bluuebunny/crossref_metadata_2025 huggingface dataset:
Complexities of the San Andreas fault near San Gorgonio Pass: Implications for large earthquakes
Authors: Yule Doug , Sieh Kerry
Published: November 2003

Geologic relationships and patterns of crustal seismicity constrain the three‐dimensional geometry of the active portions of San Andreas fault zone near San Gorgonio Pass, southern California. Within a 20‐km‐wide contractional stepover between two segments of the fault zone, the San Bernardino and Coachella Valley segments, folds, and dextral‐reverse and dextral‐normal faults form an east‐west belt of active structures. The dominant active structure within the stepover is the San Gorgonio Pass‐Garnet Hill faults, a dextral‐reverse fault system that dips moderately northward. Within the hanging wall block of the San Gorgonio Pass‐Garnet Hill fault system are subsidiary active dextral and dextral‐normal faults. These faults relate in complex but understandable ways to the strike‐slip faults that bound the stepover. The pattern of crustal seismicity beneath these structures includes a 5–8 km high east‐west striking step in the base of crustal seismicity, which corresponds to the downdip limit of rupture of the 1986 North Palm Springs earthquake. We infer that this step has been produced by slip on the linked San Gorgonio Pass‐Garnet Hill‐Coachella Valley Banning (SGP‐GH‐CVB) fault. This association enables us to construct a structure contour map of the fault plane. The large step in the base of seismicity downdip from the SGP‐GH‐CVB fault system probably reflects a several kilometers offset of the midcrustal brittle‐plastic transition. (U/Th)/He thermochronometry supports our interpretation that this south‐under‐north thickening of the crust has created the region's 3 km of topographic relief. We conclude that future large earthquakes generated along the San Andreas fault in this region will have a multiplicity of mostly specifiable sources having dimensions of 1–20 km. Two tasks in seismic hazard evaluation may now be attempted with greater confidence: first, the construction of synthetic seismograms that make useful predictions of ground shaking, and second, theoretical investigations of the role of this complexity in retarding the propagation of future seismic ruptures.
Wind‐induced, cross‐frontal exchange on Georges Bank: A mechanism for early summer on‐bank biological particle transport
Authors: Chen Changsheng , Schlitz Ronald J. , Lough R. Gregory , Smith Keston W. , Beardsley Robert , Manning James P.
Published: November 2003

Water exchange across the tidal‐mixing front on the southern flank of Georges Bank (GB) is examined using a two‐dimensional (2D) primitive equation ocean model. The model domain features a cross‐frontal transect including a June 1999 hydrographic (CTD)/ADCP study made as part of the U.S. GLOBEC Northwest Atlantic/Georges Bank program. The model was initialized with temperature and salinity fields taken on the 15 June 1999 CTD section and run prognostically with tidal forcing, measured winds, and representative surface heat flux. The results show that fluctuations of wind plus tidal mixing can play the following essential role in the short‐term transport of water and particles from the stratified region to the mixed region on GB in early summer, when stratification is just developing with a weak thermocline at a depth of about 10 m. First, a passing weather front drives a wind‐induced on‐bank Ekman transport of the upper part of the water column at the tidal‐mixing front and associated particles in the surface mixed layer. Then, when the wind relaxes or changes direction, the water in the on‐bank extension of the front (above the thermocline) mixes quickly through enhanced tidal motion in shallower depths of water. As a result, particles that are advected along the extended front stay in the previously well‐mixed region of the bank. Surface heating tends to increase the strength of the thermocline and reduce the thickness of the surface mixed layer. This in turn accelerates the on‐bank movement of the front under an easterly wind favorable for Ekman transport and thus enhances the on‐bank, cross‐frontal transport of particles. Since the wind‐induced, cross‐frontal on‐bank transport of water can occur episodically during passages of meteorological fronts, these could produce a larger net cross‐frontal flux than that produced by just tidal forcing on equivalent timescales. Therefore wind‐induced processes can be important in the on‐bank cross‐frontal flux of copepods and other zooplankton species that exhibit shallow maxima in their vertical distributions over the southern flank of GB in early summer.
Space‐time dependency modeling using general classes of flexible stationary variogram models
Authors: Fernández‐Casal Rubén , González‐Manteiga Wenceslao , Febrero‐Bande Manuel
Published: November 2003

In this paper we describe a generalization of theShapiro and Botha[1991]approach for the case of anisotropy in two components with a view to obtaining flexible stationary variogram models suitable for modeling spatiotemporal dependency. Additionally, instead of choosing the empirical semivariogram estimator, the use of a nonparametric kernel estimator of the semivariogram is proposed. The work also includes an application to wind speed data and a simulation study. It can be observed in the simulations that the use of flexible models avoids problems of bad specification that may arise when parametric models are used and, in addition, that the local linear semivariogram estimator produces significantly better results than those obtained with the empirical estimator.
Implementation of Noah land surface model advances in the National Centers for Environmental Prediction operational mesoscale Eta model
Authors: Ek M. B. , Mitchell K. E. , Lin Y. , Rogers E. , Grunmann P. , Koren V. , Gayno G. , Tarpley J. D.
Published: November 2003

