bluuebunny/crossref_metadata_2025 huggingface dataset:
Ground‐based remote sensing of methane height profiles with a tunable diode laser heterodyne spectrometer
Authors: Koide M. , Taguchi M. , Fukunishi H. , Okano S.
Published: February 2004

Height distributions of methane in the troposphere and stratosphere were derived from high resolution absorption spectra observed with a ground‐based tunable diode laser heterodyne spectrometer. The center wavenumber of the measured methane absorption line is 1223.1561 cm−1. In the retrieval of methane height profiles, a volume mixing ratio of methane was assumed to have a constant value in the troposphere and to decrease with a constant rate in the stratosphere. The tropospheric mixing ratio and the decreasing rate in stratosphere were derived to be 1.7±0.1 ppmv and −0.06 ppmv/km, respectively, for measurements at Tsukuba (36.0°N, 140.1°E) on December 17 and 20, 1991.
Structure function as a tool in AE and Dst time series analysis
Authors: Takalo J. , Lohikoski R. , Timonen J.
Published: February 2004

A new method to analyse the structure function (SF) has been constructed and used in the analysis of the AE time series for the years 1978–85 and Dst time series for 1957–84. It is shown that this SF analysis makes a clear distinction between affine and periodicity dominated time series, and it displays the essential periodicities of the series in a range relevant to its characteristic time scale. The AE time series is found to be affine such that the scaling exponent changes at a time scale of 113 (±9) minutes. On the other hand, in the SF function analysis, the Dst data are dominated by the 24‐hour and 27‐day periods. The 27‐day period is modulated by the annual variation.
Kinematic considerations for mantle mixing
Authors: Metcalfe Guy , Bina Craig R. , Ottino J. M.
Published: February 2004

Recent experimental and computational studies show that “islands” (unmixed regions that do not interact with surrounding regions) are ubiquitous features in chaotically advecting fluids. Such islands quite naturally account for the geochemically inferred coexistence of apparently distinct, long‐lived geochemical heterogeneity with relatively homogeneous regions of an actively convecting mantle. These results also indicate that mixing patterns—the set of islands and folds characterizing the large‐scale material advection— are sensitive to small variations in the rheology of the fluid. Therefore, interpretation of numerical simulations of mantle transport and mixing is less straightforward than currently supposed. Computational studies of analytic flow solutions with systematically introduced and controlled errors indicate that mantle simulations are unlikely to accurately compute individual trajectories for even moderate time, but that trajectory ensembles can be accurately computed for long time. Significantly, computations also indicate that mixing and transport results may not evolve smoothly with increased rheological realism.
The contribution of topographic scattering to teleseismic coda in southern California
Authors: Revenaugh Justin
Published: February 2004

Given that seismic coda is largely the result of scattering near the receiver, a tie to geological complexity, i.e., to crustal heterogeneity, is expected, but a systematic and predictive understanding of the important aspects of geology is lacking. We have developed a technique for mapping the origins of coda energy as recorded by regional networks that provides insight into the proximal generation of seismic coda. Here, the role of topography in the production of surface‐propagating coda energy, both as a scatterer and as a proxy of shallow geologic structure, is examined for the portion of the San Andreas fault system within the Southern California Seismic Network. We find significant correlation of P to Rg scattering potential with topographic roughness that extends to relatively subtle topography. The correlation peaks at a migration velocity of ∼2.9 km/s, confirming the identification of scattered Rg energy and offering an alternative means of estimating regional shallow velocity structure.
The efficiency of “viscous interaction” between the solar wind and the magnetosphere during intense northward IMF events
Authors: Tsurutani Bruce T. , Gonzalez W. D.
Published: February 2004

We examined 11 cases when the interplanetary magnetic field (IMF) was intensely northward (> 10 nT) for long durations of time (> 3 hours), to quantitatively determine an upper limit on the efficiency of solar wind energy injection into the magnetosphere. We have specifically selected these large BN events to minimize the effects of magnetic reconnection. Many of these cases occurred during intervals of high‐speed streams associated with coronal mass ejections when viscous interaction effects might be at a maximum. It is found that the typical efficiency of solar wind energy injection into the magnetosphere is 1.0 × 10−3 to 4.0 × 10−3, 100 to 30 times less efficient than during periods of intense southward IMFs. Other energy sinks not included in these numbers are discussed. Estimates of their magnitudes are provided.
Vertical distribution of heat generation in the Nissho Granitic Pluton, Hokkaido, Japan
Authors: Furukawa Yoshitsugu
Published: February 2004

Vertical distribution of radiogenic heat generation is estimated for the Nissho granitic pluton emplaced in the upper crust of the Kuril arc. The estimated profile shows that heat generation steeply decreases with depth. Using the exponential model the thickness of the layer with relatively high heat generation is estimated to be 7±2 km; this thickness is in the range of those estimated in heat flow provinces on continents. It is considered that this upward concentration of heat generation is caused by magmatic processes such as the gravitational differentiation in the magma chamber. In the upper crust of evolving arcs, where the continental‐type crust is growing, magmatic processes in chambers of granitic magmas could be important for the upward concentration of heat generation.
First incoherent‐scatter measurements of the equatorial E layer obtained with the ALTAIR radar
Authors: Tsunoda Roland T.
Published: February 2004

