occurs mostly between 108w and 58e where a meridional land sea contrast exists and it is characterized by a temporary rainfall and convection decrease over west africa preonset dates onset dates and summer rainfall amount over the sahel are uncorrelated during the period 1968 90 the atmospheric dynamics associated with the abrupt itcz shift has been investigated between the preonset and the onset stages the heat low dynamics associated with the itf controls the circulation in the low and midlevels its meridional circulation intensity is the highest at the beginning of the monsoon onset this can lead to 1 increased convective inhibition in the itcz through intrusion of dry and subsiding air from the north and 2 increased potential instability through a greater inland moisture advection and a higher monsoon depth induced by a stronger cyclonic circulation in the low levels through higher vertical wind shear due to westerly monsoon wind and midlevel african easterly jet aej increases through enhancement of the instability character of the aej and through increased shortwave radiation received at the surface during the monsoon onset once the rainfall minimum occurred due to the convective inhibition the accumulated potential instability breaks the convective inhibition the inertial instability of the monsoon circulation is released and the associated regionalscale circulation increases leading to the abrupt shift of the itcz then the itcz moves north up to 108n where thermodynamical conditions are favorable it is suggested by the authors that the abrupt shift of the itcz initiated by the amplification of the heat low dynamics could be due to an interaction with the northern orography of the atlas ahaggar mountains subsidence over and north of this orography due to both the northern branches of the heat low and of the northern hadleytype cell contributes to enhance the high geopotentials north of these mountains and the associated northeasterly winds this leads to the development of a leeward trough that reinforces the heat low dynamics maintaining an active convective itcz through enhanced moist air advection from the ocean increasing the northern hadley circulation which reinforces the high geopotentials and the interaction with the orography through a positive feedback the fact that an abrupt shift of the itcz is only observed on the western part of west africa may result from the enhancement of moisture advection which comes from the west and has a stronger impact west of the greenwich meridian the northwest southeast orientation of the atlas ahaggar crest can induce the interaction with the heat low first in the east where the mountains are nearer to the itf than in the west and second in the west another consequence of the possible orography induced interaction with the atmospheric circulation is that the induced leeward trough increasing the cyclonic vorticity in the heat low may stimulate moisture convergence in the oceanic itcz near the western coast of west africa

melting runoff and the formation of frozen lakes in a mixed snow and blue ice field in dronning maud land antarctica large scale melting phenomena such as meltwater drainage channels and meltwater accumulation basins of frozen lakes were surveyed on the land ice mass in jutulgryta dronning maud land antarctica during the norwegian antarctic research expedition in 1989 90 nare 1989 90 the largest frozen lake that was observed was close to 1 km in width these melting features were also detected in a landsat thematic mapper image recorded on 12 february 1990 then during nare 1993 94 a 5year glaciological programme was started in this area in spite of negative air temperatures and the presence of a frozen ice surface sub surface melting and runoff were found within the uppermost metre in blue ice fields the sub surface melting is a consequence of solar radiative penetration and absorption within the ice i e the solid state greenhouse effect temperatures in blue ice were about 6 c higher than for snow internal melt and meltwater transport were observed throughout the 1 month of measurements the conditions for active melting in jutulgryta are probably marginal a slight increase of air temperatures can result in more classical surface melting whereas a cooling may disable sub surface melting studies of how the extent and characteristics of the melting features change with time can be particularly valuable as indicators of climate change this ongoing programme clearly identifies the importance of analyzing how these melting features originate of mapping their present areal distribution of determining how sensitive they are to climate change and of studying changes in the past and possible changes in the future

retreating alpine glaciers increased melt rates due to accumulation of dust vadret da morteratsch switzerland the automatic weather station aws on the snout of the vadret da morteratsch switzerland has delivered a unique 12 year meteorological dataset from the ablation zone of a temperate glacier this dataset can be used to study multi annual trends in the character of the surface energy budget since 2003 there has been a substantial darkening of the glacier tongue due to the accumulation of mineral and biogenic dust the typical surface albedo in summer has dropped from 0 32 to 0 15 we have analysed the implications of the lowered albedo for the energy balance and the annual ablation for the 4 year period 2003 06 the decreased albedo caused an additional removal of about 3 5 m of ice calculations with an energy balance model show that the same increase in ablation is obtained by keeping the ice albedo fixed to 0 32 and increasing the air temperature by 1 7 k our analysis confirms that for retreating glaciers the deposition of dust from exposed side moraines on the glacier surface constitutes an important feedback mechanism the mineral dust stimulates the growth of algae lowers the surface albedo enhances the melt rates and thereby facilitates the further retreat of the glacier snout

in situ sampled snow particle sizes of the east antarctic ice sheet and their relation to physical and remotely sensed snow surface parameters knowledge of snow properties across antarctica is important in estimating how climate could potentially influence the mass balance of the antarctic ice sheet however measuring these variables has proven to be challenging because appropriate techniques have not yet been developed and extensive datasets of field estimates are lacking the goal of this study was to estimate the relationship between field observed snow particle size parameters from across the east antarctic ice sheet and a suite of spatial datasets i e topography remote sensing data using a principal component analysis pca five snow particle size parameters were correlated to spatial datasets of the following five groups 1 relief properties such as elevation and slope 2 remote sensing data from moderate resolution imaging spectroradiometer modis and synthetic aperture radar sar sensors 3 spatially interpolated data i e 10 m maps of temperature and approximate snow accumulation in kg m 2 a 1 4 field retrieved data on surface roughness and 5 in situ elevation and distance from the coast the results show that the relief parameter slope correlated best with the snow particle length and area r 0 76 r 0 80 further the pca indicated that the different remote sensing parameters correlated differently with the size parameters and that the most common parameter in visual analysis particle length grain diameter is not always the optimal parameter to characterize the snow particle size as for example area correlates better to slope and aspect than length

thermally induced icequakes detected on blue ice areas of the east antarctic ice sheet over a year of seismic observations 5000 short duration icequakes were detected by a permanent broadband station installed at the princess elisabeth base located 180 km inland in eastern dronning maud land east antarctica icequake detection via seismic waveform pattern recognition indicates the presence of two dominating clusters of events totalizing 1500 icequakes the corresponding icequake locations point towards two distinct zones of outcropping blue ice areas bias located respectively at 4 and 1 km from the seismic station both on the leeward side of a nunatak protruding through the ice sheet the temporal occurrence of these icequakes suggests a close genetic link with thermal contraction of ice caused by significant surface cooling controlled in summer by variations in diurnal solar radiation and in winter by strong cooling during cold katabatic regimes further analysis demonstrates the dependence of these icequakes on the absolute surface temperature and on its temporal change besides providing information on the ice fracture mechanics and rheology investigations of thermal icequakes may be regarded as a ground based proxy for the monitoring of the thermal state of bias and characterization of ice sheet ablation zones

