bluuebunny/crossref_metadata_2025 huggingface dataset:
The Coast Belt Thrust System: Evidence of Late Cretaceous shortening in southwest British Columbia
Authors: Journeay J. M. , Friedman R. M.
Published: February 2008

The Coast Belt Thrust System (CBTS) is the leading edge of a west vergent contractional belt that formed along the inboard margin of the Insular superterrane in late Cretaceous time. The foreland of this contractional belt comprises a system of east dipping frontal thrusts that imbricate Jurassic and Early Cretaceous supracrustal arc sequences and related plutonic suites of the Western Coast Belt (WCB). These faults root eastward into an imbricate zone of folded thrusts and out‐of‐sequence reverse faults across which the metamorphic gradient has been structurally inverted. To the east and structurally above the imbricate zone is a folded stack of high‐pressure thrust sheets comprising metamorphosed island arc and oceanic rocks of the Central Coast Belt (CCB). These rocks represent the exhumed crustal root of the CBTS. Metamorphosed volcanic and volcaniclastic rocks that occur in thrust sheets of the imbricate zone yield U‐Pb zircon dates which support a correlation with lower‐plate Jurassic and Early Cretaceous arc sequences of the WCB. Structural and geochronologic data indicate a two‐stage history of Late Cretaceous shortening. During the early stage of shortening, supracrustal arc and related basin sequences along the inboard margin of the Insular superterrane were structurally imbricated and accreted to the toe (footwall) of a westward prograding accretionary complex made up of previously assembled terranes of the CCB. These early‐stage structures are represented by folded thrusts in the imbricate and hinterland zones of the CBTS. The timing of this early‐stage thrusting is bracketed by the emplacement of synorogenic plutonic suites, which yield U‐Pb zircon dates of 97 ± 1 Ma and 96 +6/−3 Ma. Late‐stage shortening involved both thin‐skinned thrusting and folding of Jura‐Cretaceous arc sequences in the WCB foreland and out‐of‐sequence thrusting of higher‐grade thrust sheets in the imbricate and hinterland zones of the CBTS. In the foreland this episode of deformation is bracketed by late‐and postkinematic plutons, which yield U‐Pb zircon dates of 94 ± 2 Ma and 91 +4/−3 Ma, respectively. In the imbricate zone, this episode of deformation is bracketed by the emplacement of synkinematic and postkinematic plutons, which yield U‐Pb zircon dates of 96 +6/−3 Ma and 94 +6/−5 Ma, respectively. The development of thick‐skinned out‐of‐sequence thrusts in the imbricate and hinterland zones of the CBTS signals a northeastward migration of the deformation front in Late Cretaceous time. This shift in the locus of thrusting resulted in southwestward telescoping and structural inversion of the metamorphic hinterland and may account for the complex stacking order and thermal history of the Southern Coast Belt.
Current land cover in the tropics and its potential for sequestering carbon
Authors: Houghton R. A. , Unruh J. D. , Lefebvre P. A.
Published: February 2008

Emissions of carbon dioxide and other greenhouse gases from human activity are increasing the concentrations of these gases in the atmosphere. The Earth is expected to warm as a result, with consequences that are potentially highly disruptive to human societies. Reductions in the use of fossil fuels and in rates of deforestation worldwide will reduce emissions of CO2, but atmospheric concentrations will continue to increase unless emissions are reduced by more than 60% (about 4.5 billion tons of carbon annually). Reforestation seems to offer one of the few means for reducing the atmospheric concentration of CO2over periods as short as human generations. We report here an approach for evaluating the potential for reforestation to help stabilize or even reduce the concentration of CO2in the atmosphere. Reforestation is defined broadly to include tree plantations, natural regrowth of secondary forests, and the practice of agroforestry. Our premise is that human use of the land has generally reduced woody biomass and that such lands have a potential for reaccumulating carbon if appropriately managed. We used published ground studies together with global vegetation index data from the NOAA 7 satellite to estimate current land cover in tropical regions. Then, superimposing this map of current land cover over maps depicting the distribution of vegetation cover prior to human disturbance, we obtained an estimate of about 3200 X 106ha in the tropics (almost 60% of the total land area considered) where woody biomass had been decreased, and where carbon might again be sequestered. We calculated the amount of carbon that could be withdrawn from the atmosphere and stored in woody biomass if several management options were implemented. Biomass accumulations were determined from forestry statistics. Application of the data on biomass to the areas suitable for accumulation of carbon yielded an estimate of potential accumulation of 160‐170 Pg carbon, an amount equivalent to the accumulation of carbon in the atmosphere since the start of the industrial revolution, or to about 25 years of fossil fuel emissions at current rates. Estimates of both area and potential accumulation of carbon were crude, probably not better than ±50%. They are useful for suggesting the role that tropical lands might play in stabilizing atmospheric concentrations of CO2, but they should not be used to suggest specific management options in individual countries. As maps with higher spatial resolution become available, however, the method should provide more precise estimates overall and in specific locations.
Plasma potential deformation due to localized large‐amplitude electron plasma waves
Authors: Sato Naoyuki , Hatakeyama Rikizo , Sato Noriyoshi
Published: February 2008