We describe the first incoherent‐scatter (IS) radar measurements made of the daytime E layer at equatorial latitudes. Using ALTAIR, a steerable IS radar located in the Kwajalein Atoll, we not only show that the E‐layer profiles are consistent with those obtained in situ by rockets, we present the first direct evidence of a latitudinal gradient in plasma density in the bottomside E layer that extended from 3°N dip latitude to beyond 6°N. We suggest that the gradient involves the electrodynamic transport of metallic ions, e.g., the gradient could be produced by the equatorial metallic‐ion fountain or possibly by the dumping of metallic ions at the base of the E layer by the wind‐shear mechanism for sporadic E. We close with a brief discussion of the implications of such a gradient on the equatorial electrojet.
Plasmoid formation and evolution in a numerical simulation of a substorm
Authors: Slinker S. P. , Fedder J. A. , Lyon J. G.
Published: February 2004

Plasmoids are thought to occur as a consequence of the formation of a near‐Earth neutral line during the evolution of a geomagnetic substorm. Using a 3D, global MHD simulation of the interaction of the Earth's magnetosphere with the solar wind, we initiate a substorm by a southward turning of the Interplanetary Magnetic Field (IMF) after a long period of steady northward field. A large plasmoid is formed and ejected. We show field line maps of its shape and relate its formation time to the progress of the substorm as indicated by the cross polar potential. Because of the large region of closed field in the magnetotail at the time of the substorm, this plasmoid is longer in axial dimension than is typically observed. We compare the simulation results with the type of satellite observations which have been used to argue for the existence of plasmoids or of traveling compression regions (TCRs) in the lobes or magnetosheath. The simulation predicts that plasmoid passage would result in a strong signal in the cross tail electric field.
Nightside electron flux measurements at Mars by the Phobos‐2 HARP instrument
Authors: Shutte N. , Gringauz K. , Király P. , Kotova G. , Nagy A. F. , Rosenbauer H. , Szegö K. , Verigin M.
Published: February 2004

All the available nightside electron data obtained during circular orbits at Mars from the Phobos‐2 HARP instrument have been examined in detail and are summarized in this paper. An electron flux component with energies exceeding that of the unperturbed solar wind was observed inside the magnetosheath, indicating the presence of acceleration mechanism(s). The character of the electron fluxes measured in the magnetotail cannot be classified in any simple manner; however, there is a correlation between the electron fluxes measured well inside this region and the unperturbed solar wind ram pressure.
The reaction O(³P) + HOBr: Temperature dependence of the rate constant and importance of the reaction as an HOBr stratospheric loss process
Authors: Nesbitt F. L. , Monks P. S. , Payne W. A. , Stief L. J. , Toumi R.
Published: February 2004

The absolute rate constant for the reaction O(³P) + HOBr has been measured between T=233K and 423K using the discharge‐flow kinetic technique coupled to mass spectrometric detection. The value of the rate coefficient at room temperature is (2.5±0.6) × 10−11 cm³ molecule−1 s−1 and the derived Arrhenius expression is (1.4±0.5) × 10−10 exp[(−430±260)/T] cm³ molecule−1 s−1. From these rate data the atmospheric lifetime of HOBr with respect to reaction with O(³P) is about 0.6h at z = 25 km which is comparable to the photolysis lifetime based on recent measurements of the UV cross section for HOBr. Implications for HOBr loss in the stratosphere have been tested using a 1D photochemical box model. With the inclusion of the rate parameters and products for the O + HOBr reaction, calculated concentration profiles of BrO increase by up to 33% around z = 35 km. This result indicates that the inclusion of the O + HOBr reaction in global atmospheric chemistry models may have an an impact on bromine partitioning in the middle atmosphere.
Rotational Raman scattering and the ring effect in zenith‐sky spectra
Authors: Fish D. J. , Jones R. L.
Published: February 2004

The technique of zenith‐sky spectroscopy is widely used to measure the vertical columns of O3, NO2, OClO and BrO in the atmosphere. In this paper, a model to simulate the effect of rotational Raman scattering by O2 and N2 on zenith‐sky spectra is presented. The model is used to calculate the Raman‐scattering cross‐section for zenith‐sky measurements and this cross‐section is shown to correspond closely to the measured Ring cross‐section, supporting the case that Raman scattering is the major cause of the Ring effect. Raman scattering is also shown to reduce the depths of structured molecular absorptions in scattered light spectra, leading to a general underestimation of the slant columns of molecules measured by zenith‐sky spectroscopy which can be significant in some cases. This effect varies with solar zenith angle, so will affect particularly attempts to retrieve the vertical profile of an absorber from the variation of slant column with zenith angle. The calculated Ring cross‐section is used to infer the proportion of multiply‐scattered light which enters a zenith‐sky spectrometer at twilight, and thus to estimate the magnitude of the corresponding underestimation of measured slant columns.
Nighttime hydrogen peroxide production on sulfuric‐acid‐aerosols involving nitrate and sulfate radicals
Authors: Pedersen Thorvald
Published: February 2004

A novel nighttime reaction sequence involving 1) nitrate radicals, 2) sulfate radicals and ultimately 3) hydrogen peroxide is proposed. According to a grossly simplified model calculation this sequence may lead to a twofold increase in the background hydrogen peroxide level during one night. This increase may be accumulated over a long period. Presumably an increased level of hydrogen peroxide will mean increased ozone depletion in the lower stratosphere. Proper modelling and more experimental work is needed to assess the importance of this proposed source of hydrogen peroxide.
Ozone trends deduced from combined Nimbus 7 SBUV and NOAA 11 SBUV/2 data
Authors: Hollandsworth S. M. , McPeters R. D. , Flynn L. E. , Planet W. , Miller A. J. , Chandra S.
Published: February 2004

