bluuebunny/crossref_metadata_2025 huggingface dataset:
Digital elevation model grid size, landscape representation, and hydrologic simulations
Authors: Zhang Weihua , Montgomery David R.
Published: February 2004

High‐resolution digital elevation data from two small catchments in the western United States are used to examine the effect of digital elevation model (DEM) grid size on the portrayal of the land surface and hydrologic simulations. Elevation data were gridded at 2‐, 4‐, 10‐, 30‐, and 90‐m scales to generate a series of simulated landscapes. Frequency distributions of slope (tan B), drainage area per unit contour length (a), and the topographic index (a/tan B) were calculated for each grid size model. Frequency distributions of a/tan B were then used in O'Loughlin's (1986) criterion for predicting zones of surface saturation and in TOPMODEL (Beven and Kirkby, 1979) for simulating hydrographs. For both catchments, DEM grid size significantly affects computed topographic parameters and hydrographs. While channel routing dominates hydrograph characteristics for large catchments, grid size effects influence physically based models of runoff generation and surface processes. A 10‐m grid size provides a substantial improvement over 30‐ and 90‐m data, but 2‐ or 4‐m data provide only marginal additional improvement for the moderately to steep gradient topography of our study areas. Our analyses suggest that for many landscapes, a 10‐m grid size presents a rational compromise between increasing resolution and data volume for simulating geomorphic and hydrological processes.
Global patterns of carbon dioxide emissions from soils
Authors: Raich James W. , Potter Christopher S.
Published: February 2004

We use semi‐mechanistic, empirically based statistical models to predict the spatial and temporal patterns of global carbon dioxide emissions from terrestrial soils. Emissions include the respiration of both soil organisms and plant roots. At the global scale, rates of soil CO2efflux correlate significantly with temperature and precipitation; they do not correlate well with soil carbon pools, soil nitrogen pools, or soil C:N. Wetlands cover about 3% of the land area but diminish predicted CO2emissions by only about 1%. The estimated annual flux of CO2from soils to the atmosphere is estimated to be 76.5 Pg C yr−1, 1–9 Pg greater than previous global estimates, and 30–60% greater than terrestrial net primary productivity. Historic land cover changes are estimated to have reduced current annual soil CO2emissions by 0.2–2.0 Pg C yr−1in comparison with an undisturbed vegetation cover. Soil CO2fluxes have a pronounced seasonal pattern in most locations, with maximum emissions coinciding with periods of active plant growth. Our models suggest that soils produce CO2throughout the year and thereby contribute to the observed wintertime increases in atmospheric CO2concentrations. Our derivation of statistically based estimates of soil CO2emissions at a 0.5° latitude by longitude spatial and monthly temporal resolution represents the best‐resolved estimate to date of global CO2fluxes from soils and should facilitate investigations of net carbon exchanges between the atmosphere and terrestrial biosphere.
Dating of vein Specularite using internal (U+Th)/4He isochrons
Authors: Wernicke Rolf S. , Lippolt Hans J.
Published: February 2004

Hematite, an ubiquitous iron oxide, is commonly found enriched with uranium and other elements supplied by the ore solution from which it had formed. The decay of the incorporated uranium to stable lead produces alpha particles which become 4He atoms via electron capture. In hematite this helium production may provide a convenient ‘clock’ which records the time elapsed since the iron oxide became closed enough to prevent quantitative helium escape (Wernicke and Lippolt, 1993a; 1993b). Recently, Lippolt et al. (1993) reported high retention qualities of specular hematite for 4He over geologic periods of time (activation energies above 116 [KJ/mol] and diffusion coefficients smaller than 10−30 [m2 s−1] at room temperature, and closure temperatures above 200°C).

Here the concentrations of U and Th have been measured together with radiogenic 4He at four different locations inside two specularites. The U‐He concentrations co‐varied sufficiently among the locations for an internal helium isochron of Late Jurassic age to be obtained from each specularite. The study suggests that specularite is a prolific chronometer and might allow a routine approach of the helium (isochron) method to obtain crystallization/cooling ages.
Chimneys on the Earth's inner‐outer core boundary?
Authors: Bergman Michael I. , Fearn David R.
Published: February 2004

Convection occurs in the “mushy” zone at the solid/liquid boundary of a non‐eutectic melt freezing from below when the Rayleigh number Ram exceeds some critical value Ramc,. Nonlinear processes can then lead to the rising fluid being concentrated in narrow “chimneys”. The focusing occurs because a fluid parcel rising in the mushy zone finds itself undersaturated in the solvent, resulting in encompassed dendrites remelting, and porosity, and hence permeability, increasing. This reduces the Darcy friction and increases the flow in an upwelling region, leading eventually to a solid‐free chimney. A larger downwelling region of higher solid fraction becomes necessary to feed the chimney. Here, we are interested in applying these ideas to the Earth's core. Many discussions of compositional convection in the Earth's core tacitly assume that it will be in the form of chimney convection rising from the mushy zone at the inner‐outer core boundary. We question this assumption here because the Chandrasekhar number Qm of flow through the dendrites may be large. Magnetic drag then supplants Darcy friction as the primary retarding force. Because the magnetic drag is independent of permeability and length‐scale, and thus porosity, the focusing mechanism that results in chimneys no longer operates. Although Ram is likely to remain highly super‐critical, the nonlinear convection may assume a form different from chimney convection, in spite of lateral variations in permeability.
Plasma distribution functions in the Earth's magnetotail (XGSM∼ −42RE) at the time of a magnetospheric substorm: GEOTAIL/LEP observation
Authors: Machida S. , Mukai T. , Saito Y. , Hirahara M. , Obara T. , Nishida A. , Terasawa T. , Maezawa K.
Published: February 2004