There appears a drastic potential drop along a collisionless magnetized plasma flow in the presence of localized large‐amplitude electron plasma waves generated externally. The phenomenon is attributed to ponderomotive force on electrons and nonlinear electron acceleration due to enhanced wave damping.
Kinematic model of active deformation in central Asia
Authors: Avouac Jean‐Philippe , Tapponnier Paul
Published: February 2008

The velocity field of present‐day deformation in Central Asia is modelled using a set of four rotating blocks (Siberia, Tarim, Tibet, India) on a spherical earth. A best‐fit is inverted on the basis of estimated shortening‐rates across the main thrust zones (Himalayas, Tien Shan) and measured slip‐rates along the principal strike‐slip faults (Altyn Tagh and Karakorum) separating those blocks. The fit to the data implies that nearly all the present convergence between India and Asia can be accounted for by slip‐partitioning on these four zones, with as much as 50% absorbed by northeastwards extrusion of Tibet. This suggests that localised deformation governs the present mechanical behaviour of the Central Asian lithosphere.
A fine‐particle sodium tracer for long‐range transport of the Kuwaiti oil‐fire smoke
Authors: Lowenthal Douglas H. , Borys Randolph D. , Rogers C. Fred , Chow Judith C. , Stevens Robert K. , Pinto Joe P. , Ondov John M.
Published: February 2008

Evidence for long‐range transport of the Kuwaiti oil‐fire smoke during the months following the Persian Gulf War has been more or less indirect. For example, high concentrations of aerosol particles containing soot and oil‐combustion tracers such as vanadium observed at great distances from the Middle East may have come from sources other than the oil fires. However, more‐recent data on the aerosol chemistry of Kuwaiti oil‐fire plumes provides a direct link between those fires and aerosols collected at the Mauna Loa Observatory (MLO) during the late spring and summer of 1991.

By itself, temporal covariation of fine‐particle concentrations of elemental carbon, sulfur, and the noncrustal V / Zn ratio in MLO aerosols suggested a link to large‐scale oil‐combustion sources, but not necessarily to Kuwait. However, high concentrations of fine‐particle (0.1–1.0 µm diameter) NaCl were observed in the “white” oil‐fire plumes over Kuwait during the summer of 1991. Further analysis of the Mauna Loa data indicates strong temporal correspondence between the noncrustal V / Zn and noncrustal Na / Zn ratios and strong consistency between the noncrustal Na to noncrustal V ratios found at Mauna Loa and in the Kuwaiti oil‐fire plume. In the absence of other demonstrable sources of fine‐particle Na, these relationships provide a direct link between the Kuwaiti oil fires and aerosol composition observed at MLO.
Accurate location of nuclear explosions at Azgir, Kazakhstan, from satellite images and seismic data: Implications for monitoring decoupled explosions
Authors: Sykes Lynn R. , Deng Jishu , Lyubomirskiy Paul
Published: February 2008

The 10 largest tamped nuclear explosions detonated by the Former Soviet Union in and near two salt domes near Azgir were relocated using seismic data and the locations of shot points on a SPOT satellite image taken in 1988. Many of the shot points are clearly recognized on the satellite image and can be located with an accuracy of 60 m even though testing was carried out at those points many years earlier, i. e. between 1966 and 1979. Onsite inspections and a local seismic monitoring network combined with our accurate locations of previous explosions would insure that any cavities that remain standing from those events could not be used for undetected decoupled nuclear testing down to a very small yield. Since the Azgir area, like much of the Pre‐Caspian depression, is arid, it would not be a suitable place for constructing large cavities in salt by solution mining and then using them for clandestine nuclear testing.
The 1992 Landers earthquake sequence: Earthquake occurrence and structural heterogeneities
Authors: Zhao Dapeng , Kanamori Hiroo
Published: February 2008

The June 28, 1992, Mw 7.3 Landers earthquake occurred in the southeastern Mojave Desert, California. Over 10,000 aftershocks of the earthquake were recorded by the Caltech‐USGS Southern California Seismic Network (SCSN) in 1992. To investigate the relationship between complexities in the crustal structure and variations in seismicity, we have used a tomographic method to invert 145,098 P wave arrival times from 3740 Landers earthquake aftershocks and 1148 other events recorded by 60 permanent and temporary SCSN stations. We determined a detailed P wave tomographic image with a spatial resolution of about 5 km and relocated the hypocenters with the obtained 3‐D velocity model. The results show a correlation between seismicity patterns and velocity patterns and a tendency for regions rich in seismicity to be associated with higher velocities. The higher velocity areas are considered to be strong and brittle parts of the fault zone, which are apt to generate earthquakes. In contrast, low velocity areas are probably more ductile and weaker, allowing aseismic slippage.
Radiative feedback of polar stratospheric clouds on Antarctic temperatures
Authors: Rosenfield Joan E.
Published: February 2008

