bluuebunny/crossref_metadata_2025 huggingface dataset:
Atmospheric radical production by excitation of vibrational overtones via absorption of visible light
Authors: Donaldson D. J. , Frost G. J. , Rosenlof K. H. , Tuck A. F. , Vaida V.
Published: February 2004

We present calculations using a radiative transfer model which predict that in the lower stratosphere at high zenith angles, significant enhancements to the photodissociation rates of HNO3 and HNO4 can result from visible wavelength excitation of OH overtone vibrations containing sufficient energy to cleave the O‐O and N‐O bonds. The results indicate that atmospheric chromophores such as HONO2, HO2NO2 and H2O2, could make a potentially significant contribution to the production of HOx and NOx. Calculating the relative importance of their effect requires better knowledge of the absolute absorption cross sections, both for vibrational overtones and in the near UV. Stratospheric air masses in which this process could be important are those that experience lengthy exposure at high solar zenith angles: the outer regions of the polar winter vortex and the polar summer anticyclone. We note that the general mechanism may have application elsewhere, such as in the atmospheres of other planets and in generating the diffuse interstellar bands associated with molecular clouds.
Seasonal emissions of isoprene and other reactive hydrocarbon gases from the ocean
Authors: Broadgate Wendy J. , Liss Peter S. , Penkett Stuart A.
Published: February 2004

In this paper we show evidence that isoprene emission from the oceans is strongly seasonally dependent and is correlated with the chlorophyll content of the water from measurements in the North Sea and Southern Ocean. We estimate the seasonally averaged flux of isoprene to the atmosphere to be 1.7 × 107 molecules cm−2 s−1, which may be significant for atmospheric chemistry in locations remote from land as it is the only known source of atmospheric isoprene in these regions. We observe a strong seasonal cycle of several other NMHCs in seawater at high latitudes, with a maximum in summer. This will distort current estimates of the annual marine flux of NMHCs to the atmosphere which may need to be reduced by up to an order of magnitude to account for lower emissions in winter.
Local increases in auroral electron precipitation which were not accompanied by a corresponding increase in the electric potential of the auroral electron acceleration region
Authors: Calvert W. , Hardy D. A.
Published: February 2004

The Oedipus C rocket that was launched from Poker Flats, Alaska in November 1995 has detected significant local increases in the observed auroral electron precipitation flux during an auroral substorm which were not accompanied by a corresponding increase in the electric potential of the auroral electron acceleration region. The energy of the electrons which contributed to these increases in flux were also found to extend well below the electric potential energy of these electrons at the top of the acceleration region, thereby requiring a related loss in energy inside the acceleration region. This loss in energy must therefore be attributed to a wave instability which extracts energy from the electrons which are scattered into the loss cone inside the electron acceleration region to cause the discrete aurora during a substorm.
Temporal gravity and height changes of the Yellowstone Caldera, 1977–1994
Authors: Arnet Felix , Kahle Hans‐Gert , Klingelé Emile , Smith Robert B. , Meertens Charles M. , Dzurisin Dan
Published: February 2004

This paper describes the longest record of gravity measurements in the area of the Yellowstone caldera, Wyoming. The temporal gravity changes, at the ±12 µGal (10−8 ms−2) precision level, are compared with changes in heights from leveling and GPS. The gravity field decreased across the caldera from 1977 to 1983 during the uplift and attained a maximum decrease of up to −60± 2 µGal along the Caldera axis. The gravity field then reversed polarity to increasing values, of up to 60±12 µGal between 1986 and 1993. The ratio between height and gravity changes varied during the entire time, but converged over the latter period following the free‐air gravity gradient. General ground deformation deduced from leveling showed caldera‐wide uplift of ∼15 mm/a during the period of gravity decrease, then from leveling and GPS, subsidence of ∼25 mm/a during the gravity increase.
Global ocean thermohaline conveyor at present and in the Late Quaternary
Authors: Seidov Dan , Haupt Bernd J.
Published: February 2004

Operation modes of the global ocean thermohaline conveyor at present, at the last glacial maximum, and at a subsequent meltwater event (MWE) are revisited using a combination of a global ocean circulation model and a semi‐Lagrangian trajectory tracing model. The trajectory tracing model helps to visualize the true three‐dimensional water transport that is not accessible within traditional ocean circulation modeling. Our simulations confirm that the glacial mode of the conveyor was substantially weaker as compared to the present day mode. However, the simulations indicate that major changes of the deep global ocean conveyor occurred only at the MWE. These changes led to reversal of the Indian‐Atlantic branch of the deep conveyor due to complete cessation of North Atlantic Deep Water production caused by a very localized meltwater impact.
Partial melt compositions of carbonated peridotite at 3 GPa and role of CO2 in alkali‐basalt magma generation
Authors: Hirose Kei
Published: February 2004

Partial melt compositions of natural carbonated peridotite (KLB‐1 + 2.5 wt% CO2) have been determined at 3 GPa using the diamond aggregate method. Melt obtained at 1350 °C is carbonatitic, and with increasing temperature melt composition becomes silicate‐rich. These melts are lower in SiO2 and Al2O3 and higher in MgO and CaO compared to dry partial melts of KLB‐1 generated at the same pressure. The 1400 and 1450 °C liquids have melilititic compositions, which are in good agreement with those of natural alkali‐basalts from continental regions. At higher temperatures, partial melts are richer in SiO2, and the compositions of liquids at 1475 and 1525 °C approximate nephelinite and basanite respectively. However, they deviate from natural alkaline rocks in that the CaO/(CaO+MgO) ratios are smaller, suggesting that the natural nephelinite and basanite magmas were formed at lower pressures. The compositional trend of natural alkaline rocks, melilitites‐nephelinites‐basanites, may reflect the effect of decreasing pressure.
Areal and point precipitation intensity changes: Implications for the application of climate models
Authors: Osborn Timothy J.
Published: February 2004