reconstructing thermal properties of firn at summit greenland from a temperature profile time series we have constrained the value for thermal diffusivity of near surface snow and firn at summit station greenland using a fourier type analysis applied to hourly temperature measurements collected from eight thermistors in a closed off air filled borehole between may 2004 and july 2008 an implicit finite difference method suggests that a bulk diffusivity of 25 3m2 a 1 is the most reasonable for representing macroscale heat transport in the top 30 m of firn and snow this value represents an average diffusivity and in a conduction only model generates temperature series whose phase shifts with depth most closely match those of the summit borehole data rms difference between measurements and model output is 6 days this bulk value derived numerically and corroborated analytically is useful over large tracts of the greenland ice sheet where density and microstructure are unknown

spectral transmission and implications for the partitioning of shortwave radiation in arctic sea ice we present a new set of values for the spectral extinction coefficients k for the interior of first year fy and multi year my arctic sea ice during the summer melt season measured during sheba surface heat budget of the arctic ocean program and at barrow alaska usa results for fy ice are consistent with previously reported values and differences can be understood in terms of variations in the concentration of biological and suspended particulate material the values for the interior of my ice are lower than previously reported for both bare and ponded ice for bare my ice the new kvalues predict a substantial increase in the solar radiation transmitted through the ice into the upper mixed layer ponded my ice is only slightly more transparent than previously reported and fy ice values are generally consistent with previously reported values assuming an asymmetry parameter of 0 94 the extinction coefficients are consistent with a volume scattering coefficient of 77 m 1 that is constant from 400 to at least 720 nm

temperature measurements and heat transfer in near surface snow at the south pole to study near surface heat flow on the antarctic ice sheet snow temperatures were measured at south pole station to a depth of 3 m at 15 min intervals during most of 1992 solar heating and water vapor transport were negligible during the 6 month winter as was inter grain net thermal radiation leaving conduction as the dominant heat transport mechanism the rate of temperature change at depth over 15 min intervals was smaller than that at the surface by one order of magnitude at 20 cm depth and two orders of magnitude at 1 m depth a finite difference model with conduction as the only heat transfer mechanism and measured temperatures as the upper and lower boundary conditions was applied to foursets of three thermistors each the thermal conductivity was estimated as that which minimized the difference between modeled and measured 15 min changes in temperatures at the center thermistor the thermal conductivity obtained at shallow depths above 40 cm was lower than that given by existing parameterizations based on density probably because the snow grains were freshly deposited cold and poorly bonded a model using only vertical conduction explains on average 87 ofthe observed 15 min temperature changes at less than 60 cm depth and 92 below 60 cm the difference between modeled andmeasured temperature changes decreased with depth the discrepancies between model and observation correlated more strongly with the air snow temperature difference than with the product of that difference with the square of the wind speed suggesting that the residual errors are due more to non vertical conduction and to sub grid scale variabilis of the conductivity than to windpumping the residual heating rate not explained by the model of vertical conduction exceeds 0 2 w m 3 only in the top 60 cm of the near surface snow

water infiltration underneath single ring permeameters and hydraulic conductivity determination summary a single ring permeameter is suitable for measurement of soil hydraulic conductivity at a large field scale because of its simple structure easy operation portability small amount of recharging water and particularly because of its variable radius the authors established a simple single ring permeameter which consists of a hollow cylinder that is simply inserted into the top soil based on the theories of the philip and nestingen methods for single ring permeameter tests this paper presents new equations for describing 1 d infiltration within the inserted depth of the single ring infiltrometer and 3 d flow beyond the depth under both gravity and soil suction forces the soil hydraulic parameters of hydraulic conductivity and soil suction were optimized based on the declines of the ponded water depth within the single ring cylinder the new method was validated using numerical simulations of the declines of the water column within the cylinder through the variably saturated flow modflow vsf modflow the new method was then successfully applied in laboratory troughs and on a hillslope in huanjiang county northwest guangxi in southwest china the results demonstrate that the hydraulic conductivity determined by the new method is more accurate than those from the 1 d green ampt method and the 3 d nestingen method

falling head ponded infiltration with evaporation comment reference ecol article 1994 002doi 10 1016 0022 1694 94 90013 2 url http www elsevier com wps find journaldescription cws home 503343 description description record created on 2005 12 09 modified on 2016 11 26

surface layer response to topographic solar shading in antarctica s dry valleys 1 the effects of topographic shading on local flow transitioning and atmospheric surface layer properties are investigated using observational data from the miers valley one of the dry valleys of antarctica a unique data set was collected during a 9 day period in the summer of 2012 using an eddy covariance system and a sound detection and ranging that provided vertical profiles of wind and turbulence characteristics in the surface layer and the lower part of the boundary layer within the miers valley this data set is ideal for investigating the dynamics of flow transitioning due to topographic shading without the atmosphere experiencing complete darkness the lack of atmospheric humidity soil moisture and surface vegetation in the dry valleys creates an atmosphere within which the microclimatic responses are amplified and as a result the valley atmosphere is extremely sensitive to solar radiation the entire measured valley boundary layer up to 250 m above ground level feels the transition from an unstable to a stable stratification as the surface temperature drops by 10 c in response to the topographic shading wavelet analysis reveals the dynamics of flow deceleration stagnation and oscillations as the flow transitions from an unstable to a stable boundary layer the larger air mass along valley scales to the longer terrain fetch and as the shade is cast over the valley it retains some of the longer wavelengths of the flow the cross valley component influenced by the slopes is quicker to adjust to short period oscillations and takes around three more hours before it couples with the oscillatory pattern of the along valley flow

