bluuebunny/crossref_metadata_2025 huggingface dataset:
Cretaceous paleomagnetic results from western Tibet and tectonic implications
Authors: Chen Y. , Cogné J.‐P. , Courtillot V. , Tapponnier P. , Zhu X. Y.
Published: February 2008

We present paleomagnetic results obtained from samples collected in the summer of 1989 along a 1000 km traverse between Yecheng (Xinjiang) and Shiquanhe (Tibet) in the western Qinghai‐Xizang Plateau (along ∼80°E longitude). During this field trip, 480 paleomagnetic cores in Jurassic to Tertiary limestones and sandstones were drilled at 49 sites; 400 were measured. Isothermal remanent magnetization analysis indicates the existence of high coercivity minerals, and thermal, rather than alternating field demagnetization, was found to be more efficient in isolating paleomagnetic directions. The characteristic magnetization has rather low unblocking temperatures (250–560°C) in most limestone samples and higher unblocking temperatures (400°C–680°C) in the sandstone samples. About half of the measured samples show the present geomagnetic field or aberrant directions. The remainder display stable multicomponent magnetizations. The stable characteristic magnetizations indicate (1) a probable Jurassic remagnetization; (2) a Cretaceous (120‐80 Ma) magnetization which passes a fold test, yielding a mean pole at 66.2°N, 245.0°E (A95=5.1°, N=14 sites); and (3) a large scatter of Tertiary directions, which may be due to tectonic problems and/or remagnetization in the sampling zone. The Cretaceous paleodirections from Aksaichin and Longmuco (11 sites on the Qiangtang (North Tibet) block) are very similar to those from Shiquanhe (three sites on the Lhasa (South Tibet) block), separated by 300 km. This suggests that the North and South Tibet blocks formed a single unit at least as early as the Cretaceous. Comparing our results with previous paleomagnetic work on the Tibetan plateau, it is found that the paleolatitude of 10.6°±5.1° obtained from this study for a reference at Domar (33.75°N, 80.4°E) is close to that (9.6°±2.8°) obtained by Achache et al. (1984) and Lin and Watts (1988) from the Takena formation (110‐100 Ma) in the Lhasa region (30°N, 91°E). In addition, it appears that the southern margin of the Tibetan blocks (i.e., Eurasia) occupied an E‐W trending position at about 7°±6°N latitude. Paleodeclination differences between the western and eastern Tibetan blocks suggest internal deformations of the plateau at different scales (from 1 to 1000 km). According to differences in paleomagnetic declinations, the arcuate shape of the blocks would have been partly acquired after the collision.
The Pre‐Cenozoic magmatic history of the Thurston Island Crustal Block, west Antarctica
Authors: Pankhurst R. J. , Millar I. L. , Grunow A. M. , Storey B. C.
Published: February 2008

New Rb‐Sr and K‐Ar geochronological data are presented for the majority of known pre‐Cenozoic outcrops in Thurston Island, the Jones Mountains, and the western Eights Coast, which collectively represent the basement geology of the Thurston Island crustal block of West Antarctica. Almost all are of calc‐alkaline igneous or metaigneous rocks, and indicate long‐standing proximity to a magmatic arc. The observable history began with Late Carboniferous (309±5 Ma) emplacement of mantle‐derived orthogneiss precursors in eastern Thurston Island. Nd model ages from these and later igneous rocks suggest that the underlying crust is no older than about 1200–1400 Ma throughout the area. A variety of cumulate gabbros was emplaced soon after gneiss formation, followed by crust‐contaminated diorites that have Triassic mineral cooling dates of 240–220 Ma. In the nearby Jones Mountains, the oldest exposed rock is a muscovite‐bearing granite with an Early Jurassic age of 198±2 Ma; its initial 87Sr/86Sr ratio of 0.710 and ϵNdt values of −5 to −7 indicate either anatexis or, at least, a high degree of crustal input during magma genesis. This belongs to a suite of such granites known throughout the Antarctic Peninsula and related to earliest rifting of the Gondwana supercontinent. The subsequent evolution of the Thurston Island area was dominated by I‐type magmatism, apparently in two major episodes at 152–142 Ma (Late Jurassic granites) and 125–110 Ma (Early Cretaceous bimodal suite). Most of these magmas had initial 87Sr/86Sr ratios of 0.705–0.706 and ϵNdt values of +2 to −4 and were derived from slightly enriched mantle or from juvenile lower crust. They are thought to signify subduction of Pacific Ocean floor as in the adjacent parts of West Antarctica, although the Late Jurassic episode was of greater intensity in Thurston Island than elsewhere. The Cretaceous magmatism was intense and of Andean‐type. Between 100 and 90 Ma, volcanism in the Jones Mountains became predominantly silicic, with increasing incorporation of crustal components (initial 87Sr/86Sr ratios of 0.706–0.709 and ϵNdt values of −3 to −6), as subduction‐related magmatism ceased in this part of the margin.
Source complexity of the 1988 Armenian Earthquake: Evidence for a slow after‐slip event
Authors: Kikuchi Masayuki , Kanamori Hiroo , Satake Kenji
Published: February 2008

