bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of lidar measurements of ice clouds at multiple incidence angles
Authors: Noel Vincent , Roy Gilles , Bissonnette Luc , Chepfer Hélène , Flamant Pierre
Published: October 2002

The focus of this paper is the retrieval of the oscillation angle of crystals around the horizontal plane, in low‐level ice clouds, using the lidar depolarization ratio. An ice cloud located between 0.5 and 2.25 km of altitude has been studied. Measurements were taken near Montreal, on February 2nd, 2000, with a 1.06‐μm lidar with scanning capability and dual polarization. The scanning observations show high variations of both backscattering coefficient and depolarization ratio, that are usually associated with horizontally‐oriented crystals. A technique has been developed to retrieve the average crystals oscillation angle: the evolution of the measured lidar depolarization ratio with the lidar beam incidence angle on the cloud is compared with simulations of lidar depolarization ratio computed through ray‐tracing. For the fore mentioned case, the average crystal oscillation angle is estimated to be 12° and the relative quantity of oriented ice crystals in the cloud to be 20%.
Vulnerability of climate on Earth to sudden changes in insolation
Authors: Bendtsen Jørgen , Bjerrum Christian J.
Published: October 2002

The cooling of the Earth after a large sudden change in the solar insolation is buffered by the large heat reservoir in the ocean. For the present day temperature distribution it takes at least one decade to cool down the ocean to the freezing point of seawater. With a simple coupled climate model the influence of the radiative forcing expected to follow an extra‐terrestrial impact or from extensive volcanic activity is determined. We show that the radiative forcing associated with an impact of a similar size to the one which occurred at the K/T‐boundary, has a significant influence on the climate system, and that the outcome of such an impact is critically dependent upon the initial thermal state of the ocean. Ultimately, such an impact could have led to a complete ice‐covered Earth due the combined effect from the decreased insolation and the ice‐albedo feedback.
Northwest Pacific subtropical countercurrent on isopycnal surface in summer
Authors: Chu Peter C. , Li Rongfeng , You Xiaobao
Published: October 2002

A three‐dimensional absolute velocity field on the isopycnal surface in the northwest Pacific subtropical region in the summer is calculated from the Navy's Generalized Digital Environmental Model (GDEM) climatological temperature and salinity data on a 0.5° × 0.5° grid using the P‐vector method. GDEM for the area was built from historical (1930–1997) temperature and salinity profiles. The basic current system, consisting of North Equatorial Current, Kuroshio and its recirculation, Subtropical Countercurrent (STCC), is identified. STCC occurs from the surface to the level of σθ = 25.8 between 18°N and 23.5°N, with a maximum velocity around 0.1 m/s. At σθ = 23.5, STCC originates east of Luzon Strait at around 122.5°E and meanders eastward. As σθ increases, its origin shifts toward northeast. Comparison between velocity and potential vorticity fields leads to the conclusion that the STCC core is above the southern boundary of the subtropical mode water.
Very‐long‐period volcanic earthquakes beneath Mammoth Mountain, California
Authors: Hill David P. , Dawson Phillip , Johnston Malcolm J. S. , Pitt A. M. , Biasi Glenn , Smith Ken
Published: October 2002

Detection of three very‐long‐period (VLP) volcanic earthquakes beneath Mammoth Mountain emphasizes that magmatic processes continue to be active beneath this young, eastern California volcano. These VLP earthquakes, which occurred in October 1996 and July and August 2000, appear as bell‐shaped pulses with durations of one to two minutes on a nearby borehole dilatometer and on the displacement seismogram from a nearby broadband seismometer. They are accompanied by rapid‐fire sequences of high‐frequency (HF) earthquakes and several long‐period (LP) volcanic earthquakes. The limited VLP data are consistent with a CLVD source at a depth of ∼3 km beneath the summit, which we interpret as resulting from a slug of fluid (CO2–saturated magmatic brine or perhaps basaltic magma) moving into a crack
Interactive coupled ensemble: A new coupling strategy for CGCMs
Authors: Kirtman Ben P. , Shukla J.
Published: October 2002

This paper presents a new strategy for coupling state‐of‐the‐art oceanic and atmospheric general circulation models. The procedure is to use multiple realizations of the atmospheric GCM coupled to a single realization of the ocean GCM. The ensemble mean state of the atmospheric GCM fluxes are coupled to the ocean model thereby affecting the evolution of the coupled system. The traditional approach for generating a coupled ensemble is to apply the ensemble averaging to a collection of individual realizations a posteriori. This interactive ensemble technique is distinct from the traditional procedure because here the ensemble mean of the atmospheric models continuously interacts with the ocean model as the coupled system evolves. Simulation experiments with and without the interactive ensemble are described. The interactive ensemble coupled model produces realistic ENSO events that are irregular. This technique also dramatically improves the simulation of the global teleconnection associated with ENSO, and the ENSO‐monsoon relationship.
Correlations among the optical properties of cirrus‐cloud particles: Implications for spaceborne remote sensing
Authors: Reichardt J. , Reichardt S. , Behrendt A. , McGee T. J.
Published: October 2002