evolution of interannual warm and cold events in the southeast atlantic ocean extreme warm episodes in the southeast atlantic ocean known as benguela ninos have devastating envi ronmental impacts and have been shown to be remotely forced to place these extreme events into perspective the investigation is here extended to minor warm events as well as to cold episodes to this end different sets of observations have been combined with outputs from a numerical simulation of the tropical atlantic for the period 1982 99 it is shown that both warm and cold surface events develop regularly in the same specific region along the coast of angola and namibia some cold events compete in magnitude with major warm episodes local sea air heat flux exchanges do not seem to precondition the sea surface in the angola benguela region prior to the arrival of an event most warm and cold episodes are large scale events despite their limited surface signature they appear to be generated by wind anomalies in the western and central equatorial atlantic in the same way as benguela ninos seasonal fluctuations of the depth and shape of the tropical thermocline seem partly to control the way subsurface anomalies eventually impact the surface during austral summer surface anomalies create an identifiable pool centered near 158s whereas in winter they show an elongated pattern along the coast stretching toward the equator local upwelling or downwelling favorable wind regimes as well as local net heat fluxes may modulate the surface expression of events

practical estimates of field saturated hydraulic conductivity of bedrock outcrops using a modified bottomless bucket method 1 the bottomless bucket bb approach nimmo et al 2009a is a cost effective method for rapidly characterizing field saturated hydraulic conductivitykfsof soils and alluvial deposits this practical approach is of particular value for quantifying infiltration rates in remote areas with limited accessibility a similar approach for bedrock outcrops is also of great value for improving quantitative understanding of infiltration and recharge in rugged terrain we develop a simple modification to the bb method for application to bedrock outcrops which uses a nontoxic quick drying silicone gel to seal the bb to the bedrock these modifications to the field method require only minor changes to the analytical solution for calculatingkfs on soils we investigate the reproducibility of the method with laboratory experiments on a previously studied calcarenite rock and conduct a sensitivity analysis to quantify uncertainty in our predictions we apply the bb method on both bedrock and soil for sites on pahute mesa which is located in a remote area of the nevada national security site the bedrock bb tests may require monitoring over several hours to days depending on infiltration rates which necessitates a cover to prevent evaporative losses our field and laboratory results compare well to kfs values inferred from independent reports which suggests the modified bb method can provide useful estimates and facilitate simple hypothesis testing the ease with which the bedrock bb method can be deployed should facilitate more rapid in situ data collection than is possible with alternative methods for quantitative characterization of infiltration into bedrock

sea surface temperature fields associated with west african rainfall anomaly types abstract four west african rainfall anomaly types are defined in relation to the northern summer rainfall departure signs in the sahel and in the guinean region in order to investigate the statistical links between interannual variability of west african rainfall and sea surface temperature sst through the period 1950 90 composite analysis depicts the setup of four different mean sst anomaly fields drought over all of west africa is associated with the growth of positive sst anomalies in the eastern pacific and in the indian ocean and negative sst anomalies in the northern atlantic and in the gulf of guinea in contrast drought limited to the sahel corresponds mostly to a northward expansion of positive sst anomalies in the southern atlantic and negative sst anomalies in the northern atlantic northward expansion of negative sst anomalies in the southern atlantic positive sst departures in the northern atlantic and development of negative sst anomalies in the eastern pacific appear to be synchron

temperatures heating rates and vapour pressures in near surface snow at the south pole a finite volume model is used to simulate 9 years 1995 2003 of snow temperatures at the south pole the upper boundary condition is skin surface temperature derived from routine upwelling longwave radiation measurements while the lower boundary condition is set to the seasonal temperature gradient at 6 5 m depth taken from prior measurements at the south pole we focus on statistics of temperature heat fluxes heating rates and vapour pressures in the top metre of snow but present results from the full depth of the model 6 5 m the monthly mean net heat flux into the snow agrees with results from previous studies performed at the south pole on shorter timescales the heating rates and vapour pressures show large variability the net heat flux into the snow which is between 5wm 2 in the monthly mean can be greater than 20 w m 2 on hourly timescales on sub daily timescales heating rates exceed 40 k d 1 in the top 10 cm of the snow subsurface temperatures and therefore heating rates are more variable during winter april september due to increased synoptic activity and the presence of a strong surface based atmospheric temperature inversion the largest vapour pressures 60 70 pa and vertical gradients of vapour pressure are found in the top metre of snow during the short summer december january in contrast during the long winter the low temperatures result in very small vapour pressures and insignificant vapour pressure gradients the high summertime vapour pressure gradients may be important in altering the isotopic composition of snow and ice on the antarctic plateau

surface glaciochemistry of taylor valley southern victoria land antarctica and its relationship to stream chemistry we have analysed a series of surface samples from the alpine glaciers of taylor valley southern victoria land antarctica for their geochemical composition this was done to better establish the role of glaciochemical variation on the chemical composition of meltwater streams emanating from the glaciers the chemistry of the snow and ice changes with proximity to the ocean and with elevation of the glacier surface the aeolian transport of dry valley dust as indicated by both chemical and particulate matter variations is a major process affecting the overall glacier chemistry and the chemistry of the meltwaters streams originating on the western edges of the glaciers are more impacted by the aeolian input as they are in the direct path of the major regional wind direction our data strongly suggest that the variation in stream geochemistry in taylor valley is a result in part of the differences in chemical composition of glacier melt copyright 2003 john wiley sons ltd

spatial and temporal variation of sublimation on antarctica results of a high resolution general circulation model in this paper we use output of a high resolution general circulation model echam 3 t106 resolution 1 1 x 1 1 to study the spatial and temporal variation of sublimation on antarctica first we compare model results with available observations of sublimation rates the yearly cycle with small latent heat fluxes during the winter is well reproduced and the agreement with sparsely available spot observations is fair the model results suggest that a significant 10 15 of the annual precipitation over antarctica is lost through sublimation and that sublimation plays an important role in the formation of blue ice areas a preliminary analysis of the atmospheric boundary layer moisture budget shows that the spatial variation of sublimation in the coastal zone of east antarctica can be explained by variations of horizontal advection of dry air dry air advection and thus surface sublimation is enhanced in areas where katabatic winds are strong and have a large downslope component and where the antarctic topography drops suddenly from the plateau to the coastal zone in areas where horizontal advection is small like the plateau and the large ice shelves special conditions must be met to make significant sublimation at the surface possible

