timing and origin of recent regional ice mass loss in greenland within the last decade the greenland ice sheet gris and its surroundings have experienced record high surface temperatures mote 2007 box et al 2010 ice sheet melt extent fettweis et al 2011 and record low summer sea ice extent nghiem et al 2007 using three independent data sets we derive for the first time consistent ice mass trends and temporal variations within seven major drainage basins from gravity fields from the gravity recovery and climate experiment grace tapley et al 2004 surface ice velocities from inteferometric synthetic aperture radar insar rignot and kanagaratnam 2006 together with output of the regional atmospheric climate modelling racmo2 gr ettema et al 2009 and surface elevation changes from the ice cloud and land elevation satellite icesat sorensen et al 2011 we show that changing ice discharge d surface melting and subsequent run off m r and precipitation p all contribute in a complex and regionally variable interplay to the increasingly negative mass balance of the gris observed within the last decade interannual variability in p along the northwest and west coasts of the gris largely explains the apparent regional mass loss increase during 2002 2010 and obscures increasing m r and d since the 1990s in winter 2002 2003 and 2008 2009 accumulation anomalies in the east and southeast temporarily outweighed the losses by m r and d that prevailed during 2003 2008 and after summer 2010 overall for all basins of the gris the decadal variability of anomalies in p m r and d between 1958 and 2010 w r t 1961 1990 was significantly exceeded by the regional trends observed during the grace period 2002 2011 2012 elsevier b v

seasonal and interannual global surface mass variations from multisatellite geodetic data 1 monthly global surface mass distribution changes are estimated in the spherical harmonic domain with a complete spectrum up to degree and order 50 the estimates are derived by inverting gps displacement series measured at roughly 450 continuously tracking sites and ocean bottom pressure obp estimates of a data assimilated ocean circulation model from 1993 to 2004 the inversion uses a hybrid estimator after singular value decomposition of the normalized measurement equations with reduced reliance on a priori spectral information the results are then compared and combined with gravity recovery and climate experiment grace gravity data to provide enhanced spectral and geographic coverage high fidelity degree 1 surface mass variation coefficients are recovered corresponding to equivalent geocenter motion with better than 0 5 mm annual amplitude precisions in all three components a clear annual surface mass cycle occurs in both gps obp and grace derived results there is very good agreement among the low degree spherical harmonic coefficients and in global geographic pattern but with significant regional differences in amplitudes annual variations of average mass over the global oceans antarctica and greenland are then derived total surface mass over both antarctica and greenland peak in their respective summers due to increased atmospheric mass large interannual variations have also been found involving several continents in the 11 year gps obp solution the patterns of variation suggest that the recent satellite laser ranging slr observation of a reversal in trend of the earth s oblateness may be largely an interannual surface mass cycle with considerable contribution from the northern continents

use of borehole imaging to improve understanding of the in situ stress orientation of central and northern england and its implications for unconventional hydrocarbon resources abstract new interest in the potential for shale gas in the united kingdom uk has led to renewed exploration for hydrocarbons in the carboniferous age bowland hodder shales under central and northern england following an incidence of induced seismicity from hydraulic fracturing during 2010 at preese hall lancashire the publically available databases quantifying the in situ stress orientation of the united kingdom have shown to be inadequate for safe planning and regulation of hydraulic fracturing this paper therefore reappraises the in situ stress orientation for central and northern england based wholly on new interpretations of high resolution borehole imaging for stress indicators including borehole breakouts and drilling induced tensile fractures these analyses confirm the expected north northwest south southeast orientation of maximum horizontal in situ stress identified from previous studies e g evans and brereton 1990 the dual caliper data generated by evans and brereton 1990 yields a mean shmax orientation of 149 87 with a circular standard deviation of 66 9 however the use of borehole imaging without incorporation of results from older dual caliper logging tools very significantly decreases the associated uncertainty with a mean shmax orientation of 150 9 with a circular standard deviation of 13 1 the use of high resolution borehole imaging is thus shown to produce a more reliable assessment of in situ stress orientation the authors therefore recommend that the higher resolution of such imaging tools should therefore be treated as a de facto standard for assessment of in situ stress orientation prior to rock testing use of borehole imaging should be formally instituted into best practice or future regulations for assessment of in situ stress orientation prior to any hydraulic fracturing operations in the uk

a first look at the structure of the wave pouch during the 2009 predict grip dry runs over the atlantic abstractin support of the national science foundation pre depression investigation of cloud systems in the tropics nsf predict and national aeronautics and space administration genesis and rapid intensification processes nasa grip dry run exercises and national oceanic and atmospheric administration hurricane intensity forecast experiment noaa ifex during the 2009 hurricane season a real time wave tracking algorithm and corresponding diagnostic analyses based on a recently proposed tropical cyclogenesis model were applied to tropical easterly waves over the atlantic the model emphasizes the importance of a lagrangian recirculation region within a tropical wave critical layer the so called pouch where persistent deep convection and vorticity aggregation as well as column moistening are favored for tropical cyclogenesis distinct scenarios of hybrid wave vortex evolution are highlighted it was found that easterly waves without a pouch or with a shallow pouch did not develop although not all wav

the multiple vortex nature of tropical cyclogenesis abstract this study explores the extent to which potential vorticity pv generation and superposition were relevant on a variety of scales during the genesis of tropical storm allison allison formed close to shore and the combination of continuous doppler radar satellite aircraft and surface observations allows for the examination of tropical cyclogenesis in great detail preceding allison s genesis pv superposition on the large scale created an environment where decreased vertical shear and increased instability surface fluxes and low level cyclonic vorticity coexisted this presented a favorable environment for meso scale pv production by widespread convection and led to the formation of surface based meso scale vortices termed convective burst vortices cbvs the cbvs seemed to form in association with intense bursts of convection and rotated around each other within the meso circulation field one cbv eventually superposed with a mesoscale convective vortex mcv resulting in a mor

african easterly wave variability and its relationship to atlantic tropical cyclone activity abstract automatic tracking of vorticity centers in european centre for medium range weather forecasts analyses has been used to develop a 20 yr climatology of african easterly wave activity the tracking statistics at 600 and 850 mb confirm the complicated easterly wave structures present over the african continent the rainy zone equatorward of 15 n is dominated by 600 mb activity and the much drier saharan region poleward of 15 n is more dominated by 850 mb activity over the atlantic ocean there is just one storm track with the 600 and 850 mb wave activity collocated based on growth decay and genesis statistics it appears that the 850 mb waves poleward of 15 n over land generally do not get involved with the equatorward storm track over the ocean instead there appears to be significant development of 850 mb activity at the west african coast in the rainy zone around 10 n 10 w which it is proposed is associated with latent heat release based on the tracking statistics it has been shown th

genesis of hurricane julia 2010 within an african easterly wave developing and nondeveloping members from wrf letkf ensemble forecasts abstractin this study the predictability of and parametric differences in the genesis of hurricane julia 2010 are investigated using 20 mesoscale ensemble forecasts with the finest resolution of 1 km results show that the genesis of julia is highly predictable with all but two members undergoing genesis despite the high predictability substantial parametric differences exist between the stronger and weaker members notably the strongest developing member exhibits large upper tropospheric warming within a storm scale outflow during genesis in contrast the nondeveloping member has weak and more localized warming due to inhibited convective development and a lack of a storm scale outflow a reduction in the rossby radius of deformation in the strongest member aids in the accumulation of the warmth while little contraction takes place in the nondeveloping member the warming in the upper troposphere is responsible for the development of meso scale surface pressure falls and a meso surface low i