Three plasma burst events were observed with the Low Energy Particle (LEP) instrument onboard GEOTAIL at XGSM=−42 RE. Two of these events were detected when the spacecraft was in the plasma sheet. In these events, the first signature of the burst was the tailward flow of the accelerated electrons with energies of about 5 keV. This was followed by the appearance of the tailward streaming ions with energies > 20 keV. Importantly, these tailward streaming ions were observed together with the non‐streaming ions of the plasma sheet which had not experienced acceleration or heating. Then the electron distribution function started to develop an elongated core component at < 1 keV and isotropic or perpendicularly heated structure at > 1keV. These two events lasted for about two minutes. The spacecraft was in the tail lobe before the third event took place. In this event the first signature was the bistreaming electrons with peak energy at 2 keV. After a short interval of the flux decrease, hot electrons with energy ∼3 keV appeared. The velocity distribution function of the ions had an incomplete shell structure with an average tailward velocity of ∼900 km/sec. The non‐streaming component was absent in this case. It is suggested that in the first two events the spacecraft was in the plasma jet emanating from the near Earth neutral line, while it traversed the edge of the plasmoid in the third event. The associated substorm onset can be identified for the first event after which the disturbance continued.
The shallow attenuation structure of the fast‐spreading East Pacific Rise near 9°30′N
Authors: Christeson G. L. , Wilcock W. S. D. , Purdy G. M.
Published: February 2004

Direct measurements of Q values in the shallow crust are difficult to obtain due to the lack of energy turning in this region. We analyze a unique data set consisting of seven refraction experiments carried out with both the source and receiver near the seafloor. This experimental geometry allows us to resolve the shallow compressional wave attenuation structure of young crust at the East Pacific Rise. All models depict a low‐Q layer 2A (apparent Q=11–22), and several models resolve a layer 2B with a much higher Q (apparent Q > 70). This structure is consistent with a layer 2A composed of extrusives overlying a layer 2B composed of sheeted dikes.
A Two‐Dimensional Model Study of the QBO Signal in SAGE II NO2 and O3
Authors: Chipperfield M. P. , Gray L. J. , Kinnersley J. S. , Zawodny J.
Published: February 2004

Calculations of the QBO signal in SAGE II O3 and NO2 data between 1984 and 1991 are presented and have been investigated by using a two‐dimensional model. The isentropic 2D model is a fully interactive radiative‐dynamical‐chemical model in which the eddy fluxes of chemical species are calculated in a consistent manner. The QBO in the model has been forced by relaxing the equatorial zonal wind toward the observations at Singapore allowing the comparison of the model with observations from specific years. The model reproduces the observed vertical structure of the equatorial ozone anomaly with the well‐known transition from dynamical to photochemical control at around 28km. The model also reproduces the observed vertical structure of the SAGE II observed NO2 anomaly. The model studies have shown that it is the QBO modulation of NO2 which is the main cause of QBO signal in O3 above 30km. The model also reproduces the observed latitudinal structure of the QBO signals in O3 and NO2. Due to the differing horizontal distribution of O3 and NOy the ozone signal shows a distinct phase change in the subtropics whereas the NO2 anomaly gives a broader signal.
Radon recording of Uttarkashi earthquake
Authors: Virk H. S. , Singh Baljinder
Published: February 2004

Spatial and temporal distribution of radon is recorded in both soil‐gas and groundwater using two different techniques, viz. track etch method and emanometry. Radon recording stations have been set up at one site in Amritsar and four sites in the Kangra valley (Himachal Pradesh) under the Himalayan seismicity project. The track‐etch method gives integrated measurement of radon over a week or a fortnight whereas emanometry is used for daily recording of radon activity in soil‐gas and groundwater.

The Uttarkashi earthquake (mb = 6.5, MS = 7.0) occurred on October 20, 1991 (Oct. 19 U.T.) in the Garhwal Himalayas (30.78°N, 78.77°E) about 330 km from our recording stations in the Kangra valley and about 450 km from Amritsar, respectively. Radon anomalies were recorded at all sites in Kangra valley and Amritsar about a week before the Uttarkashi earthquake, which clearly establishes that radon changes can be effective for forecasting some earthquakes.
Shear wave splitting in the records of the German Regional Seismic Network
Authors: Vinnik L. P. , Krishna V. G. , Kind R. , Bormann P. , Stammler K.
Published: February 2004

