bluuebunny/crossref_metadata_2025 huggingface dataset:
Along‐axis variations in oceanic crustal density and their contribution to gravity anomalies at slow‐spreading ridges
Authors: Minshull T. A.
Published: February 2004

Gravity data from mid‐ocean ridges are routinely used to infer crustal thickness variations. Commonly, the contribution to the gravity anomaly from mantle density variations are taken into account, but variations in crustal density are rarely considered. Wide‐angle seismic experiments conducted in the same locations as detailed gravity surveys on the mid‐Atlantic Ridge show that the crustal thickness inferred from gravity data can deviate substantially from that derived from seismic data, particularly in the vicinity of ridge offsets. This discrepancy may be partly attributed to unmodeled crustal density variations: at slow‐spreading ridges, crust formed near ridge offsets has consistently lower velocity than crust formed near segment centers, and a corresponding density reduction of up to 20% may be inferred.
On the association of terrestrial gamma‐ray bursts with lightning and implications for sprites
Authors: Inan Umran S. , Reising Steven C. , Fishman Gerald J. , Horack John M.
Published: February 2004

Measurements of ELF/VLF radio atmospherics (sferics) at Palmer Station, Antarctica, provide evidence of active thunderstorms near the inferred source regions of two different gamma‐ray bursts of terrestrial origin [Fishman et al., 1994]. In one case, a relatively intense sferic occurring within ±1.5 ms of the time of the gamma‐ray burst provides the first indication of a direct association of this burst with a lightning discharge. This sferic and many others launched by positive cloud‐to‐ground (CG) discharges and observed at Palmer during the periods studied exhibit ‘slow tail’ waveforms, indicative of continuing currents in the causative lightning discharges. The slow tails of these sferics are similar to those of sferics originating in positive CG discharges that are associated with sprites.
Evidence of large scale ozone depletion within the Arctic Polar Vortex 94/95 based on airborne LIDAR measurements
Authors: Wirth M. , Renger W.
Published: February 2004

Measurements with an airborne lidar performed during the Arctic winter 1994/95 show, that the ozone mixing ratio declined by about 50% throughout the polar vortex in the period from the beginning of February to mid of March in a sharp defined altitude band from 420 K to 520 K potential temperature. The simultaneous detection of the stratospheric aerosol density provides evidence that this depletion was not caused by dynamical processes but by chemical reactions.
Stratospheric meteorological conditions for the 3–12 Nov 1994 ATMOS/ATLAS‐3 measurements
Authors: Manney G. L. , Swinbank R. , O'Neil A.
Published: February 2004

During the ATLAS‐3 mission (3–12 Nov 1994), United Kingdom Meteorological Office fields show that the SH vortex was still strong below about 700 K (∼16 hPa), with coherent vortex fragments apparent up to about 1300 K (∼3 hPa). The SH vortex was shifted off the pole toward 270°E throughout ATLAS‐3, although its shape varied from day to day. SH temperatures were increasing during ATLAS‐3; temperatures below 188 K were last seen 35–45 days before the mission, but were below 195 K as late as 2 Nov 1994. The NH polar vortex had developed at levels above about 550 K (∼35 hPa). Simulated high‐resolution potential vorticity (PV) fields clearly show low latitude air being drawn up around the polar vortices in both hemispheres. These fields indicate that meteorological analyses underestimate the amount of atmospheric variability, including the strength of local PV gradients, and small‐scale structure. Structure such as that in the simulated fields can result in apparent discrepancies between tracer measurements and PV fields.
Transport in sandstone: A study based on three dimensional microtomography
Authors: Auzerais F. M. , Dunsmuir J. , Ferréol B. B , Martys N. , Olson J. , Ramakrishnan T. S. , Rothman D. H. , Schwartz L. M.
Published: February 2004

High resolution imaging of the microstructure of Fontainebleau sandstone allows a direct comparison between theoretical calculations and laboratory measurements. While porosity, pore‐volume‐to‐surface ratio, permeability, and end point relative permeability are well predicted by our calculations, we find that electrical resistivity and wetting phase residual saturation are both overestimated.
Solar UVB measurements with the double‐ and single‐monochromator Brewer ozone spectrophotometers
Authors: Bais A. F. , Zerefos C. S. , McElroy C. T.
Published: February 2004

In this work, the new double‐monochromator version of the Brewer Ozone Spectrophotometer, especially designed for spectral UV measurements, is briefly described and its measurements are compared with those obtained by a conventional, single‐monochromator Brewer instrument. The comparison shows that the performance of the new instrument is much superior in the low UVB wavelengths (λ<305 nm), because of the much higher stray‐light rejection capability of the instrument. The conventional Brewer spectrophotometer is capable of recording accurately solar UVB spectra at wavelengths greater than about 300 nm. The error in UVB dose calculations made using data from the conventional Brewer is estimated to be of the order of +1%, while the absolute irradiances at wavelengths below 300 nm may be overestimated by more than 10%, depending on the measured wavelength and the solar zenith angle.
A physical adsorption model of the dependence of ClONO2 heterogeneous reactions on relative humidity
Authors: Henson Bryan F. , Wilson Kevin R. , Robinson Jeanne M.
Published: February 2004

We present a model of heterogeneous reactivity based on physical adsorption that describes the observed relative humidity dependence of the ClONO2 reaction probability with H2O and HCl on sulfuric acid tetrahydrate ice surfaces (SAT) and with H2O on nitric acid trihydrate (NAT). The laboratory data are modeled using only two parameters for a given system, the measured reaction probability on a neat H2O ice surface, and a constant from the BET theory which describes the fraction of an acid hydrate surface covered by H2O as a function of relative humidity. The model indicates that ClONO2 reactivity with both HCl and H2O on SAT and with H2 O on NAT is controlled by the surface coverage of H2O. In contrast, the reaction of ClONO2 +HCl on NAT is better described by an alternative model based on reactivity in solutions formed within a porous ice by capillary liquid absorption.
Reply to “The VAN earthquake predictions,” by D. A. Rhoades and F. F. Evison
Authors: Varotsos P. , Lazaridou M.
Published: February 2004

Rhoades and Evison [1996] indicated a technical flaw in the procedure of Mulargia and Gasperini [1992] and also made many useful remarks and fundamental suggestions on the correct way for performing a statistical evaluation of an earthquake prediction method. We think that these suggestions should be carefully followed by statisticians in the future.

