the roles of tropical and subtropical wind stress anomalies in the el nino modoki onset the el nino modoki is separated into two types el nino modoki i and el nino modoki ii which are characterized by substantially different mechanism according to comparisons between the evolution of air sea coupled processes and heat budget analyses this study discovered the distinct dynamical mechanism of the onset of el nino modoki ii compared to that of el nino modoki i for el nino modoki i westerly wind anomalies in the western pacific appear earlier than warm sea surface temperature sst anomalies in the central tropical pacific in addition zonal advection is responsible for changes in mixed layer temperature in the nino 4 region during the developing phase in spring and summer however warm sst anomalies accompany easterly anomalies in the central tropical pacific and there are no westerly anomalies in the western tropical pacific during the developing phase in spring and summer for el nino modoki ii for el nino modoki ii ekman feedback is the major contributor to changes in mixed layer temperature according to reanalysis data the 2 5 layer model results and coupled model simulations anomalous westerly wind stress in the subtropical north pacific and easterly wind stress in the central eastern tropical pacific can lead to equatorward and westward oceanic current anomalies thus enhancing meridional and zonal convergences at upper layer because anomalous convergence at upper layer can inhibit upwelling motion in the central tropical pacific sst anomalies in the central tropical pacific tend to be warm even without anomalous westerlies in the western pacific

the factors influencing the abrasion efficiency of saltating grains on a clay crusted playa the entrainment and subsequent transport of pm10 particulate matter 10 m has become an important and challenging focus of research for both scientific and practical applications arid and semi arid environments are important sources for the atmospheric loading of pm10 although the emission of this material is often limited by surface crusts it has been suggested that the primary mechanisms through which pm10 is released from a crusted surface are abrasion by saltating grains or disturbance by agricultural and recreational activities to examine the importance of saltation abrasion in the emission of pm10 a series of field wind tunnel tests were conducted on a clay crusted surface near desert wells arizona in a previous part of this study it was found that the emission rate varies linearly with the saltation transport rate although there can be considerable variation in this relationship this paper more closely examines the source of the variability in the abrasion efficiency the amount of pm10 emitted by a given quantity of saltating grains the abrasion efficiency was found to vary with the susceptibility of the surface to abrasion the ability of the sand to abrade that surface and the availability of material with a caliper size 10 m within the crust specifically the results of the study show that the abrasion efficiency is related to the crust strength the amount of surface disturbance and the velocity of the saltating grains it is concluded that the spatial and temporal variability of these controls on the abrasion efficiency imposes severe contextual limitations on experimentally derived models and can make theoretical models too complex and impractical to be of use copyright 2001 john wiley sons ltd

north pacific temperature and precipitation response to el nino like equatorial heating sensitivity to forcing location this study investigates the sensitivity of oceanic and atmospheric response in the extra tropics especially in the north pacific to the position of equatorial el nino like heating within a slab ocean climate model in a suite of numerical experiments we impose an idealized equatorial sea surface temperature sst anomaly in the pacific and systematically vary its longitudinal position along the equator to mimic different flavors of el nino we find that regardless of the forcing location the induced sst pattern closely resembles a positive phase of the pacific decadal oscillation with a characteristic warming along the north american coast as part of an arc shaped pattern accompanied by wind anomalies around the aleutian low however the extent and magnitude of the coastal warming vary nonmonotonically when the forcing shifts westward along the equator the strongest response is found when the equatorial forcing is located in the central pacific close to the dateline in contrast precipitation response over southern california is strongest for an eastern pacific warming centered at 150 w even though its magnitude is highly uncertain since the boundary between dry and wet precipitation anomalies passes through this region we repeat the experiments for cold i e la nina like anomalies and observe a significant asymmetry in the sst and atmospheric response between the warm and cold cases finally our experiments suggest that tropical heating or cooling over the western pacific warm pool generates the largest tropical rainfall response and hence the largest global mean sst anomaly

the physics of wind blown loess implications for grain size proxy interpretations in quaternary paleoclimate studies abstract loess deposits are recorders of aeolian activity during past glaciations since the size distribution of loess deposits depends on distance to the dust source and environmental conditions at the source during transport and at deposition loess particle size distributions and derived statistical measures are widely used proxies in quaternary paleoenvironmental studies however the interpretation of these proxies often only considers dust transport processes to move beyond such overly simplistic proxy interpretations and toward proxy interpretations that consider the range of environmental processes that determine loess particle size distribution variations we provide a comprehensive review on the physics of dust particle mobilization and deposition furthermore using high resolution bulk loess and quartz grain size datasets from a last glacial interglacial sequence we show that because grain size distributions are affected by multiple often stochastic processes changes in these distributions over time allow multiple interpretations for the driving processes consequently simplistic interpretations of proxy variations in terms of only one factor e g wind speed are likely to be inaccurate nonetheless using loess proxies to understand temporal changes in the dust cycle and environmental parameters requires i a careful site selection to minimize the effects of topography and source distance and ii the joint use of bulk and quartz grain size proxies together with high resolution mass accumulation rate calculations if possible

wind tunnel evaluation of a wedge shaped aeolian sediment trap abstract a detailed set of tests in a wind tunnel investigated the characteristics of flow and sampling efficiency of a low cost sediment trap that can be used in wind tunnels and field applications the trap is constructed of thin sheet aluminum and has a wedge shape 32 internal inlet angle with a 20 500 mm rectangular inlet orifice that extends 40 mm beyond the wedge form relatively unimpeded airflow through the trap is achieved by the large exit area 130 500 mm which is covered with fine stainless steel mesh 62 5 m openings 60 porosity and collected all but the finer silt sediment sizes despite its angular shape the trap has good characteristics of flow and a very high sampling efficiency 90 over a wide range of wind velocities because of its near isokinetic characteristics of flow results also indicate that this trap and others that have wide side profiles are very sensitive to incident wind angle incident angles 5 significantly reduce the sampling efficiency and promote scour around the trap inlet

initial transient response of the winter polar stratospheric vortex to idealized equatorial pacific sea surface temperature anomalies in the ncar waccm abstractperpetual winter simulations using the ncar whole atmosphere community climate model waccm are conducted to document the differences of the initial transient response of the boreal winter northern hemisphere stratospheric polar vortex to central cpw and eastern pacific warming epw events idealized patches of positive sea surface temperature sst anomalies are superimposed onto a climatological sst field to mimic canonical cpw and epw forcings a 20 member ensemble was created by varying initial atmospheric conditions for both cpw and epw cases in the ensemble average the vortex weakens under both cpw and epw forcing indicated by a negative zonal mean zonal wind tendency this tendency is mainly tied to changes in the eddy driven mean meridional circulation mmc a negative anomaly in the eddy momentum flux convergence also plays a secondary role in the weakening the vortex response however differs dramatically among individual ensemble members a few ensemble members exhibit initial

