bluuebunny/crossref_metadata_2025 huggingface dataset:
Structure and dynamics of sporadic layers of ionization in the ionospheric E region
Authors: Kagan L. M. , Bakhmet'eva N. V. , Belikovich V. V. , Tolmacheva A. V. , Kelley M. C.
Published: October 2003

Layers of ionization that appear in the ionospheric E region sporadically in time have been named sporadic‐E layers, or Es. These sporadic ionization layers play a crucial role in small‐scale irregularity generation (as they guarantee a plasma density gradient necessary for gradient‐drift processes to develop) and in providing reliability of radio communication and navigation. Despite the fact that Es layers have been studied since the late sixties, a method to visualize the Es horizontal structure was suggested for the first time only recently [Kagan et al., 2000]. In the present paper we propose a new type of experiment for the reconstruction of the patchy‐type Es structure and dynamics using a combination of the above‐mentioned method with the method of artificial periodic irregularities (API) [Belikovich et al., 1999]. This combined method allows us for the first time to carry out Es tomography, to trace the three‐dimensional (3‐D) dynamics of sporadic ionization clouds and their associated 3‐D neutral motions, and to study the effects of high‐frequency radio waves on the sporadic‐E layers. The procedure includes recording of the Es horizontal structure and dynamics with an all‐sky camera via radio‐wave‐induced optical emissions in combination with measurements of the Es vertical structure and dynamics by the API method. Both methods complement each other and can be used simultaneously. The experiment is to be equipped with a powerful HF radio wave transmitter, all‐sky cameras, an ionosonde, and an HF digital receiver.
An accelerated boundary integral equation scheme for propagation over the ocean surface
Authors: Awadallah Ra'id S. , Lamar Michael T. , Kuttler James R.
Published: October 2003

In two recent papers, C. L. Rino, H. Ngo and V. Kruger (RNK) proposed a novel scheme for tropospheric propagation over one‐dimensional (1D) terrain or ocean surfaces. This scheme is based on a boundary integral equation (BIE) formalism, the iterative solution of which is carried out efficiently via the method of ordered multiple interactions (MOMI). An important merit of the RNK scheme is the fact that, being a BIE‐based model, it rigorously accounts for the effect of the multiple‐scale ocean surface roughness on the propagated field. In their most recent paper, C. L. Rino and V. Kruger suggested that the accelerated version of MOMI proposed by H.‐T. Chou and J. T. Johnson (MOMI/CJ) could substantially enhance the efficiency of their scheme. Motivated by this suggestion, this paper proposes a combined RNK/CJ algorithm for propagation over finitely conducting (FC) ocean surfaces. While maintaining its accuracy, the proposed scheme enhances the computational efficiency of the rigorous RNK model by reducing the number of mathematical operations needed in the iterative solution of the governing BIE.
Foreland basin magmatism in the Western Moroccan Meseta and geodynamic inferences
Authors: Roddaz Martin , Brusset Stéphane , Soula Jean‐Claude , Béziat Didier , Ben Abbou Mohamed , Debat Pierre , Driouch Youssef , Christophoul Frédéric , Ntarmouchant Ahmed , Déramond Joachim
Published: October 2003

Basaltic magmatism occurs in the Hercynian foreland basin of the Western Moroccan Meseta as pillow lavas flows interbedded with “flysch” deposits and sills of dolerite and gabbro. A sedimentological and tectonic study shows that the deposition of the flysch, and thus the intrusion of the lava flows and sills, was controlled by the northwestward propagation of thrust‐related folds in the wedge‐top depozone of a syncontractional foreland basin system. The pillow lavas appear as either massive sheets of stacked lava flows or thin lava flows interlayered with the syntectonic turbiditic deposits. The sills are composed of several mafic units (up to six in the most evolved Marziqallal sill) cut through by granophyric veins, which can be interpreted as a result of in situ crystallization. The pillows lava basalts and the dolerites/gabbros are calc‐alkaline and cogenetic. A discussion of the possible mechanisms of magma production in subduction related orogens leads us to conclude that this foreland basin magmatism was generated in a retrolithospheric setting. A comparison with the other Early Carboniferous volcanic and plutonic rocks of the Western and Eastern Mesetas shows that calc‐alkaline foreland basin magmatism was widespread in the entire Mesetan domain and was probably a result of wet melting of the metasomatised mantle lithosphere of the overriding plate. Because the Moroccan Hercynides are likely to have been a result of continental subduction and the magmatism is observed at a distance of more than 500 km from the suture, it is suggested that the retroforeland basin magmatism was a result of either dehydration of a shallow dipping (∼15°) foregoing oceanic slab, or underplating of the continental lithosphere ending with slab breakoff beneath the foreland basin.
New paleomagnetic constraints on central Asian kinematics: Displacement along the Altyn Tagh fault and rotation of the Qaidam Basin
Authors: Chen Yan , Gilder Stuart , Halim Nadir , Cogné Jean Pascal , Courtillot Vincent
Published: October 2003

