bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of inner core rotation and obliquity on the inner core wobble and the free inner core nutation
Authors: Guo Jun‐Yi , Ning Jin‐Sheng
Published: October 2002

The inner core wobble and the free inner core nutation are studied. A simple Earth model is adopted to derive all the results analytically. As new results over earlier work, the formulas of the frequencies of these two modes taking into account of the rotation rate and the obliquity of the inner core relative to the mantle are obtained. The formula for the inner core wobble is also used to study the inner core rotation relative to the mantle under some other assumptions.
A local, crossing‐path study of attenuation and anisotropy of the inner core
Authors: Helffrich George , Kaneshima Satoshi , Kendall J.‐M.
Published: October 2002

We report results from studying a region under the north Pacific using 46 ray paths along east‐west and north‐south directions to study the nature of inner core anisotropy, and find an anisotropy signal in differential PKPBC–PKPDF at about the resolution of the data, with north‐south paths faster than east‐west, but no dependence of attenuation on wavespeed or depth in this part of the inner core. Inner core Q is 130−52+255 between 140–340 km depth. The observations also provide constraints on the degree of homogeneous meridional anisotropy possibly present in the core, to between 0.1 and 0.6% velocity differences in the fast and slow directions, significantly smaller than the 2–4% axi‐symmetric anisotropy in the inner core. The small meridional component to anisotropy argues against significant contributions to anisotropy from low‐order inner core convection or stresses imposed on the inner core by the outer core field.
Analysis of local seismo‐acoustic events in the Korean Peninsula
Authors: Il‐Young Che , Jun Myung‐Soon , Jeon Jeong‐Soo , Min Kyung Duck
Published: October 2002

In order to discriminate between man‐made explosions and earthquakes, a preliminary seismo‐acoustic analysis was performed in the Korean Peninsula from August 1999 to December 2000. During this time, 202 seismo‐acoustic events were identified as blasts. These events were concentrated in specific regions: a rock quarry, an open‐pit mine and a construction site, which were identified by field survey. All of these events occurred within 200 km of a seismo‐acoustic array. We applied ray‐tracing methods to the atmosphere using local meteorological observations to understand the short‐distance propagation characteristics of infrasonic signals. Calculated infrasonic traveltime using a local meteorological model fits well with observed traveltime from a quarry. Local winds make possible infrasonic wave ducts in the lower atmosphere, and allow infrasonic wave arrival at short distances. Ray tracing using a local meteorological model has been used for the association between seismic and infrasonic signals.
Implications of iodine chemistry for daytime HO2 levels at Rishiri Island
Authors: Kanaya Yugo , Yokouchi Yoko , Matsumoto Jun , Nakamura Kenji , Kato Shungo , Tanimoto Hiroshi , Furutani Hiroshi , Toyota Kenjiro , Akimoto Hajime
Published: October 2002

The observed midday maximum in the mixing ratio of HO2 at Rishiri Island in June 2000 was ∼10 pptv, but photochemical box model simulations overpredicted HO2 at this location by an average of 70%. This overestimation was significant only when the mixing ratio of NO was lower than 300 pptv, and was coincident with overprediction of the NO/NO2 ratio. We detected several organoiodines, presumably emitted from seaweeds, and propose the presence of the IO radical. IO could reduce HO2 mixing ratios via the formation of HOI that may subsequently be scavenged by aerosols or lost by photolysis and may also convert NO to NO2 directly. Model calculations with known iodine chemistry could reproduce the observed HO2 with 12–25 pptv of IO. Although iodine chemistry is unlikely to explain the entire discrepancy in HO2, several pptv of IO could significantly reduce HO2 mixing ratios and NO/NO2 ratios.
A global view of bio‐physical coupling from SeaWiFS and TOPEX satellite data, 1997–2001
Authors: Wilson Cara , Adamec David
Published: October 2002

Vertical fluxes of nutrient‐rich water from below the nutricline to the ocean surface can be a limiting factor affecting surface chlorophyll, and the depth of the nutricline plays an important role in the regulation of surface productivity. Because subsurface nutrient data is less available than physical oceanographic data, satellite chlorophyll (SC) data has been compared to satellite sea‐level anomalies (SLA), because SLA largely reflects changes in the thermocline depth, and the thermocline and nutricline are often colocated. Here global correlations between 46 months of TOPEX SLA and SeaWiFS SC are examined. These two measurements are predominately negatively correlated as smaller SLA implies a shallower thermocline/nutricline, which will increase the surface nutrient flux and increase phytoplankton concentrations. However, there are large areas in all ocean basins where the correlations suggest that SC are affected by processes other than thermocline depth changes.
Subcratonic low‐velocity layer and flood basalts
Authors: Vinnik Lev , Farra Veronique
Published: October 2002

Teleseismic recordings of several seismograph stations are processed with the aid of the S receiver function technique [Farra and Vinnik, 2000]. The data provide evidence of a strong reduction of S velocity at a depth around 360 km (station BOSA) and 280–300 km (station LBTB) in the East of southern Africa. A similar feature is found in the Tunguska basin of the Siberian platform from the recordings of station NRIL. In both regions large volumes of flood basalts have been erupted 190–180 Ma and 250 Ma ago, respectively. The coincidence suggests a causal relation between the two phenomena. This relation implies that the low‐velocity anomalies migrate with the plates.
Dispersive and repetitive Pc5 mode microinjections in the inner magnetosphere
Authors: Sarafopoulos D. V.
Published: October 2002