It is demonstrated that the long‐term‐mean intensity of an area‐mean precipitation timeseries and the long‐term‐mean intensities at the points within the area of interest can change by different relative amounts if the spatial scale of precipitation events changes. This effect is problematic when trying to derive fine‐scale climate change scenarios from the statistics of area‐mean grid‐box precipitation simulated by climate models. Examples of this effect are given using model predictions of changing intensity and changing precipitation type (synoptic or convective).
Far‐field seismogram perturbations induced by topographic heterogeneity
Authors: Gaffet Stéphane , Massinon Bernard
Published: February 2004

The far‐field contribution of the wavefield diffracted by topographical heterogeneities located in the vicinity of sources is analyzed in the case of nuclear explosions detonated inside the Taourirt Tan Afella massif, Algeria. The far‐field scattered field is strongly shaped by the geometry of the topography and by the source location inside the mountain. Focusing and defocusing of the pP wave are shown. Back‐scattering inside of the massif appears in the coda of the pP phase. For specific take‐off angles, ie for given teleseismic distances, broadening of the pS diffracted field may appear. This broadening is explained by the simultaneous arrival of the pS and the P surface wave to S converted wave, with similar polarizations.
Evidence for extensive degassing of the Hawaiian Mantle Plume from helium‐carbon relationships at Kilauea Volcano
Authors: Hilton David R. , McMurtry Gary M. , Kreulen Rob
Published: February 2004

We report helium and carbon isotope and abundance characteristics of solfataras and steam fumaroles located within and around the central summit caldera of Kilauea volcano, Hawaii. Kilauea fluids are characterized by high‐³He ‘hotspot’ ³He/4He ratios of between 13.7 and 15.9 RA (where RA = air ³He/4He) together with CO2/³He and δ13C(CO2) values of 4.6–8.4 (×109) and −3.4 to −3.6‰, respectively. We combine our measurements with CO2 flux estimates to reconstruct the ³He characteristics of Kilauea parental magma allowing an estimate of the ³He characteristics of the Kilauea mantle source. Derived ³He contents of ∼3.3×10−11 cm³STP/g indicate that Kilauea magma sources are highly depleted in primordial ³He, compared to model estimates of magma sources supplying both spreading ridges and ocean islands. Our results are consistent with the notion that the Hawaiian plume has undergone extensive degassing prior to incorporation into the source region of Kilauea volcano. We suggest that degassing of mantle plumes, at Hawaii and possibly elsewhere, can act as an important control on the range of ³He/4He ratios observed to characterize ocean island basalts (OIBs); in turn, this can affect the relationship between helium isotopes and other tracers of mantle sources. Plume degassing can also explain the puzzling observation that the ³He content of most OIBs is less than that of mid‐ocean ridge basalts (MORBs).
Ulysses observations of the northward extension of the heliospheric current sheet
Authors: Forsyth R. J. , Balogh A. , Smith E. J. , Gosling J. T.
Published: February 2004

After passing through the northern polar regions of the heliosphere during the summer of 1995, the Ulysses spacecraft has been gradually returning towards lower equatorial latitudes, reaching 30°N in August 1996 at about which time low speed solar wind from the streamer belt was once again observed. This paper reports on the Ulysses magnetic field observations, beginning from this time, concentrating on encounters with the heliospheric current sheet. These encounters restarted at a latitude of 25.5°N, a higher latitude than might be expected at solar activity minimum. We show that this early reappearance was due to a northward deflection of the current sheet caused by a long‐lived active region at the corresponding heliographic longitude in the photosphere.
Evidence for formation of OH radicals from the reaction of O3 with alkenes in the gas phase
Authors: Paulson Suzanne E. , Sen Atish D. , Liu Ping , Fenske Jill D. , Fox Matthew J.
Published: February 2004

A series of experiments investigating the formation of OH radicals from O3‐alkene reactions are described. Pairs of OH tracer compounds—aromatic and aliphatic hydrocarbons—were added to O3‐alkene mixtures in small quantities. Under these conditions, a large fraction of the tracer is consumed, resulting in a much larger signal than in experiments using excess tracer. The average decay ratios of tracer pairs in 30 experiments were within 7% of those predicted by literature rate constants for tracer‐OH reactions, strongly supporting the hypothesis that OH is formed directly from O3 reaction with alkenes.
Chronology of the episode 54 eruption at Kilauea Volcano, Hawaii, from GOES‐9 satellite data
Authors: Harris Andrew J. L. , Keszthelyi Laszlo , Flynn Luke P. , Mouginis‐Mark Peter J. , Thornber Carl , Kauahikaua James , Sherrod David , Trusdell Frank , Sawyer Michael W. , Flament Pierre
Published: February 2004

