snow grain size profiles deduced from microwave snow emissivities in antarctica spaceborne microwave radiometers are an attractive tool for observing antarctic climate because their measurements are related to the snow temperature however the conversion from microwave emission to snow temperature is not simple and strongly depends on the emissivity through snow properties this difficulty in predicting the snow property profile for antarctic conditions is the main bottleneck in the retrieval of accurate climate information from microwave radiometers we attempt to explain the vertically polarized emissivity at 19 3 and 37 ghz derived from brightness temperatures acquired by the special sensor microwave imager ssm i and physical temperature from the era 40 re analysis in antarctica the snow emissivities at 19 3 and 37 ghz are nearly equal although a decrease with frequency is expected to explain this we consider various profiles of snow grain size and density and predict their emissivity using a dense medium radiative transfer dmrt model the results show that the emissivities cannot be explained by constant profiles of grain size and density heterogeneous snowpacks need to be considered we first test random variations of snow density and grain radius with depth and then monotonic and continuous variations in the snow grain radius in both cases we show that an overall increase of the snow grain radius with depth is required to match the observed emissivity in antarctica in addition two parameters characterizing the snow grain profiles are retrieved and compared with 1 in situ measurements of grain size at various locations in east antarctica 2 grain size estimated using visible spaceborne radiometers and 3 a semi empirical relationship for grain growth

open and almost shut case for explosive eruptions vent processes determined by so2 emission rates at karymsky volcano kamchatka vent processes were examined at karymsky volcano kamchatka by measuring so2 emissions using a correlation spectrometer cospec continuous high sensitivity cospec measurements and physical observations were collected on 11 and 12 september 1999 when karymsky was producing small ashy eruptions every 5 20 min each eruptive event began with an explosion and audible rumbling lasting 30 s followed in some cases by audible chugging lasting to 2 min gas plumes accompanied each event and almost without exception the plumes dissipated and became invisible despite significant so2 emissions variations in so2 output show distinctive patterns that correlate with eruption activity maximum so2 output occurred following each explosion and then declined rapidly to low but detectable levels in contrast a second type of event often associated with audible chugging was characterized by high so2 output long after the initial ash blast variations in degassing at karymsky can be explained by secondary boiling gas pressure accumulation and vent resealing we developed a new application of the cospec technique to study the dynamic vent processes of erupting volcanoes this application provides insights into the processes that occur at the otherwise inaccessible vents of erupting volcanoes particularly when a volcano changes from passive degassing and small explosions to degassing patterns that may precede a larger and more dangerous eruption

cryosphere applications of nscat data though designed to measure vector winds over the ocean new imaging techniques facilitate the use of nasa scatterometer data nscat in cryosphere studies nscat provides data of unprecedented coverage resolution and quality which when coupled with the scatterometer image reconstruction with filtering sirf algorithm enables images of spl sigma sup o at resolutions approaching 8 km over stationary targets such images are useful in ice mapping and classification and multidecadal studies are possible by comparison with seasat scatterometer sass data the utility of nscat data in polar ice studies is illustrated through a review of two cryosphere applications of nscat data 1 sea ice mapping and tracking and 2 ice sheet change in greenland and antarctica the wide swath and frequent revisit coupled with incidence and azimuth angle diversity makes nscat data very effective in mapping the extent of sea ice in greenland snow and ice facies are clearly delineated on the basis of the seasonally dependent radar backscattering cross section due to sensitivity of radar backscatter to diagenetic changes occurring at and beneath the surface comparison of nscat and sass data enables study of change in greenland between 1978 and 1996

a review on phreatic eruptions and their precursors abstract an analysis of the reported information on 132 historical phreatic events indicates that most of these 115 were not followed by a magmatic or phreatomagmatic eruption only in 18 cases precursory phenomena are reportedly lacking whereas they are recognized for the majority 72 of the considered cases these precursors have been analyzed as a function of the kind of phreatic event and of its possible triggering mechanism unfortunately the quality of the available information is poor however data suggest that anomalous seismicity ground deformation changes in the output chemistry and temperature of fumaroles and thermal springs are potential mid term precursors whereas seismic tremor is a common short term precursor

spatial resolution improvement of ssm i data with image restoration techniques a space variant image restoration algorithm has been developed with the aim of improving the spatial resolution of ssm i special sensor microwave imager passive microwave imagery due to the conical scanning of the instrument the relative geometry of the data samples changes over the scan this change is accounted for by using a space variant point spread function in the restoration algorithm application of this algorithm to a scene from the weddell sea results in an image with enhanced ice edge and coast definition as a result ice concentration estimates near the edge agree more closely with higher resolution optical data from avhrr

retrieving snowpack properties and accumulation estimates from a combination of sar and scatterometer measurements this study combines two satellite radar techniques low resolution c ku band scatterometer and high resolution c band synthetic aperture radar sar for glaciological studies in particular mass balance estimations three parameters expressing the mean backscattering and its dependency on azimuth and incidence angle are used to describe and classify the antarctic ice sheets backscattering behavior simple linear regression analyses are carried out between ground truth accumulation data and the sar backscattering coefficient along continuous profile lines from this we parameterize the accumulation rate separately for certain snow pack regimes we find that sar data can be used to map mass balance changes however only within limited areas applying this method therefore generally requires accurate ground truth for regional calibration together with additional information regarding mean air temperature or elevation this investigation focuses on the area of dronning maud land antarctica we present the first high resolution accumulation map based on sar data for the surrounding area of the epica deep ice core drilling site kohnen which is compared to reliable ground truth records as well as to a surface mass balance map interpolated from these at low resolution

growth of greenland ice sheet measurement measurements of ice sheet elevation change by satellite altimetry show that the greenland surface elevation south of 72 degrees north latitude is increasing the vertical velocity of the surface is 0 20 0 06 meters per year from measured changes in surface elevations at 5906 intersections between geosat paths in 1985 and seasat in 1978 and 0 28 0 02 meters per year from 256 694 intersections of geosat paths during a 548 day period of 1985 to 1986

ers 1 radar and field observed characteristics of autumn freeze up in the weddell sea ers 1 satellite microwave radar data are analyzed to investigate changes in sea ice characteristics during a period when a drifting ice camp was deployed in the weddell sea antarctica synthetic aperture radar and scatterometer data are calibrated and geolocated to derive a time series of c band backscatter coefficient corresponding with simultaneous surface measurements during the austral autumn freeze up thermistor strings were implanted in the snow and ice at a number of local and regional sites surface measurements at these sites indicate that up to 50 of the surface of ice floes surviving the summer were flooded with an unconsolidated saline slush layer at the snow ice interface consisting of approximately half seawater and half ice of meteoric origin the slush was typically 5 30 cm thick and covered by a 20 to 50 cm thick dry snow layer results show that the microwave radar backscatter characteristics of this perennial ice region responded sensitively to changes in air temperature and corresponding changes in turbulent flux of heat at the surface of the sea ice at ice concentrations exceeding 95 the modulation of the regional backscatter coefficient by wind speed and direction was negligible warm summer conditions persisted for around 2 weeks after ice camp deployment on february 7 day 38 with air temperatures of around 3 to 5 c prior to the onset of autumn freeze up from february 26 day 57 onward cooling began and snow ice growth proceeded as air temperatures fell to below 20 c altogether between february 7 day 38 and march 15 1992 day 75 the backscatter coefficient time series measured by each radar indicated that fell by several decibels during the freezing and transformation of the layer of saturated saline basal snow into snow ice this change is caused by a reduction in the permittivity and thus the scattering intensity of the basal snow as a function of the disappearance by freezing of the saltwater saturated layer these results suggest the possibility of monitoring the timing and autumn freeze up transition of regional ice signatures as a means of quantifying the proportion of flooded perennial sea ice

rapid change of snow surface properties at vostok east antarctica revealed by altimetry and radiometry we present results of snow surface properties using the envisat dual frequency altimeter at s 3 2 ghz and ku 13 6 ghz bands and the amsr e microwave radiometer at frequencies ranging between 6 and 36 ghz in the vostok region east antarctica the altimetric time series observed between 2002 and 2008 show variations at 3 different time scales daily seasonal and inter annual that correlate directly with variations in the snow surface properties in this study we focus on the analysis of the rapid daily event occurring on february 14th 2005 that created a jump of the backscatter coefficient of up to 5 3 db at the s band and 2 5 db at the ku band the ratio of v h polarization brightness temperature slowly decreased in december and january 2005 and suddenly increased on february 14th 2005 the origin of this rapid event is investigated using aws data from vostok station altimetric and radiometric data simultaneously both snow surface density and roughness are found to vary during this event this event is shown to be synchronous with strong wind occuring during a period of anomalous wind direction and the presence of surface hoar these particular conditions certainly modified the snow surface roughness and thus impacted the altimetric signal we finally investigate the impact of this event on the calculation of the regional ice sheet mass balance using different corrections of height with echo shape variations it is shown to be negligible only if the full echo shape correction legresy et al 2006 is used