surface energy balance in the ablation zone of langfjordjokelen an arctic maritime glacier in northern norway glaciers in northern and southern norway are subject to different daily and seasonal cycles of incoming solar radiation which is presumably reflected in the importance of net solar radiation in their surface energy balance we present a 3 year continuous record from an automatic weather station in the ablation zone of the ice cap langfjordjokelen one of the most northerly glaciers of mainland norway despite its location at 708 n langfjordjokelen was found to have a maritime climate with an annual mean air temperature of 1 08c frequent cloud cover and end of winter snow depths over 3m in all three years the main melt season was may october but occasional melt events occurred on warm cloudy winter days net solar and longwave radiation together accounted for 58 of the melt energy with a positive contribution by net longwave radiation 7 the sensible and latent heat fluxes supplied the remainder of the melt energy cloud optical thickness over langfjordjokelen was larger than on two glaciers in southern norway especially in the summer months this resulted in a smaller contribution of net solar radiation to surface melt on langfjordjokelen the effect of the higher latitude on net solar radiation was found to be small

comment on variable head ponded infiltration under constant or variable rainfall by j r philip keywords time equation reference ecol article 1996 002doi 10 1029 95wr03645 url http www agu org journals wr record created on 2005 12 09 modified on 2016 08 08

snow crystal growth with varying surface temperatures and radiation penetration the temperature field is derived for a sinusoidally varying surface temperature with varying solar radiation penetration the growth rates of snow crystals are calculated to explain the rapidly growing layers of faceted crystals i e depth hoar that form just below the surface at high altitudes and in polar snow the solutions also show that a layer of wet snow can exist just below the surface even on days when the surface temperature remains sub freezing

infiltration into fractured bedrock experiment performed on fractured ash flow tuff water was released from a 3 4m 2 infiltration plot divided into 12 square subplots with a head of 0 04 m over a period of 800 days this experiment revealed peculiar infiltration patterns not amenable to current infiltration models which were originally developed for infiltration into soils over a short duration in particular we observed that in part of the infiltration plot the infiltration rate abruptly increased a few weeks into the infiltration tests we suggest that these anomalies result from increases in fracture permeability during infiltration which may be caused by swelling of clay fillings and or erosion of infill debris interaction of the infiltration water with subsurface natural cavities lithophysal cavities could also contribute to such anomalies this paper provides a conceptual model that partly describes the observed infiltration patterns in fractured rock and highlights some of the pitfalls associated with direct extension of soil infiltration models to fractured rock over a long period

firn air depletion as a precursor of antarctic ice shelf collapse since the 1970s the sudden rapid collapse of 20 of ice shelves on the antarctic peninsula has led to large scale thinning and acceleration of its tributary glaciers the leading hypothesis for the collapse of most of these ice shelves is the process of hydrofracturing whereby a water filled crevasse is opened by the hydrostatic pressure acting at the crevasse tip this process has been linked to observed atmospheric warming through the increased supply of meltwater importantly the low density firn layer near the ice shelf surface providing a porous medium in which meltwater can percolate and refreeze has to be filled in with refrozen meltwater first before hydrofracturing can occur at all here we build upon this notion of firn air depletion as a precursor of ice shelf collapse by using a firn model to show that pore space was depleted in the firn layer on former ice shelves which enabled their collapse due to hydrofracturing two climate scenario runs with the same model indicate that during the 21st century most antarctic peninsula ice shelves and some minor ice shelves elsewhere are more likely to become susceptible to collapse following firn air depletion if warming continues into the 22nd century similar depletion will become widespread on ice shelves around east antarctica our model further suggests that a projected increase in snowfall will protect the ross and filchner ronne ice shelves from hydrofracturing in the coming two centuries

a study of the surface mass balance in dronning maud land antarctica using automatic weather stations we use data from four automatic weather stations awss in dronning maud land east antarctica to study the surface mass balance and its components distinct differences were found between the moisture climates of the high plateau the katabatic wind zone and the coastal ice shelves significant undersaturation occurs year round in the katabatic wind zone while on the high plateau and on the coastal ice shelf the air is usually close to saturation in summer absorption of shortwave radiation at the snow surface enhances surface sublimation at all sites removing 3 9 of the annual solid precipitation significant summer melting is an equally important ablation term near the coast but vanishes inland vertically integrated column drifting snow sublimation was estimated using two different methods this process appears to be similar to or greater in magnitude than surface sublimation because intervals between significant precipitation events may last as long as several months sublimation and melt cause extended periods of surface ablation in summer in summer all ablation processes together remove 15 56 of the solid precipitation or 6 27 on an annual basis

on the numerical resolution in a thermodynamic sea ice model the numerical integration of the heat conduction equation is one of the main components in a thermodynamic sea ice model the spatial resolution in the ice normally varies from a minimum of three layers up to a few tens of layers the temporal resolution varies from a few minutes up to hours in this paper the impact of numerical resolution on the prediction of a one dimensional thermodynamic ice model is studied analytical solutions for idealized cases were derived and compared with the numerical results for the full ice model groups of simulations were made applying average climatic weather forcing data corresponding to the ice freezing ice thermal equilibrium and ice warm up seasons special attention was paid to the effect of model spatial resolution early in the freezing season the influence of resolution on model predictions is not significant when the shortwave radiation becomes large its absorption within the ice or snow cover was found to modulate the effect of numerical resolution on predictions of ice temperature and surface heat fluxes e g the model run with a coarse spatial resolution yielded large daily variations in surface temperature resolution also affects the in ice temperature profile for process studies a two layer scheme for the solar radiation penetrating into the ice is suitable for a fine spatial resolution ice model

solar heating rates and temperature profiles in antarctic snow and ice observations of temperature maxima at about 10 cm depth in cold antarctic snow during summer have previously been explained by proposing that solar heating is distributed with depth whereas thermal infrared cooling is localized at the surface the solid state greenhouse an increase in temperature from the surface to 10 cm depth t 4 k found by rusin 1961 on the antarctic plateau was successfully reproduced by schlatter 1972 in a combined radiative transfer and heat transfer model

falling head ponded infiltration it is remarkable that the green ampt or delta function solution for falling head ponded infiltration takes precisely the same functional form as that for constant head infiltration only the values of the constants change falling head infiltration experiments are thus as amenable to green ampt analysis as more complicated constant head experiments