an experimental study on the susceptibility of crusted surfaces to wind erosion a comparison of the strength properties of biotic and salt crusts abstract penetrometry has been employed in a number of studies investigating the strength of crusted sediments as related to their stability to particle impact in aeolian systems despite the early success of this procedure questions remain concerning the effect of the angle of penetration the role of fatigue and the relative importance of the ultimate strength as compared to the elasticity of the crust this paper reports on a series of penetrometer and wind tunnel experiments that consider these effects in the context of both salt and biotic crusts the results demonstrate that the angle of penetration is not important but the density of penetrations is the decreased strength observed with high densities of penetration repeated loading and continual impact in wind tunnel experiments provides further confirmation that sedimentary crusts progressively become weaker during mass transport events the elasticity of the surface appears to be at least as important to consider as the ultimate strength although much stronger the salt crusts were found to break down and erode sooner than biotic crusts in wind tunnel studies the notable elasticity of biotic crusts appears to afford them some protection against abrasion

underground gravity survey in alpine regions an underground gravity study was carried out under extreme conditions of the alpine regions the lead zinc mine bleiberg carinthia was selected as an example to show the possibilities and limitations of the subsurface gravity method for in situ density determinations gravity measurements were made in two vertical mine shafts passing through triassic sedimentary rocks of the bleiberg unit the main prblem in gravity data reduction in extremely rugged topography is the accurate calculation of the terrain effect on underground stations a general discussion of the various corrections required for the gravity measurements in the mine is presented the mean interval densities in the two shafts in limestone dolomite and schists formations were determined as 2 76 and 2 77 g cm 3 respectively with an accuracy of better than 0 01 g cm 3 for a depth interval of 50 m the interval densities provide valuable information about the lithological and structural changes in the shaft surroundings and also agree well with the representative hand sample densities in the second part the applications of subsurface horizontal gravity surveys in exploration are discussed since the influence of topography is less underground because of the greater distance to the surface subsurface surveys have definite advantages over surface surveys and can be very helpful in locating anomalous density zones in the mines an example of gravity survey with a station spacing of 10 m at a depth of about 540 m is presented

induced gravity anomalies and seismic energy as a basis for prediction of mining tremors the results of prediction of occurrence of mining tremors and bursts in the course of the exploitation of the remaining part of the hard coal in seam 510 of the mine pstrowski upper silesia have been presented in the paper the exploitation has taken place under extremely difficult conditions hazardous for the mining crew

absolute gravity measurements at uk tide gauges absolute gravity near 3 of the united kingdom s uk core tide gauges was repeatedly measured using an fg5 gravimeter over a period of 3 4 years to determine vertical land movements at those gauges the absolute gravity sites were established at newlyn and aberdeen in 1995 and in lerwick in 1996 assuming a height change of 1 mm causes a change in gravity of 0 2 gal we see vertical land movements of 1 0 1 4 mm yr at newlyn 3 8 1 6 mm yr at lerwick and 0 9 3 1 mm yr at aberdeen these land movements are within the error estimates in agreement with land movement predicted by a model of post glacial rebound subsidence to ensure that our absolute gravimeter is giving accurate results it has been regularly intercompared with other absolute gravimeters and was verified to be in agreement at the 2 gal level

geomechanical response to seasonal gas storage in depleted reservoirs a case study in the po river basin italy 1 underground gas storage ugs in depleted hydrocarbon reservoirs is a strategic practice to cope with the growing energy demand and occurs in many places in europe and north america in response to summer gas injection and winter gas withdrawal the reservoir expands and contracts essentially elastically as a major consequence of the fluid gas and water pore pressure fluctuations depending on a number of factors including the reservoir burial depth the difference between the largest and the smallest gas pore pressure and the geomechanical properties of the injected formation and the overburden the porous medium overlying the reservoir is subject to three dimensional deformation with the related cyclic motion of the land surface being both vertical and horizontal we present a methodology to evaluate the environmental impact of underground gas storage and sequestration from the geomechanical perspective particularly in relation to the ground surface displacements long term records of injected and removed gas volume and fluid pore pressure in the lombardia gas field northern italy are available together with multiyear detection of vertical and horizontal west east displacement of the land surface above the reservoir by an advanced permanent scatterer interferometric synthetic aperture radar psinsar analysis these data have been used to calibrate a 3 d fluid dynamic model and develop a 3 d transversally isotropic geomechanical model the latter has been successfully implemented and used to reproduce the vertical and horizontal cyclic displacements on the range of 8 10 mm and 6 8 mm respectively measured between 2003 and 2007 above the reservoir where a ugs program has been underway by stogit eni s p a since 1986 following a 5 year field production life because of the great economical interest to increase the working gas volume as much as possible the model addresses two ugs scenarios where the gas pore overpressure is pushed from the current 103 pi where pi is the gas pore pressure prior to the field development to 107 pi and 120 pi results of both scenarios show that there is a negligible impact on the ground surface with deformation gradients that remain well below the most restrictive admissible limits for the civil structures and infrastructures

interdecadal change of the structure of the enso mode and its impact on the enso frequency in the late 1970s the enso cycle exhibited frequency change the oscillation period increased from 2 4 yr high frequency during 1962 75 to 4 6 yr low frequency during 1980 93 observations suggest that this frequency change was accompanied by a significant change in the structure of the coupled enso mode in comparison with the high frequency regime the structure of the coupled mode in the low frequency regime shows three distinctive features during the warm phase of enso the eastward shift of the westerly anomalies the meridional expansion of the westerly anomalies and the weaker intensity of the easterly anomalies in the eastern pacific to test the robustness of the relationship between the oscillation period and the structure of the coupled mode the authors designed empirical atmospheric models based on observations and coupled them with the ocean model of zebiak and cane numerical experiments demonstrate that the enso period is sensitive to changes in the wind anomaly pattern in a way much like the observed enso frequency structure relation the increase of the enso period after 1980 is mainly due to the eastward shift of the zonal wind stress with respect to the sst anomalies physical explanations of the dependence of enso frequency on the structure of the coupled mode are provided by diagnosing the relative contributions of the thermocline feedback and zonal advection feedback on enso evolution

contribution of aeolian sand to backbarrier marsh sedimentation abstract the frequency of island overwash is commonly assumed to be the main factor regulating sand flux to backbarrier marshes however aeolian transport of sand across a barrier has received little attention in saltmarsh research the contribution of aeolian sand to backbarrier marshes is examined here with marsh cores and measurements of wind blown sediment transport across transgressive and regressive parts of a barrier island backbarrier marshes fronted by a wide washover fan or a high elevation dune ridge were supplied with aeolian sand that significantly contributed to vertical accretion especially near the marsh barrier island edge the percent volume of the marsh originating from aeolian sand based on the upper 1 cm of marsh sediment decreased by an order of magnitude only 20 m from the dune marsh boundary sandy beds sampled in every marsh core at depth are composed of aeolian sand and were likely emplaced over time after storms deposited a sandy washover fan near the marsh and or reduced vegetation cover across the island sand beds preserved within backbarrier marsh deposits are commonly thought to have been emplaced rapidly during a storm however post storm aeolian transport should also be considered as an important mechanism for forming sand beds over a longer period of time within saltmarsh strata the contribution of aeolian sand to backbarrier marsh accretion should increase as sea level continues to rise causing many barrier islands to narrow thereby reducing transport distances between the dune and marsh along developed coastlines however anthropogenic factors associated with increased development largely decrease the connectivity between the dunes and backbarrier marsh