shallow s wave attenuation and actively degassing magma beneath taal volcano philippines taal volcano philippines is one of the world s most dangerous volcanoes given its history of explosive eruptions and its close proximity to populated areas a real time broadband seismic network was recently deployed and has detected volcano tectonic events beneath taal our source location analysis of these volcano tectonic events using onset arrival times and high frequency seismic amplitudes points to the existence of a region of strong attenuation near the ground surface beneath the east flank of volcano island in taal lake this region is beneath the active fumarolic area and above sources of pressure contributing inflation and deflation and it coincides with a region of high electrical conductivity the high attenuation region matches that inferred from an active seismic survey conducted at taal in 1993 these features strongly suggest that the high attenuation region represents an actively degassing magma body near the surface that has existed for more than 20 years

passive polarimetric microwave signatures observed over antarctica windsat fully polarimetric passive microwave observations expressed in the form of the stokes vector were analyzed over the antarctic ice sheet the vertically and horizontally polarized brightness temperatures first two stokes components from windsat are shown to be consistent with previous studies azimuthal modulations in the third and fourth stokes components were analyzed and related to surface topography roughness and snow morphology a second harmonic sine function of the azimuth angle was used to estimate the orientation angle of snow features such as topographic slope and sastrugi the results show good agreement with the orientations derived in a previous study using scatterometer data at similar frequencies seasonal variability in the third and fourth stokes components is discussed a consistent pattern of response emerged for 10 7 ghz under winter conditions the large contribution of multiple volume scattering causes a high and regionally varying 10 7 ghz fourth stokes signal under summer conditions surface scattering dominates and results in a high 10 7 ghz third stokes signal the third and fourth stokes observations at 37 ghz were found to correspond to the smaller penetration depth at this higher frequency resulting in a low difference between the amplitudes of summer and winter the study demonstrates the potential of the spaceborne fully polarimetric passive microwave radiometers in monitoring the thermal and morphological properties of large ice sheets

relative partitioning of acoustic and seismic energy during strombolian eruptions the relative elastic energy partitioning during strombolian eruptions can be estimated from acoustic pressure and seismic velocity records we outline methods for determining acoustic and seismic energies for sensors deployed within several kilometers of erupting vents we use these energies to introduce the concept of the volcano acoustic seismic ratio g or vasr which is the ratio of elastic energy propagated through the atmosphere and into the earth eruption vasr is a physical diagnostic of explosive degassing that is appropriate for comparing eruption mechanisms at individual and between various volcanoes here we assess acoustic and seismic energies and corresponding vasr for discrete strombolian explosive events at karymsky and erebus volcanoes we attribute the relatively high and stable vasr at erebus g 8 standard deviation 41 to repeatable source conditions occurring at the surface of a persistent lava lake with accompanying strong coupling to the atmosphere lower and more variable vasr at karymsky g 0 18 in 1998 to g 1 51 in 1991 with standard deviations of 93 and 313 respectively is attributed to changing conditions within a narrow partially choked conduit variable seismoacoustic energy partitioning for karymsky as manifested by the large vasr standard deviation suggests that conduit conditions affecting vasr which include magma properties conduit obstruction or fragmentation depths can evolve both during the course of an explosion and between successive events d 2005 elsevier b v all rights reserved

azimuth variation in microwave scatterometer and radiometer data over antarctica while designed for ocean observation scatterometer and radiometer data have proven very useful in a variety of cryosphere studies over large regions of antarctica ice sheet and bedrock topography and the snow deposition drift and erosional environment combine to produce roughness on various scales roughness ranges from broad basin scale ice sheet topography at spl sim 100 km wavelengths to large spatially coherent dune fields at spl sim 10 km wavelength to erosional features on the meter scale known as sastrugi these roughness scales influence the microwave backscattering and emission properties of the surface combining to introduce azimuth angle dependencies in the satellite observation data in this paper the authors explore the use of nasa scatterometer nscat data european remote sensing ers advanced microwave instrument ami scatterometer mode data and special sensor microwave imager ssm i data to study surface roughness effects in antarctica all three sensors provide strong evidence of azimuth modulation which is correlated with the surface slope environment and results in a katabatic wind flow regime due to its broad azimuth coverage nscat data appears to be the best suited for azimuth angle observations a simple empirical model for the azimuth variation in the radar backscatter is developed and an algorithm for computing the parameters of the model from nscat data at a fine scale is presented results indicate relationships exist between the azimuthal variation of the data and the orientation of the surface slope and small scale roughness relative to the sensor look direction

seismicity accompanying the 1999 eruptive episode at telica volcano nicaragua abstract telica volcano nicaragua is a persistently restless basaltic andesite stratovolcano located in the central american volcanic front a high rate of low frequency seismic events lfs has been recorded at telica since the installation of a single vertical component 1 hz seismic sensor teln near its summit in 1993 due to the high rate of lfs at telica traditional methods of forecasting volcanic activity based on increases in the overall rate of seismicity are not applicable therefore an understanding of the nature of precursory changes in telica s seismicity is necessary to forecast future volcanic activity in may 1999 a nine month eruptive episode started at telica consisting of phreatic to phreatomagmatic explosions here we analyse over 29 000 seismic events recorded during a fifteen month period of seismicity bracketing this eruptive episode in an attempt to retrospectively identify precursory changes in seismicity seismic event rates between january 1999 and march 2000 show a reduction in the lf event rate three months before the onset of eruptive activity closely followed by a short lived swarm of high frequency hf 5 hz events after a three month data gap a second reduction in the lf event rate started in august 1999 directly following eruptive activity in august and approximately two months before a series of explosions in october 1999 this reduction in the lf event rate was closely followed by a short lived swarm of hf events that was coincident with the onset of numerous 22 short lived but populous lf multiplets a further reduction in event rate for both lfs and hfs is evident in the months between the october 1999 explosions and explosions on the 29th of december 1999 we suggest that these changes in seismicity reflect a transition from open system degassing to closed system degassing at telica and could signify a change in the volcanic system preceding future episodes of phreatic to phreatomagmatic activity at telica and similar persistently restless volcanic systems worldwide we note that these signals are for phreatic to phreatomagmatic activity and thus may not pertain to magmatic volcanism or to other persistently restless volcanoes prior to their magmatic activity

azimuthal modulation of c band scatterometer spl sigma sup 0 over southern ocean sea ice in a continuing evaluation of the ers 1 c band scatterometer as a tool for studying polar sea ice the authors evaluate the azimuthal modulation characteristics of antarctic sea ice ers 1 ami scatterometer mode data sets from several study regions dispersed in the antarctic seasonal sea ice pack are evaluated for azimuthal modulation when appropriate the incidence angle dependence is estimated and removed in a study region before determining whether azimuthal modulation is present in the data other comparisons are made using the fore and aft beam measurement difference the results show that over the ice pack azimuthal modulation is less than 1 db at the scale of observation of the ers 1 c band scatterometer

greenland snow accumulation estimates from satellite radar scatterometer data data collected by the c band ers 2 wind scatterometer escat the ku band adeos 1 nasa scatterometer nscat and the ku band seawinds on quikscat qscat satellite instruments are used to illustrate spatiotemporal variability in snow accumulation on the greenland ice sheet microwave radar backscatter images of greenland are derived using the scatterometer image reconstruction sir method at 3 day intervals over the periods 1991 1998 and 1996 1997 for escat and nscat respectively the backscatter coefficient normalized to 40 incidence a and gradient in backscatter b in the range 20 60 are compared with historical snow accumulation data and recent measurements made in the program for arctic regional climate assessment parca shallow snow pits empirical relationships derived from these comparisons reveal different exponential relationships between c and ku band a values and dry snow zone mean annual accumulation q frequency difference images between overlapping scatterometer images suggest that c band data are more sensitive to snow layering and buried inhomogeneities whereas ku band data are more sensitive to volume scattering from recently accumulated snow direct comparisons between nscat b values and in situ q measurements show a linear relationship between ln q and b with a negative rank correlation of r 0 8 the root mean square residual in fitting regression line equation ln q 3 08 17 83b to the data is 0 05 m snow water equivalent this simple ku band empirical relationship is exploited to investigate decadal changes in dry snow zone accumulation between seasat 1978 and nscat 1996 additional comparisons between nscat and recent qscat 1999 data reveal significant upslope shifts in the dry snow line along the southwestern flank of the ice sheet recent acceleration in the increase in intensity of scattering is observed in the percolation zone suggesting increased melting between 2000 and 3000 m elevation in the southern half of the ice sheet

extent of low accumulation wind glaze areas on the east antarctic plateau implications for continental ice mass balance persistent katabatic winds form widely distributed localized areas of near zero net surface accumulation on the east antarctic ice sheet eais plateau these areas have been called glaze surfaces due to their polished appearance they are typically 2 200km2 in area and are found on leeward slopes of ice sheet undulations and megadunes adjacent leeward high accumulation regions isolated dunes are generally smaller and do not compensate for the local low in surface mass balance smb we use a combination of satellite remote sensing and field gathered datasets to map the extent of wind glaze in the eais above 1500m elevation mapping criteria are derived from distinctive surface and subsurface characteristics of glaze areas resulting from many years of intense annual temperature cycling without significant burial our results show that 11 2 1 7 or 950 143 103 km2 of the eais above 1500m is wind glaze studies of smb interpolate values across glaze regions leading to overestimates of net mass input using our derived wind glaze extent we estimate this excess in three recent models of antarctic smb at 46 82 gt the lowest input model appears to best match the mean in regions of extensive wind glaze