We analyzed teleseismic P and S waves using a multiple‐event deconvolution method to investigate the source process of the Spitak, Armenia, earthquake of December 7, 1988. Teleseismic long‐period body waves exhibit complex waveforms, significantly more complex than those normally seen for an event of this size. We identified two groups of subevents. One is a group of strike‐slip events during the first 20 s. The other is a dip‐slip event initiating at about 30 s after the initial rupture. The tensor sum of all the subevents is essentially strike‐slip (strike=302°, dip=59°, rake=143°) with a scalar moment of 1.47×1019 N m. The seismic moment of the dip‐slip event (strike=89°, dip=60°, rake=88°) is 5.6 ×1018 N m, nearly 40% of the total, and the moment release rate is slower than the other subevents with a strike‐slip mechanism. We call this event a slow after‐slip event. The mechanism of the after‐sup event is consistent with the present‐day deformation pattern in the Caucasus where north‐south compression is predominant due to the continental collision between the Arabian plate and the Russian Platform. This result suggests that in a region where both strike slip motion and crustal shortening are taking place, like southern California, a large strike‐slip event may accompany large thrust events and vice versa. In order to determine the total coseismic deformation pattern, it is essential to resolve these multiple events in time, space, and mechanism.
Elastic properties of hydrogrossular garnet and implications for water in the upper mantle
Authors: O'Neill Bridget , Bass Jay D. , Rossman George R.
Published: February 2008

The single‐crystal elastic properties of a hydrous silicate garnet, hibschite (Ca3Al2(SiO4)1.72(H4O4)1.28), were measured using Brillouin spectroscopic techniques. The adiabatic bulk modulus of hibschite, Ks = 99.8±1.0 GPa, and the shear modulus, μ = 64.3±0.5 GPa, are 40% lower than the bulk and shear moduli for anhydrous grossular garnet Ca3Al2(SiO4)3. This increased compressibility of hydrogarnet is attributed to increased hydrogen bonding with pressure in the H4O4 tetrahedron. Density considerations indicate that hydrogarnet is likely to be stable relative to an assemblage with H2O as a separate phase throughout the upper mantle and probably the transition zone. Assuming garnet to be the sole repository for mantle water, the seismic wave velocities of a “wet” eclogitic layer are 6–8% lower than those of dry eclogite. A hydrated eclogitic layer several times thicker than the oceanic crust would probably be required for a water‐rich region of the mantle to be seismologically detectable. Lesser quantities of mantle water than those implied by the above scenario may be invisible to seismic techniques.
On pyroclastic flow emplacement
Authors: Battaglia Maurizio
Published: February 2008

In this note I investigate some theoretical characteristics of pyroclastic flow deposits, assuming that these flows are Bingham fluids, probably the simplest non‐Newtonian fluids. Pyroclastic flows are modeled as laminar debris flows moving on an inclined plane, and their physics is discussed within the classical framework of lubrication theory. Using general hydrodynamics methods, I show that the arrestment and emplacement of pyroclastic flows may be seen as the time‐asymptotic limit of their equations of motion. This limit is found to be a nonlinear ordinary differential equation, whose solution gives the shape of pyroclastic flow deposits. The model suggests that these flows stop when the supply of material from the source is depleted; deposit thickness is controlled principally by the flow yield stress τz, a parameter characteristic of Bingham fluids, while deposit length, a measure of flow mobility, depends on τz, on the source flux q0, and on the slope θ of the solid substrate. Even in this simple model, theoretical analysis shows a complex correlation between flow parameters and deposit profiles.
Formation of left‐lateral fractures within the Summit Ridge Shear Zone, 1989 Loma Prieta, California, Earthquake
Authors: Johnson Arvid M. , Fleming Robert W.
Published: February 2008

The 1989 Loma Prieta, California, earthquake is characterized by the lack of major, throughgoing, coseismic, right‐lateral faulting along strands of the San Andreas fault zone in the epicentral area. Instead, throughout the Summit Ridge area there are zones of tension cracks and left‐lateral fracture zones oriented about N45°W, that is, roughly parallel to the San Andreas fault in this area. The left‐lateral fractures zones are enigmatic because their left‐lateral slip is opposite to the right‐lateral sense of the relative motion between the Pacific and North American plates. We suggest that the enigmatic fractures can be understood if we assume that coseismic deformation was by right‐lateral shear across a broad zone, about 0.5 km wide and 4 km long, beneath Summit Ridge. The shear zone has an orientation of about N70° W and is oblique to the San Andreas fault zone, which has a trend of N45° to 50°W, so that right‐lateral shearing, along with some dilation, can account for the orientation of the fracture zones. Using an analog, kinematic model of the Summit Ridge shear zone and the observable geometric parameters (a shear zone about 0.5 km wide, an acute angle of 25° between the tension cracks and the shear‐zone walls, left‐lateral slip of 5 cm, and spacing of about 100 m in the tension cracks) we estimate that the amount of right‐lateral shift across the Summit Ridge shear zone was on the order of 1.4 m. This is comparable to the amount of slip for coseismic faulting at depth, 1.9 to 2.4 m, as computed by several investigators. Thus contrary to most previous reports on the Loma Prieta earthquake, which assert that coseismic, right‐lateral ground rupture was restricted to considerable (greater than 4 km) depths in the epicentral area, we find that nearly all the right‐lateral offset is represented at the ground surface by the Summit Ridge shear zone.
A simulated Antarctic ast ice ecosystem
Authors: Arrigo Kevin R. , Kremer James N. , Sullivan Cornelius W.
Published: February 2008