enso like and enso induced tropical pacific decadal variability in cgcms abstractoutputs from coupled general circulation models cgcms are used in examining tropical pacific decadal variability tpdv and their relationships with el nino southern oscillation enso herein tpdv is classified as either enso induced tpdv eit or enso like tpdv elt based on their correlations with a decadal modulation index of enso amplitude and spatial pattern eit is identified by the leading eof mode of the low pass filtered equatorial subsurface temperature anomalies and is highly correlated with the decadal enso modulation index this mode is characterized by an east west dipole structure along the equator elt is usually defined by the first eof mode of subsurface temperature of which the spatial structure is similar to enso generally this mode is insignificantly correlated with the decadal modulation of enso eit closely interacts with the residuals induced by enso asymmetries both of which show similar spatial structures on the other hand elt is controlled by slowly varying oc

saltating particles playa crusts and dust aerosols at owens dry lake california as part of the multinational lake owens dust experiment lode we have studied the generation of dust storms on the south sand sheet of owens dry lake california an anthropogenically desiccated playa reported to be the single greatest source of particulate matter in north america during march 1993 we performed an intensive field study including eight significant dust storms building on our prior work 1978 1984 and preliminary studies 1991 1992 we studied sources and magnitude of coarse saltating particles the meteorological conditions that allow them to become mobile across the flat playa of owens dry lake and how the motion of saltating particles across different types of playa surfaces results in the generation of pm10 dusts aerosol particles smaller than 10 m aerodynamic diameter saltating grains of lacustrine sand and broken crust abrade and disaggregate the playa surface into fine aerosols and the resulting pm10 concentrations recorded during major dust storms are among the highest ever recorded in north america on 23 march 1993 we measured a 2 h concentration on the playa of 40 620 g m 3 as far as we can determine the highest ambient pm10 value ever recorded in the u s a abrasion of salt silt clay crusts by saltation is shown to be responsible for all but a small part of one dust storm the quantity sand run saltating particle transport multiplied by wind run is shown to be very closely correlated with dust aerosol concentration finally we have established that on lake bed studies are essential for quantitative prediction of dust events on the owens dry lake bed despite the difficult conditions encountered

simulation of the seasonal cycle of the tropical pacific ocean abstract in a general circulation model of the tropical pacific ocean forced with climatological seasonally varying winds equatorial upwelling and downwelling in adjacent latitudes play central roles in closing the oceanic circulation the transport of the eastward north equatorial countercurrent decreases in a downstream direction because fluid is lost to downwelling into the thermocline where there is equatorward motion although this fluid converges onto the equatorial undercurrent the latter s transport decreases because of equatorial upwelling the upwelling on the other hand enhances the transport of the westward south equatorial current seasonally the countercurrent and south equatorial current are intense during the northern hemisphere summer and fall at which time the thermocline has a pronounced trough near 3 n and a ridge near 10 n and are weak in the spring when latitudinal thermal gradients are small and when the southeast trades are relatively weak these variations are out of phase

induced gravity anomalies and rock burst risk in coal mines a case history1 the use of the gravity method to predict rock bursts in mines is based on the relationship between the development of a dilatancy process in the exploited rock mass and the time dependent gravity anomalies induced by this phenomenon the differences between successive observations of anomalies and the time behaviour of their trend amplitudes as precursors of preceding changes of rock stability are interpreted the centres of zones of induced rock density variation are determined by computing the position of singular points of the differences between anomalies two gravity surveys have been carried out in the radbod coal mine germany the first survey took place at the level of the dickebank seam depth 1030 m the second in the sonnenschein seam depth 1090 m the observations were made with worden and lacoste romberg d type gravimeters the differences between successive anomalies were less than 100 gal in the case of the dickebank seam the position of singular points demonstrates the effect of two approaching longwalls on a previously mined out seam and on the gallery in which the gravity observations were made in the case of the sonnenschein seam the trend amplitudes show distinct variations in the formation of the approaching longwall below the edges of all previously mined out seams in particular the effect of a remnant pillar has caused the largest gravity gradients this result corresponds to the existence of a zone of rock burst hazard known from test drilling the computed singular points are grouped together under the remnant pillar indicating two local hazard zones both results the observed development of rock instability with time and the information about the position of the disturbed rock mass relative to the mine workings are of importance subsurface gravity surveying can therefore be a valuable tool for predicting rock bursts

the observed impacts of the two types of el nino on the north equatorial countercurrent in the pacific ocean this study investigates the interannual variations in the north equatorial counter current necc associated with the eastern pacific and the central pacific types of el nino using observational analysis and ocean simulations we show that the wind stress anomalies during the two el nino types are of comparable amplitude but have different spatial structures which results in significant and distinct variations in the necc the necc shifts southward and intensifies during the developing phase of el nino but the variations are confined in the central eastern pacific for the eastern pacific type and the western central pacific for the central pacific type these differences can be attributed to modulations in equatorial kelvin wave and tropical rossby wave propagation as well as ekman pumping plain language summary the north equatorial counter current necc is an eastward flowing surface current that transports a significant amount of water from the warm pool in the western pacific to the east variations in the necc exert profound effects on the tropical pacific climate and need to be better understood this study conducts statistical analyses and ocean model experiments to show that different flavors of el nino can displace the necc location and alter its intensity in distinct ways the cause and the physical mechanisms behind the distinct impacts are identified and verified using specific el nino events of each flavor the findings reported in this study contribute to advance our understanding of el nino diversity and its impacts on the circulation and variability of the pacific ocean

contrasting eastern pacific and central pacific types of enso abstract surface observations and subsurface ocean assimilation datasets are examined to contrast two distinct types of el nino southern oscillation enso in the tropical pacific an eastern pacific ep type and a central pacific cp type an analysis method combining empirical orthogonal function eof analysis and linear regression is used to separate these two types correlation and composite analyses based on the principal components of the eof were performed to examine the structure evolution and teleconnection of these two enso types the ep type of enso is found to have its sst anomaly center located in the eastern equatorial pacific attached to the coast of south america this type of enso is associated with basinwide thermocline and surface wind variations and shows a strong teleconnection with the tropical indian ocean in contrast the cp type of enso has most of its surface wind sst and subsurface anomalies confined in the central pacific and tends to onset develop and decay in situ

tensile test of natural microbiotic crust abstract the mechanical properties of microbiotic crust are important to stabilize sandy surfaces in arid and semi arid regions we developed a new experimental approach to perform the tensile test of natural microbiotic crust the modulus of elasticity ultimate stress and one dimensional stress strain relation was obtained the microbiotic crust we measured exhibits linear elastic behavior firstly and then breaks this mechanical character was applied to the study of the rupture of microbiotic crust under the impact of one saltating grain a very simple dimensionless variable was suggested to quantitatively assess surface stability