The free availability of GOES satellite data every 15 minutes makes these data an attractive tool for studying short‐term changes on cloud‐free volcanoes in the Pacific basin. We use cloud‐free GOES‐9 data to investigate the chronology of the January 1997, episode 54 eruption of Kilauea Volcano, Hawaii. Seventy‐six images for this effusive eruption were collected over a 60‐hour period and show the opening and shutdown of active fissures, the draining and refilling of the Pu‘u ‘O‘o lava lake, and the cessation of activity at the ocean entry.
Implications of small comets for the noble gas inventories of Earth and Mars
Authors: Swindle Timothy D. , Kring David A.
Published: February 2004

Frank et al. [1986a,b] proposed the possibility of large numbers of small comets impacting the Earth. Using the parameters for the small comets suggested by Frank and Sigwarth [1993], we find that, over the lifetime of the solar system, such small comets would deliver far more Ar, Kr, and Xe to the atmospheres of Earth and Mars than those atmospheres presently contain if, as Frank and Sigwarth [1993] assumed, the small comets formed in very cold regions far from the Sun. Comets can be greatly depleted in noble gases if they form relatively close to the Sun (for example, near Jupiter), but this source region is inconsistent with other features of the proposed model. Alternatively, if the comets did form in very cold regions far from the Sun, the current flux would have to be at least a factor of 30,000 higher than the long‐term average.
Numerical simulation of plasma processes occurring in the ram region of the tethered satellite
Authors: Singh Nagendra , Leung W. C.
Published: February 2004

Plasma processes affecting collection of electrons by a conducting body in a magnetized plasma are studied using a fully 3‐dimensional particle‐in‐cell simulation, including a relative drift (Vo) between the plasma and the body. The main focus of the paper is on the plasma processes occurring in the ram region when the body potential Φo > Wo /e where Wo is the ram energy of the ions in the rest frame of the body. The potential structure near the body and the resulting flow of electrons and ions are critically examined to determine the sources of free energy for exciting plasma waves, which can possibly accelerate electrons to superthermal energies. Simulations reveal that the E × Bo drift of the electrons in the body's sheath, shifted toward the ram region and extended along the magnetic field Bo, produces sufficiently large relative drifts between the electrons and ions across Bo to excite lower hybrid waves. It is estimated that such drifts in the sheath of the tethered satellite was able to produce lower hybrid waves which could accelerate the electrons up to a few hundred electron volts.
A geometrical method for migrating 3D or 2.5D seismic reflection data
Authors: Pivot F.
Published: February 2004

Classical processing of 2.5D land seismic surveys has shown to yield unsatisfactory images, even though shot gathers show clear reflections and a good signal to noise ratio. If some major interfaces are easily identified within the stack volume, their 3D geometry remains difficult to appreciate because of a lack of continuity in the cross‐receiver line direction. The theoretical aspects of an alternate method allowing a construction of these 3D structures are presented here. This method geometrically migrates picked reflection traveltimes on good quality shot gathers without amplitude or frequency considerations. It is tested on a synthetic dataset from a 3D smoothly deformed reflector that is well recovered by the technique and applied to major reflections of a 2.5D seismic survey, allowing a successful reconstruction of the reflectors.
Odd nitrogen formed by energetic electron precipitation as calculated from TIROS data
Authors: Callis Linwood B.
Published: February 2004

Daily odd nitrogen formation due to energetic electron precipitation has been calculated for 840101 through 841231. Electron energy spectra between 4.25 and 1050 keV were used as derived from TED and MEPED observations made aboard NOAA spacecraft. Results indicate the importance of electron precipitation to the middle atmospheric NOy budget between 70 and 111 km. The column NOy source for 42≤Z≤111 km and for invariant latitudes between 63° and 76° in both hemispheres is calculated to be ≈13 times that of the global source of NOy derived from N2O. This source is larger in the southern hemisphere and is dominated by electrons which deposit their energy above 80 km.
Evidence for HBr production due to minor channel branching at mid‐latitudes
Authors: Chartrand D. J. , McConnell J. C.
Published: February 2004

Recently, Nolt et al. [1997] have presented HBr measurements over the height range 20–36 km. We have compared model calculations with these measurements and find definitive evidence for non‐zero branching ratios for HBr production from either HO2+BrO, k1b, or OH+BrO, k2b. For k1b, best agreement between modelled and observed HBr concentrations is obtained if the branching ratio increases from ∼0.4% at 20 km, to about 2% at 34 km with no additional contribution from the OH+BrO branch. However, a height‐independent value of 1% also produces reasonable results. This branching ratio contradicts the study of Mellouki et al. [1994]. For OH+BrO, the best value of k2b appears to be 2–3%, if k1a = 0 which is comparable to the recently determined branching ratio for HCl production from the analogous chlorine reaction, OH+ClO.
Ulysses' return to the slow solar wind
Authors: McComas D. J. , Bame S. J. , Barraclough B. L. , Feldman W. C. , Funsten H. O. , Gosling J. T. , Riley P. , Skoug R. , Balogh A. , Forsyth R. , Goldstein B. E. , Neugebauer M.
Published: February 2004

