the existence of free rossby waves during january 1979 abstract the large scale transient components of atmospheric flow have been studied for many years observational studies indicate that large amplitude regularly westward propagating waves appear episodically in the atmosphere these waves have spatial structures and frequencies enticingly similar to those of external rossby modes obtained theoretically from the linearized baroclinic equations in the present study the episode of 10 28 january 1979 is studied by expanding global objective analyses into the normal modes of a global baroclinic quasi geostrophic model linearized about the observed nonseparable zonal mean wind field several coherent regularly propagating waves are found one of the most significant of these the r31 or 16 day mode is examined in detail although the observed structure is similar in some ways to the theoretically derived structure there are important discrepancies these discrepancies are examined more closely using upper air soundings from antarctica the experimental res

oceanic effects on polar motion determined from an ocean model and satellite altimetry 1993 2001 1 mass redistribution and motion in the oceans are major driving forces of geodetic variations including polar motion length of day geocenter and gravity field changes we examine oceanic contribution to polar motion using estimates from a data assimilating ocean general circulation model and satellite radar altimeter observations the data include model estimates of variations in oceanic mass obp and meridional and zonal velocities sea level anomalies from topex poseidon t p satellite altimeter measurements and steric sea surface height changes deduced from the model are also used to estimate obp effects estimated oceanic contributions from both the model and t p show considerably better agreement with polar motion observations compared with results from previous studies the improvement is particularly significant at intraseasonal timescales both obp and ocean current variations provide important contributions to polar motion at intraseasonal timescales the oceans appear to be a dominant contributor to residual polar motion not accounted for by the atmosphere the oceans also play an important role in seasonal excitation combined obp and ocean current contributions explain much of the residual semiannual variability

climatology of normal mode rossby waves abstract three years of twice daily nmc global operational analyses were projected onto normal mode rossby waves to produce a climatology of these waves for zonal wavenumbers 1 through 4 annual average geopotential amplitudes at 50 kpa are about 5 gpm for the gravest symmetric meridional mode and 10 and 20 gpm for the next two meridional model although the amplitude for a given time and latitude can greatly exceed the average seasonal average amplitudes differ by less than 25 from the annual average the modes frequencies drift during the course of a year but this variation is not correlated with season autocorrelations of rossby wave time series become negligible for lags greater than approximately ten days which is of the order of the wave period for all ten modes examined geopotential fluctuations exist in both northern and southern hemispheres

structural evolution of harmaliyah oil field eastern saudi arabia the history of structural growth of the harmaliyah oil field in eastern saudi arabia was studied by means of a series of paleostructural maps to determine if early entrapment of hydrocarbons played an important role in preserving the high porosity of the kimmeridgian upper jurassic arab d reservoir the arab d has been affected by shallow or preburial diagenesis a common feature in arabian upper jurassic calcarenitic reservoirs closure forming the structural trap in the arab d at harmaliyah oil field developed principally during the late turonian late cretaceous during kimmeridgian late jurassic early turonian late cretaceous time shallow or preburial diagenesis of the calcarenitic arab d reservoir rocks seems to have played a major part in preservation of por sity before the porosity was filled with hydrocarbons

modelling the pole tide and its effect on the earth s rotation summary the pole tide is the response of the ocean to incremental centrifugal forces associated with the chandler wobble the tide has a potentially important effect on the period and damping of the wobble but it is at present not well constrained by observations here we construct both analytical and numerical models for the pole tide the analytical models consider the tide first in a global ocean and then in an enclosed basin on a beta plane the results are found to approach equilibrium linearly with decreasing frequency and inversely with increasing basin depth the numerical models solve laplace s tidal equations over the world s oceans using realistic continental boundaries and bottom topography the results indicate that the effects of the non equilibrium portion of the deep ocean tide on the chandler wobble period and damping are negligible