Dispersive fluxes of energetic electrons with a period of 4 min are identified in the morning sector of the inner plasma sheet and have been measured via the Interball/DOK‐2 instrument. These fluxes are termed “repetitive microinjections” because, as we establish, each microinjection constitutes an individual entity that exhibits energy dispersion like the classical substorm‐associated injections. We suggest that these repetitive dispersions are produced from a wavy isospectrum surface, such as a meandering injection boundary near the Earth, combined with a radially outward gradient of energetic electrons. The Greenland ground station magnetometers, at local times similar to that of Interball, record intense Pc5 pulsations with 4 min period and peak‐to‐peak amplitudes of up to 80 nT. We speculate that the Pc5 pulsations are produced by small‐scale Birkeland currents that propagate along the magnetic field lines and have been supplied from small‐scale vortices in the plasma sheet.
Prospects for decadal prediction of the North Atlantic Oscillation (NAO)
Authors: Eden Carsten , Greatbatch Richard J. , Lu Jian
Published: October 2002

For certain, but realizable, states of the thermohaline and wind driven circulation of the North Atlantic Ocean, we demonstrate the possibility of making statements regarding the likely range of values to be taken by the annual average of the NAO‐index on time scales out to a decade. Given that the North Atlantic is currently in such a predictable state, a simple surrogate model yields a prediction that the NAO index is more likely to be positive than negative for the next couple of years, followed by several years in which the NAO index is more likely to be negative.
Ocean color variability in the Tasman Sea
Authors: Tilburg Charles E. , Subrahmanyam Bulusu , O'Brien James J.
Published: October 2002

The Tasman Sea contains the largest noncoastal surface chlorophyll‐a concentrations within the South Pacific Ocean. Observations of ocean color from SeaWiFS demonstrate that the chlorophyll‐a seasonal cycle is characterized by a large austral spring bloom and a much smaller fall bloom separated by periods of lower concentrations, typical of communities within the North Atlantic Ocean. However, the seasonal cycle of the mixed layer depth of the Tasman Sea is much more similar to the North Pacific Ocean, whose persistent winter stratification results in relatively constant chloropohyll‐a concentrations. Examination of eddy kinetic energy from satellite altimetry (TOPEX/Poseidon and ERS‐2 blended product) reveals that the western Tasman Sea contains a large number of eddies originating within the East Australian Current that coincide spatially with the blooms. Upwelling and downwelling associated with these eddies greatly increase vertical mixing within the upper ocean, offsetting the normally shallow winter mixed layer, which leads to a chlorophyll‐a seasonal cycle much like that of the North Atlantic Ocean.
Warming, salting and origin of the Tyrrhenian Deep Water
Authors: Fuda J.‐L. , Etiope G. , Millot C. , Favali P. , Calcara M. , Smriglio G. , Boschi E.
Published: October 2002

Data collected from 1996 to 2001 down to 3,500 m in the Tyrrhenian sub‐basin with ship‐handled and moored instruments show 5‐year T and S trends (0.016 °C/yr, 0.008/yr) that are the largest ever evidenced in Mediterranean deep waters. This is not consistent with the usual hypothesis that Tyrrhenian Deep Water (TDW) is a mixture of eastern water flowing from the Sicily Channel and western water flowing from the Sardinia Channel partly since both are reported to encounter lower trends. We argue that TDW might result from a dense water formation process occurring within the Tyrrhenian itself, in a region never reported up to now, east of the Bonifacio Strait. Whatever the validity of our hypothesis, climatic changes are occurring in the whole sea and are efficiently specified with long time series.
Towards a reliable GCM estimation of contrail radiative forcing
Authors: Marquart Susanne , Mayer Bernhard
Published: October 2002

Selected results of the ECHAM4 general circulation model are compared with sophisticated radiative transfer model calculations in order to investigate the performance of the ECHAM4 radiation schemes with respect to the radiative forcing (RF) of contrails. The mean shortwave RF is found to be in accordance with radiative transfer model results. For the longwave part it is shown that the effective emissivity approach combined with the assumption of maximum‐random cloud overlap used in the standard ECHAM4 leads to a considerable underestimation of the longwave contrail RF. Hence, this approach cannot be recommended for calculating the longwave RF of optically thin clouds in general. As an alternative, more adequate results of a modified version of the ECHAM4 longwave scheme are discussed.
Entropy, energy, and proximity to criticality in global earthquake populations
Authors: Main Ian G. , Al‐Kindy Fahad H.
Published: October 2002

We examine the question of proximity of the global earthquake population to the critical point characterised by the energy E and entropy S based on annual frequency data from the Harvard CMT catalogue. The results are compared with a theoretical model corresponding to a Boltzmann probability density distribution of the form p(E) ∝ E−B−1e−E/θ. The data are consistent with the model predictions for fluctuations in the characteristic energy θ at constant B value, of the form S∼B〈lnE〉. This approximation is valid for large θ, relative to the maximum possible event size, confirming that the Earth is perpetually in a near‐critical state, reminiscent of self‐organized criticality. However, the results also show fluctuations of ±10% in entropy that may be more consistent with the notion of intermittent criticality. A more precise definition of the two paradigms, and a similar analysis of numerical models, are both needed to distinguish between these competing models.
Annual and seasonal variations of atmospheric CO2, N2O and CO concentrations retrieved from NOAA/TOVS satellite observations
Authors: Chédin Alain , Hollingsworth Anthony , Scott Noelle A. , Serrar Soumia , Crevoisier Cyril , Armante Raymond
Published: October 2002