In order to better understand the tectonic evolution of central Asia under the influence of the India‐Asia collision, we carried out a paleomagnetic study of 1500 cores from 106 sites along the Altyn Tagh fault, in the Qaidam and Tarim basins, and on the Tibetan plateau. Samples were mainly collected from Jurassic to Neogene siltstones and sandstones. In most cases stepwise thermal demagnetization unblocks low and high temperature components carried by magnetite and hematite. Low temperature components are north and down directed and lie close to the recent geomagnetic field. High temperature components from 10 of 13 age/locality groups pass fold and/or reversal tests and likely represent primary remanent magnetizations. The ten overall mean directions display a complex pattern of vertical‐axis block rotations that are compatible with a tectonic model of clockwise rotation of the Qaidam Basin and concomitant left‐lateral slip on the Altyn Tagh fault. Two of the ten localities are rotated significantly counterclockwise; they lie adjacent to the Altyn Tagh fault zone, consistent with the idea that left‐lateral strike‐slip motion occurred along it. The age of counterclockwise rotation near the eastern extremity of the fault was dated as younger than 19 Ma. Three widely spread areas within the Qaidam Basin exhibit similar and significant clockwise rotations, on the order of 20°, with respect to the North China Block, Tarim and Eurasia. The mean of the three values is thought to represent the total rotation of Qaidam. Because the youngest rocks displaying clockwise rotations are Oligocene, the main phase of Qaidam Basin rotation, and hence shear on the Altyn Tagh fault, took place after or near the end of the Oligocene (∼24 Ma). Upper Neogene strata located on the Qaidam Basin are not significantly rotated, thus tectonic deformation acting since the Upper Neogene (∼5 Ma) is not resolvable by paleomagnetic methods. Given a 20° ± 5° clockwise rotation of the Qaidam Basin with respect to the Tarim Basin, the maximum left‐lateral displacement on the Altyn Tagh fault since 24 Ma is 500 ± 130 km.
Computational Bayesian maximum entropy solution of a stochastic advection‐reaction equation in the light of site‐specific information
Authors: Kolovos Alexander , Christakos George , Serre Marc L. , Miller Cass T.
Published: October 2003

This work presents a computational formulation of the Bayesian maximum entropy (BME) approach to solve a stochastic partial differential equation (PDE) representing the advection‐reaction process across space and time. The solution approach provided by BME has some important features that distinguish it from most standard stochastic PDE techniques. In addition to the physical law, the BME solution can assimilate other sources of general and site‐specific knowledge, including multiple‐point nonlinear space/time statistics, hard measurements, and various forms of uncertain (soft) information. There is no need to explicitly solve the moment equations of the advection‐reaction law since BME allows the information contained in them to consolidate within the general knowledge base at the structural (prior) stage of the analysis. No restrictions are posed on the shape of the underlying probability distributions or the space/time pattern of the contaminant process. Solutions of nonlinear systems of equations are obtained in four space/time dimensions and efficient computational schemes are introduced to cope with complexity. The BME solution at the prior stage is in excellent agreement with the exact analytical solution obtained in a controlled environment for comparison purposes. The prior solution is further improved at the integration (posterior) BME stage by assimilating uncertain information at the data points as well as at the solution grid nodes themselves, thus leading to the final solution of the advection‐reaction law in the form of the probability distribution of possible concentration values at each space/time grid node. This is the most complete way of describing a stochastic solution and provides considerable flexibility concerning the choice of the concentration realization that is more representative of the physical situation. Numerical experiments demonstrated a high solution accuracy of the computational BME approach. The BME approach can benefit from the use of parallel processing (the relevant systems of equations can be processed simultaneously at each grid node and multiple integrals calculations can be accelerated significantly, etc.).
Observed regional and climatological associations between spring and summer precipitation over northern central Eurasia
Authors: Ye Hengchun
Published: October 2003

Regional patterns of association between spring and summer precipitation over northern central Eurasia are examined based on 60 years (1936–1995) of station precipitation records. Rotated principal component analysis and correlation analysis are performed to reveal regional teleconnections. This study found that summer precipitation is positively correlated with spring precipitation over areas east of the Caspian Sea and west of China. Summer precipitation over and west of the northern Ural Mountains is positively correlated, while summer precipitation over central Siberia is negatively correlated to spring precipitation over northern European Russia. Persistent summer wind anomalies in the middle and lower troposphere are found to be associated with spring precipitation conditions and thus may be responsible for the observed summer precipitation anomalies. Also, orographic lifting may be another contributor to enhanced local moisture recycling in the identified areas. Knowledge of regional patterns of association between summer and spring precipitation will help us to better predict summer precipitation anomalies, especially regarding the possible persistence of droughts.
On the role of heat fluxes in the uptake of anthropogenic carbon in the North Atlantic
Authors: Völker Christoph , Wallace Douglas W. R. , Wolf‐Gladrow Dieter A.
Published: October 2003