long term time lapse microgravity and geotechnical monitoring of relict salt mines marston cheshire u k the area around the town of northwich in cheshire u k has a long history of catastrophic ground subsidence caused by a combination of natural dissolution and collapsing abandoned mine workings within the underlying triassic halite bedrock geology in the village of marston the trent and mersey canal crosses several abandoned salt mine workings and previously subsiding areas the canal being breached by a catastrophic subsidence event in 1953 this canal section is the focus of a long term monitoring study by conventional geotechnical topographic and microgravity surveys results of 20 years of topographic time lapse surveys indicate specific areas of local subsidence that could not be predicted by available site and mine abandonment plan and shaft data subsidence has subsequently necessitated four phases of temporary canal bank remediation ten years of microgravity time lapse data have recorded major deepening negative anomalies in specific sections that correlate with topographic data gravity 2d modeling using available site data found upwardly propagating voids and associated collapse material produced a good match with observed microgravity data intrusive investigations have confirmed a void at the major anomaly the advantages of undertaking such long term studies for near surface geophysicists geotechnical engineers and researchers working in other application areas are discussed

interannual variability in the mid and low latitude western north pacific abstract twenty two years 1967 88 of hydrographic data collected by the japan meteorological agency along the 137 e meridian and surface wind data compiled by florida state university fsu were analyzed to study the interannual variability in the western north pacific in the midlatitude region north of 22 n the dominant signal in the dynamic height field was the interannual path variations of the kuroshio whereas the eastward transport of the kuroshio itself had no significant changes between the straight path and meander path years the net transport of the kuroshio system including recirculations showed a 30 increase during the meander path years in the straight path years when the net transport was small the kuroshio tended to take a straight path with a strong recirculation developed to the south the interannual path variations of the kuroshio strongly influenced the water mass movement in the midlatitudes during the kuroshio meander years we found that a significant portion of the north p

constraints on density changes in the funnel shaped caldera inferred from gravity monitoring of the lusi mud eruption abstract from its inception may 29 2006 the lusi mud eruption has continuously erupted fluids boiling mud and clasts through large active vents approximately 100 m in diameter in 2016 we conducted a dynamic gravity survey dg using a network built over four locations and two continuous gravity monitoring cg experiments to monitor the eruption activity the cg was done for 8 days from june 2nd to june 10th and for 9 days from august 20th to august 29th 2016 atmospheric pressure and atmospheric temperature variations were recorded during each experiment to constrain potential environmental effects and earth and oceanic tide effects were removed from gravity signals cg and dg atmospheric pressure effects were removed from cg gravity signals at the station closest to the hydrothermal pond the dg survey results show a gravity increase of 0 009 mgal month 1 which we interpret as the growth of the mud edifice in the central area cg monitoring shows that gravity variations occur at a period of 12 13 h with amplitudes reaching up to 0 020 mgal we interpret this as relating to density variation of the rising mud mixture fluids coarse mud clasts the observed 12 13 h period variations appear to indicate that tides may have some control on the density change of rising mud mixture by triggering the release of gas trapped at depth our 3d gravity results around the lusi vents show that density variations range from 100 kg m 3 to 775 kg m 3 similarly vent diameters better constrain density contrasts occurring within the caldera zone which is more likely to range between 400 and 450 kg m 3 and is equivalent respectively to 27 and 31 of gas ratio change over time

the impact of eastern pacific versus central pacific el ninos on the north equatorial countercurrent in the pacific ocean 1 using a three dimensional ocean reanalysis data product the influence of two types of the el ninos on the north equatorial countercurrent necc across the pacific basin is examined in this study eastern pacific el ninos ep el ninos exert a significant impact on the interannual changes of the necc whereas central pacific el ninos cp el ninos have little influence from the developing to mature phase of the ep el ninos that occursfrequently in the latter half of a calendar year the necc tends to intensify and shift southward while the ep el nino related position changes of the necc is out of phase with its seasonal position changes the ep el nino related intensity variability of the necc is in phase with its seasonal modulation during both types of el ninos the el nino modulated wind stress curl forcing changes the upper ocean thickness modifying the necc intensity and central position the weaker and shorter fluctuations of wind stress curl forcing during the cp el nino events induce irregular and insignificant changes of the necc

the north equatorial countercurrent and heat storage in the western pacific ocean during 1982 83 a sequence of extreme climate anomalies known as an el nino southern oscillation episode was observed in the tropical pacific ocean during 1982 831 2 models suggest that oceanic circulation has an important role in the formation of such anomalies1 3 4 by altering the pattern of sea surface temperature through advection the baroclinic structure of the upper 500 m of the ocean has been monitored routinely in the western pacific since 1979 providing indirect current measurements by the geostrophic method these observations reported here show large changes in the near equatorial currents during 1982 83 which are consistent with currents observed in the central and eastern pacific5 6 in particular the north equatorial countercurrent necc flowed with 25 50 increased strength during the early phase then weakened almost to zero flow the west pacific heat pool cooled by more than 1 c observed changes in circulation were large enough to alter surface heat storage by advection although other potentially important processes may not be negligible

a wind tunnel study of particle kinematics during crust rupture and erosion abstract sediments with protective crusts of varying type were subjected to particles fed from an upwind source during wind tunnel experiments carried out to compare their ability to resist erosion and alter the kinematics of the saltation cloud a laser doppler anemometer measured the distribution of particle velocity for saltators impacting each crusted surface and for particles ejected from this same surface inclusive of ricochets biotic crusts grown on sand in an environmental chamber were able to withstand erosion over several hours of continuous particle impact as compared to brittle salt crusts which regardless of wind speed or sodium chloride concentration eroded fully within one half hour despite the appearance of deep pits and grooves on the ruptured crusts loss of mass dominated over particle trapping on these rough surfaces while decreasing salt concentration between 320 g kg 1 and 80 g kg 1 generally was found to be associated with an increase in the mass flux of particles ejected from the surface little to no correlation with either wind speed or particle impact speed was observed the range over which varying salt concentration affects the momentum of ejected particles is rather narrow within 160 g kg 1 temporal changes in the velocity distribution of ejected particles with crust rupture and deflation are complicated by variations in crust strength with depth this is especially true of biotic crusts and weak salt crusts fast moving particles associated with the upper 40 of the cumulative velocity distribution generally demonstrate little variation from the control surfaces and probably represent ricochets in comparison those within the lower 60 of the distribution are significantly affected by crust rupture and erosion and may include low energy rebounds as well as the entrainment of new particles loosened from within the crust while such measurements are exceedingly rare they are needed for the validation of physically based models of crust erosion

recent developments in underground gravity surveys1 underground gravity observations in deep coal mines using the conventional gravity meters worden type master and lacoste romberg model d both of which have been adapted to the fire damp regulations can be accurate to 10 and 3 gal respectively for underground determination of the vertical gradient of gravity the lacoste romberg meter is used together with a specially designed measuring tower using this euipment an accuracy in tower gradient observations of 30 e was obtained to apply the equipment to precision gravity observations in underground situations an additional correction i e a gallery correction is needed high accuracy in correction is achieved by a new method of three dimensional modelling the gravity effect is computed for bodies with a surface approximated by triangular elements which are generated from corner points of the body the combination of gallery correction with tower gradient data leads to a new method for in situ density determination it offers the possibility of horizontal instead of vertical density profiling to demonstrate the effectiveness of the developments in underground observations the localization of a pump room is presented microgravity and tower gradient observations were carried out to detect the cavity the horizontal gradient was also calculated to give a more reliable location

