bluuebunny/crossref_metadata_2025 huggingface dataset:
Single‐link cluster analysis of earthquake aftershocks: Decay laws and regional variations
Authors: Davis Scott D. , Frohlich Cliff
Published: February 2008

Using single‐link cluster analysis, we investigate how various properties of aftershock sequences depend on their tectonic regime and focal depth. For International Seismological Centre earthquakes of mb ≥ 4.8, we find that earthquakes deeper than 70 km have the fewest and smallest aftershock sequences. Even after accounting for differences in detectability and maximum magnitude, we find that ridgetransform earthquakes have smaller aftershock sequences than shallow subduction zone earthquakes. Among different subduction zones, we find that zones with high moment release rates possess larger aftershock sequences. Comparing ridge‐transform zones, we find those with slower spreading rates possess larger aftershock sequences. By transposing origin times of several different aftershock sequences as if all had main shocks occurring at time zero, we are able to study the properties of aftershock sequences which individually have too few aftershocks to study by other means. Secondary events determined by single‐link cluster analysis follow a modified Omori's (power law) decay for time separations of 0.1 day to 20 days from the parent event, with p values ranging from 0.539±0.022 (intermediate‐ and deep‐focus earthquakes) to 0.928±0.024 (ridge‐transform earthquakes). We find that earthquake foreshocks and multiplets also follow a modified Omori's law. At greater times from the main shock the decay is steeper than a power law decay, more like an exponential decay. Aftershocks in the Adak catalog (mb ≥ 2.0) show a marked decrease in activity between 40 and 50 km depth. We speculate that the observed differences in number of aftershocks and p values may be caused by variations in fault heterogeneity or in fluid pressures.
Hurricane‐induced surge and currents on the Texas‐Louisiana shelf
Authors: Signorini S. R. , Wei J. S. , Miller C. D.
Published: February 2008

This study consists of numerical model simulations of hurricane‐induced surge and currents on the Texas‐Louisiana shelf. The numerical experiment includes the simulation of multiple hurricane tracks with landfalling points along the Texas‐Louisiana coast. A parallel storm that traverses the entire Texas‐Louisiana coastline is also modeled to assess the difference in shelf response between landfalling and parallel storms. The grid extends from the Texas‐Mexico border to the Gulf Coast of Florida, with the ocean open boundary seaward of the shelf break. Along‐shelf and cross‐shelf surge and current variability are assessed as a function of shoreline geometry and bottom topography. A complementary one‐dimensional mixed layer model is used to evaluate the vertical structure of the currents and the maximum depth of hurricane influence. The choice of landfalling storm tracks is based principally on historical storm tracks for the Texas‐Louisiana area. Storm intensity, i.e., central pressure depression, for all storms is set equal to the 10‐year recurrence interval central pressure. Strong cyclonic flow is induced by the hurricane wind field within a distance from the storm's center equal to 3 to 5 times the storm's radius of maximum winds. Far‐field hurricane winds generate a northward moving coastal jet along the west coast of Florida, particularly for the landfalling storms. The far‐field continental shelf currents are topographically steered by the shoreline and bathymetry. There is strong evidence of a cyclonic‐anticyclonic eddy pair being generated in the wake of the parallel storm traveling eastward over the continental shelf. An intercomparison of the one‐ and two‐dimensional models shows that for depths less than 50 m, the combined use of the surge and mixed layer models permits a description of the vertical and horizontal hurricane‐induced current patterns. The surge height computations for a given storm strength point to the importance of several factors that determine surge levels as a function of offshore distance. These factors are bathymetry, topography, angle of approach of the storm, distance to landfall location, and shelf width. The most dramatic increase in surge levels occurs in depths less than 10 m, where the surge profile mirrors the changes in the bottom slope. In contrast, the sensitivity of surge dynamics to shelf width is neither strong nor consistent. A narrow spread of maximum surge values is observed. Each transect is examined individually to explain local behavior and the reason for the modest variation in surge values among dissimilar geographical areas. No critical dependence on the exact storm angle exists for storm angles within the range of angles associated with maximum surge generation (within 20° counterclockwise from the shore‐normal direction). Since the landfalling storms used in this study fall into this category, no significant dependence of surge height on the landfalling angle is observed.
Measurement of the hydrodynamic modulation of centimeter waves
Authors: Miller Sarah J. , Shemdin Omar H.
Published: February 2008

An investigation of the hydrodynamic modulation of 1‐ to 3.5‐cm wind waves in a wave tank is described. The modulation of short waves at wind speeds from 4 to 10 m s−1 was due to a mechanically generated 2‐s surface wave. Measurement of the surface slope was obtained using a laser‐optical slope sensor. The equilibrium height wave number spectrum was determined using the two components of the slope frequency spectrum. It was found to be consistent with k−3.75 cosp (θ/2), where p is a decreasing function of k and wind speed. The linear modulation transfer function was found to be 2–3 times that predicted by a linearized action‐conservation model based on Hughes' (1978) theory, and to increase with wind speed. Phase agreement is also unsatisfactory, the modulation being in phase with the oscillating current at high wind speeds.
Wind‐induced mesoscale features in a coupled ice‐ocean system
Authors: Ikeda M.
Published: February 2008