However, we do not agree with Rhoades and Evison's [1996] opinion that objective tests of the performance of the VAN‐method, using independent data, cannot begin until the method and the null hypothesis have been fully formulated. In our opinion the main question in the present debate is whether our predictions can be ascribed to chance. Such a test has already been carried out in this issue by Aceves et al. [1996], although they make it clear that they have tested the significance of our predictions and not the overall success of our method.
The use of X‐ray diffraction in support of calorimetry for the characterization of some nitric acid hydrates possibly involved in the polar stratospheric clouds formation
Authors: Ji K. , Petit J. C. , Négrier P. , Haget Y.
Published: February 2004

The use of a Guinier‐Simon device has enabled us, firstly, to obtain the XRD (X‐Ray Diffraction) lines of three stoichiometric hydrates namely NAT, NAD and NAM (Nitric Acid Trihydrate, Nitric Acid Dihydrate, Nitric Acid Monohydrate) secondly, to detect the presence of these hydrates in mixtures and also to determine their formation temperature. The latter information is essential to understand the mechanism of formation of PSCs (Polar Stratospheric Clouds).
Domain structures in single crystal magnetite below the Verwey Transition as observed with a low‐temperature magnetic force microscope
Authors: Moloni Katerina , Moskowitz Bruce M. , Dahlberg E. Dan
Published: February 2004

The magnetic domain structures on the {110} plane of magnetite (Fe3O4) below the Verwey transition (Tv=120K) were studied using a Low‐Temperature Magnetic Force Microscope (LTMFM). At 298K, domain structures consisted of arrays of 180°, 109° and 71° walls, typical for magnetite with cubic anisotropy. At 77K (below Tv), the cubic style patterns disappeared and transformed into uniaxial patterns consistent with the uniaxial magnetocrystalline symmetry of the low‐temperature monoclinic phase of magnetite. We also observed two distinct styles of domain patterns below Tv: (1) wide domains separated by straight 180° walls along the in‐plane [100] easy axis; and (2) intricate wavy walls with reverse spike domains characteristic of out‐of‐plane easy axes. This intimate mixture of domain styles within adjacent areas of the crystal reflects variations in the direction of the magnetic easy axes in different regions produced by c‐axis twinning of the crystal below Tv The thermal dependence of planar and wavy‐wall patterns show little change from 77K until 110K, where patterns disappear. Upon cooling back to 77K, domain structures are different from the initial 77K states, indicating that renucleation of different domain states occurs by cycling near Tv.
Fluctuations of the repetition period of Pc1 Pearl pulsations
Authors: Guglielmi A. , Feygin F. , Mursula K. , Kangas J. , Pikkarainen T. , Kalisher A.
Published: February 2004

In this paper we investigate fluctuations of the repetition period of geomagnetic Pc1 pearl pulsations. Starting from calculated repetition period we present a general formula for the deviation of the repetition period as a function of wave frequency and stochastic parameters of the medium along the ray trace. We then apply this formula for a dipole magnetic field with a simple plasma distribution, and show that a linear correlation between repetition period and its deviation is predicted. This correlation and the frequency dependence of fluctuations are then compared with experimental values measured from selected Pc1 pearl events observed in Finland.
Zeeman splitting of the 61 Gigahertz oxygen (O2) line in the mesosphere
Authors: Hartmann G. K. , Degenhardt W. , Richards M. L. , Liebe H. J. , Hufford G. A. , Cotton M. G. , Bevilacqua R. M. , Olivero J. J. , Kämpfer N. , Langen J.
Published: February 2004

Zeeman splitting of O2 molecular states in the Earth's upper atmosphere leads to polarized emission spectra. A 61 GHz radiometer operated as part of the Millimeter‐wave Atmospheric Sounder (MAS), a core payload instrument of the NASA Space Shuttle ATLAS missions, observed such emissions. This instrument's high resolution spectrometer (200 kHz) allows us to verify for the first time Zeeman effect model calculations for the upper atmosphere in some detail. The results suggest some interesting new aspects for the research of the upper atmosphere.
Greenhouse warming and changes in the seasonal cycle of temperature: Model versus observations
Authors: Mann Michael E. , Park Jeffrey
Published: February 2004

Thomson [1995] argues that an enhanced green‐house effect may be altering the seasonal cycle in temperature. We compare trends in the amplitude and phase of the seasonal cycle in observational temperature data in the northern hemisphere with the response of two general circulation models to increased CO2 concentrations. Sizeable amplitude decreases are observed in both models and observations. Significant phase delays (ie, later seasonal transitions) are found in the simulations, opposite to the phase advances isolated in the observations. The retreat of winter sea ice in high‐latitude regions appears to explain the models' response to CO2 increase. Much of the variability in the observational data is not predicted by the models.
A novel method to measure the solar wind speed
Authors: Issautier Karine , Meyer‐Vernet Nicole , Moncuquet Michel , Hoang Sang
Published: February 2004

