bluuebunny/crossref_metadata_2025 huggingface dataset:
Statistical analysis of thorium and fast neutron data at the lunar surface
Authors: Gasnault O. , Feldman W. C. , d'Uston C. , Lawrence D. J. , Maurice S. , Chevrel S. D. , Pinet P. C. , Elphic R. C. , Genetay I. , Moore K. R.
Published: October 2003

A comparison is conducted between the remotely sensed abundances of thorium (through gamma‐ray spectroscopy) and major chemical elements (through fast neutron spectroscopy) on the lunar surface. These are key elements in the investigation of lunar evolution. Correlations of variations of thorium abundance and fast neutron flux are analyzed on a spatial scale of 180 km through the construction of a covariance map. This technique is an unbiased mathematical method for developing the borders of major formations such as the Procellarum KREEP Terrane. Although thorium variations are positively correlated with those of the fast neutron flux over most of the lunar nearside, several locations within the Procellarum KREEP Terrane have negative correlations. This anticorrelation may denote an emplacement for these materials by transport of impact ejecta. Furthermore, analysis of these data reveals the presence of a distinctive structure in the northwest corner of Oceanus Procellarum marked by a ring of enhanced thorium. This structure may be related to an ancient impact basin. The confirmation of such a ring of thorium around the major basins inside Procellarum KREEP Terrane would reinforce the hypothesis of the redistribution of thorium during impact from shallow depth.
Enhanced productivity led to increased organic carbon burial in the euxinic North Atlantic basin during the late Cenomanian oceanic anoxic event
Authors: Kuypers Marcel M. M. , Pancost Richard D. , Nijenhuis Ivar A. , Sinninghe Damsté Jaap S.
Published: October 2003

Three Cenomanian/Turonian (C/T, ∼93.5 Ma) black shale sections along a northeast‐southwest transect in the southern part of the proto‐North Atlantic Ocean were correlated by stable carbon isotope stratigraphy using the characteristic excursion in δ13C values of both bulk organic matter (OM) and molecular fossils of algal chlorophyll and steroids. All three sites show an increase in marine organic carbon (OC) accumulation rates during the C/T Oceanic Anoxic Event (OAE). The occurrence of molecular fossils of anoxygenic photosynthetic green sulfur bacteria, lack of bioturbation, and high abundance of redox sensitive trace metals indicate sulfidic conditions, periodically reaching up into the photic zone before as well as during the C/T OAE. During the C/T OAE, there was a significant rise of the chemocline as indicated by the increase in concentrations of molecular fossils of green sulfur bacteria and Mo/Al ratios. The presence of molecular fossils of the green strain of green sulfur bacteria indicates that euxinic conditions periodically even occurred at very shallow water depths of 15 m or less during the C/T OAE. However, bottom water conditions did not dramatically change as indicated by more or less constant V/Al and Zn/Al ratios at site 367. This suggests that the increase in OC burial rates resulted from enhanced primary productivity rather than increased anoxia, which is supported by stable carbon isotopic evidence and a large increase in Ba/Al ratios during the C/T OAE. The occurrence of the productivity event during a period of globally enhanced organic carbon burial rates (i.e., the C/T OAE) points to a common cause possibly related to the formation of a deep water connection between North and South Atlantic basins.
Isotope study of moisture sources, recharge areas, and groundwater flow paths within the eastern Batinah coastal plain, Sultanate of Oman
Authors: Weyhenmeyer Constanze E. , Burns Stephen J. , Waber H. Niklaus , Macumber Phil G. , Matter Albert
Published: October 2003

Oxygen and hydrogen isotope analyses of rainfall samples collected on the eastern Batinah coastal plain of northern Oman between 1995 and 1998 indicate two different principal water vapor sources for precipitation in the area: a northern, Mediterranean source and a southern, Indian Ocean source. As a result, two new local meteoric water lines were defined for the study area. Isotopic analyses of groundwater samples from over 200 springs and wells indicate that the main source of water to the Batinah coastal alluvial aquifer is high‐altitude rainfall from the adjacent Jabal Akhdar Mountains, originating from a combination of northern and southern moisture sources. The groundwater recharged at high‐altitude forms two plumes of water which is depleted in the heavy isotopes 18O and 2H and stretches from the mountains across the coastal plain to the sea, thereby retaining a chemical homogeneity horizontally and vertically down to a depth exceeding 300 m. In contrast, in areas adjacent to these two plumes the alluvial aquifer is geochemically stratified. Near the coast, saline intrusion results in abrupt changes in chloride concentrations and isotope values.
Methane efflux from boreal wetlands: Theory and testing of the ecosystem model Ecosys with chamber and tower flux measurements
Authors: Grant R. F. , Roulet N. T.
Published: October 2003