A one‐dimensional time marching radiative transfer model has been used to investigate the potential effects of polar stratospheric clouds (PSCs) on winter and spring temperatures in the Antarctic lower stratosphere. High, middle, and low PSC amounts were specified from lidar backscatter profiles and were chosen to represent the likely range of PSC amounts present in the Antarctic region. The computed effects of the PSCs on temperatures depend strongly on the surface temperature and on the extent of tropospheric cloudiness, and range from a maximum increase of 6 K for a high amount of PSCs over a warm surface and clear troposphere to a maximum decrease of 2 K for a high amount of PSCs over a cold surface and a troposphere with high clouds. The average effect is unlikely to be more than a 1 or 2 K temperature change.
Effects of Doppler shifts and source perspectives on extreme ultraviolet images of ion populations moving in the inner magnetosphere
Authors: Murphy D. L. , Chiu Y. T.
Published: February 2008

The effects of solar EUV line resonance scattering by a population of ions in gyration, bounce and drift motion in the magnetosphere are formulated and demonstrated numerically with the O+ 834 Å line as test example. It is shown that anisotropies of motion induced by the geomagnetic field and source perspective effects caused by 834 Å earthshine profoundly affect the morphology and magnitude of the EUV line images, thus enhancing the effects of Doppler shifts on narrow EUV lines. These effects have little impact, though, on relatively wide resonance scattering lines such as the He+ 304 Å line.
Magnetic domain structures on a natural single crystal of magnetite
Authors: Özdemir Özden , Dunlop David J.
Published: February 2008

Well‐defined domain structures with the theoretically expected angles of 71°, 109° and 180° between adjacent domain magnetizations are observed on a 3‐mm octahedral crystal of magnetite sectioned parallel to a {110} crystallographic plane. A regular and readily interpretable array of closure domains, of the style predicted by Landau and Lifschitz [1935], is seen at free surfaces such as crystal edges and cracks. Closure and body domains form along adjacent <111> easy axes in the interior of magnetite crystals, but the closure domains are suppressed near surfaces that do not contain two sets of <111> axes, that is if the domain structure is viewed on a plane that makes a large angle with {110}. From the measured correlation between the width of a domain and its length, we obtain estimates of (0.91 ± 0.17) × 10−3 J/m² for the domain wall energy and 1.28 × 10−11 J/m for the exchange constant in magnetite. The latter figure is close to the value 1.33 × 10−11 J/m reported by Heider and Williams [1988]. Our study shows that the internal domain structures in multidomain magnetite are generally simple. More complicated patterns appear on unfavourably oriented viewing surfaces, but are not representative of the interior structure.
Low P‐wave velocity at the base of the mantle
Authors: Garnero Edward J. , Grand Stephen P. , Helmberger Donald V.
Published: February 2008

A tool for investigating P‐wave (VP) structure at the base of the mantle is presented. SKS waves at distances around 107° are incident upon the core‐mantle boundary (CMB) with a slowness that allows for coupling with diffracted P‐waves (Pd) at the base of the mantle. The P‐wave diffraction occurs at both the SKS entrance and exit locations of the outer core. The resulting phase, SPdKS, arrives slightly later in time than SKS, having a wave path through the mantle and core very close to SKS. The difference time between SKS and SPdKS most strongly depends on VP at the base of the mantle near SKS core entrance and exit points. Digitized long‐period (5‐15s) observations from deep focus Tonga events recorded by North American WWSSN and Canadian Seismographic Network stations, and South American events recorded by European and Eurasian WWSSN stations exhibit anomalously large SPdKS‐SKS difference times. SKS and the later arriving SPdKS are separated by several seconds more than predictions made by the global average PREM model. Models having a pronounced low‐velocity zone in VP at the base of the mantle best predict the observations. These models are perturbations of the PREM model, whereby the lowermost 50–100 km of the D″ layer has a negative VP gradient, with the mantle‐side CMB VP reduced from PREM by 5% (to 13.0 km/s) at the base of the mantle.
A novel approach to domain imaging in natural Fe/Ti oxides by spin‐polarized scanning electron microscopy
Authors: Haag M. , Allenspach R.
Published: February 2008

A novel approach to magnetic domain imaging in rock magnetism is described. Spin‐polarized scanning electron microscopy is a technique that can map domain patterns on a submicron scale and moreover completely differentiate the information on magnetism and morphology. We demonstrate the applicability of the technique to problems of rock magnetism by identifying the domain configuration in a natural ore grain consisting of two Fe/Ti‐oxide phases. Strong contrast enhancement can be achieved by covering the specimen with ultrathin Fe overlayers. We compare our approach to existing domain imaging techniques and discuss the potential of this method to obtain detailed insight into the microscopic magnetization processes relevant to rock magnetism.
Some consequences of the Shift Theorem for multispacecraft measurements
Authors: Chapman Sandra C. , Dunlop Malcom W.
Published: February 2008

