bluuebunny/crossref_metadata_2025 huggingface dataset:
Global, multiyear variations of optical thickness with temperature in low and cirrus clouds
Authors: Tselioudis George , Rossow William B.
Published: February 2004

The International Satellite Cloud Climatology Project (ISCCP) dataset is used to correlate variations of cloud optical thickness and cloud temperature in today's atmosphere. The analysis focuses on low and cirrus clouds. Cold low clouds show increases in cloud optical thickness with temperature consistent with adiabatic behavior, while warm low clouds primarily show decreases in cloud optical thickness with temperature. An exception are subtropical low clouds which show a tendency for increases in optical thickness with temperature, particularly during El Niño years. High and middle latitude cirrus clouds show increases in optical thickness with temperature. In subtropical and tropical latitudes, cirrus cloud optical thicknesses show a complicated behavior that could be related to changes in the dynamical regime in which the clouds are formed.
Self‐organized criticality of plastic shear bands in rocks
Authors: Poliakov A. N. B. , Herrmann H. J.
Published: February 2004

We show that the shear bands that appear during the pure shear numerical simulations of rocks with a non‐associated plastic flow rule form fractal networks. The system drives spontaneously into a state in which the length distribution of shear bands follows a power law (self‐organized criticality) with exponent 2.07. The distribution of local gradients in deviatoric strain rate has different scaling exponents for each moment, in particular the geometrical fractal dimension is 1.7. Samples of granodiorite sheared under high confining pressure from the Pyrenees are analyzed and their properties compared with the numerical results.
Alvin magnetic survey of zero‐age crust: CoAxial Segment Eruption, Juan de Fuca Ridge 1993
Authors: Tivey Maurice A. , Johnson H. Paul
Published: February 2004

Magnetic profiles obtained by deep submersible ALVIN across a newly erupted lava flow on the Juan de Fuca Ridge (JDFR) show strong magnetic anomaly fields (>20,000 nT) and high crustal magnetization (>50 A/m contrast) relative to the surrounding older lavas. These results are consistent with previous ideas that extrusive crust is initially highly magnetized. Within the high amplitude magnetic anomaly over the center of the flow, there is a clearly defined deep, “notch‐like” magnetic low. This notch may indicate thermal demagnetization associated with a subsurface feeder dike, weakly magnetized intrusives or altered extrusive rock. If the former mechanism is active, the notch should disappear with time as the dike cools.
Quasi‐periodic oscillations of the magnetopause during northward sheath magnetic field
Authors: Kokubun S. , Kawano H. , Nakamura M. , Yamamoto T. , Tsuruda K. , Hayakawa H. , Matsuoka A. , Frank L. A.
Published: February 2004

The Geotail satellite quasi‐periodically crossed the dawn flank of magnetopause more than ten times during an interval of 1.5 hours on November 4, 1992. Magnetopause crossings were characterized by quasi‐periodic pulses of a sawtooth wave form in the magnetic field and the plasma flow components tangential to the magnetopause. The magnetic field strength in the magnetosheath was larger than that in the magnetosphere. The direction of magnetic field outside the magnetopause current layer was northward with antisunward tilt, indicating the draping of magnetic field on the magnetopause. Boundary normals of wavy magnetopause systematically incline sunward on the upstream side, while they tend to incline antisunward with considerable deviation on the downstream side. Comparison with other multiple crossing events suggests that the November 4 event exhibits wavy structure of the dawn flank magnetopause associated with the northward interplanetary magnetic field.
OH emission and gravity waves (including a breaking wave) in all‐sky imagery from Bear Lake, UT
Authors: Swenson Gary R. , Mende Stephen B.
Published: February 2004

A new type of all‐sky imager, using a high resolution, bare CCD, was operated at Utah State University Observatory at Bear Lake Utah during fall‐winter, 1991–2 on clear nights. The purpose was to image OH airglow in the 7500–9000 Å spectral region for correlative measurements with UARS satellite instrumentation. Examination of some 20 nights of data, some OH wave activity (interpreted as gravity wave phenomena) has been observed on all images and the spatial extent of the waves typically covered the entire viewing field (including overhead). Images are presented including examples of multiple wave sources and a (one time observed) complex breaking wave. The unique chaotic structure, which evolved over an hour, developed a distorted phase front followed by a very short wavelength ‘rippled’ structure.
Impact of increased CO2 on simulated ENSO‐like phenomena
Authors: Knutson Thomas R. , Manabe Syukuro
Published: February 2004

The impact of a CO2‐induced global warming on ENSO‐like fluctuations in a global coupled ocean‐atmosphere GCM is analyzed using two multi‐century experiments. In the 4×CO2 experiment, CO2 increases by a factor of four in the first 140 years and then remains constant at 4×CO2 for another 360 years; in the control experiment, CO2 remains constant at 1×CO2 for 1000 years. The standard deviation of tropical Pacific SST fluctuations (7°N–7°S, 173°E–120°W; 2 to 15 year timescales) is 24% lower in the 4×CO2 experiment than in the control experiment; for the model's Southern Oscillation Index, a 19% decrease occurs, whereas for central tropical Pacific rainfall, a 3% increase occurs. An important feature of the control simulation is the internally generated modulation of variability on a multi‐century timescale, which is comparable in magnitude to the changes occurring with 4×CO2. We conclude that despite an order 5 K warming of the tropical Pacific, and order 50% increase in time‐mean atmospheric water vapor under 4×CO2 conditions, ENSO‐like SST fluctuations in the coupled model do not intensify, but rather decrease slightly in amplitude.
The GPS flight experiment on TOPEX/POSEIDON
Authors: Melbourne William G. , Davis E. S. , Yunck Thomas P. , Tapley Byron D.
Published: February 2004