A robust model of CH4 emission from terrestrial ecosystems should be capable of simulating the temporal and spatial variability that characterizes field measurements. Such a model should couple a biologically based treatment of microbial CH4 transformations with a physically based treatment of heat, solute, and gas transfer vertically and laterally through soils. These processes are coupled in the ecosystem model Ecosys, which was tested against CH4 effluxes measured with surface chambers and a flux tower at a beaver pond in the BOREAS Northern Study Area. Spatial and temporal variation of CH4 effluxes in the model encompassed that measured by surface chambers and the flux tower. Both modeled and measured CH4 effluxes rose from <0.05 μmol m−2 s−1 and <0.01 g C m−2 d−1 at sites above the pond to >1.0 μmol m−2 s−1 and >0.5 g C m−2 d−1 at the pond margin. Larger effluxes occurred in the model when warming pond sediments generated episodic bubbling events. Annual CH4 effluxes in the model rose from <1 g C m−2 at sites above the pond to 76 g C m−2 at the pond margin. Annual totals included several brief but rapid efflux events during thawing and warming of soil and pond sediments that are frequently missed by surface measurements. Annual CH4 effluxes predicted after 100 years under an IS92a‐driven climate change scenario rose by ∼20% from the pond, but changed little from the surrounding landscape, indicating topographic variation in response of CH4 effluxes to climate change.
A comparison of tomographic and geodynamic mantle models
Authors: Becker Thorsten W. , Boschi Lapo
Published: October 2003

We conduct a comprehensive and quantitative analysis of similarities and differences between recent seismic tomography models of the Earth's mantle in an attempt to determine a benchmark for geodynamic interpretation. After a spherical harmonic expansion, we find the spectral power and radial correlation of each tomographic model as a function of depth and harmonic degree. We then calculate the correlation, at the same depths and degrees, between all possible pairs of models, to identify stable and model‐dependent features (the former being usually of longer spatial wavelength than the latter). We can therefore evaluate the degree of robust structure that seismologists have mapped so far and proceed to calculate ad hoc mean reference models. Tomographic models are furthermore compared with two geodynamic subduction models that are based on plate motion reconstructions. We find systematically low intermediate‐wavelength correlation between tomography and convective reconstruction models and suggest that the inadequate treatment of the details of slab advection is responsible. However, we confirm the presence of stable, slab‐like fast anomalies in the mid‐mantle whose geographic pattern naturally associates them with subduction. This finding, in addition to our analysis of heterogeneity spectra and the absence of strong minima in the radial correlation functions besides the one at ~700 km, supports the idea of whole mantle convection with slab penetration through the 660 km phase transition, possibly accompanied by a reorganization of flow.
CaSiO3 and CaTiO3 perovskite‐melt partitioning of trace elements: Implications for gross mantle differentiation
Authors: Corgne Alexandre , Wood Bernard J.
Published: October 2003

We report the results of CaSiO3 perovskite‐melt partitioning experiments conducted at conditions relevant to the uppermost lower mantle. Partition coefficients, measured by LA‐ICPMS, show that CaSiO3 perovskite has a strong affinity for REE, Y, Th and U, making CaSiO3 the most likely host for these elements in the lower mantle. Comparison with the low‐pressure analogue CaTiO3 shows that large ions partition similarly into the Ca‐sites of the two perovskites. Thus CaTiO3 may be used as a model to investigate the factors controlling the partitioning of many trace ions into CaSiO3. Combined fractionation of MgSiO3 and CaSiO3 perovskites during an early magma ocean has been suggested as a means of enriching the lower mantle in silica. Our results show, however, that the chondritic upper mantle ratios of refractory lithophile elements would be lost after ∼17% of perovskite fractionation. A large perovskitic layer `hidden' in the lower mantle is therefore improbable.
Recent and future changes in Arctic sea ice simulated by the HadCM3 AOGCM
Authors: Gregory J. M. , Stott P. A. , Cresswell D. J. , Rayner N. A. , Gordon C. , Sexton D. M. H.
Published: October 2003

The HadCM3 AOGCM has been used to undertake an ensemble of four integrations from 1860 to 1999 with forcings due to all major anthropogenic and natural climate factors. The simulated decreasing trend in average Arctic sea ice extent for 1970–1999 (−2.5% per decade) is very similar to observations. HadCM3 indicates that internal variability and natural forcings (solar and volcanic) of the climate system are very unlikely by themselves to have caused a trend of this size. The simulated decreasing trend in Arctic sea ice volume (−3.4% per decade for 1961–1998) is less than some recent observationally based estimates. Extending the integrations into the 21st century, Arctic sea ice area and volume continue to decline. Area decreases linearly as global‐average temperature rises (by 13% per K), and volume diminishes more rapidly than area. By the end of the century, in some scenarios, the Arctic is ice‐free in late summer.
Properties of near surface marine sediments from wavelet correlation analysis
Authors: Kritski A. , Yuen D. A. , Vincent A. P.
Published: October 2003

We present the first results from applying the wavelet correlation analysis to study physical properties of near top marine sediments. This technique applied to the synthetic and field data yields well resolved group velocity dispersion curves for the first two shear modes and surface waves. This method can be potentially useful for detecting of different seismic modes at frequencies masked by other neighboring modes. This novel technique is superior to traditional cross‐correlation and Fourier analysis for inferring the physical properties of near surface marine sediments, such as density, porosity variations in depth and distance under diverse field conditions.
Evaluating measurements of new particle concentrations, source rates, and spatial scales during coastal nucleation events using condensation particle counters
Authors: Hämeri K. , O'Dowd C. D. , Hoell C.
Published: October 2003

