bluuebunny/crossref_metadata_2025 huggingface dataset:
On the correlation between tropopause pressure and ozone above central Europe
Authors: Hoinka K. P. , Claude H. , Köhler U.
Published: February 2004

For a period of twenty years the correlation between local readings of total ozone collected above Hohenpeissenberg are correlated with local measurements of the tropopause pressure above Munich. Regionally averaged values of ozone columns provided by TOMS are additionally correlated with tropopause pressure derived from ECMWF analyses. The correlation coefficient between total ozone and tropopause pressure results to 0.48±0.02 (local data) and 0.55±0.02 (regional mean values). A vertical displacement of the tropopause by one kilometre is associated with an ozone anomaly of 13 Dobson units.
New model for ULF Pc5 pulsations: Alfvén cones
Authors: Bellan P. M.
Published: February 2004

It is proposed that nightside auroral Pc 5 signals are inertial Alfvén resonance cones excited by localized field‐aligned current pulses in the distant magnetotail.
Anisotropy of magnetic susceptibility of magnetically oriented rock powders
Authors: Aubourg C. , Bakhtari H. , Rochette P.
Published: February 2004

To estimate the maximum magnetic anisotropy of the ensemble of magnetic carriers present in a rock, we measured the Anisotropy of Magnetic low field Susceptibility (AMS) of magnetically oriented rock powder. We studied basaltic rock (Chaîne des Puys, Massif Central France) and metasediments (Coffs Harbour, Australia). In the basaltic powder, PSD titanomagnetites show maximum anisotropy of L ≈ 1.16. In the metasediments, the foliation anisotropy is constant (F ≈ 1.3) controlled by iron‐bearing phyllosilicates. The linear anisotropy goes up to L ≈ 2 in pyrrhotite bearing rocks. In contrast, magnetite bearing samples show low linear anisotropy (L < 1.1).
Evaluation of sulfate aerosols indirect effect in marine stratocumulus clouds using observation‐derived cloud climatology
Authors: Kogan Zena N. , Kogan Yefim L. , Lilly Douglas K.
Published: February 2004

The indirect shortwave effect of anthropogenic sulfate aerosol augmentation in marine stratocumulus clouds has been evaluated using global cloud climatology, sulfate aerosol data from a chemical model, and cloud albedo augmentation obtained from a large‐eddy simulation (LES) cloud model with explicit microphysics. It is found that the annually and globally (over the oceans) averaged indirect shortwave forcing is −1.1 Wm−2 with a hemispheric difference of 0.4 Wm−2. Given the many uncertainties in the aerosol‐CCN‐cloud microstructure links, this estimate, most likely, should be considered as an upper limit of the aerosol indirect forcing. The hemispheric forcing has a strong seasonal cycle with the Northern Hemisphere (NH) forcing exceeding the Southern Hemisphere (SH) forcing during the NH spring and summer and the SH forcing prevailing during the SH spring and summer. We also estimate that the single layer St/Sc contributes most to the aerosol indirect forcing (60%) with an additional 25% from the St/Sc overlapped with Ci/Cs/Cc, and 15% from St/Sc overlapped with As/Ac.
On the assessment and uncertainty of atmospheric trace gas burden measurements with high resolution infrared solar occultation spectra from space by the ATMOS Experiment
Authors: Abrams M. C. , Chang A. Y. , Gunson M. R. , Abbas M. M. , Goldman A. , Irion F. W. , Michelson H. A. , Newchurch M. J. , Rinsland C. P. , Stiller G. P. , Zander R.
Published: February 2004

The Atmospheric Trace Molecule Spectroscopy (ATMOS) instrument is a high resolution Fourier transform spectrometer that measures atmospheric composition from low Earth orbit with infrared solar occultation sounding in the limb geometry. Following an initial flight in 1985, ATMOS participated in the Atmospheric Laboratory for Applications and Science (ATLAS) 1, 2, and 3 Space Shuttle missions in 1992, 1993, and 1994 yielding a total of 440 occultation measurements over a nine year period. The suite of more than thirty atmospheric trace gases profiled includes CO2, O3, N2O, CH4, H2O, NO, NO2, HNO3, HCl, HF, ClONO2, CCl3F, CCl2F2, CHF2Cl, and N2O5. The analysis method has been revised throughout the mission years culminating in the ‘version 2’ data set. The spectroscopic error analysis is described in the context of supporting the precision estimates reported with the profiles; in addition, systematic uncertainties assessed from the quality of the spectroscopic database are described and tabulated for comparisons with other experiments.
Attenuation of broad‐band (50–1500 Hz) seismic waves in granitic rocks near the Earth’ surface
Authors: Holliger K. , Bühnemann J.
Published: February 2004

We report Q‐estimates from borehole‐to‐tunnel seismic experiments at Nagra's “Grimsel Test Site” (GTS). The probed granitic rocks are cut by brittle faults but do not show any signs of pervasive weathering. Q‐values estimated from P‐wave first arrivals by the spectral ratio and rise time methods range from about 20 to 60 with a median value of 35 and a standard error of 20% or less. The surprisingly low Q‐values inferred indicate that even outside the weathering zone, seismic attenuation in some parts of the uppermost crystalline crust may be very high.
Flux chamber measurements of anomalous CO2 emission from the flanks of Mammoth Mountain, California
Authors: Rahn T. A. , Fessenden J. E. , Wahlen M.
Published: February 2004