We present the impact tests that preceded the most recent operational upgrades to the land surface model used in the National Centers for Environmental Prediction (NCEP) mesoscale Eta model, whose operational domain includes North America. These improvements consist of changes to the “Noah” land surface model (LSM) physics, most notable in the area of cold season processes. Results indicate improved performance in forecasting low‐level temperature and humidity, with improvements to (or without affecting) the overall performance of the Eta model quantitative precipitation scores and upper air verification statistics. Remaining issues that directly affect the Noah LSM performance in the Eta model include physical parameterizations of radiation and clouds, which affect the amount of available energy at the surface, and stable boundary layer and surface layer processes, which affect surface turbulent heat fluxes and ultimately the surface energy budget.
Observations of blowing snow at the South Pole
Authors: Mahesh Ashwin , Eager Rebecca , Campbell James R. , Spinhirne James D.
Published: November 2003

Observations of blowing snow from visual observers' records as well as ground‐based infrared and lidar measurements at South Pole Station are analyzed to obtain the first climatology of blowing snow over the Antarctic Plateau. Occurrence frequencies of blowing snow, wind direction and speed during blowing snow events, typical snow layer heights, as well as optical depths are determined. Blowing snow is recorded in roughly one third of the visual observations and occurs under a narrow range of wind directions. Blowing snow layers are usually less than 400 m in thickness but can exceed 1000 m. During blowing snow conditions, these near‐surface layers are apparent in lidar backscatter profiles. These layers emit radiances similar to those from optically thin clouds frequently seen over the Antarctic Plateau. Because the near‐surface blowing snow layers are frequently present, they are a factor in space‐borne laser altimetry and other satellite remote sensing.
Shallow‐water carbonates record marginal to open ocean Quaternary paleoceanographic evolution
Authors: Sakai Saburo
Published: November 2003

The oxygen and carbon isotopic composition of shallow‐water carbonates and their fossil components can be important tools for understanding Quaternary paleoceanographic conditions of marginal seas, including coral reef regions. However, most previous paleoceanographic studies using isotopes have been based on pelagic or hemipelagic sediments because the original δ18O and δ13C values of shallow‐water carbonates are normally altered by postdepositional diagenesis. This study shows that marginal to open ocean isotopic signals can be preserved in carefully cleaned low‐Mg calcitic planktic foraminifers of shallow‐water carbonates, even when the isotopic values of the carbonate host rock have been altered by meteoric fluids and subaerial exposure. The two studied core sections were collected from the mid‐Quaternary Ryukyu Group (southwestern Japan), which consists mainly of bioclastic grainstone‐packstone, rhodolith floatstone‐rudstone, and large foraminiferal floatstone corresponding to open shelf to shelf slope facies, from the southwest Ryukyu Islands, Japan. Down core δ18O records of planktic foraminifers in the Ryukyu Group imply that sea surface temperatures (SST) in the northwestern Pacific increased ∼2.0°C at the beginning of oxygen isotope stage 19 (post mid‐Pleistocene revolution (MPR)). This warming may have triggered the expansion of reef complex deposits as large as those now in the Ryukyu Islands and was approximately coeval with the lower section of the Australian Great Barrier Reef. SST warming due to the expansion of the Western Pacific Warm Pool (WPWP) toward the north and south subtropical regions is a possible mechanism for reef expansion and initiation of the coral reefs of the Western Pacific region.
Direct assessment of groundwater vulnerability from single observations of multiple contaminants
Authors: Worrall Fred , Kolpin Dana W.
Published: December 2003

Groundwater vulnerability is a central concept in pollution risk assessment, yet its estimation has been largely a matter of expert judgment. This work applies a method for the direct calculation of vulnerability from monitoring well observations of pesticide concentrations. The method has two major advantages: it is independent of the compounds being examined, and it has a direct probabilistic interpretation making it ideal for risk assessment. The methodology was applied to data from a groundwater monitoring program in the midwestern United States. The distribution of the vulnerabilities was skewed toward zero. Spatial distribution of the vulnerabilities shows them to be controlled by both regional and local factors. Methods are presented for estimating the necessary sample sizes for vulnerability studies. The further application of the approach developed in this study to understanding groundwater pollution is discussed.
Effect of isolated fractures on accelerated flow in unsaturated porous rock
Authors: Su Grace W. , Nimmo John R. , Dragila Maria I.
Published: December 2003