Condensation particle counters (CPCs), used to examine particle production in the coastal environment, are evaluated for their ability to differentiate ultrafine sizes between 3 and 10 nm, along with their ability to count high total particle number concentrations encountered during coastal nucleation events. Four ultrafine particles counters, with a 3 nm detection limit, were deployed in a spatial array comprising a triangular distribution with nodes approximately 100 m apart (two at 3 m height, one at 10 m). A fourth node was deployed at 20 m. The 10 m and 20 m node comprised additional CPCs with detection limits of 5 and 10 nm. Size cutoff efficiency calibrations were performed in the field, and all CPCs were found to be within the manufacturer's specifications. During the nucleation events it was found that peak particle concentrations of the order of 180,000 cm−3 were encountered, and as a result, coincidence calibrations were also performed in the laboratory. It was found that, at concentrations over 100,000 cm−3, the CPCs significantly underestimated the true concentrations by a factor of about 5–6. Total particle concentrations were also measured using a 30‐times dilution system and an ultrafine CPC, along with integrated total concentration derived from the ultrafine Differential Mobility Particle Sizer (DMPS). Comparison of laboratory‐derived corrections for coincidence and both the diluted CPC total concentrations and DMPS concentrations revealed very good agreement and confirmed that peak particle concentrations during coastal nucleation bursts result in new particle concentrations as high as 1.2 × 106 cm−3. The DMPS total concentration was somewhat lower than the diluted CPC concentration, suggesting that the recommended method of measuring such high concentrations is to dilute the sample significantly. The lower concentrations from the DMPS are partially due to the 10 min integration time being insufficient to resolve peaks seen by the CPC operated at 1 Hz. Taking the corrected concentrations in account, 3 nm particle source rates were calculated to be >105 cm−3 s−1. The spatial array of CPCs revealed that within the general coastal nucleation plume, there are numerous microplumes with spatial scales of the order of 10–100 m when sampling is conducted near the source region. Further from the source region these microplumes merge into the general coastal plume.
Modeling the effect of denitrification on Arctic ozone depletion during winter 1999/2000
Authors: Davies S. , Chipperfield M. P. , Carslaw K. S. , Sinnhuber B.‐M. , Anderson J. G. , Stimpfle R. M. , Wilmouth D. M. , Fahey D. W. , Popp P. J. , Richard E. C. , von der Gathen P. , Jost H. , Webster C. R.
Published: October 2003

We have used the SLIMCAT three‐dimensional chemical transport model together with observations from the Stratospheric Aerosol and Gas Experiment (SAGE III) Ozone Loss and Validation Experiment (SOLVE) and the Third European Stratospheric Experiment on Ozone (THESEO 2000) to quantify the effect of denitrification on Arctic ozone loss. We have used two different denitrification schemes in the model: one based on the sedimentation of ice particles containing cocondensed nitric acid trihydrate (NAT) and the other based on large NAT particles. The model was forced using both UK Meteorological Office (UKMO) and European Centre for Medium‐Range Weather Forecasts (ECMWF) analyses. In the Arctic lower stratosphere the UKMO analyzed temperatures are similar to the ECMWF, except at temperatures near the ice point where the UKMO analyses are colder by over 2 K. Consequently, the UKMO analyses predicted large regions of ice clouds, in contrast to the ECMWF. The denitrification scheme based on large NAT particles gives the best agreement with ER‐2 NOy observations for both sets of meteorological analyses. Although the ice scheme and UKMO analyses also produce denitrification, the vertical extent of denitrification and renitrification does not agree as well with the observed NOy. Uncertainties in the budget of ClOy observations from the ER‐2 prevent an indirect validation of the best model denitrification scheme based on these data. The denitrified model runs give the best agreement with the observed HCl and ClONO2 reservoirs in mid March. However, UKMO‐forced runs generally overestimate the observed ClOx during the same period. The denitrified model runs indicate that by late March 56–74% O3 loss had occurred at 460 K and that denitrification contributed 21–30% of this loss. The model runs showing the largest O3 depletion (forced by UKMO analyses) agree well with ER‐2 and ozone sonde data, although these runs overestimated ClOx.
Evidence for inertia gravity waves forming polar stratospheric clouds over Scandinavia
Authors: Dörnbrack Andreas , Birner Thomas , Fix Andreas , Flentje Harald , Meister Alexander , Schmid Heidi , Browell Edward V. , Mahoney Michael J.
Published: October 2003

At three successive days at the end of January 2000 the Deutsches Zentrum für Luft‐ und Raumfahrt (DLR) airborne lidar Ozone Lidar Experiment explored mountain‐wave‐induced polar stratospheric clouds above the Scandinavian mountain ridge. Global analyses and mesoscale modeling are applied to explain their complex internal structure and their day‐to‐day variability. Depending on the synoptical‐scale meteorological conditions, stratospheric temperature anomalies of different amplitude and horizontal extent are generated by the upward propagating mountain waves. Short‐term excitation of about 6 hours resulted in localized stratospheric temperature anomalies directly above the mountain ridge as for 25 January 2000. In this case, the elevation of the observed clouds differed not much from the synoptic‐scale clouds upstream above the Norwegian Sea. On the other hand, long‐lasting flow past the Scandinavian mountain ridge formed huge 400‐km horizontally extending stratospheric ice clouds in altitudes as much as 5 km above the elevation of the upstream clouds just 1 day later. Inertia gravity waves with horizontal wavelengths of about 350 km are responsible for their formation. For the first time a predicted temperature minimum far downstream of the mountains could be proofed by the observation of an isolated stratospheric ice cloud above Finland. The observed particles are classified in terms of their measured optical properties such as backscatter ratio and depolarization. In all cases, mountain waves generated ice clouds. In contrast to the nitric acid trihydrate tail of the ice cloud on 25 January the same classification results in a tail of liquid supercooled ternary solutions droplets 1 day later. The particle structure downstream of the mountains is very complex and needs detailed microphyical modeling and interpretation.
Stable isotope composition of waters in the Great Basin, United States 1. Air‐mass trajectories
Authors: Friedman Irving , Harris Joyce M. , Smith George I. , Johnson Craig A.
Published: October 2003