After ten long years of wandering the uncharted seas, Ulysses returned to his home port of Ithaca. Similarly, after its unprecedented five year odyssey through the previously uncharted regions over the poles of the Sun, the Ulysses spacecraft has returned to the slow, variable solar wind which dominates observations near the ecliptic plane. Solar wind plasma and magnetic field observations from Ulysses are used to examine this return from the fast polar solar wind through the region of solar wind variability and into a region of slow solar wind from the low latitude streamer belt. As it journeyed equatorward, Ulysses encountered a large corotating interaction region and associated rarefaction region on each solar rotation. Due to these repeated interactions, Ulysses also observed numerous shocks, all of which have tilts that are consistent with those expected for shocks generated by corotating interaction regions. Eventually, Ulysses emerged into a region of unusually steady slow solar wind, indicating that the tilt of the streamer belt with respect to the solar heliographic equator was smaller than the width of the band of slow solar wind from the streamer belt.
Free surface effects on the propagation of dynamic rupture
Authors: Nielsen Stefan B.
Published: February 2004

Dynamic rupture of reverse and normal fault intersecting the surface are investigated. In the case of a normal fault nucleating at depth and propagating upwards, coupling of rupture‐radiated stress and free boundary conditions at the surface may induce a shallow secondary nucleation anticipating up to a few seconds the arrival of the main rupture front. Indeed, the free surface induces normal stress fluctuations modifying the fault frictional strength. No significant effect on rupture velocity is observed in the case of reverse faulting. These incidences are explained by a stress analysis and illustrated by some numerical simulations in the case of dynamic normal faulting in a homogeneous half‐space. The described effects could explain some observations of high frequency radiation close to the surface in documented shallow earthquakes like in Kalamata, 1986 [Bouin, 1994].
Measurement of NO and NOy emission indices during SUCCESS
Authors: Campos T. L. , Weinheimer A. J. , Zheng J. , Montzka D. D. , Walega J. G. , Grahek F. E. , Vay S. A. , Collins J. E. , Wade L. O. , Sachse G. W. , Anderson B. E. , Brune W. H. , Tan D. , Faloona I. , Baughcum S. L. , Ridley B. A.
Published: February 2004

Exhaust measurements in the wake vortex regime of the NASA Boeing 757 aircraft were made during the SUbsonic aircraft: Contrails and Cloud Effects Special Study. Emission indices for NO and NOy were calculated from in situ measurements taken on board the NASA DC‐8 for plumes aged 20–300 seconds. The average NO emission index is 7.5 g NO2/kg fuel for mean conditions of 37 kft altitude, 0.7 Mach and 0.34 kg/s fuel flow rate. Comparison is made between measured indices and predictions based on ground engine test data and a fuel flow model. Measurements are positively correlated but are on average 22% higher than predictions, with considerable scatter and systematic deviations in measurements made under low thrust conditions. These conditions are lower than typical in commercial cruise operation of the 757, for which the model was optimized. No statistically significant change in nitrogenous emissions is observed for an order of magnitude change in fuel sulfur content. Estimation of the NO2 from photochemical calculations implies a contribution to NOx of 5–19%. Examination of exhaust composition shows that 95% of the NOy is in the form of NOx.
Biogeochemical significance of transport exopolymer particles in the Indian Ocean
Authors: Kumar M. Dileep , Sarma V. V. S. S. , Ramaiah N. , Gauns M. , de Sousa S. N.
Published: February 2004

The behavior of Transparent Exopolymer Particles (TEP), produced by biochemical processes, was studied for the North Indian Ocean, an area of global biogeochemical significance, during 1996 southwest monsoon. Very different behavior of TEP was found between waters of the Arabian Sea and the Bay of Bengal. The TEP concentrations were lower in the Bay of Bengal due to faster scavenging from water column because of interaction with mineral particles. They were higher and occurred even in intense sub‐oxic layers in the Arabian Sea. Our results support the mineral ballast theory in the Bay of Bengal and also reveal the hitherto not noticed organic matter reservoir, which seems to be in surplus, to meet the higher carbon demand by bacteria in denitrifying waters of the Arabian Sea.
Particulate sizing and emission indices for a jet engine exhaust sampled at cruise
Authors: Hagen D. , Whitefield P. , Paladino J. , Trueblood M. , Lilenfeld H.
Published: February 2004

Particle size and emission indices measurements for jet engines, primarily the Rolls Royce RB211 engines on a NASA 757 aircraft are reported. These data were used to estimate the fraction of fuel sulfur that was converted to particulates. These measurements were made in‐situ with the sampling aircraft several kilometers behind the source. Some complimentary ground measurements on the same source aircraft and engines are also reported. Significant differences are seen between the ground observations and the in‐situ observations, indicating that plume processes are changing the aerosol's characteristics.
Trends of ozone in the troposphere
Authors: Oltmans S. J. , Lefohn A. S. , Scheel H. E. , Harris J. M. , Levy H. , Galbally I. E. , Brunke E.‐G. , Meyer C. P. , Lathrop J. A. , Johnson B. J. , Shadwick D. S. , Cuevas E. , Schmidlin F. J. , Tarasick D. W. , Claude H. , Kerr J. B. , Uchino O. , Mohnen V.
Published: February 2004

Using a set of selected surface ozone (nine stations) and ozone vertical profile measurements (from six stations), we have documented changes in tropospheric ozone at a number of locations. From two stations at high northern hemisphere (NH) latitudes there has been a significant decline in ozone amounts throughout the troposphere since the early 1980s. At midlatitudes of the NH where data are the most abundant, on the other hand, important regional differences prevail. The two stations in the eastern United States show that changes in ozone concentrations since the early 1970s have been relatively small. At the two sites in Europe, however, ozone amounts increased rapidly into the mid‐1980s, but have increased less rapidly (or in some places not at all) since then. Increases at the Japanese ozonesonde station have been largest in the lower troposphere, but have slowed in the recent decade. The tropics are sparsely sampled but do not show significant changes. Small increases are suggested at southern hemisphere (SH) midlatitudes by the two surface data records. In Antarctica large declines in the ozone concentration are noted in the South Pole data, and like those at high latitudes of the NH, seem to parallel the large decreases in the stratosphere.
On the place of the pseudo‐breakup in a magnetospheric substorm
Authors: Rostoker Gordon
Published: February 2004