Fractures that begin and end in the unsaturated zone, or isolated fractures, have been ignored in previous studies because they were generally assumed to behave as capillary barriers and remain nonconductive. We conducted a series of experiments using Berea sandstone samples to examine the physical mechanisms controlling flow in a rock containing a single isolated fracture. The input fluxes and fracture orientation were varied in these experiments. Visualization experiments using dyed water in a thin vertical slab of rock were conducted to identify flow mechanisms occurring due to the presence of the isolated fracture. Two mechanisms occurred: (1) localized flow through the rock matrix in the vicinity of the isolated fracture and (2) pooling of water at the bottom of the fracture, indicating the occurrence of film flow along the isolated fracture wall. These mechanisms were observed at fracture angles of 20 and 60 degrees from the horizontal, but not at 90 degrees. Pooling along the bottom of the fracture was observed over a wider range of input fluxes for low‐angled isolated fractures compared to high‐angled ones. Measurements of matrix water pressures in the samples with the 20 and 60 degree fractures also demonstrated that preferential flow occurred through the matrix in the fracture vicinity, where higher pressures occurred in the regions where faster flow was observed in the visualization experiments. The pooling length at the terminus of a 20 degree isolated fracture was measured as a function of input flux. Calculations of the film flow rate along the fracture were made using these measurements and indicated that up to 22% of the flow occurred as film flow. These experiments, apparently the first to consider isolated fractures, demonstrate that such features can accelerate flow through the unsaturated zone and should be considered when developing conceptual models.
A stochastic model of space‐time variability of mesoscale rainfall: Statistics of spatial averages
Authors: Kundu Prasun K. , Bell Thomas L.
Published: December 2003

A characteristic feature of rainfall statistics is that they depend on the space and time scales over which rain data are averaged. A previously developed spectral model of rain statistics that is designed to capture this property predicts power law scaling behavior for the second moment statistics of area‐averaged rain rate on the averaging length scale L as L → 0. In the present work a more efficient method of estimating the model parameters is presented and used to fit the model to the statistics of area‐averaged rain rate derived from gridded radar precipitation data from TOGA‐COARE. Statistical properties of the data and the model predictions are compared over a wide range of averaging scales. An extension of the spectral model scaling relations to describe the dependence of the average fraction of grid boxes within an area containing nonzero rain (the “rainy area fraction”) on the grid scale L is also explored.
Field validation of the DNDC model for greenhouse gas emissions in East Asian cropping systems
Authors: Cai Zucong , Sawamoto Takuji , Li Changsheng , Kang Guoding , Boonjawat Jariya , Mosier Arvin , Wassmann Reiner , Tsuruta Haruo
Published: November 2003

Validations of the DeNitrification‐DeComposition (DNDC) model against field data sets of trace gases (CH4, N2O, and NO) emitted from cropping systems in Japan, China, and Thailand were conducted. The model‐simulated results were in agreement with seasonal N2O emissions from a lowland soil in Japan from 1995 to 2000 and seasonal CH4 emissions from rice fields in China, but failed to simulate N2O and NO emissions from an Andisol in Japan as well as NO emissions from the lowland soil. Seasonal CH4 emissions from rice cropping systems in Thailand were poorly simulated because of site‐specific soil conditions and rice variety. For all of the simulated cases, the model satisfactorily simulated annual variations of greenhouse gas emissions from cropping systems and effects of land management. However, discrepancies existed between the modeled and observed seasonal patterns of CH4 and N2O emissions. By incorporating modifications based on the local soil properties and management, DNDC model could become a powerful tool for estimating greenhouse gas emissions from terrestrial ecosystems.
Millennial‐scale variability of deep‐water temperature and δ18Odw indicating deep‐water source variations in the Northeast Atlantic, 0–34 cal. ka BP
Authors: Skinner L. C. , Shackleton N. J. , Elderfield H.
Published: December 2003

Paired measurements of Mg/Ca and δ18Occ (calcite δ18O) in benthic foraminifera from a deep‐sea core recovered on the Iberian Margin (MD99‐2334K; 37°48′N, 10°10′W; 3,146 m) have been performed in parallel with planktonic δ18Occ analyses and counts of ice‐rafted debris (IRD). The synchrony of temperature changes recorded in the Greenland ice cores and in North Atlantic planktonic δ18Occ allows the proxy records from MD99‐2334K to be placed confidently on the GISP2 time‐scale. This correlation is further corroborated by AMS 14C‐dates. Benthic Mg/Ca measurements in MD99‐2334K permit the reconstruction of past deep‐water temperature (Tdw) changes since ∼34 cal. ka BP (calendar kiloyears before present). Using these Tdw estimates and parallel benthic δ18Occ measurements, a record of deep‐water δ18O (δ18Odw) has been calculated. Results indicate greatly reduced Tdw in the deep Northeast Atlantic during the last glaciation until ∼15 cal. ka BP, when Tdw warmed abruptly to near‐modern values in parallel with the onset of the Bølling‐Allerød interstadial. Subsequently, Tdw reverted to cold glacial values between ∼13.4 and ∼11.4 cal. ka BP, in parallel with the Younger Dryas cold reversal and the H0 ice‐rafting event. Similar millennial‐scale Tdw changes also occurred during the last glaciation. Indeed, throughout the last ∼34 cal. ka, millennial δ18Odw and Tdw changes have remained well coupled and are linked with IRD pulses coincident with Heinrich events 3, 2, 1, and the Younger Dryas, when transitions to lower Tdw and δ18Odw conditions occurred. In general, millennial Tdw and δ18Odw variations recorded in MD99‐2334K describe an alternation between colder, low‐δ18Odw and warmer, high δ18Odw conditions, which suggests the changing local dominance of northern‐sourced North Atlantic Deep Water (NADW) versus southern‐sourced Antarctic Bottom Water (AABW). The observed similarity of the Tdw and GISP2 δ18Oice records would therefore suggest a common component of variability resulting from the coupling of NADW formation and Greenland climate. A link between Greenland stadials and the incursion of cold, low‐δ18Odw AABW in the deep Northeast Atlantic is thus implied, which contributes to the relationship between Greenland climate and the millennial benthic δ18Occ signal since ∼34 cal. ka BP.
Stimulation of electron Bernstein modes by perpendicular ion beams
Authors: Brinca A. L. , Romeiras F. J. , Gomberoff L.
Published: November 2003