ice melt rates during volcanic eruptions within water drained low pressure subglacial cavities subglacial volcanism generates proximal and distal hazards including large scale flooding and increased levels of explosivity direct observation of subglacial volcanic processes is infeasible therefore we model heat transfer mechanisms during subglacial eruptions under conditions where cavities have become depressurized by connection to the atmosphere we consider basaltic eruptions in a water drained low pressure subglacial cavity including the case when an eruption jet develops such drained cavities may develop on sloping terrain where ice may be relatively shallow and where gravity drainage of meltwater will be promoted we quantify for the first time the heat fluxes to the ice cavity surface that result from steam condensation during free convection at atmospheric pressure and from direct and indirect radiative heat transfer from an eruption jet our calculations indicate that the direct radiative heat flux from a lava fountain a dry end member eruption jet to ice is c 25 kw m 2 and is a minor component the dominant heat transfer mechanism involves free convection of steam within the cavity we estimate the resulting condensation heat flux to be c 250 kw m 2 absorption of radiation from a lava fountain by steam enhances convection but the increase in condensing heat flux is modest at c 25 kw m 2 overall heat fluxes to the ice cavity surface are likely to be no greater than c 300 kw m 2 these are comparable with heat fluxes obtained by single phase convection of water in a subglacial cavity but much less than those obtained by two phase convection

a drive point application of the guelph permeameter method for coarse textured soils abstract the guelph permeameter gp is a widely used well auger hole method for in situ determination of field saturated hydraulic conductivity kfs and sorptive number in the vadose or unsaturated zone its application can be difficult however in gravelly materials which are problematic to auger and in un cohesive sandy materials which collapse during the augering process or upon wetting of the unlined well we circumvented these issues by replacing the gp well with a conically tipped well screen or drive point which is pushed driven rotated or vibrated to the desired depth we also developed a steady flow analysis to account for the fact that water discharge through the drive point screen is solely radial rather than both radial and vertical as in the original gp method the hydrus 2d numerical simulation model was used to determine appropriate shape values cdp for the drive point analysis and an empirical regression equation was developed to convert the discrete cdp values into continuous shape functions for porous materials with negligible moderate strong and very strong capillarity in a well sorted medium coarse sand the drive point method produced kfs and values which were plausible and consistent with other data from the field site the original gp method on the other hand under estimated the drive point results by factors of 2 1 3 1 which may have been caused by progressive collapse of the unlined gp well and or gradual sinking of the gp outflow tip into the unprotected well base it was concluded that the drive point gp method can provide convenient and accurate estimates of kfs and in materials where hydraulic properties are not substantially altered by the disturbance of drive point installation

on the triggering of benguela ninos remote equatorial versus local influences 1 the relative importance of remote and local influences in the development of benguela ninos is examined using observations and a coupled general circulation model capable of simulating interannual variability in the tropical atlantic while previous studies have emphasized the role of equatorially excited kelvin waves the present study finds that meridional wind anomalies along the southwest african coast contribute substantially both observations and model output indicate that sea surface temperatures along the southwest african coast respond rapidly to changes in meridional wind stress these wind anomalies form part of a basin scale weakening of the subtropical anticyclone that extends to the equator as the weakening begins three months before the peak of the event it might have some predictive potential results also indicate that the close correlation between benguela and atlantic ninos in observations might result from the large spatially coherent wind stress anomalies associated with the weakened anticyclone

timing and regional patterns of snowmelt on antarctic sea ice from passive microwave satellite observations an improved understanding of the temporal variability and the spatial distribution of snowmelt on antarctic sea ice is crucial to better quantify atmosphere ice ocean interactions in particular sea ice mass and energy budgets it is therefore important to understand the mechanisms that drive snowmelt both at different times of the year and in different regions around antarctica in this study we combine diurnal brightness temperature differences dtb 37ghz and ratios tb 19ghz tb 37ghz to detect and classify snowmelt processes we distinguish temporary snowmelt from continuous snowmelt to characterize dominant melt patterns for different antarctic sea ice regions from 1988 89 to 2014 15 our results indicate four characteristic melt types on average 38 9 6 0 of all detected melt events are diurnal freeze thaw cycles in the surface snow layer characteristic of temporary melt type a less than 2 reveal immediate continuous snowmelt throughout the snowpack i e strong melt over a period of several days type b in 11 7 4 0 type a and b take place consecutively type c and for 47 8 6 8 no surface melt is observed at all type d continuous snowmelt is primarily observed in the outflow of the weddell gyre and in the northern ross sea usually 17 days after the onset of temporary melt comparisons with snow buoy data suggest that also the onset of continuous snowmelt does not translate into changes in snow depth for a longer period but might rather affect the internal stratigraphy and density structure of the snowpack considering the entire data set the timing of snowmelt processes does not show significant temporal trends

a model assessment of satellite observed trends in polar sea ice extents 1 for more than three decades now satellite passive microwave observations have been used to monitor polar sea ice here we utilize sea ice extent trends determined from satellite data for both the northern and southern hemispheres for the period 1972 73 2004 and assess and interpret them using results from simulations by eleven climate models in the northern hemisphere nh observations show a statistically significant decrease of sea ice extent and an acceleration of sea ice retreat during the past three decades however from the modeled natural variability of sea ice extents in control simulations we conclude that the acceleration is not statistically significant and should not be extrapolated into the future most of the models like the observations show an absence of a prominent seasonal cycle in the trend values both observations and model simulations show that climate variability in sea ice extent in the southern hemisphere sh is much larger than in the nh and that the sh sea ice extent trends are not statistically significant citation vinnikov k y d j cavalieri and c l parkinson 2006 a model assessment of satellite observed trends in polar sea ice extents geophys res lett 33 l05704 doi 10 1029 2005gl025282

a 5 year record of surface energy and mass balance from the ablation zone of storbreen norway a 5 year record of data from an automatic weather station aws operating in the ablation zone of storbreen norway has been used to calculate the local surface energy and mass balance the aws observations cover five mass balance years with an unusually strong mass deficit on storbreen the average energy flux q contributing to melt for the period 2001 06 is 113wm 2 of this the net shortwave radiation flux is the dominant contributor 92wm 2 followed by the sensible heat flux 20 wm 2 and the latent heat flux 9 w m 2 the net longwave radiation 6w m 2 and the subsurface heat flux 2 w m 2 contribute negatively to the budget net radiation thus produces 76 of the melt while the turbulent fluxes and the subsurface heat flux produce 24 of the total melt the seasonal mean incoming shortwave radiation is remarkably constant between the years whereas variations in temperature and reflected shortwave radiation albedo explain most of the interannual variation in melt the modelled ablation compares well with the measured ablation from stake readings the sensitivity of the energy balance model was examined by varying the surface roughness length of momentum and the sensitivity of the calculated melt by perturbations of temperature wind speed and relative humidity