Lidar measurements of Arctic (67.9°N) cirrus clouds reveal a strong positive correlation between particle depolarization ratio and extinction‐to‐backscatter (lidar) ratio for ambient cloud temperatures above ∼−45°C, and an anti‐correlation for colder temperatures. Similar correlations are evident in a 2‐year midlatitude (53.5°N) cirrus data set. These data suggest that robust relationships may exist between these particle optical properties that will facilitate the retrieval of cirrus extinction profiles from polarization‐sensitive (spaceborne) elastic‐backscatter lidars.
Competitive adsorption of atmospheric trace gases onto ice at 228 K: HNO3/HCl, 1‐Butanol/Acetic acid and 1‐Butanol/HCl
Authors: Sokolov O. , Abbatt J. P. D.
Published: October 2002

For HNO3/HCl, 1‐butanol/acetic acid and 1‐butanol/HCl, adsorption isotherms have been measured at 228 K in an ice‐coated flow tube with both gases present at pressures between 10−6 and 10−4 torr. For HNO3/HCl, the uptake of each gas is lowered by the presence of the other in the surface saturated regime, but the total surface coverage of adsorbed gases is similar to the coverage of HNO3 adsorbing alone. There is no delay to the onset of the displacement of one adsorbed acid by the other and HNO3 bonds more strongly than HCl. Competition also occurs between 1‐butanol and acetic acid in the saturated regime of their isotherms, but not in a manner consistent with a two‐species Langmuir model. By contrast, 1‐butanol is not affected by the presence of a saturated surface of HCl.
Lunar mare basalt flow units: Thicknesses determined from crater size‐frequency distributions
Authors: Hiesinger H. , Head J. W. , Wolf U. , Jaumann R. , Neukum G.
Published: October 2002

Accurate lava flow unit thicknesses estimates are necessary to place constraints on volcanic flux estimates. We refine the technique of using the shape of crater size‐frequency distribution (CSFD) curves to estimate the thickness of individual lunar mare flow units. We find that a characteristic knee often observed in CSFD curves is reasonably interpreted to represent the presence of two lava flow units separated in time, and that the diameter at which this knee occurs is related to the thickness of the overlying flow unit. Examination of 58 curves with this characteristic knee in several lunar nearside basins (Oceanus Procellarum, Imbrium, Tranquillitatis, Humorum, Cognitum, Nubium, and Insularum) allowed us to identify flow units that have not been detected in low‐sun images. We found that the range of flow unit thickness is ∼20–220 m and the average is ∼30–60 m. This technique expands considerably the ability to assess lava flow unit thicknesses and volumes on the Moon and planets.
Dynamics and longevity of an initially stratified mantle
Authors: Gonnermann Helge M. , Manga Michael , Mark Jellinek A.
Published: October 2002

We performed laboratory experiments of thermochemical convection in order to determine the rate at which an initially density‐stratified, and hence layered, mantle will be homogenized. In the experiments, two layers of fluid with similar viscosities are superposed and heated from below. Initially, in the “stratified” regime, mechanical entrainment into both layers occurs by viscous coupling and theoretical models for the entrainment rate agree well with our experimental data. Over time entrainment and mixing reduce the density difference between the layers until the “doming” regime is reached. The density interface becomes unstable, thermal plumes of the dense fluid penetrate into the overlying layer and the entrainment rate reaches a constant. Applying our results to the Earth's mantle, we confirm that it is possible for a compositionally distinct layer to persist over the age of the Earth, even if the initial density difference is less than 2%.
A systematic spatiotemporal test of the critical point hypothesis for large earthquakes
Authors: Zöller Gert , Hainzl Sebastian
Published: October 2002

The critical point hypothesis for large earthquakes predicts two different precursory phenomena in space and time, an accelerating moment release and the growth of the spatial correlation length. The objective of this work is to investigate both methods with respect to their predictive power. A systematic statistical test based on appropriate random earthquake catalogs allows to quantify the correlations of a precursory pattern with the subsequent mainshock activity. The analysis of target earthquakes in California since 1960 with magnitudes M ≥ Mcut reveals that these correlations increase systematically with growing Mcut, and correlations at greater than 95% confidence are observed for Mcut ≥ 6.5 in the case of the spatial correlation length. In particular, the seismicity patterns are found to be significantly correlated with each of the largest earthquakes (M ≥ 7.0), individually. The acceleration of the moment release has a similar trend, but is less significant.
A new strategy for assimilating SST data for ENSO predictions
Authors: Tang Youmin , Kleeman Richard
Published: October 2002

With a simple 3D Var assimilation scheme, a new strategy for assimilating sea surface temperature (SST) observations has been proposed in this paper. The strategy involves assimilating two proxy data, SST and subsurface thermal data, into the ocean model. An ensemble of predictions for the Niño3 region SST anomalies (SSTA) is performed to validate the new strategy. The results show that the new strategy can effectively improve Niño3 SSTA predictions at all lead times, in particular for lead times over 6 months, and for the predictions of El Niño episodes. The prediction skills of the Niño3 SSTA attained by the new scheme can be as high as those attained by the assimilation of subsurface data and sea level height. Comparisons between two schemes of SST assimilations suggest that the impact of observations on the initializations of ENSO predictions could greatly depend on how the observations were assimilated.
A revised shock time of arrival (STOA) model for interplanetary shock propagation: STOA‐2
Authors: Moon Y.‐J. , Dryer M. , Smith Z. , Park Y. D. , Cho K. S.
Published: October 2002