The precision orbit determination (POD) experiment on TOPEX/POSEIDON using the Global Positioning System (GPS) is yielding concrete results. Orbit consistency and accuracy tests indicate that GPS is routinely providing satellite altitude with an accuracy of better than 3 cm. Here we review the GPS experiment, its basic concepts, POD techniques and key results, and discuss the possible cost and performance benefits that may flow to future missions.
Spatial and temporal characteristics of giant undulations
Authors: Nishitani N. , Hough G. , Scourfield M. W. J.
Published: February 2004

A giant undulation event observed at SANAE, Antarctica (L = 4) is reported. During the event the geomagnetic activity was high, as was the case in previously reported observations of giant undulations. Data were recorded by all‐sky and small field‐of‐view TV cameras, from 2346 UT on September 10, to 0007 UT on September 11 (MLT ∼ 2200 h) 1987. The fine temporal and spatial resolution of the TV data made a detailed study of the undulation possible. The average wavelength was 170 km and the amplitude of the wave increased from 70 km to 140 km in 10 minutes. Wave propagation, measured at different positions on the undulation, was duskward with a phase speed of 540 to 650 m/s. An inner structure, propagating at a speed of 2.5 to 4.0 km/s, about 3 times as fast as the undulation form, was observed just poleward of the undulation boundary, indicating the presence of strong velocity shear. The linear theory of the velocity shear instability is examined as a possible generation mechanism on the basis of these observations.
A new class of forward‐reverse shock pairs in the solar wind
Authors: Gosling J. T. , McComas D. J. , Phillips J. L. , Weiss L. A. , Pizzo V. J. , Goldstein B. E. , Forsyth R. J.
Published: February 2004

A new class of forward‐reverse shock pairs in the solar wind has been discovered using Ulysses observations at high heliographic latitudes. These shock pairs are produced by expansion of coronal mass ejections, CMEs, that have internal pressures that are higher than, and speeds that are comparable to, that of the surrounding solar wind plasma. Of six certain CMEs observed poleward of S31°, three have associated shock pairs of this nature. We suggest that high internal CME pressures may exist primarily for events that have high speeds close to the surface of the Sun.
Highly rotationally excited NO(υ,J) in the thermosphere from CIRRIS 1A limb radiance measurements
Authors: Armstrong P. S. , Lipson S. J. , Dodd J. A. , Lowell J. R. , Blumberg W. A. M. , Nadile R. M.
Published: February 2004

Earthlimb spectra of thermospheric NO fundamental band emissions, obtained in the CIRRIS 1A Space Shuttle experiment, have been analyzed using nonlinear least‐squares spectral fitting. Absolute NO(υ≥1,J) column densities have been determined in the 100 to 260‐km tangent height region and inverted to yield altitude‐dependent number densities for both a rotationally thermalized and a highly rotationally excited population component. Emissions from high‐J levels are predicted to dominate the Δυ=2 overtone bands during the daytime. The rotationally excited population is found to decrease more at night than the rotationally thermalized component. In addition, radiance from the CO υ=1→0 fundamental band is observed in the NO R‐branch band head region, with greater relative importance at night. The derived CO rotational temperatures are significantly greater than modeled local kinetic temperatures. These results provide important inputs to models of NO(υ,J) formation mechanisms, and of the chemistry, radiative processes, and energy budget of the thermosphere.
Temperature averages and rates of stratospheric reactions
Authors: Murphy D. M. , Ravishankara A. R.
Published: February 2004

Use of zonal average temperatures is common in numerical modeling of stratospheric chemistry. In most cases, this approach is accurate. The exceptions are when a heterogeneous reaction or a thermal process which is highly non‐linear in temperature is involved. The differences between use of an average temperature and more realistic temperature are presented for cases where temperature fluctuations are of importance in the stratosphere. In particular, the rates of reactions of HCl in sulfate aerosols are significantly underestimated by the use of zonal average temperatures. Errors associated with using monodispersed aerosols in place of a size distribution are also addressed.
On the cross‐field diffusion of ions in one‐ and two‐dimensional hybrid simulations of collisionless shocks
Authors: Giacalone Joe
Published: February 2004

It can be demonstrated analytically that under certain geometries used in numerical simulations of collisionless shocks in which there is at least one ignorable spatial coordinate, the transport of particles across the magnetic field is essentially zero. This notion is tested using one‐ and two‐dimensional hybrid simulations (kinetic ions/ fluid electrons). We find, as the theorem predicts, the particles treated kinetically are tied to the same field line on which they start.
Determination of the infrared cross sections and global warming potentials of 1,1,2‐trifluoroethane (HFC‐143)
Authors: Clerbaux C. , Colin R.
Published: February 2004

