bluuebunny/crossref_metadata_2025 huggingface dataset:
Particle acceleration at corotating reverse shocks in the southern hemisphere: Ulysses results
Authors: Desai M. I. , Marsden R. G. , Sanderson T. R. , Balogh A. , Forsyth R. J. , Gosling J. T.
Published: February 2004

We have correlated the ∼1 MeV proton intensity (J) measured at corotating reverse shocks detected by Ulysses in the southern hemisphere with two parameters that characterise the strength of the shock. Between 6°–29°S J is essentially independent of the shock strength, whereas between 29°–41°S J is well correlated with the same. The poor correlation from 6°S to 29°S is attributed to variations in the background intensity caused by changes in solar activity. Our results also show that J is independent of the shock normal angle at all latitudes. We compensate for the effects of a fluctuating background by assuming that reverse shocks associated with two adjacent compression regions observed during a ∼26 day period accelerate particles out of the same seed population. The relation between the ratio of the proton intensities and the ratios of the shock parameters for such reverse shock‐pairs indicates that the shock acceleration efficiency increases with the shock strength but is independent of the normal angle.
Ulysses electron distributions fitted with Kappa functions
Authors: Maksimovic Milan , Pierrard Viviane , Riley Pete
Published: February 2004

We fit Kappa functions to 16,000 velocity distribution functions measured in the solar wind by the electron plasma instrument on board Ulysses. Statistically, the electron distributions are observed to have important high velocity tails in the fast solar wind but are closer to a Maxwellian in the slow wind. We also discuss how this result could support a recent kinetic model of the solar wind proposed by Maksimovic, Pierrard and Lemaire [1997].
High‐resolution temperature profiles measured with stratospheric balloons near the Andes Mountains
Authors: de la Torre A. , Alexander P. , Giraldez A.
Published: February 2004

A spectral analysis of two balloon soundings of temperature performed in the troposphere and lower stratosphere over the Andes Mountains in Argentina with a vertical resolution of 10 m has been performed. The first and second soundings, launched at the same location, were performed during unusually calm and disturbed atmospheric conditions respectively. Considerable deviations from the −3 value predicted for the spectral slopes in the power‐law range by current saturation theories are found. These departures are reduced if the data resolution at disposal is diminished, thereby eliminating the highest wavelength harmonics. Slopes do not clearly steepen with increasing height as suggested by other authors and topography seems to be responsible for this fact at low altitudes. The spectral amplitude increase with height detected from recent lidar data is corroborated only in the sounding with calm atmospheric conditions. Spectra are found to scale with the buoyancy frequency not as simply as suggested by the saturation models.
Advection and diffusion of Indonesian Throughflow Water within the Indian Ocean South Equatorial Current
Authors: Gordon Arnold L. , Ma Shubin , Olson Donald B. , Hacker Peter , Ffield Amy , Talley Lynne D. , Wilson Douglas , Baringer Molly
Published: February 2004

Warm, low salinity Pacific water weaves through the Indonesian Seas into the eastern boundary of the Indian Ocean. The Indonesian Throughflow Water (ITW) adds freshwater into the Indian Ocean as it spreads by the advection and diffusion within the Indian Ocean's South Equatorial Current (SEC). The low salinity throughflow trace, centered along 12°S, stretches across the Indian Ocean, separating the monsoon dominated regime of the northern Indian Ocean from the more typical subtropical stratification to the south. ITW is well represented within the SEC thermocline, extending with concentrations above 80% of initial characteristics from the sea surface to 300‐m within the eastern half of the Indian Ocean, with 60% concentration reaching well into the western Indian Ocean. The ITW transport within the SEC varies from 4 to 12 × 106 m³ sec−1, partly in response to variations of the injection rate at the eastern boundary and to the likelihood of a zonally elongated recirculation cell between the Equatorial Counter Current and the SEC within the Indian Ocean. Lateral mixing disperses the ITW plume meridionally with an effective isopycnal mixing coefficient of 1.1 to 1.6 × 104 m²sec−1.
Distribution of radiogenic heat generation in the arc's crust of the Hokkaido Island, Japan
Authors: Furukawa Yoshitsugu , Shinjoe Hironao
Published: February 2004

Radiogenic heat generation was measured for rocks collected in the vertical section of the crust of the arc exposed in the Hokkaido island, Japan. Measured heat generation value of metasediments is nearly constant of ∼1.0 µW/m³ and independent of the metamorphic grade. Using the measured heat generation value, together with the published heat generation data of a granitic body emplaced in this section, vertical profile of heat generation in the crust is constructed. The estimated heat generation profile shows steep decrease with depth, but is not lower than a value of ∼1.0 µW/m³ in the upper crust. In the lower crust metabasites are dominant, and heat generation value is one order of magnitude lower than that in the upper crust. Surface heat flow derived from the crustal heat generation is estimated to be ∼25 mW/m². When the crustal heat generation is considered, temperature at the bottom of the crust estimated from surface heat flow becomes ∼300°C lower. This temperature difference corresponds to the viscosity variation of more than three orders of magnitude, which is important for understanding lithosphere dynamics.
The static compressibility of gypsum
Authors: Stretton Iona C. , Schofield Paul F. , Hull Steve , Knight Kevin S.
Published: February 2004