The CO2 fluxes involved in the mass mortality of large stands of timber on the flanks of Mammoth Mountain in California's Sierra Nevada were measured and spatial and temporal inhomogeneities observed. Our estimate of the integrated flux over the total area of tree‐kill is on the order of 400 t day−1. Small scale spatial variability most likely reflects varying degrees of shallow bedrock fracture and soil compaction. Temporal variability suggests a fast response to subsurface conditions such as seismically induced crack propagation, degassing of intruded magma, or changing groundwater/soil moisture conditions.
Wintertime stratospheric ozone changes over Japan since 1991
Authors: Zhao Yongjing , Kondo Yutaka
Published: February 2004

Total ozone and ozonesonde data obtained in Sapporo (43°N), Tsukuba (36°N), Kagoshima (32°N), and Naha (26°N) since 1991 were analyzed to study the stratospheric ozone changes over Japan. It was found that sizable total ozone anomalies occurred in the winters of 1992/93 and 1994/95 at the four stations, although the duration and magnitude of the ozone decreases were different between the two periods. Ozone profiles showed increases in ozone concentration above 26 km in the winter of 1991/92 and the most pronounced ozone depletion in the winter of 1992/93 at the four stations. The altitude regions of significant ozone losses in Sapporo, Tsukuba, and Kagoshima in the winter of 1994/95 were higher than those in 1992/93. The latitudinal differences in the degree of ozone losses between 26°N and 43°N since 1991 are presented. The effects of the volcanic aerosol from the Pinatubo eruption and Quasi Biennial Oscillation (QBO) on total ozone are discussed.
Cloud condensation nucleus activity of the organic component of biomass smoke particles
Authors: Novakov T. , Corrigan C. E.
Published: February 2004

Natural and anthropogenic water‐soluble inorganic aerosol species are efficient cloud condensation nuclei (CCN). Biomass smoke particles, although composed mostly of organic material, are also known to be efficient CCN. However, because smoke particles consist of mixtures of organic and inorganic species, it has not been established whether the organic component is intrinsically CCN active or is intrinsically inactive and rendered CCN active only through association with water‐soluble inorganic species. Here we report results of laboratory experiments on smoke particles produced by combustion of eucalyptus, redwood, and cellulose which show that their water‐soluble organic fraction is principally derived from smoldering combustion of the cellulosic fuel content. Because cellulose smoke particles are entirely organic, water soluble, and CCN active (at 0.5% and 0.3% supersaturation), we conclude that the water‐soluble organic species in smoke particles from smoldering biomass combustion are responsible for their intrinsic CCN activity.
On the ability of phase transitions and viscosity layering to induce long wavelength Heterogeneity in the mantle
Authors: Tackley Paul J.
Published: February 2004

The ability of phase transitions and a viscosity jump at 660 km depth to induce long‐wavelength flow in the mantle is systematically investigated using three‐dimensional numerical simulations of internally‐heated convection at convective vigors (as indicated by the Rayleigh number Ra) ranging from mildly supercritical to greater than the Earth's current regime. Cases with neither a viscosity jump nor phase changes display a steadily decreasing wavelength with increasing Ra, as expected. Increasing the lower mantle viscosity by a factor of 30 induces significantly longer wavelengths, but the “reddening” effect decreases with increasing Ra; this is explained in large part by the decrease in effective Rayleigh number due to increasing the lower mantle viscosity. In contrast, the effect of phase transitions is minor at low Ra but increases sharply at geodynamically relevant Ra, potentially increasing the mean wavelength of thermal heterogeneity by factors of greater than 10. Conclusions regarding the relative importance of the two effects are thus highly dependent on Ra.
Monte Carlo modelling of TRM and CRM acquisition and comparison of their properties in an ensemble of interacting SD grains
Authors: Shcherbakov V. P. , Sycheva N. K. , Lamash B. E.
Published: February 2004

Numerical modelling of TRM and of Haigh's model of CRM acquisition was performed using the Monte‐Carlo method. It was confirmed that for noninteracting particles, i.e. at small volume concentration c < 1% CRM < TRM as was predicted earlier by Stacey and Banerjee and at large grain size, ≈ (0.1–0.2) µm, it may reach values ≈ (4–10)‥ However for strongly interacting systems, i.e. c > (l–3)%, CRM may be ≥ TRM, though CRM can not exceed TRM more than twice. The relative stability to thermodemagnetisation is always higher for TRM than for CRM.
Aftershock sequence of the 1994, Mw 6.8, Liwa Earthquake (Indonesia): Seismic Rupture process in a volcanic arc
Authors: Widiwijayanti Christina , Déverchère Jacques , Louat Rémy , Sébrier Michel , Harjono Hery , Diament Michel , Hidayat Dannie
Published: February 2004

We present the aftershock activity following the February 15, 1994, Mw 6.8 earthquake which was strongly felt in southern Sumatra, Indonesia, near the Great Sumatran Fault (GSF). At this place, the slip rate is supposed to be low; neverthless, three M>6 events occurred along this segment during this century. No significant instrumental microseismicity has ever been recorded there. We use data from both the regional Indonesian network and a local seismic array operating 11 days after the mainshock during one month. Aftershocks mostly locate in a broad zone of 55 × 20 km² near two active NW‐trending strike‐slip segments of the GSF separated by a recent caldera, Suwoh. During the experiment, the NW segment (from Suwoh up to 15 km SE of the Ranau lake caldera, an old right‐stepover pull‐apart) was very active. As first suggested by the aftershock distribution and the lack of coseismic rupture at the surface, the 20 focal mechanisms determined provide evidence for various post‐seismic stress adjustments on secondary faults located in the Ranau‐Suwoh paleo‐pull‐apart graben. Less than 20% of the aftershocks are directly linked to the main rupture, a nearly pure right‐lateral strike‐slip faulting reaching 25 km depth. A narrow seismic gap underlines the active volcanic area of Suwoh. We conclude that the rupture process along the GSF is controlled both by volcanism and structures, and that the volcanic activity affects the mechanical properties of the crust only in a narrow zone.
Geodetic inversion for the fault model of the 1994 Shikotan Earthquake
Authors: Ozawa Shinzaburo
Published: February 2004