We have examined a possibility for improvement of the STOA (Shock Time Of Arrival) model for interplanetary shock propagation. In the STOA model, the shock propagating velocity is given by Vs ∼ R−N with N = 0.5, where R is the heliocentric distance. Noting observational and numerical findings that the radial dependence of shock wave velocity depends on initial shock wave velocity, we suggest a simple modified STOA model (STOA‐2) which has a linear relationship between initial coronal shock wave velocity (Vis) and its deceleration exponent(N), N = 0.05 + 4 × 10−4Vis, where Vis is a numeric value expressed in units of km s−1. Our results show that the STOA‐2 model not only removes a systematic dependence of the transit time difference predicted by the previous STOA model on initial shock velocity, but also reduces the number of events with large transit time differences.
Recent trends in hydrologic balance have enhanced the terrestrial carbon sink in the United States
Authors: Nemani Ramakrishna , White Michael , Thornton Peter , Nishida Kenlo , Reddy Swarna , Jenkins Jennifer , Running Steven
Published: October 2002

Climate data show significant increases in precipitation and humidity over the U.S. since 1900, yet the role of these hydro‐climatic changes on the reported U.S. carbon sink is incompletely understood. Using a prognostic terrestrial ecosystem model, we simulated 1900–1993 continental U.S. carbon fluxes and found that increased growth by natural vegetation was associated with increased precipitation and humidity, especially during the 1950–1993 period. CO2 trends and warmer temperatures had a lesser effect. Two thirds of the increase in observed forest growth rates could be accounted for by observed climatic changes, including the confluence of earlier springs and wetter autumns leading to a lengthening of the vegetation carbon uptake period. However, regional differences in precipitation trends produced differing regional carbon sink responses. The strong coupling between carbon and hydrologic cycles implies that global carbon budget studies, currently dominated by temperature analyses, should consider changes in the hydrologic cycle.
Tsunami earthquakes as transient phenomena
Authors: Seno Tetsuzo
Published: October 2002

Recent modeling of tsunami waveforms caused by tsunami earthquakes indicates that fault slip occurred along the subduction boundary close to the trench axis. On the other hand, it is well known that seismicity is generally very low within ca. 50 km from the trench axis, and this has been attributed to the stable frictional sliding properties of the subducted unconsolidated sediments. This makes tsunamigenic slip near the trench difficult to explain. In order to solve this dilemma, I propose that transition from stable sliding to nearly zero friction, with a velocity‐weakening property, occurs as a result of areal increase of zones of elevated fluid pressure, which may make fairly rapid seismic slip possible following the breakage of asperities at normal seismogenic depths. This transition can be identified as seismic reflections with negative polarities, which may help to rate hazards for a coming large tsunami earthquake
Mapping organic coatings on atmospheric particles
Authors: Russell Lynn M. , Maria Steven F. , Myneni Satish C. B.
Published: October 2002

To date there is no direct evidence of the distribution or characteristics of organic compounds in individual particles because techniques for chemically identifying organic compounds are not sufficiently sensitive to detect molecules or functional groups with masses below 10−15 g [Husar and Shu, 1975]. Here we present detailed maps of organic groups (aromatic, alkyl, ketonic carbonyl and carboxylic carbonyl groups) and inorganic ions (potassium, carbonate, calcium) in individual dry particles with diameters ranging from 0.2 to 10 μm using a new technique for aerosol characterization by soft X‐ray spectromicroscopy at atmospheric pressure. The maps show both the compounds present in individual particles and regions of different compositions within particles. The particle compositions on surfaces are enhanced in shorter chain or more oxygenated groups, providing the first observations of surface active carboxylic acids in organic coatings in atmospheric particles.
Climate driven changes in the oxidation pathways of atmospheric sulfur
Authors: Alexander B. , Savarino J. , Barkov N. I. , Delmas R. J. , Thiemens M. H.
Published: October 2002

Ice cores have provided a wealth of information about past atmospheric composition and climate variability. However, relatively little is known about how the chemistry of the atmosphere has responded to natural climate change and anthropogenic influences. The oxygen isotopes (δ17O and δ18O) of sulfate serve as a recorder of the relative amounts of gas and aqueous‐phase oxidation pathways in the atmosphere. This quality, along with its stability, renders sulfate an ideal proxy to investigate changes in oxidation pathways of S(IV) species in present and ancient atmospheres. The oxygen isotopic composition of sulfate in eight samples from the Vostok, Antarctica ice core, covering one full climate cycle, is presented. Assuming tropospheric‐derived sulfate only, isotope data reveal that the ratio of gas‐phase over aqueous‐phase oxidation of S(IV) species was greater during the last glacial than the surrounding interglacial periods.
Global climate sensitivity to land surface change: The Mid Holocene revisited
Authors: Diffenbaugh Noah S. , Sloan Lisa C.
Published: October 2002

Land surface forcing of global climate has been shown both for anthropogenic and non‐anthropogenic changes in land surface distribution. Because validation of global climate models (GCMs) is dependent upon the use of accurate boundary conditions, and because changes in land surface distribution have been shown to have effects on climate in areas remote from those changes, we have tested the sensitivity of a GCM to a global Mid Holocene vegetation distribution reconstructed from the fossil record, a first for a 6 ka GCM run. Here we demonstrate that large areas of the globe show statistically significant temperature sensitivity to these land surface changes and that the magnitude of the vegetation forcing is equal to the magnitude of 6 ka orbital forcing, emphasizing the importance of accurate land surface distribution for both model validation and future climate prediction.
Viscoelastic deformation from North Anatolian Fault Zone earthquakes and the eastern Mediterranean GPS velocity field
Authors: Hearn Elizabeth H. , Hager Bradford H. , Reilinger Robert E.
Published: October 2002