This investigation studies the characteristics of electron cyclotron harmonic waves generated by almost monoenergetic perpendicular ion beams. Its motivation is twofold: (1) the new type of free energy source, beams made up of protons, alpha particles, and multiply ionized carbon, nytrogen or oxygen ions, has recently been observed in the geoplasma, and (2) the classical mechanism associated with the stimulation of these electrostatic modes is unable to explain some of their observed features, namely the fine structure sometimes seen in the emission bands and the occurrence of multiple harmonics with the higher branches lying above the upper hybrid frequency. The appropriate dispersion equation supports the developed analysis and determines the properties of this new excitation mechanism. Its characteristics contribute to overcome difficulties encountered by the standard paradigm in the interpretation of several types of electron Bernstein emissions.
Effects of the solar wind electric field and ionospheric conductance on the cross polar cap potential: Results of global MHD modeling
Authors: Merkine V. G. , Papadopoulos K. , Milikh G. , Sharma A. S. , Shao X. , Lyon J. , Goodrich C.
Published: December 2003

The behavior of the cross polar cap potential, ΦPC, under strong solar wind conditions is studied using global MHD simulations. Simulations using two typical values of the ionospheric Pedersen conductance in agreement with others show that the cross polar cap potential is reduced compared to the corresponding potential in the solar wind due to the stagnation of the magnetosheath flow and the existence of parallel potentials. However, it is the ionospheric conductance that affects the value of ΦPC the most: the transpolar potential saturates only for high enough ionospheric conductance. A mechanism in which the ionospheric conductance changes the properties of the magnetosheath flow is proposed. This mechanism assumes mapping of the electrostatic potential in the ideal MHD system and yields a self‐consistent response of the reconnection and transpolar potentials to changes in the ionospheric conductance.
Eurasian snow cover, more skillful in predicting U.S. winter climate than the NAO/AO?
Authors: Cohen Judah L. , Saito Kazuyuki
Published: December 2003

Successfully predicting the phase and strength of the dominant winter mode of variability for the Northern Hemisphere (NAO/AO) is considered the most important future breakthrough in winter climate prediction; however skillful prediction of the index has been elusive. In this Letter we present a snow index constructed from observed summer and fall anomalies that is more highly correlated than the observed value of the winter AO with winter surface temperatures in the eastern United States. Ease of use and the potential for greater predictive skill could potentially render forecasting the phase and strength of the NAO/AO irrelevant as a tool for prediction of U. S. winter surface temperatures.
Relationship between CME velocity and active region magnetic energy
Authors: Venkatakrishnan P. , Ravindra B.
Published: December 2003

We find an empirical relationship between the initial speed of Coronal Mass Ejection (CME) and the potential magnetic field energy of the associated active region (AR) that closely resembles the Sedov relation between the speed of a blast wave and the blast energy. We conclude that it is the magnetic energy of an AR that drives the CME. The restructuring of the AR field lines in the corona which can push material with Alfven speed and thus inject energy into the plasma on a time scale shorter than the dynamical time of the corona, is a likely process that can drive the CME. The empirical relationship allows the prediction of the maximum speed of a CME that can result from an AR of a given magnetic energy.
Elemental composition determined by PIXE analysis of the insoluble aerosol particles in EPICA‐Dome C ice core samples representing the last 27000 years
Authors: Ghermandi Grazia , Cecchi Rodolfo , Capotosto Margherita , Marino Federica
Published: November 2003

107 samples from the first 581 m of the EPICA ice core, Dome C, East Antarctica, representing a 27000 year record, were analysed by the PIXE technique. The concentrations of several elements (Na, Mg, Al, Si, S, Cl, K, Ca, Ti, Mn, Fe) were determined in the insoluble particles, collected by filtration from the melted ice samples. The average elemental ratios for Holocene and LGM are in agreement with continental crust values. The element depositional fluxes, evaluated from PIXE concentration data by means of the EPICA ice accumulation rate, are smaller in the Holocene than during Glacial times, confirming the differences in dust loads in the atmosphere during the contrasting climatic conditions. In Holocene, the fraction of the insoluble particle mass (estimated as the sum of the measured element oxides) agrees well with the total dust mass as determined from Coulter Counter measurements, but during the LGM the particle counting shows a larger dust mass.
Co‐seismic slip, post‐seismic slip, and largest aftershock associated with the 1994 Sanriku‐haruka‐oki, Japan, earthquake
Authors: Yagi Yuji , Kikuchi Masayuki , Nishimura Takuya
Published: November 2003