The unit cell parameters of deuterated gypsum have been extracted from Rietveld analysis of neutron powder diffraction data, obtained during compression of powdered gypsum up to 5.4 GPa. The unit‐cell of gypsum compresses anisotropically, with the largest compression along the b‐axis. The static compressibility has been determined by fitting the data to a third‐order Birch‐Murnaghan equation of state. This yields values of 45±1 GPa for the bulk modulus and 2.0±0.2 for its pressure derivative.
Volcanic aerosol perturbations and strong El Niño events: No general correlation
Authors: Self S. , Rampino M. R. , Zhao J. , Katz M. G.
Published: February 2004

We test the hypothesis that El Niño/Southern Oscillation (ENSO) events are caused or enhanced by volcanic aerosol perturbations using two methods: 1) A case‐by‐case comparison of the 16 strongest El Niño events of the last 150 years with the characteristics of the largest concurrent volcanic events, and 2) Comparison of the timing of strong El Niño events and the independently determined record of stratospheric optical depth (τ) perturbations. Many eruptions that occurred near times of strong El Niño years produced small amounts of stratospheric aerosols, in many cases the relative timing of the two events argues against triggering. The correlation of 4 of 11 peaks in global stratospheric optical depth (τ ≥ 0.025) within 3 years of strong El Niño events over the last 150 years is what would be expected by chance. Moreover, five strong El Niños occurred between 1915 and 1960, when the stratosphere was largely free of volcanic aerosols. Of the three strongest tropical volcanic aerosol perturbations that coincided with or were followed by strong El Niños in the period studied (Krakatau in 1883, El Chichón in 1982, and Pinatubo in 1991), the two modern ones occurred after the earliest SST warming of the El Niño events. The coincidence of these two phenomena indicates no causative relationship.
Venus tail ray observation near Earth
Authors: Grünwaldt H. , Neugebauer M. , Hilchenbach M. , Bochsler P. , Hovestadt D. , Bürgi A. , Ipavich F. M. , Reiche K.‐U. , Axford W. I. , Balsiger H. , Galvin A. B. , Geiss J. , Gliem F. , Gloeckler G. , Hsieh K. C. , Kallenbach R. , Klecker B. , Livi S. , Lee M. A. , Managadze G. G. , Marsch E. , Möbius E. , Scholer M. , Verigin M. I. , Wilken B. , Wurz P.
Published: February 2004

In June, 1996, Venus passed through a very close inferior conjunction with the Sun. At that time the CTOF detector of the CELIAS mass spectrometer experiment on the SOHO spacecraft near Earth's L1 Lagrangian point was measuring heavy ions in the solar wind ∼4.5 × 107 km downstream of Venus. Close to the time predicted by simple geometric arguments for passage of SOHO through the Venus wake, CTOF made three encounters with unusual fluxes of O+ and C+ ions. Their energy distributions resembled those of tail rays originating in the Venus ionosphere or ionopause region rather than of ions produced in the corona of neutral atoms that surrounds the planet. The C+ abundance was ≈ 10% of O+. The observed O+ speed was very close to the simultaneous solar wind speed and the O+ temperature was a cool 5600 K/amu. The flux densities for the three events were (2.4–4.4) × 10³ cm−2s−1.
Transient response of a coupled model to estimated changes in greenhouse gas and sulfate concentrations
Authors: Haywood J. M. , Stouffer R. J. , Wetherald R. T. , Manabe S. , Ramaswamy V.
Published: February 2004

This study investigates changes in surface air temperature (SAT), hydrology and the thermohaline circulation due to the the radiative forcing of anthropogenic greenhouse gases and the direct radiative forcing (DRF) of sulfate aerosols in the GFDL coupled ocean‐atmosphere model. Three 300‐year model integrations are performed with increasing greenhouse gas concentrations only, increasing sulfate aerosol concentrations only and increasing greenhouse gas and sulfate aerosol concentrations. A control integration is also performed keeping concentrations of sulfate and carbon dioxide fixed. The global annual mean SAT change when both greenhouse gases and sulfate aerosols are included is in better agreement with observations than when greenhouse gases alone are included. When the global annual mean SAT change from a model integration that includes only increases in greenhouse gases is added to that from a model integration that includes only increases in sulfate, the resulting global SAT change is approximately equal to that from a model integration that includes increases in both greenhouse gases and sulfate aerosol throughout the integration period. Similar results are found for global annual mean precipitation changes and for the geographical distribution of both SAT and precipitation changes indicating that the climate response is linearly additive for the two types of forcing considered here. Changes in the mid‐continental summer dryness and thermohaline circulation are also briefly discussed.
Ring current modeling in a realistic magnetic field configuration
Authors: Fok M.‐C. , Moore T. E.
Published: February 2004

A 3‐dimensional kinetic model has been developed to study the dynamics of the storm time ring current in a dipole magnetic field. In this paper, the ring current model is extended to include a realistic, time‐varying magnetic field model. The magnetic field is expressed as the cross product of the gradients of two Euler potentials and the bounce‐averaged particle drifts are calculated in the Euler potential coordinates. A dipolarization event is modeled by collapsing a tail‐like magnetosphere to a dipole‐like configuration. Our model is able to simulate the sudden enhancements in the ring current ion fluxes and the corresponding ionospheric precipitation during the substorm expansion.
Kinetic Alfvén waves and plasma transport at the magnetopause
Authors: Johnson Jay R. , Cheng C. Z.
Published: February 2004