Estimates of the parameters of shear‐wave splitting in the records of SKS and SKKS of the new German Regional Seismograph Network (GRSN) for one‐layer model show large azimuthal variations at some stations of the network. It is found that the variations are compatible with the presence of two anisotropic mantle layers in the region of the South German Triangle (SGT); the fast direction in the upper layer is between N‐S and NE‐SW, close to the previously reported estimates of the fast direction in the sub crustal lithosphere of the SGT. The fast direction in the lower, presumably asthenospheric layer is close to E‐W. The estimates of the effective fast direction for one‐layer model at the stations of the GRSN confirm the previously noted tendency of the fast direction of mantle anisotropy in Central Europe to change from 50°–70° in the western part of the region to 100°–120° in the eastern part. A correlation of this change with a bending of the present‐day direction of maximum horizontal stress in the crust suggests that anisotropy in the asthenosphere of Central Europe can be related to the Alpine orogeny.
Generation of slow‐mode waves in front of the dayside magnetopause
Authors: Yan M. , Lee L. C.
Published: February 2004

Slow‐mode waves have been observed to appear frequently in front of the dayside magnetopause. It is found based on two‐dimensional global MHD simulations that slow‐mode waves are generated through the interaction between the bow shock and various MHD waves (fast‐mode, Alfven‐mode, or slow‐mode waves) in the upstream solar wind. The generated slow‐mode waves stay in front of the magnetopause for a long time (over 15 minutes) before the wave energy is convected away tailward. Since various waves are often present in the solar wind, this mechanism may lead to the frequent appearance of slow‐mode waves in front of the magnetopause.
Rate constants for the reactions of OH with CH3Cl, CH2Cl2, CHCl3, and CH3Br
Authors: Hsu K.‐J. , DeMore W. B.
Published: February 2004

Rate constants for the reactions of OH with CH3Cl, CH2Cl2, CHCl3, and CH3Br have been measured by a relative rate technique in which the reaction rate of each compound was compared to that of HFC‐152a (CH3CHF2) and (for CH2Cl2) HFC‐161 (CH3CH2F). Using absolute rate constants for HFC‐152a and HFC‐161, which we have determined relative to those for CH4, CH3CCl3, and C2H6, temperature dependent rate constants of both compounds were derived. The derived rate constant for CH3Br is in good agreement with recent absolute measurements. However, for the chloromethanes all the rate constants are lower at atmospheric temperatures than previously reported, especially for CH2Cl2 where the present rate constant is about a factor of 1.6 below the JPL 92‐20 value. The new rate constant appears to resolve a discrepancy between the observed atmospheric concentrations and those calculated from the previous rate constant and estimated release rates.
The African Superswell
Authors: Nyblade Andrew A. , Robinson Scott W.
Published: February 2004

Maps of residual bathymetry in the ocean basins around the African continent reveal a broad bathymetric swell in the southeastern Atlantic Ocean with an amplitude of about 500m. We propose that this region of anomalously shallow bathymetry, together with the contiguous eastern and southern African plateaus, form a superswell which we refer to as the African superswell. The origin of the African superswell is uncertain. However, rifting and volcanism in eastern Africa, as well as heat flow measurements in southern Africa and the southeastern Atlantic Ocean, suggest that the superswell may be attributed, at least in part, to heating of the lithosphere.
New aspects of whistler waves driven by an electron beam studied by a 3‐D electromagnetic code
Authors: Nishikawa Ken‐Ichi , Buneman Oscar , Neubert Torsten
Published: February 2004

We have restudied electron beam driven whistler waves with a 3‐D electromagnetic particle code. The simulation results show electromagnetic whistler wave emissions and electrostatic beam modes like those observed in the Spacelab 2 electron beam experiment. It has been suggested in the past that the spatial bunching of beam electrons associated with the beam mode may directly generate whistler waves. However, the simulation results indicate several inconsistencies with this picture: (1) whistler waves continue to be generated even after the beam mode space charge modulation looses its coherence, (2) the parallel (to the background magnetic field) wavelength of the whistler wave is longer than that of the beam instability, and (3) the parallel phase velocity of the whistler wave is smaller than that of the beam mode. The complex structure of the whistler waves in the vicinity of the beam suggest that the transverse motion (gyration) of the beam and background electrons is also involved in the generation of whistler waves.
The subcritical, quasi‐parallel, switch‐on shock
Authors: Farris M. H. , Russell C. T. , Fitzenreiter R. J. , Ogilvie K. W.
Published: February 2004

The conditions that lead to subcritical, quasi‐parallel bow shocks are very rare. Even more rarely, a subcritical, quasi‐parallel shock can also be termed a switch‐on shock, where the tangential component of the magnetic field, which is very small upstream, is said to “switch on” downstream. The Rankine‐Hugoniot conservation relations predict that the jump in the tangential component of the magnetic field across the shock is very large for these upstream conditions. In this study, we find that the measured jumps in the plasma conditions are in accord with predictions made by the Rankine‐Hugoniot conservation relations. The structure of the switch‐on shock, not predicted by the Rankine‐Hugoniot equations, is very similar to that of the subcritical, quasi‐perpendicular shock, with the exception that the precursor wave in front of the shock ramp damps more slowly.
Heterogeneity spectrum and scale‐anisotropy in the upper crust revealed by the German Continental Deep‐Drilling (KTB) Holes
Authors: Wu Ru‐Shan , Xu Zhengyu , Li Xiao‐Ping
Published: February 2004