We show that atmospheric concentration variations of major greenhouse gases (CO2, N2O, CO) may be retrieved from observations of the National Oceanic and Atmospheric Administration (NOAA) polar meteorological satellite series. The method relies on the analysis of the differences between the observations and simulations from a radiative transfer model using collocated radiosonde data and fixed gas concentrations as the prime input. Over the time period considered (July 1987 – September 1991), the results are in good agreement with present knowledge of the atmospheric cycles (seasonal, annual) of the gases. A reanalysis of the more than 20 years archive of NOAA observations has considerable promise for an improved knowledge of the carbon cycle.
Quasi‐Lagrangian measurements in the lower stratosphere reveal an energy peak associated with near‐inertial waves
Authors: Hertzog A. , Vial F. , Mechoso C. R. , Basdevant C. , Cocquerez P.
Published: October 2002

In March 2001, three superpressure balloons were launched from Kiruna, Sweden (67.9°N, 21.1°E). The balloons drifted for several weeks in the stratospheric polar vortex at about 19 km. The corresponding trajectories exhibit cycloid‐like patterns due to the presence of near‐inertial waves. Consistently, it is found that the intrinsic‐frequency spectra of the horizontal velocity components are enhanced around the inertial frequency in reference to the generally assumed power‐law distribution. A large spectral gap is also found between gravity waves and Rossby waves in the polar stratosphere, in contrast to the continuum found in the equatorial lower stratosphere.
Dust vertical distribution in the Caribbean during the Puerto Rico Dust Experiment
Authors: Reid Jeffrey S. , Westphal Douglas L. , Livingston John M. , Savoie Dennis L. , Maring Hal B. , Jonsson Haflidi H. , Eleuterio Daniel P. , Kinney James E. , Reid Elizabeth A.
Published: October 2002

As part of Puerto Rico Dust Experiment (PRIDE), a Piper Navajo research aircraft, equipped with particle probes and an airborne Sun photometer, was deployed to Puerto Rico in July 2000. During the study, mid‐visible optical depths in Puerto Rico due to dust reached 0.5. In the middle of the summer transport season, the vertical distributions of dust were similar to that commonly assumed in the region with dust concentrated in the Saharan Air Layer (SAL) aloft. However, during the first half of the study period, dust had the highest concentrations in the marine and convective boundary layers, with lower dust concentrations above the trade inversion despite the presence of a strong SAL. Supporting meteorology suggests that the state of the monsoon on the coast of Africa influences the nature of the vertical distribution of dust in the Caribbean.
Offshore Ekman transport and Ekman pumping off Peru during the 1997–1998 El Niño
Authors: Halpern David
Published: October 2002

Satellite ocean vector wind measurements are used to describe onshore‐offshore Ekman transport and Ekman pumping/suction (i.e., downward/upward velocity) in the coastal ocean at 15°S off Peru, where upwelling is the dominant physical process. Normal and El Niño conditions are defined for May 1992 – April 1997 and May 1997 – May 1998, respectively. During normal conditions, both Ekman suction and offshore Ekman transport produced upwelling. During the El Niño, the May–August speed of Ekman pumping (−9 × 10−6 m s−1) was nearly 4 times larger than the normal speed of Ekman suction and offshore Ekman transport nearly doubled. The strong Ekman pumping may be the source for the deepened coastal thermocline during El Niño, although the evidence is not conclusive because of the absence of in situ observations.
Impacts of the Indian Ocean on the ENSO cycle
Authors: Yu Jin‐Yi , Mechoso Carlos R. , McWilliams James C. , Arakawa Akio
Published: October 2002

This study examines the impacts of the Indian Ocean on the ENSO (El Niño‐Southern Oscillation) cycle by performing experiments with a coupled atmosphere‐ocean general circulation model (CGCM). In one of the experiments, the ocean model domain includes only the tropical Pacific Ocean (the Pacific Run). In the other experiment, the ocean model domain includes both the Indian and tropical Pacific Oceans (the Indo‐Pacific Run). The experiment results show that the CGCM simulation of ENSO including both the Indian and tropical Pacific Oceans tends to be more realistic than that including the tropical Pacific Ocean only. In particular, the Indo‐Pacific Run produces ENSO events with larger amplitude and greater variability on decadal time scales. The interactive Indian Ocean also affects the surface heat flux anomalies in the Indian Ocean during the ENSO cycle and surface wind stress anomalies in both the tropical Indian and Pacific Oceans. There are indications that both surface heat flux and wind stress are actively forcing a portion of the interannual variability in the Indian Ocean during the ENSO cycle.
Observed solar modulation of galactic cosmic ray intensity in the outer heliosphere, 1997–2001
Authors: Van Allen J. A. , Webber W. R.
Published: October 2002