modeling time series of microwave brightness temperature at dome c antarctica using vertically resolved snow temperature and microstructure measurements time series of observed microwave brightness temperatures at dome c east antarctic plateau were modeled over 27 months with a multilayer microwave emission model based on dense medium radiative transfer theory the modeled time series of brightness temperature at 18 7 and 36 5 ghz were compared with advanced microwave scanning radiometer eos observations the model uses in situ high resolution vertical profiles of temperature snow density and grain size the snow grain size profile was derived from near infrared nir reflectance photography of a snow pit wall in the range 850 1100 nm to establish the snow grain size profile from the nir reflectance and the specific surface area of snow two empirical relationships and a theoretical relationship were considered in all cases the modeled brightness temperatures were overestimated and the grain size profile had to be scaled to increase the scattering by snow grains using a scaling factor and a constant snow grain size below 3 m depth i e below the image derived snow pit grain size profile brightness temperatures were explained with a root mean square error close to 1 k most of this error is due to an overestimation of the predicted brightness temperature in summer at 36 5 ghz

anisotropy repeating earthquakes and seismicity associated with the 2008 eruption of okmok volcano alaska 1 we use shear wave splitting sws analysis and double difference relocation to examine temporal variations in seismic properties prior to and accompanying magmatic activity associated with the 2008 eruption of okmok volcano alaska using bispectrum cross correlation a multiplet of 25 earthquakes is identified spanning five years leading up to the eruption each event having first motions compatible with a normal fault striking ne sw cross correlation differential times are used to relocate earthquakes occurring between january 2003 and february 2009 the bulk of the seismicity prior to the onset of the eruption on 12 july 2008 occurred southwest of the caldera beneath a geothermal field earthquakes associated with the onset of the eruption occurred beneath the northern portion of the caldera and started as deep as 13 km subsequent earthquakes occurred predominantly at 3 km depth coinciding with the depth at which the magma body has been modeled using geodetic data automated sws analysis of the okmok catalog reveals radial polarization outside the caldera and a northwest southeast polarization within we interpret these polarizations in terms of a magma reservoir near the center of the caldera which we model with a mogi point source sws analysis using the same input processing parameters for each event in the multiplet reveals no temporal changes in anisotropy over the duration of the multiplet suggesting either a short term or small increase in stress just before the eruption that was not detected by gps or eruption triggering by a mechanism other than a change of stress in the system

multidisciplinary observations of the 2011 explosive eruption of telica volcano nicaragua implications for the dynamics of low explosivity ash eruptions we present multidisciplinary observations of the march june 2011 vei 2 eruptive episode of the basalticandesite telica volcano nicaragua which allow for a comprehensive study of the eruption mechanics of low explosivity eruptions at persistently active volcanoes the observations are from a dense network of seismic and gps instrumentation augmented by visual observations of the eruptive episode geochemical and petrologic analysis of eruptive products plume so2 measurements and temperature measurements of fumaroles inside and outside the active vent the 2011 eruptive episode was telica s most explosive since 1999 and consisted of numerous vulcanian explosions with maximum column heights of 1 5 2 km above the crater rim depositing a low volume of dominantly hydrothermally altered ash based on observed variations in seismicity temperature and so2 flux the lack of deformation of the edifice the non juvenile origin of and predominance of accretionary lapilli in the ash we propose that temporary sealing of the hydrothermal system between similar to 0 5 and 2 km depth allowed pressure to build up prior to vulcanian explosions making this a phreatic eruptive episode

studies of the location of azimuth modulation minima for ku band ocean radar backscatter an extensive data set of radar backscatter measurements at 14 ghz was used to evaluate the locations of the azimuthal modulation minima relative to the cross wind directions it was found that the minima were significantly offset from the cross wind directions toward the downwind direction for the horizontal polarization data these offsets were substantially smaller for the vertical polarization data simple scattering model calculations based on the two scale scattering approach also show similar offsets implications of these results for the geophysical model function are discussed

thermal deformation and degassing remote sensing time series ce 2000 2017 at the 47 most active volcanoes in latin america implications for volcanic systems

observation and characterization of radar backscatter over greenland characterization of the microwave signature of the greenland snow surface enables delineation of the different snow facies and is a tool for tracking the effects of climate change a new empirical observation model is introduced that uses a limited number of parameters to characterize the snow surface based on the dependence of radar backscatter on incidence angle azimuth angle spatial gradient and temporal rate of change the individual model parameters are discussed in depth with examples using data from the nasa scatterometer nscat and from the c band european remote sensing ers satellite advanced microwave instrument in scatterometer mode the contribution of each model term to the overall accuracy of the model is evaluated the relative contributions of the modeled dependencies vary by region two studies illustrating applications of the model are included first interannual changes over the greenland ice sheet are investigated using nine years of ers data surface changes are observed as anomalies in the spl sigma spl deg model parameters second intraannual variations of the surface are investigated these changes are observed in the average backscatter normalized to a given observation geometry the results indicate that the model can be used to obtain a more complete understanding of multiyear change and to obtain low variance high temporal resolution observations of intraannual changes the model may be applied for increased accuracy in scatterometer synthetic aperture radar sar and wide angle sar studies

snow facies over ice sheets derived from envisat active and passive observations this paper aims to separate different snow regions over the terrestrial ice sheets based on their measured microwave signatures it takes advantage of coregistered data from passive and active sensors on the environmental satellite envisat to directly derive a snow facies indicator in a point by point basis this paper represents the first attempt of this kind in exploiting nadir viewing and dual frequency data from both altimeter and radiometer sensors the approach is based on a clustering method such representation of the data by means of fewer clusters necessarily loses fine details but achieves simplification in geographical representation and eases the description of the condition of the ice sheets in 2004 our approach broadens the description of the snow pack by taking into account characteristics such as surface roughness grain size stratification and snowmelt effects whereas the latter has often solely been considered in most previous work such partition of the ice sheets might help to better understand relationships between microwave signatures and snow morphology it could also be useful for estimating elevation uncertainty in altimeter data which in turn is essential to correctly interpret the significance of the rates of elevation change in a changing climate and to convert elevation change to snow mass change

high resolution temperature observations of a trapped nonlinear diurnal tide influencing cold water corals on the logachev mounds abstract a high resolution thermistor string mooring of 120 m length was used to measure turbulence processes in the water layer above the foot of a densely populated cold water coral mound at 919 m depth at the southeast slope of rockall bank in the logachev area north east atlantic ocean as expected from previous current observations the temperature data reveal a dominant diurnal tidal periodicity associated with topography trapped weakly bottom intensified waves these baroclinic diurnal waves are driven to near resonance around the mound and have vertical amplitudes exceeding the mooring line their horizontal excursion length matches the size of the mound which causes a residual current around and flux up the mound as their particle velocities also match the phase speed of the wave traveling around the mound these waves can become highly nonlinear and show largest turbulence due to wave breaking at the transition from warming downslope to cooling upslope tidal phase averaged over the entire 9 day time series and the 120 m vertical range mean turbulent kinetic energy dissipation amounts to 2 2 1 1 10 7 w kg 1 and mean vertical eddy diffusivity to 9 5 10 3 m2 s 1 with short term variations over four orders of magnitude such large turbulence more than 100 times larger than open ocean values and comparable with that observed in tidally energetic shelf break shallow sea areas will affect the nutrient replenishment of the cold water corals

extent and duration of antarctic surface melting the extent and duration of surface melting on the antarctic ice shelves and margins of the antarctic ice sheet are derived from satellite passive microwave data for 1978 87 the occurrence of surface melting in daily maps of t b is indicated by a marked increase in microwave brightness temperature t b which is caused by moisture in the near surface firn t b increases of more than 30 deg above the annual mean t b are chosen to indicate melting most antarctic surface melting occurs during december and january the observed melting is correlated with regional air temperatures but some melt patterns also appear to be related to katabatic wind effects the correlations suggest that the surface melting in antarctica increases about 3 5 10 6 d km 2 per degree of summer temperature increase the surface melt index duration times area of melting calculated for antarctica is 24 10 6 d km 2 averaged over nine summers the observed inter annual and regional variability is large surface melting was most extensive during the 1982 83 summer 36 10 6 d km 2 and least extensive during the 1985 86 summer 15 10 6 d km 2 the data indicate a decline in surface melting over the 9 years but meaningful inferences regarding trends in surface melting are precluded by the large inter annual variability