A quasi‐geostrophic, mesoscale eddy‐resolving model is coupled with free‐drifting sea ice to examine mesoscale oceanic structures, which are induced by wind forcing on a nonuniform ice distribution, and redistribution of sea ice. Initial concentration of sea ice has anomalies on the motionless ocean, and the sea ice is suddenly forced by a wind stress. Differences in Ekman transport between the high (low) concentration area and the surrounding area generate dipole eddylike features in the ocean with anticyclonic and cyclonic eddies on the right (left) and left (right), respectively, looking in the downwind direction. Redistribution of ice by the ocean circulation continues after the wind ceases, forming arch or hammer head shapes of ice anomalies. Interactions with the other anomalies can produce various shapes, which could lead to misinterpretation of ocean flow field. It is suggested that to detect ocean flow field in an ice‐covered area (not near the ice edge), trajectories should be used instead of shapes of ice cover.
Biological production models as elements of coupled, atmosphere‐ocean models for climate research
Authors: Platt Trevor , Sathyendranath Shubha
Published: February 2008

Process models of phytoplankton production are discussed with respect to their suitability for incorporation into global‐scale numerical ocean circulation models. Exact solutions are given for integrals over the mixed layer and the day of analytic, wavelength‐independent models of primary production. Within this class of model, the bias incurred by using a triangular approximation (rather than a sinusoidal one) to the variation of surface irradiance through the day is computed. Efficient computation algorithms are given for the nonspectral models. More exact calculations require a spectrally sensitive treatment. Such models exist but must be integrated numerically over depth and time. For these integrations, resolution in wavelength, depth, and time are considered and recommendations made for efficient computation. The extrapolation of the one‐(spatial)‐dimension treatment to large horizontal scale is discussed.
Climatological perspectives, oceanographic and meteorological, on variability in the subtropical convergence zone in the northwestern Atlantic
Authors: Hanson Howard P. , Cornillon Peter , Halliwell George R. , Halliwell Vicki
Published: February 2008

We discuss the large‐scale setting for the Frontal Air‐Sea Interaction Experiment (FASINEX). A climatology of the west‐central North Atlantic, derived from various data sets, is presented, and the meteorological and oceanographic context for FASINEX is thereby established. While the atmospheric and oceanic processes of interest during the intensive phases of FASINEX are not resolved in this large‐scale study, we are able to show how these scales produce an environment favorable to the smaller‐scale processes of frontogenesis that are the subject of other contributions in this issue.
A study of the sources and sinks of methane and methyl chloroform using a global three‐dimensional Lagrangian tropospheric tracer transport model
Authors: Taylor John A. , Brasseur G. P. , Zimmerman P. R. , Cicerone R. J.
Published: February 2008

Sources and sinks of methane and methyl chloroform are investigated using a global three‐dimensional Lagrangian tropospheric tracer transport model with parameterized hydroxyl and temperature fields. By comparison with methyl chloroform observations a global average tropospheric hydroyl radical concentration of 6.4×105 cm−3 was found to be consistent with published methyl chloroform emission data for the year 1980. Published methyl chloroform emissions data for 1981–1984 were found to be inconsistent with the observed methyl chloroform concentration increases. A large decrease in hydroxyl radical concentrations could explain the disagreement between the emission data and atmospheric methyl chloroform concentrations, but this is unlikely. Using the hydroxyl radical field calibrated to the methyl chloroform observations, the globally averaged release of methane and its spatial and temporal distribution were investigated. Two source function models of the spatial and temporal distribution of the flux of methane to the atmosphere were developed. The first model was based on the assumption that methane is emitted as a proportion of net primary productivity (NPP). With the average hydroxyl radical concentration fixed, the methane source term was computed as ∼623 Tg CH4, giving an atmospheric lifetime for methane ∼8.3 years. The second model identified source regions for methane from rice paddies, wetlands, enteric fermentation, termites, and biomass burning based on high‐resolution land use data. This methane source distribution resulted in an estimate of the global total methane source of ∼611 Tg CH4, giving an atmospheric lifetime for methane ∼8.5 years. The most significant difference between the two models were predictions of methane fluxes over China and South East Asia, the location of most of the world's rice paddies, indicating that either the assumption that a uniform fraction of NPP is converted to methane is not valid for rice paddies, or that NPP is underestimated for rice paddies, or that present methane emission estimates from rice paddies are too high. Using a recent measurement of the reaction rate of hydroxyl radical and methane by Vaghjiani and Ravishankara (G. L. Vaghjiani and A. R. Ravishankara, Rate coefficient for the reaction of OH and CH4: Implications to the atmospheric lifetime and budget of methane, submitted to Nature, 1990) (hereinafter referred to as Vaghjiani and Ravishankara, 1990) leads to estimates of the global total methane source for SF1 of ∼524 Tg CH4 giving an atmospheric lifetime of ∼10.0 years and for SF2 ∼514 Tg CH4 yielding a lifetime of ∼10.2 years. These results are provisional pending any revision of the reaction rate for hydroxyl radical and methyl chloroform.
Precipitating relativistic electrons: Their long‐term effect on stratospheric odd nitrogen levels
Authors: Callis L. B. , Baker D. N. , Blake J. B. , Lambeth J. D. , Boughner R. E. , Natarajan M. , Klebesadel R. W. , Gorney D. J.
Published: February 2008