We propose a novel method to measure in situ the bulk speed of a space plasma. It is based on the analysis of the electrostatic field spectrum produced by the Doppler‐shifted thermal fluctuations of the plasma ions which can be measured with a sensitive receiver at the terminals of a passive electric antenna. We present a preliminary application in the solar wind using the data acquired in the ecliptic plane by the Unified Radio and Plasma experiment (URAP) on the Ulysses spacecraft. This should allow us to extend to the bulk speed the method of thermal noise spectroscopy which already gives an accurate in situ diagnosis of the electron density and bulk temperature. This method can be complementary to classical electrostatic analyzers for both interplanetary and magnetospheric studies.
Simultaneous PMSE observations with ALOMAR‐SOUSY and EISCAT‐VHF radar during the ECHO‐94 Campaign
Authors: Bremer Jürgen , Hoffmann Peter , Singer Werner , Meek Christopher E. , Rüster Rüdiger
Published: February 2004

During the ECHO‐94 campaign PMSE have been observed with the ALOMAR‐SOUSY radar on 53.5 MHz at Andenes (69.28°N; 16.02°E) and with the EISCAT‐VHF radar on 224 MHz at Tromsø (69.58°N; 19.21°E). Comparisons of simultaneous measurements demonstrate generally good agreement between PMSE structures derived by both equipments. A detailed comparison shows differences caused by the mesospheric mean wind field as well as differences of the local dynamic or thermodynamic state at both measuring places.
Thermal expansion of forsterite up to the melting point
Authors: Bouhifd M. A. , Andrault D. , Fiquet G. , Richet P.
Published: February 2004

As determined from powder X‐ray diffraction experiments with synchrotron radiation, the thermal expansion coefficient of forsterite increases smoothly from 2.8 to 4.5 K−1 from 400 K to 2160 K. No anomalous increases of the cell parameters are observed near the melting point. The consistency between the observed and calculated value of the initial slope of the melting curve of forsterite suggests that defects do not make a large contribution to thermal expansion near the melting point. Along with previous results, the new data confirm the influence of anharmonicity on the high‐temperature heat capacity of forsterite and indicate that both the Grüneisen parameter and αKT (α = thermal expansion coefficient, KT = bulk modulus) have nearly constant values at high temperatures.
First Composition Measurements of Energetic Neutral Atoms
Authors: Lui A. T. Y. , Williams D. J. , Roelof E. C. , McEntire R. W. , Mitchell D. G.
Published: February 2004

Energetic neutral atoms (ENAs) were detected by the Energetic Particles and Ion Composition (EPIC) instrument on the Geotail spacecraft during a magnetic storm on October 29–30, 1994. The energetic particles could be identified as neutrals because the direction of the particle flux steadily tracked the direction of the Earth and was uncorrelated with the changing orientation of the ambient magnetic field as the spacecraft viewed the dayside magnetosphere for ∼16 hours. These observations provide the first composition measurements of ENAs, yielding the storm‐time evolution of ENA fluxes of hydrogen, helium, and oxygen separately as well as their energy spectra. ENA fluxes and the rate of recovery of Dst are both roughly steady, consistent with charge exchange being a significant energy loss process for the storm‐time ring current. For total energies above 200 keV, the intensity of ENA oxygen is the highest, followed by hydrogen, and then by helium. These observations enable us to deduce the line‐of‐sight (LOS) integrals of the products nHjion and nHfion, where nH=hydrogen geocorona density, jion=differential ion flux, and fion=phase space density (PSD), for ion species H+, He+ and O+ at energies between ∼60 and ∼600 keV. A ∼50–60 keV Maxwellian fits the O+ LOS PSD fairly well but fits the He+ and the H+ only poorly.
Latitudinal distribution of upper stratospheric ClO as derived from Space Borne Microwave Spectroscopy
Authors: Aellig C. P. , Kämpfer N. , Rudin C. , Bevilacqua R. M. , Degenhardt W. , Hartogh P. , Jarchow C. , Künzi K. , Olivero J. J. , Croskey C. , Waters J. W. , Michelsen H. A.
Published: February 2004

Latitudinal distributions of upper stratospheric ClO measured by MAS during the three ATLAS missions are presented for northern hemisphere (NH) spring equinox in 1992, southern hemisphere (SH) early fall in 1993, and NH fall in 1994. The MAS ClO results are shown along with correlative MLS observations. The results of both instruments consistently show the same latitudinal features. The ClO maximum in the NH spring occurs at mid latitudes, whereas the latitudinal ClO maximum in both the NH and SH fall occurs at high latitudes. The volume mixing ratio maxima were significantly higher in the fall (0.7–0.8 ppbv) than in spring (0.5–0.6 ppbv). Qualitatively, these results are consistent with calculations of several 2‐D models.
Evidence for upper mantle anisotropy beneath southern Germany from Love and Rayleigh wave dispersion
Authors: Friederich W. , Huang Z.‐X.
Published: February 2004

We advance evidence for the existence of seismic anisotropy in the upper mantle beneath Southern Germany from the dispersion of Love and Rayleigh waves. The evidence is based upon a substantial Love‐Rayleigh discrepancy observed between periods of 40 s and 120 s. An isotropic mantle model clearly fails to explain the observed dispersion curves. Systematic inversion experiments with transversely isotropic models show that anisotropy at depths between 70 km and 200 km is sufficient to explain the observed dispersion curves. Our data require neither anisotropy at greater depths nor anisotropy in the crust though we cannot exclude its presence there. A search for azimuthal anisotropy of Rayleigh wave propagation indicates a weak, but possibly insignifant azimuthal anisotropy of about 1% for periods less than 40 s with fast directions between 20 and 50 degrees east of north. At larger periods azimuthal anisotropy is less than 1% and the fast directions scatter considerably as period varies.
Possible links between ozone and temperature profiles
Authors: Fortuin J. Paul F. , Kelder Hennie
Published: February 2004