The influence of the overturning circulation on the anthropogenic carbon sink in the North Atlantic is investigated with a simple box model. The net air‐sea flux of anthropogenic carbon in the North Atlantic is the result of two opposing fluxes: The first is the uptake caused by the disequilibrium between the rapidly rising atmospheric pCO2 and the dissolved carbon content in the ocean, depending mainly on the water exchange rate between mixed layer and interior North Atlantic ocean. Superimposed is a second flux, related to the northward transport of heat within the Atlantic basin, that is directed out of the ocean, contrary to conventional wisdom. It is caused by a latitudinal gradient in the ratio of seawater alkalinity to total dissolved inorganic carbon that in turn is related to the cooling and freshening of surface water on its way north. This flux depends strongly on the vertical structure of the upper branch of the overturning circulation and on the distribution of undersaturation and supersaturation of CO2 in Atlantic surface waters. A data‐based estimate of anthropogenic carbon inventory in the North Atlantic is consistent with a dominance of the disequilibrium flux over the heat‐flux‐related outgassing at the present time, but, in our model, does not place a strong constraint on the net anthropogenic air‐sea flux. Stabilization of the atmospheric pCO2 on a higher level will change the relative role of the two opposing fluxes, making the North Atlantic a source of anthropogenic carbon to the atmosphere. We discuss implications for the interpretation of numerical carbon cycle models.
Quantitative bedrock geology of the conterminous United States of America
Authors: Peucker‐Ehrenbrink Bernhard , Miller Mark W.
Published: October 2003

We quantitatively analyze the area‐age distribution of bedrock based on data from the most recent geologic map of the conterminous United States of America [King and Beikman, 1974a, 1974b], made available in digital form by the United States Geologic Survey. The area‐age distribution agrees surprisingly well with older data [Higgs, 1949] but provides much higher temporal resolution. The mean stratigraphic age of all sedimentary bedrock is ∼134 Myr; that of Tertiary‐Cambrian sediments is ∼104 Myr. The analysis also reveals area coverage of some minor lithologies, such as ultramafic rocks that cover ∼0.15% of the conterminous United States. Area coverage of 162 lithostratigraphic units is made available as an Excel data sheet.
Deliquescence behavior of organic/ammonium sulfate aerosol
Authors: Brooks Sarah D. , Wise Matthew E. , Cushing Melinda , Tolbert Margaret A.
Published: October 2003

Recent studies have shown that tropospheric aerosols composed of internal mixtures of organics with sulfates are quite common with the organic composing up to 50% of the particle mass. The influences of the organics on the chemical and physical properties of the aerosol are not known. In this paper, we report the solubility of a series of dicarboxylic acids in saturated ammonium sulfate solution as a function of temperature. We also report the deliquescence relative humidity (DRH) of the pure dicarboxylic acids and of mixtures of dicarboxylic acids with ammonium sulfate. For the systems studied, we find that the presence of water‐soluble dicarboxylic acids caused deliquescence to occur at a lower relative humidity (RH) than pure ammonium sulfate. In contrast, the less soluble dicarboxylic acids had no measurable effect on the deliquescence relative humidity of ammonium sulfate.
Types of elastic nonlinearity of sedimentary soils
Authors: Pavlenko Olga V. , Irikura Kojiro
Published: October 2003

Vertical array records of the 1995 Kobe earthquake showed clearly nonlinearity of soil behavior. Although there have been few observational validations, earlier scientific publications on soil nonlinearity appeared since 1970's. In theoretical studies, nonlinearity has been introduced in constitutive relations as the quadratic correction to Hooke's law, but the question of the types of soil nonlinearity was not investigated. Here we show, on the basis of data processing and nonlinear system identification technique, that sediments represent physical systems possessing mostly odd types of nonlinearity. Even‐order nonlinearities become comparable with odd‐order ones only in special cases, like liquefied soils. Though the even and odd nonlinearities have much in common, the frequencies of combination harmonics, shapes of seismic solitary waves, and other nonlinear phenomena are different in these two cases. On the whole, the nonlinearity in soils leads to changes in spectra of propagating seismic signals: the spectra tending to take the form of E(f)∼f–n.
Seismicity and crustal structure related to the Miyake‐jima volcanic activity in 2000
Authors: Nishizawa A. , Ono T. , Otani Y.
Published: October 2003

The largest earthquake swarm ever recorded in Japan began off the islands of Miyake‐jima, Kozu‐shima and Nii‐jima, and was linked to volcanic activity on Miyake‐jima, at the northern end of the volcanic front of the Izu‐Ogasawara (Bonin) arc. Ocean bottom seismographic observations made directly above the swarm region gave clear indication of a magmatic intrusion. The hypocenter distribution shows a vertical sheet, 2 km wide and at a depth of 12–20 km, that broadens markedly at depths up to 12 km. The P wavespeed structure obtained from a seismic refraction survey shows no significant difference in the characteristics of the shallow crust between the strong swarm region and inactive region. However, a low wavespeed region was detected 10–15 km northwest of Miyake‐jima.
Estimates of vertical crustal motion derived from differences of TOPEX/POSEIDON and tide gauge sea level measurements
Authors: Nerem R. S. , Mitchum G. T.
Published: October 2003

We have computed estimates of the rate of vertical crustal motion from differences of sea level measurements made by the TOPEX/POSEIDON radar altimeter and a globally distributed network of 114 tide gauges. A rigorous error analysis was performed which suggests the accuracy of the estimated vertical rates is approximately 1–2 mm/year for roughly half of the tide gauges, which is sufficiently accurate to detect a variety of geophysical phenomena. While only a cursory analysis of the estimated crustal motion rates was performed, we observed many interesting phenomena including significant uplift at volcanic islands in the Pacific and uplift of 7–9 mm/year along the southwest coast of Alaska. The results reported here will be useful in a variety of geophysical studies, as well as for validation of similar estimates of vertical crustal motion provided by precise geodetic techniques such as SLR, DORIS, GPS, and VLBI.
Observation of dust and anthropogenic aerosol plumes in the Northwest Pacific with a two‐wavelength polarization lidar on board the research vessel Mirai
Authors: Sugimoto Nobuo , Matsui Ichiro , Shimizu Atsushi , Uno Itsushi , Asai Kazuhiro , Endoh Tatsuo , Nakajima Teruyuki
Published: October 2003