Using electron count rate data at geostationary orbit, daily energy spectra, extending from 30 keV to 15 MeV, have been developed for trapped relativistic electrons at 6.6 RE These spectra have been used to model the flux of these electrons into the atmosphere at 120 km. Energy deposition calculations permit daily sources of HOx and NOy to be calculated at auroral and subauroral latitudes due to relativistic electron precipitation (REP) for the period June 13, 1979, through June 4, 1988. Both short‐term and long‐term source variations are quite large over the period considered. The long‐term variation of the NOy source is found to reach a maximum in late 1984 and early 1985, with significant declines thereafter. Daily Solar Backscattered Ultraviolet (SBUV) O3 data show a significant response to these precipitation events. Two‐dimensional model calculations have been carried out for the period 1979 to 1990 with REP effects included through June 4, 1988. Results suggest that globally integrated NOy has increased by 35–40% from 1979 to early 1985 with declines thereafter. The largest long‐term increases are found in the lower stratosphere at the high latitudes. Comparisons of Limb Infrared Monitor of the Stratosphere (LIMS), Solar Mesospheric Explorer (SME), Stratospheric Aerosol and Gas Experiment (SAGE), and SAGE II NO2 data are consistent with these calculations. The results suggest that a significant contribution to the anomalously large and unexplained global O3 declines between 1979 and 1985 has been made by the catalytic destruction of O3 by odd nitrogen in the lower stratosphere at mid to high latitudes. The results also provide evidence for a clear and strong linkage between solar variability, the state of the magnetosphere, and the chemical climatological state of the middle and lower atmosphere.
Charge exchange contamination of CRIT‐II Barium CIV Experiment
Authors: Swenson G. R. , Mende S. B. , Meyerott R. E. , Rairden R. L.
Published: February 2008

Experiments have been recently performed which attempted to confirm Critical Ionization Velocity (CIV) ioinzation by deploying chemicals at high velocity in the ionosphere. Specifically, the CRIT‐II Rocket performed a barium release in the ionosphere where observations of Ba+ resonant emissions following the release are believed to have resulted from the CIV process. Calculations are presented here which suggest a significant fraction (if not all) of the Ba+ observed likely resulted from charge exchange with the thermosphere ions and not through CIV processes. The results presented here are pertinent to other CIV experiments performed in the ionosphere. It is recommended that laboratory measurements of the charge exchange cross section between O+ and Ba as well as other metal vapors used in CIV experiments be made.
EXOS‐D observations of electric field fluctuations and charged particle precipitation in the polar cusp
Authors: Matsuoka A. , Mukai T. , Hayakawa H. , Kohno Y. ‐I. , Tsuruda K. , Nishida A. , Okada T. , Kaya N. , Fukunishi H.
Published: February 2008

EXOS‐D has observed irregular and spiky electric fields at the polar cusp in the altitude range of 4,000 to 10,000 km. The oscillations have amplitude of tens of mV/m and a broadband spectrum. We have found that high‐frequency (> 0.5 Hz) oscillations are associated with the precipitation of magnetosheath‐originated plasma, i.e., ion in the energy range of 0.1 to 1 keV/e and electron above 100eV/e. Oscillatory electric fields can also be observed all along the auroral oval, but they are more intense and more frequently seen at the cusp. The nature of these oscillation is discussed in terms of two possible mechanisms; i.e., 1) Doppler‐shifted quasi‐static structure of field‐aligned current, 2) Alfven waves propagated along magnetic field lines. We suggest that the high‐frequency turbulence in the polar cusp region is due to Alfven waves propagated from the magnetopause where interplanetary and geomagnetic field lines are reconnected and the magnetosheath plasma is injected into the polar cusp.
The role of quasi‐stationary planetary waves in the retrieval of concentrations from satellite measurements
Authors: Varotsos Constantinos , Cartalis Constantinos
Published: February 2008

Two recently proposed Reference Atmospheres for the vertical and latitudinal distribution of temperature in the middle atmosphere yield concentration values of nitric oxide (NO) which differ by as much as 25% at high latitudes during winter. The role of the quasi ‐ stationary planetary waves in the temperature distribution at high latitudes during winter is investigated with respect to the above mentioned NO difference. Considering this role, the initial difference is reduced to about 15% maximum.
VHF radar observation of gravity wave critical layers in the mid‐latitude summer mesopause region
Authors: Yi Fan , Klostermeyer Jürgen , Rüster Rüdiger
Published: February 2008

Observations with the SOUSY VHF Radar in the mesopause region during summer 1989 show layers of strong echo intensity and wind speeds increasing with height. Occasionally, quasi‐monochromatic internal gravity waves occur in the bottom side of the echo layer and vanish in the height interval around the echo intensity maximum which tends to increase with increasing wave amplitude. The data analysis can be performed using a Boussinesq and a WKB approximation. It shows that the horizontal phase trace velocity of the observed gravity waves is equal to the background wind velocity at the height of the echo intensity maximum. The observations thus represent nonlinear gravity wave‐critical level encounters producing strong turbulence in the neutral gas. But the estimated energy dissipation rates are too small to produce neutral gas turbulence at scales equal to half the radar wavelength yielding an additional indication for a yet unidentified mechanism generating small‐scale structures in the electron gas.
Differences between magnetic domain imaging observations and theory
Authors: Ye Jun , Merrill Ronald T.
Published: February 2008