the use of gps horizontals for loading studies with applications to northern california and southeast greenland received 23 august 2012 revised 15 january 2013 accepted 20 january 2013 published 25 april 2013 1 we describe how gps measurements of horizontal crustal motion can be used to augment vertical crustal motion measurements to improve and extend gps studies of surface loading we show that the ratio of the vertical displacement to the horizontal displacement combined with the direction of the horizontal motion can help determine whether nearby loading is concentrated in a small region for example in a single lake or glacier and where that region is we illustrate this method by applying it to two specific cases an analysis of gps data from northern california to monitor the level of lake shasta and the analysis of data from a single gps site in southeast greenland to determine mass variability of two large nearby outletglaciers helheim glacier and midgaard glacier the californiaexampleserves largely as a proof of concept where the results can be assessed by comparing with independent observations lake shasta tide gauge data in this case our greenland results show that both helheim and midgaard have experienced notable interannual variations in mass loss rate over the last decade helheim sm ass loss accelerated rapidly in mid 2003 decelerated in late 2005 and increased again in 2008 2009 before returning to about its pre 2003 rate in late 2010 midgaard s mass loss accelerated in mid 2004 and remained more or less constant before returning to its pre 2003 rate in late 2008

the role of vortical hot towers in the formation of tropical cyclone diana 1984 abstract a high resolution 3 km horizontal grid spacing near cloud resolving numerical simulation of the formation of hurricane diana 1984 is used to examine the contribution of deep convective processes to tropical cyclone formation this study is focused on the 3 km horizontal grid spacing simulation because this simulation was previously found to furnish an accurate forecast of the later stages of the observed storm life cycle the numerical simulation reveals the presence of vortical hot towers or cores of deep cumulonimbus convection possessing strong vertical vorticity that arise from buoyancy induced stretching of local absolute vertical vorticity in a vorticity rich prehurricane environment at near cloud resolving scales these vortical hot towers are the preferred mode of convection they are demonstrated to be the most important influence to the formation of the tropical storm via a two stage evolutionary process i preconditioning of the local environment via diabatic production of mul

the impact of moist frontogenesis and tropopause undulation on the intensity size and structural changes of hurricane sandy 2012 abstractthis study examines the relative roles of moist frontogenesis and tropopause undulation in determining the intensity size and structural changes of hurricane sandy using a high resolution cloud resolving model a 138 h simulation reproduces sandy s four distinct development stages i rapid intensification ii weakening iii steady maximum surface wind but with large continued sea level pressure slp falls and iv reintensification results show typical correlations between intensity changes sea surface temperature and vertical wind shear during the first two stages the large slp falls during the last two stages are mostly caused by sandy s northward movement into lower tropopause regions associated with an eastward propagating midlatitude trough where the associated lower stratospheric warm air wraps into the storm and its surrounding areas the steady maximum surface wind occurs because of the widespread slp falls with weak gradients lacking significant inward advection of absolute

acceleration of the contribution of the greenland and antarctic ice sheets to sea level rise 1 ice sheet mass balance estimates have improved substantially in recent years using a variety of techniques over different time periods and at various levels of spatial detail considerable disparity remains between these estimates due to the inherent uncertainties of each method the lack of detailed comparison between independent estimates and the effect of temporal modulations in ice sheet surface mass balance here we present a consistent record of mass balance for the greenland and antarctic ice sheets over the past two decades validated by the comparison of two independent techniques over the last 8 years one differencing perimeter loss from net accumulation and one using a dense time series of time variable gravity we find excellent agreement between the two techniques for absolute mass loss and acceleration of mass loss in 2006 the greenland and antarctic ice sheets experienced a combined mass loss of 475 158 gt yr equivalent to 1 3 0 4 mm yr sea level rise notably the acceleration in ice sheet loss over the last 18 years was 21 9 1 gt yr2 for greenland and 14 5 2 gt yr2 for antarctica for a combined total of 36 3 2 gt yr2 this acceleration is 3 times larger than for mountain glaciers and ice caps 12 6 gt yr2 if this trend continues ice sheets will be the dominant contributor to sea level rise in the 21st century

a global view of equatorial waves and tropical cyclogenesis abstractthis study investigates the number of tropical cyclone formations that can be attributed to the enhanced convection from equatorial waves within each basin tropical depression td type disturbances i e easterly waves were the primary tropical cyclone precursors over the northern hemisphere basins particularly the eastern north pacific and the atlantic in the southern hemisphere however the number of storms attributed to td type disturbances and equatorial rossby waves were roughly equivalent equatorward of 20 n tropical cyclones formed without any equatorial wave precursor most often over the eastern north pacific and least often over the western north pacific the madden julian oscillation mjo was an important tropical cyclone precursor over the north indian south indian and western north pacific basins the mjo also affected tropical cyclogenesis by modulating the amplitudes of higher frequency waves each wave type reached the attribution threshold 1 5 times more often and tropi

genesis of tropical storm debby 2006 within an african easterly wave roles of the bottom up and midlevel pouch processes abstractthe bottom up generation of low level vortices lvs and midlevel vortices mvs during the genesis of tropical storm debby 2006 and the roles of a midlevel marsupial pouch associated with an african easterly wave aew are examined using an 84 h simulation with the finest grid size of 1 33 km results show that several mvs are generated in leading convective bands and then advected rearward into stratiform regions by front to rear ascending flows because of different lagrangian storm scale circulations mvs and lvs are displaced along different paths during the early genesis stages mvs propagate cyclonically inward within the aew pouch while experiencing slow intensification and merging under the influence of converging flows the mvs merging into a mesovortex is accelerated as they come closer to each other in the core region in contrast the low level lagrangian circulation is opened as a wave trough prior to tropical depression td stage so the lvs tend to escape from the pouch r

the extreme melt across the greenland ice sheet in 2012 1 the discovery of the 2012 extreme melt event across almost the entire surface of the greenland ice sheet is presented data from three different satellite sensors including the oceansat 2 scatterometer the moderate resolution imaging spectroradiometer and the special sensor microwave imager sounder are combined to obtain composite melt maps representing the most complete melt conditions detectable across the ice sheet satellite observations reveal that melt occurred at or near the surface of the greenland ice sheet across 98 6 of its entire extent on 12 july 2012 including the usually cold polar areas at high altitudes like summit in the dry snow facies of the ice sheet this melt event coincided with an anomalous ridge of warm air that became stagnant over greenland as seen in melt occurrences from multiple ice core records at summit reported in the published literature such a melt event is rare with the last significant one occurring in 1889 and the next previous one around seven centuries earlier in the medieval warm period given its rarity the 2012 extreme melt across greenland provides an exceptional opportunity for new studies in broad interdisciplinary geophysical research