The Global Warming Potentials (GWPs) of CH2F‐CHF2 (HFC‐143) have been estimated for different time horizons. Radiative forcings associated with this CFC alternative have been derived relative to CFC‐11 and CO2 by introducing laboratory measured absorption cross sections into a coupled chemical‐radiative model.
Gas transfer velocities for SF6 and ³He in a small pond at low wind speeds
Authors: Clark Jordan F. , Schlosser Peter , Wanninkhof Rik , Simpson H. James , Schuster William S. F. , Ho David T.
Published: February 2004

Gas transfer velocities for two gases, SF6 (sulfur hexafluoride) and ³He, were determined in a small pond by injecting a mixture of these gases into the water and monitoring the decline of their concentrations over the next eight days. For wind speeds between 1.5–2.5 m s−1, no variations of gas transfer velocity with wind speed could be resolved with our data. Gas transfer velocities at wind speeds greater than 3 m s−1 were substantially larger and consistent with other lake tracer experiments. From the ratio of gas transfer velocities for SF6 and 3He we calculated the Schmidt number exponent to be 0.57±0.07.
Microbial‐mineral floc associated with nascent hydrothermal activity on CoAxial Segment, Juan de Fuca Ridge
Authors: Juniper S. Kim , Martineu P. , Sarrazin J. , Gélinas Y.
Published: February 2004

Following a June 1993 seafloor eruption at CoAxial Segment, Juan de Fuca Ridge, extensive accumulation of microbial‐mineral floc was observed in association with abundant diffuse venting on new lava flows, and around less extensive new venting on older basalts. Microscopic and SEM examination revealed a diverse assemblage of microbial forms contained within a poorly organized organo‐mineral matrix. Samples more closely resembled microbial floc described from other hydrothermal areas than the layered bacterial mats observed after the eruption at 9°N on the East Pacific Rise. Iron and silica were the major compositional elements in all samples, with the latter likely important in preserving microbial remains. Organic carbon content was on the order of 3–4%. Enzyme assays indicated the presence of autotrophic CO2 fixation and potential for sulfide oxidation. Floc covered 7–14% of the seafloor on the hydrothermally active part of the new lava flow. We discuss the possibility that the CoAxial floc originated as ejecta from the sub‐seafloor hydrothermal system rather than from in situ production around vent openings.
Spatial statistics of snowmelt flow: Data from lysimeters and aerial photos
Authors: Sommerfeld Richard A. , Bales Roger C. , Mast Alisa
Published: February 2004

The two‐dimensional, horizontal spatial statistics of meltwater flow through a Wyoming snowpack were investigated using two independent methods: meltwater flow from arrays of closely spaced lysimeters and a survey of snow surface brightness on aerial photos. Both methods suggested a characteristic distance of about 6 m over which the respective phenomena were correlated. If a characteristic distance for meltwater flow could be related to snow characteristics such as slope and aspect, modeling of meltwater related phenomena would be facilitated. If the aerial photo data could be shown to be related to the flow data, as these results suggest, a convenient technique for determining meltwater spatial statistics from aerial photos would be available.
An estimation of the elastic thickness of the lithosphere in the Canary Archipelago using admittance function
Authors: Dañobeitia J. J. , Canales J. P. , Dehghani G. A.
Published: February 2004

A recent compilation of shipborne gravity and bathymetry data has been used to determine the Effective Elastic Thickness (EET) of the lithosphere beneath the Canary Islands volcanic complex by means of the admittance technique. As a first approach, we have computed the admittance, which is interpreted in terms of isotropic elastic plate thickness, with an EET of 23 km. Nevertheless, the proximity of the West African Continental Margin (WACM), together with the lateral variability in lithosphere structure in part caused by the large volcanic history of the Canaries, require a slightly different approach. To minimize the influence of the margin and to check whether or not any significant variation in EET occurs related to the known Canary hotspot, we have computed the admittance following the isochron lines. The results show a higher EET (35 km) than that obtained by the first approach but slightly smaller than that predicted by the cooling plate model.
Integrated stress determination by joint inversion of hydraulic tests and focal mechanisms
Authors: Yin J. M. , Cornet F. H.
Published: February 2004

An inversion method, based on a genetic algorithm, is proposed for interpreting jointly various kinds of stress data in order to overcome the limitation, in number and quality, of each data set. The method has been applied to results from hydraulic tests in boreholes and to focal mechanisms of induced seismicity observed within the same depth interval. The regional stress field is described by two symmetrical tensors. The first one represents the stress at a given depth and the second one the vertical stress gradient. Results indicate that one of the principal directions is vertical. They are consistent with all but one of the hydraulic tests considered in the inversion and with about 70% of the focal mechanisms. This inversion confirms previous results suggesting that, for the scale of these induced microseismic events, the regional stress field cannot be determined solely from an inversion of the fault plane solutions.
Finding sets of acceptable solutions with a genetic algorithm with application to surface wave group dispersion in Europe
Authors: Lomax Anthony , Snieder Roel
Published: February 2004

We discuss the use of a genetic algorithm (GA) to invert data for many acceptable solutions, in contrast to inversion for a single, “optimum” solution. The GA is a directed search method which does not need linearization of the forward problem or a starting model, and it can be applied with a very large model‐space. Consequently, fewer assumptions are required and a greater range of solutions is examined than with many other inversion methods.