the gravimetric detection of mining subsidence a series of gravity measurements were taken over a period of time c 150 days each above two adjacent working coal faces precise level and gravity measurements were taken along the same profile before during and after seam extraction the observed change in gravity agrees well with the level data the combined data sets illustrate the validity of a simple bouguer relationship for the gravity gradient the results of two dimensional modelling are used to estimate the gravitational effect of the extracted material a local feature detected only on the gravity signal may be due to an outcropping limestone layer this controlled experiment demonstrates the possibility of using high precision gravity measurements as a substitute for level measurements particularly in surveys of large areal extent where the cost of obtaining comprehensive coverage by level methods may be prohibitive

soil crusting on sandy soils and its influence on wind erosion abstract under rainfall a crust forms at the surface of most soils for soils rich enough in clay clay content 5 it is well known that a physical crust is responsible for a supply limitation of particles available for wind erosion sandy soils are very prone to crusting as well as to wind erosion indeed structural sieving crusts develop on sandy soils even after light rainfalls this kind of crust shows a loose sand layer at the surface overlying a thin layer where fine particles are concentrated the main objectives of this study were to determine whether such a crust formation limits the availability of 1 sand grains for entrainment into saltation and 2 fine particles for uptake into a vertical wind erosion flux suspension in atmosphere of particles

analysis of exploitation induced gravity changes at wairakei geothermal field gravity changes corrected for subsidence of up to 1 000 300 gal have occurred in the 1km2 area of the production bore field at wairakei and smaller decreases extend over a 50km2 surrounding area the largest part of these decreases occurred during the 1960s since then the net gravity change for the whole field has been zero indicating mass flow equilibrium the principal causes of gravity change have been deep liquid pressure drawdown which resulted in formation of a steam zone subsequent saturation changes in the steam zone liquid temperature decline and groundwater level changes gravity models suggest saturation of the steam zone was 0 7 0 1 in 1962 and decreased to 0 6 by 1972 gravity increases in the northern and eastern bore field since the early 1970s are attributed to cool water invading the steam zone

observations and mechanisms of a simple stochastic dynamical model capturing el nino diversity abstractel nino southern oscillation enso has significant impact on global climate and relevance for seasonal forecasts recently a simple modeling framework was developed that captures the enso diversity where state dependent stochastic wind bursts and nonlinear advection of sea surface temperature are coupled to a simple ocean atmosphere model that is otherwise deterministic linear and stable in this article the coupled model is compared with observations using reanalysis data over the last 34 yr where the observed non gaussian statistics and the overall mechanisms of enso are both captured by the model then the formation mechanisms of both the central pacific cp and the traditional el nino in the model are systematically studied first ocean rossby waves induced by easterly trade wind anomalies facilitate the heat content buildup then the reflected ocean kelvin waves and the nonlinear advection lead to positive sst anomalies in the cp region and create a cp el nino second two formation

the changing influences of enso and the pacific meridional mode on mesoscale eddies in the south china sea abstractthis study finds that the correlation between el nino southern oscillation enso and the activity of mesoscale oceanic eddies in the south china sea scs changed around 2004 the mesoscal

effects of ocean initial perturbation on developing phase of enso in a coupled seasonal prediction model coupled prediction systems for seasonal and inter annual variability in the tropical pacific are initialized from ocean analyses in ocean initial states small scale perturbations are inevitably smoothed or distorted by the observational limits and data assimilation procedures which tends to induce potential ocean initial errors for the el nino southern oscillation enso prediction here the evolution and effects of ocean initial errors from the small scale perturbation on the developing phase of enso are investigated by an ensemble of coupled model predictions results show that the ocean initial errors at the thermocline in the western tropical pacific grow rapidly to project on the first mode of equatorial kelvin wave and propagate to the east along the thermocline in boreal spring when the surface buoyancy flux weakens in the eastern tropical pacific the subsurface errors influence sea surface temperature variability and would account for the seasonal dependence of prediction skill in the nino3 region it is concluded that the enso prediction in the eastern tropical pacific after boreal spring can be improved by increasing the observational accuracy of subsurface ocean initial states in the western tropical pacific

a wind tunnel study of the resilience of three fungal crusts to particle abrasion during aeolian sediment transport abstract this study is a comparison of the strength stability and resistance to abrasion of monospecific sand crusts formed by three species of free living fungi aureobasidium pullulans trichoderma harzianum and absidia corymbifera compared to three photoautotrophs examined in a previous study the fungal crusts were thicker and stronger in flexure by a factor of two or more in addition to the morphological properties of these fungi the organic substrate required for growth contributes to the total crust strength wind tunnel tests in which the crusts were subjected to particle impact from an upwind sediment source nominally 0 014 kg m 1 s 1 and varied levels of freestream velocity u showed that crusts comprised of trichoderma and absidia were stable at wind velocities under 10 m s 1 crusts of aureobasidium generally ruptured at velocities well below this level and to a much greater extent the distinctive morphologies and metabolic rates of the three fungi appear to explain these differences as compared to the wind tunnel experiments independent tests of crust strength in flexure which were intended to simulate crust flaking were found to be less sensitive indicators of relative crust stability in aeolian settings analysis of the time rate of expansion of the perimeter of crust loss indicates that this relation is approximately exponential with the exception of low wind velocities near the threshold for grain ejection where the momentum of the saltators at impact appears to be of prime importance

estimation of seismic velocities and gas hydrate concentrations a case study from the shenhu area northern south china sea abstract in the shenhu area of the northern south china sea scs canyon systems and focused fluid flow systems increase the complexity of the gas hydrate distribution in the region it also induces difficulties in predicting the hydrate reservoir characteristics and quantitatively evaluating reservoir parameters in this study several inversion methods have been executed to estimate the velocities of strata and gas hydrate concentrations along a profile in the shenhu area the seismic data were inverted to obtain the reflection coefficient of each stratum via a spectral inversion method stratigraphic horizons were then delineated by tracking the inverted reflectivities based on the results of spectral inversion a low frequency velocity field of the strata was constructed for acoustic impedance inversion using a new iterative algorithm for acoustic impedance inversion reflection coefficients were converted into velocities and the velocity variations of the strata along a 2d seismic line were then obtained subsequently gas hydrate saturations at well sh2 were estimated via the shale corrected resistivity method the chloride ion concentration method and three different rock physics models the results were then compared to determine the optimal rock physics model and the modified wood equation mwe was found to be appropriate for this area finally the inverted velocities and mwe were used to predict the distribution and concentrations of gas hydrates along the seismic line the estimated spatial distribution of gas hydrates is consistent with that from sonic logging and resistivity data at well sh2 and with the drilling results therefore this method is applicable in areas with no well data or with few wells and provides an effective tool for predicting and evaluating gas hydrates using seismic data