improved methods for observing earth s time variable mass distribution with grace using spherical cap mascons we discuss several classes of improvements to gravity solutions from the gravity recovery and climate experiment grace mission these include both improvements in background geophysical models and orbital parameterization leading to the unconstrained spherical harmonic solution jpl rl05 and an alternate jpl rl05m mass concentration mascon solution benefitting from those same improvements but derived in surface spherical cap mascons the mascon basis functions allow for convenient application of a priori information derived from near global geophysical models to prevent striping in the solutions the resulting mass flux solutions are shown to suffer less from leakage errors than harmonic solutions and do not necessitate empirical filters to remove north south stripes lowering the dependence on using scale factors the global mean scale factor decreases by 0 17 to gain accurate mass estimates ocean bottom pressure obp time series derived from the mascon solutions are shown to have greater correlation with in situ data than do spherical harmonic solutions increase in correlation coefficient of 0 08 globally particularly in low latitude regions with small signal power increase in correlation coefficient of 0 35 regionally in addition to reducing the error rms with respect to the in situ data reduction of 0 37 cm globally and as much as 1 cm regionally greenland and antarctica mass balance estimates derived from the mascon solutions agree within formal uncertainties with previously published results computing basin averages for hydrology applications shows general agreement between harmonic and mascon solutions for large basins however mascon solutions typically have greater resolution for smaller spatial regions in particular when studying secular signals

case study of an intense african easterly wave abstract the life cycle of an intense african easterly wave aew over the african continent is examined using european centre for medium range weather forecasts ecmwf operational analyses meteosat satellite images and synoptic observations this system the strongest aew of 2000 can be tracked from central north africa into the eastern atlantic ocean where it is associated with the genesis of hurricane alberto synoptic analysis of the kinematic and thermodynamic fields is supplemented by analysis of potential vorticity pv allowing exploration at the role of multiple scales in the evolution of this aew the authors analysis promotes the division of the aew life cycle into three distinctive phases i initiation the aew development is preceded by a large convective event composed of several mesoscale convective systems over elevated terrain in sudan this convection provides a forcing on the baroclinically and barotropically unstable state that exists over tropical north africa ii baroclini

interannual variability of greenland ice losses from satellite gravimetry 1 using extended satellite gravity measurements from the gravity recovery and climate experiment grace here we show that ice losses in southeast greenland appear to have slowed down dramatically since late 2007 while those in the west especially northwest greenland show continued accelerations in recent years over the period april 2002 to november 2009 averaged ice loss rates in eastern greenland 120 31 gt yr are still significantly larger than those in the west 86 3 22 gt yr however the estimated ice loss rate from glaciers in northwest greenland has increased from 30 9 8 gt yr over the first few years 2002 2005 to 128 2 33 gt yr for the more recent period 2007 2009 while the loss rate in southeast greenland for the more recent period has become almost negligible down from 109 28 gt yr of just a few years ago the rapid change in the nature of the regional ice mass in southeast and northwest greenland in the course of only several years further reinforces the idea that the greenland ice sheet mass balance is very vulnerable to regional climate conditions the dramatic slow down of ice loss in southeast greenland observed by grace provides an independent verification of similar reports from other remote sensing data the observed significant interannual variability of greenland ice mass change suggests that it is very challenging to quantify greenland s long term ice mass change rates and some observed apparent accelerations might simply be a reflection of the interannual variability

a reconciled estimate of ice sheet mass balance we combined an ensemble of satellite altimetry interferometry and gravimetry data sets using common geographical regions time intervals and models of surface mass balance and glacial isostatic adjustment to estimate the mass balance of earth s polar ice sheets we find that there is good agreement between different satellite methods especially in greenland and west antarctica and that combining satellite data sets leads to greater certainty between 1992 and 2011 the ice sheets of greenland east antarctica west antarctica and the antarctic peninsula changed in mass by 142 49 14 43 65 26 and 20 14 gigatonnes year 1 respectively since 1992 the polar ice sheets have contributed on average 0 59 0 20 millimeter year 1 to the rate of global sea level rise

genesis of hurricane julia 2010 within an african easterly wave low level vortices and upper level warming abstractwhile a robust theoretical framework for tropical cyclogenesis tcg within african easterly waves aews has recently been developed little work explores the development of low level meso scale vortices llvs and a meso scale surface low in relation to deep convection and upper tropospheric warming in this study the development of an llv into hurricane julia 2010 is shown through a high resolution model simulation with the finest grid size of 1 km the results presented expand upon the connections between llvs and the aew presented in previous studies while demonstrating the importance of upper tropospheric warming for tcg it is found that the significant intensification phase of hurricane julia is triggered by the pronounced upper tropospheric warming associated with organized deep convection the warming is able to intensify and expand during tcg owing to formation of a storm scale outflow beyond the rossby radius of deformation results confirm previous ideas by demonstrating that th

increasing rates of ice mass loss from the greenland and antarctic ice sheets revealed by grace 1 we use monthly measurements of time variable gravity from the grace gravity recovery and climate experiment satellite gravity mission to determine the ice mass loss for the greenland and antarctic ice sheets during the period between april 2002 and february 2009 we find that during this time period the mass loss of the ice sheets is not a constant but accelerating with time i e that the grace observations are better represented by a quadratic trend than by a linear one implying that the ice sheets contribution to sea level becomes larger with time in greenland the mass loss increased from 137 gt yr in 2002 2003 to 286 gt yr in 2007 2009 i e an acceleration of 30 11 gt yr2 in 2002 2009 in antarctica the mass loss increased from 104 gt yr in 2002 2006 to 246 gt yr in 2006 2009 i e an acceleration of 26 14 gt yr2 in 2002 2009 the observed acceleration in ice sheet mass loss helps reconcile grace ice mass estimates obtained for different time periods

data adaptive detection of transient deformation in geodetic networks author s walwer d calais e ghil m abstract 2016 american geophysical union all rights reserved the recent development of dense and continuously operating global navigation satellite system gnss networks worldwide has led to a significant increase in geodetic data sets that sometimes capture transient deformation signals it is challenging however to extract such transients of geophysical origin from the background noise inherent to gnss time series and even more so to separate them from other signals such as seasonal redistributions of geophysical fluid mass loads in addition because of the very large number of continuously recording gnss stations now available it has become impossible to systematically inspect each time series and visually compare them at all neighboring sites here we show that multichannel singular spectrum analysis m ssa a method derived from the analysis of dynamical systems can be used to extract transient deformations seasonal oscillations and background noise present in gnss time series m ssa is a multivariate nonparametric statistical method that simultaneously exploits the spatial and temporal correlations of geophysical fields the method allows for the extraction of common modes of variability such as trends with nonconstant slopes and oscillations shared across time series without a priori hypotheses about their spatiotemporal structure or their noise characteristics we illustrate this method using synthetic examples and show applications to actual gps data from alaska to detect seasonal signals and microdeformation at the akutan active volcano the geophysically coherent spatiotemporal patterns of uplift and subsidence thus detected are compared to the results of an idealized model of such processes in the presence of a magma chamber source

transformation of a large monsoon depression to a tropical storm during tcm 93 abstract data obtained during two aircraft observing periods aop from the tcm 93 mini field experiment are used to describe the transformation between 5 and 10 n of a large depression in the western north pacific monsoon trough into a tropical cyclone over a 36 h period the transformation is defined to occur in three stages although a large mesoscale convective system mcs was present along the eastern periphery of the monsoon depression during the preorganization stage characterized by observations from the first aop the overall convective organization of the broad circulation is weak the structure of the mcs provided a midlevel subsynoptic contribution to the vorticity of the monsoon depression and contributed to a shift in the center of the monsoon depression circulation between 800 and 600 mb toward the mcs location however the presence of unsaturated downdrafts associated with the mcs perturbed the low level thermodynamic conditions and contributed to the rapid decay of the mcs slow intens