Dust and anthropogenic aerosol plumes from the Asian continent were observed in the Northwest Pacific (32.0° to 38.0°N, 146.5°E) with a two‐wavelength polarization lidar on board the research vessel Mirai during the MR01‐K02 cruise (May 14 to 28, 2001). Dust aerosols were identified from the aerosol depolarization ratio at 532 nm and the ratio of the backscattering coefficient at 1064 nm and 532 nm. High aerosol density air masses with a low depolarization ratio and a small wavelength ratio (indicating small particle size) were also detected in the plume. The distribution patterns of the dust and the spherical aerosols were conceptionally explained by the model prediction for dust and sulfate with the Chemical Weather Forecast System (CFORS). Aerosols with large particle size but with low depolarization ratio were also observed in between the layers of dust and sulfate. This indicates that the aerosols were possibly an internal mixture of dust and sulfate.
Simultaneous observation of the vertical gradients of refractivity in the atmosphere and electron density in the lower ionosphere by radio occultation amplitude method
Authors: Liou Y. A. , Pavelyev A. G. , Huang C. Y. , Igarashi K. , Hocke K.
Published: October 2003

It is shown that the refractivity and temperature vertical gradients may be retrieved using radio occultation (RO) amplitude data only. For the considered RO events the vertical gradient of refractivity found from the amplitude data shows good correspondence at two frequencies and changes in interval ±2–±5 N‐units/km (between heights 5–10 km) up to ±1–±2 N‐units/km (between heights 12–21 km). The corresponding magnitudes of temperature gradient change from negative values 4– 9°K/km at the height 8–14 km to positive 1–3 °K/km above 20.5 km. Sharp changes of temperature gradient ±6–±9 °K/km are found in the tropopause at the heights between 14–20 km. The height of the equatorial tropopause is found to be equal 16.8 km in correspondence with UCAR data. The vertical gradient of electron density in the sporadic E‐layer of the ionosphere has been retrieved from the same RO event. Two maximum values of the positive gradient of about 29·109 and 28·109 [m−3km−1] are located at heights 93.5 and 99 km. Simultaneous observations of the vertical gradients of refractivity in the atmosphere and ionosphere would be useful to investigate connections between meteorological and space weather phenomena.
Interannual variability in methane growth rate simulated with a coupled Ocean‐Atmosphere‐Chemistry model
Authors: Johnson C. E. , Stevenson D. S. , Collins W. J. , Derwent R. G.
Published: October 2003

We assess the contribution made to the interannual variability of the global methane accumulation rate from its atmospheric sink using the STOCHEM tropospheric chemistry model coupled to the HadCM3 climate model. For both control and climate change scenarios, the standard deviation of the detrended accumulation rate was 1.4 ppbv/yr for the period 1990–2009, compared with the measured standard deviation of 3.1 ppbv/yr for the period 1984–1999. As the model emissions have no variability, the methane sink processes in the model are responsible for all the simulated variability of the methane accumulation rate. This appears to explain a significant fraction of the observed variability and was well correlated with simulated water vapour. The largest component of the model interannual variability is derived from the El‐Niño Southern Oscillation cycle in the coupled Ocean‐Atmosphere model, and this mode of variation is shown to be present in the methane accumulation rate.
Satellite retrieval of aerosol absorption over the oceans using sunglint
Authors: Kaufman Y. J. , Martins J. V. , Remer L. A. , Schoeberl M. R. , Yamasoe M. A.
Published: October 2003

Aerosol absorption of sunlight, in particular by black carbon ‐ soot and dark organic material produced from incomplete combustion of fossil fuel and from vegetation fires, is emerging as a key component of climate forcing. However, global characterization of black carbon emissions, distribution and absorption of sunlight cannot be determined within a factor of 5. Here we propose that the oceanic sunglint can be used as a bright background against which aerosol absorption can be measured from space. The method can map global ocean glint every 4–10 days and determine the distribution of aerosol absorption optical thickness with an error of ±25% for aerosol optical thickness of 0.2 to 0.4. 18 % of the ocean observations are for this range of optical thicknesses. The monthly average aerosol absorption is estimated to have an error of ±12% and uncertainty in the single scattering albedo of ±0.02. We outline a satellite design to perform the measurements.
Up‐gully flow in the great plains region: A mechanism for perturbing the nighttime lower atmosphere?
Authors: Balsley B. , Fritts D. , Frehlich R. , Jones R. M. , Vadas S. , Coulter R.
Published: October 2003