We show how shift theorem yields a routine quantitative test to determine whether a structure seen by two or more spacecraft is a quasistatic convecting object, such as a boundary layer. The test indicates the frequency range over which the data is consistent with a structure which is coherent between spacecraft, planar, and time independent in its rest frame. A cluster of four non coplanar spacecraft is required to determine the velocity of the structure in the spacecraft frame. Whether or not the data is found to be consistent with quasistatic convecting object, this analysis of the data from four non coplanar spacecraft yields the convection velocity of the plasma given the dispersion relation or vice versa, as well as the wavevectors corresponding to given frequency components. The test for coherence, planarity and time independence is shown to be robust against detector and systematic inter‐spacecraft timing and positional uncertainties. Random errors will affect a finite frequency range, in principle this can be determined to restrict the frequency range over which the test can be applied.
Anisotropic magnetic susceptibility in the continental lower crust and its implications for the shape of magnetic anomalies
Authors: Florio G. , Fedi M. , Rapolla A. , Fountain D. M. , Shive P. N.
Published: February 2008

Magnetic anisotropy measurements on samples from the lower continental crust were made to test the hypothesis that anisotropy may cause deflection of the peak‐to‐trough axes of magnetic anomalies caused by mid‐ to lower crustal sources. Average anisotropy (P′) for these samples is 1.5 but can be as high as 3.4. Felsic granulite facies rocks show the highest anisotropy. Magnetic sources with P′ equal to the maximum determined in this study can cause azimuthal rotations of magnetic anomalies by up to about 25°, but P′ lower than or equal to 1.5 causes no significant rotation. Comparison of the model results to the abnormal shape of some magnetic anomalies in southern Italy indicate that these anomalies cannot be related easily to a strong and coherent AMS of the source rocks. The most probable explanation of such shapes is the existence of a strong remanent magnetization in subsequently rotated source bodies.
An ionospheric travelling convection vortex event observed by ground‐based magnetometers and by Viking
Authors: Vogelsang H. , Lühr H. , Voelker H. , Woch J. , Bösinger T. , Potemra T. A. , Lindqvist P. ‐A.
Published: February 2008

A transient ionospheric travelling convection vortex (ITCV) event was recorded by the EISCAT magnetometer cross in northern Scandinavia on April 21, 1986 around 8:40 MLT. Simultaneously, the near‐conjugate satellite VIKING observed strong magnetic and electric field variations on closed magnetic field lines. The signatures seen by the spacecraft are consistent with a passage through two oppositely directed field‐aligned current tubes. The total upward and downward currents turned out to be matched within a region of ∼ 1000 km in the ionosphere. Because of the close spatial and temporal proximity of both observations we interpret the field‐aligned currents as being associated with the ITCV. This is the first time that in‐situ measurements of the currents connecting the ITCV to the source region close to the magnetopause have been published. Both the current density and the dimensions of the current tubes could be estimated here.
Transmission characteristics of VLF/ELF radio waves through the Jovian ionosphere
Authors: Nagai Ken , Ohta Kenji , Hobara Yasuhide , Hayakawa Masashi
Published: February 2008

The propagation characteristics of whistler‐mode waves through the plausible profiles of the Jovian ionosphere have been investigated by means of full‐wave numerical computations. There were three different profiles examined in detail: an irregular profile based on Pioneer measurements, a more‐idealized smoother profile, and a smooth profile with a low‐altitude ledge. The whistler transmission losses for the Pioneer profiles with several ledges are found to be extremely large in a wide frequency range from 1 to 10 kHz at both day and night, even at a high magnetic latitude. The latitudinal dependence of the transmission loss for the smooth electron density profiles corresponding approximately to the lower edge of the Pioneer profiles, is estimated such that the loss at magnetic latitude greater than 50° is less than 10 dB at night and day. But the transmission loss exhibits a dramatic increase with the decrease in latitude from 30° ∼40°, especially at higher frequency and at day. The presence of a possible ledge in the bottom ionosphere is found to result in an oscillatory behaviour of transmission loss due to the development of a standing wave pattern between relative density maxima. The possible utilization of these theoretical characteristics is suggested to study the coupling of lightning energy to whistlers in the Jovian magnetosphere and also lightning properties from the whistler observations by future deep spacecrafts.
Continuous lidar measurements of stratospheric aerosols and ozone after the Pinatubo eruption. Part I: Dial ozone retrieval in presence of stratospheric aerosol layers
Authors: D‧Altorio Alfonso , Masci Fabrizio , Rizi Vincenzo , Visconti Guido , Boschi Enzo
Published: February 2008