A simple two‐dimensional (z,t) model of first year sea ice structure and dynamics is coupled to a high resolution, time‐dependent model of microalgal growth in which simulated physiological responses are determined by ambient temperature, spectral irradiance, nutrient concentration, and salinity. The physical component utilizes atmospheric data to simulate congelation ice growth, initial brine entrapment, desalination, and nutrient flux. Temperature gradient, sea ice salinity, brine salinity, and brine volume are also computed. The biological component is based on the concept of a maximum temperature‐dependent algal growth rate which is reduced by limitations imposed from insufficient light or nutrients, as well as suboptimal salinity. Estimated gross primary productivity is reduced by respiration and grazing terms. Preliminary simulations indicate that, during a bloom, microalgae are able to maintain their vertical position relative to the lower congelation ice margin and are not incorporated into the crystal matrix as the ice sheet thickens. Model results imply that land fast sea ice contains numerous microhabitats that are functionally distinct based upon the unique suite of processes that control microalgal growth and accumulation within each. In the early stages of the spring bloom, high brine salinity inhibits microalgal growth at all depths within the congelation ice, except near the skeletal layer. Light is predicted to be the limiting resource throughout the congelation ice and platelet ice at this time. Later in the bloom when environmental conditions are more favorable for algal growth, model results suggest that biomass accumulation in the upper congelation ice is controlled by microzooplankton grazing, Microalgae in the skeletal layer and upper platelet ice are susceptible to nutrient limitation at this time due to diminished flux and high nutrient demand. Light limits microalgal growth in the lower platelet ice throughout the bloom. Results indicate that land fast sea ice in McMurdo Sound can support a production rate of approximately 0.5 g C m−2d−1under optimal conditions, 76% of which is associated with the platelet layer where rates of nutrient exchange are relatively high. While adjustments in any biological coefficient will alter the magnitude of production in the model, the range of results permitted by uncertainty in their values is well within the bounds likely to result from normal variations in snow cover, or from the uncertainty in the rate of nutrient flux.
Circulation in the Timor Sea
Authors: Cresswell George , Frische Andrea , Peterson Jan , Quadfasel Detlef
Published: February 2008

In October 1987 and March 1988, measurements were taken across the Sahul shelf and the southwestern end of the Timor Strait to the edge of Indonesian waters. The shipboard instrumentation comprised a conductivity‐temperature‐depth (CTD) rosette, an acoustic Doppler current profiler (ADCP) and a Pegasus dropsonde. Complementary data came from satellite‐tracked drifters, continental shelf moorings, and a Nansen bottle survey in 1976. Pegasus and ADCP measurements in the strait suggested a total transport of about 7 Sv toward the Indian Ocean, with about half of this in the upper 350 m. However, transports may at times be higher, because a drifter in July 1983 revealed speeds of l m s−1 in the strait, twice those measured on the surveys. Data from moored current meters implied a transport on the shelf of roughly 1 Sv, except in the autumn transition of the monsoon in 1985 when it exceeded 3 Sv. Water properties measured on the 1987 and 1988 surveys suggested components from the Flores and Banda seas, Indian Ocean Central Water and a high‐salinity subsurface plume from evaporation on the inner Sahul shelf.
Satellite observations of a polar low over the Norwegian Sea by special sensor microwave imager, Geosat, and TIROS‐N operational vertical sounder
Authors: Claud Chantal , Mognard Nelly M. , Katsaros Kristina B. , Chedin Alain , Scott Noelle A.
Published: February 2008

Many polar lows are generated at the boundary between sea ice and the ocean, in regions of large temperature gradients, where in situ observations are rare or nonexistent. Since satellite observations are frequent in high‐latitude regions, they can be used to detect polar lows and track their propagation and evolution. The Special Sensor Microwave/I mager (SSM/I) providing estimates of surface wind speed, integrated cloud liquid water content, water vapor content, and precipitation size ice‐scattering signal over the ocean; the Geosat radar altimeter measuring surface wind speed and significant wave height; and the TIROS‐N Operational Vertical Sounder (TOVS) allowing the determination of temperature and humidity profiles in the atmosphere have been used in synergy for a specific case which occurred in the Norwegian Sea on January, 23–24 1988. All three instruments show sharp atmospheric gradients associated with the propagation of this low across the ocean, which permit the detection of the polar low at a very early stage and tracking it during its development, propagation, and decay. The wind speed gradients are measured with good qualitative agreement between the altimeter and SSM/I. TOVS retrieved fields prior to the formation of the low confirm the presence of an upper level trough, while during the mature phase baroclinicty can be observed in the 1000–500 hPa geopotential thicknesses. Comparisons between satellite‐retrieved products and analyses of the operational Norwegian limited area model (150‐ and 50‐ km mesh) highlight the importance of satellites for the monitoring of such mesoscale phenomena.
Comparison of T‐phase spectra and tsunami amplitudes for tsunamigenic and other earthquakes
Authors: Walker D. A. , Bernard E. N.
Published: February 2008