stress induced borehole elongation a comparison between the four arm dipmeter and the borehole televiewer in the auburn geothermal well the nature and origin of borehole elongation recorded by the four arm dipmeter calipers is studied utilizing information obtained from hydraulic fracturing stress measurements and borehole televiewer data taken in a well located in auburn new york a preferred orientation n10 w s10 e 10 and a less prominant e w orientation of borehole elongation was observed on two runs of the dipmeter comparisons of borehole geometry determined using the televiewer and the dipmeter show that both tools give the same orientation of borehole elongtion provided that the zone of elongation is longer than 30 cm comparisons of dipmeter caliper data with orientation of in situ stress and natural fractures obtained from hydrofracturing tests and televiewer data show that the n10 w s10 e borehole elongations 1 are axisymmetric 2 are aligned with the minimum horizontal stress sh and 3 are not associated with natural fractures intersecting the well these elongations are interpreted as stress induced well bore breakouts the e w elongation direction is characterized by an asymmetric borehole cross section in thinly bedded rocks and is not caused by breakouts this asymmetric geometry can be discriminated from breakouts using the oriented electric measurements provided by the dipmeter this study demonstrates that the dipmeter can be used to determine the orientation of sh by mapping breakouts confirming the results of earlier less detailed studies and provides a firm basis for mapping regional stress patterns using existing dipmeter data

genesis of tropical storm eugene 2005 from merging vortices associated with itcz breakdowns part ii roles of vortex merger and ambient potential vorticity abstract in this study the roles of merging midlevel mesoscale convective vortices mcvs and convectively generated potential vorticity pv patches embedded in the intertropical convergence zone itcz in determining tropical cyclogenesis are examined by calculating pv and absolute vorticity budgets with a cloud resolving simulation of tropical storm eugene 2005 results show that the vortex merger occurs as the gradual capture of small scale pv patches within a slow drifting mcv by another fast moving mcv thus concentrating high pv near the merger s circulation center with its peak amplitude located slightly above the melting level the merging phase is characterized by sharp increases in surface heat fluxes low level convergence latent heat release and upward motion lower tropospheric pv surface pressure falls and growth of cyclonic vorticity from the bottom upward melting and freezing appear to affect markedly the vertical structures of diabatic heating convergence absolute vorticity

antarctica greenland and gulf of alaska land ice evolution from an iterated grace global mascon solution we have determined the ice mass evolution of the antarctica and greenland ice sheets ais and gis and gulf of alaska goa glaciers from a new grace global solution of equal area surface mass concentration parcels mascons in equivalent height of water the mascons were estimated directly from the reduction of the inter satellite k band range rate kbrr observations taking into account the full noise covariance and formally iterating the solution the new solution increases signal recovery while reducing the grace kbrr observation residuals the mascons were estimated with 10 day and 1 arc degree equal area sampling applying anisotropic constraints an ensemble empirical mode decomposition adaptive filter was applied to the mascon time series to compute annual mass balances the details and causes of the spatial and temporal variability of the land ice regions studied are discussed the estimated mass trend over the total gis ais and goa glaciers for the time period 1 december 2003 to 1 december 2010 is 380 plus or minus 31 gt a exp 1 equivalent to 1 05 plus or minus 0 09 mma exp 1 sea level rise over the same time period we estimate the mass acceleration to be 41 plus or minus 27 gt a exp 2 equivalent to a 0 11 plus or minus 0 08 mm a exp 2 rate of change in sea level the trends and accelerations are dependent on significant seasonal and annual balance anomalies

satellite gravity measurements confirm accelerated melting of greenland ice sheet using time variable gravity measurements from the gravity recovery and climate experiment grace satellite mission we estimate ice mass changes over greenland during the period april 2002 to november 2005 after correcting for the effects of spatial filtering and limited resolution of grace data the estimated total ice melting rate over greenland is 239 23 cubic kilometers per year mostly from east greenland this estimate agrees remarkably well with a recent assessment of 224 41 cubic kilometers per year based on satellite radar interferometry data grace estimates in southeast greenland suggest accelerated melting since the summer of 2004 consistent with the latest remote sensing measurements

acceleration of greenland ice mass loss in spring 2004 in 2001 the intergovernmental panel on climate change projected the contribution to sea level rise from the greenland ice sheet to be between 0 02 and 0 09 m from 1990 to 2100 ref 1 however recent work has suggested that the ice sheet responds more quickly to climate perturbations than previously thought particularly near the coast here we use a satellite gravity survey by the gravity recovery and climate experiment grace conducted from april 2002 to april 2006 to provide an independent estimate of the contribution of greenland ice mass loss to sea level change we detect an ice mass loss of 248 36 km3 yr 1 equivalent to a global sea level rise of 0 5 0 1 mm yr 1 the rate of ice loss increased by 250 per cent between the periods april 2002 to april 2004 and may 2004 to april 2006 almost entirely due to accelerated rates of ice loss in southern greenland the rate of mass loss in north greenland was almost constant continued monitoring will be needed to identify any future changes in the rate of ice loss in greenland

numerical simulation of the meso β scale structure and evolution of the 1977 johnstown flood part ii inertially stable warm core vortex and the mesoscale convective complex abstract a mesoscale warm core vortex associated with the mesoscale convective complex mcc that produced the 1977 johnstown flood is examined using a three dimensional nested grid model simulation of the flood episode in the simulation the vortex plays a key role in determining the evolution of the mcc a squall line and the distribution of heavy precipitation the vortex has a space scale of 100 200 km in diameter and a time scale of more than 18 hours its low pressure center extends from the midtroposphere down to the surface and its maximum vorticity occurs between 850 and 700 mb a pool of cool moist downdraft air develops in the surface to the 850 mb layer beneath the warm core while a cold dome forms in the vicinity of the tropopause above the warm core following forcing from repeated deep convection prior to model initial time the vortex is initiated by mesoscale ascent associated with a traveling meso scale wave genesis takes place in a nearly saturated slightly conditionally unstabl

computations of the viscoelastic response of a 3 d compressible earth to surface loading an application to glacial isostatic adjustment in antarctica and canada s u m m a r y we develop a 3 d finite element model to study the viscoelastic response of a compressible earth to surface loads the effects of centre of mass motion polar wander feedback and selfconsistent ocean loading are implemented to assess the model s accuracy we benchmark the numerical results against a semi analytic solution for spherically symmetric structure we force our model with the ice 5g global ice loading history to study the effects of laterally varying viscosity structure on several glacial isostatic adjustment gia observables including relative sea level rsl measurements incanada and present day time variable gravity and uplift rates in antarctica canadian rsl observations have been used to determine the earth s globally averaged viscosity profile antarcticgps uplift rates have been used to constrainantarcticgia models and gia time variable gravity and uplift signals are error sources for grace and altimeter estimates of present day antarctic ice mass loss and must be modelled and removed from those estimates computinggia results for a 3 d viscosity profile derived from a realistic seismic tomography model and comparing with results computed for 1 d averages of that 3 d profile we conclude that 1 a gia viscosity model based on canadian relative sea level data is more likely to represent a canadian average than a true global average 2 the effects of 3 d viscosity structure on grace estimates of present day antarctic mass loss are probably smaller than the difference between gia models based on different antarctic deglaciation histories and 3 the effects of 3 d viscosity structure on antarctic gps observations of present day uplift rate can be significant and can complicate efforts to use gps observations to constrain 1 d gia models