power series solution for falling head ponded infiltration with evaporation 1 assumptions for many of the derived analytical infiltration models are either a constant infiltration rate or a constant head at the soil surface for many realistic infiltration situations a falling head boundary condition is more appropriate philip showed that both the wetting profiles and the cumulated infiltration in one dimensional infiltration into homogenous soil with constant head at the upper boundary can be written as a power series in t presently it is shown that a power series solution can be applied for falling head infiltration with evaporation when comparing with the constant head solution the falling head solution differs only from the second term i e the sorptivity remains unchanged a result which can be applied to falling head infiltrometer technique the effect of a constant evaporation rate in the falling head scenario appears from the third term in the presented numerical examples the retention model by van genuchten and the hydraulic conductivity model by mualem are applied by comparing the wetting profiles obtained with a fem solution it is shown that the discrepancies between the models are very small also the estimation of the time at which the pond is emptied is concordant the infiltration model is compared with a model by parlange and colleagues and a simple infiltrometer method for determining the saturated hydraulic conductivity is proposed

ice flow modelling to constrain the surface mass balance and ice discharge of san rafael glacier northern patagonia icefield we simulate the ice dynamics of the san rafael glacier srg in the northern patagonia icefield 46 7 s 73 5 w using glacier geometry obtained by airborne gravity measurements the full stokes ice flow model elmer ice is initialized using an inverse method to infer the basal friction coefficient from a satellite derived surface velocity mosaic the high surface velocities 7 6 km a 1 near the glacier front are explained by low basal shear stresses 1 km a 1 we force the model using different surface mass balance scenarios taken or adapted from previous studies and geodetic elevation changes between 2000 and 2012 our results suggest that previous estimates of average surface mass balance over the entire glacier were likely too high mainly due to an overestimation in the accumulation area we propose that most of srg imbalance is due to the large ice discharge 0 83 0 08 gt a 1 and a slightly positive 0 08 0 06 gt a 1 the committed mass loss estimate over the next century is 0 34 0 03 gt a 1 this study demonstrates that surface mass balance estimates and glacier wastage projections can be improved using a physically based ice flow model

a comparative stability analysis of atlantic and pacific nino modes abstractel nino southern oscillation enso in the pacific and the analogous atlantic nino mode are generated by processes involving coupled ocean atmosphere interactions known as the bjerknes feedback it has been argued that the atlantic nino mode is more strongly damped than enso which is presumed to be closer to neutrally stable in this study the stability of enso and the atlantic nino mode is compared via an analysis of the bjerknes stability index this index is based on recharge oscillator theory and can be interpreted as the growth rate for coupled modes of ocean atmosphere variability using observational data an ocean reanalysis product and output from an ocean general circulation model the individual terms of the bjerknes index are calculated for the first time for the atlantic and then compared to results for the pacific positive thermocline feedbacks in response to wind stress forcing favor anomaly growth in both basins but they are twice as large in the pacific compared to the atlanti

modeling the isotopic composition of antarctic snow using backward trajectories simulation of snow pit records 1 the quantitative interpretation of isotope records d 18 o dd and d excess in ice cores can benefit from a comparison of observed meteorology with associated isotope variability for this reason we studied four isotope records from snow pits in western dronning maud land dml antarctica covering the period 1998 2001 timing and magnitude of snowfall events on these locations were monitored using sonic height rangers for the distinguished snowfall events we evaluated the isotopic composition of the moisture during transport by combining backward trajectory calculations with isotopic modeling using a rayleigh type distillation model mcim the initial isotope ratio of the moisture was determined frommonthlymeanisotopefields fromageneralcirculation model echam4 the trajectory analysis showed that the southern atlantic ocean is the major moisture sourceforprecipitationindml modelingresultsalongthetrajectoriesrevealedthatmostof the isotopic depletion occurred during the last day of the transport finally a diffusion model was applied to describe the diffusion in the firn layer such that the modeled isotopes couldbecomparedwiththeobservedisotoperecords theresultingmodeledisotopeprofiles were mostly in good agreement with the observed seasonal variability in the snow however at low temperatures especially on the antarctic interior magnitude of the total distillation was underestimated regarding the d excess parameter our results show a large influence of advection height on the final value of d excess in precipitation this in turn points to the importance of the vertical structure of d excess over the oceanic source region which obscures the classical interpretation of this parameter in terms of temperature and relative humidity in the moisture source region

comment on falling head ponded infiltration by j r philip reference ecol article 1995 001doi 10 1029 94wr02565 url http www agu org record created on 2005 12 09 modified on 2016 08 08

baseline characteristics of a debris covered snow covered gorge in a typical japanese mountainous terrain abstract debris covered snow covered gorges dsgs are common in the mountainous environment of the japanese alps in the western pacific region but are almost absent in subdued landscapes where snow melting rates are higher our study demonstrates that the effect of debris coverage on the shrinkage of snow covered gorges of the japanese alps results in differences in how the gorges respond to climate change which has been neglected in predictions of future water availability snow covered gorges and glacial meltwater make important contributions to drinking water irrigation water and hydropower supply in the japanese alps region global warming is expected to increase mountainous river discharge and snowmelt in the short term but long term predictions are uncertain therefore detailed and reliable baseline data about the mountainous environment of the japanese alps and its effects on the cryosphere are essential for predicting the future hydrosphere of japan however field investigations in this region are difficult and to date studies have not collected enough data to fully understand the processes involved supraglacial debris influences the terminus dynamics and can thereby modify the migration of a snow covered gorge under climate change recent studies have found several dsgs that are stagnant i e almost non flowing in the mountainous environments of southwest saskatchewan canada two surface samples were taken on 24 june 2014 and 27 june 2014 to determine the mean grain size of sediment at the site it was found that dsgs extended for several kilometres through valleys in this region our results indicated that the maximum temperature within 10 cm of the ground surface varied from 10 c to 15 c which may be the crucial baseline factor for the existence of dsgs although the increasing rates of meltwater discharge and surface lowering indicate that these snow covered gorges are currently shrinking their fronts remain remarkably stable a phenomenon that has also been observed in other regions the significance of debris cover and its impact on regional differences in the mountainous environment of the japanese alps has not been established in the mountainous valley belt of the region in this study we report the baseline characteristics of dsg during the beginning of the snowmelt period in the extreme mountainous environment region of the japanese alps