Instruments on Pioneer 10, Voyager 1 and Voyager 2 measure galactic cosmic ray intensity (>80 MeV/nucleon) as the spacecraft move along their solar system escape trajectories. As of 1 June 2001, their respective heliocentric radial distances were 78 AU (in approximately the antapex direction from the Sun), 81 AU and 64 AU (the latter two in approximately the apex direction). The principal finding of this paper is that all three spacecraft were still under the delayed influence of increasing solar activity during cycle 23 and were, therefore, inside the modulation boundary of the heliosphere. Also the combined evidence favors essential antapex‐apex symmetry in the large scale modulation medium. The contents of this paper are generally concordant with studies by other groups of authors but are unique in the inclusion of the recent four years of antapex data from Pioneer 10.
Topography within circular grabens: Implications for polygon origin, Utopia Planitia, Mars
Authors: Buczkowski Debra L. , McGill George E.
Published: October 2002

Very large, fracture‐bounded polygons occur in Acidalia and Utopia Planitiae, Mars. Two models for the origin of these large polygons postulate drape folding of a sedimentary cover material over an uneven buried surface, with the strain enhancement needed to explain the large size due to differential compaction. Throughout the polygonal terrain are circular grabens inferred to overlie buried crater rims. Drape folding models predict that (1) these circular grabens will bound topographic lows and (2) the surface relief and percent compaction within circular grabens will be proportional to ring diameters. Relief and compaction within 8 circular grabens have been determined by gridding MOLA data in ArcView. All 8 fulfill the first prediction, and 7 of them fulfill the second prediction. These results support a sedimentary origin for polygonal terrain materials, and thus are consistent with the past existence of an “ocean” in the martian lowland.
Transient eddies in the southern hemisphere of Mars
Authors: Hinson D. P. , Wilson R. J.
Published: October 2002

Mars Global Surveyor is providing the first observations of transient eddies in the southern hemisphere of Mars. We derive basic properties of the traveling eddies that appear in midwinter (Ls = 134°–148°) through analysis of radio occultation measurements at 67°–70°S latitude. The dominant mode has a period of ∼2 solar days and a zonal wavenumber s = 3. Strong zonal variations in eddy amplitude signal the presence of a possible “storm zone” at 150°–330°E longitude. Within this longitude band the eddies achieve peak amplitudes at the 300‐Pa pressure level of ∼7 K in temperature and 10–15 m s−1 in meridional wind speed. The minimum temperature associated with the eddies is ∼2 K colder than saturation of CO2, close to the threshold where nucleation and growth of new ice particles can occur. A simulation by a Mars general circulation model produces traveling eddies that closely resemble the observations.
Comparison of aerosol properties derived from Sun photometer data and ground‐based chemical measurements
Authors: Corbin Katherine C. , Kreidenweis Sonia M. , Vonder Haar Thomas H.
Published: October 2002

Aerosol optical depth (AOD) data from the Aerosol Robotic Network (AERONET) instrument at Goddard Space Flight Center were compared with surface chemical data from the Interagency Monitoring of Protected Visual Environments (IMPROVE) sampler at Washington, D.C. for the years 1995–1997. These sites were the only ones in the two networks in close enough proximity to make such a comparison. The Spearman correlation coefficients between AOD and boundary‐layer aerosol properties derived from the IMPROVE data ranged from about 0.42 to 0.55. The relatively weak correlations for these urban sites are consistent with findings in previous studies, and are most likely due to the lack of information on the vertical profiles of aerosol mass concentration, composition, and relative humidity.
Effects of nonlinear rheology on degree 2 harmonic deformation in a spherical self‐gravitating earth
Authors: Wu Patrick
Published: October 2002

The effect of non‐linear rheology on surface displacements, gravitational potential perturbation and ∂tJ2 (or J2‐dot) for a self‐gravitating spherical earth is studied using a finite element code coupled to Poisson's equation. Four earth models investigated are: a model with uniform linear rheology throughout the mantle and three others containing nonlinear rheology in the whole mantle, upper mantle and lower mantle respectively. The effect of self‐gravitation is shown to be non‐negligible. The effects of nonlinear rheology in different parts of the mantle on surface displacements and potential have also been shown to be large. ∂tJ2 due to cyclic glaciation of the Laurentian, Fennoscandian, Barents Sea and Antarctic ice sheets over realistic oceans is also computed for all four rheology models. The model with nonlinear lower mantle cannot be ruled out by the observed data.
The draping of heliospheric magnetic fields upstream of coronal mass ejecta
Authors: Jones G. H. , Rees A. , Balogh A. , Forsyth R. J.
Published: October 2002

The propagation of a fast coronal mass ejection through the interplanetary medium results in compression and draping of existing heliospheric magnetic fields, forming an upstream sheath. Such sheaths are a common context for planar magnetic structures, where the magnetic field is ordered into laminar sheets. A technique is presented to estimate the location of spacecraft with respect to the large‐scale structure of ejecta which they encounter. The technique employs the characteristics of sheath planar magnetic structures, assuming that they are formed by field‐line draping. The technique's results for four magnetic clouds encountered by the Ulysses spacecraft are compared to those of a flux rope model. Very good agreement is found, suggesting that this is a promising technique for estimating an ejection's location from single‐spacecraft data.
Spectral representation of rain profiles and diurnal variations observed with TRMM PR over the equatorial area
Authors: Takayabu Yukari N.
Published: October 2002