drivers of ascat c band backscatter variability in the dry snow zone of antarctica c band backscatter parameters contain information about the upper snowpack firn in the dry snow zone the wide incidence angle diversity of the advanced scatterometer ascat gives unprecedented characterisation of backscatter anisotropy revealing the backscatter response to climatic forcing the a isotropic component and m2 bi sinusoidal azimuth anisotropy parameters are investigated here in conjunction with data from atmospheric and snowpack models to identify the backscatter response to surface forcing parameters wind speed and persistence precipitation surface temperature density and grain size the long term mean a parameter is successfully recreated with a regression using these drivers indicating strong links between the a parameter and precipitation on long timescales while the ascat time series is too short to determine which factors drive observed trends factors influencing the seasonal and short timescale variability are revealed on these timescales a strongly responds to the propagation of surface temperature cycles anomalies downward through the firn via direct modulation of the dielectric constant the influence of precipitation on a is small at shorter timescales the m2 parameter is controlled by wind speed and persistence through modification of monodirectionally aligned surface roughness this variability indicates that throughout much of coastal antarctica a microwave snapshot is generally not representative of longer term conditions

multifrequency microwave emission fromthe dome c area on the east antarctic plateau temporal and spatial variability the antarctic plateau that extends for several hundred kilometers with an average altitude of close to 3000 m a s l is the highest part of the east antarctic ice cap this area provides unique opportunities for various scientific disciplines including glaciology and atmospheric and earth sciences in addition there is growing interest in using the antarctic plateau for calibrating and validating data of satellite borne microwave radiometers thanks to the size structure and spatial homogeneity of this area and the thermal stability of deeper snow layers in this paper we analyze the temporal and spatial variabilities of multifrequency microwave emission from the area surrounding the dome c scientific station using advanced microwave scanning radiometer data collected throughout 2005 moreover a multilayer coherent electromagnetic model is used for estimating the contribution of snow layers to emission at various frequencies the results are consistent with the physical structure of the ice sheet and with its seasonal and spatial variations

comparison of microwave backscatter anisotropy parameterizations of the antarctic ice sheet using ascat the c band eumetsat advanced scatterometer ascat was launched in 2007 and provides backscatter measurements with excellent azimuth and incidence angle diversity in polar regions c band backscatter measurements can be used to retrieve near surface snow firn properties such as grain size and accumulation rate however the antarctic ice sheet ais exhibits strong microwave backscatter anisotropy as a function of both incidence and azimuth angles and this anisotropy must be well understood before such physical parameter retrieval can be accurately performed this paper presents a detailed comparison of several different parameterizations of both the azimuth and the incidence anisotropy parameterizations used here result in residuals similar to the radiometric performance of ascat indicating accurate characterization of the anisotropy the analysis of these parameterizations provides an insight into the physical mechanisms taking place near the surface of the ais 30 day composite maps of several parameters are presented and discussed in the context of near surface glaciology this anisotropy characterization will form the basis of a technique for extraction of physical parameters of the ais

multiangle backscattering observations of continental surfaces in ku band 13 ghz from satellites understanding the signals particularly in arid regions backscattering in ku band 13 ghz over continen tal surfaces is analyzed with the tropical rainfall measurement mission precipitation radar instruments incidence angles from 0 to 18 along with observations from the topex poseidon nadir looking altimeter and the quikscat scatterometer inci dence angles around 50 the signals from the three instruments are very consistent the backscattering tends to decrease with increasing vegetation density as expected making it possible to classify vegetation density with active microwaves over the northern african desert a very large spatial variability of the backscattering is observed with both surface and volume scatter ings contributing to the signals the use of multiangle observations does help characterizing the desert types but in some areas the ambiguity of the signals is still unexplained the french chinese joint mission chinese french oceanic satellite will carry two active microwave instruments with a large range of incidence angles from 0 to 50 we show that the combined use of ob servations at low and high incidence angles adds information particularly over desert surfaces

on the influence of cold water coral mound size on flow hydrodynamics and vice versa using a combination of in situ observations and idealistic 2 d nonhydrostatic numericalsimulations the relation between cold water coral cwc mound size and hydrodynamics is explored forthe rockall bank area in the north atlantic ocean it is shown that currents generated by topographicallytrapped tidal waves in this area cause large isopycnal depressions resulting from an internal hydrauliccontrol above cwc mounds the oxygen concentration distribution is used as a tracer to visualize the flowbehavior and the turbulent mixing above the mounds by comparing two cwc mounds of different sizesand located close to each other it is shown that the resulting mixing is highly dependent on the size of themound the effects of the hydraulic control for mixing nutrient availability and ecosystem functioning arealso discussed

sea ice identification using dual polarized ku band scatterometer data this paper describes a classification algorithm using dual polarized scatterometer measurements to identify the edge of the sea ice cover the distinct polarization scattering signatures of sea ice and open water are discussed and illustrated with the dual polarized radar measurements from the seasat a scatterometer sass the analysis of sass data suggests that the ratio of vertical and horizontal polarization backscatter denoted as the copol ratio is a useful discriminator of sea ice and open ocean a simple classification algorithm using the thresholds of the copol ratio and backscatter levels is proposed the feasibility of this algorithm is demonstrated using the sass data from the single sided dual polarization mode the results indicate that the dual polarized measurements from the nasa scatterometer nscat can be used to produce routine maps of sea ice edges

assessing the likelihood and magnitude of volcanic explosions based on seismic quiescence abstract volcanic eruptions are generally forecast based on strong increases in monitoring parameters such as seismicity or gas emissions above a relatively low background level e g voight 1988 sparks 2003 because of this forecasting individual explosions during an ongoing eruption or at persistently restless volcanoes is difficult as seismicity gas emissions and other indicators of unrest are already in a heightened state therefore identification of short term precursors to individual explosions at volcanoes already in heightened states of unrest and an understanding of explosion trigger mechanisms is important for the reduction of volcanic risk worldwide seismic and visual observations at telica volcano nicaragua demonstrate that a episodes of seismic quiescence reliably preceded explosions during an eruption in may 2011 and b the duration of precursory quiescence and the energy released in the ensuing explosion were strongly correlated precursory seismic quiescence is interpreted as the result of sealing of shallow gas pathways leading to pressure accumulation and eventual catastrophic failure of the system culminating in an explosion longer periods of sealing and pressurization lead to greater energy release in the ensuing explosion near real time observations of seismic quiescence at restless or erupting volcanoes can thus be useful for both timely eruption warnings and for forecasting the energy of impending explosions

the importance of the permanent thermocline to the cold water coral carbonate mound distribution in the ne atlantic abstract a prominent feature of the nw european continental slope is the presence of numerous cold water coral carbonate mounds that are clustered in a number of provinces these provinces occupy a relatively narrow depth range along the continental slope 95 of all coral carbonate mounds identified on the irish seabed have their mound bases between 500 and 1000 m water depths with a peak in distribution at 650 m water depth the distribution in mound base depths is skewed with a tail extending from the maximum at 650 m to deeper depths this distribution brackets the depth of the permanent thermocline in the ne atlantic 600 1000 m formed below the base of the winter mixed layer it is shown that the permanent thermocline is associated with the strongest residual near seabed current flow with typical residual current speeds up to 2 3 times larger at the thermocline depth compared to other depths the strong vertical density gradient associated with the permanent thermocline together with the steep continental slope at those depths also enhances the energy of certain periodic motions such as internal waves and baroclinic tidal currents these dynamic conditions favour mound growth through the promotion of significant along slope sediment transport and also provide large across slope sediment movement and organic matter fluxes the stability of the thermocline structure is likely the key in providing favourable conditions over long time scales that allow mound growth through sediment baffling processes

late stage volatile saturation as a potential trigger for explosive volcanic eruptions magma reservoirs typically accumulate over hundreds to thousands of years yet geochemical analyses of volcanic rocks from campi flegrei suggest activity there was triggered by injections of volatile rich magma only days before the eruption

recent changes in the microwave scattering properties of the antarctic ice sheet time series satellite microwave data are used to monitor and quantify changes in the scattering properties of the antarctic ice sheet daily ers scatterometer escat and special sensor microwave imager ssm i image data acquired since 1992 are analyzed to understand the seasonal and interannual changes over the ice sheet for regions of the ice sheet where azimuthal modulation is negligible seasonal cycles are observed in both the escat amplitude spl sim 0 5 db and ssm i data amplitude spl sim 10 k these cycles are attributed to seasonal changes in surface temperature interannual variability in the time series signatures appears to be associated with accumulation there is also evidence to suggest that shifts in the wind direction can alter the backscatter through azimuthal modulation over the period 1992 97 large trends are observed in the escat 1 k yr sup 1 signatures over several regions in antarctica these changes typically occur over ice shelves and at the margins of the ice sheet where previous melt events have occurred and where accumulation is relatively high 300 mm yr sup 1 it is likely the large changes result from the successive burial of an efficient scattering layer formed by refreezing after a melt event prior to 1992 there is also evidence to suggest that similarly large changes can be observed in the interior of the ice sheet due to the burial of depth hear layers in order to monitor long term change in the properties of the antarctic ice sheet it is necessary to remove the seasonal cycle from time series microwave data such anomaly data can then be used to understand the link between escat and ssm i with accumulation and wind shifts