We have modeled linear viscoelastic relaxation of a uniform‐viscosity asthenosphere following large earthquakes in the Aegean‐Anatolian region during the 20th century to evaluate whether this process contributes significantly to the regional velocity field. We address in particular whether southward motion of the Aegean Sea region relative to central Anatolia (and thus extension of western Turkey) can be attributed to a postseismic strain pulse. Our models show that postseismic relaxation of a thick (250 km) viscoelastic substrate cannot generate the observed extension in western Turkey, regardless of the choice of viscosity. We also find that the asthenosphere viscosity must exceed about 5 × 1020 Pa s, at least north of the North Anatolian Fault Zone (NAFZ), to be consistent with low GPS site velocities in the Black Sea region and highly localized strain around the fault.
Power law decay in model predictability skill
Authors: Chu Peter C. , Ivanov Leonid M. , Kantha Lakshmi H. , Melnichenko Oleg V. , Poberezhny Yuri A.
Published: October 2002

Ocean predictability skill is investigated using a Gulf of Mexico nowcast/forecast model. Power law scaling is found in the mean square error of displacement between drifting buoy and model trajectories (both at 50 m depth). The probability density function of the model valid prediction period (VPP) is asymmetric with a long and broad tail on the higher value side, which suggests long‐term predictability. The calculations demonstrate that the long‐term (extreme long such as 50–60 day) predictability is not an "outlier" and shares the same statistical properties as the short‐term predictions.
Observations of circulation and coastal exchange characteristics in southern Lake Michigan during 2000 winter season
Authors: Rao Y. R. , Murthy C. R. , McCormick M. J. , Miller G. S. , Saylor J. H.
Published: October 2002

Intermittent satellite images collected over in the last few years have revealed episodic late winter‐spring plumes coinciding with northerly storms in southern Lake Michigan. A major inter‐disciplinary observational program was initiated to study the importance of these episodic events on nearshore‐offshore transport and the subsequent ecological consequences. In this paper, high density observations of winds and currents made during the winter of 2000 are analyzed to study the variability of the coastal circulation and the physical mechanisms resulting in the alongshore and cross‐shore transport in the lake. The measurements of currents show the signature of forced two‐gyre circulation in the southern basin. During northerly storm episodes the combination of directly wind forced currents and northward propagating vorticity wave generate significant offshore transport in this region.
Heterogeneous and catalytic uptake of ozone on mineral oxides and dusts: A Knudsen cell investigation
Authors: Michel A. E. , Usher C. R. , Grassian V. H.
Published: October 2002

The uptake of ozone on various mineral powders has been studied using a Knudsen cell apparatus at T = 296 K. Samples included α‐Al2O3, α‐Fe2O3, SiO2, China loess and Saharan sand. Reactive uptake coefficients, γBET, were measured for the various particles and found to be 8 ± 5 × 10−5 for α‐Al2O3, 1.8 ± 0.7 × 10−4 for α‐Fe2O3 and 5 ± 3 × 10−5 for SiO2. The authentic dust samples were found to have γBET values of 2.7 ± 0.9 × 10−5 for China loess and 6 ± 3 × 10−5 for Saharan sand. Variations in the reactivity of the Saharan sand were observed as a function of sample treatment. Under the conditions of this study, heterogeneous uptake of ozone is catalytic and results in the destruction of ozone.
Airborne Lidar and in‐situ Aerosol Observations of an Elevated Layer, Leeward of the European Alps and Apennines
Authors: Nyeki S. , Eleftheriadis K. , Baltensperger U. , Colbeck I. , Fiebig M. , Fix A. , Kiemle C. , Lazaridis M. , Petzold A.
Published: October 2002

An elevated layer was observed during airborne lidar and in‐situ aerosol measurements, leeward of the European Alps and Apennine mountains. The layer was encountered during the Mesoscale Alpine Program (MAP) in autumn 1999, and extended >200 km at an altitude ∼4100 m asl over the northern Adriatic sea. Detailed meteorological analysis suggested that mountain venting followed by advection was responsible for formation of the layer. Evidence for particle nucleation was found in six profiles, and was associated with regions of cloud outflow. Despite determination of the average aerosol mass concentration within the layer (∼1.8 (SO4) μg m−3), an estimate of export to the free troposphere was complicated by the complex structure of the planetary boundary layer.
Solar Wind Variations Related to Fluctuations of the North Atlantic Oscillation
Authors: Boberg Fredrik , Lundstedt Henrik
Published: October 2002

A study on a possible solar wind interaction with the North Atlantic Oscillation (NAO) is performed. Results are presented suggesting a relationship between the NAO index and the electric field strength E of the solar wind. A possible scenario for the suggested interaction is that an electromagnetic disturbance is generated by the solar wind in the global electric circuit of the ionosphere. This disturbance is then dynamically propagating downward through the atmosphere and subsequently influencing the large‐scale pressure system in the North Atlantic region. A relationship is also evident on longer time‐scales when using the group sunspot number as a proxy for the solar wind.
Effective electrical conductivity of 3‐D heterogeneous porous media
Authors: Hautot Sophie , Tarits Pascal
Published: October 2002