Isentropic trajectories, calculated using the NOAA/Climate Monitoring and Diagnostics Laboratory's isentropic transport model, were used to determine air‐parcel origins and the influence of air mass trajectories on the isotopic composition of precipitation events that occurred between October 1991 and September 1993 at Cedar City, Utah, and Winnemucca, Nevada. Examination of trajectories that trace the position of air parcels backward in time for 10 days indicated five distinct regions of water vapor origin: (1) Gulf of Alaska and North Pacific, (2) central Pacific, (3) tropical Pacific, (4) Gulf of Mexico, and (5) continental land mass. Deuterium (δD) and oxygen‐18 (δ18O) analyses were made of precipitation representing 99% of all Cedar City events. Similar analyses were made on precipitation representing 66% of the precipitation falling at Winnemucca during the same period. The average isotopic composition of precipitation derived from each water vapor source was determined. More than half of the precipitation that fell at both sites during the study period originated in the tropical Pacific and traveled northeast to the Great Basin; only a small proportion traversed the Sierra Nevada. The isotopic composition of precipitation is determined by air‐mass origin and its track to the collection station, mechanism of droplet formation, reequilibration within clouds, and evaporation during its passage from cloud to ground. The Rayleigh distillation model can explain the changes in isotopic composition of precipitation as an air mass is cooled pseudo‐adiabatically during uplift. However, the complicated processes that take place in the rapidly convecting environment of cumulonimbus and other clouds that are common in the Great Basin, especially in summer, require modification of this model because raindrops that form in the lower portion of those clouds undergo isotopic change as they are elevated to upper levels of the clouds from where they eventually drop to the ground.
Stable isotope compositions of waters in the Great Basin, United States 3. Comparison of groundwaters with modern precipitation
Authors: Smith George I. , Friedman Irving , Veronda Guida , Johnson Craig A.
Published: October 2003

Groundwater samples from wells and springs, scattered over most of the Great Basin province, were collected and analyzed for their isotopic makeup. They were augmented by previously published isotopic data on groundwaters from southeast California and by several hundred unpublished isotopic analyses. The ratio of 2H (deuterium, D) to 1H, in water samples from valleys in parts of California, Idaho, Nevada, Oregon, and Utah, are here compared with the winter, summer, and annual isotopic compositions of precipitation falling in or near the sampled areas. The main goal of this study was to identify basins where the groundwaters have isotopic compositions that are “lighter” (depleted in the heavier isotope, D) relative to modern winter precipitation. Where these basins do not adjoin substantially higher terrain, we consider those light groundwaters to be of Pleistocene age and thus more than 10,000 years old. Where the groundwater is 10 to 19‰ lighter than local winter precipitation, we consider it to be possibly an indication of Pleistocene water; where the δD makeup is >20‰ lighter, we consider it to be probably Pleistocene water. More than 80 sites underlain by waters of possible or probable Pleistocene age were identified.
Primary particle emissions from residential coal burning: Optical properties and size distributions
Authors: Bond Tami C. , Covert David S. , Kramlich John C. , Larson Timothy V. , Charlson Robert J.
Published: October 2003

Particles generated by combustion of fossil fuels contribute to climate forcing by absorbing and scattering visible light. Residential combustion takes place in homes for heating or cooking purposes and is thought to contribute a large fraction of the global burden of anthropogenic primary particles. We present optical properties and size distributions of particulate matter emitted from three types of coal burned in residential combustors: bituminous coal, hard coal briquettes, and lignite. Emissions from these coals differ significantly and can be partially explained by differences in coal composition. For bituminous coal, particulate matter emission factors are somewhat greater than those used in current emission inventories. We observe particles for which the light absorption is weak and has a strong spectral dependence. For hard coal briquettes and lignite, emitted light absorption is low, and based on our measurements, current inventories of light‐absorbing aerosols significantly overestimate the contribution from these sources. Hard coal briquettes produce very few particles in the optically active size range. For all coals tested the size distributions required to represent the average of the emitted particles are broader than atmospheric size distributions, with geometric standard deviations between 2.2 and 3.0.
Stratospheric transport by planetary wave mixing as observed during CRISTA‐2
Authors: Riese M. , Manney G. L. , Oberheide J. , Tie X. , Spang R. , Küll V.
Published: October 2003