A quasi‐two‐dimensional model is developed to calculate domain structures in magnetite grains containing two to 20 domains. The calculation shows that “domains” do not consist of uniformly magnetized regions, consistent with the conclusions previously carried out on sub‐micron grains, but that they become more uniformly magnetized for grains containing several domains, consistent with domain imaging results. In spite of improvement over previous calculations, there remains a significant difference between the number of domains observed and calculated.
Stable isotopic constraints on the nature of the syntectonic fluid regime of the Canadian Cordillera
Authors: Nesbitt Bruce E. , Muehlenbachs Karlis
Published: February 2008

Oxygen, hydrogen and carbon isotopic analyses of rocks from the Canadian Cordillera document regional variations in the origins and evolution of crustal fluids. High temperature systems in unmetamorphosed, felsic volcanic rocks are characterized by low δ 18O values. Veins in regional metamorphic rocks are characterized by δ 18O values that reflect approximate oxygen isotopic equilibration of the fluids with regional rock units. The δ D studies indicate that both systems were dominated by meteoric water. The δ 13C values for vein carbonate indicate a regional lithologic control on δ13C values. The data indicate that convection of surface fluids to depths of 10 or more kilometers during orogenesis was common. The existence of deep convection cells involving meteoric water further indicates that fluid pressures to these depths must have been approximately hydrostatic. Regional structural style appears to exert an important control on the depth of penetration of surface fluids.
Combined EISCAT and All‐Sky Camera observations of auroral structures
Authors: Girard L. , Senior C.
Published: February 2008

Discrete arc structures were identified from EISCAT data on March 11, 1984 which were simultaneously recorded on All‐Sky camera pictures from the Kilpisjärvi station in Finland. From the electric field measurements supplied by the tri‐static UHF facility, some privileged orientation has been found through the requirement of a uniform tangential electric field across the arc structure, which corresponds to the preferential arc alignment as deduced from camera pictures. Additional fold structures, resolved by the All‐Sky camera, develop along the preexisting arcs which still organize the electric field fluctuations in their vicinity.
The West Mageik Lake Sill Complex as an analogue for magma transport during the 1912 Eruption at the Valley of Ten Thousand Smokes, Alaska
Authors: Lowenstern Jacob B. , Wallmann Peter C. , Pollard David D.
Published: February 2008

We compare the structure and intrusive history of the West Mageik Lake sill complex to possible conduits for magma transport during the 1912 eruption at the nearby Valley of Ten Thousand Smokes (VTTS), on the Alaska Peninsula, to shed light on some of the enigmatic aspects of the 1912 eruption, including its unusual feeder system and eruptive sequence. At West Mageik Lake, Late Tertiary (?) rhyolitic magma propagated along a roughly east‐west trend as sills that followed bedding planes and through‐going joint sets in the Jurassic Naknek siltstone. This demonstrates the feasibility of arc‐parallel transport of rhyolitic magma as sills at shallow crustal levels.
Short period wave generation in Moss Landing Harbor caused by offshore landslides induced by the Loma Prieta Earthquake
Authors: Gardner‐Taggart Joan M. , Barminski Robert F.
Published: February 2008

Short period waves were observed in the Moss Landing Harbor approximately 2 minutes after the October 17, 1989 Loma Prieta earthquake. Offshore submarine landslides in the region of wave generation was noted by scuba divers and recorded by side scanning sonographs, fathometer records and ROV video footage taken in the area after the quake. These waves are believed to have been generated by offshore submarine landslides along the canyon walls of the Monterey Canyon directly offshore of the Moss Landing Marine Laboratories.
A picosecond accuracy relativistic VLBI model via Fermi normal coordinates
Authors: Shahid‐Saless Bahman , Hellings Ronald W. , Ashby Neil
Published: February 2008

We use Fermi normal coordinates to construct transformations relating solar system barycentric coordinates to local inertial geocentric coordinates. We then calculate relativistic corrections to terrestrial VLBI measurements. We develop our formalism to include corrections needed for picosecond accuracy. We also include a calculation of photon time delay which includes effects arising from the motion of gravitational sources.
Mean winds, tides and gravity waves in the upper middle atmosphere during ALOHA‐90
Authors: Vincent R. A. , Lesicar D.
Published: February 2008

Wind measurements made with a partial reflection radar located on Christmas Island (2°N, 157°W) are used to describe the dynamical state of the equatorial mesopause region during ALOHA‐90. Time mean westward (easterly) winds prevailed at most heights, and reached their maximum values of about −60 ms−1 near 85 km, but the mean meridional motions were weak. Strong oscillations due to the 24, 12, and 8 hr atmospheric tides were also observed in both wind components. The inferred vertical wavelengths were large, even for the diurnal tide. On the nights of 22 and 25 March, when airborne lidar observations were made in the vicinity of Christmas Island, the prevailing and tidal winds combined to produce especially strong westward winds ( −100 ms−1). Gravity wave activity was also high during March/April, especially for short period waves, although considerable day‐to‐day variability was noted.
A cautionary tale for palaeomagnetists: A spurious apparent single component remanence due to overlap of blocking‐temperature spectra of two components
Authors: Dinarès‐Turell J. , McClelland E.
Published: February 2008