convective contribution to the genesis of hurricane ophelia 2005 abstract the convection occurring in the tropical depression that became hurricane ophelia 2005 was investigated just prior to tropical storm formation doppler radar showed a deep wide intense convective cell of a type that has been previously thought to occur in intensifying tropical depressions but has not heretofore been documented in detail the updraft of the cell was 10 km wide 17 km deep had updrafts of 10 20 m s 1 throughout its mid to upper levels and contained a cyclonic vorticity maximum the massive convective updraft was maintained by strong positive buoyancy which was maximum at about the 10 km level probably aided by latent heat of freezing evaporative cooling and precipitation drag occurred in the rain shower of the cell but were insufficient to produce a strong downdraft or gust front outflow to force the updraft the convective updraft was fed by a layer of strong inflow that was several kilometers deep wind induced turbulence just above the ocean surface enriched the equi

genesis of typhoon chanchu 2006 from a westerly wind burst associated with the mjo part i evolution of a vertically tilted precursor vortex abstract although previous studies have shown the relationship between the madden julian oscillation mjo and tropical cyclogenesis tcg many scale interactive processes leading to tcg still remain mysterious in this study the larger scale flow structures and evolution during the pregenesis genesis and intensification of typhoon chanchu 2006 near the equator are analyzed using ncep s final analysis satellite observations and 11 day nested numerical simulations with the advanced research weather research and forecast model arw wrf results show that the model could reproduce the structures and evolution of a synoptic westerly wind burst wwb associated with the mjo during the genesis of chanchu including the eastward progression of a wwb from the indian ocean into the pacific ocean the modulation of the associated quasi symmetric vortices the initial slow spinup of a northern pre chanchu disturbance at the northeastern periphery of the wwb and its general track and intensification it i

synoptic scale influence of the saharan air layer on tropical cyclogenesis over the eastern atlantic abstract the formations of hurricane andrew tropical storm ernesto and hurricane luis which occurred respectively during the 1992 1994 and 1995 hurricane seasons over the eastern atlantic have been investigated by utilizing the european centre for medium range weather forecasts ecmwf gridded data analyses these cases were selected to illustrate the contrasting influences of the saharan air layer sal on tropical cyclogenesis analyses results show that tropical storm ernesto 1994 and hurricane luis 1995 formed from the merger of the low level 925 hpa and midlevel 700 hpa vortices over the eastern atlantic within the monsoon trough enhanced by surges in the trades midlevel vortices associated with each case appear to evolve from african wave troughs enhanced by cyclonic shear vorticity of the midtropospheric jet which existed to the south of an sal anticyclonic eddy as an elongated wind maximum vorticity budget calculations suggest that vortex stretching dominated the enhancement of

thermodynamic aspects of tropical cyclone formation abstractthe thermodynamic aspects of tropical cyclone tc formation near the center of the wave pouch a region of approximately closed lagrangian circulation within the wave critical layer are examined through diagnoses of a high resolution numerical simulation and dropsonde data from a recent field campaign it is found that the meso area near the pouch center is characterized by high saturation fraction small difference in equivalent potential temperature e between the surface and the middle troposphere and a short incubation time scale updrafts tend to be more vigorous in this region presumably because of reduced dry air entrainment while downdrafts are not suppressed the thermodynamic conditions near the pouch center are thus critically important for tc formation the balanced responses to convective and stratiform heating at the pregenesis stage are examined using the sawyer eliassen equation deep convection is concentrated near the pouch center the strong radial and vertical gradients o

tropical storm development from african easterly waves in the eastern atlantic a comparison of two successive waves using a regional model as part of nasa amma 2006 abstract two successive african easterly waves aews from august 2006 are analyzed utilizing observational data the european centre for medium range weather forecasts reanalysis and output from the national center for atmospheric research national oceanic and atmospheric administration weather research and forecasting model wrf to understand why the first wave does not develop over the eastern atlantic while the second wave does the first aew eventually forms hurricane ernesto over the caribbean sea but genesis does not occur over the eastern atlantic the second wave although weaker than the first over land leaves the west african coast and quickly intensifies into tropical storm debby west of the cape verde islands this study shows that the environmental conditions associated with the first aew s passage inhibited development these conditions include strong low and midtropospheric vertical wind shear owing to a stronger than normal african easterly jet lower than normal relative humidity a

annual variations in gps measured vertical displacements near upernavik isstrom greenland and contributions from surface mass loading in response to present day ice mass loss on and near the greenland ice sheet steady crustal uplifts have been observed from the network of global positioning system gps stations mounted on bedrock in addition to the secular uplift trends the gps time series also show prominent annual variability here we examine the annual changes of the vertical displacements measured at two gps stations srmp and upvk near upernavik isstrom in western greenland we model elastic loading displacements due to various surface mass loading including three non ice components atmospheric pressure ocean bottom pressure continental water storage and one ice component i e surface mass balance smb we find that the contribution from atmospheric pressure changes can explain 46 and 78 of the annual amplitude observed in the gps verticals at srmp and upvk respectively we also show that removing the predicted loading displacements due to smb adversely increases the annual variance of the gps residuals however using the gps data alone we cannot identify the exact cause s of this discrepancy because the annual loading displacements are sensitive to the smb changes from over 85 of the ice sheet area alternatively by differencing vertical displacements between the two stations we find a good agreement between the modeled differential smb loading displacements and the gps residuals after removing non ice components our study highlights the necessity of correcting for non ice loading contributions in the gps measurements of crustal deformation to infer ice mass changes in greenland at annual periods

greenland ice sheet mass balance distribution of increased mass loss with climate warming 2003 07 versus 1992 2002 we derive mass changes of the greenland ice sheet gis for 2003 07 from icesat laser altimetry and compare them with results for 1992 2002 from ers radar and airborne laser altimetry the gis continued to grow inland and thin at the margins during 2003 07 but surface melting and accelerated flow significantly increased the marginal thinning compared with the 1990s the net balance changed from a small loss of 7 3g t a 1 in the 1990s to 171 4g t a 1 for 2003 07 contributing 0 5 mm a 1 to recent global sea level rise we divide the derived mass changes into two components 1 from changes in melting and ice dynamics and 2 from changes in precipitation and accumulation rate we use our firn compaction model to calculate the elevation changes driven by changes in both temperature and accumulation rate and to calculate the appropriate density to convert the accumulation driven changes to mass changes increased losses from melting and ice dynamics 17 206 gt a 1 are over seven times larger than increased gains from precipitation 10 35 gt a 1 during a warming period of 2 k 10 a 1 over the gis above 2000 m elevation the rate of gain decreased from 44 to 28 gt a 1 while below 2000 m the rate of loss increased from 51 to 198 gt a 1 enhanced thinning below the equilibrium line on outlet glaciers indicates that increased melting has a significant impact on outlet glaciers as well as accelerating ice flow increased thinning at higher elevations appears to be induced by dynamic coupling to thinning at the margins on decadal timescales