The fault parameters of the 1994 Shikotan earthquake were determined by inverting all available geodetic data using an iterative linearized least‐squares method. A one‐fault inversion shows that a shallow‐dip fault‐plane model does not reproduce the minor deformation observed on Shikotan island, while a steep‐dip model can fit all the data well. Multifault inversion shows that a fault‐plane divided into two subfaults lengthwise is the best fitting model based on Akaike's Information Criteria [AIC] for shallow‐dip faulting mechanism. This model yields a very high stress drop, 40 MPa, on the deeper subfault. For a steep‐dip model, a fault plane divided into two subfaults sideways gives the minimum AIC. All the computations for models consisting of two to eight subfaults show that the chi‐square values of the shallow‐dip models are about 10% higher than those of the steep‐dip models. Considering the high stress drop, the larger chi‐square value, and the requirements of a complex subfault system for the shallow‐dip model, we reach the conclusion that the steep‐dip model is more suitable to explain the geodetic observations.
Resolution of the Scripps/NOAA Marine Gravity Field from satellite altimetry
Authors: Marks Karen M.
Published: February 2004

The July 1995 declassification of the entire Geosat GM satellite altimeter data set enabled a joint Scripps/NOAA effort to compute a new (version 7.2) marine gravity field on a 2‐minute grid. This gravity field covers the world' oceans between 72°N and 72°S, and is derived from a combination of ERS‐1 and Geosat GM and ERM data. An earlier NOAA Geosat‐only gravity field solution was confined to the southern latitudes because the 1992 declassification was limited to GM data south of 30°S. A simple coherence analysis between accurately‐navigated ship gravity profiles and comparable gravity profiles obtained from the gravity grids reveals that the Scripps/NOAA gravity field is coherent with ship gravity down to ∼≥ 23–30 km. This slight increase in resolution over the previous NOAA Geosat‐only gravity field (short‐wavelength resolution of ∼26–30 km) implies that the increased spatial coverage provided by the ERS‐I altimeter, when combined with Geosat, improves the solution. Coherence analyses between satellite gravity and ship topography, and ship gravity and ship topography, show that even shorter wavelength gravity anomalies (∼13 km) are present in sea‐surface measurements made by ship. Even so, the Scripps/NOAA marine gravity field does an excellent job of resolving most of the short‐wavelength gravity anomalies covering the world’ oceans.
Gravity anomalies of the Mid‐Atlantic Ridge north of the Kane Fracture Zone
Authors: Fujimoto H. , Seama N. , Lin J. , Matsumoto T. , Tanaka T. , Fujioka K.
Published: February 2004

High‐resolution gravity and multibeam bathymetric data were newly obtained from the Mid‐Atlantic Ridge (MAR) between latitudes 23°30′N and 28°N. Mantle Bouguer anomalies (MBA) show magmatic accretion focused at discrete centers along the spreading axis except near the oblique portion of the MAR between 24°30′–24°50′N. The MBA also indicates that crustal production near the TAG hydrothermal field has been relatively low during the last 2–3 My. The MBA show 120°‐striking off‐axis traces, indicating northward migration of the oblique portion and northward extension of the segments south of the oblique zone despite a long‐wavelength southward deepening of the axial topography. Observed gravity anomalies support a tectonic interpretation proposed from morphology and geomagnetic anomalies that the segment south of the oblique zone has extended northward by repeatedly adding short segments which migrated westward through asymmetric spreading in the oblique zone.
Evolution of plasmaspheric ions at geosynchronous orbit during times of high geomagnetic activity
Authors: Elphic R. C. , Weiss L. A. , Thomsen M. F. , McComas D. J. , Moldwin M. B.
Published: February 2004

The evolution of the plasmasphere, the region of relatively dense cold plasma surrounding the Earth, is strongly dependent on magnetospheric activity. Here we report on plasmaspheric evolution as observed at geosynchronous orbit in association with magnetopause crossings and storm sudden commencements (SSCs). The occurrence frequency distributions at geosynchronous orbit of both magnetopause‐associated and SSC‐associated plasmaspheric ions is peaked near 1400 LT, with an overall range from 1000 LT to beyond 1800 LT. This is greatly skewed from the average plasmaspheric distribution at 6.6 RE, which peaks closer to 1800 LT. The evolution of SSC‐associated plasmaspheric ions is tracked using a superposed epoch analysis: lower‐activity SSCs produce minor changes from the pre‐SSC local time distribution; after geomagnetically‐effective SSCs, the ions appear almost immediately at earlier local times, spanning the late morning to dusk local time sector for hours. These observations are consistent with (1) a push of plasmaspheric material inward over the spacecraft due to magnetospheric compression and (2) the prompt penetration of a convection electric field.
Ice core data of atmospheric carbon monoxide over Antarctica and Greenland during the last 200 years
Authors: Haan D. , Martinerie P. , Raynaud D.
Published: February 2004