geophysical constraints on a modified crust below the rayn anticlines eastern saudi arabia abstract the gravity anomaly signature for a regional trans rayn geophysical traverse trgt across rayn anticlines ra illustrates alternating bouguer anomaly b a highs and lows highs over the anticline axes and lows in flanking sub basins we demonstrate for the first time that the bipolar gravity signatures actually camouflage a more extensive b a low of amplitude 63 mgal and wavelength 750 km developed between the qatar and amar arches 2d gravity modeling for trgt infers a 3 layer crustal model for ra i a regionally extensive upper crustal layer 10 15 km thick of lighter density by 0 02 g cm3 compared to normal upper continental crust ii a mid crustal 10 km thick transition layer of intermediate density and iii the lower mafic crust of higher than normal density the moho dips westward from 37 3 below ghawar anticline ga to 47 and 47 6 km below the kbs amar arches with a lateral density change in the lower crust following the same direction crustal thinning by as much as 22 occurred below ga the altered crust directly correlating to the basement uplift on its top and mantle uplift at its base an inverse correlation between crustal thicknesses and vp vs is observed for the entire ra displaying highest vp vs 1 93 and poisson s ratio 0 443 for the ga crust

hydrological and oceanic effects on polar motion from grace and models 1 terrestrial water storage tws and ocean bottom pressure obp are major contributors to the observed polar motion excitations second only to atmospheric mass movement however quantitative assessment of the hydrological and oceanic effects on polar motion remains unclear because of the lack of global observations in this paper hydrological and oceanic mass excitations to polar motion are investigated using monthly tws and obp derived from the gravity recovery and climate experiment grace for january 2003 until december 2008 the results from this analysis are compared with hydrological model excitations from the european center for medium range weather forecasts ecmwf and oceanic model excitations obtained from the jet propulsion laboratory jpl using estimating the circulation and climate of the ocean ecco results show that the grace derived obp and tws better explain the geodetic residual polar motion excitations for the px component at the annual period while the grace obp and ecmwf hydrological angular momentum agree better with the geodetic residuals for the annual py excitation grace ocean and hydrology excitations better explain the geodetic residuals for the semiannual py excitation however the jpl ecco and ecmwf models better explain the intraseasonal geodetic residual of polar motion excitation in the px and py components the grace data demonstrate much higher intraseasonal variability than either the models or the geodetic observations

atmospheric excitation of polar motion during the gig 91 measurement campaign daily determinations of the earth s pole position from global positioning system gps observations acquired during the first gps iers and geodynamics gig experiment held during january 22 1991 to february 13 1991 are interpreted in terms of atmospheric wind and pressure fluctuations as parameterized by the atmospheric angular momentum aam functions all available aam functions spanning the gig 91 period have been collected and compared to the observations in the time and polar motion domains the greatest level of agreement is obtained using the total wind plus pressure functions from the japanese meteorological agency jma where the pressure term is computed by assuming the inverted barometer approximation in this case the correlation coefficient between the observed and jma induced polar motion series is 0 91 for the x component and 0 72 for the y component the rms of the difference between the observed and jma induced series is 0 71 mas for the x component and 0 69 mas for the y component and the percentage of the variance of the observed series explained by the jma induced series is 83 for the x component and 48 for the y component thus it is demonstrated that atmospheric wind and pressure fluctuations are largely responsible for exciting the rapid polar motions observed during gig 91

temporal variability of the antarctic circumpolar current observed from satellite altimetry sea level measurements by the seasat altimeter were used to study the temporal variability of the antarctic circumpolar current between july and october 1978 large scale zonal coherence in the cross stream sea level difference was observed indicating a general increase in the surface geostrophic velocity of the current around the southern ocean the result demonstrates the power of satellite altimetry to monitor the variability of large scale ocean currents