We report stratospheric DIAL (DIfferential Absorption Lidar) ozone observations in presence of large amount of volcanic aerosols, which strongly affect the inversion of the backscattering signals. The retrieval method is based on the use of three wavelengths, two from the O3 DIAL (308 and 351nm) and a third one from an aerosol lidar (589nm) operated at the same site (L‧Aquila, Italy; 42°N,13°E). For each measurement session the relationships between the backscattering ratios at different wavelengths are fitted with an appropriate size distribution of the aerosols. The aerosol optical properties determined with this procedure allow to correct the ozone profiles. The ozone data are compared whenever possible with balloon ozonesonde measurements taken at S.Pietro Capofiume (Italy, 45°N, 11°E) or Hohenpeissenberg (Germany, 48°N, 11°E) and they generally show a good agreement. The ozone profiles can be retrieved with an indetermination that, within the aerosol layer, ranges between ±15 to ±35%. A systematic intercomparison is reported with data of other stations to assess the reliability of the method.
Continuous lidar measurements of stratospheric aerosols and ozone after the Pinatubo eruption Part II: Time evolution of ozone profiles and of aerosol properties
Authors: D‧Altorio Alfonso , Masci Fabrizio , Rizi Vincenzo , Visconti Guido , Verdecchia Marco
Published: February 2008

Two lidar systems, an aerosol lidar and an O3 Differential Absorption Lidar (DIAL), have been routinely operated at the same site (L‧Aquila, Italy; 42°N, 13°E) since August 1991. The multiwavelength analysis of the lidar signals allows to retrieve parameters related to equivalent aerosol size distributions and their optical properties. These are needed to correct the ozone DIAL profiles from the disturbance introduced by the stratospheric volcanic aerosols. The method and the confidence of the retrieved ozone profiles are discussed in a companion paper. Here we present the whole measurement series of ozone and backscattering ratio profiles during the period from August 1991 to December 1992. In addition, for some observations, the mode radius and the dispersion of the representative aerosol size distribution are reported. The time evolutions of aerosol surface area density and mass mixing ratio are also discussed within the uncertainties of the retrieval algorithm.
Airborne brightness temperature measurements of the polar winter troposphere as part of the Airborne Arctic Stratosphere Experiment II and the effect of brightness temperature variations on the diabatic heating in the lower stratosphere
Authors: Valero Francisco P. J. , Platnick Steven , Kinne Stefan , Pilewskie Peter , Bucholtz Anthony
Published: February 2008

In this paper we report radiometric measurements of tropospheric brightness temperatures obtained during the AASE II experiment. These measurements represent the first attempt to characterize effective radiative temperatures as seen from above the troposphere during the Arctic winter. The reported measurements include brightness temperatures at 6.7 and 10.5μm as seen from the NASA DC‐8 aircraft flying at about 11 km altitude. We also present radiative transfer calculations to estimate the effect of tropospheric brightness temperature on the lower stratospheric heating rates. Because of the recent massive eruption of the Pinatubo volcano, we also discuss the effects of a volcanic aerosol layer. It is concluded that small particles like the volcanic aerosol or PSCs type 1 do not affect stratospheric heating rates by much; on the other hand, larger particles, PSCs types 2 and 3, may have significant effects on heating rates and consequently on dynamics of the lower stratosphere. The dynamical effects of local stratospheric temperature variations are briefly discussed.
The Venus atmospheric response to solar cycle variations
Authors: Keating Gerald M. , Hsu N. Christina
Published: February 2008

Atmospheric drag measurements from the orbital decay of the Pioneer Venus Orbiter and Magellan spacecraft have recently been obtained of the Venus dayside and nightside atmosphere between 130 and 210 km during a period of low solar activity. These new measurements, combined with the earlier Pioneer Venus drag measurements (1978–80) obtained near the maximum of the 11‐year solar cycle, have allowed the detection of the detailed response of temperature, atomic oxygen and carbon dioxide to solar variations. We have found a weak but detectable temperature response on the dayside which is in accord with the response predicted by Keating and Bougher when they assumed very strong CO2 radiative cooling resulting from atomic oxygen exciting CO2 into 15 micron emission. This same radiative process may cause strong cooling in the Earth's upper atmosphere with the doubling of CO2 in the future. With decreasing solar activity, the O/CO2 ratio in the lower thermosphere is found to decrease, apparently due to decreased photodissociation of CO2 and lower temperatures. The percent decrease in atomic oxygen with decreasing solar activity on the dayside is found to be approximately the same as the percent decreases of atomic oxygen transported to the nightside. A very weak response of nightside temperatures to solar activity variations has also been detected.
Chapman's airglow mechanism resurrected?
Authors: Schofield Keith
Published: February 2008

A reanalysis is summarized of a previously unquestioned, sole source of kinetic data, on the reaction of NaO with O‐atom. It is apparent that there are significant uncertainties in the kinetic mechanism of the experiments. Moreover, it appears plausible that these reaction rate data do not relate to NaO but rather to Na2O. This conclusion has the potential for resolving a dilemma concerning the chemiluminescent excitation mechanism of sodium in the airglow and in long duration meteor trails. It remains conceivable that Chapman's originally suggested scheme is valid and recently proposed alternative explanations invoking a role for NaO(A²Σ+) are unnecessary.
A Stokesian model of areal clear‐sky direct radiation for mountainous terrain
Authors: Ranzi Roberto , Rosso Renzo
Published: February 2008