Studies using data gathered during CASES‐99 show that when the near‐surface nighttime wind direction shifts through the “up‐gully” direction of a significant gully near the tower, the flow produces a pronounced but localized upward surge of vertical velocity up to at least 55 m. This surge generates an outward propagating wave packet having horizontal and vertical wavelengths on the order of 100–250 m with tilted wave fronts consistent with upward phase propagation. The wave packet is observable (with significant delays) by other sensors out to 850 m. As a working hypothesis we assume that the up‐gully flow is constricted and strengthened as it progresses up the narrowing gully. We theorize that, upon exiting the gully, the flow has a pronounced and tightly confined vertical component that in turn produces a packet of internal propagating gravity waves.
Lidar backscatter to extinction, mass and area conversions for stratospheric aerosols based on midlatitude balloonborne size distribution measurements
Authors: Jäger Horst , Deshler Terry
Published: October 2003

Size distributions of the stratospheric sulfuric acid aerosol derived from balloonborne particle counter measurements from Laramie, Wyoming, are used to calculate ratios of particle extinction, mass, and surface area to particle backscatter, and the wavelength dependences of particle backscatter and extinction. These ratios may then be used to infer particle extinction, mass, and area from midlatitude lidar data in the spectral range 355 nm to 1064 nm for the time period 1991 to 1999. The conversions are defined in four height intervals from the tropopause to 30 km with a time resolution of four months. Results of conversions from earlier studies are included to span the time period 1979 to 1999. The eruptions of El Chichón (1982) and Pinatubo (1991) strongly influence these conversions. Extended background levels are observed prior to El Chichón and since about 1997.
Complex images of Moho and variation of Vp/Vs across the Himalaya and South Tibet, from a joint receiver‐function and wide‐angle‐reflection approach
Authors: Galvé A. , Sapin M. , Hirn A. , Diaz J. , Lépine J.‐C. , Laigle M. , Gallart J. , Jiang M.
Published: October 2003

Teleseismic receiver functions (RF) allow us to image the spatial variation of the crust‐mantle boundary (Moho) along a tight array spanning from south of the Himalayas to the centre of the Tibetan Plateau. This approach is cross‐tested with wide‐angle reflection imaging (WARR). Highlighted by each of the two independent methods, a complex architecture of the Moho with dipping and overlapping segments indicating lithospheric imbrication, is confirmed. The joint use of the two methods reveals an increase of the average crustal P‐to‐S‐wave‐velocity ratio from south to the centre of the Lhasa block. This may be due to lowered S‐wave velocity confined in specific layers, that may be interpreted as partial melt. This accounts for half of the relative increase in the delay of direct teleseismic S‐wave arrivals with respect to P‐wave arrivals from south to north, suggesting a similar anomaly in the shallower mantle.
Lost sunspot cycle in the beginning of Dalton minimum: New evidence and consequences
Authors: Usoskin I. G. , Mursula K. , Kovaltsov G. A.
Published: October 2003

We have recently suggested that one solar cycle was lost in the beginning of the Dalton minimum during 1790s [Usoskin et al., 2001]. Earlier, this cycle has been combined with the preceding activity to form the exceptionally long solar cycle 4 in 1784‐1799 with an irregular phase evolution. Here we show that historical data of auroral occurrence provide independent evidence for the existence of the new cycle. Using a heliospheric model we demonstrate that 10Be or any other cosmogenic isotope data do not exclude the possibility of a new cycle. We also discuss the other implications of the new cycle for solar activity, in particular the cycle length distribution and the Waldmeier relation between the cycle amplitude and the length of the ascending and descending phase. Including the new cycle also restores the Gnevyshev‐Ohl rule of cycle pairing and removes the phase catastrophe in the beginning of the Dalton minimum.
Effects of clouds on erythemal and total irradiance as derived from data of the Argentine Network
Authors: Cede Alexander , Blumthaler Mario , Luccini Eduardo , Piacentini Rubén D. , Nuñez Liliana
Published: October 2003

Ultraviolet (UV) erythemal and total (300–3000 nm) irradiance measurements of the Argentine Servicio Meteorológico Nacional Network were related to ground‐based cloud observations. No geographical dependence was observed in the effects of each cloud‐type on the irradiance, from tropical to Antarctic regions. For overcast conditions, median transmittance percentages with respect to the clearsky situation of 81%, 44% and 36% at high, medium and low clouds respectively for erythemal irradiance, and 83%, 30% and 23% for total irradiance were determined, similar to results at mid‐latitudes of the Northern Hemisphere. Irradiance enhancement by broken cloud fields is more pronounced from 5 to 7 octas cloud coverage and can last even hours, with peak instantaneous values of 113% for erythemal and 133% for total irradiance, with respect to the very clean clearsky situation. In each case, the total irradiance is usually more attenuated and also more enhanced by clouds than the erythemal irradiance.
On the relationship between Dasuopu Snow Accumulation and the Asian Summer Monsoon
Authors: Zhao Hongxu , Moore G. W. K.
Published: October 2003

The Asian summer monsoon (ASM) is an important component of the global climate system. We investigate the relationship that exists between it and the snow accumulation record from an ice core drilled on the Dasuopu glacier in the Himalayas. This ice core record has been proposed as a proxy to study variability in the ASM. We argue that there is a weak direct expression of the ASM in the snow accumulation time series from the ice core. This is the result of the extreme elevation of the ice core site and the surface‐trapped characteristic of the atmospheric moisture transport associated with the ASM. We will present evidence of a coupling between Dasuopu snow accumulation (DSA) and the Hadley and Walker circulations. In particular, we argue that the recent reduction in snow accumulation at the site is the result of an intensification of the regional Hadley circulation.
Biomass burning and fossil fuel signatures in the upper troposphere observed during a CARIBIC flight from Namibia to Germany
Authors: Mühle J. , Brenninkmeijer C. A. M. , Rhee T. S. , Slemr F. , Oram D. E. , Penkett S. A. , Zahn A.
Published: October 2003