surface expressions of the ghawar structure saudi arabia abstract the ghawar anticline is approximately 225 km long and 25 km wide in the subsurface but the surface structural expression is not obvious identifying subtle structural imprints in the young mio pliocene sedimentary cover is therefore of great importance in developing a structural growth model for the ghawar field the ghawar area between the jafurah sand desert to the east and the rubayda dahna sand deserts to the west is characterized by a rougher topography when compared to the surrounding rather smooth flat areas this rough geomorphology of the structure can also be noticed on the satellite images a geomorphologic elevation map of the area and a subsurface structural contour map of the top arab d upper jurassic reservoir reveal very similar geometric shapes calcareous sandstone deposits of the youngest hofuf formation mio pliocene cap the structural highs along the axis of the anticline and spectacular fractures caves mesas and monumental geomorphologic features have developed in the escarpments fractures in the dam formation middle miocene are not as conspicuous as in the hofuf formation but indigenous fractures are clearly recognized in this formation a match between the directions of some topographic lineaments and projected surface traces of subsurface faults from seismic cross sections can be observed however at the field locations faults have yet to be defined on the surface surface indications suggest that the structure has been active until the present day elevations of a bedding plane on the shedgum plateau reveal a 0 25 dip angle which cannot be distinguished on the surface by the human eye the movements that occurred during the 4 million years since the pliocene period reveal an average tilting of 0 06 per one million years

regional atmospheric angular momentum contributions to polar motion excitation we focus on a regional analysis of the equatorial components of the effective atmospheric angular momentum eaam functions that are responsible for excitation of polar motion these functions are computed from the ncep ncar 40 year reanalysis project data both globally and in 108 geographic sectors for the period from 1968 to 1997 we investigate regional contributions of these atmospheric angular momentum functions to the short period oscillations of geodetically determined polar motion directly and to the global eaam excitation functions themselves we examine two excitation terms in parallel both excluding and including the inverted barometer ib formulation which adjusts the atmosphere to account for an isostatic equilibrium response from the ocean to overlying pressure the ib formulation tends to decrease effective atmospheric variability in the case of pressure terms without ib the largest contributions to the equatorial components of eaam functions originate in the south pacific north atlantic and north pacific regions however application of the ib correction may result in the dominance of eurasia and north america instead with nearly all southern hemisphere contributions disappearing oscillations of the polar motion excitation function are mainly coherent with variations of the pressure term of the eaam excitation functions over northern mid latitude land areas distinct oscillations appear to occur in two frequency bands 25 75 days and 75 125 days in both prograde and retrograde directions which correspond to counterclockwise and clockwise polar motion respectively coherence and cross spectral analyses are performed to determined degree of agreement and common amplitude respectively we examine the atmospheric functions with respect to one important region in eurasia and note a propagating horizontal influence within the atmosphere

the rotation of the earth earth rotation studies are reviewed for the 1987 1990 time period it is noted that the emphasis in these studies has shifted from improvements in the observational techniques to interpreting and gaining greater understanding of the variations of the earth rotations there have been progressive improvements in the accuracy and the temporal resolution of earth rotation measurements

causes of rapid motions of the earth s pole analysis of new highly accurate geodetic data reveals rapid motions of the earth s pole with peak to peak variations of 0 002 to 0 020 seconds of arc fluctuating on timescales between two weeks and several months comparison with meteorological excitation estimates shows that these motions are at least partially driven by surface air pressure changes as modified by the response of sea level to atmospheric loading such geodetic measurements thus potentially provide a novel means of observing the dynamics of the atmosphere and oceans at very low spatial wavenumbers

atmospheric and oceanic excitation of the earth s wobbles during 1980 2000 1 because of the action of various geophysical excitation mechanisms the earth does not rotate about its figure axis so it wobbles as it rotates here the effectiveness of atmospheric and oceanic processes in exciting the earth s wobbles during 1980 2000 is evaluated using estimates of atmospheric angular momentum from the national centers for environmental prediction national center for atmospheric research ncep ncar reanalysis project and estimates of oceanic angular momentum from the estimating the circulation and climate of the ocean ecco consortium s simulation of the general circulation of the oceans on intraseasonal timescales atmospheric surface pressure changes are found to be the single most effective process exciting the earth s wobbles explaining about twice as much of the observed variance as do either atmospheric wind or ocean bottom pressure changes and nearly 4 times as much of the observed variance as do oceanic currents however on interannual timescales ocean bottom pressure changes are found to be the single most effective process exciting the earth s wobbles explaining more than 5 times as much of the observed variance as do atmospheric wind and pressure changes combined and more than twice as much of the observed variance as do oceanic currents within the chandler band it is found that during 1980 2000 atmospheric and oceanic processes have enough power to excite the chandler wobble and are significantly coherent with it the single most important mechanism exciting the chandler wobble is found to be ocean bottom pressure variations atmospheric and oceanic processes do not appear to have enough power to excite the earth s wobbles to their observed levels on pentadal and longer timescales although series longer than the 21 yearlong series used here need to be studied in order to obtain greater statistical significance of this result