We analyzed continuous GPS data to investigate the spatio‐temporal distribution of co‐seismic slip, post‐seismic slip, and largest aftershock associated with the 1994 Sanriku‐haruka‐oki, Japan, earthquake (Mw = 7.7). To get better resolution for co‐seismic and post‐seismic slip distribution, we imposed a weak constraint as a priori information of the co‐seismic slip determined by seismic wave analyses. We found that the post‐seismic slip during 100 days following the main‐shock amount to as much moment release as the main‐shock, and that the sites of co‐seismic slip and post‐seismic slip are partitioning on a plate boundary region in complimentary fashion. The major post‐seismic slip was triggered by the mainshock in western side of the co‐seismic slip, and the extent of the post‐seismic slip is almost unchanged with time. It rapidly developed a shear stress concentration ahead of the slip area, and triggered the largest aftershock.
Unexpectedly high aerosol load in the free troposphere over central Europe in spring/summer 2003
Authors: Mattis Ina , Ansmann Albert , Wandinger Ulla , Müller Detlef
Published: November 2003

We observed particle extinction coefficients of 5–30 Mm−1 and particle optical depths of 0.03–0.11 at UV and visible wavelengths in the free troposphere from May to July, 2003. In May and early June distinct aerosol layers could be observed above the boundary layer (typically between 3–7‐km height). In contrast, the aerosol distribution became vertically more homogeneous and stretched to the tropopause by the end of June and in July. Most probably, severe forest fires in Siberia in the spring of 2003 caused this enhanced free tropospheric background. The observations were made with a Raman lidar operating at 355 and 532‐nm wavelength at Leipzig, Germany. This lidar allows a clear identification of aged smoke in terms of spectrally resolved backscatter and extinction coefficients, particle optical depths, Ångström exponents, extinction‐to‐backscatter ratios, and depolarization ratio.
A Madden‐Julian Oscillation in tropospheric ozone
Authors: Ziemke J. R. , Chandra S.
Published: December 2003

This study shows evidence of a Madden‐Julian Oscillation (MJO) in tropospheric ozone. Tropospheric ozone is derived using differential measurements of total column ozone and stratospheric column ozone from total ozone mapping spectrometer (TOMS) and microwave limb sounder (MLS) instruments. Two broad regions of significant MJO signal are identified in the tropics, one in the western Pacific and the other in the eastern Pacific. Over both regions, MJO variations in tropospheric ozone represent 5–10 Dobson Unit (DU) peak‐to‐peak anomalies. These variations are significant compared to mean background amounts of around 20 DU or less over most of the tropical Pacific. MJO signals of this magnitude would need to be considered when investigating and interpreting particular pollution events since ozone is a precursor of the Hydroxyl (OH) radical, the main oxidizing agent of pollutants in the lower atmosphere.
Use of Total Organic Carbon (TOC) as tracer of diffuse infiltration in a dolomitic karstic system: The Nerja Cave (Andalusia, southern Spain)
Authors: Batiot Christelle , Liñán Cristina , Andreo Bartolomé , Emblanch Christophe , Carrasco Francisco , Blavoux Bernard
Published: November 2003

Recent studies in several karstic systems in France have highlighted that Total Organic Carbon (TOC) was a relevant parameter in order to characterise the behaviour of aquifers, to differentiate the water types that participate in karstic flow (fast infiltration, unsaturated zone, saturated zone) and to evaluate their vulnerability. This study on TOC dynamics at the experimental site of the Nerja Cave has been performed to test the potential of this tracer in a particular climatic (Mediterranean climate), lithologic (dolomitic marbles) and hydrodynamic (diffuse flow behaviour) context. TOC evolution, compared to those of classical tracers used in hydrogeology, permits the understanding of the hydrodynamical behaviour of the unsaturated zone of this dolomitic aquifer, whose response to precipitation is slower than that commonly obtained in karstic aquifers of calcareous nature.
Modeling El Niño and its tropical teleconnections during the last glacial‐interglacial cycle
Authors: Otto‐Bliesner Bette L. , Brady Esther C. , Shin Sang‐Ik , Liu Zhengyu , Shields Christine
Published: December 2003

Simulations with the NCAR Climate System Model (CSM), a global, coupled ocean‐atmosphere‐sea ice model, for the last glacial‐interglacial cycle reproduce recent estimates, based on alkenones and Mg/Ca ratios, of sea surface temperature (SST) changes and gradients in the tropical Pacific and predict weaker El Niños/La Niñas compared to present for the Holocene and stronger El Niños/La Niñas for the Last Glacial Maximum (LGM). Changes for the LGM (Holocene) are traced to a weakening (strengthening) of the tropical Pacific zonal SST gradient, wind stresses, and upwelling and a sharpening (weakening) of the tropical thermocline. Results suggest that proxy evidence of weaker precipitation variability in New Guinea and Ecuador are explained not only by changes in El Niño/La Niña but also changes in the atmospheric circulation and hydrologic cycle.
Recent shifts in the state of the North Pacific
Authors: Bond N. A. , Overland J. E. , Spillane M. , Stabeno P.
Published: December 2003