The long‐term time series of global ozone from the Nimbus‐7 SBUV (Nov. 1978–June 1990) are extended through June 1994 by using measurements from the NOAA‐11 SBUV/2. The data sets are merged based upon comparisons during the 18‐month overlap period in which both instruments were operational. During this period, the average offset between the two time series is less than 2% in total ozone, and less than 6% in Umkehr layers 1–10. A linear‐regression trend model is applied to the extended time series to calculate updated trends as a function of latitude and altitude. Trends through June 1994 are 1.5‐2% per decade less negative than through June 1990 in the tropical middle stratosphere (35–40 km) and in the upper stratosphere (45–50 km) at mid‐latitudes. In the lower stratosphere, the trends are nearly 1.5% per decade more negative in the southern hemisphere tropical regions to 25°S, but remain relatively unchanged elsewhere. The seasonal structure of the total ozone trends is similar to past trend study results, but the magnitude of the seasonal trend can vary by 2% per decade depending on the length of the time series. Both TOMS (through April 1993) and SBUV total ozone time series show small negative trends in the equatorial region, though they are not statistically significant at the 2‐σ level.
An observation of the greenhouse radiation associated with carbon monoxide
Authors: Evans W. F. J. , Puckrin E.
Published: February 2004

Ground‐based measurements of the downward thermal emission spectra from the clear sky have been made in the spring and autumn seasons. These measurements clearly show the presence of the carbon monoxide emission band between 2000–2200 cm−1. A simulation of the background emission has been performed using the FASCD3P line‐by‐line radiation code. The simulation has been used to isolate the downward thermal emission that is attributed uniquely to carbon monoxide. From these measurements the actual downward greenhouse radiation flux from carbon monoxide has been determined to vary between 0.06 W/m² ± 16% and 0.11 W/m² ± 10%, depending on the time of year and other meteorological factors. A comparison to the longwave fluxes associated with other important greenhouse gases suggests that carbon monoxide itself may be a radiatively important trace gas in the atmosphere, and may make a significant contribution to the radiation imbalance of the atmosphere.
Oxygen isotopes in western Australian coral reveal Pinatubo aerosol‐induced cooling in the Western Pacific Warm Pool
Authors: Gagan Michael K. , Chivas Allan R.
Published: February 2004

We present a 12‐year (1981–93) near‐weekly oxygen‐isotope (δ18O) record from a western Australian (Ningaloo Reef) Porites lobata coral precisely positioned to record the sea‐surface temperature (SST) variation of the Leeuwin Current. The predictability of the Ningaloo Reef coral‐based SSTs may be unparalleled since it can be shown that SST changes in the Western Pacific Warm Pool (WPWP) are strongly correlated with, and lead by about 2.5 years, SST changes in the Leeuwin Current. Consequently, the ordinary SST variation in the Ningaloo coral record can be anticipated and removed to reveal unexpected cooling of 0.6°C (1992) and 0.9°C (1993) following the June 1991 eruption of Mt. Pinatubo. This cooling signal at Ningaloo Reef is likely to be produced by Pinatubo aerosol‐induced cooling of the southwestern WPWP averaging 0.5°C by early 1992 which is sustained at least through early 1993. It is suggested that this magnitude of volcanic cooling in the southwestern WPWP could have prolonged, in part, the extended 4‐year (1991–94) negative phase of the Southern Oscillation.
The style of the Tyrrhenian subduction
Authors: Marotta Anna Maria , Sabadini Roberto
Published: February 2004

Momentum and energy equations are solved simultaneously for an incompressible viscous fluid in order to model the changes in the shape of a subducted slab when active convergence between the subducting and overriding plates comes to the end and slab pull becomes the dominant tectonic mechanism. This model can be applied to the Tyrrhenian domain, where it has been suggested that active convergence terminated about 7–9 Myr ago. During the active phase the angle of immersion of the slab at intermediate depths between 100 and 270 km is small, about 45°–50°, and large, about 80°–90°, at depths greater than 300 km. The phase of passive gravitational sinking is characterized by a substantial modification in the shape of the slab, with a large angle of immersion of 70° now at intermediate depths, decreasing to 50° in proximity of the tip of the slab. When the shape of the modelled slab is compared with the seismogenic portion of the subducted Ionian lithosphere in the Tyrrhenian, our results are consistent with subduction driven by slab pull and with cessation of active convergence between 7–9 Myr before present.
Mineral magnetic record of environment in Late Pleistocene and Holocene sediments, Lake Manas, Xinjiang, China
Authors: Jelinowska A. , Tucholka P. , Gasse F. , Fontes J. C.
Published: February 2004