modeling time series of microwave brightness temperature in antarctica this paper aims to interpret the temporal variations of microwave brightness temperature at 19 and 37 ghz and at vertical and horizontal polarizations in antarctica using a physically based snow dynamic and emission model sdem sdem predicts time series of top of atmosphere brightness temperature from widely available surface meteorological data era 40 re analysis to do so it successively computes the heat flux incoming the snowpack the snow temperature profile the microwaves emitted by the snow and finally the propagation of the microwaves through the atmosphere up to the satellite since the model contains several parameters whose value is variable and uncertain across the continent the parameter values are optimized for every 50 km 50 km pixel simulation results show that the model is inadequate in the melt zone where surface melting occurs on at least a few days a year because the snowpack structure and its temporal variations are too complex in contrast the accuracy is reasonably good in the dry zone and varies between 2 and 4 k depending on the frequency and polarization of observations and on the location at the antarctic scale the error is larger where wind is usually stronger suggesting either that meteorological data are less accurate in windy regions or that some neglected processes e g windpumping surface scouring are important at dome c in calm conditions a detailed analysis shows that most of the error is due to inaccuracy of the era 40 air temperature 2 k finally the paper discusses the values of the optimized parameters and their spatial variations across the antarctic

stable and unstable phases of elevated seismic activity at the persistently restless telica volcano nicaragua abstract telica volcano nicaragua is a persistently restless volcano with daily seismicity rates that can vary by orders of magnitude without apparent connection to eruptive activity low frequency lf events are dominant and peaks in seismicity rate show little correlation with eruptive episodes presenting a challenge for seismic monitoring and eruption forecasting a short period seismic station teln has been operated on telica s summit since 1993 and in 2010 the installation of a six station broadband seismic and eleven station continuous gps network the tesand network was completed to document in detail the seismic characteristics of a persistently restless volcano between our study period of november 2009 and may 2013 over 400 000 events were detected at the tesand summit station tbtn with daily event rates ranging from 5 to 1400 we present spectral analyses and classifications of 200 000 events recorded by the tesand network between april 2010 and march 2013 and earthquake locations for a sub set of events between july 2010 and february 2012 in 2011 telica erupted in a series of phreatic vulcanian explosions six months before the 2011 eruption we observe a sudden decrease in lf events concurrent with a swarm of high frequency hf events followed by a decline in overall event rates which reached a minimum at the eruption onset we observe repeated periods of high and low seismicity rates and suggest these changes in seismicity represent repeated transitions between open system and closed system degassing we suggest that these short and long term transitions between open to closed system degassing form part of a long term pattern of stable vs unstable phases at telica stable phases are characterised by steady high rate seismicity and represent stable open system degassing whereas unstable phases are characterised by highly variable seismicity rates and represent repeated transitions from open to closed system degassing where the system is unable to sustain steady open system degassing these observations have implications for seismic monitoring at persistently restless volcanoes as the recognition of unstable seismic phases may indicate the open system degassing process cannot be sustained and explosions are likely

a comparison between active and passive microwave measurements of the antarctic ice sheet and their association with the surface katabatic winds the intensity of the seasat altimeter return power over antarctica varies in strong correlation with the intensity of model katabatic winds it is also strongly correlated with the polarization of the passive microwave signal at 37 ghz of the nimbus 7 smmr data it is shown that this is most likely the result of the wind induced micro roughness of the ice surface

phase equilibria trigger for explosive volcanic eruptions 1 a mechanism for explosive volcanic eruptions based on multicomponent phase equilibria modelling of four explosive volcanic systems is proposed in each system either isochoric or isobaric crystallization where either crystals or crystals and exsolved fluid are chemically fractionated from melt leads inevitably to near solidus dynamical instability culminating in violent explosive eruption driving this instability is a dramatic increase in the volume fraction of fluid bubbles in the magma exceeding the limit for magma fragmentation this phenomenon is independent of magma decompression country rock may be weak allowing magma to remain in lithostatic equilibrium with its host rock or strong leading to divergence of magma and lithostatic pressure bubbles may be retained or expelled during crystallization instability is the inevitable outcome of crystallization at shallow levels in the crust for all four systems regardless of the mechanical state of host country rock we speculate that this phase equilibria mechanism driving explosive eruptions has general significance

imaging the dynamics of magma propagation using radiated seismic intensity 1 at shallow depth beneath the earth s surface magma propagates through strongly heterogeneous volcanic material inversion of buoyancy and or solidification have strong impacts on the dynamics of propagation without any change of magma supply in this paper we study the spatial and time evolution of magma intrusions using induced seismicity we propose a new method based on ratio analysis of estimates of radiated seismic intensities recorded at different stations during seismic swarms by applying this method to the january 2010 piton de la fournaise volcano eruption we image complex dike propagation dynamics which strongly differ from a model of constant velocity dike propagation we provide a new method to image in real time the dynamics of dike propagation and to infer the position of eruptive fissures

carbonate mound development at the sw rockall trough margin based on high resolution tobi and seismic recording abstract in 2002 high resolution sidescan sonar images of a mound area at the sw rockall trough margin were recorded with the tobi deep towed sidescan sonar processed tobi images with a pixel resolution of 6 m provide a unique overview of the carbonate mound distribution and related sedimentary features around the mounds three morphologically distinct areas can be recognised on the tobi mosaic in area i between 500 and 600 m water depth upslope of the mounds giant sediment waves are found with wavelengths up to 500 m with wave crests of more than 10 km long and with an amplitude of up to 30 m reflected with a high backscatter on the tobi image area ii between 600 and 1000 m water depth along the upper margin flank is characterised by clustered and isolated carbonate mounds forming elongated ridges with an orientation perpendicular to the slope sedimentary structures such as flow ridges sediment waves local scouring at the foot of some mounds and draping of sediment around mounds indicate the influence of strong near bed currents oriented in two main current directions parallel to the margin as well as in a similar direction as the mound clusters the mound clusters are several kilometres long can be over 380 m high and are dissected by downslope directed channels on the tobi image the mounds appear as regions of high backscatter caused by the presence of cold water coral colonies on the sediment and by distinct shadows all mounds have their tops at a specific depth level 500 600 m water depth area iii between 900 and 1200 m water depth below the mounds is characterised by disturbed sediments with distinct slump scars and flow ridges 2d high resolution seismic profiling perpendicular and parallel to the slope across the mounds does in general not reveal strong internal reflectors within the mounds in contrast three strong reflectors can be observed in the sedimentary sequence underneath the mounds the upper reflector c10 of early pliocene age is an erosional unconformity above which most of the mounds and sediment waves seem to have developed the second erosional unconformity c20 of middle miocene age is formed by an apparent irregular surface that locally is dissected by some small faults reflectors c10 and c20 have been found in two different mound clusters in the mound area indicating that mound development possibly started after formation of reflector c20 the third reflector forms the acoustic basement which is locally dissected by some small faults that are located below the mounds at least two stages of mound formation are recognised on the seismic profiles

are the ashes from the latest eruptions 2010 2016 at turrialba volcano costa rica related to phreatic or phreatomagmatic events abstract the initial eruptive episodes of explosive eruptions are classified as phreatic if the amount of juvenile material scoria glass pumice is null and the amount of fresh accidental lithics and hydrothermally altered lithics is substantial phreatic eruptions have been in some cases recognized as precursory events preceding phreatomagmatic and magmatic eruptive phases usually the lithological features of tephra deposits are investigated and sampled in the field investigation of ash samples under binocular microscope or by back scattered electron bse microscope images of polished sections is usually considered sufficient to typify the fragmentation mechanism of the eruption the opening eruptive phases at turrialba volcano together with the formation of new intracraters i e 2010 2012 2014 and the enlargement of the western crater 29 october 2014 to present were classified in previous papers and internal reports as phreatic we studied a series of ash samples erupted from 2010 to 2016 with the aim of understanding the fragmentation processes characterizing the vent opening phases we used sem eds analyses in addition to field and microscopic investigation results showed a composition of accidental lithics of fresh to hydrothermally altered clasts and secondary minerals 82 98 besides juvenile andesite fragments 2 18 which leads us to revisit the classification of the initial eruptive phases of turrialba as phreatomagmatic our method allowed the detection of a juvenile component directly involved in an effective magma water interaction which was possible only by a scrutinous examination of the glass surface textures by sem in the range size between 3 and 3 5 phi we recommend such a type of investigation when the identification of fresh magma in a new eruption is crucial for the preparedness and hazard evaluation at active volcanoes

discrimination of geophysical phenomena in satellite radar interferograms various geophysical phenomena are recorded in the interference patterns formed by differencing two synthetic aperture radar sar images the fringes generated by the topographic relief can be removed using a digital elevation model dem the remaining fringes map the change in satellite to ground range which occurred between the acquisition times of the two images by comparing different pairs of images spanning different intervals of time it is possible to discriminate between geophysical signal and interferometric artifact here we apply this pair wise logic to the area around the 1992 landers california earthquake using sar images acquired by the ers 1 satellite the range varies with time as a constant step impulsive or sloping function examples of each type include a dem error an aftershock two atmospheric perturbations and postseismic afterslip respectively their signatures are identified and separated using the pair wise logic