We apply the GA to fundamental Rayleigh group dispersion estimates for paths across Central Europe and across the East European Platform to determine “average”, layered S velocity models separately for each region. The use of the GA allows an identical model parameterization and broad parameter search range to be used for both regions. The scatter of acceptable solutions shows velocity‐depth trade‐offs around the Moho, indicates the depth resolution of the inversion, and shows the uncertainty in upper mantle, S velocity estimates. The results indicate that a thicker crust and up to 0.3 km/sec (7%) higher S wave velocities in the upper 100 km of the mantle under the older East European Platform than under Central Europe explain most of the differences in the data sets.
Anomalous HNO3/NOx ratio of remote tropospheric air: Conversion of nitric acid to formic acid and NOx?
Authors: Chatfield Robert B.
Published: February 2004

The N oxidation ratio, [HNO3]/ [NOx], in the free troposphere is measured at ∼ 1 to 9 (averaging ∼5), consistently lower than the values of 15–100 which known theory suggests to be reached rapidly. This discrepancy casts doubt on current models' abilities to predict effects of NO sources on remote [NO], and so also [O3] and [OH]. HNO3‐to‐NOx recycling processes involving HCHO in solution are appealing explanations for the ratio. Known chemical theory are illustrated using a Lagrangian box model of the mid‐troposphere which simulates characteristic episodes from NOx input to HNO3 washout. Ratio and budget constraint equations for NOy, can usefully restrict conceivable explanations of missing chemistry of fast nitrogen cycling; most explanations could be called “fast‐cycles” or “re‐NOx‐ification.” These equations also show how current global models may suggest spuriously good N oxidation ratios and errors in OH. Aerosol or cloud droplets reactions with HCHO may produce (a) formic acid (which needs an appropriate source) and NOx, or alternatively, (b) hydroxymethyl nitrate (or methyl dinitrate), which might supply a large, variable amount of “missing NOy” not currently measurable except by NOy instruments.
Observations of the 5‐day wave in the mesosphere and lower thermosphere
Authors: Wu D. L. , Hays P. B. , Skinner W. R.
Published: February 2004

The 5‐day planetary wave has been detected in the winds measured by the High Resolution Doppler Imager (HRDI) on the Upper Atmosphere Research Satellite (UARS) in the mesosphere and lower thermosphere (50–110 km). The appearances of the 5‐day wave are transient, with a lifetime of 10–20 days in the two‐year data set. The structures of selected 5‐day wave events are in generally good agreement with the (1,1) Rossby normal mode for both zonal and meridional components. A climatology of the 5‐day wave is presented for an altitude of 95 km and latitudes mainly between 40°S and 40°N.
A bounce‐averaged kinetic model of the ring current ion population
Authors: Jordanova V. K. , Kozyra J. U. , Khazanov G. V. , Nagy A. F. , Rasmussen C. E. , Fok M.‐C.
Published: February 2004

A bounce‐averaged ring current kinetic model for arbitrary pitch angle, including losses due to charge exchange and Coulomb collisions along ion drift paths, is developed and solved numerically. Results from simplified model runs, intended to illustrate the effects of adiabatic drifts and collisional losses on the proton population, are presented. The processes of i) particle acceleration under the conditions of time‐independent magnetospheric electric fields; ii) a predominant loss of particles with small pitch angles due to charge exchange; and iii) a buildup of a low‐energy population caused by the Coulomb drag energy degradation, are discussed.
Simulation of coda wave envelope in depth dependent scattering and absorption structure
Authors: Hoshiba Mitsuyuki
Published: February 2004

Coda waves are considered to be composed of scattered waves. For simplicity, previous models of coda wave generation have often assumed spatial uniformity of scattering and absorption. To account for possible depth dependent attenuation, the energy density of coda waves are synthesized using the Monte Carlo simulation method with multiple isotropic scattering assumption. Uniform velocity structure is assumed and impulsive point source is used. In depth dependent structures given in this paper, the synthesized envelopes give coda Q−1 decreasing with increasing lapse time, which has been observationally known well but has not been adequately explained with uniform models. The energy density becomes asymptotically close to a common decay curve irrespective of epicentral distances as the lapse time increases. However, the amount of the energy density from two sources is different at the same receiver at even the same lapse time for the same radiation energy when the focal depths are different. Theoretical basis of the conventional coda normalization method is examined in cases of the strong depth dependent attenuation structure.
A comparison of satellite laser ranging and seismicity data in the Aegean Region
Authors: Jackson James , Haines John , Holt William
Published: February 2004

In this study we compare the strain rates obtained from earthquake moment tensors in the time interval 1911–92 in Greece with measured velocities of SLR stations relative to Eurasia. We find that the SLR measurements do not require strain different in orientation from that seen in the earthquakes, but simply more of it. The clearest deficit is in the SE Aegean where earthquakes this century can account for virtually none of the measured SLR strain rates. By contrast, in the northern Aegean and NW Turkey the earthquakes can account for a substantial part (>50%) of the measured strain rates. By using both geodetic and seismic data to localize apparent deficits in seismically‐released strain, this study represents a first step towards using space‐based geodesy for crude regional seismic risk assessment.
stress pulses in southern Italy
Authors: Marzocchi Warner , Mulargia Francesco
Published: February 2004