The first polar ice core measurements of carbon monoxide compatible with atmospheric data were obtained using an improved experimental protocol. A new CO extraction method has been developed with special care to eliminate any CO contamination. The procedure has been applied to ice core samples originating from Antarctica and Greenland in order to reconstruct past CO variations over the last 200 years. Consistent results in terms of atmospheric concentrations are obtained. We find that CO concentration started to increase over Greenland around 1850 and that, by contrast, CO levels at high southern latitudes remained fairly constant between 1860 and 1916. Based on available data on past CO sources, a scenario is proposed for the CO increase observed in Greenland. In addition, our Greenland CO results suggest that simulations of preindustrial CO distribution could have underestimated CO concentrations mainly in the northern hemisphere leading to an overestimate of the change since preindustrial times, and to an underestimate of the past interhemispheric gradient of carbon monoxide.
Lagrangian measurement of subsurface poleward flow between 38°N and 43°N along the West Coast of the United States during summer, 1993
Authors: Collins Curtis A. , Garfield Newell , Paquette Robert G. , Carter Everett
Published: February 2004

Subsurface Lagrangian measurements at about 140 m showed that the path of the California Undercurrent lay next to the continental slope between San Francisco (37.8°N) and St. George Reef (41.8°N) during mid‐summer 1993. The mean speed along this 500 km path was 8 cms−1. The flow at this depth was not disturbed by upwelling centers at Point Reyes or Cape Mendocino. Results also demonstrate the ability to acoustically track floats located well above the sound channel axis along the California coast.
The measurement of tropospheric OH radicals by laser‐induced fluorescence spectroscopy during the POPCORN Field Campaign
Authors: Hofzumahaus A. , Aschmutat U. , Heßling M. , Holland F. , Ehhalt D. H.
Published: February 2004

A highly sensitive OH measurement instrument has been developed. It is based on laser‐induced fluorescence (LIF) detection of OH using the A²Σ+v′ = 0‐X²Π v″ = 0 transition at 308.15 nm at low pressure. The LIF instrument detects OH directly and with high specificity, a fact that was demonstrated by recording laser excitation spectra (Q1(3), Q21(3) and P1(1) lines) of ambient OH. For high time resolution (typ. 60–100 s), the laser wavelength was modulated on‐/off‐ resonance with the P1(1) line. Here, we report some of the OH measurements obtained by this technique during its first application in a tropospheric field campaign (“POPCORN”), which was conducted in August 1994 in a rural environment in the North‐East of Germany. These include diurnal OH concentration profiles with maximum OH concentrations up to 1.4×107cm−3at noon. Minimum OH concentrations were measured in the morning and evening down to the detection limit of (3–6) × 105cm−3(SNR=2, measurement time 1 min.). During the day, OH fluctuations were observed on a time scale of minutes and hours. These were highly correlated to the flux of the solar UV radiation which is responsible for the primary OH production by photolysis.
A three‐dimensional view of the stratosphere‐to‐troposphere exchange in the GFDL SKYHI Model
Authors: Eluszkiewicz Janusz
Published: February 2004

A three‐dimensional perspective on the stratosphere‐to‐troposphere exchange is provided by trajectory calculations based on winds from the GFDL SKYHI general circulation model. For particles initialized at the 350 K isentropic surface, the exchange is initially (for up to 30 days) more vigorous in the summer hemisphere, in agreement with the isentropic results of Chen [1995]. However, on longer time scales the relative importance of the exchange in the winter hemisphere increases, as particles in that hemisphere descend more rapidly towards the extratropical tropopause. These results illustrate the importance of cross‐isentropic transport for the stratosphere‐to‐troposphere exchange on seasonal time scales.
Joint distributions of potential vorticity and inert trace constituent in CCM2 and UW θ‐σ model simulations
Authors: Zapotocny Tom H. , Lenzen Allen J. , Johnson Donald R. , Reames Fred M. , Politowicz Philip A. , Schaack Todd K.
Published: February 2004

This letter describes an experiment that examines the ability of the University of Wisconsin (UW) hybrid isentropic‐sigma (θ‐σ) and sigma (σ) coordinate models and the NCAR Community Climate Model 2 (CCM2) to transport and conserve the joint distributions of isentropic potential vorticity (Pθ) and a source‐free inert trace constituent related to the initial distribution of Pθ called proxy ozone (O3), during 10‐day isentropic integrations. Under the idealized conditions of this experiment, the governing equations for the atmospheric continuum require that the initial joint distribution of Pθ and O3 be conserved, thereby establishing a test of model accuracy from statistical comparisons of paired values of O3 and Pθ. Any decrease in the initial correlation of unity of Pθ and O3 after integration is an objective measure of a model's skill. Results show that correlation coefficients for the UW θ‐σ model remain higher than those from CCM2 and the UW σ model, demonstrating an inherent advantage in the simulation of trace constituent transport relative to dynamical processes in isentropic versus sigma coordinate models.
Evidence of secular changes in rainfall data from the tropical western and central Pacific Over a 20‐year period
Authors: Maliekal Jose A. , Petroski Thomas J.
Published: February 2004