With a multiple linear regression analysis ozone and temperature trends are determined for a cold and warm half‐year cycle, based on concurrent ozone and temperature data recorded at various ozonesonde stations over the past decades. It is attempted to quantify the derived temperature trends, either in terms of radiative cooling caused by the trends in ozone and other greenhouse gases, or in terms of changes in the vertical advection regime. In the lower stratosphere, it is found that an increase in the ascent‐rate of air over the observed period often explains the observed cooling and ozone depletion, whereas higher up in the stratosphere the temperature trends are often in agreement with radiative transfer calculations. With the ozone and temperature residuals, correlation profiles are constructed, as well as sensitivity curves which give the local air temperature response to local changes in ozone. These sensitivity curves are compared with radiative transfer calculations for the stratosphere.
Mantle transition zone beneath Eurasia
Authors: Vinnik Lev , Kosarev Grigoriy , Petersen Natalia
Published: February 2004

Mantle Pds (Fig. 1) converted phases are detected in the records of 11 seismograph stations in easternmost Russia and China. These data reveal neither a strong depression on the 660‐km discontinuity nor a layer of partial melting atop the 410‐km discontinuity that were found previously beneath this region in studies using long‐period underside SH reflections and multiple ScS reverberations. Apparently, a significant deepening of the 660‐km discontinuity occurs only if the subducted plate penetrates the discontinuity, which is not the case in the study region. Most estimates of thickness of the mantle transition zone (MTZ) in Eurasia based on the Pds data are a few kilometres larger than the standard value (250 km), and suggest that the average thickness of the MTZ beneath Eurasia is about 10 kilometres more than beneath the surrounding oceans.
The ocean tide gravimetric loading reconsidered
Authors: Llubes M. , Mazzega P.
Published: February 2004

In 1994–95, a set of new global ocean tide models computed by different teams was made available to the scientific community. These models were derived from the analysis of satellite altimetric data, numerical hydrodynamics or a combination of both. The task is now to evaluate their relative accuracy, in particular with independent data. The data bank prepared by the International Center for Earth Tides (ICET, Melchior 1994) gives us a unique opportunity to compare the tidal models by testing their capability to predict the induced gravimetric loading effects. The more recent versions (released in 1995) of the models by Ma et al. (1994) and by Schrama and Ray (1994) both completed at high latitudes by the Le Provost et al. (1994) FES94.1 model have the best scores for the semidiurnal M2 wave, with a standard deviation (SD) of the gravimetric data residues less than 0.540 µgal. Schwiderski (1980) and Egbert et al. (1994) models give the smallest residual SD, about 0.370 µgal, for the diurnal O1 component. However, the ordering of the models may change when we focus on some particular regions of the globe.
Reaction probability of peroxyacetyl radical on aqueous surfaces
Authors: Villalta Peter W. , Lovejoy Edward R. , Hanson David R.
Published: February 2004

The uptake coefficient for the loss of peroxyacetyl radical, CH3C(O)O2 (PA), on H2O is measured to be 0.0043 (+0.0024/−0.0015) at 274±3 K. Uptake measurements onto aqueous solutions of sodium ascorbate yield limits for the PA Henry's law coefficient in H2O (≤ 0.1 M atm−1) and the CH3C(O)O2 hydrolysis rate coefficient (≥ 7 × 105 M−1 s−1) at ∼275 K. These measurements support the hypothesis that PA heterogeneous reaction can mediate the loss of PAN in fog (Roberts et al., submitted manuscript, J. Geophys. Res., 1995). The most likely products of PA hydrolysis are HO2 and acetic acid. PA hydrolysis may be a significant source of odd hydrogen at night as well as an important source of acetic acid in the atmosphere.
Seasonal variations of water vapor in the lower stratosphere inferred from ATMOS/ATLAS‐3 measurements of H2O and CH4
Authors: Abbas M. M. , Michelsen H. A. , Gunson M. R. , Abrams M. C. , Newchurch M. J. , Salawitch R. J. , Chang A. Y. , Goldman A. , Irion F. W. , Manney G. L. , Moyer E. J. , Nagaraju R. , Rinsland C. P. , Stiller G. P. , Zander R.
Published: February 2004

Stratospheric measurements of H2O and CH4 by the Atmospheric Trace Molecule Spectroscopy (ATMOS) Fourier transform spectrometer on the ATLAS‐3 shuttle flight in November 1994 have been examined to investigate the altitude and geographic variability of H2O and the quantity H = (H2O + 2CH4) in the tropics and at mid‐latitudes (8 to 49°N) in the northern hemisphere. The measurements indicate an average value of 7.24±0.44 ppmv for H between altitudes of about 18 to 35 km, corresponding to an annual average water vapor mixing ratio of 3.85±0.29 ppmv entering the stratosphere. The H2O vertical distribution in the tropics exhibits a wave‐like structure in the 16‐ to 25‐km altitude range, suggestive of seasonal variations in the water vapor transported from the troposphere to the stratosphere. The hygropause appears to be nearly coincident with the tropopause at the time of observations. This is consistent with the phase of the seasonal cycle of H2O in the lower stratosphere, since the ATMOS observations were made in November when the H2O content of air injected into the stratosphere from the troposphere is decreasing from its seasonal peak in July–August.
Evaluation of simulations of terrestrial precipitation in UK Met. Office/Hadley Centre Climate Change Experiments
Authors: Airey M. J. , Hulme M. , Johns T. C.
Published: February 2004