a vortical hot tower route to tropical cyclogenesis abstract a nonhydrostatic cloud model is used to examine the thermomechanics of tropical cyclogenesis under realistic meteorological conditions observations motivate the focus on the problem of how a midtropospheric cyclonic vortex a frequent by product of mesoscale convective systems during summertime conditions over tropical oceans may be transformed into a surface concentrated warm core tropical depression as a first step the vortex transformation is studied in the absence of vertical wind shear or zonal flow within the cyclonic vorticity rich environment of the mesoscale convective vortex mcv embryo the simulations demonstrate that small scale cumulonimbus towers possessing intense cyclonic vorticity in their cores vortical hot towers vhts emerge as the preferred coherent structures the vhts acquire their vertical vorticity through a combination of tilting of mcv horizontal vorticity and stretching of mcv and vht generated vertical vorticity horizontally localized and exhibiting conve

gps measurements of crustal uplift near jakobshavn isbrae due to glacial ice mass loss 1 we analyze 2006 2009 data from four continuous global positioning system gps receivers located between 5 and 150 km from the glacier jakobshavn isbrae west greenland the gps stations were established on bedrock to determine the vertical crustal motion due to the unloading of ice from jakobshavn isbrae all stations experienced uplift but the uplift rate at kangia north only 5 km from the glacier front was about 10 mm yr 1 larger than the rate at ilulissat located only 45 km further away this suggests that most of the uplift is due to the unloading of the earth s surface as jakobshavn thins and loses mass our estimate of jakobshavn s contribution to uplift rates at kangia north and ilulissat are 14 6 1 7 mm yr 1 and 4 9 1 1 mm yr 1 respectively the observed rates are consistent with a glacier thinning model based on repeat altimeter surveys from nasa s airborne topographic mapper atm which shows that jakobshavn lost mass at an average rate of 22 2 km3 yr 1 between 2006 and 2009 at kangia north and ilulissat the predicted uplift rates computed using thinning estimates from the atm laser altimetry are 12 1 0 9 mm yr 1 and 3 2 0 3 mm yr 1 respectively the observed rates are slightly larger than the predicted rates the fact that the gps uplift rates are much larger closer to jakobshavn than further away and are consistent with rates inferred using the atm based glacier thinning model shows that gps measurements of crustal motion are a potentially useful method for assessing ice mass change models

tropical cyclogenesis associated with rossby wave energy dispersion of a preexisting typhoon part i satellite data analyses abstract the structure and evolution characteristics of rossby wave trains induced by tropical cyclone tc energy dispersion are revealed based on the quick scatterometer quikscat and tropical rainfall measuring mission trmm microwave imager tmi data among 34 cyclogenesis cases analyzed in the western north pacific during 2000 01 typhoon seasons six cases are associated with the rossby wave energy dispersion of a preexisting tc the wave trains are oriented in a northwest southeast direction with alternating cyclonic and anticyclonic vorticity circulation a typical wavelength of the wave train is about 2500 km the tc genesis is observed in the cyclonic circulation region of the wave train possibly through a scale contraction process the satellite data analyses reveal that not all tcs have a rossby wave train in their wakes the occurrence of the rossby wave train depends to a certain extent on the tc intensity and the background flow whether or not a rossby wave train can finally lead to cy

improving the estimate of the secular variation of greenland ice mass in the recent decades by incorporating a stochastic process abstract the irregular interannual variations observed in the greenland ice sheet gris mass balance can be interpreted as stochastic these variations often have large amplitudes and if not accounted for correctly in the mass change model parameterization could have profound impacts on the estimate of the secular trend and acceleration here we propose a new mass trajectory model that includes both the conventional deterministic components and a stochastic component this new model simultaneously estimates the secular rate and acceleration seasonal components and the stochastic component of mass changes simulations show that this new model improves estimates of model parameters especially accelerations over the conventional model without stochastic component using this new model we estimate an acceleration of 1 6 1 3 gt yr2 in mass change minus means mass loss for 2003 2017 using the gravity recovery and climate experiment grace data and an acceleration of 1 1 1 3 gt yr2 using the modeled surface mass balance plus observed ice discharge the corresponding rates are estimated to be 288 2 12 7 gt yr and 274 9 13 0 gt yr the greatest discrepancies between the new and the conventional model parameter determinations are found in the acceleration estimates 1 6 gt yr2 vs 7 5 gt yr2 from the grace data the estimated accelerations using the new method are apparently smaller than those estimated by other studies in terms of mass loss our quantitative analysis elucidates that the acceleration estimate using the conventional method is the lower bound i e 7 5 gt yr2 for 2003 2017 while the acceleration estimated by the new method lies in the middle of the possible ranges it is also found that these discrepancies between the new and the conventional methods diminish with sufficiently long 20 yr observation records

grace observes small scale mass loss in greenland using satellite gravity data between february 2003 and january 2008 we examine changes in greenland s mass distribution on a regional scale during this period greenland lost mass at a mean rate of 179 25 gt yr equivalent to a global mean sea level change of 0 5 0 1 mm yr rates increase over time suggesting an acceleration of the mass loss driven by mass loss during summer the largest mass losses occurred along the southeastern and northwestern coast in the summers of 2005 and 2007 when the ice sheet lost 279 gt and 328 gt of ice respectively within 2 months in 2007 a strong mass loss is observed during summer at elevations above 2000 m for the first time since the start of the observations

tropical cyclogenesis associated with rossby wave energy dispersion of a preexisting typhoon part ii numerical simulations abstract the cyclogenesis events associated with the tropical cyclone tc energy dispersion are simulated in a 3d model a new tc with realistic dynamic and thermodynamic structures forms in the wake of a preexisting tc when a large scale monsoon gyre or a monsoon shear line flow is present maximum vorticity generation appears in the planetary boundary layer pbl and the vorticity growth exhibits an oscillatory development this oscillatory growth is also seen in the observed rainfall and cloud top temperature fields the diagnosis of the model output shows that the oscillatory development is attributed to the discharge and recharge of the pbl moisture and its interaction with convection and circulation the moisture convection feedback regulates the tc development through controlling the atmospheric stratification raindrop induced evaporative cooling and downdraft pbl divergence and vorticity generation on one hand ascending motion associated with deep convection transports moisture upward and le

origins of the european regional stress field abstract we present a study of the origins of the european regional stress field intraplate stresses due to various plate boundary forces and intraplate stress sources were predicted using an elastic finite element analysis the finite element mesh consists of about 1629 nodes in a network of 3117 triangular elements which provide a spatial resolution of about 1 the study builds on the previous modelling studies through consideration of a wide range of plausible forces acting along the collisional eastern and southern plate boundaries and importantly through the inclusion of forces due to other lateral density variations within the lithosphere such as those associated with the continental margins and high topography the modelling was constrained by more than 1800 stress indicators from the world stress map project which provide information about the orientation of the observed maximum horizontal compressive stress sh the torque associated with the ridge push force is well constrained and the principal source of uncertainty relates to the boundary conditions used to represent the collisional resistance acting along the eastern and southern boundaries a gradient in the collisional resistance increasing in magnitude from west to east is assumed to act along the southern plate boundary whereas the eastern boundary is modelled as a pinned margin at 46 e the sh orientation and magnitude of the regional stress field was found to be largely invariant to the boundary conditions used to represent the tectonic forces acting along the eastern and southern margins and is characterized by a nearly uniform nw se compression with a magnitude in the range of 10 20 mpa averaged over a 100 km thick lithosphere lateral density variations within the continental areas of europe were found to reduce the magnitude of the predicted stresses but do not have a significant effect on the orientation of the regional stress field