The winters of 1999–2002 for the North Pacific were characterized by spatial patterns in sea level pressure anomaly (SLPA) and sea surface temperature anomaly (SSTA) with little resemblance to those of the leading pattern of North Pacific climate variability, the Pacific Decadal Oscillation (PDO). In essence, the southeastern (northern) portion of the North Pacific was subject to atmospheric forcing characteristic of that before (after) the major regime shift of 1976–77. Recent major changes in the ecosystems off the west coast of the United States and continued conditions similar to those of the early 1990s in the Gulf of Alaska, Bering Sea, and Sea of Okhotsk are consistent with these SLPA and SSTA patterns. Our result illustrates that a single indicator such as the PDO is incomplete in characterizing North Pacific climate.
A new climate‐vegetation equilibrium state for Tropical South America
Authors: Oyama Marcos Daisuke , Nobre Carlos Afonso
Published: December 2003

The existence of multiple climate‐vegetation equilibria in Tropical South America is investigated under present‐day climate conditions with the use of an atmospheric general circulation model coupled to a potential vegetation model. Two stable equilibria were found. One corresponds to the current biome distribution. The second is a new equilibrium state: savannas replace eastern Amazonian forests and a semi‐desert area appears in the driest portion of Northeast Brazil. If sustainable development and conservation policies were not able to halt the increasing environmental degradation in those areas, then land use changes could, per se, tip the climate‐vegetation system towards this new alternative drier stable equilibrium state, with savannization of parts of Amazonia and desertification of the driest area of Northeast Brazil, and with potential adverse impacts on the rich species diversity in the former region and water resources in the latter.
Aliased tidal signatures in continuous GPS height time series
Authors: Penna N. T. , Stewart M. P.
Published: December 2003

Coordinate time series are often derived from continuous GPS data processed as discrete 24 hour solutions. Under this regimen, residual semi‐diurnal and diurnal crustal tide signatures are under‐sampled, resulting in aliased periodic signals in the coordinate time series. A secondary aliasing effect, well known from satellite altimetry studies but generally ignored in GPS analysis, arises from the repeat period of the satellite orbits being longer than the Nyquist period of the semi‐diurnal and diurnal tidal signatures. This paper derives the theoretical periods for these two aliasing effects for the principal semi‐diurnal and diurnal tidal constituents. The presence of both types of aliased signals in GPS time series is then demonstrated using simulated GPS data and also considered for time series derived from real GPS data. It is shown that the beating of the two aliased signals invariably results in spurious signatures in the time series with semi‐annual and annual periods.
Modification of the solar wind electron velocity distribution at interplanetary shocks
Authors: Fitzenreiter R. J. , Ogilvie K. W. , Bale S. D. , Viñas A. F.
Published: December 2003

We analyze a small selection of interplanetary shocks of moderate strength, observed by instruments aboard the Wind spacecraft. We find electron signatures of heating and acceleration that are similar to those found at Earth's high Mach number bow shock. Upstream, velocity distributions have the signature of shock‐accelerated electrons with the characteristic time of flight velocity cutoff with bump‐on‐tail reduced distributions observed in coincidence with Langmuir waves. Downstream, the distributions broaden with the stronger shocks showing flat‐topped distributions and accompanying beams, such as are seen on the high entropy side of Earth's bow shock. We apply the Liouville mapping analysis of Hull et al. [1998, 2001] to one of the interplanetary shocks and compute the deHoffman‐Teller electrostatic potential across the shock using the electron moments to map the observed upstream distribution to the downstream region. The mapping successfully reproduces the inflated phase density and beam signatures of the observed downstream electron velocity distribution.
Evaluation of statistical convection patterns for real‐time ionospheric specifications and forecasts
Authors: Bekerat Hamed A. , Schunk Robert W. , Scherliess Ludger
Published: December 2003

Statistical models of high‐latitude plasma convection have been used in a wide range of studies pertaining to the ionosphere and thermosphere, and they are beginning to be used in various space weather applications. However, the statistical convection models only provide average, not instantaneous, convection patterns, and it is not clear if they are real convection patterns or blurred images of convection. It is also unclear how reliable these convection models are for applications involving ionosphere‐thermosphere specifications and forecasts. To address these issues, a quantitative analysis was conducted of the Weimer [2001] empirical convection model, which is the most comprehensive model of high‐latitude convection that has been constructed to date. First, criteria were established to determine whether or not a modeled convection pattern was correct for a given set of geophysical conditions. The criteria adopted were reasonable but stringent. Then the cross‐track ion drift velocities obtained from Weimer [2001] were compared with the corresponding velocities measured by the DMSP F13 satellite. The comparisons were done for nearly a year (1998) of satellite crossings of the northern polar region (4430 successive crossings). The results indicate that the Weimer [2001] model is able to produce the gross structure in the convection pattern, i.e., it is good in a statistical sense. However, it does not adequately capture the mesoscale spatial structure and convection magnitudes observed by the DMSP satellite. Typically, it was able to capture real (instantaneous) convection features in only about 6% of the satellite crossings. Although empirical convection patterns are invaluable for scientific applications, these results have important implications for using empirical convection models in space weather applications.
A meshless formulation for geodynamic modeling
Authors: Hansen D. L.
Published: November 2003