A study of magnetic parameters was carried out on a Late Pleistocene and Holocene sedimentary sequence (5 m) from Lake Manas (northern Xinjiang, China), that has already been analysed for bulk sediment mineralogy, stables isotopes from carbonates and biogenic material. Magnetic minerals confirm major changes in palaeoenvironmental and palaeohydrological conditions that were deduced from other methods. They also provide complementary information on changes in the lake system during the early and middle Holocene. The most important mineral magnetic change results from the authigenic formation of ferrimagnetic greigite, Fe3S4 during the lacustrine episodes dated from ∼8.7 kyr B.P. to ∼5.5 kyr B.P. (380–335 cm) and from ∼4.5 kyr B.P. to ∼3.5 kyr B.P. (320–285 cm) respectively. Our data also indicate an abrupt break in sedimentary conditions which coincides with a short‐term return towards dry climatic conditions around 3.5 kyr B.P., which was only suggested from other proxy data.
An intercomparison of plasma turbulence at three comets: Grigg‐Skjellerup, Giacobini‐Zinner, and Halley
Authors: Tsurutani Bruce T. , Glassmeier K. ‐H. , Neubauer F. M.
Published: February 2004

We examine and intercompare the LF plasma wave turbulence at three comets: Grigg‐Skjellerup (GS), Giacobini‐Zinner (GZ), and Halley (H). All three have power spectral peaks at the local ion cyclotron frequency (the pump wave) at ∼10−2 Hz, and a power‐law fall‐off at higher frequencies that suggest the development of turbulent cascades [Acuna, 1986]. The power laws for the three comets are approximately f−1.9, f−1.9 and f−2.1, respectively. However, other than the similarities in the power spectra, we find the magnetic field turbulence is considerably different at the three comets. Phase steepening is demonstrated to occur at the trailing edges of the GS waves. This is probably due to nonlinear steepening plus dispersion of the left‐hand mode components. A coherency analysis of GZ turbulence indicates that it is primarily composed of right‐handed mode components, i.e., the turbulence is “whistler‐mode”. This too can be explained by nonlinear steepening plus dispersion of the magnetosonic waves. At the level of GS and GZ turbulence development when the spacecraft measurements were made, classical three‐wave processes, such as the decay or modulation instabilities do not appear to play important roles. It is most likely that the nonlinear steepening and dispersive time scales are more rapid than three‐wave processes, and the latter had not had time to develop for the relatively “new” turbulence. The wave turbulence at Halley is linearly polarized. The exact nature of this turbulence is still not well understood at this time. Several possibilities are suggested, based on our preliminary analyses.
Effect of improved subgrid scale transport of tracers on uptake of bomb radiocarbon in the GFDL Ocean General Circulation Model
Authors: Duffy P. B. , Eltgroth P. , Bourgeois A. J. , Caldeira K.
Published: February 2004

We show that the Gent‐McWilliams tracer transport parameterization greatly improves the ability of the GFDL ocean general circulation model to simulate vertical profiles of both temperature and bomb radiocarbon with a single set of model parameter values. This parameterization, which includes new advection terms as well as isopycnal mixing, has previously been shown to greatly improve simulated temperature fields. Here, we show that it does not markedly affect the already good simulation of oceanic absorption of bomb radiocarbon, and discuss the reasons for this result.
Metallic emission lines during the impacts L and Q1 of comet P/Shoemaker Levy 9 in Jupiter
Authors: Roos‐Serote M. , Barucci A. , Crovisier J. , Drossart P. , Fulchignoni M. , Lecacheux J. , Roques F.
Published: February 2004

High resolution spectroscopy of the impacts and impact sites of comet P/Shoemaker‐Levy 9 in Jupiter has been performed at the Pic‐du‐Midi observatory, France. The transient emission of seven emission lines from five different metals (Na, Fe, Ca, Li, K) and of the Hα line have been identified in spectra from the fresh impact sites of fragments L and Q1.
Near‐ir spectroscopy of Jupiter at the time of comet Shoemaker‐Levy 9 Impacts: Emissions of CH4, H3+ and H2
Authors: Encrenaz Th. , Schulz R. , Stüwe J. A. , Wiedemann G. , Drossart P. , Crovisier J.
Published: February 2004

Near‐infrared emissions of the SL9 impact sites of Jupiter have been recorded on July 16–18, 1994, at ESO (La Silla, Chile). A very strong emission of methane was recorded between 3.50 and 3.56 µm, shortly after impact H, showing evidence for a temporary increase of the Jovian stratospheric temperature. Emissions of H2 (2.12 µm) and H3+ (3.53 µm) were also detected above some of the impact sites, several hours after the impacts. The observed H3+ emissions, however, seem to be at least partly contaminated by the southern aurora. A strong continuum was also detected at 2.12 µm over most of the impact sites, presumably due to intense scattering of reflected sunlight by stratospheric haze.
Do stratospheric aerosol droplets freeze above the ice frost point?
Authors: Koop T. , Biermann U. M. , Raber W. , Luo B. P. , Crutzen P. J. , Peter Th.
Published: February 2004

Laboratory experiments are presented which show that liquid stratospheric aerosol droplets under polar winter conditions do not freeze for temperatures higher than the water ice saturation temperature (frost point). Calorimetric measurements of the freezing of supercooled H2SO4/HNO3/H2O bulk solutions with concentrations typical of the polar stratospheric aerosol exhibit very small freezing rates, which excludes the possibility of homogeneous freezing of the droplets for temperatures above the frost point. Even heterogeneous formation of H2SO4 and HNO3 hydrates at these temperatures is a very inefficient process unless the stratosphere offers nuclei better suited for nucleation than those present in the laboratory experiments, which appears to be unlikely. Only ice was found to be a potential nucleus suited for the formation of the hydrates, which could cause the hydrates to freeze at temperatures below the frost point.
Radar wind profiler observations of solar semidiurnal atmospheric tides
Authors: Whiteman C. David , Bian X.
Published: February 2004