Large amplitude compressional type ULF waves can propagate from the magnetosheath to the magnetopause where there are large gradients in density, pressure and magnetic field. These gradients efficiently couple compressional waves with shear/kinetic Alfvén waves near the Alfvén field‐line resonance location (ω=k∥υA). We present a solution of the kinetic‐MHD wave equations for this process using a realistic equilibrium profile including full ion Larmor radius effects and wave‐particle resonance interactions for electrons and ions to model the dissipation. For northward IMF a KAW propagates backward to the magnetosheath. For southward IMF the wave remains in the magnetopause but can propagate through the k∥=0 location. The quasilinear theory predicts that transport due to KAWs at the magnetopause primarily results from the perpendicular electric field coupling with magnetic drift effects with diffusion coefficient D⟂ ∼ 109 m²/s. For southward IMF additional transport can occur because magnetic islands form at the k∥=0 location. Due to the broadband nature of the observed waves these islands can overlap leading to stochastic transport which is larger than that due to quasilinear effects.
Geochemical estimates of denitrification in the Arabian Sea and the Bay of Bengal during WOCE
Authors: Howell Evan A. , Doney Scott C. , Fine Rana A. , Olson Donald B.
Published: February 2004

High quality World Ocean Circulation Experiment (WOCE) data are used in conjunction with an isopycnal mixing model to calculate nitrate deficits due to denitrification in the oxygen minima of both the Arabian Sea and the Bay of Bengal. Basin‐scale, integral denitrification rates are estimated by combining the nitrate deficits with water mass ages computed for the same regions based on the chlorofluorocarbon (CFC‐11) distributions. Nitrate deficits exceeding 12 µmol; kg−1 are observed for the Arabian Sea during the 1995 southwest monsoon. The estimated basin‐scale nitrate deficit integrated over the oxygen minimum layer is 63±20 Tg N, and the annual loss rate is 21±7 Tg N y−1. The basin‐scale nitrate deficit is about half other, recent inventory estimates, with most of the discrepancy in the bottom half of the oxygen minimum below the secondary nitrite maximum. No signature of active, water column denitrification was observed in the Bay of Bengal during the 1995 northeast monsoon.
Surface impedance time domain reflectometry for the determination of ice depth
Authors: Garner Stephen J. , Thiel David V. , O'Keefe Steven G.
Published: February 2004

The analysis of the surface impedance of a horizontally stratified earth is similar to the impedance of a step‐wise discontinuous lossy transmission line. Time Domain Reflectometry (TDR) is commonly used in transmission line assessment to determine the location of faults. There are electrical conditions where TDR can be applied to a two layered subsurface to determine the time of flight of the EM wave and hence the thickness of the top layer. When the upper layer resistivity is sufficiently contrasted over a conductive second layer, then transforming surface impedance data measured across a broad band of frequencies into the time domain allows one to determine the time of flight to the subsurface boundary.

If the maximum frequency, frequency step size and number of steps are optimised for the two layers a periodicity appears in the surface impedance profile. It is demonstrated through computer modelling that a layer of ice on rock or sea water gives a return time of flight equal to the separation time of peaks in the time domain surface impedance profile. The technique requires a vertically polarised transmitter which steps up to the high frequency (HF) range. For example an ice layer of 30 to 400 meters thickness requires frequencies up to 5MHz.

In this paper, the basic theory for the use of TDR techniques in the interpretation of the surface impedance data is explained, and computer modelling results are presented
Is the hydroxyl radical formed in the gas‐phase ozonolysis of alkenes?
Authors: Schäfer C. , Horie O. , Crowley J. N. , Moortgat G. K.
Published: February 2004

The hypothesis that OH radicals are generated in the ozonolysis of alkenes was tested by measuring the relative conversion of a pair of alkanes added to selected alkene‐O3 systems. The results were compared with OH‐initiated relative removal (via H2O2 photolysis) and with the expected relative rates based on literature data. We find that the removal of alkanes is not consistent with their reaction with OH. These results suggest that there is no compelling experimental data in support of OH formation in the ozonolysis of alkenes.
In‐situ measurement of Cl2 and O3 in a stratospheric solid rocket motor exhaust plume
Authors: Ross M. N. , Ballenthin J. O. , Gosselin R. B. , Meads R. F. , Zittel P. F. , Benbrook J. R. , Sheldon W. R.
Published: February 2004

The concentration of Cl2 in the stratospheric exhaust plume of a Titan IV launch vehicle was measured with a neutral mass spectrometer carried on a WB‐57F aircraft at 18.9 km altitude. Twenty nine minutes after a twilight Titan IV launch, the mean Cl2 concentration across an 8 km wide plume was 126 ± 44 ppbv, consistent with model predictions that a large fraction of the HCl in solid rocket motor exhaust is converted into Cl2 by afterburning reactions in the hot plume. Co‐incident measurements with ultraviolet absorption photometers also carried on the aircraft show that ozone concentration in the plume was not different from ambient levels. This is consistent with model predictions that nighttime SRM launches will not cause transient ozone loss in the lower stratosphere. The measured Cl2 concentration equals 15% of the ambient ozone concentration suggesting that transient ozone reduction in SRM plume wakes can be expected after daytime launches when solar ultraviolet radiation will photolyze the exhaust plume Cl2.
Phase equilibrium of gas hydrate: Implications for the formation of hydrate in the deep sea floor
Authors: Zatsepina Olga Ye. , Buffett Bruce A.
Published: February 2004