It is common to view the expansive phase of a magnetospheric substorm as a large amplitude disturbance. As a result, any magnetic disturbance that has the normal characteristics of an expansive phase onset but has an amplitude below some subjective limit is not classed as an expansive phase onset but is labelled, instead, as a pseudo‐breakup. In this paper it will be shown that a pseudo‐breakup is, in fact, a disturbance which represents the same physical process as the onset of an expansive phase or any of the subsequent intensifications. Examination of simultaneous interplanetary magnetic field data suggests the possibility that a pseudo‐breakup is distinguished from the onset or intensifications of an expansive phase by its occurrence during a period of increasing energy input into the magnetosphere. Thus, the pseudo‐breakup is not accompanied by a large scale poleward motion of the high latitude edge of the auroral oval in the substorm disturbed region characteristic of an expansive phase.
Ice crystal nucleation and growth in contrails forming at low ambient temperatures
Authors: Jensen E. J. , Toon O. B. , Pueschel R. F. , Goodman J. , Sachse G. W. , Anderson B. E. , Chan K. R. , Baumgardner D. , Miake‐Lye R. C.
Published: February 2004

A model of ice crystal nucleation and growth in a diluting aircraft exhaust plume is used to evaluate the physical processes responsible for the ice number densities and size distributions measured on May 4, 1996. Predicted ice crystal size distributions are compared with observations at about 70 seconds plume age. The simulated crystals grow to about 2 µm radius within 2–3 seconds, then remain approximately constant in size until 30–60 seconds plume age when crystal sublimations begins. The calculated crystal size distribution has approximately the same volume mode radius as the observed size distribution (1–2 µm); however, the model does not predict as many crystals larger than 2 µm radius as indicated by the measurements. Due to the low ambient temperature (−61°C), large ice supersaturations are generated in the plume, and all exhaust soot particles and ambient aerosols entrained into the plume before about 1 second plume age are activated to ice nuclei. The simulations indicate that if the soot particle emission index is on the order of 2×1012 particles (kg fuel)−1 or lower and freshly nucleated sulfate aerosols are too small to freeze in the young plume, then the majority of the contrail ice crystals may be nucleated on ambient aerosols entrained into the exhaust plume.
Recent forecast skill for the El Niño/Southern Oscillation
Authors: Ghil Michael , Jiang Ning
Published: February 2004

We outline a relationship between three slowly varying characteristics of the coupled ocean‐atmosphere system in the tropical Pacific: (i) quasi‐periodicity, (ii) extended predictability, and (iii) approximate low dimensionality. The Southern Oscillation Index (SOI) and Niño‐3 sea surface temperatures characterize climatic variations in the tropical Pacific; these two time series are usually anticorrelated. This low‐dimensional characterization suggests that much of the system's seasonal‐to‐interannual predictability depends on the regular behavior of the two scalar time series under consideration. The predictive skill of two idealized models is studied, showing the strong connection between regularity and predictability. El‐Niño/Southern‐Oscillation (ENSO) predictability is then assessed for current forecast models. When the periodic component of the ENSO signal is strong, it results in higher forecast skill. This skill decreases when the anti‐correlation between SOI and Niño‐3 temperature anomalies is lost, as it has been in the first half of this decade.
Influences of anthropogenic and oceanic forcing on recent climate change
Authors: Folland Chris K. , Sexton David M. H. , Karoly David J. , Johnson Colin E. , Rowell David P. , Parker David E.
Published: February 2004

We report a new approach to climate change detection and attribution using an atmospheric general circulation model (AGCM), complementary to the traditional approach using coupled ocean‐atmosphere models (CGCM). Ensembles of simulations were run with an AGCM forced with the observed history of sea‐surface temperature (SST) and sea‐ice extent and repeated with a variety of forcing factors added incrementally. SST changes alone give a warming of only about 0.15°C in annual global land surface air temperature between 1950 and 1994. Addition of changing greenhouse gases, including off‐line calculations of tropospheric ozone, give a further warming of 0.15°C, still 0.2 °C less than observed. This deficit in warming derives from the Northern Hemisphere (NH) winter half‐year as the summer half‐year NH temperature is well‐simulated. In the lower stratosphere, little cooling is simulated using the observed changes of SST alone but increasing the concentration of greenhouse gases and decreasing the concentration of stratospheric ozone leads to a cooling close to that observed. Inclusion of changes to tropospheric ozone with other forcing factors, the first time this has been attempted, gives good simulations of tropospheric and stratospheric temperature changes; these are significantly more similar to observations than using SST variations alone. Despite the uncertainties, these simulations strongly indicate a discernible anthropogenic effect on the annual mean thermal structure of the atmosphere, the first time this has been shown in the presence of the observed variations of SST and sea‐ice extent.
Whistler mode wave coupling effects on electron dynamics in the near Earth magnetosphere
Authors: Matsoukis S. K. , Chapman S. , Rowlands G.
Published: February 2004