Crustal heterogeneities and their statistical characteristics bear important information about the dynamic processes and evolution of the crust. The velocity well‐log data from the German Continental Deep Drilling Project (KTB) offer a rare opportunity to measure directly the properties of crustal heterogeneities. In this study, we first estimated the power spectrum of crustal heterogeneities from the P‐velocity well‐logs of the two holes. For the first time, a power‐law spectrum of crustal heterogeneities was directly observed in the spatial wavelength range from a few meters to a few kilometers. The slope of the vertical 1D power spectrum of the random velocity perturbations is about 1.1, corresponding to a flicker‐noise random medium. The scale‐anisotropy ratio (aspect ratio) and the horizontal spectral slope of crustal heterogeneities were also estimated by cross‐correlation analysis between these two holes to be about 1.8 and 2.0, respectively.
Observation of ion‐cyclotron turbulence at small values of magnetic‐field‐aligned current
Authors: Amatucci W. E. , Koepke M. E. , Carroll J. J. , Sheridan T. E.
Published: February 2004

Fluctuations in plasma density are observed in the ion‐cyclotron frequency range in a Q‐machine plasma column at values of magnetic‐field‐aligned current significantly below the critical value for current‐driven electrostatic ion‐cyclotron (CDEIC) waves. These fluctuations arise from the inhomogeneous energy‐density driven (IEDD) instability, are relatively broadband, and can have large amplitude compared to CDEIC fluctuations. These results impact the interpretation of ion heating and acceleration in the ionosphere, especially at low‐altitude where magnetic‐ field‐aligned current densities estimated to be large enough to be supercritical to current‐driven or beam‐driven electrostatic ion‐cyclotron waves are rarely detected.
Signatures of energy‐time dispersed electron fluxes measured by Freja
Authors: Clemmons J. H. , Boehm M. H. , Paschmann G. E. , Haerendel G.
Published: February 2004

Two measurements of velocity‐dispersed electron fluxes at altitudes near 1750 km are reported. The energy‐time signatures of both observations are interpreted in terms of a simple time‐of‐flight (TOF) scenario. The first measurement occurred at low magnetic latitude (∼62°) and consisted of three injection events. Analysis yields a source location near the equator ∼6.5 RE from the spacecraft and provides evidence that the injections were periodic. The injections are interpreted as being the result of interactions with waves near the earthward edge of the equatorial plasma sheet, and the presence of fine structure in the fluxes with timescales of a few hundred ms provides new information on the injection process. Analysis of the second measurement leads to the determination of a source location about 850 km above the spacecraft. Although the simple model is able to explain the observations at small pitch angles, the measurements at large pitch angles require that the model be refined, and a modification which invokes pitch‐angle diffusion is suggested.
Large‐scale auroral plasma density cavities observed by Freja
Authors: Lundin R. , Eliasson L. , Haerendel G. , Boehm M. , Holback B.
Published: February 2004

Freja, the joint Swedish and German scientific satellite, has an orbit inclination that allows it to traverse the auroral oval tangentially and stay for minutes on field lines connected to the auroral energization region. One signature of the auroral energization process is the heating/transverse energization of ionospheric ions. Associated with such transverse heating/energization of ionospheric ions is a depletion of cold plasma in the topside ionosphere. We have studied several Freja passes at ≈1700 km altitude with long time periods of plasma depletion and transverse ion acceleration. Inside these depletion regions the density may decrease by more than two orders of magnitude (from 1000 to ≈10 cm−3). This suggests that transverse ion heating is indeed a very strong mechanism for plasma density depletion in the topside ionosphere.
Evidence for Komatiite‐type lavas on Mars from Phobos ISM data and other observations
Authors: Reyes David P. , Christensen Philip R.
Published: February 2004

Data from the Phobos 2 Imaging Spectrometer for Mars (ISM), compiled by Mustard et al. [1993], and other observations support the existence of komatiitic lavas on Mars. Mustard et al. [1993] determined from ISM data that the composition of the low‐albedo materials covering the Syrtis Major plateau originally consisted of augite‐bearing basalt containing both augite and pigeonite, with no appreciable amount of olivine. This description is consistent with a komatiitic basalt. Komatiite is significant for the Earth because it contains a high amount of MgO, implying generation under unique circumstances compared to more typical basaltic compositions and may be similarly important for Mars.
Atmospheric gravity waves from the impact of comet Shoemaker‐Levy 9 with Jupiter
Authors: Ingersoll A. P. , Kanamori H. , Dowling T. E.
Published: February 2004

We study the effect of the Jovian water cloud on internal gravity waves generated by the impact of comet SL9. Vertical structure follows Voyager data to the 1‐bar level, a moist adiabat from 1 to 5 bars, and a dry adiabat below the 5‐bar level. The waves are trapped in the moist layer and propagate horizontally. Their speed is related to the vertical integral of the Brunt‐Väisälä frequency, and varies as the square root of the water abundance (130 m/s for solar composition). The amplitudes are large, e.g., ±1 K at a distance of 8000 km for an energy of 1027 ergs. The circular ripples should be detectable one or two days after the impact in thermal infrared and visible images.
On possible magnetospheric dust interactions of comet Shoemaker‐Levy 9 at Jupiter
Authors: Ip W.‐H. , Prangé R.
Published: February 2004