We calculate the solubility of methane gas over a range of pressure and temperature. The gas is dissolved in liquid water, which coexists with free gas at high temperature or solid hydrate at low temperature and high pressure. We show that solubility is significantly altered by the presence or absence of the hydrate phase. When hydrate is absent at high temperatures, our calculations reproduce experimentally observed increases in solubility with decreasing temperature. When hydrate is present, however, we find that the gas solubility decreases sharply with decreasing temperature. Such an abrupt decrease in solubility permits hydrate to crystallize directly from the aqueous solution, without the need of any free gas. This result has important implications for the formation of gas hydrate in marine environments, where the gas supply may not be sufficient to provide free gas. We apply our calculations at typical pressure and temperature conditions in marine sediments to establish the gas concentration needed to stabilize hydrate. Estimates of the vertical distribution of hydrate in marine sediments and the rate of accumulation are obtained using simple models of hydrate formation.
Seismic activity at the Cerro Prieto Geothermal Area (Mexico) from August 1994 to December 1995, and its relationship with tectonics and fluid exploitation
Authors: Fabriol H. , Munguía L.
Published: February 2004

A continuous monitoring of the Cerro Prieto geothermal field was carried out from August 1994 to December 1995 to investigate the seismicity of tectonic origin and the seismicity triggered by exploitation activities. Hypocenters for 148 events were located mainly around the northern end of the Cerro Prieto fault and within the geothermal zone. The estimated focal depths range mostly from 1 to 6 km, for earthquakes with magnitudes from 0.5 to 4.6. It was difficult to distinguish between natural and triggered seismicity. We observed a single case of an earthquake for which a correlation in time and space seems plausible with a sharp increase of fluid injection in a well located at less than 1 km from the epicenter. Fault plane solutions of 26 events with magnitudes between 2.8 and 4.6 indicate right‐lateral strike‐slip motion for earthquakes that occur near the Cerro Prieto and Imperial faults. Inside the geothermal zone, events with normal components of motion were recorded, as expected from the extensional stress regime of the pull‐apart basin laying between both faults.
Preliminary estimates of plate convergence in the Caucasus Collision Zone from global positioning system measurements
Authors: Reilinger R. E. , McClusky S. C. , Souter B. J. , Hamburger M. W. , Prilepin M. T. , Mishin A. , Guseva T. , Balassanian S.
Published: February 2004

Global Positioning System (GPS) measurements (1991–1994) traversing the Greater and Lesser Caucasus mountains indicate a minimum N‐S shortening of 10±2 mm/yr. This represents approximately 30–50% of the NUVEL‐1A convergence rate between the Arabian and Eurasian plates. The remainder of the convergence appears to be accommodated in the areas south of the Lesser Caucasus, by a combination of right‐lateral strike‐slip faulting on planes oriented N 120°E, and shortening on thrust faults with similar orientations. More dense GPS observations conducted in the epicentral area of the April 29, 1991, Ms=7.0 Racha, Georgia earthquake, which occurred along the southern boundary fault of the Greater Caucasus mountains, indicate N‐S shortening following the earthquake which we interpret as due to post‐seismic slip. This mechanism may contribute to the substantially lower shortening rates derived from seismic moment tensors compared with tectonic estimates of shortening rates in the Caucasus.
Corrections for zenith scattered light DOAS
Authors: Platt U. , Marquard L. , Wagner T. , Perner D.
Published: February 2004

A variety of physical processes can influence the accuracy of the results obtained by Zenith Scattered Light ‐ Differential Optical Absorption Spectroscopy (ZSL‐DOAS) measurements of stratospheric species (like NO2, OClO, BrO and O3). The magnitude of errors that may result, if these effects are ignored, as well as correction methods are discussed.
Elastic constants and anisotropy of forsterite at high pressure
Authors: da Silva Cesar , Stixrude Lars , Wentzcovitch Renata M.
Published: February 2004

We have determined from first principles the athermal elastic constant tensor of Mg2SiO4 forsterite with the plane wave pseudopotential method over a wide range of pressure (0–100 GPa) that encompasses the full range over which forsterite has been observed experimentally. The computed elastic constants are in excellent agreement with experimental data up to the maximum pressure of the experiments (16 GPa). We calculate the single‐crystal elastic anisotropy from the elastic constants. We find that the anisotropy is strong (azimuthal P‐ and S‐wave anisotropy: 25% and 20%, respectively, polarization anisotropy: 15%), in agreement with experiment, and that it depends weakly on pressure over the range 0–25 GPa, in contrast to the behavior of other silicates and oxides.
Shear‐wave splitting and fracture alignments at the Northwest Geysers, California
Authors: Lou M. , Shalev E. , Malin P. E.
Published: February 2004