This paper evaluates the simulation of precipitation in four successive versions of the UK Met. Office/Hadley Centre global climate model (GCM) that have been used to perform climate change experiments. The precipitation fields over land from the control integrations of these four experiments are compared with observed precipitation on a global scale and for selected regions. Globally, improvements in simulating mean monthly precipitation patterns occur with successive simulations. The poorest correlations and highest root mean square errors occur in the boreal summer months. A major improvement in the simulation of the South Asian summer monsoon by the most recent versions of the model is noted. The pattern of temporal variability in the later versions over global land areas is generally well simulated. The observed pattern of temporal correlation between the Southern Oscillation Index and precipitation anomalies has improved in the latest model version.
Shock‐induced phase transition of MnO around 90GPa
Authors: Noguchi Yuichi , Kusaba Keiji , Fukuoka Kiyoto , Syono Yasuhiko
Published: February 2004

Shock compression experiments on single crystal MnO grown by the Verneuil method have been carried out for the pressure range of 41–114GPa using both propellant and two‐stage light‐gas guns. The shock states, recorded with the inclined mirror method, were analyzed by the free‐surface approximation and impedance‐match solution. The observed shock compression curve of MnO with the rock salt structure(B1) is found to be slightly more compressible than that measured statically to 60GPa using a diamond‐anvil cell. We observed a phase transition around 90GPa with a volume decrease of approximately 8%. The present phase transition pressure falls on a trend of B1‐B2(CsCl‐type structure) transformation among alkaline earth metal monoxides, rather than transformation to the B8(NiAs‐type structure) that wüstite (FeO) demonstrates.
Near‐simultaneous bow shock crossings by WIND and IMP 8 on December 1, 1994
Authors: Slavin J. A. , Szabo A. , Peredo M. , Lepping R. P. , Fitzenreiter R. J. , Ogilvie K. W. , Owen C. J. , Steinberg J. T.
Published: February 2004

Near‐simultaneous dawn‐side bow shock crossings by WIND and IMP 8 on December 1, 1994 are analyzed to determine shock location and shape and to examine the changes in shock structure and the foreshock MHD wave properties with increasing downstream distance. The WIND and IMP 8 crossings took place at sun‐Earth‐spacecraft angles of 64.7° and 115.3°, respectively. The solar wind speed and interplanetary magnetic field magnitude were near their long‐term average values. However, the orientation of the IMF was unusual in that it rotated from an angle of ∼50–60° to the sun‐Earth line at the beginning of the interval of shock crossings to less than 20° just after the final crossings. The ratio of the downstream to upstream components of the magnetic field tangential to the shock decreases from 4.1 at WIND to 3.1 at IMP 8 in general agreement with theory. In addition, the overshoot in the shock magnetic ramp observed at WIND is greatly diminished by the downstream distance of IMP 8. In the foreshock, MHD waves with periods of 10–20 s and amplitudes of 3–6 nT were observed at both spacecraft. However, at WIND they have a strong compressional component which is much weaker farther downstream at IMP 8. Unexpectedly, the radial distance of the shock at both spacecraft is only ∼80–85% of that predicted by recent models. Motivated by this event, we have statistically analyzed a larger data set of bow shock crossings which took place under quasi‐field‐aligned flow conditions. On this basis it is suggested that magnetosheath thickness may decrease by ∼10% as the IMF becomes increasingly flow aligned.
Interplanetary observations of solar g‐mode oscillations?
Authors: Riley Pete , Sonett C. P.
Published: February 2004

By applying spectral techniques to magnetic field and plasma data from Helios 1 and 2, Pioneer 1 and 2, and Voyager 1 and 2 missions, an attempt has been made to find evidence for solar g‐mode oscillations in the solar wind. It is demonstrated that analysis employing simple spectral techniques is unlikely to detect such oscillations. Using the multi‐taper method, however, many ‘significant’ lines are identified. Unfortunately, we cannot conclude that such lines are necessarily the signature of solar g‐mode oscillations because (i) these lines do not appear to be stationary; (ii) there is no evidence for the predicted signatures of asymptotic g‐modes; and (iii) the statistics of these lines do not deviate significantly from pseudo‐randomly generated data. We suggest that the difference between our conclusions and previous studies lies in the criteria used to identify these lines.
Recent decreases in Arctic summer ice cover and linkages to atmospheric circulation anomalies
Authors: Maslanik James A. , Serreze Mark C. , Barry Roger G.
Published: February 2004

Sea ice data from November 1978 through September 1995 for the Arctic Ocean and peripheral seas indicate that summer ice coverage has been below normal in recent years, with extreme minima in 1990, 1993, and 1995. The net trend in summer ice cover over the 17‐year period is −0.6% per year, with the extent of the perennial ice pack reduced by 9% in 1990–1995 compared with 1979–1989. The reductions are greatest in the Siberian sector of the Arctic Ocean. Linkages are proposed between these ice anomalies and a sharp increase since 1989 in the frequency of low pressure systems over the central Arctic.
Heterogeneous interactions of BrO and ClO: Evidence for BrO surface recombination and reaction with HSO3−/SO32−
Authors: Abbatt Jonathan P. D.
Published: February 2004