The plasma interaction of the dust coma of comet Shoemaker‐Levy 9 with the Jovian magnetosphere could result in the possible generation of a field‐aligned electric current system connecting the impinging dust cloud with the Jovian ionosphere. If the current flow is intense enough, transient auroral activity might be produced as a result. In this event, enhanced level of auroral and radio emissions would be expected an hour or so before the atmospheric impact.
Freja observations of heating and precipitation of positive ions
Authors: Eliasson L. , André M. , Eriksson A. , Norqvist P. , Norberg O. , Lundin R. , Holback B. , Koskinen H. , Borg H. , Boehm M.
Published: February 2004

The experiments on board Freja are designed to measure auroral particle energization processes with very high temporal and spatial resolution. One main scientific objective is to study ion heating transverse to the magnetic field lines in the auroral region. The Freja orbit with an inclination of 63° allows us to make detailed measurements in the nightside auroral oval during all disturbance levels. We concentrate here on two different observations of transverse ion energization at an altitude of about 1700 km in the northern hemisphere auroral region. The three‐dimensional ion mass spectrograph has shown that both heavy and light ions are heated to energies most often in the range from a few eV to some hundred eV. Transversely heated ions are, however, also seen up to the present high energy limit of the hot plasma instrument, 4.5 keV. Ion conics are produced in regions with anisotropic electron fluxes as well as in regions of intense keV proton precipitation. Waves above the lower hybrid frequency are observed in the events presented in this report. These waves may play an important role in the ion heating process. The Freja data indicate that the waves are generated in different ways in these events. Thus, this preliminary investigation confirms that several scenarios are needed to explain the heating of ionospheric plasma and shows some of the possibilities for future studies.
The speeds of coronal mass ejections in the solar wind at mid heliographic latitudes: Ulysses
Authors: Gosling J. T. , Bame S. J. , McComas D. J. , Phillips J. L. , Goldstein B. E. , Neugebauer M.
Published: February 2004

Six CMEs have been detected in the Ulysses plasma observations poleward of S31°. The most striking aspect of these mid‐latitude CMEs was their high speeds; the overall average speed of these CMEs was ∼ 740 km s−1, which was comparable to that of the rest of the solar wind at these latitudes. This average CME speed is much higher than average CME speeds observed in the solar wind in the ecliptic or in the corona close to the Sun. The evidence indicates that the CMEs were not pushed up to high speeds in interplanetary space by interaction with trailing high‐speed plasma. Rather, they simply seem to have received the same basic acceleration as the rest of the solar wind at these mid‐latitudes. Our results suggest that the basic acceleration process for many CMEs at all latitudes is essentially the same as for the normal solar wind. Frequently most of this acceleration must occur well beyond 6 solar radii from Sun center.
Indirect detection of the Martian helium corona
Authors: Barabash S. , Norberg O.
Published: February 2004

The ion composition mass spectrometer ASPERA on board the PHOBOS 2 spacecraft detected particles with M/q=4 in the vicinity of Mars. A significant difference between the measured particle velocity and the solar wind velocity suggests that these ions are of planetary origin, apparently He+ from ionisation within the Martian helium corona. The particles had typical energies of either more than 10 keV or about 500 eV. The former correspond to ion pickup in the solar wind and the latter might be ions extracted from the upper ionosphere by an electric field. The observed density of pickup He+ ions was 0.02–0.1 cm−3 and the He+ density in the plasmasheet was of 0.2–0.7 cm−3. According to a recent model of the Martian neutral atmosphere [Moroz et al, 1991], the He+ density could reach 0.2 cm−3 at the Phobos orbit. Such values give mass densities comparable to those of the solar wind. Thus, helium may play a role in the solar wind mass loading process near Mars.
On ion acoustic turbulence and the nonlinear evolution of kinetic Alfvén waves in aurora
Authors: Wahlund J.‐E. , Louarn P. , Chust T. , de Feraudy H. , Roux A. , Holback B. , Dovner P‐O. , Holmgren G.
Published: February 2004

Wave data from the recently launched Freja satellite, show a close relationship between Alfvén wave activity and ion acoustic wave activity within auroral energization regions. The Alfvén wave activity becomes especially strong (several 100 mV/m) in localized regions with horizontal scales of a few hundred meters to a km (few tens of Hz in the S/C reference system). In some cases these signatures become more electrostatic‐like and filled with broadband, high frequency electrostatic turbulence up to 15 kHz. This broadband electrostatic turbulence has an amplitude comparable to the larger scale electric signatures, and is identified as ion acoustic waves. We argue that these signatures have evolved from solitary kinetic Alfvén waves (SKAW), and may be important for auroral energization processes.
Observations of ion acoustic fluctuations in the auroral topside ionosphere by the FREJA S/C
Authors: Wahlund J.‐E. , Louarn P. , Chust T. , de Feraudy H. , Roux A. , Holback B. , Cabrit B. , Eriksson A. I. , Kintner P. M. , Kelley M. C. , Bonnell J. , Chesney S.
Published: February 2004

The widespread existence of naturally excited broadband electrostatic wave activity up to 15 kHz, with predominantly parallel polarization, have been detected in the topside auroral ionosphere by the wave experiment onboard the Freja S/C. Amplitudes of a few mV/m electric field fluctuations and a few % density fluctuations are typically observed, but stronger cases are quite common. These emissions are most often observed within the auroral energization region according to the plasma instrument data, and coincide frequently with Alfvén wave activity from a few Hz to tens of Hz. This suggests that the electrostatic emission is linked to the nonlinear evolution of kinetic Alfvén waves.
using the NOAA/AVHRR to study stratospheric aerosol optical thicknesses following the Mt. Pinatubo Eruption
Authors: Long Craig S. , Stowe Larry L.
Published: February 2004