The magnetic properties of the upper Cretaceous red‐limestones from the Montsec thrust sheet in the Pyrenees reveal an unusual arrangement of the unblocking temperatures and coercivities of the magnetic mineral phases, which leads to an apparently single‐component remanence being isolated on thermal demagnetization. That this is an artefact of the almost complete overlap of the blocking temperature spectra of the two real components, can be deduced from alternating field and thermal demagnetization of a composite isothermal remanent magnetization (IRM). When two IRM components are imparted to the sample, at right angles to each other and each affecting grains with different coercivities, thermal demagnetizations of the composite IRM does not isolate the components but alternating field demagnetization does, illustrating the superiority of the latter treatment in this case.
The Katmai Scientific Drilling Project, surface phase: Investigation of an exceptional igneous system
Authors: Eichelberger J. C. , Hildreth W. , Papike J. J.
Published: February 2008

Explosive volcanism is the response of magma to rapid decompression. Inherent complexity of volcanoes and lack of observations at depth in young systems are impediments to proper understanding of this important phenomenon. The Katmai Scientific Drilling Project is an interdisciplinary surface and drilling investigation of an exceptionally large and relatively simple explosive volcanic event that occurred in Alaska's Aleutian Range in 1912. The surface phase of the project is now largely complete, and results are presented in the papers that follow.
An analytic solution to the steady‐state double adiabatic equations
Authors: Gombosi Tamas I.
Published: February 2008

20 moment transport equations applicable to low β plasmas of thermal origin in rotating planetary magnetospheres are presented. An analytic solution is found for a set of simplified equations describing the steady‐state transport of collisionless plasma neglecting heat flow effects, which is also known as the double adiabatic situation [Chew et al., 1956]. The new element of this analytic solution is a closed form solution for the variation of the parallel flow velocity, u∥, along magnetic field lines. The solution is significantly different from the often used assumption that, in the collisionless regime, the divergence of the parallel flow velocity is negligible (cf. [Burgers, 1969]). It is shown that only T⟂/B remains constant along the field line (as predicted by earlier calculations), while the density, parallel temperature and parallel Mach number vary as n/B∝1/u∥, T∥⧜1/u∥², and M∥⧜u∥², respectively (in contrast to earlier predictions of n/B=const, T∥=const, and M∥=const.).
Measurement of cloud integrated backscattering coefficient with a nephelometer
Authors: Novakov T. , Rivera‐Carpio C. , Schmidt R. C. , Rogers C. F.
Published: February 2008

We describe the application of a nephelometer to in‐situ, real‐time measurement of the integrated backscattering coefficient σbs of cloud drops. For thin and moderately thick clouds, this quantity is related to the cloud albedo A, for 0° zenith solar radiation, through the relation A=σbsL, where L is the geometric cloud thickness. The instrument was used in a field experiment on El Yunque peak in Puerto Rico. The measured σbs values are in agreement with results of Mie theory calculations, using independently measured cloud drop concentration and size distribution.
Chemical and thermal constraints on models of Thermal Springs Valley of Ten Thousand Smokes, Alaska
Authors: Lowell R. P. , Keith T. E. C.
Published: February 2008

Thermal (15–30°C) springs issuing from 1912 ash‐flow tuff in the mid‐valley region of the Valley of Ten Thousand Smokes consist of meteoric water that may have been heated by an incompletely cooled lens of welded tuff upvalley from the springs. Conductive cooling of the thermal waters along the flow path is the likely cause for the difference between the observed spring temperatures and the source temperature inferred from chemical geothermometry. Conductive cooling alone can not easily account for the seasonal fluctuations in spring temperatures, however. Mixing of the thermal waters with cold meteoric waters would seem a likely possibility; but thermal water chemistry is constant, indicating that mixing does not occur after the water leaves the zone of heating. Even if mixing occurred, simple mixing models do not account totally for the observed temperature differences of the springs from late spring to summer. The geochemical and thermal data argue for a complex hydrological and thermal regime.
Attenuation of vertical S‐wave amplitude from Wadati‐Benioff earthquakes in Washington
Authors: Cohee B. P.
Published: February 2008

Regression of 842 vertical S‐wave seismograms from 45 microearthquakes sampling the Wadati‐Benioff source zone beneath western Washington suggests a regional control of ground amplitude at 7 to 10 Hz frequency. Mean station amplitude residuals fall in two distinct populations that are geographically coincident with the tectonic regions of the Coast Range‐Puget Lowlands to the west (yielding smaller amplitudes) and the Cascade Range to the east (yielding larger amplitudes). The mean 10 Hz response spectral velocity recorded by the eastern stations is twice that of the western stations. The amplitudes suggest attenuation properties, averaged over the uppermost 60 km, are different for the two regions.
HCL dissolved in solid mixtures of nitric acid and ice: Implications for the polar stratosphere
Authors: Marti James , Mauersberger Konrad , Hanson David
Published: February 2008