Rainfall data from the tropical western and central Pacific over the period from 1971 to 1990 show both decadal and interannual variability. A statistically significant secular trend may be used to model the overall rainfall variability. However, locally weighted regression analysis reveals that this increasing trend stalls in the early 1980's, and reverses its course by the year 1990. Decomposition of individual rainfall time series into low frequency, seasonal, and irregular components facilitates the isolation of the time varying annual cycle and the elucidation of the interannual signal. Strong or prolonged warm El Niño‐Southern Oscillation events dominate the interannual variability during the study period. The decadal scale variation in the annual cycle is so systematic, in fact, there is approximately a 20% reduction in its amplitude between 1971 and 1982. In addition, the long‐term change in the seasonal component appears to modulate the much shorter‐term interannual signal.
Water vapor and cloud feedback over the tropical oceans: Can we use ENSO as a surrogate for climate change?
Authors: Lau K.‐M. , Ho C.‐H. , Chou M.‐D.
Published: February 2004

Based on experiments with the Goddard Earth Observing System (GEOS) global climate model, we find that the basic patterns of anomalous water vapor greenhouse effect and cloud radiative forcing during ENSO are primarily determined by the basin‐wide dynamical response to large scale sea surface temperature (SST) forcing. There is no supergreenhouse effect in the sense of unstable interaction due to local thermodynamics and water vapor radiative feedback on interannual time scales. About 80% of the clear sky water vapor greenhouse sensitivity to SST deduced from ENSO anomalies are due to the transport of water vapor by the large scale circulation. The sensitivity of water vapor greenhouse effect to SST due to radiative feedback is found to be about 1.8 Wm−2/°C, much smaller than the values of 6–9 Wm−2/°C previously estimated from satellite observations from ENSO conditions. Our results show that regionally based interannual variability should not be used to infer radiative feedback sensitivity for climate change unless proper corrections are made for the effect of the large scale circulation.
A new model for the emplacement of Columbia River basalts as large, inflated Pahoehoe Lava Flow Fields
Authors: Self S. , Thordarson Th. , Keszthelyi L. , Walker G. P. L. , Hon K. , Murphy M. T. , Long P. , Finnemore S.
Published: February 2004

Extensive flows of the Columbia River Basalt (CRB) Group in Washington, Oregon, and Idaho are dominantly inflated compound pahoehoe sheet lavas. Early studies recognized that CRB lavas are compound pahoehoe flows, with textures suggesting low flow velocities, but it was thought that the great thickness and extent of the major flows required very rapid emplacement as turbulent floods of lava over a period of days or weeks. However, small volume (< 1 km³) compound pahoehoe flows on Kilauea, Hawai'i, demonstrate that such flows can thicken by at least an order of magnitude through gradual inflation and the same mechanism has been proposed for larger (10–20 km3) pahoehoe flows in Iceland. The vertical distribution of vesicles and other morphologic features within CRB lava flows indicate that they grew similarly by inflation. Small pahoehoe lobes at the base and top of many CRB pahoehoe lava flows indicate emplacement in a gradual, piecemeal manner rather than as a single flood. We propose that each thick CRB sheet flow was active for months to years and that each group of flows produced by a single eruption (a flow field) was emplaced slowly over many years.
Climate forcing by stratospheric ozone depletion calculated from observed temperature trends
Authors: Zhong Wenyi , Toumi Ralf , Haigh Joanna D.
Published: February 2004

The radiative forcing of the surface‐troposphere system caused by stratospheric ozone depletion in the 1980s is calculated using observed values of change in ozone, from TOMS data, and temperature, from MSU data. The seasonal variation of the ozone and temperature trends produces strong seasonal and latitudinal variations in radiative forcing. The balance between peak positive solar forcing and maximum negative longwave forcing shifts the peak negative forcing at the South Pole from November to October. The time difference between peak ozone loss and maximum temperature decrease results in net positive values in Southern Hemisphere mid‐latitudes in August and September. Positive values also occur at low latitudes in both hemispheres. The globally and annually averaged net radiative forcing is about −0.025Wm−2 between 1979 and 1990, much less than that previously reported using fixed dynamical heating model temperature changes, although inclusion of the ozone 14 µm band would somewhat narrow this gap. Ozone radiative forcing is very sensitive to the vertical profile of temperature change.
Polar vortex conditions during the 1995–96 Arctic Winter: MLS CLO and HNO3
Authors: Santee M. L. , Manney G. L. , Read W. G. , Froidevaux L. , Waters J. W.
Published: February 2004

Microwave Limb Sounder (MLS) measurements of lower stratospheric ClO and HNO3 during the 1995–96 Arctic winter are presented. The 1995–96 Arctic winter was both colder and more persistently cold than usual, leading to an enhancement in lower stratospheric ClO of greater magnitude, vertical extent, and duration than previously observed in the Arctic. Vortex concentrations of HNO3 in mid‐December were large due to diabatic descent. Trajectory calculations indicate that localized severe depletions of gas‐phase HNO3 in mid‐February and early March did not arise from entrainment of midlatitude air into the vortex and were therefore probably related to polar stratospheric cloud (PSC) formation. A strong correlation between temperature and gas‐phase HNO3 was evident, consistent with recurring PSC condensation and evaporation cycles.
HNO3/NOx ratio in the remote troposphere During MLOPEX 2: Evidence for nitric acid reduction on carbonaceous aerosols?
Authors: Hauglustaine D. A. , Ridley B. A. , Solomon S. , Hess P. G. , Madronich S.
Published: February 2004