A summary of rainfall statistics over the equatorial area (10°N–10°S), observed by a space‐borne precipitation radar of the Tropical Rainfall Measuring Mission (TRMM), is presented utilizing all nadir data of PR2a25 version 5 for the period of 1998–1999. Spectral representation of rain profiles is introduced, and convective and stratiform rain characteristics over land and over ocean are examined. With 0.3 mm hr−1 rain‐top threshold, convective: stratiform rain ratios at 2–4 km over land and over ocean are, 61:39 and 50:50 in amount, 20:80 and 17:83 in area, respectively. For diurnal variations over ocean, two types of rain vary almost synchronously, with an early‐morning maximum in 03–06 LT, indicating that direct radiative effect is the dominant diurnal control. Over land, convective rain has a distinct maximum of afternoon showers in 15–18 LT, while stratiform rain has a midnight (24–03LT) maximum. Also shown is that afternoon showers are more frequent but nighttime rain is stronger, suggesting contributions from large‐scale disturbances.
Can soot particles emitted by airplane exhaust contribute to the formation of aviation contrails and cirrus clouds?
Authors: Alcala‐Jornod Carine , van den Bergh Hubert , Rossi Michel J.
Published: October 2002

Flame soot samples taken as surrogates for aviation soot have been generated under two limiting conditions of combustion in a rich and lean flame resulting in grey and black soot, respectively. Absolute mean surface residence times τs of H2O adsorbed on soot ranging from 400 to 150 ms have been measured for black soot at 243K and for grey soot at 193K, respectively. The kinetic parameters for desorption of H2O adsorbed on grey and black soot are Ea = 7 ± 0.5 and 9 ± 0.6 kcal/mol, logA/s−1 = 8.8 ± 0.5 and 8.5 ± 0.5, respectively. We conclude that soot aerosol may be coated with H2O molecules in a sulfur‐free pathway once the particles have cooled down to 500K in the plume of aviation exhaust.
A dynamical framework to understand and predict the major Northern Hemisphere mode
Authors: Cohen Judah , Salstein David , Saito Kazuyuki
Published: October 2002

The dynamics of the leading mode of boreal winter and its excitation by varying boundary conditions remain mostly unclear. A novel framework is presented to explain the evolution of this dominant winter mode. It is shown that there exists a dichotomy of pathways with the characteristics of the dominant mode dependent upon the pathway taken. All winters examined fall into one of the two different dynamic evolutions presented, the knowledge of which clarifies prior uncertainties associated with the dominant mode and provides excellent potential for the successful prediction of subsequent winter mean climate states.
Seismic anisotropy in the top 400 km of the inner core beneath the “eastern” hemisphere
Authors: Niu Fenglin , Wen Lianxing
Published: October 2002

Depth variation in seismic anisotropy at the top 400 km of the inner core beneath the “eastern” hemisphere is investigated by comparing the differential travel times of PKP phases recorded at distances from 127° to 160°. At distances less than about 150°, there is no noticeable difference in differential travel times for PKP phases sampling both the polar and the equatorial paths. At greater distances, however, PKIKP phases arrive systematically earlier (about 0 ∼ 0.5 second) in the polar path than in the equatorial path. These observations suggest that, in the “eastern” hemisphere, seismic anisotropy exists only in depths greater than about 200 km below the inner core boundary (ICB) with seismic velocities along the polar paths (an average of 27.6° from the earth's spin axis) being 0.4% faster than those along the equatorial paths.
Edge‐based finite element approach to the simulation of geoelectromagnetic induction in a 3‐D sphere
Authors: Yoshimura Ryokei , Oshiman Naoto
Published: October 2002

We present a new simulator based on an edge‐based finite element method (FEM) for computing the global‐scale electromagnetic (EM) induction responses in a 3‐D conducting sphere excited by an external source current for a variety of frequencies. The formulation is in terms of the magnetic vector potential. The edge‐element approach assigns the degrees of freedom to the edges rather than to the nodes of the element. This edge‐element strictly satisfies the discontinuity of the normal boundary conditions without considering the enforced normal boundary conditions that are usually practiced in a node‐based FEM. To verify our simulation code, we compare our results with those of other solvers for two test computations, corresponding to azimuthally symmetric and asymmetric models. The results are in good agreement with one another.
Elemental and Isotopic Chloride Geochemistry and Fluid Flow in the Nankai Trough
Authors: Spivack Arthur J. , Kastner Miriam , Ransom Barbara
Published: October 2002

The first transect of pore fluid Cl− profiles across the deformation front of an accretionary prism and underthrust section, Nankai Trough, and the first Cl isotopic profile in this environment are presented. These demonstrate that there is channelized horizontal episodic flow through most of the section arcward of the deformation front and in the lowermost section seaward of the deformation front. In the underthrust sediments, channels appear to be continuous. Fluid velocities, within the channels, based on Cl− gradients, are 13 ± 5cm/year. The near balance of depth‐integrated flow and the subduction of pore fluid indicates that flow episodes are frequent. δ37Cl values are lower than seawater throughout the section, averaging −6.1 per mil. This demonstrates fluid/mineral exchange of Cl and suggests that subducted solids carry enriched δ37Cl that is efficiently recycled from deeper levels in the subduction zone back into seawater and may be responsible for the seawater/mantle δ37Cl fractionation.
The ion environment near Europa and its role in surface energetics
Authors: Paranicas C. , Ratliff J. M. , Mauk B. H. , Cohen C. , Johnson R. E.
Published: October 2002