NOAA has been archiving weekly and monthly gridded analyses of “radiatively equivalent” aerosol optical thickness over oceans on magnetic tape since June 29, 1989. These analyses are derived from the Advanced Very High Resolution Radiometer (AVHRR) on board the NOAA‐11 polar orbiting environmental satellite. The eruption of Mt. Pinatubo in June 1991 and the ensuing dispersal of aerosol particles in the stratosphere occurred after two complete years of observations with essentially “background” particle concentrations in the stratosphere. This fortunate timing means that computing the difference between the average of the first two years of tropospheric aerosols and the “Post‐Pinatubo” period of tropospheric and stratospheric aerosols provides a means of observing the evolution of the stratospheric aerosol cloud. Time series of zonal averages of these difference fields are presented and analyzed. These analyses indicate that by the end of 1993, the stratospheric aerosol optical thickness declined from its peak value in late Summer of 1991 to levels that are no longer detectable with AVHRR data.
Freja observations of electromagnetic ion cyclotron ELF waves and transverse oxygen ion acceleration on auroral field lines
Authors: Erlandson R. E. , Zanetti L. J. , Acuña M. H. , Eriksson A. I. , Eliasson L. , Boehm M. H. , Blomberg L. G.
Published: February 2004

Extremely low‐frequency (ELF) magnetic and electric field plasma wave emissions were recorded on 2 October 1993 on auroral field lines by the Magnetic Field Experiment during Freja orbit 4770. The ELF wave frequencies were below the local oxygen gyrofrequency (25 Hz) and between the helium and proton gyrofrequencies (100 to 400 Hz). The ELF waves, interpreted as electromagnetic ion cyclotron (EMIC) waves, were observed in a region of inverted‐V‐type electron precipitation. The EMIC waves were correlated over time with auroral and lower energy (≈100 eV) electrons, which are both possible sources of free energy, and also with transversely accelerated oxygen ions. The waves above the helium gyrofrequency were more closely correlated with the transverse oxygen ion acceleration than the waves below the oxygen gyrofrequency. These observations are consistent with a scenario in which electron beams generate EMIC waves, which then produce transverse oxygen ion acceleration through a gyroresonant interaction.
An experimental investigation of the spin‐up of a neutrally stratified fluid core
Authors: Davis R. G.
Published: February 2004

The spin‐up of a homogeneous fluid in a rotating hemisphere with a solid equatorial plane has been examined experimentally. For the case of small Rossby number, applicable to the Earth, fluid is spun‐up by vortex stretching via a small order Ek1/2, where Ek is the Ekman number, vertical velocity induced by Ekman layer pumping. The experimental results compare well with the predictions of the linear theory of Greenspan and Howard (1963). Inertial waves generated by the impulse were observed and their frequency measured.
Seismic azimuthal anisotropy beneath the Pakistan Himalayas
Authors: Sandvol Eric A. , Ni James F. , Hearn Thomas M. , Roecker Steve
Published: February 2004

Teleseismic S, SKS and SKKS data, collected from a temporary broadband array across the Himalayan front in Pakistan, are analyzed for shear‐wave splitting parameters. The SKS and SKKS phases have ray paths originating from both the South Pacific and Colombia which have azimuths approximately 40° apart with respect to the Pakistan array. If significant seismic azimuthal anisotropy is present we should observe splitting associated with one of these ray paths. No evidence was seen for any shear‐wave splitting beneath any of the stations in the array. Teleseismic S waves were also used in order to provide better azimuthal coverage for the shear‐wave splitting measurements. We were able to correct for any source‐side anisotropy when needed. No receiver‐side splitting was observed in any of the S wave data. The lack of shear‐wave splitting beneath the Pakistan array indicates that there is no appreciable large‐scale azimuthal anisotropy beneath this part of the Himalayas. Therefore, if there is any significant strain in the upper mantle beneath this area, it must either be vertically oriented, or, if horizontal, vertically vary in such a way that the integrated effect on S wave splitting is null.
The significance of detailed structure in the boundary layer to thermal radiation at the surface in climate models
Authors: Zhao Wenzhong , Kuhn William R. , Drayson S. Roland
Published: February 2004

This study used a mid‐latitude measurement of diurnal variations in the boundary layer to simulate thermal radiation for a clear sky. The emissivity growth method was used for the absorption by the five major greenhouse gases averaged over 10 cm−1 from line by line calculations. The vertical resolution of the model was 0.6 mb at the ground surface, and gradually increases to 100 mb in the middle troposphere. The importance to the calculated surface and outgoing infrared radiation due to detailed boundary layer structure and diurnal variations is demonstrated. Thus there is a need to carefully consider the near surface atmosphere in construction of radiation models for use in climate studies.
Isothermal plateau fission‐Track age for a paleomagnetic excursion in the Mamaku Ignimbrite, New Zealand, and implications for Late Quaternary stratigraphy
Authors: Shane Phil , Black Tasha , Westgate John
Published: February 2004