direct measurements of upper ocean currents and water properties across the tropical pacific during the 1990s abstract meridional sections of upper ocean zonal currents potential temperature and salinity are estimated at ten longitudes from 143 e to 95 w using conductivity temperature depth and acoustic doppler current profiler data from 172 synoptic sections taken in the tropical pacific between 138 e and 86 w mostly in the 1990s data reduction is carried out in a potential isopycnal and mixed layer framework to preserve a sharp pycnocline a mixed layer water property extrema and velocity extrema mean zonal currents potential temperatures and salinities are produced at each longitude the seasonal cycles of these fields are also estimated as well as a simple el nino southern oscillation enso cycle zonal sections along the equator are also presented properties of the near equatorial zonal currents including transports temperatures and salinities are estimated separately from the synoptic sections the seasonal cycles of these quantities and their correlations with the southern oscillation index are investigated the work is distinguished from most existing literature in that direct estimates of zonal velocity are combined with contemporaneous temperature and salinity data allowing trans pacific estimates of near equatorial current transports and properties including those of the northern branch of the south equatorial current the new guinea coastal undercurrent and the equatorial undercurrent

an analysis of soil crust strength in relation to potential abrasion by saltating particles wind erosion depends on the ease with which particles can be detached from the soil surface but suitable tests to characterize this property are not available two possible methods to determine surface soil strength in the field were therefore compared on a range of artificially crusted surfaces these were made by spraying or tension wetting aggregates 10 2 2 0 5 and 0 5 mm from a structurally unstable sandy loam followed by drying each test involved measuring the force exerted on a probe driven at a steady rate into the surface using either a flat tipped 0 6 mm diameter penetrometer or a flat ended cylindrical punch with inner and outer diameters of 5 and 6 mm respectively both probes showed that crusts could be produced reproducibly depending on the probe and aggregate size penetration mainly occurred either as a result of aggregates being deflected out of the pathway of the probe or by genuine rupture of aggregates or of the crusted surface the penetrometer because it was comparable to the size of sand grains gave results that can be used to characterize surface erodibility to saltating particles the punch gave results that would be unsuitable for this purpose as would other strength tests that are on too large a scale penetrometer results were analyzed to calculate the energy required for penetration it was thus possible to demonstrate that only the spray wetted fine aggregates had a surface that could undergo large scale rupture by saltating sand grains for all other surfaces saltating particles would be unable to supply sufficient energy to rupture aggregates or the crusted surface erosion could only occur by a slower process of abrasion in which smaller particles or aggregates are chipped away from the surface however it is shown that saltating particles could rupture the interaggregate bonding in the 2 0 5 mm aggregate surfaces thus permitting creep an alternative and potentially simpler way of characterizing surface erodibility by using a surface modulus of elasticity is also discussed our results demonstrate that the small diameter penetrometer is a promising technique for characterizing erodibility of aggregated and crusted surfaces 1997 by john wiley sons ltd

decadal changes of enso persistence barrier in sst and ocean heat content indices 1958 2001 decadal changes of el nino southern oscillation enso persistence barriers in various indices of sea surface temperature sst and ocean heat content ohc are examined in this study using observations and ocean data assimilation products for the period 1958 2001 it is found that the sst indices in the eastern and central equatorial pacific exhibit very different decadal barrier variability the variability is large for the eastern pacific sst indices nino1 2 and nino3 whose persistence barriers shifted abruptly in 1976 1977 and 1989 1990 in contrast the central pacific sst indices nino3 4 and nino4 experienced little decadal barrier variability and have had their persistence barriers fixed in spring in the past four decades the zonal mean ohc index averaged over the equatorial pacific shows decadal barrier changes similar to those in the eastern pacific sst indices and always leads the nino3 sst barrier by about one season it is noticed that the sst persistence barrier appeared first in the eastern pacific before 1976 1977 first in the central pacific between 1976 1977 and 1989 1990 and almost simultaneous in both the eastern and central pacific after 1989 1990 these timings coincide with the westward propagating eastward propagating and standing pattern of enso sst anomalies observed in these three periods these results suggest that enso sst anomalies in the equatorial pacific can be considered to consist of two different processes a central pacific process whose phase transition such as onset and barrier always happen in spring and an eastern pacific process whose phase transition and barrier change from decade to decade and are influenced by changes in the mean thermocline depth along the equatorial pacific

two types of el nino events cold tongue el nino and warm pool el nino abstract in this study two types of el nino events are classified based on spatial patterns of the sea surface temperature sst anomaly one is the cold tongue ct el nino which can be regarded as the conventional el nino and the other the warm pool wp el nino the ct el nino is characterized by relatively large sst anomalies in the nino 3 region 5 s 5 n 150 90 w while the wp el nino is associated with sst anomalies mostly confined to the nino 4 region 5 s 5 n 160 e 150 w in addition spatial patterns of many atmospheric and oceanic variables are also distinctively different for the two types of el nino events furthermore the difference in the transition mechanism between the two types of el nino is clearly identified that is the discharge process of the equatorial heat content associated with the wp el nino is not efficient owing to the spatial structure of sst anomaly as a result it cannot trigger a cold event it is also demonstrated that zonal advective feedback i e zonal adve

accurate evaluation of ocean tide loading effects for gravity in nearshore region the fg5 measurements at sakurajima volcano in kagoshima bay japan we detected 5 10 microgal diurnal semidiurnal gravity signals of ocean tide origin by the fg5 absolute gravimeter at two stations in sakurajima volcano located 300 m and 2500 m away from the shore we computed the gravity originating both from the global ocean tides and from the local ones in kagoshima bay considering the fine scale sealand distribution around the stations the observed fg5 records and the theoretical ocean tides agreed well with each other in both amplitude and phase indicating that the oceanic loading effects can be predicted to an accuracy better than 2 microgal within several hundred meters of the shore in sakurajima the apparently puzzling errors that have so far arisen on nearshore lacoste measurements were resolved by the correction of the effects

temporal aspects of the abrasion of microphytic crusts under grain impact wind tunnel simulations of the response of two moss crusts to grain impact indicate that given sufficient time these surfaces will deteriorate under very low wind velocities only slightly above u t for the loose saltating grains in parallel with these experiments the frequency distributions of ultimate strength and penetration energy were determined for each of the two crust types via penetrometry pohlia was found to be stronger than tortula but even so both of these crusts had ultimate strengths 20 350 times higher than the force delivered by a single grain impacting each surface at a velocity of 1 ms 1 in comparison the modulus of deformation and penetration energy data were very similar for the two surface types especially for the weakest areas of crust development this observation is in accord with the wind tunnel simulations that also found no consistent difference in the response of these two crust types to impact in comparison with crusts formed by clay and salt fibrous microphytic crusts are morphologically complex and typically weak the notable elasticity of these surfaces does reduce the force of grain impact and thereby provides some protection against rupture one of the central conclusions of this study suggests that not only is the particle kinetic energy at impact important in crust breakdown but also tiny fractures at points of localized stress concentration contribute to a progressive reduction in the integrity of the filament net in some of the experiments conducted as part of this study up to 50 or more minutes of constant bombardment was required to produce small abrasion marks on selected areas of the microphytic crust this study prepares a foundation for future experiments needed to examine the breakdown of complex crusts formed in nature copyright 2002 john wiley sons ltd