volcanic ash leachates a review and recommendations for sampling methods tephra in plumes can scavenge and thereby rapidly deposit volatiles including sulphur halogen and metal species these may then be leached e g by rainfall potentially releasing heavy loadings to soils and water bodies several eruptions have resulted in contamination of pasture sometimes with serious impacts on livestock water quality has also been an issue in some areas affected by tephra fall this work synthesises the literature on volcanic ash leachates and considers the controls on volatile adsorption general trends emerge for basaltic intermediate and silicic tephra as well as for variable particle size and transport distance the applications of ash leachate data to plume gas geochemistry calculation of volatile budgets and environmental impact assessment are evaluated comparisons for different eruptions are hampered by disparities in leachate analysis techniques a standardised methodology is therefore proposed to facilitate future health impact assessment and volcanological interpretation of results from different sites

understanding the timing of eruption end using a machine learning approach to classification of seismic time series abstract the timing and processes that govern the end of volcanic eruptions are not yet fully understood and there currently exists no systematic definition for the end of a volcanic eruption currently end of eruption is established either by generic criteria typically 90 days after the end of visual signals of eruption or criteria specific to a given volcano we explore the application of supervised machine learning classification methods support vector machine logistic regression random forest and gaussian process classifiers and define a decisiveness index d to evaluate the consistency of the classifications obtained by these models we apply these methods to seismic time series from two volcanoes chosen because they display contrasting styles of eruption telica nicaragua and nevado del ruiz colombia we find that for both volcanic systems the end date we obtain by classification of seismic data is 2 4 months later than end dates defined by the last occurrence of visual eruption such as ash emission this finding is in agreement with previous general definitions of eruption end and is consistent across models our classifications have a higher correspondence of eruptive activity with visual activity than with database records of eruption start and end we analyze the relative importance of the different features of seismic activity used in our models e g peak event amplitude daily event counts and find little consistency between the two volcanic systems in terms of the most important features which determine whether activity is eruptive or non eruptive these initial results look promising and our approach may offer a robust tool to help determine when an eruption has ended in the absence of visual confirmation

sea ice extent mapping using ku band scatterometer data although spaceborne scatterometers such as the nasa scatterometer have inherently low spatial resolution resolution enhancement techniques can be used to increase the utility of scatterometer data in monitoring sea ice extent in the polar regions a key parameter in the global climate the resolution enhancement algorithm produces images of a and b where a is the normalized radar backscatter coefficient o at 40 incidence and b is the incidence angle dependence of o dual polarization a and b parameters are used to identify sea ice and ocean pixels in composite images the a copolarization ratio and vertically polarized b are used as primary classification parameters to discriminate between sea ice and open ocean estimates of the sea ice extent are obtained using linear and quadratic mahalanobis distance discriminant boundaries the distribution parameters needed for the quadratic estimate are taken from the linear estimate the o error variance is used to reduce errors in the linear and mahalanobis ice ocean classifications noise reduction is performed through binary image region growing and erosion dilation techniques the resulting edge closely matches the nasa team algorithm special sensor microwave imager derived 30 ice concentration edge a 9 month data set of global sea ice extent maps is produced with one 6 day average map every 3 days

toward a robust retrieval of snow accumulation over the antarctic ice sheet using satellite radar 1 the sensitivity of radar measurements to snow accumulation rate is determined by the firn volume characteristics of the ice sheets here we present a new approach for calculating the volume backscattering of dry firn which is combined with recently developed empirical parameterizations of firn grain size and density as functions of depth surface temperature and accumulation rate to this end dense medium radiative transfer theory is applied to calculate the volume scattering and absorption coefficients the coefficients for the density transition between snow and dense firn are evaluated using polynomial interpolation for testing the method we used measured accumulation rates envisat asar c band wide swath mode images and quikscat ku band backscattering data from dronning maud land antarctica the comparison between measured and simulated backscattering coefficients shows that no tuning parameter is necessary to obtain the correct absolute level of scattering intensity the robustness of accumulation rate retrievals depends on the consideration of technical and environmental factors due to the presence of sastrugi on the ice sheet surface the measured intensities are sensitive to the radar look direction wind compaction of snow and depth hoar formation change the depth dependent snow density and grain size profiles theoretical simulations revealed that the backscattering coefficient at c band is more sensitive to changes of accumulation rates than at ku band penetration depths can vary significantly dependent on radar frequency and firn characteristics this has to be taken into account when comparing accumulation rates from different locations

correlations between so2 flux and long period seismicity at galeras volcano the 14 january 1993 eruption of galeras volcano in colombia which killed six scientists and three tourists1 was followed by a larger eruption on 23 march 19932 both eruptions were preceded by episodes of long period seismicity the source of long period seismic events has been modelled extensively3 8 as the resonance within a fluid filled crack induced by pressure transients in the fluid5 7 here we use the so2 flux from galeras volcano measured remotely to infer the degassing history during the episode of long period events preceding the 23 march eruption so2 flux and long period seismicity have been monitored separately elsewhere to forecast volcanic activity9 13 our results show how the combination and correlation of the two methods can be used to interpret the movement of gases from the magma body to the surface and to monitor the pressure buildup leading to an eruption at explosive volcanoes

relating microwave backscatter azimuth modulation to surface properties of the greenland ice sheet azimuth dependence of a normalized radar cross section over the greenland ice sheet is modeled with a simple surface scattering model the model assumes that azimuth anisotropy in surface roughness at scales of 3 300 m is the primary mechanism driving the modulation to evaluate the contribution of azimuth anisotropy in surface roughness to the radar backscatter the model is compared to models based on isotropic surface roughness the models are inverted to estimate snow surface properties using measurements from the c band european remote sensing satellite advanced microwave instrument in scatterometer mode results indicate that the largest mesoscale rms surface slopes are found in the lower portions of the dry snow zone estimates of the preferential direction in surface roughness are highly correlated with katabatic wind fields over greenland which is consistent with wind formed sastrugi as the dominant mechanism causing azimuth modulation of the maximum improvement of the azimuth modulation surface model compared to its isotropic counterparts occurs in the lower regions of the dry snow zone where the azimuth variability of is the largest in regions with azimuth modulation over 1 db the mean root mean square error estimate of the azimuth dependent surface scattering model is 0 46 db compared with 0 70 db for similar models using isotropic roughness

measurements of volcanic so2 and co2 fluxes by combined doas multi gas and ftir observations a case study from turrialba and telica volcanoes over the past few decades substantial progress has been made to overcome the technical difficulties of continuously measuring volcanic so2 emissions however measurements of co2 emissions still present many difficulties partly due to the lack of instruments that can directly measure co2 emissions and partly due to its strong atmospheric background in order to overcome these difficulties a commonly taken approach is to combine differential optical absorption spectroscopy doas by using novac scan doas instruments for continuous measurements of crateric so2 emissions and electrochemical ndir multi component gas analyser system multi gas instruments for measuring co2 so2 ratios of excerpts of the volcanic plume this study aims to quantify the representativeness of excerpts of co2 so2 ratios measured by multi gas as a fraction of the whole plume composition by comparison with simultaneously measured co2 so2 ratios using cross crater fourier transform infrared spectroscopy ftir two study cases are presented telica volcano nicaragua with a homogenous plume quiescent degassing from a deep source and ambient temperature and turrialba volcano costa rica which has a non homogeneous plume from three main sources with different compositions and temperatures our comparison shows that in our easier case telica ftir and multi gas co2 so2 ratios agree within a factor about 3 in our complicated case turrialba multi gas and ftir yield co2 so2 ratios differing by approximately 13 25 at most these results suggest that a fair estimation of volcanic co2 emissions can be provided by the combination of doas and multi gas instruments for volcanoes with similar degassing conditions as telica or turrialba based on the results of this comparison we report that by the time our measurements were made telica and turrialba were emitting approximately 100 and 1 000 t day 1 of co2 respectively

windsat passive microwave polarimetric signatures of the greenland ice sheet windsat has systematically collected the first global fully polarimetric passive microwave data over both land and ocean as the first spaceborne polarimetric microwave radiometer it was designed to measure ocean surface wind speed and direction by including the third and fourth stokes parameters which are mostly related to the asymmetric structures of the ocean surface roughness although designed for wind vector retrieval windsat data are also collected over land and ice and this new data has revealed for the first time significant land signals in the third and fourth stokes parameter channels particularly over greenland and the antarctic ice sheets the third and fourth stokes parameters show well defined large azimuth modulations that appear to be correlated with geophysical variations particularly snow structure melting and metamorphism and have distinct seasonal variation the polarimetric signatures are relatively weak in the summer and are strongest around spring this corresponds well with the formation and erosion of the sastrugi in the dry snow zone and snowmelt in the soaked zone in this paper we present the full polarimetric signatures obtained from windsat over greenland and use a simple empirical observation model to quantify the azimuthal variations of the signatures in space and time

l band ice sheet brightness temperatures at dome c antarctica spectral emission modelling temporal stability and impact of the ionosphere the temporal thermal stability size structure and spatial uniformity of antarctic plateau regions such as dome c make them ideal candidates for external calibration and validation or radiometric performance monitoring of planned space borne l band radiometers such as the soil moisture and ocean salinity smos radiometer as experimental observations do not exist at this frequency a combination of historical ka xand c band data are used together with electromagnetic and ionospheric models to extrapolate to this longer wavelength dome c is demonstrated to exhibit negligible seasonal variability 0 1k and may prove to be a suitable candidate provided the effects of atmospheric and ionospheric perturbations can be mitigated