Planetary waves drive the mean meridional circulation of the stratosphere and at the same time facilitate quasi‐horizontal mixing of trace gases. This paper presents significant day‐to‐day variability of stratospheric trace gas fields associated with large planetary wave activity observed during the second mission of the Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) experiment. Geopotential height data of the UK Met Office show that the CRISTA‐2 observations in the Southern Hemisphere winter were made during a period of extremely large amplitudes of both wave‐1 and wave‐2. The planetary wave‐1, usually a quasi‐stationary feature, moved eastward with the traveling planetary wave‐2. The large amplitudes of both wave‐1 and wave‐2 led to a significant displacement of the edge of the polar vortex toward the tropics (down to 30°S). As a result of the large wave amplitudes and favorable phase alignment, the anticyclone drawing up tropical air was unusually strong, and thus considerable wave‐induced trace gas flux from the tropics toward midlatitudes was observed, mainly in the form of a pronounced planetary‐scale tongue advected out of the tropics around the vortex and into the anticyclone. Quantitative transport calculations based on a sequential data assimilation system highlight the importance of such transport events for trace gas eddy‐flux in the Southern Hemisphere winter stratosphere.
Influence of climate change over the 20th Century on four French glacier mass balances
Authors: Vincent C.
Published: October 2003

Winter and summer mass balance measurements from four French glaciers have been used to assess the sensitivity of mass balance to climatic fluctuations. The sensitivity of summer ablation to temperature is maximum in low‐elevation zones (1.4 m water equivalent (w.e.) °C−1 at 1800 m above sea level (asl)) and decreases with altitude (0.5 m w.e. °C−1 at 2900 m asl). As a consequence, the sensitivity of equilibrium line altitude to temperature is 60–70 m °C−1. This is half the value previously reported in the literature, implying that alpine glacier retreat scenarios for the 21st Century have been largely overestimated. Winter accumulation can be as high as 3 times the amount of precipitation recorded downvalley. These relationships between mass balance and meteorological data were then used to reconstruct the mass balances of these four glaciers back to 1907 using old maps and photogrammetric measurements. Model sensitivity analysis shows that a 25–30% increase in precipitation would compensate a 1°C temperature rise for the mass balances of glaciers. From these results the 20th Century may be divided into four periods: two steady state periods, 1907–1941 and 1954–1981, during which the mass of glaciers remained almost constant, and two deficit periods, 1942–1953 and 1982–1999, marked by a sharp reduction in glacier mass. Regarding mean ablation at 2800 m asl, a 22 W m−2 increase in energy balance is required to explain the ablation difference between the two most recent periods, 1954–1981 and 1982–1999. According to the energy balance analysis the increase in air temperature explains more than 60% of this ablation rise.
Vertical variability of aerosol properties observed at a continental site during the Lindenberg Aerosol Characterization Experiment (LACE 98)
Authors: Petzold A. , Fiebig M. , Flentje H. , Keil A. , Leiterer U. , Schröder F. , Stifter A. , Wendisch M. , Wendling P.
Published: October 2003

In the summer of 1998, an aerosol column closure experiment was conducted over eastern Germany as part of the Lindenberg Aerosol Characterization Experiment (LACE 98). The experimental platforms involved were two aircraft equipped with aerosol in situ instrumentation, an airborne aerosol backscatter lidar and solar irradiance sensors (upwelling and downwelling) to measure optical and microphysical aerosol properties relevant for radiative forcing in the entire atmospheric column from the boundary layer to the tropopause region. Using Mie theory and reasonable assumptions on the particle complex refractive index, the hemispheric backscatter fraction and spectral light scattering coefficients were calculated from the measured aerosol size distribution data. A comparison between optical parameters derived from particle size distribution measurements and optical properties measured by independent techniques yields an uncertainty range of ±30% for the calculated aerosol optical parameters. Detailed information on the vertical variability of the particle size distribution, the aerosol extinction coefficient and the hemispheric backscatter fraction is given, which is applicable for a realistic representation of aerosol properties in climate models. The estimated daily averaged aerosol shortwave radiative forcing varies from −33 ± 12 to −12 ± 5 W m−2, and respective aerosol optical depths at λ = 0.710 μm range from 0.18 to 0.06.
Ozone depletion in Northern Hemisphere winter/spring 1999/2000 as measured by the Global Ozone Monitoring Experiment on ERS‐2
Authors: Eichmann K.‐U. , Weber M. , Bramstedt K. , Burrows J. P.
Published: October 2003

During the SOLVE/THESEO 2000 campaign the Global Ozone Monitoring Experiment (GOME) sampled the Arctic region from January to April 2000. Results from the GOME total ozone measurements are presented to highlight the peculiarity of the 1999/2000 Arctic winter/spring season in relation to earlier years. Chemical ozone loss calculations have been derived from daily vortex‐averaged ozone profile measurements from GOME. Between 12 February and 13 March 2000, an accumulated chemical ozone loss of 1.3 ± 0.3 ppmv at 475 K isentropic height was derived within the polar vortex. This amounts to a daily chemical depletion rate of 43 ppbv per day (42%). Using 25 January 2000 as a reference date, where six GOME ozone profile measurements were available, an ozone loss of 1.8 ± 0.4 ppmv (49%, 37 ppbv/day) can be derived. The GOME vortex average ozone volume mixing ratios at 475 K agrees well with results from the three‐dimensional chemical transport model SLIMCAT and weekly mean values derived from higher‐resolution ozone sonde measurements. The low vertical resolution of the GOME measurements leads to an overestimation of ozone after the vortex was split into parts in the middle of March. The accumulated chemical column loss (400–600 K) corrected for diabatic effects is 114 ± 10 DU between 25 January and 13 March. By comparing midlatitude ozone volume mixing ratios from GOME to passive ozone tracer data from SLIMCAT, an ozone loss of about 12% is estimated at 475 K isentropic level within the potential vorticity range between 20 and 30 PVU. This value is statistically insignificant because of uncertainties in model transport.
Moisture budget of the Arctic atmosphere from TOVS satellite data
Authors: Groves David G. , Francis Jennifer A.
Published: October 2003