geothermal reservoir monitoring with a combination of absolute and relative gravimetry microgravity monitoring is a valuable tool for mapping the redistribution of subsurface mass and for assessing changes in fluid recharge from reservoir boundaries associated with geothermal exploitation to further the development of a high precision absolute relative hybrid gravity measurement technique we conducted measurements using an absolute gravimeter in two geothermal fields in japan the absolute gravity measurements were performed in the central production areas to directly measure gravity changes caused by fluid withdrawal we succeeded in measuring long term trends within an accuracy of a few microgals in the okuaizu and ogiri fields which have been producing electricity for several years absolute measurements in the center of the field provide reliable and local reference datum anchor points for more widely distributed relative gravity measurements in the ogiri field we carried out time lapse hybrid measurements with this combination of absolute and relative gravimetry and delineated the

first detection of absolute gravity change caused by earthquake unequivocal coseismic gravity change was detected for the first time by absolute gravimetry the measurements were done just one day before and only 7 days after a m6 1 earthquake m6 1 the absolute gravity change was 6 microgal significantly larger than the observational error of about 1 microgal of particular interest is that the observed spatial gravity variations agree remarkably well with those expected from an elastic dislocation model constructed on displacement data alone the result strongly encourages us to perform a simultaneous inversion of both gravity and displacements to have better insight of earthquakes

linkage between interannual variation of the east asian intraseasonal oscillation and mei yu onset abstractthe mei yu onset over the middle to lower reaches of the yangtze river valley mlyrv varies considerably from early june to mid july which leads to large interannual changes in rainy seas

spatiotemporal gravity changes at miyakejima volcano japan caldera collapse explosive eruptions and magma movement 1 calderas are ubiquitous topographic features of volcanos yet caldera formation itself has not been recorded intensively by modern measurement techniques here we report the spatiotemporal gravity changes before and after caldera collapse at the miyakejima volcano japan in 2000 a gravity decrease of as much as 145 gal 1 gal 10 8 m s2 at the summit area since june 1998 was detected 2 days prior to the collapse interpreted as reflecting the formation of a large void beneath the volcano gravity changes detected after the initiation of collapse can mostly be corrected by the effect of collapsed topography from which a rapid rate of collapse of more than 1 6 107 m3 d can be inferred correcting for the effect of topography change we identified a temporal decrease in gravity from the middle of july to late august despite ground subsidence the gravity decrease is interpreted as a reduction of the density in a cylindrical conduit attributed to water inflow from an ambient aquifer that also promoted intensive magma water interaction and subsequent explosive eruptions from september to at least november 2000 gravity values at all sites increased significantly by a degree that cannot be explained by ground displacement alone we interpret this temporal evolution as primarily due to magma ascent and refilling of the conduit

three evolution patterns of central pacific el nino 1 three evolution patterns are identified for the central pacific cp type of el nino based on events that occurred during 1958 2007 1 a symmetric decaying pattern whose sea surface temperature anomalies grow and decay symmetrically with respect to a peak phase 2 a prolonged decaying pattern that decays slowly and is followed by a warm event in the eastern pacific ep and 3 an abrupt decaying pattern that terminates rapidly after the peak and is followed by a cold event in the ep the depth of the equatorial thermocline is found to determine which evolution pattern occurs if the cp el nino occurs in a recharged thermocline state i e deeper than normal depth an ep warming may appear in the decaying phase of the cp event to slow down the decay giving rise to the prolonged decaying pattern if the thermocline is in a discharged state i e shallower than normal depth an ep cooling may occur to abruptly terminate the cp el nino if the thermocline is in a neutral state i e normal depth the cp event may have a symmetric pattern of growth and decay although a few exceptions exist these results indicate that the equatorial thermocline state at the peak phase of a cp el nino event can be a potential predictor of the way the event may decay

wind erosion of crusted soil sediments saltating particles increase the rate of dust release from sediments in arid and semi arid areas they also break interparticle bonds in aggregated and crusted soils thereby increasing the number of particles available for entrainment this pilot study examines rates of erosion in relation to the flux of saltating grains for three crusted sediments of different strengths dislodgement of surface particles decreases with increasing crust strength as measured by a cylindrical flat ended penetrometer in addition initial dust release from craters formed by single impactors in unaggregated soil is examined in relation to the associated saltator the volume of material removed depends linearly on the kinetic energy of the abraders

the 4d microgravity method for waterflood surveillance part ii gravity measurements for the prudhoe bay reservoir alaska between 1994 and 2002 a series of experiments was conducted at prudhoe bay alaska aimed at the development of an effective 4d or time lapse gravity technique theoretical investigations had pointed out the potential for monitoring water injection in the 2500 m deep reservoir but it was not clear that gravity measurements of sufficient accuracy could be made in the arctic environment during the course of these experiments new techniques and instrumentation were introduced and perfected for both gravity and position measurements gravity stations are located using high precision global positioning system gps techniques without permanent monuments robust methods for meter drift control have improved noise resistance in relative gravimeter surveys absolute gravity measurements with a field portable instrument maintain absolute gravity levels among surveys a 4d gravity difference noise of 12 gal standard deviation has been established at prudhoe bay for gps controlled relative gravimeter surveys

el nino modoki and its possible teleconnection 1 using observed data sets mainly for the period 1979 2005 we find that anomalous warming events different from conventional el nino events occur in the central equatorial pacific this unique warming in the central equatorial pacific associated with a horseshoe pattern is flanked by a colder sea surface temperature anomaly ssta on both sides along the equator empirical orthogonal function eof analysis of monthly tropical pacific ssta shows that these events are represented by the second mode that explains 12 of the variance since a majority of such events are not part of el nino evolution the phenomenon is named as el nino modoki pseudo el nino modoki is a classical japanese word which means a similar but different thing the el nino modoki involves ocean atmosphere coupled processes which include a unique tripolar sea level pressure pattern during the evolution analogous to the southern oscillation in the case of el nino hence the total entity is named as el nino southern oscillation enso modoki the enso modoki events significantly influence the temperature and precipitation over many parts of the globe depending on the season the impacts over regions such as the far east including japan new zealand western coast of united states etc are opposite to those of the conventional enso the difference maps between the two periods of 1979 2004 and 1958 1978 for various oceanic atmospheric variables suggest that the recent weakening of equatorial easterlies related to weakened zonal sea surface temperature gradient led to more flattening of the thermocline this appears to be a cause of more frequent and persistent occurrence of the enso modoki event during recent decades