Nonlinear electron whistler mode wave particle interactions in the near earth magnetosphere suggest several candidate mechanisms for phase space diffusion of electrons into the loss cone to provide a source of auroral precipitating electrons. A unidirectional whistler mode wave propagating parallel to the background magnetic field and interacting with an electron can be shown to produce resonance (trapping of electrons) but the process is not stochastic. Chaos can be introduced by resonance between electrons that mirror many times in the earth's field, and a whistler wavefield. Here, we show that an electron interacting with two oppositely directed, parallel propagating whistler mode waves exhibits stochastic behaviour in addition to resonance. The background field is uniform, so that stochasticity arises solely due to the presence of the wavefield without requiring bounce motion of electrons between mirror points. Stochasticity first appears for wave amplitudes not inconsistent with observations at disturbed times in the near earth magnetosphere and therefore may contribute to pitch angle diffusion.
Depolarization of lidar returns by small ice crystals: An application to contrails
Authors: Mishchenko Michael I. , Sassen Kenneth
Published: February 2004

Measurements of the lidar linear depolarization ratio δ can be a powerful remote sensing technique for characterizing the microphysics of contrail particles. Since young contrails often consist of relatively small ice crystals, the quantitative interpretation of lidar measurements requires accurate theoretical computations of δ for polydisperse, randomly oriented nonspherical particles with size parameters ranging from zero to at least several tens, thus ruling out most of the currently available numerical techniques. In this paper we use the recently improved T‐matrix method and compute δ for polydispersions of randomly oriented ice spheroids, circular cylinders, and Chebyshev particles with sizes typical of young contrails. We show that ice crystals with effective radii as small as several tenths of a micron can already produce δ exceeding 0.5 at visible wavelengths. This may explain the frequent occurrence of large δ values for very young contrails. We also show that observed increases of δ with the contrail's age can be explained either by a rapid increase of the particle size parameter from essentially zero to about 5 or by assuming that the contrail particles originate as perfect spheres and then acquire a certain degree of asphericity.
Initial results from WING, the continuous GPS network in the western Pacific area
Authors: Kato Teruyuki , Kotake Yoshiko , Nakao Shigeru , Beavan John , Hirahara Kazuro , Okada Masami , Hoshiba Mitsuyuki , Kamigaichi Osamu , Feir Renato B. , Park Pil Ho , Gerasimenko Mikhail D. , Kasahara Minoru
Published: February 2004

To investigate tectonic deformation in the western Pacific, a continuous GPS tracking network has been established, and named the Western Pacific Integrated Network of GPS (WING). Between 1995 and March 1997 we establised ten new sites. Data for the period July 1995 to October 1996 were analyzed, together with data from International GPS Service for Geodynamics (IGS) global sites, to estimate daily coordinates. A fiducial‐free approach was used to obtain the most accurate baseline estimates. To fix the estimated coordinates to the terrestrial reference frame, the Tsukuba IGS site is assumed to be moving westward relative to the stable Eurasian continent at ∼2 cm/yr according to Heki's [1996] estimate. We find that: (1) velocities of sites well within oceanic plates are in good agreement with rigid plate motion models; (2) sites close to plate boundaries are all affected by the deformation at those boundaries, among which back‐arc rifting (spreading) is clearly visible at the Mariana and Okinawa troughs; (3) sites in eastern Asia are moving east to east‐southeast relative to the stable Eurasian continent, suggesting long distance effects of the northward collision of India with Asia.
Capillary sealing in sedimentary basins: A clear field example
Authors: Revil A. , Cathles L. M. , Shosa J. D. , Pezard P. A. , de Larouzière F. D.
Published: February 2004

Pore fluid overpressures as high as 2 MPa (full lithostatic) are observed at ODP Site 975 starting at depths of 145 mbsf (meters below the sea floor). Sediment porosity increases to near surface values below the top of overpressure, while compaction and pressures above the seal are normal. Spikes in the density log and degassing of core from the overpressured zone indicate the presence of gas. The high porosity sediments are far too permeable to allow the generation and maintainance of fluid overpressures by disequilibrium compaction alone. The presence of two fluid phases in a layered sequence of fine and coarse sediment suggests capillary sealing, and this is shown to be quantitatively feasible.
Absorption of sunlight by water vapor in cloudy conditions: A partial explanation for the cloud absorption anomaly
Authors: Crisp D.
Published: February 2004

The atmospheric radiative transfer algorithms used in most global general circulation models underestimate the globally‐averaged solar energy absorbed by cloudy atmospheres by up to 25 Wm−2. The origin of this anomalous absorption is not yet known, but it has been attributed to a variety of sources including oversimplified or missing physical processes in these models, uncertainties in the input data, and even measurement errors. Here, a sophisticated atmospheric radiative transfer model was used to provide a more comprehensive description of the physical processes that contribute to the absorption of solar radiation by the Earth's atmosphere. We found that the amount of sunlight absorbed by a cloudy atmosphere is inversely proportional to the solar zenith angle and the cloud top height, and directly proportional to the cloud optical depth and the water vapor concentration within the clouds. Atmospheres with saturated, optically‐thick, low clouds absorbed about 12 W m−2 more than clear atmospheres. This accounts for about 1/2 to 1/3 of the anomalous absorption. Atmospheres with optically thick middle and high clouds usually absorb less than clear atmospheres. Because water vapor is concentrated within and below the cloud tops, this absorber is most effective at small solar zenith angles. An additional absorber that is distributed at or above the cloud tops is needed to produce the amplitude and zenith angle dependence of the observed anomalous absorption.
Crustal anisotropy in the Ural Mountains Foredeep from teleseismic receiver functions
Authors: Levin Vadim , Park Jeffrey
Published: February 2004