T‐phase spectral strengths and seismic moments from earlier studies for tsunamigenic and nontsunamigenic earthquakes off Alaska, the Aleutians, northern Honshu, and central Honshu are compared to tsunami height recordings from coastal tide gauges and deep‐ocean pressure recorders. Tsunamigenic earthquakes have larger seismic moments and T‐phase spectral strengths than nontsunamigenic earthquakes. Pacific‐wide tsunamigenic earthquakes had well‐recorded water waves on the deep‐ocean pressure gauges, while water waves for the regional tsunamis could be found only on coastal tide gauges in close proximity to the earthquake epicenters. Thresholds of T‐phase spectral strengths required for tsunamigenesis are estimated for each of the areas investigated. On comparing tsunami heights, seismic moments, and spectral strengths for two Pacific‐wide tsunamis generated by earthquakes with similar source locations, we note that the earthquake with the larger tsunami has the larger T‐phase spectral strength but smaller seismic moment. We conclude that T‐phase spectral strengths may be useful in estimating tsunami energy.
A shell‐derived time history of bomb 14C on Georges Bank and its Labrador Sea implications
Authors: Weidman Christopher R. , Jones Glenn A.
Published: February 2008

Bomb‐produced radiocarbon has been used in the past as an important tracer of ocean circulation and as a valuable tool for calculating CO2 air‐sea exchange. However, previous studies of the ocean's time‐varying bomb 14C record have been confined exclusively to analyzing banded corals, and thus their application has been limited to the lower latitudes. The first time history of bomb 14C from the high‐latitude North Atlantic Ocean is obtained from a 54‐year‐old mollusc specimen, (Bivalvia) Arctica islandica, which was collected live from Georges Bank (41°N) in 1990. The annual growth bands of its shell were analyzed for Δ14C using accelerator mass spectrometry, producing a Δ14C time history from 1939 to 1990. The depleted condition of the Georges Bank bomb 14C signal relative to two coral‐derived North Atlantic Δ14C time histories suggests a significant deepwater source for the waters on Georges Bank. Supported by previous work linking the origin of waters on Georges Bank to the Labrador Sea, the Δ14C budget on Georges Bank is modeled as Labrador Sea water, which largely becomes confined to the shelf and partially equilibrates with the atmosphere during a 1‐year transit time from the Labrador Sea to Georges Bank. This model is also used to estimate a time history of bomb 14C for the Labrador Sea. Prebomb Δ14C values calculated for the surface Labrador Sea suggest that a greater inventory of bomb 14C has accumulated here than has previously been reported. However, the estimated prebomb average Δ14C (−70.6‰) for this period is nearly identical to the −70‰ previously calculated for the prebomb source of North Atlantic Deep Water and is in agreement with Transient Tracers in the Ocean subsurface tritium data from the central Labrador Sea. Deduced variations in the ventilation and/or 14CO2 uptake rates in the Labrador Sea correspond with observed changes in surface salinity of the Labrador Sea, suggesting a reduction in deepwater formation during the late 1960s and 1970s.
A mixed‐layer study of the formation of Levantine intermediate water
Authors: Lascaratos Alex , Williams Richard G. , Tragou Elina
Published: February 2008

A mixed‐layer model is used to investigate the formation of Levantine Intermediate Water (LIW) over the Eastern Mediterranean. The one‐dimensional model is initialized with climatological hydrography and integrated over the Levantine basin with forcing by climatological surface fluxes. Realistic and repeated seasonal mixed‐layer cycles are obtained if the annual surface heat input and water loss are offset by a parameterized horizontal advection. The model integrations show that LIW is formed during winter in the mixed layer of the Northwestern Levantine. The preferred formation region for LIW is found through idealized experiments to be controlled by the preconditioning of the hydrography, especially that of the cold, cyclonic Rhodes gyre, rather than by the pattern of the climatological fluxes. The annual‐mean formation rate of LIW is estimated to be 1.0 Sv using the climatological surface fluxes. The magnitude of the annual surface fluxes alters the formation rate and modifies the formation region. An additional annual heat flux reduces the formation rate of LIW, whereas an extra cooling enhances it, as well as forming waters denser than LIW in the center of the Rhodes gyre.
Summer sea surface temperature variability off Vancouver Island from satellite data
Authors: Fang Wendong , Hsieh William W.
Published: February 2008

Satellite‐sensed advanced very high resolution radiometer (AVHRR) sea surface temperature (SST) data over eight summers (1984–1991) were used to analyze the summer SST patterns of variability off the west coast of Vancouver Island. Empirical orthogonal function (EOF) analysis of the spatial variance for 133 nearly cloud‐free summer images was performed. The first EOF mode, which resembled the mean of all images, showed a strong cool water band located at the northwest corner of Vancouver Island, a cool tongue extending seaward from the Strait of Juan de Fuca and a warm patch off Barkley Sound. The second mode revealed topographically controlled upwelling: cool water over the shelf region with its seaward boundary roughly following the 200‐m depth contour, plus a cold eddy located just north of the Juan de Fuca Canyon. The third mode displayed cool water extending southwestward off Brooks Peninsula, while the fourth mode showed a cool water plume extending off Cape Scott at the northern tip of Vancouver Island. These four modes accounted for 33, 12, 10, and 5% of the SST variance, respectively. The temporal amplitude of these EOF modes revealed how the SST features changed as summer progressed. From these images, we also constructed an overall seasonal coolness index, which revealed the summers of 1986 and 1991 to have the coolest coastal water, with both summers immediately preceding an El Niño.
Sea spray dispersion over the ocean surface: A numerical simulation
Authors: Zhuang Y. , Lozowski E. P. , Wilson J. D. , Bird G.
Published: February 2008