mass transport waves amplified by intense greenland melt and detected in solid earth deformation the annual cycle and secular trend of greenland mass loading are well recorded in measurements of solid earth deformation horizontal crustal displacements can potentially track the spatiotemporal detail of mass changes with great fidelity our analysis of greenland crustal motion data reveals that a significant excitation of horizontal amplitudes occurs during the intense melt years we discover that solitary seasonal waves of substantial mass transport 1 67 0 54 gt month traveled at an average speed of 7 1 km month through rink glacier in 2012 we deduce that intense surface melting enhanced either basal lubrication or softening of shear margins or both causing the glacier to thin dynamically in summer the newly routed upstream subglacial water was likely to be both retarded and inefficient thus providing a causal mechanism for the prolonged ice transport to continue well into the winter months as the climate continues to produce increasingly warmer spring and summer amplified seasonal waves of mass transport may become ever more present with important ramifications for the future sea level rise

genesis of pre hurricane felix 2007 part i the role of the easterly wave critical layer abstract the formation of pre hurricane felix 2007 in a tropical easterly wave is examined in a two part study using the weather research and forecasting wrf model with a high resolution nested grid configuration that permits the representation of cloud system processes the simulation commences during the wave stage of the precursor african easterly wave disturbance here the simulated and observed developments are compared while in part ii of the study various large scale analyses physical parameterizations and initialization times are explored to document model sensitivities in this first part the authors focus on the wave vortex morphology its interaction with the adjacent intertropical convergence zone complex and the vorticity balance in the neighborhood of the developing storm analysis of the model simulation points to a bottom up development process within the wave critical layer and supports the three new hypotheses of tropical cyclone formation proposed recently by dunkerton montgome

oceanic cyclogenesis as induced by a mesoscale convective system moving offshore part ii genesis and thermodynamic transformation abstract the genesis of intense cyclonic vorticity in the boundary layer and the transformation of a low level cold pool to a warm core anomaly associated with the long lived mesoscale convective systems mcss which produced the july 1977 johnstown flash flood and later developed into a tropical storm are examined using a 90 h real data simulation of the evolution from a continental mcs vortex to an oceanic cyclone storm system it is shown that the midlevel vortex trough at the end of the continental mcs s life cycle is characterized by a warm anomaly above and a cold anomaly below the mesovortex as it drifts toward the warm gulf stream water plays an important role in initiating and organizing a new mcs and a cyclonic shear vorticity band at the southern periphery of the previously dissipated mcs it is found from the vorticity budget that the vorticity band is amplified through stretching of absolute vorticity as it is wrapped around in a slantwise manner toward the cyclone center then the as

the genesis of hurricane guillermo texmex analyses and a modeling study abstract the transformation of a mesoscale convective system into hurricane guillermo was captured by aircraft and doppler wind data during the tropical experiment in mexico the early phase of the system evolves in a way very similar to previously documented mesoscale convective systems with a midlevel mesocyclone developing in the stratiform precipitation region more unusually the cyclone extends to low altitudes a weak cyclone is discernable even in the 300 m altitude wind field after another day of evolution a small surface based warm core cyclone is observed to develop within the relatively cold air associated with the mesocyclone aloft this mesocyclone develops into a hurricane over the subsequent day a nonhydrostatic axisymmetric numerical model is used to explore the evolution of the initially cold core midlevel vortex into a tropical cyclone a mesoscale midlevel showerhead is switched on in an initially quiescent tropical atmosphere overlying a warm ocean surface evaporation of t

analysis of african easterly wave structures and their role in influencing tropical cyclogenesis abstract composite structures of african easterly waves aews that develop into named tropical cyclones in the atlantic are compared and contrasted with nondeveloping aews using the 40 yr ecmwf re analysis era 40 data and satellite brightness temperature between 1979 and 2001 developing aews are characterized by a more distinctive cold core structure two days before reaching the west african coast as they move westward the convective activity increases further in the vicinity of the guinea highlands region at the same time the aew trough increases its vorticity at low levels consistent with a transformation toward a more warm core structure before it reaches the ocean as the aew moves over the ocean convection is maintained in the trough consistent with the observed tropical cyclogenesis the nondeveloping aew has a similar evolution before reaching the coast except that the amplitudes are weaker and there is less convective activity in the guinea highlands region the nondeveloping aew composite

geodetic measurements reveal short term changes of glacial mass near jakobshavn isbrae greenland from 2007 to 2017 abstract the global positioning system gps and gravity recovery and climate experiment grace provide important geodetic datasets to study glacial mass change applying the multichannel singular spectral analysis to the gps measured vertical and horizonal crustal displacement and grace derived vertical displacement near jakobshavn isbrae ji in western greenland from 2007 to 2017 we reconstruct the short term loading displacements due to ice mass changes both the vertical and east displacements show strong seasonal variability they also reveal three episodes of transient displacements downward and eastward motion from late 2007 to around 2010 sustained upward and westward motion from 2010 to early 2013 and downward and eastward motion till late 2016 we also forward model the seasonal and transient displacements caused by surface mass balance smb and glacier dynamics our model agrees well with the geodetic observations and provides quantitative insights into the contribution from smb and ice dynamics to the ice mass changes we find that smb is the dominant contributor to the seasonal and transient displacements at three out of four gps sites aasi ilul and qeqe while at the fourth gps site kaga that is closest to the glacier the contributions to the transient displacements from smb and glacier dynamics are comparable the forward modeling also suggests that the dynamic mass change in the ji catchment underwent strong seasonal variations and these variations correlated more with the seasonal retreat and advance of the calving front than with the changes of glacial velocities our altimetry results reveal that the frontal portion of ji catchment lost 34 gt in 2012 and this loss of ice declined to only 11 gt in 2016 due to widespread thickening along the main flowline

effect of borehole deviation on breakout orientations well bore breakouts are zones of spalling and fracture that form on opposite sides of a well bore and tend to change the cross sectional shape of the borehole from circular to roughly elliptical in vertical holes drilled in areas where one principal stress sv is vertical breakouts tend to form at opposite ends of the borehole diameter parallel to the least compressive horizontal principal stress direction sh this paper uses an analytical elastic solution for stress at the wall of a borehole to analyze the rotation of breakout orientations away from the direction of sh as the borehole deviates from the direction of the vertical principal stress the calculated orientations of breakouts in deviated boreholes depend on the type of faulting regime in which the well was drilled i e normal strike slip or thrust on the deviation angle o of the borehole axis from vertical on the angle between the horizontal projection of the borehole axis and the direction of sh and on the relative magnitudes of the three principal stresses sh sh the greatest compressive horizontal stress and sv in the strike slip faulting regime regardless of the values of sv sh and sh a borehole must deviate at least 35 from vertical before the horizontal projection of the breakout orientation differs by more than 10 from sh in the normal and thrust faulting regimes however the borehole deviation angle ocrit required to rotate projected breakout orientations by 10 from sh approaches zero as the value of sh approaches that of sh in the thrust faulting regime only about 3 of all combinations of sv sh and sh will produce ocrit values less than 10 while about 12 of all such combinations will yield ocrit 10 in the normal faulting regime about 12 and 33 of such combinations will yield ocrit 20 in the thrust and normal faulting regimes respectively careful study of changes in breakout orientation as a function of borehole deviation may improve the resolution of inferred stress directions when studying breakouts in deviated boreholes in these two faulting regimes