The relationship between the physical properties and the effective electrical conductivity of porous structures is studied using three‐dimensional (3‐D) models of random porosity. Synthetic electric (DC) and electromagnetic (EM) field data are calculated for a 3‐D electrical conductivity model with a random porosity p (p = 2 − 70%) embedded in a homogeneous half‐space. The effective conductivity of the random porosity model is obtained from inversion of the synthetic data and agrees with a modified Archie's law. We applied percolation theory to our random porosity model to explain the variation of effective conductivity with p. We found that EM and DC data do not provide the same effective conductivity at a particular porosity but they do provide the same volume fraction of interconnected conductive elements. This volume fraction depends on the percolation threshold pc. It follows a law of the form ∼p above pc and ∼p2.2 below pc.
Observed reductions of surface solar radiation at sites in the United States and worldwide from 1961 to 1990
Authors: Liepert Beate G.
Published: October 2002

Surface solar radiation revealed an estimated 7 W/m2 or 4% decline at sites worldwide from 1961 to 1990. Here I find that the strongest declines occurred in the United States sites with 19 W/m2 or 10%. The clear sky optical thickness effect accounts for −8 W/m2 and the cloud optical thickness effect for −18 W/m2 in three decades. If the observed increases in cloud cover frequencies are added to the clear sky and cloud optical thickness effect, the higher all sky reduction in solar radiation in the United States can be explained. It is shown that solar radiation declined below cloud‐free sky because of the reduction of the cloud‐free fraction of the sky itself and because of the reduction of clear sky optical thickness. Solar radiation exhibits no significant changes below cloud‐covered sky because reduced cloud optical thickness is compensated by increased frequencies of hours with overcast skies.
First deep seismic reflection images of the Eastern Alps reveal giant crustal wedges and transcrustal ramps
Authors:   TRANSALP Working Group, Gebrande Helmut , Lüschen Ewald , Bopp Michael , Bleibinhaus Florian , Lammerer Bernd , Oncken Onno , Stiller Manfred , Kummerow Jörn , Kind Rainer , Millahn Karl , Grassl Herfried , Neubauer Franz , Bertelli Luca , Borrini Daniela , Fantoni Roberto , Pessina Camillo , Sella Mattia , Castellarin Alberto , Nicolich Rinaldo , Mazzotti Alfredo , Bernabini Marcello
Published: October 2002

The Alps are considered as a classical example for an orogen created by continental plate collision. In this study we present new images obtained from deep seismic reflection profiling in the Eastern Alps between Munich and Venice which give rise to examine and revise existing concepts. The seismic sections exhibit a prominent bi‐verging reflection pattern at crustal scale. A major ramp‐like structure, outcropping at the Inn‐Valley fault, can be traced southward over 80 km into the mountain root where relics of the subducted Penninic ocean are expected. New models of the evolution of the Eastern Alps show an upper/lower crustal decoupling along transcrustal thrust faults with opposite thrust directions of both the European and the Adriatic‐African continents.
Relationship between the planetary‐scale circulation over East Asia and the intensity of the South Asian Summer Monsoon
Authors: Xu Jianjun , Chan Johnny C. L.
Published: October 2002

By partitioning the monthly mean horizontal winds at various tropospheric levels into the vertical mean and vertical shear components, the kinetic energy of the shear flow (Ks) averaged between June and September within the box (40°–100°E, 0–20°N) is found to be strongly related to the South Asia summer monsoon (SASM), and is therefore defined as the SASM index (SASMI) to represent the intensity of the SASM. When the value of the SASMI is large, positive (negative) temperature anomalies are found over the Asian landmass (Indian Ocean). This gives rise to an above‐normal north‐south land‐sea temperature gradient. As a result, low‐level southwesterlies extend all the way from the Indian sub‐continent to the Philippines, which result in a monsoon trough over south China. The southerlies to the north of this trough converge with the northerlies in the midlatitudes over northern China to form a monsoon frontal trough.
Evidence of the Gulf Stream's influence on tropical cyclone intensity
Authors: Bright Robert J. , Xie Lian , Pietrafesa Leonard J.
Published: October 2002

Historical storm data and satellite imagery are analyzed to determine the intensity changes and storm‐related characteristics of 53 coastal and landfalling tropical cyclones (TCs) from Florida to North Carolina that passed over the Gulf Stream (GS) during the period 1944–2000. It appears that less intense storms (Category 2 or weaker), as well as those occurring earlier in the Atlantic hurricane season, are more likely to be strengthened by the GS. In addition, 81% of the Category 2 or weaker storms that intensified based on both maximum wind speed (MWS) and minimum central pressure (MCP) had tracks approximately parallel to the GS, while 3 of the 5 major (Category 3–5) hurricanes that intensified based on both MWS and MCP tracked perpendicular to the GS. The presence of an upstream mid‐latitude trough could have contributed to the intensification of the weaker TCs by steering them along the GS.
Thermal evidence of water exchange through a coastal aquifer: Implications for nutrient fluxes
Authors: Moore Willard S. , Krest James , Taylor Glenn , Roggenstein Edward , Joye Samantha , Lee Rosalynn
Published: October 2002

We report the discovery of a semi‐confined, high permeability zone (HPZ) 2 meters below the sea bed where exchanges between coastal aquifers and the ocean occur. A temperature probe placed in the HPZ recorded a 1°C semidiurnal cycle. The cycle was in phase with the tide, indicating tidal pumping was driving water exchange through the HPZ. We use these temperature variations to quantify water exchange between the HPZ and the ocean. Water in the HPZ is enriched in nutrients and radium; both total dissolved nitrogen and phosphorus correlate strongly with dissolved 226Ra. We use these correlations and previously quantified subterranean fluxes of 226Ra to demonstrate that this system may be a significant source of nutrients to the coastal ocean.
Elastic wave propagation along a set of parallel fractures
Authors: Nakagawa Seiji , Nihei Kurt T. , Myer Larry R.
Published: October 2002