The Arctic atmospheric moisture budget is an important component of the Arctic climate system, and moisture transport is a major mechanism by which both local and hemispheric atmospheric processes affect the Arctic Ocean. The lack of humidity data over the Arctic Ocean severely hampers present understanding of climatological and time‐varying features of the Arctic moisture budget. We combine daily satellite precipitable water retrievals from the NASA/NOAA TIROS Operational Vertical Sounder (TOVS) Polar Pathfinder data set with wind fields from the NCEP‐NCAR Reanalysis to create a new high‐resolution data set of the Arctic atmospheric moisture budget from October 1979 to December 1998. Products are at a horizontal resolution of (100 km)2 and include daily fields of precipitable water and precipitable water flux profiles at 16 vertical levels and net precipitation (i.e., precipitation minus evaporation, P‐E). We show that these retrievals compare well with rawinsonde‐derived moisture transport and reanalysis products, yet capture spatial and temporal variability that other data sets cannot owing to the sparse coverage of the conventional observation network in the Arctic Ocean. Our method yields an average annual net precipitation of 15.1 cm yr−1 over the polar cap (poleward of 70°N) and 12.9 cm yr−1 over the Arctic Basin. Poleward moisture transport into the Arctic is greatest from June to August and smallest in December. Over regions of known storm tracks, especially in the North Atlantic sector, we find that transient circulation features account for 32% of the net precipitation in the Greenland‐Iceland‐Norwegian Seas, 90% in the Nansen Basin, and 74% in the Arctic basin as a whole.
Small‐scale temperature variations in the vicinity of NLC: Experimental and model results
Authors: Rapp M. , Lübken F.‐J. , Müllemann A. , Thomas G. E. , Jensen E. J.
Published: October 2003

Gravity waves (GWs) are a ubiquitious dynamical feature of the polar summer mesopause region. During three summer campaigns, in 1991, 1993 and 1994, we launched seven sounding rockets from the north Norwegian island Andøya. Each of these payloads carried an ionization gauge capable of measuring the total atmospheric density at a high spatial resolution. From these measurements, temperature profiles were determined for altitudes between 70 and 110 km, with an altitude resolution of 200 m. The temperature profiles reveal significant rms variations that are as large as 6 K at 80 km, 10 K at 85 km, and even 20 K at 95 km. During three out of the seven launches a bright noctilucent cloud (NLC) was simultaneously detected by our ground‐based lidar and by rocket‐borne in situ experiments. During these flights, the NLC is located close to a local temperature minimum below the mesopause. We then estimated gravity wave parameters from accompanying falling sphere and chaff wind observations and found signatures that the wave periods during the NLC cases were on the order of 7–9 hours, with corresponding horizontal wavelengths of 600–1000 km. Motivated by these observations, we used a microphysical model of NLC generation and growth to study the interaction between GWs and NLC. Based on recently measured and modeled temperatures and water vapor mixing ratios, and our gravity wave parameter estimates, we find that the NLC layer indeed follows the motion of the cold phase of the wave by means of a complex interplay between ice crystal sedimentation, transport by the vertical wind, and simultaneous growth. It turns out that the history of individual particles significantly influences the observed properties of NLC. Furthermore, we find that GWs with periods longer than 6.5 hours amplify NLC while waves with shorter periods tend to destroy NLC. In addition, we can only find a correlation between local temperature minima and the location of the NLC provided that the wave periods are longer than ∼6 hours, which is consistent with our wave parameter estimates.
Correlation dimensions of climate subsystems and their geographic variability
Authors: Gan Thian Yew , Wang Qiang , Seneka Michael
Published: October 2003

The correlation dimension D2 of precipitation (Canada and Africa), air temperature (Canada, New Zealand, and Southern Hemisphere), geo‐potential height (Canada), and unregulated streamflow (Canada, USA, and Africa) were estimated using the Hill procedure of Mikosch and Wang [1995] and the bias correction of Wang and Gan [1998]. After bias correction, it seems that D2 is distinct between climate subsystems, such that for precipitation, it is between 8 and 9, for streamflow, it is between 7 and 9, for temperature, it is between 10 and 11, and for geo‐potential heights, it is between 12 and 14. The results seem to suggest that climate might be viewed as a loosely coupled set of fairly high‐dimensional subsystems and that different climate variables can yield different D2 values. Further, results also suggest that the D2 values of the climate subsystems studied, generally, have low geographic variability, as found between the precipitation data of Western Canada and Uganda, between the streamflow data of basins representing wide range climate and scales from Canada, USA, and Africa, and among the temperature data of Western Canada, New Zealand, and the southern hemisphere, and that the original D2 values analyzed from Canadian geo‐potential heights are similar to that of Western Europe, eastern North America, and Germany. There is at most a weak relationship among basin physical characteristics, location, basin scale, and streamflow D2, while climatic influence is more obvious, as shown by drier basins having slightly higher D2 values than basins of wetter climate, basins from temperate climate having higher D2 values than those from cold or hot climates, and comparable D2 values between precipitation and streamflow data.
Temporal and spatial patterns of the interannual variability of total ozone in the tropics
Authors: Camp Charles D. , Roulston Mark S. , Yung Yuk L.
Published: October 2003