During a CARIBIC flight from Namibia to Germany in July 2000, air influenced by recent convective injection of biomass burning emissions was intersected in the vicinity of the ITCZ at an altitude of 10 km. The observed CO enhancement ratios for non‐methane hydrocarbons (NMHCs) and methyl halides are consistent with those reported for fresh biomass burning plumes. Air masses affected by transcontinental transport of natural gas emissions, most probably from the Gulf of Mexico, were encountered over the Mediterranean Sea. These are one of the few observations of deep convection of biomass burning emissions to the upper troposphere and of long range transport of natural gas emissions reported so far. The observations demonstrate the importance of deep convection for the chemistry of the upper troposphere and the potential of commercial aircraft for atmospheric research.
Implications of geometry, age and depositional history of a shallow confining layer in a coastal groundwater basin, Monterey County, California, USA
Authors: Erskine J. A. , Fisher A. T.
Published: October 2003

We mapped the geometry of a shallow confining layer within the Salinas Valley aquifer system, northern Monterey County, California, using indicator geostatistics. The confining layer was previously interpreted to be mainly Holocene in age, having been deposited as a single unit during post‐Wisconsin sea‐level rise. We interpret this layer in our field area to be associated with Isotope Stages 5 (84–121 kyr) based on three independent arguments: layer geometry, with three distinct clay units rather than one;14C analyses of peat samples; and consideration of required rates of coastal uplift. The complex stratigraphy of the confining layer likely resulted from deposition over existing topography, erosion during exposure, and uplift during three intervals of sea level rise and fall. Similarly complex layering may occur in other coastal basins, influencing groundwater resource development, remediation and protection in these settings.
Reformation of perpendicular shocks: Hybrid simulations
Authors: Hellinger P. , Trávnícek P. , Matsumoto H.
Published: October 2003

We show that in one‐dimensional hybrid simulations supercritical perpendicular shocks have a well‐defined, slightly oscillating structure (including foot, ramp, overshoot, and undershoot) for hot upstream protons and low Mach numbers. In this case the reflected protons are able to stop the shock steepening at proton scales. However, for colder upstream protons and/or higher Mach numbers simulated shocks show a nonstationary feature, namely a periodic reappearance of a new shock front. These nonstationary shocks simulated by one‐dimensional hybrid code have shock front gradient scales that are governed only by the spatial resolution used in the code. Consequently, we conclude that the one‐dimensional hybrid code is not suitable for description of perpendicular nonstationary shocks.
Anisotropic features of the Alpine lithosphere in Northern Spain
Authors: Díaz J. , Gallart J. , Ruiz M. , Pulgar J. A. , López C. , González‐Cortina J. M.
Published: October 2003

As part of an extensive seismic research carried out in the last years at the Northern part of Iberia affected by the Alpine compressional tectonics, the mantle anisotropic features have been investigated with the shear‐wave splitting technique. Two N‐S transects across the western Pyrenees and the eastern part of the Cantabrian Mountains were instrumented. In both cases the average fast velocity direction (FVD) and the delay times are remarkably consistent. The δt values are less than 1 s and the average FVD is close to E/W, subparallel to the trend of the Pyrenean belt. However, in each station the results show a significant variation of the splitting parameters with respect to the backazimuthal direction. This azimuthal dependence is compatible with synthetic models including two distinct anisotropic layers and suggests a complex distribution at depth of the anisotropic features, to be related with imprints of different geodynamic processes in the area.
Why is the Bay of Bengal less productive during summer monsoon compared to the Arabian Sea?
Authors: Prasanna Kumar S. , Muraleedharan P. M. , Prasad T. G. , Gauns M. , Ramaiah N. , de Souza S. N. , Sardesai S. , Madhupratap M.
Published: October 2003

The Bay of Bengal is traditionally considered to be a less productive basin compared to the Arabian Sea. We explore the reasons for this in the central Bay during summer. Copious rainfall and river water freshen the upper layers of the Bay by 3–7 psu during summer, and SST was warmer by 1.5–2°C than in the central Arabian Sea. This leads to a strongly stratified surface layer. The weaker winds over the Bay are unable to erode the strongly stratified surface layer, thereby restricting the turbulent wind‐driven vertical mixing to a shallow depth of <20 m. This inhibits introduction of nutrients from below, situated close to the mixed layer bottom, into the upper layers. While advection of nutrients rich water into the euphotic zone makes the Arabian Sea highly productive, this process is unlikely in the Bay of Bengal.
Transit time distributions in Lake Issyk‐Kul
Authors: Waugh Darryn W. , Vollmer Martin K. , Weiss Ray F. , Haine Thomas W. N. , Hall Timothy M.
Published: October 2003