Previous studies on elastic wave propagation in fractured media have demonstrated that a single planar fracture supports fracture interface waves and that two plane parallel fractures support fracture channel waves. Here, the results are presented for plane wave propagation through an infinite number of plane parallel fractures with equal fracture spacing and fracture stiffnesses. Analysis of the dispersion equations for this fractured system demonstrates that these waves exhibit symmetric and antisymmetric particle motions, degenerate to classical Rayleigh‐Lamb plate waves when the fractures are completely open, and possess dispersive velocities that are functions of both the fracture stiffness and spacing. Time‐frequency analysis performed on a series of laboratory ultrasonic transmission measurements on a fractured rock analog shows good agreement with the theoretical predictions.
Deconvolution of u‐channel paleomagnetic data near geomagnetic reversals and short events
Authors: Guyodo Yohan , Channell James E. T. , Thomas Ray G.
Published: October 2002

The deconvolution scheme of Oda and Shibuya [1996], designed for half‐core data from the pass‐through magnetometer aboard the Joides Resolution, has been adapted for treatment of u‐channel data. The program was tested using u‐channels from Ocean Drilling Program (ODP) Site 1090. A significant increase in resolution of the u‐channel data can be achieved by deconvolution, resulting in data comparable with that obtained by continuous discrete sampling. Large amplitude changes of the magnetization vector revealed by the deconvolution treatment are in good agreement with the results obtained on discrete samples extracted from the same u‐channels. Application of this procedure to u‐channel data from ODP Sites 983 and 984, over a short time interval around 1.255 Ma, permitted enhanced definition of the so‐called Bjorn geomagnetic event.
Modification of the electron density profile near the upper hybrid layer during radio wave heating of the ionosphere
Authors: Gondarenko N. A. , Guzdar P. N. , Milikh G. M. , Ossakow S. L.
Published: October 2002

High frequency (HF) radio waves can modify the electron density profile of the ionosphere in the upper hybrid resonance region (UHR). The spatial and temporal development of this modification was investigated using a multi‐frequency Doppler diagnostic system at the TROMSØ facility [Lobachevsky et al., 1992]. We present the results of the simulations of the density profile modification near the upper hybrid resonance height for the parameters relevant to the experiment and show that the spatio‐temporal development of the density modification is quantitatively modelled by the mode conversion and the radio wave heating.
Dynamical reconstruction of the record low column ozone over Europe on 30 November 1999
Authors: Allen Douglas R. , Nakamura Noboru
Published: October 2002

The assembly of the record‐low total column ozone observed over Europe on 30 November 1999 is investigated using a three‐dimensional reconstruction based on POAM, SAGE, and HALOE data and a passive tracer advected by UKMO winds on isentropic surfaces. The reconstruction reproduces TOMS observation to within 10–20 DU over the northern hemisphere and agrees well with select ozonesonde profiles in the mid‐ to high latitudes, although values in the vicinity of the ozone minimum are systematically higher than TOMS. Relative role is quantified for the disparate dynamical processes that contributed constructively to the low‐ozone episode: poleward intrusion of ozone‐poor subtropical air in the lowermost stratosphere, adiabatic lifting of ozone maximum, and displacement of ozone‐poor Arctic vortex air aloft. Of these, the first two are found to account for about three quarters of the reconstructed column anomaly between 320 and 1900 K whereas the last for about one quarter.
Dark slope streaks on Mars: Are aqueous processes involved?
Authors: Ferris J. C. , Dohm J. M. , Baker V. R. , Maddock T.
Published: October 2002

Concentrations of dark slope streaks occur in the equatorial latitudes of Mars, mostly where magmatic‐driven activity dominates the geologic record. Although originally ascribed to wet debris flows, all the most recent published hypotheses concerning these features focus on processes which disturb a brighter dusty mantle to expose a darker substrate. These mechanisms invoke dry mass wasting or eolian processes, excluding a role for water. In light of the geographic, geologic, and morphologic considerations, and the new information provided from the Mars Orbital Camera and the Mars Orbital Data Altimeter, we reexamine fluvial processes as a viable explanation for some of the dark slope streaks. In our opinion, two contrasting processes for the formation of dark slope streaks, dust avalanching and spring discharge, represent endpoints on a continuum of progenitors. It may be that some of these features result from dry mass wasting or eolian processes, some from fluvial processes, and some from a mechanism(s) not yet conceived. A spring discharge origin for the formation of the dark slope streaks has profound implications, including Mars having limited, but currently active, fluvial processes acting upon its surface, as well as near‐surface aquifers.
Is Tropical Atlantic Variability driven by the North Atlantic Oscillation?
Authors: Wu Lixin , Liu Zhengyu
Published: October 2002

The role of the North Atlantic Oscillation (NAO) on the genesis of the Tropical Atlantic Variability (TAV) is studied in a coupled ocean‐atmosphere general circulation model using two modeling approaches of partial coupling and partial blocking. It is found that the NAO is not a necessary precondition for the genesis of the TAV although it can enhance climate variability in the tropical North Atlantic significantly via extratropical‐tropical teleconnections. Instead, local ocean‐atmosphere interaction plays a dominant role for the full development of TAV. Our results do not rule out the possible influence of ENSO on TAV.
Irrigation's influence on precipitation: Texas High Plains, U.S.A.
Authors: Moore Nathan , Rojstaczer Stuart
Published: October 2002