The solubility of HCl in polar stratospheric cloud (PSC) particles plays an important role in the heterogeneous chemistry of the lower polar stratosphere. New laboratory studies are reported showing a strong dependence of the HCl solubility on the HNO3 content in ice particles. At 200 K and a partial HCl pressure of 10−6 Torr, the HCl content in NAT is 0.35 mol%, decreasing about a factor of 3 for every 10 fold decrease in the substrate's HNO3 content. At an HCl pressure of 10−7 Torr the content is about 40% of that at 10−6 Torr. HCl dissolved in pure water ice at these partial pressures is less than 0.002 mol%. The surface coverage of HCL on small ice samples was estimated to be about 0.1 monolayer at 10−6 Torr exposure.
Absence of large shield volcanoes and calderas on the Moon: Consequence of magma transport phenomena?
Authors: Head James W. , Wilson Lionel
Published: February 2008

Large shield volcanoes and calderas are not observed on the Moon. Theoretical assessments show that melt ascending from the mantle will stall at rheological traps or at the shallower density trap at the base of the low‐density lunar crust. Magma will then only reach the surface along dikes propagated from these deep reservoirs, and such events will be infrequent and characterized by very large‐volume eruptions. These conditions favor the formation of sinuous rules, single long flows, and widespread flow units, rather than abundant small eruptions from a central edifice. The absence of large shield volcanoes and calderas on the Moon is interpreted to be related to the fact that shallow neutral buoyancy zones and magma reservoirs are not favored on the Moon.
Evidence for trapped anomalous cosmic ray oxygen ions in the inner magnetosphere
Authors: Grigorov N. L. , Kondratyeva M. A. , Panasyuk M. I. , Tretyakova Ch. A. , Adams J. H. , Blake J. B. , Schulz M. , Mewaldt R. A. , Tylka A. J.
Published: February 2008

A series of measurements of 5–30 MeV/nucleon oxygen ions made with track detector stacks on Cosmos satellites show isotropic angular distributions during solar energetic particle events. Solar‐quiet times, on the other hand, have highly anisotropic distributions suggestive of a trapped‐particle component. Detailed Monte Carlo simulations confirm this interpretation and allow us to measure the trapped and cosmic‐ray contributions to the observed fluxes. Our data are fully consistent with anomalous cosmic‐ray ions, rather than radial diffusion from the outer zone, as the source of the trapped particles.
Lunar neutron leakage fluxes as a function of composition and hydrogen content
Authors: Feldman W. C. , Reedy R. C. , McKay D. S.
Published: February 2008

Areas of the Moon that might have enhanced concentrations of hydrogen are discussed. The fluxes of thermal, epithermal, and fast neutrons escaping from the lunar surface were calculated for eight different compositions and several hydrogen contents. These flux ratios depend on composition and are very sensitive to the hydrogen content. Their measurement using flight‐proven techniques from lunar orbit should allow detection and identification of hydrogen residing in either permanently shaded cold traps near the lunar poles or mature regoliths. Knowledge of composition, especially of Fe and Ti, improves the thresholds for hydrogen detection and also could allow identification of Gd and Sm.
MHD wave coupling in inhomogeneous media
Authors: Wright Andrew N.
Published: February 2008

The coupling of different MHD waves is important for an understanding of laboratory, space, and solar plasmas. In this paper we investigate fast and Alfvén mode coupling in the cold plasma limit. The medium is assumed to have an invariant direction (e.g., slab or axisymmetric models) and carries an arbitrary solenoidal background magnetic field. Wave fields are Fourier analysed with wave number kβ in the invariant direction. The coupled linearised wave fields are then expanded in a power series (of kβ) to yield a decoupled hierarchy of inhomogeneous wave equations. The higher order terms in the series represent wave coupling phenomena such as the resonant excitation of Alfvén waves, and the damping of a magnetospheric cavity mode.
Evidence of a relation between El NIno and QBO, and for an El Nino in 1991–92
Authors: Angell J. K.
Published: February 2008

The possibility of a relation between El Nino and the quasi‐biennial oscillation (QBO) in equatorial low stratosphere is investigated. Based on the 9 El Ninos and 16 quasi‐biennial variations in 50 mb zonal wind at Singapore between 1954 and 1991, the sea‐surface temperature (SST) in eastern equatorial Pacific has averaged nearly 0.5°C warmer one season after QBO east‐wind maximum than 4–5 seasons before and after this maximum, but this difference in temperature is not statistically significant. Because of the difference in period of these oscillations (2 1/4 years on average in the case of the QBO, about 4 1/2 years on average in the case of El Nino), there can not be an El Nino associated with every QBO east‐wind maximum, i.e., any relation between El Nino and QBO east‐wind maximum has to “skip a beat” on occasion. This paper presents evidence for a pattern in this “skip”, such that an El Nino is associated with a QBO east‐wind maximum except when the El Nino associated with the previous east‐wind maximum was a major one and/or the SST maximum followed the previous east‐wind maximum by a few seasons. On the basis of this pattern an El Nino would not have been expected in 1989 or 1990 (because the El Nino of 1987 was a major one) but would be expected in 1991 or 1992 in association with the QBO east‐wind maximum projected to occur in the northern summer of 1992. Comparison with earlier “skips” shows that an El Nino would be most likely before the next east‐wind maximum, or at the end of 1991. Because it would follow the aborted warm event of 1990, it probably would not be a major El Nino.
A comparison of induced magnetotails of planetary bodies: Venus, Mars, and Titan
Authors: Luhmann J. G. , Russell C. T. , Schwingenschuh K. , Yeroshenko Ye.
Published: February 2008