Semidiurnal solar tides in the mid‐latitude troposphere are investigated using harmonic analysis of 404 MHz radar profiler wind data obtained from a wide longitude zone in the U.S. The tides are apparent above a 1000‐m‐deep surface layer and increase in amplitude with height, attaining speeds of 0.5–0.7 m/s at 5–7 km. Observed wind characteristics agree well with tidal characteristics obtained with a dynamical model driven by observed global semidiurnal horizontal pressure gradients.
Early Earth's climate: Cloud feedback from reduced land fraction and ozone concentrations
Authors: Jenkins Gregory S.
Published: February 2004

Two features of early Earth—reduced ozone (O3) concentration and land fraction are investigated with a general circulation model (GCM). These features are components of a paradox (Faint‐Young Sun paradox) which has intrigued researchers for more than two decades. In this study, land fraction and O3 concentrations are uniformly reduced by 100 percent. The reduction in O3 takes place in the troposphere and stratosphere with all other variables held constant including present‐day land fraction. Two sensitivity tests under global ocean conditions are reported: one case with implied oceanic poleward transports of heat, the other case with no implied oceanic poleward transports of heat. The results show that the removal of land under present‐day conditions increases cloud fractions and cool surface temperatures, unless heat is transported poleward by oceans. In a third sensitivity test with zero O3 concentrations, global mean air temperatures are increased by 2 K because of an increase in upper tropospheric and lower stratospheric clouds. The clouds enhance the greenhouse effect within the troposphere, increasing downward longwave radiation to the surface, melting sea ice and snow. Similar studies using radiative‐convective models which do not include interactive clouds do not show such surface warming.
Correlation analysis between subduction in the last 180 Myr and lateral seismic structure of the lower mantle: geodynamical implications
Authors: Kývalová Hana , Čadek Ondřej , Yuen David A.
Published: February 2004

We have calculated the correlation between four recent tomographic models and reconstructions of past subduction sites to estimate the present positions of the lithospher subducted during the Cenozoic and the Mesozoic. A significant correlation is found at a depth of about 1000 km for subduction younger than 120 Myr, while remnants of subduction older than 120 Myr are detected close to the core‐mantle boundary (CMB). Somewhere in the depth range of 1300–2600 km a gap exists where no significant correlation is found in any time. The results suggest that the slabs do not pass through the lower mantle continuously. It is possible that both regimes, the catastrophic and the steady‐state, may be important for different time periods. Fast seismic anomalies close to the CMB may be associated with a past catastrophic event, while the good correlation in the upper part of the lower mantle may be explained by a steady‐state model. Other explanations for the very good correlation found at a depth of about 1000 km are either a predicted perovskite phase transition or a chemical boundary suggested by seismic array analysis.
The Shikotan Earthquake of October 4, 1994: Lithospheric earthquake
Authors: Kikuchi Masayuki , Kanamori Hiroo
Published: February 2004

A large Mw=8.2 earthquake occurred off Shikotan Is., one of the Kurile Is., on October 4, 1994. We inverted 32 body‐wave records to determine the rupture pattern using an iterative deconvolution method. The mechanisms of the subevents were allowed to vary during rupture. The source parameters obtained are: the location of the initial break = (43.48°N, 147.40°E); the centroid depth = 56 km; (strike, dip, rake) = (49°, 75°, 125°) for the total source; the seismic moment Mo = 2.6×1021 Nm (Mw=8.2); source time duration T = 42 s; the average rupture velocity ν = 2.5 km/s. We also determined the mechanism using long‐period Love and Rayleigh waves from 14 stations. The solution for a finite source distributed over a depth range from 0 to 90 km is (strike, dip, rake) = (54°, 76°, 129°) with Mo = 2.3×1021 Nm, in good agreement with that from body waves. Referring to the extent of the aftershock area and the subevent distribution, we estimated the fault area S = 120 × 60 km², the average slip D=5.6m, and the stress drop Δσ=11 MPa. We computed synthetic waveforms as well as static displacements using either the steep or the low‐angle plane as the fault plane, and found that the steep‐dip fault model fits the data better. Our result (the mechanism, large centroid depth, high stress drop) strongly suggests that the 1994 Shikotan earthquake is a lithospheric earthquake: an intra‐plate event that ruptures through a substantial part of the subducting oceanic lithosphere. This type of lithospheric earthquake is relatively common.
Effect of source depth correction on the estimation of earthquake size
Authors: Romanelli Fabio , Panza Giuliano F.
Published: February 2004

The relationship between surface wave magnitude, Ms, and seismic moment, Mo, of earthquakes is essential for the estimation of seismic risk in any region. In the hypothesis of constant stress drop, theoretical models predict that Log Mo and Ms are related by a linear law. The slope most commonly found in the literature is around 1.5. Here we show that the application to the Ms values of the necessary correction for the focal depth, gives a general increment of the correlation coefficient, and that a slope around 1.0 is consistent with the global data, while for regionalized data it can vary from about 1.0 to 2.0.
The contribution of flux transfer events to convection
Authors: Lockwood M. , Cowley S. W. H. , Smith M. F. , Rijnbeek R. P. , Elphic R. C.
Published: February 2004