falling head ponded infiltration in the nonlinear limit the green and ampt infiltration solution represents only an extreme example of behavior within a larger class of very nonlinear delta function diffusivity soils the mathematical analysis of these soils is greatly simplified by the existence of a sharp wetting front below the soil surface solutions for more realistic delta function soil models have recently been presented for infiltration under surface saturation without ponding after general formulation of the problem solutions for a full suite of delta function soils are derived for ponded surface water depleted by infiltration exact expressions for the cumulative infiltration as a function of time or the drainage time as a function of the initial ponded depth may take implicit or parametric forms and are supplemented by simple asymptotic expressions valid for small times and small and large initial ponded depths as with surface saturation without ponding the green ampt model overestimates the effect of the soil hydraulic conductivity at the opposing extreme a low conductivity model is identified that also takes a very simple mathematical form and appears to be more accurate than the green ampt model for larger ponded depths between these two the nonlinear limit of gardner s soil is recommended as a physically valid first approximation relative discrepancies between different soil models are observed to reach a maximum for intermediate values of the dimensionless initial ponded depth and in general are smaller than for surface saturation without ponding

climate science tropical atlantic warm events sea surface temperatures in the eastern equatorial atlantic ocean are subject to year to year variations reanalysis data and model simulations suggest that advection of warm water from north of the equator can drive some of the warm events

effects of bubbles cracks and volcanic tephra on the spectral albedo of bare ice near the transantarctic mountains implications for sea glaciers on snowball earth 1 spectral albedo was measured along a 6 km transect near the allan hills in east antarctica the transect traversed the sequence from new snow through old snow firn and white ice to blue ice showing a systematic progression of decreasing albedo at all wavelengths as well as decreasing specific surface area ssa and increasing density broadband albedos under clear sky range from 0 80 for snow to 0 57 for blue ice and from 0 87 to 0 65 under cloud both air bubbles and cracks scatter sunlight their contributions to ssa were determined by microcomputed tomography on core samples of the ice although albedo is governed primarily by the ssa and secondarily by the shape of bubbles or snow grains albedo also correlates highly with porosity which as a proxy variable would be easier for ice sheet models to predict than bubble sizes albedo parameterizations are therefore developed as a function of density for three broad wavelength bands commonly used in general circulation models visible near infrared and total solar relevance to snowball earth events derives from the likelihood that sublimation of equatorward flowing sea glaciers during those events progressively exposed the same sequence of surface materials that we measured at allan hills with our short 6 km transect representing a transect across many degrees of latitude on the snowball ocean at the equator of snowball earth climate models predict thick ice or thin ice or open water depending largely on their albedo parameterizations our measured albedos appear to be within the range that favors ice hundreds of meters thick

the interaction of katabatic winds and the formation of blue ice areas in east antarctica blue ice areas bias are an extreme example of a local mass balance gradient and are furthermore reasonably stable in time and space owing to local feed back mechanisms a meteorological experiment performed in and around a blue ice area in dronning maud land east antarctica showed that during driftingsnow conditions surface wind speed over the blue ice behind the mountain barrier is equal to that away from the mountains when corrected for surface roughness and stability this implies that use of diagnostic katabatic wind models to estimate divergence of drifting snow can be extended to the situation where nunataks are involved in preventing the drifting snow from passing which is the case for most bias a diagnostic model is tested for a two dimensional profile in terre adelie after which it is applied to entire east antarctica the present order of magnitude estimate shows that areas sensitive to blue ice formation appear where precipitation is low and mean annual wind speed is high i e in dronning maud land and the drainage basin of lambert glacier the results appeared to be especially sensitive to a change in inversion strength a decrease in inversion strength weakens the katabatic flow and thus the amount of snowdrift transport reducing the area where bias can develop

water flow through temperate glaciers understanding water movement through a glacier is fundamental to several critical issues in glaci ology including glacier dynamics glacier induced floods and the prediction of runoff from glacierized drainage basins to this end we have synthesized a conceptual model of water movement through a temper ate glacier from the surface to the outlet stream pro cesses that regulate the rate and distribution of water input at the glacier surface and that regulate water movement from the surface to the bed play important but commonly neglected roles in glacier hydrology where a glacier is covered by a layer of porous perme able firn the accumulation zone the flux of water to the glacier interior varies slowly because the firn tempo rarily stores water and thereby smooths out variations in the supply rate in the firn free ablation zone in con trast the flux of water into the glacier depends directly on the rate of surface melt or rainfall and therefore varies greatly in time water moves from the surface to the bed through an upward branching arborescent net work consisting of both steeply inclined conduits formed by the enlargement of intergranular veins and gently inclined conduits spawned by water flow along the bottoms of near surface fractures crevasses engla cial drainage conduits deliver water to the glacier bed at a limited number of points probably a long distance downglacier of where water enters the glacier englacial conduits supplied from the accumulation zone are quasi steady state features that convey the slowly varying water flux delivered via the firn their size adjusts so that they are usually full of water and flow is pressurized in contrast water flow in englacial conduits supplied from the ablation area is pressurized only near times of peak daily flow or during rainstorms flow is otherwise in an open channel configuration the subglacial drainage system typically consists of several elements that are distinct both morphologically and hydrologically an up glacier branching arborescent network of channels in cised into the basal ice conveys water rapidly much of the water flux to the bed probably enters directly into the arborescent channel network which covers only a small fraction of the glacier bed more extensive spatially is a nonarborescent network which commonly includes cav ities gaps between the glacier sole and bed channels incised into the bed and a layer of permeable sediment the nonarborescent network conveys water slowly and is usually poorly connected to the arborescent system the arborescent channel network largely collapses during winter but reforms in the spring as the first flush of meltwater to the bed destabilizes the cavities within the nonarborescent network the volume of water stored by a glacier varies diurnally and seasonally small temper ate alpine glaciers seem to attain a maximum seasonal water storage of 200 mm of water averaged over the area of the glacier bed with daily fluctuations of as much as 20 30 mm the likely storage capacity of subglacial cavities is insufficient to account for estimated stored water volumes so most water storage may actually occur englacially stored water may also be released abruptly and catastrophically in the form of outburst floods