The crustal seismic activity in southern Italy during the last three centuries has been analyzed in order to confirm or disprove the evidence of a northward migration of earthquake epicenters from Calabria towards southern Apennines and Irpinia that we have found in a previous work. The results suggest such a migration to be statistically significant at a velocity of about 13 km/yr. This, in turns, stands for the existence of stress pulses propagating northward along the Apennine axis.
Seasonal variation of atmospheric nitric acid over the South Pole in 1992
Authors: Van Allen Renate , Liu Xu , Murcray Frank J.
Published: February 2004

We conducted year‐round measurements of mid infrared atmospheric emission over the South Pole in 1992. We were able to observe a large seasonal change of the total column of nitric acid (HNO3) vapor. During the summer, the HNO3 column abundance was about 2×1016 molecules/cm². There was a small increase in the fall. A rapid decrease of 50% was observed in late June, soon after the stratospheric temperature reached the threshold for formation of type I polar stratospheric clouds (PSCs). By early July, the stratospheric temperature was cold enough to form type II PSCs, and the HNO3 column decreased to 7×1015 molecules/cm². Measured nitric acid values in the spring remained extremely low even after the stratosphere warmed well above PSC temperatures. This may indicate permanent removal of HNO3 by gravitational settling, or long‐term sequestering in large particles. Normal summer values were not observed until the vortex dissipated and allowed the lateral transport of HNO3, to the south polar region.
Subevent rake and random scattering effects in realistic strong ground motion simulation
Authors: Zeng Yuehua , Anderson John G. , Su Feng
Published: February 2004

Recently Zeng et al. (1994) proposed a composite source model for convolution with synthetic Green's functions for computing strong ground motion due to a complex rupture process of a large earthquake. The composite source consists of sub‐events with a distribution of sizes, distributed randomly on the fault. In this paper, we extend our discussion of the source by allowing subevent rake to vary within the positive strain quadrant and by including the effect of the random lateral heterogeneity of the earth by adding scattered waves into the Green's function computed from a layered elastic earth model. Both of these variations contribute towards equalizing different components of the high frequency waveform train. The random scattering has the stronger effect on increasing the amplitudes of the nodal components. The early part of these scattered coda waves also tends to elongate the strong shaking of the earthquake.
Rapid changes in LLBL thickness
Authors: Hapgood Mike , Lockwood Mike
Published: February 2004

We employ data from two spacecraft, at the dawn flank of the magnetopause, to investigate fluctuations in the thickness of the low‐latitude boundary layer (LLBL). We show the LLBL is considerably thinner shortly after the detection of a flux transfer event than it was during the event. These data are shown to be consistent with the theory of transient increases in the open LLBL thickness caused by a pulse of enhanced reconnection at the magnetopause.
Dynamic observation of indentation process
Authors: Yoshioka Naoto , Yoshioka Masato
Published: February 2004

Indentation experiments were performed with a pyramidal Vickers indenter on glass samples to observe the dynamic process of indentation. Successive picture images of indentation were taken by a CCD camera through a microscope. The change in diagonal length of the indentation was measured as a function of time of the order of several tens of milliseconds. The results show that the initial process of indentation is highly dependent on the collision velocity of the indenter when it comes into contact with the sample. Higher collision velocities yield larger rates of initial increase in diagonal length. An empirical equation was obtained that is similar to a visco‐elastic Voigt model. It is suggested that local heating due to friction between the indenter and the sample or adiabatic compression reduced the viscosity of the sample material. The dynamic effect observed may be a cause of the change in resistance that is seen in the rate‐dependent rock friction.
Velocity and associated echo power variations in the summer polar mesosphere
Authors: Rüster R.
Published: February 2004

VHF radar measurements have been made for 32 days in the summer polar mesosphere at Andenes (69°N, 16°E) in Northern Norway. For specific time intervals a significant correlation between wave‐induced velocity oscillations and corresponding echo power variations has been found. In particular, the height dependence of amplitude and phase of the different waves has been studied in detail. The observed waves in the velocity field, which are also present in the temperature field, occasionally appear in corresponding echo power variations possibly due to the existence of ice particles in the summer polar mesosphere.
Attenuation distance of low frequency waves upstream of the pre‐dawn bow shock: GEOTAIL and ISEE 3 comparison
Authors: Sugiyama T. , Terasawa T. , Kawano H. , Yamamoto T. , Kokubun S. , Frank L. A. , Ackerson K. , Tsurutani B. T.
Published: February 2004

We have made a statistical study of the spatial distribution of low frequency waves (∼0.01–0.1 Hz) in the region upstream of the pre‐dawn to dawn side bow shock (−50 Re < X < 15 Re) using both GEOTAIL and ISEE‐3 magnetometer data. We have found that the wave amplitude dependence on D and Xs, where D is the distance from the bow shock and Xs the x‐coordinate position of shock foot point of the IMF, can be described by a functional form of A exp(Xs/LX ‐ D/LD), with the characteristic attenuation distances, LX = 62 ± 12 Re and LD = 59 ± 38 Re.
The bootstrap method in space physics: Error estimation for the minimum variance analysis
Authors: Kawano H. , Higuchi T.
Published: February 2004