The uptake coefficients (γ) for loss of BrO and ClO radicals on surfaces characteristic of participate material in the atmosphere have been measured using a coated‐wall flow tube coupled to a resonance fluorescence detector. Neither radical is lost efficiently at 213 K on sulfuric acid (60 to 70 wt%), pyrex or ice surfaces, with BrO uptake coefficients ranging from 5 × 10−4 to 1 × 10−3 on these surfaces and with ClO uptake coefficients smaller than 1×10−4. Based on the observation by mass spectrometry of Br2 formation coincident with BrO loss on ice surfaces, it is believed that radical self‐reaction is occurring on the surface. Finally, for BrO it was observed that the uptake coefficient on 23 wt% aqueous solutions of NaCl at 253 K was small (< 3 × 10−3) but that it could be significantly enhanced when sulfur(IV) species were added to the solution, either by exposure to gas phase SO2 or by the addition of Na2SO3. Aside from the BrO/S(IV) reactions which may promote condensed‐phase free‐radical chemistry, these findings imply that heterogeneous interactions of BrO and ClO in the atmosphere will be insignificant with respect to gas‐phase processes.
A Large 13CO deficit in the lower Antarctic stratosphere due to “ozone hole” chemistry: Part II, Modeling
Authors: Müller Rolf , Brenninkmeijer Carl A. M. , Crutzen Paul J.
Published: February 2004

Recently, isotopically extremely light CO (δ13C = −32 to −43‰) was found in whole air samples from the high southern‐latitude lower stratosphere (Part I). To investigate the cause of these unprecedented observations, we simulate in a photochemical model the typical history of air masses at polar latitudes in the lowermost stratosphere over austral winter and spring. The model results show that the observations may be explained by the very efficient isotope fractionation in the reaction R1: CH4 + Cl → HCl + CH3. Extremely high levels of Cl atom concentrations prevail in the polar lower stratosphere in austral spring for a period of about 10 days after most ozone is lost. Therefore, R1 becomes very efficient, leading to a very high rate of buildup of HCl and an unusually high isotopic CO fractionation.
ATMOS/ATLAS‐3 measurements of stratospheric chlorine and reactive nitrogen partitioning inside and outside the November 1994 Antarctic Vortex
Authors: Rinsland C. P. , Gunson M. R. , Salawitch R. J. , Michelsen H. A. , Zander R. , Newchurch M. J. , Abbas M. M. , Abrams M. C. , Manney G. L. , Chang A. Y. , Irion F. W. , Goldman A. , Mahieu E.
Published: February 2004

Partitioning between HCl and ClONO2 and among the main components of the reactive nitrogen family (NO, NO2, HNO3, ClONO2, N2O5, and HO2NO2) has been studied inside and outside the Antarctic stratospheric vortex based on ATMOS profiles measured at sunrise during the 3–12 November 1994 ATLAS‐3 Shuttle mission. Elevated mixing ratios of HCl in the lower stratosphere with a peak of ∼2.9 ppbv (10−9 parts per volume) were measured inside the vortex near 500 K potential temperature (∼19 km). Maximum ClONO2 mixing ratios of ∼1.2, ∼1.4, and ∼0.9 ppbv near 700 K (∼25 km) were measured inside, at the edge, and outside the vortex, respectively. Model calculations reproduce the higher levels of HCl and NOx (NO + NO2) inside the lower stratospheric vortex both driven by photochemical processes initiated by low 03. The high HCl at low O3 results from chemical production of HCl via the reaction of enhanced Cl with CH4, Limited production of ClONO2, and the descent of inorganic chlorine from higher altitudes.
Cloud properties derived from surface MFRSR measurements and comparison with GOES results at the ARM SGP Site
Authors: Min Qilong , Harrison Lee C.
Published: February 2004

We describe a family of inversion methods to infer the optical depth, τ, of warm clouds from surface measurements of spectral irradiance. Our most complex retrieval also uses the total liquid water path measured by a microwave radiometer to obtain the effective radius, re, of the cloud droplets. We apply these retrievals to data from the Atmospheric Radiation Measurement (ARM) Program, and compare our results to those produced by the GOES satellite for episodes where total overcast was observed. Our surface‐based estimates of τ agree with those from GOES when the optical depths are <10, but are consistently larger by as much as a factor of 2 when optical depths are greater. We show that the uncertainties associated with the surface‐based retrievals are less than those done from a satellite, and argue from the time series of the observations and the statistics of the measurements that the disagreement is not merely a consequence of the larger spatial average sampled by the satellite.
Validation of ozone profile retrievals from infrared ground‐based solar spectra
Authors: Pougatchev N. S. , Connor B. J. , Jones N. B. , Rinsland C. P.
Published: February 2004

A direct validation of ozone profile retrievals from IR ground‐based high resolution solar spectra has been performed. The spectra were recorded at 0.0035 to 0.01 cm−1 resolution on 11 days between February and October 1994 at the Network for the Detection of Stratospheric Change station in Lauder, New Zealand (45.04°S, 169.68°E, 0.37 km altitude) and analyzed for the O3 profile with a line‐by‐line forward model and semiempirical application of the optimal estimation inversion technique of Rodgers. The line parameters on the 1992 HITRAN compilation were assumed in the analysis. Retrieved ozone columns in three atmospheric layers (0.37–12 km, 12–20 km, and 20–100 km) have been compared with correlative ozonesondes, microwave and Dobson spectrometer data from the same site. IR total and O3 columns above 20 km agree with Dobson and microwave measurements to better than 2%. For the layers 0.37–12 km and 12–20 km the differences between IR and integrated ozonesondes are −7±5% and 2±4%, respectively. Special exercises have been performed to show the applicability of the retrieval method to spectra with a resolution ∼0.02 cm−1 and better.
Detection of P‐wave reflector in D″ beneath the south‐western Pacific using double‐array stacking
Authors: Yamada A. , Nakanishi I.
Published: February 2004