The Pioneer Venus orbiter (PVO), PHOBOS 2, and Voyager 1 spacecraft have together provided observations of three planetary bodies with induced magnetotails: Venus, Mars, and Titan. During the extended mission of PVO, the tail of Venus was probed at an altitude of ∼1.3 planetary radii, which provided a more appropriate basis for comparison with the Mars data (at ∼2.7 planetary radii), and Titan data (∼2.5 planetary radii downstream), than the previously analyzed Venus tail data obtained near PVO apoapsis (∼12 planetary radii). A parallel examination of the magnetic properties of these tails at downstream distances within 3 planetary radii reveals the following similarities and differences. In the cases of Venus and Mars, which are always embedded in the supermagnetosonic solar wind flow, the tail lobe fields are smoothly joined to the draped magnetosheath fields at their outer boundaries, but separated in the center by a distinct, and sometimes narrow, current sheet. The tail of Mars has a cross section that is wider, when scaled by the planet radius, than that at Venus (as found by earlier MARS spacecraft experiments), a lobe field strength that is about the same as that at Venus in spite of the factor of ∼3 smaller interplanetary field at Mars, and a cross‐tail field strength that exceeds that at Venus by ∼1.5 times. The tail of Titan appears similar to the others except that there is no bow shock and little or no draped magnetosheath field signature since the surrounding magnetospheric plasma flow is submagnetosonic (although super‐Alfvenic). The lobe field strengths are about half those at Venus and Mars, while the cross‐tail field is almost negligible. The near‐Titan tail diameter is close to the body diameter. In place of the smooth transition to a draped magnetosheath field at the tail boundaries, as seen at Venus and Mars, the Titan observations show current sheets where the field rotates to its external orientation. It is shown that the Titan wake magnetic signature can be simulated with a model field composed of a cylindrical boundary containing antiparallel axial “tail lobe” fields, surrounded by a field described by streamlines of incompressible flow around a cylinder. Simulation of the magnetic fields observed at Mars and Venus, on the other hand, requires a draped magnetosheath field model with an appropriately oriented comet‐tail‐like model in its interior.
He2+ heating at a quasi‐parallel shock
Authors: Fuselier S. A. , Lennartsson O. W. , Thomsen M. F. , Russell C. T.
Published: February 2008

We present the first observations of solar wind He2+ heating downstream from the Earth's quasi‐parallel shock. These observations show that in conjunction with protons, two different regions are observed. In regions where the proton distribution is cooler, more dense, and similar to that observed downstream from quasi‐perpendicular shocks, the He2+ distribution is shell‐like, also similar to that observed downstream from quasi‐perpendicular shocks. In regions where the proton distribution is hotter, less dense, and Maxwellianlike, the He2+ distribution is also Maxwellianlike without evidence for a shell. These observations support the interpretation that the nearly isotropic proton and He2+ distributions are produced through the strong interaction of a very dense specularly reflected proton beam with the incident solar wind, while the cooler proton distributions and shell‐like He2+ distributions are produced in a manner similar to that at the quasi‐perpendicular bow shock.
The proton scattering mean free path for the May 7, 1978, solar flare event
Authors: Debrunner H. , Grädel H. , Lockwood J. A.
Published: February 2008

The scattering mean free paths of solar flare protons in the rigidity ranges 195–396 MV (20–80 MeV) and from about 1.5 to 5 GV for the May 7, 1978, solar cosmic ray event were found to be 1.7±0.1 AU and 3.9±0.4 AU, respectively. These scattering mean free paths are compared with those deduced for other scatter‐free solar cosmic ray events. The rigidity dependence of λ11 can be described by λ[AU] = 2.0 (P[GV])0.4 for 0.1 < P < 5 GV.
Collisionless conductivity and stochastic heating of the plasma sheet in the geomagnetic tail
Authors: Horton Wendell , Tajima T.
Published: February 2008

The chaotic single particle orbits in the geomagnetic tail are used to calculate the collisionless conductivity. It is shown that the stochasticity from inhomogeneous magnetic fields leads to a power law decay of the single particle correlation function similar to an elastic collisional process. The height‐integrated dissipative part of the collisionless conductivity governs the irreversible stochastic heating of the plasma sheet. Both exponentially growing reconnection type magnetic perturbations and a sinusoidal pulse with a half period up to 1 hour in duration are used to analyze the plasma sheet heating.
Numerical tracing of energetic particle drifts in a model magnetosphere
Authors: Reeves G. D. , Belian R. D. , Fritz T. A.
Published: February 2008

We present results from a model developed to study the motion of impulsively injected energetic particles which become trapped in the Earth's magnetic field at geosynchronous orbit. The model is based on numerically solving the analytic expressions for the bounce average gradient and curvature drift in a model magnetic field. The predicted motion of trapped geosynchronous particles in the Tsyganenko and Usmanov (1982) model (TU‐82) has characteristics which are not predicted by less sophisticated models. We investigate the motion of drifting particles predicted by the model under various conditions such as: Kp level, pitch angle, orientation of the magnetic field, and location of the origin of the drift shell. As a test of the predictions of the model, we apply it to observations of a substorm injection event which took place on October 16, 1983, and was observed by three geosynchronous satellites. The injection region for this event is found to span approximately 45° from near midnight to near 2100 LT. We also report the existence of a “periphery” outside the central injection where either injected ions or electrons, but not both, are observed with dispersionless signatures. The internal consistency of the predictions of the structure of the injection region using remote observations from the three geostationary satellites and the TU‐82 field model is found to be quite good.
Comparative terrestrial planet thermospheres: 1. Solar cycle variation of global mean temperatures
Authors: Bougher S. W. , Roble R. G.
Published: February 2008