The recently constructed gridded Merged Ozone Data (MOD) set, combining the monthly mean column abundances collected by the Total Ozone Mapping Spectrometer (TOMS) and the Solar Backscatter Ultraviolet (SBUV and SBUV/2) instruments, provides a nearly continuous record from late 1978 to 2000 on a 5° × 10° latitude‐longitude grid. The precision of these measurements and their calibration allow very small signals, ∼1% of total column ozone, to be clearly seen. Using MOD, we have carried out an empirical orthogonal function (EOF) study of the temporal and spatial patterns of the interannual variability of total column ozone in the tropics. The first four EOFs of our study capture over 93% of the variance of the deseasonalized data. The leading two EOFs of our study, respectively accounting for 42% and 33% of the variance, display structures attributable to the quasi‐biennial oscillation (QBO), with influence from a decadal oscillation. The third EOF (15% of the variance) represents an interaction between the QBO and an annual cycle. The fourth EOF (3% of the variance) is related to the El Niño ‐ Southern Oscillation. This EOF decomposition is robust; nearly identical patterns occur in the decomposition of various equatorial latitude bands of MOD and similar patterns occur in the analysis of the deseasonalized TOMS data set, a shorter record with a more finely resolved spatial grid. For comparison, similar decompositions were performed for dynamical fields from the reanalysis product from the National Centers for Environmental Prediction and the National Center for Atmospheric Research. Using these analyses, we found possible connections between the deduced patterns in ozone and the climate variables.
On temperature inversions and the mesospheric surf zone
Authors: Sassi F. , Garcia R. R. , Boville B. A. , Liu H.
Published: October 2003

Mesospheric thermal inversions are investigated in a numerical simulation with the Whole Atmosphere Community Climate Model, an upward extension of the National Center for Atmospheric Research's Community Climate Model. The seasonal character, spatial extent, and magnitude of the inversion layers are realistic during winter. In the model, the occurrence of wintertime inversions is a direct consequence of the rapid decay with height of vertically propagating planetary waves, which induces large temperature perturbations in the upper mesosphere to maintain hydrostatic equilibrium. The magnitude of the inversions is highly correlated with planetary wave amplitude, so that large inversions develop during episodes of planetary wave amplification. Gravity waves do not play a major direct role in the formation of the inversions because the largest thermal tendencies associated with gravity wave breaking occur well above the range of altitudes where inversions are found. However, gravity waves play an essential indirect role because they set up a critical line in the upper mesosphere where Rossby waves break in the mesospheric surf zone.
A Lagrangian analysis of stratospheric ozone variability and long‐term trends above Payerne (Switzerland) during 1970–2001
Authors: Koch Gisela , Wernli Heini , Staehelin Johannes , Peter Thomas
Published: October 2003

A systematic Lagrangian investigation is performed of wintertime high‐resolution stratospheric ozone soundings at Payerne, Switzerland, from January 1970 to March 2001. During the winter season, ozone variability is largest in the lower stratosphere (p > 120 hPa) where the trend is not statistically significant (on the 95%‐level) considering the whole time period. A significant negative trend (−5% per decade) exists only above this level. For every ozone sounding, 10‐day backward trajectories have been calculated on 16 isentropic levels using NCEP reanalysis data. Both the minimum/maximum latitude and potential vorticity (PV) averaged along the trajectories are used as indicators of the air parcels' “origin.” A detailed case study of an ozone minihole (198 Dobson units; 1 DU = 0.001 atm cm) in November 2000 reveals that this extreme event was due to the concurrent transport to central Europe of subtropical air in the lowermost stratosphere (where the climatological ozone gradient points to the north) and of polar air in the lower to middle stratosphere (where the ozone gradient is reversed). The importance of transport for the understanding of single ozone profiles is confirmed by the statistical analysis which shows that negative/positive ozone deviations generally coincide with transport from regions with climatologically low/high ozone values. Some important differences arise when considering the layers from 340–440 K and 460–700 K separately. In the lower layer the frequency of transport from the subtropics has increased since 1970 which leads to a (statistically not significant) ozone decrease. The stable relationship between PV and ozone for the 32‐year period indicates either no direct chemical impact or no temporal change of this impact. In the upper layer the PV‐ozone relationship changes significantly after 1987, and a separate trend analysis for air masses transported from the polar, midlatitude and subtropical regions shows negative ozone trends in all three categories (with a maximum for the polar region). This is not direct evidence for, but would be in agreement with, an increased chemical ozone depletion in the Arctic since the late 1980s. The reasons for the negative trend in the midstratospheric air masses with subtropical origin that are in qualitative agreement with recent satellite observations are presently unknown.
Concentration trends and mixing states of particulate oxalate in Arctic boundary layer in winter/spring
Authors: Hara Keiichiro , Osada Kazuo , Matsunaga Katsuji , Sakai Tetsu , Iwasaka Yasunobu , Furuya Keiichi
Published: October 2003