The minimum variance analysis technique introduced by Sonnerup and Cahill (1967) is a useful tool in space physics. However the statistical errors appearing in this method are difficult to estimate accurately because of the complicated form of the eigenvalue decomposition. To deal with this problem, this paper introduces the bootstrap method (Efron, 1979) which replaces analytical solutions with repeated simple calculations. We apply this method to the estimation of the statistical errors in the minimum variance direction and the average component in the minimum variance direction, and show that this method accurately estimates the errors.
vapour pressures of H2SO4/HNO3/HCl/HBr/H2O solutions to low stratospheric temperatures
Authors: Luo Beiping , Carslaw Kenneth S. , Peter Thomas , Clegg Simon L.
Published: February 2004

Vapour pressures of H2O, HNO3, HCl and HBr over supercooled aqueous mixtures with sulphuric acid have been calculated using an activity coefficient model, for 185 K < T < 235 K, 0 < wt%(H2SO4) + wt%(HNO3) < 70, and assuming HCl and HBr to be minor constituents. Predicted vapour pressures agree well with most laboratory data, and give confidence in the validity of the model. The results are parameterized as simple formulae, which reproduce the model results to within 40% and cover the entire stratospherically relevant range of composition and temperature.
Ozone profiles at McMurdo Station, Antarctica during the spring of 1993; Record low ozone season
Authors: Johnson B. J. , Deshler T. , Zhao R.
Published: February 2004

Record low ozone was measured by balloon‐borne ozonesondes (40 flights) at McMurdo Station, Antarctica (78°S) during the 1993 austral spring. Total column ozone declined by 55% from an initial 275 Dobson Units (DU) on 30 August to a minimum of 130±7 DU on 2 October. Ozone within the 12–20 km showed a 95% decrease from an initial 138 DU in August to a record low 7 DU on 19 October. Probable causes of the 1993 record low ozone, based on balloon‐borne observations at McMurdo include: the presence of the Pinatubo volcanic aerosol layer between 11 and 16 km (though decreased from the 1992 season); a colder than normal stratosphere over McMurdo (183 K minimum); and a relatively stable polar vortex which delayed the intrusion of high levels of ozone from outside the polar vortex wall until after 22 October. These conditions provided an optimum environment for the formation of polar stratospheric clouds (PSCs), essential to the heterogeneous chemistry that subsequently leads to the catalytic destruction of ozone by reactive chlorine.
Effect of stratospheric aerosol on ozone profile from BUV measurements
Authors: Torres Omar , Bhartia P. K.
Published: February 2004

Results of a simulation study on the effects of optically thick stratospheric sulfate aerosol layers on the backscattered ultraviolet radiation (buv) in the range 256–340 nm are presented. In general, the increased Mie scattering produced by the aerosols results in an enhancement of the buv radiation. The increase is approximately linear with optical depth and strongly depends on solar zenith angle and aerosol layer altitude in relation to the ozone maximum. The effect is greatest at those wavelenghts whose contribution functions peak in the vicinity of the densest part of the aerosol layer. The aerosol induced perturbation of the buv field affects the ozone profile retrieval from space measurements by the SBUV experiment. In the tropical stratosphere, the retrieved ozone between 25 and 45 km is underestimated as a result of increased Mie scattering. On the other hand, an algorithm related effect causes the retrieved ozone below 25 km to be overestimated by an amount similar to the stratospheric deficit.
Radiative damping of gravity waves in the terrestrial planetary atmospheres
Authors: Imamura Takeshi , Ogawa Toshihiro
Published: February 2004

We investigated the scale‐dependent radiative damping of internal gravity waves on the limit of amplitude growth with height in the altitude region 60–120 km of the terrestrial planetary atmospheres. The radiative damping due to the CO2 15 µm radiation limits wave propagation much more effectively in the Mars atmosphere than in the Earth's atmosphere. Though radiative damping is as effective in the Venus atmosphere as in the Mars atmosphere at ∼120 km altitude, it is not so effective below ∼100 km altitude. The damping due to molecular diffusion is significant compared to radiative damping above ∼80 km altitude on the Earth and above ∼120 km altitude on Mars, whereas on Venus it is not significant even above ∼120 km altitude.
Intracomparison tests of the FG5 absolute gravity meters
Authors: Sasagawa Glenn S. , Klopping Fred , Niebauer Timothy M. , Faller James E. , Hilt Richard L.
Published: February 2004

The FG5 series absolute gravimeters have an estimated instrumental accuracy of 1–2 µGal (1‐2 × 10−8 ms−2). A number of instrument comparisons were conducted with six FG5 instruments over a period of 9 months; the predecessor series JILA4 instrument was also used. The standard deviation of mean g values (averaged over 24–48 h), as observed by different instruments, is 1.8 µGal. Observations taken within 48 h typically agree within 2 µGal, and the maximum observed disagreement is 6 µGal for two observations taken 37 days apart. Individual data sets of 100–250 measurements (16–42 min duration) show minimum standard deviations of 7–8 µGal, placing an upper bound on instrument noise. The data are not corrected for local water‐table effects or regional atmospheric loading, and thus the observed repeatability is probably an underestimate of the instrument accuracy. The observed instrument agreement is consistent with the instrumental accuracy estimate. Ignoring deficiencies in modeling environmental gravity signals, this accuracy level should allow resolution of vertical motions at the sub‐centimeter level.
Estimation of an earthquake focal mechanism from a satellite radar interferogram: Application to the December 4, 1992 Landers aftershock
Authors: Feigl Kurt L. , Sergent Arnaud , Jacq Dominique
Published: February 2004