It is shown from flux transfer event (FTE) occurrence statistics, observed as a function of MLT by the ISEE satellites, that recent 2‐dimensional analytic theories of the effects of pulsed Petschek reconnection predict FTEs to contribute between 50 and 200 kV to the total reconnection voltage when the magnetosheath field points southward. The upper limit (200 kV) allows the possibility that FTEs provide all the antisunward transport of open field lines into the tail lobe. This range is compared with the voltages associated with series of FTEs signatures, as inferred from ground‐based observations, which are in the range 10–60 kV. We conclude that the contribution could sometimes be made by a series of single, large events; however, the voltage is often likely to be contributed by several FTEs at different MLT.
Seasonal variations in the atmospheric distribution of a reactive chlorine compound, tetrachloroethene (CCl2=CCl2)
Authors: Wang Charles J.‐L. , Blake Donald R. , Rowland F. Sherwood
Published: February 2004

Tropospheric mixing ratios of CCl2=CCl2 were measured at remote surface locations in the Pacific between 71°N and 47°S during September and December of 1989, and March and June of 1990. The observed gradient of decreasing concentrations from the northern to southern hemisphere, and very low concentrations in the southern hemisphere throughout the year, indicates a predominant input from the northern hemisphere. Our seasonal measurements in the northern hemisphere showed maximum CCl2=CCl2 concentrations occurring in the late winter and minimum concentrations occurring in the late summer. This distinct seasonal variation is strongly coupled to the atmospheric abundance of hydroxyl radical, the only important species responsible for CCl2=CCl2 removal. Using the estimated global CCl2=CCl2 emissions the lifetime is calculated to be about 5.4 months which is in good agreement with the 4.0 month estimate obtained from the inverse ratio of its measured hydroxyl reaction rate constant compared with that of methylchloroform (CH3CCl3).
High pressure effects on thermal properties of MgO
Authors: Inbar Iris , Cohen R. E.
Published: February 2004

Using the non‐empirical Variational Induced Breathing (VIB) model, the thermal properties of periclase (MgO) under high pressures and temperatures are investigated using molecular dynamics, which includes all anharmonic effects. Equations of state for temperatures up to 3000K and pressures up to 310 GPa were calculated. Bulk modulus, thermal expansivity, Anderson‐Grüneisen parameter, thermal pressure, Grüneisen parameter and their pressure and temperature dependencies are studied in order to better understand high pressure effects on thermal properties. The results agree very well with experiments and show that the thermal expansivity decreases with pressure up to about 100 GPa (η=0.73), and is almost pressure and temperature independent above this compression. It is also effected by anharmonicity at zero pressure and temperatures above 2500K. The thermal pressure changes very little with increasing pressures and temperatures, and the Grüneisen parameter is temperature independent and decreases slightly with pressure.
Sample support in a single fracture: Considering the definition and control of the support of a water sample
Authors: Silliman Stephen E.
Published: February 2004

Defining and controlling the support of a field measurement (the volume or area over which the measurement is averaged) are critical components of statistical and/or geostatistical analysis of a data base. For the present study, the seemingly simple task of collecting a water sample from a single fracture is used to illustrate potential difficulties in defining and controlling the support of that sample. Two definitions of sample support are considered for this problem. First, one could argue that the support is equal to the volume of water collected. Second, one could argue for a support defined in terms of the area of the fracture surface contacted by the water collected. Collection of water samples with constant volume is relatively straight forward in a field situation. Collection of a water sample which involves contact with a specified area of the fracture, however, is not as straight forward. In the case of negligible regional flow, a constant sample area can be approximated by requiring that the sample volume collected be linearly proportional to the locally averaged aperture (thus requiring an independent measure of the local aperture). In the case of regional flow with continuous sampling, a constant area within each sample can be approximated by matching the up gradient width of the capture zone of the sampler (thus requiring knowledge of the local aperture and hydraulic gradient). These examples illustrate how difficult it may be to define and control the support for even these simple measurements. Further, they illustrate that the choice of support may be closely related to the purpose for which the measurement is collected. Additional attention to the problem of defining / controlling sample supports has the potential to pay substantial dividends in the areas of scaling and field design / analysis.
H2O2 in snow, air and open pore space in firn at Summit, Greenland
Authors: Bales Roger C. , Losleben Mark V. , McConnell Joseph R. , Fuhrer Katrin , Neftel Albrecht
Published: February 2004

Measurements of H2O2 in firn gas down to a 1.7‐m depth showed a consistent trend, with higher firn‐gas concentrations generally associated with higher concentrations in the firn at the same depth. However, firn to firn‐gas concentration ratios still exhibited a seasonal dependence, suggesting that for summer layers equilibrium has not yet been reached. The time to reach equilibrium between firn and firn gas is at least weeks. Snowfall and fog deposit several times more H2O2 than the surface snow will retain at equilibrium, supporting the idea that surface snow is a temporary reservoir for H2O2. Thus from an equilibrium standpoint, the snow‐pack should be a source of atmospheric H2O2 in the summer as well as fall, resulting in higher daytime concentrations than would occur based on just atmospheric photochemical reactions. But firn‐gas measurements reported here were generally near or lower than those in the atmosphere, suggesting that degassing is too slow to significantly influence atmospheric H2O2 levels.
Comment on “Problems of UV‐B radiation measurements in biological research: Critical remarks on current techniques and suggestions for improvements” by H. Tüg and M. E. M. Baumann
Authors: McKenzie R. L. , Johnston P. V.
Published: February 2004