The double‐array (event‐ and receiver‐array) stacking is applied to the P‐wave data from 6 Fiji Is. events recorded by a local network of short‐period seismographs in Japan to investigate Vp structure in the lowermost mantle. A signal which may be interpreted as the reflection from a discontinuity at 170 km above the CMB (core‐mantle boundary) is observed between P and PcP in the stacked record. As compared with the receiver‐array stacking with a small number of stations applied to a single event, the double‐array stacking is effective to detect the weak signal of PdP.
Dissolved and particulate trace metals in hydrothermal plumes at the Mid‐Atlantic Ridge
Authors: James R. H. , Elderfield H.
Published: February 2004

Seawater samples from the non‐buoyant plume have been collected at the TAG (26°N) and Snakepit (23°N) hydrothermal sites on the Mid‐Atlantic Ridge (MAR), and analysed for dissolved (<0.4 µm) and particulate (>0.4 µm) trace metals. Up to 50% of vent fluid Fe is present in the <0.4 µm fraction in the non‐buoyant plume. Increases in particulate concentrations of Cd are accompanied by a reduction in dissolved Cd to levels below ambient seawater. We show that dissolved Cd is scavenged from seawater in the buoyant section of the plume while Cd re‐dissolves from the particles in the non‐buoyant plume. Up to 43% of hydrothermally injected Cu is found in the <0.4 µm fraction in the non‐buoyant plume.
Long‐term temperature trends in the middle and upper atmosphere
Authors: Golitsyn G. S. , Semenov A. I. , Shefov N. N. , Fishkova L. M. , Lysenko E. V. , Perov S. P.
Published: February 2004

We analyse data from weekly rocket temperature soundings up to 75 km carried out since mid‐1960s at polar (Heiss Island, 80.6°N and Molodezhnaya, 67.7°S), temperate (Volgograd, 48.7°N and Balkhash, 46.8°N) and tropical (Thumba, 8.5°N) latitudes. All records show significant cooling which is of the order of a few degrees K at 30–40 km, 10 K at 50 km and 20 K at 60–70 km. In the mesosphere the temperature trends are estimated from the hydroxyl rotational temperature records which start in 1957 at Zvenigorod (55.7°N) and Abastumani (41.8°N). These are related to the mesopause at 87 km and also show a cooling of about 30 K during the time. The cooling is qualitatively consistent with increasing concentration of greenhouse gases but may also reflect the changing chemistry of stratosphere and mesosphere, which is clearly seen in increasing emission intensities of hydroxyl during the last decades. Therefore the stratosphere and mesosphere may be regions with the strongest signals of global change.
Axial temperature gradients in dielectric samples in the laser‐heated diamond cell
Authors: Manga Michael , Jeanloz Raymond
Published: February 2004

Temperature gradients inside the laser‐heated diamond cell are not measured in the axial direction, along the optic axis, yet can bias estimates of the peak temperatures achieved in optically thin (dielectric) samples such as Mg‐silicate perovskite. Thermal diffusion calculations show that the observed thermal‐radiation spectrum is not significantly affected by axial temperature gradients. The apparent (measured) temperature underestimates the actual peak sample temperature by 350–850 K for 4000 < T < 6000 K.
Seafloor magnetotelluric sounding above axial seamount
Authors: Heinson Graham , Constable Steven , White Antony
Published: February 2004

Axial Seamount is a large, active, ridge axis volcano located on the central segment of the Juan de Fuca Ridge in the northeast Pacific Ocean. Magnetotelluric (MT) data have been collected at three sites, approximately 4 km apart around the eastern rim of the volcano, during a 65‐day deployment. MT responses, in the bandwidth of 10²–105 s, are almost isotropic, with a weakly‐defined principal direction of strike parallel to the main topographic trends of Axial Seamount, and are relatively flat over the whole bandwidth. Apparent resistivities are of the order of 7–20 Ωm, and phases are as low as 30° at the short periods. Diagonal terms of the MT tensor are an order of magnitude smaller than the off‐diagonal terms, suggesting that three‐dimensional effects on the data are minimal. Two‐dimensional inversions suggest that seafloor bathymetry and the distant coastlines have a surprisingly small effect on the MT response, and one‐dimensional inversions fit the MT data to within the errors with no serial correlation in the residuals. A low crustal resistivity is the most robust part of the model, probably due to seawater in fractures and possibly due to a magma chamber. An electrical asthenosphere, although less well constrained, exists over a depth range 30–60 km, and the resistivity of this region is compatible with about 8% fraction of melt.
Changes in longitudinal distribution of the partial pressure of CO2 (pCO2) in the central and western equatorial Pacific, west of 160°W
Authors: Inoue Hisayuki Y. , Ishii Masao , Matsueda Hidekadzu , Ahoyama Michio , Asanuma Ichio
Published: February 2004

We describe spatial and temporal variations in the partial pressure of carbon dioxide (pCO2) in the central and western equatorial Pacific on the basis of measurements conducted for the periods between 1987 and 1994. Surface water pCO2 data indicate the significant differences in longitudinal distribution depending on the ocean conditions. We examine the relationship between the area showing higher surface pCO2 values and the El Niño/Southern Oscillation phenomenon by using the Southern Oscillation Index. Results indicate that the area showing higher surface pCO2 values correlates with the SOI, which suggests significant intra‐ and interannual fluctuations of CO2 outflux from the central and western equatorial Pacific.
A comparison of measurements from ATMOS and instruments aboard the ER‐2 aircraft: Halogenated gases
Authors: Chang A. Y. , Salawitch R. J. , Michelsen H. A. , Gunson M. R. , Abrams M. C. , Zander R. , Rinsland C. P. , Elkins J. W. , Dutton G. S. , Volk C. M. , Webster C. R. , May R. D. , Fahey D. W. , Gao R.‐S. , Loewenstein M. , Podolske J. R. , Stimpfle R. M. , Kohn D. W. , Proffitt M. H. , Margitan J. J. , Chan K. R. , Abbas M. M. , Goldman A. , Irion F. W. , Manney G. L. , Newchurch M. J. , Stiller G. P.
Published: February 2004