A meshless continuum formulation is presented. The formulation resembles the element free Galerkin method, where discrete nodes (or particles) are mutually attached via shape functions constructed from moving least squares approximations. No reference to any type of mesh is made. The performance of the present formulation is superior to the performance of other methods in problems involving strain localization, fracture, contact, or extreme deformations. This paper documents the construction of discrete equations as well as continuum‐mechanical details concerning the behavior of ductile as well as brittle solids. In the meshless analysis both Eulerian and Lagrangian shape functions can be applied. Eulerian shape functions are calculated from the nodes' spatial coordinates and are constantly updated. In contrast, the Lagrangian shape functions are calculated from the nodes' convected material coordinates. The Lagrangian shape functions provide the most stable simulations, whereas Eulerian shape functions lead to numerical instabilities. It is demonstrated how the meshless formulation provides an objective framework for studying crustal strain localizations as the meshless method does not suffer from the mesh sensitivity of the finite element method. In addition, examples on applications in fracture and contact problems are given through ductile necking and folding.
Location of long‐period events below Kilauea Volcano using seismic amplitudes and accurate relative relocation
Authors: Battaglia Jean , Got Jean‐Luc , Okubo Paul
Published: December 2003

We present methods for improving the location of long‐period (LP) events, deep and shallow, recorded below Kilauea Volcano by the permanent seismic network. LP events might be of particular interest to understanding eruptive processes as their source mechanism is assumed to directly involve fluid transport. However, it is usually difficult or impossible to locate their source using traditional arrival time methods because of emergent wave arrivals. At Kilauea, similar LP waveform signatures suggest the existence of LP multiplets. The waveform similarity suggests spatially close sources, while catalog solutions using arrival time estimates are widely scattered beneath Kilauea's summit caldera. In order to improve estimates of absolute LP location, we use the distribution of seismic amplitudes corrected for station site effects. The decay of the amplitude as a function of hypocentral distance is used for inferring LP location. In a second stage, we use the similarity of the events to calculate their relative positions. The analysis of the entire LP seismicity recorded between January 1997 and December 1999 suggests that a very large part of the LP event population, both deep and shallow, is generated by a small number of compact sources. Deep events are systematically composed of a weak high‐frequency onset followed by a low‐frequency wave train. Aligning the low‐frequency wave trains does not lead to aligning the onsets indicating the two parts of the signal are dissociated. This observation favors an interpretation in terms of triggering and resonance of a magmatic conduit. Instead of defining fault planes, the precise relocation of similar LP events, based on the alignment of the high‐energy low‐frequency wave trains, defines limited size volumes.
Effects of lateral mixing on the mean state and eddy activity of an equatorial ocean
Authors: Pezzi L. P. , Richards K. J.
Published: December 2003

Numerical experiments are performed using an ocean general circulation model (OGCM) to assess the impact of the form of lateral mixing of momentum and tracers on the state of an equatorial ocean. It is found that the large‐scale structure of both the velocity and temperature fields are very sensitive to the imposed parameterization of lateral mixing in the model. With uniform values for the viscosity and diffusion coefficient across the domain, a decrease in these coefficients increases the activity of tropical instability waves (TIW), resulting in an increase in the sea surface temperature of the cold tongue, and thus overcoming the cold bias often found in ocean models of the equatorial Pacific. However, there is an associated increase in the strength of the Equatorial Under‐Current (EUC) to unrealistic levels. It is found that the strength of the EUC can be limited, while little affecting the TIW activity, by applying an enhanced level of mixing in the vicinity of the equator. This enhanced mixing is used to model the effect of the observed interleaving of water masses across the equator. Both the level and distribution of eddy kinetic energy (associated with TIWs) varies with the level and orientation of the lateral mixing. An examination of the main energy conversion terms of mean to eddy energy reveals that both the barotropic and baroclinic energy conversion terms are important for the production of TIWs. The relative role of each of these conversion terms changes as the lateral mixing is decreased. At low levels of lateral mixing, barotropic instability is found to dominate the production of total eddy energy. Including enhanced mixing at the equator decreases this barotropic production, but surprisingly increases the baroclinic production away from the equator.
A comparative study of O3 formation in the Houston urban and industrial plumes during the 2000 Texas Air Quality Study
Authors: Daum P. H. , Kleinman L. I. , Springston S. R. , Nunnermacker L. J. , Lee Y.‐N. , Weinstein‐Lloyd J. , Zheng J. , Berkowitz C. M.
Published: December 2003