Measurements of sulfur hexafluoride (SF6) and chlorofluorocarbons (CFCs) are used to constrain the timescales for deep‐water renewal in Lake Issyk‐Kul. As these tracers have different tropospheric histories their combination provides more transport information than one tracer alone. In particular, from these measurements the mean, Γ, and standard deviation, σ, of the distributions of transit times since water made last contact with the surface can be tightly constrained. Γ is older than the age determined from SF6 and younger than the ages from the CFCs, and increases from around 4 yrs at 200 m to around 10.5 yrs at the deepest location (655 m). σ also increases with depth and equals around 0.7 to 0.8 Γ, which corresponds to large ranges of transit times, and implies mixing processes play a major role in the transport. The approach used can also be applied to similar tracer measurements in the oceans and groundwaters to constrain transport in these geophysical systems.
Atmospheric pressure corrections in geodesy and oceanography: A strategy for handling air tides
Authors: Ponte Rui M. , Ray Richard D.
Published: October 2003

Global pressure data are often needed for processing or interpreting modern geodetic and oceanographic measurements. The most common source of these data is the analysis or reanalysis products of various meteorological centers. Tidal signals in these products can be problematic for several reasons, including potentially aliased sampling of the semidiurnal solar tide as well as the presence of various modeling or timing errors. Building on the work of Van den Dool and colleagues, we lay out a strategy for handling atmospheric tides in (re)analysis data. The procedure also offers a method to account for ocean loading corrections in satellite altimeter data that are consistent with standard ocean‐tide corrections. The proposed strategy has immediate application to the on‐going Jason‐1 and GRACE satellite missions.
Martian sedimentary rock stratigraphy: Outcrops and interbedded craters of northwest Sinus Meridiani and southwest Arabia Terra
Authors: Edgett Kenneth S. , Malin Michael C.
Published: October 2003

Layers in the upper martian crust record a complex history of deposition and erosion. We examined a region between 2°–9°N, 1°–8°W and found that light‐toned, layered, sedimentary rocks in northwest Sinus Meridiani also occur in southwest Arabia Terra, where they are mantled by dust. The rocks are divided into four distinct stratigraphic units. Impact craters of diameters 30–60 km are interbedded with the ∼200 m‐thick units, attesting to their antiquity, revealing the presence of temporal unconformities between units, and indicating that the sequence spans considerable time. A crater at 8°N, 7°W, containing hundreds of repeated sedimentary layers, is stratigraphically lower than most of the four‐unit section. The layers in the crater formed in a different environment than the layered material outside the crater. Deciphering the geologic history of Mars requires recognition that the planet has more than a cratered surface; its crust is a cratered volume.
Constraints on the viscosity of the continental crust and mantle from GPS measurements and postseismic deformation models in western Mongolia
Authors: Vergnolle Mathilde , Pollitz Fred , Calais Eric
Published: October 2003

We use GPS measurements and models of postseismic deformation caused by seven M6.8 to 8.4 earthquakes that occurred in the past 100 years in Mongolia to assess the viscosity of the lower crust and upper mantle. We find an upper mantle viscosity between 1 × 1018 and 4 × 1018 Pa s. The presence of such a weak mantle is consistent with results from independent seismological and petrological studies that show an abnormally hot upper mantle beneath Mongolia. The viscosity of the lower crust is less well constrained, but a weak lower crust (3 × 1016 to 2 × 1017 Pa s) is preferred by the data. Using our best fit upper mantle and lower crust viscosities, we find that the postseismic effects of viscoelastic relaxation on present‐day horizontal GPS velocities are small (<2 mm yr−1) but still persist 100 years after the 1905, M8.4, Bolnay earthquake. This study shows that the GPS velocity field in the Baikal‐Mongolia area can be modeled as the sum of (1) a rigid translation and rotation of the whole network, (2) a 3–5 mm yr−1 simple shear velocity gradient between the Siberian platform to the north and northern China to the south, and (3) the contribution of postseismic deformation, mostly caused by the 1905 Bolnay‐Tsetserleg sequence and by the smaller, but more recent, 1957 Bogd earthquake.
Development and application of a state‐of‐the‐science plume‐in‐grid model
Authors: Karamchandani Prakash , Seigneur Christian , Vijayaraghavan Krishnakumar , Wu Shiang‐Yuh
Published: October 2003

We describe the development, evaluation, and application of a new plume‐in‐grid model for investigating the subgrid‐scale effects, associated with NOx emissions from large elevated point sources, on O3 formation. Traditional Eulerian air quality models cannot resolve the strong concentration gradients created by plumes emitted from large point sources. Although several plume‐in‐grid approaches have been used in the past to address this issue, they have been limited by their simplistic simulation of plume dispersion and/or chemistry and their lack of treatment of the effect of turbulence on plume chemistry. In the plume‐in‐grid model presented here, the embedded reactive plume model combines a state‐of‐the‐science puff model with a gas‐phase chemistry mechanism that is consistent with that used in the host grid model. The puff model uses a second‐order closure scheme, allowing for a more accurate treatment of dispersion and the influence of turbulent concentration fluctuations on chemical rates. It also allows the splitting and merging of puffs to account for wind shear effects, varying chemistry across the plume, and interplume and intraplume interactions. The combined puff/chemistry model is embedded into an Eulerian grid model. Results from the application of this model to the northeastern United States, a domain containing some of the largest NOx‐emitting power plants in the United States, show that the plume‐in‐grid treatment leads to significant differences in surface O3 and HNO3 concentrations.
Asian aerosols in North America: Frequency and concentration of fine dust
Authors: VanCuren Richard A. , Cahill Thomas A.
Published: October 2003