A trajectory simulation approach has been used to calculate sea spray dispersion above the ocean surface as a function of droplet size, emission rate, and meteorological conditions. By numerically simulating the stochastic turbulent trajectories of a large number of ejected sea spray droplets of various sizes and ejection speeds, the vertical profile of sea spray concentration was deduced from the average residence time of the droplets in each of a set of horizontal layers within the first 10 m above the ocean surface.
Optimal estimation of parameters for a two‐dimensional hydrodynamical model of the Arabian Gulf
Authors: Lardner R. W. , Al‐Rabeh A. H. , Gunay N.
Published: February 2008

The parameters of a two‐dimensional numerical tidal model of the Arabian Gulf are estimated by optimal assimilation of data from tide gauges at several of the Saudi Aramco tide stations. The parameters estimated are the bottom drag coefficient and a correction to the bathymetry and are in general allowed to be position dependent. Significant improvements in the predictions of the model are obtained. The method used is based on the minimization of a cost function measuring the difference between the observed and computed water heights at the tide stations, the gradient of the cost function being computed by the adjoint method. The parameter functions are approximated by piecewise constant or piecewise linear approximations, and the cost function is minimized using the quasi‐Newton algorithm CONMIN. It is found in general that in order to obtain stable estimates, it is necessary to include in the cost function a term that penalizes large variations in the parameter functions. Techniques are developed to reduce the storage demands of the algorithm sufficiently to permit the assimilation of 29 days of tidal data.
Mixing processes in Crater Lake, Oregon
Authors: McManus James , Collier Robert W. , Dymond Jack
Published: February 2008

Subsurface hydrothermal activity dominates the heat and salt budgets of the deep water column in Crater Lake, Oregon. From a time series of conductivity‐temperature‐depth data and data from a thermistor chain mooring, we estimate that the net hydrothermal heat flow is ∼1 W m−2 and the corresponding salt flux is ∼5 μg m−2 s−1. This paper discusses the observation of these fluxes and the mechanisms and time scales of mixing responsible for the redistribution of these properties through the water column. Free convection and wind mixing homogenize the upper 200 m of the lake twice annually. Deep‐lake ventilation occurs during early winter and to some extent during late spring. However, since the deep lake does not reach atmospheric saturation with respect to dissolved oxygen at any time during the year, ventilation of the deep water appears to be incomplete. During periods of seasonal stratification, the active input of hydrothermally enriched fluids produces heterogeneities and instabilities in the density structure of the deep lake that may drive deep‐lake mixing. As a result of these and other mixing processes. Crater Lake remains relatively well mixed, despite its great depth.
Ventilation and transport of thermocline and intermediate waters in the northeast Pacific during recent El Niños
Authors: Van Scoy Kim A. , Druffel Ellen R. M.
Published: February 2008

We present time series of tritium (3H) concentrations in seawater from stations in the eastern subpolar (50°N, 145°W) and subtropical (28°N, 122°W) North Pacific. In the eastern subpolar North Pacific the tritium gradient between surface water and North Pacific Intermediate Water is smallest during years that coincide with El Niño events. In the eastern subtropical North Pacific between 200 and 400 m the tritium signature suggests that the water is of subpolar origin during non‐El Niño years. During El Niño years, the water at this location is devoid of tritium. We hypothesize that the El Niño phenomenon alters both the ventilation of thermocline and intermediate waters in the eastern subpolar North Pacific, as well as the transport of this water to the eastern subtropical gyre. Combined with satellite altimeter data, these results offer both a mechanism and a time frame by which subpolar water ventilates the vast reservoir of the subtropical North Pacific.
Estimation of open boundary conditions with the adjoint method
Authors: Seiler U.
Published: February 2008

The adjoint method is used to assimilate observations into a quasi‐geostrophic ocean model for a midlatitude jet. The domain has four open boundaries. Control variables used in this study are the lateral boundary values of stream function and relative vorticity. As a basic step, simulated data are assimilated (“identical‐twin” approach), and the effects of reducing the amount of observations as well as changing their distribution in space and time are investigated. Special attention is paid to the problem of how well the unobserved parts of the model trajectory are resolved. First, data are assimilated as two‐dimensional maps at certain time intervals. Subsequently, continuous assimilation is performed along satellite ground tracks. The solution deteriorates somewhat in the satellite scenario, for which the data set is relatively sparse. However, the model can still be well fitted to the “truth.” It is also shown that the deeper layers are constrained by the upper layer information.
Equatorial variability and resonance in a wind‐driven Indian Ocean model
Authors: Jensen Tommy G.
Published: February 2008