Mamaku Ignimbrite, the youngest of the large, welded ignimbrite sheet‐forming eruptions from the Taupo Volcanic Zone in New Zealand, is dated at 230±12 ka by the isothermal plateau fission‐track (ITPFT) method on glass. This age is older and more precise than that indicated by previous studies, requiring the revision of loess/paleosol coverbed chronologies. The eruption occurred during a paleomagnetic excursion allowing the ignimbrite to be easily distinguished from other eruptive events by paleomagnetic methods. This excursion is one of the few such events recorded in igneous rocks in the Southern Hemisphere, may be widely recorded in New Zealand, and is now temporally well constrained.
Observation by Ulysses of hot (∼270 keV) coronal particles at 32° south heliolatitude and 4.6 AU
Authors: Armstrong T. P. , Haggerty D. , Lanzerotti L. J. , Maclennan C. G. , Roelof E. C. , Pick M. , Simnett G. M. , Gold R. E. , Krimigis S. M. , Anderson K. A. , Lin R. P. , Sarris E. T. , Forsyth R. , Balogh A.
Published: February 2004

An unusual event of streaming 60 keV‐2 MeV ions (with energy spectrum peaked ∼270 keV) and of 42–315 keV electrons occurred during the passage of a coronal mass ejection (CME) over the Ulysses spacecraft June 9–13, 1993, located at helioradius 4.6 AU and heliolatitude 32° south. The topology of the interplanetary magnetic field (IMF) within the CME has been identified as a helical magnetic flux rope by Gosling et al. [1994]. The ion and electron pitch angle distributions (PADs) had a bidirectional component in the outer (large‐pitch) regions of the flux rope, while there were strongly unidirectional (antisunward) beams in the inner (small‐pitch) core of the structure, where the electron PADs also displayed a distinctive depletion of electrons moving inward (sunward). Because the core ion beam was narrow, we can associate the observed energy spectrum in the peak direction of the beam (characterized by a Maxwellian with kT = 270 keV) directly with the spectrum injected in the inner heliosphere. The well‐defined spatial structure of the event and the absence of any clear signatures of local interplanetary shock acceleration during the period June 9–17 implies that the injection source could have been a long‐lived hot coronal ion population. The “weak scattering” electron PAD implies that the other (antisunward) end of the core of the flux rope was magnetically connected, not back to the sun, but rather to the outer heliosphere.
On the absence of plasma wave emissions and the magnetic field orientation in the distant magnetosheath
Authors: Coroniti F. V. , Greenstadt E. W. , Moses S. L. , Tsurutani B. T. , Smith E. J.
Published: February 2004

In early September, 1983 ISEE‐3 made a long traversal of the distant dawnside magnetosheath starting near x = −150 RE downstream. The distant magnetosheath often contains moderately intense plasma wave emissions at frequencies from several hundred Hz to 5 kHz. However, over time scales of many days, a clear correlation exists between the occurrence of the plasma waves and the cone angle (θxB) between the magnetic field and the plasma flow velocity (x‐direction). For θxB large (small), the plasma wave amplitudes are near background (high). Sudden ( < 1 minute) changes in the local magnetic field orientation produce correspondingly sudden changes in the wave amplitudes. Statistically, the wave amplitudes decrease continuously with increasing θxB.
Observations of the remnants of the ultrarelativistic electrons injected by the strong SSC of 24 March 1991
Authors: Looper M. D. , Blake J. B. , Mewaldt R. A. , Cummings J. R. , Baker D. N.
Published: February 2004

Data from the SAMPEX spacecraft has shown the presence near L = 1.9 of the remnants of the ultrarelativistic electrons (above 15 MeV) injected into the magnetosphere on 24 March 1991. The decay of the electrons has been tracked since July 1992. The electrone‐folding lifetime is in the range of six to twelve months, and the location in L of the peak intensity moved inward by ∼0.05 units in one year. The inferred electron lifetime is similar to that of ∼0.5 MeV electrons, which is in agreement with extrapolation to higher energies of the theoretical estimates of Lyons and Thorne (1972).
Contribution of photosynthesized carbon to the methane emitted from paddy fields
Authors: Minoda T. , Kimura M.
Published: February 2004

Emission rates of CH4 from paddy soil with and without rice straw applications were measured with pot experiments to estimate the contribution of rice straw to total CH4 emissions during the growing season. The CH4 derived from rice straw was calculated to be 50.4% of the total emission. 13CO2 uptake experiments were carried out three times from Aug. 8 to Sept. 18 to estimate the contribution of photosynthesized carbon to CH4 emission. The contribution percentages of photosynthesized carbon to the total CH4 emitted to the atmosphere were 72–110% around Aug. 8, 29–36% around Aug. 30, and 13–17% around Sept. 18, 1993.
Complexity in a spatially uniform continuum fault model
Authors: Shaw Bruce E.
Published: February 2004