The [HNO3]/[NOx] ratio is generally overestimated by a factor of 5–10 in photochemical models in comparison to tropospheric measurements. In this study, the heterogeneous reduction of HNO3 into NO on carbonaceous aerosols [Lary et al., 1996] has been introduced in a photochemical box‐model on the basis of black carbon mass densities measured during MLOPEX 2. This recycling to NOx decreases the [HNO3]/[NOx] ratio close to observed values. The concomitant increase in modeled NOx concentration is also in better agreement with the observations, and has substantial implications for the ozone budget in the remote atmosphere. Large uncertainties in the estimate of black carbon surface area and of accomodation coefficients preclude definitive conclusions until more detailed measurements are carried out.
Determination of H2O2 and organic peroxides in cloud‐and rain‐water on the Kleiner Feldberg during FELDEX
Authors: Sauer F. , Schuster G. , Schäfer C. , Moortgat G. K.
Published: February 2004

This letter reports high‐pressure liquid chromatography (HPLC) measurements of H2O2 and organic hydroperoxides in cloud‐ and rain‐water. Observations were conducted on the Kleiner Feldberg (Germany) from late October to late November 1995, within the FELDEX‐campaign. It was the first campaign ever in which organic peroxides were determined in cloud‐water. H2O2 was found with concentrations of <0.008–3.19 µmol · 1−1. Hydroxymethyl hydroperoxide (HOCH2OOH, HMHP) and 1‐hydroxyethyl hydroperoxide (CH3CH(OH)OOH, 1‐HEHP) were observed with concentrations in the range of <0.008–1.0 µmol · 1−1 (HMHP) and <0.008–0.28 µmol · 1−1 (1‐HEHP). The ratio of the sum of organic peroxides over the total amount of peroxides (H2O2+organic peroxides) was 0–81%. The concentrations of S(IV) and H2O2 in the samples were anticorrelated. The results indicate that organic peroxides, such as HMHP and 1‐HEHP, should be included into modelling studies of the aqueous phase oxidation of S(IV).
Initial rupture of earthquakes in the 1995 Ridgecrest, California Sequence
Authors: Mori Jim , Kanamori Hiroo
Published: February 2004

Close examination of the P waves from earthquakes ranging in size across several orders of magnitude shows that the shape of the initiation of the velocity waveforms is independent of the magnitude of the earthquake. A model in which earthquakes of all sizes have similar rupture initiation can explain the data. This suggests that it is difficult to estimate the eventual size of an earthquake from the initial portion of the waveform. Previously reported curvature seen in the beginning of some velocity waveforms can be largely explained as the effect of anelastic attenuation; thus there is little evidence for a departure from models of simple rupture initiation that grow dynamically from a small region. The results of this study indicate that any “precursory” radiation at seismic frequencies must emanate from a source region no larger than the equivalent of a M0.5 event (i.e. a characteristic length of ∼10 m). The size of the nucleation region for magnitude 0 to 5 earthquakes thus is not resolvable with the standard seismic instrumentation deployed in California.
Interseismic horizontal deformation in northern Honshu and its relationship with the subduction of the Pacific Plate in the Japan Trench
Authors: Shen‐Tu Bingming , Holt William E.
Published: February 2004

We investigate the origin of the geodetically observed interseismic horizontal deformation in northern Honshu by comparing shear strain rates, principal strain rates, and velocity fields determined from geodetic data with those calculated from the elastic dislocation models involving interplate motion at the Japan trench. The agreement between the observed and predicted directions of the principal strain axes indicates that the geodetic strain field in northern Honshu is primarily elastic strain transmitted from the Japan trench. In order to match the strain rate tensors and velocity magnitudes obtained from the geodetic data, the dislocation model requires that 35% to 60% of the NUVEL1‐A Pacific‐North American plate motion is locked at the plate interface along the Japan trench. The down‐dip depth limit of the locked zone is inferred to be 55 km, which is consistent with the seismic data in the Japan trench.
UV absorption spectra of H2O/HNO3 films
Authors: Berland B. S. , Foster K. L. , Tolbert M. A. , George S. M.
Published: February 2004

The ultraviolet (UV) absorption spectra were measured for amorphous and crystalline H2O/HNO3 films representative of polar stratospheric clouds (PSCs). Film compositions were determined using laser induced thermal desorption (LITD). Pure HNO3 films showed a broad absorption peak with a maximum absorbance at λ ≈ 195 nm. The absorbances of amorphous H2O/HNO3 films were also broad and peaked at λ=196–198 nm. The absorption cross sections increased slightly for more dilute films, although the band shape was nearly independent of the H2O content This increase in cross section was consistent with a change in the absorbing species from molecular HNO3 to ionic NO3−. The major absorbing species in crystalline NAT, NAD, and NAM is also NO3− and these films all had very similar UV absorption spectra. Their absorption peaks were all at λ ≈ 200 nm and the band shapes were nearly identical.
Transmittance of a cloud is wavelength‐dependent in the UV‐range
Authors: Seckmeyer G. , Erb R. , Albold A.
Published: February 2004

Spectral irradiance measured at two stations at different altitudes (the Zugspitze‐summit at 2964 m a.s.l. and the Fraunhofer‐Institute for Atmospheric Environmental Research at 730 m a.s.l., 8 km apart in horizontal direction) was used to examine the spectral attenuation of the UV‐irradiance by a homogeneous cloud‐layer at an altitude of about 1200 m. Calculating the ratio of the global spectral irradiance beneath a homogenous cloud‐cover (22 October, 1995) to the global spectral irradiance on a cloudless day (24 October, 1995) both measured at the valley station, delivered the spectral transmittance of the cloud. By means of data measured on the Zugspitze on the same two days possible differences in the atmospheric conditions above 2964 m were eliminated and thus the influence of the cloud on the UV‐irradiance at Garmisch‐Partenkirchen was separated. The transmittance of the cloud‐layer was found to be wavelength‐dependent, ranging from 45% in the UVA to 60% in the UVB. Therefore it can be assumed that clouds are not generally “grey” (i.e. that the attenuation is dependent on wavelength).
A historical record of ammonium concentrations from a glacier in the Alps
Authors: Döscher A. , Gäggeler H. W. , Schotterer U. , Schwikowski M.
Published: February 2004