A numerical isopycnal ocean model has been designed and applied to model the Indian Ocean north of 25°S. Vertical normal modes are used in the open boundary conditions and for selections of initial layer depths. A 21‐year integration with a reduced Hellerman‐Rosenstein monthly averaged wind stress has been made with 3.5‐layer and 1.5‐layer versions of the model. Both solutions reproduce the main features of the observed wind‐driven seasonal circulation in the Indian Ocean above the main thermocline. The transient semiannual equatorial surface jets are more intense, more coherent, and in better phase agreement with observations when three layers are active. The associated undercurrents below the main thermocline are also included in the 3.5‐layer model solution. Second baroclinic‐mode, reflecting, equatorial Kelvin and Rossby waves combine to give a semiannual, resonant basin mode. Experiments with an equatorial band of semiannual zonal winds suggest a very strong response of the Indian Ocean to wind forcing with this period. Further, the amplitudes of the 28–30 day oscillations in the western equatorial model region are found to be strongly damped with depth; they have upward phase propagation and downward energy propagation.
Climatology of the East Antarctic ice sheet (100°E to 140°E) derived from automatic weather stations
Authors: Allison Ian , Wendler Gerd , Radok Uwe
Published: February 2008

A decade ago, automatic weather stations (AWS) were placed in remote areas of Antarctica where little or no information on the meteorological conditions was available. These stations report to the ARGOS data collection system onboard polar orbiting satellites of the NOAA series. The Australian National Antarctic Research Expeditions (ANARE) and the United States Antarctic Research Program (USARP) of the National Science Foundation (with logistic support from the French Expéditions Polaires Françaises (EPF)) have built up two AWS data nets in East Antarctica. There are a total of 16 stations in the area 55°–145°E and 65°–75°S, stretching from sea level to above 3000 m altitude. The records of 10 of these stations are sufficiently long to be adequate for a climatological study of the basic parameters of surface temperature, pressure, and wind and have been used in this study. The station data were reduced to a common format and interpreted jointly to describe the broad‐scale climatic features of the ice sheet. Climatological results include (1) an absolute lowest minimum temperature of −84.6°C at Dome C; (2) no minimum below −40°C at D10 near the coast; (3) a “coreless” winter temperature regime, without seasonal temperature trends for 6 months, at all stations; (4) mean surface wind speeds increasing to maxima near, rather than at, the coast; (5) high directional constancy in all seasons, with directions closer to the fall line in winter and during night hours than in summer and during day hours; (7) a distinct semiannual pressure variation with a main minimum in spring (September) and a secondary minimum in autumn (March); and (8) interrelationships among surface temperature, pressure, and wind related to the ice sheet topography.
A two‐dimensional zonally averaged transport model including convective motions and a new strategy for the numerical solution
Authors: Strand Asbjørn , Hov Øystein
Published: February 2008

A two‐dimensional zonally averaged transport model of the atmosphere up to 10 mbar (∼33 km) has been developed. The transport is described by an effective stream function and a diffusion tensor derived from a three‐dimensional general circulation model. The numerical solution of the transport equations has been given special attention, and a positive definite mass conservative advection scheme which produces small numerical diffusion has been modified for use in the model. In addition to the vertical transport described by the transport equations, a parameterization of the vertical mixing due to convective clouds and frontal circulation is included in the model. The model has been tested with different tracers which indicated a realistic representation of the atmospheric transport.
The quasi‐two‐day wave observed in the equatorial middle atmosphere
Authors: Harris T. J. , Vincent R. A.
Published: February 2008

An oscillation with a period near 2 days is found in radar wind measurements made in the upper mesosphere and lower thermosphere at Christmas Island (2°N, 157° W) in the central Pacific. The oscillation is particularly strong in the meridional wind component, and seems to be present almost continuously ir the 80–100 km height region, although some intermittency is evident. Wave amplitudes are especially large about one month after the solstices, in July/August and in January/February, at times coincident with large 2‐day wave events in the summer mesosphere at extratropical latitudes. Power spectral and complex demodulation techniques are used to study the amplitude and frequency variations of the oscillation as a function of height and time. Downward phase propagation is found, consistent with upward energy propagation, and with a vertical wavelength of about 70 km. An unusual feature is a shift in wave period from near 50 hours in July/August to 48 hours in January/February, when the largest amplitudes (up to 45 m s−1 ) are observed. A 16‐hour oscillation is also found at times when the 2‐day wave amplitudes are largest. The observations are consistent with the 2‐day wave being a manifestation of the (3, 0) Rossby‐gravity normal mode. Another, weaker oscillation, is also found in the meridional wind field at a period near 44 hours. This oscillation may be due to the (2, 0) normal mode.
Effect of saltation bombardment on the entrainment of dust by wind
Authors: Shao Y. , Raupach M. R. , Findlater P. A.
Published: February 2008

Saltation is the wind‐driven, hopping motion of sand‐sized particles across an erodible surface. This mode of motion not only transports sand and similar materials in its own right but can also initiate (through bombardment of the surface) the entrainment and subsequent transport by suspension of smaller dust particles. In this paper, we report a wind tunnel study of the effect of saltation bombardment on dust entrainment. The technique is to allow sand grains to saltate from an upwind sand source onto a bed of dust particles. The experiment confirms that the ejection of dust particles by saltation bombardment (as opposed to detachment of dust particles by aerodynamic forces) is the principal mechanism for the natural entrainment of dust by wind. The data are used to examine the dependence of the dust emission flux Fd (mass per unit ground area per unit time) upon the friction velocity u*; it is found that Fd is closely proportional to the streamwise flux of saltating sand grains, which in turn is approximately proportional to u*3 At a given u*, Fd increases as the size of the bombarding sand grains increases. On the basis of the hypothesis that Fd is proportional to the kinetic energy flux of the saltating sand grains, we derive theoretically the result that Fd scales with the streamwise saltating sand grain flux and thence approximately with u*3, as observed in this experiment.
Increased transmission of ultraviolet radiation to the surface due to stratospheric scattering
Authors: Davies Roger
Published: February 2008