Radial and transverse teleseismic receiver functions (RFs) at GSN station ARU, in central Eurasia, display variation in back‐azimuth ψ consistent with a 1‐D anisotropic crustal structure. In a broad ψ range, the transverse RFs possess a strong phase at ∼5‐sec delay relative to direct P, with a polarity reversal at ψ ∼ 50°. The radial RFs peak at the transyerse‐RF polarity reversal for this converted phase. The first motion of the transverse RFs varies with ψ also, reversing polarity at ψ ∼ 345°. The azimuthal variation can be modeled by a 5‐layer velocity profile with substantial (15%) seismic anisotropy in both the lowermost crust and a low‐velocity surface layer. Assuming hexagonal symmetry, the lowermost crust has a tilted “slow” symmetry axis i.e. an oblate phase velocity surface. The strike of the axis is oblique to the north‐south Urals trend, but deviates <20° from the mantle fast‐axis inferred from SKS splitting. The magnitude and tilt of the model's anisotropy suggests that fine layering and/or aligned cracks augment mineral‐orientation anisotropy near the top and bottom of the crust.
Measurement of charge transfer in sprite‐producing lightning using ELF radio atmospherics
Authors: Cummer S. A. , Inan U. S.
Published: February 2004

Transient high altitude optical emissions referred to as “sprites” are believed to occur as a result of the transfer of large amounts of charge (∼100–300 C) from cloud altitudes of 5–10 km to the ground. Using a general subionospheric ELF propagation model, we quantitatively interpret magnetic field waveforms of ELF radio atmospherics originating in mid‐western U.S. lightning discharges and observed at Stanford (∼1800 km range) to determine the temporal variation of the lightning current and thereby measure the charge transfer during the stroke. For 6 sprite‐producing lightning current waveforms observed on July 24, 1996, we find that 25 to 325 coulombs of charge was transferred during the first 5 ms of the discharges, assuming a 10 km altitude for the initial charge.
Subsidence at The Geysers Geothermal Field, N. California from a comparison of GPS and leveling surveys
Authors: Mossop Antony , Segall Paul
Published: February 2004

Between 1994 and 1996 three GPS surveys were conducted in The Geysers region of northern California. Our aim was to constrain models of the stresses and strains induced by geothermal power production in that region. Each survey spanned The Geysers geothermal field and consisted of typically 40 monuments. These monuments had been previously employed in a series of first order leveling surveys during the 1970's. This earlier study had determined that The Geysers region was subsiding, with a maximum rate of 0.048 ± 0.0055 m/yr between 1973 and 1977. In order to be able to directly compare the leveling and GPS surveys we transform them to the same reference frame using the GEOID 96 geoid model. For the period 1977–1996 we determine a maximum susbsidence rate of 0.047 ± 0.002 m/yr. We then model this subsidence using a series of point sources of contraction and find their optimal configuration by applying the random cost method and the F‐test. The minimum volume strain that we find consistent with this subsidence is approximately 5 × 10−4. Such a strain cannot be explained by a thermoelastic mechanism, but does seem to be consistent with poroelastic deformation and a quasi‐static reservoir bulk modulus, K, of ≤ 3.6 × 109 Pa.
Sensitivity of SS precursors to topography on the upper‐mantle 660‐km discontinuity
Authors: Chaljub Emmanuel , Tarantola Albert
Published: February 2004

The sensitivity of SS precursors to the presence of topography on the 660‐km discontinuity is addressed using an axisymmetric finite difference approximation to the SH wave propagation in the Earth mantle. Numerical experiments are lead to quantify the bias in both wavelength and amplitude committed in estimating depth information on the upper‐mantle discontinuities from ray inversion of SdS arrival times. It is further shown that long period S660S arrival‐times do not provide information on the deepening of the ‘660‧ in presence of a velocity increase expected as the thermal signature of a subducting slab.
MLS observations of ClO and HNO3 in the 1996–97 Arctic Polar Vortex
Authors: Santee M. L. , Manney G. L. , Froidevaux L. , Zurek R. W. , Waters J. W.
Published: February 2004

Microwave Limb Sounder (MLS) measurements of lower stratospheric ClO and gas‐phase HNO3 are presented for the 1996–97 Arctic winter. The horizontal and vertical extent of enhanced ClO were smaller in 1997 than in 1996, as was the degree of enhancement. This is consistent with differences in the evolution and vertical structure of temperatures in the two years. Gas‐phase HNO3 abundances, which increased in early winter due to diabatic descent, exhibited a decreasing trend from mid to late winter in all six Arctic winters observed by MLS, probably due to increasing HNO3 photolysis throughout this period.
HALOE observations of the vertical structure of chemical ozone depletion in the Arctic Vortex during winter and early spring 1996–1997
Authors: Müller Rolf , Grooß Jens‐Uwe , McKenna Daniel S. , Crutzen Paul J. , Brühl Christoph , Russell James M. , Tuck Adrian F.
Published: February 2004