pre eruptive inflation caused by gas accumulation insight from detailed gas flux variation at sakurajima volcano japan sulfur dioxide so2 emission rate observations were made at sakurajima volcano japan to quantify the relationship between the so2 emission rate and inflation prior to vulcanian explosions the explosions associated with precursory inflation events were preceded by decreases in so2 emission rates by 10 60 min the amounts of accumulated gas were calculated using time series of so2 emission rate the amounts of accumulated so2 and increases in strain records before the explosions showed a positive correlation the volume increase of a deformation source calculated using the strain records was of the comparable order of magnitude as the volume of the accumulated volcanic gas the results suggest that the inflations before the explosions were caused by the gas accumulation

azimuthal anisotropy of scatterometer measurements over land studies of the earth s land surface involving scatterometers are becoming an increasingly important application field of microwave remote sensing similarly to scatterometer observations of ocean waves the backscattering coefficient sigma0 response of land surfaces depends on both the incidence and azimuth angle under which the observations are made in order to retrieve geophysical parameters from scatterometer data it is necessary to account for azimuthal modulation effects of the backscattered signal in the present study this paper localizes the regions affected by a strong azimuthal signal dependence when observed with the european remote sensing satellite scatterometer and the seawinds scatterometer on quikscat qscat the possible physical reasons for the azimuthal effects relating the very detailed qscat azimuthal response to the spatial orientation of special topographic features and land cover within the sensor footprint were then discussed different methods for normalizing the backscattering coefficient with respect of observation azimuth angle were also proposed and evaluated first the mean local incidence angle of the sensor footprint using the shuttle radar topography mission digital elevation model dem were modeled and concluded that the resolution of the dem is too coarse to characterize most of the observed azimuthal effects a more effective way of normalizing the backscatter with respect to azimuth is then found to be by using historical backscatter observations to statistically determine the expected backscatter at each observation azimuth and incidence angle as well as time of the year the efficiency of this method is limited to the availability of past measurements for each location on the earth

vertically extensive and unstable magmatic systems a unified view of igneous processes volcanoes are an expression of their underlying magmatic systems over the past three decades the classical focus on upper crustal magma chambers has expanded to consider magmatic processes throughout the crust a transcrustal perspective must balance slow plate tectonic rates of melt generation and segregation in the lower crust with new evidence for rapid melt accumulation in the upper crust before many volcanic eruptions reconciling these observations is engendering active debate about the physical state spatial distribution and longevity of melt in the crust here we review evidence for transcrustal magmatic systems and highlight physical processes that might affect the growth and stability of melt rich layers focusing particularly on conditions that cause them to destabilize ascend and accumulate in voluminous but ephemeral shallow magma chambers

temporal variations of repeating low frequency volcanic earthquakes at ngauruhoe volcano new zealand abstract a persistent swarm of micro earthquakes was observed at ngauruhoe volcano new zealand from 2005 to 2010 marking the first unrest episode at the volcano since 1975 detailed waveform and spectral analysis of the continuous seismic record revealed eight earthquake families f1 f8 within a sequence of 8561 low frequency earthquakes an analysis of stacked waveforms of each family allowed the families to be linked systematically into four super families that may indicate four different mechanisms and or source locations or geometries the first super family mostly occurred in 2005 and showed stable waveforms and no significant evolution the second super family was dominant over a two year period starting in mid 2006 and displayed a slow evolution with progressively higher frequency the third super family emerged from early 2008 with intermittent occurrence and high seismicity and progressed to higher peak frequency in 2010 the fourth super family was mainly observed from late 2008 to mid 2009 and had the highest peak frequency in 2009 the observed evolutionary pattern may be driven by a modest multi year input of gas and heat from a deeper relict magmatic zone into the shallow volcano hydrothermal system the interplay of gas from below and seasonal meltwater from above may have modulated the seismic activity and may relate to repeated over pressurization and failure of constricted evolving pathways within a pervasive crack system

patterns of volcanotectonic seismicity and stress during the ongoing eruption of the soufriere hills volcano montserrat 1995 2007 abstract the ongoing eruption of the soufriere hills volcano montserrat has been accompanied throughout by varying levels of high frequency volcanotectonic vt seismicity these earthquakes reflect the brittle response of the host rock to stresses generated within the magmatic system and thus reveal interesting and useful information about the structure of the volcanic conduit system and processes occurring within it in general systematic changes in the rate location and fault plane solutions of vt earthquakes correspond to changes in the volcano s behavior and indicate that the main conduit for the eruption is a dike or system of dikes trending ne sw and centered beneath the eruptive vent to date the eruption has comprised three extrusive phases separated by two 1 2 year long periods of residual activity prior to the start of each extrusive phase vt earthquakes with fault plane solution p axes oriented perpendicular to inferred regional maximum compression dominate the data set consistent with stresses induced by the inflation of the mid level conduit system 90 rotated vt fault plane solutions are also observed preceding a change in eruption style from effusive to explosive in 1997 while increases in the rate of vt earthquakes precede eruption phase onsets high rates of vt seismicity are also observed during the first period of residual activity and in this case appear to reflect the relaxation of host rock following withdrawal of magma from the mid crustal system most vt earthquakes are located directly beneath the eruptive vent although two distal vt clusters were observed during the first six months of the eruption late 1995 early 1996 both of these distal clusters likely resulted from stresses generated during the establishment of the main conduit system

understanding magmatic processes at telica volcano nicaragua crystal size distribution and textural analysis telica volcano in nicaragua currently exhibits persistent activity with continuous seismicity and degassing yet it has not produced lava flows since 1529 to provide insight into magma chamber processes including replenishment and crystallization crystal size distribution csd profiles of plagioclase feldspar phenocrysts were determined for quaternary telica basalts and basaltic andesites textural analysis of 14 highly crystalline lavas 20 vol phenocrysts indicates that the samples are dominated by sieve textured plagioclase feldspar phenocrysts whose origin requires thermochemical disequilibrium within the magmatic system the csd curves display an inverse relationship between phenocryst length and population density concave up patterns observed for the telica lava samples can be represented by linear segments that define two crystal populations a steeply sloping segment for small crystals 1 5 mm in length the two crystal populations may be explained by magma replenishment and a mixing model in which a mafic magma is introduced to a stable chamber that is petrologically and geochemically evolving residence times calculated using the defined linear segments of the csd curves suggest these magmatic processes occur over timescales on the order of decades to centuries the crystal size distribution and textural analysis advocate for the current persistent activity as being consistent throughout telica s historic and prehistoric eruptive periods and driven by replenishment of mafic magma

katabatic wind intensity and direction over antarctica derived from scatterometer data although satellite radar scatterometers are initially designed to measure ocean surface wind speed and direction they also provide important observations over continental ice sheets data from the seasat scatterometer analysed over a sector of antarctica show that the signal is strongly dependent on the incidence angle of observation but that it also depends on azimuth ledroit et al 1992 the minimum values of the backscatter coefficient the ratio of backscattered versus incident power are always observed in the direction of katabatic winds a theoretical analysis shows that the backscatter coefficient must be very sensitive to the sastrugi slopes and orientations which are streamlined features formed on the snow surface in the wind direction parish and bromwich 1987 satellite scatterometers can thus map the characteristics of sastrugis of importance for the interpretation of microwave measurements above ice sheets this indirectly provides the intensity and direction of these very persistent and strong winds which play a important role in the behaviour of the atmosphere and ocean in high southern latitudes

mechanisms of unrest and eruption at persistently restless volcanoes insights from the 2015 eruption of telica volcano nicaragua many of earth s volcanoes experience well defined states of quiescence and unrest with unrest occasionally culminating in eruption some volcanoes however experience an unusually protracted i e decades long period of noneruptive unrest and are thus categorized as persistently restless volcanoes prvs the processes that drive persistently restless volcanism are poorly understood as our knowledge of prvs is currently based on a small number of case studies here we examine multidisciplinary observations of the 2015 eruptive episode at telica volcano nicaragua in the context of its long term behavior we suggest that the latter phases of the 2015 eruption were ultimately driven by destabilization of its shallow magma reservoir based on previous geodetic seismic studies of telica geirsson et al 2014 https doi org 10 1016 j jvolgeores 2013 11 009 rodgers et al 2013 https doi org 10 1016 j jvolgeores 2013 08 010 and 2015 https doi org 10 1016 j jvolgeores 2014 11 012 and on multiparameter observations at telica over a 7 year period we propose that three distinct states of unrest occur at telica over decadal timescales a stable open state involving steady conduit convection and two distinct unstable states that may lead to eruptions in the weak sealing state phreatic explosions result from steady conduit convection underlying a weak seal in the destabilized state destabilization of the top of the convecting magma in the conduit leads to rapid accumulation of high pressures leading to strong impulsive phreatomagmatic explosions our observations and interpretations suggest that continuous seismic ground based deformation gas emission and thermal monitoring and interpretation of these data within a paradigm of sustained conduit convection modulated by episodes of sealing and destabilization of shallow magma reservoirs may allow robust forecasting of eruption potential energy and duration at telica and similar prvs worldwide