Ozone formation in the Houston area during a period of high ozone concentrations that occurred on 29 August 2000 during the TexAQS 2000 study is examined to understand differences in the sources of O3 precursors and the rate and efficiency of ozone formation over the city of Houston and the industrialized Ship Channel region to the east of Houston. From late morning through late afternoon on 29 August, a period of stagnation occurred, allowing accumulation of O3 and product species separately over downtown Houston and the Houston Ship Channel. Three aircraft flights were made in the region, starting from about 0900 CST and extending to about 1700 CST. A localized plume of high O3 ranging between 120 and 200 ppb was observed over the Ship Channel on all of these aircraft flights. Over the same time period, O3 concentrations over the city were much lower ranging between 40 and 90 ppb. NOx concentrations measured in the two regions in the late morning were roughly the same, but hydrocarbon reactivities over the industrial area were much higher, by as much as a factor of 10. Photochemical box model calculations constrained by observations of NOx, hydrocarbons, O3, and other stable species indicated that the instantaneous ozone formation rate was much lower (3–18 ppb/h) over downtown Houston than it was over the Ship Channel (3–80 ppb/h). The much faster O3 formation rates and higher concentrations observed over the Ship Channel are attributed to the much higher hydrocarbon reactivity, the majority of which was contributed by low molecular weight alkenes. These high hydrocarbon reactivities also caused O3 over the Ship Channel to be produced with much higher efficiency than over urban Houston. Comparison of photochemical product distributions suggests that O3 formation in the urban area is much more hydrocarbon limited than in the Ship Channel, consistent with the geographic distribution of major hydrocarbon sources in the area.
Springtime trans‐Pacific atmospheric transport from east Asia: A transit‐time probability density function approach
Authors: Holzer Mark , McKendry Ian G. , Jaffe Dan A.
Published: November 2003

The atmosphere is known to episodically transport dust, aerosols, and gaseous pollutants from industrialized east Asia, the Gobi desert, and Siberian wild fires to western North America. We give a novel characterization of the climatological springtime transport from these regions and of the probability of transport “events,” that is, long‐range transport of high concentrations with minimal dispersion. Our primary transport diagnostic is the transit‐time probability density function (pdf), , which is a tracer‐independent measure of the flow that allows us to isolate the role of transport from other factors such as source variability and chemistry. The pdf approach, unlike typical back‐trajectory analyses, captures transport due to all possible paths and accounts for both resolved advection and subgrid processes. We use a numerical model of the global atmosphere (Model of Atmospheric Transport and Chemistry (MATCH)) driven by National Centers for Environmental Prediction reananlysis data to establish the springtime statistics of daily averages of . A suitably defined average of quantifies the climatological mass fraction of air from the source region per interval of transit times, or ages. Over the North American west coast, this fraction peaks at transit times of ∼8 days in the upper troposphere (∼6 days later at the surface) for the dust and pollution regions and at 12–14 days for the Siberian region. An analysis of the variability of at fixed transit time allows us to identify transport events and to estimate their probability of occurrence. This is illustrated for transport events to the “Pacific Northwest” (PNW) region of North America, defined as (43.8°–53.3°N) × (115.3°–124.7°W). Correlations between averaged over the PNW and the winds at any point in the atmosphere identify large‐scale anomaly structures of the flow that correspond to favorable transport to the PNW.
A method for analyzing how various parts of clouds influence each other's brightness
Authors: Várnai Tamás , Marshak Alexander
Published: November 2003

This paper proposes a method for obtaining new information on three‐dimensional (3‐D) radiative effects that arise from horizontal radiative interactions in heterogeneous clouds. Unlike current radiative transfer models, it can not only calculate how 3‐D effects change radiative quantities at any given point but can also determine which areas contribute to these 3‐D effects, to what degree, and through what mechanisms. The new method uses Monte Carlo radiative transfer simulations to generate numerous photon trajectories through the cloud field, and then it examines the radiative processes along each trajectory. After describing the proposed method, the paper illustrates its new capabilities both for detailed case studies and for the statistical processing of large data sets. Because the proposed method makes it possible, for the first time, to link a particular change in cloud properties to the resulting 3‐D effect, it can be used to develop new types of radiative transfer parameterizations. Encouraging initial results suggest that such parameterizations will be able to incorporate 3‐D effects in practical applications currently limited to 1‐D theory, such as remote sensing of cloud properties and dynamical cloud modeling.
Earthshine and the Earth's albedo: 1. Earthshine observations and measurements of the lunar phase function for accurate measurements of the Earth's Bond albedo
Authors: Qiu J. , Goode P. R. , Pallé E. , Yurchyshyn V. , Hickey J. , Montañés Rodriguez P. , Chu M.‐C. , Kolbe E. , Brown C. T. , Koonin S. E.
Published: November 2003

We have been making sustained observations of the earthshine from Big Bear Solar Observatory in California since late 1998. We also have intermittent observations from 1994–1995. We have reinvigorated and modernized a nearly forgotten way of measuring the Earth's albedo, and hence its energy balance, previously studied by A. Danjon and his followers for about 25 years early in the last century using their observations of the earthshine from France. This is the first in a series of papers covering observations and simulations of the Earth's reflectance from photometric and spectral observations of the Moon. Here, we develop a modern method of measuring, instantaneously, the large‐scale reflectance of the Earth. From California we see the Moon reflecting sunlight from the third of the Earth to the west of us in our evening (before midnight, which is during the Moon's rising phase) and from the third of the Earth to our east in our morning (after midnight, which is during the Moon's declining phase). We have precisely measured the scattering from the Moon as a function of lunar phase, which enables us to measure, in a typical night's observations, the Earth's reflectance to an accuracy of 2.0% (equivalent to measuring the Earth's emission temperature to ∼0.8 K). We have also identified the lunar phase function as the major source of discrepancy between Danjon's estimates of the albedo and more recent measurements. The albedo is due to the interplay of cloud cover and different landscapes.