Using the interferometric fringes generated by the phase difference between a pair of synthetic‐aperture radar (SAR) images acquired by the ERS‐1 satellite, we estimate the focal mechanism of a small, shallow thrust earthquake. The inversion procedure is an iterative, linearized least‐squares algorithm based on a standard elastic dislocation formulation for coseismic displacements. Our preferred estimate is a thrust focal mechanism with its hypocenter at (N34.35° ± 0.4 km, W116.91° ± 0.2 km, 2.6 ± 0.3 km depth) on a plane dipping southward beneath the San Bernardino Mountains, with a moment magnitude (Mw) of 5.4. The strike, dip, and rake are N106°E ± 7°, 28° ± 4°, and 93° ± 4°, respectively on a fault 3.1 ± 0.5 km wide and 2.9 ± 0.4 km long. The precision of these estimates is competitive with seismological determinations.
Long‐term monitoring of carbon and oxygen isotope ratios of stratospheric CO2 over Japan
Authors: Gamo Toshitaka , Tsutsumi Makoto , Sakai Hitoshi , Nakazawa Takakiyo , Machida Toshinobu , Honda Hideyuki , Itoh Tomizo
Published: February 2004

We have been measuring stable isotopic ratios of carbon (δ13C) and oxygen (δ18O) of carbon dioxide in the stratosphere (18–35 km altitudes) over Japan since 1985, presenting here the first temporal δ13C and δ18O records between 1985 and 1991. The stratospheric δ13C is gradually decreasing due to anthropogenic effects with a rate of approximately −0.03‰ y−1, which is similar to the tropospheric value. The previously found 18O enrichment in stratospheric CO2 has been maintained almost steadily during the 6 years, with a monotonous δ18O increase with increasing altitude up to 35 km over Japan.
Mesospheric temperature inversions as seen by ISAMS in December 1991
Authors: Leblanc Thierry , Hauchecorne Alain , Chanin Marie‐Lise , Rodgers Clive , Taylor Fred , Livesey Nathaniel
Published: February 2004

A large number of mesospheric temperature inversion layers have been observed locally in recent decades, notably by the network of French lidars. It is shown in this paper that the Improved Stratospheric and Mesospheric Sounder on board the Upper Atmosphere Research Satellite is able to detect the presence of temperature inversions, and thus allows the study of their occurrence and characteristics on a global scale. During December 1991, inversions of large amplitude (greater than 20 K) are seen almost every day, especially in mid latitudes, with extent varying typically from 105 to 106 km². Several particularly large inversions were observed at the end of the month. Their correlation with assimilated stratospheric winds is consistent with the interpretation that gravity waves propagate unfiltered through the stratosphere in the regions of strong winds, and break in the mesosphere.

The combination of high resolution lidar measurements and global satellite coverage is expected to lead to a better understanding of this significant feature of the winter mesosphere at middle latitudes.
Rate constant for the reaction of OH radical with HFC‐365mfc (CF3CH2CF2CH3)
Authors: Mellouki Abdelwahid , Téton Sophie , Le Bras Georges
Published: February 2004

Rate constant for the reaction of OH with HFC‐365mfc (CF3CH2CF2CH3) has been measured at a total pressure of 100 Torr, using the laser photolysis ‐ laser induced fluorescence technique. The obtained kinetic data were used to derive the following Arrhenius expression over the temperature range 269–370 K : k = (1.68±0.21) × 10−12 exp[‐(1585±80)/T] cm³ molecule−1 s−1. At 298 K, the measured rate coefficient was : k = (8.69±0.74) × 10−15 cm³ molecule−1 s−1. This study is the first investigation to be reported on this reaction. Using our kinetic data, the tropospheric lifetime of CF3CH2CF2CH3 is estimated to be 7.8 years.
Hybrid simulations of the saturated Farley‐Buneman instability in the ionosphere
Authors: Oppenheim Meers , Otani Niels , Ronchi Corrado
Published: February 2004

Numerical simulations of the Farley‐Buneman instability in 2–1/2 dimensions using particle ions and fluid electrons show the growth, saturation and nonlinear behavior of two‐stream waves. This hybrid technique models the saturated state of the instability for a much longer period of time than the pure particle codes that preceded it. While focusing principally on modeling the topside E region equatorial electrojet, many of these results apply to the auroral two‐stream instability as well. The following features are seen in all our hybrid simulations: (1) wave growth at an angle offset from the electron drift direction where the angle depends on the strength of the driving electric field, (2) nonlinear coupling to waves traveling perpendicular to the propagation direction of the principal two‐stream waves, (3) a saturated wave phase velocity at or above the sound speed but well below the velocity predicted by linear theory and (4) phase velocities which remain almost constant as a simulated radar sweeps from a horizontal direction to nearly vertical. The nonlinear electron motion dominates the behavior of these waves. Further, these simulations indicate that ion kinetic effects are not essential for the saturation of the instability and that electron temperature effects have a minor impact on the final saturated state.
Permeability dependence of streaming potential in rocks for various fluid conductivities
Authors: Jouniaux Laurence , Pozzi Jean‐Pierre
Published: February 2004