The global direct flux of clear‐sky incoming solar radiation over a given portion of terrain (e.g., the surface of a drainage basin) is modeled by using the Stokes' formula. Accordingly, line integration is substituted for surface integration to describe topographic variability. This allows for separating the effects of solar radiation geometry and terrain configuration. Application to a small alpine basin shows this model to provide accurate results also when a major portion of the terrain is in shadow. It can be applied to estimate radiative fluxes in hydrological models at the scale of small catchments and at the GCM scale when topography is complex.
Trends in total ozone over southern African stations between 1979 and 1991
Authors: Kalicharran S. , Diab R. D. , Sokolic F.
Published: February 2008

Trends in total ozone for the period 1979 to 1991 over the southern African subcontinent and the southern ocean islands of Marion and Gough and the South African Antarctic base of SANAE are examined. Version 6 TOMS data are used. With the exception of the low latitude stations (Nairobi and Harare), where a marginally increasing trend (+0.2% and +0.3%, respectively) was observed, the other stations all exhibited a decreasing trend in total ozone over the 13 year period, ranging between −1.1 and −2.6% over most of South Africa, increasing with latitude to reach −20.6% at SANAE. Inter‐annual fluctuations at Nairobi are dominated by a QBO, with maximum ozone occurring during the westerly phase of the QBO. At the extratropical locations, ozone peaks and troughs are anti‐correlated with those at Nairobi and the QBO signal is less well developed and modulated by the seasonal cycle.
Effect of hot N(4S) atoms on the NO solar cycle variation in the lower thermosphere
Authors: Gérard J. ‐C. , Shematovich V. I. , Bisikalo D. V.
Published: February 2008

The variation of the nitric oxide peak density near 110 km with solar activity is calculated using a photochemical diffusive model of thermospheric odd nitrogen. This model includes the reaction of translationally excited (“hot”) nitrogen atoms with O2 as a source of nitric oxide, in addition to the classical photochemistry. It is confirmed that the dissociation of N2 by energetic photoelectrons due to the ionization of atmospheric constituents by solar soft X rays is an important source of atomic nitrogen which controls the observed NO maximum near 110 km. The consideration of the hot N(4S) source increases the NO peak density by 45 to 60% dependent on the solar activity level considered. The calculated NO peak density increases by a factor of ∼3.5 from low to high solar activity conditions, in agreement with the Solar Mesosphere Explorer satellite observations. The absolute concentrations calculated in the model with an N(²D) effective yield of 54% from N2 electron impact dissociation are midway between the two sets of solar cycle NO variation measurements currently available.
Mapping and energization in the magnetotail: 1. Magnetospheric boundaries
Authors: Kaufmann Richard L. , Larson Douglas J. , Beidl Paul , Lu Chen
Published: February 2008

A set of boundaries was chosen to model the principal observed magnetospheric regions. Those regions which extended out to the distant magnetotail were defined at xsm = −20 RE. The Tsyganenko (1989) magnetic field model (T89) was used to project the boundaries down to the ionosphere. It was found that all field lines which passed within 3 RE of the magnetopause projected to the dayside ionosphere. Dayside arcs therefore generally map to the low‐latitude boundary layer, the cusp/cleft, or the entry layer. The nightside auroral zone, and therefore field lines associated with the substorm current diversion process, primarily traced to portions of the plasma sheet that do not come in direct contact with flowing solar wind plasma. Several mapping problems were encountered. The first involved identifying certain boundaries in the magnetosphere model. The flanks of the magnetotail are not modeled realistically. As a result, we had difficulty in defining a T89 magnetopause in the equatorial plane. Other problems were that some magnetotail boundaries may have no ionospheric signature, and that some boundaries are influenced by cross‐field plasma drift. Plasma boundaries are not tangent to field lines when drift is present, but all mapping was done by following field lines. Uncertainties of about 1° of latitude in the resulting ionospheric projections were found for each 1 RE of drift near midnight at xsm = −20 RE. The steady state magnetotail then was subdivided out to xsm = −22 RE according to the expected characteristics of charged particle orbits. Orbits were traced in the modified Harris magnetic field model, with parameters adjusted to approximate the shapes of T89 magnetic field lines. The one‐dimensional Harris model was used to eliminate some drift effects. This permitted a detailed study of each separate subregion. Curves defining various orbit types were projected to the ionosphere. It is suggested that low‐ or middle‐altitude satellites may be able to detect regions of quasi‐adiabatic and nonadiabatic equatorial orbits by monitoring the loss cones. For these highly field aligned loss cone particles, we found that the net effect of the complex interaction with the current sheet can be explained by an extremely simple model. The model involves shifting all generally field‐aligned ions as a block through an energy‐dependent “scatter” angle. When viewed microscopically, the resulting pitch angle changes are highly structured. Macroscopically it may be possible to describe the process in terms of pitch angle diffusion.
Narrow‐band electrostatic noise generated by an electron velocity space hole
Authors: Richard Robert T. , Ashour‐Abdalla Maha , Coroniti Ferdinand V.
Published: February 2008