This paper gives the composition, energy spectra, and time variability of energetic ions measured just upstream of Europa. From 100 keV to 100 MeV, ion intensities vary by less than a factor of ∼5 among Europa passes considered between 1997 and 2000. We use the data to estimate the radiation dose rate into Europa's surface for depths 0.01 mm – 1 m. We find that in a critical fraction of the upper layer on Europa's trailing hemisphere, energetic electrons are the principal agent for radiolysis, and their bremsstrahlung photon products, not included in previous studies, dominate the dose below about 1 m. Because ion bombardment is more uniform across Europa's surface, the radiation dose on the leading hemisphere is dominated by the proton flux. Differences exist between this calculation and published doses based on the E4 wake pass. For instance, proton doses presented here are much greater below 1 mm.
Empirical relationships between aerosol mass concentrations and Ångström parameter
Authors: Kusmierczyk‐Michulec J. , de Leeuw G. , Gonzalez C. Robles
Published: October 2002

Empirical relations between aerosol mass concentrations and Ångström parameters α were derived from simultaneous optical and chemical measurements on the Baltic in March 1998. The relations apply to mass concentrations of sea salt aerosol (SSA), black carbon (BC) and organic carbon (OC), expressed in terms of their ratio to the total particulate matter (TPM). Using these relations to calculate the mass concentrations of these aerosol components for a different season or a different area, yields favorable results. The relations were obtained and verified for Ångström parameters 0.2 ≤ α ≤ 1.43.
Modelling regional responses by marine pelagic ecosystems to global climate change
Authors: Boyd Philip W. , Doney Scott C.
Published: October 2002

Current coupled ocean‐atmosphere model (COAM) projections of future oceanic anthropogenic carbon uptake suggest reduced rates due to surface warming, enhanced stratification, and slowed thermohaline overturning. Such models rely on simple, bulk biogeochemical parameterisations, whereas recent ocean observations indicate that floristic shifts may be induced by climate variability, are widespread, complex, and directly impact biogeochemical cycles. We present a strategy to incorporate ecosystem function in COAM's and to evaluate the results in relation to region‐specific ecosystem dynamics and interannual variability using a template of oceanic biogeographical provinces. Illustrative simulations for nitrogen fixers with an off‐line multi‐species, functional group model suggest significant changes by the end of this century in ecosystem structure, with some of the largest regional impacts caused by shifts in the areal extent of biomes.
How does snow impact the albedo of vegetated land surfaces as analyzed with MODIS data?
Authors: Jin Yufang , Schaaf Crystal B. , Gao Feng , Li Xiaowen , Strahler Alan H. , Zeng Xubin , Dickinson Robert E.
Published: October 2002

Albedo derived from MODIS observations is found to be very stable during November 2000–January 2001. We analyze shortwave albedo under snow and snow‐free conditions by IGBP land cover types. Snow changes the spectral property of the surface reflectivity and causes high heterogeneity in the surface albedo between and within land types. The mean black sky (or direct beam) albedo at local solar noon for snow‐covered forests is less than 0.30 in the shortwave (0.3–5.0 μm), but it reaches 0.57 for snow‐covered grassland and barren. Although we are unable to further separate within‐class albedos with fractional tree cover, we find that the normalized difference snow index (NDSI) is highly correlated with surface albedo and hence can be taken as a measure of snow, soil and canopy fraction.
Magnetic field topology during July 14–16 2000 (Bastille Day) solar CME event
Authors: Rastätter L. , Hesse M. , Kuznetsova M. , Gombosi T. I. , DeZeeuw D. L.
Published: October 2002

The July 14–16, 2000 (Bastille Day) event was marked by an extraordinary level of geomagnetic activity following the impact of a large magnetic cloud onto the Earth's magnetosphere at 14:38 on July 15, 2000. The strong increase of the solar wind speed, and density and the large amplitude and variability of By and Bz gives rise to dramatic topological changes of unexpected magnitude in the magnetic field of the near‐Earth magnetosphere. This event is one of the first real events comprehensively modeled with the adaptive grid MHD simulation scheme BATS‐R‐US. Magnetic field line integrations were performed with the model output to obtain the three‐dimensional magnetic topology and the magnetic mapping between the northern and the southern hemisphere of the Earth.
Aeromagnetic and gravity anomaly constraints for an early Paleozoic subduction system of Victoria Land, Antarctica
Authors: Ferraccioli F. , Bozzo E. , Capponi G.
Published: October 2002

In Victoria Land three fault‐bounded tectonostratigraphic terranes are generally recognized: the Robertson Bay Terrane, the Bowers Terrane and the Wilson Terrane. Accretion and suturing of terranes at the East Antarctic Craton margin is usually related to west‐dipping subduction during the early Paleozoic Ross Orogen: however, nature of subduction‐related basement under the Bowers and Robertson Bay terranes is still debated and this adds uncertainty to existing tectonic models. This paper interprets aeromagnetic and gravity data against geologic and geochemical evidence to elaborate a new tectonic model for Victoria Land. We propose that the contrasting magnetic and gravity signatures over the northern and southern Bowers Terrane are linked to different basement rocks, specifically, buried oceanic basement beneath the northern Bowers Terrane and continental basement beneath the southern Bowers Terrane. The relevant linear magnetic anomaly in Central Victoria Land might also be a previously unrecognized suture within the Wilson Terrane.
Localization of abrupt change in the North Atlantic thermohaline circulation
Authors: Johnson Helen L. , Marshall David P.
Published: October 2002