mass balance of the greenland ice sheet from 1958 to 2007 we combine estimates of the surface mass balance smb of the greenland ice sheet for years 1958 to 2007 with measurements of the temporal variability in ice discharge d to deduce the total ice sheet mass balance during that time period we find a robust correlation r2 0 83 between anomalies in smb and in d which we use to reconstruct a continuous series of total ice sheet mass balance we find that the ice sheet was losing 110 70 gt yr in the 1960s 30 50 gt yr or near balance in the 1970s 1980s and 97 47 gt yr in 1996 increasing rapidly to 267 38 gt yr in 2007 multi year variations in ice discharge themselves related to variations in smb cause 60 20 more variation in total mass balance smb and therefore dominate the ice sheet mass budget copyright 2008 by the american geophysical union

utilization of observations of well bore failure to constrain the orientation and magnitude of crustal stresses application to continental deep sea drilling project and ocean drilling program boreholes

scale interactions during the formation of typhoon irving the development of typhoon irving is investigated using a variety of data including special research aircraft data from the tropical cyclone motion tcm 92 experiment objective analyses satellite data and traditional surface and sounding data the development process is treated as a dry adiabatic vortex dynamics problem and it is found that environmental and mesoscale dynamics mutually enhance each other in a cooperative interaction during cyclone formation synoptic scale interactions result in the evolution of the hostile environment toward more favorable conditions for storm development mesoscale interactions with the low level large scale circulations and with other midlevel mesoscale features result in development of vorticity in the midlevels and enhancement of the low level vorticity associated with the developing surface cyclone multiple developments of mesoscale convective systems after the storm reaches tropical depression strength suggests both an increase in low level confluence and a tendency toward recurrent development of associated mesoscale convective vortices this is observed in both aircraft data and satellite imagery where subsequent interactions including mergers with the low level tropical depression vortex are observed a contour dynamics experiment suggests that the movement of mesoscale convective systems in satellite imagery corresponds well to the movement of their associated midlevel vortices results from a simple baroclinic experiment show that the midlevel vortices affect the large scale low level circulation in two ways 1 initially interactions between midlevel vortices produce a combined vortex of greater depth 2 interaction between midlevel vortices and the low level circulation produces a development downward of the midlevel vorticity this strengthens the surface vortex and develops a more cohesive vortex that extends from the surface through the midtroposphere

geodetic and model data reveal different spatio temporal patterns of transient mass changes over greenland from 2007 to 2017 abstract much of the research to understand the ice mass changes of greenland ice sheet gris has focused on detecting linear rates and accelerations at decadal or longer periods the transient short term non secular mass changes show large variability and if not properly accounted for can introduce significant biases into estimates of long term ice mass loss rates and accelerations despite the growing number of geodetic observations in terms of spatial coverage types of observables and the extent of the time series studies of the transient mass changes over gris are lacking to address this limitation we apply multi channel singular spectral analysis to the gravity recovery and climate experiment grace mass concentrations mascon surface mass balance smb model output and ice discharge data to determine the transient mass changes over greenland over the decade 2007 to 2017 the goal of this analysis is to elucidate the spatio temporal variability of the ice mass change for the entire gris both the mascon and smb transient mass changes are characterized by a sustained mass gain from late 2007 to early 2010 a sustained mass loss from early 2010 to early 2013 and a mass gain from early 2013 to mid 2015 global positioning system sites deployed along the coast of greenland showed uplift from early 2010 to early 2013 and subsidence from early 2013 to 2015 consistent with the corresponding ice mass loss and gain of the entire gris the peak to peak amplitude of the transient mass change was estimated to be 294 27 gt from grace mascons and 252 16 gt from the smb where the latter value includes the effect of ice discharge the transient mass change due to ice discharge accounted for less than 10 of the total transient mass change our regional assessment reveals that the central west southwest northeast and southeast regions display similar time varying patterns as we found for the entire gris but the north and northwest regions show different patterns atmospheric circulation anomalies as measured by the greenland blocking index gbi are able to explain most of these transient anomalies more specifically high gbi associated high temperature was one of the main reasons for the transient mass loss of the entire gris during 2010 2012 while low gbi can explain the transient mass gain during 2013 2015 contrasting behaviors of precipitation anomalies in east and west greenland under abnormally high or low gbi conditions may explain the different patterns of the transient mass change in the northwest and the rest of greenland

numerical study of convection observed during the winter monsoon experiment using a mesoscale two dimensional model abstract a two dimensional version of the pennsylvania state university mesoscale model has been applied to winter monsoon experiment data in order to simulate the diurnally occurring convection observed over the south china sea the domain includes a representation of part of borneo as well as the sea so that the model can simulate the initiation of convection also included in the model are parameterizations of mesoscale ice phase and moisture processes and longwave and shortwave radiation with a diurnal cycle this allows use of the model to test the relative importance of various heating mechanisms to the stratiform cloud deck which typically occupies several hundred kilometers of the domain frank and cohen s cumulus parameterization scheme is employed to represent vital unresolved vertical transports in the convective area the major conclusions are ice phase processes are important in determining the level of maximum large scale heating and vertical motion because there is a strong anvil componen

drilling induced tensile wall fractures implications for determination of in situ stress orientation and magnitude abstract detailed investigation of failure of the borehole wall in two scientific drilling projects the german ktb kontinentales tiefbohrprogramm der bundesrepublik deutschland and the european geothermal research project at soultz sous forets france has lead to new insight in the phenomena of tensile fractures induced in the wellbore wall during drilling comparison of the orientation of the fractures with the orientation of the horizontal principal stress known from breakout and hydraulic fracturing analysis demonstrates that these fractures are reliable indicators of the orientation of the maximum horizontal principal stress s h a model for the initiation of the fractures is presented which points out the important influences of a the tectonic stress state b increased mud pressures during drilling operation and c thermal stresses induced by circulation of relatively cold drilling mud analysis of drilling induced fractures in the gpk1 borehole at soultz sous forets where the magnitude of s h is known from hydraulic fracturing experiments demonstrates the validity of this model for the initiation of the fractures further a new method is proposed to estimate the magnitude of s h from the occurrence of drilling induced fractures and knowledge of thermally induced stress and pumping pressure during drilling the method is successfully applied to both ktb boreholes an independent method to estimate the magnitude of s h based on the analytical calculation of the stress intensity factor for drilling induced fractures taking into consideration both increased mud pressure and thermal stress is also presented application of this method confirms the results derived with the analysis described above additionally the evaluation of the orientation of the fractures with respect to the wellbore axis indicates that over major depth sections of the investigated wells the vertical stress is a principal stress