Ammonia is the primary gaseous alkaline species in the atmosphere over Europe, neutralising up to 70% of the original acidity in precipitation [Buijsman et al., 1987]. It is directly involved in the conversion of sulphur dioxide and nitrogen oxides into the aerosol phase. Furthermore, ammonium contributes considerably to the nitrogen deposition and soil acidification which causes extensive changes in plant communities in many ecosystems [Moore, 1995; Rohde et al., 1995]. However, in Europe continuous long‐term measurements of atmospheric ammonia or ammonium in precipitation are lacking. Here, we present a continuous, high‐resolution record of ammonium in precipitation for the time period 1780 to 1980 deduced from an ice core recovered from a high‐altitude glacier in the Alps. The ammonium level remained constant from 1780 to 1870 and increased afterwards by a factor of three. This trend shows that ammonia emissions in Europe have substantially increased in the last 100 years.
The effect of spatial variations in unresolved topography on gravity wave drag in the Martian atmosphere
Authors: Joshi M. M. , Lawrence B. N. , Lewis S. R.
Published: February 2004

Recent three dimensional simulations of the Martian atmosphere have shown that gravity wave drag is a large, and possibly dominant, term in the momentum balance above 50 km. In previous simulations, a constant value was used for the topographic variance on scales smaller than the model grid. Spatial variations in this quantity are now taken into account, and the results described. The topographic variance has its highest amplitude in the Tharsis and Hellas regions. Correspondingly, relatively low breaking levels are found here. Longitudinal variations in breaking levels and hence accelerations are very large, as are zonal asymmetries in zonal wind u. These asymmetries are expected to play a role in planetary wave propagation in the Martian middle atmosphere. Momentum balances are found to be dependent on nonlinear coupling terms in the momentum equations due to the high zonal winds and small planetary radius. At the equinoxes two regimes exist. One is where breaking levels are very low: here accelerations and eddy diffusion coefficients resulting from the parameterization of gravity wave breaking in the model are also very low. The other regime is where breaking levels are higher, and winds are stronger. In this region, vertical mixing is also very weak. These results give further credence to the idea that breaking thermal tides cause the intense vertical diffusion that has been inferred from observations at the Martian equinox.
Dayside moving auroral transients related to LLBL dynamics
Authors: Moen J. , Evans D. , Carlson H. C. , Lockwood M.
Published: February 2004

The NOAA‐12 satellite skimmed through a region of dayside auroral activity over Svalbard on January 12, 1992. A sequence of auroral forms from two separated onset sites in the postnoon sector drifted westward towards magnetic noon. The auroral forms were associated with a population of injected magnetosheath plasma mixed with a secondary component of magnetospheric ions (>30 keV) that is a key signature of the low‐latitude boundary layer (LLBL). The direction of motion of the cleft auroral forms and the basic features of the NOAA particle spectrograms indicate that the transients are related to LLBL on open field lines. The auroral transients are consistent with footprints of reconnection at the dayside magnetopause which is both patchy in space and sporadic in time.
Proton temperature anisotropy in the magnetosheath: Hybrid simulations
Authors: Gary S. Peter , McKean Michael E. , Winske Dan
Published: February 2004

Scattering by enhanced fluctuations from the electromagnetic proton cyclotron instability imposes an upper bound on the proton temperature anisotropy of the form T⟂p/T∥p −1 = Sp/β∥pαp. Here β∥p is the proton β based on T∥p and the directional subscripts indicate directions perpendicular and parallel to the background magnetic field. This paper describes the analysis of the proton temperature anisotropy in two‐dimensional hybrid simulations of quasi‐perpendicular shocks and their associated magnetosheaths. Three simulations are considered: at low, intermediate, and high upstream Mach numbers. Considering results from well downstream of all three shocks as one data set, an upper bound on the proton temperature anisotropy fits the above equation with αp=0.5. This compares favorably to αp values from other simulations and from sheath observations.
Low‐temperature fluid flow through sulfidic sediments from TAG: Modification of fluid chemistry and alteration of mineral deposits
Authors: Mills Rachel A. , Clayton Trevor , Alt Jeffrey C.
Published: February 2004

Low‐temperature fluid flow has been identified as an important component of the heat, mass and chemical flux at sites of active venting. One way to study the movement of water through hydrothermal deposits is to analyse the pore‐fluids extracted from sulfidic sediments. The composition of diffuse flow fluids in one sediment core from the south of the active TAG mound reflects the dilution of high‐temperature, black smoker fluids, with modification inside the mound during ongoing circulation. Fluid modification includes conductive cooling, removal of Si from solution and entrainment and removal of U from seawater which can represent significant sinks of these elements. Precipitation of clay minerals and Fe‐oxides is currently occurring within this sediment core generating ochreous type material subsurface. Extensive low‐temperature alteration of basaltic material at the core‐top is apparent in conjunction with supergene enrichment of Cu and Mn.
Factors controlling the variances of seismic velocity, density, thermal conductivity and heat production of cores from the KTB Pilot Hole
Authors: Huenges Ernst
Published: February 2004