Using bias‐corrected Nexrad precipitation estimates and spatial statistics of rainfall intensity, we examine the influence of irrigation on summer precipitation in the Texas High Plains. In this region, human alteration of the surface water and energy balance has been extreme. Irrigation enhances precipitation downwind, yielding storms of greater duration, length, and accumulation. Irrigation water is not a significant source of moisture feeding precipitation; rather, the cool, wet surface increases low‐level instability, triggering storms. We estimate that an additional 6% to 18% of summer precipitation attributable to irrigation falls ∼90 km downwind of the irrigated region.
Composition measurements above the Southern Solar Polar Region around the solar activity maximum by the Ulysses COSPIN/LET instrument
Authors: Hofer M. Y. , Marsden R. G. , Sanderson T. R. , Tranquille C.
Published: October 2002

In November 2000, during the second southern polar passage (SPP), the Ulysses spacecraft reached its highest heliographic latitude (80.2°) at a solar radial distance of ∼2.27 AU. The first SPP in 1994 took place as the level of solar activity was approaching the minimum between the cycles 22 and 23. The recent high‐latitude observations during the second SPP in 2000/2001 correspond to near‐maximum activity conditions with a large number of transient phenomena. These heliospheric conditions are reflected in the energetic particle composition data covering the energy range 4–20 MeV/n recorded by the COSPIN/‐LET instrument. Most of the particles observed at high heliographic latitudes had their origin in solar energetic particle events. Furthermore, the results suggest coronal mass ejection‐driven shock acceleration of coronal material as the source.
Subsidence at Kiska Volcano, Western Aleutians, detected by satellite radar interferometry
Authors: Lu Zhong , Masterlark Tim , Power John , Dzurisin Daniel , Wicks Charles
Published: October 2002

Sequential interferometric synthetic aperture radar images of Kiska, the westernmost historically active volcano in the Aleutian arc, show that a circular area about 3 km in diameter centered near the summit subsided by as much as 10 cm from 1995 to 2001, mostly during 1999 and 2000. An elastic Mogi‐type deformation model suggests that the source is within 1 km of the surface. Based on the shallow source depth, the copious amounts of steam during recent eruptions, and recent field reports of vigorous steaming and persistent ground shaking near the summit area, we attribute the subsidence to decreased pore‐fluid pressure within a shallow hydrothermal system beneath the summit area.
En echelon ridge and trough structures on Europa
Authors: Michalski Joseph R. , Greeley Ronald
Published: October 2002

Europa's surface is tectonically and morphologically complex. Europan ridges, bands, ridged bands, double ridges, complex ridges, and troughs are collectively referred to as lineaments. Some lineaments are fault zones and exhibit sets of en echelon ridge and trough structures (EERTS). EERTS can be used to interpret the stress field in which the lineaments formed. These observations suggest that some lineaments at low latitudes initially formed as shear zones, rather than as purely tensional fractures as is commonly assumed. From stepping directions of EERTS and the offset directions of the lineaments in which they occur, we infer that some EERTS form as a result of compressional stress and others form as a result of tensional stress. EERTS that are inferred to form in compression are morphologically indistinguishable from EERTS that form in tension. The presence of tensional EERTS may support a diapiric origin for some ridges.
Age‐dependent seismic thickness and mechanical strength of the Australian lithosphere
Authors: Simons Frederik J. , van der Hilst Rob D.
Published: October 2002

We present constraints on the regional variations of the seismic and mechanical thickness of the Australian lithosphere. We infer the seismic thickness from a waveform tomographic model of S‐wave speed, and as a proxy for the elastic thickness we use the wavelength at which the coherence of surface topography and Bouguer gravity drops below half of its long‐wavelength maximum. Our results show that on scales <1000 km the relationship between the age of the crust and the thickness of the lithosphere is more complicated than longer‐wavelength or global averages suggest. Recent geochemical and geodynamical evidence for small‐scale secular variations of the composition and stability of continental cratons further illustrates the complexity of the age dependence of seismo‐mechanical lithospheric properties on regional scales.
Influence of the El Niño‐La Niña cycle on satellite‐derived primary production in the California Current
Authors: Kahru Mati , Mitchell B. Greg
Published: October 2002

Time series of phytoplankton net primary production (NPP) for the California Current were derived using satellite data and the VGPM primary productivity model for a 5‐year period (1997–2001) including the 1997–98 El Niño. NPP had a strong annual periodicity correlated with the El Niño‐La Niña cycle. The most obvious effects of the El Niño on NPP were 100‐300 km off the coast: a reduction by 30% off Southern California but an increase by 40% off Baja California. During its peak El Niño decreased NPP by 10–15% (1.5 Tg C month−1) in the 1000‐km band off Southern California but increased by 20–30% off Northern and Southern Baja (4 Tg C month−1). The total annual NPP was lowest during the El Niño years of 1997–1998 and peaked in 2000. Trends of increasing NPP and zooplankton volume were observed off Central and Southern California.
Ambient light emission from hydrothermal vents on the Mid‐Atlantic Ridge
Authors: White Sheri N. , Chave Alan D. , Reynolds George T. , Van Dover Cindy L.
Published: October 2002