Narrow‐band Electrostatic Noise (NEN) is a common occurrence in the Earth's distant magnetotail. NEN is observed in a frequency range (100‐316 Hz) that falls roughly between the electron and ion plasma frequencies. This mode may result from holes in the electron distribution function associated with slow shocks. An instability that is associated with this mode is studied using numerical simulations. The growth of the instability depends on the size and shape of the hole. The hole mode can also be driven unstable by either an anisotropy in the electron distribution function or an ion beam. In all these cases the instability saturates at a low level and only a fraction of the available free energy is released.
Parametric excitation of the electrostatic whistler and Z mode by auroral kilometric radiation
Authors: Hui C. ‐H. , Seyler C. E.
Published: February 2008

By using a two‐dimensional magnetized electron plasma simulation model it is found that an X mode which is presumed to be the dominant component of auroral kilometric radiation can parametrically decay into an electrostatic whistler and a Z mode. The electrostatic whistler grows to large amplitude, and the associated parallel electric field accelerates electrons to several kiloelectron volts. It is proposed that this mechanism is a possible origin of Z mode radiation, broadband electrostatic noise, and energetic parallel electron beams.
Magnetohydrodynamic theory of field line resonances in the magnetosphere
Authors: Cheng C. Z. , Chang T. C. , Lin C. A. , Tsai W. H.
Published: February 2008

The linearized ideal magnetohydrodynamic (MHD) equations are cast into a set of global differential equations from which the field line resonance equations of the shear Alfvén waves and slow magnetosonic waves are obtained naturally for finite beta plasmas in general magnetic field geometries with flux surfaces. The coupling between the shear Alfvén waves and the magnetosonic waves is through the combined effects of geodesic magnetic field curvature and plasma pressure. For axisymmetric magnetospheric equilibria there is no coupling between the shear Alfvén waves and the slow magnetosonic waves because the geodesic magnetic field curvature vanishes. We derive the asymptotic singular solutions of the MHD equations near the field line resonant surface. We perform numerical solutions of the field line resonance equations for a dipole magnetic field with constant plasma pressure and density along the magnetic field line. Similar to previous studies, the shear Alfvén wave field line resonant frequency is roughly given by ω ≈ cL−4 ρ−1/2, where the coefficient c is roughly constant with respect to the L shell distance and ρ is the plasma mass density. The slow magnetosonic wave resonant frequency is roughly proportional to P/ρL², where P is the plasma pressure, and is much smaller than the shear Alfvén wave resonant frequency even for equatorial plasma beta as high as unity.
Electromagnetic ion cyclotron waves stimulated by modest magnetospheric compressions
Authors: Anderson B. J. , Hamilton D. C.
Published: February 2008

The relationship between sudden impulses and enhancements or onset of Pc 1 at high‐latitude ground stations is well established. It has been proposed that increased hot proton temperature anisotropy resulting from convection during magnetospheric compression is responsible for the enhancement in Pc 1 emissions via generation of electromagnetic ion cyclotron (EMIC) waves in the dayside outer equatorial magnetosphere (e.g., Olson and Lee, 1983). We use AMPTE/CCE magnetic field and particle data to test this suggestion. Compression‐induced Pc 1 events are very common in the AMPTE/CCE data set: among isolated sudden (<5 min) magnetic field increases of 10 nT or greater in the 8‐16 MLT/L > 6 region, 47% are associated with EMIC wave onset at the satellite. Compressions energize particles via earthward convection, so the association of local Pc 1 onsets with compressions may be either a temporal effect or merely the result of inward transport to the spacecraft of plasma previously unstable to EMIC waves. EMIC waves occur 10‐20% of the time in the outer magnetosphere, which is considerably less than the occurrence rate of Pc 1 with compressions, suggesting that convection alone does not account for compression Pc 1 onset. To test whether the plasma is more unstable to EMIC waves after compressions than before, the proton distribution (1‐300 keV) measured at the peak of the compression is used together with an image dipole model to calculate the distribution that would result from adiabatic expansion back to the precompression state. Comparison of the EMIC wave growth rates from the measured compression and extrapolated expansion distributions provide an indication of the compression‐induced enhancement of EMIC wave activity. Differences in wave growth of several orders of magnitude are found, indicating significant increases in EMIC wave activity. The results suggest that enhancements in dynamic pressure pump the energetic proton distributions in the outer magnetosphere, driving EMIC waves. Waves are expected to be generated most readily close to the magnetopause, and transient pressure pulses may be associated with bursts of EMIC waves, which would be observed on the ground in association with ionospheric transient signatures.
Superposed epoch analysis of pressure and magnetic field configuration changes in the plasma sheet
Authors: Kistler L. M. , Baumjohann W. , Nagai T. , Möbius E.
Published: February 2008