approximate analysis of falling head lined borehole permeameter the falling head lined borehole permeameter consists of a snugly fitting tube extending to the base of a vertical borehole in unsaturated soil water is suddenly introduced into the tube to standard depth and the subsequent time course of water depth is observed soil water data in the amazon basin has been secured with this instrument we develop an approximate analysis based on a green ampt model with the flow treated as a gravity perturbed spherically symmetrical pressure capillarity driven flow

snow atmosphere coupled simulation at dome c antarctica using a snow atmosphere coupled model the evolution of the surface and near surface snow temperature is modeled at dome c antarctica during the period 20 30 january 2010 firstly the detailed multilayer snow model crocus is run in stand alone mode with meteorological input forcing data provided by local meteorological observations the snow model is able to simulate the evolution of surface temperature with good accuracy it reproduces the observed downward propagation of the diurnal heatwave into the upper 50 cm of the snowpack reasonably well secondly a fully coupled 3 d snow atmosphere simulation is performed with the arome regional meteorological model for which the standard single layer snow parameterization is replaced by crocus in spite of a poor simulation of clouds the surface and near surface snow temperatures are correctly simulated showing neither significant bias nor drifts during the simulation period the model reproduces particularly well the average decrease of the diurnal amplitude of air temperature from the surface to the top of the 45 m instrumented tower this study highlights the potential of snow atmosphere coupled models over the antarctic plateau and the need to improve cloud microphysics and data assimilation over polar regions

sea surface temperature variability in the tropical southeast atlantic ocean and west african rainfall 1 evidence is presented of a connection between sea surface temperature sst variability in the tropical southeast atlantic ocean off angola and boreal summer rainfall over coastal west africa the strongest relationships exist between april may sst in the angola benguela frontal zone area may june latent heat fluxes in this area and july august rainfall over the region 5 w 5 e 5 n 10 n anomalously wet summers in this region are also characterised by a weaker african easterly jet a stronger tropical easterly jet and in many cases reduced rainfall further north over the southern sahel

coupled effects of canal lining and multi layered soil structure on canal seepage and soil water dynamics ponding tests were conducted in the shiyang river basin in northwest china to assess canal leakage characteristics four anti seepage constructions concrete lining pebble lining clay lining plus compacted canal bed compacted canal bed only were performed on four canal sections which were situated in multi layered soils the canal sections were tested using a two stage approach first a stable water level was maintained followed by a stage where the water level in the canal section was permitted to drop the canal seepage rate and the soil water content near the canal bed were monitored during the stable and dropping stages soil texture bulk density and hydraulic conductivity were tested in each canal section and soil layer double ring infiltration tests were performed to investigate infiltration behaviour from the canal sections the saturated unsaturated flow model hydrus 2d was applied to simulate canal seepage and the local soil water response the simulation results compared well with the monitored data indicating that the model can reliably simulate canal seepage under these complex soil structures and different canal liners both experimental results and numerical modelling show that the clay lining plus compacted canal bed provides the best anti seepage performance followed by compacted canal bed only then pebble and concrete lining simulation results also predicted that the soil water content was discontinuous at the interface of distinct soil layers and that the range and form of wetting front varied greatly in the four canal sections with a larger wetted area for the more permeable canals simulations were performed to study the sensitivity on canal seepage of to the permeability of each soil lining layer and the lining effect on canal seepage the results confirmed by double ring infiltration tests indicated that the canal lining is not the only dominant factor affecting canal seepage the soil permeability can also influence the seepage greatly especially where there exists a low permeability layer e g compacted soil layer close to the canal

seismic multiplet response triggered by melt at blood falls taylor glacier antarctica 1 meltwater input often triggers a seismic response from glaciers and ice sheets it is difficult however to measure melt production on glaciers directly while subglacial water storage is not directly observable therefore we document temporal changes in seismicity from a dry based polar glacier taylor glacier antarctica during a melt season using a synthesis of seismic observation and melt modeling we record icequakes using a dense six receiver network of three component geophones and compare this with melt input generated from a calibrated surface energy balance model in the absence of modeled surface melt we find that seismicity is well described by a diurnal signal composed of microseismic events in lake and glacial ice during melt events the diurnal signal is suppressed and seismicity is instead characterized by large glacial icequakes we perform network based correlation and clustering analyses of seismic record sections and determine that 18 of melt season icequakes are repetitive multiplets the epicentral locations for these multiplets suggest that they are triggered by meltwater produced near a brine seep known as blood falls our observations of the correspondingp wave first motions are consistent with volumetric source mechanisms we suggest that surface melt enables a persistent pathway through this cold ice to an englacial fracture system that is responsible for brine release episodes from the blood falls seep the scalar moments for these events suggest that the volumetric increase at the source region can be explained by melt input

a benchmark dataset of in situ antarctic surface melt rates and energy balance abstract surface melt on the coastal antarctic ice sheet ais determines the viability of its ice shelves and the stability of the grounded ice sheet but very few in situ melt rate estimates exist to date here we present a benchmark dataset of in situ surface melt rates and energy balance from nine sites in the eastern antarctic peninsula ap and coastal dronning maud land dml east antarctica seven of which are located on ais ice shelves meteorological time series from eight automatic and one staffed weather station neumayer ranging in length from 15 months to almost 24 years serve as input for an energy balance model to obtain consistent surface melt rates and energy balance results we find that surface melt rates exhibit large temporal spatial and process variability intermittent summer melt in coastal dml is primarily driven by absorption of shortwave radiation while non summer melt events in the eastern ap occur during fohn events that force a large downward directed turbulent flux of sensible heat we use the in situ surface melt rate dataset to evaluate melt rates from the regional atmospheric climate model racmo2 and validate a melt product from the quikscat satellite

warm events in the tropical atlantic abstract sea surface temperature in the eastern equatorial atlantic ocean undergoes anomalous warming events of 1 2 c every few years the warm anomalies reach their maximum strength in northern hemisphere summer when equatorial upwelling normally brings cold thermocline water to the surface by compositing surface observations from a 28 year record we are able to identify consistent features in anomalies of sst and winds the composites show that the sst anomalies in northern summer are confined to the eastern equatorial region with reduced zonal winds to the west and reduced northward trade winds to the east accompanying these changes in winds are enhanced convection near the equator caused by a southward shift and intensification of the intertropical convergence zone later in the year sst south of the equator becomes elevated as a result by spring of the year following the equatorial anomaly convection in the western side of the basin is much higher than normal to understand the ocean dynami