This paper presents a statistical analysis of about 50000 petrophysical data measured on core samples from the Continental Deep Drilling Project (KTB) of the Federal Republic of Germany. The scattering of the data must be taken into consideration using empirical relationships between pairs of parameters, e.g., sound velocity, density, heat production and thermal conductivity. Such covariances of parameters were calculated and used to find the principle components by applying factor analysis. The reduction of parameters by factor analysis may help other scientists to concentrate on the essential parameters to be measured. About 50% of the variance of all data can be explained by one background variable, the so‐called “lithology factor”. The variables that load a factor are either highly correlated or anticorrelated. The lithology factor combines gamma spectroscopy data, density and the mineral contents of quartz, amphibole, garnet and white mica. Seismic velocities and porosity data, however, were less well related to the lithology factor. Therefore, the KTB data indicate that correlation between seismic velocity and one of the lithology factor loading variables is unlikely. The lithology factor distinguishes 3 major “rock types”: metabasites, gneisses and an intermediate type. The variance of the petrophysical parameters within the rock types, plotted in crossplots, show the level of validity of commonly used relationships among these parameters. Measurements under ambient and simulated in‐situ conditions are included to enable discussion of chemical, mineralogical and microstructural characteristics of the rocks.
High heat flow in the trans‐Hudson Orogen, Central Canadian Shield
Authors: Guillou‐Frottier L. , Jaupart C. , Mareschal J. C. , Gariépy C. , Bienfait G. , Cheng L. Z. , Lapointe R.
Published: February 2004

Nine new heat flow and heat production measurements are presented for the Trans‐Hudson Orogen, an Early Proterozoic Province between the Archean Superior and Hearne Provinces of the Canadian Shield. Seventeen heat flow values now available in this region range between 23 and 81 mW.m−2. The highest value is anomalous and is due to heat refraction effects in and around highly conducting quartzite formations. When refraction effects are accounted for, the Flin Flon and Thompson belts appear as distinct crustal blocks with different mean heat flow values of 42±3(s.d.) mW.m−2 and 54±8(s.d.) mW.m−2. Such differences can be accounted for by variations in the amount of felsic rocks in the uppermost 15 km of the crust. Comparison between heat flow and elastic thickness studies show that variations in elastic thickness of the lithosphere are not thermally induced.
Production pattern of alkenones in the Mediterranean Sea
Authors: Ternois Yann , Sicre Marie‐Alexandrine , Boireau Anne , Marty Jean‐Claude , Miquel Juan‐Carlos
Published: February 2004

Time‐series of downward alkenone fluxes have been investigated at 200 m depth over a one year sediment trap experiment, in the Northwestern Mediterranean Sea. Alkenone flux maxima occurred in autumn and to a lesser extent in May, during the spring bloom. Temperature estimates calculated from the UK′37 index revealed that alkenone producers preferentially develop in subsurface waters (at about 50 m) in spring, whereas the autumn alkenone production occurred upper in the water column (around 30 m). Examination of the core‐top UK′37 index values at various sites of the Northwestern Mediterranean basin, suggested that the spring bloom period do not significantly imprint the temperatures recorded in the sediments. The sedimentary temperature estimates would rather reflect annually integrated SST, with a major influence of the autumnal post‐bloom development of the coccolithophores in the euphotic zone.
On the cause of 1/f‐power spectral scaling in borehole sonic logs
Authors: Bean Christopher J.
Published: February 2004

Borehole logs provide in situ information about the scaling of fluctuations in the elastic properties of rock. A surprising finding has been the widespread 1/fβ‐type (0.5 < β < 1.5) scaling of borehole sonic log power spectra, yielding no clear correlation with geological age, type or history, raising questions about the reliability and origin of these findings. Ubiquitous fractures, for example, have been evoked as the most likely explanation of these results. Firstly, we show that the smoothing effects of the logging tool must be taken into account in order to obtain reliable values of β. We then investigate the scaling properties of lithology only in perfectly exposed metamorphic rock, by explicitly excluding fractures. We find clear 1/f scaling for reconstructed velocity data based solely on lithological variations. Although fractures are certainly important in contributing to 1/f fluctuations in borehole logs, intrinsic geology may also play a significant role.
The impact of solar radiation on the Quasi‐Biennial Oscillation of ozone in the tropical stratosphere
Authors: Huang Theresa Y. W.
Published: February 2004

The feedback of the radiative forcing caused by the ozone QBO in the tropics on the ozone variation itself is examined with a 2‐D model. Simulations show that the effect of the QBO in solar heating on the ozone and meridional circulation oscillations are negligible, which contradicts the proposal of Hasebe (1994). The impact of the ozone variation on the photolysis QBO is also presented and is shown to be important. Its overall effect is to damp the amplitude of ozone oscillation through its modulation of the oxygen photolysis rate.
Modeling and inverse Q imaging of ground penetrating radar waves in 1 and 2d
Authors: Bano Maksim
Published: February 2004

As in the case of seismic attenuation, dielectric loss or radar attenuation may be related to the quality factor Q which is given by the ratio of the real to imaginary parts of effective (or total) dielectric permittivity. The frequency dependence of both parts of the effective permittivity would imply the broadening (absorption) and distortion (dispersion) of the radar pulse when it travels into the earth, so the radar pulse is not stationary. Therefore the classical deconvolution and migration methods, used currently in seismic processing, do not always work well in the case of GPR data. In order to compensate for radar attenuation (absorption and dispersion) two methods (in ID and 2D) are proposed. These methods are based on the weighted downward extrapolation of the electric field in the frequency domain. The results are tested and illustrated using synthetic and real radargrams in 1 and 2D.