determination of oceanic dynamic barometer corrections to atmospheric excitation of earth rotation the excitation of earth s rotation by atmospheric pressure fluctuations on timescales from days to years is modified by the oceanic response to the pressure load that response has often been approximated as a static inverted barometer ib change in sea level but evidence from theory and both tide gauge and altimetric data suggests that the ib poorly models the sea level response at short periods static models also fail to account for the currents induced by the pressure loading the actual dynamic response of the oceans to barometric loads depends on frequency and on the spatial structure of the loading this work presents a green s function approach to determining the rotational effects of that oceanic response the green s functions characterize the rotational effects of the oceanic response to pressure loads described spatially by individual spherical harmonics for each harmonic of forcing they were computed at nine periods ranging from 4 days to 18 years and interpolated at intermediate periods computations were based on solutions to the author s dynamic spherical harmonic ocean tide model the effects on rotation of the dynamic barometer oceanic response are obtained by a convolution type combination of the green s functions with actual atmospheric pressure data results for data spanning the past decade will be illustrated using harmonically decomposed national center for environmental prediction ncep and european centre for medium range weather forecasts ecmwf pressure fields

rapid ocean signals in polar motion and length of day 1 non tidal variability in ocean currents and bottom pressure is substantial at short periods but relating the associated signals in ocean angular momentum oam to observed polar motion and length of day fluctuations has been difficult our simulations using a barotropic ocean model reveal a clear connection between the estimated oam signals and both polar motion and length of day at periods of 3 10 days the dynamic response of the oceans to barometric pressure plays an important role in the excitation of rapid rotation signals the impact of oam variability is most clear when using gps based earth orientation measurements with little temporal smoothing using the gps series and accounting for oam in addition to atmospheric effects yields substantial improvements in the excitation budget for rapid polar motion and length of day the comparisons with earth rotation data provide a useful check on the rapid ocean variability simulated by the barotropic model

hydrocarbon habitat in main producing areas saudi arabia current hydrocarbon production in saudi arabia is from reservoirs of cretaceous and jurassic age geochemical studies of the sediments and oils suggest that the hydrocarbons were derived from two separate source rock provinces oil production from the large fields in the southern part of the area is from jurassic carbonate reservoirs most of these oils were derived from thermally mature thinly laminated organic rich carbonate rocks of jurassic age callovian oxfordian these source rocks were deposited in an intrashelf basin which is limited to the southern part of the main producing areas extensive vertical migration of oils originating in these sediments is prevented by superjacent evaporite seals deposited during the late jurassic fields in the northern producing areas appear to have derived their hydrocarbons from a source rock province on the north production from cretaceous clastic and carbonate reservoirs is limited to the northeastern part of the producing areas this distribution may be explained by limitation of thermally mature cretaceous source rocks to the northeastern areas or by the local lack of subjacent evaporite seals to separate these reservoirs from jurassic source rocks thermal maturation studies indicate that the hydrocarbons in mesozoic reservoirs migrated into the present traps during the early tertiary