Shear‐wave splitting is commonly observed on three‐component microearthquake seismograms recorded at the Northwest Geysers geothermal field, California. The polarization of leading shear waves around each recording station is predominantly N10°–40°E, suggesting that the shear‐wave splitting is caused mainly by pervasive, north‐northeast orientated anisotropy. Time delays between the leading and second shear waves can be as large as 10ms/km to 30ms/km. We propose that the direction and magnitude of this shear wave splitting is due to the presence of pervasive, stress‐aligned secondary fractures related to several northwest‐trending, right‐lateral faults in the Geysers area.
The determination of shock ramp width using the noncoplanar magnetic field component
Authors: Newbury J. A. , Russell C. T. , Gedalin M.
Published: February 2004

We determine a simple expression for the ramp width of a collisionless fast shock, based upon the relationship between the noncoplanar and main magnetic field components. By comparing this predicted width with that measured during a shock observation, the shock velocity can be determined from a single spacecraft. For a range of low‐Mach, low‐β bow shock observations made by ISEE‐1 and ‐2, ramp widths determined from two‐spacecraft comparison and from this noncoplanar component relationship agree within 30%. When two‐spacecraft measurements are not available or are inefficient, this technique provides a reasonable scale size estimation for low Mach shocks.
A direct divider method for self‐affine fractal profiles and surfaces
Authors: De Santis Angelo
Published: February 2004

Many profiles and surfaces of interest in geology and geophysics can be modelled by self‐affine fractals. The divider method was the first method introduced in fractal analysis, is generally suitable for self‐similar fractals, and has been adapted by Brown [1987] using a multi‐step approach to estimate the fractal dimension of self‐affine profiles. Here, we improve the method in order to be a 1‐step technique, but showing also that it is in practice another form of the variance method. Then, we generalise the divider method to self‐affine fractal surfaces. The method is tested with application to synthetic one‐ and two‐dimensional functions of known fractal dimension.
Energetic electron precipitation from the inner zone
Authors: Abel Bob , Thorne Richard M. , Vampola A. L.
Published: February 2004

Energetic electron precipitation flux from the Earth's inner radiation belt (L≤2) is usually below the detection threshold of current satellite instrumentation. Theoretical estimates of the longitudinally and interhemispherically averaged rate of precipitation have been obtained by evaluating the equilibrium electron pitch angle distribution in the loss cone due to pitch angle scattering. The results are normalized to CRRES MEA measurements of the trapped flux. An energy deposition code is employed to evaluate ion production rates in the middle atmosphere. We demonstrate that inner zone electron precipitation is an important mesospheric energy source for L≥1.35 and that it can be the dominant ionization source at altitudes between 60 and 80 km. For E≳1MeV the energetic electron deposition declines monotonically with decreasing L, in agreement with the trend implied by observations at L≥2.
Endogenous magma degassing and storage at Mount Etna
Authors: Allard Patrick
Published: February 2004

Combining SO2 plume emissions from Mt. Etna in 1975–1995 with the magma S content suggests that between 3.5 and 5.9 km³ of basalt were degassed for sulfur over two decades, only 10–20% of which actually extruded. Except during extensive lava outbreak (1992), the SO2 flux was mostly supplied by endogenous degassing of non‐erupted basalt, replaced at a time‐averaged rate of 4.5–8 m³/s. The unerupted degassed magma cannot be accomodated by the upper plumbing system (whose maximum capacity is estimated at 0.6 km³), nor by simple intrusive growth of the volcanic pile. Being denser than undegassed melt, most of it was probably removed by gravitational convection in sub‐volcanic feeders. Ultimately, part of this degassed magma may solidify within the crust, contributing to the accretion of a wide ‘plutonic‧ complex, ≥3 times larger than the volcano itself, that has grown within its sedimentary basement.
On the winding of the IMF spiral for slow and fast wind within the inner heliosphere
Authors: Bruno R. , Bavassano B.
Published: February 2004

Magnetic field and plasma hourly data, recorded within the inner heliosphere from 1975 through mid 1981, have been used to test the interplanetary magnetic field configuration as predicted by the Parker theory against observed interplanetary magnetic field spiral configuration. Following this theory, magnetic field lines should always be aligned with wind flow direction when observed in a reference system corotating with the Sun. Our observations showed a general tendency for the field lines to be more tightly wound with respect to the predicted spiral configuration in agreement with similar studies performed around and beyond 1 AU by other authors. If we set the corotation radius b = 20 Rs we obtain an average overwinding of about 2.7° ± 0.3°. Our results also showed that field lines associated with fast and slow wind have different winding offsets with respect to the predicted Parker spiral. A possible explanation might be in a different value of the corotating radius b depending on the speed of the wind. A value of b = 20 Rs for slow wind would suggest a b = 12 Rs for fast wind.
Intermittent short‐duration magnetic field anomalies in the Io torus: Evidence for plasma interchange?
Authors: Kivelson Margaret Galland , Khurana Krishan K. , Russell Christopher T. , Walker Raymond J.
Published: February 2004