A spectral imaging camera was used to observe light emission from high‐temperature, deep‐sea vents at three hydrothermal sites on the Mid‐Atlantic Ridge (MAR): Logatchev, Snake Pit, and Lucky Strike. Ambient light measured at these sites is similar to that observed at sites along the East Pacific Rise and the Juan de Fuca Ridge, with components from both thermal and non‐thermal sources. The shrimp species Rimicaris exoculata, which is found on the MAR but not in the Eastern Pacific, possesses a unique photoreceptor capable of detecting low light levels. It is not yet known if R. exoculata “sees” vent light. However, since the characteristics of vent light appear to be unrelated to geographical location, the exclusion of R. exoculata from the Eastern Pacific is probably unrelated to differences in ambient light conditions.
Three‐dimensional P‐wave velocity structure of Iwate volcano, Japan from active seismic survey
Authors: Tanaka S. , Hamaguchi H. , Nishimura T. , Yamawaki T. , Ueki S. , Nakamichi H. , Tsutsui T. , Miyamachi H. , Matsuwo N. , Oikawa J. , Ohminato T. , Miyaoka K. , Onizawa S. , Mori T. , Aizawa K.
Published: October 2002

The three‐dimensional P‐wave velocity structure of the Iwate volcano, northeastern Japan, is determined to depths of 2 km through an active seismic survey conducted in October 2000. Seismic tomography is applied to approximately 2700 travel‐time data. The most prominent discovery is an existing of column‐like high‐velocity body (Vp > 5.4 km/s) that extends vertically for 2 km beneath the caldera. While the western part of the volcano extending from the caldera is characterized by a moderate‐velocity region (4.8 < Vp < 5.4 km/s), the summit and eastern flank of the volcano are covered with very low‐velocity material (Vp < 4 km/s) which represent relatively younger volcanic edifices. The spatial difference in the velocity structures between the western and eastern parts of the volcano is explained by the evolutionary history of the volcano. And we find that the western structure may give constraints on the volcanic activity in 1998.
Tidal effects on submarine groundwater discharge into the ocean
Authors: Taniguchi Makoto
Published: October 2002

Semi‐monthly, diurnal and semi‐diurnal variations of Submarine Groundwater Discharge (SGD) were found in Osaka bay, Japan, by continuous measurements of SGD using newly developed automated seepage meters. SGD increased sharply from neap to spring tide with semi‐monthly period. SGD also changes with diurnal and semi‐diurnal periods due to changes in hydraulic gradient between the groundwater and seawater in the coastal zone. SGD variations with semi‐monthly period by neap‐spring tidal pumping is much larger than those with diurnal and semi‐diurnal variations by tidal height changes.
Potential causes of abrupt climate events: A numerical study with a three‐dimensional climate model
Authors: Goosse H. , Renssen H. , Selten F. M. , Haarsma R. J. , Opsteegh J. D.
Published: October 2002

A multi‐millennia simulation performed with a three‐dimensional climate model under constant forcing shows abrupt climate events lasting for several centuries caused by a spontaneous transition to an infrequently visited state of the oceanic thermohaline circulation. This state is characterized by a more southern location of the main area of deep ocean convection in the North Atlantic and implies a large cooling in the mid and high latitudes of the northern hemisphere. This transition of the thermohaline circulation occurs spontaneously less than once in 5000 years in the model, but such transitions can also be triggered by a reduction of the solar irradiance.
Crustal structure of the Chicxulub Impact crater imaged with magnetotelluric exploration
Authors: Unsworth Martyn , Enriquez Oscar Campos , Belmonte Salvador , Arzate Jorge , Bedrosian Paul
Published: October 2002

The electrical resistivity structure of the Chicxulub Impact crater has been imaged using broadband magnetotelluric exploration. A 1–2 km thick sequence of conductive Tertiary sedimentary rocks was imaged within the crater. The shallow resistivity of this layer increases across the cenote ring. This is primarily due to a decrease in porosity, although the groundwater composition may have some effect. While this layer reduces the sensitivity of MT, several features can be discerned beneath it. In the center of the crater the structural high is imaged as a region of high resistivity. In the outer part of the crater, lower resistivities in the upper crust may be due to mineralization or hydrothermal alteration.
Relating inferred HNO3 flux values to the denitrification of the 1999–2000 Arctic vortex
Authors: Northway Megan J. , Popp Peter J. , Gao Ru‐Shan , Fahey David W. , Toon Geoff C. , Bui T. Paul
Published: October 2002

Extensive populations of large HNO3‐containing particles were observed in situ in the 1999–2000 Arctic winter vortex. Assuming nitric acid trihydrate (NAT) composition, the associated values of instantaneous gravitational flux of HNO3 are between 1·108 and 5·1010 molec cm−3 km day−1 and are the largest ever derived from in situ measurements. The relationship between these observed populations and observed denitrification in the 1999–2000 Arctic vortex is developed using constraints of NAT formation and sedimentation. This analysis of the 1999–2000 winter provides a useful guide to interpreting future observations of polar stratospheric clouds and denitrification in the polar regions.
Trying to bring the magnetopause to a standstill
Authors: De Keyser J. , Darrouzet F. , Roth M.
Published: October 2002

Satellite observations of the magnetospheric boundary (magnetopause and boundary layer) show it to be a very dynamic place, in part due to boundary motion. We present a straightforward technique for identifying boundary motion and for recovering magnetopause and boundary layer structure in a reference frame that comoves with the boundary, that is, a frame in which it is at a standstill.