surface airflow over east antarctica abstract surface winds over the antarctic interior occur mainly due to the strong radiational cooling of the ice slopes as a consequence such winds exhibit a high degree of persistence with a predominant direction closely related to the terrain orientation using detailed contour maps of the interior ice topography and representative values of the mean wintertime strength of the temperature inversion it is possible to infer the terrain induced accelerations a simple diagnostic equation system is formulated from which a time averaged surface airflow pattern of east antarctica is generated the results appear consistent with observations the occurrence of localized anomalously strong katabatic winds is explained as a result of typographically forced patterns of cold air convergence depicted in the airflow analysis

water mass characteristics and sill dynamics in a subpolar cold water coral reef setting at stjernsund northern norway the stjernsund located in subpolar setting at 70 5 n off northern norway hosts a thriving cold water coral reef community on a morainic sill dives with manned submersible jago identified the different reef zones and sedimentary facies on top and on the slopes of the sill hydrographic investigations indicate different water mass distribution east and west of the sill winter mode water and norwegian coastal water variability depends on the runoff and freshwater discharge into the fjord atlantic water dynamics are almost entirely tidally driven high resolution ctd time series covering a full tidal cycle demonstrate mixing processes occurring east of the sill additionally the different bathymetric distribution of living corals on the western and eastern slope of the sill portrays the dependence on these tidal dynamics the living corals thrive just below the isopycnal of 27 5 kg m 3 which marks the boundary between norwegian coastal water and atlantic water

effect of snow surface metamorphism on aquarius l band radiometer observations at dome c antarctica the antarctic plateau presents ideal characteristics to study the relationship between microwave observations and snow ice properties it is also a promising target for radiometer calibration and sensor intercalibration which are critical for applications requiring subkelvin accuracy such as sea surface salinity retrievals this paper presents the spaceborne aquarius l band radiometric observations collected since august 2011 over the antarctic plateau and it focuses on their temporal evolutions at dome c 75 1 circ hbox s 123 35 circ hbox e aquarius operates three radiometers with a sensitivity of 0 15 k over the oceans allowing us to analyze small variations in brightness temperature tb and changes with incidence angles over the antarctic plateau aquarius tbs have a relatively low annual standard deviation 0 2 0 9 k where melting never occurs however the analysis of the tb time series at dome c revealed significant variations up to 2 5 k in summer first these variations are compared with a remote sensing grain index gi based on high frequency 89 and 150 ghz shallow penetration tb channels variations in the ratio of tbs observed at horizontal and vertical polarizations are synchronous with gi changes second aquarius tb variations are compared with the presence of hoar crystals on the surface identified using surface based near infrared photographs the largest and longest changes in tbs correspond to periods with hoar crystals on the surface therefore in spite of the deep penetration of the l band radiation evolutions of the snow properties near the surface which usually change rapidly and irregularly do influence l band observations collection of accurate snow surface measurements and thorough analyses of the l band observations are thus needed to use the antarctic plateau as a calibration inter calibration target

counter current convection in a volcanic conduit abstract volcanoes of strombolian type are able to maintain their semi permanent eruptive states through the constant convective recycling of magma within the conduit leading from the magma chamber in this paper we study the form of this convection using an analytic model of degassing two phase flow in a vertical channel we provide solutions for the flow at small grashof and large prandtl numbers and we suggest that permanent steady state counter current convection is only possible if an initial bubbly counter current flow undergoes a regime transition to a churn turbulent flow we also suggest that the magma in the chamber must be under pressured in order for the flow to be maintained and that this compromises the assumed form of the flow

observations of the antarctic ice sheet with the seasat scatterometer relation to katabatic wind intensity and direction the seasat a satellite scatterometer radar initially designed to measure ocean wind intensity and direction also provided observations on the antarctic ice sheet the signal of the back scatter coefficient decreases strongly from 10 to 20 db when the incidence angle of the observations increases from 0 to 65 an additional 5 db signal is found which is correlated with the direction and intensity of katabatic winds independent of the incidence angle and polarization of the signal by using simplified models of the volume scattering within the snowpack which is mostly sensitive to snow grain size and surface scattering from the air snow interface which depends on roughness it is evident that the signal of the scatterometer could result from the effects of snow dunes at low incidence angle and of micro roughness and volume back scatter at incidence angles greater than 25 the instrument therefore provides a means of measuring the direction and intensity of katabatic winds

the surface windfield over the antarctic ice sheets the intense radiative cooling of air over the ice slopes of antarctica generates a surface wind regime that is strongly controlled by topography and plays a key role in determining the behaviour of the atmosphere and ocean in high southern latitudes1 7 resultant surface winds are intimately linked to the orientation of the ice terrain fig 1 and display the highest degree of persistence found on earth the close coupling between wind and topography allows estimation of the former if the latter is known with some precision here we report on time averaged near surface airflow over the antarctic continent during winter diagnosed from a recent accurate synthesis of terrain slopes and from estimates of the lower atmospheric temperature structure the simulated drainage pat tern exhibits strong spatial variability with the airflow concentrated into several zones near the coastal margin these confluence regions are responsible for strong persistent katabatic winds over downstream coastal stretches and are indicative of zones of greatest katabatic potential

sustained long period seismicity at shishaldin volcano alaska abstract from september 1999 through april 2004 shishaldin volcano aleutian islands alaska exhibited a continuous and extremely high level of background seismicity this activity consisted of many hundreds to thousands of long period lp 1 2 hz earthquakes per day recorded by a 6 station monitoring network around shishaldin the lp events originate beneath the summit at shallow depths 0 3 km volcano tectonic events and tremor have rarely been observed in the summit region such a high rate of lp events with no eruption suggests that a steady state process has been occurring ever since shishaldin last erupted in april may 1999 following the eruption the only other signs of volcanic unrest have been occasional weak thermal anomalies and an omnipresent puffing volcanic plume the lp waveforms are nearly identical for time spans of days to months but vary over longer time scales the observations imply that the spatially close source processes are repeating stable and non destructive event sizes vary but the rate of occurrence remains roughly constant the events range from magnitude 0 1 to 1 8 with most events having magnitudes

seismic observations of redoubt volcano alaska 1989 2010 and a conceptual model of the redoubt magmatic system abstract seismic activity at redoubt volcano alaska has been closely monitored since 1989 by a network of five to ten seismometers within 22 km of the volcano s summit major eruptions occurred in 1989 1990 and 2009 and were characterized by large volcanic explosions episodes of lava dome growth and failure pyroclastic flows and lahars seismic features of the 1989 1990 eruption were 1 weak precursory tremor and a short 23 hour long intense swarm of repetitive shallow long period lp events centered 1 4 km below the crater floor 2 shallow volcano tectonic vt and hybrid earthquakes that separated early episodes of dome growth 3 13 additional swarms of lp events at shallow depths precursory to many of the 25 explosions that occurred over the more than 128 day duration of eruptive activity and 4 a persistent cluster of vt earthquakes at 6 to 9 km depth in contrast the 2009 eruption was preceded by a pronounced increase in deep lp dlp events at lower crustal depths 25 to 38 km that began in mid december 2008 two months of discontinuous shallow volcanic tremor that started on january 23 2009 a strong phreatic explosion on march 15 and a 58 hour long swarm of repetitive shallow lp events the 2009 eruption consisted of at least 23 major explosions between march 23 and april 5 again accompanied by shallow vt earthquakes several episodes of shallow repetitive lp events and dome growth continuing until mid july increased vt earthquakes at 4 to 9 km depth began slowly in early april possibly defining a mid crustal magma source zone magmatic processes associated with the 2009 eruption seismically activated the same portions of the redoubt magmatic system as the 1989 1990 eruption although the time scales and intensity vary considerably among the two eruptions the occurrence of precursory dlp events suggests that the 2009 eruption may have involved the rise of magma from lower crustal depths based on the evolution of seismicity during the 1989 1990 and 2009 eruptions the redoubt magmatic system is envisioned to consist of a shallow system of cracks extending 1 to 2 km below the crater floor a magma storage or source region at roughly 3 to 9 km depth and a diffuse magma source region at 25 to 38 km depth close tracking of seismic activity allowed the alaska volcano observatory to successfully issue warnings prior to many of the hazardous explosive events that occurred in 2009

resolution enhancement of spaceborne scatterometer data a method for generating enhanced resolution radar images of the earth s surface using spaceborne scatterometry is presented the technique is based on an image reconstruction technique that takes advantage of the spatial overlap in scatterometer measurements made at different times to provide enhanced imaging resolution the reconstruction algorithm is described and the technique is demonstrated using both simulated and actual seasat a scatterometer sass measurements the technique can also be used with ers 1 scatterometer data the sass derived images which have approximately 4 km resolution illustrate the resolution enhancement capability of the technique which permits utilization of both historic and contemporary scatterometer data for medium scale monitoring of vegetation and polar ice the tradeoff between imaging noise and resolution inherent in the technique is discussed