Streaming potentials have been measured on sandstone and limestone samples in a large range of permeabilities. The electrokinetic coupling coefficient increases with permeability and we explain this effect by the related variation of surface conductivity. A model is proposed to study this effect for various fluid conductivities and it is shown that the dependence of the electrokinetic coupling coefficient on permeability is stronger for high fluid resistivity and is weaker for lower fluid resistivity. When fluid resistivity is below 1 Ω.m permeability and streaming potential are no more related.
Ice flow dynamics of the Greenland Ice Sheet from SAR interferometry
Authors: Rignot E. , Jezek K. C. , Sohn H. G.
Published: February 2004

Synthetic‐aperture radar (SAR) interferograms produced from ESA's ERS‐1 satellite, provide the first synoptic view of ice flow dynamics of the western sector of the Greenland Ice Sheet. Glacial motion is detected in the radar ranging direction at millimetric scales, across a complete sequence of snow accumulation and melting regimes, despite significant variations in their radar scattering properties. Ice flow evolves from a slow, regular motion at the higher elevations. At lower elevations, motion is strongly convoluted by meter‐scale undulations in surface topography, which have a unique interferometric signature that enables a novel approach for retrieving flow direction. Inferred flow directions, combined with surface displacements in the radar ranging direction, yield ice velocity estimates that are within 6% of in‐situ measurements gathered along a 40 km survey line. Application of repeat‐pass SAR interferometry to the entire Greenland Ice Sheet should enable precise mapping of its ice flow dynamics at an unprecedented level of spatial detail.
Isolated deep earthquakes and the fate of subduction in the mantle
Authors: Lundgren Paul , Giardini Domenico
Published: February 2004

The locations of earthquakes with depth in the mantle provide direct evidence of the trajectory and state of stress of subducting lithosphere. The occurrence over the last decade of isolated large deep earthquakes outside the main Wadati‐Benioff zones in the Kurile, Izu‐Bonin, and Chile deep seismic areas (in addition to the observed flat distributions of deep seismicity beneath the Banda Sea and Fiji Plateau areas and the large number of deep earthquakes located away from the main slab in the Tonga arc) supports recent tomographic and other seismological studies, leading to a reconsideration of slabs as simple planar structures sinking undeformed into the lower mantle. The focal geometries of these isolated earthquakes, which often exhibit near vertical compressional stresses, are distinct from adjacent events in the main Wadati‐Benioff zone. They are also different in orientation from events in the deflecting toe of the slab and from the stress orientation expected if the deflected slab acts as a stress guide. These isolated mantle earthquakes are interpreted to take place in subducted lithosphere that has deflected to a horizontal posture at the base of the upper mantle. Conversely, the deep seismicity in the adjacent Wadati‐Benioff zone is associated with the deflection of the subducting lithosphere.
Post‐Gondwana geomorphic evolution of southwestern Africa: Implications for the controls on landscape development from observations and numerical experiments
Authors: Gilchrist Alan R. , Kooi Henk , Beaumont Christopher
Published: February 2004

The relationship between morphology and surficial geology is used to quantify the denudation that has occurred across southwestern Africa since the fragmentation of Gondwana during the Early Mesozoic. Two main points emerge. Significant denudation, of the order of kilometers, is widespread except in the Kalahari region of the continental interior. The denudation is systematically distributed so that the continental exterior catchment, draining directly to the Cape basin, is denuded to a greater depth than the interior catchment inland of the Great Escarpment The analysis also implies that the majority of the denudation occurred before the beginning of the Cenozoic for both the exterior and interior catchments. Existing models of landscape development are reviewed, and implications of the denudation chronology are incorporated into a revised conceptual model. This revision implies that the primary effect of rifting on the subsequent landscape evolution is that it generates two distinct drainage regimes. A marginal upwarp, or rift flank uplift, separates rejuvenated rivers that drain into the subsiding rift from rivers in the continental interior that are deflected but not rejuvenated. The two catchments evolve independently unless they are integrated by breaching of the marginal upwarp. If this occurs, the exterior baselevel is communicated to the interior catchment that is denuded accordingly. Denudation rates generally decrease as the margin evolves, and this decrease is reinforced by the exposure of substrate that is resistant to denudation and/or a change to a more arid climate. The observations do not reveal a particular style of smaller‐scale landscape evolution, such as escarpment retreat, that is responsible for the differential denudation across the region. It is proposed that numerical model experiments, which reflect the observational insights at the large scale, may identify the smaller‐scale controls on escarpment development if the model and natural systems are analogous. Four numerical experiments are presented in which the roles of antecedent topography, resistant substrate, climate change, and lowering the baselevel of the interior catchment are investigated for an initially high elevation margin bordered by an escarpment. The model results suggest several styles of landscape evolution that are compatible with the observations. Escarpments may retreat in a regular manner, but they also degrade and are destroyed, only to reform at the drainage divide between exterior and interior catchments.