station coordinates baselines and earth rotation from lageos laser ranging 1976 1984 satellite laser range slr measurements to lageos from may 1976 to january 1984 have been used to compute earth rotation parameters and the geocentric positions of 57 laser tracking station sites occupied during this interval the station position determinations were part of a simultaneous solution which includes lageos orbit elements in 15 day arcs and earth rotation parameters in 3 day subarcs using residuals from a 7 7 year lageos long arc lla 8402 systematic differences between the terrestrial reference frames implied by the university of texas station coordinate solution lsc 8402 and by previous solutions computed at the university of texas ut and at goddard space flight center gsfc are reviewed the new solution resolves a 0 72 m z axis difference between the terrestrial reference system origins inferred from the gsfc solution sl5 and the previous ut solution lsc 8112 the implied origins of the lsc 8402 solution and the sl5 solution are consistent to less than 60 mm in all components and after removing orientation and scale differences the coordinates for 26 common tracking stations have an rms difference of less than 80 mm the rms difference in baseline length for 22 station pairs used in the recent crustal dynamics project very long baseline interferometry vlbi slr intercomparison experiment is 50 mm between the gsfc and ut laser solutions and 40 mm between the ut laser solution and the vlbi solution the earth rotation parameters computed in 3 day intervals have an internal precision of 2 marc sec 62 mm at the earth s surface for xp and yp and 0 15 ms 70 mm at the equator for ut1 the estimated accuracy of the series based on dual baseline vlbi intercomparisons is approximately 2 marc sec for xp and yp and 0 2 ms for ut1 the effects of plate motion on the determination of the secular drift in polar motion using the 7 7 year series is shown to be at the level of 1 marc sec yr finally baseline changes have been investigated by repeated station coordinate determinations using 60 day subsets of the 7 7 year interval of the lageos data set in each 60 day solution interval orbit elements were estimated at 15 day intervals and earth rotation parameters were determined at 5 day intervals for the 4 year period beginning in january 1980 baseline length changes inferred by the successive 60 day solutions were found to be in general agreement with the motions predicted by the am1 2 plate motion model of minster and jordan

the korudag anticlinorium in the south thrace basin northwest turkey a super giant petroleum trap complex the sedimentary sequence of the south thrace basin northwest turkey comprises upper cretaceous holocene sediments in this basin the korudag anticlinorium which is the subject of this study is located between the aegean sea in the west and the sea of marmara to the east the anticlinorium which is approximately 300 km 186 mi long and 40 km 25 mi wide was formed by effects of the neotethys subduction accretion complex and istranca massif collision during the late early miocene the korudag anticlinorium was deformed to its present day structure by the oldest splay of the north anatolian fault upper middle miocene and the northern branch of the north anatolian fault naf n not earlier than 200 ka organic geochemical analysis oil and gas to source rock correlation and basin modeling studies suggest that the korudag anticlinorium should be charged by hydrocarbons generated from the karaagac ceylan regionally and mezardere formations gas and oil are being produced from the korudag anticlinorium and its subparallel anticlines in the north marmara degirmenkoy seymen cayirdere karacali yulafli tekirdag sevindik and vakiflar gas plus oil fields mapping done as part of this study indicates that the korudag anticlinorium has not yet been tested and explored comprehensively

the cenozoic kinematics of qatar evidence for high angle faulting along the dukhan anticline abstract new geological mapping and observations made across qatar favor a fault controlled model for the dukhan structure in the western part of the peninsula over previous fold related and regional erosion models regional stratigraphic relationships and sedimentology record significant fault localized accommodation development this miocene basin development may reflect far field extension in the foreland of coeval thrusting in oman the subsequent change in regional tectonics to convergence across the zagros front is interpreted to have led to basin inversion and the development of the present day topography and outcrop distribution

european vegetation during marine oxygen isotope stage 3 european vegetation during representative warm and cold intervals of stage 3 was inferred from pollen analytical data the inferred vegetation differs in character and spatial pattern from that of both fully glacial and fully interglacial conditions and exhibits contrasts between warm and cold intervals consistent with other evidence for stage 3 palaeoenvironmental fluctuations european vegetation thus appears to have been an integral component of millennial environmental fluctuations during stage 3 vegetation responded to this scale of environmental change and through feedback mechanisms may have had effects upon the environment the pollen inferred vegetation was compared with vegetation simulated using the biome 3 5 vegetation model for climatic conditions simulated using a regional climate model regcm2 nested within a coupled global climate and vegetation model genesis biome despite some discrepancies in detail both approaches capture the principal features of the present vegetation of europe the simulated vegetation for stage 3 differs markedly from that inferred from pollen analytical data implying substantial discrepancy between the simulated climate and that actually prevailing sensitivity analyses indicate that the simulated climate is too warm and probably has too short a winter season these discrepancies may reflect incorrect specification of sea surface temperature or sea ice conditions and may be exacerbated by vegetation climate feedback in the coupled global model