Recent climate model experiments, as well as paleoclimate records, suggest that the meridional overturning circulation or “thermohaline circulation” in the Atlantic Ocean could change abruptly as a result of global warming, and that this could have a significant impact on European climate. We use a reduced‐gravity model to investigate the response of the Atlantic overturning circulation to changes in forcing. We find that variability at decadal and higher frequencies is confined to a single hemisphere. This implies that (a) overturning variability resulting from high frequency changes in buoyancy forcing in the Labrador and Greenland Seas will be limited to the North Atlantic, and (b) any observed decadal and higher frequency fluctuations in North Atlantic overturning can only result from changes in the surface fluxes within the North Atlantic basin itself. These results suggest that Southern Ocean wind forcing is not important for North Atlantic overturning on decadal and shorter timescales.
Wavelength dependence of aerosol optical thickness in the UV‐B band
Authors: Kirchhoff V. W. J. H. , Silva A. A. , Pinheiro D. K.
Published: October 2002

The optical thickness of the atmosphere, τat, was deduced from measurements of narrowband direct solar UV‐B (280–320 nm) radiation. This is the radiation that is strongly absorbed in the stratosphere by ozone, especially near the lower limit wavelength of these measurements, 306.3 nm. Measurement campaigns were organized to obtain radiation data at different sites, for different kinds of aerosol, using the same methods and instruments, in order to deduce the atmospheric optical thickness for different atmospheric conditions. The measurements were made with a Brewer spectrophotometer at each site. This instrument measures also the atmospheric ozone and sulphur dioxide columns, and therefore it is possible to deduce the aerosol optical thickness, τae. The possibility of additional absorptions in the UV‐B band, especially formaldehydes, is investigated. Two data sets are examined: C. Grande and S. Paulo. A large percentage of the data show that the wavelength dependence of the aerosol optical thickness is one that appears to increase with wavelength. In other words, the difference between the absolute values at 320.1 and 306.3 nm, is positive for the majority of cases. However, this difference is not always larger than the uncertainty/error of the measurement. This intriguing result opposes the Angstrom law, applicable to a much larger dynamic range in wavelength. For the C. Grande data (with generally larger values of optical thickness), the difference is positive in 16 out of 19 cases, but there are only 4 cases when the difference is larger than the error. For the S. Paulo morning data, however, the opposite is true. The difference is positive with only one exception, and there are 13 cases out of 17 where the difference is larger than the error.
Dynamic response to valley breeze circulation in Santa María del Oro, a volcanic lake in Mexico
Authors: Serrano David , Filonov Anatoliy , Tereshchenko Irina
Published: October 2002

The paper discusses the dynamic response to valley breeze circulation in Santa Maria del Oro, a volcanic lake in Mexico. Hourly records of wind measurements were used to construct a hydrodynamical model of the level fluctuations of the lake's water as well as integrated drift currents. The calculations show that the valley breeze circulation stimulates barotropic seiches in the lake with a period of 2.6 minutes and maximal level in the southwest part up to 18 mm. The drift current form two circulating rings having an opposite directions: anticyclonical in northern part of the lake and cyclonical in the southern. At the external edge of these rings the current speed can reach 20 cm/s. The measurements have shown that most part of the year the lake is strongly stratified. The maximal vertical temperature gradients are over 1°C/m in November and August, in a layer of 17–20 m.
Global comparison of magnetospheric ion fluxes and auroral precipitation during a substorm
Authors: Mende S. B. , Frey H. U. , Immel T. J. , Mitchell D. G. , son‐Brandt P. C: , Gérard J.‐C.
Published: October 2002

Integrated fluxes from global images taken by the High Energy Neutral Atom (HENA) and the far ultraviolet (FUV) imagers on the IMAGE spacecraft were compared for a six‐hour period, during which a reasonably intense substorm occurred. HENA and the FUV proton auroral imager (SI‐12) monitor emissions which are representative of trapped and precipitating magnetospheric proton fluxes, respectively. For several hours prior to substorm onset, measurements of the fluxes of lower energy (10–16 and 16–27 keV) magnetospheric Energetic Neutral Atoms (ENA‐s) by HENA and precipitating auroral protons by FUV SI‐12 show strong similarities, with the implication that, in general, proton precipitation is controlled by a steady pitch angle diffusion process. Less similarity is seen between ENA‐s and the auroral electron precipitation, which is monitored with the FUV Wideband Imaging Camera. Prior to substorm onset, ENA intensity at large radial distance (L > 8) is reduced while the overall integrated ENA flux increases signifying earthward motion and accumulation of the plasma. About 20 minutes before onset, the auroral fluxes decrease while the ENA intensity continues to grow. The observations are consistent with a pre‐onset increase in plasma pressure in the inner magnetosphere without an increase in precipitation showing more efficient trapping perhaps by the distorted nightside magnetosphere. At substorm onset the increase in precipitation intensity is very sudden while the more gradual intensification of the energetic ENA‐s continues. At onset the electron aurora shows an increase in intensity of one order of magnitude, while the increase in precipitating proton flux is only 50%. The intensification of the precipitation is relatively short lived (∼10 minutes) while the ENA substorm enhancements last about an hour.
The semiannual variation of great geomagnetic storms
Authors: Svalgaard L. , Cliver E. W. , Ling A. G.
Published: October 2002