Recently, Rice [1993] pointed out that, up to now, the self‐organizing models which have produced complex nonperiodic sequences of events have all been sensitive to the spatial discretization used, and thus did not have a well defined continuum limit. He went on the suggest that spatial nonuniformity or “inherent discreteness” may be a necessary ingredient in allowing the complexity to develop in these systems. In this paper, I present a counterexample to this suggestion: a spatially uniform model with a well defined continuum limit is shown to give rise to complex nonperiodic sequences. The complexity arises in the deterministic model from inertial dynamics with a velocity‐weakening frictional instability, with the instability being stabilized at short lengthscales by a viscous term. The numerical results are shown to be independent of the spatial discretization for discretizations small compared to the viscous lengthscale. Furthermore, the qualitative features of the complexity produced are seen to be invariant with respect to two very different types of small scale cutoffs, implying a universality of the results with respect to the details of the small scale cutoff.
Evidence of an ion composition boundary (protonopause) in bi‐ion fluid simulations of solar wind mass loading
Authors: Sauer Konard , Bogdanov Alexander , Baumgärtel Klaus
Published: February 2004

The interaction of the solar wind with cometary plasma is studied in the framework of a collisionless 2D bi‐ion fluid plasma model which allows for different bulk velocities of the light and heavy ions. It is shown that an ion composition boundary is formed which is impenetrable for the protons but presents no barrier to the magnetic field flux. The magnetic field is transported further downstream by the charge‐neutralizing electrons which follow the heavy ions through the boundary. We believe that this new type of plasma boundary can explain the observed ion composition boundary at comets (cometopause, pile‐up boundary), at Mars (planetopause, massloading boundary) and at Venus (rarefaction wave, intermediate transition).
Distances to the termination shock and heliopause from a simulation analysis of the 1992–93 heliospheric radio emission event
Authors: Steinolfson R. S. , Gurnett D. A.
Published: February 2004

A new heliospheric radio emission event observed by Voyagers 1 and 2 in mid‐1992 is believed to have been produced by the interaction of an interplanetary shock with the heliopause. The shock is thought to have originated near the Sun during a period of intense solar activity in late‐May and early‐June, 1991. The observed travel time of the shock to the heliopause is 408 days; the initial speed is estimated to be between 600 and 800 km/s. We use a numerical gasdynamic simulation of an interplanetary shock, propagating through an equilibrium solution of the solar wind/interstellar medium interaction, to compute the distances to the termination shock and the heliopause that are consistent with these observations. For a shock speed of 600 km/s, the termination shock is located at 92 AU, and the heliopause is located at 128 AU. These distances increase to 112 AU and 156 AU when the shock speed is increased to 800 km/s.
Geomorphological width functions and the random cascade
Authors: Marani Marco , Rinaldo Andrea , Rigon Riccardo , Rodriguez‐Iturbe Ignacio
Published: February 2004

We examine the geomorphological width functions of several river basins through the formalism of conservative (microcanonical) random cascades and we compare the results with those of more conventional fractal and multifractal analyses. We suggest that the spatial patterns of aggregation described by the width functions analyzed show common recurrent characters and that the implications of the robust identification of the singularity spectra via Legendre transforms are supported also by random cascade rationale.
Assessing the ability of the Köppen System to delineate the general world pattern of climates
Authors: Triantafyllou G. N. , Tsonis A. A.
Published: February 2004

The Köppen climate classification system [Köppen, 1923] is a scheme that provides an objective numerical basis for defining regional climatic types based on temperature and precipitation. Through the years it has been used as a scientific and teaching tool for prescribing the general world pattern of climates. Here for the first time an evaluation of the system is performed by employing coextensive temperature and precipitation data over the N. Hemisphere for the last 140 years. First the global pattern of climate type sensitivity is obtained. From this pattern it is discovered that several climate types exhibit a rather strong variability. Since all climate types depend on temperature we then tested whether or not the above variability is due to the fact that over the last 140 years the global climate system exhibits a well documented positive temperature trend known as global warming. We found that the Köppen system is rather insensitive to the observed global warming and concluded that overall the system performs rather poorly over Europe and Asia whereas it appears adequate over N. America and N. Africa.
Fluid flow and heat transport near the critical point of H2O
Authors: Ingebritsen S. E. , Hayba D. O.
Published: February 2004

Near‐critical extrema in the properties of water may influence flow patterns in hydrothermal systems, but singularities in equations of state for H2O at its critical point have inhibited quantitative modeling. Posing governing equations in terms of pressure (P) and enthalpy (H) avoids these singularities and facilitates computation. Numerical simulations with a P‐H based model show little near‐critical enhancement in heat transfer for systems in which flow is driven by fixed pressure drops. However, in density‐driven systems, near‐critical variations in fluid properties can enhance convective heat transfer by a factor of 10² or more (“superconvection”) if permeability is sufficiently high. Near‐critical two‐phase processes (“heat pipes”) are at least equally effective at dissipating thermal energy. The restriction to high‐permeability environments within a fairly narrow P‐H window suggests that superconvection may be quite rare in natural systems
Fossil strain from the 1811–1812 New Madrid Earthquakes
Authors: Rydelek Paul A. , Pollitz Fred F.
Published: February 2004

Observations of postseismic deformation generally suggest that the effects of postseismic viscoelastic relaxation may persist for many decades after an earthquake. In particular, strain effects from the three great earthquakes that occurred in the New Madrid seismic zone in 1811–1812 may influence present day measurements of ground deformation in this active seismic region of the central United States. Forward calculations using an earth rheology that may be appropriate for a continental intraplate region and a simple fault model for the 1811–1812 sequence suggest that postseismic relaxation may be an important factor in driving the unexpectedly high rate of shear deformation recently observed in the southern New Madrid Seismic Zone.