Global average models for the thermospheres of Venus, Earth, and Mars are used to calculate the solar cycle variations of the global mean temperatures using the compositional profiles for each planet. All models use the same absolute solar EUV and UV fluxes but scaled for planetary distances. Photochemistry appropriate to each planet is used (or assumed) with similar rate coefficients for common physical and chemical processes. In particular, the CO2 15‐μm cooling rates for all three planets are determined using a common rate coefficient for collisional excitation of the CO2 bending mode by atomic oxygen (relaxation rate 10−12 cm³ s−1). Solar EUV and UV heating efficiencies are calculated self‐consistently for Earth, but prescribed for Venus (15/22%) and Mars (18/22%) according to independent calculations. Eddy diffusion profiles are prescribed for each planet in accord with previous studies that compared model predictions with available satellite observations. The global mean models are run to steady state for both solar minimum (F10.7 = 70) and solar maximum (F10.7 = 240) conditions. The results show that the solar cycle global mean exospheric temperature variation is about 76 K for Venus (172 to 248 K), 518 K for Earth (737 to 1255 K), and 110 K for Mars (180 to 290 K). A thermal balance analysis shows that the small exospheric temperature variation on Venus occurs because of the strong radiative damping by CO2 15‐μm cooling. The peak CO2 cooling occurs at the altitude of maximum solar heating, and efficiently radiates it to space. On Earth, the increased solar heating occurs at a higher altitude than the peak in the infrared cooling. Consequently, it must be thermally conducted down to the altitude of the peak infrared cooling before it is radiated to space. An increase in the thermally conducted heat flux requires an increase in the vertical temperature gradient which results in a larger exospheric temperature variation. On Mars, the increased solar heating also occurs at a higher altitude than the peak cooling and likewise must be conducted downward before radiating to space. Furthermore, CO2 cooling is not as effective on Mars as it is on Venus because of lower O/CO2 ratios. These two factors yield a Mars solar cycle variation of global mean temperatures that is larger than for Venus.
Maximum power flux of auroral kilometric radiation
Authors: Benson Robert F. , Fainberg Joseph
Published: February 2008

The maximum auroral kilometric radiation (AKR) power flux observed by distant satellites has been increased by more than a factor of 10 from previously reported values. This increase has been achieved by a new data selection criterion and a new analysis of antenna spin modulated signals received by the radio astronomy instrument on ISEE 3. The method relies on selecting AKR events containing signals in the highest‐frequency channel (1980, kHz), followed by a careful analysis that effectively increased the instrumental dynamic range by more than 20 dB by making use of the spacecraft antenna gain diagram during a spacecraft rotation. This analysis has allowed the separation of real signals from those created in the receiver by overloading. Many signals having the appearance of AKR harmonic signals were shown to be of spurious origin. During one event, however, real second harmonic AKR signals were detected even though the spacecraft was at a great distance (17 RE) from Earth. During another event, when the spacecraft was at the orbital distance of the Moon and on the morning side of Earth, the power flux of fundamental AKR was greater than 3×10−13 W m−2 Hz−1 at 360 kHz normalized to a radial distance r of 25 RE assuming the power falls off as r−2. A comparison of these intense signal levels with the most intense source region values (obtained by ISIS 1 and Viking) suggests that multiple sources were observed by ISEE 3.
The structure of tangential discontinuities: 1. Results of hybrid simulations
Authors: Cargill P. J. , Eastman T. E.
Published: February 2008

One‐dimensional hybrid numerical simulations of tangential discontinuities (TDs) are presented for parameters representative of both the solar wind and magnetopause. For parameters common at the frontside magnetopause near local noon (antiparallel magnetic field and density gradients) it is found that TDs have a number of characteristic features that could be detected at the magnetopause. There is an overshoot in the magnetic field intensity on the low‐density side of the TD. The overshoot is of the order of 20% for density ratios of 10 but can be somewhat larger for other parameters. It extends typically over a few ion Larmor radii. The various plasma quantities all vary on their own characteristic length scale, so that a given set of conditions on either side should result in a (possibly) unique structure. It is found that the key parameters in determining TD structure are the density (and ion temperature) ratios, the plasma beta on the magnetosheath side, and the value of the electric potential difference across the TD. The relative orientation of the magnetic fields on either side of the TD does not appear to be of critical importance. For typical solar wind conditions (density and field gradients parallel) the magnetic field profile does not possess an overshoot but it does extend over 2–3 ion Larmor radii. The presence of a cross‐field plasma flow is shown to slightly modify the magnetic field profile, but the velocity profile is very sensitive to the sign of the flow (and hence the motional electric field). It is also shown that the TD structure is dependent on the assumed initial conditions. When the TD is initially chosen to be wider than the width that would result from the evolution of an infinitesimally thin initial TD, there is little further evolution. The currents in the TD layer can be a considerable fraction of the ion thermal speed, so that relaxation via plasma microinstabilities could arise. A detailed comparison with observed magnetopause crossings will be presented in a future article.