The occurrence frequency of the largest geomagnetic storms from 1868–1998 exhibits a well‐defined semiannual modulation with more than twice as many storms occurring during equinoctial months than at the solstices. To examine the cause of this seasonal imbalance, we empirically obtained a new geomagnetic index aam that has the same seasonal and Universal Time variation as the am index. In effect, this extends the am index backward in time to 1868. By normalizing the aam time series for Ψ, the angle between the solar wind flow direction and Earth's dipole, we removed 75% of the amplitude of the six‐month wave in monthly averages of aam and ∼75% of the seasonal discrepancy in the numbers of great storms. We obtained similar percentages for the (unmodified) am index over the shorter 1959–1998 interval. These results indicate that most, though not all, of the discrepancy in storm counts between the equinoxes and solstices is due to an equinoctial effect.
Cosmic ray access to Jupiter's magnetosphere
Authors: Selesnick R. S.
Published: October 2002

Cosmic ray access to Jupiter's magnetosphere is investigated by numerical calculations of cosmic ray trajectories in the combined magnetic fields of the planetary dipole and the magnetospheric current sheet. Entry along the current sheet allows cosmic rays to reach closer to Jupiter than they would in a dipole planetary magnetic field alone. Observations of galactic cosmic rays from Galileo show that the calculations underestimate the true cutoff rigidities at equatorial radial distances >10 RJ, but that the calculated ∼14 GV cutoff rigidity at 10 RJ is a reasonable estimate.
Mechanism for Sea Surface Temperature Cooling In the Gulf of Oman during Winter
Authors: Luis Alvarinho J. , Kawamura Hiroshi
Published: October 2002

We report on sea surface temperature (SST) cooling in the Gulf of Oman during winter monsoon 1993 using evidence from the advanced very high resolution radiometer (AVHRR). A combination of the AVHRR SST and scatterometer‐based momentum and heat fluxes is used to discuss the SST‐cooling mechanism. Cold SST evolves in the gulf during an intense outbreak of wintertime winds. The turbulence generated by these winds in the surface atmospheric boundary layer depletes large heat from the sea surface and cause 1–2°C SST cooling during January–March. Additionally, the alongshore component of the wind stress promotes Ekman dynamics and further enhances SST cooling along the periphery of the gulf.
Acceleration of interstellar helium pickup ions at the Earth's bow shock: GEOTAIL observation
Authors: Oka M. , Terasawa T. , Noda H. , Saito Y. , Mukai T.
Published: October 2002

After ionization in the solar wind, He+ pickup ions of the interstellar origin are expected to be accelerated at heliospheric shocks (the termination shock, CIR (co‐rotating interaction region) shocks, and planetary bow shocks), and to become the seed population for anomalous cosmic rays. Although there are many theoretical attempts to treat the 'injection' process of the helium pickup ions at these shocks, there has been little direct observational evidence. In this report we present in situ identification of the initial acceleration process of pickup He+ at the bow shock.
OH column abundance over Table Mountain Facility, California: Annual average 1997–2000
Authors: Mills F. P. , Cageao R. P. , Nemtchinov V. , Jiang Y. , Sander S. P.
Published: October 2002

The column abundance of OH over Table Mountain Facility, California, (TMF) has been measured regularly since July 1997 using the Fourier‐transform Ultraviolet Spectrometer. The annual average OH column observed for 1998–2000 is 10–20% larger than that observed by another group over Tokyo for 1992–1995; 30–65% smaller than that observed by other groups over Colorado and New Mexico for 1980–1996; and 15–30% smaller than calculated by photochemical models. The Tokyo annual average and model estimates are within the range of geophysical variability for the OH column observed over TMF but the Colorado and New Mexico annual averages are not. This suggests the possibility of systematic errors in one or more of the data sets.
Time‐series of zenith radiance and surface flux under cloudy skies: Radiative smoothing, optical thickness retrievals and large‐scale stationarity
Authors: von Savigny C. , Davis A. B. , Funk O. , Pfeilsticker K.
Published: October 2002

Cloudy sky zenith radiance time‐series covering spatial scales a few meters up to 200–400 km measured by a ground‐based photometer at 753 nm are investigated with 2nd‐order structure functions, and compared to broad‐band short‐wave column transmittance. A previously reported scale break occurs at scales on the order of the vertical cloud extension due to radiative smoothing (i.e., lateral photon transport by diffusion in optically thick clouds). We use simulated radiance and flux fields for 3D clouds to explain why optical depths can be extracted with reasonable accuracy from surface fluxes by using 1D radiative transfer theory at large‐enough scales. We also show clear evidence of a transition from nonstationary to stationary behavior, i.e., a scale break, occurring at spatial scales of a few tens of kilometers. We argue that this qualitative change in the correlations of remotely observed radiation fields is likely to carry over to the most highly variable inherent cloud property, namely optical depth.
Evidence of liquid water in recent debris avalanche on Mars
Authors: Baratoux D. , Mangold N. , Delacourt C. , Allemand P.
Published: October 2002

The identification of landforms associated to liquid water on Mars is a major goal for the understanding of the geologic and climatic evolution of this planet. In the region of Reull Vallis, near Hellas basin, lobate debris aprons are recent landforms due to the creep of water ice mixed with rocks. Among these landforms, one unusually long debris apron has a tongue‐shape and gross morphology that indicates a different mechanism of deposition. This study demonstrates, using topographic data from Viking DEM and MOLA (Mars Observer Laser Altimeter) that the geometric parameters of this feature support the presence of liquid water during its flow. This landform is therefore comparable in size to the most developed wet debris avalanches on Earth. Its late Amazonian age questions the presence of near‐surface liquid water in the recent geological past of Mars.