Using an elemental signature for Asian dust derived from events in April 1998, we probed a long‐term set of routine aerosol samples to develop the first empirical assessment of the frequency and intensity of dust transport from Asia to midlatitude North America. Our data reveal a pattern of consistent, frequent transport that contradicts the episodic characterization derived from short‐term studies and anecdotal reports. We find that fine (<2.5 μm) Asian dust is a regular component of the troposphere over the eastern Pacific and western North America and is common, at least in spring, across North America. Typical Asian fine dust concentrations (24‐hour average) are between 0.2 and 1 μg/m3 and only very rarely exceed 5 μg/m3. Our data also indicate that Asian dust is concentrated in an altitude zone ranging from about 500 to 3000 m MSL, consistent with isentropic transport processes previously observed in the western Pacific.
A two‐dimensional simulation of the isotopic composition of water vapor and methane in the upper atmosphere
Authors: Ridal Martin , Siskind David E.
Published: October 2003

A chemical oxidation scheme where CH3D produces HDO has been incorporated into a two‐dimensional model to simulate the transport and isotopic composition chemistry of stratospheric methane and water. The model results show that deuterium ratios in water and methane are good tracers of stratospheric dynamics. Comparisons with measurements by the ATMOS instrument suggest that the modeled methane isotopic ratio is too low in the upper stratosphere and mesosphere. The very low amount of CH4 and CH3D in the middle to upper stratosphere makes the isotopic ratio for methane more sensitive to model uncertainties than the isotopic ratio of water vapor. One reason for the too low isotopic ratio values may be that the reaction rates in the oxidation of CH3D are slower than assumed. The isotopic ratio for methane was very sensitive to changes in the rate constants for the reactions of CH3D with OH, O(1D) and Cl, while the water vapor isotopic ratio only shows small changes.
Evaluation of midlatitude cloud properties in a weather and a climate model: Dependence on dynamic regime and spatial resolution
Authors: Tselioudis George , Jakob Christian
Published: October 2003

In this study, the midlatitude cloud fields produced by a climate (GISS) and a weather (ECMWF) model are evaluated against satellite observations. Monthly ensembles of model cloud property distributions for the four seasons are compared with similar ensembles from satellite retrievals. The weather model is run in both forecast and “climate” mode in order to evaluate the importance of the exact representation of the atmospheric conditions in these ensemble comparisons. The weather and climate models are evaluated at different resolutions that cover the range used in today's climate and weather prediction simulations. Cloud property evaluations are separated into broadly defined dynamic regimes that cover the range of large‐scale midlatitude motions. Quantitative evaluation tables are produced that rank the performance of the different model versions used in the study. The evaluation analysis reveals several common features between the two models. Those are the overestimation of cloud optical depth in all dynamic regimes, the underestimation of cloud cover in the large‐scale descent regime and the underestimation of cloud top height in the large‐scale descent regime. It is also shown that, in the radiative balance calculations, the models compensate for the overestimation of cloud optical depth through the underprediction of cloud cover. The comparison of the forecast and “climate” runs of the ECMWF model shows remarkably similar statistical properties of the clouds in the two runs. The analysis of runs with different resolutions reveals large improvement when going from a 4° × 5° 9‐layer to a 2° × 2.5° 32‐layer run with the GISS GCM, much of which is caused by the increase in vertical resolution. A comparison of a T42 and a T106 run of the same vertical resolution with the ECMWF GCM does not show considerable differences between the two model versions.
Sensitivity of tracer transports and stratospheric ozone to sea surface temperature patterns in the doubled CO2 climate
Authors: Rind David , Lerner Jean , Perlwitz Judith , McLinden Chris , Prather Michael
Published: October 2003

Two sets of sea surface temperature/sea ice changes are used to test the sensitivity of tracer transport to the pattern of warming in the doubled CO2 climate. One set (2CO2WT) has greater tropical and high latitude sea surface temperature changes than the other (2CO2), although both fall within the range of plausible response. Simulations were done both with and without interactive ozone. Results show that the SST pattern affects the circulation change throughout the troposphere and middle atmosphere; the ozone interaction affects primarily the upper stratosphere, but through wave‐mean flow interaction has effects that extend down into the upper troposphere. Both experiments feature increased tropospheric/stratospheric exchange at low latitudes and greater vertical mixing within the troposphere; only the WT experiments result in increased interhemispheric transport and a more direct circulation in the high latitude stratosphere. Ozone increases in the upper stratosphere and decreases in the lower stratosphere in all the simulations, with greater transport of high latitude ozone into the troposphere in the WT runs. At sea level there is a more positive phase of the Arctic Oscillation (AO)‐type oscillation, and this is also true at 100 mbar, but there is no significance in the middle troposphere and the sign is different in the middle stratosphere. Many of these results differ from those generated in older versions of the GISS GCMAM despite the same SST forcing due to differences in control run characteristics, which has implications for model intercomparison experiments.