The relative enhancement of ultraviolet radiation reaching the surface due to scattering by stratospheric aerosols is shown to be consistent with single‐scattering theory, rather than the photon‐trapping effect described by some recent studies. The enhancement is greatest for large solar zenith angles when there is a significant absorbing layer below the stratospheric aerosol. Under appropriate conditions of ozone depletion and the presence of volcanic aerosol this enhancement makes it possible for the UV flux reaching the surface at high southern latitudes to exceed the peak flux at the equator, but only for wavelengths shorter than about 290 nm.
Third Soviet‐American Gases and Aerosols (SAGA 3) experiment: Overview and meteorological and oceanographic conditions
Authors: Johnson J. E. , Koropalov V. M. , Pickering K. E. , Thompson A. M. , Bond N. , Elkins J. W.
Published: February 2008

The primary goal of the third joint Soviet‐American Gases and Aerosols (SAGA 3) experiment was to study trace gases and aerosols in the remote marine boundary layer. SAGA 3/leg 1 took place from February 13 to March 13, 1990, aboard the former Soviet R/V Akademik Korolev and consisted of five equatorial transects (designated transects 1 through 5) between 15°N and 10°S on a cruise track from Hilo, Hawaii, to Pago‐Pago, American Samoa. Specific objectives were to study (1) the oceanic distribution and air‐sea exchange of biogenic trace gases; (2) photochemical cycles of C‐, S‐, and N‐containing gases in the marine boundary layer; (3) the distribution of aerosol particles in the marine boundary layer and their physical and chemical properties; (4) interhemispheric gradients and latitudinal mixing of trace gases and aerosols; and (5) stratospheric aerosol layers. SAGA 3/leg 2 continued from March 17 to April 7, 1990, with one more equatorial transect between American Samoa and the northern coast of the Philippines (transect 6) followed by a final transect to Singapore (transect 7). During leg 2, most former Soviet measurements continued, but with the exception of measurements of nitrous oxide (N2O) and selected halocarbons in the air and surface waters all American measurements ceased. This paper briefly summarizes the chemical measurements made by SAGA 3 investigators and presents in some detail the meteorological and hydrological characteristics encountered during SAGA 3. The meteorological analysis is based on atmospheric soundings of temperature, humidity, winds, sea surface temperature, postcruise back trajectories of winds, and satellite imagery. In general, the meteorology during SAGA 3 was typical of the location and time of year. Exceptions to this include an incipient El Niño that never developed fully, a poorly defined ITCZ on 4 of 6 equator crossings, wind speeds that were 20% greater than the decadal mean, a convective event that brought midtropospheric air to the surface (on Julian day 59), and transport of northern hemispheric air to 18°S during a synoptic scale tropical disturbance.
Spatial and temporal variability of heat, water vapor, carbon dioxide, and momentum air‐sea exchange in a coastal environment
Authors: Crawford Timothy L. , McMillen Robert T. , Meyers Tilden P. , Hicks Bruce B.
Published: February 2008

The spatial and temporal variability of heat, moisture, momentum, and CO2 turbulent fluxes in a coastal environment were assessed using simultaneous eddy correlation measurements from a tower, a boat, and an aircraft platform. The flux measurements were made using new instrument systems, including new CO2 and H2O sensors, low‐flow distortion packages, and careful sensor motion correction systems. The flux tower was operated on the windward beach of Florida's Bahia Honda Key, while the boat was stationed upwind between 1 and 15 km offshore. The airplane flew transects 10 to 20 m above the ocean surface, along flight paths extending from the tower to 40 km offshore. Dissolved CO2 in the coastal waters and atmospheric CO2 concentrations were continuously measured throughout the experiment. The results indicate good agreement among the different sensing systems and demonstrate that air‐to‐sea trace gas, momentum, and energy flux density measurements are achievable from both a boat and an aircraft. Further, the observations emphasize the complex temporal and spatial trends possible in a coastal region. Due to the nonequilibrated boundary layer, generated by spatial trends, nearshore measurements are not representative of either the entire coastal region or of the open ocean. The observed 10 W m−2 sensible heat flux was time‐invariant but did vary spatially with surface temperature, which was strongly correlated with ocean depth. The 100 to 200 W m−2 evaporative moisture flux dominated energy exchange and varied both in space and in time. No consistent diurnal variation was observed, but the spatial trend also followed surface temperature. As expected, momentum flux scaled with wind speed. CO2 exchange showed large spatial and temporal variance. Spatially, the surface temperature warmed as the shore was approached and CO2 was apparently driven off. Temporally, CO2 exchange varied greatly, as did ΔpCO2 which ranged from +50 to −100 ppm. This large variability in ΔpCO2 is thought to illustrate the importance of biological and physical processes and to explain the large CO2 fluxes observed (not always in the same direction) in this and other flux studies in nearshore conditions. Ten kilometers from shore, where the spatial and temporal variability was less, CO2 transfer velocities were of the order of 0.1 cm s−1.
Application of a space‐time stochastic model for daily precipitation using atmospheric circulation patterns
Authors: Bogardi Istvan , Matyasovszky Istvan , Bardossy Andras , Duckstein Lucien
Published: February 2008