dust emission from wet and dry playas in the mojave desert usa the interactions between playa hydrology and playa surface sediments are important factors that control the type and amount of dust emitted from playas as a result of wind erosion the production of evaporite minerals during evaporative loss of near surface ground water results in both the creation and maintenance of several centimeters or more of loose sediment on and near the surfaces of wet playas observations that characterize the texture mineralogic composition and hardness of playa surfaces at franklin lake soda lake and west cronese lake playas in the mojave desert california along with imaging of dust emission using automated digital photography indicate that these kinds of surface sediment are highly susceptible to dust emission the surfaces of wet playas are dynamic surface texture and sediment availability to wind erosion change rapidly primarily in response to fluctuations in water table depth rainfall and rates of evaporation in contrast dry playas are characterized by ground water at depth consequently dry playas commonly have hard surfaces that produce little or no dust if undisturbed except for transient silt and clay deposited on surfaces by wind and water although not the dominant type of global dust salt rich dusts from wet playas may be important with respect to radiative properties of dust plumes atmospheric chemistry windborne nutrients and human health published in 2007 by john wiley sons ltd

improved extended reconstruction of sst 1854 1997 abstract an improved sst reconstruction for the 1854 1997 period is developed compared to the version 1 analysis in the western tropical pacific the tropical atlantic and indian oceans more variance is resolved in the new analysis this improved analysis also uses sea ice concentrations to improve the high latitude sst analysis and a modified historical bias correction for the 1939 41 period in addition the new analysis includes an improved error estimate analysis uncertainty is largest in the nineteenth century and during the two world wars due to sparse sampling the near global average sst in the new analysis is consistent with the version 1 reconstruction the 95 confidence uncertainty for the near global average is 0 4 c or more in the nineteenth century near 0 2 c for the first half of the twentieth century and 0 1 c or less after 1950

determination of reservoir properties at wairakei geothermal field using gravity change measurements abstract exploitation of a liquid dominated geothermal system generally results in the transfer of mass within or out of the system and causes measurable changes in gravity when the rate of mass transfer is controlled by the permeability of the reservoir rocks then the analysis of measured gravity changes can yield values for reservoir properties for two such cases we derive permeability or permeability thickness transmissivity and storativity one case is during the early stages of exploitation when a two phase zone is rapidly expanding calculations using a numerical reservoir simulation model show that for wairakei the gravity changes associated with permeabilities of 50 and 100 md would be clearly distinguishable 50 gal in less than 2 years a measured gravity change of 415 gal between 1950 and 1961 suggests a permeability of 100 md which is consistent with values obtained from well tests the second case is during reinjection into a deep liquid zone overlain by a two phase zone gravity changes of up to 120 gal associated with reinjection at wairakei are analysed using analytical models theis solution the measured gravity changes are matched by those of a model with isotropic permeability having a permeability thickness kh of 9 9 d m and a storativity of 9 2 10 6 m pa 1 if a model having anisotropic horizontal permeability is used the derived values for kh are 18 2 and 5 4 d m and the storativity is 8 7 10 6 m pa 1

interannual variability of the north pacific subtropical countercurrent and its associated mesoscale eddy field interannual changes in the mesoscale eddy field along the subtropical countercurrent stcc band of 188 258n in the western north pacific ocean are investigated with 16 yr of satellite altimeter data enhanced eddy activities were observed in 1996 98 and 2003 08 whereas the eddy activities were below average in 1993 95 and 1999 2002 analysis of repeat hydrographic data along 1378e reveals that the vertical shear between the surface eastward flowing stcc and the subsurface westward flowing north equatorial current nec was larger in the eddy rich years than in the eddy weak years by adopting a 2 layer reduced gravity model it is shown that the increased eddy kinetic energy level in 1996 98 and 2003 08 is because of enhanced baroclinic instability resulting from the larger vertical shear in the stcc nec s background flow the cause for the stcc nec s interannually varying vertical shear can be sought in the forcing by surface ekman

wind transport of sand surfaces crusted with photoautotrophic microorganisms abstract wind tunnel experiments show that while surfaces inoculated with photoautotrophic organisms are stable in winds up to 19 m s 1 only filamentous cyanobacteria especially nostoc commune afford considerable protection against abrasion from windborne particles crusts formed by the polysaccharide secreting alga chlamydomonas acidophila break down easily under impact the entrainment of large low density aggregates possibly contributing to higher transport rates than would otherwise be expected for untreated sediment surface disintegration encompasses a suite of complex scale dependent processes which vary with the structure thickness and strength of the crust independent measurements of crust strength based on flexure testing are in good agreement with wind tunnel evaluation of crust stability the accommodation of a relatively large amount of deformation without rupture is an important property of fibrous photoautotrophic mats perhaps outweighing consideration of their peak strength

rock burst forecasting and genetic research in coal mines by microgravity method microgravity can be used for predicting rock bursts for the first time gravity anomalies related to rock bursts have been recorded the methodology developed has led to the first successful predictions the depth of the rock burst focus might be determined on the basis of analytical downward continuation of related gravity anomalies the focus is treated as a singular point of the gravity potential and its derivatives the rock burst gravity anomalies might be explained on the basis of the assumed dilatancy process that causes the rock burst the mean density change of the rock mass threatened with rock bursts can be estimated from the corresponding rock burst gravity anomalies

a microgravimetric network in east central greece an area of potential seismic hazard summary the eastern mediterranean is a region of complex tectonic processes and associated horizontal and vertical displacements a high precision gravity network has been established in the atalanti area of central greece to monitor temporal gravity changes on an annual or more frequent basis a total of 68 sites have been measured in 1981 and 1982 with a maximum single instrument standard deviation of 0 08 gravity units after a least squares network adjustment analysis of the gravity differences between the two measuring epochs exhibits no change of gravity over the network with a precision of 0 1 1 gravity units it is proposed that the gravity values given form a stable base for continued observations which will enable the authors to resurvey the region in the event of precursory foreshocks observation of the atlantic network will continue on an annual basis preserving the same observation sequence for reasons of symmetry

yardang evolution from maturity to demise yardangs are enigmatic wind parallel ridges sculpted by aeolian processes that are found extensively in arid environments on earth and mars no general theory exists to explain the long term evolution of yardangs curtailing modeling of landscape evolution and dynamics of suspended sediment release we present a hypothesis of yardang evolution using relative rates of sediment flux interyardang corridor downcutting yardang denudation substrate erodibility and substrate clast content to develop and sustain yardangs corridor downcutting must exceed yardang vertical denudation and deflation however erosion of substrate yields considerable quantities of sediment that shelters corridors slowing downcutting we model the evolution of yardangs through various combinations of rates and substrate compositions demonstrating the life span suspended sediment release and resulting landscape evolution we find that yardangs have a distinct and predictable evolution with inevitable demise and unexpectedly dynamic and autogenic erosion rates driven by subtle differences in substrate clast composition

role of sea surface temperatures in forcing circulation anomalies driving u s great plains pluvial years abstractin the u s great plains gp diagnosing precipitation variability is key in developing an understanding of the present and future availability of water in the region building on previous

a conceptual model of wind erosion of soil surfaces by saltating particles a conceptual model is described for the prediction of wind erosion rates dependent on the distribution of impact energy delivered to the surface by saltating grains p ei and the distribution of local surface strength p es methods are presented for the measurement of both distributions and consequent loss of material from the bed it is concluded that saltating sand grains can rupture weak crusts under even moderate wind conditions and that the rate of erosion will depend on the shape of the distribution tails copyright 1999 john wiley sons ltd