circular geological structures outcropping in the sedimentary basins of saudi arabia abstract a number of circular geological structures outcrop in the sedimentary basins of saudi arabia several are reviewed here to assess their mode of origin they are unrelated to each other are easily seen on aerial imagery and their origins are assessed here on the basis of new fieldwork and reflection seismic data the structures range in size from hundreds of meters to several kilometers in diameter jabal rayah 28 39 n 37 11 30 e is 5 km in diameter with ring faults and anomalously steep dips in siluro devonian strata reflection seismic data demonstrate that underlying strata are structureless and jabal rayah is interpreted as a probable impact structure ash shutbah 21 37 08 n 45 39 21 e is 2 3 km in diameter and consists of a zone of concentric sub horizontal folds in mesozoic carbonates surrounding a central area of disharmonic steeply plunging folds and a mass of stratigraphically anomalous sandstone there are dissolution structures in the vicinity and although this is a viable explanation the uniquely large and complex nature of ash shutbah suggests an alternative origin by impact reflection seismic data show that underlying strata in the vicinity of ash shutbah are structureless a province of at least 100 circular structures occurs in northeast saudi arabia aerial imagery and reflection seismic data shows that these structures are a mixture of bioherms and dissolution collapse features the kidan crater 22 06 53 n 53 26 38 e is a subcircular feature approximately 100 m in diameter exposed in quaternary sabkha between large sand dunes in the rub al khali field investigation reveals an unfaulted bowl with a slightly fractured floor in sabkha facies 3d reflection seismic data shows a small fault underlying the crater leading to a fluid escape interpretation for the depression

wrench tectonics in abu dhabi united arab emirates recent studies of the geodynamics and tectonic history of the arabian plate throughout geologic time have revealed that wrench forces played an important role in the structural generation and deformation of petroleum basins and reservoirs of the united arab emirates the tectonic analysis of abu dhabi revealed that basin facies evolution were controlled by wrench tectonics examples are the pre cambrian salt basin the permo triassic and jurassic basins in addition several sedimentary patterns were strongly influenced by wrench tectonics the lower cretaceous shuaiba platform margin and associated reservoirs is a good example wrench faults difficult to identify by conventional methods were examined from a regional perspective and through careful observation and assessment of many factors subsurface structural mapping and geoseismic cross sections supported by outcrop studies and geomorphological features revealed a network of strike slip faults in abu dhabi structural modelling of these wench forces including the use of strain ellipses was applied both on regional and local scales this effort has helped in reinterpreting some structural settings some oil fields were interpreted as en echelon buckle folds associated with ne sw dextral wrench faults several flower structures were interpreted along nw se sinistral wrench faults which have significant hydrocarbon potential synthetic and antitheticmore strike slip faults and associated fracture systems have played a significant role in field development and reservoir management studies four field examples were discussed less

application of landsat imagery to oil exploration in niobrara formation denver basin wyoming the niobrara formation produces oil from fractures in several places in the denver basin the niobrara is an oil prone mature source rock that entered the oil generating window during the laramide orogeny the laramide orogeny began with maximum compressive stress oriented east northeast during the late cretaceous to paleocene and ended with maximum stress oriented to the northeast in the eocene we believe the eocene phase activated northeast trending extension fractures that may have acted as pathways for migration and loci for storage of oil locally generated in the niobrara theoretically the fracture pressures related to oil generation in the niobrara would preferentially open and fill this northeast trending fracture system using landsat imagery to map fracture in the northern part of the denver basin we have identified areas prospective for niobrara oil production within an exploration fairway that is based on subsurface isopach and resistivity mapping support for this concept is the location of wells reported to produce oil from the niobrara along a zone of northeast trending lineaments