On Galileo's inbound pass through the Io plasma torus in December 1995, we detected intermittent, short‐duration increases in the magnetic field magnitude, notable by their abrupt onset and subsequent abrupt recovery to the previous level. The events were small and brief, with an average field change of 15.7 nT (1–2% of the background field) and an average duration of ∼26 s. They were observed first shortly after data at high time resolution were first acquired at a radial distance of 7.7 RJ from Jupiter's center. The last and most clearly‐defined signature, with exceptionally sharp boundaries, was observed at 6.03 RJ, about 12 minutes before closest approach to Io. The magnetic pressure change across the boundaries of these structures was ∼10 to ∼33 nPa, the latter value in a region with background plasma pressure of 60 nPa. Thus, although of small amplitude in the magnetic field, they represent large changes in the pressure. Abrupt changes in the measurements of the other fields and particles instruments correlate with some of the magnetic signatures. In this paper, we present the magnetometer data for these unusual signatures, discuss the limits on particle density changes that they imply, the significance of their spatial distribution, and their relationship to transport of plasma in the torus.
The continuing search for an anthropogenic climate change signal: Limitations of correlation‐based approaches
Authors: Legates David R. , Davis Robert E.
Published: February 2004

Several recent studies claim to have found evidence of large‐scale climate changes that were attributed to human influences. These assertions are based on increases in correlation over time between general circulation model prognostications and observations as derived from a centred pattern correlation statistic. We argue that the results of such studies are inappropriate because of limitations and biases in these statistics which leads us to conclude that the results of many studies employing these statistics may be erroneous and, in fact, show little evidence of a human fingerprint in the observed records.
The Pele Plume (Io): Observations with the Hubble Space Telescope
Authors: Spencer John R. , Sartoretti Paola , Ballester Gilda E. , McEwen Alfred S. , Clarke John T. , McGrath Melissa A.
Published: February 2004

In July 1996, with the Hubble Space Telescope (HST), we observed the Pele plume silhouetted against Jupiter at a wavelength of 0.27µm, the first definitive observation of an Io plume from Earth. The height, 420 ± 40 km, was greater than any plume observed by Voyager. The plume had significantly smaller optical depth at 0.34 and 0.41µm, where it was not detected. The wavelength dependence of the optical depth can be matched by a plume either of fine dust, with minimum mass of 1.2 × 109 g and maximum particle size of 0.08µm, or of SO2 gas with a column density of 3.7 × 1017 cm−2 and total mass of 1.1 × 1011 g. Our models suggest that early Voyager imaging estimates of the minimum mass of the Loki plume [Collins, 1981] may have been too large by a factor of ∼ 100. We may have detected the Pele plume in reflected sunlight, at 0.27µm, in July 1995, but did not see it 21 hours earlier, so the plume may be capable of rapid changes.
Source regions of the slow solar wind
Authors: Woo Richard , Martin Jan M.
Published: February 2004

While the fast solar wind is generally thought to originate from coronal holes, the source of the slow solar wind is only known to be associated with the highly structured and highly variable streamer belt. There is growing evidence from multiple‐station intensity scintillation measurements of solar wind velocity—often referred to as IPS for interplanetary scintillation—that the slow wind originates in localized regions of the solar corona overlying the streamer belt. In this paper, velocity structure in the corona is investigated based on estimates obtained from the power spectra of single‐station intensity scintillation measurements. These measurements were conducted with the S‐ and X‐band (13 and 3.6 cm wavelengths, respectively) radio signals of Voyager 2 during its superior conjunctions in 1979 and 1982. Unlike previous studies, simultaneous estimates of density fluctuation from the same intensity scintillation measurements were available to provide the coronal context for the velocity measurements. Solar eclipse pictures show that with increasing heliocentric distance, coronal streamers taper to narrow extensions or stalks of angular size 1–2° by a few solar radii. Prominent enhancements in density fluctuation characterizing such streamer stalks are found to coincide with the low speed wind measured by Voyager 2, leading to the first observational evidence for streamer stalks as the long sought coronal sources of the slow solar wind.
Bending thin lithosphere causes localized “Snapping” and not distributed “crunching”: Implications for Abyssal Hill Formation
Authors: Buck W. Roger
Published: February 2004

Horizontal loads (i.e. pushes or pulls) on the lithosphere are thought to produce significant, localized, dip‐slip faults, but vertical loads are generally considered to produce broadly distributed bending or flexure. The same processes of weakening or yielding that lead to localization of deformation on faults during lithospheric stretching or shortening can produce highly localized faulting during lithospheric bending. Localized bending, or “snapping” should occur when the bending moment begins to decrease with increasing plate curvature. If yielding causes a reduction in cohesion then thin brittle layers may respond to bending in the “snapping” mode while thicker layers respond in a more distributed “crunching” mode. For a Mohr‐Coulomb layer floating on an invicid substrate it is the ratio of the cohesion to the average shear stress needed to overcome friction that controls the mode of bending. The average horizontal stress on the layer also affects the mode of bending. For estimated rock properties, a brittle layer has to be less than a few, up to perhaps 10 km thick, to break in a localized way. Lithosphere at many mid‐ocean ridges is thought to be only a few kilometers thick and also may be a site of vertical loading. The localized snapping mode of bending may produce abyssal hills at fast‐spreading mid‐ocean ridges.
Uptake of NOy on wave‐cloud ice particles
Authors: Weinheimer A. J. , Campos T. L. , Walega J. G. , Grahek F. E. , Ridley B. A. , Baumgardner D. , Twohy C. H. , Gandrud B. , Jensen E. J.
Published: February 2004