Using data from 41 substorm events in the near‐Earth magnetotail, we have combined plasma, energetic ion, and magnetic field data from the AMPTE/IRM spacecraft to perform a superposed epoch analysis of changes in the total pressure and in the magnetic field configuration as a function of time relative to substorm onset. We find that unloading is evident in the total pressure profile, with the pressure beginning to decrease at onset time and reaching a minimum about 45 min later. The pressure decreases by ∼20%. The pressure increase associated with the growth phase is not evident in this analysis. This indicates that the pressure changes during the growth phase are not as uniform for the different substorms as the pressure changes during the expansion phase. To study the changes in the magnetic field configuration, we have determined the development of the plasma pressure profiles in z for an average of data from 15 to 19 RE. We combined this information with the known radial gradient in the total pressure to determine the field configuration changes during a substorm. The stretching of the field during the growth phase is clearly evident in this analysis. At substorm onset, the field line dipolarization begins on the innermost field lines and then progresses to the outer field lines. The field lines map the closest to the Earth about 45 min after substorm onset, and then begin to stretch out again during the recovery phase of the substorm.
Heat flux solutions of the 13‐moment approximation transport equations in a multispecies gas
Authors: Wu Jian , Taieb Charley
Published: February 2008

A steady state analytical solution of the heat flux equation in the 13‐moment approximation is obtained, where temperature gradient, regimes changing from subsonic to supersonic flow situations, and effects of drift velocity between species, say diffusion‐thermal effects, are taken into account. From such a general solution, validity conditions of Fourier's law are examined. A solution for a collisionless regime based upon the above solution is achieved. Then, the high‐latitude topside ionosphere with a mixture of the ionized constituents O+ and H+ and neutrals is studied. Heat flux is derived for the two ionized constituents in a regime where the gradient of the aligned velocity component is less important than collision frequencies. Heat fluxes of O+ and H+ ions in this situation are further simplified considering that H+ ion concentration is smaller than O+ ion concentration. With the help of the European incoherent scatter (EISCAT)‐VHF data, O+ and H+ heat fluxes in the high‐latitude topside ionosphere are calculated with the above solutions. Results are compared to those obtained with Fourier's law. We find that Fourier's law underestimates significantly heat fluxes in this case, especially for H+. Thermal conduction is calculated, both with our general solution and with the Fourier's law. For the H+ ion thermal conduction, Fourier's law may lead to an inverse variation with altitude when compared to our solution, which gives an inverse contribution to the H+ ion energy balance and to the H+ temperature. H+ ion heat flux is upward not only in the supersonic regime shown by DE 1 data but also in the subsonic regime at lower altitude in the high‐latitude topside ionosphere, as shown by EISCAT data.
Three‐dimensional nonsteady compressible magnetohydrodynamic fluctuations in the solar wind
Authors: Lou Yu‐Qing
Published: February 2008

We investigate some basic properties of three‐dimensional nonsteady compressible magnetohydrodynamic (MHD) perturbations in a polytropic radial MHD wind with spherical symmetry. At a large radial distance r, we derive analytical solutions for MHD slow‐ and fast‐type perturbations for several rational values of the polytropic index γ. The propagation characteristics of MHD slow‐type perturbations, which are more magnetic at large r, are very similar to those of Alfvénic perturbations; namely, there exists the same characteristic frequency fnof;c for both types of perturbations, and the transverse magnetic field perturbation associated with MHD slow‐type perturbations also tends to dominate the background radial magnetic field at large r except in the zero frequency limit. The propagation characteristics of MHD fast‐type perturbations, which are more acoustic at large r, depend upon the value of γ because the sound speed CS in the wind scales as ∼r−(γ‐1) at large r. For the typical case of γ < 2, MHD fast‐type perturbations always propagate relative to the wind. For the atypical case of γ > 2, acoustic perturbations actually become MHD slow perturbations at large r because CS is now slower than the Alfvén speed CA, which scales as ∼r−1 at large r, and these acoustic perturbations do not propagate relative to the wind, yet the wind advects them radially outward. For the special case of γ = 2, there exists another characteristic frequency fnof;a. For perturbation frequency fnof; > fnof;a, acoustic perturbations propagate relative to the wind, whereas for fnof; < fa, they appear standing relative to the wind. We discuss the relevance of these results, both MHD fast‐ and slow‐type perturbations with γ < 2, to interplanetary fluctuations in the inner solar wind. In particular, we interpret the increasing trends with r of the relative density and magnetic field fluctuations observed in high‐speed solar winds within 0.3 to 1 AU as manifestation of MHD fast‐ and slow‐type perturbations.
On the cause of thin current sheets in the near‐Earth magnetotail and their possible significance for magnetospheric substorms
Authors: Schindler K. , Birn J.
Published: February 2008

The formation of thin current sheets in the near‐Earth magnetotail during substorm growth phases is addressed in terms of a simple model. An appropriate part of the unperturbed magnetotail is represented by a plane sheet model. Perturbations are applied to the upper and to the left boundaries, representing the magnetopause and the near‐Earth tail boundary, where the perturbation at the latter models the interaction between the tail and the inner magnetosphere. Treating the perturbation as ideal (dissipation‐free), we found that singular current sheets develop in the midplane of the tail. The analytical results are explored numerically. Using realistic dimensions of the domain considered, the influence of the earthward boundary on current sheet formation dominates. It is argued that current sheet formation of this type plays an important role in the processes associated with the onset of magnetospheric substorms.