Particulate organic species contribute to the formation of cloud condensation nuclei and may play a role in the formation/growth of condensation nuclei. The field measurements in this paper investigated size distribution and mixing states of particulate oxalate (one of major organic compounds in aerosol particles) in the Arctic boundary layer in during the winter and spring. The variation of particulate oxalate concentration correlated well with nss‐SO42− concentration. This correlation may be due to the direct emissions of oxalate and its precursors of oxalate from anthropogenic sources. The molar ratio of oxalate to nss‐SO42− was found to gradually increase from winter to early spring with the recovery of solar radiation to the Arctic Circle. Individual aerosol particle analysis by means of laser microprobe mass spectrometry showed that most of the oxalate was internally mixed with sulfate in fine particle mode (0.2–2.0 μm).
Thermal infrared spectroscopy of experimentally shocked anorthosite and pyroxenite: Implications for remote sensing of Mars
Authors: Johnson Jeffrey R. , Hörz Friedrich , Lucey Paul G. , Christensen Philip R.
Published: October 2003

The feldspar and pyroxene mineralogies on Mars revealed by the Thermal Emission Spectrometer (TES) on Mars Global Surveyor likely record a variety of shock effects, as suggested by petrologic analyses of the Martian meteorites and the abundance of impact craters on the planet's surface. To study the effects of shock pressures on thermal infrared spectra of these minerals, we performed shock recovery experiments on orthopyroxenite and anorthosite samples from the Stillwater Complex (Montana) over peak pressures from 17 to 63 GPa. We acquired emissivity and hemispherical reflectance spectra (350–1400 cm−1; ∼7–29 μm) of both coherent chips and fine‐grained powders of shocked and unshocked samples. These spectra are more directly comparable to remotely sensed data of Mars (e.g., TES) than previously acquired absorption or transmission spectra of shocked minerals. The spectra of experimentally shocked feldspar show systematic changes with increasing pressure due to depolymerization of the silica tetrahedra. For the spectra of chips, this includes the disappearance of small bands in the 500–650 cm−1 region and a strong band at 1115 cm−1, and changes in positions of a strong band near 940 cm−1 and the Christiansen feature near 1250 cm−1. Spectra of the shocked powders show the gradual disappearance of a transparency feature near 830 cm−1. Fewer changes are observed in the pyroxene spectra at pressures as high as 63 GPa. Spectra of experimentally shocked minerals will help identify more precisely the mineralogy of rocks and soils not only from TES but also from Mars instruments such as miniTES and THEMIS.
STORM: An empirical storm‐time ionospheric correction model 1. Model description
Authors: Araujo‐Pradere E. A. , Fuller‐Rowell T. J. , Codrescu M. V.
Published: October 2003

Using data from 75 ionosonde stations and 43 storms, and based on the knowledge gained from simulations from a physically based model, we have developed an empirical ionospheric storm‐time correction model. The model is designed to scale the quiet time F region critical frequency (foF2) to account for storm‐time changes in the ionosphere. The model is driven by a new index based on the integral of the apindex over the previous 33 hours weighted by a filter obtained by the method of singular value decomposition. Ionospheric data were sorted as a function of season and latitude and by the intensity of the storm, to obtain the corresponding dependencies. The good fit to the data at midlatitudes for storms during summer and equinox enable a reliable correction, but during winter and near the equator, the model does not improve significantly on the quiet time International Reference Ionosphere predictions. This model is now included in the international recommended standard IRI2000 [Bilitza, 2001] as a correction factor for perturbed conditions.
Calibrating short‐timescale tropospheric phase fluctuations seen by a radio telescope: Limits from subreflector and Cassegrain feed ring radiometer placement
Authors: Linfield Roger
Published: October 2003

Water vapor radiometers (WVRs) measure tropospheric brightness temperatures and use those measurements to infer path delay. Calibration of short‐timescale phase fluctuations at a radio telescope requires that the WVR and radio telescope sample a similar volume of the troposphere. Using a statistical (Kolmogorov frozen flow) model of tropospheric fluctuations, the short‐timescale calibration capability of two WVR configurations has been quantified. The first configuration is a WVR mounted, with its own antenna, on the back side of the main radio telescope subreflector, giving a conical beam that is coaxial with the main cylindrical near‐field beam of the large telescope. The second configuration uses a Cassegrain feed ring, with the WVR and radio astronomy feeds at different positions on the ring. This second configuration gives a cylindrical calibration near‐field beam, offset in angle to the main cylindrical beam. An important application of short‐timescale phase calibration is improving the coherence of high‐frequency interferometric observations. For two cases of current/near future interest (86 GHz very long baseline interferometry with the Very Long Baseline Array; 350 GHz observations with the Atacama Large Millimeter Array, ALMA), useful calibration could be achieved with either geometry (coaxial conical beam or offset cylindrical beam). For a coaxial conical beam, a 2° WVR beam width would allow significant coherence improvement, but a beam width ≤1° (full width at half maximum) is needed for optimum performance. For an offset cylindrical beam, the desired angular offset (on the sky) is ≤1° for 43 GHz Very Large Array observations, or ≤0.3° for 350 GHz ALMA observations.