We wish to comment on the paper titled “Problems of UV‐B radiation in biological research. Critical remarks on current techniques and suggestions for improvements”, by Helmut Tüg and Marcus Baumann (hereafter T&B), which appeared in the April 15 issue of Geophysical Research Letters (21, 8, 689–692, 1994).
Hydrolysis of N2O5 and ClONO2 on the H2SO4/HNO3/H2O ternary solutions under stratospheric conditions
Authors: Zhang Renyi , Leu Ming‐Taun , Keyser Leon F.
Published: February 2004

The reaction probabilities of N2O5 and ClONO2 with H2O on liquid sulfuric acid surfaces have been reexamined to determine the effect of HNO3 on these two hydrolysis rates, using a fast flow reactor coupled to a chemical ionization mass spectrometer. The measurements were carried out by maintaining constant H2O and HNO3 partial pressures and by varying temperatures between 227 and 195 K in order to mimic compositions representative of stratospheric aerosols. For experiments excluding HNO3, the reaction probability of N2O5 hydrolysis was found to be near 0.1, independent of temperature and H2SO4 content. This is in agreement with results previously measured under similar conditions. In the presence of gaseous HNO3 at stratospheric concentrations, the reaction probability was observed to decrease from about 0.09 at 218 K to about 0.02–0.03 at 195 K for PH2O = 3.8 × 10−4−1.0 × 10−3 Torr, showing that incorporation of HNO3 into liquid sulfuric acid greatly retarded the N2O5 hydrolysis. The ClONO2 reaction with H2O on liquid sulfuric acid, on the other hand, did not appear to be affected by the presence of HNO3.
Palomar observations of the R impact of comet Shoemaker‐Levy 9: I. Light curves
Authors: Nicholson P. D. , Gierasch P. J. , Hayward T. L. , McGhee C. A. , Moersch J. E. , Squyres S. W. , Van Cleve J. , Matthews K. , Neugebauer G. , Shupe D. , Weinberger A. , Miles J. W. , Conrath B. J.
Published: February 2004

We present near‐infrared observations from Palomar observatory of the impact of fragment R of comet Shoemaker‐Levy 9 with Jupiter on 21 July 1994. Two instruments were used to image the event at 3.2 and 4.5 microns simultaneously. The lightcurves from these image sequences both show two faint precursor flashes, a bright main peak, and several oscillations over the following hour. We identify the precursor flashes with the entry of the bolide into Jupiter's upper atmosphere, and with the post‐impact ejecta plume rising above the planet's limb. The main peak is due to the re‐entry of the collapsing plume into Jupiter's atmosphere and the resultant shock heating.
A simplified model for predicting high pressure thermal expansion of MgO
Authors: Wang K. , Reeber R. R.
Published: February 2004

Thermal expansion of MgO, periclase, is approximated by contributions from a quasi‐harmonic perfect crystal and its equilibrium high temperature/pressure defects. We demonstrate that the influence of thermal defects on high pressure thermal expansion is very small and may be neglected at lower mantle conditions. Following that, a simple relationship has been obtained between high pressure thermal expansion and the thermal expansion of a quasi‐harmonic perfect crystal at zero pressure. Our estimation of MgO thermal expansion at the core‐mantle boundary is 9.36 × 10−6K−1.
Nitrogen and oxygen photochemistry following SL9
Authors: Moses Julianne I. , Allen Mark , Gladstone G. Randall
Published: February 2004

The collision of SL9 with Jupiter caused many new molecular species to be deposited in the Jovian stratosphere. We use a photochemical model to follow the evolution of the impact‐derived species. Our results regarding the nitrogen and oxygen compounds are presented here. NH3 photolysis initiates the nitrogen photochemistry. Much of the nitrogen ends up in N2, nitrogen‐sulfur compounds, and HCN, but NH3 and nitriles such as C2H3CN may also exist in observable quantities a year or so after the impacts. Oxygen species survive for a long time in the Jovian stratosphere. The only major oxygen‐containing compounds that exhibit dramatic changes in the lower stratosphere in the first year following the impacts are SO, SO2, and OCS — H2O, CO2, and CO are comparatively stable. We discuss the important photochemical processes operating on the nitrogen and oxygen species in the Jovian stratosphere, make predictions concerning the temporal variation of the major species, and identify molecules that might act as good tracers for atmospheric dynamics.
Seasonal variations of water vapor in the tropical lower stratosphere
Authors: Mote Philip W. , Rosenlof Karen H. , Holton James R. , Harwood Robert S. , Waters Joe W.
Published: February 2004

Measurements of stratospheric water vapor by the Microwave Limb Sounder aboard the Upper Atmosphere Research Satellite show that in the tropical lower stratosphere, low‐frequency variations are closely related to the annual cycle in tropical tropopause temperatures. Tropical stratospheric air appears to retain information about the tropopause conditions it encountered for over a year as it rises through the stratosphere. We use a two‐dimensional Lagrangian model to relate MLS measurements to the temperature that tropical air parcels encountered when crossing the 100 hPa surface.
Freezing behavior of stratospheric sulfate aerosols inferred from trajectory studies
Authors: Tabazadeh A. , Toon O. B. , Hamill Patrick
Published: February 2004