In a flight through a wave cloud during SUCCESS on 2 May 1996, simultaneous forward‐ and aft‐facing NOy inlets were used to infer the amount of condensed‐phase NOy present on ice particles that were up to a few minutes old. Condensed‐phase amounts were 25–75 pptv, or 10–20% of gas‐phase NOy. Given the rapid HNO3 uptake on ice observed in the laboratory, a model calculation implies that virtually all of the gas‐phase HNO3 will be depleted in the first 1–2 minutes after the appearance of ice. Thus the NOy observations are consistent with the laboratory results only if the ambient HNO3/NOy ratio is 10–20%.
Current‐voltage characteristics of the tethered satellite system: Measurements and uncertainties due to temperature variations
Authors: Chang C. L. , Drobot A. T. , Papadopoulos K. , Wright K. H. , Stone N. H. , Gurgiolo C. , Winningham J. D. , Bonifazi C.
Published: February 2004

One of the primary goals of the Tethered Satellite System reflight mission (TSS‐1R) is to determine the current‐voltage characteristics of the TSS satellite orbiting in the ionosphere. While the collected current was measured directly with high reliability, the satellite potential could only be deduced from a circuit model or from interpretation of measurement data below satellite potentials of 500 Volts. The greatest uncertainty in the circuit model is the value of tether resistance R. We have provided quantitative calibration of the resistance based on instrument data for Vs < 100 Volts. We have reached the important conclusion that the R value in the TSS circuit model is correlated to temperature changes associated with the diurnal cycles along the TSS flight path. We have also applied the calibrated R value in the TSS circuit equation to construct the I‐V curves that extend to high voltages. The resulting I‐V characteristics are presented with error bounds on satellite potential to indicate the uncertainty associated with the tether resistance determination. The I‐V relation exhibits different scalings in the high (> 100 Volts) and low (< 10 Volts) voltage regimes, which indicates a fundamental transition for the current collection physics in the ionospheric plasma surrounding the satellite.
Supercooled cirrus cloud formation modified by nitric acid pollution of the upper troposphere
Authors: Laaksonen Ari , Hienola Jukka , Kulmala Markku , Arnold Frank
Published: February 2004

We have investigated nitric acid induced cirrus cloud formation in the upper troposphere. Our theoretical model investigations were made in the light of recent upper tropospheric gaseous nitric acid observations which show higher than expected nitric acid abundances. Our investigations indicate markedly increased cloud condensation nuclei number densities due to nitric acid induced aerosol activation. Our findings suggest that nitric acid may substantially modify supercooled cirrus cloud formation at temperatures above −40°C and thereby influence climate.
Modulated electron plasma waves observed in the tail lobe: Geotail waveform observations
Authors: Kojima H. , Furuya H. , Usui H. , Matsumoto H.
Published: February 2004

We present the results of the Geotail waveform observation on the electrostatic plasma waves with their frequency close to the local electron plasma frequency in the tail lobe. Those waves, which we call “electron plasma waves” in the present paper, are strongly modulated in their amplitudes and are very similar to the modulated Langmuir waves observed by previous spacecraft in the various regions. From the detailed analyses, we conclude that they include the Langmuir waves and 5 types of the Electron Cyclotron Harmonic (ECH) waves. Finally, we introduce an interesting event that the observed waves change from the ECH waves to the Langmuir waves in a short period within one second.
El Niño and climate change
Authors: Trenberth Kevin E. , Hoar Timothy J.
Published: February 2004

A comprehensive statistical analysis of how an index of the Southern Oscillation changed from 1882 to 1995 was given by Trenberth and Hoar [1996], with a focus on the unusual nature of the 1990–1995 El Niño‐Southern Oscillation (ENSO) warm event in the context of an observed trend for more El Niño and fewer La Niña events after the late 1970s. The conclusions of that study have been challenged by two studies which deal with only the part of our results pertaining to the length of runs of anomalies of one sign in the Southern Oscillation Index. They therefore neglect the essence of Trenberth and Hoar, which focussed on the magnitude of anomalies for certain periods and showed that anomalies during both the post‐1976 and 1990‐mid‐1995 periods were highly unlikely given the previous record. With updated data through mid 1997, we have performed additional tests using a regression model with autoregressive‐moving average (ARMA) errors that simultaneously estimates the appropriate ARMA model to fit the data and assesses the statistical significance of how unusual the two periods of interest are. The mean SOI for the post‐1976 period is statistically different from the overall mean at <0.05% and so is the 1990‐mid‐1995 period. The recent evolution of ENSO, with a major new El Niño event underway in 1997, reinforces the evidence that the tendency for more El Niño and fewer La Niña events since the late 1970s is highly unusual and very unlikely to be accounted for solely by natural variability.
A formulation of a wave‐activity flux for stationary Rossby waves on a zonally varying basic flow
Authors: Takaya Koutarou , Nakamura Hisashi
Published: February 2004

A new formulation of an approximate conservation relation is proposed for stationary Rossby waves on a zonally varying basic flow, utilizing that A (proportional to wave enstrophy) and ε (proportional to wave energy) are both related to the wave activity pseudomomentum. For stationary Rossby waves, it is shown in the limit of a small‐amplitude, plane wave on a slowly varying, unforced non‐zonal flow that a particular linear combination of A and ε, namely, M ≡ (A + ε)/2, is independent of the wave phase, even if unaveraged, and is conserved under steady, unforced and nondissipative conditions. It is also shown that the three‐dimensional flux of M is parallel to the local group velocity in the WKB limit. The flux could be a useful diagnostic tool, as shown in an example that presents a “snapshot” of the three‐dimensional propagation of a stationary Rossby wavetrain in the real atmosphere. Our conservation relation is a generalization of that for stationary Rossby waves on a zonally‐uniform basic flow derived by Plumb.
Frequency‐dependent anisotropy in Wellington, New Zealand
Authors: Marson‐Pidgeon Katrina , Savage Martha Kane
Published: February 2004