We compare volume mixing ratio profiles of N2O, CFC‐11, CFC‐12, CCl4, SF6, and HCl in the mid‐latitude lower stratosphere measured by the ATMOS Fourier transform spectrometer on the ATLAS‐3 Space Shuttle Mission with in situ measurements acquired from the NASA ER‐2 aircraft during Nov 1994. Good agreement is found between ATMOS and in situ correlations of [CFC‐11], [CFC‐12], and [SF6] with [N2O]. ATMOS measurements of [CCl4] are 15% high compared to ER‐2 data, but agree within the systematic uncertainties. ATMOS observations of [HCl] vs [N2O] are within ∼10% of ER‐2 data for [HCl] > 1 ppbv, but exceed in situ measurements by larger fractional amounts for smaller [HCl]. ATMOS measurements of [ClONO2] agree well with values inferred from in situ observations of [ClO], [NO], and [O3]. The sum of [HCl] and [ClONO2] observed by ATMOS, supplemented by a minor contribution from [ClO] estimated with a photochemical model, is consistent with the levels of inorganic chlorine inferred from in situ measurements of chlorine source gases.
Detection and location of red sprites by VLF scattering of subionospheric transmissions
Authors: Dowden R. L. , Brundell J. B. , Lyons W. A. , Nelson T.
Published: February 2004

Scattering by the conductive columns of red sprites of VLF waves (“VLF sprites”) traveling in the Earth‐ionosphere waveguide is characterized by wide angle scattering (to 180°). This enabled the first VLF detection of sprite conductivity and is now used routinely for sprite detection and location by measurement of the phase and amplitude at both of the frequencies transmitted by NAA, NSS, NLK and NPM. In a blind test using only one VLF receiver and the first three of these transmitters, all of the VLF events fitting the criteria for VLF sprites were found to correspond to optical sprites and virtually all of the sprites observed optically corresponded to VLF events. Using only a single receiver in the high noise environment of local thunderstorms enabled the range to the sprite to be found to within 100 km and the direction to within 90°. Use of a large number (∼10) of suitably spaced antennas greatly increases the location accuracy and provides some information on the lateral structure of sprite conductivity.
vertical patterns of free and forced climate variations
Authors: Vinnikov Konstantin Ya. , Robock Alan , Stouffer Ronald J. , Manabe Syukuro
Published: February 2004

Observations of the vertical structure of atmospheric temperature changes over the past three decades show that while the global‐average lower atmosphere has warmed, the upper troposphere and lower stratosphere have cooled. While these changes may be due to observed anthropogenic increases of greenhouse gases, decreases of lower stratospheric ozone, and increases of tropospheric aerosols, the changes may also have been caused by natural unforced internal fluctuations of the climate system. Here we use the results of a 1000‐year simulation from a mathematical model of the coupled ocean‐atmosphere‐land system performed without any changes in external forcing, so that we may consider its variations as a surrogate for free, internally‐generated, natural fluctuations of the climate system. When the global mean surface air temperature is warm in the model, the lower troposphere, upper troposphere and lower stratosphere are also warm over most of the Earth, in contrast to the observations of the last three decades and to model simulations of the forced climate response due to increased greenhouse gases. The observed temperature change of the past three decades is therefore unlikely to have been caused solely by natural internal variations of the climate system, thereby strengthening the argument that these changes can at least partly be attributed to anthropogenic activities.
Methyl iodide in the Greenland/Norwegian Seas and the tropical Atlantic Ocean: Evidence for photochemical production
Authors: Happell James D. , Wallace Douglas W. R.
Published: February 2004

CH3I was measured in open ocean waters during two cruises to the tropical Atlantic Ocean and a late fall cruise to the Greenland and Norwegian Seas (GSNS). In warm, tropical surface waters subject to high solar irradiance, average CH3I saturation anomalies were positive (1.5–7.7 pmol kg−1), indicating a sea‐to‐air flux. This contrasted with negative saturation anomalies (−0.65±0.02 pmol kg−1) measured in cold surface waters of the open ocean GSNS subject to low‐light. High latitude oceans may therefore be a significant sink for atmospheric CH3 during the fall and winter. The locations and/or seasons where samples were analyzed were all characterized by relatively low biological production and the CH3I saturation anomaly along 19°S decreased from 7.7±0.6 to 3.4±0.4 pmol kg−1 when entering a more productive upwelling zone. Taken together these observations suggest a chemical, as opposed to biological, production mechanism for this compound in the open ocean. Within the open ocean of the GSNS, multiple linear regression between the observed CH3I saturation anomaly and variables including light intensity, water temperature, CFC‐11 saturation (indicator of gas exchange and deep mixing), and distance from the Norwegian Coastal Current (indicator of coastal or southern sources) showed that light intensity was the only significant predictor, explaining 79% of the variance. Photochemical production may therefore be dominant source of CH3I within the open ocean and this may have important implications for the large‐scale, seasonal cycling of iodine between the ocean and the atmosphere.