Space‐time series of daily precipitation amount conditioned on daily circulation pattern (CP) types are calculated. A stochastic hydroclimatological model is used to define daily precipitation under the climate of eastern Nebraska. Principal component analysis and k means method result in nine CP types in west central United States on the basis of 40 years of data. Both the probability and the amount of daily precipitation are strongly related to CP types. The approach can be used to predict the regional or local hydrological effect of climate change.
Alkyl nitrates, nonmethane hydrocarbons, and halocarbon gases over the equatorial Pacific Ocean during SAGA 3
Authors: Atlas E. , Pollock W. , Greenberg J. , Heidt L. , Thompson A. M.
Published: February 2008

The third joint Soviet‐American Gases and Aerosols (SAGA 3) experiment was a research cruise conducted aboard the Akademik Korolev in February and March 1990. The cruise covered a region of the equatorial Pacific Ocean from 15°N to 10°S latitude and 144° to 165°W longitude. On this cruise we collected samples for the measurement of alkyl nitrates (RONO2), nonmethane hydrocarbons (NMHC) and several halocarbon gases. Though there are few data available for comparison in this region of the marine boundary layer, the mixing ratios of the trace gases we measured are within the range of prior measurements in the remote atmosphere. Latitudinal gradients were found for trace gases with predominantly anthropogenic sources, e.g., methylene chloride, tetrachloroethylene, and acetylene; higher concentrations in the North Pacific atmosphere decreased slowly across the Equator to the South Pacific. More stable gases, e.g. methyl chloride and methyl bromide, had no pronounced variation across the equator. A biogenic source of two organobromine compounds, bromoform and dibromochloromethane, was indicated by maximum mixing ratios of these species over the equator where indicators of biological productivity (e.g., chlorophyll) in the surface ocean water also maximized. Alkyl nitrates were found at levels higher than predicted from steady state calculations based on measured mixing ratios of hydrocarbons and NO. The measured levels of RONO2 suggest long‐range transport as one mechanism contributing to elevated concentrations of alkyl nitrates in the remote troposphere. However, the distributions of C2 and C3 alkyl nitrates over the equator were similar to the organobromine gases. This distribution suggests a possible oceanic source for alkyl nitrates to the atmosphere.
Studies of the Kuwait oil fire plume during midsummer 1991
Authors: Daum P. H. , Al‐Sunaid A. , Busness K. M. , Hales J. M. , Mazurek M.
Published: February 2008

This paper reports aircraft observations of the Kuwait oil fire plume conducted during the period July 31‐August 17, 1991. During this study the plume was transported almost exclusively to the south of Kuwait over the Persian Gulf and the Arabian Peninsula. The plume base was generally found to be well above the surface, in some cases as high as 1–2 km; plume tops did not exceed 5 km. Aerosol mass (based on measured aerosol constituents) in the central section of the plume, ca. 150–200 km downwind of the source region, was found to be >500 μg/m3, with number densities in the size range (approximate) 0.2 < d < 3 μm (where d is diameter) as high as 30,000/cm3. The aerosol was composed of (in order of approximate contribution to mass) inorganic salts, elemental carbon, and organic carbon. Sodium chloride constituted a surprisingly large component of the soluble inorganic mass. The aerosol particles appeared to function as good cloud condensation nuclei, with a large fraction of accumulation mode particles (by number) activated at a supersaturation of 0.6%. Under conditions in which the plume was relatively compact, transmittance of solar radiation to the surface was only 10–20%. Plume albedo was observed to be as low as 2–3% close to the source region, consistent with the high elemental‐carbon concentrations present in the plume. Trace gas concentrations were consistent with fuel composition and with current knowledge of atmospheric chemical processes. Sulfur dioxide concentrations close to the source region were found to be as high as 300–400 ppb. The emissions factor for S (expressed as a percentage) was estimated to be 1.8%, which is consistent with estimates of a fuel sulfur content of 2–2.5%. SO2 was found to be only slowly oxidized (<1%/h). Nitrogen oxide concentrations were found to be quite low (<50 ppb near the source, decreasing to 1–2 ppb well downwind), which is consistent with a crude oil nitrogen source. Despite relatively low concentrations, sufficient NOx was present to act as a catalyst to generate excess ozone in the plume as the plume was transported downwind and dispersed.
Effect of anthropogenic sulfate aerosols on low‐level cloud albedo over oceans
Authors: Kim Yongseung , Cess Robert D.
Published: February 2008

By reducing cloud droplet size, anthropogenic sulfate aerosols are capable of increasing cloud albedo and thus possibly changing the climate. To test the detectability of this effect, we examined satellite‐measured low‐level cloud albedo off the east coasts of North America and Asia at mid‐latitudes where anthropogenic sulfate sources are large and aerosols are transported eastward over the oceans by prevailing westerlies. The satellite data demonstrate enhanced cloud albedo near the coastal boundaries where sulfate concentrations are large. Similar trends are absent over ocean regions of the southern hemisphere that are removed from anthropogenic sulfate sources.