Shear‐wave splitting measurements are made using teleseismic S, ScS and SKS waveforms recorded at the GDSN broadband station SNZO, situated in South Karori, New Zealand. The average S and SKS delay times are around 2 to 3 s, among the highest in the world. The average ScS delay time is significantly smaller, around 1 s. This discrepancy appears to be due to differences in dominant frequency. The most likely cause of frequency‐dependent anisotropy is oriented heterogeneities with a scale‐length much smaller than the wavelength. The fast polarizations range between 21° and 79°, with an average NE‐SW direction which is sub‐parallel to the trend of the local geologic structure and the strike of the Hikurangi subduction zone. Azimuthal variations in delay time, which cannot be explained by differences in period, may be due to a dipping axis of symmetry, or laterally varying anisotropy, or a more complicated symmetry system.
Transformation of contrails into cirrus during SUCCESS
Authors: Minnis Patrick , Young David F. , Garber Donald P. , Nguyen Louis , Smith William L. , Palikonda Rabindra
Published: February 2004

Three contrail systems were analyzed with geostationary satellite data to document the conversion of the contrails to cirrus clouds. Two unique contrails, a pair of figure eights and a NASA DC‐8 oval, were tracked for more than 7 hours. A cluster of contrails from commercial aircraft lasted over 17 hours. The figure eights produced a cirrus cloud having a maximum extent of 12,000 km²; the commercial cluster reached an area of ∼35,000 km². The contrail‐cirrus were thin with optical depths between 0.2 and 0.5. In all cases, cloud particle size increased as the contrails developed into cirrus clouds. The climatic impact of contrails will be greater than would be estimated if only linear contrails, those typically observed in satellite imagery, are considered. Additional research is required to obtain reliable statistics on contrail growth and lifetime.
Rate change observed at JPLM after the Northridge Earthquake
Authors: Heflin Michael , Dong Danan , Donnellan Andrea , Hurst Ken , Jefferson David , Watkins Michael , Webb Frank , Zumberge James , Dauger Deborah , Lyzenga Gregory
Published: February 2004

Geodetic time series determined with the Global Positioning System indicate that the geodetic rate of a permanent site in Pasadena, California (JPLM) changed significantly after the 17 January 1994 Northridge California earthquake. Subtracting the pre‐quake rate and co‐seismic offset leaves 30±4 mm of integrated eastward excess motion observed in the three years following the earthquake. North and vertical components show excess motion of −11 plusmn;3 mm and 25±11 mm respectively. Local surveys to three additional points near JPLM changed by no more than 6 mm E, 3 mm N, and 15 mm V during the two years after the earthquake, ruling out the possibility of a local effect at the JPLM monument. The direction and size of the post‐seismic displacements at JPLM are not consistent with additional slip on the fault which ruptured. The most rapid accumulation of excess motion occurs immediately after the earthquake, suggesting a relationship between the two events.
Detection of hydrothermal plumes along the Southeast Indian Ridge near the Amsterdam‐St. Paul Plateau
Authors: Scheirer Daniel S. , Baker Edward T. , Johnson Kevin T. M.
Published: February 2004

A new self‐contained profiling instrument, attached to 91 lowerings of waxcores and dredges along a 1600 km stretch of the Southeast Indian Ridge, found six sites having optical back‐scatter anomalies indicative of hydrothermal plumes from high‐temperature seafloor venting. At five other sites, back‐scatter anomalies were less distinct, and at the remaining sites, anomalies were absent. These are the first documented hydrothermal sites along this intermediate‐rate spreading center and are among the very few yet discovered in the Indian Ocean basin. Some profiles exhibit complex back‐scatter anomalies suggestive of multiple sources of seafloor discharge. At one site, near‐bottom temperature anomalies of ∼0.1°C and the recovery of a vent‐specific barnacle provide the first precise seafloor location of active venting in the deep Indian Ocean. Although this study is only reconnaissance in nature, venting along this portion of the SEIR appears to be significantly less than predicted by global correlations of plume incidence as a function of spreading rate. Nevertheless, these sites may be important as biological connections between distinct faunal assemblages of Atlantic and Pacific vent fields.
Infrared spectral absorption of nearly invisible cirrus clouds
Authors: Smith W. L. , Ackerman S. , Revercomb H. , Huang H. , DeSlover D. H. , Feltz W. , Gumley L. , Collard A.
Published: February 2004

The SUbsonic aircraft Contrail and Cloud Effects Special Study (SUCCESS) was conducted 8 April–10 May 1996 to better understand the radiative properties of high level ice crystal clouds produced by anthropogenic (i.e., jet aircraft) and natural (i.e., weather) causes. In this paper multispectral radiance data observed during SUCCESS from the high flying NASA ER‐2 aircraft are presented to demonstrate that nearly ‘invisible’ high level layers of very small ice particles can cause very significant absorption (50% or more) of the upwelling infrared radiation to space.