We discuss observations by the Halogen Occultation Experiment on the Upper Atmosphere Research Satellite in the lower stratosphere in the Arctic vortex during winter and spring 1996–1997. Using HF as a chemically conserved tracer, we identify chemical ozone depletion and chlorine activation, despite variations caused by dynamical processes. For the Arctic vortex region, significant chemical ozone loss (up to two thirds around 475 K potential temperature) due to extensive activation of the inorganic chlorine reservoir is deduced, as observed similarly for previous winters. Chemical reductions in column ozone of up to 70–80 Dobson units (DU) in the lower stratosphere are calculated. Both chlorine activation and ozone loss inside the vortex, however, are more variable than observed in previous years.
GCM analysis of local influences on ice core δ signals
Authors: Krinner Gerhard , Genthon Christophe , Jouzel Jean
Published: February 2004

A high resolution GCM is used to examine the effect of changes in local surface climate parameters on the ice sheets that can influence the interpretation of the isotopic signal of the ice from deep cores. The model suggests that the 10°C difference between the LGM surface temperature deduced from borehole thermometry and that deduced from the water isotope analysis to a great extent may be due to a modification of the precipitation seasonality in central Greenland. For central East Antarctica, the model tends to suggest a weak opposite bias.
Breakup of the electron current layer during 3‐D collisionless magnetic reconnection
Authors: Drake J. F. , Biskamp D. , Zeiler A.
Published: February 2004

The structure of the electron current layer which forms in the dissipation region during magnetic reconnection in a collisionless plasma is explored by advancing the 3 ‐ D electron magnetohydrodynamic (EMHD) equations. The current layer thins down below the electron skin depth c/ωpe and then breaks up into a fully turbulent distribution of swirling vortices, The turbulence is sufficiently strong that current is largely shunted into the plane of the magnetic reconnection. The results are consistent with the absense of electron scale current layers in satellite observations of the magnetosphere.
Relation of ongoing deformation rates to the subduction zone process in southern Alaska
Authors: Sauber Jeanne , McClusky Simon , King Robert
Published: February 2004

The rate and orientation of ongoing strain associated with subduction of the Pacific plate and the accretion of the Yakutat terrane to southern Alaska has been estimated at 13 sites from Global Positioning System measurements made in June 1993 and 1995. Along the Gulf of Alaska coast near Cape Yakataga, the average rate of deformation, relative to Fairbanks, was ≈38 mm/yr at N32°W. Further inland, above the region where the dip of the downgoing Pacific plate changes from about 10° to >30°, the deformation rate was ≈12mm/yr at N26°W. In the Sourdough/Paxson area, the deformation rate drops to 2–5 mm/yr and suggests a low short‐term deformation rate across the Denali fault. Elastic straining of the overriding plate due to back‐slip on a main thrust zone with an average dip of about 10° can account for the overall rate and distribution of short‐term compressional strain across south central Alaska. Above the transitional region between unstable and stable sliding we suggest that strain associated with ≈15 mm/yr of right‐lateral strike‐slip occurs also. If the strain accumulated since the two 1899 earthquakes (bothMW=8.1) from the offshore Pamplona fault zone to south of the Border Ranges fault (down‐dip width ≈100 km) was seismically released on a single fault it would correspond to a M=8.1 earthquake.
An impact plume model for atmospheric holes in the FUV dayglow
Authors: Boslough Mark B. E. , Gladstone G. Randall
Published: February 2004

A transient decrease in FUV dayglow emission from a ∼ 10³ km² region of Earth's upper atmosphere is one expected outcome of the collision of a stony meteoroid as small as 50 cm in diameter. Computational models of the entry of projectiles between 210 and 21,000 kg predict the ejection of low‐density plumes of air from the stratosphere and mesosphere at velocities of up to 5 km/s. The plumes reach an altitude of over 1000 km, displacing the atomic O‐rich thermosphere, and replacing it with photoelectron‐ and O‐poor air from beneath 80 km. The FUV dayglow is normally dominated by O emissions so the plume appears as a dark spot when viewed from above. FUV dayglow holes are reported at rates ∼ 104–106 larger than the impact flux of objects in the size range modeled here, suggesting either 1) the observed rate is greatly overestimated, 2) there is an additional mechanism, or 3) much smaller impactors (which we have not modeled) can also generate FUV darkening plumes.
Mapping the outer LLBL with SuperDARN double‐peaked spectra
Authors: Schiffler Andreas , Sofko George , Newell Patrick T. , Greenwald Ray
Published: February 2004

A SuperDARN HF radar pair (Saskatoon‐Kapuskasing) has been used to measure Doppler spectra of backscatter from the dayside F‐layer. Normally the spectra are single‐peaked, but a small fraction exhibit a double‐peaked (D‐P) signature. On the 2D convection maps, these D‐P spectra occur in range cells located poleward of the convection reversal. A comparison with DMSP SSJ/4 particle data measurements and their mapping to magnetospheric boundaries shows that the D‐P spectra are concentrated just equatorward of the magnetopause, in regions of spatially/temporally structured soft electron precipitation (about 300 eV) where the highly variable flux can reach 2–5 ergs/cm²/s. The D‐P spectra are most easily explained in terms of scattering from small‐scale vortices of size less than the radar resolution of 45 km. The D‐P spectral measurements are illustrated by SuperDARN and DMSP data for a dayside event on Feb. 20, 1995, when northward IMF conditions prevailed. We conclude that HF radar D‐P observations can be used to map in real time the dayside 2D ionospheric footprint of the outer LLBL.