Temperature histories based on 10‐day back trajectories for six ER‐2 flights during AASE I (1989) and AAOE (1987) are presented. These trajectories along with the properties of the observed PSC (polar stratospheric cloud) particles are used here to infer the physical state of the preexisting sulfuric acid aerosols. Of all the ER‐2 flights described here, only the PSCs observed on the flights of January 24 and 25, 1989 are consistent with the thermo‐dynamics of liquid ternary solutions of H2SO4/HNO3/H2O (Type Ib PSCs). For these two days, back trajectories indicate that the air mass was exposed to SAT (sulfuric acid tetrahydrate) melting temperatures about 24 hours prior to being sampled by the ER‐2. For the remaining ER‐2 flights (January, 16, 19, and 20 for the AASE I campaign and August 17 for the AAOE campaign), the observed PSCs were probably composed of amorphous solid solutions of HNO3 and H2O (Type Ic PSCs). Formation of such Type Ic PSCs requires the presence of solid H2SO4 aerosols since liquid aerosols yield ternary solutions. The 10‐day back trajectories of these flights indicate that the air mass was not exposed to SAT melting temperatures during the past week and had experienced cooling/warming cycles prior to being sampled by the ER‐2. These temperature histories, recent laboratory measurements and the properties of glassy solids suggest that stratospheric H2SO4 aerosols may undergo a phase transition to SAT upon warming at ∼ 198 K after going through a cooling cycle to about 194 K or lower.
Contrail formation: Homogeneous nucleation of H2SO4/H2O droplets
Authors: Kärcher B. , Peter Th. , Ottmann R.
Published: February 2004

Homogeneous nucleation of sub‐nanometer H2SO4/H2O germs, their growth and freezing probability in the cooling wake of a subsonic jet aircraft at tropopause altitude are investigated. Heteromolecular condensation, water uptake, and coagulation cause a small subset of the germs to grow into nm‐sized solution droplets which overcome the Kelvin barrier. These droplets efficiently take up water vapor from the gas phase, dilute rapidly, and may eventually freeze as water ice. However, results discussed for the case of a B 747 airliner suggest that under threshold conditions for the onset of contrail formation, a visible contrail is not likely to be produced by this mechanism. The sensitivity of the calculations to uncertainties in the nucleation theory underlines the need for detailed measurements of the particle microphysics in young aircraft plumes.
A new algorithm for improved ionospheric electron density modeling
Authors: Richards P. G. , Torr D. G. , Hagan M. E. , Buonsanto M. J.
Published: February 2004

This paper presents an algorithm that allows physical, time‐dependent, ionospheric models to reproduce the measured F2 peak electron density (NmF2). The algorithm uses the measured NmF2 to adjust the entire altitude density profile in the model as it steps in time. Thus the algorithm provides an internal constraint to the electron density in addition to the usual initial and boundary constraints. If the plasma temperatures are also well modeled, the new algorithm allows a faithful reproduction of electron density profiles throughout the entire F2 layer to high altitudes. The algorithm offers a simple method of parameterizing electron density profiles from incoherent scatter radars and also extending bottom side measurements into the topside ionosphere. The improved accuracy of the model electron density will allow more accurate studies of ionospheric emissions, energy budget, and minor species densities. There may be other non‐ionospheric physical systems where a similar algorithm could be applied. Any system where remote sensing measurements provide internal constraints would be a candidate.
Stable carbon isotope measurements of atmospheric organic acids in Los Angeles, California
Authors: Sakugawa Hiroshi , Kaplan Isaac R.
Published: February 2004

Atmospheric organic acids are ubiquitous constituents of urban smog and haze and are also present in the atmospheres of rural and largely uninhabited areas (e.g., the Amazon Rain Forest Basin). We report here source characterization of atmospheric organic acids in Los Angeles by measurements of their stable carbon isotopic ratios, e.g., 13C/12C(δ13C). The study was performed by separating formic and acetic acids using ion chromatography exclusion (ICE) and isolating milligram quantities of individual organic acids from atmospheric rain samples. Authentic reference samples of formic and acetic acids were used to determine that only a negligible isotope fractionation of δ13C value occurs after the ICE separation. During 1991–1992, rainwaters were collected in Los Angeles to isolate formic and acetic acids for the isotope measurements. Results presented in this paper demonstrate a significant isotopic difference between the mean δ13C value for acetic acid (−20.5‰) and formic acid (−30.1‰). We conclude from these results that the formic acid is derived from mixing of formic acid from direct emissions with the acid formed by secondary oxidation processes in the atmosphere, most probably from aldehydes, whereas acetic acid originates only from direct source emissions.
Comparison of ClO measurements by airborne and spaceborne microwave radiometers in the Arctic winter stratosphere 1993
Authors: Crewell S. , Fabian R. , Künzi K. , Nett H. , Wehr T. , Read W. , Waters J.
Published: February 2004

In February 1993 measurements of chlorine monoxide ClO, one of the key substances in catalytic ozone destruction, were performed over Scandinavia by two microwave receivers, the Submillimeter Atmospheric Sounder (SUMAS) on board the German research aircraft FALCON and the Microwave Limb Sounder (MLS) on board the Upper Atmospheric Research Satellite (UARS). High ClO concentrations (>1ppb) inside the polar vortex at approximately 20km altitude were detected by both experiments. A comparison shows good agreement of both sensors in the location of enhanced ClO.